Chronic ethanol feeding causes depression of mitochondrial elongation factor Tu in the rat liver: implications for the mitochondrial ribosome.

Chronic ethanol feeding is known to negatively impact hepatic energy metabolism. Previous studies have indicated that the underlying lesion responsible for this may lie at the level of the mitoribosome. The aim of this study was to characterize the structure of the hepatic mitoribosome in alcoholic male rats and their isocalorically paired controls. Our experiments revealed that chronic ethanol feeding resulted in a significant depletion of both structural (death-associated protein 3) and functional [elongation factor thermo unstable (EF-Tu)] mitoribosomal proteins. In addition, significant increases were found in nucleotide elongation factor thermo stable (EF-Ts) and structural mitochondrial ribosomal protein L12 (MRPL12). The increase in MRPL12 was found to correlate with an increase in the levels of the 39S large mitoribosomal subunit. These changes were accompanied by decreased levels of nuclear- and mitochondrially encoded respiratory subunits, decreased amounts of intact respiratory complexes, decreased hepatic ATP levels, and depressed mitochondrial translation. Mathematical modeling of ethanol-mediated changes in EF-Tu and EF-Ts using prederived kinetic data predicted that the ethanol-mediated decrease in EF-Tu levels could completely account for the impaired mitochondrial protein synthesis. In conclusion, chronic ethanol feeding results in a depletion of mitochondrial EF-Tu levels within the liver that is mathematically predicted to be responsible for the impaired mitochondrial protein synthesis seen in alcoholic animals.

Adenine nucleotide changes in the remnant liver: An early signal for regeneration after partial hepatectomy.

UNLABELLED: Liver regeneration after partial hepatectomy (PHx) is orchestrated by multiple signals from cytokines and growth factors. We investigated whether increased energy demand on the remnant liver after PHx contributes to regenerative signals. Changes in the tissue's energy state were determined from adenine nucleotide levels. Adenosine triphosphate (ATP) levels in remnant livers decreased markedly and rapidly (to 48% of control by 30 seconds post-PHx) and remained significantly lower than those in sham-operated controls for 24 to 48 hours. The ATP decrease was not reflected in corresponding increases in adenosine diphosphate (ADP) and adenosine monophosphate (AMP), resulting in a marked decline in total adenine nucleotides (TAN). We found no evidence of mitochondrial damage or uncoupling of oxidative phosphorylation. Multiple lines of evidence indicated that the decline in TAN was not caused by increased energy demand, but by ATP release from the liver. The extent of ATP loss was identical after 30% or 70% PHx, whereas fasting or hyperglycemia, conditions that greatly alter energy demand for gluconeogenesis, affected the ATP/ADP decline but not the loss of TAN. Presurgical treatment with the alpha-adrenergic antagonist phentolamine completely prevented loss of TAN, although changes in ATP/ADP were still apparent. Importantly, phentolamine treatment inhibited early signaling events associated with the priming stages of liver regeneration and suppressed the expression of c-fos. Pretreatment with the purinergic receptor antagonist suramin also partly suppressed early regenerative signals and c-fos expression, but without preventing TAN loss. CONCLUSION: The rapid loss of adenine nucleotides after PHx generates early stress signals that contribute to the onset of liver regeneration.

S-adenosyl-L-methionine co-administration prevents the ethanol-elicited dissociation of hepatic mitochondrial ribosomes in male rats.

BACKGROUND: Chronic ethanol feeding to male rats has been shown to result in decreased mitochondrial translation, depressed respiratory complex levels and mitochondrial respiration rates. In addition, ethanol consumption has been shown to result in an increased dissociation of mitoribosomes. S-adenosyl-L-methionine (SAM) is required for the assembly and subsequent stability of mitoribosomes and is depleted during chronic ethanol feeding. The ability of dietary SAM co-administration to prevent these ethanol-elicited lesions was investigated. METHODS: Male Sprague-Dawley rats were fed a nutritionally adequate liquid diet with ethanol comprising 36% of the calories according to a pair-fed design for 28 days. For some animals, SAM was supplemented in the diet at 200 mg/l. Liver mitochondria were prepared and mitoribosomes isolated. Respiration rates, ATP levels, respiratory complex levels, and the extent of mitoribosome dissociation were determined. RESULTS: Twenty-eight days of ethanol feeding were found to result in decreased SAM content, depressed respiration, and increased mitoribosome dissociation. No changes in mitochondrial protein content; levels of respiratory complexes I, III, and V; complex I activities; and ATP levels were detected. Co-administration of SAM in the diet was found to prevent ethanol-induced SAM depletion, respiration decreases and mitoribosome dissociation. CONCLUSIONS: Taken together, these findings suggest (1) that mitoribosome dissociation precedes respiratory complex depressions in alcoholic animals and (2) that dietary supplementation of SAM prevents some of the early mitochondrial lesions associated with chronic ethanol consumption.