The emerging role of leptin in humans

Leptin is an adipocyte-secreted hormone which plays a key role in energy homeostasis. Recent advances in leptin physiology have revealed that the main role of this hormone in humans is to signal energy availability in energy-deficient states. 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. Moreover, recent "proof of concept" studies involving leptin administration to humans further support its critical role in regulating energy homeostasis, neuroendocrine and immune function as well as insulin resistance in states of energy/caloric deprivation. Leptin's potential role in the therapy of several disease states, including hypothalamic amenorrhea, anorexia nervosa and syndromes of insulin resistance is under intensive investigation.

Low-dose leptin reverses skeletal muscle, autonomic, and neuroendocrine adaptations to maintenance of reduced weight

Maintenance of a reduced body weight is accompanied by decreased energy expenditure that is due largely to increased skeletal muscle work efficiency. In addition, decreased sympathetic nervous system tone and circulating concentrations of leptin, thyroxine, and triiodothyronine act coordinately to favor weight regain. These "weight-reduced" phenotypes are similar to those of leptin-deficient humans and rodents. We examined metabolic, autonomic, and neuroendocrine phenotypes in 10 inpatient subjects (5 males, 5 females [3 never-obese, 7 obese]) under 3 sets of experimental conditions: (a) maintaining usual weight by ingesting a liquid formula diet; (b) maintaining a 10% reduced weight by ingesting a liquid formula diet; and (c) receiving twice-daily subcutaneous doses of leptin sufficient to restore 8 am circulating leptin concentrations to pre-weight-loss levels and remaining on the same liquid formula diet required to maintain a 10% reduced weight. During leptin administration, energy expenditure, skeletal muscle work efficiency, sympathetic nervous system tone, and circulating concentrations of thyroxine and triiodothyronine returned to pre-weight-loss levels. These responses suggest that the weight-reduced state may be regarded as a condition of relative leptin insufficiency. Prevention of weight regain might be achievable by strategies relevant to reversing this leptin-insufficient state.

Fat and energy partitioning: longitudinal observations in leptin-treated adults homozygous for a Lep mutation

OBJECTIVE

Partitioning of body energy content in the aleptinemic ob/ob mouse differs from that in wild-type mice, but it is not known whether parallel differences exist between humans with leptin (Lep) gene mutations and healthy adults. The objective of this study was to evaluate body composition in three leptin-treated Turkish adults homozygous for a missense mutation (C-->T substitution at codon 105 resulting in Arg-->Trp) of Lep.

RESEARCH METHODS AND PROCEDURES

Subjects, one male and two female Turkish family members, were evaluated at baseline and treated for 18 months with r-MetHuLeptin. Patient data (fat mass, energy content) were compared with adult sex-specific predicted values (adjusted for weight, height, and age) derived in healthy control subjects.

RESULTS

Weight loss with leptin treatment was substantial, ranging from 43.9% to 52.1%. At baseline and with leptin treatment, the two women had a fat mass and energy content similar (+/-12%) to predicted values. Baseline fat and energy content in the male patient was high compared with predicted values (e.g., fat +33%) but approached and reached normal values (e.g., fat, +2%) after 18 months of leptin therapy.

DISCUSSION

Adult women with Lep mutations had body composition similar to normal women at baseline and with leptin treatment. In contrast, the man with a Lep mutation had high body fat in the untreated state but a normal male phenotype with leptin administration, possibly secondary to androgenic fat partitioning effects. Fat and energy partitioning can, thus, be quantitatively assessed and linked with potential hormonal mechanisms in humans with inherited disturbances in energy regulation.

Glycoengineering: the effect of glycosylation on the properties of therapeutic proteins

Therapeutic proteins have revolutionized the treatment of many diseases but low activity or rapid clearance limits their utility. New approaches have been taken to design drugs with enhanced in vivo activity and half-life to reduce injection frequency, increase convenience, and improve patient compliance. One recently used approach is glycoengineering, changing protein-associated carbohydrate to alter pharmacokinetic properties of proteins. This technology has been applied to erythropoietin and resulted in the discovery of darbepoetin alfa (DA), a hyperglycosylated analogue of erythropoietin that contains two additional N-linked carbohydrates, a threefold increase in serum half-life and increased in vivo activity compared to recombinant human erythropoietin (rHuEPO). The increased serum half-life allows for less frequent dosing to maintain target hemoglobin levels in anemic patients. Carbohydrates on DA and other molecules can also increase molecular stability, solubility, increase in vivo biological activity, and reduce immunogenicity. These properties are discussed.

Intraperitoneal leptin regulates lipid metabolism in ethanol supplemented Mus musculas heart

Diseases of the heart and blood vessels are a major cause of illness and disability worldwide. The relationship between ethanol consumption and cardiovascular disease are both complex and interconnected. Our aim of this study was to explore the effect of leptin on lipid metabolism in ethanol supplemented mice. Male Swiss mice (Mus musculas) weighing 25+/-2 g were administered ethanol (6.32 g kg(-1) body weight) for the first 30 days. Subsequently, ethanol fed mice were given intraperitoneal injections of exogenous mouse recombinant leptin (230 microg kg(-1) body weight) every alternate day for 15 days. Food and water intake and total body weight were measured every day and at the end of the experimental period of 45 days, plasma and cardiac lipids were analyzed. Exogenous leptin injections to ethanol fed mice significantly (P < 0.05) prevented the accumulation of total cholesterol, phospholipids (PL), triglycerides (TG) and free fatty acids (FFA) in the mouse heart and blood as compared to the untreated ethanol fed mice whereas, the plasma concentration of free cholesterol was significantly increased on leptin administration as compared to normal untreated mice. Moreover leptin administration significantly elevated the activities of cardiac lipoprotein lipase (LPL) and plasma lecithin cholesterol acyl transferase (LCAT) and significantly reduced the activities of cardiac HMG CoA reductase and cholesterol ester synthase (CES) on leptin administration to ethanol fed mice. Thus we could postulate that an increase in systemic leptin level prevents the accumulation of lipids in the plasma and heart of ethanol treated mice.

