Potential of Egg White Ovomucin and Its Hydrolysates in Mitigating Enteric Infections as an Antimicrobial Alternative
Creators: Bao, Xiaoyu
Publisher: name: University of Alberta Library
Year: 2024

<p>Ovomucin, accounting for ~3.5% of egg white, is a mucin-type glycoprotein and composed of ~ 33% carbohydrate content with 2.6-8% sialic acid. Ovomucin and its derived hydrolysates possess various biological activities, including anti-adhesive, anti-oxidative, and immunomodulatory activities. The overall objectives of this thesis were to investigate the anti-adhesive effect of ovomucin hydrolysates against bacterial adhesion to intestinal epithelia and their beneficial effect on intestinal barrier function against chemical and pathogenic challenges using in vitro and in vivo models.<br>
Using lipopolysaccharide (LPS)-treated differentiated human colorectal adenocarcinoma cells (Caco-2), ovomucin-protex 26L hydrolysate (OP) at concentrations of 0.1 mg/mL, 0.5 mg/mL, and 1.0 mg/mL significantly restored the transepithelial electrical resistance (TEER) values and decreased the paracellular FITC-dextran (4 kDa and 40 kDa) flux permeability. OP also significantly maintained the expression levels of tight junction proteins, including occludin and ZO-1, and preserved their structures and cell surface localization. Additionally, OP dramatically inhibited the phosphorylation of mitogen-activated protein kinase (MAPK) p38, extracellular signal-regulated kinase ½ (ERK1/2), and the activation and nucleus-translocation of nuclear factor κB (NF-κB) p65.<br>
The anti-adhesive and anti-inflammatory effects of OP, along with ovomucin-pepsin/pancreatin hydrolysate (OPP), were also investigated in enterotoxigenic Escherichia coli (ETEC) K88-challenged porcine small intestinal epithelial cells (IPEC-J2) and Caco-2 cells. OP and OPP both effectively inhibited ETEC K88 adhesion to the surfaces of intestinal epithelial cells and removal of sialic acids impaired their anti-adhesive capacities. Besides, OP restored epithelial permeability as indicated by elevated TEER values in IPEC-J2 cells. However, restored expression of tight junction proteins, including claudin-3, occludin, and ZO-1, were only observed in Caco-2 cells. OP and OPP suppressed activation of MAPK and NF-κB p65 signaling pathways in both cell lines. ETEC K88-associated virulence in activating calcium/calmodulin dependent protein kinase 2 (CaMK Ⅱ), elevating intracellular Ca2+ concentration, and inducing oxidative stress were attenuated by OP and OPP.<br>
To study the in vivo potential of ovomucin (OVM), OP, and OPP in preventing bacterial adhesion, colonization, and disease severity, a Citrobacter rodentium-induced colitis model was used. Supplementation of OVM, OP, and OPP in a basal diet did not impact body weight throughout the 4-week experimental period. At 7-d post-infection (7 dpi), OP treatment significantly reduced C. rodentium load in the gut of mice. OP and OVM both attenuated colitis severity evidenced by lower levels of colonic pathology and inflammatory cytokines/chemokines. However, the OPP group showed increased pathological severity with significantly decreased microbial diversity in the gut microbiota. In vitro culture of C. rodentium demonstrated that OPP better promoted bacterial growth in the minimal medium and showed numerically higher C. rodentium adhesion to mouse rectal epithelial cells (CMT-93) compared to OP. <br>
To study the potential of OP as an antimicrobial alternative in preventing enteric infection, ETEC K88-infected 21-day weaned piglets were used. Ovalbumin is the most abundant protein in chicken egg white, ovalbumin-protex 26L hydrolysate (OVAP) was also included in this study. ETEC K88 infection induced diarrhea in piglets, triggered inflammatory responses, and disrupted intestinal integrity in intestinal mucosa. OP supplementation changed the diarrhea pattern of piglets after ETEC K88 inoculation, improved the morphology of jejunum, and mediated the production of pro-inflammatory cytokines in jejunal and colonic mucosa. Notably, OVAP supplementation significantly decreased ETEC K88 abundance in the piglet colon.<br>
In summary, this thesis demonstrated the potential of ovomucin and its hydrolysate, particularly OP, as an anti-adhesive substance to inhibit pathogenic infection and benefit intestinal function and health.</p>