Mint oils: in vitro anti-inflammatory effects tested in porcine alveolar macrophages

Essential oils as feed additives are being investigated for promoting health in piglets due to their anti-inflammatory activity. The objective of the study was to measure the in vitro anti-inflammatory effects of peppermint oil and spearmint oil with porcine alveolar macrophages as host immune responses. Briefly, macrophages were harvested from the bronchial lavage of 6 pigs at 6 weeks of age, and then seeded into 24-well plate with at 106 cells/mL. After 24 h incubation at 37oC and 5% CO2, cells were treated with mint oil or lipopolysaccharide (LPS) by randomized complete block design with 12 replicates. The treatments were 2 × 5 factorial arrangement with 2 doses of LPS (0 or 1 μg/mL) and 5 doses of mint oil (0, 25, 50, 100, 200 µg/mL). The supernatants were collected after another 24 h incubation to measure the concentration of tumor necrosis factor alpha (TNF-α) by ELISA assay. Cell viability was also tested by the MTT assay. Data were analyzed using the MIXED procedure of SAS 9.4. Administration of both mint oils and LPS did not impact the PAM cell viability of macrophages. LPS challenge significantly stimulated (P < 0.05) TNF-α secretion from macrophages. In the non-challenge group, peppermint oil reduced (P < 0.05) TNF-α production at 25, 50, and 100 μg/mL, whereas spearmint oil reduced (P < 0.05) TNF-α concentration from 50 to 200 μg/mL. In the LPS challenge group, both mint oils linearly inhibited (P < 0.001) TNF-α secretion from LPS-challenged macrophages with 200 μg/mL as the strongest dose. Results of the current study indicated that both peppermint and spearmint oils had anti-inflammatory activities in vitro. In vivo animal trials will be conducted to evaluate their impacts on animal health and performance