Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: KEGG:D06522 (Silica)
 2,396 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The phospholipid and lipid metabolism of mouse peritoneal macrophages has been studied in the presence of various silicogenic dusts and asbestos particles. These extensive kinetic studies were possible as a reproducible method was developed to determine these major cellular constituents after labelling macrophages with 1-14C-oleic acid. The following results have been obtained so far: 1. Silicogenic dusts activate a phospholipase A in macrophages leading to a concentration and time-dependent degradation of lecithin and cephalin. 2. Using low doses of SiO2 (less than 1 mg/10(7) cells) the split-off free fatty acid can still be transesterified into the triglycerides. 3. High doses of silica (greater than 2 mg/10(7) cells) induce also a lipolysis. 4. Silica specifically inhibits a plasma membrane-bound acyltransferase 5. Asbestos particles induce in long-term cultures a moderate degradation of diacylphospholipids with transesterification of 1-14C-oleic acid into the triglycerides.
 ...
PMID:The activation of phospholipase A in macrophages after the phagocytosis of silica and other cytotoxic dusts. 19 65

The relationship between biochemical changes in bronchoalveolar lavage fluid (BALF), serum and the lung of different dustexposed rats was studied. Wistar rats were divided into 5 groups: 1. Xingkong chrysotile asbestos (CH-As); 2. Dust in a sieve selection workshop of Xingkong asbestos mine (Dust-Wo); 3. Silica group (SiO2); 4. Titanium dioxide (TiO2) and 5. Normal control group (Control). All the rats were killed in three months after experiment. The results showed that the level of alveolar macrophages (AM), lactic dehydrogenase (LDH) and acid phosphatase (AcP) in each group was marked by related to collagen, lung fat, ceruloplasmin (Cp) and hydroxyproline (HoP) by r and t-test. Among the LDH from BALF, culture fluid and serum, there was also a marked relationship. So the authors pointed out that the BALF especially AM and LDH test could serve as a good and valuable index for detection the condition of pneumoconiosis.
 ...
PMID:[The relationship of biochemical changes among bronchoalveolar lavage fluid serum and lung on dust-exposed rats]. 166 Aug 48

Next to oxygen silicium is the most common substance of our environment. It occurs mostly in form of quartz (SiO2). In the past silica was usually mentioned in connection with foreign body granulomas in dermatological papers. Recently relations between occupational silica exposure and several diseases were reported. Silica exposure was related to the development of scleroderma, lupus erythematodes and sarcoidosis. Pathogenetic connections may be due to a stimulating effect on fibroblasts and due to immunmodulating properties of silica.
 ...
PMID:[Quartz--its relevance for dermatology]. 283 Oct 19

The dynamics of the biological response of pulmonary tissue to silica dust (silica earth from Piotrowice, Poland, recommended as a domestic reference fibrogenic standard) was studied in rats after single-shot intratracheal instillation of a suspension of 20 mg of the dust for one, three, and seven months. Silica dust provoked pronounced pulmonary fibrosis as inferred from increased collagen content together with pathomorphological alteration (silicotic nodules). The lung burden of silica dust affected the lysosomal subfraction as manifested by an increase in its protein content with concomitant stimulation (release and presumably induction) of beta-glucuronidase and cathepsin D and a transient (up to three months) stimulation of lipid peroxidation. Stimulation of activity of lysosomal enzymes and lipid peroxidation mediated by silica dust may reflect destructive metabolic processes resulting in the development of pulmonary fibrosis as the sign of a pathological repair mechanism. The extent of the effects brought about by silica earth testify that it may be recommended as a reference standard for evaluating the potential health hazard from industrial exposure to dusts containing SiO2.
 ...
PMID:Silica earth provoked lung fibrosis with stimulation of lysosomal enzymes and lipid peroxidation in rats. 283 69

