125 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.

Evaluation of Four Plant Extract Repellents for Management of the European Red Ant Myrmica rubra (Hymenoptera: Formicidae)

Spearmint oil, peppermint oil, neem oil, and d-limonene were tested as nest site repellents against the colonization of the invasive European red ant, Myrmica rubra (L.) in both laboratory and field trials. In a laboratory assay, a 10% (v/v) solution of each extract repelled M. rubra colonies from nesting in plant pots filled with moist soil compared to water-treated controls, when applied as a dip to pots. Extracts also repelled colonies compared to a water control in a second laboratory experiment, where pots were dipped 15 d prior to the start of the experiment. In a 2008 field comparison, 20 plant pots, filled with moist potting soil, were dipped in either 10% (v/v) spearmint oil or peppermint oil, 70% (v/v) neem oil, or a water control and left in infested sites. Seven control pots were colonized over 3 mo, while none of the extract-treated pots were colonized. This field trial was repeated for a 15-wk duration in 2009 with the addition of a 10% (v/v) d-limonene solution as a treatment, and a change in neem oil concentration to 10% (v/v). Spearmint and peppermint oils repelled M. rubra colonies for the duration of the experiment. Neem oil and d-limonene repelled colonies for 3 and 4 wk, respectively. These extracts, especially mint oils, show potential as low-hazard repellents against M. rubra in greenhouse and nursery settings, and could reduce the number of new infestations incurred by the transport of plant stock.

Comparative study of larvicidal activity of commercial essential oils from aromatic rosemary, vanilla, and spearmint against the mosquito Aedes aegypti

Laojun S, Chaiphongpachara T. 2020. Comparative study of larvicidal activity of commercial essential oils from aromatic rosemary, vanilla, and spearmint against the mosquito Aedes aegypti. Biodiversitas 21: 2383-2389. Dengue fever is a dangerous mosquito-borne viral disease of humans. This disease is caused by dengue virus, a member of the genus Flavivirus of the family Flaviviridae. The Aedes aegypti mosquito is a principal vector for this virus. To control Ae. aegypti populations, there is extensive focus on larval eradication, because breeding sites are often close to human populations, especially man-made containers. The objective of this research was to evaluate the efficacy of commercial essential oils from rosemary (Rosmarinus officinalis), vanilla (Vanilla planifolia), and spearmint (Mentha spicata) with regard to larvicidal activity against Ae. aegypti larvae after 24 and 48-hours of exposure in the laboratory. The results showed highly efficacious larvicidal activity, with median lethal doses (LC50) of 0.23, 0.10, and 0.12 ppm after 24-hour exposure to commercial rosemary, vanilla, and spearmint oil, respectively. The results of this study will be useful for the control of a common dengue vector and may replace the use of pesticides that may have broad environmental impacts.

Efficacy of Active Ingredients From the EPA 25(B) List in Reducing Attraction of Aedes aegypti (Diptera: Culicidae) to Humans

Mosquitoes of the Aedes genus are vectors for dengue, chikungunya, Zika, and yellow fever viruses. Mosquito repellents are an effective way to prevent mosquito bites and reduce the spread of mosquito-borne diseases. In the early 90s, the U.S. Environmental Protection Agency (EPA) published a list of active ingredients that pose minimum risk to human health that can be used as pesticides or repellents without passing the EPA registration process. The present study examined the efficacy of 21 of the active ingredients listed by the EPA 25 (B) exempt list and five commercially available sprays that only contained active ingredients from the EPA 25(B) list in repelling female Aedes aegypti (L.) females. We performed choice bioassays in a controlled laboratory environment, using a Y-tube olfactometer to determine attraction rates of humans to female Ae. aegypti in the presence of one of the 21 active ingredients and five commercially available repellent sprays. We found that cinnamon oil, peppermint oil, spearmint oil, lemongrass oil, and garlic oil reduced mosquito attraction to human odor. Of the five commercial repellent sprays, only one reduced mosquito attraction for up to 30 min in our assay. The EPA 25 (B) list contains active ingredients that under the conditions of our assay repel Ae. aegypti.

Essential oils as tick repellents on clothing

Essential oils show promise as natural alternatives to synthetic tick repellents, but few studies have investigated their repellent efficacy in vivo or under field conditions. Here, blanket-drags and standardised walks were employed to evaluate tick acquisition by 1 m2 cotton blankets or cotton trousers, respectively, in woodland edge habitats of known high tick abundance. Blankets and trousers had been treated with one of 5% oregano, rosemary, spearmint or thyme oils, 20% DEET (N,N-diethyl-3-methylbenzamide) (positive control) or ethanol excipient-only (negative control). The number of ticks present on the blankets or trousers differed significantly between treatments: spearmint oil treatments resulted in significantly fewer ticks than the negative controls for both blankets and trousers and significantly fewer ticks were present on the oregano oil treated blankets. For ticks that did attach to the trousers, the rate of drop off within 3 min was significantly higher for trousers treated with spearmint oil or thyme oil than ethanol, oregano oil and rosemary oil. No reduction in repellence was detected over a 24 h period between treatment and testing. The results suggest that 5% oregano and spearmint oils exhibit potential as natural clothing repellents, with an effective equivalence to 20% DEET.