Mélanie Nadeau

Effects of androgens on adipocyte differentiation and adipose tissue explant metabolism in men and women.

Objective  To examine the effects of aromatizable or nonaromatizable androgens on abdominal subcutaneous (SC) and omental (OM) adipose tissue lipid metabolism and adipogenesis in men and women.

Pathways of adipose tissue androgen metabolism in women: depot differences and modulation by adipogenesis

The objective was to examine pathways of androgen metabolism in abdominal adipose tissue in women. Abdominal subcutaneous (SC) and omental (OM) adipose tissue samples were surgically obtained in women. Total RNA was isolated from whole adipose tissue samples and from primary preadipocyte cultures before and after induction of differentiation. Expression levels of several steroid-converting enzyme transcripts were examined by real-time RT-PCR. Androgen conversion rates were also measured. We found higher expression levels in SC compared with OM adipose tissue for type 1 3beta-hydroxysteroid dehydrogenase (3beta-HSD-1; P < 0.05), for aldo-keto reductase 1C3 (AKR1C3; P < 0.0001), for AKR1C2 (P < 0.0001), and for the androgen receptor (P < 0.0001). 17beta-HSD-2 mRNA levels were lower in SC adipose tissue (P < 0.05). Induction of adipocyte differentiation led to significantly increased expression levels in SC cultures for AKR1C3 (4.7-fold, P < 0.01), 11-cis-retinol dehydrogenase (6.9-fold, P < 0.02), AKR1C2 (5.6-fold, P < 0.004), P-450 aromatase (5.7-fold, P < 0.02), steroid sulfatase (3.1-fold, P < 0.02), estrogen receptor-beta (11.8-fold, P < 0.01), and the androgen receptor (4.0-fold, P < 0.0005). Generally similar but nonsignificant trends were obtained in OM cultures. DHT inactivation rates increased with differentiation, this effect being mediated by dexamethasone alone, through a glucocorticoid receptor-dependent mechanism. In conclusion, higher mRNA levels of enzymes synthesizing and inactivating androgens are found in differentiated adipocytes, consistent with higher androgen-processing rates in these cells. Glucocorticoid-induced androgen inactivation may locally modulate the exposure of adipose cells to active androgens.

Alterations of plasma metabolite profiles related to adipose tissue distribution and cardiometabolic risk

Metabolomic profiling of obese individuals revealed altered concentrations of many metabolites, especially branched-chain amino acids (BCAA), possibly linked to altered adipose tissue BCAA catabolism. We tested the hypothesis that some features of this metabolite signature relate closely to visceral obesity and concomitant alterations in cardiometabolic risk factors. We also postulated that alterations in BCAA-catabolizing enzymes are predominant in visceral adipose tissue. Fifty-nine women (BMI 20-41 kg/m(2)) undergoing gynecologic surgery were recruited and characterized for overall and regional adiposity, blood metabolite levels using targeted metabolomics, and cardiometabolic risk factors. Adipose samples (visceral and subcutaneous) were obtained and used for gene expression and Western blot analyses. Obese women had significantly higher circulating BCAA and kynurenine/tryptophan (Kyn/Trp) ratio than lean or overweight women (P < 0.01). Principal component analysis confirmed that factors related to AA and the Kyn/Trp ratio were positively associated with BMI, fat mass, visceral or subcutaneous adipose tissue area, and subcutaneous adipocyte size (P ≤ 0.05). AA-related factor was positively associated with HOMA-IR (P ≤ 0.01). Factors reflecting glycerophospholipids and sphingolipids levels were mostly associated with altered blood lipid concentrations (P ≤ 0.05). Glutamate level was the strongest independent predictor of visceral adipose tissue area (r = 0.46, P < 0.001). Obese women had lower expression and protein levels of BCAA-catabolizing enzymes in visceral adipose tissue than overweight or lean women (P ≤ 0.05). We conclude that among metabolites altered in obesity plasma concentrations of BCAA and the Kyn/Trp ratio are closely related to increased adiposity. Alterations in expression and protein levels of BCAA-catabolizing enzymes are predominant in visceral adipose tissue.

