Dietary Betaine Promotes Generation of Hepatic S‐Adenosylmethionine and Protects the Liver from Ethanol‐Induced Fatty Infiltration

Previous studies have shown that ethanol feeding to rats alters methionine metabolism by decreasing the activity of methionine synthetase. This is the enzyme that converts homocysteine in the presence of vitamin B₁₂ and N⁵‐methyltetrahydrofolate to methionine. The action of the ethanol results in an increase in the hepatic level of the substrate N⁵‐methyltetrahydrofolate but as an adaptive mechanism, betaine homocysteine methyltransferase, is induced in order to maintain hepatic S‐adenosylmethionine at normal levels. Continued ethanol feeding, beyond 2 months, however, produces depressed levels of hepatic S‐adenosylmethionine. Because betaine homocysteine methyltransferase is induced in the livers of ethanolfed rats, this study was conducted to determine what effect the feeding of betaine, a substrate of betaine homocysteine methyltransferase, has on methionine metabolism in control and ethanol‐fed animals. Control and ethanol‐fed rats were given both betainelacking and betaine‐containing liquid diets for 4 weeks, and parameters of methionine metabolism were measured. These measurements demonstrated that betaine administration doubled the hepatic levels of S‐adenosylmethionine in control animals and increased by 4‐fold the levels of hepatic S‐adenosylmethionine in the ethanol‐fed rats. The ethanol‐induced infiltration of triglycerides in the liver was also reduced by the feeding of betaine to the ethanol‐fed animals. These results indicate that betaine administration has the capacity to elevate hepatic S‐adenosylmethionine and to prevent the ethanol‐induced fatty liver.