To understand the effect of the commercial processing of diatomaceous earths (DEs) on their ultim... more To understand the effect of the commercial processing of diatomaceous earths (DEs) on their ultimate surface structure and potential toxicity, we investigated the influence of the industrial processing and the nature of the deposit. Two flux calcined specimens from different deposits, DE/1-FC and DE/2-FC, and the simply calcined sample DE/1-C, from the same deposit as DE/1-FC, were compared in both their bulk and their surface properties. X-ray diffraction (XRD) analysis in a heating chamber revealed the presence of cristobalite in all samples, more abundant on the flux calcined ones. The crystal lattice is probably imperfect, as the Rtransition, visible by XRD in DE/1-FC and DE/2-FC, is not detected by differential scanning calorimetry. Progressive etching with HF solutions suggests that most of the crystalline phase is at the core and not at the outer region of the samples. The combined use of spectroscopic (UV-vis and IR) and calorimetric techniques (heat of adsorption of water as a measure of hydrophilicity) reveals that DE/1-FC and DE/2-FC particles have an external layer of glass, absent in DE/1-C, where iron impurities act as network-forming and sodium ions as modifier species, with few patches of a hydrophobic phase, the latter relatable to a heated pure silica phase. When tested on a macrophage cell line (MH-S) in comparison with appropriate positive and negative controls (an active and an inactive quartz dust, respectively), only DE/1-C exhibited a cell damage and activation similar to that of active quartz (measured by lactate dehydrogenase release, peroxidation of membrane lipids and synthesis of NO). It is likely that the presence of a vitreous phase mitigates or even eliminates the cellular responses of silica in DE.
A well-defined silica nanoparticle model system was developed to study the effect of the size and... more A well-defined silica nanoparticle model system was developed to study the effect of the size and structure of aggregates on their membranolytic activity. The aggregates were stable and characterized using transmission electron microscopy, dynamic light scattering, nitrogen adsorption, small-angle X-ray scattering, infrared spectroscopy, and electron paramagnetic resonance. Human red blood cells were used for assessing the membranolytic activity of aggregates. We found a decreasing hemolytic activity for increasing hydrodynamic diameter of the nanoparticle aggregates, in contrast to trends observed for isolated particles. We propose here a qualitative model that considers the fractal structure of the aggregates and its influence on membrane deformation to explain these observations. The open structure of the aggregates means that only a limited number of primary particles, from which the aggregates are built up, are in contact with the cell membrane. The adhesion energy is thus expected to decrease resulting in an overall lowered driving force for membrane deformation. Hence, the hemolytic activity of aggregates, following an excessive deformation of the cell membrane, decreases as the aggregate size increases. Our results indicate that the aggregate size and structure determine the hemolytic activity of silica nanoparticle aggregates.
ABSTRACT The inhalation of crystalline silica dusts causes lung inflammation and the development ... more ABSTRACT The inhalation of crystalline silica dusts causes lung inflammation and the development of silicosis and lung cancer. Inhalation of amorphous silica dusts seems to elicit no adverse biological response. The large variability in toxicity elicited by quartz dusts having different origins may be assigned to differences in the surface structures of the particles. When a silica particle is in contact with body fluids, adsorption and surface reactions with endogenous molecules (e.g. proteins and pulmonary surfactant) take place. These reactions can modify the surface properties of the silica particles and consequently modulate the pathogenic responses elicited. In this work we study the adsorp- tion of bovine serum albumin (BSA) on different amorphous and crystalline silica dusts, the occurrence of conformational changes of the protein during the adsorption process, and the effect of some surface properties (hydrophilicity, presence at the surface of metal impurities and defects) on the amount of proteins adsorbed.
Free-radical chemistry as a means to evaluate lunar dust health hazard in view of future missions... more Free-radical chemistry as a means to evaluate lunar dust health hazard in view of future missions to the moon / Turci,
Surface Chemistry in Biomedical and Environmental Science
ABSTRACT The inhalation of crystalline silica dusts causes lung inflammation and the development ... more ABSTRACT The inhalation of crystalline silica dusts causes lung inflammation and the development of silicosis and lung cancer. Inhalation of amorphous silica dusts seems to elicit no adverse biological response. The large variability in toxicity elicited by quartz dusts having different origins may be assigned to differences in the surface structures of the particles. When a silica particle is in contact with body fluids, adsorption and surface reactions with endogenous molecules (e.g. proteins and pulmonary surfactant) take place. These reactions can modify the surface properties of the silica particles and consequently modulate the pathogenic responses elicited. In this work we study the adsorp- tion of bovine serum albumin (BSA) on different amorphous and crystalline silica dusts, the occurrence of conformational changes of the protein during the adsorption process, and the effect of some surface properties (hydrophilicity, presence at the surface of metal impurities and defects) on the amount of proteins adsorbed.
