Insulin and Endothelin in the Acute Regulation of Adiponectin in Vivo in Humans

Large Reduction in Adiponectin During Pregnancy Is Associated With Large-for-Gestational-Age Newborns

CONTEXT

Fetuses exposed to an obese intrauterine environment are more likely to be born large-for-gestational age (LGA) and are at increased risk of obesity in childhood and cardiovascular disease and/or type 2 diabetes mellitus as adults, but which factors that influence the intrauterine environment is less clear.

OBJECTIVE

To investigate the association between circulating levels of leptin and adiponectin, measured multiple times during pregnancy, and birth weight and prevalence of LGA or small-for-gestational-age infants. The association between birth weight and messenger RNA (mRNA) expression of adiponectin receptors and genes involved in nutrient transport in the placenta was also investigated.

DESIGN

Population-based prospective cohort [substudy of the STORK study (STORe barn og Komplikasjoner, translated as Large Babies and Complications)] from 2001 to 2008.

SETTING

University hospital. Patients or other participants: 300 women.

MAIN OUTCOME MEASURES

Oral glucose tolerance test was performed twice along with adiponectin and leptin levels measured four times during pregnancy.

RESULTS

Circulating adiponectin was lower in mothers who gave birth to LGA offspring or had fetuses with high intrauterine abdominal circumference late in pregnancy. Adiponectin decreased most from early to late pregnancy in mothers who gave birth to LGA offspring, and the decrease was an independent predictor of birth weight. Adiponectin receptor 2 and system A amino acid transporter mRNA expression in placentas was negatively correlated with birth weight and was lower in placentas from LGA infants.

CONCLUSIONS

Our findings suggest that maternal adiponectin may be an important predictor of fetal growth and birth weight, independent of body mass index and insulin resistance.

Assessment of adiponectin level in obese and lean Nepalese population and its possible correlation with lipid profile: A cross-sectional study

OBJECTIVE

Adiponectin- one of the most important adipokines plays a pivotal role in carbohydrate and lipid metabolism and vascular biology. Changing food trend and lifestyle has tremendously affected the health status of Nepalese population. Studies have shown that between 1996 and 2006 obesity in Nepal has increased from 1.6% to 10%. Studies have been conducted in Nepal on the prevalence of obesity and its correlation with lipid profile. But based on our knowledge, this is the first study correlating adiponectin with obesity and lipid profile in Nepal. This piece of work will certainly help to assess the impact of obesity in Nepalese population.

MATERIALS AND METHODS

Fifty four obese and Thirty six normal/lean participants were included from different locations of Kathmandu Valley. Anthropometric measurements like age, BMI, Waist circumference, hip circumference, waist to hip ratio, mid thigh circumference and chest circumferences were taken from each participant. Blood glucose, lipid profile and serum adiponectin levels were measured from overnight fasting samples.

RESULTS

Significant differences were observed in BMI, Waist Circumference, Hip Circumference, Waist to Hip Ratio (WHR) and Chest circumference between obese and normal groups. Fasting Blood Glucose, Serum Triglyceride, HDL Cholesterol, LDL Cholesterol, Total Cholesterol/HDL ratio, Non-HDL Cholesterol and Adiponectin Levels were significant between the groups. Inverse correlations were observed between adiponectin level and BMI, Waist Circumference, Hip Circumference, Waist to Hip ratio, Chest Circumference, Fasting Blood Glucose, Triglyceride, Total Cholesterol/HDL ratio, LDL/HDL Cholesterol ratio and Non-HDL Cholesterol levels. Positive correlation was found between adiponectin and HDL Cholesterol levels.

CONCLUSION

Our study showed significant inverse association of serum adiponectin with obesity and lipid profile parameters except for Serum HDL Cholesterol level in Nepalese population.

Hormone therapy is associated with better body composition and adipokine/glucose profiles: a study with monozygotic co-twin control design

OBJECTIVE

The aim of this study was to evaluate the possibility of preventing the metabolic health consequences of postmenopausal hypogonadism with the use of long-term hormone therapy (HT).

METHODS

We used a monozygotic co-twin control design including 10 twin pairs (aged 56-62 y) discordant for HT (duration of HT, 2-10 y). In addition, 14 premenopausal women (aged 29-35 y) who did not use HT were studied to evaluate the differences in metabolic health between the premenopausal and postmenopausal states. Body composition was determined, and waist-to-hip ratio was used as an estimate for fat distribution. Serum sex steroids, sex hormone-binding globulin, and serum lipid and glucose profiles were analyzed. The serum levels of adiponectin, monocyte chemotactic protein-1, and leptin, as well as their local transcript levels in adipose tissue, skeletal muscle, and leukocytes, were measured.

