Leptin elimination in hyperleptinaemic peritoneal dialysis patients

Leptin and ghrelin in chronic kidney disease: their associations with protein-energy wasting

BACKGROUND

This study aimed to evaluate plasma concentrations of leptin and total ghrelin in children with chronic kidney disease (CKD) and assess their roles in protein-energy wasting (PEW).

METHODS

This study consisted of three different CKD populations [CKD group (20 patients with non-dialysis CKD), dialysis group (39 patients on dialysis), and kidney transplant (KTx) group (35 KTx recipients)] and control group (18 healthy children). Plasma leptin and total ghrelin levels were measured. Multi-frequency bioimpedance analysis was used for the assessment of fat and lean mass. PEW was defined using criteria including body mass, muscle mass, growth, serum albumin level, and protein intake.

RESULTS

While plasma leptin levels did not differ among the study groups, total ghrelin levels were significantly higher in the dialysis group (P < 0.001). Seven dialysis patients (18%) and one CKD patient (5%) but none of the KTx recipients met the criteria of PEW. Dialysis patients with PEW had lower plasma leptin levels compared to their counterparts (P = 0.018); however, total ghrelin levels did not differ between the two groups (P = 0.10). Low leptin level in dialysis patients was independently associated with lower fat mass index (P < 0.001) and lower height-specific SD scores of BMI (P = 0.019).

CONCLUSIONS

PEW is prevalent in dialysis patients. Low levels of leptin seem to be associated with PEW. Our result suggests that low leptin levels may be a consequence rather than a cause of PEW. Longitudinal studies are required to investigate this complex relationship between leptin and PEW in pediatric dialysis patients.

Study of Serum Levels of Leptin, C-Reactive Protein and Nutritional Status in Hemodialysis Patients

Background:

Leptin is secreted by adipose tissue and decreases appetite. However, the role of leptin in the pathogenesis of hemodialysis (HD)-related malnutrition has not been fully evaluated.

Objectives:

The aim of study was to investigate the association between the serum leptin levels, serum C-reactive protein (CRP) levels, and nutritional status in hemodialysis patients.

Patients and Methods:

This analytical descriptive study included 45 hemodialysis patients and 40 healthy subjects. Biochemical parameters and serum leptin levels were measured. The nutritional status was evaluated using a food frequency questionnaire (FFQ) and the calculation of the body mass index (BMI).

Results:

Serum leptin (P < 0.05) and albumin (P < 0.0001) levels and BMI (P < 0.001) of HD patients were significantly lower, while CRP levels were significantly higher than those of controls (P < 0.0001). HD patients consumed the lower daily servings of the food groups compared to the control subjects (P < 0.0001). A significant positive correlation between serum levels of leptin and albumin and BMI was demonstrated. No significant correlations were identified between leptin level, CRP level, and other variables.

Conclusions:

The findings suggest that low levels of leptin may be a contributory factor for malnutrition in HD patients. Further studies are required to ascertain the significance of leptin levels in relation to nutritional factors in hemodialysis patients.

Association between serum leptin levels and peritoneal dialysis: A meta-analysis

There is limited information available with regard to the association between serum leptin levels, or other adipokines, and serum lipid levels and insulin sensitivity in patients undergoing peritoneal dialysis (PD). Thus, the aim of the present study was to perform a meta-analysis investigating this association. Potential relevant studies were identified through searching the following databases: MEDLINE, Science Citation Index, Cochrane Library, PubMed, Embase, CINAHL, Chinese Biomedical, Chinese Journal Full-Text and Weipu Journal. Statistical analyses were calculated using version 12.0 STATA software. In total, 21 case-control studies comprising 1,187 subjects (574 patients and 613 controls) were collected for the meta-analysis. The results identified a statistically significant difference in the serum levels of leptin when comparing the PD patients with the healthy controls [controls vs. cases, standardized mean difference (SMD), 2.09; 95% confidence interval (CI), 1.58-2.59; P<0.001]. Furthermore, ethnicity-subgroup analysis indicated that the PD patients of Asian and Caucasian populations were associated with increased serum levels of leptin (Asian population, SMD, 2.05; 95% CI, 1.48-2.62; P<0.001; Caucasian population, SMD, 2.19; 95% CI, 1.19-3.18; P<0.001). Therefore, serum leptin levels may be used as a prognostic marker for PD.

