Bile acids increase alveolar epithelial permeability via mitogen-activated protein kinase, cytosolic phospholipase A2 , cyclooxygenase-2, prostaglandin E2 and junctional proteins.

BACKGROUND AND OBJECTIVE: Bile acid (BA) aspiration is associated with various lung diseases. It was hypothesized that BA may induce changes in alveolar epithelium permeability and contribute to the pathogenesis of lung injury. METHODS: Human alveolar epithelial cells were grown in monolayer and stimulated with a major component of BA, chenodeoxycholic acid (CDCA). Transepithelial electrical resistance (TER) and paracellular fluxes were measured to assess permeability alteration. Prostaglandin E2 ( PGE2 ) production was measured, and its effect on TER and junctional proteins (JP) was also examined. Reverse transcription polymerase chain reaction and Western blots were used to investigate the expression of messenger RNA and JP. RESULTS: CDCA induced significant p38 and c-Jun N-terminal kinase (JNK) phosphorylation, cytosolic phospholipase A2 (cPLA2 ) and cyclooxygenase-2 (COX-2) messenger RNA expression, PGE2 production, TER reduction and decay of JP (including occludin, zonula occludens-1 (ZO-1) and E-cadherin, in which ZO-1 had maximal change). CDCA also increased paracellular fluxes, which was abolished by dexamethasone. Both CDCA and PGE2 contributed to TER reduction in an identical trend and a dose-response manner. PGE2 also reduced ZO-1 expression, which was similar to that observed by CDCA stimulation. Pretreatment with inhibitors of p38 (SB203580), JNK (SP600125), cPLA2 (mepacrine) and COX-2 (NS398) as well as dexamethasone reversed the CDCA-induced PGE2 production, TER reduction and decay of ZO-1. CONCLUSIONS: The increase in alveolar permeability was associated with decay of JP. BA may induce permeability alteration through the upregulation of mitogen-activated protein kinase, cPLA2 , COX-2, PGE2 and JP, which may contribute to the pathogenesis of BA-associated lung injury.