Resistin In Adipocytes Research Articles

Effects of rosuvastatin and metformin on resistin levels in subcutaneous, epicardial and perivascular adipose tissues of patients with ischemic heart disease

Abstract The aim of the study was to assess the level of resistin in local fat depots and the possibility of correcting the level of resistin using rosuvastatin and metformin. Methods This study was performed at the Federal State Budgetary Institution's Research Institute for Complex Issues of Cardiovascular Diseases. The study included 84 patients with ischemic heart disease (IHD), who were planned to undergo coronary artery bypass grafting (CABG). The average age of the patients was 63.8 (50.1; 68.6) years. Patients were included in the study after they provided written informed consent. In order to study the combined effect of atorvastatin and metformin on the functional activity of adipocytes in the SAT, EAT, and PVAT, isolated adipocytes were cultured for 24 hours with the addition of drugs at different concentrations: 1 μmol/L atorvastatin (SigmaAldrich, China) + 1 mmol/L metformin (USP, Norway); 5 μmol/L atorvastatin + 10 mmol/L metformin. Then, the expression of mRNA resistin genes (RSTN) was assessed. Statistical analysis was performed using GraphPad Prism 6 (GraphPad Software), nonparametric tests, and multivariate statistics methods. Results The level of RSTN expression in the EAT was the highest compared to the SAT (2.6 times, p=0.0014) and the PVAT (1.9 times, p=0.0017). The level of secretion of the resistin in the culture medium of adipocytes corresponded to the expression of the resistin gene. Cultivation of adipocytes with rosuvastatin showed that low concentrations (1 μmol/L) did not have a significant effect on the functional activity of adipocytes. At the same time, 5 μmol/L rosuvastatin reduced the level of RSTN expression and protein secretion, but only in subcutaneous adipocytes in compared with control. Culturing adipocytes with metformin at a concentration of 10 mmol/L reduced the level of RSTN expression and protein secretion in the culture medium in all three adipose tissues. At the same time, 1 mmol/L metformin did not have a significant effect. The use of a combination of the drugs rosuvastatin and metformin at various concentrations led to a decrease in the RSTN expression in the SAT, EAT, and PVAT, but only when 5 μmol/L rosuvastatin + 10 mmol/L metformin were used. Conclusion Thus, the level of resistin in adipocytes of adipose tissue of patients with IHD is influenced only by rosuvastatin at a concentration of 5 μmol/L and only on adipocytes of adipose tissue, reducing the level of RSTN expression and protein secretion in the culture medium. Metformin was more effective than rosuvastatin and at high concentrations (10 mmol/L) reduced RSTN expression and protein secretion in the culture medium regardless of the localization of adipocytes. The combined use of high concentrations of rosuvastatin (5 μmol/L) and metformin (10 mmol/L) of patients with IHD had a comparable effect with metformin at a concentration of 10 mmol/L. Funding Acknowledgement Type of funding sources: None.

Role of atorvastatin in improving the inflammation-induced adipokine imbalance in mice with acute myocardial infarction

To investigate the effect of acute myocardial infarction (AMI)-activated inflammation on adipokine imbalance and the therapeutic effects of statin. Methods: A total of 32 C57BL/6 mice were divided into 4 groups: a sham group, an AMI group, a low-dose atorvastatin [2 mg/(kg.d)] group and a high-dose atorvastatin [20 mg/(kg.d)] group. AMI models were established by surgical coronary artery ligation. Plasma levels of high sensitive C reaction protein (hs-CRP), adiponectin and resistin were measured. Adiponectin and resistin expressions were determined. In addition, mouse 3T3-L1 preadipocytes in vitro were differentiated and they were stimulated by oxidized low density lipoprotein (ox-LDL). The protein expressions of adiponectin and resistin in adipocytes were detected. The effects of atorvastatin on ox-LDL-induced adipokine imbalance in adipocytes were identified. Results: The plasma levels of hs-CRP and resistin in AMI mice were significantly increased, whereas the plasma levels of adiponectin were remarkably decreased. However, atorvastatin treatment blocked the changes in the plasma levels of hs-CRP, resistin and adiponectin in AMI mice in a dose-dependent manner. Consistent findings regarding the adipose expressions of the two adipokines were obtained. The plasma levels of hs-CRP were positively correlated with resistin but negatively with adiponectin. In vitro study, ox-LDL increased resistin protein and adiponectin expressions in adipocytes, which were dose-dependently reversed by atorvastatin. Conclusion: Inflammation activation in AMI mice leads to adipokine imbalance. Atorvastatin ameliorates the AMI-induced adipokine imbalance via anti-inflammation.

