Acute effects of simultaneous intraperitoneal infusion of glucose and amino acids

How to Improve the Biocompatibility of Peritoneal Dialysis Solutions (without Jeopardizing the Patient's Health)

Peritoneal dialysis (PD) is an important, if underprescribed, modality for the treatment of patients with end-stage kidney disease. Among the barriers to its wider use are the deleterious effects of currently commercially available glucose-based PD solutions on the morphological integrity and function of the peritoneal membrane due to fibrosis. This is primarily driven by hyperglycaemia due to its effects, through multiple cytokine and transcription factor signalling-and their metabolic sequelae-on the synthesis of collagen and other extracellular membrane components. In this review, we outline these interactions and explore how novel PD solution formulations are aimed at utilizing this knowledge to minimise the complications associated with fibrosis, while maintaining adequate rates of ultrafiltration across the peritoneal membrane and preservation of patient urinary volumes. We discuss the development of a new generation of reduced-glucose PD solutions that employ a variety of osmotically active constituents and highlight the biochemical rationale underlying optimization of oxidative metabolism within the peritoneal membrane. They are aimed at achieving optimal clinical outcomes and improving the whole-body metabolic profile of patients, particularly those who are glucose-intolerant, insulin-resistant, or diabetic, and for whom daily exposure to high doses of glucose is contraindicated.

How to Overcome Anabolic Resistance in Dialysis-Treated Patients?

A current hypothesis is that dialysis-treated patients are "anabolic resistant" i. e., their muscle protein synthesis (MPS) response to anabolic stimuli is blunted, an effect which leads to muscle wasting and poor physical performance in aging and in several chronic diseases. The importance of maintaining muscle mass and MPS is often neglected in dialysis-treated patients; better than to describe mechanisms leading to energy-protein wasting, the aim of this narrative review is to suggest possible strategies to overcome anabolic resistance in this patient's category. Food intake, in particular dietary protein, and physical activity, are the two major anabolic stimuli. Unfortunately, dialysis patients are often aged and have a sedentary behavior, all conditions which per se may induce a state of "anabolic resistance." In addition, patients on dialysis are exposed to amino acid or protein deprivation during the dialysis sessions. Unfortunately, the optimal amount and formula of protein/amino acid composition in supplements to maximixe MPS is still unknown in dialysis patients. In young healthy subjects, 20 g whey protein maximally stimulate MPS. However, recent observations suggest that dialysis patients need greater amounts of proteins than healthy subjects to maximally stimulate MPS. Since unneccesary amounts of amino acids could stimulate ureagenesis, toxins and acid production, it is urgent to obtain information on the optimal dose of proteins or amino acids/ketoacids to maximize MPS in this patients' population. In the meantime, the issue of maintaining muscle mass and function in dialysis-treated CKD patients needs not to be overlooked by the kidney community.

The osmo-metabolic approach: a novel and tantalizing glucose-sparing strategy in peritoneal dialysis

Peritoneal dialysis (PD) is a viable but under-prescribed treatment for uremic patients. Concerns about its use include the bio-incompatibility of PD fluids, due to their potential for altering the functional and anatomical integrity of the peritoneal membrane. Many of these effects are thought to be due to the high glucose content of these solutions, with attendant issues of products generated during heat treatment of glucose-containing solutions. Moreover, excessive intraperitoneal absorption of glucose from the dialysate has many potential systemic metabolic effects. This article reviews the efforts to develop alternative PD solutions that obviate some of these side effects, through the replacement of part of their glucose content with other osmolytes which are at least as efficient in removing fluids as glucose, but less impactful on patient metabolism. In particular, we will summarize clinical studies on the use of alternative osmotic ingredients that are commercially available (icodextrin and amino acids) and preclinical studies on alternative solutions under development (taurine, polyglycerol, carnitine and xylitol). In addition to the expected benefit of a glucose-sparing approach, we describe an ‘osmo-metabolic’ approach in formulating novel PD solutions, in which there is the possibility of exploiting the pharmaco-metabolic properties of some of the osmolytes to attenuate the systemic side effects due to glucose. This approach has the potential to ameliorate pre-existing co-morbidities, including insulin resistance and type-2 diabetes, which have a high prevalence in the dialysis population, including in PD patients.

