Crystalline Silica Particles Research Articles

Strain and Species Variations in Pulmonary Responses to Inhaled Min-U-Sil Crystalline Silica Particles in Mice

chambers for 5 days at 100 or 250 mg m~ 3 . Following the exposure period, cells and fluids from sham and silica-exposed animals were recovered by bronchoalveolar lavage (BAL). Granulocytes, as well as lactate dehydrogenase (LDH), N-acetylglucomsaminidase (NAG) and protein values were measured in BAL fluids at several postexposure time periods. In addition, the lungs of exposed mice were processed for BrdU pulmonary cell labeling, histopathological and morphometric analysis. The results showed that a 5 day exposure to silica produced a sustained, but low-level inflammatory response, measured up through 6 months postexposure in the lungs of black and beige mice. Cell labelling of terminal airway and lung parenchymal cells in beige and black mice were enhanced over corresponding unexposed controls. The results demonstrated minor differences in the pulmonary inflammatory or cell proliferative responses between the two strains of silicaexposed mice. Preliminary morphometric analysis of pulmonary lesions among silica-exposed beige and black mice did not show a dose response relationship, however, the lesions were similar in nature and in distribution at 6 months postexposure. In general, the mice demonstrated a mild response to silica exposure when compared to the two strains of rats. We had expected to observe a reduced pulmonary response to inhaled silica particles in the neutrophil-defective beige mouse relative to the normal C57 black mouse. However, the species effect (i.e. reduced responsiveness in mice) seemed to take precedence over the differences in response among the two strains. Although it has been reported by others that exposure to silica may cause pulmonary fibrosis in mice, our results following acute exposures indicate that the two strains of mice tested here are much less responsive to the toxic effects of silica when compared to exposed rats.

Non-fibrous inorganic particles in bronchoalveolar lavage fluid of pottery workers.

To study the actual exposure of pottery workers to silica particles, as their risk of silicosis is potentially high because of the presence of inhalable crystalline silica particles in the workplace. Nine pottery workers underwent bronchoalveolar lavage. The recovered fluid was analysed for cytological and mineralogical content by analytical transmission electron microscopy. The data were compared with those obtained from a control group composed of seven patients with sarcoidosis and six patients with haemoptysis. Cytological results showed a similar profile in exposed workers and controls, whereas in patients with sarcoidosis a lymphocytic alveolitis was found. Microanalysis of the particulate identified the presence of silicates, CRSs, and metals. Pottery workers had higher numbers of total particles and CRSs, and had a higher silicate/metal ratio. In five workers, the presence of zirconium silicate was also detected. Patients with sarcoidosis had the lowest number of particles, and an inverted silicate/metal ratio. Microanalysis by transmission electron microscope can provide useful information to assess occupational exposure to dusts.

Time course of chemotactic factor generation and neutrophil recruitment in the lungs of dust-exposed rats.

The time course of neutrophil recruitment into the lung, neutrophilic chemotactic activity, and the gene expression of neutrophilic chemokines by lavaged cells was determined after intratracheal instillation of various particles. Low-toxicity, low-solubility dusts such as titanium dioxide (TiO2) particles, as well as fibrogenic crystalline silica and nonfibrogenic amorphous silica particles were instilled into the lungs of rats. Results showed that all three dusts induced neutrophilic inflammation as early as 5 h after exposure. Both crystalline and amorphous silica elicited higher degrees of pulmonary inflammation when compared with TiO2 particles. Maximal infiltration of neutrophils into the lungs occurred 5 to 6 h after intratracheal instillation of the dusts. The inflammatory response was transient for TiO2 and amorphous silica, i.e., evident at 2 days after exposure but not different from controls at 10 days after exposure. In contrast, inflammatory effects were sustained through a 10-day period following exposures to crystalline silica. Chemotactic activity for neutrophils was detected directly in bronchoalveolar lavage (BAL) fluids of dust-exposed rats within 2 h after exposure, but not in the BAL fluids of saline- or unexposed rats. The chemotactic activity was correlated with the influx and disappearance of neutrophils into alveolar regions of the lung in TiO2- and amorphous silica-exposed rats. The mRNA expression of two known neutrophil chemotactic cytokines in BAL cells, macrophage inflammatory protein-2 (MIP-2) and KC, also correlated with chemotactic activity and acute and pulmonary inflammatory responses. MIP-2 mRNA was expressed prior to the detection of chemotactic activity in BAL fluids. However, the mRNA expressions of MIP-2 and KC were transient for rats that were exposed to these dusts as KC and MIP-2 message were no longer detectable in BAL cells after 2 days of recovery. Although both neutrophilic chemotactic activity and inflammation remained prominent 10 days after exposure to crystalline silica, MIP-2 expression could not be detected in BAL cells. Thus, we conclude that MIP-2 is likely to be only one of several cytokines involved in mediating neutrophilic inflammation following a single instillation of crystalline silica.

