Neither nitrite nor nitric oxide mediate toxic effects of nitroglycerin on mitochondria.

It is commonly accepted that the major effect of nitroglycerin (NG) is realized through the release of nitric oxide (NO) catalyzed by aldehyde dehydrogenase-2 (ALDH2). In addition, it has been shown that NG inhibits mitochondrial respiration. The aim of this study was to clarify whether NG-mediated inhibition of mitochondrial respiration is mediated by NO. In rat liver mitochondria, NG inhibited complex-I-dependent respiration and induced reactive oxygen species (ROS) production, preferentially at complex I. Both effects were insensitive to chloral hydrate, an ALDH2 inhibitor. Nitrite, an NG intermediate, had no influence on either mitochondrial respiration or the production of ROS. NO inhibited preferentially complex I but did not elevate ROS production. Hemoglobin, an NO scavenger, and blue light had contrary effects on mitochondria inhibited by NO or NG. In summary, our data suggest that although NG induces vasodilatation via NO release, it causes mitochondrial dysfunction via an NO-independent pathway.

Effect of estrogen on mitochondrial function and intracellular stress markers in rat liver and kidney following trauma-hemorrhagic shock and prolonged hypotension.

Trauma-hemorrhage (T-H) is known to impair tissue perfusion, leading to tissue hypoxia, and thus affecting mitochondria, the organelles with the highest oxygen demand. In a model of T-H and prolonged hypotension without fluid resuscitation, administration of a small volume of 17beta-estradiol (E2), but not vehicle, prolonged the survival of rats for 3 h, even in the absence of fluid resuscitation. The main finding of this study is that T-H followed by prolonged hypotension significantly affects mitochondrial function, endoplasmic reticulum (ER) stress markers and free iron levels, and that E2 ameliorated all these changes. All of these changes were observed in the liver but not in the kidney. The sensitivity of mitochondrial respiration to exogenous cytochrome c can reflect increased permeability of the outer mitochondrial membrane for cytochrome c. Increased levels of free iron are indicative of oxidative stress, but neither oxidative nor nitrosylative stress markers changed. The spliced isoform of XBP1 mRNA (an early marker of ER stress) and the expression of C/EBP homologous protein (CHOP) (a protein regulating ER stress-induced apoptosis) were elevated in T-H animals but remained unchanged if T-H rats received E2. Both the prevention of elevated sensitivity of mitochondrial respiration to cytochrome c and a decrease in ER stress by E2 maintain functional integrity of the liver and may help the organ during prolonged hypotension and following resuscitation. A decrease in free iron levels by E2 is more relevant for resuscitation, often accompanied by oxidative stress reaction. Thus, E2 appears to be a novel hormonal adjunct that prolongs permissive hypotension during lengthy transportation of the injured patient between the injury site and the hospital in both civilian and military injuries.

Reperfusion does not induce oxidative stress but sustained endoplasmic reticulum stress in livers of rats subjected to traumatic-hemorrhagic shock.

Oxidative stress is believed to accompany reperfusion and to mediate dysfunction of the liver after traumatic-hemorrhagic shock (THS). Recently, endoplasmic reticulum (ER) stress has been suggested as an additional factor. This study investigated whether reperfusion after THS leads to increased oxidative and/or ER stress in the liver. In a rat model, including laparotomy, bleeding until decompensation, followed by inadequate or adequate reperfusion phase, three time points were investigated: 40 min, 3 h, and 18 h after shock. The reactive oxygen and nitrogen species and its scavenging capacity (superoxide dismutase 2), the nitrotyrosine formation in proteins, and the lipid peroxidation together with the status of endogenous antioxidants (alpha-tocopherylquinone-alpha-tocopherol ratio) were investigated as markers for oxidative or nitrosylative stress. Mitochondrial function and cytochrome P450 isoform 1A1 activity were analyzed as representatives for hepatocyte function. Activation of the inositol-requiring enzyme 1/X-box binding protein pathway and up-regulation of the 78-kDa glucose-regulated protein were recorded as ER stress markers. Plasma levels of alanine aminotransferase and Bax/Bcl-XL messenger RNA (mRNA) ratio were used as indicators for hepatocyte damage and apoptosis induction. Oxidative or nitrosylative stress markers or representatives of hepatocyte function were unchanged during and short after reperfusion (40 min, 3 h after shock). In contrast, ER stress markers were elevated and paralleled those of hepatocyte damage. Incidence for sustained ER stress and subsequent apoptosis induction were found at 18 h after shock. Thus, THS or reperfusion induces early and persistent ER stress of the liver, independent of oxidative or nitrosylative stress. Although ER stress was not associated with depressed hepatocyte function, it may act as an early trigger of protracted cell death, thereby contributing to delayed organ failure after THS.

Antimycin A and lipopolysaccharide cause the leakage of superoxide radicals from rat liver mitochondria.

Here we show that both Antimycin A, a respiratory chain inhibitor inducing apoptosis, and endotoxic shock, a syndrome accompanied by both necrosis and apoptosis, cause not only an increase but also the leakage of superoxide radicals (O(2)(*-)) from rat heart mitochondria (RHM), while O(2)(*-) generated in intact RHM do not escape from mitochondria. This was shown by a set of O(2)(*-)-sensitive spin probes with varying hydrophobicity. The levels of O(2)(*-) detected in intact RHM gradually increase as the hydrophobicity of spin probes increases and were not sensitive to superoxide dismutase (SOD) added to the incubation medium. Both Antimycin A and endotoxic shock elevated O(2)(*-) levels. Elevated O(2)(*-) levels became sensitive to SOD but in a different manner. The determination of O(2)(*-) with water-soluble PPH was fully sensitive to SOD, while the determination of O(2)(*-) with the more hydrophobic CMH and CPH was only partially sensitive to SOD, suggesting the release of a portion of O(2)(*-) into the surrounding medium.