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

Nocardia cyriacigeorgica causes bovine mastitis, reduces milk quantity and quality, and is often re-sistant to antimicrobials. Selenomethionine (SeMet) is a form of selenium, an essential trace el-ement. Although SeMet reduced ROS-mediated apoptosis and intramammary infections. How-ever, protective effects of SeMet on N. cyriacigeorgica-infected bovine mammary epithelial cells (bMECs) are unclear. The objective was to evaluate whether SeMet mitigated N. cyriacigeorgi-ca-induced inflammatory injury, oxidative damage and apoptosis in bMECs. Cells were cultured with or without being pretreated 40 µM of SeMet for 12 h, then challenged N. cyriacigeorgica (MOI=5:1) for 6 h. Although N. cyriacigeorgica was resistant to lincomycin, erythromycin, en-rofloxacin, penicillin, amoxicillin, cephalonium, cephalexin, and ceftriaxone, 40 μM SeMet in-creased cell viability and inhibited LDH release in infected bMECs. Furthermore, N. cyriacigeor-gica 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 evi-dent with transmission electron microscopy. SOD and GSH-px activities were down regulated after 3, 6 or 12 h, whereas 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 ac-tivities were upregulated (P < 0.05), MDA and ROS concentrations were downregulated (P < 0.05), and apoptosis was reduced (P < 0.05). In conclusion, 40 μM SeMet alleviated inflammation, oxi-dative stress and apoptosis induced by N. cyriacigeorgica in bMECs cultured in vitro.