Relationship between serum resistin concentrations and insulin resistance in nonobese, obese, and obese diabetic subjects

Adipokines in inflammation and metabolic disease

The worldwide epidemic of obesity has brought considerable attention to research aimed at understanding the biology of adipocytes (fat cells) and the events occurring in adipose tissue (fat) and in the bodies of obese individuals. Accumulating evidence indicates that obesity causes chronic low-grade inflammation and that this contributes to systemic metabolic dysfunction that is associated with obesity-linked disorders. Adipose tissue functions as a key endocrine organ by releasing multiple bioactive substances, known as adipose-derived secreted factors or adipokines, that have pro-inflammatory or anti-inflammatory activities. Dysregulated production or secretion of these adipokines owing to adipose tissue dysfunction can contribute to the pathogenesis of obesity-linked complications. In this Review, we focus on the role of adipokines in inflammatory responses and discuss their potential as regulators of metabolic function.

Adipocyte-myocyte crosstalk in skeletal muscle insulin resistance; is there a role for thyroid hormone?

PURPOSE OF REVIEW

To review original research studies and reviews that present data on adipocyte-myocyte crosstalk in the development of skeletal muscle insulin resistance with a specific focus on thyroid hormone.

RECENT FINDINGS

Adipose tissue communicates with skeletal muscle not only through free fatty acids but also through secretion of various products called adipokines. Adipokines came out as governors of insulin sensitivity and are deregulated in obesity. In addition to well known leptin, adiponectin, interleukin-6 and tumor necrosis factor-alpha, newer adipokines like retinol-binding protein 4 have been associated with insulin resistance. There is mounting evidence that not only adipose tissue but also skeletal muscle produces and secretes biologically active proteins or 'myokines' that facilitate metabolic crosstalk between organ systems. In recent years, increased expression of myostatin, a secreted anabolic inhibitor of muscle growth and development, has been associated with obesity and insulin resistance. Both hypothyroidism and hyperthyroidism affect insulin sensitivity in multiple ways that might overlap adipocyte-myocyte crosstalk. Recent studies have provided new insights in effects of processing of the parent hormone T4 to the active T3 at the level of the skeletal muscle.

SUMMARY

Adipocyte-myocyte crosstalk is an important modulator in the development of skeletal muscle insulin resistance. Thyroid disorders are very common and may have detrimental effects on skeletal muscle insulin resistance, potentially by interacting with adipocyte-myocyte crosstalk.

Effect of telmisartan on selected adipokines, insulin sensitivity, and substrate utilization during insulin-stimulated conditions in patients with metabolic syndrome and impaired fasting glucose

Objective

Telmisartan improves glucose and lipid metabolism in rodents. This study evaluated the effect of telmisartan on insulin sensitivity, substrate utilization, selected plasma adipokines and their expressions in subcutaneous adipose tissue (SAT) in metabolic syndrome.

Design and methods

Twelve patients with impaired fasting glucose completed the double-blind, randomized, crossover trial. Patients received telmisartan (160 mg/day) or placebo for 3 weeks and vice versa with a 2-week washout period. At the end of each period, a hyperinsulinemic euglycemic clamp (HEC) combined with indirect calorimetry was performed. During HEC (0, 30, and 120 min), plasma levels of adipokines were measured and a needle biopsy (0 and 30 min) of SAT was performed.

Results

Fasting plasma glucose was lower after telmisartan compared with placebo (P<0.05). There were no differences in insulin sensitivity and substrate utilization. We found no differences in basal plasma adiponectin, resistin and tumour necrosis factor α (TNFα), but an increase was found in basal leptin, after telmisartan treatment. Insulin-stimulated plasma adiponectin (P<0.05), leptin and resistin (P<0.001) were increased, whereas TNFα was decreased (P<0.05) after telmisartan treatment. Expression of resistin, but not adiponectin, TNFα and leptin was increased after telmisartan treatment.

Conclusions

Despite the decrease in fasting plasma glucose, telmisartan does not improve insulin sensitivity and substrate utilization. Telmisartan increases plasma leptin as well as insulin-stimulated plasma adiponectin, leptin and resistin, and decreases plasma TNFα during HEC. Changes in plasma adipokines cannot be explained by their expressions in SAT. The changes in plasma adipokines might be involved in the metabolic effects of telmisartan in metabolic syndrome.

Short-term overfeeding may induce peripheral insulin resistance without altering subcutaneous adipose tissue macrophages in humans

OBJECTIVE

Chronic low-grade inflammation is a feature of obesity and is postulated to be causal in the development of insulin resistance and type 2 diabetes. The aim of this study was to assess whether overfeeding induces peripheral insulin resistance in lean and overweight humans, and, if so, whether it is associated with increased systemic and adipose tissue inflammation.

RESEARCH DESIGN AND METHODS

Thirty-six healthy individuals undertook 28 days of overfeeding by +1,250 kcal/day (45% fat). Weight, body composition, insulin sensitivity (hyperinsulinemic-euglycemic clamp), serum and gene expression of inflammation markers, immune cell activation, fat cell size, macrophage and T-cell numbers in abdominal subcutaneous adipose tissue (flow cytometry and immunohistochemistry) were assessed at baseline and after 28 days.

RESULTS

Subjects gained 2.7 +/- 1.6 kg (P < 0.001) and increased fat mass by 1.1 +/- 1.6% (P < 0.001). Insulin sensitivity decreased by 11% from 54.6 +/- 18.7 to 48.9 +/- 15.7 micromol/(kg of FFM)/min (P = 0.01). There was a significant increase in circulating C-reactive protein (P = 0.002) and monocyte chemoattractant protein-1 (P = 0.01), but no change in interleukin-6 and intercellular adhesion molecule-1. There were no changes in fat cell size, the number of adipose tissue macrophages or T-cells, or inflammatory gene expression and no change in circulating immune cell number or expression of their surface activation markers after overfeeding.

CONCLUSIONS

Weight gain-induced insulin resistance was observed in the absence of a significant inflammatory state, suggesting that inflammation in subcutaneous adipose tissue occurs subsequent to peripheral insulin resistance in humans.

Adipocytokines in sleep apnea syndrome

OBJECTIVE

Biomarkers of adipose tissue may affect glucose and lipid metabolism and present pro-inflammatory properties, thus could be involved in the pathobiochemistry of cardiovascular disease (CVD). The coexistence of sleep apnea syndrome (OSA) and metabolic risk factors of CVD is worth explaining. The aim of the study was to compare the serum adipocytokines in subjects with and without OSA, who had all elevated body mass index (BMI).

METHODS

Overweight (BMI: 25.0-29.9 kg/m2) and obese (BMI: 30.0-39.9 kg/m2) OSA-suspected Caucasian males, aged 30-63, with no acute disease or chronic disorder underwent polysomnographic evaluation to select OSA-positive (AHI > or = 5) and OSA-negative (AHI <5) subjects. Four subgroups were created of 18 persons each: Over(weight)-OSA-Neg, Over-OSA-Pos, Obese-OSA-Neg, Obese-OSA-Pos. In all subjects, plasma carbohydrate and lipid metabolism parameters, and serum uric acid, resistin and leptin concentrations were determined.

RESULTS

A decreased resistin level was observed in Over-OSA-Pos vs. Over-OSA-Neg subjects (P=0.037) as well as in Obese-OSA-Pos vs. Obese-OSA-Neg (P=0.045). No differences in leptin concentrations were observed. A positive correlation between leptin and BMI was in both overweight subgroups and a negative one between resistin and fasting glucose was in both obese subgroups.

CONCLUSIONS

OSA may decrease the serum resistin level in subjects with excess body mass and also may contribute to glucose metabolism, but has no influence on the leptin level.

Relationship between resistin and aPAI-1 levels with insulin resistance in Saudi children

BACKGROUND

Association of resistin with insulin resistance (IR) in humans is still controversial and few studies have investigated the association of plasminogen activator inhibitor-1 (PAI-1) with IR in children. The purpose of the present study was therefore to evaluate serum levels of resistin and active PAI-1 (aPAI-1) in Saudi children and their association with the various obesity-related complications.

