Brown Adipose Tissue - The New Weapon to Fight Obesity?

Obesity develops when energy intake exceeds energy expenditure. Brown adipose tissue, in contrast to white adipose tissue, dissipates large amounts of chemical energy through a process called uncoupled respiration, which is mediated by uncoupling protein-1 (UCP-1). This mitochondrial process results in increased fatty acid oxidation and the generation of heat (thermogenesis). Given these functions, brown adipose tissue has recently emerged as an appealing target for enhanced energy expenditure to favor body weight loss and glucose metabolism. In fact, animal studies have demonstrated that the activation of brown adipose tissue or the acquisition of brown-fat characteristics within white adipose depots ("browning of white fat") can completely protect against obesity and related metabolic complications. In addition to classic white and brown adipose tissues, an intermediate type of fat has recently been described -"beige" or "brite" adipose tissue. UCP-1 expressing beige adipocytes can emerge within white-fat stores upon cold exposure, adrenergic stimulation, or distinct genetic alterations. Once activated, they possess similar thermogenic activity as brown adipocytes. The number of genetic and hormonal factors contributing to such a "browning" phenotype is constantly growing. Understanding the biology of beige/ brown adipose tissue development and function has gained additional signifi cance with the recent discovery that active brown fat is present in adult humans and can be detected by FDG-PET scan. However, to date, no pharmacological approaches exist to harness its energy-dissipating function in humans. Hence, the race is on for developing novel anti-obesity therapeutics targeting brown fat.