Myricetin suppresses oxidative stress-induced cell damage via both direct and indirect antioxidant action

Abstract

We evaluated the cytoprotective effect of myricetin on oxidative stress damaged cells by assessment of the scavenging effect of reactive oxygen species (ROS) and the activities of antioxidant enzymes. Myricetin showed the scavenging effect of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals on intracellular ROS. In addition, myricetin restored the activity and protein expression of cellular antioxidant defense enzymes such as superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) reduced by hydrogen peroxide (H₂O₂) treatment. H₂O₂-induced cellular DNA and lipid damages, and myricetin was found to prevent the DNA damage shown by inhibition of DNA tail and it decreased nuclear phospho-histone H2A.X expression, which are both markers for DNA strand breakage. Membrane lipid peroxidation was also attenuated as shown by inhibition of TBARS formation and of fluorescence intensity of diphenyl-1-pyrenylphosphine (DPPP). These results suggest that myricetin protects cells against H₂O₂-induced cell damage via inhibition of ROS generation and activation of antioxidant enzymes.

Introduction

The univalent reduction of molecular oxygen results in the generation of ROS including superoxide anions, hydroxyl radicals as well as hydrogen peroxide (Halliwell and Gutteridge, 1984a, Halliwell and Gutteridge, 1984b, Gutteridge and Halliwell, 2000). Excessive ROS can damage sugars, proteins, polyunsaturated lipid, and DNA, thus leading to degenerative processes and diseases (Halliwell and Gutteridge, 1988, Sawada, 2009, Wakamatsu et al., 2008, Eleuteri et al., 2009, Mirshafiey and Mohsenzadegan, 2008, Hori and Nishida, 2009, Du et al., 2008, Roessner et al., 2008). However, aerobic organisms have antioxidant defense systems, protecting against oxidative stress-induced damage. These enzymatic defense mechanisms include superoxide dismutase (SOD), which catalyses the dismutation of the superoxide anion to H₂O₂; catalase (CAT), which converts H₂O₂ to water and an oxygen molecule; and seleno-dependent glutathione peroxidase (GPx), which catalyses the degradation of H₂O₂ and hydroperoxide through the utilization of glutathione (Liochev and Fridovich, 2007, Goldstone et al., 2006).

Flavonoids are structurally heterogenous polyphenolic compounds, which are widely distributed in plant foods, and which may exert beneficial effects, including protection from cardiovascular disease, cancer, diabetes, and neurodegenerative disorders (Steinmetz and Potter, 1991, Grassi et al., 2009, Mandel et al., 2008, Lu et al., 2008, Richter et al., 1999). Most of these beneficial effects originate from their potent antioxidant and free radical scavenging properties, as well as their ability to modulate many cellular enzyme functions (Abdel-Raheem et al., 2009, Zhang et al., 2009, Piao et al., 2008, Middleton et al., 2000). Flavonoids can provide both short and long-term protection against oxidative stress via a variety of mechanisms including acting as antioxidants themselves, directly neutralizing toxic ROS through the donation of hydrogen ions, inducing antioxidant enzymes, or modulating cell signaling pathways (Williams et al., 2004).

Myricetin (3,3′,4′,5,5′,7-hexahydroxylflavone) is a natural flavonoid, found in many fruits, vegetables, herbs, and other plants. Recently, it has been reported that myricetin is highly effective with respect to scavenging ROS and exhibits a cytoprotective effect against oxidative stress (Shimmyo et al., 2008, Dajas et al., 2003, Fawcett et al., 2002, Molina-Jiménez et al., 2004, Molina-Jiménez et al., 2005), anti-inflammatory effect (Park et al., 2008, Wang and Mazza, 2002, Alexandrakis et al., 2003), and anti-mutagenic effect (Hayder et al., 2008, Duthie and Dobson, 1999). The present study focused on investigating the cytoprotective effect of myricetin via activation of antioxidant defense enzymes.