Cysteamine toxicity in patients with cystinosis

Cysteamine toxicity presenting with acute encephalopathy and spastic tetraparesis

Cystinosis is a lysosomal storage disorder usually presenting with renal disease in infancy. As soon as the diagnosis is made, cysteamine (a cystine-depleting medication), is started, significantly improving life expectancy. We describe a young woman taking lifelong cysteamine for nephropathic cystinosis, who became acutely encephalopathic with a spastic tetraparesis secondary to cysteamine toxicity, which was potentially worsened by copper deficiency. On replacing copper and reducing the dose of cysteamine, she made a full neurological recovery. We discuss the case, and review cystinosis and what is known about cysteamine toxicity.

Addressing the psychosocial aspects of transition to adult care in patients with cystinosis

Cystinosis is a rare autosomal-recessive lysosomal storage disease that progressively affects multiple organs beginning with the kidneys. Patients require lifelong multidisciplinary care for the management of kidney disease and progressive extra-renal manifestations, and thus, they are especially fragile and vulnerable during transition from pediatric to adult care. Previous documents have provided guidance to help the medical transition of these highly burdened patients. Patients and their families often experience great psychological distress and face significant social challenges; for these reasons, they often need help from psychologists, social workers, and other psychosocial professionals. Due to the rarity of the disease, most psychosocial professionals have no expertise in this disorder and require advice. To this end, a steering committee (SC) composed of six experts, including pediatric nephrologists, psychologists, and social workers with experience in the care for patients with cystinosis, have identified and addressed seven key questions related to psychosocial challenges of the disease and the burden of treatment. Ten additional international experts (the extended faculty, EF) were invited to answer these questions. Since robust evidence is lacking, as in many rare diseases, conclusions were based on collective agreement between members of the SC and the EF, and the consolidated answers were summarized into expert opinion statements. The present document contains information on the concerns and psychosocial burden of patients with cystinosis and of their caregivers, and provides practical advice for timely and appropriate support to facilitate the transition to adult care.

Cysteamine-mediated blockade of the glycine cleavage system modulates epithelial cell inflammatory and innate immune responses to viral infection

Transient blockade of glycine decarboxylase (GLDC) can restrict de novo pyrimidine synthesis, which is a well-described strategy for enhancing the host interferon response to viral infection and a target pathway for some licenced anti-inflammatory therapies. The aminothiol, cysteamine, is produced endogenously during the metabolism of coenzyme A, and is currently being investigated in a clinical trial as an intervention in community acquired pneumonia resulting from viral (influenza and SARS-CoV-2) and bacterial respiratory infection. Cysteamine is known to inhibit both bacterial and the eukaryotic host glycine cleavage systems via competitive inhibition of GLDC at concentrations, lower than those required for direct antimicrobial or antiviral activity. Here, we demonstrate for the first time that therapeutically achievable concentrations of cysteamine can inhibit glycine utilisation by epithelial cells and improve cell-mediated responses to infection with respiratory viruses, including human coronavirus 229E and Influenza A. Cysteamine reduces interleukin-6 (IL-6) and increases the interferon-λ (IFN-λ) response to viral challenge and in response to liposomal polyinosinic:polycytidylic acid (poly I:C) simulant of RNA viral infection.

Cysteamine hydrochloride affects ocular development and triggers associated inflammation in zebrafish

The increasing use of cosmetics has raised widespread concerns regarding their ingredients. Cysteamine hydrochloride (CSH) is a newly identified allergenic component in cosmetics, and therefore its potential toxicity needs further elucidation. Here, we investigated the in vivo toxicity of CSH during ocular development utilizing a zebrafish model. CSH exposure was linked to smaller eyes, increased vasculature of the fundus and decreased vessel diameter in zebrafish larvae. Moreover, CSH exposure accelerated the process of vascular sprouting and enhanced the proliferation of ocular vascular endothelial cells. Diminished behavior in response to visual stimuli and ocular structural damage in zebrafish larvae after CSH treatment were confirmed by analysis of the photo-visual motor response and pathological examination, respectively. Through transcriptional assays, transgenic fluorescence photography and molecular docking analysis, we determined that CSH inhibited Notch receptor transcription, leading to an aberrant proliferation of ocular vascular endothelial cells mediated by Vegf signaling activation. This process disrupted ocular homeostasis, and induced an inflammatory response with neutrophil accumulation, in addition to the generation of high levels of reactive oxygen species, which in turn promoted the occurrence of apoptotic cells in the eye and ultimately impaired ocular structure and visual function during zebrafish development.

Enteric-Coated Cysteamine Bitartrate in Cystinosis Patients

Cystinosis is a severe inherited metabolic storage disease caused by the lysosomal accumulation of cystine. Lifelong therapy with the drug cysteamine bitartrate is necessary. Cysteamine cleaves intralysosomal cystine, and thereafter, it can exit from the organelle. The need for frequent dosing every 6 h and the high prevalence of gastrointestinal side effects lead to poor therapy adherence. The purpose of our study was to improve cysteamine treatment by comparing the efficacy of two cysteamine formulas. This is highly relevant for the long-term outcome of cystinosis patients. The cystine and cysteamine levels of 17 patients taking immediate-release cysteamine (IR-cysteamine/Cystagon^®) and 6 patients taking encapsulated delayed-release cysteamine (EC-cysteamine) were analyzed. The EC-cysteamine levels showed a near-ideal pharmacokinetic profile indicative of delayed release (longer T_max and T_min), and the corresponding cystine levels showed few fluctuations. In addition, the C_max of IR-cysteamine was greater, which was responsible for unbearable side effects (e.g., nausea, vomiting, halitosis, lethargy). Treatment with EC-cysteamine improves the quality of life of cystinosis patients because the frequency of intake can be reduced to 2-3 times daily and it has a more favorable pharmacokinetic profile than IR-cysteamine. In particular, cystinosis patients with no access to the only approved delayed-release cysteamine Procysbi^® could benefit from a cost-effective alternative.

