Adipocytokines: mediators linking adipose tissue, inflammation and immunity

There has been much effort recently to define the role of adipocytokines, which are soluble mediators derived mainly from adipocytes (fat cells), in the interaction between adipose tissue, inflammation and immunity. The adipocytokines adiponectin and leptin have emerged as the most abundant adipocyte products, thereby redefining adipose tissue as a key component not only of the endocrine system, but also of the immune system. Indeed, as we discuss here, several adipocytokines have a central role in the regulation of insulin resistance, as well as many aspects of inflammation and immunity. Other adipocytokines, such as visfatin, have only recently been identified. Understanding this rapidly growing family of mainly adipocyte-derived mediators might be of importance in the development of new therapies for obesity-associated diseases.

Adiponectin, TNF-α and inflammatory cytokines and risk of type 2 diabetes: A systematic review and meta-analysis

AIMS

There has been growing evidence that adiponectin, tumor necrosis factor-α (TNF-α) and inflammatory cytokines involved in insulin resistance and may be attractive candidates for assessing risk of the incident type 2 diabetes (T2DM). A systematic review and meta-analysis of prospective studies was conducted to assess the associations of levels of serum adiponectin, TNF-α and inflammatory markers (Interleukin-1 beta (IL-1β), Interleukin-6 (IL-6), Interleukin-18 (IL-18), C-reactive protein (CRP)) with risk of T2DM.

MATERIALS/METHODS

We searched PubMed, ISI Web of Knowledge, EMBASE, and Cochrane Library databases up until February 1, 2016 for eligible studies which were matched to search subjects. Either fixed-effects or random-effects models were used to estimate the summary risk incorporated between study variations.

RESULTS

19 studies comprising a total of 39,136 participants and 7924 cases were included in the meta-analysis. Our findings showed that an obvious association of elevated CRP levels with T2DM risk (relative risk [RR] 1.48 [95% CI 1.26-1.71]), with the absence of publication bias. For IL-6, the meta-analysis involved 16 cohorts with a total of 24,929 participants and 4751 cases. Using data from all trials, a strong positive correlation (1.32 [1.14, 1.51]) was observed between basal plasma IL-6 and T2DM, whereas relatively lower relation between TNF-α (1.16 [0.87, 1.45]), IL-18 (1.45 [1.16, 1.73]), IL-1β (0.87, [0.59, 1.15]) and independently increased risk to occurrence of T2DM. Conversely, we also found that the level of adiponectin decreased significantly in patients with T2DM. Sensitivity analyses further supported the associations.

CONCLUSIONS

This meta-analysis indicates that T2DM risk as whole was strongly associated with elevated levels of inflammatory cytokines (IL-1β, IL-6, IL-18, CRP), TNF-α and low levels of adiponectin. Despite an overall detectable association in the meta-analysis, considerable heterogeneity existed between studies. Further work is needed, it seems clear that a complex interplay of inflammation and the development of DM. Moreover, these biomarkers are predictors of T2DM subjects and should take more attention to measure levels of these as well as to target therapy/interventions.

Mineralocorticoid receptor blockade reverses obesity-related changes in expression of adiponectin, peroxisome proliferator-activated receptor-gamma, and proinflammatory adipokines

BACKGROUND

In obesity, decreases in adiponectin and increases in proinflammatory adipokines are associated with heart disease. Because adipocytes express mineralocorticoid receptor (MR) and MR blockade reduces cardiovascular inflammation and injury, we tested the hypothesis that MR blockade reduces inflammation and expression of proinflammatory cytokines in adipose tissue and increases adiponectin expression in adipose tissue and hearts of obese mice.

METHODS AND RESULTS

We determined the effect of MR blockade (eplerenone, 100 mg/kg per day for 16 weeks) on gene expression in retroperitoneal adipose and heart tissue from obese, diabetic db/db mice (n=8) compared with untreated obese, diabetic db/db mice (n=10) and lean, nondiabetic db/+ littermates (n=11). Expression of tumor necrosis factor-alpha, monocyte chemoattractant protein-1, plasminogen activator inhibitor type 1, and macrophage protein CD68 increased, and expression of adiponectin and peroxisome proliferator-activated receptor-gamma decreased in retroperitoneal adipose tissue from obese versus lean mice. In addition, adiponectin expression in heart was reduced in obese versus lean mice. MR blockade prevented these obesity-related changes in gene expression. Furthermore, treatment of undifferentiated preadipocytes with aldosterone (10(-8) mol/L for 24 hours) increased mRNA levels of tumor necrosis factor-alpha and monocyte chemoattractant protein-1 and reduced mRNA and protein levels of peroxisome proliferator-activated receptor-gamma and adiponectin, supporting a direct aldosterone effect on gene expression.

CONCLUSIONS

MR blockade reduced expression of proinflammatory and prothrombotic factors in adipose tissue and increased expression of adiponectin in heart and adipose tissue of obese, diabetic mice. These effects on adiponectin and adipokine gene expression may represent a novel mechanism for the cardioprotective effects of MR blockade.

