RARE DISEASE
Cystinuria type B
Cystinuria type B
Cystinuria type B
Drug discovery
0
drugs
With orphan designations
Overview
Cystinuria type B is an autosomal recessive (or incompletely dominant) genetic disorder caused by mutations in the SLC7A9 gene, impairing renal cystine reabsorption and leading to recurrent cystine kidney stones. Heterozygous carriers often exhibit elevated urinary cystine excretion and rare stone formation. Diagnosis involves genetic testing, urine chromatography, and stone analysis.
Key Information
Burden
Recurrent stones: >60% recurrence rate; 70% develop chronic kidney disease (CKD), with 5% progressing to end-stage kidney disease [1][9][11].
Morbidity: Frequent urologic interventions (e.g., PCNL, lithotripsy) and higher infection risk [14][19].
Sex disparity: Males often present earlier (<3 years) and with more aggressive disease [6][11].
Therapies
First-line: High fluid intake (>3 L/day), urinary alkalinization (target pH >7.0) with potassium citrate, and sodium/protein restriction [1][8][13].
Second-line: Thiol drugs (tiopronin preferred over D-penicillamine) to solubilize cystine [3][8][13].
Emerging options: α-lipoic acid and tolvaptan under investigation [3][13].
Categories: rare genetic diseases, rare inborn errors of metabolism, rare renal diseases, rare transplant-related disorders
Research Papers
86 drug discovery papers about Cystinuria type B, with 1 first-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
86 drug discovery papers about Cystinuria type B, with 1 first-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
categories:
Small molecules
small molecules
2025-08-29 | Association of Clinical Biochemists in Ireland Annual Conference
Cystinuria is an autosomal recessive metabolic disorder characterized by defective reabsorption of cystine and dibasic amino acids (lysine, arginine, and ornithine) in the proximal renal tubules and small intestine.The condition involves mutations in two key genes: SLC3A1 and SLC7A9.The SLC3A1 gene encodes the rBAT protein, while the SLC7A9 gene encodes the b0,+AT protein.Cystinuria is classified into three types based on genetic mutations: Type A (SLC3A1 defects), Type B (SLC7A9 defects), and Type AB (mutations in both genes).Cystinuria is characterised by persistently elevated levels of cystine in the urine, with or without urinary cystine stones formation.In contrast, transient neonatal cystinuria (TNC) is observed in newborns with initially high cystine levels that decrease over the first two years of life due to immature renal amino acid transport.Confirmatory diagnosis involves measuring urinary amino acid levels, with cystine typically exceeding 1000 mol/ g creatinine.In this report, we describe a case of TNC that developed in a 15-month-old boy who was born extremely premature at 24 weeks and 3 days gestation.Immediately after birth, he required intubation and mechanical ventilation due to respiratory distress and poor Apgar score.At 40 days old, the boy was re-admitted with a non-functioning ileostomy, necessitating a stoma revision and adhesion lysis.During this admission, he experienced multi-system dysfunction including eA240
2025-07-09 | A Case of Cystinuria With Compound Heterozygous Mutations Both in SLC3A1 and SLC7A9 Genes.
Cystinuria is an autosomal recessively inherited genetic disorder, and is typically classified into type A, caused by mutations in SLC3A1, or type B, caused by mutations in SLC7A9. While the predominance of the genotypes varies among countries, due to lack of a large scale cohort, the characterization of mutations in SLC3A1 or SLC7A9 is still limited in East Asia. A 61-year-old male patient admitted to the department of nephrology, with a chief complaint of fever, chillness and left flank pain for a week. The patient had a past history of recurrent urolithiasis, with a frequency of at least 1 to 2 times a year. Computed tomography visualized 1 cm-sized stone at distal ureter, which was removed by retrograde ureteroscopy. The stone analysis documented 100% of cystine, indicating an underlying genetic disorder, cystinuria. Whole genome sequencing from peripheral blood unveiled 3 heterozygous missense mutations in coding exons of SLC3A1 gene, and 2 heterozygous missense mutations in coding exons of SLC7A9 gene. We here report a case of cystinuria with compound heterozygous mutations both in SLC3A1 and SLC7A9 genes, with a total of 5 mutant alleles in a patient.
