LIPOPOLYSACCHARIDE INDUCES DISSEMINATED ENDOTHELIAL APOPTOSIS REQUIRING CERAMIDE GENERATION

The endotoxic shock syndrome is characterized by systemic inflammation , multiple organ damage, circulatory collapse and death. Systemic rele ase of tumor necrosis factor (TNF)-alpha and other cytokines purported ly mediates this process. However, the primary tissue target remains u nidentified. The present studies provide evidence that endotoxic shock results from disseminated endothelial apoptosis. Injection of lipopol ysaccharide (LPS), and its putative effector TNF-alpha, into C57BL/6 m ice induced apoptosis in endothelium of intestine, lung, fat and thymu s after 6 h, preceding nonendothelial tissue damage. LPS or TNF-alpha injection was followed within 1 h by tissue generation of the pro-apop totic lipid ceramide. TNF-binding protein, which protects against LPS- induced death, blocked LPS-induced ceramide generation and endothelial apoptosis, suggesting systemic TNF is required for both responses. Ac id sphingomyelinase knockout mice displayed a normal increase in serum TNF-alpha in response to LPS, yet were protected against endothelial apoptosis and animal death, defining a role for ceramide in mediating the endotoxic response. Furthermore, intravenous injection of basic fi broblast growth factor, which acts as an intravascular survival factor for endothelial cells, blocked LPS-induced ceramide elevation, endoth elial apoptosis and animal death, but did not affect LPS-induced eleva tion of serum TNF-alpha. These investigations demonstrate that LPS ind uces a disseminated form of endothelial apoptosis, mediated sequential ly by TNF and ceramide generation, and suggest that this cascade is ma ndatory for evolution of the endotoxic syndrome.