The lung-brain axis in neurodegeneration: inflammatory, immune, and vascular mechanisms with therapeutic implications

Neurodegenerative and chronic pulmonary diseases represent major global health challenges and have widely been investigated separately. Emerging evidence indicates the existence of a lung-brain axis, through which pulmonary pathology and environmental exposures can influence neurological health. The current review highlights the mechanistic and clinical evidence linking chronic lung inflammation, air pollution, and immune dysregulation to the onset and progression of Alzheimer's disease (AD), Parkinson's disease (PD), Multiple sclerosis (MS), and amyotrophic lateral sclerosis (ALS). A pathway-based framework is presented in which lung inflammation, systemic cytokine release, oxidative stress, blood-brain barrier disruption, immune priming, and protein misfolding mediate lung-to-brain communication. Associations between chronic obstructive pulmonary disease, asthma, particulate matter exposure, and adverse neurological outcomes including cognitive decline, brain atrophy, disease progression, and elevated neurodegenerative risk are emphasized. Specific mechanisms are addressed, including immune-mediated effects in multiple sclerosis, inhalation-driven protein aggregation in Parkinson's disease, and vascular and oxidative injury contributing to dementia and amyotrophic lateral sclerosis. COVID-19 is considered a clinical model of acute lung-brain axis disruption, demonstrating inflammation-driven neurocognitive consequences, and its role in this context was also highlighted. Additionally, potential preventive and therapeutic strategies are discussed, highlighting pulmonary health and environmental exposure reduction as modifiable factors that may help mitigate neurological disease. This integrative review underscores the clinical relevance of the lung-brain axis and calls for interdisciplinary strategies to improve neurological outcomes through pulmonary and environmental interventions.