A novel synthetic erionite fibre radiolabelled with (57)Co.

The aim was to produce a radiolabelled fibre suitable for long-term carcinogenesis studies. To this end, we have successfully synthesised erionite fibres by a method adapted to incorporate (57)Co into the crystal framework. Morphologically the fibres are straight, of median length 2.5 microm, with 11% of fibres > 8 microm long, and median width 0.32 microm. These values are comparable to natural Oregon erionite. Autoradiography confirmed that the (57)Co was associated with the fibres themselves. The stability of the radiolabel in vivo was examined by instilling 1 mg of synthetic erionite into the lungs of F-344 rats. About half of the thoracic content of (57)Co was cleared in the first week, and over the following 5 weeks the remainder was cleared slowly with a half-time of 120 days. After 6 weeks the urinary excretion of (57)Co was only 0.054% of the initial lung content per day. This represented fibre dissolution plus any leaching of (57)Co from the fibres. It can be concluded that the (57)Co is bound into the erionite fibres with sufficient stability in vivo for studying their effects in relation to translocation to the pleura.

Increased expression of epidermal growth factor receptor in rat pleural mesothelial cells correlates with carcinogenicity of mineral fibres.

Asbestos fibres have been shown to stimulate the mitogen-activated protein kinase signalling cascade in rat pleural mesothelial (RPM) cells after autophosphorylation of the epidermal growth factor receptor (EGFR). We examined if mineral fibres with known carcinogenicity can be discriminated from materials with less or no carcinogenicity by their ability to up-regulate expression of EGFR protein in RPM cells in vitro. Crocidolite and erionite, two fibrous preparations with marked potential to induce mesothelioma, were associated with increases in EGFR protein expression over sham controls, whereas chrysotile asbestos and milled (non-fibrous) crocidolite did not. Intense patterns of EGFR protein expression were linked to RPM cells phagocytosing long fibres. To determine the role of EGFR expression in these cells, we assessed cell proliferation using an antibody against proliferating cell nuclear antigen (PCNA) in combination with an antibody against EGFR. In these co-localization studies, cells showed intense staining for EGFR protein 24 h before being PCNA positive at 48 h. These results suggest that carcinogenic fibres induce EGFR and initiate cell signalling cascades in mesothelial cells, leading to cell proliferation and carcinogenesis.

Cell Signaling in Mesothelial Cells by Asbestos: Evidence for the Involvement of Oxidative Stress in the Regulation of the Epidermal Growth Factor Receptor.

Asbestos has been shown to stimulate the mitogen-activated protein kinase signaling cascade after autophosphoryiation of the epidermal growth factor recptor (EGF-R), an event important in regulating the response of cells to extracellular signals. In studies reported here, we have examined whether mineral fibers with known carcinogenicity can be discriminated from nonpathogenic fibers by their ability to upregulate expression of EGF-R protein in mesothelial cells. Crocidolite and erionite, two fibrous preparations known to induce mesothelioma, increased expression of EGF-R protein in a time- and dose-dependent manner, whereas milled (nonfibrous) crocidolite and chrysotile asbestos, two preparations with much less or no ability to induce mesothelioma, did not. Intense patterns of EGF-R protein expression were linked to mesothelial cells phagocytosing long fibers as observed by phase-contrast microscopy. To determine the importance of EGF-R expression in these cells, we assessed downstream signaling events in rat pleural mesothelial (RPM) cells by looking at the induction of activator protein-1 (AP-I), a transcription factor that controls the transition to S phase in the cell cycle, leading to cell proliferation. Crocidolite induced AP-I in RPM cells in a dose-dependent manner, and this induction of AP-I in RPM cells was inhibited by coincubation with tyrphostin AG 1478, a potent inhibitor of the EGF-R. To examine the mechanism of induction of EGF-R in RPM cells by asbestos, RPM cells were treated with crocidolite in the presence and absence of the antioxidant N-acetylcysteine (NAC). Reduced glutathione (GSH) was examined as a marker of oxidative stress and the expression of EGF-R protein was measured. Crocidolite asbestos caused a dose-dependent depletion of GSH in RPM cells, and the presence of NAC ameliorated the expression of EGF-R protein by crocidolite. Our data suggest that carcinogenic fibers induce EGF-R via a mechanism involving oxidative stress initiating cell signaling cascades in mesothelial cells leading to cell proliferation and carcinogenesis.

The construction and validation of a high containment nose-only rodent inhalation facility.

A new nose-only inhalation facility for rodents has been designed and built for operation within a high containment glove box facility. All operations using the equipment, whether concerned with aerosol generation or animal handling and exposure are conducted under high containment with total operator protection. The facility has been used to investigate known carcinogenic fibres such as the amphiboles. It has been designed to be resistant to most chemicals, under the conditions of an experiment, and can be used with radioactive material within the limitations which would be imposed for radiological protection. This paper describes the construction and validation of the equipment using titanium dioxide.