The role of falling leptin levels in the neuroendocrine and metabolic adaptation to short-term starvation in healthy men

Leptin deficiency: clinical implications and opportunities for therapeutic interventions

The discovery of leptin has significantly advanced our understanding of the metabolic importance of adipose tissue and has revealed that both leptin deficiency and leptin excess are associated with severe metabolic, endocrine, and immunological consequences. We and others have shown that a prominent role of leptin in humans is to mediate the neuroendocrine adaptation to energy deprivation. Humans with genetic mutations in the leptin and leptin receptor genes have deregulated food intake and energy expenditure leading to a morbidly obese phenotype and a disrupted regulation in neuroendocrine and immune function and in glucose and fat metabolism. Observational and interventional studies in humans with (complete) congenital leptin deficiency caused by mutations in the leptin gene or with relative leptin deficiency as seen in states of negative energy balance such as lipoatrophy, anorexia nervosa, or exercise-induced hypothalamic and neuroendocrine dysfunction have contributed to the elucidation of the pathophysiological role of leptin in these conditions and of the clinical significance of leptin administration in these subjects. More specifically, interventional studies have demonstrated that several neuroendocrine, metabolic, or immune disturbances in these states could be restored by leptin administration. Leptin replacement therapy is currently available through a compassionate use program for congenital complete leptin deficiency and under an expanded access program to subjects with leptin deficiency associated with congenital or acquired lipoatrophy. In addition, leptin remains a potentially forthcoming treatment for several other states of energy deprivation including anorexia nervosa or milder forms of hypothalamic amenorrhea pending appropriate clinical trials.

Interleukin-6 and leptin as markers of energy metabolic changes in advanced ovarian cancer patients

The progression of the neoplastic disease is characterized by specific alterations of energy metabolism and by symptoms like fatigue, anorexia, nausea, anaemia, immunodepression and poor performance status (PS). The main cause of these symptoms and metabolic abnormalities is the chronic action of proinflammatory cytokines released both by tumour and immune cells. The present study aimed to assess the relationship between markers of inflammation (C-Reactive Protein, Fibrinogen, proinflammatory cytokines) and energy metabolic status (BMI, leptin, oxidative stress) according to clinical parameters in 104 ovarian cancer patients at different stage and, moreover, to evaluate prospectively the changes of these parameters in accordance to tumour response in a subgroup of 70 advanced stage ovarian cancer patients. Advanced stage and poor PS were associated to high-grade inflammation and impaired energy metabolism. Among inflammatory mediators, interleukin (IL)-6 had a central role as predictive factor of leptin, reactive oxygen species and glutathione peroxidase. In turn, leptin considered the key marker of the nutritional status and energy metabolism, was independently determined from stage and IL-6, not only from BMI. Moreover, the evaluation of the changes of these parameters during the course of the neoplastic disease in the subgroup of advanced ovarian cancer patients clearly unveils the central role of IL-6 and leptin as early markers of the metabolic alterations and symptoms associated to disease progression in advanced stage ovarian cancer. Their assessment should be included in monitoring disease outcome, especially when cancer is no longer curable and quality of life becomes the primary endpoint.

Overtrained horses alter their resting pulsatile growth hormone secretion

The influence of intensified and reduced training on nocturnal growth hormone (GH) secretion and elimination dynamics was studied in young (1.5 yr) Standardbred geldings to detect potential markers indicative for early overtraining. Ten horses trained on a treadmill for 32 wk in age-, breed-, and gender-matched fixed pairs. Training was divided into four phases (4, 18, 6, and 4 wk, respectively): 1) habituation to high-speed treadmill trotting, 2) normal training, in which speed and duration of training sessions were gradually increased, 3) in this phase, the horses were divided into 2 groups: control (C) and intensified trained (IT) group. In IT, training intensity, duration, and frequency were further increased, whereas in control these remained unaltered, and 4) reduced training (RT). At the end of phases 2, 3, and 4, blood was sampled overnight every 5 min for 8 h for assessment of GH secretory dynamics using pulse detection, deconvolution analysis, and approximate entropy (ApEn). Intensified training induced overtraining (performance decreased by 19% compared with C), which was associated with an increase in concentration peaks number (3.6 vs. 2.0, respectively), a smaller peak secretion pattern with a prolonged half-life (15.2 vs. 7.3 min, respectively), and an increased ApEn (0.89 vs. 0.49, respectively). RT did not lead to full recovery for the overtrained horses. The increased irregularity of nocturnal GH pulsatility pattern is indicative of a loss of coordinated control of GH regulation. Longer phases of somatostatin withdrawal are hypothesized to be the underlying mechanism for the observed changes in GH pulsatility pattern.

