Researchers Hope to Tap Into Leeches’ Medical Promise
It is a slimy black bloodsucker that lives in swamps, but to some scientists the dreaded leech represents a real chance to tackle some of the world’s most difficult medical problems.
To researchers at British firm Biopharm Ltd., the world’s largest commercial leech farm, the creature is seen as a rich source of possible new drugs.
“Leeches have a highly specialized lifestyle, and they have evolved in such a way that they produce many substances other animals don’t possess,” said Bob Wallis, Biopharm director of research and development.
Medieval practitioners, who used leeches by the bucketful to bleed patients of “diseased blood,” may not have been the quack doctors history says they were. Wallis says their ideas may have been dubious, but they were on the right track.
Most leeches feed on blood and face unique difficulties because wounds naturally clot. To keep feeding, leeches must produce chemicals that prevent a wound from closing or blood from clotting. A normal pin prick will bleed for 10 minutes, but a leech bite will ooze blood for 10 hours.
Biopharm hopes to isolate these novel substances and earn cash by licensing them out to pharmaceutical firms that can seek to turn them into useful drugs.
Wallis said Swiss firm Ciba-Geigy AG and Germany’s Hoechst AG are both in Phase III clinical trials for drugs derived from a substance called hirudin. If the drugs successfully combat blood clotting they may be used to treat heart attacks and vein thrombosis--the formation of potentially lethal blood clots.
The unusual diet of the leech also means that it could provide clues to a large range of possible drugs beyond just blood-clotting medicines.
Most leech bites are painless, and it is thought a painkiller is injected into the unwitting host. Wallis believes there is a leech-based local anesthetic just waiting to be discovered inside the leech’s mouth.
“Undoubtedly there are painkillers in there, but we have no idea what they are,” he said.
Leeches also are believed to produce a molecule that inhibits an enzyme that causes the human lung disease emphysema. “The time is close when we are going to start looking at an emphysema treatment,” Wallis said.
Biopharm, which nestles in a southern Welsh valley, was founded in 1984 and at the time was the world’s only commercial leech farm. The firm is privately owned and despite having only 20 employees maintains sales offices in the United States, France, Italy and Japan.
Its motto is “the Biting Edge of Science” and it produces more than 50,000 leeches a year.
The company has examples of many of the hundreds of leech species. Among them is the giant Amazon leech, which can grow to 18 inches in length. This monster, discovered by Biopharm founder Roy Sawyer, has already yielded a unique clot-dissolving substance called hementin.
But only a tiny fraction of Biopharm’s leeches are used for research. The majority, of a type known as hirudo medicinalis, are sold to hospitals where they are used in plastic surgery and the reattachment of severed body parts.
Though leeches are mostly used as a last resort, they are increasingly recognized as a vital surgeon’s tool. From supplying just four British hospitals 11 years ago Biopharm now supplies 150 in Britain and many more in 29 countries abroad.
But how does a bloodsucker help reattach a severed hand?
The surgeon’s problem is this: Arteries that supply the body with blood are thick-walled and easily sewn back together, but veins that drain blood are thinner and present a much more difficult problem.
A constant flow of blood needs to be created to keep the hand alive while the veins mesh together; otherwise, blood flowing in cannot get out and the severed part will become bloated with blood and die.
Enter the leeches.
By feeding on the body part, they can drain blood and prevent clotting until the circulation is moving naturally again.
One stumbling block seems obvious--patient reluctance to have leeches applied to their wounds. The most common reaction to leeches was famously summed up by Humphrey Bogart in the 1951 film “African Queen.”
“If there’s anything in the world I hate, its leeches--the filthy little devils,” Bogie’s character squirmed.
But Wallis says the leeches are so effective that patient fears are soon overcome. “If it’s a choice between having your ear or not having it, then the leech becomes a pretty persuasive argument,” he said.
The practice has led to some gruesome but successful operations. The record for the most leeches used on a single patient was an American man in 1995 who had 1,000 Biopharm animals used on his severed scalp.
In Britain the title is held by a man who had both hands reattached with the help of about 600 leeches.
But for the leech itself the ending is not quite so happy. To prevent the spread of blood-borne diseases like AIDS, each leech is destroyed after feeding.