Immunohistochemical detection of advanced glycosylation end-products in the peritoneum and its possible pathophysiological role in CAPD

Care of the pediatric patient on chronic peritoneal dialysis

Peritoneal dialysis is the most commonly prescribed dialysis modality for infants and young children with kidney failure worldwide. Provision of high-quality care for the pediatric patient on chronic peritoneal dialysis requires a multidisciplinary approach and a strong collaboration with the patient and their caregiver. This article not only reviews current recommendations and advances in the care of pediatric patients on peritoneal dialysis with a focus on the provision of high-quality care and improvement in outcomes, but it also draws attention to health care disparities that exist locally and globally.

Effect of Dialysis Modalities on All-Cause Mortality and Cardiovascular Mortality in End-Stage Kidney Disease: A Taiwan Renal Registry Data System (TWRDS) 2005-2012 Study

Introduction: End-stage kidney disease (ESKD) patients who need renal replacement therapy need to face a dialysis modality decision: the choice between hemodialysis (HD) and peritoneal dialysis (PD). Although the global differences in HD/PD penetration are affected by health-care policies, these two modalities may exert different effects on survival in patients with ESKD. Although Taiwan did not implicate PD as first policy, we still need to compare patients’ outcomes using two modalities in a nation-wise database to determine future patients’ care and health policies. Methods: We used the nationwide Taiwan Renal Registry Data System (TWRDS) database from 2005 to 2012 and included 52,900 patients (48,371 on HD and 4529 on PD) to determine all-cause and cardiovascular mortality among ESKD patients. Results: Age-matched survival probability from all-cause mortality was significantly lower in patients on PD than in those on HD (p < 0.05). The adjusted hazard ratios of 3-year and 5-year all-cause and cardiovascular mortality were significantly higher in PD compared with HD. The presence of comorbid conditions including myocardial infarction, coronary artery disease (CAD), diabetes mellitus (DM), hypoalbuminemia, hyperferritinemia and hypophosphatemia was related with significantly higher all-cause and CV mortality in PD patients. No significant difference was noted among younger patients <45 years of age regardless of DM and/or comorbid conditions. Conclusion: Although PD did not have the survival advantage compared to HD in all dialysis populations, PD was related with superior survival in younger non-DM patients, regardless of the presence of comorbidities. Similarly, for younger ESKD patients without the risk of CV disease, both PD and HD would be suitable dialysis modalities.

Dialysis Duration and Glucose Exposure Amount Do Not Increase Mortality Risk in Peritoneal Dialysis Patients: A Population-Based Cohort Study From 2004 to 2012

Background

Although the bio-incompatibility of glucose-based peritoneal dialysis (PD) solution is well documented, it is used worldwide. How PD duration and the amount of dialyzate glucose exposure affect survival in patients with end-stage renal disease remain inconclusive due to improper study designs in the extant literature.

Methods

All incident patients with PD from 2004 to 2007 who were older than 18 years in Taiwan were included. Patients were censored when they received a transplant or at the end of 2012. Glucose exposure through PD solution was calculated by the mean glucose contained per liter when receiving PD. For those who had already shifted to hemodialysis (HD) and survived longer than 2, 3, and 4 years (the index dates), the cause-specific Cox regression model was used to make the survival comparison by PD duration and mean glucose concentration in these three cohorts, respectively. The model was adjusted by demographics, case-mix, time cohort (2004–2005 vs. 2006–2007), peritonitis episode (none vs. ≥once), and mean PD solution glucose exposure (tertile).

Results

A total of 3,226 patients were included, with a mean age of 53.4 ± 15.2 years, 44.6% being male, and 34.2% having diabetes mellitus. The 1, 2, 3, and 4-year survival rates were 94, 87, 80, and 74%, while technical survival rates were 86, 70, 56, and 45%, respectively. The overall transplant events were 309 (9.6%) only. There were 389, 495, and 553 incident patients with PD shifting to HD included in 2-, 3-, and 4-year cohort, respectively. The population with moderate glucose concentration exposure had the highest mortality, and the high glucose concentration exposure had non-significant lower mortality in each cohort. In various fixed time-window cohorts, the duration of PD treatment did not increase mortality risk after adjustments. In addition, glucose exposure did not affect the mortality rate.

Conclusion

For incident PD patients with PD duration no longer than 4 years, neither PD duration nor glucose exposure amount increases the long-term mortality risk.

Quantification of Degradation Products Formed during Heat Sterilization of Glucose Solutions by LC-MS/MS: Impact of Autoclaving Temperature and Duration on Degradation

Heat sterilization of glucose solutions can lead to the formation of various glucose degradation products (GDPs) due to oxidation, hydrolysis, and dehydration. GDPs can have toxic effects after parenteral administration due to their high reactivity. In this study, the application of the F0 concept to modify specific time/temperature models during heat sterilization and their influence on the formation of GDPs in parenteral glucose solutions was investigated using high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS). Glucose solutions (10%, w/v) were autoclaved at 111 °C, 116 °C, and 121 °C for different durations. The GDPs glyoxal, methylglyoxal, glucosone, 3-deoxyglucosone/3-deoxygalactosone, 3,4-dideoxyglucosone-3-ene, and 5-hydroxymethylfurfural were quantified after derivatization with o-phenylenediamine by an optimized LC-MS/MS method. For all GDPs, the limit of detection was <0.078 μg/mL, and the limit of quantification was <0.236 μg/mL. The autoclaving time of 121 °C and 15 min resulted in the lowest levels of 3-DG/3-DGal and 5-HMF, but in the highest levels of GO and 2-KDG. The proposed LC-MS/MS method is rapid and sensitive. So far, only 5-HMF concentrations are limited by the regulatory authorities. Our results suggest reconsidering the impurity limits of various GDPs, especially the more toxic ones such as GO and MGO, by the Pharmacopoeias.

Identification and quantification of glucose degradation products in heat-sterilized glucose solutions for parenteral use by thin-layer chromatography

During heat sterilization of glucose solutions, a variety of glucose degradation products (GDPs) may be formed. GDPs can cause cytotoxic effects after parenteral administration of these solutions. The aim of the current study therefore was to develop a simple and quick high-performance thin-layer chromatography (HPTLC) method by which the major GDPs can be identified and (summarily) quantified in glucose solutions for parenteral administration. All GDPs were derivatized with o-phenylenediamine (OPD). The resulting GDP derivatives (quinoxalines) were applied to an HPTLC plate. After 20 minutes of chamber saturation with the solvent, the HPTLC plate was developed in a mixture of 1,4-dioxane-toluene-glacial acetic acid (49:49:2, v/v/v), treated with thymol-sulfuric acid spray reagent, and heated at 130°C for 10 minutes. Finally, the GDPs were quantified by using a TLC scanner. For validation, the identities of the quinoxaline derivatives were confirmed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Glyoxal (GO)/methylglyoxal (MGO) and 3-deoxyglucosone (3-DG)/3-deoxygalactosone (3-DGal) could be identified and quantified in pairs, glucosone (2-KDG), 5-hydroxymethylfurfural (5-HMF), and 3,4-dideoxyglucosone-3-ene (3,4-DGE) each individually. For 2-KDG, the linearity of the method was demonstrated in the range of 1–50 μg/mL, for 5-HMF and 3,4-DGE 1–75 μg/mL, for GO/MGO 2–150 μg/mL, and for 3-DG/3-DGal 10–150 μg/mL. All GDPs achieved a limit of detection (LOD) of 2 μg/mL or less and a limit of quantification (LOQ) of 10 μg/mL or less. R² was 0.982 for 3.4-DGE, 0.997 for 5-HMF, and 0.999 for 2-KDG, 3-DG/3-DGal, and GO/MGO. The intraday precision was between 0.4 and 14.2% and the accuracy, reported as % recovery, between 86.4 and 112.7%. The proposed HPTLC method appears to be an inexpensive, fast, and sufficiently sensitive approach for routine quantitative analysis of GDPs in heat-sterilized glucose solutions.

Low-GDP, pH-neutral solutions preserve peritoneal endothelial glycocalyx during long-term peritoneal dialysis

BACKGROUND

During peritoneal dialysis (PD), solute transport and ultrafiltration are mainly achieved by the peritoneal blood vasculature. Glycocalyx lies on the surface of endothelial cells and plays a role in vascular permeability. Low-glucose degradation product (GDP), pH-neutral PD solutions reportedly offer higher biocompatibility and lead to less peritoneal injury. However, the effects on the vasculature have not been clarified.

METHODS

Peritoneal tissues from 11 patients treated with conventional acidic solutions (acidic group) and 11 patients treated with low-GDP, pH-neutral solutions (neutral group) were examined. Control tissues were acquired from 5 healthy donors of kidney transplants (control group). CD31 and ratio of luminal diameter to vessel diameter (L/V ratio) were evaluated to identify endothelial cells and vasculopathy, respectively. Immunostaining for heparan sulfate (HS) domains and Ulex europaeus agglutinin-1 (UEA-1) binding was performed to assess sulfated glycosaminoglycans and the fucose-containing sugar chain of glycocalyx.

RESULTS

Compared with the acidic group, the neutral group showed higher CD31 positivity. L/V ratio was significantly higher in the neutral group, suggesting less progression of vasculopathy. Both HS expression and UEA-1 binding were higher in the neutral group, whereas HS expression was markedly more preserved than UEA-1 binding in the acidic group. In vessels with low L/V ratio, which were found only in the acidic group, HS expression and UEA-1 binding were diminished, suggesting a loss of glycocalyx.

CONCLUSION

Peritoneal endothelial glycocalyx was more preserved in patients treated with low-GDP, pH-neutral solution. The use of low-GDP, pH-neutral solutions could help to protect peritoneal vascular structures and functions.

