Carbon in Intimate Contact with Quartz Reduces the Biological Activity of Crystalline Silica Dusts

Ghiazza, Mara; Tomatis, Maura; Doublier, Sophie; Grendene, Francesca; Gazzano, Elena; Ghigo, Dario; Fubini, Bice

doi:10.1021/tx300299v

Cited by 9 publications

(13 citation statements)

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“…All quartz samples were tested for their potential to generate carbon-centred radicals after 10, 30 and 60 min of incubation with formate ion. The homolytic cleavage of the hydrogen-carbon bond in formate was followed by spin trapping technique and quantified with EPR spectroscopy, as carried out in several previous studies with quartz dusts [ 20 , 41 – 43 ]. Representative EPR/spin trapping spectra of the [DMPO–COO] • – adduct obtained in the presence of sodium formate at 60 min and double-integration of the reaction kinetics are reported in Fig.…”

Section: Resultsmentioning

confidence: 99%

Revisiting the paradigm of silica pathogenicity with synthetic quartz crystals: the role of crystallinity and surface disorder

et al. 2015

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BackgroundExposure to some - but not all - quartz particles is associated to silicosis, lung cancer and autoimmune diseases. What imparts pathogenicity to any single quartz source is however still unclear. Crystallinity and various surface features are implied in toxicity. Quartz dusts used so far in particle toxicology have been obtained by grinding rocks containing natural quartz, a process which affects crystallinity and yields dusts with variable surface states. To clarify the role of crystallinity in quartz pathogenicity we have grown intact quartz crystals in respirable size.MethodsQuartz crystals were grown and compared with a fractured specimen obtained by grinding the largest synthetic crystals and a mineral quartz (positive control). The key physico-chemical features relevant to particle toxicity - particle size distribution, micromorphology, crystallinity, surface charge, cell-free oxidative potential - were evaluated. Membranolysis was assessed on biological and artificial membranes. Endpoints of cellular stress were evaluated on RAW 264.7 murine macrophages by High Content Analysis after ascertaining cellular uptake by bio-TEM imaging of quartz-exposed cells.ResultsQuartz crystals were grown in the submicron (n-Qz-syn) or micron (μ-Qz-syn) range by modulating the synthetic procedure. Independently from size as-grown quartz crystals with regular intact faces did not elicit cellular toxicity and lysosomal stress on RAW 264.7 macrophages, and were non-membranolytic on liposome and red blood cells. When fractured, synthetic quartz (μ-Qz-syn-f) attained particle morphology and size close to the mineral quartz dust (Qz-f, positive control) and similarly induced cellular toxicity and membranolysis. Fracturing imparted a higher heterogeneity of silanol acidic sites and radical species at the quartz surface.ConclusionsOur data support the hypothesis that the biological activity of quartz dust is not due to crystallinity but to crystal fragmentation, when conchoidal fractures are formed. Besides radical generation, fracturing upsets the expected long-range order of non-radical surface moieties - silanols, silanolates, siloxanes - which disrupt membranes and induce cellular toxicity, both outcomes associated to the inflammatory response to quartz.Electronic supplementary materialThe online version of this article (doi:10.1186/s12989-016-0136-6) contains supplementary material, which is available to authorized users.

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Section: Resultsmentioning

confidence: 99%

Revisiting the paradigm of silica pathogenicity with synthetic quartz crystals: the role of crystallinity and surface disorder

et al. 2015

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“…The overall antioxidant function seen in Figure 7B is believed to be a combination of UV absorption, ROS scavenging in the graphene sack interior, and possible passivation of a portion of the TiO 2 surfaces by close contact with internal conforming graphene structures (see SI) in a manner analogous to the passivation of silica by carbon black following co-grinding to produce intimate contact. 72 …”

