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PubMed2005

Radiologically recognized pleural changes in nonpneumoconiotic silica-exposed coal miners.

OBJECTIVES: Whether nonpneumoconiotic silica-exposed coal miners develop radiologically recognizable pleural changes was studied. METHODS: In a retrospective follow-up study, the oldest and the most recent chest X-rays of 765 workers with a profusion category lower than 1/0 according to the International Labour Office were read. RESULTS: Altogether 720 (94.1%) workers had no abnormalities, and 45 (5.9%) showed some pleural alteration in the first X-ray. In 43 (6%) of the 720 with no initial abnormalities, some pleural change was detected in the last X-ray. There was a statistical difference (P = 0.022) according to silica exposure category [low: 5 (2.4%); medium: 8 (6%); high: 30 (8%)]. The relative risk for any pleural alteration was significantly increased in relation to the silica-exposed group [medium: odds ratio (OR) 5.72, 95% confidence interval (95% CI) 1.4-23.5, P = 0.016; high: OR 7.62, 95% CI 2.1-27.2, P = 0.002] and to rib alterations (OR 3.74, 95% CI 1.4-9.7, P = 0.007). In 19 (2.6%) workers with no alterations initially, a costophrenic sinus alteration was detected later. Again the silica exposure categories [low: 1 (0.5%); medium: 3 (2.2%); high: 15 (4.2%)] differed significantly (P = 0.033). The relative risk of costophrenic sinus obliteration was significantly increased in relation to the silica-exposed group [medium: OR 8.59, 95% CI 0.7-113, P = 0.102; high: OR 16.44, 95% CI 1.5-177, P = 0.021]. The appearance of two costophrenic sinus obliterations and the disappearance of four were detected in the last chest X-ray of the 45 workers with some pleural alteration initially. CONCLUSIONS: Costophrenic sinus obliteration can be found in nonpneumoconiotic silica-exposed coal miners and seems to be associated with silica exposure intensity.

Adult↗
PubMedDate not supplied

Repair strength of etched vs silica-coated metal-ceramic and all-ceramic restorations.

The purpose of this in vitro study was to examine shear bond strengths of composite resin to metal-exposed porcelain-fused-to-metal (PFM) and all-ceramic restorations after silica coating or etching with 5% hydrofluoric acid (HF). Specimens were fabricated for each of the following groups: two all-ceramic materials [a feldspathic porcelain (Vita Mark II) and a leucite-reinforced glass-ceramic (IPS Empress)], and one noble metal-ceramic (Orplid Keramik I alloy; Vita VMK 68 N felspathic veneer ceramic). These groups were repaired with resin composites after different pretreatment methods. In one metal-ceramic subgroup the surface exhibited a 50% metal and 50% ceramic exposure. In the silica-coating groups, the specimen surfaces were air abraded with silica acid-modified Al2O3 (CoJet Sand) and treated corresponding to the porcelain repair with resin composite. For control groups, the surfaces were etched with 5% HF for 60 seconds and treated in the same way as the silica-coated groups. After 24 hours of storage (distilled water, 37 degrees C) and an additional 24 hours of thermocycling (1150 x 5 degrees C/55 degrees C) the specimens were debonded using a shear bond strength test (n = 15). In all groups the silica coat repair achieved equal or significantly higher bond strengths than did the etching technique (p < 0.05, Mann-Whitney U test). In the metal-exposed group, the mean bond strength increased from 7.3 MPa to 16.3 MPa following the silica-coat repair. Results indicated that silica coating represents a suitable treatment for the intraoral repair of the materials tested in the present study.

Acid Etching, Dental↗
PubMedDate not supplied

Silica and renal diseases: no longer a problem in the 21st century?

Silicosis and other occupational diseases are still important even in the most developed countries. In fact, at present, silica exposure may be a risk factor for human health not only for workers but also for consumers. Furthermore, this exposure is associated with many other different disorders besides pulmonary silicosis, such as progressive systemic sclerosis, systemic lupus erythematosus, rheumatoid arthritis, dermatomyositis, glomerulonephritis and vasculitis. The relationships between these silica-related diseases need to be clarified, but pathogenic responses to silica are likely to be mediated by interaction of silica particles with the immune system, mainly by activation of macrophages. As regards renal pathology, there is no single specific clinical or laboratory finding of silica-induced nephropathy: renal involvement may occur as a toxic effect or in a context of autoimmune disease, and silica damage may act as an additive factor on an existing, well-established renal disease. An occupational history must be obtained for all renal patients, checking particularly for exposure to silica, heavy metals, and solvents.

