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Table 2 Overview of in vitro genotoxicity outcomes obtained with crystalline silica of respirable size in in vitro studies

From: An updated review of the genotoxicity of respirable crystalline silica

Sample characteristics Test system Outcomes Reference
DQ12 quartz milled to 410 nm average diameter (100–800 nm). Used as positive control Micronuclei (MN) in human PBL pooled from 2 donors (similar to OECD test guideline 487) after 24 h incubation in the absence of metabolic activation. Dose-response study. No increase in MN in the concentration range testing at 32, 100, 320 and 1000 μg/ml. Particle number at lowest concentration was 5.32 × 109 [17]
DQ12 quartz as positive control in evaluation bentonite genotoxicity.
GSD: 2.0 μm, surface area: 5.7 m2/g
Bentonite particles (BP; 6.8 and 6.5% CS). GSD 2.7 and 2.5 μm. Surface area: 60 and 108 m2/g
COMET and MN in Human B cell line (HM2.CIR), at concentrations 30–240 μg/ml
COMET and MN in Human B cell line (HM2.CIR), at concentrations 30, 60, 180, 240 μg/ml
Slightly NS elevation of MN and COMET in cell line, after 24 h exposure to highest concentration (240 μg/ml). At 72 h of exposure all values are increased.
Dose-dependent increase in MN and COMET above concentrations of 60 and 120 μg/ml, respectively; but only at 24 h. At 48 and 72 h all BP samples show increased MN and COMET.
Bentonite particles show a stronger effect than DQ12 quartz.
[18]
Pure milled quartz from mineral source (respirable, surface area 4. 2 m2/g) and vitreous silica (respirable, 5.0 m2/g). Size range determined with SEM between 0.5 and 5 μm Macrophage cell line (RAW 264.7) and epithelial cell line (A549) were incubated 4 or 24 h.
Concentrations 5–80 μg/cm2.
MN frequency and % tail DNA (comet) were assessed
Only quartz and not vitreous silica caused changes in % tail DNA, but exclusively in RAW cell line and not in A549 cells.
The effect was visible both at 4 and 24 h.
Particle uptake was assessed and noted to be similar in both cell types, although quantitative data are lacking
[19]
DQ12 (3 μm) as reference particles for fibre study to elucidate effect of mineral composition
Quenching all particles with aluminium lactate
Primary rat alveolar macrophages, 2 h incubation with 200 μg/cm2
Primary rat alveolar macrophages, 2 h incubation with 200 μg/cm2
Tail intensity in comet assay was induced 20-fold over control in the presence of significant cytotoxicity induced by DQ12
Particle toxicity and tail moment induction was reduced to control levels by pre-incubation with aluminium lactate (100 uM)
[20]
[20]
DQ12 quartz as positive control in study aiming to investigate metal nanoparticles. ToxTracker reporter assay in mouse embryonic stem (mES) cells. GFP induction and cell viability were determined with flow cytometry. mES cells were exposed to quartz particles (6.25, 25, 50 and 100 μg/mL) for 24 h DNA damage reporter (Bscl2) and the general stress reporter (Btg2) genes were not induced by treatment with any concentration of quartz. Only the anti-oxidant reporter gene was induced in a concentration dependent way. No genotoxicity was observed in mES cells using the comet assay. [21]
Ground Min-U-Sil (CS) with mean size of 3.7 um and purity of 99.5% CS.
Aged versus freshly ground CS
Human bronchial epithelial cells (BEAS-IIB) and lung cancer cells with altered (H460) or deficient (H1299) p53 expression Freshly fractured or aged silica produced divergent cellular responses in certain downstream cellular events, including ROS production, apoptosis, cell cycle and chromosomal changes, and gene expression. Exposure to freshly fractured silica also resulted in a rise in aneuploidy in cancer cells with a significantly greater increase in p53-deficient cells [22]
Quartz Q1 with mean size (D50) of 12.1 μm. 0.89 m2/gram and DQ12 (D50, 3 μm)) with or without different organosilane coatings (PTMO, SIVO 160) and Al-lactate as control inhibitor Primary rat alveolar macrophages, 1.5–2 × 105 cells per well, 2 h incubation with 75 μg/cm2 Both Q1 and DQ12 caused significant DNA damage in comet assay associated to cytotoxicity (LDH leakage). Both toxicity and DNA damage were blocked by pre-treatment of DQ12 with Al-lactate or organosilane compounds. Surface binding was found to be effective up to 168 h after treatment in artificial lysosomal fluid (pH 4.5). [20]