The two tumor necrosis factor receptors mediate opposite effects on differentiation and glucose metabolism in human adipocytes in primary culture

Prevention of Metabolic Syndrome by Phytochemicals and Vitamin D

In recent years, attention has focused on the roles of phytochemicals in fruits and vegetables in maintaining and improving the intestinal environment and preventing metabolic syndrome. A high-fat and high-sugar diet, lack of exercise, and excess energy accumulation in the body can cause metabolic syndrome and induce obesity, diabetes, and disorders of the circulatory system and liver. Therefore, the prevention of metabolic syndrome is important. The current review shows that the simultaneous intake of phytochemicals contained in citruses and grapes together with vitamin D improves the state of gut microbiota and immunity, preventing metabolic syndrome and related diseases. Phytochemicals contained in citruses include polyphenols such as hesperidin, rutin, and naringin; those in grapes include quercetin, procyanidin, and oleanolic acid. The intake of these phytochemicals and vitamin D, along with prebiotics and probiotics, nurture good gut microbiota. In general, Firmicutes are obese-prone gut microbiota and Bacteroidetes are lean-prone gut microbiota; good gut microbiota nurture regulatory T cells, which suppress inflammatory responses and upregulate immunity. Maintaining good gut microbiota suppresses TNF-α, an inflammatory cytokine that is also considered to be a pathogenic contributor adipokine, and prevents chronic inflammation, thereby helping to prevent metabolic syndrome. Maintaining good gut microbiota also enhances adiponectin, a protector adipokine that prevents metabolic syndrome. For the prevention of metabolic syndrome and the reduction of various disease risks, the intake of phytochemicals and vitamin D will be important for human health in the future.

Receptor Specificity Engineering of TNF Superfamily Ligands

The tumor necrosis factor (TNF) ligand family has nine ligands that show promiscuity in binding multiple receptors. As different receptors transduce into diverse pathways, the study on the functional role of natural ligands is very complex. In this review, we discuss the TNF ligands engineering for receptor specificity and summarize the performance of the ligand variants in vivo and in vitro. Those variants have an increased binding affinity to specific receptors to enhance the cell signal conduction and have reduced side effects due to a lowered binding to untargeted receptors. Refining receptor specificity is a promising research strategy for improving the application of multi-receptor ligands. Further, the settled variants also provide experimental guidance for engineering receptor specificity on other proteins with multiple receptors.

Association of TNF-α Gene Expression and Release in Response to Anti-Diabetic Drugs from Human Adipocytes in vitro

INTRODUCTION

TNF-α, a proinflammatory cytokine secreted by activated immune cells, and overexpression of it in adipocytes, has an important role in insulin resistance progression and diabetes development.

AIM AND OBJECTIVE

Subcutaneous adipocytes derived from mesenchymal stem cells were used for in vitro analysis to find the role of antidiabetic drugs on TNF-α in high glucose-fed adipocytes.

METHODS

In vitro adipocytes were used along with variable concentration of anti-diabetic drugs. The level of TNF-α was measured by ELISA and the mRNA level was quantified using SYBR-Green real-time PCR. All data were statistically analyzed.

RESULTS

The level of TNF-α and the mRNA expression were observed and analyzed with normal adipocytes. TNF-α level and expression of it showed agonistic behavior, ie no change at low concentration while enhances with the increase of glucose. The level was decreased significantly when the adipocytes were treated with metformin (p=0.015) and pioglitazone (p=0.020). A combination of drugs showed that the expression of TNF-α was almost the same as for metformin alone. However, insulin increases the TNF-α expression as for pioglitazone.

DISCUSSION

Such a report on adipocytes may be helpful for clinical benefits to understand the additional mechanism of adipocytes on the release and expression of TNF-α. However, anti-diabetic drugs including insulin up-regulate the TNF-α gene expression in mild or severe glucose load.

The Inflammatory and Hemostatic Cardiovascular Risk Markers During Acute Hyperglycemic Crisis in Type 1 and Type 2 Diabetes

BACKGROUND

We analyzed cardiovascular inflammatory (C-reactive protein (CRP), interleukin 6 (IL-6)), haemostatic (homocysteine) risk markers in lean and obese patients at admission and acute hyperglicemic crisis (AHC) resolving, involving diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic state (HHS).

METHODS

In that context, we included group A: N = 20 obese, B: N=20 lean patients with DKA; C: N = l0 obese, D: N=10 lean patients with HHS; E: N = 15 obese, F: N=15 lean controls. CRP IL-6, homocysteine were determined by ELISA.

RESULTS

Our results showed that CRP IL-6, and homocysteine levels decreased in all groups: (A: p<0.001; B: p<0.001, C: p<0.05; D: p<0.001 mg/L), (A: p<0.001 B: p<0.001, C: p<0.001, D: p<0.01 pg/mL), (A: p<0.001, B: p <0.001; C: p<0.05, D: p=0.001 μmol/L), respectively, at resolving AHC. However, CRP persisted higher (p<0.001, p<0.01), IL-6 lower (p<0.05, p<0.001), while homocysteine levels turned out to be similar to controls.

CONCLUSIONS

AHC is associated with increased inflammatory and hemostatic cardiovascular risk markers. Also, insulin therapy in AHC has had more pronounced favorable effect on IL-6 and homocystein than on CRP.

