Bifidobacterium BX520 supplementation prevents neuroinflammation in necrotizing enterocolitis by inhibiting IDO1 through the gut-brain axis

Abstract

Abstract Background Necrotizing enterocolitis (NEC) is a severe gastrointestinal disease in premature infants. Among children who have survived NEC, one of the most important long-term complications observed is the occurrence of severe neurological dysfunction. However, the pathway leading to NEC-related neurological dysfunction remains unclear. Recent studies suggest that gut microbiota dysbiosis mediated kynurenine metabolism disorder may be an important etiological factor for central nervous system (CNS) injury in NEC. Indoleamine 2,3-dioxygenase 1 (IDO1) is the key enzyme in this metabolic pathway, which facilitates the conversion of tryptophan into kynurenine and its entry from the gut into the brain, thereby promoting the activation of microglia. Therefore, this study aims to explore the potential of preventing brain inflammation in NEC by modulating the IDO1-kynurenine axis through targeted intervention in the gut microbiota. Methods Metabolomic analysis and 16S rRNA sequencing were performed on fecal samples from 12 NEC patients and 12 healthy controls. Serum levels of indole metabolites were measured using ELISA. The NEC model was established using 4-day-old SD rats, which were subjected to asphyxia, cold treatment and LPS intervention. Quantitative PCR (qPCR) and Western blot were utilized to determine transcriptional and protein levels of relevant markers. Pathological changes in intestinal and brain tissues were assessed using Hematoxylin-eosin (HE) staining and Nissl staining. Results Metabolomic analysis revealed that the tryptophan-kynurenine metabolic pathway was abnormally activated in the fecal samples of NEC patients, while the level of indole-3-aldehyde (IAld) in serum was significantly reduced. In the NEC rat model, abnormal IDO1 activation was observed in the hippocampus, along with elevated mRNA and protein levels of the inflammatory factors IL-1β and NF-κB in hippocampal tissue. 16S rRNA sequencing revealed a significant reduction in the abundance of Bifidobacterium in NEC patients. Supplementation with Bifidobacterium BX520, which produces high levels of indole metabolites, significantly reduced weight loss and mortality in the NEC group. Additionally, HE staining showed that BX520 significantly reduced intestinal damage and inflammation in NEC. Furthermore, Bifidobacterium BX520 significantly activated ileal aryl hydrocarbon receptor(AHR) and increased the mRNA expression of tight junction proteins ZO1 and Occludin in the ileum. WB results showed that BX520 significantly inhibited the IDO1 protein level in the hippocampus of NEC rats and markedly reduced the expression of inflammatory factors IL-1β and NF-κB. Intervention on NEC with the IDO1 inhibitor 1-MT demonstrated that targeted inhibition of IDO1 could significantly decrease the levels of IL-1β and NF-κB proteins in the brain of NEC. Conclusion The supplementation of Bifidobacterium BX520, which produces high-yield indole metabolites, can improve the intestinal barrier by activating the intestinal AHR in NEC, and inhibit the expression of brain IDO1, thereby ameliorating the brain IL-1β and NF-κB inflammatory responses in NEC.