Such conditions are associated with increased levels of oxidative stress in the lung and several studies have therefore focused on the antioxidant/oxidants balance in CF, with particular interest on GSH and GSH-associated enzymes [1], [2]. GSH is one of the major water-soluble antioxidants and its chemical properties make selleck products it able to play a role also in mucolysis, regulation of inflammation, immune response and cell viability [1]. Interestingly, GSH concentrations are markedly reduced in CF airways and plasma [8], and several factors (e.g. chronic inflammation, oxidative stress, impaired CFTR-mediated GSH transport) may contribute to this effect. Gamma-glutamyltransferase (GGT) is a membrane-bound enzyme involved in the metabolism and recuperation of extracellular glutathione by cells.
GGT is also involved in S-nitrosoglutathione and leukotrienes metabolisms [9], [10] and several studies documented its role in promoting pro-oxidant reactions, thanks to the highly reactive GSH-derivative cysteinyl-glycine [11]. Indeed, cysteinyl-glycine can be considered as a marker of GGT activity and its ability in promoting protein S-thiolation was also shown [12]. GGT expression can be induced by oxidative stress [13], [14] and inflammatory cytokines, such as TNF-alpha, IFN-alpha and �Cbeta (see [11] for a recent review). Interestingly, a significant increase in GGT activity was described in the bronchoalveolar lavage of young children with pulmonary inflammation due to CF [15] and such increase was interpreted as a response to inflammation-related oxidative stress, likely providing bronchial cells with a mechanism for an increased recovery of extracellular glutathione [1], [15].
Higher GGT activities were also detected in vitro in cultured CF cell lines [4], [16], suggesting that the GGT increase in CF lungs may be directly related with CFTR defective function. Nevertheless other non-epithelial sources should be taken into account when considering the GGT increase in CF lungs. In particular, some studies demonstrated the expression of GGT in human lymphoid cells and an increase of GGT activity was described in the granulocytic cell lineage along with cell maturation [17], during differentiation of lymphocytes [18] and monocytes/macrophages [19].
In neutrophils GGT is localized in microsomal and granular fractions and released upon neutrophils activation with calcium-ionophore “type”:”entrez-nucleotide”,”attrs”:”text”:”A23187″,”term_id”:”833253″,”term_text”:”A23187″A23187 [9], [17], [20]. The aim of the present work was to assess the origin and the biochemical characteristics of the GGT detectable in CF sputum in comparison with the enzyme released by activated neutrophils, in order to appraise the contribution of inflammation-derived GGT to the increased activity described in CF lungs. Materials and Methods Chemicals Unless otherwise indicated, all reagents Dacomitinib were from Sigma Chemical Co.