Pharmacological alternatives to oxytetracycline as potential treatment of flexural limb deformities in foals: a preliminary in vitro cell viability and proliferation study

Flexural limb deformities are a widespread condition in foals. Oxytetracycline is a common conservative treatment option with relaxing effects on the muscle-tendon-unit, potentially mediated through a matrix-metalloproteinase (MMP)-inhibitor mechanism. Its high therapeutic dose for this indication, potential negative side effects, and the guidelines for prudent use of antimicrobials make investigating alternatives desirable. In this study, the influence of substances with potentially similar mechanisms of action, however without antimicrobial properties, on viability and proliferation of juvenile myofibroblasts was assessed in vitro. Myofibroblasts from forelimb superficial digital flexor tendons and accessory ligaments of the deep digital flexor tendon from 6 foals, euthanized for reasons unrelated to this study, were cultured and characterized. The myofibroblasts were incubated with oxytetracycline, the MMP-inhibitors incyclinide, ilomastat, aprotinin, pentoxifylline, the lathyrogenic agent β-aminopropionitrile fumarate and Dulbecco's modified eagle medium as control. Colorimetric cell viability (MTS) and crystal violet assays assessed their viability and proliferation capacities. The morphology and immunohistochemistry profile of the cultured cells was consistent with tendon and ligament myofibroblasts. All test substances were biocompatible, shown by the absence of significant differences with cells incubated with medium, demonstrating the absence of cytotoxic or anti-proliferative effect on juvenile myofibroblasts in the tested concentrations in this preliminary study.