Studies on the activities of tannins and related compounds from medicinal plants and drugs. I. Inhibitory effects on lipid peroxidation in mitochondria and microsomes of liver.

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Abstract
The inhibitory effects of 25 tannins and related compounds on the lipid peroxidation induced by ADP and ascorbic acid in rat liver mitochondria, and on that induced in rat liver microsomes by ADP and NADPH, were determined. All of the tannins, except for some polyphenols of low MW and methylated polyphenols, showed significant inhibition in these 2 systems at the concentration of 1 .mu.g/ml. Almost complete inhibition of the lipid peroxidation in the 2 systems was shown by some ellagitannins such as pedunculagin, isoterchebin, etc., at the dose of 5 .mu.g/ml. Marked differences of the inhibitory activities were observed among the tannins depending on the tannin structure, including the stereoisomerism in the monomer of condensed tannin, and on the experimental system used. The inhibitory effects of most of the hydrolyzable tannins were higher than those of the condensed tannins in both systems. Some monomeric polyphenols, represented by (-)-epigallocatechin gallate, showed inhibitory effects stronger than those of the condensed tannins in these systems, particularly on the lipid peroxidation induced by ADP and NADPH. The inhibitory effects of these tannins in both systems were very much stronger than that of .alpha.-tocopherol.