Bait worms and heavy metals
What happens when someone consumes cadmium-contaminated food or water? That's easier to ask than answer, since you can't just feed burgers laced with this carcinogen to sophomore lab rats (poisoning human research subjects just isn't kosher these days).

Faced with this dilemma, scientists typically turn to lab animals. They've found that rodents fight heavy metals by directing the liver to produce a metal-binding protein called metallothionein or MT. MT binds to cadmium and other toxic metals and detoxifies them for storage in the liver or kidney. It's an intelligent system -- the more toxic metal present, the more MT the body produces.

Since it turns out that humans use essentially the same mechanism to deal with toxic metals, scientists can use rodents for toxicology experiments where repetition improves the reliability of results. But the use of rodents still attracts flack from animal rights activists, and they aren't as cheap as you might expect. "The government regulations are very stringent," says Paul Chien, a biologist at San Francisco University, a private Jesuit institution. "To keep lab rats, you essentially have to run a hospital." And that raises the price tag of toxicology studies.

Question: If humans and rodents use the same enzyme for the same purpose, what about smaller simpler, cheaper organisms? It turns out that there is one that's small, cheap and unlikely to irritate advocates of animal rights.

In fact, this scientific wonder is not a mammal -- or even a vertebrate -- but rather something you can buy for a dollar a dozen at bait shops. Right. We're talking nightcrawlers, formally Lumbricus terrestris, bait worm of choice to millions of freshwater fishing fanatics.
Eat lead, worm!
By injecting precise doses of toxic metals into the worms' body cavity, Chien and Art Furst, a retired University of San Francisco toxicologist, who together developed the technique, have activated the same enzyme system that detoxifies metals in rodents and people. Their results show the same comparative toxicity of the metals in worms, rats and humans, Chien says. "There is no qualitative difference between our results and those in rats and humans." Thus excess copper is most toxic to all three, followed by cadmium and zinc.

Using cheap animals to do cheap, rapid tests of the detoxification system, Chien and Furst have found that zinc, an essential trace mineral, sparks the production of MT in the body. This finding "reminds people about getting the appropriate amounts of zinc," Chien says. But he notes that copper binds tightly to MT, making less MT available to protect against the toxicity of other heavy elements.

Worms are certainly cheap: the rats for a major set of toxicology tests might cost $200,000, compared to just $450 for the worms, Chien adds. And you could always go ice fishing with the survivors...

The nightcrawler research may also help explain how selenium protects against mercury poisoning. Although indigenous people in Greenland have been exposed to high levels of mercury, they show no symptoms of mercury poisoning, probably because they get so much selenium in their diets. "Selenium may replace the sulfur on MT," says Chien, "and make the protein more potent in binding metals."

Eat broccoli, worm!
Nightcrawlers may also be helpful for testing antioxidants as cancer preventatives (antioxidants are chemicals that detoxify damaging chemicals called free radicals in the body.) The technique relies on the fact that when more heavy metal is available in the body, the liver makes more MT.

To test the antioxidants, Chien's lab doses a worm with antioxidants like broccoli extract or beta carotene. Then they give the worm a shot of heavy metal and measure how much MT is produced. "If you add the antioxidant, you can see the body does not produce as much MT," he reports. "Therefore we assume the body is being protected by the antioxidant and less MT is needed."

The bait-shop rat wannabes are also being used to test the best time to administer antidotes to arsenic, lead, cadmium and mercury. That experiment has so many variables, Furst says, that it "would be too expensive for rodents."

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