Time Profiles of Peritoneal and Renal Clearances of Different Uremic Solutes in Incident Peritoneal Dialysis Patients

Nutrition in Peritoneal Dialysis

The use of peritoneal dialysis (PD) has been associated with improved quality of life, cost-effectiveness, and better outcomes for patients with kidney failure. However, many patients utilizing PD for replacement therapy face numerous nutritional hurdles. As the use of PD continues to increase worldwide, malnutrition has become an increasingly recognized concern for patients undergoing PD. The nephrology community needs to recognize and treat malnutrition to promote optimal nutritional states for our patients. In this review, we discuss several factors that contribute to malnutrition and protein-energy wasting and explore the benefits and limitations of nutritional parameters used to assess protein-calorie malnutrition. We also emphasize updated guidelines on daily caloric, protein, and micronutrient recommendations, as well as their effects on electrolyte homeostasis.

Phosphate Control in Peritoneal Dialysis Patients: Issues, Solutions, and Open Questions

Hyperphosphatemia is a common complication in advanced chronic kidney disease and contributes to cardiovascular morbidity and mortality. The present narrative review focuses on the management of phosphatemia in uremic patients receiving peritoneal dialysis. These patients frequently develop hyperphosphatemia since phosphate anion behaves as a middle-size molecule despite its low molecular weight. Accordingly, patient transporter characteristics and peritoneal dialysis modalities and prescriptions remarkably influence serum phosphate control. Given that phosphate peritoneal removal is often insufficient, especially in lower transporters, patients are often prescribed phosphate binders whose use in peritoneal dialysis is primarily based on clinical trials conducted in hemodialysis because very few studies have been performed solely in peritoneal dialysis populations. A crucial role in phosphate control among peritoneal dialysis patients is played by diet, which must help in reducing phosphorous intake while preventing malnutrition. Moreover, residual renal function, which is preserved in most peritoneal dialysis patients, significantly contributes to maintaining phosphate balance. The inadequate serum phosphate control observed in many patients on peritoneal dialysis highlights the need for large and well-designed clinical trials including exclusively peritoneal dialysis patients to evaluate the effects of a multiple therapeutic approach on serum phosphate control and on hard clinical outcomes in this high-risk population.

Improving the adsorption performance of urea by using polyhydroxy groups to modify two-dimensional Ti3C2Tx

Wearable artificial kidney can provide continuous dynamic dialysis for uremia patients. For the sake of practical application, the critical step is to find an adsorbent that can effectively remove urea and have excellent biological compatibility. The layered Ti3C2Tx (DL-Ti3C2Tx) with high specific surface area and good dispersion was prepared by a two-step etching method. From the first principles calculation, urea can be adsorbed by different groups (-F, -O, -OH) on the surface of Ti3C2Tx, among which -OH has the greatest binding energy to urea. Therefore, DL-Ti3C2Tx was modified with different alkali solutions (KOH, NaOH, LiOH) to introduce -OH on the surface, which can increase the adsorption capacity of urea. The experimental results showed that DL-Ti3C2Tx (LiOH-Ti3C2Tx) after treated by LiOH had the highest urea adsorption efficiency, and the urea removal rate of LiOH-Ti3C2Tx was still higher than 92% when the urea concentration was 500 mg/L. In the Simulated dialysate, Ti3C2Tx treated with three kinds of alkali solutions still maintained a good adsorption efficiency for urea, and still had a certain adsorption capacity after recycling for four times. Biocompatibility experiments showed that Ti3C2Tx in different concentrations did not cause hemolysis of erythrocyte, and had no obvious damage to vascular endothelial cells. This study greatly improves the urea adsorption efficiency of MXene, which has a broad application prospect in the selection of adsorbent for wearable artificial kidney.

On the importance of the interplay of residual renal function with clinical outcomes in end-stage kidney disease

Chronic kidney disease (CKD) is one of the most important public health concerns of the century, and is associated with high rates of morbidity, mortality and social costs. CKD evolving towards end-stage kidney disease (ESKD) is on the rise resulting in a greater number of patients requiring peritoneal dialysis (PD) and hemodialysis (HD). The aim of this manuscript is to review the current literature on the interplay of residual renal function (RRF) with clinical outcomes in ESKD. The persistence of RRF is one of the most important predictors of decreased morbidity, mortality, and better quality of life in both PD and HD patients. RRF contributes to the well-being of ESKD patients through various mechanisms including higher clearance of solutes, maintenance of fluid balance, removal of uremic toxins and control of electrolytes. Furthermore, RRF has beneficial effects on inflammation, anemia, malnutrition, diabetes mellitus, obesity, changes in the microbiota, and cardiac diseases. Several strategies have been proposed to preserve RRF, such as blockade of the renin-angiotensin-aldosterone system, better blood pressure control, incremental PD and HD. Several clinical trials investigating the issue of preservation of RRF are ongoing. They are needed to broaden our understanding of the interplay of RRF with clinical outcomes in ESKD.

Impact on change in serum beta 2 microglobulin by combination therapy of peritoneal dialysis and hemodialysis: a 12-month preliminary observational study

Background

In the Japanese guidelines on combination peritoneal dialysis (PD) and hemodialysis (HD) therapy, patients with serum beta 2 microglobulin (β2MG) levels less than 30 mg/L are recommended. And PD patients with β2MG more than 30 mg/L are considered to transfer to the PD + HD combination therapy. However, the resultant changes in serum β2MG levels by the introduction of PD + HD combination therapy and the factors influencing the change have not clearly elucidated.

Methods

We retrospectively studied 11 PD patients (mean age 56.4 ± 12.9 years, 10 males) with baseline β2MG levels > 30 mg/L with respect to changes in β2MG and its related factors for 12 months after the introduction of combination therapy of PD plus once a week HD (4 h) using a high-performance dialyzer. Laboratory data including hemoglobin, albumin, C-reactive protein, blood urea nitrogen, creatinine, and the patients’ demographic profiles, and HD-related factors, such as Kt/V and blood flow rate, were assessed.

Results

Serum β2MG levels decreased statistically significantly after the introduction of combination therapy: from 36.7 ± 6.7 mg/L at 0 months, to 33.4 ± 6.1 mg/L at 3 months (p = 0.030, compared to baseline), 32.9 ± 4.5 mg/L at 6 months (p = 0.009), and 33.3 ± 5.3 mg/L at 12 months (p = 0.023), respectively. However, only 27–36% patients achieved target β2MG levels of < 30 mg/L during the observation period. Regarding influencing factors, serum albumin levels, blood flow rates of HD, residual renal function and baseline β2MG were associated with a decrease in serum β2MG levels on univariate analysis. In multivariate analysis, serum albumin at 3 and 12 months correlated significantly with Δβ2MG (β =  − 0.990, p = 0.032 at 3 months, β =  − 0.551, p = 0.033 at 12 months). Urine volume at 12 months correlated significantly with Δβ2MG (β = 0.507, p = 0.019).

Conclusions

Combination therapy of PD and HD might reduce serum β2MG levels, but with marginal efficacy. Our preliminary data indicate that the combination therapy of PD and once weekly HD is not sufficient to significantly decrease serum β2MG levels. Additional HD prescriptions, such as increase in blood flow rate and hemodiafiltration, need to be tested in order to improve β2MG levels in these patients.

Altered gut microbiota and gut-derived p-cresyl sulfate serum levels in peritoneal dialysis patients

Peritoneal dialysis (PD) is a renal replacement therapy for end-stage renal disease. Gut microbiota-derived uremic solutes, indoxyl sulfate (IS), p-cresyl sulfate (PCS), and trimethylamine-N-oxide (TMAO) accumulate in PD patients. The objective was to explore the gut microbiota and their influence on uremic toxins in PD patients and healthy controls (HC). Fecal samples were collected from PD patients (n = 105) and HC (n = 102). 16S rRNA gene regions were sequenced for gut microbiota analysis. IS, PCS, and TMAO levels were measured using HPLC-MS. PD patients exhibited lower alpha diversity and altered gut microbiota composition compared to HC. At the genus level, PD patients showed increased abundance of opportunistic pathogenic bacteria, and decreased abundance of beneficial bacteria. Three Operational Taxonomic Units discriminated PD patients from HC. Phenylalanine metabolism increased in PD, whereas tryptophan metabolism was unaltered. Low serum PCS did not necessarily mean healthier due to the loss of alpha diversity, increased Proteobacteria and opportunistic pathogenic bacteria. High serum PCS was mainly caused by elevated p-cresol-producing bacteria, enriched amino acid related enzymes, and enhanced sulfur metabolism, rather than declined residual renal function. In patients with different urine volumes, the gut microbiota alpha diversity and composition were unaltered, but serum IS and TMAO were significantly elevated in anuric patients. In conclusion, the gut microbiota abundance, composition, and function were altered in PD patients, which increased the PCS levels. We provided a better understanding of the microbiota-metabolite-kidney axis in PD patients. Targeting certain bacteria could decrease the PCS levels, whereas preserving the residual renal function could reduce the IS and TMAO levels.

