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

High Expression Level of PPARγ in CD24 Knockout Mice and Gender-Specific Metabolic Changes: A Model of Insulin-Sensitive Obesity

Background: The heat-stable HSA/CD24 gene encodes a protein that shows high expression levels in adipocyte precursor cells but low levels in terminally differentiated adipocytes. Its high expression in many types of human cancer suggests an association between cancer, diabetes, and obesity, which is currently unclear. In addition, peroxisome proliferator-activated receptor gamma (PPARγ) is a regulator of adipogenesis that plays a role in insulin sensitivity, lipid metabolism, and adipokine expression in adipocytes. Aim: To assess gender-dependent changes in CD24 KO and its association with PPARγ expression. Experimental approach: WT and CD24 KO mice were monitored from birth up to 12 months, and various physiological and molecular characteristics were analysed. Mean body weight and adipose mass were higher in KO mice than in WT mice. Male, but not female, KO mice showed increased insulin sensitivity, glucose uptake, adipocyte size, and PPARγ expression than WT mice. In addition, enteric bacterial populations, assessed through high-throughput sequencing of stool 16S rRNA genes, were significantly different between male KO and WT mice. Conclusions: CD24 may negatively regulate PPARγ expression in male mice. Furthermore, the association between the CD24 and insulin sensitivity suggests a possible mechanism for diabetes as a cancer risk factor. Finally, CD24 KO male mice may serve as a model of obesity and insulin hyper-sensitivity.

Peripheral adiponectin levels in anxiety, mood, trauma- and stressor-related disorders: A systematic review and meta-analysis

BACKGROUND

Anxiety, mood, trauma- and stressor-related disorders confer increased risk for metabolic disease. Adiponectin, a cytokine released by adipose tissue is associated with these disorders and obesity via inflammatory processes. Available data describing associations with mental disorders remain limited and conflicted.

METHODS

A systematic search was conducted for English, peer-reviewed articles from inception until February 2019 that assessed for serum or plasma adiponectin levels in adults with an anxiety, mood or trauma-related disorder. Diagnoses were determined by psychiatric interview, based on DSM-IV, DSM-5 or ICD-10 criteria. Analyses were performed using STATA 15 and Standardized mean difference (SMD) with 95% confidence interval was applied to pool the effect size of meta-analysis studies.

RESULTS

In total 65 eligible studies were included in the systematic review and 30 studies in this meta-analysis. 19,178 participants (11,262 females and 7916 males), comprising healthy adults and adults with anxiety, mood and trauma-related disorders, were included. Overall results indicated an inverse association between adiponectin levels and examined mental disorders. Specifically, patients with an anxiety disorder (SMD  = -1.18 µg/mL, 95% CI, -2.34; -0.01, p  = 0.047); trauma or stressor-related disorder (SMD  =  -0.34 µg/mL, 95% CI, -0.52; -0.17, p  = 0.0000) or bipolar disorder (SMD  =  -0.638 µg/mL, 95% CI, -1.16, -0.12, p  = 0.017) had significant lower adiponectin levels compared to healthy adults.

LIMITATIONS

Heterogeneity, potential publication bias, and lack of control for important potential confounders were significant limitations.

CONCLUSION

Peripheral adiponectin levels appear to be inversely associated with anxiety, mood, trauma- and stressor related disorders and may be a promising biomarker for diagnosis and disease monitoring.

