Association of the serum leptin concentration with weight loss in chronic hemodialysis patients

Increased Expression of the Leptin Gene in Adipose Tissue of Patients with Chronic Kidney Disease-The Possible Role of an Abnormal Serum Fatty Acid Profile

Chronic kidney disease (CKD) is associated with an increased level of leptin and an abnormal fatty acid (FA) profile in the serum. However, there are no data on the associations between them, and the reason for increased serum levels in patients with CKD is not well elucidated. Recently, we found that a CKD-related abnormal FA profile caused significant changes in the expression of genes involved in lipid metabolism in hepatocytes. The aim of this study was to examine whether leptin gene expression in subcutaneous adipose tissue (SAT) of patients with CKD may contribute to increased serum levels of this adipokine and whether the abnormal serum FA profile observed in CKD patients has an impact on leptin gene expression in adipocytes. The FA profile was measured in serum samples from patients with CKD and controls by GC–MS. The relative mRNA levels of leptin were measured in SAT by Real-Time PCR. Moreover, the effect of the CKD-related abnormal FA profile on leptin gene expression was studied in in vitro cultured 3T3-L1 adipocytes. Patients with CKD had higher concentrations of serum leptin than controls and higher expression level of the leptin gene in SAT. They also had increased serum monounsaturated FAs and decreased polyunsaturated FAs. The incubation of adipocytes with FAs isolated from CKD patients resulted in an increase of the levels of leptin mRNA. Increased leptin gene expression in SAT may contribute to elevated concentrations of these adipokine in patients with CKD. CKD-related alterations of the FA profile may contribute to elevated serum leptin concentrations in patients with CKD by increasing the gene expression of this adipokine in SAT.

Changes in gene expressions of hypothalamic neuropeptides controlling feeding behaviors in bilateral nephrectomized rats

Anorexia is one of the most widespread eating disorders that appears to contribute to malnutrition in patients with advanced kidney dysfunction. The changes of neuropeptides controlling feeding behaviors synthesized in the hypothalamus under several physiological condition could induce anorexia. While several mechanisms underlying uremic anorexia have been proposed, the changes of hypothalamic neuropeptides controlling feeding behaviors of uremic patients are poorly understood. The gene expressions of hypothalamic neuropeptides controlling feeding behaviors were evaluated after bilateral nephrectomy, which is a model of acute kidney dysfunction, by in situ hybridization histochemistry. Food consumption decreased markedly in bilateral nephrectomized rats. The mRNA levels of corticotrophin-releasing hormone, proopiomelanocortin, cocaine- and amphetamine-regulated transcript, which suppress feeding behavior, were significantly higher in bilateral nephrectomized rats than in sham-operated rats. On the other hand, the mRNA levels of Agouti-related peptide, neuropeptide Y, melanin-concentrating hormone, and orexin, which promote feeding behavior, were significantly lower in bilateral nephrectomized rats than in sham-operated rats. In addition, the plasma level of leptin, which has an anorexic effect, increased after bilateral nephrectomy. The results suggest that hypothalamic neuropeptides controlling feeding behaviors may be involved in the development of anorexia in bilateral nephrectomized rats. This report is the first step to elucidating the physiological mechanisms of anorexia in patients with kidney dysfunction.

Uremic Toxicity: Present State of the Art

The uremic syndrome is a complex mixture of organ dysfunctions, which is attributed to the retention of a myriad of compounds that under normal condition are excreted by the healthy kidneys (uremic toxins). In the area of identification and characterization of uremic toxins and in the knowledge of their pathophysiologic importance, major steps forward have been made during recent years. The present article is a review of several of these steps, especially in the area of information about the compounds that could play a role in the development of cardiovascular complications. It is written by those members of the Uremic Toxins Group, which has been created by the European Society for Artificial Organs (ESAO). Each of the 16 authors has written a state of the art in his/her major area of interest.

The impact of peripheral serotonin on leptin-brain serotonin axis, bone metabolism and strength in growing rats with experimental chronic kidney disease

Chronic kidney disease (CKD) results in decreased bone strength. Serotonin (5-HT) is one of the critical regulators of bone health, fulfilling distinct functions depending on its synthesis site: brain-derived serotonin (BDS) favors osteoblast proliferation, whereas gut-derived serotonin (GDS) inhibits it. We assessed the role of BDS and peripheral leptin in the regulation of bone metabolism and strength in young rats with 5/6 nephrectomy. BDS synthesis was accelerated during CKD progression. Decreased peripheral leptin in CKD rats was inversely related to BDS content in the hypothalamus, brainstem and frontal cortex. Serotonin in these brain regions affected bone strength and metabolism in the studied animals. The direct effect of circulating leptin on bone was not shown in uremia. At the molecular level, there was an inverse association between elevated GDS and the expression of cAMP responsive element-binding protein (Creb) gene in bone of CKD animals. In contrast, increased expression of activating transcription factor 4 (Atf4) was shown, which was associated with GDS-dependent transcription factor 1 (Foxo1), clock gene - Cry-1, cell cycle genes: c-Myc, cyclins, and osteoblast differentiation genes. These results identified a previously unknown molecular pathway, by which elevated GDS can shift in Foxo1 target genes from Creb to Atf4-dependent response, disrupting the leptin-BDS - dependent gene pathway in the bone of uremic rats. Thus, in the condition of CKD the effect of BDS and GDS on bone metabolism and strength can't be distinguished.

Inflammatory Cytokines as Uremic Toxins: "Ni Son Todos Los Que Estan, Ni Estan Todos Los Que Son"

Chronic kidney disease is among the fastest growing causes of death worldwide. An increased risk of all-cause and cardiovascular death is thought to depend on the accumulation of uremic toxins when glomerular filtration rate falls. In addition, the circulating levels of several markers of inflammation predict mortality in patients with chronic kidney disease. Indeed, a number of cytokines are listed in databases of uremic toxins and uremic retention solutes. They include inflammatory cytokines (IL-1β, IL-18, IL-6, TNFα), chemokines (IL-8), and adipokines (adiponectin, leptin and resistin), as well as anti-inflammatory cytokines (IL-10). We now critically review the cytokines that may be considered uremic toxins. We discuss the rationale to consider them uremic toxins (mechanisms underlying the increased serum levels and evidence supporting their contribution to CKD manifestations), identify gaps in knowledge, discuss potential therapeutic implications to be tested in clinical trials in order to make this knowledge useful for the practicing physician, and identify additional cytokines, cytokine receptors and chemokines that may fulfill the criteria to be considered uremic toxins, such as sIL-6R, sTNFR1, sTNFR2, IL-2, CXCL12, CX3CL1 and others. In addition, we suggest that IL-10, leptin, adiponectin and resistin should not be considered uremic toxins toxins based on insufficient or contradictory evidence of an association with adverse outcomes in humans or preclinical data not consistent with a causal association.

