Inhibition of p38 Mitogen‐Activated Protein Kinase Ameliorates Cytokine Up‐Regulated Shigatoxin‐1 Toxicity in Human Brain Microvascular Endothelial Cells

Brain injury in hemolytic-uremic syndrome (HUS) may be enhanced by inflammatory cytokine up-regulation of endothelial cell sensitivity to shigatoxin (Stx). The present study investigated whether inflammatory cytokine up-regulation of Stx toxicity could be ameliorated by inhibiting candidate signal transduction pathways. Exposure of human brain endothelial cells (HBECs) to tumor necrosis factor (TNF) greatly increased Stx-1 and Stx-2 cytotoxicity; this was reduced by inhibition of p38 mitogen-activated protein kinase (MAPK), but not c-Jun kinase. SB203580, a specific inhibitor of p38 MAPK, reduced TNF-stimulated Stx cytotoxicity in HBECs, TNF-stimulated (125)Stx-1 binding to intact HBECs, the cellular content of Gb3 (galactose alpha 1,4, galactose ss 1,4, glucose-ceramide) (the Stx receptor), and TNF-stimulated Gb3 synthase and glucosylceramide synthase activities but did not affect lactosylceramide synthase activities or mRNA content. Thus, inhibition of p38 MAPK substantially reduces inflammatory cytokine up-regulation of Stx-receptor synthesis and cell-surface expression, thereby decreasing Stx cytotoxicity. Inhibition of p38 MAPK may be of therapeutic benefit in HUS.