Chronic Kidney Disease Interplay with Comorbidities and Carbohydrate Metabolism: A Review

Chronic kidney disease (CKD) poses a global health challenge, engendering various physiological and metabolic shifts that significantly impact health and escalate the susceptibility to severe illnesses. This comprehensive review delves into the intricate complexities of CKD, scrutinizing its influence on cellular growth homeostasis, hormonal equilibrium, wasting, malnutrition, and its interconnectedness with inflammation, oxidative stress, and cardiovascular diseases. Exploring the genetic, birth-related, and comorbidity factors associated with CKD, alongside considerations of metabolic disturbances, anemia, and malnutrition, the review elucidates how CKD orchestrates cellular growth control. A pivotal focus lies on the nexus between CKD and insulin resistance, where debates persist regarding its chronological relationship with impaired kidney function. The prevalence of insulin abnormalities in CKD is emphasized, contributing to glucose intolerance and raising questions about its role as a precursor or consequence. Moreover, the review sheds light on disruptions in the growth hormone and insulin-like growth factor axis in CKD, underscoring the heightened vulnerability to illness and mortality in cases of severe growth retardation. Wasting, a prevalent concern affecting up to 75% of end-stage renal disease (ESRD) patients, is analyzed, elucidating the manifestations of cachexia and its impact on appetite, energy expenditure, and protein reserves. Taste disturbances in CKD, affecting sour, umami, and salty tastes, are explored for their implications on food palatability and nutritional status. Independent of age and gender, these taste alterations have the potential to sway dietary choices, further complicating the management of CKD. The intricate interplay between CKD, inflammation, oxidative stress, and cardiovascular diseases is unraveled, emphasizing the profound repercussions on overall health. Additionally, the review extends its analysis to CKD's broader impact on cognitive function, emotional well-being, taste perception, and endothelial dysfunction. Concluding with an emphasis on dietary interventions as crucial components in CKD management, this comprehensive review navigates the multifaceted dimensions of CKD, providing a nuanced understanding essential for developing targeted therapeutic strategies.

The magnitude of undernutrition and associated factors among adult chronic kidney disease patients in selected hospitals of Addis Ababa, Ethiopia

BACKGROUND

Undernutrition is a common comorbidity in chronic kidney disease patients which augments the progression of the disease to an end-stage renal disease, renal dysfunction and related morbidity and mortality. However, in Ethiopia, there is a dearth of research evidence in this regard. Therefore, this study aimed to assess the magnitude of undernutrition and its associated factors among adult chronic kidney disease patients.

METHODS

An institution-based cross-sectional study was conducted in selected hospitals of Addis Ababa from May to August 2018. Data were collected by structured and pretested questionnaires. Patients' charts were reviewed from their medical profiles. Body mass index was calculated from anthropometric measurements using calibrated instruments. Serum albumin level was determined by reference laboratory standard procedure. Data were entered into Epi- data version 3.1 and exported to SPSS version 21 for analysis. Descriptive statistics were calculated and presented by tables, graphs and texts. Binary and multivariable logistic regression analyses were computed and the level of statistical significance was declared at p-value <0.05.

RESULTS

From the total sample size of 403 participants, 371 were involved in the study. The prevalence of undernutrition (BMI<18.5) among adult chronic kidney disease patients was 43.1% (95% CI: 38%-48%). Undernutrition (BMI<18.5) was significantly higher among patients with diabetic nephropathy [AOR = 2.00, 95% CI, 1.09-2.66], serum albumin value less than 3.8g/dl [AOR = 4.21: CI, 2.07-5.07], recently diagnosed with diabetes mellitus [AOR = 2.36, 95% CI, 1.03-3.14] and stage V chronic kidney disease [AOR = 3.25:95% CI, 1.00-3.87].

CONCLUSION

Undernutrition in chronic kidney disease patients was significantly higher among patients with diabetic nephropathy, patients on stage V chronic kidney disease, recently diagnosed with diabetes mellitus and serum albumin value less than 3.8g/dl.

Resting Energy Expenditure in Peritoneal Dialysis Patients

Objectives

This study aimed to evaluate whether resting energy expenditure (REE) of patients undergoing peritoneal dialysis (PD) therapy differs from that of healthy individuals, as well as to investigate the factors associated with REE in this sample of patients.

Design

Cross-sectional study.

Setting

Dialysis Unit of the Nephrology Division, Federal University of Sao Paulo–Oswaldo Ramos Foundation, Brazil.

Subjects and Methods

The study examined the REE of 37 patients (20 males, age 44.5 ± 13 years) undergoing PD therapy. Only patients older than 18 years, on PD for at least 3 months, without catabolic illness, and with normal thyroid function were included. Patients were pair matched for age and gender with 37 healthy individuals. REE was measured by indirect calorimetry. Body composition was assessed by dual-energy x-ray absorptiometry in the patients and by bioelectrical impedance in the healthy individuals.

