Oxidative activity of 17ß-hydroxysteroid dehydrogenase on testosterone in male abdominal adipose tissues and cellular localization of 17ß-HSD type 2.

Testosterone can be converted into androstenedione (4-dione) by 17ß-hydroxysteroid dehydrogenase (HSD) activity likely performed by 17ß-HSD type 2. Our objective was to evaluate the rate of testosterone conversion to 4-dione as well as expression and localization of 17ß-HSD type 2 in omental (OM) vs. subcutaneous (SC) adipose tissues of men. Formation of 4-dione from testosterone was significantly higher in homogenates (p ≤ 0.001) and explants (p ≤ 0.01) of OM than SC tissue. Microscopy analyses and biochemical assays in cell fractions localized the enzyme in the vasculature/endothelial cells of adipose tissues. Conversion of testosterone to 4-dione was weakly detected in most OM and/or SC preadipocyte cultures. Positive correlations were found between 17ß-HSD type 2 activity in whole tissue and BMI or SC adipocyte diameter. We conclude that conversion of testosterone to 4-dione detected in abdominal adipose tissue is caused by 17ß-HSD type 2 which is localized in the vasculature of the adipose compartment.

Gene expression levels of Casein kinase 1 (CK1) isoforms are correlated to adiponectin levels in adipose tissue of morbid obese patients and site-specific phosphorylation mediated by CK1 influences multimerization of adiponectin.

White adipose tissue has now been recognized as an important endocrine organ secreting bioactive molecules termed adipocytokines. In obesity, anti-inflammatory adipocytokines like adiponectin are decreased while pro-inflammatory factors are over-produced. These changes contribute to the development of insulin resistance and obesity-associated diseases. Since members of the casein kinase 1 (CK1) family are involved in the regulation of various signaling pathways we ask here whether they are able to modulate the functions of adiponectin. We show that CK1δ and ε are expressed in adipose tissue and that the expression of CK1 isoforms correlates with that of adiponectin. Furthermore, adiponectin co-immunoprecipitates with CK1δ and CK1ε and is phosphorylated by CK1δ at serine 174 and threonine 235, thereby influencing the formation of adiponectin oligomeric complexes. Furthermore, inhibition of CK1δ in human adipocytes by IC261 leads to an increase in basal and insulin-stimulated glucose uptake. In summary, our data indicate that site-specific phosphorylation of adiponectin, especially at sites targeted by CK1δ in vitro, provides an additional regulatory mechanism for modulating adiponectin complex formation and function.

The ghrelin O-acyltransferase-ghrelin system reduces TNF-α-induced apoptosis and autophagy in human visceral adipocytes.

AIMS/HYPOTHESIS: Proinflammatory and proapoptotic cytokines such as TNF-α are upregulated in human obesity. We evaluated the association between ghrelin isoforms (acylated and desacyl ghrelin) and TNF-α in obesity and obesity-associated type 2 diabetes, as well as the potential role of ghrelin in the control of apoptosis and autophagy in human adipocytes. METHODS: Plasma concentrations of the ghrelin isoforms and TNF-α were measured in 194 participants. Ghrelin and ghrelin O-acyltransferase (GOAT) levels were analysed by western-blot, immunohistochemistry and real-time PCR in 53 biopsies of human omental adipose tissue. We also determined the effect of acylated and desacyl ghrelin (10 to 1,000 pmol/l) on TNF-α-induced apoptosis and autophagy-related molecules in omental adipocytes. RESULTS: Circulating concentrations of acylated ghrelin and TNF-α were increased, whereas desacyl ghrelin levels were decreased in obesity-associated type 2 diabetes. Ghrelin and GOAT were produced in omental and subcutaneous adipose tissue. Visceral adipose tissue from obese patients with type 2 diabetes showed higher levels of GOAT, increased adipocyte apoptosis and increased expression of the autophagy-related genes ATG5, BECN1 and ATG7. In differentiating human omental adipocytes, incubation with acylated and desacyl ghrelin reduced TNF-α-induced activation of caspase-8 and caspase-3, and cell death. In addition, acylated ghrelin reduced the basal expression of the autophagy-related genes ATG5 and ATG7, while desacyl ghrelin inhibited the TNF-α-induced increase of ATG5, BECN1 and ATG7 expression. CONCLUSIONS/INTERPRETATION: Apoptosis and autophagy are upregulated in human visceral adipose tissue of patients with type 2 diabetes. Acylated and desacyl ghrelin reduce TNF-α-induced apoptosis and autophagy in human visceral adipocytes.

