Neutrophil apoptosis and dysfunction in uremia

The high prevalence of bacterial infections among patients with end-stage r enal disease suggests that "professional" phagocytes such as neutrophils ar e functionally impaired. This dysfunction has been ascribed to uremic toxin s, malnutrition, and dialysis. The aim of this study was to investigate the contribution of apoptosis to neutrophil dysfunction in uremia. Neutrophils harvested from uremic patients (n = 6) and age-/gender-matched healthy con trol subjects (n = 6) were incubated with either 50% autologous plasma or 1 0% fetal calf serum. After 24-h incubation, apoptosis was quantified by flo w cytometry by using propidium iodide nuclear staining. Neutrophils from he althy volunteers were also incubated with either 50% heterologous normal or uremic plasma. After 24-h incubation, apoptosis was quantified by flow cyt ometry and transmission electron microscopy. In addition, superoxide produc tion was determined by measuring the capacity to reduce ferri- to ferro-cyt ochrome C by using bp-phorbol 12-beta-myristate 13-alpha-acetate or N-formy l methionyl-leucyl-phenylalanine (fMLP) for stimulus. Phagocytosis was dete rmined by the uptake of C-14-labeled heat-killed Staphylococcus aureus. Com pared with normal neutrophils, uremic neutrophils demonstrated greater apop tosis in the presence of autologous plasma (9 +/- 4 versus 19 +/- 6%, P = 0 .01) as well as 10% fetal calf serum (19 +/- 7 versus 31 +/- 6%, P = 0.03). Furthermore, compared with normal neutrophils exposed to heterologous norm al plasma, those exposed to heterologous uremic plasma exhibited higher apo ptosis rates (19 +/- 3 versus 40 +/- 5%, P = 0.002), lower fMLP-stimulated superoxide production (22.6 +/- 2.5 versus 15.5 +/- 1.1 nmol O-2(. 1)/3.12 x 10(5) cells/30 min, P = 0.01), and a lower phagocytosis index (38 +/- 3% versus 27 +/- 5%, P = 0.04). Apoptosis correlated inversely with fMLP-stimu lated superoxide production (r = -0.60, P = 0.04) and phagocytosis (r = -0. 57, P = 0.05). These results suggest that uremic neutrophils undergo accele rated in vitro apoptosis. Furthermore, uremic plasma accelerates apoptosis of normal neutrophils, resulting in a dysfunctional pattern that is similar to that observed in uremia.