HMW Adiponectin Research Articles

Synergistic effects of ascorbic acid and thiazolidinedione on secretion of high molecular weight adiponectin from human adipocytes

To test the hypothesis that ascorbic acid (AA) and thiazolidinedione (TZD) would have additive effects on HMW adiponectin secretion by virtue of different modes of action. We determined the effects of supplementation of AA and/or TZD on expression and secretion of total and HMW adiponectin from human Simpson-Golabi-Behmel syndrome (SGBS) adipocytes in the absence or presence of the proinflammatory cytokine TNFα. AA supplementation significantly increased secretion of HMW adiponectin (1.7-fold) without altering adiponectin expression or total adiponectin secretion. TZD significantly increased expression (3-fold) and secretion of total (1.4-fold) but not HMW adiponectin. Combined supplementation resulted in a significant increase in expression (3-fold) and secretion of total (1.8-fold) and HMW (5-fold) adiponectin. Similar results were seen in cells co-treated with TNFα. These data show that AA and TZD have synergistic rather than simple additive effects on secretion of HMW adiponectin from human adipocytes and raise the possibility that differences in AA levels may contribute to the variability in adiponectin multimer profiles and efficacy of TZD in humans. Our results also provide a rationale for longitudinal clinical trials investigating the effects of AA supplementation with or without TZD on adiponectin and metabolic profiles.

Daily physical activity, fasting glucose, uric acid, and body mass index are independent factors associated with serum fibroblast growth factor 21 levels

Fibroblast growth factor 21 (FGF21) levels have been linked with beneficial effects on glucose and lipid metabolism in animals. It is elevated in humans with the metabolic syndrome. This study investigates independent factors associated with serum FGF21 levels. Cross-sectional study done in healthy blue-collar workers. A medical history was taken, and FGF21 (measured using an ELISA commercial kit), glucose, uric acid, plasma lipids, total/high-molecular weight (HMW) adiponectin, and retinal-binding protein 4 (RBP4) were measured in 210 individuals with (n=81) and without (n=129) metabolic syndrome. The median of serum FGF21 levels were higher in subjects with metabolic syndrome (339.5 vs 276.4 ng/l, P=0.01). Serum FGF21 levels correlated positively with body mass index (BMI; r=0.23, P=0.001) and age (r=0.17, P=0.01). After adjusting for age and BMI, a significant positive correlation persisted for fasting glucose, uric acid, and physical activity in both males (r=0.21, r=0.11, and r=0.19, all P<0.05) and females (r=0.20, r=0.19, and r=0.14, all P<0.05). In addition, FGF21 also correlates negatively with RBP4 (r=-0.27, P=0.02), total (r=-0.26, P=0.03), and HMW adiponectin (r=-0.30, P=0.01) in women. A multiple linear regression model analysis identified that BMI (standardized beta (SB)=0.247; P=0.008), glucose (SB=0.226; P=0.003), uric acid (SB=0.191; P=0.04), and physical activity (SB=0.223; P=0.004) are independent factors influencing serum FGF21 levels (F=10.05, r(2)=0.19, P<0.001). In addition, fasting hyperglycemia > or =100 mg/dl, excess body weight with BMI > or =25 kg/m(2), and uric acid > or =5.5 mg/dl predicted higher serum FGF21 levels. Serum FGF21 levels are influenced by BMI, fasting glycemia, uric acid, and physical activity.

