Human Platelets Research Articles

Isorhynchophylline inhibits platelet activation and thrombus formation.

Isorhynchophylline is a Chinese herbal medicine and has multiple effects such as anti-inflammatory and neuroprotective effects. Whether isorhynchophylline has anti-thrombotic property is unknown. This study aims to evaluate its role in platelet function. Human platelets were incubated with isorhynchophylline (0, 10, 20 and 40 μM) at 37°C for 1 hour to detect platelet aggregation and activation, receptors level, spreading and calcium mobilization. Additionally, isorhynchophylline (5 mg/kg) was injected into mice to measure in vivo hemostasis and thrombosis. Isorhynchophylline dose-dependently reduced platelet aggregation, ATP secretion, P-selectin expression and αIIbβ3 activation induced by collagen-related peptide (CRP) or thrombin without affecting surface level of receptors αIIbβ3, GPIbα, and GPVI. Meanwhile, isorhynchophylline-treated platelets showed reduced spreading. Moreover, isorhynchophylline reduced platelet calcium mobilization, phosphatidylserine exposure and the phosphorylation of PLCγ2 and PKCα. Furthermore, administration of isorhynchophylline into mice impaired platelet hemostatic function and arterial/venous thrombosis without affecting coagulation. In conclusion, Isorhynchophylline impairs platelet function and arterial/venous thrombosis, implying its potential to be a novel agent for treating thrombotic or cardiovascular diseases.

Highly efficient generation of mature megakaryocytes and functional platelets from human embryonic stem cells

BackgroundPlatelet transfusion therapy has made a great breakthrough in clinical practice, and the differentiation of human embryonic stem cells (hESCs) to produce functional platelets has become a new potential approach, however, efficient generation of functional platelets still faces great challenges. Here, we presented a novel approach to highly and efficiently generate mature megakaryocytes (MKs) and functional platelets from hESCs.MethodsIn hypoxic conditions, we successfully replicated the maturation process of MKs and platelets in a controlled in vitro environment by introducing an optimal combination of cytokines at various stages of development. This method led to the generation of MKs and platelets derived from hESCs. Subsequently, mature MKs and functional platelets were further comprehensively investigated and characterized using a variety of methodologies, including flow cytometry analysis, RT-qPCR validation, Giemsa-Wright’s staining, immunofluorescent staining, RNA transcriptome analysis, and DNA ploidy analysis. Additionally, the in vivo function of platelets was evaluated through the transplantation using thrombocytopenia model mice.ResultsUnder our 3D differentiation conditions with four sequential stages, hESCs could be efficiently induced into mature MKs, with 95% expressing CD41aCD42a or 90% expressing CD41aCD42b, and those MKs exhibited polyploid properties, produced filamentous proplatelet structures and further generated platelets. Furthermore, 95% of platelets showed CD42b+CD62p+ phenotype upon the stimulation with ADP and TRAP-6, while 50% of platelets exhibited the ability to bind PAC-1, indicating that hESC-derived platelets possessed the in vitro functionality. In mice models of thrombocytopenia, hESC-derived platelets effectively restored hemostasis in a manner comparable to human blood-derived platelets. Further investigation on the mechanism of this sequential differentiation revealed that cellular differentiation and molecular interactions during the generation of hESC-derived MKs and platelets recapitulated the developmental trajectory of the megakaryopoiesis and thrombopoiesis.ConclusionsThus, our results demonstrated that we successfully established a highly efficient differentiation of hESCs into mature MKs and functional platelets in vitro. The in vivo functionality of hESC-derived platelets closely resembles that of natural human platelets, thus offering a promising avenue for the development of functional platelets suitable for future clinical applications.