Results

The REE of PD patients was similar to that of pair-matched controls (1372 ± 266 and 1453 ± 252 kcal/day respectively, p = 0.13) even when adjusted for lean body mass and gender ( p = 0.56). The REE of PD patients was positively correlated with lean body mass ( r = 0.60, p < 0.01), fat mass ( r = 0.43, p < 0.01), body mass index (r = 0.60, p < 0.01), serum glucose (r = 0.36, p < 0.05), and protein equivalent of nitrogen appearance (PNA; r = 0.42, p < 0.01). There were no correlations between REE and glucose absorption, dialysis-related parameters, C-reactive protein, and energy or protein intake by 3-day food diary. In the multiple linear regression analysis, using REE as the dependent variable, the final model showed that lean body mass and female gender were determinants of REE in PD patients ( R2 = 0.44). When separate analysis by gender was performed, REE correlated directly with body fat in female patients (r = 0.70, p < 0.01) but not in male patients ( r = 0.29, p = 0.21). On the other hand, lean body mass was significantly correlated with REE in male patients ( r = 0.78, p < 0.01) but not in female patients ( r = 0.47, p = 0.06).

Conclusions

This study showed that REE of PD patients did not differ from that of healthy individuals. The strong association between body fat and REE in female patients remains to be further investigated.

Effects of Combined Resistance Plus Aerobic Training on Body Composition, Muscle Strength, Aerobic Capacity, and Renal Function in Kidney Transplantation Subjects

Lima, PS, de Campos, AS, de Faria Neto, O, Ferreira, TCA, Amorim, CEN, Stone, WJ, Prestes, J, Garcia, AMC, and Urtado, CB. Effects of combined resistance plus aerobic training on body composition, muscle strength, aerobic capacity, and renal function in kidney transplantation subjects. J Strength Cond Res XX(X): 000-000, 2019-Immunosuppression and a sedentary lifestyle may exacerbate complications such as early graft dysfunction and muscle loss, and reduce patient survival after kidney transplantation (KT). Therefore, the purpose of this study was to evaluate changes in body composition (BC), muscular strength, aerobic, and renal function in KT subjects submitted to combined resistance plus aerobic training. Twelve KT subjects were randomly assigned into groups: (G1) 12 weeks of combined training (3 males and 4 females, 54 ± 3 years); or (G2) nonexercise control (5 females, 43 ± 18 years). The subjects were evaluated for BC (dual-energy X-ray absorptiometry), estimated V[Combining Dot Above]O2peak, right-hand maximal grip strength (RHMGS) and left-hand maximal grip strength (LHMGS), and renal function. Post-training revealed that G1 reduced body fat percentage (p = 0.046), uric acid (Δ = -0.87; p = 0.023), urea (Δ = -9.43; p = 0.032), and creatinine (Δ = -0.15; p = 0.045), increased fat-free mass, estimated V[Combining Dot Above]O2peak, RHMGS, LHMGS (p < 0.05), and estimated glomerular filtration rate (eGFR) (Δ = 11.64; p = 0.017). G2 increased urea (Δ = 8.20; p = 0.017), creatinine (Δ = 0.37; p = 0.028), and decreased eGFR (Δ = -16.10; p = 0.038). After 12 weeks, urea (Δ = 24.94; p = 0.013), uric acid (Δ = 1.64; p = 0.044), and creatinine (Δ = 0.9; p = 0.011) were lower, whereas eGFR (Δ = 36.51; p = 0.009) was higher in G1. These data indicate that combined training instigates positive changes in BC, muscular strength, aerobic capacity, and renal function after KT.

Muscle wasting in chronic kidney disease

Loss of lean body mass is a relevant component of the cachexia, or protein energy wasting (PEW), syndrome. Reduced muscle mass seems to be the most solid criterion for the presence of cachexia/PEW in patients with chronic kidney disease (CKD), and those with greater muscle mass loss have a higher risk of death. Children with CKD have many risk factors for lean mass and muscle wasting, including poor appetite, inflammation, growth hormone resistance, and metabolic acidosis. Mortality risks in patients with CKD increases as body mass index (BMI) and weight decreases. However, data regarding cachexia/PEW and muscle wasting in children with CKD is scarce due to lack of consensus in diagnostic criteria and an appropriate investigative methodology. Further research is urgently needed to address this important complication in the pediatric CKD setting, which may have fundamental impact on clinical outcomes.

Vegetarian Diet in Chronic Kidney Disease-A Friend or Foe

Healthy diet is highly important, especially in patients with chronic kidney disease (CKD). Proper nutrition provides the energy to perform everyday activities, prevents infection, builds muscle, and helps to prevent kidney disease from getting worse. However, what does a proper diet mean for a CKD patient? Nutrition requirements differ depending on the level of kidney function and the presence of co-morbid conditions, including hypertension, diabetes, and cardiovascular disease. The diet of CKD patients should help to slow the rate of progression of kidney failure, reduce uremic toxicity, decrease proteinuria, maintain good nutritional status, and lower the risk of kidney disease-related secondary complications (cardiovascular disease, bone disease, and hypertension). It has been suggested that plant proteins may exert beneficial effects on blood pressure, proteinuria, and glomerular filtration rate, as well as results in milder renal tissue damage when compared to animal proteins. The National Kidney Foundation recommends vegetarianism, or part-time vegetarian diet as being beneficial to CKD patients. Their recommendations are supported by the results of studies demonstrating that a plant-based diet may hamper the development or progression of some complications of chronic kidney disease, such as heart disease, protein loss in urine, and the progression of kidney damage. However, there are sparse reports suggesting that a vegan diet is not appropriate for CKD patients and those undergoing dialysis due to the difficulty in consuming enough protein and in maintaining proper potassium and phosphorus levels. Therefore, this review will focus on the problem as to whether vegetarian diet and its modifications are suitable for chronic kidney disease patients.

