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Bekker GJ, Oshima K, Araki M, Okuno Y, Kamiya N. Binding Mechanism between Platelet Glycoprotein and Cyclic Peptide Elucidated by McMD-Based Dynamic Docking. J Chem Inf Model 2024; 64:4158-4167. [PMID: 38751042 DOI: 10.1021/acs.jcim.4c00100] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/28/2024]
Abstract
The cyclic peptide OS1 (amino acid sequence: CTERMALHNLC), which has a disulfide bond between both termini cysteine residues, inhibits complex formation between the platelet glycoprotein Ibα (GPIbα) and the von Willebrand factor (vWF) by forming a complex with GPIbα. To study the binding mechanism between GPIbα and OS1 and, therefore, the inhibition mechanism of the protein-protein GPIbα-vWF complex, we have applied our multicanonical molecular dynamics (McMD)-based dynamic docking protocol starting from the unbound state of the peptide. Our simulations have reproduced the experimental complex structure, although the top-ranking structure was an intermediary one, where the peptide was bound in the same location as in the experimental structure; however, the β-switch of GPIbα attained a different conformation. Our analysis showed that subsequent refolding of the β-switch results in a more stable binding configuration, although the transition to the native configuration appears to take some time, during which OS1 could dissociate. Our results show that conformational changes in the β-switch are crucial for successful binding of OS1. Furthermore, we identified several allosteric binding sites of GPIbα that might also interfere with vWF binding, and optimization of the peptide to target these allosteric sites might lead to a more effective inhibitor, as these are not dependent on the β-switch conformation.
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Affiliation(s)
- Gert-Jan Bekker
- Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Kanji Oshima
- Bio-Pharma Research Laboratories, Kaneka Corporation, 1-8 Miyamae-cho, Takasago-cho, Takasago, Hyogo 676-8688, Japan
| | - Mitsugu Araki
- Graduate School of Medicine, Kyoto University, 53 Shogoin-Kawaharacho, Sakyo-ku, Kyoto 606-8507, Japan
| | - Yasushi Okuno
- Graduate School of Medicine, Kyoto University, 53 Shogoin-Kawaharacho, Sakyo-ku, Kyoto 606-8507, Japan
| | - Narutoshi Kamiya
- Graduate School of Information Science, University of Hyogo, 7-1-28 minatojima Minami-machi, Chuo-ku, Kobe, Hyogo 650-0047, Japan
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2
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Hoefer T, Rana A, Niego B, Jagdale S, Albers HJ, Gardiner EE, Andrews RK, Van der Meer AD, Hagemeyer CE, Westein E. Targeting shear gradient activated von Willebrand factor by the novel single-chain antibody A1 reduces occlusive thrombus formation in vitro. Haematologica 2021; 106:2874-2884. [PMID: 33054112 PMCID: PMC8561297 DOI: 10.3324/haematol.2020.250761] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2020] [Indexed: 12/12/2022] Open
Abstract
Intraluminal thrombus formation precipitates conditions such as acute myocardial infarction and disturbs local blood flow resulting in areas of rapidly changing blood flow velocities and steep gradients of blood shear rate. Shear rate gradients are known to be pro-thrombotic with an important role for the shear-sensitive plasma protein von Willebrand factor (VWF). Here, we developed a single-chain antibody (scFv) that targets a shear gradient specific conformation of VWF to specifically inhibit platelet adhesion at sites of SRGs but not in areas of constant shear. Microfluidic flow channels with stenotic segments were used to create shear rate gradients during blood perfusion. VWF-GPIbα interactions were increased at sites of shear rate gradients compared to constant shear rate of matched magnitude. The scFv-A1 specifically reduced VWF-GPIbα binding and thrombus formation at sites of SRGs but did not block platelet deposition and aggregation under constant shear rate in upstream sections of the channels. Significantly, the scFv A1 attenuated platelet aggregation only in the later stages of thrombus formation. In the absence of shear, direct binding of scFv-A1 to VWF could not be detected and scFV-A1 did not inhibit ristocetin induced platelet agglutination. We have exploited the pro-aggregatory effects of SRGs on VWF dependent platelet aggregation and developed the shear-gradient sensitive scFv-A1 antibody that inhibits platelet aggregation exclusively at sites of shear rate gradients. The lack of VWF inhibition in non-stenosed vessel segments places scFV-A1 in an entirely new class of anti-platelet therapy for selective blockade of pathological thrombus formation while maintaining normal haemostasis.
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Affiliation(s)
- Thomas Hoefer
- Baker Heart and Diabetes Institute, Melbourne; TH and AR contributed equally to this work.
| | - Akshita Rana
- Australian Centre for Blood Diseases, Monash University, Melbourne; TH and AR contributed equally to this work.
| | - Be'eri Niego
- Australian Centre for Blood Diseases, Monash University, Melbourne.
| | - Shweta Jagdale
- Baker Heart and Diabetes Institute, Melbourne; Australian Centre for Blood Diseases, Monash University, Melbourne.
| | - Hugo J Albers
- Applied Stem Cell Technologies, University of Twente, Enschede; BIOS Lab-on-a-Chip, University of Twente, Enschede.
| | - Elizabeth E Gardiner
- ACRF Department of Cancer Biology and Therapeutics, John Curtin School of Medical Research, Australian National University, Canberra.
| | - Robert K Andrews
- Australian Centre for Blood Diseases, Monash University, Melbourne.
| | | | - Christoph E Hagemeyer
- Baker Heart and Diabetes Institute, Melbourne; Australian Centre for Blood Diseases, Monash University, Melbourne.
| | - Erik Westein
- Baker Heart and Diabetes Institute, Melbourne; Australian Centre for Blood Diseases, Monash University, Melbourne; CEH and EW contributed equally to this work.