The roles of regulatory-compliant media and inflammatory/oxytocin priming selection in enhancing human mesenchymal stem/stromal cell immunomodulatory properties

Osteoarthritis (OA) represents a significant global health burden without a known disease modifying agent thereby necessitating pursuit of innovative therapeutic approaches. The infrapatellar fat pad (IFP) serves as a reservoir of mesenchymal stem/stromal cells (MSC), and with adjacent synovium plays key roles in joint disease affecting local inflammatory responses. Therapeutically, IFP-MSC have garnered attention for their potential in OA treatment due to their immunomodulatory and regenerative properties. However, optimizing their therapeutic efficacy necessitates a comprehensive understanding of how growth medium and inflammatory/hormonal priming influence their behavior. In this study, we isolated and expanded IFP-MSC in three different growth media: DMEM + 10% fetal bovine serum (FBS), DMEM + 10% human platelet lysate (HPL), and xeno-/serum-free synthetic (XFSF) medium. Subsequently, cells were induced with an inflammatory/fibrotic cocktail (TIC) with or without oxytocin (OXT). We evaluated various parameters including growth kinetics, phenotype, immunomodulatory capacity, gene expression, and macrophage polarization capacity. Our results revealed significant differences in the behavior of MSC cultured in different media. IFP-MSC cultured in HPL and XFSF exhibited superior growth kinetics and colony-forming abilities compared to those cultured in FBS. Furthermore, both HPL and XFSF media enhanced the expression of MSC markers (> 90%) and potentiated their immunomodulatory properties. Notably, XFSF-conditioned IFP-MSC demonstrated the highest attenuation of peripheral blood mononuclear cell (PBMC) proliferation, indicating their robust immunosuppressive capacity. Additionally, TIC priming further augmented the immunomodulatory functionality of MSC, with IFP-MSC exhibiting enhanced suppression of PBMC proliferation upon TIC priming. Of particular interest, gene expression analysis revealed distinct patterns in TIC + OXT induced MSC compared to TIC only induced, with upregulation of genes associated with immunomodulatory and regenerative functions. Furthermore, TIC + OXT priming promoted M2 polarization in macrophages, suggesting a potential therapeutic strategy for immune-mediated inflammatory joint conditions including OA. Our findings highlight the critical influence of growth medium and inflammatory/hormonal priming on MSC behavior and therapeutic potential. XFSF and HPL media offer promising alternatives to FBS, enhancing MSC growth and immunomodulatory properties. Moreover, TIC + OXT priming represents a novel approach to augment MSC immunomodulation and promote M2 polarization, providing insights into potential therapeutic strategies for OA and other immune-mediated inflammatory conditions.

Effect of In Vitro Low-Impulse Laser Irradiation on Morphofunctional Properties of Human Platelets.

We studied morphofunctional features of human platelets exposed in vitro to low-pulse laser radiation (LPLR) with different wavelengths. Platelet-rich plasma (PRP) was irradiated at wavelengths of 635, 488, and 355 nm. LPLR with λ=635 nm and 1 W power after 10 min caused degranulation of many platelets, formation of small platelet conglomerates, and accelerated platelet adhesion on glass. LPLR with λ=635 nm and 2 mW and LPLR with λ=488 nm did not cause significant changes in the morphofunctional platelet status. LPLR with λ=355 nm induced massive platelets' deformation, sharp decrease in their morphofunctional status without activation.

Utility of acid citrate dextrose‐acidification for platelet volume reduction protocols in the transfusion service

AbstractBackgroundVolume‐reduced platelets can minimize circulatory overload, allergic transfusion reactions, or out‐of‐group plasma infusion. Our center adopted a volume reduction protocol that includes acidification with acid citrate dextrose solution A (ACD‐A) before centrifugation and without any rest period prior to resuspension allowing a better turnaround time for platelet issue.Study Design and MethodsThis report compares corrected count increments (CCIs) from full‐volume and ACD‐A acidified volume‐reduced human platelets in a retrospective study at a single hospital and in a mouse model.ResultsAt a pediatric tertiary care hospital, 530 patients received conventional apheresis platelets during the 20‐month study period. Among all patients, the expected 4‐h mean CCI was 9.8 (95% CI: 8.7, 10.9) for full‐volume platelets, and 8.8 (95% CI: 7.3, 10.6) for ACD‐acidified volume‐reduced platelets (p = .29). A statistically significant difference (p = .01) was identified in the expected 24‐h mean CCI: 6.3 (95% CI: 5.5–7.0) with full‐volume platelet, 4.7 (95% CI: 3.6–6.0) with ACD‐acidified volume‐reduced platelet. Limiting CCI calculations to patients with Hematology/Oncology/Hematopoietic Progenitor Cell Transplant diagnosis (n = 296, 56%) indicated a statistically significant difference in both 4‐ and 24‐h predicted CCIs, showing lower CCIs in ACD‐acidified volume‐reduced platelet, although these were still similar to the CCIs observed in all patients and considered to be clinically acceptable responses similar to other volume reduction protocols. The recovery of count‐adjusted, volume‐reduced platelets was significantly lower in mice, suggesting a procedure‐related defect.DiscussionACD‐A acidification of platelets before volume reduction decreases turnaround time for platelet issue and provides clinically allowable 4‐h and 24‐h platelet increments.

