Peritoneal Fluid‐Derived Small Extracellular Vesicle Proteins as Potential Biomarkers for Endometriosis: A Case–Control Study

ABSTRACT Objective To demonstrate the presence of peritoneal fluid (PF)‐derived small extracellular vesicles (sEVs) in endometriosis and control samples, to characterise their protein content and to define endometriosis‐specific biomarkers within the sEV proteome. Design Case–control experimental study. Setting Academic endometriosis centre. Sample PF samples from women between 18 and 49 years old ( n = 63). Methods sEVs were enriched using size exclusion chromatography (SEC), and characterised by nanoparticle tracking analysis (NTA), immunoblotting and mass spectrometry, according to surgically‐defined disease stage and cycle phase (control, rASRM stages I–II and III–IV endometriosis, in proliferative, secretory, and menstrual phases). FragPipe was used for protein identification. Main Outcome Measures Protein content of sEVs from control and endometriosis PF samples. Results sEVs were identified in PF of women by NTA, immunoblotting and mass spectrometry. Four proteins were significantly different across all samples: fructose‐bisphosphate aldolase A (ALDOA: 3.12‐fold increase in control samples, p = 0.0164), heat shock protein 90‐alpha (HSP90AA1: 2.14‐fold increase in control samples, p = 0.0245), collagen alpha‐1 (XV) chain (COL15A1: 1.83‐fold increase in control samples, p = 0.0421), and protein S100‐A10 (2.54‐fold increase in endometriosis samples, p = 0.0421). Conclusions PF‐derived sEVs differ between endometriosis and control patients. Concentrations vary regardless of cycle phase and disease stage, and this difference appears to be reflected in the proteomics analysis. However, higher sampling numbers are needed to confirm findings and functional assays to be performed delineate sEV function in endometriosis pathophysiology. Correlating PF‐derived sEV proteins with those in blood or urine could help further understand endometriosis and lead to the identification of biomarkers for diagnosis.