The UK-based researchers have suggest the antioxidant effects of green tea polyphenols could be reversed when the compounds are used in nano-formulations after research published in Nanomedicine compared the effects of different polyphenol forms on white blood cells.
Led by Professor Diana Anderson from the University of Bradford, UK, the researchers revealed that the known antioxidant properties of polyphenols such as epigallocatechin gallate (EGCG) and theaflavins can be reversed when they are used in their nanoparticle form.
The findings showed that when used in bulk form, these polyphenols exhibited their anticipated antioxidant responses, but the nanoform at higher concentrations had the reverse effect and exhibited statistically significant pro-oxidant effects, which can cause increased DNA damage.
“Both the compounds in the bulk form produced statistically significant concentration-dependent reductions in DNA damage,” revealed the authors. “In contrast, when used in the nano-particle form both theaflavin and EGCG, although initially causing a reduction, produced a concentration-dependent statistically significant increase in DNA damage.”
"We didn't expect these changes," explained Anderson. "When my PhD student came to me with the results, she assumed she'd made a mistake. But it struck me that I'd seen this happen before - in a study we published in 1994 describing a dose-related switch of properties in Vitamin C in the presence of hydrogen peroxide.”
“At the time I didn't think much about it, but this is the first time I've seen this happen with the nano-form of a compound," explained Anderson.
During the research, Anderson and her colleagues used white blood cells (lymphocytes) from healthy volunteers and cancer patients to assess the potential anti-cancer effects of tea polyphenols. The polyphenols were presented in both bulk and nano- forms and compared against of anti-cancer drugs to measure their protection against DNA damage.
The authors explained that many previous studies have suggested polyphenols to be increasingly useful as anti-cancer compounds, and may also offer beneficial effects to healthy, non-cancer cells due to their antioxidant properties that can quench free radical species.
However Anderson reveals that the results of DNA damage tests revealed conflicting findings for the bulk and nano- forms of the polyphenols.
“These observations support the notion that theaflavins and EGCG act as both antioxidants and pro-oxidants, depending on the form in which they are administered,” concluded the researchers.
Anderson warned that many researchers and R&D departments are looking into using nano forms of nutrients in efforts to boost their bioavailability and efficacy, “but this study shows that the nanoform doesn't always produce a more effective response.”
“In this case, it suggests that the bulk form of tea polyphenols is more useful as a chemopreventive."