Use of pure bicarbonate-buffered peritoneal dialysis fluid reduces the incidence of CAPD peritonitis.

BACKGROUND: Advances in bag connection technology have reduced the incidence of peritonitis in CAPD patients but there is little information on the effect of the new peritoneal dialysis fluids. METHODS: We studied the incidence of CAPD peritonitis for about 3 years in 100 incident patients--50 patients dialysed with lactate-buffered solution, pH 5.5 and containing glucose degradation products (GDP) (lactate group), and 50 patients with pure bicarbonate-buffered solution, pH 7.4 and low GDP (bicarbonate group). Patients in both groups were similar in age, sex, length of time on CAPD, connection technology and handling of dialysis. RESULTS: In the lactate group, 74 episodes of peritonitis were recorded compared with 43 in the bicarbonate group, i.e. one episode per 21 patient-months with the lactate dialysis fluid and one episode per 36 patient-months with the bicarbonate dialysis fluid (OR 0.58, 95% CI 0.37-0.91, P = 0.017). A total of 3369 exchanges per episode of peritonitis were recorded for bicarbonate compared with 2004 exchanges per episode of peritonitis in the lactate group. The majority of organisms isolated in both groups were Gram-positive bacteria, with a predominance of the oropharyngeal and cutaneous endogenous flora. Three episodes of fungal peritonitis occurred in the lactate group and none in the bicarbonate group. CONCLUSIONS: Our results suggest that the pure bicarbonate-buffered peritoneal dialysis fluid appears to reduce the frequency of peritonitis in CAPD patients possibly in relation to greater biocompatibility and maintenance of peritoneal membrane structural integrity. Similar results can probably relate to all low-GDP solutions.     

Benefits of switching from a conventional to a low-GDP bicarbonate/lactate-buffered dialysis solution in a rat model

BACKGROUND: Long-term exposure to standard peritoneal dialysis fluid (PDF) results in alterations in peritoneal morphology and function. Studies investigating the long-term effects on the peritoneum of a low-glucose degradation product (GDP) bicarbonate/lactate-buffered PDF demonstrated its superior biocompatibility. We examined the potential of the low-GDP bicarbonate/lactate-buffered solution to reverse or reduce standard PDF-induced peritoneal alterations. METHODS: Female Wistar rats received twice daily intraperitoneal infusions with either a lactate-buffered solution with 3.86% glucose at pH 5.5 (Dianeal, referred to as standard PDF), or a low-GDP bicarbonate/lactate-buffered solution with 3.86% glucose at physiologic pH (Physioneal, referred to as bicarbonate/lactate PDF) for different periods of time: (1) 12 weeks Dianeal (N= 9); (2) 12 weeks Physioneal (N= 9); (3) 20 weeks Dianeal (N= 11); (4) 20 weeks Physioneal (N= 10); (5) 12 weeks Dianeal followed by 8 weeks Physioneal (N= 10). RESULTS: Chronic standard PDF exposure resulted in loss of ultrafiltration capacity, increased VEGF expression and vascular density, higher advanced glycation end product (AGE) accumulation, up-regulation of TGF-beta expression, and development of fibrosis compared to low-GDP bicarbonate/lactate-buffered PDF. The PDF-induced alterations were time-dependent. Crossover from standard PDF to low-GDP bicarbonate/lactate PDF resulted in a less impaired ultrafiltration (UF), less pronounced VEGF expression and neoangiogenesis, and less severe AGE accumulation, TGF-beta expression, and fibrosis compared to continuous standard PDF exposure for 20 weeks. CONCLUSION: Low-GDP bicarbonate/lactate-buffered PDF has the potential to slow down standard PDF-induced peritoneal membrane damage.     

The in vitro biocompatibility performance of a 25 mmol/L bicarbonate/10 mmol/L lactate-buffered peritoneal dialysis fluid

