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PubMed1994

Anti-topoisomerase I antibodies in silica-associated systemic sclerosis. A model for autoimmunity.

OBJECTIVE: To determine the frequency and type of autoantibodies present in patients with systemic sclerosis (SSc) associated with an established environmental toxin. METHODS: Clinical data and sera were available from 14 men with silica-associated SSc who had developed SSc after at least 2 years of exposure to silica at work. Controls included 27 men with silicosis without SSc. Autoantibodies were measured by immunodiffusion, immunoblotting, and functional inhibition of topoisomerase I (topo I). RESULTS: Nine of the 14 patients with silica-associated SSc had anti-topo I antibodies. All anti-topo I antibodies in the patients with silica-associated SSc and in 14 anti-topo I-positive patients with idiopathic SSc were directed at an active site of topo I, or at least sterically inhibited its function. One patient with silica-associated SSc had anticentromere antibodies. Unexpectedly, 2 patients with silicosis who had no symptoms of a connective tissue disease had autoantibodies to Ro/SS-A and La/SS-B autoantigens. CONCLUSION: Anti-topo I antibodies are the predominant autoantibodies present in silica-associated SSc. The generation of anti-topo I antibodies in genetically susceptible individuals may depend partly on the patient's sex and on the site of organ involvement, and may be triggered by silica particles acting as an immune adjuvant.

Aged↗
PubMed2002

Probing the silica surfaces by red blood cells.

BACKGROUND: The polymorphic forms of silica (silicon dioxide; SiO(2)) interact with the cell membranes of many mammalian cells, including red blood cells (RBCs), causing hemolysis. The electrostatic factor, which is believed to be a major contributor to the silica-cell contact, might have potential interest for the study of cell surface properties. The surface properties of SiO(2) particles are also of interest. METHODS: Washed human RBCs interacted with the particles of highly dispersed fumed silica (Aerosil A-300) and silicas (nine samples) obtained from the initial A-300 by its dehydroxylation at various thermal conditions. Their light scatter (forward and side light scatter) in 0.01% silica solution was measured uninterruptedly within the first 5 min of the reaction by flow cytometry (flow erythrogram). The hemolytic effect of SiO(2) particles was evaluated by photometric measurement of hemoglobin in the supernatant 90 min after the reaction. RESULTS: Light scatter of affected RBCs and the degree of hemolysis revealed that the surface properties of SiO(2) particles had various effects on the RBCs. After thermal reduction of the surface hydroxyl groups, the membranotoxic effect of silica increased and then decreased. CONCLUSIONS: RBCs offer a convenient and informative model for examining the surface properties of silica.

Cell Membrane↗
PubMed1998

Capillary electrochromatography with novel stationary phases. I. Preparation and characterization of octadecylsulfonated silica.

A novel silica-based stationary phase was developed for use in capillary electrochromatography (CEC) at relatively high electroosmotic flow (EOF). The silica was first bonded with a relatively hydrophilic layer bearing strong sulfonic acid groups. To this charged polar sublayer, octadecyl functions were covalently attached to yield the nonpolar top layer. This novel stationary phase, referred to as octadecylsulfonated silica (ODSS), was packed in bare fused-silica capillaries or in capillaries with the same coating as the sublayer on the silica-based stationary phase. The resulting packed columns were evaluated in CEC using alkylbenzenes as the test model solutes. Good separations can be achieved in less than 8 min, much faster than when using a regular octadecyl silica capillary column. Due to the permanent negative charge provided by the sulfonated sublayer on both the capillary walls and the silica particles, the magnitude of the EOF remained more or less constant over a wide range of pH, and its magnitude can be conveniently varied by the applied voltage.

Benzene↗
PubMed2006

Applications of silica supports in affinity chromatography.

The combined use of silica-based chromatographic supports with immobilized affinity ligands can be used in many preparative and analytical applications. One example is the use of silica-based affinity columns in HPLC, giving rise to a method known as high-performance affinity chromatography (HPAC). This review discusses the role that silica has played in the development of affinity chromatography and HPAC and the applications of silica in these methods. This includes a discussion of the types of ligands that have been employed with silica and the methods by which these ligands have been immobilized. Various formats have also been presented for the use of silica in affinity chromatographic methods, including assays involving direct or indirect analyte detection, on-line or off-line affinity extraction, and chiral separations. The use of silica-based affinity columns in studies of biological systems based on zonal elution and frontal analysis methods will also be considered.

Adsorption↗
PubMed1999

Silica-induced generation of reactive oxygen species in Rat2 fibroblast: role in activation of mitogen-activated protein kinase.

