Steady-state pharmacokinetics and pharmacodynamics of cysteamine bitartrate in paediatric nephropathic cystinosis patients

Cysteamine Suppresses Cancer Cell Invasion and Migration in Glioblastoma through Inhibition of Matrix Metalloproteinase Activity

Glioblastoma (GBM) cells are highly invasive, infiltrating the surrounding normal brain tissue, thereby limiting the efficacy of surgical resection and focal radiotherapy. Cysteamine, a small aminothiol molecule that is orally bioavailable and approved for cystinosis, has potential as a cancer treatment by inhibiting tumor cell invasion and metastasis. Here we demonstrate that these potential therapeutic effects of cysteamine are likely due to the inhibition of matrix metalloproteinases (MMPs) in GBM. In vitro assays confirmed that micromolar concentrations of cysteamine were not cytotoxic, enabling the interrogation of the cellular effects without confounding tumor cell loss. Cysteamine's inhibition of MMP activity, especially the targeting of MMP2, MMP9, and MMP14, was observed at micromolar concentrations, suggesting the mechanism of action in suppressing invasion and cell migration is by inhibition of these MMPs. These findings suggest that achievable micromolar concentrations of cysteamine effectively inhibit cancer cell invasion and migration in GBM, supporting the potential for use as an adjunct cancer treatment.

A New and Rapid LC-MS/MS Method for the Determination of Cysteamine Plasma Levels in Cystinosis Patients

Cystinosis is a rare lysosomal storage disorder caused by autosomal recessive mutations in the CTNS gene that encodes for the cystine transporter cystinosin, which is expressed on the lysosomal membrane mediating the efflux of cystine. Cysteamine bitartrate is a cystine-depleting aminothiol agent approved for the treatment of cystinosis in children and adults. In this study, we developed and validated a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the determination of cysteamine levels in plasma samples. This LC-MS/MS method was validated according to the European Medicines Agency (EMA)'s guidelines for bioanalytical method validation. An ultra-performance liquid chromatograph (UPLC) coupled with a 6470 mass spectrometry system was used for cysteamine determination. Our validated method was applied to plasma samples from n = 8 cystinosis patients (median, interquartile range (IQR) = 20.5, 8.5-26.0 years). The samples were collected before cysteamine oral administration (pre-dose) and 1 h after (post-dose). Our bioanalytical method fulfilled the regulatory guidelines for method validation. The cysteamine plasma levels in pre-dose samples were 2.57 and 1.50-3.31 μM (median and IQR, respectively), whereas the post-dose samples reported a cysteamine median concentration of 28.00 μM (IQR: 17.60-36.61). Our method allows the rapid determination of cysteamine plasma levels. This method was successfully used in cystinosis patients and, therefore, could be a useful tool for the evaluation of therapy adherence and for future pharmacokinetic (PK) studies involving a higher number of subjects.

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.

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.

A comparison of immediate release and delayed release cysteamine in 17 patients with nephropathic cystinosis

Background

Nephropathic cystinosis is a rare and severe metabolic disease leading to an accumulation of cystine in lysosomes which especially harms kidney function. A lifelong therapy with the aminothiol cysteamine can delay the development of end-stage renal disease and the necessity of kidney transplantation. The purpose of our study was to compare the effectiveness of immediate-release and delayed-release cysteamine on cystine and cysteamine levels as well as assessing the onset of adverse effects.

Methods

We retrospectively analysed cystine and cysteamine levels of 17 patients after a single dose of immediate-release cysteamine (Cystagon®, Mylan Pharmaceuticals, Canonsburg, PA and Recordati Pharma GmbH) as well as a single dose of delayed-release cysteamine (Procysbi®; Horizon Pharma USA and Chiesi Farmaceutici S.p.A., Parma, Italy) respectively. Data were collected during a period of three years in the context of optimizing the individual treatment regimens. The dose of DR-cysteamine was reduced to 70% of the equivalent dose of IR-cysteamine. The efficacy of both formulas in depleting white blood cells’ cystine levels and their side effects were compared.

Results

Immediate (IR)- and delayed-release (DR) cysteamine effectively decreased intracellular cystine levels under the target value of 0.5 nmol cystine/mg protein, while fewer side effects occurred under DR-cysteamine. Mean maximum levels of cysteamine were reached after 60 min with IR-cysteamine and after 180 min with DR-cysteamine.

Conclusion

A therapy with DR-cysteamine is as effective as IR-cysteamine while less side effects were reported. Our data show that DR-cysteamine should be dosed higher than 70% of the equivalent dose of IR-cysteamine in order to decrease cystine levels over an extended period of time. Moreover, our data suggest increasing the dosing scheme of Procysbi® to three times daily, to prevent a rapid decrease and achieve a steadier decline in cystine levels. Due to the more convenient dosing scheme, DR-cysteamine might ameliorate therapy adherence and improve patients’ quality of life.

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).

