An autopsy study of the peritoneal cavity from patients on continuous ambulatory peritoneal dialysis

Does Enalapril Prevent Peritoneal Fibrosis Induced by Hypertonic (3.86%) Peritoneal Dialysis Solution?

Objective

Peritoneal fibrosis (PF) is one of the most serious causes of failure in continuous ambulatory peritoneal dialysis (PD). Although the underlying mechanism responsible for the genesis of PF is still unknown, transforming growth factor p (TGFβ1) has been shown to be associated with PF. Angiotensin converting enzyme inhibitors have been shown to prevent the stimulating effect of growth factors. The aim of the present study was to investigate the effect of enalapril on peritoneal function and morphology in a rat model of experimental PF.

Methods

Twenty-one albino Wistar rats were divided into three groups: ( 1 ) the control group (C) received 10 mL isotonic saline intraperitoneally (IP), ( 2 ) the dextrose (Dx) group 10 mL 3.86% dextrose PD solution IP, and ( 3 ) the enalapril-treated group (ENA) 10 cc 3.86% dextrose PD solution IP plus 100 mg/L enalapril in drinking water. After 4 weeks, a 1-hour peritoneal equilibration test was performed with 20 mL 2.27% dextrose PD solution. Dialysate-to-plasma urea ratio (D/P urea), glucose reabsorption (D1/D0 glucose), ultrafiltration (UF) volume, and levels of dialysate protein, TGFβ1, and cancer antigen 125 (CA125) were determined. The parietal peritoneum was evaluated histologically by light microscopy.

Results

Administration of enalapril resulted in preserved UF (-0.2 ± 0.7 mL vs 1.7 ± 0.3 mL, p < 0.05), protein loss (2.3 ± 0.5 g/L vs 1.6 ± 0.2 g/L, p > 0.05), and peritoneal thickness (77 ± 7 μ vs 38 ± 5 μ, p < 0.001). D/P urea increased significantly in the Dx group ( p < 0.05). Both higher levels of TGFβ1 (undetectable vs 298 ± 43 pg/mL, p < 0.001) and lower levels of CA125 in dialysate effluent (0.94 ± 0.5 U/L vs 0.11 ± 0.1 U/L, p > 0.05) were determined in the Dx group.

Conclusion

These findings show that peritoneal morphology and function tests were dramatically deranged in the Dx group. The same properties were partially preserved in the ENA group. The production of TGFβ1 was significantly reduced but peritoneal thickness was not completely inhibited. In conclusion, by inhibiting the production of TGFβ1, enalapril can preserve peritoneal histology, peritoneal function, and remodeling of mesothelial cells.

TGF-β1 Induced by High Glucose is Controlled by Angiotensin-Converting Enzyme Inhibitor and Angiotensin II Receptor Blocker on Cultured Human Peritoneal Mesothelial Cells

Background

Loss of peritoneal function is a major complication associated with long-term peritoneal dialysis. Observed changes include loss and degeneration of the mesothelium, submesothelial thickening, alterations in the structure and number of blood vessels, and reduplication of the vascular basement membrane. Exposure to high glucose concentrations in peritoneal dialysis solutions is known to cause injury to cultured human peritoneal mesothelial cells (HPMC) as a result of overexpression of transforming growth factor beta 1 (TGF-β1). Previous studies have demonstrated that angiotensin II (AII) increases expression of TGF-β1 in a number of different cell types; although this has not been demonstrated in HPMC.

Objective

To clarify possible mechanisms involved in peritoneal fibrosis, we investigated whether HPMC expressed AII-forming pathway mRNA and whether increases in AII induced by high glucose contribute to the production of TGF-β1. We also examined the effects of the angiotensin-converting enzyme inhibitor (ACEI) perindoprilat and the AII receptor blocker (ARB) candesartan on expression of TGF-β1 and proliferation of HPMC.

Methods

Expression of mRNA for the AII-forming pathway and TGF-β1 in HPMC was examined by reverse transcriptase-polymerase chain reaction (RT-PCR) and quantitative RT-PCR. Levels of AII and TGF-β1 following 48 hours of incubation of the cells in a range of glucose concentrations were measured by enzyme immunoassay and enzyme linked immunosorbent assay respectively. The effect of glucose on cell proliferation was examined using the water-soluble tetrazolium salt WST-1 and [3H]-thymidine uptake. We also investigated the effect of ACEI and ARB on the expression of TGF-β1 and the proliferation of HPMC incubated at high glucose for 48 hours.

Results

AII-forming pathway mRNA was detected in HPMC, with expression of angiotensinogen, angiotensin-converting enzyme (ACE), AII type 1 receptor, and TGF-β1 mRNA increasing following exposure to glucose according to glucose concentration. High glucose was also shown to increase the production of AII and TGF-β1 and decrease the proliferation of HPMC. In contrast, we found that both the ACEI and the ARB attenuated the increase in TGF-β1 production and reduced cell proliferation caused by exposure to high glucose. These effects were greater with a combination of the two drugs.

Conclusion

The present study provides evidence that ( 1 ) HPMC express mRNA for the AII-forming pathway; ( 2 ) ACEI and ARB inhibit the TGF-β1 production induced by high glucose; ( 3 ) the AII-forming pathway is one mechanism by which high glucose causes production of TGF-β1. In addition to having antihypertensive and renal-protective effects, combination therapy with an ACEI and an ARB may also be effective in preventing loss of peritoneal function and decreasing peritoneal fibrosis.

Peritoneal Function: The Role of Aquaporins

The aquaporins (AQPs) constitute a large family of water channels that play a part in transcellular water movement in many tissues. They are particularly abundant and important in the kidney and the lung. Derangement of AQP structure or function leads to a variety of water-balance disorders. Aquaporin-1 (AQP1) is constitutively expressed in the endothelial cells of the capillaries and venules that provide the ultrasmall pores predicted by the three-pore model of water movement during peritoneal dialysis. The ultrasmall pores are critical for ultrafiltration. In addition, AQP1 and AQP3 are constitutively expressed in peritoneal mesothelial cells. The expression of those AQPs is upregulated by hyperosmolality. Reduced expression or function of AQP1 may be responsible for some cases of ultrafiltration failure, but further evidence is required to establish that link.

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.

