Diabetes Mellitus: Metabolic Effects and Oxidative Stress

Diabetes mellitus is a complex polygenic pathology, which is characterized by numerous metabolic disorders. Progressive hyperglycemia developing during this disease causes clinically significant tissue damage and is considered as a main risk factor of micro- and macrovascular complications leading to retinopathy, nephropathy, and neuropathy. Hyperglycemia depended oxidative stress and impairments in nitric oxide bioavailability play an essential role in the pathogenesis of diabetes and its complications. Homeostasis of glucose maintained by metabolic effects of insulin includes an increase of glucose uptake by skeletal muscles and suppression of glucose production by the liver. M. Brownlee (2005) put forward a hypothesis assuming that oxidative stress is the main mechanism of diabetic tissue damages. According to this hypothesis, mitochondrial dysfunction and superoxide anion radical hyperproduction by mitochondria is the principal mechanism of activation of four pathways of hyperglycemia-induced impairments under diabetes. Two cell signaling cascades regulate the glucose homeostasis: insulin-mediated glucose uptake (IMGU) in skeletal muscles, liver, and heart and glucose-stimulated insulin secretion (GSIS) in pancreatic β-cells. In addition to nonspecific irreversible oxidative damage of DNA, protein and lipid molecules reactive oxygen and nitrogen species induce cell and tissue damage, activating a number of cell stress-sensitive signaling cascades. Stress-dependent serine phosphorylation of insulin receptor substrate (IRS) proteins decreases its capacity for tyrosine phosphorylation and may accelerate degradation of IRS. This process underlies the molecular mechanism of oxidative stress-induced insulin resistance

Calcium-Induced Mitochondrial Permeability Transitions: Parameters of Ca 2+ Ion Interactions with Mitochondria and Effects of Oxidative Agents

We evaluated the parameters of Ca2+-induced mitochondrial permeability transition (MPT) pore formations, Ca2+ binding constants, stoichiometry, energy of activation, and the effect of oxidative agents, tert-butyl hydroperoxide (tBHP), and hypochlorous acid (HOCl), on Ca2+-mediated process in rat liver mitochondria. From the Hill plot of the dependence of MPT rate on Ca2+ concentration, we determined the order of interaction of Ca2+ ions with the mitochondrial sites, n = 3, and the apparent Kd = 60 ± 12  µM. We also found the apparent Michaelis–Menten constant, Km, for Ca2+ interactions with mitochondria to be equal to 75 ± 20  µM, whereas that in the presence of 300  µM tBHP was 120 ± 20  µM. Using the Arrhenius plots of the temperature dependences of apparent mitochondrial swelling rate at various Ca2+ concentrations, we calculated the activation energy of the MPT process. ΔEa was 130 ± 20  kJ/mol at temperatures below the break point of the Arrhenius plot (30–34 °C) and 50 ± 9 kJ/mol at higher temperatures. Ca2+ ions induced rapid mitochondrial NADH depletion and membrane depolarization. Prevention of the pore formation by cyclosporin A inhibited Ca2+ -dependent mitochondrial depolarization and Mg2+ ions attenuated the potential dissipation. tBHP (10–150 µM) dose-dependently enhanced the rate of MPT opening, whereas the effect of HOCl on MPT depended on the ratio of HOCl/Ca2+. The apparent Kmof tBHP interaction with mitochondria in the swelling reaction was found to be Km= 11 ± 3 µM. The present study provides evidence that three calcium ions interact with mitochondrial site with high affinity during MPT. Ca2+-induced MPT pore formations due to mitochondrial membrane protein denaturation resulted in membrane potential dissipation. Oxidants with different mechanisms, tBHP and HOCl, reduced mitochondrial membrane potential and oxidized mitochondrial NADH in EDTA-free medium and had an effect on Ca2+-induced MPT onset

Role of mitochondrial calcium in hypochlorite induced oxidative damage of cells

Hypochlorite (HOCl) is one of the most important mediators of inflammatory processes. Recent evidence demonstrates that changes in intracellular calcium pool play a significant role in the damaging effects of hypochlorite and other oxidants. Mitochondria are shown to be one of the intracellular targets of hypochlorite. But little is known about the mitochondrial calcium pool changes in HOCl-induced mitochondrial dysfunction. Using isolated rat liver mitochondria, we showed the oxidative damage of mitochondria (GSH oxidation and mixed protein-glutathione formation without membrane lipid peroxidation) and alterations in the mitochondrial functional parameters (decrease of respiratory activity and efficiency of oxidative phosphorylation, NADH and FADH coenzyme levels, and membrane potential) under hypochlorite action (50e300mM). Simultaneously, the mitochondrial calcium release and swelling were demonstrated. In the presence of EGTA, the damaging effects of HOCl were less pronounced, reflecting direct involvement of mitochondrial Ca2+ in mechanisms of oxidant-induced injury. Furthermore, exposure of HeLa cells to hypochlorite resulted in a considerable increase in cytoplasmic calcium concentrations and a decrease in mitochondrial ones. Applying specific inhibitors of calcium transfer systems, we demonstrated that mitochondria play a key role in the redistribution of cytoplasmic Ca2+ ions under hypochlorite action and act as mediators of calcium release from the endoplasmic reticulum into the cytoplasm

