Active Constituents and Mechanisms of Xinshubao Tablets in Coronary Vasorelaxation

Background: Xinshubao tablet (XSB), a traditional Chinese medicine (TCM) formula composed of five medicinal herbs, is used clinically to alleviate cardiovascular diseases. This study aimed to investigate the coronary vasodilatory effects of XSB and its individual herbs, exploring its active constituents and the underlying mechanisms. Methods: The vasorelaxant effects of XSB and its individual herbal intestinal absorption solutions (IASs) were evaluated by ex vivo coronary artery ring assays. The chemical constituents of the best active herbal IAS were qualitatively identified using ultra-performance liquid chromatography–quadrupole time-of-flight mass spectrometry (UPLC–Q-TOF-MS). Molecular docking and ex vivo assays were used to predict and validate the bioactive constituents and mechanisms responsible for coronary vasorelaxation. Results: Vasodilation experiments revealed that XSB-IAS and its individual herb IAS exhibited varying degrees of vasodilatory effects, in the range of 0.8–18 g raw materials/mL. At 6, 12, and 18 mg of raw materials/mL, Crataegus pinnatifida Bge (Shanzha) exhibited vasodilation rates of 26.45% ± 1.8%, 36.57% ± 3.5%, and 45.16% ± 6.3%, which were obviously higher than those of the other individual herbs. Fifty constituents in Shanzha IAS were identified by UPLC-Q-TOF-MS. Vasodilation-related protein–protein interaction (PPI) network revealed NOS3 as a core regulatory target. Molecular docking demonstrated that among the identified constituents, isochlorogenic acid B, betulin, etc., displayed binding affinity to NOS3. Isochlorogenic acid B was further validated to exhibit vasodilatory effects in the ranges of 0.05–2.5 mM. Mechanistic results showed that isochlorogenic acid B improved vasodilation by inhibiting Ca2+ influx through both voltage-dependent and receptor-operated Ca2+ channels, activating K+ channels, and exhibiting endothelium-dependent vasorelaxation. Conclusions: This study provides insights into the material basis and mechanisms underlying the vasorelaxant effects of XSB. Isochlorogenic acid B was firstly found to exert the coronary vasodilatory effect. This study can also contribute to the identification of efficacy-related quality markers in TCM.