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

Efficacy and tolerability of sevelamer carbonate in hyperphosphatemic patients who have chronic kidney disease and are not on dialysis

BACKGROUND AND OBJECTIVES

Sevelamer carbonate is an improved, buffered form of sevelamer hydrochloride developed for the treatment of hyperphosphatemia in patients with chronic kidney disease. This study investigated the ability of sevelamer carbonate to control serum phosphorous in hyperphosphatemic patients who had chronic kidney disease and were not on dialysis.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This was an open-label, dosage-titration study. Patients with serum phosphorus > or =5.5 mg/dl were enrolled (n = 46). Sevelamer carbonate was administered for 8 wk. Patients were supplemented with native vitamin D (400 IU). The primary efficacy parameter was the change from baseline in serum phosphorous. Secondary measures included the percentage of serum phosphorus responders; changes in serum lipids, calcium-phosphorus product, and bicarbonate; and safety and tolerability.

RESULTS

Sevelamer carbonate treatment resulted in a statistically significant decrease in mean serum phosphorous levels from baseline to end of treatment. A total of 75% of patients with stage 4 and 70% of patients with stage 5 chronic kidney disease achieved the target serum phosphorous at the end of treatment. There were statistically significant decreases in serum calcium-phosphorus product and total and low-density lipoprotein cholesterol at the end of treatment and a statistically significant increase in mean serum bicarbonate levels (from 16.6 to 18.2 mEq/L). Sevelamer carbonate was well tolerated.

CONCLUSIONS

Sevelamer carbonate is an effective and well-tolerated therapy for the control of phosphorous levels in hyperphosphatemic patients who have chronic kidney disease and are not on dialysis.

Acidose metabólica na doença renal crônica: abordagem nutricional

A acidose metabólica é uma das complicações da doença renal crônica e está associada ao aumento do catabolismo protéico, à diminuição da síntese de proteínas e ao balanço nitrogenado negativo. A dieta tem forte influência sobre a geração de ácidos, podendo contribuir, portanto, para determinar a gravidade da acidose no paciente com doença renal crônica. Alguns pesquisadores têm observado que é possível estimar a excreção ácida renal, e que o cálculo dessa carga ácida a partir de alguns componentes da dieta, permitiria uma predição apropriada dos efeitos da dieta na acidose metabólica. Este artigo é uma comunicação sobre as bases fisiológicas, bem como as implicações clínicas da acidose em pacientes com doença renal crônica e a influência da dieta no balanço ácido-básico desses pacientes.

A proposed nomenclature and diagnostic criteria for protein-energy wasting in acute and chronic kidney disease

The recent research findings concerning syndromes of muscle wasting, malnutrition, and inflammation in individuals with chronic kidney disease (CKD) or acute kidney injury (AKI) have led to a need for new terminology. To address this need, the International Society of Renal Nutrition and Metabolism (ISRNM) convened an expert panel to review and develop standard terminologies and definitions related to wasting, cachexia, malnutrition, and inflammation in CKD and AKI. The ISRNM expert panel recommends the term 'protein-energy wasting' for loss of body protein mass and fuel reserves. 'Kidney disease wasting' refers to the occurrence of protein-energy wasting in CKD or AKI regardless of the cause. Cachexia is a severe form of protein-energy wasting that occurs infrequently in kidney disease. Protein-energy wasting is diagnosed if three characteristics are present (low serum levels of albumin, transthyretin, or cholesterol), reduced body mass (low or reduced body or fat mass or weight loss with reduced intake of protein and energy), and reduced muscle mass (muscle wasting or sarcopenia, reduced mid-arm muscle circumference). The kidney disease wasting is divided into two main categories of CKD- and AKI-associated protein-energy wasting. Measures of chronic inflammation or other developing tests can be useful clues for the existence of protein-energy wasting but do not define protein-energy wasting. Clinical staging and potential treatment strategies for protein-energy wasting are to be developed in the future.

