Studies on Inhibition Mechanism of Autoxidation by Tannins and Flavonids. II.1) : Inhibition Mechanism of Caffeetannins Isolated from Leaves of Artemisia Species on Lipoxygenase Dependent Lipid Peroxidation

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Abstract
Inhibitory effects of caffeoylquinic acids isolated from leaves of Artemisia species and other related compounds on the lipoxygenase dependent peroxidation of linoleic acid were studied by kinetic and electron spin resonance (ESR) measurements. The order of inhibition activity was as follows: 3,5-dicaffeoylquinic acid (ID50 = 2.0 .times. 10-5 M) = rosmarinic acid > geraniin (2.8 .times. 10-5 M) > .alpha.-tocopherol (3.7 .times. 10-5 M) > chlorogenic acid (7.5 .times. 10-5 M) = caffeic acid > ferulic acid (2.5 .times. 10-4 M). This order coincided well with that obtained from the measurement of radical scavenging activities of these compounds against 1,1-diphenyl-2-picryl hydrazyl. The inhibition profile of these compounds on lipid peroxidation in the lipoxygenase system was quite similar to those obtained previously in the biological systems of rat liver mitochondria and microsomes. In the separate ESR measurements in alkaline dimethyl sulfoxide solution, all caffeoylquinic acids exhibited relatively stable ESR signals assigned as a radical derived from the one-electron oxidation of dihydroxyphenyl group. From these results, it was concluded that the radical scavenging mechanism is commonly operative in both chemical and biological peroxidation systems.

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