Inhaled particles and respiratory disease

Inhaled particles and respiratory disease

Altered calcium homeostasis and cell injury in silica-exposed alveolar macrophages.

There is evidence to suggest that cell injury induced in alveolar macrophages (AM) following phagocytic activation by silica particles may be mediated through changes in intracellular free calcium [Ca2+]i. However, the mechanism of silica-induced cytotoxicity relative to [Ca2+]i overloading is not yet clear. To provide a better insight into this mechanism, isolated rat AMs were exposed to varying concentrations of crystalline silica (particle size < 5 microns in diameter) and the fluctuation in their [Ca2+]i and cell integrity were quantitatively monitored with the fluorescent calcium probe, Fura-2 AM, and the membrane integrity indicator, propidium iodide (PI). Results from this study indicate that silica can rapidly increase [Ca2+]i in a dose-dependent manner with a characteristic transient calcium rise at low doses (< 0.1 mg/ml) and an elevated and sustained rise at high doses (> 0.1 mg/ml). Depletion of extracellular calcium [Ca2+]o markedly inhibited the [Ca2+]i rise (approximately 90%), suggesting that Ca2+ influx from extracellular source is a major mechanism for silica-induced [Ca2+]i rise. When used at low doses but sufficient to cause a transient [Ca2+]i rise, silica did not cause significant increase in cellular PI uptake during the time of study, suggesting the preservation of membrane integrity of AMs under these conditions. At high doses of silica, however, a marked increase in PI nuclear fluorescence was observed. Depletion of [Ca2+]o greatly inhibited cellular PI uptake, induced by 0.1 mg/ml or higher doses of silica. This suggests that Ca2+ influx, as a result of silica activation, is associated with cell injury. Indeed, our results further demonstrated that the low dose effect of silica on Ca2+ influx is inhibited by the Ca2+ channel blocker nifedipine. At high doses of silica (> 0.1 mg/ml), cell injury was not prevented by nifedipine or extracellular Ca2+ depletion, suggesting that other cytotoxic mechanisms, i.e., nonspecific membrane damage due to lipid peroxidation, are also responsible for the silica-induced cell injury. Silica had no significant effect on cellular ATP content during the time course of the study, indicating that the observed silica-induced [Ca2+]i rise was not due to the impairment of Ca(2+)-ATPase pumps, which restricts Ca2+ efflux. Pretreatment of the cells with cytochalasin B to block phagocytosis failed to prevent the effect of silica on [Ca2+]i rise. Taken together, these results suggest that the elevation of [Ca2+]i caused by silica is due mainly to Ca2+ influx through plasma membrane Ca2+ channels and nonspecific membrane damage (at high doses).(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of particle size and modulation frequency on the photoacoustic spectra of silica powders

Investigations of the infrared spectra of crystalline and amorphous silica particles of different sizes (0.05, 5, 10, 15, 30, 45, and 260 μm) in the range of 400-4000 cm -1 using Fourier transform infrared/photoacoustic spectroscopy are reported. The change in the intensity I of the signal with porosity ∈ of powders follows the ∈/(1-∈) dependence for strong bands and ∈ dependence for weaker bands are predicted by the theory of McGovern et al. For strong bands, I also follows the empirical relation I∼D -n , where D is the particle diameter in cm and n=0.34-0.42

Surface and Bulk Infrared Modes of Crystalline and Amorphous Silica Particles: A Study of the Relation of Surface Structure to Cytotoxicity of Respirable Silica

