ABSTRACT
Objective:To investigate the protective effect and mechanism of dexamethasone in lung ischemia/reperfusion injury (LIRI) rats.Methods:① Part one experiment: 24 Sprague-Dawley (SD) rats were divided into four groups according to the random number method ( n = 6): standard ventilation group (N group), normal saline group (NS group), LIRI group, and dexamethasone+LIRI group (DEX group). The rat model of LIRI was established by clamping the left pulmonary hilum for 1 hour and reperfusing it for 2 hours. The DEX group was given dexamethasone 3 mg/kg 5 minutes before reperfusion, and NS group was injected with normal saline. Group N did not receive any treatment. The left lung tissue of the rats in each group were taken alive 2 hours after reperfusion. The lung tissue was harvested for lung wet/dry mass ratio (W/D) measurement. Hematoxylin-eosin (HE) staining and electron microscopy was used to observe the pathological changes of lung tissue and to assess the degree of injury. Ultrastructural changes of lung tissue were observed under electron microscope. The levels of tumor necrosis factor-α (TNF-α), interleukin (IL-1β, IL-6) in lung tissue were detected by enzyme linked immunosorbent assay (ELISA). The expressions of phosphorylated protein kinase B (p-AKT) was detected by Western Blot. ② Part two experiment: intervention with phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) pathway inhibitor LY294002 to further explore the mechanism of dexamethasone in reducing lung injury induced by LIRI. Twenty-four SD rats were divided into four groups according to the random number method ( n = 6): N group, LIRI group, DEX group, and dexamethasone+LY294002+LIRI group (LY group). All the groups except the LY group were treated with membrane and intervention according to part one experiment. The LY group was injected with LY294002 0.3 mg/kg after injection of dexamethasone. The expressions of M1 macrophage polarization markers CD11c, CD16, and M2 macrophage polarization markers CD206, Arg1 were detected by immunohistochemistry. Results:① Part one experiment: compared with N group, the morphological and ultrastructural changes of lung tissue in the LIRI group were significantly changed, lung injury score, lung W/D ratio and TNF-α, IL-1β, IL-6 levels were significantly increased, and p-AKT expression was significantly decreased. Compared with the LIRI group, the morphological and ultrastructural changes of the lung tissue in the DEX group were significantly improved, and the lung injury score was reduced (5.00±0.89 vs. 8.83±0.75), lung W/D ratio and TNF-α, IL-1β, IL-6 levels were significantly decreased [lung W/D ratio: 6.25±0.56 vs. 8.27±0.72, TNF-α(ng/L): 93.28±16.42 vs. 205.90±25.30, IL-1β(ng/L): 130.10±10.81 vs. 209.10±19.20, IL-6 (ng/L): 195.80±21.17 vs. 310.50±20.77], p-AKT expression was significantly increased [p-AKT/AKT: (57.58±8.80)% vs. (36.62±9.25)%], and the differences were statistically significant (all P < 0.05). There was no significant difference in each index between NS group and N group. ② Part two experiment: compared with the N group, the expression of macrophage polarization markers CD11c, CD16, CD206 and Arg1 in the LIRI group were significantly increased. Compared with the LIRI group, the expressions of CD11c and CD16 in the lung tissue of the DEX group were significantly decreased, and the expressions of CD206 and Arg1 were significantly increased. The intervention of PI3K/AKT signaling pathway inhibitor LY294002 significantly blocked the effect of dexamethasone on LIRI-mediated macrophage polarization (CD11c immunohistochemical score: 7.20±0.36 vs. 5.00±0.34, CD16 immunohistochemical score: 8.20±0.48 vs. 7.40±0.64, CD206 immunohistochemical score: 5.80±0.59 vs. 7.40±0.28, Arg1 immunohistochemical score: 7.20±0.72 vs. 8.80±0.48, all P < 0.05). Conclusions:Dexamethasone pretreatment can alleviate the intrapulmonary inflammatory response and lung injury caused by LIRI in rats. The mechanism of action is related to the polarization direction of pulmonary macrophagesvia activation of the PI3K/AKT pathway by dexamethasone.
