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Query: UMLS:C0028754 (obesity)
 124,988 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Obesity etiology and treatment have been fraught with disappointment for researchers, because the mechanisms regulating fuel homeostasis and adiposity are incompletely understood. It can now be hypothesized in the light of new evidences that the control of body weight and composition depends upon an axis with three interrelated and self-controlled components: 1) food intake; 2) nutrient turnover and thermogenesis and 3) body fat stores, all of which underly complex feedback mechanisms. This approach considers two of the most relevant recent findings in the field (leptin and beta 3-adrenoceptors), adding new views to previous metabolic models of obesity. This perspective supplies some additional clues to the understanding of body composition regulation as well as the potential involvement of genetic and hypothalamic disorders in the onset of obesity.
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PMID:Regulation of energy balance and adiposity: a model with new approaches. 914 47

Leptin, the product of the ob gene, reduces body fat in genetically obese animals and circulates in elevated concentrations in the blood of obese patients. Polymorphic markers situated in the proximity of the human ob gene have recently been suggested to be linked to morbid obesity. We have studied the possible association between the microsatellite markers near the ob gene and morbid obesity in 252 morbidly obese patients with a mean body mass index (BMI) of 43 +/- 7 kg/m2, and 151 lean controls with a mean BMI of 22 +/- 2 kg/m2, and searched for linkage of these gene markers to obesity in 76 affected sib-pairs (BMI > or = 32). No significant association was observed between any of the eight microsatellite markers and morbid obesity, and affected-sib-pair analysis failed to show linkage of three selected ob gene markers to obesity in the sibships. There was a strong positive correlation between serum leptin levels and BMI in morbidly obese patients; a carrier status for either of the two most prevalent alleles of the microsatellite marker D7S530 in the vicinity of the ob gene was associated with serum leptin levels in the obese subjects. Two of the markers (D7S2519, D7S649) showed a significant relation to the weight-losing response to a 16-week very-low-calorie dietary intervention. We have thus been able to confirm a tight relationship between serum leptin and body mass but have found no evidence for genetic linkage of the ob gene markers to morbid obesity in a population considered to represent a genetic isolate and to be an ideal model for studies of complex disorders.
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PMID:Markers for the gene ob and serum leptin levels in human morbid obesity. 915 Jul 18

The cloning of human and mouse cDNAs from brain that encode high affinity leptin receptors was recently reported. We have physically localized the human leptin receptor gene (LEPR) to a region at 1p31, between the anonymous microsatellite markers D1S515 and D1S198. The genomic structure of the human leptin receptor gene, corresponding to the published human brain cDNA sequence, spans over 70 kb and includes 20 exons. Since the leptin receptor gene is a candidate gene for obesity, and because of its proximity to D1S198, a marker previously linked to insulin secretion, the LEPR gene was sequenced in 20 non-diabetic Pima Indians chosen for extremes in percent body fat and in their acute insulin response to intravenous glucose. Seven polymorphic sites were identified. Two of these polymorphisms, Lys109Arg and Gln223Arg, are amino acid substitutions in the extracellular domain of the leptin receptor, one polymorphism is a silent substitution, and four occur in non-coding regions of the leptin receptor. Four of these sites are in linkage disequilibrium with one another. Nucleotides at three noncoding polymorphic sites were found exclusively in obese Pima Indians. This demonstrates an association between variation at the leptin receptor gene and obesity in humans.
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PMID:Structure and sequence variation at the human leptin receptor gene in lean and obese Pima Indians. 915 41

In 112 obese compared with 42 lean children, we found that serum leptin is elevated early in the evolution of childhood-onset obesity (28.4 +/- 1.4 vs. 4.5 +/- 0.4 ng/ml in lean children, P < 0.0001) and correlates with adiposity. Obese children also had higher serum leptin normalized to fat mass. Despite high serum leptin, obese children ingested 2-3 times more calories than did lean control subjects (P < 0.0001) and gained weight rapidly (10.2 +/- 0.3 vs. 2.9 +/- 0.1 kg/year in control subjects, P < 0.0001). Girls had higher leptin levels than did boys, in obese as well as in nonobese children, and showed a closer correlation between adiposity and serum leptin. Elevation of serum leptin was comparable before and after puberty in obese boys, but puberty further increased leptin levels in obese girls (36 +/- 3 ng/ml), resulting in a clear sexual dimorphism with pubertal obese boys (22 +/- 5 ng/ml, P < 0.005). In conclusion, increased serum leptin reflects but does not halt fat deposition in childhood obesity. After normalization to body adiposity, leptin was found to be increased independently by obesity status, female sex, and female sexual maturation.
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PMID:Circulating leptin in normal children and during the dynamic phase of juvenile obesity: relation to body fatness, energy metabolism, caloric intake, and sexual dimorphism. 916 70

Zucker fatty (fa/fa) rats exhibit overt obesity, hypercholesterolemia, hyperlipidemia, and hyperglycemia as recessive traits. The fa mutation has been determined to be a missense mutation in the extracellular domain of the leptin receptor. We report herein the construction of CHO cells that stably express the fa-type leptin receptor and the characterization of this receptor using mRNA expression levels of the immediate early genes, c-fos, c-jun, and jun-B, which are induced by leptin as a criterion of signal transduction. The fa-type receptor not only exhibits a slightly reduced leptin-binding affinity, but also performs reduced signal transduction.
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PMID:Leptin receptor of Zucker fatty rat performs reduced signal transduction. 916 83

