Bacillus amyloliquefaciens Regulates the Keap1/Nrf2 Signaling Pathway to Improve the Intestinal (Caco-2 Cells and Chicken Jejunum) Oxidative Stress Response Induced by Lipopolysaccharide (LPS)

This article aims to investigate the mechanism by which <i>Bacillus amyloliquefaciens</i> alleviates lipopolysaccharide (LPS)-induced intestinal oxidative stress. The study involved two experimental subjects: human colorectal adenocarcinoma (Caco-2) cells and Arbor Acres broiler chickens. The experiment involving two samples was designed with the same treatment groups, specifically the control (CK) group, lipopolysaccharide (LPS) group, <i>Bacillus amyloliquefaciens</i> (JF) group, and JF+LPS group. In the Caco-2 experiment, we administered 2 μg/mL of LPS and 1 × 10⁶ CFU/mL of JF to the LPS and JF groups, respectively. In the broiler experiment, the LPS group (19-21 d) received an abdominal injection of 0.5 mg/kg BW of LPS, whereas the JF group was fed 1 × 10⁷ CFU/g of JF throughout the entire duration of the experiment (1-21 d). The results indicated the following: (1) JF significantly decreased the DPPH free radical clearance rate and hydrogen peroxide levels (<i>p</i> < 0.05). (2) JF significantly enhanced the total antioxidant capacity (T-AOC), superoxide dismutase (SOD), and glutathione peroxidase (GSH Px) activity in Caco-2 cells (<i>p</i> < 0.05), while concurrently reducing malondialdehyde (MDA) content (<i>p</i> < 0.05). (3) Compared to the CK group, JF significantly increased the mRNA expression levels of <i>nuclear factor-erythroid 2-related factor 2</i> (<i>Nrf2</i>), <i>heme oxygenase-1</i> (<i>HO-1</i>), SOD, <i>catalase</i> (<i>CAT</i>), GSH-Px, <i>interleukin-4</i> (<i>IL-4</i>), <i>interleukin-10</i> (<i>IL-10</i>), Claudin, Occludin1, <i>zonula occludens-1</i> (<i>ZO-1</i>), and <i>mucin 2</i> (<i>MUC2</i>) in Caco-2 cells (<i>p</i> < 0.05), while concurrently reducing the mRNA expression of <i>Kelch-like ECH-associated protein 1</i> (<i>Keap1</i>), <i>tumor necrosis factor-alpha</i> (<i>TNF-α</i>), <i>interleukin-1β</i> (<i>IL-1β</i>), and <i>interleukin-8</i> (<i>IL-8</i>) (<i>p</i> < 0.05). In comparison to the LPS group, the JF+LPS group demonstrated a significant increase in the mRNA expression of <i>Nrf2</i>, <i>SOD</i>, <i>GSH-Px</i>, and <i>IL-4</i>, as well as <i>Occludin1</i>, <i>ZO-1</i>, and <i>MUC2</i> in Caco-2 cells (<i>p</i> < 0.05), alongside a decrease in the mRNA expression of <i>Keap1</i>, <i>TNF-α</i>, and <i>IL-1β</i> (<i>p</i> < 0.05). (4) In broiler chickens, the JF group significantly elevated the levels of T-AOC, CAT, and GSH-Px in the jejunum while reducing MDA content (<i>p</i> < 0.05). Furthermore, the CAT level in the JF+LPS group was significantly higher than that observed in the LPS group, and the levels of MDA, TNF-α, and IL-1β were significantly decreased (<i>p</i> < 0.05). (5) In comparison to the CK group, the JF group exhibited a significant increase in <i>Nrf2</i> levels in the jejunum of broiler chickens (<i>p</i> < 0.05). Notably, the mRNA expression levels of <i>IL-4</i>, <i>IL-10</i>, <i>Claudin</i>, <i>Occludin1</i>, <i>ZO-1</i>, and <i>MUC2</i> were reduced (<i>p</i> < 0.05), while the mRNA expression levels of <i>Keap1, TNF-α</i>, and <i>IL-1β</i> also showed a decrease (<i>p</i> < 0.05). Furthermore, the mRNA expression levels of <i>Nrf2</i>, <i>Occludin1</i>, <i>ZO-1</i>, and <i>MUC2</i> in the JF+LPS group were significantly elevated compared to those in the LPS group (<i>p</i> < 0.05), whereas the mRNA expression levels of <i>Keap1</i> and <i>TNF-α</i> were significantly diminished (<i>p</i> < 0.05). In summary, JF can enhance the intestinal oxidative stress response, improve antioxidant capacity and intestinal barrier function, and decrease the expression of inflammatory factors by regulating the <i>Keap1</i>/<i>Nrf2</i> signaling pathway.