Protective Effects Of N-3 Polyunsaturated Fatty Acids On Oxidative Damages To Bovine Mammary Epithelial Cells

Bovine mammary epithelial cells are important site of milk synthesis and and secretion,which are closely related to milk yield and quality.The mammary epithelial cells of high-yielding cows,especially those in peak lactation,are prone to oxidative stress.It is an effective way to keep mammary gland healthy and lactate by protecting mammary epithelial cells from oxidative damages and enhancing their antioxidant ability through the eliminations of all kinds of oxidative reaction factors.N-3 PUFAs is an important lipid nutrient element in the body,and dietary supplementation of n-3 PUFAs can improve the antioxidant capacity of the body and resist oxidative stress response.In this study,the relationship between subclinical mastitis and antioxidant capacity was explored by comparing the activities of antioxidant enzyme in the milk of healthy with subclinical mastitic bovine,and the protective effects of n-3 PUFAs on oxidative damage of MAC-T cells by using a LPS-induced oxidative stress model of MAC-T cells.The main research results are as follows:(1)Relationship between subclinical mastitis and antioxidant capacity in bovine.The activity and content of antioxidant capacities in milk of bovine without mastitis were determined.It was found that the activities of SOD,CAT,GSH-Px and GST in milk of bovine with subclinical mastitis were significantly reduced compared with those of healthy bovine(p<0.01 or p<0.05),while the content of MDA in milk of bovine with subclinical mastitis was significantly increased compared with that of health bovine(p<0.01).(2)Investigation of the protective effects of n-3 PUFAs on MAC-T cells from LPS-induced oxidative damages MAC-T cells cultured in vitro were treated with LPS to establish a cell model of oxidative damages.The effects of n-3 PUFAs on LPS-induced oxidative damage in MAC-T cells were investigated by detecting the activity of antioxidant enzymes,the content of MDA and the degree of DNA damage in different treatment groups.The results showed that,compared with the control group,the activities of SOD,CAT,GSH-Px and GST in cells of LPS treatment group were significantly decreased(p<0.01),and the content of MDA was significantly increased(p<0.01),and the degree of DNA damage was enhanced.N-3 PUFAs pretreatment group could significantly inhibit the decrease of SOD and CAT activities induced by LPS(p<0.01),MDA content increased(p<0.01)and DNA damage.Compared with normal control group,the activities of SOD and GST,the content of MDA and the degree of DNA damage in n-3 PUFAs group were not significantly different.(3)N-3 PUFAs promotes the translocation of Nrf2 from cytoplasm to nucleus and activation of the Keap1-Nrf2-ARE antioxidant pathway.Western blotting and immunofluorescence staining were used to detect the expression of Nrf2 protein in the cytoplasm and nucleus to explore whether n-3 PUFAs could activate Nrf2 to achieve antioxidant protection.The results showed that,compared with the control group,the expression of Nrf2 protein in the cytoplasm was significantly decreased and that in the nucleus was significantly increased after treatment with LPS.After pretreatment with different concentrations of n-3 PUFAs,the expression of Nrf2 protein in the cytoplasm increased with the increase of n-3 PUFAs concentration,and the expression of Nrf2 protein in the nucleus increased more significantly.In conclusion,the activity of antioxidant enzymes in milk of bovine with subclinical mastitis decreased.In addition,n-3 PUFAs could increase the activity of antioxidant enzymes,reduce MDA content,alleviate the degree of DNA damage,enhance the translocation into the nuclear Nrf2,activate the antioxidant Keap1 Nrf2-ARE signaling pathways in the MAC-T cells,to protect cells from the oxidative damages induced by LPS.The findings of this study might provide a theoretical basis for the application of n-3 PUFAs in the prevention and treatment of mastitis in bovine.