Excessive inflammation reactions with a cytokine storm in the lungs have historically been thought as the primary cause of fatal acute respiratory distress syndrome (ARDS). However, interruption of inflammatory cytokine activation failed to attenuate ARDS, suggesting that other therapies are required to treat this illness and improve survival. Etoposide (ET), a cytotoxic agent, and prednisolone (PSL), a corticosteroid with strong anti-inflammatory activity, have been used to treat other disease involving similar cytokine-activated macrophages and hemophagocytic activity. However, they have not been previously tested as ARDS therapeutics alone or in combination. In the present study, we used a fatal ARDS mouse model induced via administration of a-galactosylceramide and lipopolysaccharide, which resulted in the development of severe lung injury with hypercytokinemia and hemophagocytosis, all of which were observed in ARDS patients infected with highly pathogenic respiratory viruses. The ET and PSL combination therapy, but not ET or PSL alone, reduced the recruitment and activation of inflammatory cells including macrophages, natural killer T cells, and neutrophils, and significantly improved the survival rate in this model. Furthermore, whereas ET alone improved lung edema, it did not increase the survival rate, indicating the necessity of PSL in the treatment of ARDS. Surprisingly, combination therapy did not reduce the production of cytokines and chemokines in the lungs, demonstrating that inflammatory cells, rather than hypercytokinemia, are the direct target of these compounds and primary cause of ARDS-related death. Thus, combination therapy with ET and PSL that targets inflammatory cells has the potential to attenuate fatal ARDS.
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