Pre- and post-translational negative effect of beta-adrenoceptor agonists on adiponectin secretion: in vitro and in vivo studies

Adiponectin and cardiovascular inflammatory responses

Obesity is recognized as a cause of many metabolic and cardiovascular disorders through its ability to promote chronic systemic inflammation. Recent studies have found that adipose tissues secrete numerous cytokines that are referred to as adipokines. Although most adipokines induce inflammation, adiponectin inhibits inflammatory reactions and protects against metabolic and cardiovascular diseases. This review focuses on the anti-inflammatory properties of adiponectin in various experimental systems, especially with respect to cardiovascular diseases.

The effects of the surgical removal of subcutaneous adipose tissue on energy expenditure and adipocytokine concentrations in obese women

OBJECTIVE

To analyze the effects of the surgical removal of subcutaneous adipose tissue by ultrasound-assisted megalipoplasty (UAM) on energy expenditure and adipocytokine concentrations in obese women.

METHODS

Fifteen premenopausal obese women with BMI 37.5+/-6.3 kg/m(2) (range: 30.7-53.6 kg/m(2)) underwent UAM. Body composition (by DEXA), resting metabolic rate (REE) by indirect calorimetry, insulin resistance (by the HOMA method), leptin, C-reactive protein, interleukin-6, resistin and adiponectin were measured before and 1, 3, 28 and 180 days after the procedure.

RESULTS

UAM significantly reduced fat mass at day 3, without further changes in the following days. REE increased at day 3 after UAM, returned to baseline levels at day 28 and significantly declined at day 180. Leptin levels transiently increased after UAM and then declined according to fat mass reduction. C-reactive protein, interleukin-6 and resistin levels acutely increased after UAM and then returned to the baseline levels. Adiponectin levels acutely declined after the procedure and then stabilized to a plasma level slightly lower than at baseline. Insulin resistance deteriorated in the acute post-operative phase and then improved.

CONCLUSION

The surgical removal of subcutaneous fat was associated to an acute inflammatory reaction with high REE and insulin-resistance. Later on, the metabolic effects of fat mass removal appeared, with a reduction of leptin levels and REE and an improvement of insulin resistance.

Adiponectin, obesity and atherosclerosis

The circulating protein adiponectin has been the subject of immense interest ever since it was first discovered in the mid-1990s. The protein is uniquely produced and secreted by mature adipocytes and is believed to have important anti-inflammatory and anti-diabetic effects; low levels have been shown to be predictive of future type 2 diabetes and cardiovascular disease. This review discusses adiponectin in relation to obesity, inflammation, insulin resistance and atherosclerosis.

Serum adiponectin levels and lifestyle factors in Japanese men

Adiponectin plays an important role in the development of various lifestyle-related diseases such as obesity, hypertension, type II diabetes mellitus, hyperlipidemia, and metabolic syndrome, leading to the development of heart and vascular diseases. However, the determinants that affect circulating adiponectin levels, including lifestyle factors, have still not been thoroughly investigated, in a general male population in particular. A total of 109 healthy Japanese male subjects (mean age, 55 +/- 14 years) with constant lifestyles were enrolled. All were on no medication. Fasting serum adiponectin levels were measured with an enzyme-linked immunosorbent assay. Each subject's lifestyle was assessed by the self-administered Breslow Questionnaire (a well-established method to estimate various lifestyles) with minor modifications. Partial correlation analysis for serum adiponectin levels, after controlling age and all lifestyle factors, revealed a significant and independent negative correlation between serum adiponectin levels and body mass index (BMI) (r = -0.222, P = 0.025), and a significant and independent positive correlation between serum adiponectin levels and sleep duration (r = 0.252, P = 0.011). No significant correlations were observed between adiponectin and other lifestyle factors. These data suggest that increased BMI and shorter sleep duration may be significant independent risks for low serum adiponectin levels in healthy males. Therefore, these factors may be intervention targets to modulate adiponectin to its proper levels for the prevention of cardiovascular disorders.

β-adrenoceptor agonists downregulate adiponectin, but upregulate adiponectin receptor 2 and tumor necrosis factor-α expression in adipocytes

Recently, the insulin-sensitizing adipokine adiponectin and the insulin resistance-inducing adipokine tumor necrosis factor-alpha (TNF-alpha) were reported to inhibit each other's production in adipocytes. We investigated the effects of two beta(3)-adrenoceptor agonists, 5-[(2R)-2-[[(2R)-2-(3-chlorophenyl)-2-hydroxyethyl]amino]propyl]-1,3-benzodioxole-2,2-dicarboxylate (CL-316,243) and (+/-)-(R(*),R(*))-[4-[2-[[2-(3-chlorophenyl)-2-hydroxyethyl]amino]propyl]phenoxy]acetic acid (BRL37344), on the gene expression of adiponectin, two adiponectin receptors, and TNF-alpha in adipose tissues of C57BL/6J mice. CL-316,243 and BRL37344 downregulated adiponectin, but upregulated adiponectin receptor 2 (not receptor 1) in epididymal or/and subcutaneous white adipose tissues and in brown adipose tissue. TNF-alpha expression was upregulated only in epididymal adipose tissue. To further explore these effects, we treated differentiated 3T3-L1 adipocytes with the non-selective beta-adrenoceptor agonist isoproterenol. As a result, adiponectin receptor 2 (but not receptor 1) gene expression and TNF-alpha protein expression increased, but gene expression and secretion of adiponectin decreased. The upregulation of adiponectin receptor 2 by isoproterenol is most likely via beta(2),beta(3)-adrenoceptors, adenylyl cyclases, and protein kinase A (PKA). However, the accompanying activation of AMP-activated protein kinase (AMPK) may inhibit this upregulation. Our results suggest that upregulation of TNF-alpha and downregulation of adiponectin by beta-adrenoceptor activation may contribute to the pathogenesis of catecholamine-induced insulin resistance, and that upregulation of adiponectin receptor 2 may be a feedback result of reduced adiponectin.

Adiposity and cardiovascular disorders: disturbance of the regulatory system consisting of humoral and neuronal signals

Obesity, a major healthcare issue, is associated with significant cardiovascular morbidities, including hypertension and atherosclerosis. Numerous intensive studies conducted this decade have revealed that adipose tissue is a major endocrine organ that secretes a variety of bioactive substances, termed adipocytokines. Adipocytokine secretion profiles are altered as obesity develops, which may increase the risk of obesity-related cardiovascular disorders. For instance, leptin is upregulated in obese subjects and plays important roles in the pathophysiology of obesity-related atherogenesis through multiple mechanisms, such as its proliferative, proinflammatory, prothrombotic, and prooxidant actions. In contrast, adiponectin, which is downregulated in obese subjects, has protective effects against cardiovascular disorders at various atherogenic stages. In addition to these factors secreted by adipose tissue, neuronal circuits involving autonomic nerves are now being recognized as an important metabolic regulatory system and have thus attracted considerable attentions. Alterations in fat accumulation in intraabdominal organs, such as visceral adipose tissue and the liver, send afferent neuronal signals to the brain, leading to modulation of sympathetic tonus and thereby affecting the vasculature. Moreover, these humoral and neuronal signaling pathways communicate with each other, resulting in cooperative metabolic regulation among tissues/organs throughout the body. Further elucidation of these regulatory systems is anticipated to lead to new approaches to devising therapeutic strategies for the metabolic syndrome.

