title: Antioxidative effects of green tea polyphenols on free radical initiated and photosensitized peroxidation of human low density lipoprotein.
abstract: Antioxidative effects of the main polyphenolic components extracted from green tea leaves, i.e. (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG), (-)-epigallocatechin gallate (EGCG) and gallic acid (GA), against free radical initiated peroxidation of human low density lipoprotein (LDL) were studied. The peroxidation was initiated either thermally by a water-soluble initiator 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH), or photochemically by a triplet sensitizer benzophenone (BP). The reaction kinetics was monitored by the uptake of oxygen and the depletion of alpha-tocopherol (TOH) presented in the native LDL. Kinetic analysis of the antioxidation process demonstrates that these green tea polyphenols are effective antioxidants against both AAPH-initiated and BP-photosensitized LDL peroxidation. The antioxidative action of the green tea polyphenols includes trapping the initiating and/or propagating peroxyl radicals with the activity sequence EC>EGCG>ECG>EGC>GA for the AAPH initiated peroxidation, and reducing the alpha-tocopheroxyl radical to regenerate alpha-tocopherol with the activity sequence of ECG>EC>EGCG>EGC>GA and ECG>EGCG>GA>EC>EGC for the AAPH-initiated and BP-photosensitized peroxidations respectively.
authors.affiliation: National Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou, 730000, Gansu, China.
authors.forename: Z
authors.initials: Z
authors.lastname: Liu
authors.forename: L P
authors.initials: LP
authors.lastname: Ma
authors.forename: B
authors.initials: B
authors.lastname: Zhou
authors.forename: L
authors.initials: L
authors.lastname: Yang
authors.forename: Z L
authors.initials: ZL
authors.lastname: Liu
mesh_terms: D000975:Antioxidants / Q000494:pharmacology*; D002392:Catechin / Q000031:analogs & derivatives / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D005609:Free Radicals / Q000378:metabolism; D005707:Gallic Acid / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D015227:Lipid Peroxidation / Q000187:drug effects* / Q000528:radiation effects; D008077:Lipoproteins, LDL / Q000097:blood / Q000187:drug effects* / Q000378:metabolism; D010636:Phenols / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D010777:Photochemistry; D011108:Polymers / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D013662:Tea / Q000737:chemistry*
chemical_list: D000975:Antioxidants; D005419:Flavonoids; D005609:Free Radicals; D008077:Lipoproteins, LDL; D010636:Phenols; D011108:Polymers; D013662:Tea; D005707:Gallic Acid; D002392:Catechin; C062669:epicatechin gallate; C045651:epigallocatechin gallate; C057580:gallocatechol