Abstract 4134384: Sotagliflozin, a Dual Inhibitor of Sodium-Glucose Transporters 1 and 2, Elicits Cardioprotective Effects Through Attenuation of Platelet Activation and Thrombosis

Sodium-glucose cotransporter (SGLT) inhibitors are used in the treatment of type 2 diabetes mellitus (T2DM) and chronic kidney disease (CKD). In the SCORED trial, sotagliflozin (SOTA), a dual SGLT1/2 inhibitor, demonstrated significant reductions in both myocardial infarction (MI) and stroke in patients with T2DM and CKD. These results suggest a cardiovascular (CV) benefit of SOTA in patients with T2DM and CKD who are at increased risk of thromboembolic disease. To investigate the underlying mechanism of CV protection, we evaluated the effects of SOTA on platelet activation and thrombus formation, in both in vivo and ex vivo models, to understand its effects on MI and stroke. Washed human platelets treated with SOTA were stimulated with various agonists and platelet activation was assessed via lumi-aggregometry and flow cytometry. In whole blood, SOTA was evaluated for its potential to reduce platelet adhesion and thrombus formation in the perfusion flow chamber and Total Thrombus formation Analysis System (TTAS) assays. In vivo , mice dosed with SOTA were assessed for thrombus formation at the site of injury in real-time in the cremaster arteriole injury model. To determine the effect of SOTA on hemostasis, we assessed coagulation parameters ex vivo in human whole blood using thromboelastography. Finally, bleeding time was measured in vivo in mice dosed with SOTA using the tail bleeding assay. In washed platelets, SOTA inhibits platelet activation and aggregation in a dose-dependent manner. Similarly, a dose-dependent decrease in platelet adhesion and thrombus formation was observed in whole blood assays. In vivo , platelet accumulation and fibrin formation were decreased in mice dosed with SOTA, however no effect is observed in coagulation parameters or bleeding time. SOTA inhibits platelet activation and thrombus formation with no impact on coagulation parameters or bleeding potential. These findings highlight a potential mechanism through which SOTA reduces the risk of stroke and MI in patients with T2DM and CKD, underscoring the importance of further investigation into the role of SOTA in CV protection, particularly in patients suffering from both T2DM and CKD at high risk of thromboembolic events.

Human platelet lysate combined with mesenchymal stem cells pretreated with platelet lysate improved cardiac function in rats with myocardial infarction

Myocardial infarction (MI) is a leading cause of heart failure, disability and mortality worldwide. In this study, the effects of intramyocardial injection of human platelet lysate (HPL), bone marrow mesenchymal stem cells pretreated with HPL (PMSCs), and PMSC lysate (lys), alone and in combination were investigated on MI-induced by LAD ligation in male Wistar rats. The experiment was carried out on sham, vehicle (Veh), HPL, PMSCs, PMSC lysate (PMSC lys), HPL + PMSCs, and HPL + PMSC lys groups. SBP, DBP, and ± dp/dt max were monitored by the PowerLab physiograph. The MSC characteristics and CD31, NKX2.5, and cardiac troponin I (cTnI) contents were determined by flow cytometry, immunohistochemistry, and immunofluorescence, respectively. SBP, DBP, and ± dp/dt max that decreased in the MI group were recovered by HPL, PMSC, PMSC lys, HPL + PMSC, and HPL + PMSC lys treatments. CD31 density was higher in all treated groups compared to the Veh group. CD31 density in the HPL + PMSCs and HPL + PMSC lys groups was higher than in the PMSCs group. The number of Dil+/NKX2.5 + and Dil+/cTnI + cells was higher in the HPL + PMSCs group compared to the PMSCs group. The HPL and PMSCs mitigates heart injuries and cardiac dysfunction after MI. HPL provides an appropriate environment for cardiomyocyte differentiation from PMSCs.