METHODS

In this cross-sectional study, 73 boys and 77 girls with varying body mass index (BMI) were recruited. They were assessed for anthropometric measures and fasting serum levels of glucose, insulin, lipid profile, resistin, angiotensin II (ANG II) and aPAI-1.

RESULTS

Resistin was positively correlated with hips (r = 0.33, P < 0.01), waist (r = 0.23, P < 0.05) and BMI (r = 0.33, P < 0.01). The association of resistin with the markers of obesity was also significant in girls but lost significance in boys. aPAI-1 was positively correlated with total cholesterol (r = 0.24; P < 0.01), triglycerides (r = 0.2, P < 0.05), HOMA-IR (r = 0.26, P < 0.01) and insulin (r = 0.26, P < 0.01). The significant association of aPAI-1 with IR was also true in girls but lost significance in boys.

CONCLUSION

Resistin is not correlated with IR and further studies are needed to explore the role of resistin especially in childhood obesity. In contrast, increased levels of PAI-1 may contribute to the risk of cardiovascular diseases related to obesity and insulin resistance in children. The observed gender-related differences in the association between resistin, aPAI-1 with obesity markers and IR could be attributed to sexual dimorphism in body fat distribution.

Metabolic effects of obesity: A review

With the many recent advances in the biomedical world, vast changes are taking place in our growing knowledge of the physiological aspects of almost all the tissues and organs of the human body. One of the most prevalent topics of discussion is the question of obesity and its effect on the metabolic changes in the human body. The original classical role of adipose tissue as an energy storage organ has been greatly modified. We now know that it is an endocrine organ, producing adipokines like leptin, adiponectin, visfatin, resistin, apelin, etc, which modulate metabolic processes in the body. Since obesity is associated with an increase in the adipose tissue mass, these hormones may be expected to be produced in increased concentrations and may thus have a significant impact on the macronutrient metabolism. Further, these adipokines may interact with long term energy modulators like insulin. Even though the scientific community has started unravelling the mysteries of the close linkage between obesity, its hormones and their physiological effects, a lot still remains to be discovered. The present discussion makes an attempt to trace the basic modern day concepts of the role of obesity in various metabolic processes.

Diabetic cardiomyopathy: signaling defects and therapeutic approaches

Diabetes mellitus is the world's fastest growing disease with high morbidity and mortality rates, predominantly as a result of heart failure. A significant number of diabetic patients exhibit diabetic cardiomyopathy; that is, left ventricular dysfunction independent of coronary artery disease or hypertension. The pathogenesis of diabetic cardiomyopathy is complex, and is characterized by dysregulated lipid metabolism, insulin resistance, mitochondrial dysfunction and disturbances in adipokine secretion and signaling. These abnormalities lead to impaired calcium homeostasis, ultimately resulting in lusitropic and inotropic defects. This article discusses the impact of these hallmark factors in diabetic cardiomyopathy, and concludes with a survey of available and emerging therapeutic modalities.

Influence of exercise intensity in older persons with unchanged habitual nutritional intake: skeletal muscle and endocrine adaptations

Long-term adherence to training programmes is difficult to attain. Yet, the benefits of exercise to general health and well-being are undeniable. Any measure to demonstrate the minimum required exercise for maximal benefit to a person is a promising avenue towards increasing the uptake and adherence to physical activity for the general public. The purpose of this study was to compare the effects of two different intensities of resistance training in healthy older adults. We hypothesised that compared to high-intensity resistance exercise, relatively low training intensity could also improve in vivo markers of healthy physiologic and endocrine functions in previously sedentary older individuals. Thirty (out of a possible 34 recruited) older adults were randomly assigned to low (LowR, i.e. approximately 40% one repetition maximum (1RM)) versus high-resistance training (HighR, i.e. approximately 80% 1RM) for 12 weeks. Neither intervention significantly impacted upon body composition markers including: body mass index (BMI), waist/hip ratio and bioelectric impedance. Muscle strength data showed an advantage for the HighR protocol with 51 +/- 4% and 22.4 +/- 10.2% (P < 0.05) improvements in 1RM strength and bilateral knee extension torque, respectively, compared with 17 +/- 1% and 10.3 +/- 4.7% (P < 0.05) increments in 1RM strength and bilateral torque in the LowR group. Unilateral torque did not change significantly in either group. Quadriceps muscle thickness data also showed a significantly greater benefit of the HighR protocol (5.8 +/- 2.6% increase) compared with the LowR protocol (no change). Functional ability tests, including Get-up-and-go (GUG), Standing from lying and the 6-min walk, showed changes of -11.6 +/- 4.8%, -15.6% and 8.5 +/- 1.7% (P < 0.05), respectively, in HighR compared with only one significant improvement in the LowR, namely a -10.8 +/- 3% (P < 0.05) improvement in the GUG test. Overnight fasting serum levels of IGFBP-3 increased, NPY decreased and TNF-alpha decreased significantly in the LowR group. Serum levels of glucose increased and NPY decreased significantly in HighR. Circulating levels of I, IL-6 and IGF-1 did not change with either intervention. In vivo physiologic changes show functional advantages for older persons carrying out high-resistance training. At the endocrine level, such an advantage is not clear. In fact, in terms of changes in sera levels of fasting glucose, IGFBP-3 and TNF-alpha, there appears to be an advantage to carrying out the lower intensity exercises for the aged populations where endocrine adaptations are key.

Hyperresistinemia - a novel feature in systemic infection during human pregnancy

PROBLEM

Resistin, originally described as an adipokine, has emerged as a potent pro-inflammatory protein associated with both acute and chronic inflammation. Moreover, resistin has been proposed as a powerful marker of sepsis severity, as well as a predictor of survival of critically ill non-pregnant patients. The aim of this study was to determine whether pyelonephritis during pregnancy is associated with changes in maternal plasma resistin concentrations.

METHODS OF STUDY

This cross-sectional study included the following groups: (i) normal pregnant women (n = 85) and (ii) pregnant women with pyelonephritis (n = 40). Maternal plasma resistin concentrations were determined by ELISA. Non-parametric statistics was used for analyses.

RESULTS

(i) The median maternal plasma resistin concentration was higher in patients with pyelonephritis than in those with a normal pregnancy (P < 0.001); (ii) among patients with pyelonephritis, the median maternal resistin concentration did not differ significantly between those with and without a positive blood culture (P = 0.3); (iii) among patients with pyelonephritis who were diagnosed with systemic inflammatory response syndrome (SIRS), those who fulfilled > or =3 criteria for SIRS had a significantly higher median maternal plasma resistin concentration than those who met only two criteria; and (iv) maternal WBC count positively correlated with circulating resistin concentration (r = 0.47, P = 0.02).

CONCLUSION

Hyperresistinemia is a feature of acute pyelonephritis during pregnancy. The results of this study support the role of resistin as an acute-phase protein in the presence of bacterial infection during pregnancy.

Transcription of human resistin gene involves an interaction of Sp1 with peroxisome proliferator-activating receptor gamma (PPARgamma)

BACKGROUND

Resistin is a cysteine rich protein, mainly expressed and secreted by circulating human mononuclear cells. While several factors responsible for transcription of mouse resistin gene have been identified, not much is known about the factors responsible for the differential expression of human resistin.