RESULTS

Long-term HT was associated with a healthier amount and distribution of body fat. No difference was seen in serum lipid concentrations between HT users and their nonusing identical twin sisters, but fasting serum glucose and glycated hemoglobin levels were 5% and 3% lower in HT users than in nonusers, respectively. Among the adipokines analyzed, the most notable finding was a 15% lower level of monocyte chemotactic protein-1 in HT users, particularly with respect to its suggested mediator role between obesity and insulin resistance.

CONCLUSIONS

Long-term HT is associated with healthier amount and distribution of body fat and better adipocytokine profile, with concomitant signs of improved insulin sensitivity.

Insulin infusion reduces hepatocyte growth factor in lean humans

OBJECTIVE

Plasma Hepatocyte Growth Factor (HGF) is significantly elevated in obesity and may contribute to vascular disease, metabolic syndrome or cancer in obese individuals. The current studies were done to determine if hyperinsulinemia increases plasma HGF.

MATERIALS/METHODS

Twenty-two participants (10 women/12 men, BMI 20.6-34.5 kg/m(2), age 18-49 years) underwent a hyperinsulinemic euglycemic clamp with measurement of HGF at baseline and steady state. Relationships between baseline HGF, anthropometrics, triglycerides, liver enzymes, c-reactive protein and adiponectin were also evaluated.

RESULTS

Fasting HGF was positively correlated (P<0.050) with weight (r=0.63), BMI (r=0.55), waist circumference (r=0.68), WHR (r=0.48), triglycerides (r=0.44), alanine aminotransferase (r=0.74) and γ-glutamyl transpeptidase (r=0.56), but not c-reactive protein or adiponectin. In stepwise regression, alanine aminotransferase and insulin sensitivity accounted for significant variation in fasting HGF. A significant effect of insulin to suppress HGF during the clamp (P=0.029) was found after adjustment for BMI. HGF was reduced 7% at steady state in the lean subjects only (437.1 ±57.8 vs 405.4±72.0 pg/ml; P=0.030).

CONCLUSIONS

The positive correlation of HGF with hepatic enzymes suggests liver may be a significant source of circulating HGF in lean subjects. The strong correlation of plasma HGF with adiposity and the lack of an effect of insulin to increase HGF during the clamp in obese subjects suggest that adiposity, rather than elevated insulin levels, may be the major contributor to plasma HGF in obese subjects. Thus, a reduction in plasma HGF through weight loss is likely the best way to decrease comorbidities mediated by this angiogenic and mitogenic factor.

Nonalcoholic steatohepatitis versus steatosis: adipose tissue insulin resistance and dysfunctional response to fat ingestion predict liver injury and altered glucose and lipoprotein metabolism

Nonalcoholic fatty liver disease (NAFLD) ranges from simple steatosis (SS) to nonalcoholic steatohepatitis (NASH). Though liver-related risk seems confined to NASH, it is currently unclear whether NASH has a higher risk of cardiovascular disease (CVD) and diabetes than SS as a result of the coexistence of obesity and other cardiometabolic confounders. Adipose tissue is an emerging modulator of liver disease in NAFLD and of cardiometabolic disease in the general population. We evaluated in SS and NASH (1) glucose homeostasis and cardiovascular risk profile and (2) the effect of adipose tissue dysfunction, assessed in fasting conditions and postprandially, on liver injury, glucose and lipoprotein metabolism, and markers of early atherosclerosis. Forty nonobese, nondiabetic, normolipidemic biopsy-proven NAFLD patients (20 with SS and 20 with NASH) and 40 healthy subjects, matched for overall/abdominal adiposity and metabolic syndrome, underwent an oral fat load test, with measurement of plasma triglyceride-rich lipoproteins, oxidized low-density lipoproteins, adipokines, and cytokeratin-18 fragments, and an oral glucose tolerance test with minimal model analysis to yield glucose homeostasis parameters. Circulating endothelial adhesion molecules were measured, and adipose tissue insulin resistance (adipose IR) index and visceral adiposity index were calculated. Despite similar fasting values, compared to SS, NASH showed a more atherogenic postprandial lipoprotein profile, an altered adipokine response (i.e., higher resistin increase and an adiponectin fall), and hepatocyte apoptosis activation after fat ingestion. Adipose IR index, endothelial adhesion molecules, and hepatic insulin resistance progressively increased across NAFLD stages. NASH, but not SS, showed an impaired pancreatic β-cell function. On multiple regression analysis, adipose IR index and postprandial adiponectin independently predicted liver histology and altered cardiometabolic parameters.