Protein and Energy Depletion in Chronic Hemodialysis Patients: Clinical Applicability of Diagnostic Tools

Protein and energy depletion states are common and associated with increased morbidity and mortality in chronic hemodialysis (CHD) patients. Therefore, proper use of diagnostic tools to assess depleted states in CHD patients is critical. Assessment of protein and energy status can be done by an array of methodologies that include simple estimates of the visceral and somatic pools of protein to more refined techniques to measure protein and energy balance. The nutritional and metabolic derangements in the CHD population are highly complex and can be confounded by multiple comorbidities and fluid shifts between body compartments. Therefore, assessment of protein and energy status in CHD patients requires a wide range of methodologies that not only identify depleted states but also monitor nutrition therapy and predict clinical outcome. Most important, these methods require cautious and individualized interpretation in order to minimize the interference of comorbid conditions frequently observed in the CHD population. Currently, there is not a single method that can be considered the gold standard for assessment of protein and energy status in CHD patients. Therefore, a combination of methods is recommended. In this review, we describe available methods to assess protein and energy status, with special considerations pertaining to CHD patients.

[Fitness and quality of life in kidney transplant recipients: case-control study]

BACKGROUND AND OBJECTIVES

We analyzed the levels of fitness, muscle structure and quality of life of adults after kidney transplant and healthy adults.

PATIENTS AND METHODS

A total of 16 kidney transplant patients and 21 healthy controls performed several fitness test, isokinetic evaluation of knee flexion and extension and ultrasonography muscle thickness assessment. They also completed the quality of life questionnaire SF-36.

RESULTS

Physical fitness, muscle structure and quality of life of the kidney transplant recipients were significantly poorer than the controls. The transplant patients performed less well in the "get up and go" and "sit to stand" test (p<.001) as well as in assessments of muscle structure, strength and power. The patients had a poorer score in their quality of life assessments, differing from the controls in domains of physical function, physical role, general health and social function (p<.001).

DISCUSSION

Fitness, strength and muscle mass are diminished in kidney transplant patients, resulting in a poorer quality of life which might entail an increased risk to their health.

Phosphate overload directly induces systemic inflammation and malnutrition as well as vascular calcification in uremia

Hyperphosphatemia contributes to increased cardiovascular mortality through vascular calcification (VC) in patients with chronic kidney disease (CKD). Malnutrition and inflammation are also closely linked to an increased risk of cardiovascular death in CKD. However, the effects of Pi overload on inflammation and malnutrition remain to be elucidated. The aim of the present study was to investigate the effects of dietary Pi loading on the interactions among inflammation, malnutrition, and VC in CKD. We used control rats fed normal diets and adenine-induced CKD rats fed diets with different Pi concentrations ranging from 0.3% to 1.2% for 8 wk. CKD rats showed dietary Pi concentration-dependent increases in serum and tissue levels of TNF-α and urinary and tissue levels of oxidative stress markers and developed malnutrition (decrease in body weight, serum albumin, and urinary creatinine excretion), VC, and premature death without affecting kidney function. Treatment with 6% lanthanum carbonate blunted almost all changes induced by Pi overload. Regression analysis showed that serum Pi levels closely correlated with the extent of inflammation, malnutrition, and VC. Also, in cultured human vascular smooth muscle cells, high-Pi medium directly increased the expression of TNF-α in advance of the increase in osteochondrogenic markers. Our data suggest that dietary Pi overload induces systemic inflammation and malnutrition, accompanied by VC and premature death in CKD, and that inhibition of Pi loading through dietary or pharmacological interventions or anti-inflammatory therapy may be a promising treatment for the prevention of malnutrition-inflammation-atherosclerosis syndrome.

A low serum bicarbonate concentration as a risk factor for mortality in peritoneal dialysis patients

BACKGROUND AND AIM

Metabolic acidosis is common in patients with chronic kidney disease and is associated with increased mortality in hemodialysis patients. However, this relationship has not yet been determined in peritoneal dialysis (PD) patients.

METHODS

This prospective observational study included a total of 441 incident patients who started PD between January 2000 and December 2005. Using time-averaged serum bicarbonate (TA-Bic) levels, we aimed to investigate whether a low serum bicarbonate concentration can predict mortality in these patients.

RESULTS

Among the baseline parameters, serum bicarbonate level was positively associated with hemoglobin level and residual glomerular filtration rate (GFR), while it was negatively associated with albumin, C-reactive protein (CRP) levels, peritoneal Kt/V urea, and normalized protein catabolic rate (nPCR) in a multivariable linear regression analysis. During a median follow-up of 34.8 months, 149 deaths were recorded. After adjustment for age, diabetes, coronary artery disease, serum albumin, ferritin, CRP, residual GFR, peritoneal Kt/V urea, nPCR, and percentage of lean body mass, TA-Bic level was associated with a significantly decreased risk of mortality (HR per 1 mEq/L increase, 0.83; 95% CI, 0.76-0.91; p < 0.001). In addition, compared to patients with a TA-Bic level of 24-26 mEq/L, those with a TA-Bic level < 22 and between 22-24 mEq/L conferred a 13.10- and 2.13-fold increased risk of death, respectively.