The in vitro biocompatibility performance of a 25 mmol/L bicarbonate/10 mmol/L lactate-buffered peritoneal dialysis fluid. BACKGROUND: The biocompatibility profile of a new peritoneal dialysis (PD) solution (Physioneal 35) was determined using a selection of in vitro assay systems. Physioneal 35 is buffered by a combination of 25 mmol/L bicarbonate and 10 mmol/L lactate, thereby providing a solution with a total of 35 mmol/L of alkali to complement the currently available 25 mmol/L bicarbonate and 15 mmol/L lactate combination solution, Physioneal 40. In addition, the new solution contains a calcium concentration of 1.75 mmol/L rather than 1.25 mmol/L present in Physioneal 40. Physioneal 35 and 40 are manufactured in double chamber bag systems that permit separation of glucose from the buffer during sterilization. When the two chambers are mixed just before patient use, the resulting solution has a neutral pH and reduced glucose degradation content. Physioneal 35 was evaluated for its cytotoxicity potential using a murine fibroblast assay, its acute effect on human neutrophil and human peritoneal mesothelial cell function, and its in vitro potential to form advanced glycation end products (AGE). The biocompatibility characteristics of this new formulation were compared with that of a conventional, lactate-based solution and to that of its parent formulation, Physioneal 40. METHODS: Proliferation of murine fibroblasts was determined after exposure to dialysis fluids for 72 hours. Cell viability was assayed by the ability to take up neutral red dye. Human neutrophils were exposed for 15 minutes to dialysis fluids, and their ATP content and phorbol 12-myristate 13-acetate (PMA) stimulated chemiluminescence response was determined as a measure of viability and respiratory burst activity, respectively. Cellular interleukin (IL)-1beta-driven IL-8 synthesis by human mesothelial cells following acute exposure to dialysis fluids was also assessed. Advanced glycation end product formation in the dialysis fluids was measured after 5 and 20 days of incubation with human serum albumin (HSA) as the model protein. RESULTS: In all assays employed, the biocompatibility profile of Physioneal 35 was similar to that of the Physioneal 40 parent formulation. Physioneal 35 showed a significant improvement in biocompatibility performance compared to a pH neutralized conventional lactate-buffered peritoneal dialysis solution in the murine fibroblast assay. In the acute exposure assays, human neutrophil viability and respiratory burst were significantly improved compared with the acidic, conventional solution; however, no statistically significant improvement were seen in mesothelial cells. AGE formation, which is thought to be an important mechanism by which glucose and glucose degradation products cause structural and functional changes of the peritoneal membrane, was significantly lower in Physioneal 35 compared with the conventional dialysis solution. CONCLUSION: The biocompatibility profile of Physioneal 35 was similar to that of the original Physioneal 40 bicarbonate/ lactate-buffered dialysis solution, confirming that differences in both buffer content and calcium concentration do not affect biocompatibility performance. Both bicarbonate/lactate formulations (Physioneal 35 and Physioneal 40) were more biocompatible than a conventional lactate-buffered dialysis solution in this in vitro biocompatibility assessment.     

In vivo and in vivo effects of amino-acid-based and bicarbonate-buffered peritoneal dialysis solutions with regard to peritoneal transport and cytokines/prostanoids dialysate concentrations

Background: Increasing evidence suggests that conventional PD solutions are detrimental to host defence mechanisms of peritoneal cells. We tested a new amino-acid-based and bicarbonate-buffered PD solution under in vivo and in vitro conditions. Method: During a prospective cross-over randomized intraindividual study 10 CAPD patients were investigated with three different solutions: Amino/Bic, 1% amino acid, 34 mmol/l bicarbonate; Glu/Bic, 1.5% glucose, 34 mmol/l bicarbonate; and Glu/Lac, 1.5% glucose, 35 mmol/l lactate. A PET was performed and transport properties (clearance, D/P ratio, MTAC) were calculated. Prostanoid and cytokine concentrations were measured in serum and the 6 h effluent. Using an in vitro model, mononuclear leukocytes of healthy donors were also incubated with the test fluid. In vivo results. Peritoneal clearance and MTAC of small solutes (creatinine, urea) were not significantly altered by amino acids or bicarbonate. Peritoneal permeability and transperitoneal excretion of higher-weight protein molecules ({beta}2-microglobulin, albumin, IgG) were increased with Amino/Bic compared to Glu/Lac (P<0.05) (D/P ratio albumin: Amino/Bic, 0.027±0.003; Glu/Bic, 0.023±0.003; Glu/Lac, 0.022±0.002). Application of Amino/Bic was accompanied by an increased effluent concentration of Il-6, Il-8, TNF&agr; PGE2, and 6-keto-PGR1a (P<0.05). Dialysate nitrite/nitrate and cGMP concentrations (as indicators of NO generation) did not differ between the solutions. In vitro results. Both bicarbonate fluids demonstrated a better preservation of the mitochondrial dehydrogenases activity (MTT assay) compared to Glu/Lac (P <0.01) (Amino/Bic: 80.6±3.2%; Glu/Bic: 86.0±1.8%; Glu/Lac, 64.9±2.3%, referred to RPMI as control). Constitutive and LPS stimulated release of Il-1{beta} and Il-6 was less suppressed with both bicarbonate fluids (P<0.05) LPS-stim. Il-6 release: Amino.Bic, 33.0±6.6%; Glu/Bic, 65.5±10.3%; Glu/Lac, 1.5±0.7% referred to RPMI). Conclusion: Application of an amino-acid/bicarbonate solution resulted in a small but significant increase in peritoneal permeability. Also increased concentrations of various cytokines/prostanoids were measured in the effluent. According to in vitro testing with mononuclear phagocytes both bicarbonate-buffered fluids were to the same extent less inhibitory to certain cell functions than lactate-buffered solution.     