CONCLUSION

Adipose tissue dysfunction, including a maladaptive adipokine response to fat ingestion, modulates liver injury and cardiometabolic risk in NAFLD.

Low circulating adiponectin levels are associated with insulin resistance in non-obese peritoneal dialysis patients

In patients with end-stage renal disease (ESRD), circulating adipokine levels are increased due to decreased renal clearance, irrespective of obesity. However, whether adipokines play a role in the development of insulin resistance (IR) in non-obese ESRD patients is unknown. We conducted a cross-sectional study to identify factors associated with IR in 62 non-obese patients on peritoneal dialysis (PD). Non-obesity was defined as body mass index (BMI) <25 kg/m(2). IR was determined using homeostatic model assessment-IR (HOMA-IR). We also measured serum concentrations of adiponectin, leptin, resistin, high-sensitivity C-reactive protein (hsCRP), and IL-6. The average BMI of the study patients was 21.6 kg/m(2). When patients were divided into two groups according to the median value of HOMA-IR, serum adiponectin levels were significantly lower in patients with HOMA-IR > 1.85 than in those with HOMA-IR ≤1.85, whereas serum concentrations of leptin and resistin did not differ between the two groups. In addition, log-transformed HOMA-IR was negatively correlated with adiponectin (γ = -0.464, P < 0.001) and log-transformed high-density lipoprotein cholesterol (γ = -0.250, P = 0.050) and positively correlated with age (γ = 0.334, P = 0.008) and triglyceride (γ = 0.392, P = 0.002). However, resistin, log-transformed leptin and log-transformed hsCRP were not associated with HOMA-IR. In a multiple linear regression model, adiponectin was independently associated with HOMA-IR (β = -0.023, P = 0.015). In conclusion, this study suggests that low circulating adiponectin levels might be involved in IR even in non-obese patients undergoing PD.

Glucocorticoid effects on adiponectin expression

Maintenance of energy metabolism and glucose homeostasis is achieved by the regulatory effects of many hormones and their interactions. Glucocorticoids produced from adrenal cortex and adiponectin produced by adipose tissue play important roles in the production, distribution, storage, and utilization of energy substrates. Glucocorticoids are involved in the activation of a number of catabolic processes by affecting the expression of a plethora of genes, while adiponectin acts primarily as an insulin sensitizer. Both are regulated by a number of physiological and pharmacological factors. Although the effects of glucocorticoids on adiponectin expression have been extensively studied in different in vitro, animal and clinical study settings, no consensus has been reached. This report reviews the primary literature concerning the effects of glucocorticoids on adiponectin expression and identifies potential reasons for the contradictory results between different studies. In addition, methods to gain better insights pertaining to the regulation of adiponectin expression are discussed.

Caloric restriction increases adiponectin expression by adipose tissue and prevents the inhibitory effect of insulin on circulating adiponectin in rats

Aging is associated with redistribution of body fat and the development of insulin resistance. White adipose tissue emerges as an important organ in controlling life span. Caloric restriction (CR) delays the rate of aging possibly modulated partly by altering the amount and function of adipose tissue. Adiponectin is a major adipose-derived adipokine that has anti-inflammatory and insulin-sensitizing properties. This study examined the effects of CR on adiposity and gene expression of adiponectin, its receptors (AdipoR1 and AdipoR2) in adipose tissue and in isolated adipocytes of Brown Norway rats that had undergone CR for 4 months or fed ad libitum. The study also determined plasma concentrations of adiponectin and insulin in these animals and whether insulin infusion for 7 days affects adiponectin expression and its circulating concentrations under CR conditions. CR markedly reduced body weight as anticipated, epididymal fat mass and adipocyte size. CR led to an increase in plasma free fatty acid and glycerol (both twofold), and adipose triglyceride lipase messenger RNA (mRNA) in adipose tissue and isolated adipocytes (both >2-fold). Adiponectin mRNA levels were elevated in adipose tissue and adipocytes (both >2-fold) as was plasma adiponectin concentration (2.8-fold) in CR rats. However, CR did not alter tissue or cellular AdipoR1 and AdipoR2 expression. Seven days of insulin infusion decreased adiponectin mRNA in adipose tissue but did not reverse the CR-induced up-regulation of circulating adiponectin levels. Our results suggest that the benefits of CR could be, at least in part, dependent on enhanced expression and secretion of adiponectin by adipocytes.

