Leptin treatment has vasculo-protective effects in lipodystrophic mice.

Lipodystrophy syndromes (LDs) are characterized by loss of adipose tissue, metabolic complications such as dyslipidemia, insulin resistance, and fatty liver disease, as well as accelerated atherosclerosis. As a result of adipose tissue deficiency, the systemic concentration of the adipokine leptin is reduced. A current promising therapeutic option for patients with LD is treatment with recombinant leptin (metreleptin), resulting in reduced risk of mortality. Here, we investigate the effects of leptin on endothelial to mesenchymal transition (EndMT), which impair the functional properties of endothelial cells and promotes atherogenesis in LD. Leptin treatment reduced inflammation and TGF-ß2-induced expression of mesenchymal genes and prevented impairment of endothelial barrier function. Treatment of lipodystrophic- and atherosclerosis-prone animals (Ldlr-/-; aP2-nSrebp1c-Tg) with leptin reduced macrophage accumulation in atherosclerotic lesions, vascular plaque protrusion, and the number of endothelial cells with mesenchymal gene expression, confirming a reduction in EndMT in LD after leptin treatment. Treatment with leptin inhibited LD-mediated induction of the proatherosclerotic cytokine growth/differentiation factor 15 (GDF15). Inhibition of GDF15 reduced EndMT induction triggered by plasma from patients with LD. Our study reveals that in addition to the effects on adipose tissue function, leptin treatment exerts beneficial effects protecting endothelial function and identity in LD by reducing GDF15.

The Effect of FGF21 and Its Genetic Variants on Food and Drug Cravings, Adipokines and Metabolic Traits.

Fibroblast growth factor 21 (FGF21) is a regulator of addictive behavior. Increasing evidence suggests an impact of FGF21 on eating behavior, food and drug cravings and on other adipokines like insulin-like growth factor 1 (IGF-1) or adiponectin. We investigated the association of serum FGF21 and genetic variants with aspects of food and drug craving and obesity related metabolic parameters including serum adipokine levels. Standardized questionnaires, blood samples and anthropometric data of the Sorbs cohort (n = 1046) were analyzed using SPSS. For genetic analyses, the FGF21-locus ±10 kb was genotyped and analyzed using PLINK. Validation was conducted in a second independent cohort (n = 704). FGF21 was significantly associated with alcohol and coffee consumption, smoking and eating behavior (disinhibition). We confirmed correlations of FGF21 serum levels with IGF-1, adiponectin, pro-enkephalin, adipocyte fatty-acid-binding protein, chemerin and progranulin. FGF21 genetic variants were associated with anthropometric and metabolic parameters, adipokines, food and drug craving while strongest evidence was seen with low-density lipoprotein cholesterol (LDL-C). We highlight the potential role of FGF21 in food and drug cravings and provide new insights regarding the link of FGF21 with other adipokines as well as with metabolic traits, in particular those related to lipid metabolism (LDL-C).

Leptin decreases circulating inflammatory IL-6 and MCP-1 in mice.

Leptin influences inflammation and immune response. Dose-dependent effects of leptin on biomarkers of inflammation have not been studied in vivo, so far. Leptin-deficient low-density lipoprotein receptor (LDLR) knockout (LDLR-/- ;ob/ob) female mice were treated with three different leptin doses or saline for 12 weeks. The effect of leptin on plasma interleukin (IL)-6 and monocyte chemoattractant protein (MCP)-1 concentrations and Il-6 and Mcp-1 mRNA expression in vivo were assessed. Macrophage infiltration in epididymal adipose tissue (epiAT) after leptin treatment was determined by quantitative immunohistochemical analysis. Aortic root atherosclerotic lesions were analyzed by oil red O staining. Mean plasma IL-6 and MCP-1 decreased significantly in the 3.0 mg/kg BW/day group as compared to control mice (both P < 0.01). Messenger RNA expression of Il-6 and Mcp-1 was significantly down-regulated by leptin treatment in different adipose tissues in vivo. Characteristic crown-like structures formed by adipose tissue macrophages were significantly reduced by leptin treatment in epiAT. Recombinant leptin dose-dependently diminished plaque area in the aortic root. Leptin administration within the subphysiological to physiological range diminishes circulating pro-inflammatory IL-6 and MCP-1. Reduction of Il-6 and Mcp-1 gene expression in adipose tissue, as well as decreased adipose tissue macrophage infiltration might contribute. © 2018 BioFactors, 45(1):43-48, 2019.

