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Di Martino RMC, Maxwell BD, Pirali T. Deuterium in drug discovery: progress, opportunities and challenges. Nat Rev Drug Discov 2023; 22:562-584. [PMID: 37277503 PMCID: PMC10241557 DOI: 10.1038/s41573-023-00703-8] [Citation(s) in RCA: 54] [Impact Index Per Article: 54.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/12/2023] [Indexed: 06/07/2023]
Abstract
Substitution of a hydrogen atom with its heavy isotope deuterium entails the addition of one neutron to a molecule. Despite being a subtle change, this structural modification, known as deuteration, may improve the pharmacokinetic and/or toxicity profile of drugs, potentially translating into improvements in efficacy and safety compared with the non-deuterated counterparts. Initially, efforts to exploit this potential primarily led to the development of deuterated analogues of marketed drugs through a 'deuterium switch' approach, such as deutetrabenazine, which became the first deuterated drug to receive FDA approval in 2017. In the past few years, the focus has shifted to applying deuteration in novel drug discovery, and the FDA approved the pioneering de novo deuterated drug deucravacitinib in 2022. In this Review, we highlight key milestones in the field of deuteration in drug discovery and development, emphasizing recent and instructive medicinal chemistry programmes and discussing the opportunities and hurdles for drug developers, as well as the questions that remain to be addressed.
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Affiliation(s)
| | | | - Tracey Pirali
- Department of Pharmaceutical Sciences, Università del Piemonte Orientale, Novara, Italy.
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Semicarbazide-Sensitive Amine Oxidase (SSAO) and Lysyl Oxidase (LOX) Association in Rat Aortic Vascular Smooth Muscle Cells. Biomolecules 2022; 12:biom12111563. [DOI: 10.3390/biom12111563] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2022] [Revised: 10/11/2022] [Accepted: 10/12/2022] [Indexed: 11/17/2022] Open
Abstract
Vascular smooth muscle cells (VSMCs) are the main stromal cells in the medial layer of the vascular wall. These cells produce the extracellular matrix (ECM) and are involved in many pathological changes in the vascular wall. Semicarbazide-sensitive amine oxidase (SSAO) and lysyl oxidase (LOX) are vascular enzymes associated with the development of atherosclerosis. In the vascular smooth muscle cells, increased SSAO activity elevates reactive oxygen species (ROS) and induces VSMCs death; increased LOX induces chemotaxis through hydrogen peroxide dependent mechanisms; and decreased LOX contributes to endothelial dysfunction. This study investigates the relationship between SSAO and LOX in VSMCs by studying their activity, protein, and mRNA levels during VSMCs passaging and after silencing the LOX gene, while using their respective substrates and inhibitors. At the basal level, LOX activity decreased with passage and its protein expression was maintained between passages. βAPN abolished LOX activity (** p < 0.01 for 8 vs. 3 and * p < 0.05 for 5 vs. 8) and had no effect on LOX protein and mRNA levels. MDL72527 reduced LOX activity at passage 3 and 5 (## p < 0.01) and had no effect on LOX protein, and mRNA expression. At the basal level, SSAO activity also decreased with passage, and its protein expression was maintained between passages. MDL72527 abolished SSAO activity (**** p < 0.0001 for 8 vs. 3 and * p < 0.05 for 5 vs. 8), VAP-1 expression at passage 5 (** p < 0.01) and 8 (**** p < 0.0001), and Aoc3 mRNA levels at passage 8 (* p < 0.05). βAPN inhibited SSAO activity (**** p < 0.0001 for 5 vs. 3 and 8 vs. 3 and * p < 0.05 for 5 vs. 8), VAP-1 expression at passage 3 (* p < 0.05), and Aoc3 mRNA levels at passage 3 (* p < 0.05). Knockdown of the LOX gene (**** p < 0.0001 for Si6 vs. Sictrl and *** p < 0.001 for Si8 vs. Sictrl) and LOX protein (** p < 0.01 for Si6 and Si8 vs. Sictrl) in VSMCs at passage 3 resulted in a reduction in Aoc3 mRNA (#### p < 0.0001 for Si6 vs. Sictrl and ### p < 0.001 for Si8 vs. Sictrl) and VAP-1 protein (# p < 0.05 for Si8 vs. Sictrl). These novel findings demonstrate a passage dependent decrease in LOX activity and increase in SSAO activity in rat aortic VSMCs and show an association between both enzymes in early passage rat aortic VSMCs, where LOX was identified as a regulator of SSAO activity, protein, and mRNA expression.
