Substrate Specificity of Human Cytochrome P450 (CYP) 2C Subfamily and Effect of Azole Antifungal Agents on CYP2C8

Abstract

-PURPOSE: The metabolic activities of aminopyrine N-demethylation and tolbutamide methylhydroxylation by the human hepatic cytochrome P450 (P450 or CYP) 2C subfamily were compared and the effects of azole antifungal agent on the drug-metabolizing activity of CYP2C8 were investigated. METHODS: Aminopyrine N-demethylation and tolbutamide methylhydroxylation by CYP2C8, CYP2C9, and CYP2C19 were determined by the previous reported methods. The effects of five azole antifungal agents, fluconazole, itraconazole, ketoconazole, miconazole, and voriconazole, on the aminopyrine N-demethylation activity by CYP2C8 were investigated. RESULTS: With regard to aminopyrine N-demethylation, CYP2C19 had the lowest Michaelis constant (Km) and CYP2C8 had the highest maximal velocity (Vmax) among the CYP2C subfamily members. The Vmax/Km values for CYP2C8 were the highest, followed by CYP2C19. For tolbutamide methylhydroxylation, the Km and Vmax for CYP2C19 were three and six times higher than the corresponding values for CYP2C9, and the Vmax/Km value for CYP2C19 was twice that for CYP2C9, whereas hydroxylated tolbutamide formed by CYP2C8 was not detected. Fluconazole, itraconazole, and voriconazole at a concentration of 2 or 10 µM neither inhibited nor stimulated CYP2C8-mediated aminopyrine Ndemethylation activity at substrate concentrations around the Km (5 mM). However, ketoconazole and miconazole noncompetitively inhibited CYP2C8-mediated aminopyrine N-demethylation with the inhibitory constant values of 1.98 and 0.86 µM, respectively. CONCLUSION: These results suggest that ketoconazole and miconazole might inhibit CYP2C8 clinically.

Induction by Phenobarbital of Phase I and II Xenobiotic-Metabolizing Enzymes in Bovine Liver: An Overall Catalytic and Immunochemical Characterization

“…An increasing amount of a cross-reacting CYP2C protein was observed in the liver of PB-treated cattle, thus partially confirming transcriptional results (i.e., CYP2C31 and CYP2C42 ). Bovine CYP2C-dependent catalytic activities were evaluated by using the broad substrates aminopyrine [ 95 , 120 , 121 ], chlorpheniramine [ 122 , 123 ], and 7-MFMC [ 94 , 101 , 123 ]. Phenobarbital significantly increased the in vitro metabolism ( N- demethylation) of the abovementioned substrates, and especially of 7-MFMC.…”

Non-Alcoholic Steatohepatitis Decreases Microsomal Liver Function in the Absence of Fibrosis

“…Because N-demethylation of 13 C-aminopyrine has been shown to be the rate-limiting step, it has been assumed that the ABT reflects the activity of the cytochrome P450-dependent mono-oxygenase system and gives a global assessment of this system. It has been demonstrated that the N-demethylation of aminopyrine is catalyzed most efficiently by CYP2C19 and CYP2C8, followed by CYP2D6, 2C18, 1A2 and 2B6; and to a lesser extent by CYP2C9, 2A6, 1A1 and 3A4 [5,6]. Aminopyrine metabolism is mostly dependent on hepatic metabolic capacity (functional hepatic mass) rather than on portal blood flow [7].…”

EFFECT OF SIMVASTATIN ON THE GROWTH INHIBITION OF Candida albicans

“…Their mechanism of action occurs by inhibiting the enzyme 14α-demethylase (14 DM), an important cytochrome P-450 enzyme in the ergosterol biosynthesis route, which catalyzes the oxidative removal of the 14α-methyl group from lanosterol (ZHANG et al, 2016;NIWA;IMAGAWA, 2016;SUI et al, 2017). Azole, bound to the active site of this enzyme, competes with the substrate for binding).…”