Leptin restores markers of female fertility in lipodystrophy.

OBJECTIVES: Female reproductive dysfunction occurs in patients with pathological loss of adipose tissue, i.e. lipodystrophy (LD). However, mechanisms remain largely unclear and treatment effects of adipocyte-derived leptin have not been assessed in LD animals. METHODS: In the current study, C57Bl/6 LD mice on a low-density lipoprotein receptor knockout background were treated with leptin or saline for 8 weeks and compared to non-LD controls. RESULTS: The number of pups born was 37% lower in breeding pairs consisting of LD female mice x non-LD male mice (n = 3.3) compared to LD male mice x non-LD female mice (n = 5.2) (p < 0.05). Mean uterus weight was significantly lower in the saline-treated LD group (18.8 mg) compared to non-LD controls (52.9 mg; p < 0.0001) and increased significantly upon leptin treatment (46.5 mg; p < 0.001). The mean number of corpora lutea per ovary was significantly lower in saline-treated LD animals compared to non-LD controls (p < 0.01) and was restored to non-LD control levels by leptin (p < 0.05). Mechanistically, mRNA expression of ovarian follicle-stimulating hormone receptor (p < 0.01) and estrogen receptor ß (p < 0.05), as well as of pituitary luteinizing hormone ß subunit (p < 0.001) and follicle-stimulating hormone ß subunit (p < 0.05), was significantly upregulated in LD mice compared to non-LD controls. In addition, mean time to vaginal opening as a marker of puberty onset was delayed by 12.5 days in LD mice (50.9 days) compared to non-LD controls (38.4 days; p < 0.001). CONCLUSIONS: Female LD animals show impaired fertility which is restored by leptin. Future studies should assess leptin as a subfertility treatment in human leptin-deficiency disorders.

Betatrophin levels are increased in women with gestational diabetes mellitus compared to healthy pregnant controls.

OBJECTIVE: Betatrophin has recently been introduced as a novel adipokine/hepatokine, which promotes pancreatic ß cell proliferation and improves glucose tolerance in several mouse models of insulin resistance. However, regulation of betatrophin in gestational diabetes mellitus (GDM), as well as its association with markers of obesity, such as glucose and lipid metabolism, inflammation, and renal function, have not been elucidated. DESIGN AND METHODS: Circulating betatrophin was quantified in 74 women with GDM and 74 healthy and gestational age-matched controls by ELISA. In a subset of the study population comprising of 85 patients (41 previous controls, 44 previous women with GDM), postpartum betatrophin levels were measured in a follow-up study. RESULTS: Median (interquartile range) serum betatrophin levels were higher in women with GDM (1.79 (0.53) µg/l) as compared to non-diabetic pregnant controls (1.58 (0.44) µg/l) (P=0.002). In multivariate analysis, GDM status was an independent and positive predictor of circulating betatrophin (P=0.001). Furthermore, betatrophin levels were significantly higher during gestation (1.70 (0.53) µg/l) as compared to postpartum levels (1.55 (0.66) µg/l) (P=0.028). Moreover, postpartum irisin remained a positive and independent predictor of postpartum betatrophin concentrations. CONCLUSIONS: Women with GDM have significantly higher betatrophin levels as compared to healthy pregnant controls and GDM status positively predicts circulating betatrophin. Furthermore, postpartum levels are significantly lower as compared to betatrophin concentrations during pregnancy. Moreover, irisin is a significant predictor of postpartum betatrophin levels.

Effects of weight loss and exercise on apelin serum concentrations and adipose tissue expression in human obesity.