Role of Surfactant in Peritoneal Dialysis

Evidence is reviewed that demonstrates how the mesothelial cell in the normal peritoneum and comparable serosal cavities secretes surface-active phospholipid (SAPL) as a means of protecting itself and the membrane it forms with its neighbors. It is shown how SAPL, if adsorbed (reversibly bound) to mesothelium, can impart excellent lubricity, antiwear and release (antistick) properties, while impeding surgical adhesion formation. More-speculative benefits include acting as a deterrent to fibrosis and as a barrier to both protein leakage and pathogen invasion by spanning cell junctions. Such spanning would also “pin down” cell corners, impeding peeling as the first step in exfoliation encountered in prolonged continuous ambulatory peritoneal dialysis (CAPD). The molecular mechanism underlying each of these possible functions is adsorption. Morphological and hydrophobicity studies are discussed as validation for such an adsorbed lining and how it can be fortified by administering exogenous SAPL.

Any role for SAPL in ultrafiltration is much more controversial. However, a surfactant lining can explain the very high permeability of the membrane to lipid-soluble drugs, implying that it is a barrier to water-soluble solutes. The clinical and animal evidence is conflicting but would seem to be best explained by a role for the barrier in promoting semipermeability, and hence the osmotic driving force for water transmission. Thus, adsorption of exogenous SAPL in CAPD patients with low ultrafiltration seems to restore this barrier function. The future direction for surfactant in CAPD would seem to rest with the physical chemists in producing formulations that optimize adsorption, probably involving a compromise between water solubility and surface activity of the phospholipids selected. It might even warrant using the interdialytic interval for re-adsorbing SAPL without the problem of dilution by a large volume of dialysate.

Neoangiogenesis in the Peritoneal Membrane

Objective

This study reviews relevant publications on the peritoneal vasculature and tries to establish morphological–functional relationships.

Design

The design is a review article.

Results

Recent morphological studies in peritoneal dialysis (PD) patients have shown the presence of diabetiform neoangiogenesis in long-term peritoneal dialysis. The same abnormalities could be induced in rats administered a high glucose dialysis solution daily for 20 weeks. The animals showed functional abnormalities in peritoneal transport similar to those found in long-term PD patients. Evidence was obtained in patients that vascular endothelial growth factor could be involved in glucose-induced peritoneal neoangiogenesis.

Conclusions

Diabetiform peritoneal neoangiogenesis is an important pathogenetic factor in ultrafiltration failure in long-term peritoneal dialysis patients.

How Can We Standardize Peritoneal Thickness Measurements in Experimental Studies in Rats?

Objective

The various methods of measuring peritoneal thickness in experimental studies in rats have yielded conflicting results. Also, no standard method exists to assess histologic findings in peritoneal morphology. We therefore undertook the present study to create a reproducible and standard method for assessing rat peritoneal histology in experimental studies.

Methods

Parietal peritoneal samples from 61 Wistar albino rats were used in the study. Excepting the skin, the whole abdominal wall from each rat was cut two-dimensionally (longitudinally and horizontally), fixed in formalin, and processed routinely for light microscopy. Slides were divided into two groups according to the direction of the inner abdominal muscle fibers in the sections. Longitudinal and horizontal sections of abdominal muscle were evaluated. For every section, one histopathology image was captured from a light microscope to an IBM-compatible computer. Peritoneal thickness (mean of the maximum and the minimum) and submesothelial area (SMA) were drawn on the image. A computer program then automatically performed measurements. Two different measurement methods were compared, based on the same sections.

Results

The mean peritoneal thickness was 91 ± 8 μm in the longitudinal sections and 75 ± 7 μm in the horizontal sections ( p < 0.05). Measurements of the SMA were found to be 47,762 ± 4,374 μm2 for the longitudinal sections and 40,389 ± 3,631 μm2 for the horizontal sections ( p < 0.05). In both types of sections, a positive correlation (96% for longitudinal and 90% for horizontal) was found between the SMA and the peritoneal thickness ( p < 0.01). The SMA measurements correlated significantly with functional properties [ratio of the dialysate concentration of glucose initially and after a 1-hour dwell (D1/D0 glucose), ultrafiltration, and protein loss; p < 0.01].

Conclusion

Peritoneal thickness can be measured as a mean of the minimum and maximum values. That measurement strongly correlates with submesothelial area. Both types of sections can be used, but the horizontal and longitudinal sections show systematic differences. All samples in a study should be taken using the same section pattern, either longitudinal or horizontal.

Ex Vivo Analysis of Dialysis Effluent-Derived Mesothelial Cells as an Approach to Unveiling the Mechanism of Peritoneal Membrane Failure

During peritoneal dialysis (PD), the peritoneum is exposed to bioincompatible dialysis fluids, which causes progressive fibrosis and angiogenesis and, ultimately, ultrafiltration failure. In addition, repeated episodes of peritonitis or hemoperitoneum may accelerate all these processes. Fibrosis has been classically considered the main cause of peritoneal membrane functional decline. However, in parallel with fibrosis, the peritoneum also displays increases in capillary number (angiogenesis) and vasculopathy in response to PD. Nowadays, there is emerging evidence pointing to peritoneal microvasculature as the main factor responsible for increased solute transport and ultrafiltration failure. However, the pathophysiologic mechanism(s) involved in starting and maintaining peritoneal fibrosis and angiogenesis remain(s) elusive. Peritoneal stromal fibroblasts have been considered (for many years) the cell type mainly involved in structural and functional alterations of the peritoneum; whereas mesothelial cells have been considered mere victims of peritoneal injury caused by PD. Recently, ex vivo cultures of effluent-derived mesothelial cells, in conjunction with immunohistochemical analysis of peritoneal biopsies from PD patients, have identified mesothelial cells as culprits, at least in part, in peritoneal membrane deterioration. This review discusses recent findings that suggest new peritoneal myofibroblastic cells may arise from local conversion of mesothelial cells by epithelial-to-mesenchymal transition during the repair responses that take place in PD. The transdifferentiated mesothelial cells may retain a permanent mesenchymal state, as long as initiating stimuli persist, and contribute to PD-induced fibrosis and angiogenesis, and hence to membrane failure. Future therapeutic interventions could be designated in order to prevent or reverse epithelial-to-mesenchymal transition of mesothelial cells, or its pernicious effects.

