[Effects of obesity on alveolar bone resorption and gut microbiota in periodontitis mice].

<b>Objective:</b> To study the effects of obesity on alveolar bone loss and gut microbiota in mice with periodontitis. <b>Methods:</b> Twenty-four seven-week-old female C57BL/6J mice were randomly divided into four groups based on table of random numbers (<i>n</i>=6 in each group): normal-fat diet group (NFD group), high-fat diet group (HFD group), normal-fat diet and periodontitis group (NFD_PD group) and high-fat diet and periodontitis group (HFD_PD group). NFD and HFD groups were fed with normal or high-fat diet for twelve weeks respectively; NFD_PD and HFD_PD groups were induced to periodontitis by ligating the bilateral maxillary second molars with 5-0 silk thread at the fourth week after feeding with normal or high-fat diet respectively. The body weight was measured weekly. The mice were euthanized for collecting the samples at the end of the 12th week. Liver, kidneys, perirenal and retroperitoneal fat were weighed. Serum was collected to detect the level of serum lipids and inflammatory factors. The right maxilla bones were scanned by micro-CT. HE staining was performed to observe the periodontal tissue. The cecum contents were collected for gut microbiota 16S rRNA gene sequencing. Spearman correlation analysis was performed to analyze the correlation between the abundance of gut microbiota and serum inflammatory level and CT value. <b>Results:</b> After 12 weeks of high-fat diet fed, the body weight of HFD group [(26.52±1.96) g] was significantly higher than that of NFD group [(20.95±0.63) g] (<i>t</i>=6.63, <i>P</i><0.001). The body weight of HFD_PD group [(23.82±1.12) g] was significantly higher than that of NFD_PD group [(20.73±0.47) g] (<i>t</i>=6.23, <i>P</i>=0.001). The serum levels of total cholesterol, triglyceride and low density lipoprotein in HFD group and HFD_PD group were significantly higher than those in NFD group and NFD_PD group (<i>P</i><0.01). The distance from the cemento-enamel junction to the alveolar bone crest (CEJ-ABC) on the mesial site of maxillary second molar in HFD_PD group [(647.46±47.46) μm] was significantly higher than that in NFD_PD group [(440.48±68.08) μm] (<i>t</i>=5.58, <i>P</i><0.001). HE staining showed that the maxillary second molar attachment loss, collagen fiber destruction and inflammatory cell infiltration were more significant serious in HFD_PD group compared with NFD_PD group. The levels of interleukin (IL)-1β, IL-6 and monocyte chemotactic protein-1 (MCP-1) of serum in HFD_PD group [(17.11±1.92), (31.61±3.20) and (204.42±35.96) ng/L, respectively] were significantly higher than those in NFD_PD group [(10.44±1.65), (19.96±2.09) and (147.36±10.76) ng/L, respectively] (<i>P</i><0.001, <i>P</i><0.001, <i>P</i>=0.004). The 16S rRNA gene analysis revealed that the <i>Bacteroides/Firmicutes</i> ratio in HFD_PD group (4.00±3.30) was significantly higher than that in NFD_PD group (0.62±0.19) (<i>t</i>=2.50, <i>P</i>=0.030). The abundance of <i>Oscillospira</i> in HFD_PD group [(12.25±0.05) %] was significantly higher than that in NFD_PD group [(2.80±0.01) %] (<i>t</i>=4.64, <i>P</i><0.001). The abundance of <i>Parabacteroides</i> in HFD_PD group [(0.25±0.27)% ] was significantly lower than that in NFD_PD group [(2.04±0.02)%] (<i>t</i>=2.32, <i>P</i>=0.043). The β-diversity analysis of gut microbiota based on Bray-Curtis distance showed that samples of HFD_PD group and NFD_PD group were obviously grouped. Correlation analysis showed that the abundance of <i>Oscillospira</i> was positively correlated with IL-1β, IL-6, MCP-1 concentration and CEJ-ABC value in serum significantly (<i>r</i> values were 0.80, 0.79, 0.80, 0.89, <i>P</i><0.05). The abundance of <i>Parabacteroides</i> was negatively correlated with IL-1β, IL-6 concentration and CEJ-ABC value in serum significantly (<i>r</i> values were -0.71, -0.71, -0.86, -0.95, <i>P</i><0.05). <b>Conclusions:</b> Obesity promotes alveolar bone resorption in periodontitis mice and changes the gut microbiota. <i>Oscillospira</i> and <i>Parabacteroides</i> may play a key role.