OBJECTIVE: Apelin is an adipokine which plays a role in the regulation of glucose homeostasis and may contribute to the link between increased adipose tissue mass and obesity related metabolic diseases. Here we investigate the role of omental and subcutaneous (SC) adipose tissue apelin and its receptor APJ mRNA expression in human obesity and test the hypothesis that changes in circulating apelin are associated with reduced fat mass in three weight loss intervention studies. METHODS: Apelin serum concentration was measured in 740 individuals in a cross-sectional (n = 629) study including a subgroup (n = 161) for which omental and SC apelin mRNA expression has been analyzed and in three interventions: 12 weeks exercise (n = 60), 6 months calorie-restricted diet (n = 19), 12 months after bariatric surgery (n = 32). RESULTS: Apelin mRNA is significantly higher expressed in adipose tissue of patients with type 2 diabetes and correlates with circulating apelin, BMI, body fat, C-reactive protein, and insulin sensitivity. Obesity surgery-induced weight loss causes a significant reduction in omental and SC apelin expression. All interventions led to significantly reduced apelin serum concentrations which significantly correlate with improved insulin sensitivity, independently of changes in BMI. CONCLUSIONS: Reduced apelin expression and serum concentration may contribute to improved insulin sensitivity beyond significant weight loss.

Fibroblast growth factor-21 serum concentrations are associated with metabolic and hepatic markers in humans.

Rather than a traditional growth factor, fibroblast growth factor-21 (FGF21) is considered to be a metabolic hormone. In the current study, we investigated serum FGF21 levels in the self-contained population of Sorbs. Serum FGF21 concentrations were quantified by ELISA and correlated with IGF1 as well as metabolic, renal, hepatic, inflammatory, and cardiovascular parameters in 913 Sorbs from Germany. Moreover, human IGF1 protein secretion was investigated in FGF21-stimulated HepG2 cells. Median FGF21 serum concentrations were 2.1-fold higher in subjects with type 2 diabetes mellitus (141.8 ng/l) compared with controls (66.7 ng/l). Furthermore, nondiabetic subjects with FGF21 levels below the detection limit of the ELISA showed a more beneficial metabolic profile compared with subjects with measurable FGF21. Moreover, FGF21 was significantly lower in female compared with male subjects after adjustment for age and BMI. In multiple regression analyses, circulating FGF21 concentrations remained independently and positively associated with gender, systolic blood pressure, triglycerides, and γ glutamyl transferase whereas a negative association was observed with IGF1 in nondiabetic subjects. Notably, FGF21 significantly inhibited IGF1 secretion into HepG2 cell culture supernatants in preliminary in vitro experiments. FGF21 serum concentrations are associated with facets of the metabolic syndrome, hepatocellular function, as well as GH status.

Amyloid precursor protein expression is induced by tumor necrosis factor alpha in 3T3-L1 adipocytes.

Amyloid precursor protein (APP) has been characterized as an adipocyte-secreted protein that might contribute to obesity-related insulin resistance, inflammation, and dementia. In the current study, regulation of APP by the proinflammatory and insulin resistance-inducing cytokine tumor necrosis factor (TNF) alpha was determined in 3T3-L1 adipocytes. Interestingly, APP protein synthesis and mRNA expression were significantly increased by TNFalpha in a time-dependent manner with maximal induction observed after 24 h of treatment. Furthermore, TNFalpha induced APP mRNA expression dose-dependently with maximal 6.4-fold upregulation seen at 100 ng/ml effector. Moreover, inhibitor experiments suggested that TNFalpha-induced APP expression was mediated by nuclear factor kappa B. Taken together, we show for the first time a potent upregulation of APP by TNFalpha suggesting a potential role of this adipocyte-secreted protein in TNFalpha-induced insulin resistance and inflammatory disease.

Interleukin-1beta is a positive regulator of TIARP/STAMP2 gene and protein expression in adipocytes in vitro.

