Antioxidant Properties of Lippia alba Essential Oil: A Potential Treatment for Oxidative Stress-Related Conditions in Plants and Cancer Cells

(Mill.) N.E.Br. ex Britton and P. Wilson is used in folk medicine of Central and South America for its biological activities: i.e., antifungal, antibacterial, antiviral, and anti-inflammatory. Based on ethnopharmacological information and the increasing interest in this species, this work aimed to test a possible wide use of its essential oil (EO) in pharmaceutical and horticultural applications. Therefore, we focused the attention on the antioxidant activity of the oil as a possible tool to overcome the oxidative stress in both applications. For this purpose, we have chosen three aggressive breast cancer cell lines and two horticultural species ( L. and L.) that are very sensitive to salt stress. We determined the antioxidant activity of EO through the quantification of phenols and flavonoids. Regarding tomato and bean plants under salt stress, EO was used for the first time as a seed priming agent to enhance plant salt tolerance. In this case, the seed treatment enhanced the content of phenolic compounds, reduced power and scavenger activity, and decreased membrane lipid peroxidation, thus mitigating the oxidative stress induced by salt. While in breast cancer cells the EO treatment showed different responses according to the cell lines, i.e., in SUM149 and MDA-MB-231 the EO decreased proliferation and increased antioxidant activity and lipid peroxidation, showing high cytotoxic effects associated with the release of lactate dehydrogenase, vice versa no effect was observed in MDA-MB-468. Such antioxidant activity opens a new perspective about this essential oil as a possible tool to counteract proliferation in some cancer cell lines and in horticulture as a seed priming agent to protect from oxidative damage in crops sensitive to salinity.