Gut-brain axis in Alzheimer's disease: neuroinflammatory mechanisms and immunopharmacological interventions

Despite being defined pathologically by amyloid-β plaques, chronic neuroinflammation and neurofibrillary tangles, the drugs that target these processes directly (lecanemab and donanemab) have only modest effects on the clinical course of Alzheimer's disease (AD) and significant safety concerns have been identified, so there is renewed interest in upstream, systemic contributors to disease. This review aims to provide a synthesis of the latest mechanistic and clinical evidence that gut microbiota dysbiosis is associated with Alzheimer's disease with a specifically immunopharmacological focus. We will explore how the gut-brain axis pathways (vagal, immune, endocrine and microbial-metabolite signaling) converge to trigger microglial and astrocytic activation via toll-like receptor 4/NF-κB and complement-primed NLRP3 inflammasome signaling, which is also directly activated by amyloid-β and tau. Then we review the immunopharmacological interventions intended to break this axis - probiotic supplementation (some consistent benefit - although mild) and sodium oligomannate, with strong preclinical and case report signals that need human trials (in 2026) and polyphenols and GLP-1 receptor agonists, which have a persistent disconnect between mechanistic promise and clinical efficacy, including a definitive null result for semaglutide in 2026. Translative directions are addressed to nanotechnology-based delivery systems for improving bioavailability and blood-brain barrier penetration, as well as emerging precision-medicine, AI-driven approaches in the selection of treatments based on microbiome information. It is our opinion that because the gut-brain-immune axis is a mechanistically supported and potentially highly scalable therapeutic target, complementary to amyloid and tau therapies, the development of future therapies should match the inflammatory, metabolic and microbial phenotypes.