Analysis of Polyphenolic Composition, Antioxidant Power and Stress-Response Effects of Fractionated Perilla Leaf Extract on Cells In Vitro

Background/Objectives: The Perilla frutescens plant has historically been used to protect against inflammation and redox stress. This has been attributed in part to the high content of various polyphenols. Despite this, the complement of polyphenolic components in Perilla extract is not yet fully defined. The aim of this study was to characterise the polyphenolic composition in Perilla extract, and its effect on the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2), which during inflammation and oxidative stress binds to the antioxidant response element (ARE) found on the promoter of phase II antioxidant enzymes. Methods: Following extraction using four solvents of different properties, the total phenolic, flavonoid and ortho-diphenolic content of Perilla extract were determined. Individual phenolic compounds were identified and quantified by RP-HPLC. Dual Luciferase assay using a reporter plasmid containing a human NQO1 ARE-luciferase fusion was employed to determine the potential protective effect of the Perilla fractions against redox stress. Results: HPLC analysis revealed that the highest phenolic content was present in the polar extracts. A total of 35 distinct polyphenolic compounds were identified, with rosmarinic acid being the major constituent. On cells in vitro, the methanol Perilla fraction showed protection against redox stress, with the luciferase assay displaying up to 1.5 fold increase in the induction of the human NQO1 ARE-luciferase reporter. Conclusions: While Perilla extract seems to be mainly protecting against inflammation and redox stress through the action of rosmarinic acid, further work is required on the synergystic effects between different polyphenols.