Exposure to silica has been associated with progressive pulmonary inflammation and fibrosis. While the fibroblasts play an important role in the pathogenesis of silicosis, the direct interaction between silica and fibroblasts is poorly understood. We observed that silica particles stimulated intracellular ROS generation in Rat2 fibroblast, evidenced by DCFH oxidation. Silica-induced DCFH oxidation was inhibited by catalase and DPI, a flavoenzyme inhibitor. Additionally, the time course of elevation of the intracellular ROS was paralleled by the increases of MEK and ERK phosphorylation. Silica-induced ERK phosphorylation was also effectively attenuated by catalase and DPI. However, SOD enhanced the silica-induced ERK phosphorylation, indicating a role for H(2)O(2) in ERK activation. Furthermore, ERK and MEK phosphorylation are reproduced by H(2)O(2) treatment. Taken together, these results demonstrate that silica stimulates ROS production via flavoenzyme-dependent mechanism in Rat2 fibroblasts and the H(2)O(2), in turn, serves as a signal transduction element in activating MEK-ERK pathway.

Animals↗
PubMed1997

Aqueous Suspensions of Fumed Silica and Adsorption of Proteins

Thermally stimulated depolarization spectra of frozen aqueous suspensions of fumed silica show a dependence of relaxation processes on the concentration of silica (CSiO2) due to a change in the particle-particle interaction (their electrical double layers) and the concentration of bulk water (ice) with increasing CSiO2. A significant fraction of agglomerates of primary particle aggregates are not decomposed in aqueous suspensions of fumed silica. The thickness of an interfacial water layer perturbed by the silica surface or protein molecules was estimated from the dependence of 1H NMR signal intensity of unfrozen water on temperature below 273 K, separating the signals of water molecules weakly and strongly bound to the surface. Protein molecules adsorbed on fumed silica aggregates form hydrogen bonds with identical withSiOH or identical withSiO- groups by amino groups, e.g., H+NR from the zwitterion fragments. Aqueous suspensions of mechanochemically activated fumed silica do not lose protein adsorption ability during a long period in which the particles remain as microscaled agglomerates. According to AM1-SM1 calculations, complexes such as identical withSiO(H)···H+NRCOO- are stabilized in aqueous suspensions of silica and the protein desorption rate decreases with increasing molecular weight of proteins.

Journal Article↗
PubMed1997

Compounding Fumed Silicas into Polydimethylsiloxane: Bound Rubber and Final Aggregate Size

The properties of mechanically mixed suspensions of fumed silicas in polydimethylsiloxane (PDMS) were studied. The work focuses on two aspects: (i) Adsorption of PDMS onto silicas by means of the mechanical mixing of the bulk polymer and untreated or chemically modified fumed silicas. The silica-PDMS suspensions were completely dispersed or only swollen by a solvent, depending on the filler concentration, the silica surface chemistry, and the polymer molecular weight. The bound rubber content of the different preparations was determined by a weight difference technique and by carbon analysis of the samples and was compared with previously reported values in similar systems. (ii) The effect of the mechanical mixing on the final aggregate size of the silica and on the polymer molecular weight distribution. One PDMS and silicas of different surface area and surface chemistry were used. The final size of the aggregates after a long mixing time with the bulk polymer was approximately the same in all cases. Copyright 1997 Academic Press. Copyright 1997Academic Press

Journal Article↗
PubMed2000

Adsorption of Ethyl(hydroxyethyl)cellulose onto Silica Particles: The Role of Surface Chemistry and Temperature.

The adsorption characteristics of an ethyl(hydroxyethyl)cellulose (EHEC) polymer onto colloidal silica particles from aqueous solution have been investigated. The influence of solution temperature and the silica surface chemistry on EHEC adsorption isotherms and adsorbed layer thicknesses have been determined in an attempt to elucidate the mechanisms of adsorption. As the hydrophobicity of the silica particles are increased by physical and chemical treatment, the plateau EHEC adsorbed amount increased, while the corresponding adsorbed layer thickness decreased. The estimated free energy of adsorption (DeltaG(o)(ads)) was shown to be dependent on the silica surface chemistry, but did not correlate directly with silica's advancing water contact angle and suggests that EHEC adsorption is not directly controlled by hydrophobicity alone. As the solution temperature increased from 18 to 37 degrees C, the plateau coverage of EHEC increased while the layer thickness generally decreased, this concurred with a reduction in the solvency. For hydrophilic and dehydrated silica particles, DeltaG(o)(ads) decreased in magnitude with increasing temperature, whereas for chemically treated silica, DeltaG(o)(ads) increased with temperature. These findings are discussed with respect to the specific interactions between EHEC segments and surface sites, which control the adsorption mechanisms of cellulose polymers. Copyright 2000 Academic Press.

