How do CdSe/ZnS Quantum Dots Disrupt Actin Dynamics?

By Samudrapom DamReviewed by Susha Cheriyedath, M.Sc.Apr 23 2024

A paper recently published in the journal International Journal of Molecular Sciences investigated the impact of cadmium selenide/zinc sulfide (CdSe/ZnS) quantum dots (QDs) on in vitro actin dynamics.

Toxicity of QDs

QDs represent novel nanomaterials/semiconductor nanoparticles with different emergent characteristics like tunable optical properties, photobleaching resistance, and bright fluorescence. These attributes underscore their usefulness within the biomedical domain.

Moreover, QDs can be conjugated with ligands, profoundly impacting their stability and interaction dynamics with the environment. This specificity enhancement, achieved through coordination with biological agents like peptides and antibodies, positions QDs as promising candidates for drug delivery, especially in cancer therapy.

However, despite their immense potential, concerns regarding QDs' toxicity have hindered widespread adoption. Core material leakage is a primary cause of QD toxicity, necessitating the use of a shell to cover the core. This shell renders the QDs water-soluble and provides a surface for ligand coordination, thereby mitigating toxic effects.

Yet, QD toxicity is far more intricate than initially presumed. Multiple factors, including QD type, concentration, size, route of exposure, and functional groups, collectively determine their toxicity.

In particular, the toxicity of QDs and their nonspecific interactions with cellular proteins present significant challenges in biomedical research. Studies have been conducted to elucidate these interactions, revealing spontaneous binding of QDs with intracellular proteins like G-actin. This interaction disrupts G-actin's function by altering its secondary structure, impeding the formation of a normal actin cytoskeleton.

The Study

In this study, researchers investigated the adverse effects of QDs by focusing on actin depolymerization and polymerization, one of the most crucial cellular processes. Specifically, several biomolecular techniques were used to investigate the impact of CdSe/ZnS QDs on actin dynamics.

Water-soluble CdSe/ZnS QDs coated with a carboxylic acid end group were obtained, and fluorometer emission, energy dispersive X-Ray spectroscopy (EDS), and dynamic light scattering (DLS) were performed to characterize the QDs.

For the experiments, one mg Pyrene-labeled muscle actin was homogenized in 50 µL of de-ionized sterile water and kept on ice. This actin was divided into two vials, each containing 25 µL of homogenized G-actin.

To prepare the G-actin stock, the content of each vial was diluted with general actin buffer to achieve a 0.4 mg/mL working concentration. After two hours of incubation, the diluted vials were centrifuged at 14,000 rpm at 4 °C for 30 minutes and then placed on ice prior to use in experiments.

For the spin-down assays, a 250 µg aliquot of beta-muscle actin was resuspended in 250 µL of general actin buffer to create a one mg/mL muscle actin solution, which was left on ice for 30 minutes before experiments.

The researchers conducted actin polymerization assessment through spin-down and fluorometer-based assays, while actin depolymerization assessment was done using fluorometer-based assays. They also investigated the ability of QDs to bind to filamentous actin (F-actin) and induce actin bundling using spin-down assays.

Research Findings

The research findings revealed significant insights into the effects of CdSe/ZnS QDs on cellular processes, shedding light on their potential toxicity.

The emission peak of CdSe/ZnS QDs at 630 nm aligned with manufacturer specifications, with a hydrodynamic diameter of 23.88 nm. EDS confirmed the presence of key elements, including cadmium, selenide, zinc, sulfide, carbon, and oxygen. Interestingly, QDs exhibited a biphasic behavior: lower concentrations stimulated actin polymerization, while higher concentrations inhibited it.

In spin-down assays, low QD concentrations (0.1–0.5 µM) promoted actin polymerization, but concentrations exceeding 1 µM hindered the process. Similarly, fluorometer-based assays revealed that higher QD concentrations (20 nM) inhibited actin polymerization, while lower concentrations (2.5 nM) stimulated it. Notably, 5 nM QD concentration struck a balance between inhibition and stimulation.

Furthermore, QDs demonstrated a role in actin depolymerization, with higher concentrations inducing complete depolymerization. They also bound to filamentous actin (F-actin), leading to bundling at specific concentrations.

These findings unveil a novel mechanism whereby QDs disrupt cellular processes and exert toxicity, highlighting the need for further investigation into their impact on biological systems.

Journal Reference

Chand, A., Le, N., Kim, K. (2024). CdSe/ZnS Quantum Dots’ Impact on In Vitro Actin Dynamics. International Journal of Molecular Sciences, 25(8), 4179. https://doi.org/10.3390/ijms25084179, https://www.mdpi.com/1422-0067/25/8/4179

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