Pharmacokinetics of recombinant methionyl human leptin after subcutaneous administration: variation of concentration-dependent parameters according to assay.

CONTEXT: Recombinant human leptin (r-metHuLeptin) has demonstrated efficacy in improving hormonal and metabolic parameters in leptin-deficient states, but pharmacokinetic parameters after sc administration have not yet been published. In addition, the effect of potential variability across different leptin assays on concentration-dependent pharmacokinetic parameters remains unknown. OBJECTIVE: The objective of the study was to characterize pharmacokinetic parameters after sc r-metHuLeptin administration using three commercially available leptin assays (Linco, Diagnostic Systems Laboratories, and Alpco). DESIGN, SETTING, PATIENTS, AND INTERVENTION: We analyzed pharmacokinetic profiles in five lean and five obese men after sc administration of physiological (0.01 mg/kg) and pharmacological (0.3 mg/kg) doses of r-metHuLeptin. MAIN OUTCOME MEASURES: Leptin pharmacokinetic parameters were measured. RESULTS: Measurement of leptin produced typical pharmacokinetic profiles in all assays with time to maximal concentration and half-life of approximately 3 h. Diagnostic Systems Laboratories consistently measured leptin higher than Linco, with Alpco measuring intermediate between or similar to Linco. There was high correlation among assays (R(2) ranging from 0.89 to 0.98, all P < 0.01). Concentration-dependent parameters such as maximal concentration, area under the curve, and clearance were significantly different among assays, whereas concentration-independent parameters such as time to maximal concentration and half-life were generally not different. CONCLUSIONS: We report novel data on leptin pharmacokinetic parameters after sc administration, which will be relevant for the future therapeutic use of r-metHuLeptin. Although commercially available assays demonstrated high correlation, they can provide substantially different measures of leptin levels. This demonstrates the importance of standardizing leptin assays for diagnosing patients with relative leptin deficiency, determining appropriate doses of r-metHuLeptin for administration, and monitoring response to therapy.

Independent circadian and sleep/wake regulation of adipokines and glucose in humans.

Leptin and adiponectin play important physiological roles in regulating appetite, food intake, and energy balance and have pathophysiological roles in obesity and anorexia nervosa. To assess the relative contributions of day/night patterns in behaviors (sleep/wake cycle and food intake) and of the endogenous circadian pacemaker on observed day/night patterns of adipokines, in six healthy subjects we measured circulating leptin, soluble leptin receptor, adiponectin, glucose, and insulin levels throughout a constant routine protocol (38 h of wakefulness with constant posture, temperature, and dim light, as well as identical snacks every 2 h) and throughout sleep and fasting periods before and after the constant routine. There were significant endogenous circadian rhythms in leptin, glucose, and insulin, with peaks around the usual time of awakening. Sleep/fasting resulted in additional systematic decreases in leptin, glucose, and insulin, whereas wakefulness/food intake resulted in a systematic increase in leptin. Thus, the day/night pattern in leptin is likely caused by combined effects from the endogenous circadian pacemaker and day/night patterns in behaviors. Our data imply that alterations in the sleep/wake schedule would lead to an increased daily range in circulating leptin, with lowest leptin upon awakening, which, by influencing food intake and energy balance, could be implicated in the increased prevalence of obesity in the shift work population.

Serum adiponectin levels are inversely associated with overall and central fat distribution but are not directly regulated by acute fasting or leptin administration in humans: cross-sectional and interventional studies.

Adiponectin is an adipocyte-secreted protein that circulates in high concentrations in the serum and acts to increase insulin sensitivity. Previous studies have shown that serum adiponectin is inversely associated with fat mass and insulin resistance in humans and that acute fasting decreases adipose tissue adiponectin mRNA expression in rodents. Whether acute energy deprivation, body fat distribution, or serum hormone levels are associated with circulating adiponectin in humans remains largely unknown. To identify predictors of serum adiponectin levels, we evaluated the association of adiponectin with several anthropometric, metabolic, and hormonal variables in a cross-sectional study of 121 women without a known history of diabetes. We also performed interventional studies to assess whether fasting for 48 h and/or leptin administration regulates serum adiponectin in healthy men and women. Our cross-sectional study shows that, in addition to overall obesity, central fat distribution is an independent negative predictor of serum adiponectin and suggests that adiponectin may represent a link between central obesity and insulin resistance. In addition, estradiol is negatively and independently associated with adiponectin, whereas there is no association between serum adiponectin and leptin, cortisol, or free testosterone levels. Our interventional studies demonstrate that neither fasting for 48 h, resulting in a low leptin state, nor leptin administration at physiological or pharmacological doses alters serum adiponectin levels. Further studies are needed to fully elucidate the physiology of adiponectin in humans and its role in the pathogenesis of insulin-resistant states.