CONCLUSIONS

This study showed that a low serum bicarbonate concentration is an independent risk factor for mortality in PD patients. This relationship between low bicarbonate levels and adverse outcome could be related to enhanced inflammation and a more rapid loss of RRF associated with metabolic acidosis. Large randomized clinical trials to correct acidosis are warranted to confirm our findings.

Vegetarianism: advantages and drawbacks in patients with chronic kidney diseases

Vegetarian diet is a very old practice that is liable to confer some health benefits. Recent studies have demonstrated that modification of the dietary pattern with a reduction of animal protein intake and increased consumption of plant-based foods could influence cardiovascular risk profile and mortality rate. Moreover, phosphate bioavailability from plant proteins is reduced. These statements could lead to some benefits for chronic kidney disease (CKD) patients. This review summarizes the characteristics and benefits of vegetarian diets in the general population and the potential beneficial effects of such a diet on phosphate balance, insulin sensitivity, and the control of metabolic acidosis in CKD patients. Potential drawbacks exist when a vegetarian diet is associated with protein intake that is too restrictive and/or insufficient energy intake, justifying an early and regular nutritional follow-up jointly assumed by a nephrologist and a renal dietitian.

Red meat snacks for chronic hemodialysis patients: effect on inflammatory activity (a pilot study)

RATIONAL

Among the alternatives to reverse chronic hemodialysis protein-energy malnutrition is the enhancement of intradialytic oral nutritional therapy. Although foods of animal origin are a source of nutrients and represent a feasible diet, there is uncertainty about their health consequences.

OBJECTIVES

We assessed the relationship of intradialytic high-protein red meat snack supplementation with patient inflammatory status and protein losses (nitrogen) during this supplementation. Fourteen patients submitted to low-flux chronic hemodialysis for one month were divided into two groups receiving 2 g (group 1) and 29 g (group 2) of oral intradialytic protein during the initial phase, respectively. In the subsequent phase, group 1 was supplemented with 27 g protein (a red meat snack) for a total of 29 g per dialysis. Group 2 continued to receive 29 g protein. Nutritional status, total nitrogen losses through the dialysate and acute inflammatory phase protein (CRP) were assessed before and after dialysis. Reuse of the dialyzer was also determined on each occasion.

MAIN FINDINGS

Red meat supplementation did not interfere with CRP, nitrogen loss through the dialysate (18 ± 7 to 19 ± 4 g in group 1, ns, and 20 ± 7 to 21 ± 4 g in group 2, ns) or with nutritional status. However, the data showed a positive correlation between pre- and post-hemodialysis CRP values (r = 0.84, p < 0.01) in both groups, suggesting an increase of the values after ultrafiltration. Reuse of the dialyzer was not correlated with CRP values.

PRINCIPLE CONCLUSIONS

The results suggest that snacks were not acutely correlated with increased inflammatory levels and indicated that a protein-rich red meat snack may be beneficial for chronic hemodialysis patients.

Cachexia and protein-energy wasting in children with chronic kidney disease

Children with chronic kidney disease (CKD) are at risk for "cachexia" or "protein-energy wasting" (PEW). These terms describe a pathophysiologic process resulting in the loss of muscle, with or without loss of fat, and involving maladaptive responses, including anorexia and elevated metabolic rate. PEW has been defined specifically in relation to CKD. We review the diagnostic criteria for cachexia and PEW in CKD and consider the limitations and applicability of these criteria to children with CKD. In addition, we present an overview of the manifestations and mechanisms of cachexia and PEW. A host of pathogenetic factors are considered, including systemic inflammation, endocrine perturbations, and abnormal neuropeptide signaling, as well as poor nutritional intake. Mortality risk, which is 100- to 200-fold higher in patients with end-stage renal disease than in the general population, is strongly correlated with the components of cachexia/PEW. Further research into the causes and consequences of wasting and growth retardation is needed in order to improve the survival and quality of life for children with CKD.

Wasting in chronic kidney disease

Wasting/cachexia is prevalent among patients with chronic kidney disease (CKD). It is to be distinguished from malnutrition, which is defined as the consequence of insufficient food intake or an improper diet. Malnutrition is characterized by hunger, which is an adaptive response, whereas anorexia is prevalent in patients with wasting/cachexia. Energy expenditure decreases as a protective mechanism in malnutrition whereas it remains inappropriately high in cachexia/wasting. In malnutrition, fat mass is preferentially lost and lean body mass and muscle mass is preserved. In cachexia/wasting, muscle is wasted and fat is relatively underutilized. Restoring adequate food intake or altering the composition of the diet reverses malnutrition. Nutrition supplementation does not totally reverse cachexia/wasting. The diagnostic criteria of cachexia/protein-energy wasting in CKD are considered. The association of wasting surrogates, such as serum albumin and prealbumin, with mortality is strong making them robust outcome predictors. At the patient level, longevity has consistently been observed in patients with CKD who have more muscle and/or fat, who report better appetite and who eat more. Although inadequate nutritional intake may contribute to wasting or cachexia, recent evidence indicates that other factors, including systemic inflammation, perturbations of appetite-controlling hormones from reduced renal clearance, aberrant neuropeptide signaling, insulin and insulin-like growth factor resistance, and metabolic acidosis, may be important in the pathogenesis of CKD-associated wasting. A number of novel therapeutic approaches, such as ghrelin agonists and melanocortin receptor antagonists are currently at the experimental level and await confirmation by randomized controlled clinical trials in patients with CKD-associated cachexia/wasting syndrome.

