Identification of the Main Human Cytochrome P450 Enzymes Involved in Safrole 1'-Hydroxylation

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• 作者：Yune-Fang Ueng ; Chih-Hang Hsieh ; Ming-Jaw Don ; Chin-Wen Chi ; and Li-Kang Ho
• 刊名：Chemical Research in Toxicology
• 出版年：2004
• 出版时间：August 2004
• 年：2004
• 卷：17
• 期：8
• 页码：1151 - 1156
• 全文大小：74K
• 年卷期：v.17,no.8(August 2004)
• ISSN：1520-5010

文摘

Safrole is a natural plant constituent, found in sassafras oil and certain other essential oils.The carcinogenicity of safrole is mediated through 1'-hydroxysafrole formation, followed bysulfonation to an unstable sulfate that reacts to form DNA adducts. To identify the maincytochrome P450 (P450) involved in human hepatic safrole 1'-hydroxylation (SOH), wedetermined the SOH activities of human liver microsomes and Escherichia coli membranesexpressing bicistronic human P450s. Human liver (n = 18) microsomal SOH activities were inthe range of 3.5-16.9 nmol/min/mg protein with a mean value of 8.7 ± 0.7 nmol/min/mg protein.In human liver (n = 3) microsomes, the mean K_m and V_max values of SOH were 5.7 ± 1.2 mMand 0.14 ± 0.03 mol/min/nmol P450, respectively. The mean intrinsic clearance (V_max/K_m)was 25.3 ± 2.3 L/min/nmol P450. SOH was sensitive to the inhibition by a CYP2C9 inhibitor,sulfaphenazole, and CYP2E1 inhibitors, 4-methylpyrazole and diethyldithiocarbamate. Theliver microsomal SOH activity showed significant correlations with tolbutamide hydroxylation(r = 0.569) and chlorzoxazone hydroxylation (r = 0.770) activities, which were the modelreactions catalyzed by CYP2C9 and CYP2E1, respectively. Human CYP2C9 and CYP2E1showed SOH activities at least 2-fold higher than the other P450s. CYP2E1 showed an intrinsicclearance 3-fold greater than CYP2C9. These results demonstrated that CYP2C9 and CYP2E1were the main P450s involved in human hepatic SOH.