Generation of Functioning Platelets from Mature Megakaryocytes Derived from CD34+ Umbilical Cord Blood Cells.

Clinically patients with thrombocytopenia are in urgent need of platelet transfusion, thus it is necessary to produce the platelets in large scale in vitro to meet the clinical needs. In this study, we developed efficient protocol to generate functioning platelets by differentiating umbilical cord blood (CB)-derived CD34+ cells into mature megakaryocytes. Under our condition, up to 85% of mature megakaryocytes were generated from CB-derived CD34+ cells, and over 75% CD42b+CD62p+ platelets were produced. The megakaryocytes at day 12 after the differentiation had the similar gene expression pattern to natural mature megakaryocytes, and AMPK and insulin signal pathway were activated to inhibit the apoptosis and benefit platelet release. There were up to 72% of the platelets that could bind with PAC1, which is the highest rate of CB CD34+ cell-derived platelets to play function in vitro to date. The recovery of hemostasis and coagulation was similar in thrombocytopenia mice injected with CB CD34+ cell-derived platelets and with human blood-derived platelets, respectively, and it is the first time to demonstrate that human CB CD34+ cell-derived platelets were functional invivo. Therefore, our findings open a new avenue to provide an in vitro efficient approach to generate functional platelets for clinical applications.

Structure-derived insights from blood factors binding to the surfaces of different adenoviruses

The tropism of adenoviruses (Ads) is significantly influenced by the binding of various blood factors. To investigate differences in their binding, we conducted cryo-EM analysis on complexes of several human adenoviruses with human platelet factor-4 (PF4), coagulation factors FII (Prothrombin), and FX. While we observed EM densities for FII and FX bound to all the species-C adenoviruses examined, no densities were seen for PF4, even though PF4 can co-pellet with various Ads. Similar to FX, the γ-carboxyglutamic acid (Gla) domain of FII binds within the surface cavity of hexon trimers. While FII binds equally to species-C Ads: Ad5, Ad6, and Ad657, FX exhibits significantly better binding to Ad5 and Ad657 compared to Ad6. Although only the FX-Gla domain is observed at high-resolution (3.7 Å), the entire FX is visible at low-resolution bound to Ad5 in three equivalent binding modes consistent with the 3-fold symmetric hexon. Only the Gla and kringle-1 domains of FII are visible on all the species-C adenoviruses, where the rigid FII binds in an upright fashion, in contrast to the flexible and bent FX. These data suggest that differential binding of FII and FX may shield certain species-C adenoviruses differently against immune molecules, thereby modulating their tropism.

Differences in human and commercial hybrid pig platelet activation induced by borosilicate glass beads in a modified chandler loop-system.

The pig (Sus scrofa) is the most widely used large animal model in Europe, with cardiovascular research being one of the main areas of application. Adequate refinement of interventional studies in this field, meeting the requirements of Russell and Burch's 3 R concept, can only be performed if blood-contacting medical devices are hemocompatible. Because most medical devices for cardiovascular interventional procedures are developed for humans, they are tested only for compatibility with human blood. The aim of this study was therefore to determine whether there are differences in behavior of human and porcine platelets from commercial hybrid pigs when they come into contact with borosilicate glass, which was used as an exemplary thrombogenic material. For this purpose, changes in platelet count, platelet volume and platelet expression of the activation markers CD61, CD62P and CD63 were measured using a modified chandler loop-system simulating the fluidic effects of the bloodflow. Commercial hybrid pig and human platelets showed significant adhesions to borosilicate glass but the commercial hybrid pigs platelets showed a significantly higher tendency to adhere to borosilicate glass. In contrast to human platelets the platelets of commercial hybrid pigs showed significant activation after 4 to 8 minutes exposure to borosilicate glass and there were differences among the ratios of surface and activation markers in between the platelets of both species.

Informing pregnancy dose via target-mediated drug disposition modeling and simulations for a recombinant human monoclonal antibody.