Acceleration of neutrophil apoptosis by glucose-containing peritoneal dialysis solutions: role of caspases.

Commercial, glucose-containing peritoneal dialysis (PD) solutions have deleterious effects on leukocytes and mesothelial cells that contribute to an impaired peritoneal defense. However, the molecular mechanisms of these deleterious effects are poorly understood. The effect of PD solutions on neutrophil viability, the molecular mechanisms of cell death, its functional consequences, and the possibilities for pharmacologic modulation have now been studied. The effect of newly available, bicarbonate-buffered PD solutions were further investigated. Lactate-buffered, glucose-containing PD solutions increased the apoptosis rate of cultured neutrophils (control media versus 4.25% glucose PD solution: 31 +/- 3% versus 52 +/- 3% apoptosis at 24 h, P < 0.001). Bicarbonate-buffered, 4.25% glucose-containing PD solutions with low concentration of glucose degradation products did not increase the rate of apoptosis. Apoptosis induced by lactate-buffered, 4.25% glucose PD solutions was not related to hyperosmolality or acidic pH and was not reproduced by increasing the glucose concentration by the addition of glucose to a commercial, lactate-buffered fluid. Neutrophil apoptosis was associated with caspase-3 activation. Inhibition of caspase-3 by the use of the caspase-3 inhibitor acetyl-Asp-Glu-Val-Asp-fmk or the broad-spectrum caspase inhibitor benzyloxycarbonyl-Val-Ala-DL-Asp-fluoromethylketone (zVAD-fmk) prevented features of apoptosis, such as morphologic changes, internucleosomal DNA degradation, and the appearance of hypodiploid cells and increased the number of viable, trypan blue-excluding neutrophils. Furthermore, zVAD-fmk increased neutrophil phagocytosis of bacteria. However, the caspase-1 inhibitor acetyl-Tyr-Val-Ala-Asp-aldehyde did not prevent cell death. These data suggest that unidentified components in commercial, lactate-buffered, high-glucose PD fluid accelerate the rate of neutrophil apoptosis. Glucose degradation products may be such unidentified components. Acceleration of neutrophil apoptosis may contribute to the impaired local defense system of patients undergoing PD.     

Effects of pH-neutral, bicarbonate-buffered dialysis fluid on peritoneal transport kinetics in children

BACKGROUND: Due to their superior biocompatibility, pH-neutral solutions are beginning to replace acidic lactate-buffered peritoneal dialysis (PD) fluids. We hypothesized that pH-neutral and acidic solutions might differentially affect peritoneal transport in the early dwell phase, due to differences in ionic shifts and initial peritoneal vasodilation. Such differences may become clinically relevant in patients with frequent short cycles on automated PD (APD). METHODS: Twenty-five children were treated with a lactate-buffered (35 mmol/L, pH 5.5) or a bicarbonate-buffered PD solution (34 mmol/L, pH 7.4) in randomized order on two sequential days. Each day a four-hour Standardized Permeability Analysis (SPA) was performed, followed by overnight APD (7 cycles, fill volume 1000 mL/m2, dwell time 75 min). Functional peritoneal surface area was dynamically assessed using the three-pore model. RESULTS: While intraperitoneal pH was constant at 7.41 +/- 0.03 throughout the SPA with bicarbonate fluid, the dialysate remained acidic for more than one hour with lactate solution (pH 7.12 +/- 0.08 at 1 h). Total pore area was 60% higher during the first 30 minutes of the dwell than under steady-state conditions, without a difference between acidic and pH-neutral fluid. Net base gain, intraperitoneal volume kinetics, glucose absorption, ultrafiltration rate, effective lymphatic absorption and the transport of urea, potassium, beta2-microglobulin and albumin were similar with both fluids. However, phosphate and creatinine elimination were 10% lower with bicarbonate PD fluid, resulting in corresponding significant decreases in the 24-hour clearances of these solutes. CONCLUSION: The peritoneal surface area is not measurably influenced by pH-neutral PD fluid. Creatinine and phosphate elimination appears to be slightly reduced with bicarbonate fluid; this observation awaits clarification in extended therapeutical trials.     

