The slowing of ischemic energy demand in preconditioned myocardium

Influence of diabetes mellitus duration on the efficacy of ischemic preconditioning in a Zucker diabetic fatty rat model

Augmented mortality and morbidity following an acute myocardial infarction in patients with diabetes mellitus Type 2 (T2DM) may be caused by increased sensitivity to ischemia reperfusion (IR) injury or altered activation of endogenous cardioprotective pathways modified by T2DM per se or ischemic preconditioning (IPC). We aimed to investigate, whether the duration of T2DM influences sensitivity against IR injury and the efficacy of IPC, and how myocardial glucose oxidation rate was involved. Male Zucker diabetic fatty rats (homozygote (fa/fa)) at ages 6-(prediabetic), 12- (onset diabetes) and 24-weeks of age (late diabetes) and their age-matched non-diabetic controls (heterozygote (fa/+) were subjected to IR injury in the Langendorff model and randomised to IPC stimulus or control. T2DM rats were endogenously protected at onset of diabetes, as infarct size was lower in 12-weeks T2DM animals than in 6- (35±2% vs 53±4%; P = 0.006) and 24-weeks animals (35±2% vs 72±4%; P<0.0001). IPC reduced infarct size in all groups irrespective of the presence of T2DM and its duration (32±3%; 20±2%; 36±4% respectively; (ANOVA P<0.0001). Compared to prediabetic rats, myocardial glucose oxidation rates were reduced during stabilisation and early reperfusion at onset of T2DM, but these animals retained the ability to increase oxidation rate in late reperfusion. Late diabetic rats had low glucose oxidation rates throughout stabilisation and reperfusion. Despite inherent differences in sensitivity to IR injury, the cardioprotective effect of IPC was preserved in our animal model of pre-, early and late stage T2DM and associated with adaptations to myocardial glucose oxidation capacity.

Myocardial Preconditioning: Characteristics, Mechanisms, and Clinical Applications

Perioperative myocardial ischemia and dysfunction re main prevalent after cardiac surgery despite the use of conventional measures to provide myocardial protec tion. Myocardial preconditioning is a powerful, endog enously regulated means of myocardial protection that may also have some clinical usage for patients undergo ing cardiac surgical procedures. The paradoxical con cept of using ischemia as a stimulus for myocardial protection has been studied extensively in animals and humans. The specific characteristics and constituents of preconditioning have been well identified. The mecha nism remains to be completely elucidated due to differ ences among species and experimental models. Some pharmacologic agents are capable of mimicking the classic mechanism of ischemic preconditioning. Pharma cologic and ischemic preconditioning may have signifi cant clinical use and therapeutic efficacy as a means of providing myocardial protection during cardiac surgery, especially in procedures that do not use cardioplegia and cardiopulmonary bypass, such as minimally inva sive coronary artery bypass grafting. This article re views the characteristics, mechanisms, potential clini cal applications, and therapeutic efficacy of myocardial preconditioning.

Resveratrol, a unique phytoalexin present in red wine, delivers either survival signal or death signal to the ischemic myocardium depending on dose

Recent studies have demonstrated the cardioprotective abilities of resveratrol, a polyphenolic antioxidant present in red wine. Resveratrol can also kill cancer cells at relatively higher doses by exerting a death signal. We reasoned that resveratrol might possess the ability to protect the cells at lower doses as observed during pharmacological preconditioning of the heart, while at higher doses cause cell death as found for cancer cells. To test this hypothesis, rats were randomly fed for 14 days by gavaging any of the four doses of resveratrol - 2.5, 5.0, 25 or 50 mg/kg - while vehicle-fed animals served as placebo control. After 14 days, isolated working hearts were prepared from both experimental and control animals, and the hearts were subjected to 30-min global ischemia followed by 2 h of reperfusion. The rats fed either 2.5 or 5 mg/kg dose of resveratrol for 14 days provided cardioprotection as evidenced by improved post-ischemic ventricular recovery and reduction of myocardial infarct size and cardiomyocyte apoptosis compared to control. In contrast, the hearts fed either 25 or 50 mg/kg dose of resveratrol depressed cardiac function and increased myocardial infarct size and number of apoptotic cells. The results for Western blots and RT-PCR demonstrated an increase of protein and RNA transcripts of redox proteins including thioredoxin (Trx)-1, Trx-2, glutaredoxin (Grx)-1, Grx-2, redox factor Ref-1 as well as redox-sensitive transcription factor NFkappaB, and survival factors such as phosphorylated-Akt (p-Akt), and Bcl-2 in the animals fed lower doses (2.5 and 5 mg/kg) of resveratrol, while the reverse was true for the animals fed higher doses (25 and 50 mg/kg) of resveratrol. The results thus indicate that at lower doses (2.5 or 5 mg/kg), resveratrol exerts survival signal by up-regulating anti-apoptotic and redox proteins Akt and Bcl-2, while at higher doses (>25 mg/kg), it potentiates a death signal by down-regulating redox proteins and up-regulating pro-apoptotic proteins.

