Peritoneal dialysis and peritoneal fibrosis: molecular mechanisms, risk factors and prospects for prevention

Peritoneal dialysis (PD) leads to structural and functional changes in the peritoneal membrane, the endpoint of which is peritoneal fibrosis. Peritoneal fibrosis is diagnosed in 50% and 80% of PD patients within 1 and 2 years of treatment initiation, respectively. A key role in the development of peritoneal fibrosis is played by mesothelial-mesenchymal transformation, a complex biological process of transition from mesothelium to mesenchyme. This review summarizes the current knowledge on the changes in peritoneal function and morphology, the molecular mechanisms of peritoneal fibrosis development, and its clinical consequences during PD. Special attention is given to established and potential risk factors for peritoneal fibrosis, and existing prevention strategies are considered.

Aging of the Peritoneal Dialysis Membrane

Long-term peritoneal dialysis as currently performed, causes structural and functional alterations of the peritoneal dialysis membrane. This decay is brought about by the continuous exposure to commercially available glucose-based dialysis solutions. This review summarizes our knowledge on the peritoneum in the initial phase of PD, during the first 2 years and the alterations in function and morphology in long-term PD patients. The pseudohypoxia hypothesis is discussed and how this glucose-induced condition can be used to explain all peritoneal alterations in long-term PD patients. Special attention is paid to the upregulation of hypoxia inducing factor-1 and the subsequent stimulation of the genes coding for glucose transporter-1 (GLUT-1) and the growth factors transforming growth factor-β (TGFβ), vascular endothelial growth factor (VEGF), plasminogen growth factor activator inhibitor-1 (PAI-1) and connective tissue growth factor (CTGF). It is argued that increased pseudohypoxia-induced expression of GLUT-1 in interstitial fibroblasts is the key factor in a vicious circle that augments ultrafiltration failure. The practical use of the protein transcripts of the upregulated growth factors in peritoneal dialysis effluent is considered. The available and developing options for prevention and treatment are examined. It is concluded that low glucose degradation products/neutral pH, bicarbonate buffered solutions with a combination of various osmotic agents all in low concentration, are currently the best achievable options, while other accompanying measures like the use of RAAS inhibitors and tamoxifen may be valuable. Emerging developments include the addition of alanyl glutamine to the dialysis solution and perhaps the use of nicotinamide mononucleotide, available as nutritional supplement.

Relative Contributions of Pseudohypoxia and Inflammation to Peritoneal Alterations with Long-Term Peritoneal Dialysis Patients

Long-term peritoneal dialysis (PD) is associated with alterations in peritoneal function, like the development of high small solute transfer rates and impaired ultrafiltration. Also morphologic changes can develop, the most prominent being loss of mesothelium, vasculopathy and interstitial fibrosis. Current research suggests peritoneal inflammation as the driving force for these alterations. In this review the available evidence for inflammation is examined and a new hypothesis is put forward consisting of high glucose-induced pseudohypoxia. Hypoxia of cells is characterized by a high NADH/NAD+ ratio in their cytosol. Pseudohypoxia is similar, but occurs when excessive amounts of glucose are metabolized, as is the case for peritoneal interstitial cells in PD. The glucose- induced high NADH/NAD+ ratio upregulates the hypoxia-inducible factor-1 gene, which stimulates not only the glucose transporter-1 gene, but also many profibrotic genes like TGFβ, VEGF, PAI-1 and CTGF, all known to be involved in the development of peritoneal fibrosis. This review discusses the causes and consequences of pseudohypoxia in PD and the available options for treatment and prevention. Reducing peritoneal exposure to the excessively high dialysate glucose load is the cornerstone to avoid the pseudohypoxia-induced alterations. This can partly be done by the use of icodextrin, or by combinations of low molecular weight osmotic agents, all in a low dose. The addition of alanyl-glutamine to the dialysis solution needs further clinical investigation.

