Timothy R. Quinlan

TNFα and increased chemokine expression in rat lung after particle exposure

Abstract Macrophage inflammatory protein 2 (MIP-2) and CINC (Cytokine-Induced-Neutrophil-Chemoattractant) are members of the chemokine family of inflammatory and immunoregulatory cytokines. MIP-2 and CINC exhibit potent neutrophil chemotactic activity and are thought to be key mediators of inflammatory cell recruitment in response to tissue injury and infection. In the present studies, we examined the potential involvement of MIP-2 and CINC in particle-elicited inflammation in the rat lung and the role of TNFα in particle-induced chemokine expression. Acute intratracheal instillation exposure of F344 rats to α quartz or titanium dioxide was shown to markedly increase steady-state levels of MIP-2 and CINC mRNA in lung tissue; a response which was associated with a significant increase in neutrophils in the bronchoalveolar lavage fluid. Additional studies demonstrated that acute inhalation of crocidolite fibers by rats also induced increased MIP-2 and CINC expression. Since previous studies had demonstrated that TNFα stimulates MIP-2 and CINC expression in vitro and that particle exposure induces TNFα production in rat lung we examined the role of TNFα in a quartz-induced MIP-2 gene expression. We demonstrated that passive immunization of mice against TNFα markedly attenuated the increased lung MIP-2 mRNA seen in response to a quartz inhalation. Collectively, these findings suggest that the chemokines MIP-2 and CINC play a role in neutrophil recruitment to the rat lung after particle exposure and indicate that particle-induced expression of these chemokines is mediated, at least in part, by production of TNFα.

Mechanisms of asbestos-induced nitric oxide production by rat alveolar macrophages in inhalation and in vitro models.

To evaluate the contribution of reactive nitrogen species to inflammation by asbestos, Fischer 344 rats were exposed to crocidolite or chrysotile asbestos by inhalation to determine whether increases occurred in nitric oxide (NO.) metabolites from alveolar macrophages (AMs). AMs from animals inhaling asbestos showed significant elevations (p < .05) in nitrite/nitrate levels which were ameliorated by NG-monomethyl-L-arginine (NMMA), an inhibitor of inducible nitric oxide synthase (iNOS) activity. Temporal patterns of NO. generation from AMs correlated with neutrophil influx in bronchoalveolar lavage samples after asbestos inhalation or bleomycin instillation, another model of pulmonary fibrosis. To determine the molecular mechanisms and specificity of iNOS promoter activation by asbestos, RAW 264.7 cells, a murine macrophage-like line, and AMs isolated from control rats were exposed to crocidolite asbestos in vitro. These cells showed increases in steady-state levels of iNOS mRNA in response to asbestos and more dramatic increases in both iNOS mRNA and immunoreactive protein after addition of lipopolysaccharide (LPS). After transfection of an iNOS promoter/luciferase reporter construct, RAW 264.7 cells exposed to LPS, crocidolite asbestos and its nonfibrous analog, riebeckite, revealed increases in luciferase activity whereas cristobalite silica had no effects. Studies suggest that NO. generation may be important in cell injury and inflammation by asbestos.

Activation of Early Cellular Responses by Asbestos: Induction of c-FOS and c-JUN Protooncogene Expression in Rat Pleural Mesothelial Cells

Asbestos fibers belong to a family of ubiquitous mineral silicates. Two types of malignancies have been documented in respiratory tract and pleura following inhalation of asbestos. Bronchogenic carcinoma, arising in the tracheobronchialepithelium, is a tumor found in individuals exposed occupationally to asbestos. Since this tumor is rarely found in non-smoking asbestos workers, asbestos is thought to act mainly as a co-carcinogen or tumor promoter in the development of this disease (Mossman et al. 1990). However, the development of malignant mesothelioma in the pleura is not associated with cigarette smoking. The generally accepted view is that amphibole asbestos acts as a complete carcinogen in the development of mesothelioma (Mossman et al.1990).