Adipokines in the treatment of diabetes mellitus and obesity

Mulberry leaves ameliorate diabetes via regulating metabolic profiling and AGEs/RAGE and p38 MAPK/NF-κB pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Mulberry leaves have been used as traditional hypoglycemic medicine-food plant for thousand years in China. According to traditional Chinese medicine theory, type 2 diabetes mellitus (T2DM) belongs to the category of XiaoKe. Presently, the research of mulberry leaf hypoglycemic and lipid-lowering direction is mature, but the curative effects of alkaloids, flavonoids, polysaccharides, and other bioactive ingredients and the related mechanism is still unclear.

AIM OF THE STUDY

This paper aims to study the efficacy and mechanism of alkaloids, flavonoids, polysaccharides, and other bioactive components in mulberry leaves in the treatment of T2DM individually.

MATERIALS AND METHODS

The determination of levels of fasting blood glucose (FBG), triglyceride (TG) and total cholesterol (T-Cho), and pyruvate kinase (PK), hexokinase (HK), and alanine aminotransferase (ALT/GPT) of in plasma of diabetic mice. Urine metabolomics was analyzed by UPLC-QTOF/MS to evaluate differential metabolites from multiple metabolic pathways. The glucose uptake of HepG2 cells and 3T3-L1 cells. Expression of Caspase-3 and caspase-9, inflammatory injury and p38MAPK/NF-κB signaling pathway in GLUTag cells.

RESULTS

Our study revealed alkaloids, flavonoids, and polysaccharides in mulberry leaf could increase the levels of PK, HK, and ALT/GPT, and decrease the levels of TG and T-Cho significantly, and regulate glucose, amino acid, and lipid metabolism. Furthermore, 1-deoxynojirimycin (DNJ) and isoquercitrin (QG) both could increase glucose uptake and promote differentiation of HepG2 cells, increase PPARγ, C/EBPα and SREBP-l expression in 3T3-L1 cells, and inhibit AGEs-induced injury and apoptosis in GLUTag cells, reduce the expression of proteins related to AGEs/RAGE and p38MAPK/NF-κB pathway. Notably, isoquercitrin exhibited more pronounced anti-diabetic efficacy.

CONCLUSIONS

The alkaloids, flavonoids, and polysaccharides from mulberry leaf exhibited hypoglycemic activity through the regulation of glucose, amino acid, and lipid metabolism. 1-DNJ and QG increased glucose uptake and promoted differentiation of HepG2 cells, increased PPARγ, C/EBPα and SREBP-l expression in 3T3-L1 cells, and inhibited AGEs-induced injury and apoptosis in GLUTag cells via the AGEs/RAGE and p38 MAPK/NF-κB pathway.

Angiogenesis in obesity

PURPOSE

Angiogenesis is considered as a major progenitor in the progression of obesity. The current manuscript enumerates the extrinsic role of angiogenesis in obesity.

RESULT

High caloric diet and lack of physical exercise are the most common causes of obesity and related metabolic conditions. A grossly elevated levels of fat in adipose tissue escalate certain complications which further worsen the state of obesity. Enlargement of white adipose tissue (WAT), deposition of fat mass, proliferation of endothelial cells, production of inflammatory cytokines induces the formation of denovo capillaries from parent microvasculature. Also, several intracellular signaling pathways precipitate obesity. Though, angiostatic molecules (endostatin, angiostatin and TNP-470) have been designed to combat obesity and associated complications.

CONCLUSION

Adipose tissue trigger growth of blood capillaries, and in turn adipose tissue endothelial cells promote pre-adipocyte proliferation. Modulation of angiogenesis and treatment with angiostatic substances may have the potential to impair the progression of obesity.

Estimated Association Between Cytokines and the Progression to Diabetes: 10-year Follow-Up From a Community-Based Cohort

CONTEXT

The long-term association between multiple cytokines and progression to diabetes is still uncertain.

OBJECTIVE

To identify which cytokines could predict progression to prediabetes and type 2 diabetes over 10 years.

METHODS

The study included 912 participants aged 40 to 69 years at baseline from the Ansung cohort, part of the Korea Genome Epidemiology Study. At baseline, a 75-g oral glucose tolerance test and 8 cytokines were measured: plasminogen activator inhibitor 1 (PAI-1), resistin, interleukin 6, leptin, monocyte chemoattractant protein 1, tumor necrosis factor alpha, retinol binding protein 4 (RBP4), and adiponectin. People with normal glucose tolerance (NGT, n = 241) and prediabetes (n = 330) were followed-up biennially for 10 years. Multinomial logistic regression analysis was used to evaluate the predictability of cytokines on the new-onset prediabetes and type 2 diabetes.

RESULTS

At 10 years, 38 (15.8%) and 82 (34.0%) of those with NGT had converted to prediabetes and type 2 diabetes, respectively. Of those with prediabetes, 228 (69.1%) had converted to type 2 diabetes. In people with NGT or prediabetes at baseline, the highest tertile of RBP4 was associated with a 5.48-fold and 2.43-fold higher risk of progression to type 2 diabetes, respectively. The odds for converting from NGT to prediabetes in the highest tertile of PAI-1 and the lowest tertile of adiponectin were 3.23 and 3.37, respectively. In people with prediabetes at baseline, those in the highest tertile of resistin were 2.94 time more likely to develop type 2 diabetes (all P < 0.05).