Endothelial lipase is localized to follicular epithelial cells in the thyroid gland and is moderately expressed in adipocytes.

Endothelial lipase (EL), a member of the triglyceride lipase gene family, has been shown to be a key player in HDL metabolism. Northern blots revealed that EL was highly expressed in endothelium, thyroid, lung, placenta, liver, and testis. In liver and adrenal gland, EL protein was localized with vascular endothelial cells but not parenchymal cells. EL was shown to be upregulated in tissues such as atherosclerotic plaque where it was located in macrophages, endothelial cells, and medial smooth muscle cells. The purpose of this study was to investigate the cellular localization of EL in thyroid and other tissues where EL is known to be expressed. Besides its presence in vascular endothelial and smooth muscle cells, EL protein was detected in the epithelial cells that line the follicles within the thyroid gland. EL-specific immunostaining was also found near the cell surface as well as in the cytoplasm of adipocytes. Using immunoblots, EL expression was confirmed in cultured human omental and subcutaneous adipocytes. EL expression, however, was not found in preadipocytes. These findings suggest that EL plays a role in thyroid and adipocyte biology in addition to its well-known role in endothelial function and HDL metabolism.

Aromatase expression in abdominal omental/visceral and subcutaneous fat depots: a comparison of pregnant and obese women.

OBJECTIVE: To investigate total and promoter expression of aromatase in subcutaneous and omental (visceral) fat and compare this expression in pregnant and obese women. DESIGN: Cross-sectional study. SETTING: Academic hospital. PATIENT(S): Six women undergoing elective cesarean section and three women undergoing bariatric surgery. INTERVENTION(S): Subcutaneous and omental fat obtained during surgery. MAIN OUTCOME MEASURE(S): Total aromatase and promoter expression was measured by polymerase chain reaction and protein levels by Western blotting. RESULT(S): Total aromatase expression was significantly higher in omental compared with subcutaneous fat from pregnant women; this pattern was reversed in obese women. Aromatase messenger RNA in omentum was significantly higher in pregnancy than obesity, and this was linked to an up-regulation of promoter II (PII). Promoter 1.4 (P1.4) expression was lower than PII, and there was no difference in P1.4 expression between the two fat depots from pregnant subjects. In obese women both P1.4 and PII were up-regulated in subcutaneous compared with omental depots, with P1.4 expression greater than that of PII. Aromatase protein levels were extremely low in fat depots of pregnant women and undetectable in obese women. CONCLUSION(S): There are differences between total aromatase and promoter expression in subcutaneous and omental fat from pregnant compared with obese women. These differences support the evidence that the fat depots are derived from different cell lineages and that the promoter-derived aromatase translation varies according to physiologic/pathophysiologic status.

Effects of laparoscopic Roux-en-Y gastric bypass on glucose-6 phosphate dehydrogenase activity in obese type 2 diabetics.

