Roles of adipocyte derived hormone adiponectin and resistin in insulin resistance of type 2 diabetes

Sex-specific characterization of aortic function and inflammation in a new diet-induced mouse model of metabolic syndrome

Perivascular adipose tissue (PVAT) expansion promotes inflammation and vascular dysfunction in metabolic syndrome (MetS), but the sexual dimorphisms of PVAT are poorly understood. Using a new mouse model of diet-induced MetS, we characterized the aorta and determined the influence of PVAT on vascular function in males and females. Six-week-old C57BL/6 mice were fed either a high-fat diet (43% kcal in food) with high sugar and salt in their drinking water (10% high fructose corn syrup and 0.9% NaCl; HFSS), or a normal chow diet (NCD) for 10 weeks. The aorta was characterized at endpoint using pin myography, flow cytometry, bulk RNA-sequencing, GSEA analysis, and histology. Compared to NCD-fed mice, HFSS-fed mice displayed higher weight gain, fasting blood glucose, systolic blood pressure, aortic fibrosis, and perivascular adipocyte cross-sectional area, regardless of sex (p < .05). Circulating adiponectin levels were also higher in HFSS-fed males compared to NCD males. PVAT enhanced U46619-mediated contraction in HFSS males only. HFSS increased the expression of immune regulation genes in female PVAT and ion transport genes in male PVAT but had no effect on total numbers of immune cells in the aorta in either sex. Despite having similar effects on metabolic parameters in males and females, HFSS caused contrasting effects on vascular function with and without PVAT. These data highlight the sexual dimorphisms of PVAT in regulating the vasculature in healthy and diseased states.

Adipokines in pregnancy

Reproductive success consists of a sequential events chronology, starting with the ovum fertilization, implantation of the embryo, placentation, and cellular processes like proliferation, apoptosis, angiogenesis, endocrinology, or metabolic changes, which taken together finally conduct the birth of healthy offspring. Currently, many factors are known that affect the regulation and proper maintenance of pregnancy in humans, domestic animals, or rodents. Among the determinants of reproductive success should be distinguished: the maternal microenvironment, genes, and proteins as well as numerous pregnancy hormones that regulate the most important processes and ensure organism homeostasis. It is well known that white adipose tissue, as the largest endocrine gland in our body, participates in the synthesis and secretion of numerous hormones belonging to the adipokine family, which also may regulate the course of pregnancy. Unfortunately, overweight and obesity lead to the expansion of adipose tissue in the body, and its excess in both women and animals contributes to changes in the synthesis and release of adipokines, which in turn translates into dramatic changes during pregnancy, including those taking place in the organ that is crucial for the proper progress of pregnancy, i.e. the placenta. In this chapter, we are summarizing the current knowledge about levels of adipokines and their role in the placenta, taking into account the physiological and pathological conditions of pregnancy, e.g. gestational diabetes mellitus, preeclampsia, or intrauterine growth restriction in humans, domestic animals, and rodents.

The circadian rhythm: an influential soundtrack in the diabetes story

Type 2 Diabetes Mellitus (T2DM) has been the main category of metabolic diseases in recent years due to changes in lifestyle and environmental conditions such as diet and physical activity. On the other hand, the circadian rhythm is one of the most significant biological pathways in humans and other mammals, which is affected by light, sleep, and human activity. However, this cycle is controlled via complicated cellular pathways with feedback loops. It is widely known that changes in the circadian rhythm can alter some metabolic pathways of body cells and could affect the treatment process, particularly for metabolic diseases like T2DM. The aim of this study is to explore the importance of the circadian rhythm in the occurrence of T2DM via reviewing the metabolic pathways involved, their relationship with the circadian rhythm from two perspectives, lifestyle and molecular pathways, and their effect on T2DM pathophysiology. These impacts have been demonstrated in a variety of studies and led to the development of approaches such as time-restricted feeding, chronotherapy (time-specific therapies), and circadian molecule stabilizers.

Hepatokines and Adipokines in Metabolic Syndrome

Hepatokines and adipokines are secretory proteins derived from hepatocytes and adipocytes, respectively. These proteins play a main role in the pathogenesis of metabolic syndrome (MetS), characterized by obesity, dysglycemia, insulin resistance, dyslipidemia, and hypertension. Adipose tissue and liver are important endocrine organs because they regulate metabolic homeostasis as well as inflammation because they secrete adipokines and hepatokines, respectively. These adipokines and hepatokines communicate their action through different autocrine, paracrine and endocrine pathways. Liver regulates systemic homeostasis and also glucose and lipid metabolism through hepatokines. Dysregulation of hepatokines can lead to progression toward MetS, type 2 diabetes (T2D), inflammation, hypertension, and other diseases. Obesity is now a worldwide epidemic. Increasing cases of obesity and obesity-associated metabolic syndrome has brought the focus on understanding the biology of adipocytes and the mechanisms occurring in adipose tissue of obese individuals. A lot of facts are now available on adipose tissue as well. Adipose tissue is now given the status of an endocrine organ. Recent evidence indicates that obesity contributes to systemic metabolic dysfunction. Adipose tissue plays a significant role in systemic metabolism by communicating with other central and peripheral organs via the production and secretion of a group of proteins known as adipokines. Adipokine levels regulate metabolic state of our body and are potent enough to have a direct impact upon energy homeostasis and systemic metabolism. Dysregulation of adipokines contribute to obesity, T2D, hypertension and several other pathological changes in various organs. This makes characterization of hepatokines and adipokines extremely important to understand the pathogenesis of MetS. Hepatokines such as fetuin-A and leukocyte cell-derived chemotaxin 2, and adipokines such as resistin, leptin, TNF-α, and adiponectin are some of the most studied proteins and they can modulate the manifestations of MetS. Detailed insight into the function and mechanism of these adipokines and hepatokines in the pathogenesis of MetS can show the path for devising better preventative and therapeutic strategies against this present-day pandemic.

Potential benefits of egg white hydrolysate in the prevention of Hg-induced dysfunction in adipose tissue

Aim: To investigate the effects of egg white hydrolysate (EWH) on the lipid and glycemic metabolism disruption in the white adipose tissue (WAT) dysfunction induced by mercury (Hg). Experimental: Wistar rats were treated for 60 days: control (saline, intramuscular - i.m.); hydrolysate (EWH, gavage, 1 g kg^-1 day^-1); mercury (HgCl₂, i.m., 1^st dose 4.6 μg kg^-1, subsequent doses 0.07 μg kg^-1 day^-1) and hydrolysate-mercury (EWH-HgCl₂). Hg level and histological analyses were performed in epididymal WAT (eWAT), pancreas and liver. GRP78, CHOP, PPARα, PPARγ, leptin, adiponectin, and CD11 mRNA expressions were analyzed in eWAT. The plasma lipid profile, glucose, and insulin levels were measured. Antioxidant status was also evaluated in the plasma and liver. Results: EWH intake prevented the reduced eWAT weight, adipocyte size, insulin levels, and antioxidant defenses and the increased glucose and triglyceride levels induced by Hg exposure; hepatic glutathione levels were higher in rats co-treated with EWH. The increased mRNA expression of CHOP, PPARα, and leptin induced by Hg was reduced in co-treated rats. EWH did not modify the elevated mRNA expression of GRP78, PPARγ and adiponectin in Hg-treated rats. Increased levels of Hg were found in the liver; the co-treatment did not alter this parameter. EWH prevented the morphological and metabolic disorder induced by Hg, by improving antioxidant defenses, inactivating pro-apoptotic pathways and normalizing the mRNA expression of PPARs and adipokines. Its effects enabled an increase in insulin levels and a normal balance between the fat storage and expenditure mechanisms in WAT. Conclusions: EWH may have potential benefits in the prevention and management of Hg-related metabolic disorders.