Higher total ghrelin levels are associated with higher insulin-mediated glucose disposal in non-diabetic maintenance hemodialysis patients

BACKGROUND & AIMS

Insulin resistance is common in maintenance hemodialysis (MHD) and it can contribute to exceedingly high mortality in MHD patients. Ghrelin is a gastric hormone whose total plasma concentration is increased in MHD. Emerging data suggest a potential role of ghrelin to modulate intermediate metabolism but the metabolic impact of ghrelin in chronic kidney disease is unknown. The current study aimed at assessing the potential relationships between ghrelin and insulin sensitivity in MHD.

METHODS

Total (T-Ghr) and acylated (A-Ghr) ghrelin as well as insulin-mediated glucose disposal [(M): hyperinsulinemic-euglycemic clamp] were measured in non-diabetic non-obese ambulatory MHD patients (n=19, 16 Males). C-reactive protein (CRP) was also measured since systemic inflammation is associated with insulin resistance in non-renal patients and inflammation is negatively modulated by ghrelin in experimental models.

RESULTS

Compared to control subjects (C: n=9, 7 Males), MHD had similar body fat and resting energy expenditure but reduced M and increased CRP (P<0.05). MHD also had higher T-(P<0.05) but not A-Ghr. M was associated positively with T-Ghr and negatively with CRP in linear regression analysis in MHD. In stepwise multiple regression analysis only T-Ghr remained associated with M (P<0.05) in a model including A-Ghr and CRP.

CONCLUSIONS

Insulin sensitivity is associated negatively with systemic inflammation and positively with total plasma ghrelin in non-diabetic MHD patients. Based on available knowledge these results suggest a potential novel role of ghrelin in preserving insulin sensitivity in MHD.

Gene expression profiling in the remnant kidney model of wild type and kinin B1 and B2 receptor knockout mice

Angiotensin-converting enzyme inhibitors are the most efficient pharmacologic agents to delay the development of end-stage renal disease (ESRD). This is a multipharmacologic approach that inhibits angiotensin II formation while increasing kinin concentrations. Considerable attention has been focused on the role of decreased angiotensin II levels; however, the role of increased kinin levels is gaining in interest. Kinins affect cellular physiology by interacting with one of two receptors being the more inducible B1 and the more constitutive B2 receptors. This study utilizes the mouse remnant kidney of 20 weeks duration as a model of ESRD. Whole mouse genome microarrays were used to evaluate gene expression in the remnant kidneys of wild type, B1 and B2 receptor knockout animals. The microarray data indicate that gene families involved in vascular damage, inflammation, fibrosis, and proteinuria were upregulated, whereas gene families involved in cell growth, metabolism, lipid, and protein biosynthesis were downregulated in the remnant kidneys. Interestingly, the microarray analyses coupled to histological evaluations are suggestive of a possible protective role of kinins operating through the B2 receptor subtype in this model of renal disease. The results highlight the potential of microarray technology for unraveling complex mechanisms contributing to chronic renal failure.

Correction of chronic metabolic acidosis for chronic kidney disease patients

BACKGROUND

Metabolic acidosis is a feature of chronic kidney disease (CKD) due to the reduced capacity of the kidney to synthesise ammonia and excrete hydrogen ions. It has adverse consequences on protein and muscle metabolism, bone turnover and the development of renal osteodystrophy. Metabolic acidosis may be corrected by oral bicarbonate supplementation or in dialysis patients by increasing the bicarbonate concentration in dialysate fluid.

OBJECTIVES

To examine the benefits and harms of treating metabolic acidosis in patients with CKD, both prior to reaching end-stage renal disease (ESRD) or whilst on renal replacement therapy (RRT), with sodium bicarbonate or increasing the bicarbonate concentration of dialysate.

SEARCH STRATEGY

We searched CENTRAL (The Cochrane Library, issue 4 2005), Cochrane Renal Group's specialised register (October 2005), MEDLINE (1966 - October 2005) and EMBASE (1980 - October 2005).

SELECTION CRITERIA

Randomised controlled trials (RCTs), crossover RCTs and quasi-RCTs investigating the correction of chronic metabolic acidosis in adults or children with CKD.

