Different
strategies for cardiac protection: metabolic, ionic, signaling
Metin Avkiran
Centre for Cardiovascular Biology and Medicine, King’s College,
London,
and The Rayne Institute, St Thomas’ Hospital, London, UK
Correspondence: Dr Metin Avkiran, Centre for Cardiovascular Biology
and Medicine,
The Rayne Institute, St Thomas’ Hospital
Lambeth Palace Road, London SE1 7EH, UK, e-mail: metin.avkiran@kcl.ac.uk
Introduction
Cardiovascular disease remains a leading cause of death worldwide.
For example, cardiovascular mortality, arising principally from
ischemic heart disease, accounts for 40% of all deaths before
the age of 74 years in European countries.[1]
Despite the availability of preventative treatments, patients
often present at an advanced stage of coronary artery disease,
with atherosclerotic plaques that are liable to cause abrupt coronary
occlusion, myocardial infarction, and death. Currently, the most
effective method of reducing mortality in patients who suffer
such an abrupt coronary occlusion is to achieve rapid reperfusion,
by thrombolysis or mechanical disruption of the occlusive coronary
thrombus and plaque. However, it is well established that for
reperfusion to be of optimal benefit (by salvaging ischemic myocardium
from necrosis and thereby maintaining ventricular function), it
has to be achieved rapidly after the onset of ischemia. Unfortunately,
many patients with acute myocardial infarction do not receive
the full benefit of reperfusion because they suffer from delays
in reporting to hospital and/or receiving appropriate treatment.[2]
Furthermore, there is evidence that the phenomenon of ‘reperfusion-induced
injury’ may detract from the undoubted benefits of coronary flow
restoration.[3]
There are currently no clinically proven therapies that are used
widely to enhance the myocardium’s tolerance to ischemia and thereby
extend the time-window for tissue salvage by reperfusion, or to
further enhance the benefits of reperfusion by attenuating reperfusion-induced
injury. If available, such therapies would be expected to be of
value not only in the management of acute myocardial infarction
but also in cardiac surgery, where the heart is often subjected
to periods of global ischemia and reperfusion. In the surgical
setting, these may find application as adjuvant therapies and
be used in conjunction with existing cardioprotective strategies,
such as cardioplegic arrest or intermittent ventricular fibrillation,
to enhance postischemic myocardial viability and function.
From the above, it is apparent that the development of effective
treatments for the direct protection of ischemic and reperfused
myocardium should provide cardiologists and cardiac surgeons with
novel therapeutic options and would be expected to have a beneficial
impact on the mortality and morbidity associated with ischemic
heart disease. The objective of this article is to highlight several
approaches to cardiac protection that have received attention
in recent years, some of which have already reached the stage
of clinical evaluation. These approaches have aimed to improve
myocardial tolerance to ischemia and improve its viability and
function after reperfusion, by manipulating cellular metabolism
or ion transport and by understanding (and subsequently exploiting)
the signaling mechanisms that regulate myocardial susceptibility
to injury, in particular those that are responsible for the powerful
endogenous protection afforded by adaptive phenomena such as ischemic
preconditioning (Figure 1).
Figure 1. Potential approaches to cardiac protection. GIK,
glucose-insulin-potassium; NHE, sodium/hydrogen exchanger; p38
MAPK, p38 mitogen-activated protein kinase.
Metabolic approaches
Under normal, aerobic conditions, the myocardium can utilize a
variety of substrates (eg, free fatty acids, glucose, lactate)
to produce the energy required to maintain its viability and function,
in the form of adenosine triphosphate (ATP), primarily through
oxidative metabolism. In contrast, in ischemic myocardium, the
metabolism of glucose to lactate by anaerobic glycolysis becomes
the main source of ATP generation.[4]
As reviewed recently,[5,6]
in myocardium subjected to ischemia and reperfusion, significant
functional benefit may be obtained by using interventions that
inhibit fatty acid metabolism and/or stimulate glucose metabolism,
in particular glucose oxidation. This may be achieved by the administration
of glucose and insulin, a concept which has received renewed attention[7]
following encouraging clinical findings with glucose-insulin-potassium
(GIK) treatment, from a metaanalysis[8] and a prospective, randomized
clinical trial,[9] in patients with acute myocardial
infarction. Interestingly, recent experimental data suggest that
GIK therapy may also help maintain systolic and diastolic ventricular
function following transient ischemia that does not produce irreversible
myocardial injury.[10] A likely mechanism
for the benefits of GIK therapy is reduced free fatty acid metabolism
(through decreases in both circulating fatty acids and myocardial
fatty acid uptake), although other mechanisms such as increased
glycolytic ATP synthesis may also contribute.[7]
Alternatively, glucose oxidation may be increased by pharmacological
stimulation of the rate-limiting enzyme in this process, the pyruvate
dehydrogenase complex.[5] For example, dichloroacetate,
which stimulates pyruvate dehydrogenase activity, has been shown
to enhance glucose oxidation and thereby increase cardiac work
and efficiency during reperfusion of isolated hearts subjected
to global ischemia.[11] However, a low potency
and short in vivo half-life limit the clinical utility of dichloroacetate.[5]
Another approach to alter the balance between fatty acid oxidation
and glucose oxidation beneficially is to inhibit key enzymes in
the former process. The antianginal drug trimetazidine has been
shown recently to inhibit mitochondrial long-chain 3-ketoacyl
coenzyme A thiolase, a critical enzyme in fatty acid oxidation,
and thereby increase glucose oxidation.[12]
Presumably through such an effect on myocardial metabolism, trimetazidine
has also been shown to attenuate the intracellular acidosis and
the intracellular accumulation of sodium that develop in isolated
hearts during ischemia, and to improve the postischemic recovery
of systolic and diastolic function.[13] It
is clear, therefore, that myocardial injury and dysfunction during
ischemia and reperfusion may be attenuated through a variety of
interventions targeted at myocardial metabolism.
Ionic approaches
Ischemia is associated with a disruption of myocardial ionic homeostasis,
which results in the intracellular accumulation of sodium and
calcium and the extracellular accumulation of potassium. These
ionic disturbances, some of which (in particular the intracellular
accumulation of calcium, or ‘calcium overload’) may be further
exacerbated during early reperfusion, have been linked causally
with the unfavorable consequences of ischemia and reperfusion,
such as arrhythmias, contractile dysfunction, and myocardial necrosis.[14]
As such, ion translocating proteins have been favored targets
for putative cardioprotective agents. One ion translocating protein
which has received particular attention in recent years is the
sodium/hydrogen exchanger (NHE), which is activated during ischemia
and reperfusion[15] and is believed to contribute
to the intracellular accumulation of sodium, and consequently
calcium, in myocardial cells (Figure 2).[16]
Figure 2. Putative mechanism of calcium overload during
myocardial ischemia and reperfusion. Increased activity of the
sodium/hydrogen exchanger (NHE), primarily as a result of intracellular
acidosis, occurs concomitantly with inhibition of the sodium/potassium
pump (Na/K pump) and leads to the intracellular accumulation of
sodium. This in turn produces calcium influx through reverse-mode
sodium/calcium exchange (NCE).
Since the mid-1990s, several new drugs that selectively
target the cardiac NHE and inhibit its activity have been developed
and shown to attenuate severe arrhythmias, limit the extent of
myocardial necrosis (ie, infarct size), and preserve myocardial
contractile function in a variety of models of ischemia and reperfusion.[16,17]
Interestingly, relative to ischemic preconditioning, the magnitude
of the protection afforded by NHE inhibition appears to be comparable
or, if the ischemic period is prolonged, even greater.[18–20]
One of the new NHE inhibitors, cariporide, has also been tested
clinically in two recent studies. Rupprecht et al[21]
have obtained data from a cohort of 100 patients with acute
anterior myocardial infarction, which suggested that cariporide
could preserve tissue viability and contractile function when
used as in conjunction with direct coronary angioplasty. These
encouraging findings need to be confirmed by larger clinical studies.
Théroux et al[22] have determined the effects
of cariporide in a much larger, combined phase-II/phase-III study
(the GUARDIAN [Guard During Ischemia Against Necrosis] study),
which involved patients in a variety of high-risk ischemic situations.
The results of this study indicated no significant benefit of
cariporide in patients with unstable angina or non-ST-elevation
myocardial infarction and those undergoing a high-risk percutaneous
coronary intervention.[22] However, in patients
undergoing high-risk coronary artery bypass graft surgery, there
was a significant reduction in the primary endpoint (incidence
of death or myocardial infarction), with the highest dose of cariporide
(12.1% [89/734] vs. 16.2% [120/743] in the placebo group, P =
0.03).[22] These data suggest that the experimental
promise of NHE inhibition may be fulfilled clinically, at least
in the setting of coronary artery bypass graft surgery.
The interest in the intracellular accumulation of sodium and calcium
as potential causal factors in ischemia and reperfusion-induced
injury has also led to recent studies with pharmacological inhibitors
of other ion translocating proteins, such as the sodium/calcium
exchanger[23] and the sodium/bicarbonate symporter,[24]
in cellular models of simulated ischemia. However, there
is inadequate whole heart and in vivo data with such agents and
they have not reached the stage of clinical evaluation.
Signaling
Until recently, for many cardiovascular investigators, ‘signaling’
was something they occasionally did while driving. However, the
burgeoning interest in the mechanisms that underlie the powerful
cardioprotective adaptation that is initiated by ischemic preconditioning[25]
has encouraged an intense interest in the intracellular signaling
pathways that operate in myocardial cells, particularly those
that are mediated through protein phosphorylation reactions catalyzed
by enzymes known as protein kinases.
There appears to be general agreement that protein kinase C plays
a pivotal role in initiating the adaptive signaling mechanisms
that underlie ischemic preconditioning.[26–28]
However, distal components of the relevant signaling pathways
have not been definitively identified. For example, considerable
confusion surrounds the role p38 mitogen-activated protein kinase
(p38 MAPK) in preconditioning,[29] since p38
MAPK has been suggested to be a critical mediator of both the
preconditioning response[30,31] and ischemic
injury.[32–34]
The identity of the ‘end effector’ of ischemic preconditioning
also remains unclear. Although the mitochondrial ATP-sensitive
potassium channel had been suggested to serve such a function,[35]
more recent evidence indicates a more proximal, triggering role
for this channel in the activation of the relevant signaling pathways.[36]
Interest in the signaling pathways that determine myocardial susceptibility
to injury during ischemia and reperfusion has also included those
pathways that may regulate myocyte loss through programmed cell
death, or apoptosis. In this context, experiments in a variety
of models have suggested that activation of antiapoptotic pathways,
such as those mediated via extracellular signal-regulated kinase
(also known as p42/p44 MAPK)[37] and Akt/protein
kinase B,[38,39] may provide functional benefit
during ischemia and reperfusion, by preserving myocardial viability.
