Secretory factors from human adipose tissue and their functional role.

Obesity is characterized by an expanded adipose tissue mass. Recent data suggest that adipose tissue is a multi-functional organ rather than simply a passive storage site for excess energy. It has been clearly demonstrated that human adipose tissue produces a variety of secretory factors that exert multiple effects at both the local and the systemic level. To date, >100 products, covering a broad range of protein families as well as many fatty acids and prostaglandins, have been reported to be secreted by adipose tissue. The source of these secreted factors is not only mature fat cells but also poorly-identified cells present in the stromal-vascular fraction including macrophages. Secreted factors of particular interest include many cytokines or chemokines, such as TNF-alpha, IL-6, IL-8, as well as plasminogen activator inhibitor-1, angiotensin-II, leptin, and adiponectin. In the obese state the expression and secretion of these factors is disturbed. With the exception of adiponectin, most circulating factors are elevated. From this perspective, obesity can be described as a pro-inflammatory condition. In addition, regional differences in adipose expression of many of these factors have been found. There is now growing evidence that many secretory factors play an important role in the pathophysiology of the metabolic and cardiovascular complications of obesity. The question arising from these observations is how the secretory pattern of adipose tissue can be modified by dietary and pharmacological measures to reduce the health risks of obesity.