Substance Derived From Horseshoe Crab Blood Helps Save At-Risk Human Patients

Horseshoe crabs have become true blue-blood donors.

The strange sea creature, which resembles a horse’s hoof with a spikelike tail and startles some beach goers along the U.S. Atlantic coast, is helping to fight disease and save human lives.

New techniques using horseshoe crab blood may soon both detect and battle endotoxins that have invaded the human bloodstream. Endotoxins, chemical poisons released from some bacteria, are harmless unless they enter the bloodstream. Then even minute quantities can kill.

Scientists working at nearby Woods Hole Marine Biological Laboratory discovered in the mid-1960s that the horseshoe crab’s blood, which turns blue when exposed to air, clots when exposed to endotoxins.

Every year now, thousands of horseshoe crabs are harvested and hauled alive to laboratories, where they donate some of their blood as a diagnostic tool. Crab blood turns blue because it contains hemocyanin, a copper-based molecule that carries oxygen throughout the circulatory system.

More than 1,000 crabs a week give blood during peak summer months here at Associates of Cape Cod, one of the nation’s largest crab labs. Like human donors, horseshoe crabs are not harmed by the experience. They are all returned home to the sea.

The end product is a white powder that experts the world over use to detect bacterial contamination or disease.

“Many of our customers are pharmaceutical companies,” said Stanley Watson, president of Associates of Cape Cod. “Anytime they make a solution or product to be injected into the human body, they have to be sure these products are free of endotoxins.”

The horseshoe crab substance has also been used to diagnose illnesses such as meningitis because it can detect endotoxins associated with it.

Patients who are coming out of surgery, undergoing chemotherapy or who have been treated for serious burns are particularly susceptible to septic shock caused by such endotoxins.

“Doctors don’t know whether a patient’s in septic shock or not, it’s just by clinical observation,” Watson said. “We hope to develop a test to detect septic shock, and a method to treat it.

Some electronic companies use the white powder produced from the crab blood to detect damaged computer chips. The chips are so small that the presence of a single bacterium across two little elements in a chip could be enough to short it out.

Horseshoe crabs are playing an important role in another area of research--the human eye, its functions and failings. The crab’s two large lateral eyes have been studied more than any other animal’s, because of the size and simplicity of their structure and because they function much like most vertebrate eyes.

“We’re trying to understand how the human eye and the brain work together to give us vision,” said Robert Barlow, a professor of neuroscience at Syracuse University. “And we feel there is a good chance of answering this question with the visual system of the horseshoe crab.”

One of Earth’s oldest inhabitants, the horseshoe crab, which has seen the dinosaurs come and go, has survived virtually unchanged for some 360 million years. Only four species survive. Three of them live along the shores of Southeast Asia and nearby islands. Their American cousins populate the Atlantic coast from Maine to the Yucatan Peninsula on the Gulf of Mexico.

Adult horseshoe crabs can measure more than 2 feet long, and despite their fearsome appearance, are harmless. “There’s this false conception by both the public and the fishing community that these things either kill fish or are dangerous to humans,” said Maureen Powers, a Vanderbilt University neuroscientist.