Shiga Toxin-associated Hemolytic Uremic Syndrome: Combined Cytotoxic Effects of Shiga Toxin and Lipopolysaccharide (endotoxin) on Human Vascular Endothelial Cells in Vitro

This study explores the in vitro relationship between Shiga toxin-producing Shigella spp. and Escherichia coli and the development of vascular complications in humans following bacillary dysentery. We propose that lipopolysaccharide (LPS; endotoxin) may combine with Shiga toxin to facilitate vascular damage characteristic of hemolytic uremic syndrome. We have examined the direct cytotoxic effects of Shiga toxin and LPS on human umbilical vein endothelial cells (HUVEC) in culture. Shiga toxin alone was cytotoxic to HUVEC, whereas LPS was noncytotoxic at concentrations at or below 10 micrograms/ml. Combinations of LPS with Shiga toxin resulted in a synergistic cytotoxic effect. The synergistic cytotoxic response of HUVEC to Shiga toxin plus LPS was dose dependent for both agents and was maximal at 24 h of exposure. This synergistic response was enhanced by preincubation of HUVEC with LPS. LPS (1 micrograms/ml) alone depressed HUVEC protein synthesis in a transient manner and enhanced the protein synthesis-inhibiting activity of Shiga toxin. The synergistic cytotoxic activity of LPS analogs was as follows, in decreasing order: complete LPS = diphosphoryl lipid A greater than monophosphoryl lipid A greater than deacylated LPS. These results are consistent with a role for Shiga toxin and LPS in the development of hemolytic uremic syndrome at the level of the vascular endothelium in humans.