Lipopolysaccharide (LPS) induced acute lung injury and neuroinflammation in a new mouse model of COVID-19 disease
Authors: Milicic Stanic Branka , Duggal Nisha , Shults Nataliia , Ji Hong , de Souza Aline M.A. , Hawks Seth , Wu Xie , Saavedra Juan , Sandberg Kathryn 
Published: May 2023

Objective: Due to their affordability and availability, rodents are the most often employed experimental animals to explore disease mechanisms. Rats and mice's resistance to SARS-CoV-2 infection is impeding a worldwide effort to study the pathogenesis of COVID-19. Our aim was to develop a suitable small animal model of COVID-19 disease to investigate mechanisms of brain and lung inflammation. Methods: Lipopolysaccharide (LPS) was administered intraperitoneally to wildtype (WT) and angiotensin converting enzyme 2 knockout (ACE2KO) mice of the C57BI/6 strain in order to mimic the cytokine storm that results from COVID-19. Since the SARS‐CoV‐2 utilizes human ACE2 as the receptor for entry with subsequent downregulation of ACE2, these mice deficient in ACE2 gene may have a similar mechanism observed in COVID‐19 patients. We selected a minimal dose (500ug/kg) and time period (3h) when several cytokines were elevated to determine the severity of lung injury using a point-counting method on tissue sections stained with hematoxylin and eosin. The data are expressed as a mean percentage of grid points located in the superficial and peribronchial area in up to 20 fields. Congestion, neutrophil infiltration, percentage of peribronchial and superficial intrapulmonary hemorrhage and alveolar space area were all assessed. Results: To see the effect of LPS, WT mice (WT-G) were injected with a minimal dose of LPS (WT LPS-G). We observed a much larger percentage of peribronchial intrapulmonary hemorrhage in WT LPS-G compared to WT-G [(%): WT LPS-G, 12.3±1.8 vs. WT-G, 6.67±1.3; p<0.05; n=5]. Significantly higher percentage of the peribronchial congestion was seen in the LPS group [(%): WT LPS-G, 1.78±0.46 vs. WT-G, 0.770±0.18; p<0.05; n=5]. We implemented this lung histology scoring criteria in ACE2KO mice to see effect of LPS in mice deficient in ACE2 gene. The LPS-injected ACE2KO mice (ACE2KO LPS-G) exhibited a higher percentage of peribronchial intrapulmonary hemorrhage compared to WT-G [(%): ACE2KO LPS-G, 10.6±2.1 vs. WT-G, 6.67±1.3; p<0.05; n=5], peribronchial neutrophil infiltration [(%): ACE2KO LPS-G, 2.50±0.68 vs. WT-G, 0.640±0.54; p<0.05; n=5] and superficial neutrophil infiltration [(%): LPS-G, 2.14±0.59 vs. WT-G, 0.720±0.56; p<0.05; n=5]. These lung pathologies led to 1.6-fold higher lung histopathology scores in the ACE2KO LPS-G compared to WT-G for peribronchial intrapulmonary hemorrhage, 3.9-fold higher scores for peribronchial neutrophil infiltration and 3.0-fold higher scores for superficial neutrophil infiltration. On-going studies are investigating injury in brain since COVID-19 exacerbates brain pathologies. Conclusion: Research on the tissue-specific etiology of the disease will greatly benefit from the creation of this distinctive COVID-19 animal model. This model will facilitate studies investigating diagnostics, prognosis and response to treatments in COVID-19 disease. TL1TR001431 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.