Biocompatibility pattern of a bicarbonate/lactate-buffered peritoneal dialysis fluid in APD: a prospective, randomized study.

BACKGROUND: In chronic ambulatory peritoneal dialysis, bicarbonate-buffered fluids, with their neutral pH and less advanced glycosylation end-products (AGE) and glucose degradation products (GDP), have better biocompatibility than conventional peritoneal dialysis (PD) solutions. That difference may be more beneficial in automated peritoneal dialysis (APD), due to its more frequent exchanges and longer contact times with fresh dialysate. We performed a prospective, randomized study in APD patients to compare the biocompatibility of conventional and bicarbonate/lactate-buffered PD fluids. METHODS: We randomized 14 APD patients to have APD with either conventional or bicarbonate/lactate-based fluids. After 6 months, both groups changed to the other solution. The overall observation period was 12 months. After 1 and 5 months and again after 7 and 11 months, phagocytotic and respiratory burst capacities of effluent peritoneal macrophages were determined. Plasma interleukin (IL)-6 and C-reactive protein (CRP) as well as effluent IL-6, CRP, transforming growth factor (TGF)-beta 1, AGE and CA125 concentrations were measured. Inflow pain was quantified using a patient questionnaire. RESULTS: Respiratory burst capacity remained unchanged and phagocytotic activity increased significantly during APD (P<0.001) with the bicarbonate/lactate fluid. Effluent IL-6 release was significantly lower than with the lactate fluid (P<0.05). While in the effluent TGF-beta 1 was unaffected, AGE concentration was lower after bicarbonate/lactate treatment (P<0.05). Effluent CA125 concentration, an indicator of mesothelial cell integrity, was higher (P<0.05) in neutral effluents. Finally, patients' inflow pain diminished (P = 0.05) when using the neutral fluid. CONCLUSIONS: The use of a neutral PD fluid in APD improved patients' inflow pain as well as biocompatibility parameters reflecting enhanced phagocytotic activity of peritoneal macrophages, reduced constitutive inflammatory stimulation (IL-6), reduced AGE accumulation in the peritoneal cavity and better preservation of the mesothelial cell integrity. From the biocompatibility point of view, a neutral fluid with low GDP content can be recommended as the primary choice for APD.     

Continuous Flow Peritoneal Dialysis: Solution Formulation and Biocompatibility

When peritoneal dialysis was introduced several years ago an important alternative dialysis therapy to hemodialysis was made available for the treatment of end-stage chronic disease. However, a continuous search for new developments and technologies is necessary to find the optimal peritoneal dialysis fluid (PDF) to preserve peritoneal membrane function as long as possible. Conventional PDFs are known to compromise the functional integrity of the peritoneal membrane as a consequence of their acidic pH in combination with their high lactate content, as well as the high concentrations of glucose and glucose degradation products (GDPs) present in currently used conventional solutions. Novel solutions such as bicarbonate-buffered PDF (at neutral pH) display improved in vitro biocompatibility as compared to conventional, acidic lactate-buffered PDF. Since these novel solutions are manufactured in dual-chambered bags they also contain fewer GDPs, thus further reducing their potential toxicity and protein glycation. Clinically the novel solutions reduce inflow pain and improve peritoneal membrane transport characteristics, ultrafiltration capacity, and effluent markers of peritoneal membrane integrity. The concept of continuous flow peritoneal dialysis (CFPD) is another approach to optimize PDF. The technique of CFPD not only enables the individualization of acid-base correction by variable concentrations of HCO₃⁻ but may also help to restore peritoneal cell functions by neutral pH, reduced glucose load, diminished GDP content, and reduced advanced glycation end product (AGE) formation, thereby potentially contributing to the improved preservation of peritoneal membrane function.     

Long-term exposure to new peritoneal dialysis solutions: Effects on the peritoneal membrane