ACE Inhibitor and At1-Receptor Blocker Attenuate the Production of Vegf in Mesothelial Cells

Objective

Human mesothelial cells (HMC) are a major source of intraperitoneal vascular endothelial growth factor (VEGF) and by that are presumably involved in complications of long-term peritoneal dialysis (PD), such as ultrafiltration failure. This prompted us to look for agents that reduce basic mesothelial VEGF production and abrogate VEGF-overproduction induced by proinflammatory cytokines such as tumor necrosis factor alpha (TNF-α) and interleukin-1α (IL-1α). Angiotensin-converting enzyme (ACE) inhibition was found to preserve peritoneal function and ameliorate morphologic changes in a rat PD model. The present in vitro study was designed to investigate the effect of the ACE inhibitors captopril and enalapril, and the angiotensin II type 1-receptor (AT1) antagonist losartan on mesothelial VEGF synthesis.

Methods

HMC were isolated from omental tissue and taken into culture. VEGF antigen concentrations were measured in the cell supernatant by ELISA. VEGF mRNA levels were determined by real-time polymerase chain reaction.

Results

Incubation of HMC with captopril (100 - 1000 μmol/L) resulted in a concentration-dependent attenuation of VEGF synthesis. Incubation with captopril (500 - 1000 – μmol/L), enalapril (100 - 1000 μmol/L), and losartan (1 100 μmol/L) significantly decreased inflammatory mediator (TNF-α, IL-1α)-induced mesothelial VEGF overproduction.

Conclusion

The results indicate that ACE inhibitors and AT1-receptor blockers are capable of effectively attenuating the overproduction of VEGF due to proinflammatory cytokine stimuli. These data suggest that locally produced angiotensin II in the peritoneal cavity may be a potential therapeutic target in ultrafiltration failure during long-term PD.

Changes in Water Transport across the Peritoneum during Treatment with Continuous Ambulatory Peritoneal Dialysis in Selected Patients with and without Peritonitis

Background

The natural course of longitudinal changes in peritoneal permeability and membrane area has been studied mostly by performing single-dwell studies in selected patients during treatment with peritoneal dialysis.

Purpose

To evaluate the permeability characteristics of the peritoneal membrane by measuring drained ultrafiltration volume relative to initial glucose concentration in dialysis fluid from the start to the end of continuous ambulatory peritoneal dialysis (CAPD) treatment in a selected cohort of patients with and without peritonitis.

Design

A retrospective analysis of a group of patients whose peritoneal function was prospectively followed by recording drained ultrafiltration volume and glucose concentration in dialysis fluid for each dwell time, every day, during the time in CAPD treatment. Mean values from a 1-month period starting after the first 3 weeks of CAPD treatment were compared with the mean values from the last month of treatment. Approximately 11 500 exchanges were analyzed. Evaluations were done separately for short (day) and long (night) dwell times.

Patients and Statistics

Of 132 patients commencing CAPD treatment in the time period selected for inclusion, 51 had enough data to be included in this study. Of these, 29 patients experienced one or more episodes of successfully treated peritonitis. The selection of patients was not based upon patient characteristics, but upon criteria to satisfy predefined demands, such as number of measurements in each period, time since an episode of peritonitis, and time on CAPD treatment. Data were analyzed in three different groups: patients with episodes of peritonitis, patients without peritonitis, and both groups together. To assess changes between monthly mean at the start and at the end of CAPD, paired t-test was performed. Patients were also stratified into two groups according to low and high glucose in dialysis fluid at the start of CAPD (cutoff = 2 g/dL). Additionally, we used linear regression analyses to predict the level of drained ultrafiltration volume for a given level and change in glucose concentration. Mean treatment time for the entire group was 20 months (median 14.3 months), ranging from 6 to 69 months.

Results

No statistical differences in glucose concentrations were found between the periods compared. In the entire group there was an increase in ultrafiltration volume from the start to the end of CAPD treatment, for both day ( p = 0.009) and night ( p = 0.013) exchanges. Also, for patients without peritonitis, an increase appeared for day ( p = 0.046) and night exchanges ( p = 0.053). However, for the cohort with peritonitis, only an insignificant increase was indicated. Patient characteristics, diabetic patients, the need for glucose in dialysis fluid when commencing CAPD treatment, the number of episodes of peritonitis, and time on CAPD did not influence the change in ultrafiltration. Regression analyses showed higher ultrafiltration response to a given level and change in glucose concentration at the end of CAPD treatment compared to the start values, also for the cohort with peritonitis. The regression coefficient between these variables was also significantly changed for both day ( p < 0.0001) and night ( p = 0.027) exchanges.

Conclusion

A significant change in the regression coefficient between glucose in dialysis fluid and ultrafiltration volume reflects an increase in ultrafiltration response to a given level and change in glucose concentration during time on CAPD treatment. A parallel change after 5- and 9-hour dwells can be explained by a decrease in peritoneal surface area combined with a lesser decrease in peritoneal conductivity. However, changes in Starling forces across the peritoneal membrane are possible even in the absence of changes in peritoneal membrane characteristics.

Atorvastatin Improves Peritoneal Sclerosis Induced by Hypertonic PD Solution in Rats

Background

Peritoneal sclerosis is a complication of peritoneal dialysis and results in ultrafiltration failure. It is related to chronic peritoneal injury due to dialysis solution content and recurrent peritonitis. Statins have anti-inflammatory properties which may be of value in modulating responses to injury. We evaluated the capacity of atorvastatin to modify peritoneal alterations secondary to hypertonic glucose.

Methods

Thirty-two non-uremic rats were divided into three groups: group I (Sham) rats received no treatment (n=11), group II received hypertonic (3.86%, 10 ml/day) PD solution (n=10) and group III received hypertonic PD solution (10 ml/day) plus 80 mg/L atorvastatin in drinking water (n=11). After four weeks, a one-hour peritoneal equilibration test (PET) was performed with 3.86% PD solution. Dialysate-to-plasma urea ratio (D/P urea), glucose reabsorption (D1/D0 glucose), ultrafiltration volume (UF), dialysate protein, TGF-ß1 and VEGF levels were determined.

Results

Administration of atorvastatin resulted in preserved UF (4.9±0.8 vs 7.5±0.6 mL, p <0.01), protein loss (2.2±0.2 vs 2.1±0.1 g/L, p >0.05), and peritoneal thickness (53±3 vs 26±4 μm, p <0.01). D1/D0 glucose was significantly reduced in the dextrose group (0.70±0.02 vs 0.56±0.04, p <0.01). Both higher levels of TGF-ß1 (206±40 vs 474±120 pg/mL, p<0.05), and VEGF in dialysate effluent (4±0.4 vs 7.9±3 pg/mL, p>0.05), was determined in the dextrose group.

