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Transforming growth factor (TGF) β is the central cytokine in fibrotic liver diseases. We analyzed whether hepatoprotective adiponectin directly interferes with TGFβ1 signaling in primary human hepatocytes (PHH). Adiponectin induces the TGFβ decoy receptor BMP-and activin-membrane-bound inhibitor (BAMBI) in PHH. Overexpression of BAMBI in hepatoma cells impairs TGFβ-mediated phosphorylation of SMAD2 and induction of connective tissue growth factor. BAMBI is lower in human fatty liver with a higher susceptibility to liver fibrosis and negatively correlates with BMI of the donors. Hepatic BAMBI is reduced in rodent models of liver inflammation and fibrosis. In summary, the current data show that hepatoprotective effects of adiponectin include induction of BAMBI which is reduced in human fatty liver and rodent models of metabolic liver injury.

Galectin-3 plays a role in atherosclerotic diseases, and the effect of adiponectin that protects from atherosclerotic diseases on monocytic galectin-3 was analysed. Adiponectin reduced galectin-3 mRNA, its cellular and soluble form, and this effect was impaired in T2D cells. Cellular galectin-3 was higher in monocytes of overweight than normal-weight donors and was highest in T2D cells. Cellular galectin-3 positively correlated with the BMI of the donors and negatively with soluble monocyte galectin-3. Circulating levels of total adiponectin did not correlate with cellular or soluble galectin-3 indicating that additional factors contribute to higher cellular monocytic galectin-3 in obesity and T2D.

The abundance of the adiponectin receptors, AdipoR1 and AdipoR2, and the effects of the antidiabetic adipokine adiponectin in monocytes of normal-weight and overweight controls and type 2 diabetic patients (T2D) were analyzed. AdipoR1 and AdipoR2 mRNAs were increased in monocytes of obese controls and T2D patients when compared to normal-weight controls, and AdipoR1 mRNA positively correlated to AdipoR2 mRNA, the waist to hip ratio and systemic adiponectin. However, AdipoR1 and AdipoR2 proteins were lower in monocytes of T2D compared to normal-weight donors. Induction of IL-6 and IL-8 by adiponectin, an effect involving p38 MAPK, was also reduced in T2D monocytes.

The adiponectin paralog CORS-26 (collagenous repeat-containing sequence of 26kDa protein) is a member of the C1q/TNF-alpha molecular superfamily. CORS-26 is a secreted protein and baculovirus-produced CORS-26 released in the supernatant of insect cells forms stable trimers. Adiponectin exerts anti-inflammatory effects in LPS-treated monocytic cells and CORS-26 also reduces IL-6 and TNF-alpha secretion but does not increase IL-10. Suppression of NFkappaB signalling may explain the anti-inflammatory actions of CORS-26. Furthermore CORS-26 protein was detected in human monocytic and dendritic cells. The present data demonstrate for the first time that CORS-26 forms trimers, exerts anti-inflammatory properties and that it is expressed in monocytic cells. Therefore CORS-26 may provide a new target for pharmacological drugs in inflammatory diseases like the metabolic syndrome.

Aldehyde oxidase 1 (AOX1) is highly abundant in the liver and oxidizes aldehydes thereby generating reactive oxygen species. Enzymes involved in detoxification of aldehydes are expressed in adipocytes and alter adipogenesis, therefore the functional role of AOX1 in adipocytes was analyzed. AOX1 mRNA was higher in visceral compared to subcutaneous human adipose tissue but AOX1 protein was detected in both fat depots. AOX1 expression in adipocytes was confirmed by immunohistochemistry and immunoblot. AOX1 was induced during adipocytic differentiation and was downregulated by fenofibrate in differentiated cells. Knock-down of AOX1 in preadipocytes led to impaired lipid storage and adiponectin release in the differentiated cells. These data indicate that AOX1 is essential for adipogenesis and may link energy and drug metabolism.

Low levels of high-density lipoprotein (HDL)-cholesterol represent an independent cardiovascular risk factor and, besides reduced physical activity, mechanisms leading to decreased HDL-cholesterol levels are not known. We aimed to test the hypothesis, that adiponectin provides a missing link between type 2 diabetes and low levels of HDL-cholesterol, independent from common metabolic risk factors. 523 patients with type 2 diabetes were investigated for adiponectin serum levels and parameters of lipid metabolism. Even after correction for age, gender, BMI and fasting insulin concentration, serum levels of adiponectin were highly significant (P