Collagen-induced Aggregation Research Articles

Effect of toxins from different periodontitis-associated bacteria on human platelet function.

Periodontitis is caused by a dysbiosis of oral bacteria resulting in alveolar bone destruction and teeth loss. The role of platelets in pathogenesis of periodontitis is a subject of research. The release of toxins from periodontitis-associated bacteria may influence platelet function and contribute to the modulation of hemostatic or inflammatory responses. Therefore, we explored platelet function upon exposure to defined toxins: leukotoxin A from Aggregatibacter actinomycetemcomitans (LtxA), a synthetic version of the C14-Tri-LAN-Gly peptide from Fusobacterium nucleatum (C14), and lipopolysaccharides from Porphyromonas gingivalis (LPS). Light transmission aggregometry was performed after the addition of toxins to platelet-rich plasma in different doses. Flow cytometry was used to identify inhibitory effects of toxins by measuring phosphorylation of the vaso-dilator-stimulated phosphoprotein or to identify activating effects by the detection of CD62P expression. The release of chemokines derived from washed platelets was determined by immunoassays. Collagen-induced threshold aggregation values were diminished upon incubation with LtxA and C14, accompanied with an increase of vaso-dilator-stimulated phosphoprotein (VASP) phosphorylation, indicating platelet inhibition. In contrast, LPS did not affect aggregation but slightly enhanced CD62P expression under co-stimulation with low-dose thrombin pointing to slight platelet activation. The three toxins did not relevantly influence the secretion of chemokines. Although weak, the investigated toxins differently influenced human platelet function. LtxA and C14 mediated inhibitory effects, whereas LPS contributed to a slight activation of platelets. Further analysis of specific cellular responses mediated by bacterial toxins may render novel targets and suggestions for the treatment of periodontitis.

Physiological platelet aggregation assay to mitigate drug-induced thrombocytopenia using a microphysiological system

Developing a reliable method to predict thrombocytopenia is imperative in drug discovery. Here, we establish an assay using a microphysiological system (MPS) to recapitulate the in-vivo mechanisms of platelet aggregation and adhesion. This assay highlights the role of shear stress on platelet aggregation and their interactions with vascular endothelial cells. Platelet aggregation induced by soluble collagen was detected under agitated, but not static, conditions using a plate shaker and gravity-driven flow using MPS. Notably, aggregates adhered on vascular endothelial cells under gravity-driven flow in the MPS, and this incident increased in a concentration-dependent manner. Upon comparing the soluble collagen-induced aggregation activity in platelet-rich plasma (PRP) and whole blood, remarkable platelet aggregate formation was observed at concentrations of 30 µg/mL and 3 µg/mL in PRP and whole blood, respectively. Moreover, ODN2395, an oligonucleotide, induced platelet aggregation and adhesion to vascular endothelial cells. SYK inhibition, which mediated thrombogenic activity via glycoprotein VI on platelets, ameliorated platelet aggregation in the system, demonstrating that the mechanism of platelet aggregation was induced by soluble collagen and oligonucleotide. Our evaluation system partially recapitulated the aggregation mechanisms in blood vessels and can contribute to the discovery of safe drugs to mitigate the risk of thrombocytopenia.

Clinical significance for assessing adaptive hemostasis changes during multiple pregnancy after in vitro fertilization