Myocardial energy metabolism in ischemic preconditioning and cardioplegia: a metabolic control analysis

For both, cardioplegia (CP) and ischemic preconditioning (IP), increased ischemic tolerance with reduction in infarct size is well documented. These cardioprotective effects are related to a limitation of high energy phosphate (HEP) depletion. As CP and IP have to be assumed to act by different mechanisms, their effects on myocardial HEP metabolism cannot be assumed to be identical. Therefore, a systematic analysis of myocardial HEP metabolism for both procedures and their combination was performed, addressing the question whether there are different effects on myocardial HEP metabolism by IP and CP. In this study, metabolic control analysis was used to analyze the regulation of HEP metabolism. In open chest pigs subjected to 45 min LAD occlusion (index ischemia), CP and IP preserved myocardial ATP (control (C) 0.14 +/- 0.05 micromol/g wwt; CP: 0.95 +/- 0.14, IP: 0.61 +/- 0.12; p<0.05 C vs. CP and IP) and reduced myocardial necrosis (infarct size IA/RA: C: 90.0 +/- 3.0%; CP: 0.0 +/- 0.0% but patchy necroses; IP: 5.05 +/- 2.1%; p<0.05 C vs. CP and IP). The effects on HEP metabolism, however, were different: CP acted predominantly by slowing down the breakdown of phosphocreatine (PCr) during early phases of ischemia (C: DeltaPCr 0-2 min: 5.24 +/- 0.32 micromol/g wwt; CP: DeltaPCr 0-2 min: 3.38 +/- 0.23 micromol/g wwt, p<0.05 vs. C), leaving ATP breakdown during later stages unaffected (C: DeltaATP 5-45 min: 1.77 +/- 0.11 micromol/g wwt CP: DeltaATP 5-45 min: 1.59 +/- 0.28 micromol/g wwt, n.s. vs. C). In contrast to CP, in IP PCr breakdown was even increased (IP: DeltaPCr 0-2 min: 7.06 +/- 0.34 micromol/g wwt, p<0.05 vs. C), but ATP depletion greatly attenuated (IP: DeltaATP 5-45 min: 0.48 +/- 0.10 micromol/g wwt, p<0.05 vs. C and CP). Combining IP and CP yielded an additive effect with slowing down the breakdown of both PCr (IP+CP: DeltaPCr 0-2 min: 5.09+/- 0.35 micromol/g wwt, p<0.05 vs. C and IP) and ATP (IP+CP: DeltaATP 5-45 min: 0.56 +/- 0.48 micromol/g wwt, p<0.05 vs. C and CP), resulting in a higher ATP content at the end of index ischemia (1.86 +/- 0.46 micromol/g wwt, p<0.05 vs. C, CP and IP). Compared to IP, combining IP+CP achieved also a further reduction in infarct size (IA/RA: 0.0 +/- 0.0%, p<0.05 vs IP) and--compared to CP--a disappearance of the patchy necroses. The concept of major differences in myocardial HEP metabolism during CP and IP is further supported at a molecular level by metabolic control analysis. CP but not IP slowed down the CK reaction velocity at high PCr levels. In contrast to CP exerting a continuous decline in vATPase for any given ATP level, in IP myocardium ATPase reaction velocity was even increased at higher ATP contents, whereas a marked decrease in ATPase reaction velocity was found if ATP levels decreased. The equilibrium of the CK-reaction remained unchanged following CP, whereas IP induced a changing CK equilibrium, which was the more shifted towards PCr the more myocardial HEP content decreased. The data demonstrate different effects of CP and IP on myocardial HEP metabolism, i.e. PCr and ATP breakdown as well as the apparent equilibrium of the creatine kinase (CK)-reaction. For these reasons the combination of the two protective interventions has an additive effect.