RLYB212 is a human monoclonal anti-human platelet antigen (HPA)-1a immunoglobulin gamma 1 in clinical development as a subcutaneous injection for the prevention of maternal alloimmunization to fetal HPA-1a leading to fetal and neonatal alloimmune thrombocytopenia (FNAIT). This analysis developed a target-mediated drug disposition (TMDD) model to simultaneously characterize RLYB212 pharmacokinetics (PK) and HPA-1a-positive platelet dynamics in HPA-1b/b (HPA-1a-negative) volunteers. The model was then used to perform simulations to inform a dosing regimen in a phase II clinical study in pregnant women, where simulations accounted for physiological changes throughout pregnancy. Allometric scaling (0.75) for clearance and intercompartment transfer rate and volume (1) was included in the base model to account for variations in body weight. A 0.06 mg RLYB212 dose with a loading dose of 0.12 mg was identified as the optimal dosing regimen of RLYB212, which maintained exposures below the target upper boundary of ~10 ng/mL throughout pregnancy. This work presents an application of the TMDD model that advances the quantitative clinical pharmacology toolkit to understand monoclonal antibody PK in pregnancy.

Comparative analysis of Lox-1 and CD36 expression in human platelets and on circulating microparticles during ARDS-induced coagulopathy

IntroductionAcute respiratory distress syndrome (ARDS) patients are at risk of thrombosis through mechanisms implicating oxidized low-density lipoprotein (oxLDL). Endothelial cells, immune cells and platelets were reported to express scavenger receptors for oxLDL: Lox-1 and CD36. We hypothesized that platelets shed a soluble Lox-1 ectodomain (sLox-1) and release CD36–bearing procoagulant microparticles (MPs), that both become elevated in subjects with ARDS-induced coagulopathy. MethodsUsing anti-extracellular and anti-intracellular Lox-1 antibodies, we first tested by western blot whether platelets express Lox-1 and shed sLox-1 upon activation. Next, we measured sLox-1 in blood plasma of 23 healthy donors and 48 ARDS Omega patients with and without coagulopathy, and assessed the corresponding MP fraction for Lox-1/sLox-1 and CD36. We evaluated mechanisms of sLox-1-MP association. Recombinant proteins were used as controls. ResultsResting platelets expressed abundant CD36 (7.8 ng/μg protein extract) which was released upon oxLDL stimulation, but undetectable levels of full-length 37 kDa Lox-1 receptor or 24 kDa sLox-1 (below 10 pg/μg). In an RNAseq meta-analysis, platelets expressed negligible OLR1, the mRNA encoding Lox-1, compared to CD36. A subset of ARDS patients showed elevated plasma sLox-1 and MP-associated sLox-1 compared to healthy controls that was positively associated with 90-day survival and low coagulopathy. MP-associated CD36 was reduced in ARDS plasma compared to healthy donors and did not correlate with survival, coagulopathy, or sLox-1. oxLDL promoted sLox-1 binding to CD36-deficient MPs. ConclusionsLox-1 arising from a non-platelet cell source associates with circulating MPs which could serve a protective role in ARDS.

Functional Foods in Preventing Human Blood Platelet Hyperactivity-Mediated Diseases-An Updated Review.

A systematic search of the PUBMED database from 2000 to 2023 was conducted using the selected keywords: "functional foods", "polyphenols", "fatty acids", "herbs", fruits and vegetables", "cardioprotective agents", "plant", "platelet aggregation", "platelet activation", "clinical and non-clinical trial", "randomized", and "controlled". Potent natural antiplatelet factors have been described, including omega-3 fatty acids, polyphenols, and other phytochemicals. Antiplatelet bioactive compounds in food that can prevent platelet hyperactivity and thus may prevent several platelet-mediated diseases, including cardiovascular disease. This narrative review describes the work during 2000-2023 in developing functional foods from natural sources with antiplatelet effects.

Management of human leukocyte antigen-mediated platelet transfusion refractoriness: Brief synopsis and recent literature review.

Management of human leukocyte antigen-mediated platelet transfusion refractoriness: Brief synopsis and recent literature review.

Platelet Extracellular Vesicles Loaded Gelatine Hydrogels for Wound Care.

