Investigation of the antioxidant and membranotropic activity of the quinozaline alkaloid triptantrin in different model systems

A comparative study of antioxidant (radical-scavenging) properties of triptantrin, which is a quinazoline alkaloid with anti-inflammatory activity that occurs in many species of higher plants and microorganisms, including the human microbiome, in systems containing 2,2’-azobis (2-methylpropionamidin) dihydrochloride and luminol, or hemoglobin, hydrogen peroxide, and luminol was performed and the impact of the alkaloid on the permeability of planar bilayer lipid membranes was assessed. Trolox was used as a reference antioxidant, and ascorbic acid and dihydroquercetin were used as standards. The antioxidant activity of triptantrin in both systems was much lower than that of the reference and standard antioxidants. The substances formed the following series according to antioxidant activity: dihydroquercetin > trolox > ascorbic acid > triptantrin, with the antioxidant potential of the latter being 1000 times lower than that of trolox and 3000 times lower than that of the bioflavonoid dihydroquercetin. Triptantrin did not cause significant changes in permeability of planar bilayer membranes when applied at concentrations of 0.5–10 μg/mL. The data show that triptantrin lacks considerable radical-scavenging and membranotropic activities; therefore one can assume that the high antiinflammatory activity that has been reported for triptantrin is neither related to an ability to neutralize reactive oxygen species nor to effects on cell membrane permeability. The putative mechanisms that underlie the biological effects of triptantrin are discussed.