BACKGROUND: Chronic exposure to peritoneal dialysis fluid (PDF) affects the peritoneum, but precise causative factors are incompletely understood. We examined the effects of standard and new PDF on peritoneal function and structure. METHODS: Female Wistar rats received twice daily intraperitoneal infusions of a standard lactate-buffered 3.86% glucose PDF at pH 5.5 (Dianeal) (N= 12), a low glucose degradation product (GDP) containing bicarbonate/lactate-buffered 3.86% glucose PDF at pH 7.4 (Physioneal) (N= 12), a lactate-buffered amino acid-based PDF at pH 6.7 (Nutrineal) (N= 12) or Earle's Balanced Salt Solution at pH 7.4 (EBSS) (N= 12) during 12 weeks. RESULTS: Net ultrafiltration was lower after treatment with standard PDF, but not with low-GDP bicarbonate/lactate-buffered and amino acid-based PDF, compared to EBSS. Peritonea exposed to standard PDF were characterized by an increased expression of vascular endothelial growth factor (VEGF), microvascular proliferation as well as submesothelial fibrosis, which were not observed in other groups. Staining for methylglyoxal adducts was prominent in the standard PDF-exposed group, mild in the low GDP bicarbonate/lactate-buffered group and absent in the other groups. Standard PDF induced accumulation of advanced glycation end products (AGEs) and up-regulation of the receptor for AGE (RAGE). AGEs accumulation was absent and RAGE expression was only modestly increased in low-GDP bicarbonate/lactate-buffered and amino acid-based PDF. CONCLUSION: Long-term in vivo exposure to standard PDF adversely affects peritoneal function and structure. A low-GDP bicarbonate/lactate-buffered and amino acid-based PDF better preserved peritoneal integrity and may thus improve the longevity of the peritoneal membrane. GDPs and associated accelerated AGE formation are the main causative factors in PDF-induced peritoneal damage.     

Hemodynamic effects of peritoneal dialysis solutions on the rat peritoneal membrane: role of acidity, buffer choice, glucose concentration, and glucose degradation products.

Conventional peritoneal dialysis fluids (PDF) are unphysiologic because of their hypertonicity, high glucose and lactate concentrations, acidic pH, and presence of glucose degradation products (GDP). Long-term exposure to conventional PDF may cause functional and structural alterations of the peritoneal membrane. New PDF have a neutral pH, a low GDP content, and contain bicarbonate or lactate as the buffer. Intravital microscopy was used to analyze the vasoactive effects of conventional and new PDF on the rat peritoneal membrane. A conventional, acidic pH, lactate-buffered 4.25% glucose PDF induced maximal vasodilation of mesenteric arteries, resulting in a doubling of the arteriolar flow and a 20% increase of the perfused capillary length per area. The hemodynamic effects of conventional PDF were similar after pH-adjustment with NaOH, indicating that acidity per se is not essential for the changes. Superfusion by a pH-neutral, lactate-buffered PDF with low GDP content caused only a transient arterial vasodilation despite continuous exposure, with a commensurate effect on arteriolar flow and capillary recruitment. Application of a pH-neutral, bicarbonate-buffered PDF with low GDP content did not affect the hemodynamic parameters. Resterilization of the bicarbonate solution increased GDP levels and completely restored the vasodilatory capacity. The corresponding 1.5% glucose PDF induced similar but less pronounced changes. Conventional PDF have important vasoactive effects on the peritoneal circulation, mainly because of the presence of GDP and transiently because of high lactate concentrations. Capillary recruitment may increase effective peritoneal vascular surface area. In addition, chronic vasodilation may induce structural adaptations in the blood vessel wall, contributing to vascular sclerosis. PDF with reduced GDP content induce no major hemodynamic effects and may thus have the potential to better preserve peritoneal vascular integrity.     

Leukotriene B4 and tumor necrosis factor release from leukocytes: effect of peritoneal dialysate.

The effect of peritoneal dialysate on the capacity of peripheral blood polymorphonuclear (PMNL) and mononuclear leukocytes (MNC) to release leukotriene B4 (LTB4) and tumor necrosis factor alpha (TNF alpha) was investigated in vitro. Following density gradient separation, aliquots of 5 x 10(6) PMNL or MNC were incubated in peritoneal dialysis fluid containing 1.5% glucose or Hanks' buffer (= control) for 1-2 h at 37 degrees C. TNF alpha and LTB4 production was stimulated with Escherichia coli lipopolysaccharide (LPS) and calcium ionophore A23187, respectively. MNC incubated in buffer and LPS produced (mean +/- SD) 1,006 +/- 522 pg TNF alpha/5 x 10(6) cells; no significant amounts of TNF alpha were detectable in the presence of dialysate. An inhibition of TNF alpha release was also observed in MNC exposed to bicarbonate-buffered dialysates (pH 7.40) and 4.25% and 1.5% glucose solution with physiologic osmolality. Incubation of PMNL in Hanks' buffer followed by A23187 stimulation led to production of 29.1 +/- 19.2 ng LTB4/5 x 10(6) cells, whereas glucose-incubated cells were refractory to ionophore stimulation (less than 0.1 ng LTB4/5 x 10(6) cells). The failure of dialysate-exposed leukocytes to release inflammatory mediators in response to adequate stimuli may contribute to the impairment of cellular host defense in the setting of continuous ambulatory peritoneal dialysis.     

