Inflammatory and Functional Responses Induced by Normobaric and Hyperbaric Hyperoxia in Mice Lungs

Abstract

AimWe aimed to validate a lung injury model developed for small animals submitted to hyperoxia and hyperbaric environment.MethodsAfter approval by the Institutional Ethics Committee (CEUA, code: 016/17), 95 adult male BALB/c mice were used in three protocols. Protocol I: 45 mice were distributed into 5 groups. Each group was exposed to 100% oxygen in a hyperbaric chamber under pressures of 1, 1.5, 2, 2.5, and 3 atmospheres absolute (ata), and survival curves and LC50 were calculated for each pressure. Protocol II: 25 mice were distributed into 5 groups and then exposed to 50% of the LC50 achieved at the same pressure levels. Protocol III: 20 mice were distributed into 4 groups (3ata, hyperbaric hyperoxia; HIPEROX, normobaric hyperoxia; HIPERBAR, hyperbaric normoxia; CTRL, ambient air).ResultsData are expressed as mean±SEM. Survival time was inversely proportional to ambient pressure. The LC50 obtained were 70.3, 33.1, 15.2, 9.7 and 5.9 h 100%O2, respectively. In protocol II, tissue damping (G) was significantly higher in 1ata than in the other groups (1ata 6.78±3.4; 1.5ata 3.4±0.4; 2ata 3.7±2; 2.5ata 2.8±0.6; 3ata 2.7±0.6; CTRL 1.94±0.2 cmH2O/mL, p=0.0007 vs control, ANOVA) and between 1ata and CTRL in tissue elastance (H) (51.4±29.1 vs 18.72±1.3 cmH2O/mL, p= 0.009, ANOVA). Superoxide dismutase activity in groups of hyperbaric hyperoxia was statistically higher than CTRL (2.5ata: 20.20±0.22; 3ata: 20.04±0.09 vs CTRL: 16.83±0.25 U/mg protein, p>0.001, ANOVA). Apoptosis was more evident in 1ata, 1.5ata and 3ata groups than in CTRL (1ata: 0.13±0.01; 1.5ata 0.15±0.01 and 3ata: 0.22±0.01 vs CTRL: 0.08±0.004 positive/total cells, p>0.05, ANOVA). The 1ata group had more collapsed alveoli (72.01±2.3 vs CTRL 41.39±5.6%, p>0.01, ANOVA) and 1.5ata group had more inflammatory cells (1.5ata: 8.4±0.6 vs CTRL: 4.5±0.2 × 10−3/μm2 PMN cells p<0.001, ANOVA) when compared to all other groups. In protocol III, Newtonian resistance [Rn, 0.62±0.03 (3ata); 0.75±0.06 (HIPEROX); 0.43±0.12 (HIPERBAR); 0.15±0.01 (CTRL) cmH2O/mL, p<0.03, ANOVA], tissue viscance [2.7±0.2 (3ata); 2±0.09 (HIPEROX); 2.1±0.1 (HIPERBAR); 1.9±0.1 (CTRL) cmH2O/mL, p<0.05, ANOVA] and inflammatory infiltrate [5.2±0.3 (3ata); 6.5±0.6 (HIPEROX); 4.4±0.3 (HIPERBAR); 4.5±0.2 (CTRL) × 10−3/μm2 PMN cells, p<0.05, ANOVA] were worst in the hyperbaric hyperoxic groups. SOD activity was increased in hyperoxia [20.04±0.09 (3ata); 19.54±0.1 (HIPEROX); 19.7±0.4 (HIPERBAR); 16.83±0.25 (CTRL) U/mg protein, p<0.001, ANOVA]. Moreover, the most significant apoptotic stimulus was found in groups 3ata and HIPERBAR [0.22±0.01 (3ata); 0.12±0.02 (HIPEROX); 0.17±0.01 (HIPERBAR); 0.08±0.004 (CTRL), p<0.01, ANOVA].ConclusionWe achieved a model to generate acute lung injury, whose pattern changes as exposure moves across the normobaric hyperoxia to hyperbaric hyperoxia spectrum, accompanied by an overall bimodal response in mechanics, histopathological expression, antioxidant activity and apoptosis.Support or Funding InformationCNPq, FAPERJ, FINEP, CAPES (Brazil)