Elevated superoxide generation in mononuclear phagocytes by treatment with 1α hydroxyvitamin D₃: Changes in kinetics and in oxidase cytozsolic factor P47

The effect of 1α-hydroxyvitamin D₃ (1αOHD₃) treatment on the superoxide production of phagocytic cells in patients undergoing continuous ambulatory peritoneal dialysis (CAPD) was studied. A 3-day treatment of CAPD patients with 3 μg per day of 1αOHD₃ (high-dose treatment) significantly increased NADPH oxidase and killing activities in peritoneal macrophages and peripheral blood monocytes (P<0.001) as compared with low-dose (0.25 μg/day of 1αOHD₃) treatment or nontreatment. The high oxidase activity observed in macrophages and monocytes after the treatment with 1αOHD₃, correlated significantly to the increase in the amount of the cytosolic factor p47 of the NADPH oxidase as detected by western blotting analysis. Superoxide production by the peripheral blood neutrophils of these patients only slightly increased with 1αOHD₃ treatment, and the amount of p47 was not affected by 1αOHD₃ administration. In order to evaluate the significance of the oxidase cytosolic factor in dictating oxidase activity, a reconstitution of NADPH oxidase was conducted by mixing macrophage cytosols and membranes in a cell-free system. The addition of macrophage cytosol from patients on high-dose treatment to macrophage membranes from patients in all of the categories of treatment resulted in significantly higher (P<0.001) superoxide production as opposed to the macrophage cytosol from nontreated patients. These results suggest that 1,25(OH)₂D₃ causes an increase in NADPH oxidase activity in the peritoneal macrophages and monocytes of CAPD patients by inducing synthesis and elevating the amount of the cytosolic factor p47. The increased killing of staphylococci by these cells is probably due to the elevation of superoxide generation, which is the major mechanism for the killing of invasive pathogens.