Effects of ethanol on lipid metabolism in adipose tissue

Ethanol impairs differentiation of human adipocyte stromal cells in culture

BACKGROUND

Bioinformatic resources suggest that adipose tissue expresses mRNAs for alcohol dehydrogenases (ADHs) and ALDH2, and epidemiological studies indicate that heavy alcohol use reduces adipose tissue mass. We therefore characterized the expression of alcohol metabolizing enzymes in human, rat and mouse adipose tissue, preadipocytes, and adipocytes, the ability of adipocytes to metabolize ethanol, and the effects of ethanol on differentiation of human adipose stromal cells (hASCs).

METHODS

Adipose tissue, preadipocytes, and adipocytes were collected from rodents or from humans undergoing bariatric surgery. hASCs were differentiated in vitro using standard methods. Gene expression and cellular differentiation were analyzed by Western blotting, RT-PCR, and microscopy.

RESULTS

Class I ADH was expressed in human > mouse > rat adipose tissue, whereas ALDH2 was high in all samples. ADH, catalase, and ALDH2 were induced during differentiation of hASCs. The presence of 50 mM ethanol markedly reduced the differentiation of hASCs; this effect was associated with inhibition of expression of transcription factors required for differentiation, but did not depend on the ability of the cells to metabolize ethanol.

CONCLUSIONS

Human adipose tissue expresses alcohol oxidizing enzymes. The presence of ethanol at physiologically relevant concentrations inhibits differentiation of hASCs. Ethanol could alter adipose tissue biology, inducing a form of acquired lipodystrophy, which is consistent with epidemiological studies.

Adaptation of lipogenesis and lipolysis to dietary ethanol

The effect of dietary ethanol on metabolic fates of glucose and ethanol, and activities of lipoprotein lipase and hormone-sensitive lipase in several tissues of miniature pigs were determined in vitro. Ethanol and glucose were used at similar rates for fatty acid synthesis in liver and brain and CO2 production in liver. Ethanol was preferred over glucose for fatty acid and CO2 production in ileal mucosal cells. Glucose was the preferred substrate for lipogenesis and oxidation to CO2 in adipose tissue and skeletal muscle, and for oxidation to CO2 in brain. Dietary ethanol decreased glucose and ethanol conversion to fatty acids in ileal mucosa and brain, respectively. Dietary ethanol had no effect on the capacity of liver, adipose tissue, and skeletal muscle to convert either glucose or ethanol to long-chain fatty acids. The capacity to oxidize ethanol, but not glucose, to CO2 in liver was increased by dietary ethanol. No dietary ethanol effect was observed in other tissues. The capacity for removal of plasma triglycerides (based on lipoprotein lipase activity) tended to increase in adipose tissue and skeletal muscle of pigs fed ethanol. Mobilization of long-chain fatty acids from adipose tissue (based on hormone-sensitive lipase activity), triglyceride concentration in plasma, and percentage of lipid in liver remained unchanged when ethanol was fed. Livers of ethanol-fed pigs, however, were larger than livers of control pigs. Our results indicate that feeding miniature pigs 21-37% of total caloric intake as ethanol causes significant metabolic adaptations of lipid metabolism in liver and ileal mucosa, but not in adipose tissue, skeletal muscle, and brain. The ethanol feeding, however, did not cause fatty livers or hyperlipidemia.

Studies on the serum lipid and lipoproteins in steatosis of the liver

In a medical department, specialized in liver diseases, 45 patients (33 men and 12 women) suffering from steatosis of the liver have been examined with reference to serum lipid abnormalities. Twenty-eight of the patients were chronic alcoholics. Annual check-ups, including biopsy of the liver, were made to evaluate the development of the steatosis. The patients did not receive treatment with drugs or diet. Thirteen patients showed hypercholesterolemia, 16 increased serum triglyceride and 8 increased serum phosphorus lipid. Two showed a type I lipoprotein anomaly and 33 a type II-like pattern, defined as increased beta-lipoprotein associated with increase of serum cholesterol, was found in four cases. Three had a type III and three a type IV abnormal pattern, with increased pre-beta-lipoprotein and serum triglyceride levels. Correlation analysis revealed correlations between pre-beta-lipoprotein and serum triglyceride as well as between serum triglyceride and serum free fatty acid levels.