Effects of zinc supplementation on serum zinc and leptin levels, BMI, and body composition in hemodialysis patients

PROJECT

The aim of this study was to determine the effects of zinc supplementation on serum zinc and leptin levels as well as on anthropometric status and some biochemical parameters in hemodialysis (HD) patients.

PROCEDURE

In this randomized, double-blind, and placebo-controlled trial, sixty HD patients were randomly divided into groups to receive a daily supplement of 100mg elemental Zn (supplemented group) or placebo (control group) for 60 days. Anthropometric measurements were taken using standard calibrated instruments. Serum zinc and leptin levels were determined by atomic absorption and ELISA method respectively before and after intervention.

RESULTS

Zinc supplementation resulted in significant increase in the mean serum zinc level in the experimental group while changes observed in the placebo group were not significant. The mean serum leptin in women part of the experimental group was decreased significantly after supplementation. After adjusting for age, BMI, body fat (%), serum zinc and dietary Zn intake, a negative and significant association was observed between serum zinc and leptin levels in all subjects (β=-0.33, P=0.03) as a result of Zn supplementation.

CONCLUSIONS

More studies are needed to clarify the mechanisms by which serum leptin level is influenced as a result of zinc supplementation in HD patients.

Leptin and plasminogen activator inhibitor-1 levels in children on chronic dialysis

PURPOSE

In this study, it is aimed to compare the serum leptin and PAI-1 levels and evaluate their relationship in children on hemodialysis (HD) and peritoneal dialysis (PD).

METHOD

Thirty-six patients on HD (mean age: 15.0 ± 2.8 years), 19 patients on PD (mean age: 13.0 ± 3.5 years) and 15 healthy subjects (mean age: 14.5 ± 2.7 years) were included in the study. Laboratory investigations included blood count, biochemical parameters, serum iron, iron binding capacity, parathormone, erythrocyte sedimentation rate, C-reactive protein (CRP), prothrombin time (PT), partial thromboplastin time (PTT), fibrinogen, serum leptin and PAI-1 levels.

RESULTS

Serum leptin levels were significantly higher in HD group than in control group when the effects of BMI and sex were controlled, while PD and control groups had similar leptin levels. PAI-1 levels were also significantly higher in HD group than in control group, while there was no statistically significant difference in PAI-1 levels of PD and control group. PAI-1 levels and leptin levels were significantly correlated, which was independent of the effect of BMI in both HD and PD groups when they are evaluated separately.

CONCLUSION

Results of our study showed that HD patients had higher leptin and PAI-1 levels and leptin and PAI-1 levels were correlated significantly in both patient groups. The effect of elevated serum leptin and PAI-1 levels on the cardiovascular complications remains to be established.

Fasting serum leptin level correlates with mid-arm fat area in peritoneal dialysis patients

Leptin correlates with body fat content and plays a pivotal role in inflammatory response. This study aimed to investigate the relationships of fasting serum leptin levels and the anthropometric fat components among peritoneal dialysis (PD) patients. Fasting blood samples were obtained from 40 PD patients. Leptin levels were measured using a commercial enzyme-linked immunosorbent assay kit. Body weight (r=0.424; P=0.006), waist circumference (r=0.352; P=0.026), body mass index (BMI; r=0.483; P=0.002), body fat mass (r=0.352; P=0.026), high sensitivity C-reactive protein (hs-CRP; r=0.494; P=0.001), triceps skinfold thickness (TSF; r=0.505; P=0.001), mid-arm circumference (MAC; r=0.471; P=0.002), and mid-arm fat area (MAFA; r=0.564; P<0.001) were positively correlated, while high density lipoprotein (HDL)-cholesterol (r=-0.345; P=0.028) was negatively correlated with fasting serum leptin levels among the PD patients. Multivariate forward stepwise linear regression analysis showed that MAFA (R(2)=0.318, P=0.011) was the independent predictor of fasting serum leptin levels among the PD patients. In conclusion, fasting leptin level was positively associated with body fat composition (body weight, waist circumference, BMI, body fat mass, TSF, MAC, and MAFA) and hs-CRP among PD patients, and MAFA was the independent predictor of fasting serum leptin levels among the PD patients.