User-friendly and ultra-stable all-inclusive gold tablets for cysteamine detection

To date, a range of nanozymes has been reported for their enzyme-mimicking catalytic activity such as solution-based sensors. However, in remote areas, the need for portable, cost-effective, and one-pot prepared sensors is obvious. In this study, we report the development of a highly stable and sensitive gold tablet-based sensor for cysteamine quantification in human serum samples. The sensor is produced in two steps: synthesis of a pullulan-stabilized gold nanoparticle solution (pAuNP-Solution) using a pullulan polymer as a reducing, stabilizing, and encapsulating agent and then, casting the pAuNP-Solution into a pullulan gold nanoparticle tablet (pAuNP-Tablet) by a pipetting method. The tablet was characterized by UV-vis, DLS, FTIR, TEM, and AFM analyses. The pAuNP-tablet exhibited a high peroxidase-mimetic activity via a TMB-H₂O₂ system. The presence of cysteamine in the system introduced two types of inhibition which were dependent on the cysteamine concentration. By determining Michaelis-Menten's kinetic parameters, we gained mechanistic insights into the catalytic inhibition process. Based on the catalytic inhibition capability of cysteamine, the limit of detection (LoD) was calculated to be 69.04 and 82.9 μM in buffer and human serum samples, respectively. Finally, real human serum samples were tested, demonstrating the applicability of the pAuNP-Tablet for real-world applications. The % R values in human serum samples were in the range of 91-105% with % RSD less than 2% for all replicas. The stability tests over 16 months revealed the ultra-stable properties of the pAuNP-Tablet. Overall, with a simple fabrication method and a novel employed technique, this study contributes to the advancement of tablet-based sensors and helps in cysteamine detection in clinical settings.

Hepatic lipid metabolism disorders and immunotoxicity induced by cysteamine in early developmental stages of zebrafish

Cysteamine, a sulfhydryl compound, is an intermediate in the metabolism of coenzyme A to taurine in living organisms. However, the potential side effects of cysteamine such as hepatotoxicity in pediatric patients have been reported in some studies. To evaluate the impact of cysteamine on infants and children, larval zebrafish (a vertebrate model) were exposed to 0.18, 0.36 and 0.54mM cysteamine from 72 hpf to 144 hpf. Alterations in general and pathological evaluation, biochemical parameters, cell proliferation, lipid metabolism factors, inflammatory factors and Wnt signaling pathway levels were examined. Increased liver area and lipid accumulation were observed in liver morphology, staining and histopathology in a dose-dependent manner with cysteamine exposure. In addition, the experimental cysteamine group exhibited higher alanine aminotransferase, aspartate aminotransferase, total triglyceride and total cholesterol levels than the control group. Meanwhile, the levels of lipogenesis-related factors ascended whereas lipid transport-related factors descended. Oxidative stress indicators such as reactive oxygen species, MDA and SOD were upregulated after cysteamine exposure. Afterwards, transcription assays revealed that biotinidase and Wnt pathway-related genes were upregulated in the exposed group, and inhibition of Wnt signaling partially rescued the abnormal liver development. The current study found that cysteamine-induced hepatotoxicity in larval zebrafish is due to inflammation and abnormal lipid metabolism, which is mediated by biotinidase (a potential pantetheinase isoenzyme) and Wnt signaling. This provides a perspective on the safety of cysteamine administration in children and identifies potential targets for protection against adverse reactions.

Cystinosis

Cystinosis is a very rare autosomal recessive lysosomal storage disorder with an incidence of 1 : 150,000 - 1 : 200,000, and is caused by mutations in the CTNS gene encoding the lysosomal membrane protein cystinosin, which transports cystine out of the lysosome into the cytoplasm. As a result, accumulation of cystine occurs in almost all cells and tissues, especially in the kidneys, leading to multiple organ involvement. Introduction of drug therapy with cysteamine in the mid 1980s, along with the availability of renal replacement therapy in childhood, have dramatically improved patient outcome. Whereas patients used to die without therapy with end-stage renal failure during the first decade of life, nowadays most patients live well into adulthood without renal replacement therapy, and several reach 40 years. There is robust evidence that early initiation and sustained lifelong therapy with cysteamine are both essential for morbidity and mortality. The rarity of the disease and the multi-organ involvement present an enormous challenge for those affected and the providers of care for this patient group.

Cysteamine affects skeletal development and impairs motor behavior in zebrafish

Cysteamine is a kind of feed additive commonly used in agricultural production. It is also the only targeted agent for the treatment of cystinosis, and there are some side effects in clinical applications. However, the potential skeletal toxicity remains to be further elucidated. In this study, a zebrafish model was for the first time utilized to synthetically appraise the skeletal developmental defects induced by cysteamine. The embryos were treated with 0.35, 0.70, and 1.05 mM cysteamine from 6 h post fertilization (hpf) to 72 hpf. Substantial skeletal alterations were manifested as shortened body length, chondropenia, and abnormal somite development. The results of spontaneous tail coiling at 24 hpf and locomotion at 120 hpf revealed that cysteamine decreased behavioral abilities. Moreover, the level of oxidative stress in the skeleton ascended after cysteamine exposure. Transcriptional examination showed that cysteamine upregulated the expression of osteoclast-related genes but did not affect osteoblast-related genes expression. Additionally, cysteamine exposure caused the downregulation of the Notch signaling and activating of Notch signaling partially attenuated skeletal defects. Collectively, our study suggests that cysteamine leads to skeletal developmental defects and reduces locomotion activity. This hazard may be associated with cysteamine-mediated inhibition of the Notch signaling and disorganization of notochordal cells due to oxidative stress and apoptosis.

Evaluation of NACA and diNACA in human cystinosis fibroblast cell cultures as potential treatments for cystinosis

Background

Cystinosis is a rare autosomal recessive lysosomal storage disease, associated with high morbidity and mortality. Mutations in the CTNS gene disable a membrane protein responsible for the transport of cystine out of the lysosome. Loss of transporter function leads to intralysosomal cystine accumulation and long-term damage to various tissues and organs, including the kidneys, eyes, liver, muscles, pancreas, and brain. The only cystine-depletion therapy for treatment of cystinosis is cysteamine which requires frequent administration of high doses and often causes gastrointestinal pain as well as pungent sulfurous odor in patients. The current in vitro study evaluated antioxidants, N-acetylcysteine amide (NACA; NPI-001) and (2R,2R′)-3,3′-disulfanediyl bis(2-acetamidopropanamide) (diNACA; NPI-002), as potential treatments for cystinosis.

Methods

Cytotoxicity of cysteamine, NACA and diNACA was evaluated in cultured human cystinotic fibroblasts (HCFs). HCFs were cultured in 96 well plates incubated for 0–72 h in the presence of 25, 50 or 75 μM each of either cysteamine, NACA or diNACA along with an untreated control. Media was removed and cell viability assessed. Next, cystine-depleting activities of cysteamine, NACA and diNACA were screened in HCFs cell culture utilizing an inexpensive, proven colorimetric assay. HCFs were seeded and allowed to reach approximately 80% confluence before the addition of the test articles: 50 μM of either cysteamine, NACA or diNACA in media along with an untreated control. HCFs were incubated, harvested, and cystine was reduced to cysteine, the concentration of which was then determined per quantity of protein compared to a cysteine standard. Statistically significant cystine depletion was determined by paired t-test versus untreated control (p < 0.05).

