ESTABLISHMENT OF A HIGHLY SENSITIVE LEPTIN RADIOIMMUNOASSAY AND DETECTION OF INCREASED LEPTIN LEVELS IN HYPERLIPIDEMIA AND PREGNANCY

ABSTRACT

The highly effective antibody has been obtained by immunizing rabbits with recombinant leptin many times. The leptin is iodinated with the chloramine-T method and purified with a Sephadex-G25 chromatography column. The reaction between antigen and antibody is carried out by a one-step balance method and cultured at 4°C for 24 h; the binding and free antigen was then separated by PR reagent. The determining range of this method is about 0.5–24 ng/mL; limited detection level is 0.45 ng/mL, relative standard deviation in a group, and among groups, are less than 5.4% and 8%, respectively. The level of blood leptin in 277 samples of normal persons, in 112 samples of overweight persons (weight/hieght m² ≥ 25) and 224 samples of hyperlipidemic patients have been measured by this method. It is demonstrated that the level of blood leptin in males is much lower than that of the females, and becomes elevated with increased age. Serum leptin level in overweight persons and hyperlipidemic patients is also much higher than that of normal groups (P<0.01). Serum leptin of 21 workers in our lab at 8:00AM and 4:00PM has been tested. It was found that there are no differences between the two time points. The same results are obtained within age groups. Leptin levels of pregnant women's serum is higher than those of the control group (P<0.001). Leptin in newborn's serum is significantly lower than those of mothers (P<0.01). There is no obvious correlation between leptin level of mother and newborns by correlation analysis (r = 0.19, P>0.05). The body weight and body weight index of pregnant women are well correlated with their serum leptin levels (r = 0.33 and 0.35, P<0.05). The body weight and body weight index of newborns are well correlated with their serum leptin levels (r = 0.54 and 0.49, P<0.001). The serum leptin level of pregnant women is not correlated with newborn's body weight (r = 0.10). These results have shown that the proposed method is stable, simple, and specific, being sensitive enough to determine leptin levels in human serum or plasma.     

Serum leptin levels during the menstrual cycle of healthy fertile women.

Leptin is a protein, produced by adipose tissue, which has cytokine and hormonal properties. Serum leptin levels can be considered as a measure of body fat mass, and are involved in regulation of body weight. Previous studies suggest that leptin may have an additional role in reproduction, and there is also evidence for involvement in the hypothalamic-pituitary-gonadal axis. In this study, we investigate the possible changes in serum leptin concentration throughout the menstrual cycle. Samples were collected from apparently healthy, fertile women at different stages in their menstrual cycle, timed precisely according to the luteinising hormone (LH) surge. Mean serum leptin levels were significantly higher in the luteal phase (median 11.4 ng/mL) than in the follicular phase (median 10.0 ng/mL) (P < 0.001). In addition, mean serum leptin levels correlated with body mass index (r = 0.54, P < 0.05), but showed no correlation with luteal-phase progesterone levels. Results showed that levels of serum leptin vary during the menstrual cycle, and add to the mounting evidence that leptin has a role in reproduction. These fluctuations should be taken into account whenever studies are performed using female subjects.     

瘦素、RAAS与高血压的关系

目的 探讨瘦素和肾素-血管紧张素-醛固酮系统（RAAS）与高血压的相互关系及病理生理机制.方法 采用放射免疫方法测定91例高血压患者及67名健康志愿者的血清瘦素、血浆肾素活性（PRA）、血管紧张素Ⅱ（AngⅡ）和醛固酮（ALD））水平;同时测量身高、体重,计算体质指数（BMI）.结果 ①同组内女性瘦素水平均显著高于男性（P＜0.01）;高血压组女性瘦素水平显著高于正常组女性（P＜0.01）;高血压组男性瘦素水平也显著高于对照组男性（P＜0.05）.②高血压患者血清瘦素、PRA、收缩压（SBP）和舒张压（DBP）均显著高于对照组（P＜0.01）; AngⅡ水平也明显高于对照组（P＜0.05）,而BMI和ALD水平与对照组比较无明显变化.③直线相关统计分析显示,高血压组患者血清瘦素的升高与PRA、AngⅡ、BMI和SBP呈正相关（PRA：r =0.52,P＜0.01;AngⅡ：r=0.43,P＜0.01;BMI：r =0.55,P＜0.01;SBP：r=0.33,P＜0.05）,而与ALD和DBP无相关性;对照组瘦素仅与BMI呈高度正相关（r=0.54,P＜0.01）,其它指标均无相关性.结论 血清瘦素水平对血压的影响与性别有关,高血压患者存在瘦素抵抗,瘦素可通过影响RAAS的活性使血压升高,主要为收缩压（SBP）的增高.     

