Differential NRF2 Methylation and PD-1 Expression in Normal Tissues of Colorectal Adenoma and Carcinoma across Sexes.

Purpose: Metachronous cancer following the cure of the primary cancer could be related with the tumor microenvironment. Recently it has been known that nuclear factor erythroid 2-related factor 2 (NRF2), a key transcription factor regulates immune checkpoint expression, including programmed cell death-ligand 1 (PD-L1), a well-known checkpoint molecule. The aim of this study was to investigate the roles of NRF2 and PD-1 in the tumor microenvironment using the normal colon tissue, with a focus on sex-specific differences.

Materials and methods: A total of 280 participants were enrolled including 66 healthy controls (HC), 109 patients with colorectal adenoma (AD), and 105 patients with colorectal cancer (CRC). Quantitative real-time polymerase chain reaction (PCR) for NRF2 and PD-1 and methylation-specific PCR for NRF2 were performed with normal mucosal tissue above the 20 cm from anal verge.

Results: NRF2 methylation levels were significantly lower in the AD and CRC groups compared to the HC in both sexes. PD-1 mRNA expression was significantly reduced in the AD and CRC groups compared to the HC group. In terms of sex males showed significantly lower PD-1 mRNA levels in the AD and CRC groups, whereas females displayed significantly higher PD-1 expression in the AD group but significantly lower levels in the CRC group. In conclusion there were significant differences in NRF2 methylation and PD-1 expression in the normal mucosal tissue among CRC, AD, and HC groups, suggesting that metachronous lesions might arise from this underlying tumor microenvironment.

Conclusions: Our results suggest that mRNA expressions of NRF2 and PD-L1 in the normal colon tissue may serve as early molecular markers in colorectal carcinogenesis with distinct sex-specific patterns.