Identification and Characterization of Methylated and Ring-Fission Metabolites of Tea Catechins Formed in Humans, Mice, and Rats
作者:Xiaofeng Meng、Shengmin Sang、Nanqun Zhu、Hong Lu、Shuqun Sheng、Mao-Jung Lee、Chi-Tang Ho、Chung S. Yang
DOI:10.1021/tx010184a
日期:2002.8.1
(-)-Epigallocatechin gallate (EGCG), the most abundant tea catechin, has been proposed to be beneficial to human health based on its strong antioxidative and other biological activities in vitro. Inadequate knowledge regarding the bioavailability and biotransformation of EGCG in humans, however, has limited our understanding of its possible beneficial health effects. In this study, 4',4"-di-O-methyl-EGCG (4',4"-DiMeEGCG) was detected in human plasma and urine by LC/MS/MS following green tea ingestion. Both 4',4"-DiMeEGCG and EGCG reached peak plasma values (20.5 +/- 7.7 and 145.4 +/- 31.6 nM, respectively, in 4 subjects) at 2 h after the dose. The half-lives of 4',4"-DiMeEGCG and EGCG were 4.1 +/- 0.8 and 2.7 +/- 0.9 h, respectively. The cumulative urinary excretion of 4',4"-DiMeEGCG during a 24 h period was 140.3 +/- 48.6,mug, about 5-fold higher than that of EGCG, but the excreted 4',4"-DiMeEGCG and EGCG in urine only accounted for about 0.1% of ingested EG-CG. (-)-5-(3',4',5'-Trihydroxyphenyl)-gamma-valerolactone (M4) and (-)-5-(3',4'-dihydroxyphenyl)-gamma-valerolactone (M6), along with another possible ring-fission metabolite, (-)-5-(3',5'-dihydroxyphenyl)-gamma-valerolactone (M6'), were detected in human urine after green tea ingestion. The cumulative excretion of M4, M6', and M6 during a 24 h period ranged from 75,mug to 1.2 mg, 0.6 to 6 mg, and 0.6 to 10 mg, respectively. The combined excretion of all three ring-fission metabolites accounted for 1.5-16% of ingested catechins. M4, M6', and M6 were all observed after the ingestion of pure EGCG or EGC by human subjects, whereas only M6 was produced after EC ingestion. These metabolites as well as monomethylated EGCG were detected in mice and rats after tea or EGCG administration, and the tissue levels reflected the rather low bioavailability of EGCG in rats. The presently characterized methylated EGCG metabolites and ring-fission products exist in substantial quantities and may contribute to the biological activities of tea.
(-)-表没食子儿茶素-3- gallate(EGCG),茶叶中最丰富的儿茶素,因其在体外具有强大的抗氧化和其他生物活性,已提出对人类健康有益。然而,对人体内EGCG的生物利用度和生物转化了解不足,限制了我们对其可能有益健康效果的理解。在本研究中,绿茶摄入后,通过液相色谱-串联质谱法(LC/MS/MS)在人体血浆和尿液中检测到4',4"-二-O-甲基-EGCG(4',4"-DiMeEGCG)。4',4"-DiMeEGCG和EGCG在给药后2小时达到血浆峰值浓度(分别为20.5 ± 7.7 nM和145.4 ± 31.6 nM,在4名受试者中测得)。4',4"-DiMeEGCG和EGCG的半衰期分别为4.1 ± 0.8小时和2.7 ± 0.9小时。在24小时内,4',4"-DiMeEGCG的累积尿排泄量为140.3 ± 48.6微克,约为EGCG排泄量的5倍,但在尿液中排泄的4',4"-DiMeEGCG和EGCG仅占摄入EG.cg的约0.1%。在绿茶摄入后的人尿中检测到(-)-5-(3',4',5'-三羟基苯基)-γ-戊内酯(M4)、(-)-5-(3',4'-二羟基苯基)-γ-戊内酯(M6),以及另一种可能的环裂解代谢物,(-)-5-(3',5'-二羟基苯基)-γ-戊内酯(M6')。在24小时内,M4、M6'和M6的累积排泄量分别为75微克至1.2毫克、0.6至6毫克和0.6至10毫克。所有三种环裂解代谢物的联合排泄量占摄入儿茶素的1.5%-16%。M4、M6'和M6在人类受试者摄入纯EGCG或EGC后被观察到,而在摄入EC后仅产生M6。这些代谢物以及单甲基化EGCG在茶或EGCG给药后被检测到存在于小鼠和大鼠中,组织水平反映了大鼠中EGCG的较低生物利用度。目前表征的甲基化EGCG代谢物和环裂解产物存在大量,并可能有助于茶的生物活性。