Results

Neither cysteamine, NACA nor diNACA at 25, 50 or 75 μM caused cytotoxicity in HCFs. Treatment with all tested concentrations (25, 50 or 75 µM) of either NACA or diNACA at 48 or 72 h resulted in statistically significant increases in cell viability, relative to untreated control, whereas the higher concentrations (50 or 75 µM) of cysteamine achieved statistical significance at both timepoints but not the lowest concentration (25 µM). All test articles depleted cystine from HCFs compared to control. NACA depletion of cystine was statistically superior to cysteamine at 6, 24 and 48 h and numerically greater at 72 h. DiNACA depletion of cystine was statistically superior to cysteamine at 6 and 48 h, slightly numerically greater at 24 h and slightly less at 72 h.

Conclusions

NACA and diNACA were non cytotoxic to HCFs and significantly increased cell viability. Cystine reduction was determined as percent of control after incubation with 50 µM of NACA, diNACA or cysteamine in HCFs cell culture for 6, 24, 48 and 72 h. Of the three test articles, NACA exhibited most rapid and greatest potency in cystine reduction. Rank order potency for cystine reduction over time was observed, NACA > diNACA ≥ cysteamine. Therefore, further study of NACA and diNACA as potential treatments for cystinosis is warranted.

Expert guidance on the multidisciplinary management of cystinosis in adolescent and adult patients

Cystinosis, a rare autosomal recessive lysosomal storage disorder, results in an abnormal accumulation of the amino acid cystine in multiple organs and tissues of the body. Renal symptoms typically develop in the first few months of life, with extra-renal manifestations becoming apparent over the next 10–20 years, which require coordinated multidisciplinary care. Here, we describe a consensus-based guidance to support the management of adolescents and adults living with cystinosis. The programme was led by a Steering Committee (SC) of six experts in the management of patients with cystinosis, who identified a list of 15 key questions reflecting the multi-organ effects of cystinosis. An Extended Faculty (EF) of eight additional specialists was invited to answer the questions via an online digital platform using a quasi-Delphi approach. The consolidated answers were summarized into recommendations. Where evidence was lacking, recommendations were developed using collective expert consensus. The EF was asked to agree/disagree with the clinical recommendations. The expert-agreed clinical recommendations provide guidance that considers both renal and extra-renal systems. The topics covered are advice on fertility and family planning, consideration of the nervous, muscular, ophthalmic, cardio-respiratory, endocrine, dermatological and gastrointestinal systems, as well as guidance on dental care, diet, lifestyle, and improving quality of life and psychological well-being. In summary, this work outlines recommendations and a checklist for clinicians with a vision for improving and standardizing the multidisciplinary care for patients with cystinosis.

Muscle and Bone Impairment in Infantile Nephropathic Cystinosis: New Concepts

Cystinosis Metabolic Bone Disease (CMBD) has emerged during the last decade as a well-recognized, long-term complication in patients suffering from infantile nephropathic cystinosis (INC), resulting in significant morbidity and impaired quality of life in teenagers and adults with INC. Its underlying pathophysiology is complex and multifactorial, associating complementary, albeit distinct entities, in addition to ordinary mineral and bone disorders observed in other types of chronic kidney disease. Amongst these long-term consequences are renal Fanconi syndrome, hypophosphatemic rickets, malnutrition, hormonal abnormalities, muscular impairment, and intrinsic cellular bone defects in bone cells, due to CTNS mutations. Recent research data in the field have demonstrated abnormal mineral regulation, intrinsic bone defects, cysteamine toxicity, muscle wasting and, likely interleukin-1-driven inflammation in the setting of CMBD. Here we summarize these new pathophysiological deregulations and discuss the crucial interplay between bone and muscle in INC. In future, vitamin D and/or biotherapies targeting the IL1β pathway may improve muscle wasting and subsequently CMBD, but this remains to be proven.

Drug Repurposing in Rare Diseases: An Integrative Study of Drug Screening and Transcriptomic Analysis in Nephropathic Cystinosis

Diagnosis and cure for rare diseases represent a great challenge for the scientific community who often comes up against the complexity and heterogeneity of clinical picture associated to a high cost and time-consuming drug development processes. Here we show a drug repurposing strategy applied to nephropathic cystinosis, a rare inherited disorder belonging to the lysosomal storage diseases. This approach consists in combining mechanism-based and cell-based screenings, coupled with an affordable computational analysis, which could result very useful to predict therapeutic responses at both molecular and system levels. Then, we identified potential drugs and metabolic pathways relevant for the pathophysiology of nephropathic cystinosis by comparing gene-expression signature of drugs that share common mechanisms of action or that involve similar pathways with the disease gene-expression signature achieved with RNA-seq.

What role for cysteamine in the defence against infection?

The aminothiol cysteamine has many potential therapeutic applications and is also an endogenous molecule, produced in the body via the activity of pantetheinase enzymes such as vanin-1. This simple small molecule is highly reactive in biological settings and much is yet unknown about its endogenous role in innate immunity to infection, including the impact of cysteamine on bacterial pathogens. We discuss the literature surrounding its biochemistry and challenges to its development as well as the multiple beneficial properties which have been uncovered that support research into its development as novel antimicrobial therapy.

A novel sustained-release cysteamine bitartrate formulation for the treatment of cystinosis: Pharmacokinetics and safety in healthy male volunteers

The strict intake regimen of cysteamine bitartrate formulations, associated with side effects, is a concern for the treatment compliance in cystinosis therapy. Therefore, there is a need for a cysteamine formulation with an improved pharmacokinetic profile. This study investigated the pharmacokinetics, safety and tolerability of a new sustained‐release cysteamine dosage form, PO‐001, in healthy volunteers. This was a randomized, investigator‐blinded, three‐way cross‐over study to compare single doses (600 mg) of PO‐001 with Cystagon^® (immediate‐release) and Procysbi^® (delayed‐release). Collected blood samples were analyzed for plasma cysteamine concentrations and pharmacokinetic parameters were estimated by noncompartmental analysis. In addition, plasma cysteamine concentrations were analyzed using a population pharmacokinetic approach using NONMEM^®. Pharmacokinetics showed clear sustained‐release characteristics of PO‐001 over time with a lower C_max and longer T_max compared to Cystagon^® and Procysbi^®. All treatment‐emergent adverse events were of mild severity, with the exception of two subjects who reported moderate severity gastrointestinal problems including vomiting and diarrhea, which were related to Cystagon^® intake. Population PK simulations showed a favourable PK profile based on C_max and C_trough concentrations at steady state. In conclusion, a single dose of 600 mg PO‐001 was well tolerated with no findings of clinical concern. This new cysteamine bitartrate formulation showed pharmacokinetics of a sustained‐release formulation, which may be beneficial for the treatment of cystinosis patients. This study supports advancing this type of sustained‐release formulation into a subsequent study to confirm reduced dosing frequency with efficient control of white blood cells (WBCs) cystine levels. Netherlands Trial Registry (NTR) (NL67638.056.18).

