Targeting Hexokinase II to mitochondria to modulate energy metabolism and reduce ischemia-reperfusion injury in heart

Mitochondrially bound hexokinase II (mtHKII) has long been known to confer cancer cells with their resilience against cell death. More recently, mtHKII has emerged as a powerful protector against cardiac cell death. mtHKII protects against ischaemia-reperfusion (IR) injury in skeletal muscle and heart, attenuates cardiac hypertrophy and remodelling, and is one of the major end-effectors through which ischaemic preconditioning protects against myocardial IR injury. Mechanisms of mtHKII cardioprotection against reperfusion injury entail the maintenance of regulated outer mitochondrial membrane (OMM) permeability during ischaemia and reperfusion resulting in stabilization of mitochondrial membrane potential, the prevention of OMM breakage and cytochrome C release, and reduced reactive oxygen species production. Increasing mtHK may also have important metabolic consequences, such as improvement of glucose-induced insulin release, prevention of acidosis through enhanced coupling of glycolysis and glucose oxidation, and inhibition of fatty acid oxidation. Deficiencies in expression and distorted cellular signalling of HKII may contribute to the altered sensitivity of diabetes to cardiac ischaemic diseases. The interaction of HKII with the mitochondrion constitutes a powerful endogenous molecular mechanism to protect against cell death in almost all cell types examined (neurons, tumours, kidney, lung, skeletal muscle, heart). The challenge now is to harness mtHKII in the treatment of infarction, stroke, elective surgery and transplantation. Remote ischaemic preconditioning, metformin administration and miR-155/miR-144 manipulations are potential means of doing just tha

Ischemic preconditioning, insulin, and morphine all cause hexokinase redistribution

Association of hexokinase (HK) with mitochondria preserves mitochondrial integrity and is an important mechanism by which cancer cells are protected against hypoxic conditions. Maintenance of mitochondrial integrity also figures prominently as a major characteristic of many cardioprotective manipulations. In this study, we provide evidence that cardioprotective interventions may promote HK redistribution from the cytosol to the mitochondria in the heart. Isolated Langendorff-perfused rat hearts (n=6/group) were subjected to normoxic perfusion (control, Con), three 5-min ischemia-reperfusion periods (ischemic preconditioning, IPC), 1 U/l insulin (Ins), or 1 mu M morphine (Mor). Hearts were immediately homogenized and centrifuged to obtain whole cell, cytosolic, and mitochondrial fractions. HK, lactate dehydrogenase (LDH), and citrate synthase (CS) enzyme activities were determined. No change in LDH or CS present in the cytosol fraction relative to whole cell activity was observed with any of the cardioprotective interventions. By contrast, HK present in the cytosol fraction relative to whole cell activity decreased significantly (P <0.05) with all cardioprotective interventions, from 0.58 +/- 0.03 (Con) to 0.46 +/- 0.04 (IPC), 0.41 +/- 0.01 (Ins), and 0.45 +/- 0.02 (Mor). In addition, HK relative to CS activity in the mitochondrial fraction increased significantly with cardioprotection, from 0.15 +/- 0.001 (Con) to 0.21 +/- 0.002 (IPC), 0.18 +/- 0.003 (Ins), and 0.21 +/- 0.005 (Mor). Our novel data suggest that well-known cardioprotective interventions share a common end-effector mechanism of cytosolic HK translocation. Association of HK with mitochondria may promote inhibition of the mitochondrial permeability transition pore and thereby reduce cell death and apoptosi

Commonly used numbers of microspheres affect cardiac vascular resistance

The main goal of the study was to examine how the microsphere technique affects the hemodynamics and mitochondrial energy status of the Langendorff-perfused rat heart. The hearts were perfused at a constant flow with Tyrode solution. NADH videofluorometry of the surface of the left ventricle was used to record the mitochondrial energy status as indication of regional ischemia. The effects of seven successive (separated by 10 min) injections of 0.1 ml of saline or (0.05% Tween 20; polysorbate 20, Sigma-Aldrich, St. Louis, MO, U.S.A.) or (0.05% Tween 20 + microspheres) were studied. The number of microspheres per injection were: #1 (2,500), #2 (5,000), #3 (10,000), #4 (20,000), #5 (40,000), #6 (40000), and #7 (80000). The anti-aggregation agent Tween always caused a biphasic response in perfusion pressure. Compared with the Tween effect, the injection of microspheres caused an initial change (mm Hg) in perfusion pressure of #1 (-10), #2 (NS), #3 (NS), #4 (+7.5), #5 (+12.3), #6 (+14.4), #7 (+18.3), and a delayed change (10 min after injection) of #1 (-22.2), #2 (-6.0), #3 (-4.1), #4 (-4.5), #5 (NS), #6 (NS), and #7 (+5.9). The microspheres caused a significant delayed increase in NADH only for injection #6 and #7. Similar results were found for different durations of the input function or when hearts were perfused at constant perfusion pressure. In hearts without flow reserve (10 muM adenosine), Tween injections were without effect, whereas three successive injections of 60,000 microspheres each only caused increases in perfusion pressure and NADH. The data demonstrate that in hearts with flow reserve present, even very low numbers of microspheres (2,000/g heart) cause large decreases in perfusion pressure without obvious signs of ischemia. When flow reserve was exhausted by either microsphere loading or adenosine addition, microspheres only caused increases in perfusion pressure and resulted in detectable ischemia (NADH). It is concluded that microspheres affect the vascular resistance of the heart and that these effects are flow reserve dependen