The ventral premammillary nucleus links fasting-induced changes in leptin levels and coordinated luteinizing hormone secretion

Physiological conditions of low leptin levels like those observed during negative energy balance are usually characterized by the suppression of luteinizing hormone (LH) secretion and fertility. Leptin administration restores LH levels and reproductive function. Leptin action on LH secretion is thought to be mediated by the brain. However, the neuronal population that mediates this effect is still undefined. The hypothalamic ventral premammillary nucleus (PMV) neurons express a dense concentration of leptin receptors and project to brain areas related to reproductive control. Therefore, we hypothesized that the PMV is well located to mediate leptin action on LH secretion. To test our hypothesis, we performed bilateral excitotoxic lesions of the PMV in adult female rats. PMV-lesioned animals displayed a clear disruption of the estrous cycle, remaining in anestrus for 15-20 d. After apparent recovery of cyclicity, animals perfused in the afternoon of proestrus showed decreased Fos immunoreactivity in the anteroventral periventricular nucleus and in gonadotropin releasing hormone neurons. PMV-lesioned animals also displayed decreased estrogen and LH secretion on proestrus. Lesions caused no changes in mean food intake and body weight up to 7 weeks after surgery. We further tested the ability of leptin to induce LH secretion in PMV-lesioned fasted animals. We found that complete lesions of the PMV precluded leptin stimulation of LH secretion on fasting. Our findings demonstrate that the PMV is a key site linking changing levels of leptin and coordinated control of reproduction.

Prospective study of gut hormone and metabolic changes after adjustable gastric banding and Roux-en-Y gastric bypass

Objective

The objective of this study was to quantify hormones that regulate energy and glucose homeostasis in order to establish possible mechanisms for the greater efficacy of Roux-en-Y gastric bypass (RYGB) compared with laparascopic adjustable gastric banding (LAGB) in achieving weight loss and improved insulin sensitivity.

Design

Longitudinal study of patients undergoing LAGB (n=15) and RYGB (n=28) who were studied prior to surgery and at 2, 12, 26 and 52 wks afterwards.

Measurements

Fasting blood samples were drawn at each visit. Postprandial blood samples were also obtained prior to surgery and at 26 and 52 wks. Samples were assayed for peptide YY (PYY), ghrelin, glucagon-like peptide-1 (GLP-1), glucose, insulin, leptin, thyrotropic hormone (TSH), free T₄ and free T₃.

Results

At one year there was greater weight loss in RYGB compared with LAGB patients (30% vs 15%), but final body mass index was similar (34 vs 33 kg/m²). At wk 52, area under the curve (AUC) for PYY in RYGB subjects was greater than LAGB (P<0.01). GLP-1 levels at 30 min post-meal were three-fold greater after RYGB compared with LAGB (P<0.001). Conversely, ghrelin AUC increased after LAGB at wk 52 (P<0.05) but tended to decrease after RYGB. Fasting glucose, insulin, and leptin, and HOMA-IR decreased in both groups over time but were significantly lower at wk 52 after RYGB compared with LAGB. The change in leptin correlated significantly with weight loss in LAGB (r=0.86) and RYGB (r=0.77), however, HOMA-IR correlated significantly with weight loss only in LAGB (r=0.78), and not RYGB (r=0.15). There was a significant decrease in free T₃ (P<0.01) after RYGB.

Conclusions

Differences in levels of gut hormones may play a role in promoting greater weight loss and insulin sensitivity after RYGB compared with LAGB, however, weight loss may be limited by decreases in free T₃ and leptin.

The endocrinopathies of anorexia nervosa

OBJECTIVE

To describe the hormonal adaptations and alterations in anorexia nervosa.

METHODS

We performed a PubMed search of the English-language literature related to the pathophysiology of the endocrine disorders observed in anorexia nervosa, and we describe a case to illustrate these findings.

RESULTS

Anorexia nervosa is a devastating disease with a variety of endocrine manifestations. The effects of starvation are extensive and negatively affect the pituitary gland, thyroid gland, adrenal glands, gonads, and bones. Appetite is modulated by the neuroendocrine system, and characteristic patterns of leptin and ghrelin concentrations have been observed in anorexia nervosa. A thorough understanding of refeeding syndrome is imperative to nutrition rehabilitation in these patients to avoid devastating consequences. Although most endocrinopathies associated with anorexia nervosa reverse with recovery, short stature, osteoporosis, and infertility may be long-lasting complications. We describe a 20-year-old woman who presented with end-stage anorexia nervosa whose clinical course reflects the numerous complications caused by this disease.

CONCLUSIONS

The effects of severe malnutrition and subsequent refeeding are extensive in anorexia nervosa. Nutrition rehabilitation is the most appropriate treatment for these patients; however, it must be done cautiously.

