Bee K. Tan

Secretion of adiponectin by human placenta: differential modulation of adiponectin and its receptors by cytokines.

Aims/hypothesisPregnancy, a state of insulin resistance, is associated with elevated levels of cytokines and profound alterations in metabolism. Serum adiponectin, an adipokine with anti-inflammatory and insulin-sensitising properties, has been shown to be lower in patients with gestational diabetes mellitus, a state of greater insulin resistance than normal pregnancies. Hypothesising that the human placenta is a source of adiponectin, we investigated its expression and secretion, and the regulation by cytokines of adiponectin and its receptors.MethodsReal-time RT-PCR, radioimmunoassay, Western blotting, radioligand binding and immunofluorescent analyses were applied to demonstrate the expression, secretion and functionality of placental adiponectin.ResultsAdiponectin gene expression and protein were found in the human term placenta, with expression primarily in the syncytiotrophoblast. RIA of conditioned media from explant experiments revealed that the placenta can secrete adiponectin in vitro. Addition of conditioned media to HEK-293 cells transfected with the gene for adiponectin receptor-1 (ADIPOR1) altered the phosphorylation status of extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase, an effect abolished after preabsorption with adiponectin antibody. Cytokines, including TNF-α, IFN-γ, IL-6 and leptin, differentially modulated placental adiponectin receptors as well as adiponectin gene expression and secretion. Interestingly, in placentae from women with gestational diabetes mellitus, we observed significant downregulation of adiponectin mRNA, significant upregulation of ADIPOR1 expression, and a non-significant increase in ADIPOR2 expression.Conclusions/interpretationOur results indicate that the human placenta produces and secretes adiponectin, and that adiponectin and its receptors are differentially regulated by cytokines and their expression altered in women with gestational diabetes mellitus. Collectively, our novel data suggest that adiponectin may play a role in adapting energy metabolism at the materno-fetal interface.

Identification of Nesfatin-1 in Human and Murine Adipose Tissue: A Novel Depot-Specific Adipokine with Increased Levels in Obesity

Nesfatin-1 is a recently identified anorexigenic peptide derived from its precursor protein, nonesterified fatty acid/nucleobindin 2 (NUCB2). Although the hypothalamus is pivotal for the maintenance of energy homeostasis, adipose tissue plays an important role in the integration of metabolic activity and energy balance by communicating with peripheral organs and the brain via adipokines. Currently no data exist on nesfatin-1 expression, regulation, and secretion in adipose tissue. We therefore investigated NUCB2/nesfatin-1 gene and protein expression in human and murine adipose tissue depots. Additionally, the effects of insulin, dexamethasone, and inflammatory cytokines and the impact of food deprivation and obesity on nesfatin-1 expression were studied by quantitative RT-PCR and Western blotting. We present data showing NUCB2 mRNA (P < 0.001), nesfatin-1 intracellular protein (P < 0.001), and secretion (P < 0.01) were significantly higher in sc adipose tissue compared with other depots. Also, nesfatin-1 protein expression was significantly increased in high-fat-fed mice (P < 0.01) and reduced under food deprivation (P < 0.01) compared with controls. Stimulation of sc adipose tissue explants with inflammatory cytokines (TNFalpha and IL-6), insulin, and dexamethasone resulted in a marked increase in intracellular nesfatin-1 levels. Furthermore, we present evidence that the secretion of nesfatin-1 into the culture media was dramatically increased during the differentiation of 3T3-L1 preadipocytes into adipocytes (P < 0.001) and after treatments with TNF-alpha, IL-6, insulin, and dexamethasone (P < 0.01). In addition, circulating nesfatin-1 levels were higher in high-fat-fed mice (P < 0.05) and showed positive correlation with body mass index in human. We report that nesfatin-1 is a novel depot specific adipokine preferentially produced by sc tissue, with obesity- and food deprivation-regulated expression.

