Flavonoids as Potent Scavengers of Hydroxyl Radicals

Abstract

Oxidative stress is a fundamental principle in the pathophysiology of many diseases. It occurs when the production of reactive oxygen species exceeds the capacity of the cell defense system. The hydroxyl radical is a reactive oxygen species that is commonly formed in vivo and can cause serious damage to biomolecules, such as lipids, proteins, and nucleic acids. It plays a role in inflammation-related diseases, like chronic inflammation, neurodegeneration, and cancer. To overcome excessive oxidative stress and thus to prevent or stop the progression of diseases connected to it, scientists try to combat oxidative stress and to find antioxidant molecules, including those that scavenge hydroxyl radical or diminish its production in inflamed tissues. This article reviews various methods of hydroxyl radical production and scavenging. Further, flavonoids, as natural plant antioxidants and essential component of the human diet, are reviewed as compounds interacting with the production of hydroxyl radicals. The relationship between hydroxyl radical scavenging and the structure of the flavonoids is discussed. The structural elements of the flavonoid molecule most important for hydroxyl radical scavenging are hydroxylation of ring B and a C2-C3 double bond connected with a C-3 hydroxyl group and a C-4 carbonyl group. Hydroxylation of ring A also enhances the activity, as does the presence of gallate and galactouronate moieties as substituents on the flavonoid skeleton.

Flavonoid Accumulation Behavior in Response to the Abiotic Stress: Can a Uniform Mechanism Be Illustrated for All Plants?

“…They have been considered as a secondary (non-enzymatic) reactive oxygen spe-cies scavenging system in plants and humans [36]. Flavonoids exhibit direct scavenging of reactive oxygen species [36] one of the ways scavenging reactive oxygen species, flavonoids can easily donate hydrogen atom. Thus, while reactive oxygen species are inactivated by flavonoids, flavonoids return to phenoxyl radical [37].…”

Screening of Polyphenol Composition and Antiradical Capacity of Wild Erica arborea: A Native Plant Species from the Portuguese Flora

“…Our results also shown that flavonoids (kaempferol, myricetin, quercetin and luteolin glycosides) and phenolic acids (chlorogenic, neochlorogenic and caffeic acids) are associated with the antiradical activity. These compounds act as scavengers of various oxidizing species such as superoxide anion, hydroxyl radical or peroxy radicals and as quenchers of singlet oxygen [23] and their antiradical capacity arise from their ability to inhibit lipid peroxidation, chelate redox-active metals, and reduce all processes involving reactive oxygen species [24]. They may exert protection of cell structures through different mechanisms, and one in particular is their ability to increase the levels of the powerful intracellular antioxidant enzymes [25,26].…”

Probing Reducing Power for Ferryl Phytoglobins of Several Phenolic Compounds Using Their Kinetic Profiles Assisted by Chemometric Methods

“…Phenolic compounds can act as visual signals for attracting pollinating insects, phytoalexins, photoreceptors, detoxifying agents, scavenger of reactive oxygen species (ROS) such as H 2 O 2 , hydroxyl, peroxyl or alkoxyl radical; they also, contribute to different flavours and colour shades in flowers, leaves, fruits and vegetables, protect the plant cells against UV radiation, fungal, bacterium or virus pathogens, parasites and herbivores, etc. [5][6][7][8][9][10][11][12].…”

“…Flavonoids are present in all part of the plants, especially the photosynthesising plant cells of a wide range of vascular plants; up to date over 8000 flavonoid compounds have been identified and the number is still increasing. Chemically, they all have characteristic C 6 -C 3 -C 6 benzo--pyrone skeleton consists of two benzene rings (A and B, Table 1) connected through heterocyclic pyran ring (C) [5,6,8,17]. Flavonoids generally, occur in plants as glycosides (O-glycoside or C-glycoside) with a monosaccharide or disaccharide attached, but also as aglycones or methylated and sulfated derivatives [9,11].…”

“…Flavonoids generally, occur in plants as glycosides (O-glycoside or C-glycoside) with a monosaccharide or disaccharide attached, but also as aglycones or methylated and sulfated derivatives [9,11]. Flavonoids can be divided into several classes based on the structure of the carbon skeleton, substitution, conjugation, degree of hydroxylation and degree of polymerization such as, flavones, flavonols, flavanones, flavanols, isoflavones, flavanonols and anthocyanidins [5,8,18]. UV-Vis spectral features of flavonoids display two major absorption bands in the region from 200-400 nm, which are known as band I (300-385 nm) and band II (250-285 nm) [9,19,20].…”