A Method for Generating Pulmonary Neutrophilia Using Aerosolized Lipopolysaccharide
Summary
We describe a method for inducing neutrophilic pulmonary inflammation by challenge to aerosolized lipopolysaccharide by nebulization, to model acute lung injury. In addition, basic surgical techniques for lung isolation, tracheal intubation and bronchoalveolar lavage are also described.
Abstract
Acute lung injury (ALI) is a severe disease characterized by alveolar neutrophilia, with limited treatment options and high mortality. Experimental models of ALI are key in enhancing our understanding of disease pathogenesis. Lipopolysaccharide (LPS) derived from gram positive bacteria induces neutrophilic inflammation in the airways and lung parenchyma of mice. Efficient pulmonary delivery of compounds such as LPS is, however, difficult to achieve. In the approach described here, pulmonary delivery in mice is achieved by challenge to aerosolized Pseudomonas aeruginosa LPS. Dissolved LPS was aerosolized by a nebulizer connected to compressed air. Mice were exposed to a continuous flow of LPS aerosol in a Plexiglas box for 10 min, followed by 2 min conditioning after the aerosol was discontinued. Tracheal intubation and subsequent bronchoalveolar lavage, followed by formalin perfusion was next performed, which allows for characterization of the sterile pulmonary inflammation. Aerosolized LPS generates a pulmonary inflammation characterized by alveolar neutrophilia, detected in bronchoalveolar lavage and by histological assessment. This technique can be set up at a small cost with few appliances, and requires minimal training and expertise. The exposure system can thus be routinely performed at any laboratory, with the potential to enhance our understanding of lung pathology.
Introduction
Lipopolysaccharide (LPS) is a cell wall component of gram negative bacteria1. Challenge to LPS is a well-documented model of acute lung injury, a syndrome characterized by acute neutrophilic inflammation and edema2. In addition, pulmonary neutrophilia is also a hallmark of chronic obstructive pulmonary disease (COPD)3, and LPS challenge in humans has been used to model COPD exacerbations4. Thus, experimental models of LPS exposure are clinically relevant and valuable tools to understand human pathology.
The objective of the pulmonary delivery of aerosolized LPS described here is to generate a neutrophilic inflammatory response in the conducting and respiratory airways, without systemic involvement. Several techniques of LPS challenge have been described previously. Intra-venous injection of LPS is the most commonly used route of administration. Although this technique is easily accessible, the primary damage is to the endothelium, with secondary destruction of the pulmonary epithelium following neutrophil migration to the lung. Intra-venous administration also induces systemic inflammation2, which may complicate the clinical picture in animal models. Systemic inflammation is in contrast not observed with intra-tracheal administration. This technique, however, is labor intensive and requires anesthetics as well as considerable training5,6 . Furthermore, pulmonary deposition by this route of administration is dependent on breathing7. Thus, pulmonary deposition is affected by the depth of anesthesia needed for the intra tracheal administration and variable deposition in the airways may be observed. In contrast, pulmonary delivery with aerosolized LPS requires minimal training, and can easily be accomplished on a large number of animals with little or no variation between individuals5,8 . A recent study confirms that aerosol delivery is superior to the intra-tracheal route with regard to deposition, and that more relevant doses of LPS induce neutrophilic inflammation with this model8.
Previous studies have demonstrated that challenge to aerosolized Psuedomonas aeruginosa LPS generates a marked inflammatory response in the airway lumen and lung parenchyma, including the alveolar spaces9,10. The inflammation is characterized by a predominance of neutrophils and presence of pulmonary edema, and can thus be used to address pathogenesis of acute lung injury and gain further knowledge of the mechanisms contributing to disease pathology.
Protocol
Representative Results
Discussion
Aerosolized LPS generates an inflammatory response in the airways, characterized by neutrophils in the epithelial submucosa, spaces surrounding the conducting airways, as well as the alveolar spaces. This is, together with the increased total protein content in BALF, indicative of plasma leakage, representative of the pathology of acute lung injury. As LPS induces a sterile inflammation, the reaction is independent of the adaptive immune response, and there are limitations to the relevance to bacterial infections. The te…
Disclosures
The authors have nothing to disclose.
Acknowledgements
We would like to thank Kerstin Thim (AstraZeneca, Lund, Sweden), Benita Dahlberg and Dr. Anders Eklund (Karolinska Institutet, Stockholm, Sweden) as well as Dr. Martin Stampfli (McMaster University, Hamilton, ON, Canada) for skillful assistance and expert advice.
