Effects of unfractionated and fractionated heparins on myeloperoxidase activity and interactions with endothelial cells: possible effects on the pathophysiology of equine laminitis.

As heparins are sometimes used to prevent equine laminitis, the interactions between equine neutrophil myeloperoxidase (MPO), unfractionated (UFH) and fractionated low molecular weight (LMWH) heparins and digital endothelium have been investigated. The effects of the heparins on purified equine MPO activity were tested by immunocapture followed by enzymatic detection. Endothelium-MPO interactions were assessed by measuring total and active MPO uptake by arterial and venous digital endothelial cells in culture with or without the addition of heparins. A dose-dependent MPO inhibition by UFH and LMWH was seen, with the greatest reduction in MPO activity noted with the highest concentration of LMWH. The MPO capture was greater in arterial cells, but heparins better inhibited MPO capture in venous cells. The activity of cell-bound MPO was almost completely suppressed by the heparins, and no differences were observed between UFH and LMWH. The results confirm the anti-inflammatory properties of heparins and allow a better understanding of the potential role of MPO in laminitis.