Microanalysis of eating behavior of three leptin deficient adults treated with leptin therapy

Leptin deficiency has been associated with extreme obesity and hyperphagia in rodents and humans. A rare genetic disorder in humans yields the absence of the hormone leptin, extreme obesity, and a ravenous appetite. Reports on these rare cases have indicated that therapy using leptin injections can yield significant weight loss and changes in appetite. The aim of this report on acute leptin therapy in three leptin deficient adults was to provide a microanalysis of changes in eating behavior and ratings of hunger and satiety. In addition to substantial weight loss, 15 weeks of leptin therapy was associated with approximately 50% reduction in food intake and substantial changes in ratings of hunger and satiety before most meals. After short-term leptin therapy, the three participants ate until ratings indicated they were satiated, which was comparable to the ratings before leptin therapy. These findings suggest that one of the primary effects of acute leptin therapy may be to reduce the ravenous hunger associated with leptin deficiency, resulting in reduced food intake and significant weight loss. These results are discussed in the context of the scientific literature pertaining to leptin and its effects on appetite and obesity.

Effect of three treatment schedules of recombinant methionyl human leptin on body weight in obese adults: a randomized, placebo-controlled trial

AIM

The aim of this study was to evaluate the effect on body weight and safety of subcutaneously administered recombinant leptin in obese adults and to evaluate whether the timing of recombinant leptin administration influences efficacy.

METHODS

A randomized, double-blind, placebo-controlled, multicentre study was designed, comprising of a 3-week dietary lead-in followed by a 12-week leptin or placebo treatment period. A total of 284 overweight and obese (body mass index 27-37.0 kg/m(2)) predominantly white (98%) women (66%) and men (34%) with a mean (+/-s.d.) 46.8+/-10.4 years of age were randomized into three treatment groups with three matching placebo groups. Recombinant leptin was administered by subcutaneous injection [10 mg/morning, 10 mg/evening or 20 mg/day (10 mg twice daily)]. Patients were counselled at baseline to reduce dietary intake by 2,100 kJ/day (500 kcal/day), and dietary advice was reinforced every 2-4 weeks.

RESULTS

No statistically significant change in body weight occurred with recombinant leptin treatment compared with placebo treatment in any treatment group. No clinically significant adverse effects were observed with the exception of an increase in injection-site reactions in patients treated with recombinant leptin (83%) vs. placebo (36%).

CONCLUSIONS

Administration of recombinant leptin to an overweight and obese population, in addition to a mildly energy-restricted diet, was not efficacious in terms of weight loss at the doses and schedules studied. The hypothesis that nocturnal administration of recombinant leptin might have a specific effect on weight loss was not supported.

Engineering a pharmacologically superior form of leptin for the treatment of obesity

Leptin plays a central role in the homeostasis of body weight through its regulatory effects on appetite and energy expenditure, yet in trials as a therapeutic agent for the treatment of obesity in humans it has been disappointing. The poor clinical efficacy of leptin results from its short circulating half-life, low potency and poor solubility, necessitating large and frequent doses to obtain even modest clinical benefit. Engineered Fc-leptin immunofusins, consisting of the Fc fragment of an immunoglobulin gamma chain followed by leptin, exhibit improved pharmacological properties with very consistent and potent biological activities. Furthermore, in extending the circulating half-life of the protein in vivo from a few minutes for leptin to many hours for Fc-leptin, these proteins have the potential to reduce drastically the dosage and frequency of administration required to obtain clinical benefit. The results of this study show that the engineered leptin immunofusins described here have significantly enhanced pharmacological properties in comparison with the recombinant leptin that was used in clinical trials. As such, they could represent an important step towards a therapeutically superior form of leptin if the disappointing performance of leptin in early clinical trials was due to its poor pharmacological properties rather than any conceptual weakness in the strategy of using leptin for the treatment of obesity and its related disorders.

Génétique de l'obésité humaine

BACKGROUND

Both genetic and environmental aspects are recognized in the obesity field but we are not able to elucidate multiple genes and gene-environment interactions with the present resources and tools used in the study of this complex disease. The purpose of this paper is to present some examples of the knowledge acquired in the field of obesity genetics and the new ongoing tools and developments that aim at studying the contribution of genes to obesity and their response to environmental changes.

MAIN POINTS

In rare cases of monogenic obesities, genetic tools have proved extremely powerful for identifying the genes responsible and for defining new syndromes. However, in common obesity, most studies include the search for genotype-phenotype associations without taking into account the influence of environment (diet, sedentary lifestyle) in the relationship. Among the limitations to this integrated approach, one can cite the difficulty of having large enough samples as well as biocomputing tools that are still in their infancy for accessing the question of multiple interactions with no "a priori hypotheses". This picture will probably change rapidly in the future.

PERSPECTIVE

Large databases and DNA and biological sample banks will be available with updated environmental information and precise phenotypes thanks especially to European working groups. The capacity for studying multiple genes at once at the DNA or RNA levels is rapidly growing. Finally, tremendous progress in biocomputing will allow the integration of information from different sources (i.e. environment, phenotype, genotype, gene expression) and thus improve our ability to deal with complexity.

Genetic and hereditary aspects of childhood obesity

Genetic factors are involved in the regulation of body weight and in determining individual responses to environmental factors such as diet and exercise. The identification and characterization of monogenic obesity syndromes have led to an improved understanding of the precise nature of the inherited component of severe obesity and has had undoubted medical benefits, whilst helping to dispel the notion that obesity represents an individual defect in behaviour with no biological basis. For individuals at highest risk of the complications of severe obesity, such findings provide a starting point for providing more rational mechanism-based therapies, as has successfully been achieved for one disorder, congenital leptin deficiency.

Human leptin: an adipocyte hormone with weight-regulatory and endocrine functions

Leptin is synthesized and secreted primarily by adipocytes, and is present in serum in direct proportion to the amount of adipose tissue. The primary role of leptin is to provide to the central nervous system a signal of energy intake and energy stores in the body so that the hypothalamus can efficiently maintain a stable body weight. The receptor for leptin in the hypothalamus signals by activation of an associated janus kinase which phosphorylates signal transducer and activator of transcription (STAT) proteins that regulate neuronal gene expression. Genetic mutations in leptin and its receptor can result in obesity in both rodents and humans, supporting a central role for leptin in the regulation of body weight. Leptin has also been implicated in a variety of physiological processes other than body weight homeostasis. Many of these functions are mediated through the central nervous system; however, the presence of leptin receptors in tissues throughout the body suggests that leptin can also have direct effects on cells and tissues. Serum leptin levels have been associated with cardiovascular risk factors after correction for adiposity. Leptin can promote platelet aggregation, which requires expression of functional leptin receptors on the platelet. Leptin-induced increases in sympathetic nerve activity have been suggested to contribute to hypertension, and leptin has been observed to increase oxidative stress in cultured endothelial cells. Many of these pathophysiologic effects of leptin on the vasculature are most likely of importance when leptin levels are elevated in obese subjects due to resistance to the weight-reducing effects of the hormone. An improved understanding of the effects of leptin on the vasculature will provide valuable insight into the relationship between obesity and cardiovascular disease.