METHODOLOGY/PRINCIPAL FINDING

We show that the minimal promoter of human resistin lies within approximately 80 bp sequence upstream of the transcriptional start site (-240) whereas binding sites for cRel, CCAAT enhancer binding protein alpha (C/EBP-alpha), activating transcription factor 2 (ATF-2) and activator protein 1 (AP-1) transcription factors, important for induced expression, are present within sequences up to -619. Specificity Protein 1(Sp1) binding site (-276 to -295) is also present and an interaction of Sp1 with peroxisome proliferator activating receptor gamma (PPARgamma) is necessary for constitutive expression in U937 cells. Indeed co-immunoprecipitation assay demonstrated a direct physical interaction of Sp1 with PPARgamma in whole cell extracts of U937 cells. Phorbol myristate acetate (PMA) upregulated the expression of resistin mRNA in U937 cells by increasing the recruitment of Sp1, ATF-2 and PPARgamma on the resistin gene promoter. Furthermore, PMA stimulation of U937 cells resulted in the disruption of Sp1 and PPARgamma interaction. Chromatin immunoprecipitation (ChIP) assay confirmed the recruitment of transcription factors phospho ATF-2, Sp1, Sp3, PPARgamma, chromatin modifier histone deacetylase 1 (HDAC1) and the acetylated form of histone H3 but not cRel, C/EBP-alpha and phospho c-Jun during resistin gene transcription.

CONCLUSION

Our findings suggest a complex interplay of Sp1 and PPARgamma along with other transcription factors that drives the expression of resistin in human monocytic U937 cells.

Association of resistin and adiponectin with different clinical blood pressure phenotypes

We investigated whether the resistin (Res) and adiponectin (Adp) levels are associated with different clinical blood pressure (BP) phenotypes. Among 465 consecutive never-treated white subjects, we excluded those with diabetes mellitus; impaired glucose metabolism; history of any cardiovascular disease or other concurrent medical condition; secondary hypertension; ongoing vasoactive treatment. Three separate clinic BP measurements and ambulatory BP monitoring were implemented to divide 328 subjects (aged 48±6 years; 172 males) into hypertensives (n=105), masked hypertensives (n=41), white-coat hypertensives (n=52) and normotensives (n=130). Participants underwent echocardiography and oral glucose tolerance testing, whereas, from fasting venous blood samples metabolic profile, plasma Res and Adp levels were assessed. Hypertensives and masked hypertensives showed higher log(10)(Res) and lower log(10)(Adp) levels compared with normotensives, whereas white-coat hypertensives had similar levels of these adipokines compared with normotensives. Common correlates for both of the adipokines were 24-h systolic BP, standing/sitting difference of both diastolic BP and heart rate, and waist circumference. Hypertensive and masked hypertensive compared with normotensive phenotype were independently associated with log(10)(Res) with odds ratios of 1.24 (1.08-1.44), and 1.16 (1.09-1.34) and log(10)(Adp) with 0.74 (0.65-0.87), and 0.81 (0.67-0.95), respectively. Increased Res and decreased Adp plasma levels are associated with out-of-clinic hypertension, whereas they did not determine white-coat hypertension.

Plasma adipokine and inflammatory marker concentrations are altered in obese, as opposed to non-obese, type 2 diabetes patients

Elevated plasma free fatty acid (FFA), inflammatory marker, and altered adipokine concentrations have been observed in obese type 2 diabetes patients. It remains unclear whether these altered plasma concentrations are related to the diabetic state or presence of obesity. In this cross-sectional observational study, we compare basal plasma FFA, inflammatory marker, and adipokine concentrations between obese and non-obese type 2 diabetes patients and healthy, non-obese controls. A total of 20 healthy, normoglycemic males (BMI <30 kg/m²), 20 non-obese (BMI <30 kg/m²) and 20 obese (BMI >35 kg/m²) type 2 diabetes patients were selected to participate in this study. Groups were matched for age and habitual physical activity level. Body composition, glycemic control, and exercise performance capacity were assessed. Basal blood samples were collected to determine plasma leptin, adiponectin, resistin, tumor necrosis factor α (TNFα), interleukin-6 (IL-6), high-sensitivity C-reactive protein (hsCRP) and FFA concentrations. Plasma FFA, inflammatory marker (hsCRP, IL-6, TNFα), adipokine (adiponectin, resistin, leptin), and triglyceride concentrations did not differ between non-obese diabetes patients and healthy, normoglycemic controls. Plasma FFA, IL-6, hsCRP, leptin, and triglyceride levels were significantly higher in the obese diabetes patients when compared with the healthy normoglycemic controls (P < 0.05). Furthermore, plasma hsCRP and leptin levels were significantly higher in the obese versus non-obese diabetes patients (P < 0.05). Significant correlations between plasma parameters and glycemic control were observed, but disappeared after adjusting for trunk adipose tissue mass. Elevated plasma leptin, hsCRP, IL-6, and FFA concentrations are associated with obesity and not necessarily with the type 2 diabetic state.

Plasma resistin concentration determined by common variants in the resistin gene and associated with metabolic traits in an aged Japanese population

AIMS/HYPOTHESIS

Resistin is a cytokine derived from adipose tissue and is implicated in obesity-related insulin resistance and type 2 diabetes mellitus. Polymorphisms of the resistin gene (RETN) have been shown to affect the plasma resistin concentration. The aims of this study were to identify polymorphisms of RETN that influence plasma resistin concentration and to clarify the relation between plasma resistin level and metabolic disorders in an aged Japanese cohort.

METHODS

The study participants comprised 3133 individuals recruited to a population-based prospective cohort study (KING study). Plasma resistin concentration, BMI, abdominal circumference, blood pressure, fasting plasma glucose and serum insulin concentrations, HbA(1c) content and serum lipid profile were measured in all participants. The HOMA index of insulin resistance (HOMA-IR) was also calculated. Eleven polymorphisms of RETN were genotyped.

RESULTS

A combination of ANOVA and multiple linear regression analysis in screening and large-scale subsets of the study population revealed that plasma resistin concentration was significantly associated with rs34861192 and rs3745368 polymorphisms of RETN. Multiple linear regression analysis with adjustment for age and sex also showed that the plasma resistin level was significantly associated with serum concentrations of HDL-cholesterol, triacylglycerol and insulin, as well as with BMI.

CONCLUSIONS/INTERPRETATION

Our results implicate the rs34861192 and rs3745368 polymorphisms of RETN as robust and independent determinants of plasma resistin concentration in the study population. In addition, plasma resistin level was associated with dyslipidaemia, serum insulin concentration and obesity.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00262691.

Effect of adipose tissue on the sexual dimorphism in metabolic flexibility

Metabolic flexibility is the ability to transition between fat oxidation (fasting state) and glucose oxidation (fed state). We hypothesized that adipose tissue inflammation and lipid metabolism contribute to sexual dimorphism in metabolic flexibility. Respiratory quotient (DeltaRQ, metabolic flexibility) and nonesterified fatty acids (NEFAs) before and during euglycemic-hyperinsulinemic clamp were measured in healthy young women (n = 22) and men (n = 56). Adiponectin levels were measured in plasma. Abdominal subcutaneous adipose tissue gene expression was measured by quantitative reverse transcriptase polymerase chain reaction. As compared with men, women had higher DeltaRQ (0.14 +/- 0.04 vs 0.09 +/- 0.04, P < .01). Fasting RQ and fat cell size were not different between sexes. As compared with men, women had lower insulin-suppressed NEFAs (P < .05); greater adiponectin levels; and higher expression of adipogenesis, fatty acid storage, and oxidation genes (PPARgamma2, PCK1, SCD1, and PPARalpha; P < .05). There were no sex differences in messenger RNA of macrophage markers or chemokines. Stepwise regression analysis revealed that the only adipose tissue characteristics that influenced metabolic flexibility in women were SCD1 and PCK1 messenger RNA (model R(2) = 0.49, P < .05); in men, these were serum adiponectin and insulin-suppressed NEFAs (model R(2) = 0.34, P < .05). Healthy young women are more metabolically flexible than men, driven by an increase in insulin-stimulated glucose oxidation rather than differences in fasting fat oxidation. Women have greater capacity for insulin suppression of NEFAs despite similar chemokine and macrophage content in adipose tissue. Combined, these results provide evidence for a role of adipose tissue characteristics in the sexual dimorphism of metabolic flexibility.