Surface IR (infrared) modes of crystalline and fumed (amorphous) silica particles, calcined at temperatures up to 1095 degrees C, have been studied by Fourier transform infrared spectroscopy. The ability of these same particles to lyse cells has been measured by a hemolysis protocol. The untreated crystalline and amorphous materials differ by a factor of 40 in specific surface area, and the intensity per unit mass of the sharp surface silanol band near 3745 cm-1 in the amorphous material is an order of magnitude larger than in the crystalline material. A similar difference is observed in the lysing potential of the two materials. The intensity of the silanol band increases after calcination for both materials, reaching peak values near 500 degrees C, followed by a dramatic drop at higher calcination temperatures, and reaching negligible values for materials calcined near 1100 degrees C. The lysing potential data follow essentially the same pattern for both crystalline and fumed silica. These results are consistent with the hypothesis that the surface silanol groups are involved in cell lysis. Further experiments are suggested to evaluate the relationship between the surface structure of silica particles and their potential cytotoxicity.

Surface and bulk infrared modes of crystalline and amorphous silica particles: a study of the relation of surface structure to cytotoxicity of respirable silica.

Surface IR (infrared) modes of crystalline and fumed (amorphous) silica particles, calcined at temperatures up to 1095 degrees C, have been studied by Fourier transform infrared spectroscopy. The ability of these same particles to lyse cells has been measured by a hemolysis protocol. The untreated crystalline and amorphous materials differ by a factor of 40 in specific surface area, and the intensity per unit mass of the sharp surface silanol band near 3745 cm-1 in the amorphous material is an order of magnitude larger than in the crystalline material. A similar difference is observed in the lysing potential of the two materials. The intensity of the silanol band increases after calcination for both materials, reaching peak values near 500 degrees C, followed by a dramatic drop at higher calcination temperatures, and reaching negligible values for materials calcined near 1100 degrees C. The lysing potential data follow essentially the same pattern for both crystalline and fumed silica. These results are consistent with the hypothesis that the surface silanol groups are involved in cell lysis. Further experiments are suggested to evaluate the relationship between the surface structure of silica particles and their potential cytotoxicity.

Adhesive formulations manipulated by the addition of fumed colloidal silica

3 HEALTH AND SAFETY DATA Silicosis is associated with the inhalation of microscopic particles of crystalline silica. However, fumed silica is amorphous and below the particle sizes associated with lung damage [4]. But it is reported that breathing air contaminated with a high concentration of hydrophobic fumed silica can cause nausea, dizziness and eye irritation. The manufacturer recommends that a dust mask be worn while using hydrophobic silica. It is a good practice to wear a dust mask and polyethylene gloves when using either grade of fumed silica. Both grades are capable of removing oils from the skin. 0.014 1.76 amorphous 8.0-10.0 0.2%* none 0.007 1.46 amorphous 3.5-4.2 none 3.0%t Hydrophilic ES. Hydrophobic RS. Particle size (diameter in !-tm) Refractive index X-ray form pRin water Surface ammonia Moisture content

Enhancement by BCG of macrophage-like suppressor cells that inhibit the expression of cytotoxic T-cell effector function

The expression of alloimmune splenic T-cell-mediated cytotoxicity, as determined by the 51Cr release assay, in animals undergoing allograft rejection, was observed to be inhibited by a cell present in the plastic-adherent fractions of the spleens. The activity of the suppressor cell, induced by the presence of the allograft, was enhanced if the animals were treated with BCG: The latter also potentiated the rejection response. The suppressor cell acted at the cytolytic phase of the effector function so that there was a measurable increase in the response if the suppressor cells were removed from the immune spleens prior to the assay. The cell responsible for the suppressor activity was macrophage-like in its characteristics, being of light density, adherent to glass surfaces, Thy-1-negative and sensitive to the toxic effects of crystalline silica particles.