Improvement in insulin sensitivity by weight loss does not affect hyperinsulinemia-mediated reduction in total and high molecular weight adiponectin: a MONET study

Acute hyperinsulinemia reduces total and high molecular weight (HMW) adiponectin levels in humans. Whether an increase in insulin sensitivity (IS) is accompanied by a greater suppressive effect of hyperinsulinemia on adiponectin levels is unknown, however. To clarify the inhibitory role of insulin on adiponectin, total and HMW adiponectin levels were measured during acute hyperinsulinemia before and after an improvement in insulin sensitivity in response to weight loss. Forty-six overweight and obese postmenopausal women were randomized to either 6-month caloric restriction (CR) alone (n = 22), or CR with resistance training (CR+RT, n = 24). IS (hyperinsulinemic-euglycemic clamp) was assessed before and after weight loss. Total and HMW adiponectin levels were measured by ELISA at baseline, 90, 160, and 180 min of each clamp. Relative mean body weight loss was -8.0% ± 4.4% for both groups (CR: -7.7% ± 3.8%; CR+RT: -8.2% ± 5.0%). IS increased significantly, by 18.4% ± 25.3% (CR: 19.3% ± 29.7%; CR+RT: 17.7% ± 21.0%). Before each intervention, total and HMW adiponectin levels in both groups significantly decreased in response to hyperinsulinemia (total: -8.4% ± 19.4%; HMW: -3.2% ± 13.2%). Despite the improvement in IS seen after each intervention, a similar pattern of reduction to that before weight loss was observed in total and HMW adiponectin levels during hyperinsulinemia. These results establish that total and HMW adiponectin levels decline during a hyperinsulinemic-euglycemic clamp. Also, the insulin-sensitizing effect of weight loss via caloric restriction alone or with resistance training does not amplify the reduction in adiponectin levels observed during hyperinsulinemia in healthy postmenopausal women.

Preeclampsia and adiponectin in cord blood

AIMS

To compare cord blood concentrations of total adiponectin in the offspring of pregnancies with and without preeclampsia.

METHODS

Using a Luminex analyzer, cord blood adiponectin was measured in 182 singleton pregnancies with preeclampsia and compared to adiponectin measured in 511 singleton pregnancies without preeclampsia.

RESULTS

Adiponectin levels in cord blood increased with increasing gestational age, but overall, crude levels were similar in pregnancies with and without preeclampsia. However, in pregnancies with early delivery (weeks 32-36), and in pregnancies with delivery after spontaneous contractions, adiponectin levels were higher in the preeclampsia group.

CONCLUSION

In preterm pregnancies and in pregnancies with spontaneous contractions, adiponectin levels in cord blood were higher in the preeclampsia group than in pregnancies without preeclampsia, maybe reflecting the need to optimize energy in preeclampsia.

Genetic architecture of plasma adiponectin overlaps with the genetics of metabolic syndrome-related traits

OBJECTIVE

Adiponectin, a hormone secreted by adipose tissue, is of particular interest in metabolic syndrome, because it is inversely correlated with obesity and insulin sensitivity. However, it is not known to what extent the genetics of plasma adiponectin and the genetics of obesity and insulin sensitivity are interrelated. We aimed to evaluate the heritability of plasma adiponectin and its genetic correlation with the metabolic syndrome and metabolic syndrome-related traits and the association between these traits and 10 ADIPOQ single nucleotide polymorphisms (SNPs).

RESEARCH DESIGN AND METHODS

We made use of a family-based population, the Erasmus Rucphen Family study (1,258 women and 967 men). Heritability analysis was performed using a polygenic model. Genetic correlations were estimated using bivariate heritability analyses. Genetic association analysis was performed using a mixed model.

RESULTS

Plasma adiponectin showed a heritability of 55.1%. Genetic correlations between plasma adiponectin HDL cholesterol and plasma insulin ranged from 15 to 24% but were not significant for fasting glucose, triglycerides, blood pressure, homeostasis model assessment of insulin resistance (HOMA-IR), and C-reactive protein. A significant association with plasma adiponectin was found for ADIPOQ variants rs17300539 and rs182052. A nominally significant association was found with plasma insulin and HOMA-IR and ADIPOQ variant rs17300539 after adjustment for plasma adiponectin.

CONCLUSIONS

The significant genetic correlation between plasma adiponectin and HDL cholesterol and plasma insulin should be taken into account in the interpretation of genome-wide association studies. Association of ADIPOQ SNPs with plasma adiponectin was replicated, and we showed association between one ADIPOQ SNP and plasma insulin and HOMA-IR.