A hypothesis is presented for the action of silica-treated macrophages on protein synthesis in fibroblasts and also a method for the isolation of silica-attached materials in lung tissue. The increased protein synthesis in the fibroblasts is due, at least partly, to an increase in mRNA. Silica prevents the suppressing "macrophage effect" of macrophage-originated ribonuclease on fibroblasts. However, under certain conditions, collagen synthesis is stimulated by silica-treated macrophage preparations to such an extent that the effect cannot be explained by the inhibition of macrophage ribonuclease alone. We therefore postulate the existence of a fibrogenic factor, which is released by the macrophages. This factor has been demonstrated and can be purified from lung homogenate of SiO2-treated rats.
 ...
PMID:Fibroblast RNA and macrophage proteins (including the fibrogenic factor) in experimental silicosis. 619 86

Silica (SiO2) or related substances such as silicone ([-R2Si-O-]n), which is used in plastic surgery, or asbestos (e.g. chrysotile; 3MgO.2SiO2.H2O) have 'adjuvant effects'. In a study of scleroderma patients in Germany more than 78% had experienced exposure to silicate dust. T-cell receptor (TcR) V beta gene analysis on CD4- CD8- double-negative alpha beta T cells from scleroderma patients, using polymerase chain reaction (PCR), showed that certain V beta genes, V beta 5, V beta 7 and V beta 17, were predominantly expressed in the cells. We found that certain V beta repertoires, V beta 5.3 and V beta 6.7, were predominantly expressed on fractionated T cells with a high Ca2+ level that had been stimulated by chrysotile in vitro. The intracellular Ca2+ level in human peripheral blood mononuclear cells (PBMC) increased after incubation with silica or chrysotile. Interleukin-2 (IL-2) release from PMBC also rose significantly with chrysotile stimulation, but no change was observed when major histocompatibility complex (MHC) class II DP/DR positive cells were depleted. Therefore, our results support the possibility that silicate acts as a superantigen.
 ...
PMID:Polyclonal human T-cell activation by silicate in vitro. 792 6

Silica and ferric oxide are common industrial exposures. Studies have indicated that all commonly occurring forms of crystalline silica can cause fibrotic lung disease. There is evidence to indicate that crystalline silica is carcinogenic in humans who have not developed silicosis, while amorphous silica is not carcinogenic in humans. An important biological response to particles deposited deep in the lung is their engulfment by pulmonary alveolar macrophages (AM). To assess the role of AM in silica-induced lung disease, particle size distribution and surface area of crystalline, gelled, precipitated, and fumed silica, ferric oxide, and aluminum oxide were characterized; the cytotoxicity of the particles to hamster and rat AM in vitro was measured at 0.0-0.5 mg/1 x 10(6) cells at 24 and 48 h using dye exclusion procedures. The count medium diameter for aluminum oxide, ferric oxide, and amorphous silica was equal to or less than 0.38 microns, while for crystalline silica the value was 0.83 microns. The surface areas for the amorphous silicas and the aluminum oxide ranged from 253 to 125 m2/g with gelled silica having the highest value; the values for crystalline silica and ferric oxide were 4.3 and 10.8 m2/g, respectively. Crystalline silica (1.6%) was detected in the fumed silica, while none was detected in precipitated or gelled silica. With gelled silica, based on the dose of the particle, the viability of the hamster AM decreased to 27% at 0.05 mg and to zero at 0.1 mg at 24 h. At doses of 0.05 and 0.1 mg of crystalline, precipitated, or fumed silica, the percent viability decreased significantly to 76-67% and 51-42%, respectively, and to zero at 0.5 mg. Macrophages viable at 24 h decreased further at 48 h compared with the control culture. The ferric oxide and the aluminum oxide showed minimal to no changes in viability. Similar results for the particles were obtained with rat AM. The results indicate that precipitated and fumed amorphous silica tested at equivalent doses are equally as toxic to AM lavaged from two species of rodents as crystalline silica; gelled silica is more toxic than crystalline. Ferric oxide and aluminum oxide are noncytotoxic in this system. The results of this study indicate that the dose as well as the surface area and surface characterization are important determinants in the cytotoxicity of hamster and rat AM to these particles.
 ...
PMID:Influence of particle dose on the cytotoxicity of hamster and rat pulmonary alveolar macrophage in vitro. 805 15