Hypoadiponectinemia in type 2 diabetes mellitus in men is associated with sympathetic overactivity as evaluated by cardiac 123I-metaiodobenzylguanidine scintigraphy

Hypoadiponectinemia is associated with insulin resistance. However, there is very limited information about the relationship between plasma adiponectin and cardiac autonomic nervous function. We tested the hypothesis that hypoadiponectinemia is associated with cardiac sympathetic overactivity in patients with type 2 diabetes mellitus. Thirty-three male type 2 diabetic patients not on insulin treatment were classified into a hypoadiponectinemia group (plasma adiponectin concentration, <4.0 microg/mL; age, 58.6 +/- 8.6 years [mean +/- SD]; n = 14) and an age-matched normoadiponectinemia group (serum adiponectin concentration, >/=4.0 microg/mL; age, 58.2 +/- 8.1 years; n = 19). In each patient, baroreflex sensitivity, heart rate variability, plasma norepinephrine concentration, and cardiac (123)I-metaiodobenzylguanidine (MIBG) scintigraphic findings were assessed. Compared with the normoadiponectinemia group, the hypoadiponectinemia group had a higher body mass index (P < .01), higher plasma concentrations of glucose and insulin (P < .05 and P < .01, respectively), higher homeostasis model assessment of insulin resistance (HOMA-IR) values (P < .005), higher plasma triglyceride levels (P < .05), and lower plasma high-density lipoprotein cholesterol levels (P < .05). In the hypoadiponectinemia group, the autonomic function measurements included a lower baroreflex sensitivity (P< .05) and a lower delayed myocardial uptake of (123)I-MIBG (P < .01) with a higher washout rate (P < .05). Multiple regression analysis revealed that the plasma adiponectin level was independently associated with HOMA-IR (F = 9.916) and the percent washout rate of (123)I-MIBG (F = 5.985). Our results suggest that in middle-aged men with type 2 diabetes mellitus, hypoadiponectinemia is associated with cardiac sympathetic overactivity as determined by (123)I-MIBG scintigraphy.

Regulation of adiponectin and leptin secretion and expression by insulin through a PI3K-PDE3B dependent mechanism in rat primary adipocytes

Adiponectin is intimately involved in the regulation of insulin sensitivity, carbohydrate and lipid metabolism, and cardiovascular functions. The circulating concentration of adiponectin is decreased in obesity and Type 2 diabetes. The present study attempts to elucidate the mechanisms underlying the regulation of adiponectin secretion and expression in rat primary adipocytes. The beta-agonist, isoprenaline, decreased adiponectin secretion and expression in a dose-dependent manner in primary adipocytes. Importantly, such an inhibitory effect could be blocked by insulin. The opposing effects of isoprenaline and insulin could be explained by differential regulation of intracellular cAMP levels, since cAMP analogues suppressed adiponectin secretion and expression in a fashion similar to isoprenaline, and insulin blocked the inhibitory effects of the cAMP analogue hydrolysable by PDE (phosphodiesterase). A specific PDE3 inhibitor, milrinone, and PI3K (phosphoinositide 3-kinase) inhibitors abolished the effects of insulin on adiponectin secretion and expression. In the same studies, leptin secretion and expression displayed a similar pattern of regulation to adiponectin. We conclude that insulin and beta-agonists act directly at the adipocytes in opposing fashions to regulate the production of adiponectin and leptin, and that a PI3K-PDE3B-cAMP pathway mediates the effects of insulin to restore beta-agonist/cAMP-suppressed secretion and expression of these two adipokines.

Modulation of adiponectin and leptin during refeeding of female anorexia nervosa patients

CONTEXT

Several studies assessed adiponectin levels in anorexia nervosa (AN) patients, however, data regarding the dynamics of changes in adiponectin levels during refeeding of these patients is limited and contradicting.

OBJECTIVE

Our objective was to assess adiponectin levels and the distribution of its different isoforms in AN patients before and after long-term refeeding, and to relate them to alterations in body mass index, leptin, insulin sensitivity, and additional endocrine parameters.

DESIGN, SETTING, AND PARTICIPANTS

We conducted a longitudinal controlled study of 38 female adolescent malnourished AN inpatients, with 13 young, lean, healthy women serving as controls. Blood samples were obtained upon admission and thereafter at 1, 3, and 5 months (at target weight).

MAIN OUTCOME MEASURES

Changes in body mass index, leptin, adiponectin, insulin sensitivity, and adiponectin multimeric forms were measured.

RESULTS

At admission, leptin levels of AN patients were significantly lower, whereas insulin sensitivity (assessed by homeostasis model assessment-insulin resistance), adiponectin levels, and the ratio of high molecular weight (HMW) adiponectin to total adiponectin were significantly higher compared with controls. During weight recovery, leptin levels and homeostasis model assessment-insulin resistance increased significantly, whereas adiponectin and HMW adiponectin/total adiponectin ratio decreased significantly, to levels similar to controls. An initial increase in adiponectin levels was observed after 1 month of refeeding. There was no correlation between adiponectin and either T(4) or cortisol levels.

CONCLUSIONS

Our study demonstrates hyperadiponectinemia, increased adiponectin HMW isoform, and increased insulin sensitivity in adolescent AN female patients and reversal of these findings with weight rehabilitation. We hypothesize that increased adiponectin levels may have a protective role in maintaining energy homeostasis during extreme malnourishment.

Chronic ethanol feeding to rats decreases adiponectin secretion by subcutaneous adipocytes

Chronic ethanol feeding to mice and rats decreases serum adiponectin concentration and adiponectin treatment attenuates chronic ethanol-induced liver injury. Although it is clear that lowered adiponectin has pathophysiological importance, the mechanisms by which chronic ethanol decreases adiponectin are not known. Here, we have investigated the impact of chronic ethanol feeding on adiponectin expression and secretion by adipose tissue. Rats were fed a 36% Lieber-DeCarli ethanol-containing liquid diet or pair-fed control diet for 4 wk. Chronic ethanol feeding decreased adiponectin mRNA but had no effect on adiponectin protein in subcutaneous adipose tissue. Chronic ethanol feeding also reduced adiponectin secretion by isolated subcutaneous and retroperitoneal adipocytes despite the maintenance of equivalent intracellular concentrations of adiponectin between subcutaneous adipocytes from ethanol- and pair-fed rats. Treatment with brefeldin A suppressed adiponectin secretion by subcutaneous adipocytes from pair-fed rats but had little effect after ethanol feeding. In subcutaneous adipocytes from pair-fed rats, adiponectin was enriched in endoplasmic reticulum (ER)/Golgi relative to plasma membrane; however, after chronic ethanol feeding, adiponectin was equally distributed between plasma membrane and ER/Golgi fractions. In conclusion, chronic ethanol feeding impaired adiponectin secretion by subcutaneous and retroperitoneal adipocytes; impaired secretion likely contributes to decreased adiponectin concentrations after chronic ethanol feeding.

Effect of aerobic training on plasma levels and subcutaneous abdominal adipose tissue gene expression of adiponectin, leptin, interleukin 6, and tumor necrosis factor alpha in obese women

Adipocytokines secreted by adipose tissue are suggested to play a role in the development of obesity-related complications. Regular aerobic exercise has been shown to reduce the risk of metabolic complications in obese subjects. The aim of this study was to investigate the effect of aerobic training on gene expression in subcutaneous abdominal adipose tissue (SCAAT) and on plasma levels of several adipocytokines in obese women. Twenty-five obese sedentary premenopausal women (body mass index, 32.18 +/- 3.17 kg/m(2)) underwent a 12-week aerobic exercise program, with a frequency of 5 d/wk and intensity corresponding to 50% of individual maximal oxygen consumption (V(.-)(O(2)max)) consisting of 2 sessions per week of supervised aerobic exercise and 3 sessions per week of home-based exercise on a bicycle ergometer. Before and after the aerobic training, (V(.-)(O(2)max)) and body composition were measured and plasma and SCAAT biopsy samples (in a subgroup of 8 subjects) were obtained for determination of plasma and messenger RNA levels of adipocytokines (leptin, adiponectin, interleukin 6, tumor necrosis factor alpha). The aerobic training resulted in an increase of subjects' V o(2)max by 12.8% (24.6 +/- 3.9 vs 27.7 +/- 4.8 mL x min(-1) x kg(-1), P < .05). Body weight and fat mass were reduced by 5.9% (88.5 +/- 8.2 vs 83.3 +/- 7.7 kg, P < .001) and 6.4% (38.8 +/- 4.2% vs 36.3 +/- 4.6%, P < .001), respectively, and the revised QUantitative Insulin sensitivity ChecK Index (QUICKI) increased (0.43 +/- 0.06 vs 0.48 +/- 0.06, P < .05) during the aerobic training. No aerobic training-induced changes in messenger RNA levels of the investigated genes in SCAAT were observed. A decrease of plasma leptin (24.3 +/- 8.7 vs 18.1 +/- 8.3 ng/mL, P < .05) was detected, whereas plasma levels of other cytokines remained unchanged. In moderately obese females, 3 months' aerobic training did not promote changes in the adipose tissue gene expression or plasma levels of the adipocytokines (except for leptin) involved in a regulation of lipid and carbohydrate metabolism.

