cis-9,trans-11-Conjugated Linoleic Acid Exerts an Anti-inflammatory Effect in Bovine Mammary Epithelial Cells afterEscherichia coliStimulation through NF-κB Signaling Pathway

The anti-inflammatory effects of cis-9,trans-11-conjugated linoleic acid (cis-9,trans-11-CLA) in diverse cells have been demonstrated in recent studies. The present study was conducted to observe the anti-inflammatory effects and involved mechanisms of CLA in bovine mammary epithelial cells (BMECs) exposed to Escherichia coli. According to the gene expression of IL-6, to optimize the treatment period and dose of CLA, 50 and 100 μM CLA were chosen to pretreat the cells for a period of 48 h. BMECs were exposed to 1 × 107 /mL E. coli for 6 h (ECO group), and cells were pretreated with 50 and 100 μM CLA for 48 h followed by E. coli challenge (C50 and C100 groups). After E. coli challenge, compared with that in the CON group (control group), the gene expressions of pro-inflammatory cytokines (IL-1β and IL-6), chemokines (IL-8 and CCL-20), and antimicrobial peptide BNBD5 were increased, while the gene expression of the anti-inflammatory cytokine IL-10 was decreased significantly; CLA reversed this inflammation effect. Pretreatment with CLA also repressed the secretion of IL-6, IL-8, and TNF-α from BMECs in the culture medium following E. coli challenge. Therefore, cis-9,trans-11-CLA exerted anti-inflammatory effects in BMECs. The cells that were pretreated with CLA expressed remarkably lower levels of phospho-p65, phospho-IκB, and TLR4 and a higher level of PPARγ after E. coli challenge at the gene and protein levels. Compared to that in the ECO group, the nuclear translocation of phospho-p65 was suppressed when CLA was added. Combined with the above results, 50 μM CLA showed a better anti-inflammatory effect. In conclusion, CLA can reduce inflammation caused by E. coli in bovine mammary epithelial cells, and this effect is mediated through the TLR4-NF-κB pathway and PPARγ participation.