Serum ghrelin levels in obese patients: the relationship to serum leptin levels and soluble leptin receptors levels

Ghrelin is a new endogenous ligand for the growth hormone secretagogue receptor. It activates the release of growth hormone from the pituitary and it also participates in the regulation of energy homeostasis. The aim of the study was to characterize changes in serum ghrelin levels in obese subjects and their relationship to the serum levels of leptin and soluble leptin receptor. Eight obese patients (6 women and 2 men) with body mass index (BMI) 40.3+/-13.4 kg.m(-2) and eight healthy controls (5 women and 3 men) with BMI 22.7+/-1.3 kg.m(-2) were examined. The ghrelin serum levels (165.0+/-58.1 vs. 343.37+/-81.96; p<0.001) and soluble leptin receptor serum levels (7.25+/-3.44 vs. 21.80+/-4.99; p<0.0001) were significantly lower in obese patients. The leptin serum levels (23.45+/-12.90 vs. 6.41+/-2.96; p<0.005) were significantly higher compared to the lean subject group. In both measured groups the levels of serum leptin significantly positively correlated with BMI. We proved a significantly lower serum ghrelin levels in the group of obese patients in comparison with the control group.     

The influence of very-low-calorie-diet on serum leptin, soluble leptin receptor, adiponectin and resistin levels in obese women

The aim of our study was to determine whether adipocyte-derived hormones leptin, adiponectin and resistin contribute to the improvement of insulin sensitivity after very-low calorie diet (VLCD). Therefore, serum levels of these hormones were measured in fourteen obese females before and after three weeks VLCD and in seventeen age- and sex-matched healthy controls. Body mass index, HOMA index, serum insulin and leptin levels in obese women before VLCD were significantly higher than in control group (BMI 48.01+/-2.02 vs. 21.38+/-0.42 kg/m(2), HOMA 10.72+/-2.03 vs. 4.69+/-0.42, insulin 38.63+/-5.10 vs. 18.76+/-1.90 microIU/ml, leptin 77.87+/-8.98 vs. 8.82+/-1.52 ng/ml). In contrast, serum adiponectin and soluble leptin receptors levels were significantly lower in obese women before VLCD than in the control group. No differences were found in serum glucose and resistin levels between the obese group before VLCD and the control group. VLCD significantly decreased BMI, HOMA index, serum glucose, insulin and leptin levels and increased soluble leptin receptor levels. The changes in serum adiponectin and resistin levels in obese women after VLCD did not reach statistical significance. We conclude that leptin and soluble leptin receptor levels were affected by VLCD while adiponectin and resistin concentrations were not. Therefore, other mechanisms rather than changes in the endocrine function of the adipose tissue are probably involved in the VLCD-induced improvement of insulin sensitivity.     

Impact of tuberculosis on serum leptin levels in patients with HIV infection

AIM: Tuberculosis (TB) and human immunodeficiency virus (HIV) are classical wasting diseases accompanied by immunosuppression. As leptin is involved in the weight regulation and cellular immunity, we investigated the role of leptin levels in the co-infection of HIV and TB (HIV-TB). METHODS: The study group consists of the patients with asymptomatic HIV infection (n = 20), patients with HIV-TB co-infection (n = 20) and healthy control subjects (n = 20). Serum leptin levels and the concentrations of IFN-gamma, TNF-alpha, IL-12 and IL-4 cytokines were measured by ELISA before the start of the treatment. CD4+ T-cell counts were determined in patients with HIV and HIV-TB by flow cytometry. Body mass index (BMI) of the study subjects was calculated. RESULTS: Serum leptin levels and BMI were significantly lower in the patients with HIV-TB than control and HIV subjects. Multivariate regression analysis showed that serum leptin concentration was significantly dependent on BMI and sex but not on age and the disease groups. The leptin levels did not correlate either with CD4+ T-cell counts or with any of the serum cytokines in HIV and HIV-TB patients. CONCLUSION: Thus our finding suggests that the leptin concentrations were strongly associated with BMI and gender but not with the disease state or with the circulating cytokine levels.     

