Radioactive Tracing of Testosterone Reveals Minimal Formation of 5α-DHT in SGBS Cells and Human Primary Adipocytes

Abstract

Hyperandrogenism is associated with polycystic ovary syndrome (PCOS), acne, and alopecia. In PCOS, subcutaneous fat has been shown to contribute to hyperandrogenism through increased testosterone (T) production which is accompanied by an increase in the intra-adipose 5α-dihydrotestosterone (5α-DHT):T ratio. However, whether 5α-DHT is produced in isolated adipocytes is uncertain. Here we investigated the ability of subcutaneous human adipocytes to synthesize and inactivate 5α-DHT in a model of subcutaneous white adipocytes, Simpson-Golabi-Behmel syndrome (SGBS) cells, and primary adipocytes. We quantified the transcripts of genes involved in the biosynthesis of 5α-DHT (AKR1C3, SRD5A1, SRD5A2, and HSD17B6) and the inactivation of 5α-DHT (AKR1C1 and AKR1C2). We found that genes that inactivate 5α-DHT were more abundantly transcribed than genes that biosynthesize 5α-DHT. This trend was reflected by radioisotope tracing. We developed a radiochromatographic method involving high-performance liquid chromatography and in-line detection of radioactive analytes with precision and accuracy within the 15% tolerance allowable by the US Food and Drug Administration criteria for analytical assays. The lower limit of detection and quantification for 5α-DHT was 3.4 pg and 15 pg, respectively. The formation of 5α-DHT was barely detectable when starting with either 10 nM T or 3α-androstanediol (3α-diol). Conversely, 5α-DHT was rapidly metabolized to 3α-diol but not 3β-diol. 3α-Diol was the major metabolite despite comparable levels of AKR1C1 and AKR1C2 transcripts. The same result was observed in both cell lines. Our data reveal that adipocytes do not biosynthesize 5α-DHT from testosterone. By contrast, 5α-DHT is rapidly metabolized by AKR1C2 in subcutaneous adipocytes.

Keywords: PCOS; adipocytes; androgen metabolism; hyperandrogenism.

Figure 1.

Potential pathways for 5α-DHT biosynthesis and its metabolism in human adipocytes. The canonical pathway is depicted in purple, the 5α-Adione pathway in pink, the backdoor pathway in teal, and the Δ⁵-Adiol pathway in brown. Gene names are given in italics.

Figure 2.

A, Radiochromatrographic separation of testosterone (T), 5α-DHT, 3α-diol, and 3β-diol on a C8 column. B, Calibration curves of T, 3β-diol, 3α-diol, and 5α-DHT.

Figure 3.

Simpson-Golabi-Behmel syndrome (SGBS) differentiation. A, Oil Red O staining of SGBS cells at preadipocyte stage and at full differentiated state at 4× magnification (1000 μm scale bar). At full differentiation and 20× magnification (100 μm scale bar), SGBS cells show lipid droplets and nuclei. B, Oil Red O staining extraction quantification through differentiation; n = 4. C. GLUT4 messenger RNA (mRNA)/GAPDH mRNA quantification through differentiation; n = 3. D, SRD5A1, SRD5A2, HSD17B6, AKR1C1, AKR1C2, and AKR1C3 mRNA quantification through differentiation, n = 3. All quantification is represented as mean ± SEM.

Figure 4.

Metabolism of A, testosterone (T); B, 5α-DHT; and C, 3α-diol in a 96-hour time course. Protein concentration refers to cell lysates. All quantification is represented as mean ± SEM; n = 4.

Figure 5.

Fully differentiated primary cells. A, SRD5A1, SRD5A2, HSD17B6, AKR1C1, AKR1C2, and AKR1C3 messenger RNA quantification at full differentiation. Metabolism of B, testosterone (T); C, 5α-DHT; and D, 3α-diol in a 96-hour time course. E, Radioactivity is present in aqueous layer of samples, an indicator of androgen elimination through conjugation. Protein concentration refers to cell lysates. All quantification is represented as mean ± SEM; n = 3.