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Xue L, Singla RK, Qin Q, Ding Y, Liu L, Ding X, Qu W, Huang C, Shen Z, Shen B, Miao L. Exploring the complex relationship between vitamin K, gut microbiota, and warfarin variability in cardiac surgery patients. Int J Surg 2023; 109:3861-3871. [PMID: 37598356 PMCID: PMC10720796 DOI: 10.1097/js9.0000000000000673] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2023] [Accepted: 08/02/2023] [Indexed: 08/22/2023]
Abstract
BACKGROUND AND OBJECTIVES Due to the high individual variability of anticoagulant warfarin, this study aimed to investigate the effects of vitamin K concentration and gut microbiota on individual variability of warfarin in 246 cardiac surgery patients. METHODS The pharmacokinetics and pharmacodynamics (PKPD) model predicted international normalized ratio (INR) and warfarin concentration. Serum and fecal samples were collected to detect warfarin and vitamin K [VK1 and menaquinone-4 (MK4)] concentrations and gut microbiota diversity, respectively. In addition, the patient's medical records were reviewed for demographic characteristics, drug history, and CYP2C9, VKORC1, and CYP4F2 genotypes. RESULTS The PKPD model predicted ideal values of 62.7% for S-warfarin, 70.4% for R-warfarin, and 76.4% for INR. The normal VK1 level was 1.34±1.12 nmol/ml (95% CI: 0.33-4.08 nmol/ml), and the normal MK4 level was 0.22±0.18 nmol/ml (95% CI: 0.07-0.63 nmol/ml). The MK4 to total vitamin K ratio was 16.5±9.8% (95% CI: 4.3-41.5%). The S-warfarin concentration of producing 50% of maximum anticoagulation and the half-life of prothrombin complex activity tended to increase with vitamin K. Further, Prevotella and Eubacterium of gut microbiota identified as the main bacteria associated with individual variability of warfarin. The results suggest that an increase in vitamin K concentration can decrease anticoagulation, and gut microbiota may influence warfarin anticoagulation through vitamin K2 synthesis. CONCLUSION This study highlights the importance of considering vitamin K concentration and gut microbiota when prescribing warfarin. The findings may have significant implications for the personalized use of warfarin. Further research is needed to understand better the role of vitamin K and gut microbiota in warfarin anticoagulation.
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Affiliation(s)
- Ling Xue
- Department of Pharmacy
- Department of Pharmacology, Faculty of Medicine, UPV/EHU, Spain
| | - Rajeev K. Singla
- Joint Laboratory of Artificial Intelligence for Critical Care Medicine, Department of Critical Care Medicine and Institutes for Systems Genetics, Frontiers Science Center for Disease-related Molecular Network, West China Hospital, Sichuan University, Chengdu, People’s Republic of China
- School of Pharmaceutical Sciences, Lovely Professional University, Phagwara, Punjab, India
| | | | - Yinglong Ding
- Department of Cardiovascular Surgery, The First Affiliated Hospital of Soochow University
| | | | | | | | | | - Zhenya Shen
- Department of Cardiovascular Surgery, The First Affiliated Hospital of Soochow University
| | - Bairong Shen
- Joint Laboratory of Artificial Intelligence for Critical Care Medicine, Department of Critical Care Medicine and Institutes for Systems Genetics, Frontiers Science Center for Disease-related Molecular Network, West China Hospital, Sichuan University, Chengdu, People’s Republic of China
| | - Liyan Miao
- Department of Pharmacy
- College of Pharmaceutical Sciences
- Institute for Interdisciplinary Drug Research and Translational Sciences, Soochow University, Suzhou
- National Clinical Research Center for Hematologic Diseases, The First Affiliated Hospital of Soochow University, Jiangsu
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The Effects of Osteoporotic and Non-osteoporotic Medications on Fracture Risk and Bone Mineral Density. Drugs 2021; 81:1831-1858. [PMID: 34724173 PMCID: PMC8578161 DOI: 10.1007/s40265-021-01625-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/11/2021] [Indexed: 12/26/2022]
Abstract
Osteoporosis is a highly prevalent bone disease affecting more than 37.5 million individuals in the European Union (EU) and the United States of America (USA). It is characterized by low bone mineral density (BMD), impaired bone quality, and loss of structural and biomechanical properties, resulting in reduced bone strength. An increase in morbidity and mortality is seen in patients with osteoporosis, caused by the approximately 3.5 million new osteoporotic fractures occurring every year in the EU. Currently, different medications are available for the treatment of osteoporosis, including anti-resorptive and osteoanabolic medications. Bisphosphonates, which belong to the anti-resorptive medications, are the standard treatment for osteoporosis based on their positive effects on bone, long-term experience, and low costs. However, not only medications used for the treatment of osteoporosis can affect bone: several other medications are suggested to have an effect on bone as well, especially on fracture risk and BMD. Knowledge about the positive and negative effects of different medications on both fracture risk and BMD is important, as it can contribute to an improvement in osteoporosis prevention and treatment in general, and, even more importantly, to the individual's health. In this review, we therefore discuss the effects of both osteoporotic and non-osteoporotic medications on fracture risk and BMD. In addition, we discuss the underlying mechanisms of action.