Sex differences in markers of metabolic syndrome and adipose tissue inflammation in obesity-prone, Osborne-Mendel and obesity-resistant, S5B/Pl rats

The current study examined the role of sex differences in the development of risk factors associated with obesity and its comorbidities using models that differ in their susceptibility to develop obesity, obesity-resistant S5B/Pl (S5B) and obesity-prone Osborne-Mendel (OM) rats. Male and female rats were fed a low fat or high fat diet (HFD) and markers of metabolic syndrome (MetSyn) and expression of inflammatory cytokines/chemokines in visceral and subcutaneous adipose depots were measured. We hypothesized that male and female OM and S5B rats would exhibit differential responses to the consumption of HFD and that females, regardless of susceptibility to develop obesity, would display decreased obesity-related risk factors. Results suggested that consumption of HFD increased adiposity and fasting glucose levels in male OM and S5B rats, decreased circulating adiponectin levels in male S5B rats, and increased body weight and triglyceride levels in male OM rats. The consumption of HFD increased body weight and adiposity in female OM rats, not female S5B rats. Overall, female rats did not meet criteria for MetSyn, while male rats consuming HFD met criteria for MetSyn. Visceral and subcutaneous adipose tissue inflammation was higher in male rats. In visceral adipose tissue, HFD consumption differentially altered expression of cytokines in male and female S5B and OM rats. These findings suggest that resistance to obesity in males may be overridden by chronic consumption of HFD and lead to increased risk for development of obesity-related comorbidities, while female rats appear to be protected from the adverse effects of HFD consumption.

Systemic Metabolic Alterations Correlate with Islet-Level Prostaglandin E2 Production and Signaling Mechanisms That Predict β-Cell Dysfunction in a Mouse Model of Type 2 Diabetes

The transition from β-cell compensation to β-cell failure is not well understood. Previous works by our group and others have demonstrated a role for Prostaglandin EP3 receptor (EP3), encoded by the Ptger3 gene, in the loss of functional β-cell mass in Type 2 diabetes (T2D). The primary endogenous EP3 ligand is the arachidonic acid metabolite prostaglandin E₂ (PGE₂). Expression of the pancreatic islet EP3 and PGE₂ synthetic enzymes and/or PGE₂ excretion itself have all been shown to be upregulated in primary mouse and human islets isolated from animals or human organ donors with established T2D compared to nondiabetic controls. In this study, we took advantage of a rare and fleeting phenotype in which a subset of Black and Tan BRachyury (BTBR) mice homozygous for the Leptin^ob/ob mutation—a strong genetic model of T2D—were entirely protected from fasting hyperglycemia even with equal obesity and insulin resistance as their hyperglycemic littermates. Utilizing this model, we found numerous alterations in full-body metabolic parameters in T2D-protected mice (e.g., gut microbiome composition, circulating pancreatic and incretin hormones, and markers of systemic inflammation) that correlate with improvements in EP3-mediated β-cell dysfunction.

The GEF Cytohesin-2/ARNO Mediates Resistin induced Phenotypic Switching in Vascular Smooth Muscle Cells

The pro-inflammatory adipokine resistin induces a phenotypic switch of vascular smooth muscle cells (VSMC), a process decisive for atherosclerosis, including morphological changes, increased synthetic activity, proliferation and migration. The guanine-exchange factor ARNO (Cytohesin-2) has been shown to be important for morphological changes and migration of other cell types. In this study we dissected the role of ARNO in resistin induced VSMC phenotypic switching and signalling. Firstly, treatment with the cytohesin inhibitor Secin H3 prevented the resistin mediated induction of morphological changes in VSMC. Secondly, Secin H3 treatment as well as expression of an inactive ARNO (EK) reduced resistin induced VSMC synthetic activity, as assessed by matrix metalloproteinase 2 (MMP-2) expression, as well as the migration into a wound in vitro compared to ARNO WT expression. Thirdly, we found ARNO to influence MMP-2 expression and migration via activation of p38 MAPK and the JNK/AP-1 pathway. Interestingly, these processes were shown to be dependent on the binding of PIP₃, as mutation of the ARNO PH-domain inhibited VSMC migration, MMP-2 expression as well as p38 MAPK and JNK signalling. Thus, we demonstrate that ARNO is an important link in resistin dependent cell signalling leading to morphological changes, MMP-2 production and migration of VSMC.

AMPK α1 mediates the protective effect of adiponectin against insulin resistance in INS-1 pancreatic β cells

The fat-derived protein adiponectin is known to reverse the effects of insulin resistance and to lower blood glucose levels. The AMP-activated protein kinase (AMPK) signalling pathway plays a central role in metabolism and energy homeostasis. Here, to investigate the role of AMPK in the protective effect of adiponectin against insulin resistance, we established the model of high-glucose (HG)- and high-lipid (HL)-induced insulin resistance in INS-1 pancreatic β cells. We found that 25mM of glucose and 0.4mM of palmitic acid treatment significantly increased cell apoptosis and impaired insulin secretion in INS-1 cells. However, recombinant human adiponectin dramatically reduced HG- and/or HL-induced cell apoptosis and greatly improved insulin secretion. Interestingly, adiponectin treatment also activated AMPK signalling pathway by increasing the phosphorylation of Thr172 in the AMPK α subunit; 10μM of compound C, a potent AMPK inhibitor, blocked the protective effects of adiponectin against HG/HL-induced insulin resistance. Furthermore, knockout experiments by CRISPR/Cas9 technology showed that AMPK α1, but not AMPK α2, is involved in the protective effects of adiponectin. Taken together, adiponectin reversed the effects of insulin resistance via AMPK α1, which provides a novel insight into the protective mechanism of adiponectin and may be used as a new strategy for the treatment of type 2 diabetes. SIGNIFICANCE OF THE STUDY: Adiponectin can reverse the effects of insulin resistance and lower blood glucose levels. Here, adiponectin reduced HG/HL-induced cell apoptosis and greatly improved insulin secretion. These effects were blocked by AMPK inhibitor, compound C. Specifically, we found that AMPK α1, but not AMPK α2, mediates the protective effects of adiponectin, which provides a novel insight into the protective mechanism of adiponectin against insulin resistance.