BACKGROUND: Glucose-6-phosphate dehydrogenase (G6PD) is the rate-limiting enzyme of the pentose phosphate pathway that provides the majority of NADPH required for lipid biosynthesis. G6PD overexpression has been implicated in insulin resistance, hyperlipidemia, and increased oxidative stress in animals. This study examines G6PD expression in obese diabetic and nondiabetic subjects pre- and post-laparoscopic Roux-en-Y gastric bypass (LRYGB). METHODS: Patients undergoing LRYGB were recruited for the IRB-approved study and placed in either the diabetic (n = 11) or nondiabetic group (n = 16) (diabetic, HbA1c > 6.5%; nondiabetic, HbA1c < 6.0%). Blood samples were collected at baseline and throughout the first 3 postoperative months. Liver, adipose, and omental samples were taken during surgery. Results are expressed as mean ± SEM and were compared statistically using the Mann-Whitney test. RESULTS: The two groups were not significantly different at baseline except for fasting glucose and HbA1c. G6PD activity (nm/min/mg protein) was significantly higher in red blood cells (RBCs) (3.12 ± 1.39 vs. 0.67 ± 0.14) and liver (17.23 ± 2.40 vs. 9.74 ± 2.18) in diabetics compared to nondiabetics. There was good correlation between increased liver G6PD activity and the severity of diabetes as measured by HbA1c (r (2) = 0.525) and fasting glucose (r (2) = 0.542). No significant difference was found in the adipose or omental G6PD expression. Both groups experienced a significant increase in G6PD blood activity shortly following surgery (1 week) followed by a reduction 3 months after surgery. CONCLUSION: These results are the first ever seen in human subjects and demonstrate increased G6PD activity in diabetics compared to nondiabetics. These results suggest a correlation between G6PD activity and the severity of type 2 diabetes. The early increases in G6PD activity after LRYGB were unexpected and longer follow-up is needed to determine the effects of LRYGB on G6PD activity.

Dehydroepiandrosterone (DHEA) treatment in vitro inhibits adipogenesis in human omental but not subcutaneous adipose tissue.

Dehydroepiandrosterone (DHEA), a precursor sex steroid, circulates in sulphated form (DHEAS). Serum DHEAS concentrations are inversely correlated with metabolic syndrome components and in vivo/in vitro studies suggest a role in modulating adipose mass. To investigate further, we assessed the in vitro biological effect of DHEA in white (3T3-L1) and brown (PAZ6) preadipocyte cell lines and human primary preadipocytes. DHEA (from 10(-8)M) caused concentration-dependent proliferation inhibition of 3T3-L1 and PAZ6 preadipocytes. Cell cycle analysis demonstrated unaltered apoptosis but indicated blockade at G1/S or G2/M in 3T3-L1 and PAZ6, respectively. Preadipocyte cell-line adipogenesis was not affected. In human primary subcutaneous and omental preadipocytes, DHEA significantly inhibited proliferation from 10(-8)M. DHEA 10(-7)M had opposing effects on adipogenesis in the two fat depots. Subcutaneous preadipocyte differentiation was unaffected or increased whereas omental preadipocytes showed significantly reduced adipogenesis. We conclude that DHEA exerts fat depot-specific differences which modulate body composition by limiting omental fat production.

The gene expression of the main lipogenic enzymes is downregulated in visceral adipose tissue of obese subjects.

Contradictory findings regarding the gene expression of the main lipogenic enzymes in human adipose tissue depots have been reported. In this cross-sectional study, we aimed to evaluate the mRNA expression of fatty acid synthase (FAS) and acetyl-CoA carboxilase (ACC) in omental and subcutaneous (SC) fat depots from subjects who varied widely in terms of body fat mass. FAS and ACC gene expression were evaluated by real time-PCR in 188 samples of visceral adipose tissue which were obtained during elective surgical procedures in 119 women and 69 men. Decreased sex-adjusted FAS (-59%) and ACC (-49%) mRNA were found in visceral adipose tissue from obese subjects, with and without diabetes mellitus type 2 (DM-2), compared with lean subjects (both P < 0.0001). FAS mRNA was also decreased (-40%) in fat depots from overweight subjects (P < 0.05). Indeed, FAS mRNA was significantly and positively associated with ACC gene expression (r = 0.316, P < 0.0001) and negatively with BMI (r = -0.274), waist circumference (r = -0.437), systolic blood pressure (r = -0.310), serum glucose (r = -0.277), and fasting triglycerides (r = -0.226), among others (all P < 0.0001). Similar associations were observed for ACC gene expression levels. In a representative subgroup of nonobese (n = 4) and obese women (n = 6), relative FAS gene expression levels significantly correlated (r = 0.657, P = 0.034; n = 10) with FAS protein values. FAS protein levels were also inversely correlated with blood glucose (r = -0.640, P = 0.046) and fasting triglycerides (r = -0.832, P = 0.010). In conclusion, the gene expression of the main lipogenic enzymes is downregulated in visceral adipose tissue from obese subjects.

