Induction of monooxygenase and transferase activities in rat by dietary administration of flavonoids.

1. The influence of the dietary flavonoids, chrysin, quercetin, tangeretin, flavone and flavanone, on the components of the rat liver drug-metabolizing enzyme system was examined and compared with two well-known synthetic flavonoids 7,8-benzoflavone and 5,6-benzoflavone. 2. Polyhydroxylated molecules such as quercetin and chrysin, produced no significant changes on phase I and phase II enzyme activities. 3. Flavone was the most potent inducer, and resulted in a mixed type of induction. 7-Ethoxycoumarin O-deethylase (ECOD), 7-ethoxyresorufin O-deethylase (EROD) and pentoxyresorufin depentylase (PROD) activities were increased 2, 30 and 15-fold respectively. p-Nitrophenol UDP-glucuronyltransferase (UDPGT 1), p-hydroxybiphenyl UDP-glucuronyltransferase (UDPGT 2) and glutathione transferase (GST) activities were also induced. 4. Flavanone, which differs from flavone only by the degree of unsaturation of the pyrone ring, produced only a weak increase in monooxygenase activity, but the increase in phase II enzyme activities was as great as that for flavone treatment. 5. Tangeretin displayed a mixed pattern of induction, with increases in ECOD, EROD and PROD, and UDPGT 1 and UDPGT 2 activities, but these were less than with flavone treatment. 6. 7,8-Benzoflavone and 5,6-benzoflavone showed induction patterns similar to those of 3-methylcholanthrene. Nevertheless dietary treatment with 5,6-benzoflavone caused changes which were not as great as those usually described when this compound is administered i.p.