Targeting GSK-3β to Modulate the Wnt Pathway: A Promising Neuroprotective Strategy for Alzheimer’s Disease

Alzheimer's disease (AD) is marked by amyloid-β plaques and neurofibrillary tangles. Glycogen synthase kinase-3β (GSK-3β) is a promising therapeutic target for mitigating several AD-related pathologies via modulation of the Wnt pathway. However, nonspecific GSK-3β inhibition by indirubin-3'-oxime (IMX) may result in significant off-target effects, necessitating the development of brain-targeted delivery systems. Solid lipid nanoparticles (SLNs) are biocompatible nanocarriers for brain-targeted delivery of therapeutics. Polysorbate 80 (PS80) and stearic acid (SA)-modified SLNs encapsulating IMX (PS80-SA SLNs-IMX) were prepared using the solvent injection method. The formula was optimized using full factorial design (FFD). The optimized formulation was biophysically characterized. The neuroprotective efficacy of PS80-SA SLNs-IMX was then evaluated <i>in vitro</i> using cell lines (IMR-32 & N2a). Biodistribution study was carried out in Wistar rats to evaluate the site-specific distribution of IMX and SLNs. The optimized PS80-SA SLNs-IMX exhibited a particle size of 185.7 ± 2.7 nm, a polydispersity index of 0.22 ± 0.01, a ζ potential of -21.02 ± 1.53 mV, and an entrapment efficiency of 99.4 ± 0.12%. Surface morphology analysis revealed that they are spherical in shape, and <i>in vitro</i> release study revealed the sustained release of PS80-SA SLNs-IMX until 48 h. Accelerated stability study results revealed the formulation stability with negligible changes in the PS, PDI, and ZP up to 6 months. MTT assay results have shown that PS80-SA SLNs-IMX has a negligible cytotoxic effect. ROS and neuroprotective assays have demonstrated antioxidant and neuroprotective effects of PS80-SA SLNs-IMX against OKA-induced neurotoxicity. ELISA depicted a significant reduction in Aβ1-42 and p-tau upon treatment with PS80-SA SLNs-IMX. Western blot analysis confirmed the effect of PS80-SA SLNs-IMX on the inhibition of GSK-3β and the activation of the Wnt pathway. Biodistribution study results revealed that PS80-SA SLNs-IMX has a significant increase in brain concentration when compared to naïve IMX, indicating the brain-specific distribution of PS80-SA SLNs-IMX. In conclusion, PS80-SA SLNs-IMX demonstrated enhanced neuronal cell uptake and significant neuroprotective activity <i>in vitr</i>o. To our knowledge, this is the first report of PS80-SA SLNs-IMX with high entrapment and robust neuroprotection in an okadaic acid (OKA)-induced tauopathy model, underscoring the translational potential for AD therapy.