Matrix metalloproteinases with gelatinolytic activity induced by Paracoccidioides brasiliensis infection.

Matrix metalloproteinases (MMPs) modulate extracellular matrix turnover, inflammation and immunity. We studied MMP-9 and MMP-2 in experimental paracoccidioidomycosis. At 15 and 120 days after infection (DAI) with virulent Paracoccidioides brasiliensis, MMP-9 was positive by immunohistochemistry in multinucleated giant cells, in mononuclear cells with macrophage and lymphocyte morphologies and also in fungal cells in the lesions of susceptible and resistant mice. Using gelatin zymography, pro- and active MMP-9 and active MMP-2 were detected in all infected mice, but not in controls. Gelatinolytic activity was not observed in P. brasiliensis extracts. Semiquantitative analysis of gelatinolytic activities revealed weak or absent MMP-2 and strong MMP-9 activity in both mouse strains at 15 DAI, declining at 120 DAI. Avirulent P. brasiliensis-infected mice had residual lesions with MMP-9-positive pseudoxantomatous macrophages, but no gelatinase activity at 120 DAI. Our findings demonstrate the induction of MMPs, particularly MMP-9, in experimental paracoccidioidomycosis, suggesting a possible influence in the pattern of granulomas and in fungal dissemination.

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.

Depot-specific steroidogenic gene transcription in human adipose tissue.

CONTEXT: Sex steroids (androgens and oestrogens) and corticosteroids (glucocorticoids and mineralocorticoids) have a major impact on fat distribution. Several genes involved in steroid synthesis and metabolism, such as 11beta-hydroxysteroid dehydrogenase type 1 and aromatase, are known to be expressed within adipose tissue, thus modulating local steroid levels; however, our knowledge of which genes are expressed and at what level is incomplete. OBJECTIVE: To detect by real-time quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) which of 13 key steroidogenic genes are transcribed within human adipose tissue and to assess whether mRNA levels differ significantly between the subcutaneous abdominal and omental adipose depots. PATIENTS: Eight women undergoing caesarean section [age 29.1 +/- 6.5 years, body mass index (BMI) 28.9 +/- 8.4 kg/m(2)]. RESULTS: Genes transcribed in both depots were StAR (steroidogenic acute regulatory protein), CYP11A1 (side-chain cleavage enzyme), HSD3B2 (3beta-hydroxysteroid dehydrogenase type 2), CYP21B (21-hydroxylase), CYP19 (aromatase), HSD11B1 (11beta-hydroxysteroid dehydrogenase type 1), HSD17B3, HSD17B5, HSD17B7 (17beta-hydroxysteroid dehydrogenase types 3, 5 and 7) and SRD5A2 (5alpha-reductase type 2). All but SRD5A2 varied significantly in abundance between depots. CYP17 (17alpha-hydroxylase), CYP11B1 (11beta-hydroxylase) and CYP11B2 (aldosterone synthase) transcription were not detected. CONCLUSIONS: This study confirms and significantly extends our knowledge of steroidogenic gene expression within adipose tissue, showing that transcript levels are depot specific. We have demonstrated that de novo synthesis from cholesterol of sex steroids, cortisol and aldosterone is not possible because of the absence of key steroidogenic mRNAs. Instead, the pattern of transcription suggests that 11-deoxycorticosterone, a mineralocorticoid, would be the ultimate product of any de novo adipose synthesis.

