Tick protein tapped to attack blood clots.

Tick protein tapped to attack blood clots

Low on the list of nature's most popular animals creeps the tick. Described by one entomologist as an "ugly bag of skin," this squatty, slow-crawling relative of the spider has an unwavering thirst for fresh blood and is a common carrier of disease, including Rocky Mountain spotted fever and Lyme disease. But if a scientific hunch proves correct, thousands of people threatened by blood clots may someday have kinder words for ticks.

From an extract of the "soft" tick Ornithodoros moubata, researchers have purified a peptide, or small protein, which they speculate may have therapeutic value as an anticoagulant. Physicians often use anticoagulant drugs to prevent blood clots in patients recuperating from heart attacks, stroke or major surgery, but not without risking serious side effects. For instance, heparin -- the anticoagulant most commonly prescribed for heart attack and stroke patients -- can cause abnormal bleeding, bruises, rashes, aching bones or burning feet. And in a small fraction of patients, lethal clots may form despite heparin treatment.

Like heparin, the newly isolated tick anticoagulant peptide (TAP) interrupts the chain of enzyme reactions that produces fibrin, an insoluble mesh of protein that gives structure to a blood clot. But "unlike other clot preventers, such as heparin, this isolated tick anticoagulant acts only on [clotting] factor Xa, and not on other enzymes in the clot chain or on platelets," biochemist George P. Vlasuk told SCIENCE NEWS. "Hence, there might be fewer side effects if this anticoagulant could ever be used clinically."

Vlasuk and his colleagues at Merck Sharp & Dohme Research Laboratories in West Point, Pa., describe their work in the May 4 SCIENCE.

"One interesting sidelight," adds Vlasuk, is that "ticks cause Lyme disease.... If we knew more about how they naturally use a blood anticoagulant to feed, we might be able to control ticks by developing an antibody to a tick anticoagulant." Researchers have already developed such "tick vaccines" for livestock, derived from anticoagulants other than TAP (SN: 3/25/89, p.186).

"But it's a leap of faith at this point to extrapolate from soft ticks to the deer [Lyme disease] tick," cautions Richard Endris of Merck Sharp & Dohme in Rahway, N.J., who served as an entomological consultant on the study. Noting that this species feeds much more slowly than O. moubata, he says, "The same [anticoagulant] mechanism might not occur in the deer tick."