Astragaloside IV Mediates the PI3K/Akt/mTOR Pathway to Alleviate Injury and Modulate the Composition of Intestinal Flora in ApoE-/- Atherosclerosis Model Rats

Abstract

Background: Atherosclerosis (AS) is a chronic inflammatory vascular disease with a complex pathogenesis. Astragaloside IV (AST IV), the primary active component of Astragalus, possesses anti-inflammatory, antioxidant, and immunomodulatory properties. This research aims to investigate the outcome of AST IV on AS and its potential molecular mechanism.

Methods: A high-fat diet (21% fat, 50% carbohydrate, 20% protein, 0.15% cholesterol, and 34% sucrose) was utilized to feed Apolipoprotein E deficient (ApoE^-/-) SD rats for 8 weeks, followed by continuous intragastric administration of AST IV for 8 weeks. Biochemical detection was conducted for serum lipid levels and changes in vasoactive substances. After Masson staining, aortic root oil red O staining, and Hematoxylin Eosin (HE) staining, the efficacy of AST IV was verified using quantitative reverse transcription polymerase chain reaction (qRT-PCR). The mRNA expression levels of inflammatory factors and endothelial dysfunction-related biomarkers in rat aortic root tissues were appraised. The changes in the composition of intestinal flora in rats after AST IV treatment were appraised using Image J (Multi-point Tool). Western blot was used to evaluate phosphatidylinositol-3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/Akt/mTOR) pathway-related protein levels in rat aortic root tissues.

Results: AST IV administration alleviated the pathological symptoms of AS rats. AST IV administration reduced serum total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), endothelin-1 (ET-1) and angiotensin (Ang)-II (Ang-II) levels, and augmented serum high-density lipoprotein cholesterol (HDL-C) and nitric oxide (NO) levels. At the same time, AST IV administration inhibited the levels of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), IL-1β, vascular cell adhesion molecule-1 (VCAM-1), matrix metalloproteinase-2 (MMP-2), macrophage inflammatory protein-1 (MCP-1), and intercellular adhesion molecule-1 (ICAM-1) in the aortic root tissue of AS rats. In addition, the intestinal flora changed significantly after AST IV administration. The number of Bifidobacterium, Lactobacillus, and Bacteroides augmented significantly, and Enterobacter, Enterococcus, Fusobacterium, and Clostridium significantly decreased. Mechanistically, AST IV administration inhibited the phosphorylation of PI3K, Akt, and mTOR in AS rats. When combined with Dactolisib (BEZ235) (a PI3K/Akt/mTOR pathway inhibitor), AST IV could further inhibit phosphorylation and reduce inflammation.

Conclusion: AST IV has a potential anti-AS effect, which can improve the pathological changes of the aorta in ApoE^-/- rats fed with a high-fat diet, reduce the level of inflammatory factors, and modulate the composition of intestinal flora via the PI3K/Akt/mTOR pathway.

Keywords: PI3K/Akt/mTOR; astragaloside IV; atherosclerosis; gut microbiota.