Type 2 Diabetes in Octogenarians Is Associated with Decreased Low Molecular Weight Adiponectin

Background: Adiponectin circulates in the blood in three different multimer isoforms, of which the high molecular weight form (HMW) is presumed to mediate insulin sensitivity. We examined whether adiponectin oligomer distribution is associated with aging and type 2 diabetes (T2D) in octogenarians without characteristic features of metabolic syndrome. Methods: The study included 154 octogenarians (58 men, 96 women), 24 normoglycemic middle-aged controls (11 men, 13 women; mean age 44 years), and 33 middle-aged individuals (14 men, 19 women; mean age 55 years) with T2D. Based on oral glucose tolerance test 62 octogenarians had normal, 63 impaired glucose tolerance, and 29 octogenarians had newly detected T2D. Serum adiponectin multimer isoforms were measured after overnight fast by enzyme-linked immunosorbent assays. Results:Compared to the normoglycemic middle-aged control group, male normoglycemic octogenarians revealed significantly higher total adiponectin and all adiponectin isoforms. The same was true for females with the exception of low molecular weight (LMW) adiponectin, which was not statistically higher in octogenarians. Male and female octogenarians with T2D had significantly higher levels of total, HMW, and middle molecular weight (MMW) adiponectin, but not LMW adiponectin, than middle-aged individuals with T2D. Female, but not male, octogenarians revealed significantly lower total adiponectin than normoglycemic octogenarians. Compared with normoglycemic octogenarians, male and female octogenarians with T2D were characterized by significantly lower LMW adiponectin. In male and female octogenarians, total adiponectin and all multimer isoforms were directly correlated with HDL cholesterol. LMW adiponectin in octogenarians of both sexes was inversely correlated with glucose level at 2-hour oral glucose tolerance test. Conclusions: Serum levels of total adiponectin as well as its HMW and MMW isoforms were significantly higher in octogenarians with normoglycemia or T2D than in corresponding middle-aged control groups. In male and female octogenarians without metabolic syndrome, T2D was associated with lower LMW adiponectin, while the HMW and MMW isoforms were not statistically different.

Metabolic And Vascular Responses Acutely Affected By Meal Consumption And Exercise

Lifestyle strongly regulates vascular and metabolic function, with physical activity eliciting acute, short- and long-term effects. We examined risk factor changes after a single exercise session in sedentary people. PURPOSE: To determine how glucose control, arterial elasticity and inflammatory markers respond to a single bout of moderate intensity exercise performed the day before or immediately prior to a standardized mixed meal. METHODS: Participants (5M/6F) were young (26 y±1), normal BMI (22.7 ± 0.3), untrained (VO2peak 25 ± 1 ml/kg/min), but generally healthy. The test meal (670 kcal, 45/40/15% energy as CHO/fat/pro) was consumed on 3 separate mornings. One trial (no-exercise) was after refraining from moderate-to-vigorous activity for ≥3 days. On the other 2 trials, a 45-min exercise bout at 75% HRmax was performed either 17-hr (prior afternoon) or 1-hr (same morning) before the meal. RESULTS: Post-meal energy expenditure increased (24% above baseline at 1-hr) and fuel oxidation shifted toward CHO but there were no differences between trials. Fasting glucose (83±1 mg/dl) and insulin (6.1±0.8 μIU/ml) were similar among trials, but 3-hr post-meal AUC's were reduced by 9 & 19% (p<0.05), respectively, on the acute exercise trial. Small artery elasticity, measured by diastolic pulsewave contour analysis, was reduced 18-20% from 1-3 hours (p < 0.01) after the meal on the no-exercise trial. This post-meal decline was prevented on both exercise trials, demonstrating both acute and residual benefits of exercise. In contrast, large artery elasticity was not significantly affected by the meal or exercise. After prior-day exercise, fasting SBP (110±1 mmHg) and DBP (61±1) were reduced (p < 0.05) by 3 and 2 mmHg, respectively. These effects may be mediated in part by changes in inflammatory markers like ICAM-1 and VCAM-1, which were reduced 5-6% (p<0.03) by prior-day exercise, C-reactive protein (40% lower after acute exercise) and visfatin (7% lower after acute and prior day exercise). Other putative cyto-/adipokines (IL6, HMW adiponectin, e-selectin) were unchanged. CONCLUSION: These results demonstrate that exercise has positive benefits on metabolic and vascular outcomes in untrained young people that begin to accrue after a single moderate exercise session. Supported by NIH Grant P20 DKRR024215

