Jonathan Cowman

Age-related changes in platelet function are more profound in women than in men

Age is a risk factor for cardiovascular disease (CVD), however the effect of age on platelet function remains unclear. Ideally, platelet function should be assayed under flow and shear conditions that occur in vivo. Our study aimed to characterise the effect of age on platelet translocation behaviour using a novel flow-based assay that measures platelet function in less than 200 μl of blood under conditions of arterial shear. Blood from males (n = 53) and females (n = 56), ranging in age from 19–82 and 21–70 respectively were perfused through custom-made parallel plate flow chambers coated with immobilised human von Willebrand Factor (VWF) under arterial shear (1,500s−1). Platelet translocation behaviour on VWF was recorded by digital-image microscopy and analysed. The study showed that aging resulted in a significant decrease in the number of platelet tracks, translocating platelets and unstable platelet interactions with VWF. These age related changes in platelet function were more profound in women than in men indicating that age and gender significantly impacts on platelet interactions with VWF.

Dynamic platelet function on von Willebrand factor is different in preterm neonates and full-term neonates: changes in neonatal platelet function.

Essentials It is unclear if platelet function differs between preterm and full‐term neonates. Platelet behavior was characterized using a flow‐based assay on von Willebrand Factor (VWF). Preterms had increased platelet interaction with VWF and glycoprotein Ibα expression. Platelets from preterm neonates behave differently on VWF compared to full‐term neonates.

Platelet behaviour on von Willebrand Factor changes in pregnancy: Consequences of haemodilution and intrinsic changes in platelet function

Platelet function in pregnancy is poorly understood. Previous studies of platelet function in pregnancy have used non-physiological assays of platelet function with conflicting results. This study using a physiological assay of platelet function investigated platelet interactions with von Willebrand Factor (VWF) in blood from healthy pregnant women and healthy non-pregnant controls. Blood samples (200 µl) from third-trimester pregnancies (n = 21) and non-pregnant controls (n = 21) were perfused through custom-made parallel-plate flow chambers coated with VWF under arterial shear (1,500 s−1). Multi-parameter measurements of platelet interactions with the immobilized VWF surface were recorded by digital-image microscopy and analysed using custom-designed platelet-tracking software. Platelet interactions with VWF decreased in healthy third-trimester pregnant participants relative to controls. This effect is most likely due to haemodilution which occurs physiologically during pregnancy. Interestingly, platelets in blood from pregnant participants translocated more slowly on VWF under arterial-shear conditions. These decreases in platelet translocation speed were independent of haemodilution, suggesting intrinsic changes in platelet function with pregnancy.

Dynamic platelet function is markedly different in patients with cancer compared to healthy donors

Abstract Despite a fivefold increased risk of thromboembolism in patients with cancer, the mechanism of arterial thromboembolism is poorly understood. To address this, we investigated platelet function in cancer patients and healthy controls using an assay that mimics the arterial vasculature. Blood samples from cancer patients (n = 36) and healthy controls (n = 22) were perfused through custom-made parallel-plate flow chambers coated with von Willebrand factor (VWF) under arterial shear (1,500 s−1). Multiparameter measurements of platelet interactions with the immobilized VWF surface were recorded by digital-image microscopy and analyzed using custom-designed platelet-tracking software. Six measured parameters that characterize in detail the surface motion and surface binding of several hundred platelets per blood sample differed significantly in those with cancer from the healthy donors. In particular, it was found that patients with cancer had decreased numbers of platelets interacting, translocating and adhering to VWF. There were also reductions in the speed and distances that platelets traveled on VWF in comparison to healthy controls. Platelet function differed between those with early-stage cancer compared to those with later stage cancer. Patients with advanced cancer had an increased number of platelets stably adhering to VWF and greater platelet surface coverage after a given time of interaction. To the best of our knowledge, our results demonstrate for the first time that dynamic platelet function is markedly different in patients with cancer compared to healthy donors.

Successful kidney transplantation normalizes platelet function

Abstract Background Uraemic platelet dysfunction is not completely understood, in part due to non-physiological platelet function assays. We have developed a physiological flow-based assay that quantifies platelet function in microlitre volumes of blood under arterial shear. The aim of this study was to characterize platelet function before and after kidney transplantation. Methods Ten patients scheduled for living donor kidney transplant surgery and nine healthy controls were analysed using the assay. The motional parameters of platelet behaviour on von Willebrand factor (VWF) were recorded using customized platelet tracking software. The assay was repeated 3–8 weeks post-transplant in the transplant group and at an interval of >3 weeks in normal healthy volunteers. Results Platelet–VWF interactions were markedly reduced in the 10 pre-transplant patients compared with the healthy controls. In seven patients with immediate graft function, dynamic platelet function returned to normal (despite a small decrease in haemoglobin and haematocrit), but remained markedly abnormal in the three patients with delayed graft function (DGF). Conclusions Dynamic platelet function returned to normal following transplantation in those with immediate graft function. This early improvement was not observed in those with DGF. There may be important clinical implications, as patients with DGF are more likely to undergo invasive procedures, including transplant biopsies and insertion of central venous catheters.

MRS2179: a novel inhibitor of platelet function.

Background Antiplatelet agents, such as aspirin and P2Y12 inhibitors, are essential in the secondary prevention of cardiovascular disease [1]. Despite effective treatment with these drugs, many patients still suffer ischemic events. This suggests the need for additional antiplatelet therapy. The P2Y1 receptor is a seven transmembrane G protein coupled receptor responsible for platelet shape change and reversible aggregation [2]. Animal studies have shown that antagonists of the P2Y1 receptor, such as MRS2179, inhibit platelet aggregation [3]. The effect of P2Y1 inhibition in man is not yet clear. To address this we characterised platelet function in human blood using a novel shearmediated dynamic assay.

PS-276 Preterm Infants Exhibit Increased Platelet Adhesion To Vwf Under Conditions Of Arterial Shear

Background/aims Preterm infants have higher rates of haemorrhagic diathesis and respiratory complications than terms and adults. Platelets play a key role in haemostasis but detailed platelet function testing in neonate populations are lacking mainly due to the large blood volume requirements. To address this we developed a physiologically relevant assay on vonWillebrand factor that mimics platelet behaviour in vivo at arterial shear conditions. Methods A prospective clinical study of blood from preterms < 32 weeks (n = 21), terms (n = 12) and adults (n = 48). 200 μl of blood for each donor was labelled with a florescent dye for visualisation of platelets in real-time. The blood was perfused over parallel plate flow chambers coated with purified vonWillebrand Factor (vWF). Platelet interactions with the surface were imaged via video microscopy at high speed (500 frames at 30 frames/second). In-vivo when platelets are exposed to activated vWF they tether, roll and translocate. For the first time ever we managed to image these platelet behaviours using a custom designed platelet tracking algorithm. Results Preterms had significantly more numbers of static platelets (54 ± 55 vs. 26 ± 4 and 28 ± 2 SEM, p < 0.0001). In the preterm cohort there were increased numbers of platelets translocating on the vWF surface (359 ± 25 vs. 277 ± 25 and 307 ± 10 SEM, p = 0.05) compared with the terms and adults. Clinical outcomes showed significantly high levels of RDS (76.19%), CLD (38.09%) IVH (28.57%) and pulmonary haemorrhage (23.8%). Conclusions The behaviour of platelets on vWF is significantly different in preterms and could explain the increased tendency to bleeding and development of RDS and CLD in premature neonates. The tiny volume of blood needed to perform this test has major implications for its use in a clinical setting.