The 24-Month Changes in Body Fat Mass and Adipokines in Patients Starting Peritoneal Dialysis

♦ BACKGROUND: Peritoneal dialysis (PD) is characterized by a gain in fat mass. The fat tissue is a complex endocrine organ that releases various adipokines. In this study, we prospectively examined serial changes of fat composition and adipokines in patients undergoing PD. ♦ METHODS: Body composition was assessed by computed tomography (CT). Nutrition status and adipokines (leptin, adiponectin, interleukin [IL]-6, and tumor necrosis factor [TNF]-α) were assessed on the 7th day and 6 months, 12 months, and 24 months after the start of PD. ♦ RESULTS: Fifty-four patients (28 men), with a mean age of 53.2 ± 13.2 years, were enrolled. Baseline fat mass, especially subcutaneous fat mass, was correlated with baseline leptin (ρ = 0.612), adiponetin (ρ = -0.477), and interleukin-6 (IL-6) (ρ = 0.391). Visceral fat mass was correlated with leptin (ρ = 0.545) and adiponectin (ρ = -0.514). Baseline adiponectin was negatively correlated with baseline leptin (ρ = -0.363). While body weight and leptin increased during the 24 months, serum adiponectin decreased in that period. The changes in visceral and subcutaneous fat mass were greater in the first 12 months and 6 months, respectively. There was no difference in IL-6 and TNF-α. Eight patients died during the follow-up period (mean 47.4 months). Twenty-seven patients continued PD. Increased baseline and serial change of IL-6 level were risk factors for mortality. After adjusting for age, sex, diabetes mellitus (DM), and coronary vascular disease (CVD), the significance of the IL-6 level disappeared. ♦ CONCLUSIONS: Baseline subcutaneous fat in patients starting PD is correlated with baseline adipokine levels rather than visceral fat. The increase in subcutaneous fat was greatest in the first 6 months. While leptin and adiponectin increased and decreased respectively, IL-6 did not change in the first 24 months.

Challenges of Providing Nutrition Support in the Outpatient Dialysis Setting

Malnutrition is prevalent in maintenance hemodialysis (MHD) patients and has been strongly associated with increased morbidity and mortality. There are numerous contributors to the development, occurrence, and persistence of malnutrition in the MHD patient. Intensive diet counseling and use of enteral supplements may not be effective interventions for patients exhibiting high nutrition risk. More aggressive nutrition options such as enteral and parenteral support are less often used and have associated risks. Intradialytic parenteral nutrition (IDPN) as a form of PN delivered during the dialysis procedure is a convenient and attractive convention that is underused because of its history and controversy. There is a lack of randomized controlled trials demonstrating improved morbidity and mortality with all nutrition support interventions in MHD patients. This research is particularly crucial for IDPN in order to render change in Medicare reimbursement. Qualification of patients for this therapy is difficult because of the very strict coverage criteria. For those patients who do qualify for IDPN, clinician nutrition support knowledge is essential for safe administration of solutions and effective physical, metabolic, and nutrition management of the patient. Attention to other factors that contribute to malnutrition in MHD such as treatment adequacy and comorbid conditions is important; however, the early detection of malnutrition in the MHD patient with appropriate level of nutrition intervention is critical. Future improved understanding of the malnutrition of uremia will allow for development and investigation of other strategies that are anti-catabolic or anabolic.

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.

Leptin as an uremic toxin: Deleterious role of leptin in chronic kidney disease

White adipose tissue secretes a large variety of compounds named adipokines amongst which, leptin exhibits pleiotropic metabolic actions. Leptin is an anorexigenic hormone, secreted in proportion of fat mass, with additional effects on the regulation of inflammation, cardiovascular system, immunity, hematopoiesis and bone metabolism. Chronic kidney disease (CKD) is characterized by an increase of plasma leptin concentration that may be explained by a lack of renal clearance. Hyperleptinemia plays a key role in the pathogenesis of complications associated with CKD such as cachexia, protein energy wasting, chronic inflammation, insulin resistance, cardiovascular damages and bone complications. Leptin is also involved in the progression of renal disease through its pro-fibrotic and pro-hypertensive actions. Most of the adverse effects of leptin have been documented both experimentally and clinically. Leptin may therefore be considered as an uremic toxin in CKD. The aim of this review is to summarize the pathophysiological and clinical role of leptin in in vitro studies, experimental models, as well as in patients suffering from CKD.

Leptin in chronic kidney disease: a link between hematopoiesis, bone metabolism, and nutrition

Anemia, dyslipidemia, malnutrition, together with mineral and bone disorders are common complications in patients with chronic kidney disease (CKD). All are associated with increased risk of mortality. Leptin is a small peptide hormone that is mainly but not exclusively produced in adipose tissue. It is also secreted by normal human osteoblasts, subchondral osteoblasts, placental syncytiotrophoblasts, and the gastric epithelium. Leptin binds to its receptors in the hypothalamus to regulate bone metabolism and food intake. Leptin also has several other important metabolic effects on peripheral tissues, including the liver, skeletal muscle, and bone marrow. Leptin is cleared principally by the kidney. Not surprisingly, serum leptin appears to increase concurrently with declines in the glomerular filtration rate in patients with CKD. A growing body of evidence suggests that leptin might be closely related to hematopoiesis, nutrition, and bone metabolism in CKD patients. Results are conflicting regarding leptin in patients with CKD, in whom both beneficial and detrimental effects on uremia outcome are found. This review elucidates the discovery of leptin and its receptors, changes in serum or plasma leptin levels, the functions of leptin, relationships between leptin and the complications mentioned above, and pharmaceutical interventions in serum leptin levels in patients with CKD.

The adipose tissue as an endocrine organ

During the past 2 decades, results of both basic science and clinical studies have changed the physicians' views about adipocyte pathophysiology. Since leptin was discovered in 1994, white adipose tissue was recognized as an endocrine organ and an important source of biologically active substances with local and/or systemic action called adipokines. Inappropriate secretion of several adipokines by the excessive amount of white adipose tissue seems to participate in the pathogenesis of obesity-related pathologic processes including endothelial dysfunction, inflammation, atherosclerosis, diabetes mellitus, and chronic kidney disease. In this review endocrine action of selected adipokines (mainly leptin and adiponectin) in the context of kidney diseases is discussed. Specifically, the role of these adipokines in malnutrition, chronic kidney disease progression, and pathogenesis of cardiovascular complications is presented.