Adult complications of nephropathic cystinosis: a systematic review

While nephropathic cystinosis is classically thought of as a childhood disease, with improved treatments, patients are more commonly living into adulthood. We performed a systematic review of the literature available on what complications this population faces as it ages. Nearly every organ system is affected in cystinosis, either from the disease itself or from sequelae of kidney transplantation. While cysteamine is known to delay the onset of end-stage kidney disease, its effects on other complications of cystinosis are less well determined. More common adult-onset complications include myopathy, diabetes, and hypothyroidism. Some less common complications, such as neurologic dysfunction, can still have a profound impact on those with cystinosis. Areas for further research in this area include additional study of the impact of cysteamine on the nonrenal manifestations of cystinosis, as well as possible avenues for new and novel treatments.

Bone Disease in Nephropathic Cystinosis: Beyond Renal Osteodystrophy

Patients with chronic kidney disease (CKD) display significant mineral and bone disorders (CKD-MBD) that induce significant cardiovascular, growth and bone comorbidities. Nephropathic cystinosis is an inherited metabolic disorder caused by the lysosomal accumulation of cystine due to mutations in the CTNS gene encoding cystinosin, and leads to end-stage renal disease within the second decade. The cornerstone of management relies on cysteamine therapy to decrease lysosomal cystine accumulation in target organs. However, despite cysteamine therapy, patients display severe bone symptoms, and the concept of “cystinosis metabolic bone disease” is currently emerging. Even though its exact pathophysiology remains unclear, at least five distinct but complementary entities can explain bone impairment in addition to CKD-MBD: long-term consequences of renal Fanconi syndrome, malnutrition and copper deficiency, hormonal disturbances, myopathy, and intrinsic/iatrogenic bone defects. Direct effects of both CTNS mutation and cysteamine on osteoblasts and osteoclasts are described. Thus, the main objective of this manuscript is not only to provide a clinical update on bone disease in cystinosis, but also to summarize the current experimental evidence demonstrating a functional impairment of bone cells in this disease and to discuss new working hypotheses that deserve future research in the field.

Effects of long-term cysteamine treatment in patients with cystinosis

Cystinosis is a rare autosomal-recessive lysosomal storage disease with high morbidity and mortality. It is caused by mutations in the CTNS gene that encodes the cystine transporter, cystinosin, which leads to lysosomal cystine accumulation. Patients with infantile nephropathic cystinosis, the most common and most severe clinical form of cystinosis, commonly present with renal Fanconi syndrome by 6-12 months of age, and without specific treatment, almost all will develop end-stage renal disease (ESRD) by 10-12 years of age. Early corneal cystine crystal deposition is a hallmark of the disease. Cystinosis also presents with gastrointestinal symptoms (e.g., vomiting, decreased appetite, and feeding difficulties) and severe growth retardation and may affect several other organs over time, including the eye, thyroid gland, gonads, pancreas, muscles, bone marrow, liver, nervous system, lungs, and bones. Cystine-depleting therapy with cysteamine orally is the only specific targeted therapy available for managing cystinosis and needs to be combined with cysteamine eye drops for corneal disease involvement. In patients with early treatment initiation and good compliance to therapy, long-term cysteamine treatment delays progression to ESRD, significantly improves growth, decreases the frequency and severity of extrarenal complications, and is associated with extended life expectancy. Therefore, early diagnosis of cystinosis and adequate life-long treatment with cysteamine are essential for preventing end-organ damage and improving the overall prognosis in these patients.

Multidisciplinary approach for patients with nephropathic cystinosis: model for care in a rare and chronic renal disease

Care for patients with chronic and rare diseases is complex, especially considering the lack of knowledge about the disease, which makes early and precise diagnosis difficult, as well as the need for specific tests, sometimes of high complexity and cost. Added to these factors are difficulties in obtaining adequate treatment when available, in raising patient and family awareness about the disease and treatment compliance. Nephropathic cystinosis is among these diseases. After more than 20 years as a care center for these patients, the authors propose a follow-up protocol, which has been used with improvement in the quality of care and consists of a multidisciplinary approach, including care provided by a physician, nurse, psychologist, nutritionist and social worker. In this paper, each field objectively exposes how to address points that involve the stages of diagnosis and its communication with the patient and their relatives or guardians, covering the particularities of the disease and the treatment, the impact on the lives of patients and families, the approach to psychological and social issues and guidelines on medications and diets. This protocol could be adapted to the follow-up of patients with other rare diseases, including those with renal involvement. This proposal is expected to reach the largest number of professionals involved in the follow-up of these patients, strengthening the bases for the creation of a national protocol, observing the particularities of each case.

Allogeneic HSCT transfers wild-type cystinosin to nonhematological epithelial cells in cystinosis: First human report

Cystinosis is an autosomal recessive lysosomal storage disorder characterized by the defective transport of the amino acid cystine out of the lysosome due to a deficiency of cystinosin, the lysosomal cystine transporter. Patients have lysosomal cystine accumulation in various tissues, leading to cellular stress and damage, particularly in the kidney, cornea, and other extrarenal tissues. Cysteamine, a cystine-depleting agent, improves survival and delays the progression of disease, but it does not prevent the development of either renal failure or extrarenal complications. Furthermore, the drug has severe adverse effects that significantly reduce patient compliance. Allogeneic hematopoietic stem cell transplantation (HSCT) is currently established as a therapeutic option for many inborn errors of metabolism, where the main pathologic driving factor is an enzyme deficiency. Recent studies in the cystinosis mouse-model suggested that HSCT could be a curative treatment alternative to cysteamine therapy. We treated a 16-year-old boy who had infantile cystinosis and side effects of cysteamine therapy with HSCT. We were able to demonstrate successful transfer of the wild-type cystinosin protein and CTNS mRNA to nonhematological epithelial cells in the recipient, as well as a decrease in the tissue cystine-crystal burden. This is the first report of allogeneic HSCT in a patient with cystinosis, the prototype of lysosomal membrane-transporter disorders.

