Effects of oxalate on HK-2 cells, a line of proximal tubular epithelial cells from normal human kidney

Purpose: Oxalate, a metabolic end product, is a major constituent of majority of renal stones. Previous studies with LLC-PK1 cells, a line of proximal renal epithelial cells of porcine origin, have shown that oxalate produces time and concentration dependent effects on the growth and viability of these cells. We assessed the possibility that oxalate may be toxic to HK-2 cells, a line of human proximal renal epithelial cells. Materials and Methods: HK-2 cells were maintained in Dulbecco's modified Eagle's medium supplemented with fetal bovine serum and antibiotics. Cells were exposed to oxalate for various intervals. Trypan blue exclusion criteria were used to assess membrane integrity, cell morphology was assessed by hematoxylin and eosin staining and crystal violet staining was used to measure cell density. DNA synthesis was measured by [H-3]-thymidine incorporation and superoxide production was measured by the nitroblue tetrazolium reduction method. Results: Exposure of HK-2 cells to oxalate produced time and concentration dependent increase in the membrane permeability to trypan blue and changes in the light microscopic appearance of the cells. Long-term exposure to oxalate resulted in an increase in DNA synthesis and alterations in cell viability with net cell loss after exposure to high oxalate concentrations. Conclusions: To our knowledge the results provide the first direct demonstration of the toxic effects of oxalate in HK-2 cells, a line of human renal epithelial cells, and suggest that hyper-oxaluria may contribute to renal tubular damage associated with calcium oxalate stone disease.