Influence of acute aerobic exercise on adiponectin oligomer concentrations in middle-aged abdominally obese men

Exercise intensity may induce changes in total adiponectin and adiponectin oligomer levels. However, the effects of acute aerobic exercise on total adiponectin and adiponectin oligomers in middle-aged abdominally obese men remain unknown. The purpose of this study was to investigate the influence of aerobic exercise intensity on changes in the concentrations of total adiponectin and adiponectin oligomers (high–molecular weight [HMW] and middle– plus low–molecular weight [MLMW] adiponectin), and the endocrine mechanisms involved in exercise-induced changes in adiponectin oligomer profiles in middle-aged abdominally obese men. Using a crossover design, 9 middle-aged abdominally obese men (age, 54.1 ± 2.4 years; body mass index, 27.9 ± 0.6 kg/m2) underwent 2 trials that consisted of 60 minutes of stationary cycle exercise at either moderate-intensity (ME) or high-intensity (HE) aerobic exercise (50% or 70% of peak oxygen uptake, respectively). Blood samples were collected to measure the concentrations of adiponectin oligomers, hormones (catecholamines, insulin, and growth hormone), metabolites (free fatty acid, glycerol, triglyceride, and glucose), and cytokines (interleukin-6 and tumor necrosis factor–α). After exercise, plasma catecholamine concentrations were higher during HE than during ME (P < .05). Total adiponectin concentration decreased at the end of HE (P < .05), but remained unchanged after ME. The HMW adiponectin concentration did not change at either intensity, whereas the MLMW concentration decreased at the end of HE (P < .05). The ratio of HMW to total adiponectin concentration increased significantly (P < .05), whereas the ratio of MLMW to total adiponectin concentration decreased significantly (P < .05), at the end of HE. The percentage changes in epinephrine concentration from baseline to the end of exercise were correlated with the percentage changes in total adiponectin concentration (r = −0.67, P < .05) and MLMW adiponectin concentration (r = −0.82, P < .05) from baseline to the end of HE. Our results indicate that the change in total adiponectin was mainly due to a change in MLMW adiponectin concentration during high-intensity exercise in middle-aged abdominally obese men. Epinephrine may partially regulate the decrease in total and MLMW adiponectin concentrations during high-intensity exercise.

Characterization of Wistar–Kyoto rats showing hyperadiponectinemia

Aims Wistar–Kyoto rats (HA-WKY) kept in the author's laboratory showed higher levels of serum adiponectin (approximately 4-fold) compared with Wistar–Kyoto/Izm rats (WKY/Izm), a WKY standard strain, at 6 weeks old. In a preliminary study, HA-WKY but not WKY/Izm showed hyperinsulinemia and severe hypercholesterolemia when fed a high-fat diet. This study analyzed the differences between HA-WKY and WKY/Izm to investigate the causes of hyperadiponectinemia. Main methods Six-week-old male HA-WKY and WKY/Izm were used for an analysis of adiponectin-related factors. Key findings The main intermediates in the adiponectin signaling pathway, AMP-activated protein kinase and peroxisome proliferator-activated receptor α, were activated at similar levels in liver and skeletal muscle between HA-WKY and WKY/Izm, although HA-WKY had not only higher adiponectin concentrations but also extremely high levels of high-molecular weight (HMW, polymer) adiponectin, which is the active form. The main difference between HA-WKY and WKY/Izm was the existence of adiponectin, mainly middle-molecular weight (MMW, hexamer) and HMW adiponectin multimers, in skeletal muscle extracts from WKY/Izm but not HA-WKY. Skeletal muscle in WKY/Izm expressed much higher amounts of T-cadherin, a receptor for MMW and HMW adiponectin multimers, than that in HA-WKY. In contrast, there was no significant difference in the expression level of adiponectin receptor 2 for trimer, MMW, and HMW adiponectin multimers. Significance The results suggested that the existence of adiponectin in WKY/Izm skeletal muscle was due to the binding of serum adiponectin. The difference in serum adiponectin concentrations between HA-WKY and WKY/Izm could come from the difference in adiponectin binding to skeletal muscle.