L-carnitine is an osmotic agent suitable for peritoneal dialysis

Excessive intraperitoneal absorption of glucose during peritoneal dialysis has both local cytotoxic and systemic metabolic effects. Here we evaluate peritoneal dialysis solutions containing L-carnitine, an osmotically active compound that induces fluid flow across the peritoneum. In rats, L-carnitine in the peritoneal cavity had a dose-dependent osmotic effect similar to glucose. Analogous ultrafiltration and small solute transport characteristics were found for dialysates containing 3.86% glucose, equimolar L-carnitine, or combinations of both osmotic agents in mice. About half of the ultrafiltration generated by L-carnitine reflected facilitated water transport by aquaporin-1 (AQP1) water channels of endothelial cells. Nocturnal exchanges with 1.5% glucose and 0.25% L-carnitine in four patients receiving continuous ambulatory peritoneal dialysis were well tolerated and associated with higher net ultrafiltration than that achieved with 2.5% glucose solutions, despite the lower osmolarity of the carnitine-containing solution. Addition of L-carnitine to endothelial cells in culture increased the expression of AQP1, significantly improved viability, and prevented glucose-induced apoptosis. In a standard toxicity test, the addition of L-carnitine to peritoneal dialysis solution improved the viability of L929 fibroblasts. Thus, our studies support the use of L-carnitine as an alternative osmotic agent in peritoneal dialysis.     

The new peritoneal dialysis solutions: friends only, or foes in part?

Over the past decade new solutions for peritoneal dialysis have been developed in an effort to reduce the bioincompatibility of conventional glucose-containing, lactate-buffered solutions, and thereby to improve the clinical outcomes of peritoneal dialysis. The new solutions contain either other non-glucose osmotic agents, such as glucose polymers or amino acids, or have a neutral pH; the buffer content is altered in some of the new solutions. In vitro and in vivo studies have shown the biocompatibility of these new solutions to be superior to that of standard solutions. In this paper, available clinical data on the use of these new solutions are reviewed. In general, the data indicate improved biocompatibility of the new solutions; a number of studies, however, detected no superiority when levels of accepted markers of biocompatibility, such as vascular endothelial growth factor or hyaluronic acid, were measured. This finding could be explained by the assumption that the new peritoneal dialysis solutions not only induce less damage to the peritoneal membrane but also better maintain repair mechanisms, which apparently are associated with enhanced release of such markers.     

Improved biocompatibility of bicarbonate/lactate-buffered PDF is not related to pH.

BACKGROUND: Chronic exposure to conventional peritoneal dialysis fluid (PDF) is associated with functional and structural alterations of the peritoneal membrane. The bioincompatibility of conventional PDF can be due to hypertonicity, high glucose concentration, lactate buffering system, presence of glucose degradation products (GDPs) and/or acidic pH. Although various investigators have studied the sole effects of hyperosmolarity, high glucose, GDPs and lactate buffer in experimental PD, less attention has been paid to the chronic impact of low pH in vivo. METHODS: Rats received daily 10 ml of either conventional lactate-buffered PDF (pH 5.2; n=7), a standard bicarbonate/lactate-buffered PDF with physiological pH (n=8), bicarbonate/lactate-buffered PDF with acidic pH (adjusted to pH 5.2 with 1 N hydrochloride, n=5), or bicarbonate/lactate buffer, without glucose, pH 7.4 (n=7). Fluids were instilled via peritoneal catheters connected to implanted subcutaneous mini vascular access ports for 8 weeks. Control animals with or without peritoneal catheters served as control groups (n=8/group). Various functional (2 h PET) and morphological/cellular parameters were analyzed. RESULTS: Compared with control groups and the buffer group, conventional lactate-buffered PDF induced a number of morphological/cellular changes, including angiogenesis and fibrosis in various peritoneal tissues (all parameters P<0.05), accompanied by increased glucose absorption and reduced ultrafiltration capacity. Daily exposure to standard or acidified bicarbonate/lactate-buffered PDF improved the performance of the peritoneal membrane, evidenced by reduced new vessel formation in omentum (P<0.02) and parietal peritoneum (P<0.008), reduced fibrosis (P<0.02) and improved ultrafiltration capacity. No significant differences were found between standard and acidified bicarbonate/lactate-buffered PDF. During PET, acidic PDF was neutralized within 15 to 20 min. CONCLUSION: The bicarbonate/lactate-buffered PDF, acidity per se did not contribute substantially to peritoneal worsening in our in vivo model for PD, which might be explained by the buffering capacity of the peritoneum.     

