Quantitation of phenylpropanoids and iridoids in insulin‐sensitising extracts of Leonurus sibiricus L. (Lamiaceae)

Introduction Leonurus sibiricus L. is regularly used in traditional Mongolian medicine including for the treatment of symptoms of diabetes mellitus. Objectives To provide a validated quantitation method for the quality control of Leonurus sibiricus and to prove in vitro insulin-sensitisation, thereby supporting the traditional use of Leonurus sibiricus. Methodology Pulverised Leonurus sibiricus material was either extracted with methanol or methanol:water (25:75, v/v). HPLC-CAD (charged aerosol detector) separations were performed on a Luna Phenyl-Hexyl column with water and acetonitrile (both modified with 0.1% formic acid) as mobile phase. Gradient elution was employed using theophylline as internal standard. Tentative peak identification was facilitated by HPLC-MS. Validation was carried out according to ICH (International Conference on Harmonisation) guidelines. Potential insulin-sensitisation of accordant extracts was assessed in glucose uptake experiments in C2C12 myocytes and protein tyrosine phosphatase 1B (PTP1B) enzyme assays. Results Thirty-six compounds were tentatively identified based on their retention times, UV spectra, MS fragments and data from literature. They comprise phenolcarboxylic acids, flavonoids, iridoid glycosides, and phenylpropanoids, among which acetylharpagide, ajugoside, lavandulifolioside, and verbascoside were selected for quantitation. The methanol extract contained 0.42% combined iridoids, and 1.58% combined phenylpropanoids. Validation showed good accuracy, intermediate precision and robustness. The methanol extract of Leonurus sibiricus led to a 1.5 fold increase in insulin-stimulated cellular glucose uptake and inhibition of PTP1B by 40% at a concentration of 10 µg/mL. Conclusion HPLC-CAD analysis allowed sensitive quantitation of the selected marker compounds in Leonurus sibiricus, thereby providing a reliable tool for its quality control. Copyright © 2015 John Wiley & Sons, Ltd.