Non-invasive intradermal imaging of cystine crystals in cystinosis

IMPORTANCE

Development of noninvasive methodology to reproducibly measure tissue cystine crystal load to assess disease status and guide clinical care in cystinosis, an inherited lysosomal storage disorder characterized by widespread cystine crystal accumulation.

OBJECTIVE

To develop an unbiased and semi-automated imaging methodology to quantify dermal cystine crystal accumulation in patients to correlate with disease status.

DESIGN, SETTING AND PARTICIPANTS

101 participants, 70 patients and 31 healthy controls, were enrolled at the University of California, San Diego, Cystinosis Clinics, Rady Children's Hospital, San Diego and at the annual Cystinosis Research Foundation family conference for an ongoing prospective longitudinal cohort study of cystinosis patients with potential yearly follow-up.

EXPOSURES

Intradermal reflectance confocal microscopy (RCM) imaging, blood collection via standard venipuncture, medical record collection, and occasional skin punch biopsies.

MAIN OUTCOMES AND MEASURES

The primary outcome was to establish an automated measure of normalized confocal crystal volume (nCCV) for each subject. Secondary analysis examined the association of nCCV with various clinical indicators to assess nCCV's possible predictive potential.

RESULTS

Over 2 years, 57 patients diagnosed with cystinosis (median [range] age: 15.1 yrs [0.8, 54]; 41.4% female) were intradermally assessed by RCM to produce 84 image stacks. 27 healthy individuals (38.7 yrs [10, 85]; 53.1% female) were also imaged providing 37 control image stacks. Automated 2D crystal area quantification revealed that patients had significantly elevated crystal accumulation within the superficial dermis. 3D volumetric analysis of this region was significantly higher in patients compared to healthy controls (mean [SD]: 1934.0 μm3 [1169.1] for patients vs. 363.1 μm3 [194.3] for controls, P<0.001). Medical outcome data was collected from 43 patients with infantile cystinosis (media [range] age: 11 yrs [0.8, 54]; 51% female). nCCV was positively associated with hypothyroidism (OR = 19.68, 95% CI: [1.60, 242.46], P = 0.02) and stage of chronic kidney disease (slope estimate = 0.53, 95%CI: [0.05, 1.00], P = 0.03).

CONCLUSIONS AND RELEVANCE

This study used non-invasive RCM imaging to develop an intradermal cystine crystal quantification method. Results showed that cystinosis patients had increased nCCV compared to healthy controls. Level of patient nCCV correlated with several clinical outcomes suggesting nCCV may be used as a potential new biomarker for cystinosis to monitor long-term disease control and medication compliance.

Challenges for cysteamine stabilization, quantification, and biological effects improvement

The aminothiol cysteamine, derived from coenzyme A degradation in mammalian cells, presents several biological applications. However, the bitter taste and sickening odor, chemical instability, hygroscopicity, and poor pharmacokinetic profile of cysteamine limit its efficacy. The use of encapsulation systems is a good methodology to overcome these undesirable properties and improve the pharmacokinetic behavior of cysteamine. Besides, the conjugation of cysteamine to the surface of nanoparticles is generally proposed to improve the intra-oral delivery of cyclodextrin-drug inclusion complexes, as well as to enhance the colorimetric detection of compounds by a gold nanoparticle aggregation method. On the other hand, the detection and quantification of cysteamine is a challenging mission due to the lack of a chromophore in its structure and its susceptibility to oxidation before or during the analysis. Derivatization agents are therefore applied for the quantification of this molecule. To our knowledge, the derivatization techniques and the encapsulation systems used for cysteamine delivery were not reviewed previously. Thus, this review aims to compile all the data on these methods as well as to provide an overview of the various biological applications of cysteamine focusing on its skin application.

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.

An Open-Label Investigation of the Pharmacokinetics and Tolerability of Oral Cysteamine in Adults with Cystic Fibrosis

Background and Objective

Cysteamine is licensed for use in nephropathic cystinosis but preclinical data suggest a role in managing cystic fibrosis (CF). This study aimed to determine whether oral cysteamine is absorbed in adult CF patients and enters the bronchial secretions. Tolerability outcomes were also explored.

Methods

Patients ≥18 years of age, weighing >50 kg with stable CF lung disease were commenced on oral cysteamine bitartrate (Cystagon^®) 450 mg once daily, increased weekly to 450 mg four times daily. Serial plasma cysteamine concentrations were measured for 24 h after the first dose. Participants were reviewed every week for 6 weeks, except at 4 weeks. Plasma cysteamine concentrations were measured 8 h after dosing when reviewed at 1, 2 and 3 weeks and 6 h after dosing when reviewed at 5 weeks. Sputum cysteamine concentration was also quantified at the 5-week assessment.

Results

Seven of the ten participants reported adverse reactions typical of cysteamine, two participants discontinued intervention. Following the first 450-mg dose, mean (SD) maximum concentration (C_max) was 2.86 (1.96) mg/l, the time corresponding to C_max (T_max) was 1.2 (0.7) h, the half-life (t_½) was 3.7 (1.7) h, clearance (CL/F) 89.9 (30.5) L/h and volume of distribution (V_d/F) 427 (129) L. Cysteamine appeared to accumulate in sputum with a median (interquartile range) sputum:plasma cysteamine concentration ratio of 4.2 (0.98–8.84).

