Targeting integrin and integrin signaling in treating thrombosis

A novel ITGA2B double cytosine frameshift variant (c.1986_1987insCC) leads to Glanzmann's thrombasthenia in a cat

BACKGROUND

Glanzmann's thrombasthenia (GT) is a congenital platelet disorder affecting approximately 1:1 000 000 people globally and characterized by impaired platelet aggregation and clot retraction. Autosomal recessive, loss-of-function, variants in ITGA2B or ITGB3 of the αIIbβ3 receptor cause the disease in humans. A cat affected by Glanzmann's and macrothrombocytopenia was presented to the UC Davis VMTH.

HYPOTHESIS/OBJECTIVES

Severe thrombopathia in this cat has an underlying genetic etiology.

ANIMALS

A single affected patient, 2 age-matched clinically healthy controls, and a geriatric population (n = 20) of normal cats.

METHODS

Physical examination and clinical pathology tests were performed on the patient. Flow cytometry and platelet aggregometry analyses for patient phenotyping were performed. Patient and validation cohort gDNA samples were extracted for Sanger sequencing of a previously identified ITGA2B (c.1986delC) variant. Reverse transcriptase PCR was performed on patient and healthy control PRP samples to verify ITGA2B variant consequence.

RESULTS

A novel c.1986_1987insCC autosomal recessive variant in ITGA2B was identified. This variant was absent in a population of 194 unrelated cats spanning 44 different breeds. Complete loss of ITGA2B transcript and protein expression was verified by RT-PCR and flow cytometry, explaining the underlying etiology of GT, and likely macrothrombocytopenia, in this cat.

CONCLUSIONS AND CLINICAL IMPORTANCE

This study emphasizes the role of precision medicine in cardiovascular disease of cats and identified yet another variant that may be of utility for screening in the feline population. This study provides a small-volume, standardized, successful protocol for adequate platelet RNA isolation and subsequent molecular assessment of gene expression in cats.

Therapeutic effects and molecular mechanisms of natural products in thrombosis

Thrombotic disorders, such as myocardial infarction and stroke, are the leading cause of death in the global population and have become a health problem worldwide. Drug therapy is one of the main antithrombotic strategies, but antithrombotic drugs are not completely safe, especially the risk of bleeding at therapeutic doses. Recently, natural products have received widespread interest due to their significant efficacy and high safety, and an increasing number of studies have demonstrated their antithrombotic activity. In this review, articles from databases, such as Web of Science, PubMed, and China National Knowledge Infrastructure, were filtered and the relevant information was extracted according to predefined criteria. As a result, more than 100 natural products with significant antithrombotic activity were identified, including flavonoids, phenylpropanoids, quinones, terpenoids, steroids, and alkaloids. These compounds exert antithrombotic effects by inhibiting platelet activation, suppressing the coagulation cascade, and promoting fibrinolysis. In addition, several natural products also inhibit thrombosis by regulating miRNA expression, anti-inflammatory, and other pathways. This review systematically summarizes the natural products with antithrombotic activity, including their therapeutic effects, mechanisms, and clinical applications, aiming to provide a reference for the development of new antithrombotic drugs.

Roles of Integrin in Cardiovascular Diseases: From Basic Research to Clinical Implications

Cardiovascular diseases (CVDs) pose a significant global health threat due to their complex pathogenesis and high incidence, imposing a substantial burden on global healthcare systems. Integrins, a group of heterodimers consisting of α and β subunits that are located on the cell membrane, have emerged as key players in mediating the occurrence and progression of CVDs by regulating the physiological activities of endothelial cells, vascular smooth muscle cells, platelets, fibroblasts, cardiomyocytes, and various immune cells. The crucial role of integrins in the progression of CVDs has valuable implications for targeted therapies. In this context, the development and application of various integrin antibodies and antagonists have been explored for antiplatelet therapy and anti-inflammatory-mediated tissue damage. Additionally, the rise of nanomedicine has enhanced the specificity and bioavailability of precision therapy targeting integrins. Nevertheless, the complexity of the pathogenesis of CVDs presents tremendous challenges for monoclonal targeted treatment. This paper reviews the mechanisms of integrins in the development of atherosclerosis, cardiac fibrosis, hypertension, and arrhythmias, which may pave the way for future innovations in the diagnosis and treatment of CVDs.

A novel GATA1 variant p.G229D causing the defect of procoagulant platelet formation

INTRODUCTION

GATA1 is one of the master transcription factors in hematopoietic lineages development which is crucial for megakaryocytic differentiation and maturation. Previous studies have shown that distinct GATA1 variants are associated with varying severities of macrothrombocytopenia and platelet dysfunction.

OBJECTIVE

To determine the underlying pathological mechanisms of a novel GATA1 variant (c. 686G > A, p. G229D) in a patient with recurrent traumatic muscle hematomas.

METHODS

Comprehensive phenotypic analysis of the patient platelets was performed. Procoagulant platelet formation and function were detected using flow cytometry assay and thrombin generation test (TGT), respectively. The ANO6 expression was measured by qPCR and western blot. The intracellular supramaximal calcium flux was detected by Fluo-5N fluorescent assay.

RESULTS

The patient displayed mild macrothrombocytopenia with defects of platelet granules, aggregation, and integrin αIIbβ3 activation. The percentage of the procoagulant platelet formation of the patient upon the stimulation of thrombin plus collagen was lower than that of the healthy controls (40.9 % vs 49.0 % ± 5.1 %). The patient platelets exhibited a marked reduction of thrombin generation in platelet rich plasma TGT compared to the healthy controls (peak value: ∼70 % of the healthy controls; the endogenous thrombin potential: ∼40 % of the healthy controls). The expression of ANO6 and intracellular calcium flux were impaired, which together with abnormal granules of the patient platelets might contribute to defect of procoagulant platelet function.

CONCLUSIONS

The G229D variant could lead to a novel platelet phenotype characterized by defective procoagulant platelet formation and function, which extended the range of GATA1 variants associated platelet disorders.

Integrinβ-1 in disorders and cancers: molecular mechanisms and therapeutic targets

Integrinβ-1 (ITGB1) is a crucial member of the transmembrane glycoprotein signaling receptor family and is also central to the integrin family. It forms heterodimers with other ligands, participates in intracellular signaling and controls a variety of cellular processes, such as angiogenesis and the growth of neurons; because of its role in bidirectional signaling regulation both inside and outside the membrane, ITGB1 must interact with a multitude of substances, so a variety of interfering factors can affect ITGB1 and lead to changes in its function. Over the past 20 years, many studies have confirmed a clear causal relationship between ITGB1 dysregulation and cancer development and progression in a wide range of benign diseases and solid tumor types, which may imply that ITGB1 is a prognostic biomarker and a therapeutic target for cancer treatment that warrants further investigation. This review summarizes the biological roles of ITGB1 in benign diseases and cancers, and compiles the current status of ITGB1 function and therapy in various aspects of tumorigenesis and progression. Finally, future research directions and application prospects of ITGB1 are suggested. Video Abstract.

Integrin β Expression as a New Diagnostic Marker for Arteriovenous Thrombosis: A Single-Center Prospective Study

Integrin β plays an important role in the pathogenesis of thrombosis and inflammation, and it may be a shared pathogenic mechanism between arterial and venous thromboses. With the goal of identifying new treatment targets for thrombotic diseases and specific diagnostic markers for venous thromboembolism (VTE), this prospective clinical study was performed to clarify the relationship between integrin and thrombosis. The levels of integrin β1-3, interleukin-6 (IL-6), and C-reactive protein were significantly higher in patients with acute myocardial infarction (AMI; n = 44) and acute VTE (n = 43) compared to healthy controls (n = 33). The IL-6 and integrin β1-3 levels were also significantly higher in the AMI group compared to the VTE and control groups. Logistic regression analysis identified IL-6 and integrin β1-3 levels as independent risk factors for thrombotic disease. Based on the receiver-operating characteristic curve, Youden index, sensitivity, and specificity, the diagnostic accuracy value for VTE was greater than 0.8 when integrins β1, β2, and β3 were combined. Overall, these results suggest that integrin β levels can contribute to improving the diagnosis and treatment of arteriovenous thrombosis.

