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 Bacillus amyloliquefaciens 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, Bacillus amyloliquefaciens (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 (p < 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 (p < 0.05), while concurrently reducing malondialdehyde (MDA) content (p < 0.05). (3) Compared to the CK group, JF significantly increased the mRNA expression levels of nuclear factor-erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1), SOD, catalase (CAT), GSH-Px, interleukin-4 (IL-4), interleukin-10 (IL-10), Claudin, Occludin1, zonula occludens-1 (ZO-1), and mucin 2 (MUC2) in Caco-2 cells (p < 0.05), while concurrently reducing the mRNA expression of Kelch-like ECH-associated protein 1 (Keap1), tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β), and interleukin-8 (IL-8) (p < 0.05). In comparison to the LPS group, the JF+LPS group demonstrated a significant increase in the mRNA expression of Nrf2, SOD, GSH-Px, and IL-4, as well as Occludin1, ZO-1, and MUC2 in Caco-2 cells (p < 0.05), alongside a decrease in the mRNA expression of Keap1, TNF-α, and IL-1β (p < 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 (p < 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 (p < 0.05). (5) In comparison to the CK group, the JF group exhibited a significant increase in Nrf2 levels in the jejunum of broiler chickens (p < 0.05). Notably, the mRNA expression levels of IL-4, IL-10, Claudin, Occludin1, ZO-1, and MUC2 were reduced (p < 0.05), while the mRNA expression levels of Keap1, TNF-α, and IL-1β also showed a decrease (p < 0.05). Furthermore, the mRNA expression levels of Nrf2, Occludin1, ZO-1, and MUC2 in the JF+LPS group were significantly elevated compared to those in the LPS group (p < 0.05), whereas the mRNA expression levels of Keap1 and TNF-α were significantly diminished (p < 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 Keap1/Nrf2 signaling pathway.