Functionalization-Dependent Induction of Cellular Survival Pathways by CdSe Quantum Dots in Primary Normal Human Bronchial Epithelial Cells

Abstract

Quantum dots (QDs) are semiconductor nanocrystals exhibiting unique optical properties that can be exploited for many practical applications ranging from photovoltaics to biomedical imaging and drug delivery. A significant number of studies have alluded to the cytotoxic potential of these materials, implicating Cd-leaching as the causal factor. Here, we investigated the role of heavy metals in biological responses and the potential of CdSe-induced genotoxicity. Our results indicate that, while negatively charged QDs are relatively noncytotoxic compared to positively charged QDs, the same does not hold true for their genotoxic potential. Keeping QD core composition and size constant, 3 nm CdSe QD cores were functionalized with mercaptopropionic acid (MPA) or cysteamine (CYST), resulting in negatively or positively charged surfaces, respectively. CYST-QDs were found to induce significant cytotoxicity accompanied by DNA strand breakage. However, MPA-QDs, even in the absence of cytotoxicity and reactive oxygen species formation, also induced a high number of DNA strand breaks. QD-induced DNA damage was confirmed by identifying the presence of p53 binding protein 1 (53BP1) in the nuclei of exposed cells and subsequent diminishment of p53 from cytoplasmic cellular extracts. Further, high-throughput real-time PCR analyses revealed upregulation of DNA damage and response genes and several proinflammatory cytokine genes. Most importantly, transcriptome sequencing revealed upregulation of the metallothionein family of genes in cells exposed to MPA-QDs but not CYST-QDs. These data indicate that cytotoxic assays must be supplemented with genotoxic analyses to better understand cellular responses and the full impact of nanoparticle exposure when making recommendations with regard to risk assessment.

Quantum dots: bright and versatile in vitro and in vivo fluorescence imaging biosensors

“…Negatively charged QDs with MPA (methoxy propyl acetate) capping ligands showed to be relatively noncytotoxic compared to positively charged, cystamine capped, QDs. In contrast, genetical analysis revealed that MPA-QDs induced a high number of DNA-strand breaks 498 due to the upregulation of metallothioneins, which bind the Cd ions that leached from the core and thus reduce the ability for DNA repair. ROI can also induce nucleobase damage of DNA, which is attributed to the abstraction of hydrogen atoms from nucelobases and ribosyl groups.…”

Coating of Quantum Dots strongly defines their effect on lysosomal health and autophagy

“…[59] Specifically regarding QDs, studies have until now only reported that there is a lack of ROS induction by MPA-coated QDs. [34,35] Apart from ROS levels, we looked further into the impact of QD exposure on lysosomal health and autophagy. As a first step we evaluated the influence of QDs on the number and size of lysosomes.…”

The Comet Assay: Automated Imaging Methods for Improved Analysis and Reproducibility

“…Analysis of the DNA “comet” tail and nucleoid shape as well as the migration pattern allows for relative assessment of DNA damage. Our previous studies have implemented the comet assay for monitoring the genotoxic effects of cadmium selenide nanoparticles on normal human bronchial epithelial (NHBE) cells7.…”