Modulation of Neutrophil Apoptosis by Uremic Plasma during Hemodialysis

Abstract

During hemodialysis (HD), blood-membrane interactions lead to activation of several circulating cells and plasma proteins. The resultant activation and/or release of mediators can modulate the structure, function and survival of circulating neutrophils. Little is known of plasma factors that influence apoptosis of neutrophils in hemodialyzed patients. Hence, we investigated the effect of uremic plasma obtained during HD on the survival of neutrophils obtained from healthy volunteers. Neutrophils harvested from healthy volunteers were incubated in ultrafiltered culture medium supplemented with either 50% heterologous normal plasma obtained from healthy volunteers (n = 15) or 50% uremic plasma collected from long-term HD patients dialyzed with cuprophan (CU) (n = 8), cellulose triacetate (CTA) (n = 8) or polysulfone (PS) (n = 8) dialyzers. Plasma samples were drawn predialysis, 15 min after starting dialysis, and postdialysis. After 24-hour incubation, neutrophil aliquots were processed for quantification of apoptosis by flow cytometry, using propidium iodide DNA staining. In addition, tumor necrosis factor α (TNFα) and interleukin-10 (IL-10) were measured in normal and predialysis uremic plasma samples. Neutrophils from healthy volunteers exposed to heterologous normal plasma samples exhibited 10.3 ± 1.2% apoptosis. In contrast, the proportion of apoptosis was significantly higher among neutrophils exposed to predialysis (28.5 ± 2.3%, p < 0.0001), 15 min (23.0 ± 2.4%, p < 0.0001), or postdialysis uremic plasma samples (25.7 ± 2.3%, p < 0.0001). Compared to neutrophils exposed to predialysis uremic plasma samples, a significantly lower proportion of apoptosis was observed in neutrophils exposed to the 15-min plasma samples among patients dialyzed with CU (26.4 ± 2.9 vs. 18.2 ± 3.5%; p < 0.001) but not with CTA or PS dialyzers. Futher, CU membranes induced the greatest percentage decrease in neutrophil apoptosis at 15 min. There was a direct correlation between neutrophil apoptosis and plasma levels of TNFα (r = 0.424, p = 0.02) and IL-10 (r = 0.744, p < 0.0001). The results of the study suggest that normal neutrophils exposed to uremic plasma undergo accelerated in vitro apoptosis compared to those incubated with normal plasma. Further, during HD, the apoptosis-inducing activity of uremic plasma is modulated by the use of dialyzers with different degrees of biocompatibility. The identification of soluble factors that are responsible for the increased apoptosis-inducing activity of uremic plasma needs to be further investigated.