Circulating resistin levels are not associated with obesity or insulin resistance in humans and are not regulated by fasting or leptin administration: cross-sectional and interventional studies in normal, insulin-resistant, and diabetic subjects.

Resistin is a novel adipocyte-secreted hormone proposed to link obesity with diabetes. Studies in mice have revealed conflicting data however, and the physiological role of circulating resistin in humans remains unknown. We conducted cross-sectional studies in 123 middle-aged women and 120 healthy young subjects and found that serum resistin levels did not correlate with markers of adiposity, including body mass index, waist-to-hip ratio, or fat mass, or insulin resistance assessed by homeostasis model, lipid profile, or serum leptin levels; but females had higher resistin levels than males (P < 0.02). We also found no difference in serum resistin levels between lean healthy and obese insulin-resistant nondiabetic and type 2 diabetic adolescents. Finally, to evaluate the effect of food deprivation and/or leptin administration on resistin levels, we performed interventional studies that revealed no significant difference in resistin levels after 48 h of fasting and/or leptin administration at either physiological or pharmacological doses. We conclude that circulating resistin is unlikely to play a major role in insulin resistance or energy homeostasis in humans.

Increased leptin levels in preeclampsia: associations with BMI, estrogen and SHBG levels.

UNLABELLED: Leptin is secreted mainly by the white adipose tissue but is also synthesized in several non-adipose tissue organs including the placenta. Serum leptin levels are increased in normal pregnancies and are higher in preeclamptic than normal pregnant women. There is, however, a lack of empirical evidence of an independent association of serum leptin levels and preeclamsia. We have studied cross-sectionally 18 3rd trimester preeclamptic women, 28 3rd trimester and 30 2nd trimester control women to confirm the reported increase of serum leptin in preeclampsia and to assess whether elevated leptin levels in preeclampsia increase the variance explained by body mass index (BMI), androgens, estrogens and/or sex hormone binding globulin (SHBG). Anthropometric, demographic and hormonal data were analyzed using linear and logistic regression models. RESULTS: Leptin is significantly increased in preeclampsia by univariate analysis, but use of multivariate analysis indicates that the elevated leptin levels are not associated with preeclampsia independently from BMI, estrogens and SHBG. CONCLUSION: This study confirms that leptin levels are higher in women with preeclampsia than in controls and demonstrates that serum leptin levels do not add to the prediction of preeclampsia after accounting for BMI, estrogen and SHBG levels of preeclamptic women.

Effect of dieting on plasma leptin, soluble leptin receptor, adiponectin and resistin levels in healthy volunteers.

OBJECTIVE: Recent findings demonstrating important effects of the adipokines on metabolism, energy homeostasis and body weight regulation have prompted research on the possible role of negative energy balance in altering adipocytokine regulation. The goal of this study was to evaluate the effects of a hypocaloric diet in healthy normal-weight volunteers. An additional goal was to help clarify the contribution of restricted caloric intake to altered plasma adipokine levels in the eating disorders anorexia nervosa and bulimia nervosa. DESIGN: Participants were studied before and after a 4-week reduced-calorie diet (1000-12000 kcal/day). patients Subjects included 15 healthy, normal-weight women (age 22 +/- 3 years). MEASUREMENTS: Plasma concentrations of leptin, soluble leptin receptor protein (sOB-R), adiponectin, resistin, thyroid hormones and beta-hydroxybutyrate were determined following overnight fast before and after the 4-week reduced-calorie diet. RESULTS: Subjects lost a mean of 3.4 +/- 2.1 kg in response to the reduced-calorie diet. The weight loss phase was associated with a 60.3% decrease in plasma leptin levels (P < 0.001), a 43.5% increase in sOB-R levels (P < 0.002) and a 16.2% decrease in plasma adiponectin levels (P < 0.04). There was no significant change in plasma resistin levels. CONCLUSIONS: These results demonstrate that a modest decrease in energy intake sustained over several weeks may play an important role in altering levels of plasma leptin and sOB-R. The findings also provide preliminary evidence that, in contrast to previous results in obese subjects, caloric restriction with accompanying weight loss in healthy, normal-weight volunteers may lead to decreased circulating adiponectin levels. Additional studies will be needed to clarify the contribution of altered energy intake to abnormalities in cytokine levels in the eating disorders.