Indeed, it has been suggested that activation of such antiapoptotic
pathways by growth factors may present a promising new approach
to the attenuation of reperfusion-induced injury.[40]
It is likely that research into the intracellular signaling pathways
that mediate ischemic preconditioning and those that modulate
myocardial susceptibility to injury and dysfunction during ischemia
and reperfusion (either by mimicking or independently of preconditioning)
will continue unabated for some years to come. The hope is that
such work will identify critical pathways which subsequently can
be exploited to therapeutic benefit, through either pharmacological
or genetic manipulation.
Conclusion
Exciting new data continue to emerge from the search for metabolic,
ionic, and signaling strategies for the protection of the myocardium
during ischemia and reperfusion. Although these strategies have
been discussed under separate headings in this article, it should
be noted that the cellular processes manipulated by such strategies
impact upon each other. For example, altered myocardial metabolism
can undoubtedly modulate cellular ionic balance (eg, by altering
the activity of ion translocating proteins) and signal transduction
(eg, by regulating protein phosphorylation reactions). Similarly,
activation or inhibition of targeted signaling molecules can produce
responses by positively or negatively affecting the activities
of metabolic enzymes or ion translocating proteins. Greater understanding
of the crossregulatory mechanisms that operate between distinct
cellular processes and the consequences of their manipulation
during ischemia and reperfusion is likely to lead the way in the
development of effective new cardioprotective therapies which
will fulfill an important void in the physicians’ arsenal in the
battle against ischemic heart disease.
REFERENCES
- Corrected and republished in:
 |
Eur Heart J 1997 Dec;18(12):1231-48 |
The burden of cardiovascular diseases mortality in Europe.
Task Force of the European Society of Cardiology on Cardiovascular
Mortality and Morbidity Statistics in Europe.
Sans S, Kesteloot H, Kromhout D.
Institute of Health Studies, Barcelona, Spain.
PMID: 9458415 [PubMed - indexed for MEDLINE]
-
Time to treatment of acute myocardial infarction revisited.
Cannon CP.
Cardiovascular Division, Brigham and Women's Hospital, Boston,
MA 02115, USA.
Time to treatment in acute myocardial infarction (MI) has been
of great interest since the advent of thrombolytic therapy.
The paradigm that has emerged is that rapid achievement of reperfusion,
with either thrombolysis or primary angioplasty, minimizes infarct
size, reduces the degree of left ventricular dysfunction, and
improves survival. Recent studies have confirmed the benefit
of reducing time to treatment with thrombolysis (between onset
of pain to initiation of thrombolysis) and that of more rapid
drug reperfusion time with more aggressive thrombolytic regimens
(between initiation of thrombolytic therapy and actual achievement
of reperfusion). Furthermore, their effects are additive (and
in some cases synergistic), confirming the benefit of rapid
reperfusion. For primary angioplasty, the same relationship
has been observed: More rapid treatment seems to be associated
with improved outcome. The "door-to-balloon" time
is a major determinant of overall time to reperfusion and, as
such, is a crucial component of the overall strategy. This paradigm
can also be extended to the prehospital phase of treating acute
MI in two ways: 1) for patients to rapidly identify the symptoms
of acute MI and to present earlier to the hospital is critical
in reducing overall time to treatment and 2) in emergency medical
care, rapid identification of MI patients, electrocardiographic
monitoring, and defibrillation as needed for ventricular arrhythmias
has been shown to be lifesaving. Thus, time to treatment in
the current era of aggressive management of acute MI extends
far beyond the original description to every aspect of acute
MI care.
Publication Types:
|
Review
|
|
Review, academic |
PMID: 10091021 [PubMed - indexed for MEDLINE]
-
-
Reperfusion induced injury: manifestations, mechanisms, and
clinical relevance.
Hearse DJ, Bolli R.
Cardiovascular Research, Rayne Institute, St Thomas's Hospital,
London, United Kingdom.
Although reperfusion is an absolute prerequisite for the survival
of ischaemic tissue, it is not necessarily without hazard. Many
(but not all) cardiologists are of the opinion that some component
of reperfusion may be detrimental and able to inflict injury
over and above that attributable to the ischaemia. In this article
we define four sequelae of reperfusion which might be designated
as "reperfusion injury", we identify possible underlying
mechanisms, and consider whether any of these forms of reperfusion
injury are of clinical relevance.
Publication Types:
|
Review
|
|
Review, tutorial |
PMID: 1571929 [PubMed - indexed for MEDLINE]
-
-
Glucose for the heart.
Depre C, Vanoverschelde JL, Taegtmeyer H.
Department of Internal Medicine, Division of Cardiology, University
of Texas Houston Medical School 77030, USA.
Publication Types:
|
Review
|
|
Review, tutorial |
PMID: 9927407 [PubMed - indexed for MEDLINE]
-
[Treating ischemic heart disease by pharmacologically improving
cardiac energy metabolism].
[Article in French]
Lopaschuk GD.
University of Alberta, Edmonton, Canada.
THE ISCHEMIA-ENERGY RELATIONSHIP: A growing number of experimental
and clinical studies have demonstrated that improving heart
energy metabolism can have a positive effect on the consequences
of myocardial ischemia. By enhancing myocardial carbohydrate
metabolism, it is possible to improve cardiac function and/or
limit tissue damage. It is known however that a high level of
circulating fatty acids reduces myocardial glucose metabolism,
a situation which is observed in most cases of symptomatic myocardial
ischemia and which can further aggravate ischemic damage. PHARMACOLOGICAL
OPTIONS: A certain number of pharmacological possibilities are
available for stimulating glucose metabolism directly or indirectly
by inhibiting fatty acid beta-oxidation. The effect of trimetazidine
is based on this action and we have recently demonstrated in
isolated perfused rat hearts with high concentrations of fatty
acids that trimetazidine stimulates glucose oxidation. Clinical
studies have also demonstrated that trimetazidine has a protective
effect on heart tissue during episodes of myocardial ischemia.
Pharmacologically improving cardiac energy metabolism with drugs
such as trimetazidine could be a new promising approach to the
treatment of cardiovascular diseases.
PMID: 9893703 [PubMed - indexed for MEDLINE]-
-
Energy substrate metabolism, myocardial ischemia, and targets
for pharmacotherapy.
Taegtmeyer H, King LM, Jones BE.
University of Texas-Houston Medical School, Department of Medicine,
77030, USA.
Myocardial ischemia is essentially a metabolic event. In this
review we will try to distill the essence of a complex series
of molecular reactions triggered by the sudden reduction or
cessation of blood flow to the heart. We recognize that it is
difficult to describe even simple metabolic changes occurring
in ischemia without a brief recap of pathways of energy transfer
in the normal myocardium. We will therefore begin with a description
of the energy substrate supply to a system that is best defined
as the heart's remarkable ability for efficient conversion of
chemical into mechanical energy. At the core of the system are
rates of oxidative phosphorylation of adenosine diphosphate
(ADP) that exactly match rates of adenosine triphosphate (ATP)
hydrolysis. We will then describe the consequences of a sudden
interruption to this balance, namely ischemia. At the same time
we will explore metabolic strategies that may be employed to
lessen the consequences of ischemia on contractile function,
highlighting areas of future research and clinical investigation.
The review is not meant to be comprehensive. Its main aim is
to discuss the concept of pharmacotherapy as an intervention
in altered cellular metabolism, akin to the concept of reperfusion
therapy as an intervention in obstructed coronary arteries.
Publication Types:
|
Review
|
|
Review, tutorial |
PMID: 9737487 [PubMed - indexed for MEDLINE]
-
-
Comment in:
|
Circulation. 1997 Aug 19;96(4):1074-7
|
|
Circulation. 1998 Jun 9;97(22):2278-9 |
Glucose-insulin-potassium therapy for treatment of acute
myocardial infarction: an overview of randomized placebo-controlled
trials.
Fath-Ordoubadi F, Beatt KJ.
Medical Research Council Clinical Sciences Centre, Postgraduate
Medical School, and Department of Cardiology, Hammersmith Hospital,
London, UK. 100412.3302@compuserve.com
BACKGROUND: Glucose-insulin-potassium (GIK) therapy has been
advocated for the treatment of acute myocardial infarction.
However, the results from the clinical trials have been inconclusive,
largely because of the small number of patients recruited and
discrepancies between protocols used in these studies. METHOD
AND RESULTS: A systematic MEDLINE search for all the randomized
placebo-controlled studies of GIK therapy in acute myocardial
infarction was made, and a meta-analysis of the mortality data
was performed. Fifteen trials were identified, 5 were excluded
because of poor randomization, and 1 was excluded because recruitment
was limited to diabetic patients. The 9 remaining trials with
a total of 1932 patients were included in the analysis. Hospital
mortality was reduced from 21% (205 of 972 patients) in the
placebo group to 16.1% (154 of 956) in the GIK group (P=.004;
odds ratio, 0.72; 95% confidence interval [CI], 0.57 to 0.90).
The proportional mortality reduction was 28% (CI, 10% to 43%).
The number of lives saved per 1000 patients treated was 49 (95%
CI, 14 to 83). CONCLUSIONS: The findings indicate that GIK therapy
may have an important role in reducing the in-hospital mortality
after acute myocardial infarction. The value of this therapy
in the era of thrombolysis and acute revascularization by primary
angioplasty can be fully resolved only by conducting a large
randomized mortality study.
Publication Types:
|
Meta-analysis |
PMID: 9286943 [PubMed - indexed for MEDLINE]
-
-
Comment in:
|
Circulation. 1997 Aug 19;96(4):1074-7
|
|
Circulation. 1998 Jun 9;97(22):2278-9 |
Glucose-insulin-potassium therapy for treatment of acute
myocardial infarction: an overview of randomized placebo-controlled
trials.