Aim: to assess adaptive hemostasis changes in multiple dichorionic pregnancy after in vitro fertilization (IVF). Materials and Methods. A prospective observational randomized controlled trial was conducted by examining 58 and 46 pregnant women with multiple dichorionic diamniotic twins resulting from applying assisted reproductive technologies (ART) and spontaneous delivery (comparison group), respectively. Hemostasis parameters were studied as follows: activated partial thromboplastin time (APTT), prothrombin time (PT), thrombin time (TT), fibrinogen, antithrombin, protein C, protein S, functions of protein С (РrоС Global test), D-dimer, platelet aggregation with adenosine-5-diphosphate (ADP), ristocetin, and collagen. Results. A high coagulation potential was revealed, more prominent after using ART (p < 0.05). Fibrinogen level gradually increased while gestation age increased, whereas APTT, PT and TT level decreased. In the group with natural conception, fibrinogen increased by 22 % in the second trimester, reaching 4.5 g/L (95 % CI = 4,2–4,8) and by 6 % in the third trimester, reaching 4.8 g/L (95 % CI = 4,3–5,4), whereas in the IVF group – by 26 %, reaching 5.3 g/L (95 % CI = 4,7–5,6) and by 21 %, reaching (6.5 g/L; 95 % CI = 5,2–6,8) in relevant trimester of pregnancy, respectively. Antithrombin level was lower in IVF patients – 76.8 % (95 % CI = 72.6 – 81.0) in the second trimester, reaching 70.6 % (95 % CI = 64.8–76.4) in the third trimester (p < 0.001). Protein C level did not differ significantly between groups and was low within the reference range. The aggregatogram demonstrated a high platelet hemostatic potential in IVF patients (p < 0.05) as early as in the first trimester: ADP-induced aggregation – 68.3 % (95 % CI = 62.9–73.7), ristocetin-induced aggregation – 53.1 % (95 % = CI 48.7–58.5), collagen-induced aggregation – 58.4 % (95 % CI = 52.1–64.7). In the third trimester, both platelet aggregation and functional activity (ADP-induced aggregation – 64.5 % [95 % CI = 59.3–69.7], ristocetin-induced aggregation – 68.4 % [95 % CI = 63.2–73.6], collagen-induced aggregation – 50.7 % [95 % CI = 44.3–57.1]; p < 0.05) and D-dimer level persistently increased, also more prominently in the IVF group (1.60 ± 0.46 ng/ml; p < 0.05). Conclusion. Gestational adaptation in induced multiple pregnancies is at high risk of breach in compensatory mechanisms and requires monitoring for timely detection of decompensation signs and their correction to prolong pregnancy till optimal delivery time frame.

Abstract 3094: Traditional Chinese Medicine Buyang Huanwu Decoction Regulates The Platelet Gpvi And Its Downstream Protein Signaling Pathways,inhibiting Thrombosis And Preventing Cardiovascular Disease.

Background: Coronary heart disease Qi-Deficiency and Blood Stasis Syndrome will lead to the body of platelets disorders, blood viscosity, conducive to the formation of thrombosis, Buyang Huanwu Decoction (BYHWD) is a classic Chinese medicine treatment of Qi-Deficiency and Blood Stasis Syndrome. Platelet glycoprotein VI (GPVI) plays a crucial role in collagen-induced activation and aggregation of platelets. GPVI has become the focus of new approaches to antithrombotic therapy. Methods: After 6 weeks of irregular sleep deprivation in rats with syndrome of deficiency of qi and blood stasis formed, the coronary heart disease model was established by ligation of the left anterior descending coronary artery in rats. The dosage of 1 mL/100 g was given by intragastric administration for 14 days after operation. Results: The purpose of this study was to investigate the effects of BYHWD on platelet granule secretion and platelet function in vitro. We found that BYHWD can significantly reduce the platelet aggregation induced by ADP and collagen, significantly reduce the median expression of CD62p and the ratio of activated platelets, and reduce the concentration of fluorescent calcium ions in platelets. Under the electron microscope observation found that under the action of BYHWD, the ultrastructure of rat platelets pseudopodia reduced, aggregation reduced, rat coronary inner wall platelets, thrombus mass adhesion reduced, and the inner wall was smoother. In addition, BYHWD can regulate GPVI and its downstream proteins. Compared with the coronary heart disease group with syndrome of blood stasis, BYHWD can significantly reduce the expression of GPVI. Significantly reduced the expression of Syk, CALDAG-GEFI, significantly reduced the expression of IP 3 and significantly reduced the degree of PLCγ 2 of rats. Decreased the degranulation reaction of the rat blood, significantly decreased the level of TXA 2 , 5-HT in the rat blood, and significantly decreased the content of the rat blood COX-1 in the rat serum. Conclusion: Therefore, BYHWD can regulate GPVI and its downstream protein signaling pathways, reduce platelet over-activation, degranulation reaction, thereby inhibiting thrombosis, protecting heart function and preventing cardiovascular disease.