Usefulness of C-Reactive Protein to High-Molecular-Weight Adiponectin Ratio to Predict Insulin Resistance and Metabolic Syndrome in Japanese Men

We questioned whether the ratio of C-reactive protein to high-molecular-weight adiponectin (C/A ratio), compared to each value alone, is more useful to predict insulin resistance and/or metabolic syndrome. We measured serum CRP and HMW adiponectin levels in 841 Japanese men who had participated in an annual health checkup. Correlations of the C/A ratio with metabolic parameters were assessed, and its predictive values for insulin resistance and MetS were compared with CRP or HMW adiponectin alone. The C/A ratio was higher in subjects with MetS (n = 114) than in those without MetS (0.46 ± 0.67 vs. 0.23 ± 0.39, p<0.0001). The C/A ratio was correlated with a larger number of metabolic parameters than CRP, but the correlation was comparable to HMW adiponectin. Likewise, the area under the curve of the C/A ratio in receiver operator characteristic analysis for MetS was greater than that of CRP, but comparable to that of HMW adiponectin. However, the AUC of the C/A ratio in ROC analysis for insulin resistance (HOMA-IR >2.5) was greater than that of CRP or HMW adiponectin alone. While the C/A ratio provided little advantage to predict MetS, it might be more useful to predict insulin resistance than CRP or HMW adiponectin alone.

Effects of Telmisartan on Insulin Resistance in Japanese Type 2 Diabetic Patients

PPARgamma agonists are widely used in type 2 diabetic patients to reduce insulin resistance. Recently, telmisartan, an AT1 receptor antagonist, was reported to function as a partial agonist of PPARgamma based on in vitro experiments. The aim of the present study was to investigate whether the PPARgamma enhancing activity of telmisartan is exerted clinically in diabetic patients. We compared the effects of telmisartan with those of candesartan, on insulin sensitivity, the serum levels of various adipocytokines and oxidative stress. In total, 85 Japanese type 2 diabetic patients with hypertension, maintained on 8 mg per day of candesartan, were randomly assigned to the TM group (candesartan switched to 40 mg of telmisartan, n=38) or the CD group (no treatment change, n=47). After 3 months, oxidized lipids were significantly decreased only in the TM group. Although the homeostasis assessment model of insulin resistance (HOMA-R) tended to be improved and serum concentrations of HDL-cholesterol and HMW adiponectin tended to be increased only in the TM group, these alterations were too small to be significant by unpaired t-test. Interestingly, in subgroup analysis, the alterations of HOMA-R, serum concentrations of oxidized lipids, and HMW adiponectin were more apparent in obese TM group subjects and the changes reached statistical significance. Switching from candesartan to telmisartan in obese subjects increases serum adiponectin and improves both insulin resistance and oxidative stress, while these effects were not statistically apparent in the total patient population. These results support the idea that telmisartan exerts its PPARgamma enhancing activity clinically in obese type 2 diabetic patients.

Effects of Regular Aerobic Exercise on HMW adiponectin Concentration

Effects of Regular Aerobic Exercise on HMW adiponectin Concentration

High–molecular weight adiponectin is associated with coronary artery angiographic findings in Asian Indians