Humans↗
PubMed1992

Instillation of chemotactic factor to silica-injected lungs lowers interstitial particle content and reduces pulmonary fibrosis.

Silica-induced pulmonary fibrosis usually follows exposure to increased levels of this particulate and its retention in interstitial macrophages of the lung. It is suggested that accelerated clearance of particles from the pulmonary interstitium may ameliorate subsequent fibrosis. To test this hypothesis, one group of mice received 2-mg intratracheal (IT) silica; some particles were phagocytized and cleared during the subsequent inflammatory response, other particles were translocated across the epithelium to reach interstitial macrophages by 2 weeks. These mice later showed increased fibroblast growth, a doubling of lung collagen levels and large silicotic nodules by 16 weeks when much of the silica was still present in the lung. A second group of mice received IT silica, then 2 and 3 weeks later received IT injections of N-formyl-L-methionyl-leucyl-phenylalanine (FMLP), a leukocyte chemoattractant. Subsequently, a significant increase in inflammatory cells was seen and silica was observed mostly in phagocytes within the alveolar spaces. Few interstitial particles were found at 4 weeks, and extensive fibrosis did not develop by 16 weeks; only a few small nodules were seen and little silica was present in the lung. The results indicate that clearance of interstitial particles by a controlled inflammatory response is possible, and that removal of silica from the interstitium decreases the fibrotic response.

Animals↗
PubMed2002

[Study on the silica-induced cytotoxicity and hprt gene mutagenisis in rat lung fibroblasts and alveolar type II epithelial cells].

OBJECTIVE: To explore the differences of the silica-induced inhibition on cellular proliferation and hprt gene mutagenesis between lung fibroblasts and alveolar type II cells. METHODS: The proliferation inhibitive cytotoxicity was detected by MTT (3-[4,5-Dimethylthiazolzyl]-2,5-Diphenyl Tetrazolium Bromide) colorimetric method. Mutation in the hprt gene was screened by culture in the presence of the toxic purine analog, 6-thioguanine (6-TG). RESULTS: Under the same circumstances of silica exposure, alveolar type II cells was more sensitive than lung fibroblasts for proliferation inhibition. The median proliferation inhibition concentration (IC50) of silica on epithelial was 140 micrograms/cm2, whereas IC50 of silica on fibroblasts was 282 micrograms/cm2. At the same doses of silica, the hprt gene mutation frequency in type II cells (84.2 x 10(-6))-156.6 x 10(-6) was statistically higher than that in fibroblasts (67.6 x 10(-6)-114.3 x 10(-6), P < 0.05). CONCLUSION: There were significant differences of both silica-induced cell proliferation inhibition and hprt gene mutation between rat lung fibroblasts and type II epithelial cells. In vitro, cultured rat alveolar type II cells were more sensitive in cytotoxicity and hprt gene mutagenesis to silica dust than lung fibroblasts were.

Animals↗
PubMed2004

[In-situ sol-gel preparation of nano silica porous layer capillary columns and their applications in gas chromatography].

A new method is described to prepare nano silica porous layer columns by using in-situ sol-gel synthesis technology. By the interaction of ethyl acetate and water glass solution, the nano silica was synthesized on the inner surface of fused silica capillary. The influence of reaction conditions on the morphology surface area, pore volume and pore size was investigated. The experimental results demonstrate that when the mole ratio of ethyl acetate to silica was 0.82, the particle size of the superfine silica powder was in the range of 25-50 nm, the BET specific surface area was 420 m2/g, and the total pore volume was 0.68 cm3/g. The nano silica porous layer on the inner surface of fused silica capillary was formed by bonding reactions through cross-linked polysiloxane chains, and deactivated by 1 g/L KCl. The column shows sufficient selectivity, stable retention performance, proper resistance to water, good reproducibility, and unique activity. The column is suitable for the analysis of chlorofluorocarbons, halohydrocarbons, sulfur compounds, and light hydrocarbons C1-C4.

