Isoflavones antioxidant capacity

Isoflavones, a special kind of polyphenols, show similar behaviour regarding absorption and metabolism to this family of compounds. Thus, Scalbert et al [12] put forward two primary sources of evidence concerning the absorption of polyphenols first, indirect evidence for their absorption through the gut barrier as can be seen from the increase in the antioxidant capacity of the plasma following the consumption of polyphenol-rich foods, and second, their recovery in urine after the ingestion of given amounts of a particular polyphenol. 

An ex vivo study with rat hepatocytes found a strong correlation between the cytotoxicity of a flavonoid and its ability to induce an early collapse of the mitochondrial transmembrane potential [6]. In contrast, nontoxic flavonoids had no effect on the transmembrane potential. As discussed previously, the ability of flavonoids and isoflavones to inhibit mitochondrial respiration and adenosine triphosphate (ATP) synthesis or uncouple oxidative phosphorylation represents a potential mechanism whereby they can trigger dissipation of the transmembrane potential and thus cytochrome c-dependent apoptosis. Thus, it is interesting to note that epicatechin, which had little or no proapoptotic effect in cancer cells [64] and exerted antiapoptotic effects in primary culture models [7,8,59], had essentially no inhibitory effect against complex I, II, or HI activity and FoFi-ATPase activity [24,25]. However, the preceding discussion has also indicated that the pro- or antiapoptotic effects of flavonoids may be explained by more specific mechanisms, potentially independently of their antioxidant capacity. These include effects on protein kinase cascades and gene expression, including MARK and the Bcl-2 family of proteins. 

Heneman, K.M., Chang, H.C., Prior, R.L., and Steinberg, F.M. 2007. Soy protein with and without isoflavones fails to substantially increase postprandial antioxidant capacity. J Nutr Biochem 18, 46-53. 

Vega-Lopez, S., Yeum, K.J., Lecker, J.L., Ausman, L.M., Johnson, E.J., Devaraj, S., Jialal, I., and Lichtenstein, A.H. 2005. Plasma antioxidant capacity in response to diets high in soy or animal protein with or without isoflavones. Am J Clin Nutr 81, 43 9. 

Flavonoid Compounds based on two benzene rings linked by a three-carbon chain. They are important pigments and nutraceuticals due to their antioxidant capacity. Flavonoids include anthocyanins, chalcones, flavones, flavonols, and isoflavones. 

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