Pharmacokinetics of human leptin in mice and rhesus monkeys

Cholesterol reduction by immunization with a PCSK9 mimic

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a plasma protein that controls cholesterol homeostasis. Here, we design a human PCSK9 mimic, named HIT01, with no consecutive 9-residue stretch in common with any human protein as a potential heart attack vaccine. Murine immunizations with HIT01 reduce low-density lipoprotein (LDL) and cholesterol levels by 40% and 30%, respectively. Immunization of cynomolgus macaques with HIT01-K21Q-R218E, a cleavage-resistant variant, elicits high-titer PCSK9-directed antibody responses and significantly reduces serum levels of cholesterol 2 weeks after each immunization. However, HIT01-K21Q-R218E immunizations also increase serum PCSK9 levels by up to 5-fold, likely due to PCSK9-binding antibodies altering the half-life of PCSK9. While vaccination with a PCSK9 mimic can induce antibodies that block interactions of PCSK9 with the LDL receptor, PCSK9-binding antibodies appear to alter homeostatic levels of PCSK9, thereby confounding its vaccine impact. Our results nevertheless suggest a mechanism for increasing the half-life of soluble regulatory factors by vaccination.

Alterations in Microbiota and Metabolites Related to Spontaneous Diabetes and Pre-Diabetes in Rhesus Macaques

Spontaneous type 2 diabetes mellitus (T2DM) macaques are valuable resources for our understanding the pathological mechanism of T2DM. Based on one month’s fasting blood glucose survey, we identified seven spontaneous T2DM macaques and five impaired glucose regulation (IGR) macaques from 1408 captive individuals. FPG, HbA1c, FPI and IR values were significant higher in T2DM and IGR than in controls. 16S rRNA sequencing of fecal microbes showed the significantly greater abundance of Oribacterium, bacteria inhibiting the production of secondary bile acids, and Phascolarctobacterium, bacteria producing short-chain fatty acids was significantly lower in T2DM macaques. In addition, several opportunistic pathogens, such as Mogibacterium and Kocuria were significantly more abundant in both T2DM and IGR macaques. Fecal metabolites analysis based on UHPLC-MS identified 50 differential metabolites (DMs) between T2DM and controls, and 26 DMs between IGR and controls. The DMs were significantly enriched in the bile acids metabolism, fatty acids metabolism and amino acids metabolism pathways. Combining results from physiochemical parameters, microbiota and metabolomics, we demonstrate that the imbalance of gut microbial community leading to the dysfunction of glucose, bile acids, fatty acids and amino acids metabolism may contribute to the hyperglycaemia in macaques, and suggest several microbes and metabolites are potential biomarkers for T2DM and IGR macaques.

Atomistic mechanism of leptin and leptin-receptor association

The leptin-leptin receptor complex is at the very core of energy homeostasis and immune system regulation, among many other functions. In this work, we built homology models of leptin and the leptin binding domain (LBD) of the receptor from humans and mice. Docking analyses were used to obtain the coordinates of the native leptin-LBD complexes and a mixed heterodimer formed by human leptin and mouse LBD. Molecular dynamics (MD) simulations were performed using all models (monomers and heterodimers) as initial coordinates and the GROMACS program. The overall structural and dynamical behaviors are similar for the three complexes. Upon MD simulations, several new interactions appear. In particular, hydrophobic interactions, with more than 90% persistence, seem to be the most relevant for the stability of the dimers, as well as the pair formed by Asp85_Lep and Arg468_LBD. This in silico analysis provides structural and dynamical information, at the atomistic level, about the mechanism of leptin-LBD complex formation and leptin receptor activation. This knowledge might be used in the rational drug design of therapeutics to modulate leptin signaling.Communicated by Ramaswamy H. Sarma.

Evidence of growth hormone effect on plasma leptin in diet-induced obesity and diet-resistant rats

Background

Plasma leptin is regulated by several factors, including growth hormone (GH), which influences the pathophysiology of obesity.

Objective

To demonstrate the short-term effect of GH on plasma leptin levels in 3 conditions in vivo with the different amount of body fat mass.

Methods

Adult male Wistar rats were fed with standard chow or hypercaloric diet (HC). The HC rats were demonstrated as HC-feeding obese (HC-O) and HC-feeding resistant (HC-R) rats. Then, they were treated with GH or saline for 3 days. Basal plasma leptin levels were measured at 24 and 32 h. For meal-induced condition, all rats were fed for 2 hand plasma leptin was measured. Further 16-h fasting period, plasma leptin, insulin, and insulin sensitivity indexes were determined.

Results

The short-term GH treatment decreased basal plasma leptin at 32 h after the first GH injection in HC-O rats. However, GH treatment had no effect on meal-induced plasma leptin in all rats. Furthermore, GH treatment attenuated fasting effect on plasma leptin in control and HC-R rats. The insulin resistance (IR) induced by the short-term GH treatment was demonstrated by higher fasting plasma insulin and the increased homeostasis model of IR in HC-R rats.

Conclusions

The study demonstrates the important role of greater fat mass in HC-O rats, which results in decreased basal plasma leptin after short-term GH treatment. For meal-induced condition, GH had no effect on plasma leptin in all rats. Interestingly, GH could attenuate fasting effect on plasma leptin in rats that have lower fat mass.

Cardiac leptin overexpression in the context of acute MI and reperfusion potentiates myocardial remodeling and left ventricular dysfunction

BACKGROUND

Acute MI induces leptin expression in the heart, however the role of myocardial leptin in cardiac ischemia and reperfusion (IR) remains unknown. To shed light on the effects of elevated levels of leptin in the myocardium, we overexpressed cardiac leptin and assessed local remodeling and myocardial function in this context.