Conclusion

Exposure to hypertonic glucose solution resulted in alterations in peritoneal transport manifested by a rapid dissipation of the glucose gradient and resultant impaired UF response. Administration of atorvastatin led to prevention of these alterations. We suggest that the anti-inflammatory properties of statins are useful in providing protection of the peritoneal membrane from the effects of hypertonic glucose.

Peritoneal dialysis: from bench to bedside and bedside to bench

For patients with end-stage kidney disease unable to receive a kidney transplant, replacement of kidney function with dialysis is necessary to extend life. Peritoneal dialysis (PD) and hemodialysis (HD) are the two major forms of dialysis therapy. HD involves the passage of blood via an extracorporeal circuit whereby removal of small solutes, toxins, and water is achieved across a synthetic, semipermeable dialysis membrane. In contrast, in PD, the dialysis membrane is the highly vascularized internal lining of the peritoneal cavity. Intraperitoneal installation of hypertonic high glucose PD solution creates a transmembrane osmotic and diffusive gradient that facilitates water removal [ultrafiltration (UF)], convection, and diffusion of uremic toxins. Insight into the physiology of solute and water transport across the peritoneal membrane has been enhanced by the proposal of the ′'three-pore model'' of peritoneal membrane transport. Transport characteristics and UF capacity of the peritoneal membrane vary among individuals, and deleterious changes in the membrane may ensue over time. The degree to which these changes are a direct consequence of the type and composition of currently available PD solutions, recurrent infectious episodes, genetic differences among individuals, or a combination thereof is the subject of intense study. Adverse consequences resulting from the systemic and local metabolic effects of intraperitoneal glucose exposure, infection of the PD fluid, PD catheter dysfunction, and patient burnout from self-care often limit the long-term success of the therapy. Research aimed at addressing these challenges will examine the use of more biocompatible PD solutions and strategies aimed at attenuating progressive peritoneal membrane injury.

Are the Mesothelial-to-Mesenchymal Transition, Sclerotic Peritonitis Syndromes, and Encapsulating Peritoneal Sclerosis Part of the Same Process?

Mesothelial-to-mesenchymal transition (MMT) is an autoregulated physiological process of tissue repair that in uncontrolled conditions, such as peritoneal dialysis (PD), can lead to peritoneal fibrosis. The maximum expression of sclerotic peritoneal syndromes (SPS) is the encapsulating peritoneal sclerosis (EPS) for which no specific treatment exists. The SPS includes a wide range of peritoneal fibrosis that appears progressively and is considered as a reversible process, while EPS does not. EPS is a serious complication of PD characterized by a progressive intra-abdominal inflammatory process that results in bridles and severe fibrous tissue formation which cover and constrict the viscera. Recent studies show that transdifferentiated mesothelial cells isolated from the PD effluent correlate very well with the clinical events such as the number of hemoperitoneum and peritonitis, as well as with PD function (lower ultrafiltration and high Cr-MTC). In addition, in peritoneal biopsies from PD patients, the MMT correlates very well with anatomical changes (fibrosis and angiogenesis). However, the pathway to reach EPS from SPS has not been fully and completely established. Herein, we present important evidence pointing to the MMT that is present in the initial peritoneal fibrosis stages and it is perpetual over time, with at least theoretical possibility that MMT initiated the fibrosing process to reach EPS.

The peritoneal osmotic conductance is low well before the diagnosis of encapsulating peritoneal sclerosis is made

Encapsulating peritoneal sclerosis (EPS) is a serious condition whose frequency is increasing the longer the duration of peritoneal dialysis. To identify prognostic indicators of EPS, we studied here longitudinal changes in peritoneal membrane function of patients who later developed this complication. We identified all patients with an unequivocal diagnosis of EPS who began their peritoneal dialysis in our unit over a 20-year period and matched each of them for dialysis duration and age with four control patients who completed their dialysis. The dialysate/plasma creatinine ratio increased with time in both groups but was significantly higher in the patients with EPS only at the time their dialysis was discontinued. The ultrafiltration capacity was significantly worse for at least 2 years before stopping dialysis, diverging further at the time dialysis ceased, suggesting reduced osmotic conductance in the EPS patients. Both the glucose exposure rate for the 5 years preceding stoppage of dialysis and exposure to the osmotic agent icodextrin were significantly higher. Residual renal function was less in the EPS group, but there was no significant difference in the rates of peritonitis compared to the control group. The 24 h peritoneal protein clearance was not significantly different in EPS patients, possibly due to a greater fibrous matrix. Thus, our study shows that regular peritoneal membrane function tests can identify most patients at high risk of developing EPS before its occurrence.

The renin-angiotensin-aldosterone system in peritoneal dialysis: is what is good for the kidney also good for the peritoneum?

Morphological changes of the peritoneal membrane that occur over time among patients on peritoneal dialysis include fibrosis and neoangiogenesis. While the pathophysiologic mechanisms underlying these changes are not fully understood, the activation of the renin-angiotensin-aldosterone system (RAAS) may have an important role. Components of the RAAS are constitutively expressed within peritoneal mesothelial cells, and are upregulated in the presence of acute inflammation and chronic exposure to peritoneal dialysate. The high glucose concentration, low pH, and the presence of glucose degradation products in peritoneal dialysis solutions have all been implicated in modulation of peritoneal RAAS. Furthermore, activation of the RAAS, as well as the downstream production of transforming growth factor-beta, contributes to epithelial-to-mesenchymal transformation of mesothelial cells, resulting in progressive fibrosis of the peritoneal membrane. This process also leads to increased vascular endothelial growth factor production, which promotes peritoneal neoangiogenesis. Functionally, these changes translate into reduced ultrafiltration capacity of the peritoneal membrane, which is an important cause of technique failure among patients on long-term peritoneal dialysis. This brief review will describe our current state of knowledge about the role of peritoneal RAAS in peritoneal membrane damage and potential strategies to protect the membrane.

Surgical management of peritoneal dialysis peritonitis: the impact of peritoneal sclerosis

BACKGROUND

Peritonitis is a life-threatening complication of peritoneal dialysis. Peritoneal sclerosis is associated with long-term peritoneal dialysis. The aim of this study was to assess the effect of peritoneal sclerosis on outcomes following laparotomy for peritoneal dialysis peritonitis.