The impact of interleukin (IL)-1beta on tumor necrosis factor alpha-induced adipose-related protein (TIARP)/six-transmembrane protein of prostate 2 (STAMP2) was determined in adipocytes. TIARP/STAMP2 mRNA synthesis was significantly stimulated by IL-1beta in a dose- and time-dependent fashion in 3T3-L1 adipocytes. Signaling studies suggested that janus kinase 2, nuclear factor kappaB, and p44/42 mitogen-activated protein kinase are involved in IL-1beta-induced TIARP/STAMP2 mRNA expression. Furthermore, IL-1beta, TNFalpha, and IL-6 showed synergistic stimulatory effects on TIARP/STAMP2 gene expression. Moreover, both TIARP/STAMP2 mRNA synthesis and protein expression were induced by IL-1beta in fully differentiated human mesenchymal stem cell-derived adipocytes (hMSC-Ad). Taken together, TIARP/STAMP2 is highly upregulated in 3T3-L1 cells and hMSC-Ad by IL-1beta and might, therefore, modulate proinflammatory and insulin resistance-inducing effects of IL-1beta.

Secretory products from human adipocytes stimulate proinflammatory cytokine secretion from human endothelial cells.

Hyperplasia and hypertrophy of fat cells can be found in obesity and increased adiposity is associated with endothelial dysfunction as an early event of atherosclerosis. However, it is unclear whether human adipocytes directly influence endothelial protein secretion. To study the crosstalk between fat and endothelial cells, human umbilical venous endothelial cells (HUVECs) were cultured in infranatants (Adipo) of primary differentiated human adipocytes. Interestingly, significantly increased secretion of 23 cytokines and chemokines from HUVECs was detected in four independent experiments after Adipo stimulation by protein array analysis detecting a total of 174 different proteins. Among those, time-dependent Adipo-induced upregulation of cytokine secretion in HUVECs was confirmed by ELISA for interleukin (IL)-8, monokine induced by gamma interferon, macrophage inflammatory protein (MIP)-1beta, MIP-3alpha, monocyte chemoattractant protein-1, and IL-6. Factors besides adiponectin, leptin, resistin, and tumor necrosis factor alpha appear to mediate these stimulatory effects. Our findings suggest that endothelial cell secretion is significantly influenced towards a proinflammatory pattern by adipocyte-secreted factors.

Serum levels of adipocyte fatty acid binding protein are increased in gestational diabetes mellitus.

OBJECTIVE: Adipocyte fatty acid binding protein (AFABP) was recently introduced as a novel adipokine, serum levels of which independently correlate with the development of the metabolic syndrome and cardiovascular disease in humans. In the current study, we investigated serum concentrations of AFABP in patients with gestational diabetes mellitus (GDM) as compared with healthy pregnant controls matched for gestational age and fasting insulin. DESIGN AND METHODS: AFABP was determined by ELISA in controls (n=80) and GDM patients (n=40) and correlated to clinical and biochemical measures of renal function, glucose and lipid metabolism, as well as inflammation, in both groups. RESULTS: Median serum AFABP concentrations were significantly elevated in subjects with GDM (22.9 microg/l) as compared with healthy pregnant controls (18.3 microg/l; P<0.05). Furthermore, GDM was independently associated with AFABP concentrations in multiple regression analysis (P<0.05). In addition, markers of adiposity (body mass index, serum leptin), triglycerides and serum creatinine were independently associated with circulating AFABP (P<0.05). CONCLUSIONS: Maternal AFABP concentrations are significantly increased in GDM. The adipokine might contribute to the increased metabolic and cardiovascular risk of the disease.

Tissue inhibitor of metalloproteinase-1 mRNA production and protein secretion are induced by interleukin-1 beta in 3T3-L1 adipocytes.

