[High-fat diet promotes the impact of periodontitis on gut microbiota and glucose metabolism].

Objective: To study whether high-fat diet could aggravate the effect of periodontitis on gut microbiota and glucose metabolism. Methods: Twenty-four male SD rats were randomly and equally divided into four groups based on table of random numbers (n=6 in each group): control group, in which rats were given normal chow diet; periodontitis group, in which periodontitis was induced by ligating bilateral maxillary second molars with 5-0 silk thread; high-fat diet group, in which rats were given high-fat diet; high-fat diet+periodontitis group, in which rats were given high-fat diet and periodontitis was induced at the end of the 8th week. Fasting blood glucose and glucose tolerance were measured at the end of the 12th week. Then the rats were euthanized and the cecum content was collected. The microbial 16S rRNA gene sequencing was performed on the Illumina MiSeq platform. The taxonomy of the sequences was analyzed through RDP Classifier (http://rdp.cme.msu.edu/) against the SILVA (SSU123) 16S rRNA database. Pearson correlation analysis was performed to analyze the correlation between changes in gut microbiota and blood glucose. Results: After 4 weeks of periodontitis induction, the fasting blood glucose levels of the periodontitis group and the high-fat diet group were (4.93±0.28) and (5.25±0.24) mmol/L, respectively, which were significantly higher than that of the control group [(4.56±0.20) mmol/L] (P<0.05) with glucose intolerance. The fasting blood glucose level of high-fat diet+periodontitis group [(5.53±0.14) mmol/L] was significantly higher than that of periodontitis group and high-fat diet group, respectively (P<0.05), with the glucose tolerance curve higher than that of periodontitis group. The 16S rRNA gene analysis revealed that the Bacteroides/Firmicutes ratio in the periodontitis group is (0.37±0.23), which was significantly lower than that of the control group (0.68±0.05) (P<0.05). The relative abundance of Lachnospiraceae_NK4A136_group in the periodontitis group was (14.03±6.38)%, which was significantly lower than that of the control group [(28.21±4.82)%] (P<0.05). The relative abundance of Allobaculum [(4.27±2.67)%], Ruminococcaceae_UCG_005 [(3.70±0.90)%], Blautia [(0.63±0.45)%] in the periodontitis group were significantly higher than those of the control group [(0.60±0.72) %, (0.43±0.16) %, (0.13±0.13) %, respectively](P<0.05). Compared with periodontitis group, the relative abundance of Proteobacteria in high-fat diet+periodontitis group [(3.06±0.90)%] was significantly higher than that of the periodontitis group [(1.40±0.98)%] (P<0.05). The principal coordinate analysis and similarity analysis based on the Bray-Curtis distance showed that samples of the high-fat diet+periodontitis group clustered separately from the periodontitis group and the high-fat diet group. The results of correlation analysis showed that the abundance of Lachnospiraceae_NK4A136_group was negatively correlated with fasting blood glucose and glucose levels after loading for 60 and 120 minutes (r=-0.56, -0.50, -0.42, respectively) (P<0.05). The abundance of Allobaculum, [Eubacterium]_coprostanoligenes_group, Peptococcaceae_uncultured, [Ruminococcus]_torques_group, and several genera belonging to the Proteobacteria were positively correlated with glucose levels after loading for 120 minutes (P<0.05). Conclusions: Periodontitis might be closely related to impaired gut microbiota and glucose metabolism, and the effect could be aggravated by high-fat diet.