Peroxynitrite Scavenging Activity of Indole Derivatives: Interaction of Indoles with Peroxynitrite

Abstract

One of the products of nitrogen-derived free radicals, peroxynitrite (ONOO(-)), is formed by the reaction of superoxide anion (O(2)(*-)) with nitric oxide (NO). ONOO(-) can cause damage to proteins and DNA through nitration. In particular, proteins and their constituent amino acids have been proven to be extremely sensitive to ONOO(-). However, the lack of specific endogenous defense enzymes to protect against ONOO(-) has prompted many researchers to search for endogenous scavengers. We previously found 5-hydroxytryptamine (HT), which is an indole derivative (ID), to be an efficient ONOO(-) scavenger. In the present study, the interaction of several other indoles was further investigated: tryptophan (TRP), 5-hydroxyL-tryptophan (HLT), HT, N-acetyl-5-hydroxytryptamine (AHT), 5-methoxyindole-3-acetate (MIA), 5-methoxytryptamine (MT), and melatonin. The ONOO(-) scavenging activity of ID was assayed by measuring the formation of oxidized dihydrorhodamine-123 (DHR-123). The scavenging efficacy was expressed as the IC(50), denoting the concentration of each indole required to cause 50% inhibition of DHR-123 formation. In a separate in vitro study, the protective effect of IDs against ONOO(-)-induced nitration of bovine serum albumin was investigated. Nitration was quantified using an immunoassay with a monoclonal anti-nitrotyrosine antibody, and a horseradish peroxidase-conjugated anti-mouse secondary antibody from sheep. The results revealed that the inhibitory activities of indoles were as follows: HLT, IC(50) = 0.73 microM; HT, IC(50) = 1.03 microM; and AHT, IC(50) = 0.98 microM), showing relatively strong activities against ONOO(-). Interestingly, TRP, MIA, MT, and melatonin were less effective. Regarding the protection of albumin by IDs, the data showed that the formation of ONOO(-) was inhibited in a dose-dependent manner. Further probing of the mode of the interaction of indoles revealed that the hydroxyl groups in IDs are required for the enhanced scavenging action. It was concluded that several indole derivatives with hydroxyl groups are effective scavengers against ONOO(-), and that the scavenging efficacy depends on the presence of hydroxyl groups located within the indole ring structure.

Protective effect of tryptophan against dextran sulfate sodium- induced experimental colitis

“…On the other hand, indole derivatives via kynurenine pathway have been reported to have anti-oxidative effects as scavengers of peroxynitrite (16). Moreover, serotonin, 5-hydroxytryptophan (5-HTP), N-acetylserotonin (NAS), and melatonin which are metabolized via serotonin pathway have been reported to have several anti-oxidative effects (17)(18)(19)(20).…”

Melatonin: An Established Antioxidant Worthy of Use in Clinical Trials

“…Not only melatonin but also several of its metabolites can detoxify free radicals and their derivatives (57)(58)(59). Studies also reveal that melatonin eliminates the decomposition products of ONOO in the presence of physiological carbon dioxide concentrations (60)(61)(62). Melatonin also supports several intracellular enzymatic antioxidant enzymes, including SOD and glutathione peroxidase (GSH-Px) (63,64).…”

Recent Developments of Melatonin Related Antioxidant Compounds

“…Paradoxically, the toxicity of NO . involves oxidation reactions, but nitric oxide itself is only a weak oxidant [100]. Several lines of evidence indicate that peroxynitrite is formed in vivo.…”