Loratadine as an Anti-inflammatory Agent Against Clostridium difficile Toxin B

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) 1 alpha expression in PBMCs. We identified loratadine as the safest representative antihistamine for therapeutic development. Loratadine inhibited toxin B-induced MIP-1 alpha 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-1 alpha 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. Loratadine, a Food and Drug Administration-approved antihistamine, inhibits toxin B-mediated proinflammatory macrophage inflammatory protein 1 alpha secretion from immune cells. Its anti-inflammatory effect ameliorates intestinal inflammation in Clostridium difficile-infected animals. Loratadine may be repurposed to optimize existing therapies.