Early Detection Device For Exposure To Chemical Warfare Agents Being Developed

The earliest sign of exposure to agents such as sarin and soman – words that were foreign to many Americans pre-Sept. 11 – are the seemingly innocent contractions of small groups of muscles, like an eye twitch, the researchers says.

They are pooling their knowledge about central nervous system toxins and the electromyogram, or EMG, that records the electrical activity of muscles, to develop an early detection device that may one day be worn by soldiers and rescue workers at risk; it may have applications as well for crop dusters, farmers and others who work around insecticides, similar, albeit less lethal, versions of these compounds called organophosphates.

"Chemical warfare agents kill by disrupting normal communication between nerves and muscles so that muscles can no longer relax," said Dr. Jerry J. Buccafusco, pharmacologist at the Medical College of Georgia. "The diaphragm muscles stop contracting so you can't breathe. The drugs get into your brain and your involuntary respiratory drive center – which makes you breathe while you sleep – goes into spasm. On top on that, you are going to have copious secretions because the cholinergic system (key to the nerve-muscle interaction that enables breathing) also is involved in secretions and sweating. So you drown in your own secretions, unable to breathe."

But at the earliest sign of confused communication between the brain and the nerves and muscles it controls, soldiers and others in close proximity might still be saved; Dr. Buccafusco and Dr. Carlo De Luca, a biomedical engineer at Boston University, want to maximize that chance.

"We believe we will see changes in the EMG signal that will be indicative of organophosphates in the body before they begin to do serious damage inside the body," Dr. De Luca said. "We have high hopes we can do that."

The National Institutes of Health recently increased those hopes by awarding a two-year, Small Business Innovation Research award jointly to Dr. De Luca's, biotech company, Altec, Inc., and Dr. Buccafusco's company, Prime Behavior Testing Laboratories.

Chemical warfare agents, insecticides and even some drugs for treating Alzheimer's disease work by inhibiting cholinesterase, an enzyme that breaks down acetylcholine, a key neurotransmitter in the body and brain involved in learning, memory and the neuromuscular system, Dr. Buccafusco said.

In fact, muscle contractions occur because a nerve triggers a muscle and it does that by releasing acetylcholine. "The reason you can move, say, your arm back and forth is because you have an enzyme called cholinesterase that's destroying acetylcholine virtually as it is being released," he said. "So you have this really sophisticated system that allows you to fire and relax in millisecond amounts of time."

The Germans actually developed chemical warfare agents by looking at the different inhibitors of cholinesterase. For example, eye drops used to relieve the dangerously high intraocular pressure of glaucoma use carbamates to temporarily tie up the enzyme cholinesterase, so that aceylcholine lingers longer, constricting the pupil and temporarily increasing the fluid outflow channel of the eye. When the Germans looked at phosphates, they found the phosphate group stuck to the target site, creating an essentially irreversible bond that renders cholinesterase inactive and leaves muscles contracted.

Dr. De Luca calls the surface EMG signal the "most underused bio-signal in the body." But he and Dr. Buccafusco believe the same technology that assesses the muscle weakness of a patient in rehab can be modified to serve as well on the front lines of battlefields and farmlands.

Dr. Buccafusco has been studying acetylcholine and cholinesterase inhibitors for years, both in evaluating potential new treatments for Alzheimer's disease and in determining how soldiers, farmers and others are impacted by chronic exposure to sub-toxic doses of organophosphates that may linger in war zones or family farms.

On the current project with Dr. De Luca, he has preliminary data on Rhesus monkeys at the Alzheimer's Research Center at MCG, using a phosphate-based glaucoma drug rather than dangerous chemical warfare agents.

The tests show the EMG was able to detect superficial muscle twitches in human-like primates before secondary, cold-like symptoms set in. "So, at least in that particular experiment, it seems the answer is ‘yes,' peripheral muscles seem to be more sensitive."

This does not surprise him because the highest release rate, turnover rate and breakdown rate for acetylcholine is in the neuromuscular system. As soon as the monkeys show the cold-like signs of increased salivation and eye secretion, they are given an antidote to avoid pain or distress.

The primate studies will be expanded over the next six months to include giving memory tests to the monkeys – who initially should actually have improved cognition because of the decreased breakdown of acetylcholine – to obtain the EMG signal under confounding conditions. However, with longer-term exposure, the cognition benefit likely will go away because of the irreversible nature of these agents.

Boston researchers will use the collected data to develop sophisticated algorithms that will be placed in a prototype that eventually could be clinically tested. Included in the detection device is a tracking system so that soldiers or others using the device could be rapidly found and treated.

The researchers are still discussing the most effective style and position for the device, everything from a wristband to a shoulder patch to a device that's periodically squeezed.

Dr. De Luca said his spinoff company, which turns scientific findings into real applications, is "one of the most fascinating things I've done in my life." Dr. Buccafusco agrees that the opportunity to apply research is a great one. "One of my dreams as a child was to some day help the government deal with catastrophe. This is one of the things most scientists dream about. If I can do that in a small way, help a soldier survive or help a farmer in the fields, it's great."