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3
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Arce NA, Cao W, Brown AK, Legan ER, Wilson MS, Xu ER, Berndt MC, Emsley J, Zhang XF, Li R. Activation of von Willebrand factor via mechanical unfolding of its discontinuous autoinhibitory module. Nat Commun 2021; 12:2360. [PMID: 33883551 PMCID: PMC8060278 DOI: 10.1038/s41467-021-22634-x] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Accepted: 03/16/2021] [Indexed: 01/05/2023] Open
Abstract
Von Willebrand factor (VWF) activates in response to shear flow to initiate hemostasis, while aberrant activation could lead to thrombosis. Above a critical shear force, the A1 domain of VWF becomes activated and captures platelets via the GPIb-IX complex. Here we show that the shear-responsive element controlling VWF activation resides in the discontinuous autoinhibitory module (AIM) flanking A1. Application of tensile force in a single-molecule setting induces cooperative unfolding of the AIM to expose A1. The AIM-unfolding force is lowered by truncating either N- or C-terminal AIM region, type 2B VWD mutations, or binding of a ristocetin-mimicking monoclonal antibody, all of which could activate A1. Furthermore, the AIM is mechanically stabilized by the nanobody that comprises caplacizumab, the only FDA-approved anti-thrombotic drug to-date that targets VWF. Thus, the AIM is a mechano-regulator of VWF activity. Its conformational dynamics may define the extent of VWF autoinhibition and subsequent activation under force.
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Affiliation(s)
- Nicholas A Arce
- Aflac Cancer and Blood Disorders Center, Children's Healthcare of Atlanta, Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, USA
| | - Wenpeng Cao
- Department of Bioengineering, Department of Mechanical Engineering & Mechanics, Lehigh University, Bethlehem, PA, USA
| | - Alexander K Brown
- Biodiscovery Institute, School of Pharmacy, University of Nottingham, Nottingham, UK
| | - Emily R Legan
- Aflac Cancer and Blood Disorders Center, Children's Healthcare of Atlanta, Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, USA
| | - Moriah S Wilson
- Aflac Cancer and Blood Disorders Center, Children's Healthcare of Atlanta, Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, USA
| | - Emma-Ruoqi Xu
- Biodiscovery Institute, School of Pharmacy, University of Nottingham, Nottingham, UK
| | - Michael C Berndt
- Faculty of Health Sciences, Curtin University, Perth, WA, Australia
| | - Jonas Emsley
- Biodiscovery Institute, School of Pharmacy, University of Nottingham, Nottingham, UK
| | - X Frank Zhang
- Department of Bioengineering, Department of Mechanical Engineering & Mechanics, Lehigh University, Bethlehem, PA, USA.
| | - Renhao Li
- Aflac Cancer and Blood Disorders Center, Children's Healthcare of Atlanta, Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, USA.
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4
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Brown E, Ozawa K, Moccetti F, Vinson A, Hodovan J, Nguyen TA, Bader L, López JA, Kievit P, Shaw GD, Chung DW, Osborn W, Fu X, Chen J, Lindner JR. Arterial Platelet Adhesion in Atherosclerosis-Prone Arteries of Obese, Insulin-Resistant Nonhuman Primates. J Am Heart Assoc 2021; 10:e019413. [PMID: 33880941 PMCID: PMC8200741 DOI: 10.1161/jaha.120.019413] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Background Platelet–endothelial interactions are thought to contribute to early atherogenesis. These interactions are potentiated by oxidative stress. We used in vivo molecular imaging to test the hypothesis that platelet–endothelial interactions occur at early stages of plaque development in obese, insulin‐resistant nonhuman primates, and are suppressed by NADPH‐oxidase‐2 inhibition. Methods and Results Six adult rhesus macaques fed a Western‐style diet for a median of 4.0 years were studied at baseline and after 8 weeks of therapy with the NADPH‐oxidase‐2‐inhibitor apocynin (50 mg/kg per day). Six lean control animals were also studied. Measurements included intravenous glucose tolerance test, body composition by dual‐energy X‐ray absorptiometry, carotid intimal medial thickness, carotid artery contrast ultrasound molecular imaging for platelet GPIbα (glycoprotein‐ Ibα) and vascular cell adhesion molecule‐1, and blood oxidative markers on mass spectrometry. Compared with lean controls, animals on a Western‐style diet were obese (median body mass: 16.0 versus 8.7 kg, P=0.003; median truncal fat: 49% versus 20%, P=0.002), were insulin resistant (4‐fold higher insulin–glucose area under the curve on intravenous glucose tolerance test, P=0.002), had 40% larger carotid intimal medial thickness (P=0.004), and exhibited oxidative signatures on proteomics. In obese but not lean animals, signal enhancement on molecular imaging was significantly elevated for GPIbα and vascular cell adhesion molecule‐1. The signal correlated modestly with intimal medial thickness but not with the degree of insulin resistance. Apocynin significantly (P<0.01) reduced median signal for GPIbα by >80% and vascular cell adhesion molecule‐1 signal by 75%, but did not affect intimal medial thickness, body mass, or intravenous glucose tolerance test results. Conclusion In nonhuman primates, diet‐induced obesity and insulin resistance leads to platelet–endothelial adhesion at early atherosclerotic lesion sites, which is associated with the expression of pro‐inflammatory adhesion molecules. These responses appear to be mediated, in part, through oxidative pathways.
