17-Hydroxylase/C17,20-lyase (CYP17) is not the enzyme responsible for side-chain cleavage of cortisol and its metabolites

The question addressed in this study was the nature of the enzyme required to remove the side-chain of 17-hydroxycorticosteroids, leading in the case of cortisol to the excretion of 11β-hydroxyandrosterone, 11-oxo-androsterone and the corresponding etiocholanolones. We questioned whether it could be CYP17, the 17-hydroxylase/17,20-lyase utilized in androgen synthesis. The conversion of exogenous cortisol to C 19 steroids in patients with complete 17-hydroxylase deficiency (17HD) was studied rationalizing that if CYP17 was involved no C 19 steroids would be formed. The urinary excretion of the four 11-oxy-C 19 steroids as well as many of the major C 21 cortisol metabolites were measured by GC/MS. Our results showed that the conversion of cortisol to C 19 steroids was normal in 17HD indicating that a currently unidentified enzyme must be responsible for this transformation. A secondary goal was to determine to what extent 11-oxy-C 19 steroids were metabolites of cortisol or adrenal synthesized 11β-hydroxyandrostenedione. Since cortisol-treated 17HD patients cannot produce androstenedione, all C 19 11-oxy-metabolites excreted must be derived from exogenous cortisol. The extent to which 17HD patients have lower relative excretion of C 19 steroids should reflect the absence of 11β-hydroxyandrostenedione metabolites. Our results showed almost all of 11-oxo-etiocholanolone and 11β-hydroxyetiocholanolone were cortisol metabolites, but in contrast the excretion of 11β-hydroxyandrosterone was less than 10% that of normal individuals, indicating that in excess of 90% must be a metabolite of 11β-hydroxyandrostenedione.