ABSTRACT
Objective To investigate the role and mechanism of mitochondrial DNA (mtDNA) in rats with ventilator-induced lung injury (VILI) via Toll-like receptor 9 (TLR9)-myeloid differentiation factor 88 (MyD88) signaling pathway. Methods Thirty adult male Sprague-Dawley (SD) rats were randomly divided into three groups (each n = 10): spontaneous breathing group, normal tidal volume (VT) group (NVT group, VT = 8 mL/kg), and high VT group (HVT group, VT = 40 mL/kg). Rats in the NVT group and HVT group were ventilated mechanically with a positive end-expiratory pressure (PEEP) of 0 and the fraction of inspired oxygen (FiO2) at 0.50. After 4 hours of ventilation, the blood from the rats' hearts was collected and the rats were sacrificed, the levels of interleukins (IL-6, IL-1β) and tumor necrosis factor-α (TNF-α) in serum were determined with enzyme-linked immune sorbent assay (ELISA). The bronchoalveolar lavage fluid (BALF) was collected for a determination of total protein by using the bicinchoninic acid (BCA) assay. The lung tissues were harvested to determine the wet/dry (W/D) ratio. The changes in pathobiology of lung tissue were observed with hematoxylin and eosin (HE) staining. The protein expression levels of mtDNA-encoded cytochrome C oxidase subunit Ⅳ (COX-Ⅳ), TLR9, MyD88 and nuclear factor-κB p65 (NF-κB p65) in lung tissues were determined by immunohistochemistry. Results The histopathology of lung tissues indicated that lungs from animals ventilated with HVT developed marked lung inflammation changes, whereas no major histological change was observed in animals ventilated with NVT or spontaneously breathing. The pathological score in HVT group was significantly higher than that of spontaneous breathing group and NVT group (3.50±0.41 vs. 0.25±0.09, 0.33±0.10, both P < 0.05). Compared with spontaneous breathing group and NVT group, the ratio of W/D in the HVT group was significantly increased (6.42±0.41 vs. 4.14±0.04, 4.28±0.11, both P < 0.05), the contents of total proteins in BALF were significantly increased (g/L: 0.43±0.04 vs. 0.13±0.01, 0.14±0.01, both P < 0.05), and serum IL-6, IL-1β and TNF-α levels were also increased [IL-6 (μg/L): 1.15±0.17 vs. 0.42±0.10, 0.46±0.04; IL-1β (μg/L): 6.73±0.38 vs. 2.08±0.90, 2.19±0.18; TNF-α (μg/L): 4.10±0.11 vs. 1.12±0.10, 1.14±0.04; all P < 0.05]. Immunohistochemistry results demonstrated that the proteins of COX-Ⅳ, TLR9, MyD88 and NF-κB p65 in HVT group were shown in brown, which meant strongly expressed. However, these proteins in spontaneous breathing group and NVT group were uncolored or shown in buff, which meant unexpressed or weakly expressed. The results of quantitative analysis indicated that the immunoreactive scores (IRS) of COX-Ⅳ, TLR9, MyD88 and NF-κB p65 in HVT group were significantly higher than those in spontaneous breathing group and NVT group (COX-Ⅳ IRS: 8.80±2.17 vs. 0.80±0.45, 1.40±0.55;TLR9 IRS: 8.40±2.51 vs. 1.00±0.71, 1.20±0.84; MyD88 IRS: 9.40±1.52 vs. 1.40±0.55, 1.60±0.55; NF-κB p65 IRS: 9.80±2.05 vs. 1.00±0.71, 1.20±0.84; all P < 0.05). There was no significant difference in all of the parameters between spontaneous breathing group and NVT group (all P > 0.05). Conclusion mtDNA contributes significantly to VILI by activating the TLR9-MyD88 signaling pathway, resulting in subsequent secretion of NF-κB p65 and the proinflammatory cytokines, which induce acute inflammatory injury of lung tissue.