Adiponectin Release Research Articles

Cytokine-mediated modulation of leptin and adiponectin secretion during in vitro adipogenesis: Evidence that tumor necrosis factor-α- and interleukin-1β-treated human preadipocytes are potent leptin producers

Over the last decade, compelling evidence has been presented that cytokines affect adipocyte tissue formation and function. In this study we explored the effect of pro-inflammatory (i.e. interleukin (IL)-1β, IL-6, interferon (IFN)-γ, and tumor necrosis factor (TNF)-α) versus anti-inflammatory cytokines (i.e. IL-4, IL-10, and transforming growth factor (TGF)-β 1) on leptin and adiponectin secretion during in vitro human adipogenesis. Confirmative to previous reports, conversion of precursor preadipocytes into mature adipocytes was completely inhibited upon exposure to TNF-α, IL-1β, IFN-γ, or TGF-β 1. Hence, all these anti-adipogenic cytokines prevented release of adipocyte-specific adiponectin. IFN-γ also strongly reduced leptin production (≥85%). However, TNF-α, IL-1β, and TGF-β 1 stimulated leptin production from preadipocytes in the absence of mature adipocytes (20.6 ± 5.4 ng/ml, 100.8 ± 18.2 ng/ml, and 5.4 ± 0.4 ng/ml, respectively, compared to 6.6 ± 0.8 ng/ml in control adipocyte cultures on day 21; n = 4). IL-4, IL-6 and IL-10 did not, or only slightly, affect adipocyte differentiation and their hormonal secretion. In conclusion, adiponectin and leptin are both synthesized by adipocytes, whereas leptin is also produced by preadipocytes upon TNF-α or IL-1β stimulation. These data suggest that preadipocytes could contribute more to total circulating leptin levels than has been previously considered, especially in diseased conditions were these pro-inflammatory factors play a prominent role.

Release and regulation of leptin, resistin and adiponectin from human placenta, fetal membranes, and maternal adipose tissue and skeletal muscle from normal and gestational diabetes mellitus-complicated pregnancies

The aim of this study was to determine the release and regulation of leptin, resistin and adiponectin from human placenta and fetal membranes, and maternal subcutaneous adipose tissue and skeletal muscle obtained from normal and gestational diabetes mellitus (GDM)-complicated pregnancies at the time of Cesarean section. Tissue explants were incubated in the absence (basal control) or presence of 10 mug/ml lipopolysaccharide (LPS), 10, 20 or 40 ng/ml tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-6 and IL-8, 1 microM phorbol myristate acetate, 10, 20 and 40 mM glucose, 0.1, 1 and 10 microM insulin and 0.1 1 and 10 microM dexamethasone, progesterone and estrogen. After an 18-h incubation, the medium was collected and the release of leptin, resistin and adiponectin was quantified by ELISA. Human gestational tissues and maternal tissues released immunoreactive leptin, resistin and adiponectin; however, there was no difference in the release of either resistin or adiponectin between normal pregnant women and women with gestational diabetes. The release of leptin was significantly higher in placenta, amnion and choriodecidua obtained from normal pregnant women compared with women with GDM. However, in maternal tissues, the situation was reversed, with adipose tissue and skeletal muscle obtained from women with GDM releasing significantly greater amounts of leptin. In adipose tissue and skeletal muscle the release of leptin was significantly greater in insulin-controlled GDM compared with diet-controlled GDM, and leptin release from adipose tissue was significantly correlated with maternal body mass index. In all tissues tested, there was no effect of incubation with LPS, IL-6, IL-8 or TNF-alpha on leptin, resistin or adiponectin release. PMA significantly increased the release of resistin from placenta and adipose tissue. Insulin increased placental resistin release, whereas the hormones dexamethasone, progesterone and estrogen significantly decreased placental resistin release. The data presented in this study demonstrate that dysregulation of leptin metabolism and/or function in the placenta may be implicated in the pathogenesis of GDM. Furthermore, resistin release is greatly affected by a variety of inflammatory mediators and hormones.