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Kinetic isotope effects and synthetic strategies for deuterated carbon-11 and fluorine-18 labelled PET radiopharmaceuticals. Nucl Med Biol 2021; 96-97:112-147. [PMID: 33892374 DOI: 10.1016/j.nucmedbio.2021.03.011] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2021] [Revised: 03/19/2021] [Accepted: 03/30/2021] [Indexed: 11/22/2022]
Abstract
The deuterium labelling of pharmaceuticals is a useful strategy for altering pharmacokinetic properties, particularly for improving metabolic resistance. The pharmacological effects of such metabolites are often assumed to be negligible during standard drug discovery and are factored in later at the clinical phases of development, where the risks and benefits of the treatment and side-effects can be wholly assessed. This paradigm does not translate to the discovery of radiopharmaceuticals, however, as the confounding effects of radiometabolites can inevitably show in preliminary positron emission tomography (PET) scans and thus complicate interpretation. Consequently, the formation of radiometabolites is crucial to take into consideration, compared to non-radioactive metabolites, and the application of deuterium labelling is a particularly attractive approach to minimise radiometabolite formation. Herein, we provide a comprehensive overview of the deuterated carbon-11 and fluorine-18 radiopharmaceuticals employed in PET imaging experiments. Specifically, we explore six categories of deuterated radiopharmaceuticals used to investigate the activities of monoamine oxygenase (MAO), choline, translocator protein (TSPO), vesicular monoamine transporter 2 (VMAT2), neurotransmission and the diagnosis of Alzheimer's disease; from which we derive four prominent deuteration strategies giving rise to a kinetic isotope effect (KIE) for reducing the rate of metabolism. Synthetic approaches for over thirty of these deuterated radiopharmaceuticals are discussed from the perspective of deuterium and radioisotope incorporation, alongside an evaluation of the deuterium labelling and radiolabelling efficacies across these independent studies. Clinical and manufacturing implications are also discussed to provide a more comprehensive overview of how deuterated radiopharmaceuticals may be introduced to routine practice.
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Demidov VV. Site-specifically deuterated essential lipids as new drugs against neuronal, retinal and vascular degeneration. Drug Discov Today 2020; 25:1469-1476. [DOI: 10.1016/j.drudis.2020.03.014] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2019] [Revised: 03/07/2020] [Accepted: 03/23/2020] [Indexed: 01/10/2023]
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Basov A, Fedulova L, Vasilevskaya E, Dzhimak S. Possible Mechanisms of Biological Effects Observed in Living Systems during 2H/ 1H Isotope Fractionation and Deuterium Interactions with Other Biogenic Isotopes. Molecules 2019; 24:E4101. [PMID: 31766268 PMCID: PMC6891295 DOI: 10.3390/molecules24224101] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2019] [Revised: 11/01/2019] [Accepted: 11/11/2019] [Indexed: 12/11/2022] Open
Abstract
This article presents the original descriptions of some recent physics mechanisms (based on the thermodynamic, kinetic, and quantum tunnel effects) providing stable 2H/1H isotope fractionation, leading to the accumulation of particular isotopic forms in intra- or intercellular space, including the molecular effects of deuterium interaction with 18O/17O/16O, 15N/14N, 13C/12C, and other stable biogenic isotopes. These effects were observed mainly at the organelle (mitochondria) and cell levels. A new hypothesis for heavy nonradioactive isotope fractionation in living systems via neutron effect realization is discussed. The comparative analysis of some experimental studies results revealed the following observation: "Isotopic shock" is highly probable and is observed mostly when chemical bonds form between atoms with a summary odd number of neutrons (i.e., bonds with a non-compensated neutron, which correspond to the following equation: Nn - Np = 2k + 1, where k ϵ Z, k is the integer, Z is the set of non-negative integers, Nn is number of neutrons, and Np is number of protons of each individual atom, or in pair of isotopes with a chemical bond). Data on the efficacy and metabolic pathways of the therapy also considered 2H-modified drinking and diet for some diseases, such as Alzheimer's disease, Friedreich's ataxia, mitochondrial disorders, diabetes, cerebral hypoxia, Parkinson's disease, and brain cancer.