Leptin expression and leptin receptor gene polymorphisms in growth hormone deficiency patients

Growth hormone deficiency (GHD) patients have lower weight, height, bone age, insulin-like growth factor 1 (IGF-1) levels, GH levels, fat metabolism and skeletal growth. The association of leptin with GHD characteristics and the effect of gene variants of leptin on GHD are unknown. Our aim was to examine the association of circulating leptin levels and common genetic variants in leptin (LEP) and leptin receptor (LEPR) genes with anthropometric measures, circulating hormone concentrations and GHD. A case control study of 125 GHD cases and 159 control subjects were characterized for bone age, body mass index (BMI), height, weight, leptin, IGF-1, GH and their genotype at the leptin promoter G-2548A, and LEPR variants, K109R and Q223R, at Chung Shan Medical University Hospital. Leptin levels were significantly associated with lower bone age, weight and BMI in GHD patients. Leptin levels were also significantly associated with reduced IGF-1 levels in girls but not boys in both groups. The frequency of LEPR223 [A/G or A/A] genotype was significantly higher than the LEPR223 G/G genotype in the GHD group. The LEPR223 [A/G or A/A] genotype was significantly associated with increased weight and BMI in the control group, but not in the GHD group. In conclusion, the GHD group carried a significantly higher frequency of the LEPR [G/A or A/A] genotype and of the A allele (LEPR223R). The LEPR223R polymorphism affected weight and BMI in control, but not in GHD patients, suggesting that the effect of LEPR223 [A/G or A/A] genotype was counteracted by other factor(s) in GHD patients.     

Markers for the gene ob and serum leptin levels in human morbid obesity

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 ≥ 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. Received: 25 October 1996 / Revised: 4 December 1996     

Normal leptin expression, lower adipogenic ability, decreased leptin receptor and hyposensitivity to Leptin in Adolescent Idiopathic Scoliosis

Leptin has been suggested to play a role in the etiology of Adolescent Idiopathic Scoliosis (AIS), however, the leptin levels in AIS girls are still a discrepancy, and no in vitro study of leptin in AIS is reported. We took a series of case-control studies, trying to understand whether Leptin gene polymorphisms are involved in the etiology of the AIS or the change in leptin level is a secondary event, to assess the level of leptin receptor, and to evaluate the differences of response to leptin between AIS cases and controls. We screened all exons of Leptin gene in 45 cases and 45 controls and selected six tag SNPs to cover all the observed variations. Association analysis in 446 AIS patients and 550 healthy controls showed no association between the polymorphisms of Leptin gene and susceptibility/severity to AIS. Moreover, adipogenesis assay of bone mesenchymal stem cells (MSCs) suggested that the adipogenic ability of MSCs from AIS girls was lower than controls. After adjusting the differentiation rate, expressions of leptin and leptin receptor were similar between two groups. Meanwhile, osteogenesis assay of MSC showed the leptin level was similar after adjusting the differentiation rate, but the leptin receptor level was decreased in induced AIS osteoblasts. Immunocytochemistry and western blot analysis showed less leptin receptors expressed in AIS group. Furthermore, factorial designed studies with adipogenesis and osteogenesis revealed that the MSCs from patients have no response to leptin treatment. Our results suggested that Leptin gene variations are not associated with AIS and low serum leptin probably is a secondary outcome which may be related to the low capability of adipogenesis in AIS. The decreased leptin receptor levels may lead to the hyposensitivity to leptin. These findings implied that abnormal peripheral leptin signaling plays an important role in the pathological mechanism of AIS.     

Leptin expression in breast nipple aspirate fluid (NAF) and serum is influenced by body mass index (BMI) but not by the presence of breast cancer.