Fath-Ordoubadi F, Beatt KJ.
Medical Research Council Clinical Sciences Centre, Postgraduate
Medical School, and Department of Cardiology, Hammersmith Hospital,
London, UK. 100412.3302@compuserve.com
BACKGROUND: Glucose-insulin-potassium (GIK) therapy has been
advocated for the treatment of acute myocardial infarction.
However, the results from the clinical trials have been inconclusive,
largely because of the small number of patients recruited and
discrepancies between protocols used in these studies. METHOD
AND RESULTS: A systematic MEDLINE search for all the randomized
placebo-controlled studies of GIK therapy in acute myocardial
infarction was made, and a meta-analysis of the mortality data
was performed. Fifteen trials were identified, 5 were excluded
because of poor randomization, and 1 was excluded because recruitment
was limited to diabetic patients. The 9 remaining trials with
a total of 1932 patients were included in the analysis. Hospital
mortality was reduced from 21% (205 of 972 patients) in the
placebo group to 16.1% (154 of 956) in the GIK group (P=.004;
odds ratio, 0.72; 95% confidence interval [CI], 0.57 to 0.90).
The proportional mortality reduction was 28% (CI, 10% to 43%).
The number of lives saved per 1000 patients treated was 49 (95%
CI, 14 to 83). CONCLUSIONS: The findings indicate that GIK therapy
may have an important role in reducing the in-hospital mortality
after acute myocardial infarction. The value of this therapy
in the era of thrombolysis and acute revascularization by primary
angioplasty can be fully resolved only by conducting a large
randomized mortality study.
Publication Types:
|
Meta-analysis |
PMID: 9286943 [PubMed - indexed for MEDLINE]
-
-
Metabolic modulation of acute myocardial infarction. The
ECLA (Estudios Cardiologicos Latinoamerica) Collaborative Group.
Diaz R, Paolasso EA, Piegas LS, Tajer CD, Moreno MG, Corvalan
R, Isea JE, Romero G.
Department of Cardiology, Instituto Cardiovascular de Rosario,
Rosario, Argentina.
BACKGROUND: Several trials have been performed in the past using
glucose, insulin, and potassium infusion (GIK) for the treatment
of acute myocardial infarction (AMI). Because of continuing
uncertainty about the potential role of this therapeutic intervention,
we conducted a randomized trial to evaluate the impact of a
GIK solution during the first hours of AMI. METHODS AND RESULTS:
Four hundred seven patients with suspected AMI admitted within
24 hours of symptoms onset were enrolled. In a ratio of 2:1,
268 patients were allocated to receive GIK (high- or low-dose)
and 139 to receive control. Phlebitis and serum changes in the
plasma concentration of glucose or potassium were observed more
often with GIK. A trend toward a nonsignificant reduction in
major and minor in-hospital events was observed in patients
allocated to GIK. In 252 patients (61.9%) treated with reperfusion
strategies, a statistically significant reduction in mortality
(relative risk [RR] 0.34; 95% CI: 0.15 to 0.78; 2P=0.008) and
a consistent trend toward fewer in-hospital events in the GIK
group were observed. CONCLUSIONS: Our results confirm that a
metabolic modulation strategy in the first hours of an AMI is
feasible, applicable worldwide, and has mild side effects. The
statistically significant mortality reduction in patients who
underwent a reperfusion strategy might have important implications
for the management of AMI patients. It is now essential to perform
a large-scale trial to reliably determine the magnitude of benefit.
Publication Types:
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Clinical trial
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Multicenter study
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Randomized controlled trial |
PMID: 9867443 [PubMed - indexed for MEDLINE]
-
Glucose-insulin-potassium preserves systolic and diastolic
function in ischemia and reperfusion in pigs.
Zhu P, Lu L, Xu Y, Greyson C, Schwartz GG.
Cardiovascular Research Institute, University of California,
San Francisco, California 94121, USA.
Clinical and experimental studies have suggested benefit of
treatment with intravenous glucose-insulin-potassium (GIK) in
acute myocardial infarction. However, patients hospitalized
with acute coronary syndromes often experience recurrent myocardial
ischemia without infarction that may cause progressive left
ventricular (LV) dysfunction. This study tested the hypothesis
that anticipatory treatment with GIK attenuates both systolic
and diastolic LV dysfunction resulting from ischemia and reperfusion
without infarction in vivo. Open-chest, anesthetized pigs underwent
90 min of moderate regional ischemia (mean subendocardial blood
flow 0.3 ml x g(-1) x min(-1)) and 90 min reperfusion. Eight
pigs were treated with GIK (300 g/l glucose, 50 U/l insulin,
and 80 meq/l KCl; infused at 2 ml x kg(-1) x h(-1)) beginning
30 min before ischemia and continuing through reperfusion. Eight
untreated pigs comprised the control group. Regional LV wall
area was measured with orthogonal pairs of sonomicrometry crystals.
GIK significantly increased myocardial glucose uptake and lactate
release during ischemia. After reperfusion, indexes of regional
systolic function (external work and fractional systolic wall
area reduction), regional diastolic function (maximum rate of
diastolic wall area expansion), and global LV function (LV positive
and negative maximum rate of change in pressure with respect
to time) recovered to a significantly greater extent in GIK-treated
pigs than in control pigs (all P < 0.05). The findings suggest
that the clinical utility of GIK may extend beyond treatment
of acute myocardial infarction to anticipatory metabolic protection
of myocardium in patients at risk for recurrent episodes of
ischemia.
PMID: 10666092 [PubMed - indexed for MEDLINE]-
Cardiac efficiency is improved after ischemia by altering
both the source and fate of protons.
Liu B, Clanachan AS, Schulz R, Lopaschuk GD.
Department of Pediatrics, University of Alberta, Edmonton, Canada.
Cardiac efficiency is decreased in hearts after severe ischemia.
We determined whether reducing the production of H+ from glucose
metabolism or inhibiting the clearance of H+ via Na(+)-H+ exchange
could increase cardiac efficiency during reperfusion. This was
achieved using dichloroacetate (DCA) to stimulate glucose oxidation
and 5-(N,N-dimethyl)-amiloride (DMA) to inhibit Na(+)-H+ exchange,
respectively. Isolated working rat hearts were subjected to
30 minutes of global ischemia and 60 minutes of reperfusion.
Glycolysis and oxidation rates of glucose, lactate, and palmitate
were measured. Recovery of cardiac work, O2 consumption (MVO2),
and rates of acetyl-coenzyme A and ATP production during reperfusion
were determined. After ischemia, cardiac work recovered to 35
+/- 5% of preischemic values in control hearts (n = 23), although
MVO2, tricarboxylic acid (TCA) cycle activity, and ATP production
from glycolysis and oxidative metabolism rapidly recovered to
preischemic levels. This decrease in cardiac efficiency was
accompanied by a substantial production of H+ from glucose metabolism
DCA caused a 2.2-fold increase in glucose oxidation, a 46 +/-
17% decrease in H+ production, a 1.6-fold increase in cardiac
efficiency, and a 2.0-fold increase in cardiac work during reperfusion
(n = 17). Inhibition of Na(+)-H+ exchange with DMA did not alter
TCA cycle activity and ATP production rates but did result in
a 1.8-fold increase in cardiac efficiency and a 1.7-fold increase
in cardiac work (n = 12). These data show that cardiac efficiency
and the contractile function after ischemia can be improved
by either reducing the rate of H+ production from glucose metabolism
during reperfusion or inhibiting the clearance of H+ via Na(+)-H+
exchange. Our data suggest that an increased requirement for
ATP to restore ischemia-reperfusion-induced alterations in ion
homeostasis contributes to the decrease in cardiac efficiency
and contractile function after ischemia.
PMID: 8888686 [PubMed - indexed for MEDLINE]-
-
Comment in:
|
Circ Res. 2000 Mar 17;86(5):487-9 |
The antianginal drug trimetazidine shifts cardiac energy
metabolism from fatty acid oxidation to glucose oxidation by
inhibiting mitochondrial long-chain 3-ketoacyl coenzyme A thiolase.
Kantor PF, Lucien A, Kozak R, Lopaschuk GD.
Cardiovascular Research Group and the Division of Pediatric
Cardiology, University of Alberta, Edmonton, Canada.
Trimetazidine is a clinically effective antianginal agent that
has no negative inotropic or vasodilator properties. Although
it is thought to have direct cytoprotective actions on the myocardium,
the mechanism(s) by which this occurs is as yet undefined. In
this study, we determined what effects trimetazidine has on
both fatty acid and glucose metabolism in isolated working rat
hearts and on the activities of various enzymes involved in
fatty acid oxidation. Hearts were perfused with Krebs-Henseleit
solution containing 100 microU/mL insulin, 3% albumin, 5 mmol/L
glucose, and fatty acids of different chain lengths. Both glucose
and fatty acids were appropriately radiolabeled with either
(3)H or (14)C for measurement of glycolysis, glucose oxidation,
and fatty acid oxidation. Trimetazidine had no effect on myocardial
oxygen consumption or cardiac work under any aerobic perfusion
condition used. In hearts perfused with 5 mmol/L glucose and
0.4 mmol/L palmitate, trimetazidine decreased the rate of palmitate
oxidation from 488+/-24 to 408+/-15 nmol x g dry weight(-1)
x minute(-1) (P<0.05), whereas it increased rates of glucose
oxidation from 1889+/-119 to 2378+/-166 nmol x g dry weight(-1)
x minute(-1) (P<0.05). In hearts subjected to low-flow ischemia,
trimetazidine resulted in a 210% increase in glucose oxidation
rates. In both aerobic and ischemic hearts, glycolytic rates
were unaltered by trimetazidine. The effects of trimetazidine
on glucose oxidation were accompanied by a 37% increase in the
active form of pyruvate dehydrogenase, the rate-limiting enzyme
for glucose oxidation. No effect of trimetazidine was observed
on glycolysis, glucose oxidation, fatty acid oxidation, or active
pyruvate dehydrogenase when palmitate was substituted with 0.8
mmol/L octanoate or 1.6 mmol/L butyrate, suggesting that trimetazidine
directly inhibits long-chain fatty acid oxidation. This reduction
in fatty acid oxidation was accompanied by a significant decrease
in the activity of the long-chain isoform of the last enzyme
involved in fatty acid beta-oxidation, 3-ketoacyl coenzyme A
(CoA) thiolase activity (IC(50) of 75 nmol/L). In contrast,
concentrations of trimetazidine in excess of 10 and 100 micromol/L
were needed to inhibit the medium- and short-chain forms of
3-ketoacyl CoA thiolase, respectively. Previous studies have
shown that inhibition of fatty acid oxidation and stimulation
of glucose oxidation can protect the ischemic heart. Therefore,
our data suggest that the antianginal effects of trimetazidine
may occur because of an inhibition of long-chain 3-ketoacyl
CoA thiolase activity, which results in a reduction in fatty
acid oxidation and a stimulation of glucose oxidation.