Relationships between the serum levels of soluble leptin receptor and free and bound leptin in non-pregnant women of reproductive age and women undergoing controlled ovarian hyperstimulation

BACKGROUND: The aim of this study was to investigate the relationships between the serum levels of soluble leptin receptor (SLEPR), and total, free and bound leptin, and the change in the serum SLEPR level during an IVF cycle. METHODS: Serum concentrations of leptin and SLEPR were measured in 50 Japanese women of reproductive age, and 20 patients participating in an IVF programme. The total leptin was fractionated into free and bound portions by gel filtration chromatography. RESULTS: The SLEPR level was negatively correlated with the body mass index (BMI) (r = -0.548, P < 0.0001), total leptin (r = -0.433, P < 0.0001), the percentage of free leptin (r = -0.732, P < 0.0001) and the absolute free leptin concentration (r = -0.506, P < 0.0001). The SLEPR level was positively correlated with the percentage of bound leptin (r = 0.730, P < 0.0001), whereas there was little variation in the absolute bound leptin concentration, regardless of the BMI or SLEPR concentration. During the IVF cycle, total and free leptin elevated during maximal ovarian stimulation, whereas there was no significant difference in the SLEPR concentration. CONCLUSIONS: The results demonstrate a skillful mechanism where a change in the serum SLEPR level regulates, in part, the biological activity of leptin in the circulation.     

The relationship between plasma leptin and nutritional status in chronic hemodialysis patients

Leptin serves an important role in suppressing appetite in mice and is known to be elevated in chronic renal failure (CRF) patients. But clinical significance of leptin as an appetite-reducing uremic toxin, remains to be determined. So we studied the relationship between plasma leptin and nutritional status in 46 chronic hemodialysis (HD) patients. Pre HD leptin was measured and divided by body mass index (BMI) to give adjusted leptin levels. KT/Vurea (K, dialyzer urea clearance; T, duration of HD; V, volume of distribution of urea), C-reactive protein (CRP), plasma insulin and nutritional parameters such as serum albumin, normalized protein catabolic rate (nPCR), subjective global assessment (SGA), BMI and mid-arm muscle circumference (MAMC) were also measured. Mean plasma leptin levels were 8.13+/-2.91 ng/mL (male 3.15+/-0.70; female 14.07+/-6.14, p<0.05). Adjusted leptin levels were positively correlated with nPCR (male r=0.47, p<0.05; female r=0.46, p<0.05), SGA (male r=0.43, p<0.05; female r=0.51, p<0.05) and MAMC (male r=0.60, p<0.005; female r=0.61, p<0.05). They did not correlate with KT/Vurea, serum albumin, hematocrit, bicarbonate, insulin and CRP. Presence of DM and erythropoietin therapy had no effect on leptin levels. These results suggest that leptin is a marker of good nutritional status rather than a cause of protein energy malnutrition in chronic HD patients.     

Variation in plasma leptin levels in young Iranian children with cystic fibrosis

Introduction

Poor weight gain is one of the most important mortality hazards in cystic fibrosis (CF) patients. The mechanisms that may hinder body weight regulation are not completely understood. Leptin and its role in fat mass could be related to control of weight gain in CF patients. As the previous data are conflicting, we aimed to investigate serum leptin level in Iranian CF children compared to a control group.

