Enhanced expression of pulmonary gamma-glutamylcysteine synthetase heavy subunit in rats exposed to cadmium aerosols.Toxicol Appl Pharmacol. 2000 Mar 15; 163(3):249-59.TA
This investigation sought to determine the effect of cadmium (Cd) aerosol exposure on the pulmonary expression of the heavy subunit (HS) of gamma-glutamylcysteine synthetase (gamma-GCS), the rate-limiting enzyme in de novo synthesis of glutathione (GSH). Using Northern hybridization analysis, we demonstrated that CdO inhalation caused time- and dose-dependent increases in the steady-state levels of gamma-GCS-HS mRNA that were highly correlated with lung Cd burden. Observed increases in gamma-GCS-HS gene expression were maximal 2 h following a single aerosol exposure to Cd and appeared to be triggered by an oxidant stress, characterized by a decline in the reduced to oxidized glutathione ratio. Immunoblotting of proteins in lung extracts from treated and untreated animals produced a single protein band corresponding to a molecular weight of 73 kDa. Elevated levels of gamma-GCS-HS mRNA and gamma-GCS-HS protein in lungs of Cd-exposed animals were also accompanied by higher gamma-GCS enzymatic activity and elevations in glutathione (GSH). Immunohistochemical and in situ hybridization studies were used to identify compartments in the lung where Cd-induced expression of gamma-GCS-HS was localized. The most prominent staining for gamma-GCS-HS protein and gamma-GCS-HS mRNA was observed in the alveolar epithelium of Cd-exposed animals. Quantitative image analysis confirmed a good agreement between relative levels of protein and mRNA transcripts for gamma-GCS-HS. These observations suggest that resistance to Cd toxicity in the lung may reflect the ability of specific lung cells to upregulate gamma-GCS expression and increase de novo GSH synthesis as an adaptive response.