The case for Increased Peritoneal Dialysis Utilization in Low- and Lower-Middle-Income Countries

Peritoneal dialysis (PD) has several advantages compared to hemodialysis (HD), but there is evidence showing underutilization globally, especially in low-income and lower-middle-income countries (LLMICs) where kidney replacement therapies (KRT) are often unavailable, inaccessible, and unaffordable. Only 11% of all dialysis patients worldwide use PD, more than 50% of whom live in China, the United States of America, Mexico, or Thailand. Various barriers to increased PD utilization have been reported worldwide including patient preference, low levels of education, and lower provider reimbursement. However, unique but surmountable barriers are applicable to LLMICs including the excessively high cost of providing PD (related to PD fluids in particular), excessive cost of treatment borne by patients (relative to HD), lack of adequate PD training opportunities for doctors and nurses, low workforce availability for kidney care, and challenges related to some PD outcomes (catheter-related infections, hospitalizations, mortality, etc.). This review discusses some known barriers to PD use in LLMICs and leverages data that show a global trend in reducing rates of PD-related infections, reducing rates of modality switches from HD, and improving patient survival in PD to discuss how PD use can be increased in LLMICs. We therefore, challenge the idea that low PD use in LLMICs is unavoidable due to these barriers and instead present opportunities to improve PD utilization in LLMICs.

Association between Cardiac Outcomes and Indoxyl Sulfate Levels in Hemodialysis Patients: A Cross-sectional Study

Objective Indoxyl sulfate (IS) is a protein-bound uremic toxin that is associated with cardiovascular events and mortality in hemodialysis (HD) patients. However, the factors affecting the levels of IS are currently unclear. This study aimed to investigate the factors influencing serum IS concentrations in HD patients. Methods We included 100 HD patients from Guangdong Provincial People's Hospital. Baseline characteristics, including sex, age, clinical features, duration of HD, echocardiography findings, electrocardiogram results, and biochemical indicators, were collected and analyzed in relation to serum total-form IS levels. Results Among all 100 patients, serum IS levels were significantly higher in patients aged ≥ 60 years, males, and patients with mitral regurgitation and inadequate dialysis. Among patients aged < 60 years, IS levels were significantly higher among patients with mitral regurgitation compared with those without. Furthermore, multiple linear regression analysis identified sex, age, ventricular septal thickness, and mitral regurgitation as factors independently associated with serum IS (STDβ = -0.475, 0.162, -0.153, 0.142, and 0.136, respectively; all P < 0.05) adjusted for body mass index, smoking, and fasting plasma glucose. Conclusions Male sex, age ≥ 60 years, ventricular septal thickness, and mitral regurgitation are factors associated with high total serum IS concentrations in Chinese HD patients. Elevated IS levels may play a role in the process of mitral regurgitation in HD patients < 60 years old.

Peritoneal dialysis modality transition and impact on phosphate and potassium serum levels

Peritoneal dialysis (PD) modalities affect solute removal differently. However, the impacts of switching PD modalities on serum levels of biomarkers of different sizes are not known. Our objective was to analyze whether a change in the PD modality associates with the levels of two routine biochemical laboratories. In this multicentric prospective cohort study. we selected all patients who remained on a PD modality for at least 6 months and switched PD modality. Patients were also required to be treated with the same PD modality for at least 3 months before and after the modality change. The primary outcome was change in potassium and phosphate serum levels. We identified 737 eligible patients who switched their PD modality during the study. We found mean serum phosphate levels increased during the 3 months after switching from CAPD to APD and conversely decreased after switching to from APD to CAPD. In contrast, for potassium the difference in the mean serum levels was comparable between groups switching from CAPD to APD, and vice versa. In conclusion, CAPD seems to be as efficient as APD for the control of potassium serum levels, but more effective for the control of phosphate serum levels. The effect of a higher removal of middle size molecules as result of PD modalities in terms of clinical and patient-reported outcomes should be further explored.

Association of Plasma Uremic Solute Levels with Residual Kidney Function in Children on Peritoneal Dialysis

BACKGROUND AND OBJECTIVES

Residual native kidney function confers health benefits in patients on dialysis. It can facilitate control of extracellular volume and inorganic ion concentrations. Residual kidney function can also limit the accumulation of uremic solutes. This study assessed whether lower plasma concentrations of uremic solutes were associated with residual kidney function in pediatric patients on peritoneal dialysis.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Samples were analyzed from 29 pediatric patients on peritoneal dialysis, including 13 without residual kidney function and ten with residual kidney function. Metabolomic analysis by untargeted mass spectrometry compared plasma solute levels in patients with and without residual kidney function. Dialytic and residual clearances of selected solutes were also measured by assays using chemical standards.

RESULTS

Metabolomic analysis showed that plasma levels of 256 uremic solutes in patients with residual kidney function averaged 64% (interquartile range, 51%-81%) of the values in patients without residual kidney function who had similar total Kt/V_urea. The plasma levels were significantly lower for 59 of the 256 solutes in the patients with residual kidney function and significantly higher for none. Assays using chemical standards showed that residual kidney function provides a higher portion of the total clearance for nonurea solutes than it does for urea.

CONCLUSIONS

Concentrations of many uremic solutes are lower in patients on peritoneal dialysis with residual kidney function than in those without residual kidney function receiving similar treatment as assessed by Kt/V_urea.

Lipid microsphere-coated PGE1 improves peritoneal transport and reduces inflammation in peritoneal dialysis: A randomized clinical pilot trial

OBJECTIVE

To evaluate the effects of lipid microspheres coated with prostaglandin E1 (lipo-PGE1) on peritoneal transport function and inflammation in patients with end-stage renal disease undergoing continuous ambulatory peritoneal dialysis (CAPD).

METHODS

In total, 89 patients were randomly allocated to the lipo-PGE1 and control groups. All the patients received conventional treatment, and those in the lipo-PGE1 group received lipo-PGE1 intravenously for 2 weeks. The levels of β2-microglobulin (β2-MG), cystatin C, albumin, urea, creatinine, interleukin-6 (IL-6), matrix metalloproteinase-2 (MMP-2), and high-sensitivity C-reactive protein (hs-CRP) were measured before and at 1 and 2 weeks after treatment.

RESULTS

In the lipo-PGE1 group, the peritoneal clearance rates of β2-MG, cystatin C, and albumin were significantly increased comparing with pre-treatment values, and the IL-6 appearance rate (AR) in the peritoneal dialysate and the serum levels of IL-6 and hs-CRP were markedly decreased (p < 0.05). The lipo-PGE1 group had significantly higher peritoneal clearance rates of β2-MG and cystatin C and lower IL-6 AR in the peritoneal dialysate than the control group (p < 0.05).

CONCLUSIONS

Lipid microspheres coated with prostaglandin E1 may increase the peritoneal clearance of moderately sized molecules and macromolecules with insignificant effect on the clearance of small molecules. The reduction in IL-6 level following treatment with lipo-PGE1 may alleviate inflammation.

KDOQI US Commentary on the 2020 ISPD Practice Recommendations for Prescribing High-Quality Goal-Directed Peritoneal Dialysis

The recently published 2020 International Society for Peritoneal Dialysis (ISPD) practice recommendations regarding prescription of high-quality goal-directed peritoneal dialysis differ fundamentally from previous guidelines that focused on "adequacy" of dialysis. The new ISPD publication emphasizes the need for a person-centered approach with shared decision making between the individual performing peritoneal dialysis and the clinical care team while taking a broader view of the various issues faced by that individual. Cognizant of the lack of strong evidence for the recommendations made, they are labeled as "practice points" rather than being graded numerically. This commentary presents the views of a work group convened by the National Kidney Foundation's Kidney Disease Outcomes Quality Initiative (KDOQI) to assess these recommendations and assist clinical providers in the United States in interpreting and implementing them. This will require changes to the current clinical paradigm, including greater resource allocation to allow for enhanced services that provide a more holistic and person-centered assessment of the quality of dialysis delivered.