In the genetic mutant mouse models ob/ob or db/db, leptin deficiency or resistance, respectively, results in severe obesity and the development of a syndrome resembling NIDDM. One of the earliest manifestations in these mutant mice is hyperinsulinemia, suggesting that leptin may normally directly suppress the secretion of insulin. Here, we show that pancreatic islets express a long (signal-transducing) form of leptin-receptor mRNA and that beta-cells bind a fluorescent derivative of leptin (Cy3-leptin). The expression of leptin receptors on insulin-secreting beta-cells was also visualized utilizing antisera generated against an extracellular epitope of the receptor. A functional role for the beta-cell leptin receptor is indicated by our observation that leptin (100 ng/ml) suppressed the secretion of insulin from islets isolated from ob/ob mice. Furthermore, leptin produced a marked lowering of [Ca2+]i in ob/ob beta-cells, which was accompanied by cellular hyperpolarization and increased membrane conductance. Cell-attached patch measurements of ob/ob beta-cells demonstrated that leptin activated ATP-sensitive potassium channels (K(ATP)) by increasing the open channel probability, while exerting no effect on mean open time. These effects were reversed by the sulfonylurea tolbutamide, a specific inhibitor of K(ATP). Taken together, these observations indicate an important physiological role for leptin as an inhibitor of insulin secretion and lead us to propose that the failure of leptin to inhibit insulin secretion from the beta-cells of ob/ob and db/db mice may explain, in part, the development of hyperinsulinemia, insulin resistance, and the progression to NIDDM.
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PMID:Leptin suppression of insulin secretion by the activation of ATP-sensitive K+ channels in pancreatic beta-cells. 916 85

Leptin is a signaling protein that in its mutant forms has been associated with obesity and Type II diabetes. The lack of sequence similarity has precluded analogies based on structural resemblance to known systems. Backbone NMR signals for mouse leptin (13C/15N -labeled) have been assigned and its secondary structure reveals it to be a four-helix bundle cytokine. Helix lengths and disulfide pattern are in agreement with leptin as a member of the short-helix cytokine family. A three-dimensional model was built verifying the mechanical consistency of the identified elements with a short-helix cytokine core.
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PMID:Leptin is a four-helix bundle: secondary structure by NMR. 916 7

Serum leptin levels are elevated in subjects with exogenous obesity, indicating that obesity is associated with leptin resistance. Since in man no abnormalities have yet been found in either the genes for leptin or its receptor, the mechanism of leptin resistance in obesity remains unknown. To determine if resistance might be related to leptin binding by a serum component, we assessed the carrier status of leptin in serum. The presence of a specific leptin binding factor in human serum has been established by (1) demonstrating [125I]-leptin binding to a serum component that is saturable and specifically displaceable only by unlabeled leptin and not by human growth hormone, pork insulin, insulin-like growth factors I and II, luteinizing or follicle stimulating hormones, transforming growth factor-beta 1, interleukin-6, or leukemia inhibiting factor; (2) fractionating the leptin bound serum complex and the serum leptin binding component on a molecular sieving column revealing a mass of approximately 450 kDa; and (3) identifying an inverse correlation between the concentration of serum leptin and the quantity of the leptin binding component. It is suggested that binding of leptin by this serum component may influence the physiologic response to leptin.
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PMID:Demonstration of a leptin binding factor in human serum. 916 40

In non-diabetic subjects, insulin concentrations and insulin resistance are clearly connected, and both correlate with leptin levels, making interpretations about mechanisms difficult. In non-insulin-dependent (Type 2) diabetes mellitus (NIDDM), however, insulin concentrations and insulin resistance are less closely associated. Therefore, we examined the relationship of plasma leptin concentrations within insulin resistance and insulin levels in 32 subjects with NIDDM, who underwent measurement of insulin resistance with an insulin sensitivity test. Plasma leptin was measured with an in-house monoclonal immunoradiometric assay. Fasting leptin level correlated with BMI (r = 0.78; p < 0.001), metabolic clearance rate of glucose (= -0.44; p = 0.015), and fasting specific insulin (r = 0.58; p = 0.001), but not with age, cholesterol, triglycerides or blood pressure (r = -0.26 to 0.21; p = NS). In linear regression analysis, after adjustment for BMI and gender, leptin concentrations correlated with those of insulin (partial r = 0.42; p = 0.025), but not insulin resistance (partial r = -0.10; p = NS). We conclude that in NIDDM, concentrations of plasma leptin are closely related to those of insulin per se and to obesity, but not to insulin resistance. Insulin may be an important regulator of leptin concentration in NIDDM.
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PMID:Relationships between plasma leptin and insulin concentrations, but not insulin resistance, in non-insulin-dependent (type 2) diabetes mellitus. 917 Dec 53

Receptor subunits for the neurocytokine ciliary neurotrophic factor (CNTF) share sequence similarity with the receptor for leptin, an adipocyte-derived cytokine involved in body weight homeostasis. We report here that CNTF and leptin activate a similar pattern of STAT factors in neuronal cells, and that mRNAs for CNTF receptor subunits, similarly to the mRNA of leptin receptor, are localized in mouse hypothalamic nuclei involved in the regulation of energy balance. Systemic administration of CNTF or leptin led to rapid induction of the tis-11 primary response gene in the arcuate nucleus, suggesting that both cytokines can signal to hypothalamic satiety centers. Consistent with this idea, CNTF treatment of ob/ob mice, which lack functional leptin, was found to reduce the adiposity, hyperphagia, and hyperinsulinemia associated with leptin deficiency. Unlike leptin, CNTF also reduced obesity-related phenotypes in db/db mice, which lack functional leptin receptor, and in mice with diet-induced obesity, which are partially resistant to the actions of leptin. The identification of a cytokine-mediated anti-obesity mechanism that acts independently of the leptin system may help to develop strategies for the treatment of obesity associated with leptin resistance.
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PMID:Ciliary neurotrophic factor corrects obesity and diabetes associated with leptin deficiency and resistance. 917 39


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