Abstract

Plants have been useful sources of new biologically active compounds. However, traditional ethno-medical approaches may draw attention to one or other clinical claim, but only specific scientific investigation can validate their effects. The aim of this study was to examine whether an extract of Melilotus officinalis leaves interferes with reactive oxygen/nitrogen species (ROS/RNS) during the course of human neutrophil respiratory bursts, and to establish the lowest concentration at which it still has antioxidant activity by means of luminol amplified chemiluminescence (LACL). We also studied its ability to counteract lipid peroxidation (LPO) in human cells. Before investigating its antioxidant effects on human cells, we analysed its scavenging activity against ABTS^●+, hydroxyl radical, superoxide anion, and Fremy’s salt (the last three by means of electron paramagnetic resonance [EPR] spectrometry). The extract of M. officinalis exerted its anti-ROS/RNS activity in a concentration-dependent manner, with significant effects being observed for even very low concentration: 20 μg/ml without L-arginine (L-Arg) and 10 μg/ml when L-Arg was added to the formyl-methionyl-leucyl-phenylalanine (fMLP) test. LPO assay confirmed these results, which were paralleled by the EPR study. These findings are interesting for improving the antioxidant network and restoring redox balance in human cells, and extend the possibility of using plant-derived molecules to antagonise the oxidative stress generated in living organisms. 

Key words: Melilotus officinalis extract, antioxidant activity, human neutrophils, respiratory bursts, chemiluminescence, lipoperoxidation, electron paramagnetic resonance.