Molecular mechanism for adiponectin-dependent M2 macrophage polarization: link between the metabolic and innate immune activity of full-length adiponectin

The anti-inflammatory effects of globular adiponectin (gAcrp) are mediated by IL-10/heme oxygenase 1 (HO-1)-dependent pathways. Although full-length (flAcrp) adiponectin also suppresses LPS-induced pro-inflammatory signaling, its signaling mechanisms are not yet understood. The aim of this study was to examine the differential mechanisms by which gAcrp and flAcrp suppress pro-inflammatory signaling in macrophages. Chronic ethanol feeding increased LPS-stimulated TNF-α expression by Kupffer cells, associated with a shift to an M1 macrophage polarization. Both gAcrp and flAcrp suppressed TNF-α expression in Kupffer cells; however, only the effect of gAcrp was dependent on IL-10. Similarly, inhibition of HO-1 activity or siRNA knockdown of HO-1 in RAW264.7 macrophages only partially attenuated the suppressive effects of flAcrp on MyD88-dependent and -independent cytokine signatures. Instead, flAcrp, acting via the adiponectin R2 receptor, potently shifted the polarization of Kupffer cells and RAW264.7 macrophages to an M2 phenotype. gAcrp, acting via the adiponectin R1 receptor, was much less effective at eliciting an M2 pattern of gene expression. M2 polarization was also partially dependent on AMP-activated kinase. flAcrp polarized RAW264.7 macrophages to an M2 phenotype in an IL-4/STAT6-dependent mechanism. flAcrp also increased the expression of genes involved in oxidative phosphorylation in RAW264.7 macrophages, similar to the effect of flAcrp on hepatocytes. In summary, these data demonstrate that gAcrp and flAcrp utilize differential signaling strategies to decrease the sensitivity of macrophages to activation by TLR4 ligands, with flAcrp utilizing an IL-4/STAT6-dependent mechanism to shift macrophage polarization to the M2/anti-inflammatory phenotype.

A novel ELISA system for selective measurement of human adiponectin multimers by using proteases

BACKGROUND

Adiponectin, an antiatherogenic adipocyte-derived protein exists in human blood as multiple isoforms--trimeric low molecular weight (LMW), albumin-binding LMW (Alb-LMW), hexameric middle molecular weight (MMW), and high molecular weight (HMW) forms. We developed a novel ELISA system to detect total human adiponectin and the selective level of each adiponectin multimer for investigating the distribution of these levels in human blood.

METHODS

Two monoclonal antibodies that were raised against human adiponectin were used to construct a sandwich ELISA to measure adiponectin levels. Adiponectin multimers were selectively measured after sample pretreatment with two proteases that specifically digested the trimeric forms or both the hexameric and trimeric forms.

RESULTS

The ELISA had a dynamic range of 0.075-4.8 ng/ml. Intraassay variations (CV) were 5.3% (total adiponectin), 4.1% (MMW+HMW), and 3.3% (HMW). Comparison of the results of ELISA and quantitative western blot analysis of multimeric adiponectin in serum samples revealed good correlation (LMW+Alb-LMW, r=0.873; MMW, r=0.907; HMW, r=0.950). Each of the three forms of adiponectin multimer levels closely correlated with total adiponectin levels in healthy subjects.

CONCLUSIONS

This ELISA system can be used to further investigate the physiological roles of human adiponectin multimers.

Increased adiponectin is negatively linked to the local inflammatory process in patients with rheumatoid arthritis

Adiponectin has been shown to exert insulin-sensitizing, anti-atherogenic, and anti-inflammatory properties in metabolic diseases. It has been suggested that adiponectin may play a role in rheumatoid arthritis (RA). To assess adiponectin in serum and synovial fluid from patients with RA and osteoarthritis (OA), and in serum from healthy controls. Adiponectin and CRP levels were analyzed by ELISA. The clinical activity of RA patients was assessed according to the 28 joint count Disease Activity Score. Synovial fluid adiponectin was significantly higher in RA than in OA patients (p<0.001). Adiponectin was negatively associated with the leukocyte count in RA synovial fluid (r=-0.45, p<0.05). Serum adiponectin was higher in RA compared to healthy controls (p<0.02), however comparable to OA patients. Serum adiponectin was higher than in synovial fluid in both diseases (p<0.001). In general, women had higher adiponectin levels than men. Adiponectin was not related to age, disease duration, body mass index, or disease activity of RA patients. Adiponectin is decreased in synovial fluid compared to serum indicating that peripheral fat stores are major producers of adiponectin into the blood stream. However, increased synovial fluid adiponectin in RA patients may counterpart the local inflammatory process.

A novel enzyme-linked immunosorbent assay specific for high-molecular-weight adiponectin

Human plasma contains at least three forms of adiponectin: a trimer, a hexamer, and a high-molecular-weight (HMW) multimer. We purified HMW adiponectin from human plasma using its affinity to gelatin and obtained monoclonal antibodies against it. On Western blot analysis, the reactivity of these monoclonal antibodies was shown to be restricted to a non-heat-denatured form of adiponectin molecules. On heating, the collagen-like domain of adiponectin molecules became denatured, and thus the trimer form could not be maintained. From these, monoclonal antibodies against HMW adiponectin were suggested to react with the intact trimer of adiponectin. With these monoclonal antibodies, we developed a sandwich ELISA system for quantifying adiponectin in human serum. Its specificity was verified by analysis of serum fractions separated by gel-filtration chromatography, and our ELISA system was found to be HMW adiponectin-specific. With this novel ELISA, the HMW adiponectin concentrations were 8.4 +/- 5.5 microg/ml (mean +/- SD) in healthy women and 6.2 +/- 3.6 microg/ml in healthy men. Also, serum with a lower HMW adiponectin concentration was shown to have a lower HMW ratio (i.e., HMW adiponectin/total adiponectin).