Section: Discussionmentioning

confidence: 99%

Antioxidant chemistry of graphene-based materials and its role in oxidation protection technology

et al. 2014

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Two-dimensional nanomaterials have potential as a new class of antioxidants that combine physical barrier function with ultrahigh surface area for free radical scavenging. This work presents the first measurements of the chemical reactivities of graphene-based materials toward a set of model free radicals and reactive oxygen species using electron paramagnetic resonance spectroscopy (EPR) and sacrificial dye protection assays. Graphene-based materials are shown to protect a variety of molecular targets from oxidation by these species, and to be highly effective as hydroxyl-radical scavengers. When hydroxyl radical is produced photolytically, the overall antioxidant effect is a combination of preventative antioxidant activity (UV absorption) and ·OH radical scavenging. Few-layer graphene is more active than monolayer graphene oxide, despite its lower surface area, which indicates that the primary scavenging sites are associated with the sp2-carbon network rather than oxygen-containing functional groups. To explain this trend, we propose that GO is a weak hydrogen donor, due to the non-phenolic nature of most OH groups on GO, which reside at basal sp3-carbon sites that do not allow for radical resonance stabilization following hydrogen donation. As an example application of graphene antioxidant behavior, we show that encapsulation of TiO2 nanoparticles in graphene nanosacks reduces undesired photo-oxidative damage to nearby organic target molecules, which suggests graphene encapsulation as a new approach to managing adverse environmental or health impacts of redox-active nanomaterials.

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“…Indeed, VS is less active in ˙OH release than Qz-1 and Qz-3. Moreover, neither VS nor Qz-3 are able to catalyze carbon-centered radicals, contrary to Qz-1 [ 41 , 47 ].…”

Section: Discussionmentioning

confidence: 99%

Why does the hemolytic activity of silica predict its pro-inflammatory activity?

et al. 2014

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BackgroundThe hemolytic activity of inhaled particles such as silica has been widely investigated in the past and represents a usual toxicological endpoint to characterize particle reactivity despite the fact that red blood cells (RBCs) are not involved in the pathogenesis of pulmonary inflammation or fibrosis caused by some inhaled particles. The inflammatory process induced by silica starts with the activation of the inflammasome, which leads to the release of mature IL-1β. One of the upstream mechanisms causing activation of the inflammasome is the labilization of the phagolysosomal membrane after particle phagocytosis. Considering RBC lysis as a model of membrane damage, we evaluated the relationship between hemolytic activity and inflammasome-dependent release of IL-1β for a panel of selected silica particles, in search of the toxicological significance of the hemolytic activity of an inhaled particle.MethodsWell-characterized silica particles, including four quartz samples and a vitreous silica, with different surface properties and hemolytic potential were tested for their capacity to induce inflammasome-dependent release of IL-1β in LPS-primed primary murine peritoneal macrophages by ELISA and Western blot analysis. The mechanisms of IL-1β maturation and release were clarified by using ASC-deficient cells and inhibitors of phagocytosis and cathepsin B.ResultsThe silica samples induced dose-dependent hemolysis and IL-1β release of different amplitudes. A significant correlation between IL-1β release and hemolytic activity was evidenced (r = 0.827) by linear regression analysis. IL-1β release was completely abolished in ASC-deficient cells and reduced by inhibitors, confirming the involvement of the inflammasome and the requirement of phagocytosis and cathepsin B for activation.ConclusionsThe same physico-chemical properties of silica particles which are relevant for the lysis of the RBC membrane also appear implicated in the labilization of the phagolysosome, leading to inflammasome activation and release of the pro-inflammatory cytokine IL-1β. These findings strengthen the relevance of the hemolysis assay to predict the pro-inflammatory activity of silica dusts.Electronic supplementary materialThe online version of this article (doi:10.1186/s12989-014-0076-y) contains supplementary material, which is available to authorized users.

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Carbon in Intimate Contact with Quartz Reduces the Biological Activity of Crystalline Silica Dusts

Cited by 9 publications

References 45 publications

Revisiting the paradigm of silica pathogenicity with synthetic quartz crystals: the role of crystallinity and surface disorder

Revisiting the paradigm of silica pathogenicity with synthetic quartz crystals: the role of crystallinity and surface disorder

Antioxidant chemistry of graphene-based materials and its role in oxidation protection technology

Why does the hemolytic activity of silica predict its pro-inflammatory activity?

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