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Affiliation(s)
- Eran Brown
- Knight Cardiovascular Institute Portland OR
| | - Koya Ozawa
- Knight Cardiovascular Institute Portland OR
| | | | - Amanda Vinson
- Oregon National Primate Research CenterOregon Health & Science University Portland OR
| | | | | | - Lindsay Bader
- Oregon National Primate Research CenterOregon Health & Science University Portland OR
| | | | - Paul Kievit
- Oregon National Primate Research CenterOregon Health & Science University Portland OR
| | | | | | | | - Xiaoyun Fu
- Bloodworks Research Institute Seattle WA
| | | | - Jonathan R Lindner
- Knight Cardiovascular Institute Portland OR.,Oregon National Primate Research CenterOregon Health & Science University Portland OR
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5
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Ngo T, Kim K, Bian Y, Nam G, Park HJ, Lee K, Cho GS, Ryu JM, Lim KM, Chung JH. Antithrombotic effect of SP-8008, a benzoic acid derivative, through the selective inhibition of shear stress-induced platelet aggregation. Br J Pharmacol 2019; 177:929-944. [PMID: 31648364 PMCID: PMC7024737 DOI: 10.1111/bph.14894] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2019] [Revised: 07/30/2019] [Accepted: 09/05/2019] [Indexed: 01/23/2023] Open
Abstract
Background and Purpose Bleeding is one of the most critical adverse effects of antithrombotic drugs, and many efforts have been made to discover novel antiplatelet agents without bleeding complications. Shear stress‐induced platelet aggregation (SIPA), where the interaction of von Willebrand factor (vWF) and platelet glycoprotein (GP) Ib constitutes the initial step, is a promising target to overcome bleeding problems, as SIPA occurs only in pathological conditions. Here, we describe SP‐8008, a novel modulator of vWF–GP Ib interactions and evaluated its antiplatelet/antithrombotic effects. Experimental Approach Newly synthesized compounds were screened for antiplatelet effects in vitro, using human platelets exposed to high shear stress. Aggregation, intracellular calcium level, granule secretion, and integrin activation were assessed. Molecular modelling using virtual docking and flow cytometry were used to evaluate effects on vWF–GP Ib interactions. Antithrombotic effects in vivo were determined in rats, using arterial thrombosis and shear stress‐specific thrombosis. Transection tail bleeding time was used to evaluate adverse effects. Key Results SP‐8008 was a potent inhibitor of SIPA, with IC50 of 1.44 ± 0.09 μM. SP‐8008 effectively and broadly blocked shear stress‐induced platelet activation events, without any significant toxicity. Importantly, SP‐8008 was highly selective against SIPA, effectively interfering with vWF–GP Ib engagement. Most importantly, SP‐8008 exerted significant antithrombotic effects in vivo in both shear stress‐specific and arterial thrombosis, without prolonging bleeding time. Conclusions and Implications Our results demonstrated that SP‐8008 can be a novel selective antiplatelet agent with improved safety profile.
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Affiliation(s)
- Thien Ngo
- College of Pharmacy, Seoul National University, Seoul, Korea
| | - Keunyoung Kim
- College of Pharmacy, Seoul National University, Seoul, Korea
| | - Yiying Bian
- College of Pharmacy, Seoul National University, Seoul, Korea
| | - Gibeom Nam
- School of Pharmacy, Sungkyunkwan University, Suwon, Korea
| | - Hyun-Ju Park
- School of Pharmacy, Sungkyunkwan University, Suwon, Korea
| | - Kiho Lee
- College of Pharmacy, Korea University, Sejong, Korea
| | - Geum-Sil Cho
- Research Headquarters, Shin Poong Pharm. Co. Ltd., Ansan, Korea
| | - Jei-Man Ryu
- Research Headquarters, Shin Poong Pharm. Co. Ltd., Ansan, Korea
| | - Kyung-Min Lim
- College of Pharmacy, Ewha Womans University, Seoul, Korea
| | - Jin-Ho Chung
- College of Pharmacy, Seoul National University, Seoul, Korea
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6
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Chen 陈温纯 W, Voos KM, Josephson CD, Li R. Short-Acting Anti-VWF (von Willebrand Factor) Aptamer Improves the Recovery, Survival, and Hemostatic Functions of Refrigerated Platelets. Arterioscler Thromb Vasc Biol 2019; 39:2028-2037. [PMID: 31315441 DOI: 10.1161/atvbaha.119.312439] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
OBJECTIVE Refrigeration-induced binding of VWF (von Willebrand factor) to platelets contributes to the rapid clearance of refrigerated platelets. In this study, we investigate whether inhibiting VWF binding by a DNA-based aptamer ameliorates the clearance of refrigerated platelets without significantly impeding hemostatic functions. Approach and Results: Platelets were refrigerated with or without aptamer ARC1779 for 48 hours. VWF binding, the effective lifetime of ARC1779, platelet post-transfusion recovery and survival, and the hemostatic function were measured. ARC1779 treatment during refrigeration inhibited the platelet-VWF interaction. ARC1779-treated refrigerated murine platelets exhibited increased post-transfusion recovery and survival than untreated ones (recovery of ARC1779-treated platelets: 76.7±5.5%; untreated: 63.7±0.8%; P<0.01. Half-life: 31.4±2.36 hours versus 28.1±0.86 hours; P<0.05). A similar increase was observed for refrigerated human platelets (recovery: 49.4±4.4% versus 36.8±2.1%, P<0.01; half-life: 9.2±1.5 hours versus 8.7±0.9 hours, ns). The effective lifetime of ARC1779 in mice was 2 hours. Additionally, ARC1779 improved the long-term (2 hours after transfusion) hemostatic function of refrigerated platelets (tail bleeding time of mice transfused with ARC1779-treated refrigerated platelets: 160±65 seconds; untreated: 373±96 seconds; P<0.01). The addition of an ARC1779 antidote before transfusion improved the immediate (15 minutes after transfusion) hemostatic function (bleeding time of treated platelets: 149±21 seconds; untreated: 320±36 seconds; P<0.01). CONCLUSIONS ARC1779 improves the post-transfusion recovery of refrigerated platelets and preserves the long-term hemostatic function of refrigerated platelets. These results suggest that a short-acting inhibitor of the platelet-VWF interaction may be a potential therapeutic option to improve refrigeration of platelets for transfusion treatment.
