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Extraadrenal 21-Hydroxylation by CYP2C19 and CYP3A4: Effect on 21-Hydroxylase Deficiency

Department of Pediatrics (L.G.G., N.H., V.A., W.L.M.), University of California San Francisco, San Francisco, California 94143-0978; and Department of Endocrinology-LIM42 (L.G.G., B.B.M., T.A.S.S.B.), Hospital das Clinicas da Universidade de São Paulo, 05403-900 São Paulo, Brazil

Address all correspondence and requests for reprints to: Prof. Walter L. Miller, Department of Pediatrics, HSE-1401, 513 Parnassus Avenue, University of California, San Francisco, San Francisco, California 94143-0978. E-mail: wlmlab{at}ucsf.edu.

Context: 21-Hydroxylase deficiency (21OHD) is caused by CYP21A2 gene mutations disrupting the adrenal 21-hydroxylase, P450c21. CYP21A2 mutations generally correlate well with the 21OHD phenotype, but some children with severe CYP21A2 mutations have residual 21-hydroxylase activity. Some hepatic P450 enzymes can 21-hydroxylate progesterone, but their physiological relevance in modifying 21OHD is not known.

Objective: We determined the ability of CYP2C19 and CYP3A4 to 21-hydroxylate progesterone and 17-hydroxyprogesterone (17OHP), determined the impact of the common P450 oxidoreductase (POR) variant A503V on these activities, and examined correlations between CYP2C19 variants and phenotype in patients with 21OHD.

Methods: Bacterially expressed, N-terminally modified, C-His-tagged human P450c21, CYP2C19, and CYP3A4 were combined with bacterially expressed wild-type and A503V POR. The 21-hydroxylation of radiolabeled progesterone and 17OHP was assessed, and the Michaelis constant (Km) and maximum velocity (Vmax) of the reactions were measured. CYP2C19 was genotyped in 21OHD patients with genotypes predicting severe congenital adrenal hyperplasia.

Results: Compared to P450c21, the Vmax/Km for 21-hydroxylation of progesterone by CYP2C19 and CYP3A4 were 17 and 10%, respectively. With both forms of POR, the Km for P450c21 was approximately 2.6 µM, the Km for CYP2C19 was approximately 11 µM, and the Km for CYP3A4 was approximately 110 µM. Neither CYP2C19 nor CYP3A4 could 21-hydroxylate 17OHP. The CYP2C19 ultrametabolizer allele CYP2C19*17 was homozygous in one of five patients with a 21OHD phenotype that was milder than predicted by the CYP21A2 genotype.

Conclusions: CYP2C19 and CYP3A4 can 21-hydroxylate progesterone but not 17OHP, possibly ameliorating mineralocorticoid deficiency, but not glucocorticoid deficiency. Multiple enzymes probably contribute to extraadrenal 21-hydroxylation.