Adverse Drug Effect Profiles of Gp2b/3a Inhibitors: A Comparative Review of the Last Two Decades

ST-Elevation Myocardial Infarction and non-ST Elevation Myocardial Infarction belong to the acute coronary syndrome group of diseases. These conditions are characterized by the complete or partial blockage of one or several coronary arteries, resulting in myocardial injury or necrosis. Various medications are used in their treatment, with the most recent addition being Glycoprotein IIb/IIIa inhibitors. They work by hindering the activity of glycoprotein IIb/IIIa receptors, which, in turn, prevents the clumping of platelets. Some of the GpIIb/IIIa inhibitors available in this category include abciximab, tirofiban, eptifibatide, roxifiban, and orbofiban. With this comprehensive literature review, we aimed to explore the potential adverse effects of these medications and compare the three in terms of their side effects profile. We searched through PubMed and Google Scholar and pinpointed 13 articles aligned with our inclusion criteria: six articles utilized eptifibatide, four were related to abciximab, and three used tirofiban. In 85% of the cases, a severe drop in platelet count, reaching as low as 1000/μL, was reported. Additionally, several other side effects were noted: one case documented multiple bruising spots appearing around the patient's body, two cases reported diffuse alveolar hemorrhage, and one case described a cardiac tamponade resulting from hemorrhagic pericarditis. Our study highlights the crucial significance of keeping a watchful eye on and comprehending the potential drawbacks linked to these medications in cardiovascular treatment. The necessity of researching these medications and their side effects is also evident, as this will significantly enhance the quality of treatment provided.

Flow Chamber Analyses in Cardiovascular Research: Impact of Platelets and the Intercellular Crosstalk with Endothelial Cells, Leukocytes, and Red Blood Cells

Platelets are main drivers of thrombus formation. Besides platelet aggregate formation, platelets interact with different blood cells such as red blood and white blood cells (RBCs, WBCs) and endothelial cells (ECs), to promote thrombus formation and inflammation. In the past, the role of different proteins in platelet adhesion, activation, and aggregate formation has been analyzed using platelets/mice with a genetic loss of a certain protein. These knock-out mouse models have been investigated for changes in experimental arterial thrombosis or hemostasis. In this review, we focused on the Maastricht flow chamber, which is a very elegant tool to analyze thrombus formation under flow using whole blood or different blood cell components of genetically modified mice. Besides, the interaction of platelets with RBCs, WBCs, and ECs under flow conditions has been evaluated with regard to thrombus formation and platelet-mediated inflammation. Importantly, alterations in thrombus formation as emerged in the flow chamber frequently reflect arterial thrombosis in different mouse models. Thus, the results of flow chamber experiments in vitro are excellent indicators for differences in arterial thrombosis in vivo. Taken together, the Maastricht flow chamber can be used to (1) determine the severity of platelet alterations in different knock-out mice; (2) analyze differences in platelet adhesion, aggregation, and activation; (3) investigate collagen and non-collagen-dependent alterations of thrombus formation; and (4) highlight differences in the interaction of platelets with different blood/ECs. Thus, this experimental approach is a useful tool to increase our understanding of signaling mechanisms that drive arterial thrombosis and hemostasis.

Antagonistic Roles of Human Platelet Integrin αIIbβ3 and Chemokines in Regulating Neutrophil Activation and Fate on Arterial Thrombi Under Flow

BACKGROUND

Platelets and neutrophils are the first blood cells accumulating at sites of arterial thrombus formation, and both cell types contribute to the pathology of thrombotic events. We aimed to identify key interaction mechanisms between these cells using microfluidic approaches.

METHODS

Whole-blood perfusion was performed over a collagen surface at arterial shear rate. Platelet and leukocyte (in majority neutrophil) activation were microscopically visualized using fluorescent markers. The contributions of platelet-adhesive receptors (integrin, P-selectin, CD40L) and chemokines were studied by using inhibitors or antibodies and using blood from patients with GT (Glanzmann thrombasthenia) lacking platelet-expressed αIIbβ3.

RESULTS

We observed (1) an unknown role of activated platelet integrin αIIbß3 preventing leukocyte adhesion, which was overcome by short-term flow disturbance provoking massive adhesion; (2) that platelet-expressed CD40L controls the crawling pattern and thrombus fidelity of the cells on a thrombus; (3) that continued secretion of platelet substances promotes activation of identified neutrophils, as assessed by (fMLP [N-formylmethionyl-leucyl-phenylalanine, a potent chemotactic agent and leukocyte activator] induced) [Ca2+]i rises and antigen expression; (4) and that platelet-released chemokines activate the adhered cells in the order of CXCL7>CCL5>CXCL4. Furthermore, postsilencing of the platelets in a thrombus suppressed the leukocyte activation. However, the leukocytes on thrombi did no more than limitedly form neutrophil extracellular traps, unless stimulated with phorbol ester or lipopolysaccharide.

CONCLUSIONS

Together, these findings reveal a multifaceted regulation of adhesion and activation of neutrophils by platelets in a thrombus, with a balanced role of several platelet-adhesive receptors and a promoting role of platelet-released substances. This multivalent nature of neutrophil-thrombus interactions offers novel prospects for pharmacological intervention.

Repurposing of rilpivirine for preventing platelet β3 integrin-dependent thrombosis by targeting c-Src active autophosphorylation

BACKGROUND

HIV-infected individuals are known to be at higher risk for thrombotic cardiovascular disease (CVD), which may also be differentially affected by components of anti-HIV drugs. To identify the effects of a series of FDA-approved anti-HIV drugs on platelet aggregation in humans, focusing on the novel pharmacological effects of rilpivirine (RPV), a reverse transcriptase inhibitor, on platelet function both in vitro and in vivo and the mechanisms involved.

METHODS AND RESULTS

In vitro studies showed that RPV was the only anti-HIV reagent that consistently and efficiently inhibited aggregation elicited by different agonists, exocytosis, morphological extension on fibrinogen, and clot retraction. Treatment of mice with RPV significantly prevented thrombus formation in FeCl3-injured mesenteric vessels, postcava with stenosis surgery, and ADP -induced pulmonary embolism models without defects in platelet viability, tail bleeding, and coagulation activities. RPV also improved cardiac performance in mice with post-ischemic reperfusion. A mechanistic study revealed that RPV preferentially attenuated fibrinogen-stimulated Tyr773 phosphorylation of β3-integrin by inhibiting Tyr419 autophosphorylation of c-Src. Molecular docking and surface plasmon resonance analyses showed that RPV can bind directly to c-Src. Further mutational analysis showed that the Phe427 residue of c-Src is critical for RPV interaction, suggesting a novel interaction site for targeting c-Src to block β3-integrin outside-in signaling.

CONCLUSION

These results demonstrated that RPV was able to prevent the progression of thrombotic CVDs by interrupting β3-integrin-mediated outside-in signaling via inhibiting c-Src activation without hemorrhagic side effects, highlighting RPV as a promising reagent for the prevention and therapy of thrombotic CVDs.

MTH1 protects platelet mitochondria from oxidative damage and regulates platelet function and thrombosis

Human MutT Homolog 1 (MTH1) is a nucleotide pool sanitization enzyme that hydrolyzes oxidized nucleotides to prevent their mis-incorporation into DNA under oxidative stress. Expression and functional roles of MTH1 in platelets are not known. Here, we show MTH1 expression in platelets and its deficiency impairs hemostasis and arterial/venous thrombosis in vivo. MTH1 deficiency reduced platelet aggregation, phosphatidylserine exposure and calcium mobilization induced by thrombin but not by collagen-related peptide (CRP) along with decreased mitochondrial ATP production. Thrombin but not CRP induced Ca2+-dependent mitochondria reactive oxygen species generation. Mechanistically, MTH1 deficiency caused mitochondrial DNA oxidative damage and reduced the expression of cytochrome c oxidase 1. Furthermore, MTH1 exerts a similar role in human platelet function. Our study suggests that MTH1 exerts a protective function against oxidative stress in platelets and indicates that MTH1 could be a potential therapeutic target for the prevention of thrombotic diseases.

Soluble endoglin reduces thrombus formation and platelet aggregation via interaction with αIIbβ3 integrin

BACKGROUND

The circulating form of human endoglin (sEng) is a cleavage product of membrane-bound endoglin present on endothelial cells. Because sEng encompasses an RGD motif involved in integrin binding, we hypothesized that sEng would be able to bind integrin αIIbβ3, thereby compromising platelet binding to fibrinogen and thrombus stability.

METHODS

In vitro human platelet aggregation, thrombus retraction, and secretion-competition assays were performed in the presence of sEng. Surface plasmon resonance (SPR) binding and computational (docking) analyses were carried out to evaluate protein-protein interactions. A transgenic mouse overexpressing human sEng (hsEng+) was used to measure bleeding/rebleeding, prothrombin time (PT), blood stream, and embolus formation after FeCl3-induced injury of the carotid artery.

