Study on microwave radiation aggravating the impairment of cognitive functions in mice with experimental periodontitis

To explore the effects of microwave radiation on cognitive function and neuroinflammation in mice with experimental periodontitis, providing experimental evidence for understanding how environmental exposure may be linked to the risk of neurodegenerative diseases by modulating chronic inflammation as a shared pathological mechanism.

This study was approved by the Animal Ethics Committee of the Academy of Military Medical Sciences. C57BL/6J mice were randomly divided into a control group (C group, untreated), a microwave radiation group (R group, exposed to microwave radiation only), a periodontitis group (P group, ligation-induced periodontitis only), and a periodontitis + microwave radiation group (PR group, ligation-induced periodontitis plus microwave radiation exposure). A periodontitis model was established using the silk ligation method. Eight weeks after modeling, the R and PR groups were subjected to whole-body microwave radiation at 2800 MHz and 10 mW/cm² for 10 h/day for 7 consecutive days. Behavioral tests were conducted: the open field test and elevated plus maze test were used to assess anxiety-like behavior, the Y-maze test to evaluate spatial memory, and the novel object recognition test to assess learning and memory abilities. Micro-CT, hematoxylin & eosin staining (HE), and quantitative real-time polymerase chain reaction (qPCR) were used to analyze periodontal tissue pathology and local inflammation. Serum and brain levels of lipopolysaccharide (LPS), interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) were measured using enzyme-linked immunosorbent assay (ELISA). The composition of the oral microbiota was analyzed based on 16S rRNA sequencing.

Behavioral tests showed that anxiety-like behavior was significantly exacerbated in the R and PR groups, and spatial and recognition memory impairments in the PR and P groups were more severe compared with the R and C groups, respectively (P < 0.05). Histological and molecular biological analyses revealed that periodontal inflammation infiltration, alveolar bone resorption, and local expression of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6) were further exacerbated in the PR and P groups compared with the R and C groups, respectively (P < 0.05). ELISA results showed that in serum, LPS levels in group P and group PR were increased compared with group C and group R, respectively. The levels of TNF-α, IL-1β, and IL-6 in group PR were significantly higher than those in group P and group R, with a synergistic increase in TNF-α level (P < 0.05). In brain tissue, LPS and TNF-α, IL-1β, IL-6 levels in group P were significantly higher than those in group C; all the above indicators in group PR were significantly higher than those in group P and group R, and LPS and IL-6 levels showed a synergistic increase (P < 0.05). Oral microbiota analysis found that microwave radiation further reduced microbial diversity on the basis of periodontitis, leading to increased relative abundances of Lactobacillus and Enterococcus, and decreased relative abundances of Staphylococcus. Correlation analysis confirmed that these differential bacterial genera were positively correlated with brain inflammation levels and negatively correlated with cognitive function indicators.

Microwave radiation exposure can exacerbate cognitive impairment in mice with experimental periodontitis, and its mechanism may be related to aggravated local periodontal damage, disruption of oral microbiota homeostasis, and subsequent induction of systemic and central neuroinflammatory cascades.