Effects of chronic ethanol consumption on the rate of rat liver mitochondrial protein turnover and synthesis

Effects of chronic ethanol feeding on the protein composition of mitochondrial ribosomes

Chronic ethanol feeding has been shown to decrease the number of functionally active mitochondrial ribosomes by 55%. In this work, 55S mitochondrial ribosomes were isolated from rat liver and their constitutive proteins characterized by two-dimensional polyacrylamide gel electrophoresis and quantified by densitometry. A total of 86 proteins were found to be associated with the mitochondrial ribosome. This compares with 70 isolated from cytoplasmic ribosomes. In addition, mitochondrial ribosomal proteins were found to be significantly less basic than their cytoplasmic counterparts. Chronic ethanol feeding was found to significantly decrease the levels of a number of constitutive proteins of the mitochondrial ribosome when compared to those isolated from pair-fed controls. Sucrose density gradient analyses revealed a significant decrease in the number of intact 55S ribosomes. It is suggested that ethanol-elicited alterations in specific constitutive proteins of the mitochondrial ribosome may lead to impaired assembly of the monosome and that this may result in lower levels of those displaying functional activity.

Cytotoxicity of short-chain alcohols

Ethanol and other short-chain alcohols elicit a number of cellular responses that are potentially cytotoxic and, to some extent, independent of cell type. Aberrations in phospholipid and fatty acid metabolism, changes in the cellular redox state, disruptions of the energy state, and increased production of reactive oxygen metabolites have been implicated in cellular damage resulting from acute or chronic exposure to short-chain alcohols. Resulting disruptions of intracellular signaling cascades through interference with the synthesis of phosphatidic acid, decreases in phosphorylation potential and lipid peroxidation are mechanisms by which solvent alcohols can affect the rate of cell proliferation and, consequently, cell number. Nonoxidative metabolism of short-chain alcohols, including phospholipase D-mediated synthesis of alcohol phospholipids, and the synthesis of fatty acid alcohol esters are additional mechanisms by which alcohols can affect membrane structure and compromise cell function.

Differential effects of chronic ethanol consumption on hepatic mitochondrial and cytoplasmic ribosomes

The effects of chronic ethanol consumption on the properties of mitochondrial and cytoplasmic ribosomes were investigated in rat liver. Sedimentation properties of purified mitochondrial (55S) and cytoplasmic (80S) ribosomes were determined by analyses on sucrose density gradients. Mitochondrial ribosomes from control animals moved further in the gradients than did those isolated from ethanol-fed rats, which suggests that ethanol ribosomes have a lower molecular weight. In addition, mitochondrial from ethanol-fed animals contained a lower percentage of ribosomes present as the intact monosome, suggesting that ethanol may have an effect on the stability of the functional mitochondrial ribosomes. This was confirmed by the presence of the larger 39S subunit in preparations from ethanol-fed animals. No such ethanol-related alterations were seen with cytoplasmic ribosomes. The protein composition of mitochondrial cytoplasmic ribosomes was investigated using two-dimensional gel electrophoresis, followed by two-dimensional densitometry. As indicated by differences in protein staining intensity, ethanol consumption seemed to alter the concentration of seven mitochondrial ribosomal proteins. In contrast, no such changes were observed in the protein pattern from cytoplasmic ribosomes. Observations in this study provide for the possibility that alterations in the amounts of selected proteins in the mitochondrial ribosome lead to impaired assembly of the ribosome. These ethanol-related structural changes may be responsible for the decreased activity of mitochondrial ribosomes that results in impaired hepatic mitochondrial protein synthesis (W.B. Coleman and C.C. Cunningham, Biochim. Biophys, Acta 1058:178-186, 1991). Furthermore, this study reemphasizes the increased susceptibility of the hepatic mitochondrial translation system, compared with the cytoplasmic system to chronic ethanol consumption.

Protective influence of zinc against the deleterious effects of ethanol in postimplantation rat embryos in vivo

Zinc is a cofactor for alcohol dehydrogenase, the ethanol metabolizing enzyme. Ethanol-induced zinc deficiency could decrease ethanol metabolism, resulting in an increase in circulating and tissue ethanol levels. This may cause retardation in embryonic growth and development. The influence of zinc supplementation on ethanol-induced embryopathy was studied by the simultaneous administration of ethanol and zinc to pregnant SD rats from gestational day 6 through 12. Ethanol was given in the form of a liquid diet and zinc was administered intraperitoneally. The ethanol group received the liquid ethanol diet, the ethanol+zinc group received the ethanol diet and zinc and the pair-fed control group was given an isocaloric control diet. Embryos were explanted from all groups on day 12 of gestation. Embryos of animals treated with ethanol alone exhibited a significantly higher rate of resorption and retarded embryonic growth and development compared to the pair-fed control group. The embryonic protein content, crown-rump length, the number of somites and embryonic morphological score were significantly reduced in the ethanol-treated group. In addition, serum zinc concentration also was lower. Compared to embryos from ethanol-treated animals, embryos from ethanol+zinc treated animals showed a significantly higher number of somites; cardiac development was more advanced and embryonic protein content was higher. These observations suggest that zinc supplementation of ethanol-treated pregnant rats may have some protective influence against the embryopathic effects of ethanol.