Journal Article↗
PubMed1993

Binding of the cationic dye, Janus green B, as a measure of the specific surface area of crystalline silica in aqueous suspension.

Twelve preparations of crystalline silica, with a wide range of particle sizes, were assayed by a new method, which measures surface adsorption of the cationic dye Janus green B to crystalline silica samples in a buffered aqueous suspension. The same samples were also assayed for total surface area by the Brunauer-Emmett-Teller (BET) method of surface adsorption of nitrogen gas. A strong linear correlation was found between the two methods of measurement (r = 0.977). Reproducible specific surface area measurements by the Janus green B adsorption method were made on 2-mg samples using ordinary visible wave-length spectrophotometric equipment, whereas the BET method necessitated sample sizes in excess of 100 mg and more specialized instrumentation. Five size-fractionated preparations from the same Min-U-Sil alpha-quartz sample showed an increase in BET surface area and Janus green B binding per unit weight with decreasing particle size. Among four standard alpha-quartz samples tested, Min-U-Sil 5 and F600 had the lowest specific surface areas, whereas DQ-12 and Chinese standard alpha-quartz had much higher surface areas. The synthetic silica preparations cristobalite and tridymite had intermediate surface areas. Binding by the cationic dye Janus green B is consistent with a surface charge mechanism and provides a useful new technique for the assessment of surface characteristics of crystalline silica samples. Its linear relationship to surface area suggests that the ratio of aqueous surface charge to surface area is constant for different crystalline silica preparations. Comparison of surface areas for different preparations of crystalline silica is important in understanding the relative activities of these preparations in studies on mechanisms of silicosis and silica-induced lung cancer.

Azo Compounds↗
PubMed1994

The inhibition of silica-induced lung inflammation by dexamethasone as measured by bronchoalveolar lavage fluid parameters and peroxynitrite-dependent chemiluminescence.

The inhalation of silica has been shown to produce a dramatic inflammatory and toxic response within the lungs of humans and laboratory animals. Currently, no effective treatment exists for workers who may have been exposed to the inhalation of silica. The objective of this study was to develop an animal model in which we could evaluate the effect that anti-inflammatory steroids have on the acute silica-induced pulmonary inflammatory response. Male Fischer 344 rats were pretreated with either dexamethasone (2 mg/kg) or saline vehicle (i.p.) on days 1, 3, and 5. On day 6, the animals from the two groups were then intratracheally instilled with either silica (20 mg/0.5 ml saline vehicle) or saline vehicle (0.5 ml). Twenty-four hours after the instillations in the non-steroid group, significant increases occurred in total protein, total number of cells, neutrophils, and lymphocytes recovered from the lungs of animals treated with silica compared to saline controls. Silica also caused dramatic increases in the luminol-dependent chemiluminescence (LDCL) of lung tissue and bronchoalveolar lavage (BAL) cells. The LDCL reaction was markedly decreased by either superoxide dismutase (SOD) or N-nitro-L-arginine methyl ester hydrochloride (L-NAME). SOD is involved in the enzymatic breakdown of superoxide anion, while L-NAME, a nitric oxide (NO) synthase inhibitor, prevents the formation of NO. When the superoxide anion and NO react, they form the highly oxidizing substance peroxynitrite. This study then implicates peroxynitrite as an agent which may be involved in the silica-induced oxidant lung injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Inhalation↗
PubMed2003

Silica accumulation in Triticum aestivum L. and Dactylis glomerata L.

The silica accumulation in orchard grass (Dactylis glomerata L.) and wheat (Triticum aestivum L.) has been studied in plant samples grown under defined conditions in a pot trial. The plant habit and the quantity of biomineralised silica within the selected Gramineae depend to a remarkable extent on the soil. The plants grew with different soil pH values and silica additives. By means of atomic absorption spectrometry, the silicon enrichment in different plant parts was determined. In dried plant parts the silica bodies can be well distinguished by variable pressure scanning electron microscopy in the back scattering mode. They are located in silica cells below the epidermis and in epidermal appendices (bristles, prickle hairs). The silica bodies showed a defined morphology, structure and composition which was elucidated by the combined performance of scanning electron microscopy in combination with X-ray spectroscopy, solid-state nuclear resonance, X-ray diffraction and Raman spectroscopy. The composition was near to stoichiometric SiO(2) (41 weight% silicon, 56 weight % oxygen), and the SiO(4/2)tetrahedra were arranged preferentially in three-dimensional networks; a smaller proportion was in chains and layers. The silica bodies with an overall amorphous structure contained crystalline precipitates, which could be indexed by alpha-quartz.