Adiponectin and its receptors in patients with chronic hepatitis C

BACKGROUND/AIMS

There is increasing interest in the influence of excess body weight and associated metabolic factors on the liver. In patients with non-alcoholic steatohepatitis, lower levels of adiponectin were associated with higher grades of hepatic steatosis and necroinflammatory activity, suggesting a pathophysiological role for this adipokine in liver disease.

METHODS

We studied 194 consecutive patients with untreated chronic HCV, to assess the relationship between adiponectin and its receptors and hepatic steatosis, fibrosis and inflammation.

RESULTS

Significant negative correlations between serum adiponectin and male gender, body mass index and serum insulin were observed. However, there was no association between serum adiponectin and stage of fibrosis and lower levels of serum adiponectin were associated with the presence of steatosis in males only. In contrast, there was a significant increase in serum adiponectin and hepatic adiponectin immunoreactivity with increasing inflammation. The hepatic mRNA expression of the adiponectin receptors, AdipoR1 and AdipoR2, displayed significant but opposite associations with phosphoenolpyruvate carboxykinase (PEPCK) gene expression, a substitute marker of hepatic insulin sensitivity.

CONCLUSIONS

In patients with chronic HCV, adiponectin was associated with steatosis only in males and was paradoxically increased with inflammation. Our results suggest that the role of adiponectin in chronic liver diseases may be linked to gender and etiology.

Role of the xenobiotic receptor in inflammatory bowel disease

BACKGROUND

Gene-environment interplay modulates inflammatory bowel diseases (IBD). Dioxin-like compounds can activate the aryl hydrocarbon receptor (AhR) and alter macrophage function as well as T-cell polarization. We hypothesized that attenuation of the AhR signaling pathway will ameliorate colitis in a murine model of IBD.

METHODS

Dextran sulfate sodium (DSS) colitis was induced in C57BL/6 AhR null mice (AhR(-/-) ), heterozygous mice (AhR(-/+) ), and their wildtype (WT) littermates. Clinical and morphopathological parameters were used to compare the groups.

PATIENTS

AhR pathway activation was analyzed in biopsy specimens from 25 IBD patients and 15 healthy controls.

RESULTS

AhR(-/-) mice died before the end of the treatment. However, AhR(-/+) mice exhibited decreased disease activity compared to WT mice. The AhR(-/+) mice expressed less proinflammatory cytokines such as tumor necrosis factor alpha (TNF-α) (6.1- versus 15.7-fold increase) and IL17 (23.7- versus 67.9-fold increase) and increased antiinflammatory IL-10 (2.3-fold increase) compared with the AhR(+/+) mice in the colon. Colonic macrophage infiltration was attenuated in the AhR(-/+) group. AhR and its downstream targets were significantly upregulated in IBD patients versus control (CYP1A1 -19.9, and IL8- 10-fold increase).

CONCLUSIONS

Attenuation of the AhR receptor expression resulted in a protective effect during DSS-induced colitis, while the absence of AhR exacerbated the disease. Abnormal AhR pathway activation in the intestinal mucosa of IBD patients may promote chronic inflammation. Modulation of AhR signaling pathway via the diet, cessation of smoking, or administration of AhR antagonists could be viable strategies for the treatment of IBD.

Testosterone therapy decreases subcutaneous fat and adiponectin in aging men

OBJECTIVE

Testosterone therapy increases lean body mass and decreases total fat mass in aging men with low normal testosterone levels. The major challenge is, however, to determine whether the metabolic consequences of testosterone therapy are overall positive. We have previously reported that 6-month testosterone therapy did not improve insulin sensitivity. We investigated the effect of testosterone therapy on regional body fat distribution and on the levels of the insulin-sensitizing adipokine, adiponectin, in aging men with low normal bioavailable testosterone levels.

DESIGN

A randomized, double-blinded, placebo-controlled study on 6-month testosterone treatment (gel) in 38 men, aged 60-78 years, with bioavailable testosterone <7.3 nmol/l, and a waist circumference >94 cm.

METHODS

Central fat mass (CFM) and lower extremity fat mass (LEFM) were measured by dual X-ray absorptiometry. Subcutaneous abdominal adipose tissue (SAT), visceral adipose tissue (VAT), and thigh subcutaneous fat area (TFA) were measured by magnetic resonance imaging. Adiponectin levels were measured using an in-house immunofluorometric assay. Coefficients (b) represent the placebo-controlled mean effect of intervention.