Do probiotics effectively ameliorate glycemic control during gestational diabetes? A systematic review

BACKGROUND

Gestational diabetes mellitus (GDM) is defined as any degree of glucose intolerance with onset or first recognition during pregnancy. The aim of this work was to systematically review all studies in which probiotic supplements were used during pregnancy and analyse the effects on GDM.

METHODS

The data were collected using the medical subheading (MeSH) terms: ("diabetes, gestational"[MeSH Terms] OR ("diabetes"[All Fields] AND "gestational"[All Fields]) OR "gestational diabetes"[All Fields] OR ("gestational"[All Fields] AND "diabetes"[All Fields])) AND ("probiotics"[MeSH Terms] OR "probiotics"[All Fields]). The search included original articles written in English/Portuguese and published between 2012 and 2017.

RESULTS

Of the 31 articles identified, seven met the inclusion criteria and were included in this review. In these studies, the sample size ranged from 60 to 373 women with GDM, which was between 24 and 40 weeks of pregnancy (second and third trimesters). Results demonstrated that probiotics used during pregnancy in women with GDM may improve glycaemic control and reduce VDL cholesterol, triglycerides, and inflammatory markers.

CONCLUSIONS

The present systematic review highlights the importance of probiotics for glycemic control and decrease of inflammatory markers in GDM. Further long-term studies should be conducted to elucidate this interaction.

Egg white hydrolysate shows insulin mimetic and sensitizing effects in 3T3-F442A pre-adipocytes

Insulin resistance and inflammation in adipose tissue is a key mechanism underlying metabolic syndrome, a growing health problem characterized by diabetes, obesity and hypertension. Previous work from our research group has demonstrated the potential of egg white ovotransferrin derived bioactive peptides against hypertension, oxidative stress and inflammation in vitro and in vivo. Egg white hydrolysate (EWH) has also shown anti-hypertensive effects in spontaneously hypertensive rats. Given the interplay among hypertension, inflammation, oxidative stress and metabolic syndrome, the objective of the study was to test the EWH on differentiation, insulin signaling and inflammatory responses in 3T3-F442A pre-adipocytes. Our study suggested that EWH could promote adipocyte differentiation as shown by increased lipid accumulation, increased release of adiponectin and upregulation of peroxisome proliferator associated receptor gamma (PPARγ) and CCAAT/ enhancer binding protein alpha (C/EBP-α). In addition to enhanced insulin effects on the upregulation of protein kinase B/Akt phosphorylation, EWH treatment increased extracellular signal regulated kinase 1/2 (ERK1/2) phosphorylation to a level similar to that of insulin, indicating insulin sensitizing and mimetic properties of the EWH. EWH further attenuated cytokine induced inflammatory marker; cyclooxygenase -2 (COX-2) by 48.78%, possibly through the AP-1 pathway by down regulating c-Jun phosphorylation in adipocytes. Given the critical role of adipose in the pathogenesis of insulin resistance and metabolic syndrome, EWH may have potential applications in the prevention and management of metabolic syndrome and its complications.

Molecular cloning of feline resistin and the expression of resistin, leptin and adiponectin in the adipose tissue of normal and obese cats

Resistin, one of the adipokines that has a cycteine-rich C-terminus, is considered to relate to the development of insulin resistance in rats. However, in cats, there is little knowledge regarding resistin. In this study, we cloned the feline resistin cDNA from adipose tissue by RT-PCR. The feline resistin clone contained an entire open reading frame encoding 107 amino acids that had 72.8%, 75.4%, 50.9% and 51.8% homology with bovine, human, mouse and rat homologues, respectively. In both subcutaneous and visceral adipose tissues, the transcription levels of feline resistin mRNA were significantly higher in obese cats than normal cats, and those of feline adiponectin mRNA were significantly lower in obese cats than normal cats. However, there was no difference in the expression of feline leptin between normal and obese cats. On the other hand, in both normal and obese cats, there were no significant differences in resistin, leptin and adiponectin mRNA levels between subcutaneous and visceral adipose tissues. In cats, the altered expression of resistin and adiponectin mRNA with obesity may contribute to the pathogenesis of insulin resistance and subsequent diabetes mellitus. In addition to feline adiponectin, the feline resistin cDNA clone obtained in this study will be useful for further investigation of the pathogenesis of obesity in cats.

Egg consumption and risk of incident type 2 diabetes in men: the Kuopio Ischaemic Heart Disease Risk Factor Study

BACKGROUND

The prevalence of type 2 diabetes (T2D) is increasing around the world. Eggs are a major source of cholesterol, which has been associated with elevated blood glucose and an increased risk of T2D. However, there are limited and conflicting data from prospective population studies on the association between egg consumption and risk of T2D.

OBJECTIVE

We investigated the association between egg consumption and risk of incident T2D in middle-aged and older men from eastern Finland.

DESIGN

The study included 2332 men aged 42-60 y in 1984-1989 at the baseline examinations of the prospective, population-based Kuopio Ischaemic Heart Disease Risk Factor Study. Dietary intakes were assessed with 4-d food records at baseline. Incident T2D was assessed by self-administered questionnaires; by fasting and 2-h oral-glucose-tolerance-test blood glucose measurement at re-examination rounds 4, 11, and 20 y after baseline; and by record linkage to a hospital discharge registry and reimbursement register of diabetes medication expenses. Cox proportional hazards regression analyses were used to estimate associations with the risk of incident T2D. Associations with the metabolic risk markers at baseline and at the 4-y examinations were analyzed by ANCOVA.

RESULTS

During an average follow-up of 19.3 y, 432 men developed T2D. After adjustment for potential confounders, those in the highest compared with the lowest egg intake quartile had a 38% (95% CI: 18%, 53%; P-trend across quartiles <0.001) lower risk of incident T2D. Analyses with metabolic risk markers also suggested an inverse association with fasting plasma glucose and serum C-reactive protein but not with serum insulin. The associations between cholesterol intake and risk of T2D, plasma glucose, serum insulin, and C-reactive protein were mainly nonsignificant, especially after accounting for egg consumption.

CONCLUSION

Higher egg intake was associated with a lower risk of T2D in this cohort of middle-aged and older men.

