Platelet adhesion and signaling induced by the octapeptide primary binding sequence (KOGEOGPK) from type III collagen

Efficient co-expression of recombinant human fusion collagen with prolyl 4-hydroxylase from Bacillus anthracis in Escherichia coli

Collagen family members, the most abundant proteins in the human body, are widely used in biomedical fields and tissue engineering industries. However, the applications of collagen remain mostly relying on material derived from native tissues due to its extremely complex post-translational modifications like proline hydroxylation, which hinder the large-scale exogenous production of collagen. In the current study, we propose a novel prolyl hydroxylated recombinant human fusion collagen containing multiple native cell-interaction sites derived from human type Ⅰ and Ⅲ collagen with good biocompatibility and thermal stability. To obtain prolyl hydroxylated collagen, prolyl 4-hydroxylases from Bacillus anthracis, Arabidopsis thaliana, and Dactylosporangium sp. RH1 were co-expressed with collagen in Escherichia coli (E. coli), respectively. Among of which, prolyl 4-hydroxylase (P4H) from Bacillus anthracis showed the highest hydroxyl rate with 63.6%. Furthermore, a yield of hydroxylated collagen at 0.8 g/L was achieved by fed-batch fermentation in a 5 L fermenter with the productivity of 0.0267 g·L^-1 ·h^-1 . Compared with non-hydroxylated recombinant collagen, hydroxylated recombinant collagen showed significant improvements in thermal stability and biocompatibility. Taken this together, our studies provide a promising method for further development of collagen application in biomaterials engineering. A novel recombinant human fusion collagen with multiple motifs derived from both human type I and Ⅲ collagen exhibits good biocompatibility and thermal stability as higher molecular weight of ∼120kDa. By co-expression recombinant collagen and P4H genes in Escherichia coli, the maximum hyp in the recombinant collagen reached 63.6%, and a yield of hydroxylated collagen at 0.8 g/L was achieved by fed-batch fermentation in a 5 L fermenter. This article is protected by copyright. All rights reserved.

Inhibition of Arginine Methylation Impairs Platelet Function

Protein arginine methyltransferases (PRMTs) catalyze the transfer of methyl groups to arginine residues in proteins. PRMT inhibitors are novel, promising drugs against cancer that are currently in clinical trials, which include oral administration of the drugs. However, off-target activities of systemically available PRMT inhibitors have not yet been investigated. In this work, we study the relevance of arginine methylation in platelets and investigate the effect of PRMT inhibitors on platelet function and on the expression of relevant platelet receptors. We show that (1) key platelet proteins are modified by arginine methylation; (2) incubation of human platelets with PRMT inhibitors for 4 h results in impaired capacity of platelets to aggregate in response to thrombin and collagen, with IC₅₀ values in the μM range; and (3) treatment with PRMT inhibitors leads to decreased membrane expression and reduced activation of the critical platelet integrin α_IIbβ₃. Our contribution opens new avenues for research on arginine methylation in platelets, including the repurposing of arginine methylation inhibitors as novel antiplatelet drugs. We also recommend that current and future clinical trials with PRMT inhibitors consider any adverse effects associated with platelet inhibition of these emerging anticancer drugs.

Molecular underpinnings of integrin binding to collagen-mimetic peptides containing vascular Ehlers-Danlos syndrome-associated substitutions