A Turbidimetric Analysis to Monitor Collagen-Induced Aggregation of Pretreated Human Platelets

A Turbidimetric Analysis to Monitor Collagen-Induced Aggregation of Pretreated Human Platelets

A Turbidimetric Analysis to Monitor Collagen-Induced Aggregation of Pretreated Human Platelets

A Turbidimetric Analysis to Monitor Collagen-Induced Aggregation of Pretreated Human Platelets

High platelet adrenergic activity and concomitant activation of the pituitary/medullar axis as alarming laboratory parameters in ACS survivors-the STRESS-AMI study.

Kinetics of stress-related biological parameters were determined in acute coronary syndrome (ACS) patients undergoing complex cardiovascular rehabilitation. We determined platelet functionality in the absence/presence of a selective alpha-2 adrenergic receptor inhibitor, atipemazole parallel with salivary cortisol levels at enrolment, and at 3- and 12-months follow-up in 75 ACS patients with percutaneous coronary intervention. Pharmacological/non-pharmacological secondary prevention methods have been efficiently applied. Baseline aggregometry indicated platelet hyperactivity, decreasing gradually and being significantly reduced late, at 12 months (p < 0.05). Cortisol levels followed similar kinetics (p < 0.05). Baseline epinephrine-induced aggregations (EIA) significantly correlated with most of the other platelet agonists, even at subsequent time-points. Patients with upper-quartile EIA at enrolment (EIA-UQ) had significantly higher ADP- and collagen-induced aggregations at enrolment, at 3- and 12-months follow-up as well, indicating that high adrenergic response in the acute phase is accompanied by general platelet hyperactivity and predicts sustained platelet activation. In the EIA-UQ group higher cardiac biomarker release, elevated C-reactive protein and cortisol levels, and lower baseline left ventricular ejection fraction were detected.Atipemazole significantly reduced platelet aggregation induced by several platelet agonists, being most potent and comparable to full in vitro P2Y12 inhibition on collagen-induced aggregations (p < 0.05), indicating that catecholamines might serve as promt/long-term modulators of platelet function. Despite effective CCR programme and dual antiplatelet therapy, prolonged activation of sympathetic neuroendocrine system and general platelet hyperactivity can be detected up to one year in ACS patients with high adrenergic platelet activity. Moreover, initial high adrenergic activity is accompanied by clinical parameters associated to increased cardiovascular risk, therefore early identification of these patients might support complex optimal long-term therapy.

Antiplatelet effects of the CEACAM1-derived peptide QDTT

Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) restricts platelet activation via platelet collagen receptor GPVI/FcRγ-chain. In this study, screening against collagen-induced platelet aggregation was performed to identify functional CEACAM1 extracellular domain fragments. CEACAM1 fragments, including Ala-substituted peptides, were synthesized. Platelet assays were conducted on healthy donor samples for aggregation, cytotoxicity, adhesion, spreading, and secretion. Mice were used for tail bleeding and FeCl3-induced thrombosis experiments. Clot retraction was assessed using platelet-rich plasma. Extracellular segments of CEACAM1 and A1 domain-derived peptide QDTT were identified, while N, A2, and B domains showed no involvement. QDTT inhibited platelet aggregation. Ala substitution for essential amino acids (Asp139, Thr141, Tyr142, Trp144, and Trp145) in the QDTT sequence abrogated collagen-induced aggregation inhibition. QDTT also suppressed platelet secretion and “inside-out” GP IIb/IIIa activation by convulxin, along with inhibiting PI3K/Akt pathways. QDTT curtailed FeCl3-induced mesenteric thrombosis without significantly prolonging bleeding time, implying the potential of CEACAM1 A1 domain against platelet activation without raising bleeding risk, thus paving the way for novel antiplatelet drugs.

Differential inhibition of platelet function by cilostazol in combination with clopidogrel.

