Mechanism of alkaloid-based inhibition of aldose reductase: Computational perspectives and experimental validations.

Excessive aldose reductase activity drives the polyol-pathway damage that underlies diabetic cataract, neuropathy and nephropathy, yet few safe, potent AR inhibitors have reached the clinic. Here we integrated virtual screening, atomistic simulation and enzymology to evaluate six natural alkaloids-calycanthine, rutaecarpine, glaucine, sparteine, berbamine and tetrandrine-as prospective AR antagonists. A 2500-compound AutoDock Vina screen singled out these scaffolds for high predicted affinity (≤ - 7.0 kcal mol), chemotype diversity and favorable in silico developability. Docking located all ligands within the catalytic cleft; 200-ns MD trajectories plus free-energy landscapes revealed that rutaecarpine and the bis-benzylisoquinolines tetrandrine and berbamine clamp the anion-binding and specificity pockets simultaneously, collapsing conformational space into a single deep basin. MM/PBSA analysis ranked tetrandrine highest (ΔG = -35.8 ± 2.5 kcal mol) followed by rutaecarpine (-23.0 ± 1.3 kcal mol) and berbamine (-19.4 ± 2.7 kcal mol); per-residue decomposition highlighted Phe122, Trp219 and Leu300 as recurring hot-spots. In vitro, the same hierarchy emerged: tetrandrine inhibited recombinant human AR with an IC₅₀ of 1.56 ± 0.23 μM, outperforming quercetin (2.37 ± 0.27 μM), while rutaecarpine and berbamine yielded IC₅₀ values of 4.84 ± 0.81 and 7.35 ± 0.78 μM, respectively. Lineweaver-Burk and Michaelis-Menten plots demonstrated non-competitive inhibition, aligning with the MD-inferred pocket-clamping mechanism. ADMET profiling identified rutaecarpine as the most balanced lead (Lipinski-compliant, moderate hERG/CYP risk), whereas tetrandrine's hERG liability and low solubility call for scaffold refinement. This study validates bis-benzylisoquinoline and indolo-quinazolinone frameworks as privileged AR inhibitory chemotypes and showcases an end-to-end computational-experimental pipeline that rapidly converts ethnopharmacological molecules into mechanistically characterized leads for managing diabetic complications.