The adipokine tissue inhibitor of metalloproteinase (TIMP)-1 is upregulated when weight is gained and promotes adipose tissue development. In the present study, the effect of insulin resistance-inducing and proinflammatory interleukin (IL)-1 beta on TIMP-1 gene expression and secretion was investigated in 3T3-L1 adipocytes. Interestingly, protein secretion and mRNA production of TIMP-1 were significantly stimulated by IL-1 beta. Thus, IL-1 beta induced TIMP-1 secretion in a dose-dependent manner with maximal 3.5-fold upregulation seen at 0.67 ng/ml IL-1 beta relative to untreated cells. Furthermore, TIMP-1 mRNA synthesis was significantly stimulated by IL-1 beta in a dose-dependent fashion with 2.5-fold induction seen at IL-1 beta concentrations as low as 0.02 ng/ml and maximal 8.1-fold upregulation found at 20 ng/ml effector. Induction of TIMP-1 mRNA was also time dependent with maximal 9.6-fold upregulation detectable after 8 h of IL-1 beta treatment. Signaling studies suggested that janus kinase 2 is involved in IL-1 beta-induced TIMP-1 mRNA expression. Taken together, our results demonstrate that the TIMP-1 expression is selectively upregulated by proinflammatory IL-1 beta, supporting a direct association between insulin resistance, inflammation, and adipose tissue development in obesity.

Serum levels of the atherosclerosis biomarker sTWEAK are decreased in type 2 diabetes and end-stage renal disease.

Recently, circulating soluble tumor necrosis factor-like weak inducer of apoptosis (sTWEAK) was introduced as a potential biomarker which is downregulated in atherosclerosis. In the current study, we hypothesized that sTWEAK serum levels are decreased in end-stage renal disease and in patients with type 2 diabetes mellitus (T2DM) since both conditions are high-risk states for atherosclerotic disease. Soluble TWEAK was quantified by ELISA in control patients (n=60) with a glomerular filtration rate above 50 ml/min and patients on chronic hemodialysis (CD, n=60) and correlated to clinical and biochemical measures of renal function, glucose, and lipid metabolism, as well as inflammation. 30 control patients and 32 CD patients presented with T2DM. Mean serum sTWEAK concentrations were significantly lower in CD and T2DM patients with lowest concentrations seen when both conditions were present (control/-T2DM: 669 +/- 201 microg/l; control/+T2DM: 516 +/- 187 microg/l; CD/-T2DM: 402 +/- 128 microg/l; CD/+T2DM: 317 +/- 132 microg/l; all comparisons between groups p<0.05). In univariate analyses, sTWEAK was negatively correlated with fasting glucose in both, control and CD patients. In multivariate analyses, CD and T2DM remained independently associated with circulating sTWEAK. Taken together, circulating sTWEAK concentrations are decreased in end-stage renal disease and T2DM. Furthermore, both conditions have an additive and independent negative effect on sTWEAK levels. Our results support the view that circulating sTWEAK might be a novel biomarker of atherosclerosis.

Secretory products from human adipocytes impair endothelial function via nuclear factor kappaB.

Hyperplasia and hypertrophy of fat cells can be found in obesity, and increased adiposity is associated with endothelial dysfunction as an early event of atherosclerosis. However, it is unclear whether human adipocytes directly influence endothelial function. To study the crosstalk between fat and endothelial cells, human umbilical venous endothelial cells (HUVECs), and human coronary artery endothelial cells (HCAECs) were cultured in infranatants (Adipo) of primary differentiated human adipocytes. Interestingly, incubation of HUVECs and HCAECs with Adipo significantly increased monocyte adhesion 7.3 and 2.2-fold, respectively. VCAM-1, ICAM-1, and E-selectin in HUVECs were upregulated 3.9, 3.0, and 9.5-fold, respectively, under these conditions. Furthermore, Adipo significantly stimulated NFkappaB activity 1.9-fold. The NFkappaB inhibitor MG-132 and heat inactivation significantly reversed Adipo-stimulated monocyte adhesion. TNFalpha-neutralizing antibodies partly reversed Adipo-induced monocyte adhesion. In contrast, thiazolidinedione-pretreatment of human adipocytes did not alter the effects of Adipo. Adipo did not show cytotoxic effects. Taken together, we demonstrate that endothelial dysfunction is induced by adipocyte-secreted factors via NFkappaB partly dependent on TNFalpha.

Plasminogen activator inhibitor-1 expression and secretion are stimulated by growth hormone and interleukin-6 in 3T3-L1 adipocytes.

