Abstract
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.
Footnotes
This work was supported by the National Science Council [Grant NSC99-2314-B-006-041]; and National Cheng Kung University Hospital [Grants 95-04, 98-03-006].
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
doi:10.1124/jpet.111.181560.
↵ The online version of this article (available at http://jpet.aspetjournals.org) contains supplemental material.
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ABBREVIATIONS:
- ALI
- acute lung injury
- ARDS
- acute respiratory distress syndrome
- IL
- interleukin
- BAL
- bronchoalveolar lavage
- aSMase
- acidic sphingomyelinase
- nSMase
- neutral sphingomyelinase
- LPS
- lipopolysaccharide
- S1P
- sphingosine-1-phosphate
- MAPK
- mitogen-activated protein kinase
- PBS
- phosphate-buffered saline
- CHL
- chlorpromazine
- Sph-24
- sphingolactone-24
- SKI-II
- sphingosine kinase inhibitor II
- SB203580
- 4-[4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-1H-imidazol-5-yl]pyridine
- FBS
- fetal bovine serum
- PI
- propidium iodide
- GAPDH
- glyceraldehyde-3-phosphate dehydrogenase
- FTY720
- 2-amino-2-[2-(4-octylphenyl)ethyl]propane-1,3-diol.
- Received March 12, 2011.
- Accepted June 30, 2011.
- Copyright © 2011 by The American Society for Pharmacology and Experimental Therapeutics
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