A cysteine-rich adipose tissue-specific secretory factor inhibits adipocyte differentiation

Involvement of iNOS and NO in TNF-alpha-downregulated resistin gene expression in 3T3-L1 adipocytes

OBJECTIVE

In order to characterize the regulation of resistin gene expression, we explore the effect of tumornecrosis factor-alpha (TNF-alpha) on resistin mRNA expression and its underlying mechanism in 3T3-L1 adipocytes.

METHODS AND PROCEDURES

Differentiated 3T3-L1 adipocytes were treated for 24 h with 0-10 ng/ml of TNF-alpha or with 2.5 ng/ml of TNF-alpha for 0-24 h, and then resistin mRNA levels were measured by northern blotting. To further explore the involvement of nitric oxide (NO) in TNF-alpha-regulated resistin expression, the effect of the NO donor, sodium nitroprusside (SNP), on resistin mRNA levels in adipocytes and the effect of the nitric oxide synthase (NOS) inhibitors, N(G)-nitro-L-arginine methyl ester (L-NAME), and S,S'-1,3-phenylene-bis(1,2-ethanediyl)-bis-isothiourea.2HBr (PBITU), on the TNF-alpha effect in adipocytes were examined. The effects of TNF-alpha on inducible NOS (iNOS) protein expression in adipocytes were also measured by western blotting.

RESULTS

Our results showed that TNF-alpha caused a dose-dependent reduction in resistin mRNA levels. This effect seemed to be associated with the TNF-alpha-induced expression of iNOS. The results showed that TNF-alpha induced iNOS expression and release of NO after 24-h treatment of differentiated 3T3-L1 adipocytes. Pretreatment with L-NAME and PBITU significantly reversed the TNF-alpha-induced downregulation of resistin expression, while treatment with SNP mimicked the inhibitory effect of TNF-alpha on resistin expression. In addition, pretreatment with protein tyrosine kinase (PTK) inhibitors, genistein and AG-1288, prevented TNF-alpha-induced iNOS expression and subsequent resistin downregulation.

DISCUSSION

Our data suggest that TNF-alpha suppresses resistin expression by inducing iNOS expression, thus causing overproduction of NO, which downregulates resistin gene expression.

Adipokines: the missing link between insulin resistance and obesity

White adipose tissue was believed to be just an energy-storage organ, but it is now recognized to be an active participant in energy homoeostasis and physiological functions such as immunity and inflammation. Macrophages are components of adipose tissue and actively participate in its activities. Adipose tissue is known to express and secrete a variety of products known as 'adipokines', including leptin, adiponectin, resistin and visfatin, as well as cytokines and chemokines such as tumor necrosis factor-alpha, interleukin-6 and monocyte chemoattractant protein-1. The release of adipokines by either adipocytes or adipose tissue-infiltrated macrophages leads to a chronic subinflammatory state that could play a central role in the development of insulin resistance and type 2 diabetes, and the increased risk of cardiovascular disease associated with obesity.

Adipocytokine and ghrelin levels in relation to cardiovascular disease risk factors in women at midlife: longitudinal associations

BACKGROUND

There are limited data concerning the relationships between changes in adipocytokines and cardiovascular disease (CVD) risk factors.

OBJECTIVE

To examine the longitudinal associations between leptin, adiponectin, resistin and ghrelin levels and CVD risk factor levels in women at midlife.

DESIGN

Prospective, observational study.

SUBJECTS AND MEASUREMENTS

Leptin, adiponectin, resistin, ghrelin levels and CVD risk factors were measured in specimens collected from 40 women at 3 points in time corresponding to the pre-, peri- and postmenopause stages of their natural menopause transition.

RESULTS

In longitudinal analyses adjusted for CVD risk factors and leptin at the previous menopausal stage, aging, education, smoking and physical activity, greater increases in leptin over the menopause transition were associated with greater decreases in high-density lipoprotein cholesterol (HDL-c) and greater increases in diastolic blood pressure, glucose, insulin and insulin resistance (all P < 0.05). Larger decreases in adiponectin over the menopause transition were associated with greater increases in systolic blood pressure, insulin and insulin resistance and with greater decreases in HDL-c. Greater increases in ghrelin levels over the menopausal transition were associated with greater low-density lipoprotein cholesterol increases (P = 0.014). Resistin was not associated with CVD risk factor changes.

CONCLUSION

There were significant adverse associations of adipocytokines and ghrelin with multiple CVD risk factor changes in women across midlife. Given that this time period is dynamic for CVD risk, these data underscore the need for additional prospective studies.

Analysis of genetic variations in the resistin gene shows no associations with obesity in women

Resistin is thought to be involved in the development of obesity and insulin resistance. Polymorphisms in the gene encoding resistin could contribute to this link, but different studies have yielded contradictory results. In this study, we investigated whether polymorphisms in resistin are involved in the development of obesity in a Belgian female population. We selected three single-nucleotide polymorphisms (SNPs; rs1862513, rs3745367, and rs3745369) and compared their genotype and allele frequencies between female obese patients (N = 541) and control individuals (N = 235). This analysis showed association with neither obesity for any of the variants nor with the haplotypes of these SNPs. Furthermore, we also investigated whether these variants have an influence on BMI. After Kruskal-Wallis analysis, we found that there was no difference in BMI between the genotypes for all variants. Together, these results suggest that these variants in resistin are not associated with obesity in the female population.

Adiponectin and resistin response in the onset of obesity in male and female rats

OBJECTIVE

Studying the sex-dependent response of adiponectin and resistin adipose tissue expression and circulating levels in the onset of dietary obesity.

METHODS AND PROCEDURES

Male and female 4-week-old Wistar rats were fed a control or cafeteria (CAF) diet for 15 days. Body weight and energy intake were monitored. Gonadal (visceral), retroperitoneal (visceral) and inguinal (subcutaneous) white adipose tissue (WAT) depots were collected. Serum adiponectin and resistin and tissue mRNA levels were analyzed by western blot and reverse transcription-PCR, respectively. Serum levels of insulin, tumor necrosis factor-alpha (TNFalpha), and glucose were measured by enzyme-linked immunosorbent assay and by a glucose sensor. Insulin resistance was assessed by the homeostasis model assessment (HOMA).

RESULTS

Energy intake and adipose-tissue weight were significantly increased in the CAF rats, with higher increase in visceral than in subcutaneous fat, especially in females. The effective production of adiponectin and resistin (total levels adjusted per WAT weight) was decreased in the CAF groups, more markedly in females for adiponectin. This decrease was associated with the tendency to lower WAT mRNA levels for resistin, but not for adiponectin. Insulin levels were not significantly altered. Fasting glucose was slightly increased in CAF females. HOMA score was not significantly increased by CAF feeding, although it tended to be increased in a few CAF females.

DISCUSSION

Decrease of WAT adiponectin and resistin-effective production seems an early response to obesity development under a high-fat (CAF) diet, with sex-associated differences. This can probably be related to a physiological role of both adipokines modulating the insulin signaling system.

A polymorphism in the resistin gene promoter is related to increased C-reactive protein levels in patients with coronary artery disease

BACKGROUND

Resistin, a novel adipocyte-derived peptide, has been linked to inflammatory process and coronary artery disease (CAD). The -420C>G polymorphism located in the resistin gene (RETN) promoter has recently been suggested to play a potential role in proinflammatory conditions (e.g., atherogenesis). However, whether this polymorphism has any effect on the inflammatory process in patients with stable CAD is unclear.

METHODS

The RETN -420C>G polymorphism was determined by using PCR-restriction fragment length polymorphism. Plasma lipid profiles, glucose and high-sensitivity C-reactive protein (hs-CRP) were measured in fasting state.

RESULTS

Patients with variant genotypes (CG+GG) had significantly higher levels of hs-CRP than CC carriers (adjusted p<0.001). In addition, the variant genotypes were observed to be independently associated with higher hs-CRP levels (>3 mg/L, p=0.004). However, no association was found between this polymorphism and plasma lipids or glucose levels.

CONCLUSION

Our data suggest that the RETN -420C-to-G variant is associated with increased CRP levels in patients with stable CAD, suggesting that the RETN -420C>G polymorphism may be potentially involved in the inflammatory component of atherogenesis through an enhanced production of CRP.

