Quantum dots (QDs) are potentially advantageous tools for both diagnostics and therapeutics due to their light emitting characteristics. The impact of QDs on biological systems however, is not fully understood. The aim of this project therefore, was to investigate the interaction of a series of different surface modifies QDs with macrophages and their subsequent toxicity. CdTe/CdSe (core), ZnS (shell) QDs with either an organic, COOH or NH2 polyethylene glycol (PEG) surface coatings were used. Fluorescent COOH polystyrene beads (PBs) at (Ø) 20nm and 200nm were also studied. J774.A1 murine ‘macrophage-like' cells were treated for two hours with QDs (40nM) of PBs ($50μg.ml^{-1}$) in the presence of 10% FCS prior to assessment of cellular uptake via confocal microscopy and flow cytometry. COOH and $NH_{2}$ (PEG) QDs, as well as 20nm and 200nm PBs entered macrophages within 30 minutes, and were found to locate within endosomes, lysosomes and the mitochondria. T.E.M. also illustrated particles, including organic QDs, to be present inside J774.A1 cells within membrane- bound vesicles at two hours. Organic QDs were unable to be visualised via fixed cell confocal microscopy. Live cell confocal microscopy (without 10% FCS) did suggest however, that organic QDs entered cells in low quantities up to 30 minutes, after which fluorescence declined. Particle toxicity was determined over 48 hours via the MTT, LDH and GSH assays, as well as via assessment of their potential to produce the pro-inflammatory cytokine (TNF-α) and effect cytosolic $Ca^{2+}$ signalling in the J774.A1 cells. Organic QDs were found to be highly toxic at all time points and concentrations used. Both COOH and $NH_{2 }$ (PEG) QDs induced significant (p<0.0001) cytotoxicity (MTT and LDH assays) at 80nM after 48 hours, as well as significant (p<0.01) GSH depletion over 24 hours at all doses, as well as increasing the level of cytosolic $Ca^{2+}$ at 40nM when assessed over 30 minutes. Organic and NH2 (PEG) QDs were found to significantly increase TNF-α production after 24 hours at 80nM. The findings of this study demonstrate that QDs differ in their uptake by macrophages according to their surface coating, with the organic surface coated QDs being the most toxic. At sub-lethal concentrations, in the presence of 10% FCS, the COOH and $NH_{2}$ (PEG) QDs are taken up resulting in GSH depletion and modulated $Ca^{2+}$ signalling, with $NH_{2}$ (PEG) QDs and organic QDs only eliciting limited TNF-α production. Interestingly however, despite these observations, QD surface coating does not affect the intracellular fate of these NPs, with all of the different surface coated QDs observed to be present in endosomes, lysosomes and the mitochondria within J774.A1 macrophage cells. Therefore, in conclusion, the surface coating of QDs plays a significant role in their interaction with macrophages, their uptake and their subsequent toxicity.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:506385 |
| Date | January 2009 |
| Creators | Clift, Martin James David |
| Contributors | Stone, Vicki |
| Publisher | Edinburgh Napier University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://researchrepository.napier.ac.uk/Output/2557 |
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