A Randomized Clinical Trial with a 0.6% Amino Acid/1.4% Glycerol Peritoneal Dialysis Solution

Background

Glucose is an accepted osmotic agent for peritoneal dialysis (PD) although it has several drawbacks. Some of these drawbacks have been addressed by the introduction of solutions with low glucose degradation products and physiological pH in dual-chambered bags. Despite this achievement, there is a need for alternative osmotic agents. This randomized clinical trial analyzes 3-month's clinical experience with a mixture of 0.6% amino acids and 1.4% glycerol.

Methods

The study was performed at the renal units of the University Hospitals Ghent, Belgium, and Utrecht, The Netherlands. Stable PD patients were randomized for either protocol A (test solution, n = 5) or protocol B (control regimen, n = 5). In both protocols, there was a run-in phase of 1 month with a dialysis regimen of 2 × 2 L 2.27% glucose solution (Dianeal; Baxter, Nivelles, Belgium), 1 × 2 L Extraneal (Baxter), and 1 × 2 L glucose solution (Dianeal). After this month-long run-in period, patients in group A received during 3 months 2 × 2 L amino acid/glycerol solution, 1 × 2 L Extraneal, and at least 1 × 2 L of a classic glucose solution.

Results

Glucose absorption decreased in the test group during the test phase (from 84.2 ± 8.7 to 11.7 ± 11.6 g/24 hours, p = 0.001). Dialysate levels of cancer antigen 125 (CA125) increased in the test group, from 17.5 ± 11.0 to 32.4 ± 4.6 units/L ( p = 0.04), whereas, in the control group, the levels remained stable (15.5 ± 8.7 and 14.9 ± 9.8 units/L respectively, p = 0.4). There were no differences in serum urea, serum bicarbonate, serum osmolarity, serum albumin, or parameters related to skin-fold thickness or serum glycerol levels between control and test solutions. No differences were observed in obtained ultrafiltration after a 4-hour dwell with 2.27% glucose or the test solution, both measured at week 4 of the run-in period and week 12 of the test period.

Conclusion

This study demonstrated that the use of a new 0.6% amino acid/1.4% glycerol-containing dialysis solution is safe and well tolerated. Glucose load was reduced significantly and dialysate CA125 levels improved significantly. Ultrafiltration was comparable with that of a 2.27% glucose solution. All these factors, in combination with the potential nutritional benefits, can contribute to a beneficial impact on the success of the PD technique. Further long-term studies in larger patient groups are warranted to explore the potential of this promising new solution.

Solutions for peritoneal dialysis in children: recommendations by the European Pediatric Dialysis Working Group

The purpose of this article is to provide recommendations on the choice of peritoneal dialysis (PD) fluids in children by the European Pediatric Dialysis Working Group. The literature on experimental and clinical studies with PD solutions in children and adults was analyzed together with consensus discussions within the group. A grading was performed based on the international KDIGO nomenclature and methods. The lowest glucose concentration possible should be used. Icodextrin may be applied once daily during the long dwell, in particular in children with insufficient ultrafiltration. Infants on PD are at risk of ultrafiltration-associated sodium depletion, while anuric adolescents may have water and salt overload. Hence, the sodium chloride balance needs to be closely monitored. In growing children, the calcium balance should be positive and dialysate calcium adapted according to individual needs. Limited clinical experience with amino acid-based PD fluids in children suggests good tolerability. The anabolic effect, however, is small; adequate enteral nutrition is preferred. CPD fluids with reduced glucose degradation products (GDP) content reduce local and systemic toxicity and should be preferred whenever possible. Correction of metabolic acidosis is superior with pH neutral bicarbonate-based fluids compared with single-chamber, acidic, lactate-based solutions. Prospective comparisons of low GDP solutions with different buffer compositions are still few, and firm recommendations cannot yet be given, except when hepatic lactate metabolism is severely compromised.

