Acute lung injury (ALI) is a commonly encountered respiratory disease and its prognosis is poor when the treatment is not provided promptly and properly. However no specific pharmacologic treatment is currently available for ALI, although recently several supportive drugs have been under scrutiny. We studied anti-inflammatory effects of pentoxifylline (PF), a methylated xanthine, and ONO-5046, a synthetic neutrophil elastase inhibitor on lipopolysaccharide (LPS)-induced ALI in vitro.

To establish an in vitro model of LPS-induced ALI, primary rat alveolar macrophages and peripheral neutrophils in various ratios (1:0, 5:1,1:1,1:5,0:1) were co-cultured with transformed rat alveolar epithelial cells (L2 cell line) or vascular endothelial cells (IP2-E4 cell line) under LPS stimulation. Each experiment was divided into five groups-control, LPS, LPS+PF, LPS+ONO, and LPS+PF+ONO. We compared LPS-induced superoxide anion productions from primary rat alveolar macrophages and peripheral neutrophils in various ratios, and the resultant cytotoxxicity on L2 cells or IP2-E4 cells between groups. In addition we also compared the productions of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, monocyte chemotactic protein(MCP)-1, IL-6, and IL-10 as will as mRNA expressions of TNF-α, inducible nitric oxide synthetase(iNOS), and MCP-1 from LPS-stimulated primary rat alveolar macrophages between groups.

(1) PF and ONO-5046 in each or both showed a trend to suppress LPS-induced superoxide anion productions from primary rat alveolar macrophages and peripheral neutrophils regardless of their ratio, except for the LPS+PF+ONO group with the 1:5 ratio, although statistical significance was limited to a few selected experimental conditions. (2) PF and ONO-5046 in each or both showed a trend to prevent IP2-E4 cells from LPS-induced cytotoxicity by primary rat alveolar macrophages and peripheral neutrophils regardless their ratio, although statistical significance was limited to a few selected experimental conditions. The effects of PF and/or ONO-5046 on LPS-induced L2 cell cytotoxicity varied according to expaerimental conditions. (3) PF showed a trend to inhibit LPS-induced productions of TNF-α, MCP-1, and IL-10 from primary rat alveolar macrophages. ONO-5046 alone didnot affect the LPS-induced productions of proinflammatory cytokines from primary rat alveolar macrophages but the combination of PF and ONO-5046 showed a trend to suppress LPS-induced productions of TNF-αand IL-10 PF and ONO-5046 in each or both showed a trend to increase LPS-induced IL-β and IL-6 productions from primary rat alveolar macrophages. (4) PF and ONO-5046 in each or both showed atrend to attenuate LPS-induced mRNA expressions of TNF-α and MCP-1 from primary rat alveolar macrophages but at the same time showed a trend increase iNOS mRNA expression.

These results suggest that PF and ONO-5046 may play a role in attenuating inflammation in LPS-induced ALI and that further study is needed to use these drugs as a new supportive therapeutic strategy for ALI.