Tumor necrosis factor-alpha inhibits leptin production in subcutaneous and omental adipocytes from morbidly obese humans

This study was undertaken to examine the regulation of leptin production from human adipocytes by tumor necrosis factor-alpha (TNFalpha). Adipocytes were isolated from adipose tissue obtained during bariatric surgical procedures (17 women and 3 men; body mass index, 52.5 +/- 2.4 kg/m2; age, 40 +/- 3 yr) and cultured in suspension. Leptin release from sc adipocytes was inhibited 17.7 +/- 5.2% (P < 0.01), 21.6 +/- 4.3% (P < 0.005), and 37.1 +/- 7.2% (P < 0.05) by 1, 10, and 100 ng/mL TNFalpha, respectively, after 48 h in culture. At 100 ng/mL, significant inhibition of leptin release (25.8 +/- 9.7%; P < 0.05) was detected by 24 h. TNFalpha (10 ng/mL) had no effect on dexamethasone (0.1 micromol/L)-stimulated leptin production in sc adipocytes. In omental adipocytes TNFalpha inhibited leptin release 21.0 +/- 9.6% and 40.8 +/- 6.3% at 10 and 100 ng/mL by 48 h (P < 0.05). Significant inhibition ofleptin release from omental adipocytes was observed at 24 h with 100 ng/mL TNFalpha (P < 0.05). Anti-TNFalpha antibody completely blocked TNFalpha inhibition of leptin release. The ob messenger ribonucleic acid was significantly reduced (23.6 +/- 5.9%) after 48 h of TNFalpha (100 ng/mL) treatment (P < 0.025). TNFalpha had no effect on glucose uptake or lactate production in sc and omental adipocytes. The data suggest that the direct paracrine effect of adipose-derived TNFalpha is inhibition of leptin production.     

Regulation of leptin release by troglitazone in human adipose tissue

In pieces of human subcutaneous adipose tissue incubated in primary culture for 48 hours, the release of leptin was stimulated by 50% in the presence of 3.3 micromol/L troglitazone. Insulin (0.1 nmol/L) and dexamethasone (200 nmol/L) stimulated leptin release by 30% and 300%, respectively. Troglitazone in combination with either insulin or dexamethasone had no effect on leptin release. Instead, troglitazone inhibited leptin release in the presence of both dexamethasone and insulin. The stimulatory effect of troglitazone on leptin release was also mimicked by 1 micromol/L 15-deoxy-delta(12-14)prostaglandin J2 (dPGJ2). However, if the concentration of dPGJ2 was increased to 10 micromol/L in the presence of dexamethasone, there was a decrease in leptin release, as well as of lactate formation and lipolysis. These data indicate that both stimulatory and inhibitory effects of troglitazone and dPGJ2 can be seen on leptin release by human adipose tissue.     

Intrinsic site-specific differences in the expression of leptin in human adipocytes and its autocrine effects on glucose uptake.

Leptin, the ob gene product of adipocytes, regulates body weight by actions on the satiety center in the hypothalamus, but it may also have peripheral effects on the metabolic actions of insulin. In human mature adipocytes isolated from omental (OM) and s.c. tissue, we found that leptin (10 and 100 ng/mL) significantly reduced insulin-mediated glucose uptake by 40% (P<0.05). The effects were rapid and sustained. A U-shaped dose-response curve was obtained, and high leptin concentrations (>100 ng/mL) were without effect. Leptin did not affect basal glucose uptake in adipocytes and had no effect on insulin-stimulated glucose uptake in human preadipocytes. Because leptin may thus have autocrine effects, we examined leptin production from OM and s.c. adipocytes. Western blotting of leptin from 96-h conditioned medium showed greater leptin secretion from s.c. than OM adipocytes, with a ratio of 3.2 (SE +/-0.3, P<0.01). Long-term ceiling cultures were used to examine intrinsic differences in leptin expression under closely controlled conditions. Confocal immunofluorescence microscopy of 12- to 16-day-old ceiling-cultured adipocytes showed that sc adipocytes contained 3.4-fold more leptin (SE +/-0.5, P<0.01) than OM adipocytes, indicating an intrinsic site-specific difference in leptin production. The autocrine effects of leptin to inhibit insulin-stimulated glucose uptake and subsequent lipogenesis in adipose tissue may, therefore, be less in OM adipocytes and may play a role in determining visceral obesity.     