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Affiliation(s)
- Alexander Basov
- Department of Fundamental and Clinical Biochemistry, Kuban State Medical University, Krasnodar 350063, Russia;
- Department of Radiophysics and Nanotechnology, Kuban State University, Krasnodar 350040, Russia
| | - Liliya Fedulova
- The V.M. Gorbatov Federal Research Center for Food Systems of Russian Academy of Sciences, Moscow 109316, Russia; (L.F.); (E.V.)
| | - Ekaterina Vasilevskaya
- The V.M. Gorbatov Federal Research Center for Food Systems of Russian Academy of Sciences, Moscow 109316, Russia; (L.F.); (E.V.)
| | - Stepan Dzhimak
- Department of Radiophysics and Nanotechnology, Kuban State University, Krasnodar 350040, Russia
- The V.M. Gorbatov Federal Research Center for Food Systems of Russian Academy of Sciences, Moscow 109316, Russia; (L.F.); (E.V.)
- Federal Research Center the Southern Scientific Center of the Russian Academy of Sciences, Rostov-on-Don 344006, Russia
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Pestov NB, Kalinovsky DV, Larionova TD, Zakirova AZ, Modyanov NN, Okkelman IA, Korneenko TV. Properties of a cryptic lysyl oxidase from haloarchaeon Haloterrigena turkmenica. PeerJ 2019; 7:e6691. [PMID: 30984480 PMCID: PMC6452851 DOI: 10.7717/peerj.6691] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2018] [Accepted: 02/26/2019] [Indexed: 11/20/2022] Open
Abstract
Background Lysyl oxidases (LOX) have been extensively studied in mammals, whereas properties and functions of recently found homologues in prokaryotic genomes remain enigmatic. Methods LOX open reading frame was cloned from Haloterrigena turkmenica in an E. coli expression vector. Recombinant Haloterrigena turkmenica lysyl oxidase (HTU-LOX) proteins were purified using metal affinity chromatography under denaturing conditions followed by refolding. Amine oxidase activity has been measured fluorometrically as hydrogen peroxide release coupled with the oxidation of 10-acetyl-3,7-dihydroxyphenoxazine in the presence of horseradish peroxidase. Rabbit polyclonal antibodies were obtained and used in western blotting. Results Cultured H. turkmenica has no detectable amine oxidase activity. HTU-LOX may be expressed in E. coli with a high protein yield. The full-length protein gives no catalytic activity. For this reason, we hypothesized that the hydrophobic N-terminal region may interfere with proper folding and its removal may be beneficial. Indeed, truncated His-tagged HTU-LOX lacking the N-terminal hydrophobic signal peptide purified under denaturing conditions can be successfully refolded into an active enzyme, and a larger N-terminal truncation further increases the amine oxidase activity. Refolding is optimal in the presence of Cu2+ at pH 6.2 and is not sensitive to salt. HTU-LOX is sensitive to LOX inhibitor 3-aminopropionitrile. HTU-LOX deaminates usual substrates of mammalian LOX such as lysine-containing polypeptides and polymers. The major difference between HTU-LOX and mammalian LOX is a relaxed substrate specificity of the former. HTU-LOX readily oxidizes various primary amines including such compounds as taurine and glycine, benzylamine being a poor substrate. Of note, HTU-LOX is also active towards several aminoglycoside antibiotics and polymyxin. Western blotting indicates that epitopes for the anti-HTU-LOX polyclonal antibodies coincide with a high molecular weight protein in H. turkmenica cells. Conclusion H. turkmenica contains a lysyl oxidase gene that was heterologously expressed yielding an active recombinant enzyme with important biochemical features conserved between all known LOXes, for example, the sensitivity to 3-aminopropionitrile. However, the native function in the host appears to be cryptic. Significance This is the first report on some properties of a lysyl oxidase from Archaea and an interesting example of evolution of enzymatic properties after hypothetical horizontal transfers between distant taxa.
