Fluorosilicic acid induces DNA damage and oxidative stress in bone marrow mesenchymal stem cells.

Excess fluoride in water can produce changes in tooth enamel mineralization and lead to diseases such as dental or skeletal fluorosis. The present study aimed to assess the genotoxic effects, oxidative stress, and osteoblastic mineralization induced by fluorosilicic acid (FA) in murine bone marrow-derived mesenchymal stem cells (BM-MSCs). BM-MSCs were isolated from the femurs and tibias of rats and cultured under standard conditions. Cells exposure occurred for 3, 7, 14, and 21 days to different concentrations of FA (0.6-9.6 mg/L). Cytotoxicity was observed in 14 and 21 days of exposure for all concentrations of FA (cell proliferation below 60%), and for 3 and 7 days, in which the proliferation was above 80%. Alkaline comet assay results demonstrated significant increased damage at concentrations of 0.3-2.4 mg/L, and the micronucleus test showed increased rates for micronucleus (1.2-2.4 mg/L) and nuclear buds (NBUDs) (0.3-2.4 mg/L) (P < 0.05/Dunnett's test). An alkaline comet assay modified by repair endonuclease (FPG) was used to detect oxidized nucleobases, which occurred at 0.6 mg/L. The oxidative stress was evaluated by lipid peroxidation (TBARS) and antioxidant activity (TAC). Only lipid peroxidation was increased at concentrations of 0.6 mg/L and 1.2 mg/L (P < 0.001/Tukey's test). The osteogenesis process determined the level of extracellular matrix mineralization. The mean concentration of Alizarin red increased significantly in 14 days at the 0.6 mg/L concentration group (P < 0.05/Tukey's test) compared to the control group, and a significant difference between the groups regarding the activity of alkaline phosphatase (ALP) was observed. Unlike other studies, our results indicated that FA in BM-MSCs at concentrations used in drinking water induced genotoxicity, oxidative stress, and acceleration of bone mineralization.

Fatal Fluorosilicic Acid Exposure After a Motor Vehicle Crash: A Case Report.

ABSTRACT: Fluorosilicic acid (FSA) is a corrosive liquid used in manufacturing and other processes. High-level exposures to FSA cause fluoride toxicity resulting in profound hypocalcemia, potentially leading to sudden death. Prompt recognition of exposure risk allows appropriate environmental management precautions, reducing the risk of further casualties. Herein, we present a case report of death due to FSA exposure sustained during a motor vehicle crash involving a truck transporting the material and the management thereof.

Intravitreal safety profiles of sol-gel mesoporous silica microparticles and the degradation product (Si(OH)4).

Mesoporous silica has attracted significant attention in the drug delivery area; however, impurities can be a source of toxicity. The current study used commercial microparticles produced at large scale in a well-controlled environment. Micrometer sized mesoporous silica particles were acquired through a commercial vendor and pore structures were characterized by SEM. The three silica particle formulations had a diameter of 15 micrometers and three different pore sizes of 10 nm, 30 nm, and 100 nm. The fourth formulation had particle size of 20-40 micrometers with 50 nm pores. Before in vivo tests, an in vitro cytotoxicity test was conducted with silicic acid, derived from the sol-gel particles, on EA.hy926 cells. Low concentration (2.5 µg/mL) of silicic acid showed no cytotoxicity; however, high concentration (25 µg/mL) was cytotoxic. In vivo intravitreal injection demonstrated that 15 um silica particles with 10 nm pore were safe in both rabbit and guinea pig eyes and the particles lasted in the vitreous for longer than two months. Formulations of with larger pores demonstrated variable localized vitreous cloudiness around the sol-gel particle depot and mild inflammatory cells in the aqueous humor. The incidence of reaction trended higher with larger pores (10 nm: 0%, 30 nm: 29%, 50 nm: 71%, 100 nm: 100%, p < .0001, Cochran Armitage Trend Test). Sol-gel mesoporous silica particles have uniform particle sizes and well-defined pores, which is an advantage for implantation via a fine needle. Selected formulations may be used as an intraocular drug delivery system with proper loading and encapsulation.

Combined toxicity of arsenite and dimethylarsenic acid on the freshwater diatom Nitzschia palea.

