Putatively Identified Sarmentoside-B Removes Oligomerized Amyloid Peptide from Neurons by Inhibiting mTOR and Restoring Lysosomal Function, in In Vitro Alzheimer’s Disease Model

Background/Objectives: Alzheimer’s disease (AD) is characterized by beta-amyloid (Aβ) plaque deposition, which impairs several cellular processes, including autophagy. Considering the multifactorial nature of AD, the development of therapies acting on alternative molecular targets is necessary. In this study, we evaluated the neuroprotective effect of a molecule from the hydrozoan Eudendrium carneum and investigated its impact on autophagy-related pathways. Methods: The secretion of E. carneum was fractionated by RP-HPLC according to its neuroprotective activity in SH-SY5Y cells exposed to oAβ42, evaluated using LDH and MTT assays. The purified molecule (named EC5), characterized by mass spectrometry, was evaluated regarding in silico toxicity and calcium dynamics. Neuronal lysosomal morphology was assessed using the LysoTracker probe, and cathepsin D activity was determined using a synthetic substrate. The expression of autophagy-related proteins (mTOR, LAMP-1, and LC3B) was evaluated by dot blotting, and amyloid plaque clearance was quantified using Thioflavin-T staining. Results: The steroid glycoside putatively identified as Sarmentoside B (EC5) exhibited neuroprotective effects and showed no toxicity or alterations in neuronal calcium or sodium channel dynamics. EC5 restored lysosomal morphology and cathepsin D activity, reversing the impairment induced by oAβ42. Furthermore, EC5 reduced mTOR expression, and this interaction was supported by molecular docking analysis. Lysosomal restoration promoted the clearance of oAβ42 aggregates, as evidenced by Thioflavin-T staining, resulting in reduced neuronal death. Conclusions: EC5, putatively identified as Sarmentoside B, exerts neuroprotective effects against oAβ42-induced toxicity by promoting autophagy-related amyloid clearance, highlighting its therapeutic potential for AD.