Biocompatibility of a bicarbonate/lactate-buffered PD fluid tested with a double-chamber cell culture system.

OBJECTIVE: In peritoneal dialysis (PD), neutrally buffered PD fluids with lower concentrations of glucose degradation products (GDP) have tested superior to conventional fluids in terms of biocompatibility. However, conventional in vitro studies provoke debate because, due to the lack of subsequent equilibration with the blood, they do not resemble the true intraperitoneal situation of PD. METHODS: We established a double-chamber cell culture system with peritoneal mesothelial cells seeded on top of a permeable membrane, with a physiological buffer below. Thus adequately reflecting the in vivo equilibration pattern, we compared a conventional fluid with a neutral bicarbonate/lactate-buffered PD solution. Using an exchange pattern adapted from an 8-hour continuous ambulatory PD regimen, cell viability was assessed with an MTT assay, and cell function via constitutive and stimulated interleukin (IL)-6 release. As an indicator of potential induction of fibrosis and as a parameter of mesothelial cell integrity, respectively, transforming growth factor-beta 1 (TGF-beta1) generation and cancer antigen 125 (CA125) release were measured. RESULTS: The conventional solution significantly compromised mesothelial cell viability and function in terms of mitochondrial activity (p < 0.05) and stimulated IL-6 release (p < 0.05). The bicarbonate/lactate fluid had no effect on cell viability or IL-6 release and turned out to be equivalent to the properties of the growth medium. Whereas lactate-incubated cells did not respond to IL-1beta stimulation, bicarbonate/lactate-treated cells adequately increased IL-6 release after stimulation (p < 0.0005). Release of TGF-beta1 and CA125 did not differ between the different fluids and the control. CONCLUSIONS: Due to the sustained equilibration process, the double-chamber cell culture model allows a more realistic insight into mesothelial cell viability and function in terms of PD. As in classic in vitro studies, an adverse effect of conventional PD solutions on mesothelial cells was overt in the present cell culture system. The neutral bicarbonate/lactate-buffered fluid with low GDP content, however, did not interfere with mesothelial cell vitality or function, indicating superior biocompatibility.

Histochemical distribution and expression of aquaporin 1 in the peritoneum of patients undergoing peritoneal dialysis: relation to peritoneal transport.

BACKGROUND: Aquaporin 1 (AQP-1) channels have been claimed to be responsible for osmotically driven free-water movement across the peritoneal membrane. Data about AQP-1 expression and its location in the human peritoneum related to clinical findings concerning ultrafiltration (UF) and free-water transport are still lacking. METHODS: Fifty-seven peritoneal biopsy specimens obtained from peritoneal dialysis (PD) patients were investigated. AQP-1 expression was detected by means of immunohistochemistry and a semiquantitative scoring system. Histological findings were related to peritoneal transport properties measured by means of an extended peritoneal equilibration test (PET) using dextran 70 as a volume marker. RESULTS: AQP-1 expression in the peritoneum was detected in both vascular endothelial cells (capillaries and small venules; score, 2.96 +/- 0.92) and the mesothelial cell layer (score, 2.31 +/- 1.54). There was significantly greater AQP-1 expression in vascular endothelial cells of patients showing increased thickness of the submesothelial fibrous layer of the peritoneum greater than 400 microm compared with less than 400 microm. Free-water transport through AQP-1 was 42% +/- 12% from total UF after 1 hour. There was a significant correlation between AQP-1 expression and free-water transport after 1 hour of equilibration with 3.86% glucose in the PET (r = 0.753; P < 0.001). CONCLUSION: Our data indicate that AQP-1 is located not only in the endothelial cell layer of capillaries and small vessels in the peritoneum of PD patients, but also in the mesothelial cell layer. AQP-1 expression correlated with free-water transport after 1 hour of equilibration, reaching a significant part from total UF at this time.

Efficacy and safety of a 7.5% icodextrin peritoneal dialysis solution in patients treated with automated peritoneal dialysis.