The toxicity and bioavailability of single arsenic species have been widely investigated, however, the biological effects of mixed arsenic species co-existing in natural waters still remain unknown. The objective of this work was to discern the adverse effects of combined arsenite (As(III)) and dimethylarsenic acid (DMA) on diatom Nitzschia palea. The combined ecotoxicity of As(III) and DMA on N. palea was observed to be time-dependent and showed dose-effect relation. The toxicity of DMA and As(III) mixture was higher than individual DMA or As(III) when the As(III) concentration was in the range of 0.085-0.316 mg L-1. As the As(III) concentration increased from 0.487 to 0.858 mg L-1, the antagonistic effect was found, which could be due to the higher thiols contents in the thiol-containing proteins (e.g., frustulins, silaffins and other glycoproteins). The content of malondialdehyde (MDA) in the treatment of mixed arsenic species was found to be at the same level compared to the As-free control after 72 h of exposure, indicating that the co-toxicity of As(III) and DMA on diatom frustules was not significant. Furthermore, the increase of frustule formation rate in the mixture of EC50 As(III)-EC10 DMA at 72 h exposure time indicated that the damaged diatom cell walls was likely repaired gradually. The results from this study suggested that the effects of co-existed arsenic species were concentration-specific and should be considered in the risk assessment of arsenic and development of water quality criteria for the protection of aquatic ecosystems.

Comparison of the toxicity of fluoridation compounds in the nematode Caenorhabditis elegans.

Fluorides are commonly added to drinking water in the United States to decrease the incidence of dental caries. Silicofluorides, such as sodium hexafluorosilicate (Na2 SiF6 ) and fluorosilicic acid (H2 SiF6 ), are mainly used for fluoridation, although fluoride salts such as sodium fluoride (NaF) are also used. Interestingly, only the toxicity of NaF has been examined and not that of the more often used silicofluorides. In the present study, the toxicities of NaF, Na2 SiF6 , and H2 SiF6 were compared. The toxicity of these fluorides on the growth, feeding, and reproduction in the alternative toxicological testing organism Caenorhabditis elegans was examined. Exposure to these compounds produced classic concentration-response toxicity profiles. Although the effects of the fluoride compounds varied among the 3 biological endpoints, no differences were found between the 3 compounds, relative to the fluoride ion concentration, in any of the assays. This suggests that silicofluorides have similar toxicity to NaF.

Cytotoxicity of ammonium hexafluorosilicate on human gingival fibroblasts.

Ammonium hexafluorosilicate (SiF), which is claimed to significantly improve occlusion of dentinal tubules, was proposed as a novel desensitizer for dentine hypersensitivity (DH). However, the cytotoxicity of SiF on oral cells is lacking. The purpose of this study was to investigate the cytotoxicity of SiF on human gingival fibroblasts (hGFs) under different dosages (0.001%, 0.01%, 0.1%, and 1%) and treatment durations (1, 5, 10, and 30min). Cell proliferation, mitochondrial membrane potential (MMP) and cell cycle were tested by MTT assay, JC-1 staining and flow cytometry, respectively. Glutathione (GSH) depletion was analyzed to further investigate the underlying mechanism of SiF-induced cytotoxicity. MTT assay showed that there was significantly lower number of viable cells when the hGFs were treated with 0.01% (10min), 0.1% (10 and 30min) and 1% (5, 10, and 30min) SiF than the control group (p<0.05). MMP decreased and GSH depletion increased dramatically along with higher concentrations (0.1% and 1% SiF) and prolonged times (10 and 30min). DNA synthesis [S (%)] of cells treated with 0.1% and 1% SiF (5, 10, and 30min) was significantly lower than the control group (p<0.05). Our results indicate exposure to up to 0.01% SiF for less than 5min causes low or no cytotoxicity in vitro.

Silicosis in mice: effects of dose, time, and genetic strain.

