Exosomes are cell-derived, phospholipid bilayer-enclosed vesicles that play important roles in intercellular interactions and regulate many biological processes. Accumulating evidence suggests that serum exosomes are potential biomarkers for the early diagnosis of cancer. To aid the downstream molecular analyses of tumour-secreted exosomes, purified exosomes are highly desirable. However, current techniques for exosome isolation are time-consuming and highly instrument-dependent, with limited specificity and recovery. Thus, rapid and efficient methods are strongly needed for both basic research and clinical applications. Here, we present a novel strategy for facile exosome isolation from human serum by taking advantage of the specific interaction of TiO₂ with the phosphate groups on the lipid bilayer of exosomes. Due to their simplicity and highly affinitive binding, model exosomes can be reversibly isolated with a high recovery (93.4%). Downstream characterization and proteome profiling reveal that high-quality exosomes can be obtained from human serum by this TiO₂-based isolation method in 5 min, which is a fraction of the time required for the commonly used ultracentrifugation method. We identified 59 significantly up-regulated proteins by comparing the serum exosomes of pancreatic cancer patients and healthy donors. In addition to the 30 proteins that were reported to be closely related to pancreatic cancer, we found an additional 29 proteins that had not previously been shown to be related to pancreatic cancer, indicating the potential of this novel method as a powerful tool for exosome isolation for health monitoring and disease diagnosis.

Significance: Human angiotensin-converting enzyme 2 (ACE2) is the most widely known entry receptor for SARS-CoV-2. The possible involvement of other cellular components in viral entry mechanisms remains unknown. Vimentin is expressed in human endothelial cells, binds to SARS-CoV-2-spike, and expedites SARS-CoV-2 entry. Treatment of lung ACE2/A549 carcinoma cells with purified vimentin or coculture of ACE2/A549 cells with HEK-293 cells expressing vimentin increased ACE2-dependent viral entry. CR3022 antibody blocked vimentin interaction with SARS-CoV-2-spike and inhibited SARS-CoV-2 entry. Vimentin could facilitate SARS-CoV-2 infection and contribute to vascular complications associated with COVID-19.

EED MS ² spectra were used to generate candidate topologies and guide selection of fragment(s) for MS ³ analysis. Isotoplogies indistinguishable at the MS ² level may be differentiated by CID-EED MS ³ analysis.