The effects of moderate ethanol consumption on the liver of the monkey, Macaca fascicularis

Although evidence has accumulated for the cardioprotective effects of moderate ethanol consumption, little is known about the effects on the liver of consuming the equivalent of two drinks per day. The objective of this study was to determine the effects of moderate ethanol administration on the hepatic content of enzymes involved in ethanol oxidation, on hepatic lipid accumulation, and on serum markers of liver function/damage in the monkey, Macaca fascicularis.

Ovariectomized, adult monkeys were maintained for 34 months on an atherogenic diet containing cholesterol 1.21 mg/kJ. They were trained to drink ethanol plus vehicle at a dose of 0.5 g/kg body weight, which was administered 5 days a week for 2 years. Blood was collected for ethanol concentrations (1 hr after ethanol administration) and was also assayed for gamma-glutamyltransferase, alanine aminotransferase (ALT), and alkaline phosphatase (ALP) activities. Liver obtained at necropsy was analyzed for triglyceride and cholesterol contents and for alcohol dehydrogenase, cytochrome P450 2E1, and cytochrome P450 3A4 by Western blots.

The blood ethanol concentrations measured 1 hr after ethanol administration were relatively constant over the 2-year dosing period. Hepatic levels of alcohol dehydrogenase and the cytochrome P450s were not significantly different between ethanol-consuming animals and control animals. Ethanol-associated increases in liver triglyceride were not significant due to high variability in hepatic lipid content in both the controls and ethanol consumers. However, covariance analyses using pretreatment concentrations of plasma cholesterol and apolipoprotein A-I suggested that the ethanol-related increase in hepatic free cholesterol was significant. Relative to controls, alcohol consumers had higher levels of serum ALT and a transient increase in ALP at 5 months.

The observations made in this study on primates administered an atherogenic diet suggest that moderate ethanol ingestion has modest effects on the liver, including slightly increased ALT and ALP values. However, additional studies will be required to verify that this level of consumption is hepatotoxic when ingested over extended periods. This is still a concern because some human studies suggest that levels of ethanol considered to be cardioprotective cause liver injury when consumed over a lifetime.