Upregulated TNF Expression 1 Year After Bariatric Surgery Reflects a Cachexia-Like State in Subcutaneous Adipose Tissue

Background

Adipose tissue dysfunction contributes to obesity-associated chronic diseases. In the first year after bariatric surgery, obese patients significantly improve their metabolic status upon losing weight. We aimed to investigate whether changes in subcutaneous adipose tissue gene expression reflect a restoration of a healthy lean phenotype after bariatric surgery.

Methods

Thirty-one severely obese patients (BMI ≥ 40 kg/m²) were examined before and after surgery. subcutaneous adipose tissue (SAT) was collected during and 1 year after bariatric surgery. SAT from 20 matched lean and overweight patients (BMI < 30 kg/m²) was collected during elective abdominal surgery. Baseline characteristics and SAT gene expression relevant to glucose and lipid metabolism, inflammation, and apoptosis were analyzed.

Results

After surgery, mean BMI decreased from 46.1 ± 6.3 to 31.1 ± 5.7 kg/m² and homeostasis model assessment of insulin resistance from 5.4 ± 5.3 to 0.8 ± 0.8. SAT expression of most analyzed inflammatory cytokines, growth factors, and metabolic and cell surface markers was greatly downregulated even compared to the lean cohort. In contrast, gene expression of TNF and CASP3 was significantly upregulated. Elastic net regression analysis showed that fasting glucose levels and CASP3 predicted increased TNF expression in the post-obese group.

Conclusions

Gene expression patterns in SAT 1 year after bariatric surgery point to a reduced inflammation. The unexpected high TNF expression in SAT of post-obese subjects is most likely not an indicator for inflammation, but rather an indicator for increased lipolysis and adipose tissue catabolism. Notably, after bariatric surgery SAT gene expression reflects a cachexia-like phenotype and differs from the lean state.

Electronic supplementary material

The online version of this article (doi:10.1007/s11695-016-2477-5) contains supplementary material, which is available to authorized users.

The association of oxidative stress and pro-inflammatory cytokines in diabetic patients with hyperglycemic crisis

AIMS

To investigate the relationship between oxidative stress and serum levels of pro-inflammatory cytokines in diabetic patients with hyperglycemic crisis.

METHODS

Seventy-three patients presenting to hospital with diabetic ketoacidosis or non-ketotic hyperglycemia were studied. Superoxide dismutase (SOD) activity, malondialdehyde (MDA) content, total antioxidant capacity (TAC), 8-iso-prostaglandin F2α (8-iso-prostaglandinF2α, 8-iso-PGF2α), tumor necrosis factor receptor-I (TNF-RI), interleukin -1β (IL-1β), tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) levels were measured in all patients. The patients were then given an intravenous infusion of insulin 0.1U • kg-1 • h-1, as well as fluids, symptomatic therapy and parenteral and intravenous nutrition.

RESULTS CONCLUSION

Patients with hyperglycemic crises have significantly increased oxidative stress and dysregulated serum pro-inflammatory cytokines that can be effectively treated by intensive insulin therapy.

TWEAK prevents TNF-α-induced insulin resistance through PP2A activation in human adipocytes

Visceral fat is strongly associated with insulin resistance. Obesity-associated adipose tissue inflammation and inflammatory cytokine production are considered key mediators of insulin signaling inhibition. TWEAK is a relatively new member of the TNF cytokine superfamily, which can exist as full length membrane-associated (mTWEAK) and soluble (sTWEAK) isoforms. Although TWEAK has been shown to have important functions in chronic inflammatory diseases its physiological role in adipose tissue remains unresolved. In this study, we explore the molecular mechanisms involved in the modulation of TNF-α-induced effects on insulin sensitivity by sTWEAK in a human visceral adipose cell line and also in primary human adipocytes obtained from visceral fat depots. Our data reveal that sTWEAK ameliorates TNF-α-induced insulin resistance on glucose uptake, GLUT4 translocation and insulin signaling without affecting other metabolic effects of TNF-α such as lipolysis or apoptotis. Co-immunoprecipitation experiments in adipose cells revealed that pretreatment with sTWEAK specifically inhibits TRAF2 association with TNFR1, but not with TNFR2, which mediates insulin resistance. However, sTWEAK does not affect other downstream molecules activated by TNF-α, such as TAK1. Rather, sTWEAK abolishes the stimulatory effect of TNF-α on JNK1/2, which is directly involved in the development of insulin resistance. This is associated with an increase in PP2A activity upon sTWEAK treatment. Silencing of the PP2A catalytic subunit gene overcomes the dephosphorylation effect of sTWEAK on JNK1/2, pointing to PP2A as a relevant mediator of sTWEAK-induced JNK inactivation. Overall, our data reveal a protective role of TWEAK in glucose homeostasis and identify PP2A as a new driver in the modulation of TNF-α signaling by sTWEAK.

Lack of direct insulin-like action of visfatin/Nampt/PBEF1 in human adipocytes

Visfatin, a protein identified as a secretion product of visceral fat in humans and mice, is also expressed in different anatomical locations, and is known as pre-B cell-colony enhancing factor (PEBF1). It is also an enzyme displaying nicotinamide phosphoribosyltransferase activity (Nampt). The evidence that levels of visfatin correlate with visceral fat mass has been largely debated and widely extended to other regulations in numerous clinical studies and in diverse animal models. On the opposite, the initial findings regarding the capacity of visfatin/Nampt/PEBF1 to bind and to activate the insulin receptor have been scarcely reproduced, and even were contradicted in recent reports. Since the putative insulin mimicking effects of visfatin/Nampt/PEBF1 have never been tested on mature human adipocytes, at least to our knowledge, we tested different human visfatin batches on human fat cells freshly isolated from subcutaneous abdominal fat and exhibiting high insulin responsiveness. Up to 10 nM, visfatin was devoid of clear activatory action on glucose transport in human fat cells while, in the same conditions, insulin increased by more than threefold the basal 2-deoxyglucose uptake. Moreover, visfatin was unable to mimic the lipolysis inhibition induced by insulin. Visfatin definitively cannot be considered as a direct activator of insulin signalling in human fat cells. Nevertheless itsin vivo effects on insulin release and on glucose handling deserve to further study the role of this multifunctional extracellular enzyme in obese and diabetic states.

