Impaired Platelet Aggregation Research Articles

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

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. Severe thrombopathia in this cat has an underlying genetic etiology. A single affected patient, 2 age-matched clinically healthy controls, and a geriatric population (n = 20) of normal cats. 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. 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. 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.

MONOCLONAL GAMMOPATHY OF CLINICAL SIGNIFICANCE

Aside from the risk to evolve to MM or WM, or to be associated with AL amyloidosis or POEMS syndrome, the M-protein in persons with MGUS can cause “per se” the so-called “monoclonal gammopathies of clinical significance –MGCS” resulting in neurologic, skin, ocular, bleeding or other disorders. The monoclonal gammopathy of renal significance (MGRS), coined to highlight renal damage, different from cast nephropathy or amyloid deposition, linked to the M-protein is not discussed here. In patients with MGUS and peripheral neuropathy (PN), and no evidence of AL amyloidosis or POEMS, a causal relationship must be considered. In the IgM type, a gammopathy-associated PN is likely (50% are MAG positive) while in the IgG and IgA types a CIDP with coincidental MGUS is the most likely diagnosis. The main skin conditions related to M-proteins are: 1) cryoglobulin (IgG/IgM) vasculatis with petechiae, purpura or ulcers, 2) Schnitzler syndrome (IgM, chronic urticaria, fever, artralgia), 3) pyoderma gangrenosum (IgA, ulcers with central necrosis), 4) necrobiotic xanthogranuloma (IgG, yellow papules, nodules, plaques), 5) escleromixedema (IgG-lambda, mucine dermal deposition with occasional systemic involvement –cardiomyopathy, pulmonary fibrosis or reduced esophageal motility-) or 6) acquired generalized cutis laxa (lambda, elastolysis of the skin –premature ageing-, occasionally associated with kidney –fibrillar glomerulopathy-, heart or lung involvement). The most frequent ocular M-protein related condition is crystalline keratopathy (Ig deposition, corneal thickening, photophobia, visual loss). Bleeding can result from acquired von Willebrand deficiency or by impaired platelet aggregation induced by the M-protein. In summary, The M-protein in MGUS can cause relevant clinical conditions. If a causal relationship is proven or highly suspected, therapy against the plasma cell clone (rituximab-based in IgM-types and bortezomib-based, even including ASCT, in non-IgM) must be timely initiated.

Rhomb-I, a P–I metalloproteinase from Lachesis muta rhombeata venom degrades vessel extra cellular matrix components and impairs platelet aggregation

Rhomb-I, a 23-kDa metalloproteinase was isolated from L. m. rhombeata venom. Its dimethylcasein proteolysis was abolished by metal chelators, and slightly enhanced by Ca2+ and Mg2+ ions, but inhibited by Co2+, Zn2+ and α2-macroglobulin. In aqueous solution, rhomb-I autoproteolyzed to a 20- and 11-kDa fragments at 37 °C. The amino acid sequence showed high homology with other snake venom metalloproteinases. Rhomb-I causes hemorrhage that may be ascribed to hydrolysis of essential basement membrane, extracellular matrix and plasma proteins. It preferentially cleaves the α-chains of fibrin (ogen). Rhomb-I inhibited convulxin- and von Willebrand factor (vWF)-induced aggregation on human platelets without significant effect on collagen-stimulated aggregation or other effectors. It digests vWF into a low-molecular-mass multimers of vWF and a rvWF-A1 domain to a 27-kDa fragment as revealed by western blotting with mouse anti-rvWF A1-domain IgG. Incubation of platelets with rhomb-I resulted in adhesion to and cleavage of platelet receptors glycoprotein (GP)Ibα and GPVI to release a 55-kDa soluble form. Both membrane glycoproteins GPIbα that binds vWF, together with GPVI which binds collagen, play a key role in mediating platelet adhesion/activation and can initiate (patho)physiological thrombus formation. Conclusions: rhomb-I is implicated in the pathophysiology of Lachesis envenoming by disrupting vasculature, hemostasis and platelet aggregation through impairing vWF-GPIb axis and blocking GPVI-collagen binding.

