Oxalate crystallization in the kidney in the presence of hyperuricemia

It has been a long time since uric acid was suggested to be a promoting factor in calcium oxalate stones, and a number of in vitro studies have been carried out on the relationship between uric acid or urate and calcium oxalate. Concerning in vivo studies, urate or calcium oxalate stone-forming diets were given alone in most cases, and diets that induce formation of stones with different composition have not been given in combinations. We administered a low-concentration oxalemic diet, and a mixed diet containing oxalic acid and uric acid, and biochemically and histologically studied the effects of oxalate and uric acid on kidney stone formation. In the kidney of the animals given the mixed diet, formation of crystalloids of uric acid or urate was evident when no crystallization was noted in the kidney of those given the low concentration oxalemic diet alone. The morphological differences in the uric acid and urate crystalloids in the kidney and the process leading to crystallization of calcium oxalate were examined under transmission and scanning electron microscopy. Histological examination indicated that these uric acid crystals and urate crystals serve as seeds and induce formation and epitaxial growth of calcium oxalate crystals. Our in vivo study provides additional evidence that uric acid is a promoting factor in calcium oxalate stone formation.