Selenomethionine Mitigates Effects of Nocardia cyriacigeorgica-Induced Inflammation, Oxidative Stress, and Apoptosis in Bovine Mammary Epithelial Cells

<i>Nocardia cyriacigeorgica</i> causes bovine mastitis, reduces milk quantity and quality, and is often resistant to antimicrobials. Selenomethionine (SeMet) is a form of selenium, which reduces reactive oxygen species (ROS)-mediated apoptosis and intramammary infections. However, the protective effects of SeMet on <i>N. cyriacigeorgica</i>-infected bovine mammary epithelial cells (bMECs) are unclear. The objective of this study was to evaluate whether SeMet mitigated <i>N. cyriacigeorgica</i>-induced inflammatory injury, oxidative damage and apoptosis in bMECs. Cells were cultured with or without being pretreated with 40 µM of SeMet for 12 h, then challenged with <i>N. cyriacigeorgica</i> (multiplicity of infection = 5:1) for 6 h. Although <i>N. cyriacigeorgica</i> was resistant to lincomycin, erythromycin, enrofloxacin, penicillin, amoxicillin, cephalonium, cephalexin, and ceftriaxone, 40 μM SeMet increased cell viability and inhibited lactate dehydrogenase release in infected bMECs. Furthermore, <i>N. cyriacigeorgica</i> significantly induced mRNA production and protein expression of TNF-α, IL-1β, IL-6, and IL-8 at 6 h. Cell membrane rupture, cristae degeneration and mitochondria swelling were evident with transmission electron microscopy. Superoxide dismutase (SOD) and glutathione peroxidase (GSH-px) activities were down-regulated after 3, 6, or 12 h, whereas malondialdehyde (MDA) and ROS contents were significantly upregulated, with cell damage and apoptosis rapidly evident (the latter increased significantly in a time-dependent manner). In contrast, bMECs pretreated with 40 μM SeMet before infection, SOD, and GSH-px activities were upregulated (<i>p</i> < 0.05); MDA and ROS concentrations were downregulated (<i>p</i> < 0.05), and apoptosis was reduced (<i>p</i> < 0.05). In conclusion, 40 μM SeMet alleviated inflammation, oxidative stress and apoptosis induced by <i>N. cyriacigeorgica</i> in bMECs <i>cultured</i> in vitro.