Daidzein as an antioxidant of lipid: effects of the microenvironment in relation to chemical structure.
Isoflavone daidzein (D, pK a1 = 7.47 +/- 0.02 and pK a2 = 9.65 +/- 0.07) was, through a study of the parent compound and its three methyl anisol derivatives 7-methyldaidzein (7-Me-D, pK a = 9.89 +/- 0.05), 4'-methyldaidzein (4'-Me-D, pK a = 7.43 +/- 0.03), and 7,4'-dimethyldaidzein (7,4'-diMe-D), found to retard lipid oxidation in liposomal membranes through two mechanisms: (i) radical scavenging for which the 4'-OH was more effective than the 7-OH group in agreement with the oxidation potentials: 0.69 V for 4'-OH and 0.92 V for 7-OH versus Ag/AgCl in acidic solution and 0.44 V for 4'-O(-) and 0.49 V for 7-O(-) in alkaline solution and (ii) change in membrane fluidity through incorporation of the isoflavones, in effect hampering radical mobility. The radical scavenging efficiency measured by the rate of the reaction with the ABTS(*)(+) in aqueous solution followed the order D > 7-Me-D > 4'-Me-D > 7,4'-diMe-D, as also found for antioxidant efficiency in liposomes when oxidation was initiated with the water-soluble AAPH radical and monitored as the formation of conjugate dienes. For oxidation initiated by the lipid-soluble AMVN radical, the antioxidant efficiency was ranked as 4'-Me-D > D > 7,4'-diMe-D > 7-Me-D, and change in fluorescence anisotropy of fluorescent probes bound to the membrane surface or inside the lipid bilayer confirmed the effects of isoflavones on the membrane fluidity, especially for 7,4'-diMe-D.
State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, China.
Jun
J
Liang
Yu-Xi
YX
Tian
Li-Min
LM
Fu
Tian-He
TH
Wang
Hai-Jun
HJ
Li
Peng
P
Wang
Rui-Min
RM
Han
Jian-Ping
JP
Zhang
Leif H
LH
Skibsted
D000975:Antioxidants / Q000737:chemistry* / Q000494:pharmacology*; D016166:Free Radical Scavengers / Q000737:chemistry / Q000494:pharmacology; D007529:Isoflavones / Q000737:chemistry* / Q000494:pharmacology*; D007700:Kinetics; D008051:Lipid Bilayers / Q000138:chemical synthesis / Q000737:chemistry; D015227:Lipid Peroxidation / Q000187:drug effects*; D008081:Liposomes / Q000138:chemical synthesis / Q000737:chemistry; D008560:Membrane Fluidity / Q000187:drug effects; D010084:Oxidation-Reduction
D000975:Antioxidants; D016166:Free Radical Scavengers; D007529:Isoflavones; D008051:Lipid Bilayers; D008081:Liposomes; C004742:daidzein