Bone disease in nephropathic cystinosis is related to cystinosin-induced osteoclastic dysfunction

Background

Bone impairment is a poorly described complication of nephropathic cystinosis (NC). The objectives of this study were to evaluate in vitro effects of cystinosin (CTNS) mutations on bone resorption and of cysteamine treatment on bone cells [namely human osteoclasts (OCs) and murine osteoblasts].

Methods

Human OCs were differentiated from peripheral blood mononuclear cells (PBMCs) of patients and healthy donors (HDs). Cells were treated with increasing doses of cysteamine in PBMCs or on mature OCs to evaluate its impact on differentiation and resorption, respectively. Similarly, cysteamine-treated osteoblasts derived from murine mesenchymal stem cells were assessed for differentiation and activity with toxicity and proliferation assays.

Results

CTNS was expressed in human OCs derived from HDs; its expression was regulated during monocyte colony-stimulating factor- and receptor activator of nuclear factor-κB-dependent osteoclastogenesis and required for efficient bone resorption. Cysteamine had no impact on osteoclastogenesis but inhibited in vitro HD osteoclastic resorption; however, NC OC-mediated bone resorption was impaired only at high doses. Only low concentrations of cysteamine (50 μM) stimulated osteoblastic differentiation and maturation, while this effect was no longer observed at higher concentrations (200 µM).

Conclusion

CTNS is required for proper osteoclastic activity. In vitro low doses of cysteamine have beneficial antiresorptive effects on healthy human-derived OCs and may partly correct the CTNS-induced osteoclastic dysfunction in patients with NC. Moreover, in vitro low doses of cysteamine also stimulate osteoblastic differentiation and mineralization, with an inhibitory effect at higher doses, likely explaining, at least partly, the bone toxicity observed in patients receiving high doses of cysteamine.

Teenagers and young adults with nephropathic cystinosis display significant bone disease and cortical impairment

BACKGROUND

Bone impairment appears to be a novel complication of nephropathic cystinosis despite cysteamine therapy. Its exact underlying pathophysiology is nevertheless unclear. The objective of this study was to evaluate bone status among patients included in the French Crystobs study.

METHODS

In addition to clinical data, bone status was evaluated using biomarkers (ALP, PTH, 25-D, 1-25D, FGF23), DXA (spine and total body), and high-resolution peripheral quantitative computed tomography (HR-pQCT) at the tibia and radius. Results were compared to age- and gender-matched healthy controls (1:2 basis) from the local reference cohorts.

RESULTS

At a median age of 22.5 (10.2-34.6) years, 10 patients with nephropathic cystinosis were included (2 receiving conservative therapies, 2 undergoing hemodialysis, 6 with a past of renal transplantation); 7 out of 10 patients complained of a bone symptom (past of fracture, bone deformations, and/or bone pain). Biochemicals and spine DXA did not show any significant abnormalities. Using HR-pQCT, significant decreases in cortical parameters (e.g., cortical thickness 850 (520-1100) versus 1225 (480-1680) μm; p < 0.05) and total volumetric bone mineral density (290 (233-360) versus 323 (232-406) mg/cm³; p < 0.05) were observed in cystinotic patients in comparison to controls at the tibia. There were no differences for trabecular parameters. Similar results were observed at the radius.

CONCLUSIONS

In this pilot study, bone impairment (rather cortical than trabecular) is a significant clinical problem in nephropathic cystinosis; 70% of patients displayed significant bone symptoms, during teenage or young adulthood. This new complication should be known by physicians because of its potential dramatic impact on quality of life.

Cysteamine, an Endogenous Aminothiol, and Cystamine, the Disulfide Product of Oxidation, Increase Pseudomonas aeruginosa Sensitivity to Reactive Oxygen and Nitrogen Species and Potentiate Therapeutic Antibiotics against Bacterial Infection

Cysteamine is an endogenous aminothiol produced in mammalian cells as a consequence of coenzyme A metabolism through the activity of the vanin family of pantetheinase ectoenzymes. It is known to have a biological role in oxidative stress, inflammation, and cell migration. There have been several reports demonstrating anti-infective properties targeting viruses, bacteria, and even the malarial parasite. We and others have previously described broad-spectrum antimicrobial and antibiofilm activities of cysteamine. Here, we go further to demonstrate redox-dependent mechanisms of action for the compound and how its antimicrobial effects are, at least in part, due to undermining bacterial defenses against oxidative and nitrosative challenges. We demonstrate the therapeutic potentiation of antibiotic therapy against Pseudomonas aeruginosa in mouse models of infection. We also demonstrate potentiation of many different classes of antibiotics against a selection of priority antibiotic-resistant pathogens, including colistin (often considered an antibiotic of last resort), and we discuss how this endogenous antimicrobial component of innate immunity has a role in infectious disease that is beginning to be explored and is not yet fully understood.

Nephropathic Cystinosis: Symptoms, Treatment, and Perspectives of a Systemic Disease

Cystinosis is a rare autosomal recessive lysosomal storage disorder caused by mutations in the CTNS gene. Main dysfunction is a defective clearance of cystine from lysosomes that leads to accumulation of cystine crystals in every tissue of the body. There are three different forms: infantile nephropathic cystinosis, which is the most common form, juvenile nephropatic, and non-nephropathic cystinosis. Mostly, first symptom in infantile nephropathic cystinosis is renal Fanconi syndrome that occurs within the first year of life. Another prominent symptom is photophobia due to corneal crystal deposition. Cystine depletion therapy with cysteamine delays end-stage renal failure but does not stop progression of the disease. A new cysteamine formulation with delayed-release simplifies the administration schedule but still does not cure cystinosis. Even long-term depletion treatment resulting in bypassing the defective lysosomal transporter cannot reverse Fanconi syndrome. A future perspective offering a curative therapy may be transplantation of CTNS-carrying stem cells that has successfully been performed in mice.

A systematic literature review of cysteamine bitartrate in the treatment of nephropathic cystinosis

OBJECTIVES

To summarize available clinical evidence for cysteamine bitartrate preparations in the treatment of nephropathic cystinosis as identified through a systematic literature review (SLR).

METHODS

We searched MEDLINE, MEDLINE In-Process and Embase using Ovid with a predefined search strategy through 19 January 2016. All publicly available clinical reports on the use of delayed-release (DR) cysteamine bitartrate (Procysbi ¹ ) or immediate-release (IR) cysteamine bitartrate (Cystagon ² ) in patients with cystinosis were included.

