Abstract 140: Magnesium Lithospermate B Inhibits Blood Coagulation and Platelet Aggregation: Novel Mechanism of a Traditional Drug for Cardiovascular Diseases

Magnesium lithospermate B (MLB) is one of the major components of Salvia miltiorrhiza root (Danshen). Danshen extracts have been used to control cardiovascular disease for centuries. In 2005, intravenous injection of Danshen depside salt was approved in China for treatment of chronic angina. Although clinical observations have suggested that Danshen extracts inhibited thrombosis, the exact mechanism has not been adequately explored. Using an in vitro whole blood clotting assay, we observed that MLB (250 μM) significantly reduced clot size. Both the clot wet and dry weights were decreased following treatment (108.3 mg vs. 63.5 mg, and 32.8 mg vs. 18.5 mg, p<0.05, respectively). Using thromboelastography, we found that MLB markedly decreased the mechanical strength of the clot and modestly delayed initiation of coagulation in cell-free blood plasma prepared by centrifugation (10,000 хg, 10 min). Under confocal microscopy, we further observed that MLB significantly reduced the density of the fibrin network formed in plasma following thrombin treatment, suggesting that MLB targets coagulation factors to inhibit coagulation. Recent network pharmacology analyses predict that MLB may interact with VWF, factor XIII (FXIII), or thrombin in the coagulation cascade. We found that MLB did not inhibit VWF-dependent platelet agglutination induced by botrocetin. ELISA revealed that MLB also did not significantly alter the binding of activated FXIII (FXIIIa) to fibrinogen. However, when native FXIII from blood plasma was used for the same assay, MLB significantly reduced the binding of FXIIIa to fibrinogen. Since generation of FXIIIa from FXIII is thrombin-dependent, these data suggest that MLB inhibits thrombin activity or thrombin generation. Indeed, we found that MLB markedly inhibited thrombin-induced gel-filtered human and mouse platelet aggregation. These data demonstrated a novel role for MLB in the inhibition of blood coagulation and platelet aggregation, likely through direct inhibition of thrombin function, although we cannot exclude its additional anti-thrombotic activities. Thus, purified MLB may represent an efficient, low-cost agent for treatment of artery and deep vein thrombosis.