Omental 11beta-hydroxysteroid dehydrogenase 1 correlates with fat cell size independently of obesity.

OBJECTIVES: In ideopathic obesity, there is evidence that enhanced cortisol regeneration within abdominal subcutaneous adipose tissue may contribute to adiposity and metabolic disease. Whether the cortisol regenerating enzyme, 11beta-hydroxysteroid dehydrogenase type 1 (11betaHSD1), or glucocorticoid receptor (GRalpha) levels are altered in other adipose depots remains uncertain. Our objective was to determine the association between 11betaHSD1 and GRalpha mRNA levels in four distinct adipose depots and measures of obesity and the metabolic syndrome. RESEARCH METHODS AND PROCEDURES: Adipose tissue biopsies were collected from subcutaneous (abdominal, thigh, gluteal) and intra-abdominal (omental) adipose depots from 21 women. 11betaHSD1 and GRalpha mRNA levels were measured by real-time polymerase chain reaction. Body composition, fat distribution, fat cell size, and blood lipid, glucose, and insulin levels were measured. RESULTS: 11betaHSD1 mRNA was highest in abdominal subcutaneous (p < 0.001) and omental (p < 0.001) depots and was positively correlated with BMI and visceral adiposity in all depots. Omental 11betaHSD1 correlated with percent body fat (R = 0.462, p < 0.05), fat cell size (R = 0.72, p < 0.001), and plasma triglycerides (R = 0.46, p < 0.05). Conversely, GRalpha mRNA was highest in omental fat (p < 0.001). GRalpha mRNA was negatively correlated with BMI in the abdominal subcutaneous (R = -0.589, p < 0.05) and omental depots (R = -0.627, p < 0.05). Omental GRalpha mRNA was inversely associated with visceral adiposity (R = -0.507, p < 0.05), fat cell size (R = -0.52, p < 0.01), and triglycerides (R = -0.50, p < 0.05). DISCUSSION: Obesity was associated with elevated 11betaHSD1 mRNA in all adipose compartments. GRalpha mRNA is reduced in the omental depot with obesity. The novel correlation of 11betaHSD1 with omental fat cell size, independent of obesity, suggests that intracellular cortisol regeneration is a strong predictor of hypertrophy in the omentum.

Mitogen-activated protein kinases, inhibitory-kappaB kinase, and insulin signaling in human omental versus subcutaneous adipose tissue in obesity.

MAPKs and inhibitory-kappaB kinase (IKK) were suggested to link various conditions thought to develop in adipose tissue in obesity (oxidative, endoplasmic reticulum stress, inflammation) with insulin resistance. Yet whether in obesity these kinases are affected in a fat-depot-differential manner is unknown. We assessed the expression and phosphorylation of these kinases in paired omental and abdominal-sc fat biopsies from 48 severely obese women (body mass index > 32 kg/m(2)). Protein and mRNAs of p38MAPK, ERK, c-Jun kinase-1, and IKKbeta were increased 1.5-2.5-fold in omental vs. sc fat. The phosphorylated (activated) forms of these kinases were also increased to similar magnitudes as the total expression. However, phosphorylation of insulin receptor substrate-1 on Ser312 (equivalent of murine Ser307) was not increased in omental, compared with sc, fat. Consistently, fat tissue fragments stimulated with insulin demonstrated that tyrosine phosphorylation and signal transduction to Akt/protein kinase B in omental fat was not inferior to that observable in sc fat. Comparison with lean women (body mass index 23.2 +/- 2.9 kg/m(2)) revealed similar ERK2 and IKKbeta expression and phosphorylation in both fat depots. However, as compared with lean controls, obese women exhibited 480 and 270% higher amount of the phosphorylated forms of p38MAPK and c-Jun kinase, respectively, in omental, but not sc, fat, and this expression level correlated with clinical parameters of glycemia and insulin sensitivity. Increased expression of stress-activated kinases and IKK and their phosphorylated forms in omental fat occurs in obesity, potentially contributing to differential roles of omental and sc fat in the pathophysiology of obesity.