In vitro hyperresponsiveness to tumor necrosis factor-alpha contributes to adipokine dysregulation in omental adipocytes of obese subjects

CONTEXT

In obesity, adipocyte hypertrophy and macrophage infiltration lead to overproduction of proinflammatory adipokines, which play a crucial role in the metabolic syndrome. The molecular mechanisms underlying this overproduction are still unsettled. The role of TNF-alpha also remains controversial in human obesity.

OBJECTIVE

We revisited the contribution of TNF-alpha to adipokine dysregulation in central obesity. We more particularly assessed the involvement of TNF-alpha vs. other stromal-vascular cell (SVC)-secreted factors and searched for potential differential responses to TNF-alpha between adipocytes of lean and obese individuals.

DESIGN AND PARTICIPANTS

Primary cultures of omental adipocytes from obese and nonobese age- and sex-matched subjects were used. For some experiments, we generated media previously conditioned by SVCs, which mimic adipocyte microenvironment.

RESULTS

Adipocytes of obese subjects mainly overexpressed adipokines, in comparison with those of lean ones, when cultured in SVC-conditioned media. This was abrogated by immunoneutralization of TNF-alpha, indicating that among the numerous factors secreted by SVCs, TNF-alpha is a crucial contributor to adipokine dysregulation. Accordingly, adipocytes of obese subjects overproduced adipokines in response to direct exposure of TNF-alpha. This hyperresponsiveness was mediated by TNF-alpha receptor 1 and hyperactivation of the nuclear factor-kappaB (NF-kappaB) pathway. Correspondingly, NF-kappaB activity was increased in adipocytes of obese subjects and correlated with adipocyte size, adipokine expression, and in vivo insulin resistance. Eventually adipokine overexpression in adipocytes of obese subjects was prevented by NF-kappaB inhibitors.

CONCLUSIONS

In obesity, TNF-alpha that is [corrected] over other SVC-secreted factors, a crucial determinant of adipokine dysregulation acts on enlarged adipocytes, which are hyperresponsive to this triggering signal [corrected]

Local inflammation and hypoxia abolish the protective anticontractile properties of perivascular fat in obese patients

BACKGROUND

Inflammation in adipose tissue has been implicated in vascular dysfunction, but the local mechanisms by which this occurs are unknown.

METHODS AND RESULTS

Small arteries with and without perivascular adipose tissue were taken from subcutaneous gluteal fat biopsy samples and studied with wire myography and immunohistochemistry. We established that healthy adipose tissue around human small arteries secretes factors that influence vasodilation by increasing nitric oxide bioavailability. However, in perivascular fat from obese subjects with metabolic syndrome (waist circumference 111+/-2.8 versus 91.1+/-3.5 cm in control subjects, P<0.001; insulin sensitivity 41+/-5.9% versus 121+/-18.6% in control subjects, P<0.001), the loss of this dilator effect was accompanied by an increase in adipocyte area (1786+/-346 versus 673+/-60 mum(2), P<0.01) and immunohistochemical evidence of inflammation (tumor necrosis factor receptor 1 12.4+/-1.1% versus 6.7+/-1%, P<0.001). Application of the cytokines tumor necrosis factor receptor-alpha and interleukin-6 to perivascular fat around healthy blood vessels reduced dilator activity, resulting in the obese phenotype. These effects could be reversed with free radical scavengers or cytokine antagonists. Similarly, induction of hypoxia stimulated inflammation and resulted in loss of anticontractile capacity, which could be rescued by catalase and superoxide dismutase or cytokine antagonists. Incubation with a soluble fragment of adiponectin type 1 receptor or inhibition of nitric oxide synthase blocked the vasodilator effect of healthy perivascular adipose tissue.

CONCLUSIONS

We conclude that adipocytes secrete adiponectin and provide the first functional evidence that it is a physiological modulator of local vascular tone by increasing nitric oxide bioavailability. This capacity is lost in obesity by the development of adipocyte hypertrophy, leading to hypoxia, inflammation, and oxidative stress.