Reduced levels of adiponectin in sleep apnea syndrome

BACKGROUND

To investigate adiponectin levels in an obese population with and without obstructive sleep apnea syndrome (OSAS) and the acute modifications in adiponectin after a whole-night control by auto continuous positive air pressure (CPAP).

METHODS

46 obese subjects [22 males, 24 females, age 55.1+/-11.4 yr, body mass index (BMI) 38.9+/-6.5 kg/m2]: 11 OSAS with apnea/hypopnea index (AHI) from 10/h to 30/h, 14 OSAS with AHI >30/h and 21 without OSAS. Thirty-seven normal weight healthy subjects (20 males, 17 females, age 31.3+/-9.5 yr, BMI 21.5+/-1.8 kg/m2). Serum adiponectin levels, biochemical parameters, anthropometric measurements, pulmonary function, pulse-oxymetry and polisomnography.

RESULTS

The 3 groups of obese patients were comparable for gender, BMI, age, fat mass, fat free mass, hip and waist circumference, waist-to-hip ratio (WHR), systolic and diastolic blood pressure and glycometabolic parameters. Adiponectin levels were significantly reduced in obese patients compared to healthy normal weight subjects (8.1+/-3.5 vs 11.3+/-4.8 microg/ml p<0.001) In particular, adiponectin showed a trend to decrease according to the severity of OSAS. No differences in adiponectin levels were found after a whole-night control by Auto CPAP.

CONCLUSIONS

OSAS is associated with reduced levels of adiponectin independently of insulin-resistance and BMI. These low adiponectin levels may contribute to the increased mortality seen in such patients.

Cold exposure suppresses serum adiponectin levels through sympathetic nerve activation in mice

OBJECTIVE

Several lines of evidence suggest important roles for adiponectin in glucose and lipid metabolism and atherosclerosis. However, the mechanisms regulating serum adiponectin levels and adiponectin production are still not completely understood. Our aim was to determine whether adiponectin synthesis is physiologically regulated by the sympathetic nervous system (SNS).

RESEARCH METHODS AND PROCEDURES

Mice were exposed to cold (4 degrees C) for 12 hours and for 24 hours with or without inhibition of noradrenaline synthesis or pan-beta adrenergic function, followed by measurement of serum adiponectin concentrations and levels of adiponectin and uncoupling protein (UCP) 1 expressions in various white adipose tissues (WATs).

RESULTS

Cold exposure significantly reduced serum adiponectin concentrations without changing body weights or WAT sizes in either subcutaneous or intra-abdominal fat tissues. The serum adiponectin reduction was associated with a decrease in adiponectin mRNA expression in subcutaneous, epididymal, and mesenteric fat tissues. In these adipose tissues, UCP1 expression was markedly enhanced, suggesting SNS activation in these tissues. Administration of alpha-methyl-p-tyrosine or a combination of SR59230A and propranolol reversed the cold-exposure-induced decreases in serum adiponectin concentrations and adiponectin mRNA expression in these tissues. In contrast, in retroperitoneal fat, the effects of cold exposure on adiponectin and UCP1 expressions were strikingly weak but were not reversed by SNS inhibitors.

DISCUSSION

SNS physiologically regulates serum adiponectin levels and adiponectin synthesis in WATs in vivo, although responsiveness to SNS stimulation differs markedly among WATs. Sympathetic activation might be involved in development of the metabolic syndrome by modulation of serum adiponectin concentrations.

Adiponectin downregulates its own production and the expression of its AdipoR2 receptor in transgenic mice

Adiponectin (ApN) is an adipokine whose expression and plasma levels are inversely related to obesity and insulin-resistant states. The in vivo effects of a chronic expression of exogenous ApN restricted to adipose tissue are unclear. Moreover, the regulatory effects of ApN on its own expression and on that of its receptors are still unknown. In this study, we generated transgenic (Tg) mice with moderate expression of exogenous ApN targeted to adipose tissue (native full-length ApN being placed under control of the adipocyte promoter aP2). After a transient overexpression of ApN in young pups, we intriguingly observed a reduction of ApN mRNA levels and protein content in fat depots, together with a decrease of circulating ApN in adult mice. As a result, the phenotype of these adult mice included glucose intolerance, insulin resistance, and increased adiposity. Reduced expression of ApN in fat tissue was associated with diminished expression of uncoupling protein 2 involved in energy dissipation, and higher expression of fatty acid synthase, a key enzyme of lipogenesis, and of TNFalpha implicated in insulin resistance. Concomitantly, the expression of the ApN receptor AdipoR2 that mediates action of full-length ApN was downregulated, while that of AdipoR1 was unaffected. In agreement with the in vivo studies, recombinant ApN added to the culture medium of 3T3-F442A adipocytes caused a decrease in AdipoR2 and ApN mRNA levels. This treatment did not affect the expression of AdipoR1. Eventually, we demonstrated a contrario that AdipoR2 (but not R1) was specifically upregulated in fat of ApN(-/-) mice. Our in vivo and in vitro data provide evidence for a novel regulatory feedback loop by which ApN downregulates its own production and the expression of its AdipoR2 receptor.

Endothelin-1 inhibits adiponectin secretion through a phosphatidylinositol 4,5-bisphosphate/actin-dependent mechanism

Adiponectin is an adipokine with profound insulin-sensitizing, anti-inflammatory, and anti-atherogenic properties. Plasma levels of adiponectin are reduced in insulin resistant states such as obesity, type 2 diabetes and cardiovascular disease. However, the mechanism(s) by which adiponectin concentrations are decreased during disease development is unclear. Studies have shown that endothelin-1 (ET-1), a vasoconstrictor peptide, affects adipocyte glucose metabolism and secretion of adipokines such as leptin, resistin, and adiponectin. The goal of our study was to determine the mechanism by which ET-1 decreases adiponectin secretion. 3T3-L1 adipocytes were treated for 24h with ET-1 (10nM) and then stimulated with vehicle or insulin (100 nM) for a period of 1-2h. Chronic ET-1 (24h) treatment significantly decreased basal and insulin-stimulated adiponectin secretion by 66% and 47%, respectively. Inhibition of phosphatidylinositol 4,5-bisphosphate (PIP(2)) hydrolysis by the PLCbeta inhibitor, U73122, or exogenous addition of PIP(2):histone carrier complex (1.25:0.625 microM) ameliorated the decrease in basal and insulin-stimulated adiponectin secretion observed with ET-1. However, treatment with exogenous PIP(2):histone carrier complex and the actin depolymerizing agent latrunculin B (20 microM) did not reverse the ET-1-mediated decrease in adiponectin secretion. In conclusion, we demonstrate that ET-1 inhibits basal and insulin-stimulated adiponectin secretion through PIP(2) modulation of the actin cytoskeleton.