Visceral adiposity and endothelial lipase.

CONTEXT: Overexpression of endothelial lipase (EL) has been shown to reduce plasma high-density lipoprotein cholesterol levels in animal models. However, the extent to which EL contributes to modulate the deteriorated high-density lipoprotein profile observed in obesity in humans is less clear. OBJECTIVES: The objectives of this study were to investigate the association between levels of obesity and visceral adiposity in particular and plasma EL concentrations. METHODS: Postheparin plasma EL concentrations were measured by ELISA and visceral adiposity by computed tomography in a sample of 80 sedentary men in good health. EL mRNA levels in abdominal sc and omental adipose tissues obtained during abdominal hysterectomies were measured in another sample of 14 women. RESULTS: Plasma EL levels were positively correlated with body mass index (R = 0.46, P < 0.0001), visceral adipose tissue accumulation (R = 0.44, P < 0.0001), and a proatherogenic lipid profile including increased plasma cholesterol and triglycerides. However, EL mRNA levels were similar in sc and omental AT and were 10,000-fold lower than lipoprotein lipase mRNA levels in those tissues. CONCLUSIONS: Increased visceral adiposity is significantly correlated with elevated plasma EL levels, but this association is unlikely to be causal and may reflect other common metabolic alterations.

Lipoprotein lipase activity/mass ratio is higher in omental than in subcutaneous adipose tissue.

BACKGROUND: Lipoprotein lipase (LPL) is important for lipid deposition in adipose tissue (AT) and responds rapidly to changes in the nutritional state. Animal experiments indicate that short-term regulation of LPL is mainly post-translational. Different processing of LPL in different AT depots may play a role in the distribution of lipids in the body. MATERIALS AND METHODS: Lipoprotein lipase mRNA, mass and activity were measured in pieces of omental adipose tissue (OAT) and subcutaneous adipose tissue (SAT) from 15 subjects undergoing gastrointestinal surgery (four male and 11 female subjects, mean age 54 +/- 5 years, BMI 28 +/- 2 kg m(-2)). RESULTS: Lipoprotein lipase activity was higher in OAT than in SAT (18 +/- 2.1 compared with 12 +/- 1.6 mU g(-1), P < 0.01), whereas LPL mass was lower in OAT than in SAT (100 +/- 9 compared with 137 +/- 16 mU g(-1), P < 0.05). Consequently, the specific LPL activity (ratio of activity over mass) was approximately twofold greater in OAT compared with SAT. There was correlation between LPL mRNA and LPL activity in SAT (P < 0.05) and a similar tendency in OAT (P = 0.08). There were strong correlations (P < 0.01) for mRNA abundance as well as for LPL activity between the two depots. In contrast there was no correlation between the LPL mass and LPL mRNA or activity in any of the depots. CONCLUSIONS: These results indicate that long-term regulation, as reflected in the mRNA abundance, is similar in the two types of adipose tissue. The displayed activity reflects the mRNA abundance and the fraction of newly synthesized LPL molecules which the post-translational mechanism allows to become/remain active. This fraction was on average twofold greater in OAT compared with SAT.

Differences in transport of fatty acids and expression of fatty acid transporting proteins in adipose tissue of obese black and white women.

We have reported that the rate of de novo triglyceride (TG) synthesis by omental, but not subcutaneous, adipose tissue was higher in African-American women (AAW) than in Caucasian women (CAW). The purpose of this study was to explore the potential mechanisms underlying this increase. Toward that end, we determined the activities of key enzymes in the pathway of TG synthesis, the rates of uptake of fatty acids by adipocytes, mRNA and protein levels of the fatty acid-transporting proteins FAT/CD36 and FATP, and mRNA and protein levels of PPARgamma in omental fat of AAW and CAW. The results showed 1) no difference in the activity of phosphofructokinase, glycerol-3-phosphate dehydrogenase, or diacylglycerol acyltransferase; 2) a higher rate of fatty acid uptake by adipocytes of the AAW; 3) an increase in the mRNA and protein levels of CD36 and FATP4 in the fat of the AAW; and 4) an increase in the mRNA and protein levels of PPARgamma, which can stimulate the expression of CD36 and FATP. These results suggest that the increase in the transport of fatty acid, which is mediated by the overexpression of the transport proteins in the omental adipose tissue of the AAW, might contribute to the higher prevalence of obesity in AAW.

