Ignacio Granja and John R. Asplin are employed by Litholink. John R. Asplin is a consultant to Oxthera Corp. David S. Goldfarb is a consultant for Takeda and Keryx and a speaker for CME Quintiles, Mission and owner, Ravine Group. There are no patents, products in development or marketed products to declare. This does not alter the authors’ adherence to all the PLOS ONE policies on sharing data and materials, as detailed online in the guide for authors.
Conceived and designed the experiments: OO RB JA DG. Performed the experiments: OO RB IG JA DG. Analyzed the data: JA RB DG. Contributed reagents/materials/analysis tools: JA IG. Wrote the paper: OO DG RB JA.
Sodium thiosulfate (STS) reduced calcium stone formation in both humans and genetic hypercalciuric stone forming (GHS) rats. We sought to measure urine chemistry changes resulting from STS administration in people.
STS was given to healthy and hypercalciuric stone forming adults. Five normal non-stone forming adults (mean age 33 years), and 5 people with idiopathic hypercalciuria and calcium kidney stones (mean age 66 years) participated. Two baseline 24-hour urine collections were performed on days 2 and 3 of 3 days of self-selected diets. Subjects then drank STS 10 mmol twice a day for 7 days and did urine collections while repeating the self-selected diet. Results were compared by non-parametric Wilcoxon signed rank test. The primary outcome was the resulting change in urine chemistry.
STS administration did not cause a significant change in urinary calcium excretion in either group. In both groups, 24 hour urinary ammonium (P = 0.005) and sulfate excretion (P = 0.007) increased, and urinary pH fell (P = 0.005); citrate excretion fell (P<0.05) in hypercalciuric participants but not in non-stone formers. Among stone formers with hypercalciuria, 3 of 5 patients had measurement of serum HCO3 concentration after the STS period: it did not change. The net effect was an increase in supersaturation of uric acid, and no change in supersaturation of calcium oxalate or calcium phosphate.
The basis for studies demonstrating that STS prevented stones in rats and people was not reflected by the changes in urine chemistry reported here. Although serum HCO3 did not change, urine tests suggested an acid load in both non-stone forming and hypercalciuric stone-forming participants. The long term safety of STS needs to be determined before the drug can be tested in humans for long-term prevention of stone recurrence.
Sodium thiosulfate (STS) has a number of uses in medicine, the most well known of which is its role as an antidote for cyanide poisoning. It acts via the conversion of cyanide to the more water-soluble thiocyanate which is readily excreted in urine
Two studies, one in genetic hypercalciuric stone-forming (GHS) rats and one in humans, have shown a decrease in the incidence of kidney stones following STS administration
Our study sought to investigate whether urine chemistries of humans on STS therapy would suggest efficacy in reducing urinary lithogenicity, and whether evidence for an associated acid load would be present.
The study population consisted of two distinct arms.
The second group consisted of an equal number of participants with a mean age of 66 years. This group included 4 men and 1 woman all of whom had been seen and evaluated as outpatients in the Metabolic Stone Clinic and who were documented calcium stone formers with a history of hypercalciuria, specifically with 24 hour urine calcium measurements of greater than 300 mg/d on collections done within a year prior to the study, while following a self-selected diet. We identified 10 eligible patients seen in the Metabolic Stone Clinic in recent months and the first 5 who were contacted and agreed to participate were enrolled. The participants were recruited between January-April, 2011. The mean serum creatinine concentration was 1.1+0.1 mg/dl (range 0.9–1.2 mg/dl) and the mean estimated glomerular filtration rate was 74.2+12.4 ml/min/1.73 m2 (range 60.0- 91.0 ml/min/1.73 m2). Three patients had calcium stones composed of calcium oxalate and calcium phosphate, the latter component constituting 20, 40, or 50% of analyzed stones. The other 2 patients did not provide stones for analysis but had radio-opaque stones seen on plain abdominal radiography. Patients over the age of 80 were excluded from the study. Patients who had hypercalciuria in the past but did not have hypercalciuria on baseline collections done immediately prior to STS administration were not excluded. All patients were prescribed a diet demonstrated in a randomized controlled trial to reduce the incidence of recurrent stones in participants with hypercalciuria (more dietary calcium, less animal protein, sodium and oxalate).
The patients were selected at random and solicited for participation. The study was approved by the institutional review board of the New York Harbor VA Healthcare System and registered with Clinicaltrials.gov as NCT01088555. The study was performed under US Food and Drug Administration Investigational New Drug number 106,424. All subjects provided written consent to participate in the study.
