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Molecular Endocrinology and Oncology Research Center (K.B., C.R., C.B., V.L.-T., A.T.), and Gynecology Unit (P.D., M.D., P.L.), Laval University Medical Research Center, Québec, Canada G1V 4G2
Address all correspondence and requests for reprints to: André Tchernof, Ph.D., Molecular Endocrinology and Oncology Research Center, Laval University Medical Research Center, 2705 Laurier Boulevard (T3-67), Québec, PQ, Canada G1V 4G2. E-mail: andre.tchernof{at}crchul.ulaval.ca.
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Abstract |
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-hydroxysteroid dehydrogenase (3-HSD-3, AKR1C2) in female sc and omental adipose tissue and in preadipocyte primary cultures. 17ß-HSD-5 preferentially synthesizes testosterone from the inactive adrenal precursor androstenedione, whereas 3-HSD-3 inactivates dihydrotestosterone. mRNAs of both enzymes were detected in adipose tissue from the omental and sc compartments. Real-time PCR quantification indicated a 3-fold higher 3-HSD-3 expression compared with 17ß-HSD-5, and the expression of both enzymes tended to be higher in the sc vs. the omental depot. Accordingly, dose-response and time-course experiments performed in preadipocyte primary cultures indicated that 3-HSD activity was higher than 17ß-HSD activity (13-fold maximum velocity difference). We measured 3-HSD activity in omental and sc adipose tissue samples of 32 women for whom body composition and body fat distribution were evaluated by dual-energy x-ray absorptiometry and CT, respectively. We found that androgen inactivation in omental adipose tissue through 3-HSD activity was significantly higher in women with elevated vs. low visceral adipose tissue accumulation (1.7-fold difference; P < 0.05). Moreover, omental adipose tissue 3-HSD activity was positively and significantly associated with CT-measured visceral adipose tissue (r = 0.43; P < 0.02) and omental adipocyte diameter (r = 0.42; P < 0.02). These results indicate that local androgen inactivation is a predominant reaction in female abdominal adipose tissue, with the greatest conversion rates observed in the presence of abdominal visceral obesity. Increased androgen inactivation in omental adipose tissue of abdominally obese women may impact locally on the regulation of adipocyte metabolism. |
Introduction |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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, IL-6, their soluble receptors, leptin, plasminogen activator inhibitor-1, TGF-ß, angiotensinogen, IGF-1, and acylation-stimulating protein (1). In addition, several steroidogenic enzymes or steroid-converting activities have been detected in adipose tissue (reviewed in Ref.2). mRNA and/or activity of aromatase (3, 4), 3ß-hydroxysteroid dehydrogenase (3ß-HSD) (5), type 1 11ß-HSD (6), types 2 and 3 17ß-HSD (3, 4, 7), 7-hydroxylase (5), 17-hydroxylase (8), 5-reductase (9, 10), and UDP-glucuronosyltransferase (UGT)2B15 (11) have all been detected. The physiological relevance of steroid conversions in adipose tissue has been intensely studied recently. For example, a study by Corbould et al. (4) found that the ratio of type 3 17ß-HSD to aromatase expression in intraabdominal adipose tissue was correlated positively with waist circumference and body mass index, suggesting that female adipose tissue is increasingly androgenic with central obesity. The generation of active cortisol through the expression of type 1 11ß-HSD in abdominal adipose tissue, which has been shown to increase exposure of omental adipocytes to cortisol (12), also appears to be of particular interest. Studies by Bujalska et al. (13) and Masuzaki et al. (14) recently led to the suggestion that increased expression of 11ß-HSD-1 in abdominal adipose tissue may represent a common molecular etiology for visceral obesity and the metabolic syndrome. These studies dramatically emphasize the potential importance of steroid conversions in adipose tissue. The impact of other adipose tissue steroidogenic enzymes that would decrease or increase the exposure of omental adipocytes to active steroids in a manner similar to the 17ß-HSD-3/aromatase ratio for androgens or 11ß-HSD-1 for cortisol remains to be established.