Genetic architecture of the APM1 gene and its influence on adiponectin plasma levels and parameters of the metabolic syndrome in 1,727 healthy Caucasians

The associations of the adiponectin (APM1) gene with parameters of the metabolic syndrome are inconsistent. We performed a systematic investigation based on fine-mapped single nucleotide polymorphisms (SNPs) highlighting the genetic architecture and their role in modulating adiponectin plasma concentrations in a particularly healthy population of 1,727 Caucasians avoiding secondary effects from disease processes. Genotyping 53 SNPs (average spacing of 0.7 kb) in the APM1 gene region in 81 Caucasians revealed a two-block linkage disequilibrium (LD) structure and enabled comprehensive tag SNP selection. We found particularly strong associations with adiponectin concentrations for 11 of the 15 tag SNPs in the 1,727 subjects (five P values <0.0001). Haplotype analysis provided a thorough differentiation of adiponectin concentrations with 9 of 17 haplotypes showing significant associations (three P values <0.0001). No significant association was found for any SNP with the parameters of the metabolic syndrome. We observed a two-block LD structure of APM1 pointing toward at least two independent association signals, one including the promoter SNPs and a second spanning the relevant exons. Our data on a large number of healthy subjects suggest a clear modulation of adiponectin concentrations by variants of APM1, which are not merely a concomitant effect in the course of type 2 diabetes or coronary artery disease.

Role of resistin in obesity, insulin resistance and Type II diabetes

Resistin is a member of a class of cysteine-rich proteins collectively termed resistin-like molecules. Resistin has been implicated in the pathogenesis of obesity-mediated insulin resistance and T2DM (Type II diabetes mellitus), at least in rodent models. In addition, resistin also appears to be a pro-inflammatory cytokine. Taken together, resistin, like many other adipocytokines, may possess a dual role in contributing to disease risk. However, to date there has been considerable controversy surrounding this 12.5 kDa polypeptide in understanding its physiological relevance in both human and rodent systems. Furthermore, this has led some to question whether resistin represents an important pathogenic factor in the aetiology of T2DM and cardiovascular disease. Although researchers still remain divided as to the role of resistin, this review will place available data on resistin in the context of our current knowledge of the pathogenesis of obesity-mediated diabetes, and discuss key controversies and developments.

Fasting serum levels of adiponectin, ghrelin, and leptin in men with spinal cord injury

OBJECTIVES

To measure serum levels of adiponectin, ghrelin, and leptin in men with spinal cord injury (SCI) and to investigate possible correlations between these serum levels and various factors, such as body mass index (BMI), age, injury level, and duration of injury.

DESIGN

Cross-sectional.

SETTING

A university hospital that is a tertiary referral center.

PARTICIPANTS

Eighty-nine men with traumatic neurologically complete SCI (30 with tetraplegia, 59 with paraplegia) and 37 age- and BMI-matched male controls. Subjects with SCI were injured at the mean age +/- standard error of 28.5+/-1.0 years (range, 14.7-59.1 y) and the mean injury duration was 10.8+/-0.7 years (range, 1.1-27.7 y).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Serum levels of adiponectin, ghrelin, and leptin and BMI.

RESULTS

Serum leptin levels in subjects with SCI (mean, 7.0+/-0.5 mg/mL) [corrected] were significantly higher than those in able-bodied controls (mean, 4.7+/-0.6 mg/mL) [corrected] (P<.01). The group with tetraplegia had higher serum leptin levels than the group with paraplegia, but this did not reach a statistically significant level (8.2+/-1.1 ng/mL vs 6.4+/-0.5 mg/mL [corrected] P=.097). There were significant differences in serum leptin levels among the 3 groups by 1-way analysis of variance (P=.008). Serum adiponectin levels in subjects with SCI (7.1+/-0.5 mg/mL) [corrected] were higher than those in able-bodied controls (5.6+/-0.5 mg/mL) [corrected] but this was not statistically significant (P=.08). In contrast, serum levels of ghrelin in subjects with SCI (302.0+/-17.5 pg/mL) were similar to those in the controls (264.0+/-27.0 pg/mL) (P=.24). Serum leptin levels correlated positively with BMI (SCI, r=.698, P<.001; controls, r=.782, P<.001), whereas serum adiponectin (SCI, r=-.527, P<.001; controls, r=-.315, P=.057) and ghrelin (SCI, r=-.368, P<.001; controls, r=-.447, P=.006) levels correlated negatively with the BMI in both subjects with SCI and controls.

CONCLUSIONS

Men with SCI have significantly higher serum leptin levels than able-bodied controls, and serum leptin levels correlated with the degree of neurologic deficit. Men with SCI had a tendency toward higher serum adiponectin level than able-bodied controls. Serum levels of ghrelin in men with SCI were similar to those of controls.

Increased plasma adiponectin concentrations in poorly controlled patients with phenylketonuria normalize with a strict diet: evidence for catecholamine-mediated adiponectin regulation and a complex effect of phenylketonuria diet on atherogenesis risk factors

Adiponectin (Adpn), an adipose tissue-derived hormone, prevents endothelial inflammation and early atherogenesis. Classic phenylketonuria (PKU), an inborn error of phenylalanine (Phe) metabolism, results in a reduction of catecholamine biosynthesis and requires treatment with lifelong low-Phe diet to prevent mental dysfunction and allow proper intellectual development. In this study, we evaluated the effect of the quality of PKU diet on plasma Adpn concentrations and related biochemical indices of endothelial dysfunction and atherogenesis. Patients with PKU were divided into groups A (n = 18), who were on a strict diet, and B (n = 18), who were on a loose diet, after evaluation of their 30-day dietetic diaries and measurement of Phe blood concentrations. Twenty healthy children of similar ages and body mass indexes served as controls (group C). Group A patients had normal circulating catecholamines and Adpn and decreased tumor necrosis factor alpha concentrations and low-density lipoprotein cholesterol/apolipoprotein B ratio compared with groups B and C. Despite these favorable parameters, however, homocysteine concentration was twice as high in group A compared with groups B and C. Interestingly, group B patients under loose dietary control had significantly elevated Adpn concentrations compared with groups A and C and increased tumor necrosis factor alpha and an unfavorable lipid profile, but normal levels of homocysteine. These data support the hypothesis that catecholamines inhibit Adpn secretion and that the elevated Adpn of the poorly controlled patients might moderate their risk for endothelial dysfunction and atherogenesis. Homocysteine production appears to be unfavorably affected by a strict PKU diet, diverging from the rest of the atherogenesis risk factors, which were improved in the well-controlled patients.

Serum adiponectin levels in adult male patients with obstructive sleep apnea hypopnea syndrome

BACKGROUND

Adiponectin has been found to be associated with the pathogenesis of diabetes, obesity and some cardiovascular diseases, which usually coexist with obstructive sleep apnea hypopnea syndrome (OSAHS). However, an association between adiponectin and OSAHS has rarely been reported.

OBJECTIVES

To investigate the levels of serum adiponectin in adult male patients with OSAHS.

METHODS

Following polysomnographic examination, 86 adult male habitual snorers were divided into simple snorers (control group) and OSAHS patients (OSAHS group) who were further divided into mild, moderate and severe OSAHS subgroups based on their apnea hypopnea index (AHI). There was no significant difference in age, body mass index (BMI), fasting blood glucose (FBG) and insulin resistance expressed as homeostasis model assessment (HOMA) between the two groups. The serum adiponectin levels were measured by radioimmunoassay.

RESULTS

Serum adiponectin levels were significantly lower in the OSAHS group than in the control (p < 0.01). Such a decrease in adiponectin level was most significant in patients with moderate and severe OSAHS. Pearson correlation analysis showed that in OSAHS patients, serum adiponectin level was negatively correlated with BMI, waist (WC) and neck (NC) circumferences, AHI and HOMA, but positively correlated with nadir pulse oxyhemoglobin saturation (nadir SpO2). After controlling for HOMA, BMI, NC and WC in OSAHS patients, a partial correlation analysis showed that adiponectin levels were negatively correlated with AHI but positively correlated with nadir SpO2. Multiple logistic regression analysis indicated that adiponectin was independently associated with OSAHS.

CONCLUSIONS

Serum adiponectin levels were significantly lower in OSAHS patients than in simple snorers. OSAHS may cause a decrease in serum adiponectin level.