Therapeutic Options for Preservation of Residual Renal Function in Patients on Peritoneal Dialysis

Dialysis is not the ideal renal replacement therapy because it does not fully restore all kidney functions. Increasing evidence suggests that preservation of residual renal function is associated with a survival benefit, a decrease in morbidity, better nutrition, a lower level of inflammatory markers, an improved quality of life, and cost savings by obviating the need for more peritoneal dialysis exchanges and possibly by reducing the requirement for antihypertensive agents, phosphate binders, and erythropoietin. In the present article, we review the impact of residual renal function on patient outcomes and the renoprotective strategies available in patients on peritoneal dialysis.

Removal of Protein-Bound Uremic Toxins by Liposome-Supported Peritoneal Dialysis

Background:Protein-bound uremic toxins (PBUTs) are poorly cleared by peritoneal dialysis (PD). This study aimed to enhance PBUT removal in PD by adding a binder to the peritoneal dialysate and to evaluate the feasibility and efficacy of liposome-supported PD (LSPD) to increase the removal of PBUTs compared with albumin PD.Methods:Removal of p-cresyl sulfate (PCS), indoxyl sulfate (IS), and indole-3-acetic acid (3-IAA) was first evaluated in an in vitro PD model using artificial plasma preloaded with test solutes. Male Sprague-Dawley rats (n = 24) were then subjected to 5/6 nephrectomy and fed for 16 weeks to establish end-stage renal failure, after which they were treated with either conventional glucose-based PD, albumin-based PD, or liposome-based PD. Removal of PBUTs and small water-soluble solutes was determined during a 6-hour PD dwell.Results:In vitro experiments showed that adding albumin as a toxin binder to the dialysate markedly increased the removal of PCS, IS, and 3-IAA compared with the control. The uptake capacity of liposomes was comparable with that of albumin for PCS and 3-IAA, though slightly inferior for IS. In vivo PD in uremic rats demonstrated that LSPD resulted in higher intraperitoneal concentrations and more total mass removal for PBUTs than the conventional glucose-based PD, which was comparable with albumin PD.Conclusions:Supplementing conventional glucose-based PD solutions with a binder could efficiently increase the removal of PBUTs. This preliminary study suggested that LSPD may be a promising alternative to albumin PD for increasing PBUT removal in the development of next-generation PD solutions for PD patients.

In vitro efficacy and safety of a system for sorbent-assisted peritoneal dialysis

A system for sorbent-assisted peritoneal dialysis (SAPD) was designed to continuously recirculate dialysate via a tidal mode using a single lumen peritoneal catheter with regeneration of spent dialysate by means of sorbent technology. We hypothesize that SAPD treatment will maintain a high plasma-to-dialysate concentration gradient and increase the mass transfer area coefficient of solutes. Thereby, the SAPD system may enhance clearance while reducing the number of exchanges. Application is envisaged at night as a bedside device (12 kg, nighttime system). A wearable system (2.0 kg, daytime system) may further enhance clearance during the day. Urea, creatinine, and phosphate removal were studied with the daytime and nighttime system (n = 3 per system) by recirculating 2 liters of spent peritoneal dialysate via a tidal mode (mean flow rate: 50 and 100 mL/min, respectively) for 8 h in vitro. Time-averaged plasma clearance over 24 h was modeled assuming one 2 liter exchange/day, an increase in mass transfer area coefficient, and 0.9 liters ultrafiltration/day. Urea, creatinine, and phosphate removal was 33.2 ± 4.1, 5.3 ± 0.5, and 6.2 ± 1.8 mmol, respectively, with the daytime system and 204 ± 28, 10.3 ± 2.4, and 11.4 ± 2.1 mmol, respectively, with the nighttime system. Time-averaged plasma clearances of urea, creatinine and phosphate were 9.6 ± 1.1, 9.6 ± 1.7, and 7.0 ± 0.9 mL/min, respectively, with the nighttime system and 10.8 ± 1.1, 13.4 ± 1.8, and 9.7 ± 1.6 mL/min, respectively, with the daytime and nighttime system. SAPD treatment may improve removal of uremic toxins compared with conventional peritoneal dialysis, provided that peritoneal mass transport will increase.

Protein-Bound Uremic Toxins in Hemodialysis Patients Relate to Residual Kidney Function, Are Not Influenced by Convective Transport, and Do Not Relate to Outcome

Protein-bound uremic toxins (PBUTs) are predominantly excreted by renal tubular secretion and hardly removed by traditional hemodialysis (HD). Accumulation of PBUTs is proposed to contribute to the increased morbidity and mortality of patients with end-stage kidney disease (ESKD). Preserved PBUT excretion in patients with residual kidney function (RKF) and/or increased PBUT clearance with improved dialysis techniques might improve the prognosis of patients with ESKD. The aims of this study are to explore determinants of PBUTs in HD patients, and investigate whether hemodiafiltration (HDF) lowers PBUT plasma concentrations, and whether PBUTs are related to the outcome. Predialysis total plasma concentrations of kynurenine, kynurenic acid, indoxyl sulfate, indole-3-acetic acid, p-cresyl sulfate, p-cresyl glucuronide, and hippuric acid were measured by UHPLC-MS at baseline and after 6 months of follow-up in the first 80 patients participating in the CONvective TRAnsport Study (CONTRAST), a randomized controlled trial that compared the effects of online HDF versus low-flux HD on all-cause mortality and new cardiovascular events. RKF was inversely related to kynurenic acid (p < 0.001), indoxyl sulfate (p = 0.001), indole-3-acetic acid (p = 0.024), p-cresyl glucuronide (p = 0.004) and hippuric acid (p < 0.001) plasma concentrations. Only indoxyl sulfate decreased by 8.0% (−15.3 to 34.6) in patients treated with HDF and increased by 11.9% (−15.4 to 31.9) in HD patients after 6 months of follow-up (HDF vs. HD: p = 0.045). No independent associations were found between PBUT plasma concentrations and either risk of all-cause mortality or new cardiovascular events. In summary, in the current population, RKF is an important determinant of PBUT plasma concentrations in HD patients. The addition of convective transport did not consistently decrease PBUT plasma concentrations and no relation was found between PBUTs and cardiovascular endpoints.

The “Heart” of Peritoneal Dialysis: Residual Renal Function

The CANUSA study originally reported the importance of total small-solute clearance in predicting survival of peritoneal dialysis (PD) patients. However, subsequent reanalysis of data from the CANUSA study clearly demonstrated that the predictive power for mortality in PD patients was largely attributable to residual renal function (RRF) and not to the dose of PD. While this should not lead to the assumption that the dose of PD is unimportant, it does clearly indicate that the contribution of residual renal clearance and PD clearance to the overall survival of PD cannot be considered equivalent. In a previous study, we also demonstrated the importance of loss of RRF in predicting a heightened risk of mortality and cardiovascular death in PD patients. In this review, we focus our discussion on the different potential mechanisms that explain the important link between RRF and cardiovascular disease and survival of PD patients. We provide evidence to explain why RRF is so important to patients receiving long-term PD treatment and why it should be regarded as the “heart” of PD.

Prescribing high-quality peritoneal dialysis: The role of preserving residual kidney function

Maintenance of residual kidney function (RKF) is independently associated with increased survival in patients with end-stage renal disease. Presence of RKF is also associated with improved volume status, better nutritional status, reduced erythropoietin requirement, and decreased rate of peritonitis in patients on peritoneal dialysis (PD). Thus, the preservation of RKF is an important therapeutic end point in the management of patients on PD. Measurement of RKF in PD patients should be based on the mean of 24-h urinary creatinine and urea clearances, and ideally, this should be done quarterly. Compared to those started on hemodialysis, patients initiated on PD appear to have slower decline in RKF. The choice of PD modality should be based on patient preference, as there is no clear evidence to date showing one modality is superior than the other in preserving RKF. Peritoneal dialysates with neutral pH and low glucose degradation products seem to have a favorable effect on RKF. An angiotensin-converting enzyme inhibitor or angiotensin receptor blocker should be used whenever possible to preserve RKF and reduce cardiac mortality. Both loop diuretics and icodextrin can be utilized to maintain fluid balance in PD patients. However, caution should be taken to avoid volume depletion which could accelerate RKF decline. Short-term use of aminoglycosides does not have a detrimental impact on RKF, but prolonged use (>3 weeks) should be avoided to minimize the risk of ototoxicity. Lastly, potential nephrotoxic agents such as intravenous contrast should be used judiciously.