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Affiliation(s)
- Wenchun Chen 陈温纯
- From the Aflac Cancer and Blood Disorders Center, Children's Healthcare of Atlanta, Department of Pediatrics (W.C., K.M.V., C.D.J., R.L.), Emory University School of Medicine, Atlanta, GA
| | - Kayleigh M Voos
- From the Aflac Cancer and Blood Disorders Center, Children's Healthcare of Atlanta, Department of Pediatrics (W.C., K.M.V., C.D.J., R.L.), Emory University School of Medicine, Atlanta, GA
| | - Cassandra D Josephson
- From the Aflac Cancer and Blood Disorders Center, Children's Healthcare of Atlanta, Department of Pediatrics (W.C., K.M.V., C.D.J., R.L.), Emory University School of Medicine, Atlanta, GA.,Department of Pathology (C.D.J), Emory University School of Medicine, Atlanta, GA
| | - Renhao Li
- From the Aflac Cancer and Blood Disorders Center, Children's Healthcare of Atlanta, Department of Pediatrics (W.C., K.M.V., C.D.J., R.L.), Emory University School of Medicine, Atlanta, GA
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7
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The Glycoprotein Ib-IX-V Complex. Platelets 2019. [DOI: 10.1016/b978-0-12-813456-6.00010-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/17/2023]
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8
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Chen W, Druzak SA, Wang Y, Josephson CD, Hoffmeister KM, Ware J, Li R. Refrigeration-Induced Binding of von Willebrand Factor Facilitates Fast Clearance of Refrigerated Platelets. Arterioscler Thromb Vasc Biol 2017; 37:2271-2279. [PMID: 29097365 DOI: 10.1161/atvbaha.117.310062] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2017] [Accepted: 10/23/2017] [Indexed: 11/16/2022]
Abstract
OBJECTIVE Apheresis platelets for transfusion treatment are currently stored at room temperature because after refrigeration platelets are rapidly cleared on transfusion. In this study, the role of von Willebrand factor (VWF) in the clearance of refrigerated platelets is addressed. APPROACH AND RESULTS Human and murine platelets were refrigerated in gas-permeable bags at 4°C for 24 hours. VWF binding, platelet signaling events, and platelet post-transfusion recovery and survival were measured. After refrigeration, the binding of plasma VWF to platelets was drastically increased, confirming earlier studies. The binding was blocked by peptide OS1 that bound specifically to platelet glycoprotein (GP)Ibα and was absent in VWF-/- plasma. Although surface expression of GPIbα was reduced after refrigeration, refrigeration-induced VWF binding under physiological shear induced unfolding of the GPIbα mechanosensory domain on the platelet, as evidenced by increased exposure of a linear epitope therein. Refrigeration and shear treatment also induced small elevation of intracellular Ca2+, phosphatidylserine exposure, and desialylation of platelets, which were absent in VWF-/- platelets or inhibited by OS1, which is a monomeric 11-residue peptide (CTERMALHNLC). Furthermore, refrigerated VWF-/- platelets displayed increased post-transfusion recovery and survival than wild-type ones. Similarly, adding OS1 to transgenic murine platelets expressing only human GPIbα during refrigeration improved their post-transfusion recovery and survival. CONCLUSIONS Refrigeration-induced binding of VWF to platelets facilitates their rapid clearance by inducing GPIbα-mediated signaling. Our results suggest that inhibition of the VWF-GPIbα interaction may be a potential strategy to enable refrigeration of platelets for transfusion treatment.
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Affiliation(s)
- Wenchun Chen
- From the Aflac Cancer and Blood Disorders Center, Children's Healthcare of Atlanta, GA (W.C., S.A.D., Y.W., C.D.J., R.L.); Department of Pediatrics (W.C., S.A.D., Y.W., C.D.J., R.L.) and Department of Pathology (C.D.J.), Emory University School of Medicine, Atlanta, GA; Blood Research Institute, BloodCenter of Wisconsin, Milwaukee (K.M.H.); and Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock (J.W.)
| | - Samuel A Druzak
- From the Aflac Cancer and Blood Disorders Center, Children's Healthcare of Atlanta, GA (W.C., S.A.D., Y.W., C.D.J., R.L.); Department of Pediatrics (W.C., S.A.D., Y.W., C.D.J., R.L.) and Department of Pathology (C.D.J.), Emory University School of Medicine, Atlanta, GA; Blood Research Institute, BloodCenter of Wisconsin, Milwaukee (K.M.H.); and Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock (J.W.)
| | - Yingchun Wang
- From the Aflac Cancer and Blood Disorders Center, Children's Healthcare of Atlanta, GA (W.C., S.A.D., Y.W., C.D.J., R.L.); Department of Pediatrics (W.C., S.A.D., Y.W., C.D.J., R.L.) and Department of Pathology (C.D.J.), Emory University School of Medicine, Atlanta, GA; Blood Research Institute, BloodCenter of Wisconsin, Milwaukee (K.M.H.); and Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock (J.W.)
| | - Cassandra D Josephson
- From the Aflac Cancer and Blood Disorders Center, Children's Healthcare of Atlanta, GA (W.C., S.A.D., Y.W., C.D.J., R.L.); Department of Pediatrics (W.C., S.A.D., Y.W., C.D.J., R.L.) and Department of Pathology (C.D.J.), Emory University School of Medicine, Atlanta, GA; Blood Research Institute, BloodCenter of Wisconsin, Milwaukee (K.M.H.); and Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock (J.W.)