Evaluation of nutrient intake in early post kidney transplant recipients

The purpose of our study was to evaluate the dietary intake of kidney transplant recipients (KTRs) and assess oral intake related nutrition problems. Fifty patients who had undergone kidney transplantation were included: 24 males, 26 females. The mean age was 46.8 ± 11.2 years, height was 161.3 ± 8.3 cm, and body weight was 60.5 ± 8.7 kg. We conducted nutrition education based on the diet guideline for KTRs (energy 32 kcal/kg of ideal body weight [IBW], protein 1.3 g/kg of IBW) and neutropenic diet guideline before discharge. Dietary intake of the patients at 1 month after transplantation was investigated by 3-day food records. Body weight and laboratory values for nutritional status and graft function were also collected. Body weight was significantly decreased from admission to discharge. Body weight from discharge to 1 month and 3 months after transplantation was increased but was not significant. Biochemical measurements were generally improved but the number of patients with hypophosphatemia increased. The daily dietary intake of energy and protein was adequate (33.1 kcal/kg, 1.5 g/kg, respectively). However, the dietary intake of calcium, folate, and vitamin C did not meet the Korean Recommended Nutrient Intake of vitamins and minerals (86.8%, 62.4%, and 88.0%, respectively). Patients with low intake of calcium, folate, and vitamin C presented low intake in milk and dairy products, vegetables, and fruits, and these foods were related to restricted food items in neutropenic diet. More attention should be paid on improving quality of diet, and reconsideration of present neutropenic diet guideline is necessary. These results can be used to establish evidence-based medical nutrition therapy guideline for KTRs.

Insulin resistance in patients with chronic kidney disease

Metabolic syndrome and its components are associated with chronic kidney disease (CKD) development. Insulin resistance (IR) plays a central role in the metabolic syndrome and is associated with increased risk for CKD in nondiabetic patients. IR is common in patients with mild-to-moderate stage CKD, even when the glomerular filtration rate is within the normal range. IR, along with oxidative stress and inflammation, also promotes kidney disease. In patients with end stage renal disease, IR is an independent predictor of cardiovascular disease and is linked to protein energy wasting and malnutrition. Systemic inflammation, oxidative stress, elevated serum adipokines and fetuin-A, metabolic acidosis, vitamin D deficiency, depressed serum erythropoietin, endoplasmic reticulum stress, and suppressors of cytokine signaling all cause IR by suppressing insulin receptor-PI3K-Akt pathways in CKD. In addition to adequate renal replacement therapy and correction of uremia-associated factors, thiazolidinedione, ghrelin, protein restriction, and keto-acid supplementation are therapeutic options. Weight control, reduced daily prednisolone dosage, and the use of cyclosporin decrease the risk of developing new-onset diabetes after kidney transplantation. Improved understanding of the pathogenic mechanisms underlying IR in CKD may lead to more effective therapeutic strategies to reduce uremia-associated morbidity and mortality.

Adipokines as uremic toxins

The adipose tissue has pleiotropic functions far beyond the mere storage of energy, and it secretes a number of hormones and cytokines, called adipokines, which have biological effects that impact heath and disease. Adipokines are markedly elevated in the plasma of uremic patients, mainly due to decreased renal excretion. They have pluripotent signaling effects on inflammation/oxidative stress (leptin, adiponectin, resistin), protein-energy wasting (leptin, adiponectin), insulin signaling (adiponectin, leptin, visfatin), endothelial dysfunction (visfatin), and vascular damage (adiponectin, leptin, resistin), which are prevalent in uremic patients. Obesity superimposed to uremia may further aggravate hyperadipokinemia, with the exception of adiponectinemia, which is mitigated by adiposity. Among adipokines and until more data become available, only leptin may be considered as a full uremic toxin owing to adverse effects on protein-energy wasting, cardiovascular damage, inflammation, and the immune system, which have been documented both clinically and experimentally. Resistin and visfatin display some features of uremic toxins, but more data are needed to consider these adipokines as true uremic toxins. In contrast, high levels of adiponectin and chemerin seen in uremia appear to be beneficial. Further research is needed to investigate whether selective removal of leptin, resistin, and visfatin and increments of adiponectin and chemerin levels may have clinical relevance in uremic patients.

Longitudinal study of leptin levels in chronic hemodialysis patients

Background

The influence of serum leptin levels on nutritional status and survival in chronic hemodialysis patients remained to be elucidated. We conducted a prospective longitudinal study of leptin levels and nutritional parameters to determine whether changes of serum leptin levels modify nutritional status and survival in a cohort of prevalent hemodialysis patients.

Methods

Leptin, dietary energy and protein intake, biochemical markers of nutrition and body composition (anthropometry and bioimpedance analysis) were measured at baseline and at 6, 12, 18 and 24 months following enrollment, in 101 prevalent hemodialysis patients (37% women) with a mean age of 64.6 ± 11.5 years. Observation of this cohort was continued over 2 additional years. Changes in repeated measures were evaluated, with adjustment for baseline differences in demographic and clinical parameters.

Results

Significant reduction of leptin levels with time were observed (linear estimate: -2.5010 ± 0.57 ng/ml/2y; p < 0.001) with a more rapid decline in leptin levels in the highest leptin tertile in both unadjusted (p = 0.007) and fully adjusted (p = 0.047) models. A significant reduction in body composition parameters over time was observed, but was not influenced by leptin (leptin-by-time interactions were not significant). No significant associations were noted between leptin levels and changes in dietary protein or energy intake, or laboratory nutritional markers. Finally, cumulative incidences of survival were unaffected by the baseline serum leptin levels.

Conclusions

Thus leptin levels reflect fat mass depots, rather than independently contributing to uremic anorexia or modifying nutritional status and/or survival in chronic hemodialysis patients. The importance of such information is high if leptin is contemplated as a potential therapeutic target in hemodialysis patients.

