Texas and the United Kingdom have found that a
chemical from green tea reduces HIV's ability to infect
from the University of Sheffield and Baylor College of
Medicine in Houston found that as little as two cups of
green tea could provide enough of the chemical
epigallocatechin gallate (EGCG) to inhibit HIV cell
binding by 40%.
However, they do
not recommend that people start drinking gallons of
green tea as an HIV preventative. Rather, they are
conducting research to find out if EGCG or a chemical
like it would make a good HIV drug.
gallate is a catechin, one of a large family of
chemicals called bioflavonoids that are found in tea, red
wine, and many fruits and vegetables. Most are colored
red or purple and/or taste bitter; many have
antioxidant properties and have been investigated for
some time as possible anticancer and cardiovascular drugs.
Christina Nance and her team found that EGCG exerts a more
direct effect on HIV infection. The molecule likes to bind
to CD4, the cell-surface molecule which HIV first
binds to as well.
discovered by Japanese scientists in 2003, but by using
computers to image the exact shape of the proteins and
working out the electronic processes involved, Nance's
team worked out that ECGC sticks to exactly the same
amino acid (component) of the CD4 molecule as does
gp120--the "docking module" of HIV.
"When it binds
there, the gp120 envelope protein--and thus
HIV--can't [bind]," Nance said. Her team's
findings are published in a recent issue of The
Journal of Allergy and Clinical Immunology.
The history of
HIV medicine is full of promising-looking compounds from
plants that had some effect on the HIV virus in the test
tube but, when tested in animals and humans, either
produced no effect or only did so at toxic doses. The
previous Japanese research had indicated that the same
would be true of EGCG -- huge doses would be needed.
But Nance said
that "physiological levels" of EGCG -- that is, 0.2
micromoles per liter, or the amount in just a cup or two of
green tea -- inhibited HIV binding by 40%.
The team is now
using computer-imaging tools to examine more closely the
way that EGCG binds to CD4 in the hope of developing
improved molecules that will bind to it more closely.
It is also
investigating the possibility of a small trial of ECGC in
humans to see if it blocks HIV infection in real life.
If EGCG or
something like it does lead to an HIV treatment, it won't be
a first. The story of the integrase inhibitors, which
has now finally resulted in the launch of a new drug,
raltegravir, started when researchers looked at
substances derived from green coffee beans.
And another drug
now undergoing trials, bevirimat, was derived from
chemicals found in birch-tree bark.
Will a mug of
English Breakfast have the same effect? No. Black tea
leaves contain EGCG, but in much lower quantities. That's
because black tea leaves are fermented, a process in
which many of the catechins are oxidized to
darker-colored molecules called theaflavin and thearubigen.
(Gus Cairns, Gay.com/U.K.)