SPP1 and nephrolithiasis: Most of the studies that focused on both proteins were conducted in either laboratory animals[18,21] or in Madin Darby canine kidney cell culture (MDCK)[22], which may not be representative of the real situation in canine renal tissue in vivo. However the conflicting roles of THP and OPN makes the study of their reaction toward kidney stone formation also valuable for the explanation of the pathogenesis of renal oxalosis in dogs.