In-Silico discovery of 17alpha-hydroxywithanolide-D as potential neuroprotective allosteric modulator of NMDA receptor targeting Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder marked by cognitive decline, memory impairment, and behavioral alterations. The N-methyl-D-aspartate (NMDA) receptor has emerged as a promising target for AD pharmacotherapy due to its role in the disease's pathogenesis. This study leverages advanced computational methods to screen 80 active constituents of Withania somnifera (Ashwagandha), a traditional herb known for its neuroprotective effects, against the NMDA receptor, using FDA-approved Ifenprodil as a reference. Our blind virtual screening results demonstrated that all tested compounds could bind to various domains of the NMDA receptor, with binding energies ranging from - 4.1 to -11.9 kcal/mol, compared to Ifenprodil's -7.8 kcal/mol. Binding preference analysis revealed 7 compounds bound to the A-chain, 37 to the B-chain, 7 to the C-chain, and 29 to the D-chain of the receptor. Notable binding was observed predominantly at the Amino Terminal Domain (ATD) core site, some at the ATD-Ligand Binding Domain (LBD) interface, and a few at the Transmembrane Domain (TMD). Particularly, 17alpha-hydroxywithanolide D, with a binding energy of -11.9 kcal/mol, emerged as a prime candidate for further investigation. Molecular dynamics simulations of this compound revealed key interactions, including direct hydrogen bonding with residues ASP165, ARG431, THR433, LYS466, and TYR476 on the D-chain, as well as additional hydrophobic and water-bridging interactions. These simulations highlighted the compound's influence on dynamic conformational states of the GluN1b-GluN2B receptor complex, modulating interactions between GluN1b Lys178 and GluN2B Asn184. Furthermore, the compound affected the distance between LBD heterodimers and the tension within the LBD-M30 linker, demonstrating its potential to modulate NMDA receptor activity. This comprehensive study not only underscores the therapeutic promise of Withania somnifera derivatives for AD but also provides a detailed molecular basis for their efficacy, offering valuable insights for targeted drug development and innovative therapeutic strategies against Alzheimer's disease.