Monogenic obesity in humans

Until relatively recently, the small number of identifiable inherited human diseases associated with marked obesity were complex, pleiotropic developmental disorders, the molecular basis for which were entirely obscure. The molecular basis for many of these complex syndromes, such as Bardet Beidl syndrome, has been revealed, providing novel insights into processes essential for human hypothalamic function and energy balance. In addition to these discoveries, which were the fruits of positional cloning, the molecular constituents of the signaling pathways responsible for the control of mammalian energy homeostasis have been identified, largely through the study of natural or artificial mutations in mice. We discuss the increasing number of human disorders that result from genetic disruption of the leptin-melanocortin pathways that have been identified. Practical implications of these findings for genetic counseling, prognostication, and even therapy have already emerged.

Clinical evidence that hyperinsulinaemia independent of gonadotropins stimulates ovarian growth

OBJECTIVE

Ovarian enlargement is a constant feature of syndromes of extreme insulin resistance. The objective of this study is to show the role of insulin on ovarian growth in the presence of low gonadotropin levels.

PATIENTS

Seven young patients with syndromes of extreme insulin resistance (five with lipodystrophy, one with Type B syndrome and one with Rabson-Mendenhall syndrome) were studied.

MEASUREMENTS

Baseline LH concentrations and luteinizing hormone releasing hormone (LHRH) tests were performed. Total testosterone, insulin and C-peptide values were measured. Pelvic ultrasounds were performed.

RESULTS

Four patients were prepubertal (age range 7-10 years old) and had prepubertal gonadotropin levels, and 2 of the 4 who were tested did not respond to LHRH (NIH 10 and RM-PAL). Three patients were Tanner stage 4 (age range 13-17 years old) and had low gonadotropins that did not respond to LHRH stimulation test. All seven patients had marked hyperinsulinaemia and 6 of 7 had at least one enlarged ovary. Testosterone values were increased in 4 of 7 patients.

CONCLUSION

This represents the first example of the pathologic role of insulin to stimulate ovarian growth with low circulating gonadotropins. Thus, while ovarian growth and steroidogenesis are normally stimulated by gonadotropins at puberty, hyperinsulinaemia stimulates pathologic growth of the ovary and an androgenic steroid profile that is active at all ages. We suggest that these patients constitute a model to separate the effect of insulin from gonadotropin in stimulating ovarian growth and/or steroidogenesis.

Long-term efficacy of leptin replacement in patients with generalized lipodystrophy

Ectopic fat accumulation has been implicated as a contributing factor in the abnormal metabolic state of obesity. One human model of ectopic fat deposition is generalized lipodystrophy. Generalized lipodystrophy is a rare disorder characterized by a profound deficiency of adipose tissue with resultant loss of triglyceride storage capacity and reduced adipokines, including leptin. Subjects with generalized lipodystrophy and reduced leptin levels often have an increased appetite leading to hyperphagia. Excess fuel consumption, coupled with a lack of adipose tissue, contributes to the significant ectopic triglyceride accumulation in the muscle and liver seen in these subjects. This ectopic fat, along with the deficiency in leptin signaling and perhaps other adipokines, likely contributes to insulin resistance, diabetes, and hepatic steatosis. We report here the long-term effects of leptin replacement in a cohort of these subjects. Fifteen patients with generalized lipodystrophy were treated with twice-daily recombinant methionyl human leptin (r-metHuLeptin) for 12 months. We evaluated metabolic parameters at baseline and every 4 months. Antidiabetes medications were decreased or discontinued as necessary. Reductions were seen in serum fasting glucose (from 205 +/- 19 to 126 +/- 11 mg/dl; P < 0.001), HbA1c (from 9 +/- 0.4 to 7.1 +/- 0.5%; P < 0.001), triglycerides (from 1,380 +/- 500 to 516 +/- 236 mg/dl; P < 0.001), LDL (from 139 +/- 16 to 85 +/- 7 mg/dl; P < 0.01), and total cholesterol (from 284 +/- 40 to 167 +/- 21 mg/dl; P < 0.01). HDL was unchanged (from 31 +/- 3 to 29 +/- 2 mg/dl; P = 0.9). Liver volumes were significantly reduced (from 3,663 +/- 326 to 2,190 +/- 159 cm3; P < 0.001), representing loss of steatosis. Decreases were seen in total body weight (from 61.8 +/- 3.6 to 57.4 +/- 3.4 kg; P = 0.02) and resting energy expenditure (from 1,929 +/- 86 to 1,611 +/- 101 kcal/24 h; P < 0.001). R-metHuLeptin led to significant and sustained improvements in glycemia, dyslipidemia, and hepatic steatosis. Leptin represents the first novel, effective, long-term treatment for severe forms of lipodystrophy.

Effects of Leptin on Biliary Lipids: Potential Consequences for Gallstone Formation and Therapy in Obesity

Gallstone disease is exceptionally common, occurring especially in Western populations, with cholesterol gallstones predominating. Currently, it is believed that obesity is the most consistent and important risk factor for the development of cholesterol gallstones. Obesity has been shown to be associated with the supersaturation of bile with cholesterol because of increased hepatic secretion of the sterol. In accord with current information from experimental studies, leptin appears to be involved in biliary cholesterol secretion and cholesterol gallstone formation in humans. This review summarizes the current information on the role of obesity in biliary lipid secretion as well as the effect of leptin and its potential consequences for gallstone formation and therapy in the obese.

Leptin treatment induces loss of bone marrow adipocytes and increases bone formation in leptin-deficient ob/ob mice

Normal mice and leptin-deficient ob/ob mice were treated with leptin to study effects on osteogenesis and adipogenesis in bone marrow. Leptin treatment significantly decreased bone marrow adipocyte size and number in ob/ob mice while increasing bone formation, BMC, and BMD. The results suggest that, in leptin-sensitive animals, the reduction in marrow adipocytes has positive effects on bone formation.

INTRODUCTION

Adipocytes, osteoblasts, and osteoclasts have leptin receptors, and leptin can also affect bone metabolism indirectly through its receptors in the hypothalamus. We examined the effects of leptin treatment on bone formation, BMD, and marrow adipocyte population in normal mice and leptin-deficient ob/ob mice.

