Examining inflammatory mechanisms and potential cytoprotective therapeutics in animal models of Shiga toxin induced kidney injury

Abstract

Shiga toxin-producing enterohemorrhagic Escherichia coli (EHEC) is an emerging food- and water-borne pathogen, causing approximately 73,000 annual infections in the United States and an estimated 1.5 million infections globally. E. coli O157:H7, the most frequently associated EHEC strain, is primarily transmitted through consumption of contaminated ground beef and produce and leads to hemorrhagic colitis in humans. In 5% to 15% of infected patients, circulating Shiga toxins (Stx1, Stx2) cause hemolytic uremic syndrome (HUS), characterized by the presence of thrombocytopenia, hemolytic anemia, and thrombotic microangiopathy, contributing to acute kidney injury (AKI). Current treatment is supportive and antibiotic therapy is contraindicative as it increases toxin production. Therapeutics for EHEC-induced HUS need to be identified to minimize kidney injury and uncontrolled coagulopathy. Well-characterized animal models of HUS and EHEC infection are available and provide avenues for potential therapeutic discovery. Baboons (Papio) challenged with endotoxin-free Shiga toxins develop full spectrum HUS, and mice infected with Stx2-producing Citrobacter rodentium (Cr Stx2+), a genetically modified enteric mouse pathogen, develop severe Stx2-mediated kidney injury. Initial studies have shown that soluble thrombomodulin (sTM), an anti-coagulant, is a promising therapeutic in preventing severe kidney injury in pediatric patients. In these studies, we determined whether complement was activated in baboons challenged with Shiga toxins, and evaluated whether intraperitoneal injection of sTM would reduce disease severity from mice infected with Cr Stx2+. D-dimer and cell injury markers (HMGB1, histones) confirmed the presence of coagulopathy and cell injury in Stx challenged baboons. Studies revealed that complement activation is not required for the development of thrombotic microangiopathy and HUS induced by EHEC Shiga toxins in these pre-clinical models. Soluble thrombomodulin treatment in Cr Stx2+ infected mice significantly decreased colonization but did not alter mortality. However, gene expression of kidney injury markers (NGAL, KIM-1) decreased significantly compared to no treatment indicating sTM-associated cytoprotectivity. The C. rodentium mouse model does not develop the coagulopathy seen in HUS patients and sTM treatment may be more effective in the baboon toxemia model. Soluble thrombomodulin is a promising therapeutic for EHEC-induced HUS and should be further evaluated in Stx challenged baboons.