Material and methods

Forty-three CF patients aged from 3 to 120 months and 43 age-matched controls were enrolled. Patients were recruited from the outpatient clinic of the Children''s Medical Center Hospital. Controls were visited in the general outpatient clinic for an annual check-up. Both groups were divided into three subgroups based on age: 3 to 12 months, 13 to 48 months, and 49 to 120 months. Body mass index (BMI) was calculated for all the participants. Serum leptin levels were measured applying a solid phase enzyme-linked immunosorbent assay (ELISA).

Results

Leptin levels and BMI values were significantly different between patients and controls (p = 0.02, p < 0.001, respectively) but only patients aged 13–48 months had significantly higher levels of leptin than age-matched controls (p = 0.016). Overall male patients’ mean leptin level was significantly higher than in female patients (p = 0.032) and male controls (p < 0.001).

Conclusions

Leptin level in our patients was significantly higher than controls. It seems that leptin levels during infancy are higher than in adult patients. Further studies are required on specific genotypes, gender and age to reveal the probable correlation with BMI and leptin levels in CF patients from different ethnic groups.     

Serum leptin levels,bone mineral density and osteoblast alkaline phosphatase activity in elderly men and women

Although primarily secreted by adipose cells, leptin, a polypeptide hormone that influences body weight, satiety and lipid metabolism, and its receptor are also expressed in human osteoblasts. Leptin plays a role in the central, hypothalamic modulation of bone formation, as well as locally within the skeleton by enhancing differentiation of bone marrow stroma into osteoblasts and inhibiting its differentiation into osteoclasts and adipocytes. The purpose of this investigation was to compare serum leptin values in 100 postmenopausal women (age 62-97) and 31 men (age 72-92) to bone mineral density (BMD) measurements made by dual X-ray absorptiometry and additionally to biochemical markers of bone resorption and formation, including crosslinked collagen N-telopeptides (NTx), aminoterminal extension procollagen propeptides (PINP) and bone-specific alkaline phosphatase (bAP). The circulating level of leptin directly correlated with body mass index (BMI) (r=0.61-0.78, P<0.001) and was modestly, but significantly and positively associated with bAP activity (r=0.24-0.33, P<0.01) in the sera of men and women after adjustment for BMD, age and BMI. The association of circulating leptin levels with bAP, a specific marker of osteoblast activity suggests that leptin levels influence osteoblast activity in vivo in elderly women and men.     

Serum leptin levels in different types of hypertension during pregnancy

We determined the serum levels of leptin in 96 pregnant women with body mass index between 20 to 30, 30 normal (NP), 26 with mild preeclampsia (MPE), 27 with severe preeclampsia (SPE), 6 with chronic hypertension plus preeclampsia (CHT+PE) and 7 with chronic hypertension (CHT). A significant (p < 0.01) decrease in leptin levels was observed in the SPE group when compared with the NP group. On the contrary, significant (p < 0.05) increases were observed in the CHT and CHT+PE groups when compared with the NP group. Leptin levels were significantly higher in the MPE (p < 0.001), CHT (p < 0.01) and CHT+PE (p < 0.5) groups when compared with the SPE. No significant differences were observed in the CHT group when compared with CHT+PE. Moreover, a positive correlation was encountered (r = 0.6, p < 0.001) between platelet number and leptin levels for all the patients with preeclampsia. These results suggest that leptin levels may be useful metabolic parameter in different types of hypertension during pregnancy.     

Predictive value of serum and follicular fluid leptin concentrations during assisted reproductive cycles in normal women and in women with the polycystic ovarian syndrome