MATERIALS AND METHODS

At the age of 15 weeks, mice were implanted with Alzet osmotic pumps for subcutaneous delivery of treatment solutions (saline, 2.5 microg leptin/day, or 10 microg leptin/day) for 14 days at a delivery rate of 0.25 microl/h. Bone formation was assessed using fluorochrome labels, cell populations were quantified using histomorphometry, and bone densitometry was measured using DXA. We also used a Luminex Beadlyte assay system to quantify cell survival markers in bone marrow samples.

RESULTS AND CONCLUSIONS

Results indicate that both doses of leptin decreased the number of marrow adipocytes in ob/ob mice by >20% (p < 0.05) compared with PBS-treated ob/ob mice. The decrease in adipocyte number with leptin treatment is accompanied by an increase in concentration of the apoptosis marker caspase-3 in bone marrow adipocytes and hematopoietic cells. Both leptin doses also significantly (p < 0.05) increased the percentage of fluorochrome-labeled tibial endosteal surface by >30% compared with PBS-treated ob/ob mice. Leptin treatment increased whole body BMC by >30% in the ob/ob mice receiving the highest leptin dose. Leptin treatment provided no increase in bone formation, BMC, or BMD in normal, leptin-replete mice.

Effect of leptin replacement on brain structure in genetically leptin-deficient adults

The hormone leptin profoundly affects body weight and metabolism. Three human adults (two women, 35 and 40 yr old; one man, age 27) have been identified with a recessive mutation in the ob gene, which is homologous to the mutation in ob/ob mice, and produces leptin deficiency and morbid obesity. Because leptin replacement increases brain weight and changes brain protein and DNA content in ob/ob mice, we hypothesized that analogous treatment of leptin-deficient humans would alter brain tissue composition. Volumetric T1-weighted magnetic resonance images of the brain were acquired before and at 6 and 18 months after initiation of replacement therapy (daily sc injections of recombinant methionyl human leptin), which produced dramatic loss in body weight. We used voxel-based morphometry to test for increased gray matter tissue concentration after initiation of leptin replacement and detected increases at 6 months in the anterior cingulate gyrus, the inferior parietal lobule, and the cerebellum. These increases were maintained for over 18 months, with identical stereotaxic coordinates of the maxima for the effects. Our findings suggest that leptin can have sustained effects on tissue composition in the human brain and broaden the potential spectrum of leptin's influence beyond feeding behavior and endocrine function.

Leptin reverses nonalcoholic steatohepatitis in patients with severe lipodystrophy

Severe lipodystrophy is characterized by diminished adipose tissue and hypoleptinemia, leading to ectopic triglyceride accumulation. In the liver, this is associated with steatosis, potentially leading to nonalcoholic steatohepatitis (NASH). We investigated the prevalence of NASH and the effect of leptin replacement in these patients. Ten patients with either generalized lipodystrophy (8 patients) or Dunnigan's partial lipodystrophy (2 patients) were included in this analysis. Paired liver biopsy specimens were obtained at baseline and after treatment with recombinant methionyl human leptin (r-metHuLeptin), mean duration 6.6 months. The extents of portal and parenchymal inflammation, steatosis, ballooning, presence of Mallory bodies, and fibrosis in liver biopsy specimens were scored using a previously validated system developed to assess NASH activity. Histological disease activity was defined as the sum of ballooning, steatosis, and parenchymal inflammation scores. We concurrently tested serum triglycerides and aminotransferases and estimations of liver volume and fat content by magnetic resonance imaging. Eight of 10 patients met histological criteria for NASH at baseline. After treatment with r-metHuLeptin, repeat histological examinations showed significant improvements in steatosis (P = .006) and ballooning injury (P = .005), with a reduction of mean NASH activity by 60% (P = .002). Fibrosis was unchanged. Significant reductions were seen in mean serum triglycerides (1206-->226 mg/dL, P = .002), glucose (220-->144 mg/dL, P = .02), insulin (46.4-->24.8 muIU/mL, P = .004), ALT (54-->24 U/L, P = .02), AST (47-->22 U/L, P = .046), liver volume (3209-->2391 cm(3), P = .007), and liver fat content (31-->11%, P = .006). In conclusion, r-metHuLeptin therapy significantly reduced triglycerides, transaminases, hepatomegaly, and liver fat content. These reductions were associated with significant reductions in steatosis and the hepatocellular ballooning injury seen in NASH.

Exogenous leptin restores in vitro T cell proliferation and cytokine synthesis in patients with common variable immunodeficiency syndrome

Common variable immunodeficiency (CVID) is a primary immunodeficiency characterized by hypogammaglobulinemia. Leptin has been implicated as an antiapoptotic compound as well as a stimulant of the immune response. Leptin administration is capable of reversing the immune deficiency that occurs upon starvation. We investigated a possible role for leptin in CVID; a condition associated with lowered plasma leptin levels. Thirty-eight patients were studied. Addition of leptin to the tissue culture media of PBMC from CVID patients increased the proliferative response of lymphocytes to mitogens and decreased activation-induced apoptosis of these cells. IL-2 and specially IL-4 production also increased significantly upon addition of leptin to the PBMC cultures. Our results suggest that leptin may be involved in some of the cellular defects observed in CVID and indicate a novel therapeutic strategy to improve immune function in these patients.

The long-term effect of recombinant methionyl human leptin therapy on hyperandrogenism and menstrual function in female and pituitary function in male and female hypoleptinemic lipodystrophic patients

