Metabolic activation of o-phenylphenol to a major cytotoxic metabolite, phenylhydroquinone: role of human CYP1A2 and rat CYP2C11/CYP2E1.
1. The in vitro metabolic activation of o-phenylphenol has been evaluated as yielding a toxic metabolite, 2,5-dihydroxybiphenyl (phenylhydroquinone), by p-hydroxylation in liver microsomes of rat and human. The involvement of rat CYP2C11, CYP2E1 and human CYP1A2 in the p-hydroxylation of o-phenylphenol is suggested. 2. 2,3- and phenylhydroquinone, which induced DNA single-strand scission in the presence of 1 microM CuCl2, were the most cytotoxic chemicals examined to cultured mammalian cell lines among o-phenylphenol, m-phenylphenol, p-phenylphenol, 2,2'-, 4,4'-, 2,3- and phenylhydroquinone. 3. Rat and human liver microsomes catalysed the formation of phenylhydroquinone, but not 2,3-dihydroxybiphenyl, using o-phenylphenol as a substrate. A higher rate of metabolic activation of o-phenylphenol was observed with livers of the male than the female rats by 5.6- and 2.6-fold respectively. 4. Inhibitory antibodies against the male-specific CYP2C11 inhibited hepatic o-phenylphenol p-hydroxylation in the male F344 and Sprague-Dawley rat by > 70%. Liver microsomes from the isoniazid-treated rats produced 1.8- and 3-fold induction of o-phenylphenol p-hydroxylation and chlorzoxazone 6-hydroxylation (a CYP2E1-dependent activity) respectively. 5. Human CYP1A2, expressed by baculovirus-mediated cDNA expression systems, exhibited a remarkably higher capacity for o-phenylphenol p-hydroxylation at concentrations of 5 (> 5-fold), 50 (> 2-fold) and 500 microM (> 2-fold) than CYP2A, CYP2B, CYP2Cs, CYP2D6, CYP2E1 and CYP3A4 on the basis of pmol P450. 6. Among various CYP inhibitors tested here, 7,8-benzoflavone and furafylline, typical human CYP1A2 inhibitors, inhibited the microsomal p-hydroxylation of o-phenylphenol in human livers most potently by 70 and 50% respectively. 7. The results thus indicate the involvement of rat CYP2C11/CYP2E1 and human CYP1A2 in the hepatic p-hydroxylation of o-phenylphenol.
Ozawa
S
S
Division of Pharmacology, National Institute of Health Sciences, Tokyo, Japan. sozawa@nihs.go.jp
Ohta
K
K
Miyajima
A
A
Kurebayashi
H
H
Sunouchi
M
M
Shimizu
M
M
Murayama
N
N
Matsumoto
Y
Y
Fukuoka
M
M
Ohno
Y
Y
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D001711:Biotransformation; D001713:Biphenyl Compounds / Q000493:pharmacokinetics* / Q000633:toxicity; D019388:Cytochrome P-450 CYP1A2 / Q000378:metabolism*; D019392:Cytochrome P-450 CYP2E1 / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D000072467:Cytochrome P450 Family 2; D003580:Cytochromes; D005419:Flavonoids; D006801:Humans; D006873:Hydroquinones / Q000493:pharmacokinetics* / Q000633:toxicity; D006900:Hydroxylation; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D008114:Liver Neoplasms, Experimental; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D010636:Phenols / Q000493:pharmacokinetics*; D011108:Polymers / Q000493:pharmacokinetics*; D059808:Polyphenols; D051381:Rats; D011916:Rats, Inbred F344; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000378:metabolism; D039181:Steroid 16-alpha-Hydroxylase; D013250:Steroid Hydroxylases / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D001713:Biphenyl Compounds; D003580:Cytochromes; D005419:Flavonoids; D006873:Hydroquinones; D007527:Isoenzymes; D010636:Phenols; D011108:Polymers; D059808:Polyphenols; D011994:Recombinant Proteins; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D019392:Cytochrome P-450 CYP2E1; D001189:Aryl Hydrocarbon Hydroxylases; C504573:CYP1A2 protein, human; C450279:CYP2C11 protein, rat; C017170:Cyp1a2 protein, rat; D019388:Cytochrome P-450 CYP1A2; D000072467:Cytochrome P450 Family 2; D039181:Steroid 16-alpha-Hydroxylase; C066330:phenylhydroquinone