Leptin in humans: lessons from translational research

Leptin has emerged over the past decade as a key hormone in not only the regulation of food intake and energy expenditure but also in the regulation of neuroendocrine and immune function as well as the modulation of glucose and fat metabolism as shown by numerous observational and interventional studies in humans with (complete) congenital or relative leptin deficiency. These results have led to proof-of-concept studies that have investigated the effect of leptin administration in subjects with complete (congenital) leptin deficiency caused by mutations in the leptin gene as well as in humans with relative leptin deficiency, including states of lipoatrophy or negative energy balance and neuroendocrine dysfunction, as for instance seen with hypothalamic amenorrhea in states of exercise-induced weight loss. In those conditions, most neuroendocrine, metabolic, or immune disturbances can be restored by leptin administration. Leptin replacement therapy is thus a promising approach in several disease states, including congenital complete leptin deficiency, states of energy deprivation, including anorexia nervosa or milder forms of hypothalamic amenorrhea, as well as syndromes of insulin resistance seen in conditions such as congenital or acquired lipodystrophy. In contrast, states of energy excess such as garden-variety obesity are associated with hyperleptinemia that reflects either leptin tolerance or leptin resistance. For those conditions, development of leptin sensitizers is currently a focus of pharmaceutical research. This article summarizes our current understanding of leptin's role in human physiology and its potential role as a novel therapeutic option in human disease states associated with a new hormone deficiency, ie, leptin deficiency.

r-metHuLeptin improves highly active antiretroviral therapy-induced lipoatrophy and the metabolic syndrome, but not through altering circulating IGF and IGF-binding protein levels: observational and interventional studies in humans

OBJECTIVE

Leptin is an adipocyte secreted hormone and an important regulator of neuroendocrine, metabolic, and immune function. Both r-metHuLeptin and IGF1 administration result in reduced central adipose tissue in subjects with highly active antiretroviral therapy-induced metabolic syndrome (HAART-MS) but whether the effects of leptin are mediated through increasing IGF levels remains unknown.

METHODS

To assess whether r-metHuLeptin improves the HAART-MS by regulating circulating IGF and IGFBPs, we first conducted a cross-sectional study of 118 men and women with HIV infection and >6 months of exposure to antiretroviral medications to examine any association between circulating IGF1 and leptin levels. We also performed a randomized, double-blinded, placebo-controlled, crossover trial of recombinant human leptin (r-metHuLeptin) administration to seven HIV positive men with lipoatrophy and leptin deficiency (leptin <3 ng/ml) related to antiretroviral medication use.

RESULTS

In the observational study, leptin levels were inversely associated with circulating IGF1 levels after adjusting for age and gender (r=0.27 P=0.002), but this inverse association became non-significant after adjustment for % body fat and exercise. In the interventional leptin study, leptin levels increased significantly during r-metHuLeptin treatment (from 1.34+/-0.20 ng/ml at baseline to 17+/-5.05 ng/ml after 8 weeks P=0.046) and metabolic parameters improved including reduced fasting insulin levels and reduced homeostasis model assessment-insulin resistance (HOMA-IR). Despite the increase in circulating leptin levels, there was no change in IGF1, IGF2, free IGF1, or IGF-binding proteins during the 2-month treatment period.

CONCLUSION

The effects of r-metHuLeptin in patients with HAART-MS are not mediated through increasing IGF or IGFBP levels.

Cord blood leptin and adiponectin as predictors of adiposity in children at 3 years of age: a prospective cohort study

OBJECTIVES

Leptin and adiponectin are adipocyte-secreted hormones that regulate energy homeostasis and metabolism. Because their roles in the neonatal period and in early childhood are poorly understood, we aimed in this prospective cohort study to determine the extent to which umbilical cord blood leptin and adiponectin concentrations predict measures of adiposity and growth at 3 years of age.

PATIENTS AND METHODS

We studied 588 children participating in the prospective prebirth cohort study Project Viva. We examined associations of cord blood leptin and adiponectin levels with weight changes during the first 6 months of life, 3-year circulating leptin and adiponectin concentrations, and the following adiposity-related outcomes at 3 years of age: BMI z score, height-for-age z score, and sums of triceps and subscapular skinfold thicknesses to represent overall adiposity, as well as subscapular/triceps skinfold ratio to represent central adiposity.

RESULTS

Cord blood leptin and adiponectin were each directly associated with the duration of gestation and birth weight for gestational age z scores. Cord blood leptin levels were negatively associated with change in weight-for-length, weight-for-age, and length-for-age z scores between birth and 6 months of age. Similarly, cord blood adiponectin was negatively associated with change in weight-for-length and weight-for-age z scores. After adjusting for several maternal and child factors related to obesity, each 10 ng/mL increment of cord blood leptin was associated with a reduction in BMI z score and higher leptin levels at 3 years but not with skinfold thicknesses. Each 10 microg/mL increment of cord blood adiponectin was positively associated with a higher subscapular skinfold thickness/triceps skinfold thickness ratio at 3 years.

CONCLUSIONS

Lower cord blood leptin levels are associated with smaller size at birth but more pronounced weight gain in the first 6 months of life and higher BMI at 3 years of age. Cord blood adiponectin levels are also directly associated with birth weight for gestational age, inversely associated with weight gain in the first 6 months of life, and predict an increase in central adiposity at age 3 years.

Pharmacokinetics of subcutaneous recombinant methionyl human leptin administration in healthy subjects in the fed and fasting states: regulation by gender and adiposity

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 approximately 7 ng/mL in lean men, approximately 20 ng/mL in obese men and approximately 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 (C(max)) and area under the serum concentration-time curve from time zero to infinity (AUC(infinity)) [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 approximately 70 ng/mL in lean men, approximately 100 ng/mL in obese men and approximately 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 approximately 150 ng/mL in lean men, approximately 300 ng/mL in obese men and approximately 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 approximately 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.