Lipodystrophy patients are hypoleptinemic and insulin resistant. Women have enlarged polycystic ovaries, hyperandrogenism, and amenorrhea. We have determined the role of correction of hypoleptinemia on these metabolic and neuroendocrine parameters. Ten females and 4 males with generalized lipodystrophy were treated with recombinant methionyl human leptin (r-metHuLeptin) in physiologic doses in an open-labeled study for a period of 12 and 8 months, respectively. In the female group, serum free testosterone decreased from 39.6 +/- 11 to 18.9 +/- 4.5 ng/dL (P < 0.01) and serum sex hormone binding globulin increased from 14 +/- 2.5 to 25 +/- 4.8 nmol/L (P < 0.02). Luteinizing hormone (LH) responses to LH releasing hormone were more robust after therapy and significantly changed in the youngest group of 3 female patients (P < 0.01). Ovarian ultrasound showed a polycystic ovarian disease pattern in all patients and did not change after therapy. Eight of the 10 patients had amenorrhea prior to therapy and all 8 developed normal menses after therapy. In the male group, serum testosterone tended to increase from 433 +/- 110 to 725 +/- 184 ng/dL (P = 0.1) and sex hormone binding globulin also increased from 18.25 +/- 2.6 to 27 +/- 1.7 nmol/L (P < 0.04) following r-metHuLeptin therapy. Serum LH response to LH releasing hormone did not show significant changes. Five additional hypoleptinemic male subjects with minimal metabolic abnormalities underwent normal pubertal development without receiving r-metHuLeptin therapy. In both genders, insulin-like growth factor increased significantly and there were no differences in growth hormone, thyroid, or adrenal hormone levels following r-metHuLeptin therapy. Glycemic parameters significantly improved after r-metHuLeptin therapy in both groups. Hypoglycemic medications were discontinued in 7 of 12 patients and dramatically reduced in 5 patients. r-metHuLeptin therapy plays an important role in insulin sensitivity. In females, it plays an additional role in normalizing menstrual function. This is likely to occur both from increasing insulin sensitivity and from restoring LH pulsatility. The persistent hypoleptinemic state in these subjects did not inhibit pubertal development.

Leptin: structure, function and biology

Leptin is an adipocyte-derived hormone that acts as a major regulator for food intake and energy homeostasis. Leptin deficiency or resistance can result in profound obesity, diabetes, and infertility in humans. Since its discovery, our understanding of leptin's biological functions has expanded from anti-obesity to broad effects on reproduction, hematopoiesis, angiogenesis, blood pressure, bone mass, lymphoid organ homeostasis, and T lymphocyte systems. Leptin orchestrates complex biological effects through its receptors, expressed both centrally and peripherally. Leptin receptor belongs to the class I cytokine receptor superfamily. At least five isoforms of leptin receptor exist, primarily because of alternate splicing. The longest form is capable of full signal transduction. The short forms may serve as leptin binding proteins and play a role in leptin transporting across the blood-brain barrier. In this review, we present the crystal structure of leptin and the structural comparison with other four-helical cytokines, discuss the leptin-receptor binding models based on other cytokine-receptor complex structures, and summarize the most recent progress on leptin signal transduction pathways--especially its link to peripheral lipid metabolism through AMP-activated protein kinase and hepatic stearoyl-CoA desaturase-1 pathways. Furthermore, we propose the structure based design of leptin analogs with increased stability, improved potency, enhanced blood-brain barrier transport, and extended time action for future therapeutic application.

Prevention and reversal of renal injury by leptin in a new mouse model of diabetic nephropathy

Diabetic nephropathy is the leading cause of end-stage renal disease, for which effective therapy to prevent the progression at advanced stages remains to be established. There is also a long debate whether diabetic glomerular injury is reversible or not. Lipoatrophic diabetes, a syndrome caused by paucity of adipose tissue, is characterized by severe insulin resistance, dyslipidemia, and fatty liver. Here, we show that a genetic model of lipoatrophic diabetes (A-ZIP/F-1 mice) manifests a typical renal injury observed in human diabetic nephropathy that is associated with glomerular hypertrophy, diffuse and pronounced mesangial widening, accumulation of extracellular matrix proteins, podocyte damage, and overt proteinuria. By crossing A-ZIP/F-1 mice with transgenic mice overexpressing an adipocyte-derived hormone leptin, we also reveal that leptin completely prevents the development of hyperglycemia and nephropathy in A-ZIP/F-1 mice. Furthermore, continuous leptin administration to A-ZIP/F-1 mice by minipump beginning at 40 weeks of age significantly alleviates the glomerular injury and proteinuria. These findings demonstrate the therapeutic usefulness of leptin at least for a certain type of diabetic nephropathy. The model presented here will serve as a novel tool to analyze the molecular mechanism underlying not only the progression but also the regression of diabetic nephropathy.

The delicate balance between fat and muscle: adipokines in metabolic disease and musculoskeletal inflammation

Adipose tissue has evolved as a complex organ with functions far beyond the mere storage of energy. Chronic oversupply of calories, common to Western-style diets, frequently goes hand-in-hand with an altered secretion pattern of adipokines and elevated plasma free fatty acid levels, known to modulate insulin sensitivity in skeletal muscle. Intramyocellular accumulation of lipids directly attenuates insulin signaling within myocytes via distinct kinases. Obesity is also accompanied by an enhanced basal inflammatory tone, originating from adipocytes and adipose tissue-associated macrophages. In addition, adipocytes accumulate within the skeletal muscle and exert direct paracrine effects on muscle insulin sensitivity.

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.

Effects of exogenous leptin on satiety and satiation in patients with lipodystrophy and leptin insufficiency

To examine leptin's role in human appetite regulation, we studied recombinant methionyl human leptin's effects on satiation and satiety in a model of leptin insufficiency, lipodystrophy. Eight females with hypoleptinemia and lipodystrophy were given sc injections of A-100 (maximal dose, 200% of that predicted to normalize serum leptin) for 4 months. Satiation and satiety were determined before and again during leptin treatment. Satiation was measured as the time to voluntary cessation of eating from a standardized food array after a 12-h fast. Satiety was determined as the time to hunger sufficient to consume a full meal after consumption of a standardized preload. During leptin treatment, satiation time decreased (41.2 +/- 18.2 to 19.5 +/- 10.6 min; P = 0.01), satiety time increased (62.9 +/- 64.8 to 137.8 +/- 91.6 min; P = 0.04), energy consumed to produce satiation decreased (2034 +/- 405 to 1135 +/- 432 kcal or 8.5 +/- 1.7 to 4.7 +/- 1.8 MJ; P < 0.01), and the amount of food desired in the postabsorptive state decreased (P < 0.02). Ghrelin concentrations also decreased during leptin administration (284.3 +/- 127.9 to 140.6 +/- 104.5 pmol/liter; P < 0.002). We conclude that increased leptin in patients with lipodystrophy results in less caloric, shorter, more satiating meals and longer-lived satiety. These data support the hypothesis that leptin plays an important, permissive role in human appetite regulation.

