Glucose, insulin and potassium (GIK) during reperfusion mediates improved myocardial bioenergetics

Insulin Postconditioning Reduces Infarct Size in the Porcine Heart in a Dose-Dependent Manner

AIM

Insulin and glucose may have opposite effects when used to reduce ischemia-reperfusion injury. When insulin is administered alone, feeding state determines tolerance and further induces metabolic and hormonal changes. Higher insulin doses are needed for similar activation of cardioprotective Akt signaling in the fed compared to the fasted pig heart. Thus, the aim of the study was to investigate the effects of 2 prespecified insulin doses on infarct size, apoptosis, metabolism, and cardiac function in a clinically relevant, randomized large animal model using conventional percutaneous catheter intervention techniques and including different fasting states.

METHODS AND RESULTS

Twenty-seven female pigs were subjected to 40-minute ischemia and 120-minute reperfusion. Pharmacological postconditioning with intracoronary infusions administered over 3 × 30 seconds was performed at immediate reperfusion. Animals were randomly assigned to 3 groups-preexperimental fasting and intracoronary saline ( controls), preexperimental fasting and 0.1U of insulin ( fasted Ins_0.1U), and preexperimental feeding and 1.0U of insulin ( fed Ins_1.0U). A significant reduction in infarct size was demonstrated in the fed Ins_1.0U group ( P = .047) but not in the fasted Ins_0.1U group ( P = .531) compared to controls (infarct size normalized to area at risk ± standard deviation: controls 70.2% ± 12.9%, fasted Ins_0.1U 65.0% ± 9.4%, and fed Ins_1.0U 54.4% ± 7.3%). Infarct limitation was associated with more uncleaved caspase-3 in the area of risk and the infarcted area, lower circulating free fatty acids, and less increase in heart rate during reperfusion. Fed animals had higher levels of glucose, carnitine, potassium, and normetanephrine and higher heart rate at baseline compared to controls.

CONCLUSION

Insulin postconditioning reduced infarct size in the in vivo pig heart, but the beneficial effects were restricted to the highest dose, which is limited by side effects and can only be given to nonfasted animals. The finding challenges successful general use of insulin in the treatment of reperfusion injury in clinical acute myocardial infarction.

Cardiac damage associated with stress hyperglycaemia and acute coronary syndrome changes according to level of presenting blood glucose

OBJECTIVE

To determine the prevalence of stress hyperglycaemia in people presenting with acute coronary syndrome (ACS), and the relationships between admission glucose and cardiac damage, cardiovascular mortality and morbidity.

METHODS

In a prospective observational study people presenting with ACS at the Gold Coast Hospital had their admission glucose (AG) level tested to determine stress hyperglycaemia. A range of measurements supplemented this data including troponin levels, category of ACS and major adverse coronary events (MACEs) were obtained through hospital records and patient follow-up post-discharge.

RESULTS

One hundred eighty-eight participants were recruited. The prevalence of stress hyperglycaemia in ACS was 44% with 31% having a previous diagnosis of type 2 diabetes and 7.7% had undiagnosed diabetes. The stress hyperglycaemic group had a significantly higher median troponin levels compared to participants with normal blood glucose levels on admission (p<0.05) however the highest presenting glucose group (>15 mmol/L) had troponin levels similar to people presenting with normal blood glucose levels and ACS (p>0.05).

CONCLUSIONS

Cardiac necrosis as measured by troponin levels is significantly increased in people with ACS and stress hyperglycaemia. This study found that one in four participants presenting with ACS and an admission glucose of >7.0 had no previous diagnosis for diabetes.

PRACTICE IMPLICATION

Consistently ordering HbA1C testing on patients with high AG can enable earlier diagnosis and treatment of diabetes.

Citric Acid Cycle Intermediates in Cardioprotection

Over the last decade, there has been a concerted clinical effort to deliver on the laboratory promise that a variety of maneuvers can profoundly increase cardiac tolerance to ischemia and/or reduce additional damage consequent upon reperfusion. Here we will review the proximity of the metabolic approach to clinical practice. Specifically, we will focus on how the citric acid cycle is involved in cardioprotection. Inspired by cross-fertilization between fundamental cancer biology and cardiovascular medicine, a set of metabolic observations have identified novel metabolic pathways, easily manipulable in man, which can harness metabolism to robustly combat ischemia-reperfusion injury.

