Citrate provides protection against oxalate and calcium oxalate crystal induced oxidative damage to renal epithelium

Purpose: Oxalate and calcium oxalate (CaOx) crystals are injurious to renal epithelial cells. The injury is caused by the production of reactive oxygen species (ROS). Citrate is a well-known inhibitor of CaOx crystallization and as such it is one of the major therapeutic agents prescribed. Since citrate increases cellular reduced nicotinamide adenine dinucleotide phosphate and glutathione (GSH), we hypothesized that exogenously administered citrate should act as an antioxidant and protect cells from oxalate induced injury. Materials and Methods: We exposed LLC-PK1 and MDCK cells to 500 muM/ml oxalate or 150 mug/cm(2) calcium oxalate crystals for 30, 60 and 180 minutes with or without 3 mg/ml citrate in the medium. We determined cell viability by lactate dehydrogenase release and trypan blue exclusion, ROS involvement by changes in hydrogen peroxide and GSH, and lipid peroxidation by quantifying 8-isoprostane. Results: The presence of citrate was associated with significant decrease in lactate dehydrogenase release (p <0.001) and staining with trypan blue (p <0.05). In addition, there was a significant increase in GSH (p <0.005) and a decrease in the production of hydrogen peroxide (p <0.05) and 8-isoprostane (p <0.0005) secretion into the culture medium when citrate was present in the medium. Conclusions: Citrate protects cells from oxalate and CaOx crystal induced injury by preventing lipid peroxidation through a decrease in ROS production. The results provide additional data for the beneficial role of citrate therapy for CaOx nephrolithiasis.