Determinants of Peritoneal Solute Transport Rates in Newly Started Nondiabetic Peritoneal Dialysis Patients

Objective

An overrepresentation of a fast peritoneal transport status in new peritoneal dialysis (PD) patients with extensive comorbidity has been reported in some studies. High mass transfer area coefficients (MTACs) of low MW solutes suggest the presence of a large effective peritoneal surface area. The mechanism is unknown. It might include comorbidity, chronic inflammation, or an effect of mesothelial cell mass on peritoneal transport by the production of vasoactive substances. To investigate their relative importance in early PD, peritoneal permeability characteristics in incident PD patients were analyzed for relationships with comorbidity, serum concentrations of inflammatory markers, and products of the mesothelial cells that can be detected in dialysate.

Design

A cross-sectional study.

Setting

A university hospital.

Methods

46 patients who fulfilled the following inclusion criteria were analyzed: a standard peritoneal permeability analysis (SPA) within 6 months after the start of PD, no peritonitis prior to the SPA, older than 18 years, and without diabetes mellitus as a primary renal disease. The patients were divided into tertiles based on the MTAC creatinine: slow, medium, and fast transport groups. The Davies comorbidity score was used to assess comorbidity. Serum and dialysate samples obtained during the SPA were used to determine hyaluronan, interleukin (IL)-6, vascular endothelial growth factor (VEGF), and cancer antigen 125 (CA125). The dialysate concentrations of these substances were expressed as their dialysate appearance rates.

Results

No significant differences were present in the three transport groups for comorbidity, serum concentrations of inflammatory markers, or serum VEGF. Interleukin-6 and VEGF concentration attributed to local VEGF production were not different between the tertiles. Levels of VEGF were higher in the medium transport group compared to the slow transport group ( p = 0.02); CA125 was higher in the fast transport group compared to the medium transport group ( p = 0.01). When analyzed as continuous variables, MTAC creatinine was related to VEGF ( r = 0.33, p < 0.05) and CA125 ( r = 0.41, p = 0.03). In linear regression analysis, VEGF influenced the association between CA125 and MTAC creatinine; IL-6 weakened this association only marginally.

Conclusion

A fast peritoneal transport status in incident nondiabetic PD patients was not related to comorbidity. The relationships found between VEGF, CA125, and MTAC creatinine may suggest a role of VEGF in the regulation of the vascular peritoneal surface area, possibly already before structural abnormalities have developed. Our analyses are consistent with the hypothesis that mesothelial cell mass is an important determinant of the peritoneal transport status in incident nondiabetic PD patients without previous peritonitis. Of the many potential mediators produced by mesothelial cells, VEGF was more important than the inflammation marker IL-6.

Effect of Scavenging Circulating Reactive Carbonyls by Oral Pyridoxamine in Uremic Rats on Peritoneal Dialysis

Pyridoxamine, a reactive carbonyl (RCO) scavenger, can ameliorate peritoneal deterioration in uremic peritoneal dialysis (PD) rats when given via dialysate. We examined the effects of scavenging circulating RCOs by oral pyridoxamine. Rats underwent nephrectomy and 3 weeks of twice daily PD either alone or with once daily oral pyridoxamine. PD solution was supplemented with methylglyoxal, a major glucose-derived RCO, to quench intraperitoneal pyridoxamine. Oral pyridoxamine achieved comparable blood and dialysate pyridoxamine concentrations, suppressed pentosidine accumulation in the blood but not in the mesenterium or dialysate, and reduced the increases in small solute transport and mesenteric vessel densities, with no effects on submesothelial matrix layer thickening or serum creatinine. Thus, reducing circulating RCOs by giving oral pyridoxamine with PD provides limited peritoneal protection. However, orally given pyridoxamine efficiently reaches the peritoneal cavity and would eliminate intraperitoneal RCOs. Oral pyridoxamine is more clinically favorable and may be as protective as intraperitoneal administration.

Differential effects of transforming growth factor-beta on the synthesis of connective tissue growth factor and vascular endothelial growth factor by peritoneal mesothelial cell

BACKGROUND

Previous studies found that transforming growth factor-beta (TGF-beta) plays a conflicting role in peritoneal fibrosis. We hypothesise that TGF-beta acts on peritoneal mesothelial cells (PMC) via VEGF and CTGF as downstream mediators.

METHODS

The effect of TGF-beta in primary culture of rat PMC was studied. VEGF and CTGF mRNA expression was examined by real time quantitative polymerase chain reaction (RT-QPCR), and VEGF antigen level in cell supernatant by ELISA.

RESULTS

Incubation of rat PMC with TGF-beta resulted in a time- (3-72 h) and concentration- (0-50 pg/ml) dependent increase in VEGF mRNA expression, and VEGF protein level in the cell supernatant. When stimulated with TGF-beta 100 pg/ml, there was a 20-fold up-regulation of VEGF mRNA expression (p < 0.001). The CTGF mRNA expression and protein level of PMC was slightly increased at low concentration of TGF-beta (50 pg/ml) but decreased at a higher concentration (100 pg/ml or above). The effect of TGF-beta on PMC CTGF, but not VEGF, gene expression was inhibited by Smad decoy oligodeoxynucleotide. The effect of TGF-beta on PMC VEGF gene expression and protein synthesis was inhibited by PD98059 (a specific MAP kinase inhibitor) and chelerythrine (a specific protein kinase C inhibitor), but not cholera toxin (activator of cyclic AMP) or herbimycin A (inhibitor of protein tyrosine kinase). The up-regulation of CTGF mRNA expression was inhibited by PD98059, but not chelerythrine, cholera toxin or herbimycin A. Furthermore, CTGF gene expression in TGF-beta-stimulated PMC was inhibited by co-administration of recombinant VEGF.

CONCLUSIONS

Our data demonstrate that TGF-beta induces PMC production of VEGF and CTGF via different signalling pathways. At high concentration of TGF-beta, VEGF production predominates and CTGF production was inhibited. Since CTGF and VEGF have different biologic effects, our results may explain the complex activity of TGF-beta in peritoneal physiology.