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

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

Effect of aquaporin 1 on mouse peritoneal mesothelial cells after a long-term peritoneal dialysis

Aquaporin 1 (AQP1) is one member of the aquaporin family, also the deeply studied one. It is widely located on the endothelial cells, but the effect of AQP1 on the peritoneal mesothelial cells (PMCs) after long-term peritoneal dialysis (PD) has not been reported before. We divided normal mice into two groups, control group and dialysis group, to confirm the fibrotic changes and expression of APQ1 on peritoneal mesothelial cells. Then we assigned normal mice and AQP1 knockout mice into four groups: Control group, normal dialysis group, AQP1 knockout control group and AQP1 knockout dialysis group. The two dialysis groups received 4.25% glucose dialysis for 28 days. We found that mice in both dialysis groups showed peritoneal fibrotic changes, which were most severe in the AQP1 knockout dialysis group; the peritoneal thickness in the AQP1 knockout dialysis group was also thicker than that in the dialysis group (P < .05). We used electron microscopy to detect ultrastructural changes and observed changes in microvilli and vacuolar degeneration in mesothelial cells from all groups except the control group. The basement membranes were damaged in the AQP1 knockout dialysis group, and peritoneal mesothelial cells were disrupted and detached in this group. Together our findings indicate that AQP1 plays an important role in maintaining the physiological functions of peritoneal mesothelial cells, and AQP1 can protect mesothelial cells during dialysis.

Non-invasive assessment of peritoneal membrane alterations

The peritoneal dialysis membrane is subject to remodelling in the course of peritoneal dialysis. In the absence of longitudinal morphological studies, this process is mainly studied indirectly by the investigation of changes in peritoneal transport. Non-invasive assessment of the peritoneum is also possible by assessment of substances that originate from peritoneal tissues and can be determined either as their gene expression in peritoneal effluent cells and/or as proteins in peritoneal effluent. Three of these biomarkers will be discussed, because longitudinal data are available. Cancer antigen 125 (CA 125) is present on the mesothelium,while its gene (MUC 16) is expressed in peritoneal effluent cells and is related to dialysate CA 125 protein. The constitutive production and the small intra-individual variability of 15% indicate its usefulness as a follow-up marker of mesothelial cell mass. Dialysate appearance rate is higher on biocompatible than on conventional solutions, but both decrease during long-term follow-up. Interleukin-6 (Il-6) is present in peritoneal effluent due to both transport from the circulation and local intraperitoneal production. Its appearance rate is unrelated to its gene expression in peritoneal cells. The intra-individual variation of effluent Il-6 averages 28%, hampering the interpretation of cross-sectional values. The relationships between effluent Il-6 and peritoneal transport have been interpreted as microinflammation, but are difficult to interprete due to mathematical coupling. Plasminogen activator inhibitor-1 (PAI-1) is encoded by the SERPINE 1 gene. A relationship is present between effluent concentration and gene expression. PAI-1 production is stimulated by glucose. PAI-1 appearance rate increases with PD duration. The sensitivity of effluent PAI-1 for the diagnosis of encapsulating peritoneal sclerosis was 100% one year prior to the diagnosis and the specificity 56%. It can be concluded that the discussed biomarkers are useful extensions to transport in assessment of the peritoneum during dialysis.  

Peritoneal dialysis induces alterations in the transcriptome of peritoneal cells before detectible peritoneal functional changes

Long-term peritoneal dialysis (PD) is associated with functional and structural alterations of the peritoneal membrane. Inflammation may be the key moment, and, consequently, fibrosis may be the end result of chronic inflammatory reaction. The objective of the present study was to identify genes involved in peritoneal alterations during PD by comparing the transcriptome of peritoneal cells in patients with short- and long-term PD. Peritoneal effluent of the long dwell of patients with stable PD was centrifuged to obtain peritoneal cells. The gene expression profiles of peritoneal cells using microarray between patients with short- and long-term PD were compared. Based on microarray analysis, 31 genes for quantitative RT-PCR validation were chosen. A 4-h peritoneal equilibration test was performed on the day after the long dwell. Transport parameters and protein appearance rates were assessed. Genes involved in the immune system process, immune response, cell activation, and leukocyte and lymphocyte activation were found to be substantially upregulated in the long-term group. Quantitative RT-PCR validation showed higher expression of CD24, lymphocyte antigen 9 ( LY9), TNF factor receptor superfamily member 4 ( TNFRSF4), Ig associated-α ( CD79A), chemokine (C-C motif) receptor 7 ( CCR7), carcinoembryonic antigen-related cell adhesion molecule 1 ( CEACAM1), and IL-2 receptor-α ( IL2RA) in patients with long-term PD, with CD24 having the best discrimination ability between short- and long-term treatment. A relationship between CD24 expression and genes for collagen and matrix formation was shown. Activation of CD24 provoked by pseudohypoxia due to extremely high glucose concentrations in dialysis solutions might play the key role in the development of peritoneal membrane alterations.

