Bradykinin and nitric oxide generation by dialysis membranes can be blunted by alkaline rinsing solutions

Bradykinin and nitric oxide generation by dialysis membranes can be blunted by alkaline rinsing solutions. Background Bradykinin (BK) generation following the first contact of blood with the dialysis materials is thought to enhance hypersensitivity reactions (HSRs). Some of the effects of BK are mediated by nitric oxide (NO). We have recently reported that the pH of diluted blood modulates the kinin system. The present study was aimed to investigate the role of the pH of culture media and filter-washing solutions and BK and NO generation, either in vitro and ex vivo. Methods BK was measured by a specific enzyme-linked immunosorbent assay (ELISA), and NO synthase (NOS) activity by 3 H-citrulline production after incubation with 3 H-arginine and nitrites by using the Griess reagent. In in vitro experiments, NOS activity was detected in endothelial cells (ECs) cultured with graded BK concentrations at various pH values. Blood from 30 patients in regular dialysis was ex vivo circulated in one single passage through minifilters prerinsed with pH 7 or pH 8 phosphate buffer (PB) solutions. The out-flowing blood was tested for BK and nitrite content and was incubated with cultured ECs to evaluate its capacity to modulate NOS activity. Results BK induced in vitro a dose-dependent increase in NOS activity of ECs, which was mediated by tyrosine kinase phosphorylation. NO generation was enhanced at pH 7.2, which remained unchanged at pH 7.6. In ex vivo experiments, blood out-flowing after one passage on filters washed with pH 7 PB solutions had increased BK levels ( P P P r = 0.54, P Conclusions BK and NO generation are modulated by environmental pH. Rinsing the blood and dialysate compartments of filters with an alkaline solution prior to use may mitigate the activation of mediators likely to be involved in some HSRs.