Scientists look at fracture healing, lung damage from bleeding, EPM, foal pneumonia, and more

by Denise Steffanus

EQUINE research foundations raise funds to support studies that benefit the horse industry. In the United States, the Grayson-Jockey Club Research Foundation, American Quarter Horse Foundation, Morris Animal Foundation, and many other foundations established by universities, associations, breed organizations, and individuals devote millions of dollars each year to research that enhances the health and welfare of the horse.

Recent studies have investigated a wide range of problems that challenge the horse and drain dollars from horse owners' pockets. Below are some research projects of particular interest to those in the Thoroughbred industry.

Accelerated fracture repair

Fractures in horses take as long as four months to a year to fully repair. Complications arise in many cases when the horse must bear weight on the injury or when laminitis develops in the opposite limb. Alicia Bertone, D.V.M., Ph.D., recently completed a study at Ohio State University that uses gene therapy to inject bone morphogenetic protein--a specialized protein that aids in fracture repair--directly into the fracture site to accelerate healing.

"There are body proteins--biologic proteins--that go up naturally at the site of the fracture," said Bertone. "The most potent one identified to date is bone morphogenetic protein: BMP. There is quite a bit of research in other species that shows that these BMPs can accelerate bone healing."

According to Bertone, human surgeons place surgical sponges soaked in BMP at the site of spinal injury to hasten bone fusion, but the BMP materials typically cost about $5,000. "It's complicated and expensive," she said. Bertone's study aimed to find a cost-effective means to provide BMP treatment to horses.

"What we did was take the gene for the BMP, which is much faster and easier to produce, and we put it into a viral vector," Bertone said. "Viruses have become experts in getting genes into cells; that's how they replicate and make you sick. They are the best method to bring genes into cells. So we take these viruses and make them non-pathogenic--they don't make the horse sick--and we put the BMP gene in this viral vector, and then we inject it into a fracture."

Bertone's study used BMP therapy to accelerate healing in splint bone fractures.

"Basically, that study is completed, and our results look very promising," she said. "I think it will become a cost-effective treatment."

Lung damage from bleeding

Exercise-induced pulmonary hemorrhage (EIPH) occurs in most racehorses during peak performance. Different theories exist as to why bleeding in the lungs occurs.

Some researchers believe it is caused when the huge equine heart pumps at maximum force and causes the horse's blood pressure to soar to a level that makes small blood vessels burst. Other researchers theorize that bleeding results from mechanical weakness in certain parts of the lungs created by repetition of movement, much like bending a paper clip repeatedly causes it to break.

After an episode of EIPH, scar tissue typically forms during healing, which compounds the condition. "This results in a vicious cycle of racing, scarring, and bleeding," said Frederik Derksen, D.V.M., Ph.D., professor of large animal clinical sciences at Michigan State University and one of the world's leading authorities in equine respiratory disease.

Derksen has undertaken the task of testing the medication Enalapril for its effectiveness in preventing the formation of scar tissue in the lungs.

"This is not a medication meant to prevent bleeding itself," Derksen explained, "but to alleviate the damage caused by blood in the lungs."

In human medicine, Enalapril is in a class of medications called angiotensin-converting enzyme (ACE) inhibitors, which are used to control high blood pressure. It decreases certain chemicals that tighten blood vessels, enabling blood to flow more smoothly and the heart to pump blood more efficiently.

New EPM diagnostics

Research is complete on three diagnostic tools to detect the neurological disease equine protozoal myeloencephalitis (EPM). The Western blot test, which has been the gold standard, does not distinguish between an active infection and benign exposure. Scientists hope these new tests will solve that problem.

Molecular biologist Daniel Howe, Ph.D., and his colleagues at the University of Kentucky's Maxwell H. Gluck Equine Research Center have developed an enzyme-linked immunosorbent assay (ELISA) test that concentrates on detection of a surface protein of the protozoan Sarcocystis neurona that causes EPM rather than the multitude of proteins screened by the Western blot test.

Howe said 50% of the samples he tests are positive for antibodies to S. neurona, but not all these horses have an active infection.

"We hope we can use these assays to distinguish a horse that simply has been infected with Sarcocystis neurona but has no disease versus the horse that has been infected and is clinically affected," Howe said. "Obviously, I think that would be the biggest benefit, and there is still some work we are doing to try to achieve that."

