Most drugs and xenobiotics are metabolized by a small number of hepatic cytochrome P450 enzymes. All drug metabolizing P450 enzymes receive electrons from NADPH through a single flavoprotein known as NADPH-P450 reductase. We have recently identified mutations in NADPH P450 reductase from patients with disordered steroidogenesis. Polymorphisms in the drug metabolizing enzymes, especially cytochrome P450s are well known to be responsible for variations in drug responses. My preliminary work on mutant and polymorphic P450 reductase suggests that many drug metabolizing P450 enzymes are severely affected by an abnormal P450 reductase enzyme. Since all liver P450 enzymes need P450 reductase for activity, it is seems likely that changes in P450 reductase may produce drug responses that are phenotypically similar to one or more cytochrome P450 mutations / polymorphisms. As an example, in the first report of P450 reductase mutations, the disease profile of hormonally impaired patients suggested a defect in P450c17 or P450c21 but no mutation in any of these enzymes was found and it was the defective P450 reductase that produced a phenotypic response similar to defective P450c17 and P450c21. Sequencing data from normal population has revealed several variants of NADPH P450 reductase enzyme. These P450 reductase variants are being tested for the electron transfer activities towards various cytochrome P450 enzymes. First set of P450 reductase mutations had been tested for activity towards P450c17 and aromatase (CYP19A1).

Growth, Adrenarche and Polycystic Ovary Syndrome

Androgenic steroids are required for a wide range of functions necessary for life, from the salt balance by mineralocorticoids, sugar balance by glucocorticoids to the growth reproductive and sexual functions by sex steroids. Human androgens are made from dehydroepiandrosterone (DHEA). DHEA is made from cholesterol by only two enzymes; P450scc, the cholesterol side-chain cleavage enzyme, and P450c17, which catalyzes both 17-hydroxylase and 17,20 lyase activities. P450c17 is qualitative regulator of steroidogenesis. In the absence of P450c17 (e.g. in adrenal zona glomerulosa, ovarian glomerulosa) 17-deoxysteroids (progesterone, corticosterone, aldosterone) are produced. When 17-hydroxylase activity is present, cortisol is produced; when both hydroxylase and lyase activities are present, C-19 androgen precursors are produced. Production of DHEA rises rapidly at adrenarche and peaks at around 20-25 years of age and then declines slowly with age. Adrenarche is the event when adrenal cortex begins to make androgens and it is independent of the puberty and occurs in both sexes. Recent clinical data suggest that premature, exaggerated adrenarche is an early sign of polycystic ovary syndrome (PCOS), which affects around 5% of women of reproductive age and is the most common of endocrine disorders. It has been shown that the ratio of hydroxylase to lyase activities of P450c17 is regulated by serine phosphorylation and interaction with cytochrome b5. Identification of the kinase that phosphorylates P450c17 and serves as a trigger for adrenarche is of fundamental importance in human biology. Moreover, adrenopause, the decline in production of androgens with old age, could be controlled by activation of same kinase or deactivation of phosphatases that dephosphorylate P450c17. I have identified Phosphatase 2A (PP2A) and phosphoprotein SET (also called TAF-1) are regulators of P450c17 phosphorylation.