Two enzymes from the aldoketoreductase (AKR) family 1C, namely type 5 17ß-HSD (17ß-HSD-5, AKR1C3) and type 3 3-HSD (3-HSD-3, AKR1C2) were recently characterized by Dufort et al. (15, 16). 17ß-HSD-5 is involved in forming testosterone from androstenedione (4-dione), and 3-HSD-3 catalyzes the conversion of the active androgen dihydrotestosterone (DHT) to the inactive metabolite 5-androstan-3,17ß-diol (3-diol). Thus, 17ß-HSD-5 is involved in the formation of active androgens, whereas 3-HSD-3 is an important step in their inactivation. Expression of these enzymes in a wide variety of tissues suggests a potential importance in local synthesis and inactivation of active androgens in peripheral tissues. We hereby report on the expression and activity of 17ß-HSD-5 and 3-HSD-3 in female sc and omental adipose tissue as well as primary preadipocyte cultures.
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Subjects and Methods |
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Women of this study were recruited through the elective surgery schedule of the Gynecology Unit of the Laval University Medical Research Center for studies on adipose tissue metabolism. Thirty-two healthy women aged 40–60 yr undergoing abdominal gynecological surgery were included in the present analysis. All women of the study elected for total (n = 31) or subtotal (n = 1) abdominal hysterectomies, some with salpingo-oophorectomy of one (n = 5) or two (n = 19) ovaries. Reasons for surgery included one or more of the following: menorrhagia (n = 11), myoma (n = 18), pelvic pain (n = 11), benign cyst (n = 1), endometriosis (n = 7), cystitis (n = 3), and hydrosalpinx (n = 3). Medication included thyroid hormones (n = 3), GnRH agonist and/or hormone therapy (n = 9), lipid lowering (n = 1) or antihypertensive therapy (n = 8), nonsteroidal antiinflammatory drugs (n = 4), antidepressants (n = 9), antivertigo (n = 1), antiseizure (n = 1), and asthma (n = 6) medication. Seven women were taking nutritional supplements (vitamins, iron, calcium, or glucosamine). Other types of medication included digoxin, acetaminophen, aspirin, allergy medicine, antibiotics, mesalamine, and antispasmodic medicine. Approbations by the medical ethics committees of Laval University and Laval University Medical Research Center were obtained. All subjects provided written informed consent before their inclusion in the study.
Body fatness and body fat distribution measurements
These tests were performed on the morning of or a few days before the surgery. Measures of total body fat mass, fat percentage, and fat-free mass were determined by dual-energy x-ray absorptiometry, using a Hologic QDR-2000 densitometer and the enhanced array whole-body software V5.73A (Hologic Inc., Bedford, MA). Measurement of abdominal sc and visceral adipose tissue cross-sectional areas was performed by computed tomography (CT) as previously described (17), using a GE Light Speed 1.1 CT scanner (General Electric Medical Systems, Milwaukee, WI) and the Light Speed QX/I 1.0 production software. Subjects were examined in the supine position, with arms stretched above the head. The scan was performed at the L4-L5 vertebrae level using a scout image of the body to establish the precise scanning position. The quantification of visceral adipose tissue area was done by delineating the intraabdominal cavity at the innermost aspect of the abdominal and oblique muscle walls surrounding the cavity and the posterior aspect of the vertebral body with the computer interface of the scanner. Deep sc adipose tissue area was determined by measuring the surface between the sc fascia and the muscle wall across the whole surface of the scan. Adipose tissue was highlighted and computed using an attenuation range of –190 to –30 Hounsfield units. The coefficient of variation between two analyses from the same observer (n = 10) were 0, 2.14, 1.60, and 1.32% for total, visceral, superficial sc, and deep sc adipose tissue areas, respectively. The coefficient of variation between two analyses from two different observers (n = 10) were 0, 2.19, 2.65, and 2.10% for total, visceral, superficial sc, and deep sc adipose tissue areas, respectively.
