In vitro effects of low-calcium peritoneal dialysis solutions on peritoneal macrophage functions

The use of low-calcium peritoneal dialysis solutions (PDS) for continuous ambulatory peritoneal dialysis is becoming widely accepted to reduce the risk of serum hypercalcemia in patients taking calcium salts as phosphate binders. We compared the in vitro effects of low-calcium PDS (1,000 mumol calcium/L), calcium-free buffer, and buffers with increasing calcium concentrations (500 to 5,000 mumol calcium/L) on peritoneal macrophage (PMO) functions. Peritoneal macrophages isolated from 10 continuous ambulatory peritoneal dialysis patients were incubated in the different solutions and tested for phagocytic and killing capacity, superoxide generation (cytochrome-C reduction and lucigenin-enhanced chemiluminescence), and the rate of myeloperoxidase-dependent oxidative metabolism (luminol-enhanced chemiluminescence). All functions of the PMO incubated in calcium-free buffer were significantly suppressed compared with the PMO incubated in calcium buffers. No dose-dependent increase of a single PMO function could be found after incubating the PMO in calcium buffer with increasing concentrations. Incubation of PMO in otherwise identical PDS containing 1,000, 1,450, or 1,750 mumol calcium/L did not result in significantly different PMO functions. Acidic PDS (pH 5.3 to 5.5) suppressed all measured PMO functions as compared with their neutralized counterparts (pH 7.4), irrespective of the calcium concentration. Results of our in vitro study show that low-calcium PDS does not suppress PMO functions any more than standard-calcium PDS (1,750 mumol calcium/L) does.