An increase in the redox state during reperfusion contributes to the cardioprotective effect of GIK solution

This study aimed at determining whether glucose-insulin-potassium (GIK) solutions modify the NADH/NAD(+) ratio during postischemic reperfusion and whether their cardioprotective effect can be attributed to this change in part through reduction of the mitochondrial reactive oxygen species (ROS) production. The hearts of 72 rats were perfused with a buffer containing glucose (5.5 mM) and hexanoate (0.5 mM). They were maintained in normoxia for 30 min and then subjected to low-flow ischemia (0.5% of the preischemic coronary flow for 20 min) followed by reperfusion (45 min). From the beginning of ischemia, the perfusate was subjected to various changes: enrichment with GIK solution, enrichment with lactate (2 mM), enrichment with pyruvate (2 mM), enrichment with pyruvate (2 mM) plus ethanol (2 mM), or no change for the control group. Left ventricular developed pressure, heart rate, coronary flow, and oxygen consumption were monitored throughout. The lactate/pyruvate ratio of the coronary effluent, known to reflect the cytosolic NADH/NAD(+) ratio and the fructose-6-phosphate/dihydroxyacetone-phosphate (F6P/DHAP) ratio of the reperfused myocardium, were evaluated. Mitochondrial ROS production was also estimated. The GIK solution improved the recovery of mechanical function during reperfusion. This was associated with an enhanced cytosolic NADH/NAD(+) ratio and reduced mitochondrial ROS production. The cardioprotection was also observed when the hearts were perfused with fluids known to increase the cytosolic NADH/NAD(+) ratio (lactate, pyruvate plus ethanol) compared with the other fluids (control and pyruvate groups). The hearts with a high mechanical recovery also displayed a low F6P/DHAP ratio, suggesting that an accelerated glycolysis rate may be responsible for increased cytosolic NADH production. In conclusion, the cardioprotection induced by GIK solutions could occur through an increase in the cytosolic NADH/NAD(+) ratio, leading to a decrease in mitochondrial ROS production.

The effect of insulin on the heart: Part 2: Effects on function during and post myocardial ischaemia

Insulin infusion has been advocated in the treatment of myocardial ischaemia and myocardial infarction. There is evidence from experimental animal studies for a protective effect of high-dose insulin administration in myocardial ischaemia and myocardial infarction. In some relatively small study populations a reduction in mortality was reported in those patients who received glucose-insulin-potassium (GIK) during myocardial infarction, which was confirmed in two meta-analyses. However, it has not been possible to reproduce these positive results in large randomised clinical trials. (Neth Heart J 2010;18:255-9.).

Opioid receptor agonist reduces myocardial ischemic injury when administered during early phase of myocardial ischemia

AIM OF THE STUDY

Postresuscitation myocardial dysfunction is one of the leading causes of early death after initial success of resuscitation, the mechanisms of postresuscitation myocardial dysfunction remain controversial. We hypothesize that ischemia injury, rather than reperfusion injury is the major cause of postresuscitation myocardial dysfunction. We proposed to investigate the separate effects of ischemia and reperfusion injury on postresuscitation myocardial dysfunction.

METHODS

Thirty-three Langendorff-perfused isolated rat hearts were subjected to 15 min of global ischemia followed by 120 min of reperfusion. Pentazocine was utilized as a myocardial protective agent, either before ischemia or during reperfusion. All hearts were randomized into 3 groups: (1) "ischemia protection", in which pentazocine was infused 10 min prior to global ischemia, (2) "reperfusion protection", in which pentazocine was infused during 2h of reperfusion and (3) "control", with no pentazocine infusion. Left ventricular (LV) functions were measured by the maximal rate of LV pressure rise (dP/dt(max)) and decline (-dP/dt(max)), the maximal LV diastolic pressure (LVDP). The incidences of postischemic arrhythmias were measured.

RESULTS

When pentazocine was administered before onset of ischemia, the LV systolic and diastolic functions were significantly greater, and the postischemic arrhythmias were significantly less in comparison to those with reperfusion protection (p<0.05) and the control group (p<0.05).

CONCLUSIONS

In this model, the severity of postischemic myocardial dysfunction was less when the heart was protected during ischemia. Ischemia injury may therefore be the major cause of postresuscitation myocardial dysfunction.