Conclusion

Oral cysteamine is absorbed and enters the bronchial secretions in patients with CF. Although adverse reactions were common, the majority of patients continued with cysteamine. Further trials are required to establish the risk benefit ratio of cysteamine therapy in CF.

Cysteamine broadly improves the anti-plasmodial activity of artemisinins against murine blood stage and cerebral malaria

BACKGROUND

The potential emergence and spread of resistance to artemisinins in the Plasmodium falciparum malaria parasite constitutes a major global health threat. Hence, improving the efficacy of artemisinins and of artemisinin-based combination therapy (ACT) represents a major short-term goal in the global fight against malaria. Mice defective in the enzyme pantetheinase (Vnn3) show increased susceptibility to blood-stage malaria (increased parasitaemia, reduced survival), and supplementation of Vnn3 mutants with the reaction product of pantetheinase, cysteamine, corrects in part the malaria-susceptibility phenotype of the mutants. Cysteamine (Cys) is a small, naturally occurring amino-thiol that has very low toxicity in vivo and is approved for clinical use in the life-long treatment of the kidney disorder nephropathic cystinosis.

METHODS

The ability of Cys to improve the anti-plasmodial activity of different clinically used artemisinins was tested. The effect of different CYS/ART combinations on malarial phenotypes (parasite blood-stage replication, overall and survival from lethal infection) was assessed in a series of in vivo experiments using Plasmodium strains that induce either blood-stage (Plasmodium chabaudi AS) or cerebral disease (Plasmodium berghei ANKA). This was also evaluated in an ex vivo experimental protocol that directly assesses the effect of such drug combinations on the viability of Plasmodium parasites, as measured by the ability of tested parasites to induce a productive infection in vivo in otherwise naïve animals.

RESULTS

Cys is found to potentiate the anti-plasmodial activity of artesunate, artemether, and arteether, towards the blood-stage malaria parasite P. chabaudi AS. Ex vivo experiments, indicate that potentiation of the anti-plasmodial activity of artemisinins by Cys is direct and does not require the presence of host factors. In addition, potentiation occurs at sub-optimal concentrations of artemisinins and Cys that on their own have little or no effect on parasite growth. Cys also dramatically enhances the efficacy and protective effect of artemisinins against cerebral malaria induced by infection with the P. berghei ANKA parasite.

CONCLUSION

These findings indicate that inclusion of Cys in current formulations of ACT, or its use as adjunct therapy could improve the anti-plasmodial activity of artemisinin, decrease mortality in cerebral malaria patients, and prevent or delay the development and spread of artemisinin resistance.

How should patients with cystine stone disease be evaluated and treated in the twenty-first century?

Cystinuria continues to be one of the most challenging stone diseases. During the latest decades our knowledge of the molecular basis of cystinuria has expanded. Today 160 different mutations in the SLC3A1 gene and 116 in the SLC7A9 gene are listed. The full implications of type A, B or AB status are not yet fully understood but may have implications for prognosis, management and treatment. Despite better understanding of the molecular basis of cystinuria the principles of recurrence prevention have remained essentially the same through decades. No curative treatment of cystinuria exists, and patients will have a life long risk of stone formation, repeated surgery, impaired renal function and quality of life. Therapy to reduce stone formation is directed towards lowering urine cystine concentration and increasing cystine solubility. Different molecules that could play a role in promoting nucleation and have a modulating effect on cystine solubility may represent new targets for cystinuria research. Investigation of newer thiol-containing drugs with fewer adverse effects is also warranted. Determining cystine capacity may be an effective tool to monitor the individual patient's response. Compliance in cystinuric patients concerning both dietary and pharmacological intervention is poor. Frequent clinical follow-up visits in dedicated centres seem to improve compliance. Cystinuric patients should be managed in dedicated centres offering the complete range of minimal invasive treatment modalities, enabling a personalized treatment approach in order to reduce risk and morbidity of multiple procedures.

Impairment of chaperone-mediated autophagy leads to selective lysosomal degradation defects in the lysosomal storage disease cystinosis

Metabolite accumulation in lysosomal storage disorders (LSDs) results in impaired cell function and multi-systemic disease. Although substrate reduction and lysosomal overload-decreasing therapies can ameliorate disease progression, the significance of lysosomal overload-independent mechanisms in the development of cellular dysfunction is unknown for most LSDs. Here, we identify a mechanism of impaired chaperone-mediated autophagy (CMA) in cystinosis, a LSD caused by defects in the cystine transporter cystinosin (CTNS) and characterized by cystine lysosomal accumulation. We show that, different from other LSDs, autophagosome number is increased, but macroautophagic flux is not impaired in cystinosis while mTOR activity is not affected. Conversely, the expression and localization of the CMA receptor LAMP2A are abnormal in CTNS-deficient cells and degradation of the CMA substrate GAPDH is defective in Ctns^−/− mice. Importantly, cysteamine treatment, despite decreasing lysosomal overload, did not correct defective CMA in Ctns^−/− mice or LAMP2A mislocalization in cystinotic cells, which was rescued by CTNS expression instead, suggesting that cystinosin is important for CMA activity. In conclusion, CMA impairment contributes to cell malfunction in cystinosis, highlighting the need for treatments complementary to current therapies that are based on decreasing lysosomal overload.

