Cellular Uptake of Nanoparticles versus Small Molecules: A Matter of Size

Abstract

The primary function of the cell membrane is to protect cells from their surroundings. This entails a strict regulation on controlling the exchange of matter between the cell and its environment. A key factor when considering potential biological applications of a particular chemical structure has to do with its ability to internalize into cells. Molecules that can readily cross cell membranes are frequently needed in biological research and medicine, since most therapeutic entities are designed to modulate intracellular components. However, the design of molecules that do not penetrate cells is also relevant toward, for example, extracellular contrast agents, which are most widely used in clinical diagnosis. Small molecules have occupied the forefront of biomedical research until recently, but the past few decades have seen an increasing use of larger chemical structures, such as proteins or nanoparticles, leading to unprecedented and often unexpectedly novel research. Great achievements have been made toward understanding the rules that govern cellular uptake, which show that cell internalization of molecules is largely affected by their size. For example, macromolecules such as proteins and nucleic acids are usually unable to internalize cells. Intriguingly, in the case of nanoparticles, larger sizes seem to facilitate internalization via endocytic pathways, through which the particles remain trapped in lysosomes and endosomes. In this Account, we aimed at presenting our personal view of how different chemical structures behave in terms of cell internalization due to their size, ranging from small drugs to large nanoparticles. We first introduce the properties of cell membranes and the main mechanisms involved in cellular uptake. We then discuss the cellular internalization of molecules, distinguishing between those with molecular weights below 1 kDa and biological macromolecules such as proteins and nucleic acids. In the last section, we review the biological behavior of nanoparticles, with a special emphasis on plasmonic nanoparticles, which feature a high potential in the biomedical field. For each group of chemical structures, we discuss the parameters affecting their cellular internalization but also strategies that can be applied to achieve the desired intracellular delivery. Particular attention is paid to approaches that allow conditional regulation of the cell internalization process using external triggers, such as activable cell penetrating peptides, due to the impact that these systems may have in drug delivery and sensing applications. The Account ends with a "Conclusions and Outlook" section, where general lessons and future directions toward further advancements are briefly presented.

Surface chemistry of gold nanoparticles for health-related applications

“…For AuNP-based nanomedicines, the size and surface charges are important factors to determine their cellular uptake efficiency. 110,111 Circulating AuNPs with an enhanced permeability and retention (EPR) effect benets their selective accumulation at tumour sites. Cellular uptake of AuNPs with strongly negatively charged surface is very hard.…”

Elucidating the mechanism of cyclodextrins in the treatment of Niemann-Pick Disease Type C using crosslinked 2-hydroxypropyl-β-cyclodextrin

“…Our data also showed that the cellular uptake was key for the activity of either types of CDs. The crosslinked CDs were mainly taken up via an energy-dependent process (likely endocytosis), which could be expected considering that their large molecular weight would hamper their diffusion through the cell membrane [52]. In contrast, the fact that monomeric HPβCD uptake was only reduced at 4 °C and not under energy depleting conditions would support the theory that a diffusive process might be involved [53].…”

A rational design of a cancer-specific and lysosome-targeted fluorescence nanoprobe for glutathione imaging in living cells

“…It has been well-documented that nanoprobes often accumulated in lysosomes via the interplay of size and surface charge: (1) nanostructure could be taken up by cells by the energy-dependent endocytosis pathway whose destination is lysosomes; 65,66 (2) the positively charged amino moiety enables the nanoparticles to enter into lysosomes. 45,58,67,68 To inspect the subcellular targeting ability of DTFN, HeLa cells pre-treated with DTFN were co-incubated with Lyso-Tracker Red and Mito-Tracker Red, respectively. As displayed in Fig.…”