Leptin transport across the blood-brain barrier: implications for the cause and treatment of obesity.

Leptin has emerged as a major regulator of adiposity. Leptin is released into the blood from fat cells and circulates to the brain where it crosses the blood-brain barrier (BBB) to act at receptors within the central nervous system to affect appetite, thermogenesis, and a number of other actions. In humans and in many rodent models, resistance to leptin appears to be a chief cause of obesity. Determining the cause of leptin resistance is fundamental to developing strategies for the use of leptin in obesity. The literature characterizing the transport of leptin across the BBB is reviewed. This literature strongly suggests that the cause of leptin resistance is due a decreased transport of leptin across the BBB in obese humans and rodents. The main cause of this resistance appears to be an impairment in the activity of the transporter rather than just simply saturation at higher doses. Strategies to overcome impaired BBB transport are reviewed, including the use of allosteric regulators and the delivery of material by the intrathecal route.