Identification of chemerin receptor (ChemR23) in human endothelial cells: chemerin-induced endothelial angiogenesis

Chemerin acting via its distinct G protein-coupled receptor CMKLR1 (ChemR23), is a novel adipokine, circulating levels of which are raised in inflammatory states. Chemerin shows strong correlation with various facets of the metabolic syndrome; these states are associated with an increased incidence of cardiovascular disease (CVD) and dysregulated angiogenesis. We therefore, investigated the regulation of ChemR23 by pro-inflammatory cytokines and assessed the angiogenic potential of chemerin in human endothelial cells (EC). We have demonstrated the novel presence of ChemR23 in human ECs and its significant up-regulation (P<0.001) by pro-inflammatory cytokines, TNF-alpha, IL-1beta and IL-6. More importantly, chemerin was potently angiogenic, as assessed by conducting functional in-vitro angiogenic assays; chemerin also dose-dependently induced gelatinolytic (MMP-2 & MMP-9) activity of ECs (P<0.001). Furthermore, chemerin dose-dependently activated PI3K/Akt and MAPKs pathways (P<0.01), key angiogenic and cell survival cascades. Our data provide the first evidence of chemerin-induced endothelial angiogenesis and MMP production and activity.

Omentin-1, a Novel Adipokine, Is Decreased in Overweight Insulin-Resistant Women With Polycystic Ovary Syndrome: Ex Vivo and In Vivo Regulation of Omentin-1 by Insulin and Glucose

OBJECTIVE—Polycystic ovary syndrome (PCOS) is associated with insulin resistance and obesity. Recent studies have shown that plasma omentin-1 levels decrease with obesity. Currently, no data exist on the relative expression and regulation of omentin-1 in adipose tissue of women with PCOS. The objective of this study was to assess mRNA and protein levels of omentin-1, including circulating omentin-1, in omental adipose tissue of women with PCOS and matched control subjects. Ex vivo and in vivo regulation of adipose tissue omentin-1 was also studied. RESEARCH DESIGN AND METHODS—Real-time RT-PCR and Western blotting were used to assess mRNA and protein expression of omentin-1. Plasma omentin-1 was measured by enzyme-linked immunosorbent assay. The effects of d-glucose, insulin, and gonadal and adrenal steroids on adipose tissue omentin-1 were analyzed ex vivo. The in vivo effects of insulin (hyperinsulinemia) on omentin-1 levels were also assessed by a prolonged insulin-glucose infusion. RESULTS—In addition to decreased plasma omentin-1 levels in women with PCOS (P < 0.05), compared with control subjects, there was significantly lower levels of omentin-1 mRNA (P < 0.01) and protein (P < 0.05) in omental adipose tissue of women with PCOS (P < 0.01). Furthermore, in omental adipose tissue explants, insulin and glucose significantly dose-dependently decreased omentin-1 mRNA expression, protein levels, and secretion into conditioned media (P < 0.05, P < 0.01). Also, hyperinsulinemic induction in healthy subjects significantly reduced plasma omentin-1 levels (P < 0.01). CONCLUSIONS—Our novel findings reveal that omentin-1 is downregulated by insulin and glucose. These may, in part, explain the decreased omentin-1 levels observed in our overweight women with PCOS.

Omentin : a novel link between inflammation, diabesity, and cardiovascular disease

Obesity has reached pandemic proportions and is associated with serious cardiometabolic sequelae including insulin resistance, diabetes, dyslipidemia, hypertension, and cardiovascular disease, where adipose tissue-secreted cytokines, that is, adipokines, have been implicated in these processes. Omentin is a novel adipokine preferentially produced by visceral adipose tissue with insulin-sensitizing effects, where circulating levels are decreased in insulin-resistant states, for example, obesity and diabetes. With respect to vascular biology, omentin causes vasodilatation of blood vessels and attenuates C-reactive protein-induced angiogenesis potentially via the nuclear factor B signaling pathway, a potent proinflammatory signaling pathway. Thus, omentin may have beneficial effects on the metabolic syndrome and could potentially be used as a biologic marker and/or pharmacologic agent in this respect.