To assess the antiplatelet effect of cilostazol clinically, we compared the effects of cilostazol in combination with clopidogrel on various platelet function tests. We recruited patients with ischemic stroke at high risk of recurrence who were treated with clopidogrel alone within 180days after stroke onset. Subjects underwent baseline platelet function tests, and were then randomly assigned to receive dual antiplatelet therapy (DAPT) comprising clopidogrel and cilostazol or clopidogrel monotherapy (SAPT). After 6months, platelet function was measured again and compared to that at baseline in each group, and the rate of change was compared between groups. Thirty-four patients were enrolled, but 4 patients were excluded for various reasons. In total, 30 subjects (13 in DAPT and 17 in SAPT group) were analyzed. Adenosine diphosphate- and collagen-induced aggregation, VerifyNow P2Y12 reaction units, vasodilator-stimulated phosphoprotein (platelet reactivity index: PRI) and plasma p-selectin concentration were significantly lower (P = 0.004, 0.042, 0.049, 0.003 and 0.006 respectively), while VerifyNow % inhibition was significantly higher at 6months compared to baseline (P = 0.003) in the DAPT group only. Comparison of the rate of change in each parameter from baseline to 6months showed that while PRI decreased at a greater rate (P = 0.012), VerifyNow % inhibition increased at a greater rate (P = 0.003) in the DAPT group than the SAPT group. The inhibitory effects of adjunctive cilostazol added to clopidogrel on platelet function differed by type of platelet function test. VerifyNow % inhibition and PRI were more inhibited than the other platelet function tests. CSPS.com substudy in TWMU (UMIN000026672), registered on April 1, 2017. This study was performed as a substudy of CSPS.com (UMIN000012180, registered on October 31, 2013) and was retrospectively registered.

Investigating the catalytic efficiency of C22-Fatty acids with LOX human isozymes and the platelet response of the C22-oxylipin products

Polyunsaturated fatty acids (PUFAs) have been extensively studied for their health benefits because they can be oxidized by lipoxygenases to form bioactive oxylipins. In this study, we investigated the impact of double bond placement on the kinetic properties and product profiles of human platelet 12-lipoxygenase (h12-LOX), human reticulocyte 15-lipoxygenase-1 (h15-LOX-1), and human endothelial 15-lipoxygenase-2 (h15-LOX-2) by using 22-carbon (C22) fatty acid substrates with differing double bond content. With respect to kcat/KM values, the loss of Δ4 and Δ19 led to an 18-fold loss of kinetic activity for h12-LOX, no change in kinetic capability for h15-LOX-1, but a 24-fold loss for h15-LOX-2 for both C22–FAs. With respect to the product profiles, h12-LOX produced mainly 14-oxylipins. For h15-LOX-1, the 14-oxylipin production increased with the loss of either Δ4 and Δ19, however, the 17-oxylipin became the major species upon loss of both Δ4 and Δ19. h15-LOX-2 produced mostly the 17-oxylipin products throughout the fatty acid series. This study also investigated the effects of various 17-oxylipins on platelet activation. The results revealed that both 17(S)-hydroxy-4Z,7Z,10Z,13Z,15E,19Z-DHA (17-HDHA) and 17-hydroxy-4Z,7Z,10Z,13Z,15E-DPAn6 (17-HDPAn6) demonstrated anti-aggregation properties with thrombin or collagen stimulation. 17-hydroxy-7Z,10Z,13Z,15E,19Z-DPAn3 (17-HDPAn3) exhibited agonistic properties, and 17-hydroxy-7Z,10Z,13Z,15E-DTA (17-HDTA) showed biphasic effects, inhibiting collagen-induced aggregation at lower concentrationsbut promoting aggregation at higher concentrations. Both 17-hydroxy-13Z,15E,19Z-DTrA (17-HDTrA), and 17-hydroxy-13Z,15E-DDiA (17-HDDiA) induced platelet aggregation. In summary, the number and placement of the double bonds affect platelet activation, with the general trend being that more double bonds generally inhibit aggregation, while less double bonds promote aggregation. These findings provide insights into the potential role of specific fatty acids and their metabolizing LOX isozymes with respect to cardiovascular health.

