Appearance Of Platelet Aggregates Research Articles

Microscopic Description of Platelet Aggregates Induced by Escherichia coli Strains.

In addition to their role in haemostasis, platelets are also involved in the inflammatory and antimicrobial process. Interactions between pathogens and platelets, mediated by receptors can lead to platelet activation, which may be responsible for a granular secretion process or even aggregation, depending on the bacterial species. Granular secretion releases peptides with bactericidal activity as well as aggregating factors. To our knowledge, these interactions have been poorly studied for Escherichia coli (E. coli). Few studies have characterised the cellular organization of platelet-E. coli aggregates. The objective of our study was to investigate the structure of platelet aggregates induced by different E. coli strains as well as the ultrastructure of platelet-E. coli mixtures using a scanning and transmission electron microscopy (SEM and TEM) approach. Our results show that the appearance of platelet aggregates is mainly dependent on the strain used. SEM images illustrate the platelet activation and aggregation and their colocalisation with bacteria. Some E. coli strains induce platelet activation and aggregation, and the bacteria are trapped in the platelet magma. However, some strains do not induce significant platelet activation and are found in close proximity to the platelets. The structure of the E. coli strains might explain the results obtained.

Practical issues that should be considered when planning the implementation of pathogen reduction technology for plateletpheresis

Pathogen reduction technology (PRT) is associated with increased blood safety through the inactivation of virus, bacteria and parasites. Dilution of platelet (PLT) concentrates in platelet additive solution (PAS) is a requirement for applying PRT, and that it is associated with various practical issues: increasing PLT target yields to compensate for loss of PLTs through PRT, extended apheresis donation time due to PAS addition at the end of the procedure, and the appearance of PLT aggregates. We proposed to program higher target PLT yields for plateletpheresis donations to compensate for PLTs lost due to PRT processing. To verify the feasibility of this approach, a paired study of the Amicus 3.11 and Trima 5.22 apheresis separators was performed using 196 procedures carried out on the same 98 donors. The Amicus 3.11 presented a higher collection efficiency (CE: 78.02 vs. 69.63; p < 0.0001) and collection rate (CR: 8.3 vs. 7.00; p < 0.0001); it was also faster (56.92 vs. 62.60; p < 0.0001) than the Trima 5.22 apheresis device. However, analysis of the donor group with higher pre-procedure PLT counts showed similar productivity results for the Amicus and Trima. The percentage of PLT aggregates detected was higher with the TA than the AM (8.62% vs. 3.88%, p = 0.04). Overall, both separators are entirely suitable for collecting hyper-concentrated PLTs that are subsequently diluted in PAS for PRT, without excessively increasing the donation time. PLT aggregation can occur after apheresis collection but most of them disappear by day 1. Further investigation is needed to study the clinical impact of PLT aggregation.

Platelet Aggregates Detected by a Conventional Hematology Analyzer Method Is a Risk Factor for Stroke or a Predictive Factor in Patients With Chronic-Stage Cerebral Infarction

Assessment of platelet activation and/or function is important for primary and secondary prevention of vascular events. To test the hypothesis that determination of platelet aggregation in patients with chronic-stage cerebral infarction (CI) provides a simple measure of risk for ischemic stroke, we used a conventional hematology analyzer to detect aggregates and to assess the efficacy of antiplatelet agents in preventing spontaneous aggregate formation. Platelet aggregates were measured in citrated blood from 142 magnetic resonance imaging confirmed CI patients and 97 controls without CI (nonstroke). Aggregates were detected in 1 of 36 (2.8%) nonstroke subjects without risk factors, but in 24 of 52 (46.2%) nonstroke subjects with risk factors (odds ratio [OR], 3.32; 95% confidence interval [CI], 1.10-10.00), in 21 of 35 (60.0%) nonstroke subjects with a predictive factor (carotid artery intima-media thickness [IMT] >1.1 mm) (OR, 9.13; 95% CI, 2.70-30.48), and in 31 of 63 (49.2%) CI patients who had not received antiplatelet therapy (OR, 2.16; 95% CI, 1.12-4.17). After adjusting for other risk factors, the appearance of platelet aggregates was correlated only with IMT ≥1.1 mm. The rate of appearance of platelet aggregates was 0.33-fold lower in patients on antiplatelet therapy compared with those not on antiplatelet therapy (24.1%; 19 of 79 CI patients). Patients with platelet aggregates in the blood are considered at high risk for ischemic stroke, because the appearance of aggregates is associated with increased IMT. Our method is suitable for screening platelet function in high-risk patients and for examining the efficacy of antiplatelet agents.