METHODS AND RESULTS

Cardiac leptin overexpression was stimulated in mice undergoing IR by a single intraperitoneal injection of leptin antagonist (LepA). All mice exhibited a normal pattern of body weight gain. A rapid, long-term upregulation of leptin mRNA was demonstrated in the heart, adipose, and liver tissues in IR/LepA-treated mice. Overexpressed cardiac leptin mRNA extended beyond postoperative day (POD) 30. Plasma leptin peaked 7.5 hours postoperatively, especially in IR/LepA-treated mice, subsiding to normal levels by 24 hours. On POD-30 IR/LepA-treated mice demonstrated cardiomyocyte hypertrophy and perivascular fibrosis compared to IR/saline controls. Echocardiography on POD-30 demonstrated eccentric hypertrophy and systolic dysfunction in IR/LepA. We recorded reductions in Ejection Fraction (p<0.001), Fraction Shortening (p<0.01), and Endocardial Fraction Area Change (p<0.01), and an increase in Endocardial Area Change (p<0.01). Myocardial remodeling in the context of IR and cardiac leptin overexpression was associated with increased cardiac TGFβ ligand expression, activated Smad2, and downregulation of STAT3 activity.

CONCLUSIONS

Cardiac IR coinciding with increased myocardial leptin synthesis promotes cardiomyocyte hypertrophy and fibrosis and potentiates myocardial dysfunction. Plasma leptin levels do not reflect cardiac leptin synthesis, and may not predict leptin-related cardiovascular morbidity. Targeting cardiac leptin is a potential treatment for cardiac IR damage.

Animal models of obesity and diabetes mellitus

More than one-third of the worldwide population is overweight or obese and therefore at risk of developing type 2 diabetes mellitus. In order to mitigate this pandemic, safer and more potent therapeutics are urgently required. This necessitates the continued use of animal models to discover, validate and optimize novel therapeutics for their safe use in humans. In order to improve the transition from bench to bedside, researchers must not only carefully select the appropriate model but also draw the right conclusions. In this Review, we consolidate the key information on the currently available animal models of obesity and diabetes and highlight the advantages, limitations and important caveats of each of these models.

Expression of the clock gene Rev-erbα in the brain controls the circadian organisation of food intake and locomotor activity, but not daily variations of energy metabolism

The nuclear receptor REV-ERBα is part of the molecular clock mechanism and is considered to be involved in a variety of biological processes within metabolically active peripheral tissues as well. To investigate whether Rev-erbα (also known as Nr1d1) in the brain plays a role in the daily variations of energy metabolism, feeding behaviour and the sleep-wake cycle, we studied mice with global (GKO) or brain (BKO) deletion of Rev-erbα. Mice were studied both in a light/dark cycle and in constant darkness, and then 24-hour variations of Respiratory quotient (RQ) and energy expenditure, as well as the temporal patterns of rest-activity and feeding behaviour, were recorded. The RQ increase of GKO mice was not detected in BKO animals, indicating a peripheral origin for this metabolic alteration. Arrhythmic patterns of locomotor activity were only found in BKO mice. By contrast, the circadian rhythm of food intake was lost both in GKO and BKO mice, mostly by increasing the number of daytime meals. These changes in the circadian pattern of feeding behaviour were, to some extent, correlated with a loss of rhythmicity of hypothalamic Hcrt (also named Orx) mRNA levels. Taken together, these findings highlight that Rev-erbα in the brain is involved in the temporal partitioning of feeding and sleep, whereas its effects on energy metabolism are mainly exerted through its peripheral expression.

Use and Importance of Nonhuman Primates in Metabolic Disease Research: Current State of the Field

Obesity and its multiple metabolic sequelae, including type 2 diabetes, cardiovascular disease, and fatty liver disease, are becoming increasingly widespread in both the developed and developing world. There is an urgent need to identify new approaches for the prevention and treatment of these costly and prevalent metabolic conditions. Accomplishing this will require the use of appropriate animal models for preclinical and translational investigations in metabolic disease research. Although studies in rodent models are often useful for target/pathway identification and testing hypotheses, there are important differences in metabolic physiology between rodents and primates, and experimental findings in rodent models have often failed to be successfully translated into new, clinically useful therapeutic modalities in humans. Nonhuman primates represent a valuable and physiologically relevant model that serve as a critical translational bridge between basic studies performed in rodent models and clinical studies in humans. The purpose of this review is to evaluate the evidence, including a number of specific examples, in support of the use of nonhuman primate models in metabolic disease research, as well as some of the disadvantages and limitations involved in the use of nonhuman primates. The evidence taken as a whole indicates that nonhuman primates are and will remain an indispensable resource for evaluating the efficacy and safety of novel therapeutic strategies targeting clinically important metabolic diseases, including dyslipidemia and atherosclerosis, type 2 diabetes, hepatic steatosis, steatohepatitis, and hepatic fibrosis, and potentially the cognitive decline and dementia associated with metabolic dysfunction, prior to taking these therapies into clinical trials in humans.