Hexosamines regulate leptin production in human subcutaneous adipocytes

The hexosamine biosynthetic pathway has recently been proposed as a mechanism through which cells "sense" nutrient flux to regulate leptin release. This study was undertaken to examine the regulation of leptin production by hexosamines in human adipocytes. Adipose tissue UDP-N-acetylglucosamine, an end product of hexosamine biosynthesis, was elevated 3.2-fold, and ob messenger ribonucleic acid was elevated 2-fold in the sc adipose tissue of 17 obese [body mass index (BMI), 41.3+/-12.0 kg/m2; age, 31+/-5 yr] subjects compared to 14 lean (BMI, 23.4+/-1.6 kg/m2; age, 33+/-11 yr) subjects. Serum leptin was increased 2.7-fold in the obese subjects. A significant positive relationship was found between adipose tissue UDP-N-acetylglucosamine and BMI (Spearman correlation = 0.576; P = 0.0007) and between UDP-N-acetylglucosamine and serum leptin (Spearman correlation = 0.4650; P = 0.0145). Treatment of isolated sc adipocytes with 1 mmol/L glucosamine, an intermediate product in UDP-N-acetylglucosamine biosynthesis, increased leptin release 21.4+/-17.6% (mean +/- SD) over control (P = 0.0365) and 74.5+/-82.8% over control (P = 0.0271) in adipocytes from lean (BMI, 23.2+/-1.6 kg/m2; n = 6) and obese (BMI, 55.4+/-13.0 kg/m2,; n = 9) subjects, respectively, by 48 h of culture. Inhibition of UDP-N-acetylglucosamine biosynthesis with 6-diazo-5-oxo-norleucine reduced glucose-stimulated leptin release from cultured adipocytes 21.8+/-32.4% (P = 0.0395; n = 12) and ob gene expression 19.9+/-18.9% (P = 0.0208; n = 8) by 48 h of treatment. These findings suggest that hexosamine biosynthesis regulates leptin production in human adipose tissue.     

Serum leptin level as an indicator to predict the clinical efficacy of troglitazone in patients with type 2 diabetes mellitus

Troglitazone is effective in approximately 50% in patients with type 2 diabetes (NIDDM). In this study, we investigated the relations between serum leptin levels and clinical efficacy of troglitazone. Forty-five type 2 diabetic patients (23 men and 22 women) from our outpatient clinic were treated with troglitazone 400 mg daily for 12 weeks. Fasting plasma glucose (FPG), HbA1c, body weight, serum insulin and leptin concentrations were measured before and after troglitazone treatment. After 12 weeks of troglitazone treatment, FPG (before versus after, 179+/-33 vs. 138+/-26 mg/dl, mean+/-SD), HbA1c (7.8+/-1.3 vs. 6.9+/-1.0%), IRI (8.3+/-4.3 vs. 6.3+/-3.4 microU/ml) and HOMA-R index (homeostasis model assessment of insulin resistance) (3.8+/-2.4 vs. 2.2+/-1.3) decreased significantly, while body mass index (BMI) slightly increased (26.3+/-3.5 vs. 26.6+/- 3.6 kg/m(2)), and serum leptin remained unchanged (8.5+/-7.2 vs. 9.1+/-8.7 ng/ml). Reduction in FPG (DeltaFPG) after troglitazone treatment were correlated with reduction in HOMA-R (DeltaHOMA-R) (r=0.721, P<0.0001). DeltaFPG was correlated with serum leptin (r=0.441, P<0.01), HOMA-R (r=0.460, P<0.01) and FPG (r=-0.781, P<0.0001) at baseline, but not with BMI and serum IRI at baseline. Furthermore, serum leptin at baseline was significantly correlated with DeltaHOMA-R (r=0.634, P<0.01). Leptin concentration before treatment therefore, can be used as an predictor for clinical efficacy of troglitazone in patients with type 2 diabetes.     