Serum resistin is reduced by glucose and meal loading in healthy human subjects

Resistin is an adipokine that induces insulin resistance in mice; serum concentrations are decreased by fasting and increased by feeding. Adiponectin, another adipokine, improves insulin sensitivity. The aims of this study were to determine the effects of glucose and meal loading on serum resistin and total and high-molecular weight (HMW) adiponectin in humans and to explore potential determinants of fasting serum resistin and of changes in resistin. Serum resistin and total and HMW adiponectin were measured by enzyme-linked immunosorbent assay in young, lean, nondiabetic subjects during 75-g oral glucose tolerance test (OGTT) and meal tolerance test (MTT). Resistin single nucleotide polymorphism (SNP) -420 was typed. Serum resistin was decreased at 60 and 120 minutes during OGTT compared with baseline (n = 36, 1-way repeated-measures analysis of variance, P < .0001; Scheffe, P = .0457 and P < .0001, respectively). Serum resistin was also reduced at 240 minutes during MTT (n = 33, 1-way repeated measures analysis of variance, P < .0001; Scheffe, P = .0002). Multiple regression analysis adjusted for age, sex, and body mass index revealed that the reductions in serum resistin were dependent on baseline resistin levels. Subjects with greater baseline concentrations of resistin experienced more pronounced declines in resistin (OGTT, unstandardized regression coefficient (beta) = -0.19, P = .0005; MTT, beta = -0.63, P < .0001). Serum total and HMW adiponectin was unchanged. Fasting serum resistin was positively correlated with the G allele number of SNP -420 (beta = 7.70, P = .01) and white blood cell count (beta = 0.007, P = .0001) adjusted for age, sex, and body mass index. Therefore, in young, lean, nondiabetic humans, serum resistin was reduced by glucose and meal loading; the reduction in resistin was greater in subjects with higher fasting resistin. Fasting resistin was correlated with SNP -420 and white blood cell count.

Long-term effects of central leptin and resistin on body weight, insulin resistance, and beta-cell function and mass by the modulation of hypothalamic leptin and insulin signaling

To determine the long-term effect of central leptin and resistin on energy homeostasis, peripheral insulin resistance, and beta-cell function and mass, intracerebroventricular (ICV) infusion of leptin (3 ng/h), resistin (80 ng/h), leptin plus resistin, and cerebrospinal fluid (control) was conducted by means of an osmotic pump for 4 wk on normal rats and 90% pancreatectomized diabetic rats fed 40% fat-energy diets. Overall, the effects were greater in diabetic rats than normal rats. Leptin infusion, causing a significant reduction in food intake, decreased body weight and epididymal fat. However, resistin and leptin plus resistin reduced epididymal fat with decreased serum leptin levels in comparison with the control. Unlike serum leptin, only resistin infusion lowered serum resistin levels. Central leptin increased glucose infusion rates during euglycemic hyperinsulinemic clamp and suppressed hepatic glucose production in the hyperinsulinemic state in comparison with the control. However, central leptin did not affect glucose-stimulated insulin secretion and beta-cell mass. Central resistin infusion also increased peripheral insulin sensitivity, but not as much as leptin. Unlike leptin, resistin significantly increased first-phase insulin secretion during hyperglycemic clamp and beta-cell mass by augmenting beta-cell proliferation. These metabolic changes were associated with hypothalamic leptin and insulin signaling. ICV infusion of leptin potentiated signal transducer and activator of transcription 3 phosphorylation and attenuated AMP kinase in the hypothalamus, but resistin had less potent effects than leptin. Leptin enhanced insulin signaling by potentiating IRS2-->Akt pathways, whereas resistin activated Akt without augmenting insulin receptor substrate 2 phosphorylation. In conclusion, long-term ICV infusion of leptin and resistin independently improved energy and glucose homeostasis by modulating in different ways hypothalamic leptin and insulin signaling.

Role of resistin as a marker of inflammation in systemic lupus erythematosus

INTRODUCTION

Resistin is a cystein-rich secretory adipokine. It is proposed to have proinflammatory properties in humans. The aim of this study was to determine associations between serum levels of resistin and markers of inflammation and bone mineral density (BMD) in female patients with systemic lupus erythematosus (SLE).

METHODS

One hundred sixty-three female patients with SLE (20 to 82 years old) were examined in a cross-sectional study. Venous blood samples were analyzed for resistin, erythrocyte sedimentation rate (ESR), C-reactive protein, creatinine, fasting lipids, complements, tumor necrosis factor-alpha, interleukin (IL)-1beta, IL-6, sIL-6R (soluble IL-6 receptor), ICTP (C-terminal telopeptide of type I collagen), and PINP (N-terminal propeptide of type I procollagen). Simple and multiple regression analyses as well as logistic regression analyses were performed. Resistin in serum was compared with 42 healthy female controls with respect to age.

RESULTS

Serum resistin levels in controls were similar to those of patients with SLE. Markers of inflammation and current dose of glucocorticosteroids correlated positively to resistin in serum. Markers of renal function, number of prevalent vertebral fractures, and BMD were also significantly associated with resistin. In a multiple regression model, ESR, creatinine, C3, current glucocorticosteroid dose, high-density lipoprotein, and BMD radius remained significantly associated with resistin. In logistic regression analyses with resistin as the independent variable, a significant association was found with ESR (normal or elevated) but not with S-creatinine or z score for hip and radius total.

CONCLUSION

Although resistin measurements did not differ between patients and controls, resistin was clearly associated with general inflammation, renal disease, treatment with glucocorticosteroids, and bone loss. We hypothesize that resistin has proinflammatory and disease-promoting properties in SLE. Further studies are needed to elucidate the mechanism behind these associations.

Adipokines and the peripheral and neural control of energy balance

Adipokines are secreted by adipose tissue and control various physiological systems. Low leptin levels during fasting stimulate feeding, reduce energy expenditure, and modulate neuroendocrine and immune function to conserve energy stores. On the other hand, rising leptin levels in the overfed state prevent weight gain by inhibiting food intake and increasing energy expenditure. These actions are mediated by neuronal circuits in the hypothalamus and brainstem. Leptin also controls glucose and lipid metabolism by targeting enzymes such as AMP-activated protein kinase and stearoyl-coenzyme A desaturase-1 in liver and muscle. Likewise, adiponectin and resistin control energy balance and insulin sensitivity via central and peripheral targets. As highlighted in this review, there are distinct as well as common signaling pathways for adipokines. Understanding adipokine signaling in the brain and other organs will provide insights into the pathogenesis and treatment of obesity, diabetes and various metabolic disorders.

Perinatal changes of plasma resistin concentrations in pregnancies with normal and restricted fetal growth

BACKGROUND

The adipocytokine resistin inhibits adipogenesis and induces insulin resistance. Intrauterine growth-restricted (IUGR) neonates have reduced fat mass and changes of endocrine/metabolic mechanisms, predisposing to insulin resistance and metabolic syndrome in adult life.

OBJECTIVES

To investigate plasma resistin concentrations in maternal, fetal and neonatal samples from IUGR and appropriate-for-gestational-age (AGA) pregnancies and correlate them with respective insulin concentrations.

METHODS

Plasma resistin and insulin concentrations were determined in 40 mothers and their 20 IUGR and 20 AGA singleton full-term fetuses and neonates on postnatal day 1 (N1) and day 4 (N4).

RESULTS

No significant differences in resistin concentrations were observed between AGA and IUGR groups. In the AGA group, maternal resistin concentrations were significantly lower compared to fetal, N1 and N4 ones (p = 0.003, p = 0.017 and p = 0.039, respectively). Maternal resistin concentrations positively correlated with fetal ones (r = 0.527, p = 0.02). In the IUGR group, maternal resistin concentrations were significantly lower compared to N1 (p < 0.001) and positively correlated with N4 concentrations (r = 0.626, p = 0.007). In both groups, the effect of gender, mode of delivery, parity and adjusted birth weight (customized centiles) on resistin concentrations was not significant. No correlation between resistin and insulin concentrations was documented.

CONCLUSIONS

Lack of difference in resistin concentrations between IUGR and AGA groups, and lack of correlation between resistin and insulin concentrations as well as customized centiles, possibly suggests that resistin may not be directly involved in the regulation of insulin sensitivity and adipogenesis in the perinatal period. Mode of delivery and parity are not associated with circulating resistin concentrations.