Plasma lipid-lipoprotein and glucose measurements
Blood samples were obtained after a 12-h fast on the morning of surgery. Fasting plasma glucose concentration was measured by an enzymatic colorimetric method (Sigma Chemical Co., St. Louis, MO). Cholesterol and triglyceride levels were measured in plasma and lipoprotein fractions with a Technicon RA-500 analyzer (Bayer Corp., Etobicoke, Ontario, Canada) using enzymatic methods, as previously described (18). The high-density lipoprotein (HDL) fraction was obtained after precipitation of low-density lipoprotein (LDL) in fasting plasma with heparin and MnCl2. The cholesterol content was measured before and after the precipitation step to determine LDL and HDL cholesterol content.
Adipose tissue sampling
Paired omental and sc adipose tissue samples were collected during the surgical procedure and immediately carried to the laboratory in 0.9% saline preheated at 37 C. A portion of the biopsy was used for adipocyte and preadipocyte isolation, and the remaining tissue was immediately frozen at -80 C for subsequent analyses.
Preadipocyte isolation and primary cultures
Tissue samples were digested with collagenase type I in Krebs-Ringer-Henseleit (KRH) buffer for 45 min at 37 C according to a modified version of the Rodbell method (19). Adipocyte suspensions were filtered through nylon mesh and washed three times with KRH buffer. For cell size measurements, mature adipocyte suspensions were visualized using a contrast microscope attached to a camera and computer interface. Pictures were taken, and the Scion Image software was used to measure the size of 250 adipocytes. Preadipocytes were isolated using a modified method previously described by Hauner et al. (20, 21). Briefly, the residual KRH buffer of the adipocyte isolation was centrifuged and the pellet was washed in DMEM-F12 supplemented with 10% fetal bovine serum, 2.5 µg/ml amphotericin B, 1.00 U/ml penicillin, and 50 g/ml streptomycin. Cells were treated with erythrocyte lysis buffer (154 mM NH4Cl, 10 mM KHCO3, and 0.1 mM EDTA, pH 7.5) and washed again with DMEM-F12. Preadipocytes were placed in 12-well culture plates and cultured at 37 C under a 5% CO2 atmosphere. Medium was changed every 2–3 d. The absence of significant endothelial cell contamination was ascertained by measuring levels of vascular endothelial growth factor R2 in cell lysates and culture medium of two of the cultures used in the present experiments with the human serum vascular endothelial growth factor R2 Quantikine kit (R&D Systems, Minneapolis, MN).
Reverse transcriptase (RT)-PCR
Total RNA was isolated using Trizol (Invitrogen Life Technologies, Carlsbad, CA) following the manufacturer’s recommendations. RT was done with the Ambion Retroscript kit (Ambion Inc., Austin, TX) using random decamer primers for 3-HSD-3 and a specific 3' primer for 17ß-HSD-5. PCR amplification conditions were 95 C for 30 sec, 58 C for 1 min, and 72 C for 2 min for 38 cycles. PCR primers used were 5'-ACC-TCC-AGA-GGT-TCC-GAG-AAG-TAA-AGC-TTT-GGA-GGT-3' and 5'-GGA-ATT-CTT-TAT-TGT-ATT-TCT-GGC-CTA-TGG-AGT-GAG-3' for 17ß-HSD-5 and 5'-CGG-GTT-CCA-CCA-TAT-TGA-TTC-TGC-ACA-TGT-T-3' and 5'-GGA-ATT-CGA-TGG-GCT-TAG-CTG-TAG-CTT-3' for 3-HSD-3. PCR products were separated on 2% agarose gels and stained with ethidium bromide.
