Idiopathic calcium oxalate kidney stones form while attached to Randall plaques, the subepithelial deposits on renal papillary surfaces. Plaque formation and growth mechanisms are poorly understood. Plaque formation elsewhere in the body is triggered by reactive oxygen species and oxidative stress. This review explores possible reactive oxygen species involvement in plaque formation and calcium oxalate nephrolithiasis. A search of various databases for the last 8 years identified literature on reactive oxygen species involvement in calcium oxalate nephrolithiasis. The literature was reviewed and results are discussed. Under normal conditions reactive oxygen species production is controlled, increasing as needed and regulating crystallization modulator production. Reactive oxygen species overproduction or decreased antioxidants lead to oxidative stress, inflammation and injury, and are involved in stone comorbidity. All major chronic inflammation markers are detectable in stone patient urine. Patients also have increased urinary excretion of the IαI and the thrombin protein families. Results of a recent study of 17,695 participants in NHANES III (National Health and Nutrition Examination Survey) showed significantly lower antioxidants, carotene and β-cryptoxanthin in those with a kidney stone history. Animal model and tissue culture studies revealed that high oxalate, calcium oxalate and calcium phosphate crystals provoked renal cell reactive oxygen species mediated inflammatory responses. Calcium oxalate crystals induce renin up-regulation and angiotensin II generation. Nonphagocytic NADPH oxidase leads to reactive oxygen species production mediated by protein kinase C. The P-38 MAPK/JNK transduction pathway is turned on. Transcriptional and growth factors, and generated secondary mediators become involved. Chemoattractant and osteopontin production is increased and macrophages infiltrate the renal interstitium around the crystal. Phagocytic NADPH oxidase is probably activated, producing additional reactive oxygen species. Localized inflammation, extracellular matrix and fibrosis develop. Crystallization modulators have a significant role in inflammation and tissue repair. Based on available data, Randall plaque formation is similar to extracellular matrix mineralization at many body sites. Renal interstitial collagen becomes mineralized, assisting plaque growth through the interstitium until the mineralizing front reaches papillary surface epithelium. Plaque exposure to pelvic urine may also be a result of reactive oxygen species triggered epithelial sloughing.

Urine contains compounds that modulate the nucleation, growth and aggregation of crystals as well as their attachment to renal epithelial cells. These compounds may function to protect the kidneys against: 1, the possibility of crystallization in tubular fluid and urine, which are generally metastable with respect to calcium salts, 2, crystal retention within the kidneys thereby preventing stone formation and 3, possibly against plaque formation at the nephron basement membrane. Since oxalate is the most common stone type, the effect of various modulators on calcium oxalate (CaOx) crystallization has been examined in greater details. Most of the inhibitory activity resides in macromolecules such as glycoproteins and glycosaminoglycans while nucleation promotion activity is most likely sustained by membrane lipids. Nephrocalcin, Tamm-Horsfall protein, osteopontin, urinary prothrombin fragment 1, and bikunin are the most studied inhibitory proteins while chondroitin sulfate (CS), heparan sulfate (HS) and hyaluronic acid (HA) are the best studied glycosaminoglycans. Crystallization modulating macromolecules discussed here are also prominent in cell injury, inflammation and recovery. Renal epithelial cells on exposure to oxalate and CaOx crystals produce some of the inflammatory molecules such as monocyte chemoattractant protein-1 (MCP-1) with no apparent role in crystal formation. In addition, macrophages surround the CaOx crystals present in the renal interstitium. These observations indicate a close relationship between inflammation and nephrolithiasis.

Reactive oxygen species, inflammation and calcium oxalate nephrolithiasis