Meta-Analysis of Adiponectin as a Biomarker for the Detection of Metabolic Syndrome

Previous studies revealed the potential significance of circulating adiponectin levels with respect to the diagnosis and prediction of metabolic syndrome, but uncertainty has been noted across different cohorts. Systematic evaluation was performed for diagnostic accuracy and predictivity of adiponectin variation for metabolic syndrome in enrolled studies including 1,248 and 6,020 subjects, respectively. Adiponectin can identify metabolic syndrome with moderate accuracy (area under the curve = 0.81, 95% CI: 0.77–0.84). Heterogeneity analysis revealed that an increasing index of insulin resistance was independently associated with improving the performance of adiponectin upon metabolic syndrome diagnosis (ratio of diagnostic odds ratio = 3.89, 95% CI: 1.13–13.9). In addition, reductions in adiponectin were associated with increasing metabolic syndrome incidence in a linear dose-response manner. The risk of hypoadiponectinemia with metabolic syndrome was especially increased in men (P < 0.05). Further Mendelian randomization analysis identified that the amplified risk could be attributed to increased susceptibility (up to 7%) to insulin resistance compared with women. In conclusion, adiponectin measurement might have potential benefits in the detection of metabolic syndrome. Factors that affect insulin resistance should be considered for adjustment in future assessments.

Obstructive sleep apnea: Influence of hypertension on adiponectin, inflammatory markers and dyslipidemia

Obstructive sleep apnea (OSA) is a common but often unrecognized condition with potentially serious complications. The aim of this study was to explore the possible mechanisms linking hypertension (HT), a common cardiovascular disease (CVD), with obstructive sleep apnea (OSA) by investigating the levels of morning and evening serum adiponectin, inflammatory markers (TNF-α, IL-6), and lipid profiles in OSA patients with and without HT. Four groups were enrolled in this case-control analytic study: control, OSA, OSA+HT, and HT groups, each of which included 22 subjects. The results revealed low morning and evening serum adiponectin levels in patients with OSA and OSA+HT compared with their control and HT counterparts. Serum adiponectin levels declined progressively with increasing severity of OSA. Also, morning adiponectin levels were significantly decreased at the same time that a loss of the normal diurnal rhythm was observed in the OSA and OSA+HT groups. Both TNF-α and IL-6 levels were significantly increased in the OSA and OSA+HT groups compared with levels in the control and HT groups. Altered lipid profiles was noticed in the same groups. These findings were more pronounced in the OSA+HT than in the OSA group. In conclusion, the biochemical findings of this study demonstrate predominantly low adiponectin levels, increased levels of inflammatory markers, and atherogenic lipid profiles in OSA patients with HT compared with those of the other patients studied. This highlights the possible contributing role of these factors to the pathogenesis of HT as a common cardiovascular complication in OSA patients.

Leptin and calorie intake among different nicotine dependent groups

BACKGROUND

Exposure to nicotine via tobacco smoking may influence leptin release and decrease food intake among smokers. However, the effect of nicotine exposure on leptin and food intake among different nicotine dependent groups is unclear.

OBJECTIVE

We aimed to measure leptin and calorie intake among different nicotine dependent groups.

DESIGN

Cross-sectional study.

SETTING

Research department in school of medical sciences.

PATIENTS AND METHODS

Subjects were selected by purposive (non-probability) sampling and categorized as having low, moderate and high nicotine dependency based on the Fagerstrom Test for Nicotine Dependence (FTND) score. Diet was recorded by interview. Anthropometry, blood pressure, body composition, lipid profile, and physical activity level were measured accordingly. Fasting serum leptin was measured using a commercial ELISA kit.

MAIN OUTCOME MEASURE(S)

Nicotine dependency, 24-hour diet, clinical anthropometric and clinical measurements.

RESULTS

In 107 Malay male smokers leptin concentration was inversely correlated with nicotine dependence. However, body weight, smoking period, blood pressure, body composition, lipid profile and physical activity level were not significantly different among low, moderately and highly dependent smoking groups. Leptin concentration and total calorie intake were also not significantly different among these groups.

CONCLUSION

Leptin concentration was inversely correlated with nicotine dependence, but leptin concentration and total calorie intake status were not significantly different among our different nicotine dependency subjects.

LIMITATIONS

Purposive sampling for subject recruitment and inaccurate information in the self-administered questionnaire.

Smoking and diabetes: is the association mediated by adiponectin, leptin, or C-reactive protein?