Collagens carry out critical extracellular matrix (ECM) functions by interacting with numerous cell receptors and ECM components. Single glycine substitutions in collagen III, which predominates in vascular walls, result in vascular Ehlers-Danlos syndrome (vEDS), leading to arterial, uterine, and intestinal rupture and an average life expectancy of <50 years. Collagen interactions with integrin α₂β₁ are vital for platelet adhesion and activation; however, how these interactions are impacted by vEDS-associated mutations and by specific amino acid substitutions is unclear. Here, we designed collagen-mimetic peptides (CMPs) with previously reported Gly → Xaa (Xaa = Ala, Arg, or Val) vEDS substitutions within a high-affinity integrin α₂β₁-binding motif, GROGER. We used these peptides to investigate, at atomic-level resolution, how these amino acid substitutions affect the collagen III-integrin α₂β₁ interaction. Using a multitiered approach combining biological adhesion assays, CD, NMR, and molecular dynamics (MD) simulations, we found that these substitutions differentially impede human mesenchymal stem cell spreading and integrin α₂-inserted (α₂I) domain binding to the CMPs and were associated with triple-helix destabilization. Although an Ala substitution locally destabilized hydrogen bonding and enhanced mobility, it did not significantly reduce the CMP-integrin interactions. MD simulations suggested that bulkier Gly → Xaa substitutions differentially disrupt the CMP-α₂I interaction. The Gly → Arg substitution destabilized CMP-α₂I side-chain interactions, and the Gly → Val change broke the essential Mg²⁺ coordination. The relationship between the loss of functional binding and the type of vEDS substitution provides a foundation for developing potential therapies for managing collagen disorders.

The collαgen III fibril has a "flexi-rod" structure of flexible sequences interspersed with rigid bioactive domains including two with hemostatic roles

Collagen III is critical to the integrity of blood vessels and distensible organs, and in hemostasis. Examination of the human collagen III interactome reveals a nearly identical structural arrangement and charge distribution pattern as for collagen I, with cell interaction domains, fibrillogenesis and enzyme cleavage domains, several major ligand-binding regions, and intermolecular crosslink sites at the same sites. These similarities allow heterotypic fibril formation with, and substitution by, collagen I in embryonic development and wound healing. The collagen III fibril assumes a "flexi-rod" structure with flexible zones interspersed with rod-like domains, which is consistent with the molecule's prominence in young, pliable tissues and distensible organs. Collagen III has two major hemostasis domains, with binding motifs for von Willebrand factor, α2β1 integrin, platelet binding octapeptide and glycoprotein VI, consistent with the bleeding tendency observed with COL3A1 disease-causing sequence variants.

Propolis Modifies Collagen Types I and III Accumulation in the Matrix of Burnt Tissue

Wound healing represents an interactive process which requires highly organized activity of various cells, synthesizing cytokines, growth factors, and collagen. Collagen types I and III, serving as structural and regulatory molecules, play pivotal roles during wound healing. The aim of this study was to compare the propolis and silver sulfadiazine therapeutic efficacy throughout the quantitative and qualitative assessment of collagen types I and III accumulation in the matrix of burnt tissues. Burn wounds were inflicted on pigs, chosen for the evaluation of wound repair because of many similarities between pig and human skin. Isolated collagen types I and III were estimated by the surface plasmon resonance method with a subsequent collagenous quantification using electrophoretic and densitometric analyses. Propolis burn treatment led to enhanced collagens and its components expression, especially during the initial stage of the study. Less expressed changes were observed after silver sulfadiazine (AgSD) application. AgSD and, with a smaller intensity, propolis stimulated accumulation of collagenous degradation products. The assessed propolis therapeutic efficacy, throughout quantitatively and qualitatively analyses of collagen types I and III expression and degradation in wounds matrix, may indicate that apitherapeutic agent can generate favorable biochemical environment supporting reepithelization.

Safety and efficacy of protease-activated receptor-1 antagonists in patients with coronary artery disease: a meta-analysis of randomized clinical trials

BACKGROUND

Thrombin receptor antagonists blocking protease-activated receptor-1 (PAR-1) on platelets represent a new class of oral antiplatelet agents for patients with atherothrombotic disease manifestations.

OBJECTIVES

We investigated the safety and efficacy of PAR-1 antagonists in patients with coronary artery disease (CAD).

PATIENTS/METHODS

Randomized, placebo-controlled trials of the PAR-1 antagonists atopaxar or vorapaxar in CAD patients were identified. The primary safety endpoint was the composite of Thrombolysis In Myocardial Infarction (TIMI) clinically significant bleeding. The primary efficacy endpoint was the composite of death, myocardial infarction (MI) or stroke.