PMID: 10720420 [PubMed - indexed for MEDLINE]
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Comment in:
|
Cardiovasc Res. 2000 Sep;47(4):637-9 |
Changes in intracellular sodium and pH during ischaemia-reperfusion
are attenuated by trimetazidine. Comparison between low- and
zero-flow ischaemia.
El Banani H, Bernard M, Baetz D, Cabanes E, Cozzone P, Lucien
A, Feuvray D.
Laboratoire de Physiologie Cellulaire, Universite Paris XI,
Orsay, France.
OBJECTIVE: The aim of this study was to investigate whether
trimetazidine (TMZ; 10(-6)M), which has been shown to inhibit
fatty acid oxidation, reduces the ionic imbalance induced by
ischaemia and reperfusion, especially through an attenuation
in intracellular changes in H(+) and Na(+). METHODS: Isovolumic
rat hearts receiving 5.5 mM glucose and 1.2 mM palmitate as
metabolic substrates were exposed to zero-flow ischaemia (TI)
or low-flow ischaemia (LFI - coronary flow decreased by an average
of 90%) (30 min at 37 degrees C) and then reperfused. 23Na nuclear
magnetic resonance (NMR) spectroscopy was used to monitor intracellular
Na(+) (Na(+)(i)) and 31P NMR spectroscopy was used to monitor
intracellular pH (pH(i)). RESULTS: During LFI the major effect
of TMZ was a significant reduction in intracellular acidosis,
whereas during TI the main effect of TMZ was a significant reduction
in Na(+)(i) gain. In addition, the further gain in Na(+)(i)
that occurred during the first minutes of reperfusion following
TI, and to a far lesser extent following LFI, was suppressed
in TMZ-treated hearts and also suppressed when hearts were perfused
without fatty acid. In both LFI and TI, TMZ-induced attenuation
of ionic imbalance was associated with a significantly improved
recovery of ventricular function on reperfusion, as assessed
by a lower increase in diastolic pressure and an increased recovery
of developed pressure. CONCLUSION: Our data provide evidence
that specific myocardial metabolic modulation plays a significant
role in reducing ionic imbalance during ischaemia and reperfusion.
PMID: 10974217 [PubMed - indexed for MEDLINE]
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-
The contribution of ionic imbalance to ischemia/reperfusion-induced
injury.
Pierce GN, Czubryt MP.
Ion Transport Laboratory, St. Boniface General Hospital Research
Centre, Winnipeg, Manitoba, Canada.
Recent data from a number of independent laboratories have implicated
ionic disturbances within the myocardium as being a critical
contributory factor in injury to the heart during ischemia/reperfusion.
The present treatise discusses the data supporting a role for
Ca2+, Na+ and K+ in ischemic/reperfusion injury. The mechanism
whereby intracellular ionic homeostasis becomes altered is the
focus of the review. In particular, the evidence in support
of an involvement of abnormal ion movements through Na+/H+ exchange,
Na+ channels and the ATP-sensitive K+ channel in ischemic/reperfusion
injury is advanced.
Publication Types:
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Review
|
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Review, academic |
PMID: 7760373 [PubMed - indexed for MEDLINE]
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The acid test: Na+/H+ exchange and its inhibitors in acute
myocardial ischaemia.
Avkiran M.
The Rayne Institute, St Thomas' Hospital, London, U.K.
PMID: 10381850 [PubMed - indexed for MEDLINE]-
-
Rational basis for use of sodium-hydrogen exchange inhibitors
in myocardial ischemia.
Avkiran M.
Cardiovascular Research, The Rayne Institute, St. Thomas' Hospital,
London, United Kingdom.
The cardiac sarcolemmal Na+/H+ exchanger extrudes intracellular
H+ in exchange for Na+, in an electroneutral process. Of the
6 mammalian exchanger isoforms identified to date, the Na+/H+
exchanger (NHE)-1 is believed to be the molecular homolog of
the sarcolemmal Na+/H+ exchanger. The exchanger is activated
primarily by a reduction in intracellular pH (intracellular
acidosis), although such activation is subject to modulation
by a variety of endogenous mediators (e.g., catecholamines,
thrombin, endothelin) through receptor-mediated mechanisms.
A large body of preclinical evidence now suggests that inhibition
of the sarcolemmal Na+/H+ exchanger attenuates many of the unfavorable
consequences of acute myocardial ischemia and reperfusion. Much
of this evidence has been obtained with recently developed potent,
selective inhibitors of the exchanger, such as HOE-642 (cariporide)
and its structurally related congener HOE-694, in studies using
both in vitro and in vivo models of ischemia and reperfusion
in a variety of species. The data from these studies indicate
that Na+/H+ exchange inhibition leads to a decreased susceptibility
to severe ventricular arrhythmia, attenuates contractile dysfunction,
and limits tissue necrosis (i.e., decreases infarct size) during
myocardial ischemia and reperfusion. Such protection is likely
to arise, at least in part, from attenuation of "Ca2+ overload,"
which has been linked causally with all of these pothologic
phenomena. The consistent and marked cardioprotective benefit
that has been observed with cariporide and related compounds
in preclinical studies suggests that Na+/H+ exchange inhibition
may represent a novel and effective approach to the treatment
of acute myocardial ischemia in humans.
Publication Types:
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Review
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|
Review, tutorial |
PMID: 10482175 [PubMed - indexed for MEDLINE]
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-
The myocardial Na(+)-H(+) exchange: structure, regulation,
and its role in heart disease.
Karmazyn M, Gan XT, Humphreys RA, Yoshida H, Kusumoto K.
Department of Pharmacology and Toxicology, University of Western
Ontario, London, Ontario, Canada. mkarm@julian.uwo.ca
The Na(+)-H(+) exchange (NHE) is a major mechanism by which
the heart adapts to intracellular acidosis during ischemia and
recovers from the acidosis after reperfusion. There are at least
6 NHE isoforms thus far identified with the NHE1 subtype representing
the major one found in the mammalian myocardium. This 110-kDa
glycoprotein extrudes protons concomitantly with Na(+) influx
in a 1:1 stoichiometric relationship rendering the process electroneutral,
and its activity is regulated by numerous factors, including
phosphorylation-dependent processes. There is convincing evidence
that NHE mediates tissue injury during ischemia and reperfusion,
which probably reflects the fact that under conditions of tissue
stress, including ischemia, Na(+)-K(+) ATPase is inhibited,
thereby limiting Na(+) extrusion, resulting in an elevation
in [Na(+)](i). The latter effect, in turn, will increase [Ca(2+)](i)
via Na(+)-Ca(2+) exchange. In addition, NHE1 mRNA expression
is elevated in response to injury, which may further contribute
to the deleterious consequence of pathological insult. Extensive
studies using NHE inhibitors have consistently shown protective
effects against ischemic and reperfusion injury in a large variety
of experimental models and has led to clinical evaluation of
NHE inhibition in patients with coronary artery disease. Emerging
evidence also implicates NHE1 in other cardiac disease states,
and the exchanger may be particularly critical to postinfarction
remodeling responses resulting in development of hypertrophy
and heart failure.
Publication Types:
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Review
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|
Review, tutorial |
PMID: 10532945 [PubMed - indexed for MEDLINE]
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Na+/H+ exchanger activity does not contribute to protection
by ischemic preconditioning in the isolated rat heart.
Shipolini AR, Yokoyama H, Galinanes M, Edmondson SJ, Hearse
DJ, Avkiran M.
Cardiovascular Research, The Rayne Institute, St Thomas' Hospital,
London, UK.
BACKGROUND: Despite evidence that pharmacological inhibition
of the Na+/H+ exchanger (NHE) is cardioprotective, activation
of NHE has been proposed as a protective mechanism of ischemic
preconditioning (PC). METHODS AND RESULTS: In isolated rat ventricular
myocytes (n=8 to 11 per group) loaded with the fluorescent pH
indicator C-SNARF-1, we showed that HOE-642 (HOE) was a potent
inhibitor of the sarcolemmal NHE (80% inhibition at 1 micromol/L);
such inhibition was readily reversible by washout of the drug.
We confirmed that 1 micromol/L HOE produces significant and
reversible inhibition of NHE activity in isolated rat hearts
as well (n=4), and in this model, we tested (n=8 per group)
whether the presence of the drug during (1) the prolonged period
of ischemia (40 or 60 minutes) or (2) the preceding brief periods
of PC ischemia (3 minutes plus 5 minutes) modulates the protective
efficacy of PC. In protocol 1, HOE was infused for 5 minutes
immediately before the prolonged ischemic period. With 40 minutes
of prolonged ischemia, the postischemic recovery of left ventricular
developed pressure (LVDP) was 15+/-2% in controls and was improved
to 45+/-7% with HOE (P<.05), 55+/-5% with PC (P<.05),
and 68+/-2% with PC+HOE (P<.05 versus all groups). When the
prolonged ischemic period was extended to 60 minutes, an additive
effect of PC and HOE was readily apparent and LVDP recovery
with PC+HOE (66+/-2%) was almost double that observed with HOE
(37+/-4%) or PC (34+/-5%) alone (P<.05). In protocol 2, HOE
was infused for 3 minutes immediately before each episode of
PC ischemia and was subsequently washed out before a 40-minute
prolonged ischemic period (HOE+PC). LVDP recovery was 34+/-4%
in controls and was improved to 57+/-2% with PC (P<.05) and
55+/-3% with HOE+PC (P<.05). Improved recovery of LVDP was
matched by reduced creatine kinase leakage in all cases. CONCLUSIONS:
Because coadministration of HOE (at a concentration sufficient
to inhibit NHE activity) did not reduce the efficacy of PC in
either protocol, we conclude that NHE activity does not contribute
to the cardioprotective actions of PC. On the contrary, NHE
inhibition during the prolonged ischemic period may enhance
the protection afforded by PC.
