Decreased Liver Kinase B1 Expression and Impaired Angiogenesis in a Murine Model of Bronchopulmonary Dysplasia.

Bronchopulmonary dysplasia (BPD) is characterized by impaired lung alveolar and vascular growth. We investigated the hypothesis that neonatal exposure to hyperoxia leads to persistent BPD phenotype caused by decreased expression of liver kinase B1 (LKB1), a key regulator of mitochondrial function. We exposed mouse pups from Postnatal Day (P)1 through P10 to 21% or 75% oxygen. Half of the pups in each group received metformin or saline intraperitoneally from P1 to P10. Pups were killed at P4 or P10 or recovered in 21% O2 until euthanasia at P21. Lung histology and morphometry, immunofluorescence, and immunoblots were performed to detect changes in lung structure and expression of LKB1; downstream targets AMPK, PGC-1α, and electron transport chain (ETC) complexes; and Notch ligands Jagged 1 and delta-like 4. LKB1 signaling and in vitro angiogenesis were assessed in human pulmonary artery endothelial cells (exposed to 21% or 95% O2 for 36 hours. Levels of LKB1, phosphorylated AMPK, PGC-1α, and ETC complexes were decreased in lungs at P10 and P21 in hyperoxia. Metformin increased LKB1, phosphorylated AMPK, PGC-1α, and ETC complexes at P10 and P21 in pups exposed to hyperoxia. Radial alveolar count was decreased, and mean linear intercept increased in pups exposed to hyperoxia at P10 and P21; these were improved by metformin. Lung capillary density was decreased in hyperoxia at P10 and P21 and was increased by metformin. In vitro angiogenesis was decreased in human pulmonary artery endothelial cells by 95% O2 and was improved by metformin. Decreased LKB1 signaling may contribute to decreased alveolar and vascular growth in a mouse model of BPD.

Epidemiology of Cause of Death in Pediatric Acute Respiratory Distress Syndrome.

OBJECTIVES: Investigations of acute respiratory distress syndrome in adults suggest hypoxemia is an uncommon cause of death. However, the epidemiology of death in pediatric acute respiratory distress syndrome is not well characterized. We aimed to describe the cause, mode, and timing of death in pediatric acute respiratory distress syndrome nonsurvivors. We hypothesized that most deaths would be due to nonpulmonary factors, rather than hypoxemia. DESIGN: Retrospective, decedent-only analysis. SETTING: Two large, academic PICUs. PATIENTS: Nonsurvivors with pediatric acute respiratory distress syndrome. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Of 798 subjects with pediatric acute respiratory distress syndrome, there were 153 nonsurvivors (19% mortality). Median time to death was 6 days (interquartile range, 3-13 d) after pediatric acute respiratory distress syndrome onset. Patients dying less than 7 days after pediatric acute respiratory distress syndrome onset had greater illness severity and worse oxygenation. Patients dying less than 7 days were more likely to die of a neurologic cause, including brain death. Patients dying greater than or equal to 7 days after pediatric acute respiratory distress syndrome onset were more commonly immunocompromised. Multisystem organ failure predominated in deaths greater than or equal to 7 days. Withdrawal of therapy was the most common mode of death at all timepoints, accounting for 66% of all deaths. Organ dysfunction was common at time of death, irrespective of cause of death. Refractory hypoxemia accounted for only a minority of pediatric acute respiratory distress syndrome deaths (20%). CONCLUSIONS: In pediatric acute respiratory distress syndrome, early deaths were due primarily to neurologic failure, whereas later deaths were more commonly due to multisystem organ failure. Deaths from neurologic causes accounted for a substantial portion of nonsurvivors. Refractory hypoxemia accounted for only a minority of deaths. Our study highlights limitations associated with using death as an endpoint in therapeutic pediatric acute respiratory distress syndrome trials.

Association of Response to Inhaled Nitric Oxide and Duration of Mechanical Ventilation in Pediatric Acute Respiratory Distress Syndrome.

