Hydroxyl radical reactions and the radical scavenging activity of β-carboline alkaloids

beta-Carbolines are bioactive pyridoindole alkaloids occurring in foods, plants and the human body. Their activity as hydroxyl radical ((OH)-O-center dot) scavengers is reported here by using three different methods: deoxyribose degradation, hydroxylation of benzoate and hydroxylation of 2'-deoxyguanosine to give 8-hydroxy-2'-deoxyguanosine (8-OHdG) as assessed by RP-HPLC (MS). Fenton reactions (Fe2+/Fe3+ plus H2O2) were used for (OH)-O-center dot generation, and the radical increased in the presence of ascorbic acid or 6-hydroxydopamine as pro-oxidants. beta-Carbolines were scavengers of (OH)-O-center dot in the three assays and in the presence of pro-oxidants. Tetrahydro-beta-carboline-3-carboxylic acids were active against the hydroxylation of 2'-deoxyguanosine. beta-Carbolines reacted with hydroxyl radicals ((OH)-O-center dot) affording hydroxy-beta-carbolines, whereas tetrahydro-beta-carbolines gave oxidative and degradation products. On the basis of IC50 and reaction rates (k), beta-Carbolines (norharman and harman), and tetrahydro-beta-carbolines (tetrahydro-beta-carboline, 1-methyltetrahydro-beta-carboline and pinoline) were good (OH)-O-center dot radical scavengers and their activity was comparable to that of the indole, melatonin, which is an effective hydroxyl radical scavenger and antioxidant. (C) 2014 Elsevier Ltd. All rights reserved.