RESULTS

Under flow conditions, supplementation of human whole blood with sEng led to a smaller thrombus size. sEng inhibited platelet aggregation and thrombus retraction, interfering with fibrinogen binding, but did not affect platelet activation. SPR binding studies demonstrated that the specific interaction between αIIbβ3 and sEng and molecular modeling showed a good fitting between αIIbβ3 and sEng structures involving the endoglin RGD motif, suggesting the possible formation of a highly stable αIIbβ3/sEng. hsEng+ mice showed increased bleeding time and number of rebleedings compared to wild-type mice. No differences in PT were denoted between genotypes. After FeCl3 injury, the number of released emboli in hsEng+ mice was higher and the occlusion was slower compared to controls.

CONCLUSIONS

Our results demonstrate that sEng interferes with thrombus formation and stabilization, likely via its binding to platelet αIIbβ3, suggesting its involvement in primary hemostasis control.

A mechanism of platelet integrin αIIbβ3 outside-in signaling through a novel integrin αIIb subunit-filamin-actin linkage

The communication of talin-activated integrin αIIbβ3 with the cytoskeleton (integrin outside-in signaling) is essential for platelet aggregation, wound healing, and hemostasis. Filamin, a large actin crosslinker and integrin binding partner critical for cell spreading and migration, is implicated as a key regulator of integrin outside-in signaling. However, the current dogma is that filamin, which stabilizes inactive αIIbβ3, is displaced from αIIbβ3 by talin to promote the integrin activation (inside-out signaling), and how filamin further functions remains unresolved. Here, we show that while associating with the inactive αIIbβ3, filamin also associates with the talin-bound active αIIbβ3 to mediate platelet spreading. Fluorescence resonance energy transfer-based analysis reveals that while associating with both αIIb and β3 cytoplasmic tails (CTs) to maintain the inactive αIIbβ3, filamin is spatiotemporally rearranged to associate with αIIb CT alone on activated αIIbβ3. Consistently, confocal cell imaging indicates that integrin α CT-linked filamin gradually delocalizes from the β CT-linked focal adhesion marker-vinculin likely because of the separation of integrin α/β CTs occurring during integrin activation. High-resolution crystal and nuclear magnetic resonance structure determinations unravel that the activated integrin αIIb CT binds to filamin via a striking α-helix→β-strand transition with a strengthened affinity that is dependent on the integrin-activating membrane environment containing enriched phosphatidylinositol 4,5-bisphosphate. These data suggest a novel integrin αIIb CT-filamin-actin linkage that promotes integrin outside-in signaling. Consistently, disruption of such linkage impairs the activation state of αIIbβ3, phosphorylation of focal adhesion kinase/proto-oncogene tyrosine kinase Src, and cell migration. Together, our findings advance the fundamental understanding of integrin outside-in signaling with broad implications in blood physiology and pathology.

Case report: reuse of tirofiban leads to very severe thrombocytopenia

Background

Telofiban is a class of small molecule non-peptide tyrosine derivatives containing RGD sequences. It is the only platelet surface glycoprotein (GP) IIb/IIIa receptor antagonist (GPI) currently marketed in China. In patients with ST-segment elevation myocardial infarction(STEMI) who receive percutaneous coronary intervention (PCI) with a heavy thrombotic load, postoperative intravenous tirofiban can prevent complications of myocardial ischemia due to sudden coronary artery occlusion. With the increase in the clinical use of tirofiban, the number of adverse reactions related to thrombocytopenia induced by tirofiban has gradually increased. Still, most of them have thrombocytopenia after the first use. We report one case of very severe thrombocytopenia following the reuse of tirofiban.

Case summary

A 65-year-old man of Han nationality, 170 cm in height, 85 kg in weight, and 29.4 BMI, suffered from cerebral infarction 13 years ago and left with right limb movement disorder. Five days before this hospitalization, the patient underwent PCI, and three stents were implanted. After the operation, anti-platelet tirofiban and nadroparin calcium were given, and no thrombocytopenia was found. The patient still retains 80% stenosis due to anterior descending branches and plans to undergo PCI again half a month later. The patient with a history of hypertension, type 2 diabetes, diabetic nephropathy, and cerebral infarction usually took 100 mg of aspirin and 75 mg of clopidogrel, antiplatelet therapy, and had no history of food and drug allergy. One day after discharge, the patient suddenly felt chest tightness and wheezing. The laboratory showed hypersensitivity troponin 2.85 ng/ml (normal 0-0.0268 ng/ml), and the admission ECG showed ST-T changes in leads I, aVL, V5-V6. On the 6th day of hospitalization, PCI was performed, a stent was implanted in the proximal section of the anterior descending branch opening, and tirofiban(10 ug/kg, 3 min bolus, then 0.1 ug/kg/min) antiplatelet therapy was given after surgery. About 10 min after the tirofiban infusion, the patient suddenly shivered, accompanied by convulsions, accompanied by elevated body temperature (up to 39.4°C), accompanied by epistaxis and microscopic hematuria. An urgent blood test showed that the platelets dropped to 1 × 109/L, tirofiban and aspirin stopped immediately, and the antiplatelet therapy of clopidogrel was retained. After infusion of methylprednisolone sodium succinate and gamma globulin, the patient's platelets gradually recovered, and the patient was successfully discharged seven days later in stable condition.

Conclusion

This case is typical of severe thrombocytopenia caused by reusing tirofiban. This case may provide new insights into: 1. Patients who did not have thrombocytopenia after the first use of tirofiban may still have extremely severe thrombocytopenia after re-exposure to tirofiban. Routine platelet count monitoring and early identification of thrombocytopenia are the essential links. 2. Thrombocytopenia caused by re-exposure to tirofiban may have a faster onset, deeper degree, and slower recovery due to antibodies retained after the first exposure to tirofiban; 3. Platelet transfusions may not be necessary for patients with severe thrombocytopenia; 4. Immunosuppressants help suppress the body's immune response, promote platelet recovery, and can be reduced or discontinued when platelets rise and may be safe; 5. After tirofiban for PCI, continuing the maintenance dose of clopidogrel may be safe if the patient has no significant bleeding events.

Efficacy and safety of intracoronary versus intravenous tirofiban in patients with ST-segment elevation myocardial infarction undergoing primary percutaneous coronary intervention: A meta-analysis of randomized controlled trials

Background

Effective antiplatelet therapy is critical for patients with ST-segment elevation myocardial infarction (STEMI) and receiving primary percutaneous coronary interventions (PPCI). Intracoronary (IC) and intravenous (IV) administration of tirofiban are commonly used during the procedure of PPCI. However, which is the better administration route of tirofiban have not been fully evaluated.

Methods

A comprehensive literature search of RCTs that comparing IC with IV tirofiban in STEMI patients undergoing PPCI was conducted, which were published as of May 7, 2022, in PubMed, Embase, Cochrane Library, Web of Science, Scopus and ClinicalTrials.gov. The primary efficacy endpoint was 30-day major adverse cardiovascular events (MACE) and the primary safety endpoint was in-hospital bleeding events.

Results

This meta-analysis included 9 trials involving 1177 patients. IC tirofiban significantly reduced the incidence of 30-day MACE (RR 0.65, 95% CI: 0.44 to 0.95, P = 0.028) and improved the rate of the thrombolysis in myocardial infarction (TIMI) grade 3 flow in high-dose (25 μg/kg) group (RR = 1.13, 95% CI: 0.99-1.30, P = 0.001), in-hospital (WMD 2.03, 95% CI: 1.03 to 3.02, P < 0.001), and 6-month left ventricular injection fraction (LVEF) (WMD 6.01, 95% CI: 5.02 to 6.99, P < 0.001) compared with IV. There was no significant difference in the incidences of in-hospital bleeding events (RR 0.96, 95% CI: 0.67 to 1.38, P = 0.82) and thrombocytopenia (RR 0.63, 95% CI: 0.26 to 1.57, P = 0.32) between the two groups.

Conclusions

IC tirofiban significantly improved the incidence of TIMI 3 in the high-dose group, in-hospital and 6-month LVEF, and reduced the 30-day MACE incidence without increasing the risk of bleeding compared with IV.

