Effect Of The Apoptosis Inducing Factor In Neuronal Apoptosis Of Rat Brains With Chronic Fluorosis

Objective: Aim of the study is to investigate whether the non-caspasedependent pathway mediated by apoptosis-inducing factor(AIF) can participate the procesure of neuronal apoptosis in brains of the rats with chronic fluorosis and discuss the mechanism by detecting the rate of neuronal apoptosis, the expressions of AIF and caspase at protein level. Methods: 60 Sprague Dawley(SD) rats(half male and half female) were divided randomly into two groups, i.e., Control group fed with tap water with fluoride content <0.5 mg/L and Fluorine group in which sodium fluoride was added into drinking water with fluoride content of 50 mg/L. Both groups were fed with standard food with fluorine content <0.5 mg/ kg. The experiment period was 10 months. Dental fluorosis was observed; fluoride contents in urine and bone were detected by fluorin-ion selective electrode method. Histopathological changes in brains of the rats were examined by HE and Nissl stainings. The protein expressions of AIF as well as caspase-3 and caspase-9 were detected by immune-histochemistry for the distribution in the cerebral cortex and hippocampus, and by western blotting for protein expressions in these brain regions. Apoptosis rates of the neurons in the cerebral cortex and hippocampus of rats were measured by flow cytometry. Results: Dental fluorosis with different degrees, higher levels of fluoride contents in urine and bone were detected in the rats with chronic fluorosis as compared to those of the rats in the Control group rats(P<0.05). No obvious changes in histopathology examined by HE staining were observed in brains of the rats with chronic fluorosis. Nevertheless, decreased colors and small numbers of nissl bodies were observed in brains of the rats wich chronic fluorosis as compared with the rats in the Control group. The results by immune-histochemistry showed that the numbers of the positive stained neural cells and the color degree in these cells in the temporal cortex of the rats in the Fluoride group were higher than those of the rat brains in the Control group(P < 0.05). However, no changes of the histopathological examinations were found in the frontal and occipital cortices of the rats with chronic fluorosis(P > 0.05). The results by Western blotting result showed that protein expression of AIF(57-k Da) in the mitochondria of rat brains in Fluorine group was obviously lower than that of the Control group, and while the level of AIF in the nucleus of the cells was significantly higher than that of the control. The levels of casepase 3 and 9 at protein level were significantly increased in brains of the rats with chronic fluorosis as compared to the controls. Accorded to the data of flow cytometry outcome, apoptosis rate in the neurons of the hippocampus and cortex of rats in the Fluorine group was significantly higher than those of the controls(P<0.05). Conclusion: The results suggest that both the AIF mediated non-caspase dependent apoptotic pathway and casepase dependent pathoway participate in the procedure of neuronal apoptosis, which may be one of the mechanism in brain damage.