The Effect of 4-Methylcatechol on Platelets in Familial Hypercholesterolemic Patients Treated with Lipid Apheresis and/or Proprotein Convertase Subtilisin Kexin 9 Monoclonal Antibodies.

Elevated low-density lipoprotein (LDL) cholesterol levels lead to atherosclerosis and platelet hyperaggregability, both of which are known culprits of arterial thrombosis. Normalization of LDL cholesterol in familial hypercholesterolemia (FH) is not an easy task and frequently requires specific treatment, such as regularly performed lipid apheresis and/or novel drugs such as proprotein convertase subtilisin kexin 9 monoclonal antibodies (PCSK9Ab). Moreover, a high resistance rate to the first-line antiplatelet drug acetylsalicylic acid (ASA) stimulated research of novel antiplatelet drugs. 4-methylcatechol (4-MC), a known metabolite of several dietary flavonoids, may be a suitable candidate. The aim of this study was to analyse the antiplatelet effect of 4-MC in FH patients and to compare its impact on two FH treatment modalities via whole-blood impedance aggregometry. When compared to age-matched, generally healthy controls, the antiplatelet effect of 4-MC against collagen-induced aggregation was higher in FH patients. Apheresis itself improved the effect of 4-MC on platelet aggregation and blood from patients treated with this procedure and pretreated with 4-MC had lower platelet aggregability when compared to those solely treated with PCKS9Ab. Although this study had some inherent limitations, e.g., a low number of patients and possible impact of administered drugs, it confirmed the suitability of 4-MC as a promising antiplatelet agent and also demonstrated the effect of 4-MC in patients with a genetic metabolic disease for the first time.

Effects of uridine and nucleotides on hemostasis parameters

Several purinergic receptors have been identified on platelets which are involved in hemostatic and thrombotic processes. The aim of the present study was to investigate the effects of uridine and its nucleotides on platelet aggregation and hemostasis in platelet-rich plasma (PRP) and whole blood. The effects of uridine, UMP, UDP, and UTP at different final concentrations (1 to 1000 µM) on platelet aggregation were studied using an aggregometer. In PRP samples, platelet aggregation was induced by ADP, collagen and epinephrine 3min after addition of uridine, UMP, UDP, UTP and saline (as a control). All thromboelastogram experiments were performed at 1000 µM final concentrations of uridine and its nucleotides in whole blood. UDP and UTP were also tested in thromboelastogram with PRP. Our results showed that UDP, and especially UTP, inhibited ADP- and collagen-induced aggregation in a concentration-dependent manner. In whole blood thromboelastogram experiments, UDP stimulated clot formation while UTP suppressed clot formation. When thromboelastogram experiments were repeated with PRP, UTP's inhibitory effect on platelets was confirmed, while UDP's stimulated clot forming effect disappeared. Collectively, our data showed that UTP inhibited platelet aggregation in a concentration-dependent manner and suppressed clot formation. On the other hand, UDP exhibited distinct effects on whole blood or PRP in thromboelastogram. These data suggest that the difference on effects of UTP and UDP might have arisen from the different receptors that they stimulate and warrant further investigation with regard to their in vivo actions on platelet aggregation and hemostasis.

Role of GPR56 in Platelet Activation and Arterial Thrombosis.