Real-time PCR
First-strand cDNA synthesis was accomplished using 5 µg of the isolated RNA in a reaction containing 200 U of Superscript II Rnase H-RT (Invitrogen), 300 ng of oligo-dT18, 500 µM deoxynucleotide triphosphate, 10 mM dithiothreitol, and 34 U of porcine RNase inhibitor (Amersham Pharmacia, Piscataway, NJ) in a final volume of 50 µl. The resulting products were then treated with 1 µg of RNase A for 30 min at 37 C and purified thereafter with Qiaquick PCR purification kits (QIAGEN, Valencia, CA). For quantitative PCR analyses, a Light-Cycler PCR (Roche Diagnostics, Laval, Québec, Canada) was used to measure the expression of 3-HSD-3 and 17ß-HSD-5 using the following sets of primers: 5'-CCG-TCA-AAT-TGG-CAA-TAG-AAG-CC-3', 5'-CAA-CTC-TGG-TCG-ATG-GGA-ATT-GCT-3', 5'-CAA-CCA-GGT-AGA-ATG- TCA-TCC-GTA-T-3', and 5'-ACC-CAT-CGT-TTG-TCT-CGT-TGA-3', respectively for 3-HSD-3 and 17ß-HSD-5 cDNAs. The FastStart DNA Master SYBR green kit (Roche Diagnostics) was used in a final reaction volume of 20 µl containing 3 mM MgCl2, 20 ng of each primer, and 20 ng of the cDNA template. The PCR was carried out according to the following conditions: 95 C for 10 min and 50 cycles of 95 C for 10 sec, 58 C for 5 sec, and 72 C for 8 sec with a temperature transition of 3 C/sec. PCR results were normalized according to glucose-6-phosphate dehydrogenase expression levels using the following primers: 5'-CAG-CGC-CTC-AAC-AGC-CAC-AT-3' and 5'-AAG-GGC-TTC-TCC-ACG-ATG-ATG-C-3'.
Enzymatic activities
3-HSD and 17ß-HSD activities were measured in preadipocyte primary cultures and in whole-tissue homogenates. Preadipocyte cultures were grown in six- or 12-well culture plates. Culture medium was changed for fresh medium containing the corresponding 14C-labeled steroid (PerkinElmer Life Sciences Inc., Boston, MA), 87 nM DHT as substrate for 3-HSD activity and 73 nM androstenedione for 17ß-HSD activity, and cells were incubated for 3, 6, 12, and 24 h for cultures treated with DHT and for 6, 12, 24, and 36 h for cultures treated with androstenedione. For measures in adipose tissue homogenates, tissue samples were homogenized with a Polytron in 50 mM sodium phosphate buffer (pH 7.4), 20% glycerol, 1 mM EDTA, 1 mM reduced nicotinamide adenine dinucleotide phosphate, and 1 mM nicotinamide adenine dinucleotide phosphate. 14C-labeled steroid substrates were added, and reactions were performed at 37 C in a final volume of 1 ml for 24 h. Steroids from culture media and tissue homogenates were extracted twice with 1 vol ether as described previously (16). The organic phases were pooled and evaporated to dryness. The steroids, including reference standards, were solubilized in 50 µl dichloromethane and applied to Silica Gel 60 TLC plates (Merck, Darmstadt, Germany) using 10-µl calibrated micropipettes. The separation was done by migration in toluene-acetone (4:1), the radioactivity was detected using a Storm 860 PhosphorImager (Amersham Pharmacia Biotech Inc.), and quantification was done using the ImageQuant software version 5.1 (Amersham Pharmacia Biotech, Uppsala, Sweden). Proteins in each tissue or cell sample were quantified by the method of Lowry and used in the calculation of activity values.
Statistical analyses
A paired t test procedure was used to compare real-time PCR-measured expression levels of 3-HSD-3 vs. 17ß-HSD-5 or enzyme activities in sc vs. omental adipose tissue. The Welch ANOVA was used to compare means between subjects with low or high visceral fat areas. Spearman rank correlation coefficients were computed to quantify associations between steroid-converting activities and adiposity measures. A level of 
0.05 was considered as statistically significant. Analyses were performed using the JMP statistical software (SAS Institute, Cary, NC).
