Control of adenine nucleotide metabolism in hepatic mitochondria from rats with ethanol-induced fatty liver

Abstract

Male rats developed fatty liver after being fed on an ethanol-containing diet for 31 days. Liver mitochondria from these animals catalysed ATP synthesis at a slower rate when compared with mitochondria from pair-fed control rats (control mitochondria), and demonstrated lowered respiratory control with succinate as substrate, owing to a decrease in the State-3 respiratory rate. Respiration in the presence of uncoupler was comparable in mitochondria from both groups of rats. Translocation of both ATP and ADP was decreased in mitochondria from ethanol-fed rats, with ADP uptake being lowered more dramatically by ethanol feeding. Parameters influencing adenine nucleotide translocation were investigated in mitochondria from ethanol-fed rats. Experiments performed suggested that lowered adenine nucleotide translocation in these mitochondria is not the result of inhibition of the translocase by either long-chain acyl-CoA derivatives or unesterified fatty acids. Analysis of endogenous adenine nucleotides in these mitochondria revealed lowered ATP concentrations, but no decrease in total adenine nucleotides. In experiments where the endogenous ATP in these mitochondria was shifted to higher concentrations by incubation with oxidizable substrates or defatted bovine serum albumin, the rate of ADP translocation was increased, with a linear correlation being observed between endogenous ATP concentrations and the rate of ADP translocation. The depressed ATP concentration in mitochondria from ethanol-fed rats suggests that the ATP synthetase complex is replenishing endogenous ATP at a slower rate. The lowered ATPase activity of the ATP synthetase observed in submitochondrial particles from ethanol-fed animals suggests a decrease in the function of the synthetase complex. A decrease in the rate of ATP synthesis in mitochondria from ethanol-fed rats is sufficient to explain the decreased ADP translocation and State-3 respiration.

Modification of the Mitochondrial Proteome in Response to the Stress of Ethanol-dependent Hepatotoxicity

“…Isolation of Rat Liver Mitochondria-Coupled liver mitochondria were prepared by differential centrifugation of liver homogenates (34,35) using ice-cold mitochondria isolation medium containing 0.25 M sucrose, 1 mM EDTA, and 5 mM Tris-HCl, pH 7.5. Protease inhibitors were added to the isolation buffer to prevent protein degradation (10).…”

Chronic alcohol consumption increases the sensitivity of rat liver mitochondrial respiration to inhibition by nitric oxide

“…Human hemoglobin and liver mitochondria were prepared as previously described. 24,25 Cytochrome c oxidase and citrate synthase activities were determined spectrophotometrically. 26,27 Oxygen and NO concentrations were measured simultaneously using Clark-type electrodes (Instech, Plymouth Meeting, PA; Harvard Apparatus, Holliston, MA) in a 1.0-mL sealed Perspex chamber, magnetically stirred at 37°C.…”

Novel interactions of mitochondria and reactive oxygen/nitrogen species in alcohol mediated liver disease

“…Conclusive evidence shows that chronic alcohol exposure depresses the activities of all the oxidative phosphorylation complexes by approximately 30%-50%, exce pt Complex Ⅱ [15,16] . Inhibition of mitochondrial protein synthesis due to alcohol-mediated damage to the mitochondrial DNA [13,17] and ribosomes [18,19] is proposed to contribute to decreased functioning of the oxidative phosphorylation system and depressed rates of ATP synthesis [20,21] . Recently, studies by Cunningham and colleagues have shown that both hepatic energy charge and NADH-linked respiration are decreased in mitochondria isolated from liver of non-human primates allowed to consume alcohol for 18 mo [22] ; thus recapitulating the findings observed in rodent studies.…”