A role of PKC in the improvement of energy metabolism in preconditioned heart

Objectives. A possible link between activation of PKC and improvement of energy metabolism during reperfusion in ischemic preconditioning hearts was examined. Methods. Isolated perfused rat hearts were preconditioned by 5-min ischemia and 5-min reperfusion in the presence and absence of a PKC inhibitor polymyxin B (50 μM) and then subjected to 40-min sustained ischemia and subsequent 30-min reperfusion. In another set of experiments, the hearts pretreated with and without a PKC activator PMA (15 pmol/5 min) were subjected to the sustained ischemia and reperfusion. Myocardial high-energy phosphates, glycolytic intermediates and mitochondrial oxygen consumption capacity were determined at appropriate experimental sequences. Results. Preconditioning enhanced the recovery of cardiac function such as left ventricular developed pressure, heart rate and rate-pressure product of the reperfused heart, suppressed the release of creatine kinase, enhanced the reperfusion-induced restoration of myocardial high-energy phosphates, attenuated the reperfusion-induced accumulation in glucose 6-phosphate and fructose 6-phosphate contents, abolished the ischemia-induced increase in tissue lactate content and prevented the ischemia-induced decrease in mitochondrial oxygen consumption capacity. Treatment of the perfused heart with PMA mimicked the effects of preconditioning on post-ischemic contractile function, enzyme release, levels of myocardial energy store, glycolytic intermediates and lactate, and mitochondrial function. Polymyxin B-treatment abolished the preconditioning-induced recovery of post-ischemic contractile function, the suppression of the release of CK, the restoration of myocardial energy store, and the preservation of mitochondrial function, whereas it did not cancel the improvement of glycolytic intermediate levels and the reduction in tissue lactate accumulation. Post-ischemic contractile function was closely related to restoration of high-energy phosphates and mitochondrial oxygen consumption capacity in all hearts subjected to ischemia/reperfusion. Conclusion. The results suggest that activation of PKC and preservation of mitochondrial function are closely linked with each other in the preconditioned heart, which may lead to the improvement of post-ischemic contractile function. Received: 29 January 1999, Returned for 1. revision: 26 February 1999, 1. Revision received: 27 April 1999, Returned for 2. revision: 18 May 1999, 2. Revision received: 12 July 1999, Returned for 3. revision: 26 July 1999, 3. Revision received: 25 October 1999, Accepted: 3 November 1999     

How increased oxidative stress promotes longevity and metabolic health: The concept of mitochondrial hormesis (mitohormesis)

Recent evidence suggests that calorie restriction and specifically reduced glucose metabolism induces mitochondrial metabolism to extend life span in various model organisms, including Saccharomyces cerevisiae, Drosophila melanogaster, Caenorhabditis elegans and possibly mice. In conflict with Harman’s free radical theory of aging (FRTA), these effects may be due to increased formation of reactive oxygen species (ROS) within the mitochondria causing an adaptive response that culminates in subsequently increased stress resistance assumed to ultimately cause a long-term reduction of oxidative stress. This type of retrograde response has been named mitochondrial hormesis or mitohormesis, and may in addition be applicable to the health-promoting effects of physical exercise in humans and, hypothetically, impaired insulin/IGF-1-signaling in model organisms. Consistently, abrogation of this mitochondrial ROS signal by antioxidants impairs the lifespan-extending and health-promoting capabilities of glucose restriction and physical exercise, respectively. In summary, the findings discussed in this review indicate that ROS are essential signaling molecules which are required to promote health and longevity. Hence, the concept of mitohormesis provides a common mechanistic denominator for the physiological effects of physical exercise, reduced calorie uptake, glucose restriction, and possibly beyond.     

Role of glycolysis in the energy production for the non-mechanical myocardial work in isolated pig hearts*

Summary

Background: The dissociation of mechanical from non-mechanical energy utilisation can be studied using BDM (2,3-butanedione monoxime), which inhibits the actin-myosin interaction without inhibiting Ca²⁺ transport. The objective of the present study was to establish if increasing the non-mechanical energy demand of perfused isolated pig hearts by dobutamine stimulation requires glycolysis with increased exogenous glucose uptake.

Methods: Five isolated pig hearts (CTRL) were perfused for 90?min at constant flow (1?ml?g^?1?min^?1) with non-recirculating blood containing 30?mM BDM and 26?MBq/l of fluorine-18 2-fluoro-2-deoxyglucose (¹⁸FDG). This was compared with five hearts (DOBU) subjected to the same protocol for the first 30?min and then to dobutamine (1.5?μM) for the following 30?min and dobutamine (4?μM) for the last 30?min. Five other isolated hearts were perfused as for the DOBU group but without BDM (CTRLDOBU). Using a clinical PET scanner, glucose uptake was assessed by estimating ¹⁸FDG uptake using linear regression. The slope variations were compared using a global test of coincidence.