Influence of reverse signaling via membrane TNF-alpha on cytotoxicity of NK92 cells

Membrane tumor necrosis factor-alpha (mTNF-alpha) serves as a receptor transducing signals into mTNF-alpha-bearing cells. Among human peripheral blood mononuclear cells, natural killer (NK) cells have been reported to be the only cell type constitutively expressing mTNF-alpha, which is involved in the cytotoxicity of resting NK cells. Using an IL-2-dependent human NK cell line, NK92, which constitutively expresses mTNF-alpha, we examined the effect of reverse signaling via mTNF-alpha on cellular activities. When the cells were prestimulated with soluble TNFR1 (sTNFR1) which activated mTNF-alpha-mediated reverse signaling, the cytotoxicity of NK92 cells was significantly increased. Further investigation demonstrated that prestimulation with sTNFR1 augmented exocytosis and mRNA transcription of two cytotoxic molecules, perforin and granzyme B, which could serve as underlying molecular mechanisms by which mTNF-alpha-mediated reverse signaling promoted cytotoxicity of NK cells toward K562 cells. On the other hand, pretreatment of NK92 with sTNFR1 boosted the expression of FasL and TNF-alpha, including both the secretory and membrane forms. These molecules also contribute to the NK-mediated cytotoxicity, although K562 cells are Fas-negative and sTNF-alpha-resistant. Interestingly, the mTNF-alpha reverse signaling was found to act synergistically with IL-2 on NK-mediated cytotoxicity. This synergy markedly promoted the production of secretory as well as membrane cytotoxic molecules which may be responsible for the enhanced NK92-mediated cytotoxicity. Our observations suggest that, via reverse signaling, constitutively expressed mTNF-alpha may sensitize NK cells to activating stimuli, such as IL-2, resulting in increased NK-mediated cytotoxicity through promoting the production of multiple cytotoxic effector molecules.

Blockade of tumor necrosis factor (TNF) receptor type 1-mediated TNF-alpha signaling protected Wistar rats from diet-induced obesity and insulin resistance

TNF-alpha plays an important role in the pathogenesis of obesity and insulin resistance in which the effect of TNF-alpha signaling via TNF receptor type 1 (TNFR1) largely remains controversial. To delineate the role of TNFR1-mediated TNF-alpha signaling in the pathogenesis of this disorder, a TNFR1 blocking peptide-Fc fusion protein (TNFR1BP-Fc) was used for the present study. Wistar rats were fed a high-fat/high-sucrose (HFS) diet for 16 wk until obesity and insulin resistance developed. In comparison with increased body weight and fat weight, enlarged adipocytes, and hypertriglyceridemia in the obese state, the subsequent 4-wk treatment with TNFR1BP-Fc resulted in significant weight loss characterized by decreased fat pad weight and adipocyte size and reduced plasma triglycerides. Furthermore, obesity-induced insulin resistance, including hyperinsulinemia, elevated C-peptide, higher degree of hyperglycemia after glucose challenge, and less hypoglycemic response to insulin, was markedly improved, and the compensatory hyperplasia and hypertrophy of pancreatic islets were reduced. Interestingly, treatment with TNFR1BP-Fc markedly suppressed systemic TNF-alpha release and its local expression in pancreatic islets and muscle and adipose tissues. In addition, blockage of TNFR1-mediated TNF-alpha signaling in obese rats significantly enhanced tyrosine phosphorylation of insulin receptor substrate 1 (IRS-1) in the muscle and fat tissues. Our results strongly suggest a pivotal role for TNFR1-mediated TNF-alpha signaling in the pathogenesis of obesity and insulin resistance. Thus, TNFR1BP-Fc may be a good candidate for the treatment of this disease.

Aromatase expression in women's cancers

Estrogen has been positively linked to the pathogenesis and growth of three common women's cancers (breast, endometrium and ovary). A single gene encodes the key enzyme for estrogen biosynthesis named aromatase, inhibition of which effectively eliminates estrogen production in the entire body. Aromatase inhibitors successfully treat breast cancer, whereas their roles in endometrial and ovarian cancers are less dear. Ovary, testis, adipose tissue, skin, hypothalamus and placenta express aromatase normally, whereas breast, endometrial and ovarian cancers overexpress aromatase and produce local estrogen exerting paracrine and intracrine effects. Tissue specific promoters distributed over a 93 kilobase regulatory region upstream of a common coding region alternatively control aromatase expression. A distinct set of transcription factors regulates each promoter in a signaling pathway- and tissue-specific manner. In cancers ofbreast, endometrium and ovary, aromatase expression is primarly regulated by increased activity of the proximally located promoter 1.3/II region. Promoters I.3 and II lie 215 bp from each other and are coordinately stimulated by PGE2 via a cAMP-PKA-dependent pathway. In breast adipose fibroblasts exposed to PGE2 secreted by malignant epithelial cells, activation of PKC potentiates cAMP-PKA-dependent induction ofaromatase. Thus, inflammatory substances such as PGE2 may play important roles in inducing local production of estrogen that promotes tumor growth.

Expression of p107 and p130 during human adipose-derived stem cell adipogenesis

Within the first 24h of hormonally stimulated adipocyte differentiation, murine 3T3-L1 preadipocytes undergo a mitotic expansion phase prior to terminal differentiation. During this time, the cell cycle regulatory proteins, p130 and p107 undergo dramatic differential expression and the transient increase in expression of p107 appears to be required for terminal differentiation. Recently, human adipose-derived human stem cells (hASC) of mesenchymal origin have been used as a model of human adipocyte differentiation and we sought to determine if differentiating hASC undergo clonal expansion and if the regulated expression of p130/p107 was similar to that observed during 3T3-L1 adipogenesis. Results indicate that differentiating hASC, unlike 3T3-L1 cells do not undergo clonal expansion and p130 expression gradually diminishes across differentiation. However, p107 expression is transiently increased during hASC differentiation in a manner analogous to 3T3-L1 cells suggesting a similar role for p107 in terminal differentiation in human adipocytes.