The adhesion G protein-coupled receptor GPR56 mediates cell-cell and cell-extracellular matrix interactions. To examine the function of GPR56 in platelet activation and arterial thrombosis, we generated GPR56-knockout mice and evaluated GPR56 expression in human and mouse platelets. The results revealed that the levels of the GPR56 N-terminal fragment were significantly higher on the first day after myocardial infarction than on the seventh day in the plasma of patients with ST-segment-elevation myocardial infarction. Next, we investigated the effects of GPR56 on platelet function in vitro and in vivo. We observed that collagen-induced aggregation and adenosine triphosphate release were reduced in Gpr56 -/- platelets. Furthermore, P-selectin expression on the Gpr56 -/- platelet surface was also reduced, and the spreading area on immobilized collagen was decreased in Gpr56 -/- platelets. Furthermore, collagen-induced platelet activation in human platelets was inhibited by an anti-GPR56 antibody. Gpr56 -/- mice showed an extended time to the first occlusion in models with cremaster arteriole laser injury and FeCl3-induced carotid artery injury. GPR56 activated the G protein 13 signaling pathway following collagen stimulation, which promoted platelet adhesion and thrombus formation at the site of vascular injury. Thus, our study confirmed that GPR56 regulated the formation of arterial thrombosis. Inhibition of the initial response of GPR56 to collagen could significantly inhibit platelet activation and thrombus formation. Our results provide new insights for research into antiplatelet drugs.

The Relationship between Premature Adrenarche and Platelet Aggregation.

Premature adrenarche has been associated with an increase in adrenal androgens, and the hyperandrogenic hormonal environment is known to lead to increased platelet aggregation. Here, we evaluated the effects of premature adrenarche (PA) on platelet aggregation in platelet-rich plasma samples from female patients. The study included 40 female patients diagnosed with PA between February 2014 and June 2018 and 30 healthy female individuals in the control group. Adenosine diphosphate (ADP) and collagen-induced platelet aggregation were studied with the photometric aggregometry method. There was no significant difference in the platelet count or volume values between the participants with PA and the control group. Additionally, the ADP-induced maximum aggregation time, value, and slope values did not significantly differ between the patient and control groups (p>0.05). However, the collagen-induced maximum aggregation time, value, and slope values were significantly higher in the patient group (p < 0.001). Increased collagen-induced platelet aggregation was detected in female patients with PA. As PA is associated with a higher risk of cardiovascular events later in life, close follow-up of PA in this respect may be beneficial.

Impact of Tyrosine Kinase Inhibitors Applied for First-Line Chronic Myeloid Leukemia Treatment on Platelet Function in Whole Blood of Healthy Volunteers In Vitro.

The tyrosine kinase inhibitors (TKIs) imatinib, dasatinib, bosutinib, and nilotinib are established for first-line treatment of chronic myeloid leukemia (CML) but may cause side effects such as bleeding and thrombotic complications. We investigated the impact of TKIs on platelet function ex vivo in anticoagulated whole blood (WB) samples from healthy adults by lumiaggregometry and PFA-100 test. Samples (n = 15 per TKI) were incubated for 30 minutes with TKI at therapeutically relevant final concentrations. Aggregation and ATP release were induced by collagen (1 µg/mL), arachidonic acid (0.5 mmol/L), and thrombin (0.5 U/mL). Imatinib, bosutinib, and nilotinib significantly increased collagen-induced aggregation compared with controls. In addition, for bosutinib and nilotinib, a significant increase in aggregation after induction with arachidonic acid was detected. ATP-release and PFA-100 closure times were not influenced significantly by these three TKI. In contrast, dasatinib demonstrated a concentration-dependent inhibition of collagen-induced aggregation and ATP release and a significant prolongation of the PFA-100 closure time with the collagen/epinephrine cartridge. Aggregation and ATP release by other agonists as well as closure time with the collagen/ADP cartridge were not influenced significantly. In conclusion, we clearly show a concentration-dependent inhibition of collagen-induced platelet function in WB by dasatinib confirming prior results obtained in platelet-rich plasma. Bosutinib and nilotinib exerted no impairment of platelet activation. On the contrary, both TKI showed signs of platelet activation. When comparing our results with existing data, imatinib in therapeutic relevant concentrations does not impair platelet function.

