Effect of iodine-enriched eggs on metabolic activation of benzo(a)pyrene to mutagens and drug-metabolizing enzyme activities in rat hepatic tissue

Rats were fed a diet containing 10% (w/w) ordinary egg (OE) powder or iodine-enriched egg (IE) powder, which was prepared especially for this experiment and contained 100-150 times more iodine than the OE, for 60 days. A part of each group was intraperitoneally injected with polychlorinated biphenyl (PCB) at 5 days before sacrifice. The metabolic capacity for transformation of benzo[a]pyrene (BP) to mutagenic metabolites, cytochrome P-450 (P-450) content, and glutathione S-transferase (GST), sulfotransferase (ST) and UDP-glucuronyltransferase (UDPGT) activities in the liver were investigated. Compared to rats fed the OE diet, the metabolic capacity for activation of BP determined by the Ames test was significantly lower in those fed the IE diet. PCB treatment significantly increased the metabolic capacity regardless of experimental diets; however, the increased metabolic capacity after PCB treatment in animals fed the IE diet was still significantly lower at some BP dose levels than that in animals fed the OE diet. The P-450 contents as well as the various conjugating enzyme activities tended to be lower in the IE-fed group compared with the OE-fed group. Drug-metabolizing activities were generally induced by PCB in both dietary groups. The PCB-induced P-450 contents were found to be significantly lower in the IE group than in the OE group, but there was no difference in the increase in conjugating enzyme activities between the two groups. Based upon these findings, it is suggested that the lowering effects of the IE on the BP mutagenicity may be at least partially due to a reduction of some P-450 linked drug-metabolizing enzyme activities involved in the activation of BP.