The effect of troglitazone on plasma homocysteine,hepatic and red blood cell S-adenosyl methionine,and S-adenosyl homocysteine and enzymes in homocysteine metabolism in Zucker rats

We studied the effect of troglitazone on the plasma concentrations of homocysteine (tHcy), the erythrocyte and hepatic concentrations of S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH), and the hepatic activities of cystathionine-beta-synthase (C beta S) and methylenetetrahydrofolate reductase (MTHFR) in lean and fatty Zucker rats (a model of insulin resistance). Four groups of female Zucker rats were studied. Troglitazone (200 mg/kg) was administered by gavage daily for 3 weeks to lean and fatty Zucker rats. The other 2 groups served as controls. The blood parameters were determined at days 0, 10, and 21. The hepatic SAM and SAH concentrations and MTHFR and C beta S were measured in the 3-week liver samples. Plasma homocysteine fell significantly in all troglitazone-treated animals from a mean +/- SD of 7.6 +/- 1.5 micromol/L to 4.5 +/- 1.1 micromol/L (P <.02) but not in control animals (5.7 +/-1.8 micromol/L to 5.9 +/- 1.8 micromol/L). The decreases induced by troglitazone in homocysteine were seen in both the lean and the fatty Zucker rats. This was accompanied by significant rises in the hepatic concentrations of SAH and SAM + SAH. In addition, a significant decline in the hepatic SAM/SAH ratio was observed. The mean +/- SD hepatic C beta S (expressed as nmol of cystathionine formed at 37 degrees C) in the troglitazone-treated rats was 1,226 +/- 47 nmol/h/mg protein, which was significantly higher than that in the control group (964 +/- 64 nmol/h/mg protein; P =.03). We conclude that troglitazone lowers plasma homocysteine in insulin-resistant animals. The homocysteine-lowering effects of troglitazone may be mediated in part by a shift in the concentrations of tHcy and its related metabolites from the blood to the liver as well as by an upregulation of hepatic C beta S activity. These data support the hypothesis that insulin may regulate homocysteine metabolism through regulation of hepatic C beta S activity, although activity of other hepatic enzymes not studied here may also contribute to these observations.     

Interleukin-6 regulates human adipose tissue lipid metabolism and leptin production in vitro

Adipose tissue IL-6 expression is increased in obesity and is a strong predictor of abnormalities in adipocyte and systemic metabolism. We used adipose tissue organ culture to test the direct effects of IL-6 on leptin expression, lipolysis, and lipoprotein lipase activity. To assess possible interactions with the hormonal milieu, IL-6 effects were tested in the presence or absence of insulin and/or glucocorticoid [dexamethasone (dex)]. Because omental (Om) and abdominal sc depots differ in IL-6 expression, their responses to exogenous IL-6 were compared. Although IL-6 had no significant effects under basal conditions, culture with the combination of IL-6 and dex, compared with dex alone, for 2 d increased leptin in both depots [+95 +/- 30% (sc) and +67 +/- 19% (Om), P < 0.01]; IL-6 did not affect leptin production when added in the presence of insulin. Culture with IL-6 in the absence of hormones moderately increased lipolysis during culture in both sc and Om [+79 +/- 23% (sc) and +26 +/- 9% (Om), each P < 0.01]. IL-6 markedly reduced the high levels of lipoprotein lipase activity in tissue cultured with insulin plus dex. We conclude that high local concentrations of IL-6 can modulate leptin production and lipid metabolism in human adipose tissue.     

Regulation of leptin release by insulin,glucocorticoids, G(i)-coupled receptor agonists,and pertussis toxin in adipocytes and adipose tissue explants from obese humans in primary culture

The basal release of leptin by adipocytes from massively obese human subjects incubated for 48 hours in serum-free suspension culture was comparable to that by explants of subcutaneous adipose tissue from the same obese individuals. There was no stimulation due to dexamethasone or insulin alone of leptin release by adipocytes. However, the combination of insulin and dexamethasone doubled leptin release by adipocytes. The release of leptin was also stimulated by agonists of G(i)-coupled receptors (prostaglandin E(2) [PGE(2)], brimonidine [an alpha(2) catecholamine agonist] and cyclopentyladenosine [CPA]) in the presence of dexamethasone. Leptin release by these agents was further enhanced by insulin in both adipocytes and adipose tissue. Pertussis toxin, which irreversibly inactivates G(i) heterotrimers, inhibited leptin release and abolished the stimulatory effects of G(i)-coupled receptor agonists. However, pertussis toxin did not block the stimulation of leptin release by insulin in either adipose tissue or adipocytes. These data indicate that the release of leptin by human adipocytes cultured for 48 hours in a serum-free medium is comparable to that by explants of adipose tissue except that dexamethasone stimulation of leptin release requires the presence of insulin.     