Dietary fish oil positively regulates plasma leptin and adiponectin levels in sucrose-fed, insulin-resistant rats

Insulin resistance and adiposity induced by a long-term sucrose-rich diet (SRD) in rats could be reversed by fish oil (FO). Regulation of plasma leptin and adiponectin levels, as well as their gene expression, by FO might be implicated in these findings. This study was designed to evaluate the long-term regulation of leptin and adiponectin by dietary FO in a dietary model of insulin resistance induced by long-term SRD in rats and to determine their impact on adiposity and insulin sensitivity. Rats were randomized to consume a control diet (CD; n = 25) or an SRD (n = 50) for 7 mo. Subsequently, the SRD-fed rats were randomized to consume SRD+FO or to continue on SRD for an additional 2 mo. Long-term SRD induced overweight and decreased both plasma leptin and adiponectin levels without change in gene expression. Dyslipidemia, adiposity, and insulin resistance accompanied these modifications. Shifting the source of fat to FO for 2 mo increased plasma levels of both adipokines, reversed insulin resistance and dyslipidemia, and improved adiposity. These results were not associated with modifications in gene expression. These results suggest that increasing both adipokines by dietary FO might play an essential role in the normalization of insulin resistance and adiposity in dietary-induced, insulin-resistant models.

The emerging role of adipocytokines as inflammatory mediators in inflammatory bowel disease

Anorexia, malnutrition, altered body composition and development of mesenteric obesity are well known features of inflammatory bowel disease (IBD). Recent data suggest that dysregulation of protein secretion by white adipose tissue is involved in these manifestations of patients with IBD. Adipocytes are recently recognized as endocrine cells that secrete a variety of bioactive substances known as adipocytokines. There is evidence that adipocytokines are involved in inflammatory and metabolic pathways in human beings. Overexpression of adipocytokines such as leptin, adiponectin and resistin in mesenteric adipose tissue of operated patients with Crohn's disease has recently been reported, suggesting that mesenteric adipocytes in IBD may act as immunoregulating cells. Therefore, it could be suggested that adipocytokines play an important role in the disease pathogenesis. Moreover, modulators of mesenteric adipose function have been suggested as potential therapeutic drugs in IBD. In this review, the importance of white adipose tissue function and adipocytokines, is discussed with respect to IBD.

Circulating adiponectin reflects severity of liver disease but not insulin sensitivity in liver cirrhosis

BACKGROUND

The adipocytokine adiponectin has been proposed to play important roles in the regulation of energy homeostasis, insulin sensitivity and shows anti-inflammatory properties.

AIM

In this study we investigated the role of circulating adiponectin in different chronic liver diseases, its regulation by systemic anti-tumour necrosis factor (TNF)-alpha treatment and its hepatic metabolism.

PATIENTS AND METHODS

Plasma adiponectin levels were determined in 87 patients with liver cirrhosis of different aetiologies, seven patients with alcoholic steatohepatitis undergoing systemic anti-TNF-alpha treatment, in 11 patients with liver cirrhosis receiving transjugular intrahepatic portosystemic shunt implantation and in 21 healthy controls.

RESULTS

Adiponectin levels were significantly higher in all subjects with liver cirrhosis of different aetiologies when compared with healthy controls and increased dependent on Child-Pugh classification. In subjects with alcoholic steatohepatitis, systemic anti-TNF-alpha treatment caused a significant decrease in circulating adiponectin. Adiponectin concentrations were similar in portal, hepatic and peripheral veins. No correlation between adiponectin levels and insulin resistance was found in any patient group.

CONCLUSIONS

Our data suggest that circulating adiponectin is increased in liver cirrhosis independent of the aetiology of liver disease. We suggest that high adiponectin levels in chronic liver disease might reflect one of the body's anti-inflammatory mechanisms in chronic liver diseases.

Adiponectin is expressed in the brown adipose tissue and surrounding immature tissues in mouse embryos

Adiponectin is one of the adipocytokines, which are adipose-specific secretory factors. We examined its expression during embryogenesis. Transcripts of adiponectin were detected at a late stage of embryogenesis on embryonic (E) day E16.5. In situ hybridization showed that adiponectin transcripts were localized in brown adipose tissues (BATs) and surrounding immature tissues in mouse embryos. Immunohistochemistry using a specific anti-adiponectin antibody showed that the distribution of adiponectin closely parallels that of its mRNA. Adiponectin was also detected in serum at day E16.5, and its concentration peaked at birth. By contrast, transcripts of both the adiponectin receptors 1 and 2 were already expressed by day E12.5 in many tissues. Thus, their expression profile differed from that of adiponectin itself. Furthermore, experiments using primary cultures of brown adipocytes showed that adiponectin is regulated in brown adipocytes by various modulators, similar to its regulation in white adipose tissues (WATs). These data indicate that adiponectin has important roles in glucose and lipid metabolism during the perinatal period.

Plasma levels of adiponectin, a novel adipocyte-derived hormone, in sleep apnea

OBJECTIVE

Obstructive sleep apnea (OSA) is associated with obesity, sympathetic activation, systemic inflammation, and cardiovascular morbidity. Obesity, beta-adrenergic agonists, and inflammation are linked to decreased expression and/or secretion of an adipose tissue-derived antiatherogenic hormone, adiponectin. The purpose of the study was to investigate whether OSA affected plasma levels of adiponectin, which might help explain OSA-associated cardiovascular morbidity.

RESEARCH METHODS AND PROCEDURES

We randomly selected 68 otherwise healthy male subjects, either with moderate/severe OSA [apnea-hypopnea index (AHI)>or=20; n=35] or without OSA (AHI<or=5; n=33). The diagnosis of OSA was made based on prospective full polysomnography. Adiponectin was measured before polysomnography between 8 and 10 pm.

RESULTS

AHI was higher in the OSA group (49.5+/-4.4 vs. 2.9+/-0.4 events/h; p<0.001). OSA subjects were also more obese, with greater BMI (33+/-1 vs. 30+/-1; p=0.016) and percentage body fat (29+/-1% vs. 26+/-1%; p=0.030). Adiponectin levels were 7.67+/-0.73 and 6.33+/-0.51 microg/mL in the OSA and non-OSA groups, respectively, and this difference was significant in covariate analysis (taking into account age, hemodynamic characteristics, measures of body fat, and OSA severity) (p=0.009). After excluding from both groups the subjects with extreme BMI, such that the OSA and non-OSA study cohorts had similar BMI and percentage body fat, subjects with OSA had significantly higher plasma adiponectin (8.49+/-0.92 vs. 6.32+/-0.55 microg/mL; p=0.042), differences also evident in covariate analysis (p=0.017).

DISCUSSION

Plasma adiponectin levels are elevated in otherwise healthy subjects with OSA. Therefore, low adiponectin is unlikely to explain the association between OSA and cardiovascular disease.

Adiponectin: action, regulation and association to insulin sensitivity

Adiponectin is a novel adipocyte-specific protein, which, it has been suggested, plays a role in the development of insulin resistance and atherosclerosis. Although it circulates in high concentrations, adiponectin levels are lower in obese subjects than in lean subjects. Apart from negative correlations with measures of adiposity, adiponectin levels are also reduced in association with insulin resistance and type 2 diabetes. Visceral adiposity has been shown to be an independent negative predictor of adiponectin. Thus, most features of the metabolic syndrome's negative associations with adiponectin have been shown. Adiponectin levels seem to be reduced prior to the development of type 2 diabetes, and administration of adiponectin has been accompanied by lower plasma glucose levels as well as increased insulin sensitivity. Furthermore, reduced expression of adiponectin has been associated with some degree of insulin resistance in animal studies indicating a role for hypoadiponectinaemia in relation to insulin resistance. The primary mechanisms by which adiponectin enhance insulin sensitivity appears to be through increased fatty acid oxidation and inhibition of hepatic glucose production. Adiponectin levels are increased by thiazoledinedione treatment, and this effect might be important for the enhanced insulin sensitivity induced by thiazolidinediones. In contrast, adiponectin levels are reduced by pro-inflammatory cytokines especially tumour necrosis factor-alpha. In summary, adiponectin in addition to possible anti-inflammatory and anti-atherogenic effects appears to be an insulin enhancer, with potential as a new pharmacologic treatment modality of the metabolic syndrome and type 2 diabetes.

