Asbestos-induced lung epithelial permeability: potential role of nonoxidant pathways

Cytotoxic and Apoptotic Effect of Nanoclinoptilolite on Canine Osteosarcoma Cell Lines

Introduction

Clinoptilolite has antiviral, antibacterial, anti-inflammatory, antidiabetic, and anticancer properties due to its biological activities. In various cancer cell culture studies, it has been reported effective against tumour cells and gave positive results in treatment of various tumours in dogs. No study was found on the effects of the nanoparticulate form, nanoclinoptilolite, on cancer cells. The aim of this study was to determine its cytotoxic and apoptotic effects in canine osteosarcoma (OSA) cell culture.

Material and Methods

Doses at 50% inhibitory concentration were determined by measuring the dose- and duration-dependent cytotoxicity of nanoclinoptilolite on canine D-17 osteosarcoma cells by methylthiazol tetrazolium (MTT) test for 24 h, 48 h, and 72 h. Murine caspase-3 and -7 activity and expression levels of the BAX and BCL2 genes were measured using RT-PCR to investigate the apoptotic effect.

Results

Nanoclinoptilolite decreased cell viability and induced caspase-3- and -7-mediated apoptosis in treated canine OSA cells. Furthermore, its application to canine OSA cells downregulated the expression of BCL2 and upregulated the expression of proapoptotic BAX.

Conclusion

Clinoptilolite, which was previously demonstrated to have anticancer properties, decreased cell viability effectively and rapidly and increased the apoptotic cell ratio in a novel use in nanoparticle form, exhibiting this effect by increasing the BAX/BCL2 ratio.

Shape-Related Toxicity of Titanium Dioxide Nanofibres

Titanium dioxide (TiO₂) nanofibres are a novel fibrous nanomaterial with increasing applications in a variety of fields. While the biological effects of TiO₂ nanoparticles have been extensively studied, the toxicological characterization of TiO₂ nanofibres is far from being complete. In this study, we evaluated the toxicity of commercially available anatase TiO₂ nanofibres using TiO₂ nanoparticles (NP) and crocidolite asbestos as non-fibrous or fibrous benchmark materials. The evaluated endpoints were cell viability, haemolysis, macrophage activation, trans-epithelial electrical resistance (an indicator of the epithelial barrier competence), ROS production and oxidative stress as well as the morphology of exposed cells. The results showed that TiO₂ nanofibres caused a cell-specific, dose-dependent decrease of cell viability, with larger effects on alveolar epithelial cells than on macrophages. The observed effects were comparable to those of crocidolite, while TiO₂ NP did not decrease cell viability. TiO₂ nanofibres were also found endowed with a marked haemolytic activity, at levels significantly higher than those observed with TiO₂ nanoparticles or crocidolite. Moreover, TiO₂ nanofibres and crocidolite, but not TiO₂ nanoparticles, caused a significant decrease of the trans-epithelial electrical resistance of airway cell monolayers. SEM images demonstrated that the interaction with nanofibres and crocidolite caused cell shape perturbation with the longest fibres incompletely or not phagocytosed. The expression of several pro-inflammatory markers, such as NO production and the induction of Nos2 and Ptgs2, was significantly increased by TiO₂ nanofibres, as well as by TiO₂ nanoparticles and crocidolite. This study indicates that TiO₂ nanofibres had significant toxic effects and, for most endpoints with the exception of pro-inflammatory changes, are more bio-active than TiO₂ nanoparticles, showing the relevance of shape in determining the toxicity of nanomaterials. Given that several toxic effects of TiO₂ nanofibres appear comparable to those observed with crocidolite, the possibility that they exert length dependent toxicity in vivo seems worthy of further investigation.

Phagocytosis of crocidolite asbestos induces oxidative stress, DNA damage, and apoptosis in mesothelial cells

Phagocytosis of asbestos fibers may be a necessary step for asbestos-induced injury to mesothelial cells, but this has not been established because quantification of fiber uptake is difficult and ways to increase fiber phagocytosis without also increasing total dose were not available. We quantified phagocytosis by counting intracellular fibers after removing adherent fibers with trypsin; we selectively increased fiber phagocytosis by coating crocidolite asbestos fibers with the adhesive serum protein vitronectin (VN), which we have shown increases fiber uptake via integrins. We measured various aspects of asbestos-induced cytotoxicity: intracellular oxidation by the shift of fluorescence of cells loaded with an oxidative probe, DNA strand breakage by the alkaline unwinding ethidium bromide fluorometric assay, apoptosis by annexin V binding and by nuclear morphology, and cell-cycle progression. We found that, compared with control fibers or particles, asbestos increased intracellular oxidation, DNA strand breakage, and apoptosis. Selective increases in fiber uptake by VN-coating of the fibers further increased the oxidation, DNA strand breakage, and apoptosis, and induced a cell-cycle arrest in G2/M. Selective decreases in fiber uptake by cytochalasin or by integrin blockade with RGD peptides inhibited several of these measures of injury. We conclude that phagocytosis is important and perhaps necessary for asbestos-induced injury to mesothelial cells.