Insulin and Metformin Regulate Circulating and Adipose Tissue Chemerin

OBJECTIVE To assess chemerin levels and regulation in sera and adipose tissue from women with polycystic ovary syndrome (PCOS) and matched control subjects. RESEARCH DESIGN AND METHODS Real-time RT-PCR and Western blotting were used to assess mRNA and protein expression of chemerin. Serum chemerin was measured by enzyme-linked immunosorbent assay. We investigated the in vivo effects of insulin on serum chemerin levels via a prolonged insulin-glucose infusion. Ex vivo effects of insulin, metformin, and steroid hormones on adipose tissue chemerin protein production and secretion into conditioned media were assessed by Western blotting and enzyme-linked immunosorbent assay, respectively. RESULTS Serum chemerin, subcutaneous, and omental adipose tissue chemerin were significantly higher in women with PCOS (n = 14; P < 0.05, P < 0.01). Hyperinsulinemic induction in human subjects significantly increased serum chemerin levels (n = 6; P < 0.05, P < 0.01). In adipose tissue explants, insulin significantly increased (n = 6; P < 0.05, P < 0.01) whereas metformin significantly decreased (n = 6; P < 0.05, P < 0.01) chemerin protein production and secretion into conditioned media, respectively. After 6 months of metformin treatment, there was a significant decrease in serum chemerin (n = 21; P < 0.01). Importantly, changes in homeostasis model assessment–insulin resistance were predictive of changes in serum chemerin (P = 0.046). CONCLUSIONS Serum and adipose tissue chemerin levels are increased in women with PCOS and are upregulated by insulin. Metformin treatment decreases serum chemerin in these women.

Cardiometabolic Aspects of the Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is the most common endocrine disorder amongst women of reproductive age and is associated with various metabolic perturbations, in addition to chronic anovulation and factors related to androgen excess. In general, women live longer than men and develop cardiovascular disease at an older age. However, women with PCOS, as compared with age- and body mass index-matched women without the syndrome, appear to have a higher risk of insulin resistance, hyperinsulinemia, glucose intolerance, dyslipidemia, and an increased prothrombotic state, possibly resulting in a higher rate of type 2 diabetes mellitus, fatty liver disease, subclinical atherosclerosis, vascular dysfunction, and finally cardiovascular disease and mortality. Further alterations in PCOS include an increased prevalence of sleep apnea, as well as various changes in the secretion and/or function of adipokines, adipose tissue-derived proinflammatory factors and gut hormones, all of them with direct or indirect influences on the complex signaling network that regulates metabolism, insulin sensitivity, and energy homeostasis. Reviews on the cardiometabolic aspects of PCOS are rare, and our knowledge from recent studies is expanding rapidly. Therefore, it is the aim of the present review to discuss and to summarize the current knowledge, focusing on the alterations of cardiometabolic factors in women with PCOS. Further insight into this network of factors may facilitate finding therapeutic targets that should ameliorate not only ovarian dysfunction but also the various cardiometabolic alterations related to the syndrome.

Metformin Decreases the Adipokine Vaspin in Overweight Women With Polycystic Ovary Syndrome Concomitant With Improvement in Insulin Sensitivity and a Decrease in Insulin Resistance