Leptin is an adipocyte-derived hormone which plays a central role in the regulation of body weight and energy homeostasis and in signalling to the brain that adequate energy stores are available for reproduction. Although leptin may affect reproduction by regulating the hypothalamic-pituitary-gonadal axis, recent in-vitro observations indicate that leptin may also have direct intra-ovarian actions. Leptin concentrations were measured in women who succeeded in becoming pregnant within three cycles of in-vitro fertilization (IVF) or gamete intra-fallopian transfer (n = 53), in women who failed to become pregnant within three cycles (n = 50), and in women with polycystic ovarian syndrome (PCOS) (n = 22). It was found that lower follicular fluid leptin concentrations were a marker of assisted reproduction treatment success in normal women. Women with PCOS had higher leptin concentrations than women without such a diagnosis, but this was due to their higher body mass index (BMI). After adjustment for age and BMI, women with PCOS who became pregnant tended to have lower mean follicular fluid leptin concentrations than women with PCOS who did not succeed at becoming pregnant. Further studies exploiting the strengths of the IVF model are needed to assess whether the prognostic role for follicular fluid leptin in human reproduction is independent of other factors, and to elucidate the underlying mechanisms.     

Plasma leptin and insulin in C57BI/6J mice on a high-fat diet: relation to subsequent changes in body weight

It has been proposed that leptin and insulin through central effects are involved in the regulation of energy balance and body weight. Whether circulating leptin or insulin levels predict subsequent changes in body weight is, however, not known. We examined plasma leptin and insulin at 2, 3, 6, 9 and 12 months of age in C57BI/6J mice given a normal diet (n = 12) or a high-fat diet (58% fat on a caloric base; n = 15). Plasma leptin levels increased by age and correlated with body weight in the entire material (r = 0.81, P < 0.001). Also plasma insulin increased by high-fat diet and correlated across all age periods with body weight (r = 0.56, P < 0.001). In mice, given normal diet, plasma leptin or insulin did not correlate to subsequent changes in body weight at any of the time points studied. However, in mice given the high-fat diet, plasma leptin at 6 (r = -0.57, P = 0.027) and 9 months of age (r = -0.56, P = 0.042) as well as plasma insulin at 6 (r = - 0.51, P = 0.049) and 9 months (r = -0.58, P = 0.037) correlated inversely to the change in body weight during the subsequent 3-month period. Hence, both leptin and insulin are negative predictors for future weight gain in high-fat fed mice. This suggests that when the regulation of body weight is challenged by a high-fat diet, leptin and insulin act to restrain or prevent future weight gain. This in turn may suggest that impairment of these (probably central) actions of leptin and insulin might underlie excessive increase in body weight under such conditions.     

Serum leptin levels in asthmatic children treated with an inhaled corticosteroid.

BACKGROUND: Recent observations suggest the presence of an interaction between leptin and the inflammatory system; however, there is no adequate knowledge about the role of leptin in atopic states such as asthma. OBJECTIVES: To evaluate the potential role of leptin in relation to bronchial asthma and inhaled corticosteroid therapy. METHODS: Twenty-three children with mild-to-moderate, newly diagnosed asthma enrolled in this 2-period trial. The control group consisted of 20 age- and sex-matched children. Serum leptin levels were measured in patients at initiation and after 4 weeks of budesonide treatment and were compared with control group measurements. RESULTS: Asthmatic children had higher mean +/- SD serum leptin levels at admission (19.3 +/- 5.1 ng/mL) than after budesonide treatment (10.6 +/- 1.6 ng/mL) and vs control group measurements (9.8 +/- 1.6 ng/mL) (P < .001). There was a significant correlation between serum leptin levels before and after budesonide treatment (r = 0.68; P = .007). Mean +/- SD body mass indices in patients and controls were 16.7 +/- 2.1 and 16.9 +/- 2.6 kg/m2, respectively. Serum leptin levels did not correlate with body mass indices before budesonide treatment in the study group (r = -0.13; P = .65) but correlated well after budesonide treatment (r = 0.58; P = .009) and in the control group (r = 0.65; P = .008). CONCLUSIONS: The role of leptin elevation in children with asthma might be a regulatory mechanism rather than being etiologic, but a question may be raised whether it is possible that leptin may contribute to poor patient outcomes. Further research, both basic and clinical, is essential to explain the exact mechanism.     