PMID: 9396463 [PubMed - indexed for MEDLINE]-
Inhibition of the Na(+)/H(+) exchanger confers greater cardioprotection
against 90 minutes of myocardial ischemia than ischemic preconditioning
in dogs.
Gumina RJ, Buerger E, Eickmeier C, Moore J, Daemmgen J, Gross
GJ.
Department of Pharmacology and Toxicology, Medical College of
Wisconsin, Milwaukee 53226, USA.
BACKGROUND: This study compared the efficacy of ischemic preconditioning
(IPC) and sodium-hydrogen exchanger (NHE)-1 inhibition to reduce
infarct size (IS) induced by a 90-minute ischemic insult and
examined the interaction between NHE-1 inhibition and IPC. METHODS
AND RESULTS: In a canine infarct model, either IPC, produced
by 1 or four 5-minute coronary artery occlusions, or the specific
NHE-1 inhibitor BIIB 513, 0.75 or 3.0 mg/kg, was administered
15 minutes before either a 60- or 90-minute coronary artery
occlusion followed by 3 hours of reperfusion. IS was determined
by TTC staining and expressed as a percentage of the area at
risk (IS/AAR). Although both IPC and BIIB 513 at 0.75 mg/kg
produced comparable and significant reductions in IS/AAR in
the 60-minute occlusion model, insignificant reductions in IS/AAR
were observed in the 90-minute occlusion model. However, BIIB
513 at 3.0 mg/kg markedly reduced IS in both models (P<0.05).
Next, to examine the interaction between NHE-1 blockade and
IPC, BIIB 0.75 mg/kg was administered either before IPC or during
the washout phase of IPC before 90 minutes of coronary artery
occlusion. Both combinations resulted in a greater-than-additive
reduction in IS/AAR (P<0.05). CONCLUSIONS: These data demonstrate
that although IPC and NHE-1 inhibition provide comparable protection
against 60 minutes of myocardial ischemia, NHE-1 inhibition
is more efficacious than IPC at protecting against a 90-minute
ischemic insult. Furthermore, the combination of NHE-1 inhibition
and IPC produces a greater-than-additive reduction in IS/AAR,
suggesting either that NHE activity limits the efficacy of IPC
or that different mechanisms are involved in the cardioprotective
effect of IPC and NHE-1 inhibition.
PMID: 10604890 [PubMed - indexed for MEDLINE]-
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Protection of the myocardium during ischemia and reperfusion
: Na(+)/H(+) exchange inhibition versus ischemic preconditioning.
Avkiran M.
Publication Types:
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Editorial |
PMID: 10604882 [PubMed - indexed for MEDLINE]
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-
Comment in:
|
Circulation. 2000 Jun 27;101(25):2874-6 |
Cardioprotective effects of the Na(+)/H(+) exchange inhibitor
cariporide in patients with acute anterior myocardial infarction
undergoing direct PTCA.
Rupprecht HJ, vom Dahl J, Terres W, Seyfarth KM, Richardt
G, Schultheibeta HP, Buerke M, Sheehan FH, Drexler H.
2nd Department of Internal Medicine, Johannes Gutenberg-University,
Mainz, Germany. rupprecht@2-med.klinik.uni-mainz.de
BACKGROUND: Activation of Na(+)/H(+) exchange in myocardial
ischemia and/or reperfusion leads to calcium overload and myocardial
injury. Experimental studies have shown that Na(+)/H(+) exchange
inhibitors can attenuate Ca(2+) influx into cardiomyocytes.
We therefore performed a multicenter, randomized, placebo-controlled
clinical trial to test the hypothesis that inhibition of Na(+)/H(+)
exchange limits infarct size and improves myocardial function
in patients with acute anterior myocardial infarction (MI) treated
with direct PTCA. METHODS AND RESULTS: One hundred patients
were randomized to receive placebo (n=51) or a 40-mg intravenous
bolus of the Na(+)/H(+) exchange inhibitor cariporide (HOE 642)
(n=49) before reperfusion. Global and regional left ventricular
functions were analyzed by use of paired contrast left ventriculograms
performed before and 21 days after PTCA and myocardial enzymes
(ie, creatine kinase ?CK, CK-MB, and LDH) as markers for myocardial
tissue injury were evaluated. At follow-up, the ejection fraction
was higher (50% versus 40%; P<0.05) and the end-systolic
volume was lower (69.0 versus 97.0 mL; P<0.05) in the cariporide
group. Significant improvements in some indices of regional
wall motion abnormalities were observed, such as the percentage
of chords with hypokinesis < -2 SD (P=0.045) and the severity
of hypokinesis in the border zone of the infarct region (P=0.052).
In addition, CK, CK-MB, or LDH release was significantly reduced
in the cariporide patients. CONCLUSIONS: Our findings suggest
that inhibition of Na(+)/H(+) exchange by cariporide may attenuate
reperfusion injury and thereby improve the recovery from left
ventricular dysfunction after MI.
Publication Types:
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Clinical trial
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Multicenter study
|
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Randomized controlled trial |
PMID: 10869261 [PubMed - indexed for MEDLINE]
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-
Inhibition of the sodium-hydrogen exchanger with cariporide
to prevent myocardial infarction in high-risk ischemic situations.
Main results of the GUARDIAN trial. Guard during ischemia against
necrosis (GUARDIAN) Investigators.
Theroux P, Chaitman BR, Danchin N, Erhardt L, Meinertz T,
Schroeder JS, Tognoni G, White HD, Willerson JT, Jessel A.
BACKGROUND: The transmembrane sodium/hydrogen exchanger maintains
myocardial cell pH integrity during myocardial ischemia but
paradoxically may precipitate cell necrosis. The development
of cariporide, a potent and specific inhibitor of the exchanger,
prompted this investigation of the potential of the drug to
prevent myocardial cell necrosis. METHODS AND RESULTS: A total
of 11 590 patients with unstable angina or non-ST-elevation
myocardial infarction (MI) or undergoing high-risk percutaneous
or surgical revascularization were randomized to receive placebo
or 1 of 3 doses of cariporide for the period of risk. The trial
failed to document benefit of cariporide over placebo on the
primary end point of death or MI assessed after 36 days. Doses
of 20 and 80 mg every 8 hours had no effect, whereas a dose
of 120 mg was associated with a 10% risk reduction (98% CI 5.5%
to 23.4%, P=0.12). With this dose, benefit was limited to patients
undergoing bypass surgery (risk reduction 25%, 95% CI 3.1% to
41.5%, P=0.03) and was maintained after 6 months. No effect
was seen on mortality. The rate of Q-wave MI was reduced by
32% across all entry diagnostic groups (2.6% versus 1.8%, P=0.03),
but the rate of non-Q-wave MI was reduced only in patients undergoing
surgery (7.1% versus 3.8%, P=0.005). There were no increases
in clinically serious adverse events. CONCLUSIONS: No significant
benefit of cariporide could be demonstrated across a wide range
of clinical situations of risk. The trial documented safety
of the drug and suggested that a high degree of inhibition of
the exchanger could prevent cell necrosis in settings of ischemia-reperfusion.
Publication Types:
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Clinical trial
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Randomized controlled trial |
PMID: 11120691 [PubMed - indexed for MEDLINE]
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Cardioprotective effects of KB-R7943: a novel inhibitor of
the reverse mode of Na+/Ca2+ exchanger.
Ladilov Y, Haffner S, Balser-Schafer C, Maxeiner H, Piper
HM.
Physiologisches Institut, Justus-Liebig-Universitat, D-35392
Giessen, Germany.
The novel inhibitor of the reverse mode of the Na+/Ca2+ exchanger
(NCE) KB-R7943 (KB) was tested in isolated rat cardiomyocytes
exposed to 80 min of simulated ischemia [substrate-free anoxia,
extracellular pH (pHo) of 6.4] and 15 min of reoxygenation (pHo
7.4). At pHo 6.4, 20 micromol/l KB was required for complete
inhibition of the reverse mode of NCE. Treatment with 20 micromol/l
KB only during anoxia did not influence the onset of rigor contracture
and intracellular pH (pHi) (monitored with 2', 7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein)
but significantly reduced the cytosolic accumulation of Ca2+
(monitored with fura 2) and Na+ (monitored with sodium-binding
benzofuran isophthalate). During reoxygenation, cardiomyocytes
developed hypercontracture. This was significantly reduced by
anoxic KB treatment. To investigate this protection against
reoxygenation-induced injury in the whole heart, we exposed
Langendorff-perfused rat hearts to 110 min of anoxia (pHo 6.4)
and 50 min of reoxygenation (pHo 7.4). Application of 20 micromol/l
KB during anoxia significantly reduced the reoxygenation-induced
enzyme release. We conclude that KB offers significant protection
of cardiomyocytes against Ca2+ and Na+ overload during anoxia
and hypercontracture or enzyme release on reoxygenation.
PMID: 10362665 [PubMed - indexed for MEDLINE]-
Importance of bicarbonate transport for protection of cardiomyocytes
against reoxygenation injury.
Schafer C, Ladilov YV, Siegmund B, Piper HM.
Physiologisches Institut, Justus-Liebig-Universitat Giessen,
D-35392 Giessen, Germany.
Isolated cardiomyocytes from adult rats were incubated in anoxic
bicarbonate-buffered media at extracellular pH (pH(o)) 6.4 until
a cytosolic Ca(2+) overload and intracellular pH (pH(i)) of
6.4 were reached. On reoxygenation, the pH of the medium was
changed to 7.4 to activate the Na(+)/H(+)exchanger (NHE) and
the Na(+)-HCO(-)(3) symporter (NBS). The reoxygenation was performed
in the absence or presence of the NHE inhibitor HOE-642 (3 micromol/l)
and/or the NBS inhibitor DIDS (0.5 mmol/l), as in bicarbonate-free
media. In reoxygenated control cells pH(i) rapidly recovered
to the preanoxic level, and a burst of spontaneous oscillations
of cytosolic Ca(2+) occurred, accompanied by the development
of hypercontracture. When NBS and NHE were simultaneously inhibited
during reoxygenation, pH(i) recovery was prevented, Ca(2+) oscillations
were attenuated, and hypercontracture was abolished. Sole inhibition
of NBS or NHE showed no protection against hypercontracture.