Serum zinc, plasma ghrelin, leptin levels, selected biochemical parameters and nutritional status in malnourished hemodialysis patients

This study was performed to investigate the serum zinc (Zn), plasma ghrelin, leptin levels and nutritional status, and to evaluate the potential association between malnutrition and these investigated parameters in malnourished hemodialysis (HD) patients. Fifteen malnourished HD patients, aged 42.9 +/- 2.11 years, who underwent the HD for 46.44 +/- 7.1 months and 15 healthy volunteers, aged 41.0 +/- 2.17 years, were included in this study. The nutritional status of the subjects was determined by the subjective global assessment (SGA). Anthropometric measurements were taken by bioelectrical impedance after HD. Blood samples were collected for the analysis of zinc (Zn), ghrelin, leptin, and selected blood parameters. The HD patients consumed less energy and nutrients than controls. In HD patients, body weight, body mass index (BMI) (p < 0.001), basal metabolic rate (BMR), body fat, lean body mass (LBM), serum Zn, copper (Cu) (p < 0.05), sodium (Na) (p < 0.01), glucose (p < 0.05), albumin (p < 0.01), total cholesterol (p < 0.001), and ghrelin (p < 0.05) were lower whereas body water ratio (p < 0.001), serum potassium (K) (p < 0.01), inorganic phosphorous (Pi), blood urea nitrogen, creatinine (p < 0.001), and plasma insulin (p < 0.05) levels were higher than the controls. No difference existed between HD patients and controls regarding plasma leptin levels. There were positive correlations for body weight-fasting glucose and body weight-leptin (p < 0.05), body weight-BMI and body weight-LBM (p < 0.01); body fat-leptin (p < 0.05); BMI-fasting glucose, BMI-leptin, and BMI-body fat (p < 0.05); albumin-hemoglobin and albumin-insulin (p < 0.05). Negative correlation was found for SGA score-ghrelin (p < 0.05). Malnutrition in HD patients may result from inadequate energy and nutrient intake and low Zn and ghrelin levels. Zinc supplementation to the diets of HD patients may be of value to prevent the malnutrition.

Serum leptin, insulin resistance, and body fat after renal transplantation

OBJECTIVE

Our objective was to evaluate serum levels of leptin, body mass index (BMI), body-fat percentage (BF%), and insulin resistance in the first year after renal transplantation.

DESIGN

This study involved a prospective, observational cohort.

SETTING

The setting was a transplant unit of a university teaching hospital in Porto Alegre, Brazil.

PATIENTS

Thirty-two patients who underwent renal transplantation were prospectively followed for 1 year. A control group of 19 healthy individuals, matched by sex, age, and BMI, was included in the study.

METHODS

Body mass index and BF% were measured according to anthropometric measures, serum leptin was measured by radioimmunoassay, and the homeostasis model assessment (HOMA) was used as an index of insulin resistance. Anthropometric measures and biochemical markers were evaluated prospectively, starting at transplant time and then every 3 months for up to 1 year.

RESULTS

Leptin levels were increased before transplantation, and decreased significantly in the first year (median, 11.9 [interquartile range, 9.2 to 25.2] to 9.3 [4.9 to 16.4] ng/mL; P < .001). The HOMA values presented a similar pattern, decreasing from 2.4 +/- 1.5 (mean +/- SD) before transplantation, to 1.5 +/- 1.1 (P = .001) at 3 months after transplantation, but increasing to 2.0 +/- 1.7 at month 12 after transplantation (P = not significant). The BMI and BF% increased significantly in the first year after transplantation (23.3 +/- 2.7 kg/m(2) vs. 24.4 +/- 2.7 kg/m(2), P = .001, and 23.71% +/- 7.79% vs. 25.63% +/- 7.68%, P = .002, respectively). According to multivariate regression analysis, HOMA levels and BF% independently predicted leptin levels after transplantation.