| | - Karin M Hoffmeister
- From the Aflac Cancer and Blood Disorders Center, Children's Healthcare of Atlanta, GA (W.C., S.A.D., Y.W., C.D.J., R.L.); Department of Pediatrics (W.C., S.A.D., Y.W., C.D.J., R.L.) and Department of Pathology (C.D.J.), Emory University School of Medicine, Atlanta, GA; Blood Research Institute, BloodCenter of Wisconsin, Milwaukee (K.M.H.); and Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock (J.W.)
| | - Jerry Ware
- From the Aflac Cancer and Blood Disorders Center, Children's Healthcare of Atlanta, GA (W.C., S.A.D., Y.W., C.D.J., R.L.); Department of Pediatrics (W.C., S.A.D., Y.W., C.D.J., R.L.) and Department of Pathology (C.D.J.), Emory University School of Medicine, Atlanta, GA; Blood Research Institute, BloodCenter of Wisconsin, Milwaukee (K.M.H.); and Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock (J.W.)
| | - Renhao Li
- From the Aflac Cancer and Blood Disorders Center, Children's Healthcare of Atlanta, GA (W.C., S.A.D., Y.W., C.D.J., R.L.); Department of Pediatrics (W.C., S.A.D., Y.W., C.D.J., R.L.) and Department of Pathology (C.D.J.), Emory University School of Medicine, Atlanta, GA; Blood Research Institute, BloodCenter of Wisconsin, Milwaukee (K.M.H.); and Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock (J.W.).
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9
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Glycoprotein Ibα inhibitor (CCP-224) prevents neutrophil-platelet aggregation in Sickle Cell Disease. Blood Adv 2017; 1:1712-1716. [PMID: 28966995 DOI: 10.1182/bloodadvances.2017006742] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Key Points
CCP-224 attenuates neutrophil-platelet aggregation in SCD patient blood. CCP-224 has the potential to prevent vaso-occlusion in SCD patients.
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10
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Donnet T, Ravanat C, Eckly A, Maurer E, Alame G, Ziessel C, Mangin PH, Freund M, Cazenave JP, Gachet C, Rendu F. Dehydration of blood platelets by zeodration: in vitro characterization and hemostatic properties in vivo. Transfusion 2015; 55:2207-18. [DOI: 10.1111/trf.13121] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2014] [Revised: 02/23/2015] [Accepted: 02/28/2015] [Indexed: 12/13/2022]
Affiliation(s)
- Thibault Donnet
- UMR_S949 EFS Alsace; INSERM, Université De Strasbourg; Strasbourg
- Faculté De Médecine Pitié-Salpêtrière; UMR_S956 INSERM, UPMC; Paris France
| | | | - Anita Eckly
- UMR_S949 EFS Alsace; INSERM, Université De Strasbourg; Strasbourg
| | - Eric Maurer
- UMR_S949 EFS Alsace; INSERM, Université De Strasbourg; Strasbourg
| | - Ghina Alame
- UMR_S949 EFS Alsace; INSERM, Université De Strasbourg; Strasbourg
| | | | - Pierre H. Mangin
- UMR_S949 EFS Alsace; INSERM, Université De Strasbourg; Strasbourg
| | - Monique Freund
- UMR_S949 EFS Alsace; INSERM, Université De Strasbourg; Strasbourg
| | | | - Christian Gachet
- UMR_S949 EFS Alsace; INSERM, Université De Strasbourg; Strasbourg
| | - Francine Rendu
- Faculté De Médecine Pitié-Salpêtrière; UMR_S956 INSERM, UPMC; Paris France
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11
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Metharom P, Berndt MC, Baker RI, Andrews RK. Current state and novel approaches of antiplatelet therapy. Arterioscler Thromb Vasc Biol 2015; 35:1327-38. [PMID: 25838432 DOI: 10.1161/atvbaha.114.303413] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2014] [Accepted: 03/19/2015] [Indexed: 01/22/2023]
Abstract
An unresolved problem with clinical use of antiplatelet therapy is that a significant number of individuals either still get thrombosis or run the risk of life-threatening bleeding. Antiplatelet drugs are widely used clinically, either chronically for people at risk of athero/thrombotic disease or to prevent thrombus formation during surgery. However, a subpopulation may be resistant to standard doses, while the platelet targets of these drugs are also critical for the normal hemostatic function of platelets. In this review, we will briefly examine current antiplatelet therapy and existing targets while focusing on new potential approaches for antiplatelet therapy and improved monitoring of effects on platelet reactivity in individuals, ultimately to improve antithrombosis with minimal bleeding. Primary platelet adhesion-signaling receptors, glycoprotein (GP)Ib-IX-V and GPVI, that bind von Willebrand factor/collagen and other prothrombotic factors are not targeted by drugs in clinical use, but they are of particular interest because of their key role in thrombus formation at pathological shear.
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Affiliation(s)
- Pat Metharom
- From the Faculty of Health Sciences, Curtin University, Perth, Western Australia, Australia (P.M., M.C.B); Western Australian Centre for Thrombosis and Haemostasis, Murdoch University, Perth, Western Australia, Australia (R.I.B.); and Australian Centre for Blood Diseases, Department of Clinical Haematology, Monash University, Melbourne, Victoria, Australia (R.K.A.)
| | - Michael C Berndt
- From the Faculty of Health Sciences, Curtin University, Perth, Western Australia, Australia (P.M., M.C.B); Western Australian Centre for Thrombosis and Haemostasis, Murdoch University, Perth, Western Australia, Australia (R.I.B.); and Australian Centre for Blood Diseases, Department of Clinical Haematology, Monash University, Melbourne, Victoria, Australia (R.K.A.).
| | - Ross I Baker
- From the Faculty of Health Sciences, Curtin University, Perth, Western Australia, Australia (P.M., M.C.B); Western Australian Centre for Thrombosis and Haemostasis, Murdoch University, Perth, Western Australia, Australia (R.I.B.); and Australian Centre for Blood Diseases, Department of Clinical Haematology, Monash University, Melbourne, Victoria, Australia (R.K.A.)
| | - Robert K Andrews
- From the Faculty of Health Sciences, Curtin University, Perth, Western Australia, Australia (P.M., M.C.B); Western Australian Centre for Thrombosis and Haemostasis, Murdoch University, Perth, Western Australia, Australia (R.I.B.); and Australian Centre for Blood Diseases, Department of Clinical Haematology, Monash University, Melbourne, Victoria, Australia (R.K.A.)