The role of resistin as a regulator of inflammation: Implications for various human pathologies

Resistin was originally described as an adipocyte-secreted peptide that induced insulin resistance in rodents. Increasing evidence indicates its important regulatory roles in various biological processes, including several inflammatory diseases. Further studies have shown that resistin in humans, in contrast to its production by adipocytes in mice, is synthesized predominantly by mononuclear cells both within and outside adipose tissue. Possible roles for resistin in obesity-related subclinical inflammation, atherosclerosis and cardiovascular disease, non-alcoholic fatty liver disease, rheumatic diseases, malignant tumors, asthma, inflammatory bowel disease, and chronic kidney disease have already been demonstrated. In addition, resistin can modulate several molecular pathways involved in metabolic, inflammatory, and autoimmune diseases. In this review, current knowledge about the functions and pathophysiological implications of resistin in different human pathologies is summarized, although there is a significant lack of firm evidence regarding the specific role resistin plays in the "orchestra" of the numerous mediators of inflammation.

Resistin induces insulin resistance by both AMPK-dependent and AMPK-independent mechanisms in HepG2 cells

Resistin is a 12.5-KDa cysteine-rich peptide that has been implicated in the impairment of glucose homeostasis via the AMP-activated protein kinase (AMPK) pathway in a rodent model. However, the role resistin plays in humans is controversial. This study investigated the effect of resistin on glucose metabolism and insulin signaling using human recombinant resistin and small interfering RNA (siRNA) against AMPKalpha2 to treat the human liver HepG2 cells. The mRNA of key genes involved in glucose metabolism and the insulin-signaling pathway were detected by real-time RT-PCR. Phosphorylation levels of Akt and AMPK were measured by western blot. The incorporation of D-[U-(14)C] glucose into glycogen was quantitated by liquid scintillation counting. The results demonstrate that resistin stimulated expressions of glucose-6-phosphatase (G6Pase), phosphoenolypyruvate carboxykinase (PEPCK), and suppressor of cytokine signaling 3 (SOCS-3), repressed the expressions of insulin receptor substrate 2(IRS-2) and glucose transporter 2(GLUT2). In addition, resistin inhibited the insulin-induced phosphorylation of Akt independent of AMPK. In conclusion, our findings suggest that resistin induces insulin resistance in HepG2 cells at least partly via induction of SOCS-3 expression and reduction of Akt phosphorylation through an AMPK-independent mechanism. Resistin also increases glucose production via AMPK-mediated upregulated expression of the genes encoding hepatic gluconeogenic enzymes, G6Pase, and PEPCK.

Association of plasma levels of resistin with subcutaneous fat mass and markers of inflammation but not with metabolic determinants or insulin resistance

The aim of the present study was to investigate the relationship of plasma resistin levels with determinants of the metabolic syndrome (MetS) and anthropometric parameters in healthy Korean subjects. Plasma resistin levels were determined in 276 subjects. In subjects with MetS, the plasma resistin levels were not significantly increased compared to those without MetS (8.3+/-4.3 ng/mL vs. 8.5+/-3.6 ng/mL, respectively, P=0.84). In addition, the plasma resistin levels were not correlated with the body mass index, the waist circumference, homeostasis model assessment-insulin resistance (HOMA-IR), fasting plasma glucose or insulin levels. However, the plasma resistin levels were positively correlated with the abdominal subcutaneous fat (r=0.18, P<0.01) in all subjects and correlated with TNF alpha(r=-0.16, P<0.05) and hsCRP (r=0.15, P<0.05) in subjects without MetS but not with MetS. With multiple linear regression analysis, these linear associations remained to be significant. The results of this study show that plasma resistin levels in humans were not associated with markers of insulin resistance, obesity or other determinants of the MetS.

Adipokine serum levels are related to liver histology in severely obese patients undergoing bariatric surgery

BACKGROUND

Leptin, adiponectin, and resistin are adipokines linked to the development of insulin resistance, which plays a central role in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). We aimed to define adipokine serum levels in severely obese patients undergoing bariatric surgery and to correlate these with anthropometric and metabolic variables, liver function tests, and histopathological parameters of NAFLD and nonalcoholic steatohepatitis (NASH).

METHODS

Surgical liver biopsies were obtained from 50 bariatric patients with no history of liver disease or significant alcohol consumption. Serum leptin, adiponectin, and resistin levels were measured, and histology was assessed using Brunt's and Kleiner's scoring systems.

RESULTS

Waist/hip ratio was significantly higher in men (p = 0.0001), and leptin (p = 0.036) and adiponectin (p = 0.0001) serum levels were higher in women. Forty-one of 50 patients (82%) had histological NAFLD, including 10 (20%) with NASH. Nine patients (18%) had normal liver histology (obese control subgroup). In NAFLD patients, serum adiponectin was negatively correlated with activity grade and fibrosis stage, resistin was negatively correlated with steatosis grade (p = 0.033), while leptin was not related to histology. Leptin/adiponectin ratio showed positive association with stage (p = 0.044). In the subgroup of NASH patients, adiponectin was negatively correlated only with stage (p = 0.01), while there was no correlation between leptin, resistin, or leptin/adiponectin and histology.

CONCLUSIONS

Serum adiponectin and resistin levels are related to liver histology in bariatric patients and may be indicative of the histological severity of NAFLD and the extent of hepatic steatosis, respectively. Serum leptin levels are not informative of underlying liver histology in severely obese patients.

High resistin and interleukin-6 levels are associated with gestational diabetes mellitus

Resistin is a cysteine-rich adipokine originally described as a molecular link between obesity and insulin resistance in rodents. In this study, we hypothesised that serum resistin concentrations are elevated in patients with gestational diabetes mellitus (GDM) when compared with pregnant women with normal glucose tolerance (NGT) and related to proinflammatory interleukin-6 (IL-6) and other factors conferring insulin resistance. Serum resistin and IL-6 were measured by enzyme-linked immunosorbent assay (ELISA) in 81 women with GDM, 82 women with NGT between 24 and 31 weeks of gestation and 25 healthy non-pregnant women. Resistin concentrations were significantly higher in the GDM (21.9 [17.55-25.40] ng/ml) than in the NGT group (19.03 [15.92-23.91] ng/ml, p = 0.047), as well as in the non-pregnant women (14.8 [13.7-16.6] ng/ml, p < 0.0001). Serum IL-6 levels were elevated in the GDM (1.0 [0.7-1.5] pg/ml) as compared with the NGT group (0.8 [0.5-1.1] pg/ml, p = 0.006) and the non-pregnant controls (0.7 [0.5-1.1] pg/ml, p = 0.04). Multiple regression analysis revealed that in the pregnant women circulating resistin was related to serum IL-6 (beta = 0.33, p = 0.0004) but not to insulin or the index of insulin resistance. It is concluded that the finding of high resistin and IL-6 levels in women with gestational diabetes might confirm a role of low-grade inflammation in the pathogenesis of GDM.

Serum resistin correlates with central obesity but weakly with insulin resistance in Chinese children and adolescents

OBJECTIVE

Resistin has been linked with obesity and hypothesized as a potential marker of insulin resistance in addition to being linked with acute inflammation. However, these links are still highly controversial in humans. Our goal was to examine resistin levels in relation to obesity, insulin resistance and inflammation markers in a large population of Asian children and adolescents.

METHODS

Children and adolescents (n=3472) aged 6-18 years, boys (n=1765) and girls (n=1707), were assessed for body size parameters, pubertal development, blood lipids, glucose, insulin, resistin, C-reactive protein (CRP), adiponectin and complement C3 (C3) levels.

RESULTS

Resistin increased with central obesity in both genders but not with simple adiposity in boys. Several markers associated with central obesity correlated in a gender-specific fashion with plasma resistin. Waist circumference, fat-mass percentage, waist-to-height ratio and body mass index (BMI) positively correlated with resistin in both genders. Blood lipids such as triglycerides, nonesterified fatty acids (NEFA) and low-density lipoprotein cholesterol, diastolic and systolic blood pressure correlated positively with resistin in boys. NEFA, high-density lipoprotein cholesterol (negatively) and inflammation markers, such as CRP and C3, positively correlated with resistin in girls. There was no correlation between resistin and adiponectin, and no association of adiponectin with resistin quintiles in either boys or girls. In both boys and girls, resistin tended to decrease with age, with girls having higher levels than boys. Few indices of insulin resistance were linked with plasma resistin in either gender.

