AOPP-induced activation of human neutrophil and monocyte oxidative metabolism:: A potential target for N-acetylcysteine treatment in dialysis patients

Background. Oxidative stress largely contributes to hemodialysis-associated lethal complications, thus explaining the urgent need of antioxidant-based therapeutic strategies in hemodialysis patients. We previously identified advanced oxidation protein products (AOPP) in the uremic plasma as exquisite markers of oxidative stress and potent mediators of monocyte activation. The present study was aimed at searching whether (1) AOPP can also trigger activation of polymorphonuclear neutrophils (PMN), and (2) whether AOPP-induced activation could be inhibited by N-acetylcysteine (NAC), a widely used compound which has been shown to prevent oxidative injury to kidney. Methods. Both human serum albumin (HAS) AOPP (i.e., HOCl-modified HSA in vitro preparations and AOPP extracted from plasma of hemodialysis patients) were tested for their capacity to trigger phagocyte nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and myeloperoxidase (MPO)-dependent activities as measured by lucigenin- and luminol-amplified chemiluminescence (CL), respectively, as compared to receptor-dependent [opsonized zymosan or receptor-independent phorbol myristate acetate (PMA)]. The effect of PMN priming by platelet-activating factor (PAF), and the effect of NAC on normal monocyte and on normal or hemodialysis patient's (N = 16) PMN oxidative responses were compared. Results. HSA-AOPP triggered in a HOCl dose-dependent manner both NADPH-oxidase- and MPO-dependent CL of PMN. This latter was further enhanced by PAF priming. Plasma-derived AOPP obtained from hemodialysis patients also triggered PMN respiratory burst. NAC significantly reduced HSA-AOPP-mediated responses of normal monocyte and of normal and uremic PMN but had no significant effect on opsonized zymosan- or PMA-induced CL responses. Conclusion. This dual potential of NAC to inhibit phagocyte oxidative responses induced by HSA-AOPP without affecting those mediated by compounds mimicking pathogens supports the proposal of a therapeutic trial with NAC aimed at reducing oxidative stress-related inflammation in hemodialysis patients.