It has been postulated that the hepatocarcinogenicity of a choline-devoid diet in rats stems from peroxidation of liver lipids. We have investigated whether the diet contains conjugated dienes that could account directly for those detected in liver lipids of rats fed a choline-devoid diet. Analyses were performed on samples of corn oil and of a partially hydrogenated fat used to prepare semipurified choline-devoid and choline-supplemented diets, and on fat extracted from two pairs of diets, one set containing 5% corn oil and 10% partially hydrogenated fat, and the other only corn oil (15%). The analyses consisted of quantitation of conjugated dienes by UV spectrophotometry, separation of fatty acids with conjugated dienes by HPLC, and quantitation of trans fatty acids by IR spectrophotometry. Small levels of conjugated diene and trans fatty acids were present in the corn oil, but much higher amounts were found in the partially hydrogenated fat. HPLC analysis yielded distinct elution profiles for the fatty acids with conjugated dienes present in the two fats, and similar results were obtained with fat extracted from the diets. However, no differences were observed between choline-devoid and control choline-supplemented diets. The results indicate that caution must be exercised in interpreting data from UV analysis of tissue lipids of rats fed diets containing a partially hydrogenated fat.
Rodents kept on a choline devoid (CD) diet up to 14 months develop hepatic lesions progressing through two broad stages. The first is characterized by severe steatosis and increase in cell turnover, the second by a gradual clearance of the deposited fat and fibrosis. Hepatocellular carcinomas eventually arise in rats fed for over 12 months, even though the animals aer not exposed to chemical carcinogens. It has been suggested that the diet may trigger generated thereby may be responsible for initiation of liver cancer and promotion. The radicals would lead to DNA damage, and the altered DNA in a proliferating liver would result in initiation of the carcinogenic process. In this communication we present evidence that the diet used in the above studies contained stable fatty acid isomers with conjugated dienes, which are absorbed and deposited in rat liver. This finding cast doubts on whether a CD diet does indeed cause a peroxidation of cellular membrane lipids. Electron spin resonance (ESR) spectroscopy was also used to investigate whether any abnormal pattern of free radicals exists in the liver of rats fed a CD diet. No significant differences were noted in ESR spectra of either transition metal-centered signals, or organic free radicals.
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