The association of plasma adiponectin levels with hypertensive retinopathy

OBJECTIVE

Previous studies have demonstrated that low plasma adiponectin concentrations are associated with essential hypertension. It has also recently been shown that adiponectin plays an essential role in the modulation of angiogenesis. These data led us to hypothesize that adiponectin might contribute to end-organ damage in hypertension.

METHODS

In the present study we have evaluated the relationship between plasma adiponectin concentrations and hypertensive retinopathy. One hundred and ten patients newly diagnosed with essential hypertension (EHT) (mean age, 46.79+/-5.0 years; body mass index (BMI), 26.47+/-2.23 kg/m(2); male/female ratio, 58/52) and 57 healthy normotensive control subjects (NT) (mean age, 46.84+/-5.4 years; BMI, 26.66+/-2.65 kg/m(2); male/female ratio, 33/24) were enrolled.

RESULTS

Plasma adiponectin levels were significantly lower in EHT than in NT (P < 0.001). In addition, adiponectin concentrations were strongly correlated with systolic and diastolic blood pressures in EHT (r = -0.757, P < 0.001; r = -0.761, P < 0.001) while there was no correlation in the NT group. Plasma adiponectin in patients with grade 0 hypertensive retinopathy (n = 52) was significantly higher than that of the patients with grade 1 (n = 30) and 2 (n = 28) hypertensive retinopathy (P < 0.001 for each). Plasma adiponectin in patients with grade 0 hypertensive retinopathy was also significantly lower than that in the NT group (P < 0.001). The estimated threshold of plasma adiponectin concentration for hypertensive retinopathy was 17 microg/ml. This critical adiponectin level served largely to separate patients with retinopathy from those without.

CONCLUSION

Our results have shown that plasma adiponectin concentrations decrease progressively with higher grades of hypertensive retinopathy even after correction for other atherogenic risk factors, suggesting that a critical adiponectin level is needed for the development of retinopathy.

Adiponectin, obesity, and cardiovascular disease

Several adipocyte-secreted factors have been demonstrated to potentially link obesity, insulin resistance, and cardiovascular disease. Among those, adiponectin is an insulin-sensitizing and anti-inflammatory adipokine, concentrations of which are decreased in obesity-associated metabolic and vascular disorders. Recently, two adiponectin receptors (AdipoR) have been isolated and adenosine monophosphate kinase (AMPK), as well as acetyl coenzyme A carboxylase (ACC), appear to be critical downstream mediators for various effects of this adipokine. In addition to beneficial metabolic effects, adiponectin seems to be vasoprotective by interfering with various atherogenic processes. Of clinical interest, thiazolidinediones (TZDs) which are used in the treatment of type 2 diabetes stimulate adiponectin expression and secretion whereas several hormones dysregulated in insulin resistance and obesity downregulate this adipokine. The current knowledge on regulation and function of adiponectin in obesity, insulin resistance, and cardiovascular disease is summarized in this review and its clinical implications are discussed.

Adiponectin concentrations in sera from patients with type 2 diabetes are negatively associated with sympathovagal balance as evaluated by power spectral analysis of heart rate variation

OBJECTIVE

To investigate whether cardiac autonomic activity, particularly sympathovagal balance as estimated by power spectral analysis (PSA) of heart rate variation (HRV), is associated with serum adiponectin concentrations in patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

We studied 105 patients with type 2 diabetes (51 women and 54 men). Serum adiponectin concentrations were measured by sandwich enzyme-linked immunosorbent assay. HRV was determined automatically every 5 min over 24 h using Holter electrocardiographic recording. PSA of R-R intervals was performed using fast Fourier transformation. Low-frequency (both sympathetic and parasympathetic activities), high- frequency (pure parasympathetic activity), and the ratio of low-frequency-to-high-frequency power (LF-to-HF ratio), an index of sympathovagal balance, were used as indexes of cardiac autonomic activity.

RESULTS

We found no significant correlation between serum adiponectin and low-frequency or high-frequency power in patients with diabetes. Serum adiponectin concentration correlated negatively with the 24-h LF-to-HF ratio (r = -0.343, P = 0.0009) and creatinine clearance (r = -0.411, P < 0.0001). Serum adiponectin concentrations were significantly higher in patients with overt albuminuria than in those with normoalbuminuria or microalbuminuria. In multivariate analysis controlling for sex, BMI, glycemic control, lipid profile, and renal function, serum adiponectin concentration showed an independent negative association with 24-h LF-to-HF ratio (beta = -0.332, P = 0.020). Furthermore, sex, HDL cholesterol, and renal function retained significant influence on the serum adiponectin concentration in patients with diabetes.

CONCLUSIONS

Sympathovagal balance favoring relative sympathetic activation was associated with low serum concentrations of adiponectin in patients with type 2 diabetes.

Leptin treatment markedly increased plasma adiponectin but barely decreased plasma resistin of ob/ob mice

Adiponectin (ApN) and leptin are two adipocytokines that control fuel homeostasis, body weight, and insulin sensitivity. Their interplay is still poorly studied. These hormones are either undetectable or decreased in obese, diabetic ob/ob mice. We examined the effects of leptin treatment on ApN gene expression, protein production, secretion, and circulating levels of ob/ob mice. We also briefly tackled the influence of this treatment on resistin, another adipocytokine involved in obesity-related insulin resistance. Leptin-treated (T) obese mice (continuous sc infusion for 6 days) were compared with untreated lean (L), untreated obese (O), and untreated pair-fed obese (PF) mice. Blood was collected throughout the study. At day 3 or day 6, fat pads were either directly analyzed (mRNA, ApN content) or cultured for up to 24 h (ApN secretion). The direct effect of leptin was also studied in 3T3-F442A adipocytes. Compared with L mice, ApN content of visceral or subcutaneous fat and ApN secretion by adipose explants were blunted in obese mice. Accordingly, plasma ApN levels of O mice were decreased by 50%. Leptin treatment of ob/ob mice increased ApN mRNAs, ApN content, and secretion from the visceral depot by 50-80%. Leptin also directly stimulated ApN mRNAs and secretion from 3T3-F442A adipocytes. After 6 days of treatment, plasma ApN of ob/ob mice increased 2.5-fold, a rise that did not occur in PF mice. Plasma resistin of T mice was barely decreased. Leptin treatment, but not mere calorie restriction, corrects plasma ApN in obese mice by restoring adipose tissue ApN concentrations and secretion, at least in part, via a direct stimulation of ApN gene expression. Such a treatment only minimally affects circulating resistin. ApN restoration could, in concert with leptin, contribute to the metabolic effects classically observed during leptin administration.

