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A BIOASSAY-GUIDED INVESTIGATION INTO THE CANCER CHEMOPREVENTIVE POTENTIAL OF SELECTED NON-DIETARY PLANTS AND SELECTED FLAVONOIDS

Zavoianu, A-G (2020) A BIOASSAY-GUIDED INVESTIGATION INTO THE CANCER CHEMOPREVENTIVE POTENTIAL OF SELECTED NON-DIETARY PLANTS AND SELECTED FLAVONOIDS. Doctoral thesis, Liverpool John Moores University.

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Abstract

A selection of twelve non-dietary plants were subjected to Soxhlet extraction with n-hexane and methanol and the crude extracts were screened for Nrf2 induction potential using a AREc32 cell-based luciferase gene reporter assay. Screening for free-radical scavenging activity using the DPPH assay was also performed. The highest increase in Nrf2 induction was achieved by the methanol extract of Centaurea dichroa Boiss.& Heldr. (CD-Me, 250 µg/ml), with a 22.7-fold to control induction, followed by the n-hexane extract of Solanum anguivi Lam. (SA-He, 100 µg/ml), with 20.2-fold to control induction.The Nrf2/ARE signaling pathway was also up-regulated by two other methanol extracts, of Centaurea pamphylica Boiss. & Heldr. (CP-Me, 100 µg/ml) and Gardenia ternifolia Schumach. & Thonn. (GT-Me, 750 µg/ml), with 11.22-fold and 8.94-fold to control luciferase induction, respectively. The bioassay guided investigation led to further fractionation of the bioactive methanol extracts so that the less polar methanolic fractions F3 and F4 of CP-Me and GT-Me increased Nrf2 activity more than their respective crude extracts; up to 12.6 - 13.4-fold for CP-Me fractions, and up to 11.6 – 12.6-fold for GT-Me fractions. Moreover, compounds isolated from the bioactive fractions indicated flavonoid type structures, identifying sakuranetin for the first time in Gardenia ternifolia Schumach.& Thonn. Stachyose, mannitol and betulinic acid were also identified as precipitates from solvent extraction. Because of limited amount of material, various types of flavonoids such as flavones, flavanones and flavonols were purchased with the purpose of screening them for Nrf2 activity in AREc32 cells. The flavonoids alone increased the luciferase activity to no more than 3.1-fold (hesperetin, 40 µM), with most reaching slightly above 2-fold induction, indicating a possible synergy in the way of action of the natural products since mixtures of compounds showed higher bioactivity in the same assay. Fractions F3 of CP-Me and GT-Me showed the highest free radical-scavenging potential in the DPPH assay, with IC50 values of 0.072 mg/ml and 0.132 mg/ml respectively (IC50 exerted by positive control quercetin was 0.005 mg/ml). Finally, all flavonoids tested offered protection against oxidative stress induced by ethacrynic acid (ETA) in MCF-7 cells (LD50=68.5 µM), with the flavone velutin (2.5 µM) and flavanone sakuranetin (20 µM) increasing the LD50 of ETA more than 200 times, while all flavonoid pretreatment conditions generally increased the LD50 of ETA more than 9 times.

Item Type: Thesis (Doctoral)
Uncontrolled Keywords: cancer chemoprevention; AREc32; Nrf2; Gardenia ternifolia; Centaurea dichroa; Solanum anguivi; ethacrynic acid
Subjects: R Medicine > RS Pharmacy and materia medica
T Technology > TP Chemical technology
Divisions: Pharmacy & Biomolecular Sciences
Date Deposited: 17 Sep 2020 19:16
Last Modified: 18 Sep 2020 08:21
DOI or Identification number: 10.24377/LJMU.t.00013638
Supervisors: Ritchie, K, Sarker, S and Nahar, L
URI: https://researchonline.ljmu.ac.uk/id/eprint/13638

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