RESULTS

LEFM was decreased (b = -0.47 kg, P = 0.07) while CFM did not change significantly (b = -0.66 kg, P = 0.10) during testosterone therapy. SAT (b = -3.0%, P = 0.018) and TFA (b = -3.0%, P < 0.001) decreased, while VAT (b = 1.0%, P = 0.54) remained unchanged. Adiponectin levels decreased during testosterone therapy (b = -1.3 mg/l, P = 0.001).

CONCLUSION

Testosterone therapy decreased subcutaneous fat on the abdomen and lower extremities, but visceral fat was unchanged. Moreover, adiponectin levels were significantly decreased during testosterone therapy.

Resistin is associated with biomarkers of inflammation while total and high-molecular weight adiponectin are associated with biomarkers of inflammation, insulin resistance, and endothelial function

OBJECTIVE

Adiponectin and resistin have been linked to inflammation, endothelial dysfunction, and/or insulin secretion or resistance. It remains to be elucidated which of these adipokines is associated primarily with biomarkers of all or only some of these categories, i.e. biomarkers of inflammation, endothelial dysfunction, and/or insulin secretion or insulinemia.

DESIGN AND METHODS

We studied 1065 healthy women, Nurses' Health Study participants, who provided blood samples in 1989-1990. A cross-sectional analysis was conducted to assess the relationships between total and high-molecular weight (HMW) adiponectin and resistin with inflammatory markers and biomarkers of endothelial dysfunction, insulin secretion, and insulinemia.

RESULTS

Resistin was positively associated with the inflammatory markers soluble tumour necrosis factor-alpha receptor II and interleukin-6 but not with any biomarkers of endothelial function, glycemia, insulinemia, or markers of insulin secretion after multivariate adjustment for age and body mass index (BMI). In both crude and multivariate analyses, total adiponectin was inversely associated with insulin, proinsulin, C-peptide, HbA1c, sE-selectin, and C-reactive protein (CRP) levels. HMW adiponectin was inversely associated with circulating insulin, proinsulin, C-peptide, HbA1c, sE-selectin, and CRP concentrations, even after adjustment for age, BMI, lifestyle factors, exercise, the use of medications as well as the other biomarkers of interest. Total and HMW adiponectin demonstrated negative associations with soluble intercellular adhesion molecule-1, which became nonsignificant after adjustment for confounders, whereas positive associations between soluble vascular cell adhesion molecule-1 and total adiponectin became significant only after multivariate adjustment.

CONCLUSIONS

Total and HMW adiponectin are inversely associated with markers of insulin secretion/insulinemia, endothelial function, and inflammation. Resistin is positively associated only with markers of inflammation.

Role of adipokines in the obesity-inflammation relationship: the effect of fat removal

During the past 10 years, there has been a dramatic increase in the prevalence of obesity in the United States and other developed nations. Recent studies indicate that adipose tissue is an endocrine organ producing numerous proteins, collectively referred to as adipokines, with broad biological activity, that play an important autocrine role in obesity-associated complications. Adipose tissue in general and visceral fat in particular are thought to be key regulators of inflammation. Inflammation is heavily involved in the onset and development of atherothrombotic disease. Moreover, chronic inflammation may also represent a triggering factor in the origin of the metabolic syndrome and type 2 diabetes mellitus. According to a hypothesis, stimuli such as overnutrition, physical inactivity, and aging would result in cytokine hypersecretion and eventually lead to insulin resistance and diabetes in genetically or metabolically predisposed individuals. This article discusses the current understanding of important adipokines thought to be involved in the metabolic and cardiovascular risk associated with obesity. Available evidence linking fat removal by liposuction to modification of cardiovascular risk and vascular inflammatory markers in the obese patient is also presented. Most studies have shown that liposuction produces beneficial effects on insulin resistance and vascular inflammation in the obese patient, reducing its cardiovascular risk. Besides having a significant role in body contouring of the obese patient at the end of the lengthy process of bariatric surgery and massive weight loss, plastic surgery should be incorporated into a multifaceted program of lifestyle changes that allows the obese patient to obtain weight loss and, more importantly, to maintain the reduced weight in the long term.

Adiponectin as a potential biomarker of vascular disease

The increasing prevalence of diabetes and its complications heralds an alarming situation worldwide. Obesity-associated changes in circulating adiponectin concentrations have the capacity to predict insulin sensitivity and are a link between obesity and a number of vascular diseases. One obvious consequence of obesity is a decrease in circulating levels of adiponectin, which are associated with cardiovascular disorders and associated vascular comorbidities. Human and animal studies have demonstrated decreased adiponectin to be an independent risk factor for cardiovascular disease. However, in animal studies, increased circulating adiponectin alleviates obesity-induced endothelial dysfunction and hypertension, and also prevents atherosclerosis, myocardial infarction, and diabetic cardiac tissue disorders. Further, metabolism of a number of foods and medications are affected by induction of adiponectin. Adiponectin has beneficial effects on cardiovascular cells via its antidiabetic, anti-inflammatory, antioxidant, antiapoptotic, antiatherogenic, vasodilatory, and antithrombotic activity, and consequently has a favorable effect on cardiac and vascular health. Understanding the molecular mechanisms underlying the regulation of adiponectin secretion and signaling is critical for designing new therapeutic strategies. This review summarizes the recent evidence for the physiological role and clinical significance of adiponectin in vascular health, identification of the receptor and post-receptor signaling events related to the protective effects of the adiponectin system on vascular compartments, and its potential use as a target for therapeutic intervention in vascular disease.

