Auburn veterinary researchers hope to solve laminitis puzzle

Veterinarians and horse owners are familiar with laminitis, a crippling disease that can strike almost any horse. Although researchers have attempted to solve the puzzle of why and how the disease occurs for more than 40 years, there are still many gaps in the knowledge of the disease process—and, due to that lack of knowledge, we are still without effective treatments for the disease.

But a new approach is underway at Auburn University as researchers use molecular biology techniques to look for the pattern of gene expression that occurs in this disease often referred to as founder.

"We are examining the affected tissues in the horse's foot, and screening for genes which are activated in the early stages of laminitis," said Dr. Jim Belknap, head of the Equine Section of AU's College of Veterinary Medicine.

Laminitis commonly occurs secondary to numerous diseases including colic, severe bacterial infections (such as advanced cases of pneumonia, uterine infection subsequent to retained placenta, and diarrhea), exposure to black walnut shavings, grain overload, and ingestion of lush green pasture.

In laminitis, systemic derangements from these diseases lead to disruption of the blood flow to the horse's feet which results in deterioration of the laminae, the tissue binding the coffin bone (third phalanx) to the hoof wall. With loss of support of the laminae, the horse's weight forces the coffin bone downward, tearing all of the laminar attachments and resulting in crippling lameness. The coffin bone can literally come through the bottom of the horse's foot, commonly leading to humane destruction of the animal.

"The frustrating part is that we know which horses are likely to develop laminitis, but we still do not have adequate knowledge of the disease process to know what drugs to treat these horses with to keep many of these horses from foundering," said Dr. Belknap, who grew up on his family's Land O Goshen Farms near Louisville, Ky.

"Researchers have had little luck finding a mediator in the horse's bloodstream that causes this disease process,” he said. “We feel the reason is that the majority of the important gene activation is occurring in the foot itself. Our goal is to find what genes are being  activated in the horse's foot in that critical time period following the initiating disease process but before the crippling laminar destruction occurs."

Initial results from the AU research have demonstrated that inflammatory mediators (proteins/molecules that cause physiologic changes) are expressed by cells within the laminae early in the laminitic process. In this research, microscopic probes were made specifically for a gene of interest. The probes will attach to the RNA expressed by the gene in any cell in which the gene is activated. Dr. Belknap says that by finding the expression of these inflammatory mediators known as cytokines, they may have identified one of the initial steps in the process that leads to destruction of the foot's laminae.

"We are very excited about the first results,” he said. “The presence of inflammatory mediators in the affected horse's feet early in the laminitic process tells us to give all at-risk horses a high level of anti-inflammatory drugs very early on to block these mediators. We had been using lower doses to avoid stomach ulcers and kidney damage, but these results indicate that we should consider using higher dosages of anti-inflammatories as it is much more likely that the horses will be destroyed due to laminitis than due to complications from the drug therapy." 

The study's first steps were geared toward investigation of the presence of inflammatory and vascular mediators. Dr. Belknap's group is now using a totally non-biased approach to investigate genes activated in the early stage of laminitis.

"Up to this point, researchers including us have only looked at mediators that we have thought may be involved in laminitis due to theories or extrapolation from distantly related human diseases,” he said. “The danger of this is that, by biasing our research toward our favorite mediator, we may miss a total family of mediators that is critical to the disease process.

"In this unbiased molecular cloning technique, we will isolate numerous genes that undergo higher expression in the laminitic horse. Using this technique, we are likely to find genes/mediators that are important in the development of laminitis that no one has previously considered. The exciting part to me is that the discovery of a novel mediator or family of mediators important in laminitis may lead to an effective treatment. These techniques have resulted in some very important discoveries in different human diseases.”

While the potential discoveries of genetic research are seemingly endless, he says that it is unrealistic to believe that this project will show one particular gene to be "the key" to preventing laminitis. However, he is hopeful the AU work might uncover a multiple-gene process which could possibly be treated with medicine designed for other diseases that involve activation of the same genes.