Protein-bound uremic toxins are associated with cognitive function among patients undergoing maintenance hemodialysis

Patients with chronic kidney disease have a greater risk of cognitive impairment. Cerebral uremic solute accumulation causes uremic encephalopathy; however, the association of protein-bound uremic toxins on cognitive function remains unclear. The present study aimed to investigate the association of two protein-bound uremic toxins, namely indoxyl sulfate (IS) and p-cresyl sulfate (PCS), on cognitive function in patients receiving hemodialysis (HD) for at least 90 days. Circulating free form IS and PCS were quantified by liquid chromatography/mass spectrometry. Mini-Mental State Examination (MMSE) and Cognitive Abilities Screening Instrument (CASI) were used to evaluate cognitive function. In total, 260 HD patients were recruited with a mean age of 58.1 ± 11.3 years, of which, 53.8% were men, 40% had diabetes, and 75.4% had hypertension. The analysis revealed that both free IS and free PCS were negatively associated with the CASI score and MMSE. After controlling for confounders, circulating free IS levels persisted to be negatively associated with MMSE scores [β = −0.62, 95% confidence interval (CI): −1.16 to −0.08] and CASI scores (β = −1.97, 95% CI: −3.78 to −0.16), mainly in the CASI domains of long-term memory, mental manipulation, language ability, and spatial construction. However, there was no correlation between free PCS and total MMSE or total CASI scores after controlling for confounders. In conclusion, circulating free form IS, but not PCS is associated with lower cognitive function test scores in HD patients. Thus, a further study is needed to evaluate whether a decrease in free IS levels can slow down cognitive decline in HD patients.

Lower serum beta-2 microglobulin levels are associated with worse survival in incident peritoneal dialysis patients

Background

There is a general consensus that elevated serum beta-2 microglobulin (B2M) levels measured at a single time-point are significantly associated with mortality in patients on maintenance dialysis. To date, the majority of prior studies that have examined B2M-associated mortality have been conducted in prevalent hemodialysis patients with little residual renal function (RRF). However, studies in incident peritoneal dialysis (PD) patients are lacking. Moreover, changes in serum B2M levels over time have not been considered in this population.

Methods

We examined the association of time-updated and baseline serum B2M levels with mortality in a 10-year cohort of 725 incident PD patients who were maintained on dialysis between January 2006 and December 2011 using Cox proportional hazards regression analyses. Patients were categorized into tertiles according to B2M levels.

Results

During a median follow-up of 38 (interquartile range 23-64) months, 258 (35.4%) deaths occurred, including 106 (14.6%) and 86 (11.9%) deaths from cardiovascular and infectious causes, respectively. The lowest B2M tertile was associated with a higher risk of all-cause and infectious mortality compared with the middle tertile: the hazard ratios (95% confidence interval) for all-cause deaths were 2.12 (1.38-3.26) and 2.20 (0.96-5.05) in time-varying analyses and 1.52 (1.07-2.17) and 2.41 (1.19-4.88) in baseline analyses. Subgroup analyses showed that this association was particularly observed in females, older patients, those with comorbidities such as diabetes, a lower body mass index, lower albumin levels or those with higher RRF (all P for interactions <0.05).

Conclusions

In incident PD patients, lower B2M levels were independently associated with overall and infectious mortality. These associations can be potentially modified by malnutrition, inflammation and RRF.

Atherosclerotic vascular disease is more prevalent among black ESKD patients on long-term CAPD in South Africa

Background

Occurrence of cardiovascular disease (CVD) in the setting of chronic kidney disease (CKD) can be described as a “cruel alliance”, with CVD responsible for about half of all deaths among CKD patients. Chronic kidney disease patients are more likely to die from CVD than progress to end stage kidney disease (ESKD). Dyslipidaemia, a known traditional risk factor for CVD, is highly prevalent among CKD patients and with an even higher frequency among ESKD patients on dialytic therapies. Prolonged exposure of continuous ambulatory peritoneal dialysis (CAPD) patients to high glucose concentrations in CAPD fluid have been associated with increased risk of cardiovascular events. In this study, we investigated the relationship of atherosclerotic vascular disease (AsVD) to clinical and echocardiographic parameters among black South Africans with CKD (stage 3) and ESKD on CAPD and haemodialysis (HD).

Methods

This was a cross-sectional study of 40 adult (18–65 years) non-diabetic CKD patients (kidney disease outcome quality initiative [KDOQI] stage 3), 40 ESKD patients on CAPD, 40 ESKD patients on HD and 41 age and sex-matched healthy controls. An interviewer-administered questionnaire was used to obtain information on participants’ sociodemographic and cardiovascular risk factors. Anthropometric parameters were measured. Serum blood samples were analysed for creatinine, albumin and lipid profile; lipoprotein ratios, Framingham’s risk score and the 10-year risk of developing coronary heart disease (CHD) were calculated. Echocardiography was performed on all patients and carotid intima media thickness (CIMT) was measured in both right and left carotid arteries at 1 cm proximal to the carotid bulb. Spearman’s rank correlation and binary logistic regression were conducted to determine the relationship of AsVD to clinical and echocardiographic parameters.

Results

Atherosclerotic vascular disease was most prevalent among ESKD patients on CAPD (70%, n = 28/40). Chronic kidney disease and HD patients exhibited a similar prevalence (47.5%, n = 19/40), while the prevalence in controls was 17.1% (n = 7/41). Presence of AsVD was associated with significantly older age, higher waist hip ratio (WHR), left ventricular mass index (LVMI) and Framingham’s 10-year risk of developing CHD. Significant differences in clinical and echocardiographic parameters were observed when the study groups were compared. Age and LVH independently predicted AsVD.

Conclusion

Atherosclerotic vascular disease was more prevalent among CAPD patients compared to pre-dialysis CKD and HD patients. Among all lipoprotein ratios assessed, non-HDL-C showed the most consistent significant difference between the groups. Age (> 40 years) and presence of LVH were independent predictors of AsVD.

Association of Lower Serum Bilirubin With Loss of Residual Kidney Function in Peritoneal Dialysis Patients

Bilirubin is recognized as an endogenous antioxidant, and low serum bilirubin is reported to be associated with the progression of kidney disease. However, it is unclear whether serum bilirubin levels are associated with the loss of residual kidney function (RKF) in peritoneal dialysis (PD) patients. This study investigated the relationship between serum total bilirubin and loss of RKF. We prospectively followed 94 PD patients who started PD in our hospital between June 2006 and May 2016. Ten patients who had chronic liver disease or cirrhosis were excluded. Patients were divided into three groups based on serum total bilirubin concentration tertiles: tertile 1 (T1) < 0.3, T2 = 0.3, and T3 ≥ 0.4 mg/dL. We estimated the relationship between serum bilirubin and loss of RKF, defined as daily urine volume (<100 mL) within 3 years after starting PD, using a Cox proportional hazards model. During the 3-year observation period, 22 patients lost RKF. The incidence rate of loss of RKF increased linearly with the decrease in serum total bilirubin levels (P for trend < 0.05). After adjusting for confounding factors, low serum total bilirubin level was shown to be an independent predictor of loss of RKF (hazard ratio [HR] for every 0.1 mg/dL decrease, 1.50; 95% confidence interval [CI], 1.01-2.51; HR [95%CI] for T2 and T1 [vs. T3] 2.03 [0.65-7.88] and 3.70 [1.00-15.9]). This study suggests that low serum total bilirubin levels are associated with the loss of RKF in PD patients.

Uremic Toxin Clearance and Cardiovascular Toxicities

Uremic solutes contribute to cardiovascular disease in renal insufficiency. In this review we describe the clearance of selected uremic solutes, which have been associated with cardiovascular disease. These solutes—indoxyl sulfate (IS), p-cresol sulfate (PCS), phenylacetylglutamine (PAG), trimethylamine-n-oxide (TMAO), and kynurenine—exemplify different mechanisms of clearance. IS and PCS are protein-bound solutes efficiently cleared by the native kidney through tubular secretion. PAG and TMAO are not protein-bound but are also cleared by the native kidney through tubular secretion, while kynurenine is not normally cleared by the kidney. Increases in the plasma levels of the normally secreted solutes IS, PCS, TMAO, and PAG in chronic kidney disease (CKD) are attributable to a reduction in their renal clearances. Levels of each of these potential toxins are even higher in patients on dialysis than in those with advanced chronic kidney disease, which can be accounted for in part by a low ratio of dialytic to native kidney clearance. The rise in plasma kynurenine in CKD and dialysis patients, by contrast, remains to be explained. Our ability to detect lower levels of the potential uremic cardiovascular toxins with renal replacement therapy may be limited by the intermittency of treatment, by increases in solute production, and by the presence of non-renal clearance. Reduction in the levels of uremic cardiovascular toxins may in the future be achieved more effectively by inhibiting their production.