Ribosome dysfunction underlies SLFN14-related thrombocytopenia

AbstractPathogenic missense variants in SLFN14, which encode an RNA endoribonuclease protein that regulates ribosomal RNA (rRNA) degradation, are known to cause inherited thrombocytopenia (TP) with impaired platelet aggregation and adenosine triphosphate secretion. Despite mild laboratory defects, the patients displayed an obvious bleeding phenotype. However, the function of SLFN14 in megakaryocyte (MK) and platelet biology remains unknown. This study aimed to model the disease in an immortalized MK cell line (imMKCL) and to characterize the platelet transcriptome in patients with the SLFN14 K219N variant. MK derived from heterozygous and homozygous SLFN14 K219N imMKCL and stem cells of blood from patients mainly presented with a defect in proplatelet formation and mitochondrial organization. SLFN14-defective platelets and mature MK showed signs of rRNA degradation; however, this was absent in undifferentiated imMKCL cells and granulocytes. Total platelet RNA was sequenced in 2 patients and 19 healthy controls. Differential gene expression analysis yielded 2999 and 2888 significantly (|log2 fold change| >1, false discovery rate <0.05) up- and downregulated genes, respectively. Remarkably, these downregulated genes were not enriched in any biological pathway, whereas upregulated genes were enriched in pathways involved in (mitochondrial) translation and transcription, with a significant upregulation of 134 ribosomal protein genes (RPGs). The upregulation of mitochondrial RPGs through increased mammalian target of rapamycin complex 1 (mTORC1) signaling in SLFN14 K219N MK seems to be a compensatory response to rRNA degradation. mTORC1 inhibition with rapamycin resulted in further enhanced rRNA degradation in SLFN14 K219N MK. Taken together, our study indicates dysregulation of mTORC1 coordinated ribosomal biogenesis is the disease mechanism for SLFN14-related TP.

Mammalian STE20-like kinase-1/2 are activated in human platelets stimulated by collagen or thrombin and play a vital role in collagen-activated platelets

IntroductionMammalian ste20-like kinases-1/2 (MST1/2), the core kinases of the Hippo pathway, play critical roles in the biology of hematopoietic cells via noncanonical mechanisms and contributes to megakaryocyte differentiation, polyploidization, and maturation to produce platelets. However, the role of MST1/2 in platelet functions remains unclear. Materials and methodsIn this study, we investigated this topic by determining platelet aggregation and through flow cytometry, ATP release assay, clot retraction assay, and immunoblotting analysis. ResultsWe found that MST1/2 were rapidly phosphorylated and activated upon platelet stimulation by thrombin and collagen. XMU-MP-1, a specific inhibitor of MST1/2, blocks the activation of MST1/2 in platelets. Inhibitor-pretreated platelets showed impaired platelet aggregation and dense-granule secretion mediated by collagen, thrombin, and U46619, whereas ristocetin or ADP mediated platelet aggregation was unaffected by XMU-MP-1. Although platelet-mediated clot retraction was not affected by MST1/2 inhibitors, integrin αIIbβ3 activation was significantly attenuated in XMU-MP-1-treated platelets. Moreover, MST1/2 inhibition significantly attenuated the mobilization of platelet calcium ions and the secretion of α-granules induced by convulxin. ConclusionsThis study is the first to demonstrate that MST1/2 play vital roles in human platelets and contributes to collagen-induced platelet activation and aggregation.

Novel variants in GALE cause syndromic macrothrombocytopenia by disrupting glycosylation and thrombopoiesis

AbstractGlycosylation is recognized as a key process for proper megakaryopoiesis and platelet formation. The enzyme uridine diphosphate (UDP)-galactose-4-epimerase, encoded by GALE, is involved in galactose metabolism and protein glycosylation. Here, we studied 3 patients from 2 unrelated families who showed lifelong severe thrombocytopenia, bleeding diathesis, mental retardation, mitral valve prolapse, and jaundice. Whole-exome sequencing revealed 4 variants that affect GALE, 3 of those previously unreported (Pedigree A, p.Lys78ValfsX32 and p.Thr150Met; Pedigree B, p.Val128Met; and p.Leu223Pro). Platelet phenotype analysis showed giant and/or grey platelets, impaired platelet aggregation, and severely reduced alpha and dense granule secretion. Enzymatic activity of the UDP-galactose-4-epimerase enzyme was severely decreased in all patients. Immunoblotting of platelet lysates revealed reduced GALE protein levels, a significant decrease in N-acetyl-lactosamine (LacNAc), showing a hypoglycosylation pattern, reduced surface expression of gylcoprotein Ibα-IX-V (GPIbα-IX-V) complex and mature β1 integrin, and increased apoptosis. In vitro studies performed with patients-derived megakaryocytes showed normal ploidy and maturation but decreased proplatelet formation because of the impaired glycosylation of the GPIbα and β1 integrin, and reduced externalization to megakaryocyte and platelet membranes. Altered distribution of filamin A and actin and delocalization of the von Willebrand factor were also shown. Overall, this study expands our knowledge of GALE-related thrombocytopenia and emphasizes the critical role of GALE in the physiological glycosylation of key proteins involved in platelet production and function.