Effect of troglitazone on tumor necrosis factor alpha and transforming growth factor beta expression and action in human adipocyte precursor cells in primary culture

Troglitazone is a member of the class of thiazolidinediones that are known to act as insulin-sensitizing agents. Administration of these compounds ameliorates insulin resistance in type 2 diabetic patients, but may also promote weight gain. The main site of action is adipose tissue, where troglitazone binds to and activates the nuclear receptor peroxisome proliferator-activated receptor gamma2. The aim of this study was to investigate whether troglitazone is able to affect the adipose expression and function of tumor necrosis factor alpha (TNF-alpha) and transforming growth factor beta (TGF-beta). Both TNF-alpha and TGF-beta blocked adipose differentiation in vitro and led to a marked reduction in glycerol-3-phosphate dehydrogenase activity, a marker enzyme of adipose differentiation, by 69% +/- 11% and 75% +/- 15%, respectively. Addition of 2 mumol/L troglitazone significantly reduced this inhibitory effect of both cytokines on glycerol-3-phosphate dehydrogenase activity. Peroxisome proliferator-activated receptor gamma messenger RNA (mRNA) was reduced by TNF-alpha in freshly isolated adipocytes. This effect was completely counteracted by troglitazone, whereas TGF-beta had no immediate effect on peroxisome proliferator-activated receptor gamma mRNA. Moreover, troglitazone alone promoted adipose differentiation in a time- and dose-dependent manner. Troglitazone treatment was found to result in a marked reduction of TNF-alpha mRNA expression in human preadipocytes to 54% +/- 13% compared with untreated cultures. Furthermore, troglitazone was observed to partially antagonize the inhibitory effect of TNF-alpha on insulin-stimulated 2-deoxy-glucose uptake in newly differentiated human fat cells. In conclusion, troglitazone exerts a potent adipogenic activity in human preadipocytes, which may be mediated by suppression of the endogenous production of TNF-alpha and by counteracting the antiadipogenic effect of TGF-beta. In addition, troglitazone improved insulin-stimulated glucose uptake in differentiated fat cells.     

Hormonal regulation of 18S RNA, leptin mRNA, and leptin release in adipocytes from hypothyroid rats

The present studies were designed to examine the regulation of leptin release in primary cultures of adipocytes from fed hypothyroid rats incubated with hormones for 24 hours. Leptin release was increased in the presence of dexamethasone, while the decrease in leptin mRNA content over a 24-hour incubation was reduced by dexamethasone. Dexamethasone did not affect the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA or 18S RNA content of adipocytes. Insulin increased leptin release by adipocytes in both the absence and presence of dexamethasone. Although insulin also prevented the loss of leptin mRNA, this effect was less than that observed for GAPDH mRNA or 18S RNA content. In isolated adipocytes, the loss of almost half the 18S RNA content over a 24-hour incubation was prevented in the presence of insulin but not oxytocin or epidermal growth factor (EGF). The specific β₃ catecholamine agonist Cl 316,243 inhibited the effects of dexamethasone on leptin release and leptin mRNA accumulation, as did EGF, without affecting 18S RNA content. Oxytocin inhibited the increase in leptin release due to dexamethasone without affecting leptin mRNA levels. These data indicate that although dexamethasone and insulin are positive regulators of leptin release, only dexamethasone specifically prevented the loss of leptin mRNA in cultured rat adipocytes. In contrast, insulin, but not dexamethasone, prevented the marked loss in 18S RNA observed over a 24-hour incubation of rat adipocytes.     

Leptin is released from the human brain: influence of adiposity and gender.

Leptin, a 16-kDa circulating protein primarily derived from adipocytes, is an important factor in the regulation of appetite and energy expenditure. Using simultaneous arterio-venous blood sampling, several organs were assessed with regard to their individual roles in leptin metabolism in healthy male and female subjects constituting a range of body mass indices. Plasma leptin levels were unchanged after passage through the hepatosplanchnic and forearm circulations. In contrast, concentrations in the renal vein were consistently lower than those in the renal artery (-15%; P<0.005), indicating net extraction, whereas the brain was observed to be a net leptin releaser. Concentrations in the internal jugular vein were significantly higher than arterial levels in lean females (change, 3.0+/-1.2 ng/mL; P<0.02) and in obese males (body mass index, >28 kg/m2), but not lean (change, 2.3+/-2.3 vs. 0.1+/-0.1 ng/mL, respectively; P<0.05), indicating a probable influence of both gender and adiposity on brain leptin release. An attempt to grossly localize the site of brain release by using cerebral venous scans to distinguish between jugular venous drainage from cortical and subcortical brain areas revealed no region-specific secretion. These data raise the possibility that the brain is a nonadipose source of leptin. In addition, the higher level of brain release observed in females may contribute to the well documented gender differences in overall plasma leptin levels.     

