Differential Recognition of Nanoparticle Protein Corona and Modified Low-Density Lipoprotein by Macrophage Receptor with Collagenous Structure.

Key practical challenges such as understanding the immunological processes at the nanoscale and controlling the targeting and accumulation of nano-objects in vivo now further stimulate efforts to underpin phenomenological knowledge of the nanoscale with more mechanistic and molecular insight. Thus, the question as to what constitutes nanoscale biological identity continues to evolve. Certainly nanoparticles in contact with a complex biological milieu develop a biological identity, differing from the original nanomaterial, now referred to as the "biomolecular corona". However, this surface-adsorbed layer of biomolecules may in some circumstance lead to different forms of receptor-particle interactions not evident only from the identity of the surface-adsorbed biomolecules and hard to predict or detect by current physicochemical methods. Here we show that scavenger receptors may recognize complex as yet unidentified biomolecular surface layer motifs, even when no current physicochemical analysis is capable of doing so. For instance, fluorescently labeled SiO2 nanoparticles in a biological milieu are strongly recognized by the macrophage receptor with collagenous structure (MARCO) in even dense biological media (human serum) apparently using a form of binding with which most of the MARCO's known ligands ( e. g., LPS, modified LDL) fail to compete. Such observations may suggest the need for a much stronger emphasis on nanoscale receptor-corona and other biomolecular interaction studies if one wishes to unravel how biomolecular recognition drives outcomes in the nanoscale biological domain.

Human DMBT1-Derived Cell-Penetrating Peptides for Intracellular siRNA Delivery.

Small interfering RNA (siRNA) is a promising molecule for gene therapy, but its therapeutic administration remains problematic. Among the recently proposed vectors, cell-penetrating peptides show great promise in in vivo trials for siRNA delivery. Human protein DMBT1 (deleted in malignant brain tumor 1) is a pattern recognition molecule that interacts with polyanions and recognizes and aggregates bacteria. Taking advantage of these properties, we investigated whether specific synthetic DMBT1-derived peptides could be used to formulate nanoparticles for siRNA administration. Using an electrophoretic mobility shift assay and UV spectra, we identified two DMBT1 peptides that could encapsulate the siRNA with a self- and co-assembly mechanism. The complexes were stable for at least 2 hr in the presence of either fetal bovine serum (FBS) or RNase A, with peptide-dependent time span protection. ζ-potential, circular dichroism, dynamic light scattering, and transmission electron microscopy revealed negatively charged nanoparticles with an average diameter of 10-800 nm, depending on the reaction conditions, and a spherical or rice-shaped morphology, depending on the peptide and ß-helix conformation. We successfully transfected human MCF7 cells with fluorescein isothiocyanate (FITC)-DMBT1-peptide-Cy3-siRNA complexes. Finally, DMBT1 peptides encapsulating an siRNA targeting a fluorescent reporter gene showed efficient gene silencing in MCF7-recombinant cells. These results lay the foundation for a new research line to exploit DMBT1-peptide nanocomplexes for therapeutic siRNA delivery.

Mapping of Molecular Structure of the Nanoscale Surface in Bionanoparticles.

Characterizing the orientation of covalently conjugated proteins on nanoparticles, produced for in vitro and in vivo targeting, though an important feature of such a system, has proved challenging. Although extensive physicochemical characterization of targeting nanoparticles can be addressed in detail, relevant biological characterization of the nanointerface is crucial in order to select suitable nanomaterials for further in vitro or in vivo experiments. In this work, we adopt a methodology using antibody fragments (Fab) conjugated to gold nanoparticles (immunogold) to map the available epitopes on a transferrin grafted silica particle (SiO2-PEG8-Tf) as a proxy methodology to predict nanoparticle biological function, and therefore cellular receptor engagement. Data from the adopted method suggest that, on average, only ∼3.5% of proteins grafted on the SiO2-PEG8-Tf nanoparticle surface have a favorable orientation for recognition by the cellular receptor.

In situ characterization of nanoparticle biomolecular interactions in complex biological media by flow cytometry.

Nanoparticles interacting with, or derived from, living organisms are almost invariably coated in a variety of biomolecules presented in complex biological milieu, which produce a bio-interface or 'biomolecular corona' conferring a biological identity to the particle. Biomolecules at the surface of the nanoparticle-biomolecule complex present molecular fragments that may be recognized by receptors of cells or biological barriers, potentially engaging with different biological pathways. Here we demonstrate that using intense fluorescent reporter binders, in this case antibodies bound to quantum dots, we can map out the availability of such recognition fragments, allowing for a rapid and meaningful biological characterization. The application in microfluidic flow, in small detection volumes, with appropriate thresholding of the detection allows the study of even complex nanoparticles in realistic biological milieu, with the emerging prospect of making direct connection to conditions of cell level and in vivo experiments.