Nanoparticle form of tea polyphenols reverses antioxidant
10 September 2012
The beneficial health property of tea polyphenols is reversed
when they are prepared as nanoscale particles instead of a bulk form,
according to researchers from the University of Bradford.
Natural chemicals found in tea are known to have potential for
the treatment and prevention of a number of human cancers, but this
research shows that the known antioxidant properties of these
substances can be reversed when they are used in their nanoparticle
form. Antioxidants prevent damage to DNA and other molecules which
can be caused by free radicals.
Led by Professor Diana Anderson from Bradford’s School of Life
Sciences, the research compared the antioxidant responses of two
polyphenols, called ECGC and theaflavins. These were provided by Dr
Gupta, Director of the Indian Institute of Toxicology Research
(IITR). 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.
“We didn’t expect these changes,” says Professor 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 nanoform of a compound.”
During the research, lymphocytes (a type of white blood cell)
were treated with the platinum-based chemotherapeutic drugs,
oxaliplatin and satraplatin. These drugs bind to DNA efficiently,
forming a variety of links that block replication and transcription,
and affect signalling pathways which trigger death in cancer cells.
At the same time, the lymphocytes were treated with the polyphenols,
both in their bulk forms and their nanoforms. The relative
modifications in DNA damage caused by the different forms and
concentrations of the polyphenols was measured by Comet assay tests.
“It’s not clear why this switch happens,” says Professor
Anderson. “It may be dependent on the compound and on the type of
cancer under investigation. And of course in vivo research may show
different results again. But it’s certainly of interest that these
natural polyphenol antioxidants may not always behave as
chemopreventives. Nanotechnology has preceded nanotoxicology by a
number of years and we nanotoxicologists are having to catch up.”
The study may have implications for the development of new drugs
based on nanotechnology.The antioxidant properties of tea
polyphenols are well documented, and there is a great deal of
research being undertaken to harness these properties and apply them
in new medicines. However, studies such as this show that whilst
nanotechnology has shown enormous benefit in many areas of science,
its application in medicine may not be simple.
“Using nanoforms of chemicals is increasingly being looked at in
an effort to boost the efficacy of drugs, 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.”
Tea phenols in bulk and nanoparticle form modify DNA damage in
human lymphocytes from cancer patients and healthy individuals
treated in vitro with platinum-based chemotherapeutic drugs.
Published online ahead of print on 4 Sept in Nanomedicine.