Antiresistin RNA Oligonucleotide Ameliorates Diet-Induced Nonalcoholic Fatty Liver Disease in Mice through Attenuating Proinflammatory Cytokines

The aim of this study was to determine whether inhibition of resistin by a synthetic antiresistin RNA (oligonucleotide) oligo ameliorates metabolic and histological abnormalities in nonalcoholic fatty liver disease (NAFLD) induced by high-fat diet (HFD) in mice. The antiresistin RNA oligo and a scrambled control oligo (25 mg/kg of body weight) were i.p. injected to HFD mice. Serum metabolic parameters and hepatic enzymes were measured after 4-week treatment. The treatment significantly reduced epididymal fat and attenuated the elevated serum resistin, cholesterol, triglycerides, glucose, and insulin with an improved glucose tolerance test. Antiresistin RNA oligo also normalized serum AST and ALT levels with improved pathohistology of NAFLD. Immunoblotting and qRT-PCR revealed that decreased protein and mRNA expression of resistin in fat and liver tissues of the treated mice were associated with reduction of adipose TNF-α and IL-6 expression and secretion into circulation. mRNA and protein expression of hepatic phosphoenolpyruvate carboxykinase (PEPCK) and sterol regulatory element-binding protein-1c (SREBP-1c) were also significantly decreased in the treated mice. Our results suggest that resistin may exacerbate NAFLD in metabolic syndrome through upregulating inflammatory cytokines and hepatic PEPCK and SREBP-1c. Antiresistin RNA oligo ameliorated metabolic abnormalities and histopathology of NAFLD through attenuating proinflammatory cytokines.

Milk-derived tripeptides IPP (Ile-Pro-Pro) and VPP (Val-Pro-Pro) promote adipocyte differentiation and inhibit inflammation in 3T3-F442A cells

Milk derived tripeptides IPP (Ile-Pro-Pro) and VPP (Val-Pro-Pro) have shown promise as anti-hypertensive agents due to their inhibitory effects on angiotensin converting enzyme (ACE). Due to the key inter-related roles of hypertension, chronic inflammation and insulin resistance in the pathogenesis of metabolic syndrome, there is growing interest in investigating established anti-hypertensive agents for their effects on insulin sensitivity and inflammation. In this study, we examined the effects of IPP and VPP on 3T3-F442A murine pre-adipocytes, a widely used model for studying metabolic diseases. We found that both IPP and VPP induced beneficial adipogenic differentiation as manifested by intracellular lipid accumulation, upregulation of peroxisome proliferator-activated receptor gamma (PPARγ) and secretion of the protective lipid hormone adiponectin by these cells. The observed effects were similar to those induced by insulin, suggesting potential benefits in the presence of insulin resistance. IPP and VPP also inhibited cytokine induced pro-inflammatory changes such as reduction in adipokine levels and activation of the nuclear factor kappa B (NF-κB) pathway. Taken together, our findings suggest that IPP and VPP exert insulin-mimetic adipogenic effects and prevent inflammatory changes in adipocytes, which may offer protection against metabolic disease.

Periodontal treatment with topical antibiotics improves glycemic control in association with elevated serum adiponectin in patients with type 2 diabetes mellitus

OBJECTIVES

Chronic inflammation of periodontitis aggravates glycemic control in type 2 diabetic patients through aggravation of insulin resistance. Increased or decreased release of various inflammatory mediators, such as high sensitivity C-reactive protein (hs-CRP), tumor necrosis factor (TNF)-α, interleukin (IL)-6 and adipokines, such as adiponectin, leptin, and resistin, are presumed to be responsible for developing and progressing insulin resistance. The purpose of this study was to examine the effects of periodontal treatment on glycemic control, serum inflammatory mediators and adipokines in type 2 diabetes patients with periodontitis.

METHODS

Twenty-one type 2 diabetic patients with periodontitis received periodontal treatment with topical antibiotics (intervention group) and 8 patients did not receive periodontal treatment (control group). Periodontal examination, including probing pocket depth (PPD) and bleeding on probing (BOP), and blood sampling were performed at baseline, 2 and 6 months after periodontal treatments. Glycated hemoglobin (HbA1c), hs-CRP, TNF-α, IL-6, adiponectin, leptin, and resistin were analyzed.

RESULTS

In the intervention group, improvements of PPD and BOP, decrease in HbA1c and elevation of serum adiponectin were observed, while in the control group, all parameters were not changed. Generalized linear model revealed that changes of serum adiponectin and TNF-α and change of BOP correlated significantly with the reduction of HbA1c at 6 months after periodontal treatments.

CONCLUSION

The results demonstrated that periodontal treatment improves periodontal status and glycemic control with elevation of serum adiponectin in type 2 diabetic patients. The results suggest that HbA1c is reduced by amelioration of insulin resistance due to elevated serum adiponectin after periodontal treatments.

Adiponectin as a routine clinical biomarker

Adiponectin is a protein synthesized and secreted predominantly by adipocytes into the peripheral blood. However, circulating adiponectin level is inversely related with body weight, especially visceral fat accumulation. The mechanism of this paradoxical relation remains obscure. Low circulating adiponectin concentrations (hypoadiponectinemia; <4 μg/mL) are associated with a variety of diseases, including dysmetabolism (type 2 diabetes, insulin resistance, hypertension, dyslipidemia, metabolic syndrome, hyperuricemia), atherosclerosis (coronary artery disease, stroke, peripheral artery disease), sleep apnea, non-alcoholic fatty liver disease, gastritis and gastro-esophageal reflux disease, inflammatory bowel diseases, pancreatitis, osteoporosis, and cancer (endometrial cancer, postmenopausal breast cancer, leukemia, colon cancer, gastric cancer, prostate cancer). On the other hand, hyperadiponectinemia is associated with cardiac, renal and pulmonary diseases. This review article focuses on the significance of adiponectin as a clinical biomarker of obesity-related diseases. Routine measurement of adiponectin in patients with lifestyle-related diseases is highly recommended.

Hydroethanolic extract of Pyrostegia venusta (Ker Gawl.) Miers flowers improves inflammatory and metabolic dysfunction induced by high-refined carbohydrate diet

ETHNOPHARMACOLOGICAL RELEVANCE

Pyrostegia venusta is used in traditional Brazilian medicine as a general tonic to treat any inflammatory disease. Several studies have demonstrated that medicinal plants constitute a therapeutic approach for the treatment of obesity-related metabolic and inflammatory disarrangement. Accordingly, we investigated the effects of hydroethanolic extract of Pyrostegia venusta flowers (PvHE) supplementation for the treatment of inflammatory and metabolic dysfunction induced by high-refined-carbohydrate (HC) diet.

MATERIAL AND METHODS

The BALB/c mice were fed chow or HC diet for 8 weeks. Part of these animals was fed with HC diet supplemented with PvHE on the 9th week until the 12th week. At the end of the dietary intervention, animals were sacrificed.

RESULTS

We observed that PvHE decreased adiposity and adipocyte area; improved glucose intolerance; reduced serum triacylglycerol levels and systemic inflammatory cells; and also reduced some inflammatory mediators levels in adipose tissue and liver.

CONCLUSION

The results showed that PvHE has beneficial effects and may treat inflammatory and metabolic dysfunction induced by HC diet, that are associated to a negative modulation of the inflammatory process at systemic and local levels.