Corrections by melatonin of liver mitochondrial disorders under diabetes and acute intoxication in rats

The aim of the present work was to investigate the mechanisms of oxidative damage of the liver mitochondria under diabetes and intoxication in rats as well as to evaluate the possibility of corrections of mitochondrial disorders by pharmacological doses of melatonin. The experimental (30 days) streptozotocin-induced diabetes mellitus caused a significant damage of the respiratory activity in rat liver mitochondria. In the case of succinate as a respiratory substrate, the ADP-stimulated respiration rate V3 considerably decreased (by 25%, p<0-05) as well as the acceptor control ratio (ACR) V3/V2 markedly diminished (by 25%, /p<0-01). We observed a decrease of the ADP-stimulated respiration rate V3 by 35% (p<0-05), with glutamate as substrate. In this case, ACR also decreased (by 20%, p<0-05). Surprisingly, the phosphorylation coefficient ADP/O did not change under diabetic liver damage. Acute rat carbon tetrachloride-induced intoxication resulted in considerable decrease of the phosphorylation coefficient because of uncoupling of the oxidation and phosphorylation processes in the liver mitochondria. The melatonin administration during diabetes (10mg - kg-1 body weight, 30days, daily) showed a considerable protective effect on the liver mitochondrial function, reversing the decreased respiration rate V3 and the diminished ACR to the control values both for succinate-dependent respiration and for glutamate-dependent respiration. The melatonin administration to intoxicated animals (10mg - kg-1 body weight, three times) partially increased the rate of succinate-dependent respiration coupled with phosphorylation. The impairment of mitochondrial respiratory plays a key role in the development of liver injury under diabetes and intoxication. Melatonin might be considered as an effector that regulates the mitochondrial function under diabetes. Copyright © 2011 John Wiley & Sons, Ltd

Rat liver mitochondrial damage under acute or chronic carbon tetrachloride-induced intoxication: Protection by melatonin and cranberryflavonoids

Incurrent societies, the riskof toxic liver damagehasmarkedly increased. The aimof thepresentwork was to carry out further research into the mechanism(s) of livermitochondrial damage inducedby acute (0.8 g/kgbodyweight, single injection) or chronic (1.6 g/ kg bodyweight, 30 days, biweekly injections) carbon tetrachloride–induced intoxication and to evaluate the hepatoprotective potential of the antioxidant, melatonin, as well as succinate and cranberryflavonoids in rats. Acute intoxication resulted in considerable impairment of mitochondrial respiratory parameters in the liver. The activity of mitochondrial succinate dehydrogenase (complex II) decreased (by 25%, pb0.05). Short-term melatonin treatment (10 mg/kg, three times) of rats did not reduce the degree of toxicmitochondrial dysfunction but decreased the enhanced NO production. After 30-day chronic intoxication, no significant change in the respiratory activity of livermitochondriawas observed, despite marked changes in the redox-balance of mitochondria. The activities of the mitochondrial enzymes, succinate dehydrogenase and glutathione peroxidase, as well as that of cytoplasmic catalase in liver cells were inhibited significantly. Mitochondria isolated from the livers of the rats chronically treated with CCl4 displayed obvious irreversible impairments. Long-term melatonin administration (10 mg/kg, 30 days, daily) to chronically intoxicated rats diminished the toxic effects of CCl4, reducing elevated plasma activities of alanine aminotransferase and aspartate aminotransferase and bilirubin concentration, prevented accumulation of membrane lipid peroxidation products in rat liver and resulted in apparent preservation of the mitochondrial ultrastructure. The treatment of the animals by the complex of melatonin (10 mg/kg) plus succinate (50 mg/kg) plus cranberryflavonoids (7 mg/kg) was even more effective in prevention of toxic liver injury and liver mitochondria damage

Hepatotoxic Effects of Acetaminophen. Protective Properties of Tryptophan Derivatives

Rat intoxication with acetaminophen (APAP) (500–1500 mg/kg body weight, intragastrically) caused a considerable dose dependent decrease in reduced glutathione (GSH) level in both liver cell cytoplasm and mitochondria (at the dose 1500 mg/kg body weight by 60% and 33%, respectively). The decrease in cytoplasmic GSH level was more pronounced than in mitochondria. Despite of significant mitochondrial GSH depletion we did not observe any inactivation of the mitochondrial enzymes: succinate dehydrogenase, α-ketoglutarate dehydrogenase, glutathione peroxidase, and also any decrease in the respiratory activity of liver mitochondria isolated from APAP-intoxicated rats. We have investigated hepatoprotector properties of tryptophan derivatives, melatonin and N-acetyl-nitrosotryptophan (a nitric oxide donor). The pineal gland hormone, melatonin, a known antioxidant (10 mg/kg body weight), did not prevent intramitochondrial GSH, but decreased the APAP hepatotoxicity evaluated as the decrease in the activity of marker enzymes of hepatic damage, ALT and AST and total bilirubin content in blood plasma of intoxicated rats, whereas NNT did not exhibit any hepatoprotective effects

