Muramidase-released protein (MRP) is now being recognized as a critical indicator of the virulence and pathogenicity of Streptococcus suis (S. suis). However, the identification of viable therapeutics for S. suis infection was hindered by the absence of an explicit mechanism for MRP-actuated inflammation. Dihydroartemisinin (DhA) is an artemisinin derivative with potential anti-inflammatory activity. The modulatory effect of DhA on the inflammatory response mediated by the virulence factor MRP remains obscure. This research aimed to identify the signaling mechanism by which MRP triggers the innate immune response in mouse spleen and cultured macrophages. With the candidate mechanism in mind, we investigated DhA for its ability to dampen the pro-inflammatory response induced by MRP. The innate immune response in mice was drastically triggered by MRP, manifesting as splenic and systemic inflammation with splenomegaly, immune cell infiltration, and an elevation in pro-inflammatory cytokines. A crucial role for Toll-like receptor 4 (TLR4) in coordinating the MRP-mediated inflammatory response via nuclear factor-kappa B (NF-κB) activation was revealed by TLR4 blockade. In addition, NF-κB-dependent transducer and activator of transcription 3 (STAT3) and mitogen-activated protein kinases (MAPKs) activation was required for the inflammatory signal transduction engendered by MRP. Intriguingly, we observed an alleviation effect of DhA on the MRP-induced immune response, which referred to the suppression of TLR4-mediated actuation of NF-κB-STAT3/MAPK cascades. The inflammatory response elicited by MRP is relevant to TLR4-dependent NF-κB activation, followed by an increase in the activity of STAT3 or MAPKs. DhA mitigates the inflammation process induced by MRP via blocking the TLR4 cascade, highlighting the therapeutic potential of DhA in targeting S. suis infection diseases.

Apoptosis of intestinal epithelial cells following oxidative stress is a major cause of mucosal barrier dysfunction and is associated with the pathogenesis of various gastrointestinal diseases. Although L-tryptophan (Trp) is known to improve intestinal integrity and function, a beneficial effect of N-acetyl serotonin (NAS), a metabolite of Trp, on the apoptosis of enterocytes and the underlying mechanisms remain largely unknown. In the present study, we showed that porcine enterocytes treated with 4-hydroxy-2-nonenal (4-HNE), a metabolite of lipid peroxidation, led to upregulation of apoptotic proteins, including Bax and cleaved caspase-3, and reduction of tight junction proteins. These effects of 4-HNE were significantly abrogated by NAS. In addition, NAS reduced ROS accumulation while increasing the intracellular concentration of glutathione (GSH), and the abundance of the Nrf2 protein in the nucleus and its downstream target proteins. Importantly, these protective effects of NAS were abrogated by Atra, an inhibitor of Nrf2, indicating a dependence on Nrf2 signaling. Taken together, we demonstrated that NAS attenuated oxidative stress-induced cellular injury in porcine enterocytes by regulating Nrf2 signaling. These findings provide new insights into a functional role of NAS in maintaining intestinal homeostasis.

The aryl hydrocarbon receptor (AhR) is a transcription factor that regulates the immune system through complicated transcriptional programs. Genistein, an AhR ligand, exhibits anti-inflammatory properties. However, its role in modulating immune responses via the AhR signaling pathway remains unclear. In this study, 360 male Arbor Acre broilers (1-day-old) were fed a basal diet supplemented with 40 or 80 mg/kg genistein and infected with or without Clostridium perfringens (Cp). Our results demonstrated that genistein ameliorated Cp-induced intestinal damage, as reflected by the reduced intestinal lesion scores and improved intestinal morphology and feed-to-gain ratio. Moreover, genistein increased intestinal sIgA, TGF-β, and IL-10, along with elevated serum IgG, IgA, and lysozyme levels. Genistein improved intestinal AhR and cytochrome P450 family 1 subfamily A member 1 (CYP1A1) protein levels and AhR⁺ cell numbers in Cp-challenged broilers. The increased number of AhR⁺CD163⁺ cells in the jejunum suggested a potential association between genistein-induced AhR activation and anti-inflammatory effects mediated through M2 macrophage polarization. In IL-4-treated RAW264.7 cells, genistein increased the levels of AhR, CYP1A1, CD163, and arginase (Arg)-1 proteins, as well as IL-10 mRNA levels. This increase was attenuated by the AhR antagonist CH223191. In summary, genistein activated the AhR signaling pathway in M2 macrophages, which enhanced the secretion of anti-inflammatory cytokines and attenuated intestinal damage in Cp-infected broilers Cp.