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.

Cysteamine (Cystagon®) adherence in patients with cystinosis in Spain: successful in children and a challenge in adolescents and adults

Background

Cysteamine has improved survival and prognosis in cystinosis. Increasing numbers of patients reach adulthood and face new challenges such as compliance that wanes over time. The aim of this study was to evaluate adherence to cysteamine treatment in a group of cystinotic patients in Spain in an attempt to identify potential therapy pitfalls and improve the overall care of affected individuals. Despite the impact of cysteamine on prognosis, there is a paucity of data regarding adherence.

Method

Thirty-four cystinotic patients (21 male) 38% ≥18 years were enrolled in a voluntary, anonymous survey. Replies were obtained from patients (15/34), mothers (11/34), fathers (4/34) and both parents (4/34).

Results

Patient age (median and interquartile range) at diagnosis was 1 year (0.57–1), and patient age at Cystagon® initiation was also 1 year (0.8–1.8). Sixteen (47%) were kidney transplant (KTx) recipients; six were retransplanted. Age at first KTx 10 years (8.7–13.7). Patient understanding of multiorgan involvement in cystinosis: 4.1 organs reported; eye 97% and kidney 91%. Cysteamine was given by mother (100%) and father (83%) in <11 year olds, or self-administered (94%) in ≥11 year olds. Four daily doses in 89% versus 56% in <11 year olds or ≥11 year olds, with fixed schedule in 94% versus 50% in <11 or ≥11 year olds and progressive loss of reminders over time. Furthermore, 44% complained of unpleasant smell. Motivation for treatment compliance was 100% versus 40% in <11 versus ≥11 year olds, respectively. Disease impact in patients <18 years is as follows: school (29%), social (14%), ‘feeling different’ (10%); in patients ≥18 years: ‘feeling different’ (62%), professional (39%) and job absenteeism (31%). Referring physician: paediatric nephrologist (94%) and nephrologist (63%) in <11 versus ≥11 year olds. Ophthalmological follow-up: 83% versus 38% in <11 versus ≥11 year olds. Patient opinion of physician expertise: paediatric nephrologist (94%) and nephrologist (44%). New treatment options (65%) and better information (42%) were demanded to improve adherence.

Conclusion

Treatment with Cystagon is effective in young patients. However, adherence diminishes over time in adolescents and adults despite disease impact. Strategies such as better information on the disease, patient self-care promotion and facilitated transition to adult healthcare services are required to improve compliance and the clinical management of cystinosis.

High throughput assay for evaluation of reactive carbonyl scavenging capacity

Many carbonyl species from either lipid peroxidation or glycoxidation are extremely reactive and can disrupt the function of proteins and enzymes. 4-hydroxynonenal and methylglyoxal are the most abundant and toxic lipid-derived reactive carbonyl species. The presence of these toxics leads to carbonyl stress and cause a significant amount of macromolecular damages in several diseases. Much evidence indicates trapping of reactive carbonyl intermediates may be a useful strategy for inhibiting or decreasing carbonyl stress-associated pathologies. There is no rapid and convenient analytical method available for the assessment of direct carbonyl scavenging capacity, and a very limited number of carbonyl scavengers have been identified to date, their therapeutic potential being highlighted only recently. In this context, we have developed a new and rapid sensitive fluorimetric method for the assessment of reactive carbonyl scavengers without involvement glycoxidation systems. Efficacy of various thiol- and non-thiol-carbonyl scavenger pharmacophores was tested both using this screening assay adapted to 96-well microplates and in cultured cells. The scavenging effects on the formation of Advanced Glycation End-product of Bovine Serum Albumin formed with methylglyoxal, 4-hydroxynonenal and glucose-glycated as molecular models were also examined. Low molecular mass thiols with an α-amino-β-mercaptoethane structure showed the highest degree of inhibitory activity toward both α,β-unsaturated aldehydes and dicarbonyls. Cysteine and cysteamine have the best scavenging ability toward methylglyoxal. WR-1065 which is currently approved for clinical use as a protective agent against radiation and renal toxicity was identified as the best inhibitor of 4-hydroxynonenal.

•

We describe a rapid method for assessment of reactive carbonyl scavengers.

•

We evaluated the carbonyl scavenger activity of various pharmacophores.

•

α-amino-β-mercaptoethane structure showed the highest degree of activity.

