Peripheral factors in the metabolic syndrome: the pivotal role of adiponectin.

Several recently published reports, including ours, suggest that adiponectin is a strong proinflammatory agent. Indeed, exposure of human placenta and adipose tissue to adiponectin induces the production of interleukin-1beta (IL-1beta), IL-6, tumor necrosis factor alpha (TNF-alpha), and prostaglandin E2 (PGE2). We have previously shown that adiponectin is a powerful inducer of proinflammatory cytokines production by macrophages. The reported anti-inflammatory effect of adiponectin may be due to the induction of macrophage tolerance to further adiponectin exposure or to other proinflammatory stimuli including the Toll-like receptor (TLR) 3 ligand polyI:C and the TLR4 ligand lipopolysaccharide (LPS). We now present additional data supporting the hypothesis that adiponectin is a strong proinflammatory adipokine. More specifically, we demonstrate that adiponectin induces IL-1beta and IL-8 from THP-1 macrophage cell line. The effect of adiponectin is not restricted to differentiated THP-1 macrophages but it is evident at lower levels in undifferentiated THP-1 monocytes promoting TNF-alpha, IL-6, and IL-8 production. Thus, its high levels in the circulation of lean subjects render their macrophages resistant to several proinflammatory stimuli including its own thus acting in effect as an anti-inflammatory agent. Lowering of its high levels, as a consequence of increased body mass index (BMI), renders macrophages sensitive to any proinflammatory insult.