Abstract
Oxidative stress (OS) is one of the main limiting factors affecting the length of lactation and milk quality in dairy cows. For high-producing dairy cows, the OS of mammary glands is a serious problem. Green tea polyphenols (GTP), found mainly in tea, are a combination of many phenols. GTP have a good effect on antioxidation, inflammation resistance, obesity, fat cell metabolism improvement, and lowering of blood lipid. Therefore, we studied the role of GTP on OS in dairy cows and further investigated whether GTP alleviates oxidative damage of bovine mammary epithelial cells (BMECs) induced by hydrogen peroxide (H2O2) and its underlying molecular mechanism. In this study, 500 μM of H2O2 for 12 h incubation was chosen as the condition of the OS model of BMECs. In addition, the present results found that treatment with GTP alleviated the oxidative damage induced by H2O2 [the activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT) were significantly increased, and the contents of malondialdehyde (MDA), 8-isoprostaglandin (8-iso-PG), 8-oxo-deoxyguanosine (8-OHdG), and protein carbonyl (PC) and caspase-3 and caspase-9 activities were significantly reduced]. These effects are related to the activation of the erythrocyte-derived nuclear factor 2-like protein 2 (NFE2L2) signaling pathway and the inactivation of the caspase/Bcl-2 apoptotic pathway. When NFE2L2 short interfering RNA (siRNA) was used to downregulate the expression of NFE2L2 in cultured BMECs, NFE2L2-siRNA transfection abolished the protective effect of GTP on H2O2-induced intracellular reactive oxygen species (ROS) accumulation and apoptosis. In addition, the mitogen-activated protein kinase (MAPK) inhibition test further proved that GTP relieved H2O2-induced oxidative damage by activating the NFE2L2 signaling pathway, which was achieved by activating the extracellular-regulated kinase 1/2 (ERK1/2) signaling pathway. Overall, the results indicate that GTP has a beneficial effect on the redox balance of BMECs. In addition, GTP might be a latent antioxidant in vivo, which can be administered to ruminants during stressful periods such as the perinatal period.
Highlights
Dairy cows are one of the most economically important animals, and they produce almost all the dairy products in the daily diet of human beings
500 μM of H2O2 for 12 h incubation was chosen as the condition of the oxidative stress (OS) model of bovine mammary epithelial cells (BMECs)
Our results found that Green tea polyphenols (GTP) can activate the NFE2L2 pathway in H2O2-damaged BMECs and increase the expression of HMOX1 and NQO1, which is consistent with the study by Ma et al [11] and Song et al [26]
Summary
Dairy cows are one of the most economically important animals, and they produce almost all the dairy products in the daily diet of human beings. Continuous OS damages the health of bovine mammary cells and affects milk production and the quality of dairy products [1]. Reducing and preventing OS of bovine mammary cells is of great significance for promoting the healthy lactation of dairy cows. Mammary epithelial cells undergo highintensity metabolism, and produce a large amount of reactive oxygen species (ROS), which can cause inflammation. OS can affect the lactation time and milk quality of dairy cows [3]. Compared with those of healthy-yield dairy cows, the mammary tissues of high-producing cows pass more blood flow, which makes their mammary epithelial cells more prone to OS. The inhibition of OS is essential in preventing apoptosis in BMECs [5, 6]
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