Shear Stress Promotes Platelet Surface Desialylation, Platelet Count Drop, and Microvesiculation: Do Platelets Need to be Sugar-Coated?

Introduction. Mechanical circulatory support (MCS) devices restore hemodynamics and are lifesaving for patients with advanced heart failure and, recently, for patients with severe COVID-19. Long-term MCS is associated with bleeding complications, often requiring multiple transfusions of blood products or reoperations. To date, due to undefined etiology, device-related bleeding lacks efficient therapeutic management. We have shown that hypershear stress, existing within device-supported circulation promotes platelet dysfunction associated with pro-apoptosis, downregulation of key adhesion receptors, impaired platelet aggregation, and microvesiculation - all contributors to bleeding. Recent studies have also shown that glycosylation of platelet surface receptors, i.e. the platelet "sugar coat," plays a major role in the regulation of platelet function and lifespan. Here, we tested the hypothesis that hypershear stress promotes platelet surface desialylation, thus facilitating platelet count drop and increased microvesiculation. Methods. Human platelets were obtained from ACD-anticoagulated blood of healthy volunteers via gel filtration on Sepharose 2B. Gel-filtered platelets were exposed to neuraminidase and continuous shear stress (30 or 70 dyne/cm2,10 min) in a hemodynamic shearing device. Optionally, platelets were pretreated with oseltamivir, a common neuraminidase inhibitor. Platelets were co-stained with fluorophore-conjugated SNA lectin, binding terminal 2,6-linked sialic acid moieties, and anti-CD41 antibody. Multi-colored flow cytometry was performed to quantify platelet surface sialylation, platelets, and microparticles; fluorescent nanobeads SPHEROTM were used as a size standard. The surface density of platelet sialylation was calculated as median fluorescence intensity normalized to forward scatter indicating platelet size. The platelet neuraminidase activity was quantified using fluorogenic substrate 4-methylumbelliferyl-N-acetylneuraminic acid (MUNANA) and was presented as µM of substrate per min. Results. Platelet exposure to both hypershear stress and neuraminidase-1 induced platelet surface desialylation as indicated by the significant decrease of SNA lectins' binding density on platelets (Fig.1A). Platelet desialylation induced by shear stress and neuraminidase was associated with a notable decrease in platelet count and an increase in platelet-derived microparticles (Fig.1B). Interestingly, neuraminidase reinforced shear-mediated desialylation, platelet count drop, and microvesiculation. Oseltamivir slightly inhibited shear-mediated desialylation, preserved platelet count (30% increase vs. shear), and decreased microparticle generation (29% decrease vs. shear). Exposure to 70 dyne/cm2 shear stress resulted in a 9.5-fold increase in platelet neuraminidase activity as compared to basal level: 0.85 ± 0.61 µM/min vs 0.05 ± 0.03 µM/min, respectively (Mean ± SD, p < 0.01, one-way ANOVA). Conclusions. Shear stress promotes platelet surface desialylation with the associated reduction in platelet count and increased microvesiculation. Neuraminidase inhibition restores platelet count and decreases microparticle generation caused by hypershear. Shear-mediated increase of platelet neuraminidase activity is considered a plausible mechanism for shear-mediated platelet deglycosylation. Developing therapeutic strategies for preservation of platelet sialylation offers significant translational potential for pharmacologic management of MCS-related platelet dysfunction and bleeding coagulopathy. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

The use of a low-flux hemo-dialyzer is associated with impaired platelet aggregation in patients undergoing chronic hemodialysis.

