Salmonella typhimurium (S.T) is a common cause of acute, self-limiting food-borne diarrhea with severe intestinal inflammation and intestinal barrier damage. Oleanolic acid (OA), isolated from almost 2000 plant species, has been shown to have anti-inflammatory roles. The purpose of this study was to investigate the potential protective effects of OA on S.T-induced diarrhea and enteritis and to elucidate its anti-inflammatory mechanisms. A total of eighty BALB/c mice (4-week-old) were randomly divided into the control group (no S.T, no OA), the S.T group (S.T only), the S.T + OA group (S.T plus 100 mg kg⁻¹ OA) and the OA group (100 mg kg⁻¹ OA only). Compared with the S.T group, OA administration significantly reduced clinical symptoms and weight loss, and the severity of diarrhea and intestinal structural damage was significantly alleviated, which was confirmed by a decrease in the diarrhea index (DI) and jejunal histological damage. In addition, in the infected jejunum, OA maintained the expression and localization of occludin, claudin-1 and ZO-1 to protect the jejunal barrier, thereby maintaining the integrity of the gut barrier. Finally, OA treatment not only reduced the levels of COX-2 and iNOS but also inhibited the secretion of pro-inflammatory cytokines, such as IL-1β, IL-6 and TNF-α. Furthermore, western blotting results showed that OA treatment significantly inhibited IκB phosphorylation and degradation in intestinal tissues and the nuclear translocation of p65, and OA also decreased the level of TLR4 and the activation of the MAPK pathway. To summarise, OA can maintain the intestinal tight junction barrier and prevent diarrhea caused by S.T. as well as reduce intestinal inflammation through the NF-κB and MAPK signaling pathways.

Antibacterial peptides (APMs) are a new type of antibacterial substance. The relationship between their structure and function remains indistinct; in particular, there is a lack of a definitive and fixed template for designing new antimicrobial peptides. Previous studies have shown that porcine Protegrin-1 (PG-1) exhibits considerable antimicrobial activity and cytotoxicity. In this study, to reduce cytotoxicity and increase cell selectivity, we designed histidine-rich peptides based on the sequence template RR(XY)₂X^DPGX(YX)₂RR-NH₂, where X represents I, W, V, and F. The results showed that the peptides form more β-hairpin structures in a lipid-rich environment that mimics cell membranes. Among them, the antimicrobial peptide HV2 showed strong antibacterial activity against Gram-negative strains and almost no toxicity to normal cells. The results of our analysis of its antibacterial mechanism showed that peptide HV2 acts on the bacterial cell membrane to increase its permeability, resulting in cell membrane disruption and death. Furthermore, peptide HV2 inhibited bacterial movement in a concentration-dependent manner and had a more robust anti-inflammatory effect by inhibiting the production of TNF-α. In summary, peptide HV2 exhibits high bactericidal activity and cell selectivity, making it a promising candidate for future use as an antibiotic.

The proposal of the gut–lung axis has profoundly reshaped our understanding of the mechanisms underlying respiratory diseases. As a crucial component of this axis, the gut microbiota plays a central role in pulmonary immune regulation through inter-organ communication mediated by metabolic products. However, a systematic integration of mechanisms explaining how gut microbes achieve precise cross-organ immune regulation remains elusive. Existing research predominantly focuses on descriptive observations, such as the association between early-life microbiota dysbiosis and an increased risk of asthma and chronic obstructive pulmonary disease (COPD), as well as the frequent occurrence of acute respiratory distress syndrome (ARDS) and pulmonary fibrosis (PF), often accompanied by gut microbiome disruption. This paper focuses on three key gut microbial metabolites—short-chain fatty acids (SCFAs), tryptophan metabolites, and polyamines (PAs)—to examine their roles in immune regulation, maintenance of barrier function, and modulation of metabolic signaling networks. Based on the latest experimental and clinical evidence, this study systematically elucidates how dysbiosis of the gut microbiota, a key component of the gut-lung axis, crosses physiological barriers to exacerbate pulmonary inflammation. Regarding intervention strategies, probiotics, fecal microbiota transplantation (FMT), and CRISPR-Cas systems have demonstrated significant therapeutic potential in restoring gut microbial balance. Finally, this paper outlines future research directions, emphasizing the need to further explore non-invasive microbial sampling techniques, molecular interaction mechanisms of the gut-lung axis, and personalized microbiome-based diagnostic and therapeutic strategies to provide new insights for the prevention and treatment of respiratory diseases involving gut microbiota.