Researchers find how rhubarb remedy eases cholera
Nathan Seppa
For centuries, Chinese and Japanese healers have used traditional medicines to combat the overwhelming diarrhea that comes with cholera. Researchers in Japan have identified a natural compound responsible for the effectiveness of one rhubarb-based remedy, a finding that could lead to even better pharmaceutical therapies.
The scientists tested a formulation called Daio-Kanzo-to. One chemical in the mixture, rhubarb galloyl-tannin, inhibits cholera toxin's effects on hamster cells in a test tube, the researchers found. The rhubarb compound binds to the toxin and apparently disables it, the researchers report in the March 5 issue of the Proceedings of the National Academy of Sciences.
The team also tested rhubarb galloyl-tannin and other chemical constituents of the traditional remedy by injecting them one by one into the intestines of mice and rabbits exposed to cholera toxin. Rhubarb galloyl-tannin reduced fluid accumulation in the intestines—a sign of severe diarrhea—10 times better than the next-best ingredient did, says study coauthor Masatoshi Noda, a molecular microbiologist of the Chiba University Graduate School of Medicine in Japan.
"This is a beautiful example of taking this sort of traditional information and chasing it down to the pharmaceutical level," says John J. Mekalanos, a microbiologist at Harvard Medical School in Boston.
The current standard of care for people with cholera is oral-rehydration therapy—plenty of fluids mixed with some essential salts. Drugs can also help by killing Vibrio cholera, the bacterium that makes the toxin.
Although rhubarb galloyl-tannin worked best in this study when given before the animals were exposed to cholera toxin, Noda says he thinks it could help people with cholera as part of a "triple therapy," with antibiotics and oral rehydration. Still unclear, says Mekalanos, is how well rhubarb galloyl-tannin would penetrate the mucous membrane that lines intestines and get at cholera toxin in an infected person.
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References:
Oi, H., … and M. Noda. 2002. Identification in traditional herbal medications and confirmation by synthesis of factors that inhibit cholera toxin-induced fluid accumulation. Proceedings of the National Academy of Sciences 99(March 5):3042–3046. Abstract available at http://dx.doi.org/10.1073/pnas.052709499.
Further Readings:
Badizadegan, K., et al. 2000. Floating cholera toxin into epithelial cells: Functional association with caveolae-like detergent-insoluble membrane microdomains. International Journal of Medical Microbiology 290:403–408.
Sources:
John J. Mekalanos
Harvard Medical School
200 Longwood Avenue
Boston, MA 02115
Masatoshi Noda
Department of Molecular Infectiology
Graduate School of Medicine
Chiba University
1-8-1 Inohana, Chuo-ku
Chiba 260-8670
Japan
From Science News, Volume 161, No. 13, March 30, 2002, p. 205.