In patients with chronic hemodialysis (HD), both abnormal thrombotic and bleeding events are commonly observed. Uremic platelet dysfunction is one of the important attributing factors. Moreover, HD may also result in aggregation dysfunction of platelets during the therapeutic procedure. However, how the HD process affects platelet and coagulation function is unknown and dialyzer membrane flux could have an impact on it. We aimed to compare the impacts of low-flux and high-flux HD on the platelet function of patients undergoing chronic HD. This was a cross-sectional study conducted in the HD unit of E-Da hospital in Taiwan. A total of 78 patients with maintenance HD three times per week for more than one year, including 40 with high- and 38 with low-flux hemodialysis, were recruited. Their platelet functions were evaluated using an in vitro platelet function analyzer (PFA-100) before and after the HD session. Of the 78 patients undergoing HD, 60 (76%) had prolonged pre-dialysis collagen/epinephrine (CEPI) and collagen/adenosine diphosphate closure times. Those receiving low-flux dialyzer had a significant increase in CEPI closure time (pre-dialysis 212.3 ± 62.1 seconds. post-dialysis 241.5 ± 64.3 seconds, P = .01), but not collagen/adenosine diphosphate closure time, after HD. After adjusting confounding factors, only the low-flux dialyzer demonstrated an independent association with the prolonged CEPI closure time after HD therapy (odds ratio = 23.31, 95% CI: 1.94-280.61, P = .01). We observed that impaired platelet aggregation is prevalent in patients undergoing chronic HD. Therefore, the use of low-flux dialyzers may further worsen platelet aggregation after dialysis. Patients with uremic bleeding diathesis should take precautions. We suggest that further studies using flow cytometry should be conducted to explore the mechanism of dialysis flux and platelet activity during HD.

Gemtuzumab Ozogamicin Treatment Results in Decreased Proliferation and Differentiation of Human Megakaryocytes but Does Not Inhibit Mature Platelet Function.

Mylotarg (Gemtuzumab ozogamicin [GO]), an antibody drug conjugate comprising a CD33-directed antibody linked to calicheamicin, is approved for use in certain acute myeloid leukemia patients. Following reports of prolonged thrombocytopenia and hemorrhagic events in a subset of patients, a detailed series of in vitro and ex vivo studies was performed at the request of regulators, both to look at the effects of GO on platelet production and to determine whether treatment with GO was likely to affect platelet aggregation under a variety of conditions. Treatment with GO resulted in cellular cytotoxicity and/or decreased differentiation during human megakaryocyte development. However, GO did not impair platelet aggregation under the experimental conditions evaluated. Ultimately, the effect of GO on megakaryocyte development observed in our studies was determined to have no impact on the risk-benefit assessment in the intended patient population, as thrombocytopenia is a known side effect of GO, and monitoring of platelet counts in patients is already strongly recommended.

Importance of catecholamine signaling in the development of platelet exhaustion after traumatic injury

BackgroundImpaired ex vivo platelet aggregation is common in trauma patients. The mechanisms driving these impairments remain incompletely understood, but functional platelet exhaustion due to excessive in vivo activation is implicated. Given platelet adrenoreceptors and known catecholamine surges after injury, impaired ex vivo platelet aggregation in trauma patients may be linked to catecholamine‐induced functional platelet exhaustion. ObjectiveTo determine the relationship of catecholamines with platelet‐dependent hemostasis after injury and to model catecholamine‐induced functional platelet exhaustion in healthy donor platelets. Patients/MethodsWhole blood was collected from 67 trauma patients as part of a prospective cohort study. Platelet aggregometry and rotational thromboelastometry were performed, and plasma epinephrine (EPI) and norepinephrine (NE) concentrations were measured. The effect of catecholamines on healthy donor platelets was examined in a microfluidic model, with platelet aggregometry, and by flow cytometry examining surface markers of platelet activation. ResultsIn trauma patients, EPI and NE were associated with impaired platelet aggregation (both p < 0.05), and EPI was additionally associated with decreased viscoelastic clot strength, increased fibrinolysis, and mortality (all p < 0.05). In healthy donors, short duration incubation with EPI enhanced platelet aggregation, platelet adhesion under flow, and increased glycoprotein IIb/IIIa activation, while weaker effects were observed with NE. Compared with short incubation, longer incubation with EPI resulted in decreased platelet adhesion, platelet aggregation, and surface expression of glycoprotein IIb/IIIa. ConclusionsThese findings suggest sympathoadrenal activation in trauma patients contributes to impaired ex vivo platelet aggregation, which mechanistically may be explained by a functionally exhausted platelet phenotype under prolonged exposure to high plasma catecholamine levels.