Photoperiod-Induced Increases in Bone Mineral Apposition Rate in Siberian Hamsters and the Involvement of Seasonal Leptin Changes

The adipokine leptin regulates energy balance, appetite, and reproductive maturation. Leptin also acts on bone growth and remodeling, but both osteogenic and anti-osteogenic effects have been reported depending on experimental conditions. Siberian hamsters (Phodopus sungorus) have natural variation in circulating leptin concentrations, where serum leptin is significantly decreased during the short day (SD)-induced winter state. In summer long day (LD) photoperiods, appetite and body adiposity increase with associated central leptin insensitivity. This natural change in leptin secretion was exploited to investigate leptin's effect on bone growth. Hamsters were injected with calcium-chelating fluorescent dyes to measure bone mineral apposition rate (MAR). Measurements were initially obtained from 5-week and 6-month-old animals maintained in low leptin (SD) or high leptin (LD) states. A further study investigated effects of chronic administration of recombinant mouse leptin to hamsters housed in SD and LD conditions; growth plate thickness and bone density were also assessed. As expected, a reduction in body mass was seen in hamsters exposed to SD, confirming the phenotype change in all studies. Serum leptin concentrations were significantly reduced in SD animals in all studies. MAR was reproducibly and significantly increased in the femurs of SD animals in all studies. Vitamin D and growth plate thickness were significantly increased in SD animals at 6 months. No effect on bone density was observed in any study. Taken together these data suggest that bone growth is associated with the low leptin, winter, lean state. In leptin-treated animals, there was a significant interaction effect of leptin and photoperiod. In comparison to their vehicle counterparts, SD animals had decreased and LD animals had increased MAR, which was not apparent prior to leptin administration. In conclusion, increased MAR was associated with low serum leptin levels in early life and sustained over 6 months, implying that leptin has a negative effect on bone growth in this model. The unexpected finding that MAR increased after peripheral leptin administration in LD suggests that leptin exerts different effects on bone growth dependent on initial leptin status. This adds further weight to the hypothesis that leptin-treated LD animals display central leptin resistance.

Leptin pharmacokinetics in male mice

Pharmacokinetics of leptin in mammals has not been studied in detail and only one study has examined more than one time point in non-mutant mice and this was in a female mice. This is the first study to describe leptin distribution over a detailed time course in normal male mice. A physiologic dose (12 ng) of radiolabelled leptin was injected into adult male mice via the lateral tail vein and tissues were dissected out and measured for radioactivity over a time course of up to two hours. Major targets were the digestive tract, kidneys, skin and lungs. The brain was not a major target, and 0.15% of the total dose was recovered from the brain 5 min after administration. Major differences appear to exist in the distribution of leptin between the male and female mice, indicating a high degree of sexual dimorphism. Although the half-lives were similar between male and female mice, almost twice the proportion of leptin was recovered from the digestive tract of male mice in comparison to that reported previously for females. This would seem to indicate a major difference in leptin distribution and possibly function between males and females.

Pharmacokinetics of leptin in female mice

Pharmacokinetics of leptin in mammals has received limited attention and only one study has examined more than two time points and this was in ob/ob mice. This study is the first to observe the distribution of leptin over a time course in female mice. A physiologic dose (12 ng) of radiolabelled leptin was injected in adult female mice via the lateral tail vein and tissues were dissected out and measured for radioactivity over a time course up to two hours. Major targets for administered leptin included the liver, kidneys, gastrointestinal tract and the skin while the lungs had high concentrations of administered leptin per gram of tissue. Leptin was also found to enter the lumen of the digestive tract intact from the plasma. Very little of the dose (<1 %) was recovered from the brain at any time. Consequently we confirm that the brain is not a major target for leptin from the periphery, although it may be very sensitive to leptin that does get to the hypothalamus. Several of the major targets (GI tract, skin and lungs) for leptin form the interface for the body with the environment, and given the ability of leptin to modulate immune function, this may represent a priming effect for tissues to respond to damage and infection.

Leptin applications in 2015: what have we learned about leptin and obesity?

PURPOSE OF REVIEW

To summarize previous and current advancements for leptin therapeutics, we described how leptin may be useful in leptin deficient states such as lipodystrophy, for which leptin was recently approved, and how it may be useful in the future for typical obesity.

RECENT FINDINGS

The discovery of leptin in 1994 built the foundation for understanding the pathophysiology and treatment of obesity. Leptin therapy reverses morbid obesity related to congenital leptin deficiency and appears to possibly treat lipodystrophy, a finding which has led to the approval of leptin for the treatment of lipodystrophy in the USA and Japan. Typical obesity, on the other hand, is characterized by hyperleptinemia and leptin tolerance. Thus, leptin administration has proven ineffective for inducing weight loss on its own but could possibly be useful in combination with other therapies or for weight loss maintenance.

SUMMARY

Leptin is not able to treat typical obesity; however, it is effective for reversing leptin deficiency-induced obesity and is possibly useful in lipodystrophy. New mechanisms and pathways involved in leptin resistance are continuously discovered, whereas the development of new techniques and drug combinations which may improve leptin's efficacy and safety regenerate the hope for its use as an effective treatment for typical obesity.

