Pulmonary oxygen toxicity. Bronchoalveolar lavage demonstration of early parameters of alveolitis

K2P2.1 (TREK-1) potassium channel activation protects against hyperoxia-induced lung injury

No targeted therapies exist to counteract Hyperoxia (HO)-induced Acute Lung Injury (HALI). We previously found that HO downregulates alveolar K_2P2.1 (TREK-1) K⁺ channels, which results in worsening lung injury. This decrease in TREK-1 levels leaves a subset of channels amendable to pharmacological intervention. Therefore, we hypothesized that TREK-1 activation protects against HALI. We treated HO-exposed mice and primary alveolar epithelial cells (AECs) with the novel TREK-1 activators ML335 and BL1249, and quantified physiological, histological, and biochemical lung injury markers. We determined the effects of these drugs on epithelial TREK-1 currents, plasma membrane potential (Em), and intracellular Ca²⁺ (iCa) concentrations using fluorometric assays, and blocked voltage-gated Ca²⁺ channels (Ca_V) as a downstream mechanism of cytokine secretion. Once-daily, intra-tracheal injections of HO-exposed mice with ML335 or BL1249 improved lung compliance, histological lung injury scores, broncho-alveolar lavage protein levels and cell counts, and IL-6 and IP-10 concentrations. TREK-1 activation also decreased IL-6, IP-10, and CCL-2 secretion from primary AECs. Mechanistically, ML335 and BL1249 induced TREK-1 currents in AECs, counteracted HO-induced cell depolarization, and lowered iCa²⁺ concentrations. In addition, CCL-2 secretion was decreased after L-type Ca_V inhibition. Therefore, Em stabilization with TREK-1 activators may represent a novel approach to counteract HALI.

The Galleria mellonella Infection Model for Investigating the Molecular Mechanisms of Legionella Virulence

Legionella species evolved virulence factors to exploit protozoa as replicative niches in the environment. Cell culture infection models demonstrated that many of these factors also enable the bacteria to thrive in human macrophages; however, these models do not recapitulate the complex interactions between macrophages, lung epithelial, and additional immune cells, which are crucial to control bacterial infections. Thus, suitable infection models are required to understand which bacterial factors are important to trigger disease. Guinea pigs and, most frequently, mice have been successfully used as mammalian model hosts; however, ethical and economic considerations impede their use in high-throughput screening studies of Legionella isolates or small molecule inhibitors.Here, we describe the larvae of the lepidopteran Galleria mellonella as insect model of Legionella pathogenesis. Larvae can be obtained from commercial suppliers in large numbers, maintained without the need of specialized equipment, and infected by injection. Although lacking the complexity of a mammalian immune system, the larvae mount humoral and cellular immune responses to infection. L. pneumophila strain 130b and other prototype isolates withstand these responses and use the Defective in organelle trafficking/Intracellular multiplication (Dot/Icm) type IV secretion system (T4SS ) to inject effectors enabling survival and replication in hemocytes, insect phagocytes, ultimately leading to the death of the larvae. Differences in virulence between L. pneumophila isolates or gene deletion mutants can be analyzed using indicators of larval health and immune induction, such as pigmentation, mobility, histopathology, and survival. Bacterial replication can be measured by plating hemolymph or by immunofluorescence microscopy of isolated circulating hemocytes from infected larvae. Combined, these straightforward experimental readouts make G. mellonella larvae a versatile model host to rapidly assess the virulence of different Legionella isolates and investigate the role of specific virulence factors in overcoming innate host defense mechanisms.

Nasal High Flow in Room Air for Hypoxemic Bronchiolitis Infants

Background: Bronchiolitis is the most common reason for hospital admission in infants, with one third requiring oxygen therapy due to hypoxemia. It is unknown what proportion of hypoxemic infants with bronchiolitis can be managed with nasal high-flow in room air and their resulting outcomes. Objectives and Settings: To assess the effect of nasal high-flow in room air in a subgroup of infants with bronchiolitis allocated to high-flow therapy in a recent multicenter randomized controlled trial. Patients and Interventions: Infants allocated to the high-flow arm of the trial were initially treated with room air high-flow if saturations were ≥85%. Subsequently, if oxygen saturations did not increase to ≥92%, oxygen was added and FiO₂ was titrated to increase the oxygen saturations. In this planned sub-study, infants treated during their entire hospital stay with high-flow room air only were compared to infants receiving either standard-oxygen or high-flow with oxygen. Baseline characteristics, hospital length of stay and length of oxygen therapy were compared. Findings: In the per protocol analysis 64 (10%) of 630 infants commenced on high-flow room air remained in room air only during the entire stay in hospital. These infants on high-flow room air were on average older and presented with moderate hypoxemia at presentation to hospital. Their length of respiratory support and length of stay was also significantly shorter. No pre-enrolment factors could be identified in a multivariable analysis. Conclusions: In a small sub-group of hypoxemic infants with bronchiolitis hypoxemia can be reversed with the application of high-flow in room air only. Trial registration: ACTRN12615001305516.

The Guinea pig model of legionnaires' disease

The guinea pig pneumonia model mimics Legionnaires' disease as seen in immunocompromised humans, with high untreated fatality rates and as such lends itself to studies of experimental chemotherapy. Guinea pig infection is also used to assess relative virulence of different Legionella bacterial strains, and has also been used to study host immune defenses. Here I describe the method used to produce Legionella sp. pneumonia in the guinea pig using the intratracheal infection technique. This method uses directly observed intratracheal injection of a bacterial suspension, requiring surgical exposure of the trachea.

Targeted lung expression of interleukin-11 enhances murine tolerance of 100% oxygen and diminishes hyperoxia-induced DNA fragmentation

Acute lung injury is a frequent and treatment-limiting consequence of therapy with hyperoxic gas mixtures. To determine if IL-11 is protective in oxygen toxicity, we compared the effects of 100% O2 on transgenic mice that overexpress IL-11 in the lung and transgene (-) controls. IL-11 markedly enhanced survival in 100% O2 with 100% of transgene (-) animals dying within 72-96 h and > 90% of transgene (+) animals surviving for more than 10 d. This protection was associated with markedly diminished alveolar-capillary protein leak, endothelial and epithelial membrane injury, lipid peroxidation, and pulmonary neutrophil recruitment. Significant differences in copper zinc superoxide dismutase and catalase activities were not noted and the levels of total, reduced and oxidized glutathione were similar in transgene (+) and (-) animals. Glutathione reductase, glutathione peroxidase, and manganese superoxide dismutase activities were slightly higher in transgene (+) as versus (-) mice after 100% O2 exposure, and IL-11 diminished hyperoxia-induced expression of IL-1 and TNF. Hyperoxia also caused cell death with DNA fragmentation in the lungs of transgene (-) animals and IL-11 markedly diminished this cell death response. These studies demonstrate that IL-11 markedly diminishes hyperoxic lung injury. They also demonstrate this protection is associated with small changes in lung antioxidants, diminished hyperoxia-induced IL-1 and TNF production, and markedly suppressed hyperoxia-induced DNA fragmentation.