OBJECTIVES: Literature regarding appropriate use of inhaled nitric oxide for pediatric acute respiratory distress syndrome is sparse. This study aims to determine if positive response to inhaled nitric oxide is associated with decreased mortality and duration of mechanical ventilation in pediatric acute respiratory distress syndrome. DESIGN: Retrospective cohort study. SETTING: Large pediatric academic medical center. PATIENTS OR SUBJECTS: One hundred sixty-one children with pediatric acute respiratory distress syndrome and inhaled nitric oxide exposure for greater than or equal to 1 hour within 3 days of pediatric acute respiratory distress syndrome onset. INTERVENTIONS: Patients with greater than or equal to 20% improvement in oxygenation index or oxygen saturation index by 6 hours after inhaled nitric oxide initiation were classified as "responders." MEASUREMENTS AND MAIN RESULTS: Oxygenation index, oxygen saturation index, and ventilator settings were evaluated prior to inhaled nitric oxide initiation and 1, 6, 12, and 24 hours following inhaled nitric oxide initiation. Primary outcomes were mortality and duration of mechanical ventilation. Baseline characteristics, including severity of illness, were similar between responders and nonresponders. Univariate analysis showed no difference in mortality between responders and nonresponders (21% vs 21%; p = 0.999). Ventilator days were significantly lower in responders (10 vs 16; p < 0.001). Competing risk regression (competing risk of death) confirmed association between inhaled nitric oxide response and successful extubation (subdistribution hazard ratio = 2.11; 95% CI, 1.41-3.17; p < 0.001). Response to inhaled nitric oxide was associated with decreased utilization of high-frequency oscillatory ventilation and extracorporeal membrane oxygenation and lower hospital charges (difference in medians of $424,000). CONCLUSIONS: Positive response to inhaled nitric oxide was associated with fewer ventilator days, without change in mortality, potentially via reduced use of high-frequency oscillatory ventilation and extracorporeal membrane oxygenation. Future studies of inhaled nitric oxide for pediatric acute respiratory distress syndrome should stratify based on oxygenation response, given the association with favorable outcomes.

Hyperoxia-induced airflow restriction and Renin-Angiotensin System expression in a bronchopulmonary dysplasia mouse model.

Mechanisms underlying hyperoxia-induced airflow restriction in the pediatric lung disease Bronchopulmonary dysplasia (BPD) are unclear. We hypothesized a role for Renin-Angiotensin System (RAS) activity in BPD. RAS is comprised of a pro-developmental pathway consisting of angiotensin converting enzyme-2 (ACE2) and angiotensin II receptor type 2 (AT2), and a pro-fibrotic pathway mediated by angiotensin II receptor type 1 (AT1). We investigated associations between neonatal hyperoxia, airflow restriction, and RAS activity in a BPD mouse model. C57 mouse pups were randomized to normoxic (FiO2 = 0.21) or hyperoxic (FiO2 = 0.75) conditions for 15 days (P1-P15). At P15, P20, and P30, we measured airflow restriction using plethysmography and ACE2, AT1, and AT2 mRNA and protein expression via polymerase chain reaction and Western Blot. Hyperoxia increased airflow restriction P15 and P20, decreased ACE2 and AT2 mRNA, decreased AT2 protein, and increased AT1 protein expression. ACE2 mRNA and protein remained suppressed at P20. By P30, airflow restriction and RAS expression did not differ between groups. Hyperoxia caused high airflow restriction, increased pulmonary expression of the pro-fibrotic RAS pathway, and decreased expression of the pro-developmental in our BPD mouse model. These associated findings may point to a causal role for RAS in hyperoxia-induced airflow restriction.

alpha-Adrenergic response and myofilament activity in mouse hearts lacking PKC phosphorylation sites on cardiac TnI.

Protein kinase C (PKC)-mediated phosphorylation of cardiac myofilament (MF) proteins has been shown to depress the actomyosin interaction and may be important during heart failure. Biochemical studies indicate that phosphorylation of Ser(43) and Ser(45) of cardiac troponin I (cTnI) plays a substantial role in the PKC-mediated depression. We studied intact and detergent-extracted papillary muscles from nontransgenic (NTG) and transgenic (TG) mouse hearts that express a mutant cTnI (Ser43Ala, Ser45Ala) that lacks specific PKC-dependent phosphorylation sites. Treatment of NTG papillary muscles with phenylephrine (PE) resulted in a transient increase and a subsequent 62% reduction in peak twitch force. TG muscles showed no transient increase and only a 45% reduction in force. There was a similar difference in maximum tension between NTG and TG fiber bundles that had been treated with a phorbol ester and had received subsequent detergent extraction. Although levels of cTnI phosphorylation correlated with these differences, the TG fibers also demonstrated a decrease in phosphorylation of cardiac troponin T. The PKC-specific inhibitor chelerythrine inhibited these responses. Our data provide evidence that specific PKC-mediated phosphorylation of Ser(43) and Ser(45) of cTnI plays an important role in regulating force development in the intact myocardium.