Adiponectin is an abundant protein hormone that belongs to a family of adipokines. It is expressed mostly by adipocytes and is an important regulator of lipid and glucose metabolism. Adiponectin is an insulin sensitizing hormone with anti-diabetic, anti-inflammatory and anti-atherogenic properties (1). It has been shown that the amount of adiponectin in blood reduces in cases of patients suffering from Type 2 diabetes mellitus or coronary artery diseases, or who are insulin-resistant (2-6).
Human adiponectin consists of 244 amino acid residues and has a distinct domain structure: It contains both collagen-like and globular C1q-like domains. Collagen-like parts of three adiponectin molecules can form a triple coiled coil structure very similar to that in collagen (7). C1q-like domains form a “head” of adiponectin globula (Figure 1) and share a considerable degree of structural similarity to complement component C1q.
In blood, adiponectin is found as trimers (low molecular weight form, LMW), hexamers (medium molecular weight form, MMW) and higher order multimers (high molecular weight form, HMW). HMW adiponectin consists of 12-18 monomers (8-9). It has been suggested that different oligomeric forms exist in blood as separate moieties and do not convert into one another (10). Adiponectin oligomers are capable of binding Ca2+ ions, which are thought to participate in the maintenance of conformational stability of adiponectin (11).
The concentration of total adiponectin in the blood is approximately 3-30 μg/ml, whereas the concentration of the closest structural homolog of adiponectin, C1q, is approximately 80-200 μg/ml. Therefore, it is critical that anti-adiponectin antibodies do not crossreact with human C1q (12). Some authors describe significant gender differences in adiponectin level in healthy adults. These differences could contribute to discrepancies in adiponectin concentrations reported by various authors. It has been suggested that the concentration of the HMW form of adiponectin or HMW/total adiponectin ratio correlates with insulin resistance and metabolic syndrome better than just the concentration of total adiponectin (13-14).
Reagents for the development of a reliable adiponectin assay
HyTest offers several anti-human adiponectin monoclonal antibodies (MAbs) and a native purified adiponectin that are suitable for the development of adiponectin specific immunoassays.
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