Tea polyphenols protect bovine mammary epithelial cells from hydrogen peroxide-induced oxidative damage in vitro

Periparturient dairy cows are subjected to altered intracellular reduction-oxidation (redox) balance due to the high metabolic rates and physiological adaptations characteristic of the transition into lactation. Such conditions could alter oxidative stress status. The objective of this study was to investigate the cytoprotective effects of tea polyphenols (TP) in cultured bovine mammary epithelial cells (BMEC) exposed to hydrogen peroxide (H₂O₂)-induced oxidative stress. To establish oxidative stress, isolated BMEC were exposed to increasing concentrations of H₂O₂ (0, 100, 200, 400, 600, 800, and 1,000 μM) for 0, 2, 4, 6, 8, 12, and 24 h. Doses of TP (0, 60, 80, and 100 μg/ mL) were evaluated by pretreatment of BMEC for 0, 2, 4, 6, 8, 12 and 24 h, followed by an H₂O₂ (600 μM per culture well) challenge for 6 h. Bovine mammary epithelial cells were preincubated for 30 min with or without 2,4-dinitrochloro-benzene (DNCB), then cultured with or without TP (100 μg/ mL) for another 12 h followed by H₂O₂ (600 μM per culture well) exposure. There were 5 replicate cultures for each treatment in each experiment. Treatment with 600 μM H₂O₂ per culture well for 6 h induced oxidative damage of BMEC, indicating this system could be used to establish an oxidative stress model. After H₂O₂ (600 μM per culture well) exposure, a concentration of TP of 100 μg/mL during a 12-h incubation increased cell viability, decreased intracellular reactive oxygen species accumulation, and increased the abundance of nuclear factor-erythroid 2-related factor 2 (NFE2L2). Furthermore, TP upregulated mRNA abundance of genes in the NFE2L2 and mitogen-activated protein kinase (MAPK) pathways of BMEC. The DNCB assay allowed further confirmation that the induction of NFE2L2 and HMOX-1 in response to TP was mediated through the sustained upregulation of the abundance of MAPK3/1 [formerly known as extracellular regulated kinases 1/2] and MAPK11/12/13/14 (formerly known as p38). Overall, results indicate that TP has beneficial effects on BMEC redox balance; it can reduce cellular oxidative stress-related injury and may potentially serve as an antioxidant against oxidative stress in dairy cows.