Researchers have synthesized tannic acid-coated magnetic beads capable of extracting membrane vesicles called “exosomes” from biological fluids with 60% efficiency. This novel method will make it easier and faster to isolate exosomes from laboratory samples, while the chemical composition of the exosomes will help detect cancer in its early stages. The study supported by a grant from the Presidential Program of the Russian Science Foundation (RSF) was published in the Journal of Materials Chemistry B.
Cells in the human body “communicate” through exosomes — tiny membrane vesicles that are released into the intercellular space and carry proteins, fats, nucleic acids, and other molecules. Since the exosomes’ contents replicate the chemical composition of the cell they split off from, they can be used as molecular markers to identify various diseases. For example, the presence in exosomes of proteins and RNA typical of cancer cells is compelling evidence of incipient cancer.
However, exosome-based diagnostics is not yet widely used in clinical practice because these vesicles are as small as viruses and therefore difficult to isolate. A recently proposed approach uses magnetic beads to capture exosomes from biological samples, such as blood. The surface of the beads is coated with molecules, such as antibodies, that specifically bind to exosomes and hold them in place, and the bead-exosome complexes are then extracted from the biological sample using a magnet. However, this approach has been rather inefficient, prompting researchers to improve the beads’ ability to bind to exosomes.
A joint team from the Skolkovo Institute of Science and Technology, Lomonosov Moscow State University and the Kulakov National Medical Research Center for Obstetrics, Gynecology and Perinatology of the Russian Ministry of Health has improved magnetic beads by applying a layer of tannic acid onto their surface. The researchers synthesized beads of iron oxide and calcium carbonate (chalk and marble are the most common forms of the latter) and then coated their surface with a layer of polyvinylpyrrolidone and polyallylaminohydrochloride polymers or albumin, which specifically bind to exosomes. Finally, the resulting complexes were held in tannic acid which settled on the surface along with the other molecules.
The researchers placed the magnetic beads in a solution containing a predetermined amount of exosomes to assess the efficiency of binding, then removed the beads with a magnet and measured the remaining amount of membrane vesicles.