Site-specific albumination of a therapeutic protein with multi-subunit to prolong activity in vivo

Albumin fusion/conjugation (albumination) has been an effective method to prolong in vivo half-life of therapeutic proteins. However, its broader application to proteins with complex folding pathway or multi-subunit is restricted by incorrect folding, poor expression, heterogeneity, and loss of native activity of the proteins linked to albumin. We hypothesized that the site-specific conjugation of albumin to a permissive site of a target protein will expand the utilities of albumin as a therapeutic activity extender to proteins with a complex structure. We show here the genetic incorporation of a non-natural amino acid (NNAA) followed by chemoselective albumin conjugation to prolong therapeutic activity in vivo. Urate oxidase (Uox), a therapeutic enzyme for treatment of hyperuricemia, is a homotetramer with multiple surface lysines, limiting conventional approaches for albumination. Incorporation of p-azido-l-phenylalanine into two predetermined positions of Uox allowed site-specific linkage of dibenzocyclooctyne-derivatized human serum albumin (HSA) through strain-promoted azide-alkyne cycloaddition (SPAAC). The bio-orthogonality of SPAAC resulted in the production of a chemically well-defined conjugate, Uox-HSA, with a retained enzymatic activity. Uox-HSA had a half-life of 8.8 h in mice, while wild-type Uox had a half-life of 1.3 h. The AUC increased 5.5-fold (1657 vs. 303 mU/mL x h). These results clearly demonstrated that site-specific albumination led to the prolonged enzymatic activity of Uox in vivo. Site-specific albumination enabled by NNAA incorporation and orthogonal chemistry demonstrates its promise for the development of long-acting protein therapeutics with high potency and safety.

PASylation of Murine Leptin Leads to Extended Plasma Half-Life and Enhanced in Vivo Efficacy

Leptin plays a central role in the control of energy homeostasis and appetite and, thus, has attracted attention for therapeutic approaches in spite of its limited pharmacological activity owing to the very short circulation in the body. To improve drug delivery and prolong plasma half-life, we have fused murine leptin with Pro/Ala/Ser (PAS) polypeptides of up to 600 residues, which adopt random coil conformation with expanded hydrodynamic volume in solution and, consequently, retard kidney filtration in a similar manner as polyethylene glycol (PEG). Relative to unmodified leptin, size exclusion chromatography and dynamic light scattering revealed an approximately 21-fold increase in apparent size and a much larger molecular diameter of around 18 nm for PAS(600)-leptin. High receptor-binding activity for all PASylated leptin versions was confirmed in BIAcore measurements and cell-based dual-luciferase assays. Pharmacokinetic studies in mice revealed a much extended plasma half-life after ip injection, from 26 min for the unmodified leptin to 19.6 h for the PAS(600) fusion. In vivo activity was investigated after single ip injection of equimolar doses of each leptin version. Strongly increased and prolonged hypothalamic STAT3 phosphorylation was detected for PAS(600)-leptin. Also, a reduction in daily food intake by up to 60% as well as loss in body weight of >10% lasting for >5 days was observed, whereas unmodified leptin was merely effective for 1 day. Notably, application of a PASylated superactive mouse leptin antagonist (SMLA) led to the opposite effects. Thus, PASylated leptin not only provides a promising reagent to study its physiological role in vivo but also may offer a superior drug candidate for clinical therapy.

Effects of energy status and diet on Bdnf expression in the ventromedial hypothalamus of male and female rats

Sex differences exist in the regulation of energy homeostasis in response to calorie scarcity or excess. Brain-derived neurotrophic factor (BDNF) is one of the anorexigenic neuropeptides regulating energy homeostasis. Expression of Bdnf mRNA in the ventromedial nucleus of the hypothalamus (VMH) is closely associated with energy and reproductive status. We hypothesized that Bdnf expression in the VMH was differentially regulated by altered energy balance in male and female rats. Using dietary intervention, including fasting-induced negative energy status and high-fat diet (HFD) feeding-induced positive energy status, along with low-fat diet (LFD) feeding and HFD pair-feeding (HFD-PF), effects of diets and changes in energy status on VMH Bdnf expression were compared between male and female rats. Fasted males but not females had lower VMH Bdnf expression than their fed counterparts following 24-hour fasting, suggesting that fasted males reduced Bdnf expression to drive hyperphagia and body weight gain. Male HFD obese and HFD-PF non-obese rats had similarly reduced expression of Bdnf compared with LFD males, indicating that dampened Bdnf expression was associated with feeding a diet high in fat instead of increased adiposity. Decreased BDNF signaling during HFD feeding would increase a drive to eat and may contribute to diet-induced obesity in males. In contrast, VMH Bdnf expression was stably maintained in females when energy homeostasis was disturbed. These results suggest sex-distinct regulation of central Bdnf expression by diet and energy status.

Metreleptin: first global approval

Metreleptin is an analogue of the human hormone leptin being developed by Amylin Pharmaceuticals (a subsidiary of Bristol-Myers Squibb) for the subcutaneous treatment of metabolic disorders including lipodystrophy. The compound is expected to improve insulin sensitivity, hypertriglyceridaemia and hyperglycaemia in patients with lipodystrophy who are unresponsive to conventional treatment. Metreleptin has been approved in Japan as a leptin therapy for the treatment of lipodystrophy. Amylin has also completed a submission for regulatory approval to the US FDA for metreleptin in the treatment of diabetes mellitus and/or hypertriglyceridaemia in patients with rare forms of lipodystrophy. Clinical development of the drug is also underway in the USA for the treatment of type 1 diabetes. Amgen was previously assessing the use of metreleptin as a treatment for amenorrhoea; however, it appears that development in this indication has been discontinued. This article summarizes the milestones in the development of metreleptin leading to this first approval for lipodystrophy.