柱梁接合部における梁端溶接部の構造性能に関する研究

博士（工学）神戸大

Ischemic preconditioning affects hexokinase activity and HKII in different subcellular compartments throughout cardiac ischemia-reperfusion

Gurel E, Smeele KM, Eerbeek O, Koeman A, Demirci C, Hollmann MW, Zuurbier CJ. Ischemic preconditioning affects hexokinase activity and HKII in different subcellular compartments throughout cardiac ischemia-reperfusion. J Appl Physiol 106: 1909-1916, 2009. First published February 19, 2009; doi:10.1152/japplphysiol.90537.2008.-The glycolytic enzyme hexokinase (HK) is suggested to play a role in ischemic preconditioning (IPC). In the present study we determined how ischemic preconditioning affects HK activity and HKI and HKII protein content at five different time points and three different subcellular fractions throughout cardiac ischemia-reperfusion. Isolated Langendorff-perfused rat hearts (10 groups of 7 hearts each) were subjected to 35 min ischemia and 30 min reperfusion (control groups); the IPC groups were pretreated with 3 times 5-min ischemia. IPC was without effect on microsomal HK activity, and only decreased cytosolic HK activity at 35 min ischemia, which was mimicked by decreased cytosolic HKII, but not HKI, protein content. In contrast, mitochondrial HK activity at baseline and during reperfusion was elevated by IPC, without changes during ischemia. No effect of IPC on mitochondrial HK I protein content was observed. However, mitochondrial HK II protein content during reperfusion was augmented by IPC, albeit not following the IPC stimulus. It is concluded that IPC results in decreased cytosolic HK activity during ischemia that could be explained by decreased HKII protein content. IPC increased mitochondrial HK activity before ischemia and during reperfusion that was only mimicked by increased HK II protein content during reperfusion. IPC was without effect on the phosphorylation status of HK before ischemia. We conclude that IPC is associated with 1) a biphasic response of increased mitochondrial HK activity before and after ischemia, 2) decreased cytosolic HK activity during ischemia, and 3) cellular redistribution of HKII but not HK

Hexokinase cellular trafficking in ischemia-reperfusion and ischemic preconditioning is altered in type I diabetic heart

Diabetes mellitus (DM) has been reported to alter the cardiac response to ischemia-reperfusion (IR). In addition, cardioprotection induced by ischemic preconditioning (IPC) is often impaired in diabetes. We have previously shown that the subcellular localisation of the glycolytic enzyme hexokinase (HK) is causally related to IR injury and IPC protective potential. Especially the binding of HK to mitochondria and prevention of HK solubilisation (HK detachment from mitochondria) during ischemia confers cardioprotection. It is unknown whether diabetes affects HK localisation during IR and IPC as compared to non-diabetes. In this study we hypothesize that DM alters cellular trafficking of hexokinase in response to IR and IPC, possibly explaining the altered response to IR and IPC in diabetic heart. Control (CON) and type I diabetic (DM) rat hearts (65 mg/kg streptozotocin, 4 weeks) were isolated and perfused in Langendorff-mode and subjected to 35 min I and 30 min R with or without IPC (3 times 5 min I). Cytosolic and mitochondrial fractions were obtained at (1) baseline, i.e. after IPC but before I, (2) 35 min I, (3) 5 min R and (4) 30 min R. DM improved rate-pressure product recovery (RPP; 71 +/- A 10 % baseline (DM) versus 9 +/- A 1 % baseline (CON) and decreased contracture (end-diastolic pressure: 24 +/- A 8 mmHg (DM) vs 77 +/- A 4 mmHg (CON)) after IR as compared to control, and was associated with prevention of HK solubilisation at 35 min I. IPC improved cardiac function in CON but not in DM hearts. IPC in CON prevented HK solubilisation at 35 min I and at 5 min R, with a trend for increased mitochondrial HK. In contrast, the non-effective IPC in DM was associated with solubilisation of HK and decreased mitochondrial HK at early reperfusion and a reciprocal behaviour at late reperfusion. We conclude that type I DM significantly altered cellular HK translocation patterns in the heart in response to IR and IPC, possibly explaining altered response to IR and IPC in diabetes

