Androgen inactivation and steroid-converting enzyme expression in abdominal adipose tissue in men

We examined 5 alpha-dihydrotestosterone (5 alpha-DHT) inactivation and the expression of several steroid-converting enzymes with a focus on aldoketoreductases 1C (AKR1C), especially AKR1C2, in abdominal adipose tissue in men. AKR1C2 is mainly involved in the conversion of the potent androgen 5 alpha-DHT to its inactive forms 5 alpha-androstane-3 alpha/beta,17 beta-diol (3 alpha/beta-diol). Subcutaneous (s.c.) and omental (Om) adipose tissue biopsies were obtained from 21 morbidly obese men undergoing biliopancreatic derivation surgery and 11 lean to obese men undergoing general abdominal surgery. AKR1C2 mRNA and 5 alpha-DHT inactivation were detected in both s.c. and Om adipose tissue. After incubation of preadipocytes with 5 alpha-DHT, both 3 alpha-diol and 3 beta-diol were produced through 3 alpha/beta-ketosteroid reductase (3 alpha/beta-HSD) activity. In preadipocyte cultures, 3 alpha-reductase activity was significantly predominant over 3 beta-reductase activity in cells from both the s.c. and Om compartments. Expression levels of AKR1C1, AKR1C3 and of the androgen receptor were significantly higher in s.c. versus Om adipose tissue while mRNA levels of 17 beta-HSD-2 (hydroxysteroid dehydrogenase type 2) and 3 (alpha ->beta)-hydroxysteroid epimerase were significantly higher in Om fat. 3 alpha/beta-HSD activity was mainly detected in the cytosolic fraction, suggesting that AKR1C may be responsible for this reaction. Experiments with isoform-specific AKR1C inhibitors in preadipocytes showed that AKR1C2 inhibition significantly decreased 3 alpha-HSD and 3 beta-HSD activities (3 alpha-HSD: 30 +/- 24% of control for s.c. and 32 +/- 9% of control for Om, 3 beta-HSD: 44 +/- 12% of control for s.c.). When cells were incubated with both AKR1C2 and AKR1C3 inhibitors, no significant additional inhibition was observed. 5 alpha-DHT inactivation was significantly higher in mature adipocytes compared with preadipocyte cultures in 's.c. adipose tissue, as expressed per microgram total protein (755 +/- 830 versus 245 +/- 151 fmol 3 alpha/beta-diol per mu g protein over 24h, P < 0.05 n=10 cultures). 5 alpha-DHT inactivation measured in tissue homogenates was significantly higher in the s.c. depot compared with Om fat (117 39 versus 79 +/- 38 fmol 3 alpha/beta-diol per mu g prot over 24 It, P < 0.0001). On the other hand, Om 3 alpha/beta-HSD activity was significantly higher in obese men (body mass index (BMI)>= 30 kg/m(2)) compared with lean and over-weight men (84 +/- 37 versus 52 +/- 30 fmol 3 alpha/beta-diol per mu g protein over 24 h, P < 0.03). No difference was found in s.c. 3 alpha/beta-HSD activity between these groups. Positive correlations were found between s.c. 5 alpha-DHT inactivation rate and circulating levels of the androgen metabolites androsterone-glucuronide (r=0-41, P < 0.02) and 3 alpha-diol-glucuronide (r=0.38, P < 0.03) and with the adrenal precursor androstenedione (r=0.42, P < 0.02). In conclusion, androgen inactivation was detected in abdominal adipose tissue in men, with higher 3 alpha/beta-HSD activity in the s.c. versus Om depot. Higher Om 5 alpha-DHT inactivation rates were found in obese compared with lean men. Further studies are required to elucidate whether local androgen inactivation in abdominal adipose tissue is involved in the modulation of adipocyte metabolism and regional fat distribution in men.