UC Davis

OBJECTIVE: The pharmacokinetic characteristics of human leptin were examined in rhesus monkeys and in C57BL/6J mice fed a normal chow or a high-fat diet.DESIGN: For the monkey study, in nine rhesus monkeys (body weight 12.4±2.4 kg; mean±s.d.), recombinant met-human leptin was injected intravenously or subcutaneously (1 mg/kg). For the mouse study, after 6 months of feeding C57BL/6J mice a high-fat diet (body weight 32.9±3.6 g; n=8) or a control diet (24.5±1.2 g; n=6), recombinant met-human leptin was administered intraperitoneally (10 μg/g). Blood samples were collected for leptin measurement at specific time points after leptin administration.MEASUREMENTS: Plasma leptin concentrations were determined by radioimmunoassay and pharmacokinetic analysis was performed.RESULTS: Disposition of human leptin in rhesus monkeys was biphasic following intravenous administration, with a terminal phase half-life of 96.4±16.5 min and clearance of 1.8±0.2 ml/min/kg. Subcutaneously administered leptin was absorbed slowly, perhaps by a zero-order process as leptin levels appeared to plateau and remained elevated throughout the 8 h sampling period. In C57BL/6J mice, the absorption and elimination of human leptin were both first-order following intraperitoneal administration. Pharmacokinetic parameters did not differ between normal-weight mice fed a chow diet and obese mice fed a high-fat diet. The elimination half-life was 47.0±26.4 min in mice fed a high-fat diet and 49.5±12.0 min in mice fed a control diet.CONCLUSION: The kinetics of leptin in rhesus monkeys were biphasic and clearance was similar to values previously reported in humans. The estimated half-life was 96.4 min in rhesus monkeys and 49.5 min in normal weight mice. The was no difference in leptin kinetics between high-fat fed and control mice, suggesting that the increased baseline leptin levels in the obese mice are due to increased leptin production and secretion.