Chlorofluorocarbons↗
PubMed2005

[Effects of taurine on the expression of nitric oxide synthase in lung of rats exposed to silica].

OBJECTIVE: To evaluate the effects of taurine in diet on the expression of inducible nitric oxide synthase (iNOS) in rat lung induced by silica. METHODS: Wistar rats were established by direct tracheal instillation of silica into rat lungs exposed surgically, and the animals of taurine-treated group were silica-instilled with a diet containing taurine. The taurine concentration of serum was analyzed by means of HPLC. The expression of iNOS protein in paraffin-embedded lung sections with Streptavidin/peroxidase (SP) immunohistochemistry on tissue microarray was measured by Image-Pro Plus. RESULTS: The concentration of taurine in serum of taurine-treated group was significantly higher than those in saline-treated and silica-treated groups (P < 0.05). The activities of total NOS and iNOS in BALF supernatant and iNOS positive area percentage of rat lung in silica-treated group were at the peak on 14th day, which were 1.84 U/ml, 1.12 U/ml and 5.42% more respectively than those in saline-treated group (P < 0.05). There were no significant differences between taurine-treated group and silica-treated group in total NOS and iNOS activities of BALF supernatant, and iNOS positive area of the lung (P > 0.05). CONCLUSION: Treatment with taurine hardly influences on the increase in expression of nitric oxide synthase in rat lung induced by silica dust.

Animals↗
PubMed1991

Silica and lung cancer: a controversial issue.

The role of crystalline silica in lung cancer has long been the subject of controversy. In this article, we review the main experimental and epidemiological studies dealing with this problem. Some evidence for a genotoxic potential of crystalline silica has been obtained in the rare in vitro studies published to date. In vivo studies have shown that crystalline silica is carcinogenic in the rat; the tumour types appear to vary according to the route of administration. In addition, an association between carcinogenic and fibrogenic potency has been observed in various animal species exposed to crystalline silica. An excess of lung cancer related to occupational exposure to crystalline silica is reported in many epidemiological studies, regardless of the presence of silicosis. However, most of these studies are difficult to interpret because they do not correctly take into account associated carcinogens such as tobacco smoke and other occupational carcinogens. An excess of lung cancer is generally reported in studies based on silicosis registers. Overall, experimental and human studies suggest an association between exposure to crystalline silica and an excess of pulmonary malignancies. Although the data available are not sufficient to establish a clear-cut causal relationship in humans, an association between the onset of pneumoconiosis and pulmonary malignancies is probable. In contrast, experimental observations have given rise to a pathophysiological mechanism that might account for a putative carcinogenic potency of crystalline silica.

Animals↗
PubMed2006

[Determination and analysis of silica particles surface alumino-silicate occlusion].

OBJECTIVE: To investigate the methods of determining aluminum silicate coated on the surface of silica particles and analyze the role of surface occlusion on development of silicosis. METHODS: Respirable dust samples were collected on filters using 2 L/min flow in tungsten mines and pottery factories of Jiangxi province, and tin mines of Guanxi province. Dust particles were analyzed by a multiple-voltage scanning electron microscopy-energy dispersive X-ray spectroscopy (MVSEM-EDS) using 20 KeV and 5 KeV electron beam accelerating voltages. Changes in the silicon to aluminum X-ray line intensity ratio between the two voltages are compared particle by particle. This provided an index that distinguishes a silica particle that was homogeneously aluminum-contaminated from a clay coated silica particle. RESULTS: The total of 3,982 dust particles from 47 dust samples of seven pottery factories, three tin mines and three tungsten mines were analyzed in this study. Significant difference of aluminum silicate coated on the surface of silica particle was shown between particles from pottery factories and tin mines. The average sample percentage of respirbale-sized silica particles alumino-silicate occlusion in the pottery factories (45%) was higher than that in the tin mines (18%) and tungsten mines (13%). CONCLUSION: Higher percentages silica particles alumino-silicate occlusion is observed in the pottery factories than that in metal mines. These surface analysis results help to understand differences in risk of silicosis when exposure is normalized to cumulative respirable surface silica dust.