Each participant undertook 2 baseline 24 hour urine collections over two consecutive days during which they were instructed to keep detailed food diaries while eating their self-selected diets. Oral doses of STS were then taken by the subjects for 7 days after the completion of the baseline urine collections. STS was dispensed by the research pharmacist to the patients and taken home for self-adminstration. The dose was 10 mmol (5 ml of a 2 M solution) twice a day, replicating the protocol described by Yatzidis. The taste and smell of STS precludes blinding the study. On days 5, 6 and 7, subjects replicated the diets they had documented during the pre-STS baseline urine collections. On days 6 and 7 of the medication administration period, participants undertook a second set of two 24 hour urine collections. Food diaries were not collected; they were simply used to allow subjects to replicate diets. Three of the 5 stone forming participants also had basic metabolic panels, including serum bicarbonate levels, checked prior to STS administration and on day 7 of taking STS; the other 2 did not have post-STS serum measurements because of logistical problems.
During the urine collections, the urine was maintained at room temperature. An antimicrobial and a urine volume marker were added to each urine container and then a 50 ml aliquot of urine was obtained. The participants performed the urine collections at home, and then mailed their urine collections to Litholink Corp (Chicago, IL) for analysis
In each 24 hour urine sample, we measured calcium, chloride, creatinine, magnesium, sodium, potassium, phosphate, ammonium, and uric acid concentrations by standard laboratory technique using a Beckman Synchron CX5 (Beckman Instruments, Brea, CA, USA). pH was measured by glass electrode. Oxalate was measured by enzyme assay using oxalate oxidase (Trinity Biotech, Bray, Ireland). Citrate was measured by enzyme assay using citrate lyase (Mannheim Bohringer, Mannheim, Germany). From these analyses supersaturation (SS) was calculated with respect to calcium oxalate, calcium phosphate, and uric acid using the iterative computer program EQUIL 2
Thiosulfate and sulfate were measured by ion chromatography using a Dionex ICS 2000 system (Dionex Corp., Sunnyvale, CA). Samples were loaded into a 25-µl loop using an autosampler and injected onto an AG-11 guard column and AS-11 analytical column in series, with KOH as the mobile phase. Ion peaks were detected using a conductivity meter with the eluent background conductivity suppressed using an anion self-regenerating suppressor. We have found thiosulfate to be stable in urine under the collection conditions used in this study.
Results of baseline and post-STS urine collections were compared by non- parametric Wilcoxon signed rank test and the effects of STS in controls and hypercalciuric stone forming participants were compared by Mann Whitney U test. Statistical data were generated and analyzed with a commercially available software package, Systat (Point Richmond, CA, USA). Results were expressed as mean±SD and differences were considered statistically significant at
All 10 patients enrolled completed the study without any lost to follow-up. The results of all participants were included. The results of STS administration in both the normal participants, the hypercalciuric participants and the 2 groups combined are presented in
NORMAL CONTROLS | HYPERCALCIURIC STONE FORMERS | COMBINED | |||||||
Baseline | Post-STS | P-value | Baseline | Post-STS | P-value | Baseline | Post-STS | P value | |
Ca (mg) | 111.5±24.9 | 147±43.9 | 0.08 | 279.3±155.6 | 277.9±143.9 | 0.89 | 195.4±137.4 | 212.5±121.7 | 0.17 |
Na (meq) | 186.6±66.8 | 198.1±61.4 | 0.5 | 172.1±46.4 | 198.8±48.4 | 0.22 | 179.4±54.8 | 198.4±52.1 | 0.20 |
K (meq) | 97.2±25.0 | 82.9±22.0 | 0.22 | 69.8±15.8 | 66.0±18.8 | 0.69 | 83.5±30.7 | 74.4±21.3 | 0.24 |
Creatinine (mg) | 1171.3±377.2 | 1235.8±422.1 | 0.14 | 1748.8±255.7 | 1858.2±378.0 | 0.14 | 1460.1±430.0 | 1547.0±500.3 | 0.04 |
pH | 6.67±0.39 | 6.08±0.40 | <0.05 | 6.09±0.58 | 5.76±0.52 | <0.05 | 6.39±0.56 | 5.95±0.48 | 0.005 |
NH4 (meq) | 24.8±5.9 | 43.4±17.3 | <0.05 | 36.3±6.1 | 55.8±11.2 | <0.05 | 31.6±7.6 | 49.6±15.2 | 0.005 |
Citrate (mg) | 740.6±504.7 | 713.9±548.6 | 0.5 | 605.9±195.1 | 444.0±221.1 | <0.05* | 673.3±367.7 | 579.0±419.2 | 0.03 |
PO4 (mg) | 805.±410 | 831±496 | 0.5 | 1152±297 | 1033±263 | 0.08 | 979±384 | 932±390 | 0.57 |
SO4 (meq) | 44.1±18.8 | 85.8±29.3 | 0.08 | 44.1±13.5 | 98.9±16.0 | <0.05 | 44.1±15.4 | 94.5±22.8 | 0.007 |
Ox (mg) | 37.8±15.1 | 36.3±17.3 | 0.9 | 42.5±14.5 | 42.4±16.8 | 0.50 | 40.2±14.2 | 39.3±16.4 | 0.80 |
UA (mg) | 583±260 | 586±228 | 0.65 | 712±161 | 742±157 | 0.50 | 648±215 | 664±202 | 0.96 |
SS UA | 0.19±0.13 | 0.5±0.36 | <0.05 | 0.76±0.62 | 1.38±0.89 | <0.05 | 0.47±0.52 | 0.94±0.79 | 0.005 |
SS CaP | 0.74±0.2 | 0.55±0.33 | 0.5 | 1.66±1.04 | 1.03±0.80 | 0.14 | 1.20±0.86 | 0.79±0.63 | 0.09 |
SS CaOx | 3.18±0.4 | 3.58±0.63 | 0.22 | 7.14±3.59 | 8.17±4.99 | 0.69 | 5.16±3.18 | 5.88±4.13 | 0.33 |
SS = supersaturation, CaOx = calcium oxalate, CaP = calcium phosphate, UA = uric acid; P values by Wilcoxon signed-rank test; *: effect in hypercalciuric participants different than effect in normal controls; P<0.05 by Mann-Whitney U test.