Obesity hypertension: the regulatory role of leptin

Leptin is a 16-kDa-peptide hormone that is primarily synthesized and secreted by adipose tissue. One of the major actions of this hormone is the control of energy balance by binding to receptors in the hypothalamus, leading to reduction in food intake and elevation in temperature and energy expenditure. In addition, increasing evidence suggests that leptin, through both direct and indirect mechanisms, may play an important role in cardiovascular and renal regulation. While the relevance of endogenous leptin needs further clarification, it appears to function as a pressure and volume-regulating factor under conditions of health. However, in abnormal situations characterized by chronic hyperleptinemia such as obesity, it may function pathophysiologically for the development of hypertension and possibly also for direct renal, vascular, and cardiac damage.

Changes in body fat mass in patients after starting peritoneal dialysis

BACKGROUND

Peritoneal dialysis (PD) is characterized by gain in fat mass. Visceral fat mass is associated with metabolic syndrome and atherosclerosis rather than subcutaneous fat mass. In addition, the change in visceral fat mass is a more reliable predictor of survival in PD patients. In this study, we prospectively examined serial changes in fat composition and nutritional status and analyzed factors associated with gain in fat mass in patients undergoing PD.

METHODS

Body composition was assessed by bioelectric impedance analysis (BIA) and computed tomogram (CT). Nutrition status was assessed by Subjective Global Assessment (SGA), protein equivalent of nitrogen appearance (nPNA), serum albumin, C-reactive protein (CRP), and lipid profile. All measurements except BIA were performed on the seventh day and at 6 and 12 months after the start of PD.

RESULTS

60 patients (30 men; mean age 55.0 ± 12.5 years) were enrolled. Increase in body weight continued during the 12 months but visceral and subcutaneous fat mass increased during the first 6 months and decreased during the second 6 months. While hematocrit and serum albumin decreased during the first 6 months, they did not change during the second 6 months. Serum creatinine, total cholesterol, and triglyceride increased similarly to the weight pattern. While nPNA decreased during the 12 months, Kt/V, SGA, and CRP did not change. Patients that had more visceral fat mass at the start of PD had less gain of visceral fat mass during the first 6 months (r = -0.821, p = 0.002). Patients that had more subcutaneous fat mass at the start of PD had less gain of subcutaneous fat mass (r = -0.709, p = 0.015). The change in weight was not associated with the change in visceral or subcutaneous fat during the first 6 months.

CONCLUSION

Patients starting PD experience weight gain, including visceral and subcutaneous fat, during the first 6 months of PD. Patients with high baseline fat mass had less increase in fat mass than those with low baseline fat mass, regardless of visceral or subcutaneous fat mass.

Challenges of nutrition intervention for malnourished dialysis patients

Malnutrition, or protein energy wasting (PEW), is prevalent in patients with chronic kidney disease stage 5 dialysis (CKD-5). One criterion of PEW strongly associated with morbidity and mortality in CKD-5 dialysis patients is the serum albumin level. Serum albumin levels have not improved over the past 10 years. Typical intervention strategies need to be reevaluated. Intradialytic parenteral nutrition (IDPN) is a form of parenteral nutrition delivered during dialysis that is a convenient and assured route of nutrition alimentation for high-nutrition-risk PEW patients who cannot improve nutrition status by oral and enteral routes. Recent qualification criteria for IDPN changes in Medicare part D have made this therapy an available option for many more of these high-nutrition-risk PEW patients. Nutrition support knowledge in clinicians is essential to administer IDPN effectively and to optimize clinical response. An improved understanding of the milieu of uremia and PEW of CKD-5, as well as the study of nutrition interventions inclusive of IDPN, will allow for effective strategies toward improved outcomes in the future.

Leptin levels recover normally in healthy older adults after acute diet-induced weight loss

OBJECTIVES

Involuntary weight loss affects 20% of community dwelling older adults. The underlying mechanism for this disorder is unknown. Objective is to determine if failure of older persons to regain weight is associated with elevated pro-inflammatory cytokine and leptin levels.

DESIGN

Prospective diet intervention study.

SETTING

University of Washington Medical Center from 2001-2005.

PARTICIPANTS

Twenty-one younger (18-35 years old) and nineteen older (>or= 70 years old) men and women.

INTERVENTION

Each subject was placed for two weeks on a weight-maintaining diet, followed in sequence by 2 weeks of 30% caloric restriction, then 4 weeks of ad libitum food intake.

MEASUREMENTS

Plasma leptin levels, fasting serum pro-inflammatory cytokine levels, and peripheral blood mononuclear cell cytokine levels were measured.

RESULTS

Leptin levels in the two cohorts decreased after caloric restriction and increased after ad-libitum food consumption resumed. Plasma TNF alpha levels were higher in older subjects compared to younger adults. However, there was no association between changes in TNF alpha levels and changes in AUC leptin.

CONCLUSION

Leptin levels in healthy older individuals responded appropriately in a compensatory manner to changes in body weight. These data do not support a cytokine dependent elevation in leptin levels as being responsible for the failure of older adults to regain weight.

Malnutrition-inflammation-atherosclerosis syndrome in Chronic Kidney disease

Chronic kidney disease is becoming a major health problem globally and in India an alarming number of about 8 million people are suffering from this disease. Patients undergoing hemodialysis have a high prevalence of protein-energy malnutrition and inflammation. As these two conditions often occur concomitantly in hemodialysis patients, they have been referred together as 'malnutrition-inflammation-atherosclerosis syndrome' to emphasize the important association with atherosclerotic cardiovascular disease. The three factors related to the pathophysiology in these patients are dialysis related nutrient loss, increased protein catabolism and hypoalbuminemia. Inflammation in Chronic Kidney disease is the most important factor in the genesis of several complications in renal disease. Pro-inflammatory cytokines like IL-1 and TNF-alpha play a major role in the onset of metabolic alterations in Chronic Kidney disease patients. Atherosclerosis is a very frequent complication in uremia due to the coexistence of hypertension, hyperhomocysteinemia, inflammation, malnutrition and increased oxidative stress, generation of advanced glycation end products, advanced oxidation protein products, hyperlipidemia and altered structural and functional ability of HDL. LDL-cholesterol, apolipoprotein (A), apolipoprotein (B), and Lp(a) are also associated with atherosclerosis. Studies have now provided enormous data to enable the evaluation of the severity of malnutrition-inflammation-atherosclerosis syndrome as well as effective monitoring of these patients.