Nutrition assessment and management in children on peritoneal dialysis

Protein-calorie malnutrition, otherwise known as cachexia, is a common problem in children undergoing chronic peritoneal dialysis (PD) and is a frequent source of significant morbidity and mortality. Recent evidence suggests that the main factors involved in the pathogenesis are metabolic acidosis, a decreased response to anabolic hormones, and chronic inflammation, associated with hormonal imbalances and an increased metabolic rate. Given the complexity and multifactorial nature of cachexia, the assessment of nutritional status in children on PD requires a complete history and physical examination; assessment of dietary intake, biochemical indices, and anthropometry; and possibly bioimpedance analysis and combined score systems. Its management should likewise be multidisciplinary and include ensuring an adequate energy and protein intake; optimal metabolic control, with the correction of acidosis, anaemia, and hyperparathyroidism; an optimal (or at least adequate) dialysis dose; and, if necessary, prescription of specific drugs such as recombinant human growth hormone.

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.

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.

Feeding flaxseed oil but not secoisolariciresinol diglucoside results in higher bone mass in healthy rats and rats with kidney disease

Flaxseed's oil and lignan, secoisolariciresinol diglucoside (SDG), are implicated in attainment of health and treatment of renal injury and osteoporosis. To test for these benefits, weanling Han:SPRD-cy rats (n=171) with or without kidney disease were randomized to diets made with either corn oil or flaxseed oil and with or without SDG for 12 weeks. In females, weight was lower with the SDG diet. In males fed flaxseed oil, lean mass was higher and fat % was lower. In both sexes, fat % was lower in diseased rats. Bone mineral content (BMC) and density were higher in rats fed flaxseed oil and lower in diseased rats, additionally; BMC was lower in SDG-supplemented females. The benefit of flaxseed oil on body composition is sex specific but the effect on bone mass is not. Lastly, reduced weight due to early rat kidney disease is not due to loss of lean body mass.

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.

Nutrition and Metabolism in Kidney Disease

Nutritional and metabolic derangements are highly prevalent in patients with chronic kidney disease (CKD) and patients on renal replacement therapy. These derangements, which can be termed uremic malnutrition, significantly affect the high morbidity and mortality rates observed in this patient population. Uremic malnutrition clearly is related to multiple factors encountered during the predialysis stage and during chronic dialysis therapy. Several preliminary studies suggested that interventions to improve the nutritional status and metabolic status of uremic patients actually may improve the expected outcome in these patients, although their long-term efficacy is not well established. It therefore is important to emphasize that uremic malnutrition is a major comorbid condition in CKD and renal replacement therapy patients, and that all efforts should be made to try to understand better and treat these conditions effectively to improve not only mortality but also the quality of life of chronically uremic patients. In this article we review the current state of knowledge in the field of nutrition and metabolism in all stages of CKD and renal replacement therapy, including kidney transplant. We also address questions that face investigators in this field and suggest where future research might be headed.

Inflammation is associated with increased energy expenditure in patients with chronic kidney disease

BACKGROUND

Inflammation, a clinical condition observed in patients with chronic kidney disease (CKD), may be related to increased resting energy expenditure (REE).

OBJECTIVES

The main objective was to investigate the relation between inflammation and REE in patients with CKD who are not undergoing dialysis. We also aimed to analyze whether a decrease in C-reactive protein (CRP) would result in a reduction in REE.

DESIGN

This study enrolled 132 patients with CKD who were not undergoing dialysis, who had creatinine clearance from 5 to 65 mL.min(-1).1.73 m(-2), and who were 53.6 +/- 16 y old; 82 (62.1%) were men. Twenty-nine patients had clinical signs of infection. REE was measured by using indirect calorimetry, and inflammation was evaluated by using high-sensitivity CRP measurement. Patients were divided according to tertiles of CRP with the following intertertile ranges: first tertile, CRP < or = 0.14 mg/dL (n = 43); second tertile, CRP 0.15-0.59 mg/dL (n = 46); and third tertile, CRP > or = 0.60 mg/dL (n = 43). REE was measured before and after treatment in 10 patients who had inflammation or infection.

RESULTS

After adjustment for age, sex, and lean body mass, the REE of the third (1395 kcal/d; P = 0.02) and second (1355 kcal/d; P = 0.04) tertiles was significantly higher than that of the first tertile (1286 kcal/d). In the multiple linear regression analysis (n = 132), the independent determinants of REE were lean body mass, CRP, and age (R2 = 0.55). After treatment of infection in a subgroup of 10 patients, it was observed that a significant reduction in CRP concentration was accompanied by a significant reduction of 174 +/- 165 kcal that accounted for 13% of the initial REE.

CONCLUSION

This study showed that inflammation is associated with increased REE in patients with CKD.