Elevated circulating adiponectin levels in liver cirrhosis are associated with reduced liver function and altered hepatic hemodynamics

Adiponectin is a novel adipocytokine negatively correlated with parameters of the metabolic syndrome, such as body mass index (BMI), body fat mass (BFM), and circulating insulin levels. Furthermore, metabolic actions directly on the liver have been described. The aim of the present study was to characterize circulating adiponectin levels, hepatic turnover, and the association of adiponectin with key parameters of hepatic as well as systemic metabolism in cirrhosis, a catabolic disease. Circulating adiponectin levels and hepatic turnover were investigated in 20 patients with advanced cirrhosis. Hepatic hemodynamics [portal pressure, liver blood flow, hepatic vascular resistance, indocyanine green (ICG) half-life], body composition, resting energy expenditure, hepatic free fatty acids (FFA) and glucose turnover, and circulating levels of hormones (catecholamines, insulin, glucagon) and proinflammatory cytokines (IL-1beta, TNF-alpha, IL-6) were also assessed. Circulating adiponectin increased dependently on the clinical stage in cirrhosis compared with controls (15.2 +/- 1.7 vs. 8.2 +/- 1.1 microg/ml, respectively, P < 0.01), whereas hepatic extraction decreased. Adiponectin was negatively correlated with parameters of hepatic protein synthesis (prothrombin time: r = -0.62, P = 0.003; albumin: r = -0.72, P < 0.001) but not with transaminases or parameters of lipid metabolism. In addition, circulating adiponectin increased with portal pressure (r = 0.67, P = 0.003), hepatic vascular resistance (r = 0.60, P = 0.008), and effective hepatic blood flow (ICG half-life: r = 0.69, P = 0.001). Adiponectin in cirrhosis was not correlated with BMI, BFM, parameters of energy metabolism, insulin levels, hepatic FFA and glucose turnover, and circulating proinflammatory cytokines. These results demonstrate that 1) adiponectin plasma levels in cirrhosis are significantly elevated, 2) the liver is a major source of adiponectin extraction, and 3) adiponectin levels in cirrhosis do not correlate with parameters of body composition or metabolism but exclusively with reduced liver function and altered hepatic hemodynamics.

Adiponectin and atherosclerotic disease

Adiponectin has been identified as one of the "adipocytokines" that are derived only from adipose tissue, and are abundantly present in circulating blood. Adiponectin has protective actions in the initiation and progression of atherosclerosis through anti-inflammatory and anti-atherogenic effects. Adiponectin levels are decreased in obesity, type 2 diabetes, and patients with coronary artery disease (CAD). Adiponectin levels were negatively correlated with the CRP levels in patients with CAD. Adiponectin plays a crucial role in the association between obesity, type 2 diabetes, and insulin resistance. Mechanisms explaining the relationship between adiponectin and insulin resistance suggest that adiponectin and tumor necrosis factor (TNF)-alpha inhibited each other's expression and production in adipocytes. Thiazolidinediones, which are insulin-sensitizing agents, increased the production of adiponectin through directly enhancing its gene expression. The C-terminal globular domain of adiponectin may play a central role in the protective effects against atherosclerosis. Adiponectin receptors 1 (AdipoR1) and 2 (AdipoR2) are expressed ubiquitously in most organs, especially in skeletal muscle in AdipoR1, and liver in AdipoR2. With the prospect of future basic and clinical research on the molecular structure-receptor relationship, adiponectin could become a promising target for future investigations in reducing the morbidity and mortality of atherosclerotic disease.

Serum concentrations of adiponectin and leptin in patients with thyroid dysfunctions

Thyroid dysfunction is associated with metabolic changes that affect mass and adipocyte function, as well as lipid and carbohydrate metabolism. Adipose tissue performs complex metabolic and endocrine functions. Leptin and adiponectin are two of the most important adipocytokines, both involved in the regulation of intermediate metabolism. The aim of this study was to evaluate the relationships between thyroid status and circulating levels of the two adipose tissue hormones. We studied 15 patients with hyperthyroidism, 15 patients with hypothyroidism and 15 euthyroid subjects, all matched by sex, age and body mass index (BMI). Serum concentrations of free thyroxine, free tri-iodothyronine, thyrotropin, leptin and adiponectin and anthropometric parameters (weight, height, BMI) were assessed. No significant difference was found among the 3 groups, as assessed by Student's t-test, both for adiponectin and leptin. We conclude that metabolic changes associated with thyroid dysfunction are not related to variations in serum levels of adiponectin or leptin.

Update on adipocyte hormones: regulation of energy balance and carbohydrate/lipid metabolism

Hormones produced by adipose tissue play a critical role in the regulation of energy intake, energy expenditure, and lipid and carbohydrate metabolism. This review will address the biology, actions, and regulation of three adipocyte hormones-leptin, acylation stimulating protein (ASP), and adiponectin-with an emphasis on the most recent literature. The main biological role of leptin appears to be adaptation to reduced energy availability rather than prevention of obesity. In addition to the well-known consequences of absolute leptin deficiency, subjects with heterozygous leptin gene mutations have low circulating leptin levels and increased body adiposity. Leptin treatment dramatically improves metabolic abnormalities (insulin resistance and hyperlipidemia) in patients with relative leptin deficiency due to lipoatrophy. Leptin production is primarily regulated by insulin-induced changes of adipocyte metabolism. Dietary fat and fructose, which do not increase insulin secretion, lead to reduced leptin production, suggesting a mechanism for high-fat/high-sugar diets to increase energy intake and weight gain. ASP increases the efficiency of triacylglycerol synthesis in adipocytes leading to enhanced postprandial lipid clearance. In mice, ASP deficiency results in reduced body fat, obesity resistance, and improved insulin sensitivity. Adiponectin production is stimulated by thiazolidinedione agonists of peroxisome proliferator-activated receptor-gamma and may contribute to increased insulin sensitivity. Adiponectin and leptin cotreatment normalizes insulin action in lipoatrophic insulin-resistant animals. These effects may be mediated by AMP kinase-induced fat oxidation, leading to reduced intramyocellular and liver triglyceride content. The production of all three hormones is influenced by nutritional status. These hormones, the pathways controlling their production, and their receptors are promising targets for managing obesity, hyperlipidemia, and insulin resistance.

Regulation of adipocytokines and insulin resistance

It has long been known that obesity and insulin resistance are linked. Recently, it has been shown that adipocytes secrete several proteins including tumour necrosis factor-alpha, interleukin-6, resistin, and adiponectin. Since several of these so-called adipocytokines influence insulin sensitivity and glucose metabolism profoundly, they might provide a molecular link between increased adiposity and impaired insulin sensitivity. Thiazolidinediones which decrease insulin resistance and are used in the treatment of Type 2 diabetes seem to mediate part of their insulin-sensitising effects via modulation of adipocytokine expression. Furthermore, hormones such as beta-adrenergic agonists, insulin, glucocorticoids, and growth hormone might impair insulin sensitivity at least in part via up-regulation or down-regulation of adipocytokine synthesis. We summarise the current knowledge on how major adipocyte-secreted proteins are regulated by hormones and drugs influencing insulin sensitivity and discuss its implications for insulin resistance and obesity.

Regulation of adiponectin secretion by endothelin-1

Adiponectin is an adipocyte-derived hormone best known for its insulin-sensitizing ability. The expression and circulating concentration of adiponectin are decreased in type 2 diabetics and increase following treatment with thiazolidinediones. Endothelin-1 (ET-1) is a potent vasoconstrictor peptide whose levels are elevated in numerous disease states, including obesity and diabetes. ET-1 has profound effects on adipose tissue metabolism and alters the release of adipose-derived factors such as leptin and resistin, therefore we investigated the role of ET-1 in adiponectin secretion. 3T3-L1 adipocytes were treated with insulin (100 nM), ET-1 (100 nM), or the appropriate vehicle and adiponectin secretion into the media was determined by immunoblotting and densitometric analysis. Adiponectin secretion significantly increased 1h following insulin or ET-1 treatment, respectively. Pretreatment with ET-1 for 24h significantly inhibited the ability of insulin or ET-1 to acutely stimulate adiponectin secretion. The specific ET(A) receptor antagonist, BQ-610 (1 microM), significantly inhibited ET-1-stimulated adiponectin secretion. In summary, ET-1 acutely stimulates adiponectin secretion through the ET(A) receptor. Chronic exposure to ET-1 dramatically decreases the stimulatory effect of insulin and ET-1 on adiponectin secretion. Our findings suggest vascular factors such as ET-1 may play a role in the regulation of adiponectin secretion and whole body energy metabolism.

