Browsing by Author "Bravo, Denisse"
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- ItemBiomimetic, Mild Chemical Synthesis of CdTe-GSH Quantum Dots with Improved Biocompatibility(PUBLIC LIBRARY SCIENCE, 2012) Perez Donoso, Jose M.; Monras, Juan P.; Bravo, Denisse; Aguirre, Adam; Quest, Andrew F.; Osorio Roman, Igor O.; Aroca, Ricardo F.; Chasteen, Thomas G.; Vasquez, Claudio C.Multiple applications of nanotechnology, especially those involving highly fluorescent nanoparticles (NPs) or quantum dots (QDs) have stimulated the research to develop simple, rapid and environmentally friendly protocols for synthesizing NPs exhibiting novel properties and increased biocompatibility. In this study, a simple protocol for the chemical synthesis of glutathione (GSH)-capped CdTe QDs (CdTe-GSH) resembling conditions found in biological systems is described. Using only CdCl2, K2TeO3 and GSH, highly fluorescent QDs were obtained under pH, temperature, buffer and oxygen conditions that allow microorganisms growth. These CdTe-GSH NPs displayed similar size, chemical composition, absorbance and fluorescence spectra and quantum yields as QDs synthesized using more complicated and expensive methods. CdTe QDs were not freely incorporated into eukaryotic cells thus favoring their biocompatibility and potential applications in biomedicine. In addition, NPs entry was facilitated by lipofectamine, resulting in intracellular fluorescence and a slight increase in cell death by necrosis. Toxicity of the as prepared CdTe QDs was lower than that observed with QDs produced by other chemical methods, probably as consequence of decreased levels of Cd+2 and higher amounts of GSH. We present here the simplest, fast and economical method for CdTe QDs synthesis described to date. Also, this biomimetic protocol favors NPs biocompatibility and helps to establish the basis for the development of new, "greener" methods to synthesize cadmium-containing QDs.
- ItemEnhanced Glutathione Content Allows the In Vivo Synthesis of Fluorescent CdTe Nanoparticles by Escherichia coli(PUBLIC LIBRARY SCIENCE, 2012) Monras, Juan P.; Diaz, Victor; Bravo, Denisse; Montes, Rebecca A.; Chasteen, Thomas G.; Osorio Roman, Igor O.; Vasquez, Claudio C.; Perez Donoso, Jose M.The vast application of fluorescent semiconductor nanoparticles (NPs) or quantum dots (QDs) has prompted the development of new, cheap and safer methods that allow generating QDs with improved biocompatibility. In this context, green or biological QDs production represents a still unexplored area. This work reports the intracellular CdTe QDs biosynthesis in bacteria. Escherichia coli overexpressing the gshA gene, involved in glutathione (GSH) biosynthesis, was used to produce CdTe QDs. Cells exhibited higher reduced thiols, GSH and Cd/Te contents that allow generating fluorescent intracellular NP-like structures when exposed to CdCl2 and K2TeO3. Fluorescence microscopy revealed that QDs-producing cells accumulate defined structures of various colors, suggesting the production of differently-sized NPs. Purified fluorescent NPs exhibited structural and spectroscopic properties characteristic of CdTe QDs, as size and absorption/emission spectra. Elemental analysis confirmed that biosynthesized QDs were formed by Cd and Te with Cd/Te ratios expected for CdTe QDs. Finally, fluorescent properties of QDs-producing cells, such as color and intensity, were improved by temperature control and the use of reducing buffers.
- ItemHelicobacter pylori-Induced Loss of the Inhibitor-of-Apoptosis Protein Survivin Is Linked to Gastritis and Death of Human Gastric Cells(OXFORD UNIV PRESS INC, 2010) Valenzuela, Manuel; Perez Perez, Guillermo; Corvalan, Alejandro H.; Carrasco, Gonzalo; Urra, Hery; Bravo, Denisse; Toledo, Hector; Quest, Andrew F. G.Helicobacter pylori infects the human stomach and modifies signaling pathways that affect gastric epithelial cell proliferation and viability. Chronic exposure to this pathogen contributes to the onset of gastric atrophy, an early event in the genesis of gastric cancer associated with H. pylori infection. Susceptibility to H. pylori-induced cell death ultimately depends on the presence of protective host cell factors. Although expression of the inhibitor-of-apoptosis protein survivin in adults is frequently linked to the development of cancer, evidence indicating that the protein is present in normal gastric mucosa is also available. Thus, we investigated in human gastric tissue samples and cell lines whether H. pylori infection is linked to loss of survivin and increased cell death. Our results show that infection with H. pylori decreased survivin protein levels in the mucosa of patients with gastritis. Furthermore, survivin down-regulation correlated with apoptosis and loss of cell viability in gastrointestinal cells cocultured with different H. pylori strains. Finally, overexpression of survivin in human gastric cells was sufficient to reduce cell death after infection. Taken together, these findings implicate survivin as an important survival factor in the gastric mucosa of humans.