While obesity is a known risk factor for postmenopausal breast cancer, the molecular mechanisms involved are unclear. Systemic levels of leptin, the product of the ob (obesity) gene, are increased in obese individuals (body mass index, BMI, over 25) and are higher in women than men. Leptin has been found to stimulate the growth of breast cancer cells in vitro. Our goal was to determine whether leptin was 1) present in nipple aspirate fluid (NAF), and 2) whether NAF leptin levels were associated with a) levels in serum, b) obesity, and c) breast cancer. We collected and evaluated NAF specimens from 83 subjects and serum specimens from 49 subjects. NAF leptin was detectable in 16/41 (39 %) of premenopausal and 21/42 (50 %) postmenopausal subjects. NAF leptin was significantly lower (p = 0.042) in premenopausal than postmenopausal women with a BMI < 25, but not in those with a higher BMI. NAF leptin was significantly associated with BMI in premenopausal (p = 0.011) but not in postmenopausal women. Serum leptin was associated with BMI in both premenopausal and postmenopausal women (p = 0.0001 for both). NAF and serum leptin were associated in premenopausal (p = 0.02) but not postmenopausal women. Neither NAF nor serum leptin was associated with premenopausal or postmenopausal breast cancer. Our findings include that 1) leptin is present in the breast and detectable in a subset of NAF samples, 2) NAF leptin in premenopausal but not postmenopausal women parallels serum leptin levels, and 3) neither NAF nor serum levels of leptin were associated with premenopausal or postmenopausal breast cancer.     

Serum copper levels and not zinc are positively associated with serum leptin concentrations in the healthy adult population

Leptin, the obesity gene protein product, is a hormone with multiple physiological functions in the human. However, there are few reports in the literature on its role in trace element metabolism in the normal population. Therefore, we investigated the association among serum leptin, zinc, copper, and zinc/copper ratio in 570 healthy men and women aged 15 yr and older. Serum leptin assay was done with a commercial enzymelinked immunosorbent assay kit; serum zinc and copper levels were measured by an atomic absorption spectrophotometer. Serum leptin was found to be positively associated with age (r=0.254, p<0.001), sex (r=0.406, p<0.001), body mass index (BMI) (r=0.553, p<0.001), and serum copper (r=0.419, p<0.001), but negatively associated with the zinc/copper ratio (r=−0.423, p<0.001). There was no significant association between serum leptin and zinc (r=−0.131, p>0.05). When the confounding effects of age, sex, and BMI were removed, serum leptin was still positively associated with serum copper (r=0.197, p=0.02) and the serum zinc/copper ratio (r=−0.182, p=0.03). These results suggest that copper and not zinc has an effect on serum leptin levels.     

Lower serum leptin concentrations in rugby players in comparison with healthy non-sporting subjects--relationships to anthropometric and biochemical parameters

Leptin is a protein hormone synthesized by adipocytes. Its serum concentrations reflect the total body fat content. Serum leptin concentrations are significantly higher in obese than in lean people and in women than in men. However little information about the influence of physical activity on serum leptin concentrations is available. We have compared the body weight, the body mass index (BMI), the body fat content (measured by caliper as skinfold thickness) and the serum concentrations of leptin, triglycerides, total, high density and low density lipoprotein (LDL) cholesterol in 14 top rugby players and 10 healthy controls. We found that serum leptin, total and LDL cholesterol concentrations were significantly lower in the rugby players group than in the control subjects. The body weight and BMI were significantly higher in the rugby players, while the body fat content was only slightly (non-significantly) higher in the control group. The serum leptin concentrations in both groups positively correlated with the BMI and body fat content and also with LDL concentrations in the control group. The serum leptin concentrations in the rugby players were lower than in the non-sporting subjects despite a similar body fat content in both groups. We would therefore suggest the possibility that regular hard physical training decreases serum leptin concentrations not only by the decrease of total body fat content, but also by a separate mechanism, which is not directly dependent on the changes in the amount of body adipose tissue.     