Background

Although the association between cigarette smoking and risk of type 2 diabetes is well established, its mechanisms are yet to be clarified. This study examined the possible mediating effects of adiponectin, leptin, and C-reactive protein (CRP) concentrations on the smoking-diabetes association.

Methods

Between 2002 and 2011, we followed 3338 Japanese workers, aged 35–66 years, who were enrolled in the second Aichi workers’ cohort study. We used multivariable-adjusted Cox regression models to determine the hazard ratios and respective 95% confidence intervals (CIs) of the association between smoking status and risk of diabetes. A multiple mediation model with bootstrapping was used to estimate the magnitude and the respective bias-corrected (BC) 95% CIs of the indirect effects of smoking on diabetes through the three biomarkers.

Results

Relative to never smokers, the risk of diabetes was significantly elevated in current (hazard ratio 1.75, 95% CI 1.25–2.46) and ex-smokers (hazard ratio 1.54, 95% CI 1.07–2.22). The indirect effects of smoking on diabetes through adiponectin levels were statistically significant among light (point estimate 0.033, BC 95% CI 0.005–0.082), moderate (point estimate 0.044, BC 95% CI 0.010–0.094), and heavy smokers (point estimate 0.054, BC 95% CI 0.013–0.113). In contrast, neither the indirect effects of smoking on diabetes through leptin nor CRP levels were significant, as the corresponding BC 95% CIs included zero.

Conclusions

In our analysis, adiponectin concentration appeared to partially mediate the effect of smoking on diabetes, while leptin and CRP levels did not.

Plasma adiponectin is a more specific marker of fatty liver than a marker of metabolic syndrome in Japanese men

BACKGROUND

The association of plasma cardiovascular risk markers and metabolic syndrome (MetS) with non-alcoholic fatty liver disease (NAFLD) has not been well defined.

METHODS

Japanese men (n = 809) had standard anthropometric measurements done, and had their liver fat quantitated by ultrasound. Three groups were identified: (1) normal controls without significant disease, (2) preliminary-metabolic syndrome (pre-MetS) cases and (3) MetS cases. Plasma adiponectin, high sensitivity-C reactive protein (hs-CRP), HOMA-IR, lipids, lipoproteins and liver enzymes were evaluated among the three groups.

RESULTS

The prevalence of fatty liver was 13% in controls, 39% in pre-MetS and 62% in MetS. Plasma adiponectin and high density lipoprotein cholesterol (HDL-C) were significantly decreased, and HOMA-IR, hs-CRP, TG, remnant lipoproteins (RLPs) and small dense-LDL-C (sd LDL-C) were significantly increased in subjects with fatty liver compared to those without fatty liver. Multivariate analyses of serum parameters associated with fatty liver revealed that adiponectin and hs-CRP were more strongly associated with the presence of fatty liver than waist circumference. However, HOMA-IR, HDL-C, TG, RLP-C, RLP-TG and sd LDL-C were more strongly associated with waist circumference than with fatty liver. Factor analysis revealed that adiponectin and HDL-C were linked to liver enzymes, lipoproteins and HOMA-IR associated with fatty liver, but not with waist circumference.

CONCLUSIONS

Adiponectin was found to be a more specific diagnostic marker for the presence of fatty liver regardless of MetS status, and was inversely correlated with liver enzyme concentrations. However, RLPs were found to be more specifically associated with the presence of MetS.

Mild obesity reduces survival and adiponectin sensitivity in endotoxemic rats

BACKGROUND

Recent meta-analyses have reported that critically ill patients with morbid obesity (body mass index >40 kg/m(2)) have poor outcomes, but the effects and mechanisms of action of mild obesity are still unclear. The purpose of this study was to evaluate the effect of mild obesity using a lard-based, high-fat diet (HFD) on pathologic conditions and the mechanisms of adiponectin action in endotoxemic rats.

