Cystinosis. Intracellular cystine depletion by aminothiols in vitro and in vivo

Mechanism of action and impact of thiol homeostasis on efficacy of an enzyme replacement therapy for classical homocystinuria

Homocystinuria (HCU) due to cystathionine beta-synthase (CBS) deficiency is characterized by elevated plasma and tissue homocysteine levels. There is no cure, but HCU is typically managed by methionine/protein restriction and vitamin B6 supplementation. Enzyme replacement therapy (ERT) based on human CBS has been developed and has shown significant efficacy correcting HCU phenotype in several mouse models by bringing plasma total homocysteine below the clinically relevant 100 μM threshold. As the reactive nature of homocysteine promotes disulfide formation and protein binding, and ERT is unable to normalize plasma total homocysteine levels, the mechanism of action of ERT in HCU remains to be further characterized. Here we showed that only a reduced homocysteine serves as a substrate for CBS and its availability restricts the homocysteine-degrading capacity of CBS. We also demonstrated that cells export homocysteine in its reduced form, which is efficiently metabolized by CBS in the culture medium. Availability of serine, a CBS co-substrate, was not a limiting factor in our cell-based model. Biological reductants, such as N-acetylcysteine, MESNA or cysteamine, increased the availability of the reduced homocysteine and thus promoted its subsequent CBS-based elimination. In a transgenic I278T mouse model of HCU, administration of biological reductants significantly increased the proportion of protein-unbound homocysteine in plasma, which improved the efficacy of the co-administered CBS-based ERT, as evidenced by significantly lower plasma total homocysteine levels. These results clarify the mechanism of action of CBS-based ERT and unveil novel pharmacological approaches to further increase its efficacy.

Long-term effects of luteolin in a mouse model of nephropathic cystinosis

In infantile nephropathic cystinosis, variants of the CTNS gene cause accumulation of cystine in lysosomes, causing progressive damage to most organs. Patients usually present before 1 year of age with signs of renal Fanconi syndrome. Cysteamine therapy allows cystine clearance from lysosomes and delays kidney damage but does not prevent progression to end-stage kidney disease, suggesting that pathways unrelated to cystine accumulation are also involved. Among these, impaired autophagy, altered endolysosomal trafficking, and increased apoptosis have emerged in recent years as potential targets for new therapies. We previously showed that luteolin, a flavonoid compound, improves these abnormal pathways in cystinotic cells and in zebrafish models of the disease. Herein, we have investigated if prolonged luteolin treatment ameliorates kidney damage in a murine model of cystinosis. To this end, we have treated Ctns-/- mice from 2 to 8 months with 150 mg/kg/day of luteolin. No significant side effects were observed. Compared to untreated animals, analyses of kidney cortex samples obtained after sacrifice showed that luteolin decreased p62/SQSTM1 levels (p <0.001), improved the number, size, and distribution of LAMP1-positive structures (p <0.02), and decreased tissue expression of cleaved caspase 3 (p <0.001). However, we did not observe improvements in renal Fanconi syndrome and kidney inflammation. Kidney function remained normal during the time of the study. These results indicate that luteolin has positive effects on the apoptosis and endo-lysosomal defects of cystinotic proximal tubular cells. However, these beneficial effects did not translate into improvement of renal Fanconi syndrome.

Combination of disulfiram and Copper-Cysteamine nanoparticles induces mitochondria damage and promotes apoptosis in endometrial cancer

Endometrial cancer (EC) stands as one of the most prevalent gynecological malignancies affecting women, with its incidence and disease-related mortality steadily on the rise. Disulfiram (DSF), an FDA-approved medication primarily used for treating alcohol addiction, has exhibited promising anti-tumor properties. Studies have revealed DSF's capacity for enhanced anti-tumor activity, particularly when combined with copper. The novel Copper-Cysteamine (CuCy) compound, Cu3Cl(SR)2 (R[bond, double bond]CH2CH2NH2), showcases photodynamic effects and demonstrates significant anti-tumor potential under various conditions, including exposure to ultraviolet light, X-ray, microwave, and ultrasound. This study delves into exploring the synergistic anti-tumor effects and underlying mechanisms by utilizing copper-cysteamine in conjunction with DSF against endometrial cancer. The investigation involved comprehensive analyses encompassing in vitro experiments utilizing Ishikawa cells, in vivo studies, and transcriptomic analyses. Remarkably, the combined administration of both compounds at a low dose of 0.5 μM exhibited pronounced efficacy in impeding tumor growth, inhibiting blood vessel formation, and stimulating cell apoptosis. Notably, experiments involving transplanted tumors in nude mice vividly demonstrated the significant in vivo anti-tumor effects of this combination treatment. Detailed examination through transmission electron microscopy unveiled compelling evidence of mitochondrial damage, cellular swelling, and rupture, indicative of apoptotic changes in morphology due to the combined treatment. Moreover, transcriptomic analysis unveiled substantial downregulation of mitochondrial-related genes at the molecular level, coupled with a significant hindrance in the DNA repair pathway. These findings strongly suggest that the combined application of CuCy and DSF induces mitochondrial impairment in Ishikawa cells, thereby fostering apoptosis and ultimately yielding potent anti-tumor effects.

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.

ER-associated degradation in cystinosis pathogenesis and the prospects of precision medicine

Cystinosis is a lysosomal storage disease that is characterized by the accumulation of dipeptide cystine within the lumen. It is caused by mutations in the cystine exporter, cystinosin. Most of the clinically reported mutations are due to the loss of transporter function. In this study, we identified a rapidly degrading disease variant, referred to as cystinosin(7Δ). We demonstrated that this mutant is retained in the ER and degraded via the ER-associated degradation (ERAD) pathway. Using genetic and chemical inhibition methods, we elucidated the roles of HRD1, p97, EDEMs, and the proteasome complex in cystinosin(7Δ) degradation pathway. Having understood the degradation mechanisms, we tested some chemical chaperones previously used for treating CFTR F508Δ and demonstrated that they could facilitate the folding and trafficking of cystinosin(7Δ). Strikingly, chemical chaperone treatment can reduce the lumenal cystine level by approximately 70%. We believe that our study conclusively establishes the connection between ERAD and cystinosis pathogenesis and demonstrates the possibility of using chemical chaperones to treat cystinosin(7Δ).

