Mechanism Of Quantum Dots Facilitating Cu²⁺ Induced Toxicity Towards Hepatic L02 Cells And E.coli/B.subtilis Bacterial

Variou pollutants co-exist in environment and possible enter human body, some related antagonistic and additive as well as independent functions between these pollutants become possible. The current toxin evaluation normally focus on individual chemicals, which make the combined toxicity blind to people sometime, therefore the improved toxicity resulting from the synergistic function between individual toxins is worth noting.The Trojan horse technology has been developed recently to enhance some therapeutic drug uptake by smaller basic peptides.As we all know, many drug leads fail to make it into clinical trials due to the additional delivery obstacles arising from the less bioavailability and, the cellular membrane barrier even the blood-brain barrier (BBB). To deliver functional drug molecular into cells, normally methods of linking them to some receptor-specific Trojan-horse peptides, which, mediates the transcytosis of the "package" across the blood-brain barrier (BBB) and endocytosis across the plasma membrane. Such Trojan horse peptides can not only penetrate cells and tissues, but even release the carried drug in the cytoplasm and enhance the uptake of the cargos at nontoxic concentrations.Quantum dots (QDs) are luminescent nanoparticles with unique optical properties that have been exploited for molecular imaging and drug delivery. Their characteristic size-dependent variable fluorescence wavelength and surface properties are reasons for the wide applications. The surface-coating of functional groups and/or biomolecules on QDs may promote their interactions with other toxicants and present a potential risk to human body. The interaction of Cu2+with MSA-CdTe QDs has been exploited for trace Cu2+analysis. The nanoparticles might play the Trojan horse role by allowing more transition metals accumulate into living cells followed by the subsequent release of the metals leading to the higher toxicity.In this study, we focus on "Trojan horse" role of QDs. QDs (quantum dots) nanoparticles thus possible carry Cu2+causing much more cellular accumulation of Cu2+. the carrier role of MPA-CdTe QDs for Cu2+uptake was confirmed according to the following procedure using human hepatic L02 cells:Firstly, the 10 nm red shifts of QDs luminescence emission with addition of Cu2+implied the possible redox reaction between of QDs and Cu2+, and the emerged Cu element in the X-ray energy dispersive spectroscopy (EDS) data confirm the interaction of the two species. Then a small amount of MSA-CdTe QDs (2μg/ml) in a Cu2+ solution (2.5-20μg/ml) resulted in a higher cellular [Cu2+].The presence of a small amount of MPA-CdTe QDs in a Cu2+solutionresulted in a higher toxicity with up to 6-fold cell viability decrease, which was accompanied by cell morphology changes.A major mechanism of QDs enhanced toxicity of Cu2+was thus proposed as the adsorption of Cu2+ions on the negatively charged QDs surface; QDs served the role of a Trojan horse carrying Cu2+when it migrated into the cells.Considering Quantum dots (QDs) and Cu2+are known ROS (Reactive oxygen species) inducer, we investigated the combined oxidative stress and corresponding protective strategy using human hepatic L02 cells. The combined toxicity was then confirmed as ROS associated oxidative stress with up to 4-fold increase of the intracellular ROS level. NAC (N-acetylcysteine) also provided almost complete protection against the induced toxicity. Therefore the ROS associated oxidant injury are responsible for the QDs-Cu2+/Cu2+induced toxicity.The combined oxidative damage and corresponding toxicity mechanisms are keys to evaluate ecological hazards via co-exposure of QDs plus original contaminants. GST enzyme activity and Nrf2 expression in individual Cu2+ and QDs-Cu2+ treated L02 cells were investigated. Addition of QDs improved Cu2+-induced GST synthesis and Nrf2 transcription with maximum increase by 35%and 86%respectively. The increased toxicity could also be consisit with cell morphology changes, indicating QDs and/or Cu2+induced cytoprotective antioxidant enzyme GST via the Nrf2/ARE pathway.Quantum dots (QDs) represent a new kind of environmental pollutants. The combined toxicity of QDs with Cu2+is also concerned due to the increasing release of these two chemicals. E.coli, a common environmental model microbial, used to evaluated the possible synergistic toxicity and the regarding mechanism. It was observed that addition of MS A-CdTe QDs (5μg/mL) in a Cu2+solution (9-72μg/mL) resulted in a higher toxicity with up to 8-fold cell viability decrease and the elongated lag phase. The intracellular ROS levels were also improved by up to 400%. Meanwhile, accumulation of copper in the E.coli were correlated with the decreased cell viability, suggesting that a primary cause of QDs enhanced copper toxicity is through the production of superoxide anions and improved accumulation of copper in the cytoplasm.Also, the combined toxicity of QDs with Cu2+to B.subtilis, a known soil model bacterial, was investigated. It was observed that addition of MPA-CdSe QDs in a Cu2+solution resulted in a higher toxicity with up to 2-fold of cell viability decrease. The intracellular ROS levels were also improved by up to 500%compared that of Cu2+, which was consistent with induction of Antioxidant enzymes SOD and copper accumulation at higher concentrations (14 and 28μg/mL of Cu2+) in the case QDs-Cu2+. Implying the potential of QDs enhanced copper toxicity is possibly through the production of superoxide anions and improved copper cellular accumulation.TiO2 nanoparticles (NPs) possess the potential to co-exist with Cu2+in soil. The individual and combined toxicity of these two chemicals was evaluated here using Bacillus subtilis, a known soil model bacterial. Cu+(6.25～50μg/mL) alone exhibited toxicity to bacterial with cell viability andα-Amylase production decrease up to 51%and 85%, respectively. Addition of TiO2 (50 mg/mL) decreased Cu2+induced cell viability with up to 25%,while increased enzyme biosynthesis by 28 compared that of Cu+, and the growth rate and lag period didn't exhibit significant change. A primary cause of TiO2 increasing Cu2+ toxicity is assumed as·OH formation and the increased enzyme activity are considered arise from Cu2+ facilitating TiO2 degradation ability.