The identification of effective pharmacological tools for Alzheimer’s disease (AD) represents one of the main challenges for therapeutic discovery. Due to the variety of pathological processes associated with AD, a promising route for pharmacological intervention involves the development of new chemical entities that can restore cellular homeostasis. To investigate this strategy, we designed and synthetized SG2, a compound related to the thyroid hormone thyroxine, that shares a pleiotropic activity with its endogenous parent compound, including autophagic flux promotion, neuroprotection, and metabolic reprogramming. We demonstrate herein that SG2 acts in a pleiotropic manner to induce recovery in a C. elegans model of AD based on the overexpression of Aβ42 and improves learning abilities in the 5XFAD mouse model of AD. Further, in vitro ADME-Tox profiling and toxicological studies in zebrafish confirmed the low toxicity of this compound, which represents a chemical starting point for AD drug development.

Background: Alzheimer’s disease (AD) is a chronic neurodegenerative disorder characterized by progressive cognitive decline and behavioral impairments. Hydrogen sulfide (H₂S) is an endogenous gasotransmitter that exerts pleiotropic neuromodulatory, anti-inflammatory, cytoprotective, and trophic effects within the central nervous system. Objectuves: This study investigated whether chronic inhalation of naturally H₂S-rich sulphureous water, a non-invasive and clinically applicable intervention, exerts neuroprotective effects in 5XFAD mice, a transgenic model of severe AD pathology. Methods: Two-month-old male and female wild-type and 5XFAD mice underwent daily inhalation of saline or sulphureous water for eight weeks. Sulphureous water exposure was well tolerated and did not impair baseline learning or memory in either genotype. A detailed analysis of swim trajectories revealed selective enhancement of spatially accurate navigation strategies in sulphureous water-exposed 5XFAD female mice, with nearly a threefold increase in effective search behaviors, whereas male mice showed no treatment-specific effects. In addition, sulphureous water inhalation significantly reduced the number and area of 6E10⁺ and 11A1⁺ amyloid-β plaques in corticohippocampal regions and decreased cortical microglia number. Transcriptional profiling of cortical tissue revealed strong genotype-dependent upregulation of microglial, inflammatory, and stress-response genes. Sulphureous water exposure selectively modulated inflammatory and stress-response genes, including Cd11b, Cst, Sod1, Tgfb1, and Hsp90a, with distinct genotype-dependent interactions. Results: Overall, chronic inhalation of naturally H₂S-rich sulphureous water during the prodromal phase of AD-like pathology mitigated early amyloid burden, reduced cortical microgliosis, and improved qualitative aspects of spatial navigation, particularly in female mice. Conclusions: These findings warrant further translational investigation of sulphureous water inhalation as a potential preventive or disease-modifying strategy for AD in humans.