| Endemic fluorosis is a typical geochemistry disease, marked by dental fluorosis and skeletal fluorosis, involving many countries and regions, and China suffers heavy. Excess fluoride can go through the blood-brain barrier and accumulate in the brain, damaging the nervous system, while the hippocampus is a target organ of fluorosis. The effect of chronic fluorosis on brain injury has become a popular area in fluorosis research, but the mechanism of brain damage caused by fluoride has not been yet clear. The free radical injury theory has been recognized by most scholars, suggesting that the brain damage in fluorosis has something to do with elevated levels of oxidative stress caused by excessive fluoride.Exploring a drug treatment of fluorosis has become an urgent issue. Epidemiological investigations and animal experiments have shown that the dose of selenium can alleviate fluorosis, make urinary fluoride excretion, correct the oxygen free radicals and lipid metabolism disorder, restrain lipid peroxidation induced by fluoride and improve brain injury in fluorosis. So far, antagonism research about selenium on the phrenology system of fluorosis has advanced considerably. Studies on the central nervous system have been reported but lack of depth and system. In addition, in order to find the best anti-fluoride effect without toxic effects of selenium dose, it is necessary to get a smaller and safer dose of selenium against fluoride, based on the 1.5 mg/L dose in the early subchronic toxicology studies.Methods:The experiment was divided into:antagonism groups, prevention groups and treatment groups:(1) antagonism groups:240 Sague-Dwley (SD) rats were randomly divided into 8 groups of 30 each. The control group drank tap water, fluoride group drank 50mg/L of sodium fluoride solution,3 selenium-infected groups drank 0.375mg/L,0.75mg/L,1.5mg/L of sodium selenite solution,3 fluorine+selenium groups drank 50mg/L of sodium fluoride solution and the concentration gradient of 3 pairwise combination of sodium selenite solution, and the exposure time were 6 months. (2) prevention groups:120 SD rats were randomly divided into 4 groups of 30 each. Fluoride-after-water control group drank tap water before 50mg/L of sodium fluoride solution.3 fluoride-after-selenium groups were asked to drink 3 concentrations of sodium selenite solution above, then 50mg/L sodium fluoride solution, and all the time were 6 months. (3) treatment groups:120 SD rats were randomly divided into 4 groups of 30 each. Water-after-fluoride control group drank water before 50mg/L of sodium fluoride solution.3 selenium-after-fluoride groups were asked to drink 50mg/L of sodium fluoride solution, then 3 concentrations of sodium selenite solution, time for 6 months. Every group made blood fluorine and blood selenium levels, fluidity of hippocampal synaptic membrane, hippocampal PSD-93 protein and gene expression levels as the observation points to observe changing trends in the process of brain injury caused by the chronic fluorosis under different concentrations of selenium and different interventions. So we can evaluate and compare molecular mechanism of different concentrations of selenium to prevent, antagonise and treat hippocampal damage caused by oxidative stress and find the best anti-fluoride concentration of selenium, look for drug targets to treat brain injury in fluorosis and supply scientific basis for the development and application of anti-fluoride.Results:1. Antagonism groupsAfter exposure to fluoride for 6 months, rats'incisors in F group got clear stripes of chalk color with yellow and white, symptoms of dental fluorosis evident compared to that of controls; blood fluoride levels in F group were significantly increased (P<0.01) than that in the control group. It is clear that if rats have been exposed in the 50 mg/L NaF solution for 6 months, drinking water fluorosis model were reproduced successfully.Compared with the control group, the blood fluoride level of rats in F+low-selenium group (F+LSe) was significantly increased (P<0.05); in high-selenium group (HSe), the blood selenium level was significantly increased (P<0.05); in F group and F+LSe group, fluidity of hippocampal synaptic membrane significantly decreased (P<0.05); in F group, PSD-93 protein level increased by 30%, when that in F+L Se group increased by 28%, both of which showed significant differences (P<0.01); in F group, PSD-93 mRNA level increased by 34% and the difference was significant (P<0.01). The results above showed that fluorosis can cause injury of rats' hippocampal synaptosome membrane and PSD-93 expression abnormally high.Compared with the F group, the blood level in F+middle-selenium group (F+MSe) was significantly decreased (P<0.05); in F+high selenium (F+HSe) group, the blood fluoride level decreased significantly (P<0.01); in F+HSe group, the blood selenium level significantly increased (P<0.01); in F+HSe group, membrane fluidity of hippocampal synaptosome significantly increased (P<0.05); in F+HSe group, PSD-93 protein expression decreased by 18%(P<0.05); in F+LSe group, PSD-93 mRNA levels decreased by 19%(P <0.05), which in F+MSe group and F+HSe group decreased by 27% and 25%(P<0.01). The results above showed that 1.5mg/L of selenium can antagonize the hippocampal damage of rats caused by chronic fluorosis obviously.2. Prevention groupsCompared with fluoride-after-water control group (W-F), blood fluoride level significantly decreased (P<0.05) and blood selenium level significantly increased (P<0.05) in after-high selenium group (HSe-F):blood selenium level in fluoride-after-middle selenium group (MSe-F) was significantly increased (P<0.05); fluidity of hippocampal synaptic membrane in MSe-F group was significantly increased (P<0.05); in MSe-F group, PSD-93 protein expression level decreased by 34%, significantly different (P<0.01); in other groups, PSD-93 mRNA levels have not significant difference (P> 0.05). The results above showed that 0.75mg/L of selenium has obviously protective effect against hippocampal damage caused by chronic fluorosis.3. Treatment groupsCompared with water-after fluoride group (F-W), the blood fluoride and blood selenium levels in other groups were not significantly different (P> 0.05), but the blood fluoride had a decreasing trend with selenium concentration increasing; hippocampal synaptic membrane fluidity significantly increased in high-selenium-after-fluorine group (F-HSe) (P<0.05); in F-HSe group, PSD-93 protein and mRNA levels decreased by 28% and 25% respectively, significantly different (P<0.01). The results above showed that 1.5mg/L of selenium has obviously protective effect against hippocampal damage caused by chronic fluorosis.In summary, chronic fluoride exposure can cause, oxidative stress level increased and hippocampal synaptic membrane fluidity in rats decreased. Abnormal hippocampal synaptic membrane fluidity may cause PSD-93 up-regulated, while the selenium intervention can reverse the abnormity of cell/molecular levels in hippocamp organ. Different concentrations of selenium and different feeding methods have different effects. In all,1.5mg/L of selenium has a good antagonism and treatment on hippocampus damage caused by chronic fluorosis, and 0.75mg/L of selenium has a good preventive effect. PSD-93 may be a drug target for prevention and control of injuries in fluorosis. |
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