Shenlian extract improves atherosclerosis by relieving adventitial inflammation

Shenlian (SL) extract, a Chinese medicinal compound mainly pointing at inflammation response of atherosclerosis, is composed of Salvia miltiorrhizae Bunge and Andrographis paniculata (Burm.f.) Nees. Salvia miltiorrhizae Bunge has been reported to activate blood to remove stasis, while another herb, Andrographis paniculata (Burm.f.) Nees, has been revealed to clear endogenous heat toxins. The anti-atherosclerotic effects of these two herbs have been reported closely relating to inflammation. However, from the point of view of adventitial inflammation, the in-depth study of SL extract in anti-atherosclerotic effects by relieving adventitial inflammation is still unknown.

To explore the effects of adventitial inflammation in atherosclerosis progression and if SL extract could reverse the process.

A novel atherosclerosis model based on adventitial inflammation was established. High-fat diet-fed ApoE^-/- mice were implanted a cotton thread soaked with LPS on the right common carotid artery (RCCA). Meanwhile, three time points were set (week 2, 4, and 12) to accurately evaluate the effect of SL extract on the whole process of atherosclerosis with adventitial inflammation. The pathological changes of phenotype transformation of VAFs, vascular cell proliferation and collagen synthesis were observed dynamically by immunohistochemistry (IHC), BrdU method and sirius red staining. Then primary VAFs were stimulated by LPS to mirror the process of adventitial inflammation in vitro. The VAFS phenotype conversion and its function alterations including proliferation, migration, inflammatory secretion was assessed. Finally, we established a co-culture model of activated VAFs and vascular smooth muscle cells (VSMCs) to observe the impacts of activated VAFs on phenotype transformation and migration of VSMCs.

SL extract improved atherosclerosis progression by reducing lipid content, adventitial inflammation and plaque formation. HE results showed sham-operated group (Sham) appeared light infiltrated inflammation only in adventitia at week 2, and the degree of inflammation infiltrated in model was more severe than that in Sham at week 2, 4, and 12. At week 12, the sham and model group showed evidently thickened media and intima. The phenotypic transformation, proliferation and migration of vascular adventitial fibroblasts (VAFs) as well as inflammatory secretion enhanced remarkably in vivo and vitro, but SL extract reversed these changes. Moreover, SL extract downregulated JAK2-STAT3-MMP2 signal pathway. The VSMCs transformed from contractile phenotype into synthetic phenotype and the migration of VSMCs increased after co-culture with activated VAFs. In contrast, SL extract could suppress theses effects.

Taken together, atherosclerotic inflammation could be a "outside-in" signaling. Adventitial inflammation not only accelerated intimal plaque formation in atherosclerosis, but also worsened the degree of vascular lesion. And SL extract improved atherosclerosis by relieving adventitial inflammation, and the underlying mechanisms could be associated with curbing phenotypic transformation, proliferation and migration of VAFs and VSMCs.