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Takeda K, Ikenaka Y, Fourches D, Tanaka KD, Nakayama SMM, Triki D, Li X, Igarashi M, Tanikawa T, Ishizuka M. The VKORC1 ER-luminal loop mutation (Leu76Pro) leads to a significant resistance to warfarin in black rats (Rattus rattus). PESTICIDE BIOCHEMISTRY AND PHYSIOLOGY 2021; 173:104774. [PMID: 33771253 DOI: 10.1016/j.pestbp.2021.104774] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2020] [Revised: 12/10/2020] [Accepted: 01/04/2021] [Indexed: 06/12/2023]
Abstract
Well-known 4-hydroxycoumarin derivatives, such as warfarin, act as inhibitors of the vitamin K epoxide reductase (VKOR) and are used as anticoagulants. Mutations of the VKOR enzyme can lead to resistance to those compounds. This has been a problem in using them as medicine or rodenticide. Most of these mutations lie in the vicinity of potential warfarin-binding sites within the ER-luminal loop structure (Lys30, Phe55) and the transmembrane helix (Tyr138). However, a VKOR mutation found in Tokyo in warfarin-resistant rats does not follow that pattern (Leu76Pro), and its effect on VKOR function and structure remains unclear. We conducted both in vitro kinetic analyses and in silico docking studies to characterize the VKOR mutant. On the one hand, resistant rats (R-rats) showed a 37.5-fold increased IC50 value to warfarin when compared to susceptible rats (S-rats); on the other hand, R-rats showed a 16.5-fold lower basal VKOR activity (Vmax/Km). Docking calculations exhibited that the mutated VKOR of R-rats has a decreased affinity for warfarin. Molecular dynamics simulations further revealed that VKOR-associated warfarin was more exposed to solvents in R-rats and key interactions between Lys30, Phe55, and warfarin were less favored. This study concludes that a single mutation of VKOR at position 76 leads to a significant resistance to warfarin by modifying the types and numbers of intermolecular interactions between the two.
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Affiliation(s)
- Kazuki Takeda
- Laboratory of Toxicology, Department of Environmental Sciences, Faculty of Veterinary Medicine, Hokkaido University, Kita-18 Nishi-9, Kita-ku, Sapporo 060-0818, Japan
| | - Yoshinori Ikenaka
- Laboratory of Toxicology, Department of Environmental Sciences, Faculty of Veterinary Medicine, Hokkaido University, Kita-18 Nishi-9, Kita-ku, Sapporo 060-0818, Japan; Water Research Group, Unit for Environmental Sciences and Management, North-West University, Potchefstroom, South Africa
| | - Denis Fourches
- Department of Chemistry, Bioinformatics Research Center, North Carolina State University, Raleigh, NC, USA
| | - Kazuyuki D Tanaka
- Technical Research Laboratory, IKARI SHODOKU CO., Ltd., Narashino, Chiba, Japan
| | - Shouta M M Nakayama
- Laboratory of Toxicology, Department of Environmental Sciences, Faculty of Veterinary Medicine, Hokkaido University, Kita-18 Nishi-9, Kita-ku, Sapporo 060-0818, Japan
| | - Dhoha Triki
- Department of Chemistry, Bioinformatics Research Center, North Carolina State University, Raleigh, NC, USA
| | - Xinhao Li
- Department of Chemistry, Bioinformatics Research Center, North Carolina State University, Raleigh, NC, USA
| | - Manabu Igarashi
- Division of Global Epidemiology, Research Center for Zoonosis Control, Hokkaido University, Sapporo, Japan; Global Station for Zoonosis Control, Global Institution for Collaborative Research and Education, Hokkaido University, Sapporo, Japan
| | - Tsutomu Tanikawa
- Technical Research Laboratory, IKARI SHODOKU CO., Ltd., Narashino, Chiba, Japan
| | - Mayumi Ishizuka
- Laboratory of Toxicology, Department of Environmental Sciences, Faculty of Veterinary Medicine, Hokkaido University, Kita-18 Nishi-9, Kita-ku, Sapporo 060-0818, Japan.
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4
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Li S, Liu S, Yang Y, Li W. Characterization of Warfarin Inhibition Kinetics Requires Stabilization of Intramembrane Vitamin K Epoxide Reductases. J Mol Biol 2020; 432:5197-5208. [PMID: 32445640 DOI: 10.1016/j.jmb.2020.05.009] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2020] [Revised: 04/24/2020] [Accepted: 05/14/2020] [Indexed: 01/04/2023]
Abstract
Intramembrane enzymes are often difficult for biochemical characterization. Human vitamin K epoxide reductase (VKOR) is the target of warfarin. However, this intramembrane enzyme becomes insensitive to warfarin inhibition in vitro, preventing the characterization of inhibition kinetics for decades. Here we employ structural biology methods to identify stable VKOR and VKOR-like proteins and purify them to near homogeneity. We find that the key to maintain their warfarin sensitivity is to stabilize their native protein conformation in vitro. Reduced glutathione drastically increases the warfarin sensitivity of a VKOR-like protein from Takifugu rubripes, presumably through maintaining a disulfide-bonded conformation. Effective inhibition of human VKOR-like requires also the use of LMNG, a mild detergent developed for crystallography to increase membrane protein stability. Human VKOR needs to be preserved in ER-enriched microsomes to exhibit warfarin sensitivity, whereas human VKOR purified in LMNG is stable only with pre-bound warfarin. Under these optimal conditions, warfarin inhibits with tight-binding kinetics. Overall, our studies show that structural biology methods are ideal for stabilizing intramembrane enzymes. Optimizing toward their inhibitor-binding conformation enables the characterization of enzyme kinetics in difficult cases.
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Affiliation(s)
- Shuang Li
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Shixuan Liu
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Yihu Yang
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Weikai Li
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA.
