Antioxidant Activity of Isoflavones and Their Major Metabolites Using Different in Vitro Assays

Abstract

Isoflavone phytoestrogens found mainly in soybeans and clover are widely studied phytochemicals. Genistein and daidzein, the major isoflavones found in soy, have received the most attention. However, they undergo extensive metabolism in the intestine and the liver, which might affect their biological properties, e.g. their antioxidant capacities. Furthermore, the biological activities of other naturally occurring isoflavones, for instance, glycitein from soy or biochanin A from red clover, have not yet been studied in detail. The aim of this study was to investigate the antioxidant activities of six naturally occurring isoflavones and their corresponding oxidative and bacterial metabolites. The oxygen radical absorbance capacity assay as well as the in vitro oxidation of low density lipoproteins with the conjugated diene and the thiobarbituric acid reacting substances formation as end points were used. The oxidative metabolites of genistein and daidzein as well as equol exhibited the highest antioxidant activities in all three assays. With few exceptions, they were more effective than the positive controls quercetin and ascorbic acid. Formononetin, the 4'-O-methyl ether of daidzein, showed the lowest antioxidant property. Because the antioxidant efficacy of isoflavones as effective antioxidants is evident at concentrations well within the range found in the plasma of subjects consuming soy products, this biological activity could be of physiological relevance.

Protective effects of equol and their polyphenolic isomers against dermal aging: Microarray/protein evidence with clinical implications and unique delivery into human skin

“…The present findings also support the known powerful antioxidant activities of equol (Rufer & Kulling, 2006) and further elucidate which isomers of equol contribute to these positive properties. Also, differential effects of the isomers were seen with S-equol inducing the significant expression ($1.7-fold increase over racemic and R-equol) of MT1H and PCNA considered antioxidant genes protecting against metal toxicity and DNA damage (Hanada et al, 1998;Takahashi et al, 2005).…”

Astragali Radix elicits anti-inflammation via activation of MKP-1, concomitant with attenuation of p38 and Erk

“…Polyphenolic compounds from various herbs have been found to work as phytoestrogens (Mitchell et al, 2000;Gong et al, 2003;Klinge et al, 2005), antioxidants (Rüfer and Kulling, 2006), tyrosine kinase inhibitors (Kousidou et al, 2006), and anti-inflammatory compounds (Jung et al, 2007). HPLC analysis of AR displayed the presence of several secondary metabolites such as polyphenolic flavonoids including formononetin (Fig.…”

Soy, phytoestrogens and their impact on reproductive health

“…The non-genomic effects mediated by ERs usually involve rapid cellular responses leading to nitric oxide release, calcium flux, and/or activation of different signaling pathways, such as the AMP-activated protein kinase (AMPK), mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K) pathways, as observed in various cell lines (D'Eon et al, 2005;Ropero et al, 2006). In addition to their estrogenic actions, isoflavones have been reported to possess antioxidant (Rufer and Kulling, 2006) and tyrosine kinase inhibitor (Akiyama et al, 1987) properties. They may also act as peroxisome proliferator-activated receptor gamma (PPAR)c ligands (Rosen et al, 1999).…”