Physiological difference between obese (fa/fa) Zucker rats and lean Zucker rats concerning adiponectin

Obese (fa/fa) Zucker rat is a spontaneous genetic obesity model and, by comparison with lean Zucker rat, exhibits hyperphagia, hyperinsulinemia, and hyperlipidemia. The aim of this study was to examine the physiological difference concerning adiponectin between obese (fa/fa) Zucker rats and control lean Zucker rats. We therefore measured plasma adiponectin level and analyzed adiponectin and adiponectin receptor 1 mRNA expression in retroperitoneal white adipose tissue (RT WAT), brown adipose tissue (BAT), liver, and soleus muscle. We also examined the tissue mRNA expression of peroxisome proliferator–activated receptor α (PPAR α), PPAR δ, and PPAR γ, which regulate adiponectin expression sensitivity to a PPAR γ agonist shown by brown adipocytes from obese (fa/fa) Zucker rats and lean Zucker rats, by measuring adiponectin release from these cells. Plasma adiponectin levels of obese (fa/fa) Zucker rats were significantly higher than those of lean Zucker rats. Adiponectin mRNA expression levels in RT WAT were lower in obese (fa/fa) Zucker rats than in lean Zucker rats, but those in BAT were higher. Adiponectin receptor 1 expression levels in RT WAT, BAT, and liver of obese (fa/fa) Zucker rats were lower than in lean Zucker rats. The expression level of PPAR α, PPAR δ, and PPAR γ in BAT was lower in obese (fa/fa) Zucker rats than in lean Zucker rats. Moreover, the PPAR γ agonist increased adiponectin release only from the brown adipocytes isolated from lean Zucker rats. It is the conclusive difference between obese (fa/fa) Zucker rats and lean Zucker rats that plasma adiponectin levels of obese (fa/fa) Zucker rats are significantly higher than those of lean Zucker rats. Moreover, we clarified that mRNA expression level of adiponectin receptor 1 in RT WAT, BAT, and liver of obese (fa/fa) Zucker rats is low despite high plasma adiponectin level, and low expression of PPARs in BAT leads to less sensibility of adiponectin release from brown adipocytes to a PPAR γ agonist in obese (fa/fa) Zucker rats.

Metformin reduces adiponectin protein expression and release in 3T3-L1 adipocytes involving activation of AMP activated protein kinase

The drugs troglitazone and metformin are used to reduce the degree of insulin resistance in type 2 diabetes. Both compounds act through different mechanisms which might include opposing effects on the production of adiponectin, an insulin-sensitizer released by adipocytes. This study compared the effects of troglitazone and metformin on adiponectin production by 3T3-L1 adipocytes during 48 h culture. Troglitazone increased adiponectin mRNA and protein expression as well as release, whereas metformin did not affect transcription but reduced protein expression and release. The effect of metformin was also seen with phenformin, and with low-glucose culture, all conditions with a reduced mitochondrial activity and an activated AMP activated protein kinase (AMPK). Addition of the AMPK activator 5-aminoimidazole-4-carboxamide-riboside (AICAR) also caused a decrease in adiponectin protein expression. These data indicate that metformin and troglitazone exert opposing effects on adiponectin expression and release by differentiated 3T3-L1 adipocytes. The metformin-induced suppression involves an activation of AMP activated protein kinase.

Regulation of Adiponectin Expression in Human Adipocytes: Effects of Adiposity, Glucocorticoids, and Tumor Necrosis Factor α

