Fidaxomicin and OP-1118 inhibit C. difficile toxin A- and B-mediated inflammatory responses via inhibition of NF-{kappa}B activity. [PublishAheadOfPrint]

Objective: Clostridium difficile causes diarrhea and colitis by releasing toxin A and toxin B. In the human colon, both toxins cause intestinal inflammation and stimulate TNFα expression via activation of NF-B. It is well established that the macrolide antibiotic fidaxomicin is associated with reduced relapses of C. difficile infection. We showed that fidaxomicin and its primary metabolite, OP-1118, significantly inhibited toxin A-mediated intestinal inflammation in mice in vivo and toxin A-induced cell rounding in vitro. We aim to determine whether fidaxomicin and OP-1118 possess anti-inflammatory effects against toxin A and toxin B in the human colon and examine the mechanism of this response. Design: We used fresh human colonic explants, NCM460 human colonic epithelial cells, and RAW264.7 mouse macrophages to study the mechanism of fidaxomicin and OP-1118 against toxin A- and B-mediated cytokine expression and apoptosis. Results: Fidaxomicin and OP-1118 dose-dependently inhibited toxin A- and B-induced TNFα and IL-1β mRNA expression and histological damage in human colonic explants. Fidaxomicin and OP-1118 inhibited toxin A-mediated NF-B phosphorylation in human and mouse intestinal mucosa. Fidaxomicin and OP-1118 also inhibited toxin A-mediated NF-B phosphorylation and TNFα expression in macrophages, which was reversed by the NF-B activator PMA. Fidaxomicin and OP-1118 prevented toxin A- and B-mediated apoptosis in NCM460 cells, which was reversed by the addition of the PMA. PMA reversed the cytoprotective effect of fidaxomicin and OP-1118 in toxin-exposed human colonic explants. Conclusion: Fidaxomicin and OP-1118 inhibit C. difficile toxin A- and B-mediated inflammatory responses, NF-B phosphorylation, and tissue damage in human colon.

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