Cytotoxicity and lipid peroxidation-inhibiting activity of flavonoids.

Thirty-five flavonoids of seven different types, namely isoflavonoids, chalcones, dihydroflavonols, flavanols, flavanones, flavones, and flavonols were investigated for their ability to inhibit ascorbate-induced microsomal lipid peroxidation and their cytotoxicity. For each activity a structure-activity relationship was established. Subsequently, an antioxidant selectivity index, i. e., the maximal non-toxic dose divided by the IC(50) value for lipid peroxidation, was introduced. Kaempferol showed the highest antioxidant selectivity index of all flavonoids tested.