Prooxidative Activities of Tea Catechins in the Presence of Cu²⁺

Evaluation of Resveratrol Oxidationin Vitroand the Crucial Role of Bicarbonate Ions

“…Many studies reported in the literature have demonstrated that polyphenols are unstable in alkaline solutions. 6,9,10,13) A study by Jhoo et al proposed that theanaphthoquione is the main oxidative product of theaflavin, a tea polyphenol. 13) Since they found that the oxidative product of theanaphthoquione increased dramatically in alkaline solution, they proposed that OH À is involved in the theaflavin oxidation reaction via serial one-electron oxidations (a radical reaction), followed by the attack of the carbon ring of theaflavin by OH À , leading to theanaphthoquione production.…”

“…Several papers have summarized a free radical mechanism of polyphenol oxidation and proposed that metal ions and superoxide anions play a role. 6,9,10) In this context, studies have reported that superoxide dismutase (SOD) can effectively inhibit the oxidation of EGCG (a tea polyphenol), while metal ion chelaters have demonstrated some capacity to inhibit the oxidation of several phenolic compounds. 7,11,12) Since pholyphenols are unstable in alkaline solution, a study by Jhoo et al has proposed that OH À plays a role in the degradation of teaflavin, a black tea polyphenol, and identified theanaphthoquinone as the major final product of oxidation.…”

Epigallocatechin-3-gallate affects the growth of LNCaP cells via membrane fluidity and distribution of cellular zinc

“…It is known that the biological behavior of EGCG could be influenced by metal ions, especially transition metal ions (e.g., iron, zinc, and copper ions) (Chen et al, 2006;Hayakawa et al, 2004). EGCG chelates metal ions, which is an important factor that affects the bioactivity of EGCG.…”

“…Recently, several reports have focused on the interactions of catechin with metal ions (Reznichenko et al, 2006;Yu et al, 2005;Hayakawa et al, 2004;Chen et al, 2007). Catechin induces redox reactions or chelates with metal ions, especially transitional metal ions, which lead to bioactivity changes of catechin.…”

Dual effects of (+)-catechin on hemin-induced oxidative reactions: A potential pharmacological implication

“…A possible explanation for the pro-oxidant effect of catechin on hemin oxidation is that itself can be the source of H 2 O 2 which may lead to the accelerated oxidation of heme. Moreover, catechin would bind to both intact and degraded forms of heme proteins through its metal chelating effect, 12,19 which was convenient for catechin to react with dissolved oxygen in aqueous solution, and generates H 2 O 2 . Also, metal-chelating ability would make the spectral changes of hemin after the addition of (þ)-catechin different from that after the treatment of H 2 O 2 (Fig.…”