Similarities in skeletal muscle strength and exercise capacity between renal transplant and hemodialysis patients

Exercise intolerance is common in hemodialysis (HD) and renal transplant (RTx) patients. Aim of the study was to assess to what extent exercise capacity and skeletal muscle strength of RTx patients differ from HD patients and healthy controls and to elucidate potential determinants of exercise capacity in RTx patients. Exercise capacity, muscle strength, lean body mass (LBM) and physical activity level (PAL) were measured by cycle-ergometry, isokinetic dynamometry, DEXA and Baecke Questionnaire, respectively, in 35 RTx, 16 HD and 21 controls. VO2peak and muscle strength of the RTx patients were significantly lower compared to controls (p<0.01), but not different compared to HD patients. In RTx patients, strength (p<0.001), PAL (p=0.001) and age (p=0.045) were significant predictors of VO2peak. Muscle strength was related to LBM (p=0.001) and age (p=0.001), whereas gender (p<0.001) and renal function (p=0.01) turned out to be significant predictors of LBM. No effects of corticosteroids were observed. Exercise capacity and muscle strength seem equally reduced in RTx and HD patients compared to controls. In RTx patients, muscle strength and PAL are highly related to exercise capacity. Renal function appears to be a significant predictor of LBM, and through the LBM, of muscle strength and exercise capacity.

Cellular proteolysis and systemic inflammation during exacerbation in cystic fibrosis

BACKGROUND

Weight loss indicates a poor prognosis in cystic fibrosis (CF). We hypothesised that fat-free mass (FFM) depletion and increased systemic inflammation would be associated with increased cellular proteolysis during an exacerbation of the respiratory symptoms. Patients were studied prospectively from the beginning of treatment with antibiotics when admitted to the Adults CF Centre.

METHODS

Twenty six patients with CF were studied at the start and end of antibiotic treatment and 2 weeks later. Mean (95% CI) FEV1 when clinically stable was 54.1 (44.5, 62.6)% predicted. Urinary excretion of Pseudouridine (5-ribosyluracil, PSU) was determined as an indicator of cellular protein breakdown. Body composition was assessed by dual energy X-ray absorptiometry (DXA).

RESULTS

Patients had increased concentrations of PSU at all assessments (p<0.01). Those with a low FFM had greater PSU (ratio to FFMI) than those with a normal FFM at all assessments. At the start of treatment, PSU was related to FFM, C-reactive protein (CRP) (p<0.05) and tumour necrosis factor (TNF)alpha soluble receptors (sr) I and II (p<0.01). Circulating inflammatory mediators were greater in patients than in healthy subjects at all assessments.

CONCLUSION

Increased protein breakdown is associated with a low FFM and increased systemic inflammation and it may be a contributory mechanism of poor weight preservation in CF.

Impairment of small intestinal protein assimilation in patients with end-stage renal disease: extending the malnutrition-inflammation-atherosclerosis concept

BACKGROUND

Protein malnutrition is a common finding in renal disease. Recently, we showed that impaired protein assimilation (digestion and absorption) may contribute to protein malnutrition in nondiabetic patients with chronic renal failure.

OBJECTIVE

The aim of the present study was to evaluate whether these findings can be extended to the dialysis population. Moreover, relations with indexes of the malnutrition-inflammation-atherosclerosis (MIA) syndrome were investigated.

DESIGN

Protein assimilation was evaluated in 24 healthy control subjects and in 40 patients with end-stage renal disease (ESRD; 14 treated with peritoneal dialysis and 26 with hemodialysis) by means of a [13C]protein breath test, quantification of the generation rate of p-cresol, or both methods. Both approaches provide reliable information on the efficiency of protein assimilation. Breath test results were expressed as the maximum percentage recovery per hour of the administered dose of 13C (%max) and as the cumulative percentage recovery at the end of the test (%cum end). Several indexes of nutritional status, inflammation, and atherosclerosis were assessed.

RESULTS

Compared with the control subjects, ESRD patients had significantly lower breath-test derived indexes of protein assimilation [%max=3.75 +/- 0.30 compared with 4.90 +/- 0.25, P=0.006; %cum end=12.41 (5.74-23.22) compared with 16.87 (9.42-22.99), P=0.020] and a higher 24-h p-cresol generation rate corrected for dietary protein intake [3.89 (0.48-11.60) compared with 2.81 (0.21-11.20) mg p-cresol/g urea nitrogen; P=0.028]. The presence of impaired protein assimilation was associated with indexes of the MIA syndrome.

CONCLUSION

Our study provides evidence that protein assimilation is impaired in ESRD patients. Moreover, this disorder is associated with the severity of the MIA syndrome.

Metabolic Acidosis and Malnutrition in Dialysis Patients

Acidosis is a classic uremic toxin that causes protein catabolism, mainly by selective breakdown of skeletal muscle protein. However, the importance of acidosis is often overlooked in dialysis patients. In the presence of acidosis, there is activation of the ubiquitin-proteasome machinery as well as the branched-chain keto acid dehydrogenase, resulting in catabolism of muscle protein. Acidosis acts synergistically with other catabolic factors, such as inflammatory cytokines and insulin resistance, in inducing protein catabolism. There is ample laboratory evidence showing that correction of acidosis prevents the up-regulation of the ubiquitin-proteasome machinery and reduces protein degradation. Randomized control trials further show that acidosis in dialysis patients can be treated successfully by a higher dialysate bicarbonate or lactate concentration, or by oral bicarbonate supplement. Correction of mild acidosis in dialysis patients is effective in improving nutritional status and reducing the duration of hospitalization.

