Neurodegenerative and neuropsychiatric illnesses are characterized by neuroinflammation, which is driven by microglial activation, cytokine production, and breakdown of the blood-brain barrier (BBB). It is currently known that the gut microbiota plays an important role in modulating neuroimmune signaling, which in turn may trigger anxiety-like behaviors and depressive phenotypes through the microbiota-gut-brain axis. This review aims to integrate the most recent mechanistic knowledge on treatment strategies targeting the gut microbiota to modulate neuroinflammation. This review article discusses preclinical and clinical studies that investigated microbial composition, metabolite profiles, and host-microbe interactions involved in neuroinflammatory processes. However, special attention was given to signaling via the vagus nerves and bile acids, as well as to tryptophankynurenine metabolism and short-chain fatty acids (SCFAs). To examine the potential connection between the two, researchers used animal models such as germ-free animals and antibiotic-injected mice for fecal microbiota transplantation (FMT). This article defines dysbiosis as amplifying neuroinflammatory responses by altering microglial phenotypes, disrupting the blood-brain barrier, and triggering the production of pro-inflammatory cytokines. In contrast, microbiome diversity rehabilitation through the use of probiotics, prebiotics, synbiotics, and dietary modifications reduces neuroinflammatory markers and enhances cognitive and behavioral status. Clinical trials have shown considerable promise in diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), autism spectrum disorder (ASD), and depression. However, variability in treatment protocols, treatment resistance, and host-specific factors continue to pose significant challenges. This narrative review integrates mechanistic insights into microglial activation, cytokine signaling, blood-brain barrier regulation, vagal pathways, tryptophan metabolism, and short-chain fatty acids with emerging clinical evidence and therapeutic strategies, including probiotics, prebiotics, dietary modulation, and personalized microbiome-based interventions. Despite promising therapeutic potential, microbiome engineering faces important challenges, including safety concerns, lack of standardized intervention protocols, and substantial inter-individual variability in host-microbiome responses, which currently limit clinical translation. This review focuses on both neurodegenerative and neuropsychiatric disorders, examining shared neuroinflammatory mechanisms mediated by the gut-brain axis and evaluating microbiotatargeted therapeutic strategies across these disease categories. The review discusses both preventive strategies, including dietary modulation, prebiotics, and lifestyle-based microbiome interventions, as well as therapeutic approaches such as microbiota-targeted treatments aimed at mitigating neuroinflammation and disease progression.