Motivations and methods for analyzing pulsatile hormone secretion

Endocrine glands communicate with remote target cells via a mixture of continuous and intermittent signal exchange. Continuous signaling allows slowly varying control, whereas intermittency permits large rapid adjustments. The control systems that mediate such homeostatic corrections operate in a species-, gender-, age-, and context-selective fashion. Significant progress has been made in understanding mechanisms of adaptive interglandular signaling in vivo. Principal goals are to understand the physiological origins, significance, and mechanisms of pulsatile hormone secretion. Key analytical issues are: 1) to quantify the number, size, shape, and uniformity of pulses, nonpulsatile (basal) secretion, and elimination kinetics; 2) to evaluate regulation of the axis as a whole; and 3) to reconstruct dose-response interactions without disrupting hormone connections. This review will focus on the motivations driving and the methodologies used for such analyses.

Revisiting leptin's role in obesity and weight loss

Maintenance of weight loss is often unsuccessful because of metabolic adaptations that conserve energy. Studies in rodents suggest that a reduction in leptin level during weight loss signals to the brain to increase feeding and decrease energy expenditure. In this issue of the JCI, Rosenbaum et al. examined this concept in obese patients who lost weight and were maintained at 10% below their initial weight (see the related article beginning on page 2583). Brain activity responses to visual food stimuli were visualized using functional MRI. Leptin levels fell during weight loss and increased brain activity in areas involved in emotional, cognitive, and sensory control of food intake. Restoration of leptin levels maintained weight loss and reversed the changes in brain activity. Thus, leptin is a critical factor linking reduced energy stores to eating behavior. Potentially, leptin therapy could sustain weight loss by overriding the tendency toward energy conservation.

Leptin replacement improves cognitive development

Background

Leptin changes brain structure, neuron excitability and synaptic plasticity. It also regulates the development and function of feeding circuits. However, the effects of leptin on neurocognitive development are unknown.

Objective

To evaluate the effect of leptin on neurocognitive development.

Methodology

A 5-year-old boy with a nonconservative missense leptin gene mutation (Cys-to-Thr in codon 105) was treated with recombinant methionyl human leptin (r-metHuLeptin) at physiologic replacement doses of 0.03 mg/kg/day. Cognitive development was assessed using the Differential Ability Scales (DAS), a measure of general verbal and nonverbal functioning; and selected subtests from the NEPSY, a measure of neuropsychological functioning in children.

Principal Findings

Prior to treatment, the patient was morbidly obese, hypertensive, dyslipidemic, and hyperinsulinemic. Baseline neurocognitive tests revealed slower than expected rates of development (developmental age lower than chronological age) in a majority of the areas assessed. After two years, substantial increases in the rates of development in most neurocognitive domains were apparent, with some skills at or exceeding expectations based on chronological age. We also observed marked weight loss and resolution of hypertension, dyslipidemia and hyperinsulinemia.

Conclusions

We concluded that replacement with r-metHuLeptin is associated with weight loss and changes in rates of development in many neurocognitive domains, which lends support to the hypothesis that, in addition to its role in metabolism, leptin may have a cognitive enhancing role in the developing central nervous system.

Trial Registration

ClinicalTrials.gov NCT00659828

Role and regulation of adipokines during zymosan-induced peritoneal inflammation in mice

Adipokines, cytokines mainly produced by adipocytes, are active participants in the regulation of inflammation. Administration of zymosan (ZY) was used to investigate the regulation and role of adipokines during peritonitis in mice. Injection of ZY led to a significant increase in leptin levels in both serum and peritoneal lavage fluid, whereas a differential trend in local vs. systemic levels was observed for both resistin and adiponectin. The role of leptin in ZY-induced peritonitis was investigated using leptin-deficient ob/ob mice, with and without reconstitution with exogenous leptin. Leptin deficiency was associated with delayed resolution of peritoneal inflammation induced by ZY, because ob/ob mice had a more pronounced cellular infiltrate in the peritoneum as well as higher and prolonged local and systemic levels of IL-6, TNFalpha, IL-10, and chemokine (C-X-C motif) ligand 2 compared with wild-type mice. Reconstitution with exogenous leptin exacerbated the inflammatory infiltrate and systemic IL-6 levels in ob/ob mice while inhibiting production of TNFalpha, IL-10, and chemokine (C-X-C motif) ligand 2. In contrast with the important role of leptin in regulating each aspect of ZY-induced peritonitis, adiponectin deficiency was associated only with a decreased inflammatory infiltrate, without affecting cytokine levels. These findings point to a complex role for adipokines in ZY-induced peritonitis and further emphasize the interplay between obesity and inflammation.