Tubular Diseases and Stones Seen From Pediatric and Adult Nephrology Perspectives

The tubular system of the kidneys is a complex series of morphologic and functional units orchestrating the content of tubular fluid as it flows along the nephron and collecting ducts. Renal tubules maintain body water, regulate electrolytes and acid-base balance, reabsorb precious organic solutes, and eliminate specific metabolites, toxins, and drugs. In addition, decisive mechanisms to adjust blood pressure are governed by the renal tubules. Genetic as well as acquired disorders of these tubular functions may cause serious diseases that manifest both in childhood and adulthood. This article addresses a selection of tubulopathies and the underlying pathomechanisms, while highlighting the important differences in pediatric and adult nephrology care. These range from rare monogenic conditions such as nephrogenic diabetes insipidus, cystinosis, and Bartter syndrome that present in childhood, to the genetic and acquired tubular pathologies causing hypertension or nephrolithiasis that are more prevalent in adults. Both pediatric and adult nephrologists must be aware of these conditions and the age-dependent manifestations that warrant close interaction between the two subspecialties.

N-acetylcysteine and cysteamine bitartrate prevent azide-induced neuromuscular decompensation by restoring glutathione balance in two novel surf1-/- zebrafish deletion models of Leigh syndrome

SURF1 deficiency (OMIM # 220110) causes Leigh syndrome (LS, OMIM # 256000), a mitochondrial disorder typified by stress-induced metabolic strokes, neurodevelopmental regression and progressive multisystem dysfunction. Here, we describe two novel surf1-/- zebrafish knockout models generated by CRISPR/Cas9 technology. While gross larval morphology, fertility, and survival into adulthood appeared unaffected, surf1-/- mutants manifested adult-onset ocular anomalies and decreased swimming activity, as well as classical biochemical hallmarks of human SURF1 disease, including reduced complex IV expression and enzymatic activity and increased tissue lactate. surf1-/- larvae also demonstrated oxidative stress and stressor hypersensitivity to the complex IV inhibitor, azide, which exacerbated their complex IV deficiency, reduced supercomplex formation, and induced acute neurodegeneration typical of LS including brain death, impaired neuromuscular responses, reduced swimming activity, and absent heartrate. Remarkably, prophylactic treatment of surf1-/- larvae with either cysteamine bitartrate or N-acetylcysteine, but not other antioxidants, significantly improved animal resiliency to stressor-induced brain death, swimming and neuromuscular dysfunction, and loss of heartbeat. Mechanistic analyses demonstrated cysteamine bitartrate pretreatment did not improve complex IV deficiency, ATP deficiency, or increased tissue lactate but did reduce oxidative stress and restore glutathione balance in surf1-/- animals. Overall, two novel surf1-/- zebrafish models recapitulate the gross neurodegenerative and biochemical hallmarks of LS, including azide stressor hypersensitivity that was associated with glutathione deficiency and ameliorated by cysteamine bitartrate or N-acetylcysteine therapy.

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.

Spectral domain optical coherence tomography-based retinochoroidal cystine crystal score: a window into infantile nephropathic cystinosis

PRÉCIS: Cystinosis is a lysosomal storage disease leading to an accumulation of cystine crystals in several organs. We aim to comprehensively describe chorioretinal cystine crystals via spectral domain optical coherence tomography (SD-OCT) and elaborate a new biomarker for systemic disease control.

BACKGROUND/AIMS

Cystinosis is a rare lysosomal storage disease leading to an accumulation of cystine crystals in several organs. This study aims to describe the deposition of retinochoroidal crystals in infantile nephropathic cystinosis and to elucidate their potential value as an objective biomarker for systemic disease control.

METHODS

This cross-sectional study was carried out by the University Eye Hospital of the Ludwig-Maximilian University (Munich, Germany) in collaboration with the German Cystinosis Study Group. A complete ophthalmologic examination was performed, along with posterior segment SD-OCT (Spectralis; Heidelberg Engineering GmbH, Heidelberg, Germany). Retinochoroidal crystals were graded by employing a novel semiquantitative grading system-the retinochoroidal cystine crystal score (RCCCS). To quantify quality of vision, patients completed a specific questionnaire. A total of 85 eyes of 43 patients with cystinosis were included (mean age 22.3±8.8 years, range 6-39; male:female ratio=23:20).

RESULTS

Cystine crystals were detectable in all neuroretinal layers and the choroid, most frequently in the choriocapillaris. The RCCCS was negatively correlated with cysteamine intake (r=0.533, p=0.001) and positively with cystatin C, a stable parameter of renal function (r=0.496, p=0.016). Moreover, the value of the RCCCS affected subjective quality of vision. Genetic analysis indicated pronounced crystal deposition in patients with heterozygous mutations containing the 57-kb-deletion allele of the CTNS gene.

CONCLUSION

Ocular cystinosis leads to retinochoroidal crystal accumulation in every stage of the disease. Crystal deposition may be markedly influenced by oral cysteamine therapy. Therefore, the presented SD-OCT based grading system might serve as an objective biomarker for systemic disease control.

SLC7A14 imports GABA to lysosomes and impairs hepatic insulin sensitivity via inhibiting mTORC2

Lysosomal amino acid accumulation is implicated in several diseases, but its role in insulin resistance, the central mechanism to type 2 diabetes and many metabolic diseases, is unclear. In this study, we show the hepatic expression of lysosomal membrane protein solute carrier family 7 member 14 (SLC7A14) is increased in insulin-resistant mice. The promoting effect of SLC7A14 on insulin resistance is demonstrated by loss- and gain-of-function experiments. SLC7A14 is further demonstrated as a transporter resulting in the accumulation of lysosomal γ-aminobutyric acid (GABA), which induces insulin resistance via inhibiting mTOR complex 2 (mTORC2)'s activity. These results establish a causal link between lysosomal amino acids and insulin resistance and suggest that SLC7A14 inhibition may provide a therapeutic strategy in treating insulin resistance-related and GABA-related diseases and may provide insights into the upstream mechanisms for mTORC2, the master regulator in many important processes.

