Effect of cystine-binding thiol drugs on urinary cystine capacity in patients with cystinuria.
OBJECTIVE
To determine the effect of cystine-binding thiol drugs (CBTD) on urinary cystine capacity in patients with cystinuria.


METHODS
Seven cystinuric patients performed two sets of urine collections while on and off CBTD while controlling for all other variables: diet and fluid and alkali intake. They monitored and recorded their diet for 3 days and performed urine collections on days 2 and 3. They then stopped the CBTD for 7 days. On days 8, 9, and 10, they replicated their diets of days 1 through 3 and performed two more urine collections on days 9 and 10. Two patients took D-penicillamine, four took tiopronin, and one took tiopronin and captopril. The cystine capacity was determined, and the values obtained when the patient was on and off the CBTD were compared to determine whether CBTDs affect urinary cystine capacity. To measure the cystine capacity, we used a solid-phase assay in which cystine crystals are added to the urine and incubated for 48 hours. The crystals are spun down and resolubilized in high-pH buffer, and the amount of cystine in the crystals is calculated. The solid phase will take up cystine from urine (negative cystine capacity) that is supersaturated and give up cystine to an undersaturated urine (positive cystine capacity).


RESULTS
All seven patients had significant improvement in urinary cystine capacity on CBTDs. The mean cystine capacity off CBTD was -130.6 +/- 280.8, while the value during CBTD use was 43.1 +/- 131.2 (P < 0.05). On CBTDs, two patients still had negative values, but both had important improvements. The mean urinary volumes were similar on and off CBTD, indicating adequate and similar fluid intake. Urine pH values and urinary excretion of sodium and urea also were comparable, indicating consistency of citrate intake and diet.


CONCLUSIONS
Our results demonstrate that CBTDs lower the urinary supersaturation of cystine, as shown by a less-negative or more-positive cystine capacity. Cystine capacity can be measured directly, even in the presence of CBTDs. The value of this measurement lies in the potential to monitor the response to the drug, prescribe the minimum effective dose, and potentially decrease the adverse effects often associated with CBTDs.
Dolin
Daniele J
DJ
Department of Urology, St. Vincent Catholic Medical Center, 170 West 12th Streetm Cronin 205, New York, NY 10011, USA. ddolin@svcmcny.org
Asplin
John R
JR
Flagel
Leigh
L
Grasso
Michael
M
Goldfarb
David S
DS
D000284:Administration, Oral; D000328:Adult; D002216:Captopril / Q000627:therapeutic use*; D016022:Case-Control Studies; D003545:Cysteine / Q000187:drug effects* / Q000378:metabolism; D003555:Cystinuria / Q000175:diagnosis / Q000188:drug therapy*; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D010396:Penicillamine / Q000627:therapeutic use*; D011336:Probability; D011446:Prospective Studies; D012016:Reference Values; D018570:Risk Assessment; D008625:Tiopronin / Q000627:therapeutic use*; D016896:Treatment Outcome; D016482:Urinalysis
D002216:Captopril; D008625:Tiopronin; D010396:Penicillamine; D003545:Cysteine