Spinal neurocyte apoptosis in rats with chronic fluorosis and improvement after defluorination

Objective To study the spinal neurocyte apoptosis and the changes of p53 in chronic fluorosis rats, and the improvement after drinking no fluoride water. Methods One hundred twenty Wistar rats were divided into 4 groups by random number table method according to body mass, 30 rats in one group fed with high concentration NaF water (200 mg/L) to make fluorosis model and classified as high fluoride group; other 30 rats were fed with distilled water as control group; another 30 rats were fed with high concentration NaF water (200 mg/L) for 12 weeks, then fed with distilled water for 12 weeks and classified as defluorination group; the rest 30 rats were classified as defluorination control group. The content of fluoride in urine was tested after the 4th, 8th, and 12th weeks. Then the content of fluoride in urine of defluorination group and defluorination control group was tested. The high fluoride group rats and control group rats were killed after 12th week. Defluorination group rats and defluorination control group rats were killed after 24th week. Their spinal cord was collected. The expression of p53 protein in spinal cord was detected by immunohistochemistry and Western blotting. Apoptosis of the neurocyte was quantitatively analyzed by flow cytometry (FCM). Results By FCM, apoptosis of neurocyte was increased in both high fluorosis group rats and defluorination group rats compared with those in control group rats[(3.36 ± 0.71)% vs. (0.78 ± 0.65)%; (3.47 ± 0.56)% vs. (0.83 ± 0.64)%, t = 14.680, 17.003, all P 0.05)]. Immunohistochemistry and Western blotting revealed that p53 expression in spinal cord of high fluorosis group rats was increased compared with those in control group rats (422.69 ± 12.35 vs. 177.82 ± 14.16; 253.37 ± 10.42 vs. 87.14 ± 7.39, t = 77.212, 72.988, all P 0.05). Conclusions There is apoptosis of neurocytes in the spinal cord of chronic fluorosis rats; overexpression of p53 probably plays an important role in the mechanism of damage induced by excessive fluorine. Apoptosis can not be recovered after defluorination for a short time, and persistent over-expression of p53 may be one of the reasons that apoptosis of neurocytes in the spinal cord can not decrease.