CONCLUSION

In this population, plasma resistin levels are a weak biochemical marker of metabolic dysfunction defined by central obesity, adiposity and inflammation and does not predict insulin resistance. Only a small proportion of resistin variation can be explained by factors related to metabolic syndrome, suggesting that resistin is not strongly implicated in a concentration-dependent fashion in any of the examined pathologies.

Resistin acutely impairs insulin-stimulated glucose transport in rodent muscle in the presence, but not absence, of palmitate

Resistin is a cytokine implicated in the development of insulin resistance. However, there has been little investigation of the effects of resistin on fatty acid (FA) metabolism and insulin response in skeletal muscle, a key tissue for glucose disposal. The purpose of the present study was to examine the role of altered FA metabolism as a cause of resistin's inhibition of insulin-stimulated glucose transport in muscle. Isolated rat soleus muscles were incubated acutely (2 h) in the presence or absence of 600 ng/ml resistin, with or without 2 mM palmitate. Resistin acutely impaired insulin-stimulated glucose transport and Akt phosphorylation, but only in the presence of palmitate, implicating a role for altered FA metabolism. This impairment of glucose transport induced by resistin plus palmitate could be pharmacologically rescued by the inclusion of aimidazole carboxamide ribonucleotide, a stimulator of AMP-activated protein kinase and FA oxidation, as well as inhibitors of ceramide synthesis (myriocin, fumonisin). However, to our surprise, resistin actually blunted the palmitate-induced increase in muscle ceramide content; as expected, ceramide content was significantly lowered by fumonisin. In summary, the acute impairment of insulin response by resistin was manifested only in the presence of high palmitate and was alleviated when FA metabolism was manipulated (increased oxidation, inhibited ceramide synthesis). Resistin's acute impairment of insulin response does not appear to require an absolute increase in ceramide content; however, reducing ceramide content alleviated the impairment in glucose transport and insulin signaling.

The expression of rat resistin isoforms is differentially regulated in visceral adipose tissues: effects of aging and food restriction

Two variants of the adipose hormone resistin are generated by alternative splicing in Wistar rats. Here we analyzed the expression of these resistin variants in 2 main visceral adipose depots, epididymal and retroperitoneal, as well as the resistin serum concentration during aging and food restriction. Total protein levels of resistin were also analyzed in extracts from both visceral adipose depots. Resistin variants show similar patterns of relative expression in visceral adipose tissues in 3-month-old rats, representing the short variant, s-resistin, which is 15% of the full-length transcript. However, only epididymal, but not retroperitoneal, fat pad shows a decrease in both messenger RNA and protein levels of resistin isoforms with aging. Food restriction decreases adiposity index in 8- and 24-month-old animals to values even lower than those of 3-month-old animals. Food restriction decreases resistin expression in both adipose tissues in 8-month-old but not in 24-month-old rats. Interestingly, concomitant with the improvement of insulin sensitivity asserted by homeostasis model assessment, resistin serum levels decrease only in food-restricted 8-month-old animals. In contrast, food restriction up-regulates s-resistin messenger RNA in epididymal adipose tissue, whereas no significant changes are appreciated in retroperitoneal adipose tissue. These data indicate that both forms of resistin are differentially regulated by fat depot location, aging, and even nutritional status, suggesting that alternative splicing plays a key role in this differential regulation.

Relationship between serum adipocytokine levels and metabolic syndrome in menopausal women

OBJECTIVE

Adipocytokines are bioactive substances derived from adipose tissues, especially visceral fat, and play a crucial role in the development of metabolic syndrome. The aims of this study were to estimate serum levels of adipocytokines (adiponectin, resistin and TNF-alpha) and to examine the associations between adipocytokine levels and metabolic syndrome in menopausal women.

METHODS

We recruited 28 postmenopausal women with features of metabolic syndrome. For the purpose of comparing adipocytokine levels, 30 postmenopausal women without metabolic syndrome were recruited by matching age and body mass index (BMI). Serum levels of adipocytokines (adiponectin, resistin, TNF-alpha) were then determined, and any potential correlations between adipocytokine levels and metabolic syndrome were investigated.

RESULTS

There were no significant differences in adiponectin or resistin levels in women with metabolic syndrome when compared with the control group. Conversely, TNF-alpha levels were significantly higher in women with metabolic syndrome. Furthermore, multivariate logistic regression analysis indicated that TNF-alpha was significantly associated with metabolic syndrome.

CONCLUSION

Our results suggest that, among the adipocytokines (adiponectin, resistin and TNF-alpha), serum TNF-alpha levels may serve as a useful biomarker for diagnosing metabolic syndrome in menopausal women.

Energy homoeostasis: The roles of adipose tissue-derived hormones, peptide YY and Ghrelin

This review discusses the physiology of the hormones leptin, adiponectin, resistin, peptide YY, and ghrelin and how each of these contributes to energy homoeostasis, weight regulation, and the pathogenesis of obesity. The relationship these hormones have with insulin and insulin resistance is also discussed, and the potential therapeutic use of each of these hormones is also considered.

Relation of adipose tissue to metabolic flexibility

Metabolic flexibility is the capacity for skeletal muscle to shift reliance between lipids and glucose during fasting or in response to insulin. We hypothesized that body fat, adipose tissue characteristics, e.g. larger adipocytes, presence of inflammatory gene markers and impaired suppression of non-esterified fatty acids (NEFAs) during insulin infusion might be related to metabolic flexibility. We measured changes in respiratory quotient (DeltaRQ) before and during euglycemic-hyperinsulinemic clamp in healthy young males. Body fat by DXA, laboratory measurements, abdominal subcutaneous adipose tissue biopsies and fat cell size (FCS) were obtained after an overnight fast. Gene expression for 17 adipose tissue genes related to lipid synthesis, uptake, oxidation and storage, lipolysis and inflammation were measured. Reduced metabolic flexibility was associated with higher body fat, larger FCS and impaired insulin suppression of NEFAs. Metabolic flexibility was associated with higher serum adiponectin levels. Lower adipose tissue gene expression for inflammation markers was associated with greater NEFA suppression by insulin and metabolic flexibility. Combined, these results indicate that body fat, larger adipocytes, failure of insulin to suppress NEFAs, decreased adiponectin levels and inflammation markers in adipose tissue are associated with decreased insulin-stimulated glucose uptake and oxidation, which is an important component of reduced metabolic flexibility.

Inverse association between serum resistin and insulin resistance in humans

AIM

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Adipocytokines and the metabolic complications of obesity

CONTEXT

Adipose tissue is increasingly recognized as an active endocrine organ with many secretory products and part of the innate immune system. With obesity, macrophages infiltrate adipose tissue, and numerous adipocytokines are released by both macrophages and adipocytes. Adipocytokines play important roles in the pathogenesis of insulin resistance and associated metabolic complications such as dyslipidemia, hypertension, and premature heart disease.

EVIDENCE ACQUISITION

Published literature was analyzed with the intent of addressing the role of the major adipose secretory proteins in human obesity, insulin resistance, and type 2 diabetes.

EVIDENCE SYNTHESIS

This review analyzes the characteristics of different adipocytokines, including leptin, adiponectin, pro-inflammatory cytokines, resistin, retinol binding protein 4, visfatin, and others, and their roles in the pathogenesis of insulin resistance.

CONCLUSIONS

Inflamed fat in obesity secretes an array of proteins implicated in the impairment of insulin signaling. Further studies are needed to understand the triggers that initiate inflammation in adipose tissue and the role of each adipokine in the pathogenesis of insulin resistance.