Role of endogenous ET-1 in the regulation of myocardial blood flow in lean and obese humans

Endothelin is an important determinant of peripheral vascular tone, and increased endogenous endothelin activity contributes to peripheral vascular dysfunction in human obesity. The contributions of endothelin to the regulation of coronary vascular tone in health in humans have not been well studied. We hypothesized that the contribution of endothelin to the regulation of myocardial perfusion would be augmented in human obesity. Using [NH(3)]ammonia positron emission tomography (PET), we measured myocardial perfusion under resting and adenosine-stimulated conditions on two separate days, with and without concurrent exposure to BQ123, an antagonist of type A endothelin receptors (1 micromol/min IV beginning 90 min before measurement). We studied 10 lean and 9 obese subjects without hypertension, hyperlipidemia, or diabetes mellitus. We observed a BQ123-induced increase in resting myocardial perfusion of approximately 40%, not different between lean and obese subjects (BQ123-induced increase in flow: lean 0.12 +/- 0.20, obese 0.32 +/- 0.51 ml/g/min, P = 0.02 BQ123 effect, P = 0.27 comparing response across groups). Although basal flow rates varied by region of the myocardium, the BQ123 effect was seen in all regions. BMI and cholesterol were significantly related to BQ123-induced increases in basal tone in multivariable analysis. There was no baseline difference in the adenosine-stimulated increase in blood flow between lean and obese subjects, and BQ123 failed to augment these responses in either group. These observations suggest that endothelin is an important contributor to the regulation of myocardial perfusion under resting conditions in healthy lean and obese humans, with increased contributions in proportion to increasing obesity.

A genome-wide association study reveals variants in ARL15 that influence adiponectin levels

The adipocyte-derived protein adiponectin is highly heritable and inversely associated with risk of type 2 diabetes mellitus (T2D) and coronary heart disease (CHD). We meta-analyzed 3 genome-wide association studies for circulating adiponectin levels (n = 8,531) and sought validation of the lead single nucleotide polymorphisms (SNPs) in 5 additional cohorts (n = 6,202). Five SNPs were genome-wide significant in their relationship with adiponectin (P< or =5x10(-8)). We then tested whether these 5 SNPs were associated with risk of T2D and CHD using a Bonferroni-corrected threshold of P< or =0.011 to declare statistical significance for these disease associations. SNPs at the adiponectin-encoding ADIPOQ locus demonstrated the strongest associations with adiponectin levels (P-combined = 9.2x10(-19) for lead SNP, rs266717, n = 14,733). A novel variant in the ARL15 (ADP-ribosylation factor-like 15) gene was associated with lower circulating levels of adiponectin (rs4311394-G, P-combined = 2.9x10(-8), n = 14,733). This same risk allele at ARL15 was also associated with a higher risk of CHD (odds ratio [OR] = 1.12, P = 8.5x10(-6), n = 22,421) more nominally, an increased risk of T2D (OR = 1.11, P = 3.2x10(-3), n = 10,128), and several metabolic traits. Expression studies in humans indicated that ARL15 is well-expressed in skeletal muscle. These findings identify a novel protein, ARL15, which influences circulating adiponectin levels and may impact upon CHD risk.

Maternal serum adiponectin multimers in gestational diabetes

OBJECTIVE

Adiponectin, an adipokine with profound insulin-sensitizing effect, consists of heterogeneous species of multimers. These oligomeric complexes circulate as low-molecular-weight (LMW) trimers, medium-molecular-weight (MMW) hexamers and high-molecular-weight (HMW) isoforms and can exert differential biological effects. The aims of this study were to determine whether there is a change in circulating adiponectin multimers in the presence of gestational diabetes mellitus (GDM), overweight/obesity or with a treatment with sulfonylurea or insulin in patients with GDM.

STUDY DESIGN

This cross-sectional study included women with: 1) normal pregnancy (n=149); and 2) patients with GDM (n=72). Thirty-three patients with GDM were managed with diet alone. Among the others 39 diabetic patients, 17 were treated with Glyburide and 22 with insulin. The study population was further stratified by first trimester body mass index (BMI) (normal weight <25 kg/m(2) vs. overweight/obese > or =25 kg/m(2)). Serum adiponectin multimers (total, HMW, MMW and LMW) concentrations were determined by ELISA.

RESULTS

1) The median maternal serum of total, HMW, MMW and LMW were lower in patients with GDM than in those with normal pregnancies (P<0.001 for all comparisons); 2) patients with GDM had a lower HMW/total adiponectin ratio and a higher MMW/total and LMW/total adiponectin ratio than those with a normal pregnancy (P<0.001 for all comparisons); and 3) among GDM patients, there were no differences in the concentrations and relative distribution of adiponectin multimers between those who were managed with diet, and those who were treated with pharmacological agents.

CONCLUSION

1) GDM is characterized by a distinctive pattern of concentrations and relative distribution of adiponectin multimers akin to Type 2 diabetes mellitus; 2) dysregulation of adiponectin multimeres can provide a mechanistic basis for the association between adiposity and GDM.