CONCLUSIONS

In this 10-year prospective study, NGT with higher serum RBP4 and PAI-1, and with lower adiponectin were associated with new-onset prediabetes and type 2 diabetes.

Polydatin Inhibits Adipose Tissue Inflammation and Ameliorates Lipid Metabolism in High-Fat-Fed Mice

Polydatin (PD), an active component of Chinese herbs, is reported to have many biological functions, such as cardioprotective actions, anti-inflammatory activities, and antitumor effects. In this study, we investigated the effects of PD on body weight control, glucose and lipid metabolic regulation, and anti-inflammation in a high-fat-diet- (HFD-) induced obese mice model. After treatment of PD (100 mg/kg/d for 4 weeks), HFD mice reduced body weight, retroperitoneal fat mass, and adipose cell sizes; significantly lowered serum total cholesterol triglyceride (TG) and low-density lipoprotein (LDL) levels; and increased high-density lipoprotein (HDL) levels compared with the HFD control mice. Further studies showed that PD downregulated the mRNA and protein expressions of peroxisome proliferator-activated receptor gamma (PPARγ), a transcription factor involving in the regulation of adipocyte differentiation, in the retroperitoneal fat of HFD mice. Additionally, PD significantly upregulated the mRNA and protein expressions of leptin, an adipocyte-derived anorexic hormone that regulates food intake and energy expenditure, in the adipose tissues of HFD mice. Moreover, PD reduced the expression levels of monocyte chemoattractant protein-1 (MCP-1) and tumor necrosis factor-alpha (TNF-α) in the retroperitoneal and epididymal tissues of HFD mice, suggesting that PD prevented adipose tissue inflammation. In conclusion, PD may serve as a pharmaceutic candidate for obesity-related lipid metabolism, anti-inflammation, and body weight loss.

Increase of the Adiponectin/Leptin Ratio in Patients with Obesity and Type 2 Diabetes after Roux-en-Y Gastric Bypass

Bariatric surgery remains the most effective option for achieving important and sustained weight loss. We explored the effects of Roux-en-Y gastric bypass (RYGB) on the circulating levels of adiponectin, leptin, and the adiponectin/leptin (Adpn/Lep) ratio in patients with obesity and type 2 diabetes (T2D). Twenty-five T2D volunteers undergoing RYGB were included in the study, and further subclassified as patients that responded or not to RYBG, regarding remission of T2D. Anthropometric and biochemical variables were evaluated before and after RYGB. Obese patients with T2D exhibited an increase (p < 0.0001) in the Adpn/Lep ratio after RYGB. Changes in the Adpn/Lep ratio correlated better with changes in anthropometric data (p < 0.001) than with the variations of adiponectin or leptin alone. Multiple regression analysis revealed that the change in the Adpn/Lep ratio in patients with T2D was an independent predictor of the changes in body mass index (p < 0.001) and body fat percentage (p = 0.022). However, the Adpn/Lep ratio did not differ between individuals with or without T2D remission after RYGB. In summary, the current study demonstrated that after weight and body fat loss following RYGB, the Adpn/Lep ratio increased in patients with obesity and T2D.

Effect of n-3 Polyunsaturated Fatty Acid Supplementation on Metabolic and Inflammatory Biomarkers in Type 2 Diabetes Mellitus Patients

BACKGROUND

Type 2 diabetes mellitus (T2DM) is accompanied by chronic low-grade inflammation, with an imbalance in the secretion of adipokines and, worsening insulin resistance. Supplementation with n-3 PUFA in T2DM decreases inflammatory markers, the purpose of the study was to investigate the effect of n-3 PUFA supplementation on adipokines, metabolic control, and lipid profile in T2DM Mexican adults.

METHODS

In a randomized, single-blind, placebo-controlled pilot study, 54 patients with T2DM received 520 mg of DHA + EPA-enriched fish-oil (FOG) or a placebo (PG) daily. Baseline and 24-week anthropometric and biochemical measurements included glucose, insulin, glycosylated hemoglobin (Hb1Ac), leptin, adiponectin, resistin, and lipid profile; n-3 PUFA intake was calculated in g/day.

RESULTS

Waist circumference and blood glucose showed significant reductions in the FOG group (p = 0.001 and p = 0.011, respectively). Hb1Ac (p = 0.009 and p = 0.004), leptin (p < 0.000 and p < 0.000), and leptin/adiponectin ratio (p < 0.000 and p < 0.000) decreased significantly in both groups after 24 weeks (FOG and PG respectively). Serum resistin (FOG p < 0.000 and PG p = 0.001), insulin (FOG p < 0.000 and PG p < 0.000), and HOMA-IR (FOG p = 0.000 and PG p < 0.000) increased significantly in both groups. FOG had an overall improvement in the lipid profile with a significant decrease in triacylgycerols (p = 0.002) and atherogenic index (p = 0.031); in contrast, the PG group had increased total cholesterol (p < 0.000), non-HDL cholesterol (p < 0.000), and atherogenic index (p = 0.017).