P2.02: Save the Environment: Liver Transplantation Restores A Circulating Environment That Supports Healthy Platelet Aggregation Within Two Hours of Reperfusion

Introduction: Thrombocytopenia in patients with cirrhosis is common and likely multifactorial secondary to splenic sequestration, decreased thrombopoietin production, shear stress of portal hypertension, and toxic suppression of megakaryocytopoiesis. However, there is no clear association of absolute platelet count with risk of hemorrhage. Rather, platelet dysfunction, in the pro-inflammatory vasodilatory state of chronic liver disease, may be of greater importance. There is evidence that the circulating environment of severe tissue injury and shock impairs platelet aggregation in trauma patients. Using this model as our template, we hypothesized that healthy platelets treated with serum from cirrhotic patients pre-transplant would have impaired aggregation compared to those treated with serum post-portal reperfusion. Methods: Serum was collected from liver transplant recipients prior to incision, and two hours following portal reperfusion as part of the Mild Hypothermia and Acute Kidney Injury in Liver Transplantation trial (NCT03534141). Platelets (from male and female healthy platelet donors) were isolated by centrifugation, pelleted, and mixed with each of the following sera (6 of each group): buffer, autologous, gender matched healthy (heterologous), gender matched pre-transplant, and gender matched post-portal reperfusion (12% v/v) for 20min (Fig1A). Baseline aggregation was measured for 10min via multiple impedance aggregometer, then stimulated with a thrombin analog and measured for 15min. Aggregometry responses were quantified by the area under the impedance aggregation curve (AUC), normalized to autologous treated platelets. Statistical analysis was performed using one way ANOVA, with Tukey’s Honest Significant Difference testing post-hoc for pairwise comparisons. Results: Healthy platelet aggregation was markedly impaired upon treatment with pre-transplant serum, but was restored when treated with serum from the same cohort of patients two hours post-portal reperfusion (to levels similar to treatment with healthy sera, Fig1B). Healthy platelet aggregation upon treatment with post-portal reperfusion serum was significantly higher than with pre-transplant serum treatment (median relative AUC 1.4x vs -0.1x, p<0.05; Fig2). Conclusion: Healthy platelets treated with serum from cirrhotic patients immediately prior to liver transplant have impaired aggregation, while treatment with serum from the same patients two hours post-portal reperfusion restores aggregation. This suggests the circulating environment of cirrhosis may induce platelet dysfunction through soluble inhibitors, and that liver transplantation and the healthy plasma administration accompanying the reperfusion phase, may induce swift recovery of platelet aggregation capacity. Future investigations should focus on implications of this including that platelet transfusion may not achieve hemostasis until post portal-reperfusion.

MANAGEMENT OF MULTIPLE ORAL LESIONS IN A RARE SYNDROME WITH PLATELETS IMPAIRMENT

Hallerman-Streiff syndrome (HSS) is a rare congenital disease described in less than 200 cases worldwide. Skull changes, hypotrichosis, cataracts, a beaked nose, micrognathia, skin atrophy, dental anomalies, and short stature are characteristics described. A 28-year-old female patient was referred for dental care, complaining about recurrent spontaneous gingival bleeding. Intraoral examination revealed dental anomalies, periodontal disease, generalized gingival hyperplasia, and 3 nodules located on alveolar ridges. Due to extensive bleeding during periodontal treatment and medical history of bleeding episodes, a platelet aggregation test was requested, revealing impaired adrenaline-induced platelet aggregation. The following dental visits aimed to prevent hemorrhage during invasive procedures, using hemostatic agents. Nodules were removed with the aid of a high-power laser, with no intercurrences. Histologic analysis suggested the diagnosis of collagenous fibroma, a rare encounter. To date, this the first description of blood dyscrasia and oral lesions in a patients HSS.

Autophagy Ameliorates Reactive Oxygen Species-Induced Platelet Storage Lesions.