DATA COLLECTION AND ANALYSIS

Outcomes were analysed using relative risk (RR) and weighted mean difference (MD) for continuous measures.

MAIN RESULTS

We identified three trials in adult dialysis patients (n = 117). There were insufficient data for most outcomes for meta-analysis. In all three trials acidosis improved in the intervention group though there was variation in achieved bicarbonate level. There was no evidence of effect on blood pressure or sodium levels. Some measures of nutritional status/protein metabolism (e.g. SGA, NP NA) were significantly improved by correction in the one trial that looked in these in detail. There was heterogeneity of the effect on serum albumin in two trials. Serum PTH fell significantly in the two trials that estimated this, there was no significant effect on calcium or phosphate though both fell after correction. Complex bone markers were assessed in one study, with some evidence for a reduction in bone turnover in those with initial high bone turnover and an increase in low turnover patients. The studies were underpowered to assess clinical outcomes, in the one study that did there was some evidence for a reduction in hospitalisation after correction.

AUTHORS' CONCLUSIONS

The evidence for the benefits and risks of correcting metabolic acidosis is very limited with no RCTs in pre-ESRD patients, none in children, and only three small trials in dialysis patients. These trials suggest there may be some beneficial effects on both protein and bone metabolism but the trials were underpowered to provide robust evidence.

The prevalence of insulin resistance in nondiabetic nonobese patients with chronic kidney disease

This study was undertaken to evaluate the prevalence of insulin resistance (IR) and associated factors in nondiabetic, nonobese patients with chronic kidney disease (CKD) who had not yet received dialysis therapy. A group of 89 consecutive patients (42 male, 47 female) who were hospitalized in the Nephrology Clinic at Dicle University, had recently been diagnosed with CKD, and had not yet been treated with dialysis were enrolled in the study, as was a control group of 30 healthy volunteers. Diabetic and obese patients were excluded. IR was determined by the homeostasis model assessment of IR (HOMA-IR) formula. Blood samples were taken after an overnight fasting period to establish serum glucose, insulin, C-peptide, albumin, lipid profile, hematocrit, bicarbonate, and intact parathormone (iPTH) levels. The mean age of patients was 48.7+/-19.7 y (men, 49.5+/-21.5 y; women, 48.1+/-18.0 y); other mean values were as follows: glucose, 98.4+/-20.6 mg/dL; insulin, 16.7+/-16.2 microU/mL; HOMA-IR, 5.46+/-1.14; hemoglobin (Hgb), 8.7+/-1.6 g/dL; calcium-phosphorus product (Ca x P), 52.2+/-16.2 mg2/dL2; iPTH, 377.7+/-258.1 pg/mL, and bicarbonate (HCO3), 16.6+/-5.3 mEq/L. HOMA-IR was significantly higher in patients with stage 4 CKD than in controls (P<.001); serum levels of urea, creatinine clearance (CrCl), C-reactive protein (CRP), albumin, total cholesterol, high-density lipoprotein cholesterol (HDL-C), Hgb, HCO3, Ca x P, and iPTH were found to be associated with HOMA-IR when a comparison was made with the control group. According to correlation analyses of possible risk factors in patients with IR, positive correlations with age, body mass index, CRP, Ca x P product, and iPTH, and negative correlations with albumin, CrCl, Hgb, and HDL-C were found. A high percentage of IR was found, and this percentage increased as glomerular filtration rate decreased in patients with stage 4 CKD. In addition, a correlation was found between IR and parameters such as age, body mass index, CRP, Ca x P, iPTH, albumin, CrCl, Hgb, and HDL-C.