Interaction between resistin and adiponectin in the proliferation of rat vascular smooth muscle cells

We investigated the effect between resistin and adiponectin on the proliferation of vascular smooth muscle cells (VSMCs). We confirmed that resistin significantly increases the number of rat VSMCs as well as thymidine incorporation with them, whereas adiponectin diminishes resistin-induced cell proliferation. Resistin significantly increased p42/44 mitogen-activated protein kinase (MAPK) phosphorylation within rat VSMCs, whereas adiponectin inhibited resistin-induced MAPK phosphorylation. Moreover, resistin significantly increased c-fos expression, whereas adiponectin suppressed resistin-induced c-fos expression. Cell cycle progression is a tightly controlled event that is negatively regulated by cyclin-dependent kinases inhibitors (CDKIs) such as p53, p21, and p27. Resistin significantly decreased the expression of these CDKIs, whereas adiponectin restored the resistin-induced decrease in CDKIs expression. These effects were abolished in the MAPK inhibitors. In conclusion, resistin plays a role in the development of atherosclerosis, whereas adiponectin may be an important in its prevention in insulin-resistant patients.

Adiponectin mRNA in adipose tissue and its association with metabolic risk factors in postmenopausal obese women

OBJECTIVE

The present study evaluates adiponectin mRNA in visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) and also evaluates its association with metabolic risk factors in postmenopausal obese women.

DESIGN

A case control study was carried out on postmenopausal women (n=68), in which 34 were obese and 34 were non-obese. Blood sample, visceral and subcutaneous adipose tissues were obtained. Adiponectin mRNA levels were measured by Real Time-RT PCR.

RESULTS

The mean (± SEM) serum adiponectin (28.39 ± 2.52 vs. 20.56 ± 1.13), VAT (0.362 ± 0.098 vs. 0.048 ± 0.005) and SAT (0.222 ± 0.035 vs. 0.042 ± 0.007) adiponectin mRNA levels were significantly lower (p<0.001) in obese than non-obese. However, the mean VAT and SAT adiponectin mRNA levels were similar (p>0.05) between the groups. Further, the mean glucose and TG levels were significantly (p<0.01 or p<0.001) higher, while HDL was lower (p<0.01) in obese than non-obese. Furthermore, VAT adiponectin mRNA also showed significant (p<0.05) and inverse association with TG, while direct association with HDL and both the associations were independent of BMI and WC (waist circumference).

CONCLUSION

The BMI and WC independent and significant association of VAT adiponectin mRNA with TG and HDL suggest its potential modulatory role in lipid metabolism in postmenopausal obese women.

Resistin gene expression in visceral adipose tissue of postmenopausal women and its association with insulin resistance

AIM

The present study evaluates resistin mRNA expression in visceral adipose tissue (VAT) and its correlation with insulin resistance (homeostatic model assessment) in postmenopausal obese women.

MATERIALS & METHODS

A total of 68 (nonobese = 34 and obese = 34) age-matched (49-70 years) postmenopausal women were recruited for the study. Fasting blood samples were collected at admission and abdominal VAT were obtained during surgery for gall bladder stones or hysterectomy. Physical parameters (age, height, weight and BMI) were measured. Biochemical parameters (plasma insulin, plasma glucose and serum resistin) were estimated by enzymatic methods. The VAT resistin mRNA expression was evaluated by real-time PCR.

RESULTS

The relative mean (± standard deviation) VAT resistin mRNA expression in postmenopausal obese women lowered significantly by 20.4% compared with postmenopausal nonobese women (0.029 ± 0.011 vs 0.023 ± 0.013; p = 0.047). Furthermore, VAT resistin mRNA expression in postmenopausal obese women was downregulated by 0.69-fold when compared with age-matched postmenopausal nonobese women. Furthermore, the relative VAT resistin mRNA expression in postmenopausal obese women showed significant inverse association with insulin resistance (r = -0.48; p < 0.01) and serum resistin (r = -0.84; p < 0.001), while in postmenopausal nonobese women it did not show any association with both insulin resistance (r = 0.03; p > 0.05) and serum resistin (r = -0.03; p > 0.05).

CONCLUSION

The VAT resistin mRNA expression in postmenopausal obese women is associated to insulin resistance.

Over expression of resistin in adipose tissue of the obese induces insulin resistance

AIM: To compare resistin mRNA expression in subcutaneous adipose tissue (SAT) and its correlation with insulin resistance (IR) in postmenopausal obese women.

METHODS: A total of 68 postmenopausal women (non obese = 34 and obese = 34) were enrolled for the study. The women of the two groups were age matched (49-70 years). Fasting blood samples were collected at admission and abdominal SAT was obtained during surgery for gall bladder stones or hysterectomy. Physical parameters [age, height, weight, body mass index (BMI)] were measured. Biochemical (plasma insulin and plasma glucose) parameters were estimated by enzymatic methods. RNA was isolated by the Trizol method. SAT resistin mRNA expression was done by real time- reverse transcription polymerase chain reaction (RT-PCR) by using Quanti Tect SYBR Green RT-PCR master mix. Data was analyzed using independent Student’s t test, correlation and simple linear regression analysis.

RESULTS: The mean weight (52.81 ± 8.04 kg vs 79.56 ± 9.91 kg; P < 0.001), BMI (20.23 ± 3.05 kg/m²vs 32.19 ± 4.86 kg/m²; P < 0.001), insulin (8.47 ± 3.24 μU/mL vs 14.67 ± 2.18 μU/mL; P < 0.001), glucose (97.44 ± 11.31 mg/dL vs 109.67 ± 8.02 mg/dL; P < 0.001) and homeostasis model assessment index (2.01 ± 0.73 vs 3.96 ± 0.61; P < 0.001) were significantly higher in postmenopausal obese women compared to postmenopausal non obese women. The mean serum resistin level was also significantly higher in postmenopausal obese women compared to postmenopausal non obese women (9.05 ± 5.15 vs 13.92 ± 6.32, P < 0.001). Furthermore, the mean SAT resistin mRNA expression was also significantly (0.023 ± 0.008 vs 0.036 ± 0.009; P < 0.001) higher and over expressed 1.62 fold (up-regulated) in postmenopausal obese women compared to postmenopausal non obese women. In postmenopausal obese women, the relative SAT resistin mRNA expression showed positive (direct) and significant correlation with BMI (r = 0.78, P < 0.001) and serum resistin (r = 0.76, P < 0.001). Furthermore, the SAT resistin mRNA expression in postmenopausal obese women also showed significant and direct association (r = 0.45, P < 0.01) with IR, while in postmenopausal non obese women it did not show any association (r = -0.04, P > 0.05).

CONCLUSION: Increased SAT resistin mRNA expression probably leads to inducing insulin resistance and thus may be associated with obesity-related disorders in postmenopausal obese women.

