Pharmacokinetics of Subcutaneous Recombinant Methionyl Human Leptin Administration in Healthy Subjects in the Fed and Fasting States
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Background: Recombinant methionyl human leptin (r-metHuLeptin) has demonstrated efficacy in improving hormonal and metabolic parameters in leptin-deficient states, and it has been suggested that leptin replacement may reverse metabolic adaptations during weight loss interventions. The pharmacokinetics of subcutaneously administered r-metHuLeptin have been recently published, but whether pharmacokinetic parameters are altered by short-term fasting, adiposity and/or gender has not yet been evaluated.
Objective: The objective of this study was to characterize pharmacokinetic parameters following subcutaneous r-metHuLeptin administration at doses in the physiological to supra-physiological to pharmacological range in the fed state and during 3-day complete fasting in lean and obese subjects, including both men and women.
Methods: We analysed pharmacokinetic profiles in five lean men, five obese men and five lean women following subcutaneous administration of physiological (0.01 mg/kg), supra-physiological (0.1 mg/kg) and pharmacological (0.3 mg/kg) doses of r-metHuLeptin given once in the fed state and once daily during 3-day complete caloric deprivation (fasting).
Results: With r-metHuLeptin administration at 0.01 mg/kg, leptin concentrations ranged up to ∼7 ng/mL in lean men, ∼20 ng/mL in obese men and ∼30 ng/mL in lean women in the fed state. There was a significant effect of 3-day fasting: it decreased baseline leptin concentrations, peak serum concentration (Cmax) and area under the serum concentration-time curve from time zero to infinity (AUC∞) [all p < 0.0001] and increased clearance (p < 0.001), most prominently in lean men (p < 0.0001 across the groups). Administration of r-metHuLeptin at 0.1 mg/kg resulted in leptin concentrations up to ∼70 ng/mL in lean men, ∼100 ng/mL in obese men and ∼150 ng/ mL in lean women in the fed state. At this dose, there was a similar effect of fasting on the pharmacokinetic parameters as well as a decrease in the terminal-phase elimination half-life (p = 0.02), consistent with increased clearance, but the effect of fasting was less pronounced overall than with the 0.01 mg/kg dose. With r-metHuLeptin administration at 0.3 mg/kg, leptin concentrations ranged up to ∼150 ng/mL in lean men, ∼300 ng/ mL in obese men and ∼400 ng/mL in lean women in the fed state. At this dose, fasting increased clearance to a lesser degree (p = 0.046), mainly in lean men, suggesting that the fasting-induced increase in leptin clearance by the kidneys can plateau. Within each group, the subjects lost ∼3–4 kg of bodyweight after 3 days of fasting (all p < 0.0001), but the amount and time course of weight loss did not differ according to the dose of r-metHuLeptin administered or the circulating leptin concentrations achieved.
Conclusions: Short-term fasting in healthy individuals results in increased clearance of leptin; this contributes to hypoleptinaemia, which may serve as a signal to increase energy intake in the setting of caloric restriction. Obese individuals with greater energy stores at baseline have a blunted response to the fasting-induced increase in leptin clearance. Also, women have a differential response to fasting, with primarily decreased leptin production rather than increased clearance. These findings and the resulting formulas for calculating doses for r-metHuLeptin administration have important implications for future therapeutic use of r-metHuLeptin in conjunction with hypocaloric diets for the treatment of obesity.
KeywordsPramlintide Lean Woman General Clinical Research Center Fasting Study Beth Israel Deaconess Medical Center
We gratefully thank the General Clinical Research Center (GCRC) nurses at Beth Israel Deaconess Medical Center (BIDMC) for assistance with collection of the samples for this research, and the GCRC nutritionists for assistance with the isocaloric diet and fasting studies. This study was supported by NIH grant no. M01-RR01032 to the BIDMC GCRC; NIH DK grant nos. R01-58785, R01-79929 and K24 81913 and an Amgen grant and a BIDMC discretionary grant to Christos Mantzoros; and NIH grant no. K23 RR018860 to Jean Chan. Christos Mantzoros has received honorarium for one lecture and grant support through BIDMC-Harvard from Amylin, Inc. Jean Chan and Shekman Wong have no conflicts of interest to report.
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