Changes in circulating microparticles in mice with ventilator-induced lung injury

Abstract

To investigate the changes in serum level of microparticles (EMPs) in mice with ventilator-induced lung injury (VILI), and explore its significance in VILI. Forty-eight grade SPF male C57BL/6J mice were randomly divided into two groups, with 24 mice in each group: the mice in mechanical ventilation (MV) group were given high tidal volume (VT 30 mL/kg) MV for 4 hours after tracheal intubation, and those in spontaneous breathing group were spontaneously breathed for 4 hours. The apical blood of 12 mice in each group were collected, and serum levels of interleukins (IL-1β, IL-6) and tumor necrosis factor-α (TNF-α) were determined by enzyme linked immunosorbent assay (ELISA), and serum EMPs levels were determined by flow cytometer. The correlations between EMPs and IL-1β, IL-6, and TNF-α were analyzed by linear regression analysis. The lung tissues of other 12 mice in each group were harvested, and wet/dry weight (W/D) ratio was assessed. After hematoxylin-eosin (HE) staining, the morphological changes in lung tissue were observed under light microscope. After double staining of uranium acetate and lead citrate, the ultrastructural changes in lung tissue were observed with electron microscope. Compared with spontaneous breathing group, the levels of lung W/D ratio in MV group was significantly increased (5.47±0.14 vs. 4.34±0.11), the levels of IL-1β, IL-6, TNF-α and EMPs were also significantly increased [IL-1β (ng/L): 42.4±4.4 vs. 7.7±3.6, IL-6 (ng/L): 1 239.5±66.3 vs. 21.7±4.6, TNF-α (ng/L): 237.6±25.8 vs. 37.1±19.1, EMPs (cells/μL): 28.6±1.8 vs. 5.9±1.8, all P < 0.01]. It was shown by correlation analysis that EMPs were positively related with IL-1β, IL-6, and TNF-α (r value was 0.968, 0.932, 0.945, respectively, all P = 0.000). It was shown by fitting linear regression analysis that when EMPs increased by 1 cell/μL, IL-1β increased by 2.4 ng/L [95% confidence interval (95%CI) = 1.9-2.8, P < 0.001], IL-6 increased by 34.5 ng/L (95%CI = 25.1-44.0, P < 0.001), and TNF-α increased by 13.6 ng/L (95%CI = 10.3-16.9,P < 0.001). It was shown by light microscope that the structure of lung tissue and alveolar of mice in spontaneous breathing group appeared normal, while the shrinks of alveolar and disappearance of alveolar architecture were found in MV group. It was shown by electron microscopy that alveolar wall edema and thickening and broken alveolar septa were found in MV group, by contrast, the structure of alveolar was normal in spontaneous breathing group. 30 mL/kg VT ventilation for 4 hours could induce VILI with increase in EMPs, suggesting EMPs closely related to VILI, and EMPs level may be putative biomarker of VILI.