Asian Indians (AIs) have a higher prevalence and a more aggressive form of coronary artery disease (CAD), and it has been suggested that hypoadiponectinemia may have a role in this accelerated CAD. The present study was undertaken to determine the extent and severity of angiographic findings in 2 groups of CAD patients matched for age and sex, AIs (n = 29) vs whites (n = 30), and to elucidate the potential relationship between adiponectin (total and high–molecular weight [HMW] form) and the severity and extent of coronary angiographic findings in both groups. Angiographic findings were assessed using the modified Gensini index; and 2 scores, scores 1 and 2, were used to assess the severity and extent. Both Gensini index scores 1 and 2 were higher in the AI group compared with the white group (144.4 ± 87.1 vs 93.5 ± 56.3 and 127.2 ± 86.5 vs 80.1 ± 39.3, respectively; P < .05). Adiponectin levels were similar in both groups. Total adiponectin and HMW adiponectin were positively associated with Gensini index score 1 ( r = 0.62, P = .004 and r = 0.64, P = .003) and score 2 ( r = 0.51, P = .021 and r = 0.54, P = .013), respectively, in AI men, whereas there was no significant association in white men. Thus, AIs had more severe CAD compared with whites; and in AI men with CAD, total adiponectin and HMW adiponectin were associated with the severity of angiographic scores.

Secretion of adiponectin multimeric complexes from adipose tissue explants is not modified by very low calorie diet

Adiponectin is a protein abundantly secreted by the adipose tissue (AT). Plasma adiponectin levels are decreased in obese, insulin-resistant, and type 2 diabetic patients. Various multimeric complexes, i.e. high-, middle-, and low-molecular weight isoforms (HMW, MMW and LMW), are present in plasma. Here, we investigated the effect of weight reducing diet on the distribution of adiponectin isoforms in plasma and on their secretion in AT explants from obese subjects. A total of 20 obese subjects (age 37.8+/-7.3 years, body mass index 33.9+/-5.0 kg/m(2)) underwent eight weeks of very low-calorie diet (VLCD). A needle biopsy of subcutaneous abdominal AT and blood samples were taken before and after dietary intervention. AT explants were incubated in culture medium for 4 h. ELISA assay and western blot analyses were used to identify adiponectin complexes in culture media and in plasma. The distribution of adiponectin polymers in plasma was different from that secreted in human AT explants. Before VLCD, the relative amount of HMW isoform was 75.5+/-9.1% of total adiponectin in culture media and 52.2+/-11.2% in plasma. Despite the diet-induced weight loss and improvement of insulin sensitivity, VLCD neither induced change in total adiponectin level nor in the ratio of HMW to total adiponectin in plasma and in culture media of AT explants. The profile of adiponectin polymeric isoforms secreted by AT explants into culture media differs from the plasma profile. A dietary intervention leading to weight loss and improvement of insulin sensitivity was not associated with modifications of AT secretion of total or HMW adiponectin.

Adiponectin isoform distribution in women—relationship to female sex steroids and insulin sensitivity

Little is known about the associations between adiponectin and its oligomeric isoforms with female sex steroids, and the relevance of these relationships to insulin sensitivity in women. In a cross-sectional study of 32 healthy women (12 premenopausal, 10 postmenopausal, and 10 early pregnant), we investigated the correlations of total adiponectin and the high–, medium–, and low–molecular weight oligomers (HMW, MMW, and LMW, respectively) with estrogen, progesterone, adiposity, and insulin resistance. Fat mass and serum concentrations of estradiol, progesterone, insulin, glucose, and total and isoform adiponectin were measured. The homeostasis model assessment of insulin resistance (HOMA-IR) was calculated. Serum concentrations of total and HMW adiponectin were highest in postmenopausal women and lowest in pregnant women. Concentrations of the MMW and LMW isoforms were not significantly different between the 3 groups. Total adiponectin, HMW adiponectin, and MMW adiponectin were negatively associated with estradiol and progesterone; but no associations between the LMW isoform and female sex steroids were observed. Fat mass and HOMA-IR were highest in pregnant women and lowest in premenopausal women. The HOMA-IR was positively associated with fat mass, estradiol, and progesterone, and negatively associated with total, HMW, and MMW adiponectin. Multivariate stepwise regression analysis revealed that fat mass explained 34% of the variance in HOMA-IR and that total and isoform adiponectin contributed an additional 10% to 15%. In the multivariate linear regression analysis, there were significant interactions of estradiol and progesterone with adiponectin or fat mass in the associations with HOMA-IR. In conclusion, there are strong negative associations of serum adiponectin and some of its isoforms with estradiol and progesterone. Female sex steroids are likely to affect insulin sensitivity through modulation of adiponectin and body fat.