Effect of chronic ethanol consumption on hepatic mitochondrial transcription and translation

Liver mitochondria from ethanol-fed rats display an impaired ability for protein synthesis in vitro. Studies were conducted to explore the possible mechanisms which might account for this impaired capacity of ethanol mitochondria for protein synthesis. The present studies did not demonstrate any significant ethanol-induced lesion in mitochondrial nucleic acid metabolism in organelles isolated from ethanol-fed rats for any of the parameters investigated (mtDNA content, steady-state mtRNA concentration, mtRNA polymerase activity, concentration of specific mRNAs and rRNAs, mtRNA processing). An investigation of ribosome function in isolated mitochondria demonstrated significant decreases in the number of active ribosomes (55% fewer) in mitochondria from ethanol-fed rats. Initiation of protein synthesis was also significantly depressed (46%) in ethanol mitochondria. In addition, the yield of ribosomal particles from ethanol mitochondria was decreased 32% as compared to the yield of ribosomal particles from control mitochondria. However, isolated ribosomes from ethanol mitochondria were determined to be fully functional in a poly(U)-directed phenylalanine polymerization system. Soluble translation factors from ethanol mitochondria were also found to support full activity of control ribosomes in a poly(U)-directed phenylalanine polymerization system. These results suggest strongly that the ethanol-induced depression of mitochondrial protein synthesis is due to a decrease in the number of competent ribosomes in hepatic mitochondria from chronically ethanol-fed rats.

Effects of chronic ethanol consumption on the synthesis of polypeptides encoded by the hepatic mitochondrial genome

Liver mitochondria from rats fed ethanol chronically demonstrate an impaired ability to incorporate [35S]methionine into polypeptide products in vitro. This ethanol-induced effect on mitochondrial translation in vitro could not be attributed to significant differences in the methionine precursor pool sizes of ethanol and control mitochondria or to the acute effects of residual ethanol. The observed reduction of radiolabeled methionine incorporation into mitochondrial gene products of ethanol mitochondria in vitro reflects a decrease in the synthesis of all the mitochondrial gene products. However, the percentage of total radiolabel incorporated into each gene product is unaffected by ethanol, suggesting an ethanol-induced coordinate depression of mitochondrial protein synthesis. Moreover, SDS-PAGE and densitometry of submitochondrial particles from ethanol-fed and control rats demonstrated that the steady-state concentration of each of the mitochondrial gene products is decreased in ethanol-fed rats. This reduction of the steady-state concentration of the mitochondrial gene products may be related to the observed depressions of oxidative phosphorylation activities associated with hepatic mitochondria from ethanol-fed rats.

Effect of chronic ethanol administration on protein catabolism in rat liver

Hepatic protein catabolism was measured in rats which were pair-fed a liquid diet containing either ethanol or isocaloric maltose-dextrin (control diet). Within 12 days after initiation of pair feeding, the level of total hepatic protein in ethanol-fed rats was 26% higher than that in pair-fed control rats. During this time interval, the catabolic rates of both short-lived [3H]puromycin-labeled proteins and long-lived native [14C]bicarbonate-labeled proteins were measured in the two groups of animals. The degradation rate of short-lived [3H]puromycinyl proteins and peptides was the same in ethanol-fed and pair-fed control rats. However, the overall catabolic rate of long-lived proteins in rats fed the ethanol liquid diet for 2-10 days was 37-40% lower than that in pair-fed controls. This difference in protein turnover was not a general phenomenon, since the time-dependent decay of [14C]proteins in the hepatic microsome fraction of ethanol-fed rats was 33% slower than that in pair-fed controls, but the apparent rate of cytosolic protein catabolism was the same in both groups of animals. The differences in protein turnover did not reflect quantitative changes in lysosomal proteases since the activities of four hepatic lysosomal cathepsins were unaffected by alcohol administration. When rats were subjected to longer periods of pair feeding (16-25 days), the difference in overall hepatic protein catabolism between ethanol-fed rats and their pair-fed controls was considerably attenuated.(ABSTRACT TRUNCATED AT 250 WORDS)

Certain biochemical effects of garlic oil on rats maintained on high fat-high cholesterol diet

The feeding of a high fat-high cholesterol (HF-HC) diet to normal rats for 1 month increased the lipid components cholesterol and triglyceride in serum, liver and kidneys and decreased the serum albumin very significantly. Administration of garlic oil (100 mg/kg b. wt/day) for 1 month together with the HF-HC diet to another group almost nullified the lipid-increasing and albumin-decreasing effects of that diet. The reduction in total lipids, cholesterol and triglycerides and the restoration to normal level of serum albumin were highly significant in the garlic oil group. Adipose tissue triglyceride lipase activity was significantly increased in both the above groups with a much greater rise in the oil group.