The role of antioxidant versus pro‐oxidant effects of green tea polyphenols in cancer prevention

Abstract

Consumption of green tea (Camellia sinensis) may provide protection against chronic diseases, including cancer. Green tea polyphenols are believed to be responsible for this cancer preventive effect, and the antioxidant activity of the green tea polyphenols has been implicated as a potential mechanism. This hypothesis has been difficult to study in vivo due to metabolism of these compounds and poor understanding of the redox environment in vivo. Green tea polyphenols can be direct antioxidants by scavenging reactive oxygen species or chelating transition metals as has been demonstrated in vitro. Alternatively, they may act indirectly by up-regulating phase II antioxidant enzymes. Evidence of this latter effect has been observed in vivo, yet more work is required to determine under which conditions these mechanisms occur. Green tea polyphenols can also be potent pro-oxidants, both in vitro and in vivo, leading to the formation of hydrogen peroxide, the hydroxyl radical, and superoxide anion. The potential role of these pro-oxidant effects in the cancer preventive activity of green tea is not well understood. The evidence for not only the antioxidant, but also pro-oxidant, properties of green tea are discussed in the present review.

Effect of Long-Term Green Tea Extract Supplementation on Peripheral Blood Leukocytes in CrossFit-Trained and Untrained Men

“…EGCG-mediated inhibition of chemokine Agata . Zak, Ilona Pokora production and chemokine interactions with their receptors on white blood cell surface may alter the range and magnitude of the inflammatory response including white blood cell count and pattern (Forester, Lambert, 2011). Our findings showed that 6-week GTE supplementation resulted in a significant increase in the absolute eosinophil count as well as eosinophil percentage in both study groups.…”

“…Green tea extract and EGCG exert the pro-oxidative effect in subjects with low baseline oxidative stress, whereas green tea poliphenols may be scavenging ROS in subjects with high baseline oxidative stress. According to Forester and Lambert suggestion, with moderate and low concentrations EGCG, low level oxidative stress may be a beneficial cue for the body to initiate induction of protective anti-oxidant systems and host immune responses (Lambert, Elias, 2010), (Forester, Lambert, 2011). Thus under same (exercise, training) conditions with increased oxidative stress, supplementation of green tea polyphenols may attenuated ROS mediated tissue damage.…”

Green Tea Catechins for Prostate Cancer Prevention: Present Achievements and Future Challenges

“…Dietary components, like vitamins and polyphenols, also contribute in maintaining intracellular redox homeostasis [26,27]. An increasing numbers of studies have demonstrated that GTPs are strong antioxidant compounds [21,28], nonetheless GTPs are also able to exert pro-oxidant effects. The pro-oxidant/antioxidant behavior of GTPs greatly depend on many experimental conditions, such as final concentration of use, temperature, pH, presence of metal ions, and differences in culture media composition [21,[29][30][31].…”

“…Transition metals are able to initiate the catechins auto-oxidation reaction, also promoting the formation of catechins-metal ions complexes. Depending on the experimental model these mechanisms have been correlated both to an antioxidant or a pro-oxidant behavior of GTCs [21,28]. Zinc is required for normal prostate metabolism due to its ability to inhibit aconitase activity determining the excretion of citrate into seminal fluid.…”

Health benefits of Green and Black Tea: A Review

“…Tea consumption has been reported to have beneficial effects against different types of cancers due to its antioxidants which have the ability to prevent and control cancer development. Many in vivo studies conducted with rodents have shown that tea protects against many types of cancer and at most stages of carcinogenesis [16].Green tea and green tea polyphenols have been shown to have anti-cancer activity in a number of laboratory studies, which could be mediated through antioxidant or pro-oxidant mechanisms [17].Green tea polyphenols such as EGCG inhibit cell viability and induce apoptosis in a number of cancer cell lines such as osteogenic sarcoma [18], lymphoblastoid cells [19], leukemia cells [20], melanoma cells [21], T lymphocytes [22] and larynx carcinoma [23]. EGC can inhibit breast cancer cell viability through induction of apoptosis, yet not in normal breast cells [24].…”