Anti-inflammatory effects of leptin and cholecystokinin on acetic acid-induced colitis in rats: role of capsaicin-sensitive vagal afferent fibers

Leptin and cholecystokinin (CCK) have a synergistic interaction in the suppression of food intake, and afford similar gastroprotective activity. The present study was designed to investigate the putative protective effects of CCK and leptin on acute colonic inflammation. Leptin or CCK-8s was injected to rats intraperitoneally immediately before and 6 h after the induction of colitis with acetic acid. CCK-A receptor antagonist (L-364,718) or CCK-B receptor antagonist (L-365,260) was injected intraperitoneally 15 min before leptin or CCK treatments. In a group of rats, vagal afferent fibers were denervated by topical application of capsaicin on the cervical vagi. Rats were decapitated at 24 h, and the distal 8 cm of the colon were removed for macroscopic scoring, determination of tissue wet weight index (WWI), histologic assessment and tissue myeloperoxidase (MPO) activity. All inflammation parameters were increased by acetic acid-induced colitis compared to control group. Leptin or CCK-8s treatment reduced these parameters in a similar manner, while co-administration of leptin and CCK was found to be more effective in reducing the macroscopic score and WWI. CCK-8s-induced reduction in the score and WWI was prevented by CCK-A, but not by CCK-B receptor antagonist, whereas neither antagonist altered the inhibitory effect of leptin on colitis-induced injury. On the other hand, perivagal capsaicin prevented the protective effects of both CCK-8s and leptin on colitis. Our results indicate that leptin and CCK have anti-inflammatory effects on acetic acid-induced colitis in rats, which appear to be mediated by capsaicin-sensitive vagal afferent fibers involving the reduction in colonic neutrophil infiltration.

Mice body weight gain is prevented after naked human leptin cDNA transfer into skeletal muscle by electroporation

BACKGROUND

In this investigation, the feasibility of gene therapy for obesity by electroporational transfer of naked plasmid with leptin cDNA into skeletal muscle was tested. Both young and adult mice were studied.

METHODS

Human leptin cDNA was attached to the human insulin precursor secretion signal peptide gene. The fused gene was then inserted into the mammalian expression vector pcDNA3.1(-) and transferred into skeletal muscle of normal female mice using electroporation.

RESULTS

During the time of exogenic gene expression, daily food intake of leptin cDNA-treated mice was observed to be lower than the control. The body weight gain was prevented efficaciously regardless of if they were young or adult. At the 7th week after gene transfer, the body weight of both young and adult leptin cDNA-treated mice was about 20% lighter than the control. Although the body weight of pair fed controlled adult mice was close to the leptin cDNA-treated mice at the 8th week, they were always heavier than the leptin cDNA-treated mice before this time. The levels of retroperitoneal fats and serum TG of leptin cDNA-treated mice were markedly lower than that of the control. The relative serum hyperleptinemic level could last for about 2 months. The expression of leptin cDNA in muscle cells was also detected by RT-PCR. The levels of serum insulin and glucose of leptin cDNA-treated mice decreased slightly. Our data also showed that the hyperleptinmia resulted in uterus expansion in young mice, but not in the adults.

CONCLUSION

The present study provides evidence of successful electroporation of naked plasmid DNA transfer for prevention or treatment of mice obesity.

Obesity: the integrated roles of environment and genetics

Obesity represents one of the most serious global health issues with approximately 310 million people presently affected. It develops because of a mismatch between energy intake and expenditure that results from behavior (feeding behavior and time spent active) and physiology (resting metabolism and expenditure when active). Both of these traits are affected by environmental and genetic factors. The dramatic increase in the numbers of obese people in Western societies reflects mostly changing environmental factors and is linked to reduced activity and perhaps also increased food intake. However, in all societies and subpopulations, there are both obese and nonobese subjects. These differences are primarily a consequence of genetic factors as is revealed by the high heritability for body mass index. Most researchers agree that energy balance and, hence, body weight are regulated phenomena. There is some disagreement about exactly how this regulation occurs. However, a common model is the "lipostatic" regulation system, whereby our energy stores generate signals that are compared with targets encoded in the brain, and differences between these drive our food intake levels, activity patterns, and resting and active metabolisms. Considerable advances were made in the last decade in understanding the molecular basis of this lipostatic system. Some obese people have high body weight because they have broken lipostats, but these are a rare minority. This suggests that for the majority of obese people, the lipostat is set at an inappropriately high level. When combined with exposure to an environment where there is ready availability of food at low energy costs to obtain it, obesity develops. The evolutionary background to how such a system might have evolved involves the evolution of social behavior, the harnessing of fire, and the development of weapons that effectively freed humans from the risks of predation. The lipostatic model not only explains why some people become obese whereas others do not, but also allows us to understand why energy-controlled diets do not work. Drug-based solutions to the obesity problem that work with the lipostat, rather than against it, are presently under development and will probably be in regular use within 5-10 y. However, several lines of evidence including genetic mapping studies of quantitative trait loci associated with obesity suggest that our present understanding of the regulatory system is still rudimentary. In particular, we know nothing about how the target body weight in the brain is encoded. As our understanding in this field advances, new drug targets are likely to emerge and allow us to treat this crippling disorder.

Gut hormones and the control of appetite

Obesity is the main cause of premature death in the UK. Worldwide its prevalence is accelerating. It has been hypothesized that a gut nutriment sensor signals to appetite centres in the brain to reduce food intake after meals. Gut hormones have been identified as an important mechanism for this. Ghrelin stimulates, and glucagon like peptide-1, oxyntomodulin, peptide YY (PYY), cholecystokinin and pancreatic polypeptide inhibit, appetite. At physiological postprandial concentrations they can alter food intake markedly in humans and rodents. In addition, in obese humans fasting levels of PYY are suppressed and postprandial release is reduced. Administration of gut hormones might provide a novel and physiological approach in anti-obesity therapy. Here, we summarize some of the recent advances in this field.

Proteinuric nephropathy in acquired and congenital generalized lipodystrophy: baseline characteristics and course during recombinant leptin therapy

Generalized lipodystrophy is characterized by adipose tissue absence, hypoleptinemia, hypertriglyceridemia, insulin resistance, diabetes, hepatomegaly, and nonalcoholic steatohepatitis. In the course of recruiting patients for treatment with recombinant leptin, we were struck by the frequency and severity of proteinuria. We evaluated 25 patients with generalized lipodystrophy. Eighteen were treated with recombinant leptin, and we have followed 15 on leptin for 4-36 months. We followed renal parameters at baseline and during follow-up visits. Renal biopsies were performed as clinically indicated. At baseline, 22 of 25 patients (88%) had elevated urine albumin excretion (>30 mg/24 h), 15 (60%) had macroalbuminuria (>300 mg/24 h), and five (20%) had nephrotic-range proteinuria (>3500 mg/24 h). Twenty-three (92%) had elevated creatinine clearance (>125 ml/min.1.73 m(2)). Eleven of 15 patients (73%) treated with recombinant leptin exhibited reduction in proteinuria, associated with reduction of hyperfiltration. Four patients who did not improve are discussed individually. Renal biopsy findings were remarkable for focal segmental glomerulosclerosis in four patients, membranoproliferative glomerulonephritis in two patients, and diabetic nephropathy in one patient. In conclusion, generalized lipodystrophy is associated with proteinuria and unique renal pathologies, including focal segmental glomerulosclerosis and membranoproliferative glomerulonephritis. The majority treated with recombinant leptin demonstrated reduction in proteinuria and hyperfiltration.

