Plasma Citrulline Levels in Horses at Risk of Acute Laminitis

Laminitis is a painful and irreversible disease in horses in which the soft tissue structures of the foot, called the laminae (connecting the coffin bone to the hoof wall), lose blood flow and deteriorate. Without the support of these laminae the coffin bone rotates downward, applying pressure to the sole of the foot and crushing the underlying structures, resulting in severe pain. Laminitis typically progresses through three stages: the early developmental stage is treatable yet undetectable, while the later acute and chronic stages are symptomatic but irreversible. Therefore, the identification of a diagnostic marker capable of detecting the developmental stage would allow earlier and more effective treatment. Laminitis is often triggered by unrelated events occurring elsewhere in the body such as gastrointestinal (GI) upset episodes, typically called “colic”, which involve intestinal epithelial cell death. Human studies have concluded that intestinal epithelium health can be measured using plasma citrulline concentrations. Citrulline is an α-amino acid circulated in the plasma that is produced mainly by intestinal epithelial cells. We hypothesized that horses in the developmental stage of laminitis would have reduced plasma citrulline concentrations resulting from intestinal epithelial cell death occurring from a GI upset episode. In this study, blood samples were collected from control horses (n=23) and horses at risk for developing laminitis (n=20). Plasma citrulline concentration was measured using chromatography based amino acid analysis. The normal range was then calculated from the control group and compared to the concentrations from horses that did or did not develop laminitis. Five of the 20 cases developed laminitis symptoms and also had reduced plasma citrulline concentrations. If decreased citrulline levels correlate with laminitis onset across a large set of samples, a simple and affordable blood test could be developed in the future to predict the likelihood of the disease progression to the acute and chronic (irreversible) stages. This would allow veterinarians to begin treatments that could significantly reduce the chance of the horse developing the condition, greatly improving their prognosis