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.     

Troglitazone improves GLUT4 expression in adipose tissue in an animal model of obese type 2 diabetes mellitus

Troglitazone has been shown to improve peripheral insulin resistance in type 2 diabetic patients and animal models. We examined the effect of troglitazone on the expression of glucose transporter 4 (GLUT4) in muscle and adipose tissue from Otsuka Long-Evans Tokushima Fatty (OLETF) rat, an animal model of obese type 2 diabetes mellitus. In addition, the effects of troglitazone on GLUT4 translocation and on glucose transport activity in adipocytes were also evaluated. Muscle and adipose tissues were isolated from 35-week-old male troglitazone-treated and untreated OLETF rats at a dose of 150 mg/kg per day for 14 days. In skeletal muscle, the protein and mRNA levels of GLUT4 were not significantly different between OLETF and control rats and they were not affected by troglitazone. On the other hand, GLUT4 protein and mRNA levels in adipose tissue from OLETF rats were significantly decreased (P<0.01) compared with control rats and they were significantly increased (1.5-fold, P<0.01) by troglitazone. Troglitazone had no major effect on GLUT4 translocation in adipocytes, but it significantly increased (1.4-fold, P<0.05) the basal and insulin-induced amounts of GLUT4 in plasma membrane (PM) in adipocytes from OLETF rats. Consistent with these results, the basal and insulin-induced glucose uptakes in adipocytes from troglitazone-treated OLETF rats were significantly increased (1.5-fold, P<0.05) compared with untreated OLETF rats. Our results suggest that troglitazone may exert beneficial effects on insulin resistance by increasing the expression of GLUT4 in adipose tissue.     

Effective use of thiazolidinediones for the treatment of glucocorticoid-induced diabetes

We evaluated the efficacy of a thiazolidinedione in the treatment of diabetes induced by glucocorticoids. We examined the effectiveness of troglitazone in seven patients with long-standing steroid-induced diabetes. Five of the seven subjects were treated with insulin alone, one was treated with both insulin and oral therapy and one was treated with oral therapy alone. The mean insulin dose in six of the seven subjects was 0.66+/-0.09 units/kg per day. Diabetes status was assessed by measuring serum fructosamine, HgbA1c, oral glucose and meal tolerance tests (OGTT and MTT) at baseline and after treatment for 5-8 weeks with troglitazone 400 mg/day. Troglitazone caused a significant decrease in fructosamine (274+/-32 vs. 217+/-22 mmol/l; P<0.01) and HgbA1C (7.8+/-0.4 vs. 7.2+/-0.4%; P<0.01) as well as decrements in the areas under the OGTT 2,308+/-156 vs. 1,937+/-127 mmol/l; P<0.05) and MTT glucose curves (4694+/-449 vs. 4057+/-437 mmol/l; P<0.05). In addition, the area under the insulin curve for the oral glucose tolerance test showed a significant increase from 27,438+/-4,488 to 41,946+/-6,048 pmol/l (P<0.05). Total and LDL cholesterol were also significantly decreased (6.4+/-0.9 vs. 5.0+/-0.6 mmol/l and 3.8+/-0.7 vs. 2.7+/-0.4 mmol/l, respectively, P<0.05). Fasting leptin values decreased by 23% despite an increase in body weight. Troglitazone is effective in the treatment of glucocorticoid-induced diabetes as manifested by lower measures of glycemia, HgbA1c, and post-prandial glucose values, while the doses of other diabetes medications remained unchanged or were reduced. The insulin-sensitizing drug also produced a marked increase in endogenous insulin secretion in response to glucose, lower total and LDL cholesterol, and decreased fasting leptin despite weight gain. Thiazolidinediones may improve diabetes-related parameters by antagonizing pathways of glucocorticoid-induced insulin resistance and by reversing adverse effects of glucocorticoids on beta cell function.     

