Comparison of the antioxidant activity of melatonin and pinoline in vitro.

Several recent experiments have shown that melatonin is an efficient antioxidant and free radical scavenger. In the present study the antioxidative effect of melatonin was compared with that of pinoline. Pinoline (6-methoxy-tetrahydro-beta-carboline) can be formed in the mammalian body under physiological conditions from 5-hydroxytryptamine or as a tricyclic metabolite of melatonin. Both melatonin and pinoline inhibited lipid peroxidation and showed comparable activity in a total antioxidant status test. Melatonin and pinoline concentration-dependently scavenged hydroxyl radicals with IC50 11.4+/-1.0 microM for melatonin and 62.3+/-3.8 microM for pinoline. These results support the importance of the indolic part of the molecule and the 5-methoxy group common to both compounds in terms of the ability of these molecules to quench the hydroxyl radicals. As pinoline has been shown to exert an antidepressant-like effect in behavioral experiments and has been reported to have a low toxicity, this compound should be further studied as a potential antidepressant with pronounced antioxidative effects. These results further support the importance of pineal gland in antioxidative protection.