Adiponectin, the Controversial Hormone

Abstract

Adiponectin is an abundant protein hormone that belongs to a family of the so-called adipokines. It is expressed mostly by adipocytes and is an important regulator of lipid, and glucose metabolism. Moreover, adiponectin is an insulin-sensitizing hormone that has anti-diabetic, antiinflammatory and anti-atherogenic properties. Previous studies have highlighted several controversial aspects of adiponectin; the most striking paradox is that, contrary to all adipose-related proteins, adiponectin decreases with obesity. This is even more surprising when considering the fact that adiponectin is the most secreted protein in adipose tissue, so it would be expected to increase proportionally to body fat. This could be related to the development of a feedback inhibition of its production during the development of obesity. Most of the contradictory data regarding Adiponectin are related to plasma values and their relationship with body fat, gender differences and insulin resistance. Additionally, there are important confounding results regarding the mechanisms of action and functions of adiponectin especially in relation to insulin resistance and inflammation. Additionally, the lack of a direct relationship between adipose tissue adiponectin expression and plasma concentrations is controversial. Another paradox is that, in general, women show significantly higher adiponectin levels than men, despite having higher body fat content. Moreover, results about the relationship between plasma adiponectin and insulin are contradictory; although adiponectin is supposed to lower hyperinsulinemia. The potential diagnostic usage of Adiponectin was a subject of increasing interest in recent years. More specific research on this hormone will help avoiding all the contradictory data regarding Adiponectin.