Results: Heart rate was at 100?±?2 b.p.m. in the CTRL group and at 180?±?7 b.p.m. in the DOBU group. ¹⁸FDG uptake was homogeneous within the whole myocardium and we observed a linear and regular increase in both the CTRL and DOBU groups (p, NS). In the CTRLDOBU group, ¹⁸FDG uptake was also homogeneous within the whole myocardium, but slopes of ¹⁸FDG uptake during dobutamine perfusion were higher than without dobutamine.

Conclusion: In blood-perfused isolated pig hearts, exogenous glucose is not necessarily required when non-mechanical energy is increased by dobutamine stimulation. These findings suggest that ATP derived from glycolysis is not necessary to preserve myocardial Ca²⁺ transport during β-adrenergic stimulation.     

Carnosine inhibits KRAS-mediated HCT116 proliferation by affecting ATP and ROS production

Carnosine is a natural dipeptide that has generated particular interest for its antioxidant, anti-aging and especially for its antiproliferative properties. In this study, we demonstrate that carnosine inhibits the proliferation of human HCT116 colon cancer cells. In this cell line, the activating KRAS mutation induces mitochondrial ROS, the signaling molecules for cell proliferation. We observed that 50-100 mM carnosine decreases ATP and ROS concentration and induces cell cycle arrest in G1 phase. In HCT116 cells these effects are related to decreased ERK1/2 phosphorylation and increased p21^waf1 protein. Our findings support the concept that carnosine could inhibit HCT116 cell growth via its antioxidant activity and its ability to affect glycolysis.     

High rates of residual fatty acid oxidation during mild ischemia decrease cardiac work and efficiency

It is unknown what effects high levels of fatty acids have on energy metabolism and cardiac efficiency during milder forms of ischemia. To address this issue, isolated working rat hearts perfused with Krebs-Henseleit solution (5 mM glucose, 100 μU/mL insulin, and 0.4 (Normal Fat) or 1.2 mM palmitate (High Fat)) were subjected to 30 min of aerobic perfusion followed by 30 min of mild ischemia (39% reduction in coronary flow). Both groups had similar aerobic function and rates of glycolysis, however the High Fat group had elevated rates of palmitate oxidation (150%), and decreased rates of glucose oxidation (51%). Mild ischemia decreased cardiac work (56% versus 40%) and efficiency (29% versus 11%) further in High Fat hearts. Palmitate oxidation contributed a greater percent of acetyl-CoA production during mild ischemia in the High Fat group (81% versus 54%). During mild ischemia glycolysis remained at aerobic levels in the Normal Fat group, but was accelerated in the High Fat group. Triglyceride, glycogen and adenine nucleotide content did not differ at the end of mild ischemia, however glycogen turnover was double in the High Fat group (248%). Addition of the pyruvate dehydrogenase inhibitor dichloroacetate to the High Fat group resulted in a doubling of the rate of glucose oxidation and improved cardiac efficiency during mild ischemia. We demonstrate that fatty acid oxidation dominates as the main source of residual oxidative metabolism during mild ischemia, which is accompanied by suppressed cardiac function and efficiency in the presence of high fat.     

The relationship between renal metabolism and proximal tubule transport during ontogeny