CONCLUSIONS

We found a beneficial effect of n-3 PUFA supplementation on waist circumference, glucose, Hb1Ac, leptin, leptin/adiponectin ratio, and lipid profile, without significant changes in adiponectin, and increases in resistin, insulin, and HOMA-IR in both groups.

Specific Strains of Lactic Acid Bacteria Differentially Modulate the Profile of Adipokines In Vitro

Obesity induces local/systemic inflammation accompanied by increases in macrophage infiltration into adipose tissue and production of inflammatory cytokines, chemokines, and hormones. Previous studies have shown that probiotics could improve the intestinal dysbiosis induced by metabolic diseases such as obesity, diabetes, and metabolic syndrome. Microorganisms could (directly or indirectly) affect adipokine levels due to their capacity to induce translocation of several intestinal microbial antigens into systemic circulation, which could lead to metabolic endotoxemia or produce immunomodulation in different organs. The aim of the present study was to select non-inflammatory lactic acid bacteria (LAB) strains with the capacity to modulate adipokine secretion by the adipose tissue. We wish to elucidate the role of potential probiotic strains in the regulation of the cross talking between immune cells such as macrophages and adipose cells. Mouse macrophage cell line RAW 264.7 was used for evaluating the ability of 14 LAB strains to induce cytokine production. The LAB strains were chosen based on their previously studied beneficial properties in health. Then, in murine adipocyte culture and macrophage–adipocyte coculture, we determined the ability of these strains to induce cytokines and leptin secretion. Tumor necrosis factor alpha, interleukin 6 (IL-6), IL-10, monocyte chemoattractant protein-1, and leptin levels were measured in cell supernatants. We also performed the detection and quantification of leptin receptor (Ob-Rb) expression in macrophage cell lines stimulated by these LAB strains. Differential secretion profile of cytokines in macrophage cells induced by LAB strains was observed. Also, the levels of Ob-Rb expression diverged among different LAB strains. In LAB-stimulated coculture cells (adipocytes and macrophages), we observed differential production of leptin and cytokines. Furthermore, we detected lower production levels in single culture than cocultured cells. The principal component analysis showed an association between the four clusters of strains established according to their inflammatory profiles and leptin adipocyte production and leptin receptor expression in macrophages. We conclude that coculture is the most appropriate system for selecting strains with the ability to modulate adipokine secretion. The use of microorganisms with low and medium inflammatory properties and ability to modulate leptin levels could be a strategy for the treatment of some metabolic diseases associated with dysregulation of immune response.

Rheumatoid arthritis, insulin resistance, and diabetes

Recent progress in the management of rheumatoid arthritis (RA) is turning attention toward comorbidities, such as diabetes. The objectives of this review are to clarify the links between RA and diabetes and to assess potential effects of disease-modifying antirheumatic drugs (DMARDs) on diabetes. The increased insulin resistance seen in RA is closely linked to the systemic inflammation induced by certain proinflammatory cytokines such as tumor necrosis factor α (TNFα) and interleukin-6. The prevalence of type 2 diabetes is increased in patients with RA. Furthermore, certain DMARDs including hydroxychloroquine, methotrexate, TNFα antagonist, and interleukin-1β antagonists seem to improve the markers of glucose metabolism. In contrast, glucocorticoids tend to adversely affect glycemic control, particularly when taken chronically. Consequently, a crucial yet insufficiently applied rule is that cardiovascular risk factors must be sought and treated routinely, particularly as the choice of the DMARD may affect glucose metabolism.

Identification of active miRNA and transcription factor regulatory pathways in human obesity-related inflammation

Background

Obesity-induced chronic inflammation plays a fundamental role in the pathogenesis of metabolic syndrome (MS). Recently, a growing body of evidence supports that miRNAs are largely dysregulated in obesity and that specific miRNAs regulate obesity-associated inflammation. We applied an approach aiming to identify active miRNA-TF-gene regulatory pathways in obesity. Firstly, we detected differentially expressed genes (DEGs) and differentially expressed miRNAs (DEmiRs) from mRNA and miRNA expression profiles, respectively. Secondly, by mapping the DEGs and DEmiRs to the curated miRNA-TF-gene regulatory network as active seed nodes and connect them with their immediate neighbors, we obtained the potential active miRNA-TF-gene regulatory subnetwork in obesity. Thirdly, using a Breadth-First-Search (BFS) algorithm, we identified potential active miRNA-TF-gene regulatory pathways in obesity. Finally, through the hypergeometric test, we identified the active miRNA-TF-gene regulatory pathways that were significantly related to obesity.

Results

The potential active pathways with FDR < 0.0005 were considered to be the active miRNA-TF regulatory pathways in obesity. The union of the active pathways is visualized and identical nodes of the active pathways were merged.

Conclusions

We identified 23 active miRNA-TF-gene regulatory pathways that were significantly related to obesity-related inflammation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12859-015-0512-5) contains supplementary material, which is available to authorized users.