In vitro activity of cysteamine against SARS-CoV-2 variants

Global COVID-19 pandemic is caused by infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Continuous emergence of new variants and their rapid spread are jeopardizing vaccine countermeasures to a significant extent. While currently available vaccines are effective at preventing illness associated with SARS-CoV-2 infection, these have been shown to be less effective at preventing breakthrough infection and transmission from a vaccinated individual to others. Here we demonstrate broad antiviral activity of cysteamine HCl in vitro against major emergent infectious variants of SARS-CoV-2 in a highly permissible Vero cell line. Cysteamine HCl inhibited infection of wild type, alpha, beta, gamma, delta, lambda, and omicron variants effectively. Cysteamine is a very well-tolerated US FDA-approved drug used chronically as a topical ophthalmic solution to treat ocular cystinosis in patients who receive it hourly or QID lifelong at concentrations 6 times higher than that required to inhibit SARS CoV-2 in tissue culture. Application of cysteamine as a topical nasal treatment can potentially1) mitigate existing infection 2) prevent infection in exposed individuals, and 3) limit the contagion in vulnerable populations.

Relationship between age at initiation of cysteamine treatment, adherence with therapy, and glomerular kidney function in infantile nephropathic cystinosis

Infantile nephropathic cystinosis, due to impaired transport of cystine out of lysosomes, occurs with an incidence of 1 in 100-200,000 live births. It is characterized by renal Fanconi syndrome in the first year of life and glomerular dysfunction progression to end-stage kidney disease by approximately 10 years of age. Treatment with oral cysteamine therapy helps preserve glomerular function, but affected individuals eventually require kidney replacement therapy. This is because glomerular damage had already occurred by the time a child is diagnosed with cystinosis, typically in the second year of life. We performed a retrospective multicenter study to investigate the impact of initiating cysteamine treatment within the first 2 months of life in some infants and comparing two different levels of adherence in patients diagnosed at the typical age. We collected 3983 data points from 55 patients born between 1997 and 2020; 52 patients with 1592 data points could be further evaluated. These data were first analyzed by dividing the patient cohort into three groups: (i) standard treatment start with good adherence, (ii) standard treatment start with less good adherence, and (iii) early treatment start. At every age, mean estimated glomerular filtration rate (eGFR) was higher in early-treated patients than in later-treated patients. Second, a generalized additive mixed model (GAMM) was applied showing that patients with initiation of treatment before 2 months of age are expected to have a 34 ml/min/1.73 m² higher eGFR than patients with later treatment start while controlling for adherence and patients' age. These data strongly suggest that oral cysteamine treatment initiated within 2 months of birth preserves kidney function in infantile nephropathic cystinosis and provide evidence of the utility of newborn screening for this disease.

Beneficial effects of starting oral cysteamine treatment in the first 2 months of life on glomerular and tubular kidney function in infantile nephropathic cystinosis

Nephropathic cystinosis is a rare lysosomal storage disease whose basic defect, impaired transport of cystine out of lysosomes, results in intracellular cystine storage. Affected individuals exhibit renal Fanconi Syndrome in infancy, end-stage kidney disease at approximately 10 years of age, and many other systemic complications. Oral cysteamine therapy mitigates the detrimental effects on glomerular function and prevents most of the late complications of the disease but has not shown benefit with respect to the early tubular damage of cystinosis. This is because cystinosis is generally diagnosed in the second year of life, after the damage to kidney tubular function has already occurred. We longitudinally evaluated 6 infants diagnosed and treated with cysteamine from before 2 months of age. The 4 infants with good compliance with cysteamine and consistently low leucocyte cystine levels maintained normal eGFR values, exhibited only minor degrees of renal Fanconi Syndrome, and maintained normal serum levels of potassium, bicarbonate, phosphate, and calcium without electrolyte or mineral supplementation through 2, 4, 10 and 16 years of age. Thus, renal Fanconi syndrome can be attenuated by early administration of cysteamine and renew the call for molecular-based newborn screening for cystinosis.

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.

Neuromuscular conditions and the impact of cystine-depleting therapy in infantile nephropathic cystinosis: A cross-sectional analysis of 55 patients

Infantile nephropathic cystinosis (INC) is a rare lysosomal storage disease caused by biallelic mutations in the cystinosin gene, leading to cystine accumulation in various organs. The aim of this cross-sectional study was to investigate neuromuscular complications in a cohort of 55 patients (aged 2.8-41.3 years, median 18.5 years) with INC. Clinical examination, jumping mechanography, clinical neurophysiology, and muscle/nerve ultrasound were performed. Physical performance, measured by mechanography, was below average in all patients. However, this reduction in physical performance was not always detected by conventional muscle power assessment. Twenty-eight percent of patients had mostly mild axial weakness of the neck flexors and/or of the abdominal rectus muscles, the latter often presenting during childhood. One adult patient had generalized muscle weakness. Two patients had evidence of specific neuromuscular conditions, which may not have been directly related to cystinosis. 30% of patients presented with mild, 7% with moderate, and 5% with severe weakness of the intrinsic muscles of the hand. Muscle wasting was more pronounced in the older cystinosis patients with multiple organ complications. Sonographic increase in muscle echogenicity corresponded only with severe weakness. Electromyography of the intrinsic hand muscles, performed in selected patients, showed myopathic, neurogenic, or mixed myopathic-neurogenic abnormalities. A particularly important finding of this study is that the neuromuscular complications were largely independent from both the age of initiation of pharmacological cystine-depleting therapy and from adherence to treatment. Significant correlation was observed between better physical performance in jumping and cysteine levels in leukocytes.