2023-12-11 | Acetazolamide and human carbonic anhydrases: retrospect, review and discussion of an intimate relationship
Acetazolamide (AZM) is a strong pharmacological sulphonamide-type (R-SO2-NH2, pKa 7.2) inhibitor of the activity of several carbonic anhydrase (CA) isoforms, notably of renal CA II (Ki, 12 nM) and CA IV (Ki, 74 nM). AZM is clinically used for about eighty years in various diseases including epilepsy and glaucoma. Pharmacological AZM increases temporarily the urinary excretion of bicarbonate (HCO3–) and sodium ions (Na+) and sustainably the urinary pH. AZM is excreted almost unchanged over several hours at high rates in the urine. Closely parallel concentrations of circulating and excretory AZM are observed upon administration of therapeutical doses of AZM. In a proof-of-principle study, we investigated the effects of the ingestion of a 250-mg AZM-containing tablet by a healthy volunteer on the urinary excretion of organic and inorganic substances over 5 h (range, 0, 0.5, 1, 1.5, 2, 3, 4, 5 h). Measured analytes included: AZM, amino acids and their metabolites such as guanidinoacetate, i.e. the precursor of creatine, of asymmetrically (ADMA) and symmetrically (SDMA) dimethylated arginine, nitrite (O = N-O–, pKa 3.4) and nitrate (O2N-O–, pKa −1.37), the major metabolites of nitric oxide (NO), the C-H acidic malondialdehyde (MDA; (CHO)2CH2, pKa 4.5), and creatinine for correction of analytes excretion. All analytes were measured by validated isotopologues using gas chromatography-mass spectrometry (GC-MS) methods. AZM excretion in the urine reached its maximum value after 2 h and was fairly stable for the next 3 h. Time series analysis by the ARIMA method was performed. AZM ingestion increased temporarily the urinary excretion of the amino acids Leu + Ile, nitrite and nitrate, decreased temporarily the urinary excretion of other amino acids. AZM decreased sustainably the urinary excretion of MDA, a biomarker of oxidative stress (i.e. lipid peroxidation). Whether this decrease is due to inhibition of the excretion of MDA or attenuation of oxidative stress by AZM is unknown. The acute and chronic effects of AZM on the urinary excretion of electrolytes and physiological substances reported in the literature are discussed in depth in the light of its extraordinary pharmacokinetics and pharmacodynamics. Tolerance development/drug resistance to AZM in chronic use and potential mechanisms are also addressed.
2023-11-13 | Pharmacological interventions for the management of cystinuria: a systematic review
Abstract Background Cystinuria is a rare genetic kidney stone disease, with no cure. Current treatments involve lowering urinary cystine levels and increasing cystine solubility. This systematic review evaluates the available literature regarding non-surgical interventions for cystinuria. Methods Key electronic databases were searched for studies that described the clinical management of cystinuria with high diuresis, alkalinizing agents and thiol-based drugs that were published between 2000 and 2022. Observational studies were included if they contained clinical investigation with at least one previous or current episode of cystine stones, urine cystine levels > 250 mg/L and patients being managed with urinary dilution, alkalinizing agents or other pharmacological agents. All included studies were assessed for study design, patient characteristics and outcomes. A qualitative and critical analysis was performed whereby study quality was assessed using Methodological Index for Non-Randomized Studies (MINORS). Two authors performed the quality assessment and excluded the studies with a low MINORS score. Results Fourteen studies met the review inclusion and quality criteria. Of the fourteen studies, two reported treatment using alkalinizing agents, six reported treatment using thiol-based drugs, and six reported combination treatment using alkalinizing agents and thiol-based drugs. These studies indicated that first-line therapies, including high fluid intake and urinary alkalinization, increased urine volume to > 3 L/day and urinary pH > 7.0, and were associated with reduced urinary cystine levels and cystine stone formation. Second-line therapy with cystine-binding thiol drugs, such as tiopronin and D-penicillamine, reduced urinary cystine levels, cystine crystal volume and increased cystine solubility, resulting in decreased cystine stone formation and stone recurrence rate. Further, combined intervention with alkalinizing agents and thiol-based drugs synergistically reduced stone recurrence. Conclusion Cystinuria treatment may require a combined approach of high diuresis, alkalinization and pharmacological interventions with regular monitoring of urinary pH, cystine levels, cystine crystal volume and solubility. However, poor adherence to treatment is relatively frequent, hence the pressing urgency for improved therapies and treatments. Graphical abstract
2023-07-07 | Realization of Amyloid-like Aggregation as a Common Cause for Pathogenesis in Diseases
Amyloids were conventionally referred to as extracellular and intracellular accumulation of Aβ42 peptide, which causes the formation of plaques and neurofibrillary tangles inside the brain leading to the pathogenesis in Alzheimer's disease. Subsequently, amyloid-like deposition was found in the etiology of prion diseases, Parkinson's disease, type II diabetes, and cancer, which was attributed to the aggregation of prion protein, α-Synuclein, islet amyloid polypeptide protein, and p53 protein, respectively. Hence, traditionally amyloids were considered aggregates formed exclusively by proteins or peptides. However, since the last decade, it has been discovered that other metabolites, like single amino acids, nucleobases, lipids, glucose derivatives, etc., have a propensity to form amyloid-like toxic assemblies. Several studies suggest direct implications of these metabolite assemblies in the patho-physiology of various inborn errors of metabolisms like phenylketonuria, tyrosinemia, cystinuria, and Gaucher's disease, to name a few. In this review, we present a comprehensive literature overview that suggests amyloid-like structure formation as a common phenomenon for disease progression and pathogenesis in multiple syndromes. The review is devoted to providing readers with a broad knowledge of the structure, mode of formation, propagation, and transmission of different extracellular amyloids and their implications in the pathogenesis of diseases. We strongly believe a review on this topic is urgently required to create awareness about the understanding of the fundamental molecular mechanism behind the origin of diseases from an amyloid perspective and possibly look for a common therapeutic strategy for the treatment of these maladies by designing generic amyloid inhibitors.
