Scientists at Iowa State are examining why hypericin, a chemical found in the St. John’s wort plant, is toxic to viruses and cancer cells when exposed to light.

St. John’s wort, which is common in the Midwest, has been traditionally used as an effective herbal remedy against depression, said Herbalist Doreen Edmundson.

Its light-reactive properties were discovered when cows became sick after grazing on the plants during the day but recovered when they were placed in a dark barn, according to the press release.

While the medical applications of the research, such as effective ways of combating AIDS and cancer, are a long way off, researchers are making progress in determining why hypericin is toxic when activated by light.

According to a press release, a recent discovery by Jacob Petrich, ISU associate chemistry professor, and his team indicates that the answer may lie in a double proton transfer.

But Doug English, graduate student in chemistry, cautioned it has yet to be proven what causes the toxicity to viruses and cancer cells.

Before Petrich’s research, it was believed that oxygen was a potential cause of the toxicity.

However, after the removal of oxygen from the experiment it was found that hypericin remained toxic.

Experiments done by Petrich indicate that when the hypericin molecule is exposed to light, hydrogen ions, or protons are ejected from the molecule.

English said this increases the protons within the surrounding area, and consequently increases the acidity of the area.

It is suspected by researchers that virus and cancer cells cannot survive in the higher acidity, but they have not eliminated other possibilities.

To test the hypotheses, Petrich used methyl groups, whose protons cannot leave, to chemically alter the hypericin.

The modified hypericin molecules did not release protons or increase the acidity of the surrounding area, indicating that the double proton transfer may be critical to the process.

“It doesn’t prove that’s why the compound has its antiviral effect,” said George Kraus, chemistry professor and chairman of the department. “But it’s an important step along the way.”

He said Petrich is trying to find a signature by which he can tell for sure the compound is exerting a specific effect.

Before researchers can begin clinical tests, they must understand what causes the effect of light on hypericin and what is responding within the hypericin, Kraus said.

But he said they have a long way to go before understanding precisely what hypericin is doing in its excited state.

Kraus said Petrich is working to “unravel that mystery.”

Meanwhile, Kraus and Susan Carpenter, professor of microbiology, immunology and preventive medicine, are working on a “molecular flashlight.”

The flashlight would be a way to activate the hypericin once it is inside the body, Kraus said.

ISU researchers were the first to observe the dependence of hypericin’s antiviral activity.

English said the short burst of a laser light was used to activate the molecule.

That enabled them to examine the excited state processes that occur after a photon of light is absorbed by the molecule, one of which was believed to be a double proton transfer, English said

But other excited state processes were also occurring at the same time.

English said they took their research to Brookhaven National Laboratory in Upton, N.Y. last March because it gave several signals that could be misinterpreted and confusing.

The Brookhaven laboratory has a laser experiment that uses fast pulses to generate fluorescence and make accurate time measurements. English said their laser experiment allowed them to “directly monitor proton transfers.”

“We’re using state of the art technology to measure the dynamics of the molecule in its excited state,” English said.

He added that Alexandre Smirnov, graduate student in chemistry, is constructing a duplicate experiment at ISU for future research.