Acid sphingomyelinase mediates IL-6 release in experimental LPS-induced lung injury

Acute lung injury (ALI) is a major cause of mortality in intensive care units. Previous studies suggest that the acid sphingomyelinase (aSMase) might modulate pulmonary oedema in experimental models of ALI. The aim of this study was to analyze the possible role of aSMase on the effects induced by lipopolysaccharide (LPS) in pulmonary artery smooth muscle cells (PASMCs). Rat PASMCs were treated with different inhibitors for 45-60 minutes and then incubated for 24 hours in the absence (Ctrl) or presence of LPS (1 μg/ml) or bacterial SMase (0.1 U/ml; Bacillus cereus). The effects of D609 (50 mg/Kg body weight: i.p.) were assessed in an experimental model of ALI (intratracheal administration of LPS; 300 μg/Kg). IL-6 levels were determined by ELISA. Exposure to LPS for 24 hours significantly increased IL-6 release by rat PASMCs. This increase was inhibited by the TLR4 antagonist TAK242, the aSMase inhibitors desipramine and D609 and the TAK-1 inhibitor 5Z-7-oxozeaenol, but not by the iNOS inhibitor 1400W. Likewise, bacterial SMase stimulated PASMCs to release IL-6 and this effect was inhibited by 5Z-7-oxozeaenol, but not by TAK242 or 1400W. Finally, intratracheal administration of LPS increased lung aSMase activity by 30% and IL-6 levels in BAL. These effects were prevented by D609. In summary, our data suggest that aSMase activation modulates the release of IL-6 induced by LPS in PASMCs through a mechanism which involves TAK-1 activation and seems to be independent of iNOS. These results suggest that aSMase may represent a potential therapeutic target in ALI associated to bacterial sepsis. Supported by Spanish MINECO (2011-28150) and ISCIII (CP12/03304).