Various adipocytokines have been described which influence insulin sensitivity and vascular function profoundly and might, therefore, potentially link obesity, insulin resistance, and atherosclerosis. Among those, plasminogen activator inhibitor (PAI)-1 is an adipose-secreted factor upregulated in obesity and insulin resistance that inhibits fibrinolysis. Furthermore, recent studies in knockout mice suggest that PAI-1 directly impairs insulin sensitivity. In the current study, the impact of growth hormone (GH) and interleukin (IL)-6 on PAI-1 mRNA synthesis and secretion was determined in 3T3-L1 adipocytes. Interestingly, 500 ng/ml GH and 30 ng/ml IL-6 increased PAI-1 secretion five-fold and 3.6-fold, respectively. Furthermore, GH and IL-6 induced PAI-1 mRNA by up to 7.3-fold, and 3.6-fold, respectively, in a time-dependent fashion with significant stimulation seen at concentrations as low as 5 ng/ml GH and 10 ng/ml IL-6. Other insulin resistance-inducing hormones which stimulated PAI-1 synthesis included insulin, TNFalpha, and dexamethasone. Studies using pharmacological inhibitors suggested that basal and GH-induced PAI-1 synthesis were at least in part mediated by p44/42 mitogen-activated protein kinase but not janus kinase 2 and phosphatidylinositol 3-kinase. Taken together, our results show a differential regulation of PAI-1 mRNA by insulin resistance-inducing hormones including GH and IL-6.

Proinflammatory adipocytokines induce TIMP-1 expression in 3T3-L1 adipocytes.

Tissue inhibitor of metalloproteinase (TIMP)-1 is an adipocyte-secreted protein upregulated in obesity which promotes adipose tissue development. Furthermore, the proinflammatory adipocytokines tumor necrosis factor alpha (TNFalpha) and interleukin (IL)-6 induce insulin resistance, and plasma concentrations are increased during weight gain. In the current study, the impact of TNFalpha and IL-6 on TIMP-1 mRNA and protein expression was determined in 3T3-L1 adipocytes. Interestingly, TNFalpha and IL-6 induced TIMP-1 protein secretion more than 3- and 2-fold, respectively. Furthermore, TIMP-1 mRNA was upregulated in a time- and dose-dependent fashion. Inhibitor experiments suggested that nuclear factor kappaB and p 44/42 mitogen-activated protein kinase are involved in both, basal and adipocytokine-induced TIMP-1 expression. Moreover, the thiazolidinedione troglitazone partly reversed TNFalpha- but not IL-6-induced TIMP-1 synthesis. Taken together, we demonstrate that TIMP-1 expression is selectively upregulated in fat cells by proinflammatory adipocytokines and might play a role in maintaining adipose tissue mass in obesity.

Isoproterenol, TNFalpha, and insulin downregulate adipose triglyceride lipase in 3T3-L1 adipocytes.

Recently, adipose triglyceride lipase (ATGL, also called desnutrin and calcium-independent phospholipase A2 [iPLA(2)] zeta) was isolated as a novel adipose-expressed triglyceride lipase which is downregulated in obesity and may contribute to obesity-associated metabolic disorders such as hyperlipidemia and insulin resistance. To clarify expression and regulation of this fat-derived lipase, ATGL mRNA was measured in 3T3-L1 adipocytes by quantitative real-time reverse transcription-polymerase chain reaction after treatment with isoproterenol, tumor necrosis factor (TNF) alpha, insulin, and growth hormone (GH) which have been shown to influence lipolysis and insulin sensitivity profoundly. Interestingly, treatment of adipocytes with 100 nM isoproterenol, 30 ng/ml TNF alpha, and 100 nM insulin for 16 h significantly decreased ATGL mRNA to 74%, 17%, and 49% of control levels, respectively. GH did not influence ATGL synthesis. The effect of isoproterenol, TNFalpha, and insulin on ATGL expression was time- and dose-dependent. Similarly, HSL mRNA was downregulated by the three hormones. Furthermore, signaling studies suggested that activation of Gs-protein-coupled pathways by forskolin and cholera toxin is sufficient to significantly downregulate ATGL mRNA. Moreover, p44/42 mitogen-activated protein kinase appears to partly mediate the negative effect of insulin but not TNFalpha on ATGL. Taken together, downregulation of ATGL by isoproterenol, TNFalpha, and insulin might contribute to dysregulated expression and function of this lipase in obesity, hyperlipidemia, and insulin resistance.