Enhanced leptin sensitivity, reduced adiposity, and improved glucose homeostasis in mice lacking exchange protein directly activated by cyclic AMP isoform 1

The prototypic second messenger cyclic AMP (cAMP) is essential for controlling cellular metabolism, including glucose and lipid homeostasis. In mammals, the majority of cAMP functions are mediated by cAMP-dependent protein kinase (PKA) and exchange proteins directly activated by cAMP (Epacs). To explore the physiological functions of Epac1, we generated Epac1 knockout mice. Here we report that Epac1 null mutants have reduced white adipose tissue and reduced plasma leptin levels but display heightened leptin sensitivity. Epac1-deficient mice are more resistant to high-fat diet-induced obesity, hyperleptinemia, and glucose intolerance. Furthermore, pharmacological inhibition of Epac by use of an Epac-specific inhibitor reduces plasma leptin levels in vivo and enhances leptin signaling in organotypic hypothalamic slices. Taken together, our results demonstrate that Epac1 plays an important role in regulating adiposity and energy balance.

Leptin treatment inhibits the progression of atherosclerosis by attenuating hypercholesterolemia in type 1 diabetic Ins2(+/Akita):apoE(-/-) mice

AIMS

The impact of leptin deficiency and its replacement in T1D remain unclear in the context of dyslipidemia and atherosclerosis. The current study has investigated the physiologic role of leptin in lipid metabolism and atherosclerosis in T1D.

METHODS AND RESULTS

The present study has employed Ins2(+/Akita):apoE(-/-) mouse model that spontaneously develops T1D, hypercholesterolemia, and atherosclerosis. At age 13 weeks, diabetic Ins2(+/Akita):apoE(-/-) mice showed leptin deficiency by ~92% compared with nondiabetic Ins2(+/+):apoE(-/-) mice. From 13 weeks to 25 weeks of age, diabetic Ins2(+/Akita):apoE(-/-) mice were treated with low-dose leptin (at 0.4 μg/g body weight daily). Leptin treatment diminished food intake by 22-27% in diabetic mice without affecting body weight and lean mass throughout the experiment. Importantly, leptin therapy substantially reduced plasma cholesterol concentrations by ~41%, especially in LDL fractions, in diabetic Ins2(+/Akita):apoE(-/-) mice. Moreover, leptin therapy decreased atherosclerotic lesion in diabetic mice by ~62% comparable to that seen in nondiabetic mice. In addition, leptin restored repressed expression of hepatic sortilin-1, a receptor for LDL clearance, and reversed altered expression of several hepatic genes involved in lipogenesis and cholesterol synthesis characteristic of diabetic mice. These findings were accompanied by normalization of reduced hepatic expression of Irs1 and Irs2 mRNA as well as their protein levels, and improved hepatic insulin-receptor signaling.

CONCLUSIONS

The present findings suggest that leptin administration may be useful to improve dyslipidemia and reduce atherosclerosis-related cardiovascular disease in human subjects with T1D.

The potential role of glutamate in the current diabetes epidemic

In the present article, we propose the perspective that abnormal glutamate homeostasis might contribute to diabetes pathogenesis. Previous reports and our recent data indicate that chronically high extracellular glutamate levels exert direct and indirect effects that might participate in the progressive loss of β-cells occurring in both T1D and T2D. In addition, abnormal glutamate homeostasis may impact all the three accelerators of the "accelerator hypothesis" and could partially explain the rising frequency of T1D and T2D.

Morbidly obese are ghrelin and leptin hyporesponders with lesser intragastric balloon treatment efficiency : ghrelin and leptin changes in relation to obesity treatment

BACKGROUND

Ghrelin and leptin recently emerged as the most influential neuroendocrine factors in the pathophysiology of obesity. The said peptides act in reciprocity and are responsible for regulation of appetite and energy metabolism. Intragastric balloons acquired worldwide popularity for obesity treatment. However, the roles of ghrelin and leptin in intragastric balloon treatment were still not systematically studied.

METHODS

A prospective single-center study included 43 Caucasians treated with BioEnterics intragastric balloon, with age range of 18-60, and divided to non-morbid (body mass index cutoff 40 kg/m(2)) or morbid type of obesity, with 12 months follow-up. Serum hormonal samples were taken from fasting patients and kept frozen until analyses.

RESULTS

Significant differences were observed in anthropometrics and there were no differences between genders or comorbidities. The baseline weight for non-morbid vs. morbid was 104 kg (90-135) vs. 128.5 kg (104-197). Weight loss was statistically different between the studied groups during the study course with a median control weight at 6 months of 92 kg (72-121) vs. 107 kg (84-163), p < 0.001. Treatment was successful for 18 (94.7%) vs. 16 (66.7%) patients, p = 0.026. Ghrelin varied from 333.3 to 3,416.8 pg/ml and leptin from 1.7 to 61.2 ng/ml, with a statistically significant time-dependent relationship. A significant difference (p = 0.04) with emphasized ghrelin peak was found in the 3rd month of treatment for non-morbidly obese subjects.

CONCLUSIONS

The importance of ghrelin and leptin in treatment-induced changes was reaffirmed. Ghrelin hyper-response in non-morbidly obese subjects characterized greater short-term treatment efficiency and landmarked an inclination to weight regain. The results suggest a potential pattern of individualization between obese patients according to body mass index towards intragastric balloon or bariatric surgery. Further studies are needed in order to get better insights in the pathophysiologic mechanisms of obesity.