Effects of Mixed Carotenoids on Adipokines and Abdominal Adiposity in Children: A Pilot Study

CONTEXT

Carotenoids have been implicated in the regulation of adipocyte metabolism.

OBJECTIVE

To compare the effects of mixed-carotenoid supplementation (MCS) versus placebo on adipokines and the accrual of abdominal adiposity in children with obesity.

DESIGN AND SETTING

Randomized (1:1), double-blind, placebo-controlled intervention trial to evaluate the effects of MCS over 6 months in a subspecialty clinic.

PARTICIPANTS

Twenty (6 male and 14 female) children with simple obesity [body mass index (BMI) > 90%], a mean age (± standard deviation) of 10.5 ± 0.4 years, and Tanner stage I to V were enrolled; 17 participants completed the trial.

INTERVENTION

MCS (which contains β-carotene, α-carotene, lutein, zeaxanthin, lycopene, astaxanthin, and γ-tocopherol) or placebo was administered daily.

MAIN OUTCOME MEASURES

Primary outcomes were change in β-carotene, abdominal fat accrual (according to magnetic resonance imaging), and BMI z-score; secondary outcomes were adipokines and markers of insulin resistance.

RESULTS

Cross-sectional analysis of β-carotene showed inverse correlation with BMI z-score, waist-to-height ratio, visceral adipose tissue, and subcutaneous adipose tissue (SAT) at baseline. MCS increased β-carotene, total adiponectin, and high-molecular-weight adiponectin compared with placebo. MCS led to a greater reduction in BMI z-score, waist-to-height ratio, and SAT compared with placebo. The percentage change in β-carotene directly correlated with the percentage change in SAT.

CONCLUSIONS

The decrease in BMI z-score, waist-to-height ratio, and SAT and the concomitant increase in the concentration of β-carotene and high-molecular-weight adiponectin by MCS suggest the putative beneficial role of MCS in children with obesity.

Lower serum levels of Meteorin-like/Subfatin in patients with coronary artery disease and type 2 diabetes mellitus are negatively associated with insulin resistance and inflammatory cytokines

Meteorin-like (Metrnl) is a newly discovered adipokine with favorable effect on insulin sensitivity. Previous studies have reported lower levels of Metrnl in obese patients. However, there is conflicting data regarding its circulating levels in type 2 diabetes mellitus (T2DM) and there is no data in patients with coronary artery disease (CAD). The aim of the present study was to evaluate the Metrnl serum level in patients with T2DM and CAD, and also to evaluate the serum levels of Metrnl with serum levels of adiponectin, IL-6 and TNF-α in patients. This study was conducted on 66 patients with CAD, 63 T2DM patients and 41 controls. The serum levels of Metrnl, adiponectin, IL-6 and TNF-α were measured using ELISA techniques. The serum levels of Metrnl were found to be lower in CAD (75.18 ± 28.48 pg/mL) and T2DM patients (73.89 ± 33.60 pg/mL) compared to the control group (95.33 ± 32.56 pg/mL) (p < 0.005 and p<0.003, respectively). Additionally, adiponectin decreased in CAD and T2DM patients as compared to the control group, while IL-6 and TNF-α were higher in CAD and T2DM patients. Metrnl showed independent association with the risk of CAD and T2DM presence. Furthermore, Metrnl illustrated a negative correlation with IL-6 and TNF-α in both CAD patients and also with BMI, insulin resistance, IL-6 and TNF-α in T2DM patients. Metrnl showed an association with CAD and T2DM presence and with components of their pathogenesis such as inflammation and insulin resistance. These results suggested a possible interaction between Metrnl and the pathogenesis of CAD and T2DM, however more studies are needed to prove this concept.

Adiponectin isoforms: a potential therapeutic target in rheumatoid arthritis?

OBJECTIVES

Several clinical studies have suggested the adipocytokine adiponectin is involved in the progression of rheumatoid arthritis (RA). From this point of view, adiponectin might present a new therapeutic target. However, as adiponectin also exerts beneficial effects in the human organism, a strategy that would allow its detrimental effects to be abolished while maintaining the positive effects would be highly favourable. To elucidate such a strategy, the authors analysed whether the different adiponectin isoforms induce diverging effects, especially with regard to rheumatoid arthritis synovial fibroblasts (RASF), a central cell type in RA pathogenesis capable of invading into and destroying cartilage.

METHODS

Affymetrix microarrays were used to screen for changes in gene expression of RASF. Messenger RNA levels were quantified by real-time PCR, protein levels by immunoassay. The migration of RASF and primary human lymphocytes was analysed using a two-chamber migration assay.

RESULTS

In RASF, the individual adiponectin isoforms induced numerous genes/proteins relevant in RA pathogenesis to clearly different extents. In general, the most potent isoforms were the high molecular weight/middle molecular weight isoforms and the globular isoform, while the least potent isoform was the adiponectin trimer. The chemokines secreted by RASF upon adiponectin stimulation resulted in an increased migration of RASF and lymphocytes.

