Effects of Oxidized Frying Oil on Proteins Related to α-Tocopherol Metabolism in Rat Liver

An oxidized frying oil (OFO) diet has been reported to induce an increase in lipid peroxidation and a reduction in vitamin E status in animal tissues. This study was performed to investigate how vitamin E metabolism is influenced by OFO. Male Wistar rats were divided into three groups, a control group (CO) and two OFO-fed groups (OF and OFE). The diet of the OFE group was supplemented with an extra 50 mg/kg of alpha-tocopherol acetate and thus contained twice as much vitamin E as that of the OF group. After six weeks on these diets, liver alpha-tocopherol levels in the OF group were the significantly lowest among the three groups. Excretion of the alpha-tocopherol metabolite, alpha-carboxyethyl hydroxychroman (alpha-CEHC) in the urine was significantly lower in the OF group than in the other two groups. There were no significant differences in protein levels of alpha-tocopherol transfer protein (alpha-TTP) and multidrug resistance protein among the three groups. Protein levels of cytochrome P450 monooxygenase (CYP) 3A, CYP4A, and catalase were markedly increased in both groups on the OFO diet. This suggests that an OFO diet may interfere with medicine metabolism and needs further investigation.