Experimental silicosis allows study of the mechanisms of lung injury, inflammation, and fibrosis. Inbred mice are an attractive species in which to study these mechanisms because of recent progress in murine immunology, molecular biology, and genetics. We exposed mice to an aerosol of silica and examined the effects of exposure dose, the evolution of disease features over time, and the variation in responses among four inbred strains. In C3H/HeN mice incremental cumulative exposure doses of cristobalite silica caused increased initial lung dust burden 12 to 16 weeks post-exposure, progressively intense pathological responses, and increased total lung collagen (hydroxyproline). The histopathological changes and total lung collagen increased progressively over time after exposure. We compared the features of silicosis in four strains of inbred mice selected for common use or immunologic reactivity 16 weeks after aerosol inhalation exposure to crystalline cristobalite silica (70 mg/m3, 5 hours/day, 12 days). C3H/HeN mice demonstrated histopathological silicotic lesions and enlarged intrapulmonary lymphoid tissue, and increased lung wet weight, bronchoalveolar lavage (BAL) recovery of macrophages, lymphocytes, and neutrophils, and total lung collagen (hydroxyproline). BALB/c mice developed slight pulmonary lesions; MRL/MpJ mice demonstrated prominent pulmonary infiltrates with lymphocytes; New Zealand Black mice developed extensive alveolar proteinaceous deposits, inflammation, and fibrosis. Our findings demonstrate orderly dose-time-response relationships, and a substantial variation of responses among inbred strains of mice. This model should prove valuable for future experimental interventions into the mechanisms of silicosis.

Osteogenic cell cytotoxicity and biomechanical strength of the new ceramic Diopside.

Diopside was prepared by sintering a powder compact composed of CaMgSi2O6 at 1573K for 2 h. In order to clarify the biocompatibility of Diopside, the cytotoxicity of Diopside against the osteogenic cell line MC3T3-E1 and the bone-Diopside interface strength were examined. On both the 14th and 21st days of incubation of MC3T3-E1 cells with Diopside, ALP activities were not significantly lower than those of the CTRL. TEM photographs of MC3T3-E1 on Diopside after 14 days of incubation showed active secretion of crystals from osteoblast-like cells. Scanning electron microscopic analysis showed that the cells on Diopside formed multiple cell layers similar to those on the CTRL both 14 and 21 days after incubation. These results showed that Diopside had no cytotoxic effect on MC3T3-E1. The pulling test showed that failure loads of Diopside were significantly lower than those of AWGC. Histologically, there was no fibrous tissue or foreign body reaction at the bone interface. SEM-EPMA showed that Diopside had attached to the bone via a calcium-phosphorus layer. SEM back-scattered electron imaging showed that the Diopside plate had degraded to a porous state 12 weeks after implantation. These findings indicate that Diopside is a biodegradable ceramic.

Cytotoxic and genotoxic effects of calcium silicates on human lymphocytes in vitro.

Calcium silicate has been considered as a possible replacement for asbestos due to its heat and fire resistance. We describe the cytotoxic and genotoxic potential of calcium silicate using peripheral human blood lymphocytes. Calcium silicates at concentrations of 10 and 100 micrograms/ml significantly increased the frequencies of chromosomal aberrations (CAs) and sister-chromatid exchanges (SCEs). The increases in CAs and SCEs were dose-dependent, though not linearly. A significant decrease in the proliferation rate index was observed with increased dose of calcium silicates. The induction of chromatid-type aberrations indicates that the clastogenic activity of calcium silicate is S-phase-dependent.

Recent studies of man-made vitreous fibers. Chronic animal inhalation studies.

The history of asbestos use and asbestos-related disease is replete with comments that the public health would have been better protected if the results of laboratory investigation, epidemiologic surveys, and clinical studies were made available at appropriate intervals during the ongoing research, rather than in the generally accepted method of awaiting completion of studies prior to reporting medical and scientific findings. No substantive evidence of long-term adverse effects has been published in workers exposed to man-made vitreous fibers. Nevertheless, in an effort to preclude a repetition of this error of omission that occurred with asbestos exposure and use, the Thermal Insulation Manufacturers Association is regularly reporting interim and final data from ongoing animal studies. A significant segment of man-made vitreous fibers have now been tested in state-of-the-art chronic studies. This paper includes the recently completed animal inhalation studies on refractory ceramic fibers and fibrous glass. It also reviews interim data on mineral wool studies.

Metsovo-tremolite asbestos fibres: in vitro effects on mutation, chromosome aberration, cell transformation and intercellular communication.

Samples of Metsovo-tremolite asbestos, previously found to be the causative agent of endemic pleural calcification and an increased level of malignant pleural mesothelioma in a rural area of north-western Greece (Metsovo area), were tested in various in vitro toxicity test systems. It was found that asbestos fibres of this type were strong inducers of micronuclei and numerical chromosomal abnormalities while they induced low levels of chromosomal aberrations in mammalian cells in culture. Furthermore, this type of asbestos can induce a low level of in vitro transformation of Syrian hamster embryo cells. The fibres had no effect on gap-junctional cell-cell communication (followed by the dye-transfer method) and did not induce any mutations in the Salmonella typhimurium strain TA102 which is known to be sensitive to the action of various oxidative agents. These results support the hypothesis generated from studies on other types of asbestos that such fibres induce tumours by causing chromosomal mutations.