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Results |
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Female sc and omental adipose tissue expressed both AKR1C mRNAs (17ß-HSD-5 and 3-HSD-3), as confirmed by RT-PCR analysis (Fig. 1A
). Expected transcripts of 1064 and 986 bp were detected in several tissue samples from various patients. In quantitative real-time PCR analysis, 3-HSD-3 expression appeared to be approximately 3-fold higher than that of 17ß-HSD-5 when normalizing band intensity for glucose-6-phosphate dehydrogenase expression (paired-t test difference P < 0.03; Fig. 1B). For both mRNAs, expression levels were higher in sc compared with omental adipose tissue.
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Figure 2 shows a thin layer chromatogram of steroid products obtained when incubating omental or sc preadipocyte primary cultures with radiolabeled DHT or 4-dione for 6 h. The products formed when incubating cells with 4-dione were testosterone, DHT, androstanedione, and estrone (Fig. 2, samples 1 and 3). When incubating cells with DHT, 3-diol and androstanedione were detected, with 3-diol being the major reaction product (Fig. 2, samples 2 and 4). Figure 3 shows the results of time-course experiment and dose-response curves. Time-course experiments showed a relatively linear 3-diol formation over 24-h incubations. Testosterone formation appeared to reach a maximum at 36 h (Fig. 3A). The formation of 3-diol from DHT was at least 4-fold higher than testosterone formation from 4-dione at all times and doses tested. Maximal stimulation of 3-HSD activity was reached at 48 nM substrate. The Michaelis-Menten constant (Km) of the enzyme was 4.34 ± 0.81 nM and the maximum velocity (Vmax) was 117.2 ± 4.0 fmol 3-diol/24 h·µg protein. Dose-response curves for testosterone formation from 4-dione also generated a Km in the nanomolar range (Km = 9.27 ± 8.23 nM), but a 13-fold lower Vmax was reached (Vmax = 8.95 ± 2.41 fmol/24 h·µg protein). Activities of both enzymes tended to be slightly higher in sc vs. omental preadipocytes (data not shown).
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Physical and metabolic characteristics of the women for whom tissue samples were available for homogenate measures are presented in Table 1. Subjects were aged 47.7 ± 5.9 yr (40.1–59.9 yr), and they covered a wide range of body mass index values (19.3–39.4 kg/m2), averaging 27.6 ± 5.0 kg/m2. CT data were missing for one woman. According to clinically recognized criteria of fasting plasma glucose concentrations (22), one subject was diabetic. A total of 16 subjects were characterized by either low HDL cholesterol, high cholesterol, high LDL cholesterol, or high triglyceride levels. However, average values of the whole group fell within the normal range (23).
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-diol formation from DHT was easily detectable in small amounts of tissue. The formation of 3-diol in omental adipose tissue was significantly higher than that of sc fat in paired t test analyses (37.5 ± 24.7 vs. 27.2 ± 20.2 fmol/24 h·µg protein; P < 0.05). The conversion rates of the other steroid product, namely androstanedione, were also significantly higher in the omental fat depot (P < 0.004). We then examined the correlations between steroid-converting activities in tissue homogenates and dual-energy x-ray absorptiometry-measured and CT-measured adiposity variables. There was no significant association between 3-HSD activity measured in sc adipose tissue and any of the adiposity or body fat distribution variables tested. However, 3-HSD activity measured in visceral adipose tissue was significantly and positively associated with visceral adipose tissue area (r = 0.43; P < 0.02; Fig. 4). A trend for a positive association between omental 3-diol formation and deep sc adipose tissue area was found (r = 0.35; P < 0.06). A significant positive association was also observed between 3-diol formation in omental adipose tissue and visceral adipocyte diameter (r = 0.41; P < 0.02; Fig. 4). Successively excluding subjects in each medication category did not modify these results. Finally, we stratified women according to a cutoff point of 100-cm2 visceral adipose tissue area (24, 25). We found that omental 3-diol formation was significantly higher in women with elevated visceral adipose tissue accumulation, whereas no significant difference was observed for sc 3-diol formation in these two subgroups (Fig. 5).