Advanced glycation end products are associated with immature angiogenesis and peritoneal dysfunction in patients on peritoneal dialysis

BACKGROUND

Deposition of advanced glycation end products (AGEs) is frequently found in the peritoneum of patients on peritoneal dialysis (PD). Angiogenesis is also observed in the peritoneum. However, the clinical significance of AGEs and angiogenesis in the peritoneum is not fully understood. We evaluated the maturation of capillary vessels and investigated whether AGEs are associated with angiogenesis and peritoneal function in the peritoneal membrane.

METHODS

Peritoneum obtained when PD catheters were removed from 61 patients with PD was analyzed. The peritoneum was immunohistochemically stained with anti-CD34 (for endothelial cells), anti-alpha smooth muscle actin (αSMA) (for pericytes), and anti-AGE antibodies. We defined CD34-positive and αSMA-negative vessels as immature capillary vessels in peritoneal membranes using serial sections. We evaluated the associations between vessel density, peritoneal function (dialysate-to-plasma ratio for creatinine (D/P creatinine)), and the degree of AGE deposition.

RESULTS

AGE accumulation in the interstitium was positively associated with the duration of PD (p < 0.01). AGE accumulation in the interstitium and vascular wall was positively correlated with the use of acidic solution (p < 0.05) and the maximum value of D/P creatinine (p < 0.05). AGE accumulation in the vascular wall was significantly associated with immature capillary density (CD34+/αSMA-) in the peritoneum (p < 0.01). Vessel density was not significantly correlated with the last measurement of D/P creatinine (p = 0.126, r = 0.202), However, immature capillary density was positively correlated with the last measurement of D/P creatinine (p < 0.05, r = 0.278).

CONCLUSIONS

AGE accumulation is significantly associated with immature angiogenesis and peritoneal dysfunction in patients undergoing PD.

Metal cations promote α-dicarbonyl formation in glucose-containing peritoneal dialysis fluids

Heat sterilization of peritoneal dialysis fluids (PDFs) leads to the formation of glucose degradation products (GDPs), which impair long-term peritoneal dialysis. The current study investigated the effects of metal ions, which occur as trace impurities in the fluids, on the formation of six major α-dicarbonyl GDPs, namely glucosone, glyoxal, methylglyoxal, 3-deoxyglucosone, 3-deoxygalactosone, and 3,4-dideoxyglucosone-3-ene. The chelation of metal ions by 2-[bis[2-[bis(carboxymethyl)amino]ethyl]amino]acetic acid (DTPA) during sterilization significantly decreased the total GDP content (585 μM vs. 672 μM), mainly due to the decrease of the glucose-oxidation products glucosone (14 μM vs. 61 μM) and glyoxal (3 μM vs. 11 μM), but also of methylglyoxal (14 μM vs. 31 μM). The glucose-dehydration products 3-deoxyglucosone, 3-deoxygalactosone, and 3,4-dideoxyglucosone-3-ene were not significantly affected by chelation of metal ions. Additionally, PDFs were spiked with eleven different metal ions, which were detected as traces in commercial PDFs, to investigate their influence on GDP formation during heat sterilization. Iron(II), manganese(II), and chromium(III) had the highest impact increasing the formation of glucosone (1.2–1.5 fold increase) and glyoxal (1.3–1.5 fold increase). Nickel(II) and vanadium(III) further promoted the formation of glyoxal (1.3 fold increase). The increase of the pH value of the PDFs from pH 5.5 to a physiological pH of 7.5 resulted in a decreased formation of total GDPs (672 μM vs 637 μM). These results indicate that the adjustment of metal ions and the pH value may be a strategy to further decrease the content of GDPs in PDFs.

Mediators of Inflammation and Fibrosis

During peritoneal dialysis, peritoneal cells are repeatedly exposed to a non-physiologic hypertonic environment with high glucose content and low pH. Current sterile dialysis solutions cause inflammation in the submesothelial compact zone, leading to fibrosis, angiogenesis, and, eventually, ultrafiltration failure. Although the normal interstitium separates the peritoneal microvasculature from the dialysis fluid and makes transperitoneal transport less efficient, changes in the submesothelial compact zone can result in progressive increases in solute transfer and ultrafiltration diminution. This peritoneal dysfunction will further be amplified with the development of an epithelial-to-mesenchymal transition of mesothelial cells and dissipation of the osmotic driving force through the increased area and solute transport that accompany neoangiogenesis of the submesothelial microvasculature. The alteration of the peritoneal membrane can be further aggravated by peritonitis, advanced glycation end-products, and glucose degradation products. Furthermore, new data are emerging to support a proinflammatory role for peritoneal adipocytes.

Encapsulating Peritoneal Sclerosis in Japan

Encapsulating peritoneal sclerosis (EPS), the most serious and classical complication of peritoneal dialysis (PD), was recognized soon after the introduction of PD. Within a little more than a decade after PD was first introduced in Japan, the country began experiencing an increasing number of EPS cases. The present paper discusses the clinical stages of EPS, the incidence of EPS in Japan and the as-yet incompletely understood mechanisms of its development, and EPS management and prevention.

Comparison of Longitudinal Membrane Function in Peritoneal Dialysis Patients According to Dialysis Fluid Biocompatibility

Introduction

Preservation of peritoneal function is essential in long-term peritoneal dialysis. Biocompatible dialysis solutions might prevent or postpone the membrane alteration resulting in ultrafiltration failure and consecutive morbidity and mortality.

Methods

We conducted an observational cohort study in which we made a longitudinal comparison between the course of peritoneal solute and fluid transport during treatment with conventional and biocompatible solutions. Therefore, prospectively collected peritoneal transport data from the yearly standard peritoneal permeability analysis were analyzed in 251 incident patients treated between 1994 and censoring in 2016. Fluid transport included small pore and free water transport. Solute transport was assessed by creatinine mass transfer area coefficient and glucose absorption. Linear mixed models including change point analyses were performed. Interaction with peritonitis was examined.

Results

One hundred thirty-five patients received conventional and 116 biocompatible solutions. Sixty-seven percent (conventional) and 64% (biocompatible) of these underwent minimally three transport measurements. Initially, biocompatible fluids showed higher small solute transport and lower ultrafiltration than conventional fluids up to 3 years. Thereafter, conventional fluids showed an increase in small solute transport (+2.7 ml/min per year; 95% confidence interval [CI]: 0.9 to 4.5) and a decrease of free water transport (−28.0 ml/min per year; 95% CI: −60.4 to 4.4). These were minor or absent in biocompatible treatment. Peritonitis induced a decrease of transcapillary ultrafiltration after 2 years on dialysis with conventional solutions (−291 ml/min per year; 95% CI: −550 to −32) while this was absent in biocompatible treatment.

Conclusion

Despite a higher initial solute transport with biocompatible solutions, these have less influence on functional long-term peritoneal alterations than conventional solutions.

Vasculopathy plays an important role during the development and relapse of encapsulating peritoneal sclerosis with conventional peritoneal dialysis solutions

Background

Encapsulating peritoneal sclerosis (EPS) is an uncommon but life-threatening complication of peritoneal dialysis (PD) therapy. The causative factors of EPS remain unclear. Pathological studies of the peritoneum affected by EPS and relationships with clinical factors including PD solutions remain lacking. The objective of this study was to examine peritoneal samples from EPS patients and to identify the associations of peritoneal pathology with different clinical factors.

Methods

Peritoneal specimens were obtained at the time of surgical enterolysis in Tsuchiya General Hospital from 1993 to 2016. A total of 223 PD patients were enrolled and analyzed. Tissues were fixed with formalin and processed with hematoxylin and eosin and Masson’s trichrome staining, as well as immunohistochemical staining for CD31 and CD68.

Results

Evaluations could be made in 174 patients who received surgical enterolysis. Conventional or pH-neutral low-glucose degradation product PD solutions were utilized during PD treatment. The conventional PD solution group showed less angiogenesis (P = 0.013) but more severe vasculopathy, in the form of a lower ratio of luminal diameter to vessel diameter (L/V ratio) (P &lt; 0.001) in association with longer PD treatment. Multivariate Cox proportional hazard models revealed that L/V ratio (per 0.1 increase, hazard ratio = 0.88, 95% confidence interval 0.77–0.99, P = 0.047) was significantly associated with a lower incidence of EPS relapse. In contrast, most of the cases in the pH-neutral solution group showed milder vasculopathy.

Conclusions

The pathology of EPS differed between conventional and pH-neutral solution groups. Vasculopathy was related to the development and relapse of EPS in the conventional solution group.

Multicenter laparoscopic evaluation of the peritoneum in peritoneal dialysis patients

Laparoscopic findings have been used to confirm peritoneal degenerations in peritoneal dialysis (PD) therapy. This study evaluated morphological changes in the peritoneum and their clinical relevance in patients undergoing PD. Laparoscopic findings at the rectovesical peritoneum were evaluated and scored using an imaging system at the time of PD catheter removal in this multicenter study. Angiogenesis evaluated by the vascular score (VS), color changes score (CCS), plaque score (PS), PD duration, history of peritonitis, dialysate/plasma creatinine (D/P Cr) levels, and age at PD termination were statistically analyzed. The VS of patients with PD duration more than 96 months was significantly decreased compared with that of the other patients and was negatively correlated with D/P Cr levels at PD termination. The CCS for patients with PD duration more than 96 months were significantly higher than those for the other patients and positively correlated with D/P Cr levels at PD termination. The PS of patients with recurring peritonitis were significantly higher than those of the other patients. Diminished vascularity and increased color changes in the peritoneum may be predictive of D/P Cr levels with peritoneal degradation. Laparoscopic evaluation of the abdominal cavity can provide detailed information about peritoneal injury.