In vivo effects of leptin on lymphocyte subpopulations in mice

Leptin, a hormone-cytokine mainly produced by the adipose tissue, has pleitropic effects on many biological system including metabolic, endocrine, and immune system. Although it is well known that leptin controls food intake on hypothalamic regions of brain, the role of leptin in hematopoietic and immune processes has been mainly investigated with in vitro and transgenic mouse studies. The aim of this study was to investigate the effects of peripheral leptin on lymphocyte subpopulation. Initially forty male Swiss albino mice were divided into five groups. Mice in group I (Control) were given serum physiologic (SP) and group L100, group L250, group L500, and group L1000 were given 100, 250, 500 and 1000 μg/kg/day recombinant mouse leptin, respectively. Leptin or SP was injected subcutaneously for the next 6 days. Daily food/water intake was recorded for each group. At the end of the study, whole blood samples (500 μl) were obtained via intracardiac punction in anesthetized mice. Leptin levels and lymphocyte subpopulations in blood samples were analyzed. We show that no in vivo dose-dependent effect of leptin is existed on lymphocyte subpopulations count in mice. Treatment of mice with high-dose leptin led to increase only CD4+ cells (P<0.05). In addition, high-dose leptin slightly increased CD3+ cells but this was not statistically confirmed (P=0.08). Notably, it was found that leptin caused insignificant changes on body weight and food intake in normal body weight mice. The data support that high-dose leptin has proliferative effect on CD4+ cells in vivo. However, more in vivo study needs to be examined to clarify how leptin affect lymphocyte subpopulations.

Fructose-fed rhesus monkeys: a nonhuman primate model of insulin resistance, metabolic syndrome, and type 2 diabetes

The incidence of insulin resistance has increased dramatically over the past several years, and we and others have proposed that this increase may at least in part be attributable to increased dietary fructose consumption. However, a major limitation to the study of diet-induced insulin resistance is the lack of relevant animal models. Numerous studies, mostly in rodents, have demonstrated that diets high in fructose induce insulin resistance; however, important metabolic differences exist between rodents and primates. Thus, the results of metabolic studies performed in primates are substantively more translatable to human physiology, underscoring the importance of establishing nonhuman primate models of common metabolic conditions. In this report, we demonstrate that a high-fructose diet in rhesus monkeys produces insulin resistance and many features of the metabolic syndrome, including central obesity, dyslipidemia, and inflammation within a short period of time; moreover, a subset of monkeys developed type 2 diabetes. Given the rapidity with which the metabolic changes occur, and the ability to control for many factors that cannot be controlled for in humans, fructose feeding in rhesus monkeys represents a practical and efficient model system in which to investigate the pathogenesis, prevention, and treatment of diet-induced insulin resistance and its related comorbidities.

The proconvulsant effects of leptin on glutamate receptor-mediated seizures in mice

The metabolic-related hormone, leptin has been suggested for clinical use as an anticonvulsant based upon data generated from in vitro and in vivo non-human studies. However, a number of other non-human experiments have demonstrated proconvulsant activity for leptin. The current study investigated potential pro- and anticonvulsant effects of leptin during exposure to either glutamate (the major endogenous excitatory neurotransmitter) or three subtype-selective glutamate receptor agonists (N-methyl-d-aspartic acid [NMDA], alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid [AMPA], and kainate). Male C57BL/6JRj mice were pretreated with leptin (0.1-10mg/kg, i.p.) and then administered doses of the glutamate receptor agonists (i.p.) that had been previously shown to result in clonic convulsions in approximately half of the animals tested. Leptin had no clear convulsant-related effects with either glutamate or AMPA, but it exhibited dose-related, proconvulsant activity (decreased latency to first occurrence of various convulsion-related signs, and increased percentage of animals exhibiting such signs) with both NMDA and kainate. The proconvulsant effects of leptin observed during the current study suggest that a cautious approach should be taken when administering leptin to individuals who may be prone to seizures.

Neonatal hyperleptinaemia programmes anxiety-like and novelty seeking behaviours but not memory/learning in adult rats

Leptin treatment during lactation programmes for leptin resistance at adulthood, evidenced by hyperleptinaemia, hyperphagia and overweight. Since leptin is known to affect stress response, emotional behaviour and memory/learning performance, the objective of the present study was to evaluate whether neonatal hyperleptinaemia programmes anxiety-like and novelty-seeking behaviours as well as memory/learning in adult male rats. During the first 10 days of lactation (from PN1 to PN10), pups were s.c. injected once per day with either 50 microL of saline (SAL) or murine leptin (LEP - 8 microg/100 g of body mass, saline diluted). Serum leptin was assessed at PN10 and at PN150. Two separate experiments were carried out: 1) experiment one: at PN137, 29 SAL and 30 LEP rats were tested in the elevated plus-maze (EPM) and, at PN142, their behaviour was assessed in the hole board (HB) arena; 2) experiment two: at PN140, a different group of rats consisting of 53 SAL and 56 LEP animals were tested in the radial arm water maze (RAWM). Serum leptin concentration was higher in the LEP group at PN10 and at PN150. LEP animals spent significantly less time in the open arms of the EPM. Furthermore, the number of nose-pokes in the HB arena was higher in LEP rats. There were no differences between groups regarding latency to find the hidden platform in the RAWM. Our results suggests that a central mechanism of leptin resistance at adulthood, caused by neonatal hyperleptinaemia, is associated with an increased level of anxiety and also that it intensifies novelty seeking-behaviour.