The Role of Tyrosine Kinase Receptors in Peritoneal Fibrosis

Peritoneal dialysis (PD) is a modality for treatment of patients with end-stage renal disease (ESRD) that depends on the structural and functional integrity of the peritoneal membrane. However, long-term PD can lead to morphological and functional changes in the peritoneum; in particular, peritoneal fibrosis has become one of the most common complications that ultimately results in ultrafiltration failure (UFF) and discontinuation of PD. Several factors and mechanisms such as inflammation and overproduction of transforming growth factor-β1 have been implicated in the development of peritoneal fibrosis, but there is no effective therapy to prevent or delay this process. Recent studies have shown that activation of multiple receptor tyrosine kinases (RTKs) is associated with the development and progression of tissue fibrosis in various organs, and there are also reports indicating the involvement of some RTKs in peritoneal fibrosis. This review will describe the role and mechanisms of RTKs in peritoneal fibrosis and discuss the possibility of using them as therapeutic targets for prevention and treatment of this complication.

New Insights into the Effects of Chronic Kidney Failure and Dialysate Exposure on the Peritoneum

♦ INTRODUCTION: Chronic uremia and the exposure to dialysis solutions during peritoneal dialysis (PD) induce peritoneal alterations. Using a long-term peritoneal exposure model, we compared the effects of chronic kidney failure (CKD) itself and exposure to either a 'conventional' or a 'biocompatible' dialysis solution on peritoneal morphology and function. ♦ METHODS: Wistar rats (Harlan, Zeist, the Netherlands) were grouped into: normal kidney function (NKF), CKD induced by 70% nephrectomy, CKD receiving daily peritoneal infusions with 3.86% glucose Dianeal (CKDD), or Physioneal (both solutions from Baxter Healthcare, Castlebar, Ireland) (CKDP). At 16 weeks, a peritoneal function test was performed, and histology, ultrastructure, and hydroxyproline content of peritoneal tissue were assessed. ♦ RESULTS: Comparing CKD with NKF, peritoneal transport rates were higher, mesothelial cells (MC) displayed increased number of microvilli, blood and lymph vasculature expanded, vascular basal lamina appeared thicker, with limited areas of duplication, and fibrosis had developed. All alterations, except lymphangiogenesis, were enhanced by exposure to both dialysis fluids. Distinct MC alterations were observed in CKDD and CKDP, the latter displaying prominent basolateral protrusions. In addition, CKDP was associated with a trend towards less fibrosis compared to CKDD. ♦ CONCLUSIONS: Chronic kidney failure itself induced peritoneal alterations, which were in part augmented by exposure to glucose-based dialysis solutions. Overall, the conventional and biocompatible solutions had similar long-term effects on the peritoneum. Importantly, the latter may attenuate the development of fibrosis.

A review of rodent models of peritoneal dialysis and its complications

This article reviews the available rodent models of peritoneal dialysis (PD) that have been developed over the past 20 years and the complications associated with their use. Although there are several methods used in different studies, the focus of this article is not to review or provide detailed summaries of these methods. Rather, this article reviews the most common methods of establishing a dialysis model in rodents, the assays used to observe function of the peritoneum in dialysis, and how these models are adapted to study peritonitis and peritoneal fibrosis. We compared the advantages and disadvantages of different methods, which should be helpful in studies of PD and may provide valuable data for further clinical studies.

Inhibition of Rho-kinase alleviates peritoneal fibrosis and angiogenesis in a rat model of peritoneal dialysis

BACKGROUND/AIMS

The present study investigated whether Rho-kinase inhibition had a therapeutic role on the pathogenesis of peritoneal fibrosis and angiogenesis.

METHODS

A rat model of peritoneal dialysis was induced by a daily intraperitoneal infusion of 4.25% Dianeal. Those rats were treated with Rho-kinase inhibitor, fasudil. Immunofluorescence, Western blot and RT-PCR were used to detect the expression of TGF-β1, Collagen I, αSMA and VEGF in each group. Microvessel density (MVD) was measured by immunohistochemistry. Rho-kinase activity was determined by western immunoblotting.

RESULTS

Rho-kinase was activated in the peritoneum of the PD group, which was inhibited by fasudil. Compared with PD group, the mRNA and protein expressions of TGF-β1, αSMA and Collagen I were significantly downregulated in fasudil treatment groups in a dose-dependent manner, and the expression of VEGF and peritoneal MVD was also significantly downregulated in fasudil treatment groups in a dose-dependent manner.