Aglycone soy isoflavones have notable immune-regulatory bioactivity, while glycosidic forms in soybean meal pose challenges for absorption. β-Glucosidase (EC 3.2.1.21) catalyzes the non-reducing terminal β-d-glucosidic bonds, releasing β-d-glucan and aglycones. This study evaluated the impact of enzymatically hydrolyzed soybean meal (ESM) using recombinant β-glucosidase from Aspergillus niger on the growth performance and intestinal immune function of broilers under Clostridium perfringens infection. Prior to the feeding trial, soybean meal was enzymatically digested with recombinant β-glucosidase, ensuring almost complete conversion of glycosides to aglycones. After a week of pre-feeding, a total 180 healthy AA broilers were randomly assigned to three groups—control, semi-replacement of ESM (50% ESM), and full-replacement of ESM (100% ESM)—with 6 replicates of 10 chickens, and the trial lasted 28 days. On the 36th day, broilers were challenged with 1 mL of 1 × 10¹⁰ CFU/mL Clostridium perfringens (Cp) via gavage for 3 days. The results showed that the substitution of ESM had no effect on the body weight gain of broilers but significantly reduced the feed consumption and feed-to-gain ratio (p < 0.01). The study revealed that Cp significantly disrupted jejunal morphology, while ESM significantly mitigated this damage (p < 0.05). Real-time PCR results demonstrated that compared to the Cp group, ESM restored Cp-induced intestinal barrier impairments (e.g., Occludin, Claudin-1, Muc2), normalized aberrant cellular proliferation (PCNA) and apoptosis (Caspase-1 and Caspase-3), and upregulated the expression of anti-inflammatory factor Il-10 while suppressing pro-inflammatory cytokines (Il-1β, Il-6, and Il-8) (p < 0.05). Moreover, flow cytometry analyses demonstrated that ESM promoted Treg cell-derived Il-10, which alleviated macrophage-derived inflammation. Substituting conventional soybean meal with β-glucosidase, enzymatically treated, significantly reduced feed consumption and alleviated the intestinal damage and immune dysfunctions induced by Clostridium perfringens infection in broilers.

Background: Shigellosis is an illness that affects young children all over the world and Shigella flexneri is one of the most common pathogens. The aim of this study was to investigate a potential beneficial effect of Weizmannia coagulans Long45 supplementation on feline-derived Shigella flexneri-induced colitis in mice, as well as potential mechanisms. Results: The results revealed that mice receiving fecal microbiota from diarrheic cats experienced significant weight loss, decreased survival rate, increased mRNA levels of inflammatory cytokines (TNF-α, IL-4, IFN-γ, IL-1β, IL-6, and IL-18), and increased cell apoptosis compared to the single DSS treatment. In contrast, mice that received fecal microbiota from healthy cats exhibited an increased body weight, increased mRNA level of ZO-1, claudin-3, and Muc2 and decreased apoptosis, indicating a protective effect. The 16S rDNA analysis revealed that the abundance of Shigella in the feces of diarrheic cats was significantly higher than that in healthy cats, while the abundance of Bacillus was lower. Using bacteria culture technology, 19 strains of Shigella flexneri were isolated from 27 fecal samples of diarrheic cats and a strain of Weizmannia coagulans Long45 was isolated from the feces of healthy cats. Further study showed that Weizmannia coagulans Long45 significantly alleviated pathological alterations and colonic barrier dysfunction by modulating the NF-κB and Nrf2 signaling pathways. Conclusions: Our data indicate that feline-derived Shigella flexneri may be a potential pathogen associated with diarrhea and intestinal barrier dysfunction. Weizmannia coagulans Long45, as a potential probiotic, can effectively alleviate Shigella-induced colitis by interfering with the Nrf2 and NF-κB signaling pathways.