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A Novel Antibody Targeting the Second Extracellular Loop of the Serotonin 5-HT2A Receptor Inhibits Platelet Function. Int J Mol Sci 2022; 23:ijms23158794. [PMID: 35955928 PMCID: PMC9369033 DOI: 10.3390/ijms23158794] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2022] [Revised: 08/02/2022] [Accepted: 08/02/2022] [Indexed: 11/17/2022] Open
Abstract
Serotonin (5-hydroxytriptamine or 5-HT) is known to be a weak platelet agonist, and is involved in thrombus formation. While 5-HT cannot induce platelet aggregation on its own, when secreted from the alpha granules, it binds to its G-protein Coupled Receptor (GPCR; i.e., 5HT2AR), thereby acting to amplify platelet functional responses (e.g., aggregation). Thus, 5HT2AR-mediated responses are more involved in the secondary amplification of platelet aggregation in the growing thrombus. Therefore, even though 5-HT can be seen as a weak inducer of platelet activation, it is an important amplifier of aggregation triggered by agonists such as ADP, collagen, and epinephrine, thereby enhancing thrombogenesis. The 5HT2AR/5HT2A signaling pathway is of clinical interest to the scientific and medical communities as it has been implicated in the genesis of several forms of cardiovascular disorders. However, efforts to develop antagonists for 5HT2AR as therapeutic agents in cardiovascular diseases have thus far failed due to these reagents having deleterious side-effects, and/or to lack of selectivity, amongst other reasons. In light of research efforts that identified that the 5HT2AR ligand binding domain resides in the second extracellular loop (EL2; amino acids P209-N233), we developed an antibody, i.e., referred to as 5HT2ARAb, against the EL2 region, and characterized its pharmacological activity in the context of platelets. Thus, we utilized platelets from healthy human donors, as well as C57BL/6J mice (10-12 weeks old) to analyze the inhibitory effects of the 5HT2ARAb on platelet activation in vitro, ex vivo, and on thrombogenesis in vivo as well as on 5HT2AR ligand binding. Our results indicate that the 5HT2ARAb inhibits 5-HT-enhanced platelet activation in vitro and ex vivo, but has no apparent effects on that which is agonist-induced. The 5HT2ARAb was also found to prolong the thrombus occlusion time, and it did so without modulating the tail bleeding time, in mice unlike the P2Y12 antagonist clopidogrel and the 5HT2AR antagonist ketanserin. Moreover, it was found that the 5HT2ARAb does so by directly antagonizing the platelet 5HT2AR. Our findings document that the custom-made 5HT2ARAb exhibits platelet function blocking activity and protects against thrombogenesis without impairing normal hemostasis.
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Affiliation(s)
- Firdos Ahmad
- Sharjah Institute for Medical Research and College of Medicine, University of Sharjah, United Arab Emirates
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Alshbool FZ, Karim ZA, Espinosa EVP, Lin OA, Khasawneh FT. Investigation of a Thromboxane A 2 Receptor-Based Vaccine for Managing Thrombogenesis. J Am Heart Assoc 2018; 7:e009139. [PMID: 29936414 PMCID: PMC6064912 DOI: 10.1161/jaha.118.009139] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/10/2018] [Accepted: 05/15/2018] [Indexed: 12/25/2022]
Abstract
BACKGROUND Despite the well-established role for the thromboxane A2 receptor (TPR) in the development of thrombotic disorders, none of the antagonists developed to date has been approved for clinical use. To this end, we have previously shown that an antibody targeted against TPR's ligand-binding domain inhibits platelet activation and thrombus formation, without exerting any effects on hemostasis. Thus, the goal of the present studies is to design a novel TPR-based vaccine, demonstrate its ability to trigger an immune response, and characterize its antiplatelet and antithrombotic activity. METHODS AND RESULTS We used a mouse keyhole limpet hemocyanin/peptide-based vaccination approach rationalized over the TPR ligand-binding domain (ie, the C-terminus of the second extracellular loop). The biological activity of this vaccine was assessed in the context of platelets and thrombotic diseases, and using a host of in vitro and in vivo platelet function experiments. Our results revealed that the TPR C-terminus of the second extracellular loop vaccine, in mice: (1) triggered an immune response, which resulted in the development of a C-terminus of the second extracellular loop antibody; (2) did not affect expression of major platelet integrins (eg, glycoprotein IIb-IIIa); (3) selectively inhibited TPR-mediated platelet aggregation, platelet-leukocyte aggregation, integrin glycoprotein IIb-IIIa activation, as well as dense and α granule release; (4) significantly prolonged thrombus formation; and (5) did so without impairing physiological hemostasis. CONCLUSIONS Collectively, our findings shed light on TPR's structural biological features, and demonstrate that the C-terminus of the second extracellular loop domain may define a new therapeutic target and a TPR vaccine-based approach that should have therapeutic applications.