Serum leptin concentration and its effect on puberty in Naqu Tibetan adolescents

This study aimed to clarify the regularity of leptin in Naqu Tibetan adolescents. This study investigated the concentration of fasting serum leptin and clarified its relationship between BMI and other indices. Healthy Naqu Tibetan adolescents aged 12-18 were investigated randomly in the study. They were divided into seven groups (each year as one group, 12 boys and 12 girls in each group); serum concentrations of leptin, estradiol, testosterone (T), follicle stimulating hormone (FSH) and luteinizing hormone (LH) were analyzed. The height and body weight of the 168 healthy Naqu Tibetan adolescents were also assessed. The leptin level in boys decreased with age but increased in girls; in boys and girls they both differed between groups (p<0.05). In boys, the leptin level was inversely correlated with body mass index (BMI), FSH, and T (p<0.05), while in girls, it was positively related to BMI, FSH, LH, and E2 (p<0.01).These findings suggested that during puberty the serum leptin concentration increased with age in girls while it decreased in boys; in the same age group, the leptin level in girls was significantly higher than in boys. Leptin may have some relationship with puberty in Tibetan adolescents.     

Evidence that triiodothyronine decreases rat serum leptin concentration by down-regulation of leptin gene expression in white adipose tissue

Conflicting results have been reported regarding the effect of triiodothyronine (T(3)) on serum leptin and adipose tissue leptin gene expression in human and animals. The aim of the present study was to evaluate the effect of administration of increasing doses of T(3) on serum leptin concentration and on leptin mRNA abundance in white adipose tissue of rats. The results presented in this paper indicate that administration of single different doses of T(3) to euthyroid rats resulted dose dependent increases of serum total T(3) concentrations which are associated with a decrease in white adipose tissue leptin mRNA level. The leptin mRNA level in white adipose tissue was negatively correlated with serum total T(3) concentration (r=-0.8, p<0.001). Like white adipose tissue leptin mRNA level, serum leptin concentration decreased after T(3) administration, and was also negatively correlated with the serum T(3) concentration (r=-0.8, p<0.001). In contrast, administration of T(3) to the same rats led to a significant increase in white adipose tissue expression of the malic enzyme gene (malic enzyme activity and malic enzyme mRNA level), a known target gene for T(3). The results indicate that T(3) exerts a selective inhibitory effect on white adipose tissue leptin gene expression in vivo. A conclusion is that T(3) decreases rat serum leptin concentration by down-regulation of leptin gene expression in white adipose tissue.     

Central leptin gene therapy blocks ovariectomy-induced adiposity

Objective: In this study, we tested the hypothesis that insufficiency of leptin restraint in the hypothalamus is responsible for promoting weight gain and adiposity after ovariectomy (ovx). Whether increasing leptin transgene expression can overcome the diminution in leptin restraint was evaluated in ovx rats. Research Methods and Procedures: Enhanced leptin or green fluorescent protein (GFP; control) transgene expression was induced by a single intracerebroventricular injection of recombinant adeno‐associated viral vector encoding either leptin gene (rAAV‐lep) or GFP gene (rAAV‐GFP; control) in acutely and chronically ovx rats. Body weight and food intake responses were monitored weekly. White adipose tissue (WAT) mass and serum levels of WAT‐derived hormones, leptin, and adiponectin were analyzed at termination of the experiments. Results and Discussion: An increase in leptin transgene expression in the hypothalamus initiated soon after ovx blocked hyperphagia and body weight gain and markedly suppressed WAT mass and adipokines, leptin, and adiponectin. Similar suppression of weight gain and adiposity and serum leptin and adiponectin levels after intracerebroventricular rAAV‐lep injection in chronically ovx rats were observed concomitant with unchanged daily food intake. These findings are consistent with the hypothesis that in the absence of ovarian steroids, the existent insufficiency of leptin restraint at the hypothalamic level can be overcome with ectopic leptin expression, thereby reinstating central control on weight and adiposity.     

