The role of methionine in carcinogenesis in vivo.

The effects of methionine on carcinogenesis and tumor development have been studied intermittently for over 35 years. These studies have generally shown that methionine confers some degree of protection against the development of liver tumors by hepatocarcinogens. Such protective effects by supplemental dietary methionine are more pronounced in animals fed methionine- and choline-deficient diets rather than methionine- and choline-adequate diets. To date few if any protective effects of methionine have been observed against tumor formation in extrahepatic tissues. The effects of methionine on hepatocarcinogenesis appear to correlate well with its effects on the liver content of S-adenosylmethionine, the chief physiologic methyl donor. Perturbation of the methyl pool is known to alter the extent of methylation of membrane phospholipids, RNA, and DNA. Thus several plausible mechanisms by which methionine may modify the carcinogenic process center upon the aberrant methylation of macromolecules.