Gut hormones and the treatment of disease cachexia

Advances in the understanding of appetite are leading to a refined concept of disease cachexia and point to novel therapeutic strategies based on the manipulation of appetite. The complex social and psychological short-term influences on appetite obscure the fact that over the longer term appetite is tightly regulated by physiological considerations; the homeostatic control of energy balance. Like obesity, which is now viewed as a disorder of homeostasis, cachexia can be seen as an adaptive response to the disease state that becomes harmful when prolonged. Several lines of evidence implicate a disorder of appetite regulation in the pathogenesis of cachexia. As the only known circulating mediator of increased appetite the peptide hormone ghrelin has attracted attention as a potential therapy. Trials in patients with various chronic illnesses, including cancer and kidney failure, have demonstrated short-term increases in energy intake. Trials in patients with emphysema and heart failure have also shown benefits in clinical outcomes such as lean body mass and exercise capacity, and longer-term trials using oral analogues are being undertaken. As well as improving nutrition, ghrelin has a number of other actions that may be useful, including an anti-inflammatory effect; of interest since many cachexias are associated with inappropriate immune activation. The manipulation of appetite, in particular by ghrelin agonism, is emerging as an exciting potential therapy for disease cachexia. Future research should focus on the ascertainment of clinically-relevant outcomes, and further characterisation of the non-nutritional effects of this pathway.

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.

The role of obesity and its bioclinical correlates in the progression of chronic kidney disease

In spite of a progressive fall in the incidence of traditional risk factors of cardiovascular morbidity (cigarette smoking, high blood pressure, and hyperlipidemia), there is an upward trend in the prevalence of obesity and chronic kidney disease (CKD). Furthermore, there is a strong correlation between body mass indices and the relative risk of progression of CKD. The close biophysiological interaction between obesity and CKD is evident by a similar occurrence of comorbidities including insulin resistance, hyperlipidermia, endothelial dysfunction, and sleep disorders. Truncal obesity is a primary component of metabolic syndrome; unlike peripheral fat, the visceral adipocytes are more resistant to insulin. In addition, lipolysis results in a release of free fatty acid and TG, whereas hypertriglycedemia is potentiated by uremic activation of fatty acid synthase. Hypertriglycedemia and low HDL cholesterol increase the relative risk of progression of CKD. Furthermore, endothelial inflammation and premature atherosclerosis are promoted by hyperhomocysteinemia and oxidation of LDL, both of which are commonly observed in CKD and obesity. Predominance of oxidative stress in both obesity and azotemia stimulate synthesis of angiotensin II, which in turn increases TGF-B and plasminogen activator inhibitor-1, thereby propagating glomerular fibrosis. Furthermore, local synthesis of angiotensinogen by adipocytes, leptin activation of sympathetic nervous system, and hyperinsulinemia contribute to the development of hypertension in obesity and CKD. In addition, increased renal tubular expression of Na-K-ATPase and a blunted response to natiuretic hormones in obesity promote salt and water retention. Glomerular hyperfiltration from systemic volume load and hypertension results in mesangial cellular proliferation and progressive renal fibrosis. In addition, maternal nutritional deprivation increases the incidence of obesity, hypertension, and diabetes in adulthood. Reduced fetal protein synthesis contributes to oxidative glomerular injury and impairment of renal morphogenesis. Thus, kidneys are poorly equipped to handle physiologic stress that may result from the rapid body growth and programmed metabolic dysfunction later in life. Finally, in order to minimize morbidity of obesity-related kidney disease, preventive strategy must include optimal maternal health care, promotion of healthy nutrition and routine physical exercise, and early detection of CKD.

Why do patients sleep on dialysis?

Sleep-associated symptoms and excessive daytime sleepiness are felt to be more common in dialysis patients. Several surveys conducted in this patient population have identified a prevalence of sleep disturbances in up to 80% of patients. This review article summarizes common disorders associated with sleep disturbances in dialysis patients, including sleep-disordered breathing, restless legs syndrome, and major depression. Special attention is given to pathophysiological processes and effective approaches for the prevention and timely treatment of these conditions, which in turn reduces the substantial morbidity associated with sleep disturbances.

Epidemiology of dialysis patients and heart failure patients

The epidemiology of maintenance dialysis patients and heart failure patients has striking similarities. Both groups have a high prevalence of comorbid conditions, a high hospitalization rate, a low self-reported quality of life, and an excessively high mortality risk, mostly because of cardiovascular causes. Observational studies in both dialysis and heart failure patients have indicated the lack of a significant association between the traditional cardiovascular risk factors and mortality, or the existence of a paradoxic or reverse association, in that obesity, hypercholesterolemia, and hypertension appear to confer survival advantages. The time discrepancy between the 2 sets of risk factors, that is, overnutrition (long-term killer) versus undernutrition (short-term killer) may explain the overwhelming role of malnutrition, inflammation, and cachexia in causing the reverse epidemiology, which may exist in more than 20 million Americans. We have reviewed the opposing views about the concept of reverse epidemiology in dialysis and heart failure patients, the recent Die Deutsche Diabetes Dialyze study findings, and the possible role of racial disparities. Contradictory findings on hyperhomocysteinemia in dialysis patients are reviewed in greater details as a possible example of publication bias. Additional findings related to intravenous iron and serum ferritin, calcium, and leptin levels in dialysis patients may enhance our understanding of the new paradigm. The association between obesity and increased death risk in kidney transplanted patients is reviewed as an example of the reversal of reverse epidemiology. Studying the epidemiology of dialysis patients as the archetypical population with such paradoxic associations may lead to the development of population-specific guidelines and treatment strategies beyond the current Framingham cardiovascular risk factor paradigm.

Resolving controversies regarding hemodiafiltration versus hemodialysis: the Dutch Convective Transport Study

Hemodialysis patients suffer from a high incidence of cardiovascular disease. Among the many predisposing factors, such as high blood pressure, dyslipidemia, and fluid overload, the accumulation of high molecular weight uremic toxins, the so-called middle molecules, may play an important role. Since convective therapies such as online hemodiafiltration have a better clearance profile for these compounds than standard hemodialysis, it has been suggested that these dialysis strategies may reduce cardiovascular morbidity and mortality. As reliable data on these issues are not available, the Dutch Convective Transport Study (CONTRAST) was recently initiated. This prospective randomized trial was designed to compare online hemodiafiltration with low-flux hemodialysis with respect to cardiovascular morbidity and mortality.

