Imaging of the internal chorion structure of rainbow trout Oncorhynchus mykiss live embryos and the distribution of quantum dots therein: Towards a deeper understanding of potential nanotoxicity

Abstract

Quantum dots (QDs) are extensively explored in biomedicine but the understanding of the mechanism underlying the uptake of colloidal QDs by biological systems is still poor. The knowledge of their distribution in tissues and their possibilities to cross biological barriers, especially at early stages of organism development, is also still limited. The potential risk of nanoparticle exposure to aquatic organisms is continuously questioned in ecotoxicology. To answer this question, we investigated the interaction (penetration and distribution) of CdSe/ZnS-COOH QDs with the chorion as well as their toxicity, cytotoxicity and genotoxicity in “eye-egg” stage embryos of rainbow trout Oncorhynchus mykiss. Results of the confocal fluorescence microscopy, fluorescence spectroscopy and 3D image analysis of O. mykiss chorion showed that it consists of three different layers and has a hexagonal pattern of pores distribution. The present study has revealed that both the accumulation and the distribution of QDs within the chorion are related to its structure. QDs are accumulated in pore canals of the external membrane of a fertilized O. mykiss egg. Our study has shown that QDs exposure induces bradycardia in O. mykiss and, as a result, cardiac toxicity in embryos. However, embryo survival rates as well as cytotoxicity and genotoxicity effects in the fish exposed to QDs for 1 day were not found to differ significantly from those in 4-day exposed fish. Results of the mathematical modelling showed the adsorption of QDs aggregates on the outer surface of the chorion leading to the oxygen-deficient microenvironment in embryos. These results represent an important step forward towards a better understanding of the mechanisms underlying QDs impacts on living organisms, which is essential for clarifying the protective properties of biological structures, and is valuable for the evaluation of nanotoxicity to fish at early development stages.