In vivo effects of leptin on lymphocyte subpopulations in mice

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

Serum leptin correlates with serum uric acid but not serum testosterone in non-obese male adolescents

To identify the serum factors that affect circulating leptin levels, we measured the serum concentrations of leptin, testosterone (T), estradiol (E), serum alanine aminotransferase, total cholesterol and uric acid (UA) in healthy male adolescents (age, 18.3 +/- 0.1 years, n=96). We also measured body mass index (BMI), percent body fat and thickness of skin fold to assess the effect of body constitution on serum leptin level. Since serum concentration of leptin significantly correlated with BMI (r=0.820, p<0.001), we analyzed the relation-ship between leptin/BMI ratio (L/BMI) and serum parameters. Analysis of data of subjects with normal serum T level showed a significant inverse correlation between L/BMI and serum T levels (n=96, r=-0.294, p<0.005), but no such correlation was present among non-obese subjects (n=70) with BMI of +/-20% of normal (22 kg/m2). There was no correlation between L/BMI and serum E level. Serum UA level significantly correlated with L/BMI in both the test group (n=96, r=0.520, p<0.001) and non-obese subjects (r=0.369, p<0.005). Stepwise multiple regression analysis showed that UA independently and significantly influenced serum leptin levels in both the test and control groups. Our results demonstrate that T weakly influences serum leptin concentration, and that UA concentrations strongly influences serum leptin in healthy male adolescents independent of their obesity level.     

Increased leptin and decreased ghrelin level after smoking cessation

Smoking cessation is associated with transient increases in body weight. Leptin and ghrelin are known to be major mediators of appetite, weight and the reward pathway. Therefore, this study assessed the changes in the plasma leptin and ghrelin level and their relationship with the body weight and appetite after smoking cessation in the Korean population. Eighteen subjects, who had stopped smoking for 2 months were enrolled in this study. The body mass index (BMI), body fat mass (BFM), waist-hip ratio (WHR), weight and appetite were measured before and after smoking cessation. In addition, the plasma leptin and ghrelin levels were measured. The BMI, BFM, WHR, weight and appetite were significantly higher than baseline in those who had gave up smoking for 2 months (p<0.05). The plasma leptin concentration increased and the plasma ghrelin level decreased after smoking cessation. The change in the leptin level was positively correlated with the change in the body mass index and body fat mass. These results do not support the direct mediation of the leptin-ghrelin-neuropeptide Y (NPY) system on weight gain after smoking cessation. It appears that weight and appetite is regulated by a more complicated mechanism after smoking cessation.     

瘦素、抵抗素、2型糖尿病间的相关性研究

目的：研究血浆瘦素与抵抗素、体重指数、腰围、腰臀比、血脂、胰岛素敏感性指数等的关系。方法：对43例新诊断2型糖尿病患者及37例糖耐量正常者，测定空腹血浆瘦素、胰岛素、血糖、血脂及抵抗素浓度。结果：相关分析显示性别、体重指数（BMI）、腰围、腰臀比、胰岛素与瘦素呈显著正相关（r分别为0.623,0.534，0.516，0.302，0.354，均P<0.01），IAI与瘦素呈显著负相关(r=-0.373,P<0.01),甘油三酯、胆固醇空腹血糖与瘦素无明显相关。瘦素与抵抗素无相关性（r=0.101,P>0.05）结论：空腹血浆瘦素水平与肥胖程度、胰岛素抵抗呈显著正相关，与抵抗素无关。瘦素可能与2型糖尿病的发病有关。     

母体不同孕期与新生儿血中瘦素水平的观察

目的 :观察母体在不同孕期血清与新生儿脐血中瘦素水平变化及其相关关系。方法 :应用放射免疫分析 ,随机对 3 0 0例孕前、孕早期、孕中期和临产时母体血清及新生儿脐血中的瘦素水平进行了检测。结果 :妇女孕早期与孕前血中瘦素之间变化基本一致 (p >0 0 5 ) ,从孕中期开始血清瘦素水平则明显升高 ,分娩时达到高峰 (p <0 0 5或p <0 0 1)。新生儿脐血中瘦素水平与孕前母体血中瘦素水平较为一致。妇女妊娠前、后血清瘦素水平均与体重、体重指数、腹围、子宫底高度、舒张压、收缩压呈正相关。新生儿脐血瘦素水平与出生体重呈正相关 ;而与其母体瘦素水平呈负相关。结论 :新生儿瘦素来自自身 ,其浓度主要由脂肪组织的积累程度决定。检测孕期母血中瘦素浓度对判断、预测胎儿体重帮助意义不大 ,但可以了解母体孕期体重增加程度 ,并对妊娠高血压综合征的临床观察和预后判断有一定价值     