Programmed Cell Death in Cystinosis

Cystinosis is a lethal autosomal recessive disease that has been known clinically for over 100 years. There are now specific treatments including dialysis, renal transplantation and the orphan drug, cysteamine, which greatly improve the duration and quality of patient life, however, the cellular mechanisms responsible for the phenotype are unknown. One cause, programmed cell death, is clearly involved. Study of extant literature via Pubmed on “programmed cell death” and “apoptosis” forms the basis of this review. Most of such studies involved apoptosis. Numerous model systems and affected tissues in cystinosis have shown an increased rate of apoptosis that can be partially reversed with cysteamine. Proposed mechanisms have included changes in protein signaling pathways, autophagy, gene expression programs, and oxidative stress.

In Vitro and In Vivo Models to Study Nephropathic Cystinosis

The development over the past 50 years of a variety of cell lines and animal models has provided valuable tools to understand the pathophysiology of nephropathic cystinosis. Primary cultures from patient biopsies have been instrumental in determining the primary cause of cystine accumulation in the lysosomes. Immortalised cell lines have been established using different gene constructs and have revealed a wealth of knowledge concerning the molecular mechanisms that underlie cystinosis. More recently, the generation of induced pluripotent stem cells, kidney organoids and tubuloids have helped bridge the gap between in vitro and in vivo model systems. The development of genetically modified mice and rats have made it possible to explore the cystinotic phenotype in an in vivo setting. All of these models have helped shape our understanding of cystinosis and have led to the conclusion that cystine accumulation is not the only pathology that needs targeting in this multisystemic disease. This review provides an overview of the in vitro and in vivo models available to study cystinosis, how well they recapitulate the disease phenotype, and their limitations.

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.

An international cohort study spanning five decades assessed outcomes of nephropathic cystinosis

Nephropathic cystinosis is a rare disease secondary to recessive mutations of the CTNS gene encoding the lysosomal cystine transporter cystinosin, causing accumulation of cystine in multiple organs. Over the years, the disease has evolved from being a fatal condition during early childhood into a treatable condition, with patients surviving into adulthood. Data on cystinosis are limited by the rarity of the disease. Here, we have investigated factors associated with kidney and growth outcome in a very large cohort of 453 patients born between 1964 and 2016 and followed in Belgium, Germany, Austria, France, Italy, Spain, The Netherlands, Turkey and United Kingdom. From the 1970s to the 1990s, the median increase in kidney survival was 9.1 years. During these years, cysteamine, a cystine-depleting agent, was introduced for the treatment of cystinosis. Significant risk factors associated with early progression to end-stage kidney disease assessed by Cox proportional multivariable analysis included delayed initiation of cysteamine therapy and higher mean leucocyte cystine levels. No significant effect on kidney function was observed for gender, pathogenic variant of the CTNS gene, and the prescription of indomethacin or renin angiotensin system blockers. Significantly improved linear growth was associated with early use of cysteamine and lower leukocyte cystine levels. Thus, our study provides strong evidence in favor of early diagnosis and optimization of cystine depletion therapy in nephropathic cystinosis.

Nephropathic cystinosis: an update on genetic conditioning

Cystinosis is an autosomal recessive lysosomal storage disorder caused by CTNS gene mutations. The CTNS gene encodes the protein cystinosin, which transports free cystine from lysosomes to cytoplasm. In cases of cystinosin deficiency, free cystine accumulates in lysosomes and forms toxic crystals that lead to tissue and organ damage. Since CTNS gene mutations were first described, many variations have been identified that vary according to geographic region, although the phenotype remains the same. Cystinosis is a hereditary disease that can be treated with the cystine-depleting agent cysteamine. Cysteamine slows organ deterioration, but cannot treat renal Fanconi syndrome or prevent eventual kidney failure; therefore, novel treatment modalities for cystinosis are of great interest to researchers. The present review aims to highlight the geographic differences in cystinosis-specifically in terms of its genetic aspects, clinical features, management, and long-term complications.

Testicular function in males with infantile nephropathic cystinosis

STUDY QUESTION

Do males with the rare lysosomal storage disease infantile nephropathic cystinosis (INC) have a chance of biological fatherhood?

SUMMARY ANSWER

Cryostorage of semen could be an option for approximately 20% of young males with INC, with surgical sperm retrieval from the centre of the testes providing additional opportunities for fatherhood.

WHAT IS KNOWN ALREADY

Biallelic mutations in the cystinosin (CTNS) gene in INC cause dysfunction in cystine transport across lysosomal membranes and cystine accumulation throughout the body. Spontaneous paternity in cystinosis has not been described, despite the availability of cysteamine treatment. Azoospermia has been diagnosed in small case series of males with INC. ART using ICSI requires few spermatozoa, either from semen or extracted surgically from the testes of azoospermic men. However, there is limited evidence to suggest this could be successful in INC.

STUDY DESIGN, SIZE, DURATION

In this prospective cohort study performed between 2018 and 2019, we performed a cross-sectional investigation of 18 male patients with INC to delineate endocrine and spermatogenic testicular function.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Serum hormone levels, semen samples (according to World Health Organization 2010 standards), and testicular ultrasound images were analysed in 18 male patients aged 15.4–40.5 years. Surgical sperm extraction was performed in two, and their testicular biopsies were investigated by light and electron microscopy. Past adherence to cysteamine treatment was assessed from medical record information, using a composite scoring system.

MAIN RESULTS AND THE ROLE OF CHANCE

Adherence to cysteamine treatment was high in most patients. Testicular volumes and testosterone levels were in the normal ranges, with the exception of two and three older patients, respectively. Serum LH levels were above the normal range in all subjects aged ≥20 years. FSH levels were elevated in all but four males: three with spermatozoa in semen and one adolescent. Inhibin B levels were shown to be lower in older men. Testicular ultrasound revealed signs of obstruction in 67% of patients. Reduced fructose and zinc seminal markers were found in 33%, including two patients with azoospermia who underwent successful surgical sperm retrieval. Histology identified fully preserved spermatogenesis in the centre of their testes, but also tubular atrophy and lysosomal overload in Sertoli and Leydig cells of the testicular periphery.

LIMITATIONS, REASONS FOR CAUTION

Limitations of this study are the small number of assessed patients and the heterogeneity of their dysfunction in cystine transport across lysosomal membranes.

