Evaluation of Platelet Functional Activity in Healthy BALB/c Mice and in EMT-6 Breast Cancer Orthotopic Model

Platelets, anuclear cell fragments circulating in the blood,can be considered as vascular wall and latent thrombosis sensors.However, the heterogeneity of normal platelet indicators is toolarge for the correct “reading” of information from these sensors.Therefore, it is necessary to fine-tune methods for assessing thefunctional state of mouse platelets in order to then check undercontrolled conditions how various pathological processes changethe state of platelets. In this work, we adapted previously developedflow cytometry platelet functional activity tests for use in bloodsamples from BALB/c mice and evaluated changes in platelet statusin an in vivo model of spontaneous metastatic breast cancer EMT-6. Continuousand endpoint flow cytometry were used. Platelet shape change, decreasedGPIb antibody binding, P-selectin exposure, integrin activation,calcium mobilization, and phosphatidylserine exposure were observed.Several functional activity differences between human and murineplatelets were obtained. First, according to all observed parameters,activation of mouse platelets in response to 2.5 µm of ADP was significantlyweaker than activation in response to 200 µm of AYPGKF (PAR4 thrombinreceptor agonist). Second, reversible activation of integrins andshape change were observed in response to ADP. The main differencebetween platelets of mice with a tumor was a significant decrease intheir number when isolated from the blood. Additionally, some responseswere diminished: binding of antibodies to GPIb, shape change, activationof integrins, and procoagulant response. The results indicate thata tumor in the terminal stage probably reduces the number of circulatingplatelets and causes their damage.