Ontogenesis of leptin expression in different adipose tissue depots in the rat

Serum leptin levels and leptin mRNA expression by adipose tissue increase with age and are mainly associated with an increase in adiposity. Regional changes in both leptin production and fat distribution contribute to circulating leptin levels and may play a role in the regulation of body weight. a capacity that changes during development. Here, we have studied leptin mRNA expression in four different white adipose tissue depots (epididymal, retroperitoneal, mesenteric, inguinal; namely, EWAT, RWAT, MWAT, IWAT) and in interscapular brown adipose tissue (IBAT). We have also studied their relationship with lipid content and adiposity changes, together with serum leptin levels in male rats at different ages (18, 55, 93, 159, 212, 294 and 355 days). Serum leptin levels increased during development, reaching stable levels at the age of 7 months, and, as expected, were highly correlated with both the adiposity index (r=0.908, P<0.01) and body weight (r=0.906, P<0.01). Leptin mRNA expression also increased with age, following characteristic ontogenic patterns in every adipose tissue depot. The patterns were similar in EWAT and RWAT: leptin expression increased very rapidly during the first 55 days for EWAT and 3 months for RWAT, with a peak in the latter at 7 months, and high expression levels were retained for the rest of the study period. In IWAT and IBAT, leptin expression increased steadily during the 12-month period studied and was significantly lower than levels in EWAT and RWAT. Leptin expression in MWAT increased progressively with age to reach levels close to those of EWAT and RWAT in 10-month-old animals. The pattern of leptin expression in both EWAT and RWAT paralleled their lipid content, and leptin mRNA expression per unit of tissue lipid content was maintained high and constant from a very young age (about 2 and 3 months, respectively). However, the expression of mRNA for leptin (expressed per unit of tissue lipid concentration) in MWAT, IWAT and IBAT increased steadily during the whole period studied, without attaining the maximal levels observed in EWAT and RWAT. MWAT, IWAT and IBAT maintained their capacity to increase leptin mRNA expression in response to an additional accumulation of lipids. Our data demonstrate that there are regional-specific differences and different rates of increase of leptin gene expression within distinct depots of WAT and BAT. These changes cannot be uniquely explained by changes in adiposity or lipid content, implying that there are regional-specific regulatory mechanisms that may depend on the attenuation with age of the beta-adrenergic inhibitory signalling pathway upon leptin expression or on other factors.     

血清Leptin在2型糖尿病、肥胖发病机制中的临床价值

目的：研究2型糖尿病血清Leptin与胰岛素,体脂分布和睾酮的关系。方法：对65例2型糖尿病患者及42例正常对照者用放免法测定血清Leptin及胰岛素。34例糖尿病患者进行75克葡萄糖耐量试验,32例行螺旋CT SSD技术测定体脂分布。30例男性糖尿病患者测定血清睾酮。结果：在调整了BMI（体重指数）,性别后,糖尿病组与对照组血清Leptin无差异。女性血清Leptin为男性的2．3倍,餐后2小时血清Leptin较空腹下降为19．19％,代谢控制不良者（空腹血糖＞14mmol)Leptin水平较低。性别,BMI,ASF（腹部皮下脂肪）是影响血清Leptin的重要因素,Leptin浓度与体重指数,胰岛素,腹部皮下脂肪显著正相关,与睾酮负相关,结论：2型糖尿病患者无异常血清Leptin,提示Leptin并非致2型糖尿病的主要因素,代谢控制不良者有Leptin缺乏,男性较低的Leptin可能与睾酮有关,性别,体重指数,腹部皮下脂肪是影响Leptin的主要因素。