Plasma histone monomers as novel diagnostic markers in adult glioblastoma

Background: Glioblastoma (GB), the most aggressive primary brain tumor in adults, has a median survival of 12-18 months and lacks reliable minimally invasive biomarkers. Traditional diagnostics are limited by invasiveness and the inability to capture dynamic tumor changes. Circulating histones, reflecting tumor burden and epigenetic alterations, have emerged as potential liquid biopsy markers, but studies in adult GB are scarce compared to pediatric gliomas. The aim of this study was to characterize the plasma histone profile in adult GB patients versus healthy controls and evaluate its diagnostic potential. Methods: Plasma samples from 44 adult GB patients and 30 age-matched healthy controls were analyzed. Plasma levels of histones H3.1 and H3.3 were quantified by ELISA. Individual histones (H2A, H2B, H3, H4, macroH2A1.1, macroH2A1.2) and histone complexes (dimers/tetramers) were measured using an established imaging flow cytometry (ImageStreamX) multichannel detection approach. Results: GB patients exhibited significantly elevated plasma levels of individual histone monomers H2A, H3, macroH2A1.1, and macroH2A1.2, as well as markedly reduced H4 levels, compared to controls. Levels of histones H3.1- and H3.3 detected in plasma, showed no significant differences. MacroH2A1.2 levels negatively correlated with age in males. Conclusions: Adult GB displays a distinct circulating histone signature dominated by elevated free monomers rather than nucleosome complexes, contrasting with pediatric gliomas. These findings provide proof of concept for plasma histone monomers as novel minimally invasive diagnostic biomarkers in adult glioblastoma.