ABSTRACT
Objective:To explore the correlation between the efficacy of <italic>Usnea diffracta</italic> in treating atherosclerosis （AS） and the altered microbial flora in rat ileum based on the interior-exterior relationship between heart and small intestine in traditional Chinese medicine （TCM）. Method:Forty-eight SD rats were randomized into a normal group （<italic>n</italic>=8） and a modeling group （<italic>n</italic>=40）. The AS model was established with high-fat diet combined with intraperitoneal injection of vitamin D<sub>3</sub>. The successfully modeled rats were further randomly divided into the model group， positive control （simvastatin， 4 mg·kg<sup>-1</sup>） group， and low- （0.7 g·kg<sup>-1</sup>）， medium- （1.4 g·kg<sup>-1</sup>）， and high-dose （2.8 g·kg<sup>-1</sup>） <italic>U. diffracta</italic> ethanol extract groups， with eight rats in each group. After four weeks of intervention， the blood， aorta， ileum， and ileum content of rats in each group were collected. The levels of serum lipopolysaccharide （LPS）， tumor necrosis factor-<italic>α </italic>（TNF-<italic>α</italic>） and interleukin 6 （IL-6） were measured by enzyme-linked immunosorbent assay （ELISA）， and the pathological changes in rat thoracic aorta was detected by hematoxylin-eosin （HE） staining. Western blot was conducted to determine the protein expression levels of tight junction protein zonula occluden （ZO-1） and Occludin in rat ileum， and the high-throughput 16S rRNA sequencing technology was employed to detect changes in microbial diversity and abundance in rat ileum of each group. Result:Compared with the normal group， the model group exhibited obvious aortic plaque deposition， increased LPS， TNF-<italic>α</italic>， and IL-6 levels （<italic>P</italic><0.01）， but decreased ZO-1 and Occludin protein expression （<italic>P</italic><0.01）. The comparison with the model group revealed that <italic>U. diffracta</italic> significantly ameliorated the aortic plaque deposition of model rats， lowered serum LPS， TNF-<italic>α</italic>， and IL-6 levels （<italic>P</italic><0.05， <italic>P</italic><0.01）， and up-regulated ZO-1 and Occludin protein expression （<italic>P</italic><0.05， <italic>P</italic><0.01）. The abundance of Proteobacteria and Bacteroidetes in the model group changed significantly in contrast to that in the normal group， and the Bacteroidetes/Firmicutes（B/F） value declined （<italic>P</italic><0.05）. Alpha and Beta diversity analysis indicated higher total number of intestinal flora species in the model group， but lower richness and uneven distribution （<italic>P</italic><0.05， <italic>P</italic><0.01）， with a large number of pathogenic bacteria enriched. The ethanol extract of <italic>U. diffracta</italic> significantly increased the B/F value， corrected the structural disorder of microbial flora in ileum， reduced pathogenic bacteria， and increased the relative abundance of probiotics. Conclusion:<italic>U. diffracta</italic> exerts the therapeutic effect against AS possibly by improving the intestinal microbial communities， strengthening the intestinal mucosal barrier function， and reducing the serum LPS and inflammatory factors.