Effects of over-expressing resistin on glucose and lipid metabolism in mice

Resistin, a newly discovered peptide hormone mainly secreted by adipose tissues, is present at high levels in serum of obese mice and may be a potential link between obesity and insulin resistance in rodents. However, some studies of rat and mouse models have associated insulin resistance and obesity with decreased resistin expression. In humans, no relationship between resistin level and insulin resistance or adiposity was observed. This suggests that additional studies are necessary to determine the specific role of resistin in the regulation of energy metabolism and adipogenesis. In the present study, we investigated the effect of resistin in vivo on glucose and lipid metabolism by over-expressing resistin in mice by intramuscular injection of a recombinant eukaryotic expression vector pcDNA3.1-Retn encoding porcine resistin gene. After injection, serum resistin and serum glucose (GLU) levels were significantly increased in the pcDNA3.1-Retn-treated mice; there was an obvious difference in total cholesterol (TC) level between the experiment and the control groups on Day 30. In pcDNA3.1-Retn-treated mice, both free fatty acid (FFA) and high density lipoprotein (HDL) cholesterol levels were markedly lower than those of control, whereas HDL cholesterol and triglyceride (TG) levels did not differ between the two groups. Furthermore, lipase activity was expressly lower on Day 20. Our data suggest that resistin over-expressed in mice might be responsible for insulin resistance and parameters related to glucose and lipid metabolism were changed accordingly.

Regulation of gut-derived resistin-like molecule beta expression by nutrients

Resistin was initially identified as a protein, secreted by adipocytes, which inhibits insulin action and adipose differentiation. The three proteins homologous to resistin were identified and given the names resistin-like molecules (RELM) alpha, beta and gamma. Resistin and RELMalpha are abundantly expressed in adipose, but RELMbeta and RELMgamma are secreted mainly from the gut. Since nutrient composition greatly affects insulin sensitivity, we investigated the regulatory effects of various nutritional factors in food on the expressions of resistin family proteins. First, mice were given diets with different nutritional compositions (high-carbohydrate, high-protein and high-fat) for 2 weeks. RELMbeta mRNA expression in the intestines was markedly suppressed by the high-protein and high-carbohydrate diets, while slightly but not significantly upregulated by the high-fat diet. In the epididymal fat, resistin expression was unchanged, while RELMalpha expression was markedly decreased by the high-carbohydrate diet. Taking into consideration that humans have neither RELMalpha nor RELMgamma, our subsequent studies focused on RELMbeta expression. We used the human colon cancer cell line LS174T. Treatments with insulin and TNFalpha as well as stearic acid, a saturated free fatty acid, upregulated RELMbeta expression, while d-glucose downregulated RELMbeta. These results suggest RELMbeta expression to be regulated directly by nutrients such as glucose and saturated free fatty acids including stearic acid, as well as by hormones including insulin and TNFalpha. These regulations may play an important role in the nutrient-associated induction of insulin resistance.

Association of adiponectin and resistin with cardiovascular events in Korean patients with type 2 diabetes: The Korean atherosclerosis study (KAS)

Adiponectin and resistin are proteins that affect insulin resistance and atherosclerosis significantly. We investigated adiponectin and resistin concentrations as predictors of cardiovascular events in Korean patients with type 2 diabetes. The study in 2001 comprised 343 unrelated patients with type 2 diabetes (65+/-9.2 years old). They were followed up for 42 months. The baseline duration of diabetes, smoking status and history of cardiovascular diseases (CVD) were recorded. BMI, blood pressures, HbA1c, lipid profiles, ECG, creatinine and urine microalbumin were measured. Adiponectin and resistin were measured using enzyme-linked immunosorbent assays. The primary endpoint was defined as one of cardiovascular death, myocardial infarct, CABG, stroke, unstable angina or overt nephropathy. Thirty-eight patients (11.1%) experienced primary endpoint during the follow-up. After adjustment for age, sex, BMI, blood pressure and lipid status, participants in the lowest quartile of adiponectin levels compared with the highest had significantly increased risk of primary endpoint (relative risk=3.03; 95% CI 1.09-8.41; p=0.034). In contrast, resistin level had no influence on the risk of primary endpoint. A low level of adiponectin, not resistin, was a significant risk factor for the development of cardiovascular events in these Korean patients with type 2 diabetes.

Viral and host correlates of serum resistin in simian AIDS

Resistin is an adipocytokine with a proposed dual role in metabolism and inflammation. In light of the ability to promote inflammatory responses, adipocytokines may prove key factors in modulating the host response to HIV. This study utilizes the simian immunodeficiency virus (SIV) model of HIV/AIDS to investigate changes in serum resistin levels following dietary intervention and SIV infection and determine associations with measures of body composition and disease severity. Resistin levels, body composition (n = 34), and insulin resistance (n = 16) were determined in healthy rhesus macaques. A subset of animals (n = 8) was placed on an atherogenic diet (AD) and subsequently inoculated with SIVmac239. Longitudinal measures of serum resistin, cytokines, viral load, lymphocyte subsets, and body composition were obtained. In healthy macaques consuming a standard diet, resistin levels correlated positively with total fat mass (r = 0.49; p < 0.01) and tissue fat percent (r = 0.53; p < 0.01) but failed to associate with measures of insulin resistance. In contrast, a negative correlation was noted between these measures of adiposity and resistin following SIV inoculation (r = -0.27; p < 0.05 and r = -0.24; p < 0.05, respectively). Viral load correlated positively with serum resistin (r = 0.32; p < 0.01). Serum levels of MCP-1 and sTNF RII demonstrated no correlation with resistin in normal animals on a standard diet, while a significant positive correlation was observed following SIV infection (r = 0.52; p < 0.0001 and r = 0.59; p < 0.0001, respectively). Findings indicate a fundamental difference in the relationship between resistin and body composition following SIV infection and suggest that elevations in resistin parallel measures of disease severity including loss of body fat and viral replication.

[Obesity, inflammation and insulin resistance: which role for adipokines]

Adipose tissue is now recognized as an endocrine organ involved in regulating physiologic and pathologic processes including inflammation. It synthesizes and secretes hormones such as leptin and adiponectin. It can secrete other products namely adipokines including cytokines and chemokines. The release of adipokines by either adipocytes or adipose tissue-infiltrated macrophages leads to a chronic sub-inflammatory state that likely plays a major role in cardiovascular complications linked to obesity and insulin resistance.

Effects of long-term exercise and diet intervention on plasma adipokine concentrations

BACKGROUND

In a randomized, controlled, 2 x 2 factorial trial on the effect of long-term changes in diet and exercise, a significant reduction in body weight and fat mass was observed. Alterations in leptin and plasminogen activator inhibitor-1 concentrations were previously reported from this study.

OBJECTIVE

We examined the separate and combined effects of a 1-y exercise and diet intervention on several adipokines; adiponectin, interleukin-6 and -8, tumor necrosis factor-alpha, monocyte chemoattractant protein-1, hepatocyte growth factor, nerve growth factor, C-reactive protein, and resistin.

DESIGN

One hundred eighty-eight men with several risk factors for diabetes and cardiovascular disease were randomly allocated to 4 groups: diet, exercise, combined diet and exercise, and control.

RESULTS

Plasma adiponectin concentrations remained unchanged, whereas body mass index and fat mass decreased after dietary changes and an increase in physical activity. In the control group, adiponectin concentrations were reduced. Analyzed according to the factorial design, only diet intervention had a significant (P = 0.03) positive effect on plasma adiponectin relative to control, and this effect was largely explained by changes in fat mass. After adjustment for change in percentage body fat, there were significant positive effects on tumor necrosis factor-alpha in all 3 intervention groups (P = 0.01 for the diet group, 0.03 for the exercise group, and 0.05 for the combined diet and exercise group). Minor changes were observed for the other adipokines. Neither baseline concentrations of nor changes in adiponectin and plasminogen activator inhibitor-1 were significantly correlated to the other adipokines, whereas concentrations of and changes in the other adipokines were significantly correlated.

CONCLUSION

Diet intervention had a significant positive effect on adiponectin concentrations, which is largely explained by a reduction in fat mass.