Progesterone metabolism in adipose cells.

The aim of the present study was to investigate pathways of progesterone metabolism in human adipose cells. Adipose tissue samples from the omental (OM) and subcutaneous (SC) fat compartments were surgically obtained in women. In isolated mature adipocytes, progesterone was converted to 20alpha-hydroxyprogesterone as the main metabolite, most likely through the activity of aldo-keto reductases 1C1, 2 and 3 (20alpha-HSD, 3alpha-HSD type 3 and 17beta-HSD type 5, respectively). In cultured preadipocytes, progesterone was converted to several metabolites identified using bidimensional thin layer chromatography, with or without the dual inhibitor of 5alpha-reductase type 1 and 2 (17beta-N,N-diethylcarbamoyl-4-methyl-4-aza-5alpha-androstan-3-one (4-MA)). Major metabolites identified in OM and SC preadipocytes which were incubated for 24h with (14)C-labelled progesterone were 20alpha-hydroxyprogesterone, 5alpha-pregnane-3alpha/beta-ol-20-one, 5alpha- and 5beta-pregnanedione, 5alpha- and 5beta-pregnane-20alpha-ol-3-one, 5alpha-pregnane-3alpha/beta-ol-20-one and 5beta-pregnane-3alpha/beta-20alpha-diol. Induction of preadipocyte differentiation increased expression levels of AKR1C1 and modified the pattern of progesterone metabolism substantially, leaving 20alpha-hydroxyprogesterone as the main metabolite generated. On the other hand, progesterone itself showed no consistent effect on adipocyte differentiation. In conclusion, preadipocytes and lipid-storing, mature adipocytes efficiently generate progesterone metabolites in women, which is consistent with rather modest effects progesterone on abdominal fat cell differentiation.

Glucocorticoid-induced androgen inactivation by aldo-keto reductase 1C2 promotes adipogenesis in human preadipocytes

Adipogenesis and lipid storage in human adipose tissue are inhibited by androgens such as DHT. Inactivation of DHT to 3α-diol is stimulated by glucocorticoids in human preadipocytes. We sought to characterize glucocorticoid-induced androgen inactivation in human preadipocytes and to establish its role in the antiadipogenic action of DHT. Subcutaneous and omental primary preadipocyte cultures were established from fat samples obtained in subjects undergoing abdominal surgeries. Inactivation of DHT to 3α/β-diol for 24 h was measured in dexamethasone- or vehicle-treated cells. Specific downregulation of aldo-keto reductase 1C (AKR1C) enzymes in human preadipocytes was achieved using RNA interference. In whole adipose tissue sample, cortisol production was positively correlated with androgen inactivation in both subcutaneous and omental adipose tissue (P < 0.05). Maximal dexamethasone (1 μM) stimulation of DHT inactivation was higher in omental compared with subcutaneous fat from men as well as subcutaneous and omental fat from women (P < 0.05). A significant positive correlation was observed between BMI and maximal dexamethasone-induced DHT inactivation rates in subcutaneous and omental adipose tissue of men and women (r = 0.24, n = 26, P < 0.01). siRNA-induced downregulation of AKR1C2, but not AKR1C1 or AKR1C3, significantly reduced basal and glucocorticoid-induced androgen inactivation rates (P < 0.05). The inhibitory action of DHT on preadipocyte differentiation was potentiated following AKR1C2 but not AKR1C1 or AKR1C3 downregulation. Specifically, lipid accumulation, G3PDH activity, and FABP4 mRNA expression in differentiated preadipocytes exposed to DHT were reduced further upon AKR1C2 siRNA transfection. We conclude that glucocorticoid-induced androgen inactivation is mediated by AKR1C2 and is particularly effective in omental preadipocytes of obese men. The interplay between glucocorticoids and AKR1C2-dependent androgen inactivation may locally modulate adipogenesis and lipid accumulation in a depot-specific manner.