From leptin to other adipokines in health and disease: facts and expectations at the beginning of the 21st century

This year marks the 20th anniversary of the discovery of leptin, which has tremendously stimulated translational obesity research. The discovery of leptin has led to realizations that have established adipose tissue as an endocrine organ, secreting bioactive molecules including hormones now termed adipokines. Through adipokines, the adipose tissue influences the regulation of several important physiological functions including but not limited to appetite, satiety, energy expenditure, activity, insulin sensitivity and secretion, glucose and lipid metabolism, fat distribution, endothelial function, hemostasis, blood pressure, neuroendocrine regulation, and function of the immune system. Adipokines have a great potential for clinical use as potential therapeutics for obesity, obesity related metabolic, cardiovascular and other diseases. After 20 years of intense research efforts, recombinant leptin and the leptin analog metreleptin are already available for the treatment of congenital leptin deficiency and lipodystrophy. Other adipokines are also emerging as promising candidates for urgently needed novel pharmacological treatment strategies not only in obesity but also other disease states associated with and influenced by adipose tissue size and activity. In addition, prediction of reduced type 2 diabetes risk by high circulating adiponectin concentrations suggests that adipokines have the potential to be used as biomarkers for individual treatment success and disease progression, to monitor clinical responses and to identify non-responders to anti-obesity interventions. With the growing number of adipokines there is an increasing need to define their function, molecular targets and translational potential for the treatment of obesity and other diseases. In this review we present research data on adipose tissue secreted hormones, the discovery of which followed the discovery of leptin 20 years ago pointing to future research directions to unravel mechanisms of action for adipokines.

Association between circulating irisin levels and the promotion of insulin resistance during the weight maintenance period after a dietary weight-lowering program in obese patients

OBJECTIVE

Weight regain is associated with the promotion of insulin resistance. The newly discovered myokine irisin, which was proposed to be involved in the management of insulin sensitivity, could play a role in this process. This study aimed to investigate the association between irisin and reduced insulin sensitivity induced by weight regain.

MATERIALS/METHODS

Insulin sensitivity was evaluated according to the homeostasis model assessment of insulin resistance (HOMA-IR) in 136 obese patients who followed an eight-week hypocaloric diet (30% reduced energy expenditure) to lose weight and was re-evaluated four or six months after treatment. Irisin plasma levels, as well as the levels of leptin, adiponectin, ghrelin and TNF-α, were quantified in a sub-cohort (n=73) from the initially studied patients at baseline (T0), at the diet endpoint (T1) and after the follow-up period (T2).

RESULTS

After a successful dietary intervention to lose weight, 50% of the patients who regained the lost weight during the follow-up period were categorized as insulin resistant (HOMA-IR≥2.5) compared with only 25% of patients who maintained the weight loss (p=0.018). Importantly, in addition to the well-studied hormones leptin and adiponectin, irisin plasma levels were statistically associated with several risk factors for insulin resistance. Indeed, the increased risk of insulin resistance during the follow-up period was related to high irisin levels at baseline (odds ratio=4.2; p=0.039).

CONCLUSIONS

Circulating irisin predicts the insulin resistance onset in association with weight regain. Therefore, irisin could be secreted as an adaptive response to counteract the deleterious effect of excess adiposity on glucose homeostasis.

Comparative effects of gastric bypass and sleeve gastrectomy on plasma osteopontin concentrations in humans

BACKGROUND

Bariatric surgery (BS) has proven to be an effective treatment for morbid obesity. Osteopontin (OPN) is a proinflammatory cytokine involved in the development of obesity. The aim of our study was to determine the effect of weight loss following BS on circulating levels of OPN in humans.

METHODS

Body composition and circulating concentrations of OPN and markers of bone metabolism were determined in obese patients who underwent Roux-en-Y gastric bypass (RYGB; n = 40) or sleeve gastrectomy (SG; n = 11).

RESULTS

Patients who underwent RYGB or SG showed decreased body weight (P < 0.001) and body fat percentage (P < 0.001) as well as lower insulin resistance. However, plasma OPN levels were significantly increased after RYGB (P < 0.001) but remained unchanged following SG (P = 0.152). Patients who underwent RYGB also showed significantly increased C-terminal telopeptide of type-I collagen (ICTP) (P < 0.01) and osteocalcin (P < 0.001) while bone mineral density tended to decrease (P = 0.086). Moreover, OPN concentrations were positively correlated with the bone resorption marker ICTP after surgery. On the other hand, patients who underwent SG showed significantly increased ICTP levels (P < 0.05), and the change in OPN was positively correlated with the change in ICTP and negatively with the change in vitamin D after surgery (P < 0.05).

CONCLUSIONS

RYGB increased circulating OPN levels, while they remained unaltered after SG. The increase in OPN levels after RYGB could be related to the increased bone resorption in relation to its well-known effects on bone of this malabsorptive procedure in comparison to the merely restrictive SG.