METHODS

A series of 63 consecutive patients underwent laparotomy for peritoneal dialysis peritonitis. Patients were divided into two groups, those with and those without simple peritoneal sclerosis identified at laparotomy. Medical, anaesthetic, and surgical notes were used for data collection. Patients with known encapsulating peritoneal sclerosis were excluded from the study.

RESULTS

Patients with simple peritoneal sclerosis had a statistically significant longer duration of peritoneal dialysis. They also had a significantly higher risk of major complications postoperatively and a greater relative risk for mortality.

CONCLUSIONS

There is an increased prevalence of simple peritoneal sclerosis with long-term peritoneal dialysis. Patients with simple peritoneal sclerosis have higher incidence of postlaparotomy complications. Patients on long-term peritoneal dialysis should be treated aggressively for peritoneal dialysis peritonitis to reduce complication/mortality rates. Evidence of simple peritoneal sclerosis at laparotomy should preclude further peritoneal dialysis.

Technical Aspects in Studying Peritoneal Morphology in Animal Models of Peritoneal Dialysis

Objective

Peritoneal biopsies are considered useful for gaining a better understanding of the pathophysiology of the peritoneum during experimental peritoneal dialysis (PD). Different peritoneal tissue samples (i.e., abdominal wall, liver, diaphragm, intestine, and omentum) may be used, but there can be artifacts due to peritoneal tissue processing.

Aim

To investigate differences in peritoneal membranes from different parts of the peritoneum, and also 2 different fixatives, in experimental PD and a peritonitis model in rats.

Methods

Peritoneal tissues from the anterior abdominal wall, liver, omentum, and intestine were taken from each of 3 groups of animals: sham, experimental PD, and peritonitis model. Tissue samples were immediately fixed with 4% formaldehyde and routinely processed for histological examination. Two parietal peritoneal tissue samples according to longitudinal and horizontal sections of anterior wall inner abdominal muscle were also taken. All samples were immediately fixed with 4% formaldehyde and B5 fixative (B5), and then routinely processed for histological examination.

Results

In all groups, histopathological findings were more commonly seen in the abdominal wall samples. There were no changes observed in peritoneal membranes other than those of anterior abdominal wall samples from both sham and PD model rats. However, there was a significant difference between anterior and posterior facets of liver in the peritonitis model. Furthermore, the antimesenteric site of intestinal peritoneum was less affected than the mesenteric site. There were no significant histopathological differences between B5 and 4% formaldehyde fixation ( p > 0.05).

Conclusion

Our results suggest that peritoneum obtained from the anterior abdominal wall is the most affected area and therefore the most suitable site to investigate peritoneal changes in the experimental rat PD model. There were no significant differences between fixation with 4% formaldehyde and B5 solution. Abdominal wall samples should be of the same direction of inner abdominal muscle, that is, horizontal sectioning should be used for measurements of the submesothelial area.

Monitoring of the peritoneal membrane

Background. Indirect methods can be used to provide valuable information about peritoneal structure and function for the indirect analysis of peritoneal membrane. Methods. The focus of this paper will be on the commonly available tools for this purpose. First, the value and clinical relevance of CA125 as a marker of mesothelial cell mass in peritoneal effluent will be evaluated. Thereafter, monitoring the peritoneal membrane by using its properties to transport solutes and water will be discussed. Results. The data obtained can be useful for tailoring dialysis adequacy, analysis of clinical problems such as ultrafiltration failure or to predict the development of peritoneal sclerosis.

Conventional versus biocompatible peritoneal dialysis fluids: more questions than answers?

The most important challenge in peritoneal dialysis (PD) is long-term preservation of peritoneal membrane structure and function. Introduction of dialysis fluids into the peritoneal cavity induces changes. These changes are related to duration of dialysis, occurrence of peritonitis and components of the dialysis solution. Bioincompatibility is considered to be the major cause of the development of morphological changes of the peritoneal membrane. pH neutral PD fluids that are low in glucose degradation products (GDP) seem to better preserve the peritoneal membrane and have less systemic effects than the conventional ones. However, the long-term effects are not clear. An overview of the effects of conventional PD fluids and glucose-based PD fluids with neutral pH in ex vivo and in vivo animal and clinical studies is presented.

Mineralocorticoid receptor blockade ameliorates peritoneal fibrosis in new rat peritonitis model

Peritoneal fibrosis (PF) is an important complication of long-term peritoneal dialysis. Although mineralocorticoid and mineralocorticoid receptor (MR) have attracted increasing attention in the field of vascular injury, including the heart, kidney, and vessels, little is known about the role of mineralocorticoid in PF. This work was designed to explore the effects of MR blockade on PF. We developed a new model of PF in rats based on mechanical scraping of the peritoneum. This model is characterized by acute-phase inflammation (neutrophil and macrophage infiltration on days 0–3) and late-phase PF (α-smooth muscle actin-positive fibroblast infiltration, type III collagen accumulation, and neoangiogenesis on days 7–14). Peritoneal thickening peaked on day 14. MR was expressed in rat peritoneum and a rat fibroblast cell line. Expression of its effector kinase [serum- and glucocorticoid-induced kinase-1 (Sgk1)], transforming growth factor-β (TGF-β), plasminogen activator inhibitor-1 (PAI-1), and CD31-positive vessels increased during the course of PF. Rats were treated with spironolactone, angiotensin receptor blockade (ARB), or angiotensin-converting enzyme inhibitor (ACEI)-ARB-spironolactone starting at 6 h after peritoneal scraping. All parameters, including peritoneal thickening, number of macrophages and CD31-positive vessels, and expression of monocyte chemoattractant protein-1, TGF-β, PAI-1, and Sgk1, were significantly suppressed by spironolactone (10 mg·kg−1·day−1). The effects of spironolactone (10 and 20 mg·kg−1·day−1) were very similar to those of triple blockade. ARB, but not ACEI, significantly reduced peritoneal thickening. Furthermore, peritoneal function assessed by peritoneal equilibration test was significantly improved by spironolactone. Our results suggest that MR is a potential target to prevent inflammation-induced PF in patients on peritoneal dialysis.

Does a history of peritoneal dialysis result in an impaired gastrointestinal life quality?