There was no evidence to suggest the development of metabolic acidosis based on the pre- and post-STS serum bicarbonate levels in the 3 stone forming patients from whom these data were collected (
Pre-STS (meq/L) | Post STS (meq/L) | |
Patient 1 | 32 | 28 |
Patient 2 | 29 | 31 |
Patient 3 | 24 | 22 |
Mean±SD | 28.3±4.0 | 27.0±4.6 |
Urine volume, creatinine, urea, and sodium excretion remained unchanged in both arms of the study pre- and post-STS, and in the combined data, confirming replication of diets over the course of the collections. Administration of the drug was well tolerated with no patients stopping therapy due to adverse events. All patients were questioned about their experience with the drug: 2 patients had transient episodes of loose or watery stools which resolved despite continued STS administration and 2 patients described foul smelling stool. No deviations from the protocol occurred.
In the first study to examine a full set of urinary analytes after administration of oral STS, neither healthy controls, nor hypercalciuric calcium stone formers, experienced statistically significant increases in urine calcium excretion or calcium oxalate or calcium phosphate supersaturation. In stone-formers, there were decreases in urine pH and citrate, and increases in ammonium excretion without a change in serum [HCO3]. Similar results occurred in the control non-stone-formers, with the exception that citrate did not fall. These effects on urine chemistry, with no net change in lithogenicity, would not explain remarkable reductions in stone activity reported in a non-controlled, non-randomized clinical study
Our urine results are also not consistent with the findings of Yatzidis et al
The present study is consistent with thiosulfate presenting a net acid load, suggested by increases in urine ammonium excretion, and decreases in citrate excretion (in stone-formers) and urine pH. The etiology of this acid load is not clear. Stool losses of bicarbonate or potential base could be an explanation, though most patients had no diarrhea and those who did, experienced it only transiently. Previous reports of metabolic acidosis after parenteral administration of STS for cyanide poisoning and calcific uremic arteriolopathy exist
Some recent literature has claimed that sodium thiosulfate is a strong acid
The urine findings are similar to those noted in GHS rats given STS
One limitation of the study is the small sample size of the 2 groups and that the groups are not matched for age. Since the primary outcome was not a comparison of the effects of the drug on the two populations we do not consider the age difference to be important. In fact, combining the results of the 2 groups demonstrated that the results were highly consistent between them with the only difference being a fall in urine citrate in hypercalciuric stone-formers but not in the non-stone-forming controls. Finding healthy people willing to take an investigational drug and do multiple urine collections among a hospital population was more difficult than finding stone formers interested in advancing the knowledge of their disorder and its potential treatment. Only after the results in the healthy group did we realize that it would be desirable to measure serum chemistry after drug administration and because of logistical issues could not get blood while participants were still taking the drug in 2 of the 5 stone formers. Since serum [HCO3] did not change in the 3 in whom it was measured despite their significant changes in urine chemistry, we do not believe this small sample is an important limitation to knowing whether an acid load was presented. The urine findings clearly show that it occurred. We cannot speculate regarding the generalizability of these findings to a broader population of calcium stone formers with these or other urinary risk factors for stone formation.
The absence of a significant change in serum [HCO3] does not necessarily confirm the safety of long-term STS administration, as the finding is potentially related to two limitations of the study: its small sample size and relatively short duration of STS administration. STS therapy for the prevention of nephrolithiasis would likely need to continue for many years, and as such, studies of at least months to years would be necessary to sufficiently rule out development of sustained metabolic acidosis. A larger study with a longer duration more similar in scale and length to that of Yatzidis
The appropriate therapy for prevention of recurrent calcium phosphate stones is unclear as no randomized controlled trials with this outcome have been completed