Naoxintong capsule limits myocardial infarct expansion by inhibiting platelet activation through the ERK5 pathway

• NXT showed obviously preventive effects, which was associated with negative control of platelet activation. • In an ischemic environment, NXT's anti-platelet activation to limit myocardial infarct expansion relies on stimulation of platelet ROS/ERK5/RAC1 signalling pathways. • Targeting the platelet ERK5 signalling pathway, NXT significantly decreased thrombus formation without increasing the risk of bleeding. In the clinic, Naoxintong capsule (NXT) has been applied in two level prevention of ischemic disease. However, its mechanism of action requires further study. This study investigated whether NXT could affect platelet function and activation under ischemic pathological conditions. Wistar rats were divided into six groups, sham, saline, NXT (250, 500, 1000 mg/kg), and aspirin group (10 mg/kg). For the pre-treatment assays, MI model was established after pre-administration of saline, NXT-L, NXT-M, NXT-H, and aspirin respectively for 14 days, and after surgery, there were no continuous treatments. For the post-treatment assay, rats were orally administered for 3 days after MI. FeCl 3 -induced thrombosis model was applied to determine the thrombus wet weight. Bleeding time was used to assess the ability of the platelets to develop a hemostatic plug. NXT decreased infarct size, decreased LDH, CK, and CK-MB values, and improved cardiac function. NXT inhibited platelets activation through reducing CD62P-positive platelets and inhibited infarct expansion by decreasing the number of CD45-positive cells and the amount of MMP9 secreted into the heart tissue. Mechanistically, NXT inhibited platelets activation through decreasing ROS levels, decreasing ERK5 phosphorylation, and increasing RAC1 phosphorylation in MI rats. Pre-treatment with NXT decreased thrombus formation and had normal bleeding times. NXT showed obviously preventive effects, which was associated with negative control of platelet activation. The above results provide a basis for clinically expanding application of NXT.