Isolation and identification of hasubanan alkaloids having anti-cholinesterase and antioxidant activity from the stem Stephania japonica

Abstract Background A recent report showed that Stephania japonica chloroform fraction has potential anticholinesterase and antioxidant activities and is able to improve learning and memory in mice. Therefore, the aim of the present study was to isolate and identify compounds from the chloroform fraction with cholinesterase inhibitory and antioxidant activity that may be useful as new candidates for the treatment of AD. Methods Chromatographic methods were used for isolation of compounds and the isolated compounds were analyzed by spectroscopic methods for structure elucidation. Acetyl- and butyryl-cholinesterase inhibitory activity were evaluated for by Ellman’s method and the antioxidant activity by several in vitro models such as DPPH and hydroxyl radicals scavenging, reducing power, total antioxidant activity, and inhibition of brain lipid peroxidation. The interaction of cholinesterase enzymes and isolated compounds were examined by molecular docking studies. Results Bioactivity guided approach led to the isolation of four compounds from the chloroform fraction and identified as aknadinine, aknadilactam, aknadicine and stephisoferuline on the basis of their 1 H-NMR and 13 C-NMR spectral data. All the compounds were of hasubanan type. They showed significant inhibition against acetylcholinesterase and butyrylcholinesterase, with at least two fold increased affinity for butyrylcholinesterase than acetylcholinesterase. The IC 50 values of the alkaloids were in the range of 9.36–14.89 µg/mL against acetylcholinesterase and 3.97–6.66 µg/mL against butyrylcholinesterase. Kinetic analysis revealed that all the four compounds exhibited mixed type of inhibition against both acetylcholinesterase and butyrylcholinesterase. The interaction of compounds with several amino acids of enzymes was supported by molecular docking studies. All the hasubanan alkaloids showed antioxidant activity in all in vitro assays and inhibited peroxidation of brain lipid. The IC 50 values of the compounds for scavenging of DPPH and hydroxyl radicals, and lipid peroxidation inhibition were found to be in the range of 5.1-40.91, 10.44–19.41, and 20.60–31.72 µg/mL, respectively. Conclusion The hasubabanan alkaloids isolated from S. japonica may represent a new class of anti-cholinesterase compounds. The multitargeted activity of hasubanan alkaloids may lead to new candidates for the treatment of AD.