Smart hydrogel particles: biomarker harvesting

The long and challenging effort to find blood-borne markers for cancer and other diseases may soon enter a new realm of success using a new nanoparticle that preferentially and rapidly removes small proteins and other molecules from blood while simultaneously protecting them from degradation.

This work, published in the journal Nano Letters, resulted from a cooperative effort between researchers at George Mason University and the CRO-IRCCS National Cancer Institute in Aviano, Italy. Lance Liotta, M.D., Ph.D., of George Mason University led this international team.

Researchers attempting to identify disease-related biomarkers in blood face two major problems, each of which the new polymer-based nanoparticles appear to overcome. One issue is that two proteins—albumin and immunoglobulin—account for 90 percent of the molecules in blood, whereas any potential biomarkers are likely to be present at only trace levels. Furthermore, many blood-borne molecules adhere to these two major proteins, so that any effort to remove these prevalent proteins to maximize an analytical signal from the trace substances is likely to also eliminate the potential biomarkers. In addition, many of the potential biomarkers are likely to be proteins, but enzymes present in blood begin degrading these proteins almost immediately after blood is removed from the body.

To solve these problems, the investigators used a copolymer of poly(N-isopropylacrylamide) (NIPAm) and acrylic acid (ACC) to create water-impregnated nanoparticles with pores of well-defined size. Water flows freely into these particles, carrying proteins and other small molecules into the polymer matrix. By controlling the pore size, the researchers were able to create particles that exclude the huge proteins albumin and immunoglobulin while admitting smaller proteins and other molecules. The ACC component acts as a negatively charged “bait” that attracts positively charged proteins, improving the particles’ performance.

Extensive tests with these nanoparticles demonstrated that protein capture is both efficient and rapid. Using both individual proteins and diluted human serum, the investigators showed that the particles remove the majority of positively charged small proteins from blood within 15 minutes. Additional tests showed that once entrapped in the particles, the proteins do not degrade. Once sequestration is complete, the particles are easily removed from blood samples via centrifugation. Their contents can then be analyzed using mass spectrometry.

Although these particles were designed to trap positively charged proteins, which predominate in nature, the researchers note that NIPAm can be copolymerized with other bait components to trap negatively charged or hydrophobic molecules, too. These investigators are preparing these nanoparticles, as well as ones that can specifically trap glycoproteins.

This work, which was supported in part by the NCI, is detailed in the paper “Smart hydrogel particles: biomarker harvesting: one-step affinity purification, size exclusion, and protection against degradation.” An abstract of this paper is available through PubMed.

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