New-found link between microbiota and obesity.

Due to the grave pathological role of obesity, worldwide research is being continued to find out the causative factors involved in it. Recent advances in this field reveal a possible relationship between the compositional pattern of gut microbiota and genesis of obesity. Several study results have shown that short-chain fatty acids (SCFAs, microbiota-induced fermentation products) and lipopolysaccharides (LPS, an integral component of Gram negative microorganisms) play the key role in linking the two. Though several SCFAs are produced as microbiota-fermentation products, three of them, i.e., butyrate, propionate and acetate have been found to be definitely involved in obesity; though individually they are neither purely obesogenic nor antiobesogenic. Out of these, butyrate and propionate are predominantly antiobesogenic. Butyrate, though a major energy source for colonocytes, has been found to increase mitochondrial activity, prevent metabolic endotoxemia, improve insulin sensitivity, possess anti-inflammatory potential, increase intestinal barrier function and protect against diet-induced obesity without causing hypophagia. Propionate has been found to inhibit cholesterol synthesis, thereby antagonizing the cholesterol increasing action of acetate, and to inhibit the expression of resistin in adipocytes. Moreover, both these SCFAs have been found to cause weight regulation through their stimulatory effect on anorexigenic gut hormones and to increase the synthesis of leptin. Unlike butyrate and propionate, acetate, which is substantially absorbed, shows more obesogenic potential, as it acts as a substrate for hepatic and adipocyte lipogenesis. High fat diet increases the absorption of LPS, which, in turn, has been found to be associated with metabolic endotoxemia and to induce inflammation resulting in obesity. Multiple independent and interrelated mechanisms have been found to be involved in such linking processes which are discussed in this review work along with some possible remedial measures for prevention of weight gain and obesity.

The forkhead transcription factor FOXO1 stimulates the expression of the adipocyte resistin gene

Resistin is known as an adipocyte-specific hormone that can cause insulin resistance and decrease adipocyte differentiation. It can be regulated by transcriptional factors, but the possible role of forkhead transcription factor FOXO1 in regulating resistin gene expression is still unknown. Using 3T3 fibroblast and C3H10T1/2 and 3T3-L1 adipocytes, we found that transient overexpression of a non-phosphorylatable, constitutively active FOXO1, but not the wild type of FOXO1 or a DNA binding-deficient FOXO1, activated resistin promoter-directed luciferase expression. However, transient overexpression of a dominant-negative FOXO1 inactivated resistin promoter activity and reduced resistin mRNA expression. These observations indicate that the action of FOXO1 on resistin gene expression requires the activation of FOXO1 and that the effect of FOXO1 depends on the phosphorylation and dephosphorylation of FOXO1. The FOXO1 protein target sites on the resistin promoter were localized to the proximal −3545 to −787bp of 5′-flanking region of the resistin promoter. A chromatin immunoprecipitation assay also showed that FOXO1 bound the resistin promoter at nucleotide regions of −1539 to −1366bp and −1016 to −835bp, but not at the regions of −795 to −632bp. Results of this study suggest that FOXO1 transcription factor likely activates the expression of adipocyte resistin gene via direct association with the upstream resistin promoter.