[Serpentine mine "Naslawice" as the source of contamination of soil and agricultural plants with metals and fibrous minerals]. / Wplyw kopalni serpentynitu "Naslawice" na zanieczyszczenie metalami i mineralami wlóknistymi gleby i roslin uprawnych.

The study was aimed at evaluation of the effect of dust, produced at crushing the serpentine, on the soil and crops in Naslawice. The serpentine dust, apart from asbestos, contains also magnesium, calcium, chromium and nickel. These elements have been determined in the soil and plants by means of the standard methods generally used in agricultural chemistry, whereas asbestos content was determined by means of X-ray diffractometry and polarization microscopy. The dust of the crops harvested contained asbestos fibres and, in the plants, the increased content of nickel an chromium was found. The highest amount of asbestos was found in soil in the area at a distance of up to 50 km from the emission source. The soil contains also the increased amounts of chromium and sporadically cadmium.

[Various ecological problems related to mining and processing of serpentine. Evaluation of non-occupational exposure of the population of Naslawice to fibrous mineral dust]. / Niektóre problemy ekologiczne towarzyszace wydobyciu i przetwarzaniu serpentynitu. Ocena narazenia pozazawodowego na mineralny pyl wlóknisty ludnosci zamieszkalej w Naslawicach.

Non-occupational exposure of the population living in the vicinity of the serpentine mining and processing mill in Naslawice was assessed. The evaluation was based on the phase analysis and determination of respirable mineral fibres content in the samples of dust fall and soil in the fields nearby the mine, as well as on the in-door and out-door measurements of airborne fibres concentration. All soil samples contained antigorite--a mineral the structure of which is close to that of chrysotile asbestos add exhibiting high biological aggressiveness. The respirable mineral fibres content in the dust fall-out and in the soil ranged from 98,000 to 480,000 per 1 mg and from 48,000 to 122,000 per 1 mg, respectively, whereas the airborne concentrations were from 2 to 1540 fibres/l (outdoor) and from 4 to 7 fibres/l (indoor). The fall of dust in the years 1989-1990, recorded at all measuring points, exceeded 200,000 kg/km2 yearly (admissible value). The airborne concentrations of respirable mineral fibres were also higher than the admissible value (1 fibre/l of the air). The results obtained indicate that the exposure of the population in Naslawice to mineral fibrous dusts has significantly exceeded to maximum admissible concentrations established for non-occupational exposure.

Variations in the carcinogenicity of tremolite dust samples of differing morphology.

Six samples of tremolite of different morphological type were prepared as dusts of respirable size and used in intraperitoneal injection studies in rats. Three "asbestiform" tremolites produced mesotheliomas in almost all animals, although with significantly different tumor-induction periods. A brittle type of fibrous tremolite which, when manipulated to prepare "respirable dust," produced a sample with relatively few asbestiform fibers remaining nonetheless produced tumors in 70% of rats. Two samples of nonfibrous tremolite produced respirable dust samples containing numerous elongated fragments with aspect ratios greater than 3:1, which therefore fitted the definition of respirable fibers. Both these samples produced relatively few tumors, although one had more long "fibers" than did the brittle tremolite that produced 70% of tumors. This study has therefore demonstrated that different morphologic forms of tremolite produce dusts with very different carcinogenic potential. Carcinogenicity does not depend simply on the number of elongated particles injected, and we need to develop methods of distinguishing carcinogenic tremolite fibers from relatively innocuous tremolite dusts, with similar numbers of elongated particles of similar aspect ratios.

Health effects of tremolite. Now and in the future.