CONCLUSIONS

We found that leptin serum levels decreased significantly over the first posttransplant year. However, the effect of transplantation on insulin resistance appears to be transitory, and BF% also increases steadily in this period. The beneficial profile of leptin levels is counterbalanced by the detrimental effects of insulin resistance and BF% that may be related to the elevated cardiovascular risk observed after transplantation.

Low serum leptin predicts mortality in patients with chronic kidney disease stage 5

OBJECTIVE

Leptin, secreted from adipose tissue, regulates food intake, energy expenditure, and immune function. It is unknown whether leptin predicts mortality in patients with chronic kidney disease stage 5 on hemodialysis therapy.

RESEARCH METHODS AND PROCEDURES

We performed a prospective cohort study of 71 patients with chronic kidney disease stage 5 in an outpatient hemodialysis center. Subjects were recruited in June 1998 and followed for 83 months. Survival was compared by the Kaplan-Meier method.

RESULTS

After 83 months of follow-up, 48 patients (68%) had died. Serum leptin concentrations at study entry were lower among all deceased patients compared with those patients who survived (5.2 +/- 9.0 microg/L; n = 48; vs. 7.7 +/- 7.8 microg/L; n = 23; p = 0.005). Baseline serum leptin concentrations were significantly lower in patients who died from cardiovascular diseases (4.7 +/- 9.4 microg/L, n = 32) or infections (4.0 +/- 2.7 microg/L; n = 10; each p < 0.05), but not cancer (9.4 +/- 7.9 microg/L; n = 6), than in survivors (7.7 +/- 7.8 microg/L; n = 23; p = 0.003). The relative risk for mortality in patients with serum leptin concentrations below the median (<2.6 microg/L) compared with patients above the median was 1.96 (95% confidence interval, 1.01 to 3.79; p = 0.04). Survival was shorter in patients with leptin concentrations below the median compared with those whose leptin concentrations were above the median (all-cause mortality, chi(2) = 5.05; p = 0.02).

DISCUSSION

Low serum leptin concentration is an independent predictor of mortality in patients with chronic kidney disease stage 5 on hemodialysis therapy.

Leptin and Renal Disease

Leptin is a mediator of metabolism and disease in a variety of organ systems, most notably as an agent of energy stores. However, its role in renal disease as an inflammatory agent as well as its potential impact on the cachexia of uremia have sparked new interest in the molecule for nephrologists. This review elucidates the complex uremic state, the historical discovery of leptin and its physiology, and the potential interactions leptin has on both the progression of kidney disease as well as the morbidity and mortality of end-stage renal disease.

Beneficial effects of icodextrin on plasma level of adipocytokines in peritoneal dialysis patients

OBJECTIVE

Leptin and adiponectin, well-recognized adipocytokines, are reported to contribute to the pathogenesis of atherosclerosis. The aim of this study was to elucidate the effects of icodextrin-based dialysis solution on adipocytokine metabolism.

METHODS

In 12 non-diabetic anuric patients on peritoneal dialysis, dialysis solution was changed from glucose-based dialysis solution to icodextrin-based dialysis solution for 6 months. Plasma levels of leptin, adiponectin, lipids (total cholesterol, HDL-cholesterol and triglyceride), insulin, blood glucose and insulin sensitivity index by the homeostasis model assessment (HOMA-IR) were compared before and after the use of the icodextrin solution.

RESULTS

Plasma leptin level was decreased from 15.6 (2.5-69.0) to 7.3 (2.9-45.9) ng/ml (P = 0.018) and plasma adiponectin level increased from 11.6 (6.2-19.6) to 17.6 (7.8-33.0) microg/ml (P = 0.002). A reduction in plasma insulin level from 33.1 (13.8-54.1) to 19.1 (5.8-37.3) muU/ml (P = 0.009) and HOMA-IR from 8.22 (3.68-15.09) to 5.15 (1.40-13.78) (P = 0.015) was observed. While plasma total cholesterol level remained similar, HDL-cholesterol level increased, from 36.0 (22-45) to 43.5 (30-69) mg/dl (P = 0.008) and the triglyceride level decreased, from 174.0 (140-250) to 116.5 (81-207) mg/dl (P = 0.012).

