The recent rapid rise in the incidence of obesity has prompted investigations into understanding the hormonal and neuronal pathways involved in body weight homeostasis in order to devise novel therapeutic strategies. The early enthusiasm for the adipocyte hormone leptin as a regulator of fat mass was largely discarded because of the apparent development of leptin resistance, as seen in obese subjects with elevated blood leptin levels. We postulated that this leptin ineffectiveness may be caused by a lack of leptin availability at target sites in the hypothalamus. To test this hypothesis, we used viral vectors to introduce the leptin gene into the brain for a sustained supply of leptin in the hypothalamus. A single injection of recombinant adeno-associated virus encoding the leptin gene (rAAV-lep) into the third cerebroventricle prevented the aging-associated gradual increase in body weight and adiposity in adult rats for 6 months of the experiment. When administered to prepubertal rats, significantly lower body weight gain and adiposity were maintained for up to 10 months of the experiment. In addition, obesity was prevented in rats introduced to a high-fat diet and also reversed in obese-prone rats maintained on a high-fat diet. Body weight homeostasis and loss of adiposity by leptin gene therapy was achieved by an increase in energy expenditure, and when the rAAV-lep titer was increased, there was also a voluntary reduction in food intake. Importantly, this therapy reduced blood levels of insulin, triglycerides and free fatty acids, the pathophysiologic correlates of the metabolic syndrome. Thus, the long-term beneficial effects of central leptin gene therapy may herald the development of newer therapeutic strategies to control the epidemic of obesity and related metabolic disorders.
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