The effects of Stöber silica nanoparticles on neuronal survival, proliferation, and on the underl... more The effects of Stöber silica nanoparticles on neuronal survival, proliferation, and on the underlying perturbations in calcium homeostasis are investigated on the well‐differentiated neuronal cell line GT1‐7. The responses to nanoparticles 50 and 200 nm in diameter are compared. The 50‐nm silica affects neuronal survival/proliferation in a dose‐dependent way, by stimulating apoptotic processes. In contrast, the 200‐nm silica does not show any toxic effect even at relatively high concentrations (292 μg mL−1). To identify the mechanisms underlying these effects, the changes in intracellular calcium concentration elicited by acute and chronic administration of the two silica nanoparticles are analyzed. The 50‐nm silica at toxic concentrations generates huge and long‐lasting increases in intracellular calcium, whereas the 200‐nm silica only induces transient signals of much lower amplitude. These findings provide the first evidence that silica nanoparticles can induce toxic effects on n...
The release of free radicals from mechanically ground mineral dusts in aqueous suspensions has be... more The release of free radicals from mechanically ground mineral dusts in aqueous suspensions has been employed to predict the possible pathogenic potential of the dusts when inhaled. Two separate free radical-generating reactions have been considered: formation of the • OH radical from hydrogen peroxide via a "Fentonlike" reaction and of a carbon centered radical, following cleavage of a carbon-hydrogen bond. The particulate examined were: variously contaminated quartz dusts, whose well-documented pathogenicity varies from one to the other source; iron-and titanium-doped alumina pigments, prepared via a mechanochemical reaction, whose pathogenic potential is unknown, and hard metal mixtures, obtained from tungsten carbide (WC) and one metal dust, namely Fe, Co, or Ni, the cobalt mixture only being a renown hazardous material. Quartz obtained by grinding coarse particles in grinding chambers composed of steel, widia, corundum, and agate, retain some characteristics of the wall chamber material, which deeply affects its capability to generate radicals and may explain the variability of quartz hazard. Insertion of ions in the mechanochemically prepared pigments imparts to the particle suspected free radical-generating properties. Among the hard metal mixtures examined, the most active is the cobalt one.
In the course of studies of the interaction of proteins with TiO2 nanoparticles, we have investig... more In the course of studies of the interaction of proteins with TiO2 nanoparticles, we have investigated the role of the medium employed in cellular tests, by measuring the variation of ζ-potential vs pH in the range 2-9 and bovine serum albumin adsorption on TiO2 P25 in the presence of either HEPES or PBS as buffers, both mimicking the physiological pH, but with different chemical nature. The two buffers yield remarkably dissimilar surface charges and protein uptake, i.e., they impart different surface characteristics to the particles which could affect the contact with cells or tissues. This may account for dissimilar toxicological outcomes among in vitro tests and particularly between in vitro vs in vivo tests, considering the high amount of phosphate ions present in body fluids.
Amorphous silicas, opposite to crystalline polymorphs, have been regarded so far as nonpathogenic... more Amorphous silicas, opposite to crystalline polymorphs, have been regarded so far as nonpathogenic, but few studies have addressed the toxicity of the wide array of amorphous silica forms. With the advent of nanotoxicology, there has been a rising concern about the safety of silica nanoparticles to be used in nanomedicine. Here, we report a study on the toxicity of amorphous nanostructured silicas obtained with two different preparation procedures (pyrolysis vs. precipitation), the pyrogenic in two very different particle sizes, in order to assess the role of size and origin on surface properties and on the cell damage, oxidative stress, and inflammatory response elicited in murine alveolar macrophages. A quartz dust was employed as positive control and monodispersed silica spheres as negative control. Pyrogenic silicas were remarkably more active than the precipitated one as to cytotoxicity, reactive oxygen species production, lipid peroxidation, nitric oxide synthesis, and production of tumor necrosis factor-a, when compared both per mass and per unit surface. Between the two pyrogenic silicas, the larger one was the more active. Silanols density is the major difference in surface composition among the three silicas, being much larger than the precipitated one as indicated by joint calorimetric and infrared spectroscopy analysis. We assume here that full hydroxylation of a silica surface, with consequent stable coverage by water molecules, reduces/inhibits toxic behavior. The preparation route appears thus determinant in yielding potentially toxic materials, although the smallest size does not always correspond to an increased toxicity.
