Inflammatory biomarkers associated with obesity and insulin resistance: a focus on lipocalin-2 and adipocyte fatty acid-binding protein.

Obesity is an important risk factor for a cluster of metabolic and cardiovascular diseases, including insulin resistance, Type 2 diabetes, nonalcoholic fatty liver disease and atherosclerosis. Systemic low-grade inflammation, characterized by elevated circulating concentrations of proinflammatory factors, has recently been proposed to be a key mediator that links obesity with its medical complications. Adipose tissue is now recognized as the major contributor to systemic inflammation associated with obesity. As obesity develops, adipose tissue is infiltrated with activated macrophages. The 'inflamed' adipose tissue secretes a large number of proinflammatory adipokines and/or cytokines, which can act either in an autocrine manner to perpetuate local inflammation or in an endocrine manner to induce insulin resistance and endothelial dysfunction. In this review, we summarize recent advances in several newly identified adipose tissue-derived inflammatory factors, with the focus on lipocalin-2 and adipocyte fatty acid-binding protein (A-FABP). Both lipocalin-2 and A-FABP possess lipid-binding properties and are important integrators of metabolic and inflammatory pathways. A growing body of evidence from experimental, epidemiological and genetic studies suggests that both lipocalin-2 and A-FABP represent a novel class of serum biomarkers for risk prediction and therapeutic intervention of obesity-related medical complications.