Cellular mechanisms causing loss of muscle mass in kidney disease

In stable adults or patients with kidney disease, the daily turnover of cellular proteins is very large, amounting to the quantity of protein in 1 to 1.5 kg of muscle. Consequently, even a small but persistent increase in protein degradation or decrease in protein synthesis leads to a substantial loss of muscle mass. In chronic kidney disease, the pathway that degrades muscle protein is the ubiquitin-proteasome system. We tested whether either of two complications of chronic kidney disease, metabolic acidosis or insulin resistance accelerates the loss of muscle protein. Metabolic acidosis activates the ubiquitin-proteasome system and this can explain an large number of clinical conditions in which metabolic acidosis also causes loss of muscle protein. Insulin deficiency as a model of insulin resistance also activates the ubiquitin-proteasome system. Both complications also activate caspase-3 and we found that this protease performs a critical initial step in breaking down the complex structure of muscle to provide actin, myosin and fragments of these proteins as substrates for the ubiquitin-proteasome system. Defects in insulin signalling processes can activate both caspase-3 and the ubiquitin-proteasome system to degrade muscle protein. Understanding mechanisms that activate protein breakdown will lead to therapies that successfully prevent the loss of muscle mass in patients with kidney disease.

Impairment of phenylalanine conversion to tyrosine inend-stage renal disease causing tyrosine deficiency

BACKGROUND

Tyrosine is not considered an indispensable amino acid because in humans phenylalanine is converted to tyrosine. Recent human studies demonstrated that tyrosine production from phenylalanine occurs not only in liver but also in kidney.

METHODS

Here we report results from studies, performed in end-stage renal disease (ESRD) patients and in healthy controls using [15N] phenylalanine and [2H4] tyrosine as tracers demonstrating the mechanism of tyrosine deficiency in patients with renal failure.

RESULTS

Phenylalanine flux (an index of protein breakdown) was identical in both groups either before or during an infusion of amino acid mixture. In contrast, tyrosine flux (representing protein breakdown and tyrosine appearance from phenylalanine) and conversion of phenylalanine to tyrosine were lower in ESRD patients [2.05 +/- 0.30 micromol/kg fat-free mass (FFM)/hour and 2.59 +/- 0.52 micromol/kg FFM/hour, before and during amino acid infusion, respectively] than in the control subjects (4.07 +/- 0.54 micromol/kg FFM/hour and 5.53 +/- 0.86 micromol/kg FFM/hour, P <0.02, ESRD vs. controls, respectively). Plasma tyrosine concentrations in ESRD patients remained 40% lower than the controls during the postabsorptive state and following amino acid replacement.

CONCLUSION

We conclude that reduced conversion of phenylalanine to tyrosine causes tyrosine deficiency in patients with ESRD prompting to propose that tyrosine replacement is potentially required in patients with ESRD.

Association of body size with outcomes among patients beginning dialysis

BACKGROUND

Although obesity confers an increased risk of mortality in the general population, observational reports on the dialysis population have suggested that obesity is associated with improved survival. These reports have generally not examined extremely high values of body mass index (BMI; in kg/m(2)), survival >1 y, or alternative measures of adiposity.

OBJECTIVE

We sought to clarify the relation between body size and outcomes among a large cohort of patients beginning dialysis.

DESIGN

Data on 418 055 patients beginning dialysis between 1 April 1995 and 1 November 2000 were analyzed by using US Renal Data System data. BMI was divided into 8 categories in increments of 3 units, ranging from < 19 to > or =37, and the relation between survival and BMI was examined by using proportional hazards regression with adjustment for demographic, laboratory, and comorbidity data.

RESULTS

High BMI was associated with increased survival in this cohort, even at extremely high BMI, after adjustment, and over a 2-y average follow-up time. This was true for whites, African Americans, and Hispanics but not for Asians. High BMI was also associated with a reduced risk of hospitalization and a lower rate of mortality in all mortality categories. Alternative estimates of adiposity, including the Benn index and estimated fat mass, yielded similar results, and adjustments for lean body mass did not substantially alter the findings.

CONCLUSIONS

High BMI is not associated with increased mortality among patients beginning dialysis. This finding does not appear to be a function of lean body mass and, although modified by certain patient characteristics, it is a robust finding.

Assessment and monitoring of uremic malnutrition

Assessment and monitoring of protein and energy nutritional status are essential to prevent, diagnose, and treat uremic malnutrition, a condition highly prevalent and associated with increased morbidity and mortality in patients with advanced kidney failure. Comprehensive assessments of protein and energy nutritional status can be achieved by several measurements to quantitatively and qualitatively estimate protein content in visceral and somatic body compartments, in addition to measurements of energy balance. However, uremic malnutrition is a complex metabolic disorder in which not only net nutrient intake is lower than nutrient requirements, leading to decreased tissue function and loss of body mass, but it is also associated with many comorbid conditions. Therefore, a clinically meaningful assessment of uremic malnutrition should include methods that are able to assess clinical outcome, identify the underlying diseases, and determine whether there is potential of benefit from nutritional interventions. Such assessment usually requires using multiple measurements concomitantly, with no definitive single method that can be considered as a "gold standard." In this review, we describe the various types of methods to assess uremic malnutrition, expanding and updating data on the readily available methods, and discuss more precise techniques to estimate protein and energy homeostasis. Special considerations of specific methods related to their clinical and/or research applicability as they pertain to renal failure are also addressed.

