OBJECTIVE: To study the effect of fluoride on the oxidative stress of the rats in endemic fluorosis of coal burning and Mn-SOD expression at mRNA and protein levels.
METHODS: SD rats were divided into 2 groups (the number of female and male in each group was the same): control group and fluorosis group. All rats of the fluorosis group were fed corn dried by burning coal from endemic fluorosis areas with high fluoride content (fluoride 17 mg/kg in feed) to establish an animal model of fluorosis. In these rats, dental fluorosis was evaluated. The fluoride content in the urine was measured by fluorine ion-elective electrode method. The hepatic tissue and serum level of malonaldehyde (MDA) and the activities of superoxide dismutase (SOD) and glutathion reductase (GR) were measured by biochemical methods. The index signs of liver function were also measured from the serum. Reverse transcription-polymerase chain reaction (RT-PCR) and Western blot were performed to detect the alterations of Mn-SOD expression in the liver at mRNA and protein levels.
RESULTS: The dental fluorosis was observed in the fluorosis group, and the incidence was 11/11. The fluoride contents [(3.50 ± 2.58) mg/L] in the urine of fluorosis rats were increased as compared with the control [(1.42 ± 0.38) mg/L] (P < 0.05). AST [(223.74 ± 71.51) U/L] and total protein [(72.43 ± 5.59) g/L] of the hepatic function index in fluorosis rats showed obviously abnormal as compared with the control [(169.28 ± 53.74) U/L and (82.36 ± 7.31) g/L], respectively (P < 0.05). In the liver the content of MDA [(10.41 ± 0.59) µmol/g protein] increased as compared to the control [(5.80 ± 1.31) µmol/g protein, P < 0.01], and the activities of SOD [(62.60 ± 8.65) U/mg protein] and GR [ (1.17 ± 0.66) U/g protein] markedly decreased in the fluorosis group compared to the control [SOD (117.28 ± 8.64) U/mg protein and GR [(8.80 ± 1.59) U/g protein; P < 0.05, P < 0.01]. The level of Mn-SOD in the liver was markedly decreased in the fluorosis group [(14.83 ± 2.50) U/mg protein] as compared with the control [(34.05 ± 5.22) U/mg protein, P < 0.01]. The levels of mRNA (0.64 ± 0.15) and protein (0.84 ± 0.13) of Mn-SOD were markedly decreased in the fluorosis group as compared with the control [(0.86 ± 0.21) and (1.04 ± 0.14)], respectively (P < 0.05, P < 0.01).
CONCLUSIONS: Fluorosis can decrease the activities of Mn-SOD, which is associated with decreased levels of mRNA and protein of Mn-SOD. Down-regulation of Mn-SOD expression may play an important role in the aggravation of oxidative stress in endemic fluorosis.