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12
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Exploiting the kinetic interplay between GPIbα-VWF binding interfaces to regulate hemostasis and thrombosis. Blood 2014; 124:3799-807. [PMID: 25293780 DOI: 10.1182/blood-2014-04-569392] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Platelet-von Willebrand factor (VWF) interactions must be tightly regulated in order to promote effective hemostasis and prevent occlusive thrombus formation. However, it is unclear what role the inherent properties of the bond formed between the platelet receptor glycoprotein Ibα and the A1 domain of VWF play in these processes. Using VWF-A1 knock-in mice with mutations that enhance (I1309V) or disrupt (R1326H) platelet receptor glycoprotein Ibα binding, we now demonstrate that the kinetic interplay between two distinct contact surfaces influences the site and extent to which platelets bind VWF. Incorporation of R1326H mutation into the major site shortened bond lifetime, yielding defects in hemostasis and thrombosis comparable to VWF-deficient animals. Similarly, disrupting this region of contact with an allosteric inhibitor impaired human platelet accrual in damaged arterioles. In contrast, the I1309V mutation near the minor site prolonged bond lifetime, which was essential for the development of a type 2B-like VWD phenotype. However, combining the R1326H and I1309V mutations normalized both bond kinetics and the hemostatic and thrombotic properties of VWF. These findings broaden our understanding of mechanisms governing platelet-VWF interactions in health and disease, and underscore the importance of combined biophysical and genetic approaches in identifying potential therapeutic avenues for treating bleeding and thrombotic disorders.
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13
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Kim K, Bae ON, Lim KM, Noh JY, Kang S, Chung KY, Chung JH. Novel antiplatelet activity of protocatechuic acid through the inhibition of high shear stress-induced platelet aggregation. J Pharmacol Exp Ther 2012; 343:704-11. [PMID: 22984226 DOI: 10.1124/jpet.112.198242] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Bleeding is the most common and serious adverse effect of currently available antiplatelet drugs. Many efforts are being made to develop novel antithrombotic agents without bleeding risks. Shear stress-induced platelet aggregation (SIPA), which occurs under abnormally high shear stress, plays a crucial role in the development of arterial thrombotic diseases. Here, we demonstrate that protocatechuic acid (PCA), a bioactive phytochemical from Lonicera (honeysuckle) flowers, selectively and potently inhibits high shear (>10,000 s(-1))-induced platelet aggregation. In isolated human platelets, PCA decreased SIPA and attenuated accompanying platelet activation, including intracellular calcium mobilization, granule secretion, and adhesion receptor expression. The anti-SIPA effect of PCA was mediated through blockade of von Willebrand factor binding to activated glycoprotein Ib, a primary and initial event for the accomplishment of SIPA. Conspicuously, PCA did not inhibit platelet aggregation induced by other endogenous agonists like collagen, thrombin, or ADP that are important in both pathological thrombosis and normal hemostasis. Antithrombotic effects of PCA were confirmed in vivo in a rat arterial thrombosis model, where PCA significantly delayed the arterial occlusion induced by FeCl(3). Of particular note, PCA did not increase bleeding times in a rat tail transection model, whereas conventional antiplatelet drugs, aspirin, and clopidogrel substantially prolonged it. Collectively, these results suggest that PCA may be a novel antiplatelet agent that can prevent thrombosis without increasing bleeding risks.
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Affiliation(s)
- Keunyoung Kim
- College of Pharmacy, Seoul National University, Seoul, Korea
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14
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Broos K, Trekels M, Jose RA, Demeulemeester J, Vandenbulcke A, Vandeputte N, Venken T, Egle B, De Borggraeve WM, Deckmyn H, De Maeyer M. Identification of a small molecule that modulates platelet glycoprotein Ib-von Willebrand factor interaction. J Biol Chem 2012; 287:9461-72. [PMID: 22232560 PMCID: PMC3308782 DOI: 10.1074/jbc.m111.311431] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2011] [Revised: 12/23/2011] [Indexed: 11/06/2022] Open
Abstract
The von Willebrand factor (VWF) A1-glycoprotein (GP) Ibα interaction is of major importance during thrombosis mainly at sites of high shear stress. Inhibitors of this interaction prevent platelet-dependent thrombus formation in vivo, without major bleeding complications. However, the size and/or protein nature of the inhibitors currently in development limit oral bioavailability and clinical development. We therefore aimed to search for a small molecule protein-protein interaction inhibitor interfering with the VWF-GPIbα binding. After determination of putative small molecule binding pockets on the surface of VWF-A1 and GPIbα using site-finding algorithms and molecular dynamics, high throughput molecular docking was performed on both binding partners. A selection of compounds showing good in silico docking scores into the predicted pockets was retained for testing their in vitro effect on VWF-GPIbα complex formation, by which we identified a compound that surprisingly stimulated the VWF-GPIbα binding in a ristocetin cofactor ELISA and increased platelet adhesion in whole blood to collagen under arterial shear rate but in contrast inhibited ristocetin-induced platelet aggregation. The selected compound adhering to the predicted binding partner GPIbα could be confirmed by saturation transfer difference NMR spectroscopy. We thus clearly identified a small molecule that modulates VWF-GPIbα binding and that will now serve as a starting point for further studies and chemical modifications to fully characterize the interaction and to manipulate specific activity of the compound.
