Methods: Wild-type (n=12) and apoE-deficient (n=12) rats (all Sprague-Dawley strain background; age, 8 weeks) were used. These rats were randomly divided into two groups of 6 rats each: control and occlusal disharmony groups. The control group received no treatment for 8 weeks. The occlusal disharmony group underwent cut-off maxillary molar cusps for 8 weeks. In rat hippocampus, formic acid-soluble Aβ40 and Aβ42 levels were determined using ELISA kits. Gene expression of β-secretase was analyzed by real time reverse transcription polymerase chain reaction. Comparisons among the groups were made by ANOVA and Tukey’s test.
Results: The occlusal disharmony group in wild-type rats showed 1.9, 1.6 and 2.0 times higher levels of Aβ40, Aβ42 and β-secretase compared to the control group, respectively (p<0.05). In apoE-deficient rats, the occlusal disharmony group also showed 1.4, 1.6 and 1.8 times higher levels of Aβ40, Aβ42 and β-secretase compared to the control group, respectively (p<0.05). Furthermore, the levels of Aβ40 and Aβ42 in the occlusal disharmony group in apoE-deficient rats was significantly higher than those in the wild-type rats (p<0.05).
Conclusions: In the rat hippocampus, deficiency of apoE and occlusal disharmony had an additive effect on Aβ production.