Resistin, an adipocytokine, offers protection against acute myocardial infarction

Resistin, an adipocyte-derived hormone, is thought to represent a link between obesity and insulin-resistant diabetes. The potential role of resistin as a cardioprotective agent has not been explored. Our hypothesis is that resistin has a cardioprotective effect that is mediated by the resistin receptor-coupled activation of PI3K/Akt/PKC/K(ATP) dependent pathways. Our studies demonstrated that pretreatment of mouse hearts with 10 nM resistin for 5 min protected the heart against I/R injury in a mouse heart perfusion model. When mouse hearts were subjected to 60 min of LAD ligation followed by 4 h of reperfusion, resistin pretreatment (33 microg/kg) for 30 min or 24 h before ligation was able to significantly reduce the infarct size/risk area. The protective effect of resistin was abolished by wortmannin, as well as by an Akt inhibitor, triciribine. Resistin's protective effect was absent in Akt kinase-deficient mutant mice. The protective effect was also blocked by chelerythrine, a PKC inhibitor, and epsilonV1-2, a PKCepsilon inhibitor. Finally, the protective effect was blocked by 5-hydroxydecanoate, which blocks the opening of mitoK(ATP) channels. Resistin-induced Akt phosphorylation in HL-1 cells was inhibited by wortmannin and triciribine. Resistin also induced PKCepsilon phosphorylation, which was blocked by triciribine. These studies demonstrate that resistin's cardioprotective effect is mediated by PI3K/Akt/PKC dependent pathways. In addition to cardiomyocytes, resistin also induced Akt phosphorylation in endothelial cells and smooth muscle cells, suggesting that resistin receptors are present in these cells. The effect of resistin on apoptosis was assessed in hearts subjected to 30 min of ischemia and 3 h of reperfusion. There were significantly fewer in situ oligo ligation-positive myocyte nuclei in mice treated with resistin. Our results show that resistin can dramatically reduce apoptosis and infarct size, thus protecting the heart against I/R injury.

Resistin Is a Key Mediator of Glucose-dependent Insulinotropic Polypeptide (GIP) Stimulation of Lipoprotein Lipase (LPL) Activity in Adipocytes

Studies on the physiological roles of the incretin hormone, glucose-dependent insulinotropic polypeptide (GIP) have largely focused on its insulinotropic action and ability to regulate beta-cell mass. In previous studies on the stimulatory effect of GIP on adipocyte lipoprotein lipase (LPL), a pathway was identified involving increased phosphorylation of protein kinase B (PKB) and reduced phosphorylation of LKB1 and AMP-activated protein kinase (AMPK). The slow time of onset of the responses suggested that GIP may have induced release of an intermediary molecule, and the current studies focused on the possible contribution of the adipokine resistin. In differentiated 3T3-L1 adipocytes, GIP, in the presence of insulin, increased resistin secretion through a pathway involving p38 mitogen-activated protein kinase (p38 MAPK) and the stress-activated protein kinase/Jun amino-terminal kinase (SAPK/JNK). The other major incretin hormone, glucagon-like peptide-1 (GLP-1), exhibited no significant effects. Chronic elevation of circulating GIP levels in the Vancouver Diabetic Fatty (VDF) Zucker rat resulted in increases in circulating resistin levels and activation of p38 MAPK or SAPK/JNK in epididymal fat tissue, suggesting the existence of identical pathways in vivo as well as in vitro. Administration of resistin to 3T3-L1 adipocytes mimicked the effects of GIP on the PKB/LKB1/AMPK/LPL pathway: increasing phosphorylation of PKB, reducing levels of phosphorylated LKB1 and AMPK, and increasing LPL activity. Knockdown of resistin using RNA interference attenuated the effect of GIP on the PKB/LKB1/AMPK/LPL pathway in 3T3-L1 adipocytes, supporting a role for resistin as a mediator.

Within-subject variation of plasma resistin levels over a 1-year period

BACKGROUND

Resistin, a recently discovered hormone, is purportedly involved in metabolic and inflammatory processes in humans and may thus be an important marker to assess disease risk in large-scale epidemiological studies.

METHODS

We assessed the reliability of human resistin levels in 63 men and 51 women aged 35-67 years with repeated measurements of resistin over a period of 1 year. Student's paired t-test was used to compare resistin concentrations at baseline and 1 year later. Intraclass correlation coefficients (ICCs) were calculated by analysis of variance.

RESULTS

There was no significant difference between resistin concentrations at baseline and after 1 year for both sexes combined or when analyzed separately for men and women. The ICCs were 0.70 (95% CI 0.59-0.78) for both sexes combined, 0.75 (95% CI 0.62-0.84) for men, and 0.66 (95% CI 0.47-0.79) for women. Resistin levels were not significantly related to age, body mass index, waist-to-hip ratio, sex, or fasting status.

CONCLUSIONS

Individual blood resistin concentrations did not significantly change over a period of 1 year, but showed a high degree of reliability. Our findings suggest that a single resistin measurement may be sufficient for risk assessment in epidemiological studies.

Conditioned medium obtained from in vitro differentiated adipocytes and resistin induce insulin resistance in human hepatocytes

Adipocyte-derived factors might play a role in the development of hepatic insulin resistance. Resistin was identified as an adipokine linking obesity and insulin resistance. Resistin is secreted from adipocytes in rodents but in humans it was proposed to originate from macrophages and its impact for insulin resistance has remained elusive. To analyze the role of adipokines in general and resistin as a special adipokine, we cultured the human liver cell line HepG2 with adipocyte-conditioned medium (CM) containing various adipokines such as IL-6 and MCP-1, and resistin. CM and resistin both induce insulin resistance with a robust decrease in insulin-stimulated phosphorylation of Akt and GSK3. Insulin resistance could be prevented by co-treatment with troglitazone but not by co-stimulation with adiponectin. As human adipocytes do not secrete resistin, HepG2 cells were also treated with resistin added into CM. CM with resistin addition induced stronger insulin resistance than CM alone pointing to a specific role of resistin in the initiation of hepatic insulin resistance in humans.

Mechanisms of obesity-associated insulin resistance: many choices on the menu

Obesity-associated insulin resistance is a major risk factor for type 2 diabetes and cardiovascular disease. In the past decade, a large number of endocrine, inflammatory, neural, and cell-intrinsic pathways have been shown to be dysregulated in obesity. Although it is possible that one of these factors plays a dominant role, many of these factors are interdependent, and it is likely that their dynamic interplay underlies the pathophysiology of insulin resistance. Understanding the biology of these systems will inform the search for interventions that specifically prevent or treat insulin resistance and its associated pathologies.

Effect of the -420C/G variant of the resistin gene promoter on metabolic syndrome, obesity, myocardial infarction and kidney dysfunction

OBJECTIVE

Resistin is an adipokine that has been suggested to be correlated with markers of inflammation and to be predictive of coronary atherosclerosis and type II diabetes in humans. A common single nucleotide polymorphism (SNP) (-420C/G) in the promoter of resistin is associated with increased resistin plasma levels and susceptibility to type II diabetes. The aim of this study was to investigate the association of the -420C/G polymorphism with metabolic syndrome, obesity, myocardial infarction and kidney disease.

DESIGN AND RESULTS

First we studied 1542 subjects from the PLIC study (a population based cohort). GG carriers showed an higher prevalence of obesity and metabolic syndrome as well as increased plasma triglycerides levels, BMI, systolic and diastolic blood pressure and cardiovascular risk according to Framingham algorithm (P < 0.05 for all). Next we investigated the presence of the -420C/G resistin polymorphism in a case-control study that included 300 subject with myocardial infarction and 300 age and sex matched controls and then we studied the role of the -420C/G SNP in 88 patients with mild to moderate renal dysfunction. No statistically significant differences in allele frequencies between the PLIC study, the myocardial infarction (MI) cases and the subjects with renal dysfunction were observed. Pro-inflammatory gene expression profiling of peripheral blood mononuclear cells failed to detect any difference between wild type subjects and carriers of the rare allele.

CONCLUSION

Our data suggest that the presence of the -420C/G SNP of the resistin gene is associated with increased obesity and metabolic syndrome, although it is not different in subjects at high cardiovascular risk such as patients with myocardial infarction or patients with renal dysfunction compared with controls.