Targeting integrin pathways: mechanisms and advances in therapy

Integrins are considered the main cell-adhesion transmembrane receptors that play multifaceted roles as extracellular matrix (ECM)-cytoskeletal linkers and transducers in biochemical and mechanical signals between cells and their environment in a wide range of states in health and diseases. Integrin functions are dependable on a delicate balance between active and inactive status via multiple mechanisms, including protein-protein interactions, conformational changes, and trafficking. Due to their exposure on the cell surface and sensitivity to the molecular blockade, integrins have been investigated as pharmacological targets for nearly 40 years, but given the complexity of integrins and sometimes opposite characteristics, targeting integrin therapeutics has been a challenge. To date, only seven drugs targeting integrins have been successfully marketed, including abciximab, eptifibatide, tirofiban, natalizumab, vedolizumab, lifitegrast, and carotegrast. Currently, there are approximately 90 kinds of integrin-based therapeutic drugs or imaging agents in clinical studies, including small molecules, antibodies, synthetic mimic peptides, antibody-drug conjugates (ADCs), chimeric antigen receptor (CAR) T-cell therapy, imaging agents, etc. A serious lesson from past integrin drug discovery and research efforts is that successes rely on both a deep understanding of integrin-regulatory mechanisms and unmet clinical needs. Herein, we provide a systematic and complete review of all integrin family members and integrin-mediated downstream signal transduction to highlight ongoing efforts to develop new therapies/diagnoses from bench to clinic. In addition, we further discuss the trend of drug development, how to improve the success rate of clinical trials targeting integrin therapies, and the key points for clinical research, basic research, and translational research.

Chloroplast-boosted photodynamic therapy for effective drug-resistant bacteria killing and biofilm ablation

Due to the misuse of various antibiotics, the problem of bacterial resistance has become more serious worldwide, and the associated diseases have significantly increased the medical burden of society. Antimicrobial photodynamic therapy (PDT) has received widespread attention because of its safety, efficiency, and facile implementation. Here, we report an oxygen-supply antibacterial agent (Ce6@CS/CP), which could enhance the efficacy of antibacterial PDT via photosynthesis of O₂. Ce6@CS/CP displayed a robust interaction with bacteria, hence facilitating the delivery efficiency of Ce6. In vitro experiments demonstrated that the photodynamic bactericidal potency of Ce6@CS/CP was remarkably greater than that of free Ce6. Furthermore, Ce6@CS/CP also exhibited superior significant antibiofilm activity to free Ce6. As a live oxygen-supply antibacterial agent, Ce6@CS/CP possesses excellent bacteria delivery ability of Ce6 and could enhance the potency of antibacterial PDT by photosynthesis, offering a new strategy for fighting against drug-resistant bacteria.

N-Stearoylethanolamine Inhibits Integrin-Mediated Activation, Aggregation, and Adhesion of Human Platelets

N-stearoylethanolamine (NSE), a lipid mediator that belongs to the N-acylethanolamine (NAE) family, has anti-inflammatory, antioxidant, and membranoprotective actions. In contrast to other NAEs, NSE does not interact with cannabinoid receptors. The exact mechanism of its action remains unclear. The aim of this study is to evaluate the action of NSE on activation, aggregation, and adhesion of platelets that were chosen as a model of cellular response. Aggregation of platelets was measured to analyze the action of NSE (10^-6-10^-10 M) on platelet reactivity. Changes in granularity and shape of resting platelets and platelets stimulated with ADP in the presence of NSE were monitored by flow cytometry, and platelet deganulation was monitored by spectrofluorimetry. In vivo studies were performed using obese insulin-resistant rats. Binding of fibrinogen to the GPIIb/IIIa receptor was estimated using indirect ELISA and a scanning electron microscopy (SEM). It was found that NSE inhibits the activation and aggregation of human platelets. Our results suggest that NSE may decrease the activation and subsequent aggregation of platelets induced by ristocetin, epinephrine, and low doses of ADP. NSE also reduced the binding of fibrinogen to GPIIb/IIIa on activated platelets. These effects could be explained by the inhibition of platelet activation mediated by integrin receptors: the GPIb-IX-V complex for ristocetin-induced activation and GPIIb/IIIa when epinephrine and low doses of ADP were applied. The anti-platelet effect of NSE complements its anti-inflammatory effect and allows us to prioritize studies of NSE as a potent anti-thrombotic agent. SIGNIFICANCE STATEMENT: N-stearoylethanolamine (NSE) was shown to possess inhibitory action on platelet activation, adhesion, and aggregation. The mechanism of inhibition possibly involves integrin receptors. This finding complements the known anti-inflammatory effects of NSE.

Comprehensive overview of COVID-19-related respiratory failure: focus on cellular interactions

The pandemic outbreak of coronavirus disease 2019 (COVID-19) has created health challenges in all parts of the world. Understanding the entry mechanism of this virus into host cells is essential for effective treatment of COVID-19 disease. This virus can bind to various cell surface molecules or receptors, such as angiotensin-converting enzyme 2 (ACE2), to gain cell entry. Respiratory failure and pulmonary edema are the most important causes of mortality from COVID-19 infections. Cytokines, especially proinflammatory cytokines, are the main mediators of these complications. For normal respiratory function, a healthy air-blood barrier and sufficient blood flow to the lungs are required. In this review, we first discuss airway epithelial cells, airway stem cells, and the expression of COVID-19 receptors in the airway epithelium. Then, we discuss the suggested molecular mechanisms of endothelial dysfunction and blood vessel damage in COVID-19. Coagulopathy can be caused by platelet activation leading to clots, which restrict blood flow to the lungs and lead to respiratory failure. Finally, we present an overview of the effects of immune and non-immune cells and cytokines in COVID-19-related respiratory failure.

Peptide therapeutics in the management of metastatic cancers

Cancer remains a leading health concern threatening lives of millions of patients worldwide. Peptide-based drugs provide a valuable alternative to chemotherapeutics as they are highly specific, cheap, less toxic and easier to synthesize compared to other drugs. In this review, we have discussed various modes in which peptides are being used to curb cancer. Our review highlights specially the various anti-metastatic peptide-based agents developed by targeting a plethora of cellular factors. Herein we have given a special focus on integrins as targets for peptide drugs, as these molecules play key roles in metastatic progression. The review also discusses use of peptides as anti-cancer vaccines and their efficiency as drug-delivery tools. We hope this work will give the reader a clear idea of the mechanisms of peptide-based anti-cancer therapeutics and encourage the development of superior drugs in the future.

Recent Advances in Nanomaterials for Diagnosis, Treatments, and Neurorestoration in Ischemic Stroke

Stroke is a major public health issue, corresponding to the second cause of mortality and the first cause of severe disability. Ischemic stroke is the most common type of stroke, accounting for 87% of all strokes, where early detection and clinical intervention are well known to decrease its morbidity and mortality. However, the diagnosis of ischemic stroke has been limited to the late stages, and its therapeutic window is too narrow to provide rational and effective treatment. In addition, clinical thrombolytics suffer from a short half-life, inactivation, allergic reactions, and non-specific tissue targeting. Another problem is the limited ability of current neuroprotective agents to promote recovery of the ischemic brain tissue after stroke, which contributes to the progressive and irreversible nature of ischemic stroke and also the severity of the outcome. Fortunately, because of biomaterials’ inherent biochemical and biophysical properties, including biocompatibility, biodegradability, renewability, nontoxicity, long blood circulation time, and targeting ability. Utilization of them has been pursued as an innovative and promising strategy to tackle these challenges. In this review, special emphasis will be placed on the recent advances in the study of nanomaterials for the diagnosis and therapy of ischemic stroke. Meanwhile, nanomaterials provide much promise for neural tissue salvage and regeneration in brain ischemia, which is also highlighted.

Tetrahydrocurcumin Downregulates MAPKs/cPLA2 Signaling and Attenuates Platelet Thromboxane A2 Generation, Granule Secretion, and Thrombus Growth

Platelet granule secretion plays a key role in atherothrombosis. Curcumin, a natural polyphenol compound derived from turmeric, exerts multiple biological activities. The current study sought to investigate the efficacy of tetrahydrocurcumin (THC, the major active metabolite of curcumin) on platelet granule secretion in vitro and thrombus formation in vivo. We found that THC significantly attenuated agonist-induced granule secretion in human gel-filtered platelets in vitro, including CD62P and CD63 expression and platelet factor 4, CCL5, and adenosine triphosphate release. These inhibitory effects of THC were partially mediated by the attenuation of cytosolic phospholipase A₂ (cPLA₂) phosphorylation, leading to a decrease in thromboxane A₂ (TxA₂) generation. Moreover, the MAPK (Erk1/2, JNK1/2, and p38 MAPK) signaling pathways were downregulated by THC treatment, resulting in reduced cPLA₂ activation, TxA₂ generation, and granule secretion. Additionally, THC and curcumin attenuated murine thrombus growth in a FeCl₃-induced mesenteric arteriole thrombosis model in C57BL/6J mice without prolonging the tail bleeding time. THC exerted more potent inhibitory effects on thrombosis formation than curcumin. Through blocking cyclooxygenase-1 activity and thus inhibiting platelet TxA₂ synthesis and granule secretion with aspirin, we found that THC did not further decrease the inhibitory effects of aspirin on thrombosis formation. Thus, through inhibiting MAPKs/cPLA₂ signaling, and attenuating platelet TxA₂ generation, granule secretion, and thrombus formation, THC may be a potent cardioprotective agent.