CONCLUSION

Icodextrin-based dialysis solution improves abnormal adipocytokine metabolism, dyslipidaemia and insulin resistance, which are known to be associated with atherosclerosis. These results suggest that the use of icodextrin-based dialysis solution might be useful in preventing atherosclerosis in PD patients. Long-term effects of icodextrin-based dialysis solution on the atherosclerosis in peritoneal dialysis patients should be tested.

Alterations of leptin and ghrelin serum concentrations in renal disease: simple epiphenomena?

The hypothesis that alterations of serum concentrations of the anorexigenic adipose tissue-derived hormone leptin or the orexigenic peptide ghrelin might help to regain appetite and fight malnutrition in patients with chronic renal failure cannot be confirmed at present. For the future, however, strategies interfering with signal transduction of these peptides in the hypothalamus might be more promising and should be investigated and further developed.

Serum leptin, body fat, and nutritional markers during the six months post-kidney transplantation

Leptin is a 16-kd protein that is thought to be a regulator of food intake and body weight. Many previous studies have reported elevated serum leptin levels in renal failure. In this study, we investigated the outcome of serum leptin and its relationship to body fat (BF), dietary intake, nutritional, and inflammatory markers after kidney transplantation (KTx). A total of 41 kidney transplant recipients were followed-up prospectively during 6 months posttransplantation. Serum leptin, albumin, transferrin, and C-reactive protein (CRP) were measured at KTx, 15 days, 3, and 6 months later. Dietary intake and BF were determined at KTx, 3, and 6 months later. A decrease in serum leptin was observed early at day 15 after KTx; this decrease was significant only in patients with BF >/= 30% of body weight. The decrease was maintained at 3 and 6 months after KTx. In multivariate analysis, an independent impact of higher percentage BF at KTx on the decrease of serum leptin was observed. Serum leptin correlated positively with BF. Conversely, no correlation was found between changes of serum leptin and changes of dietary intake. Leptin correlated positively with CRP at KTx, but not after normalization of renal function. Changes of serum leptin levels were not correlated with those of serum albumin levels. In summary, hyperleptinemia at KTx is manifest in patients with a high percentage of BF. An early and maintained correction follows KTx. Serum leptin levels did not appear to affect alimentary intake at and after KTx.

Enhanced long-term reduction of plasma leptin concentrations by super-flux polysulfone dialysers

BACKGROUND

Hyperleptinaemia in chronic haemodialysis (CHD) patients has been associated with malnutrition, which is an independent predictor of morbidity and mortality in this patient group.

METHODS

To assess the influence of HD on plasma leptin, 10 CHD patients were crossover randomized to low-flux polysulfone (PS: F 6HPS), high-flux PS (F 60S), super-flux PS (F 500S) or super-flux cellulose-tri-acetate (CTA: Tricea 150G) for 12 weeks each. Blood samples were collected at the start of the study and each 12-week period. In addition, the relationship between patient characteristics, inflammation and leptin was analysed.

RESULTS

At baseline, all groups showed similar leptin concentrations (mean 33.6+/-21.7 ng/ml). After a single HD session, a significant (P<0.01) decrease was observed with all three high permeable devices (Tricea 150G -52.7+/-6.4%; F 60S -63.1+/-5.7%; F 500S -68.7+/-8.2%), whereas leptin remained stable with low-flux PS. After 12 weeks, a marked increase was observed with low-flux PS (week 1, 30.4+/-23.0; week 12, 40.5+/-5.4 ng/ml, P = 0.05), no change with super-flux CTA and high-flux PS (Tricea 150G week 1, 29.4+/-23.7; week 12, 32.0+/-27.9 ng/ml, P = ns; F 60S week 1, 36.0+/-31.8; week 12, 33.0+/-31.2 ng/ml, P = ns), and a significant decrease with super-flux PS (week 1, 38.3+/-33.0; week 12, 29.5+/-31.9 ng/ml, P = 0.02). The change in leptin after 12 weeks was significantly different between super-flux PS, and both low-flux PS (P = 0.009) and super-flux CTA (P = 0.01). Besides interleukin-6 (IL-6) at the start of the study (P = 0.006), no correlations were observed between patient characteristics, parameters of inflammation and plasma leptin levels.