Metabolic liver disease of obesity and role of adipose tissue in the pathogenesis of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is an increasingly recognized cause of liver-related morbidity and mortality. It can develop secondary to numerous causes but a great majority of NAFLD cases occur in patients who are obese or present with other components of metabolic syndrome (hypertension, dyslipidemia, diabetes). This is called primary NAFLD and insulin resistance plays a key role in its pathogenesis. Obesity is characterized by expanded adipose tissue, which is under a state of chronic inflammation. This disturbs the normal storage and endocrine functions of adipose tissue. In obesity, the secretome (adipokines, cytokines, free fatty acids and other lipid moieties) of fatty tissue is amplified, which through its autocrine, paracrine actions in fat tissue and systemic effects especially in the liver leads to an altered metabolic state with insulin resistance (IR). IR leads to hyperglycemia and reactive hyperinsulinemia, which stimulates lipid-accumulating processes and impairs hepatic lipid metabolism. IR enhances free fatty acid delivery to liver from the adipose tissue storage due to uninhibited lipolysis. These changes result in hepatic abnormal fat accumulation, which may initiate the hepatic IR and further aggravate the altered metabolic state of whole body. Hepatic steatosis can also be explained by the fact that there is enhanced dietary fat delivery and physical inactivity. IR and NAFLD are also seen in various lipodystrophic states in contrary to popular belief that these problems only occur due to excessive adiposity in obesity. Hence, altered physiology of adipose tissue is central to development of IR, metabolic syndrome and NAFLD.

Leptin and the regulation of the hypothalamic-pituitary-adrenal axis

Leptin, the product of the obesity gene (ob) predominantly secreted from adipocytes, plays a major role in the negative control of feeding and acts via a specific receptor (Ob-R), six isoforms of which are known at present. Evidence has been accumulated that leptin, like other peptides involved in the central regulation of food intake, controls the function of the hypothalamic-pituitary-adrenal (HPA) axis, acting on both its central and peripheral branches. Leptin, along with Ob-R, is expressed in the hypothalamus and pituitary gland, where it modulates corticotropin-releasing hormone and ACTH secretion, probably acting in an autocrine-paracrine manner. Only Ob-R is expressed in the adrenal gland, thereby making it likely that leptin affects it by acting as a circulating hormone. Although in vitro and in vivo findings could suggest a glucocorticoid secretagogue action in the rat, the bulk of evidence indicates that leptin inhibits steroid-hormone secretion from the adrenal cortex. In keeping with this, leptin was found to dampen the HPA axis response to many kinds of stress. In contrast, leptin enhances catecolamine release from the adrenal medulla. This observation suggests that leptin activates the sympathoadrenal axis and does not appear to agree with its above-mentioned antistress action. Leptin and/or Ob-R are also expressed in pituitary and adrenal tumors, but little is known about the role of this cytokine in the pathophysiology.

Behavioral changes induced by cocaine in mice are modified by a hyperlipidic diet or recombinant leptin

The objective of the present study was to determine if the acute behavioral effects of cocaine acutely administered intraperitoneally (ip) at doses of 5, 10 and 20 mg/kg on white male CF1 mice, 90 days of age, would be influenced by leptin acutely administered ip (at doses of 5, 10 and 20 microg/kg) or by endogenous leptin production enhanced by a high-fat diet. The acute behavioral effects of cocaine were evaluated in open-field, elevated plus-maze and forced swimming tests. Results were compared between a group of 80 mice consuming a balanced diet and a high-fat diet, and a group of 80 mice fed a commercially available rodent chow formula (Ralston Purina) but receiving recombinant leptin (rLeptin) or saline ip. Both the high-fat-fed and rLeptin-treated mice showed decreased locomotion in the open-field test, spent more time in the open arms of the elevated plus-maze and showed less immobility time in the forced swimming test (F(1,68) = 7.834, P = 0.007). There was an interaction between diets and cocaine/saline treatments in locomotion (F(3,34) = 3.751, P = 0.020) and exploration (F(3,34) = 3.581, P = 0.024). These results suggest that anxiolytic effects and increased general activity were induced by leptin in cocaine-treated mice and that low leptin levels are associated with behavioral depression. Chronic changes in diet composition producing high leptin levels or rLeptin treatment may result in an altered response to cocaine in ethologic tests that measure degrees of anxiety and depression, which could be attributed to an antagonistic effect of leptin.

Plasma clearance and tissue distribution of radiolabeled leptin in the chicken

Leptin is an adipose and liver tissue-derived secreted protein in chickens that has been implicated in the regulation of food intake and whole-body energy balance. In this study, the metabolic clearance and tissue uptake of leptin were examined in the chicken (Gallus gallus). Four-week-old broiler males were infused with (125)I-labeled mouse leptin. Chromatography of radiolabeled leptin in plasma produced two peaks, one at 16 kDa (free leptin) and a free iodine peak. No leptin binding protein in blood was detected. Leptin was cleared with a half-life estimate of 23 min. In order to investigate the tissue distribution and uptake of radiolabeled leptin, multiple tissues were removed from infused birds at 15 and 240 min post-infusion, and trichloroacetic acid (TCA)-precipitable radioactivity was determined. The amounts of radioactivity at 15 min post-infusion in the tissues in rank order were: kidney, testis, lung, spleen, heart, liver, small and large intestine, gizzard, pancreas, bursa, leg and breast muscle, adrenals, and brain. A slightly different pattern of distribution was observed at 240 min post-infusion. We conclude from these studies that unlike mammals, no circulating leptin binding protein is present in chickens. Leptin is metabolized and cleared very rapidly from blood by the kidney.

Leptin: linking adipocyte metabolism with cardiovascular and autoimmune diseases

Leptin was originally discovered as an adipocyte-derived hormone involved in the central control of body weight and energy homeostasis. It is now clear that leptin is a pleiotropic cytokine, with activities on many peripheral cell types. These findings may help explain the surprising role of leptin in pathophysiological processes. Recent evidence suggests that leptin contributes to atherosclerosis and to the increased risk of cardiovascular disease in obese people. Leptin also appears to be involved in T-cell-dependent immunity and possibly in the development and maintenance of certain autoimmune diseases. Here, we review the role of leptin in cardiovascular and autoimmune diseases, and also briefly address the potential therapeutic use of leptin antagonists.

