# C-Ring Structure-Dependent Redox Properties of Flavonoids Regulate the Expression of Bioactivity

## TL;DR

This study shows how the C-ring structure of flavonoids affects their redox properties and biological activity, especially in gut-like conditions.

## Contribution

The study reveals how C-ring structure influences flavonoid stability, redox behavior, and sympathetic activation in acidic and neutral environments.

## Key findings

- EC was more stable than Q and Tax at pH 7, with EC forming oxidized oligomers while Tax and Q degraded.
- EC and Tax generated O2•− at pH 7 after 45 minutes, while Q only scavenged O2•− after 24 hours.
- EC increased catecholamine excretion and blood flow, suggesting a role in sympathetic activation.

## Abstract

(−)-Epicatechin (EC), taxifolin (Tax), and quercetin (Q) are flavonoids with different C-ring structures. We compared their physicochemical properties and biological activities. The comparison of their stability and redox properties was conducted at mildly acidic or neutral conditions mimicking the plant vacuole or gut, and their sympathetic hyperactivation ability was examined using catecholamine (CA) excretion and blood flow. At pH 5, flavonoids were stable, but at pH 7, their retention rates decreased in the order EC > Q > Tax. LC-MS analysis detected brown oxidized oligomers in EC, while Tax and Q primarily yielded degradation products. All flavonoids exhibited O2•− scavenging activity after incubation at pH 5. At pH 7 after 45-min, EC and Tax promoted O2•−, while Q only scavenged O2•− after 24-hr incubation, EC’s properties decreased but Tax’s properties enhanced. Computational chemistry analysis indicated EC has higher reactivity compared to Tax and Q. EC caused a significant increase in CA excretion and blood flow, which were not observed with Tax or Q or 24-h cultured EC. These results suggest that the C-ring structure of flavonoids plays a crucial role in their stability and redox properties. Furthermore, reactive oxygen species generated by flavonoids in the gut may exert beneficial effects through sympathetic activation.