Organosilane-Based Coating of Quartz Species from the Traditional Ceramics Industry: Evidence of Hazard Reduction Using In Vitro and In Vivo Tests

Abstract

The exposure to respirable crystalline silica (RCS), e.g. quartz, in industrial settings can induce silicosis and may cause tumours in chronic periods. Consequently, RCS in the form of quartz and cristobalite has been classified as human lung carcinogen category 1 by the International Agency for Research on Cancer in 1997, acknowledging differences in hazardous potential depending on source as well as chemical, thermal, and mechanical history. The physico-chemical determinants of quartz toxicity are well understood and are linked to density and abundance of surface silanol groups/radicals. Hence, poly-2-vinylpyridine-N-oxide and aluminium lactate, which effectively block highly reactive silanol groups at the quartz surface, have formerly been introduced as therapeutic approaches in the occupational field. In the traditional ceramics industry, quartz-containing raw materials are indispensable for the manufacturing process, and workers are potentially at risk of developing quartz-related lung diseases. Therefore, in the present study, two organosilanes, i.e. Dynasylan® PTMO and Dynasylan® SIVO 160, were tested as preventive, covalent quartz-coating agents to render ceramics production safer without loss in product quality. Coating effectiveness and coating stability (up to 1 week) in artificial alveolar and lysosomal fluids were first analysed in vitro, using the industrially relevant quartz Q1 as RCS model, quartz DQ12 as a positive control, primary rat alveolar macrophages as cellular model system (75 µg cm−2; 4 h of incubation ± aluminium lactate to verify quartz-related effects), and lactate dehydrogenase release and DNA strand break induction (alkaline comet assay) as biological endpoints. In vitro results with coated quartz were confirmed in a 90-day intratracheal instillation study in rats with inflammatory parameters as most relevant readouts. The results of the present study indicate that in particular Dynasylan® SIVO 160 (0.2% w/w of quartz) was able to effectively and stably block toxicity of biologically active quartz species without interfering with technical process quality of certain ceramic products. In conclusion, covalent organosilane coatings of quartz might represent a promising strategy to increase workers’ safety in the traditional ceramics industry.

Cytotoxicity of fractured quartz on human macrophages: role of the membranolytic activity of quartz and phagolysosome destabilization.

“…The suppression of the membranolytic activity when fractured quartz and RBCs are contacted in a FBS medium supports the hypothesis that serum proteins mask the surface reactive groups responsible for quartz membranolytic activity. This is in agreement with previous results [26,45,55], and corroborates what observed with other organic polymers [56][57][58]. Intriguingly, the protein coating on fractured quartz, evidenced by the change in surface charge, did not modify the cell viability impact towards THP-1 macrophages at 4 and 24 h (Fig.…”

An updated review of the genotoxicity of respirable crystalline silica

“…Ziemann et al [ 23 ] studied the cytotoxic and genotoxic effects of DQ12 quartz and new pure quartz (Q1) particles from the ceramic industry in primary rat alveolar macrophages. In the study they used several commercially available organosilane coatings to block the highly reactive silanol groups at the quartz surface.…”

“…In vivo genotoxicty responses were not included in this paper. [ 23 ] DQ12 (respirable), 6 mg total cumulative dose Instillation (intratracheal) with 3 × 2 mg each month Poly (ADP-ribose), 8-OH-dG and OGGG 1 induction were assessed in lung tissue using immunohistochemistry (IHC). A good correlation was found between all genotoxicity markers and histopathological inflammation [ 29 ] DQ12, single dose of 100 mg/kg) C57BL/6 wild-type (WT) and p47 phox−/− mice; DQ12 administered by pharyngeal aspiration In vivo oxidative DNA damage in lung tissue was not affected by quartz exposure and did not differ between p47phox− /− and WT mice.…”

Additives for reducing the toxicity of respirable crystalline silica. SILIFE project

“…As a consequence, the addition of the coating agent to quartz suspensions should increase or reduce the ς potential of the quartz (which is negative at pH > 2) and coating effectiveness can be measured in this manner. In this sense, it should be highlighted that some authors pointed out that the maximum inhibition of quartz toxicity is produced by rendering it iso-electric [24]. Moreover, the measurement of ζ potential was found to be extremely sensitive (modifications in surface charge due to the addition of less than 0.05% w/w of aminosilanes can be perfectly detected) and ζ potential is well correlated with toxicological results.…”

“…The in vitro toxicological results evidenced that the oligomeric, amino-modified siloxane SIVO160 seemed to possess considerable quartz toxicity-quenching potential. The toxicological study of the treated quartzes was completed in the project with in vivo tests, a more comprehensive information can be found in a specific paper [24]. …”