Objectives: A growing number of studies have shown that methylation biomarkers play an important role in oncogenesis. This study aimed to explore the diagnostic role of neuropeptide Y (NPY) methylation in colorectal cancer (CRC).

Methods: mRNA and protein expression, methylation, survival benefits, and immune cell infiltration were analyzed using bioinformatics tools across all tumors from The Cancer Genome Atlas. NPY methylation in CRC was further validated in CRC tissues, fecal samples, and cell lines. Analyses of NPY methylation were performed using Sequenome EpiTYPER and quantitative PCR. Retrieval of NPY expression in cell lines was tested using real-time PCR and western blotting.

Results: Bioinformatic analysis showed that the methylation level of NPY increased in most carcinomas (P<0.05). Moreover, statistical correlations were observed between NPY transcriptional expression and CD4⁺ T cells, macrophages, and dendritic cells in colon cancer (P<0.05). Similar results were obtained for CD4⁺ T cells, neutrophils, and NPY in rectal cancer (P<0.05). Our results showed that NPY was hypermethylated in CRC tissues and fecal exfoliated cells (P<0.05). Fecal NPY methylation was observed in 82.5% sensitive for primary tumors, 46.3% for intestinal polyps (including adenomatous, serrated, and inflammatory polyps), and 23.4% of healthy controls. Overall, fecal NPY methylation was 76.6% specific. For cell lines, in vivo experiments demonstrated that 5-aza-2′-deoxycytidine downregulated the methylation of NPY and restored its mRNA level (P<0.05).

Conclusions: This study indicates that NPY is hypermethylated in CRC, and that NPY methylation in fecal DNA is a potential noninvasive diagnostic biomarker for Chinese patients with CRC.