Leptin: a review of its peripheral actions and interactions

Following the discovery of leptin in 1994, the scientific and clinical communities have held great hope that manipulation of the leptin axis may lead to the successful treatment of obesity. This hope is not yet dashed; however the role of the leptin axis is now being shown to be ever more complex than was first envisaged. It is now well established that leptin interacts with pathways in the central nervous system and through direct peripheral mechanisms. In this review, we consider the tissues in which leptin is synthesized and the mechanisms which mediate leptin synthesis, the structure of leptin and the knowledge gained from cloning leptin genes in aiding our understanding of the role of leptin in the periphery. The discoveries of expression of leptin receptor isotypes in a wide range of tissues in the body have encouraged investigation of leptin interactions in the periphery. Many of these interactions appear to be direct, however many are also centrally mediated. Discovery of the relative importance of the centrally mediated and peripheral interactions of leptin under different physiological states and the variations between species is beginning to show the complexity of the leptin axis. Leptin appears to have a range of roles as a growth factor in a range of cell types: as be a mediator of energy expenditure; as a permissive factor for puberty; as a signal of metabolic status and modulation between the foetus and the maternal metabolism; and perhaps importantly in all of these interactions, to also interact with other hormonal mediators and regulators of energy status and metabolism such as insulin, glucagon, the insulin-like growth factors, growth hormone and glucocorticoids. Surely, more interactions are yet to be discovered. Leptin appears to act as an endocrine and a paracrine factor and perhaps also as an autocrine factor. Although the complexity of the leptin axis indicates that it is unlikely that effective treatments for obesity will be simply derived, our improving knowledge and understanding of these complex interactions may point the way to the underlying physiology which predisposes some individuals to apparently unregulated weight gain.

Leptin attenuates follicular apoptosis and accelerates the onset of puberty in immature rats

Human and rat granulosa cells express receptors to leptin which synergies with glucocorticoid hormones in stimulation of ovarian steroidogenesis. To examine whether leptin affects follicular development and maturation, we injected recombinant ovine leptin (300 ng-10 microg/animal) daily to immature 21 day-old female rats. Non-treated rats reached puberty at 44.5+/-1.6 (n=9) days. In contrast, in leptin treated animals, puberty was reached at 34.5+/-1.6 (n=9) days. Ovarian sections revealed hypertrophy of granulosa cells in leptin treated animals. Moreover, the number of ovulations was 2-fold higher in the treated animals compared to controls (3-4 ovulations versus 7-8 on the first three estrous cycles, P<0.001). Leptin dramatically reduced incidence of follicular apoptosis measured by TUNEL, and was already evident after 7 days of leptin injection (12% of apoptosis in leptin treated group compared to 52% in controls, P<0.001). Maximal protection against apoptosis was achieved at 1-3 microg leptin/animal. The levels of FSH, LH, progesterone and the steroidogenic factors ADX and STAR were elevated earlier in development in the leptin treated animals compared to control animals which is in line with the achievement of early puberty in the leptin treated animals compared to non treated ones. To reveal whether modulation of death and survival genes is involved in leptin attenuation of follicular apoptosis, we examined the expression of the survival gene Bcl-2 and the death gene Bax in Western blots of ovarian homogenates. There was a pronounced elevation in Bcl-2 expression during 7-14 days of leptin injections up to 16.3-fold (P<0.001) compared to Bcl-2 expression in controls. Bax expression was elevated only 3.4 fold (P<0.001), leading to an increase in the Bcl-2/Bax ratio of 4.7 fold (P<0.001). Expression of the tumor suppressor gene p 53 and the oncogene Mdm2 did not change significantly. Our data suggests that leptin may be involved in accelerating follicular maturation by attenuating follicular atresia and increasing the ratio of Bcl-2/Bax.

Perspectives in the therapeutic use of leptin

The cloning and characterisation of the protein encoded by the ob gene, called leptin, has represented an enormous advance in the knowledge we have at the present time on the control of appetite and the regulation of body weight. Animal experiments have shown that this adipocyte-derived hormone informs the hypothalamus about the magnitude of fat stores and induces changes in eating behaviour and thermogenesis directed to maintain nutritional homeostasis. Besides the CNS and adipose tissue, other tissues like the gonads, adrenals, pancreas, blood vessels, immune cells and bone are also targets for leptin action, setting the basis for the pleiotropic character of leptin. In contrast to ob(-)/ob(-) mice, which have leptin deficiency, obese patients usually exhibit hyperleptinaemia due to leptin resistance of uncertain aetiology. Patients with congenital leptin deficiency show a dramatic response to recombinant leptin therapy in terms of body weight and fat reduction. However, in contrast to animals, no thermogenic effect has been demonstrated in humans treated with leptin. Leptin-resistant obese subjects display a heterogeneous response to leptin treatment, though some patients achieve a significant weight loss when receiving high doses. New formulations are being tried with different success rates. Before leptin can play a role in the treatment of obesity, more studies are needed to discover which is the adequate dose, which the best route and form of administration and how we can select the patients who will benefit from this particular therapy. The development of new leptin analogues with high penetrating capacity to cross the blood-brain barrier and the investigation of other approaches to overcome the leptin resistance are awaited. Future applications of leptin may be directed to the treatment of infertility, wound healing and bone remodelling among others.