Autoxidative quinone formation in vitro and metabolite formation in vivo from tea polyphenol (-)-epigallocatechin-3-gallate: Studied by real-time mass spectrometry combined with tandem mass ion mapping

Abstract

Abstract(−)-Epigallocatechin-3-gallate (EGCG), the most abundant and biologically active compound in tea, has been proposed to have beneficial health effects, including prevention of cancer and heart disease. Different mechanisms of action of EGCG have been proposed, based mainly on studies in cell line systems, in which EGCG is not stable. It has been proposed that oxidation of EGCG and its production of reactive oxygen species are responsible for the biological activities such as receptor inactivation and telomerase inhibition. It is unclear, however, if this phenomenon occurs in vivo. In the present study, the stability of EGCG and product formation in Tris-HCl buffer was investigated using realtime mass spectrometry combined with tandem mass ion mapping. With real-time mass data acquisition, we demonstrate for the first time the formation of EGCG quinone, EGCG dimer quinone, and other related compounds. The structural information of the major appearing ions was provided by tandem mass analysis of each ion. A mechanism for the autoxidation of EGCG was proposed based on the structural information of these ions. None of these oxidation products were observed in the plasma samples of mice after treatment with 50 mg/kg EGCG, i.p. daily for 3 days. Instead, the methylated and conjugated metabolites of EGCG were observed. Therefore the roles of EGCG autoxidation in the biological activities of this compound in vivo remain to be investigated further.

Stability of Phenolic Compounds Isolated from Cocoa, Green Tea and Strawberries in Hank’s Balanced Salt Solution under Cell Culture Conditions.

“…In our study, EGCG was more stable than in previously reported studies mentioning a half time of EGCG at 30 min [Sang et al, 2005]. Our results are in line with the other study, in which the authors described the approximate half-time of EGCG in Tris-HCl buffer at pH 7.2 as 2 h [Sang et al, 2007]. Hong et al [2002] monitored stability of EGCG in HBSS buffer at pH 7.4 and detected oxidative products after 10 min of incubation.…”

Human Serum Albumin as an Antioxidant in the Oxidation of (−)-Epigallocatechin Gallate: Participation of Reversible Covalent Binding for Interaction and Stabilization

“…5,7) However, the galloyl moiety containing EGCg was stable for 1 h in PB with HSA at both pH 7.4 and 8.0 (Fig. 2B).…”

“…5,6) Several other factors, including temperature, oxygen concentration, antioxidant concentration, metal ions, concentration of pyrogallol-type catechins, and other tea ingredients, also affect the stability of pyrogallol-type catechins. 7) Furthermore, in vitro studies have indicated that the pyrogallol-type catechins are unstable in several cell culture media. 8,9) ROS can cause oxidative modification to sensitive proteins that can lead to changes in the protein function.…”

Evaluation of Resveratrol Oxidationin Vitroand the Crucial Role of Bicarbonate Ions

“…Then the generated semiquinone radical can quickly be oxidized by oxygen to form the corresponding quinone and superoxide anions. 19) In addition, Cu þ is also re-oxidized by oneelectron transfer to oxygen to from a superoxide anion.…”