Some effects of 3-methylcholanthrene on uridine diphosphate glucuronyltransferase in the rat and guinea pig

Dietary lipids coinduce xenobiotic metabolizing enzymes in rat liver

We examined the role of dietary lipids in regulating the activities and amounts of epoxide hydrolase, UDP-glucuronosyltransferase and glutathione S-transferase in rat liver. Male Wistar rats were fed a fat-free (FF) diet or isocaloric control diet containing 5% corn oil (CO) or 5% fish oil (FO) for 3 weeks. The activities of these enzymes were approx. 2-fold higher in rats fed the FO diet vs. the FF diet. Intermediate levels of enzyme activity were found in rats fed the CO diet. Diet-induced differences in enzyme levels were shown by immunoblotting. The highest levels of epoxide hydrolase, UDP-glucuronosyltransferase and glutathione S-transferase were detected in rats fed the FO diet. The lowest levels of these enzymes were found in rats fed the FF diet. Intermediate levels of enzyme were found in rats fed the CO diet. Thus, diet-induced differences in enzyme activities were paralleled by changes in enzyme levels. Fatty acid analysis of microsomal lipids showed that the FF diet was associated with decreased levels of n-6 fatty acids vs. the CO diet. The FO diet resulted in increased levels of n-3 fatty acids vs. the other diets.

Effect of dietary lipids on levels of UDP-glucuronosyltransferase in liver

Others have shown recently that dietary fish oil protects against acetaminophen-induced liver injury in vivo. Fish oil was protective because it increased the clearance of acetaminophen via glucuronidation. This work left unresolved the basis for increased rates of glucuronidation in animals fed fish oil. We therefore have determined how the amount and type of lipid in the diet affect the activity of liver microsomal UDP-glucuronosyltransferase activity. Male Wistar rats were fed a fat-free diet or isocaloric diets containing 5% corn oil, olive oil or fish oil for 4 weeks. The activity of UDP-glucuronosyltransferase was highest in rats fed fish oil and lowest in rats fed the fat-free diet. Treatment with corn oil and olive oil resulted in intermediate levels of activity. Diet-induced differences in amounts of UDP-glucuronosyltransferase were shown by immunoblotting and kinetic measurements. Treatment with fish oil resulted in a 3-fold increase in the amount of UDP-glucuronosyltransferase versus the fat-free diet. Corn oil and olive oil diets caused 2-fold increases in the amount of UDP-glucuronosyltransferase versus the fat-free diet. Fatty acid analysis of microsomal lipids showed that the fat-free diet was associated with decreased levels of arachidonic acid versus the corn oil or olive oil diets. The fish oil diet resulted in increased levels of omega-3 fatty acids versus the other diets.