The tryptophan metabolite 3-hydroxyanthranilic acid alleviates hyperoxia-induced bronchopulmonary dysplasia via inhibiting ferroptosis.

Bronchopulmonary dysplasia (BPD) is a prevalent chronic respiratory condition in preterm infants with an increasing incidence, severely affecting their survival rate and quality of life. Exploring the underlying mechanisms of BPD helps to develop novel effective therapeutic strategies. In this study, integrated metabolomic analyses of tracheal aspirates (TAs) from BPD infants and non-BPD infants, along with lung tissues from hyperoxia-induced experimental BPD neonatal rats and control rats, demonstrated that BPD was associated with a significant reduction in 3-hydroxyanthranilic acid (3-HAA), which was confirmed to be partly caused by tryptophan-metabolizing enzyme disorders. In vivo and in vitro models were subsequently established to assess the efficacy and underlying mechanisms of 3-HAA in relation to BPD. Compared with the BPD group, 3-HAA nebulization improved lung development and suppressed inflammation in rats. Limited proteolysis-small molecule mapping (LiP-SMap) proteomic analysis revealed the involvement of the ferroptosis pathway in the underlying mechanism by which 3-HAA alleviated hyperoxia-induced BPD injury. Ferroptosis was identified by detecting Fe(2+) levels, malondialdehyde (MDA), 4-HNE, total aldehydes, mitochondrial morphology, ferroptosis-associated protein and mRNA expression, and this dysregulation was indeed ameliorated by 3-HAA nebulization in vivo. Furthermore, a combination of LiP-SMap, molecular docking, SPR and Co-IP analyses confirmed that 3-HAA can bind directly to FTH1 and disrupt the nuclear receptor coactivator 4 (NCOA4)-FTH1 interaction. In conclusion, our study is the first to reveal that BPD is linked to the reduction of 3-HAA, and 3-HAA could inhibit the ferroptosis pathway by targeting FTH1, thereby alleviating hyperoxia-induced injury in rats and alveolar type II epithelial cells, highlighting the potential of targeting 3-HAA and ferroptosis for clinical applications in BPD.