Resistin affects lipid metabolism during adipocyte maturation of 3T3‐L1 cells

Resistin, an adipose-tissue-specific secretory factor, aggravates metabolic syndrome through impairment of glucose metabolism. Previously, we demonstrated that resistin expression was induced in both 3T3-L1 cells and primary pre-adipocytes derived from Zucker obese rats during the process of differentiation and maturation (Ikeda Y, Hama S, Kajimoto K, Okuno T, Tsuchiya H & Kogure K (2011) Biol Pharm Bull 34, 865-870). However, the biological function of resistin in adipocytes is poorly understood. In the present study, we examined the effects of resistin knockdown on the biological features of 3T3-L1 cells. We found that lipid content was significantly decreased in 3T3-L1 cells transfected with anti-resistin small interfering RNA (siRNA) after adipocyte differentiation. While expression of peroxisome proliferator activated receptor γ and CCAAT/enhancer-binding protein α was not affected, protein expression and transcriptional activity levels of carbohydrate response element binding protein (ChREBP), which upregulates transcription of lipogenic genes, decreased after anti-resistin siRNA treatment. Moreover, gene expression of fatty acid synthase and acetyl-CoA carboxylase 2, which are known to be regulated by ChREBP, were also suppressed by resistin knockdown. In contrast, activity of the fatty acid β-oxidation-regulating protein carnitine palmitoyltransferase 1 increased. These results suggest that resistin knockdown induces suppression of lipid production and activation of fatty acid β-oxidation. Consequently, resistin may affect lipid metabolism during adipocyte maturation.

Lipopolysaccharide inhibits the expression of resistin in adipocytes

Resistin is an adipocytokine leading to insulin resistance. Endotoxin/lipopolysaccharide (LPS) has been reported to decrease the expression of resistin mRNA and protein in both lean and db/db obese mice, although the underlying mechanism remains unclear. Several models such as ex vivo culture of adipose tissues, primary rat adipocytes and 3T3-L1 adipocytes were used to further characterize the effect of LPS on the expression of resistin. LPS attenuated both the resistin mRNA and protein in a time- and dose-dependent manner. In the presence of actinomycin D, LPS failed to reduce the half-life of resistin mRNA, suggesting a transcriptional mechanism. The lipid A fraction is crucial for the inhibition of resistin expression induced by LPS. Pharmacological intervention of c-Jun N-terminal kinase (JNK) reversed the inhibitory effect of LPS. LPS down-regulated CCAAT/enhancer-binding protein α (C/EBP-α; CEBPA) and peroxisome proliferator-activated receptor γ (PPAR-γ; PPARG), while activation of C/EBP-α or PPAR-γ by either over-expressing these transcriptional factors or by rosiglitazone, an agonist of PPAR-γ, blocked the inhibitory effect of LPS on resistin. C/EBP homologous protein (CHOP-10; DDIT3) was up-regulated by LPS, while a CHOP-10 antisense oligonucleotide reversed the decrement of resistin protein induced by LPS. Taken together, these results suggest that LPS inhibits resistin expression through a unique signaling pathway involving toll-like receptor 4, JNK, CHOP-10 and C/EBP-α/PPAR-γ.

Endoplasmic reticulum stress regulates adipocyte resistin expression.

OBJECTIVEResistin is a secreted polypeptide that impairs glucose metabolism and, in rodents, is derived exclusively from adipocytes. In murine obesity, resistin circulates at elevated levels but its gene expression in adipose tissue is paradoxically reduced. The mechanism behind the downregulation of resistin mRNA is poorly understood. We investigated whether endoplasmic reticulum (ER) stress, which is characteristic of obese adipose tissue, regulates resistin expression in cultured mouse adipocytes.RESEARCH DESIGN AND METHODSThe effects of endoplasmic stress inducers on resistin mRNA and secreted protein levels were examined in differentiated 3T3-L1 adipocytes, focusing on the expression and genomic binding of transcriptional regulators of resistin. The association between downregulated resistin mRNA and induction of ER stress was also investigated in the adipose tissue of mice fed a high-fat diet.RESULTSER stress reduced resistin mRNA in 3T3-L1 adipocytes in a time- and dose-dependent manner. The effects of ER stress were transcriptional because of downregulation of CAAT/enhancer binding protein-α and peroxisome proliferator–activated receptor-γ transcriptional activators and upregulation of the transcriptional repressor CAAT/enhancer binding protein homologous protein-10 (CHOP10). Resistin protein was also substantially downregulated, showing a close correspondence with mRNA levels in 3T3-L1 adipocytes as well as in the fat pads of obese mice.CONCLUSIONSER stress is a potent regulator of resistin, suggesting that ER stress may underlie the local downregulation of resistin mRNA and protein in fat in murine obesity. The paradoxical increase in plasma may be because of various systemic abnormalities associated with obesity and insulin resistance.