Uremic Toxin Clearance and Cardiovascular Toxicities

Uremic solutes contribute to cardiovascular disease in renal insufficiency. In this review we describe the clearance of selected uremic solutes, which have been associated with cardiovascular disease. These solutes-indoxyl sulfate (IS), p-cresol sulfate (PCS), phenylacetylglutamine (PAG), trimethylamine-n-oxide (TMAO), and kynurenine-exemplify different mechanisms of clearance. IS and PCS are protein-bound solutes efficiently cleared by the native kidney through tubular secretion. PAG and TMAO are not protein-bound but are also cleared by the native kidney through tubular secretion, while kynurenine is not normally cleared by the kidney. Increases in the plasma levels of the normally secreted solutes IS, PCS, TMAO, and PAG in chronic kidney disease (CKD) are attributable to a reduction in their renal clearances. Levels of each of these potential toxins are even higher in patients on dialysis than in those with advanced chronic kidney disease, which can be accounted for in part by a low ratio of dialytic to native kidney clearance. The rise in plasma kynurenine in CKD and dialysis patients, by contrast, remains to be explained. Our ability to detect lower levels of the potential uremic cardiovascular toxins with renal replacement therapy may be limited by the intermittency of treatment, by increases in solute production, and by the presence of non-renal clearance. Reduction in the levels of uremic cardiovascular toxins may in the future be achieved more effectively by inhibiting their production.

From portable dialysis to a bioengineered kidney

INTRODUCTION

Since the advent of peritoneal dialysis (PD) in the 1970s, the principles of dialysis have changed little. In the coming decades, several major breakthroughs are expected.

AREAS COVERED

Novel wearable and portable dialysis devices for both hemodialysis (HD) and PD are expected first. The HD devices could facilitate more frequent and longer dialysis outside of the hospital, while improving patient's mobility and autonomy. The PD devices could enhance blood purification and increase technique survival of PD. Further away from clinical application is the bioartificial kidney, containing renal cells. Initially, the bioartificial kidney could be applied for extracorporeal treatment, to partly replace renal tubular endocrine, metabolic, immunoregulatory and secretory functions. Subsequently, intracorporeal treatment may become possible.

EXPERT COMMENTARY

Key factors for successful implementation of miniature dialysis devices are patient attitudes and cost-effectiveness. A well-functioning and safe extracorporeal blood circuit is required for HD. For PD, a double lumen PD catheter would optimize performance. Future research should focus on further miniaturization of the urea removal strategy. For the bio-artificial kidney (BAK), cost effectiveness should be determined and a general set of functional requirements should be defined for future studies. For intracorporeal application, water reabsorption will become a major challenge.

Application of automated peritoneal dialysis in urgent-start peritoneal dialysis patients during the break-in period

Objective

Whether automated peritoneal dialysis (APD) is a feasible strategy for urgent-start peritoneal dialysis (PD) therapy during the break-in period remains unclear. This study was conducted to compare the efficacy as well as complications among three PD modes during the break-in period.

Methods

Ninety-six patients treated with urgent-start PD after catheterization were retrospectively analyzed. Patients were divided into three groups, incremental continuous ambulatory PD (CAPD) group (n = 26); APD group (n = 42); and APD–CAPD group (n = 28). Clinical parameters at the end of the break-in period and 1 month after the initiation of PD treatment were collected and analyzed.

Results

Compared with the traditional incremental CAPD, APD and APD–CAPD were superior as they could effectively remove small-molecule uremic toxins and correct electrolyte imbalance (P < 0.05), while did not increase the incidence of early complications during the break-in period (P > 0.05). However, APD led to a significant decline in albumin and pre-albumin, as compared with APD–CAPD and CAPD (P < 0.05). A PD strategy consisting 6 days of APD and 3 days of CAPD showed a great advantage in preventing excessive protein loss. There were no significant differences in all tested biochemical parameters among the three groups at 1 month after treatment (all P > 0.05).

Conclusion

Application of APD for urgent-start PD during the break-in period is feasible. A combination of APD and CAPD regimens seems to be a more reasonable mode.

Protein-bound toxins: has the Cinderella of uraemic toxins turned into a princess?

Chronic kidney disease (CKD) has emerged as a global public health problem. Although the incidence and prevalence of CKD vary from one country to another, the estimated worldwide prevalence is 8-16%. The complications associated with CKD include progression to end-stage renal disease (ESRD), mineral and bone disorders, anaemia, cognitive decline and elevated all-cause and cardiovascular (CV) mortality. As a result of progressive nephron loss, patients with late-stage CKD are permanently exposed to uraemic toxins. These toxins have been classified into three groups as a function of the molecular mass: small water-soluble molecules, middle molecules and protein-bound uraemic toxins. The compounds can also be classified according to their origin (i.e. microbial or not) or their protein-binding ability. The present review will focus on the best-characterized protein-bound uraemic toxins, namely indoxylsulfate (IS), indole acetic acid (IAA) and p-cresylsulfate (PCS, a cresol metabolite). Recent research suggests that these toxins accelerate the progression of CV disease, kidney disease, bone disorders and neurological complications. Lastly, we review therapeutic approaches that can be used to decrease toxin levels.

Influence of Residual Renal Function in Carotid Modeling as a Marker of Early Atherosclerosis in Dialysis Patients

Atherosclerosis is frequently present in patients with chronic kidney disease (CKD) treated with dialysis. We evaluated the association between residual renal function (RRF), phosphate level, inflammation and other risk factors in carotid modeling as a marker of early atherosclerosis in peritoneal dialysis (PD) compared with hemodialysis (HD) patients. We studied 39 stable PD and 53 HD patients on renal replacement therapy (RRT) for 3 to 36 months duration. B-mode ultrasonography was used to determine carotid artery intima media thickness (CIMT). We classified patients with atherosclerosis if they have CIMT >10 mm and or presence of plaque. Out of our total dialysis population studied of 92 patients, 16.3% were diabetics and 57.6% were on hemodialysis. Expectedly, PD patients had a higher RRF (P < 0.001), 24 h urine volume (P < 0.001); C-reactive protein (P = 0.047), and a lower serum phosphate (P = 0.01), PTH (P < 0.05), alkaline phosphatase (P < 0.05), and albumin levels (P < 0.001) compared to hemodialysis patients. Atherosclerosis was found in 66.3% of patients and in 100% of a diabetic population. There was no significant difference in the presence of atherosclerosis between PD and HD patients [56.4 vs 73.6% HD, respectively]. Multiple regression analysis showed age, diabetes, HD modality, RRF, phosphate, PTH and pulse pressure as independent parameters associated with atherosclerosis. Apart from the traditional risk factors like age and diabetes, our study showed a link of atherosclerosis with metabolic abnormalities secondary to renal failure. We demonstrated a novel, independent association between RRF and atherosclerosis, underlining the importance of preservation of the RRF in dialysis patients.

Incremental start to PD as experienced in Italy: results of censuses carried out from 2005 to 2014

BACKGROUND

It is not known how widely used in Italy an incremental start to in peritoneal dialysis (Incr-PD) is.

METHODS

By analyzing the peritoneal dialysis (PD) censuses conducted by the PD Study Group (GSDP-SIN) for the years 2005, 2008, 2010, 2012 and 2014 in all the Centers performing PD in Italy, the use of Incr-PD, i.e. continuous ambulatory peritoneal dialysis (CAPD) with 1 or 2 exchanges/day or automated peritoneal dialysis (APD) with 3-4 sessions/week, was examined among incident PD patients.

RESULTS

In 2014 PD was started in Italy by 1,652 patients, 455 (27.5%) of whom incrementally (Incr-CAPD 82.2% vs. Incr-APD 17.8%). Incr-PD was used in 53.5% of the 225 Centers. The number of patients and of Centers using Incr-DP increased constantly over the years up to 2012 (in 2005 Incr-PD was used in 33.4% of Centers, and in 11.9% of patients). The use of Incr-PD was greater in Centers with a more extensive PD program and greater use of PD in general. The most widely-used modality in Incr-PD was CAPD.

CONCLUSIONS

Incr-PD is used in Italy in a large number of incident PD patients. The reasons for this increase need to be clarified, as current adequacy targets are based on full-dose studies with a very low glomerular filtration rate (GFR).