To understand the effect of the commercial processing of diatomaceous earths (DEs) on their ultim... more To understand the effect of the commercial processing of diatomaceous earths (DEs) on their ultimate surface structure and potential toxicity, we investigated the influence of the industrial processing and the nature of the deposit. Two flux calcined specimens from different deposits, DE/1-FC and DE/2-FC, and the simply calcined sample DE/1-C, from the same deposit as DE/1-FC, were compared in both their bulk and their surface properties. X-ray diffraction (XRD) analysis in a heating chamber revealed the presence of cristobalite in all samples, more abundant on the flux calcined ones. The crystal lattice is probably imperfect, as the Rtransition, visible by XRD in DE/1-FC and DE/2-FC, is not detected by differential scanning calorimetry. Progressive etching with HF solutions suggests that most of the crystalline phase is at the core and not at the outer region of the samples. The combined use of spectroscopic (UV-vis and IR) and calorimetric techniques (heat of adsorption of water as a measure of hydrophilicity) reveals that DE/1-FC and DE/2-FC particles have an external layer of glass, absent in DE/1-C, where iron impurities act as network-forming and sodium ions as modifier species, with few patches of a hydrophobic phase, the latter relatable to a heated pure silica phase. When tested on a macrophage cell line (MH-S) in comparison with appropriate positive and negative controls (an active and an inactive quartz dust, respectively), only DE/1-C exhibited a cell damage and activation similar to that of active quartz (measured by lactate dehydrogenase release, peroxidation of membrane lipids and synthesis of NO). It is likely that the presence of a vitreous phase mitigates or even eliminates the cellular responses of silica in DE.
A well-defined silica nanoparticle model system was developed to study the effect of the size and... more A well-defined silica nanoparticle model system was developed to study the effect of the size and structure of aggregates on their membranolytic activity. The aggregates were stable and characterized using transmission electron microscopy, dynamic light scattering, nitrogen adsorption, small-angle X-ray scattering, infrared spectroscopy, and electron paramagnetic resonance. Human red blood cells were used for assessing the membranolytic activity of aggregates. We found a decreasing hemolytic activity for increasing hydrodynamic diameter of the nanoparticle aggregates, in contrast to trends observed for isolated particles. We propose here a qualitative model that considers the fractal structure of the aggregates and its influence on membrane deformation to explain these observations. The open structure of the aggregates means that only a limited number of primary particles, from which the aggregates are built up, are in contact with the cell membrane. The adhesion energy is thus expected to decrease resulting in an overall lowered driving force for membrane deformation. Hence, the hemolytic activity of aggregates, following an excessive deformation of the cell membrane, decreases as the aggregate size increases. Our results indicate that the aggregate size and structure determine the hemolytic activity of silica nanoparticle aggregates.
ABSTRACT The inhalation of crystalline silica dusts causes lung inflammation and the development ... more ABSTRACT The inhalation of crystalline silica dusts causes lung inflammation and the development of silicosis and lung cancer. Inhalation of amorphous silica dusts seems to elicit no adverse biological response. The large variability in toxicity elicited by quartz dusts having different origins may be assigned to differences in the surface structures of the particles. When a silica particle is in contact with body fluids, adsorption and surface reactions with endogenous molecules (e.g. proteins and pulmonary surfactant) take place. These reactions can modify the surface properties of the silica particles and consequently modulate the pathogenic responses elicited. In this work we study the adsorp- tion of bovine serum albumin (BSA) on different amorphous and crystalline silica dusts, the occurrence of conformational changes of the protein during the adsorption process, and the effect of some surface properties (hydrophilicity, presence at the surface of metal impurities and defects) on the amount of proteins adsorbed.
Free-radical chemistry as a means to evaluate lunar dust health hazard in view of future missions... more Free-radical chemistry as a means to evaluate lunar dust health hazard in view of future missions to the moon / Turci,
Surface Chemistry in Biomedical and Environmental Science
ABSTRACT The inhalation of crystalline silica dusts causes lung inflammation and the development ... more ABSTRACT The inhalation of crystalline silica dusts causes lung inflammation and the development of silicosis and lung cancer. Inhalation of amorphous silica dusts seems to elicit no adverse biological response. The large variability in toxicity elicited by quartz dusts having different origins may be assigned to differences in the surface structures of the particles. When a silica particle is in contact with body fluids, adsorption and surface reactions with endogenous molecules (e.g. proteins and pulmonary surfactant) take place. These reactions can modify the surface properties of the silica particles and consequently modulate the pathogenic responses elicited. In this work we study the adsorp- tion of bovine serum albumin (BSA) on different amorphous and crystalline silica dusts, the occurrence of conformational changes of the protein during the adsorption process, and the effect of some surface properties (hydrophilicity, presence at the surface of metal impurities and defects) on the amount of proteins adsorbed.