The clinical uses of leptin

Leptin is the first of a group of adipocyte-secreted hormones to be used clinically to treat hypoleptinemic states. In children with congenital leptin deficiency and extreme obesity, leptin induces satiety and a dramatic loss of weight. In hypoleptinemic patients with extreme insulin resistance and lipodystrophy, leptin ameliorates insulin resistance, hyperglycemia, hyperinsulinemia, dyslipidemia and hepatic steatosis. In both these leptin-deficient states, leptin therapy restores gonadotrophin secretion, as well as luteinizing hormone and thyroid-stimulating hormone pulsitility.

Monogenic human obesity syndromes

Over the past decade, we have witnessed a major increase in the scale of scientific activity devoted to the study of energy balance and obesity. This explosion of interest has, to a large extent, been driven by the identification of genes responsible for murine obesity syndromes and the novel physiological pathways revealed by those genetic discoveries. We and others recently have identified several single-gene defects causing severe human obesity. Many of these defects have occurred in molecules identical or similar to those identified as a cause of obesity in rodents. This chapter will consider the human monogenic obesity syndromes that have been characterized to date and discuss how far such observations support the physiological role of these molecules in the regulation of human body weight and neuroendocrine function.

Changes in body composition in patients with severe lipodystrophy after leptin replacement therapy

Leptin, an adipocyte hormone, when replaced in patients with lipodystrophy, improves insulin resistance, hyperglycemia, dyslipidemia, and hepatic steatosis. Changes in body composition accompany this metabolic improvement. We studied 14 patients (3 men and 11 women); 12 of who had generalized lipodystrophy (7 congenital, 5 acquired), and 2 patients had partial lipodystrophy. Body composition and related parameters were evaluated at baseline and after 4 and 12 months of leptin therapy. Baseline body mass index (BMI) was 21.7 +/- 0.8 kg/m(2), the percent body fat was 9.5% +/- 1.6%, and the serum leptin level was 1.7 +/- 0.3 ng/mL. On treatment, serum leptin levels increased by 10-fold. All patients reported a decrease in appetite on therapy. After 4 months, both daily caloric intake and resting energy expenditure (REE) decreased. The liver volume decreased (baseline = 3,055 +/- 281 cm(3); 4 months = 2,433 +/- 243 cm(3), P =.006). Dual energy x-ray absorptiometry (DEXA) demonstrated significant decreases in fat mass (5.4 +/- 0.8 kg to 5.0 +/- 0.8 kg; P =.003) and lean body mass (51.2 +/- 3.2 kg to 48.3 +/- 3.4 kg; P =.003) at 4 months on therapy. There was no impact of leptin therapy on bone mineral content, mineral density, and metabolism. Changes in body composition occurred during the first 4 months of leptin therapy, but then stabilized and were sustained thereafter.

Leptin prevents obesity induced by a high-fat diet after diet-induced weight loss in the marsupial S. crassicaudata

The aims of this study were to determine in the marsupial Sminthopsis crassicaudata, the effects of leptin on food intake, body weight, tail width (a reflection of fat stores), and leptin mRNA, after caloric restriction followed by refeeding ad libitum with either a standard or high-fat preferred diet. S. crassicaudata (n = 32), were fed standard laboratory diet (LabD; 1.01 kcal/g, 20% fat) ad libitum fo 3 days. On days 4-10, animals received LabD at 75% of basal intake and then (days 11-25) were fed either LabD or a choice of LabD and mealworms (MW; 2.99 kcal/g, 30% fat); during this time, half the animals (n = 8) in each group received either leptin (2.5 mg/kg) or PBS intraperitoneally two times daily. On day 26, animals were killed and fat was removed for assay of leptin mRNA. At baseline, body weight, tail width, and food intake were similar in each group. After caloric restriction, body weight (P < 0.001) and tail width (P < 0.001) decreased. On return to ad libitum feeding in the PBS-treated animals, body weight and tail width returned to baseline in the LabD-fed animals (P < 0.001) and increased above baseline in the MW-fed animals (P < 0.001). In the LabD groups, tail width (P < 0.001) and body weight (P < 0.001) decreased after leptin compared with PBS. In the MW groups, the increase in tail width (P < 0.001) and body weight (P = 0.001) were attenuated after leptin compared with PBS. The expression of leptin mRNA in groups fed MW were greater in PBS than in leptin-treated animals (P < 0.05). Therefore, after diet-induced weight loss, leptin prevents a gain in fat mass in S. crassicaudata; this has potential implications for the therapeutic use of leptin.

Efficacy of recombinant methionyl human leptin therapy for the extreme insulin resistance of the Rabson-Mendenhall syndrome

Recombinant methionyl human leptin (r-metHuLeptin) therapy has shown clear efficacy in the treatment of severe insulin resistance associated with lipodystrophy syndromes and low leptin levels. We treated two siblings with Rabson-Mendenhall syndrome (severe insulin resistance and presumed insulin receptor mutations). The brother and sister, aged 13 and 11 yr, respectively, had severe acanthosis nigricans, insulin resistance, and diabetes. Both were taking 2000 mg metformin and 2 mg rosiglitazone daily; the brother was also taking 300 U regular insulin daily. In contrast to our lipoatrophic patients treated with r-metHuLeptin, these two patients had a higher percent body fat and low-normal fasting triglycerides [42 mg/dl (0.37 mmol/liter), male sibling, and 33 mg/dl (0.47 mmol/liter), female sibling]. The siblings were treated with r-metHuLeptin therapy for 10 months and demonstrated a 40-60% decrease in fasting serum glucose and insulin levels and improved glycosylated hemoglobin. There was corresponding improvement in glucose and insulin tolerance during leptin therapy. This is the first report of a partial, but significant, effect of r-metHuLeptin administration in patients with extreme insulin resistance with a presumed insulin receptor mutation and low serum triglyceride levels.