Selection of modalities, prescription, and technical issues in children on peritoneal dialysis

Peritoneal dialysis (PD) is widely employed as a dialytic therapy for uraemic children, especially in its automated form (APD), that is associated with less burden of care on patient and family than continuous ambulatory PD. Since APD offers a wide range of treatment options, based on intermittent and continuous regimens, prescription can be individualized according to patient's age, body size, residual renal function, nutritional intake, and growth-related metabolic needs. Transport capacity of the peritoneal membrane of each individual patient should be assessed, and regularly monitored, by means of standardized peritoneal function tests validated in pediatric patients. To ensure maximum recruitment of peritoneal exchange area, fill volume should be scaled to body surface area and adapted to each patient, according to clinical tolerance and intraperitoneal pressure. PD solutions should be employed according to their biocompatibility and potential ultrafiltration capacity; new pH-neutral, glucose-free solutions can be used in an integrated way in separate dwells, or by appropriately mixing during the same dialytic session. Kinetic modelling software programs may help in the tailoring of PD prescription to individual patients' characteristics and needs. Owing to advances in the technology of new APD machines, greater programming flexibility, memorized delivery control, and tele-dialysis are currently possible.

Amino Acid-Based Peritoneal Dialysis Solutions for Malnutrition: New Perspectives

Protein and energy malnutrition is frequently found in patients on maintenance dialysis and is associated with an increased risk of death. Among a variety of factors involved in the development of protein and energy malnutrition, such as acidosis, insulin resistance, inflammation, and dialysate protein losses, insufficient intake of proteins and energy as a result of anorexia plays a prominent role.

Amino acid (AA)-based peritoneal dialysis (PD) solutions can induce an anabolic response in malnourished patients on continuous ambulatory PD if enough calories are ingested simultaneously. Poor appetite, however, may impede the intake of sufficient calories. Peritoneal dialysis solutions containing a mixture of AAs and glucose in a proper ratio can serve as a source of proteins and calories. Such a dialysis solution can be used in fasting patients on nocturnal automated PD as part of a regular dialysis schedule. Using a sophisticated technique involving stable isotopes, this dialysis mixture has been found to induce acute anabolic changes in whole body protein metabolism. Such a metabolic response is similar to that induced by food. Intraperitoneal AAs, in common with ingested proteins, can induce generation of hydrogen ions and urea through oxidation of specific AAs. Supplying AAs together with calories could bring about utilization of AAs for the synthesis of proteins rather than the oxidation of AAs, thereby limiting production of acid and urea. Using dialysis solutions with a buffer concentration of 40 mmol/L further contributes to maintaining acid–base homeostasis.

We advocate consideration of usage of AA/glucose dialysate when PD patients cannot comply with dietary requirements. To evaluate the long-term effects of this approach on morbidity and mortality, clinical trials with large groups of patients are needed.

Use of new peritoneal dialysis solutions in children. Kidney Int. 2008;108:S137-S144. [PMID: 18379537 DOI: 10.1038/sj.ki.5002615]

Standard peritoneal dialysis (PD) solutions with low pH and containing high concentrations of lactate and glucose have been demonstrated to negatively affect the peritoneal membrane, mesothelial cell viability, residential peritoneal cells, and also to inhibit phagocytic functions. An increasing body of experimental evidence supports the idea that the peritoneal hypervascularization and fibrosis observed in long-term PD are causally related to the acute and chronic toxicity of conventional PD solutions. A Physioneal (lactate/bicarbonate mixed buffer pH 7-7.4), Physioneal, Extraneal (7.5% icodextrin), Nutrineal (1.1% amino-acid-containing solution) regimen, for example, offers a significant reduction in carbohydrate load (approximately 40-50%), lower exposure to and absorption of glucose degradation products, reduced oxidative stress, and improved volume control when compared with a first-generation DDDD (4 x Dianeal) regimen. The positive aspects of each solution that we have observed in our patients allow a recommendation on the potential benefit of using these solutions in children treated with PD. In fact, data from the literature as well as the results of the studies reported in this paper show that in children the application of neutral pH bicarbonate/lactate-buffered solution for the standard nighttime APD prescription, icodextrin solution for a long daytime dwell, and AA-based solution in malnourished patients is safe and effective. Extended clinical trials should be encouraged to better define the PD schedules for the combined use of these solutions that may be associated with the best clinical efficacy and the highest level of biocompatibility.

