Effects of ethanol upon lipid metabolism.

Abstract

AbstractEthanol abuse produces fatty liver which cannot be prevented by supplementation in protein, minerals, vitamins, and choline. In rats, protein and choline deficiencies potentiate the effect, whereas replacement of dietary fat by medium chain triglycerides or carbohydrates decreases the capacity of ethanol to produce steatosis. Administration of a single dose of ethanol to rats represents a stressful condition associated with moderate hepatic accumulation of fatty acids derived from adipose tissue. By contrast, chronic ethanol administration produces more pronounced steatosis with a predominance of endogenously synthesized and, when available, dietary fatty acids. These accumulate because of decreased fat oxidation. Ethanol also stimulates hepatic lipogenesis. These various effects can be explained by the increase in the hepatic nicotinamide adenine dinucleotide/nicotinamide adenine dinucleotide ratio secondary to the oxidation of ethanol via the alcohol dehydrogenase pathway. In addition there are more lasting changes in intermediary metabolism, such as increased hepatic ketogenesis which could be linked to the persistent alteration in mitochondrial function and structure found after chronic ethanol ingestion. The ultrastructural changes also are characterized by proliferation of the hepatic smooth endoplasmic reticulum. The latter was documented by subfraction. This led to the description of a new pathway for ethanol metabolism, the microsomal ethanol oxidizing system, which doubles in activity after ethanol feeding. The existence of the microsomal ethanol oxidizing system may contribute to our understanding of increased cholesterol and lipoprotein synthesis. Other effects upon lipid metabolism include decreases in free fatty acids and glycerol concentrations and free fatty acid turnover which result from inhibition of peripheral fat mobilization by acetate, a metabolite of ethanol.