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5
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Nakayama SMM, Morita A, Ikenaka Y, Kawai YK, Watanabe KP, Ishii C, Mizukawa H, Yohannes YB, Saito K, Watanabe Y, Ito M, Ohsawa N, Ishizuka M. Avian interspecific differences in VKOR activity and inhibition: Insights from amino acid sequence and mRNA expression ratio of VKORC1 and VKORC1L1. Comp Biochem Physiol C Toxicol Pharmacol 2020; 228:108635. [PMID: 31639498 DOI: 10.1016/j.cbpc.2019.108635] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/04/2019] [Revised: 09/16/2019] [Accepted: 09/26/2019] [Indexed: 11/22/2022]
Abstract
Worldwide use of anticoagulant rodenticides (ARs) for rodents control has frequently led to secondary poisoning of non-target animals, especially raptors. In order to suggest some factors that may help considering the mechanism of the incidents, this study focused on the avian vitamin K 2, 3-epoxide reductase (VKOR) that is the target protein of ARs. We addressed the interspecific differences in VKOR activity and inhibition related to amino acid sequence and mRNA expression of VKORC1 and VKORC1-like1 (VKORC1L1). Poultry have been considered to be more tolerant to ARs than mammals. However, VKOR activity of owls, hawks, falcon and surprisingly, canaries, was lower and inhibited by warfarin more easily than that of chickens and turkeys. The amino acid sequence of VKORC1 and VKORC1L1 implied that the value of Ki for VKOR activity to ARs could depend on the amino acid at position 140 in the TYX warfarin-binding motif in VKORC1, and other amino acid mutations in VKORC1L1. The mRNA expression ratio of VKORC1:VKORC1L1 differed between turkey (8:1) and chicken (2:3) liver. VKORC1L1 has been reported to be resistant to warfarin compared to VKORC1. Hence, both the Ki of specific VKORC1 and VKORC1L1, and the mRNA expression ratio would cause avian interspecific difference of the VKOR inhibition. Our study also suggested the high inhibition of VKOR activities in raptors and surprisingly that in canaries as well. These factors are the most likely to contribute to the high sensitivity to ARs found in raptors.
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Affiliation(s)
- Shouta M M Nakayama
- Laboratory of Toxicology, Faculty of Veterinary Medicine, Hokkaido University, Kita18, Nishi9, Kita-ku, Sapporo 060-0818, Japan
| | - Ayuko Morita
- Laboratory of Toxicology, Faculty of Veterinary Medicine, Hokkaido University, Kita18, Nishi9, Kita-ku, Sapporo 060-0818, Japan
| | - Yoshinori Ikenaka
- Laboratory of Toxicology, Faculty of Veterinary Medicine, Hokkaido University, Kita18, Nishi9, Kita-ku, Sapporo 060-0818, Japan; Water Research Group, Unit for Environmental Sciences and Management, North-West University, Potchefstroom, South Africa
| | - Yusuke K Kawai
- Diagnostic Center for Animal Health and Food Safety, Obihiro University of Agriculture and Veterinary Medicine, Obihiro 080-8555, Japan
| | - Kensuke P Watanabe
- Laboratory of Toxicology, Faculty of Veterinary Medicine, Hokkaido University, Kita18, Nishi9, Kita-ku, Sapporo 060-0818, Japan
| | - Chihiro Ishii
- Laboratory of Toxicology, Faculty of Veterinary Medicine, Hokkaido University, Kita18, Nishi9, Kita-ku, Sapporo 060-0818, Japan
| | - Hazuki Mizukawa
- Laboratory of Toxicology, Faculty of Veterinary Medicine, Hokkaido University, Kita18, Nishi9, Kita-ku, Sapporo 060-0818, Japan
| | - Yared B Yohannes
- Laboratory of Toxicology, Faculty of Veterinary Medicine, Hokkaido University, Kita18, Nishi9, Kita-ku, Sapporo 060-0818, Japan
| | - Keisuke Saito
- Institute for Raptor Biomedicine Japan 2-2101, Hokuto, Kushiro-shi, Hokkaido 084-0922, Japan
| | - Yukiko Watanabe
- Institute for Raptor Biomedicine Japan 2-2101, Hokuto, Kushiro-shi, Hokkaido 084-0922, Japan
| | | | | | - Mayumi Ishizuka
- Laboratory of Toxicology, Faculty of Veterinary Medicine, Hokkaido University, Kita18, Nishi9, Kita-ku, Sapporo 060-0818, Japan.
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VKORC1 and VKORC1L1 have distinctly different oral anticoagulant dose-response characteristics and binding sites. Blood Adv 2019; 2:691-702. [PMID: 29581108 DOI: 10.1182/bloodadvances.2017006775] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2017] [Accepted: 01/22/2018] [Indexed: 01/11/2023] Open
Abstract
Vitamin K reduction is catalyzed by 2 enzymes in vitro: the vitamin K 2,3-epoxide reductase complex subunit 1 (VKORC1) and its isozyme VKORC1-like1 (VKORC1L1). In vivo, VKORC1 reduces vitamin K to sustain γ-carboxylation of vitamin K-dependent proteins, including coagulation factors. Inhibition of VKORC1 by oral anticoagulants (OACs) is clinically used in therapy and in prevention of thrombosis. However, OACs also inhibit VKORC1L1, which was previously shown to play a role in intracellular redox homeostasis in vitro. Here, we report data for the first time on specific inhibition of both VKOR enzymes for various OACs and rodenticides examined in a cell-based assay. Effects on endogenous VKORC1 and VKORC1L1 were independently investigated in genetically engineered HEK 293T cells that were knocked out for the respective genes by CRISPR/Cas9 technology. In general, dose-responses for 4-hydroxycoumarins and 1,3-indandiones were enzyme-dependent, with lower susceptibility for VKORC1L1 compared with VKORC1. In contrast, rodenticides exhibited nearly identical dose-responses for both enzymes. To explain the distinct inhibition pattern, we performed in silico modeling suggesting different warfarin binding sites for VKORC1 and VKORC1L1. We identified arginine residues at positions 38, 42, and 68 in the endoplasmatic reticulum luminal loop of VKORC1L1 responsible for charge-stabilized warfarin binding, resulting in a binding pocket that is diametrically opposite to that of VKORC1. In conclusion, our findings provide insight into structural and molecular drug binding on VKORC1, and especially on VKORC1L1.
