Endotoxin-induced changes of type VII collagen- cleaving matrix metalloproteinases in lamellar tissue of extracorporeally perfused equine limbs

Endotoxin-induced changes in expression of cyclooxygenase isoforms in the lamellar tissue of extracorporeally haemoperfused equine limbs

Angiogenesis and sepsis‐related equine laminitis have several features in common. Both events can be induced by endotoxin (lipopolysaccharide— LPS) and both are associated with increased expression of the enzyme cyclooxygenase (COX), of which two isoforms (COX‐1 and COX‐2) exist. To examine the causal relationship between LPS exposure and COX expression and to investigate the tissue distribution of COX in the LPS‐exposed tissue, the technique of extracorporeal haemoperfusion of isolated equine forelimbs was utilized. Perfusion was performed for 10 hr under physiological conditions (control‐perfused limbs, n = 5) and with addition of 80 ng/L of endotoxin (LPS‐perfused limbs; n = 5). After perfusion, samples of lamellar tissue were collected from the dorsal aspect of the hoof wall. Additional control samples were collected from three non‐perfused limbs. Immunohistochemical analysis was performed using antibodies against COX‐1 and COX‐2, and intensity of immunohistochemical staining was scored for each isoform. In the lamellar tissue of control‐ and LPS‐perfused limbs, there was no significant difference in COX‐1 staining intensity and distribution, whereas COX‐2 expression was significantly increased in LPS‐perfused limbs (especially in endothelial cells, fibroblasts and intravasal leucocytes as well as in epidermal basal cells at the base of the primary epidermal lamellae). These results suggest that COX‐2 and its metabolites are involved in the initiation of pathological changes seen in sepsis‐associated events such as sepsis‐related laminitis. In such cases, COX‐2 could therefore be an important therapeutic target; however, early therapy may be required as increase in COX‐2 expression occurs within 10 hr after LPS exposure.

The Equine Hoof: Laminitis, Progenitor (Stem) Cells, and Therapy Development

The equine hoof capsule, composed of modified epidermis and dermis, is vital for protecting the third phalanx from forces of locomotion. There are descriptions of laminitis, defined as inflammation of sensitive hoof tissues but recognized as pathologic changes with or without inflammatory mediators, in the earliest records of domesticated horses. Laminitis can range from mild to serious, and signs can be acute, chronic, or transition from acute, severe inflammation to permanently abnormal tissue. Damage within the intricate dermal and epidermal connections of the primary and secondary lamellae is often associated with lifelong changes in hoof growth, repair, and conformation. Decades of research contribute to contemporary standards of care that include systemic and local therapies as well as mechanical hoof support. Despite this, consistent mechanisms to restore healthy tissue formation following a laminitic insult are lacking. Endogenous and exogenous progenitor cell contributions to healthy tissue formation is established for most tissues. There is comparably little information about equine hoof progenitor cells. Equine hoof anatomy, laminitis, and progenitor cells are covered in this review. The potential of progenitor cells to advance in vitro equine hoof tissue models and translate to clinical therapies may significantly improve prevention and treatment of a devastating condition that has afflicted equine companions throughout history.