title: Tea Flavanols Block Advanced Glycation of Lens Crystallins Induced by Dehydroascorbic Acid.
abstract: Growing evidence has shown that ascorbic acid (ASA) can contribute to protein glycation and the formation of advanced glycation end products (AGEs), especially in the lens. The mechanism by which ascorbic acid can cause protein glycation probably originates from its oxidized form, dehydroascorbic acid (DASA), which is a reactive dicarbonyl species. In the present study, we demonstrated for the first time that four tea flavanols, (-)-epigallocatechin 3-O-gallate (EGCG), (-)-epigallocatechin (EGC), (-)-epicatechin 3-O-gallate (ECG), and (-)-epicatechin (EC), could significantly trap DASA and consequently form 6C- or 8C-ascorbyl conjugates. Among these four flavanols, EGCG exerted the strongest trapping efficacy by capturing approximate 80% of DASA within 60 min. We successfully purified and identified seven 6C- or 8C-ascorbyl conjugates of flavanols from the chemical reaction between tea flavanols and DASA under slightly basic conditions. Of which, five ascorbyl conjugates, EGCGDASA-2, EGCDASA-2, ECGDASA-1, ECGDASA-2 and ECDASA-1, were recognized as novel compounds. The NMR data showed that positions 6 and 8 of the ring A of flavanols were the major active sites for trapping DASA. We further demonstrated that tea flavanols could effectively inhibit the formation of DASA-induced AGEs via trapping DASA in the bovine lens crystallin-DASA assay. In this assay, 8C-ascorbyl conjugates of flavanols were detected as the major adducts using LC-MS. This study suggests that daily consumption of beverages containing tea flavanols may prevent protein glycation in the lens induced by ascorbic acid and its oxidized products.
authors.affiliation: Center for Excellence in Post-Harvest Technologies, North Carolina Agricultural and Technical State University, North Carolina Research Campus , 500 Laureate Way, Kannapolis, North Carolina 28081, United States.
authors.forename: Yingdong
authors.initials: Y
authors.lastname: Zhu
authors.affiliation: Center for Excellence in Post-Harvest Technologies, North Carolina Agricultural and Technical State University, North Carolina Research Campus , 500 Laureate Way, Kannapolis, North Carolina 28081, United States.
authors.forename: Yantao
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Center for Excellence in Post-Harvest Technologies, North Carolina Agricultural and Technical State University, North Carolina Research Campus , 500 Laureate Way, Kannapolis, North Carolina 28081, United States.
authors.forename: Pei
authors.initials: P
authors.lastname: Wang
authors.affiliation: Department of Health Science, Qatar University , Doha, Qatar.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Ahmedna
authors.affiliation: Department of Food Science, Rutgers, The State University of New Jersey , 65 Dudley Road, New Brunswick, New Jersey 08901, United States.
authors.forename: Chi-Tang
authors.initials: CT
authors.lastname: Ho
authors.affiliation: Center for Excellence in Post-Harvest Technologies, North Carolina Agricultural and Technical State University, North Carolina Research Campus , 500 Laureate Way, Kannapolis, North Carolina 28081, United States.
authors.forename: Shengmin
authors.initials: S
authors.lastname: Sang
mesh_terms: D000818:Animals; D028241:Camellia sinensis; D002417:Cattle; D003459:Crystallins / Q000378:metabolism*; D003683:Dehydroascorbic Acid / Q000633:toxicity*; D005419:Flavonoids / Q000494:pharmacology*; D017127:Glycation End Products, Advanced / Q000378:metabolism*
chemical_list: D003459:Crystallins; D005419:Flavonoids; D017127:Glycation End Products, Advanced; D003683:Dehydroascorbic Acid