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7
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Shen G, Li S, Cui W, Liu S, Liu Q, Yang Y, Gross M, Li W. Stabilization of warfarin-binding pocket of VKORC1 and VKORL1 by a peripheral region determines their different sensitivity to warfarin inhibition. J Thromb Haemost 2018; 16:1164-1175. [PMID: 29665197 PMCID: PMC6231229 DOI: 10.1111/jth.14127] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2018] [Indexed: 11/30/2022]
Abstract
Essentials VKORL1 and VKORC1 have a similar overall structure and warfarin-binding pocket. A peripheral region stabilizing this pocket controls warfarin sensitivity of the VKOR paralogs. A human single nucleotide polymorphism in this region renders VKORL1 sensitive to warfarin. A group of warfarin-resistant mutations in VKORC1 acts by disrupting peripheral interactions. SUMMARY Background The human genome encodes two paralogs of vitamin-K-epoxide reductase, VKORC1 and VKORL1, that support blood coagulation and other vitamin-K-dependent processes. Warfarin inhibits both enzymes, but VKORL1 is relatively resistant to warfarin. Objectives To understand the difference between VKORL1 and VKORC1, and the cause of warfarin-resistant (WR) mutations in VKORC1. Methods We performed systematic mutagenesis and analyzed warfarin responses with a cell-based activity assay. Mass spectrometry analyses were used to detect cellular redox state. Results VKORC1 and VKORL1 adopt a similar intracellular redox state with four-transmembrane-helix topology. Most WR mutations identified in VKORC1 also confer resistance in VKORL1, indicating that warfarin inhibits these paralogs at a common binding site. A group of WR mutations, distant from the warfarin-binding site, show significantly less resistance in VKORL1 than in VKORC1, implying that their different warfarin responses are determined by peripheral interactions. Remarkably, we identify a critical peripheral region in which single mutations, Glu37Lys or His46Tyr, drastically increase the warfarin sensitivity of VKORL1. In the background of these warfarin-sensitive VKORL1 mutants, WR mutations showing relative less resistance in wild-type VKORL1 become much more resistant, suggesting a structural conversion to resemble VKORC1. At this peripheral region, we also identified a human single nucleotide polymorphism that confers warfarin sensitivity of VKORL1. Conclusions Peripheral regions of VKORC1 and VKORL1 primarily maintain the stability of their common warfarin-binding pocket, and differences of such interactions determine their relative sensitivity to warfarin inhibition. This new model also explains most WR mutations located at the peripheral regions of VKORC1.
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Affiliation(s)
- G Shen
- Institute of Hemostasis and Thrombosis, College of Medicine, Henan University of Science and Technology, Luoyang, Henan, China
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO, USA
| | - S Li
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO, USA
| | - W Cui
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO, USA
| | - S Liu
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO, USA
| | - Q Liu
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO, USA
- Department of Forensic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Y Yang
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO, USA
| | - M Gross
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO, USA
| | - W Li
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO, USA
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8
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Warfarin and vitamin K epoxide reductase: a molecular accounting for observed inhibition. Blood 2018; 132:647-657. [PMID: 29743176 DOI: 10.1182/blood-2018-01-830901] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2018] [Accepted: 05/06/2018] [Indexed: 01/05/2023] Open
Abstract
Vitamin K epoxide reductase (VKOR), an endoplasmic reticulum membrane protein, is the key enzyme for vitamin K-dependent carboxylation, a posttranslational modification that is essential for the biological functions of coagulation factors. VKOR is the target of the most widely prescribed oral anticoagulant, warfarin. However, the topological structure of VKOR and the mechanism of warfarin's inhibition of VKOR remain elusive. Additionally, it is not clear why warfarin-resistant VKOR mutations identified in patients significantly decrease warfarin's binding affinity, but have only a minor effect on vitamin K binding. Here, we used immunofluorescence confocal imaging of VKOR in live mammalian cells and PEGylation of VKOR's endogenous cytoplasmic-accessible cysteines in intact microsomes to probe the membrane topology of human VKOR. Our results show that the disputed loop sequence between the first and second transmembrane (TM) domain of VKOR is located in the cytoplasm, supporting a 3-TM topological structure of human VKOR. Using molecular dynamics (MD) simulations, a T-shaped stacking interaction between warfarin and tyrosine residue 139, within the proposed TY139A warfarin-binding motif, was observed. Furthermore, a reversible dynamic warfarin-binding pocket opening and conformational changes were observed when warfarin binds to VKOR. Several residues (Y25, A26, and Y139) were found essential for warfarin binding to VKOR by MD simulations, and these were confirmed by the functional study of VKOR and its mutants in their native milieu using a cell-based assay. Our findings provide new insights into the dynamics of the binding of warfarin to VKOR, as well as into warfarin's mechanism of anticoagulation.
