In-vitro and in-silico cholinesterase inhibitory activity of bioactive molecules isolated from the leaves of Andrographis nallamalayana JL Ellis and roots of Andrographis beddomei CB Clarke

Cholinesterase inhibitors remain the best therapeutic strategies to treat Alzheimer's disease. In search for the potent and long-acting cholinesterase (AChE/BChE) inhibitors, we studied the inhibitory activities of three species of Andrographis genus viz, Andrographis paniculata (Burm.f.) Nees Andrographis nallamalayana J.L. Ellis , and Andrographis beddomei C.B. Clarke. It was demonstrated that the methanolic extract of these plants was able to inhibit acetylcholinesterase and butyrylcholinesterase. Furthermore, the phytochemical investigation led to the isolation of 11 known compounds. Echioidinin (1), skullcapflavone I (2), 5,2 ',6 '-trihydroxy-7-methoxyflavone (3), 5.,2 ',6 '-trihydroxy-7-methoxyflavone 2 '-O-beta-D-glucopyranoside (4), and chrysin 7-glucuronide (5) were isolated from leaves of A. nallamalayana whereas 7-O-methylwogonin (9), wogonin (10), viscidulin II (11), andrographidine C (12), andrographidine G (13), 5,8,2 '-trihydroxy-7-methoxyflavone-5-O-ss-D glucopyranoside (14) were isolated from roots of A. beddomei. Their structures were elucidated by 1H, 13CNMR spectra, mass spectrometry, and X-ray single crystal diffraction experiments. The SC-XRD and Hirshfeld Surface analysis of eight flavonoids (Compound 1, 2, 4, 6, 9, 11, 12, 13 and positive control drug galantamine hydrobromide is reported for the first time. Compound 6, 4, 10, 9 were potent inhibitors of acetylcholinesterase enzyme with IC50 values of 1.86 +/- 0.139 mu M, 3.37 +/- 0.086 mu M, 6.38 +/- 0.098 mu M, 9.11 +/- 0.116 mu M respectively. Compound 6 was more potent than the positive control, galantamine (IC50 = 4.68 +/- 0.032 mu M). All these compounds showed moderate to weak inhibitory activity against BChE. In addition, molecular docking studies were performed to explore the binding mode of the compounds, and the results were in good agreement with the experimental results. These results clearly indicate the potential of these compounds as powerful lead molecules for further investigations.