Inflammation and adipose tissue in uremia

Enhanced chronic systemic inflammation and reduced insulin sensitivity are often associated in patients with chronic renal failure, contributing to cardiovascular morbidity and mortality in these patients. Adipose tissue produces several hormones (adipocytokines including leptin, resistin, tumor necrosis factor-alpha, and adiponectin) that modulate both systemic inflammatory response and insulin action. High leptin, resistin, and tumor necrosis factor-alpha and low adiponectin are associated with proinflammatory conditions, whereas opposite patterns are commonly observed in the presence of increased insulin sensitivity, low inflammation, and reduced cardiovascular risk. Oxidative stress has also been shown recently to modulate adipocytokine production, resulting in a proinflammatory profile. Increments of plasma concentrations of both proinflammatory and anti-inflammatory adipocytokines have been reported in chronic renal failure, possibly caused by both passive accumulation from reduced renal excretion and metabolic abnormalities induced by uremia. The potential role of altered adipose tissue adipocytokine production in the onset of renal failure-associated inflammatory and metabolic derangements remains largely to be elucidated and is discussed in the current report.

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.

Skeletal muscle dysfunction in chronic renal failure: effects of exercise

A number of chronic illnesses such as renal failure (CRF), obstructive pulmonary disease, and congestive heart failure result in a significant decrease in exercise tolerance. There is an increasing awareness that prescribed exercise, designed to restore some level of physical performance and quality of life, can be beneficial in these conditions. In CRF patients, muscle function can be affected by a number of direct and indirect mechanisms caused by renal disease as well as various treatment modalities. The aims of this review are twofold: first, to briefly discuss the mechanisms by which CRF negatively impacts skeletal muscle and, therefore, exercise capacity, and, second, to discuss the available data on the effects of programmed exercise on muscle function, exercise capacity, and various other parameters in CRF.

Kt/V and nPNA in pediatric peritoneal dialysis: a clinical or a mathematical association?

The relationship between dialysis dose and nutrition is a field of particular interest in chronic pediatric dialysis (PD), and a positive correlation between ureaKt/V and nPNA has been published, suggesting a better nutritional status is associated with higher dialysis doses. However, this relationship has also been criticized as being the result of a mathematical coupling resulting from the same variables. The objective of the study was to establish the relationship between dialysis dose (Kt/V) and nutritional variables: daily protein intake (DPI), protein catabolic rate (PCR), protein equivalent of total nitrogen appearance (PNA) and nitrogen balance (NB) in dialyzed children. A cohort, prospective, observational study was carried out, for which 223 biochemical measurements were performed in 20 patients, ages 1 month to 14.3 years old (13 males), under PD for a 12-month period of follow-up. Monthly residual and total ureaKt/V, DPI, PCR, nPNA and NB were calculated, and the correlation between Kt/V and the nutritional parameters was evaluated. The Borah equation was used to calculate the nPNA. The data are reported as the mean plus or minus the standard error. All statistical comparisons were done with a paired t test, and two-way ANOVA for repeated measures was used to calculate correlations. A P <0.05 was considered significant. Mean total and residual Kt/V was 3.4+/-1.3 and 1.69+/-1.27, respectively; nPNA and PCR were 1.38+/-0.44 and 1.39+/-0.43 g/kg/day, daily protein intake (DPI) was 3.25+/-1.27 g/kg/day, and NB showed a value of 1.86+/-1.25 g/kg/day. A significant positive correlation was found between Kt/V and DPI, PCR, DPC and nPNA (all values P <0.0001), but no correlation was found between total and residual Kt/V vs. nitrogen balance ( P:ns). Total Kt/V showed a significant positive correlation with nPNA, but it did not show any correlation with nitrogen balance, suggesting that the relationship with nPNA is the result of a mathematical association calculated from the same variables.