Dactylis↗
PubMed2003

Structure of silica in Equisetum arvense.

Silicified regions in the stem and leaf of the horsetail Equisetum arvensewere studied by scanning and transmission electron microscopy. The silica was present as a thin layer on the outer surface with variation in the size of this layer depending on the part investigated. There was a dense arrangement of silica spheres with some density fluctuations. A loose arrangement of silica particles with variation in their size was found beneath this dense arrangement suggesting the agglomeration of silica. An electron diffraction pattern showed the presence of amorphous silica, with the short range order being comparable to that of silica from other chemical sources. The medium range order shows the presence of silica with a high inner surface. SAXS measurements correlate with the particle size observed in TEM, and provide values for surface fractals. A new method of plasma ashing to remove the organics is also described.

Equisetum↗
PubMed2005

Silica structure in the spicules of the sponge Suberites domuncula.

Accumulation of silica in marine organisms such as diatoms and sponges has been widely reported. The proteins depositing silica in these organisms have been identified and its structure has also been described. The ultrastructure of silica has not been studied in detail, however. Herein we describe the structure of silica in the spicules of the sponge Suberites domuncula. Peroxide treatment was performed to remove the organic compounds, thereby enabling a better study of the silica. Methods used for the study included scanning and transmission electron microscopy. Electron diffraction enabled structural comparison with silica glass at the atomic level. Small-angle X-ray scattering (SAXS) of the spicules was also conducted and structure correlation between these methods attempted. At a lower magnification, spicule needles with a smooth outer surface were visible. Diffraction results suggested a network-like structure in the spicules. Silica particles of 3 nm diameter could be measured by SAXS.

Animals↗
PubMed2003

Neopterin as a new biomarker for the evaluation of occupational exposure to silica.

OBJECTIVES: Silica is one of the most documented workplace contaminants. Long-term occupational exposure to silica is associated with an increased risk for respiratory diseases such as silicosis, tuberculosis, chronic bronchitis, chronic obstructive pulmonary disease and lung cancer. Furthermore, a variety of immune-dysfunction-related diseases has been reported in silicotic individuals. Preliminary studies indicating enhanced levels of autoantibodies and several cytokines reflect an involvement of the immune system in the pathogenesis of silicosis and resulting complications. As an early and valuable biomarker of cellular immunity, neopterin is a low-molecular-mass compound belonging to the class of pteridines. It is produced by guanosine triphosphate via interferon-gamma, following the activation of T cells. The aim of the present study was to observe the alteration of neopterin in silica exposure, and also to show whether screening of neopterin levels may be of use for assessment of occupational exposure to silica. METHODS: In this study, serum and urinary neopterin levels, both in silica-exposed workers ( n=22) and healthy volunteers ( n=20), were investigated by ELISA, spectrophotometry and HPLC techniques. RESULTS: Serum neopterin levels of control and exposed groups were measured as 5.98+ or -0.44 and 7.86+ or -1.97 nmol/l, respectively ( P<0.05). Urinary neopterin levels were also increased in the exposed group: 97.60+ or -41.42 micromol/mol creatinine for controls and 165.59+/-78.20 micromol/mol creatinine for workers ( P<0.05). At the same time, the correlation between urinary neopterin levels, serum neopterin concentration and working years, smoking status, some complaints, and silica status in the working atmosphere were evaluated. CONCLUSIONS: Our findings suggest that the following up of neopterin levels may have diagnostic value in silica-related diseases such as silicosis. Moreover, its biological monitoring should be performed in workplaces for clinical diagnosis and prognosis.

Adult↗
PubMed2006

Effects of work related confounders on the association between silica exposure and lung cancer: a nested case-control study among Chinese miners and pottery workers.

OBJECTIVE: The role of silica in the causation of lung cancer is an ongoing debate. In order to explore whether observed association between silica exposure and lung cancer is confounded by exposure to other occupational carcinogens, we updated a previously nested case-control study among a cohort of male workers in 29 Chinese mines and factories on the basis of an extended follow-up. METHODS: Five hundred and eleven lung cancer cases and 1,879 matched controls were selected. Exposure to respirable silica as well as relevant occupational confounders were quantitatively assessed based on historical industrial hygiene data. The relationship between exposure to silica and lung cancer was analyzed by conditional logistic regression analysis adjusted for exposure to arsenic, polycyclic aromatic hydrocarbons (PAHs), radon, and smoking. RESULTS: In a crude analysis adjusted for smoking only, a significant trend of increasing risk of lung cancer with exposure to silica was found for tin, iron/copper miners, and pottery workers. But after adjustment for relevant occupational confounders, no relationship between silica and lung cancer can be observed. Instead, there is a significant association between lung cancer mortality and cumulative exposure to inorganic arsenic (OR = 1.86, 95% CI: 1.14, 3.04 for each mg/m(3)-year increase) and carcinogenic PAHs (OR = 1.35, 95% CI: 1.08, 1.69 for each 100 microg/m(3)-year increase). CONCLUSION: This analysis does not provide any evidence to show that exposure to silica causes lung cancer in the absence of confounding factors.