RESULTS

A total of 41 647 patients from eight trials were included. PAR-1 antagonists were associated with higher risks of TIMI clinically significant (odds ratio [OR] 1.48, 95% confidence interval [CI] 1.39-1.57, P < 0.001), major (OR 1.46, 95% CI 1.28-1.67, P < 0.001) and minor (OR 1.67, 95% CI 1.40-2.00, P < 0.001) bleeding than placebo in the fixed-effects model. PAR-1 antagonists reduced the composite of death, MI or stroke as compared with placebo (OR 0.87, 95% CI 0.81-0.92, P < 0.001), driven by a lower risk of MI (OR 0.85, 95% CI 0.78-0.92, P < 0.001). Conversely, PAR-1 antagonists and placebo did not differ in terms of risk of death (OR 0.99, 95% CI 0.90-1.09, P = 0.81) or stroke (OR 0.96, 95% CI 0.84-1.10, P = 0.59).

CONCLUSIONS

PAR-1 antagonists decrease ischemic events in patients with CAD as compared with placebo, mainly driven by a reduction in MI, at the cost of an increased risk of clinically significant bleeding.

Platelet type III collagen binding protein (TIIICBP) presents high biochemical and functional similarities with kindlin-3

Type III collagen binding protein (TIIICBP) was previously described as a platelet membrane protein that recognizes the KOGEOGPK peptide sequence within type III collagen. In order to better characterize this protein, we performed different approaches including mass spectrometry sequencing and functional experiments. This study leads to identify high biochemical and functional similarities between TIIICBP and kindlin-3, a member of a family of focal adhesion proteins. Indeed, mass spectrometry surveys indicated that TIIICBP contains several peptides identical to kindlin-3, covering 41% of the amino acid sequence. Polyclonal antibodies raised against a kindlin-3 specific N-terminal sequence, recognized and immunoprecipitated TIIICBP from platelet lysates. Electron microscopy and flow cytometry experiments showed that kindlin-3, as well as TIIICBP, were present associated to platelet membrane and a translocation of cytosolic kindlin-3 to the platelet membrane was observed after platelet activation. Similarly to anti-TIIICBP antibodies and the KOGEOGPK peptide, anti-kindlin-3 antibodies inhibited platelet interactions with type III collagen under flow conditions and slowed down platelet aggregation induced by glycoprotein VI agonists; e.g. collagen-related peptides and convulxin. In addition, the anti-kindlin-3 antibody inhibited platelet aggregation induced by low - but not high - doses of ADP or thrombin which depends on α(IIb)β(3) integrin function. In conclusion, our results show that the peptides identified by mass spectrometry from purified TIIICBP correspond to the kindlin-3 protein and demonstrate biochemical and functional similarities between TIIICBP and kindlin-3, strengthening a key role for TIIICBP/kindlin-3 in platelet interactions with collagen by cooperating with glycoprotein VI activation and integrin clustering in focal adhesion complexes.

Review: Antiplatelet Drugs: What Comes Next?

Antiplatelet drugs are important components in the management of atherothrombotic vascular disease. However, several limitations restrict the safety and efficacy of current antiplatelet therapy in clinical practice. Interpatient variability and resistance to aspirin and/or clopidogrel has spurred efforts for the development of novel agents. Indeed, several antiplatelet drugs are at various stages of evaluation; those at advanced stage of development are the focus of this review.

Vascular PAR-1: activity and antagonism

Despite major advances in antiplatelet therapies, recurrent cardiovascular events remain high after acute coronary syndrome. Furthermore, incremental benefits achieved in the reduction of atherothrombotic events have almost always been at the expense of hemorrhagic side effects. Thrombin is the most potent platelet activating factor known and it makes important interactions with the endothelium and vascular smooth muscle with proinflammatory, proatherogenic effects. Distinct from its activity within the coagulation cascade, thrombin mediates these effects via protease-activated receptor type 1 (PAR-1) in man. This review discusses the role of PAR-1 in the vasculature and the development of novel PAR-1 antagonists. These drugs may provide important antiatherothrombotic effects without attendant bleeding complications and could represent a major breakthrough for the treatment of cardiovascular diseases.

