Anti-thrombotic and pro-angiogenic effects of Rubia cordifolia extract in zebrafish

Rubia cordifolia is a common traditional Chinese medicine that promotes blood circulation and eliminates blood stasis, and has been used to cure diseases related to blood stasis syndrome (BSS) clinically for many years. It has been previously demonstrated that anti-thrombosis and pro-angiogenesis can improve BSS. However, the anti-thrombotic and pro-angiogenic activities of Rubia cordifolia have not been well investigated.To determine the potential anti-thrombotic and pro-angiogenic activities of Rubia cordifolia and to elucidate the underlying mechanisms. In addition, the major chemical constituents of Rubia cordifolia extract (QC) were qualitatively analysed by UPLC-Q-TOF/MS to explore the association between pharmacological activity and chemical constituents.The QC samples were composed of a 95% ethanol extract and an aqueous extract following extraction using 95% ethanol. UPLC-Q-TOF/MS was used to analyse the major chemical constituents of QC. For the anti-thrombotic experiment of QC, a phenylhydrazine (PHZ)-induced AB strain zebrafish thrombosis model was used. The zebrafish larvae were stained using O-dianisidine, and the heart and caudal vein of the zebrafish were observed and imaged with a fluorescence microscope. The staining intensity of erythrocytes in the heart (SI) of each group and the morphology of thrombus in the caudal vein were used to assess the anti-thrombotic effect of QC. For the pro-angiogenic assay of QC, the intersegmental blood vessel (ISV) insufficiency model of Tg(fli-1: EGFP)y1 transgenic zebrafish (Flik zebrafish), which was induced by the VEGF receptor tyrosine kinase inhibitor II (VRI), was used. The morphology of the intact ISVs and defective ISVs was observed to evaluate the pro-angiogenic activity of QC. The mechanism involved in promoting angiogenesis was studied with real-time PCR.A total of 12 components in QC were identified based on standard compounds and references, including nine anthraquinones and three naphthoquinones. After treatment with QC, the PHZ-induced thrombosis in AB strain zebrafish larvae decreased to a certain degree, which we believe was related to its dosages, and the therapeutic effect within the 50-200 µg/mL QC treatment groups was especially prominent (P < 0.01, P < 0.001) compared to that in the PHZ model group. Similarly, QC also recovered the loss of the ISVs, which was induced by VRI in Flik zebrafish larvae, which have a certain dose-effect relationship. The pro-angiogenic activity of QC was also conspicuous (P < 0.01, P < 0.001) compared to that of the VRI model group. The following real-time PCR assay proved that QC significantly restored the VRI-induced downregulation of vWF, VEGF-A, kdrl, and flt-1 in Flik zebrafish (P < 0.05, P < 0.01, P < 0.001).A total of 12 compounds from QC were analysed by UPLC-Q-TOF/MS. The data of the pharmacological experiments demonstrated that QC presented anti-thrombotic and pro-angiogenic activities in zebrafish, and the principal active components were likely anthraquinones and naphthoquinones. Thus, the current study provided a theoretical basis for the clinical use of Rubia cordifolia as a traditional Chinese medicine in promoting blood circulation and eliminating stasis.