MATERIALS AND METHODS

Male Wistar rats underwent HFD feeding for 4 wk and were killed at 0, 1.5, and 6 h after lipopolysaccharide (LPS) injection. Plasma levels of adiponectin, nitric oxide, and interleukin 6; messenger RNA expression of adiponectin receptors (AdipoR1 and AdipoR2) in the liver and the skeletal muscle; blood biochemical test results; and histology of the liver were analyzed.

RESULTS

HFD-fed rats had a lower survival rate (12.8% versus 85.2%) and lower plasma adiponectin levels after LPS injection (P < 0.01). Messenger RNA expression of adiponectin receptors in the liver, but not the skeletal muscle, also decreased in HFD-fed rats (P < 0.05). Tissue injury and oxidative stress in the liver and plasma inflammatory mediator levels increased, and worsened lipid metabolism abnormalities were noted. The findings indicated that HFD decreased the sensitivity of adiponectin and was associated with an increase in oxidative stress and inflammation, which finally resulted in worsened liver injury and poor survival rate after LPS injection.

CONCLUSIONS

Short-term, HFD-induced, mild obesity is harmful to the septic host, reduces adiponectin sensitivity, and could be the cause of worsening pathologic conditions.

Molecular determinants of the cardiometabolic phenotype

The metabolic syndrome represents a clustering of risk factors that has been shown to predict adverse cardiovascular outcomes. Although the precise mechanisms contributing to the cardiometabolic syndrome (CMS) remain poorly defined, accumulating evidence identifies two intersecting candidate pathways responsible for inflammation and energy homeostasis in the pathophysiology that underlie cardiometabolic traits. Although currently no pharmacologic interventions specifically target CMS, future drug development efforts should attempt to capitalize on molecular nodes at the intersections of these pathways in the CMS.

The aporphine alkaloid boldine induces adiponectin expression and regulation in 3T3-L1 cells

Adiponectin is an adipokine secreted by differentiated adipocytes. Clinical studies suggest a negative correlation between oxidative stress and adiponectin levels in patients with metabolic syndrome or cardiovascular disease. Natural compounds that can prevent oxidative stress mediated inhibition of adiponectin may be potentially therapeutic. Boldine, an aporphine alkaloid abundant in the medicinal plant Peumus boldus, is a powerful antioxidant. The current study demonstrates the effects of boldine on the expression of adiponectin and its regulators, CCAAT/enhancer binding protein-alpha (C/EBPalpha) and peroxisome proliferator-activated receptor (PPAR)-gamma, in 3T3-L1 cells. Differentiated 3T3-L1 adipocytes were exposed to either hydrogen peroxide (H(2)O(2)) (100 microM) or tumor necrosis factor-alpha (TNFalpha) (1 ng/mL) for 24 hours in the presence or absence of increasing concentrations of boldine (5-100 microM). Quantitative polymerase chain reaction showed that both the oxidants decreased the mRNA levels of adiponectin, PPARgamma, and C/EBPalpha to half of the control levels. Boldine, at all concentrations, counteracted the inhibitory effect of H(2)O(2) or TNFalpha and increased the expression of adiponectin and its regulators. The effect of boldine on adiponectin expression was biphasic, with the lower concentrations (5-25 microM) having a larger inductive effect compared to higher concentrations (50-100 microM). Boldine treatment alone in the absence of H(2)O(2) or TNFalpha was also able to induce adiponectin at the inductive phase of adipogenesis. Peroxisome proliferator response element-luciferase promoter transactivity analysis showed that boldine interacts with the PPAR response element and could potentially modulate PPAR responsive genes. Our results indicate that boldine is able to modulate the expression of adiponectin and its regulators in 3T3-L1 cells and has the potential to be beneficial in obesity-related cardiovascular disease.

Association between the adiponectin promoter rs266729 gene variant and oxidative stress in patients with diabetes mellitus

AIMS

Low levels of adiponectin are associated with type 2 diabetes and coronary heart disease (CHD). Recent evidence also suggests that low levels of adiponectin are associated with increased oxidative stress. Our aim was to examine the association between the rs266729 promoter gene variant (-11377C > G) and plasma markers of oxidative stress in diabetes subjects.