WIDER IMPLICATIONS OF THE FINDINGS

This study suggests that testicular degeneration in cystinosis results from the lysosomal overload of Sertoli and Leydig cells of the testicular periphery, and that this can possibly be delayed, but not prevented, by good adherence to cysteamine treatment. Endocrine testicular function in INC may remain compensated until the fourth decade of life; however, azoospermia may occur during adolescence. Cryostorage of semen could be an option for approximately 20% of young males with INC, with surgical sperm retrieval providing additional opportunities for biological fatherhood.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the Cystinosis Foundation Germany. The authors have no competing interests to declare.

TRIAL REGISTRATION NUMBER

n/a.

Genetic burden linked to founder effects in Saguenay-Lac-Saint-Jean illustrates the importance of genetic screening test availability

The Saguenay–Lac-Saint-Jean (SLSJ) region located in the province of Quebec was settled in the 19th century by pioneers issued from successive migration waves starting in France in the 17th century and continuing within Quebec until the beginning of the 20th century. The genetic structure of the SLSJ population is considered to be the product of a triple founder effect and is characterised by a higher prevalence of some rare genetic diseases. Several studies were performed to elucidate the historical, demographic and genetic background of current SLSJ inhabitants to assess the origins of these rare disorders and their distribution in the population. Thanks to the development of new sequencing technologies, the genes and the variants responsible for the most prevalent conditions were identified. Combined with other resources such as the BALSAC population database, identifying the causal genes and the pathogenic variants allowed to assess the impacts of some of these founder mutations on the population health and to design precision medicine public health strategies based on carrier testing. Furthermore, it stimulated the establishment of many public programmes.

We report here a review and an update of a subset of inherited disorders and founder mutations in the SLSJ region. Data were collected from published scientific sources. This work expands the knowledge about the current frequencies of these rare disorders, the frequencies of other rare genetic diseases in this population, the relevance of the carrier tests offered to the population, as well as the current available treatments and research about future therapeutic avenues for these inherited disorders.

A lysosome-targeted near-infrared fluorescent probe for imaging endogenous cysteine (Cys) in living cells

Cysteine (Cys) is one of the most important essential biothiols in lysosomes. Highly selective probes for specific detection and imaging of lysosomal Cys over other biological thiols are rare. Herein, we developed a lysosome-targeted near-infrared fluorescent probe SHCy-C based on a novel NIR-emitting thioxanthene-indolium dye. Due to the turn-on fluorescence response elicited by the intramolecular charge transfer (ICT) processes before and after the reaction with Cys, probe SHCy-C exhibits high selectivity and sensitivity (16 nM) for the detection of Cys. More importantly, probe SHCy-C is found to precisely target lysosomes and achieves the "turn-on" detection and imaging of endogenous Cys in lysosomes.

Establishing an objective biomarker for corneal cystinosis using a threshold-based Spectral domain optical coherence tomography imaging algorithm

PURPOSE

The purpose of the present study was to establish a semi-automated threshold-based image segmentation algorithm to detect and objectively quantify corneal cystine crystal deposition in ocular cystinosis with anterior segment optical coherence tomography (AS-OCT).

METHODS

This prospective, observational, comparative study included 88 eyes of 45 patients from the German Cystinosis Registry Study as well as 68 eyes of 35 healthy control subjects. All eyes were imaged with AS-OCT (Cirrus HD-OCT 5000, Carl Zeiss Meditec AG, Jena, Germany). As an initial step, B-scan images were subjectively analysed for typical changes in morphology in comparison to healthy controls. Based on the experience gained, an objective semi-automated B-scan image segmentation algorithm was developed using a grey scale value-based threshold method to automatically quantify corneal crystals.

RESULTS

On AS-OCT B-scans, corneal crystals appeared as hyperreflective deposits within the corneal stroma. The crystals were distributed either in all stromal layers (43 eyes, 49%) or confined to the anterior (23 eyes, 26%) or posterior stroma (22 eyes, 25%), respectively. The novel automatic B-scan image segmentation algorithm was most efficient in delineating corneal crystals at higher grey scale thresholds (e.g. 226 of a maximum of 255). Significant differences in suprathreshold grey scale pixels were observable between cystinosis patients and healthy controls (p < 0.001). In addition, the algorithm was able to detect an age-dependent depth distribution profile of crystal deposition.

CONCLUSION

Objective quantification of corneal cystine crystal deposition is feasible with AS-OCT and can serve as a novel biomarker for ocular disease control and topical treatment monitoring.

Adherence to cysteamine in nephropathic cystinosis: A unique electronic monitoring experience for a better understanding. A prospective cohort study: CrYSTobs

INTRODUCTION

In nephropathic cystinosis (NC), adherence to cysteamine remains challenging; poor adherence is worsening the disease progression with a decline of kidney function and increase of extrarenal morbidities. Our objective was to describe adherence to cysteamine in NC patients, using electronic monitoring systems.

METHODS

Patients with confirmed NC, aged > 4 years and receiving oral cysteamine (short acting or delayed release formulation as standard of care) from 3 French reference centers, were included. Adherence to treatment was primarily assessed as the percentage of days with a good adherence score, adherence score rating from 0 (poor) to 2 (good). A descriptive analysis was performed after 1-year follow-up.

RESULTS

Seventeen patients (10 girls, median age: 13.9 (5.4-33.0) years) were included. Median age at diagnosis was 17.0 (3.0-76.9) months and age at start of cysteamine was 21.0 (15.5-116.3) months. Median daily dose of cysteamine was 1.05 (0.55-1.63) g/m²/day. Over the year, the median percentage of days with a good adherence score was 80 (1-99)% decreasing to 68 (1-99)% in patients > 11 years old. The median of average number of hours covered by treatment in a day was 22.5 (6.1-23.9) versus 14.9 (9.2-20.5) hours for delayed release versus short acting cysteamine.

CONCLUSION

Our data are the first describing a rather good adherence to cysteamine, decreasing in adolescents and adults. We described a potential interest of the delayed release formulation. Our data highlight the need for a multidisciplinary approach including therapeutic education and individualized approaches in NC patients transitioning to adulthood. Graphical abstract.