RESULTS

We identified a total of 103 publications and 10 trial records. Of these, 9 studies describe DR cysteamine bitartrate (n = 267 patients), 42 describe IR cysteamine bitartrate (n = 1,427 patients) and in 53 studies the exact preparation was not specified (n = 906 patients). The vast majority of the studies used a non-randomized study design, with randomized clinical trials (RCTs) being scarce (1 study comparing DR and IR formulation) and case reports (n = 49) being the most common study design representing 47% of the total.

CONCLUSION

A substantial evidence base for cysteamine bitartrate in the treatment of nephropathic cystinosis was identified. However, the majority of the evidence was of relatively low quality, with evidence levels of 3 or 4.

Cysteamine revisited: repair of arginine to cysteine mutations

Cysteamine is a small aminothiol endogenously derived from coenzyme A degradation. For some decades, synthetic cysteamine has been employed for the treatment of cystinosis, and new uses of the drug continue to emerge. In this review, we discuss the role of cysteamine in cellular and extracellular homeostasis and focus on the potential use of aminothiols to reconstitute the function of proteins harboring arginine (Arg) to cysteine (Cys) mutations, via repair of the Cys residue into a moiety that introduces an amino group, as seen in basic amino acid residues Lys and Arg. Cysteamine has been utilized in vitro and ex vivo in four different genetic disorders, and thus provides "proof of principle" that aminothiols can modify Cys residues. Other aminothiols such as mercaptoethylguanidine (MEG) with closer structural resemblance to the guanidinium moiety of Arg are under examination for their predicted enhanced capacity to reconstitute loss of function. Although the use of aminothiols holds clinical potential, more studies are required to refine specificity and treatment design. The efficacy of aminothiols to target proteins may vary substantially depending on their specific extracellular and intracellular locations. Redox potential, pH, and specific aminothiol abundance in each physiological compartment are expected to influence the reactivity and turnover of cysteamine and analogous drugs. Upcoming research will require the use of suitable cell and animal models featuring Arg to Cys mutations. Since, in general, Arg to Cys changes comprise about 8% of missense mutations, repair of this specific mutation may provide promising avenues for many genetic diseases.

Nephropathic cystinosis: an update

PURPOSE OF REVIEW

Over the past few decades, cystinosis, a rare lysosomal storage disorder, has evolved into a treatable metabolic disease. The increasing understanding of its pathophysiology has made cystinosis a prototype disease, delivering new insights into several fundamental biochemical and cellular processes.

RECENT FINDINGS

In this review, we aim to provide an overview of the latest advances in the pathogenetic, clinical, and therapeutic aspects of cystinosis.

SUMMARY

The development of alternative therapeutic monitoring strategies and new systemic and ocular cysteamine formulations might improve outcome of cystinosis patients in the near future. With the dawn of stem cell based therapy and new emerging gene-editing technologies, novel tools have become available in the search for a cure for cystinosis.

Inhibition of peripubertal sheep mammary gland development by cysteamine through reducing progesterone and growth factor production

Cysteamine has been used for treating cystinosis for many years, and furthermore it has also been used as a therapeutic agent for different diseases including Huntington's disease, Parkinson's disease (PD), nonalcoholic fatty liver disease, malaria, cancer, and others. Although cysteamine has many potential applications, its use may also be problematic. The effects of low doses of cysteamine on the reproductive system, especially the mammary glands are currently unknown. In the current investigation, low dose (10 mg/kg BW/day) of cysteamine did not affect sheep body weight gain or organ index of the liver, spleen, or heart; it did, however, increase the levels of blood lymphocytes, monocytes, and platelets. Most interestingly, it inhibited mammary gland development after 2 or 5 months of treatment by reducing the organ index and the number of mammary gland ducts. Plasma growth hormone and estradiol remained unchanged; however, plasma progesterone levels and the protein level of HSD3β1 in sheep ovaries were decreased by cysteamine. In addition to steroid hormones, growth factors produced in the mammary glands also play crucial roles in mammary gland development. Results showed that protein levels of HGF, GHR, and IGF1R were decreased after 5 months of cysteamine treatment. These findings together suggest that progesterone and local growth factors in mammary glands might be involved in cysteamine initiated inhibition of pubertal ovine mammary gland development. Furthermore, it may lead to a reduction in fertility. Therefore, cysteamine should be used with great caution until its actions have been further investigated and its limitations overcome.

Endocrine complications during and after adolescence in a patient with cystinosis

Cystinosis is a rare disease characterized by abnormal lysosomal cystine accumulation of cystine due to impaired lysosomal transport. We previously reported the first case of cystinosis in Korea in a 12-year-old boy with short stature, general weakness, and photophobia. The diagnosis was confirmed based on ophthalmic findings and biochemical analyses (serum leukocyte cystine measurement). Major endocrine manifestations at diagnosis included hypothyroidism, growth retardation, and hypogonadism. Despite oral cysteamine administration and renal replacement therapy, multiple complications including both endocrine and nonendocrine disorders developed during and after adolescence. In this report, we review the presenting features and factors related to the long-term complications in a patient with cystinosis.

Skeletal implications and management of cystinosis: three case reports and literature review

Hypophosphatemic rickets and short stature are observed in nephropathic cystinosis, an orphan autosomal recessive lysosomal storage disease due to a deficiency of cystinosin (CTNS gene). Although bone impairment is not common, it nevertheless appears to be more and more discussed by experts, even though the exact underlying pathophysiology is unclear. Four hypotheses are currently discussed to explain such impairment: copper deficiency, bone consequences of severe hypophosphatemic rickets during infancy, cysteamine toxicity and abnormal thyroid metabolism. In murine models, the invalidation of the CTNS gene is associated neither with renal phosphate wasting nor with renal failure, but causes severe osteopenia and growth retardation, thus raising the hypothesis of a specific underlying bone defect in cystinosis. Moreover, the in vitro ability of mesenchymal stromal cells isolated from bone marrow to differentiate along the osteoblastic lineage is reduced in patients with cystinosis as compared with cells obtained from healthy controls, this cellular abnormality being reverted after cysteamine treatment. From our experience of three pediatric patients with cystinosis and severe bone deformations having undergone a thorough biochemical evaluation, as well as a bone biopsy, we conclude that even though copper deficiency, high-doses cysteamine regimens and abnormal thyroid metabolism may worsen the bone picture in cystinosis patients, the exact pathophysiology of such impairment remains to be defined. The role of chronic hypoparathyroidism due to chronic phosphate wasting could also be discussed. In the future, larger and prospective studies should focus on this topic because of the potential major impact on patients' quality of life.