The Effect of Advanced Glycation End-Products and Aminoguanidine on Tnfα Production by Rat Peritoneal Macrophages

Objective

To evaluate the effect of advanced glycation end-products (AGEs) and the inhibitor of their formation, aminoguanidine, on tumor necrosis factor-α (TNFα) production (as a functional marker) by rat peritoneal macrophages (PMΦ).

Design

Charles River rats underwent a daily intraperitoneal injection of peritoneal dialysis solution [(PDS), 4.25 g/dL dextrose; Dialine, Travenol, Ashdod, Israel] for a 2-month period (group E). Another group of rats was subjected to the same protocol with the addition of 25 mg/kg aminoguanidine (group A). Three control groups were utilized: ( 1 ) rats that were injected daily with aminoguanidine only (group AO), ( 2 ) rats that were injected with Dulbecco's phosphate-buffered saline (group D), and ( 3 ) rats in which no intervention was carried out (group C). After 2 months, PMΦ were isolated from rat peritoneal effluent and their TNFα production measured by ELISA in cell-free culture supernatants, in both the basal state and after 24-hour stimulation with lipopolysaccharide (LPS). The concentrations of AGEs in peritoneal effluent were assayed and correlated to TNFα levels. PMΦ obtained from normal rats were then incubated for 24 hours with ( 1 ) the peritoneal effluent of each of the above respective groups, with or without LPS; ( 2 ) increasing concentrations of AGEs (0 - 250 μg/mL); and ( 3 ) increasing concentrations of aminoguanidine (0 - 7.5 mg/mL), and TNFα secretion again determined.

Results

After 2 months of daily intraperitoneal injection of PDS, in the basal state, TNFα production was significantly higher in PMΦ isolated from the peritoneal effluent groups (groups E, A, and AO) compared to controls (group C). Following LPS stimulation, a further increase in TNFα secretion was seen, with a significantly greater response in group AO versus groups E, A, and D. Effluent AGEs were markedly elevated only in group E. No correlation was found between TNFα secretion by these PMΦ and the concentration of AGEs. On incubation with the respective peritoneal effluents (groups E, A, and AO), in both the basal and stimulated state, TNFα production by PMΦ from normal rats was significantly enhanced compared to group C. Incubation with increasing concentrations of AGEs or aminoguanidine resulted in an increase of TNFα secretion by these PMΦ.

Conclusions

Following intermittent intraperitoneal administration of glucose-based PDS, rat PMΦ are chronically activated, as evidenced by increased basal TNFα secretion. The peritoneal effluent of such treated animals is capable of stimulating TNFα production by normal rat PMΦ. These data suggest that glucose-based PDS acts as a primer of PMΦ, which retain their ability to further stimulation by LPS. Although, in vitro, AGEs promote TNFα secretion by normal rat PMΦ, in vivo, their influence is probably modulated by other factors. Aminoguanidine has a specific inducing effect on rat PMΦ, independent of glucose-based PDS.

Enhanced Expression of Heat Shock Protein 47 in Rat Model of Peritoneal Fibrosis

← Objective

Peritoneal fibrosis is one of the serious complications of continuous ambulatory peritoneal dialysis therapy and is characterized by collagen accumulation. Heat shock protein 47 (HSP-47) is a collagen-specific molecular chaperon and is closely associated with collagen synthesis; however, the involvement of HSP-47 in the progression of peritoneal fibrosis is not fully understood.

← Design

To examine the serial pathological alterations caused by peritoneal fibrosis, we made an experimental model of peritoneal fibrosis by daily intraperitoneal injection of chlorhexidine gluconate (CG) in rats for 28 days and examined the expression of HSP-47 together with that of types I and III collagen, alpha-smooth muscle actin (αSMA), and ED-1 (a marker for macrophages) using immunohistochemistry. Rats treated with saline containing 15% ethanol were used as the control group.

← Results

In the control group, the peritoneal tissue was slightly thickened and HSP-47 was expressed in the peritoneum at day 28. In the CG group, the peritoneal tissue serially became thickened and fibrotic. The expression of HSP-47 was evident in mesothelial cells and submesothelial connective tissue after day 7 of treatment with CG, and increased thereafter. The expression of types I and III collagen and αSMA was proportionally strengthened during our experiments. ED-1–positive cells were present in thickened areas with abundant proliferation of collagen fiber. The number of cells positive for ED-1 increased gradually and reached a maximum at day 21.

← Conclusion

Our results indicate that, in a rat experimental model of peritoneal fibrosis, the expression of HSP-47 is associated with the progression of peritoneal fibrosis.

Superior Patient Survival for Continuous Ambulatory Peritoneal Dialysis Patients Treated with a Peritoneal Dialysis Fluid with Neutral pH and Low Glucose Degradation Product Concentration (Balance)

Background

In recent years, laboratory and clinical research has suggested the need for peritoneal dialysis fluids (PDFs) that are more biocompatible than the conventional PDFs commonly used today. Bioincompatibility of PDF has been attributed to low pH, lactate, glucose, glucose degradation products (GDPs), and osmolality. PDFs with neutral pH and low GDPs are now available commercially. In vitro and early clinical studies suggest that these solutions are indeed more biocompatible but, as of now, there is no evidence that their use improves patient outcome.

Methods

Using a dedicated database of over 2000 patients treated with PD in Korea, we were able to conduct a retrospective observational study comparing outcomes for incident continuous ambulatory PD patients treated with a standard, conventional, heat-sterilized PDF to the outcomes for patients treated with a novel, low GDP, neutral-pH PDF prepared in a dual-compartment, double-bag PD system (Balance; Fresenius Medical Care, St. Wendel, Germany). In an intention-to-treat analysis, patient and technique survival, peritonitis-free survival, and peritonitis rates were compared in 611 patients treated with Balance for up to 30 months and 551 patients with a standard PDF (stay·safe; Fresenius Medical Care) treated in the same era and with equivalent follow-up.

Results

The patients were well matched for most relevant characteristics except older age distribution for the patients treated with the standard PDF. Patients treated with Balance had significantly superior survival compared to those treated with the standard PDF (74% vs 62% at 28 months, p = 0.0032). In a multivariate Cox regression model including age, diabetes, and gender, the survival advantage persisted (relative risk of death for Balance 0.75, 95% confidence interval 0.56 – 0.99, p = 0.0465). Modality technique survival was similar in Kaplan–Meier analysis for both PDFs. No differences were detected in peritonitis-free survival or in peritonitis rates between the two solutions.

Conclusion

This study, for the first time, suggests that treatment with a novel biocompatible PDF with low GDP concentration and neutral pH confers a significant survival advantage. The exact mechanisms for such a survival advantage cannot be determined from this study. The usual criticisms of observational studies apply and the results reported here strongly warrant the undertaking of appropriately designed, randomized, controlled clinical trials.

Vascular and Interstitial Changes in the Peritoneum of Capd Patients with Peritoneal Sclerosis

Objective

To analyze morphological changes in the peritoneum of peritoneal sclerosis (PS) patients. Emphasis was put on vascular abnormalities, because the continuous exposure to glucose-based dialysis solutions could cause diabetiform changes and because longitudinal transport studies suggested the development of a large peritoneal vascular surface area.

Design

Peritoneal biopsies from continuous ambulatory peritoneal dialysis (CAPD) patients were investigated in two studies. Diabetic patients were excluded. In study 1, 11 PS biopsies were compared to three control groups varying in duration of CAPD treatment: 0 months ( n = 15), 2 – 25 months ( n = 7), and > 25 months CAPD ( n = 7). The second study was a case-control study, comparing six biopsies from the long-term control group to six PS biopsies, matched for age and duration of CAPD. All biopsies were scored for presence and type of fibrosis [Picro Sirius red, type IV collagen, α-smooth muscle actin (αSMA)] and for neoangiogenesis (factor VIII). Thickening of vascular walls by type IV collagen and vasodilation of capillaries were measured by computer-aided planimetry.

Results

In study 1 the presence of sclerosing fibrosis, deposition of interstitial type IV collagen, and the number of myofibroblasts (αSMA-positive cells) was greater in the PS biopsies than biopsies from all control groups ( p < 0.002). Moreover, the number of vessels per field was higher in PS biopsies ( p < 0.01). Vascular wall thickening of small arteries ( p < 0.008) and vasodilation of capillaries were found in PS biopsies compared to all control groups ( p < 0.007). The second study revealed differences in the presence of sclerosis but not in the extent of fibrosis between PS biopsies and their controls. The number of vessels per field in PS biopsies was higher compared to controls ( p = 0.04). Also, thickening of the vascular wall was more marked in PS biopsies ( p = 0.03). Vasodilation of capillaries was greater in PS biopsies than in controls ( p = 0.07).

Conclusion

Fibrosis of the peritoneum may precede peritoneal sclerosis. The deposition of type IV collagen and the presence of myofibroblasts in the interstitial layer could be part of a pathologic process similar to the scarring in diabetic nephropathy. Neoangiogenesis and thickening of the vascular wall by type IV collagen are consistent with glucose-induced microangiopathy. These abnormalities and the vasodilation of the capillaries can explain the high dialysate-to-plasma ratios or mass transfer area coefficients of low molecular weight solutes that can be found in long-term CAPD patients.

Advanced Glycosylation End-Products in Diabetic Rats on Peritoneal Dialysis Using Various Solutions

Objective

To evaluate and compare the effects of glucose-based solutions to those of icodextrin with respect to peritoneal transport characteristics and advanced glycosylation end-product (AGE) formation in the peritoneal membrane in a diabetic rat model of peritoneal dialysis (PD).