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Affiliation(s)
- Fatima Z Alshbool
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Texas El Paso, TX
| | - Zubair A Karim
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Texas El Paso, TX
| | | | | | - Fadi T Khasawneh
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Texas El Paso, TX
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Cooper A, Singh S, Hook S, Tyndall JDA, Vernall AJ. Chemical Tools for Studying Lipid-Binding Class A G Protein-Coupled Receptors. Pharmacol Rev 2017; 69:316-353. [PMID: 28655732 DOI: 10.1124/pr.116.013243] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2016] [Accepted: 05/15/2017] [Indexed: 12/16/2022] Open
Abstract
Cannabinoid, free fatty acid, lysophosphatidic acid, sphingosine 1-phosphate, prostanoid, leukotriene, bile acid, and platelet-activating factor receptor families are class A G protein-coupled receptors with endogenous lipid ligands. Pharmacological tools are crucial for studying these receptors and addressing the many unanswered questions surrounding expression of these receptors in normal and diseased tissues. An inherent challenge for developing tools for these lipid receptors is balancing the often lipophilic requirements of the receptor-binding pharmacophore with favorable physicochemical properties to optimize highly specific binding. In this study, we review the radioligands, fluorescent ligands, covalent ligands, and antibodies that have been used to study these lipid-binding receptors. For each tool type, the characteristics and design rationale along with in vitro and in vivo applications are detailed.
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Affiliation(s)
- Anna Cooper
- School of Pharmacy, University of Otago, Dunedin, New Zealand
| | - Sameek Singh
- School of Pharmacy, University of Otago, Dunedin, New Zealand
| | - Sarah Hook
- School of Pharmacy, University of Otago, Dunedin, New Zealand
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Dhall S, Wijesinghe DS, Karim ZA, Castro A, Vemana HP, Khasawneh FT, Chalfant CE, Martins-Green M. Arachidonic acid-derived signaling lipids and functions in impaired healing. Wound Repair Regen 2015; 23:644-56. [PMID: 26135854 DOI: 10.1111/wrr.12337] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2015] [Accepted: 05/26/2015] [Indexed: 12/30/2022]
Abstract
Very little is known about lipid function during wound healing, and much less during impaired healing. Such understanding will help identify what roles lipid signaling plays in the development of impaired/chronic wounds. We took a lipidomics approach to study the alterations in lipid profile in the LIGHT(-/-) mouse model of impaired healing which has characteristics that resemble those of impaired/chronic wounds in humans, including high levels of oxidative stress, excess inflammation, increased extracellular matrix degradation and blood vessels with fibrin cuffs. The latter suggests excess coagulation and potentially increased platelet aggregation. We show here that in these impaired wounds there is an imbalance in the arachidonic acid (AA) derived eicosonoids that mediate or modulate inflammatory reactions and platelet aggregation. In the LIGHT(-/-) impaired wounds there is a significant increase in enzymatically derived breakdown products of AA. We found that early after injury there was a significant increase in the eicosanoids 11-, 12-, and 15-hydroxyeicosa-tetranoic acid, and the proinflammatory leukotrienes (LTD4 and LTE) and prostaglandins (PGE2 and PGF2α ). Some of these eicosanoids also promote platelet aggregation. This led us to examine the levels of other eicosanoids known to be involved in the latter process. We found that thromboxane (TXA2 /B2 ), and prostacyclins 6kPGF1α are elevated shortly after wounding and in some cases during healing. To determine whether they have an impact in platelet aggregation and hemostasis, we tested LIGHT(-/-) mouse wounds for these two parameters and found that, indeed, platelet aggregation and hemostasis are enhanced in these mice when compared with the control C57BL/6 mice. Understanding lipid signaling in impaired wounds can potentially lead to development of new therapeutics or in using existing nonsteroidal anti-inflammatory agents to help correct the course of healing.
