Flavonoids from Tilia americana with anxiolytic activity in plus-maze test

The aerial parts of Tilia americana var. mexicana (Schltdl) Hardin (Tiliaceae) have been widely used in Mexican traditional medicine to relieve sleeplessness, headache, and nervous excitement. The anxiolytic effect of four extracts and several flavonoid fractions from the bracts of Tilia americana subsp.mexicana, var. mexicana (Schltdl) Hardin or Tilia mexicana (Tiliaceae) was studied. Administration of 100 mg/kg of n-hexane, ethyl acetate, and aqueous extracts to elevated plus-maze (EPM)-exposed mice displayed no anxiolytic effect; however, identical doses of methanol extract was able to increase the time percentage that mice spent in the EPM's open arms, as well as the percentage of crossings in the EPM's arms. The dose–response curve produced by methanol extract showed anxiolytic activity since 25 mg/kg; animals showed no motor activity alteration in the open field test (OFT). Methanol extract was subjected to a bioassay-guided fractionation to obtain four ascendant polarity fractions (F1–F4) which were administrated at 100 mg/kg. Data results indicate that F1 displayed the main anxiolytic effect. The purification of F1 produced a rich flavonoid anxiolytic mixture (F1C). This fraction was purified by RP-18 open chromatographic column to obtain four polar descent fractions: F1C1, F1C2, F1C3, and F1C4, respectively. Tiliroside was the major ingredient from the active fraction. High performance liquid chromatography analysis indicated that F1C was constituted principally of tiliroside, quercetin, quercitrin, kaempherol, and their glycosides. These results supported the use of Tilia americana in Mexican tradicional medicine as well as the anxiolytic effect of a rich flavonoid fraction without affect motor activity.