Green tea catechins ameliorate adipose insulin resistance by improving oxidative stress

Epidemiological data have suggested that drinking green tea is negatively associated with diabetes, and adipose oxidative stress may have a central role in causing insulin resistance, according to recent findings. The aim of this work is to elucidate a new mechanism for green tea's anti-insulin resistance effect. We used obese KK-ay mice, high-fat diet-induced obese rats, and induced insulin resistant 3T3-L1 adipocytes as models. Insulin sensitivity and adipose reactive oxidative species (ROS) levels were detected in animals and adipocytes. The oxidative stress assay and glucose uptake ability assay were performed, and the effects of EGCG on insulin signals were detected. Green tea catechins (GTCs) significantly decreased glucose levels and increased glucose tolerance in animals. GTCs reduced ROS content in both models of animal and adipocytes. EGCG attenuated dexamethasone and TNF-α promoted ROS generation and increased glucose uptake ability. EGCG also decreased JNK phosphorylation and promoted GLUT-4 translocation. EGCG and GTCs could improve adipose insulin resistance, and exact this effect on their ROS scavenging functions.

Relationship between adipocytokines and cardiovascular risk factors in patients with type 2 diabetes mellitus

The aim of this study was to explore the relationship between serum profiles of adiponectin, leptin, resistin and visfatin and traditional and non-traditional cardiovascular risk factors in patients with type 2 diabetes mellitus (T2DM). A total of 85 patients with T2DM and 30 non-diabetic controls were enrolled in the study. Levels of adipocytokines (adiponectin, leptin, resistin and visfatin), lipids (total cholesterol, triglycerides), lipoproteins [HDL-cholesterol, LDL-cholesterol, lipoprotein (a)], apolipoproteins (Apo-A1 and Apo-B), non-traditional cardiovascular risk markers [asymmetric dimethylarginine (ADMA), homocysteine] and the inflammatory marker hs-CRP were measured, and anthropometric variables were determined. Serum adiponectin levels were decreased and leptin, resistin and visfatin levels were increased in T2DM patients compared to controls. They were associated with obesity (BMI), insulin resistance (HOMA-IR) and various markers of glucose/lipid profile, inflammation and endothelial dysfunction markers. These results suggest that decreased serum adiponectin and increased leptin, resistin and visfatin levels in T2DM may be novel biochemical risk factors for cardiovascular complications.

Matrix metalloproteinases modulated by protein kinase Cε mediate resistin-induced migration of human coronary artery smooth muscle cells

BACKGROUND

Emerging evidence showed that resistin induces vascular smooth muscle cell (VSMC) migration, a critical step in initiating vascular restenosis. Adhesion molecule expression and cytoskeletal rearrangement have been observed in this progress. Given that matrix metalloproteinases (MMPs) also regulate cell migration, we hypothesized that MMPs may mediate resistin-induced VSMC migration.

METHODS

Human VSMCs were treated with recombinant human resistin at physiologic (10 ng/mL) and pathologic (40 ng/mL) concentrations for 24 hours. Cell migration was determined by the Boyden chamber assay. MMP and tissue inhibitor metalloproteinase (TIMP) mRNA and protein levels were measured with real-time PCR and ELISA. MMP enzymatic activity was measured by zymography. In another experiment, neutralizing antibodies against MMP-2 and MMP-9 were coincubated with resistin in cultured VSMCs. The regulation of MMP by protein kinase C (PKC) was determined by εV1-2, a selective PKCε inhibitor.

RESULTS

Resistin-induced smooth muscle cell (SMC) migration was confirmed by the Boyden chamber assay. Forty nanograms/milliliter resistin increased SMC migration by 3.7 fold. Additionally, resistin stimulated MMP-2 and -MMP9 mRNA and protein expressions. In contrast, the TIMP-1 and TIMP-2 mRNA levels were inhibited by resistin. Neutralizing antibodies against MMP-2 and MMP-9 effectively reversed VSMC migration. Furthermore, resistin activated PKCε, but selective PKCε inhibitor suppressed resistin-induced MMP expression, activity, and cell migration.

CONCLUSIONS

Our study confirmed that resistin increased vascular smooth muscle cell migration in vitro. In terms of mechanism, resistin-stimulated cell migration was associated with increased MMP expression, which was dependent on PKCε activation.

Association of Insulin Resistance with Serum Interleukin-6 and TNF-α Levels During Normal Pregnancy

Overview:

The purpose of this study was to evaluate the role of Tumor Necrosis Factor-α (TNF-α) in insulin resistance (IR) during normal pregnancy.

Approach:

This cross sectional study was carried out on 86 healthy pregnant women including 26, 23 and 37 individuals in the 1st, 2nd and 3rd trimesters, respectively, and in 21 healthy non pregnant women. Serum TNF-α concentration was measured by Enzyme Linked Immunosorbent Assay (ELISA) method.

Results:

There were significant differences between serum TNF-α and IL-6 levels in pregnant women as compared with maternal healthy controls. There was significant correlation between gestational age and Body Mass Index (BMI) (r = 0.28, P = 0.01). There was no significant correlation between gestational age and insulin resistance (IR). We also did not find correlations between IR and TNF-α and IR and IL-6 in pregnant women.

Conclusion:

In conclusion, our findings suggest that TNF-α and IL-6 are not greatly contributed to pregnancy induced insulin resistance in normal pregnancy.

Cord blood resistin and adiponectin in term newborns of diabetic mothers

INTRODUCTION

Adipose tissue can release hormones into the blood stream in response to specific extracellular stimuli or changes in metabolic status. Resistin, an adipose-secreted factor, is primarily involved in the modulation of insulin sensitivity and adipocyte differentiation. Adiponectin, an adipocyte-specific hormone with insulin sensitizing, anti-inflammatory and anti-atherogenic effects, is reduced in obesity and type II diabetes. The aim of the study was to assess the influence of maternal pre-existing diabetes on cord blood resistin and adiponectin at birth in relation to neonatal anthropometric parameters and cord blood insulin levels.

MATERIAL AND METHODS

A total of 60 term newborns were prospectively enrolled and categorized into three groups: 20 were macrosomic infants of pre-gestational diabetic mothers (group I), 20 were non-macrosomic infants of pre-gestational diabetic mothers (group II) and 20 were healthy non-macrosomic infants born to non-diabetic mothers serving as controls (group III). Infants' anthropometric indices were recorded. Cord blood samples for glucose, insulin, resistin and adiponectin assay, together with maternal glycosylated haemoglobin were obtained.

RESULTS

Serum insulin was increased while resistin and adiponectin were significantly decreased in infants of diabetic mothers (IDMs) compared to the control group. Serum glucose, insulin, resistin and adiponectin were comparable in group I and II. Cord serum resistin correlated positively with cord blood glucose in IDMs in both macrosomic and non-macrosomic groups. Cord serum insulin correlated positively with triceps skinfold thickness in all studied neonates. Cord serum resistin and adiponectin showed no correlation with neonatal anthropometric indices. Multiple regression analysis demonstrated that insulin, resistin and adiponectin together were highly correlated with birth weight, with adiponectin as the one responsible for this positive correlation.