Platelet transfusion is a life-saving therapy to prevent bleeding; however, the availability of platelets for transfusion is limited by the markedly short shelf life owing to the development of platelet storage lesions (PSLs). The mechanism of PSLs remains obscure. Dissection of the intracellular biological changes in stored platelets may help to reduce PSLs and improve platelet transfusion efficiency. In the present study, we explore the changes of stored platelets at room temperature under constant agitation. We found that platelets during storage showed an increased reactive oxygen species (ROS) generation accompanied with receptor shedding, apoptosis, and diminished platelet aggregation. ROS scavenger reduced platelet shedding but also impaired platelet aggregation. Autophagy is a conserved catabolic process that sequesters protein aggregates and damaged organelles into lysosomes for degradation and platelets' own intact autophagic system. We revealed that there exist a stable autophagic flux in platelets at the early stage of storage, and the autophagic flux in platelets perished after long-term storage. Treatment stored platelets with rapamycin, which stimulates autophagy in eukaryotic cells, markedly ameliorated PSLs, and improved platelet aggregation in response to extracellular stimuli.

Prenylcysteine Oxidase 1 (PCYOX1), a New Player in Thrombosis.

Prenylcysteine Oxidase 1 (PCYOX1) is an enzyme involved in the degradation of prenylated proteins. It is expressed in different tissues including vascular and blood cells. We recently showed that the secretome from Pcyox1-silenced cells reduced platelet adhesion both to fibrinogen and endothelial cells, suggesting a potential contribution of PCYOX1 into thrombus formation. Here, we show that in vivo thrombus formation after FeCl3 injury of the carotid artery was delayed in Pcyox1−/− mice, which were also protected from collagen/epinephrine induced thromboembolism. The Pcyox1−/− mice displayed normal blood cells count, vascular procoagulant activity and plasma fibrinogen levels. Deletion of Pcyox1 reduced the platelet/leukocyte aggregates in whole blood, as well as the platelet aggregation, the alpha granules release, and the αIIbβ3 integrin activation in platelet-rich plasma, in response to adenosine diphosphate (ADP) or thrombin receptor agonist peptide (TRAP). Washed platelets from the Pcyox1−/− and WT animals showed similar phosphorylation pathway activation, adhesion ability and aggregation. The presence of Pcyox1−/− plasma impaired agonist-induced WT platelet aggregation. Our findings show that the absence of PCYOX1 results in platelet hypo-reactivity and impaired arterial thrombosis, and indicates that PCYOX1 could be a novel target for antithrombotic drugs.

Multiparameter platelet function analysis of bleeding patients with a prolonged platelet function analyser closure time.

SummaryPatients referred for evaluation of bleeding symptoms occasionally have a prolonged platelet function analyser (PFA) closure time, without evidence for von Willebrand disease or impaired platelet aggregation. The aim of this study was to establish a shear‐dependent platelet function defect in these patients. Patients were included based on high bleeding score and prior PFA prolongation. Common tests of von Willebrand factor (VWF) and platelet function and exome sequencing were performed. Microfluidic analysis of shear‐dependent collagen‐induced whole‐blood thrombus formation was performed. In 14 PFA‐only patients, compared to healthy volunteers, microfluidic tests showed significantly lower platelet adhesion and thrombus formation parameters. This was accompanied by lower integrin activation, phosphatidylserine exposure and P‐selectin expression. Principal components analysis indicated VWF as primary explaining variable of PFA prolongation, whereas conventional platelet aggregation primarily explained the reduced thrombus parameters under shear. In five patients with severe microfluidic abnormalities, conventional platelet aggregation was in the lowest range of normal. No causal variants in Mendelian genes known to cause bleeding or platelet disorders were identified. Multiparameter assessment of whole‐blood thrombus formation under shear indicates single or combined effects of low–normal VWF and low–normal platelet aggregation in these patients, suggesting a shear‐dependent platelet function defect, not detected by static conventional haemostatic tests.