Understanding the hysteresis loop conundrum in pharmacokinetic/pharmacodynamic relationships

Hysteresis loops are phenomena that sometimes are encountered in the analysis of pharmacokinetic and pharmacodynamic relationships spanning from pre-clinical to clinical studies. When hysteresis occurs it provides insight into the complexity of drug action and disposition that can be encountered. Hysteresis loops suggest that the relationship between drug concentration and the effect being measured is not a simple direct relationship, but may have an inherent time delay and disequilibrium, which may be the result of metabolites, the consequence of changes in pharmacodynamics or the use of a non-specific assay or may involve an indirect relationship. Counter-clockwise hysteresis has been generally defined as the process in which effect can increase with time for a given drug concentration, while in the case of clockwise hysteresis the measured effect decreases with time for a given drug concentration. Hysteresis loops can occur as a consequence of a number of different pharmacokinetic and pharmacodynamic mechanisms including tolerance, distributional delay, feedback regulation, input and output rate changes, agonistic or antagonistic active metabolites, uptake into active site, slow receptor kinetics, delayed or modified activity, time-dependent protein binding and the use of racemic drugs among other factors. In this review, each of these various causes of hysteresis loops are discussed, with incorporation of relevant examples of drugs demonstrating these relationships for illustrative purposes. Furthermore, the effect that pharmaceutical formulation has on the occurrence and potential change in direction of the hysteresis loop, and the major pharmacokinetic / pharmacodynamic modeling approaches utilized to collapse and model hysteresis are detailed.

Drug treatment of inborn errors of metabolism: a systematic review

BACKGROUND

The treatment of inborn errors of metabolism (IEM) has seen significant advances over the last decade. Many medicines have been developed and the survival rates of some patients with IEM have improved. Dosages of drugs used for the treatment of various IEM can be obtained from a range of sources but tend to vary among these sources. Moreover, the published dosages are not usually supported by the level of existing evidence, and they are commonly based on personal experience.

METHODS

A literature search was conducted to identify key material published in English in relation to the dosages of medicines used for specific IEM. Textbooks, peer reviewed articles, papers and other journal items were identified. The PubMed and Embase databases were searched for material published since 1947 and 1974, respectively. The medications found and their respective dosages were graded according to their level of evidence, using the grading system of the Oxford Centre for Evidence-Based Medicine.

RESULTS

83 medicines used in various IEM were identified. The dosages of 17 medications (21%) had grade 1 level of evidence, 61 (74%) had grade 4, two medications were in level 2 and 3 respectively, and three had grade 5.

CONCLUSIONS

To the best of our knowledge, this is the first review to address this matter and the authors hope that it will serve as a quickly accessible reference for medications used in this important clinical field.

Pharmacokinetics of cysteamine bitartrate following intraduodenal delivery

Cysteamine is approved for the treatment of cystinosis and is being evaluated for Huntington's disease and non-alcoholic fatty liver disease. Little is known about the bioavailability and biodistribution of the drug. The aim was to determine plasma, cerebrospinal fluid (CSF), and tissue (liver, kidney, muscle) cysteamine levels following intraduodenal delivery of the drug in rats pretreated and naïve to cysteamine and to estimate the hepatic first-pass effect on cysteamine. Healthy male rats (n = 66) underwent intraduodenal and portal (PV) or jugular (JVC) venous catheterization. Half were pretreated with cysteamine, and half were naïve. Following intraduodenal cysteamine (20 mg/kg), serial blood samples were collected from the PV or the JVC. Animals were sacrificed at specific time points, and CSF and tissue were collected. Cysteamine levels were determined in plasma, CSF, and tissue. The Cmax was achieved in 5-10 min from PV and 5-22.5 min from JVC. The PV-Cmax (P = 0.08), PV-AUC0-t (P = 0.16), JVC-Cmax (P = 0.02) and JVC-AUC0-t (P = 0.03) were higher in naive than in pretreated animals. Plasma cysteamine levels returned to baseline in ≤120 min. The hepatic first-pass effect was estimated at 40%. Peak tissue and CSF cysteamine levels occurred ≤22.5 min, but returned to baseline levels ≤180 min. There was no difference in CSF and tissue cysteamine levels between naïve and pretreated groups, although cysteamine was more rapidly cleared in the pretreated group. Cysteamine is rapidly absorbed from the small intestine, undergoes significant hepatic first-pass metabolism, crosses the blood brain barrier, and is almost undetectable in plasma, CSF, and body tissues 2 h after ingestion. Sustained-release cysteamine may provide prolonged tissue exposure.

Ghrelin accelerates the healing of cysteamine-induced duodenal ulcers in rats

Background

Previous studies have shown that administration of ghrelin exhibits protective and therapeutic effects in the gut. The aim of the present investigation was to examine the influence of ghrelin administration on the course of cysteamine-induced duodenal ulcers, as well as effects on mucosal production of oxygen free radicals and duodenal antioxidant defense.