Serum leptin levels in community acquired pneumonia (CAP) are related to nutritional status and not to acute phase reaction

To determine whether leptin in patients with CAP acts as a nutritional or as an inflammatory marker and whether leptin plays any role regarding survival, we included 222 patients diagnosed of CAP, 142 men and 80 women, median age 74 years. We did not find significant differences in serum leptin levels between CAP patients and healthy controls, even after adjusting by BMI. Serum leptin levels were directly related with BMI, body fat and muscle mass and inversely related with inflammatory markers, including pro- and anti-inflammatory cytokines. Patients with positive blood cultures showed lower serum leptin and raised inflammatory markers. Although patients who died showed lower values of serum leptin, multivariate analysis showed that the prognostic value of low serum leptin levels depends on impaired nutritional status. In conclusion, we suggest that in CAP patients, leptin does not act as an inflammatory reactant but as a nutritional marker.     

Type 2 diabetes in non-obese Indian subjects is associated with reduced leptin levels: Study from Mumbai, Western India

Objective: Asian Indian subjects have a high tendency to develop Type 2 diabetes even though obesity is relatively uncommon. We evaluated the serum leptin levels in a group of non-obese Type 2 diabetic patients from Mumbai, Western India.Design: Cross sectional study.Methods: A total of 104 subjects consisting of 28 with Type 2 diabetes, 16 with impaired glucose tolerance and 60 age and sex-matched control subjects were given 75 g oral glucose tolerance test. Fasting serum leptin (IRMA), insulin and C-peptide were measured along with fasting and 2 h plasma glucose. The relation between these variables was studied by univariate and multiple regression analysis.Results: Type 2 diabetes was associated with marked (50–60%) reduction in serum leptin levels, in both men and women. Women, but not men, with impaired glucose tolerance exhibited 60% lower leptin. Serum leptin levels were positively correlated to body mass index (BMI; r = 0.501, p = 0.001) and calculated body fat percent (r = 0.525, p = 0.001) in all the study subjects with a better correlation in the normal subjects (r = 0.562 for BMI and 0.735 for body fat). On the other hand, serum leptin showed significant correlation to serum insulin (r = 0.362, p = 0.008) only in subjects with diabetes or IGT. In the multiple regression model, BMI was the only independent predictor of leptin, in all the subjects. However, in subjects with diabetes or impaired glucose tolerance, waist circumference (p = 0.003), gender (p = 0.007) and body fat (p = 0.009) were significant predictors of leptin, besides BMI. Gender-specific multiple regression revealed serum insulin as an independent predictor of leptin in men (p = 0.026). Therefore, lower serum leptin levels in diabetes is partly due to increased waist circumference, decreased BMI and male sex. These observations are consistent with the view that leptin levels in this cohort of non-obese Indians from Mumbai exhibit gender-specific relationship partly attributed to changes in serum insulin and waist circumference in men and to changes in BMI, in women.     

High circulating leptin receptors with normal leptin sensitivity in liver-specific insulin receptor knock-out (LIRKO) mice

Liver-specific insulin receptor knock-out (LIRKO) mice display hyperinsulinemia, abnormal glucose metabolism, and progressive liver dysfunction. In addition, circulating leptin levels appear to be increased more than 10-fold. However, food intake, body weight, and adipose mass are not significantly altered in LIRKO mice compared with wild-type littermates. Using a ligand immunofunctional assay, we found that the apparent increase in circulating leptin in LIRKO mice is because of an 80-fold increased serum level of soluble leptin receptor. Gene expression analysis by microarray and real time PCR reveals the liver as the source of soluble leptin receptor in LIRKO mice, with an increase in expression of the short (Ob-Ra), long (Ob-Rb), and soluble (Ob-Re) forms of the leptin receptor. Direct control of leptin receptor expression by insulin could also be demonstrated in isolated hepatocytes from normal mice. Despite the markedly increased levels of leptin receptor in their circulation, LIRKO mice exhibit normal or even enhanced leptin sensitivity, as assessed by their physiological and molecular responses to exogenous leptin administration and their lower base-line hypothalamic levels of SOCS3 mRNA. Thus, insulin signaling in the liver plays an important role in control of leptin receptor expression and shedding. In the LIRKO mouse, this is lost, leading to markedly increased leptin receptors into the circulation. These high levels of circulating leptin receptor bind leptin and likely alter its clearance, but do not inhibit leptin action and may actually potentiate leptin action. In this manner, insulin signaling in liver plays an important role in leptin homeostasis and fine modulation of leptin action.     