Dasatinib causing Intracerebral Bleeding in a Patient with Chronic Myeloid Leukaemia

Dasatinib is a potent inhibitor of BCR-ABL (break point cluster-Abelson) kinase, Src family of kinases, C-kit, and Platelet Derived Growth Factor Receptor beta (PDGFR-beta), and used in the treatment of Chronic Myeloid Leukaemia (CML), Ph-positive acute lymphoblastic leukaemia, and Acute Myeloid Leukaemia (AML). The most common side effects of dasatinib are myelosuppression, gastrointestinal disturbance, fluid retention, cutaneous eruption, and bleeding diathesis. This report is about a recently diagnosed, 45-year-old female with CML, BCR-ABL positive. After six-month therapy with imatinib, the patient developed resistance to imatinib. The treatment was changed to dasatinib 70 mg, once a day. Three months after starting the therapy, the patient showed a cytological response. While receiving dasatinib, she complained of headaches, nausea, and vomiting. Her complete blood count was within the normal limit. Coagulogram was within the normal limit. Non Contrast Computerised Tomography (NCCT) of the head showed intracerebral bleed in the right frontal area of the brain. The patient was then treated with mannitol and put on artificial ventilation. She succumbed on day fourth of the Intensive Care Unit (ICU). Dasatinib has been associated with impaired platelet aggregation, and can show fatal bleeding manifestations

Characterization of GPVI- or GPVI-CD39-Coated Nanoparticles and Their Impact on In Vitro Thrombus Formation.

Traditional antithrombotic agents commonly share a therapy-limiting side effect, as they increase the overall systemic bleeding risk. A novel approach for targeted antithrombotic therapy is nanoparticles. In other therapeutic fields, nanoparticles have enabled site-specific delivery with low levels of toxicity and side effects. Here, we paired nanotechnology with an established dimeric glycoprotein VI-Fc (GPVI-Fc) and a GPVI-CD39 fusion protein, thereby combining site-specific delivery and new antithrombotic drugs. Poly(lactic-co-glycolic acid) (PLGA) nanoparticles, NP-BSA, NP-GPVI and NP-GPVI-CD39 were characterized through electron microscopy, atomic force measurements and flow cytometry. Light transmission aggregometry enabled analysis of platelet aggregation. Thrombus formation was observed through flow chamber experiments. NP-GPVI and NP-GPVI-CD39 displayed a characteristic surface coating pattern. Fluorescence properties were identical amongst all samples. NP-GPVI and NP-GPVI-CD39 significantly impaired platelet aggregation. Thrombus formation was significantly impaired by NP-GPVI and was particularly impaired by NP-GPVI-CD39. The receptor-coated nanoparticles NP-GPVI and the bifunctional molecule NP-GPVI-CD39 demonstrated significant inhibition of in vitro thrombus formation. Consequently, the nanoparticle-mediated antithrombotic effect of GPVI-Fc, as well as GPVI-CD39, and an additive impact of CD39 was confirmed. In conclusion, NP-GPVI and NP-GPVI-CD39 may serve as a promising foundation for a novel therapeutic approach regarding targeted antithrombotic therapy.

Acetyl-CoA Carboxylase Inhibitor CP640.186 Increases Tubulin Acetylation and Impairs Thrombin-Induced Platelet Aggregation.

Acetyl-CoA carboxylase (ACC) is the first enzyme regulating de novo lipid synthesis via the carboxylation of acetyl-CoA into malonyl-CoA. The inhibition of its activity decreases lipogenesis and, in parallel, increases the acetyl-CoA content, which serves as a substrate for protein acetylation. Several findings support a role for acetylation signaling in coordinating signaling systems that drive platelet cytoskeletal changes and aggregation. Therefore, we investigated the impact of ACC inhibition on tubulin acetylation and platelet functions. Human platelets were incubated 2 h with CP640.186, a pharmacological ACC inhibitor, prior to thrombin stimulation. We have herein demonstrated that CP640.186 treatment does not affect overall platelet lipid content, yet it is associated with increased tubulin acetylation levels, both at the basal state and after thrombin stimulation. This resulted in impaired platelet aggregation. Similar results were obtained using human platelets that were pretreated with tubacin, an inhibitor of tubulin deacetylase HDAC6. In addition, both ACC and HDAC6 inhibitions block key platelet cytoskeleton signaling events, including Rac1 GTPase activation and the phosphorylation of its downstream effector, p21-activated kinase 2 (PAK2). However, neither CP640.186 nor tubacin affects thrombin-induced actin cytoskeleton remodeling, while ACC inhibition results in decreased thrombin-induced reactive oxygen species (ROS) production and extracellular signal-regulated kinase (ERK) phosphorylation. We conclude that when using washed human platelets, ACC inhibition limits tubulin deacetylation upon thrombin stimulation, which in turn impairs platelet aggregation. The mechanism involves a downregulation of the Rac1/PAK2 pathway, being independent of actin cytoskeleton.