Effect of different cooking methods on S-Alk(en)yl-L-cysteine sulfoxides profile and antiplatelet activity of onion

• Onions are predominant with organosulfur and phenolic compounds endowed with promising functional effects. • Different cooking methods effects on organosulfur composition and bioactivities of onions. • Cooking methods altered the organosulfur content and antiplatelet activity of onions. • Stir-frying cooking was found effective to retain the high amount organosulfur compounds in onion. • Onion extracts showed significant inhibition on collagen-induced antiplatelet activity. Onions are a significant source of organosulfur compounds with promising biological effects. However, the effects of different cooking methods on organosulfur composition and biological properties in onions remain unclear. Therefore, the objective of this study was to determine the composition of organosulfur compounds and the antiplatelet effect of six different onion varieties processed using different cooking methods (boiling, stir-frying, and steaming).The organosulfur compounds were quantified by measuring the S-Alk(en)ey-L-cysteine sulfoxides (ACSOs) contents utilizing and high-pressure liquid chromatography (HPLC). Results showed no significant differences in ACSOs contents among onion varieties. However, ‘Guigum' (GG) and ‘Turbo’ (TB) varieties showed the highest amount of ACSOs at 100.6 and 98.0 mg/100 g fresh weight (FW), respectively. Total ACSOs contents in the other four varieties were 62.7∼72.4 mg/100g FW, showing similar contents. Stir-fried (without the addition of water) onions retained the highest content of total ACSO, followed by steamed treated onions. However, with the boiling method, sulfur compounds were eluted and lost in the cooking water, resulted in a 46.8% loss of ACSOs. Onion extracts showed significant inhibition of the collagen-induced aggregation of rat blood platelets. The highest effect of platelet aggregation was observed in stir-fried onion extracts, whereas the lowest was in boiled extracts. Results demonstrated that stir-frying is an effective cooking method to retain the highest amount of health-beneficial organosulfur compounds in onion.

The effect of short-term refrigeration on platelet responsiveness

Storage of platelet concentrates (PC) at cold temperature (CT) is discussed as an alternative to the current standard of storage at room temperature (RT). Recently, we could show that cold-induced attenuation of inhibitory signaling is an important mechanism promoting platelet reactivity. For developing strategies in blood banking, it is required to elucidate the time-dependent onset of facilitated platelet activation. Thus, freshly prepared platelet-rich-plasma (PRP) was stored for 1 and 2 h at CT (2–6 °C) or at RT (20–24 °C), followed by subsequent comparative analysis. Compared to RT, basal and induced vasodilator-stimulated phosphoprotein (VASP) phosphorylation levels were decreased under CT within 1 h by approximately 20%, determined by Western blot analysis and flow cytometry. Concomitantly, ADP- and collagen-induced threshold aggregation values were enhanced by up to 30–40%. Furthermore, platelet-covered areas on collagen-coated slides and aggregate formation under flow conditions were increased after storage at CT, in addition to induced activation markers. In conclusion, a time period of 1–2 h for refrigeration is sufficient to induce an attenuation of inhibitory signaling, accompanied with an enhancement of platelet responsiveness. Short-term refrigeration may be considered as a rational approach to obtain PC with higher functional reactivity for the treatment of hemorrhage.

MMP-2 inhibition prevents platelet activation in ischemia/reoxygenation conditions.

Platelets play a fundamental role in myocardial infarction and the pathogenesis of ischemia/reoxygenation (I/R) injuries. They contain matrix metalloproteinases (MMPs) that are involved in arterial thrombosis. The MMP inhibitor doxycycline has been shown to exert protective effects in I/R injuries involving various organs and mechanisms. To explore the influence of doxycycline on platelet activation and MMP-2 activity during I/R. Platelets isolated from the blood of healthy human volunteers were subjected to chemical I/R conditions. The study included aerobic controls (AERO), I/R platelets and I/R platelets pretreated with doxycycline (I/R+D). The concentration of doxycycline used was standardized to 10 μM. The analysis of platelet activation markers and platelet microvesicles (PMVs) was performed using flow cytometry. Adenosine diphosphate (ADP)-induced and collagen-induced aggregation, as well as MMP-2 activity and its concentration in platelets were evaluated. Doxycycline decreased the expression of activated glycoprotein IIb/IIIa on platelets (p = 0.043). Additionally, an increased expression of CD63 was observed in buffers containing PMVs after doxycycline administration (p = 0.043). The ADP-dependent aggregation of I/R platelets was significantly lower in comparison to AERO (p = 0.022). Furthermore, there was a stronger tendency of enhanced ADP-dependent aggregation in I/R platelets pretreated with doxycycline compared to platelets that underwent I/R without doxycycline. Higher MMP-2 activity was observed in I/R+D platelets compared to I/R platelets (p < 0.01). The inhibition of platelet MMP-2 by doxycycline attenuated platelet activation and protected platelets by preserving their aggregation ability.

