Crystal-cell interaction and apoptosis in oxalate-associated injury of renal epithelial cells

Two renal epithelial cell lines, LLC-PK1 and Madin-Darby canine kidney (MDC K), were grown in monolayers and exposed to oxalate (Ox) and/or calcium oxa late (CaOx) crystals to investigate cellular responses to these challenges. In addition, LLC-PK1 cells were exposed to high concentrations of Ox for v arious time periods to investigate the role of apoptosis in Ox-associated c ell injury. Both cell types showed signs of damage when exposed to Ox. Howe ver, LLC-PK1 cells appeared more sensitive than MDCK cells. There was a sig nificant increase in release of lactate dehydrogenase into the medium and d ecrease in trypan blue exclusion by cells in the monolayer. Most noticeable was the detachment of cells from the substrate. Exposure of cells to CaOx crystals resulted in their attachment to cell surfaces followed by internal ization. Using flow cytometry for quantification of apoptotic cells, transm ission electron microscopy for morphology, and electrophoresis for DNA ladd ering detection, we observed significant apoptotic changes including conden sation and margination of nuclear chromatin, DNA fragmentation, and migrati on of phosphatidylserine of the plasma membrane from inside to the cell sur face. However, these cells also showed some necrotic changes such as loss o f plasma membrane integrity and release of lactate dehydrogenase, indicatin g that the apoptotic process was interrupted.