Peritoneal dialysis (PD) invariably induces sclerotic changes in the peritoneal membrane. The impact of these changes on the well-being of PD patients has not been studied sufficiently. In a matched-pair analysis, the gastrointestinal life quality of patients with a history of PD was compared with end-stage renal disease patients who never performed PD, using a standardized questionnaire (gastrointestinal life-quality index [GLQI]). We identified all patients in our dialysis unit who underwent PD between 1989 and 2001 and who were alive in October 2001 (PD patients; n=53). Patients who were treated by hemodialysis (HD patients) were recruited as pairs. Hemodialysis and PD patients did not differ in gastrointestinal life quality (GLQI: HD 106.0+/-16.4 points; PD 104.0+/-16.7 points; p=0.70). Gastrointestinal life quality was neither correlated with the number of peritonitis episodes, nor with the duration of PD treatment. Peritoneal dialysis treatment is not associated with a long-term impairment of gastrointestinal life quality.

Postoperative intraperitoneal adhesion pathophysiology

Aside from the normal 'ad integrum' peritoneal regeneration, the postoperative intraperitoneal adhesion formation process may be considered as the pathological part of peritoneal healing following any injury, particularly a surgical one. Despite a large body of clinical and experimental studies, its pathophysiology remains controversial. Moreover, a better understanding of the pathophysiological events and of the medical and surgical factors involved in the adhesion formation process is pivotal in any attempt to control this very frequent phenomenon and its serious consequences.

Leptin induces TGF-β synthesis through functional leptin receptor expressed by human peritoneal mesothelial cell

Marked increase in leptin concentration in spent peritoneal dialysate has been reported following continuous ambulatory peritoneal dialysis treatment. The present study was designed to determine whether functional leptin receptor is expressed by human peritoneal mesothelial cells and if so, the possible implication in dialysis. Expression of leptin receptors in cultured mesothelial cells and omental tissue was examined. The effect of leptin on the production of transforming growth factor-beta (TGF-beta) by mesothelial cells in the presence or absence of high glucose was determined using in vitro culture model of human peritoneal mesothelial cells and adipocytes. The signaling mechanism involved in leptin-induced TGF-beta synthesis by mesothelial cells was studied. Both mRNA and protein of the full-length leptin receptor are constitutively expressed in mesothelial cells. The leptin receptor expression in mesothelial cells was upregulated by glucose but not leptin. In adipocytes, glucose increased the mRNA expression and synthesis of leptin. The Janus kinase-signal transducers and activation (JAK-STAT) signal transduction pathway in mesothelial cells was activated by either exogenous or adipocytes-derived leptin. Exogenous leptin induced the release of TGF-beta by mesothelial cells. The TGF-beta synthesis induced by leptin was amplified by glucose through increased leptin receptor expression. Our novel findings reveal that functional leptin receptor is present on human peritoneal mesothelial cells. The leptin-induced TGF-beta synthesis in mesothelial cells is associated with the expression of leptin receptor and the activation of the JAK-STAT signal transduction pathway.

Effect of valsartan versus lisinopril on peritoneal sclerosis in rats

BACKGROUND

Peritoneal sclerosis (PS) is one of the most serious causes of failure in long-term peritoneal dialysis. Angiotensin II is known to promote fibrosis and inflammation in various tissues. We previously showed that ACE inhibitors (ACEIs) have beneficial effects on hypertonic PD solutions (3.86% PD) induced peritoneal alterations. The aim of this study is to compare the effects of an ACEI and a receptor blocker on peritoneal alterations induced by hypertonic PD solutions in rats.

METHODS

Forty-three non-uremic rats were divided into four groups: group I (Sham) rats received no treatment (n=11), group II received hypertonic (3.86%, 10 ml/day) PD solution (n = 10) and groups III and IV received hypertonic PD solution (10 ml/day) plus 640 mg/L valsartan (n=11) and 100 mg/L lisinopril in drinking water (n = 11). After four weeks, a one-hour peritoneal equilibration test (PET) was performed with 3.86% PD solution. Dialysate-to-plasma urea ratio (D/P urea), glucose reabsorption (D 1 /D 0 glucose), ultrafiltration volume (UF), dialysate protein, TGFbeta 1 and VEGF levels were determined.

RESULTS

Administration of valsartan or lisinopril resulted in preserved UF (8+/-0.8 and 6.7+/-0.7 vs 4.9+/-0.8 mL), D1/D0 glucose (0.69+/-0.05 and 0.62+/-0.05 vs 0.56+/-0.04) and peritoneal thickness (19.4+/-2.9 and 28.5+/-5.2 vs 53+/-3 microm), respectively. Both higher level of TGF beta 1 (206+/-40 vs 474+/-120 pg/mL, p<0.05), and VEGF in dialysate effluent (4+/-0.4 vs 7.9+/-3 pg/mL, p>0.05), was determined in the dextrose group. Both cytokines are partially inhibited by valsartan or lisinopril (p >0.05)

CONCLUSION

Exposure to hypertonic glucose solution resulted in alterations in peritoneal transport manifested by a rapid dissipation of the glucose gradient and resultant impaired UF response. Administration of valsartan or lisinopril led to attenuation of these alterations. We suggest that the equal protection of the peritoneal membrane from the effects of hypertonic glucose was achieved by receptor blockers and ACE inhibitors.

Simple peritoneal sclerosis and sclerosing peritonitis: related or distinct entities?

AIM

The etiopathogenesis of sclerosing peritonitis is still debated, with some sustaining that it is a rare form of progression of simple peritoneal sclerosis and others that it is a primitive form. The aim of the present research was to clarify this question.

MATERIAL AND METHODS

438 peritoneal biopsies from 253 patients were re-examined. 174 were obtained prior to peritoneal dialysis and 224 after various periods of dialysis. Forty biopsies were from peritoneal dialysis patients who developed sclerosing peritonitis. Peritoneal morphology was studied for signs of transition from simple sclerosis to sclerosing peritonitis.

RESULTS

Evidence was found sustaining the hypothesis that simple sclerosis to sclerosing peritonitis patients have distinct pathologies.

CONCLUSIONS

The results confirm previous observations, excluding the existence of any type of relation between simple peritoneal sclerosis to sclerosing peritonitis.