CONCLUSIONS

Infants of diabetic mothers had elevated levels of cord serum insulin and suppressed levels of cord serum resistin and adiponectin, suggesting that the regulation of these metabolic pathways is probably operational before birth. Levels were comparable in both macrosomic and non-macrosomic neonates.

Association of resistin promoter polymorphisms with plasma resistin levels and type 2 diabetes in women and men

This study's objective was to examine the associations between resistin (RETN) polymorphisms, plasma resistin levels, and type 2 diabetes risk. We conducted two nested case-control studies in postmenopausal women (359 incident cases and 359 controls) and middle-aged/elderly men (170 incident cases and 170 controls). Controls were matched (1:1) to cases by age, race, duration of follow-up, and time of blood draw. Circulating resistin levels were higher among carriers of the variant allele for rs34861192 (p<0.0001 for women, p=0.002 for men) but not rs1862513 (p=0.15 for women, p=0.14 for men). Neither polymorphism was significantly associated with risk of type 2 diabetes after adjusting for diabetes risk factors (exercise, smoking status, alcohol intake, family history of diabetes, and matching factors) among women (rs1862513: OR=1.19, 95% CI=0.80-1.77; rs34861192: OR=0.41, 95% CI=0.14-1.19) and men (rs1862513: OR=1.05, 95% CI=0.57-1.95; rs34861192: OR=0.64, 95% CI=0.14-2.89). In conclusion, RETN promoter polymorphism rs34861192 was associated with elevated circulating resistin levels, but rs1862513 was not. Neither polymorphism was associated with an increased risk for type 2 diabetes.

Patients with nonalcoholic fatty liver disease display increased serum resistin levels and decreased adiponectin levels

AIM

Resistin and adiponectin are recently discovered protein hormones, which are produced and secreted by adipocytes. Nonalcoholic fatty liver disease (NAFLD) is a metabolic syndrome, which is associated with obesity. The aim of this study was to evaluate the changes of serum adiponectin and resistin in patients with NAFLD and to determine the relationship between serum adipokine levels and clinicopathologic parameters of NAFLD.

METHODS

Forty-three patients with NAFLD and 43 controls were enrolled in this pair-matched study. Body weight, height, body mass index, abdominal wall fat thickness, waist circumference, hip circumference, and the percentage of body fat were measured. Additionally, serum lipid, glucose, alanine aminotransferase, aspartate aminotransferase, adiponectin, and resistin were determined in all individuals. Serum adiponectin and resistin levels were determined using ELISA kits.

RESULTS

Serum adiponectin levels were significantly lower in patients with NAFLD compared to the control group (control: 2.01+/-1.10 mg/l vs. NAFLD: 1.38+/-0.65 mg/l, P<0.01). Serum resistin levels were significantly elevated in patients with NAFLD compared to the control group (control: 4.70+/-3.30 ng/ml vs. NAFLD: 9.20+/-7.20 ng/ml, P<0.05). Serum adiponectin concentration was negatively correlated with the waist circumference (rho=-0.425), body mass index (rho=-0.329), percentage of body fat (rho=-0.256), abdominal wall fat thickness (rho=-0.226), and fasting blood glucose concentration (rho=-0.242), but was positively correlated with HDL (rho=0.226). Serum resistin concentration was positively correlated with waist circumference (rho=0.237). No correlation was found between resistin levels and blood pressure, fasting blood glucose concentration, triglyceride, total cholesterol, and HDL.

CONCLUSION

NAFLD patients had lower adiponectin levels and higher resistin levels. A positive correlation was found between resistin and waist circumference, whereas a negative correlation was found between adiponectin and waist circumference, body mass index, percentage of body fat, abdominal wall fat thickness, and fasting blood glucose concentration. These data suggested that hypoadiponectinemia and hyperresistinemia might be involved in the development of NAFLD.

Peripheral mononuclear cell resistin mRNA expression is increased in type 2 diabetic women

Resistin has been shown to cause insulin resistance and to impair glucose tolerance in rodents, but in humans its physiological role still remains elusive. The aim of this study was to examine whether resistin mRNA expression in human peripheral mononuclear cells (PBMCs) and its corresponding plasma levels are altered in type 2 diabetes. Resistin mRNA levels were easily detectable in human PBMC, and found to be higher in DM2 compared to healthy women (P = .05). Similarly, mononuclear mRNA levels of the proinflammatory cytokines IL-1β, TNF-α, and IL-6 were all significantly higher in DM2 compared to control women (P < .001). The corresponding plasma resistin levels were slightly, but not significantly, increased in DM2 women (P = .051), and overall, they correlated significantly with BMI (r = 0.406, P = .010) and waist circumference (r = 0.516, P = .003), but not with fasting insulin levels or HOMA-IR. Resistin mRNA expression is increased in PBMC from DM2 women, together with increased expression of the inflammatory cytokines IL-1β, TNF-α, and IL-6, independent of obesity. These results suggest that resistin and cytokines might contribute to the low-grade inflammation and the increased atherogenic risk observed in these patients.

Inverse association between serum resistin and insulin resistance in humans

AIM

To determine how serum concentrations of resistin are distributed in humans in relation to insulin resistance, type 2 diabetes, and obesity.

METHODS

Cross-sectional, descriptive study carried out in a random sample (n=713, 43% men, 18-75 years) of general population of inhabitants of the Canary Islands (Spain). Serum resistin concentration, HOMA2-IR, anthropometric parameters, drug consumption and physical activity were recorded.

RESULTS

There were no differences in resistin concentration between participants with and without diabetes (3.1+/-0.2 vs. 3.2+/-0.1ng/mL; p=0.566), or between obese and non-obese participants (3.1+/-0.1 vs. 3.2+/-0.1ng/mL; p=0.803). Individuals with abdominal obesity (waist-hip ratio [WHR] >or=1 in men or >or=0.9 in women) had lower concentrations of resistin (3.0+/-0.13 vs. 3.4+/-0.1ng/mL; p<0.001). The correlations between resistin and HOMA2-IR (r=-0.231; p<0.001) and between resistin and WHR (r=-0.202; p<0.001) were inverse. Multivariate analysis corroborated the inverse association of this cytokine with HOMA2-IR, WHR and, in women, also retained in the model the direct association between resistin and physical activity and the inverse association between resistin and antihypertensive agents.

CONCLUSIONS

In this population resistin is inversely associated with insulin resistance and abdominal obesity.

Total and high-molecular-weight adiponectin and resistin in relation to the risk for type 2 diabetes in women

BACKGROUND

Adiponectin and resistin are recently discovered adipokines that may provide a molecular link between adiposity and type 2 diabetes.

OBJECTIVE

To evaluate whether total and high-molecular-weight adiponectin and resistin are associated with future risk for type 2 diabetes, independent of obesity and other known diabetes risk factors.