Myocardial protection from ischemic preconditioning is not blocked by sub-chronic inhibition of carnitine palmitoyltransferase I

Ischemic preconditioning (IP) triggers cardioprotection via a signaling pathway that converges on mitochondria. The effects of the inhibition of carnitine palmitoyltransferase I (CPT-I), a key enzyme for transport of long chain fatty acids (LCFA) into the mitochondria, on ischemia/reperfusion (I/R) injury are unknown. Here we investigated, in isolated perfused rat hearts, whether sub-chronic CPT-I inhibition (5 days i.p. injection of 25 mg/kg/day of Etomoxir) affects I/R-induced damages and whether cardioprotection by IP can be induced after this inhibition. Effects of global ischemia (30 min) and reperfusion (120 min) were examined in hearts harvested from Control (untreated), Vehicle- or Etomoxir-treated animals. In subsets of hearts from the three treated groups, IP was induced by three cycles of 3 min ischemia followed by 10 min reperfusion prior to I/R. The extent of I/R injury under each condition was assessed by changes in infarct size as well as in myocardial contractility. Postischemic contractility, as indexed by developed pressure and dP/dt(max), was similarly affected by I/R, and was similarly improved with IP in Control, Vehicle or Etomoxir treated animals. Infarct size was also similar in the three subsets without IP, and was significantly reduced by IP regardless of CPT-I inhibition. We conclude that CPT-I inhibition does not affect I/R damages. Our data also show that IP affords myocardial protection in CPT-I inhibited hearts to a degree similar to untreated animals, suggesting that a long-term treatment with the metabolic anti-ischemic agent Etomoxir does not impede the possibility to afford cardioprotection by ischemic preconditioning.

Modest actomyosin energy conservation increases myocardial postischemic function

We have proposed that pharmacological preconditioning, leading to PKC-epsilon activation, in hearts improves postischemic functional recovery through a decrease in actomyosin ATPase activity and subsequent ATP conservation. The purpose of the present study was to determine whether moderate PKC-independent decreases in actomyosin ATPase are sufficient to improve myocardial postischemic function. Rats were given propylthiouracil (PTU) for 8 days to induce a 25% increase in beta-myosin heavy chain with a 28% reduction in actomyosin ATPase activity. Recovery of postischemic left ventricular developed pressure (LVDP) was significantly higher in PTU-treated rat hearts subjected to 30 min of global ischemia than in control hearts: 57.9 +/- 6.2 vs. 32.6 +/- 5.1% of preischemic values. In addition, PTU-treated hearts exhibited a delayed onset of rigor contracture during ischemia and a higher global ATP content after ischemia. In the second part of our study, we demonstrated a lower maximal actomyosin ATPase and a higher global ATP content after ischemia in human troponin T (TnT) transgenic mouse hearts. In mouse hearts with and without a point mutation at F110I of human TnT, recovery of postischemic LVDP was 55.4 +/- 5.5 and 62.5 +/- 14.5% compared with 20.0 +/- 2.9% in nontransgenic mouse hearts after 35 min of global ischemia. These results are consistent with the hypothesis that moderate decreases in actomyosin ATPase activity result in net ATP conservation that is sufficient to improve postischemic contractile function.