The Role of Liver in Determining Serum Colon-Derived Uremic Solutes

Evidence has shown that indoxyl sulfate (IS) and p-cresyl sulfate (PCS) may be alternative predictors of clinical outcomes in chronic kidney disease (CKD). Both toxins are derived from the gastrointestinal tract and metabolised in the liver. However, it is unclear whether the liver affects the production of IS and PCS. Here, we explore the association between IS and PCS levels in liver cirrhosis and a CKD-based cohort (N = 115). Liver and kidney function was assessed and classified by a Child-Pugh score (child A–C) and a modified version of the Modification of Diet in Renal Disease (MDRD) equation (Stages 1–4), respectively. An animal model was also used to confirm the two toxin levels in a case of liver fibrosis. In patients with early liver cirrhosis (child A), IS and PCS were significantly associated with CKD stages. In contrast, serum IS and PCS did not significantly change in advanced liver cirrhosis (child C). A stepwise multiple linear regression analysis also showed that T-PCS was significantly associated with stages of liver cirrhosis after adjusting for other confounding factors (B = -2.29, p = 0.012). Moreover, the serum and urine levels of T-PCS and T-IS were significantly lower in rats with liver failure than in those without (p<0.01, p<0.05 and p<0.01, p<0.05, respectively). These results indicated that in addition to the kidneys, the liver was an essential and independent organ in determining serum IS and PCS levels. The production rate of IS and PCS was lower in patients with advanced liver cirrhosis.

Influence of Different Payment Schemes on the Clinical Outcome in Peritoneal Dialysis Patients

♦

BACKGROUND

Cost is always a big issue for dialysis patients. In the present study, we analyzed the effect of different payment schemes on dialysis adequacy and clinical outcome in our peritoneal dialysis program. ♦

METHODS

This is a single-center cohort study. A total of 175 patients who began dialysis from January 2006 to December 2007 were included. Baseline data, including volume status, dietary intake and nutrition status, dialysis adequacy, and sodium removal were collected at 6 months after peritoneal dialysis. Based on the different payment schemes, the patients were divided into 2 groups, higher payment group (GHP, 130 cases, with more than 85% reimbursement), and lower payment group (GLP, 45 cases, with less than 50% payment or totally self-paid). Patients were followed up until dropout or until December 31, 2013. ♦

RESULTS

At baseline, patients in the 2 groups had nearly the same residual renal function. But the GLP group patients dialyzed at a lower dose (4,516.91 ± 1,768.20 mL vs 6,058.17 ± 2,013.43 mL, p < 0.001). They had lower creatinine clearance (51.64 ± 24.23 L/w vs 70.54 ± 30.27 L/w, p < 0.001), sodium removal (2.23 ± 1.29 g vs 2.77 ± 1.29 g, p = 0.027), and fluid removal (970.33 ± 545.97 mL vs 1,146.66 ± 460.93 mL, p = 0.038). Normalized by height (in meters), the GLP group patients still had a lower normalized dialysis dose (2,890.61 ± 1084.44 mL/m vs 3,761.34 ± 1,237.10 mL/m, p < 0.001). Baseline nutritional and dietary parameters were comparable except that a lower daily protein intake (42.73 ± 10.99 g vs 47.26 ± 14.30 g, p = 0.032) and higher serum urea level (23.43 ± 6.88 mmol/L vs 19.84 ± 5.92 mmol/L, p < 0.001) were presented in the GLP group. There was no difference in volume status. During the follow-up, Kaplan-Meier analysis showed that there was no significant difference in patient survival and technique survival. In multivariate Cox regression analysis, after adjusting for related factors, payment was again not a strong predictor of survival in the study population. ♦

CONCLUSION

Our study found that GLP group patients were adherent to lifestyle modification with lower dialysis doses, and they also had nearly the same long-term clinical outcome as the GHP group patients. Thus, lower dialysis doses combined with controlled dietary intake may be an effective approach to solve the dialysis problem for the low socio-economic status (SES) population.

Peritoneal Dialysis as a First versus Second Option after Previous Haemodialysis: A Very Long-Term Assessment

For renal replacement therapy, overall survival is more important than the choice of currently available individual therapy. Objectives. To compare patients and technique survival on peritoneal dialysis as first treatment (PDF) versus after previous haemodialysis (HDPD) and other indicators of follow-up. Methods. We prospectively studied 110 incident patients, during the period from August 4, 1993, to June 30, 2012, for patients and technique survival (Kaplan-Meier) (log rank P < 0.05). Results. Groups: (A) PDF: 37 patients, 24 females, age: 52.2 ± 14.9 years old, time at risk: 2123 patient-months (p/m), mean: 57 ± 42 months; (B) HDPD: 73 patients, 42 females, age: 52.45 ± 14.7 years old, time in haemodialysis: 3569.2 (p/m), range: 3-216 months, mean: 49 ± 45 months, time at risk in PD: 3700 (p/m), mean: 51 ± 49 months. Patients' survival: (A) PDF: 100%, 76.6%, 65.6%, and 19.7%; (B) HDPD: 95.4%, 65.6%, 43%, and 43% at 12, 60, 120, and 144 months, respectively, P = 0.34.

TECHNIQUE

(A) PDF: 100%, 90%, 59.8%, and 24%; (B) HDPD: 94%, 75%, 32%, and 32% at 12, 60, 120, and 144 months, respectively, P = 0.40. Conclusions. Comparable patient and technique survival were observed. Peritoneal dialysis enables a greater extension of renal replacement therapy for patients with serious difficulties continuing with haemodialysis.

Serum concentrations of p-cresyl sulfate and indoxyl sulfate, but not inflammatory markers, increase in incident peritoneal dialysis patients in parallel with loss of residual renal function

BACKGROUND

High serum concentrations of the protein-bound uremic retention solutes p-cresyl sulfate (PCS) and indoxyl sulfate (IndS) and inflammation are associated with increased cardiovascular morbidity and mortality in chronic kidney disease. Renal clearance contributes to up to 80% of the total clearance of PCS and IndS in peritoneal dialysis (PD) patients. Cross-sectional studies evaluating the impact of residual renal function (RRF) on serum concentrations of PCS, IndS, and circulating inflammatory markers have yielded conflicting results. ♢

METHODS

To clarify this issue, we carried out a prospective observational cohort study in incident PD patients (n = 35; 19 men; mean age: 55 ± 17 years). Midday blood samples were collected and analyzed for total serum PCS, IndS, C-reactive protein, and high-sensitivity interleukin 6. Peritoneal and renal clearances were calculated from urine and dialysate collections, and RRF was calculated as the mean of renal urea nitrogen and creatinine clearances. Patients were assessed 1, 6, 12, and 24 months after PD start. Differences between time points were analyzed using linear mixed models (LMMs). ♢

RESULTS

Residual renal function declined significantly over time (LMM p < 0.0001). Peritoneal clearances of both toxins tended to increase, but did not compensate for the declining renal clearances. Serum concentrations of PCS and IndS increased significantly over time (LMM p = 0.01; p = 0.0009). In contrast, total mass removal of both toxins remained stable. Circulating inflammatory markers did not change over time. ♢

CONCLUSIONS

Our data indicate that serum concentrations of PCS and IndS, but not inflammatory markers, increase in incident PD patients in parallel with loss of RRF.

p-Cresyl sulfate and indoxyl sulfate in pediatric patients on chronic dialysis

Purpose

Indoxyl sulfate and p-cresyl sulfate are important protein-bound uremic retention solutes whose levels can be partially reduced by renal replacement therapy. These solutes originate from intestinal bacterial protein fermentation and are associated with cardiovascular outcomes and chronic kidney disease progression. The aims of this study were to investigate the levels of indoxyl sulfate and p-cresyl sulfate as well as the effect of probiotics on reducing the levels of uremic toxins in pediatric patients on dialysis.

Methods

We enrolled 20 pediatric patients undergoing chronic dialysis; 16 patients completed the study. The patients underwent a 12-week regimen of VSL#3, a high-concentration probiotic preparation, and the serum levels of indoxyl sulfate and p-cresyl sulfate were measured before treatment and at 4, 8, and 12 weeks after the regimen by using fluorescence liquid chromatography. To assess the normal range of indoxyl sulfate and p-cresyl sulfate we enrolled the 16 children with normal glomerular filtration rate who had visited an outpatient clinic for asymptomatic microscopic hematuria that had been detected by a school screening in August 2011.

Results

The baseline serum levels of indoxyl sulfate and p-cresyl sulfate in the patients on chronic dialysis were significantly higher than those in the children with microscopic hematuria. The baseline serum levels of p-cresyl sulfate in the peritoneal dialysis group were significantly higher than those in the hemodialysis group. There were no significant changes in the levels of these uremic solutes after 12-week VSL#3 treatment in the patients on chronic dialysis.

