Thiosulfate reduces calcium phosphate nephrolithiasis.

An uncontrolled trial reported that sodium thiosulfate reduces formation of calcium kidney stones in humans, but this has not been established in a controlled human study or animal model. Using the genetic hypercalciuric rat, an animal model of calcium phosphate stone formation, we studied the effect of sodium thiosulfate on urine chemistries and stone formation. We fed genetic hypercalciuric rats normal food with or without sodium thiosulfate for 18 wk and measured urine chemistries, supersaturation, and the upper limit of metastability of urine. Eleven of 12 untreated rats formed stones compared with only three of 12 thiosulfate-treated rats (P < 0.002). Urine calcium and phosphorus were higher and urine citrate and volume were lower in the thiosulfate-treated rats, changes that would increase calcium phosphate supersaturation. Thiosulfate treatment lowered urine pH, which would lower calcium phosphate supersaturation. Overall, there were no statistically significant differences in calcium phosphate supersaturation or upper limit of metastability between thiosulfate-treated and control rats. In vitro, thiosulfate only minimally affected ionized calcium, suggesting a mechanism of action other than calcium chelation. In summary, sodium thiosulfate reduces calcium phosphate stone formation in the genetic hypercalciuric rat. Controlled trials testing the efficacy and safety of sodium thiosulfate for recurrent kidney stones in humans are needed.

Vegetarian compared with meat dietary protein source and phosphorus homeostasis in chronic kidney disease.

BACKGROUND AND OBJECTIVES: Patients with advanced chronic kidney disease (CKD) are in positive phosphorus balance, but phosphorus levels are maintained in the normal range through phosphaturia induced by increases in fibroblast growth factor-23 (FGF23) and parathyroid hormone (PTH). This provides the rationale for recommendations to restrict dietary phosphate intake to 800 mg/d. However, the protein source of the phosphate may also be important. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: We conducted a crossover trial in nine patients with a mean estimated GFR of 32 ml/min to directly compare vegetarian and meat diets with equivalent nutrients prepared by clinical research staff. During the last 24 hours of each 7-day diet period, subjects were hospitalized in a research center and urine and blood were frequently monitored. RESULTS: The results indicated that 1 week of a vegetarian diet led to lower serum phosphorus levels and decreased FGF23 levels. The inpatient stay demonstrated similar diurnal variation for blood phosphorus, calcium, PTH, and urine fractional excretion of phosphorus but significant differences between the vegetarian and meat diets. Finally, the 24-hour fractional excretion of phosphorus was highly correlated to a 2-hour fasting urine collection for the vegetarian diet but not the meat diet. CONCLUSIONS: In summary, this study demonstrates that the source of protein has a significant effect on phosphorus homeostasis in patients with CKD. Therefore, dietary counseling of patients with CKD must include information on not only the amount of phosphate but also the source of protein from which the phosphate derives.