METHODS AND RESULTS

Seven hundred and sixty-seven Caucasian subjects with diabetes were successfully genotyped (CC/CG/GG). Genotype data were analysed in relation to plasma total antioxidant status (TAOS) and Oxidized-LDL (Ox-LDL). Plasma adiponectin measurements were available in 206 samples. There was a significant association between genotype and plasma TAOS (CC: 42.1 +/- 13.4% vs. CG: 42.0 +/- 12.0% vs. GG: 47.9 +/- 12.0%, P = 0.02; for CC/CG vs. GG, P = 0.006). With respect to Ox-LDL, CC subjects had 8% higher plasma Ox-LDL compared with CG/GG [CC vs. CG vs. GG: 48.5 (36.3-60.2) U/L vs. 44.8 (35.6-54.1) U/L vs. 44.9 (41.2-49.1) U/L, for CC vs. CG/GG P = 0.03]. For plasma adiponectin, GG subjects had the highest levels [CC vs. CG vs. GG: 8.18 (5.69-15.38) microg/mL vs. 7.12 (5.34-12.97) microg/mL vs. 11.84 (6.98-25.25) microg/mL, P = 0.09; for CC/CG vs. GG, P = 0.05].

CONCLUSION

This study shows an association between a promoter variant in the adiponectin gene and plasma markers of oxidative stress. In line with previous studies, this work supports an antioxidant role for adiponectin which may explain its cardioprotective effect. Further prospective study is necessary to explore the effect of this gene variant in diabetes in relation to CHD risk and oxidative stress.

Low leptin but high insulin resistance of smokers in Japanese men

AIMS

To investigate the association between smoking and leptin, and to discuss their influence on diabetes in a large-scale study of Japanese men.

METHODS

A cross-sectional study was carried out in 2002. The subjects were 2836 men aged 35-66. Smoking history was investigated in a self-administered questionnaire. Blood leptin, glucose and insulin were measured.

RESULTS

Significant differences in leptin levels and homeostasis model assessment of insulin resistance (HOMA-IR) related to smoking status were observed (P=0.001 and P=0.008, respectively). The multivariate-adjusted geometric means of leptin in current, past and never smokers were 3.88, 4.08 and 4.12 ng/ml, respectively, while the means of HOMA-IR were 1.64, 1.61 and 1.49, respectively. The age-, body mass index-, and other lifestyle-adjusted prevalences of diabetes in current and never smokers were 9.2 and 4.7%, respectively. That of current smokers was significantly higher than in never smokers (P<0.001). The dose-dependent association found between the intensity of smoking and leptin levels in current smokers was statistically significant (P=0.030).

CONCLUSIONS

The present finding may explain in part an association among smoking, leptin levels and diabetes. Smoking is one of the important modifiable risk factors for the prevention of diabetes.

Hypoadiponectinemia as a marker of adipocyte dysfunction--part II: the functional significance of low adiponectin secretion

Low adiponectin expression is common in obesity and is tightly linked to insulin resistance and fat mass expansion. Whereas normal adipocytes offer effective metabolic buffering through well-controlled release and uptake of free fatty acids on demand, adipocyte expansion induced by caloric excess and modulated by genetic, regional, and systemic factors elicits major unfavorable changes in fat cell phenotypes. Large, dysfunctional adipocytes show increased lipolysis and enhanced expression and secretion of proinflammatory and pro-oxidative cytokines. Low adiponectin secretion is a hallmark of impaired adipocyte function; its secretion is inhibited by cytokines such as tumor necrosis factor alpha, interleukin 6 and plasminogen activator inhibitor 1 and by high oxidative stress induced by increased fatty acids that activate nicotinamide adenine dinucleotide phosphate-oxidase. The ensuing hypoadiponectinemia may aggravate insulin resistance and facilitate the evolution of type 2 diabetes. Only massive weight loss allows true and sustained recovery of normal fat cell function as reflected by adiponectin secretion.