[Effect of ventilator-induced lung injury on blood-brain barrier permeability in rats]

To observe the effect of ventilator-induced lung injury (VILI) on blood-brain barrier permeability in rats.

Forty-eight healthy clean male Sprague-Dawley (SD) rats were randomly divided into sham operation (Sham) group, low tidal volume (LVT) mechanical ventilation group (LVT group), normal tidal volume (NVT) mechanical ventilation group (NVT group) and high tidal volume (HVT) mechanical ventilation group (HVT group) with 12 rats in each group. After anesthesia, rats in the Sham group were intubated and kept spontaneous breathing. The rats in different tidal volume (VT) groups were mechanically ventilated by endotracheal intubation with VT of 6 mL/kg (LVT group), 10 mL/kg (NVT group), and 20 mL/kg (HVT group), respectively. The inspiration-expiration ratio of the three groups was 1:1, the ventilation frequency was 40 times/min, and the ventilation time was 3 hours. At the end of the experiment, the bronchoalveolar lavage fluid (BALF) of rats was collected, and the levels of pro-inflammatory factors [tumor necrosis factor-α (TNF-α), interleukins (IL-1β and IL-6)] in BALF were detected by enzyme-linked immunosorbent assay (ELISA). The lung tissues of rats were collected, and the lung wet/dry weight (W/D) ratio was calculated. The pathological changes of lung tissues were observed under light microscopy after hematoxylin-eosin (HE) staining, and lung injury scores were performed. The brain tissue of rats was taken to measure the brain water content, and the Evans blue (EB) content of brain tissue was measured to reflect the permeability of the blood-brain barrier. The tight junction proteins in the brain tissues were detected by Western blotting.

After 3 hours of mechanical ventilation, with the increase of VT, the degree of lung injury in VILI rats gradually increased. When VT reached 20 mL/kg, lung tissue structure was significantly injured, alveolar wall edema, alveolar congestion, lung interstitial thickening, a large number of inflammatory cells infiltrated, and the lung injury score, lung W/D ratio, and the levels of TNF-α, IL-1β and IL-6 in BALF were significantly higher than those in the Sham group [lung injury score: 10.6±1.1 vs. 1.4±1.0, lung W/D ratio: 6.6±0.8 vs. 3.7±0.6, TNF-α (ng/L): 832.9±97.9 vs. 103.8±23.3, IL-1β (ng/L): 68.9±14.1 vs. 15.7±2.6, IL-6 (ng/L): 70.8±16.4 vs. 20.3±5.4, all P < 0.05]. Lung injury in rats was accompanied by aggravating brain injury. When VT reached 20 mL/kg, brain water content and EB content in brain tissue were significantly higher than those in the Sham group [brain water content: (85.4±3.6)% vs. (68.7±2.7)%, EB content in brain tissue (μg/g): 887±78 vs. 97±14, both P < 0.05], and the protein expressions of claudin-5, occluding and zonula occluden-1 (ZO-1) in the brain tissue were significantly lower than those in the Sham group [claudin-5 protein (claudin-5/β-actin): 0.67±0.12 vs. 1.45±0.19, occludin protein (occludin/β-actin): 0.48±0.11 vs. 0.99±0.21, ZO-1 protein (ZO-1/β-actin): 0.13±0.03 vs. 0.63±0.12, all P < 0.05].

VILI can induce brain edema and increase blood-brain barrier permeability in rats, which may be related to the down-regulation of tight junction protein expression in the brain tissue.