Adiponectin translation is increased by the PPARγ agonists pioglitazone and ω-3 fatty acids

Adiponectin, made exclusively by adipocytes, is a 30-kDa secretory protein assembled posttranslationally into low-molecular weight, middle-molecular weight, and high-molecular weight homo-oligomers. PPARgamma ligand thiozolidinediones, which are widely used in the treatment of type II diabetes, increase adiponectin levels. PPARgamma also has several putative ligands that include fatty acid derivatives. Overnight treatment of rat adipocytes with pioglitazone, docosahexaenoic acid (DHA), or eicosapentaenoic acid (EPA) triggered a twofold increase in the synthesis and secretion of HMW adiponectin, and this increase was blocked by the addition of PPARgamma inhibitor GW-9662. Inhibition of glycosylation using 2,2'-dipyridyl decreased the synthesis of high-molecular weight adiponectin by pioglitazone, EPA, and DHA, but there was increased secretion of trimeric adiponectin resulting from increased translation. Although pioglitazone, DHA, and EPA increased adiponectin synthesis by more than 60%, there was no increase in total protein synthesis and no corresponding change in adiponectin mRNA expression, indicating the upregulation of translation. We examined the possibility of transacting factors in the cytoplasmic extracts from adipocytes treated with pioglitazone or DHA. In vitro translation of adiponectin mRNA was inhibited by S-100 fraction of control adipocytes and increased by S-100 extracts from adipocytes treated with pioglitazone or DHA. Consistent with this observation, both pioglitazone and DHA treatments increased the association of adiponectin mRNA with the heavier polysome fractions. Together, these data suggest that pioglitazone and the fish oils DHA or EPA are PPARgamma agonists in adipocytes with regard to adiponectin expression, and the predominant mode of adiponectin stimulation is via an increase in translation.

Reduced serum HMW adiponectin and colonic receptor expression contributes to immune dysregulation in patients with Crohnʼs Disease

Reduced serum HMW adiponectin and colonic receptor expression contributes to immune dysregulation in patients with Crohnʼs Disease

Reduced serum HMW adiponectin and colonic receptor expression contributes to immune dysregulation in patients with Crohnʼs Disease

Reduced serum HMW adiponectin and colonic receptor expression contributes to immune dysregulation in patients with Crohnʼs Disease

Plasma des-acyl ghrelin, but not plasma HMW adiponectin, is a useful cardiometabolic marker for predicting atherosclerosis in elderly hypertensive patients

Objective The coming obesity epidemic in elderly persons necessitates the establishment of new and easy-to-use cardiometabolic markers to identify individuals most likely to develop atherosclerosis among hypertensives. Methods We measured plasma HMW adiponectin and des-acyl ghrelin levels, and carotid-artery intima-media thickness (cIMT) in 263 elderly hypertensives (mean 72.6 years; 37%men). Other cardiometabolic markers, including metabolites, inflammation, and hemostasis, were also measured. Results and conclusion Both HMW adiponectin and des-acyl ghrelin levels were inversely correlated with obesity. The HMW adiponectin level was favorably associated with glucose and lipid metabolites, PAI-1 (all P < 0.05), and hs-CRP ( P = 0.07) after adjustment for age, sex, and BMI; however, it had no correlations with cIMT. In contrast, although there were no correlations between des-acyl ghrelin and cardiometabolic markers, except for a positive association with the nitrite/nitrate (NO x ) level ( P = 0.002), des-acyl ghrelin had a significant inverse correlation with cIMT ( P = 0.003). A multivariable regression analysis showed that des-acyl ghrelin, but not HMW adiponectin, was significantly associated with cIMT after adjusting for age, obesity, sex, smoking, 24-h BP, and other cardiometabolic factors ( β = −0.178, P = 0.001). Moreover, the increased risk of cIMT among those with abdominal obesity compared with non-obesity (0.833 ± 0.185 mm vs. 0.782 ± 0.163 mm, P = 0.019) was explained by the elevated 24-h BP and reduced des-acyl ghrelin level, but not by other cardiometabolic parameters. These associations were unchanged after adding NO x to the model. In conclusion, the des-acyl ghrelin level is a useful cardiometabolic marker for predicting atherosclerosis in elderly hypertensives, and the pathologic pathway linking these factors is independent of its NO bioactivity.