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9
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Vitamin K epoxide reductase and its paralogous enzyme have different structures and functions. Sci Rep 2017; 7:17632. [PMID: 29247216 PMCID: PMC5732223 DOI: 10.1038/s41598-017-18008-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2017] [Accepted: 12/05/2017] [Indexed: 01/09/2023] Open
Abstract
Vitamin K epoxide reductase (VKOR) is an essential enzyme for vitamin K-dependent carboxylation, while the physiological function of its paralogous enzyme VKOR-like (VKORL) is yet unknown. Although these two enzymes share approximately 50% protein sequence homology, the membrane topology of VKOR is still in debate. Here, we explored the differences in the membrane topology and disulfide-linked oligomerization of these two enzymes. Results from mutating the critical amino acid residues in the disputed transmembrane (TM) regions revealed that the second TM domain in the proposed 4-TM model of VKOR does not function as an authentic TM helix; supporting VKOR is a 3-TM protein, which is different from VKORL. Additionally, altering the loop sequence between the two conserved cysteine residues of VKORL affects its activity, supporting the notion that the conserved loop cysteines of VKORL are involved in its active site regeneration. However, a similar mutation in VKOR does not affect its enzymatic activity. Finally, our results show that although both VKOR and VKORL form disulfide-linked oligomers, the cysteine residues involved in the oligomerization appear to be different. Overall, the structural and functional differences between VKOR and VKORL shown here indicate that VKORL might have a different physiological function other than recycling vitamin K.
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10
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Lemke G. Phosphatidylserine Is the Signal for TAM Receptors and Their Ligands. Trends Biochem Sci 2017; 42:738-748. [PMID: 28734578 DOI: 10.1016/j.tibs.2017.06.004] [Citation(s) in RCA: 67] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2017] [Revised: 06/04/2017] [Accepted: 06/08/2017] [Indexed: 12/20/2022]
Abstract
Nature repeatedly repurposes, in that molecules that serve as metabolites, energy depots, or polymer subunits are at the same time used to deliver signals within and between cells. The preeminent example of this repurposing is ATP, which functions as a building block for nucleic acids, an energy source for enzymatic reactions, a phosphate donor to regulate intracellular signaling, and a neurotransmitter to control the activity of neurons. A series of recent studies now consolidates the view that phosphatidylserine (PtdSer), a common phospholipid constituent of membrane bilayers, is similarly repurposed for use as a signal between cells and that the ligands and receptors of the Tyro3/Axl/Mer (TAM) family of receptor tyrosine kinases (RTKs) are prominent transducers of this signal.
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Affiliation(s)
- Greg Lemke
- Molecular Neurobiology Laboratory, Salk Institute for Biological Studies, La Jolla, CA 92037, USA; Immunobiology and Microbial Pathogenesis Laboratory, Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
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11
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Chatron N, Chalmond B, Trouvé A, Benoît E, Caruel H, Lattard V, Tchertanov L. Identification of the functional states of human vitamin K epoxide reductase from molecular dynamics simulations. RSC Adv 2017. [DOI: 10.1039/c7ra07463h] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The functionally-related states of hVKORC1 predicted from MD conformations were assigned by probing their affinity to vitamin K and validated through analysis of its binding energy with VKAs.
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Affiliation(s)
- N. Chatron
- Centre de Mathématiques et de Leurs Applications (CMLA)
- ENS Cachan
- CNRS
- Université Paris-Saclay
- Cachan
| | - B. Chalmond
- Centre de Mathématiques et de Leurs Applications (CMLA)
- ENS Cachan
- CNRS
- Université Paris-Saclay
- Cachan
| | - A. Trouvé
- Centre de Mathématiques et de Leurs Applications (CMLA)
- ENS Cachan
- CNRS
- Université Paris-Saclay
- Cachan
| | - E. Benoît
- USC 1233 INRA-Vetagro Sup
- Veterinary School of Lyon
- Marcy l'Etoile
- France
| | | | - V. Lattard
- USC 1233 INRA-Vetagro Sup
- Veterinary School of Lyon
- Marcy l'Etoile
- France
| | - L. Tchertanov
- Centre de Mathématiques et de Leurs Applications (CMLA)
- ENS Cachan
- CNRS
- Université Paris-Saclay
- Cachan
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12
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The membrane topology of vitamin K epoxide reductase is conserved between human isoforms and the bacterial enzyme. Biochem J 2016; 473:851-8. [PMID: 26772871 DOI: 10.1042/bj20151223] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Accepted: 01/15/2016] [Indexed: 11/17/2022]
Abstract
The membrane topology of vitamin K epoxide reductase (VKOR) is controversial with data supporting both a three transmembrane and a four transmembrane model. The positioning of the transmembrane domains and the loops between these domains is critical if we are to understand the mechanism of vitamin K oxidation and its recycling by members of the thioredoxin family of proteins and the mechanism of action of warfarin, an inhibitor of VKOR. Here we show that both mammalian VKOR isoforms adopt the same topology, with the large loop between transmembrane one and two facing the lumen of the endoplasmic reticulum (ER). We used a redox sensitive green fluorescent protein (GFP) fused to the N- or C-terminus to show that these regions face the cytosol, and introduction of glycosylation sites along with mixed disulfide formation with thioredoxin-like transmembrane protein (TMX) to demonstrate ER localization of the major loop. The topology is identical with the bacterial homologue from Synechococcussp., for which the structure and mechanism of recycling has been characterized. Our results provide a resolution to the membrane topology controversy and support previous results suggesting a role for members of the ER protein disulfide isomerase (PDI) family in recycling VKOR.