CONCLUSIONS

Apart from low-flux PS, plasma leptin decreased considerably with all three high permeable dialysers after a single HD session. In the long run, leptin levels were lower with high-flux PS than with low-flux PS. Moreover, after switching from high-flux PS to super-flux PS (but not super-flux CTA), an additional decrease in leptin was observed. Apart from IL-6 at the start of the study, neither patient characteristics nor inflammatory parameters correlated with plasma leptin levels in this patient group.

Protein and energy nutrition among adult patients treated with chronic peritoneal dialysis

Protein-energy malnutrition (PEM) in adult patients treated with chronic peritoneal dialysis (CPD), which is highly prevalent and frequently severe in its manifestation, poses a significant therapeutic dilemma. The causes of PEM include inflammation, low nutrient intake, nutrient losses during dialysis, metabolic acidemia, coexisting illnesses, and possibly the endocrine disorders of uremia. Treatment strategies for PEM in CPD patients include the following: attempt to treat the potentially reversible causes of anorexia, increase nutrient intake (by nutritional counseling, oral food supplements, consideration of appetite stimulants and intraperitonial amino acid solutions), and the correction of metabolic acidosis. Coexisting illnesses engendering PEM should be treated. Experimental evidence suggests that such agents as anabolic steroids, human growth hormone, insulin-like growth factor-I, and L-carnitine may engender positive protein balance in these individuals. Finally, the use of anti-inflammatory agents to improve the nutritional status of malnourished CPD patients remains to be defined. There is a need to carry out clinical trials that examine whether an improvement in the nutritional status of CPD patients is associated with an improvement in their mortality, morbidity and/or quality of life.

Serum leptin concentration in peritoneal dialysis patients: determinants, longitudinal evolution and circadian rhythm

The serum concentration of leptin, an hormone secreted by adipocytes, is increased in obese and chronic renal failure patients. To determine the influence of peritoneal dialysis (PD) therapy on serum leptin levels, we analyzed its concentration in 23 patients on PD for an average of 26.8 +/- 7.1 months and compared it to that of 18 patients with chronic renal failure (creatinine clearance: 49.1 +/- 8.8 ml/min) and of 35 healthy control subjects. Leptin level was also reevaluated in 11 PD patients 9.3 +/- 1 months after the initial analysis. Finally, circadian leptin production was determined in 4 patients on automated PD (APD). Serum leptin was significantly higher in PD (31.9 +/- 7.8 ng/ml) than in chronic renal failure patients (15.2 +/- 5.9 ng/ml) and in healthy control subjects (9.6 +/- 1.1 ng/ml). Serum leptin level was significantly correlated with BMI in all three groups (except in PD males) and with the percentage of fat mass in both male and female PD patients. It did not correlate in PD patients with serum albumin concentration, free fat mass, residual diuresis, time on PD and characteristics of peritoneal permeability. At the second determination, serum leptin level had significantly increased in the PD patients although their respective BMI and serum creatinine concentration had remained virtually unchanged. Finally, in APD patients, the highest leptin level was observed at 08.00 a.m. These results demonstrate that serum leptin level is increased in PD patients and that it progressively rises under PD therapy. The circadian leptin production is delayed in APD patients probably suggesting a negative effect of the nocturnal glucose load on the regulation of its secretion.

Leptin is a negative acute phase protein in chronic hemodialysis patients

BACKGROUND

Hypoalbuminemia strongly predicts death in hemodialysis patients and results from both inflammation and malnutrition. One potential link between malnutrition and inflammation is appetite suppression triggered by inflammation. Leptin is secreted by adipose tissue and suppresses appetite, and it is also a positive acute phase protein in the rat. Factored for body weight, leptin is known to be increased in hemodialysis patients, but its relationship to inflammation is unknown.

