Inhibition of steroidogenic cytochrome P-450 enzymes in rat testis by ketoconazole and related imidazole anti-fungal drugs.

Ketoconazole, an imidazole antifungal drug, has previously been shown to diminish testosterone and cortisol production in patients as well as rat and mouse cells in vitro. Inhibition of adrenal mitochondrial cytochrome P-450 enzymes was demonstrated. In this study we tested several imidazole antifungal drugs and examined the individual steps in testicular steroidogenesis to determine which enzymes in the androgen pathway were blocked. In addition, we studied 25-hydroxyvitamin D 24-hydroxylase activity in cultured pig kidney cells (LLC-PK1) to assess a mitochondrial P-450 enzyme in another organ. All imidazoles tested inhibited both total testosterone production and 24-hydroxylase activity but the relative potencies differed. We next studied the individual testicular enzymatic steps between cholesterol and testosterone. Ketoconazole inhibited cholesterol-side-chain-cleavage enzyme (mitochondrial) and C-17,20 lyase (microsomal). The three inhibited enzymes (two testicular and one renal) are all P-450 cytochromes. Testicular 17-hydroxylase, also a P-450 cytochrome, was not inhibited even at high doses of ketoconazole. This is an interesting finding because the testicular hydroxylase and lyase have been shown to be a single protein. Non-cytochrome P-450 enzymes in the androgen pathway were not inhibited. The results demonstrate that several imidazole antifungal drugs all inhibit both microsomal and mitochondrial cytochrome P-450 enzymes in multiple organs.