Mice heterozygous for tumor necrosis factor-alpha converting enzyme are protected from obesity-induced insulin resistance and diabetes

OBJECTIVE

Tumor necrosis factor (TNF)-alpha is known to affect insulin sensitivity, glucose, and lipid metabolism through alternative and redundant mechanisms at both translational and post-translational levels. TNF-alpha exerts its paracrine effects once the membrane-anchored form is shed and released from the cell membrane. TNF-alpha cleavage is regulated by TNF-alpha converting enzyme (TACE), which regulates the function of several transmembrane proteins, such as interleukin-6 receptor and epidermal growth factor receptor ligands. The role of TACE in high-fat diet (HFD)-induced obesity and its metabolic complications is unknown.

RESEARCH DESIGN AND METHODS

To gain insights into the role of TACE in metabolic disorders, we used Tace(+/-) mice fed a standard or high-fat diet for 16 weeks.

RESULTS

We observed that Tace(+/-) mice are relatively protected from obesity and insulin resistance compared with wild-type littermates. When fed an HFD, wild-type mice exhibited visceral obesity, increased free fatty acid and monocyte chemoattractant protein (MCP)1 levels, hypoadiponectinemia, glucose intolerance, and insulin resistance compared with Tace(+/-) mice. Interestingly, Tace(+/-) mice exhibited increased uncoupling protein-1 and GLUT4 expression in white adipose tissue.

CONCLUSIONS

Our results suggest that modulation of TACE activity is a new pathway to be investigated for development of agents acting against obesity and its metabolic complications.

Aromatase excess in cancers of breast, endometrium and ovary

Pathogenesis and growth of three common women's cancers (breast, endometrium and ovary) are linked to estrogen. A single gene encodes the key enzyme for estrogen biosynthesis named aromatase, inhibition of which effectively eliminates estrogen production in the entire body. Aromatase inhibitors successfully treat breast cancer, whereas their roles in endometrial and ovarian cancers are less clear. Ovary, testis, adipose tissue, skin, hypothalamus and placenta express aromatase normally, whereas breast, endometrial and ovarian cancers overexpress aromatase and produce local estrogen exerting paracrine and intracrine effects. Tissue-specific promoters distributed over a 93-kb regulatory region upstream of a common coding region alternatively control aromatase expression. A distinct set of transcription factors regulates each promoter in a signaling pathway- and tissue-specific manner. In cancers of breast, endometrium and ovary, aromatase expression is primarly regulated by increased activity of the proximally located promoter I.3/II region. Promoters I.3 and II lie 215 bp from each other and are coordinately stimulated by PGE(2) via a cAMP-PKA-dependent pathway. In breast adipose fibroblasts exposed to PGE(2) secreted by malignant epithelial cells, PKC is also activated, and this potentiates cAMP-PKA-dependent induction of aromatase. Thus, inflammatory substances such as PGE(2) may play important roles in inducing local production of estrogen that promotes tumor growth.

In vitro adipocytic conversion in Meckel's chondrocytes in response to a fatty acid-containing medium

Chick serum (CKS) contains factors that stimulate adipocytes in Meckel's chondrocytes in vitro. In the present study, we analyzed levels of fatty acids in CKS, and further examined whether these had the potential to convert chondrocytes to adipocytes. Phenotypic changes were evaluated by light and electron microscopies, bromodeoxyuridine (BrdU) incorporation, triglyceride assays, and immunocytochemistry. We showed that CKS contained high levels of fatty acids, and a mixed medium containing 5 particular fatty acids inhibited DNA synthesis and the proliferation of chondrocytes as it facilitated their differentiation into adipocytes. The adipocytes produced were sudan-positive multilocular cells that morphologically and histochemically resembled adipocytes induced by the CKS-containing medium. Almost all lipid droplet-containing cells were positive for leptin and alpha-glycerophosphate dehydrogenase (GPDH), as evaluated by immunoperoxidase staining, and their triglyceride concentrations markedly increased during 4 to 6 days of culture. These results suggested that specific fatty acids in CKS are involved in the adipocytic conversion of Meckel's chondrocytes.

GRB14, GPD1, and GDF8 as potential network collaborators in weight loss-induced improvements in insulin action in human skeletal muscle

Obesity is associated with insulin resistance in skeletal muscle; accordingly, weight loss dramatically improves insulin action. We sought to identify molecular remodeling of muscle commensurate with weight loss that could explain improvements in insulin action. Muscle from morbidly obese women was studied before and after gastric bypass surgery. Gastric bypass surgery significantly reduced body mass by approximately 45% and improved insulin action. We then assessed mRNA profiles using a stringent statistical analysis (statistical concordance with three probe set algorithms), with validation in a cross-sectional study of lean (n = 8) vs. morbidly obese (n = 8) muscle. Growth factor receptor-bound protein 14 (GRB14), glycerol-3-phosphate dehydrogenase 1 (GPD1), and growth differentiation factor 8 (GDF8; myostatin) significantly decreased approximately 2.4-, 2.2-, and 2.4-fold, respectively, after weight loss (gastric bypass). Increased expression of these transcripts was associated with increased obesity in the cross-sectional group (lean vs. morbidly obese muscle). Each transcript was validated by real-time quantitative RT-PCR assays in both study groups. Using Ingenuity Pathway Analysis, we show that all three transcripts are involved in the same regulatory network including AKT1, IGF1, TNF, PPARG, and INS. These results suggest that GRB14, GPD1, and GDF8 are weight loss-responsive genes in skeletal muscle and that the observed transcriptional modulation of these would be expected to improve insulin signaling, decrease triglyceride synthesis, and increase muscle mass, respectively, with weight loss. Thus our data provide a possible regulatory pathway involved in the development of insulin resistance in the morbidly obese state, and improvement of insulin resistance with weight loss.

