Olea europaea leaf extract attenuates temozolomide-induced senescence-associated secretion phenotype in Glioblastoma

INTRODUCTION: Objectives: The purpose of this study is to investigate the effect of Olea europaea leaf extract (OLE) on senescence and senescence-associated secretory phenotype (SASP) caused by temozolomide (TMZ) in Glioblastoma (GB).


METHODS: Materials and Methods: A Senescence β-Galactosidase assay and a colony formation assay were used to determine the effects of OLE, TMZ, and OLE+TMZ on cellular senescence and aggressiveness of GB cell lines T98G and U87MG. mRNA expression levels of P53, a senescence factor, IL-6, MMP-9, and NF-κB1 as SASP factors and Bcl-2 and Bax as senolytic markers were assessed using RT-qPCR. Cells were double-stained with Acridine Orange (AO) and Propidium Iodide (PI) to observe the cell morphology.

RESULTS: Results: TMZ increased the senescence rate of GB cells (p<0.001). Besides, OLE+TMZ reduced the proportion of senescent cells (p<0.001) and their capability to form colonies compared to TMZ-only treated cells. In addition, OLE+TMZ co-treatment elevated the mRNA expression levels of MMP-9, IL-6, NF-κB1, p53, and the Bax/Bcl-2 ratio compared to TMZ-only treatment. Especially in U87MG cells, involvement of OLE in TMZ treatments led to an increase of more than six times in the Bax/Bcl-2 ratio compared to TMZ-only, which resulted in the induction of the apoptosis-like morphological features (p<0.0001).

DISCUSSION AND CONCLUSION: Conclusion: Collectively, our findings showed the inhibitory effect of OLE on TMZ mediated SASP-factor production in GB and, accordingly, its potential contribution to elongate the time of recurrence.