Material/Methods

Duodenal ulcers were induced in male Wistar rats by cysteamine administered intragastrically at the dose of 200 mg/kg in 1 ml of saline, 3 times at 4-h intervals. Starting 24 h after the first dose of cysteamine, rats were treated intraperitoneally twice a day with saline or ghrelin given at the dose of 4, 8 or 16 nmol/kg/dose. Seven days after administration of the first dose of cysteamine, the study was terminated.

Results

Induction of ulcers by cysteamine was accompanied by a reduction in duodenal blood flow, mucosal DNA synthesis and mucosal activity of superoxide dismutase (SOD); whereas mucosal concentration of interleukin-1β and malonyldialdehyde (MDA – an index of lipid peroxidation) were increased. Treatment with ghrelin increased healing rate of duodenal ulcers and enhanced duodenal blood flow, mucosal DNA synthesis and mucosal activity of SOD, and reduced mucosal concentration of interleukin-1β and MDA.

Conclusions

Treatment with ghrelin increases the healing rate of duodenal ulcers and this effect is related, at least in part, to improvement of duodenal mucosal blood flow, mucosal cell proliferation and antioxidant defense, as well as being related to reduction in mucosal oxidative stress and inflammatory response.

A potential new method to estimate tissue cystine content in nephropathic cystinosis

OBJECTIVES

To evaluate intestinal mucosal cystine crystal (CC) load as a way to estimate tissue cystine content in children with cystinosis.

STUDY DESIGN

Intestinal mucosal biopsies were obtained endoscopically from children (ages 2-18 years) with cystinosis. Using a special processing technique, CC within histiocytes were easily visible and enumerable in the mucosal tissue. Mean CC counts, calculated from stomach and duodenum combined (CC-GD), were correlated with duration of cysteamine treatment, estimated glomerular filtration rate (eGFR), and mean white blood cells (WBC) cystine levels.

RESULTS

Seventeen subjects (6 male) were enrolled in 2 studies from 2001 and 2003. The CC-GD count (mean 12.5 ± 1.41 crystals/histiocyte) was lower than the colonic crystal count (mean 23.6 ± 3.38, P = .0031). Nine of 17 subjects underwent repeated endoscopy 2 years later and the trend for CC-GD was to decrease over time (P = .065). Biopsies, however, were never completely depleted of CC. In subjects who were diagnosed before age 18 months, the percent change from baseline of both eGFR and CC-GD were inversely correlated (P = .026). Mean WBC cystine levels were positively correlated with CC-GD (P = .023).

CONCLUSIONS

CC are easily visible in the intestinal mucosa. CC-GD counts appear to correlate with eGFR and may help monitor response to treatment. Even when mean WBC cystine levels are low, the mucosal CC are not depleted suggesting that tissue cysteamine levels may not achieve therapeutic efficacy.

Population pharmacokinetics and pharmacodynamics of cysteamine in nephropathic cystinosis patients

BACKGROUND

Nephropathic cystinosis is an autosomal recessive disorder resulting in an impaired transport of cystine trough the lysosomal membrane causing an accumulation of free cystine in lysosomes. The only specific treatment for nephropathic cystinosis is cysteamine bitartrate. This study was aimed to describe the relationship between cysteamine plasma concentrations and white blood cell cystine levels, and to simulate an optimized administration scheme to improve the management of patients with cystinosis.

METHODS

Cysteamine and cystine concentrations were measured in 69 nephropathic cystinosis patients. A total of 250 cysteamine plasma concentrations and 243 intracellular cystine concentrations were used to perform a population pharmacokinetic and pharmacodynamic analysis. An optimized administration scheme was simulated in order to maintain cystine levels below 1 nmol half-cystine/mg of protein and to investigate the possibility of administrating the treatment less than 4 times a day (QID, recommended). The current dosing recommendations are 1.3 g/m2/day for less than 50 kg BW and 2 g/day thereafter; the maximum dose should not exceed 1.95 g/m2/day.

RESULTS

Cysteamine concentrations were satisfactorily described by a one-compartment model. Parameter estimates were standardized for a mean standard bodyweight using an allometric model. WBC cystine levels were adequately described by an indirect response model where the first-order removal rate constant is stimulated by the cysteamine concentrations.

CONCLUSIONS

According to simulations, in order to increase the percentage of patient with cystine levels below 1 nmol half-cystine/mg of protein, the current dosages could be changed as follows: 80 mg/kg/day (QID) from 10 to 17 kg, 70 mg/kg/day (QID) from 17 to 25 kg, 60 mg/kg/day (QID) from 25 to 40 kg and 50 mg/kg/day (QID) from 40 to 70 kg (these dosages remain under the maximum recommended dose). However an 8-hourly daily treatment (TID) did not provide acceptable cystine levels and should not be proposed.