Caloric restriction: impact upon pituitary function and reproduction

Reduced energy intake, or caloric restriction (CR), is known to extend life span and to retard age-related health decline in a number of different species, including worms, flies, fish, mice and rats. CR has been shown to reduce oxidative stress, improve insulin sensitivity, and alter neuroendocrine responses and central nervous system (CNS) function in animals. CR has particularly profound and complex actions upon reproductive health. At the reductionist level the most crucial physiological function of any organism is its capacity to reproduce. For a successful species to thrive, the balance between available energy (food) and the energy expenditure required for reproduction must be tightly linked. An ability to coordinate energy balance and fecundity involves complex interactions of hormones from both the periphery and the CNS and primarily centers upon the master endocrine gland, the anterior pituitary. In this review article we review the effects of CR on pituitary gonadotrope function and on the male and female reproductive axes. A better understanding of how dietary energy intake affects reproductive axis function and endocrine pulsatility could provide novel strategies for the prevention and management of reproductive dysfunction and its associated comorbidities.

Leptin does not mediate short-term fasting-induced changes in growth hormone pulsatility but increases IGF-I in leptin deficiency states

CONTEXT

States of acute and chronic energy deficit are characterized by increased GH secretion and decreased IGF-I levels.

OBJECTIVE

The objective of the study was to determine whether changes in levels of leptin, a key mediator of the adaptation to starvation, regulate the GH-IGF system during energy deficit.

DESIGN, SETTING, PATIENTS, AND INTERVENTION

We studied 14 healthy normal-weight men and women during three conditions: baseline fed and 72-h fasting (to induce hypoleptinemia) with administration of placebo or recombinant methionyl human leptin (r-metHuLeptin) (to reverse the fasting associated hypoleptinemia). We also studied eight normal-weight women with exercise-induced chronic energy deficit and hypothalamic amenorrhea at baseline and during 2-3 months of r-metHuLeptin treatment.

MAIN OUTCOME MEASURES

GH pulsatility, IGF levels, IGF and GH binding protein (GHBP) levels were measured.

RESULTS

During short-term energy deficit, measures of GH pulsatility and disorderliness and levels of IGF binding protein (IGFBP)-1 increased, whereas leptin, insulin, IGF-I (total and free), IGFBP-4, IGFBP-6, and GHBP decreased; r-metHuLeptin administration blunted the starvation-associated decrease of IGF-I. In chronic energy deficit, total and free IGF-I, IGFBP-6, and GHBP levels were lower, compared with euleptinemic controls; r-metHuLeptin administration had no major effect on GH pulsatility after 2 wk but increased total IGF-I levels and tended to increase free IGF-I and IGFBP-3 after 1 month.

CONCLUSIONS

The GH/IGF system changes associated with energy deficit are largely independent of leptin deficiency. During acute energy deficit, r-metHuLeptin administration in replacement doses blunts the starvation-induced decrease of IGF-I, but during chronic energy deficit, r-metHuLeptin administration increases IGF-I and tends to increase free IGF-I and IGFBP-3.

Leptin does not directly regulate the pancreatic hormones amylin and pancreatic polypeptide: interventional studies in humans

OBJECTIVE

Leptin and the pancreatic hormones amylin and pancreatic polypeptide are being evaluated alone or in combination for the treatment of obesity, but their physiological regulation has not yet been fully elucidated. Thus, we examined whether amylin and pancreatic polypeptide are regulated by caloric intake and/or short- and long-term energy deprivation and whether any potential regulation is mediated by changes in leptin levels.

RESEARCH DESIGN AND METHODS

We measured circulating levels of amylin and pancreatic polypeptide after 1) a 75-g glucose load in 28 healthy, normal-weight women, 2) 72-h complete energy deficiency (severe hypoleptinemia) with administration of either placebo or replacement-dose recombinant methionyl human leptin (r-metHuLeptin) in normal-weight men (n = 6) and women (n = 7), and 3) chronic mild energy deficiency (mild hypoleptinemia) in 7 women with hypothalamic amenorrhea before and after r-metHuLeptin administration for 3 months.

RESULTS

Amylin and pancreatic polypeptide levels increased 15 min after a 75-g glucose load and remained elevated at 60 and 120 min (P < 0.0001). Fasting for 72 h decreased leptin (to 21%) and amylin (to 67%) of baseline but not pancreatic polypeptide levels. Normalizing leptin levels with r-metHuLeptin did not alter the fasting-induced decrease in amylin and had no effect on pancreatic polypeptide levels. Neither amylin nor pancreatic polypeptide levels were different in leptin-deficient women with hypothalamic amenorrhea compared with weight-matched control subjects, and normalization of leptin levels with r-metHuLeptin treatment did not alter amylin or pancreatic polypeptide levels.

CONCLUSIONS

Circulating amylin levels increase after a glucose load and decrease in response to short-term complete fasting, but these changes are not mediated by leptin.

Catch-up growth following fetal growth restriction promotes rapid restoration of fat mass but without metabolic consequences at one year of age

Background

Fetal growth restriction (FGR) followed by rapid weight gain during early life has been suggested to be the initial sequence promoting central adiposity and insulin resistance. However, the link between fetal and early postnatal growth and the associated anthropometric and metabolic changes have been poorly studied.