proteins
2022-05-19 | Ca2+-mediated higher-order assembly of heterodimers in amino acid transport system b0,+ biogenesis and cystinuria.
Cystinuria is a genetic disorder characterized by overexcretion of dibasic amino acids and cystine, causing recurrent kidney stones and kidney failure. Mutations of the regulatory glycoprotein rBAT and the amino acid transporter b0,+AT, which constitute system b0,+, are linked to type I and non-type I cystinuria respectively and they exhibit distinct phenotypes due to protein trafficking defects or catalytic inactivation. Here, using electron cryo-microscopy and biochemistry, we discover that Ca2+ mediates higher-order assembly of system b0,+. Ca2+ stabilizes the interface between two rBAT molecules, leading to super-dimerization of b0,+AT-rBAT, which in turn facilitates N-glycan maturation and protein trafficking. A cystinuria mutant T216M and mutations of the Ca2+ site of rBAT cause the loss of higher-order assemblies, resulting in protein trapping at the ER and the loss of function. These results provide the molecular basis of system b0,+ biogenesis and type I cystinuria and serve as a guide to develop new therapeutic strategies against it. More broadly, our findings reveal an unprecedented link between transporter oligomeric assembly and protein-trafficking diseases.
2021-05-07 | Ca2+-mediated higher-order assembly of b0,+AT–rBAT is a key step for system b0,+biogenesis and cystinuria
Abstract Cystinuria is a genetic disorder characterized by overexcretion of dibasic amino acids and cystine, which causes recurrent kidney stones and occasionally severe kidney failure. Mutations of the two responsible proteins, rBAT and b 0,+ AT, which comprise system b 0,+ , are linked to type I and non-type I cystinuria respectively and they exhibit distinct phenotypes due to protein trafficking defects or catalytic inactivation. Although recent structural insights into human b 0,+ AT–rBAT suggested a model for transport-inactivating mutations, the mechanisms by which type I mutations trigger trafficking deficiencies are not well understood. Here, using electron cryo-microscopy and biochemistry, we discover that Ca 2+ -mediated higher-order assembly of system b 0,+ is the key to its trafficking on the cell surface. We show that Ca 2+ stabilizes the interface between two rBAT molecules to mediate super-dimerization, and this in turn facilitates the N-glycan maturation of system b 0,+ . A common cystinuria mutant T216M and mutations that disrupt the Ca 2+ site in rBAT cause the loss of higher-order assemblies, resulting in protein trafficking deficiency. Mutations at the super-dimer interface reproduce the mis-trafficking phenotype, demonstrating that super-dimerization is essential for cellular function. Cell-based transport assays confirmed the importance of the Ca 2+ site and super-dimerization, and additionally suggested which residues are involved in cationic amino acid recognition. Taken together, our results provide the molecular basis of type I cystinuria and serve as a guide to develop new therapeutic strategies against it. More broadly, our findings reveal an unprecedented link between transporter oligomeric assembly and trafficking diseases in general.