Could proteolytic enzyme modulate the interaction platelets/vessel wall in presence of asa at ultra low doses?

Acetylsalicylic acid (ASA) is known to act on platelets and vessel walls. At ultra low doses it reverses the inhibitory effects produced by a vascular fragment. Use of papain on normal platelets in vitro led to the appearance of platelet aggregation without collagen induction with a range of 20.25 ± 28.91%. In the presence of vascular fragments (without ASA), this “spontaneous” aggregation remained but was reduced (13.26 ± 27.73%). This effect was reversed by ASA treatment (29.41 ± 24.17%). Reversion of vascular inhibition by ASA was not modified by papain.

One day of estradiol treatment enhances platelet aggregation at the site of microvascular injury without altering aggregation ex vivo

Mice were implanted subcutaneously with a pellet containing 0.5 mg estradiol placebo. On the day following implantation platelet aggregation was produced in arterioles on the brain surface (pial arterioles) by injuring their endothelium in vivo with a noxious light/dye stimulus. The time between the onset of the noxious stimulus and the appearance of platelet aggregates was significantly shortened (p<.01) in the estradiol treated mice. In contrast to this enhancement of aggregation, when platelets were tested ex vivo in platelet rich plasma (PRP), aggregation to sodium arachidonate or to ADP was not altered in estradiol treated mice. Thus the enhanced aggregation observed in injured pial arterioles of estradiol treated mice may not reflect direct effects of estradiol on the platelet itself. Rather enhanced aggregation may reflect an effect of estradiol on endothelium or adjacent tissue. This effect was produced within 24 hours of achieving pregnancy levels of estradiol. The rapidity of the effect is of interest in light of earlier studies showing a similar in vivo action following 7–14 days of high estradiol levels. The rapid effect suggests that an action on megakaryocytes is an unlikely explanation for the results.

Effects of estradiol on platelet aggregation in cerebral microvessels of mice.

Mice were implanted subcutaneously with a pellet containing 0.5 mg estradiol or with a placebo. Eight to 12 days later platelet aggregation was produced in pial arterioles by injuring their endothelium in vivo with a noxious light/dye stimulus. The time between the onset of the noxious stimulus and the appearance of platelet aggregates was significantly shortened (p less than .02) by estradiol treatment in young (2 month old) mice. The same treatment had the opposite effect in 4-6 month old mice and significantly delayed the onset of aggregation (p = .01). When platelet rich plasma (PRP) was prepared, aggregation by sodium arachidonate was always inhibited in PRP from estradiol treated mice, irrespective of age. Estradiol treatment had no effect on aggregation induced ex vivo by ADP. Thus the enhanced aggregation observed in pial arterioles of young estradiol treated mice may not reflect direct effects of estradiol on the platelet itself. The data are discussed in light of the literature suggesting enhancement of ischemic vascular disease, including strokes, in patients receiving estrogens, and especially high doses of estrogens.

Effects of estradiol on platelet aggregation in mouse mesenteric arterioles and ex vivo

Mice were implanted subcutaneously with a pellet containing 0.5 mg estradiol or with a placebo. Eight to 12 days later platelet aggregation was produced in mesenteric arterioles by injuring their endothelium in vivo with a noxious light/dye stimulus. The time between the onset of the noxious stimulus and the appearance of platelet aggregates was significantly shortened (p<.01) in the estradiol treated mice. In contrast to this enhancement of aggregation, when platelets were tested ex vivo in platelet rich plasma (PRP), aggregation to sodium arachidonate was inhibited in estradiol treated mice. Aggregation of PRP by ADP was not affected by estradiol treatment of the mice. Thus the enhanced aggregation observed in injured mesenteric arterioles of estradiol treated mice may not reflect direct effects of estradiol on the platelet itself. Rather enhanced aggregation may reflect an effect of estradiol on endothelium or adjacent tissue. The data are discussed in light of other literature concerning estradiol effects in rodents, and in light of literature suggesting that an increased number of thromboembolic events occurs in humans receiving high doses of estrogens.