Acetyl-CoA carboxylase inhibition alters tubulin acetylation and aggregation in thrombin-stimulated platelets

Abstract Introduction Acetyl-CoA carboxylase (ACC), the first enzyme regulating lipid synthesis, promotes thrombus formation by increasing platelet phospholipid content. Inhibition of its activity decreases lipogenesis and increases the content in acetyl-CoA which can serve as a substrate for protein acetylation. This posttranslational modification plays a key role in the regulation of platelet aggregation, via tubulin acetylation. Purpose To demonstrate that ACC inhibition may affect platelet functions via an alteration of lipid content and/or tubulin acetylation. Methods Platelets were treated 2 hours with CP640.186, a pharmacological ACC inhibitor, prior to thrombin stimulation. Platelet functions were assessed by aggregometry and flow cytometry. Lipogenesis was measured via 14C-acetate incorporation into lipids. Lipidomics analysis was carried out on the commercial Lipidyzer platform. Protein phosphorylation and acetylation were evaluated by western blot. Results Treatment with CP640.186 drastically decreased platelet lipogenesis. However, the quantitative lipidomics analyses showed that preincubation with the compound did not affect global platelet lipid content. Interestingly, this short-term ACC inhibition was sufficient to increase tubulin acetylation level, at basal state and after thrombin stimulation. It was associated with an impaired platelet aggregation, in response to low thrombin concentration, while granules secretion was not affected. Mechanistically, we highlighted a decrease in Rac1 activity, associated with a reduced phosphorylation of its downstream effector PAK2. Surprisingly, actin cytoskeleton was not impacted but we evidenced a significant decrease in ROS production which could result from a decreased NOX2 activity. Conclusion Pharmacological ACC inhibition decreases platelet aggregation upon thrombin stimulation. The mechanism depends on increased tubulin acetylation, with subsequent alteration of the Rac1/PAK2/NOX2 signaling pathway Funding Acknowledgement Type of funding sources: Other. Main funding source(s): Fonds pour la formation à la Recherche dans l'Industrie et l'Agriculture (FRIA)

АГРЕГАЦИЯ ТРОМБОЦИТОВ У ДОНОРОВ ТРОМБОЦИТАРНОЙ МАССЫ И СВЕЖЕЗАМОРОЖЕННОЙ ПЛАЗМЫ

Currently, the most common method in clinical practice, that enables the determination of the functional state of platelets, is the method of platelet aggregation. Objectives. To study the aggregation of platelets in donors of platelet mass and fresh frozen plasma. Material and methods. The study included 31 donors of fresh frozen plasma and platelet mass. The study of platelet aggregation was carried out by the turbidimetric measurement technique on the AP2110 analyzer (ZAO «SOLAR», Minsk, Republic of Belarus) with an inductor: ADP (concentrations of 0.3 μg/ml, 0.6 μg/ml, 1.25 μg/ml and 2.5 μg/ml were used), epinephrine (concentrations of 2.5 μM and 5.0 μM were used), collagen (concentration of 2 mg/ml). Results. 33 analysis of platelet aggregation were performed in donors prior to collection of platelet mass and fresh frozen plasma. Only in 10 cases (30.3%) donors had normal platelet aggregation, hypoaggregation was detected in 15 cases (45.5%) and hyperaggregation - in 8 studies (24.2%). Impaired platelet aggregation was detected in all donors who had COVID-19 infection in their anamnesis (in 5 - hypoaggregation, in 4 - hyperaggregation). In donors who didn’t have this infection in their anamnesis, the incidence of platelet aggregation disorders was statistically significantly lower - 63.6% (in 10 - hypoaggregation, in 4 - hyperaggregation), p=0.04. The presence of COVID-19 infection in the donor’s anamnesis is an independent predictor of impaired platelet aggregation (Chi-square=7.24, p=0.007). Conclusions. The study of platelet aggregation must be mandatory before collecting platelet mass in all donors.