Resistin down-regulates insulin receptor expression, and modulates cell viability in rodent pancreatic beta-cells

The adipokine resistin is known to induce insulin resistance in rodent tissues. Increases in adipose tissue mass are known to have a negative effect on pancreatic beta-cell function, although the mechanisms are poorly understood. This study investigated the effects of resistin on insulin secretion, insulin receptor expression and cell viability in pancreatic beta-cells. BTC-6 or BRIN-BD11 cells were treated for 24h with resistin, and insulin receptor expression, insulin secretion and cell viability were measured. Incubation with 40ng/ml resistin caused significant decreases in insulin receptor mRNA and protein expression, but did not affect insulin secretion. At low concentrations, resistin caused significant increases in cell viability. These data implicate resistin as a factor that may regulate beta-cell function/viability, and suggests a potential mechanism by which increased adiposity causes beta-cell dysfunction.

Mechanical stretch enhances the expression of resistin gene in cultured cardiomyocytes via tumor necrosis factor-alpha

The heart is a resistin target tissue and can function as an autocrine organ. We sought to investigate whether cyclic mechanical stretch could induce resistin expression in cardiomyocytes and to test whether there is a link between the stretch-induced TNF-alpha and resistin. Neonatal Wistar rat cardiomyocytes grown on a flexible membrane base were stretched by vacuum to 20% of maximum elongation at 60 cycles/min. Cyclic stretch significantly increased resistin protein and mRNA expression after 2-18 h of stretch. Addition of PD-98059, TNF-alpha antibody, TNF-alpha receptor antibody, and ERK MAP kinase small interfering RNA 30 min before stretch inhibited the induction of resistin protein. Cyclic stretch increased, whereas PD-98059 abolished, the phosphorylated ERK protein. Gel-shift assay showed a significant increase in DNA-protein binding activity of NF-kappaB after stretch, and PD-98059 abolished the DNA-protein binding activity induced by cyclic stretch. DNA binding complexes induced by cyclic stretch could be supershifted by p65 monoclonal antibody. Cyclic stretch increased resistin promoter activity, whereas PD-98059 and p65 antibody decreased resistin promoter activity. Cyclic stretch significantly increased TNF-alpha secretion from myocytes. Recombinant resistin protein and conditioned medium from stretched cardiomyocytes reduced glucose uptake in cardiomyocytes, and recombinant small interfering RNA of resistin or TNF-alpha antibody reversed glucose uptake. In conclusion, cyclic mechanical stretch enhances resistin expression in cultured rat neonatal cardiomyocytes. The stretch-induced resistin is mediated by TNF-alpha, at least in part, through ERK MAP kinase and NF-kappaB pathways. Glucose uptake in cardiomyocytes was reduced by resistin upregulation.

Adipocytokines and the regulation of lipid metabolism in growth hormone transgenic and calorie-restricted mice

Chronic elevation of GH induces resistance to insulin and hyperinsulinemia in both humans and animals, whereas calorie restriction (CR) improves peripheral insulin sensitivity in many species. To investigate the mechanisms that lead to insulin resistance in animals with high levels of GH as well as the mechanisms that might improve insulin sensitivity, we fed GH-overexpressing transgenic mice ad libitum or subjected them to 30% CR. We then assayed the plasma adipocytokines levels related to insulin sensitivity, plasma lipid levels, and tissue triglycerides accumulation and examined adipocyte morphology. Furthermore, we evaluated mRNA expression and protein levels of enzymes or regulators involved in regulating hepatic lipid metabolism. Our results suggest that decreased plasma adiponectin, increased plasma resistin and cholesterol, and elevated levels of TNF-alpha and IL-6 in adipocytes may all contribute to the insulin resistance observed in GH-Tg mice. Increased accumulation of triglycerides and impaired adipocytes differentiation in GH-transgenic mice provide plausible mechanisms for the alterations of adipocytokines. Hepatic and muscle insulin resistance in these mice is probably related to excessive accumulation of fatty acids and their metabolites. An increase in plasma adiponectin and decrease in plasma IL-6, triglycerides, and cholesterol levels in response to CR may improve insulin sensitivity.

Association of Resistin Gene 3'-Untranslated Region EX4-44G-->A Polymorphism with Obesity- and Insulin-Related Phenotypes in Turkish Type 2 Diabetes Patients

Resistin, an adipocyte-secreted hormone, has been associated with obesity, insulin resistance and type 2 diabetes mellitus (T2DM) in some, but not all, rodent models. In humans, the exact function of resistin is unkown. Because 3'-untranslated region (3'-UTR) single nucleotide substitutions (SNPs) have been shown to affect gene expression, we examined the EX4-44G-->A SNP in the 3'-UTR of exon 3 within the resistin gene. The objective of this study was to investigate, for the first time in a Turkish study group, whether the 3'-UTR EX4-44G-->A variation in the resistin gene influences the development of T2DM, obesity and insulin-related phenotypes. We analyzed the genotype frequencies of the EX4-44G-->A polymorphism of the resistin gene in 116 type 2 diabetic and 102 normal subjects. Serum lipids, obesity-related and insulin-related phenotypes were analyzed. No significant difference for genotypic frequencies were observed for the BseRI restriction site in type 2 diabetic patients as compared to controls. Waist-to-hip ratio, BMI, body fat and apoAI levels were found to be affected by resistin genotype. In the control group, BMI (p < 0.01), HIS (p < 0.05) and BF (p < 0.05) levels were found to be elevated, whereas HOMA beta-cell index (p < 0.01) and apo AI (p < 0.05) levels were found to be decreased in GG genotype carriers. In the diabetic group, the GG genotype carriers were found to have higher BMI levels (p < 0.001), waist-to-hip ratio (p < 0.05), body fat (p < 0.01), HOMA (p < 0.001) and fasting insulin (p < 0.05), but lower HbA1c levels in comparison to GC + AA carriers. These data suggest that, in the Turkish study group, the EX4-44G-->A polymorphism of the resistin gene is associated with insulin and obesity-related phenotypes.

Basic endocrine products of adipose tissue in states of thyroid dysfunction

Over the past decade it has been established that adipose tissue is capable of secreting a variety of hormones, cytokines, growth factors, and other peptides that are capable of changing adipocyte biology as well as different organ systems, like the central nervous system, liver, pancreas, and skeletal muscles. Also, it is well known that changes of thyroid function are associated with marked changes in both body weight and energy expenditure. In recent years an extensive research is under way to explore the mutual roles of different adipokines and thyroid hormones. The aim of this review is to summarize our current knowledge on the role of basic peptides of adipose tissue, such as adiponectin, interleukin-6, tumor necrosis factor-alpha, and resistin, in states of altered thyroid function.

Effect of PPAR-δ agonist on the expression of visfatin, adiponectin, and resistin in rat adipose tissue and 3T3-L1 adipocytes

It has been recently reported that activation of PPAR-delta, by specific agonists or genetic manipulation, alleviates dyslipidemia, hyperglycemia, and insulin resistance in animal models of obesity and type 2 diabetes. The purpose of the present study was to determine whether the PPAR-delta agonist has a direct effect on adipokines in visceral adipose tissue of rats and in cultured adipocytes. We examined the expression of visfatin, adiponectin, and resistin mRNA in visceral adipose tissue of Wistar rats fed a high-fat diet and 3T3-L1 adipocytes treated with PPAR-delta agonist (L-165041). Body weight and biochemical measurements were performed. Rats fed a high-fat diet showed a greater increase in body weight than those fed a standard diet (P<0.05), and treatment with L-165041 (10 mg/kg/day) significantly decreased weight gain (P<0.05). The concentration of total cholesterol was lower, and HDL cholesterol was higher in L-165041-treated rats (P<0.05). In the visceral adipose tissue of L-165041-treated rats, visfatin and adiponectin mRNA levels significantly increased compared to those of the untreated rats (P<0.05). However, the expression of resistin decreased in the L-165041-treated rats. Furthermore, in cultured 3T3-L1 adipocytes, the level of visfatin and adiponectin mRNA was up-regulated in response to L-165041 treatment for nine days. By contrast, resistin mRNA levels were down-regulated by L-165041 treatment. The present study provides a novel evidence to suggest that the PPAR-delta agonist has regulatory effects on a variety of adipokines, and these effects might explain some of their metabolic function.