Association of nonalcoholic fatty liver disease with a single nucleotide polymorphism on the gene encoding leptin receptor

Leptin (Lep), a 16-kDa polypeptide hormone, exerts its action through the leptin receptor (LepRb), a member of the class I cytokine receptor family. Both leptin and LepRb probably have been implicated in pathogenesis of nonalcoholic fatty liver disease (NAFLD). This study was designed to assess the role of soluble leptin and LepRb in NAFLD and to investigate whether leptin receptor gene (LepR) single nucleotide polymorphism (SNP; ID rs6700896) influences NAFLD complicated with or without type 2 diabetes mellitus (T2DM). Blood samples from 90 obese NAFLD cases and 30 lean controls of matched age and sex were recruited in the study. Among the NAFLD patients, 32 were T2DM. Plasma leptin and LepRb levels were measured by enzyme linked immunoassay (ELISA). Lipids profile, glucose metabolic parameters, and insulin concentration were measured for all participants. Body mass index (BMI) and insulin resistance (IR) were calculated as well. Genotyping was done using SNP (rs6700986) for LepR gene. Significant difference was reported between NAFLD with or without T2DM and control regarding biochemical markers and LepR genotype and allele frequencies. Mutant homozygous and heterozygous LepR genotype and mutant allele were significantly higher in mild-severe steatosis and in NAFLD with T2DM when compared with mild steatosis and those without T2DM. Frequencies of mutant LepR polymorphism were significantly associated with IR increment. Elevated leptin level seems to be a feature of steatosis, and it appears to increase as hepatocyte steatosis develops. Moreover, polymorphism of LepR gene contributes to the onset of NAFLD by regulating lipid metabolism and affecting insulin sensitivity.     

Serum leptin levels, body fat deposition, and weight in females with anorexia or bulimia nervosa.

The objective of this retrospective study was to investigate the relation between serum leptin level and fat deposition in patients with eating disorders. 40 female inpatients with anorexia (n=24) or bulimia nervosa (n=16) were assessed for leptin level, body mass index (BMI), and percentage body fat by dual-energy X-ray absorbometry (DXA). The results show that percentage body fat is a better predictor for leptin level and clinical findings in eating disordered patients than BMI. We discuss the necessity for DXA measurements in anorectic patients for prognostic and research purposes.     

Obesity reduced the gene expressions of leptin receptors in hypothalamus and liver.

The expression of leptin receptor (OB-R) is downregulated by leptin in some cell lines. This study investigated the expressions of leptin receptors at central nerve system and peripheral site in a dietary model of obesity. Rats in the 8 week high-diet and control group were classified based on body weight gain into obese and control groups. Serum leptin and insulin concentrations were measured and gene expressions of short form of leptin receptor (OB-Ra) and long form (OB-Rb) in hypothalamus and liver were detected by RT-PCR. The levels of serum leptin in obese rats were increased compared with control rats (p<0.05). The levels of OB-Ra and OB-Rb gene expressions in both hypothalamus and liver in obese rats were reduced significantly (p<0.01). Serum leptin concentrations of obese rats had a significant negative relationship with both of OB-Ra or OB-Rb gene expression levels in hypothalamus and liver (p<0.01). On the other hand, serum insulin levels had no relationship with OB-Ra or OB-Rb gene expression levels in neither liver nor hypothalamus. Rats with diet-induced obesity have hyperleptinemia and reduced expressions of leptin receptors in hypothalamus and liver. The results suggest that a leptin downregulated OB-R expression is one of leptin resistant mechanisms for maintaining obesity.