Editors' ChoiceNanomedicine

Now You See Me, Now You Don’t

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Science Translational Medicine  15 May 2013:
Vol. 5, Issue 185, pp. 185ec81
DOI: 10.1126/scitranslmed.3006520

For some clinical applications, such as immunotherapy, enhanced nanoparticle uptake by macrophages is desirable. For applications in which prolonged blood circulation half-life is required, such as chemotherapy, clearance by macrophages is unwanted. Although several nanoparticle properties such as size and charge have been evaluated as determinants of macrophage recognition and uptake, Chao and colleagues identify a specific mechanism by which macrophages recognize superparamagnetic iron oxide (SPIO) nanocrystals, which could potentially affect the design of drug-delivery particles and imaging agents.

Macrophages like to clear nanoparticles from the body; however, the mechanism remains unclear for different types of nanoparticles. Chao et al. determined that the macrophage scavenger receptor SR-A1 could bind and mediate uptake of SPIO nanoparticles. Computer modeling revealed that the recognition of SPIO particles by macrophage SR-A1 was specifically mediated by a strong complementary interaction between the SPIO Fe-OH groups and the positively charged lysines in the collagen-like domain of SR-A1. Furthermore, the recognition of SPIO by SR-A1 could be blocked by coating the particles with layers of the neutral polymer dextran.

These in vitro and in silico findings still need to be evaluated in vivo. Nevertheless, Chao et al. expand the understanding of how macrophages recognize nanoparticles, which can be incorporated in the design of such particles for therapeutic and imaging applications that either evade or target macrophages.

Y. Chao et al., Direct recognition of superparamagnetic nanocrystals by macrophage scavenger receptor SR-AI. ACS Nano, published online 30 April 2013 (10.1021/nn400769e). [Abstract]

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