Improvement of left ventricular diastolic dynamics in prediabetic stage of a type II diabetic rat model after troglitazone treatment

Troglitazone, an oral antidiabetic agent, has hypoglycemic effects in insulin-resistant animal models and humans. This study was conducted to evaluate its effect on left ventricular diastolic dynamics of a spontaneous diabetic (DM) rat model. Twenty DM rats and 20 age-matched nonDM rats were used, and 10 of each group were treated with troglitazone as a 0.2% food admixture for 10 weeks. At 5 and 15 weeks of age, Doppler echocardiography and M-mode echocardiography were performed. Troglitazone treatment significantly improved the left ventricular diastolic dynamics of DM rats: deceleration time (msec) of early diastolic inflow decreased significantly (treated 52 +/- 3 vs untreated 64 +/- 5, p = 0.0002), and peak velocity of early transmitral inflow (cm/sec) increased significantly (treated 96 +/- 7 vs untreated 86 +/- 8, p = 0.0216). The data suggest that troglitazone improves left ventricular diastolic dynamics of a DM rat model at prediabetic stage.     

Regulation of expression of 11beta-hydroxysteroid dehydrogenase type 1 in adipose tissue: tissue-specific induction by cytokines

Patients with glucocorticoid excess develop central obesity, yet in simple obesity, circulating glucocorticoid levels are normal. We have suggested that the increased activity and expression of the enzyme 11beta-hydroxysteroid dehydrogenase type 1 (11betaHSD1) generating active cortisol from cortisone within adipose tissue may be crucial in the pathogenesis of obesity. In this study primary cultures of human hepatocytes and adipose stromal cells (ASC) were used as in vitro models to investigate the tissue-specific regulation of 11betaHSD1 expression and activity. Treatment with tumor necrosis factor-alpha (TNFalpha) caused a dose-dependent increase in 11betaHSD1 activity in primary cultures of both sc [1743.1 +/- 1015.4% (TNFalpha, 10 ng/ml); P < 0.05 vs. control (100%)] and omental [375.8 +/- 57.0% (TNFalpha, 10 ng/ml); P < 0.01 vs. control (100%)] ASC, but had no effect on activity in human hepatocytes [90.2 +/- 2.8% (TNFalpha, 10 ng/ml); P = NS vs. control (100%)]. Insulin-like growth factor I (IGF-I) caused a dose-dependent inhibition of 11betaHSD1 activity in sc [49.7 +/- 15.0% (IGF-I, 100 ng/ml]; P < 0.05 vs. control (100%)] and omental [71.6 +/- 7.5 (IGF-I, 100 ng/ml); P < 0.01 vs. control (100%)] stromal cells, but not in human hepatocytes [101.8 +/- 15.7% (IGF-I, 100 ng/ml); P = NS vs. control (100%)]. Leptin treatment did not alter 11betaHSD1 activity in human hepatocytes, but increased activity in omental ASC [135.8 +/- 14.1% (leptin, 100 ng/ml); P = 0.08 vs. control (100%)]. Treatment with interleukin-1beta induced 11betaHSD1 activity and expression in sc and omental ASC in a time- and dose-dependent manner. 15-Deoxy-12,14-PGJ2, the putative endogenous ligand of the orphan nuclear receptor peroxisome proliferator-gamma, significantly increased 11betaHSD1 activity in omental cells [179.7 +/- 29.6% (1 microM); P < 0.05 vs. control (100%)] and sc [185.3 +/- 12.6% (1 microM); P < 0.01 vs. control (100%)] ASC, and it is possible that expression of this ligand may ensure continued cortisol generation to permit adipocyte differentiation. Protease inhibitors used in the treatment of human immunodeficiency virus infection are known to cause a lipodystrophic syndrome and central obesity, but saquinavir, indinavir, and neflinavir caused a dose-dependent inhibition of 11betaHSD1 activity in primary cultures of human omental ASC. 11betaHSD1 expression is increased in human adipose tissue by TNFalpha, interleukin-1beta, leptin, and orphan nuclear receptor peroxisome proliferator-gamma agonists, but is inhibited by IGF-I. This autocrine and/or paracrine regulation is tissue specific and explains recent clinical data and animal studies evaluating cortisol metabolism in obesity. Tissue-specific 11betaHSD1 regulation offers the potential for selective enzyme inhibition within adipose tissue as a novel therapy for visceral obesity.