## 3 Results
CD, control diet; HFD, high-fat and high-cholesterol diet; + NR, a diet plus oral gavage with 0.3 g/kg BW/day of NR. ANOSIM analysis with R > 0 indicated greater among-group differences than within-group differences, and it was necessary to make group comparisons (Figure 4F). The relative abundance of the top 10 dominant phyla and the top 16 dominant genera of all samples are shown in Figure 4G,H. _Firmicutes_ (59.5%) and _Bacteroidetes_ (17.6%) were the two most abundant phyla, which accounted for 77.1% of the total of all phyla (Figure 4G). _Faecalibaculum_ (34.8%) and _Muribaculaceae_ (12.1%) were the two most abundant genera, which accounted for 46.9% of all genera (Figure 4H). Figure 3: Gene expression of lipid metabolism pathways in ApoE/- mice fed a CD or HFD, without or with NR at the end of the study. (**A**) Gene expression in cholesterol synthesis; (**B**) Gene expression in cholesterol absorption; (**C**) Gene expression in cholesterol uptake; (**D**) Gene expression in cholesterol efflux and bile acid synthesis. Data were presented as mean \(\pm\) SEM. A statistical analysis was performed using a two-way analysis of variance (ANOVA) with the main effects of diet and NR and diet/NR interaction. Means with different letters (a, b or c) indicate a significant difference from each other. CD (control), n = 10; CD + NR, n = 11; HFD, n = 10; HFD + NR, n = 10. ABCA1, Recombinant ATP Binding Cassette Transporter A1; ABCG5, ATP Binding Cassette subfamily G Member 5; ABC8, ATP Binding Cassette Subfamily G Member 8; CD, control diet; CYP7A1, Cholesterol 7-alpha hydroxylase; FXR, Farnesoid X-activated receptor; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; HFD, high-fat and high-cholesterol diet; HMGCR, Recombinant 3-hydroxy-3-methylgluturyl coenzyme a reductase; IDOL, Inducible degrader of the low-density lipoprotein receptor; LDLR, Low-density lipoprotein receptor; LXR-\(\alpha\), Recombinant liver X receptor Alpha; SREBP-2, Sterol regulatory element-binding protein-2; NPC1L1, Niemann-Pick C1-like 1; PCS89, Proprotein convertase subtilisin/kexin type 9; + NR, a diet plus oral gavage with 0.3 g/kg BW/day of NR. Figure 4: Gut microbial composition and diversity in ApeE\({}^{/}\) - mice fed with a CD or HFD, without or with NR at the end of the study. (**A**) Venn diagrams; (**B**) -diversity of richness: Observe, Chao 1, ACE, (**C**)-diversity of evenness: Shannon, Simpson, J indexes; (**D**)-diversity: (**D**) Principal component analysis (PCA) based on ASVs level; (**B**) ANSOMI analysis diagrams; (**G**) Relative abundance of phylum-level microbobia; (**B**) Relative abundance of genus-level microbobia. Data were presented as mean \(\pm\) SEM. A statistical analysis was performed using a two-way analysis of variance (ANOVA) with the main effects of diet and NR and diet’NR interaction. Means with different letters (**a** or **b**) indicated a significant difference from each other. CD (control), n = 10; CD + NR, n = 11; HFD, n = 10; HFD + NR, n = 10. CD, control diet; HFD, high-fat and high-cholesterol diet + NR, a diet plus oral gavage with 0.3 g/kg BW/day of NR. Effect of Supplementation with NR on the Relative Abundance of Gut Microbiota at Different Taxa Levels and Concentrations of SCFAs in CD- or HFD-Fed ApoE/- Mice  
At the phylum level, compared to the CD and CD + NR groups, both HFD and HFD + NR groups resulted in higher relative abundance of _Firmicutes_ and lower relative abundance of _Bacteroidees_ and _Proteobacteria_, resulting in a higher ratio of _Firmicutes_ to _Bacteroidees_ (all _P-diet_ \(<\) 0.05) (Table 2). The relative abundance of these phyla did not change with NR supplementation. The relative abundance of _Actinobacteria_ was lower in HFD + NR than HFD and CD + NR groups (_P-diet_\({}^{\ast}\)NR = 0.0016) (Table 2).