CONCLUSION

The results clearly suggest a pro-inflammatory and joint-destructive role of all adiponectin isoforms in RA pathophysiology, indicating that in chronic inflammatory joint diseases the detrimental effects outweigh the beneficial effects of adiponectin.

Inflammation mediates the association between visceral adiposity and obstructive sleep apnea in adolescents

Only a handful of studies, primarily in clinical samples, have reported an association between obesity, inflammation, and obstructive sleep apnea (OSA) in children and adolescents. No studies, however, have examined the pathogenetic link between visceral adiposity, systemic inflammation, and incident OSA in a large general population sample using objective measures of sleep and body fat. Adolescents (n = 392; mean age 17.0 ± 2.2 yr, 54.0% male) from the Penn State Child Cohort (PSCC) underwent 9-h overnight polysomnography; a DXA scan to assess body fat distribution; and a single fasting blood draw for the assessment of plasma interleukin-6 (IL-6), IL-6 soluble receptor (IL-6 sR), tumor necrosis factor alpha (TNFα), tumor necrosis factor receptor 1A (TNFR1), C-reactive protein (CRP), leptin, and adiponectin levels via ELISA. Visceral fat area was significantly elevated in moderate OSA (AHI ≥ 5), especially in boys. IL-6, CRP, and leptin were highest in adolescents with moderate OSA, even after adjusting for BMI percentile. Mediation analysis revealed that 42% of the association between visceral fat and OSA in adolescents was mediated by IL-6 (p = 0.03), while 82% of the association was mediated by CRP (p = 0.01). These data are consistent with the model of a feed-forward, vicious cycle, in which the release of proinflammatory cytokines by visceral adipocytes largely explains the association between central obesity and OSA; in turn, inflammation is also elevated in OSA independent of BMI. These findings, in a large, representative, non-clinical sample of young people, add to our understanding of the developmental pathogenesis of sleep apnea.

Effect of HTST and Holder Pasteurization on the Concentration of Immunoglobulins, Growth Factors, and Hormones in Donor Human Milk

Donor human milk (DHM) is submitted to Holder pasteurization (HoP) to ensure its microbiological safety in human milk banks but this treatment affects some of its bioactive compounds. The objective of this work was to compare the effects of HoP and high temperature short time (HTST) treatments on some bioactive compounds found in DHM. A total of 24 DHM batches were processed in a continuous HTST system (70, 72, and 75°C for 5-25 s) and by HoP (62.5°C for 30 min). The concentrations of immunoglobulins (Igs) A, G, and M, transforming growth factor-beta 2 (TGF-β₂), adiponectine, ghrelin, and leptin were measured using a multiplex system, whereas the concentration of epidermal growth factor (EGF) was determined by ELISA. In relation to Igs, IgG showed the highest preservation rates (87-101%) after HTST treatments, followed by IgA (54-88%) and IgM (25-73%). Ig retention after any of the HTST treatments was higher than after HoP (p < 0.001). Treatment times required to reduce the concentration of IgM by 90% (D-value) were 130, 88, and 49 s at 70, 72, and 75°C, while the number of degrees Celsius required to change the D-value by one factor of 10 (z-value) was 11.79°C. None of the heat treatments had a significant effect on the concentrations of TGF-β₂, EGF, adiponectin, and ghrelin. In contrast, leptin was detected only in 4 of the samples submitted to HoP, whereas it was present in all samples after the different HTST treatments, with retention rates ranging between 34 and 68%. Globally, the concentration of IgA, IgG, IgM, and leptin in DHM was significantly higher after HTST pasteurization performed in a continuous system designed to be used in human milk banks than after the HoP procedure that is routinely applied at present.

Migraine and Adiponectin: Is There a Connection?

Migraine is a common disorder, characterized by recurrent episodes of headache and associated symptoms. The full pathophysiology of migraine is incompletely delineated. Current theories suggest that it is a neurovascular disorder involving cortical depression, neurogenic inflammation and vasodilation. Various neuropeptides and cytokines have been implicated in the pathophysiology of migraine including calcitonin gene-related peptide, interleukin (IL)-1, IL-6 and tumour necrosis factor (TNF)-α. There is evidence demonstrating an association between migraine and processes associated with inflammation, atherosclerosis, immunity and insulin sensitivity. Similarly, adiponectin, an adipocytokine secreted by adipose tissue, has protective roles against the development of insulin resistance, dyslipidaemia and atherosclerosis and exhibits anti-inflammatory properties. The anti-inflammatory activities of adiponectin include inhibition of IL-6 and TNF-induced IL-8 formation, as well as induction of the anti-inflammatory cytokines IL-10 and IL-1 receptor antagonist. Adiponectin levels are also inversely correlated with C-reactive protein (CRP), TNF-α and IL-6 levels. Likewise, recent studies have shown a possible correlation between CRP, TNF-α and IL-6 and migraine attacks. In addition, insulin sensitivity is impaired in migraine and obesity is a risk factor for the transformation from episodic to chronic migraine. In this review we discuss the basic science of adiponectin and its potential connection to the pathophysiology of migraine. Future research may focus on how adiponectin levels are potentially altered during migraine attacks, and how that information can be potentially translated into migraine therapy.