Melatonin and succinate reduce rat liver mitochondrial dysfunction in diabetes

Mitochondrial dysfunction and an increase in mitochondrial reactive oxygen species in response to hyperglycemia during diabetes lead to pathological consequences of hyperglycemia. The aim of the present work was to investigate the role of a specific functional damage in rat liver mitochondria during diabetes as well as to evaluate the possibility of metabolic and antioxidative correction of mitochondrial disorders by pharmacological doses of succinate and melatonin. In rat liver mitochondria, streptozotocin-induced diabetes was accompanied by marked impairments of metabolism: we observed a significant activation of α-ketoglutarate dehydrogenase (by 60%, p<0.05) and a damage of the respiratory function. In diabetic animals, melatonin (10 mg/kg b.w., 30 days) or succinate (50 mg/kg b.w., 30 days) reversed the oxygen consumption rate V3 and the acceptor control ratio to those in nondiabetic animals. Melatonin enhanced the inhibited activity of catalase in the cytoplasm of liver cells and prevented mitochondrial glutathione-S-transferase inhibition while succinate administration prevented α-ketoglutarate dehydrogenase activation. The mitochondria dysfunction associated with diabetes was partially remedied by succinate or melatonin administration. Thus, these molecules may have benefits for the treatment of diabetes. The protective mechanism may be related to improvements in mitochondrial physiology and the antioxidative status of cells

Rat Liver Mitochondria Impairment under Acute Carbon Tetrachloride-Induced Intoxication. Effects of Melatonin

The aim of the present work was to investigate the mechanisms of oxidative damage of rat liver mitochondria in vitro, under hypochlorous acid (HOCl) induced oxidative stress, and in vivo, under acute carbon tetrachloride-induced intoxicationin rats. Hypochlorous acid (50–300 µM), the main inflammatory agent, inhibited liver mitochondria respiratory activityand caused uncoupling in the respiratory and phosporylation processes. The toxic damage of rat liver after 24 h of acute carbon tetrachloride induced intoxication (4 g/kg, intragastrically) was accompanied by a significant reduction in succinate- and glutamate-depen-dent respiration rate in state 3 (by 65%, p< 0.001, and by 50%, p< 0.01, respectively). The respiration control ratio approached 1, reflecting the loss of respirationcontrol. The phosphorylation coefficient significantly decreased due to uncoupling of the oxidation and phosphorylation processes. The mitochondrial alterations were associated with oxidation of intramitochondrial GSH by 25% (p< 0.05), the marked inhibition of succinate dehydrogenase (complex II) by 35% (p< 0.05), and the rise of blood plasma nitric oxide level by 45% (p< 0.05). The impairment of mitochondrial respiratory function may result from the inhibition of enzymatic activities in the respiratory chain and the damage of mitochondrial membrane during intoxication and plays a key role in the development of the CCl4-induced hepatotoxicity. Melatonin administration under CCl4-induced intoxication (three times at a dose of 10 mg/kg)increased the rate of succinate oxidation in state 3 by 30% (p< 0.05) and reversed the increase in glutathione peroxidase activity. Melatonin prevented an elevation of nitric oxide level in the blood plasma of intoxicated animals but did not protect mitochondrial functions under acute intoxication

Structure and antioxidant wctivity associwtions for melatonin molecule and its derivativts

Structural and electronic properties of melatonin, tryptophan, and oxidative products of these molecules were determined theoretically by performing semi-empirical and ab initio calculations. The radical scavenging effects of melatonin and tryptophan were studied using the alkoxyl and peroxyl radical- generating systems. We have shown that melatonin, rather than tryptophan, is a potent lipid antioxidant and an effective scavenger of alkoxyl- and peroxyl radicals.Изучали радикал-скэвенджерные свойства мелатонина и триптофана в системах, генерирующих алкоксильные и пероксильные радикалы(эритроциты человека, обработанные окислителем терт-бутилгидропероксид (тБГП)). Структурные и электронные свойства мелатонина, триптофана и окисленных производных данных молекул были исследованы теоретически с использованием АМ1 полуэмпирического метода иab initio метода. Высокая радикал-скэвенджерная способность мелатонина может быть обусловлена высокими значениями площади поверхности и дипольного момента молекулы, который отражает плотность заряда молекулы. С термодинамической точки зренияN1-ацетил- N2 -формил-5-метоксикинурамин(AФMK) является самым стабильным продуктом окисления мелатонина. Сравнительное исследование радикал-скэвенджерных, структурных и электронных свойства молекул мелатонина, его предшественника - триптофана продемонстрировало, что мелатонин в отличие от триптофана является потенциальным липидным антиоксидантом и эффективным скэвенджером алкоксильных и пероксильных радикалов