Abstract
The antioxidant activities of baicalin, which is a plant flavonoid, alizarin extracted from madder and green tea polyphenols extracted from green tea were studied in comparison with vitamin E or its water-soluble derivative, Trolox, in four different systems: (1) a p -iodophenol-enhanced horseradish peroxidase-luminol-perborate chemiluminescent system; (2) a hypoxanthine-xanthine oxidase-luminol chemiluminescent system; (3) lipid peroxidation in rat liver microsomes initiated by ADP-Fe2+ ; (4) lipid peroxidation in the liver of bromobenzene-intoxicated mice grouped randomly. Two chemical assays and one in vitro biological assay showed that the three natural extracts, in particular the green tea polyphenols, were very good antioxidants in their activity against iodophenol-derived phenoxyl radicals, superoxide anion radicals and lipid peroxidation in rat liver microsomes. However, the in vivo experiment showed that baicalin and alizarin were more effective than the green tea polyphenols and vitamin E in reducing the hepatic content of thiobarbituric acid-reactive substances and all three natural compounds were better than vitamin E in lowering the serum level of alanine aminotransferase in poisoned animals. It is evident that the activity of an antioxidant determined in any chemical system or even in an in vitro biological system such as rat liver microsomes can hardly represent the real activity in vivo .