Baicalein Inhibits Adipocyte Differentiation by Enhancing COX-2 Expression

Baicalein, one of the major flavonoids in Scutellaria baicalensis (Chinese Skullcap), is well known for its effects on cell proliferation, apoptosis, and inflammation. Here we show that baicalein also inhibits the adipogenesis of 3T3-L1 preadipocytes. Baicalein inhibited triglyceride accumulation during adipogenesis and significantly decreased the mRNA expression of fatty acid-binding protein (FABP), a marker of adipogenesis. Microarray analysis revealed that several genes, which are differentially expressed during adipogenesis, were modulated by baicalein treatment in 3T-L1 cells. The expression of FABP, apolipoprotein D, and insulin-like growth factor 2, which was markedly up-regulated during adipogenesis, was down-regulated by baicalein. Cyclooxygenase (COX)-2 mRNA expression, which was decreased during adipogenesis, was up-regulated by baicalein. These COX-2 mRNA expression patterns were mirrored by the expression of COX-2 protein and its enzymatic activity. NS-398, a COX-2 inhibitor, partially abrogated the baicalein-induced inhibition of adipogenensis. Thus, the anti-adipogenic effect of baicalein may be mediated by its ability to enhance the expression of COX-2, which is normally down-regulated during adipogenesis.

TNF and TNF receptor expression and insulin sensitivity in human omental and subcutaneous adipose tissue--influence of BMI and adipose distribution

Tumour necrosis factor (TNF)alpha is implicated in the relationship between obesity and insulin resistance/ type 2 diabetes. In an effort to understand this association better we (i) profiled gene expression patterns of TNF, TNFR1 and TNFR2 and (ii) investigated the effects of TNF on glucose uptake in isolated adipocytes and adipose tissue explants from omental and subcutaneous depots from lean, overweight and obese individuals. TNF expression correlated with expression of TNFR2, but not TNFR1, and TNF and TNFR2 expression increased in obesity. TNFR1 expression was higher in omental than in subcutaneous adipocytes. Expression levels of TNF or either receptor did not differ between adipocytes from individuals with central and peripheral obesity. TNF only suppressed glucose uptake in insulin-stimulated subcutaneous tissue and this suppression was only observed in tissue from lean subjects. These data support a relationship between the TNF system and body mass index (BMI), but not fat distribution, and suggest depot specificity of the TNF effect on glucose uptake. Furthermore, adipose tissue from obese subjects already appears insulin 'resistant' and this may be a result of the increased TNF levels.

Adipocyte differentiation of multipotent cells established from human adipose tissue

In this study multipotent adipose-derived stem cells isolated from human adipose tissue (hMADS cells) were shown to differentiate into adipose cells in serum-free, chemically defined medium. During the differentiation process, hMADS cells exhibited a gene expression pattern similar to that described for rodent clonal preadipocytes and human primary preadipocytes. Differentiated cells displayed the key features of human adipocytes, i.e., expression of specific molecular markers, lipolytic response to agonists of beta-adrenoreceptors (beta2-AR agonist > beta1-AR agonist >> beta3-AR agonist) and to the atrial natriuretic peptide, insulin-stimulated glucose transport, and secretion of leptin and adiponectin. hMADS cells were able to respond to drugs as inhibition of adipocyte differentiation was observed in the presence of prostaglandin F2alpha, tumour necrosis factor-alpha, and nordihydroguaiaretic acid, a natural polyhydroxyphenolic antioxidant. Thus, for the first time, human adipose cells with normal karyotype and indefinite life span have been established. They represent a novel and valuable tool for studies of fat tissue development and metabolism.

Mechanisms of increased insulin resistance in non-cirrhotic patients with chronic hepatitis C virus infection

BACKGROUND AND AIM

Evidence showing a higher prevalence of diabetes mellitus (DM) in patients with chronic hepatitis C virus (HCV) infection has been accumulating. However, the reason why chronic HCV infection promotes DM remains unknown. In the present study, the authors focused on non-cirrhotic and non-diabetic patients with chronic HCV infection and evaluated the factors responsible for increases in insulin resistance.

METHODS

Fifty-six patients diagnosed with HCV-related chronic liver disease were included. Biochemical information including body mass index (BMI), aspartate aminotransferase (AST), alanine aminotransferase, cholinesterase, triglyceride, total cholesterol, hemoglobin, platelet count, glycosylated hemoglobin, immunoreactive insulin (IRI), and serum levels of tumor necrosis factor (TNF)-alpha and HCV-RNA were determined using venous blood samples obtained from each patient after overnight fasting. Homeostasis model assessment of insulin resistance (HOMA-IR), a simple and convenient measure of insulin resistance, was also calculated. The relationship between the stage of liver fibrosis and HOMA-IR, and the clinical factors responsible for the increase in HOMA-IR in non-diabetic patients was investigated.

RESULTS

Homeostasis model assessment of insulin resistance and IRI levels increased parallel with the progression of fibrosis. Among the non-diabetic patients with mild to moderate liver fibrosis, BMI, serum levels of AST and TNF-alpha were related with HOMA-IR (BMI: r = 0.395, P = 0.041; AST: r = 0.465, P = 0.014; TNF-alpha: r = 0.396, P = 0.040). In contrast, HOMA-IR related to TNF-alpha (r = 0.526, P = 0.013) in non-diabetic patients with advanced liver fibrosis.

