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

Polyphenolic antioxidants protected against Al-phtlalocyanine tetrasulfonat e-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), w here cI(50), represents the concentrations of compounds for the 2-fold incr ease in the lag-phase of hemolysis, E-7(1) represents the compound single-e lectron oxidation potential, and P represents the octanol/water partition c oefficient. The cI(50) for quercetin and taxifolin were close, and cI(50) f or morin, kaempferol and hesperetin were lower than might be predicted by t his equation. The protection from hemolysis by azide, a quencher of singlet oxygen (O-1(2)) was accompanied by increase in cI(50) of polyphenols, indi cating that azide and polyphenols competed for the same damaging species, O -1(2) These findings point out to two factors, determining the protective e fficiency of polyphenols against O-1(2), namely, ease of electron donation and lipophilicity. (C) 2000 Elsevier Science Ireland Ltd. All rights reserv ed.