title: Effect of circulating forms of soy isoflavones on the oxidation of low density lipoprotein.
abstract: Soy isoflavones are thought to have a cardioprotective effect that is partly mediated by an inhibitory influence on the oxidation of low density lipoprotein (LDL). However, the aglycone forms investigated in many previous studies do not circulate in appreciable quantities because they are metabolised in the gut and liver. We investigated effects of various isoflavone metabolites, including for the first time the sulphated conjugates formed in the liver and the mucosa of the small intestine, on copper-induced LDL oxidation. The parent aglycones inhibited oxidation, although only 5% as well as quercetin. Metabolism increased or decreased their effectiveness. Equol inhibited 2.65-fold better than its parent compound daidzein and 8-hydroxydaidzein, not previously assessed, was 12.5-fold better than daidzein. However, monosulphated conjugates of genistein, daidzein and equol were much less effective and disulphates completely ineffective. Since almost all isoflavones circulate as conjugates, these data suggest that despite the increased potency produced by some metabolic changes, isoflavones may not be effective antioxidants in vivo unless they are deconjugated again.
authors.affiliation: School of Food Biosciences, Hugh Sinclair Human Nutrition Unit, University of Reading, Whiteknights P.O. Box 226, Reading RG6 6AP, UK.
authors.forename: Rufus
authors.initials: R
authors.lastname: Turner
authors.forename: Tobias
authors.initials: T
authors.lastname: Baron
authors.forename: Siegfried
authors.initials: S
authors.lastname: Wolffram
authors.forename: Anne Marie
authors.initials: AM
authors.lastname: Minihane
authors.forename: Aedin
authors.initials: A
authors.lastname: Cassidy
authors.forename: Gerald
authors.initials: G
authors.lastname: Rimbach
authors.forename: Peter D
authors.initials: PD
authors.lastname: Weinberg
mesh_terms: D000328:Adult; D003300:Copper / Q000037:antagonists & inhibitors; D024202:Electrophoretic Mobility Shift Assay; D006801:Humans; D007529:Isoflavones / Q000097:blood / Q000737:chemistry / Q000494:pharmacology*; D008077:Lipoproteins, LDL / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism*; D008297:Male; D015394:Molecular Structure; D010084:Oxidation-Reduction / Q000187:drug effects; D013025:Glycine max / Q000737:chemistry* / Q000378:metabolism; D013053:Spectrophotometry
chemical_list: D007529:Isoflavones; D008077:Lipoproteins, LDL; D003300:Copper