UCLA

BACKGROUND: Clostridium difficile infection (CDI) is a debilitating nosocomial infection. C. difficile produces toxins A and B, which cause inflammation. Existing therapies have issues with recurrence, cost, and safety. We aim to discover a safe, effective, and economical nonmicrobiological therapeutic approach against CDI. METHODS: We included human primary peripheral blood mononuclear cells (PBMCs), fresh human colonic explants, and humanized HuCD34-NCG mice. Toxin A+B+ VPI 10463 and A-B+ ribotype 017 C. difficile strains were used. We used single-cell RNA profiling and high-throughput screening to find actionable toxin B-dependent pathways in PBMCs. RESULTS: Histamine 1 receptor-related drugs were found among the hit compounds that reversed toxin-mediated macrophage inflammatory protein (MIP) 1α expression in PBMCs. We identified loratadine as the safest representative antihistamine for therapeutic development. Loratadine inhibited toxin B-induced MIP-1α secretion in fresh human colonic tissues. Oral loratadine (10 mg/kg/d) maintained survival, inhibited intestinal CCl3 messenger RNA expression, and prevented vancomycin-associated recurrence in the VPI 10463-infected mice and ribotype 017-infected hamsters. Splenocytes from loratadine-treated mice conferred anti-inflammatory effects to the VPI 10463-infected T/B-cell--deficient Rag-/- mice. Oral loratadine suppressed human MIP-1α expression in monocytes/macrophages in toxin B-expressing ribotype 017-infected humanized HuCD34-NCG mice. CONCLUSIONS: Loratadine may be repurposed to optimize existing therapies against CDI.