Longitudinal changes in pancreatic and adipocyte hormones following Roux-en-Y gastric bypass surgery.

Bariatric surgery is an effective treatment for severe obesity, as in addition to dramatic weight loss, co-morbidities such as type 2 diabetes are frequently resolved. Although altered gastrointestinal peptide hormone secretion and its relationship with post-surgical improvements in insulin sensitivity has been studied, much less is known about long-term changes in pancreatic and adipose tissue-derived hormones. Our objective was to conduct a comprehensive longitudinal investigation of the endocrine changes following Roux-en-Y gastric bypass surgery (RYGBP), focusing on pancreatic and adipocyte hormones and systemic markers of inflammation. Nineteen severely obese women (BMI 45.6 +/- 1.6 kg/m(2)) were studied prior to RYGBP, and at 1, 3, 6, and 12 months after RYGBP. Body composition was assessed before surgery and at 1 and 12 months. Pre-surgical adiposity was correlated with circulating adipocyte hormones (leptin, visfatin) and inflammatory molecules (IL-6, high sensitivity C-reactive protein [hsCRP], monocyte chemoattractant protein-1). As expected, RYGBP reduced fat mass and fasting insulin and glucose concentrations. In addition, reductions of fasting pancreatic polypeptide (PP) and glucagon concentrations were observed at 1 and 3 months, respectively. In the 12 months following RYGBP, concentrations of most adipocyte hormones (leptin, acylation-stimulating hormone and visfatin, but not retinol-binding hormone-4) and inflammatory molecules (IL-6, hsCRP and soluble intracellular adhesion molecule-1) were significantly reduced. Reductions of insulin resistance (measured by homeostasis model assessment of insulin resistance) were independently associated with changes of glucagon, visfatin and PP. Pre-surgical HMW adiponectin concentrations independently predicted losses of body weight and fat mass. These results suggest that pancreatic and adipocyte hormones may contribute to the long-term resolution of insulin resistance after RYGBP.

Importance of the high-molecular-mass isoform of adiponectin in improved insulin sensitivity with rosiglitazone treatment in HIV disease

The present study was designed to investigate the relationship of isoforms of adiponectin to insulin sensitivity in subjects with HIV-associated insulin resistance in response to treatment with the thiazolidinedione, rosiglitazone. The two isoforms of adiponectin, HMW (high-molecular-mass) and LMW (low-molecular-mass), were separated by sucrose-gradient-density centrifugation. The amount of adiponectin in gradient fractions was determined by ELISA. Peripheral insulin sensitivity (Rd) was determined with hyperinsulinaemic-euglycaemic clamp, whereas hepatic sensitivity [HOMA (Homoeostasis Model Assessment) %S] was based on basal glucose and insulin values. Treatment with rosiglitazone for 3 months resulted in a significant improvement in the index of hepatic insulin sensitivity (86.4+/-15% compared with 139+/-23; P=0.007) as well as peripheral insulin sensitivity (4.04+/-0.23 compared with 6.17+/-0.66 mg of glucose/kg of lean body mass per min; P<0.001). Improvement in HOMA was associated with increased levels of HMW adiponectin (r=0.541, P=0.045), but not LMW adiponectin. The present study suggests that the HMW isoform of adiponectin is important in the regulation of rosiglitazone-mediated improvement in insulin sensitivity in individuals with HIV-associated insulin resistance, particularly in the liver.

