Intestinal toxicity mechanisms of 6PPD and 6PPD-Q and their potential relevance to inflammatory bowel disease: network toxicology and experimental evidence.
TL;DR
It is demonstrated that 6PPD and 6PPD-Q induce intestinal injury, oxidative stress, and inflammatory activation in experimental models and affect molecular targets and pathways implicated in IBD.
Abstract
6PPD and its ozonation product 6PPD-quinone (6PPD-Q) are widespread tire-derived pollutants. This study combined network toxicology, clinical transcriptomics, molecular docking, and experimental validation to investigate their intestinal toxicity mechanisms and potential molecular relevance to inflammatory bowel disease (IBD), including Crohn's disease (CD) and ulcerative colitis (UC). Database screening identified 213 predicted targets for 6PPD and 165 for 6PPD-Q. Venn analysis identified 160 and 61 targets shared between 6PPD and CD- and UC-associated genes, respectively, whereas 112 and 105 targets were shared between 6PPD-Q and CD- and UC-associated genes, respectively. Network analyses showed that 6PPD-associated targets were mainly enriched in inflammatory signaling and oxidative stress-related pathways involving candidate hubs such as HIF1A, IL1B, IL6, and PTGS2. In comparison, 6PPD-Q-associated targets were enriched in kinase-signaling and mucosal-repair-related pathways involving HCK, KDR, LYN, EGFR, and MAPK14. Molecular docking predicted favorable binding poses between the compounds and the selected candidate targets, with docking scores ranging from -6.0 to -8.8 kcal/mol. Comparisons with clinical transcriptomic datasets further showed that several candidate targets were dysregulated in inflamed IBD tissues. In vivo, repeated exposure of C57BL/6 mice to 6PPD or 6PPD-Q for 40 days resulted in colon injury, reduced expression of intestinal tight-junction proteins, and increased expression of inflammatory mediators. In RAW264.7 macrophages, both compounds induced dose-dependent cytotoxicity, ROS production, and increased proinflammatory gene expression. These findings demonstrate that 6PPD and 6PPD-Q induce intestinal injury, oxidative stress, and inflammatory activation in experimental models and affect molecular targets and pathways implicated in IBD. Further studies using established experimental IBD models are warranted to determine whether these compounds exacerbate pre-existing intestinal inflammation or influence disease severity.