REGULATORY EFFECTS OF ESTROGEN AND PROGESTERONE ON THE ADIPOSE RESISTIN EXPRESSION

Resistin, a hormone secreted by adipocytes, is suggested to be an important link between obesity and diabetes. In addition, resistin gene expression increases during adipogenesis, and its serum levels are elevated in both genetically or diet-induced obese mice. To elucidate the role of resistin, the endocrine mechanisms that regulate resistin expression will be remarkable. Several studies revealed that resistin expression is regulated by hormone, including glucocorticoids, endothelin-1, etc. Gender difference in resistin expression was also reported, the expression was higher in male than female mice, and was significant enhanced after testosterone treatment in males, but not in females. In addition to resistin, estrogen has been implicated in the regulation of adipocytokines expression and secretion. Progesterone is another sex hormone possessing pivotal physiological functions in estrus cycle. A cluster of studies strongly indicated the regulatory effect of progesterone on estrogen action in various aspects, including neuro-protection, vasodilatation, and carbohydrate metabolism. We hypothesized that the resistin expression is co-regulated by both estrogen and progesterone. The aim of this study was to evaluate the regulatory effect of estrogen and progesterone on adipocyte resistin gene expression in ovariectomized (OVX) rats, isolated rat adipocytes and 3T3-L1 adipocytes in vitro. Our preliminary results show that subcutaneous injection of estradiol benzoate (EB) reduced resistin mRNA levels in adipocytes isolated from the inguinal, parametrial, perirenal, retroperitoneal, or periovarian fat deposits of OVX rats, while an in vitro study showed that estradiol treatment decreased resistin mRNA levels in cultured rat adipocytes. Both in vivo and in vitro studies show that progesterone (P4) has no regulatory effect on resistin mRNA expression in rat adipocytes. In 3T3-L1 adipocytes, both EB and P4 have no effect on resistin mRNA expression. These data suggest that estrogen is a pivotal regulator of resistin gene expression. The underlying mechanism mediate EBregulated resistin expression will be explored in the further studies. (poster)

Adipocyte resistin mRNA levels are down-regulated by laparoscopic ovarian electrocautery in both obese and lean women with polycystic ovary syndrome

The aim of this study was to investigate serum and adipocyte mRNA expression of resistin in lean and obese women with polycystic ovary syndrome (PCOS) before and 3 months after laparoscopic ovarian electrocauterization (LOE). Adipose tissue obtained from 12 women with PCOS (six obese and six lean, body mass index > 27 kg m(-1) as threshold point) before and after LOE was analysed. Gene expression of resistin was measured by semi-quantitative RT-PCR. Ten lean, age-matched healthy women served as controls. Both lean and obese women with PCOS had significantly higher fasting and 2 h insulin and homeostasis model insulin resistance index (HOMA(IR)) values and lower fasting glucose-to-insulin ratios (G(0)/I(0)) than did the controls. The serum levels of glucose and insulin and HOMA(IR) were significantly decreased, and the G(0)/I(0) ratio was significantly increased 3 months after LOE. No difference was found in serum resistin levels between controls and either obese or lean women with PCOS before LOE, nor between PCOS patients before and after LOE. However, resistin mRNA expression levels in both lean and obese women with PCOS before LOE were significantly higher than that in controls and were decreased significantly after LOE back to control levels. Local resistin activity may be actively involved in the pathogenesis of PCOS. LOE reduces insulin resistance and down-regulates resistin mRNA expression in lean and obese women with PCOS.

Proinflammatory cytokine production and insulin sensitivity regulated by overexpression of resistin in 3T3-L1 adipocytes

