Screening of acetylcholinesterase inhibitors and characterizing of phytochemical constituents from Dichocarpum auriculatum (Franch.) W.T. Wang & P. K. Hsiao through UPLC-MS combined with an acetylcholinesterase inhibition assay in vitro

Abstract

The genus Dichocarpum is endemic to East Asia, and many of them are traditionally used folk medicine in China. Dichocarpum auriculatum (Franch.) W. T. Wang et P. K. Hsiao has the effect of clearing away heat, removing toxicity, and relieving swelling in southwestern China. Intriguingly, its root and whole herb also used as remedy for the neurological disease epilepsy. However, there are not any scientific reports on the phytochemistry and pharmacological activities of D. auriculatum. Traditional and folk medicinal knowledge would be useful for finding new pharmaceutical resources. There are many evidences over the years reported that an interaction probably exists between epilepsy and Alzheimer's disease (AD). The aim of the study was to investigate the potential AChE inhibitors and the phytochemical profiles of the specie D. auriculatum. The AChE inhibitory activity of plant extracts of D. auriculatum and other 6 species from different regions of the genus Dichocarpum were evaluated in vitro assays and the UPLC-Q-TOF-MS technique was used to analyze the chemical constituents. Moreover, UPLC-ESI-MS/MS was used to determine the distribution of 12 standard compounds in samples. As a preferred source of potential acetylcholinesterase inhibitors of the genus Dichocarpum, D. auriculatum has been further investigated. The screening results show that the ability of root extracts from D. auriculatum (IC50 = 0.15 mg·mL-1) to inhibit AChE was better than other samples, it is consistent with traditional medicinal records. The phytochemical constituents of D. auriculatum was surveyed firstly by UPLC-Q-TOF-MS analysis, and 36 compounds, including 14 alkaloids, 16 flavonoids, 6 others, were identified tentatively. Further experiments showed that five compounds (columbamine, palmatine, dauricine, jatrorrhizine and berberine) from D. auriculatum were confirmed the potential inhibition of AChE activity in vitro (IC50: 0.24-6.37 μM) and UPLC-ESI-MS/MS results showed that the content of most active compounds in roots was much higher than in aerial parts. Palmatine (IC50 = 0.34 μM) and columbamine (IC50 = 0.24 μM) showed prominent AChE inhibitory activity among the tested compounds. This is the first report about the evaluation of AChE inhibitory activity and phytochemical profiles of D. auriculatum, led to the identification of 36 compounds including alkaloids and flavonoids, and five alkaloids exhibited a significant AChE inhibitory activity and had the potential as AChE inhibitors. This study provided scientific experimental basis for the traditional efficacy of neurological disease of the plant.