The proximal tubules of newborn and adult animals reabsorb a similar fraction of the filtered load of Na⁺ and H₂O (65%–70%). In tubules from adult animals, transcellular, active Na⁺ reabsorption accounts for one-third of the total, while two-thirds occur passively through the paracellular pathway, driven by hydrostatic and oncotic forces (one-third) and by cell-generated effective osmotic and ionic gradients (one-third). Since two-thirds of the Na⁺ is reabsorbed passively and does not require energy, the mature proximal tubule has a high Na⁺/O₂ molar ratio (48 Eq of Na⁺/mol of O₂). Measurements of ouabain-sensitive oxygen consumption in suspensions of proximal tubules indicate that in newborn, aerobic metabolism can support about 50% of the net Na⁺ transport rate compared with the 33% in tubules from adult animals. Independent confirmation of the direct and proportional relationship between active Na⁺ transport and ouabain-sensitive O₂ consumption exists for the adult but not for the newborn. However, measurements of epithelial conductances and of transepithelial hydrostatic and oncotic pressure differences indicate that passive paracellular fluxes can account for the remaining 50% of the proximal Na⁺ reabsorption in newborn. The high permeability of the proximal tubules of newborn animals to small molecular weight solutes suggests that cell-generated osmotic and ionic transepithelial gradients are minimal in the tubules of newborn animals. Yet in the newborn, the osmolality of the end proximal tubule fluid was found to exceed that in plasma. This indicates that osmotic gradients due to differences in reflection coefficients for preferentially reabsorbed solutes and Cl^– do exist across the proximal tubules of the newborn and suggests that these gradients may contribute to Na⁺ and H₂O reabsorption. If this is indeed the case, then the contribution of active and of hydrostatic and oncotic pressure-driven flows to the overall reabsorption of Na⁺ and fluid has been overestimated. Resolution of this discrepancy requires measurements of the reflection coefficients for HCO ₃ ^– and Cl^– in the proximal tubule of the newborn. The metabolic processes by which energy is supplied to renal proximal cells during development are also incompletely characterized. There is evidence that maturation of aerobic metabolism, Krebs cycle enzymes activity, and of the mitochondrial membrane surface area precede the development of net reabsorptive transport (Na⁺, H₂O, HCO₃, glucose). By contrast, maturation of Na⁺–K⁺-ATPase activity at the basolateral cell membrane follows that in reabsorptive transport and does not limit its development. The extent to which age-related changes in reabsorptive fluxes are due to the development of luminal membrane transport systems, to the decrease in paracellular permeability, or both remains to be determined. The high activity of enzymes in the hexosemonophosphate pathway and the high NADH/NAD ratio present during the first few weeks of extrauterine life poise the proximal tubules for high rates of biosynthesis of membrane lipids, glycoproteins, nucleic acids, and transporter proteins necessary for final differentiation.     

鼻咽癌代谢重编程与放疗抵抗

鼻咽癌是一种具有地域分布性的鼻咽上皮恶性肿瘤,放疗抵抗是鼻咽癌患者治疗失败的主要原因。代谢重编程是调控肿瘤发生发展的核心,代谢变化能够影响肿瘤的发生、发展及治疗抵抗。糖酵解、氧化磷酸化、脂肪酸氧化等代谢途径均参与肿瘤放疗敏感性的调控。肿瘤微环境变化、基因突变或基因异常表达、基因表观遗传修饰或某些信号通路异常激活是调控鼻咽癌放疗抵抗的主要机制。近年来,越来越多的研究显示,代谢重编程在鼻咽癌放疗抵抗中扮演了重要角色,可通过调控DNA损伤修复、细胞周期、凋亡与自噬、肿瘤细胞干性和免疫反应等来调节鼻咽癌细胞的放疗抗性。靶向代谢重编程可为鼻咽癌放疗增敏提供新的策略和思路。     

Molecular basis of hippocampal energy metabolism in diabetic rats: The effects of SOD mimic

Hippocampal structural changes associated with diabetes-related cognitive impairments are well described, but their molecular background remained vague. We examined whether/how diabetes alters molecular basis of energy metabolism in hippocampus readily after diabetes onset, with special emphasis on its redox-sensitivity.To induce diabetes, adult Mill Hill hybrid hooded rats received a single alloxan dose (120 mg/kg). Both non-diabetic and diabetic groups were further divided in two subgroups receiving (i) or not (ii) superoxide dismutase (SOD) mimic, [Mn(II)(pyane)Cl₂] for 7 days, i.p. Treatment of the diabetic animals started after blood glucose level ≥12 mM.Diabetes decreased protein levels of oxidative phosphorylation components: complex III and ATP synthase. In contrast, protein amounts of glyceraldehyde-3-phosphate dehydrogenase, pyruvate dehydrogenase, and hypoxia-inducible factor-1α – the key regulator of energy metabolism in stress conditions, were higher in diabetic animals. Treatment with SOD mimic restored/increased the levels of oxidative phosphorylation components and returned hypoxia-inducible factor-1α to control level, while diabetes-induced up-regulation of glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase, was additionally stimulated.To conclude, our results provide insight into the earliest molecular changes of energy-producing pathways in diabetes that may account for structural/functional disturbance of hippocampus, seen during disease progression. Also, data suggest [Mn(II)(pyane)Cl₂] as potential therapeutic agent in cutting-edge approaches to threat this widespread metabolic disorder.     

Endothelial cell metabolism in sepsis

BACKGROUND: Endothelial dysfunction in sepsis is a pathophysiological feature of septic organ failure. Endothelial cells (ECs) exhibit specific metabolic traits and release metabolites to adapt to the septic state in the blood to maintain vascular homeostasis.