DNA Tension Probes Show that Cardiomyocyte Maturation Is Sensitive to the Piconewton Traction Forces Transmitted by Integrins

Cardiac muscle cells (CMCs) are the unit cells that comprise the heart. CMCs go through different stages of differentiation and maturation pathways to fully mature into beating cells. These cells can sense and respond to mechanical cues through receptors such as integrins which influence maturation pathways. For example, cell traction forces are important for the differentiation and development of functional CMCs, as CMCs cultured on varying substrate stiffness function differently. Most work in this area has focused on understanding the role of bulk extracellular matrix stiffness in mediating the functional fate of CMCs. Given that stiffness sensing mechanisms are mediated by individual integrin receptors, an important question in this area pertains to the specific magnitude of integrin piconewton (pN) forces that can trigger CMC functional maturation. To address this knowledge gap, we used DNA adhesion tethers that rupture at specific thresholds of force (∼12, ∼56, and ∼160 pN) to test whether capping peak integrin tension to specific magnitudes affects CMC function. We show that adhesion tethers with greater force tolerance lead to functionally mature CMCs as determined by morphology, twitching frequency, transient calcium flux measurements, and protein expression (F-actin, vinculin, α-actinin, YAP, and SERCA2a). Additionally, sarcomeric actinin alignment and multinucleation were significantly enhanced as the mechanical tolerance of integrin tethers was increased. Taken together, the results show that CMCs harness defined pN integrin forces to influence early stage development. This study represents an important step toward biophysical characterization of the contribution of pN forces in early stage cardiac differentiation.

An activation specific anti-Mac-1 designed ankyrin repeat protein improves survival in a mouse model of acute lung injury

The acute respiratory distress syndrome (ARDS) is a life-threatening clinical condition. The number of ARDS cases has risen dramatically recently but specific treatment options are limited. ARDS is associated with an overshooting inflammatory response and neutrophils play a central role in its pathogenesis. Neutrophils express the integrin Mac-1 on their surface which adopts a resting and activated conformation depending on leukocyte activation. The aim of this study was to investigate the anti-inflammatory effects of the unique activation-specific anti-Mac-1 DARPin 'F7' in a mouse model of ARDS. ARDS was induced by intratracheal lipopolysaccharide (LPS) instillation and the acute (day 1-4) and chronic phase (day 5-10) were studied. After expression and purification, F7, a control DARPin and PBS, were applied daily via the intraperitoneal route. Survival and weight loss were recorded. Histological analysis of lung sections, flow cytometric leukocyte analysis of blood and bronchioalveolar lavage (BALF) were performed. Moreover, protein concentration and cytokine levels were determined in the BALF. Treatment with F7 improved survival and reduced weight loss significantly compared to treatment with the control DARPin or PBS. Neutrophil count in the BALF and peripheral blood were significantly reduced in mice treated with F7. Histology revealed significantly reduced pulmonary inflammation in the F7 treated group. Treatment with DARPin F7 inhibited neutrophil accumulation, reduced signs of local and systemic inflammation and improved survival in a mouse model of ARDS. F7 may be a novel anti-inflammatory drug candidate for the treatment of severe ARDS.

Cyclo(RGD) peptide-decorated silver nanoparticles with anti-platelet potential for active platelet-rich thrombus targeting

The development of integrated nanomedicine for prevention and early diagnosis of thrombosis is highly significant. Platelet plays a vital role in thrombotic disorders, offering an ideal target for thromboprophylaxis and imaging of thrombi. We herein fabricated cyclo(RGD) peptide-decorated AgNPs (designated cRGD-AgNPs) for active targeting platelet-rich thrombi. In vitro cytotoxicity and hemolysis assays demonstrated that cRGD-AgNPs have acceptable biocompatibility pattern. Both PEG-AgNPs (non-targeted version) and cRGD-AgNPs can inhibit agonist-mediated platelet aggregation, whereas the latter exhibited significant attenuation on platelet activation and adhesion onto collagen and fibrinogen matrix. Furthermore, the superior binding ability of cRGD-AgNPs with platelet-rich thrombus was demonstrated in static/dynamic condition in vitro. In vivo studies revealed that cRGD-AgNPs could actively target thrombi in a mouse model of carotid artery thrombi with favorable safety. Our results here suggest that cRGD-AgNPs with intrinsic anti-platelet potential might be promising nano theranostics for thromboprophylaxis and active thrombus targeting.

DisintegrinDB: The first integrated database resource of disintegrins from snake venoms

Nowadays, a large number of databases have been developed gathering different types of therapeutic peptides including antimicrobial, antiviral and scorpion toxins peptides facilitating the searching for these molecules and their structural characteristics and pharmacology. Disintegrins, a family of small non-enzymatic and cysteine-rich proteins found in the snake venom may have a potential role in terms of novel therapeutic leads for cancer treatment. Despite their therapeutic effect, no database dedicated to disintegrins is available yet. Indeed, accessible information related to disintegrins are either scattered or fragmented in different databases from which it becomes extremely difficult to collect all the properties related to a particular disintegrin without exploring numerous databases available through distinct websites. Here, we propose DisintegrinDB as a first unique resource centralizing data related to disintegrins from snake venom. DisintegrinDB aims to facilitate the search on a given disintegrin and centralizes all the information on these peptides, helping researchers to retrieve all relevant related information.

Integrins as a drug target in liver fibrosis

As the worldwide prevalence of chronic liver diseases is high and continuing to increase, there is an urgent need for treatment to prevent cirrhosis-related morbidity and mortality. Integrins are heterodimeric cell-surface proteins that are promising targets for therapeutic intervention. αv integrins are central in the development of fibrosis as they activate latent TGFβ, a known profibrogenic cytokine. The αv subunit can form heterodimers with β1, β3, β5, β6 or β8 subunits and one or more of these integrins are central to the development of liver fibrosis, however, their relative importance is not understood. This review summarises the current knowledge of αv integrins and their respective β subunits in different organs, with a focus on liver fibrosis and the emerging preclinical and clinical data with regards to αv integrin inhibitors.

Targeting the RT loop of Src SH3 in Platelets Prevents Thrombosis without Compromising Hemostasis

Conventional antiplatelet agents indiscriminately inhibit both thrombosis and hemostasis, and the increased bleeding risk thus hampers their use at more aggressive dosages to achieve adequate effect. Blocking integrin αIIbβ3 outside-in signaling by separating the β3/Src interaction, yet to be proven in vivo, may nonetheless resolve this dilemma. Identification of a specific druggable target for this strategy remains a fundamental challenge as Src SH3 is known to be responsible for binding to not only integrin β3 but also the proteins containing the PXXP motif. In vitro and in vivo mutational analyses show that the residues, especially E97, in the RT loop of Src SH3 are critical for interacting with β3. DCDBS84, a small molecule resulting from structure-based virtual screening, is structurally validated to be directed toward the projected target. It specifically disrupts β3/Src interaction without affecting canonical PXXP binding and thus inhibits the outside-in signaling-regulated platelet functions. Treatment of mice with DCDBS84 causes a profound inhibition of thrombosis, equivalent to that induced by extremely high doses of αIIbβ3 antagonist, but does not compromise primary hemostasis. Specific targets are revealed for a preferential inhibition of thrombosis that may lead to new classes of potent antithrombotics without hemorrhagic side effects.

Fibroblast growth factor-21 as a novel metabolic factor for regulating thrombotic homeostasis

Fibroblast growth factor-21 (FGF-21) performs a wide range of biological functions in organisms. Here, we report for the first time that FGF-21 suppresses thrombus formation with no notable risk of bleeding. Prophylactic and therapeutic administration of FGF-21 significantly improved the degree of vascular stenosis and reduced the thrombus area, volume and burden. We determined the antithrombotic mechanism of FGF-21, demonstrating that FGF-21 exhibits an anticoagulant effect by inhibiting the expression and activity of factor VII (FVII). FGF-21 exerts an antiplatelet effect by inhibiting platelet activation. FGF-21 enhances fibrinolysis by promoting tissue plasminogen activator (tPA) expression and activation, while inhibiting plasminogen activator inhibitor 1 (PAI-1) expression and activation. We further found that FGF-21 mediated the expression and activation of tPA and PAI-1 by regulating the ERK1/2 and TGF-β/Smad2 pathways, respectively. In addition, we found that FGF-21 inhibits the expression of inflammatory factors in thrombosis by regulating the NF-κB pathway.