Adiponectin mRNA expression in isolated subcutaneous and omental adipocytes was examined across a wide range of adiposity to determine whether adiponectin synthesis is impaired in these adipose tissue depots in obese humans. Tumor necrosis factor (TNF)alpha and dexamethasone were tested for inhibitory effects on adiponectin release from human adipocytes in vitro. Adipocytes were isolated by collagenase digestion of abdominal adipose tissue obtained from subjects undergoing surgical procedures or outpatient needle biopsy. Adiponectin and leptin mRNA were quantitated by real-time reverse transcriptase-polymerase chain reaction. Adiponectin and leptin secretion from isolated adipocytes treated with dexamethasone or TNFalpha were determined by radioimmunoassay. There was a significant negative correlation between adiponectin gene expression and BMI in subcutaneous adipocytes from 32 women (r = 0.420; p = 0.02). Adiponectin mRNA was also significantly correlated with serum adiponectin (r = 0.44; p = 0.03; n = 25). There was no correlation between adiponectin mRNA expression and BMI in omental adipocytes from 29 women. Leptin mRNA was significantly and positively correlated (r = 0.484; p = 0.01) with BMI in the same omental adipocyte mRNA preparations. In subcutaneous adipocytes from lean subjects, TNFalpha inhibited adiponectin release by 7.4 +/- 1.2% (n = 9, p < 0.05) but had no effect on adiponectin release from subcutaneous or omental adipocytes from obese subjects. Dexamethasone significantly inhibited adiponectin release with 24 hours of treatment. The data suggest that reduced adiponectin synthesis in subcutaneous adipocytes contributes to lower serum adiponectin levels in obesity and that glucocorticoids regulate adiponectin gene expression in human adipocytes. TNFalpha does not seem to directly inhibit adiponectin synthesis in human adipocytes.

Sulfasalazine and BAY 11-7082 Interfere with the Nuclear Factor-κB and IκB Kinase Pathway to Regulate the Release of Proinflammatory Cytokines from Human Adipose Tissue and Skeletal Muscle in Vitro

There is much evidence to indicate a role for adipocytokines in insulin resistance and/or type 2 diabetes mellitus. In experimental models, oral salicylates, through their ability to interfere with the nuclear factor-kappa B (NF-kappa B) transcription pathway, have been demonstrated to reverse insulin resistance. The aim of this study was to investigate whether NF-kappa B regulates the release of adipocytokines in human adipose tissue and skeletal muscle. Human sc adipose tissue and skeletal muscle (obtained from normal pregnant women) were incubated in the absence (control) or presence of two NF-kappa B inhibitors sulfasalazine (1.25, 2.5, and 5 mm) and BAY 11-7082 (25, 50, and 100 microm). After an 18-h incubation, the tissues were collected, and NF-kappa B p65 DNA-binding activity and I kappa B kinase (IKK-beta) and insulin receptor-beta protein expression were assessed by ELISA and Western blotting, respectively. The incubation medium was collected, and the release of TNF-alpha, IL-6, IL-8, resistin, adiponectin, and leptin was quantified by ELISA. Treatment of adipose tissue and skeletal muscle with sulfasalazine and BAY 11-7082 significantly inhibited the release of IL-6, IL-8, and TNF-alpha; NF-kappa B p65 DNA-binding activity; and IKK-beta protein expression (P < 0.05, by Newman-Keuls test). There was no effect of sulfasalazine and BAY 11-7082 on resistin, adiponectin, or leptin release. Both sulfasalazine and BAY 11-7082 increased the adipose tissue and skeletal muscle expression of insulin receptor-beta. The data presented in this study demonstrate that the IKK-beta/NF-kappa B transcription pathway is a key regulator of IL-6, IL-8, and TNF-alpha release from adipose tissue and skeletal muscle. Control of the IKK-beta/NF-kappa B pathway may therefore provide an alternative therapeutic strategy for regulating aberrant cytokine release and thereby alleviating insulin resistance in type 2 diabetes mellitus.

Adipose tissue metabolites and insulin resistance in nondiabetic Asian Indian men.

Obesity-related insulin resistance is associated with changes in adipose tissue release of leptin, adiponectin, and nonesterified fatty acids (NEFAs). We have previously described that persons originating from the Indian subcontinent (Asian Indians) manifest excessive insulin resistance even in the absence of obesity. Therefore, in this study, we tested the hypothesis that nondiabetic, insulin-resistant Asian Indians differ from less insulin-resistant Caucasians of similar age and body composition in adipose tissue production of leptin and adiponectin, and in suppression of plasma NEFA concentrations during hyperinsulinemia. Seventy-nine Asian Indian men were compared with 61 Caucasian men. Higher plasma NEFAs and leptin in Asian Indians (P < 0.0001 and P = 0.003 for NEFAs and leptin, respectively) and lower plasma concentrations of adiponectin (P = 0.009) were not explained by body fat content and distribution. Oral glucose tolerance test studies revealed that Caucasian men had greater suppression of plasma NEFAs than Asian Indian men. We conclude that plasma concentrations of the adipose tissue metabolites leptin and NEFAs are higher and that of adiponectin is lower in insulin-resistant Asian Indians compared with more insulin-sensitive Caucasians. These differences may contribute to the excessive prevalence of type 2 diabetes and cardiovascular disease in nonobese Asian Indians.

