Avian pathogenic Escherichia coli (APEC) is the causative agent of avian colibacillosis.
Baicalin (BA) possesses multiple pharmacological effects, but the mechanism underlying its activity in APEC-induced intestinal injury remains unknown. This study aims to investigate the protective effects and possible mechanism of BA against APEC-induced intestinal injury. Sixty 1-day-old chicks were randomly divided into 4 groups: the control group (basal diet), E. coli group (basal diet), BAI10 group (10 mg/kg BA), and BAI20 group (20 mg/kg BA). After pretreatment with BA for 15 d and subsequent induction of APEC
infection by pectoralis injection, the ileum was collected and analyzed. The results showed that BA-pretreatment demonstrated an alleviation of chicks in
diarrhea rate, mortality, and histopathological changes in intestinal tissues after APEC
infection. Additionally, following APEC
infection, BA improved the intestinal barrier by elevating
zona occludens (ZO)s (ZO-1, 2, 3),
Claudins (Claudin1, 2, 3),
Occludin, avian β-
defensin (AvBD)s (AvBD1, 2, 4),
lysozyme (Lyz)
mRNA levels and ZO-1, Claudin1, and
Occludin protein levels. Besides, the activities of total
superoxide dismutase (T-SOD),
catalase (CAT), and
glutathione peroxidase (GSH-Px) and the SOD-1 and CAT
mRNA levels and
SOD-1 protein level were elevated by BA pretreatment. BA pretreatment also decreased the
malondialdehyde (MDA) content,
heme oxygenase-1 (HO-1) and
NADH quinone oxidoreductase 1 (NQO1)
mRNA levels, and HO-1
protein level after APEC
infection. BA alleviated the APEC-induced inflammatory response, including downregulating the
mRNA levels of proinflammatory
cytokines (
tumor necrosis factor-α (TNF-α),
interleukin [IL]-1β, IL-6, IL-8) and upregulating the
mRNA levels of anti-inflammatory
cytokines (IL-4, IL-10,
IL-13,
transforming growth factor-β [TGF-β]). Furthermore, BA decreased the
mRNA and
protein levels of
phosphatidylinositol 3 kinase (PI3K),
protein kinase B (AKT), and
nuclear factor kappa-B (NF-κB) as well as the expression of the phosphorylated forms of these
proteins after APEC
infection. Collectively, our findings indicate that BA exerts a protective effect against APEC-induced intestinal injury in chicks by inhibiting the PI3K/AKT-mediated NF-κB pathway, suggesting that BA may be a potential therapeutic approach for avian colibacillosis.