Abstract: The study was aimed to investigate the effect of Passiflora edulis polysaccharide extract (PEPE) on oxidative stress-related factors of RAW264.7 cells infected with Porcine circovirus type 2 (PCV2) and explore the role of PEPE on oxidative stress.First,100 μL RAW264.7 cells of 1×10⁶ cells/mL were added into 96-well cell culture plate in each well.Cell control group and PEPE groups (25,50,100,200,400,800 and 1 600 μg/mL) were respectively set up and cultured in the incubator for 24 and 48 h,respectively.MTT assay was used to detect cell activity and screen the safe concentration range of PEPE.The experiment was then divided into the following six groups:Cell control group,virus group,PEPE high (400 μg/mL),medium (200 μg/mL) and low (100 μg/mL) dose groups and vitamin C group,among them,the cell control group was added with 10% FBS-containing DMEM culture medium,and the other groups were added with PCV2 virus liquid.After incubating for 2 h,the corresponding concentration of PEPE solution were added to the PEPE groups,the prepared VC solution was added to the VC group,and DMEM culture medium containing 10% FBS was added to cell control group and virus group,and cultured for 48 h.MTT assay was also used to detect cell activity to study the effect of PEPE on the activity of RAW264.7 cells infected with PCV2.Finally,in accordance with the above 6 test component groups,the treatment was the same as above,the cells were cultured for 12 h,and samples were collected to detect the levels of oxidative stress related factors.Griess method and DCFH-DA fluorescent probe label method were used to analyze the levels of nitric oxide (NO) and reactive oxygen species (ROS) in RAW264.7 cells supernatant.The levels of glutathione (GSH) and oxidized glutathione (GSSG) were analyzed by OPT fluorescence assay.The activities of xanthine oxidase (XOD),myeloperoxidase (MPO) and inducible nitric oxide synthase (iNOS) were analyzed by chemiluminescence technique.The results of this study showed that the safe concentration range of PEPE on RAW264.7 cells was 25-400 μg/mL.After PCV2 infected RAW264.7 cells,the cell viability was significantly reduced (P<0.05),and the PEPE group with different concentrations could improve the cell viability.The secreting levels of NO and ROS,GSSG content and activities of XOD,MPO and iNOS were significantly increased (P<0.05),while GSH content was significantly decreased (P<0.05) after PCV2 infected RAW264.7 cells.When PCV2-infected cells were treated with PEPE,the production of NO,ROS,GSSG,as well as the activities of XOD,MPO and iNOS were significantly decreased (P<0.05),while the level of GSH in 100 μg/mL PEPE treatment group was significantly increased (P<0.05).The results showed that PEPE enhanced antioxidant capacity of PCV2-infected RAW264.7 cells,which was conducive to easing the oxidative stress caused by virus infection.

Key words: Passiflora edulis polysaccharide extract (PEPE); Porcine circovirus type 2 (PCV2); oxidative stress