Sildenafil as a candidate drug for Alzheimer’s disease: Real-world patient data observation and mechanistic observations from patient-induced pluripotent stem cell-derived neurons.

Alzheimer’s disease (AD) is a chronic neurodegenerative disease needing effective therapeutics urgently. Sildenafil, one of the approved phosphodiesterase-5 inhibitors, has been implicated as having potential beneficial effect in AD. We showed that sildenafil usage is associated with reduced likelihood of AD across four new drug compactor cohorts, including bumetanide, furosemide, spironolactone, and nifedipine. For instance, sildenafil usage is associated with a 54% reduced prevalence of AD in MarketScan® (hazard ratio [HR] = 0.46, 95% CI 0.32-0.66) and a 30% reduced prevalence of AD in Clinformatics® (HR = 0.70, 95% CI 0.49-1.00) compared to spironolactone. We found that sildenafil treatment significantly reduced tau hyper-phosphorylation (pTau181, pTau205) in a dose-dependent manner in both familial and sporadic AD patient derived neurons. Further RNA-seq data analysis of sildenafil-treated AD patient iPSC-derived neurons revealed that sildenafil specifically targeting AD related genes and molecular pathways involved in axon guidance, AD-presenilin, neurogenesis, neurodegeneration, synaptic dysregulation, vascular smooth muscle contraction (VSMC) and cyclic guanosine monophosphate (cGMP)-protein kinase G (PKG) signaling pathway, mechanistically supporting the potential beneficial effect of sildenafil in AD. These real-world patient data validation and mechanistic observations from patient iPSC-derived neurons further suggested that sildenafil is a potential repurposable drug for AD. However, randomized clinical trials are required to validate sildenafil as a potential treatment of AD. To investigate the potential therapeutic benefit of sildenafil on AD outcome, we used both familial and sporadic AD patient induced pluripotent stem cells (iPSC) derived neurons to evaluate the sildenafil’s mechanism-of-action using ELISA, Western blotting, and RNA-sequencing analysis. We performed comparative gene expression profiling analysis of RNA-seq data for a male FAD patient derived iPSCs treated with and without sildenafil (100 µM) in replicates.