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Affiliation(s)
- Katleen Broos
- From the Laboratory for Thrombosis Research, Katholieke Universiteit Leuven Campus Kortrijk, E. Sabbelaan 53, B-8500 Kortrijk
| | - Mieke Trekels
- the Laboratory for Biomolecular Modelling, Department of Chemistry, Division of Biochemistry, Molecular and Structural Biology, Katholieke Universiteit Leuven, Celestijnenlaan 200G bus 2403, 3001 Heverlee, Leuven, and
| | - Rani Alphonsa Jose
- the Laboratory for Molecular Design and Synthesis, Department of Chemistry, Katholieke Universiteit Leuven, 3001 Heverlee, Belgium
| | - Jonas Demeulemeester
- the Laboratory for Biomolecular Modelling, Department of Chemistry, Division of Biochemistry, Molecular and Structural Biology, Katholieke Universiteit Leuven, Celestijnenlaan 200G bus 2403, 3001 Heverlee, Leuven, and
| | - Aline Vandenbulcke
- From the Laboratory for Thrombosis Research, Katholieke Universiteit Leuven Campus Kortrijk, E. Sabbelaan 53, B-8500 Kortrijk
| | - Nele Vandeputte
- From the Laboratory for Thrombosis Research, Katholieke Universiteit Leuven Campus Kortrijk, E. Sabbelaan 53, B-8500 Kortrijk
| | - Tom Venken
- the Laboratory for Biomolecular Modelling, Department of Chemistry, Division of Biochemistry, Molecular and Structural Biology, Katholieke Universiteit Leuven, Celestijnenlaan 200G bus 2403, 3001 Heverlee, Leuven, and
| | - Brecht Egle
- the Laboratory for Molecular Design and Synthesis, Department of Chemistry, Katholieke Universiteit Leuven, 3001 Heverlee, Belgium
| | - Wim M. De Borggraeve
- the Laboratory for Molecular Design and Synthesis, Department of Chemistry, Katholieke Universiteit Leuven, 3001 Heverlee, Belgium
| | - Hans Deckmyn
- From the Laboratory for Thrombosis Research, Katholieke Universiteit Leuven Campus Kortrijk, E. Sabbelaan 53, B-8500 Kortrijk
| | - Marc De Maeyer
- the Laboratory for Biomolecular Modelling, Department of Chemistry, Division of Biochemistry, Molecular and Structural Biology, Katholieke Universiteit Leuven, Celestijnenlaan 200G bus 2403, 3001 Heverlee, Leuven, and
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15
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Hosokawa K, Ohnishi T, Fukasawa M, Kondo T, Sameshima H, Koide T, Tanaka KA, Maruyama I. A microchip flow-chamber system for quantitative assessment of the platelet thrombus formation process. Microvasc Res 2011; 83:154-61. [PMID: 22166857 DOI: 10.1016/j.mvr.2011.11.007] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2011] [Revised: 11/08/2011] [Accepted: 11/27/2011] [Indexed: 10/14/2022]
Abstract
As the pathogenesis of arterial thrombosis often includes platelet thrombus formation (PTF), antiplatelet agents are commonly used for the prevention of thromboembolic events. Here, using a novel microchip flow-chamber system we developed to quantitatively analyze the PTF process, we evaluated the pharmacological efficacies of antiplatelet agents under different arterial shear rates. Hirudin-anticoagulated whole blood was perfused over a collagen-coated microchip at shear rates of 1000, 1500, and 2000s(-1), and PTF in the absence and presence of various antiplatelet agents was observed microscopically and quantified by measuring flow-pressure changes. The onset of PTF was measured as T(10) (time to reach 10 kPa), and AUC(10) (area under the flow pressure curve for the first 10 min) was calculated to quantify the overall stability of the formed thrombus. Aspirin and AR-C66096 (P2Y(12)-antagonist) at high concentrations (50 μM and 1000 nM, respectively) prolonged T(10) only modestly (AR-C66096>aspirin), but effectively decreased AUC(10), resulting in unstable PTF at all examined shear rates. With dual inhibition using both aspirin (25 μM) and ARC-66096 (250 nM), AUC(10) was drastically reduced. Nearly complete suppression of AUC(10) was also observed with abciximab (2 μg ml(-1)) and beraprost (PGI(2)-analog; 4 nM). Although OS-1 (GPIbα-antagonist; 100 nM) prevented complete capillary occlusion, significant amounts of microscopic thrombi were observed on the collagen surface. In contrast to abciximab and beraprost, OS-1 differentially affected PTF under higher shear conditions. Our novel analytical system is capable of distinguishing the pharmacological effects of various antiplatelet agents under physiological shear rates, suggesting that this system may aid in the determination of the appropriate type and dose of antiplatelet agent in the clinical setting.
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Affiliation(s)
- Kazuya Hosokawa
- Department of System Biology in Thromboregulation, Kagoshima University, Kagoshima 890-8520, Japan.
