TY - JOUR T1 - Defective Activity of Recombinant Cytochromes P450 3A4.2 and 3A4.16 in Oxidation of Midazolam, Nifedipine, and Testosterone JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 2287 LP - 2291 DO - 10.1124/dmd.108.021816 VL - 36 IS - 11 AU - Mitsue Miyazaki AU - Katsunori Nakamura AU - Yukiyoshi Fujita AU - F. Peter Guengerich AU - Ryuya Horiuchi AU - Koujirou Yamamoto Y1 - 2008/11/01 UR - http://dmd.aspetjournals.org/content/36/11/2287.abstract N2 - Cytochrome P4503A4 (CYP3A4) is the most abundant cytochrome P450 in adult human liver and small intestine and oxidizes numerous clinically, physiologically, and toxicologically important compounds. The metabolic activity of CYP3A4 in patients varies at least 10-fold in vivo, and CYP3A4 genetic variants are considered one of the causes of individual differences. The cDNAs for the CYP3A4*2 (S222P), *7 (G56D), *16 (T185S), and *18 (L293P) mutant alleles, found in high frequencies in Caucasians or Asians, were constructed by site-directed mutagenesis and expressed in an Escherichia coli expression system. Midazolam (MDZ), testosterone (TST), and nifedipine (NIF) were used to assess the catalytic activities of the CYP3A4 wild type (CYP3A4.1) and its variants. The catalytic activities of CYP3A4.2 and CYP3A4.16 were reduced (lower Vmax and increased Km relative to CYP3A4.1) for all substrates. The CYP3A4.7 showed lower Vmax values for MDZ and NIF (60 and 84%, respectively) and a higher Km (2-fold) for TST but not for MDZ or NIF. Although CYP3A4.18 showed low Vmax values for MDZ, NIF, and TST (88, 72, and 80% of CYP3A4.1, respectively), no significant differences were identified in the ratio Vmax/Km. In summary, CYP3A4.2 and CYP3A4.16 exhibited significantly lower activity for MDZ, TST, and NIF oxidations than CYP3A4.1. Therefore, drugs metabolized by only CYP3A should be carefully administered to patients with these alleles. The American Society for Pharmacology and Experimental Therapeutics ER -