Air Pollutants, Occupational↗
PubMed1996

Hybrid selection with cDNA-silica.

A partial length ovalbumin cDNA-silica was produced using primer extension of (dT)18-silica with annealed partial ovalbumin RNA and reverse transcriptase. This cDNA-silica was used to test whether full-length ovalbumin RNA could be selectively purified in the presence of a large excess of other (mouse muscle) RNA. The cDNA-silica synthesized had minimally 60 pmol cDNA per gram silica and had a capacity for full-length ovalbumin RNA of minimally 38 micrograms/g. Even when other RNA was present in greater than 1000-fold excess, ovalbumin RNA was selectively retained by the cDNA-silica and was eluted in yields of 43% with an enrichment which varied over the range of 29-162-fold in various experiments. These results show that even rare RNAs can be selectively purified in high yield using cDNA-silica. The importance of these results to hybrid selection and subtractive library preparation is discussed.

Adenosine Triphosphate↗
PubMed1995

Silica-induced micronuclei and chromosomal aberrations in Chinese hamster lung (V79) and human lung (Hel 299) cells.

Silica is one of the most abundant and widely used mineral groups. A large number of workers are potentially exposed to one or more forms of silica. Therefore, the potential carcinogenic hazard of silica to the exposed workers is of great concern. This study examines the genotoxic potential of silica with the micronucleus and chromosomal aberration assays using cultured Chinese hamster lung fibroblasts (V79) and human embryonic lung (Hel 299) cells. One-day-old cultures were treated with two types of silica, Min-U-Sil 5 and Min-U-Sil 10, for 24 h at concentrations of 40, 80, 160 and 320 micrograms/cm2. Both Min-U-Sils at 160 and 320 micrograms/cm2 induced micronucleus formation in V79 and Hel 299 cells. In V79 cells, a significant increase in the micronucleus frequency was also found with 40 and 80 micrograms/cm2. However, the chromosomal aberration frequency was unaffected by either Min-U-Sil 5 or 10 treatment of V79 or Hel 299 cells. Results indicated that silica, in different particle sizes, was capable of inducing micronuclei but not chromosomal aberrations in cultured animal and human lung cells and suggested that V79 cells were relatively more sensitive to silica than Hel 299 cells.

Animals↗
PubMed2006

Impact of pore structural parameters on column performance and resolution of reversed-phase monolithic silica columns for peptides and proteins.

In this work, monolithic silica columns with the C4, C8, and C18 chemistry and having various macropore diameters and two different mesopore diameters are studied to access the differences in the column efficiency under isocratic elution conditions and the resolution of selected peptide pairs under reversed-phase gradient elution conditions for the separation of peptides and proteins. The columns with the pore structural characteristics that provided the most efficient separations are then employed to optimize the conditions of a gradient separation of a model mixture of peptides and proteins based on surface chemistry, gradient time, volumetric flow rate, and acetonitrile concentration. Both the mesopore and macropore diameters of the monolithic column are decisive for the column efficiency. As the diameter of the through-pores decreases, the column efficiency increases. The large set of mesopores studied with a nominal diameter of approximately 25 nm provided the most efficient column performance. The efficiency of the monolithic silica columns increase with decreasing n-alkyl chain length in the sequence of C18<C8<C4. The resolution of proteins and peptides by reversed-phase gradient liquid chromatography on n-octadecyl, n-octyl, and n-butyl bonded monolithic silica columns is optimized. The results obtained imply the use of acetonitrile concentration gradient up to 75% for n-octadecyl and n-octyl bonded monolithic silica columns, and the use of acetonitrile concentration gradient up to 85% for n-butyl bonded monolithic silica columns. With the respect to the gradient times and flow rates, the optimum conditions are the best with n-octyl and n-butyl bonded monolithic silica columns, where the range of optimum gradient times is up to approximately 30 min and mobile phase flow rates in the range of 0.5-1 ml/min. Consequently, the best performance towards peak resolution is obtained with n-octyl bonded monolithic silica column with the respect to low concentration of organic phase gradient, fast separations and low solvent consumptions due to low flow rates.

Chromatography, Liquid↗