Cystinosis: a review

Cystinosis is the most common hereditary cause of renal Fanconi syndrome in children. It is an autosomal recessive lysosomal storage disorder caused by mutations in the CTNS gene encoding for the carrier protein cystinosin, transporting cystine out of the lysosomal compartment. Defective cystinosin function leads to intra-lysosomal cystine accumulation in all body cells and organs. The kidneys are initially affected during the first year of life through proximal tubular damage followed by progressive glomerular damage and end stage renal failure during mid-childhood if not treated. Other affected organs include eyes, thyroid, pancreas, gonads, muscles and CNS. Leucocyte cystine assay is the cornerstone for both diagnosis and therapeutic monitoring of the disease. Several lines of treatment are available for cystinosis including the cystine depleting agent cysteamine, renal replacement therapy, hormonal therapy and others; however, no curative treatment is yet available. In the current review we will discuss the most important clinical features of the disease, advantages and disadvantages of the current diagnostic and therapeutic options and the main topics of future research in cystinosis.

Management dilemmas in pediatric nephrology: Cystinosis

BACKGROUND

Cystinosis is a rare, inherited autosomal recessive disease caused by the accumulation of free cystine in lysosomes. It is treated by the administration of cysteamine, which should be monitored by trough white blood cell (WBC) cystine measurements to ensure effective treatment.

CASE-DIAGNOSIS/TREATMENT

The index case had an older brother who had previously been diagnosed with cystinosis, allowing early diagnosis of the index case at the age of 5 months. Cysteamine therapy was started at the age of 3 years; however, monitoring of WBC cystine levels did not occur on a regular basis during most of his life. Growth retardation improved after correction of electrolyte disturbances, the initiation of cysteamine therapy and treatment with recombinant human growth hormone. Renal replacement therapy was started at the age of 11 years, and renal transplantation was performed at the age of 12 years. Extra-renal cystine accumulation caused multiple endocrinopathies (including adrenal insufficiency, hypothyroidism and primary hypogonadism), neurological symptoms, pancytopenia owing to splenomegaly and portal hypertension due to nodular regenerative hyperplasia, aggravated by splenic vein thrombosis and partial portal vein thrombosis. The patient died of diffuse intra-abdominal bleeding caused by severe portal hypertension.

CONCLUSION

Cysteamine treatment should be started as early as possible, and dosage should be monitored and adapted based on trough WBC cystine levels.

RELEVANT INTERNATIONAL GUIDELINE

Emma F et al. (2014) Nephropathic cystinosis: an international consensus document. Nephrol Dial Transplant 29:iv87-iv94.

Lupus in a patient with cystinosis: is it drug induced?

A 9-year-old girl with a diagnosis of cystinosis since 2 years of age, on cysteamine therapy, presented with complaints of serositis and arthritis, and laboratory tests revealed high antinuclear antibody titers with hypocomplementemia. Kidney biopsy was not consistent with lupus nephritis. With prednisolone treatment her complaints resolved and creatinine level decreased, but on follow-up, serological features of systemic lupus erythematosus (SLE) continued. Six years after cessation of prednisolone, lupus features were reactivated, with positive antihistone antibodies and ANCA. Coincidence of cystinosis and SLE is very rare, and to the best of our knowledge this is the fourth case reported in the literature. Physicians should be aware that cystinosis patients may have some autoimmune manifestations with features of true or drug-induced lupus. In the light of this case, pathophysiology and treatment are discussed.

Cystinosis in adult and adolescent patients: Recommendations for the comprehensive care of cystinosis

INTRODUCTION

Cystinosis is a rare lysosomal systemic disease that mainly affects the kidney and the eye. Patients with cystinosis begin renal replacement therapy during the first decade of life in absence of treatment. Prognosis of cystinosis depends on early diagnosis, and prompt starting and good compliance with cysteamine treatment. Kidney disease progression, extra-renal complications and shorter life expectancy are more pronounced in those patients that do not follow treatment. The objective of this work was to elaborate recommendations for the comprehensive care of cystinosis and the facilitation of patient transition from paediatric to adult treatment, based on clinical experience. The goal is to reduce the impact of the disease, and to improve patient quality of life and prognosis.

METHODS

Bibliographic research and consensus meetings among a multidisciplinary professional team of experts in the clinical practice, with cystinotic patients (T-CiS.bcn group) from 5 hospitals located in Barcelona.

RESULTS

This document gathers specific recommendations for diagnosis, treatment and multidisciplinary follow-up of cystinotic patients in the following areas: nephrology, dialysis,renal transplant, ophthalmology, endocrinology, neurology, laboratory, genetic counselling,nursing and pharmacy.

CONCLUSIONS

A reference document for the comprehensive care of cystinosis represents a support tool for health professionals who take care of these patients. It is based on the following main pillars: (a) a multi-disciplinary approach, (b) appropriate disease monitoring and control of intracellular cystine levels in leukocytes, (c) the importance of adherence to treatment with cysteamine, and (d) the promotion of patient self-care by means of disease education programmes. All these recommendations will lead us, in a second phase, to create a coordinated transition model between paediatric and adult care services which will contemplate the specific needs of cystinosis.

Nephropathic cystinosis: an international consensus document

Cystinosis is caused by mutations in the CTNS gene (17p13.2), which encodes for a lysosomal cystine/proton symporter termed cystinosin. It is the most common cause of inherited renal Fanconi syndrome in young children. Because of its rarity, the diagnosis and specific treatment of cystinosis are frequently delayed, which has a significant impact on the overall prognosis. In this document, we have summarized expert opinions on several aspects of the disease to improve knowledge and provide guidance for diagnosis and treatment.

Improving the prognosis of nephropathic cystinosis

Cystinosis is an autosomal recessive inherited lysosomal storage disease. It is characterized by generalized proximal tubular dysfunction known as renal Fanconi syndrome and causes end-stage renal disease by the age of about 10 years if left untreated. Extrarenal organs are also affected, including the thyroid gland, gonads, pancreas, liver, muscle, and brain. Treatment consists of administration of cysteamine, resulting in depletion of cystine that is trapped inside the lysosomes. Since cysteamine has a short half-life, it should be administered every 6 hours. Recently, a new delayed-release formulation was marketed, that should be administered every 12 hours. The first studies comparing both cysteamine formulations show comparable results regarding white blood cell cystine depletion (which serves as a measure for cystine accumulation in the body), while a slightly lower daily dose of cysteamine can be used.