The effects of Stöber silica nanoparticles on neuronal survival, proliferation, and on the underl... more The effects of Stöber silica nanoparticles on neuronal survival, proliferation, and on the underlying perturbations in calcium homeostasis are investigated on the well‐differentiated neuronal cell line GT1‐7. The responses to nanoparticles 50 and 200 nm in diameter are compared. The 50‐nm silica affects neuronal survival/proliferation in a dose‐dependent way, by stimulating apoptotic processes. In contrast, the 200‐nm silica does not show any toxic effect even at relatively high concentrations (292 μg mL−1). To identify the mechanisms underlying these effects, the changes in intracellular calcium concentration elicited by acute and chronic administration of the two silica nanoparticles are analyzed. The 50‐nm silica at toxic concentrations generates huge and long‐lasting increases in intracellular calcium, whereas the 200‐nm silica only induces transient signals of much lower amplitude. These findings provide the first evidence that silica nanoparticles can induce toxic effects on n...
The release of free radicals from mechanically ground mineral dusts in aqueous suspensions has be... more The release of free radicals from mechanically ground mineral dusts in aqueous suspensions has been employed to predict the possible pathogenic potential of the dusts when inhaled. Two separate free radical-generating reactions have been considered: formation of the • OH radical from hydrogen peroxide via a "Fentonlike" reaction and of a carbon centered radical, following cleavage of a carbon-hydrogen bond. The particulate examined were: variously contaminated quartz dusts, whose well-documented pathogenicity varies from one to the other source; iron-and titanium-doped alumina pigments, prepared via a mechanochemical reaction, whose pathogenic potential is unknown, and hard metal mixtures, obtained from tungsten carbide (WC) and one metal dust, namely Fe, Co, or Ni, the cobalt mixture only being a renown hazardous material. Quartz obtained by grinding coarse particles in grinding chambers composed of steel, widia, corundum, and agate, retain some characteristics of the wall chamber material, which deeply affects its capability to generate radicals and may explain the variability of quartz hazard. Insertion of ions in the mechanochemically prepared pigments imparts to the particle suspected free radical-generating properties. Among the hard metal mixtures examined, the most active is the cobalt one.
In the course of studies of the interaction of proteins with TiO2 nanoparticles, we have investig... more In the course of studies of the interaction of proteins with TiO2 nanoparticles, we have investigated the role of the medium employed in cellular tests, by measuring the variation of ζ-potential vs pH in the range 2-9 and bovine serum albumin adsorption on TiO2 P25 in the presence of either HEPES or PBS as buffers, both mimicking the physiological pH, but with different chemical nature. The two buffers yield remarkably dissimilar surface charges and protein uptake, i.e., they impart different surface characteristics to the particles which could affect the contact with cells or tissues. This may account for dissimilar toxicological outcomes among in vitro tests and particularly between in vitro vs in vivo tests, considering the high amount of phosphate ions present in body fluids.
Amorphous silicas, opposite to crystalline polymorphs, have been regarded so far as nonpathogenic... more Amorphous silicas, opposite to crystalline polymorphs, have been regarded so far as nonpathogenic, but few studies have addressed the toxicity of the wide array of amorphous silica forms. With the advent of nanotoxicology, there has been a rising concern about the safety of silica nanoparticles to be used in nanomedicine. Here, we report a study on the toxicity of amorphous nanostructured silicas obtained with two different preparation procedures (pyrolysis vs. precipitation), the pyrogenic in two very different particle sizes, in order to assess the role of size and origin on surface properties and on the cell damage, oxidative stress, and inflammatory response elicited in murine alveolar macrophages. A quartz dust was employed as positive control and monodispersed silica spheres as negative control. Pyrogenic silicas were remarkably more active than the precipitated one as to cytotoxicity, reactive oxygen species production, lipid peroxidation, nitric oxide synthesis, and production of tumor necrosis factor-a, when compared both per mass and per unit surface. Between the two pyrogenic silicas, the larger one was the more active. Silanols density is the major difference in surface composition among the three silicas, being much larger than the precipitated one as indicated by joint calorimetric and infrared spectroscopy analysis. We assume here that full hydroxylation of a silica surface, with consequent stable coverage by water molecules, reduces/inhibits toxic behavior. The preparation route appears thus determinant in yielding potentially toxic materials, although the smallest size does not always correspond to an increased toxicity.
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