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.

Role of brain-gut axis in healing of gastric ulcers

The previous studies demonstrated the pivotal role of capsaicin-sensitive peptidergic sensory neurons and vagal nerves in the maintenance of gastric mucosal integrity. The aim of the present study was: 1). to examine the effect of the functional ablation of sensory neurons with neurotoxic dose of capsaicin and surgical vagotomy on the course of healing of gastric ulcer in rat, and 2). to compare the ulcer healing action of leptin in rats with or without capsaicin-induced inactivation of sensory neurons. Three series of experiments (A, B and C) were performed in Wistar rats with gastric ulcers induced by acetic acid method. In series A, the course of ulcer healing was compared in rats with intact and capsaicin-inactivated sensory neurons. In the series B, the effect of vagotomy on the ulcer healing and accompanying changes in GBF were determined at day 8 and 16 after ulcer induction. The rats of series C, consisting of animals with intact nerves or those with capsaicin-denervation, received the 7-day treatment with exogenous leptin (10 microg/kg i.p. twice daily) to check whether blockade of sensory nerves could influence the acceleration of ulcer healing by this peptide. Capsaicin-induced ablation of sensory neurons significantly delayed ulcer healing and this was accompanied by the significant fall in the GBF and the significant rise in the gastric mucosal gene expression of IL-1beta and TNF-alpha. Vagotomy significantly delayed ulcer healing and led to decrease in GBF at ulcer margin. Treatment with exogenous leptin significantly accelerated ulcer healing, increased the GBF at ulcer margin and upregulated mRNA for iNOS and these effects were attenuated in rats with capsaicin-deactivation of sensory neurons. We conclude that: 1). vagal and sensory neurons contribute to the gastric ulcer healing process possibly due to the increase of GBF, the limitation of inflammatory response, and overexpression of TGFalpha and iNOS resulting in NO release, and 2). the acceleration of ulcer healing by leptin was attenuated in animals with capsaicin-denervation suggesting an involvement of neuropeptides released from sensory afferent nerves in the ulcer healing effect of this hormone.

The anti-inflammatory effect of leptin on experimental colitis: involvement of endogenous glucocorticoids

The present study was designed to compare the effect of leptin on acute colonic inflammation with that of acute stress exposure, which acts via the hypothalamic-pituitary-adrenal (HPA) axis. Sprague-Dawley rats of both sexes were administered intrarectally with acetic acid. Either leptin (10 microg/kg; i.p.) or saline was injected immediately before and 6 h after the induction of colitis. A group of rats was exposed to water avoidance stress (WAS) for 30 min at the 6th h of colitis induction. RU-486 (2 mg/kg; i.p.), a glucocorticoid receptor antagonist, was injected intraperitoneally, at 12 and 1 h before the initial leptin injection, and at 1 h before the second leptin injection or exposure to WAS. Rats were decapitated at 24 h and the distal 8 cm of the colon were removed for macroscopic and microscopic scoring, determination of tissue wet weight index (WI) and tissue myeloperoxidase activity (MPO). Acetic acid-induced colitis significantly increased macroscopic and microscopic damage scores, WI and MPO, compared to control group. Exposure to acute WAS or treatment with leptin reduced the elevations in damage scores, WI and MPO induced by colitis, but no additive inhibitory effect was observed when WAS and leptin were applied together. RU-486 treatment reversed the inhibitory effects of leptin or WAS on colonic inflammation. Our results demonstrate that exogenous leptin mimics the effects of HPA axis activation on colitis-induced inflammatory process. The results also suggest that the anti-inflammatory effect of leptin involves a tissue neutrophil-dependent mechanism and is dependent on the release of glucocorticoids.

Leptin as a Potential Treatment for Obesity

Despite significant reductions in the consumption of dietary fat, the prevalence of obesity is steadily rising in western civilization. Of particular concern is the recent epidemic of childhood obesity, which is expected to increase the incidence of obesity-related disorders. The obese gene (ob) protein product leptin is a hormone that is secreted from adipocytes and functions to suppress appetite and increase energy expenditure. Leptin is an attractive candidate for the treatment of obesity as it is an endogenous protein and has been demonstrated to have potent effects on bodyweight and adiposity in rodents. Whereas leptin has been successfully used in the treatment of leptin-deficient obese patients, trials in hyperleptinemic obese patients have yielded variable results. Long-acting leptins have been tried but with no greater success. Other strategies including the use of leptin analogs and other factors that bypass normal leptin delivery systems are being developed. Identifying the mechanisms at the molecular level by which leptin functions will create new avenues for pharmaceutical targeting to simulate the intracellular effects of leptin.

Clinical features and metabolic and autoimmune derangements in acquired partial lipodystrophy: report of 35 cases and review of the literature

We describe clinical features, body fat distribution, and prevalence of metabolic abnormalities in 35 patients with acquired partial lipodystrophy (APL) seen by us over 8 years, and also review 220 cases of APL described in the literature. Based on the review and our experience, we propose that the essential diagnostic criterion for APL is the gradual onset of bilaterally symmetrical loss of subcutaneous fat from the face, neck, upper extremities, thorax, and abdomen, in the "cephalocaudal" sequence, sparing the lower extremities. Analysis of the pooled data revealed that female patients were affected approximately 4 times more often than males. The median age of the onset of lipodystrophy was 7 years. Several autoimmune diseases, in particular systemic lupus erythematosus and dermatomyositis, were associated with APL. The prevalence rates of diabetes mellitus and impaired glucose tolerance were 6.7% and 8.9%, respectively. Approximately 83% of APL patients had low complement (C) 3 levels and the presence of polyclonal immunoglobulin C3 nephritic factor. Twenty-two percent of patients developed membranoproliferative glomerulonephritis (MPGN) after a median of approximately 8 years following the onset of lipodystrophy. Compared with patients without renal disease, those with MPGN had earlier age of onset of lipodystrophy (12.6 +/- 10.3 yr vs 7.7 +/- 4.4 yr, respectively; p < 0.001) and a higher prevalence of C3 hypocomplementemia (78% vs 95%, respectively; p = 0.02). The pathogenesis of fat loss and MPGN in patients with APL remains unclear, but activation of an alternate complement pathway has been implicated. Treating the cosmetic disfigurement by surgical procedures has yielded inconsistent results. The use of thiazolidinediones to treat fat loss in patients with APL remains anecdotal. Prognosis is mainly determined by renal insufficiency due to MPGN.