Better preservation of peritoneal morphologic features and defense in rats after long-term exposure to a bicarbonate/lactate-buffered solution.

The long-term effects of a standard lactate-buffered dialysis fluid and a new, two-chamber, bicarbonate/lactate-buffered dialysis fluid (with fewer glucose degradation products and a neutral pH) were compared in an in vivo peritoneal exposure model. Rats were given daily injections, via an access port, of 10 ml of standard solution or bicarbonate/lactate-buffered solution for 9 to 10 wk. The omentum, peritoneum, and mesothelial cell layer were screened for morphologic changes. In addition, the bacterial clearing capacity of the peritoneal cells was studied. Significantly more milky spots and blood vessels were observed in the omenta of animals treated with standard solution (P < 0.03 for both parameters). Electron-microscopic analysis demonstrated dramatic changes in the appearance of the vascular endothelial cells of the milky spots and a severely damaged or even absent mesothelium on the peritoneal membrane of the standard solution-treated animals. In contrast, the mesothelium was still present in the bicarbonate/lactate-buffered solution group, although the cells lost microvilli. Both peritoneal dialysis fluids significantly increased the density of mesothelial cells (per square millimeter) on the surface of the liver and the thickness of the submesothelial extracellular matrix of the peritoneum (both P < 0.04 for both fluids versus control). A significantly better ex vivo bacterial clearing capacity was observed with peritoneal cells from the bicarbonate/lactate-buffered solution group, compared with the standard solution group (P < 0.05 in both experiments). These results demonstrate that instillation of bicarbonate/lactate-buffered solution into rats for 9 to 10 wk preserves both morphologic and immune parameters much more effectively, compared with standard solution. These findings may be of considerable clinical importance.     

Effect of PD fluid instillation on the peritonitis-induced influx and bacterial clearing capacity of peritoneal cells.

BACKGROUND: The commonly used peritoneal dialysis fluids contain glucose as the osmotic agent. Heat sterilization leads to the formation of glucose degradation products which contribute, together with glucose, to the formation of advanced glycation end-products (AGEs). AGEs have been shown to be present in the peritoneal cavity. Methods have been developed to minimize the amount of glucose degradation products in peritoneal dialysis fluids. In a rat peritoneal dialysis model, we compare the effect of a commonly used peritoneal dialysis fluid, Gambrosol, with a newly developed peritoneal dialysis fluid, PD-Bio, on the influx and functional capacity of the peritoneal cells after 2 weeks of peritoneal dialysis fluid instillation. METHODS: Three groups of animals were used: rats received daily infusion with 15 ml of either 4% Gambrosol (group 1) or 4% PD-Bio (group 2), and a control group of animals did not receive fluid (group 3). After 2 weeks of PD fluid instillation, all the animals were injected with a 0.5 ml suspension containing 3x10(8) colony-forming units of Staphylococcus aureus. The in vivo bacterial clearing capacity was determined after 15 h. RESULTS: A statistically significant higher leukocyte influx was found in the control group compared with both PD fluid-injected groups. No statistical differences in bacterial clearing were observed among the three groups, although the number of bacteria recovered from the PD-Bio group tended to be lower than that from the Gambrosol group. Moreover, in both PD fluid instillation groups, the bacteria tended to be cleared more slowly compared with the control group. The number of mesothelial cells in the PD fluid groups was significantly greater than in the control group. CONCLUSION: No differences were observed in bacterial clearing capacity, leukocyte influx and mesothelial cell number after a 2 week exposure of the peritoneal cavity to Gambrosol vs PD-Bio.     

The application of animal models to study the biocompatibility of bicarbonate-buffered peritoneal dialysis solutions

The application of animal models to study the biocompatibility of bicarbonate-buffered peritoneal dialysis solutions. Patients treated with peritoneal dialysis (PD) are at risk for development of ultrafiltration failure and peritonitis. These two significant complications can result in the termination of PD treatment. The relative unphysiologic composition of the currently used standard peritoneal dialysis fluids (PDF) is considered to be a major cause for the development of morphologic changes of the peritoneal membrane, ultimately resulting in ultrafiltration failure and probably contributing to changes in local defense mechanisms with the associated increased risk of peritonitis. In recent years, a major research focus has become the development of new and improved PD solutions. This has resulted in the development of an amino-acid-based PDF, a glucose polymer-based PDF, and several bicarbonate-buffered PDF. Typically, the first phase of biocompatibility testing of new PD solutions involves in vitro testing, employing isolated cells such as peritoneal macrophages or cell culture systems using human peritoneal mesothelial cells. The results of such evaluations are useful in providing insights into the biocompatibility performance of any given formulation, but suffer from several disadvantages, which can be better addressed using animal models. In vivo studies using animals permit the analysis of biocompatibility under conditions that allow for cell-to-cell interactions and dynamic changes in solution composition that more closely mimic the clinical situation. In this paper, we will review the use of animal models for the study of PDF biocompatibility and their application to the assessment of bicarbonate-buffered PDF.     