Bone buffering of acid and base in humans

The sources and rates of metabolic acid production in relation to renal net acid excretion and thus acid balance in humans have remained controversial. The techniques and possible errors in these measurements are reviewed, as is the relationship of charge balance to acid balance. The results demonstrate that when acid production is experimentally increased among healthy subjects, renal net acid excretion does not increase as much as acid production so that acid balances become positive. These positive imbalances are accompanied by equivalently negative charge balances that are the result of bone buffering of retained H+ and loss of bone Ca2+ into the urine. The data also demonstrate that when acid production is experimentally reduced during the administration of KHCO3, renal net acid excretion does not decrease as much as the decrease in acid production so that acid balances become negative, or, in opposite terms, there are equivalently positive HCO3- balances. Equivalently positive K+ and Ca2+ balances, and thus positive charge balances, accompany these negative acid imbalances. Similarly, positive Na+ balances, and thus positive charge balances, accompany these negative acid balances during the administration of NaHCO3. These charge balances are likely the result of the adsorption of HCO3- onto the crystal surfaces of bone mineral. There do not appear to be significant errors in the measurements.

Evidence for impaired assimilation of protein in chronic renal failure

BACKGROUND

Protein malnutrition is a common finding in chronic renal failure (CRF) and is associated with poor outcome. We hypothesized that besides inadequate dietary protein intake and alterations in metabolism, deficient protein assimilation (digestion and absorption) might contribute to the pathogenesis of protein malnutrition in uremia.

METHODS

Protein assimilation was evaluated in 64 healthy volunteers and 119 CRF patients by means of a 13C protein breath test and/or quantification of p-cresol in a 24-hour urine collection. Both approaches provide reliable information on the efficiency of protein assimilation. Breath test results were expressed as maximum percentage of administered dose of 13C (%max) and cumulative percentage at the end of the test (%cum(end)). Data were stratified according to renal function.

RESULTS

As compared to subjects with glomerular filtration rate (GFR) > or = 60 mL/min/1.73 m2, subjects with GFR < 30 mL/min/1.73 m2 demonstrated significantly lower breath test-derived parameters of protein assimilation (%max 3.97 +/- 0.23 vs. 5.20 +/- 0.23, P=0.0017; %cum(end) 13.91 +/- 0.86 vs. 17.40 +/- 0.80, P= 0.013) and significantly higher urinary output of p-cresol (54.88 mg/24 hours vs. 28.65 mg/24 hours, P= 0.0005). %max (r=0.399, P < 0.0001), %cum(end) (r=0.347, P=0.0007), and urinary p-cresol (r=-0.229, P=0.007) correlated significantly with GFR. Serum albumin correlated significantly with %max (r=0.399, P=0.0002), %cum(end) (r=0.408, P=0.0001), and urinary p-cresol output (r=-0.186, P=0.035).

CONCLUSION

Our data provide evidence that protein assimilation is impaired in CRF. This impairment might contribute to protein malnutrition in CRF.

Increased albumin and fibrinogen synthesis rate in patients with chronic renal failure

BACKGROUND

Hypoalbuminemia and hyperfibrinogenemia are frequently observed in patients with chronic renal failure (CRF) and are both associated with cardiovascular diseases. The mechanisms responsible for hypoalbuminemia and hyperfibrinogenemia in CRF are unknown.

METHODS

In the present study, both albumin and fibrinogen kinetics were measured in vivo in predialysis patients (N = 6), patients on peritoneal dialysis (N = 7) and control subjects (N = 8) using l-[1-13C]-valine.

RESULTS

Plasma albumin concentration was significantly lower in patients on peritoneal dialysis compared to control subjects (P < 0.05). Plasma fibrinogen was significantly increased in both predialysis patients (P < 0.01) as well as patients on peritoneal dialysis (P < 0.001) in comparison to control subjects. In contrast to albumin, fibrinogen is only lost in peritoneal dialysate and not in urine. The absolute synthesis rates (ASR) of albumin and fibrinogen were increased in patients on peritoneal dialysis (ASR albumin, 125 +/- 9 mg/kg/day versus 93 +/- 9 mg/kg/day, P < 0.05; ASR fibrinogen, 45 +/- 4 mg/kg/day versus 29 +/- 3 mg/kg/day, P < 0.01) compared to control subjects. Albumin synthesis is strongly correlated with fibrinogen synthesis (r2 = 0.665, P < 0.0001, N = 21). In this study, the observed hypoalbuminemia in patients on peritoneal dialysis is likely not explained by malnutrition, inadequate dialysis, inflammation, metabolic acidosis, or insulin resistance. We speculate that peritoneal albumin loss is of relevance.

CONCLUSION

Synthesis rate of albumin and fibrinogen are coordinately up-regulated. Both albumin and fibrinogen are lost in peritoneal dialysis fluid. To compensate protein loss, albumin synthesis is up-regulated, but the response, in contrast to predialysis patients, does not fully correct plasma albumin concentrations in peritoneal dialysis patients. The increase in fibrinogen synthesis introduces an independent risk factor for atherosclerosis, since plasma fibrinogen pool is enlarged.