Novel Fanconi renotubular syndromes provide insights in proximal tubule pathophysiology

The various forms of Fanconi renotubular syndromes (FRTS) offer significant challenges for clinicians and present unique opportunities for scientists who study proximal tubule physiology. This review will describe the clinical characteristics, genetic underpinnings, and underlying pathophysiology of the major forms of FRST. Although the classic forms of FRTS will be presented (e.g., Dent disease or Lowe syndrome), particular attention will be paid to five of the most recently discovered FRTS subtypes caused by mutations in the genes encoding for L-arginine:glycine amidinotransferase (GATM), solute carrier family 34 (type Ii sodium/phosphate cotransporter), member 1 (SLC34A1), enoyl-CoAhydratase/3-hydroxyacyl CoA dehydrogenase (EHHADH), hepatocyte nuclear factor 4A (HNF4A), or NADH dehydrogenase complex I, assembly factor 6 (NDUFAF6). We will explore how mutations in these genes revealed unexpected mechanisms that led to compromised proximal tubule functions. We will also describe the inherent challenges associated with gene discovery studies based on findings derived from small, single-family studies by focusing the story of FRTS type 2 (SLC34A1). Finally, we will explain how extensive alternative splicing of HNF4A has resulted in confusion with mutation nomenclature for FRTS type 4.

MFSD12 mediates the import of cysteine into melanosomes and lysosomes

Dozens of genes contribute to the wide variation in human pigmentation. Many of these genes encode proteins that localize to the melanosome-the organelle, related to the lysosome, that synthesizes pigment-but have unclear functions1,2. Here we describe MelanoIP, a method for rapidly isolating melanosomes and profiling their labile metabolite contents. We use this method to study MFSD12, a transmembrane protein of unknown molecular function that, when suppressed, causes darker pigmentation in mice and humans3,4. We find that MFSD12 is required to maintain normal levels of cystine-the oxidized dimer of cysteine-in melanosomes, and to produce cysteinyldopas, the precursors of pheomelanin synthesis made in melanosomes via cysteine oxidation5,6. Tracing and biochemical analyses show that MFSD12 is necessary for the import of cysteine into melanosomes and, in non-pigmented cells, lysosomes. Indeed, loss of MFSD12 reduced the accumulation of cystine in lysosomes of fibroblasts from patients with cystinosis, a lysosomal-storage disease caused by inactivation of the lysosomal cystine exporter cystinosin7-9. Thus, MFSD12 is an essential component of the cysteine importer for melanosomes and lysosomes.

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.

Inherited disorders of lysosomal membrane transporters

Disorders caused by defects in lysosomal membrane transporters form a distinct subgroup of lysosomal storage disorders (LSDs). To date, defects in only 10 lysosomal membrane transporters have been associated with inherited disorders. The clinical presentations of these diseases resemble the phenotypes of other LSDs; they are heterogeneous and often present in children with neurodegenerative manifestations. However, for pathomechanistic and therapeutic studies, lysosomal membrane transport defects should be distinguished from LSDs caused by defective hydrolytic enzymes. The involved proteins differ in function, localization, and lysosomal targeting, and the diseases themselves differ in their stored material and therapeutic approaches. We provide an overview of the small group of disorders of lysosomal membrane transporters, emphasizing discovery, pathomechanism, clinical features, diagnostic methods and therapeutic aspects. We discuss common aspects of lysosomal membrane transporter defects that can provide the basis for preclinical research into these disorders.

Clinical trial readiness study of distal myopathy and dysphagia in nephropathic cystinosis

BACKGROUND

Nephropathic cystinosis is a lysosomal storage disorder with late-onset systemic complications, such as myopathy and dysphagia. Currently employed outcome measures lack sensitivity and responsiveness for dysphagia and myopathy, a limitation to clinical trial readiness.

METHODS

We evaluated 20 patients with nephropathic cystinosis in two visits over the course of a year to identify outcomes sensitive to detect changes over time. Patients also underwent an expiratory muscle strength training program to assess any effects on aspiration and dysphagia.

RESULTS

There were significant differences in the Timed Up and Go Test (TUG) and Timed 25-Foot Walk (25-FW) between baseline and 1-y follow-up (P < .05). Maximum expiratory pressure (MEP) and peak cough flow (PCF) significantly improved following respiratory training (P < .05).

CONCLUSIONS

Improved respiratory outcomes may enhance patients ability to expel aspirated material from the airway, stave off pulmonary sequelae associated with chronic aspiration, and yield an overall improvement in physical health and well-being.

PQLC2 recruits the C9orf72 complex to lysosomes in response to cationic amino acid starvation

This study reveals that PQLC2, a lysosomal transporter of cationic amino acids, coordinates cellular responses to cationic amino acid availability via the regulated recruitment of a heterotrimeric protein complex containing C9orf72, SMCR8, and WDR41 to the surface of lysosomes.

The C9orf72 protein is required for normal lysosome function. In support of such functions, C9orf72 forms a heterotrimeric complex with SMCR8 and WDR41 that is recruited to lysosomes when amino acids are scarce. These properties raise questions about the identity of the lysosomal binding partner of the C9orf72 complex and the amino acid–sensing mechanism that regulates C9orf72 complex abundance on lysosomes. We now demonstrate that an interaction with the lysosomal cationic amino acid transporter PQLC2 mediates C9orf72 complex recruitment to lysosomes. This is achieved through an interaction between PQLC2 and WDR41. The interaction between PQLC2 and the C9orf72 complex is negatively regulated by arginine, lysine, and histidine, the amino acids that PQLC2 transports across the membrane of lysosomes. These results define a new role for PQLC2 in the regulated recruitment of the C9orf72 complex to lysosomes and reveal a novel mechanism that allows cells to sense and respond to changes in the availability of cationic amino acids within lysosomes.