The Effect of Silica Injections on the Rejection of Eimeria from Nonspecific Hosts

Parasites of the genus Eimeria are characteristically host specific. Peritoneal macrophages obtained from nonspecific hosts (guinea fowl and turkeys) were found to greatly reduce the viability of sporozoites of E. tenella from the chicken in vitro (Long and Millard, 1979, Parasitology 78: 239-247). We have demonstrated here that the in vivo inhibition of macrophage activity enabled infection with Eimeria to occur in a nonspecific host. It has been shown that crystalline silica particles are selectively toxic to macrophages in vivo and in vitro without altering the viability of lymphocytes (Lotzova and Cudkowicz, 1974, J. Immunol. 13: 343-345; Kessel et al., 1963, Brit. J. Exptl. Pathol. 44: 351364; Vigliani and Pernis, 1963, Adv. Tuberc. Res. 12: 230-282). After phagocytosis, silica has a cytotoxic effect on the macrophage probably by interacting with the macrophage lysosomal membrane releasing hydrolytic enzymes into the cytoplasm (Allison et al., 1966, J. Exp. Med. 124: 141-154). For the present study, silica particles were used to investigate the possible role of macrophages in the host specificity of Eimeria. Two-week-old male, White Leghorn chickens were inoculated per os with a mixture of 500,000 sporulated oocysts of turkey coccidia (a mixture of E. dispersa, E. meleagrimitis and E. adenoeides). Silica particles of an average size of 5 /im were obtained from Dr. K. Roback, Steinkoklenbergbauverein, Germany. Doses of 3 mg/0.5 ml buffered saline were injected i.v. twice daily into the wing vein. Chickens were given the silica injections by group on days 1 through 4 PI. All the feces discharged were collected and examined for oocysts daily, starting on the 5th day PI, and terminating on the 15th day PI. The combined results of two identical experiments are given in Table I. Oocysts were produced in all groups that were treated with silica; the predominant oocysts produced were identified morphologically as E. dispersa. In one of the two experiments, untreated, infected chickens discharged oocysts on only one day (5th day). Silica-treated chickens produced 17 to 126 times more oocysts over periods ranging from 5 to 15 days after oocyst inoculation. The greatest number of oocysts was discharged in all groups between 5 and 9 days PI. This corresponded with the minimum prepatent periods of Eimeria dispersa species used in this study. More oocysts were produced in those birds given the silica injections 3 to 4 days PI than those birds given the injections on days 0 through 3 PI. The treatment given 3 to 4 days PI coincided with the termination of schizogony and the start of gametogony. Thus, macrophages may play some role, either directly or indirectly, in the host specificity of coccidia by affecting the asexual cycle and perhaps the sexual cycle as well. The treatment inhibited host specific mechanism(s) of those chickens given silica on days 0 to 2 PI, but the effect was greater when silica was given 3 to 4 days PI. Thus, the mechanisms involved in the innate resistance of nonspecific hosts to Eimeria may be effective against early gametocytes. After 2 to 4 days in the chickens' circulation, most of the silica may have been sequestered in lymphoid tissue (Pearsal and Weiser, 1968, J. Reticuloendothel. Soc. 5: 107-120). The increase in the number of oocysts produced on days 13 to 15 PI may reflect the delayed effects of the silica treatment. However, more evidence is needed to adequately explain this finding. The oocysts collected from these birds completed their life cycle when inoculated into turkeys, confirming that the oocysts produced by chickens given the silica treatment were indeed turkey coccidia. Doran (1978, J. Parasitol. 64: 882-885) was able to produce a light

CYTOTOXICITY IN GRAFT-VERSUS-HOST REACTION

Graft-versus-host (GVH) reactions were induced in adult F1 hybrid mice with the i.p. injection of parental strain spleen cells. Peritoneal exudate and spleen cells of the F1 hybrids taken 8 days after the induction of GVH reaction had a nonspecific in vitro cytotoxic effect which was measured by using 51Cr-labeled target cells of parental genotype. The cytotoxic cells in the peritoneal exudates were shown to be macrophages which adhered to plastic surfaces and were sensitive to the toxic action of crystalline silica particles. Moreover, the injection of partially purified syngeneic macrophages into the F1 hybrids undergoing GVH reactions increased the cytotoxic activity of the peritoneal exudate cells obtained from these animals. These results suggest that during GVH reaction host macrophages are activated into a state of nonspecific cytotoxicity.