CONCLUSION

The Rho-kinase was activated in the peritoneum of the peritoneal dialysis rats, and the inhibition of Rho-kinase by fasudil can remarkably decrease peritoneal fibrosis and angiogenesis.

Neutral solution low in glucose degradation products is associated with less peritoneal fibrosis and vascular sclerosis in patients receiving peritoneal dialysis

BACKGROUND

The effects of novel biocompatible peritoneal dialysis (PD) solutions on human peritoneal membrane pathology have yet to be determined. Quantitative evaluation of human peritoneal biopsy specimens may reveal the effects of the new solutions on peritoneal membrane pathology. ♢

METHODS

Peritoneal specimens from 24 PD patients being treated with either acidic solution containing high-glucose degradation products [GDPs (n = 12)] or neutral solution with low GDPs (n = 12) were investigated at the end of PD. As controls, pre-PD peritoneal specimens, obtained from 13 patients at PD catheter insertion, were also investigated. The extent of peritoneal fibrosis, vascular sclerosis, and advanced glycation end-product (AGE) accumulation were evaluated by quantitative or semi-quantitative methods. The average densities of CD31-positive vessels and podoplanin-positive lymphatic vessels were also determined. ♢

RESULTS

Peritoneal membrane fibrosis, vascular sclerosis, and AGE accumulation were significantly suppressed in the neutral group compared with the acidic group. The neutral group also showed lower peritoneal equilibration test scores and preserved ultrafiltration volume. The density of blood capillaries, but not of lymphatic capillaries, was significantly increased in the neutral group compared with the acidic and pre-PD groups. ♢

CONCLUSIONS

Neutral solutions with low GDPs are associated with less peritoneal membrane fibrosis and vascular sclerosis through suppression of AGE accumulation. However, contrary to expectation, blood capillary density was increased in the neutral group. The altered contents of the new PD solutions modified peritoneal membrane morphology and function in patients undergoing PD.

Encapsulating peritoneal sclerosis: what have we learned?

Encapsulating peritoneal sclerosis (EPS) is a rare complication of peritoneal dialysis (PD), but carries significant morbidity and mortality. We review the clinical features and radiologic and histologic changes found at diagnosis of EPS. Although EPS is strongly associated with the duration of PD, the pathogenesis remains only partly understood. We discuss the mechanisms thought to underlie the abnormally thickened, sclerotic peritoneal membrane seen in long-term PD patients including epithelial to mesenchymal transition and the molecular mediators of fibrosis and angiogenesis. We review how exposure to high-glucose, nonphysiological dialysis fluids, peritonitis, and uremia may be responsible for these changes. Much remains to be learned about optimal management of EPS, both medical and surgical, because the literature lacks controlled studies. Future research challenges include defining the role of surgery, immunosuppression, and antifibrotic agents in the management of EPS. We also need to understand why some patients progress from asymptomatic peritoneal sclerosis to the extreme levels of fibrin deposition and bowel encapsulation seen in EPS. Screening PD patients for potential future EPS remains difficult, and we need strategies for monitoring patients on longer-term PD that enable us to better quantify the risk of EPS for the individual patient.

Cardiovascular risk in the peritoneal dialysis patient

Cardiovascular death is the most frequent cause of death in patients on peritoneal dialysis. Risk factors for cardiovascular death in these patients include those that affect the general population as well as those related to end-stage renal disease (ESRD) and those that are specific to peritoneal dialysis. The development of overhydration after loss of residual renal function is probably the most important cardiovascular risk factor specific to peritoneal dialysis. The high glucose load associated with peritoneal dialysis may lead to insulin resistance and to the development of an atherogenic lipid profile. The presence of glucose degradation products in conventional dialysis solutions, which leads to the local formation of advanced glycation end products, is also specific to peritoneal dialysis. Other risk factors that are not specific to peritoneal dialysis but are related to ESRD include calcifications and protein-energy wasting. When present together with inflammation and atherosclerosis, protein-energy wasting is associated with a marked increase in the risk of cardiovascular death. Obesity is not associated with increased cardiovascular risk in patients on any form of dialysis. Left ventricular hypertrophy and increased arterial stiffness are the most important risk factors for cardiovascular events in the general population.