Wnt-signaling is maintained and adipogenesis inhibited by TNFalpha but not MCP-1 and resistin

Type 2 diabetes and obesity with enlarged fat cells are associated with low-grade systemic inflammation, impaired adipogenesis as well as the recruitment of inflammatory cells into the adipose tissue. Cytokines like TNFalpha and IL-6 are secreted by the inflammatory cells and have been shown to impair normal adipocyte differentiation. An important mechanism whereby these cytokines inhibit adipogenesis is by maintaining an active Wnt-signaling pathway. Also other cytokines like MCP-1 and resistin are involved in the inflammatory process and are secreted by macrophages. If these cytokines also affect Wnt-signaling and adipocyte differentiation is currently unclear. In the present study, we show that while TNFalpha is able to maintain an active Wnt-signaling, induce inflammation and completely block adipose cell differentiation, no effect was found by either MCP-1 or resistin on these processes. Addition of the thiazolidinedione, pioglitazone, was found to antagonize the effect of TNFalpha on the Wnt-signaling process and, consequently, promote adipogenesis.

Expression of lipogenic factors galectin-12, resistin, SREBP-1, and SCD in human sebaceous glands and cultured sebocytes

The transcription factors CCAAT enhancer-binding protein alpha, beta, and delta, and peroxisome proliferator-activated receptor gamma are known to be crucial to the differentiation of adipocytes and are expressed in sebaceous gland cells. As lipogenesis is key to both adipocyte and sebocyte differentiation we hypothesize that sebocytes follow a similar program of differentiation to adipocytes. We have investigated the expression of known adipogenic factors resistin, galectin-12, sterol response-element-binding protein-1 (SREBP-1) and stearoyl-CoA desaturase in the immortalized sebaceous gland cell line SZ95 and whole skin. Reverse transcriptase-PCR analysis showed the expression of galectin-12, resistin, SREBP-1, and stearoyl-CoA desaturase mRNAs in SZ95 sebocytes. Immunoreactivity was observed for galectin-12 and SREBP-1 in the nuclei and resistin in the cytoplasm of basal sebocytes, and stearoyl CoA desaturase in the cytoplasm of basal and luminal sebocytes of human scalp skin. Expression of galectin-12, resistin, and SREBP-1 in SZ95 sebocytes was confirmed by Western blot analysis. These data provide further evidence that pathways of differentiation in adipocytes and sebocytes could be similar and therefore further understanding of sebaceous gland differentiation and lipogenesis and potential therapies for sebaceous gland disorders may be obtained from our knowledge of adipocyte differentiation.

Antidiabetic effects of cis-9, trans-11-conjugated linoleic acid may be mediated via anti-inflammatory effects in white adipose tissue

Adipose tissue may be the source of insulin desensitizing proinflammatory molecules that predispose to insulin resistance. This study investigated whether dietary fatty acids could attenuate the proinflammatory insulin-resistant state in obese adipose tissue. The potential antidiabetic effect of cis-9, trans-11-conjugated linoleic acid (c9,t11-CLA) was determined, focusing on the molecular markers of insulin sensitivity and inflammation in adipose tissue of ob/ob C57BL-6 mice. Feeding a c9,t11-CLA-enriched diet reduced fasting glucose (P < 0.05), insulin (P < 0.05), and triacylglycerol concentrations (P < 0.01) and increased adipose tissue plasma membrane GLUT4 (P < 0.05) and insulin receptor (P < 0.05) expression compared with the control linoleic acid-enriched diet. Interestingly, after the c9,t11-CLA diet, adipose tissue macrophage infiltration was less, with marked downregulation of several inflammatory markers in adipose tissue, including reduced tumor necrosis factor-alpha and CD68 mRNA (P < 0.05), nuclear factor-kappaB (NF-kappaB) p65 expression (P < 0.01), NF-kappaB DNA binding (P < 0.01), and NF-kappaB p65, p50, c-Rel, p52, and RelB transcriptional activity (P < 0.01). To define whether these observations were direct effects of the nutrient intervention, complimentary cell culture studies showed that c9,t11-CLA inhibited tumor necrosis factor-alpha-induced downregulation of insulin receptor substrate 1 and GLUT4 mRNA expression and promoted insulin-stimulated glucose transport in 3T3-L1 adipocytes compared with linoleic acid. This study suggests that altering fatty acid composition may attenuate the proinflammatory state in adipose tissue that predisposes to obesity-induced insulin resistance.

Obesity, metabolic syndrome and sleep apnoea: all pro-inflammatory states

Obesity is associated with significant morbidity and mortality and is increasing in prevalence worldwide. Associated conditions include insulin resistance (IR), diabetes, hypertension and dyslipidaemia; a clustering of these has recently been termed as metabolic syndrome. Weight gain is a major predictor of the metabolic syndrome with waist circumference being a more sensitive indicator than body mass index as it reflects both abdominal subcutaneous adipose tissue and visceral adipose tissue (VAT). VAT has more metabolic activity and secretes a number of hormones and pro-inflammatory cytokines which are linked with the metabolic abnormalities listed above. Central obesity also increases the risk of obstructive sleep apnoea syndrome (OSAS), where the sleep disordered breathing may also independently lead to/or exacerbate IR, diabetes and cardiovascular risk. The contribution of OSAS to the metabolic syndrome has been under-recognized. The putative mechanisms by which OSAS causes or exacerbates these other abnormalities are discussed. We propose that activation of nuclear factor kappa B by stress hypoxia and/or by increased adipokines and free fatty acids released by excess adipose tissue is the final common inflammatory pathway linking obesity, OSAS and the metabolic syndrome both individually and, in many cases, synergistically.

Review: Peroxisome proliferator-activated receptor gamma and adipose tissue--understanding obesity-related changes in regulation of lipid and glucose metabolism

CONTEXT

Adipose tissue is a metabolically dynamic organ, serving as a buffer to control fatty acid flux and a regulator of endocrine function. In obese subjects, and those with type 2 diabetes or the metabolic syndrome, adipose tissue function is altered (i.e. adipocytes display morphological differences alongside aberrant endocrine and metabolic function and low-grade inflammation).

EVIDENCE ACQUISITION

Articles on the role of peroxisome proliferator-activated receptor gamma (PPARgamma) in adipose tissue of healthy individuals and those with obesity, metabolic syndrome, or type 2 diabetes were sourced using MEDLINE (1990-2006).

EVIDENCE SYNTHESIS

Articles were assessed to provide a comprehensive overview of how PPARgamma-activating ligands improve adipose tissue function, and how this links to improvements in insulin resistance and the progression to type 2 diabetes and atherosclerosis.

CONCLUSIONS

PPARgamma is highly expressed in adipose tissue, where its activation with thiazolidinediones alters fat topography and adipocyte phenotype and up-regulates genes involved in fatty acid metabolism and triglyceride storage. Furthermore, PPARgamma activation is associated with potentially beneficial effects on the expression and secretion of a range of factors, including adiponectin, resistin, IL-6, TNFalpha, plasminogen activator inhibitor-1, monocyte chemoattractant protein-1, and angiotensinogen, as well as a reduction in plasma nonesterified fatty acid supply. The effects of PPARgamma also extend to macrophages, where they suppress production of inflammatory mediators. As such, PPARgamma activation appears to have a beneficial effect on the relationship between the macrophage and adipocyte that is distorted in obesity. Thus, PPARgamma-activating ligands improve adipose tissue function and may have a role in preventing progression of insulin resistance to diabetes and endothelial dysfunction to atherosclerosis.

