Electrical stimulation of the vagus nerve improves amyloid pathology in delirium superimposed on dementia

BACKGROUND: Delirium and delirium superimposed on dementia (DSD) are common complications affecting patients suffering from ongoing neurodegenerative pathologies. Peripheral surgical trauma can trigger neuroinflammation and ensuing DSD via mechanisms that remain poorly understood. Given the multifactorial therapeutic effects of neuromodulation, including vagal nerve stimulation, we have tested a minimally invasive approach to combat DSD following orthopedic surgery. METHODS: We performed orthopedic surgery on 5xFAD and CVN-AD mice and tested the efficacy of minimally invasive percutaneous vagus nerve stimulation (pVNS). We applied immunohistochemical, biochemical, and behavioral assays to evaluate the impact of surgery on postoperative delirium on DSD pathology in Alzheimer’s disease-like mice. To confirm the role of systemic factors in neuroinflammation and amyloid-β dyshomeostasis, we conducted experiments using interleukin-6 (IL-6), a cytokine commonly upregulated in postoperative delirium and in vitro co-culture assays for validation. RESULTS: In AD-like mice surgery induced acute changes in amyloid-β; perioperative treatment with pVNS effectively reduced amyloid-β load, plaque sphericity, and neuronal loss. The rescue of these pathological hallmarks led to improved delirium-like behavior, as demonstrated by the 5-choice serial reaction time task on postoperative days 1 and 2. pVNS improved microglial morphology, particularly near amyloid-β plaques. Acute isolation of microglial cells from 5xFAD mice after surgery indicated that pVNS partially enhanced key Disease-Associated Microglia (DAM) markers. The contribution of pro-inflammatory cytokines to amyloid-β aggregation was validated using an in vitro transwell culture model following Cytomix exposure, which also caused endothelial barrier disruption. Finally, we isolated IL-6 as a well-established biomarker of postoperative delirium and described its role in DSD pathology following systemic administration. CONCLUSION: These findings establish a role for neuromodulation after pVNS in regulating perioperative immunity and advance a new paradigm for perioperative interventions in patients at risk for DSD.