Updated survey of the steroid-converting enzymes in human adipose tissues

Over the past decade, adipose tissues have been increasingly known for their endocrine properties, that is, their ability to secrete a number of adipocytokines that may exert local and/or systemic effects. In addition, adipose tissues have long been recognized as significant sites for steroid hormone transformation and action. We hereby provide an updated survey of the many steroid-converting enzymes that may be detected in human adipose tissues, their activities and potential roles. In addition to the now well-established role of aromatase and 11β-hydroxysteroid dehydrogenase (HSD) type 1, many enzymes have been reported in adipocyte cell lines, isolated mature cells and/or preadipocytes. These include 11β-HSD type 2, 17β-HSDs, 3β-HSD, 5α-reductases, sulfatases and glucuronosyltransferases. Some of these enzymes are postulated to bear relevance for adipose tissue physiology and perhaps for the pathophysiology of obesity. This elaborate set of steroid-converting enzymes in the cell types of adipose tissue deserves further scientific attention. Our work on 20α-HSD (AKR1C1), 3α-HSD type 3 (AKR1C2) and 17β-HSD type 5 (AKR1C3) allowed us to clarify the relevance of these enzymes for some aspects of adipose tissue function. For example, down-regulation of AKR1C2 expression in preadipocytes seems to potentiate the inhibitory action of dihydrotestosterone on adipogenesis in this model. Many additional studies are warranted to assess the impact of intra-adipose steroid hormone conversions on adipose tissue functions and chronic conditions such as obesity, diabetes and cancer.

Abdominal Adipocyte Populations in Women with Visceral Obesity

BACKGROUND Visceral obesity is independently related to numerous cardiometabolic alterations, with adipose tissue dysfunction as a central feature. OBJECTIVE To examine whether omental (OM) and subcutaneous (SC) adipocyte size populations in women relate to visceral obesity, cardiometabolic risk factors and adipocyte lipolysis independent of total adiposity. DESIGN AND METHODS OM and SC fat samples were obtained during gynecological surgery in 60 women (mean age, 46.1±5.9 years; mean BMI, 27.1±4.5 kg/m² (range, 20.3-41.  kg/m²)). Fresh samples were treated with osmium tetroxide and were analyzed with a Multisizer Coulter. Cell size distributions were computed for each sample with exponential and Gaussian function fits. RESULTS Computed tomography-measured visceral fat accumulation was the best predictor of larger cell populations as well as the percentage of small cells in both OM and SC fat (P<0.0001 for all). Accordingly, women with visceral obesity had larger cells in the main population and higher proportion of small adipocytes independent of total adiposity (P≤0.05). Using linear regression analysis, we found that women characterized by larger-than-predicted adipocytes in either OM or SC adipose tissue presented higher visceral adipose tissue area, increased percentage of small cells and homeostasis model assessment insulin resistance index as well as higher OM adipocyte isoproterenol-, forskolin- and dbcAMP-stimulated lipolysis compared to women with smaller-than-predicted adipocytes, independent of total adiposity (P≤0.05). CONCLUSION Excess visceral adipose tissue accumulation is a strong marker of both adipocyte hypertrophy and increased number of small cells in either fat compartment, which relates to higher insulin resistance index and lipolytic response, independent of total adiposity.

Pregnancy after Bariatric Surgery: Balancing Risks and Benefits

The majority of bariatric surgeries in Canada are performed in women of reproductive age. Clinicians encounter more and more often pregnancies that occur after bariatric surgeries. The appropriate management and education of women who want to conceive after bariatric surgery is still unclear due to the lack of consistent data about maternal and neonatal outcomes following bariatric surgery. Maternal obesity during pregnancy confers a higher risk for gestational diabetes, hypertensive disorders, congenital malformations, prematurity and perinatal mortality. Generally, pregnancies in severely obese women who have undergone bariatric surgery are safe, and the women are at significantly lower risk for gestational diabetes, hypertensive disorders and large-for-gestational-age neonates, but the surgery confers a higher risk for small-for-gestational-age infants and prematurity. This review aims to provide evidence from recent publications about the risks and benefits of bariatric surgeries in the context of future pregnancies.

