Ex vivo effects of insulin on the structural integrity of equine digital lamellae

Background Laminitis has a considerable impact on the equine industry. Endocrinopathic laminitis is the most common form and affected horses often have hyperinsulinaemia due to an underlying metabolic disorder. Objectives Study design The aim of this study was to determine if insulin weakens the structural integrity of digital lamellae and to develop an ex vivo model for the study of hyperinsulinaemia-induced lamellar failure. Ex vivo experiment. Methods Results Biomechanical testing was used to assess the structural integrity of lamellar explants exposed to either medium alone (control) or medium supplemented with insulin. Lamellar explants comprised of hoof wall, lamellar tissue and distal phalanx were harvested from four adult horses with no evidence of inflammatory disease or pre-existing disease of the digit. Following an equilibration period, explants were incubated in medium or medium supplemented with insulin (2.5 mu g/ml) for 8 h prior to biomechanical testing to obtain load (N), stress (MPa), elongation to failure (mm), and Young's modulus (MPa) for each explant. Significant differences were assessed using a mixed linear model with horses as a random factor and control or insulin-treated group as a fixed factor. Lamellar explants incubated in medium supplemented with insulin failed at significantly lower load (P = 0.0001) and lower stress (P = 0.001) and had greater elongation to failure (P = 0.02). Main limitations Conclusions In addition to the ex vivo nature of the study, location-dependent variability in explant structural integrity and variable diffusion of nutrients due to explant size may have been limitations. However, the study design attempted to account for these limitations through random assignment of explants to treatment groups independent of location and by evaluating stress to failure. Insulin weakens the structural integrity of equine lamellar explants and an ex vivo model for evaluation of hyperinsulinaemia-induced lamellar failure was established.