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13
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van Gorp RH, Schurgers LJ. New Insights into the Pros and Cons of the Clinical Use of Vitamin K Antagonists (VKAs) Versus Direct Oral Anticoagulants (DOACs). Nutrients 2015; 7:9538-57. [PMID: 26593943 PMCID: PMC4663607 DOI: 10.3390/nu7115479] [Citation(s) in RCA: 59] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2015] [Revised: 10/28/2015] [Accepted: 11/05/2015] [Indexed: 12/19/2022] Open
Abstract
Vitamin K-antagonists (VKA) are the most widely used anticoagulant drugs to treat patients at risk of arterial and venous thrombosis for the past 50 years. Due to unfavorable pharmacokinetics VKA have a small therapeutic window, require frequent monitoring, and are susceptible to drug and nutritional interactions. Additionally, the effect of VKA is not limited to coagulation, but affects all vitamin K-dependent proteins. As a consequence, VKA have detrimental side effects by enhancing medial and intimal calcification. These limitations stimulated the development of alternative anticoagulant drugs, resulting in direct oral anticoagulant (DOAC) drugs, which specifically target coagulation factor Xa and thrombin. DOACs also display non-hemostatic vascular effects via protease-activated receptors (PARs). As atherosclerosis is characterized by a hypercoagulable state indicating the involvement of activated coagulation factors in the genesis of atherosclerosis, anticoagulation could have beneficial effects on atherosclerosis. Additionally, accumulating evidence demonstrates vascular benefit from high vitamin K intake. This review gives an update on oral anticoagulant treatment on the vasculature with a special focus on calcification and vitamin K interaction.
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Affiliation(s)
- Rick H van Gorp
- Department of Biochemistry, Cardiovascular Research Institute Maastricht, Maastricht University, PO Box 616, 6200 MD Maastricht, The Netherlands.
- Nattopharma ASA, 1363 Høvik, Norway.
| | - Leon J Schurgers
- Department of Biochemistry, Cardiovascular Research Institute Maastricht, Maastricht University, PO Box 616, 6200 MD Maastricht, The Netherlands.
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14
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Jaenecke F, Friedrich-Epler B, Parthier C, Stubbs MT. Membrane composition influences the activity of in vitro refolded human vitamin K epoxide reductase. Biochemistry 2015; 54:6454-61. [PMID: 26435421 DOI: 10.1021/acs.biochem.5b00716] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Human vitamin K epoxide reductase (hVKOR) is an integral membrane protein responsible for the maintenance of reduced vitamin K pools, a prerequisite for the action of γ-glutamyl carboxylase and hence for hemostasis. Here we describe the recombinant expression of hVKOR as an insoluble fusion protein in Escherichia coli, followed by purification and chemical cleavage under denaturing conditions. In vitro renaturation and reconstitution of purified solubilized hVKOR in phospholipids could be established to yield active protein. Crucially, the renatured enzyme is inhibited by the powerful coumarin anticoagulant warfarin, and we demonstrate that enzyme activity depends on lipid composition. The completely synthetic system for protein production allows a rational investigation of the multiple variables in membrane protein folding and paves the way for the provision of pure, active membrane protein for structural studies.
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Affiliation(s)
- Frank Jaenecke
- Institut für Biochemie und Biotechnologie, Martin-Luther Universität Halle-Wittenberg , Kurt-Mothes Strasse 3, D-06120 Halle/Saale, Germany.,ZIK HALOmem , Kurt-Mothes Strasse 3, D-06120 Halle/Saale, Germany
| | - Beatrice Friedrich-Epler
- Institut für Biochemie und Biotechnologie, Martin-Luther Universität Halle-Wittenberg , Kurt-Mothes Strasse 3, D-06120 Halle/Saale, Germany
| | - Christoph Parthier
- Institut für Biochemie und Biotechnologie, Martin-Luther Universität Halle-Wittenberg , Kurt-Mothes Strasse 3, D-06120 Halle/Saale, Germany
| | - Milton T Stubbs
- Institut für Biochemie und Biotechnologie, Martin-Luther Universität Halle-Wittenberg , Kurt-Mothes Strasse 3, D-06120 Halle/Saale, Germany.,ZIK HALOmem , Kurt-Mothes Strasse 3, D-06120 Halle/Saale, Germany
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15
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Structural Modeling Insights into Human VKORC1 Phenotypes. Nutrients 2015; 7:6837-51. [PMID: 26287237 PMCID: PMC4555152 DOI: 10.3390/nu7085313] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2015] [Revised: 08/03/2015] [Accepted: 08/06/2015] [Indexed: 11/17/2022] Open
Abstract
Vitamin K 2,3-epoxide reductase complex subunit 1 (VKORC1) catalyses the reduction of vitamin K and its 2,3-epoxide essential to sustain γ-carboxylation of vitamin K-dependent proteins. Two different phenotypes are associated with mutations in human VKORC1. The majority of mutations cause resistance to 4-hydroxycoumarin- and indandione-based vitamin K antagonists (VKA) used in the prevention and therapy of thromboembolism. Patients with these mutations require greater doses of VKA for stable anticoagulation than patients without mutations. The second phenotype, a very rare autosomal-recessive bleeding disorder caused by combined deficiency of vitamin K dependent clotting factors type 2 (VKCFD2) arises from a homozygous Arg98Trp mutation. The bleeding phenotype can be corrected by vitamin K administration. Here, we summarize published experimental data and in silico modeling results in order to rationalize the mechanisms of VKA resistance and VKCFD2.