Hormonal regulation of the novel adipocytokine visfatin in 3T3-L1 adipocytes.

Recently, visfatin was characterized as a novel adipo-cytokine that is upregulated in obesity and exerts insulin-mimetic effects in various tissues. To clarify expression and regulation of this adipocytokine, visfatin mRNA was measured by quantitative real-time reverse transcription-polymerase chain reaction in 3T3-L1 adipocytes during adipogenesis and after treatment with various hormones known to alter insulin sensitivity. Visfatin expression was about 6-fold higher in 3T3-L1 adipocytes in vitro as compared with epididymal fat in vivo and increased during adipogenic conversion more than 3-fold. Interestingly, 100 nM dexamethasone significantly increased visfatin mRNA by almost 1.5-fold. In contrast, 500 ng/ml growth hormone (GH), 10 ng/ml tumor necrosis factor (TNF) alpha, and 10 microM isoproterenol downregulated visfatin expression by 45%, 36%, and 43% respectively. Insulin did not influence synthesis of this adipocytokine. The effects of dexamethasone, GH, TNFalpha and isoproterenol were time- and dose-dependent. Furthermore, activation of G(s)-protein-coupled pathways by forskolin and cholera toxin was sufficient to significantly downregulate visfatin mRNA. Taken together, our results show a differential regulation of visfatin mRNA by insulin resistance-inducing hormones, supporting the view that this adipo-cytokine might be an interesting novel candidate linking core components of the metabolic syndrome such as obesity and insulin resistance.

Therapeutic perspectives of adipocytokines.

Various adipocyte-secreted factors have been described which profoundly affect insulin sensitivity and might potentially link obesity, insulin resistance and cardiovascular disease. Among those, adiponectin, visfatin and omentin appear as insulin-sensitising adipocytokines, whereas TNF-alpha, IL-6 and resistin induce insulin resistance. Moreover, leptin is a fat-derived key regulator of appetite and energy expenditure. Due to their profound effect on whole-body glucose and energy metabolism, adipocytokines have attracted interest as potential new therapeutics for diabetes mellitus and obesity. The current knowledge on function, regulation and therapeutic potential of various adipocytokines, as well as their clinical implications, are discussed in this review.

Interleukin-6 is a negative regulator of visfatin gene expression in 3T3-L1 adipocytes.

Visfatin is a novel adipocytokine exerting insulin-mimetic effects in various insulin-sensitive tissues such as liver, muscle, and fat. In contrast, interleukin (IL)-6 is a proinflammatory adipose-secreted factor that induces insulin resistance and plasma concentrations that correlate with the development of type 2 diabetes mellitus. In the present study, the impact of IL-6 on visfatin gene expression in 3T3-L1 adipocytes was determined by quantitative real-time reverse transcription-polymerase chain reaction. Interestingly, 30 ng/ml IL-6 time-dependently downregulated visfatin synthesis with a significant 40% suppression seen after 4 h of treatment. Furthermore, the addition of IL-6 for 16 h dose-dependently suppressed visfatin mRNA with significant effects first observed at concentrations as low as 3 ng/ml and a maximal 43% reduction at 30 ng/ml effector. Moreover, inhibitor studies suggested that the negative effect of IL-6 on visfatin expression is, at least in part, mediated by p44/42 mitogen-activated protein kinase. In contrast, troglitazone did not reverse the negative effect of IL-6 on visfatin synthesis under these conditions. Taken together, our study suggests that IL-6 might influence glucose tolerance in part by regulation of the novel insulin-mimetic adipocytokine visfatin.