Conclusion

The levels of the uremic toxins p-cresyl sulfate and indoxyl sulfate are highly elevated in pediatric patients on dialysis, but there was no significant effect by probiotics on the reduction of uremic toxins in pediatric dialysis patients. Therefore, studies for other medical intervention to reduce uremic toxins are also necessary in pediatric patients on dialysis.

Is residual renal function and better phosphate control in peritoneal dialysis an answer for the lower prevalence of valve calcification compared to hemodialysis patients?

INTRODUCTION

Cardiac valve calcification (CVC) has long been regarded as a consequence of abnormal calcium-phosphate metabolism in uremic patient associated with increased cardiovascular mortality in this population. We evaluated the association between residual renal function (RRF), phosphate level and valve calcification in peritoneal dialysis (PD) and hemodialysis (HD) patients.

METHODS

We studied 30 stable PD patients (60 % males; mean age 57 ± 12.36 years) and 34 HD patients (58.8 % males; mean age 50.8 ± 10.4 years) on renal replacement therapy (RRT) from 6 up to 36 months. The presence of CVC was assessed by standard bi-dimensional echocardiography. RRF was calculated by standard technique.

RESULTS

Valve calcification was more frequently found in HD compared to PD patients (70.6 vs 29.4 %, p = 0.007). Significantly lower phosphate [1.38 ± 0.41 versus 1.99 ± 0.35 mmol/L (p < 0.0001)], a higher RRF [4.09 ± 2.09 ml/min vs 0.62 ± 0.89 ml/min (p < 0.0001)], and older age [57 ± 12.36 years vs 50.8 ± 10.4 years (p = 0.033)] were observed in PD as compared to HD patients. The logistic regression analysis for the presence of valve calcification when adjusted for age and diabetes, with type of therapy, serum phosphate, RRF, CRP, and serum albumin as variables in the model, revealed significant association between the presence of valve calcification and age and RRF. The correlation between phosphate levels and RRF was even stronger in PD patients than in HD patients (r = -0.704; p = 0.0001) vs (r = -0.502; p = 0.02).

CONCLUSIONS

Our study shows that the residual renal function in PD patients contributes significantly to the maintenance of phosphate balance and may explain the lower prevalence of valve calcification in PD patients compared with HD patients in the period up to first 3 years under renal replacement therapy.

Nutrition and the kidney: recommendations for peritoneal dialysis

Protein energy wasting (PEW) is highly prevalent in peritoneal dialysis (PD) and is associated with poor outcomes, including hospitalization and mortality. Recognizing and diagnosing PEW in PD is important; although studies are limited, there are interventions that may be associated with improved outcomes. In this review of nutritional aspects of PD, we highlight some of the important causes of PEW and explore the current diagnostic tools that are used to assess PEW. Finally, we discuss the established and experimental therapies for PEW in PD.

High correlation between clearance of renal protein-bound uremic toxins (indoxyl sulfate and p-cresyl sulfate) and renal water-soluble toxins in peritoneal dialysis patients

Peritoneal dialysis (PD) is characterized by a slow continuous removal of solutes. Traditionally, dialysis adequacy is quantified by referring to the kinetics of urea nitrogen (UN) and creatinine (Cr) clearance. The efficacy of middle molecular substances and protein-bound solutes as markers for peritoneal dialysis adequacy is not clear. The aim of this cross-sectional study was to investigate correlations between the clearance of indoxyl sulfate (IS), p-cresyl sulfate (PCS), UN, and Cr in the peritoneum and kidneys and to compare the overall clearances of IS and PCS between non-anuric and anuric groups in PD patients. We recruited a total of 175 patients who had been undergoing continuous ambulatory PD (CAPD) or automated PD (APD) for at least 4 months. We measured total IS and PCS concentrations in serum, dialysate, and urine samples. Free IS and PCS concentrations were measured in all serum samples. IS and PCS clearances via both kidney and peritoneum were measured. The mean concentration of IS in the urine samples was 9.2-fold higher than that in the dialysate samples, and concentration of PCS in the urine samples was 8.5-fold higher than that in the dialysate samples. Peritoneal UN and Cr clearances were not correlated with peritoneal PCS clearance (P > 0.05) but were mildly correlated with peritoneal IS clearance. The peritoneal IS and PCS clearances in the different peritoneal equilibration test groups were similar. The renal UN and Cr clearances were strongly correlated with renal PCS and IS clearances (P > 0.89, P < 0.001). In addition, non-anuric patients showed better elimination of total PCS (10.3 mg/day [range, 1.6-19.8] vs. 5.2 mg/day [range, 0-14]; P < 0.001] and IS (37.9 mg/day [range, 25.6-56.7] vs. 24.8 mg/day [range, 17.1-41.6]; P < 0.001) than anuric patients. This cross-sectional study showed that peritoneal clearance of water-soluble solutes is not correlated with that of PCS but is mildly correlated with that of IS. However, the renal clearances of IS and PCS show strong positive correlation with the renal clearances of UN and Cr. This study confirms the important role of residual renal function in the removal of protein-bound uremic toxins.

Nutrition in patients on peritoneal dialysis

Protein-energy wasting (PEW) is prevalent among patients on dialysis and has emerged as an important risk factor for morbidity and mortality in these patients. Numerous factors, including inflammation, inadequate dialysis, insufficient nutrient intake, loss of protein during dialysis, chronic acidosis, hypercatabolic illness and comorbid conditions, are involved in the development of PEW. The causes and clinical features of PEW in patients on peritoneal dialysis and hemodialysis are comparable; assessment of the factors that lead to PEW in patients receiving peritoneal dialysis is important to ensure that PEW is managed correctly in these patients. For the past 20 years, much progress has been made in the prevention and treatment of PEW. However, the results of most nutritional intervention studies are inconclusive. In addition, the multifactorial and complicated pathogenesis of PEW makes it difficult to assess and treat. This Review summarizes the nutritional issues regarding the causes, assessment and treatment of PEW, with a focus on patients receiving peritoneal dialysis. In addition, an in-depth overview of the results of nutritional intervention studies is provided.

Residual renal function is an independent determinant of serum FGF-23 levels in dialysis patients

BACKGROUND

Both poor residual renal function (RRF) and high fibroblast growth factor 23 (FGF-23) levels are associated with arterial stiffness, left ventricular hypertrophy and increased (cardiovascular) mortality. Whether FGF-23 and RRF are interrelated is unknown.

METHODS

We performed a prospective observational cohort study in 35 peritoneal dialysis (PD) patients with evaluation at 1, 6, 12 and 24 months after start of PD. In addition, the role of RRF was assessed in a cross-sectional observational cohort study including 68 prevalent haemodialysis patients.

RESULTS

RRF significantly declined over time in PD patients. This decline was parallelled by a significant increase of both serum phosphorus and FGF-23 levels. In the prevalent dialysis cohort, RRF was found to be inversely associated with serum FGF-23 levels, independent of dialysis vintage, dialytic creatinine clearance, estimates of dietary phosphate intake (i.e. normalized protein nitrogen appearance), active vitamin D therapy and serum phosphorus and calcium levels. RRF, serum phosphorus and calcium levels and active vitamin D therapy explain 69% of the variation in FGF-23. The 38 anuric patients had higher FGF-23 levels but similar serum phosphorus levels.

CONCLUSIONS

We demonstrate an important association between RRF and FGF-23, independent of classical determinants. This favours the hypothesis that the ailing kidney directly contributes to the raised FGF-23 levels. Whether FGF-23 is associated with poor outcomes independent of RRF, or vice versa, remains to be clarified.

p-Cresylsulfate and indoxyl sulfate level at different stages of chronic kidney disease

Indoxyl sulfate and p-cresylsulfate was associated with poor clinical outcome of uremia. We explored the relationship between the two toxins and renal function in chronic kidney disease (CKD) patients. This study enrolled 103 stable CKD patients (stage 3-5 and hemodialysis (HD) patients). Serum levels of indoxyl sulfate and p-cresylsulfate were measured using ultra performance liquid chromatography. General laboratory results and patient background were also checked. Patients with advanced CKD had higher serum indoxyl sulfate, p-cresylsulfate based on ANOVA test. There were significant correlation between indoxyl sulfate and p-cresylsulfate and serum creatinine after multivariate regression analysis (B=3.59, P<0.01; B=0.93, P=0.04, respectively). In addition, there was a positive correlation between indoxyl sulfate and p-cresylsulfate level (r=0.61, P<0.01). Indoxyl sulfate and p-cresylsulfate level increased gradually while renal function declined and reached the peak at the stage of HD. Serum indoxyl sulfate level was closely associated with p-cresylsulfate level in CKD patients.

