## 1 Introduction  
Type 2 diabetes (T2D), the most common type of diabetes, affects more than 462 million people globally, or 6.28% of the world's population [1]. T2D is the main endocrine driver for the global burden of disease and has become the ninth leading cause of death [2]. Patients with T2D typically have several comorbid diseases, such as chronic kidney disease, hypertension, cardiovascular diseases (CVDs), retinopathy, neurodegenerative diseases, and cancers [3]. Among these, CVDs and chronic kidney disease are the leading causes of mortality in those with T2D [3]. Metformin has long been used as first-line medication for T2D because it is safe and inexpensive; it is the most widely prescribed drug for treating T2D [4]. Metformin is a biguanide derivative that reduces blood glucose levels through its ability to regulate energy metabolism; this regulation involves inhibiting hepatic gluconeogenesis, reducing glucose absorption, and elevating glucose utilization in peripheral tissues [5]. Numerous studies have revealed that metformin can improve inflammation, aging-related diseases, obesity, CVDs, chronic kidney disease, inflammatory bowel disease, cancers, polycystic ovarian syndrome, osteoporosis, and periodontitis [5].  
Platelets, nucleated blood cells, participate in normal hemostasis process and arterial thrombosis, which induces various CVDs and cerebrovascular diseases. The event of platelet adherence and aggregation are thought to be involved in initiating intraluminal thrombosis. While endothelial damage occurs in blood vessels, platelets adhere to the disrupted surface, and subsequently release active biological substances, thus triggering aggregation of the platelets [6]. Platelets are activated by a variety of physiological agonists (e.g., collagen, thrombin, ADP, epinephrine, and PAF). These agonists are thought to exert their effects by interacting with specific receptors on the platelet membranes. The primary effects of agonists may be enhanced by secondary effects caused by the synthesis of thromboxane A\({}_{2}\) (TxA\({}_{2}\)) from the arachidonic acid (AA) or by the secretion of ADP from the dense granules in platelets. ADP binds to two major purinergic receptors (P2Y\({}_{1}\) and P2Y\({}_{12}\)), which play an important role in potentiating platelet activation induced by other aggregating agonists [7]. Drugs that can inhibit platelet activation can also greatly diminish the danger of critical events, such as vascular death, myocardial infarction, and ischemic stroke, especially in patients with atherosclerotic vascular diseases. Clinical trials have demonstrated the beneficial effects of metformin on CVDs; in one study, metformin reduced mortality and diabetes-associated thrombotic complications, such as endothelial dysfunction (ED), myocardial infarction, acute myocarditis, and chronic heart failure [3; 8]. Metformin can directly protect injury-induced ED, which is beyond its glucose-lowering effects [9]. Metformin markedly diminished rat platelet activation through decreasing the extracellular mitochondrial DNA release, protection of mitochondrial function, and thereby reducing activated platelet-induced mitochondrial hyperpolarization-associated membrane damage [10]. Furthermore, metformin treatment could inhibit platelet aggregation in platelet-rich plasma (PRP) from the healthy human subjects [11] or type I diabetes patients [12]. Additionally, metformin was reported to decrease in vivo oxidative stress and reduce platelet activation through increasing plasma vitamin A and E or decreasing platelet superoxide anion levels in T2D patients [13; 14]. Together, metformin may, thus, have potential as a therapeutic agent for arterial thrombosis. However, relatively few studies investigated the detailed mechanisms of metformin in platelet activation. Therefore, this study investigated the underlying mechanisms of metformin in human platelets and further evaluated the in vivo effectiveness of metformin in experimental mice.