Real-time monitoring of cardiac metabolism using biosensors shows myocardial protection during ischemia-reperfusion injury with glucose-insulin-potassium administration

Cardiometabolism as an Interlocking Puzzle between the Healthy and Diseased Heart: New Frontiers in Therapeutic Applications

Cardiac metabolism represents a crucial and essential connecting bridge between the healthy and diseased heart. The cardiac muscle, which may be considered an omnivore organ with regard to the energy substrate utilization, under physiological conditions mainly draws energy by fatty acids oxidation. Within cardiomyocytes and their mitochondria, through well-concerted enzymatic reactions, substrates converge on the production of ATP, the basic chemical energy that cardiac muscle converts into mechanical energy, i.e., contraction. When a perturbation of homeostasis occurs, such as an ischemic event, the heart is forced to switch its fatty acid-based metabolism to the carbohydrate utilization as a protective mechanism that allows the maintenance of its key role within the whole organism. Consequently, the flexibility of the cardiac metabolic networks deeply influences the ability of the heart to respond, by adapting to pathophysiological changes. The aim of the present review is to summarize the main metabolic changes detectable in the heart under acute and chronic cardiac pathologies, analyzing possible therapeutic targets to be used. On this basis, cardiometabolism can be described as a crucial mechanism in keeping the physiological structure and function of the heart; furthermore, it can be considered a promising goal for future pharmacological agents able to appropriately modulate the rate-limiting steps of heart metabolic pathways.

Evaluating Novel Targets of Ischemia Reperfusion Injury in Pig Models

Coronary heart diseases are of high relevance for health care systems in developed countries regarding patient numbers and costs. Disappointingly, the enormous effort put into the development of innovative therapies and the high numbers of clinical studies conducted are counteracted by the low numbers of therapies that become clinically effective. Evidently, pre-clinical research in its present form does not appear informative of the performance of treatments in the clinic and, even more relevant, it appears that there is hardly any consent about how to improve the predictive capacity of pre-clinical experiments. According to the steadily increasing relevance that pig models have gained in biomedical research in the recent past, we anticipate that research in pigs can be highly predictive for ischemia-reperfusion injury (IRI) therapies as well. Thus, we here describe the significance of pig models in IRI, give an overview about recent developments in evaluating such models by clinically relevant methods and present the latest insight into therapies applied to pigs under IRI.

Imaging porcine cardiac substrate selection modulations by glucose, insulin and potassium intervention: A hyperpolarized [1-13 C]pyruvate study

Cardiac metabolism has received considerable attention in terms of both diagnostics and prognostics, as well as a novel target for treatment. As human trials involving hyperpolarized magnetic resonance in the heart are imminent, we sought to evaluate the general feasibility of detection of an imposed shift in metabolic substrate utilization during metabolic modulation with glucose-insulin-potassium (GIK) infusion, and thus the limitations associated with this strategy, in a large animal model resembling human physiology. Four [1-¹³ C]pyruvate injections did not alter the blood pressure or ejection fraction over 180 min. Hyperpolarized [1-¹³ C]pyruvate conversion showed a generally high reproducibility, with intraclass correlation coefficients between the baseline measurements at 0 and 30 min as follows: lactate to pyruvate, 0.85; alanine to pyruvate, 1.00; bicarbonate to pyruvate, 0.83. This study demonstrates that hyperpolarized [1-¹³ C]pyruvate imaging is a feasible technique for cardiac studies and shows a generally high reproducibility in fasted large animals. GIK infusion increases the metabolic conversion of pyruvate to its metabolic derivatives lactate, alanine and bicarbonate, but with increased variability.

Myocardial protection of insulin and potassium in a porcine ischemia-reperfusion model

BACKGROUND

We previously evaluated cardioprotective effects of glucose-insulin-potassium (GIK) in a porcine ischemia-reperfusion model; our results showed less myocardial pH decrease during ischemia and reperfusion and faster normalization of ATP and glucose during reperfusion. The proposed protective mechanism was facilitation of glucose transport for myocardial metabolism. The objective of this study was to assess the impact of insulin-potassium (IK) alone on myocardial metabolism.

METHODS

Male swine received continuous infusion of IK (IK group, n = 10), GIK (GIK group, n = 10), or standard lactated Ringer's (LR) solution (controls, n = 10). Induction of 20 minutes of ischemia in the left anterior descending (LAD) artery distribution was followed by 20 minutes of reperfusion. Real-time biosensors recorded pH and glucose levels in ischemic and nonischemic beds. Myocardial biopsies in the distribution of the LAD assessed ATP levels. Groups were compared using the Kruskal-Wallis and Mann-Whitney tests.

RESULTS

Real-time data are presented as percent change from baseline. At less than 10 minutes of ischemia, the average pH change was less for the IK group than the LR group (0.03% +/- 0.21% vs -2.06% +/- 1.23%; P = .001), and the pH change in the IK group was similar to the GIK group. After 10 minutes of ischemia and during the first 10 minutes of reperfusion, the IK group experienced pH changes that were similar to the LR group. Biopsies after 20 minutes of ischemia and 20 minutes of reperfusion showed less of a decline in ATP levels for the IK group compared to the LR group. Glucose at all time points demonstrated no statistically significant differences.

CONCLUSION

IK infusion alone demonstrates cardioprotective effects during early ischemia; however, compared to GIK infusion after 20 minutes of ischemia and reperfusion, myocardial pH and glucose levels were not sustained. Although insulin may facilitate glucose transport during ischemia, additional glucose in combination with IK enhances myocardial protection during reperfusion. This finding suggests that GIK enhancement during acute ischemia-reperfusion may improve myocardial protection.