Nutrition in children with CRF and on dialysis

The objectives of this study are: (1) to understand the importance of nutrition in normal growth; (2) to review the methods of assessing nutritional status; (3) to review the dietary requirements of normal children throughout childhood, including protein, energy, vitamins and minerals; (4) to review recommendations for the nutritional requirements of children with chronic renal failure (CRF) and on dialysis; (5) to review reports of spontaneous nutritional intake in children with CRF and on dialysis; (6) to review the epidemiology of nutritional disturbances in renal disease, including height, weight and body composition; (7) to review the pathological mechanisms underlying poor appetite, abnormal metabolic rate and endocrine disturbances in renal disease; (8) to review the evidence for the benefit of dietetic input, dietary supplementation, nasogastric and gastrostomy feeds and intradialytic nutrition; (9) to review the effect of dialysis adequacy on nutrition; (10) to review the effect of nutrition on outcome.

Peritoneal dialysis with solutions containing amino acids plus glucose promotes protein synthesis during oral feeding

Inadequate food intake plays an important role in the development of malnutrition. Recently, an increased rate of protein anabolism was shown in fasting state in patients who were on automated peritoneal dialysis with combined amino acids (AA) and glucose (G) dialysate serving as a source of both proteins and calories. This study investigated the effects of such a dialysis procedure in the daytime in the fed state in patients who were on continuous ambulatory peritoneal dialysis (CAPD). A crossover study was performed in 12 CAPD patients to compare, at 7-d intervals, a mixture of AA (Nutrineal 1.1%) plus G (Physioneal l.36 to 3.86%) versus G only as control dialysate. Whole-body protein turnover was studied by primed constant intravenous infusion of (13)C-leucine during the 9-h dialysis. For meeting steady-state conditions during whole-body protein turnover, frequent exchanges with a mixture of AA plus G were done using an automated cycler. Fed-state conditions were created by identical liquid hourly meals. Using AA plus G dialysate, as compared with the control, rates of protein synthesis increased significantly (2.02 +/- 0.08 versus 1.94 +/- 0.07 mumol leucine/kg per min [mean +/- SEM]; P = 0.039). Rates of protein breakdown and net protein balance did not differ significantly between AA plus G and G. In conclusion, dialysate that contains AA plus G also improves protein synthesis in fed CAPD patients. The use of such a mixture may contribute to long-term improvement of the nutritional status in malnourished CAPD patients with deficient food intake.

Dialysate as Food: Combined Amino Acid and Glucose Dialysate Improves Protein Anabolism in Renal Failure Patients on Automated Peritoneal Dialysis

Protein-energy malnutrition as a result of anorexia frequently occurs in dialysis patients. In patients who are on peritoneal dialysis (PD), dialysate that contains amino acids (AA) improves protein anabolism when combined with a sufficient oral intake of calories. It was investigated whether protein anabolism can be obtained with a mixture of AA plus glucose (G) as a source of proteins and calories during nocturnal automated PD (APD). A random-order cross-over study was performed in eight APD patients to compare in two periods of 7 d each AA plus G dialysate obtained by cycler-assisted mixing of one bag of 2.5 L of AA (Nutrineal 1.1%, 27 g of AA) and four bags of 2.5 L of G (Physioneal 1.36 to 3.86%) versus G as control dialysate. Whole-body protein turnover was determined using a primed continuous infusion of L-[1-13C]leucine, and 24-h nitrogen balance studies were performed. During AA plus G dialysis, when compared with control, rates of protein synthesis were 1.20 +/- 0.4 and 1.10 +/- 0.2 micromol/kg per min leucine (mean +/- SD), respectively (NS), and protein breakdown rates were 1.60 +/- 0.5 and 1.72 +/- 0.3 micromol/kg per min (NS). Net protein balance (protein synthesis minus protein breakdown) increased on AA plus G in all patients (mean 0.21 +/- 0.12 micromol leucine/kg per min; P < 0.001). The 24-h nitrogen balance changed by 0.96 +/- 1.21 g/d, from -0.60 +/- 2.38 to 0.35 +/- 3.25 g/d (P = 0.061, NS), improving in six patients. In conclusion, APD with AA plus G dialysate improves protein kinetics. This dialysis procedure may improve the nutritional status in malnourished PD patients.