Mechanism Of Surfactant And Inhaled Nitric Oxide In Ventilated Piglets With Septic Acute Lung Injury Resulted From Bacterial Peritonitis

Sepsis associated acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are often caused by bacteria, viruses, and other pathogens in the lungs, or as a result of sepsis associated with pathogens, toxins and metabolites of systemic inflammation. The inflammation itself may be regarded as innate and acquired immunal defense responsible to pathogen invasion and other assault though, it may also cause damages in unaffected lung tissue and cells. In diffusive, septic ALI, alveolar damage may result in functional and metabolic abnormality of pulmonary surfactant system, leading to atelectasis, edema and gas exchange impairment. Persistent hypoxia may cause pulmonary vasoconstriction, increasing pulmonary vascular resistance and permeability, leading to ventilation-perfusion mismatch and pulmonary hypertension. For severe ALI/ARDS, mechanical ventilation is usually required, but its mortality is still as high as 50% or more. Investigations aiming at understanding mechanisms of inflammatory injury, its initiation and consequence in septic ALI, and new therapies and interventions that may counter balance the inflammation and protect the lungs from severe damage, are intensively carried on. As pulmonary surfactant (Surf) and inhaled nitric oxide (NO) are successfully used for neonates with RDS and hypoxic respiratory failure, attempts are made to verify their efficacy in children and adults with ALI/ARDS. However, supportive results have been obtained so far from those with viral bronchiolitis, and traumatic ALI, but not in the septic ALI. In view of unsuccessful trials of Surf and inhaled NO in ALI/ARDS, we and others have been focusing on a combined use of these two therapies in various animal models of ALI induced by bacterial endotoxin, oleic acid and surfactant depletion, with variable but promising outcome. However, questions remain as to what mechanism is inside in the consistent efficacy, could it be translated into a clinical situation as new indication without substantial alteration in management, is it safe or not should these therapies are applied ? All of these questions are to beanswered, and thus the targets our current work and effort aim at.Objective:To establish an ALI model in piglets caused by bacterial peritonitis, and to investigate pathogenesis of septic ALI, and mechanism of efficacy of prophylactic surfactant (Surf) and/or inhaled nitric oxide (NO) in alleviating the septic ALI.Methods:Thirty piglets, male, 3-4 week-old, body weight 6-9 kg, were randomly allocated to groups (n=6) receiving intraperitoneal injection of Escherichia coli at 5X109 cfu/ml, followed by mechanical ventilation with a standard tidal volume of 6-8 ml/kg for 4-6 h which resulted in ALI. They were then treated as: control with no additional therapy (C), inhaled NO at 10 ppm (NO), intratracheal instillation of surfactant at phospholipids of 100 mg/kg (Surf), both surfactant and iNO (SNO) as in the NO and Surf groups. A normal group (N, n=6) was sham injected intraperitoneally with normal saline but subjected to the same ventilation mode without additional therapies. All the animals were further ventilated for 24 h. Arterial blood gas, dynamic lung compliance (Cdyn) and resistance of respiratory system (Rrs), mean system arterial pressure, and heart rate were measured at the baseline, establishment of ALI, and every 2 h during the treatment. Blood cytology, methemoglobin (MetHb), and nitrate/nitrite (NO27NO3") were measured at baseline, establishment of ALI, 12 and 24 h of the treatment. Total proteins (TP), total phospholipids (TPL), disaturated phosphatidylcholine (DSPC) were measured with biochemical methods, and minimum and maximum surface tension ( y min and v max) of TPL in bronchoalveolar lavage fluid (BALF) were measured using pulsating bubble technique. Wet-to-dry lung weight ratio (W/D), lung morphology, myeloperoxidase (MPO) and malondialdehyde (MDA), nuclear factor- k B (NF- k B) DNA binding activity, interleukin-8 (IL-8) and IL-10 mRNA, and keratinocyte growth factor (KGF) in lung tissue were determined at the end of the experiment.Statistics: Data are presented as means and standard deviation (SD). Continuous parametric data were subjected to analysis of variance (ANOVA) followed by Student-Newman-Keuls post-hoc test for between-group differences, and by paired Student t-test for within-group differences. For the lung injury score, Kruskal-Wallistest was used to detect differences across the groups, followed by the Wilcoxon-Mann-Whiteney test for differences between two groups. Pearson and Spearman correlation tests were used to analyze two variables. A p value<0.05 was regarded as statistically significant.Results:1. All the animals in the C, NO, Surf, and SNO groups developed ALI in 4.6 ± 2.9 hours after the intraperitoneal injection of E. coli, as evidenced by marked decrease of PaO2/FiO2 below 300 mmHg, and reduction of Cdyn by 30% compared to the corresponding baseline levels, and significant increase of Rrs. No such deterioration was found in the N group. During the treatment, there were persistent decreases of PaO2/FiO2 and Cdyn, and increase of Rrs in the C and NO groups. In the Surf and SNO groups, there were improvements in PaO2/FiO2, Cdyn, and Rrs at 24 hour (p<0.01, respectively).2. TP in BALF was significantly lower in the Surf and SNO groups than in the Control and NO groups (p<0.05, respectively). TPL and DSPC/TP in BALF were significantly higher in the Surf and SNO group than in the C and NO groups (p<0.01, respectively). In the C and NO groups, Y mjn and Y max were >15 mN/m and 35 mN/m, respectively, whereas in the Surf and SNO groups, values of Y min and Y max were significantly lower than those in the C and NO groups (p<0.05, respectively). Values of W/D in the C and NO groups were higher than that of the N group (p<0.01, respectively), and that in the Surf and SNO groups were higher than in the N group (p<0.05, respectively).3. There were prominent edema, infiltration of neutrophils, and collapse of alveolar in the C and NO groups. In the SNO group, there was marked improvement in edema, and infiltration of neutrophils compared with the C and NO groups (p<0.05, respectively). In the Surf and SNO groups, aeration of alveoli was significantly improved compared with C and NO groups (p<0.01, respectively).4. MPO and MDA in the lung tissue were significantly increased in the C group compared with N group (pO.Ol). In the NO, Surf, and SNO groups, these were reduced compared with the C group (PO.Ol, respectively).5. NF- k B DNA binding activity in lung tissue was significantly decreased in the SNO group compared with C group (p<0.05). IL-8 mRNA expression was significantly increased in the C group compared with N group (p<0.01). IL-8 mRNA...