Identification of novel and potent Nrf2 activators from medicinal plants

Abstract

Oxidative stress has been implicated in the pathogenesis of various age-related chronic diseases (cancer, cardiovascular disease, chronic obstructive pulmonary disease and neurodegenerative disease). The antioxidant response pathway, which is regulated by the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2), shields cells from oxidative stress by enhancing the expression of cytoprotective genes and enzymes. Transcriptional regulator Nrf2 induces the expression of detoxification enzymes (Phase II detoxifying and antioxidant enzymes) such as glutathione S-transferase (GST) and metabolic pathway enzymes for glutathione synthesis. Antioxidant therapy with the Nrf2 activation is a strategy to prevent cells from exposure to the oxidants and correct cellular redox homeostasis. Plant-derived Nrf2 activators might be used to stimulate the body's antidefense mechanisms. Our study was focused on the discovery of novel Nrf2 activators as therapeutic agents from medicinal plants. A variety of commercially available ethanolic extracts were screened for Nrf2 activity using an Nrf2-luciferase reporter cell line (AREc32), and Valeriana officinalis (root), Cynara scolymus (leaves) and Salix alba (bark) were identified to be part of the most potent samples. Sequential extraction and bioassay-guided fractionation of these plants led to the isolation of compounds identified as Nrf2 activators. NMR and LC/HRMS analysis confirmed the structures. As GST is among the Nrf2 upregulated genes, changes in GST activity upon incubation with the isolated Nrf2 activators were determined in a HepG2 cell line resulted in an increased GST activity. These compounds augmented the intracellular glutathione (GSH) and cysteinylglycine (CysGly) levels by promoting the nuclear translocation of Nrf2 that was determined by the HPLC fluorescence detection method. This thesis describes the screening of ethanolic extracts of 91 medicinal herbal samples from Integria Health care, Ballina, NSW, Australia. This study led to the isolation of 8 pure compounds that are known, but the Nrf2-ARE related pharmacological activity is reported first time with the sequential extraction of these plants. Natural products undoubtedly fulfill irreplaceable drug discovery roles and are an invaluable source for drug candidates and leads. The Nrf2-activity of these compounds has demonstrated their potential as a therapeutic agent against oxidative stress-related diseases (e.g., COPD, diabetes, cardiovascular diseases). These Nrf2 activators have been shown to activate the Nrf2-ARE pathway and its regulated genes and enzymes to protect the cells from oxidative damage. Future directions call for a further biological evaluation to illustrate the detailed mechanisms by which these Nrf2 active compounds activate the Nrf2-ARE pathway and a sufficient pharmacological investigation in vivo to confirm the prevention of oxidative stress-induced diseases.

Date of Award	2022
Original language	English