Heme-induced lung injury in human precision cut lung slices: a new model for acute lung injury.

BACKGROUND: Acute respiratory distress syndrome (ARDS) causes high mortality and has no specific pharmacological treatment. Scarcity of drugs against ARDS is in part due to the lack of models for ARDS. As raised serum heme levels are associated with higher mortality in patients with ARDS, we hypothesised that circulating heme contributes to ARDS pathology and can induce lung injury resembling human disease. We aimed to develop a new model for acute lung injury and ARDS research with heme-induced injury in human precision cut lung slices (PCLS). METHODS: We analysed heme and its degrading enzymes along with inflammatory cytokines in patients with coronavirus disease 2019 (COVID-19) and ARDS compared to healthy adult subjects. In PCLS, we studied effects of heme on cell survival, membrane integrity, the transcriptome by gene expression and the proteome by protein expression analysis or ELISA. We also tested synergistical effects with lipopolysaccharide (LPS) on cell survival in addition to heme to simulate bacterial infection. RESULTS: Patients with COVID-19 and ARDS had increased serum levels of heme and heme oxygenase 1 (HO-1) compared to controls. In PCLS, heme induced cell death in a dose-dependent manner, stimulated pro-inflammatory and injury signals and triggered changes to the extracellular matrix (ECM). Comparative analyses of the lung transcriptomic and proteomic signatures revealed 27 common markers (log2 fold change greater than 1, at adjusted (adj) p-value < 0.05 significant), most of which were inflammatory. Similar inflammatory cytokines were raised in blood from patients with COVID-19 and ARDS compared to controls. LPS did not increase cytotoxicity in addition to heme. CONCLUSION: Heme induced inflammatory cytokine release and cell death in human PCLS, resembling the patterns observed in blood samples from patients with COVID-19 and ARDS. Thus, heme-stimulated PCLS represent a novel ex vivo model for mechanistic studies for acute lung injury and ARDS.