Uremic ultrafiltrate inhibits platelet-activating factor synthesis

Background: Several studies have suggested that uremic toxins may adversely affect phagocytic leukocytes of chronic renal failure patients. Platelet-a ctivating factor (PAF) is produced by phagocytic leukocytes and is a potent mediator of inflammation which is produced by leukocytes upon appropriate stimulation. Methods: We added uremic or normal ultrafiltrate, ultrafiltrat e fractionated by reverse phase HPLC or compounds eluting at the same reten tion time as the fractionated ultrafiltrate, to normal leukocytes. Compleme nt-coated baker's yeast spores were added to stimulate phagocytosis. Total PAF was purified by thin layer chromatography and quantified by bioassay on rabbit platelets. The activities of two enzymes involved in the synthesis of PAF, phospholipase A2 (PLA2) and acetyltransferase, were measured in the presence of fractionated ultrafiltrate. Results: Ultrafiltrate from both h ealthy and uremic subjects inhibited PAF synthesis, but the inhibitory effe ct was more substantial for uremic subjects. Ultrafiltrate fractionated by HPLC showed high PAF inhibition for late eluting hydrophobic fractions. Add ition of phenol or p-cresol, two uremic toxins with similar elution pattern as the late fractions, also inhibited PAF synthesis. The activity of PLA2 and acetyltransferase was decreased in the presence of uremic ultrafiltrate . Conclusions: We observed that uremic ultrafiltrate inhibits PAF synthesis upon stimulation with complement coated baker's yeast spores. The decrease in total PAF synthesis appears to be associated with an inhibition of phos pholipase A2 and acetyltransferase activity, enzymes involved in the remode lling pathway for PAF synthesis.