In vitro and in vivo models for peritonitis demonstrate unchanged neutrophil migration after exposure to dialysis fluids.

BACKGROUND: Recurrent infections in peritoneal dialysis (PD) patients may alter the abdominal wall resulting in an impairment of its dialysis capacity. In this study we investigated both in vitro and in vivo the effects of mesothelial exposure to dialysis fluids on the migration of neutrophils and their capacity to clear a bacterial infection. METHODS: First, we evaluated neutrophil migration in an in vitro transwell model for the peritoneal membrane with monolayers of primary human mesothelial cells (MC) on the lower side and primary human endothelial cells (EC) on top of the same transwell membrane, upon exposure of MC to PD fluid (PDF)-derived components. In addition to this in vitro model, we combined chronic peritoneal exposure to PDF with a peritoneal infection model in the rat. We investigated the kinetics of the chemokine response, neutrophil recruitment and bacterial clearance. RESULTS: Known chemoattractants, such as fMLP and IL-8, strongly increased neutrophil migration across both cell layers in the in vitro model of the peritoneal membrane. Pre-incubation of the MC layer for 48 h with 55 mM glucose, a combination of two glucose degradation products, methylglyoxal and 3-deoxyglucosone, or conventional dialysis fluid (1:4 dilution), however, did not change the IL-8-induced migration of neutrophils. In concert with this finding we demonstrated an unchanged MC expression of ICAM-1 and VCAM-1 after these pre-treatments. Unexpectedly, chronic i.p. exposure to conventional PDF or a recently developed lactate/bicarbonate-buffered PDF in a rat peritoneal exposure model strongly hampered the chemokine response upon bacterial challenge. Nevertheless, neutrophil recruitment and bacterial clearance were effective and did not differ from rats not pre-exposed to PDF. CONCLUSIONS: We conclude that exposure of MC to PDF does not hamper the recruitment of functional neutrophils upon challenge.     

Mass transfer of calcium across the peritoneum at three different peritoneal dialysis fluid Ca2+ and glucose concentrations

BACKGROUND: In peritoneal dialysis, the rate of ultrafiltration has been predicted to be a major determinant of peritoneal calcium (Ca2+) removal. Hence, dialysis fluid glucose concentration should be an important factor governing the transperitoneal Ca2+ balance. The aim of this study was to test the effect of various dialysate glucose levels and selected dialysate Ca2+ levels on Ca2+ removal in peritoneal dialysis patients. METHODS: Patients (N = 8) received, during a 7-week period, 2 L of lactate (30 mmol/L)/bicarbonate (10 mmol/L)-buffered peritoneal dialysis solutions containing either 1.5% glucose and 1.0 mmol/L Ca2+ or 2.5% glucose and 1.6 mmol/L Ca2+, or 4% glucose and 2.5 mmol/L Ca2+, respectively, provided in a three-compartment bag (trio system). Patients underwent standardized (4-hour) dwells, one for each of the three dialysates to assess permeability-surface area product (PS) or mass transfer area coefficients (MTAC) for ionized and "freely diffusible" Ca2+, lactate, glucose, bicarbonate, phosphate, creatinine, and urea. RESULTS: There was a clear-cut dependence of peritoneal Ca2+ removal on the rate of ultrafiltration. For large peritoneal to dialysate Ca2+ gradients (2.5 mmol/L Ca2+ in 4% glucose) a close fit of measured to simulated data was predicted by the three-pore model using nonelectrolyte equations. For low transperitoneal Ca2+ concentration gradients, however, directly measured Ca2+ data agreed with the simulated ones only when the peritoneal Ca2+ PS was set lower than predicted from pore theory (6 mL/min). CONCLUSION: There was a marked ultrafiltration dependence of transperitoneal Ca2+ transport. Nonelectrolyte equations could be used to simulate peritoneal ion (Ca2+) transport provided that the transperitoneal ion concentration gradients were large. Based on our data 1.38 mmol/L Ca2+ in the dialysis fluid would have created zero net Ca2+ gain during a 4-hour dwell for 1.5% glucose, whereas 1.7 and 2.2 mmol/L Ca2+ would have been needed to produce zero Ca2+ gain for 2.5% glucose and 3.9% glucose, respectively.