Catechin Action

Free Radical Scavenging/Antioxidant Actions of Catechins 

Preventing Lipid Peroxidation Due to Oxidative Stress with Catechins 

---

Catechins are water-soluble however, they can be rendered insoluble by chemical reaction (Yayabe, 2001). Insoluble catechins do not lose their phenol hydroxyl groups, and their anti-bacterial and deodorising actions remain almost unaffected. In this form they are useful as natural anti-bacterial and deodorising materials for application to fibres and plastics. 

KAJiMOTO G (1963) On the antioxidative components and antiseptic components in tea. Part 111. The synergistic action of caffeine to catechin components , Nihon Shokuhin... 

SCOTT B c, BUTLER J, HALLIWELL B and ARUOMA o I (1993) Evaluation of the antioxidant actions of ferulic acid and catechins , Free Radical Res Commun, 19, 241-53. 

Concerning the mechanism of action of catechins, studies carried out on S. aureus and E. coli cells by Ikigai et al. [72] reported that their bactericidal effect is primarily involved in the damage of bacterial membranes catechins induce a rapid leakage of small molecules entrapped in the intraliposomal space, determining the aggregation of the liposomes. These actions cause damage in the membrane lipid bilayer and cell death (Table 1). 

Table 1 Mechanism of action hypothesized for catechins and proanthocyanidins... 

The mode of action of catechins on eukaryotic microorganisms has been studied little. In early investigations, Toyoshima et al. [93] suggested that catechins are able to attack the cell membrane of Trichosporon mentagrophytes causing lysis of the conidia and hyphae (Table 1). 

Model systems indicate that aldehydes may also be produced by the action of polyphenoloxidases on amino acids in the presence of catechin, all of which are present in coffee beans at some stage between green and roasted. For example, valine yields isobutanal, leucine yields isopentanal, and isoleucine yields 2-methyl-butanal.14 Some of these aldehydes probably undergo condensation reactions in the acidic medium of the roasted bean when moisture is present.15 Some dienals in green coffee beans have recently been identified as (E,E)-2,4- and (E,Z)-2,4-nonadienal and (E,E)-2,4- and (E,Z)-2,4-decadienal.18... 

Flavonoids exhibit protective action against LDL oxidation. It has been shown [145] that the pretreatment of macrophages and endothelial cells with tea flavonoids such as theaflavin digallate diminished cell-mediated LDL oxidation probably due to the interaction with superoxide and the chelation of iron ions. Quercetin and epicatechin inhibited LDL oxidation catalyzed by mammalian 15-lipoxygenase, and are much more effective antioxidants than ascorbic acid and a-tocopherol [146], Luteolin, rutin, quercetin, and catechin suppressed copper-stimulated LDL oxidation and protected endogenous urate from oxidative degradation [147]. Quercetin was also able to suppress peroxynitrite-induced oxidative modification of LDL [148],... 

Conversion of green tea catechins to black tea theaflavins, etc., by the action of Camellia sinensis polyphenoloxidase. 

Little information about the mechanism of action of flavonoids is anticipated from in vivo studies. The mechanism of catechin and morin seems to be related to an increase of the activity of detoxifying enzymes like glutathione-S-transferase and NADPH quinone reductase [198, 211]. Similarly, EGCG effect at the colonic level is associated to an increase in tissue superoxide dismutase levels, suggesting that it may act through a potentiation of the antioxidative defense [210]. 

Resveratrol has also been reported to offer protection against cardiovascular disease, such as coronary heart disease. The effects of resveratrol on factors implicated in the development of coronary heart disease - human platelet aggregation and the synthesis of eicosanoids (lipids) from arachidonate by platelets - were investigated and compared with the actions of other wine phenolics - catechin (1.39), epicatechin (7.18a), and quercetin (1.43) - and the antioxidants a-tocopherol (7.10a), hydroquinone and butylated hydroxytoluene. Resveratrol and quercetin demonstrated a dose-dependent inhibition of platelet aggregation, whereas the other compounds tested were inactive. Resveratrol also inhibited the synthesis of the eicosanoids in a dose-dependent manner, whereas the other phenolics were less effective of not effective at all. Removal of the alcohol from the wine did not diminish the effect on platelet aggregation (Pace-Asciak et al., 1995 Goldberg et al., 1995). 

Inhibitory Action of Green Tea Catechins, Gallate Esters, and Other... 

Next we evaluated a series of resveratrol analogs and catechins for their ability to compete for specific [3H]-resveratrol binding in PII fraction. Interestingly, polyphenols that display neuroprotective action are the most potent ones to compete for specific [3H]-resveratrol binding with K values ranging from 25 nM (for EGCG) to 102 nM (for resveratrol), whereas molecules including EC and EGC were inactive. 

---