Although tremolite asbestos has been well characterized since 1916, appreciation of its role in disease induction is relatively recent. It has always been understood that the morphology of tremolite is complex, and part of the slowness in recognizing it as a hazard has been definitional in nature. Reduced to simple terms the questions are, when is tremolite "asbestos-like," when is it an innocuous amorphous particle, do these forms occur together, with what confidence can they be separated for regulatory purposes, and what is the spectrum of disease potential for varying exposure? A brake on regulation is partially due to a convergence of opinion of unlikely and unintentional allies: industries producing tremolite-containing materials and some epidemiologists resisting attribution of risk to tremolite on the grounds that its known effects--pleural plaques, asbestosis, lung cancer and mesothelioma--are principally due to chrysotile, which is often contaminated with fibrous tremolite. The latter group concentrate their skepticism on internal-dose biomarker studies associating lung tremolite content with mesothelioma (but not so clearly with lung cancer or asbestosis). They ignore the basic carcinogenic quality of fibrous tremolite, shown in both animal and epidemiological studies. Evidence from the Quebec chrysotile/tremolite mining districts suggests that very low concentrations of tremolite in ambient air can be translated into high concentrations in lung, even in those without occupational exposure. Disease incidence, especially for mesothelioma, seems also to be associated with tremolite air and lung content. The risk associated with tremolite has been demonstrated in Corsica, Cyprus, the United States, and Canada. Of particular importance is an apparent increase in the proportion of mesothelioma risk attributable to tremolite, since the fibers heretofore most responsible for that disease--commercial amphiboles--have been or are being severely regulated or completely eliminated in production and use. Further, amosite and crocidolite, while still a concern, form a small fraction of "asbestos-in-place": most of this material is chrysotile and we do not really know to what degree it is contaminated with tremolite. The available evidence suggests that bulk analysis or airborne fiber analysis will not answer this question, and perhaps only animal bioaccumulation assay is sufficient. Until we know more, it seems prudent for public health to avoid dispersing chrysotile/tremolite into the environment, and, where we can, to regulate all tremolite "fibers" conservatively.

Cell toxicity, hemolytic action and clastogenic activity of asbestos and its substitutes.

The cell toxicity, hemolytic and clastogenic activity were examined in various kinds of asbestos and some asbestos substitutes with reference to the their mineralogical and physicochemical characteristics. There were thirty-five fibrous and non-fibrous samples including UICC chrysotile, size-selected samples of UICC chrysotile, chrysotile altered by heating and grinding, Yamabe (Japan) chrysotile with long and short fibers, Coalinga (U.S. A.) chrysotile with short fibers, UICC crocidolite, amosite, and 19 non-asbestos samples such as, glass fibers, calcium silicates, sepiolites and some clay minerals. The cell toxicity and the hemolytic and clastogenic activity of asbestos were the strongest for chrysotile among all of the asbestos samples tested, and their strengths varied with fiber length and with the conditions of grinding and heating. These cellular effects of Yamabe chrysotile with long fibers and size-selected UICC chrysotile with long fibers were stronger than those of chrysotile of the same origin but with short fibers. These effects were weaker in chrysotile altered by heating and grinding. Among the asbestos substitutes, the cell toxicity, hemolytic and clastogenic activities of thin glass fibers were more marked than those of thick glass fibers. The four types of sepiolite were strongly hemolytic, but their cell toxicity and clastogenicity varied according to their grade of crystallinity and/or fiber size. These effects of calcium silicates and some clay minerals were generally low but varied with mineral species. In general, the cell toxicity, hemolytic and clastogenic activities of the asbestos substitutes tested here were mild compared with those of asbestos.

[Maximum permissible levels of asbestos and other natural minerals with fibrous structure--necessity of verification]. / Najwyzsze dopuszczalne stezenia dla azbestu i innych naturalnych mineralów o strukturze wlóknistej--koniecznosc weryfikacji.

MACs of asbestos are from 2 to 20 times higher in Poland than in other Western Europe countries. The analysis of occupational diseases reported between 1983 and 1988 among workers of asbestos-cement plants has showed that Polish MAC values do not protect people from work-related asbestosis. Asbestosis was frequently diagnosed in workers employed at mining and processing of nickel ore containing admixtures of fibrous antigorite. The risk of asbestosis in workers of a nickel++ metallurgical plant was 8 times higher that in those employed at an asbestos-cement plant. In an animal study, fibrogenic, carcinogenic and mutagenic activity of antigorite was similar to the biological aggressiveness of crocidolite. Based on own studies and literature data, the following MACs for asbestos and other natural fibrous minerals were established: a) for dusts containing asbestos and other fibrous minerals except crocidolite and fibrous antigorite, total dust concentration equals 1 mg/m3 and concentration of fibres longer than 5 microns = 0.5 fibre/cm3 b) for dusts containing crocidolite and fibrous antigorite total dust concentration = 0.5 mg/m3 and concentration of fibres longer than 5 microns = 0.2 fibre/cm3.