rLj-RGD3, a novel recombinant toxin protein from Lampetra japonica, prevents coronary thrombosis-induced acute myocardial infarction by inhibiting platelet functions in rats

Recombinant Lampetra japonica RGD-peptide (rLj-RGD3), a soluble protein containing three RGD sequences, was acquired from the oral salivary glands of Lampetra japonica using recombinant DNA technology. The aim of this study was to investigate the protective effects of rLj-RGD3 against acute myocardial infarction (AMI) induced by coronary artery thrombosis, as well as the underlying mechanisms. A rat model of AMI caused by ferric chloride-induced thrombosis on the surface of the left anterior descending (LAD) coronary artery was successfully established. Rats were given various doses of rLj-RGD3 (12 μg/kg, 24 μg/kg and 48 μg/kg) via sublingual intravenous delivery 10 min before AMI. ST segment elevation was recorded by electrocardiogram (ECG) until the end of the model. Left ventricular Evans blue content and histopathological changes were examined. Blood samples were collected to determine 5-hydroxytryptamine (5-HT), β-thromboglobulin (β-TG), platelet factor 4 (PF4) and cAMP levels. The effects of rLj-RGD3 on platelet aggregation, adhesion and intracellular calcium concentrations were also measured. rLj-RGD3 significantly reduced ST segment elevation, prevented thrombus formation in the coronary artery and decreased Evans blue content in the left ventricular myocardium. Meanwhile, rLj-RGD3 exerted an inhibitory effect on adenosine diphosphate (ADP)-induced platelet aggregation and blocked platelet adhesion to collagen. Treatment with rLj-RGD3 prevented 5-HT, β-TG and PF4 release and significantly elevated intracellular cAMP levels in a dose-dependent manner but decreased the level of cytosolic-free Ca²⁺, an aggregation-inducing molecule. These results show that rLj-RGD3 can effectively reduce coronary thrombosis in AMI rats by strongly inhibiting platelet function, indicating that the recombinant RGD toxin protein rLj-RGD3 may serve as a potent clinical therapeutic agent for AMI.