Intratracheal Neomycin Attenuates TBI-induced Secondary Brain Injury via Modulation of Lung Dysbiosis and Inhibition of the NLRP3 Inflammasome.

This study is the first to investigate whether modulation of the lung microbiome after traumatic brain injury (TBI) can reduce secondary brain injury and promote neurological recovery. Moderate TBI was induced in adult male Sprague-Dawley rats, which were assigned to normal, TBI, or TBI with intratracheal neomycin treatment for three days. Bronchoalveolar lavage fluid (BAL) and lung tissues were collected on day 3, and brain neuropathology, neuroinflammation, and cognition were assessed on day 7. TBI induced marked neutrophil infiltration and alveolar interstitial edema, accompanied by elevated IL-6 and NOS2 expression in BAL fluid and increased Acinetobacter abundance (LEfSe, LDA score > 3, p < 0.05). Intratracheal neomycin treatment after TBI corrected lung dysbiosis, significantly reduced Acinetobacter abundance, and suppressed IL-6, RAGE, and NLRP3 inflammasome components (NLRP3, ASC, caspase-1, and IL-1β) in lung tissues. In the brain, neomycin improved novel object recognition, reduced IL-6, IL-1β, and NLRP3 inflammasome activation, attenuated GFAP and Iba-1 activation, decreased FJB- and TUNEL-positive cells, preserved blood-brain barrier integrity, and prevented synaptic injury. Serum IL-1β levels peaked on day 3 after TBI, but this elevation was substantially attenuated in neomycin-treated rats. Furthermore, restoration of viable Acinetobacter baumannii largely reversed the neuroprotective effects of neomycin, supporting a causal role for lung Acinetobacter in secondary brain injury after TBI. These findings suggest that early intratracheal neomycin instillation following TBI mitigates lung dysbiosis and NLRP3-mediated inflammation in both lung and brain, thereby reducing secondary brain injury via the lung-brain axis, highlighting translational therapeutic potential.