Platelet extracellular vesicles (pEVs)isolated from clinical-grade human platelet concentratesare attracting attention as a promising agent for wound healing therapies. Although pEVs have shown potential for skin regeneration, their incorporation into wound bandages has remained limitedly explored. Herein, gelatine-based hydrogel (PAH-G) foams for pEVs loading and release are formulated by crosslinking gelatine with poly(allylamine) hydrochloride (PAH) in the presence of glutaraldehyde and sodium bicarbonate. The optimized PAH-G hydrogel foam, PAH0.24G37, displayed an elastic modulus G' = 8.5 kPa at 37°C and retained a rubbery state at elevated temperatures. The excellent swelling properties of PAH0.24G37 allowed to easily absorb pEVs at high concentration (1×1011 particles mL-1). The therapeutic effect of pEVs was evaluated in vivo on a chronic wound rat model. These studies demonstrated full wound closure after 14 days upon treatment with PAH0.24G37@pEVs. The maintenance of a reduced-inflammatory environment from the onset of treatment promoted a quicker transition to skin remodeling. Promotion of follicle activation and angiogenesis as well as M1-M2 macrophage modulation are evidenced. Altogether, the multifunctional properties of PAH0.24G37@pEVs addressed the complex challenges associated with chronic diabetic wounds, representing a significant advance toward personalized treatment regimens for these conditions.

PROTACs in platelets: emerging antithrombotic strategies and future perspectives.

Proteolysis-targeted chimeras (PROTACs) are heterobifunctional compounds that selectively target proteins for degradation and are an emerging therapeutic modality to treat diseases such as cancer and neurodegenerative disorders. This review will widen the area of application by highlighting the ability of PROTACs to remove proteins from the anucleate platelets and evaluate their antithrombotic potential. Proteomic and biochemical studies demonstrated that human platelets possess the Ubiquitin Proteasomal System as well as the E3 ligase cereblon (CRBN) and therefore may be susceptible to PROTAC-mediated protein degradation. Recent findings confirmed that CRBN ligand-based PROTACs targeting generic tyrosine kinases, Btk and/or Fak lead to efficacious and selective protein degradation in human platelets. Downregulation of Btk, a key player involved in signalling to thrombosis, but not haemostasis, resulted in impaired in-vitro thrombus formation. Platelets are susceptible to targeted protein degradation by CRBN ligand-based PROTACs and have limited ability to resynthesise proteins, ensuring long-term downregulation of target proteins. Therefore, PROTACs serve as an additional research tool to study platelet function and offer new therapeutic potential to prevent thrombosis. Future studies should focus on enhancing cell specificity to avoid on-target side effects on other blood cells.

Association of HPA Antigens with Immune Thrombocytopenia: A Case-Control Study by PCR-SSP Method

Background: Human platelet antigens (HPAs) play a clinically significant role in alloimmunization and the development of immune-mediated disorders such as immune thrombocytopenia (ITP), fetal and neonatal alloimmune thrombocytopenia (FNAIT), and post-transfusion purpura (PTP). Understanding the genetic profiles of HPAs is critical for preventing and treating these conditions. Given the limitations of serological methods in determining HPA genotypes, this study aims to investigate the association between the genotypes of HPA1, HPA2, HPA3, HPA4, and HPA15 antigens and autoimmune thrombocytopenia in Lorestan Province, utilizing the PCR-SSP method. Materials and Methods: This case-control study involved 80 individuals diagnosed with ITP and 120 healthy controls. DNA samples were extracted using a commercial DNA extraction kit, with concentrations quantified via a Nanodrop spectrophotometer. Genotyping was performed using the PCR-SSP method with specific primers for each HPA gene. The genotype data were verified using previously established sample sets. The frequencies of each HPA genotype were recorded, and a comparative analysis was conducted between the patient and control groups to evaluate the study hypothesis. Results: The results revealed that individuals carrying the HPA2b allele had a 5.31-fold increased risk of developing ITP, a statistically significant finding (P < 0.05, OR = 5.31). Similarly, the presence of the HPA15b allele was associated with a 6.54-fold increased risk (P < 0.05, OR = 6.54). Conclusion: These findings, in conjunction with previous studies, suggest the need for larger-scale investigations across different populations. Such research could aid in the early diagnosis and prediction of thrombocytopenia severity, inform treatment strategies, and facilitate the removal of pathogenic antibodies from circulation.

