Green-tea study
offers hope of AIDS drug

Scientists in Texas and the United Kingdom have found that a chemical from green tea reduces HIV's ability to infect cells.

The scientists 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.

Epigallocatechin 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.

Baylor's Dr. 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.

This was 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.)