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16
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Kumar SR. Industrial production of clotting factors: Challenges of expression, and choice of host cells. Biotechnol J 2015; 10:995-1004. [PMID: 26099845 DOI: 10.1002/biot.201400666] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2015] [Revised: 04/25/2015] [Accepted: 06/01/2015] [Indexed: 12/20/2022]
Abstract
The development of recombinant forms of blood coagulation factors as safer alternatives to plasma derived factors marked a major advance in the treatment of common coagulation disorders. These are complex proteins, mostly enzymes or co-enzymes, involving multiple post-translational modifications, and therefore are difficult to express. This article reviews the nature of the expression challenges for the industrial production of these factors, vis-à-vis the translational and post-translational bottlenecks, as well as the choice of host cell lines for high-fidelity production. For achieving high productivities of vitamin K dependent proteins, which include factors II (prothrombin), VII, IX and X, and protein C, host cell limitation of γ-glutamyl carboxylation is a major bottleneck. Despite progress in addressing this, involvement of yet unidentified protein(s) impedes a complete cell engineering solution. Human factor VIII expresses at very low levels due to limitations at several steps in the protein secretion pathway. Protein and cell engineering, vector improvement and alternate host cells promise improvement in the productivity. Production of Von Willebrand factor is constrained by its large size, complex structure, and the need for extensive glycosylation and disulfide-bonded oligomerization. All the licensed therapeutic factors are produced in CHO, BHK or HEK293 cells. While HEK293 is a recent adoption, BHK cells appear to be disfavored.
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17
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18
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The Arg98Trp mutation in human VKORC1 causing VKCFD2 disrupts a di-arginine-based ER retention motif. Blood 2014; 124:1354-62. [PMID: 24963046 DOI: 10.1182/blood-2013-12-545988] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Vitamin K 2,3-epoxide reductase complex subunit 1 (VKORC1) is an enzyme localized to the endoplasmic reticulum (ER) membrane. VKORC1 catalyzes the reduction of vitamin K 2,3-epoxide to vitamin K and to vitamin K hydroquinone, the latter required by the enzyme γ-carboxylase for γ-carboxylation of all vitamin K-dependent (VKD) proteins. Until now, only 1 human VKORC1 mutation, p.Arg98Trp, is known to cause combined deficiency of VKD clotting factors type 2 (VKCFD2), a disease phenotype reported in 3 unrelated families. VKCFD2 patients suffer from spontaneous bleeding episodes because of decreased levels of γ-carboxylated VKD clotting factors. Daily supraphysiological vitamin K supplementation restores clotting for VKCFD2 patients and results in high serum levels of vitamin K 2,3-epoxide, suggesting that supplemented vitamin K is reduced in vivo. Although the p.Arg98Trp mutation results in reduced vitamin K 2,3-epoxide reductase activity, the molecular mechanism underlying this pathophysiology is unknown. Using a combination of in silico analysis and confocal microscopy, we demonstrate for the first time that VKORC1:p.Arg98Trp disrupts a di-arginine ER retention motif resulting in 20% ER colocalization only. As a consequence, VKORC1 exits the ER membrane by cellular quality control systems and results in the observed VKCFD2 phenotype.
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19
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Shearer MJ, Newman P. Recent trends in the metabolism and cell biology of vitamin K with special reference to vitamin K cycling and MK-4 biosynthesis. J Lipid Res 2014; 55:345-62. [PMID: 24489112 PMCID: PMC3934721 DOI: 10.1194/jlr.r045559] [Citation(s) in RCA: 126] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2013] [Revised: 01/30/2014] [Indexed: 12/25/2022] Open
Abstract
In contrast to other fat-soluble vitamins, dietary vitamin K is rapidly lost to the body resulting in comparatively low tissue stores. Deficiency is kept at bay by the ubiquity of vitamin K in the diet, synthesis by gut microflora in some species, and relatively low vitamin K cofactor requirements for γ-glutamyl carboxylation. However, as shown by fatal neonatal bleeding in mice that lack vitamin K epoxide reductase (VKOR), the low requirements are dependent on the ability of animals to regenerate vitamin K from its epoxide metabolite via the vitamin K cycle. The identification of the genes encoding VKOR and its paralog VKOR-like 1 (VKORL1) has accelerated understanding of the enzymology of this salvage pathway. In parallel, a novel human enzyme that participates in the cellular conversion of phylloquinone to menaquinone (MK)-4 was identified as UbiA prenyltransferase-containing domain 1 (UBIAD1). Recent studies suggest that side-chain cleavage of oral phylloquinone occurs in the intestine, and that menadione is a circulating precursor of tissue MK-4. The mechanisms and functions of vitamin K recycling and MK-4 synthesis have dominated advances made in vitamin K biochemistry over the last five years and, after a brief overview of general metabolism, are the main focuses of this review.
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Affiliation(s)
- Martin J. Shearer
- Centre for Haemostasis and Thrombosis, Guy's and St. Thomas’ NHS Foundation Trust, London SE1 7EH, UK; and
| | - Paul Newman
- Cancer Research UK London Research Institute, London WC2A 3LY, UK
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20
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Fleck SC, Pfeiffer E, Podlech J, Metzler M. Epoxide reduction to an alcohol: a novel metabolic pathway for perylene quinone-type alternaria mycotoxins in mammalian cells. Chem Res Toxicol 2014; 27:247-53. [PMID: 24428710 DOI: 10.1021/tx400366w] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
The group of perylene quinone-type Alternaria toxins contains several congeners with epoxide groups, for example, altertoxin II (ATX II) and stemphyltoxin III (STTX III). Recent studies in our laboratory have disclosed that the epoxide moieties of ATX II and STTX III are reduced to alcohols in human colon Caco-2 cells, thereby resulting in the formation of altertoxin I (ATX I) and alteichin, respectively. In the present study, this pathway was demonstrated for ATX II in three other mammalian cell lines. Furthermore, the chemical reaction of this toxin with monothiols like glutathione could be shown, and the structures of the reaction products were tentatively elucidated by UV and mass spectrometry. Chemical reaction of ATX II with dithiols capable of forming five- and six-membered rings gave rise to ATX I, thus providing a clue for the molecular mechanism of the epoxide reduction pathway of ATX II. Both epoxide reduction and glutathione conjugation appear to attenuate, but not completely abolish, the genotoxicity of ATX II.