2005-07-12 | Cystine and glutamate transport in renal epithelial cells transfected with human system x—c
Cystine and glutamate transport in renal epithelial cells transfected with human system x-c.BackgroundSystem x-c is a heterodimeric transporter, comprised of a light chain, xCT, and heavy chain, 4F2hc, which mediates the sodium-independent exchange of cystine and glutamate at the plasma membrane. In the current study we tested the hypothesis that stable transfection of Madin-Darby canine kidney (MDCK) cells with human xCT and 4F2hc results in the expression of functional system x-c.MethodsMDCK cells were transfected stably with human clones for xCT and 4F2hc. Analyses of time- and temperature-dependence, saturation kinetics, and substrate specificity of L-cystine and L-glutamate transport were carried out in control and xCT-4F2hc-transfected MDCK cells. We also measured the uptake of L-cystine inXenopus oocytes expressing human xCT and/or 4F2hc or xCT and/or rBAT (a heavy chain homologous to 4F2hc).ResultsAll of the different sets of data revealed that transport of L-cystine and L-glutamate increased significantly (twofold to threefold) in the MDCK cells subsequent to transfection with xCT-4F2hc. Moreover, uptake of L-cystine also increased (about tenfold) inXenopus oocytes expressing hxCT and h4F2hc. Biochemical analyses of L-cystine uptake in oocytes verified our findings in the transfected MDCK cells. Interestingly, in oocytes injected with rBAT with or without xCT, uptake of L-cystine was significantly greater than that in water-injected oocytes.ConclusionOur findings indicate that stable transfection of MDCK cells with xCT and 4F2hc results in a cell-line expressing a functional system x-c transporter that can utilize L-cystine and L-glutamate as substrates. This study apparently represents the first stable transfection of a mammalian cell line with system x-c. Cystine and glutamate transport in renal epithelial cells transfected with human system x-c. System x-c is a heterodimeric transporter, comprised of a light chain, xCT, and heavy chain, 4F2hc, which mediates the sodium-independent exchange of cystine and glutamate at the plasma membrane. In the current study we tested the hypothesis that stable transfection of Madin-Darby canine kidney (MDCK) cells with human xCT and 4F2hc results in the expression of functional system x-c. MDCK cells were transfected stably with human clones for xCT and 4F2hc. Analyses of time- and temperature-dependence, saturation kinetics, and substrate specificity of L-cystine and L-glutamate transport were carried out in control and xCT-4F2hc-transfected MDCK cells. We also measured the uptake of L-cystine inXenopus oocytes expressing human xCT and/or 4F2hc or xCT and/or rBAT (a heavy chain homologous to 4F2hc). All of the different sets of data revealed that transport of L-cystine and L-glutamate increased significantly (twofold to threefold) in the MDCK cells subsequent to transfection with xCT-4F2hc. Moreover, uptake of L-cystine also increased (about tenfold) inXenopus oocytes expressing hxCT and h4F2hc. Biochemical analyses of L-cystine uptake in oocytes verified our findings in the transfected MDCK cells. Interestingly, in oocytes injected with rBAT with or without xCT, uptake of L-cystine was significantly greater than that in water-injected oocytes. Our findings indicate that stable transfection of MDCK cells with xCT and 4F2hc results in a cell-line expressing a functional system x-c transporter that can utilize L-cystine and L-glutamate as substrates. This study apparently represents the first stable transfection of a mammalian cell line with system x-c.
2003-01-03 | Functional Cooperation of Epithelial Heteromeric Amino Acid Transporters Expressed in Madin-Darby Canine Kidney Cells
The heteromeric amino acid transporters b(0,+)AT-rBAT (apical), y(+)LAT1-4F2hc, and possibly LAT2-4F2hc (basolateral) participate to the (re)absorption of cationic and neutral amino acids in the small intestine and kidney proximal tubule. We show now by immunofluorescence that their expression levels follow the same axial gradient along the kidney proximal tubule (S1>S2S3). We reconstituted their co-expression in MDCK cell epithelia and verified their polarized localization by immunofluorescence. Expression of b(0,+)AT-rBAT alone led to a net reabsorption of l-Arg (given together with l-Leu). Coexpression of basolateral y(+)LAT1-4F2hc increased l-Arg reabsorption and reversed l-Leu transport from (re)absorption to secretion. Similarly, l-cystine was (re)absorbed when b(0,+)AT-rBAT was expressed alone. This net transport was further increased by the coexpression of 4F2hc, due to the mobilization of LAT2 (exogenous and/or endogenous) to the basolateral membrane. In summary, apical b(0,+)AT-rBAT cooperates with y(+)LAT1-4F2hc or LAT2-4F2hc for the transepithelial reabsorption of cationic amino acids and cystine, respectively. The fact that the reabsorption of l-Arg led to the secretion of l-Leu demonstrates that the implicated heteromeric amino acid transporters function in epithelia as exchangers coupled in series and supports the notion that the parallel activity of unidirectional neutral amino acid transporters is required to drive net amino acid reabsorption.