Discovery of quinazoline-benzothiazole derivatives as novel potent protease-activated receptor 4 antagonists with improved pharmacokinetics and low bleeding liability

Protease-activated receptor 4 (PAR4) plays a critical role in the development of pathological thrombosis, and targeting PAR4 is considered a promising strategy for improving antiplatelet therapies. Here, we reported the design of a series of quinazoline-benzothiazole-based PAR4 antagonists using a scaffold-hopping strategy. Systematic structure-activity relationship exploration leads to the discovery of compounds 20f and 20g, which displayed optimal activity (h. PAR4-AP PRP IC50 = 6.39 nM and 3.45 nM, respectively) on human platelets and high selectivity for PAR4. Both of them also showed excellent metabolic stability in human liver microsomes (compound 20f, T1/2 = 249.83 min, compound 20g, T1/2 = 282.60 min) and favourable PK profiles in rats (compound 20f, T1/2 = 5.16 h, F = 50.5 %, compound 20g, T1/2 = 7.05 h, F = 27.3 %). More importantly, neither compound prolonged the bleeding time in the mouse tail-cutting model (10 mg/kg, p.o.). These results suggest that these compounds have great potential for use in antiplatelet therapies.

Rapid method for screening of both calcium and magnesium chelation with comparison of 21 known metal chelators.

Chelation is the rational treatment modality in metal overload conditions, but chelators are often non-selective and can, hence, cause an imbalance in the homeostasis of physiological metals including calcium and magnesium. The aim of this study was to develop an affordable, rapid but sensitive and precise method for determining the degree of chelation of calcium and magnesium ions and to employ this method for comparison on a panel of known metal chelators. Spectrophotometric method using o-cresolphthalein complexone (o-CC) was developed and its biological relevance was confirmed in human platelets by impedance aggregometry. The lowest detectable concentration of calcium and magnesium ions by o-CC was 2.5μM and 2μM, respectively. The indicator was stable for at least 110days. Four and seven out of twenty-one chelators strongly chelated calcium and magnesium ions, respectively. Importantly, the chelation effect of clinically used chelators was not negligible. Structure-activity relationships for eight quinolin-8-ols showed improvements in chelation particularly in the cases of dihalogen substitution, and a negative linear relationship between pKa and magnesium chelation was observed. Calcium chelation led to inhibition of platelet aggregation in concentrations corresponding to the complex formation. A novel method for screening of efficacy and safety of calcium and magnesium ion chelation was developed and validated.

Suppressed ORAI1-STIM1-dependent Ca2+ entry by protein kinase C isoforms regulating platelet procoagulant activity

Agonist-induced rises in cytosolic Ca2+ control most platelet responses in thrombosis and hemostasis. In human platelets we earlier demonstrated that the ORAI1-STIM1 pathway is a major component of extracellular Ca2+ entry, in particular when induced via the ITAM-linked collagen receptor, glycoprotein VI (GPVI). In the present paper, using functionally defective platelets from patients with a loss-of-function mutation in ORAI1 or STIM1, we show that Ca2+ entry induced by the endoplasmic reticulum ATPase inhibitor, thapsigargin, fully relies on this pathway. We demonstrate that both the GPVI-induced and thapsigargin-induced Ca2+ entry is strongly suppressed by protein kinase C (PKC) activation, while leaving intracellular Ca2+ mobilization unchanged. Comparing effects of a PKC inhibitory panel pointed to redundant roles of beta and theta PKC isoforms in Ca2+-entry suppression. In contrast, tyrosine kinases positively regulated GPVI-induced Ca2+ entry and mobilization. Label-free and stable isotope phosphoproteome analysis of GPVI-stimulated platelets suggested a regulatory role of bridging integrator-2 (BIN2), known as important mediator of the ORAI1-STIM1 pathway in mouse platelets. Identified were 25-45 regulated phospho- sites in BIN2 and 16-18 in STIM1. Five of these were characterized as direct substrates of the expressed PKC isoforms alpha, beta delta and theta. Functional platelet testing indicated that the downregulation of Ca2+ entry by PKC resulted in suppressed phosphatidylserine exposure and plasmatic thrombin generation. Conclusively, our results indicate that in platelets multiple PKC isoforms constrain the store-regulated Ca2+ entry via ORAI1-BIN2-STIM1, and hence downregulate platelet-dependent coagulation.