Lung protective ventilation alleviates intracerebral hemorrhage-induced secondary brain and lung injury in mice via the Nrf2/HO‑1 pathway.

Background: The management of mechanical ventilation (MV) for patients with intracerebral hemorrhage (ICH) remains controversial. Lung protective ventilation (LPV) has been shown to reduce mortality in critically ill patients, such as those with acute respiratory distress syndrome (ARDS). Methods: ICH model was created in male C57BL/6 mice by injecting autologous blood into the basal ganglia, followed by LPV [tidal volume (VT) =6 mL/kg, positive end-expiratory pressure (PEEP) =5 cmH2O]. Neurobehavioral assessments were conducted at 3, 7, and 14 days, and neuronal injury was evaluated using Nissl staining. Inflammatory factors in brain tissue, serum, and bronchoalveolar lavage fluid (BALF) were analyzed by enzyme-linked immunosorbent assay (ELISA). Lung tissue was examined using hematoxylin-eosin (H&E) staining. Immunofluorescence detected Nrf2 translocation into the nucleus, and Western blot assessed Nrf2/HO-1 pathway proteins and inflammatory markers. The Nrf2 inhibitor ML385 was administered before modeling to assess the reversal of LPV's effects. Results: Conventional tidal-volume ventilation (CTV) significantly exacerbated cerebral edema compared with the ICH-only group, whereas LPV markedly reduced brain water content (wet-dry ratio). In behavioral tests, LPV‑treated mice displayed the shortest sticker removal times, highest Garcia scores, lowest Foot‑fault rates, and longest Rotarod endurance among all groups. Nissl staining revealed increased neuronal injury and apoptosis after ICH, worst in the CTV group; LPV preserved more viable neurons, indicating significant neuroprotection. Pulmonary histopathology on day 5 showed the most severe lung damage in CTV mice, intermediate damage in ICH-only mice, and significantly milder injury in LPV-treated mice. The lung wet-dry ratio was highest in CTV animals, while LPV significantly alleviated pulmonary edema. BALF cytokine analysis revealed the highest interleukin-1 beta (IL‑1β), interleukin-6 (IL‑6), and tumor necrosis factor-alpha (TNF‑α) levels in the CTV group, moderate levels in ICH, and lowest levels in LPV, indicating reduced lung inflammation. In both serum and brain tissue, LPV significantly lowered levels of IL‑1β, inducible nitric oxide synthase (iNOS), IL‑6, and TNF‑α compared with ICH and CTV groups; oxidative stress markers also improved. WB and immunofluorescence show that LPV promoted nuclear translocation of Nrf2 and upregulated downstream HO‑1. Superoxide dismutase (SOD) activity increased and malondialdehyde (MDA) levels decreased in the LPV group, consistent with activation of the Nrf2/HO‑1 antioxidant pathway. Inhibition of Nrf2 using ML385 reduced Nrf2 nuclear localization and HO‑1 expression, partially reversed LPV's anti‑inflammatory and antioxidant effects, increased iNOS, worsened brain inflammation, and diminished neurological improvement. Conclusions: Significant lung injury was evident on the 5th day after ICH. LPV alleviated neuronal damage, improved neurobehavioral outcomes, and reduced IL-6, IL-1β, and TNF-α in lung, blood, and brain. LPV activated the Nrf2/HO-1 pathway, decreasing oxidative stress. ML385 reversed LPV's protective effects on the brain and lung.