Martin Furr, D.V.M., Ph.D., chief of medicine at the Marion duPont Scott Equine Medical Center at Morven Park in Leesburg, Virginia, has completed work on a new diagnostic test that employs a computer chip to identify a pattern of activity, called gene expression, in circulating white blood cells that would indicate an active EPM infection. Gene expression means that certain genes that react to the disease begin to express proteins. Identifying those active genes and how they interact, then linking them to the specific disease that causes them is called a diagnostic signature.

"We developed a diagnostic signature for EPM that proved highly accurate, at least in the acute phase of infection--up to 28 days," Furr said.

The genomic biomarkers are expected to be able to provide information on the stage of disease and the prognosis, as well as a means to monitor the progression of the disease and its response to treatment.

William Saville, D.V.M., Ph.D., a principal researcher into EPM at Ohio State who also collaborated on Furr's project, disclosed that he and his colleagues have developed an ELISA test that detects the presence of immunoglobulin M (IgM) in serum of horses infected by S. neurona. IgM is the antibody produced in first response to an acute infection.

"Although [the test] is not perfect, we think that at least if there is IgM there, it is a very recent infection," Saville said.

Ideally, the test would be administered as soon as indications point to an EPM infection. "And if it's a very acute infection, the likelihood that it is EPM is higher, just based on the fact that it's occurring at that time," Saville said.

The question remains whether the new IgM test will be able to discern between a natural infection and antibodies produced in response to the EPM vaccine, manufactured by Fort Dodge Animal Health. "The vaccine produces very little IgM, according to the company," Saville said. "So, hopefully, yes, but it may not happen in all instances."

Magic bullet for foal pneumonia?

Respiratory disease is the most commonly reported cause of death in foals. One insidious form of the disease is pneumonia caused by Rhodococcus equi, a silent killer whose symptoms can go unnoticed for months until the infection has abscessed the foal's lungs--a point where little can be done to save its life.

Ronald Martens, D.V.M., Keith Chaffin, D.V.M, M.S., and Noah Cohen, V.M.D., Ph.D., are the principal researchers at Texas A&M University investigating R. equi. According to Martens, research has shown that foals most likely are infected with R. equi near the time of birth. Development of a vaccine to be administered to a newborn foal to prevent the disease is not practical because a vaccine would take about three weeks to achieve protection.

In a novel approach to the problem, Martens is investigating the use of a metal, gallium, to kill R. equi before it can cause clinical disease.

"Gallium works by starving the bacteria," Martens explained. "It does that because bacteria need iron to live. Gallium is very similar in some respects to iron. So the bacteria thinks it is iron and takes it in, but it can't utilize it. The gallium starts to interfere with the bacteria's DNA production. When they can't reproduce, they eventually die."

Martens said gallium is used safely in other species and to treat human cancer patients. His study has shown gallium's effectiveness in killing R. equi in test-tube studies and in laboratory mice. In preliminary tests in foals, Martens has obtained good levels of the metal in blood samples, and he has proven it is safe. The next step is to test its effectiveness in protecting foals against R. equi in a field study.

Endotoxemia blocker

Most colic deaths are caused by endotoxemia, which occurs when bacterial endotoxins are absorbed into the bloodstream through the horse's damaged gut walls, causing severe inflammation that results in shock and organ damage. The disease rapidly progresses to death.

"Endotoxins stimulate white blood cells and other cells to induce an inflammatory response that is not regulated appropriately," said Sam Jones, D.V.M., Ph.D., associate professor of equine medicine at North Carolina State University.

Jones and his colleagues believe a key player that enables certain genes to precipitate the severe inflammatory response associated with endotoxemia is the molecule p38. In this ongoing study, Jones ultimately hopes to find a drug that will block the function of p38, which he called a "linchpin" in the inflammatory process.

"Then we potentially can interfere clinically with the inflammatory response and ultimately have a treatment for endotoxemia," Jones said.

According to Jones, blocking p38 also might be useful in the treatment of laminitis or in inhibiting the inflammatory response that triggers the disease. "Many of the genes that have been identified as being involved in laminitis are regulated by p38," Jones said.

Inflammatory responses are the immune system's way of fighting disease. One of Jones's concerns is that a drug powerful enough to block the function of p38 also might suppress the immune system.

Jones said his study aims to find a drug that inhibits p38, confirm that it does the job appropriately, and assure that it can be used safely and effectively in horses.

"This is by no means something where, if these experiments work out, we now have a drug to treat endotoxemia, but we certainly have a very attractive possibility," Jones said.

Denise Steffanus is a contributing editor of Thoroughbred Times who writes frequently on veterinary and farm management topics