Cells of proximal and distal tubular origin respond differently to challenges of oxalate and calcium oxalate crystals

Abstract

LLC-PK1 and Madin-Darby canine kidney (MDCK) cells were used to study the role of free radicals in renal epithelial injury during exposure to oxalate ions (Ox) and calcium oxalate monohydrate (COM) crystals. The cell cultures were exposed for 120 or 240 min to 1.0 mmol Ox or 1.0 mmol Ox plus 500 microg/ml of COM crystals averaging 1.0 microm in size. Exposure of both LLC-PK1 and MDCK cells to Ox alone increased the leakage of lactate dehydrogenase, which was further enhanced when cells were exposed to Ox + COM crystals. The release of lactate dehydrogenase from the LLC-PK1 cell line, however, was significantly higher than that from MDCK cells. LLC-PK1 cells also showed a significant increase in malondialdehyde (MDA) content on Ox challenge. MDA content was even higher when LLC-PK1 cells were challenged with Ox + COM crystals. However, in MDCK cells, the elevated MDA content was similar in both treatment groups, suggesting that these cells may be more resistant to the calcium oxalate crystals. Glutathione peroxidase activity was decreased in both LLC-PK1 and MDCK cells. Challenging cells with Ox + COM resulted in decreased catalase activity in LLC-PK1, but increased catalase activity in MDCK cells. Superoxide dismutase activity and reduced glutathione content were not significantly different in either cell type when challenged with Ox or Ox + COM. Previous in vivo animal studies yielded indirect evidence for the increased lipid peroxidation during hyperoxaluria-induced nephrolithiasis. However, in an animal model, it is difficult to separate the effect of Ox from Ox in combination with COM crystals. This study suggests that the injury to renal tubular epithelial cells is accompanied by lipid peroxidation when exposed to Ox. The injury is augmented when COM crystals are included. LLC-PK1 cells are more susceptible to Ox-associated injury than MDCK cells.