Histological and functional characteristics of peritoneal membrane in peritoneal sclerosis of PD patients

BACKGROUND

Function and structure of peritoneal membrane (PM) are impaired on peritoneal dialysis (PD). Peritoneal sclerosis is a common finding in peritoneal biopsies (PB) of PD patients. The aim of this study was to examine the impact of peritoneal sclerosis on peritoneal function and clinical parameters in PD patients submitted to peritoneal biopsy.

METHODS

A PB was performed on 31 PD patients during catheter removal due to malfunction or after drop-out from treatment. For each patient PM transport was evaluated by the last peritoneal equilibration test before PB. Each daily glucose load was calculated. Tissue was formalin-embedded and stained for histological and immunohistochemical studies.

RESULTS

Patients with submesothelial sclerosis and those with impairment of submesothelial basement membrane and subendothelial vascular membrane were submitted to a larger daily glucose load. Peritoneal sclerosis > 50 microns was more frequent in high transporters, who were exposed to larger daily glucose load compared to medium-high transporters. Mesothelial loss is correlated to peritoneal sclerosis and vascular injuries.

CONCLUSIONS

Peritoneal sclerosis is not constant in PD patients: it is related to the loss of mesothelium integrity, to the daily glucose load of PD treatment and to vascular injuries, but apparently not to the presence of inflammatory infiltrate. It remains a matter of debate how much the peritoneal sclerosis modifies the function of PM and how new more biocompatible PD solutions could reduce PM injury.

Differential expression of receptors for advanced glycation end-products in peritoneal mesothelial cells exposed to glucose degradation products

Autoclaving peritoneal dialysate fluid (PDF) degrades glucose into glucose degradation products (GDPs) that impair peritoneal mesothelial cell functions. While glycation processes leading to formation of advanced glycation end-products (AGE) were viewed commonly as being mediated by glucose present in the PDF, recent evidence indicates that certain GDPs are even more powerful inducers of AGE formation than glucose per se. In the present study, we examined the expression and modulation of AGE receptors on human peritoneal mesothelial cells (HPMC) cultured with GDPs, conventional PDF or PDF with low GDP content. HPMC cultured with GDPs differentially modulated AGE receptors (including RAGE, AGE-R1, AGE-R2 and AGE-R3) expression in a dose-dependent manner. At subtoxic concentrations, GDPs increased RAGE mRNA expression in HPMC. 2-furaldehyde (FurA), methylglyoxal (M-Glx) and 3,4-dideoxy-glucosone-3-Ene (3,4-DGE) increased the expression of AGE-R1 and RAGE, the receptors that are associated with toxic effects. These three GDPs up-regulated the AGE synthesis by cultured HPMC. In parallel, these GDPs also increased the expression of vascular endothelial growth factor (VEGF) in HPMC. PDF with lower GDP content exerted less cytotoxic effect than traditional heat-sterilized PDF. Both PDF preparations up-regulated the protein expression of RAGE and VEGF. However, the up-regulation of VEGF in HPMC following 24-h culture with conventional PDF was higher than values from HPMC cultured with PDF containing low GDP. We have demonstrated, for the first time, that in addition to RAGE, other AGE receptors including AGE-R1, AGE-R2 and AGE-R3 are expressed on HPMC. Different GDPs exert differential regulation on the expression of these receptors on HPMC. The interactions between GDPs and AGE receptors may bear biological relevance to the intraperitoneal homeostasis and membrane integrity.

Acute-onset, steroid-sensitive, encapsulating peritoneal sclerosis in a renal transplant recipient

Encapsulating peritoneal sclerosis is a severe complication of peritoneal dialysis. Immunosuppressive drugs have been claimed to be helpful in the treatment of this disease, although the pathophysiological background is poorly understood. In this report, we present a patient with encapsulating peritoneal sclerosis after successful renal transplantation. Maintenance immunosuppressive therapy consisted of mycophenolate mofetil, tacrolimus, and low-dose corticosteroids. The patient was treated successfully with high doses of corticosteroids. A subsequent relapse of the encapsulating peritoneal sclerosis, probably resulting from fast tapering of the corticosteroid dose, responded well to an increase in corticosteroid dose. Our case strongly supports a therapeutic role for high-dose steroids in the treatment of encapsulating peritoneal sclerosis during its initial inflammatory stage.

Sclerosing encapsulating peritonitis as a complication of long-term continuous ambulatory peritoneal dialysis in Korea

Sclerosing encapsulating peritonitis (SEP) is a rare yet serious complication in patients with continuous ambulatory peritoneal dialysis (CAPD). Incidence and prevalence of this syndrome have been defined in some large populations and a few single-centre experiences, but there is no satisfactory estimate of the comparative incidence of dialysis related SEP. The pathogenesis of SEP still remains uncertain, but there could be various causative factors. The diagnosis of SEP remains based on clinical suspicion confirmed with radiologic and/or pathologic findings. The possible variable etiologies and probable distinct pathways leading to this syndrome may make a uniform therapeutic approach unlikely. To determine the prevalence, etiologic factors, clinical features, effect of dialysis duration, and outcome of SEP in Korea, patients undergoing CAPD who developed SEP were retrospectively studied in five University Hospital dialysis centres with large numbers of CAPD patients in Korea. Out of a total 3888 CAPD studied patients between January 1981 to December 2002 in those five medical centres, 31 cases developed SEP with the overall prevalence 0.8%. There were 15 men and 16 women. The mean age of these patients was 44.0 +/- 9.8 years old. The mean duration of CAPD before SEP was 70.3 +/- 41.9 months (range 9-144 months) and 67.8% of patients (21/31) had been on CAPD more than 4 years. Peritonitis, including one fungal peritonitis, was the main cause of SEP in 25 cases (80.6%). Seventy percent of these cases used beta-blocker and the mean duration of the usage was 61.7 +/- 47.6 months. Seven cases were surgically treated and others were treated conservatively with intermittent total parenteral nutrition. The mortality rate was 25.8%. In conclusion, SEP is a serious life threatening complication of CAPD, and most cases had long-term peritoneal dialysis (PD) duration more than 4 years. To reduce the incidence of SEP, careful monitoring may be needed especially in patients with long-term CAPD and peritonitis.

Selective depletion of fibroblasts preserves morphology and the functional integrity of peritoneum in transgenic mice with peritoneal fibrosing syndrome

BACKGROUND

A peritoneal fibrosing syndrome (PFS) can progressively reduce peritoneal ultrafiltration during chronic peritoneal dialysis in patients with renal failure. The pathogenesis of PFS is unclear and the role of peritoneal fibroblasts has not been evaluated experimentally.

