Zearalenone Promotes LPS-Induced Oxidative Stress, Endoplasmic Reticulum Stress, and Accelerates Bovine Mammary Epithelial Cell Apoptosis

Both zearalenone (ZEA) and lipopolysaccharide (LPS) can induce oxidative stress, and even apoptosis in bovine mammary epithelial cells (MAC-T), but not much attention has been given to the synergistic effect of ZEA and LPS. In this study, we treated MAC-T cells with different concentrations of LPS (1, 10, 50, and 100 μg/mL) and ZEA (5, 15, and 30 μM) to induce cell damage. Previous results show that MAC-T cell viability decreases with increasing LPS concentration. Meanwhile, 1 µg/mL LPS and ZEA were selected for combined treatment in subsequent studies. It was found that co-treatment with ZEA and LPS increases the accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA), decreases mitochondrial membrane potential (MMP), and superoxide dismutase (SOD), and reduces glutathione (GSH). ZEA and LPS are found to activate endoplasmic reticulum (ER) stress by increasing the expression of glucose-regulated protein 78 kDa (GRP78), activating transcription factor 6 (ATF6) and C/EBP homologous protein (CHOP). It increases cell apoptosis by suppressing the expression of the anti-apoptotic protein B-cell lymphoma-2 (Bcl-2), indicated by up-regulation of Bcl2-associated X protein (Bax) and Cysteinyl aspartate-specific proteinases 3 (caspase-3) expression. The above results suggest that the synergistic effect of ZEA and LPS aggravate cytotoxicity