Comparative analysis of exosome markers and extracellular vesicles between colorectal cancer and cancer -associated normal colonic mucosa

INTRODUCTION Exosomes are currently considered as the new biomarkers of colorectal cancer (CRC). Tetraspanins (CD9, CD63) belong to the well-known exosome markers, but can also be found on other subtypes of extracellular vesicles (EVs). OBJECTIVES The aim of this study was to estimate the expression level of exosome markers and EVs in CRC. PATIENTS AND METHODS The expression level of CD9 and CD63 antigens was evaluated by immunohistochemical staining in 109 patients diagnosed with CRC. Immunohistochemistry results were verified by nanoparticle tracking analysis (NTA), as well as the Western blot analysis and transmission electron microscopy. Exosomes isolation was performed on solid tissues. The immunohistochemical expression of both tetraspanins was compared with expression of cellular proliferation marker, Ki-67. RESULTS A higher expression level of exosome markers was observed in CRC compared with the normal colonic mucosa. The NTA revealed higher concentrations of nanoparticles in CRC tissues than in controls. There was a strong positive correlation between exosome markers and the Ki-67 antigen. The expression levels of both tetraspanins were different for lymph node staging (N stage). CONCLUSIONS Exosome markers and EVs were more pronounced in the CRC samples compared with controls. Immunohistochemical evaluation of tetraspanins reflects the results obtained by the NTA. Exocytosis appears to play an important role in the pathogenesis of CRC. To the best of our knowledge, such analysis was carried out for the first time.