1999-10-01 | Cloning and Expression of a b0,+-like Amino Acid Transporter Functioning as a Heterodimer with 4F2hc Instead of rBAT
We have cloned a transporter protein from rabbit small intestine, which, when coexpressed with the 4F2 heavy chain (4F2hc) in mammalian cells, induces a b0,+-like amino acid transport activity. This protein (4F2-lc6 for the sixth member of the 4F2 light chain family) consists of 487 amino acids and has 12 putative transmembrane domains. At the level of amino acid sequence, 4F2-lc6 shows significant homology (44% identity) to the other five known members of the 4F2 light chain family, namely LAT1 (4F2-lc1), y+LAT1 (4F2-lc2), y+LAT2 (4F2-lc3), xCT (4F2-lc4), and LAT2 (4F2-lc5). The 4F2hc/4F2-lc6 complex-mediated transport process is Na+-independent and exhibits high affinity for neutral and cationic amino acids and cystine. These characteristics are similar to those of the b0,+-like amino acid transport activity previously shown to be associated with rBAT (protein related to b0,+ amino acid transport system). However, the newly cloned 4F2-lc6 does not interact with rBAT. This is the first report of the existence of a b0,+-like amino acid transport process that is independent of rBAT. 4F2-lc6 is expressed predominantly in the small intestine and kidney. Based on the characteristics of the transport process mediated by the 4F2hc/4F2-lc6 complex and the expression pattern of 4F2-lc6 in mammalian tissues, we suggest that 4F2-lc6 is a new candidate gene for cystinuria.
small molecules
2025-08-29 | Association of Clinical Biochemists in Ireland Annual Conference
Cystinuria is an autosomal recessive metabolic disorder characterized by defective reabsorption of cystine and dibasic amino acids (lysine, arginine, and ornithine) in the proximal renal tubules and small intestine.The condition involves mutations in two key genes: SLC3A1 and SLC7A9.The SLC3A1 gene encodes the rBAT protein, while the SLC7A9 gene encodes the b0,+AT protein.Cystinuria is classified into three types based on genetic mutations: Type A (SLC3A1 defects), Type B (SLC7A9 defects), and Type AB (mutations in both genes).Cystinuria is characterised by persistently elevated levels of cystine in the urine, with or without urinary cystine stones formation.In contrast, transient neonatal cystinuria (TNC) is observed in newborns with initially high cystine levels that decrease over the first two years of life due to immature renal amino acid transport.Confirmatory diagnosis involves measuring urinary amino acid levels, with cystine typically exceeding 1000 mol/ g creatinine.In this report, we describe a case of TNC that developed in a 15-month-old boy who was born extremely premature at 24 weeks and 3 days gestation.Immediately after birth, he required intubation and mechanical ventilation due to respiratory distress and poor Apgar score.At 40 days old, the boy was re-admitted with a non-functioning ileostomy, necessitating a stoma revision and adhesion lysis.During this admission, he experienced multi-system dysfunction including eA240
2025-07-09 | A Case of Cystinuria With Compound Heterozygous Mutations Both in SLC3A1 and SLC7A9 Genes.
Cystinuria is an autosomal recessively inherited genetic disorder, and is typically classified into type A, caused by mutations in SLC3A1, or type B, caused by mutations in SLC7A9. While the predominance of the genotypes varies among countries, due to lack of a large scale cohort, the characterization of mutations in SLC3A1 or SLC7A9 is still limited in East Asia. A 61-year-old male patient admitted to the department of nephrology, with a chief complaint of fever, chillness and left flank pain for a week. The patient had a past history of recurrent urolithiasis, with a frequency of at least 1 to 2 times a year. Computed tomography visualized 1 cm-sized stone at distal ureter, which was removed by retrograde ureteroscopy. The stone analysis documented 100% of cystine, indicating an underlying genetic disorder, cystinuria. Whole genome sequencing from peripheral blood unveiled 3 heterozygous missense mutations in coding exons of SLC3A1 gene, and 2 heterozygous missense mutations in coding exons of SLC7A9 gene. We here report a case of cystinuria with compound heterozygous mutations both in SLC3A1 and SLC7A9 genes, with a total of 5 mutant alleles in a patient.
2023-12-11 | Acetazolamide and human carbonic anhydrases: retrospect, review and discussion of an intimate relationship
Acetazolamide (AZM) is a strong pharmacological sulphonamide-type (R-SO2-NH2, pKa 7.2) inhibitor of the activity of several carbonic anhydrase (CA) isoforms, notably of renal CA II (Ki, 12 nM) and CA IV (Ki, 74 nM). AZM is clinically used for about eighty years in various diseases including epilepsy and glaucoma. Pharmacological AZM increases temporarily the urinary excretion of bicarbonate (HCO3–) and sodium ions (Na+) and sustainably the urinary pH. AZM is excreted almost unchanged over several hours at high rates in the urine. Closely parallel concentrations of circulating and excretory AZM are observed upon administration of therapeutical doses of AZM. In a proof-of-principle study, we investigated the effects of the ingestion of a 250-mg AZM-containing tablet by a healthy volunteer on the urinary excretion of organic and inorganic substances over 5 h (range, 0, 0.5, 1, 1.5, 2, 3, 4, 5 h). Measured analytes included: AZM, amino acids and their metabolites such as guanidinoacetate, i.e. the precursor of creatine, of asymmetrically (ADMA) and symmetrically (SDMA) dimethylated arginine, nitrite (O = N-O–, pKa 3.4) and nitrate (O2N-O–, pKa −1.37), the major metabolites of nitric oxide (NO), the C-H acidic malondialdehyde (MDA; (CHO)2CH2, pKa 4.5), and creatinine for correction of analytes excretion. All analytes were measured by validated isotopologues using gas chromatography-mass spectrometry (GC-MS) methods. AZM excretion in the urine reached its maximum value after 2 h and was fairly stable for the next 3 h. Time series analysis by the ARIMA method was performed. AZM ingestion increased temporarily the urinary excretion of the amino acids Leu + Ile, nitrite and nitrate, decreased temporarily the urinary excretion of other amino acids. AZM decreased sustainably the urinary excretion of MDA, a biomarker of oxidative stress (i.e. lipid peroxidation). Whether this decrease is due to inhibition of the excretion of MDA or attenuation of oxidative stress by AZM is unknown. The acute and chronic effects of AZM on the urinary excretion of electrolytes and physiological substances reported in the literature are discussed in depth in the light of its extraordinary pharmacokinetics and pharmacodynamics. Tolerance development/drug resistance to AZM in chronic use and potential mechanisms are also addressed.