Urea and uremic solutes: how does peritoneal dialysis work?

The transport of urea and other solutes across the peritoneal membrane follows the general dialytic principles of diffusion and convection. Nevertheless, the unique anatomic configuration of the peritoneum suggests that specific modeling is needed to explain solute kinetics in peritoneal dialysis. The historical two-pore model of membrane transport had to be adjusted by adding a third pore, and the distributed model has further complemented this analysis. Recent findings with regard to the endothelial glycocalyx add an additional level of complexity. Unfortunately, most studies to date use only urea, glucose, and creatinine kinetics to describe transport during peritoneal dialysis and adequacy of solute removal. Studies of transport of other classes of uremic solutes are scanty but allow us to gain insight into how peritoneal dialysis works.

2009 Japanese Society for Dialysis Therapy guidelines for peritoneal dialysis

The guidelines for peritoneal dialysis (PD) of the Japanese Society for Dialysis Treatment were prepared at 2009. Upon presenting a concrete frame of PD practiced in Japan, it aims to promote PD as a standardized therapy in Japan. Notably, the guidelines recommended combination therapy of PD and hemodialysis as a part of integrated renal replacement therapy for end-stage renal disease, as well as timely PD withdrawal by peritoneal degeneration in order to prevent progression of encapsulating peritoneal sclerosis.

Contribution of residual function to removal of protein-bound solutes in hemodialysis

BACKGROUND AND OBJECTIVES

This study evaluated the contribution of residual function to the removal of solutes for which protein binding limits clearance by hemdialysis.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Solute concentrations were measured in 25 hemodialysis patients with residual urea clearances ranging from 0.1 to 6.2 ml/min per 1.73 m2. Mathematical modeling assessed the effect of residual function on time-averaged solute concentrations.

RESULTS

Dialytic clearances of the protein-bound solutes p-cresol sulfate, indoxyl sulfate, and hippurate were reduced in proportion to the avidity of binding and averaged 8±2, 10±3, and 44±13% of the dialytic urea clearance. For each bound solute, the residual clearance was larger in relation to the residual urea clearance. Residual kidney function therefore removed a larger portion of each of the bound solutes than of urea. Increasing residual function was associated with lower plasma levels of p-cresol sulfate and hippurate but not indoxyl sulfate. Wide variation in solute generation tended to obscure the dependence of plasma solute levels on residual function. Mathematical modeling that corrected for this variation indicated that increasing residual function will reduce the plasma level of each of the bound solutes more than the plasma level of urea.

CONCLUSIONS

In comparison to urea, solutes than bind to plasma proteins can be more effectively cleared by residual function than by hemodialysis. Levels of such solutes will be lower in patients with residual function than in patients without residual function even if the dialysis dose is reduced based on measurement of residual urea clearance in accord with current guidelines.

Serum protein-bound uraemic toxins and clinical outcomes in haemodialysis patients

BACKGROUND

The protein-bound uraemic toxin p-cresol is associated with immunodeficiency in haemodialysis (HD) patients. We investigated the effect of serum p-cresol, indoxyl sulphate and other variables on clinical outcomes in HD patients during a 20-month follow-up.

METHODS

We enrolled 100 stable HD patients from a single medical centre. The primary outcomes were infection-related hospitalization, cardiovascular events and all-cause mortality. Serum total and free p-cresol and indoxyl sulphate levels were measured using ultra-performance liquid chromatography. Biochemical data were collected concurrently.

RESULTS

Multivariate logistic regression analysis revealed that infection-related hospitalization correlated with free p-cresol (adjusted odds ratio: 1.70, P = 0.01) and highly sensitive C-reactive protein (hsCRP) (adjusted odds ratio: 2.07, P = 0.01); cardiovascular event was associated with free p-cresol (adjusted odds ratio: 1.78, P = 0.01) and nPCR (adjusted odds ratio: 0.01, P = 0.02); and all-cause mortality was related to albumin (adjusted odds ratio: 0.04, P = 0.01). The Kaplan-Meier method showed that free and total p-cresol were significantly associated with cardiovascular events (log-rank P < 0.01 and log-rank P < 0.01, respectively). Serum free p-cresol seemed to have a trend to correlate with infection-related hospitalization during a 20-month follow-up (log-rank P = 0.05).

CONCLUSIONS

Serum free and total p-cresol levels were significantly related to cardiovascular events. In addition, serum free p-cresol and hsCRP levels were also found to be associated with infection-related hospitalization.

Factors associated with blood concentrations of indoxyl sulfate and p-cresol in patients undergoing peritoneal dialysis

BACKGROUND

Accumulating evidence supports the important role of protein-bound uremic toxins such as indoxyl sulfate and p-cresol in uremic syndrome. They exert direct deleterious effects on a variety of cells and could link to clinical outcome. Factors relevant to indoxyl sulfate and p-cresol levels in peritoneal dialysis (PD) patients have rarely been investigated. We conducted a cross-sectional study to analyze the factors that correlate with both total and free indoxyl sulfate and p-cresol.

METHODS

182 stable PD patients with mean PD therapy duration 38.5 +/- 33.3 months were enrolled. Their mean age was 48.9 +/- 13.5 years; 62.6% (114/182) were female patients. Demographic data, including age, gender, and PD therapy duration, were reviewed and recorded. PD-associated features such as residual kidney function (RKF), peritoneal transport property, and dialysis modality were also recorded. Hemoglobin, blood urea nitrogen (BUN), serum creatinine, C-reactive protein, interleukin (IL)-6, and IL-10 were measured. Levels of total and free indoxyl sulfate and p-cresol were determined.

RESULTS

Patients without RKF had lower Kt/V and weekly creatinine clearance and higher serum creatinine and IL-6 levels. These patients also had higher total and free indoxyl sulfate levels. There was no difference in indoxyl sulfate or p-cresol levels compared to patients with different peritoneal transport properties or with different treatment modalities. Multivariate regression analysis revealed that weekly creatinine clearance and serum creatinine were independent associates of total indoxyl sulfate level; IL-6, total indoxyl sulfate, and free p-cresol were associated with free indoxyl sulfate level. Weekly creatinine clearance and free p-cresol level independently correlated with total p-cresol; while gender, total p-cresol, and free indoxyl sulfate were associated with free p-cresol level.

CONCLUSION

The free forms of indoxyl sulfate and p-cresol constituted a small portion of their total forms. The presence of RKF affected levels of free and total indoxyl sulfate. IL-6 level was significantly associated with free indoxyl sulfate level. There was a close relationship between indoxyl sulfate and p-cresol levels in their free forms in PD patients.

Nonzero Finite Wall Resistance Solution With Constant Dialyzate for Various Mass Transfer Quantities

This article deals with the theoretical investigations into dialytic mass transfer in parallel-plate hemodialyzers. The theoretical solutions presented are closed-form analytical solutions involving only exponential and algebraic polynomial functions, and are simple, economical, and convenient to use. With the help of Laplace transforms and the Galerkin method, the expressions for mixed mean concentration, local fluid-wall Sherwood number, logarithmic fluid-wall Sherwood number, local fluid Sherwood number, logarithmic fluid Sherwood number, clearance, and local concentration have been obtained. Data obtained in the present contribution are compared with earlier results and are found to be in the excellent agreement. Two solutes, urea and vitamin B12, were considered. It is observed from the above-mentioned comparison that the effect of variable dialyzate concentration on various mass transfer quantities is significant in the case of uremic small molecules. In the case of uremic middle molecules, the nonuniform concentration distribution in the dialyzate channel is only slightly affected.

Difficulty in improving malnutrition and low-grade inflammation in diabetic patients on peritoneal dialysis

Continuous ambulatory peritoneal dialysis (CAPD) is commonly used for renal replacement therapy in diabetes mellitus (DM) patients. We investigated the changes of peritoneal transport characteristics, nutritional status, and adequacy and inflammation parameters in diabetic CAPD patients (N = 17) compared to non-diabetic patients (N = 23). Peritoneal equilibrium testing, nutritional, biochemical, and anthropometric parameters and adequacy were prospectively assessed at 1 (baseline), 6 and 12 months after initiating CAPD. The levels of several nutritional parameters were lower and did not change in DM patients over time (P < 0.05) and significantly improved in the non-DM patients over time (P < 0.05). Total weekly creatinine clearance and residual renal function exhibited a rapid decline (P < 0.05) and inflammation parameter levels were higher in DM patients (P < 0.05). Our results showed the difficulty in improvement of nutritional status and inflammatory parameters in diabetic patients during at least the first year of CAPD compared to non-DM patients.