High Molecular Mass Multimer Complexes and Vascular Expression Contribute to High Adiponectin in the Fetus

High plasma adiponectin concentrations in human fetuses and neonates are unique features of early developmental stages. Yet, the origins of the high adiponectin concentrations in the perinatal period remain elusive. This study was undertaken to identify the sources and functional properties of adiponectin in utero. Tissue specimens were obtained at autopsy from 21- to 39-wk-old stillborn human fetuses. Adipose tissue and placenta were obtained at term elective cesarean section. Adiponectin complexes and expression were measured by immunodetection and real-time PCR. Adiponectin mRNA transcripts were detected in fetal sc and omental adipose depots at lower concentrations than in maternal adipose tissue. Immunoreactive adiponectin was also observed in vascular endothelial cells of fetal organs, including skeletal muscle, kidney, and brain. The absence of adiponectin in all placental cell types and lack of correlation between maternal and umbilical adiponectin indicate that umbilical adiponectin reflects its exclusive production by fetal tissues. The most prominent forms of adiponectin in fetal plasma were high and low molecular mass (HMW and LMW) multimers of 340 and 160 kDa, respectively. The proportion of the HMW complexes was 5-fold (P < 0.001) higher in umbilical plasma than in adult. The high HMW and total adiponectin levels were associated with lower insulin concentration and lower homeostasis model of assessment of insulin resistance indices in umbilical plasma, reflecting higher insulin sensitivity of the fetus compared with adult. The abundance of HMW adiponectin and its vascular expression are characteristics of human fetal adiponectin. Combined with high insulin sensitivity, fetal adiponectin may be a critical determinant of in utero growth.

Post-translational modifications of adiponectin: mechanisms and functional implications

Adiponectin is an insulin-sensitizing adipokine with anti-diabetic, anti-atherogenic, anti-inflammatory and cardioprotective properties. This adipokine is secreted from adipocytes into the circulation as three oligomeric isoforms, including trimeric, hexameric and the HMW (high-molecular-mass) oligomeric complex consisting of at least 18 protomers. Each oligomeric isoform of adiponectin exerts distinct biological properties in its various target tissues. The HMW oligomer is the major active form mediating the insulin-sensitizing effects of adiponectin, whereas the central actions of this adipokine are attributed primarily to the hexameric and trimeric oligomers. In patients with Type 2 diabetes and coronary heart disease, circulating levels of HMW adiponectin are selectively decreased due to an impaired secretion of this oligomer from adipocytes. The biosynthesis of the adiponectin oligomers is a complex process involving extensive post-translational modifications. Hydroxylation and glycosylation of several conserved lysine residues in the collagenous domain of adiponectin are necessary for the intracellular assembly and stabilization of its high-order oligomeric structures. Secretion of the adiponectin oligomers is tightly controlled by a pair of molecular chaperones in the ER (endoplasmic reticulum), including ERp44 (ER protein of 44 kDa) and Ero1-Lalpha (ER oxidoreductase 1-Lalpha). ERp44 inhibits the secretion of adiponectin oligomers through a thiol-mediated retention. In contrast, Ero1-Lalpha releases HMW adiponectin trapped by ERp44. The PPARgamma (peroxisome-proliferator-activated receptor gamma) agonists thiazolidinediones selectively enhance the secretion of HMW adiponectin through up-regulation of Ero1-Lalpha. In the present review, we discuss the recent advances in our understanding of the structural and biological properties of the adiponectin oligomeric isoforms and highlight the role of post-translational modifications in regulating the biosynthesis of HMW adiponectin.