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Background:Pyroptosis is the term for caspase-l-dependent cell death associated with pro-inflammatory cytokines.The role of alveolar macrophage (AM) pyroptosis in the pathogenesis of the acute lung injury and acute respiratory distress syndrome (ALI/ARDS) remains unclear.Methods:C57BL/6 wild-type mice were assigned to sham,lipopolysaccharide (LPS) + vehicle,LPS + acetyl-tyrosyl-valyl-alanyl-aspartyl-chloromethylketone (Ac-YVAD-CMK) and LPS + Z-Asp-Glu-Val-Asp-fluoromethylketone groups.Mice were given intraperitoneal (IP) injections of LPS.Drugs were IP injected 1 h before LPS administration.Mice were sacrificed 16 h after LPS administration,and AMs were isolated.West blot analysis for active caspase-1 and cleaved caspase-3,evaluation of lung injury and a cytokine release analysis were performed.AMs were treated with LPS and adenosine triphosphate (ATP);caspase-l-dependent cell death was evaluated using flow cytometry;the apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) pyroptosomes were examined by immunofluorescence.Results:The expression of activated caspase-1 in AMs was enhanced following LPS challenge compared with the sham group.In the ex vivo study,the caspase-1/propidium iodide-positive cells,caspase-1 specks and ASC pyroptosomes were up-regulated in AMs following LPS/ATP stimulation.The specific caspase-1 inhibitor Ac-YVAD-CMK inhibited the activation of caspase-1 and pyroptotic cell death.Ac-YVAD-CMK also reduced the lung injury,pulmonary edema and total protein in bronchoalveolar lavage fluid (BALF).In addition,Ac-YVAD-CMK significantly inhibited interleukin-β (IL-lβ) release both in serum and BALF and reduced the levels of IL-18,tumor necrosis factor-α (TNF-α),High Mobility Group Box 1 (HMGB1) in BALF during LPS-induced ALI/ARDS.Conclusions:This study reported AM pyroptosis during LPS-induced ALI/ARDS in mice and has demonstrated that Ac-YVAD-CMK can prevent AM-induced pyroptosis and lung injury.These preliminary findings may form the basis for further studies to evaluate this pathway as a target for prevention or reduction of ALI/ARDS.