In a randomized, prospective, multicenter study, we compared the safety, efficacy, and metabolic effects of a 7.5% icodextrin solution (Extraneal) with a 2.27% glucose solution for long dwell exchanges in patients undergoing automated peritoneal dialysis. Thirty-nine stable patients on automated peritoneal dialysis were randomized to receive either icodextrin (n = 20) or glucose 2.27% solution (n = 19). The study included a 2-week baseline period followed by a 12-week icodextrin treatment phase and a 2-week follow-up period when switching back to glucose. The average net ultrafiltration during the long dwell period was 278 +/- 43 mL/d for the icodextrin group and -138 +/- 81 mL/d for the control group (P < 0.001). The higher ultrafiltration volume with icodextrin was associated with higher creatinine (2.59 +/- 0.09 mL/min versus 2.16 +/- 0.11 mL/min) and urea (2.67 +/- 0.09 mL/min versus 2.28 +/- 0.12 mL/min) peritoneal clearances for the long dwell (both P < 0.001). Ultrafiltration rate per mass of carbohydrate absorbed was +5.2 +/- 1.2 microL/min/g in the icodextrin group and -5.5 +/- 2.8 microL/min/g in the glucose group (P < 0.001). In the icodextrin group, there was a decrease in serum sodium and chloride compared with baseline (P < 0.01). Total dialysate sodium removal increased in the icodextrin group from 226.7 mEq to 269.6 mEq (week 12, P < 0.001). Serum alpha-amylase activity decreased from 103 U/L to 16 U/L (P < 0.001). The total icodextrin plasma levels reached a steady-state concentration of 6,187 +/- 399 mg/L after 1 week of treatment. Urine volume and residual renal function were not specifically affected by icodextrin compared with glucose. None of the laboratory changes resulted in any reported clinically meaningful side effect. Icodextrin produced increased, sustained ultrafiltration during the long dwell period, increasing (convective) peritoneal clearance and sodium removal in automated peritoneal dialysis patients.

Dialysis with icodextrin interferes with measurement of serum alpha-amylase activity.

BACKGROUND: The glucose polymer icodextrin has gained a widespread use in peritoneal dialysis especially in patients with low ultrafiltration and high peritoneal transport properties. In patients using a once-daily exchange with icodextrin, a decreased serum amylase activity has been reported. We explored the potential underlying mechanisms of this effect. METHODS: Using standard chromolytic methods, serum amylase activity was measured in blood samples from 11 patients on icodextrin treatment and from 11 patients on conventional glucose treatment. Samples were additionally supplemented with alpha-amylase and unused icodextrin dialysis fluid. Potential complex formation between icodextrin and alpha-amylase was studied by SDS-gel electrophoresis with protein silver staining and fluorophore-assisted carbohydrate staining with the AMAC (FACE) method, which provides oligosaccharide labelling. Lipase activity was measured in parallel in all samples by two standard methods. RESULTS: Amylase activity was reduced by 90% in serum from patients using icodextrin for the long dwell (15.9+/-10.9 U/l) vs patients using standard glucose (157.1+/-23.7 U/l; P<0.001). Addition of icodextrin to serum samples from patients using conventional glucose solutions induced a dose-dependent decrease in amylase activity. The assay results indicated a substrate competition between ET7-G7PNP and icodextrin. AMAC fluorophore staining of icodextrin and subsequent gel electrophoresis failed to demonstrate complex formation between icodextrin and alpha-amylase. Unlike the amylase findings, icodextrin did not affect lipase activity. CONCLUSIONS: The present findings indicate that icodextrin competitively interacts as a substrate in the amylase assay. In support of this, fluorophore-assisted oligosaccharide electrophoresis on SDS gel failed to reveal the formation of an 'amylase/icodextrin complex'. Lipase measurement should provide an alternative and unconfounded method for diagnosing pancreatitis in icodextrin patients.

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.