Proteomic Profiling of Pre- and Post-Surgery Saliva of Glioblastoma Patients II: A Preliminary Investigation of the Complementary Low Molecular Mass Fraction

This research aimed to analyze the proteomic profile of the low-molecular mass fraction of salivary pools from patients with glioblastoma IDH wild type (GBM) to disclose the small protein and peptide components, including protein fragments, cryptides, and tumor-associated peptides, still lacking specific information in the literature, to the best of our knowledge. This fraction, corresponding to the unretained proteome fraction, was obtained by pretreating the acid-soluble fraction of saliva through Filter-Aided Sample Preparation devices with a filter molecular cutoff of 10 kDa. The fraction was analyzed by LC-MS in its entire form, without trypsin pre-digestion, following a top–down approach. Data from the analysis of pre- and post-operative salivary pools from patients with newly diagnosed and recurrent GBM were compared and discussed with data obtained in our previous study on the complementary salivary proteome fraction > 10 kDa analyzed by a bottom–up approach and data from the literature. The results highlighted a panel of GBM-associated peptide fragments from different protein precursors, namely, ANXA1, CFL1, GLUL, PFN1, H2AC12, ACTB, and HBB, which are suggested for further exploration as potential diagnostic and prognostic biomarkers and clinical applications. These findings, although providing only preliminary results on a small scale, offer new insights into the molecular characteristics of GBM tumor and lay the groundwork for further investigations on a large scale using saliva liquid biopsy for biomarker discovery and validation. The aim is to advance precision medicine and improve clinical outcomes in GBM, one of the most aggressive brain tumors with a poor prognosis, for which early diagnosis and monitoring of treatment response remain significant challenges.