A cute plasma ghrelin and leptin responses to oral feeding or intraperitoneal hypertonic glucose-based dialysate in patients with chronic renal failure

BACKGROUND

Chronic renal failure (CRF) is associated with increased plasma levels of ghrelin and leptin, but the regulation of the secretion of these hormones has been insufficiently studied, in this setting. The aim of this study was to analyze the acute effects of oral feeding or intraperitoneal 3.86% glucose-based dialysate infusion on plasma ghrelin and leptin levels in patients with CRF undergoing peritoneal dialysis (PD).

METHODS

Following a crossover design, 10 patients and eight healthy controls underwent a standardized oral intake, a 3.86% glucose-based dialysate PD exchange (patients) and placebo oral intake. We scrutinized acute changes in plasma ghrelin, leptin, glucose, insulin, and growth hormone (GH) levels.

RESULTS

In patients, total ghrelin decreased modestly immediately after oral feeding (nadir 90.6% of baseline, range 85.1, 94.5, P= 0.03) or the PD exchange test (92.2%, range 58.7, 101.9, P= 0.05) (median). Response to oral feeding was markedly blunted when compared with healthy individuals (73.8%, range 56.1, 89.1, P= 0.007) (P < 0.005 vs. patients). Plasma acyl-ghrelin had a less marked but more persistent decay after the PD exchange test (nadir 80.4%, range 55.1, 96.3, P= 0.02) than after oral intake (64.4%, range 45.6, 82.3, P= 0.005); again, changes were more intense in normal controls (47.4%, range 32.1, 67.3, P= 0.01) (P < 0.05 vs. patients). Leptin levels decreased slightly (P < 0.05) after the PD exchange in patients, but did not respond acutely to oral feeding in patients or controls.

CONCLUSION

Ghrelin secretion is partially refractory to the acute inhibitory effect of oral feeding in patients with CRF undergoing PD therapy. A 3.86% glucose-based PD exchange results in a significant decrease of plasma ghrelin levels. Plasma leptin levels are not acutely affected by oral feeding in patients with CRF or healthy individuals.

Metabolic acidosis and malnutrition-inflammation complex syndrome in chronic renal failure

Metabolic acidosis, a common condition in patients with renal failure, may be linked to protein-energy malnutrition (PEM) and inflammation, together also known as malnutrition-inflammation complex syndrome (MICS). Methods of serum bicarbonate measurement may misrepresent the true bicarbonate level, since the total serum carbon dioxide measurement usually overestimates the serum bicarbonate concentration. Moreover, the air transportation of blood samples to distant laboratories may lead to erroneous readings. In patients with chronic kidney disease (CKD) or end-stage renal disease (ESRD), a significant number of endocrine, musculoskeletal, and metabolic abnormalities are believed to result from acidemia. Metabolic acidosis may be related to PEM and MICS due to an increased protein catabolism, decreased protein synthesis, endocrine abnormalities including insulin resistance, decreased serum leptin level, and inflammation among individuals with renal failure. Evidence suggests that the catabolic effects of metabolic acidosis may result from an increased activity of the adenosine triphosphate (ATP)-dependent ubiquitin-proteasome and branched-chain keto acid dehydrogenase. In contrast to the metabolic studies, many epidemiologic studies in maintenance dialysis patients have indicated a paradoxically inverse association between mildly decreased serum bicarbonate and improved markers of protein-energy nutritional state. Hence metabolic acidosis may be considered as yet another element of the reverse epidemiology in ESRD patients. Interventional studies have yielded inconsistent results in CKD and ESRD patients, although in peritoneal dialysis patients, mitigating acidemia appears to more consistently improve nutritional status and reduce hospitalizations. Large-scale, prospective randomized interventional studies are needed to ascertain the potential benefits of correcting acidemia in malnourished and/or inflamed CKD and maintenance hemodialysis patients. Until then, all attempts should be made to adhere to the National Kidney Foundation Kidney Disease and Dialysis Outcome Quality Initiative guidelines to maintain a serum bicarbonate level in ESRD patients of at least 22 mEq/L.

Metabolic acidosis in maintenance dialysis patients: clinical considerations

Metabolic acidosis in maintenance dialysis patients: Clinical considerations. Metabolic acidosis is a common consequence of advanced chronic renal failure (CRF) and maintenance dialysis (MD) therapies are not infrequently unable to completely correct the base deficit. In MD patients, severe metabolic acidosis is associated with an increased relative risk for death. The chronic metabolic acidosis of the severity commonly encountered in patients with advanced CRF has two well-recognized major systemic consequences. First, metabolic acidosis induces net negative nitrogen and total body protein balance, which improves upon bicarbonate supplementation. The data suggest that metabolic acidosis is both catabolic and antianabolic. Emerging data also indicate that metabolic acidosis may be one of the triggers for chronic inflammation, which may in turn promote protein catabolism among MD patients. In contrast to these findings, metabolic acidosis may be associated with a decrease in hyperleptinemia associated with CRF. Several studies have shown that correction of metabolic acidosis among MD patients is associated with modest improvements in the nutritional status. Second, metabolic acidosis has several effects on bone, causing physicochemical dissolution of bone and cell-mediated bone resorption (inhibition of osteoblast and stimulation of osteoclast function). Metabolic acidosis is probably also associated with worsening of secondary hyperparathyroidism. Data on the effect of correction of metabolic acidosis on renal osteodystrophy, however, are limited. Preliminary evidence suggest that metabolic acidosis may play a role in beta2-microglobulin accumulation, as well as the hypertriglyceridemia seen in renal failure. Given the body of evidence pointing to the several systemic consequences of metabolic acidosis, a more aggressive approach to the correction of metabolic acidosis is proposed.

Elevated leptin fragments in renal failure correlate with BMI and haematopoiesis and are normalized by haemodialysis

OBJECTIVE

Leptin is an adipocyte hormone important in appetite, energy homeostasis, neuroendocrine and haematopoietic function. Patients with renal failure often have elevated total and free leptin levels. Biologically active leptin fragments (leptin(22-56) and leptin(57-92)) have been identified, but whether these fragments are affected by renal failure and/or haemodialysis (HD) is not known.

RESEARCH METHODS

Leptin, leptin(22-56) and leptin(57-92) levels were measured in 28 HD patients [14 men, 14 women, age 45.5 +/- 16.4 years, body mass index (BMI) 23.8 +/- 3.6 kg/m2] and 25 healthy controls with similar age and BMI. In 18 HD patients, leptin and fragment levels were measured before and after 2 consecutive dialysis treatments and on the intermediate, dialysis-free day.

