Circulating eosinophil cell-free DNA as a noninvasive biomarker for perforated appendicitis in pediatric patients-a proof-of-concept study

Appendicitis is the most common condition necessitating emergency abdominal surgery. While most cases are localized, 20% are complicated and result in appendix perforation. The management of non-complicated appendicitis varies across different medical centers, encompassing both surgical and non-surgical options, whereas complicated appendicitis is predominantly managed surgically. Differentiating them poses a clinical challenge, especially in pediatric patients, crucial for guiding appropriate treatment strategies. Therefore, there is an unmet need for biomarkers to distinguish the two entities. Here we examined the utility of epigenetic liquid biopsies in appendicitis. We used DNA methylation markers specific to immune and gastrointestinal epithelial cells to assess the tissue origins of plasma cell-free DNA (cfDNA) in patients with appendicitis. Appendix epithelium cfDNA was not detected in plasma samples from children with appendicitis relative to patients with abdominal pain and controls. In contrast, neutrophil and regulatory T-cell cfDNA were elevated in appendicitis enhancing the specificity and sensitivity of appendicitis diagnosis beyond the information provided by neutrophil counts. Notably, eosinophil cfDNA was most significantly elevated in children with perforated compared with non-perforated appendicitis. This finding was cross-validated using a machine-learning approach. In conclusion, eosinophil cfDNA can serve as a non-invasive biomarker for diagnosing perforated appendicitis. Our aim was to analyze the methylome of human appendix epithelial cells and identify specific methylation markers unique to the appendix, which could be applied to cfDNA. We extracted genomic DNA from three different appendix epithelial cell preparations (n=3) and assessed their methylome using Illumina 450k BeadChip arrays.