Retinoic acid attenuates oxidative injury in bovine mammary epithelial cells induced by hydrogen peroxide

The objective of this study was to explore how retinoic acid (RA) attenuates oxidative injury induced by hydrogen peroxide (H2O2) in bovine mammary epithelial cells (BMEC). Subconfluence BMEC were randomly divided into four groups with six replicates: the control group (incubated in serum-free medium without RA or H2O2 for 30 h), H2O2 group (pre-incubated for 24 h without RA, then for another 6 h with 600 μM H2O2), RA group (incubated with 1 mg/ml RA for 30 h without H2O2), and RA + H2O2 group (RA prevention group, pre-incubated with 1 mg/ml RA for 24 h and then for another 6 h with 600 mM H2O2). The results showed that the H2O2 treatment significantly decreased several measured traits, including the cell viability, glutathione peroxidase (GPX) and thioredoxin reductase (TRXR) activities, selenoprotein P (SELP) content, catalase and superoxide dismutase activities, total antioxidant capacity, and GPX1, TRXR1, and SELP gene expression, as well as GPX1 and TRXR1 protein expression. H2O2 treatment also increased the malondialdehyde and reactive oxygen species contents and induced a marked increase of several measured traits, including the arachidonic acid (ARA) concentration, cytosolic phospholipase A2 and 5-lipoxygenase gene expression and activity, and 15-hydroxy twenty-four arachidonic acid and hydroxy peroxide tetracosenic arachidonic acid contents. RA pre-treatment prevented corresponding increases in parameters related to ARA metabolism and increased the activity of TRXR. Moreover, RA pre-treatment attenuated the phosphorylation levels of p38 mitogen-activated protein kinase (MAPK) and c-Jun N-terminal kinase and effectively decreased the ARA content. These results suggest that RA protected BMEC from oxidative stress by elevating TRXR activity, which inhibited the MAPK signaling pathway and led to a decreased concentration of ARA.