Leptin antagonist reveals that the normalization of caloric intake and the thermic effect of food after high-fat feeding are leptin dependent

High-fat (HF) feeding induces a transient increase in caloric intake and enhances energy expenditure. We hypothesized that leptin is necessary for homeostatic restoration of the HF-enhanced caloric intake and may mediate the increase in uncoupling protein-1 (UCP1) in brown adipose tissue (BAT). We employed a leptin antagonist to examine the role of leptin in these biological processes. Simultaneous central administration of leptin and increasing doses of the leptin antagonist revealed a dose-dependent inhibition of leptin-induced hypothalamic signal transducer and activator of transcription-3 phosphorylation, and 7 days of infusion of the leptin antagonist produced the predicted increase in food intake and weight gain. When delivered with exogenous leptin in a 7-day infusion, the leptin antagonist blocked leptin-mediated anorexic effects as well as the increase in BAT UCP1 protein and signal transducer and activator of transcription-3 phosphorylation. Rats were then fed an HF diet (60% kcal as fat) or chow and simultaneously infused with antagonist (25 microg/day into the lateral ventricle) for 7 days and compared with vehicle-infused chow-fed rats. Daily caloric intake of both HF groups peaked on day 2. HF feeding elevated caloric intake, which nearly normalized by day 7, whereas in the presence of the antagonist, caloric intake remained elevated. Moreover, the HF-mediated augmentation in UCP1 in BAT was prevented by the antagonist. These results demonstrate that leptin is essential for the homeostatic restoration of caloric intake after HF feeding and that this leptin antagonist is able to block central leptin signaling and leptin-mediated UCP1 elevation.

Hypothalamic delivery of doxycycline-inducible leptin gene allows for reversible transgene expression and physiological responses

Our purpose was to incorporate regulation into the recombinant adeno-associated virus encoding leptin by introducing a tet-inducible promotor. This system, TET-Ob, allows for control of leptin gene expression via doxycycline in drinking water. F344XBN rats (aged 4 months) were given a hypothalamic injection of TET-Ob or control virus. During 34 days of doxycycline (doxy) administration to all rats (STAGE 1), TET-Ob rats gained 50.7% less mass, ate 10.4% less food, and had a 77.5% reduction in serum leptin as compared with controls. Doxy was then withdrawn from half of the TET-Ob rats for 32 days (TET-Ob-OFF), while half continued to receive doxy (TET-Ob-ON) (stage 2). During stage 2, TET-Ob-ON rats gained 44.8% less mass than TET-Ob-OFF and ate significantly less food than both TET-Ob-OFF and controls. Serum leptin increased to 83.4% of control values in TET-Ob-OFF, but remained very low in the in TET-Ob-ON. At death, visceral adiposity was 14.5% of controls in TET-Ob-ON animals, but had risen to 76.9% of controls in TET-Ob-OFF. A reversible increase in both leptin signal transduction in the hypothalamus and uncoupling protein expression in brown adipose was recorded. This system allows for more precise regulation of gene therapy-mediated fat loss.