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Affiliation(s)
- Sandeep Dhall
- Department of Cell Biology and Neuroscience, University of California, Riverside, California.,Department of Bioengineering Interdepartmental Graduate Program, University of California, Riverside, California
| | - Dayanjan Shanaka Wijesinghe
- Department of Surgery, Virginia Commonwealth University, Richmond, Virginia.,Hunter Holmes McGuire Veterans Administration Medical Center, Richmond, Virginia.,The Massey Cancer Center, Richmond, VA, Virginia Commonwealth University, Richmond, Virginia.,Virginia Commonwealth University Reanimation Engineering Science Center (VCURES)
| | - Zubair A Karim
- Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, Virginia
| | - Anthony Castro
- Department of Cell Biology and Neuroscience, University of California, Riverside, California
| | - Hari Priya Vemana
- Department of Pharmaceutical Sciences, College of Pharmacy, Western University of Health Sciences, Pomona, California
| | - Fadi T Khasawneh
- Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, Virginia
| | - Charles E Chalfant
- Hunter Holmes McGuire Veterans Administration Medical Center, Richmond, Virginia.,The Massey Cancer Center, Richmond, VA, Virginia Commonwealth University, Richmond, Virginia.,Virginia Commonwealth University Reanimation Engineering Science Center (VCURES).,Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, Virginia
| | - Manuela Martins-Green
- Department of Cell Biology and Neuroscience, University of California, Riverside, California.,Department of Bioengineering Interdepartmental Graduate Program, University of California, Riverside, California
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Vemana HP, Karim ZA, Conlon C, Khasawneh FT. A critical role for the transient receptor potential channel type 6 in human platelet activation. PLoS One 2015; 10:e0125764. [PMID: 25928636 PMCID: PMC4416038 DOI: 10.1371/journal.pone.0125764] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2014] [Accepted: 03/25/2015] [Indexed: 12/31/2022] Open
Abstract
While calcium signaling is known to play vital roles in platelet function, the mechanisms underlying its receptor-operated calcium entry component (ROCE) remain poorly understood. It has been proposed, but never proven in platelets, that the canonical transient receptor potential channel-6 (TRPC6) mediates ROCE. Nonetheless, we have previously shown that the mouse TRPC6 regulates hemostasis, thrombogenesis by regulating platelet aggregation. In the present studies, we used a pharmacological approach to characterize the role of TRPC6 in human platelet biology. Thus, interestingly, we observed that a TRPC6 inhibitor exerted significant inhibitory effects on human platelet aggregation in a thromboxane receptor (TPR)-selective manner; no additional inhibition was observed in the presence of the calcium chelator BAPTA. This inhibitor also significantly inhibited human platelet secretion (dense and alpha granules), integrin IIb-IIIa, Akt and ERK phosphorylation, again, in a TPR-selective manner; no effects were observed in response to ADP receptor stimulation. Furthermore, there was a causal relationship between these inhibitory effects, and the capacity of the TRPC6 inhibitor to abrogate elevation in intracellular calcium, that was again found to be TPR-specific. This effect was not found to be due to antagonism of TPR, as the TRPC6 inhibitor did not displace the radiolabeled antagonist [3H]SQ29,548 from its binding sites. Finally, our studies also revealed that TRPC6 regulates human clot retraction, as well as physiological hemostasis and thrombus formation, in mice. Taken together, our findings demonstrate, for the first time, that TRPC6 directly regulates TPR-dependent ROCE and platelet function. Moreover, these data highlight TRPC6 as a novel promising therapeutic strategy for managing thrombotic disorders.
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Affiliation(s)
- Hari Priya Vemana
- Department of Pharmaceutical Sciences, College of Pharmacy, Western University of Health Sciences, Pomona, California, United States of America
| | - Zubair A. Karim
- Department of Pharmaceutical Sciences, College of Pharmacy, Western University of Health Sciences, Pomona, California, United States of America
| | - Christine Conlon
- Department of Pharmaceutical Sciences, College of Pharmacy, Western University of Health Sciences, Pomona, California, United States of America
| | - Fadi T. Khasawneh
- Department of Pharmaceutical Sciences, College of Pharmacy, Western University of Health Sciences, Pomona, California, United States of America
- * E-mail:
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A novel antibody targeting the ligand binding domain of the thromboxane A2 receptor exhibits antithrombotic properties in vivo. Biochem Biophys Res Commun 2012; 421:456-61. [DOI: 10.1016/j.bbrc.2012.04.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2012] [Accepted: 04/02/2012] [Indexed: 11/19/2022]
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