Safety and exploratory efficacy of the novel thrombin receptor (PAR-1) antagonist SCH530348 for non-ST-segment elevation acute coronary syndrome

AIM

A previous phase 2 study of patients undergoing non-urgent PCI treated with SCH530348 plus aspirin and clopidogrel tended to reduce MACE without increased bleeding. This study evaluated the safety of SCH530348 in Japanese patients with NSTE ACS.

METHODS

Subjects (117), in whom PCI was planned, received standard-of-care (aspirin, ticlopidine, and heparin) and were randomized 4:1 to receive either SCH530348 (20 or 40 mg loading dose followed by 1 mg/d or 2.5 mg/d for 60 days) or placebo. The key safety endpoint was TIMI major and minor bleeding in the PCI cohort (n=92). The key exploratory efficacy endpoint was MACE and death within 60 days. Addition of SCH530348 to standard-of-care did not significantly increase the rate of TIMI major and minor bleeding (or non-TIMI bleeding) in the primary cohort.

RESULTS

Incidence (non-MACE) and discontinuation of AEs were similar across groups. PCI subjects treated with SCH530348 plus standard-of-care experienced a significant reduction in periprocedural MI compared with standard-of-care alone (16.9% vs 42.9%, respectively; p=0.013). There were no deaths or any other MACE.

CONCLUSION

SCH530348 added to standard-of-care did not result in excess bleeding in Japanese subjects with NSTE ACS but significantly reduced the incidence of periprocedural MI in subjects undergoing urgent PCI.

Platelet thrombin receptor antagonism and atherothrombosis

Clinical manifestations of atherothrombotic disease, such as acute coronary syndromes, cerebrovascular events, and peripheral arterial disease, are major causes of mortality and morbidity worldwide. Platelet activation and aggregation are ultimately responsible for the progression and clinical presentations of atherothrombotic disease. The current standard of care, dual oral antiplatelet therapy with aspirin and the P2Y(12) adenosine diphosphate (ADP) receptor inhibitor clopidogrel, has been shown to improve outcomes in patients with atherothrombotic disease. However, aspirin and P2Y(12) inhibitors target the thromboxane A(2) and the ADP P2Y(12) platelet activation pathways and minimally affect other pathways, while agonists such as thrombin, considered to be the most potent platelet activator, continue to stimulate platelet activation and thrombosis. This may help explain why patients continue to experience recurrent ischaemic events despite receiving such therapy. Furthermore, aspirin and P2Y(12) receptor antagonists are associated with bleeding risk, as the pathways they inhibit are critical for haemostasis. The challenge remains to develop therapies that more effectively inhibit platelet activation without increasing bleeding complications. The inhibition of the protease-activated receptor-1 (PAR-1) for thrombin has been shown to inhibit thrombin-mediated platelet activation without increasing bleeding in pre-clinical models and small-scale clinical trials. PAR-1 inhibition in fact does not interfere with thrombin-dependent fibrin generation and coagulation, which are essential for haemostasis. Thus PAR-1 antagonism coupled with existing dual oral antiplatelet therapy may potentially offer more comprehensive platelet inhibition without the liability of increased bleeding.

The Thrombin Receptor Antagonist for Clinical Event Reduction in Acute Coronary Syndrome (TRA*CER) trial: study design and rationale

BACKGROUND

The protease-activated receptor 1 (PAR-1), the main platelet receptor for thrombin, represents a novel target for treatment of arterial thrombosis, and SCH 530348 is an orally active, selective, competitive PAR-1 antagonist. We designed TRA*CER to evaluate the efficacy and safety of SCH 530348 compared with placebo in addition to standard of care in patients with non-ST-segment elevation (NSTE) acute coronary syndromes (ACS) and high-risk features.

