Low-dose lung radiotherapy for COVID-19 lung disease: a preclinical efficacy study in a bleomycin model of pneumonitis
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Abstract
Purpose
Low-dose whole lung radiotherapy (LDLR) has been proposed as a treatment for patients with acute respiratory distress syndrome associated with SARS-CoV-2 infection and clinical trials are underway. There is an urgent need for preclinical evidence to justify this approach and inform dose, scheduling and mechanisms of action.
Materials and methods
Female C57BL/6 mice were treated with intranasal bleomycin sulphate (7.5 or 11.25 units/kg, day 0), then exposed to whole lung radiation therapy (0.5, 1.0, 1.5 Gy or sham, day 3). Bodyweight was measured daily and lung tissue harvested for histology and flow cytometry on day 10. Computed tomography (CT) lung imaging was performed pre-radiation (day 3) and pre-endpoint (day 10).
Results
Bleomycin caused pneumonitis of variable severity which correlated with weight loss. LDLR at 1.0 Gy was associated with a significant increase in the proportion of mice recovering to 98% of initial bodyweight and a proportion of these mice exhibited less severe histopathological lung changes. Mice experiencing moderate initial weight loss were more likely to respond to LDLR than those experiencing severe initial weight loss. Additionally, LDLR (1.0 Gy) significantly reduced bleomycin-induced increases in interstitial macrophages, CD103+ dendritic cells and neutrophil-DC hybrids. Overall,bleomycin-treated mice exhibited significantly higher percentages of non-aerated lung in left than right lungs and LDLR (1.0 Gy) prevented further reductions in aerated lung volume in right but not left lungs. LDLR at 0.5 and 1.5 Gy did not modulate bodyweight or flow cytometric readouts of bleomycin-induced pneumonitis.
Conclusions
Our data support the concept that LDLR can ameliorate acute inflammatory lung injury, identify 1.0 Gy as the most effective dose and provide preliminary evidence that it is more effective in the context of moderate than severe pneumonitis. Mechanistically, LDLR at 1.0 Gy significantly suppressed bleomycin-induced accumulation of pulmonary interstitial macrophages, CD103+ dendritic cells and neutrophil-DC hybrids.
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SciScore for 10.1101/2021.03.03.433704: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement not detected. Randomization not detected. Blinding Lung histology: Serial 4 μm sections of the left lobe were cut and stained with haematoxylin and eosin (H&E) and Masson’s trichrome and evaluated independently by a veterinary pathologist and a pulmonary immunologist both of whom were blinded to the experimental treatment. Power Analysis not detected. Sex as a biological variable Female, 11-13 week old C57BL/6 mice (Charles River Laboratories) were administered one intranasal 40 μL dose of bleomycin sulphate (7.5 or 11.25 units/kg) or phosphate buffered saline (PBS) vehicle control under light isoflurane anaesthesia. Table 2: Resources
… SciScore for 10.1101/2021.03.03.433704: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement not detected. Randomization not detected. Blinding Lung histology: Serial 4 μm sections of the left lobe were cut and stained with haematoxylin and eosin (H&E) and Masson’s trichrome and evaluated independently by a veterinary pathologist and a pulmonary immunologist both of whom were blinded to the experimental treatment. Power Analysis not detected. Sex as a biological variable Female, 11-13 week old C57BL/6 mice (Charles River Laboratories) were administered one intranasal 40 μL dose of bleomycin sulphate (7.5 or 11.25 units/kg) or phosphate buffered saline (PBS) vehicle control under light isoflurane anaesthesia. Table 2: Resources
Experimental Models: Organisms/Strains Sentences Resources Female, 11-13 week old C57BL/6 mice (Charles River Laboratories) were administered one intranasal 40 μL dose of bleomycin sulphate (7.5 or 11.25 units/kg) or phosphate buffered saline (PBS) vehicle control under light isoflurane anaesthesia. C57BL/6suggested: NoneSoftware and Algorithms Sentences Resources Flow cytometry data were acquired on a BD Fortessa and analysed using FlowJo (version10, BD Biosciences). FlowJosuggested: (FlowJo, RRID:SCR_008520)Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).
Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:However we recognise its limitations: immune responses to bleomycin and SARS-CoV-2 are not identical, neither within the lungs nor systemically. Furthermore, our experiments were conducted exclusively in female mice aged 11-13 weeks. There is some evidence that young mice are less responsive to bleomycin than older mice (36) and it is possible that male mice would respond differently to bleomycin, LDLR or both. Furthermore, it is well established that the risk of severe COVID-19 lung disease is much greater in older patients (37), and that males are at higher risk of poor outcomes (38). Having identified bodyweight as a clinically relevant primary endpoint that correlates with the severity of bleomycin-induced pneumonitis and the associated systemic inflammatory response (39), we observed wide variation between mice in terms of rapidity and severity of weight loss, and subsequent recovery. Despite the challenges posed by this variability, our findings support the hypothesis that LDLR, delivered at a time when early histological and immunological features of lung inflammation are apparent, increases the likelihood of recovery in a subset of mice (approximately 25%). Subsequent analyses indicated that mice with moderate lung disease (measured either by lower rates of weight loss or by less marked imaging changes on CT scans) were more likely to respond to LDLR than those with severe pneumonitis. These bodyweight data are supported by histological, radiological and immunological...
Results from TrialIdentifier: No clinical trial numbers were referenced.
Results from Barzooka: We did not find any issues relating to the usage of bar graphs.
Results from JetFighter: We did not find any issues relating to colormaps.
Results from rtransparent:- Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
- No funding statement was detected.
- No protocol registration statement was detected.
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