Inhibition of phthalocyanine-sensitized photohemolysis of human erythrocytes by polyphenolic antioxidants: description of quantitative structure-activity relationships

Polyphenolic antioxidants protected against Al-phtlalocyanine tetrasulfonate-sensitized photohemolysis of human erythrocytes. A quantitative structure-activity relationship has been obtained to describe the protective effects of di- and trihydroxybenzenes: log cI(50) (muM) = (1.8620 +/- 1.5565) + (3.6366 +/- 2.8245) E-7(1) (V) - (0.4034 +/- 0.0765) log P (r(2) = 0.8367), where cI(50), represents the concentrations of compounds for the 2-fold increase in the lag-phase of hemolysis, E-7(1) represents the compound single-electron oxidation potential, and P represents the octanol/water partition coefficient. The cI(50) for quercetin and taxifolin were close, and cI(50) for morin, kaempferol and hesperetin were lower than might be predicted by this equation. The protection from hemolysis by azide, a quencher of singlet oxygen (O-1(2)) was accompanied by increase in cI(50) of polyphenols, indicating that azide and polyphenols competed for the same damaging species, O-1(2) These findings point out to two factors, determining the protective efficiency of polyphenols against O-1(2), namely, ease of electron donation and lipophilicity. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.