Acute lung injury (ALI) is characterized by
lung inflammation and diffuse infiltration of neutrophils into the alveolar space. The inhibition of alveolar neutrophil apoptosis has been implicated in the pathogenesis of ALI. Although
sphingolipids may regulate cell apoptosis, the role of
sphingolipids in activated neutrophils during ALI is not clear. In this study, we test the hypothesis that
sphingolipids would attenuate neutrophil apoptosis that contributes to the development of ALI.
Lipopolysaccharide (LPS)-stimulated human neutrophils, with or without inhibitor treatment, were analyzed for apoptosis. We found that the inhibitory effect of LPS on neutrophil apoptosis was blocked by treatment with the neutral
sphingomyelinase (nSMase) inhibitor sphingolactone-24 (Sph-24),
sphingosine kinase inhibitor II, and
p38 mitogen-activated protein kinase (MAPK) inhibitor 4-[4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-1H-imidazol-5-yl]
pyridine (
SB203580) but not by the acidic
sphingomyelinase inhibitor
chlorpromazine. LPS-activated phosphorylation of
p38 MAPK also was attenuated by treatment with Sph-24 and
sphingosine kinase inhibitor II. Furthermore, mice with LPS-induced
lung injury were treated with the nSMase inhibitor Sph-24 to evaluate its impact on
lung injury and survival. The severity of LPS-induced ALI was reduced, and the survival rate was increased in mice treated with Sph-24 compared with that in those given LPS alone. Intracellular levels of
sphingolipids in alveolar neutrophils from patients with
acute respiratory distress syndrome also were measured. We found that intracellular levels of
ceramide and phospho-p38 MAPK were elevated in alveolar neutrophils from
acute respiratory distress syndrome patients. Our results demonstrate that activation of the nSMase/
sphingosine-1-
phosphate pathway to induce
p38 MAPK phosphorylation results in inhibition of neutrophil apoptosis, which may contribute to the development of ALI.