O2 delivery and redox state are determinants of compartment-specific reactive O2 species in myocardial reperfusion

Reperfusion of the ischemic myocardium leads to a burst of reactive O(2) species (ROS), which is a primary determinant of postischemic myocardial dysfunction. We tested the hypothesis that early O(2) delivery and the cellular redox state modulate the initial myocardial ROS production at reperfusion. Isolated buffer-perfused rat hearts were loaded with the fluorophores dihydrofluorescein or Amplex red to detect intracellular and extracellular ROS formation using surface fluorometry at the left ventricular wall. Hearts were made globally ischemic for 20 min and then reperfused with either 95% or 20% O(2)-saturated perfusate. The same protocol was repeated in hearts loaded with dihydrofluorescein and perfused with either 20 or 5 mM glucose-buffered solution to determine relative changes in NADH and FAD. Myocardial O(2) delivery during the first 5 min of reperfusion was 84.7 +/- 4.2 ml O(2)/min with 20% O(2)-saturated buffer and 354.4 +/- 22.8 ml O(2)/min with 95% O(2) (n = 8/group, P < 0.001). The fluorescein signal (intracellular ROS) was significantly increased in hearts reperfused with 95% O(2) compared with 20% O(2). However, the resorufin signal (extracellular ROS) was significantly increased with 20% O(2) compared with 95% O(2) during reperfusion. Perfusion of hearts with 20 mM glucose reduced the (.)NADH during ischemia (P < 0.001) and the (.)ROS at reperfusion (P < 0.001) compared with 5.5 mM-perfused glucose hearts. In conclusion, initial O(2) delivery to the ischemic myocardium modulates a compartment-specific ROS response at reperfusion such that high O(2) delivery promotes intracellular ROS and low O(2) delivery promotes extracellular ROS. The redox state that develops during ischemia appears to be an important precursor for reperfusion ROS production.

Bioefficacy of a novel calcium-potassium salt of (-)-hydroxycitric acid

Obesity is associated with cardiovascular disease, diabetes and certain forms of cancer. Popular strategies on weight loss often fail to address many key factors such as fat mass, muscle density, bone density, water mass, their inter-relationships and impact on energy production, body composition, and overall health and well-being. (-)-Hydroxycitric acid (HCA), a natural plant extract from the dried fruit rind of Garcinia cambogia, has been reported to promote body fat loss in humans without stimulating the central nervous system. The level of effectiveness of G. cambogia extract is typically attributed solely to HCA. However, other components by their presence or absence may significantly contribute to its therapeutic effectiveness. Typically, HCA used in dietary weight loss supplement is bound to calcium, which results in a poorly soluble (<50%) and less bioavailable form. Conversely, the structural characteristics of a novel Ca2+/K+ bound (-)-HCA salt (HCA-SX or Super CitriMax) make it completely water soluble as well as bioavailable. An efficacious dosage of HCA-SX (4500 mg/day t.i.d.) provides a good source of Ca2+ (495 mg, 49.5% of RDI) and K+ (720 mg, 15% of RDI). Ca2+ ions are involved in weight management by increasing lipid metabolism, enhancing thermogenesis, and increasing bone density. K+, on the other hand, increases energy, reduces hypertension, increases muscle strength and regulates arrhythmias. Both Ca and K act as buffers in pH homeostasis. HCA-SX has been shown to increase serotonin availability, reduce appetite, increase fat oxidation, improve blood lipid levels, reduce body weight, and modulate a number of obesity regulatory genes without affecting the mitochondrial and nuclear proteins required for normal biochemical and physiological functions.

ST-segment elevation resolution and outcome in patients treated with primary angioplasty and glucose-insulin-potassium infusion

BACKGROUND

To evaluate the impact of adjunctive high-dose glucose-insulin-potassium (GIK) on ST-segment elevation resolution in patients with ST-segment elevation myocardial infarction (MI).

METHODS

As part of a randomized controlled trial of GIK versus no GIK in patients treated with primary percutaneous coronary intervention (PCI) for ST-elevation MI in a tertiary referral center, we analyzed ST-segment elevation resolution. Paired electrocardiographic recordings (baseline and 3 hours after primary PCI) were available in 612 (65%) of 940 patients.

RESULTS

We analyzed paired electrocardiograms of 310 patients randomized to GIK and 302 control patients. Baseline characteristics of the groups were comparable. Combined complete (>70%) and partial (30%-70%) resolution was more commonly observed in the GIK group (87%) when compared with the control group (78%), odds ratio 1.92 (95% CI 1.23-3.02, P = .004); 1-year mortality was lower in patients with combined complete and partial resolution compared with patients without resolution (3.8% vs 10.3%, P = .011). There was no difference in 1-year mortality between GIK and control patients (5.5% vs 4.3%, P = .58).