Adipose tissue diacylglycerol acyltransferase activity and blood lipoprotein triglyceride enrichment in women with abdominal obesity.

UNLABELLED Previous studies have suggested altered triglyceride (TG) storage in patients with abdominal obesity and blood lipid disorders. OBJECTIVE We hypothesized that women with abdominal obesity and a dysmetabolic profile have low DGAT activity in their abdominal fat compartments. METHODS Paired omental (OM) and subcutaneous (SC) adipose tissue samples were obtained surgically from 39 women undergoing abdominal hysterectomies. Body composition and fat distribution were measured by dual energy x-ray absorptiometry and computed tomography. DGAT activity was measured by acylation of sn-l,2-diacylglycerol with [(14)C] oleoyl-CoA in microsomal fractions isolated from whole adipose tissue homogenates. DGAT activity was calculated on the basis of picomoles (pmol) TG synthesized in the assay per min per mg lipid, per μg protein or per 1000 cells. RESULTS No depot differences were found when DGAT activity was reported per μg microsomal protein or per 1000 cells. DGAT activity in either depot was not associated with adipocyte diameters and blood lipid profile variables. DGAT activity per mg lipid was higher in OM than in abdominal SC adipose tissue (0.43 ± 0.20 vs. 0.34 ± 0.18 pmol/min/mg lipid, p < 0.05). OM DGAT activity was negatively correlated with OM adipocyte diameter and visceral adipose tissue area (r = -0.43, p < 0.01 and r = -0.38, p < 0.05 respectively). Plasma total, LDL and HDL TG levels were negatively associated with OM DGAT activity independent of total body fat mass (r = -0.39, p < 0.05, r = -0.46, p < 0.001 and r = -0.40, p < 0.05 respectively). CONCLUSION A defect in adipose tissue DGAT activity is predictive of adiposity and blood lipoprotein TG enrichment only when considering activity per tissue lipid mass.

Adipose tissue lamin A/C messenger RNA expression in women

Mutations in the lamin A/C gene (LMNA) cause lipodystrophy. However, little data are available on lamin A/C expression in various fat depots in women. We recruited 34 women scheduled for gynecologic surgery. Blood samples were collected on the morning of surgery to obtain a detailed lipid profile. Radiological examinations were performed to measure total body fat mass and abdominal fat accumulation. Fat samples were taken from the subcutaneous (SC) fat depot and from the greater omentum (OM) during the surgical procedure. Whole adipose tissue samples were used for total messenger RNA (mRNA) extraction and real-time polymerase chain reaction quantification of the LMNA transcript. No association was observed between lamin A/C mRNA expression, either in SC or OM fat tissue, and adiposity measures. Women with low SC lamin A/C expression, identified on the basis of the median value of SC lamin A/C mRNA expression, had a significantly altered lipid profile including lower levels of high-density lipoprotein (HDL) cholesterol and HDL(2) cholesterol and reduced HDL(2) cholesterol to HDL(3) cholesterol ratio (P < .05 for all). These women were also characterized by higher cholesterol to HDL cholesterol, low-density lipoprotein-triglycerides, very low-density lipoprotein-apolipoprotein B, and low-density lipoprotein cholesterol to HDL cholesterol (P < .05 for all). Low SC lamin A/C mRNA expression levels were also associated with significantly increased lipolysis in isolated fat cells from this fat depot. Specifically, the response to lipolytic agent isoproterenol was significantly increased at doses ranging from 10(-5) to 10(-10) mol/L (P < .05). A similar trend was observed in OM fat cells but did not reach significance. In conclusion, low lamin A/C expression in SC adipose tissue is associated with significant alterations in the lipid profile and increased fat cell lipolysis, independent of the level of total or abdominal adiposity.