Adipokines - removing road blocks to obesity and diabetes therapy

Prevention of obesity and therapeutic weight loss interventions have provided only limited long term success. Therefore there is an urgent need to develop novel pharmacological treatment strategies, which target mechanisms underlying positive energy balance, excessive fat accumulation and adverse fat distribution. Adipokines may have potential for future pharmacological treatment strategies of obesity and metabolic diseases, because they are involved in the regulation of appetite and satiety, energy expenditure, endothelial function, blood pressure, insulin sensitivity, adipogenesis, fat distribution and insulin secretion and others. There are important road blocks on the way from an adipokine candidate to the clinical use a therapeutic compound. Such road blocks include an incomplete understanding of the mechanism of action, resistance to a specific adipokine, side effects of the adipokine and others. This review focuses on the potential of selected adipokines as therapeutic tools or targets and discusses important road blocks, which currently prevent their clinical use.

Mechanisms linking excess adiposity and carcinogenesis promotion

Obesity constitutes one of the most important metabolic diseases being associated to insulin resistance development and increased cardiovascular risk. Association between obesity and cancer has also been well established for several tumor types, such as breast cancer in post-menopausal women, colorectal, and prostate cancer. Cancer is the first death cause in developed countries and the second one in developing countries, with high incidence rates around the world. Furthermore, it has been estimated that 15-20% of all cancer deaths may be attributable to obesity. Tumor growth is regulated by interactions between tumor cells and their tissue microenvironment. In this sense, obesity may lead to cancer development through dysfunctional adipose tissue and altered signaling pathways. In this review, three main pathways relating obesity and cancer development are examined: (i) inflammatory changes leading to macrophage polarization and altered adipokine profile; (ii) insulin resistance development; and (iii) adipose tissue hypoxia. Since obesity and cancer present a high prevalence, the association between these conditions is of great public health significance and studies showing mechanisms by which obesity lead to cancer development and progression are needed to improve prevention and management of these diseases.

Longitudinal variation of circulating irisin after an energy restriction-induced weight loss and following weight regain in obese men and women

OBJECTIVE

The recently discovered peptide irisin has been hypothesized to be a regulator of body metabolism. The objective of this work was to evaluate whether circulating human irisin levels are modulated by body size and changes in adiposity during an energy restriction treatment and the subsequent weight regain.

METHODS

A group of 94 obese patients (50 men, 44 women; 49.4 ± 9.4 years; BMI 35.6 ± 4.5 kg/m(2) ) participated in a weight loss program following an 8-week hypocaloric diet (-30% energy expenditure) with a weight maintenance follow-up. The patients were evaluated at 0, 8, and 24 weeks after starting treatment. In addition, 48 normal-weight subjects (16 men, 32 women; 35.71 ± 8.8 years; BMI 22.9 ± 2.2 kg/m(2) ) participated as controls. Plasma irisin, body weight, body composition, and hormones controlling energy homeostasis were measured.

RESULTS

Irisin levels were higher in obese subjects (353.1 ± 18.6 ng/mL) than in those of normal-weight (198.4 ± 7.8 ng/mL; P ≤ 0.001) and were also higher in men (340.9 ± 20 ng/mL) than in women (267.6 ± 12 ng/mL; P < 0.05). Moreover, irisin plasma levels were significantly correlated with high levels of direct and indirect adiposity markers, such as weight, BMI, waist circumference, and fat mass, as measured by bioimpedance, but not with height or leptin levels. Interestingly, irisin levels paralleled body weight reduction after the dietary treatment (week 8) and again returned to the baseline levels at 24 weeks in those patients regaining the lost weight.

CONCLUSIONS

Irisin strongly reflects body fat mass, suggesting that the irisin circulating levels are conditioned by adiposity level.

Peripheral signalling involved in energy homeostasis control

The alarming prevalence of obesity has led to a better understanding of the molecular mechanisms controlling energy homeostasis. Regulation of energy intake and expenditure is more complex than previously thought, being influenced by signals from many peripheral tissues. In this sense, a wide variety of peripheral signals derived from different organs contributes to the regulation of body weight and energy expenditure. Besides the well-known role of insulin and adipokines, such as leptin and adiponectin, in the regulation of energy homeostasis, signals from other tissues not previously thought to play a role in body weight regulation have emerged in recent years. The role of fibroblast growth factor 21 (FGF21), insulin-like growth factor 1 (IGF-I), and sex hormone-binding globulin (SHBG) produced by the liver in the regulation of body weight and insulin sensitivity has been recently described. Moreover, molecules expressed by skeletal muscle such as myostatin have also been involved in adipose tissue regulation. Better known is the involvement of ghrelin, cholecystokinin, glucagon-like peptide 1 (GLP-1) and PYY(3-36), produced by the gut, in energy homeostasis. Even the kidney, through the production of renin, appears to regulate body weight, with mice lacking this hormone exhibiting resistance to diet-induced obesity. In addition, the skeleton has recently emerged as an endocrine organ, with effects on body weight control and glucose homeostasis through the actions of bone-derived factors such as osteocalcin and osteopontin. The comprehension of these signals will help in a better understanding of the aetiopathology of obesity, contributing to the potential development of new therapeutic targets aimed at tackling excess body fat accumulation.