Materials
| Name of the material/equipment | Company | Catalog number | Comments/Description |
| Purified Pseudomonas aeruginosa LPS | Sigma-Aldrich | Harmful. Recomended purification. LPS purified from other bactria may be used. | |
| Pari LC sprint star nebulizer | PARI Respiratory Equipment Inc. | 023G1250 | |
| TSI mass flowmeter 4040 | TSI | 4040 | Alternative product from supplier may be used. |
| Saint-Gobain 15.9 mm Tygon tube | Sigma-Aldrich | Z685704 | Recomended brand. |
| Plexiglas boxes with removable lids | Custom built | N/A | 150 x 163 x 205 mm (a 2 mm hole on the side). |
| 3M Half Facepiece Reusable Respirator | 3M | 7503 | Recomended brand. |
| 3M Advanced Particulate Filters (P100) | 3M | 2291 | Recomended brand. |
| Sissors | VWR | 233-1104 | Preferred scissors may be used. |
| Forceps | VWR | 232-1313 | Preferred forceps may be used. |
| Intramedic PE50 polyethylene tube | BD | 427411 | Recomended brand. |
| Ethicon 2-0 Perma-hand silk tread | VWR | 95056-992 | Recomended brand. |
| 26 ½ gage needle | Alternative suppliers exist. | ||
| 1 mL BD slip-tip syringe, non-sterile | BD | 301025 | Alternative suppliers exist. |
| 60 mL BD Luer-Lok syringe, non-sterile, polypropolene | BD | 301035 | Alternative suppliers exist. |
| Fluka Hematoxylin-Eosin | Sigma-Aldrich | 3972 | Alternative suppliers exist. |
| Türk's solution | Merck Millipore | 109277 | |
| Table top centrifuge | Alternative manufacturers exist. | ||
| Cytospin 4 cytocentrifuge | Thermo Scientific | A78300003 | Alternative centrifuge can be used. |
| HEMA-3 stat pack | Fisher Scientific | 23-123-869 | Alternative staining kits exists. |
| Formalin solution, neutral buffered, 10% | Sigma-Aldrich | HT501128 | Alternative suppliers exist. |
References
- King, J. D., Kocincova, D., Westman, E. L., Lam, J. S. Review: Lipopolysaccharide biosynthesis in Pseudomonas aeruginosa. Innate Immun. 15, 261-312 (2009).
- Grommes, J., Soehnlein, O. Contribution of neutrophils to acute lung injury. Mol Med. 17, 293-307 (2011).
- Pesci, A., et al. Inflammatory cells and mediators in bronchial lavage of patients with chronic obstructive pulmonary disease. Eur Respir J. 12, 380-386 (1998).
- Hoogerwerf, J. J., et al. Lung Inflammation Induced by Lipoteichoic Acid or Lipopolysaccharide in Humans. Am. J. Respir. Crit. Care Med. 178, 34-41 (2008).
- Scheuchenzuber, W. J., Eskew, M. L., Zarkower, A. Comparative humoral responses to Escherichia coli and sheep red blood cell antigens introduced via the respiratory tract. Exp Lung Res. 13, 97-112 (1987).
- Asti, C., et al. Lipopolysaccharide-induced lung injury in mice. I. Concomitant evaluation of inflammatory cells and haemorrhagic lung damage. Pulm Pharmacol Ther. 13, 61-69 (2000).
- Brand, P., et al. Total deposition of therapeutic particles during spontaneous and controlled inhalations. Journal of pharmaceutical sciences. 89, 724-731 (2000).
- Liu, F., Li, W., Pauluhn, J., Trubel, H., Wang, C. Lipopolysaccharide-induced acute lung injury in rats: comparative assessment of intratracheal instillation and aerosol inhalation. Toxicology. 304, 158-166 (2013).
- Skerrett, S. J., et al. Role of the type 1 TNF receptor in lung inflammation after inhalation of endotoxin or Pseudomonas aeruginosa. American Journal of Physiology – Lung Cellular and Molecular Physiology. 276, L715-L727 (1999).
- Roos, A. B., et al. Lung epithelial-C/EBPbeta contributes to LPS-induced inflammation and its suppression by formoterol. Biochem Biophys Res Commun. 423, 134-139 (2012).
- Didon, L., et al. Lung epithelial CCAAT/enhancer-binding protein-beta is necessary for the integrity of inflammatory responses to cigarette smoke. Am J Respir Crit Care Med. 184, 233-242 (2011).
- Silverpil, E., et al. Negative feedback on IL-23 exerted by IL-17A during pulmonary inflammation. Innate Immunity. 19, 479-492 (2013).
- Mercer, P. F., et al. Proteinase-Activated Receptor-1, CCL2 and CCL7 Regulate Acute Neutrophilic Lung Inflammation. American Journal of Respiratory Cell and Molecular Biology. , (2013).
- Korkmaz, B., Horwitz, M. S., Jenne, D. E., Gauthier, F. . Neutrophil Elastase, Proteinase 3, and Cathepsin G as Therapeutic Targets in Human Diseases. Pharmacological Reviews. 62, 726-759 (2010).
- Bafadhel, M., et al. Acute Exacerbations of COPD: Identification of Biological Clusters and Their Biomarkers. Am. J. Respir. Crit. Care Med. , 201104-200597 (2011).
- Hurst, J. R., Perera, W. R., Wilkinson, T. M. A., Donaldson, G. C., Donaldson, G. C., Wedzicha, G. C. Systemic and Upper and Lower Airway Inflammation at Exacerbation of Chronic Obstructive Pulmonary. Am. J. Respir. Crit. Care Med. 173, 71-78 (2006).
- Rabe, K. F., et al. Global Strategy for the Diagnosis, Management, and Prevention of Chronic Obstructive Pulmonary Disease: GOLD Executive Summary. Am. J. Respir. Crit. Care Med. 176, 532-555 (2007).
