Preliminary assessment of the mucosal toxicity of tea tree (Melaleuca alternifolia) and rosemary (rosmarinus officinalis) essential oils on novel porcine uterus models

Antimicrobial resistance, an ever-growing global crisis, is strongly linked to the swine production industry. In previous studies, Melaleuca alternifolia and Rosmarinus officinalis essential oils have been evaluated for toxicity on porcine spermatozoa and for antimicrobial capabilities in artificial insemination doses, with the future perspective of their use as antibiotic alternatives. The aim of the present research was to develop and validate in vitro and ex vivo models of porcine uterine mucosa for the evaluation of mucosal toxicity of essential oils. The in vitro model assessed the toxicity of a wider range of concentrations of both essential oils (from 0.2 to 500 mg/mL) on sections of uterine tissue, while the ex vivo model was achieved by filling the uterine horns. The damage induced by the oils was assessed by Evans Blue (EB) permeability assay and histologically. The expression of ZO-1, a protein involved in the composition of tight junctions, was assessed through immunohistochemical and immunofluorescence analysis. The results showed that low concentrations (0.2–0.4 mg/mL) of both essential oils, already identified as non-spermicidal but still antimicrobial, did not alter the structure and permeability of the swine uterine mucosa. Overall, these findings strengthen the hypothesis of a safe use of essential oils in inseminating doses of boar to replace antibiotics.