Design

Thirty-three male Sprague–Dawley rats weighing between 275 – 300 g were divided into five groups: group C ( n = 6), control rats implanted with a catheter but not dialyzed; group D ( n = 5), diabetic rats implanted with a catheter but not dialyzed; group G ( n = 7), diabetic rats implanted with a catheter and dialyzed with standard 2.5% glucose solution for daytime exchanges and 4.25% glucose solution for overnight exchanges; group H ( n = 8), diabetic rats implanted with a catheter and dialyzed with standard 2.5% glucose solution for daytime exchanges and 7.5% icodextrin solution for overnight exchanges; group I ( n = 7), diabetic rats implanted with a catheter and dialyzed with 7.5% icodextrin solution for all exchanges. Dialysis exchanges (25 mL per exchange) were performed three times daily for a period of 12 weeks. Tissue sections were stained using a monoclonal anti-AGE antibody. One-hour peritoneal equilibration tests (PET) were performed every 4 weeks for comparison of transport characteristics.

Results

The level of immunostaining was lowest in group C and highest in group G. Significant differences in immunostaining were seen between group C and group G ( p < 0.001), group C and group H ( p = 0.001), and group C and group I ( p < 0.05). Significant differences were also found between group G and group D ( p < 0.05), and between group G and group I ( p < 0.05). Over time, the ratio of glucose concentration after 1 hour to glucose concentration at instillation (D/D0) decreased and the dialysate-to-plasma ratio (D/P) of urea increased. Significant differences in D/D0glucose and D/P urea were found between group C and group H (D/D0: 0.40 ± 0.01 vs 0.35 ± 0.01, p < 0.05; D/P urea: 0.87 ± 0.03 vs 0.97 ± 0.02, p < 0.05).

Conclusions

These results suggest that AGE formation is lower with the use of peritoneal dialysis solution containing icodextrin than with glucose-based solution. We conclude that use of icodextrin may help to slow the deterioration of the peritoneal membrane, prolonging its use for dialysis.

Effect of Duration of Chronic Peritoneal Dialysis Therapy on the Development of Peritonitis

Objective

Long-term chronic peritoneal dialysis (CPD) therapy has been associated with alterations in peritoneal membrane structure and peritoneal macrophage function. We thus reviewed our experience with the development of peritonitis among patients maintained on CPD therapy for various time periods to determine if the spectrum of organisms, rates of peritonitis, and outcome changed with the duration of CPD therapy.

Setting and Patients

Patients maintained on CPD therapy in our out-patient unit in New Haven, Connecticut.

Design

Retrospective review of the charts of patients maintained on CPD therapy (HomeChoice Cycler or Ultrabag, Baxter, McGaw Park, IL, U.S.A.) between 1 January 1997 and 31 March 1998. These patients were divided into three groups: group 1, patients maintained on CPD therapy < 12 months; group 2, patients maintained on CPD therapy for 13 - 36 months; and group 3, patients maintained on CPD therapy for ≥ 37 months.

Results

The study included 256 patients: 101 patients in group 1, 110 patients in group 2, and 45 patients in group 3. All groups of patients were similar in age. There were significantly fewer Caucasians and fewer males in group 3 in comparison to groups 1 and 2. The incidence of diabetes mellitus, coronary artery disease, and peripheral vascular disease was significantly lower among patients in group 3 in comparison to groups 1 and 2. There were 155 episodes of peritonitis during the study period for an overall rate of 1 episode in 18.7 patient-months. The overall, gram-positive, and gram-negative rates of peritonitis were not significantly different among the patients in groups 1, 2, and 3. There were more episodes of Staphylococcus aureus peritonitis among patients in group 3 in comparison to group 2 (1 episode in 59.6 vs 1 episode in 280.2 patient-months, respectively). Two weeks after the development of peritonitis, 94.6% of the patients in group 3 continued CPD therapy, while 79.4% of the patients in group 1 continued CPD therapy ( p < 0.05). No patient in group 3 transferred to hemodialysis, while 10.3% and 8.2% of the patients in groups 1 and 2 transferred to hemodialysis ( p < 0.05). The death rate 2 weeks after the onset of peritonitis was 10.3%, 9.8%, and 5.4% in groups 1, 2, and 3, respectively ( p = NS).

Conclusions

Despite the immunological and morphological changes that occur in the peritoneal cavity with increased time on CPD therapy, there was no difference in the overall, gram-positive, or gram-negative rates of peritonitis for patients maintained on CPD therapy for various time periods. Patients in group 3 continued CPD therapy more often than did patients in group 1. Patients in group 3 transferred to hemodialysis less often than did the remaining patients in the study period. The incidence of death was not significantly different for the three groups of patients.

Effect of Intraperitoneal Administration of Heparin on Advanced Glycation End-Products in Capd

Objective

To evaluate the effect of intraperitoneal (IP) administration of heparin on clearance of advanced glycation end-products (AGEs) and peritoneal dialysis efficiency.

Design

Sequential self-controlled intervention study.

Setting

University hospital, Department of Nephrology.

Patients and Methods

Pyrraline, urea, and creatinine levels in plasma and dialysate, along with AGE-derived fluorescence intensity (excitation, 370 nm; emission, 440 nm) in dialysate were measured 0, 30, and 60 days after IP administration of heparin in 11 patients on continuous ambulatory peritoneal dialysis (CAPD). Pyrraline levels were determined by ELISA.

Results

Heparin induced a significant decrease in plasma pyrraline levels; the values on days 0, 30, and 60 were 162.0 ± 89.8 μmol/L, 101.1 ± 32.1 mmol/L ( p < 0.01), and 94.0 ± 19.8 μmol/L ( p < 0.001), respectively. Heparin also induced a tendency of increased dialysate pyrraline levels and a significant increase in AGE-derived fluorescence intensity in the dialysate. The values for the latter on days 0, 30, and 60 were 51.0 ± 9.3 AU (arbitrary units/ mg of collagen), 73.5 ± 16.0 AU ( p < 0.001), and 65.6 ± 15.5 AU ( p < 0.01), respectively. Furthermore, heparin administration resulted in a significant ( p < 0.01) increase in the dialysate/plasma ratio of urea (means 0.80, 0.90, and 0.94 on days 0, 30, and 60, respectively).

Conclusion

These results suggest that a beneficial effect of IP administration of heparin is in part due to its action on AGE kinetics, supporting a potential preventive strategy for peritoneal membrane distortion in CAPD.

Early Glycated Albumin, but Not Advanced Glycated Albumin, Methylglyoxal, or 3-Deoxyglucosone Increases the Expression of Pai-1 in Human Peritoneal Mesothelial Cells

Objective

The continuous contact of glucose-containing peritoneal dialysis (PD) fluids with the peritoneum results in the intraperitoneal formation of early and advanced glycation end-products. This nonenzymatic glycation of proteins may cause morphological and functional alterations to the peritoneum, which may contribute to patient dropout from PD therapy. Because fibrinolytic system components have been demonstrated to play an important role in the balance of intraperitoneal generation and degradation of fibrin, we studied the effect of early and advanced glycated human serum albumin, methylglyoxal, and 3-deoxyglucosone on the synthesis of tissue-type plasminogen activator (tPA), as well as its specific inhibitor (PAI-1), in human peritoneal mesothelial cells (HPMC).

Methods

Antigen concentrations in the supernatants of cultured HPMC were measured by ELISA. Northern blot analysis was conducted for mRNA expression. Electrophoretic mobility shift assays were applied to demonstrate the involvement of the transcription factors nuclear factor kappa B (NF-κB) and activator protein-1 (AP-1) in signal transduction.

Results

Incubation of HPMC with early glycated albumin (GHSA) resulted in a time- and concentration-dependent increase in PAI-1 mRNA expression and antigen secretion. In contrast, no changes in PAI-1 synthesis occurred after stimulation with either the 1,2-dicarbonyl compounds methylglyoxal and 3-deoxyglucosone, or with late advanced glycation end-products. tPA synthesis was not affected by any of the tested components. Furthermore, HPMC exposed to GHSA induced NF-κB and AP-1 DNA binding activity, suggesting that GHSA-induced over-expression of PAI-1 is transcriptionally regulated by both transcription factors.

Conclusions

We conclude that Amadori modified glycated albumin upregulates PAI-1 synthesis in HPMC, possibly mediated through the activation of the transcription factors NF-κB and AP-1. The present data support the clinical relevance of the formation of glycated proteins and their involvement in pathological processes in PD patients. Thus, glycated albumin may contribute to an imbalance between intraperitoneal formation and degradation of fibrin that causes peritoneal structural alterations, with subsequent membrane failure.

The Plasma Leak–to–Response Hypothesis: A Working Hypothesis on the Pathogenesis of Encapsulating Peritoneal Sclerosis after Long-Term Peritoneal Dialysis Treatment

Encapsulating peritoneal sclerosis (EPS) is one of the most serious complications of long-term peritoneal dialysis (PD). Long-term PD therapy has been suggested as a risk factor for EPS development among patients in Japan and Australia. Although the primary mechanism of EPS development has not been clarified, histologic changes of the peritoneum associated with prolonged PD are postulated to be causally related. The present article proposes a working hypothesis—the plasma leak–to–response hypothesis—that vascular alterations in the peritoneum of long-term PD patients play a crucial role in the initiation and development of EPS.

Effects of Bicarbonate/Lactate Solution on Peritoneal Advanced Glycosylation End-Product Accumulation

Advanced glycosylation end-products (AGEs) are associated with diabetic complications and peritoneal damage after long-term peritoneal dialysis (PD) with high glucose dialysis solutions. Glucose degradation products (GDPs) derived during heat sterilization of high glucose dialysis solutions are thought to accelerate AGE formation. A new technique of separating glucose from electrolytes has yielded markedly lower GDP levels and permitted the use of dialysis solutions containing the physiologic buffer bicarbonate. Formation of AGEs in vitro with this new solution is significantly lower compared with formation of AGEs with conventional solutions.

