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The in Vivo Use of Dithiothreitol in Cystinosis

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The in Vivo Use of Dithiothreitol in Cystinosis Pediat. Res. JI: 124-131 ( 1977) Cystine storage kidney cystinosis, infantile nephropathic leukocytes dithiothreitol liver The in Vivo Use of Dithiothreitol in Cystinosis 0 DENISE DEPAPE-BRIGGER, HY GOLDMAN, AND CHARLES R. SCRIVER'" ' The de Belle Laboratory for Biochemical Genetics, Medical Research Council Group in Genetics, McGill University­ Montreal Children's Hospital Research Institute, Montreal, Quebec, Canada EDGARD DELVIN The Genetics Unit, Shriners Hospital, Montreal, Quebec, Canada ORVAL MAMER The Mass Spectrometry Unit, Royal Victoria Hospital, Montreal, Quebec, Canada Summary of INC, DTT might prevent the occurrence of irreversible phe­ notypic components by preventing cystine accumulation. Two male patients with late stage (uremic) infantile nephro­ pathic cystinosis (INC) (Table 1) were treated by mouth with the reducing agent dithiothreitol (OTT), at doses not exceeding 25 Infantile nephropathic cystinosis is a fatal autosomal recessive mg· kg- 1 body weight three times per day. Three sequential inborn error of cyst(e)ine metabolism (20, 23). Adolescent ne­ periods of observation were obtained in both patients: on thiol phropathic cystinosis ( 1, 8, 15) and adult benign cystinosis ( 15, (8.5 months); off thiol (8-9 months); on thiol again (7 months or 18, 23) are considered to be variants, perhaps allelic, of the longer). Other than nausea and vomiting at the maximum dose infantile type, in which a more benign clinical course appears to range, no apparent toxicity was.observed. One subject died in correlate with less extensive intracellular, presumably lysosomal, uremia in the 24th month of the study. storage of cystine. Dietary methods of treatment do not offset The half-cystine concentration in peripheral blood leukocytes the unknown intracellular defect of cyst(e)ine metabolism and, decreased during both treatment periods in each patient from accordingly, do not alter the clinical course of INC (2). On the initial pretreatment levels in excess of 8 nmol · mg- 1 protein other hand, we have shown ( 1, 7, 8) that the sugar thiol, threo- 1 (normal <0.1 nmol · mg- ) to 10-20% of initial values (Table 2 2 ,3-dihydroxy- l ,4-dithiolbutane ( dithiothreitol or DIT), pene­ and Fig. 1, A and B). Reduction in total number of blood trates the living cell and will correct the abnormal cystine storage leukocytes or in the neutrophil fraction, where cystine storage in cultured cystinotic fibroblasts in vitro. Earlier indications that occurs selectively in cystinosis, did not occur (Table 3) as a DIT could be administered to human subjects (7) led us to possible explanation for these findings; nor did storage of sam­ examine the effect of long term administration of DIT in two ples, a possible artifact, influence the cystine content of cys­ patients with INC. Our results indicate that DIT, or equivalent tinotic cells (Fig. 2). thiols, might offer some hope in the treatment of this inborn Multiple site rectal mucosa biopsy clearly revealed cystine error of cystine storage. storage but serial biopsies did not reflect a positive DTT re­ sponse when compared with the leukocyte assay (Table 4). High MATERIALS AND METHODS intersample variation in cystine content, even between samples taken at one time, prevented measurement of a treatment re­ PATIENTS sponse. DTT had no apparent detrimental effect on the concentration Two 8-year-old boys (SL and PF), both in the late stages of of representative proteins, including hemoglobin (Table 3), se­ INC, were enrolled in June 1973 in a trial of DIT treatment, rum insulin, and serum immunoglobulin during the treatment under conditions of informed parental consent. Typical findings trials. Renal function (glomerular and tubular) was severely concerning growth failure, cystine storage, and renal failure depressed and did not improve during the period of observation were evident in both patients (Table 1). SL died of renal failure in either patient (Table 2; Fig. 3, A and B). at 9 7 / 12 years during the later stages of this investigation. PF is Postmortem tissues from one patient revealed 10-40-fold ex­ still alive at 11 years (in April 1976). Previous observations on cess cystine accumulation in kidney cortex and liver (Table 5). their fibroblasts and leukocytes are compatible with the INC However, these levels of accumulation are at the lower range of phenotype (half-cystine content exceeded 8 nmol · mg · 1 protein or even below published values for cystine in cystinotic kidney in both patients). Patient PF has experienced 3 cm of linear and liver. growth between the 20th and 32nd month of the study, coincid­ Whereas chemical methods are not reliable for detecting and ing with the second OTT trial; there was no change in height measuring DTT in biologic fluids, preliminary evidence indicates during the first 20 months. No increase in height occurred in the that a silylated derivative of oxidized DTT can be detected in the other subject. urine of patients receiving DTT by mouth (Fig. 4). This finding suggests that the thiol is absorbed and excreted. PROTOCOL Speculation The investigation consisted of two periods of DIT treatment separated by an interval without DIT. The first treatment pe­ The defect in cystine metabolism (or transport) in cystinosis riod began in June 1973 and ended in February 1974; the second remains unknown. However, if administered early in the course trial began in October 197 4. Results on tissue cystine content 124 DITHJOTHREITOL IN CYSTINOSJS 125 are reported up to the time of death (April 1975) for SL and up DTT DOSAGE AND ROUTE OF ADMINISTRATION to November 1975 for patient PF. The concentration of creati­ The initial dosage schedule for OTT was approximately 7 nine and urea nitrogen in serum, and of cystine in leukocytes was mg· kg- 1 every 8 hr by mouth; the dose was gradually increased measured monthly in both patients. The average of several until it reached approximately 25 mg· kg- 1 every 8 hr (or I 2 determinations was used to determine the "baseline" values for capsules/day). The odor of the capsules and nausea and vomiting the CUSUM plots (see below). Rectal biopsy every 2 months associated with OTT usage at the upper dose levels affected was used in the first treatment period, but was found to be compliance with the treatment regimen and the scheduled inges­ inadequate for quantitative monitoring of the OTT response. Slit tion of OTT was not maintained consistently. lamp examination of the cornea was also performed at intervals. Enteric-coated capsules of OTT powder (250 mg) were pre­ pared by ICN or Homers Pharmaceutical Co. (Montreal). OTT was purchased from ICN (Canada). Table I . Clinical data for patients with infantile nephropathic cystinosis before dithiothreitol (DTT) trial ------ ------ PREPARATION OF SAMPLES Patient SL Patient PF Leukocytes were separated from whole blood by drawing 10 Age (yr) 7 9/12 8 2/12 ml venous blood into a syringe containing a mixture of dextran Weight age (at 50th percentile) 3 6/12 6 4/12 (2 ml) and heparin (1 ml) (5). After standing upright for 45 min Height age (at 50th percentile) 3 4/12 4 6/12 at 37° the supernatant fluid containing leukocytes was dis­ 1 Scrum crcatininc (mg·dl ') 2.6 1.6' charged into a tube. The remaining erythrocytes were then Endogenous creatrnrnc clearance 15-18' 23-24' removed by differential hypotonic Iysis; leukocytes were re­ 2 (ml·min-'/1.73 m ) covered as a button after centrifugation and stored at - 20° 2 Leukocyte half-cystine concentration 13-38' 8-17' unless sonicated immediately. The leukocytes were suspended in (nmol · mg ' protein) 1 ---- 2.0 ml water and sonicated at 22 kc·sec- (4 pulses of 15 sec ' Mean (or range) of at least three determinations. each) using an M. S. ultrasonic disintegrator and deproteinized 2 Data pooled from observations in previous 36 months; "control" immediately with 2 .0 ml sulfosalycilic acid (3 % w/v). The cys­ samples obtained immediately before first treatment trial with OTT were tine-containing supernatant was separated by centrifugation at lost in laboratory accident. 27,000 x g for 20 min, and stored at -20° until analysis. Table 2. Leukocyte half-cystine and serum creatinine values in cystinosis patients receiving dithiothreitol ( DTT) ----- - -- ·- ----- Leukocyte half-cystine Serum creatinine (mg· di I) (nmol · mg ' protein) Elapsed time in Regimen study (mo) SL PF SL PF ---·----------- Pretreatment 0 13-38 8-17 <3.0 <2.0 On OTT at zero mo 6.6 2.0 2.0 2 37.5 3.1 1.9 3 18.2 4.9 2.2 2.0 3.5 2.5 1.6 4 13.3 1.9 2.0 5 9.0 3.2 1.8 6 3.8 2.7 2.4 2.0 7 4.8 1.3 2.5 1.9 8 1.3 4.9 2.5 1.9 Off OTT at 8.5 mo 9 2.3 2.4 10 6.2 2.2 3.2 1.9 11 2.5 3.4 2.6 12 4.7 3.7 3.4 1.9 12.5 5.4 3.8 13 2.4 8.0 4.6 2.2 14 3.1 1.7 2.6 15 9.7 8.4 4.4 2 .I 16 5 .5 3.2 4 .4 2.5 On OTT again at 17 mo (SL) and 18 mo (PF) 17 9.0 5.8 5.3 2.9 18 6.4 4.6 2.7 19 6.8 4.9 20 7.4 6.2 5.0 3.0 21 2.6 4.6 5.9 2.8 22 3.6 4.0 5.3 3.2 23 1.3 6.2 3.3 24 (Died) 4.2 (Died) 3.6 25 3.6 3.4 26 3.
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