Resistin is secreted from adipocytes, and high circulating levels have been associated with obesity and insulin resistance. To investigate whether resistin could exert autocrine effects in adipocytes, we expressed resistin gene in 3T3-L1 fibroblasts using a lentiviral vector, and selected several stably-transduced cell lines under blasticidin selection.We observed that 3T3-L1 adipocytes expressing resistin have a decreased gene expression for related transcriptional factors (CCAAT/enhancer binding protein α(C/EBPα) , peroxisome proliferator-activated receptor gamma (PPARγ), and adipocyte lipid binding protein (ALBP/aP2) which is one of target genes for the PPARγ during adipocyte differentiation,. Overexpression of resistin increased the levels of three proinflammatory cytokines, tumor necrosis factor alpha (TNFα), interleukin 6 (IL-6) and monocyte chemoattractant protein-1 (MCP-1), which play important roles for insulin resistance, glucose and lipid metabolisms during adipogenesis. Furthermore, overexpressing resistin in adipocytes inhibits glucose transport 4 (GLUT4) activity and its gene expression, reducing insulin's ability for glucose uptake by 30 %.In conclusion, resistin overexpression in stably transduced 3T3-L1 cells resulted in: 1) Attenuation of programmed gene expression responsible for adipogenesis; 2) Increase in expression of proinflammatory cytokines; 3) Decrease in insulin responsiveness of the glucose transport system. These data suggest a new role for resistin as an autocrine/paracrine factor affecting inflammation and insulin sensitivity in adipose tissue.

Effect of Atorvastatin on in vitro Expression of Resistin in Adipocytes and Monocytes/Macrophages and Effect of Atorvastatin Treatment on Serum Resistin Levels in Patients with Type 2 Diabetes

Resistin is a novel cysteine-rich protein that plays a role in the development of insulin resistance and atherosclerosis. HMG-CoA reductase inhibitors (statins) possess anti-inflammatory properties that are independent of their lipid-lowering action. The aims of this study were to investigate the effect of atorvastatin on expression of resistin in vitro and to determine the effect of 6 months of treatment with atorvastatin on serum levels of resistin in patients with type 2 diabetes. 3T3-L1 adipocytes and human monocytes/macrophages and preadipocytes were incubated with 1 and 10 µmol/l atorvastatin for 24 and 48 h, followed by measurement of resistin mRNA by the quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR). Serum resistin concentration in the patients with type 2 diabetes was measured at baseline and after 6 months of atorvastatin treatment (10 mg/day). qRT-PCR analysis revealed that atorvastatin decreased resistin mRNA expression in a dose- and time-dependent manner. Serum resistin concentration tended to decrease after 6 months of atorvastatin treatment, although this decrease did not reach statistical significance. In conclusion, the findings of our in vitro study contribute to the growing volume of evidence on the anti-inflammatory and anti-atherosclerotic effects of statins, and led us to suggest that statins may control inflammatory responses by inhibiting expression of resistin mRNA. It is necessary to confirm the findings of our in vitro study by an appropriately designed large-scale clinical study.

Resistin mRNA levels are downregulated by estrogen in vivo and in vitro

Resistin, a hormone secreted by adipocytes, is suggested to be an important link between obesity and diabetes. The aim of this study was to evaluate the regulatory effect of estrogen on adipocyte resistin gene expression in ovariectomized (OVX) rats and in isolated rat adipocytes in vitro. Subcutaneous injection of estradiol benzoate reduced resistin mRNA levels in adipocytes isolated from the inguinal, parametrial, perirenal, retroperitoneal, or periovarian fat deposits of OVX rats, while an in vitro study showed that estradiol treatment decreased resistin mRNA levels in cultured rat periovarian fat adipocytes. Results of Western blotting analysis also showed that estrogen decreased adipose resistin contents in vivo and in vitro. These data suggest that estrogen is a pivotal negative regulator of resistin gene expression.

Changes in glycemia by leptin administration or high- fat feeding in rodent models of obesity/type 2 diabetes suggest a link between resistin expression and control of glucose homeostasis.