CONCLUSION

Collectively, hepatic fibrosis and inflammation appear to play key roles in the increase in insulin resistance in patients with chronic HCV infection.

Glimepiride reduces mononuclear activation of the redox-sensitive transcription factor nuclear factor-kappa B

AIMS

Glimepiride has the lowest ratio of insulin release to glucose decrease compared with other sulphonylureas. This prompted us to study in vitro and in vivo in a placebo-controlled study the effect of glimepiride on the redox-sensitive transcription factor nuclear factor-kappa B (NF-kappaB).

METHODS

Fifteen patients with type 2 diabetes on glibenclamide with a stable HbA1c over the last 6 months were included. After sampling for determination of baseline values, 10 patients were changed to an equivalent dose of glimepiride, while the placebo group was maintained at glibenclamide plus placebo. The glimepiride dose in these patients was adjusted so that no change in glucose control occurred, allowing for direct comparison. The others were kept on glibenclamide and received additional placebo. After 4 weeks of glimepiride or glibenclamide plus placebo, a second blood sample was taken. Mononuclear cells were isolated and assayed in a tissue-culture-independent electrophoretic mobility shift assay (EMSA)-based detection system for NF-kappaB binding activity, and by Western Blot for nuclear localization of NF-kappaB-p65, the cytoplasmic content of IkappaBalpha and the NF-kappaB-controlled haemoxygenase-1. Glimepiride dose-dependent inhibition of carboxymethyllysin (CML) albumin or tumour necrosis factor alpha (TNFalpha)- and H2O2-induced activation of NF-kappaB binding were determined, using isolated peripheral blood mononuclear cells from healthy volunteers, and transcriptional activity of bovine aortic endothelial cells either left untreated or induced with CML albumin incubated with or without glimepiride. Furthermore, in-vitro studies were implemented to demonstrate radical quenching properties of glimepiride in the cell-free 2,2'-azo-bis(2-aminopropane)-dihydrochloride system.

RESULTS

Baseline glucose and HbA1c remained stable in the patients switched from glibenclamide to a corresponding dose of glimepiride or kept on glibenclamide plus placebo. While in the group of patients only taking glibenclamide plus placebo the NF-kappaB binding activity did not change significantly (p = 0.58), the NF-kappaB binding activity in the group of patients taking glimepiride was reduced from 19.3 relative NF-kappaB-p65-equivalents to 15.5 relative NF-kappaB-p65-equivalents (p = 0.04). The nuclear translocation of NF-kappaB-p65 was reduced from 100% at baseline to 58% after 4 weeks (p = 0.04); the cytoplasmic localization of NF-kappaB-p65 increased from 100% to 129% (p = 0.03) and the cytoplasmic content of IkappaBalpha increased from 100% to 109% (p = 0.06). The redox-sensitive haemoxygenase-1 antigen was reduced from 100% to 82% (p = 0.04). To prove directly that glimepiride reduces NF-kappaB activation, we isolated peripheral blood mononuclear cells (PBMC) from healthy volunteers. In vitro, glimepiride reduced TNFalpha-(1 nmol/l) and CML albumin (800 nmol/l)-induced NF-kappaB activation dose dependently, being half maximal at 120 micromol/l. H2O2-mediated NF-kappaB activation was only partially reduced. In addition, glimepiride reduced NF-kappaB-dependent gene expression using a NF-kappaB-driven luciferase reporter system. Finally, a cell-free detection system showed that glimepiride has radical quenching properties.

CONCLUSION

Glimepiride can affect the activation of the redox-sensitive transcription factor NF-kappaB in vitro and in vivo.

Divergent roles for p55 and p75 TNF-alpha receptors in the induction of plasminogen activator inhibitor-1

Tumor necrosis factor-alpha (TNF-alpha) is elevated in obesity and in acute inflammatory states, and contributes to the elevated plasminogen activator inhibitor-1 (PAI-1) levels associated with these conditions. Mice genetically deficient in the p55 and p75 TNF-alpha receptors were used to study the roles of these receptors in the expression of PAI-1 in obese (ob/ob) mice, and in lean mice following acute stimulation with TNF-alpha. In ob/ob mice, p55 and p75 tumor necrosis factor-alpha receptors (TNFRs) act cooperatively to induce PAI-1 mRNA in most tissues, including the adipose tissue, kidney, heart, and liver. However, in lean mice, TNF-alpha-induced PAI-1 expression is mediated primarily by the p55 TNFR. Interestingly, PAI-1 mRNA expression in all tissues of the TNF-alpha-treated p75-deficient lean mice was significantly higher than that observed in TNF-alpha-treated wild-type mice. These observations suggest that the p75 TNFR may play a role in attenuating TNF-alpha-induced PAI-1 mRNA expression in acute inflammatory conditions. Our observation that soluble p75 TNFR was elevated in the plasma of TNF-alpha-treated mice in comparison to untreated mice supports this hypothesis. These studies thus provide insights into the TNF-alpha receptors involved in mediating and modulating the expression of PAI-1 in acute and chronic (eg, obesity) inflammatory states associated with elevated TNF-alpha.