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Affiliation(s)
- Nikolay B Pestov
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Moscow, Russia
| | | | | | - Alia Z Zakirova
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Moscow, Russia
| | - Nikolai N Modyanov
- Department of Physiology and Pharmacology, University of Toledo, Toledo, OH, United States of America
| | - Irina A Okkelman
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Moscow, Russia
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Pirali T, Serafini M, Cargnin S, Genazzani AA. Applications of Deuterium in Medicinal Chemistry. J Med Chem 2019; 62:5276-5297. [DOI: 10.1021/acs.jmedchem.8b01808] [Citation(s) in RCA: 251] [Impact Index Per Article: 50.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- Tracey Pirali
- Department of Pharmaceutical Sciences, Università del Piemonte Orientale, Largo Donegani 2, 28100 Novara, Italy
| | - Marta Serafini
- Department of Pharmaceutical Sciences, Università del Piemonte Orientale, Largo Donegani 2, 28100 Novara, Italy
| | - Sarah Cargnin
- Department of Pharmaceutical Sciences, Università del Piemonte Orientale, Largo Donegani 2, 28100 Novara, Italy
| | - Armando A. Genazzani
- Department of Pharmaceutical Sciences, Università del Piemonte Orientale, Largo Donegani 2, 28100 Novara, Italy
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Atzrodt J, Derdau V, Kerr WJ, Reid M. Deuterium- und tritiummarkierte Verbindungen: Anwendungen in den modernen Biowissenschaften. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201704146] [Citation(s) in RCA: 90] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Jens Atzrodt
- Isotope Chemistry and Metabolite Synthesis, Integrated Drug Discovery, Medicinal Chemistry; Industriepark Höchst, G876 65926 Frankfurt Deutschland
| | - Volker Derdau
- Isotope Chemistry and Metabolite Synthesis, Integrated Drug Discovery, Medicinal Chemistry; Industriepark Höchst, G876 65926 Frankfurt Deutschland
| | - William J. Kerr
- Department of Pure and Applied Chemistry, WestCHEM; University of Strathclyde; 295 Cathedral Street Glasgow Scotland G1 1XL Großbritannien
| | - Marc Reid
- Department of Pure and Applied Chemistry, WestCHEM; University of Strathclyde; 295 Cathedral Street Glasgow Scotland G1 1XL Großbritannien
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Atzrodt J, Derdau V, Kerr WJ, Reid M. Deuterium- and Tritium-Labelled Compounds: Applications in the Life Sciences. Angew Chem Int Ed Engl 2018; 57:1758-1784. [PMID: 28815899 DOI: 10.1002/anie.201704146] [Citation(s) in RCA: 407] [Impact Index Per Article: 67.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2017] [Revised: 07/27/2017] [Indexed: 12/19/2022]
Abstract
Hydrogen isotopes are unique tools for identifying and understanding biological and chemical processes. Hydrogen isotope labelling allows for the traceless and direct incorporation of an additional mass or radioactive tag into an organic molecule with almost no changes in its chemical structure, physical properties, or biological activity. Using deuterium-labelled isotopologues to study the unique mass-spectrometric patterns generated from mixtures of biologically relevant molecules drastically simplifies analysis. Such methods are now providing unprecedented levels of insight in a wide and continuously growing range of applications in the life sciences and beyond. Tritium (3 H), in particular, has seen an increase in utilization, especially in pharmaceutical drug discovery. The efforts and costs associated with the synthesis of labelled compounds are more than compensated for by the enhanced molecular sensitivity during analysis and the high reliability of the data obtained. In this Review, advances in the application of hydrogen isotopes in the life sciences are described.
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Affiliation(s)
- Jens Atzrodt
- Isotope Chemistry and Metabolite Synthesis, Integrated Drug Discovery, Medicinal Chemistry, Industriepark Höchst, G876, 65926, Frankfurt, Germany
| | - Volker Derdau
- Isotope Chemistry and Metabolite Synthesis, Integrated Drug Discovery, Medicinal Chemistry, Industriepark Höchst, G876, 65926, Frankfurt, Germany
| | - William J Kerr
- Department of Pure and Applied Chemistry, WestCHEM, University of Strathclyde, 295 Cathedral Street, Glasgow, Scotland, G1 1XL, UK
| | - Marc Reid
- Department of Pure and Applied Chemistry, WestCHEM, University of Strathclyde, 295 Cathedral Street, Glasgow, Scotland, G1 1XL, UK
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Korneenko TV, Pestov NB, Hurski AL, Fedarkevich AM, Shmanai VV, Brenna JT, Shchepinov MS. A strong developmental isotope effect in Caenorhabditis elegans induced by 5,5-deuterated lysine. Amino Acids 2017; 49:887-894. [DOI: 10.1007/s00726-017-2386-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2017] [Accepted: 01/27/2017] [Indexed: 01/17/2023]
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Schofield J, Derdau V, Atzrodt J, Zane P, Guo Z, van Horn R, Czepczor V, Stoltz A, Pardon M. Effect of deuteration on metabolism and clearance of Nerispirdine (HP184) and AVE5638. Bioorg Med Chem 2015; 23:3831-42. [DOI: 10.1016/j.bmc.2015.03.065] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2014] [Revised: 03/23/2015] [Accepted: 03/24/2015] [Indexed: 10/23/2022]
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Okkelman IA, Sukaeva AZ, Kirukhina EV, Korneenko TV, Pestov NB. Nuclear translocation of lysyl oxidase is promoted by interaction with transcription repressor p66β. Cell Tissue Res 2014; 358:481-9. [PMID: 25118846 DOI: 10.1007/s00441-014-1972-z] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2013] [Accepted: 07/21/2014] [Indexed: 11/30/2022]
Abstract
Lysyl oxidase (LOX) is an amine oxidase involved in protein cross-linking of the extracellular matrix. Less well characterized is the role that LOX plays among nuclear proteins, and molecular mechanisms of its transport to the nucleus are currently unknown. Here, we have employed yeast two-hybrid library screening and found that the LOX catalytic domain interacts with the transcription repressor p66β. This interaction has been confirmed in vitro and has been found to be accomplished through the CR2-containing domain of p66β. Moreover, co-expression of p66β and LOX in living tumor cells leads to the nuclear accumulation of LOX. Thus, p66β might be important for the regulation of LOX in the nucleus.