The fat-derived hormone adiponectin alleviates alcoholic and nonalcoholic fatty liver diseases in mice

Adiponectin has recently been shown to be a promising candidate for the treatment of obesity-associated metabolic syndromes. Replenishment of recombinant adiponectin in mice can decrease hyperglycemia, reverse insulin resistance, and cause sustained weight loss without affecting food intake. Here we report its potential roles in alcoholic and nonalcoholic fatty liver diseases in mice. Circulating concentrations of adiponectin decreased significantly following chronic consumption of high-fat ethanol-containing food. Delivery of recombinant adiponectin into these mice dramatically alleviated hepatomegaly and steatosis (fatty liver) and also significantly attenuated inflammation and the elevated levels of serum alanine aminotransferase. These therapeutic effects resulted partly from the ability of adiponectin to increase carnitine palmitoyltransferase I activity and enhance hepatic fatty acid oxidation, while it decreased the activities of two key enzymes involved in fatty acid synthesis, including acetyl-CoA carboxylase and fatty acid synthase. Furthermore, adiponectin treatment could suppress the hepatic production of TNF-alpha and plasma concentrations of this proinflammatory cytokine. Adiponectin was also effective in ameliorating hepatomegaly, steatosis, and alanine aminotransferase abnormality associated with nonalcoholic obese, ob/ob mice. These results demonstrate a novel mechanism of adiponectin action and suggest a potential clinical application of adiponectin and its agonists in the treatment of liver diseases.

The fat-derived hormone adiponectin alleviates alcoholic and nonalcoholic fatty liver diseases in mice

Adiponectin has recently been shown to be a promising candidate for the treatment of obesity-associated metabolic syndromes. Replenishment of recombinant adiponectin in mice can decrease hyperglycemia, reverse insulin resistance, and cause sustained weight loss without affecting food intake. Here we report its potential roles in alcoholic and nonalcoholic fatty liver diseases in mice. Circulating concentrations of adiponectin decreased significantly following chronic consumption of high-fat ethanol-containing food. Delivery of recombinant adiponectin into these mice dramatically alleviated hepatomegaly and steatosis (fatty liver) and also significantly attenuated inflammation and the elevated levels of serum alanine aminotransferase. These therapeutic effects resulted partly from the ability of adiponectin to increase carnitine palmitoyltransferase I activity and enhance hepatic fatty acid oxidation, while it decreased the activities of two key enzymes involved in fatty acid synthesis, including acetyl-CoA carboxylase and fatty acid synthase. Furthermore, adiponectin treatment could suppress the hepatic production of TNF-alpha and plasma concentrations of this proinflammatory cytokine. Adiponectin was also effective in ameliorating hepatomegaly, steatosis, and alanine aminotransferase abnormality associated with nonalcoholic obese, ob/ob mice. These results demonstrate a novel mechanism of adiponectin action and suggest a potential clinical application of adiponectin and its agonists in the treatment of liver diseases.

The fat-derived hormone adiponectin alleviates alcoholic and nonalcoholic fatty liver diseases in mice

Adiponectin has recently been shown to be a promising candidate for the treatment of obesity-associated metabolic syndromes. Replenishment of recombinant adiponectin in mice can decrease hyperglycemia, reverse insulin resistance, and cause sustained weight loss without affecting food intake. Here we report its potential roles in alcoholic and nonalcoholic fatty liver diseases in mice. Circulating concentrations of adiponectin decreased significantly following chronic consumption of high-fat ethanol-containing food. Delivery of recombinant adiponectin into these mice dramatically alleviated hepatomegaly and steatosis (fatty liver) and also significantly attenuated inflammation and the elevated levels of serum alanine aminotransferase. These therapeutic effects resulted partly from the ability of adiponectin to increase carnitine palmitoyltransferase I activity and enhance hepatic fatty acid oxidation, while it decreased the activities of two key enzymes involved in fatty acid synthesis, including acetyl-CoA carboxylase and fatty acid synthase. Furthermore, adiponectin treatment could suppress the hepatic production of TNF-alpha and plasma concentrations of this proinflammatory cytokine. Adiponectin was also effective in ameliorating hepatomegaly, steatosis, and alanine aminotransferase abnormality associated with nonalcoholic obese, ob/ob mice. These results demonstrate a novel mechanism of adiponectin action and suggest a potential clinical application of adiponectin and its agonists in the treatment of liver diseases.

Do regional differences in adipocyte biology provide new pathophysiological insights?

Obesity is an increasing health problem in many countries. Striking differences exist in the magnitude of the impact of different obesities on comorbidities. Individuals with peripheral obesity ('pears') possess fat distributed subcutaneously in gluteofemoral areas and the lower part of the abdomen, and are at little risk of metabolic complications. Conversely, individuals with upper-body obesity ('apples') accumulate fat in subcutaneous and visceral deposits and are more prone to metabolic and cardiovascular problems, particularly when visceral fat deposits are abundant. In this article, whether the different risk factors for obesity of 'apples' and 'pears' are largely related to the heterogeneity of function and responsiveness of the adipocytes from visceral and subcutaneous deposits is questioned. Possible pharmacological approaches to the treatment of obesity and related diseases are also considered.

Adiponectin/Acrp30, an adipocyte-specific secretory factor: physiological relevance during development

Adiponectin/Acrp30 is a fat cell-specific secretory product. The convergence of results from epidemiological, pharmacological and genetic studies over the last 2 yr has highlighted the important role that this multimeric protein complex plays in the context of insulin sensitivity. While the exact mechanism of action has not been elucidated, it is clear that adiponectin has insulin-sensitizing effects on both liver and muscle. The important role that adipose tissue plays in energy homeostasis as a storage compartment for triglycerides has been appreciated for a long time. The identification of leptin as a key hormone involved in central control of energy metabolism suggested that adipocytes also use polypeptide hormones to influence metabolic processes at distant sites. The recent progress made towards the characterization of the physiological role of adiponectin highlights the important role of adipose tissue as an endocrine organ and its central role in the fine-tuning of hepatic and muscle insulin responsiveness.

Hyperadiponectinaemia in anorexia nervosa

OBJECTIVE

Adiponectin (ApN) is a fat-derived hormone that enhances insulin sensitivity, controls body weight, prevents atherosclerosis and negatively regulates haematopoiesis and immune functions. In contrast to many proteins secreted by adipose tissue, the circulating level of ApN falls in obesity and insulin resistance states. The influence of starvation-induced depletion of fat stores on ApN concentrations is yet unknown. We therefore investigated plasma ApN in anorexia nervosa (AN).

PATIENTS AND DESIGN

We measured plasma ApN in 26 female anorectic patients and examined its relationships to several anthropometric or metabolic parameters. Twenty-four age-matched healthy female controls (C) were also studied.

RESULTS

Body mass index (BMI) and fat mass were markedly decreased in AN. However, plasma ApN levels were 30% higher in anorectic than in control subjects (P < 0.01), while a reverse pattern was observed for leptin concentrations. When normalized for fatness, ApN values almost doubled in AN. ApN levels were negatively correlated with BMI and fat mass (P < 0.05 in the combined population, AN + C). Insulin sensitivity tended to be 40% higher in AN (n = 7) than in C (n = 12) subjects, and plasma ApN levels were positively correlated with insulin sensitivity (P < 0.05 in AN + C subgroups). Total and low density lipoprotein (LDL)-cholesterol were higher, or tended to be higher, in AN, but there were no correlations between plasma ApN and plasma lipids. By contrast, ApN was related to the lipid profile, in a manner consistent with its antiatherogenic role, in healthy controls [i.e. negatively correlated with triglycerides, total and LDL-cholesterol and total/high density lipoprotein (HDL) cholesterol; P < 0.05 or less for each parameter]. In a multiple regression analysis, BMI and insulin sensitivity in AN were independent determinants for ApN levels, explaining up to approximately 80% of the variance in this measure.

CONCLUSIONS

Plasma adiponectin levels are increased in anorexia nervosa. This may, at least in part, be due to the lack of negative feedback exerted by fat mass on adiponectin production and/or to enhanced insulin sensitivity. We speculate that hyperadiponectinaemia could, in turn, contribute to maintain a state of enhanced insulin sensitivity and possibly exacerbate haematological and infectious complications of anorexia nervosa.