FIG 3.

Metabolism of cortisol and 16α-hydroxyprogesterone by gut bacteria. The cortisol side chain is metabolized in two important pathways. The first is side chain cleavage, which converts a C₂₁ glucocorticoid into a precursor to C₁₉ 11-oxyandrogens. Indeed, the conversion of 17-ketone to 17β-hydroxy by bacterial NAD(P)H-dependent 17β-HSDH along with 5α reduction by some clostridia produces a potent androgen. 16α-Hydroxyprogesterone is 16α dehydroxylated and Δ¹⁶ reduced, followed by reduction of the 3-oxo-Δ (123–125), resulting in 17α-pregnanalone.