Tetrahydro-β-carboline derivatives in aged garlic extract show antioxidant properties

This study used the hydroden peroxide scavenging assay to investigate antioxidant chemical constituents derived and separated from aged garlic extract, a unique garlic extract produced by soaking sliced garlic in an aqueous ethanol solution for > 10 mo. Four types of 1, 2,3,4-tetrahydro-beta-carboline derivatives (TH beta Cs); 1-methyl-1, 2, 3, 4-tetrahydro-beta-carboline-3-carboxylic acid, and 1-methyl-1, 2, 3, 4-tetrahydro-beta-carboline-1, 3-dicarboxylic acid (MTCdiC), from both diastereoisomers, were isolated and identified by use of liquid chromatography-mass spectrometry. All these compounds indicate strong hydrogen peroxide scavenging activities and inhibit 2, 2'-azobis(2-amidinopropane) hydrochloride-induced lipid peroxidation. Particularly, (1S, 3S)-MTCdiC had the most potent hydrogen peroxide scavenging activity, more than ascorbic acid. The (1R, 3S)- and (1S, 3S)-MTCdiC at 50-100 mu mol/L and 10-100 mu mol/L inhibited LPS-induced nitrite production. Interestingly, TH beta Cs were not detected in raw garlic and other processed garlic preparations, but they were generated and increased during the natural aging garlic extraction process. These data suggest that TH beta Cs, which are formed during the natural aging process, are potent antioxidants in aged garlic extract and thus maybe useful for the prevention of diseases associated with oxidative damage.