Adipokines and insulin resistance

Obesity is associated with an array of health problems in adult and pediatric populations. Understanding the pathogenesis of obesity and its metabolic sequelae has advanced rapidly over the past decades. Adipose tissue represents an active endocrine organ that, in addition to regulating fat mass and nutrient homeostasis, releases a large number of bioactive mediators (adipokines) that signal to organs of metabolic importance including brain, liver, skeletal muscle, and the immune system--thereby modulating hemostasis, blood pressure, lipid and glucose metabolism, inflammation, and atherosclerosis. In the present review, we summarize current data on the effect of the adipose tissue-derived hormones adiponectin, chemerin, leptin, omentin, resistin, retinol binding protein 4, tumor necrosis factor-alpha and interleukin-6, vaspin, and visfatin on insulin resistance.

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

BACKGROUND

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

OBJECTIVE

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

DESIGN

Prospective, nested, case-control study.

SETTING

United States.

PARTICIPANTS

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

MEASUREMENTS

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

RESULTS

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

LIMITATION

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

CONCLUSION

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

The usefulness of circulating adipokine levels for the assessment of obesity-related health problems

Because the prevalence of obesity has increased dramatically in recent years, one of the key targets of public health is obesity and its associated pathological conditions. Obesity occurs as a result of white adipose tissue enlargement, caused by adipocyte hyperplasia and/or hypertrophy. Recently, endocrine aspects of adipose tissue have become an active research area and these adipose tissue-derived factors are referred to as adipokines. These adipokines interact with a range of processes in many different organ systems and influence a various systemic phenomena. Therefore, dysregulated production of adipokines has been found to participate in the development of metabolic and vascular diseases related to obesity. The obese state is also known to be associated with increased local and systemic inflammation. Adipokines influence not only systemic insulin resistance and have pathophysiological roles in the metabolic syndrome and cardiovascular disease, but also contribute toward an increase in local and systemic inflammation. Thus, circulating levels of adipokines can be used as high-throughput biomarkers to assess the obesity-related health problems, including low grade inflammation. This review focuses on the usefulness of measuring circulating adipokine levels for the assessment of obesity-related health problems.

The role of adiposity as a determinant of an inflammatory milieu

With the growing prevalence of obesity, scientific interest in the biology of adipose tissue has been extended to the secretory products of adipocytes, since they have been shown increasingly to affect several aspects of the pathogenesis of obesity-related diseases. Until relatively recently, the role of adipose tissue itself in the development of obesity and its consequences was considered to be a passive one. It is now clear that, in addition to storing energy in the form of triglycerides, adipocytes also secrete a large variety of proteins, including cytokines, chemokines and hormone-like factors. This production of proatherogenic chemokines by adipose tissue is of particular interest, since their local secretion, for example by perivascular adipose depots, may provide a novel mechanistic link between obesity and associated vascular complications.

Associations of adiponectin, resistin, and tumor necrosis factor-alpha with insulin resistance

CONTEXT

Adipose tissue-derived adipokines may contribute to insulin resistance.

OBJECTIVE

We tested the hypothesis that adipokines are associated with insulin resistance in a community-based cohort and that associations are maintained in people with and without the metabolic syndrome (high vs. low risk of diabetes).

DESIGN, SETTING, AND PARTICIPANTS

We studied a cross-sectional sample of 2356 individuals attending the seventh examination (1998-2001) of the Framingham Offspring Study. We measured levels of glucose, insulin, adiponectin, resistin, and TNFalpha in fasting blood samples and defined metabolic syndrome by updated National Cholesterol Education Program criteria. We used ANOVA to test associations of adipokines with insulin resistance and multivariable logistic regression models to assess joint associations of adipokines and metabolic syndrome with insulin resistance.

MAIN OUTCOME MEASURE

Homeostasis model (HOMA-IR), with insulin resistance defined by HOMA-IR greater than the 75th percentile, was measured.

RESULTS

Age- and sex-adjusted HOMA-IR levels were inversely related to adiponectin (r = -0.40, P < 0.0001) and positively related to resistin (r = 0.13, P < 0.0001) and TNFalpha (r = 0.12, P < 0.0001). The prevalence of insulin resistance increased with decreasing tertiles of adiponectin (from 10.9% in the third to 42.5% in the first tertile; P < 0.0001) and increasing tertiles of resistin (from 19.3 to 30.9%; P < 0.0001) and TNFalpha (from 18.8 to 32.0%; P < 0.0001). Results were similar after adjustment for body mass index. These associations were present in individuals with or without the metabolic syndrome. In multivariable regression models, metabolic syndrome and adipokines individually and jointly were significantly associated with insulin resistance.

CONCLUSION

Adverse levels of adipokines are associated with insulin resistance in individuals at low or high diabetes risk.

Role of resistin in cardiac contractility and hypertrophy

Cardiovascular sequelae including diabetic cardiomyopathy constitute the major cause of death in diabetic patients. Although several factors may contribute to the development of this cardiomyopathy, the underlying molecular/cellular mechanisms leading to cardiac dysfunction are still partially understood. Recently, a novel paradigm for the role of the adipocytokine resistin in diabetes has emerged. Resistin has been proposed to be a link between obesity, insulin resistance and diabetes. Using microarray analysis, we have recently found that cardiomyocytes isolated from type 2 diabetic hearts express high levels of resistin. However, the function of resistin with respect to cardiac function is unknown. In this study we show that resistin is not only expressed in the heart, but also promotes cardiac hypertrophy. Adenovirus-mediated overexpression of resistin in cultured neonatal rat ventricular myocytes (NRVM) significantly increased sarcomere organization and cell size, increased protein synthesis and increased the expression of atrial natriuretic factor and beta-myosin heavy chain. Overexpression of resistin in NRVM was also associated with activation of the mitogen-activated protein (MAP) kinases, ERK1/2 and p38, as well as increased Ser-636 phosphorylation of insulin receptor substrate-1 (IRS-1), indicating that IRS-1/MAPK pathway may be involved in the observed hypertrophic response. Overexpression of resistin in adult cultured cardiomyocytes significantly altered myocyte mechanics by depressing cell contractility as well as contraction and relaxation velocities. Intracellular Ca(2+) measurements showed slower Ca(2+) transients decay in resistin-transduced myocytes compared to controls, suggesting impaired cytoplasmic Ca(2+) clearing or alterations in myofilament activation. We conclude that resistin overexpression alters cardiac contractility, confers to primary cardiomyocytes all the features of the hypertrophic phenotype and promotes cardiac hypertrophy possibly via the IRS-1/MAPK pathway.

Short-term treatment with ezetimibe, simvastatin or their combination does not alter circulating adiponectin, resistin or leptin levels in healthy men

OBJECTIVE

Statin therapy decreases cardiovascular morbidity and mortality, and ezetimibe, a novel cholesterol absorption inhibitor has both lipid-lowering and anti-atherosclerotic effects in animal models. As several adipokines, that is, adiponectin, high molecular weight (HMW) adiponectin, leptin and/or possibly resistin are involved in the pathogenesis of insulin resistance (IR), dyslipidaemia and atherosclerosis, we investigated whether ezetimibe and/or statin treatment may modulate serum concentrations of these four major adipokines.

RESEARCH DESIGN AND METHODS

One-centre, randomized, parallel three-group study in 72 healthy men [mean age 32 +/- 9 years, mean body mass index (BMI) 25.7 +/- 3.2 kg/m(2)].

PATIENTS

Seventy-two healthy men. Each group of 24 subjects received a 14-day treatment with either ezetimibe (10 mg/day), simvastatin (40 mg/day) or their combination. Blood was drawn before and after the 14-day treatment period.

MEASUREMENTS

Lipid levels, IR indices, serum leptin, adiponectin, HMW adiponectin and resistin concentrations. Results Neither ezetimibe nor simvastatin or their combination had any effect on serum leptin, adiponectin, HMW adiponectin and resistin concentrations. Baseline leptin levels correlated positively, while adiponectin and HMW adiponectin negatively, with BMI. Leptin concentrations correlated negatively while adiponectin and HMW adiponectin positively with plasma high-density lipoprotein-cholesterol concentrations. Resistin concentrations were not associated with BMI, lipid levels or indicators of IR.