METHODS

We followed the fate of fibroblasts producing PFS in a mouse model using fibroblast-specific protein 1 (FSP1) as a marker. PFS was induced by daily peritoneal infusions of chlorhexidine gluconate (CHG) saline into transgenic mice expressing the thymidine kinase (Delta tk) gene under the control of the FSP1 promoter (FSP1.Delta tk mice). To demonstrate the role of fibroblasts in PFS, we treated these FSP1.Delta tk mice with a nucleoside analogue to induce DNA chain termination and fibroblast death.

RESULTS

Mice receiving peritoneal infusions of CHG saline every other day for 2 weeks developed increasing numbers of FSP1+ fibroblasts in the subserosal layers of the visceral peritoneum. Mac-3+ monocytes (macrophages) subsequently accumulated over the next 2 weeks in association with increased deposition of type I collagen and increased endothelial vascularity (CD31+) in these subserosal tissues. Since these peritoneal fibroblasts expressed monocyte chemoattractant protein-1 (MCP-1), heat shock protein 47 (HSP47), and vascular endothelial growth factor (VEGF), we suspect they were partially responsible for macrophage recruitment, matrix production, and the neoangiogenesis in the subserosal tissue. Treatment of PFS in FSP1.Delta tk transgenic mice with a nucleoside analogue selectively reduced the numbers of peritoneal fibroblasts and attenuated the attendant changes in peritoneal histology. Rescuing the peritoneal membrane from chronic thickening and neoangiogenesis by reducing the number of fibroblasts also preserved ultrafiltration.

CONCLUSION

Peritoneal fibroblasts play a pivotal role in PFS, and their deletion using a fibroblasts-specific transgene was effective in preventing peritoneal fibrogenesis.

Glucose degradation products (GDP) retard remesothelialization independently of d-glucose concentration

BACKGROUND

Glucose degradation products (GDP) present in heat-sterilized dialysis fluids are thought to contribute to cellular dysfunction and membrane damage during peritoneal dialysis. To examine the effects of specific GDP on the remesothelialization process, the impact of conventional and low GDP peritoneal dialysis solutions, D-glucose, and individual GDP in a scratch-wounding model was assessed.

METHODS

Scratch (0.5 to 0.6 mm)-wounded human peritoneal mesothelial cells (HPMC) were treated, at pH 7.4, with either (1) control medium (M199), (2) laboratory-prepared heat or filter-sterilized solutions, (3) 10% to 80% vol/vol solution of Gambrosol or Gambrosol-trio (1.5% and 4.0% glucose), (4) D-glucose (5 to 80 mmol/L), or (5) individual or combined GDP [acetaldehyde, formaldehyde, glyoxal, methylglyoxal, 3-deoxyglucosone (3-DG), 5-hydroxy methylfufural (5-HMF), or 3,4-di-deoxyglucosone-3-ene (3,4-DGE)]. Wound closure was recorded by time-lapse photomicroscopy.

RESULTS

In untreated HPMC, the rate of wound closure was linear and the process was complete by 18.4 +/- 3.6 hours (N = 16). In wounded HPMC exposed to dilutions of heat-sterilized but not filtered laboratory solutions (1.5% or 4.0% glucose, pH 7.4), remesothelialization was significantly retarded (P = 0.04 and P = 0.009 vs. M199, respectively). In Gambrosol, remesothelialization was significantly retarded in both 1.5% and 4.0% solutions. In contrast in Gambrosol-trio-treated HPMC, this rate was not significantly reduced in either 1.5% or 4.0% glucose peritoneal dialysis fluids. Remesothelialization was dose-dependently retarded in HPMC exposed to 3,4-DGE (>10 microl/L), formaldehyde (>5 micromol/L) but not by exposure to the other GDP tested even at 5 times the concentration present in low glucose solutions. The rate of remesothelialization was not significantly altered by exposure to D-glucose concentrations up to 80 mmol/L.

CONCLUSION

These data identify that the formaldehyde and 3,4-DGE present in heat-sterilized peritoneal dialysis solutions are important in reducing mesothelial cell regeneration. Specifically targeting their removal may have major benefits in preserving the mesothelium during long-term peritoneal dialysis.

Antibiotic Administration in an Animal Model of Chronic Peritoneal Dialysate Exposure

♦ Objectives

The high incidence of intraperitoneal infection remains an important problem in animal models of chronic dialysate exposure. Prophylactic antibiotic administration can be used to resolve this problem, but the isolated effects of antibiotics on peritoneal membrane function and structure are unknown. The present study examined the effects of prophylactic antibiotics on infection rate and peritoneal membrane function and structure in a rat model of chronic dialysate exposure.

♦ Design

A first group of rats (A; n = 12) received 10 mL 3.86% glucose dialysate twice daily through a heparin-coated catheter. In a second group of animals (B; n = 12), oxacillin 2.5 mg/day and gentamicin 0.04 mg/day were added to the dialysate. Group C ( n= 12) was injected twice daily with an identical dose of antibiotics dissolved in 1 mL of buffer solution. Group D ( n = 12) was left untreated. Dialysate cultures were obtained regularly. After 8 weeks of exposure, peritoneal transport studies were performed and samples for histology were obtained.

♦ Results

Technique survival was 92% in group A and 100% in the remaining groups. Five rats in group A but none of the animals in the other groups developed peritonitis. The transport rates of small solutes were elevated and net ultrafiltration was decreased in group A compared to the controls. Fibrosis, as evaluated by quantifying Picro Sirius Red staining with image analysis, was significantly elevated in group A (3.48% ± 1.06% vs 0.72% ± 0.51% in group D, p < 0.05) but not in group B (0.29% ± 0.07%) or in group C (0.52% ± 0.28%). Vascular density, measured by counting the number of blood vessels that stained positive for endothelial NO synthase, was increased in both groups that were exposed to dialysate: 153.0 ± 12.9/μm2 in group A and 131.6 ± 14.3/μm2 in group B, versus 76.76 ± 12.37/μm2 in group C and 73.2 ± 10.4/μm2 in group D ( p < 0.01).

♦ Conclusions

Prophylactic administration of oxacillin and gentamicin adequately prevented intraperitoneal infection in an animal model of chronic dialysate exposure. In addition, fibrosis was absent, suggesting intra-peritoneal infection rather than dialysate exposure is a causative factor.