Impact of different ectopic fat depots on cardiovascular and metabolic diseases

Inflammatory mediators that originate in vascular and extravascular tissues promote coronary lesion formation. Adipose tissue may function as an endocrine organ that contributes to an inflammatory burden in patients at risk of cardiovascular complications. In this study, we sought to compare expression of inflammatory mediators in epicardial and subcutaneous adipose stores in patients with critical CAD. Paired samples of epicardial and subcutaneous adipose tissues were harvested at the outset of elective CABG surgery (n=42; age 65+/-10 years). Local expression of chemokine (monocyte chemotactic protein [MCP]-1) and inflammatory cytokines (interleukin [IL]-1beta, IL-6, and tumor necrosis factor [TNF]-alpha) was analyzed by TaqMan real-time reverse transcription-polymerase chain reaction (mRNA) and by ELISA (protein release over 3 hours). Significantly higher levels of IL-1beta, IL-6, MCP-1, and TNF-alpha mRNA and protein were observed in epicardial adipose stores. Proinflammatory properties of epicardial adipose tissue were noted irrespective of clinical variables (diabetes, body mass index, and chronic use of statins or ACE inhibitors/angiotensin II receptor blockers) or plasma concentrations of circulating biomarkers. In a subset of samples (n=11), global gene expression was explored by DNA microarray hybridization and confirmed the presence of a broad inflammatory reaction in epicardial adipose tissue in patients with coronary artery disease. The above findings were paralleled by the presence of inflammatory cell infiltrates in epicardial adipose stores. Epicardial adipose tissue is a source of several inflammatory mediators in high-risk cardiac patients. Plasma inflammatory biomarkers may not adequately reflect local tissue inflammation. Current therapies do not appear to eliminate local inflammatory signals in epicardial adipose tissue.

While the link between obesity and type 2 diabetes is clear on an epidemiological level, the underlying mechanism linking these two common disorders is not as clearly understood. One hypothesis linking obesity to type 2 diabetes is the adipose tissue expandability hypothesis. The adipose tissue expandability hypothesis states that a failure in the capacity for adipose tissue expansion, rather than obesity per se is the key factor linking positive energy balance and type 2 diabetes. All individuals possess a maximum capacity for adipose expansion which is determined by both genetic and environmental factors. Once the adipose tissue expansion limit is reached, adipose tissue ceases to store energy efficiently and lipids begin to accumulate in other tissues. Ectopic lipid accumulation in non-adipocyte cells causes lipotoxic insults including insulin resistance, apoptosis and inflammation. This article discusses the links between adipokines, inflammation, adipose tissue expandability and lipotoxicity. Finally, we will discuss how considering the concept of allostasis may enable a better understanding of how diabetes develops and allow the rational design of new anti diabetic treatments. Copyright (c) 2009 Elsevier B.V. All rights reserved.