Quantum dot cellular uptake and toxicity in the developing brain: implications for use as imaging probes

Abstract

Nanometer-sized luminescent semiconductor quantum dots (QDs) have been utilized as imaging and therapeutic agents in a variety of disease settings, including diseases of the central nervous system. QDs have several advantages over traditional fluorescent probes including their small size (5–10 nm), tunable excitation and emission spectra, tailorable surface functionality, efficient photoluminescence, and robust photostability, which are ideal characteristics for in vivo imaging. Although QDs are promising imaging agents in brain-related applications, no systematic evaluation of QD behavior in brain-relevant conditions has yet been done. Therefore, we sought to investigate QD colloidal stability, cellular uptake, and toxicity in vitro, ex vivo, and in vivo in the brain environment. We found that QD behavior is highly dependent on surface functionality and that treatment of cultured organotypic whole hemisphere (OWH) slices with QDs results in dose-dependent toxicity and metallothionein increase, but no subsequent mRNA expression level changes in inflammatory cytokines or other oxidative stress. QDs coated with poly(ethylene glycol) (PEG) were protected from aggregation in neurophysiologically relevant fluids and in tissue, allowing for greater penetration. Importantly, QD behavior differed in cultured slices as compared to monolayer cell cultures, and behavior in cultured slices aligned more closely with that seen in vivo. Irrespective of surface chemistry and brain-relevant platform, non-aggregated QDs were primarily internalized by microglia in a region-dependent manner both in slices and in vivo upon systemic administration. This knowledge will help guide further engineering of candidate QD-based imaging probes for neurological application.

Nanoparticle‐microglial interaction in the ischemic brain is modulated by injury duration and treatment

“…OWH brain slice culturing techniques were prepared adapted from previously published methodology. 13 Slice preparation and culturing medias are provided in Supplemental Information. For glutathione and flow cytometry measurements, three brain slices were plated per membrane insert.…”

“…9 CdSe/CdS core-shell QDs with PEG-methoxy functionality were provided by Dr Vince Holmberg in the Department of Chemical Engineering at the UW, which were proven stable at physiological conditions for ex vivo application. 13 Nanoparticle characterization, multiple particle tracking (MPT) to measure nanoparticle diffusion, trajectory analysis 30 and application of the Amsden obstruction-scaling model to calculate effective pore sizes, including all assumptions, [31][32][33][34] are detailed in Supplemental Information.…”

“…Quantum dots (QDs) and poly(amidoamine) (PAMAM) dendrimer nanoparticles, among others, have shown accumulation within activated microglia. [9][10][11][12][13] While nanoparticles can facilitate and enhance drug transport in the brain, these effects are dependent on both nanoparticle characteristics and disease state, 14 requiring further screening and study.…”

“…We use ex vivo organotypic whole hemisphere (OWH) brain slices, which have emerged as a high-throughput platform for modeling disease processes and screening therapeutic platforms, including nanoparticles. 13,15,16 The ability to obtain multiple OWH slices from a single brain reduces biological variation and enables detailed investigation of disease environments or therapeutic efficacy. OWH slices also preserve functional relationships between neighboring cells and maintain 3D-cytoarchitecture.…”

<p>The Biological Activity Research of the Nano-Drugs Based on 5-Fluorouracil-Modified Quantum Dots</p>

“…[1][2][3][4][5] Although issues regarding the cytotoxicity of QDs have been raised, the surface of QDs can be modified to reduce their toxicity towards cells, while improving their water solubility and tumor cell targeting ability. 1,[6][7][8][9] The researchers have employed various biological molecules including peptides, antibodies, proteins, and DNA to coat the surface of QDs, and these modified QDs have intensely been studied as a new class of nanoparticle probe and drug carrier in diverse biomedical research areas, ranging from cellular fluorescence imaging and diagnostics in biomedicine to environmental monitoring for public health and security. [10][11][12][13][14][15] However, the major hurdle for in vivo applications of QDs based nanomaterials is their organellespecific targeted delivery.…”