OBJECTIVE—Polycystic ovary syndrome (PCOS) is associated with insulin resistance and obesity. Vaspin (visceral adipose tissue–derived serine protease inhibitor) levels increase with hyperinsulinemia and obesity. Currently, no data exists on vaspin in PCOS women. We therefore assessed mRNA and protein levels of vaspin, including circulating vaspin, from subcutaneous and omental adipose tissue of PCOS women and matched control subjects. Ex vivo regulation of adipose tissue vaspin and the effects of metformin treatment on circulating vaspin levels in PCOS subjects were also studied. RESEARCH DESIGN AND METHODS—Real-time RT-PCR and Western blotting were used to assess mRNA and protein expression of vaspin. Serum vaspin was quantified by enzyme-linked immunosorbent assay. The effects of d-glucose, insulin, and gonadal and adrenal steroids on adipose tissue vaspin were analyzed ex vivo. RESULTS—There were significantly higher levels of circulating vaspin (P < 0.05), vaspin mRNA (P < 0.05), and protein (P < 0.05) in omental adipose tissue of PCOS women. Interestingly, in omental adipose tissue explants, glucose significantly increased vaspin protein levels and secretion into conditioned media (P < 0.001). Also, after 6 months of metformin treatment, there was a significant decrease in serum vaspin levels in PCOS women (P < 0.001). Furthermore, multivariate regression analysis revealed that following metformin therapy, changes in circulating glucose levels were predictive of changes in serum vaspin levels (P = 0.014). CONCLUSIONS—We report, for the first time, elevated serum and omental adipose tissue levels of vaspin in overweight PCOS women and ex vivo regulation of vaspin, predominantly by glucose. More importantly, metformin treatment decreases serum vaspin levels, a novel observation.

Nuclear Factor-κB Induction by Visfatin in Human Vascular Endothelial Cells: Its role in MMP-2/9 production and activation

OBJECTIVE—Visfatin is elevated in obesity and type 2 diabetes and is thought to be an inflammatory mediator within atherosclerotic lesions and to induce gelatinase activity. We investigated the activation of nuclear factor-κB (NF-κB), a well-known proinflammatory transcription factor, by visfatin in endothelial cells. RESEARCH DESIGN AND METHODS—Human endothelial cells were transfected with pNF-κB-Luc plasmid. Using quantitative PCR, Western blot analysis, and gelatin zymography, we studied NF-κB signaling in gelatinase-mediated vascular inflammation by visfatin using the NF-κB inhibitor BAY 11-7085. RESULTS—Visfatin significantly increased NF-κB transcriptional activity (P < 0.001). We also found a significant inhibition of tumor necrosis factor-α (TNF-α)-induced NF-κB activity by visfatin (P < 0.001). Furthermore, the NF-κB inhibitor significantly negated visfatin-induced matrix metalloproteinase (MMP)-2/9 mRNA expression, protein levels, and gelatinolytic activity (P < 0.001). CONCLUSIONS—Visfatin-induced NF-κB signaling in human endothelial cells affects the activation of gelatinases MMP-2 and -9, suggesting an important role of visfatin in the pathogenesis of vascular inflammation in obesity and type 2 diabetes.OBJECTIVE Visfatin is elevated in obesity and type 2 diabetes and is thought to be an inflammatory mediator within atherosclerotic lesions and to induce gelatinase activity. We investigated the activation of nuclear factor-kappaB (NF-kappaB), a well-known proinflammatory transcription factor, by visfatin in endothelial cells. RESEARCH DESIGN AND METHODS Human endothelial cells were transfected with pNF-kappaB-Luc plasmid. Using quantitative PCR, Western blot analysis, and gelatin zymography, we studied NF-kappaB signaling in gelatinase-mediated vascular inflammation by visfatin using the NF-kappaB inhibitor BAY 11-7085. RESULTS Visfatin significantly increased NF-kappaB transcriptional activity (P < 0.001). We also found a significant inhibition of tumor necrosis factor-alpha (TNF-alpha)-induced NF-kappaB activity by visfatin (P < 0.001). Furthermore, the NF-kappaB inhibitor significantly negated visfatin-induced matrix metalloproteinase (MMP)-2/9 mRNA expression, protein levels, and gelatinolytic activity (P < 0.001). CONCLUSIONS Visfatin-induced NF-kappaB signaling in human endothelial cells affects the activation of gelatinases MMP-2 and -9, suggesting an important role of visfatin in the pathogenesis of vascular inflammation in obesity and type 2 diabetes.

Investigation and current management of recurrent IVF treatment failure in the UK

Objective  To determine current practice in the management of recurrent in vitro fertilisation (IVF) treatment failure in licensed UK infertility centres.