Methodology/Principal Findings

Over the first year of post-natal life, changes in body mass index, skinfold thickness and hormonal concentrations were prospectively monitored in 94 infants in whom the fetal growth velocity had previously been measured using a repeated standardized procedure of ultrasound fetal measurements. 45 infants, thinner at birth, had experienced previous FGR (FGR+) regardless of birth weight. Growth pattern in the first four months of life was characterized by greater change in BMI z-score in FGR+ (+1.26+/−1.2 vs +0.58 +/−1.17 SD in FGR−) resulting in the restoration of BMI and of fat mass to values similar to FGR−, independently of caloric intakes. Growth velocity after 4 months was similar and BMI z-score and fat mass remained similar at 12 months of age. At both time-points, fetal growth velocity was an independent predictor of fat mass in FGR+. At one year, fasting insulin levels were not different but leptin was significantly higher in the FGR+ (4.43+/−1.41 vs 2.63+/−1 ng/ml in FGR−).

Conclusion

Early catch-up growth is related to the fetal growth pattern itself, irrespective of birth weight, and is associated with higher insulin sensitivity and lower leptin levels after birth. Catch-up growth promotes the restoration of body size and fat stores without detrimental consequences at one year of age on body composition or metabolic profile. The higher leptin concentration at one year may reflect a positive energy balance in children who previously faced fetal growth restriction.

Adipokines and the peripheral and neural control of energy balance

Adipokines are secreted by adipose tissue and control various physiological systems. Low leptin levels during fasting stimulate feeding, reduce energy expenditure, and modulate neuroendocrine and immune function to conserve energy stores. On the other hand, rising leptin levels in the overfed state prevent weight gain by inhibiting food intake and increasing energy expenditure. These actions are mediated by neuronal circuits in the hypothalamus and brainstem. Leptin also controls glucose and lipid metabolism by targeting enzymes such as AMP-activated protein kinase and stearoyl-coenzyme A desaturase-1 in liver and muscle. Likewise, adiponectin and resistin control energy balance and insulin sensitivity via central and peripheral targets. As highlighted in this review, there are distinct as well as common signaling pathways for adipokines. Understanding adipokine signaling in the brain and other organs will provide insights into the pathogenesis and treatment of obesity, diabetes and various metabolic disorders.

Central dysregulations in the control of energy homeostasis and endocrine alterations in anorexia and bulimia nervosa

In the last decades we have come to understand that the hypothalamus is a key region in controlling energy homeostasis. A number of control models have been proposed to explain the regulation of feeding behavior in physiological and pathological conditions, but all those based on imbalances of single factors fail to explain the disrupted regulation of energy supply in eating disorders such as anorexia nervosa and bulimia nervosa, as well as other psychiatric disorders. A growing amount of evidence demonstrates that many signaling molecules originated within the brain or coming from the adipose tissue or the gastro-enteric tract are involved in the highly complex process controlling food intake and energy expenditure. The recent discovery of leptin, ghrelin, and other factors have made it possible to penetrate in the still undefined pathophysiology of eating disorders with the hope of finding effective treatments for such diseases.

Alterations in the autonomic control of heart rate variability in patients with anorexia or bulimia nervosa: correlations between sympathovagal activity, clinical features, and leptin levels

Changes in body composition, hormone secretions, and heart function with increased risk of sudden death occur in eating disorders. In this observational clinical study, we evaluated sympathovagal modulation of heart rate variability (HRV) and cardiovascular changes in response to lying-to-standing in patients with anorexia (AN) or bulimia nervosa (BN) to analyze: a) differences in autonomic activity between AN, BN, and healthy subjects; b) relationships between autonomic and cardiovascular parameters, clinical data and leptin levels in patients with eating disorders. HRV, assessed by power spectral analysis of R-R intervals, blood pressure (BP) and heart rate (HR) were studied by tilt-table test in 34 patients with AN, 16 with BN and 30 healthy controls. Autonomic and cardiovascular findings were correlated with clinical data, and serum leptin levels. Leptin levels were lowered in AN vs BN and healthy subjects (p<0.0001), but both AN and BN patients showed unbalanced sympathovagal control of HRV due to relative sympathetic failure, prevalent vagal activity, impaired sympathetic activation after tilting, independently from their actual body weight and leptin levels. No significant correlations were obtained between HRV data vs clinical data, BP and HR findings, and leptin levels in eating disorders. Body mass indices (BMI) (p<0.02), and leptin levels (p<0.04) correlated directly with BP values. Our data showed alterations of sympathovagal control of HRV in eating disorders. These changes were unrelated to body weight and BMI, diagnosis of AN or BN, and leptin levels despite the reported effects of leptin on the sympathetic activity.

