Borassus flabellifer Linn haustorium methanol extract mitigates fluoride-induced apoptosis by enhancing Nrf2/Haeme oxygenase 1 –dependent glutathione metabolism in intestinal epithelial cells

Abstract

Fluoride is the most common cause of drinking water-associated toxicity and is known to induce various metabolic imbalances and dental/skeletal fluorosis. The present study analyzed the protective effect of Borassus flabellifer Linn. haustorium extract (BHE) against fluoride-induced intestinal redox metabolism and apoptosis. The total polyphenols and total flavonoids present in BHE were estimated to be 39.67 ± 5.14 mg gallic acid equivalent/g extract and 8.59 ± 0.74 mg quercetin equivalent. In cultured intestinal epithelial cells (IEC-6), sodium fluoride exposure-induced apoptosis mediated through antioxidant enzyme inhibition and subsequent oxidative damages. Further, there observed an increased expression of caspase-3, caspase-7, and apoptotic protease activating factor-1 (apaf-1) genes, increased cytochrome C release, and caspase 3/7 activity indicating the apoptosis- mediated cell death (p < 0.05). Upon pretreatment with BHE, the cytotoxic effect of fluoride was reduced by decreasing the expression of apoptotic genes and increased the cytochrome release as well as caspase 3/7 activity (p < 0.01). Providing the mechanistic basis, the expression of nuclear factor erythroid 2-related factor-2 (Nrf2)/haeme oxygenase-1 (HO1) gene was increased in the BHE pretreated cells; corroborating to these, there observed increased activity of glutathione biosynthetic enzymes (p < 0.05) and glutathione reductase. Hence, the protective effect of BHE may be mediated through Nrf2-mediated glutathione biosynthesis, the subsequent establishment of redox balance, and inhibition of apoptosis in intestinal epithelial cells.

Keywords:

• Borassus flabellifer Linn.
• Fluoride toxicity
• antioxidant activity
• apoptosis
• redox balance

Acknowledgement

Authors acknowledge King Saud University, Riyadh, Saudi Arabia for funding this research through Researchers Supporting Project No: RSP 2021/11. Authors are thankful to Kerala State Council for Science, Technology, and Environment (KSCSTE) and Rashtriya Uchchatar Shiksha Abhiyan (RUSA) for the support for infrastructure development.

Ethics approval

The study involved no human or animal models; hence, no ethical issues persist.

Informed Consent

No third party material is used in the manuscript, for which permission is required.

Authors contributions

JTJ conducted the cytoprotective analysis and data analysis under the supervision of AN. Rajagopal R., Alfarhan A., and Job J.T. contributed toward the phytochemical analysis as well as initial cytotoxicity analysis. The study was designed, qPCR experiments, and the manuscript was prepared by Dr. Narayanankutty, and the manuscript was approved by all authors.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data may be made available upon valid request.

Additional information

Funding

The study was funded by King Saud University, Riyadh, Saudi Arabia via Researchers Supporting Project No: RSP2021/11. The study was partially supported by KSCSTE- student Project Scheme [Letter No. 01519/SPS64/2019/KSCSTE and 01476/SPS64/2019/KSCSTE Dt: 16.01.2020] and Rashtriya Uchchatar Shiksha Abhiyan (RUSA), Govt. of India (File No. A1/SJC/RUSA-SPD/MRP/60/2019).