Regulation of TFEB activity and its potential as a therapeutic target against kidney diseases

The transcription factor EB (TFEB) regulates the expression of target genes bearing the Coordinated Lysosomal Expression and Regulation (CLEAR) motif, thereby modulating autophagy and lysosomal biogenesis. Furthermore, TFEB can bind to the promoter of autophagy-associated genes and induce the formation of autophagosomes, autophagosome-lysosome fusion, and lysosomal cargo degradation. An increasing number of studies have shown that TFEB stimulates the intracellular clearance of pathogenic factors by enhancing autophagy and lysosomal function in multiple kidney diseases, such as cystinosis, acute kidney injury, and diabetic nephropathy. Taken together, this highlights the importance of developing novel therapeutic strategies against kidney diseases based on TFEB regulation. In this review, we present an overview of the current data on TFEB and its implication in kidney disease.

The novel aminoglycoside, ELX-02, permits CTNSW138X translational read-through and restores lysosomal cystine efflux in cystinosis

Background

Cystinosis is a rare disorder caused by recessive mutations of the CTNS gene. Current therapy decreases cystine accumulation, thus slowing organ deterioration without reversing renal Fanconi syndrome or preventing eventual need for a kidney transplant.15-20% of cystinosis patients harbour at least one nonsense mutation in CTNS, leading to premature end of translation of the transcript. Aminoglycosides have been shown to permit translational read-through but have high toxicity level, especially in the kidney and inner ear. ELX-02, a modified aminoglycoside, retains it read-through ability without the toxicity.

Methods and findings

We ascertained the toxicity of ELX-02 in cells and in mice as well as the effect of ELX-02 on translational read-through of nonsense mutations in cystinotic mice and human cells. ELX-02 was not toxic in vitro or in vivo, and permitted read-through of nonsense mutations in cystinotic mice and human cells.

Conclusions

ELX-02 has translational read-through activity and produces a functional CTNS protein, as evidenced by reduced cystine accumulation. This reduction is comparable to cysteamine treatment. ELX-02 accumulates in the kidney but neither cytotoxicity nor nephrotoxicity was observed.

Molecular based newborn screening in Germany: Follow-up for cystinosis

BACKGROUND

Newborn screening (NBS) programs for treatable metabolic disorders have been enormously successful, but molecular-based screening has not been broadly implemented so far.

METHODS

This prospective pilot study was performed within the German NBS framework. DNA, extracted from dried blood cards was collected as part of the regular NBS program. As cystinosis has a prevalence of only 1:100,000-1:200,000, a molecular genetic assay for detection of the SMN1 gene mutation with a higher prevalence was also included in the screening process, a genetic defect that leads to spinal muscular atrophy (SMA). First tier multiplex PCR was employed for both diseases. The cystinosis screening employed assays for the three most common CTNS mutations covering 75% of German patients; in case of heterozygosity for one of these mutations, samples were screened by next generation sequencing (NGS) of the CTNS exons for 101 CTNS mutations. A detection rate of 98.5% is predicted using this approach.

RESULTS

Between January 15, 2018 and May 31, 2019, 257,734 newborns were screened in Germany for cystinosis. One neonate was diagnosed with cystinosis, consistent with the known incidence of the disease. No false positive or false negatives were detected so far. Screening, communication of findings to parents, and confirmation of diagnosis were accomplished in a multi-disciplinary setting. This program was accomplished with the cooperation of hospitals, physicians, and parents. In the neonate diagnosed with cystinosis, oral cysteamine treatment began on day 18. After 16 months of treatment the child has no clinical signs of renal tubular Fanconi syndrome.

CONCLUSIONS

This pilot study demonstrates the efficacy of a molecular-based neonatal screening program for cystinosis using an existing national screening framework.

Clinical myopathy in patients with nephropathic cystinosis

BACKGROUND

Nephropathic cystinosis is a lysosomal storage disorder. Patient survival years after renal transplantation has revealed systemic complications including distal myopathy and dysphagia.

METHODS

We evaluated 20 adult patients with nephropathic cystinosis using patient-reported and clinical outcome measures. Standard motor measures, video fluoroscopy swallow studies, and tests of respiratory function were performed. We also used Rasch analysis of an initial survey to design a 16-item survey focused on upper and lower extremity function, which was completed by 31 additional patients.

RESULTS

Distal myopathy and dysphagia were common in patients with nephropathic cystinosis. Muscle weakness ranges from mild involvement of intrinsic hand muscles to prominent distal greater than proximal weakness and contractures.

CONCLUSIONS

In addition to further characterization of underlying dysphagia and muscle weakness, we propose a new psychometrically devised, disease specific, functional outcome measures for distal myopathy in patients with nephropathic cystinosis.

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.

A 57 kB Genomic Deletion Causing CTNS Loss of Function Contributes to the CTNS Mutational Spectrum in the Middle East

Background: Nephropathic Cystinosis, the most common cause of renal Fanconi syndrome, is a lysosomal transport disorder with an autosomal recessive inheritance pattern. A large number of mutations in CTNS have been identified as causative to date. A 57 kb deletion encompassing parts of CTNS is most commonly identified in Caucasians but this allele has not been identified in individuals of Eastern Mediterranean, Middle Eastern, Persian, or Arab origin to date. Methods and Results: Implementing whole exome sequencing (WES) in a consanguineous Iranian family, we identified this large deletion affecting CTNS in a patient initially presenting with hypokalemic metabolic alkalosis symptoms and considerable proteinuria. Conclusion: We show WES is a cost and time efficient genetic diagnostics modality to identify the underlying molecular pathology in Cystinosis individuals and provide a summary of all previously reported CTNS alleles in the Middle east population. Our work also highlights the importance to consider the 57-kb deletion as underlying genetic cause in non-European populations, including the Middle East. Limited diagnostic modalities for Cystinosis in developing countries could account for the lack of previously reported cases in these populations carrying this allele. Further, our findings emphasize the utility of WES to define genetic causes in clinically poorly defined phenotypes and demonstrate the requirement of Copy number variation (CNV) analysis of WES data.

