Neutrophil activation in models of equine laminitis

Laminitis is a pathology of the equine digit resulting in failure of the dermo-epidermal interface. Inflammation is a central player in the pathophysiology. Neutrophil activation and the presence of myeloperoxidase have been observed in the black walnut heartwood extract model. However, less is known about their role in the hyperinsulinemia model. Histological sections of laminar tissue of three horses with hyperinsulinemia-induced laminitis and two control horses were immunohistochemically stained for myeloperoxidase. Insulin-induced horses showed an increased presence of myeloperoxidase in the dermal lamellae. Therefore, neutrophil activation with myeloperoxidase release seems to play a role in the pathophysiology of laminitis related to hyperinsulinemia. The second part of this study investigates the effect of juglone, a principle in the black walnut heartwood extract, on the viability of isolated neutrophils and their reactive oxygen species production by chemiluminescence after their stimulation. The effect of juglone on myeloperoxidase activity was analysed using immunologic and enzymatic assays and by a docking analysis to determine the possible interaction of juglone with the enzyme. Besides its strong inhibitory effect on reactive oxygen species production by neutrophils, juglone was able to inhibit myeloperoxidase activity by interacting with the active site of the enzyme.