In the absence of cytosolic acidosis, HOE-642 or DIDS did not
prevent hypercontracture induced by Ca(2+) overload. The results
demonstrate that simultaneous inhibition of NHE and NBS is needed
to protect myocardial cells against reoxygenation-induced hypercontracture.
PMID: 10775122 [PubMed - indexed for MEDLINE]
25. Downey JM, Cohen MV. Mechanisms
of preconditioning: correlates and epiphenomena. In: Marber MS,
Yellon DM, eds. Ischaemia: preconditioning and adaptation. Oxford:
BIOS Scientific Publishers; 1996:21–34.
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The expression of constitutively active isotypes of protein
kinase C to investigate preconditioning.
Zhao J, Renner O, Wightman L, Sugden PH, Stewart L, Miller
AD, Latchman DS, Marber MS.
Department of Cardiology, United Medical and Dental Schools
of Guy's and St Thomas' Hospitals, London, SE1 7EH, United Kingdom.
The role of protein kinase C (PKC) in ischemic preconditioning
remains controversial because of difficulties with both its
measurement and pharmacological manipulation. We investigated
preconditioning in isolated neonatal rat cardiocytes by expressing
constitutively active isotypes of PKC. Observations at differing
durations of simulated ischemia suggested beta-galactosidase
(beta-gal) activity reflected viability within transfected myocytes.
Preconditioning with 90 min of ischemia significantly increased
beta-gal activity and myocyte survival after 6 h of ischemia;
an effect abolished by PKC inhibitors. After co-transfection
with plasmids encoding beta-gal and either constitutively active
mutants of PKC-delta, PKC-alpha, wild type PKC-delta, or empty
vector, cardiocytes were subjected to 6 h of ischemia. Only
PKC-delta, rendered constitutively active by a limited deletion
within the pseudosubstrate domain, consistently increased resistance
to simulated ischemia (beta-gal activity was 85.6 +/- 11.9%
versus 53.7 +/- 6.5% (p </= 0.01) and dead myocytes 46.8
+/- 3.4% versus 68.7 +/- 2.8% (p </= 0.01)). Since transfection
was apparent in only 5-12% of cells, the results suggested a
protective bystander effect that was confirmed by co-culture
of transfected myocytes with untransfected myocytes. In neonatal
cardiocytes expression of active PKC-delta increases resistance
to simulated ischemia. This observation may provide further
insight into the mechanism and possible avenues for therapeutic
exploitation of preconditioning.
PMID: 9722533 [PubMed - indexed for MEDLINE]-
Isoform-selective activation of protein kinase C by nitric
oxide in the heart of conscious rabbits: a signaling mechanism
for both nitric oxide-induced and ischemia-induced preconditioning.
Ping P, Takano H, Zhang J, Tang XL, Qiu Y, Li RC, Banerjee
S, Dawn B, Balafonova Z, Bolli R.
Experimental Research Laboratory, Division of Cardiology, and
the Department of Physiology and Biophysics, University of Louisville,
Louisville, KY 40202, USA. ping@ntr.net
Although isoform-selective translocation of protein kinase C
(PKC) epsilon appears to play an important role in the late
phase of ischemic preconditioning (PC), the mechanism(s) responsible
for such translocation remains unclear. Furthermore, the signaling
pathway that leads to the development of late PC after exogenous
administration of NO in the absence of ischemia (NO donor-induced
late PC) is unknown. In the present study we tested the hypothesis
that NO activates PKC and that this is the mechanism for the
development of both ischemia-induced and NO donor-induced late
PC. A total of 95 chronically instrumented, conscious rabbits
were used. In rabbits subjected to ischemic PC (six 4-minute
occlusion/4-minute reperfusion cycles), administration of the
NO synthase inhibitor Nomega-nitro-L-arginine (group III), at
doses previously shown to block the development of late PC,
completely blocked the ischemic PC-induced translocation of
PKCepsilon but not of PKCeta, indicating that increased formation
of NO is an essential mechanism whereby brief ischemia activates
the epsilon isoform of PKC. Conversely, a translocation of PKCepsilon
and -eta quantitatively similar to that induced by ischemic
PC could be reproduced pharmacologically with the administration
of 2 structurally unrelated NO donors, diethylenetriamine/NO
(DETA/NO) and S-nitroso-N-acetylpenicillamine (SNAP), at doses
previously shown to elicit a late PC effect. The particulate
fraction of PKCepsilon increased from 35+/-2% of total in the
control group (group I) to 60+/-1% after ischemic PC (group
II) (P<0.05), to 54+/-2% after SNAP (group IV) (P<0.05)
and to 52+/-2% after DETA/NO (group V) (P<0.05). The particulate
fraction of PKCeta rose from 66+/-5% in the control group to
86+/-3% after ischemic PC (P<0.05), to 88+/-2% after SNAP
(P<0.05) and to 85+/-1% after DETA/NO (P<0.05). Neither
ischemic PC nor NO donors had any appreciable effect on the
subcellular distribution of PKCalpha, -beta1, -beta2, -gamma,
-delta, - micro, or -iota/lambda; on total PKC activity; or
on the subcellular distribution of total PKC activity. Thus,
the effects of SNAP and DETA/NO on PKC closely resembled those
of ischemic PC. The DETA/NO-induced translocation of PKCepsilon
(but not that of PKCeta) was completely prevented by the administration
of the PKC inhibitor chelerythrine at a dose of 5 mg/kg (group
VI) (particulate fraction of PKCepsilon, 38+/-4% of total, P<0.05
versus group V; particulate fraction of PKCeta, 79+/-2% of total).
The same dose of chelerythrine completely prevented the DETA/NO-induced
late PC effect against both myocardial stunning (groups VII
through X) and myocardial infarction (groups XI through XV),
indicating that NO donors induce late PC by activating PKC and
that among the 10 isozymes of PKC expressed in the rabbit heart,
the epsilon isotype is specifically involved in the development
of this form of pharmacological PC. In all groups examined (groups
I through VI), the changes in the subcellular distribution of
PKCepsilon protein were associated with parallel changes in
PKCepsilon isoform-selective activity, whereas total PKC activity
was not significantly altered. Taken together, the results provide
direct evidence that isoform-selective activation of PKCepsilon
is a critical step in the signaling pathway whereby NO initiates
the development of a late PC effect both after an ischemic stimulus
(endogenous NO) and after treatment with NO-releasing agents
(exogenous NO). To our knowledge, this is also the first report
that NO can activate PKC in the heart. The finding that NO can
promote isoform-specific activation of PKC identifies a new
biological function of this radical and a new mechanism in the
signaling cascade of ischemic PC and may also have important
implications for other pathophysiological conditions in which
NO is involved and for nitrate therapy.
PMID: 10082480 [PubMed - indexed for MEDLINE]-
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Ischemic preconditioning in isolated cells.
Marber MS.
Department of Cardiology, St Thomas' Hospital, King's College
London, London, England. mike.marber@kcl.ac.uk
Publication Types:
|
Review
|
|
Review, tutorial |
PMID: 10807863 [PubMed - indexed for MEDLINE]
-
-
Comment on:
|
Circ Res. 2000 May 12;86(9):989-97 |
Role of p38 mitogen-activated protein kinases in preconditioning:
a detrimental factor or a protective kinase?
Ping P, Murphy E.
Department of Medicine/Division of Cardiology, University of
Louisville, and Jewish Hospital Heart and Lung Institute, Louisville,
KY, USA. ping@ntr.net
Publication Types:
|
Comment
|
|
Review
|
|
Review, tutorial |
PMID: 10807861 [PubMed - indexed for MEDLINE]
-
Phosphorylation of tyrosine 182 of p38 mitogen-activated
protein kinase correlates with the protection of preconditioning
in the rabbit heart.
Weinbrenner C, Liu GS, Cohen MV, Downey JM.
Department of Physiology, University of South Alabama, Mobile,
AL 36688, USA.
p38 mitogen-activated protein kinase (MAPK) is known to be activated
after exposure to endotoxin, osmotic and environmental stress,
and, most recently, during ischemia/reperfusion. We investigated
whether ischemic preconditioning also causes phosphorylation
of the activation sites on p38 MAPK. Three groups of isolated
rabbit hearts were studied. Control hearts experienced 30 min
of ischemia only. The second group was preconditioned with 5
min of global ischemia and 10 min of reperfusion. Group 3 was
also ischemically preconditioned, but in the presence of 100
microM 8-(p-sulfophenyl)theophylline (SPT). Transmural left
ventricular biopsies were taken before and during the long ischemic
period. Western blot analysis with either p38 MAPK or phospho-specific
p38 MAPK (Tyr-182) antibodies showed a decreased phosphorylation
during ischemia in non-preconditioned hearts, but phosphorylation
was enhanced several fold after 10 and 20 min of ischemia in
preconditioned hearts. Furthermore, when protection from ischemic
preconditioning was blocked by SPT, increased phosphorylation
of p38 MAPK during ischemia was not present. Therefore the phosphorylation
of p38 MAPK at tyrosine 182, which is required for the kinase's
activation, occurred during ischemia only when protection from
preconditioning was evident. In a second study, changes in osmotic
fragility were measured during simulated ischemia in rabbit
cardiomyocytes. Reduced fragility in ischemically preconditioned
myocytes could be completely abolished by the specific p38 MAPK
inhibitor SB-203580. In contrast, anisomycin, an activator of
p38 MAPK and JUN kinase pathways, was found to be as protective
as ischemic preconditioning. We conclude that p38 MAPK phosphorylation
correlates with preconditioning's protection, and that its activation
may be an important step in the signal transduction cascade
of ischemic preconditioning. Copyright 1997 Academic Press Limited.
PMID: 9299362 [PubMed - indexed for MEDLINE]-
-
Comment in:
|
Circ Res. 2000 May 12;86(9):921-2 |
Adenosine A(1) receptor induced delayed preconditioning in
rabbits: induction of p38 mitogen-activated protein kinase activation
and Hsp27 phosphorylation via a tyrosine kinase- and protein
kinase C-dependent mechanism.