Aluminum↗
PubMed2006

[Expression of FasL and apoptosis in pulmonary tissue of rats exposed to silica at different time].

OBJECTIVE: To investigate the change of the expression of the FasL receptor and apoptosis in the pathology of silicosis of the rats exposed to silica and their roles. METHODS: Ninety-six wistar rats were randomizedly divided into the control group and the experimental group. The silicotic animal model was established by the direct tracheal instillation of silica into rat lungs surgically. The control rats underwent directly tracheal instillation of saline into lungs surgically. Eight rats from each group were sacrificed at different days. The expression of FasL receptor in the tissue of the model rats was detected by tissuechip microarray and immunohistochemistry and the cell apoptosis induced by silica was determined by TdT-mediated dUTP nick end-labeling method. The integral optical density of positive cells were quantitatively analyzed using Image-Pro Plus Version 4.5 for windows. RESULTS: The expression of FasL in the lung tissue of the model rats on the 7th, the 14th, the 21st, and the 28th day was significantly higher than that in the control group (P < 0.05), and peaked at the 14th day after exposure to silica. Apoptotic cells in the lung tissue of the model rats on the 1st, the 3rd, the 7th, the 14th, the 21st, and the 28th day were significantly more than those in the control group, and peaked at the 7th and the 14th day after exposure to silica. CONCLUSION: Silica can lead to apoptosis in lung tissues. FasL is expressed in all kinds of cells in the pulmonary tissues of the rats exposed to silica and leads to apoptosis. From the 7th day to 14th day, inflammatory cells dominate in apoptotic cells.

Animals↗
PubMed1983

Effect of silica on the susceptibility of mice to experimental histoplasmosis.

The role of macrophages in the innate immunity of mice to histoplasmosis was investigated using silica, which selectively inactivates macrophages. Mice given silica IV 1 day prior to challenge with live yeast cells of Histoplasma capsulatum were more susceptible to infection than were untreated controls. This increased susceptibility to Histoplasma was observed when mice were given silica at 1, 14, and 21 days prior to infection but not at 3 and 7 days. Silica treated mice that survived 30 days after challenge with a sublethal dose of Histoplasma had 23 times more viable organisms in their spleens than in those of untreated controls. The blastogenic response of spleen cells to concanavalin A and phytohemagglutinin was unaffected at 12 hr after silica injection but was significantly depressed between 1 and 21 days. In contrast, silica treatment did not affect the blastogenic response of spleen cells to lipopolysaccharide. Silica particles were cytotoxic for mouse peritoneal macrophages but not to lymphocytes in vitro. These results indicate that macrophages play an essential role in natural immunity to histoplasmosis.

Animals↗
PubMedDate not supplied

Industrial hygiene sampling and applications to ambient silica monitoring.

Interest in ambient exposures to silica has prompted an evaluation of the applicability of the industrial hygiene sampling and analysis experience. Exposure to excessive levels of silica in the workplace has long been recognized as a risk factor for the development of a variety of disabling and sometimes fatal lung diseases. Initial efforts to control occupational exposure to dust were based on reducing exposures as measured by particle-counting techniques. Because silicosis, the disease resulting from exposure to silica, occurs in the lower airways, which can be reached only by small "respirable dust" particles, size selective sampling procedures were introduced for dust monitoring. The analysis of silica in collected dust samples also has undergone development. Initial methods used involved acid digestion of soluble silicates, with subsequent chemical analysis of the insoluble "free silica" fraction. Current methodology relies on the use of X-ray diffraction and infrared technologies to quantify these materials. However, these methods are sensitive to the particle size distribution of the samples. Standard reference materials (SRMs) have been developed for use with respirable size dust samples. Ambient particulate matter is now measured using the U.S. Environmental Protection Agency sampling methods for particulate matter < or = 10 microns, which approximate the collection efficiency for thoracic fraction samplers. Because the existing calibration SRMs were produced for the measurement of occupational crystalline silica, the need to develop appropriate standards and methods for ambient silica measurements should be evaluated.