Maternal serum adiponectin multimers in gestational diabetes

OBJECTIVE

Adiponectin, an adipokine with profound insulin-sensitizing effect, consists of heterogeneous species of multimers. These oligomeric complexes circulate as low-molecular-weight (LMW) trimers, medium-molecular-weight (MMW) hexamers and high-molecular-weight (HMW) isoforms and can exert differential biological effects. The aims of this study were to determine whether there is a change in circulating adiponectin multimers in the presence of gestational diabetes mellitus (GDM), overweight/obesity or with a treatment with sulfonylurea or insulin in patients with GDM.

STUDY DESIGN

This cross-sectional study included women with: 1) normal pregnancy (n=149); and 2) patients with GDM (n=72). Thirty-three patients with GDM were managed with diet alone. Among the others 39 diabetic patients, 17 were treated with Glyburide and 22 with insulin. The study population was further stratified by first trimester body mass index (BMI) (normal weight <25 kg/m(2) vs. overweight/obese > or =25 kg/m(2)). Serum adiponectin multimers (total, HMW, MMW and LMW) concentrations were determined by ELISA.

RESULTS

1) The median maternal serum of total, HMW, MMW and LMW were lower in patients with GDM than in those with normal pregnancies (P<0.001 for all comparisons); 2) patients with GDM had a lower HMW/total adiponectin ratio and a higher MMW/total and LMW/total adiponectin ratio than those with a normal pregnancy (P<0.001 for all comparisons); and 3) among GDM patients, there were no differences in the concentrations and relative distribution of adiponectin multimers between those who were managed with diet, and those who were treated with pharmacological agents.

CONCLUSION

1) GDM is characterized by a distinctive pattern of concentrations and relative distribution of adiponectin multimers akin to Type 2 diabetes mellitus; 2) dysregulation of adiponectin multimeres can provide a mechanistic basis for the association between adiposity and GDM.

Hyperglycemia prevents the suppressive effect of hyperinsulinemia on plasma adiponectin levels in healthy humans

Adiponectin is a fat-derived hormone with insulin-sensitizing properties. In patients with type 2 diabetes plasma adiponectin levels are decreased. Since these patients are characterized by high plasma insulin and glucose concentrations, hyperinsulinemia and hyperglycemia could be responsible for the downregulation of adiponectin. Insulin decreases adiponectin levels in humans. The effect of hyperglycemia is unknown. To determine the selective effects of insulin, glucose, or their combination on plasma adiponectin, clamps were performed in six healthy males on four occasions in a crossover design: 1) lower insulinemic-euglycemic clamp (100 pmol/l insulin, 5 mmol/l glucose) (reference clamp); 2) hyperinsulinemic-euglycemic clamp (400 pmol/l insulin, 5 mmol/l glucose); 3) lower insulinemic-hyperglycemic clamp (100 pmol/l insulin, 12 mmol/l glucose); and 4) hyperinsulinemic-hyperglycemic clamp (400 pmol/l insulin, 12 mmol/l glucose). Adiponectin concentrations and high-molecular-weight (HMW)-to-total adiponectin ratio were measured at the start and end of the 6-h clamps. After the 6-h study period, total plasma adiponectin levels were significantly (P = 0.045) decreased by 0.63 microg/ml in the lower insulinemic-euglycemic clamp (clamp 1). In both euglycemic groups (clamps 1 and 2) adiponectin concentrations significantly declined (P = 0.016) over time by 0.56 microg/ml, whereas there was no change in both hyperglycemic groups (clamps 3 and 4) (P = 0.420). In none of the clamps did the ratio of HMW to total adiponectin change. We conclude that insulin suppresses plasma adiponectin levels already at a plasma insulin concentration of 100 pmol/l. Hyperglycemia prevents the suppressive effect of insulin. This suggests that, in contrast to glucose, insulin could be involved in the downregulation of plasma adiponectin in insulin-resistant patients.