A C. elegans model to study human metabolic regulation

Lipid metabolic disorder is a critical risk factor for metabolic syndrome, triggering debilitating diseases like obesity and diabetes. Both obesity and diabetes are the epicenter of important medical issues, representing a major international public health threat. Accumulation of fat in adipose tissue, muscles and liver and/or the defects in their ability to metabolize fatty acids, results in insulin resistance. This triggers an early pathogenesis of type 2 diabetes (T2D). In mammals, lipid metabolism involves several organs, including the brain, adipose tissue, muscles, liver, and gut. These organs are part of complex homeostatic system and communicate through hormones, neurons and metabolites. Our study dissects the importance of mammalian Krüppel-like factors in over all energy homeostasis. Factors controlling energy metabolism are conserved between mammals and Caenorhabditis elegans providing a new and powerful strategy to delineate the molecular pathways that lead to metabolic disorder. The C. elegans intestine is our model system where genetics, molecular biology, and cell biology are used to identify and understand genes required in fat metabolism. Thus far, we have found an important role of C. elegans KLF in FA biosynthesis, mitochondrial proliferation, lipid secretion, and β-oxidation. The mechanism by which KLF controls these events in lipid metabolism is unknown. We have recently observed that C. elegans KLF-3 selectively acts on insulin components to regulate insulin pathway activity. There are many factors that control energy homeostasis and defects in this control system are implicated in the pathogenesis of human obesity and diabetes. In this review we are discussing a role of KLF in human metabolic regulation.

Oxidative stress associated to dysfunctional adipose tissue: a potential link between obesity, type 2 diabetes mellitus and breast cancer

Diabetes mellitus and breast cancer are two important health problems. Type 2 diabetes (T2DM) and obesity are closely linked with both being associated with breast cancer. Despite abundant epidemiological data, there is no definitive evidence regarding the mechanisms responsible for this association. The proposed mechanisms by which diabetes affects breast cancer risk and prognosis are the same as the mechanisms hypothesised for the contribution of obesity to breast cancer risk. The obesity-induced inflammation promoted by adipose tissue dysfunction is a key feature, which is thought to be an important link between obesity and cancer. Inflammation induces an increase in free radicals and subsequently promotes oxidative stress, which may create a microenvironment favourable to the tumor development in obese persons. Oxidative stress is also proposed as the link between obesity and diabetes mellitus. Therefore, obesity-related oxidative stress could be a direct cause of neoplastic transformation associated with obesity and T2DM in breast cancer cells. This review is focused on the role of obesity-related oxidative stress in the context of chronic inflammation, on the time of breast cancer onset and progression, which provide targets for preventive and therapeutic strategies in the fields of diabetes and obesity-related breast cancer.

Differential chemoattractant response in adipocytes and macrophages to the action of acylation stimulating protein

Obesity is characterized by chronic low-grade inflammation with increased adipose tissue pro-inflammatory cytokine production. Acylation stimulating protein (ASP) stimulates triglyceride synthesis and glucose transport via its receptor C5L2. Circulating ASP is increased in obesity, insulin resistance and metabolic syndrome. The present study examines the effects of normal (50 nM), high physiological (200 nM) and pathological (600 nM) levels of ASP on inflammatory changes in 3T3-L1 adipocytes and J774 macrophages and the underlying mechanisms involved. Treatment with ASP for 24h increased monocyte chemoattractant protein-1 (MCP1, 800%, P<0.001) and keratinocyte-derived chemokine (KC, >150%, P<0.01) secretion in adipocytes in a dose-dependent manner, with no effect on IL-6 or adiponectin. In macrophages, ASP had no effect on these cytokines. C5a, a ligand for C5L2 and C5aR receptors, differed from ASP. Macrophage-adipocyte coculture increased MCP-1 and adiponectin secretion, and ASP further enhanced secretion (P<0.001 and P<0.05, respectively) at doses of 50 nM and 200 nM. ASP increased Ser(468) and Ser(536) phosphorylation of p65 NFκB in a time- and concentration-dependent manner (P<0.05) as well as phosphorylation of Akt Ser(473) (p=0.02). ASP and insulin stimulations of Ser(536) p65 NFκB phosphorylation were comparable (both p<0.05) but not additive. Both inhibition of PI3kinase (with wortmannin) and NFκB (with BAY11-7085) prevented ASP stimulation of MCP-1 and KC secretion in adipocytes. These findings suggest that ASP, especially at high physiologic doses, may stimulate specific inflammatory cytokines in adipocytes through PI3kinase- and NFκB-dependant pathways, thus further promoting macrophage infiltration and local inflammation in obese adipose tissue.

Six-transmembrane epithelial antigen of prostate 4 and neutrophil gelatinase-associated lipocalin expression in visceral adipose tissue is related to iron status and inflammation in human obesity

PURPOSE

Six-transmembrane epithelial antigen of prostate (STEAP)-4 and neutrophil gelatinase-associated lipocalin (NGAL) are novel adipokines related to iron homeostasis with potential roles in insulin resistance and inflammation. The aim of the present work was to evaluate the effect of obesity and iron status on gene expression levels of STEAP-4 and NGAL in visceral adipose tissue (VAT) and its implication in inflammation.

