ANTIOXIDANT ACTION OF BENZYLISOQUINOLINE ALKALOIDS

The antioxidant action of a series of benzylisoquinoline alkaloids has been investigated. Laudanosoline, protopapaverine, anonaine, apomorph ine, glaucine, boldine, bulbocapnine, tetrahydroberberine and stepholi dine produced a dose-dependent inhibition of microsomal lipid peroxida tion induced by Fe2+/ascorbate, CCl4/NADPH or by Fe3+ADP/NADPH. Apomor phine exerted the highest inhibitory effects in the three systems of i nduction used, with a potency higher than propyl gallate. Laudanosolin e was particularly effective in the first system, while bulbocapnine a nd anonaine were more potent when CCl4/NADPH or Fe3+-ADP/NADPH were us ed as inducers. Laudanosoline, protopapaverine, apomorphine, tetrahydr oberberine and stepholidine were also potent inhibitors of nitroblue t etrazolium (NBT) reduction. The presence of a free hydroxyl group or p referably of a catechol group is a feature relevant for inhibition of lipid peroxidation and NBT reduction, nevertheless the antioxidant act ivity of benzylisoquinoline alkaloids cannot be only ascribed to the f ormation of phenoxy radicals and other free radical species may be for med during aporphine and tetrahydroprotoberberine oxidation. The influ ence of this series of compounds on the time course of lipid peroxidat ion suggests that some of them, like apomorphine and boldine act as ch ain-breaking antioxidants.