TY - JOUR
T1 - Black tea increases the resistance of human plasma to lipid peroxidation in vitro, but not ex vivo
AU - Cherubini, Antonio
AU - Beal, M. Flint
AU - Frei, Balz
PY - 1999/8
Y1 - 1999/8
N2 - A number of in vitro studies have shown that polyphenols and flavonoids in tea exert significant antioxidant activity. However, epidemiologic and experimental studies have produced conflicting results. The purpose of the present study was to compare the antioxidant activity of black tea in vitro with that ex vivo. Black tea polyphenols (BTP), black tea extract (BTE), or their major polyphenolic antioxidant constituent, epigallocatechin gallate (EGCG), were added to human plasma and lipid peroxidation was induced by the water-soluble radical generator 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH). Following a lag phase, lipid peroxidation was initiated and occurred at a rate that was lowered in a dose-dependent manner by BTP. Similarly, EGCG and BTE added to plasma in vitro strongly inhibited AAPH-induced lipid peroxidation. The lag phase preceding detectable lipid peroxidation was due to the antioxidant activity of endogenous ascorbate, which was more effective at inhibiting lipid peroxidation than the tea polyphenols and was not spared by these compounds. In contrast, when eight healthy volunteers consumed the equivalent of six cups of black tea, the resistance of their plasma to lipid peroxidation ex vivo did not increase over the next 3 h. These data suggest that, despite antioxidant efficacy in vitro, black tea does not protect plasma from lipid peroxidation in vivo. The striking discrepancy between the in vitro and ex vivo data is most likely explained by the insufficient bioavailability of tea polyphenols in humans.
AB - A number of in vitro studies have shown that polyphenols and flavonoids in tea exert significant antioxidant activity. However, epidemiologic and experimental studies have produced conflicting results. The purpose of the present study was to compare the antioxidant activity of black tea in vitro with that ex vivo. Black tea polyphenols (BTP), black tea extract (BTE), or their major polyphenolic antioxidant constituent, epigallocatechin gallate (EGCG), were added to human plasma and lipid peroxidation was induced by the water-soluble radical generator 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH). Following a lag phase, lipid peroxidation was initiated and occurred at a rate that was lowered in a dose-dependent manner by BTP. Similarly, EGCG and BTE added to plasma in vitro strongly inhibited AAPH-induced lipid peroxidation. The lag phase preceding detectable lipid peroxidation was due to the antioxidant activity of endogenous ascorbate, which was more effective at inhibiting lipid peroxidation than the tea polyphenols and was not spared by these compounds. In contrast, when eight healthy volunteers consumed the equivalent of six cups of black tea, the resistance of their plasma to lipid peroxidation ex vivo did not increase over the next 3 h. These data suggest that, despite antioxidant efficacy in vitro, black tea does not protect plasma from lipid peroxidation in vivo. The striking discrepancy between the in vitro and ex vivo data is most likely explained by the insufficient bioavailability of tea polyphenols in humans.
KW - Antioxidants
KW - Flavonoids
KW - Free radicals
KW - Human study
KW - Lipid peroxidation
KW - Tea
UR - http://www.scopus.com/inward/record.url?scp=0032840225&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0032840225&partnerID=8YFLogxK
U2 - 10.1016/S0891-5849(99)00064-7
DO - 10.1016/S0891-5849(99)00064-7
M3 - Article
C2 - 10468212
AN - SCOPUS:0032840225
VL - 27
SP - 381
EP - 387
JO - Free Radical Biology and Medicine
JF - Free Radical Biology and Medicine
SN - 0891-5849
IS - 3-4
ER -