The neuroendocrine physiology of kisspeptin in the human

Kisspeptin is a 54-amino acid peptide, encoded by the KiSS-1 gene, which activates the G protein-coupled receptor GPR54. Recent evidence suggests the kisspeptin/GPR54 system is a key regulator of reproduction. GPR54-deficient mice have abnormal sexual development. Central or peripheral administration of kisspeptin stimulates the hypothalamic-pituitary-gonadal (HPG) axis in animal models. This review discusses the evidence that kisspeptin also plays a key role in human reproduction. Inactivating GPR54 mutations cause normosmic hypogonadotrophic hypogonadism in humans. Mutations which increase GPR54 signaling are associated with gonadotrophin-dependent premature puberty. Acute intravenous administration of kisspeptin to healthy human male volunteers potently increased plasma LH levels and significantly increased plasma FSH and testosterone without side effects. Plasma kisspeptin is found at low concentrations in the circulation of men and non-pregnant women, but is markedly increased in pregnancy. The placenta is believed to be the source of these high levels of circulating kisspeptin. The kisspeptin-GPR54 system is also implicated in tumour biology. Consistent with this role, plasma kisspeptin concentrations are elevated in patients with abnormal proliferation of placental tissue (gestational trophoblastic neoplasia or GTN) at presentation and fall after treatment with chemotherapy. The kisspeptin/GPR54 system therefore appears to play an important role in the regulation of reproduction in humans. Kisspeptin represents a novel tool for the manipulation of the HPG axis in humans and plasma kisspeptin may be a novel tumour marker in patients with GTN.

Deiodinases: implications of the local control of thyroid hormone action

The deiodinases activate or inactivate thyroid hormone, and their importance in thyroid hormone homeostasis has become increasingly clear with the availability of deiodinase-deficient animals. At the same time, heightened interest in the field has been generated following the discovery that the type 2 deiodinase can be an important component in both the Hedgehog signaling pathway and the G protein-coupled bile acid receptor 1-mediated (GPBAR1-mediated) signaling cascade. The discovery of these new roles for the deiodinases indicates that tissue-specific deiodination plays a much broader role than once thought, extending into the realms of developmental biology and metabolism.

Towards a pro-inflammatory and immunomodulatory emerging role of leptin

Leptin is a 16 kDa adipocyte-secreted hormone that regulates weight centrally and links nutritional status with neuroendocrine and immune function. Since its cloning in 1994, leptin's role in regulating immune and inflammatory response has become increasingly evident. Actually, the increase of leptin production that occurs during infection and inflammation strongly suggests that leptin is a part of the cytokines loop which governs the inflammatory-immune response and the host defence mechanism. Indeed, leptin stimulates the production of pro-inflammatory cytokines from cultured monocytes and enhances the production of Th1 type cytokines from stimulated lymphocytes. Several studies have implicated leptin in the pathogenesis of autoimmune inflammatory conditions such as type 1 diabetes, rheumatoid arthritis and chronic bowel disease. Obesity is characterized by elevated circulating leptin levels which might contribute significantly to the so called low-grade systemic inflammation, making obese individuals more susceptible to the increased risk of developing cardiovascular diseases, type II diabetes or inflammatory articular degenerative disease such as osteorathritis (OA). As a matter of fact, a key role for leptin in OA has been recently demonstrated since leptin exhibits, in synergy with other pro-inflammatory cytokines, a detrimental effect on articular cartilage cells by promoting nitric oxide synthesis. This review will focus prevalently on the complex relationships existing among leptin, inflammatory response and immunity, trying to provide surprising insights into leptin's role and to discuss challenges and prospects for the future.

Differential regulation of metabolic, neuroendocrine, and immune function by leptin in humans

To elucidate whether the role of leptin in regulating neuroendocrine and immune function during short-term starvation in healthy humans is permissive, i.e., occurs only when circulating leptin levels are below a critical threshold level, we studied seven normal-weight women during a normoleptinemic-fed state and two states of relative hypoleptinemia induced by 72-h fasting during which we administered either placebo or recombinant methionyl human leptin (r-metHuLeptin) in replacement doses. Fasting for 72 h decreased leptin levels by approximately = 80% from a midphysiologic (14.7 +/- 2.6 ng/ml) to a low-physiologic (2.8 +/- 0.3 ng/ml) level. Administration of r-metHuLeptin during fasting fully restored leptin to physiologic levels (28.8 +/- 2.0 ng/ml) and reversed the fasting-associated decrease in overnight luteinizing hormone pulse frequency but had no effect on fasting-induced changes in thyroid-stimulating hormone pulsatility, thyroid and IGF-1 hormone levels, hypothalamic-pituitary-adrenal and renin-aldosterone activity. FSH and sex steroid levels were not altered. Short-term reduction of leptin levels decreased the number of circulating cells of the adaptive immune response, but r-metHuLeptin did not have major effects on their number or in vitro function. Thus, changes of leptin levels within the physiologic range have no major physiologic effects in leptin-replete humans. Studies involving more severe and/or chronic leptin deficiency are needed to precisely define the lower limit of normal leptin levels for each of leptin's physiologic targets.

