Bioactive Secondary Metabolites From Lippia salsa Griseb. (Verbenaceae)

The genus Lippia (Verbenaceae) is represented in Argentina by 31 species. Many of these species are traditionally used as medicinal plants or for culinary purposes. A wide range of biological activities has been reported for plants belonging to this genus. Lippia salsa Griseb. is an endemic species from Argentina that has been scarcely studied. As part of our continuing investigation of natural products as leads for inhibiting acetylcholinesterase (AChE), an enzyme relevant for the treatment of Alzheimer's disease (AD), L. salsa was selected based on the results of a screening of AChE inhibition. The ethanolic extract obtained from the aerial parts elicited an interesting enzymatic activity with an IC50 value of 0.89 mg/ml, determined by Ellman's method. A bioassay-guided fractionation of this extract led to a semi-purified fraction with higher AChE inhibition (79.2% at 0.45 mg/ml). From this active fraction two known flavones, apigenin and luteolin, have been isolated and identified, so far. Since the ability of these flavones to inhibit cholinesterase has already been proven, it is reasonable to think that the AChE inhibition observed for L. salsa can be, at least in part, attributed to these metabolites. Apigenin and luteolin are reported here for the first time in this species. Apigenin has gained particular interests in recent years as a beneficial and health promoting agent due to its low intrinsic toxicity. On the other hand, luteolin has been identified as a potent inhibitor of Aβ fibrils, strongly implicated in AD pathology and the neurotoxicity observed with this disease. These observations suggest that L. salsa can be a source of potential multi-targets agents against AD.