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Discussion |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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-HSD-3), in abdominal adipose tissue of women. The former enzyme is involved in active androgen formation, whereas the latter is an important step in their inactivation. These recently characterized steroidogenic enzymes (15, 16) were shown to have a wide tissue distribution, which suggests a potential importance in local androgen synthesis and inactivation in peripheral tissues (15, 16). We found that expression of both enzymes was detectable in adipose tissue from the sc and omental fat compartments. Quantitative analysis revealed higher expression of 3-HSD-3. Conversions from 4-dione to testosterone and from DHT to 3-diol were observed in cultured preadipocytes, with 3-diol formation being largely predominant. Tissue homogenates from 32 women were examined for 3-HSD activity, and a positive correlation was found between CT-measured visceral adipose tissue area and 3-diol formation in the omentum. Accordingly, women with abdominal-visceral obesity were characterized by significantly higher DHT conversion rates. This study is the first to report the presence of AKR1C enzyme mRNA and activities in human adipose tissue or primary cultured preadipocytes. Results suggest that local androgen inactivation is a predominant reaction in female abdominal adipose tissue, with the greatest conversion rates observed in the presence of abdominal visceral obesity. Increased androgen inactivation in omental adipose tissue of abdominally obese women may impact locally on the regulation of adipocyte metabolism. Most studies on androgens and body fat distribution have focused on plasma levels of testosterone (26). However, the interrelationship between sex steroids and adipose tissue metabolism appears to be much more complex than what can be observed from simple plasma hormone measurements. That inactive adrenal C19 steroids may be taken up and converted into active androgens and/or estrogens in fat tissues is an increasingly well recognized phenomenon (4, 7, 27). In fact, our survey of available literature on this topic indicated that mRNA or activities of at least nine steroidogenic enzymes have been detected in fat tissues or adipose cells to date (2). The ultimate fate of steroid hormones trapped in adipose tissue appears to be dependent on specific enzyme expression patterns in each fat depot, a phenomenon that presumably allows for the local regulation of active steroid levels on a cellular basis with little or no impact on circulating hormone concentrations (2, 28, 29). This newly identified mode of hormone synthesis and inactivation in peripheral tissues has been termed intracrinology, complementary to the well known endocrine and paracrine/autocrine modes of hormone action (29). Although the absolute amount of steroids involved is small, local tissue concentration modulations are thought to be important and to exert significant biological influences locally (27).
An important study by Corbould et al. (4) recently indicated that the ratio of 17ß-HSD-3 to aromatase expression in female omental adipose tissue was positively correlated with obesity and abdominal obesity. These results suggested that testosterone formation from 4-dione, which is the predominant reaction of 17ß-HSD-3, is proportionally more important in abdominally obese women in comparison with androgen-inactivation pathways (i.e. estrogen formation through aromatase expression in that study). We hereby report on the presence of another 17ß-HSD isoform (type 5) that can account for testosterone production from androstenedione. Moreover, our finding of a predominant 3-HSD activity provides information on potentially important pathways for androgen inactivation in these tissues other than aromatase. The fact that the highest DHT inactivation rates were observed in women with visceral obesity is highly consistent with the results of Corbould et al. (4). We suggest that the increased androgen production previously observed in omental fat of abdominally obese women may occur with concomitant increases in the expression of androgen-inactivating enzymes such as 3-HSD-3.
The fact that DHT metabolism was predominant over testosterone formation in the present study is not attributable to previously documented differences in the lability of 3-HSD-3 and 17ß-HSD-5 (15, 16). 17ß-HSD-5 was previously shown to be extremely labile, with an almost complete loss of activity in HEK-293 cell homogenates compared with intact cells (15). In comparison, the reduction in 3-HSD activity, although significant, was much smaller in similar experiments (16). Accordingly, we found that 3-HSD activity was significantly reduced in tissue homogenates compared with cell cultures, which may explain the longer incubation times required to detect 3-diol formation in homogenate preparations (up to 24 h). On the other hand, 17ß-HSD activity was almost completely abolished in tissue homogenates, which prevented us from measuring this activity using reasonably small tissue biopsies. The use of intact cells in our study generated a more reliable comparison of relative differences in conversion activities.
