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

Polyphenolic antioxidants protected against Al-phthalocyanine tetrasulfonate-sensitized photohemolysis of human erythrocytes. A quantitative structure–activity relationship has been obtained to describe the protective effects of di- and trihydroxybenzenes: log cI50 (μM)=(1.8620±1.5565)+(3.6366±2.8245) E17 (V)−(0.4034±0.0765) log P (r2=0.8367), where cI50 represents the concentrations of compounds for the 2-fold increase in the lag-phase of hemolysis, E17 represents the compound single-electron oxidation potential, and P represents the octanol/water partition coefficient. The cI50 for quercetin and taxifolin were close, and cI50 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 (1O2) was accompanied by increase in cI50 of polyphenols, indicating that azide and polyphenols competed for the same damaging species, 1O2. These findings point out to two factors, determining the protective efficiency of polyphenols against 1O2, namely, ease of electron donation and lipophilicity.