Increased monoamine oxidase and semicarbazide-sensitive amine oxidase activities in white adipose tissue of obese dogs fed a high-fat diet.

Adipocytes express two types of amine oxidases: the cell surface semicarbazide-sensitive amine oxidase (SSAO) and the mitochondrial monoamine oxidase (MAO). In human abdominal subcutaneous adipose tissue, it has been reported that SSAO substrates stimulate glucose transport and inhibit lipolysis while MAO activity is decreased in obese patients when compared to age-matched controls. However, no information has been reported on visceral WAT. To further investigate the obesity-induced regulations of MAO and SSAO in white adipose tissue (WAT) from different anatomical locations, enzyme activities and mRNA abundance have been determined on tissue biopsies from control and high-fat fed dogs, an obesity model already described to be associated with arterial hypertension and hyperinsulinemia. MAO activity was increased in the enlarged omental WAT of diet-induced obese dogs, but not in their mesenteric WAT, another intra-abdominal fat depot. Subcutaneous WAT did not exhibit any change in MAO activity, as did the richest MAO-containing tissue: liver. Similarly, SSAO was increased in omental WAT of diet-induced obese dogs, but was not modified in other WAT and in aorta. The increase in SSAO activity observed in omental WAT likely results from an increased expression of the AOC3 gene since mRNA abundance and maximal benzylamine oxidation velocity were increased. Finally, plasma SSAO was decreased in obese dogs. Although the observed regulations differ from those found in subcutaneous WAT of obese patients, this canine model shows a tissue- and site-specific regulation of peripheral MAO and SSAO in obesity.

Expression and activity of 20alpha-hydroxysteroid dehydrogenase (AKR1C1) in abdominal subcutaneous and omental adipose tissue in women.

We examined the expression and activity of 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD) in abdominal adipose tissue in women. This recently characterized enzyme from the aldoketoreductase 1C family is responsible for the conversion of progesterone into 20alpha-hydroxyprogesterone. Abdominal sc (SC) and omental (OM) adipose tissue biopsies were obtained from a sample of 32 women aged 47.7 +/- 5.9 yr (body mass index 27.6 +/- 5.0 kg/m(2)) undergoing abdominal hysterectomies. Body composition and body fat distribution measurements were performed before the surgery by dual-energy x-ray absorptiometry and computed tomography, respectively. The expression of 20alpha-HSD was determined by real-time RT-PCR, and its activity was measured in whole-tissue homogenates. mRNA and activity of the enzyme were detected in both the SC and OM fat depots, the two measures being significantly higher in the SC compartment. Women characterized by a visceral adipose tissue area of 100 cm(2) or greater had an increased 20alpha-HSD conversion rate in their OM adipose tissue, compared with women without visceral obesity (13.99 +/- 2.07 vs. 7.92 +/- 0.83 fmol/microg protein per 24 h, P < 0.05). Accordingly, a positive correlation was found between OM adipose tissue 20alpha-HSD activity and computed tomography-measured visceral adipose tissue area (r = 0.36, P < 0.05). Significant positive correlations were also found between OM 20alpha-HSD activity and OM adipocyte diameter (r = 0.49, P < 0.05) and OM adipose tissue LPL activity (r = 0.36, P = 0.06). In conclusion, 20alpha-HSD activity and mRNA were detected in SC and OM adipose tissue in women, and OM 20alpha-hydroxylation of progesterone was highest in women with visceral obesity. Additional studies are required to establish whether local conversion of progesterone may impact on the metabolism and function of adipocytes located within the abdominal cavity.

