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GT160-246, a high-molecular-weight soluble anionic polymer, was tested in vitro and in vivo for neutralization of Clostridium difficile toxin A and B activities. Five milligrams of GT160-246 per ml neutralized toxin-mediated inhibition of protein synthesis in Vero cells induced by 5 ng of toxin A per ml or 1.25 ng of toxin B per ml. In ligated rat ileal loops, 1 mg of GT160-246 neutralized fluid accumulation caused by 5 microg of toxin A. At doses as high as 80 mg/loop, cholestyramine provided incomplete neutralization of fluid accumulation caused by 5 microg of toxin A. GT160-246 protected 80% of the hamsters from mortality caused by infection with C. difficile, whereas cholestyramine protected only 10% of animals. Treatment of C. difficile-infected hamsters with metronidazole initially protected 100% of the hamsters from mortality, but upon removal of treatment, 80% of the hamsters had relapses and died. In contrast, removal of GT160-246 treatment did not result in disease relapse in the hamsters. GT160-246 showed no antimicrobial activity in tests with a panel of 16 aerobic bacteria and yeast and 22 anaerobic bacteria and did not interfere with the in vitro activities of most antibiotics. GT160-246 offers a novel, nonantimicrobial treatment of C. difficile disease in humans.

Endothelial damage is characteristic of infection with Shiga toxin (Stx)-producing Escherichia coli (STEC). Because Stx-mediated endothelial cell damage at the site of infection may lead to the characteristic hemorrhagic colitis of STEC infection, we compared the effects of Stx1 and Stx2 on primary and transformed human intestinal microvascular endothelial cells (HIMEC) to those on macrovascular endothelial cells from human saphenous vein (HSVEC). Adhesion molecule, interleukin-8 (IL-8), and Stx receptor expression, the effects of cytokine activation and Stx toxins on these responses, and Stx1 and Stx2 binding kinetics and bioactivity were measured. Adhesion molecule and IL-8 expression increased in activated HIMEC, but these responses were blunted in the presence of toxin, especially in the presence of Stx1. In contrast to HSVEC, unstimulated HIMEC constitutively expressed Stx receptor at high levels, bound large amounts of toxin, were highly sensitive to toxin, and were not further sensitized by cytokines. Although the binding capacities of HIMEC for Stx1 and Stx2 were comparable, the binding affinity of Stx1 to HIMEC was 50-fold greater than that of Stx2. Nonetheless, Stx2 was more toxic to HIMEC than an equivalent amount of Stx1. The decreased binding affinity and increased toxicity for HIMEC of Stx2 compared to those of Stx1 may be relevant to the preponderance of Stx2-producing STEC involved in the pathogenesis of hemorrhagic colitis and its systemic complications. The differences between primary and transformed HIMEC in these responses were negligible. We conclude that transformed HIMEC lines could represent a simple physiologically relevant model to study the role of Stx in the pathogenesis of hemorrhagic colitis.