Prothrombotic Phenotype in COVID-19: Focus on Platelets

COVID-19 infection is associated with a broad spectrum of presentations, but alveolar capillary microthrombi have been described as a common finding in COVID-19 patients, appearing as a consequence of a severe endothelial injury with endothelial cell membrane disruption. These observations clearly point to the identification of a COVID-19-associated coagulopathy, which may contribute to thrombosis, multi-organ damage, and cause of severity and fatality. One significant finding that emerges in prothrombotic abnormalities observed in COVID-19 patients is that the coagulation alterations are mainly mediated by the activation of platelets and intrinsically related to viral-mediated endothelial inflammation. Beyond the well-known role in hemostasis, the ability of platelets to also release various potent cytokines and chemokines has elevated these small cells from simple cell fragments to crucial modulators in the blood, including their inflammatory functions, that have a large influence on the immune response during infectious disease. Indeed, platelets are involved in the pathogenesis of acute lung injury also by promoting NET formation and affecting vascular permeability. Specifically, the deposition by activated platelets of the chemokine platelet factor 4 at sites of inflammation promotes adhesion of neutrophils on endothelial cells and thrombogenesis, and it seems deeply involved in the phenomenon of vaccine-induced thrombocytopenia and thrombosis. Importantly, the hyperactivated platelet phenotype along with evidence of cytokine storm, high levels of P-selectin, D-dimer, and, on the other hand, decreased levels of fibrinogen, von Willebrand factor, and thrombocytopenia may be considered suitable biomarkers that distinguish the late stage of COVID-19 progression in critically ill patients.

Paxillin binding to the PH domain of kindlin-3 in platelets is required to support integrin αIIbβ3 outside-in signaling

BACKGROUND

Kindlin-3 is essential for supporting the bidirectional signaling of integrin αIIbβ3 in platelets by bridging the crosstalk between integrin αIIbβ3 and the cytoplasmic signaling adaptors.

OBJECTIVE

In this study, we identified a previously unrecognized paxillin binding site in the pleckstrin homology (PH) domain of kindlin-3 and verified its functional significance.

METHODS

Structure-based approaches were employed to identify the paxillin binding site in the PH domain of kindlin-3. In addition, the bidirectional signaling of integrin αIIbβ3 were evaluated in both human and mouse platelets.

RESULTS

In brief, we found that a β1-β2 loop in the PH domain of kindlin-3, an important part of the canonical membrane phospholipid binding pocket, was also involved in mediating paxillin interaction. Interestingly, the binding sites of paxillin and membrane phospholipids in the PH domain of kindlin-3 were mutually exclusive. Specific disruption of paxillin binding to the PH domain by point mutations inhibited platelet spreading on immobilized fibrinogen while having no inhibition on soluble fibrinogen binding to stimulated platelets. In addition, a membrane-permeable peptide derived from the β1-β2 loop in the PH domain of kindlin-3 was capable of inhibiting platelet spreading and clot retraction, but it had no effect on soluble fibrinogen binding to platelets and platelet aggregation. Treatment with this peptide significantly reduced thrombus formation in mice.

CONCLUSION

Taken together, these findings suggest that interaction between paxillin and the PH domain of kindlin-3 plays an important role in supporting integrin αIIbβ3 outside-in signaling in platelets, thus providing a novel antithrombotic target.

Integrins regulate stemness in solid tumor: an emerging therapeutic target

Integrins are the adhesion molecules and transmembrane receptors that consist of α and β subunits. After binding to extracellular matrix components, integrins trigger intracellular signaling and regulate a wide spectrum of cellular functions, including cell survival, proliferation, differentiation and migration. Since the pattern of integrins expression is a key determinant of cell behavior in response to microenvironmental cues, deregulation of integrins caused by various mechanisms has been causally linked to cancer development and progression in several solid tumor types. In this review, we discuss the integrin signalosome with a highlight of a few key pro-oncogenic pathways elicited by integrins, and uncover the mutational and transcriptomic landscape of integrin-encoding genes across human cancers. In addition, we focus on the integrin-mediated control of cancer stem cell and tumor stemness in general, such as tumor initiation, epithelial plasticity, organotropic metastasis and drug resistance. With insights into how integrins contribute to the stem-like functions, we now gain better understanding of the integrin signalosome, which will greatly assist novel therapeutic development and more precise clinical decisions.

Multiparameter phenotyping of platelet reactivity for stratification of human cohorts

Accurate and comprehensive assessment of platelet function across cohorts of donors may be key to understanding the risk of thrombotic events associated with cardiovascular disease, and, hence, to help personalize the application of antiplatelet drugs. However, platelet function tests can be difficult to perform and analyze; they also can be unreliable or uninformative and poorly standardized across studies. The Platelet Phenomic Analysis (PPAnalysis) assay and associated open-source software platform were developed in response to these challenges. PPAnalysis utilizes preprepared freeze-dried microtiter plates to provide a detailed characterization of platelet function. The automated analysis of the high-dimensional data enables the identification of subpopulations of donors with distinct platelet function phenotypes. Using this approach, we identified that the sensitivity of a donor's platelets to an agonist and their capacity to generate a functional response are distinct independent metrics of platelet reactivity. Hierarchical clustering of these metrics identified 6 subgroups with distinct platelet phenotypes within healthy cohorts, indicating that platelet reactivity does not fit into the traditional simple categories of "high" and "low" responders. These platelet phenotypes were found to exist in 2 independent cohorts of healthy donors and were stable on recall. PPAnalysis is a powerful tool for stratification of cohorts on the basis of platelet reactivity that will enable investigation of the causes and consequences of differences in platelet function and drive progress toward precision medicine.

Preparation and Properties of Thrombus-Targeted Urokinase/Multi-Walled Carbon Nanotubes (MWCNTs)-Chitosan (CS)-RGD Drug Delivery System

In order to improve the therapeutic effect, prolong the action time and reduce the side effects of the first generation thrombolytic drug urokinase (UK), a novel UK/multi-walled carbon nanotubes (MWCNTs)-chitosan (CS)-arginine-glycine-aspartic acid (Arg-Gly-Asp) (RGD) drug delivery system was synthesized by chemical bonding/non covalent bond modification/ultrasonic dispersion. The results showed that the diameter of the UK/MWCNTs-CS-RGD drug delivery system was about 30-40 nm, there was a layer of UK was attached to the surface of the tube wall, and the distribution was relatively uniform. The average encapsulation efficiency was 83.10%, and the average drug loading was 12.81%. Interestingly, it also had a certain sustained-release effect, and its release law was best fitted by first-order kinetic equation. Moreover, the accelerated and long-term stability test results show that it had good stability. Compared with free UK, UK/MWCNTs-CS-RGD had thrombolytic effect in vitro. In addition, MTT experiment showed that the prepared MWCNTs-CS-RGD nanomaterials had good biocompatibility. A rabbit model of carotid artery thrombosis was used to conduct targeted thrombolysis experiments in vivo. Compared with free UK, UK/MWCNTs-CS-RGD could be enriched in the thrombosis site to achieve thrombus targeting. UK/MWCNTs-CS-RGD drug delivery system was expected to become an effective thrombolytic drug for targeted therapy of thrombosis.

Platelet-Cancer Interplay: Molecular Mechanisms and New Therapeutic Avenues

Although platelets are critically involved in thrombosis and hemostasis, experimental and clinical evidence indicate that platelets promote tumor progression and metastasis through a wide range of physical and functional interactions between platelets and cancer cells. Thrombotic and thromboembolic events are frequent complications in patients with solid tumors. Hence, cancer modulates platelet function by directly inducing platelet-tumor aggregates and triggering platelet granule release and altering platelet turnover. Also, platelets enhance tumor cell dissemination by activating endothelial cell function and recruiting immune cells to primary and metastatic tumor sites. In this review, we summarize current knowledge on the complex interactions between platelets and tumor cells and the host microenvironment. We also critically discuss the potential of anti-platelet agents for cancer prevention and treatment.

