Effects of fluoride, arsenic and co-exposure on expression of Bcl-2 and Bax in hippocampus and cerebral cortex of rats

Abstract

Objective The study was designed to explore the effects of fluoride,arsenic and co-exposure on protein expression of Bcl-2 and Bax in hippocampus and cerebral cortex tissues of rats.Methods According to body weight,forty male SPF SD rats at the beginning of weaning were randomly divided into four groups.Each group was composed of 10 rats.Rats were exposed to either 120 mg/L sodium fluoride(NaF) in fluoride treated group,70 mg/L sodium arsenite (NaAsO2) in arsenite treated group,or 120 mg/L NaF and 70 mg/L NaAsO2 combined solution in arsenic-fluoride treated group by drinking water for 3 months,respectively.The control rats drank distilled water for 3 months.The protein expressions of Bcl-2 and Bax in hippocampus and cerebral cortex of rats were detected with immunohistochemistry and Western blotting.Results ①The results of immunohistochemistry assay were as follows:The Bcl-2 and Bax protein in cytoplasm of hippocampus and cerebral cortex neurons appeared as brown particles.Compared with control,NaF-exposed and NaAsO2-exposed rats,the number of Bcl-2 positive neurons of hippocampus and cerebral cortex in co-exposed rats decreased.Compared with control rats,the number of Bax positive neurons of hippocampus and cerebral cortex in NaF-exposed,NaAsO2-exposed and coexposed rats increased,especially in co-exposed rats.②The results of Western blotting assay were as follows:the protein expression levels of Bcl-2 and Bax in hippocampus of control,NaF-exposed,NaAsO2-exposed and coexposed rats were 0.84 ± 0.22,0.76 ± 0.10,0.75 ± 0.24,0.28 ± 0.05 and 0.44 ± 0.19,0.81 ± 0.14,1.22 ± 0.45,1.45 ± 0.26,respectively.The level of Bcl-2 protein expression in hippocampus of co-exposed rats was lower than that of other three groups (all P ＜ 0.05).The levels of Bax protein expression in hippocampus in the three exposure groups were all higher than that of control rats (all P ＜ 0.05),and the levels of Bax protein expression in hippocampus of NaAsO2-exposed and co-exposed rats were higher than that of NaF-exposed rats.The protein expression levels of Bcl-2 and Bax in cerebral cortex in control,NaF-exposed,NaAsO2-exposed and coexposed rats were 0.51 ± 0.18,0.50 ± 0.12,0.49 ± 0.19,0.33 ± 0.19 and 0.39 ± 0.18,0.79 ± 0.30,0.79 ± 0.35,0.80 ± 0.18,respectively.Compared with control rats,the Bax protein expressions in cerebral cortex of rats exposed to NaF,NaAsO2 and their combined solution were all higher(all P ＜ 0.05).We also found that the ratios of Bcl-2 and Bax expression in hippocampus and cerebral cortex of NaF-exposed (0.96 ± 0.28,0.69 ± 0.37),NaAsO2-exposed(0.72 ± 0.45,0.57 ± 0.10) and co-exposed rats(0.33 ± 0.05,0.37± 0.18) all markedly decreased than that of control rats(1.91 ± 1.32,1.44 ± 0.29,all P ＜ 0.05),especially in co-exposed rats.Conclusions Under certain exposure doses,fluoride and arsenic have increased Bax protein expression,decreased Bcl-2/Bax expression ratio in hippocampus and cerebral cortex of rats.Fluoride and arsenic might have synergistic effect on Bcl-2 protein expression in hippocampus and Bcl-2/Bax expression ratio in cerebral cortex of rats. Key words: Fluorine;  Arsenic ;  Apoptosis;  Bcl-2-associated X protein