Uric acid: an abettor or protector in calcium oxalate urolithiasis? Biochemical study in stone formers

Free radical induced renal damage leads to crystal retention and formation of large stones. However, the scenario behind uric acid (UA) stone formation is still a mystery, as uric acid, a risk factor of stone formation, seems to be a potent antioxidant that can protect cells from damage by reactive oxygen species. This study was intended to evaluate the role of uric acid in stone formers by assessing the oxidative stress status of the stone patients.

Determination of urinary stone forming risk factors and oxidative stress factors like plasma lipid peroxidation, protein carbonyls of stone formers and histopathological changes and uric acid deposition in stone patients kidney biopsy were studied.

Increased concentrations of urinary uric acid and oxalate in both uric acid as well as calcium oxalate stone formers were observed, whereas calcium is increased in calcium stone formers and not in the uric acid stone patients. Inhibitors such as citrate and glycosaminoglycans (GAGs) were found to be significantly decreased in all the stone patients. Histopathological studies confirmed the deposition of crystals in the damaged tubules and De Galantha staining authenticates that the damage is caused due to uric acid crystals. Increased oxidative stress is dictated by the concentrations of lipid peroxidation and protein carbonyls in stone formers. Moreover, increased activities of urinary marker enzymes substantiate the tubular damage.

We speculated that uric acid acts as a calculi forming salt rather than an antioxidant and it has no role in preventing oxidative stress pertaining to urolithiasis.