Dana A, Skarli M, Papakrivopoulou J, Yellon DM.
Hatter Institute for Cardiovascular Studies, Department of Academic
and Clinical Cardiology, and Centre for Cardiopulmonary Biochemistry,
University College London Hospitals and Medical School, London,
UK.
Transient adenosine A(1) receptor (A(1)R) activation in rabbits
induces delayed preconditioning against myocardial infarction
24 to 72 hours later. The cellular mechanisms downstream of
A(1)R mediating this delayed cardioprotection have not been
elucidated. This study examined the role of protein kinase C
(PKC) and tyrosine kinases (TKs) in the signaling cascade mediating
A(1)R-induced late preconditioning in rabbits. The small heat
shock protein Hsp27 has been shown to confer cytoskeletal protection
when in the phosphorylated state. We therefore also evaluated
the potential role of the p38 mitogen-activated protein kinase
(p38 MAPK) and Hsp27 as distal mediators of A(1)R-induced delayed
preconditioning. Pharmacological preconditioning of rabbits
with the selective A(1) agonist 2-chloro-N(6)-cyclopentyladenosine
(CCPA; 100 microgram/kg) significantly reduced myocardial infarct
size compared with control animals, after 30-minute regional
ischemia/2-hour reperfusion in vivo 24 hours later (23.7+/-3.1
versus 43.0+/-4.1%; P<0.05). This delayed protection was
abrogated by prior inhibition of either PKC with chelerythrine
chloride (5 mg/kg) or of TKs with lavendustin A (1.3 mg/kg),
suggesting that both PKC and TK are crucial for the development
of delayed preconditioning after A(1) receptor activation in
the rabbit. Myocardial tissue extracts obtained 24 hours after
CCPA treatment were analyzed for p38 MAPK catalytic activity
using an in vitro kinase assay. This showed an almost 7-fold
increase in p38 MAPK activity in myocardial samples pretreated
with CCPA compared with control hearts. Two-dimensional gel
electrophoresis revealed an increase in the phosphorylated isoforms
of Hsp27 in hearts pretreated with CCPA compared with control
hearts. Prior inhibition of either PKC or TK prevented the CCPA-induced
increase in p38 MAPK activity and phosphorylation of Hsp27.
This study identifies new components of the signaling mechanism
of A(1)R-induced delayed preconditioning. Our results suggest
an important role for both PKC and TK as mediators of late preconditioning
against infarction after A(1)R activation and, although correlative,
point to the p38 MAPK/Hsp27 pathway as a potential distal effector
of this protection.
PMID: 10807872 [PubMed - indexed for MEDLINE]
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The role of differential activation of p38-mitogen-activated
protein kinase in preconditioned ventricular myocytes.
Saurin AT, Martin JL, Heads RJ, Foley C, Mockridge JW, Wright
MJ, Wang Y, Marber MS.
Department of Cardiology, KCL, The Rayne Institute, St. Thomas'
Hospital London SE1 7EH, U.K.
Activation of protein kinase C (PKC) and more recently mitogen-activated
protein kinases (MAPKs) have been associated with the cardioprotective
effect of ischemic preconditioning. We examined the interplay
between these kinases in a characterized model of ischemic preconditioning
in cultured rat neonatal ventricular cardiocytes where ectopic
expression of active PKC-delta results in protection. Two members
of the MAPK family, p38 and p42/44, were activated transiently
during preconditioning by brief simulated ischemia/reoxygenation.
Overexpression of active PKC-delta, rather than augmenting,
completely abolished this activation. We therefore determined
whether a similar process occurred during lethal prolonged simulated
ischemia. In contrast to ischemia, brief, lethal-simulated ischemia
activated only p38 (2.8+/-0.45 vs. basal, P<0.01), which
was attenuated by expression of active PKC-delta or by preconditioning
(0.48+/-0.1 vs. ischemia, P<0.01). To determine whether reduced
p38 activation was the cause or an effect of protection, we
used SB203580, a p38 inhibitor. SB203580 reduced ischemic injury
(CK release 38.0+/-3.1%, LDH release 77.3+/-4.0%, and MTT bioreduction
127.1+/-4.8% of control, n=20, P<0.05). To determine whether
p38 activation was isoform selective, myocytes were infected
with adenoviruses encoding wild-type p38alpha or p38beta. Transfected
p38alpha and beta show differential activation (P<0.001)
during sustained simulated ischemia, with p38alpha remaining
activated (1.48+/-0.36 vs. basal) but p38beta deactivated (0.36+/-0.1
vs. basal, P<0.01). Prior preconditioning prevented the activation
of p38alpha (0.65+/-0.11 vs. ischemia, P<0.05). Moreover,
cells expressing a dominant negative p38alpha, which prevented
ischemic p38 activation, were resistant to lethal simulated
ischemia (CK release 82.9+/-3.9% and MTT bioreduction 130.2+/-6.5%
of control, n=8, P<0.05). Thus, inhibition of p38alpha activation
during ischemia reduces injury and may contribute to preconditioning-induced
cardioprotection in this model.
PMID: 11053245 [PubMed - indexed for MEDLINE]-
Inhibition of p38 mitogen-activated protein kinase decreases
cardiomyocyte apoptosis and improves cardiac function after
myocardial ischemia and reperfusion.
Ma XL, Kumar S, Gao F, Louden CS, Lopez BL, Christopher TA,
Wang C, Lee JC, Feuerstein GZ, Yue TL.
Division of Emergency Medicine, Thomas Jefferson University,
Philadelphia, PA, USA. ma1@jeflin.tju.edu
BACKGROUND: Activation of p38 mitogen-activated protein kinase
(MAPK) plays an important role in apoptotic cell death. The
role of p38 MAPK in myocardial injury caused by ischemia/reperfusion,
an extreme stress to the heart, is unknown. METHODS AND RESULTS:
Studies were performed with isolated, Langendorff-perfused rabbit
hearts. Ischemia alone caused a moderate but transient increase
in p38 MAPK activity (3.5-fold increase, P<0.05 versus basal).
Ischemia followed by reperfusion further activated p38 MAPK,
and the maximal level of activation (6.3-fold, P<0.01) was
reached 10 minutes after reperfusion. Administration of SB 203580,
a p38 MAPK inhibitor, decreased myocardial apoptosis (14.7+/-3.2%
versus 30.6+/-3.5% in vehicle, P<0.01) and improved postischemic
cardiac function. The cardioprotective effects of SB 203580
were closely related to its inhibition of p38 MAPK. Administering
SB 203580 before ischemia and during reperfusion completely
inhibited p38 MAPK activation and exerted the most cardioprotective
effects. In contrast, administering SB 203580 10 minutes after
reperfusion (a time point when maximal MAPK activation had already
been achieved) failed to convey significant cardioprotection.
Moreover, inhibition of p38 MAPK attenuated myocardial necrosis
after a prolonged reperfusion. CONCLUSIONS: These results demonstrate
that p38 MAPK plays a pivotal role in the signal transduction
pathway mediating postischemic myocardial apoptosis and that
inhibiting p38 MAPK may attenuate reperfusion injury.
PMID: 10190877 [PubMed - indexed for MEDLINE]-
An inhibitor of p38 mitogen-activated protein kinase protects
neonatal cardiac myocytes from ischemia.
Mackay K, Mochly-Rosen D.
Department of Molecular Pharmacology, Stanford University School
of Medicine, Stanford, California 94305, USA.
Cellular ischemia results in activation of a number of kinases,
including p38 mitogen-activated protein kinase (MAPK); however,
it is not yet clear whether p38 MAPK activation plays a role
in cellular damage or is part of a protective response against
ischemia. We have developed a model to study ischemia in cultured
neonatal rat cardiac myocytes. In this model, two distinct phases
of p38 MAPK activation were observed during ischemia. The first
phase began within 10 min and lasted less than 1 h, and the
second began after 2 h and lasted throughout the ischemic period.
Similar to previous studies using in vivo models, the nonspecific
activator of p38 MAPK and c-Jun NH2-terminal kinase, anisomycin,
protected cardiac myocytes from ischemic injury, decreasing
the release of cytosolic lactate dehydrogenase by approximately
25%. We demonstrated, however, that a selective inhibitor of
p38 MAPK, SB 203580, also protected cardiac myocytes against
extended ischemia in a dose-dependent manner. The protective
effect was seen even when the inhibitor was present during only
the second, sustained phase of p38 MAPK activation. We found
that ischemia induced apoptosis in neonatal rat cardiac myocytes
and that SB 203580 reduced activation of caspase-3, a key event
in apoptosis. These results suggest that p38 MAPK induces apoptosis
during ischemia in cardiac myocytes and that selective inhibition
of p38 MAPK could be developed as a potential therapy for ischemic
heart disease.
PMID: 10037715 [PubMed - indexed for MEDLINE]-
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Sarcolemmal versus mitochondrial ATP-sensitive K+ channels
and myocardial preconditioning.
Gross GJ, Fryer RM.
Department of Pharmacology and Toxicology, Medical College of
Wisconsin, Milwaukee, WI, USA. ggross@post.its.mcw.edu
Ischemic preconditioning (IPC) is a phenomenon in which single
or multiple brief periods of ischemia have been shown to protect
the heart against a more prolonged ischemic insult, the result
of which is a marked reduction in myocardial infarct size, severity
of stunning, or incidence of cardiac arrhythmias. Although a
number of substances and signaling pathways have been proposed
to be involved in mediating the cardioprotective effect of IPC,
the overwhelming majority of evidence suggests that the ATP-sensitive
potassium channel (KATP channel) is an important component of
this phenomenon and may serve as the end effector in this process.
Initially, it was hypothesized that the surface or sarcolemmal
KATP (sarc KATP) channel mediated protection observed after
IPC; however, subsequent evidence suggested that the recently
identified mitochondrial KATP channel (mito KATP) may be the
potassium channel mediating IPC-induced cardioprotection. In
this review, evidence will be presented supporting a role for
either the sarc KATP or the mito KATP in IPC and potential mechanisms
by which opening these channels may produce cardioprotection;
additionally, we will address important questions that still
need to be investigated to define the role of the sarc or mito
KATP channel, or both, in cardiac pathophysiology.