DESIGN

Prospective, nested, case-control study.

SETTING

United States.

PARTICIPANTS

1038 initially healthy women of the Nurses' Health Study who developed type 2 diabetes after blood sampling (1989 to 1990) through 2002 and 1136 matched control participants.

MEASUREMENTS

Plasma concentrations of total and high-molecular-weight adiponectin and resistin.

RESULTS

In multivariate models including body mass index, higher total and high-molecular-weight adiponectin levels were associated with a substantially lower risk for type 2 diabetes (odds ratio [OR] comparing the highest with the lowest quintiles, 0.17 [95% CI, 0.12 to 0.25] for total adiponectin and 0.10 [CI, 0.06 to 0.15] for high-molecular-weight adiponectin). A higher ratio of high-molecular-weight to total adiponectin was associated with a statistically significantly lower risk even after adjustment for total adiponectin (OR, 0.45 [CI, 0.31 to 0.65]). In the multivariate model without body mass index, higher resistin levels were associated with a higher risk for diabetes (OR, 1.68 [CI, 1.25 to 2.25]), but the association was no longer statistically significant after adjustment for body mass index (OR, 1.28 [CI, 0.93 to 1.76]).

LIMITATION

The findings apply mainly to white women and could be partly explained by residual confounding from imperfectly measured or unmeasured variables.

CONCLUSION

Adiponectin is strongly and inversely associated with risk for diabetes, independent of body mass index, whereas resistin is not. The ratio of high-molecular-weight to total adiponectin is related to risk for diabetes independent of total adiponectin, suggesting an important role of the relative proportion of high-molecular-weight adiponectin in diabetes pathogenesis.

Obesity reduces the bioavailability of nitric oxide in juveniles

OBJECTIVE

There is growing evidence that nitric oxide (NO) is critically involved in obesity and its clinical consequences like cardiovascular disease, hypertension and diabetes. We hypothesize that NO is already involved in the pathophysiology of juvenile obesity. We here determined the role of NO, its metabolites arginine and citrulline in obese and normal weight children.

DESIGN

We investigated 57 obese and 57 normal weight age- and gender-matched juveniles. Various clinical parameters as well as body measurements and intima media thickness were determined.

RESULTS

Obese juveniles revealed highly significant alterations in the NO pathway. NOX and citrulline were decreased in obese compared to normal weight juveniles and negatively correlated with body weight. Arginine was increased in obese juveniles and positively correlated with body weight. We found a significant negative correlation between NOX and oxidized low-density lipoprotein. Analysis of gamma-aminobutyric acid (GABA) revealed correlations with the NO pathway as NOX and citrulline were negatively correlated with GABA and arginine showed a positive correlation.

CONCLUSION

We show here that NO and its metabolites arginine and citrulline are already involved in juvenile obesity that may contribute to atherogenesis via reduced bioavailability of NO. Moreover, we identify GABA as a new parameter in the mechanism of obesity-related NO reduction.

A paradox: Insulin inhibits expression and secretion of resistin which induces insulin resistance

AIM: To confirm whether insulin regulates resistin expression and secretion during differentiation of 3T3-L1 preadipocytes and the relationship of resistin with insulin resistance both in vivo and in vitro.

METHODS: Supernatant resistin was measured during differentiation of 3T3-L1 preadipocytes. L6 rat myoblasts and hepatoma cell line H4IIE were used to confirm the cellular function of resistin. Diet-induced obese rats were used as an insulin resistance model to study the relationship of resistin with insulin resistance.

RESULTS: Resistin expression and secretion were enhanced during differentiation 3T3-L1 preadipocytes. This cellular differentiation stimulated resistin expression and secretion, but was suppressed by insulin. Resistin also induced insulin resistance in H4IIE hepatocytes and L6 myoblasts. In diet-induced obese rats, serum resistin levels were negatively correlated with insulin sensitivity, but not with serum insulin.

CONCLUSION: Insulin can inhibit resistin expression and secretion in vitro, but insulin is not a major regulator of resistin in vivo. Fat tissue mass affects insulin sensitivity by altering the expression and secretion of resistin.

Serum concentrations of adiponectin and characterization of adiponectin protein complexes in dogs

OBJECTIVE

To assess serum concentrations of adiponectin and characterize adiponectin protein complexes in healthy dogs.

ANIMALS

11 healthy dogs.

PROCEDURES

Sera collected from 10 dogs were evaluated via velocity sedimentation and ultracentrifugation, SDS-PAGE, western immunoblotting, and radioimmunoassay. Visceral adipose tissue (approx 90 g) was collected from the falciform ligament of a healthy dog undergoing elective ovariohysterectomy, and adiponectin gene expression was assessed via a real-time PCR procedure.

RESULTS

Adiponectin gene expression was detected in visceral adipose tissue. Serum adiponectin concentrations ranged from 0.85 to 1.5 microg/mL (mean concentration, 1.22 microg/mL). In canine serum, adiponectin was present as a multimer, consisting of a low-molecular-weight complex (180 kd); as 3 (180-, 90-, and 60-kd) complexes under denaturing conditions; as 2 (90- and 60-kd) complexes under reducing conditions; and as a dimer, a monomer, and globular head region (60, 30, and 28 kd, respectively) under reducing-denaturing conditions. It is likely that adiponectin also circulates as a high-molecular-weight (360- to 540-kd) complex in canine serum, but resolution of this complex was not possible via SDS-PAGE.

CONCLUSIONS AND CLINICAL RELEVANCE

After exposure to identical experimental conditions, adiponectin protein complexes in canine serum were similar to those detected in human and rodent sera. Circulating adiponectin concentrations in canine serum were slightly lower than concentrations in human serum. Adiponectin gene expression was identified in canine visceral adipose tissue. Results suggest that adiponectin could be used as an early clinical marker for metabolic derangements, including obesity, insulin resistance, and diabetes mellitus in dogs.

New Adipokines Linked to Obesity and Obesity-Related Diseases

Adipose tissue plays essential metabolic roles, not only serving as massive energy reservoir but also producing and releasing hormones and other biologically active molecules that regulate several metabolic activities. Adipocytes secrete a variety of factors, referred to as adipokines. Current research has identified over 50 adipocyte-secreted factors, and more are yet to be discovered. In obesity, increased production of pro-inflammatory adipokines and diminished synthesis of anti-inflammatory factors impacts on multiple functions such as appetite and energy balance, immunity, insulin sensitivity, angiogenesis, blood pressure and lipid metabolism. All are linked with higher risk for cardiovascular disease. Various adipocyte-released compounds profoundly affect insulin sensitivity and might potentially link obesity-related diseases, including atherosclerotic cardiovascular disease, type 2 diabetes mellitus, hypertension, dyslipidaemia and insulin resistance. This review aims to present some of the recent topics of selected adipokine research that may be of particular importance.