The purpose of the present study was to investigate the effect of long-term intraperitoneal use of new, neutral dialysis solution (B/L) containing bicarbonate (25 mmol/L) and lactate (15 mmol/L) on peritoneal AGE accumulation and permeability. Normal male Sprague–Dawley rats were used. Twice daily for 12 weeks, 30 mL of new solution (B/L) or conventional solution [Lac (lactate 40 mmol/L)] was injected into the peritoneal cavity of the test rats. As a control, rats that were not injected were kept for 12 weeks in the same manner as the test rats. After 12 weeks, a 2-hour peritoneal equilibration test (PET) was performed in the test rats. After the PET, the parietal peritoneum and liver were obtained for evaluation of peritoneal morphology and for immunohistochemistry for AGE. Intensity of AGE staining was semi-quantitatively graded from 0 to 3. The omentum was also obtained and immediately frozen for analysis of pentosidine content by high-performance liquid chromatography. Compared with findings in the control group, hematoxylin and eosin staining of the parietal peritoneum and liver samples revealed partial denudation of mesothelial cells in the Lac group; denudation was not remarkable in the B/L group. The B/L solution showed significantly less AGE staining in the peritoneal cavity compared to conventional solution. However, B/L solution failed to lower pentosidine levels. Intraperitoneal volume and the ratio of dialysate glucose at 2 hours to dialysate glucose at instillation (D2/D0glucose) were significantly lower and the ratio of dialysate urea to plasma urea at 2 hours (D2/P2urea) was significantly higher in the Lac and B/L groups than in the control group. Intra-peritoneal volume was significantly higher in the B/L group than in the Lac group; D2/D0glucose and D2/P2urea did not differ between the two groups.

In conclusion, peritoneal ultrafiltration decreased after long-term PD. The B/L solution showed a small but statistically significant protective effect against decreasing ultrafiltration as compared with Lac solution. The B/L solution attenuated peritoneal AGE accumulation compared with conventional solution, but did not affect peritoneal pentosidine levels. These findings indicate that biochemical kinetics of various AGE peptides are not unique, but multivalent.

Glucose Degradation Products in Peritoneal Dialysis Fluids: How they can be Avoided

♦ Objectives

A patient on peritoneal dialysis (PD) uses 3 – 7 tons of PD fluid every year. The result is considerable stress on the peritoneal tissue. Aspects of PD fluids that have been considered responsible for bioincompatibility are low pH, high osmolality, high glucose and lactate concentrations, and the presence of glucose degradation products (GDPs). However, the relative importance of each factor in PD fluid has so far not been investigated. Discovering their relative importance was the aim of the present study.

♦ Methods

Two main methods for investigating biocompatibility were used in this study: cytotoxicity measured as in vitro inhibition of cell growth, and in vitro AGE formation measured as albumin-linked fluorescence.

♦ Results

The two most important factors for determining in vitro bioincompatibility of PD fluids were the presence of GDPs, which caused both severe cytotoxicity and strong AGE promotion, and low pH, which induced severe cytotoxicity.

♦ Conclusions

The biocompatibility of PD fluids can be monitored through fairly simple in vitro methods such as cell proliferation and AGE formation. Bioincompatibility of PD fluids is caused mainly by the presence of GDPs and low pH. These findings correlate well with known clinical bioincompatibility.

The Relationship between Ultrafiltrate Volume with Icodextrin and Peritoneal Transport Pattern according to the Peritoneal Equilibration Test

♦ Objective

To establish a relationship between peritoneal transport membrane pattern, analyzed by the peritoneal equilibration test (PET), and drained volume using icodextrin (7.5% Ico) and glucose (3.86% Glu) solutions.

♦ Design

Thirty peritoneal dialysis patients were submitted to a standard 4-hour PET and divided into 4 transport categories based on dialysate-to-plasma ratio of creatinine (D/Pcr) and dialysate ratio of glucose at 4 and zero hours of the dwell (D4/D0). Patients were asked to perform exchanges for 2 consecutive nights in 10-hour dwells (2 L 3.86% Glu solution on the first night, and 2 L 7.5% Ico solution on the second night). The drained volume was measured and dialysate samples from the overnight exchanges were obtained for β2-microglobulin (B2M) levels.

♦ Results

PET classification using D/Pcr showed that 46.6% of the patients were high and high-average transporters, or 23.3% when D4/D0 was used. In spite of this difference, both methods showed significant correlation ( p = 0.0001, r = 0.862). The mean drained volumes were similar for both solutions (for 3.86% Glu, 2696 ± 369 mL; for 7.5% Ico, 2654 ± 424 mL). The high and high-average transport patients classified by D4/D0 achieved a higher ultrafiltration with 7.5% Ico than with 3.86% Glu ( p = 0.0235). When classified by D/Pcr, the difference was not significant ( p = 0.2243). In the low and low-average transport patients classified by D/Pcr, we observed a significantly lower ultrafiltration when 7.5% Ico was used compared to 3.86% Glu solution ( p = 0.0197). Using D4/D0, we saw a tendency toward lower ultrafiltration ( p = 0.0719) in the same group. We then correlated the PET results and the difference between drained volume with 7.5% Ico and 3.86% Glu solution [ΔV (I–G)]. We found a significant negative correlation between D4/D0 and ΔV (I–G) ( p = 0.002, r = –0.5390), and a positive correlation between D/Pcr and ΔV (I–G) ( p = 0.005, r = 0.4932). The levels of B2M obtained with 7.5% Ico were higher than those obtained with 3.86% Glu solution (for 7.5% Ico, 9.47 ± 6.71 μg/vol; for 3.86% Glu, 7.29 ± 4.91 μg/vol; p = 0.004). Furthermore, we found significant correlation between the total amount of B2M obtained with 7.5% Ico solution and D4/D0 ( p < 0.0001, r = –0.4493), and D/Pcr ( p < 0.0001, r = 0.5431).

♦ Conclusion

Mean drained volume was similar between the two solution groups. High transporters, as defined by D4/D0, achieved higher ultrafiltration with 7.5% Ico than with 3.86% Glu solution. This is most likely due to the higher number of small pores in the peritoneal membrane. Low transporters, as classified by D/Pcr, achieved lower ultrafiltration with 7.5% Ico than with 3.86% Glu solution. The ΔV (I–G) and the PET results showed significant correlation, confirming that high transporters have a higher ultrafiltration volume with 7.5% Ico. The total B2M mass obtained with 7.5% Ico was greater than with 3.86% Glu solution and significantly higher in the high transport patients, indicating a larger number of small pores. Thus, the ΔV (I–G) could give us an idea of the peritoneal transport pattern in peritoneal dialysis patients.

Intraperitoneal Infusion of Glucose-Based Dialysate in the Rat—An Animal Model for the Study of Peritoneal Advanced Glycation End-Products Formation and Effect on Peritoneal Transport

Objective

Glucose-based dialysate induces non enzymatic glycation within the peritoneal cavity. To evaluate the relationship between the formation of advanced glycation end-products (AGEs) and peritoneal transfer for small solutes and macromolecules, we developed a model of simulated peritoneal dialysis (PD) in normal rats.

Methods

Male albino rats of the Charles River strain were divided into two sets of 3 groups (15 – 25 rats in each group). In the experimental (E) group, the rats were intra-peritoneally (IP) injected daily with a commercially available 4.25% dextrose solution. In the control puncture (CP) group, the peritoneum was punctured daily, but no PD solution infused. In an age-matched control (CC) group, no intervention was given. Two study protocols were used. Protocol A (duration 20 weeks) consisted of a daily IP injection of 10 mL PD solution per 100 g body weight. In protocol B, a double volume of PD solution was introduced (20 mL per 100 g body weight). At 9, 16, and 20 weeks in protocol A, and at 9 weeks in protocol B, urea, creatinine, microalbumin [(MAL) measured using specific anti-rat albumin monoclonal antibody], and AGEs (measured by fluorescent assay with excitation at 370 nm and emission at 440 nm) were measured in peritoneal effluent and serum.

Results

At no time during the study were AGEs detected in serum from any group in either protocol. In both protocols, no differences were found between the control groups (CP, CC) with respect to all parameters. In protocol A, the dialysate-to-plasma ratio (D/P) of urea was significantly higher in the experimental group as compared with the control groups at 9, 16, and 20 weeks [9 weeks: 0.59 ± 0.03 (E) vs 0.39 ± 0.02 (CP) vs 0.46 ± 0.02 (CC), p < 0.0004 and p < 0.002, respectively; 16 weeks: 0.71 ± 0.08 (E) vs 0.42 ± 0.01 (CP) vs 0.46 ± 0.01 (CC), p < 0.0001 and p < 0.02, respectively; 20 weeks: 0.57 ± 0.03 (E) vs 0.39 ± 0.01 (CP) vs 0.41 ± 0.02 (CC), p < 0.002 and p < 0.004, respectively]. At 16 and 20 weeks, dialysate MAL levels were significantly increased in group E [16 weeks: 354.00 ± 80.35 μg/mL (E) vs 134.75 ± 14.36 μg/mL (CP) vs 110.69 ± 7.83 μg/mL (CC), p < 0.04 and p < 0.03, respectively; 20 weeks: 283.17 ± 14.71 μg/mL (E) vs 105.14 ± 12.11 μg/mL (CP) vs 135.50 ± 19.03 μg/mL (CC), p < 0.00001 and p < 0.0001, respectively]. In protocol B, at completion of the study (week 9), D/P urea, effluent MAL, and AGEs were significantly higher in the experimental group as compared with the control groups [D/P: 0.67 ± 0.04 (E) vs 0.46 ± 0.07 (CP) vs 0.41 ± 0.02 (CC), p < 0.0002 and p < 00001, respectively; MAL: 336.8 ± 63.30 μg/mL (E) vs 125.71 ± 16.77 μg/mL (CP) vs 119.00 ± 39.75 μg/mL (CC), p < 0.008 and p < 0.007, respectively; AGEs: 265.77 ± 33.49 U/mg creatinine (E) vs 163.10 ± 21.99 U/mg creatinine (CP) vs 83.17 ± 22.66 U/mg creatinine (CC), p < 0.02 and p < 0.001, respectively]. Peritoneal effluent AGEs were found to be significantly correlated with D/P urea and dialysate MAL ( r = 0.42, p < 0.04, and r = 0.7, p = 0.00001, respectively).

