Oral administration of a recombinant cholera toxin B subunit promotes mucosal healing in the colon

Abstract

Cholera toxin B subunit (CTB) is a component of a licensed oral cholera vaccine. However, CTB has pleiotropic immunomodulatory effects whose impacts on the gut are not fully understood. Here, we found that oral administration in mice of a plant-made recombinant CTB (CTBp) significantly increased several immune cell populations in the colon lamina propria. Global gene expression analysis revealed that CTBp had more pronounced impacts on the colon than the small intestine, with significant activation of TGFβ-mediated pathways in the colon epithelium. The clinical relevance of CTBp-induced impacts on colonic mucosa was examined. In a human colon epithelial model using Caco2 cells, CTBp, but not the non-GM1-binding mutant G33D-CTBp, induced TGFβ-mediated wound healing. In a dextran sodium sulfate (DSS) acute colitis mouse model, oral administration of CTBp protected against colon mucosal damage as manifested by mitigated body weight loss, decreased histopathological scores, and blunted escalation of inflammatory cytokine levels while inducing wound healing-related genes. Furthermore, biweekly oral administration of CTBp significantly reduced disease severity and tumorigenesis in the azoxymethane/DSS model of ulcerative colitis and colon cancer. Altogether, these results demonstrate CTBp's ability to enhance mucosal healing in the colon, highlighting its potential application in ulcerative colitis therapy besides cholera vaccination.

A recombinant cholera toxin b subunit variant (CTB-KDEL) exhibits unique colon mucosal healing effects that have therapeutic implications for inflammatory bowel disease.

“…Given that chronic inflammation and injury of the bowel, such as inflammatory bowel disease (IBD), pose an increased risk of developing colitis-associated colorectal cancer (CAC) [24,25,100,101], CTB-KDEL's effects were also examined in the azoxymethane (AOM)/DSS mouse model of CAC. Biweekly oral administration of CTB-KDEL over 9 weeks significantly reduced inflammation and tumorigenesis in this model, highlighting its therapeutic potential in intestinal injury and inflammatory bowel disease, such as ulcerative colitis (UC) [50]. Therefore, the finding that CTB-KDEL is a topical agent that facilitates TGFβ-based mucosal wound healing in UC and CAC mouse, supports a hypothesis that CTB-KDEL could help address important issues pertinent to therapeutic strategies for mucosal healing in UC.…”

“…Besides the specific T helper cell subsets, our study has also revealed that innate immune cells-including dendritic cells, natural killer cells and macrophages (both M1 and M2)-populations were increased in the colon lamina propria two weeks after CTB-KDEL oral administration [50]. Furthermore, a global gene expression analysis revealed that CTB-KDEL had more pronounced impacts on the colon than the small intestine, with significant activation of TGFβ-mediated pathways in the colon mucosa [50]. Given that there is a strong link between epithelial-derived TGFβ and innate immune cells in wound healing [92][93][94], the results provided implications for the potential utility of CTB-KDEL to promote colonic mucosal health.…”

“…Furthermore, oral administration of CTB-KDEL in mice protected against colon mucosal damage in acute colitis induced by dextran sodium sulfate (DSS). Two oral doses of as low as 1 µg of CTB-KDEL mitigated clinical signs of disease (body weight loss, decreased histopathological scores, and blunted escalation of inflammatory cytokine levels) and upregulated wound healing-related genes [50]. Interestingly, CTB-KDEL administration prevented fibrosis associated with acute colitis in mice; hence, the protein did not appear to overstimulate TGFβ signaling, at least under the conditions employed in the study.…”

“…Using CTB-KDEL [42,89], we have shown that oral administration of the CTB variant significantly altered several immune cell populations in the colon lamina propria [50].…”

“…In addition to CTB's immunostimulatory effects, CTB stimulates specific immunosuppressive effects against autoimmune disorders, excess inflammation, and allergic reactions [31,[45][46][47][48][49]. We have recently shown that oral administration of CTB-KDEL mitigates colitis in chemically-induced acute and chronic colitis mouse models [50]. Although the underlying mechanisms are not well understood, recent studies have shed some light on these immunosuppressive effects induced by CTB.…”