Resistin, but not adiponectin, inhibits dopamine and norepinephrine release in the hypothalamus

Adiponectin (Adipocyte Complement-Related Protein of 30 kDa, ACRP30) and resistin are adipocyte-derived polypeptide hormones playing a role in metabolic homeostasis. Their plasma levels are inversely (adiponectin) or directly (resistin) correlated to obesity and they have opposite effects on insulin sensitivity. Adipose tissue hormones such as leptin have been shown to modulate neurotransmitters which control feeding in the hypothalamus. We have studied the effects of adiponectin and resistin on dopamine, norepinephrine and serotonin release from hypothalamic neuronal endings (synaptosomes) in vitro. We have found that adiponectin does not modify either basal or depolarization-induced amine release, while resistin inhibits the stimulated release of dopamine and norepinephrine, leaving unaffected serotonin release. We can conclude that, similarly to leptin, but differently from adiponectin, the adipose tissue hormone resistin could affect the central mechanisms of feeding by inhibiting catecholamine release in the hypothalamus.

Resistin, but not adiponectin, inhibits dopamine and norepinephrine release in the hypothalamus

Resistin, but not adiponectin, inhibits dopamine and norepinephrine release in the hypothalamus

Treatment of insulin resistance in diabetes mellitus

Insulin resistance is a condition in which the glycemic response to insulin is less than normal. The change in insulin sensitivity leads to several sets of responses. One set effects the beta cell and leads to its accelerated destruction and the development of diabetes mellitus. The other set generates a series of nontraditional cardiovascular risk factors that result in accelerated atherosclerosis. Both of these sets of responses may have impacts on other tissues such as the nervous system. Insulin resistance is probably the result of increased visceral adiposity with increased release of free fatty acids and cytokines and a decreased release of adiponectin. Treatment of insulin resistance and its associated abnormalities can be achieved by lifestyle modification which results in weight loss, by drugs that reverse the abnormal adipocyte effects, by drugs that improve insulin sensitivity at the level of the liver and by anti-inflammatory agents that block activation of the nuclear factor kappa B cascade.

TNFalpha release by the nonfat cells of human adipose tissue.

The primary aim was to investigate the relative importance of the adipocytes vs the nonfat cells present in human adipose tissue with respect to release of immunoreactive tumor necrosis factor-alpha (TNFalpha). The second aim was to examine the correlation between body mass index (BMI) and the subsequent release of adiponectin and TNFalpha by explants of human subcutaneous and visceral adipose tissue incubated in primary culture for 48 h. We found that the maximal release of TNFalpha was seen during the first 4 h of a 48-h incubation by explants of human adipose tissue in primary culture. Over 95% of the TNFalpha released to the medium by human adipose tissue explants over a 4-h incubation came from the nonfat cells present in the adipose tissue. The release of TNFalpha by the nonfat cells released during collagenase digestion was slightly higher than that by the cells present in the adipose tissue matrix after collagenase digestion. TNFalpha release by the combined matrix and isolated nonfat cells was greater than that by explants of tissue indicating some upregulation induced by collagenase digestion. Immunoreactive TNFalpha disappeared from the medium with a half-time of approximately 10 h. There was a positive correlation coefficient of 0.79 between TNFalpha release by tissue explants and the BMI of the fat donors as well as a correlation of 0.52 between BMI and release by adipocytes. TNFalpha release negatively correlated [-0.60] with adiponectin release by adipose tissue. The release of TNFalpha was far less than that of adiponectin or IL-6, and less than that of plasminogen activator inhibitor-1, hepatocyte growth factor, or leptin over a 4-h incubation of human adipose tissue explants. TNFalpha release over 4 h was enhanced by lipopolysaccharide and inhibited by a cyclooxygenase-2 inhibitor. The release of TNFalpha by adipose tissue of obese humans is primarily due to the nonfat cells present in adipose tissue. TNFalpha is a short-lived adipokine whose release by human adipose tissue in primary culture correlates with the BMI of the fat donors.

