Tooth loss induces cognitive decline independent of low-protein diet intake in male mice

Objectives: Previous articles have shown that tooth loss is associated with cognitive decline in animal and human studies. Additionally, poor nutritional status including low-protein diet is associated with dementia. The evidence of the association of tooth loss and nutritional status is uncertain. The purpose of this study was to investigate the relationship between low-protein diet intake and cognitive decline following tooth loss in mice. Design: Male senescence-accelerated mouse-prone 8 mice were randomly allocated into sham-operated control and tooth loss groups with extracted maxillary molars: control with normal-protein diet; control with low-protein diet; bilateral maxillary molar extraction with normal-protein diet; and bilateral maxillary molar extraction with low-protein diet. After 6 months, a behavioral test was conducted, and mRNA expression and immunohistochemistry in the brain were analyzed. Results: Behavioral test revealed no effect of the interaction between tooth loss and low-protein diet intake on cognitive decline; however, tooth loss had a marked effect on cognitive decline. Real-time polymerase chain reaction showed no interaction between tooth loss and low-protein intake for Bax/Bcl-2 mRNA expression; however, tooth loss had a significant effect on Bax/Bcl-2 mRNA expression. Immunohistochemical analysis showed that the effect of tooth loss in neuronal inflammation and neuronal loss were observed in CA1 and DG region, but the effect of low-protein diet was limited in CA3. Conclusion: The present study revealed that the impact of tooth loss on cognitive decline was not dependent on the low-protein diet condition.