Activation of coagulation in C57BL/6 mice given verotoxin 2 (VT2) and the effect of co-administration of LPS with VT2

To obtain better insight into the pathogenesis of verotoxin-producing Escherichia coli-associated diseases, in this study, we explored the effect of verotoxin 2 (VT2) on coagulation in an animal model. After being given VT2 (50 ng/kg, lethal dose), C57BL/6 mice showed progressively increasing expression of TF mRNA in the kidney and brain and elevated plasma levels of thrombin-antithrombin III complex (TAT), normotest, fibrinogen, and PAI-1 paralleling the disease course over 24 hours; platelet counts were decreased at 48 hours with hemorrhage in the kidney and brain. Co-administration of lipopolysaccharide (LPS, 0.5 mg/kg) with VT2 (50 ng/kg) exhibited more prominant and/or prolonged increase in not only expression of TF and PAI-1 mRNAs in the kidney and brain but also plasma levels of TAT, fibrinogen, and PAI-1 and was associated with more remarkable hemorrhage in the tissues. Although VT2 (5 ng/kg) was not a lethal dose, co-administration of LPS (0.5 mg/kg) with VT2 (5 ng/kg) enhanced the susceptibility to VT2, resulting in more prolonged elevation of TAT levels during the first 24 hours than that in the LPS group and a second elevation at 72 hours, followed by death. Plasma IL-1beta level reached a maximum at 24 hours after VT2 (50 ng/kg) injection prior to the increase in TAT levels, whereas the increase in TNFalpha level immediately after injection was associated with the increase in PAI-1 mRNA. These observations indicate that the activation of coagulation by VT2 may occur through a mechanism different from that used by LPS, since plasma TAT levels rose in the mice immediately after LPS injection and returned to normal over 36 hours.