Physiological, pharmacological, and nutritional regulation of circulating adiponectin concentrations in humans

Adiponectin is an adipocyte hormone that links visceral adiposity with insulin resistance and atherosclerosis. It is unique among adipocyte-derived hormones in that its circulating concentrations are inversely proportional to adiposity, and low adiponectin concentrations predict the development of type 2 diabetes and cardiovascular disease. Consequently, in the decade since its discovery, adiponectin has generated immense interest as a potential therapeutic target for the metabolic syndrome and diabetes. This review summarizes current research regarding the regulation of circulating adiponectin concentrations by physiological, pharmacological, and nutritional factors, with an emphasis on human studies. In humans, plasma adiponectin concentrations are influenced by age and gender, and are inversely proportional to visceral adiposity. In vitro studies suggest that adiponectin production may be determined primarily by adipocyte size and insulin sensitivity, with larger, insulin-resistant adipocytes producing less adiponectin. While adiponectin concentrations are unchanged after meal ingestion, they are increased by significant weight loss, such as after bariatric surgery. In addition, adiponectin production is inhibited by a number of hormones, including testosterone, prolactin, glucocorticoids and growth hormone, and by inflammation and oxidative stress in adipose tissue. Smoking decreases, while moderate alcohol consumption increases, circulating adiponectin concentrations. Dietary fatty acid composition in rodents influences adiponectin production via ligand-activated nuclear receptors (PPARs); however, current evidence in humans is equivocal. In addition to PPAR agonists (such as thiazolidinediones and fibrates), a number of pharmacological agents (angiotensin receptor type 1 blockers, ACE inhibitors, and cannabinoid receptor antagonists) used in treatment of the metabolic syndrome also increase adiponectin concentrations in humans.

Adiponectin and leptin in African Americans

OBJECTIVE

African Americans (AAs) have less visceral and more subcutaneous fat than whites, thus the relationship of adiponectin and leptin to body fat and insulin sensitivity in AA may be different from that in whites.

METHODS AND PROCEDURES

Sixty-nine non-diabetic AA (37 men and 32 women), aged 33 +/- 1 year participated. The percent fat was determined by dual-energy X-ray absorptiometry, abdominal visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) volume by computerized tomography (CT), and insulin sensitivity by homeostasis model assessment (HOMA).

RESULTS

VAT was greater in men (1,619 +/- 177 cm(3) vs. 1,022 +/- 149 cm(3); P = 0.01); women had a higher percentage of body fat (34.1 +/- 1.4 vs. 24.0 +/- 1.2; P < 0.0001), adiponectin (15.8 +/- 1.2 microg/ml vs. 10.4 +/- 0.8 microg/ml; P = 0.0004) and leptin (23.2 +/- 15.8 ng/ml vs. 9.2 +/- 7.2 ng/ml; P < 0.0001). SAT and HOMA did not differ because of the sex. Adiponectin negatively correlated with VAT (r = -0.41, P < 0.05) in men, and with VAT (r = -0.55, P < 0.01), and SAT (r = -0.35, P < 0.05) in women. Adiponectin negatively correlated with HOMA in men (r = -0.38, P < 0.05) and women (r = -0.44, P < 0.05). In multiple regression, sex (P = 0.02), HOMA (P = 0.03) and VAT (P = 0.003) were significant predictors of adiponectin (adj R (2) = 0.38, P < 0.0001). Leptin positively correlated with VAT, SAT, percent fat and HOMA in men (r = 0.79, r = 0.86, r = 0.89, and r = 0.53; P < 0.001) and women (r = 0.62, r = 0.75, r = 0.83, and r = 0.55; P < 0.01). In multiple regression VAT (P = 0.04), percent body fat (P < 0.0001) and sex (P = 0.01), but not HOMA were significant predictors of serum leptin (adj R (2)= 0.82, P < 0.0001).

DISCUSSION

The relationship of adiponectin and leptin to body fat content and distribution in AA is dependent on sex. Although VAT and insulin sensitivity are significant determinants of adiponectin, VAT and percent body fat determine leptin.

Hypoadiponectinemia as a marker of adipocyte dysfunction -- Part I: the biology of adiponectin

Adiponectin is the most abundantly secreted adipocyte-derived peptide hormone, possessing an array of antidiabetogenic and cardiovascular protective effects. Acting through 2 distinct membrane receptors, adiponectin receptors 1 and 2 (which utilize 5'-adenosine monophosphate-activated protein kinase phosphorylation, p38 mitogen-activated protein kinase, and peroxisome proliferator-activated receptor alpha as key cell signaling elements), adiponectin increases hepatic and skeletal muscle sensitivity to insulin, enhances fatty acid oxidation, suppresses monocyte-endothelial interaction, supports endothelial cell growth, lowers blood pressure, and moderates adipose tissue growth. The secretion of adiponectin can be suppressed by adipose factors, which are turned on once fat cell mass increases, such as cytokines, adipose renin-angiotensin system, and increased oxidative stress. Inhibition of adiponectin secretion results in the loss of an array of mechanisms, which under normal conditions of fat cell homeostasis provide protection from insulin resistance, diabetes, and atherosclerosis.