The physiological importance of androgen inactivation in adipose tissue remains to be established. Abdominally obese women are frequently characterized by high circulating testosterone and free testosterone levels (30, 31). An interesting hypothesis to reconcile the increased circulating androgen levels in abdominally obese women on the one hand, and the elevated androgen inactivation measured in omental adipose tissue on the other, would be that high circulating androgen levels stimulate 3-HSD-3 expression and androgen inactivation in adipose tissue. According to this hypothesis, abdominal adipose tissue androgen inactivation could represent a compensatory phenomenon to prevent exposure of this tissue to excess androgens. Results presented in Fig. 3B
support the notion that 3-HSD activity is stimulated in the presence of increasing androgen concentrations. Further characterization of the promoter region of the gene coding for 3-HSD will help in determining whether androgen response elements are present on the regulatory portion of this gene.
On the other hand, a recent report by Joyner et al. (32) recently examined regional differences in DHT metabolism in cultured preadipocytes. Concordant with results of the present study, these investigators found that incubation of cell cultures with DHT led to the production of androgen metabolites such as 3-diol and androsterone. This suggested that androgen metabolism in cultured preadipocytes led to a significant reduction of available DHT, and possibly to decreases in DHT binding to the androgen receptor. This phenomenon could be of some importance when considering the effects of active androgens on adipose cell function and metabolism. Androgens have been shown to enhance the lipolytic capacity of male rat cultured adipose precursor cells by increasing the number of ß-adrenoceptors and the activity of adenylate cyclase (33). An increased fatty acid turnover has also been observed in human males treated with testosterone (34, 35), and these studies demonstrated that testosterone treatment inhibited the activity of adipose tissue lipoprotein lipase, an important regulator of lipid uptake by the adipocyte (34, 35). Taken together, available data suggest that higher androgen inactivation in omental adipose tissue of abdominally obese women may locally lower exposure of adipose cells to active androgens. This phenomenon may influence adipose cell functions and metabolism. Additional studies are needed to confirm this hypothesis.
3-HSD-3 expression has been detected in several tissues such as the prostate, brain, testis, liver, and adrenal glands (16). The pattern of androgen metabolite production observed in the present study is concordant with that of other tissues (36). We previously reported on the presence of another enzyme involved in androgen metabolism, namely UGT2B15, in both omental and sc adipose tissue of males (11). This transcript was also detected in both abdominal sc and omental adipose tissue of women (our unpublished observation). The preferred substrates of UGT2B15 being androsterone and 3-diol, it is plausible to hypothesize that a glucuronidation reaction on locally produced androgen metabolites in adipose tissue could follow androgen inactivation by 3-HSD activity and lead to androgenic signal termination.
In summary, expression of 3-HSD-3 and 17ß-HSD-5 was detected in adipose tissue from the sc and omental fat compartments of women. 3-HSD-3 expression and DHT conversion to 3-diol were predominant over 17ß-HSD-5 expression and testosterone formation from 4-dione in both tissue homogenates and preadipocyte cell cultures. A positive correlation was found between CT-measured visceral adipose tissue area and 3-diol formation in the omentum. We suggest that increased androgen inactivation in omental adipose tissue of abdominally obese women may impact on the local availability of active androgens and, therefore, on the regulation of adipocyte metabolism.
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Acknowledgments |
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Footnotes |
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Abbreviations: AKR, Aldoketoreductase; CT, computed tomography; DHT, dihydrotestosterone; HDL, high-density lipoprotein; HSD, hydroxysteroid dehydrogenase; KRH, Krebs-Ringer-Henseleit; LDL, low-density lipoprotein; UGT, UDP-glucuronosyltransferase.
Received March 27, 2003.
Accepted September 8, 2003.
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