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.
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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.