Antibacterial Photodynamic Inactivation of Fagopyrin F from Tartary Buckwheat (Fagopyrum tataricum) Flower against Streptococcus mutans and Its Biofilm.

Jaecheol Kim,Keum Taek Hwang,Ryun Hee Kim,Suna Kim,Kiuk Lee

doi:10.3390/ijms22126205

Abstract

The objective of this study was to determine reactive oxygen species (ROS) produced by fagopyrin F-rich fraction (FFF) separated from Tartary buckwheat flower extract exposed to lights and to investigate its antibacterial photodynamic inactivation (PDI) against Streptococcus mutans and its biofilm. ROS producing mechanisms involving FFF with light exposure were determined using a spectrophotometer and a fluorometer. S. mutans and its biofilm inactivation after PDI treatment of FFF using blue light (BL; 450 nm) were determined by plate count method and crystal violet assay, respectively. The biofilm destruction by ROS produced from FFF after exposure to BL was visualized using confocal laser scanning microscopy (CLSM) and field emission scanning electron microscope (FE-SEM). BL among 3 light sources produced type 1 ROS the most when applying FFF as a photosensitizer. FFF exposed to BL (5 and 10 J/cm2) significantly more inhibited S. mutans viability and biofilm formation than FFF without the light exposure (p < 0.05). In the PDI of FFF exposed to BL (10 J/cm2), an apparent destruction of S. mutans and its biofilm were observed by the CLSM and FE-SEM. Antibacterial PDI effect of FFF was determined for the first time in this study.

Highlights

This study demonstrated that fagopyrin F-rich fraction (FFF) when exposed to blue light (BL) (450 nm) produced reactive oxygen species (ROS), and the ROS production of FFF was on the basis of the type 1 mechanism
S. mutans and its biofilm were destroyed by ROS produced by photodynamic inactivation (PDI) of FFF
It was elucidated that PDI with FFF (5 μg/mL) exposed to BL (10 J/cm2 ) destroyed S. mutans biofilms, which were visually confirmed by confocal laser scanning microscopy (CLSM) and field emission scanning electron microscope (FE-SEM)

Summary

Introduction

Buckwheat plants contain protofagopyrins, which are converted to fagopyrins when the plant extract is exposed to light [1]. Both protofagopyrins and fagopyrins belong to naphthodianthrone and act as photosensitizers (PS) [1,2]. Protofagopyrins were converted to fagopyrins most rapidly when exposed to blue light (BL) and fluorescence light, and fagopyrins maintained a stable structure even when exposed to various light sources for 8 h [3]. One of naphthodianthrones structurally similar to fagopyrins and protofagopyrins, has been studied as a PS for various photodynamic effects including antibacterial effects [4,5,6]. Benković et al reported the structural characteristics of fagopyrins, which are similar to hypericin [1].

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