High levels of soluble C5b-9 complex in dialysis fluid may predict poor prognosis in peritonitis in peritoneal dialysis patients

Background We searched for indicators to predict the prognosis of infectious peritonitis by measuring levels of complement proteins and activation products in peritoneal dialysis (PD) fluid (PDF) of patients at early stages of peritonitis. We retrospectively analyzed the relationship between the levels of sC5b-9, C3 and C4 in PDF and the subsequent clinical prognosis. Methods We measured levels of sC5b-9, C3 and C4 in PDF on days 1, 2 and 5 post-onset of peritonitis in 104 episodes of infectious peritonitis in PD patients from 2008 and retrospectively compared levels with clinical outcomes. Further analysis for the presence of causative microorganisms or to demonstrate bacterial culture negative peritonitis was performed and correlated with change of levels of sC5b-9 in PDF. Results When PD patients with peritonitis were divided into groups that either failed to recover from peritonitis and were finally withdrawn from PD (group 1; n = 25) or recovered (group 2; n = 79), levels of sC5b-9, C3 and C4 in PDF were significantly higher in group 1 patients compared to those in group 2 on day5. Analysis of microorganisms showed significantly higher sC5b-9 levels in PDF of peritonitis cases caused by culture negative peritonitis in group 1 compared with group 2 when we analyzed for individual microorganisms. Of note, on day5, the sC5b-9 levels in PDF were similarly high in peritonitis caused by fungi or other organisms. Conclusion Our results suggested that levels of complement markers in PDF, especially sC5b-9, have potential as surrogate markers to predict prognosis of PD-related peritonitis

Percent change of the PDF levels of adjusted sC5b-9, C3 and C4 after onset of peritonitis.

<p>(A) shows percent change of adjusted levels in PDF of sC5b-9 (A), C3 (B) and C4 (C). (D2-D1)/D1, (D5-D2)/D2 or (D5-D1)/D1 shows changes from days 1 to 2, from days 2 and 5, or from day 1 to 5, respectively. Gray filled hatched bar is group 1 and open hatched bar is group 2. Statistical tests with Mann-Whitney U test and Bonferroni correction. ns., not significant.</p

PDF levels of adjusted sC5b-9, C3 and C4 on Day 5 for four categories of microorganisms causing peritonitis.

<p>Levels of adjusted sC5b-9, C3 and C4 in PDF were compared for four categories of microorganisms causing peritonitis on Day 5 after onset of peritonitis. (A) shows levels of adjusted sC5b-9 in PDF, (B) shows levels of adjusted C3 in PDF, and (C) shows levels of adjusted C4 in PDF. Filled bar is group 1 and open bar is group 2. Statistical tests with Mann-Whitney U test and Bonfferoni correction. ns., not significant.</p

Measurements of sC5b-9, total protein and WBC in PDFs on peritonitis days 1 and 5.

<p>All cases were categorized into gram positives, gram negatives, fungal infection (fungus) and culture negative based on identified causative microorganisms. (A) and (B) show levels of sC5b-9 in peritoneal dialysates (PDFs); (C) and (D) show levels of total protein in PDF; (E) and (F) show white blood cells (WBC) counts in PDF. (A), (C) and (E), day 1 post-onset; (B), (D) and (F), day 5 post-onset. Statistical tests with Kruskal-Wallis test followed by Mann-Whitney U test and Bonferroni correction. *, p<0.05; **, p<0.01.</p

List of causative organisms in peritonitis.

<p>List of causative organisms in peritonitis.</p

Levels of sC5b-9, C3 and C4 in PDF and relationship to species of microorganism.

<p>Levels of sC5b-9, C3 and C4 in PDF from patients with peritonitis on day 5 after onset of peritonitis and relationship to species of microorganism were investigated. <i>Staphylococcus aureus</i> includes both methicillin sensitive and methicillin resistant organisms. Gray filled hatched bar is group 1 and open hatched bar is group 2. Statistical tests with Man-Whitney U test and Bonferroni correction. Culture negative: no growth in bacterial culture examination, CNS: coagulase negative <i>Staphylococcus spp</i>., ns: not significance.</p

Comparison of Background of patients.

<p>Comparison of Background of patients.</p

Levels of adjusted sC5b-9, C3 and C4 and WBC counts in PDF of peritonitis.

<p>Levels of adjusted sC5b-9 (A), counts of WBC (B), levels of adjusted C3 (C) and levels of C4 (D) in PDF are significantly different between groups 1 and 2 on day 5 after incidences of peritonitis. Statistical tests with Mann-Whitely U test and Bonferroni correction. Each filled circle is from individual case in group 1 and each open circle is from individual case in group2.</p

Expression of membrane complement regulators, CD46, CD55 and CD59, in mesothelial cells of patients on peritoneal dialysis therapy

We investigated the expression of membrane complement regulators (CRegs), CD46, CD55 and CD59 in human mesothelial cells, and correlated with clinical background and level of complement (C) activation products in peritoneal dialysis (PD) fluids (PDF) to clarify influence of the C activation system in PD patients. Expression of CRegs was assessed on primary cultures of mesothelial cells (HPMC) harvested from PD fluid of 31 PD patients. Because expression of CD55 but not CD46 and CD59 in mesothelial cells was significantly correlated to value of dialysate-to-plasma creatinine concentration ratio (D/P Cre) (p < 0.005) as an indicator of peritoneal function, we focused on analysis of CD55 expression of HPMCs in comparison with levels of C activation products in the PDF of the PD patients, and their background factors. When comparing expression of the CRegs between systemic neutrophils and HPMC, no correlation was observed, supporting that change of CRegs’ expression in HPMC was independently occurring in the peritoneum. Expression of CD55 protein in HPMC was closely correlated with expression at the mRNA level (p < 0.0001) and was inversely correlated with levels of sC5b-9 (p < 0.05), but not C3, C4, IL6 and CA125 in the PDF. Complications of diabetes, usage of icodextrin and residual renal function were not correlated with change of CD55 expression in HPMCs. Our data show that the process of PD therapy modifies expression of CD55 on peritoneal mesothelium and triggers local C activation. These findings support efforts to modify PD therapy to limit effects on activation and regulation of the C system