Plasma Adiponectin Isoforms Distribution And Detection Of Their Bioactivity

BackgroundAdiponectin, an adipokine predominantly synthesized and secreted from adipose tissue, exists in 3 oligmeric isoforms: trimer, hexamer and high molecular weight complexes (containing 18-36 molecular) in human circulation. Animal experiments have demonstrated that adiponectin has 3 major biologic functions including an insulin sensitization/metabolic regulatory function, an anti-inflammatory/vascular protective function and an anti-ischemic/ cardioprotective function. Mounting clinical evidences have showed that the decreased human plasma adiponectin level is closely correlated with the risks and progression of metabolic syndrome, diabetes mellitus and cardiovascular disease. More importantly, the shift in adiponectin complexes distribution is closely associated with Thiazolidinedione (TZDs)-mediated increase of insulin sensitivity. However, a few data shows that there is no association between plasma adiponectin concentration and cardiovascular disease, or even shows a negtive association between them. A recently published data find that plasma adiponectin level is increased at the onset stage of obese/hyperlipidemic condition and then down-regulated, adiponectin bioactivity is decreased concomitantly. This result strongly hint us that total plasma adiponectin concentration only is not a comprehensive marker in response to the risk and development of disease. Therefore, we suggest that plasma levels of total adiponectin, adiponectin of various subtypes and their bioactivity are more efficient for preventing and prognosis of diseases.Aims1. The objective of our study were to compare total adiponectin and adiponectin isoform status in newly diagnosed Chinese type 2 diabetes patients with control subjects, and to identify an adiponectin isoform which is most closely correlated with disease.2. To isolate adiponectin isoforms from human plasma, establish a method to detect the bioactivity of human plasma adiponectin multimers and confirm which isoform is the most potent biological activity.Methods1. One hundred and seventy-four newly diagnosed type 2 diabetes outpatients and one hundred and eight normal people were enrolled in present study. Plasma total adiponectin was measured by ELISA. Plasma adiponectin multimers were analyzed by Western blot followed SDS-PAGE under nonheating nonreducing conditions.2. Plasma adiponectin isoforms were isolated by using ammonium sulfate precipitation, anion-exchange chromatography and gel filtration chromato graphy. 3. The bioactivity of purified adiponectin isoforms were detected by incubating human umbilical vein endothelial cells for one hour and then determining the phosphorylation level of AMP-activated protein kinase (AMPK).Results1. Comparison with healthy control people, plasma total adiponectin (P<0.0001) was signi?cantly lower in newly diagnosed Chinese type 2 diabetes patients. Furthermore, HMW adiponectin (P<0.05) was decreased in newly diagnosed Chinese diabetes patients.2. The three adiponectin subtypes isolated from plasma all activated AMPK and the HMW adiponectin was the most potent isoform.Conclusions1. Both circulating total adiponectin and plasma adiponectin multimers distribution altered in newly diagnosed Chinese T2DM subjects, HMW was down-regulated apparently. Plasma total adiponectin and adiponectin isoforms distribution may be the promising biomarkers for preventing and diagnosis of T2DM and cardiovascular disease.2. Our method efficiently purified adiponectin multimers from human plasma and preserved their bioactivity. HMW adiponectin was the most potent isoform. We also confirmed the feasibility of detection of the activity of adiponectin isoforms in human plasma.