Role of 11β-OH-C19 and C21 steroids in the coupling of 11β-HSD1 and 17β-HSD3 in regulation of testosterone biosynthesis in rat Leydig cells

Here we describe further experiments to support our hypothesis that bidirectional 11β-HSD1-dehydrogenase in Leydig cells is a NADP(H) regenerating system. In the absence of androstenedione (AD), substrate for 17β-HSD3, incubation of Leydig cells with corticosterone (B) or several C19- and C21-11β-OH-steroids, in the presence of [3H]-11-dehydro-corticosterone (A), stimulated 11β-HSD1-reductase activity. However, in presence of 30 μM AD, testosterone (Teso) synthesis is stimulated from 4 to 197 picomole/25,000 cells/30 min and concomitantly inhibited 11β-HSD1-reductase activity, due to competition for the common cofactor NADPH needed for both reactions. Testo production was further significantly increased (p < 0.05) to 224–267 picomole/25,000 cells/30 min when 10 μM 11β-OH-steroids (in addition to 30 μM AD) were also included. Similar results were obtained in experiments conducted with lower concentrations of AD (5 μM), and B or A (500 nM).Incubations of 0.3–6.0 μM of corticosterone (plus or minus 30 μM AD) were then performed to test the effectiveness of 17β-HSD3 as a possible NADP+ regenerating system. In the absence of AD, increasing amounts (3–44 pmol/25,000 cells/30 min) of 11-dehydro-corticosterone were produced with increasing concentrations of corticosterone in the medium. When 30 μM AD was included, the rate of 11-dehydro-corticosterone formation dramatically increased 1.3–5-fold producing 4–210 pmol/25,000 cells/30 min of 11-dehydro-corticosterone. We conclude that 11β-HSD1 is enzymatically coupled to 17β-HSD3, utilizing NADPH and NADP in intermeshed regeneration systems.

► Androgen biosynthetic enzymes such as 17α-hydroxylase, 17β-hydroxysteroid dehydrogenase and 5α-reductase require NADPH as a co-factor.
► Leydig cells contain more intracellular NADPH than NADP+ thus favoring the androgen synthetic activity.
► These androgen biosynthetic enzymes generate NADP+ which activates the 11β-HSD1-Oxidase. Therefore, when androgen precursors are delivered to the androgen synthetic pathway more NADP+ is generated to enhance a predominant oxidase activity of 11β-HSD1 in Leydig cells.