Further studies on the significance of circulating platelet aggregates induced by somatostatin in man

The aim of the present study was to further evaluate the significance of circulating platelet aggregates induced by somatostatin in insulin-dependent diabetic subjects. Eight insulin-dependent diabetics and eight normals were infused with somatostatin at increasing doses (250, 500, and 750 μg/h), each dose for 30 min. In diabetics, somatostatin induced the appearance in blood of platelet aggregates in a dose-dependent fashion, the highest level being observed with the highest dose (750 μg/h), p < 0.005. In normals, circulating platelet aggregates were detected only with the infusion of the highest rate of somatostatin ( p < 0.025). This effect of somatostatin was reversible, since it tended to disappear 30 min after the infusion was stopped. In six additional insulin-dependent diabetics, a previous infusion of phentolamine (0.5 mg/min) completely prevented the appearance of platelet aggregates by somatostatin. No significant variation of the aggregation response to both ADP and collagen and the platelet count was seen in both experiments. Somatostatin, as expected, reduced the basal concentration of plasma glucose, glucagon, and C-peptide in both diabetics and normals. On the basis of these results, we suggest that somatostatin has some proaggregating capacity in vivo, probably by interacting with adrenergic mechanisms.

Prostaglandin release and the interaction of platelets with the pulmonary vasculature of rat and guinea pig.

We have examined the isolated perfused lung as a model for studying the role of two opposing prostaglandin derivatives, prostacyclin (PGI2) and thromboxane (TXA2), in regulating the interaction between platelets and the pulmonary vascular bed. On passage of a perfusate containing either rat or human platelets through the isolated perfused rat lung, no TXA2 release was detected in the effluent from the lung, as measured by radioimmunoassay (RIA) of TXB2. After inhibition of pulmonary PGI2 synthesis however, platelet perfusion resulted in the production of TXA2 and the appearance of platelet aggregates in the perfusate. As measured in an incubation system, rat lung produces PGI2 and TXA2 in a ratio of 1:1. Guinea pig lung however, produces PGI2 and TXA2 in a ratio of 1:20. Passage of human platelets through the guinea pig2 lung resulted in TXA2 release into the effluent. Inhibitors of pulmonary TXA2 biosynthesis did not suppress its release, while perfusion with aspirin (ASA) treated platelets completely abolished TXA2 release, suggesting that TXA2 originates primarily from aggregating platelets. These results support the hypothesis that PGI2 is an important defense against intraarterial thrombosis and suggest that our model is suitable for examining platelet-pulmonary endothelial cell interaction.

PROSTACYCLIN TO PREVENT PLATELET ACTIVATION DURING CHARCOAL HÆMOPERFUSION IN FULMINANT HEPATIC FAILURE

Adverse effects associated with hypotension and the appearance of platelet aggregates in the circulation complicate charcoal hæmoperfusion of patients with fulminant hepatic failure. In an attempt to avoid these difficulties the platelet protective effect of prostacyclin (PGI 2) given intravenously before and continuously during hæmoperfusion was evaluated with an improved charcoal column design. Two of the six patients who underwent hæmoperfusion without PGI 2 had hypotension, which in one was associated with a striking rise in Swank screen filtration pressure necessitating discontinuation of hæmoperfusion after an hour. No platelet losses were observed in the six patients treated with hæmoperfusion and PGI 2 infusion, and there was significant protection from platelet activation, as assessed by the prevention of release into plasma of the platelet-specific protein β-thromboglobulin.

Circulating Platelet Aggregates and Thrombocytopenia Induced by Intravenous Infusions of Arachidonic and Lauric Acids in Guinea Pigs

Slow intravenous infusion of Na laurate (NaL) into guinea pigs caused a rapid appearance of platelet aggregates in the arterial blood and a precipitous fall in platelet counts. During the infusion of Na arachidonate (NaA) thrombocytopenia developed slowly, and few and smaller platelet aggregates appeared in the arterial blood. Considerably more guinea pigs died during or after the NaA infusion than after administration of NaL. The possibility that arachidonic acid and other long-chain fatty acids may play a role in the development of thrombosis and thromboembolism is discussed.

Platelet aggregation by platelet-clumping substance

The platelet-clumping substance isolated from rabbit plasma by the authors aggregated washed rabbit platelets, while ADP did not. The presence of AMP or adenosine did not inhibit the appearance of platelet aggregation induced by the clumping substance. Pretreatment of phosphoenol-pyruvate and pyruvate kinase on unwashed platelets did not affect the platelet aggregation by the clumping substance. It clumped human platelets and also shrimp thrombocytes. Electron microscopic findings showed that platelets to which the clumping substance was added aggregated in their original form as falt disc shapes with few pseudopods. While fusion of membrane was present, microtubules were observed in its regular form. These results showed the existence of a platelet-clumping substance in blood that is different from ADP, collagen, thrombin, adrenaline etc. and may play an important role in hemostasis and thrombogenesis.