Induction of chronic kidney failure in a long-term peritoneal exposure model in the rat: effects on functional and structural peritoneal alterations

BACKGROUND

A long-term peritoneal exposure model has been developed in Wistar rats. Chronic daily exposure to 3.86% glucose based, lactate buffered, conventional dialysis solutions is possible for up to 20 weeks and induces morphological abnormalities similar to those in long-term peritoneal dialysis (PD) patients. The possible effects of kidney failure in this model are unknown. The aim was to analyze the effects of chronic kidney failure on peritoneal function and morphology, alone and in combination with PD exposure, in a well-established, long term, peritoneal exposure model in the rat. ♢

METHODS

40 male Wistar rats were randomly assigned into four experimental groups: no nephrectomy, no peritoneal exposure (sham; n = 8); nephrectomy, no peritoneal exposure (Nx; n = 12); no nephrectomy, with peritoneal exposure (PD; n = 8); and nephrectomy, with peritoneal exposure (NxPD; n = 12). The nephrectomy consisted of a one-step 70% nephrectomy. The peritoneal exposure groups were infused once daily for 16 weeks with a 3.86% glucose-based dialysis solution. Development of chronic kidney disease was monitored during the experiment. Peritoneal function and morphological assessment of the peritoneal membrane were performed at the end of the experiment. ♢

RESULTS

During follow-up the nephrectomized groups developed uremia with remarkable renal tubular dilatation and glomerular sclerosis in the renal morphology. Functionally, uremia (Nx) and PD exposure (PD) alone showed faster small solute transport and a decreased ultrafiltration capacity, which were most pronounced in the combination group (NxPD). The presence of uremia resulted in histological alterations but the most severe fibrous depositions and highest vessel counts were present in the PD exposure groups (PD and NxPD). Significant relationships were found between the number of vessels and functional parameters of the peritoneal vascular surface area. ♢

CONCLUSION

It is possible to induce chronic kidney failure in our existing long-term peritoneal infusion model in the rat. The degree of impairment of kidney function after 16 weeks is comparable to chronic kidney disease stage IV. Uremia per se induces both functional and morphological alterations of the peritoneal membrane. An additive effect of these alterations is present with the addition of chronic kidney failure to the model. The latter makes the present long-term model important in better understanding the pathophysiology of the peritoneal membrane in PD.

Peritoneal inflammation after twenty-week exposure to dialysis solution: effect of solution versus catheter-foreign body reaction

BACKGROUND

We hypothesized that both sterile solutions and foreign body reaction to the peritoneal dialysis catheter are associated with inflammatory changes in rats exposed to hypertonic solution.

METHODS

Four hypertonic solutions (30 - 40 mL) were injected daily via needle and syringe over 20 weeks in 4 groups of rats: 4.25% standard clinical solution (LAC), LAC plus pyridoxamine (PYR), LAC plus ethyl pyruvate (EP), and a biocompatible 4% dextrose solution (BIC). Two groups received catheters: a non-injected 4-week catheter group (C4) and a group injected for 20 weeks with the BIC solution (CI). Control animals (CON) were not injected. In the C4 group, adherent cells were separated from the catheter and examined by culture and electron microscopy to ensure that animals were bacteria free prior to exposure to solution. Animals underwent transport experiments to determine mass transfer coefficients of mannitol (MTC(M)) and albumin (MTC(A)), osmotic filtration flux (J(osm)), and hydrostatic pressure-driven flux (J(p)). After euthanasia, tissues were examined for submesothelial thickness, vascular density, and immunohistochemistry for various cytokines.

RESULTS

The catheter cell layer was free of bacteria and consisted of macrophages, lymphocytes, mesothelial cells, and fibroblastic cells. Marked differences in angiogenesis and submesothelial thickening were noted for the catheter groups. Transport differences were mixed: MTC(M) was significantly less for the CI group and MTC(A) was variable among the groups. There were no differences among groups for J(osm) or J(p). Inflammatory markers in the catheter-adherent cells correlated with inflammatory changes in the tissue. These data demonstrate significant changes in submesothelial thickness, angiogenesis, transport function, and inflammatory markers between animals injected with sterile solutions over 20 weeks with and without catheters.

CONCLUSION

An indwelling catheter amplifies peritoneal inflammation from dialysis solutions through a foreign body reaction. Our data also suggest that additives to existing solutions may have limited the effect on inflammatory response to non-biocompatible solutions.