Resistin is an adipose-derived hormone that has been proposed as a link among obesity, insulin resistance, and diabetes. In agreement with a role of resistin in insulin resistance, the administration of recombinant resistin led to glucose intolerance in mice and impaired insulin action in rat liver. However, the regulation of resistin expression by physiological conditions, hormones, or agents known to modulate insulin sensitivity does not always support the association between resistin and obesity-induced insulin resistance. In the present study we investigated the effects of leptin administration on adipose resistin expression in insulin-resistant and obese ob/ob mice. We show that the expression of resistin mRNA and protein in adipose tissue is lower in ob/ob than in wild-type control mice, in agreement with the reduced adipocyte resistin mRNA level reported in several models of obesity. Leptin administration in ob/ob mice resulted in improvement of insulin sensitivity concomitant with a decrease in resistin gene expression. The lack of effect of leptin on resistin in db/db mice indicated that the leptin inhibitory action on resistin expression requires the long leptin receptor isoform. In addition, we demonstrated that the effect of leptin on resistin expression was centrally mediated. High-fat feeding in C57BL/6J wild-type mice, which is known to induce the development of obesity and insulin resistance, produced an increase in resistin expression. Interestingly, in both ob/ob and high fat-fed mice we obtained a striking positive correlation between glycemia and resistin gene expression. In conclusion, our results demonstrate that leptin decreases resistin expression and suggest that resistin may influence glucose homeostasis.

Serum and adipocyte resistin in polycystic ovary syndrome with insulin resistance.

The aim of this study was to investigate the relationship between resistin and insulin resistance in patients with polycystic ovary syndrome (PCOS). We compared serum resistin levels in 17 PCOS women and 10 lean, healthy, age-matched non-PCOS women and also compared levels of insulin receptor (IR), phosphatidylinositol-3 kinase (PI3-kinase), glucose transporter 4 (GLUT4) protein and resistin mRNA in adipocytes isolated from the omental adipose tissue of five of the PCOS patients and five age- and weight-matched, non-PCOS controls, to look for local defects in insulin action in PCOS. The PCOS group was hyperinsulinaemic and displayed an impaired insulin response in a 75 g oral glucose tolerance test and an abnormal homeostasis model insulin resistance index. Serum resistin levels were similar in PCOS patients and controls; however, resistin mRNA levels were 2-fold higher in adipocytes from PCOS patients. No correlation was found between serum resistin levels and either the BMI or testosterone levels. Western blot analysis showed that adipocyte levels of insulin receptor, PI3-kinase, and GLUT4 were respectively decreased by 56, 39.4 and 54% in PCOS patients compared with controls. These results suggest that overexpression of the resistin gene in adipocytes may be a local determinant factor in the pathogenesis of PCOS.

Transgenic and Recombinant Resistin Impair Skeletal Muscle Glucose Metabolism in the Spontaneously Hypertensive Rat

Increased serum levels of resistin, a molecule secreted by fat cells, have been proposed as a possible mechanistic link between obesity and insulin resistance. To further investigate the effects of resistin on glucose metabolism, we derived a novel transgenic strain of spontaneously hypertensive rats expressing the mouse resistin gene under the control of the fat-specific aP2 promoter and also performed in vitro studies of the effects of recombinant resistin on glucose metabolism in isolated skeletal muscle. Expression of the resistin transgene was detected by Northern blot analysis in adipose tissue and by real-time PCR in skeletal muscle and was associated with increased serum fatty acids and muscle triglycerides, impaired skeletal muscle glucose metabolism, and glucose intolerance in the absence of any changes in serum resistin concentrations. In skeletal muscle isolated from non-transgenic spontaneously hypertensive rats, in vitro incubation with recombinant resistin significantly inhibited insulin-stimulated glycogenesis and reduced glucose oxidation. These findings raise the possibility that autocrine effects of resistin in adipocytes, leading to release of other prodiabetic effector molecules from fat and/or paracrine actions of resistin secreted by adipocytes embedded within skeletal muscle, may contribute to the pathogenesis of disordered skeletal muscle glucose metabolism and impaired glucose tolerance.

Resistin gene expression in human adipocytes is not related to insulin resistance.

Obesity is an important risk factor for the development of insulin resistance and type 2 diabetes. Recently, a newly described circulating hormone resistin, which is expressed primarily in adipocytes, has been shown to antagonize insulin action in mice. Resistin, therefore, has been suggested to play a role in the pathogenesis of insulin resistance. We studied the expression of the resistin gene in primary cultured human adipocytes and preadipocytes. We also examined resistin gene expression in subcutaneous abdominal adipocytes in women (n = 24) over a wide range of body weight and insulin sensitivity. Whereas resistin gene expression was barely detectable in mature adipocytes, it was highly expressed in preadipocytes. Adipogenic differentiation of preadipocytes was associated with a time-dependent down-regulation of resistin gene expression. There was no relationship between body weight, insulin sensitivity, or other metabolic parameters and adipocyte resistin gene expression in the clinical study. Together these findings do not support an important role of adipose-tissue resistin gene expression in human insulin resistance.

