Tandem enrichment of serum exosomes and exosomal RNA with titanium dioxide

Exosomes have great potential as biomarker carriers for disease diagnosis and prognosis. In recent years, exosomal RNA (exoRNA) has become a promising candidate for the early diagnosis and prognosis of can-cers, and its pathophysiological roles in various diseases have been revealed. For example, exosome-derived mRNAs, miRNAs, circRNAs, and lncRNAs function as signalling molecules to regulate tumour growth, angiogenesis, invasion, metastasis, and the response to chemotherapy. However, the isolation of exosomes and exoRNA with high quality and purity remains challenging due to the relatively small size of exosomes and the limited amount of RNA in exosomes. In this work, we developed a novel tandem enrichment method to isolate exoRNA from serum based on the specific interaction between titanium dioxide (TiO2) and the phosphate groups on the lipid bilayer of exosomes and of the exoRNA. TiO2-based RNA isolation was first demonstrated and optimized in HeLa cells. A total of 130.9 +/- 8.34 mu g of RNA was rapidly enriched from approximately 5 x 10 6 HeLa cells within 10 min. This was a 41.5% higher yield than that using a commercial Ultrapure RNA Kit. TiO2-based tandem enrichment of exoRNA was then performed using human serum, obtaining 64.53 +/- 3.41 ng of exoRNA from 500 mu L of human serum within 30 min. A total of 2,137,902 reads, including seven types of exoRNAs, were identified from the exosomes. This method is compatible with various downstream RNA processing techniques and does not use toxic or irritating reagents, such as phenol or chloroform, providing a simple, economical, rapid, and safe ap-proach for exoRNA extraction from biological samples.(c) 2023 Elsevier B.V. All rights reserved.

Automated summary

Exosomal RNA from serum has potential as a biomarker for early cancer diagnosis and prognosis, but isolating high-quality exosomes and exoRNA remains challenging. In this study, a novel tandem enrichment method using titanium dioxide was developed to isolate exoRNA from serum. This method provides a simple, economical, rapid, and safe approach for exoRNA extraction from biological samples.