Publication Types:
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Review
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Review, tutorial |
PMID: 10325234 [PubMed - indexed for MEDLINE]
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Comment in:
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Circ Res. 2000 Sep 15;87(6):431-3 |
Opening of mitochondrial K(ATP) channels triggers the preconditioned
state by generating free radicals.
Pain T, Yang XM, Critz SD, Yue Y, Nakano A, Liu GS, Heusch
G, Cohen MV, Downey JM.
Department of Physiology, College of Medicine, University of
South Alabama, Mobile, AL 36688, USA.
The critical time for opening mitochondrial (mito) K(ATP) channels,
putative end effectors of ischemic preconditioning (PC), was
examined. In isolated rabbit hearts 29+/-3% of risk zone infarcted
after 30 minutes of regional ischemia. Ischemic PC or 5-minute
exposure to 10 micromol/L diazoxide, a mito K(ATP) channel opener,
reduced infarction to 3+/-1% and 8+/-1%, respectively. The mito
K(ATP) channel closer 5-hydroxydecanoate (200 micromol/L), bracketing
either 5-minute PC ischemia or diazoxide infusion, blocked protection
(24+/-3 and 28+/-6% infarction, respectively). However, 5-hydroxydecanoate
starting 5 minutes before long ischemia did not affect protection.
Glibenclamide (5 micromol/L), another K(ATP) channel closer,
blocked the protection by PC only when administered early. These
data suggest that K(ATP) channel opening triggers protection
but is not the final step. Five minutes of diazoxide followed
by a 30-minute washout still reduced infarct size (8+/-3%),
implying memory as seen with other PC triggers. The protection
by diazoxide was not blocked by 5 micromol/L chelerythrine,
a protein kinase C antagonist, given either to bracket diazoxide
infusion or just before the index ischemia. Bracketing preischemic
exposure to diazoxide with 50 micromol/L genistein, a tyrosine
kinase antagonist, did not affect infarction, but genistein
blocked the protection by diazoxide when administered shortly
before the index ischemia. Thus, although it is not protein
kinase C-dependent, the protection by diazoxide involves tyrosine
kinase. Bracketing diazoxide perfusion with N:-(2-mercaptopropionyl)
glycine (300 micromol/L) or Mn(III)tetrakis(4-benzoic acid)
porphyrin chloride (7 micromol/L), each of which is a free radical
scavenger, blocked protection, indicating that diazoxide triggers
protection through free radicals. Therefore, mito K(ATP) channels
are not the end effectors of protection, but rather their opening
before ischemia generates free radicals that trigger entrance
into a preconditioned state and activation of kinases.
PMID: 10988237 [PubMed - indexed for MEDLINE]
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Comment in:
|
Circ Res. 2000 Mar 31;86(6):607-9 |
Inhibition of extracellular signal-regulated kinase enhances
Ischemia/Reoxygenation-induced apoptosis in cultured cardiac
myocytes and exaggerates reperfusion injury in isolated perfused
heart.
Yue TL, Wang C, Gu JL, Ma XL, Kumar S, Lee JC, Feuerstein
GZ, Thomas H, Maleeff B, Ohlstein EH.
Departments of Cardiovascular Pharmacology, SmithKline Beecham
Pharmaceuticals, King of Prussia, PA 19406, USA.
Three major mammalian mitogen-activated protein kinases, extracellular
signal-regulated kinase (ERK), p38, and c-Jun NH(2)-terminal
protein kinase (JNK), have been identified in the cardiomyocyte,
but their respective roles in the heart are not well understood.
The present study explored their functions and cross talk in
ischemia/reoxygenation (I/R)-induced cardiac apoptosis. Exposing
rat neonatal cardiomyocytes to ischemia resulted in a rapid
and transient activation of ERK, p38, and JNK. On reoxygenation,
further activation of all 3 mitogen-activated protein kinases
was noted; peak activities increased (fold) by 5.5, 5.2, and
6.2, respectively. Visual inspection of myocytes exposed to
I/R identified 18.6% of the cells as showing morphological features
of apoptosis, which was further confirmed by DNA ladder and
terminal deoxyribonucleotide transferase-mediated dUTP nick
end labeling (TUNEL). Myocytes treated with PD98059, a MAPK/ERK
kinase (MEK1/MEK2) inhibitor, displayed a suppression of I/R-induced
ERK activation, whereas p38 and JNK activities were increased
by 70.3% and 55.0%, respectively. In addition, the number of
apoptotic cells was increased to 33.4%. With pretreatment of
cells with SB242719, a selective p38 inhibitor, or SB203580,
a p38 and JNK2 inhibitor, I/R+PD98059-induced apoptotic cells
were reduced by 42.8% and 63.3%, respectively. Hearts isolated
from rats treated with PD98059 and subjected to global ischemia
(30 minutes)/reoxygenation (1 hour) showed a diminished functional
recovery compared with the vehicle group. Coadministration of
SB203580 attenuated the detrimental effects of PD98059 and significantly
improved cardiac functional recovery. The data taken together
suggest that ERK plays a protective role, whereas p38 and JNK
mediate apoptosis in cardiomyocytes subjected to I/R, and the
dynamic balance of their activities is critical in determining
cardiomyocyte fate subsequent to reperfusional injury.
PMID: 10747006 [PubMed - indexed for MEDLINE]
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Akt promotes survival of cardiomyocytes in vitro and protects
against ischemia-reperfusion injury in mouse heart.
Fujio Y, Nguyen T, Wencker D, Kitsis RN, Walsh K.
Division of Cardiovascular Research, St Elizabeth's Medical
Center, Tufts University School of Medicine, Boston, MA 02135,
USA.
BACKGROUND: IGF-1 has been shown to protect myocardium against
death in animal models of infarct and ischemia-reperfusion injury.
In the present study, we investigated the role of the IGF-1-regulated
protein kinase Akt in cardiac myocyte survival in vitro and
in vivo. METHODS AND RESULTS: IGF-1 promoted survival of cultured
cardiomyocytes under conditions of serum deprivation in a dose-dependent
manner but had no effect on cardiac fibroblast survival. The
cytoprotective effect of IGF-1 on cardiomyocytes was abrogated
by the phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor
wortmannin. Wortmannin had no effect on cardiomyocyte viability
in the absence of IGF-1. IGF-1-mediated cytoprotection correlated
with the wortmannin-sensitive induction of Akt protein kinase
activity. To examine the functional consequences of Akt activation
in cardiomyocyte survival, replication-defective adenoviral
constructs expressing wild-type, dominant-negative, and constitutively
active Akt genes were constructed. Transduction of dominant-negative
Akt blocked IGF-1-induced survival but had no effect on cardiomyocyte
survival in the absence of IGF-1. In contrast, transduction
of wild-type Akt enhanced cardiomyocyte survival at subsaturating
levels of IGF-1, whereas constitutively active Akt protected
cardiomyocytes from apoptosis in the absence of IGF-1. After
transduction into the mouse heart in vivo, constitutively active
Akt protected against myocyte apoptosis in response to ischemia-reperfusion
injury. CONCLUSIONS: These data are the first documentation
that Akt functions to promote cellular survival in vivo, and
they indicate that the activation of this pathway may be useful
in promoting myocyte survival in the diseased heart.
PMID: 10673259 [PubMed - indexed for MEDLINE]-
Intracoronary, adenovirus-mediated Akt gene transfer in heart
limits infarct size following ischemia-reperfusion injury in
vivo.
Miao W, Luo Z, Kitsis RN, Walsh K.
Departments of Medicine and Cell Biology, Albert Einstein College
of Medicine, Bronx, NY 10461, USA.
BACKGROUND: Previous data have shown that enhanced Akt signaling
inhibits cardiac myocyte apoptosis in vitro and in vivo. To
elucidate the contribution of apoptosis to the pathogenesis
of the infarct, we investigated whether intra-coronary Akt gene
delivery could reduce gross infarct size following ischemia/reperfusion
injury. METHODS AND RESULTS: Replication-defective adenoviral
constructs encoding a myristoylated, constitutively-active form
of Akt (myrAkt) or beta -galactosidase were delivered to rat
hearts by intracoronary perfusion. Twenty-four h after gene
transduction, hearts in both groups underwent 45 min of ischemia
followed by 4 h of reperfusion. A third group of animals also
underwent ischemia-reperfusion injury but were not transduced
with an adenoviral vector. The proportion of the left ventricle
at risk was not different among the experimental groups. However,
infarct size as a proportion of the area at risk was significantly
lower in myrAkt-treated group than in the beta -galactosidase
treated group or in the control group that was not subject to
intracoronary perfusion (myrAkt=20.9+/-2.7%v beta -galactosidase=56.1+/-3.9%
and control=46.2+/-4.6%, P<0.05), as was infarct size as
a proportion of the total left ventricle (myrAkt=11.4+/-3.2
v beta -galactosidase=32. 9+/-3.3 and control=23.5+/-3.0, P<0.05).
CONCLUSIONS: These data demonstrate that Akt signaling limits
infarct size following ischemia/reperfusion injury and they
indicate that the activation of this pathway may be useful in
protecting against myocardial loss in the diseased heart. Copyright
2000 Academic Press.
PMID: 11113015 [PubMed - indexed for MEDLINE]-
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Reperfusion injury revisited: is there a role for growth
factor signaling in limiting lethal reperfusion injury?
Yellon DM, Baxter GF.
The Hatter Institute & Centre for Cardiology, University
College London Hospitals and Medical School, London, UK.
Myocardial reperfusion injury represents an important therapeutic
target. The ability of several peptide growth factors, including
transforming growth factor-beta1, insulin, insulin-like growth
factor-1, cardiotrophin-1 and fibroblast growth factors, to
modify reperfusion injury has been examined in recent studies.
The protective effects of these agents may be related to the
inhibition of apoptosis, especially during reperfusion, probably
through p42/p44 MAP kinase and PI3-kinase/Akt signaling. Growth
factor signaling may therefore represent a novel approach for
the development of pharmacological strategies that attenuate
reperfusion injury in the heart.
Publication Types:
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Review
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Review, tutorial |
PMID: 11094333 [PubMed - indexed for MEDLINE]
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