iNOS inhibitor S-methylisothiourea alleviates smoke inhalation-induced acute lung injury by suppressing inflammation and macrophage infiltration

Objective: We investigated the effects of the inducible NO synthase (iNOS) inhibitor, S-methylisothiourea (SMT), in a mouse model of smoke inhalation -induced acute lung injury (ALI) and explored the underlying molecular mechanism. Methods and analysis: A mouse model of smoke inhalation -induced ALI was established. RNA -sequencing (seq) analysis was conducted to identify the differentially expressed genes (DEGs). Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses were performed for functional annotation of DEGs. Moreover, an immunofluorescence assay using macrophage marker F4/80 was performed to assess macrophage infiltration. A hypoxia-induced HUVEC model was used to mimic smoke inhalation -induced injury in endothelial cells. Finally, a transwell assay was used to analyze the chemoattractive effects of endothelial cells on macrophages. Results: SMT markedly alleviated the pulmonary pathological symptoms, edema, and inflammatory response in the mouse smoke inhalation -induced ALI model. RNA-seq analysis revealed that SMT may diminish lung injury by regulating the levels of genes associated with inflammatory responses, cell chemokines, and adhesion. In vivo data revealed that the protective effects of SMT against smoke inhalation -induced ALI were partly achieved by inhibiting the production of adhesion molecules and infiltration of macrophages. Furthermore, in vitro data from the hypoxia-induced HUVEC model revealed that SMT reduced macrophage chemotaxis by inhibiting the production of chemokines and adhesion molecules in endothelial cells. Conclusion: iNOS inhibitor SMT protects the lungs from smoke inhalation -induced ALI by reducing the production of pro -inflammatory cytokines, adhesion molecules, and chemokines in endothelial cells, thereby inhibiting inflammation and macrophage infiltration.