A novel pathway for the photooxidation of catechin in relation to its prooxidative activity

Shunichi Shishido,Yoshimi Niwano,Taro Kanno,Hirotaka Matsuo,Takuji Nakashima,Masato Iwatsuki,Keisuke Nakamura,Rei Miyano,Hiroshi Egusa

doi:10.1038/s41598-018-31195-x

Abstract

In the present study, we evaluated the prooxidative mode of action of photoirradiated (+)-catechin at 400 nm in relation to reactive oxygen species generation and its possible application to disinfection. Photoirradiation of (+)-catechin at a concentration of 1 mg/mL yielded not only hydrogen peroxide (H2O2) but hydroxyl radical (·OH) in a total amount of approximately 20 μM in 10 min. As a result, photoirradiated catechin killed Staphylococcus aureus, and a > 5-log reduction in viable bacteria counts was observed within 20 min. Liquid chromatography-high-resolution-electrospray ionization-mass spectrometry showed that photoirradiation decreased the (+)-catechin peak (molecular formula C15H14O6) whilst it increased two peaks of a substance with the molecular formula C15H12O6 with increasing irradiation time. Nuclear magnetic resonance analysis revealed that the two C15H12O6 peaks were allocated to intramolecular cyclization products that are enantiomers of each other. These results suggest that photoirradiation induces oxidation of (+)-catechin resulting in the reduction of oxygen to generate H2O2. This H2O2 is then homolytically cleaved to ·OH, and alongside this process, (+)-catechin is finally converted to two intramolecular cyclization products that are different from the quinone structure of the B ring, as proposed previously for the autoxidation and enzymatic oxidation of catechins.

Highlights

Polyphenolic compounds are widely known for their antioxidative activity[1,2,3]
In the case of the photolysis of H2O2, as one of the artificial ·OH generation systems, the bactericidal effect depended on the photoirradiation time, indicating that bacterial death was dependent on the ·OH yield[13]
The present study demonstrated that photoirradiation of (+)-catechin has significant prooxidative potential, and can exert a bactericidal effect against S. aureus with a >5-log reduction in viable counts within 20 min

Summary

Introduction

The antioxidative activity of polyphenolic compounds is mediated by the autoxidation of phenolic hydroxyl groups[4,5], which in turn leads to radical scavenging activity against free radicals such as the superoxide anion radical (O2−·) and hydroxyl radical (·OH). In the case of the photolysis of H2O2, as one of the artificial ·OH generation systems, the bactericidal effect depended on the photoirradiation time, indicating that bacterial death was dependent on the ·OH yield[13]. This idea tempted us to combine the prooxidative activity of polyphenols and the photolysis of H2O214–16. Since the prooxidative activity of catechins has been intensively examined[7,9,10,11,17], we chose (+)-catechin as an authentic polyphenol, and the purpose of the present study was to verify the photooxidation of (+)-catechin in relation to ROS generation and bactericidal activity

Objectives

Methods

Results

Conclusion