2023-11-13 | Pharmacological interventions for the management of cystinuria: a systematic review
Abstract Background Cystinuria is a rare genetic kidney stone disease, with no cure. Current treatments involve lowering urinary cystine levels and increasing cystine solubility. This systematic review evaluates the available literature regarding non-surgical interventions for cystinuria. Methods Key electronic databases were searched for studies that described the clinical management of cystinuria with high diuresis, alkalinizing agents and thiol-based drugs that were published between 2000 and 2022. Observational studies were included if they contained clinical investigation with at least one previous or current episode of cystine stones, urine cystine levels > 250 mg/L and patients being managed with urinary dilution, alkalinizing agents or other pharmacological agents. All included studies were assessed for study design, patient characteristics and outcomes. A qualitative and critical analysis was performed whereby study quality was assessed using Methodological Index for Non-Randomized Studies (MINORS). Two authors performed the quality assessment and excluded the studies with a low MINORS score. Results Fourteen studies met the review inclusion and quality criteria. Of the fourteen studies, two reported treatment using alkalinizing agents, six reported treatment using thiol-based drugs, and six reported combination treatment using alkalinizing agents and thiol-based drugs. These studies indicated that first-line therapies, including high fluid intake and urinary alkalinization, increased urine volume to > 3 L/day and urinary pH > 7.0, and were associated with reduced urinary cystine levels and cystine stone formation. Second-line therapy with cystine-binding thiol drugs, such as tiopronin and D-penicillamine, reduced urinary cystine levels, cystine crystal volume and increased cystine solubility, resulting in decreased cystine stone formation and stone recurrence rate. Further, combined intervention with alkalinizing agents and thiol-based drugs synergistically reduced stone recurrence. Conclusion Cystinuria treatment may require a combined approach of high diuresis, alkalinization and pharmacological interventions with regular monitoring of urinary pH, cystine levels, cystine crystal volume and solubility. However, poor adherence to treatment is relatively frequent, hence the pressing urgency for improved therapies and treatments. Graphical abstract
2023-07-07 | Realization of Amyloid-like Aggregation as a Common Cause for Pathogenesis in Diseases
Amyloids were conventionally referred to as extracellular and intracellular accumulation of Aβ42 peptide, which causes the formation of plaques and neurofibrillary tangles inside the brain leading to the pathogenesis in Alzheimer's disease. Subsequently, amyloid-like deposition was found in the etiology of prion diseases, Parkinson's disease, type II diabetes, and cancer, which was attributed to the aggregation of prion protein, α-Synuclein, islet amyloid polypeptide protein, and p53 protein, respectively. Hence, traditionally amyloids were considered aggregates formed exclusively by proteins or peptides. However, since the last decade, it has been discovered that other metabolites, like single amino acids, nucleobases, lipids, glucose derivatives, etc., have a propensity to form amyloid-like toxic assemblies. Several studies suggest direct implications of these metabolite assemblies in the patho-physiology of various inborn errors of metabolisms like phenylketonuria, tyrosinemia, cystinuria, and Gaucher's disease, to name a few. In this review, we present a comprehensive literature overview that suggests amyloid-like structure formation as a common phenomenon for disease progression and pathogenesis in multiple syndromes. The review is devoted to providing readers with a broad knowledge of the structure, mode of formation, propagation, and transmission of different extracellular amyloids and their implications in the pathogenesis of diseases. We strongly believe a review on this topic is urgently required to create awareness about the understanding of the fundamental molecular mechanism behind the origin of diseases from an amyloid perspective and possibly look for a common therapeutic strategy for the treatment of these maladies by designing generic amyloid inhibitors.
proteins
2022-05-19 | Ca2+-mediated higher-order assembly of heterodimers in amino acid transport system b0,+ biogenesis and cystinuria.