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Affiliation(s)
- Stefanie C Fleck
- Institute of Applied Biosciences, Unit of Food Toxicology, Karlsruhe Institute of Technology (KIT) , Karlsruhe D-76131, Germany
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21
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Butler MS, Robertson AAB, Cooper MA. Natural product and natural product derived drugs in clinical trials. Nat Prod Rep 2014; 31:1612-61. [DOI: 10.1039/c4np00064a] [Citation(s) in RCA: 383] [Impact Index Per Article: 38.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The 25 Natural Product (NP)-derived drugs launched since 2008 and the 100 NP-derived compounds and 33 Antibody Drug Conjugates (ADCs) in clinical trials or in registration at the end of 2013 are reviewed.
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Affiliation(s)
- Mark S. Butler
- Division of Chemistry and Structural Biology
- Institute for Molecular Bioscience
- The University of Queensland
- Brisbane, Australia
| | - Avril A. B. Robertson
- Division of Chemistry and Structural Biology
- Institute for Molecular Bioscience
- The University of Queensland
- Brisbane, Australia
| | - Matthew A. Cooper
- Division of Chemistry and Structural Biology
- Institute for Molecular Bioscience
- The University of Queensland
- Brisbane, Australia
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22
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Oldenburg J, Müller CR, Rost S, Watzka M, Bevans CG. Comparative genetics of warfarin resistance. Hamostaseologie 2013; 34:143-59. [PMID: 24287886 DOI: 10.5482/hamo-13-09-0047] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2013] [Accepted: 09/25/2013] [Indexed: 11/05/2022] Open
Abstract
Warfarin and other 4-hydroxycoumarin-based oral anticoagulants targeting vitamin K 2,3-epoxide reductase complex subunit 1 (VKORC1) are administered to humans, mice and rats with different purposes in mind - to act as pesticides in high-dosage baits for killing rodents, but also to save lives when administered in low dosages as antithrombotic drugs in humans. However, high-dosage warfarin used to control rodent populations has resulted in numerous mutations causing warfarin resistance. Currently, six single missense mutations in mice, 12 distinct missense mutations in rats, as well as compound heterozygous or homozygous mutations with up to six distinct missense mutations per Vkorc1 allele have been described. Warfarin resistance missense mutations for human VKORC1 have also been found world-wide, but differ characteristically from those in rodents. In humans, 26 distinct mutations have been characterized, but occur only rarely either in heterozygous or, even rarer, in homozygous form. In this review, we summarize the known VKORC1 missense mutations causing warfarin and other 4-hydroxycoumarin drug resistance, identify genomics databases as new sources of data, explore possible underlying genetic mechanisms, and summarize similarities and differences between warfarin resistant VKORC1 variants in humans and rodents.
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Affiliation(s)
- J Oldenburg
- Prof. Dr. Johannes Oldenburg, Institute of Experimental Haematology and Transfusion Medicine, University Clinic Bonn, Sigmund Freud Str. 25, 53105 Bonn, Germany, E-mail: , Tel. +49/(0)228/287 51 75, Fax +49/(0)228/287 51 76
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23
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Taxak N, Kalra S, Bharatam PV. Mechanism-Based Inactivation of Cytochromes by Furan Epoxide: Unraveling the Molecular Mechanism. Inorg Chem 2013; 52:13496-508. [DOI: 10.1021/ic401907k] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- Nikhil Taxak
- Department
of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research (NIPER), Sector 67, S. A. S. Nagar
(Mohali), 160 062 Punjab, India
| | - Sourav Kalra
- Department
of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research (NIPER), Sector 67, S. A. S. Nagar
(Mohali), 160 062 Punjab, India
| | - Prasad V. Bharatam
- Department
of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research (NIPER), Sector 67, S. A. S. Nagar
(Mohali), 160 062 Punjab, India
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24
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Human VKORC1 mutations cause variable degrees of 4-hydroxycoumarin resistance and affect putative warfarin binding interfaces. Blood 2013; 122:2743-50. [PMID: 23982176 DOI: 10.1182/blood-2013-05-501692] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Since the discovery of warfarin-sensitive vitamin K 2,3-epoxide reductase complex subunit 1 (VKORC1), 26 human VKORC1 (hVKORC1) missense mutations have been associated with oral anticoagulant resistance (OACR). Assessment of warfarin resistance using the "classical" dithiothreitol-driven vitamin K 2,3-epoxide reductase (VKOR) assay has not reflected clinical resistance phenotypes for most mutations. Here, we present half maximal inhibitory concentrations (IC50) results for 21 further hVKORC1 mutations obtained using a recently validated cell-based assay (J Thromb Haemost 11(5):872). In contrast to results from the dithiothreitol-driven VKOR assay, all mutations exhibited basal VKOR activity and warfarin IC50 values that correspond well to patient OACR phenotypes. Thus, the present assay is useful for functional investigations of VKORC1 and oral anticoagulant inhibition of the vitamin K cycle. Additionally, we modeled hVKORC1 on the previously solved structure of a homologous bacterial enzyme and performed in silico docking of warfarin on this model. We identified one binding site delineated by 3 putative binding interfaces. These interfaces comprise linear sequences of the endoplasmic reticulum-lumenal loop (Ser52-Phe55) and the first (Leu22-Lys30) and fourth (Phe131-Thr137) transmembrane helices. All known OACR-associated hVKORC1 mutations are located in or around these putative interfaces, supporting our model.
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