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Affiliation(s)
- Irina A Okkelman
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Moscow, 117997, Russia
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Anastasia L, Rota P, Anastasia M, Allevi P. Chemical structure, biosynthesis and synthesis of free and glycosylated pyridinolines formed by cross-link of bone and synovium collagen. Org Biomol Chem 2014; 11:5747-71. [PMID: 23873348 DOI: 10.1039/c3ob40945g] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
This review focuses on the chemical structure, biosynthesis and synthesis of free and glycosylated pyridinolines (Pyds), fluorescent collagen cross-links, with a pyridinium salt structure. Pyds derive from the degradation of bone collagen and have attracted attention for their use as biochemical markers of bone resorption and to assess fracture risk prediction in persons suffering from osteoporosis, bone cancer and other bone or collagen diseases. We consider and critically discuss all reported syntheses of free and glycosylated Pyds evidencing an unrevised chemistry, original and of general utility, analysis of which allows us to also support a previously suggested non-enzymatic formation of Pyds in collagen better rationalizing and justifying the chemical events.
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Affiliation(s)
- Luigi Anastasia
- Department of Biomedical Sciences for Health, University of Milan, via F.lli Cervi 93, 20090 Segrate (Milan), Italy.
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Besouw MTP, Schneider J, Janssen MC, Greco M, Emma F, Cornelissen EA, Desmet K, Skovby F, Nobili F, Lilien MR, De Paepe A, Malfait F, Symoens S, van den Heuvel LP, Levtchenko EN. Copper deficiency in patients with cystinosis with cysteamine toxicity. J Pediatr 2013; 163:754-60. [PMID: 23651769 DOI: 10.1016/j.jpeds.2013.03.078] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/03/2012] [Revised: 01/09/2013] [Accepted: 03/28/2013] [Indexed: 12/13/2022]
Abstract
OBJECTIVES To assess whether copper deficiency plays a role in the recently described cysteamine toxicity in patients with cystinosis, and to examine whether polymorphisms in copper transporters, lysyl oxidase, and/or type I procollagen genes could be responsible for the occurrence of cysteamine toxicity in a small subset of patients with cystinosis. STUDY DESIGN Thirty-six patients with cystinosis were included: 22 with Fanconi syndrome (including 7 with cysteamine toxicity), 12 after renal transplantation, 1 receiving hemodialysis, and 1 with ocular cystinosis. Serum copper and ceruloplasmin levels and urinary copper/creatinine ratio were measured. Genes ATP7A and CTR1 (encoding copper transporters), LOX (encoding lysyl oxidase), and COL1A1 and COL1A2 (encoding type I procollagen) were analyzed in patients with (n = 6) and without (n = 5) toxicity. Fibroblast (pro)collagen synthesis was compared in patients with (n = 3) and those without (n = 2) cysteamine toxicity. RESULTS All 22 patients with Fanconi syndrome had increased urinary copper excretion. Serum copper and ceruloplasmin levels were decreased in 9 patients, including all 7 patients with cysteamine toxicity. No specific sequence variations were associated with toxicity. All fibroblasts exhibited normal (pro)collagen synthesis. CONCLUSION Patients with cystinosis with cysteamine toxicity demonstrate copper deficiency. This can cause decreased activity of lysyl oxidase, the enzyme that generates the aldehydes required for collagen cross-linking. Thus, copper supplementation might prevent cysteamine toxicity.
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Affiliation(s)
- Martine T P Besouw
- Department of Pediatric Nephrology, Leuven University Hospital, Leuven, Belgium.
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