Investigation of antioxidant activity, acute toxicity and anticholinesterasic potential of Lippia hirta (Verbenaceae)

Resumo

The genus Lippia, the second largest of the Verbenaceae family, has approximately 200 species of which approximately 120 species are found in Brazil. Since Lippia hirta has not been documented in the literature, the objective of this work was to analyze the antioxidant activity, acute toxicity and acetylcholinesterase (AChE) inhibition activity of the essential oil, crude extract and fractions from this plant species. In relation to the antioxidant activity, evaluated by the reducing power assay, it was possible to observe a relevant antioxidant behavior, especially for the essential oil (IC50= 6.26 µg.mL-1), and butanol (BuOH, IC50= 7.26 µg.mL-1) and ethyl acetate (EtOAc, IC50= 8.09 µg.mL-1) fractions, higher than the standard quercetin (IC50= 9.43 µg.mL-1) used in this assay. Low toxicity was observed for all samples and a high inhibitory potential for AChE by most fractions and especially for the alkaloid rich fraction (ARF), which was able to inhibit the enzyme by up to 100% at a concentration of 0.5 μg.mL-1, representing a strong activity. Although ARF is a complex matrix, the synergistic effect is high when compared to the standard used in the test, galantamine (IC50 = 17.8 μmol.L-1). These results stimulated the chromatographic fractionation of ARF that allowed the characterization of three alkaloids, hitherto not reported in the species, dihydrocorinanteol, vincamine and deoxycordifoline. The low toxicity, the good antioxidant activity and the excellent result for the inhibition of AChE stimulate other analyzes to determine the active compounds in the other fractions, suggesting the bio-guided fractionation as a tool of paramount importance in the phytochemical and biological analysis of Lippia hirta.