Cystinosis: practical tools for diagnosis and treatment

Cystinosis is the major cause of inherited Fanconi syndrome, and should be suspected in young children with failure to thrive and signs of renal proximal tubular damage. The diagnosis can be missed in infants, because not all signs of renal Fanconi syndrome are present during the first months of life. In older patients cystinosis can mimic idiopathic nephrotic syndrome due to focal and segmental glomerulosclerosis. Measuring elevated white blood cell cystine content is the corner stone for the diagnosis. The diagnosis is confirmed by molecular analysis of the cystinosin gene. Corneal cystine crystals are invariably present in all patients with cystinosis after the age of 1 year. Treatment with the cystine depleting drug cysteamine should be initiated as soon as possible and continued lifelong to prolong renal function survival and protect extra-renal organs. This educational feature provides practical tools for the diagnosis and treatment of cystinosis.

Cysteamine, the molecule used to treat cystinosis, potentiates the antimalarial efficacy of artemisinin

Malaria continues to be a major threat to global health. Artemisinin combination therapy (ACT) is the recommended treatment for clinical malaria; however, recent reports of parasite resistance to artemisinin in certain areas where malaria is endemic have stressed the need for developing more efficacious ACT. We report that cysteamine (Cys), the aminothiol used to treat nephropathic cystinosis in humans, strongly potentiates the efficacy of artemisinin against the Plasmodium parasite in vivo. Using a mouse model of infection with Plasmodium chabaudi AS, we observe that Cys dosing used to treat cystinosis in humans can strongly potentiate (by 3- to 4-fold) the antimalarial properties of the artemisinin derivatives artesunate and dihydroartemisinin. Addition of Cys to suboptimal doses of artemisinin delays the appearance of blood parasitemia, strongly reduces the extent of parasite replication, and significantly improves survival in a model of lethal P. chabaudi infection. Cys, the natural product of the enzyme pantetheinase, has a history of safe use for the clinical management of cystinosis. Our findings suggest that Cys could be included in novel ACTs to improve efficacy against Plasmodium parasite replication, including artemisinin-resistant isolates. Future work will include clinical evaluation of novel Cys-containing ACTs and elucidation of the mechanism underlying the potentiation effect of Cys.

Cysteamine, the natural metabolite of pantetheinase, shows specific activity against Plasmodium

In mice, loss of pantetheinase activity causes susceptibility to infection with Plasmodium chabaudi AS. Treatment of mice with the pantetheinase metabolite cysteamine reduces blood-stage replication of P. chabaudi and significantly increases survival. Similarly, a short exposure of Plasmodium to cysteamine ex vivo is sufficient to suppress parasite infectivity in vivo. This effect of cysteamine is specific and not observed with a related thiol (dimercaptosuccinic acid) or with the pantethine precursor of cysteamine. Also, cysteamine does not protect against infection with the parasite Trypanosoma cruzi or the fungal pathogen Candida albicans, suggesting cysteamine acts directly against the parasite and does not modulate host inflammatory response. Cysteamine exposure also blocks replication of P. falciparum in vitro; moreover, these treated parasites show higher levels of intact hemoglobin. This study highlights the in vivo action of cysteamine against Plasmodium and provides further evidence for the involvement of pantetheinase in host response to this infection.

The origin of halitosis in cystinotic patients due to cysteamine treatment

INTRODUCTION

Cystinosis is a rare autosomal recessive disorder characterized by the intralysosomal accumulation of cystine. Cysteamine removes cystine from the lysosome and slows down the progression of the disease. One of its side effects is the induction of halitosis, which can interfere with patients' willingness to comply with cysteamine treatment.

OBJECTIVE

To identify breath sulphur compounds causing halitosis induced by cysteamine therapy in patients with cystinosis.

STUDY DESIGN

After the ingestion of 15mg/kg cysteamine whole blood (n=4), urine (n=4) and breath (n=8) volatile sulphur compounds levels were measured every 60min over a 360min period by gas chromatography and the cysteamine plasma concentrations (n=4) were measured by high-performance liquid chromatography.

RESULTS

The expired air of cystinotic patients contained elevated concentrations of methanethiol (MT, median maximum value 0.5 (range 0-11)nmol/L) and, in particular, dimethylsulphide (DMS, median maximum value 15 (range 2-83)nmol/L). DMS concentrations higher than 0.65nmol/L are known to cause halitosis. Maximal plasma values of cysteamine (median 46 (range 30-52)micromol/L) preceded those of MT and DMS, confirming that cysteamine is converted to MT and DMS. Less than 3% of the amount of cysteamine ingested was excreted as MT and DMS via expired air and 0.002% via urine.

CONCLUSION

Halitosis induced by cysteamine intake is caused by DMS and to a lesser extent by MT, excreted via the expired air. Further studies should focus on the possibilities of reducing the formation of these volatile sulphur compounds or masking their odour, which would improve the rates of compliance with cysteamine treatment.