Anorexia nervosa is characterized by increased adiponectin plasma levels and reduced nonoxidative glucose metabolism.

The aim of the present study was to examine the effects of anorexia nervosa (AN) on adipocytokines (leptin and adiponectin) plasma concentrations and insulin-stimulated glucose disposal in adolescent and young adult women. Adiponectin and leptin plasma levels, along with insulin-stimulated glucose disposal (as measured by the euglycemic-hyperinsulinemic glucose clamp) and oxidative and nonoxidative glucose metabolism (as measured by indirect calorimetry during the last 60 min of the insulin clamp), were measured in 11 anorectic patients and 26 normal-weight healthy female controls. Leptin levels were significantly lower in AN patients, according to the reduced body mass index and their respective fat mass. On the contrary, adiponectin plasma levels were significantly higher in AN patients than in control women. Likewise, insulin-stimulated glucose disposal and nonoxidative glucose metabolism were significantly lower in AN patients. In conclusion, our study shows that young women affected by AN have higher adiponectin plasma levels than healthy female controls of similar age, despite the presence of an impairment of insulin-stimulated glucose disposal, with a prevalent failure of nonoxidative glucose metabolism. Taken together, these data suggest that the reduction of fat mass may play the major role in the control of adiponectin release, with respect to changes in insulin sensitivity.

Resistin release by human adipose tissue explants in primary culture

Resistin, also known as Fizz3 or ADSF, is a protein found in murine adipose tissue and inflammatory lung exudates. The present studies found that resistin was released by explants of human adipose tissue but the release was quite variable ranging from 3 to 158 ng/g over 48 h. The release of resistin was 250% greater by explants of omental than by explants of human subcutaneous abdominal adipose tissue. Resistin release by adipocytes was negligible as compared to that by the non-fat cells of adipose tissue. Leptin formation by adipocytes was 8-fold greater than its formation by the non-fat cells, while the formation of PAI-1 by adipocytes was 38% of that by the non-fat cells. The conversion of glucose to lactate as well as the formation of PGE 2 and IL-8 was approximately 15% of that by the non-fat cells. In contrast the release of IL-6 and IL-1β by adipocytes was 4–7% of that by the non-fat cells while the formation of resistin and IL-10 by adipocytes was 2% of that by non-fat cells. The release of adiponectin by explants ranged from 1000 to 5000 ng/g over 48 h but did not correlate with that of resistin. The present data suggest that resistin release by explants of human adipose tissue in primary culture is largely derived from the non-fat cells present in the explants.

The peroxisome proliferator-activated receptor-gamma2 Pro12Ala polymorphism.

Peroxisome proliferator-activated receptor (PPAR)-gamma is a transcription factor with a key role in adipocyte differentiation. The Ala allele of the common Pro12Ala polymorphism in the isoform PPAR-gamma2 is associated with reduced risk for type 2 diabetes. The effect on the individual is weak, but because of a prevalence of >75% of the high-risk Pro allele, the population-attributable risk is enormous. The in vivo effects of the polymorphism are secondary to alterations in adipose tissue, where PPAR-gamma2 is predominantly expressed. Moderate reduction in transcriptional activity of PPAR-gamma as a result of the polymorphism modulates production and release of adipose-derived factors. Both decreased release of insulin-desensitizing free fatty acids, tumor necrosis factor-alpha, and resistin and increased release of the insulin-sensitizing hormone adiponectin result in secondary improvement of insulin sensitivity of glucose uptake and suppression of glucose production. The population effect of this polymorphism may be modulated by environmental or genetic factors such as obesity, ethnicity, ratio of unsaturated to saturated fatty acids, and genetic background. Once diabetes has developed, the protective effect of the Ala allele may be lost, since increased vascular complications and more pronounced beta-cell dysfunction have been reported. These observations, however, are currently unexplained. In conclusion, the Pro12Ala polymorphism in PPAR-gamma2 represents the first genetic variant with a broad impact on the risk of common type 2 diabetes. The precise understanding of its mechanism may lead to novel diagnostic, preventive, and therapeutic approaches for improving the management of type 2 diabetes.