Air Pollutants, Occupational↗
PubMed2001

Histidine-functionalized silica and its copper complex as stationary phases for capillary electrochromatography.

A histidine-functionalized silica was prepared by covalent bonding of the functional groups to silane-treated silica gel. Conversion of functional groups was confirmed by infrared (IR) spectra, elemental analysis, and potentiometry. The functionality of the silica gel is 0.293 mmol g(-1). The coordination behavior of the histidine-functionalized silica was investigated by metal capacity and electron paramagnetic resonance (EPR). EPR measurements at different copper loadings were made. The results showed that the copper histidine complex might be distorted tetragonal. Both histidine-functionalized silica and its copper complex were employed as stationary phases for packed capillary electrochromatography (CEC). Electrical current was found helpful for evaluating the properties of frit construction and the stationary phase packing. Test samples include neutral compounds, inorganic anions and organic anions. Factors influencing the separation behavior have been studied. With copper-histidine functionalized silica under the condition of citrate buffer (10 mM, pH 4.0) and applied voltage of -20 kV, the separation of benzoic acid, D- and L-mandelic acid, phthalic acid and salicylic acid could be achieved within 12 min. The column efficiency for these acids was more than 1.2 x 10(5) plates m(-1), except salicylic acid.

Benzoic Acid↗
PubMed2004

Comparative study of controlled pore glass, silica gel and poraver for the immobilization of urease to determine urea in a flow injection conductimetric biosensor system.

This study compared the responses of three enzyme reactors containing urease immobilized on three types of solid support, controlled pore glass (CPG), silica gel and Poraver. The evaluation of each enzyme reactor column was done in a flow injection conductimetric system. When urea in the sample solution passed though the enzyme reactor, urease catalysed the hydrolysis of urea into charged products. A lab-built conductivity meter was used to measure the increase in conductivity of the solution. The responses of the enzyme reactor column with urease immobilized on CPG and silica gel were similar and were much higher than that of Poraver. Both CPG and silica gel reactor columns gave the same limit of detection, 0.5 mM, and the response was still linear up to 150mM. The analysis time was 4-5 min per sample. The enzyme reactor column with urease immobilized on CPG gave a slightly better sensitivity, 4% higher than the reactor with silica gel. The life time of the immobilized urease on CPG and silica gel were more than 310h operation time (used intermittently over 7 months). Good agreement was obtained when urea concentrations of human serum samples determined by the flow injection conductimetric biosensor system was compared to the conventional methods (Fearon and Berthelot reactions). These were statistically shown using the regression line and Wilcoxon signed rank tests. The results showed that the reactor with urease immobilized on silica gel had the same efficiency as the reactor with urease immobilized on CPG.

Biosensing Techniques↗
PubMed2005

Abnormal FT-IR and FTRaman spectra of ionic liquids confined in nano-porous silica gel.

A new concept of designing and synthesizing highly dispersed ionic liquids was developed through physical confinement or encapsulation of them into silica gel matrix with sol-gel process. A series of silica gel confined ionic liquids were synthesized through this process and characterized by diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS) and FTRaman analysis, and abnormal FT-IR and FTRaman spectra were observed. The silica gel matrixes confined ionic liquid BMImBF(4) were further characterized by BET analysis after the ionic liquid was almost completely washed out by acetone under refluxing conditions and meso-porous silica gel matrixes were obtained according to the N(2) adsorption measurements, which suggested that the particle-size of the dispersed ionic liquids was in nano-scale. In consideration of the results obtained together, it could be found that the abnormal FT-IR and FTRaman spectra were changed with the pore-size of the silica gel matrix. For example, obvious abnormal FT-IR and FTRaman spectra appeared when the particle-size of ionic liquid BMImBF(4) is smaller than 11 nm while they disappeared again if the corresponding particle-size >11 nm. These results indicated that nano-effect, or restriction effect, produced from the nano-pores of silica gel was the reason for the abnormal FT-IR and FTRaman spectra.

Ethanol↗
PubMed2002

Simultaneous separation of common mono- and divalent cations on a calcinated silica gel column by ion chromatography with indirect photometric detection and aromatic monoamines-oxalic acid, containing crown ethers, used as eluent.

