Lactuca racemosa Willd., Source of Antioxidants with Diverse Chemical Structures

Ethanolic extracts from the roots and aerial parts of the hitherto chemically uninvestigated lettuce species <i>Lactuca racemosa</i> Willd. (Cichorieae, Asteraceae) were chromatographically separated to obtain eight sesquiterpenoids, two apocarotenoids (loliolide and (6<i>S</i>,9<i>S</i>) roseoside), and three phenolic glucosides (apigenin 7-<i>O</i>-glucoside, eugenyl-4-<i>O</i>-<i>β</i>-glucopyranoside, and 5-methoxyeugenyl-4-<i>O</i>-<i>β</i>-glucopyranoside). Four of the isolated sesquiterpene lactones (8-<i>α</i>-angeloyloxyleucodin, matricarin, 15-deoxylactucin, and deacetylmatricarin 8-<i>β</i>-glucopyranoside) have not previously been found either in <i>Lactuca</i> spp. or in <i>Cicerbita</i> spp. In addition, HPLC-PAD chromatographic methods were used to estimate the deacetylmatricarin derivatives, luteolin 7-<i>O</i>-glucoside, and caffeic acid derivatives contents in the analyzed plant material. The aerial parts contained c. 3.0% dry weight of chicoric acid and equal amounts (0.4%) of caftaric acid and luteolin 7-<i>O</i>-glucoside. The roots contained fewer phenolic metabolites but were rich in deacetylmatricarin glucoside (c. 1.3%). The aglycone of the most abundant sesquiterpene lactone was evaluated with respect to its neuroprotective effect in H₂O₂- and 6-OHDA-treated human neuroblastoma SH-SY5Y cells. This compound, at concentrations of 10 and 50 μM, provided partial protection of undifferentiated cells, and at a concentration of 50 μM, it provided partial protection of retinoic acid-differentiated cells from H₂O₂-induced damage. In a model of 6-OHDA-evoked cytotoxicity, the sesquiterpenoid was less effective. Our findings may support the inclusion of this plant into the human diet.