Leptin and Adiponectin in the HIV Associated Metabolic Syndrome: Physiologic and Therapeutic Implications

Leptin and adiponectin represent two newly discovered adipose tissue derived hormones with important roles in energy homeostasis and insulin resistance. Their interrelations with the manifestations of the HIV associated metabolic syndrome and specific somatomorphic changes i.e. fat redistribution is reviewed. A synopsis of published studies is presented and the potential role of leptin and adiponectin is discussed. We have described an association of the HIV metabolic syndrome with a state of reduced insulin sensitivity due to adiponectin deficiency. The metabolic syndrome is also accompanied by leptin deficiency in lipoatrophic subjects and possibly by a leptin resistance state in lipohypertrophic patients. Adiponectin and / or leptin therapy in a manner similar to other leptin deficiency states may assist in the future management of such patients.

Leptin and its emerging role in children and adolescents

Leptin is an adipocyte-secreted hormone which plays a key role in energy homeostasis. Recent “proof of concept” studies involving leptin administration to humans support its critical role in regulating energy homeostasis, neuroendocrine and immune function as well as insulin resistance in states of energy/ caloric deprivation. Moreover, interventional studies in leptin deficient children and observational studies in normal girls and boys support a role for leptin as a permissive factor for the initiation of puberty in children. The potential clinical usefulness of leptin in several disease states in children and adolescents, including hypothalamic amenorrhea, eating disorders and syndromes of insulin resistance is still under investigation.

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.

Recombinant human leptin in women with hypothalamic amenorrhea

BACKGROUND

Disruptions in hypothalamic-gonadal and other endocrine axes due to energy deficits are associated with low levels of the adipocyte-secreted hormone leptin and may result in hypothalamic amenorrhea. We hypothesized that exogenous recombinant leptin replacement would improve reproductive and neuroendocrine function in women with hypothalamic amenorrhea.

METHODS

Eight women with hypothalamic amenorrhea due to strenuous exercise or low weight were studied for one month before receiving recombinant human leptin and then while receiving treatment for up to three months. Six control subjects with hypothalamic amenorrhea received no treatment and were studied for a mean (+/-SD) of 8.5+/-8.1 months.

RESULTS

Luteinizing hormone (LH) pulsatility, body weight, ovarian variables, and hormone levels did not change significantly over time in the controls and during a one-month control period before recombinant leptin therapy in the treated subjects. In contrast, recombinant leptin treatment increased mean LH levels and LH pulse frequency after two weeks and increased maximal follicular diameter, the number of dominant follicles, ovarian volume, and estradiol levels over a period of three months. Three patients had an ovulatory menstrual cycle (P<0.05 for the comparison with an expected rate of spontaneous ovulation of 10 percent); two others had preovulatory follicular development and withdrawal bleeding during treatment (P<0.05). Recombinant leptin significantly increased levels of free triiodothyronine, free thyroxine, insulin-like growth factor 1, insulin-like growth factor-binding protein 3, bone alkaline phosphatase, and osteocalcin but not cortisol, corticotropin, or urinary N-telopeptide.

CONCLUSIONS

Leptin administration for the relative leptin deficiency in women with hypothalamic amenorrhea appears to improve reproductive, thyroid, and growth hormone axes and markers of bone formation, suggesting that leptin, a peripheral signal reflecting the adequacy of energy stores, is required for normal reproductive and neuroendocrine function.

Phenotypic effects of leptin replacement on morbid obesity, diabetes mellitus, hypogonadism, and behavior in leptin-deficient adults

Genetic mutations in the leptin pathway can be a cause of human obesity. It is still unknown whether leptin can be effective in the treatment of fully established morbid obesity and its endocrine and metabolic consequences in adults. To test the hypothesis that leptin has a key role in metabolic and endocrine regulation in adults, we examined the effects of human leptin replacement in the only three adults identified to date who have genetically based leptin deficiency. We treated these three morbidly obese homozygous leptin-deficient adult patients with recombinant human leptin at low, physiological replacement doses in the range of 0.01-0.04 mg/kg for 18 months. Patients were hypogonadal, and one of them also had type 2 diabetes mellitus. We chose the doses of recombinant methionyl human leptin that would achieve normal leptin concentrations and administered them daily in the evening to model the normal circadian variation in endogenous leptin. The mean body mass index dropped from 51.2 +/- 2.5 (mean +/- SEM) at baseline to 26.9 +/- 2.1 kg/m2 after 18 months of treatment, mainly because of loss of fat mass. We document here that leptin replacement therapy in leptin-deficient adults with established morbid obesity results in profound weight loss, increased physical activity, changes in endocrine function and metabolism, including resolution of type 2 diabetes mellitus and hypogonadism, and beneficial effects on ingestive and noningestive behavior. These results highlight the role of the leptin pathway in adults with key effects on the regulation of body weight, gonadal function, and behavior.

Unraveling the multiple roles of leptin in inflammation and autoimmunity

Initially described as an antiobesity hormone, leptin has subsequently been shown also to influence hematopoiesis, thermogenesis, reproduction, angiogenesis, and immune homeostasis. Leptin links nutritional status and proinflammatory T helper 1 immune responses, and the decrease in leptin plasma concentration during food deprivation leads to impaired immune function. This review focuses on the multiple roles of leptin in chronic inflammation and autoimmunity and suggests new possible therapeutic implications for leptin modulators.