METHODS

VAT biopsies obtained from 53 subjects were used in the study. Real-time PCR and Western-blot were performed to quantify the levels of STEAP4 and NGAL in VAT as well as the association with other genes implicated in inflammatory pathways. Circulating ferritin and free iron concentrations were also determined.

RESULTS

Obese patients exhibited significantly increased STEAP4 and NGAL mRNA expression levels (P < 0.001) compared to lean subjects. Protein expression levels of NGAL (P < 0.05) and STEAP4 were also higher in the visceral fat depot of obese patients, although protein levels of STEAP4 did not reach statistical significance. A negative correlation (P < 0.05) between free iron concentrations and gene expression levels of both STEAP4 and NGAL was found, while circulating ferritin concentrations were positively correlated (P < 0.05) with NGAL mRNA after body fat (BF) adjustment. Furthermore, a significant positive association between STEAP4 and NGAL gene expression levels with inflammatory markers was also detected (P < 0.01).

CONCLUSION

These findings represent the first observation that STEAP4 and NGAL mRNA and protein levels in human VAT are related to iron status. Moreover, STEAP4 and NGAL are associated with pro-inflammatory markers suggesting their potential involvement in the low-grade chronic inflammation accompanying obesity.

The Adipose Tissue Endocrine Mechanism of the Prophylactic Protective Effect of Pioglitazone in High-Fat Diet-Induced Insulin Resistance

OBJECTIVE: To explore the adipose tissue endocrine mechanism of pioglitazone and its possible prophylactic role in insulin resistance. METHODS: Male Wistar rats were randomized to receive a normal diet (N group), a high-fat insulin resistance-inducing diet (IR group), or a high-fat diet plus treatment with pioglitazone (P group). Glucose tolerance and insulin resistance were tested at weeks 10 and 11 after starting the diet and, at week 12, adipose, liver and skeletal muscle tissue samples were taken. HepG2 cells were cultured with palmitic acid (PA), pioglitazone and PA plus pioglitazone, and RNA interference was used to downregulate adiponectin receptor (AdipoR) 2 in these cells. The mRNA and protein levels of adipokines (resistin and adiponectin), AdipoR1 and 2 and uptake of [3H]-labelled glucose were measured in the HepG2 cells. RESULTS: Resistin and adiponectin in adipose tissue and AdipoR2 in liver tissue were significantly decreased in the IR group compared with the N group. Adiponectin and AdipoR2 were significantly increased and insulin resistance significantly decreased in the P group versus the IR group. In HepG2 cells, AdipoR2 levels and glucose uptake decreased significantly when PA was ≥ 200 μM, but were elevated by pioglitazone. Small interfering RNA-AdipoR2 confirmed glucose uptake in liver was regulated by AdipoR2. CONCLUSIONS: Pioglitazone prevented insulin resistance in rats fed a high-fat diet. Liver AdipoR2-mediated glucose uptake is important in the prophylactic effect of pioglitazone on insulin resistance.

Adiponectin, a key adipokine in obesity related liver diseases

Non-alcoholic fatty liver disease (NAFLD) comprising hepatic steatosis, non-alcoholic steatohepatitis (NASH), and progressive liver fibrosis is considered the most common liver disease in western countries. Fatty liver is more prevalent in overweight than normal-weight people and liver fat positively correlates with hepatic insulin resistance. Hepatic steatosis is regarded as a benign stage of NAFLD but may progress to NASH in a subgroup of patients. Besides liver biopsy no diagnostic tools to identify patients with NASH are available, and no effective treatment has been established. Visceral obesity is a main risk factor for NAFLD and inappropriate storage of triglycerides in adipocytes and higher concentrations of free fatty acids may add to increased hepatic lipid storage, insulin resistance, and progressive liver damage. Most of the adipose tissue-derived proteins are elevated in obesity and may contribute to systemic inflammation and liver damage. Adiponectin is highly abundant in human serum but its levels are reduced in obesity and are even lower in patients with hepatic steatosis or NASH. Adiponectin antagonizes excess lipid storage in the liver and protects from inflammation and fibrosis. This review aims to give a short survey on NAFLD and the hepatoprotective effects of adiponectin.

Diabetes mellitus and insulin resistance in patients with rheumatoid arthritis: risk reduction in a chronic inflammatory disease

OBJECTIVE

To perform a systematic literature review of the potential association among molecular markers of inflammation, alterations in body composition, and insulin resistance (IR), a precursor to type 2 diabetes mellitus (DM), in rheumatoid arthritis (RA) patients. To determine the impact of tumor necrosis factor α (TNFα) as a pivotal proinflammatory cytokine in the pathophysiology of type 2 DM and RA, and the effect of antirheumatic drugs on glycemic control.

METHODS

We performed a search of PubMed to identify articles on IR and body habitus in patients with RA.