METHODS

We examined the relationship between spontaneously occurring activation of the acute phase response and leptin levels in 29 chronic hemodialysis patients. Serum samples were obtained three times weekly for six weeks and then monthly from 29 chronic hemodialysis patients, and the levels of the positive acute phase proteins [C-reactive protein (CRP), alpha1-acid glycoprotein (alpha1 AG), serum amyloid A, ceruloplasmin] and the negative acute phase proteins (albumin and transferrin) as well as leptin and interleukin-6 (IL-6) were measured.

RESULTS

Positive and negative acute phase proteins were evaluated at the maximum CRP (mean, 9.42 +/- 1.14 mg/dL) and minimum values (mean, 0.41 +/- 0.09 mg/dL). When CRP was elevated, leptin levels were significantly reduced, as were the negative acute phase proteins albumin and transferrin. Serum amyloid A, ceruloplasmin, alpha1 acid glycoprotein, and IL-6 were all significantly increased at the maximum CRP level, compatible with general activation of the acute phase response. The change in leptin correlated negatively with the change in CRP (R = 0.437, P = 0.018), as did changes in albumin (R = 0.620, P < 0.001).

CONCLUSIONS

Leptin is not increased as a consequence of inflammation in hemodialysis patients, but behaves as a negative rather than as a positive acute phase protein. Inflammation is unlikely to reduce appetite in dialysis patients through a leptin-mediated mechanism.

Increased leptin levels in serum and peritoneal fluid of patients with pelvic endometriosis

Pelvic endometriosis is an immune-related chronic inflammatory disease, characterized by ectopic implants of endometrium in the peritoneal cavity and associated with increased secretion of proinflammatory cytokines and neoangiogenesis. Leptin, the adipocyte-derived hormone, has been shown to have a role in food intake, basal metabolism, and reproductive function. Leptin levels are dynamically regulated, being elevated by inflammatory mediators and reduced by starvation. Leptin itself can influence the proinflammatory immune responses of CD4+ T lymphocytes, and reports have also shown this hormone to be an angiogenic factor in vitro and in vivo. We investigated whether leptin concentrations in serum and peritoneal fluid (PF) differed between 13 patients with different stages of endometriosis and 15 age- and body mass index-matched controls. We found a statistically significant (P < 0.05) increase in leptin levels in serum (30.3 +/- 14.8 ng/mL) and PF (35.9 +/- 17.4 ng/mL) of patients with endometriosis, compared with our control population (serum, 15.6 +/- 8.4; PF, 17.5 +/- 7.2 ng/mL). Regression equations, relating leptin to body mass index, were also significantly different in endometriosis patients, compared with controls. Higher levels of leptin were observed in the earlier stages of endometriosis than advanced-stage disease. These data suggest that the proinflammatory and neoangiogenic actions of leptin may contribute to the pathogenesis of endometriosis.

Physiological roles of the leptin endocrine system: differences between mice and humans

Leptin is a 16-kDa cytokine secreted in humans primarily but not exclusively by adipose tissues. Its concentration in blood is usually proportional to body fat mass, but is higher in women than in men not only because of a different distribution of and greater fat mass in women, but also because testosterone reduces its level in men. Leptin features in different ways during the life span. It is synthesized in the ovary, transported in the oocyte, and made by both fetus and placenta, particularly during the last month of gestation. It is made by the lactating mammary gland and ingested by the newborn infant in its milk. The prime importance of leptin is realized at puberty when it is necessary for progression to a normal adult reproductive status in females. Fasting and chronic undernutrition result in a lower level of leptin in the blood. Lack of leptin results in hunger, ensuring that the individual eat to survive, and also inhibition of reproduction, until such time as food and fat stores are adequate to supply energy for pregnancy and lactation. Thus, leptin is important for survival of the individual and survival of the species. Although an extremely rare genetic absence of leptin induces hyperphagia and obesity in humans, as it does in mice, there appears to be little role for leptin in humans in ensuring that fat stores are not in excess of adequate, that is, in preventing obesity. The mouse differs from humans in many respects, in particular in the far more drastic ways it conserves energy when it very rapidly adapts to lack of food. These include not only suppression of reproduction but also lowering of its body temperature (torpor), suppressing its thyroid function, suppressing its growth, and increasing secretion of stress hormones (from the adrenal). This review concentrates on roles of leptin in human physiology and pathophysiology but also discusses why some observations on actions of leptin in mice are not applicable to humans.

