Protective Effect of Coated Benzoic Acid on Intestinal Epithelium in Weaned Pigs upon Enterotoxigenic Escherichia coli Challenge

The study was designed to investigate the protective effect of dietary supplementation with coated benzoic acid (CBA) on intestinal barrier function in weaned pigs challenged with enterotoxigenic <i>Escherichia coli</i> (ETEC). Thirty-two pigs were randomized to four treatments and given either a basal diet or a basal diet supplemented with 3.0 g/kg CBA, followed by oral administration of ETEC or culture medium. The results showed that CBA supplementation increased the average daily weight gain (ADWG) in the ETEC-challenged pigs (<i>p</i> < 0.05). CBA also increased the serum activity of total superoxide dismutase (T-SOD) and the total antioxidant capacity (T-AOC), as it decreased the serum concentrations of endotoxin, interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in the ETEC-challenged pigs (<i>p</i> < 0.05). Interestingly, the CBA alleviated the ETEC-induced intestinal epithelial injury, as indicated by a reversal of the decrease in D-xylose absorption and a decrease in the serum levels of D-lactate and diamine oxidase (DAO) activity, as well as a decrease in the quantity of apoptotic cells in the jejunal epithelium following ETEC challenge (<i>p</i> < 0.05). Moreover, CBA supplementation significantly elevated the mucosal antioxidant capacity and increased the abundance of tight junction protein ZO-1 and the quantity of sIgA-positive cells in the jejunal epithelium (<i>p</i> < 0.05). Notably, CBA increased the expression levels of porcine beta defensin 2 (<i>PBD2</i>), <i>PBD3</i>, and nuclear factor erythroid-2 related factor 2 (<i>Nrf-2</i>), while downregulating the expression of toll-like receptor 4 (<i>TLR4</i>) in the jejunal mucosa (<i>p</i> < 0.05). Moreover, CBA decreased the expression levels of interleukin-1β (<i>IL-1β</i>), myeloid differentiation factor 88 (<i>MyD88</i>), and nuclear factor-kappa B (<i>NF-κB</i>) in the ileal mucosa upon ETEC challenge (<i>p</i> < 0.05). These results suggest that CBA may attenuate ETEC-induced damage to the intestinal epithelium, resulting in reduced inflammation, enhanced intestinal immunity and antioxidant capacity, and improved intestinal epithelial function.