Controlled etching and tapering of Au nanorods using cysteamine

While gold nanorods (AuNRs) have found many applications due to their unique optical properties, a few challenges persist in their synthesis. Namely, it is often difficult to reproducibly synthesize AuNRs with specific and monodisperse sizes, especially at shorter aspect ratios. Here, we report a method of post-synthesis precise tailoring of AuNRs by etching with cysteamine. Cysteamine selectively etches AuNRs from their ends while preserving the initial rod shape and monodispersity, making this a viable means of obtaining highly monodisperse short AuNRs down to aspect ratio 2.3. Further, we explore the effect of this etching method on two types of silica-coated AuNRs: silica side-coated and silica end-coated AuNRs. We find that the etching process is cysteamine concentration-dependent and can lead to different degrees of sharpening of the silica-coated AuNRs, forming elongated tips. We also find that cysteamine behaves only as a ligand at concentrations above 200 mM, as no etching of the AuNRs is observed in this condition. Simulations show that excitation of plasmon resonances in these sharpened AuNRs produces local electric fields twice as strong as those produced by conventional AuNRs. Thus, cysteamine etching of AuNRs is shown to be an effective means of tailoring both the size and shape of AuNRs along with their corresponding optical properties. At the same time, the resulting cysteamine coating on the etched AuNRs displays terminal amino groups that allow for further functionalization of the nanorods.

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.

Quantification of cystine in human renal proximal tubule cells using liquid chromatography-tandem mass spectrometry

Nephropathic cystinosis is characterized by abnormal intralysosomal accumulation of cystine throughout the body, causing irreversible damage to various organs, particularly the kidneys. Cysteamine, the currently available treatment, can reduce lysosomal cystine and postpone disease progression. However, cysteamine poses serious side effects and does not address all of the symptoms of cystinosis. To screen for new treatment options, a rapid and reliable high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was developed to quantify cystine in conditionally immortalized human proximal tubular epithelial cells (ciPTEC). The ciPTEC were treated with N-ethylmaleimide, lysed and deproteinized with 15% (w/v) sulfosalicylic acid. Subsequently, cystine was measured using deuterium-labeled cystine-D4, as the internal standard. The assay developed demonstrated linearity to at least 20 μmol/L with a good precision. Accuracies were between 97.3 and 102.9% for both cell extracts and whole cell samples. Cystine was sufficiently stable under all relevant analytical conditions. The assay was successfully applied to determine cystine levels in both healthy and cystinotic ciPTEC. Control cells showed clearly distinguishable cystine levels compared with cystinotic cells treated with or without cysteamine. The method developed provides a fast and reliable quantification of cystine, and is applicable to screen for potential drugs that could reverse cystinotic symptoms in human kidney cells.

Cysteamine hydrochloride eye drop solution for the treatment of corneal cystine crystal deposits in patients with cystinosis: an evidence-based review

Cystinosis is a rare, autosomal recessive disorder leading to defective transport of cystine out of lysosomes. Subsequent cystine crystal accumulation can occur in various tissues, including the ocular surface. This review explores the efficacy of cysteamine hydrochloride eye drops in the treatment of corneal cystine crystal accumulation and its safety profile.

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.

Effect of Storage Conditions on Stability of Ophthalmological Compounded Cysteamine Eye Drops

Cystinosis is a hereditary genetic disease that results in the accumulation of cystine crystals in the lysosomes, leading to many clinical manifestations. One of these manifestations is the formation of corneal cystine crystals, which can cause serious ocular complications. The only available drug to treat cystinosis is cysteamine, which breaks cystine and depletes its accumulation in the lysosomes. However, the oral form of cysteamine is not effective in treating corneal manifestations. Thus, ophthalmic solutions of cysteamine are applied. Because the commercial cysteamine eye drops are not available in most countries, hospital pharmacies are responsible for preparing "homemade" drops usually without a control of stability of cysteamine in different storage conditions. Hence, we aimed in this study to investigate the effect of different storage conditions on the stability of a cysteamine ophthalmic compounded solution. Cysteamine ophthalmic solution was prepared in the hospital pharmacy and sterilized using a candle filter. The preparations are then stored either in the freezer at -20°C or in the refrigerator at +4°C for up to 52 weeks. The amount of cysteamine hydrochloride in the preparation at different time points was determined using capillary electrophoresis (CE). Storage of the cysteamine ophthalmic preparations at +4° resulted in significant loss of free cysteamine at all time points, from 1 to 52 weeks of storage, when compared with storage in the freezer (-20°C). We demonstrate that cysteamine 0.5% compounded eye drops are easily oxidized within the first week after storage at +4°C, rendering the preparation less effective. Storage at -20°C is recommended to prevent this process.

In vitro drug release and in vivo safety of vitamin E and cysteamine loaded contact lenses

Cystinosis is an orphan disease caused by a genetic mutation that leads to deposition of cystine crystals in many organs including cornea. Ophthalmic manifestation of the disease can be treated with hourly instillation of cysteamine eye drops. The hourly eye drop instillation is tedious to the patients leading to poor compliance and additionally, significant degradation of the drug occurs within one week of opening the bottle, which further complicates this delivery approach. This paper focuses on designing a contact lens to treat the disease with improved efficacy compared to eye drops, and also exploring safety of the drug eluding contact lens in an animal model. Our goal is to design a lens that is safe and that can deliver a daily therapeutic dose of cysteamine to the cornea while retaining drug stability. We show that cysteamine diffuses out rapidly from all lenses due to its small size. Vitamin E incorporation increases the release duration of both ACUVUE^®OASYS^® and ACUVUE^® TruEye^TM but the effect is more pronounced in TruEye^TM likely due to the low solubility of vitamin E in the lens matrix and higher aspect ratio of the barriers. The barriers are not effective in hydrogel lenses, which along with the high aspect ratio in silicone hydrogels suggests that barriers could be forming at the interface of the silicone and hydrogel phases. The presence of vitamin E has an additional beneficial effect of reduction in the oxidation rates, likely due to a transport barrier between the oxygen diffusing through the silicone channels and drug located in the hydrogel phase. Based on this study, both Acuvue^®OASYS^® and ACUVUE^® TruEye^TM can be loaded with vitamin E to design a cysteamine eluting contact lenses for effective therapy of cystinosis. The lenses must be worn for about 4-5 hr. each day, which is less than the typical duration of daily-wear. The vitamin E and cysteamine loaded lenses did not exhibit any toxicity in a rabbit model over a period of 7-days.

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.