Hypoglycemic activity of Origanum vulgare L. and its main chemical constituents identified with HPLC-ESI-QTOF-MS

Origanum vulgare L. (O. vulgare) is an important medicine food homology in diabetes. The present study aimed to assess the hypoglycemic effect of the leaf extract of O. vulgare in HepG2 and HepG2-GFP-CYP2E1 (E47) cells, and disclose its potential active components by the HPLC-ESI-QTOF-MS method. Firstly, we evaluated the anti-diabetic capacity of the leaf extract of O. vulgare through inhibition of α-glucosidase activity, promotion of glucose uptake, inhibition of glycosylation and relieving of oxidative stress. Secondly, the promoter activity, the mRNA and protein expression of PEPCK and SREBP-1c, and the expression of CPY2E1 and GLUT2 in the O. vulgare mediated anti-diabetic capacity were analyzed in HepG2 and E47 cells. Finally, HPLC-ESI-QTOF-MS analysis was performed to identify the herb's main components under 280 nm irradiation. In vitro assays demonstrated that the extract inhibited α-glucosidase activity, promoted glucose uptake, inhibited glycosylation and relieved oxidative stress, which suggested that O. vulgare leaf extract has a strong hypoglycemic capacity. Moreover, mechanistic analysis also showed that the extract decreased the promoter activity and the mRNA and protein expression of PEPCK and SREBP-1c. In addition, the extract inhibited the expression of CPY2E1 and enhanced the expression of GLUT2. Moreover, the UV chromatogram at 280 nm showed six main peaks, identified as amburoside A (or 4-(3',4'-dihydroxybenzoyloxymethyl) phenyl O-β-d-glucopyranoside), luteolin 7-O-glucuronide, apigenin 7-O-glucuronide, rosmarinic acid, lithospermic acid and a novel compound, demethylbenzolignanoid, based on accurate MS data. This work supported the ethnopharmacological usage of O. vulgare as an antidiabetic herbal medicine or dietary supplement and identified its main phenolic compounds.