Caren Helbing

Caren Helbing
Department of Biochemistry and Microbiology

Research areas: amphibian metamorphosis, endocrine disruptors

A better way to test for pollutants

Learning about Dr. Caren Helbing's research may make you uneasy—the kind of unease that prompts people to switch to organic food and clothing.

That is because forty years after Rachel Carson wrote Silent Spring, Helbing's work warns us that we still don't really know how to test for chemical contaminants in the environment.

Helbing is a frog expert. For two decades she has focused on frog metamorphosis as a model for understanding how hormones work in humans. She has focused on thyroid hormone, which is behind the radical changes a tadpole undergoes to become a frog when its tails shrinks, legs grow and internal organs change.

More relevant to humans, the way thyroid hormone instructs a tadpole's brain to re-organize has direct parallels to human brains developing in the last trimester and first few weeks of life. Frogs are also sensitive to chemical contaminants in water, making them a long-standing "canary in the coalmine" animal, used as an early warning system of pollutants. As Helbing put it, not only are frogs a good tool to see if a chemical can disrupt hormones, but also how.

Helbing came to UVic in 1999 after a five year stint in cancer research at the University of Calgary, following her Ph.D. at the University of Western Ontario.

In her latest projects, Helbing uses a frog DNA array (which her lab developed) to detect which genes are activated in frog cells before and after exposure to chemicals. She then follows the frogs as they develop to look for visible physical changes or changes in behavioral due to the chemicals.

She's found several chemicals that disrupt frog development that could affect adult behavior, including the herbicide Actochlor, the flame retardant tetra-bromobisphenolA, and the antimicrobial agent Triclosan.

Her work on Triclosan (published in October 2006) attracted wide-spread media attention—with good cause.

Triclosan is everywhere. It is the active ingredient in antimicrobial soap, toothpaste, deodorants, toys and fabric. Microbiologists have long vilified the chemical as totally unnecessary and a source of antibiotic resistance. According to Helbing's work, it may be much worse: Triclosan may affect brain development in infants.

Helbing exposed tadpoles to a combination of Triclosan and thyroid hormone and found the tadpoles started to change prematurely into frogs.

The tadpoles did not respond to Triclosan alone, nor did they respond to thyroid hormone as intensely without Triclosan, giving a strong indication that Triclosan was somehow modifying the frog's response to the hormone.

Tadpoles do not normally produce thyroid hormone until just before they are ready to transform into frogs. In Helbing's first experiment, she used tadpoles who were not yet producing their own thyroid hormone which made it easy to link the effects of Triclosan to the hormone.

Helbing is currently repeating the experiment in older tadpoles. She predicts the Triclosan will hasten the changes brought on by the tadpole's endogenous thyroid to the detriment of the adult frogs.

There are several worrisome aspects to Helbing's findings. For one, if Triclosan affects thyroid hormone in humans as it does in frogs, it could be dangerous to human infants. Also, her work points to a problem with current toxicity testing.

A lot of toxicology studies assume that the effects are dose-dependent. However, hormones (or chemicals that mimic hormones) are just the opposite: they may have a greater effect at low doses. At higher doses, the body's regulatory response kicks in and dampens the effect, Helbing explains.

In her work, she found that Triclosan was affecting frogs in low concentrations, which were comparable to concentrations found in some waterways.

The implications of Helbing's work are fraught with controversy. So far there are no calls to ban Triclosan, but as other researchers build on her work, Helbing senses a storm is brewing. Based on how her frogs responded, she feels there is enough of a concern about human health to warrant fresh toxicology studies. While Helbing doesn't relish controversy, she feels that studies like hers are crucial to give policy makers more scientific data with which to work.