Ceramide Mediates Cytokine‐induced Pulmonary Edema by Inhibiting EnaC

Several lines of evidence suggest that both cytokines, such as tumor necrosis factor alpha (TNF‐α) and platelet‐activating factor (PAF), and ceramide are closely related to pulmonary edema. Ceramide acts as a messenger responsible for the signal transduction initiated by TNF‐α and PAF. Our in vivo experiments demonstrated that TNF‐α (100 ng/ml) significantly decreased mouse alveolar fluid clearance (AFC) from 19 ± 3% to 6 ± 2% (p = 0.01, n = 4) and that C 2 ‐ceramide (50 μM, a membrane‐permeable analog of ceramide) also appeared to decrease AFC from 19 ± 4% to 8 ± 6% (n=3). To determine whether ceramide affects AFC by regulating the epithelial sodium channel (ENaC), patch‐clamp experiments were performed using A549 cells, a model for alveolar type II cells. Cell‐attached recordings demonstrated that application of C 2 −ceramide (50 μM) to the apical bath reduced ENaC open probability from 0.56 ± 0.23 to 0.27 ± 0.18 (p < 0.05, n = 4). Consistent with patch‐clamp data, C 2 ‐ceramide (50 μM) also decreased transepithelial current from 9.9 ± 6.9 μA/cm 2 to 2.0 ± 1.1 μA/cm 2 (p < 0.05, n = 6) across H441 cell monolayers bathed in a Cl − ‐free solution. It has been shown that ceramide mediates PAF‐induced pulmonary edema These data together suggest that ceramide may play a pivotal role in mediating cytokine‐induced pulmonary edema by inhibiting ENaC. Supported by HL31197‐SM and DK067110 ‐HPM.