TRIAL DESIGN

TRA*CER is a prospective, randomized, double-blind, multicenter, phase III trial with an original estimated sample size of 10,000 subjects. Our primary objective is to demonstrate that SCH 530348 in addition to standard of care will reduce the incidence of the composite of cardiovascular death, myocardial infarction (MI), stroke, recurrent ischemia with rehospitalization, and urgent coronary revascularization compared with standard of care alone. Our key secondary objective is to determine whether SCH 530348 will reduce the composite of cardiovascular death, MI, or stroke compared with standard of care alone. Secondary objectives related to safety are the composite of moderate and severe GUSTO bleeding and clinically significant TIMI bleeding. The trial will continue until a predetermined minimum number of centrally adjudicated primary and key secondary end point events have occurred and all subjects have participated in the study for at least 1 year. The TRA*CER trial is part of the large phase III SCH 530348 development program that includes a concomitant evaluation in secondary prevention.

CONCLUSION

TRA*CER will define efficacy and safety of the novel platelet PAR-1 inhibitor SCH 530348 in the treatment of high-risk patients with NSTE ACS in the setting of current treatment strategies.

Safety and tolerability of SCH 530348 in patients undergoing non-urgent percutaneous coronary intervention: a randomised, double-blind, placebo-controlled phase II study

BACKGROUND

An antithrombotic drug is needed that safely reduces cardiovascular events in patients undergoing percutaneous coronary intervention (PCI). We therefore assessed the tolerability and safety of SCH 530348-an oral platelet protease-activated receptor-1 antagonist.

METHODS

We randomly assigned patients aged 45 years or older and undergoing non-urgent PCI or coronary angiography with planned PCI to an oral loading dose of SCH 530348 (10 mg, 20 mg, or 40 mg) or matching placebo in a 3:1 ratio in a multicentre international study. Those in the SCH 530348 group who subsequently underwent PCI (primary PCI cohort) continued taking an oral maintenance dose (0.5 mg, 1.0 mg, or 2.5 mg per day), and patients in the placebo group continued placebo for 60 days. The primary endpoint was the incidence of clinically significant major or minor bleeding according to the thrombolysis in myocardial infarction (TIMI) scale. Both investigators and patients were unaware of treatment allocation. Analysis was by intention to treat. This study is registered with ClinicalTrials.gov, number NCT00132912.

FINDINGS

257 patients were assigned to placebo and 773 to SCH 530348. The primary endpoint occurred in 2 (2%) of 129, 3 (3%) of 120, and 7 (4%) of 173 patients, respectively, in the SCH 530348 10 mg, 20 mg, and 40 mg groups compared with 5 (3%) of 151 patients in the placebo group (p=0.5786). TIMI major plus minor bleeding occurred in 3 (2%) of 136, 5 (4%) of 139, and 4 (3%) of 138 patients given SCH 530348 0.5 mg, 1.0 mg, and 2.5 mg once per day, respectively (p=0.7561).

INTERPRETATION

Oral SCH 530348 was generally well tolerated and did not cause increased TIMI bleeding, even when administered concomitantly with aspirin and clopidogrel. Further testing in phase III trials to accurately define the safety and efficacy of SCH 530348 is warranted.

Hydroxychavicol, a novel betel leaf component, inhibits platelet aggregation by suppression of cyclooxygenase, thromboxane production and calcium mobilization

BACKGROUND AND PURPOSE

Platelet hyperactivity is important in the pathogenesis of cardiovascular diseases. Betel leaf (PBL) is consumed by 200-600 million betel quid chewers in the world. Hydroxychavicol (HC), a betel leaf component, was tested for its antiplatelet effect.

EXPERIMENTAL APPROACH

We tested the effect of HC on platelet aggregation, thromboxane B(2) (TXB(2)) and reactive oxygen species (ROS) production, cyclooxygenase (COX) activity, ex vivo platelet aggregation and mouse bleeding time and platelet plug formation in vivo. The pharmacokinetics of HC in rats was also assessed.

