A two-hit model of sepsis plus hyperoxia causes lung permeability and inflammation

Mouse models of acute lung injury (ALI) have been instrumental for studies of the biological underpinnings of lung inflammation and permeability, but murine models of sepsis generate minimal lung injury. Our goal was to create a murine sepsis model of ALI that reflects the inflammation, lung edema, histological abnormalities, and physiological dysfunction that characterize ALI. Using a cecal slurry (CS) model of polymicrobial abdominal sepsis and exposure to hyperoxia (95%), we systematically varied the timing and dose of the CS injection, fluids and antibiotics, and dose of hyperoxia. We found that CS alone had a high mortality rate that was improved with the addition of antibiotics and fluids. Despite this, we did not see evidence of ALI as measured by bronchoalveolar lavage (BAL) cell count, total protein, C-X-C motif chemokine ligand 1 (CXCL-1) or by lung wet:dry weight ratio. Addition of hyperoxia [95% fraction of inspired oxygen (FIO2)] to CS immediately after CS injection increased BAL cell counts, CXCL-1, and lung wet:dry weight ratio but was associated with 40% mortality. Splitting the hyperoxia treatment into two 12-h exposures (0-12 h and 24-36 h) after CS injection increased survival to 75% and caused significant lung injury compared with CS alone as measured by increased BAL total cell count (92,500 vs. 240,000, P = 0.0004), BAL protein (71 vs. 103 mg/mL, P = 0.0030), and lung wet:dry weight ratio (4.5 vs. 5.5, P = 0.0005), and compared with sham as measured by increased BAL CXCL-1 (20 vs. 2,372 pg/mL, P < 0.0001) and histological lung injury score (1.9 vs. 4.2, P = 0.0077). In addition, our final model showed evidence of lung epithelial [increased BAL and plasma receptor for advanced glycation end products (RAGE)] and endothelial (increased Syndecan-1 and sulfated glycosaminoglycans) injury. In conclusion, we have developed a clinically relevant mouse model of sepsis-induced ALI using intraperitoneal injection of CS, antibiotics and fluids, and hyperoxia. This clinically relevant model can be used for future studies of sepsis-induced ALI.