The Krüppel-like factor KLF2 inhibits peroxisome proliferator-activated receptor-gamma expression and adipogenesis

Obesity is an important public health problem associated with a number of disease states such as diabetes and arteriosclerosis. As such, an understanding of the mechanisms governing adipose tissue differentiation and function is of considerable importance. We recently reported that the Krüppel-like zinc finger transcription factor KLF15 can induce adipocyte maturation and GLUT4 expression. In this study, we identify that a second family member, KLF2/Lung Krüppel-like factor (LKLF), as a negative regulator of adipocyte differentiation. KLF2 is highly expressed in adipose tissue, and studies in cell lines and primary cells demonstrate that KLF2 is expressed in preadipocytes but not mature adipocytes. Constitutive overexpression of KLF2 but not KLF15 potently inhibits peroxisome proliferator-activated receptor-gamma (PPARgamma) expression with no effect on the upstream regulators C/EBPbeta and C/EBPdelta. However, the expression of C/EBPalpha and SREBP1c/ADD1 (adipocyte determination and differentiation factor-1/sterol regulatory element-binding protein-1), two factors that feedback in a positive manner to enhance PPARgamma function, was also markedly reduced. In addition, transient transfection studies show that KLF2 directly inhibits PPARgamma2 promoter activity (70% inhibition; p < 0.001). Using a combination of promoter mutational analysis and gel mobility shift assays, we have identified a binding site within the PPARgamma2 promoter, which mediates this inhibitory effect. These data identify a novel role for KLF2 as a negative regulator of adipogenesis.

Insulin causes fatty acid transport protein translocation and enhanced fatty acid uptake in adipocytes

Fatty acid uptake into 3T3 L1 adipocytes is predominantly transporter mediated. Here we show that, during 3T3 L1 adipocyte differentiation, expression of fatty acid transport proteins (FATPs) 1 and 4 is induced. Using subcellular membrane fractionation and immunofluorescence microscopy, we demonstrate that, in adipocytes, insulin induces plasma membrane translocation of FATPs from an intracellular perinuclear compartment to the plasma membrane. This translocation was observed within minutes of insulin treatment and was paralleled by an increase in long chain fatty acid (LCFA) uptake. In contrast, treatment with TNF-alpha inhibited basal and insulin-induced LCFA uptake and reduced FATP1 and -4 levels. Thus, hormonal regulation of FATP activity may play an important role in energy homeostasis and metabolic disorders such as type 2 diabetes.

Early events involved in the development of insulin resistance in Zucker fatty rat

AIM

To clarify the mechanism by which insulin resistance develops in obesity, Zucker fatty rats (ZFR) and lean litter mates (ZLR) were temporally subjected to oral glucose tolerance tests (OGTT) at 6 and 15 weeks of age.

METHOD

As candidates for causative factors of insulin resistance, plasma leptin, free fatty acids (FFA) and tumor necrosis factor (TNF)-alpha levels were evaluated.

RESULTS

There was no difference in the body weight between the two groups at 6 weeks of age, but ZFR were significantly heavier than ZLR at 15 weeks of age. At 6 weeks of age, blood glucose levels and area under the curve of glucose (AUCg) during OGTT were not significantly different between the two groups, while plasma insulin levels and area under the curve of insulin (AUCi) in the ZFR group were significantly higher than those in the ZLR group. At 15 weeks of age, the blood glucose levels and AUCg as well as plasma insulin levels and AUCi in the ZFR group during OGTT were significantly higher than those in the ZLR group. The ratio of fasting insulin to glucose in the ZFR group was significantly higher than that in the ZLR group at 6 and 15 weeks of age. Peripheral and portal plasma leptin and FFA levels were significantly higher in ZFR than ZLR both at 6 weeks and 15 weeks of age. Meanwhile, at 6 weeks, plasma TNF-alpha levels and expression of TNF-alpha protein in subcutaneous and visceral fat tissues were similar in both groups; however at 15 weeks, these were significantly higher in the ZFR group than the ZLR group.

CONCLUSION

These results suggest that FFA rather than TNF-alpha may play an important role in early events involved in the development of insulin resistance and TNF-alpha accelerates insulin resistance together with FFA in the later stage.

The mode of action of thiazolidinediones

The thiazolidinediones (TZDs) or 'glitazones' are a new class of oral antidiabetic drugs that improve metabolic control in patients with type 2 diabetes through the improvement of insulin sensitivity. TZDs exert their antidiabetic effects through a mechanism that involves activation of the gamma isoform of the peroxisome proliferator-activated receptor (PPAR gamma), a nuclear receptor. TZD-induced activation of PPAR gamma alters the transcription of several genes involved in glucose and lipid metabolism and energy balance, including those that code for lipoprotein lipase, fatty acid transporter protein, adipocyte fatty acid binding protein, fatty acyl-CoA synthase, malic enzyme, glucokinase and the GLUT4 glucose transporter. TZDs reduce insulin resistance in adipose tissue, muscle and the liver. However, PPAR gamma is predominantly expressed in adipose tissue. It is possible that the effect of TZDs on insulin resistance in muscle and liver is promoted via endocrine signalling from adipocytes. Potential signalling factors include free fatty acids (FFA) (well-known mediators of insulin resistance linked to obesity) or adipocyte-derived tumour necrosis factor-alpha (TNF-alpha), which is overexpressed in obesity and insulin resistance. Although there are still many unknowns about the mechanism of action of TZDs in type 2 diabetes, it is clear that these agents have the potential to benefit the full 'insulin resistance syndrome' associated with the disease. Therefore, TZDs may also have potential benefits on the secondary complications of type 2 diabetes, such as cardiovascular disease.