RESULTS

Patients with RA had characteristics placing them at high risk for IR and type 2 DM. The incidence and prevalence of type 2 DM in RA was not clearly increased compared with the general population; however, studies suggested that patients with RA are likely to have IR and have increased risk of cardiovascular disease (CVD). The prevalence of type 2 DM and IR could be estimated from reports of risk factors for CVD in RA patients. The TNFα antagonists provided rapid and effective control of RA-related inflammation. Evidence indicated that extended use of TNFα antagonists in RA may provide the additional benefit of improving insulin sensitivity. These treatment-related changes may contribute to an overall reduction in the risk of type 2 DM and CVD in RA patients.

CONCLUSION

Controlling inflammation may improve insulin sensitivity and subsequently reduce the risk of developing type 2 DM in RA patients. This may also reduce the risk of CVD in this high-risk group. Future studies are required to elucidate the relationships between inflammation, body composition, IR, TNFα antagonist use, and the risk of developing type 2 DM in RA patients.

New approach in the interpretation of the adipose tissue

Az elmúlt másfél évtized kutatásai bebizonyították, hogy a zsírszövet aktív endokrin szerv, amely számos hormont választ el. A szerzők a leptin, az adiponektin, a rezisztin, a visfatin és az omentin hormonok működését mutatják be, különös tekintettel az anyagcsere-folyamatokra gyakorolt hatásukra.

Evidence for osteocalcin production by adipose tissue and its role in human metabolism

CONTEXT

The adipose tissue (AT), which is an endocrine organ, is linked to several metabolic abnormalities. Undercarboxylated osteocalcin (ucOCN) regulates insulin and adiponectin secretion.

OBJECTIVE

Our objective was to investigate the involvement of OCN in obesity and to evaluate, in vitro and ex vivo, the role of AT in the modulation of this endocrine circuit.

DESIGN, PATIENTS, AND SETTING

This transversal study involved 83 male subjects, divided according to the World Health Organization body mass index classification, evaluated at Padova's Obesity Outpatient Clinic.

METHODS

OCN, both undercarboxylated (ucOCN) and carboxylated (cOCN) forms, was measured in serum by ELISA. OCN mRNA expression and protein production were measured by quantitative RT-PCR and immunohistochemistry during in vitro adipogenesis and in sc AT (SAT) and omental AT (OAT) from normal adult men. cOCN and ucOCN release by AT in a simple growth medium was verified by ELISA.

RESULTS

Overweight and obese patients had a lower ucOCN and ucOC/OCN ratio. In the whole cohort, ucOCN/OCN ratio was negatively correlated to body mass index (rho = -0.233; P < 0.05). OCN mRNA was present in SAT and OAT and during all stages of adipogenesis, with higher expression in the first steps. Immunohistochemistry confirmed the expression of OCN protein. Both SAT and OAT were able to release cOCN and ucOCN.

CONCLUSIONS

Our data support a pathophysiological link between ucOCN and cOCN balance and obesity. OCN is present in the first phases of adipogenesis but also in human AT ex vivo. AT releases, in vitro, both ucOCN and cOCN, suggesting a possible link between AT and OCN in the regulation of metabolism.

Apelin and APJ regulation in adipose tissue and skeletal muscle of type 2 diabetic mice and humans

Apelin, an adipocyte-secreted factor upregulated by insulin, is increased in adipose tissue (AT) and plasma with obesity. Apelin was recently identified as a new player in the control of glucose homeostasis. However, the regulation of apelin and APJ (apelin receptor) expression in skeletal muscle in relation to insulin resistance or type 2 diabetes is not known. Thus we studied apelin and APJ expression in AT and muscle in different mice models of obesity and in type 2 diabetic patients. In insulin-resistant high-fat (HF)-fed mice, apelin and APJ expression were increased in AT compared with control. This was not the case in AT of highly insulin-resistant db/db mice. In skeletal muscle, apelin expression was similar in control and HF-fed mice and decreased in db/db mice. APJ expression was decreased in both HF-fed and db/db mice. Control subjects and type 2 diabetic patients were subjected to a hyperinsulinemic-euglycemic clamp, and tissues biopsies were obtained before and at the end of the clamp. There was no significant difference in basal apelin and APJ expression in AT and muscle between control and diabetic patients. However, apelin plasma levels were significantly increased in diabetic patients. During the clamp, hyperinsulinemia increased apelin and APJ expression in AT of control but not in diabetic subjects. In muscle, only APJ mRNA levels were increased in control but also in diabetic patients. Taken together, these data show that apelin and APJ expression in mice and humans is regulated in a tissue-dependent manner and according to the severity of insulin resistance.

Transcriptional targets in adipocyte biology

The global burden of metabolic disease demands that we develop new therapeutic strategies. Many of these approaches may center on manipulating the behavior of adipocytes, which contribute directly and indirectly to a host of disease processes including obesity and type 2 diabetes. One way to achieve this goal will be to alter key transcriptional pathways in fat cells, such as those regulating glucose uptake, lipid handling, or adipokine secretion. In this review, we look at what is known about how adipocytes govern their physiology at the gene expression level, and discuss novel ways that we can accelerate our understanding of this area.