The effect of osteopontin on the adhesion of calcium oxalate crystals to Madin-Darby canine kidney cells.

OBJECTIVE

We have recently reported that osteopontin protein (OPN) is present in calcium-containing urinary calculi and in rat distal tubular cells and that it is an important substance of the matrix in urinary stone formation. To investigate how OPN participates in urinary stone formation, we assessed the role of OPN in the adhesion of the surfaces of Madin-Darby canine kidney (MDCK) cells, which are distal tubular cells of the dog, to calcium oxalate crystals.

METHODS

We cultured MDCK cells with OPN, thrombin, which is an OPN inhibitor, Arg-Gly-Asp peptide and Arg-Gly-Glu peptide as a control for Arg-Gly-Asp peptide, and examined changes in adhesion of calcium oxalate crystals to the cells by scanning electron microscopy and the calcium (45Ca) concentration around the cells.

RESULTS

The 45Ca concentration in calcium oxalate crystals adhering to MDCK cells was about 1.4 times higher in MDCK cells incubated with OPN than in an MDCK-cell-negative group, and was about one half that in MDCK cells incubated with thrombin than in the group without MDCK cells.

CONCLUSION

OPN is considered to be an accelerator of urinary stone formation because of the increase in adhesion of calcium oxalate crystals to the renal distal tubular epithelium in the presence of OPN. These findings suggest that OPN plays an important role in the formation of calcium-containing urinary stones.