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UBC Theses and Dissertations

Downregulation of lipopolysaccharide-induced intestinal epithelial cell chemokine secretion by a novel MAO B inhibitor Wang, Xiaojiao


Lipopolysaccharide (LPS) is a membrane component of Gram-negative bacteria. Enzyme monoamine oxidase B (MAO B) gene and protein expression was upregulated in diseased tissue of LPS-induced periodontal mucosal chronic inflammation in rat; MAO inhibition with phenelzine reduced signs of inflammation (Ekuni et al., 2009). Current MAO inhibitors are brain permeable and clinically used to treat CNS-associated diseases. Interestingly, some of them showed promising peripheral effects. To manage chronic non-CNS inflammation, Dr. Putnins and collaborators redeveloped novel MAO B inhibitors with reduced blood-brain barrier permeability. These novel inhibitors have significantly reduced LPS-induced cytokine gene and protein expression in various epithelial and endothelial cell models via unknown mechanisms. We investigated the possible signaling pathways mediating LPS-induced interleukin-8 (IL-8) protein expression, and the mechanism by which novel MAO B inhibitor Compound B reduced such effects in intestinal epithelial cell line Caco-2 cells. Caco-2 cell differentiation was induced by culturing in Transwell-inserts for extended culture times. MAO B protein expression, levels of IL-8 secretion, total NF-kB p65 nuclear translocation, phosphorylation of NF-kB p65 at Ser536 and phosphorylation of ERK1/2, p38 and JNK MAPKs were assessed following stimulation by LPS with or without Compound B in differentiated and undifferentiated Caco-2 cultures via immunoprecipitation, ELISA, immunofluorescence and Western blotting. We showed that LPS-induced IL-8 secretion in Caco-2 cultures was independent of the common LPS-induced signaling pathways including NF-kB p65 nuclear translocation and phosphorylation of NF-kB p65 and MAPKs. MAO B protein expression was only detected in differentiated Caco-2 cultures. Compound B exhibited equal efficacy at downregulating LPS-induced IL-8 secretion in both undifferentiated and differentiated Caco-2 cultures. In summary, IL-8 downregulation by Compound B appears to be independent of the presence of MAO B protein, suggesting a possible off-target effect.

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