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

AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Inflammation and adipose tissue in uremia

Enhanced chronic systemic inflammation and reduced insulin sensitivity are often associated in patients with chronic renal failure, contributing to cardiovascular morbidity and mortality in these patients. Adipose tissue produces several hormones (adipocytokines including leptin, resistin, tumor necrosis factor-alpha, and adiponectin) that modulate both systemic inflammatory response and insulin action. High leptin, resistin, and tumor necrosis factor-alpha and low adiponectin are associated with proinflammatory conditions, whereas opposite patterns are commonly observed in the presence of increased insulin sensitivity, low inflammation, and reduced cardiovascular risk. Oxidative stress has also been shown recently to modulate adipocytokine production, resulting in a proinflammatory profile. Increments of plasma concentrations of both proinflammatory and anti-inflammatory adipocytokines have been reported in chronic renal failure, possibly caused by both passive accumulation from reduced renal excretion and metabolic abnormalities induced by uremia. The potential role of altered adipose tissue adipocytokine production in the onset of renal failure-associated inflammatory and metabolic derangements remains largely to be elucidated and is discussed in the current report.

Adiponectin in human pregnancy: implications for regulation of glucose and lipid metabolism

AIMS/HYPOTHESIS

Adiponectin is upregulated during adipogenesis and downregulated in insulin-resistant states. The mechanism(s) governing the re-arrangements from adipogenesis to facilitated lipolysis during pregnancy are unknown. Our purpose was to analyse the role of adiponectin relative to the metabolic changes in human pregnancy.

SUBJECTS, MATERIALS AND METHODS

Lean women (BMI <25 kg/m(2)) were evaluated longitudinally before conception, and in early (12-14 weeks) and late (34-36 weeks) pregnancy. Insulin sensitivity was measured using the glucose clamp technique. Venous blood and subcutaneous adipose tissue biopsies were obtained at each time point.

RESULTS

Adiponectin concentrations were lower in the third trimester than in the pregravid condition (9.9+/-1.4 vs 13.5+/-1.8 microg/ml). The hypoadiponectinaemia was reflected by a 2.5-fold decrease in white adipose tissue adiponectin mRNA. These changes were associated with a 25% increase in fat mass (23.7+/-2.9 vs 18.9+/-2.9 kg). Insulin infusion decreased high molecular weight adiponectin complexes in pregravid women (9.9+/-0.6 vs 6.2+/-0.06) and the suppressive effect of insulin was lost during pregnancy. The pregnancy-mediated changes in adiponectin were strongly correlated with basal insulin levels and insulin sensitivity (p<0.0001). The relationship between adiponectin and insulin sensitivity was related to the decreased insulin regulation of glucose utilisation (r=0.55, p<0.001) but not of endogenous hepatic glucose production.

CONCLUSIONS/INTERPRETATION

These data demonstrate that pregnancy is associated with adiponectin changes in lean women. Hypoadiponectinaemia is reflected by a lower amount of high molecular weight adiponectin and by the ratio of high to low molecular weight multimers. The adiponectin changes relate to decreased insulin sensitivity of glucose disposal rather than alterations of lipid metabolism.

Adipokines in NASH: postprandial lipid metabolism as a link between adiponectin and liver disease

Circulating levels of four adipokines (adiponectin, TNF-alpha, leptin, and resistin) and the postprandial lipid and adiponectin responses to an oral fat load were assessed in 25 non-obese, non-diabetic patients with biopsy-proven nonalcoholic steatohepatitis (NASH) and correlated with metabolic indices and liver histology. Circulating adiponectin was lower in NASH compared with controls (5,476 +/- 344 vs. 11,548 +/- 836 ng/mL; P = .00001) and on multiple regression analysis correlated negatively with liver steatosis, necroinflammation (OR = 5.0; P = .009), and fibrosis (OR = 8.0; P = .003). The magnitude of postprandial lipemia was significantly higher in NASH than in controls and was related to fasting adiponectin (beta = -0.78; P = .00003). Controls showed a significant increase in serum adiponectin in response to the fat load, whereas patients with NASH showed a slight decrease. Postprandial free fatty acids response correlated inversely with adiponectin response in both groups and independently predicted the severity of liver steatosis in NASH (beta = 0.51; P = .031). In conclusion, hypoadiponectinemia is present before overt diabetes and obesity appear and correlates with the severity of liver histology in NASH. Impaired postprandial lipid metabolism may be an additional mechanism linking hypoadiponectinemia and NASH and posing a higher cardiovascular risk to these subjects. The mechanism(s) underlying these differences are unknown, but the type of dietary fat seems to play a role. These findings may have important pathogenetic and therapeutic implications in both liver and metabolic disease.