Oxalate and calcium oxalate mediated free radical toxicity in renal epithelial cells: effect of antioxidants

In a previous study we demonstrated that oxalate induced free radical injury can promote calcium oxalate stone formation. In the present study, we tested whether the antioxidants vitamin E, superoxide dismutase (SOD), catalase and desferoxamine (DFO) can provide protection against oxalate toxicity in LLC-PK1 cells. LLC-PK1 cells were exposed to oxalate (1.0 mM) or oxalate + calcium oxalate monohydrate crystals (COM, 500 mugm) for 3, 6, and 9 h. Cellular injury was assessed by lactate dehydrogenase (LDH) release. Malondialdehyde (MDA) content, catalase and glutathione peroxidase activities were also measured. The effect of vitamin E (200 muM), DFO (1.0 mM), SOD (400 U), and catalase (400 U) on oxalate-exposed cells was tested. LLC-PK1 cells exposed to oxalate showed a significant increase in LDH release and MDA content, which was further elevated when COM crystals were added. Cellular glutathione peroxidase and catalase activities were decreased on exposure to oxalate. The addition of vitamin E, SOD, catalase and DFO significantly reduced the release of LDH and restored glutathione peroxidase and catalase activities towards the control level. The increased formation of MDA on oxalate or oxalate + COM toxicity was restored towards normalization by antioxidants and antioxidant enzymes. The protection rendered by vitamin E was greater than that of SOD, catalase and DFO. We conclude that oxalate associated free radical injury may promote stone formation by providing cellular debris for crystal nucleation and aggregation and augment crystal attachment to other tubular cells. Antioxidant administration may prevent calcium oxalate nucleation and retention in the renal tubules by preventing oxalate mediated peroxidative injury.