Investigations of branched-chain amino acids and their metabolites in animal models of cancer

Many of the features of BCAA metabolism in the tumor-bearing state are similar to the other disease states that feature involuntary weight loss and skeletal muscle atrophy. These states are generally characterized by altered BCAA availability (low BCAA intakes, elevated rates of BCAA oxidation, and gluconeogenesis), which are concurrent with activation of proteolysis and suppression of protein synthesis in skeletal muscle and ultimately lead to erosion of lean tissue mass. These features in turn imply BCAA deficiency compared with whole-body requirements and are the basis of suggestions for dietary supplementation with BCAA or their metabolites. Recent studies on BCAA supplementation in cancer focus on leucine and its derivative, beta-methyl beta-hydroxybutyrate, as regulators of skeletal muscle metabolism, although their relative efficacy is unknown. However, what would otherwise be a relatively straightforward consideration of amino acid supply and demand is confounded by the presence of the tumor and its potential utilization of BCAA for its proliferative and invasive activities. Positron emission tomography with (11)C-leucine, used for in vivo tumor imaging, points to the high avidity of tumor amino acid uptake. These features have incited research in opposing directions, probing BCAA deprivation, with a view to limiting tumor growth, as well as BCAA supplementation, with a view to supporting maintenance of host lean tissue. No clear conclusion is presently available from the sum of these efforts. Animal models with relevant clinical features are essential to determine if amino acid therapy can alter the balance between the host and the tumor in a manner that favors the host overall.

Metabolic acidosis in peritoneal dialysis patients: the role of residual renal function

BACKGROUND

Metabolic acidosis (MA) is common in chronic renal insufficiency (CRI) patients, and its pattern changes as renal function deteriorates. Although the prevalence of acidosis in peritoneal dialysis has been reported to be rather high, the causes of it have not been well studied. The present study was performed to examine the prevalence of metabolic acidosis in our continuous ambulatory peritoneal dialysis (CAPD) patients and its possible causes.

METHODS

In this cross-sectional study, we analyzed data from patients who received maintenance CAPD in our hospital and had been on dialysis for at least one month. Patients' demographic features, medications, and intercurrent medical conditions were recorded. Data including blood biochemistry, dialysis adequacy, and nutrition were collected. A serum bicarbonate concentration of less than 23 mmol/l was defined as having acidosis. The normal value of the serum anion gap (AG) was defined as 12+/- 4 mmol/l.

RESULTS

A total of 154 patients (76 males and 78 females) with age of 60.04+/- 13.92 years and the time on dialysis of 16.83+/- 21.59 months were included in this study. Sixty-six patients (43%) had a serum bicarbonate of less than 23 mmol/l, among whom 12 patients (8%) were identified as having MA with increased AG, 54 (35%) were identified as having MA with normal AG. Patients who had better residual renal function (RRF) had a significantly lower serum bicarbonate level despite their higher total KT/V(urea) as compared to those with lower RRF. In addition, patients with MA and normal AG had the highest RRF and highest total KT/V(urea). All patients with MA and increased AG had significantly lower values of dietary protein intake (DPI) as compared to their values of normalized protein nitrogen appearance (nPNA), and had higher serum urea and phosphate levels as compared with those patients without MA.

CONCLUSION

Our study suggested that CAPD patients with better RRF were more susceptible to metabolic acidosis, which was characterized by normal anion gap and hyperchloremia. Thus, we speculate that renal loss of bicarbonate may to a large extent be responsible for the occurrence of MA in these patients.

Reverse epidemiology: a spurious hypothesis or a hardcore reality?

In maintenance hemodialysis (MHD) patients, associations between demographic, clinical and laboratory values and mortality, including cardiovascular death, are significantly different and, in some cases, in the opposite direction of those derived from the general population. This phenomenon, termed 'reverse epidemiology', is not limited to MHD patients but is also observed in populations that encompass an estimated 20 million Americans including those with an advanced age, heart failure, malignancies, and AIDS. A significant portion of this reversal may be due to the overwhelming effect of the malnutrition-inflammation complex syndrome (MICS). Since two thirds of MHD patients die within 5 years of initiation of dialysis treatment, traditional cardiovascular risk factors such as obesity, hypercholesterolemia and hypertension cannot exert a long-term deleterious impact, and instead, their short-term beneficial effects on MICS provides a survival advantage. In order to improve survival and quality of life in MHD patients, extrapolated ideal norms derived from the general population should be substituted with novel norms obtained from outcome-oriented epidemiologic analyses while accounting for the differential effect of MICS in different case-mix subgroups.