F0F1 ATP synthase activity is differently modulated by coronary reactive hyperemia before and after ischemic preconditioning in the goat

The amplitude of coronary reactive hyperemia (CRH), elicited by 15 s of ischemia, is reduced in hearts subjected to 5 min of ischemic preconditioning (IP). F0F1 ATP synthase activity and ATP concentration are also altered by IP. We hypothesized that F0F1 ATP synthase is differently modulated by the inhibitor protein IF(1) during CRH elicited before (CRHnp) and after (CRHprec) IP. Hemodynamic parameters were recorded in 10 anesthetized goats. Myocardial biopsies were obtained before IP (Cnp), during CRHnp, 4 and 6 min after the onset of CRHnp, after IP (Cprec), during CRHprec, and 4 min after CRHprec. F0F1 ATP synthase activity, ATP concentration, and ATP-to-ADP ratio (ATP/ADP) were determined. Compared with CRHnp, IP blunted CRHprec. F0F1 ATP synthase activity transiently increased during CRHnp, decreased 4 min after CRHnp, and returned to control 2 min later; it was lower after IP (Cprec) and did not change during and after CRHprec. All these changes in activity were modulated by IF1. During CRHnp, ATP concentration and ATP/ADP were reduced compared with Cnp and began to rise 6 min thereafter. During Cprec, both parameters were transiently reduced but increased during and after CRHprec. Hence, during CRHnp, F0F1 ATP synthase activity transiently increases and then decreases significantly. The short-lasting inhibition of the enzyme may explain why a few seconds of occlusion do not induce IP. After IP, F0F1 ATP synthase activity is blunted, and it is not affected by a subsequent 15 s of occlusion, which induces a blunted CRHprec. These results suggest that postischemic long-lasting inhibition of F0F1 ATP synthase activity may be a feature of the preconditioned heart. The increase in ATP concentration after preconditioning is in agreement with previous reports of reduced ATP hydrolysis by cytoplasmic ATPases.

Thioredoxin regulation of ischemic preconditioning

Thioredoxins are a class of small redox-regulating proteins that appear to play a crucial role in many oxidative stress-inducible degenerative diseases. A recent study demonstrated a reduction of thioredoxin-1 (Trx1) protein in the ischemic reperfused myocardium. When the same heart was adapted to ischemic stress by preconditioning with repeated cyclic episodes of small duration of ischemia and reperfusion, there was an increased induction of Trx1 expression. Inhibition of Trx1 expression resulted in reduced postischemic ventricular recovery and increased myocardial infarct size in the preconditioned heart. Corroborating these findings, transgenic mouse hearts overexpressing Trx1 were resistant to ischemic reperfusion injury as compared with the hearts from wild-type mice. Thus, it appears that thioredoxin plays a crucial role in cardioprotection induced by preconditioning.

Regulation of glycolytic flux in ischemic preconditioning. A study employing metabolic control analysis

Exact adjustment of the Embden-Meyerhof pathway (EMP) is an important issue in ischemic preconditioning (IP) because an attenuated ischemic lactate accumulation contributes to myocardial protection. However, precise mechanisms of glycolytic flux and its regulation in IP remain to be elucidated. In open chest pigs, IP was achieved by two cycles of 10-min coronary artery occlusion and 30-min reperfusion prior to a 45-min index ischemia and 120-min reperfusion. Myocardial contents in glycolytic intermediates were assessed by high performance liquid chromatographic analysis of serial myocardial biopsies under control conditions and IP. Detailed time courses of metabolite contents allow an in-depth description of EMP regulation during index ischemia using metabolic control analysis. IP reduced myocardial infarct size (control, 90.0 +/- 3.1 versus 5.05 +/- 2.1%; p < 0.001) and attenuated myocardial lactate accumulation (end-ischemic contents, 31.9 +/- 4.47 versus 10.3 +/- 1.26 micromol/wet weight, p < 0.0001), whereby a decrease in anaerobic glycolytic flux by at least 70% could constantly be observed throughout index ischemia. By calculation of flux:metabolite co-responses, the mechanisms of glycolytic regulation were investigated. The continuous deceleration of EMP flux in control myocadium could neither be explained on the basis of substrate availability nor be attributed to regulatory "key enzymes," as multisite regulation was employed for flux adjustment. In myocardium subjected to IP, an even pronounced deceleration of EMP flux during index ischemia was observed. Again, the adjustment of EMP flux was because of multisite modulation without any evidence for flux limitation by substrate availability or a key enzyme. However, IP changed the regulatory properties of most EMP enzymes, and some of these patterns could not be explained on the basis of substrate kinetics. Instead, other regulatory mechanisms, which have previously not yet been described for EMP enzymes, must be considered. These altered biochemical properties of the EMP enzymes have not yet been described.