Increased human dermal microvascular endothelial cell survival induced by cysteamine

BACKGROUND

Cystinosis is an autosomal recessive disease caused by intralysosomal cystine accumulation, treated with cysteamine. Recently, new adverse effects of cysteamine were reported. Skin biopsies showed microvascular proliferation (angioendotheliomatosis). To examine the mechanism of angioendotheliomatosis associated with cysteamine toxicity, we examined the effect of cysteamine on human dermal microvascular endothelial cells (HDMVEC).

METHODS

After cysteamine exposure (range 0-3.0 mM) during 24 h, cell viability was measured using water soluble tetrazolium salt-1 (WST-1) in both control HDMVEC and fibroblasts. Cell proliferation and apoptosis rate were measured in HDMVEC by bromodeoxyuridine (BrdU) incorporation and caspase 3 and caspase 7 activity, respectively. Intracellular glutathione (GSH) was measured in HDMVEC after cysteamine exposure of 0, 0.1 or 1.0 mM. Medium and cysteamine were refreshed every 6 h to mimic the in vivo situation. Next, cell viability in HDMVEC was measured after 24 h of GSH exposure (range 0-10.0 mM).

RESULTS

HDMVEC viability and proliferation increased after cysteamine exposure 0.03-3.0 mM (p < 0.01) and 0.03-1.0 mM (p = 0.01) respectively; cell viability in fibroblasts was not affected by incubation with cysteamine. Apoptosis remained unaffected by incubation with 0-1.0 mM cysteamine, 3.0 mM caused increased apoptosis. Intracellular GSH was significantly increased after incubation with cysteamine 0.1 mM (p = 0.02) and 1.0 mM (p < 0.01). HDMVEC viability increased after exposure to GSH 1.0-5.0 mM (p < 0.01).

CONCLUSION

Cysteamine concentrations, similar to those described in plasma of cystinosis patients, stimulate HDMVEC viability and proliferation and increase intracellular GSH content. We postulate that this mechanism might underlie angioendotheliomatosis induced by cysteamine.

Progressive destructive bone changes in patients with cystinosis

Nephropathic cystinosis is an autosomal recessive lysosomal storage disorder in which intracellular cystine accumulates. It is caused by mutations in the CTNS gene. Clinical manifestations include renal tubular Fanconi syndrome in the first year of life, rickets, hypokalaemia, polyuria, dehydration and acidosis, growth retardation, hypothyroidism, photophobia and renal glomerular deterioration. Late complications include myopathy, pancreatic insufficiency and retinal blindness. Skeletal manifestations described in these patients include failure to thrive, osteomalacia, rickets and short stature. This paper describes progressive bony abnormalities in three unrelated patients with nephropathic cystinosis that have not been reported previously.

Copper deficiency in patients with cystinosis with cysteamine toxicity

OBJECTIVES

To assess whether copper deficiency plays a role in the recently described cysteamine toxicity in patients with cystinosis, and to examine whether polymorphisms in copper transporters, lysyl oxidase, and/or type I procollagen genes could be responsible for the occurrence of cysteamine toxicity in a small subset of patients with cystinosis.

STUDY DESIGN

Thirty-six patients with cystinosis were included: 22 with Fanconi syndrome (including 7 with cysteamine toxicity), 12 after renal transplantation, 1 receiving hemodialysis, and 1 with ocular cystinosis. Serum copper and ceruloplasmin levels and urinary copper/creatinine ratio were measured. Genes ATP7A and CTR1 (encoding copper transporters), LOX (encoding lysyl oxidase), and COL1A1 and COL1A2 (encoding type I procollagen) were analyzed in patients with (n = 6) and without (n = 5) toxicity. Fibroblast (pro)collagen synthesis was compared in patients with (n = 3) and those without (n = 2) cysteamine toxicity.

RESULTS

All 22 patients with Fanconi syndrome had increased urinary copper excretion. Serum copper and ceruloplasmin levels were decreased in 9 patients, including all 7 patients with cysteamine toxicity. No specific sequence variations were associated with toxicity. All fibroblasts exhibited normal (pro)collagen synthesis.

CONCLUSION

Patients with cystinosis with cysteamine toxicity demonstrate copper deficiency. This can cause decreased activity of lysyl oxidase, the enzyme that generates the aldehydes required for collagen cross-linking. Thus, copper supplementation might prevent cysteamine toxicity.

Cysteamine: an old drug with new potential

Cysteamine is an amino thiol with the chemical formula HSCH2CH2NH2. Endogenously, cysteamine is derived from coenzyme A degradation, although its plasma concentrations are low. Most experience with cysteamine as a drug originates from the field of the orphan disease cystinosis, in which cysteamine is prescribed to decrease intralysosomal cystine accumulation. However, over the years, the drug has been used for several other applications both in vitro and in vivo. In this article, we review the different applications of cysteamine, ending with an overview of ongoing clinical trials for new indications, such as neurodegenerative disorders and nonalcoholic fatty liver disease (NAFLD). The recent development of an enteric-coated cysteamine formulation makes cysteamine more patient friendly and will extend its applicability for both old and new indications.

A randomized controlled crossover trial with delayed-release cysteamine bitartrate in nephropathic cystinosis: effectiveness on white blood cell cystine levels and comparison of safety

BACKGROUND AND OBJECTIVES

Immediate-release cysteamine bitartrate (Cystagon; Mylan Pharmaceuticals, Canonsburg, PA) may prevent or delay kidney transplantation and other serious outcomes in patients with cystinosis, but has never been subjected to a prospective clinical trial. Cystagon efficacy requires strict lifelong dosing every 6 hours. Such a dosing schedule and Cystagon-associated side effects are often cited by patients as reasons for nonadherence.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This open-label, randomized, controlled, crossover trial was powered to show that a new delayed-release formulation of cysteamine bitartrate, RP103, taken every 12 hours, was noninferior to Cystagon for maintenance of white blood cell (WBC) cystine at levels associated with optimal outcomes in the disease.

RESULTS

Forty-three patients were randomized. Using a mixed-effects statistical analysis model, the least-squares mean peak value of WBC cystine level was 0.62±0.05 nmol 1/2 cystine/mg protein after 12 hours under RP103 and 0.54±0.05 nmol 1/2 cystine/mg protein after 6 hours under Cystagon, a difference of 0.08±0.04 nmol 1/2 cystine/mg protein (95.8% confidence interval, 0-0.16). The average steady-state total daily dose of RP103 was 82% of the incoming steady-state total daily dose of Cystagon. There were three-fold more gastrointestinal side effects compared with using Cystagon.

CONCLUSIONS

A new delayed-release Q12H formulation of cysteamine bitartrate is not inferior to the Q6H formulation (Cystagon) in maintaining low WBC cystine levels in patients with cystinosis but at a lower total daily dose.