Study of Mechanism of Action of Some Neuroprotective Agents from Indian Medicinal Plants

Abstract

The neurodegenerative conditions have characteristic pathological features such as incidence of oxidative stress, inflammation, proteins aggregation and loss of neurotransmitters. Many plant extracts and bioactives derived from them have been proven efficacious in these conditions and the bioactives are routinely utilized as the structural fingerprints to design synthetic molecules for beneficial effects in various diseased conditions. Thus, the current study was carried out with an aim to screen few extracts and the major bioactives derived from them for neuroprotective effects in various in vitro and in vivo models. Initially the molecular docking studies revealed the potential of bergenin and bacoside A to act on multiple targets related to AD and based on the results of the study, these bioactives and the plants containing these bioactives i.e. Bergenia ciliata and Bacopa monnieri were selected for evaluation of their neuroprotective effects in the in vitro and in vivo models. The crude extracts of B. ciliata were subjected to preliminary phytochemical screening followed by column chromatography using various gradients of chloroform and methanol to isolate bergenin (0.6 % yield). The standardized extracts of B. monnieri (50 % bacosides) were procured and subjected to the column chromatography using various gradients of chloroform and ethyl acetate followed by ethyl acetate and methanol for isolation of bacoside A (10.21 % yield). The isolated compounds were tested for their identity using various chromatographic and spectroscopic techniques. The extracts of B. ciliata rhizomes and its major bioactive bergenin along with standardized extracts of B. monnieri and its major bioactive bacoside A were initially evaluated in vitro on the SH-SY5Y neuroblastoma cells for testing their preliminary cytotoxicity. The extracts and test compounds were then tested for their neuroprotective effects against NMDA induced cytotoxicity in SH-SY5Y cells. The in vitro acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibition assays were also performed. Thereafter, the test compounds and extracts were screened for their preventive effects against scopolamine induced amnesia (14 days pre-treatment) and ameliorative effects against intracerebroventricular streptozotocin (ICV STZ) (28 days supplementation after induction and rest period) induced model in rats at three dose levels. The behavioral analysis in both the animal models was performed using the Morris water maze (MWM) and Y maze. The serum samples and the brain homogenates were subjected to the determination of AChE and BuChE activity coupled with the determination of the levels of GSH. The brain homogenates of the ICV STZ induced rats were subjected to the evaluation of the immunoreactivity to the major pathological hallmarks of AD-like Aβ1-42, phosphorylated tau protein and glycogen synthetase kinase 3β (GSK-3β).