Comparative chemical diversity and antioxidant activities of three species of Akebia herbal medicines

Akebia stem has long been used extensively as a rare Chinese herbal medicine. The three most significant Akebia medicinal species are Akebia quinata (Thunb.) Decne. (A. quinata), Akebia trifoliata (Thunb.) Koidz. (A. trifoliata), and Akebia trifoliata (Thunb.) Koidz. var. Australis (Diels) Rehd. (A. trifoliata. var). They have significant therapeutic effects and are widely used in the pharmaceutical and cosmetics industries. Only a few studies compared their chemical differences and antioxidant activities. To better demonstrate each species' characteristics and antioxidant properties, the ultra-performance liquid chromatography coupled with quadrupole Orbitrap mass spectrometry (UPLC-Q-Orbitrap/MS)-based metabolomics was applied to investigate the chemome diversity of three Akebia species. Their antioxidant activities were evaluated by DPPH and ABTS assays. In total, 65 different metabolites were identified, including 5 phenolic acids, 2 phenylpropanoids, 4 lignan glycosides, and 54 triterpenoid saponins. The different aglycone types of triterpenoid saponins were found to be the component differences between the three Akebia species. The chemical composition of A. trifoliata and A. trifoliata. var is similar. The 2-(3,4-dihydroxyphenyl)-ethyl-O-β-d-glucopyranoside has been found only in A. quinata. In contrast, the triterpenoid saponins akemisaponin B, akemisaponin D, oleanolic-acid-3-O-arabinopyranosyl-28-O-glucopyranosyl-glucopyranosyl-rhamnopyranosyl-arabinopyranosyl, akemisaponin C and saponin Pj1 have been found A. trifoliata and A. trifoliata. var. As a result, these six compounds can be considered marker compounds that distinguish three Akebia species. The antioxidant activities results indicated that the antioxidants of three Akebia species were the same in different antioxidative test systems. A. trifoliata (IC50: 2.28–6.97 mg·mL−1) and A. trifoliata. var (IC50: 2.09–6.87 mg·mL−1) showed 2–3 times higher antioxidant activity than A. quinata (IC50: 5.56–11.21 mg·mL−1). This study reveals the antioxidant activity differences of three Akebia species, laying a foundation for further development and utilization. This type of study can lead to the identification of a compound that, with further work and more extensive studies, has the potential to be used as a biomarker, in this case to distinguish different medicinal species.