Cytotoxic, anti-inflammatory, and α-glucosidase inhibitory effects of flavonoids from Lippia graveolens (Mexican oregano)

Lippia graveolens is a plant used for a variety of medicinal purposes and as a seasoning. Chemical investigation of a methanol extract obtained by percolation of its leaves and flowers led to the isolation of two monoterpenes (1-2) and twelve flavonoids, including two flavonols (3-4), two flavones (5-6), four flavanones (7-10), two dihydroflavonols (11-12), and two dihydrochalcone glucosides (13-14). beta-Sitosteryl glucopyranoside (15) was also isolated. The structures of all the isolates were elucidated by analysis of the NMR and MS spectra. The configuration of chiral flavonoids was determined by optical rotation and comparison with literature data. Based on the medicinal uses of the plant, the flavonoids 3-14 were tested for their ability to inhibit the activity of alpha-glucosidase, while the anti-inflammatory activity of 4 and 7-14 was evaluated in the 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced ear edema model. As a result, only the flavone 6 was a significative inhibitor of alpha-glucosidase (IC50 = 37.19 mu M), while the flavanones 9-10 and the dihydrochalcone 14 showed the best anti-inflammatory properties with IC50 values ranging from 0.72 to 1.31 mu mol/ear. The cytotoxic activity of eleven of these flavonoids (3-5 and 7-14) against five cancer human cell lines was also evaluated. The flavonol 4 inhibited moderately the proliferation of the U251 (glioblastoma) and SK-LU-1 (lung adenocarcinoma) cell lines.