Antioxidant potential of styrene pyrone polyphenols from Inonotus obliquus: A combined experimental, density functional theory (DFT) approach and molecular dynamic (MD) simulation

Abstract

Polyphenols containing styrene pyranone skeleton are unique to porous fungi. Inonotus obliquus (IO) is a medicinal and edible porous fungus. Twelve phenolic compounds containing four styryl pyranone polyphenols from IO were isolated and identified in this work. The antioxidant ability of the isolates was characterized utilizing the ferric reducing antioxidant power (FRAP) assay and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) radical scavenging test. Styrylpyranone polyphenols, especially methylinoscavin B, could capture free radicals better than other phenolic compounds, and quantum chemical calculations also confirmed this evaluation. The density functional theory (DFT) calculation data showed that Styrylpyranone polyphenols, especially methylinoscavin B, have a lower energy gap, higher softness and higher electronic chemical potential than other phenolic compounds. The bond dissociation energy values of the bond in C7ʹ O–H of the methylinoscavin B molecule are less than those in C11 and C6ʹ O–H when reacting with ∙OOH (selected as a representative free radical). On the basis of calculations, hydrogen atom transfer (HAT) is supposed to be a preferred mechanism over single electron transfer (SET) when phenolic compounds react with free radicals. Moreover, after treatment with final concentrations of 0.5, 1, 2, 3, 4 and 5 μM phelligridin E (PHE), the activity of SOD1 increased by 70.15%, 11.36%, 145.45%, 172.73%, 205.05% and 275.23%, respectively. The molecular dynamics simulation (MD) study of PHE employed SOD1 (PDB ID: 6FN8). The MD results showed that the hydrogen bonds between ASP147 of SOD1 and PHE promote GLU223-ARG224 to form a stable C coil after combining with PHE. The formation of the C Coil enhanced the stability of the electrostatic loop (EL) of SOD1 and the rate of diffusion of the superoxide anion to the active site. Styrylpyrone polyphenols of Inonotus obliquus origin have the potential to be a source of vigorous free radical scavengers and antioxidant enzyme activators.