Cystamine and cysteamine increase brain levels of BDNF in Huntington disease via HSJ1b and transglutaminase

There is no treatment for the neurodegenerative disorder Huntington disease (HD). Cystamine is a candidate drug; however, the mechanisms by which it operates remain unclear. We show here that cystamine increases levels of the heat shock DnaJ-containing protein 1b (HSJ1b) that are low in HD patients. HSJ1b inhibits polyQ-huntingtin-induced death of striatal neurons and neuronal dysfunction in Caenorhabditis elegans. This neuroprotective effect involves stimulation of the secretory pathway through formation of clathrin-coated vesicles containing brain-derived neurotrophic factor (BDNF). Cystamine increases BDNF secretion from the Golgi region that is blocked by reducing HSJ1b levels or by overexpressing transglutaminase. We demonstrate that cysteamine, the FDA-approved reduced form of cystamine, is neuroprotective in HD mice by increasing BDNF levels in brain. Finally, cysteamine increases serum levels of BDNF in mouse and primate models of HD. Therefore, cysteamine is a potential treatment for HD, and serum BDNF levels can be used as a biomarker for drug efficacy.

Strict cysteamine dose regimen is required to prevent nocturnal cystine accumulation in cystinosis

Cystinosis is an autosomal recessive disorder, caused by mutations in the lysosomal cystine carrier cystinosin, encoded by the CTNS gene. The disease generally manifests with Fanconi syndrome during the first year of life and progresses towards end stage renal disease before the age of 10 years. Cysteamine depletes intralysosomal cystine content, postpones the deterioration of renal function and the occurrence of extra-renal organ damage. Based on the pharmacokinetic data, patients with cystinosis are advised to use cysteamine every 6 h. The aim of this study was (1) to evaluate the cysteamine dose regimen in Dutch patients with cystinosis and (2) to determine morning polymorphonuclear (PMN) leukocyte cystine content 6 h vs 9 h after the last evening cysteamine dose. Only 5/22 of Dutch cystinosis patients ingested cysteamine every 6 h. Morning (8 a.m.) PMN cystine content in 11 examined patients was elevated 9 h after 12.5-15 mg/kg evening cysteamine dose compared to the value 6 h after the ingestion of the same dose (0.73+/-0.81 nmol vs 0.44+/-0.52 nmol cystine/mg protein, p =0.02). In conclusion, only the minority of Dutch cystinosis patients follows the recommended strict cysteamine dose regimen. We provide evidence that cysteamine has to be administered every 6 h, including the night, as it has much better effect for maintaining low PMN cystine levels.

Mammalian flavin-containing monooxygenases: structure/function, genetic polymorphisms and role in drug metabolism

Flavin-containing monooxygenase (FMO) oxygenates drugs and xenobiotics containing a "soft-nucleophile", usually nitrogen or sulfur. FMO, like cytochrome P450 (CYP), is a monooxygenase, utilizing the reducing equivalents of NADPH to reduce 1 atom of molecular oxygen to water, while the other atom is used to oxidize the substrate. FMO and CYP also exhibit similar tissue and cellular location, molecular weight, substrate specificity, and exist as multiple enzymes under developmental control. The human FMO functional gene family is much smaller (5 families each with a single member) than CYP. FMO does not require a reductase to transfer electrons from NADPH and the catalytic cycle of the 2 monooxygenases is strikingly different. Another distinction is the lack of induction of FMOs by xenobiotics. In general, CYP is the major contributor to oxidative xenobiotic metabolism. However, FMO activity may be of significance in a number of cases and should not be overlooked. FMO and CYP have overlapping substrate specificities, but often yield distinct metabolites with potentially significant toxicological/pharmacological consequences. The physiological function(s) of FMO are poorly understood. Three of the 5 expressed human FMO genes, FMO1, FMO2 and FMO3, exhibit genetic polymorphisms. The most studied of these is FMO3 (adult human liver) in which mutant alleles contribute to the disease known as trimethylaminuria. The consequences of these FMO genetic polymorphisms in drug metabolism and human health are areas of research requiring further exploration.

Pharmacological treatment of nephropathic cystinosis with cysteamine

Cystinosis, clinically recognised since 1903, is an autosomal recessive lysosomal storage disease caused by mutations in CTNS. This gene codes for a lysosomal cystine transporter, whose absence leads to intracellular cystine crystals, widespread cellular destruction, renal Fanconi syndrome in infancy, renal glomerular failure in later childhood and other systemic complications. Before the availability of kidney transplantation, patients affected with cystinosis uniformly died during childhood. After solid organ transplantations became successful in the 1960s, cystinosis patients survived, but eventually developed life-threatening consequences of the disease (e.g., swallowing disorders). Since the introduction of cysteamine into the pharmacological management of cystinosis, well-treated adolescent and young adult patients have experienced normal growth and maintenance of renal glomerular function. Oral cysteamine therapy is given at doses of 60 - 90 mg/kg/day q.i.d. every 6 h, and generally achieves approximately 90% depletion of cellular cystine, as measured in circulating leucocytes. Cysteamine (and kidney transplantation) have commuted the death sentence of cystinosis into a nearly normal life with a chronic disease. Because treatment with oral cysteamine can prevent, or significantly delay, the complications of cystinosis, early and accurate diagnosis, as well as proper treatment, is critical.