Conclusions

In situ generation of AGEs constitutes the chief origin of peritoneal AGEs. Advanced glycation end-products affect peritoneal permselectivity for both small and large solutes. The rat model of simulated peritoneal dialysis developed in this experiment provides a reliable method for studying peritoneal AGE formation and effect on peritoneal transfer of small solutes and macro-molecules.

Management of High Peritoneal Transporters

High transporters on chronic peritoneal dialysis are challenged by increased protein losses, high glucose absorption with associated metabolic abnormalities, and poor ultrafiltration. Furthermore, the relative risk of mortality and technique failure is higher in high transporters than in patients of other transport types. An approach for satisfactory management of such patients on peritoneal dialysis (PD) has not been clearly demonstrated.

Peritoneal Transport Characteristics with Glycerol-Based Dialysate in Peritoneal Dialysis

Background

Glycerol is a low molecular weight solute (MW 92 D) that can be used as an osmotic agent in continuous ambulatory peritoneal dialysis (CAPD). Due to its low molecular weight, the osmotic gradient disappears rapidly. Despite the higher osmolality at the beginning of a dwell, ultrafiltration has been found to be lower for glycerol compared to glucose (MW 180 D) when equimolar concentrations are used. Previous studies have shown glycerol to be safe for long-term use, but some discrepancies have been reported in small solute transport and protein loss.

Objective

To assess permeability characteristics for a 1.4% glycerol dialysis solution compared to 1.36% glucose.

Design

Two standardized peritoneal permeability analyses (SPA), one using 1.4% glycerol and the other using 1.36% glucose, in random order, were performed within a span of 2 weeks in 10 stable CAPD patients. The length of the study dwell was 4 hours. Fluid kinetics and solute transport were calculated and signs of cell damage were compared for the two solutions.

Setting

Peritoneal dialysis unit in the Academic Medical Center, Amsterdam.

Results

Median values for the 1.4% glycerol SPA were as follows: net ultrafiltration 251 mL, which was higher than that for 1.36% glucose (12 mL, p < 0.01); transcapillary ultrafiltration rate 2.12 mL/min, which was higher than that for glucose (1.52 mL/min, p = 0.01); and effective lymphatic absorption rate 1.01 mL/min, which was not different from the glucose-based solution. Calculation of peritoneal reflection coefficients for glycerol and glucose showed lower values for glycerol compared to glucose (0.03 vs 0.04, calculated with both the convection and the diffusion models). A marked dip in dialysate-to-plasma ratio for sodium was seen in the 1.4% glycerol exchange, suggesting uncoupled water transport through water channels. Mass transfer area coefficients for urea, creatinine, and urate were similar for both solutions. Also, clearances of the macromolecules P2-microglobulin, albumin, IgG, and α2-macroglobulin were not different for the two osmotic agents. The median absorption was higher for glycerol, 71% compared to 49% for glucose ( p < 0.01), as could be expected from the lower molecular weight. The use of a 1.4% glycerol solution during a 4-hour dwell caused a small but significant median rise in plasma glycerol, from 0.22 mmol/L to 0.45 mmol/L ( p = 0.02). Dialysate cancer antigen 125 and lactate dehydrogenase (LDH) concentrations during the dwell were not different for both solutions.

Conclusions

These findings show that glycerol is an effective osmotic agent that can replace glucose in short dwells and show no acute mesothelial damage. The higher net ultrafiltration obtained with 1.4% glycerol can be explained by the higher initial net osmotic pressure gradient. This was seen especially in the first hour of the dwell. Thereafter, the osmotic gradient diminished as a result of absorption. The dip in dialysate-to-plasma ratio for sodium seen in the glycerol dwell can also be explained by this high initial osmotic pressure gradient, implying that the effect of glycerol as an osmotic agent is more dependent on intact water channels than is glucose.

An Amino Acid-Based Peritoneal Dialysis Fluid Buffered with Bicarbonate versus Glucose/Bicarbonate and Glucose/Lactate Solutions: An Intraindividual Randomized Study

Objective

In order to study acute metabolic changes and peritoneal transport, amino acids as osmotic agent and bicarbonate as buffer were tested as new agents in peritoneal dialysis (PD) solutions.

Design

In a prospective, cross-over, randomized, intraindividual study, we investigated the acute metabolic changes following the application of three different PD fluids: (1) a 1% amino acid-based PD solution buffered with bicarbonate (34 mmol/L) (Amino/Bic); (2) a 1.5% glucose anhydrous-containing bicarbonate-buffered solution (34 mmol/L) (Glu/Bic); and (3) a conventional 1.5% glucose anhydrous-based dialysis solution with lactate (35 mmol/L) (Glu/Lac).

Setting

University medical center.

Patients

Ten nondiabetic patients stable on continuous ambulatory peritoneal dialysis (time on dialysis, 42.5 ± 21.5 months) were treated and monitored with the test solutions over a 6-hour dwell. Three different study days followed in a randomized order for each patient (interval of 1 – 3 weeks). Blood and dialysate samples were taken at 0.25, 0.5, 1, 2, 4, and 6 hours. Immediately after the 1-hr dwell (and after sampling), the patients received a standardized breakfast, thereby simulating usual food intake.

Results

Following the application of Amino/Bic a significant increase in plasma amino acids occurred, with peak levels (maximum 250% increase) after either the 1-hr or the 2-hr dwell. Before taking the standard meal (0.5 hr, 1 hr), the mean serum glucose level with Amino/Bic was 8% ± 13% lower than with Glu/Bic ( p = 0.06) and 14% ± 8% lower than with Glu/Lac ( p < 0.01). This difference was still significant after the standard breakfast and also for the whole dwell (average serum glucose 0.5 – 6 hr: Amino/Bic, 91 ± 6 mg/dL; Glu/Bic, 100 ± 8 mg/dL; Glu/Lac, 102 ± 7 mg/dL; p < 0.01 MANOVA). The serum insulin profiles did not differ between the fluids. A transperitoneal protein- and amino acid-related nitrogen loss of 0.49 ± 0.18 g and 0.48 ± 0.12 g per dwell was measured using Glu/Bic and Glu/Lac, while a positive balance of 1.80 ± 0.43 g was achieved with Amino/ Bic. The parameters of acid-base status (pH, HCO3, pCO2) remained nearly unchanged in the blood, irrespective of the solution used, while dialysate values differed markedly. No significant differences with respect to ultrafiltration (Amino/Bic, –68 ± 199 mL/6hr; Glu/Bic, –51 ± 89 mL/6hr; Glu/ Lac, –2 ± 134 mL/6hr) and peritoneal creatinine clearance (Amino/Bic, 4.9 ± 0.6 mL/min; Glu/Bic, 5.1 ± 0.6 mL/min; Glu/ Lac, 4.8 ± 0.5 mL/min) were measured.

Conclusions

Our results demonstrate that ultrafiltration and small solute clearance over a 6-hour dwell with a 1% Amino/Bic solution were comparable to those of 1.5% Glu/Bic and 1.5% Glu/Lac. Reduced serum glucose concentrations were found with Amino/Bic and this fluid compensated the transperitoneal protein-nitrogen loss of about three glucose dwells. Bicarbonate buffering (34 mmol/L) did not change blood acid-base status combined with either glucose or amino acids.

Preventing Peritoneal Fibrosis—Insights from the Laboratory

Objective

Peritoneal fibrosis is one of the most serious complications of peritoneal dialysis (PD). Peritoneal fibrosis is characterized by activation of the peritoneal resident cells, accumulation and deposition of excess matrix proteins within the interstitium, and neoangiogenesis and vasculopathy of the peritoneal microvasculature. Compelling evidence now exists to show that elevated glucose concentrations present as the osmotic agent in PD solutions are, per se, responsible for those detrimental changes. Until alternative osmotic agents can fully replace glucose in PD solutions, novel therapeutic strategies are essential to preserve the structural and functional properties of the peritoneum. This review highlights recent experimental data that may offer potential strategies for preservation of the peritoneal structure and improvement of clinical outcome.

Method

Literature review.

Results

Compelling evidence now exists to show that the bioincompatible nature of PD solutions—in particular, elevated glucose concentrations and glucose byproducts—play a pivotal role in the initiation of peritoneal fibrosis. Animal and in vitro studies provide some insight into methods that can potentially be employed to alleviate or retard peritoneal fibrosis. Those methods include use of alterative osmotic agents (polyglucose or amino acids), administration of TGFβ1 antagonists, gene therapy, and pharmacologic interventions.

Conclusions

Knowledge of the pathogenesis of peritoneal fibrosis has allowed independent researchers to design therapeutic strategies that abrogate excess matrix synthesis and deposition in cultured peritoneal cells and in animal models of experimental peritoneal fibrosis alike. Encouraging results have been obtained in those studies, but it remains to be determined whether the studied strategies can alleviate clinical disease. Future studies will enable us to establish specific molecules that can be targeted clinically to restrict the progressive deterioration of the peritoneal membrane as a biologic dialyzing organ.

Single Exposure of Mesothelial Cells to Glucose Degradation Products (GDPs) Yields Early Advanced Glycation End-Products (AGEs) and a Proinflammatory Response

← Background

Fluids commonly used for peritoneal dialysis (PD) have a low pH and a high glucose content. Furthermore, heat sterilization of dialysis fluids degrades some of the glucose into glucose degradation products (GDPs), such as methylglyoxal (MGO) and 3-deoxyglucosone (3-DG). Mesothelial cells (MCs) form the first line in the peritoneal cavity and are constantly exposed to these nonphysiological conditions. Since MCs play an important role in the regulation of inflammatory responses in the peritoneal cavity, we studied the kinetics of MC uptake of highly purified GDP species, along with their effect on various cellular biological and immunological parameters.