CONCLUSIONS

In patients with ST-elevation MI treated with primary PCI, addition of GIK is associated with improved ST-segment elevation resolution. ST-segment elevation resolution is related to improved 1-year survival. No benefit of GIK on 1-year outcome was observed. Future trials should investigate whether GIK-induced improvement of ST-segment elevation resolution results in more favorable clinical outcome.

Global ischemic duration and reperfusion function in the isolated perfused rat heart

Post-ischemic myocardial dysfunction has been observed in a variety of clinical situations including cardiac arrest. Potentially survivable cardiac arrest following short-term global myocardial ischemia may be of insufficient duration to cause irreversible myocyte injury, but still results in contractile and bioenergetic dysfunction. The purpose of this study was to characterize the ischemic transition from reversible to irreversible injury in the isolated perfused rat heart. Isolated, buffer perfused, male Sprague-Dawley rat hearts underwent normothermic ischemia of 15, 20, 25 or 30 min with or without 30 min of reperfusion and were freeze clamped in liquid nitrogen for bioenergetic analysis of LV tissue. Post-ischemic LV function and measurements of bioenergetic recovery were made between groups and with non-ischemic controls. Baseline LV function was similar in all groups. Post-ischemic contractile function was markedly depressed in the 25 and 30 min ischemia groups with persistent depression of high-energy phosphates, total adenine nucleotide pool, myocardial oxygen consumption, elevated CK release and evidence of significant mitochondrial edema in the 30 min group. In contrast with longer ischemic periods, the reduction in LV contractile function after 15 and 20 min of ischemia was mild, with more complete bioenergetic recovery, minimal CK release, and normal appearing mitochondrial. This data suggests a period of transition from reversible to irreversible injury occurring at approximately 20 min of normothermic global ischemia in the isolated perfused rat heart.

Insulin therapy in critically ill patients

PURPOSE OF REVIEW

The recent publication of the results of an aggressive approach to the treatment of hyperglycaemia in critically ill patients, and a rekindling of interest in the use of an infusion of glucose insulin and potassium as adjunctive therapy in a diverse group of patients with cardiovascular disease, warrants a review of the multiple effects of insulin and a review of laboratory and clinical studies.

RECENT FINDINGS

The use of an aggressive protocol to maintain normoglycaemia in critically ill patients has been demonstrated to be a beneficial technique in the critical care setting. Implementation of the protocol outside of a research setting appears to be feasible. Recent studies on the use of insulin in addition to glucose and potassium in patients with diverse cardiovascular diseases have also demonstrated positive results.

SUMMARY

This review will summarize some of the putative beneficial effects of insulin as a pharmacological agent, and review recent clinical data. Although the relative benefits of normoglycaemia in the critical care setting and the beneficial effects of insulin are difficult to differentiate, a substantial overlap exists. The extent to which these converging therapies (aggressive normoglycaemia and insulin pharmacotherapy) will be applicable to diverse clinical settings has yet to be determined.

Allopurinol improves cardiac dysfunction after ischemia-reperfusion via reduction of oxidative stress in isolated perfused rat hearts

It has been reported that the xanthine oxidase inhibitor, allopurinol, has a protective effect on ischemia - reperfusion injury, but the precise mechanism of its action is still unclear. Therefore, in the present study the mechanisms of the myocardial protection of allopurinol were evaluated in isolated perfused rat hearts. Allopurinol significantly inhibited myocardial xanthine oxidase activity, and improved left ventricular dysfunction after ischemia - reperfusion. In addition, the lactate dehydrogenase content in the coronary effluent obtained after reperfusion was significantly decreased. ATP, ADP, AMP and IMP significantly decreased, whereas inosine, hypoxanthine and xanthine significantly increased after ischemia in both the control and allopurinol groups. The concentration of xanthine was significantly decreased after ischemia - reperfusion in the allopurinol group; however, allopurinol did not affect the other purine metabolites. To evaluate the accumulation of oxidative stress, thiobarbituric acid reactive substances (TBARS) production in myocardial tissue was measured and allopurinol significantly decreased TBARS formation after ischemia - reperfusion. Finally, myocardial hydroxyl radicals were directly measured by electron spin resonance spectroscopy with the nitroxide radical 4-hydroxy-2, 2,6,6-tetramethyl-piperidine-N-oxyl. Hydroxyl radicals significantly increased immediately after reperfusion, but were significantly decreased in the allopurinol group. In conclusion, allopurinol reduced myocardial injury after ischemia-reperfusion by suppressing oxidative stress, but not by salvage of ATP. These findings may lead to the development of new therapeutic strategies for myocardial ischemia - reperfusion injury.