Humic Acids Inhibit Platelet Activation to Reduce Venous Thromboembolism in Mice

Abstract

Objective. We aimed to investigate the effects of the natural product humic acids (HA) on platelet activation and development of venous thromboembolism (VTE) in mice and further explore the relevant mechanism. Methods. Eight-week C57BL/6 mice were randomly assigned to three groups: sham operation group (n = 7), VTE group (n = 8), and VTE + HA group (n = 10). Thrombi were harvested to hematoxylin-eosin staining to evaluate the thrombolysis and recanalization of the thrombus. In addition, flow cytometry was performed to detect the expression levels of protein disulfide isomerase on endothelial-derived exosomes and glycoprotein IIb/IIIa on the surface of the activated platelets surface in plasma. Furthermore, the protein expression level of glycoprotein IIb/IIIa in thrombus was determined by immunohistochemistry and immunofluorescence. Results. The length of thrombosis in the VTE + HA group was significantly shorter than that in the VTE group ( $P=0.040$ ). No significant differences were observed in thrombolysis and recanalization between the VTE + HA group and the VTE group ( $P>0.05$ ). The content of protein disulfide isomerase carried by endothelial-derived exosomes was significantly increased in the VTE group ( $P=0.008$ ) but significantly reduced by native humic acids ( $P=0.012$ ). Compared with the VTE group, the expression of glycoprotein IIb/IIIa on activated platelet surface in the VTE + HA group was significantly decreased ( $P=0.002$ ). The concentration of plasmatic P-selectin in the VTE group was significantly higher than that in the VTE + HA group ( $P<0.001$ ). Conclusion. We demonstrate that HA possess a pharmacological property that decreases venous thrombus formation in mice. The underlying mechanism is that HA could inhibit the expression of glycoprotein IIb/IIIa on the activated platelets surface by suppressing endothelial-derived exosomes carrying on protein disulfide isomerase, thereby blocking platelet activation.