← Methods

Methylglyoxal and 3-DG were purified and added to MC cultures. Complexing to medium components or uptake by MCs was analyzed over time by HPLC of the culture supernatant and by immunocytochemistry of MCs for MGO-modified proteins. Furthermore, MCs were exposed to a single dose of MGO or 3-DG and analyzed for apoptosis, proliferation by MTT assay, and [3H]-thymidine incorporation. Incorporation of [35S]-methionine was determined in order to analyze de novo protein synthesis. Expression of the adhesion molecules intercellular adhesion molecule-1 (ICAM-1), CD44, and vascular cell adhesion molecule-1 (VCAM-1) was analyzed by cell-bound ELISA. Effects of MGO and 3-DG on cytokine production were also analyzed.

← Results

Substitution of MGO and 3-DG in culture medium resulted in a spontaneous decrease in MGO over time, whereas 3-DG levels decreased minimally. The concentration of these GDPs was more reduced in the presence of MCs, indicating binding to and/or uptake by MCs of these GDPs. Mesothelial cells that had been cultured in the presence of MGO showed positive staining with a monoclonal that specifically recognizes MGO-modified proteins, demonstrating complexing to mesothelial cellular proteins. Cell-bound ELISA showed a two- to threefold induction of expression of VCAM-1 by MGO and 3-DG; the expression of ICAM-1 and CD44 was not changed. Mesothelial cells showed a twofold increase in interleukin (IL)-6 and IL-8 production after exposure to 3-DG. Furthermore, incubation with MGO and 3-DG induced apoptosis and reduced the proliferation of cells, but did not influence protein synthesis.

← Conclusions

In the current report we demonstrate that MCs take up MGO and 3-DG and form early advanced glycation end-products. Upon short exposure to a single GDP, MCs react with enhanced cytotoxic damage and a proinflammatory response, evidenced by increased VCAM-1 expression and elevated production of IL-6 and IL-8.

By Reducing Production of Vascular Endothelial Growth Factor Octreotide Improves the Peritoneal Vascular Alterations Induced by Hypertonic Peritoneal Dialysis Solution

Objective

Chronic peritoneal dialysis (PD) may eventually result in vascular alterations of varying degree, which lead to progressive reduction in dialytic efficacy. Although the pathogenesis has not been elucidated yet, vascular endothelial growth factor (VEGF) has been proposed to play a central role in the process leading to vascular alterations.

Design

Rats were allocated to three groups: no treatment, intraperitoneal introduction of hypertonic PD solution alone, and intraperitoneal introduction of hypertonic PD solution plus octreotide. After 4 weeks, a 1-hour peritoneal equilibration test (PET) was performed. Dialysate-to-plasma urea ratio (D/P urea), glucose reabsorption (D1/D0 glucose), ultrafiltration volume (UF), and levels of dialysate protein and VEGF were determined. Peritoneal membrane histology was evaluated by light microscopy.

Results

Compared with the control group, rats treated with hypertonic PD solution showed dramatically deranged peritoneal function tests (UF: 5.8 ± 0.9 mL vs 1.3 ± 0.6 mL; D/P urea: 0.49 ± 0.1 vs 0.74 ± 0.04; D1/D0 glucose: 0.55 ± 0.05 vs 0.34 ± 0.06) and morphology (thickness: 4.6 ± 0.4 μ vs 62 ± 12 μ; neovascularisation: 0.1 ± 0.3 vessels per field vs 2.2 ± 0.3 vessels per field). Similarly, a higher level of VEGF was found in the rats treated with hypertonic PD solution. In rats treated with hypertonic solution plus octreotide, peritoneal thickness was not completely reduced (25 ± 5 μ), but peritoneal functions were protected (UF: 4.0 ± 0.5 mL; D/P urea: 0.58 ± 0.02; D1/D0 glucose: 0.51 ± 0.02). Moreover, VEGF level and neoangiogenesis were significantly less in the octreotide group than in the group treated with hypertonic dextrose alone.

Conclusion

Our data document that, by increasing the production of VEGF, a high glucose concentration can cause vascular alterations within the peritoneal membrane. Octreotide can protect against the vascular alterations and preserve peritoneal function by inhibiting overexpression of VEGF and regulating the inflammatory response in the peritoneum.

Strategies to Reduce Glucose Exposure in Peritoneal Dialysis Patients

Glucose has been used successfully for more than two decades in peritoneal dialysis, and in this regard, must be considered a safe and effective osmotic agent. Recently, however, insight has been growing about the potential for metabolic and peritoneal effects arising from long-term exposure to high glucose concentrations—for example, hyperlipidemia and loss of peritoneal ultrafiltration. Clinical concerns over exposure to excessive glucose and glucose degradation products (GDPs) during peritoneal dialysis can be significantly ameliorated by the use of non-glucose-based peritoneal dialysis (PD) solutions, in combination with more biocompatible glucose-based formulations. Peritoneal exposure to GDPs can be reduced by using low-GDP-containing glucose formulations and non glucose solutions such as amino acids and icodextrin. Peritoneal glucose exposure, hyperosmolar stress, and carbohydrate absorption can be reduced by using a combination of icodextrin and amino acids.

Structural and Functional Alterations of the Peritoneum after Prolonged Exposure to Dialysis Solutions: Role of Aminoguanidine

Objective

The effect of long-term use of high glucose dialysate on peritoneal structure and function, and its relation with accumulation of advanced glycosylation end-product (AGE) in the peritoneum was investigated in this study.

Methods

Dialysates with 4.25% glucose were injected into the peritoneal cavity of normal rats for 12 weeks without (PD, n = 7) and with (1 g/L, PD+AG, n = 7) aminoguanidine in their drinking water. Rats not having intraperitoneal (IP) injection served as control ( n = 9). After 12 weeks of IP injection, a 2-hour peritoneal equilibration test (PET) was performed using 30 mL 4.25% glucose dialysate. Intraperitoneal volume (IPV), dialysate-to-plasma urea ratio at 2 hours (D2/P2), the ratio of dialysate glucose at 2 hours to initial dialysate glucose (D2/D0), and the peritoneal fluid absorption rate (Qa) were evaluated. After the PET, samples of the parietal peritoneum were taken for hematoxylin and eosin (H&E) staining and immunohistochemical staining for AGE.

Results

The IPV and D2/D0glucose were significantly lower and Qaand D2/P2urea significantly higher in the PD group than in the control group. Aminoguanidine reversed in part the changes in IPV and D2/P2urea in the PD group; it had no effect on Qaand D2/D0glucose. The H&E staining showed a linear mesothelial lining with negligible cells and capillaries in the narrow submesothelial space in the control group. Mesothelial denudation and submesothelial infiltration of monocytes and capillary formation were observed in the PD group. Mesothelial denudation was relatively intact in the PD+AG group compared with the PD group. Submesothelial monocyte infiltration and capillary formation in the PD+AG group were not as prominent as in the PD group. Positive AGE staining was found in the submesothelial space, vascular walls, and endomysium in the PD group, while it was markedly attenuated in PD+AG group and negligible in the control group.

Conclusion

Long-term use of high glucose solutions induced peritoneal AGE accumulation and mesothelial denudation, and increased peritoneal permeability and peritoneal fluid absorption rate. Inhibition of peritoneal AGE accumulation prevented those functional and structural damages to the peritoneum.

Analysis of Non Enzymatic Glycosylation In Vivo: Impact of Different Dialysis Solutions

Background

Glucose-containing dialysis solutions in peritoneal dialysis (PC) patients induce non enzymatic glycosylation (NEG) within the peritoneal cavity. The subsequent formation of advanced glycosylation endproducts (AGEs) may be implicated in the functional deterioration of the peritoneal membrane in long-term PC patients.

Aim of the Study and Parameters

Measurement of NEG by the determination of percent glycation of albumin and IgG (GP), and of AGEs by measuring pentosidine content of protein in 4-hour effluents (Peff) and serum.

Subjects

In 5 patients each, a comparison was made between 3.86% glucose and 1.36% glucose (GP and Peff), and between 3.86% glucose and 7.5% icodextrin (Peff). Nine patients with clinically severe ultrafiltration failure (UFF) were compared to nine patients treated with PC for 1 month. Six of the patients with UFF were treated with non glucose dialysis solutions and Peff was studied again after 6 weeks.

Results

No difference was found between Peff comparing 3.86% glucose to either 1.36% glucose or icodextrin. GP were higher in 3.86% glucose than in 1.36%. Glycatedlnon glycated (G/NG) protein clearance ratios were 1.29 for albumin and 1.12 for IgG (p = 0.003). In contrast to GP, both Peff and serum pentosidine were higher in the UFF patients than in the recently started patients. Peff, but not GP, correlated with duration of PC (r = 0.67, p = 0.04). In 5 of 6 patients treated with non glucose dialysate, Peff decreased while serum pentosidine was stable. .Discussion: These data show that 4-hour Peff contents are not influenced by glucose concentration or osmolality, in contrast to GP. The relation between Peff and duration of PC, and the effect of non glucose dialysate on Peff, suggest that long-term glucose exposure is an important determinant of membrane glycosylation. Thus Peff probably reflects the long-term effects of intraperitoneal glycosylation of peritoneal membrane proteins. Treatment with non glucose dialysis solutions may result in “washout” of glycosylated proteins from the peritoneal membrane.

Biocompatibility of New Peritoneal Dialysis Solutions: What Can We Hope to Achieve?