RESULTS

Baseline leptin levels were higher in HD patients vs. controls (69.3 +/- 62.2 ng/ml vs. 30.4 +/- 32.7, P < 0.02) as were leptin(22-56) (7.14 +/- 7.04 ng/ml vs. 1.86 +/- 1.84, P < 0.02) and leptin(57-92) (5.94 +/- 6.08 ng/ml vs. 1.58 +/- 1.98, P < 0.02). Baseline leptin and fragment levels correlated significantly and independently with BMI in HD patients (r = 0.70, r = 0.59, r = 0.72, respectively, P < 0.001). After each HD session, leptin levels were reduced to levels not different from controls, but increased on the intermediate, dialysis-free day. Similar to and independently from total leptin, both leptin fragments were reduced after the first HD session to levels not different from controls. The reduction in leptin levels was higher with synthetic vs. cellulosic membrane types (37.7 +/- 23.5%vs. 18.1 +/- 21.8%, P < 0.03). Leptin correlated weakly with the erythropoietin to haematocrit ratio (T = -0.20, P = 0.14), while leptin(22-56) had a significant negative correlation with this index (T = -0.42, P < 0.01), suggesting that this fragment may favour haematopoiesis.

DISCUSSION

Leptin fragments are detected in human serum, and both leptin and leptin fragments correlate with BMI, are significantly elevated in HD patients compared to controls, and are significantly decreased by haemodialysis. The elevated leptin fragments may have important physiological significance for the anorexia, hypogonadism, and anaemia commonly seen in HD patients, but this remains to be conclusively shown by interventional trials.

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.

Initial body mass indexes have contrary effects on change in body weight and mortality of patients on maintenance hemodialysis treatment

Malnutrition is a relevant risk factor for mortality for patients on maintenance hemodialysis treatment. In a retrospective study including 377 patients who began hemodialysis treatment between 1986 and 2001, we assessed the prevalence of different statuses of nutrition and the impact of the initial status of nutrition on the change in body weight and patient survival. We found an inverse relationship between body mass index (BMI, kg/m2) and the gain in body weight and BMI within 12 months of hemodialysis treatment. Underweight and normal weight patients had a substantial increase in these parameters, greatest in underweight subjects, whereas overweight and obese patients showed only a moderate increase or none (P =.0019, P =.00036). Adjusted mortality rates showed an inverse correlation with the initial BMI (P <.0001). There was a statistically significant difference in the mortality between patients with normal weight and overweight or obesity, respectively, showing a more favorable prognosis in overweight and obese patients (P =.0007; P =.022; log-rank, normal versus overweight, P =.012). Weight loss was the greatest independent risk factor for mortality in general. Adjusted hazard ratio of death was highest in underweight patients (3.999; CI, 2.708 to 5.905; P <.0001) and decreased to 2.251 (CI, 1.795 to 2.822; P <.0001) in normal weight, 1.927 (CI, 1.390 to 2.670; P <.0001) in overweight, and 1.651 (CI, 0.841 to 3.236; P =.1439) in obese subjects when patients with weight loss were compared with patients who preserved their initial weight or gained weight. Overall, the initial BMI has an influence on the change in body weight as well as on patient survival in general and in the case of weight loss in particular.

Therapeutic effects of oral nutritional supplementation during hemodialysis

BACKGROUND

Protein-calorie malnutrition is common in chronic hemodialysis (CHD) patients and correlates with morbidity and mortality in these patients. There are limited trials evaluating the efficacy of oral nutritional supplementation in malnourished CHD patients.

METHODS

Eighty-five CHD patients with evidence of malnutrition were included in this prospective study. Patients were followed for a 3-month baseline period during which they received conventional nutrition counseling. This was followed by an intervention period, during which an oral nutritional supplement specifically formulated for CHD patients was given over a period of 6 months. An important element of this study was that the nutritional supplement was provided during dialysis to ensure compliance. Serial measurements of nutritional parameters including concentrations of serum albumin, prealbumin, transferrin as well as body mass index (BMI) and subjective global assessment (SGA) were obtained during the 9-month period.

RESULTS

The nutritional parameters did not change during the 3-month baseline period. Following administration of oral supplementation during hemodialysis, there were significant increases in concentrations of serum albumin (from 3.33 +/- 0.32 g/dL at baseline, to 3.65 +/- 0.26 g/dL at month 6, P < 0.0001) and serum prealbumin (from 26.1 +/- 8.6 mg/dL at baseline, to 30.7 +/- 7.4 mg/dL at month 6, P = 0.002). Mean SGA score increased 14% by the end of the study (P = 0.023). Although BMI and estimated dry weight increased also, these changes were not statistically significant. Serum transferrin did not change during the study period.

CONCLUSION

Oral nutritional supplementation given during hemodialysis improves nutritional markers in malnourished CHD patients.

Leptin levels are appropriate for body mass index in older men who experience involuntary weight loss

OBJECTIVES

To determine the relationship between leptin and unintentional weight loss in older adults.

DESIGN

Prospective cohort study over 2 years.

SETTING

University-affiliated Veterans Affairs Medical Center.

PARTICIPANTS

The subjects were 105 community-dwelling male veterans aged 65 and older who had participated in a prospective cohort study on nutrition and health conducted at the Veterans Affairs Puget Sound Health Care System from 1986 to 1989.

MEASUREMENTS

Anthropometric data and fasting blood specimens were collected at baseline and annually for the subsequent 2 years. Stored blood specimens were analyzed for leptin, insulin, glucose, C-reactive protein, sex hormone binding globulin, and testosterone levels.

RESULTS

Over 2 years, 75 men were weight stable (weight loss <4% of baseline) and 30 men had unintentional weight loss (weight loss>4% of baseline). The baseline body mass index (BMI) and leptin levels for the two groups were not statistically different. Positive correlations existed between leptin level and BMI at each time point for weight-stable and weight-loss subjects. Furthermore, a significant relationship existed between changes in leptin and changes in BMI over 1 year in multiple regression analysis (r =.436, P <.001 after the first year; and r =.630, P =.027 after the second year).

CONCLUSIONS

Like in younger adults, plasma leptin levels remained proportional to BMI, and changes in BMI were accurately reflected by changes in leptin levels in older individuals. Fasting leptin levels did not predict involuntary weight loss over 2 years of follow-up.