Adiponectin restrains ILC2 activation by AMPK-mediated feedback inhibition of IL-33 signaling

ILC2s are present in adipose tissue and play a critical role in regulating adipose thermogenesis. However, the mechanisms underlying the activation of adipose-resident ILC2s remain poorly defined. Here, we show that IL-33, a potent ILC2 activator, stimulates phosphorylation of AMPK at Thr172 via TAK1 in primary ILC2s, which provides a feedback mechanism to inhibit IL-33-induced NF-κB activation and IL-13 production. Treating ILC2s with adiponectin or an adiponectin receptor agonist (AdipoRon) activated AMPK and decreased IL-33-NF-κB signaling. AdipoRon also suppressed cold-induced thermogenic gene expression and energy expenditure in vivo. In contrast, adiponectin deficiency increased the ILC2 fraction and activation, leading to up-regulated thermogenic gene expression in adipose tissue of cold-exposed mice. ILC2 deficiency or blocking ILC2 function by neutralization of the IL-33 receptor with anti-ST2 diminished the suppressive effect of adiponectin on cold-induced adipose thermogenesis and energy expenditure. Taken together, our study reveals that adiponectin is a negative regulator of ILC2 function in adipose tissue via AMPK-mediated negative regulation of IL-33 signaling.

Recent advances in the measurement of adiponectin isoform distribution

PURPOSE OF REVIEW

Adiponectin has potent antidiabetic and antiatherosclerotic actions. Recent studies in animals and humans suggest that the high-molecular weight adiponectin complex, consisting of many adiponectin monomers, is the biologically active form of the peptide. This article will present recent methodological approaches for analyzing adiponectin isoform distribution.

RECENT FINDINGS

A handful of methods have been used for the isolation and measurement of high-molecular weight adiponectin, based on velocity gradient centrifugation, gel filtration chromatography and polyacrylamide gel electrophoresis. Recently, two novel sandwich enzyme-linked immuno-sorbent assays have been developed. The first makes use of antibodies raised against human high-molecular weight adiponectin and thus allows for the specific determination of high-molecular weight adiponectin in plasma. The second and more versatile enzyme-linked immuno-sorbent assay system enables the measurement of all adiponectin isoforms (i.e. low, middle and high-molecular weight) by means of selective digestion by proteases.

SUMMARY

The development and commercial availability of novel enzyme-linked immuno-sorbent assay kits enables the easy and rapid measurement of high-molecular weight adiponectin in both research and clinical practice and will undoubtedly advance further our understanding of the role of adiponectin in health and disease.

Adiponectin-deficiency exaggerates sepsis-induced microvascular dysfunction in the mouse brain

Obesity increases circulating cell-endothelial cell interactions; an early marker of inflammation in laboratory model of sepsis, but little is known about the effect of different adipokines. Adiponectin is an anti-inflammatory adipokine secreted by adipocytes. Adiponectin deficiency is implicated in exaggerated proinflammatory phenotype in both obesity and sepsis via increased proinflammatory cytokine expression. However the effect of adiponectin deficiency on circulating cell-endothelial cell interactions in polymicrobial sepsis is unknown. Furthermore although brain dysfunction in septic patients is a known predictor of death, the pathophysiology involved is unknown. In the current study, we examined the effects of adiponectin deficiency on leukocyte (LA) and platelet adhesion (PA) in cerebral microcirculation of septic mice. Adiponectin deficient (Adipoq(-/-): Adko) and background strain C57Bl/6 (wild type (WT)) mice were used. Sepsis was induced using cecal ligation and puncture (CLP). We studied LA and PA in the cerebral microcirculation using intravital fluorescent video microscopy (IVM), blood brain barrier (BBB) dysfunction using Evans Blue (EB) leakage method and E-selectin expression using dual radiolabeling technique in different WT and Adko mice with CLP. Adiponectin deficiency significantly exaggerated LA (WT-CLP:201 ± 17; Adko-CLP: ± 53 cells/mm(2); P < 0.05) and PA (WT-CLP:125 ± 17; Adko-CLP:188 ± 20 cells/mm(2); P < 0.05) in cerebral microcirculation, EB leakage (WT-CLP:10 ± 3.7; Adko-CLP:24 ± 4.3 ng/g × µl plasma; P < 0.05) and E-selectin expression (WT-CLP:0.06 ± 0.11; Adko-CLP:0.44 ± 0.053 ng/g; P < 0.05) in the brain tissue of the mice with CLP. Furthermore, E-selectin monoclonal antibody (mAb) treatment attenuated cell adhesion and BBB dysfunction of Adko-CLP mice. Adiponectin deficiency is associated with exaggerated leukocyte and PA in cerebral microcirculation of mice with CLP via modulation of E-selectin expression.

