Sodium fluoride generates ROS and alters transcription of genes for xenobiotic metabolizing enzymes in adult zebrafish (Danio rerio) liver: expression pattern of Nrf2/Keap1 (INrf2)

Abstract

Anthropogenic activities have resulted in an increase in the level of fluoride (F), a natural pollutant in water, causing great threat to the aquatic organisms including fishes. Earlier we reported that sodium fluoride (NaF) exposure alters histological ultrastructure in zebrafish (Danio rerio) liver evidenced by hyperplasia, cytoplasmic degeneration, heteropycnosis etc. In this study, zebrafish were exposed to 7.5, 15 and 30 mg NaF l⁻¹ for 30 days as well as to 15 mg NaF l⁻¹ for 90 days. In NaF treated fish, generation of reactive oxygen species (ROS), depletion of glutathione (GSH) and increase in malondialdehyde (MDA) content along with enhanced activities of oxyradical-scavenging enzymes like catalase (CAT) and superoxide dismutase (SOD) were recorded. Activity of GSH-metabolizing enzyme, glutathione-S-transferase (GST) was also enhanced. The mRNA levels of genes for xenobiotic metabolizing enzymes (XMEs) like cytochrome P450 1A (Cyp1A), NADPH Q Oxidase 1 (Nqo1) and Heme Oxygenase 1 (Ho-1) increased along with nuclear factor (erythroid-derived 2)-like 2 (Nrf2) whereas Kelch-like ECH-associated protein 1 (Keap1) decreased in the treated groups in comparison to their controls. The increase in Nrf2 protein levels in NaF treated fish confirmed its key regulatory role in F-induced oxidative stress. Chromatin condensation and nuclear fragmentations were evidenced in NaF-treated groups indicating possible induction of apoptosis. The modulation of these toxicological parameters at genetic and biochemical levels may be used as an early warning for the environmental risk assessment of F⁻ toxicity to aquatic organisms including fishes.

• Oxidative stress
• reactive oxygen species
• sodium fluoride
• xenobiotic metabolizing enzymes
• zebrafish liver

Acknowledgements

Authors are also thankful to Dr. Jolly Basak, Department of Biotechnology for her help in carrying out the Real Time PCR. D.M. is grateful for a DBT Project Fellowship and R.S. is thankful for the UGC BSR meritorious fellowship. The authors also thank the editor and the reviewers for their valuable comments, which helped to improve the article.

Declaration of interest

Authors acknowledge DBT (Department of Biotechnology) Project (No. BT/54/NE/TBP/2010) and University Grants Commission (UGC), New Delhi for the Centre for Advanced Studies (CAS) grant to the Department of Zoology. Authors declare that they have no conflict of interest.