The role of iNOS in alcohol-dependent hepatotoxicity and mitochondrial dysfunction in mice

Abstract

Nitric oxide (NO) is now known to control both mitochondrial respiration and organelle biogenesis. Under conditions of ethanol-dependent hepatic dysfunction, steatosis is increased, and this is associated with increased expression of inducible nitric oxide synthase (iNOS). We have previously shown that after chronic exposure to ethanol, the sensitivity of mitochondrial respiration to inhibition by NO is enhanced, and we have proposed that this contributes to ethanol-dependent hypoxia. This study examines the role of iNOS in controlling the NO-dependent modification of mitochondrial function. Mitochondria were isolated from the livers of both wild-type (WT) and iNOS knockout (iNOS ؊/؊ ) mice that were fed an isocaloric ethanol-containing diet for a period of 5 weeks. All animals that consumed ethanol showed some evidence of fatty liver; however, this was to a lesser extent in the iNOS ؊/؊ mice compared to controls. At this early stage in ethanol-dependent hepatic dysfunction, infiltration of inflammatory cells and the formation of nitrated proteins was also decreased in response to ethanol feeding in the iNOS ؊/؊ animals. Mitochondria isolated from wild-type ethanol-fed mice showed a significant decrease in respiratory control ratio and an increased sensitivity to NO-dependent inhibition of respiration relative to their pair-fed controls. In contrast, liver mitochondria isolated from iNOS ؊/؊ mice fed ethanol showed no change in the sensitivity to NO-dependent inhibition of respiration. In conclusion, the hepatic response to chronic alcohol-dependent cytotoxicity involves a change in mitochondrial function dependent on the induction of iNOS. (HEPATOLOGY 2004;40:565-573.)

Mitochondrial dysfunction and oxidative stress in the pathogenesis of alcohol- and obesity-induced fatty liver diseases

“…This concept is supported because increased sensitivity to NO is absent in iNOS − /− mice exposed to chronic alcohol [90]. Similarly, alcohol-associated inflammation and steatosis is abrogated in iNOS − /− mice [90,106]. Taken together, these studies demonstrate that iNOS induction is linked to alterations in NO-dependent control of mitochondrial respiration, which potentially contributes to the development of alcoholic steatohepatitis.…”

“…It is postulated that this disruption in NO signaling contributes to alcohol hepatotoxicity through inhibition of ATP synthesis, increased ROS, and inability to adapt to hypoxic stress [105]. This concept is supported because increased sensitivity to NO is absent in iNOS − /− mice exposed to chronic alcohol [90]. Similarly, alcohol-associated inflammation and steatosis is abrogated in iNOS − /− mice [90,106].…”

“…Nitric oxide (NO) and other RNS are increased in response to chronic alcohol consumption through induction of inducible nitric oxide synthase (iNOS) [82,90]. In normal healthy liver iNOS levels are very low or undetectable [91], whereas during inflammation and other disease states iNOS levels are increased in liver due to infiltrating inflammatory cells and via induction in Kupffer cells (resident liver macrophage), hepatocytes, and biliary epithelial cells [92][93][94].…”

“…Moreover, NO regulates mitochondrial respiration through reversible binding at the redoxactive heme site in cytochrome c oxidase [99][100][101] and affects mitochondrial biogenesis through interactions with soluble guanylate cyclase [102]. Studies have shown that mitochondria from chronic alcohol-fed animals are more sensitive to the inhibitory effect of NO on respiration [90,103]. While it is known that chronic alcohol consumption results in cytochrome c oxidase defects [82,90,104], it is likely that this alteration in NO responsiveness may be due to alcohol-dependent changes in interactions of NO with sites other than Complex IV.…”

“…Studies have shown that mitochondria from chronic alcohol-fed animals are more sensitive to the inhibitory effect of NO on respiration [90,103]. While it is known that chronic alcohol consumption results in cytochrome c oxidase defects [82,90,104], it is likely that this alteration in NO responsiveness may be due to alcohol-dependent changes in interactions of NO with sites other than Complex IV. It is postulated that this disruption in NO signaling contributes to alcohol hepatotoxicity through inhibition of ATP synthesis, increased ROS, and inability to adapt to hypoxic stress [105].…”