Leptin in peritoneal dialysate from continuous ambulatory peritoneal dialysis patients

The adipocyte-derived hormone leptin is the 16-kd product of the ob gene that regulates food intake and body weight. Plasma leptin level is elevated in patients with chronic renal failure, partly because of impaired clearance through the kidney. In this study, we examined whether leptin is cleared into peritoneal dialysate in patients with end-stage renal disease treated by continuous ambulatory peritoneal dialysis (CAPD). The subjects were 46 CAPD patients and 67 age- and gender-matched healthy subjects. Leptin concentration in peritoneal dialysate from CAPD patients was measurable by a sensitive enzyme-linked immunosorbent assay (ELISA), and the daily loss of leptin by the peritoneal route was estimated to correspond to the amount contained in approximately 2 L plasma. Dialysate leptin concentration correlated positively with plasma leptin level and with percent body fat measured by dual-energy X-ray absorptiometry. The dialysate-to-plasma (D/P) ratio of leptin concentration was twice higher than expected from its molecular weight. D/P ratios of beta2-microglobulin, albumin, and transferrin showed strong correlations with each other (r = 0.768 to 0.801), whereas the correlation between D/P ratios of leptin and beta2-microglobulin was less impressive (r = 0.378). This was also the case with the relationship between apparent peritoneal clearances of these macromolecules, suggesting that dialysate leptin had some origins other than passive transport of plasma leptin. To test the hypothesis that abdominal visceral fat may contribute to the unexpectedly raised peritoneal dialysate leptin concentration, multiple regression analysis was performed. Leptin concentration in peritoneal dialysate showed significant association with plasma leptin level and D/P ratio of beta2-microglobulin, and it also showed an independent association with abdominal visceral fat but not with subcutaneous fat assessed by ultrasonography. These results showed that peritoneal dialysate from CAPD patients contained a significant amount of leptin, which derived presumably from both plasma and local visceral fat tissue.

Peritoneal clearance of leptin in continuous ambulatory peritoneal dialysis

Leptin is a 16-kd protein that increases energy expenditure and limits food intake. Serum leptin (S-leptin) is elevated in dialysis patients, and little data have been reported on leptin clearance (Cl) during dialysis. We analyzed the peritoneal dialysis (PD) Cl of leptin in 15 continuous ambulatory peritoneal dialysis (CAPD) patients and compared the results to beta(2)-microglobulin (beta(2)-m), urea, and creatinine PD Cl. S-leptin was significantly elevated (Kruskal-Wallis, P < 0.005) in CAPD women (58.4 +/- 42.4 [SE] microg/L, n = 5) as compared with CAPD men (13.9 +/- 7.1, n = 10) and with healthy women (11.0 +/- 1.4, n = 13) and men (5.1 +/- 0. 9, n = 14). Correlations were found between percent of fat mass and S-leptin (P < 0.05); between S-leptin and the 24-hour PD leptin (P < 0.05); and between dialysate-to-plasma (D/P) beta(2)-m and D/P leptin (P < 0.01). PD leptin Cl (1.80 +/- 0.43 mL/min/1.73 m(2)) was higher than beta(2)-m Cl (1.22 +/- 0.31) (P < 0.01), but reduced as compared with urea Cl (8.84 +/- 1.20) (P < 0.005) and creatinine Cl (7.71 +/- 0.99) (P < 0.005). These results indicate that leptin is eliminated through the peritoneum membrane. However, peritoneal leptin clearance, as beta(2)-m, appears to be clearly restricted as compared with peritoneal transport of smaller molecules. Hence, leptin could use the same diffusion transport pathway as beta(2)-m. In addition, leptin, which has a higher molecular weight than beta(2)-m, was significantly more eliminated into the peritoneal dialysate. More studies are necessary to clarify whether this is an active leptin elimination process by peritoneal secretion or by a different restriction coefficient of diffusion through the peritoneum membrane.