Cardioprotection by ischemic preconditioning preserves mitochondrial function and functional coupling between adenine nucleotide translocase and creatine kinase

M. N. Laclau, S. Boudina, J. B. Thambo, L. Tariosse, G. Gouverneur, S. Bonoron-Adèle, V. A. Saks, K. D. Garlid and P. Dos Santos. Cardioprotection by Ischemic Preconditioning Preserves Mitochondrial Function and Functional Coupling Between Adenine Nucleotide Translocase and Creatine Kinase. Journal of Molecular and Cellular Cardiology (2001) 33, 947-956. This study investigates the effect of ischemic preconditioning on mitochondrial function, including functional coupling between the adenine nucleotide translocase and mitochondrial creatine kinase, which is among the first reactions to be altered in ischemia. Three groups of Langendorff-perfused rat hearts were studied: a control group, a group subjected to 30 min ischemia followed by 15 min reperfusion, and a group subjected to ischemic preconditioning prior to 30 min ischemia and 15 min reperfusion. Ischemic preconditioning significantly delayed the onset and amplitude of contracture during ischemia, decreased enzymatic release, and improved the recovery of heart contractile function after reperfusion. Mitochondrial function was assessed in permeabilized skinned fibers. The protective effect of preconditioning was associated with preservation of mitochondrial function, as evidenced by maintenance of the high K(1/2)for ADP in regulation of mitochondrial respiration and V(max)of respiration, the near absence of respiratory stimulation by exogenous cytochrome c, and preservation of functional coupling between mitochondrial creatine kinase and adenine nucleotide translocase. These data suggest that ischemic preconditioning preserves the structure-function of the intermembrane space, perhaps by opening the mitochondrial ATP-sensitive K(+)channel. The consequence is preservation of energy transfer processes from mitochondria to ATP-utilizing sites in the cytosol. Both of these factors may contribute to cardioprotection and better functional recovery of preconditioned hearts.

Cardioprotection with kappa-opioid receptor stimulation is associated with a slowing of cross-bridge cycling

Opioid and alpha-adrenergic receptor activation protect the heart from ischemic damage. One possible intracellular mechanism to explain this is that an improvement in ATP availability contributes to cardioprotection. We tested this hypothesis by correlating postischemic left ventricular developed pressure (LVDP) and myofibrillar Ca(2+)-dependent actomyosin Mg(2+)-ATPase from isolated rat hearts treated with the kappa-opioid receptor agonist U-50488H (1 microM) or the alpha-adrenergic receptor agonist phenylephrine (10 microM) + propranolol (3 microM). Preischemic treatment with U-50488H or phenylephrine + propranolol improved postischemic LVDP recovery by 25-30% over control hearts. Ca(2+)-dependent actomyosin Mg(2+)-ATPase was found to be 20% lower in both U-50488H- and phenylephrine + propranolol-treated hearts compared with control hearts. The kappa-opioid receptor antagonist nor-binaltorphimine (1 microM) abolished the effects of U-50488H on postischemic LVDP and actomyosin Mg(2+)-ATPase activity. Reduced actomyosin ATP utilization was also suggested in single ventricular myocytes treated with either U-50488H or the protein kinase C activator, phorbol 12-myristate 13-acetate (PMA), because U-50488H and PMA lowered maximum velocity of unloaded shortening by 15-25% in myocytes. U-50488H and phenylephrine + propranolol treatment both resulted in increased phosphorylation of troponin I and C protein. These findings are consistent with the hypothesis that kappa-opioid and alpha-adrenergic receptors decrease actin-myosin cycling rate, leading to a conservation of ATP and cardioprotection during ischemia.