Despite the bioincompatibility of the “old”, standard, high glucose, lactate-buffered peritoneal dialysis (PD) solutions, PD is itself a highly successful dialysis modality with patient survival equivalent to that of hemodialysis (HD) during the initial 3 – 5 years of dialysis therapy. Nevertheless, PD technique survival is often limited by infectious complications and alterations in the structure and function of the peritoneal membrane. These local changes also have a negative impact on patient survival owing to systemic effects such as those often seen in patients with high peritoneal transport rate and loss of ultrafiltration (UF) capacity.

Patient mortality remains unacceptably high in both HD and PD patients, with most premature deaths being associated with signs of malnutrition, inflammation, and atherosclerotic cardiovascular disease (MIA syndrome). These systemic signs are likely to be influenced by PD solutions both directly and indirectly (via changes in the peritoneal membrane). New, biocompatible PD solutions may have favorable local effects (viability and function of the peritoneal membrane) and systemic effects (for example, on MIA syndrome). Amino acid–based solution [Nutrineal (N): Baxter Healthcare Corporation, Deerfield, IL, U.S.A.] may improve nutritional status as well as peritoneal membrane viability. Bicarbonate/lactate–buffered solution [Physioneal (P): Baxter Healthcare Corporation] may ameliorate local and systemic effects of low pH, high lactate, and high glucose degradation products. Icodextrin-based solution [Extraneal (E): Baxter Healthcare SA, Castlebar, Ireland] may improve hypertension and cardiovascular problems associated with fluid overload and may extend time on therapy in patients with loss of UF capacity.

The positive effects of each of these new, biocompatible solutions have been demonstrated in several studies. It is likely that the combined use of N, P, and E solutions will produce favorable synergies in regard to both local effects (peritoneal viability) and systemic effects (less malnutrition, inflammation, and fluid overload). Solution combination is an exciting area for clinical study in the coming years. Furthermore, dialysis fluid additives such as hyaluronan, which protects and improves the function of the peritoneal membrane, may further improve PD solutions. The new, biocompatible PD solutions represent an entirely new era in the evolution of the PD therapy; they are likely to have markedly positive effects on both PD technique and PD patient survival in coming years.

Amadori Albumin and Advanced Glycation End-Product Formation in Peritoneal Dialysis using Icodextrin

Objective

To study the influence of peritoneal dialysis (PD) solutions on the formation of early glycated products and advanced glycation end-products (AGEs).

Design and Patients

The formation of both Amadori albumin and AGEs in glucose- and icodextrin-based PD fluids was analyzed in vitro and in peritoneal effluents of continuous cyclic peritoneal dialysis (CCPD) patients.

Results

Albumin incubated with glucose-based PD fluids showed a time- and glucose concentration-dependent formation of Amadori albumin and AGEs. Aminoguanidine completely inhibited AGE but not Amadori albumin formation. Albumin incubated in icodextrin resulted in the lowest levels of Amadori albumin and AGE. Amadori albumin levels in effluents of 24 CCPD patients (12 glucose and 12 icodextrin for their daytime dwells) were similar. Dialysate samples collected during a mass transfer area coefficient test in 16 CCPD patients (8 glucose, 8 icodextrin) showed an increase in Amadori albumin formation from baseline ( p < 0.0001), without a difference between the groups. In the total group, there was a positive relationship between duration on PD and dialysate Amadori albumin concentration at 240 minutes ( p = 0.03). The Amadori albumin dialysate-to-plasma (D/P) ratio at 240 minutes was 0.82 ± 0.11, and its clearance amounted to 7.71 ± 1.14 mL/min, while the albumin D/P ratio was 0.010 ± 0.003 and its clearance was 0.089 ± 0.017 mL/min. In a peritoneal biopsy of a CCPD patient, Amadori albumin was observed in the mesothelial layer and the endothelium of the peritoneum.

Conclusions

Using icodextrin-based instead of glucose-based PD fluids can largely reduce the formation of Amadori albumin and AGEs. However, CCPD patients using icodextrin during daytime dwells do not have lower effluent levels of Amadori albumin and AGEs, probably due to the exposure to glucose during their nighttime exchanges. Kinetic studies suggest washout of locally produced Amadori albumin.

Biocompatibility of Peritoneal Dialysis Fluids: Long-term Exposure of Nonuremic Rats

Objectives

Long-term peritoneal dialysis (PD) leads to structural and functional changes in the peritoneum. The aim of the present study was to investigate the long-term effects of PD fluid components, glucose and glucose degradation products (GDP), and lactate-buffered solution on morphology and transport characteristics in a nonuremic rat model.

Methods

Rats were subjected to two daily intraperitoneal injections (20 mL/day) during 12 weeks of one of the following: commercial PD fluid (Gambrosol, 4%; Gambro AB, Lund, Sweden), commercial PD fluid with low GDP levels (Gambrosol trio, 4%; Gambro AB), sterile-filtered PD fluid (4%) without GDP, or a glucose-free lactate-buffered PD fluid. Punctured and untreated controls were used. Following exposure, the rats underwent a single 4-hour PD dwell (30 mL, 4% glucose) to determine peritoneal function. Additionally, submesothelial tissue thickness, percentage of high mesothelial cells (perpendicular diameter > 2 μm), vascular density, vascular endothelial growth factor (VEGF), and transforming growth factor (TGF) β1mRNA expression were determined. Submesothelial collagen concentration was estimated by van Gieson staining.

Results

Submesothelial tissue thickness and vascular density, mediated by VEGF and TGFβ production, in the diaphragmatic peritoneum increased significantly in rats exposed to any PD fluid. Gambrosol induced a marked increased fibrosis of the hepatic peritoneum. A significant increase in high mesothelial cells was observed in the Gambrosol group only. Net ultrafiltration was reduced in the Gambrosol and in the glucose-free groups compared to untreated controls. Small solute transport was unchanged, but all groups exposed to fluids showed significantly increased lymph flow.

Conclusions

Our results show that long-term exposure to different components of PD fluids leads to mesothelial cell damage, submesothelial fibrosis, and neoangiogenesis. Mesothelial cell damage could be connected to the presence of GDP; the other changes were similar for all fluids. Peritoneal transport characteristics did not change in any consistent way and the neoangiogenesis observed was not paralleled by increased solute transport.

What Can We Do to Preserve the Peritoneum?

Background

Long-term peritoneal dialysis may lead to peritoneal membrane failure. Loss of ultrafiltration is the most important clinical abnormality. Loss of ultrafiltration is associated with an increased number of peritoneal blood vessels, with fibrotic alterations, and with loss of mesothelium. Continuous exposure to bioincompatible dialysis solutions is likely to be important in the pathogenesis of these alterations.

Methods

This article reviews the toxicity of various constituents of dialysate, current assessments of interventions, and the results of interventions aimed at preserving the peritoneum.

Results

Glucose, possibly in combination with lactate, and glucose degradation products (GDPs) are likely to be the most toxic constituents of dialysate. Diabetiform peritoneal neoangiogenesis is likely to be mediated by vascular endothelial growth factor (VEGF). Release of VEGF might be influenced by glucose-induced cellular pseudohypoxia, which is likely to be increased by exposure to lactate. Glucose and GDPs are both toxic to peritoneal cells. Glucose degradation products induce the formation of advanced glycosylation end-products at a much faster rate than does glucose itself, but the relative importance of GDPs and glucose in clinical PD has not been clarified. The effects of interventions should first be assessed in long-term animal models, followed by clinical studies on peritoneal transport and on effluent markers that may reflect the status of the peritoneum. Possible interventions aim at reducing peritoneal exposure to glucose, GDPs, and lactate. Techniques include peritoneal resting, replacing some glucose-based exchanges with amino acid–based and icodextrin-based dialysate, using bicarbonate as a buffer, and administering solutions that have a low GDP content. Exposure to various dialysis solutions with a reduced GDP content has resulted in an increase in the effluent concentration of the mesothelial cell marker CA125, irrespective of the buffer used. Experimental studies in a long-term peritoneal exposure model in rats showed that the combination of a reduction in the concentration of lactate and replacement of lactate with pyruvate resulted in a reduction of the number of peritoneal blood vessels. Results of drug therapy have been studied in various animal models. Their use in patients is still experimental.

Conclusions

Strategies to preserve the peritoneum aim at reducing membrane exposure to bioincompatible solutions. Currently available dialysis fluids that are more biocompatible are likely to have some beneficial effects. Further research on the development of dialysis solutions that use combinations of osmotic agents and alternative buffers is necessary.

Suppression of Nε-(Carboxymethyl)Lysine Generation by the Antioxidant N-Acetylcysteine

Objective

Accumulated evidence suggests that Nε-(carboxymethyl)lysine (CML), which is a dominant antigen of advanced glycation end-products (AGEs), is generated in the peritoneal cavity of patients undergoing continuous ambulatory peritoneal dialysis (CAPD), and that this process may be involved in the pathophysiology of the peritoneal injury found with CAPD treatment. Since CML is a sequential product of glycation and oxidation processes, CML generation could be suppressed by antioxidants. The aim of this in vitro study was to clarify the effect of N-acetylcysteine (NAC), an antioxidant, on CML generation from proteins under high glucose settings mimicking peritoneal dialysis solutions.

Design

Test proteins (bovine serum albumin/type I collagen) were incubated continuously for 16 weeks in glucose solutions (200 mmol/L) with or without NAC (2 mmol/L), and the generation time courses (8 and 16 weeks) of CML and furosine (the biomarker of the glycation products of the early Maillard reaction) were determined.

Results

In both proteins, furosine and CML were progressively generated in accordance with the duration of the incubation period. No apparent differences were found between solutions with and without NAC in furosine levels at the 8th and 16th weeks. However, the generation of CML was lower in the solution with NAC throughout the test periods.

Conclusion

The results showed that NAC could suppress the generation of CML. This indicates the therapeutic potential of antioxidants for the glycoxidative stress-related peritoneal injury occurring during CAPD.