CONCLUSIONS

Treatment with ezetimibe, simvastatin or their combination does not alter circulating levels of adiponectin, leptin or resistin in adult healthy men.

Long-term GH treatment is not associated with disadvantageous changes of inflammatory markers and adipocytokines in children born small for gestational age

CONTEXT

Low birth weight is associated with increased risks for adult cardiovascular disease (CVD) and diabetes mellitus type 2 (DM2). Adiponectin and resistin are hormones, considered, respectively, protective and disadvantageous regarding these risks. No data exist on the effect of long-term GH treatment on these hormones and inflammatory markers in children born small for gestational age (SGA).

OBJECTIVE

To describe longitudinal changes in inflammatory markers and adipocytokines during and after a long-term dose-response GH study.

DESIGN

Longitudinal dose-response study [group A: 1 mg/m(2) body surface area (BSA) (approximately 0.033 mg/kg/day) vs. group B: 2 mg/m(2) BSA (approximately 0.067 mg/kg/day)] and comparison with age-related controls.

PATIENTS

One hundred and three SGA children.

MEASUREMENTS

We measured adiponectin, resistin, interleukin-6 (IL-6) and C-reactive protein (CRP) levels at baseline, after 1 and 7 years of GH treatment and 6 months after discontinuation of GH.

RESULTS

Adiponectin levels decreased over time, but remained comparable with controls. Resistin levels increased and remained lower or comparable with controls. There were no significant differences between the GH dosage groups. After the GH treatment was stopped, adiponectin was decreased in group B and resistin increased in group A. GH therapy did not affect IL-6 and CRP levels at any time point. An increase in body mass index (BMI) standard deviation score (SDS) over time was associated with a decrease in adiponectin levels. None of the markers were associated with insulin sensitivity.

CONCLUSIONS

Long-term GH treatment is not associated with disadvantageous changes in adiponectin, resistin, IL-6 and CRP levels, neither during nor after GH treatment.

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.

Adipose tissue lipin-1 expression is correlated with peroxisome proliferator-activated receptor alpha gene expression and insulin sensitivity in healthy young men

CONTEXT

Lipin-1 functions in adipocyte triglyceride biosynthesis and in the regulation of gene expression, both of which may influence metabolic homeostasis.

OBJECTIVE

Our objective was to determine whether variations in adipose tissue lipin-1 expression levels influence insulin sensitivity and gene expression in young healthy human subjects.

DESIGN AND SUBJECTS

In 56 healthy young men (22.6 +/- 3.2 yr; 26.4 +/- 4.1 kg/m2) we determined insulin sensitivity by a euglycemic-hyperinsulinemic clamp, and whole body oxygen consumption and respiratory quotient by indirect calorimetry. We performed gene expression analysis in adipose tissue samples from human subjects and from lipin-1 transgenic mice using quantitative RT-PCR.

RESULTS

In healthy young men, lipin-1 expression was positively correlated with insulin sensitivity (R2 = 0.22; P < 0.01), insulin-stimulated respiratory quotient (R2 = 0.16; P < 0.01), and maximal oxygen consumption during exercise (R2 = 0.16; P < 0.01). Lipin-1 mRNA levels were also correlated with expression of genes involved in lipid oxidation, uptake, and lipolysis, both in humans and in lipin-1 transgenic mice. The strongest correlation occurred between lipin-1 and peroxisome proliferator-activated receptor alpha (R2 = 0.74; P < 1 x 10(-7)), a nuclear receptor with a key role in fatty acid oxidation.

CONCLUSION

Lipin-1 expression levels in adipose tissue of healthy young subjects and in mice are correlated with a favorable metabolic profile and expression of fatty acid oxidation genes.

Elevated plasma resistin concentrations in patients with liver cirrhosis

BACKGROUND

Resistin, an adipose-derived polypeptide hormone, has been proposed to be a candidate in insulin resistance, although its role in humans remains controversial. Liver cirrhosis (LC) is characterized by an elevated number of circulating proinflammatory cytokines, hyperinsulinemia and insulin resistance. The aim of this study was to determine the plasma resistin levels in patients with LC.

METHODS

Resistin levels were determined in 79 patients with LC and in 31 healthy controls. Patients included 34 with Child-Pugh grade A, 30 with Child's B and 15 with Child's C LC. Fasting plasma glucose, fasting plasma insulin, adiponectin, the homeostatic model assessment insulin resistance (HOMA-IR) index, quantitative insulin sensitivity check index (QUICKI) and biochemical parameters were also determined.

RESULTS

Plasma resistin levels were 7.61 +/- 6.70 ng/mL in the LC patients and 3.38 +/- 1.68 ng/mL in the controls, respectively. The plasma resistin levels were significantly elevated in patients with LC in comparison to the controls (P < 0.01). The plasma resistin levels increased in a stepwise fashion in line with a higher grade according to Child-Pugh classification. Fasting plasma insulin, adiponectin and HOMA-IR index were also significantly elevated in patients with LC in comparison to controls. Inversely, QUICKI significantly decreased in patients with LC. According to Spearman's rank correlation, log resistin showed significantly positive correlation with fasting plasma insulin, log adiponectin, HOMA-IR index, and a negative correlation with QUICKI (P < 0.01). The plasma resistin levels did not correlate with sex, body mass index and fasting plasma glucose levels.

CONCLUSION

The plasma resistin levels increased in patients with LC, thus showing a positive correlation with fasting plasma insulin, adiponectin, HOMA-IR index, and a negative correlation with QUICKI. Although a decreased extraction of resistin due to reduced liver function cannot be ruled out, resistin may contribute to insulin resistance in patients with LC. The pathophysiological roles of resistin in LC still require further investigation.

Serum resistin concentrations in growth hormone-deficient children during growth hormone replacement therapy

We performed this study to examine whether the serum resistin concentrations in growth hormone (GH)-deficient (GHD) children are influenced by administration of GH and to assess the relationship between serum resistin and free fatty acid levels during GH replacement therapy. The study included 20 prepubertal GHD children (16 boys and 4 girls) who were treated with recombinant human GH (hGH). The serum levels of resistin, insulin-like growth factor I, free fatty acid (FFA), triglyceride, cholesterol and glucose levels, leukocyte counts, and hemoglobin A(1c) were measured at baseline and after 1 month of hGH treatment. The serum resistin levels after hGH therapy were significantly higher than the basal resistin levels (median [range], 6.2 [4.9-11.8] vs 5.6 [4.4-8.3] ng/mL; P < .05), whereas the serum FFA levels were unchanged before and after treatment (0.51 [0.34-0.76] vs 0.37 [0.24-0.60] mEq/L). No significant relationship was found between serum resistin and FFA levels after hGH therapy. Body mass index, serum triglyceride, cholesterol and glucose levels, leukocyte counts, and hemoglobin A(1c) showed no significant differences before and after hGH treatment. Our results suggest that elevated serum resistin levels after 1-month hGH therapy in GHD children are not associated with the GH-induced lipolysis as found in GHD adults during short-time hGH therapy.