Left ventricular-aortic angle is associated with platelet reactivity in patients with aortic stenosis.

The impact of aortic stenosis on platelet reactivity is unclear. Previous studies reported contradicting results. The reason for this is unknown. It is known that flow alterations enhance platelet reactivity. A steep left ventricular-aortic angle (LV-AO-angle) is associated with turbulent flow in the aorta ascendens. Therefore, in this study, we hypothesized that LV-AO-angle is associated with platelet reactivity in patients with severe aortic stenosis. We included 289 patients with severe aortic stenosis and performed cardiac computertomography to assess the LV-AO-angle. Platelet function was evaluated by light transmission aggregometry. Platelet reactivity was higher in patients with a steep LV-AO-angle (ADP: <160°: 66.99% ± 20.72% vs. ≥160°: 60.66% ± 19.85%, P = 0.009; collagen: <160°: 78.67% ± 13.19% vs. ≥160°: 73.85% ± 14.44%, P = 0.003). Using Spearman correlation, ADP and collagen-induced aggregation was associated with LV-AO-angle (ADP: r = -0.19, P = 0.0009, R2 = 0.022; collagen: r = -0.21, P = 0.0004, R2 = 0.027). Apart from platelet reactivity, body weight, history of myocardial infarction and other factors were associated with steep LV-AO-angle. However, multivariate cox-regression (including body weight, comorbidities, history of MI and cardiac surgery, kidney function and laboratory parameters) revealed that LV-AO angle was a robust predictor of ADP and collagen-induced platelet aggregation. Steep LV-AO-angle is associated with enhanced platelet reactivity in patients with aortic stenosis. This could be the reason of contradicting results regarding platelet function in patients with aortic stenosis in previous studies. In addition, enhanced platelet reactivity in steep LV-AO-angle aortic stenosis patients might be a promising target in pathogenesis of aortic stenosis.

Platelet aggregation under the conditions of vortex flow in vitro in patients with chronic heart failure

Aim. To compare the effect of increased concentrations of aggregation inducers (five-fold addition) under standard conditions and under the conditions of vortex flow in vitro on platelet aggregation in patients with chronic heart failure (CHF).Materials and methods. The study included 28 patients. The activity of platelet aggregation in platelet-rich plasma (PRP) was evaluated according to light transmission curves (%) and the average size of aggregates (relative units (rel. units)). The aggregation inducer was added once at 10 seconds of the study (standard procedure) and five times at 10 seconds, 1, 2, 3, and 4 minutes of the study with a constant stirring rate of 800 rpm. The same parameters were evaluated under the conditions of vortex flow, which was created by changing the stirring rate of the PRP from 800 rpm to 0 rpm and again to 800 rpm by pressing the centrifugation button on the analyzer.Results. In the course of the study, the size of the aggregates increased in patients with CHF only under the conditions of vortex flow. When a collagen aggregation inducer was added both at the concentration of 2 mmol / l and 10 mmol / l, platelet aggregation parameters increased under the conditions of vortex flow. During the study of epinephrine-induced platelet aggregation in patients with CHF, an increase in the aggregation parameters was revealed, both at five-fold addition of the inducer and under the conditions of vortex flow compared with the standard method.Conclusion. The proposed methodological approaches to creating the conditions for vortex flow in vitro and to five-fold addition of epinephrine showed an increase in the size of the aggregates and the degree of platelet aggregation. Collagen-induced aggregation under the conditions of vortex flow revealed 7 (25%) patients with high residual platelet reactivity (HRPR), and epinephrine-induced aggregation detected 15 (54%) patients with HRPR.