Extract of Seaweed Codium fragile Inhibits Integrin αIIbβ3-Induced Outside-in Signaling and Arterial Thrombosis

Seaweeds are thought to be promising candidates for functional foods and to help prevent thrombotic and related cardiovascular diseases. Codium fragile (Suringer) Hariot has been traditionally used as a culinary ingredient, and it possesses a range of biological activities, including the inhibition of platelet function. However, the mechanism of this inhibition is unclear. The aim of this study was to examine the inhibitory effect of C. fragile in platelet function. The antiplatelet activity of C. fragile on agonist-activated platelet aggregation, granule secretion, calcium mobilization, platelet spreading, and clot retraction was assessed. The phosphorylation of c-Src, Syk, PLCγ2, and several proteins involving in the αIIbβ3 integrin outside-in signaling pathway were also studied in thrombin and CRP-stimulated platelets. The antithrombotic effect was investigated in mice using ferric chloride-induced arterial thrombus formation in vivo. Transection tail bleeding time was used to evaluate whether C. fragile inhibited primary hemostasis. The main components and contents of C. fragile ethanol extract were confirmed by GC-MS analysis. C. fragile significantly impaired agonist-induced platelet aggregation granule secretion, calcium mobilization, platelet spreading, and clot retraction. Biochemical analysis revealed that C. fragile inhibited the agonist-induced activation of c-Src, Syk, and PLCγ2, as well as the phosphorylation of PI3K, AKT, and mitogen-activated protein kinases (MAPKs). The inhibitory effect of C. fragile resulted from an inhibition of platelet αIIbβ3 integrin outside-in signal transduction during cell activation. Oral administration of C. fragile efficiently blocked FeCl₃-induced arterial thrombus formation in vivo without prolonging bleeding time. GC-MS analysis revealed that phytol was the main constituent and the total content of isomers was 160.8 mg/kg. Our results demonstrated that C. fragile suppresses not only the inside-out signaling of αIIbβ3 integrin but also outside-in signal transmission. Therefore, C. fragile could be an effective antiplatelet therapeutic candidate.

Targeting Gα13-integrin interaction ameliorates systemic inflammation

Systemic inflammation as manifested in sepsis is an excessive, life-threatening inflammatory response to severe bacterial or viral infection or extensive injury. It is also a thrombo-inflammatory condition associated with vascular leakage/hemorrhage and thrombosis that is not effectively treated by current anti-inflammatory or anti-thrombotic drugs. Here, we show that MB2mP6 peptide nanoparticles, targeting the Gα13-mediated integrin "outside-in" signaling in leukocytes and platelets, inhibited both inflammation and thrombosis without causing hemorrhage/vascular leakage. MB2mP6 improved mouse survival when infused immediately or hours after onset of severe sepsis. Furthermore, platelet Gα13 knockout inhibited septic thrombosis whereas leukocyte Gα13 knockout diminished septic inflammation, each moderately improving survival. Dual platelet/leukocyte Gα13 knockout inhibited septic thrombosis and inflammation, further improving survival similar to MB2mP6. These results demonstrate that inflammation and thrombosis independently contribute to poor outcomes and exacerbate each other in systemic inflammation, and reveal a concept of dual anti-inflammatory/anti-thrombotic therapy without exacerbating vascular leakage.

Shear and Integrin Outside-In Signaling Activate NADPH-Oxidase 2 to Promote Platelet Activation

[Figure: see text].

Cell adhesion molecule-mediated therapeutic strategies in atherosclerosis: From a biological basis and molecular mechanism to drug delivery nanosystems

Atherosclerosis (AS), characterized by pathological constriction of blood vessels due to chronic low-grade inflammation and lipid deposition, is a leading cause of human morbidity and mortality worldwide. Cell adhesion molecules (CAMs) have the ability to regulate the inflammatory response and endothelial function, as well as potentially driving plaque rupture, which all contribute to the progression of AS. Moreover, recent advances in the development of clinical agents in the cardiovascular field are based on CAMs, which show promising results in the fight against AS. Here, we review the current literature on mechanisms by which CAMs regulate atherosclerotic progression from the earliest induction of inflammation to plaques formation. In particular, we focused on therapeutic strategies based on CAMs inhibitors that prevent leukocyte from migrating to endothelium, including high-affinity antibodies and antagonists, nonspecific traditional medicinal formulas and lipid lowering drugs. The CAMs-based drug delivery nanosystem and the available data on the more reasonable and effective clinical application of CAMs inhibitors have been emphasized, raising hope for further progress in the field of AS therapy.

Phosphoproteomic Analysis of Platelets in Severe Obesity Uncovers Platelet Reactivity and Signaling Pathways Alterations

OBJECTIVE

Obesity is associated with a proinflammatory and prothrombotic state that supports atherosclerosis progression. The goal of this study was to gain insights into the phosphorylation events related to platelet reactivity in obesity and identify platelet biomarkers and altered activation pathways in this clinical condition. Approach and Results: We performed a comparative phosphoproteomic analysis of resting platelets from obese patients and their age- and gender-matched lean controls. The phosphoproteomic data were validated by mechanistic, functional, and biochemical assays. We identified 220 differentially regulated phosphopeptides, from at least 175 proteins; interestingly, all were up-regulated in obesity. Most of the altered phosphoproteins are involved in SFKs (Src-family kinases)-related signaling pathways, cytoskeleton reorganization, and vesicle transport, some of them validated by targeted mass spectrometry. To confirm platelet dysfunction, flow cytometry assays were performed in whole blood indicating higher surface levels of GP (glycoprotein) VI and CLEC (C-type lectin-like receptor) 2 in platelets from obese patients correlating positively with body mass index. Receiver operator characteristics curves analysis suggested a much higher sensitivity for GPVI to discriminate between obese and lean individuals. Indeed, we also found that obese platelets displayed more adhesion to collagen-coated plates. In line with the above data, soluble GPVI levels-indicative of higher GPVI signaling activation-were almost double in plasma from obese patients.

CONCLUSIONS

Our results provide novel information on platelet phosphorylation changes related to obesity, revealing the impact of this chronic pathology on platelet reactivity and pointing towards the main signaling pathways dysregulated.

Molecular Drivers of Platelet Activation: Unraveling Novel Targets for Anti-Thrombotic and Anti-Thrombo-Inflammatory Therapy

Cardiovascular diseases (CVDs) are the leading cause of death globally-partly a consequence of increased population size and ageing-and are major contributors to reduced quality of life. Platelets play a major role in hemostasis and thrombosis. While platelet activation and aggregation are essential for hemostasis at sites of vascular injury, uncontrolled platelet activation leads to pathological thrombus formation and provokes thrombosis leading to myocardial infarction or stroke. Platelet activation and thrombus formation is a multistage process with different signaling pathways involved to trigger platelet shape change, integrin activation, stable platelet adhesion, aggregation, and degranulation. Apart from thrombotic events, thrombo-inflammation contributes to organ damage and dysfunction in CVDs and is mediated by platelets and inflammatory cells. Therefore, in the past, many efforts have been made to investigate specific signaling pathways in platelets to identify innovative and promising approaches for novel antithrombotic and anti-thrombo-inflammatory strategies that do not interfere with hemostasis. In this review, we focus on some of the most recent data reported on different platelet receptors, including GPIb-vWF interactions, GPVI activation, platelet chemokine receptors, regulation of integrin signaling, and channel homeostasis of NMDAR and PANX1.

Synthesis and initial pharmacology of dual-targeting ligands for putative complexes of integrin αVβ3 and PAR2

Unpublished data from our labs led us to hypothesize that activated protein C (aPC) may initiate an anti-inflammatory signal in endothelial cells by modulating both the integrin αVβ3 and protease-activated receptor 2 (PAR2), which may exist in close proximity on the cellular surface. To test this hypothesis and to probe the possible inflammation-related pathway, we designed and synthesized dual-targeting ligands composed of modified versions of two αVβ3 ligands and two agonists of PAR2. These novel ligands were connected via copper-catalyzed alkyne-azide cycloadditions with polyethylene glycol (PEG) spacers of variable length. Initial in vitro pharmacology with EA.hy926 and HUVEC endothelial cells indicated that these ligands are effective binders of αVβ3 and potent agonists of PAR2. These were also used in preliminary studies investigating their effects on PAR2 signaling in the presence of inflammatory agents, and represent the first examples of ligands targeting both PARs and integrins, though concurrent binding to αVβ3 and PAR2 has not yet been demonstrated.

Conformation-Specific Blockade of αIIbβ3 by a Non-RGD Peptide to Inhibit Platelet Activation without Causing Significant Bleeding and Thrombocytopenia

Bleeding and thrombocytopenia to readministration are the most serious side effects of clinical integrin αIIbβ3 antagonists such as RGD-containing peptides. Here we show that a non-RGD peptide ZDPI, identified from skin secretions of Amolops loloensis, inhibited platelet aggregation induced by agonists, such as adenosine diphosphate, collagen, arachidonic acid, PAR1AP, and integrin αIIbβ3 allosteric activator, and reduces soluble fibrinogen binding to activated platelets without perturbing adhesion numbers on immobilized fibrinogen. Further study showed that ZDPI preferred to bind to the active conformation of integrin αIIbβ3, and thus inhibited c-Src-mediated integrin signaling transduction. In contrast to currently used clinical blockers of integrin αIIbβ3, which are all conformation-unspecific blockers, ZDPI conformation specifically binds to activated integrin αIIbβ3, subsequently suppressing platelet spreading. In vivo study revealed that ZDPI inhibited carotid arterial thrombosis with limited bleeding and thrombocytopenia. A non-RGD peptide which targets the active conformation of integrin αIIbβ3, such as ZDPI, might be an excellent candidate or template to develop antithrombotics without significant bleeding and thrombocytopenia side effects.