Resistin as an intrahepatic cytokine: overexpression during chronic injury and induction of proinflammatory actions in hepatic stellate cells

Obesity and insulin resistance accelerate the progression of fibrosis during chronic liver disease. Resistin antagonizes insulin action in rodents, but its role in humans is still controversial. The aims of this study were to investigate resistin expression in human liver and to evaluate whether resistin may affect the biology of activated human hepatic stellate cells (HSCs), key modulators of hepatic fibrogenesis. Resistin gene expression was low in normal human liver but was increased in conditions of severe fibrosis. Up-regulation of resistin during chronic liver damage was confirmed by immunohistochemistry. In a group of patients with alcoholic hepatitis, resistin expression correlated with inflammation and fibrosis, suggesting a possible action on HSCs. Exposure of cultured HSCs to recombinant resistin resulted in increased expression of the proinflammatory chemokines monocyte chemoattractant protein-1 and interleukin-8, through activation of nuclear factor (NF)-kappaB. Resistin induced a rapid increase in intracellular calcium concentration, mainly through calcium release from intracellular inositol triphosphate-sensitive pools. The intracellular calcium chelator BAPTA-AM blocked resistin-induced NF-kappaB activation and monocyte chemoattractant protein-1 expression. In conclusion, this study shows a role for resistin as an intrahepatic cytokine exerting proinflammatory actions in HSCs, via a Ca2+/NF-kappaB-dependent pathway and suggests involvement of this adipokine in the pathophysiology of liver fibrosis.

Resistin as an intrahepatic cytokine: overexpression during chronic injury and induction of proinflammatory actions in hepatic stellate cells

Obesity and insulin resistance accelerate the progression of fibrosis during chronic liver disease. Resistin antagonizes insulin action in rodents, but its role in humans is still controversial. The aims of this study were to investigate resistin expression in human liver and to evaluate whether resistin may affect the biology of activated human hepatic stellate cells (HSCs), key modulators of hepatic fibrogenesis. Resistin gene expression was low in normal human liver but was increased in conditions of severe fibrosis. Up-regulation of resistin during chronic liver damage was confirmed by immunohistochemistry. In a group of patients with alcoholic hepatitis, resistin expression correlated with inflammation and fibrosis, suggesting a possible action on HSCs. Exposure of cultured HSCs to recombinant resistin resulted in increased expression of the proinflammatory chemokines monocyte chemoattractant protein-1 and interleukin-8, through activation of nuclear factor (NF)-kappaB. Resistin induced a rapid increase in intracellular calcium concentration, mainly through calcium release from intracellular inositol triphosphate-sensitive pools. The intracellular calcium chelator BAPTA-AM blocked resistin-induced NF-kappaB activation and monocyte chemoattractant protein-1 expression. In conclusion, this study shows a role for resistin as an intrahepatic cytokine exerting proinflammatory actions in HSCs, via a Ca2+/NF-kappaB-dependent pathway and suggests involvement of this adipokine in the pathophysiology of liver fibrosis.

Resistin-like molecule alpha reduces gallbladder optimal tension

INTRODUCTION

Insulin resistance is associated with increased gallbladder volume and impaired gallbladder emptying. Resistin and resistin-like molecule alpha (RELM-alpha) are adipose-derived hormones that are believed to mediate insulin resistance. Therefore, we tested the hypothesis that administration of resistin or RELM-alpha would cause insulin resistance and diminish gallbladder contractility.

METHODS

In two sequential studies 40 eight-week-old nondiabetic lean mice were fed a chow diet for 4 weeks. In Study A, 10 mice received 20 microg of resistin IP, while in Study B 10 mice received 20 microg of RELM-alpha IP for seven days. In each study, 10 control mice received an equal volume of saline IP for seven days. At 12 weeks animals were fasted and underwent cholecystectomy, and in vitro gallbladder response to neurotransmitters was determined. Serum resistin, RELM-alpha, glucose, and insulin levels were measured. HOMA index, a measure of insulin resistance, was calculated.

RESULTS

RELM-alpha significantly increased HOMA index. RELM-alpha decreased gallbladder optimal tension, but did not alter responses to neurotransmitters. Resistin had no effect on HOMA index or on gallbladder optimal tension or response.

CONCLUSION

These data suggest that in nondiabetic lean mice: 1) resistin does not alter insulin resistance or gallbladder optimal tension, but 2) RELM-alpha increases insulin resistance and reduces gallbladder optimal tension. Therefore, we concluded that RELM-alpha may play a role in insulin-resistance mediated gallbladder dysmotility.

Plasma adiponectin concentrations in non-pregnant, normal and overweight pregnant women

AIMS

Adiponectin is an adipokine that has anti-diabetic, anti-atherogenic, anti-inflammatory and angiogenic properties. This hormone has been implicated in both the physiological adaptation to normal pregnancy and in obstetrical complications. The aims of this study were to determine normal maternal plasma concentrations of adiponectin throughout gestation and to explore the relationships between plasma adiponectin concentration, pregnancy, and maternal overweight.

METHODS

A cross-sectional study was designed to include normal pregnant (normal weight and overweight; 11-42 weeks of gestation), and non-pregnant women. Plasma adiponectin concentration was determined by immunoassay. Non-parametric statistics were used for analysis.

RESULTS

(1) Adiponectin was detectable in the plasma of all patients; (2) there was no significant differences in the median adiponectin concentration between pregnant and non-pregnant women; (3) plasma adiponectin concentrations were negatively correlated with gestational age only among normal weight pregnant women; and (4) overweight patients had significantly lower plasma adiponectin concentrations than normal weight women.

CONCLUSIONS

Consistent with the increased insulin resistance and weight gain that occur in pregnancy, adiponectin concentrations were negatively correlated with gestational age. The results of this study and the nomogram herein presented, can serve as the basis to explore the relationship between adiponectin and pregnancy complications and facilitate the clinical use of this important adipokine.

Resistin: a hormone which induces insulin resistance is increased in normal pregnancy

AIMS

Resistin, a newly discovered adipokine, is thought to play a key role in the regulation of insulin resistance. The objectives of this study were to develop a nomogram of maternal plasma concentrations of resistin from 11 weeks of gestation to term and to determine whether resistin concentrations differ between normal and overweight pregnant women.

METHODS

In this cross-sectional study, plasma concentrations of resistin were determined in normal pregnant women of normal body mass index (BMI 18.5-24.9; n=261), overweight pregnant women (BMI > or =25; n=140), and non-pregnant women of normal BMI (n=40). Blood samples were collected once from each woman between the first trimester and term. Percentiles for resistin concentration were determined for five pre-specified windows of gestational age. Plasma resistin concentration was determined by immunoassay. Non-parametric statistics were used for analysis.

RESULTS

The median maternal plasma concentration of resistin between 11 to 14 weeks of gestation in women of normal weight was significantly higher than non-pregnant women; the plasma concentration of resistin increased with gestational age.

CONCLUSIONS

Normal pregnant women have a higher median plasma concentration of resistin than non-pregnant women and the concentration of this adipokine increases with advancing gestation. Alterations in the maternal plasma concentration of resistin during pregnancy could contribute to metabolic changes of pregnancy.

Human resistin is a systemic immune-derived proinflammatory cytokine targeting both leukocytes and adipocytes

The characteristics of human resistin (RETN) are unclear and controversial despite intensive adipose-focused research. Its transcriptional and functional similarity with the murine myeloid-specific and CCAAT/enhancer binding protein epsilon (Cebpe)-dependent gene, resistin-like gamma (Retnlg), is unexplored. We examined the human CEBPE-regulatory pathway by unbiased reference and custom gene expression assays. Real-time RT-PCR analysis demonstrated lack of both the transcriptional factor CEBPE and RETN expression in adipose and muscle cells. In contrast, primary myelocytic samples revealed a concerted CEBPE-RETN transcription that was significantly elevated in inflammatory synoviocytes relative to intact peripheral blood mononuclear cells (PBMC). Mouse Cebpe and Retnlg were predictably expressed in macrophages, whereas Retn was abundant in adipocytes. Quite the opposite, a low and inconsistent RETN transcription was seen in some human white adipose tissue (WAT) biopsies without any relationship to body mass index, insulin sensitivity, or fat depot. However, in these cases, RETN was co-detected with CEBPE and the leukocyte-specific marker, EMR1, indicating the presence of inflammatory cells and their possible resistin-mediated effect on adipocytes. Indeed, addition of human resistin to WAT in culture induced, like in PBMC, the inflammatory cytokines IL6, IL8 and TNF. Importantly, the expression of the adipose-specific markers CEBPA, FABP4 and SLC2A4 was unchanged, while the expected inhibitory effect was seen with TNF. Both cytokines increased the mRNA level of CCL2 and MMP3, which may further promote inflammation in WAT. Thus, the myeloid-restricted nature of CEBPE precludes the expression of RETN in human adipocytes which, however, are targeted by this innate immune-derived proinflammatory cytokine.