Contribution of nonesterified fatty acids to insulin resistance in the elderly with normal fasting but diabetic 2-hour postchallenge plasma glucose levels: the Baltimore Longitudinal Study of Aging

Isolated postchallenge hyperglycemia (IPH) with normal fasting plasma glucose <100 mg/dL and plasma glucose with diabetic 2-hour plasma glucose >or=200 mg/dL after an oral glucose tolerance test (OGTT) is a common occurrence in the elderly. We sought to understand what unique characteristics this population might have that puts it at risk for this particular metabolic finding. We therefore conducted a longitudinal study of volunteers in the Baltimore Longitudinal Study of Aging (BLSA). All volunteers had an OGTT performed (75 g) on 2 or more occasions. We measured plasma levels of glucose, insulin, C-peptide, glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), ghrelin, leptin, adiponectin, resistin, C-reactive protein, cytokines, and their soluble receptors, as well as nonesterified free fatty acids (NEFAs). We determined that 22 subjects in BLSA had IPH, accounting for 2.1% of the BLSA population. All 22 were older than 65 years. They were then matched by age, sex, and body mass index to 12 subjects who had isolated impaired glucose tolerance (IGT) and 15 subjects with normal glucose tolerance (NGT). All subjects had normal fasting glucose levels <100 mg/dL in accordance with the American Diabetes Association Expert Committee on the Classification and Diagnosis of Diabetes Mellitus criteria (2003). We found that subjects with IPH had similar plasma insulin levels to the other 2 groups, except at the 2-hour time when their insulin levels were higher than NGT (P < .05). Although there was a clear trend for differences in the insulinogenic index, the areas under the curves for insulin, systolic blood pressure, adiponectin, and C-reactive protein across the glucose tolerance categories revealed no statistical significance. Cytokines and their soluble receptors, gut hormones, and adipokines were similar in all 3 groups. The NEFA levels were significantly elevated in the fasting state (P < .05) in the IPH compared with NGT, with IGT intermediate between the other 2 groups. The rate of clearance of NEFAs after the OGTT decreased progressively from the NGT to the IPH group (in micromoles per liter per minute: NGT, 11.9 vs IGT, 7.6 vs IPH, 3.0). We conclude that the rate of suppression of lipolysis in the elderly determines the sensitivity of glucose uptake to insulin after OGTT.

Decreased circulating protective adiponectin level is associated with angiographic coronary disease progression in patients with angina pectoris

Adipocyte cytokines regulate glucose metabolism and insulin resistance and adiponectin is thought to have a protective effect against atherosclerosis. Studies have shown that adiponectin expression is decreased in obese subjects and those with metabolic syndrome or diabetes mellitus. The purpose of this study was to investigate the relationship between circulating adipocyte cytokine concentrations and angiographic coronary artery disease (CAD) progression in patients with chest pain. Patients with stable angina pectoris who underwent repeat coronary angiograms and had serum samples at the time of first catheterization between March 1999 and January 2004 were enrolled. A modified Gensini scoring system was used to define angiographic coronary artery progression between the index and follow-up angiograms. Those who had significant angiographic progression of coronary lesions were classified into the progression group (N=55). Those who did not have CAD progression were classified into the non-progression group (N=102). Univariate analysis showed that CAD progression was associated with male gender (93% vs. 78%, p=0.038), higher baseline total cholesterol (187+/-43 vs. 173+/-39 mg/dl, p=0.037) and higher baseline fasting blood glucose (128+/-57 vs. 110+/-40 mg/dl, p=0.037). Patients in the progression group had a significantly lower serum adiponectin level (14.3+/-7.9 vs. 18.9+/-13.2 mug/ml, p=0.007) than, but resistin (28.9+/-13.4 vs. 34.4+/-26.0 ng/ml, p=0.142) and leptin (7.4+/-4.6 vs. 7.7+/-6.5 ng/ml, p=0.675) levels similar to, those in the non-progression group. In a multivariate binary logistic regression model, male gender (odds ratio 4.283, p=0.015), higher serum cholesterol (odds ratio 1.010, p=0.032) and lower serum adiponectin (odds ratio 0.959, p=0.030) were all significant independent predictors of CAD progression. In conclusion, we found that a decreased circulating level of adiponectin is associated with angiographic CAD progression in patients with angina pectoris.

The interplay between nutrients and the adipose tissue

The importance of adipose tissue in health as well as disease has been demonstrated in several studies recently, and it has become appropriate to use the term 'adipose organ' when referring to adipose tissue as a whole. The obesity epidemic, with a marked increase in the incidence of the metabolic syndrome leading to diabetes type 2 as well as cardiovascular complications, has stimulated considerable interest in adipose tissue biology. Moreover, several studies in different species have shown that limited energy intake is associated with less inflammation, improved biomarkers of health and a marked increase in longevity. In addition, there is convincing evidence that an optimal amount of adipose tissue is essential for many body functions such as immune response, reproduction and bone quality. Some nutrients and their metabolites are important as energy sources as well as ligands for many transcription factors expressed in adipose tissue, including all energy-providing nutrients both directly and indirectly as well as cholesterol, vitamin E and vitamin D. In particular, fatty acids can be effectively taken up by adipocytes and they can interact with several transcription factors crucial for growth, development and metabolic response, e.g. PPARalpha, -delta and -gamma, sterol regulatory element-binding proteins1 and 2 and liver X receptors alpha and beta). Moreover, glucose is also readily taken up and stored as fatty acids via lipogenesis in adipocytes. It is known that some metabolic signals released as proteins from adipose tissue (adipokines) are important for normal as well as pathological responses to the amount of energy stored in the adipose organ. The future challenge will be to understand the function of adipose tissue in energy homeostasis and the interplay with nutrients in order to be able to give optimal advice for the prevention and treatment of obesity.

Genetics of the metabolic syndrome

The concept of a metabolic syndrome (MetS), a cluster of pre-clinical metabolic alterations commonly associated with obesity, is the object of much debate. Genetic studies have the potential to contribute to some of the key questions, including the true nature of the cluster of pre-clinical features and whether it is associated with human genetic variation. This review summarizes the evidence for the presence of familial aggregation for the individual components of MetS and their heritability levels. It also provides an overview of the studies that have dealt with candidate genes for MetS. Potential leads from genome-wide linkage scans are also discussed. The assumption is made that obesity, ectopic fat deposition and abnormal adipose tissue metabolism are responsible for alterations in lipid metabolism, which in turn generates the commonly observed pre-clinical shifts in glucose tolerance, lipids and lipoprotein profile, blood pressure, inflammatory markers, endothelial function, and a prothrombotic state. Progress in the understanding of the genetic basis of MetS should occur as soon as a consensus is reached on the true nature of MetS, its components and diagnostic criteria.

Associations of resistin with inflammation and insulin resistance in patients with type 2 diabetes mellitus

OBJECTIVE

Resistin has been linked to obesity, type 2 diabetes, inflammation and atherosclerosis but the results of animal and human studies have been at variance. The purpose of this study was to investigate the potential roles of resistin in patients with type 2 diabetes and to evaluate the correlation between resistin and markers of obesity, inflammation, insulin resistance, metabolic parameters, diabetes control and complications.

MATERIAL AND METHODS

Fasting resistin, leptin, insulin, glucose, HbA1c, full lipid profile, C-reactive protein (CRP) (high sensitivity assay) and complete blood count were determined in 135 patients with type 2 diabetes. Univariate regression and multivariate logistic regression analyses were used to relate resistin with indices of obesity, inflammation, insulin resistance (homeostasis model, HOMA), insulin sensitivity, diabetic control, coronary heart disease (CHD) and degree of microalbuminuria.

RESULTS

Resistin showed significant (p<0.05) correlations with body mass index (BMI) "(Spearman r=0.67), waist circumference (r=0.54), fasting insulin (0.51), insulin sensitivity (r=-0.29), HOMA (r=0.30), leptin (r=0.39), CRP (r=0.29), white cell count (r=0.25) and lipid parameters but showed no significant correlation with glucose and HbA1c. Partial correlation analysis, with correction for BMI, abolished the correlation of resistin with insulin sensitivity and HOMA but not with the white cell count. When confounding factors were fixed using multiple logistic regression, resistin was not independently associated with CHD (odds ratio=1.05, p=0.08) and degree of microalbuminuria (odds ratio=1.06, p=0.24).

CONCLUSIONS

Resistin showed significant BMI-dependent associations with insulin resistance and factors linked with obesity and inflammation in patients with type 2 diabetes. Resistin may represent a link between obesity and insulin resistance via pro-inflammatory pathways.