Obesity, inflammation, and macrophages.

The World Health Organization estimates that since 1980 the prevalence of obesity has increased more than threefold throughout much of the world, and this increase is not limited to developed nations. Indeed, the incidence of obesity is increasing most rapidly among rapidly industrializing countries raising the spectre of a burgeoning epidemic in obesity-associated diseases, including diabetes, dyslipidemia, nonalcoholic fatty liver disease and atherosclerosis. Reducing the rates of obesity and its attendant complications will require both coordinated public health policy and a better understanding of the pathophysiology of obesity. Obesity is associated with low grade chronic inflammation, a common feature of many complications of obesity that appears to emanate in part from adipose tissue. In obese individuals and rodents adipose tissue macrophage accumulation is a critical component in the development of obesity-induced inflammation. The macrophages in adipose tissue are bone marrow-derived and their number is strongly correlated with bodyweight, body mass index and total body fat. The recruited macrophages in adipose tissue express high levels of inflammatory factors that contribute to systemic inflammation and insulin resistance. Interventions aimed at either reducing macrophage numbers or decreasing their inflammatory characteristics improves insulin sensitivity and decreases inflammation. Macrophage accumulation and adipose tissue inflammation are dynamic processes under the control of multiple mechanisms. Investigating the role of macrophages in adipose tissue biology and the mechanisms involved in their recruitment and activation in obesity will provide useful insights for developing therapeutic approaches to treating obesity-induced complications.