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16
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Hosokawa K, Ohnishi T, Kondo T, Fukasawa M, Koide T, Maruyama I, Tanaka KA. A novel automated microchip flow-chamber system to quantitatively evaluate thrombus formation and antithrombotic agents under blood flow conditions. J Thromb Haemost 2011; 9:2029-37. [PMID: 21827607 DOI: 10.1111/j.1538-7836.2011.04464.x] [Citation(s) in RCA: 112] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
BACKGROUND AND AIMS In the present study, we describe a newly developed microchip-based analytical system to evaluate white thrombus formation (WTF). Efficacies of various antithrombotic agents were compared under different flow conditions. METHODS Whole blood containing corn trypsin inhibitor was perfused over a microchip coated with collagen and tissue thromboplastin at the lower and higher shear rates of 240 and 600 s(-1) , and WTF process inside the microchip was quantified by monitoring a flow pressure. Parameters of T(10) (time to 10 kPa), T(10-80) (time from 10 to 80 kPa) and OT (occlusion time; time to 80 kPa) were used to evaluate the onset and the growth rate of WTF, and the capillary occlusion, respectively. RESULTS After perfusion was started, white thrombus composed of activated platelets and fibrin was formed on the coated surface. Thrombus gradually increased in size and eventually occluded the capillary. Among anticoagulants, heparin (0.5-1.0 U mL(-1)) potently prolonged T(10) at both shear rates, whereas low molecular weight heparin (1.0-2.0 IU mL(-1)) inhibited the growth of WTF at the lower shear rate. Among antiplatelet agents, abciximab (1-2 μg mL(-1)) significantly reduced the size and number of thrombi, which was additively enhanced in the presence of heparin (0.5 U mL(-1) ). OS-1 (specific GPIbα-antagonist) prevented the complete capillary occlusion. CONCLUSION The novel monitoring system of WTF may be useful in preclinical and clinical evaluations of different types of antithrombotic strategies, and their effects in combination.
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Affiliation(s)
- K Hosokawa
- Research Institute, Fujimori Kogyo Co., Yokohama, Kanagawa, Japan
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18
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Survey of the year 2008: applications of isothermal titration calorimetry. J Mol Recognit 2010; 23:395-413. [DOI: 10.1002/jmr.1025] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
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19
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Rich RL, Myszka DG. Grading the commercial optical biosensor literature-Class of 2008: 'The Mighty Binders'. J Mol Recognit 2010; 23:1-64. [PMID: 20017116 DOI: 10.1002/jmr.1004] [Citation(s) in RCA: 109] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Optical biosensor technology continues to be the method of choice for label-free, real-time interaction analysis. But when it comes to improving the quality of the biosensor literature, education should be fundamental. Of the 1413 articles published in 2008, less than 30% would pass the requirements for high-school chemistry. To teach by example, we spotlight 10 papers that illustrate how to implement the technology properly. Then we grade every paper published in 2008 on a scale from A to F and outline what features make a biosensor article fabulous, middling or abysmal. To help improve the quality of published data, we focus on a few experimental, analysis and presentation mistakes that are alarmingly common. With the literature as a guide, we want to ensure that no user is left behind.
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Affiliation(s)
- Rebecca L Rich
- Center for Biomolecular Interaction Analysis, University of Utah, Salt Lake City, UT 84132, USA
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21
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Szanto T, Vanhoorelbeke K, Toth G, Vandenbulcke A, Toth J, Noppe W, Deckmyn H, Harsfalvi J. Identification of a VWF peptide antagonist that blocks platelet adhesion under high shear conditions by selectively inhibiting the VWF-collagen interaction. J Thromb Haemost 2009; 7:1680-7. [PMID: 19624458 DOI: 10.1111/j.1538-7836.2009.03552.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
BACKGROUND Because the collagen-VWF-GPIb/IX/V axis plays an important role in thrombus formation, it represents a promising target for development of new antithrombotic agents. OBJECTIVES We used phage display to identify potential small peptides that interfere with the VWF-collagen binding and might serve as lead products for the development of possible oral antithrombotic compounds. METHODS A random linear heptamer peptide library was used to select VWF-binding peptides. RESULTS We identified a phage clone, displaying the YDPWTPS sequence, further referred to as L7-phage, that bound to VWF in a specific and a dose-dependent manner. This L7-phage specifically inhibited the VWF-collagen interaction under both static and flow conditions. Epitope mapping using deletion mutants of VWF revealed that the L7-phage does not bind to the known collagen-binding A3 domain within VWF, but to the more carboxyterminal situated C domain. This inhibition was not due to steric hindrance of the A3 domain-collagen interaction by the L7-phage. Indeed, a tetrabranched multi-antigen peptide (MAP) presenting four copies of the peptide, but not the scrambled MAP, also inhibited VWF-collagen interaction under conditions of high shear stress at a concentration of 148 nmol L(-1). CONCLUSIONS Based on these results, we conclude that we have identified the first peptide antagonist that binds to the VWF C domain and by this specifically inhibits the VWF binding to collagen, suppressing platelet adhesion and aggregation under high shear conditions. As a consequence, this peptide and its future derivates are potentially interesting antithrombotic agents.
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Affiliation(s)
- T Szanto
- Clinical Research Center, Medical and Health Science Center, University of Debrecen, Debrecen H-4012, Hungary
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Glycoprotein Ibalpha inhibitor complex structure reveals a combined steric and allosteric mechanism of von Willebrand factor antagonism. Blood 2009; 114:4883-5. [PMID: 19726719 DOI: 10.1182/blood-2009-05-224170] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Platelet glycoprotein Ibalpha (GpIbalpha) interactions with von Willebrand factor (VWF) are a critical early event in platelet adhesion, which contributes to hemostasis and thrombosis. Here we report the structure of a complex between GpIbalpha and a potent peptide inhibitor. The cyclic peptide (CTERMALHNLC) was isolated from a cysteine-constrained phage display library, and in the complex this forms one and a half turns of an amphipathic alpha-helix, the curvature of which facilitates contacts with the curved concave face of the GpIbalpha leucine-rich repeats. The peptide has only limited overlap with the VWF binding site. It effectively inhibits by stabilizing an alternative alpha-helical conformation of a regulatory loop that forms an extended beta-hairpin upon VWF binding. The structure defines a previously unrecognized binding site within GpIbalpha and represents a clear strategy for developing antiplatelet agents targeting the GpIbalpha-VWF interaction allosterically.
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