Further differentiation of 2'- and 4'-chloroflavones as inducers of hepatic microsomal monooxygenases in rats.
2'-Chloroflavone (CF) and 4'-CF were studied as inducers of cytochrome P-450-mediated monooxygenases in rat hepatic microsomes by comparison with phenobarbital (PB) and 3-methylcholanthrene (MC). As a result of interaction with the substrate 7-ethoxycoumarin (7-EC), 2'-CF-induced microsomes showed a difference spectrum different from usual type I, whereas 4'-CF-induced microsomes showed a typical type I spectrum. 2'-CF-induced microsomes increased the Vmax of aminopyrine (AM) N-demethylase activity about 1.6-fold while not affecting the apparent Km value. In contrast, 4'-CF-induced microsomes decreased the Km of 7-EC O-deethylase activity to about one fourth while significantly increasing the Vmax value. All the activities of AM N-demethylase, 7-EC O-deethylase and 6,7-dimethoxycoumarin O-demethylase in 2'-CF-induced microsomes were inhibited strongly by metyrapone and SKF 525-A, and significantly by diphenhydramine. The three enzyme activities in 4'-CF-induced microsomes were inhibited markedly by alpha-naphthoflavone and significantly by 2-bromo-4'-nitroacetophenone. These results further support the previous proposal that 2'-CF is a PB-type inducer of cytochrome P-450 while 4'-CF is a MC-type inducer.
Kato
S
S
School of Pharmacy, Hokuriku University, Kanazawa, Japan.
Yamamoto
K
K
D015660:7-Alkoxycoumarin O-Dealkylase / Q000096:biosynthesis*; D000633:Aminopyrine N-Demethylase / Q000096:biosynthesis*; D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis*; D004790:Enzyme Induction / Q000187:drug effects; D005419:Flavonoids / Q000494:pharmacology*; D008297:Male; D008748:Methylcholanthrene / Q000494:pharmacology; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D010090:Oxidoreductases, O-Demethylating / Q000096:biosynthesis*; D010634:Phenobarbital / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar
D005419:Flavonoids; C083064:4'-chloroflavone; C083063:2'-chloroflavone; D008748:Methylcholanthrene; D003577:Cytochrome P-450 Enzyme System; D010090:Oxidoreductases, O-Demethylating; C083062:scoparone O-demethylase; D015660:7-Alkoxycoumarin O-Dealkylase; D000633:Aminopyrine N-Demethylase; D010634:Phenobarbital