KEY RESULTS

HC inhibited arachidonic acid (AA) and collagen-induced platelet aggregation and TXB(2) production. HC inhibited the thrombin-induced TXB(2) production, but not platelet aggregation. SQ29548, suppressed collagen- and thrombin-induced TXB(2) production, but not thrombin-induced platelet aggregation. HC also suppressed COX-1/COX-2 enzyme activity and the AA-induced ROS production and Ca(2+) mobilization. HC further inhibited the ex vivo platelet aggregation of platelet-rich plasma (>100 nmole/mouse) and prolonged platelet plug formation (>300 nmole/mouse) in mesenteric microvessels, but showed little effect on bleeding time in mouse tail. Moreover, pharmacokinetics analysis found that more than 99% of HC was metabolized within 3 min of administration in Sprague-Dawley rats in vivo.

CONCLUSIONS AND IMPLICATIONS

HC is a potent COX-1/COX-2 inhibitor, ROS scavenger and inhibits platelet calcium signaling, TXB(2) production and aggregation. HC could be a potential therapeutic agent for prevention and treatment of atherosclerosis and other cardiovascular diseases through its anti-inflammatory and antiplatelet effects, without effects on haemostatic functions.

Antiplatelet effect of sanguinarine is correlated to calcium mobilization, thromboxane and cAMP production

Sanguinarine is a plant alkaloid present in the root of Sanguinaria canadensis and Poppy fumaria species. Sanguinarine has been used as an antiseptic mouth rinse and a toothpaste additive to reduce dental plaque and gingival inflammation. In this study, we investigated the antiplatelet effects of sanguinarine, aiming to extend its potential pharmacological applications. Sanguinarine inhibited platelet aggregation induced by arachidonic acid (AA), collagen, U46619 and sub-threshold concentration of thrombin (0.05 U/ml) with IC(50) concentrations of 8.3, 7.7, 8.6 and 4.4 microM, respectively. Sanguinarine (5-10 microM) inhibited 10-31% of platelet TXB(2) production, but not platelet aggregation induced by higher concentration of thrombin (0.1 U/ml). SQ29548, a thromboxane receptor antagonist, inhibited the AA-induced platelet aggregation but not TXB(2) production. Sanguinarine suppressed cyclooxygenase-1 (COX-1) activity (IC(50)=28 microM), whereas its effect on COX-2 activity was minimal. Sanguinarine (8, 10 microM) further inhibited the AA-induced Ca(2+) mobilization by 27-62%. In addition, SQ22536, an adenylate cyclase inhibitor, attenuated the inhibitory effect of sanguinarine toward AA-induced platelet Ca(2+) mobilization and aggregation. These results suggest that sanguinarine is a potent antiplatelet agent, which activates adenylate cyclase, inhibits platelet Ca(2+) mobilization, TXB(2) production as well as suppresses COX-1 enzyme activity. Sanguinarine may have therapeutic potential for treatment of cardiovascular diseases related to platelet aggregation.

The platelet receptor for type III collagen (TIIICBP) is present in platelet membrane lipid microdomains (rafts)

Platelet interactions with collagen are orchestrated by the presence or the migration of platelet receptor(s) for collagen into lipid rafts, which are specialized lipid microdomains from the platelet plasma membrane enriched in signalling proteins. Electron microscopy shows that in resting platelets, TIIICBP, a receptor specific for type III collagen, is present on the platelet membrane and associated with the open canalicular system, and redistributes to the platelet membrane upon platelet activation. After platelet lysis by 1% Triton X-100 and the separation of lipid rafts on a discontinuous sucrose gradient, TIIICBP is recovered in lipid raft-containing fractions and Triton X-100 insoluble fractions enriched in cytoskeleton proteins. Platelet aggregation, induced by type III collagen, was inhibited after disruption of the lipid rafts by cholesterol depletion, whereas platelet adhesion under static conditions did not require lipid raft integrity. These results indicate that TIIICBP, a platelet receptor involved in platelet interaction with type III collagen, is localized within platelet lipid rafts where it could interact with other platelet receptors for collagen (GP VI and alpha2beta1 integrin) for efficient platelet activation.