title: Sulfate but not thiosulfate reduces calculated and measured urinary ionized calcium and supersaturation: implications for the treatment of calcium renal stones.
abstract: BACKGROUND
  Urinary sulfate (SO4(2-)) and thiosulfate (S2O3(2-)) can potentially bind with calcium and decrease kidney stone risk. We modeled the effects of these species on the concentration of ionized calcium (iCa) and on supersaturation (SS) of calcium oxalate (CaOx) and calcium phosphate (CaP), and measured their in vitro effects on iCa and the upper limit of stability (ULM) of these salts.
  
  
  METHODS
  Urine data from 4 different types of stone patients were obtained from the Mayo Nephrology Clinic (Model 1). A second data set was obtained from healthy controls and hypercalciuric stone formers in the literature who had been treated with sodium thiosulfate (STS) (Model 2). The Joint Expert Speciation System (JESS) was used to calculate iCa and SS. In Model 1, these parameters were calculated as a function of sulfate and thiosulfate concentrations. In Model 2, data from pre- and post STS urines were analyzed. ULM and iCa were determined in human urine as a function of sulfate and thiosulfate concentrations.
  
  
  RESULTS
  Calculated iCa and SS values for all calcium salts decreased with increasing sulfate concentration. Thiosulfate had no effect on these parameters. In Model 2, calculated iCa and CaOx SS increased after STS treatment, but CaP SS decreased, perhaps due to a decrease in pH after STS treatment. In confirmatory in vitro experiments supplemental sulfate, but not thiosulfate, significantly increased the calcium needed to achieve the ULM of CaP and tended to increase the oxalate needed to reach the ULM of CaOx. Sulfate also significantly decreased iCa in human urine, while thiosulfate had no effect.
  
  
  CONCLUSIONS
  Increasing urinary sulfate could theoretically reduce CaOx and CaP stone risk. Although STS may reduce CaP stone risk by decreasing urinary pH, it might also paradoxically increase iCa and CaOx SS. As such, STS may not be a viable treatment option for stone disease.
authors: Department of Chemistry, University of Cape Town, Cape Town, South Africa.
authors: Allen
authors: A
authors: Rodgers
authors: Division of Nephrology and Hypertension, Mayo Clinic, Rochester, Minnesota, United States of America.
authors: Daniel
authors: D
authors: Gauvin
authors: Division of Nephrology and Hypertension, Mayo Clinic, Rochester, Minnesota, United States of America.
authors: Samuel
authors: S
authors: Edeh
authors: Department of Chemistry, University of Cape Town, Cape Town, South Africa.
authors: Shameez
authors: S
authors: Allie-Hamdulay
authors: Department of Chemistry, University of Cape Town, Cape Town, South Africa.
authors: Graham
authors: G
authors: Jackson
authors: Division of Nephrology and Hypertension, Mayo Clinic, Rochester, Minnesota, United States of America; Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota, United States of America.
authors: John C
authors: JC
authors: Lieske
mesh_terms: D000328:Adult; D000368:Aged; D002118:Calcium / Q000652:urine*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D013885:Thiosulfates / Q000652:urine*; D014545:Urinary Calculi / Q000652:urine*
chemical_list: D013885:Thiosulfates; D002118:Calcium