Pure and silica-containing Al hydroxide aerogels were prepared by the supercritical drying method. The samples were later calcined, giving rise to alumina and Si-Al mixed oxides. The materials were characterized from the points of view of their bulk and surface structures. The Si-free material before calcination is well-crystallized boehmite that converts to gamma-alumina by calcination. The silica-containing hydroxides are composed of boehmite layers with silicates in the interlayer region. The resulting mixed oxides present silica essentially in the bulk. The surface structure of alumina seems poorly sensitive to silica addition. Surface silanol groups appear only for SiO2 more than 4%. No Bronsted acidity appears. Silica addition allows mixed oxides with higher surface areas to be obtained.
 ...
PMID:Characterization of Silica-Containing Aluminum Hydroxide and Oxide Aerogels 924 Nov 85

Silica glass powder (SG-P) made by a fusing-quenching method was added as a second filler to a bioactive bone cement consisting of MgO-CaO-SiO2-P2O5-CaF2 apatite and wollastonite containing glass-ceramic powder (AW-P) and bisphenol-a-glycidyl methacrylate (Bis-GMA)-based resin, to achieve a higher mechanical strength and better handling properties in use. Five types of cement were used, containing different weight ratios of AW-P/SG-P (Group 1 = 100/0; Group 2 = 75/25; Group 3 = 50/50; Group 4 = 25/75; and Group 5 = 0/100) as filler, to evaluate the effect of SG-P content on the biological, mechanical, and handling properties. The total proportion of filler added to the cements was 85% w/w. The compressive, bending, and tensile strengths and fracture toughness of the cements increased with SG-P content. The viscosity of cements also increased with SG-P content, and every cement could be handled manually. The cements were evaluated in vivo by packing the intramedullary canals of rat tibiae. An affinity index was calculated for each cement; this was the length of bone directly apposed to cement expressed as a percentage of the total length of the cement surface. Histological examination of implanted tibiae for up to 26 weeks showed that the affinity indices decreased with SG-P content and that those of all the cement groups increased with time. At 26 weeks, Groups 1 and 2 had almost identical affnity indices (79% and 75%; no significant difference) but those of the other groups remained at <50%. Group 2 had better mechanical and handling properties than Group 1, and an SG-P content in the filler of no more than 25% w/w did not interfere strongly with the bioactivity of the cement.
 ...
PMID:Mechanical and biological properties of bioactive bone cement containing silica glass powder. 933 51

The single-site Solvation, Bond Strength, and Electrostatic (SBE) model accounts for the anomalous position of silica onthe surface acidity versus aqueous acidity correlation developed for metal oxides, by considering the solvation energy change in the protonation reaction implemented through the dielectric constant (1/epsilon(k)) and the electrostatic energy change through the Pauling bond strength to bond length ratio (s/r) of the oxide. I address here why inclusion of the solid's dielectric constant brings silica into the same correlation as other oxides like TiO2, Al2O3, and Fe2O3. The solvation and electrostatic contributions are interpreted in terms of classical concepts such as chemical hardness, polarizability, ionicity, electronegativity, and local charge densities. Silica is acidic (PZC < 7), not because of its small dielectric constant, its tetrahedral coordination, or its high bond strength alone. Surface acidity depends largely on high values of the s/r ratio. The dielectric constant of the solid affects acidity mainly by reflecting the nature of water-surface interactions. Solids with large values of epsilon(k) are interpreted as being less polarizable and more ionic so that water, a hard polar solvent, interacts favorably with such surfaces and scales similar to water-water interactions regardless of whether the metal-oxide bond is in the solid or in the aqueous state. For these oxides, pKa(s) = pKa(aq) +/- 1. Silica, with a small dielectric constant, is interpreted as being more polarizable and more covalent so that water-SiO2 interactions scale differently than for the more ionic oxides. Such an interpretation when combined with the Partial Charge Model for metal hydrolysis suggests that the surfaces of RuO2, W03, Sb2O5, and Ta2O5 should be acidic similar to silica. But, unlike silica, they would lie on the pKa correlation defined by the other oxides because of their larger dielectric constants. The mixed oxide, AlPO4, is predicted to behave like silica.
 ...
PMID:Is silica really an anomalous oxide? Surface acidity and aqueous hydrolysis revisited. 1187 60


1 2 3 4 5 6 7 8 9 10 Next >>