Pref-1, a preadipocyte secreted factor that inhibits adipogenesis

Preadipocyte factor 1 (Pref-1) belongs to the Notch/Delta/Serrate family of epidermal growth factor-like repeat-containing proteins. Pref-1 is highly expressed in 3T3-L1 cells but is extinguished during adipocyte differentiation. Pref-1 serves as an excellent marker for preadipocytes. Furthermore, Pref-1 is an inhibitor of adipogenesis. Constitutive expression of Pref-1 inhibits, whereas antisense Pref-1 enhances, 3T3-L1 adipocyte differentiation. We found that Pref-1 is synthesized as a transmembrane protein but processed to generate soluble forms, including a large 50-kDa soluble form and the small soluble forms. Furthermore, only the large soluble form, but not the small soluble or the transmembrane forms of Pref-1, is biologically active to inhibit adipogenesis. We recently elucidated that the 50-kDa soluble form of Pref-1 is released by an ADAM family member, tumor necrosis factor-alpha converting enzyme (ADMA 17). In vivo, mice lacking Pref-1 show accelerated fat deposition; conversely, mice overexpressing soluble Pref-1 in adipose tissue show a decrease in fat mass, reduced expression of adipocyte markers, and lower adipocyte-secreted factors. These findings clearly demonstrate the inhibitory effect of Pref-1 on adipogenesis in vivo.

Insulin sensitivity and resistin expression in nitric oxide-deficient rats

AIMS/HYPOTHESIS

The aim of this study was to investigate changes in insulin sensitivity and expression of the gene encoding resistin (Retn) in adipocytes from long-term nitric oxide (NO)-deficient rats.

METHODS

Male Sprague-Dawley rats received [Formula: see text]-nitro-L: -arginine methyl ester (L-NAME 0.5 mg/ml) in their drinking water for 4 weeks, while control rats received plain drinking water. During the experimental period, changes in plasma glucose, insulin and C-peptide levels were measured. After administration of L-NAME for 4 weeks, insulin sensitivity was evaluated in vivo and in vitro. An insulin binding assay was also performed to determine the number and binding affinity of insulin receptors in adipocytes. Adipocyte Retn mRNA levels were examined using northern blotting.

RESULTS

Successful induction of NO deficiency was demonstrated by an increase in systemic blood pressure. No difference in plasma glucose levels was found between the two groups. Compared with the control rats, plasma insulin and C-peptide levels were significantly decreased in the NO-deficient rats, and insulin sensitivity was significantly increased. Insulin-stimulated glucose uptake and insulin binding capacity, but not binding affinity, were significantly increased in adipocytes isolated from NO-deficient rats. In addition, adipocyte Retn mRNA levels, but not plasma resistin levels, were significantly decreased in NO-deficient rats, and the Retn mRNA levels were negatively correlated with insulin sensitivity.

CONCLUSIONS/INTERPRETATION

Insulin sensitivity was increased in NO-deficient rats and this was associated with insulin binding capacity and downregulated Retn expression. These findings suggest that NO plays a regulatory role in metabolism. Dysregulation of NO production may result in the development of metabolic disorders.

Adipose tissue-derived factors: impact on health and disease

The endocrine functions of the adipose organ are widely studied at this stage. The adipose organ, and in particular adipocytes, communicate with almost all other organs. Although some adipose tissue pads assume the functions as distinct "miniorgans," adipocytes can also be present in smaller numbers interspersed with other cell types. Although fat pads have the potential to have a significant systemic impact, adipocytes may also affect neighboring tissues through paracrine interactions. These local or systemic effects are mediated through lipid and protein factors. The protein factors are commonly referred to as adipokines. Their expression and posttranslational modifications can undergo dramatic changes under different metabolic conditions. Due to the fact that none of the mutations that affect adipose tissue trigger embryonic lethality, the study of adipose tissue physiology lends itself to genetic analysis in mice. In fact, life in the complete absence of adipose tissue is possible in a laboratory setting, making even the most extreme adipose tissue phenotypes genetically amenable to be analyzed by disruption of specific genes or overexpression of others. Here, we briefly discuss some basic aspects of adipocyte physiology and the systemic impact of adipocyte-derived factors on energy homeostasis.

Brain adipocytokine action and metabolic regulation

Adipose tissue secretes factors that control various physiological systems. The fall in leptin during fasting mediates hyperphagia and suppresses thermogenesis, thyroid and reproductive hormones, and immune system. On the other hand, rising leptin levels in the fed state stimulate fatty acid oxidation, decrease appetite, and limit weight gain. These divergent effects of leptin occur through neuronal circuits in the hypothalamus and other brain areas. Leptin also regulates the activities of enzymes involved in lipid metabolism, e.g., AMP-activated protein kinase and stearoyl-CoA desaturase-1, and also interacts with insulin signaling in the brain. Adiponectin enhances fatty acid oxidation and insulin sensitivity, in part by stimulating AMP-activated protein kinase phosphorylation and activity in liver and muscle. Moreover, adiponectin decreases body fat by increasing energy expenditure and lipid catabolism. These effects involve peripheral and possibly central mechanisms. Adipose tissue mediates interconversion of steroid hormones and secretes proinflammatory cytokines, vasoactive peptides, and coagulation and complement proteins. Understanding the actions of these "adipocytokines" will provide insight into the pathogenesis and treatment of obesity and related diseases.

Loss of resistin improves glucose homeostasis in leptin deficiency

Resistin levels are increased in obesity, and hyperresistinemia impairs glucose homeostasis in rodents. Here, we have determined the role of resistin in ob/ob mice that are obese and insulin resistant because of genetic deficiency of leptin. Loss of resistin increased obesity in ob/ob mice by further lowering the metabolic rate without affecting food intake. Nevertheless, resistin deficiency improved glucose tolerance and insulin sensitivity in these severely obese mice, largely by enhancing insulin-mediated glucose disposal in muscle and adipose tissue. In contrast, in C57BL/6J mice with diet-induced obesity but wild-type leptin alleles, resistin deficiency reduced hepatic glucose production and increased peripheral glucose uptake. Resistin deficiency enhanced Akt phosphorylation in muscle and liver and decreased suppressor of cytokine signaling-3 level in muscle, and these changes were reversed by resistin replacement. Together, these results provide strong support for an important role of resistin in insulin resistance and diabetes associated with genetic or diet-induced obesity.

Role of transcription factor NFAT in glucose and insulin homeostasis

Compromised immunoregulation contributes to obesity and complications in metabolic pathogenesis. Here, we demonstrate that the nuclear factor of activated T cell (NFAT) group of transcription factors contributes to glucose and insulin homeostasis. Expression of two members of the NFAT family (NFATc2 and NFATc4) is induced upon adipogenesis and in obese mice. Mice with the Nfatc2-/- Nfatc4-/- compound disruption exhibit defects in fat accumulation and are lean. Nfatc2-/- Nfatc4-/- mice are also protected from diet-induced obesity. Ablation of NFATc2 and NFATc4 increases insulin sensitivity, in part, by sustained activation of the insulin signaling pathway. Nfatc2-/- Nfatc4-/- mice also exhibit an altered adipokine profile, with reduced resistin and leptin levels. Mechanistically, NFAT is recruited to the transcription loci and regulates resistin gene expression upon insulin stimulation. Together, these results establish a role for NFAT in glucose/insulin homeostasis and expand the repertoire of NFAT function to metabolic pathogenesis and adipokine gene transcription.

Adipocytokines: mediators linking adipose tissue, inflammation and immunity

There has been much effort recently to define the role of adipocytokines, which are soluble mediators derived mainly from adipocytes (fat cells), in the interaction between adipose tissue, inflammation and immunity. The adipocytokines adiponectin and leptin have emerged as the most abundant adipocyte products, thereby redefining adipose tissue as a key component not only of the endocrine system, but also of the immune system. Indeed, as we discuss here, several adipocytokines have a central role in the regulation of insulin resistance, as well as many aspects of inflammation and immunity. Other adipocytokines, such as visfatin, have only recently been identified. Understanding this rapidly growing family of mainly adipocyte-derived mediators might be of importance in the development of new therapies for obesity-associated diseases.