5‐Hydroxytryptophan is a more potent in vitro hydroxyl radical scavenger than melatonin or vitamin C

Abstract

Hydroxyl radicals are involved in direct damage of important biomolecules. Potent radical scavengers such as vitamin C and indoles of the tryptophan family can avert the potential damage. Melatonin and its precursor 5-hydroxytryptophan (5-HTP) were compared with water-soluble vitamin C. Different scavenger concentrations were measured in a steady-state luminol chemiluminescence system (SLCL-system) with combined Fe(II) chloride (0.1 mm) and hydrogen peroxide (1.0 mm) as hydroxyl radical generators. 5-HTP showed highest hydroxyl radical scavenging effects with a 50% inhibition concentration (IC50) of 1.8 microm. For vitamin C an IC50 of 12.7 microm was measured, whereas melatonin in pure demineralized water was much less efficient (IC50=724 microm). A comparison between melatonin in aqueous solution and melatonin in ethanol solution revealed that melatonin was significantly more effective in pure demineralized water.

The Ability of Melatonin to Counteract Lipid Peroxidation in Biological Membranes

“…5-OH-tryptophan, the precursor of N-acetylserotonin and melatonin, was the most efficient radical scavenger in our experiments. In this regard, in a recent paper it has been demonstrated that 5-OH-tryptophan is a more potent in vitro hydroxyl radical scavenger than melatonin or vitamin C [85]. The free-radical scavenging potentials of the indole derivatives at different concentrations were also analyzed by the DPPH method and the results indicate that the indoles: 5-OH-tryptophan and N-acetylserotonin exhibited a dose-dependent free-radical scavenging ability at all of the tested concentrations.…”

Recent Developments of Melatonin Related Antioxidant Compounds

“…5), which is converted to 5-hydroxytryptophan (5-HTP), serotonin, N-acetyl serotonin, and then finally to MLT [1]. The differences of the hydroxyl scavenging behavior of these indole derivatives and vitamin C were studied [60]. 5-HTP was the most efficient radical scavenger when compare with MLT and vitamin C. Vitamin C was also more efficient than MLT and similar to 5-HTP.…”

“…Thus, whilst this agent has the potential of promoting the Fenton reaction, it also scavenges the hydroxyl radical and, at the same time, reduces the consequent rise in Fe 2+ -induced lipid peroxidation. Since hydroxyl radical cannot be detoxified enzymatically, antioxidants have evolved as endogenous scavengers to provide on-site protection against oxidative damage [60]. One such group of defense factors are indoles, which are derived from the essential amino acid tryptophan and reduce free radicals non-enzymatically by electron donation [93,94].…”

The effect of melatonin and structural analogues on the lipid peroxidation of triglycerides enriched in ω-3 polyunsaturated fatty acids

“…5-OH-tryptophan, the precursor of N-acetylserotonin and melatonin, was the most efficient radical scavenger in our experiments. In this regard, in a recent paper it has been demonstrated that 5-OH-tryptophan is a more potent in vitro hydroxyl radical scavenger than melatonin or vitamin C (Keithahn and Lerchl, 2005). The free-radical scavenging potentials of the indole derivatives at different concentrations were also analyzed by the DPPH method, and the results indicate that the indoles: 5-OHtryptophan and N-acetylserotonin exhibited a dose-dependent free-radical scavenging ability at all of the tested concentrations.…”