Cystinuria is a genetic disorder characterized by overexcretion of dibasic amino acids and cystine, causing recurrent kidney stones and kidney failure. Mutations of the regulatory glycoprotein rBAT and the amino acid transporter b0,+AT, which constitute system b0,+, are linked to type I and non-type I cystinuria respectively and they exhibit distinct phenotypes due to protein trafficking defects or catalytic inactivation. Here, using electron cryo-microscopy and biochemistry, we discover that Ca2+ mediates higher-order assembly of system b0,+. Ca2+ stabilizes the interface between two rBAT molecules, leading to super-dimerization of b0,+AT-rBAT, which in turn facilitates N-glycan maturation and protein trafficking. A cystinuria mutant T216M and mutations of the Ca2+ site of rBAT cause the loss of higher-order assemblies, resulting in protein trapping at the ER and the loss of function. These results provide the molecular basis of system b0,+ biogenesis and type I cystinuria and serve as a guide to develop new therapeutic strategies against it. More broadly, our findings reveal an unprecedented link between transporter oligomeric assembly and protein-trafficking diseases.
2021-05-07 | Ca2+-mediated higher-order assembly of b0,+AT–rBAT is a key step for system b0,+biogenesis and cystinuria
Abstract Cystinuria is a genetic disorder characterized by overexcretion of dibasic amino acids and cystine, which causes recurrent kidney stones and occasionally severe kidney failure. Mutations of the two responsible proteins, rBAT and b 0,+ AT, which comprise system b 0,+ , are linked to type I and non-type I cystinuria respectively and they exhibit distinct phenotypes due to protein trafficking defects or catalytic inactivation. Although recent structural insights into human b 0,+ AT–rBAT suggested a model for transport-inactivating mutations, the mechanisms by which type I mutations trigger trafficking deficiencies are not well understood. Here, using electron cryo-microscopy and biochemistry, we discover that Ca 2+ -mediated higher-order assembly of system b 0,+ is the key to its trafficking on the cell surface. We show that Ca 2+ stabilizes the interface between two rBAT molecules to mediate super-dimerization, and this in turn facilitates the N-glycan maturation of system b 0,+ . A common cystinuria mutant T216M and mutations that disrupt the Ca 2+ site in rBAT cause the loss of higher-order assemblies, resulting in protein trafficking deficiency. Mutations at the super-dimer interface reproduce the mis-trafficking phenotype, demonstrating that super-dimerization is essential for cellular function. Cell-based transport assays confirmed the importance of the Ca 2+ site and super-dimerization, and additionally suggested which residues are involved in cationic amino acid recognition. Taken together, our results provide the molecular basis of type I cystinuria and serve as a guide to develop new therapeutic strategies against it. More broadly, our findings reveal an unprecedented link between transporter oligomeric assembly and trafficking diseases in general.
2005-07-12 | Cystine and glutamate transport in renal epithelial cells transfected with human system x—c
Cystine and glutamate transport in renal epithelial cells transfected with human system x-c.BackgroundSystem x-c is a heterodimeric transporter, comprised of a light chain, xCT, and heavy chain, 4F2hc, which mediates the sodium-independent exchange of cystine and glutamate at the plasma membrane. In the current study we tested the hypothesis that stable transfection of Madin-Darby canine kidney (MDCK) cells with human xCT and 4F2hc results in the expression of functional system x-c.MethodsMDCK cells were transfected stably with human clones for xCT and 4F2hc. Analyses of time- and temperature-dependence, saturation kinetics, and substrate specificity of L-cystine and L-glutamate transport were carried out in control and xCT-4F2hc-transfected MDCK cells. We also measured the uptake of L-cystine inXenopus oocytes expressing human xCT and/or 4F2hc or xCT and/or rBAT (a heavy chain homologous to 4F2hc).ResultsAll of the different sets of data revealed that transport of L-cystine and L-glutamate increased significantly (twofold to threefold) in the MDCK cells subsequent to transfection with xCT-4F2hc. Moreover, uptake of L-cystine also increased (about tenfold) inXenopus oocytes expressing hxCT and h4F2hc. Biochemical analyses of L-cystine uptake in oocytes verified our findings in the transfected MDCK cells. Interestingly, in oocytes injected with rBAT with or without xCT, uptake of L-cystine was significantly greater than that in water-injected oocytes.ConclusionOur findings indicate that stable transfection of MDCK cells with xCT and 4F2hc results in a cell-line expressing a functional system x-c transporter that can utilize L-cystine and L-glutamate as substrates. This study apparently represents the first stable transfection of a mammalian