Delayed ischaemic contracture onset by empagliflozin associates with NHE1 inhibition and is dependent on insulin in isolated mouse hearts

AIMS: Sodium glucose cotransporter 2 (SGLT2) inhibitors have sodium-hydrogen exchanger (NHE) inhibition properties in isolated cardiomyocytes, but it is unknown whether these properties extend to the intact heart during ischaemia-reperfusion (IR) conditions. NHE inhibitors as Cariporide delay time to onset of contracture (TOC) during ischaemia and reduce IR injury. We hypothesized that, in the ex vivo heart, Empagliflozin (Empa) mimics Cariporide during IR by delaying TOC and reducing IR injury. To facilitate translation to in vivo conditions with insulin present, effects were examined in the absence and presence of insulin. METHODS AND RESULTS: Isolated C57Bl/6NCrl mouse hearts were subjected to 25 min I and 120 min R without and with 50 mU/L insulin. Without insulin, Empa and Cari delayed TOC by 100 and 129 s, respectively, yet only Cariporide reduced IR injury [infarct size (mean ± SEM in %) from 51 ± 6 to 34 ± 5]. Empa did not delay TOC in the presence of the NHE1 inhibitor Eniporide. Insulin perfusion increased tissue glycogen content at baseline (from 2 ± 2 µmol to 42 ± 1 µmol glycosyl units/g heart dry weight), amplified G6P and lactate accumulation at end-ischaemia, thereby decreased mtHKII and exacerbated IR injury. Under these conditions, Empa (1 µM) and Cariporide (10 µM) were without effect on TOC and IR injury. Empa and Cariporide both inhibited NHE activity, in isolated cardiomyocytes, independent of insulin. CONCLUSIONS: In the absence of insulin, Empa and Cariporide strongly delayed the time to onset of contracture during ischaemia. In the presence of insulin, both Empa and Cari were without effect on IR, possibly because of severe ischaemic acidification. Insulin exacerbates IR injury through increased glycogen depletion during ischaemia and consequently mtHKII dissociation. The data suggest that also in the ex vivo intact heart Empa exerts direct cardiac effects by inhibiting NHE during ischaemia, but not during reperfusion

Hexokinase cellular trafficking in ischemia-reperfusion and ischemic preconditioning is altered in type I diabetic heart

Diabetes mellitus (DM) has been reported to alter the cardiac response to ischemia-reperfusion (IR). In addition, cardioprotection induced by ischemic preconditioning (IPC) is often impaired in diabetes. We have previously shown that the subcellular localisation of the glycolytic enzyme hexokinase (HK) is causally related to IR injury and IPC protective potential. Especially the binding of HK to mitochondria and prevention of HK solubilisation (HK detachment from mitochondria) during ischemia confers cardioprotection. It is unknown whether diabetes affects HK localisation during IR and IPC as compared to non-diabetes. In this study we hypothesize that DM alters cellular trafficking of hexokinase in response to IR and IPC, possibly explaining the altered response to IR and IPC in diabetic heart. Control (CON) and type I diabetic (DM) rat hearts (65 mg/kg streptozotocin, 4 weeks) were isolated and perfused in Langendorff-mode and subjected to 35 min I and 30 min R with or without IPC (3 times 5 min I). Cytosolic and mitochondrial fractions were obtained at (1) baseline, i.e. after IPC but before I, (2) 35 min I, (3) 5 min R and (4) 30 min R. DM improved rate-pressure product recovery (RPP; 71 ± 10 % baseline (DM) versus 9 ± 1 % baseline (CON) and decreased contracture (end-diastolic pressure: 24 ± 8 mmHg (DM) vs 77 ± 4 mmHg (CON)) after IR as compared to control, and was associated with prevention of HK solubilisation at 35 min I. IPC improved cardiac function in CON but not in DM hearts. IPC in CON prevented HK solubilisation at 35 min I and at 5 min R, with a trend for increased mitochondrial HK. In contrast, the non-effective IPC in DM was associated with solubilisation of HK and decreased mitochondrial HK at early reperfusion and a reciprocal behaviour at late reperfusion. We conclude that type I DM significantly altered cellular HK translocation patterns in the heart in response to IR and IPC, possibly explaining altered response to IR and IPC in diabete