DMEM, or Opti-MEM, that is the Question: An Important Consideration for Extracellular Vesicle Isolation and their Downstream Applications

Abstract Serum-free synthetic media are frequently used as an alternative to extracellular vesicle-depleted serum containing media (EV-DEP) for EV production. However, the impact of this medium on EV biogenesis, release, and composition remains poorly understood. Here, we comprehensively characterised EV release by MDA-MB-231 or HEK-293T cells cultured in EV-DEP DMEM versus a serum-free synthetic medium, Opti-MEM. In Opti-MEM culture, cells released significantly more CD9- and CD63-positive EVs compared to EV-DEP DMEM. Proteomic analysis revealed that EVs from EV-DEP DMEM contained more histones and bovine proteins. Cells cultured in Opti-MEM released a substantially higher proportion of small-EVs derived from the sphingomyelinase-MVB pathway (60%) compared to EV-DEP DMEM (30%). Conversely, cells cultured in EV-DEP DMEM were more reliant upon the ROCK kinase pathway to release ectosomes (45 %) compared to OptiMEM (15 %). Where cells cultured in EV-DEP DMEM employed RabGTPase-dependent mechanisms for MVB-derived EV release (Rab3d, Rab27a, and Rab27b), cells cultured in Opti-MEM did not. Given that cells cultured in Opti-MEM vs EV-DEP DMEM produce EVs with different protein signatures from distinct molecular pathways, the choice of medium should be carefully considered when designing EV studies - particularly if they are to be used in therapeutic or immunological experiments. Competing Interest Statement The authors have declared no competing interest. Footnotes The abstract was not amended on the last resubmission to reflect the new data. The abstract now reads to inform on the new data in figure 4 and 5.