Anne Smith-Kielland

Ethanol effects on protein synthesis in nonparenchymal liver cells, hepatocytes, and density populations of hepatocytes

Rats were given ethanol chronically (20-30% of the energy) in a nutritionally sufficient diet regimen. Controls received lipid as an isoenergetic substitute for ethanol. Protein synthesis in hepatocytes isolated from ethanol-fed rats was decreased compared with controls, but not in isolated nonparenchymal liver cells. Ethanol added in vitro inhibited protein synthesis in hepatocytes by 30%, but not in nonparenchymal cells for both ethanol-fed and control rats. Protein export and protein degradation in isolated hepatocytes were not affected by long-term ethanol treatment. Isolated hepatocytes were separated according to their buoyant density in linear metrizamide gradients. They were distributed in a bell-shaped manner regardless of donor rat treatment. Cells of low density contained three times as much lipid as high density cells. They were probably enriched in periportal cells, since histologic examination indicated a predominantly periportal localization of cells containing lipid droplets. Distribution of the intra-acinar marker alanine aminotransferase supported this conclusion. Protein synthesis was similar in the low-density hepatocyte populations of the respective groups of rats, whereas it was inhibited in a high-density population of ethanol-treated rats compared to the controls. Inhibition of protein synthesis by 80 mM ethanol was lower in the low-density hepatocytes of ethanol-fed rats.

Ethanol and protein metabolism in the liver

The influence of acute and chronic ethanol administration on liver protein synthesis, secretion and degradation has been studied by various research groups. Acute ethanol administration appeared to have few if any effects on protein synthesis in vivo, but reduced the synthetic rates of both stationary and exported proteins in suspensions of isolated rat liver cells. Chronic ethanol intake for more than 4 weeks inhibited protein synthesis in vivo, and in cell preparations from treated rats. This inhibitory effect was independent of animal sex, hepatic protein content and diet. The effects of acute and chronic ethanol intake on hepatic protein export are unclear with both inhibition or no effect being reported. The effect of ethanol on liver protein degradation has only been studied to a limited extent, and the results do not indicate clear and marked effects due to ethanol. The inhibitory effect of chronic ethanol intake on hepatic protein synthesis could be of importance in the development of liver injury.

Toluene metabolism in isolated rat hepatocytes: effects of in vivo pretreatment with acetone and phenobarbital

Hepatocytes isolated from control, acetone- and phenobarbital-pretreated rats were used to study the metabolic conversion of toluene to benzyl alcohol, benzaldehyde, benzoic acid and hippuric acid at low (<100 μM) and high (100–500 μM) toluene concentrations. The baseline formation rates of toluene metabolites (benzyl alcohol, benzoic acid and hippuric acid) were 2.9±01.7 and 10.0±2.3 nmol/mg cell protein/60 min at low and high toluene concentrations, respectively. In vivo pretreatment of rats with acetone and phenobarbital increased the formation of metabolites: at low toluene concentrations 3- and 5-fold, respectively; at high toluene concentrations no significant increase (acetone) and 8-fold increase (phenobarbital). Apparent inhibition by ethanol, 7 and 60 mM, was most prominent at low toluene concentrations: 63% and 69%, respectively, in control cells; 84% and 91% in acetone-pretreated cells, and 32% (not significant) and 51% in phenobarbital-pretreated cells. Ethanol also caused accumulation of benzyl alcohol. The apparent inhibition by isoniazid was similar to that of ethanol at low toluene concentrations. Control and acetone-pretreated cells were apparently resistant towards metyrapone; the decrease was 49% and 64% in phenobarbital-pretreated cells at low and high toluene concentrations, respectively. In these cells, the decrease in presence of combined ethanol and metyrapone was 95% (low toluene concentrations). 4-Methylpyrazole decreased metabolite formation extensively in all groups. Benzaldehyde was only found in the presence of an aldehyde dehydrogenase inhibitor. Increased ratio benzoic/hippuric acid was observed at high toluene concentrations. These results demonstrate that toluene oxidation may be studied by product formation in isolated hepatocytes. However, the influence of various enzymes in the overall metabolism could not be ascertained due to lack of inhibitor specificity.

Protein synthesis in rat liver after chronic ethanol treatment

170 pm) was constructed which could be placed in either region (300 500 pm in diameter) for the determination of pyridine nucleotide fluorescence (366 + 450 nm). When the 0s tension was decreased by switching to buffer saturated with a 95% Ns and 5% CO2 gas mixture, periportal and pericentral pyridine nucleotide systems became reduced at different inflow PO2 values (Table 1). In livers from control and alcohol-treated rats, pyridine nucleotides in the pericentral region were reduced at inflow PO2 values about 70 to 110 Torr greater than those in the periportal region. However, treatment with alcohol caused pyridine nucleotides in both periportal and pericentral regions to be reduced at inflow PO2 values 120 to 160 Torr higher than controls (Table 1). Under these conditions, oxygen uptake of the perfused liver of both groups was similar (105 to 112 pmoles/g per hour). These data provide direct physical evidence that alcohol-treated liver tissue is more susceptible to tissue anoxia in both periportal and pericentral regions. At least in phenobarbital-treated rats, this phenomena appears not to be due to an increase in oxygen uptake by the liver. These studies further demonstrate that the microlight guide can readily be applied to studies of intralobular metabolic compartment&ion.