Molecular Mechanism of Changes in Gene Expression of Cytosolic Cu/Zn SOD, Lipid Peroxidation and Hepatic Function Impairments during Experimental Fluorosis

Background: Long term intake of high amount of fluoride leads to fluorosis causing metabolic, functional and structural damages affecting many tissues and organs including dental and skeletal manifestations. The liver is the most susceptible organ to fluoride toxicity because of its active and major role in digestion and detoxification.

Aim: The present study aims to elucidate the effects of sodium fluoride on hepatic function biomarkers, lipid peroxidation and gene expression of Cu/Zn SOD in albino rats.

Materials and Methods: Wistar albino rats were randomly assigned to three groups. The control rats were given 1 ml deionized water orally for 40 days. Groups II and III were administered 300 and 600 mg NaF/kg b.w. /day for the same period. Animals were sacrificed under anaesthesia, liver tissue was excised and used for biochemical and molecular analysis. The level of fluoride and lipid peroxidation (MDA) as well as reduced glutathione (GSH) content was determined. The activities of cytosolic copper/zinc superoxide dismutase (Cu/Zn SOD), aminotransferases (ALT and AST), lactate dehydrogenase (LDH) and alkaline phosphatase (ALP) in the hepatic tissue were determined. The analysis of gene expression of Cu/Zn SOD in the liver was determined using Real-time PCR.

Results: The results revealed significantly (P<0.0001) higher concentration of fluoride and MDA in the liver of rats exposed to fluoride when compared to control. The GSH content reduced significantly (P<0.0001) in fluorotic rats. The activities of hepatic function biomarkers viz; ALT, AST, LDH and ALP elevated significantly (P<0.0001) compared to the control. An elevation of 108.60% (ALP), 121.45% (AST), 33.77% (LDH) and least 24.40% (ALT) was found in rats treated with 300 mg/L fluoride and maximum elevation of 226.20% (ALP), 211.52% (AST), 57.75% (LDH) and least 56.79% (ALT) was registered in rats exposed to 600 mg/L fluoride in drinking water. The activity of cytosolic Cu/Zn SOD decreased significantly (P<0.0001) in fluorotic rats. Pearson’s bivariate correlation and simple linear regression analysis exhibited strong positive correlation between level of hepatic tissue fluoride and activities of ALT (Pearson r= 0.85), AST (Pearson r= 0.94), LDH (Pearson r= 0.89), ALP (Pearson r= 0.86) and in MDA (Pearson r=0.984) while negative correlations existed between levels of fluoride and GSH (Pearson r=-0.93) as well as activity of Cu/Zn SOD (Pearson r= -0.99). The gene expression of cytosolic Cu/Zn SOD was significantly (P<0.0001) reduced in fluorotic rats.

Conclusion: The present study revealed that fluoride declined the antioxidant activity of hepatic Cu/Zn SOD at biochemical as well as molecular level which leads to oxidative stress and tissue damage. This further affirms by increased activities of hepatic function biomarkers in correlation with high fluoride level during experimental fluorosis.