The application of unmodified silica gel (Super Micro Bead Silica Gel B-5, SMBSG B-5) as a cation-exchange stationary phase in ion chromatography with indirect photometric detection (IC-IPD) for the separation of common mono- and divalent cations (Li+, Na+, NH4+, K+, Mg2+ and Ca2+) was carried out using various aromatic monoamines [tyramine [4-(2-aminoethyl)phenol], benzylamine, phenylethylamine, 2-methylpyridine and 2,6-dimethylpyridine] as eluents. When using these amines as eluents, the peak resolution between these mono- and divalent cations was not quite satisfactory and the peak shapes of NH4+ and K+ were largely destroyed on the SMBSG B-5 silica gel column. Hence, the application of SMBSG B-5 silica gel calcinated at 200, 400, 600, 800 and 1000 degrees C for 5 h in the IC-IPD was carried out. The peak shapes of the monovalent cations were greatly improved with increasing calcination temperature and, as a result, symmetrical peaks of these mono- and divalent cations were obtained on the SMBSG B-5 silica gel calcinated at 1000 degrees C as the stationary phase. In contrast, the peak resolution between these mono- and divalent cations was not improved. Therefore, crown ethers [18-crown-6 (1,4,7,10,13,15-hexaoxacyclooctadecane), 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane)] were added to the eluent for the complete separation of these mono- and divalent cations. Excellent simultaneous separation and highly sensitive detection at 275 nm were achieved in 25 min on a column (150x4.6 mm I.D.) packed with SMBSG B-5 silica gel calcinated at 1000 degrees C by elution with 0.75 mM tyramine-0.25 mM oxalic acid at pH 5.0 containing either 1.0 mM 18-crown-6 or 10 mM 15-crown-5.

Amines↗
PubMed2000

Silica xerogel carrier material for controlled release of toremifene citrate.

Sol-gel processed silica xerogel was used as a carrier material for toremifene citrate in order to develop an implantable controlled release formulation which could be localised to a desired site providing targeted and long-lasting disease control and resulting in a reduced amount of drug needed. Toremifene citrate, an anti-estrogenic compound, was incorporated into silica xerogel matrixes during polycondensation of organic silicate, tetraethyl ortho silicate (TEOS). The effects of drug amount, drying temperature and polyethylene glycol (PEG) on the release rate of toremifene citrate and degradation of the silica xerogel matrixes were investigated. Addition of PEG (M(w) 4600/10000) decreased the specific surface area of the matrix and lowered the release rate of the drug. Reducing the amount of drug in the matrix also decreased the release rate of toremifene citrate. However, drying temperature did not affect the release rate of silica or toremifene citrate. The release profiles of toremifene citrate were according to zero order kinetics, suggesting that drug release was controlled by erosion of the silica xerogel matrix. These results suggest that the toremifene citrate release rate can be controlled to some extent by adding (PEG) or by varying the amount of drug in the silica xerogel matrix.

Delayed-Action Preparations↗
PubMed2003

Roles of silica gel in polycondensation of lactic acid in organic solvent.

Poly(lactic acid) is among the most important biodegradable, biocompatible polymers. To explore the feasibility of making poly(lactic acid) through potentially more selective enzymatic methods, the lipase-catalyzed direct polycondensation of lactic acid in organic solvents was investigated. At 37 degrees C the reaction was found to favor nonpolar solvents with larger log P values and smaller log S(w/o values. The addition of silica gel appeared to greatly enhance the lactic acid conversion (up to 98%) and the lipase stability under the reaction condition. However, upon further investigations, the silica gel itself was found to catalyze the polycondensation, in addition to the role of water removal. The conversion catalyzed by silica gel alone was actually higher than that by silica gel + lipase (or lipase alone). Up to 93% conversion of the acid functional group (or about 99.5% conversion of lactic acid monomer) was obtained in 120 h with silica gel as the catalyst. The finding is especially significant for interpreting (or reconsidering) the results of many presumably enzyme-catalyzed organic-phase reactions in the presence of silica gel.

Biocompatible Materials↗