cell line with system x-c. Cystine and glutamate transport in renal epithelial cells transfected with human system x-c. System x-c is a heterodimeric transporter, comprised of a light chain, xCT, and heavy chain, 4F2hc, which mediates the sodium-independent exchange of cystine and glutamate at the plasma membrane. In the current study we tested the hypothesis that stable transfection of Madin-Darby canine kidney (MDCK) cells with human xCT and 4F2hc results in the expression of functional system x-c. MDCK cells were transfected stably with human clones for xCT and 4F2hc. Analyses of time- and temperature-dependence, saturation kinetics, and substrate specificity of L-cystine and L-glutamate transport were carried out in control and xCT-4F2hc-transfected MDCK cells. We also measured the uptake of L-cystine inXenopus oocytes expressing human xCT and/or 4F2hc or xCT and/or rBAT (a heavy chain homologous to 4F2hc). All of the different sets of data revealed that transport of L-cystine and L-glutamate increased significantly (twofold to threefold) in the MDCK cells subsequent to transfection with xCT-4F2hc. Moreover, uptake of L-cystine also increased (about tenfold) inXenopus oocytes expressing hxCT and h4F2hc. Biochemical analyses of L-cystine uptake in oocytes verified our findings in the transfected MDCK cells. Interestingly, in oocytes injected with rBAT with or without xCT, uptake of L-cystine was significantly greater than that in water-injected oocytes. Our findings indicate that stable transfection of MDCK cells with xCT and 4F2hc results in a cell-line expressing a functional system x-c transporter that can utilize L-cystine and L-glutamate as substrates. This study apparently represents the first stable transfection of a mammalian cell line with system x-c.
2003-01-03 | Functional Cooperation of Epithelial Heteromeric Amino Acid Transporters Expressed in Madin-Darby Canine Kidney Cells
The heteromeric amino acid transporters b(0,+)AT-rBAT (apical), y(+)LAT1-4F2hc, and possibly LAT2-4F2hc (basolateral) participate to the (re)absorption of cationic and neutral amino acids in the small intestine and kidney proximal tubule. We show now by immunofluorescence that their expression levels follow the same axial gradient along the kidney proximal tubule (S1>S2S3). We reconstituted their co-expression in MDCK cell epithelia and verified their polarized localization by immunofluorescence. Expression of b(0,+)AT-rBAT alone led to a net reabsorption of l-Arg (given together with l-Leu). Coexpression of basolateral y(+)LAT1-4F2hc increased l-Arg reabsorption and reversed l-Leu transport from (re)absorption to secretion. Similarly, l-cystine was (re)absorbed when b(0,+)AT-rBAT was expressed alone. This net transport was further increased by the coexpression of 4F2hc, due to the mobilization of LAT2 (exogenous and/or endogenous) to the basolateral membrane. In summary, apical b(0,+)AT-rBAT cooperates with y(+)LAT1-4F2hc or LAT2-4F2hc for the transepithelial reabsorption of cationic amino acids and cystine, respectively. The fact that the reabsorption of l-Arg led to the secretion of l-Leu demonstrates that the implicated heteromeric amino acid transporters function in epithelia as exchangers coupled in series and supports the notion that the parallel activity of unidirectional neutral amino acid transporters is required to drive net amino acid reabsorption.
1999-10-01 | Cloning and Expression of a b0,+-like Amino Acid Transporter Functioning as a Heterodimer with 4F2hc Instead of rBAT
We have cloned a transporter protein from rabbit small intestine, which, when coexpressed with the 4F2 heavy chain (4F2hc) in mammalian cells, induces a b0,+-like amino acid transport activity. This protein (4F2-lc6 for the sixth member of the 4F2 light chain family) consists of 487 amino acids and has 12 putative transmembrane domains. At the level of amino acid sequence, 4F2-lc6 shows significant homology (44% identity) to the other five known members of the 4F2 light chain family, namely LAT1 (4F2-lc1), y+LAT1 (4F2-lc2), y+LAT2 (4F2-lc3), xCT (4F2-lc4), and LAT2 (4F2-lc5). The 4F2hc/4F2-lc6 complex-mediated transport process is Na+-independent and exhibits high affinity for neutral and cationic amino acids and cystine. These characteristics are similar to those of the b0,+-like amino acid transport activity previously shown to be associated with rBAT (protein related to b0,+ amino acid transport system). However, the newly cloned 4F2-lc6 does not interact with rBAT. This is the first report of the existence of a b0,+-like amino acid transport process that is independent of rBAT. 4F2-lc6 is expressed predominantly in the small intestine and kidney. Based on the characteristics of the transport process mediated by the 4F2hc/4F2-lc6 complex and the expression pattern of 4F2-lc6 in mammalian tissues, we suggest that 4F2-lc6 is a new candidate gene for cystinuria.
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