Expression and activity of steroid aldoketoreductases 1C in omental adipose tissue are positive correlates of adiposity in women.

We examined expression and activity of steroid aldoketoreductase (AKR) 1C enzymes in adipose tissue in women. AKR1C1 (20alpha-hydroxysteroid dehydrogenase; 20alpha-HSD), AKR1C2 (3alpha-HSD-3), and AKR1C3 (17beta-HSD-5) are involved mainly in conversion of progesterone to 20alpha-hydroxyprogesterone and inactivation of dihydrotestosterone to 5alpha-androstane-3alpha,17beta-diol. Abdominal subcutaneous and omental adipose tissue biopsies were obtained during abdominal hysterectomies in seven women with low visceral adipose tissue (VAT) area and seven age- and total body fat mass-matched women with visceral obesity. Women with elevated VAT areas were characterized by significantly higher omental adipose tissue 20alpha-HSD and 3alpha-HSD-3 mRNA abundance compared with women with low VAT accumulations (1.4- and 1.6-fold differences, respectively; P < 0.05). Omental and subcutaneous adipose tissue 3alpha-HSD activities were significantly higher in women with high vs. low VAT areas (P < 0.05 for both comparisons). Total and visceral adiposities were positively associated with omental 20alpha-HSD mRNA level (r = 0.75, P < 0.003 for fat mass; r = 0.57, P < 0.04 for VAT area) and omental 3alpha-HSD-3 mRNA level (r = 0.68, P < 0.01 for fat mass; r = 0.74, P < 0.003 for VAT area). Enzyme activities in both depots were also positively correlated with adiposity measures. Omental adipose tissue enzyme expression and activity were positively associated with omental adipocyte size and LPL activity. In conclusion, mRNA abundance and activity of AKR1C enzymes in abdominal adipose tissue compartments are positive correlates of adiposity in women. Increased progesterone and/or dihydrotestosterone reduction in abdominal adipose tissue may impact locally on fat cell metabolism.

Ovarian hormone status and abdominal visceral adipose tissue metabolism.

We examined abdominal sc and visceral adipose tissue metabolism in a sample of 19 regularly cycling premenopausal women (age 46.3 +/- 3.7 yr) and 10 women with natural menopause or pharmacological ovarian suppression (age 51.1 +/- 9.2 yr). Subcutaneous and visceral (omental, epiploic) adipose tissue biopsies were obtained during abdominal hysterectomies. Body composition and adipose tissue distribution were measured before the surgery by dual x-ray absorptiometry and computed tomography, respectively. Ovarian hormone-deficient women tended to be older (P = 0.08) and were characterized by increased visceral adipose tissue area (P < 0.05). Subcutaneous adipocyte size, lipoprotein lipase (LPL) activity, and basal lipolysis were not significantly different between groups. On the other hand, omental fat cell size was significantly higher in ovarian hormone-deficient women, compared with premenopausal women (P < 0.05). The omental/sc LPL activity ratio and omental adipocyte basal lipolysis were also significantly higher in ovarian hormone-deficient women (P < 0.05 for both comparisons). Significant positive correlations were found between visceral adipose tissue area and omental LPL activity (r = 0.54, P < 0.003), omental adipocyte basal lipolysis (r = 0.66, P < 0.0001), and omental fat cell size (r = 0.81, P < 0.0001). In multivariate analyses, ovarian status was no longer a significant predictor of adipose cell metabolism variables after visceral adipose tissue area was entered into the model, with the exception of the omental/sc LPL activity ratio, which remained independently associated with ovarian status. In conclusion, although the size of the visceral adipose tissue compartment was an important determinant of adipocyte metabolism in this depot, the increased omental/sc LPL activity ratio in ovarian hormone-deficient women supports the notion of a predominant visceral fat storage in these women.