Phenolic compounds of Heliotropium europaeum and their biological activities

Abstract

Background: Heliotropium europaeum L. is known to contain pyrrolizidine alkaloids and possesses a wide variety of biological activities. Objective: The objective of the study was to discover antioxidant phytochemical compounds in H. europaeum and assess their in vitro lipoxygenase (LOX)- and angiotensin-converting enzyme (ACE) inhibitory activities. Materials and Methods: H. europaeum herbs were extracted exhaustively by maceration using 90% aqueous ethanol. Solvent fractionation with n-hexane, dichloromethane (CH2Cl2), ethyl acetate (EtOAc), and n-butanol was performed with the dried extract until complete exhaustion. Two antioxidant active fractions (CH2Cl2and EtOAc) were combined and subjected to medium pressure liquid chromatography followed by reversed-phase high-performance liquid chromatography. Quantitative evaluation in terms of the antioxidant activities of the isolated compounds was performed using the 2,2-diphenyl-1-picrylhydrazyl assay. The potential limiting effects on the action of ACE and soybean LOX were assessed quantitatively. Results: Isolates of eight newly identified phenolic compounds from H. europaeum exhibited antioxidant and ACE- and LOX-inhibitory activities. The isolated compounds were identified as kaempferol (1), luteolin (2), quercetin (3), kaempferol-3-O-glucoside (4), and luteolin-7-O-glucoside (5), in addition to caffeic acid (6), rosmarinic acid (7), and methyl rosmarinate (8). Among the isolated compounds, quercetin possessed the most potent antioxidant activity (IC50= 8.1 μM) and ACE-inhibitory activity (IC50= 17.5 μM), whereas rosmarinic acid and its methyl ester showed the strongest LOX-inhibitory activity (IC50s = 4.2 μM and 3.6 μM, respectively). Conclusion: Our study is the first report on the phenolic constituents of the H. europaeum herbal extract and their biological activities. A total of eight phenolics were identified in this extract and isolated for the first time. Our results on H. europaeum extract constituents provide some scientific evidence on the beneficial effects of its traditional uses.