Suppressed Gene Expression of Adipocyte Resistin in an Insulin-Resistant Rat Model Probably by Elevated Free Fatty Acids

Resistin, the peptide specifically secreted from adipocytes, is a hormone antagonistic to insulin action and, thus, may serve as a link between human obesity due to adiposity and insulin resistance associated with type 2 diabetes. To test this hypothesis, we studied the gene expression of resistin in adipocytes isolated from rats fed with a fructose diet which induced insulin resistance. Compared to the control rats (C) on a normal chow diet, the fructose-fed rats (F) developed hyperinsulinemia, glucose intolerance, hypertriglyceridemia and hypertension, a profile reminiscent of the syndrome X of patients with non-insulin-dependent diabetes mellitus (NIDDM). The F rats had significantly elevated plasma free fatty acids (FFA), enlarged epididymal fat pads, and increased adipocyte size compared with the C rats. We examined the glucose transport and the relative quantity of resistin mRNA produced in the adipocytes of these two groups of rats. Compared to the C rats, the F rats had a clearly reduced insulin-stimulated glucose transport. The gene expression of resistin and other adipocyte peptides was measured on the mRNA by semiquantitative RT-PCR; the validity of this technique was established in advance with a rat-fasting and then refeeding experiment. The F rats showed a decreased expression of the resistin gene, whereas gene expression of leptin and angiotensinogen in contrast increased. Free fatty acids were found to suppress the expression of resistin gene in normal rat adipocytes. These results demonstrate that an insulin-resistant instance in the fructose diet rat model exists with the decreased gene expression of resistin.

Decreased Resistin Expression in Mice with Different Sensitivities to a High-Fat Diet

The regulation of resistin, a new adipose-derived circulating factor, is the subject of controversy. In particular, the question of its modulation in obesity led to opposite results reported by two different groups. In the current study, we assayed adipocyte resistin mRNA using fluorescent real-time RT-PCR. We studied the expression of resistin in mice which are differently sensitive to diet-induced obesity: the FVB/n strain, which poorly responds to high-fat diet and transgenic mice that express human α2A-AR in adipose tissue in the absence of β3-adrenergic receptor (AR) under the FVB genetic background which are highly sensitive to high-fat diet and develop hyperplastic obesity. We observed that FVB mice, which have no significant increased body weight after an 8-week high-fat diet period, exhibited no alteration of resistin expression. In contrast, the transgenic mice developing high-fat diet-induced obesity exhibited markedly downregulated adipocyte resistin mRNA. We also showed that obesity induced by gold thioglucose injection in FVB/n mice reduces the expression of resistin in isolated adipocytes. This argues for decreased expression of resistin as a hallmark of obesity. Moreover, our data show that feeding a high-fat diet is not a primary determinant of resistin regulation.

Resistin overexpression is induced by a beta3 adrenergic agonist in diet-related overweightness.

Resistin has been suggested as a hormone involved in insulin resistance, which may link obesity with type-2 diabetes. The aim of this work was to evaluate adipocyte resistin mRNA level in high-fat fed animals (cafeteria diet) and the influence of the treatment with the b3-adrenergic agonist tertratolol in overweight animals. Thus, female rats were assigned to three groups, which received control or cafeteria diet and intraperitoneal placebo or cafeteria diet and tertratolol administration for 30 days. Resistin mRNA levels were determined by RT-PCR. The results demonstrate that tertratolol treatment significantly prevented the excessive weight gain induced by the cafeteria regime In the same way, fat depots (perirenal, periovaric and abdominal regions) were similarly influenced by the dietary and pharmacological conditions. Interestingly, the resistin mRNA levels (arbitrary units) in adipose tissue, which remained unaffected in control and overweight animals receiving the cafeteria diet, were doubled by the b3 agonist administration. These data seem to indicate that tertratolol, in diet-related overweightiness, induces overexpression of resistin, which suggests a potential implication of the hormone in the energy balance regulation