Induction of Manganese Superoxide Dismutase Gene Expression in Bronchoepithelial Cells after Rockwool Exposure

Abstract

Superoxide dismutases play an important protective role in the lung defense against the pro-oxidative effect of fibrous dusts (e.g. crocidolite fibers). Particularly crocidolite, but also other asbestos fibers, are known to induce cellular antioxidant defense. Although rockwool, a man-made fiber made from rock, is used widely for insulation purposes, its effects on the superoxide dismutases in bronchoepithelial cells have not been investigated. Thus, the purpose of this study was to determine whether human bronchoepithelial cells (BEAS 2B) respond to rockwool fibers (115-4 experimental rockwool fiber) by induction of MnSOD mRNA and an increase of MnSOD activity levels. The results were compared with BEAS 2B cells exposed to silica (alpha-quartz: DQ12; SiO2) and UICC (Union Internationale Contre le Cancer) crocidolite (concentrations of all dusts: 0, 2, 5, 10, 25, 50 micrograms/cm2 = 0, 2.4, 6, 12, 30, 60 micrograms/ml; 24-h exposure) as control fibers. Scanning electron microscopy confirmed close dust cell contact under all experimental settings. Very low MnSOD mRNA baseline levels rose significantly (p < 0.001) in BEAS 2B cells exposed to all three dusts at 2 micrograms/cm2. However, at > 25 micrograms/cm2 MnSOD mRNA levels in silica- and crocidolite- but not in rockwool-exposed cells decreased. Slight (no significance) increases of MnSOD activity were observed which decreased at higher dust (> 5 micrograms/cm2) concentrations. These results suggest that: (1) like crocidolite and silica, rockwool accelerates MnSOD gene expression in bronchoepithelial cells; (2) an increase of MnSOD mRNA levels is not accompanied by MnSOD activity elevation; (3) in contrast to rockwool, high concentrations (> or = 25 micrograms/cm2) of crocidolite and silica reduced MnSOD activity and MnSOD mRNA levels. Because oxidants (H2O2) and crocidolite fibers were shown to reduce SOD activity, lack of active MnSOD protein may be caused by inactivation on a post-translational level. Furthermore, the decline of MnSOD mRNA and MnSOD activity levels coincides with increasing cytotoxicity. In conclusion, rockwool was demonstrated to induce MnSOD gene expression, perhaps because of its pro-oxidative effect in bronchoepithelial cells. In contrast to crocidolite and silica, rockwool fibers are not cytotoxic in this experimental setting.

The effect of stone-wool on rat lungs and on the primary culture of rat alveolar macrophages and type II pneumocytes

“…Therefore the long term effect of stone-wool on the lungs was studied. Further data on its direct toxic effects in pneumocytes and alveolar macrophages (Luoto et al, 1998;Marks-Konczalik et al, 1998) are scarce and there is only inadequate evidence for carcinogenicity of stone-wool in humans (IARC, 2002).…”

“…(iii) The effect of stone-wool on some enzymes, the activity of gamma-glutamyl transpeptidase (surface marker of type II cells -Hook, 1978;Klaveren et al, 1997), GSH-Px and GSH-Rd were determined (Kelly, 2002;Rahman and McNee, 2000;Aerts et al, 1992;Weller et al, 1997). Further, cytoplasmic Cu,Zn/SOD activity (Holley et al, 1992;Marks-Konczalik et al, 1998) and the activity of alkaline phosphatase (Richards et al, 1987) were measured. (iv) Production of MCP-1 and MIP-1α were determined by ELISA in the primary culture of alveolar macrophages and type II pneumocytes upon the effect of rockwool and crocidolite, for presumably there is some connection between the formation of free radicals and production of proinflammatory proteins, especially in alveolar macrophages and type II pneumocytes (Koyama et al, 1999;Barrett et al, 1999).…”