Affect of serum leptin on nutritional status in renal disease

Protein-energy malnutrition is a major comorbid condition in persons with renal disease. A variety of interventions have been implemented to supplement protein and energy intake in malnourished patients with renal disease, but the prevalence of protein-energy malnutrition remains high. Leptin, a hormone secreted by adipose tissue, decreases food intake via neuroendocrine systems in the hypothalamus in persons with normal renal function. Serum leptin levels are elevated in patients with chronic renal insufficiency and end-stage renal disease, and experimental evidence suggests a possible role for leptin in the development of protein-energy malnutrition in this population. Release of leptin from adipocytes may be stimulated by cytokines mediating the inflammatory response, which is frequently pronounced in patients with end-stage renal disease receiving hemodialysis and peritoneal dialysis. This article provides an overview of research conducted on serum leptin levels in different stages of renal disease, and the relationship among serum leptin, body composition, biochemical indexes, and markers of inflammation in persons with end-stage renal disease. Effects of intradialytic parenteral nutrition and anabolic factors on leptin levels and nutritional status are briefly reviewed.

Low-Molecular Weight Proteins in End-Stage Renal Disease: Potential Toxicity and Dialytic Removal Mechanisms

ABSTRACT. Low-molecular-weight proteins (LMWP) are now recognized as a distinct class of uremic toxins, and numerous compounds in this category have been identified. Dr. Henderson has spent much of his career investigating ways to enhance the removal of intermediate- and large-sized uremic retention molecules. As LMWP clearly fall under this category, it is fitting to provide a review of several aspects of this molecular class. Normal renal metabolism of LMWP is discussed along with the changes that occur during chronic renal insufficiency. The effect of end-stage renal disease on plasma LMWP concentrations is assessed. As examples of the potential uremic toxicity of this molecular class, leptin, adrenomedullin, and the compounds associated with increased susceptibility to infection are highlighted. Finally, an overview of LMWP removal mechanisms for both hemodialysis and the convective therapies is provided.

Renal clearance of endogenous leptin in hypertensive humans with or without renal artery stenosis

In humans, the kidney is involved in leptin clearance from the body. The present study was performed to assess the renal extraction of leptin in hypertensive patients with or without renal artery stenosis. Sixty-five hypertensive subjects (39 males and 26 females) underwent catheterization of the renal artery and both renal veins with blood sampling for measuring leptin levels. Blood flow to both kidneys was measured by the xenon washout technique. From these data, renal leptin uptake and renal fractional extraction of leptin were calculated. Endogenous creatinine clearance ranged from 24 to 191 ml/min in the males and from 20 to 149 ml/min in the females. In 25 patients, radiological signs of renal artery stenosis were present. Total renal leptin uptake by both kidneys averaged 141 +/- 47 ng x min(-1) x 100 g(-1). No differences in leptin uptake were found between males and females or between patients with or without renal artery stenosis. The average renal extraction fraction of leptin was 6 +/- 2%. Renal leptin uptake and renal extraction fraction of leptin did not correlate with arterial leptin concentrations or with blood pressure, endogenous creatinine clearance, or the presence or absence of renal artery stenosis. In hypertensive patients with or without renal artery stenosis, the kidney removes only a small fraction of circulating leptin from the body within one passage. This fraction remains relatively constant despite wide variations in renal function or circulating leptin.

NUTRITIONALMANAGEMENT OFMAINTENANCEDIALYSISPATIENTS: Why Aren't We Doing Better?

About 40% of patients undergoing maintenance dialysis suffer from varying degrees of protein-energy malnutrition. This is a problem of substantial importance because many measures of nutritional status correlate with the risk of morbidity and mortality. There are many causes of protein-energy malnutrition in maintenance dialysis patients. Evidence indicates that nutritional decline begins even when the reduction in glomerular filtration rate is modest, and it is likely that the observed decrease in dietary protein and energy intake plays an important role. The nutrient intake of patients receiving maintenance dialysis also is often inadequate, and several lines of evidence suggest that toxins that accumulate with renal failure suppress appetite and contribute to nutritional decline once patients are on maintenance dialysis. Recent epidemiologic studies have suggested that both increased serum levels of leptin and inflammation may reduce nutrient intake and contribute to the development of protein-energy malnutrition. It is likely that associated illnesses, which are highly prevalent, contribute to malnutrition in maintenance dialysis patients. Recent data from the United States Renal Data System registry suggest that in the United States, the mortality rate of dialysis patients is improving. However, it remains high. We offer suggestions for predialysis and dialysis care of these patients that can result in improvement in their nutritional status. Whether this improvement will result in a decrease in patient morbidity and mortality is unknown.

Increases in serum leptin levels during peritoneal dialysis are associated with inflammation and a decrease in lean body mass

Leptin, secreted from fat cells, functions as a lipostat mechanism through modulation of satiety signals. Markedly elevated leptin levels have been documented in uremic patients, especially in those who are treated by peritoneal dialysis (PD). However, the role of hyperleptinemia in uremic patients is not clear, and it is not known whether elevated leptin levels contribute to uremic anorexia and changes in body composition. In this prospective study, serum leptin, C-reactive protein (CRP), plasma insulin, and body composition (dual-energy x-ray absorptiometry) were measured in 36 patients (53 +/- 1 yr) close to start and after about 1 yr of PD. In addition, markers of dialysis adequacy and urea kinetics were followed during treatment with PD. During PD, the total body fat mass (20.5 +/- 1.0 to 22.9 +/- 1.3 kg; P < 0.01), truncal fat mass (11.5 +/- 0.7 to 13. 2 +/- 0.9 kg; P < 0.001), and serum leptin levels (20.1 +/- 3.8 to 35.6 +/- 6.8 ng/ml; P < 0.01) increased markedly, especially in patients with diabetes mellitus. Twenty-five PD patients that lost lean body mass during PD had significantly (P < 0.05) elevated initial CRP levels (14 +/- 2 mg/L) compared to 11 patients (<10 mg/L) who gained lean body mass during PD. A significant increase in serum leptin levels (20.9 +/- 4.2 to 42.7 +/- 4.0 ng/ml; P < 0.001) was observed in those patients who lost lean body mass, whereas no such change (18.4 +/- 8.4 to 19.2 +/- 6.4 ng/ml) was observed in the patients that gained lean body mass during PD treatment. The present longitudinal results demonstrate that serum leptin level and body fat content increase markedly during PD, especially in diabetic patients. Patients that lost lean body mass during PD had higher initial CRP levels and increased their serum leptin levels significantly during PD compared to those patients that gained lean body mass. Additional studies are therefore needed to elucidate the role of hyperleptinemia and inflammation in causing anorexia, protein-malnutrition, and changes in body composition during treatment with PD.