Blind bet: despite uncertain odds, many horse owners gamble on stem cell therapy

Science News, Jan 19, 2008 by Laura Beil

No animal has shaped the course of civilization more than the horse. Horses have pulled plows, herded cattle, and brought riders into battlefields and to the edges of continents. Today, horses are carrying their human companions to another frontier--the uncharted territory of stem cell medicine.

Throughout the rich history of horses, their legs have been the source of both strength and weakness. For all their size and brawn, horses move on limbs that are relatively long and slender. That arrangement provides agility and speed to 1,000 pounds of body weight, but leaves the animal at risk of injury. At a gallop, a horse places only one hoof on the ground at a time. That means at any given moment, the animal's great weight depends on a joint about the size of a baseball. No wonder then that roughly half of all performance horses end up retiring because their legs finally fail them.

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So far, no remedy for injuries or arthritis can claim stellar results. Newer treatments exist, but rest and controlled exercise remain mainstays. But now, many equine experts believe that stem cells could supply what medicine so far has not: replacement parts.

"It's very exciting and incredibly promising," says researcher Lisa Fortier of Cornell University's College of Veterinary Medicine.

Not only for horses. Researchers are exploring the potential of stem cells in human orthopedics also, and if the approach works in the equine world, it will probably work in the human one. Two-legged patients have only a fraction of the joint stress. "A horse is essentially walking around on your middle finger," Fortier says.

Recent studies of stem cell therapies have produced encouraging results, but Fortier also points out that "there is zero peer-reviewed published evidence that this actually works."

Investigations of stem cells for veterinary medicine began in earnest just this decade, as scientists throughout the world began to understand stem cells. Stem cells have the potential to become many different types of cells. Cells that have already committed to becoming muscle, bone, or any other tissue are unchangeable. Stem cells, by contrast, retain possibility.

Much controversy has embroiled research into stem cells derived from human embryos. But stem cells of a different variety--called adult-derived stem cells--reside in fat, bone marrow, and other tissues. Scientists are still sorting out the potential of these two types of stem cells, and a recent study even announced the ability to transform adult skin cells into an embryoniclike state.

Almost all veterinary work has focused on adult-derived cells, using a technique that involves removing a stem cell from fat or bone marrow and turning it into a new tendon or another component of a joint in an injured horse. Currently, injured tendons become interwoven with scar tissue after healing. Scar tissue is strong but lacks the spring of the original tendon. Elasticity is a key to with standing force: A palm tree can weather hurricane-strength winds largely because of its ability to bend.

In "most tendon injuries, when they happen, the tendon will never go back to its original mechanical flexibility," says Allison Stewart of the University of Illinois at Urbana-Champaign's College of Veterinary Medicine.

Stem cells are appealing because they could potentially grow into something that looks less like scar tissue and more like tendon--without surgery or drugs. And the price, usually only a few thousand dollars, is a small gamble for owners with high economic and emotional commitment to their horses.

Roger Smith, of the Royal Veterinary College in England, helped pioneer the movement by developing a technique in 2002 for extracting stem cells from the horse's own bone marrow, growing them in a laboratory for about 3 weeks, and then injecting them into the injured limb. Once the stem cells were surrounded by mature tendon tissue, researchers hoped that local chemical cues would induce the bone marrow stem cells to develop into tendon cells. Smith partnered with an entrepreneur to form a company, VetCell Bioscience, and began offering the treatment to horse owners.

Meanwhile, in the United States, veterinarian Robert Harman was also developing a therapy for equine orthopedics, in this ease using stem cells extracted from fat tissue on a horse's rump. His Poway, Calif.-based company, Vet-Stem, has been offering the treatment since 2003.

Most researchers, company founders among them, acknowledge that the instant commercial availability of the treatment has been a major barrier to clinical research. To gauge the effectiveness of any treatment--in people or animals--scientists commonly compare a group that receives treatment with a group that gets nothing or only an elaborately disguised sham. Neither patient nor clinician knows who gets what. But horse owners, in a virtual stampede to stem cell treatment, are loath to consent to a study where their horses might get a placebo of injected saline solution.