Covid-19: The Rollercoaster of Fibrin(Ogen), D-Dimer, Von Willebrand Factor, P-Selectin and Their Interactions with Endothelial Cells, Platelets and Erythrocytes

Severe acute respiratory syndrome coronavirus 2 (SARS-Cov-2), also known as coronavirus disease 2019 (COVID-19)-induced infection, is strongly associated with various coagulopathies that may result in either bleeding and thrombocytopenia or hypercoagulation and thrombosis. Thrombotic and bleeding or thrombotic pathologies are significant accompaniments to acute respiratory syndrome and lung complications in COVID-19. Thrombotic events and bleeding often occur in subjects with weak constitutions, multiple risk factors and comorbidities. Of particular interest are the various circulating inflammatory coagulation biomarkers involved directly in clotting, with specific focus on fibrin(ogen), D-dimer, P-selectin and von Willebrand Factor (VWF). Central to the activity of these biomarkers are their receptors and signalling pathways on endothelial cells, platelets and erythrocytes. In this review, we discuss vascular implications of COVID-19 and relate this to circulating biomarker, endothelial, erythrocyte and platelet dysfunction. During the progression of the disease, these markers may either be within healthy levels, upregulated or eventually depleted. Most significant is that patients need to be treated early in the disease progression, when high levels of VWF, P-selectin and fibrinogen are present, with normal or slightly increased levels of D-dimer (however, D-dimer levels will rapidly increase as the disease progresses). Progression to VWF and fibrinogen depletion with high D-dimer levels and even higher P-selectin levels, followed by the cytokine storm, will be indicative of a poor prognosis. We conclude by looking at point-of-care devices and methodologies in COVID-19 management and suggest that a personalized medicine approach should be considered in the treatment of patients.

High-loading Gα13-binding EXE peptide nanoparticles prevent thrombosis and protect mice from cardiac ischemia/reperfusion injury

Inefficient delivery is a major obstacle to the development of peptide-based drugs targeting the intracellular compartment. We recently showed that selectively inhibiting integrin outside-in signaling using a peptide (mP6) derived from the Gα13-binding ExE motif within the integrin β3 cytoplasmic domain had antithrombotic effects. Here, we engineered lipid-stabilized, high-loading peptide nanoparticles (HLPN), in which a redesigned ExE peptide (M3mP6) constituted up to 70% of the total nanoparticle molarity, allowing efficient in vivo delivery. We observed that M3mP6 HLPN inhibited occlusive thrombosis more potently than a clopidogrel/aspirin combination without adverse effects on hemostasis in rodents. Furthermore, M3mP6 HLPN synergized with P2Y12 receptor inhibitors or the clopidogrel/aspirin combination in preventing thrombosis, without exacerbating hemorrhage. M3mP6 HLPN also inhibited intravascular coagulation more potently than the P2Y12 inhibitor cangrelor. Postischemia injection of M3mP6 HLPN protected the heart from myocardial ischemia-reperfusion injury in a mouse model. This study demonstrates an efficient in vivo peptide delivery strategy for a therapeutic that not only efficaciously prevented thrombosis with minimal bleeding risk but also protected from myocardial ischemia-reperfusion injury in mice.

An RGD modified water-soluble fluorophore probe for in vivo NIR-II imaging of thrombosis

Venous thrombosis leads to severe symptoms and death through pulmonary embolism. There is a great need for high sensitivity imaging methods to identify acute patients who would benefit from thrombolysis. We designed a novel, organic near-infrared second-window (NIR-II) probe, which targets the glycoprotein IIb/IIIa receptor (GPIIb/IIIa) on activated platelets. The probe's structure was characterized by MALDI-TOF-MS, TEM, UV-visible absorption and NIR-II fluorescent spectroscopy. The probe's specificity for activated platelets was investigated in vitro and in vivo. Thrombosis in mice was induced by administration of FeCl₃ in the external jugular vein and imaged by using a NIR-II imager. The donor-acceptor-donor fluorescent core TTQ was prepared from donor and acceptor units. TTQ-PEG-NH₂ was synthesized by sequential modification of PEGylated TTQ, followed by c(RGD) condensation. Signal strength was continuously monitored for 24 h following TTQ-PEG-c(RGD) or non-specific fluorescent dye injection. The contralateral external jugular vein, sham surgery and a competitive inhibition experiment served as controls. TTQ-PEG-c(RGD) presented high NIR-II intensity, good stability and excellent affinity for activated platelets. The NIR-II fluorescence signal of TTQ-PEG-c(RGD) injected mice significantly increased at the thrombus site and peaked at 4 h, whereas there was no significant change in the control mice, and the competitive inhibition of the RGD antagonist suppressed the enhancement of the NIR-II fluorescence signal. Comparison between fresh and old thrombi confirmed that TTQ-PEG-c(RGD) could be used to distinguish a fresh thrombus from an old thrombus. TTQ-PEG-c(RGD) can specifically target thrombosis in vitro and in vivo, providing a potential tool for noninvasive diagnosis of early thrombi.

FAK Family Kinases in Vascular Diseases

In various vascular diseases, extracellular matrix (ECM) and integrin expression are frequently altered, leading to focal adhesion kinase (FAK) or proline-rich tyrosine kinase 2 (Pyk2) activation. In addition to the major roles of FAK and Pyk2 in regulating adhesion dynamics via integrins, recent studies have shown a new role for nuclear FAK in gene regulation in various vascular cells. In particular, FAK primarily localizes within the nuclei of vascular smooth muscle cells (VSMCs) of healthy arteries. However, vessel injury increased FAK localization back to adhesions and elevated FAK activity, leading to VSMC hyperplasia. The study suggested that abnormal FAK or Pyk2 activation in vascular cells may cause pathology in vascular diseases. Here we will review several studies of FAK and Pyk2 associated with integrin signaling in vascular diseases including restenosis, atherosclerosis, heart failure, pulmonary arterial hypertension, aneurysm, and thrombosis. Despite the importance of FAK family kinases in vascular diseases, comprehensive reviews are scarce. Therefore, we summarized animal models involving FAK family kinases in vascular diseases.

Immobilisation of an anti-platelet adhesion and anti-thrombotic drug (EP224283) on polydopamine coated vascular stent promoting anti-thrombogenic properties

Current vascular drug-eluting stents based on immuno-proliferative drugs would reduce the rate of in-stent restenosis (ISR) but may be associated with a higher risk of acute stent thrombosis due to non-selective activity. In this paper, we aimed to develop a polydopamine (PDA) coated chromium‑cobalt (CoCr) stent functionalised with EP224283 (Endotis Pharma SA), which combines both a GPIIbIIIa antagonist (tirofiban moiety) and a factor Xa inhibitor (idraparinux moiety) to reduce acute stent thrombosis. PDA-coated chromium‑cobalt (CoCr) samples were first immersed in a polyethylenimine (PEI, pH 8.5) solution to increase amine function density (36.0 ± 0.1 nmol/cm²) on the CoCr surface. In a second step, avidin was grafted onto CoCr-PDA-PEI through the biotin linkage (strategy 1) or directly by coupling reactions (strategy 2). The HABA titration proved the fixation of biotin onto CoCr-PDA-PEI surface with a density of 0.74 nmol/cm². The fixation of avidin was demonstrated by water contact angle (WCA) and surface plasmon resonance (SPR). SEM micrograph shows the flexibility of the thin layer coated onto the stent after balloon inflation. Independently of the strategy, a qualitative SEM analysis showed a reduction in platelet activation when the molecule EP224283 was immobilised on avidin. In parallel, the measurement of anticoagulant activity (anti-Xa) revealed a higher anti-factor Xa activity (2.24 IU/mL vs. 0.09 IU/mL in control) when EP224283 was immobilised on avidin. Interestingly, after seven days of degradation, the anticoagulant activity was persistent in both strategies and looked more important with the strategy 2 than in strategy 1. Throughout this work, we developed an innovative vascular stent through the immobilisation of EP224283 onto CoCr-PDA-PEI-(avidin) system, which provides a promising solution to reduce ISR and thrombosis after stent implantation.