The effects of a dialysis solution with a combination of glycerol/amino acids/dextrose on the peritoneal membrane in chronic renal failure

BACKGROUND

Long-term peritoneal dialysis (PD) with conventional glucose based, lactate-buffered PD fluids may lead to morphological and functional alterations of the peritoneal membrane. It was hypothesized that long-term exposure to a different buffer and a mixture of osmotic agents would cause less peritoneal abnormality.

OBJECTIVES

To investigate the effects of long-term exposure to a bicarbonate/lactate-buffered dialysis solution with a mixture of osmotic agents: glycerol 1.4%, amino acids 0.5%, and dextrose 1.1% (= 1% glucose) (GLAD) in a rat model with chronic kidney failure.

METHODS

All rats underwent a peritoneal catheter implantation and a 70% nephrectomy. Thereafter, the rats were randomly divided into 3 groups: GLAD, 3.86% Dianeal (Baxter, Nivelles, Belgium), and buffer (Physioneal without glucose, Baxter). All rats were infused daily for 16 weeks with the appropriate PD fluid. Afterwards, a peritoneal permeability analysis (SPARa) was performed using 3.86% Physioneal in all groups. After the SPARa, the rats were sacrificed to obtain tissue samples for morphometric determinations. Omental tissue was stained with picro Sirius red for assessment of fibrosis and with CD31 for vessel density.

RESULTS

GLAD and Dianeal showed faster small solute transport compared to the hypotonic buffer. No differences between the groups were present in ultrafiltration. Dianeal had the lowest value for free water transport and the highest protein clearances. Total triglyceride in plasma was not different between GLAD and the buffer. Vessel density after GLAD exposure (20 V/F) was very similar to the value found for the buffer solution (17 V/F); Dianeal caused a significantly higher value (35 V/F, p < 0.01). Also, the amount of fibrosis was higher in the Dianeal-exposed rats (p < 0.01).

CONCLUSION

Both hypertonic dialysis solutions increased peritoneal solute transport. GLAD exposure was associated with the best preservation of peritoneal morphology. The results of GLAD were very similar to those of the bicarbonate/lactate-buffered solution without osmotic agents. Studies in humans are needed for further assessment of GLAD.

Karl D. Nolph State of the Art Lecture: Feasible and Future Options for Salvation of the Peritoneal Membrane

A review is given of the various available strategies that can be used to protect the peritoneal membrane. A discussion of experimental studies on approaches that are still experimental, but that might be applied in patients in the future, follows. The currently available approaches include dietary sodium restriction, use of high-dose loop diuretics and of inhibitors of the renin–angiotensin system. All should preferably be combined with a dialysis prescription aimed at reducing the patient's exposure to glucose and its degradation products. The experimental studies indicate favorable effects of combining osmotic agents, together with drugs that interfere with the polyol pathway and the formation of advanced glycosylation end-products.

Experimental Study on Long-Term Exposure to a Biocompatible, Hypertonic, Pyruvate-Buffered Dialysis Solution

Background

Chronic exposure to glucose and glucose degradation products (GDPs) in dialysis solutions is involved in the pathogenesis of peritoneal neoangiogenesis and fibrosis, potentially leading to encapsulating peritoneal sclerosis (EPS). High lactate concentrations may contribute to glucose toxicity by creating a state of pseudohypoxia, which stimulates the formation of various growth factors.

Objective

To study the effects of long-term peritoneal exposure to a filter-sterilized pyruvate-buffered solution with a combination of 3 osmotic agents (amino acids, glycerol, glucose: PYRAGG) on peritoneal function and morphology.

Methods

Rats were exposed daily for a period of 20 weeks to PYRAGG, or to a conventional heat-sterilized solution (LH), or to a filter-sterilized solution (LF), after which a peritoneal function test was done and peritoneal tissue was obtained.

Results

Peritoneal solute and fluid transport characteristics at 20 weeks were similar in all groups. Fibrosis was most pronounced in the LH group compared to the others, suggesting an effect of GDPs. A marked reduction in the number of omental vessels was noted in the PYRAGG group (59% reduction compared to LH). A modest reduction (28%) was found in the LF animals. This points to a marked effect of reduced exposure to glucose.

Conclusions

PYRAGG was more biocompatible than a filter-sterilized glucose/lactate solution because it did not induce marked peritoneal abnormalities after long-term exposure. This did not lead to altered peritoneal transport characteristics. It is likely that further development of PYRAGG-like solutions will decrease the incidence of EPS.