Impact of Ambient Air Pollution on Colorectal Cancer Risk and Survival: Insights from a Prospective Cohort and Epigenetic Mendelian Randomization Study

Background: This study investigates the associations between air pollution and CRC risk and survival from an epigenomic perspective.

Methods: Using a newly developed Air Pollutants Exposure Score (APES), we utilized a prospective cohort study to investigate the associations of individual and combined air pollution exposures with CRC incidence and survival, followed by an up-to-date systematic review with meta-analysis to verify the associations. In epigenetic two-sample Mendelian randomization analyses, we examine the associations between genetically predicted DNA methylation related to air pollution and CRC risk. Further genetic colocalization and gene-environment interaction analyses provided different insights to disentangle pathogenic effects of air pollution via epigenetic modification.

Findings: During a median 12.97-year follow-up, 5,767 incident CRC cases among 428,632 participants free of baseline CRC and 533 deaths in 2,401 patients with CRC were documented in the UK Biobank. A higher APES score was associated with an increased CRC risk (HR,1.03, 95%CI,1.01-1.06; P=0.016) and poorer survival (HR,1.13, 95%CI,1.03-1.23; P=0.010), particularly among participants with insufficient physical activity and ever smokers (Pinteraction>0.05). A subsequent meta-analysis of seven observational studies, including UK Biobank data, corroborated the association between PM2.5 exposure (per 10 μg/m3 increment) and elevated CRC risk (RR,1.42, 95%CI,1.12-1.79; P=0.004; I2=90.8%). Genetically predicted methylation at PM2.5-related CpG site cg13835894 near TMBIM1/PNKD and cg16235962 near CXCR5, and NO2-related cg16947394 near TMEM110 were associated with an increased CRC risk. Gene-environment interaction analysis confirmed the epigenetic modification of aforementioned CpG sites with CRC risk and survival.

Interpretation: Our study suggests the association between air pollution and CRC incidence and survival, underscoring the possible modifying roles of epigenomic factors. Methylation may partly mediate pathogenic effects of air pollution on CRC, with annotation to epigenetic alterations in protein-coding genes TMBIM1/PNKD, CXCR5 and TMEM110.