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 too large for the correct “reading” of information from these sensors. Therefore, it is necessary to fine-tune methods for assessing the functional state of mouse platelets in order to then check under controlled conditions how various pathological processes change the state of platelets. In this work, we adapted previously developed flow cytometry platelet functional activity tests for use in blood samples from BALB/c mice and evaluated changes in platelet status in an in vivo model of spontaneous metastatic breast cancer EMT-6. Continuous and endpoint flow cytometry were used. Platelet shape change, decreased GPIb antibody binding, P-selectin exposure, integrin activation, calcium mobilization, and phosphatidylserine exposure were observed. Several functional activity differences between human and murine platelets were obtained. First, according to all observed parameters, activation of mouse platelets in response to 2.5 µm of ADP was significantly weaker than activation in response to 200 µm of AYPGKF (PAR4 thrombin receptor agonist). Second, reversible activation of integrins and shape change were observed in response to ADP. The main difference between platelets of mice with a tumor was a significant decrease in their number when isolated from the blood. Additionally, some responses were diminished: binding of antibodies to GPIb, shape change, activation of integrins, and procoagulant response. The results indicate that a tumor in the terminal stage probably reduces the number of circulating platelets and causes their damage.