MELATONIN AND STRUCTURALLY-RELATED, ENDOGENOUS INDOLES ACT AS POTENT ELECTRON-DONORS AND RADICAL SCAVENGERS IN-VITRO

The radical scavenging properties of melatonin, structurally-related i ndoles and known antioxidants were investigated in kinetic competition studies using the specific radical trapping reagent 2,2'-azino-bis(3- ethylbenz-thiazoline-6-sulfonic acid) (ABTS). In the presence of highl y reactive radicals, ABTS is oxidized to the stable thiazoline cation radical, ABTS(+) which, due to its intense green color, can be measur ed photometrically at 420 nm absorbance. The indoles melatonin, 5-meth oxytryptophol, 5-methoxyindole acetic acid and 5-methoxytryptamine as well as the phenolic and thiolic antioxidants ascorbic acid, Trolox, a nd glutathione inhibited ABTS cation radical formation and catalyzed A BTS radical cation reduction. Melatonin was the most potent radical sc avenger and electron donor when compared with the methoxylated indole analogs and the other antioxidants tested. Melatonin, the methoxylated indole analogs and the other antioxidants tested acted as potent elec tron donors which scavenged initiating and propagating radicals and re paired oxidative damage due to electrophile intermediates.