Induction of Gamma-Glutamyltransferase Activity and Consequent Pro-oxidant Reactions in Human Macrophages Exposed to Crocidolite Asbestos Alessandro Corti ,* ,1 Justine Bonetti, † Silvia Dominici,* Simona Piaggi,* Vanna Fierabracci,* Rudy Foddis,* and Alfonso Pompella* *Department of Translational Research NTMS, University of Pisa Medical School, Pisa 56126, Italy; and † Universit e de Lorraine, CITHEFOR, F-54000 Nancy, France The authors certify that all research involving human subjects was done under full compliance with all government policies and the Helsinki Declaration. 1 To whom correspondence should be addressed. Fax: (þ39) 050 2218557; E-mail: alessandro.corti@med.unipi.it. ABSTRACT Asbestos is the main causative agent of malignant pleural mesothelioma. The variety known as crocidolite (blue asbestos) owns the highest pathogenic potential, due to the dimensions of its fibers as well as to its content of iron. The latter can in fact react with macrophage-derived hydrogen peroxide in the so called Fenton reaction, giving rise to highly reactive and mutagenic hydroxyl radical. On the other hand, hydroxyl radical can as well originate after thiol-dependent reduction of iron, a process capable of starting its redox cycling. Previous studies showed that glutathione (GSH) is one such thiol, and that cellular gamma-glutamyltransferase (GGT) can efficiently potentiate GSH-dependent iron redox cycling and consequent oxidative stress. As GGT is expressed in macrophages and is released upon their activation, the present study was aimed at verifying the hypothesis that GSH/GGT-dependent redox reactions may participate in the oxidative stress following the activation of macrophages induced by crocidolite asbestos. Experiments in acellular systems confirmed that GGT-mediated metabolism of GSH can potentiate crocidolite-dependent production of superoxide anion, through the production of highly reactive dipeptide thiol cysteinyl-glycine. Cultured THP-1 macrophagic cells, as well as isolated monocytes obtained from healthy donors and differentiated to macrophages in vitro, were investigated as to their expression of GGT and the effects of exposure to crocidolite. The results show that crocidolite asbestos at subtoxic concentrations (50–250 ng/1000 cells) can upregulate GGT expression, which raises the possibility that macrophage- initiated, GSH/GGT-dependent pro-oxidant reactions may participate in the pathogenesis of tissue damage and inflammation consequent to crocidolite intoxication. Key words: crocidolite asbestos; macrophages; gamma-glutamyltransferase; glutathione; iron reduction; oxidative injury. Exposure to asbestos—a family of hydrated silicate minerals with fibrillar structure at microscopic level—represents the main risk factor for the onset of pleural mesothelioma, a highly malignant and aggressive neoplasia of the lung. The highest carcinogenic potential is owned by the mineral varieties termed amosite and crocidolite (also known as blue asbestos), whose fibers are rela- tively longer. Once inhaled microscopic fibers reach the lung pa- renchyma, where resident macrophages become activated in a typical foreign body reaction and produce reactive oxygen species (ROS: superoxide anion, hydrogen peroxide) and cytokines. Macrophages also attempt to phagocytose the fibers—but the dimensions of the latter do not allow formation of complete phagosomes, and cause rather plasma membrane ruptures lead- ing to macrophage death (reviewed by Jiang et al., 2008). Pathogenicity of asbestos is closely related with the presence of iron associated with fibers, particularly in the case of V C The Author(s) 2019. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com 476 TOXICOLOGICAL SCIENCES, 177(2), 2020, 476–482 doi: 10.1093/toxsci/kfz175 Advance Access Publication Date: 6 August 2019 Research Article Downloaded from https://academic.oup.com/toxsci/article/177/2/476/5544276 by guest on 28 September 2022