Association of plasma adiponectin concentrations with chronic lymphocytic leukemia and myeloproliferative diseases

Adiponectin, an adipocyte-secreted hormone, is an important negative regulator in the immune system and hematopoiesis. In this study, we investigated the association of adiponectin levels with chronic lymphocytic leukemia (CLL) and myeloproliferative diseases (MPDs). We measured adiponectin levels in 19 patients with CLL and 30 patients with MPD (chronic myelogenous leukemia, 15; polycythemia vera, 9; myelofibrosis, 4; essential thrombocythemia, 2). The data were (chronic myelogenous leukemia, 15; polycythemia vera, 9; myelofibrosis, 4; essential thrombocythemia, 2). The data were compared with results from a control group of healthy volunteers who were matched according to age, sex, and body mass index. The adiponectin levels in patients with CLL were lower than in the controls (4.71 +/- 1.33 microg/mL versus 16.61 +/- 3.91 microg/mL; P <.001). They were also significantly lower in patients with MPD than in the controls (8.95 +/- 1.33 microg/mL versus 16.16 +/- 4.77 microg/mL; P <.001). In addition, we compared the adiponectin levels of MPD patients who were treated with interferon (IFN) to the levels of patients who were not treated with IFN. Adipnectin levels were significantly higher in IFN-treated patients (11.03 +/- 1.39 microg/mL versus 6.87 +/- 1.79 microg/mL; P <.001). These results suggest that lymphopoiesis and myelopoiesis negatively influence adiponectin levels. Adiponectin may be related to inflammatory cytokine release. IFN therapy appears to have a positive influence on adiponectin secretion by suppressing inflammatory cytokines. Future studies are needed to prove causality and to provide insight about this hormone's mechanism of action and its potential role regarding the etiology and progression of CLL and MPD.

Serum adiponectin in a population sample of 64-year-old women in relation to glucose tolerance, family history of diabetes, autoimmunity, insulin sensitivity, C-peptide, and inflammation

The aim of the study was to describe serum adiponectin levels in a population-based sample of women with different degrees of glucose tolerance and to examine if the variability in serum adiponectin was explained by family history of diabetes, obesity, insulin resistance, glycemia, and inflammation. Repeated oral glucose tolerance tests were used in a screening procedure of a cohort of 64-year-old women to identify those with diabetes mellitus n = 210) and impaired glucose tolerance (n = 201). A random sample of women with normal glucose tolerance (NGT, n = 186) was also included. The examination included history of first-degree relatives with diabetes, anthropometry, measurement of circulating adiponectin, glutamic acid decarboxylase antibodies, blood glucose, HbA1c, insulin, proinsulin, C-peptide, high-sensitivity C-reactive protein, and homeostasis model assessment. Serum adiponectin concentration was lowest among diabetic women, highest in the random-sample NGT group, and intermediate in the impaired glucose tolerance group. This difference was partly explained by homeostasis model assessment, C-peptide, family history, and high-sensitivity C-reactive protein (R2 = 0.33, P < .001), but obesity and glycemia did not contribute to this variability in serum adiponectin. A family history of diabetes was associated with low serum adiponectin concentration independently of obesity, glycemia, or insulin sensitivity (P = .002). Glutamic acid decarboxylase-positive diabetic women (n = 17) had similar serum adiponectin as the NGT group in spite of hyperglycemia. In conclusion, serum adiponectin was lowered in women with type 2 diabetes mellitus, and this difference could only be partly explained by insulin resistance, insulin secretion, family history of diabetes, and inflammation. Family history of diabetes was independently associated with hypoadiponectinemia. Autoimmune diabetic women did not have low adiponectin levels.

Adipokines identified as new downstream targets for adiponectin: lessons from adiponectin-overexpressing or -deficient mice

Adipokines play a central role in the pathogenesis of the metabolic syndrome. Among them, adiponectin (ApN), a master regulator of immune and fuel homeostasis, is decreased. Identifying downstream adipokines targeted by ApN may help in deciphering this syndrome. We have generated transgenic mice, allowing persistent and moderate overexpression of ApN (ApN-Overex) specifically in white adipose tissue (AT). We took advantage of this model to unravel the adipokine secretion profile triggered by ApN. AT was fractionated into adipocytes and stromal-vascular cells (SVC), which were cultured for 8 h. Profiling of secretory products by antibody arrays and subsequent ELISAs showed that the secretion of three proinflammatory factors (IL-17B, IL-21, TNFα) and three hematopoietic growth factors [GF; thrombopoietin and granulocyte (macrophage) colony-stimulating-factors] was reduced in adipocytes of ApN-Overex mice compared with wild-type mice. In the SVC of these mice, besides the hematopoietic GFs, the secretion of another GF (vascular endothelial GF receptor 1), two chemokines (RANTES and ICAM-1), and two proinflammatory factors (IL-6 and IL-12p70) was reduced as well. Only one cytokine, IL-1 receptor 4, was oversecreted by SVC of ApN-Overex mice, which may exhibit anti-inflammatory properties. Most of these changes in secretion were due to corresponding changes in mRNAs. A reverse profile of adipokine expression was observed in ApN-KO mice. In conclusion, ApN regulates in vivo the secretion of downstream adipokines, thereby inducing a shift of the immune balance in both adipocytes and SVC toward a less inflammatory phenotype. These downstream adipokines may be new therapeutic targets for the management of the metabolic syndrome.