We studied the regulation of GSH and the enzymes involved in GSH regulation, γ-glutamylcysteine synthetase (γ-GCS) and γ-glutamyl transpeptidase (γ-GT), in response to the oxidants menadione, xanthine/xanthine oxidase, hyperoxia, and cigarette smoke condensate in human alveolar epithelial cells (A549). Menadione (100 μM), xanthine/xanthine oxidase (50 μM/10 mU), and cigarette smoke condensate (10%) exposure produced increased GSH levels (240 ± 6, 202 ± 12, and 191 ± 2 nmol/mg protein, respectively; P < 0.001) compared with the control level (132 ± 8 nmol/mg protein), which were associated with a significant increase in γ-GCS activity (0.18 ± 0.006, 0.16 ± 0.01, and 0.17 ± 0.008 U/mg protein, respectively; P < 0.01) compared with the control level (0.08 ± 0.001 U/mg protein) at 24 h. Exposure to hyperoxia (95% O2) resulted in a time-dependent increase in GSH levels. γ-GCS activity increased significantly at 4 h ( P < 0.001), returning to control values after 12 h of exposure. Dexamethasone (3 μM) exposure produced a significant time-dependent decrease in the levels of GSH and γ-GCS activity at 24–96 h. The activity of γ-GT did not change after oxidant treatment; however, it was decreased significantly by dexamethasone at 24–96 h. Thus oxidants and dexamethasone modulate GSH levels and activities of γ-GT and γ-GCS by different mechanisms. We suggest that the increase in γ-GCS activity but not in γ-GT activity may be required for the increase in intracellular GSH under oxidative stress in alveolar epithelial cells.
Azithromycin attenuates cigarette smoke extract-induced oxidative stress injury in human alveolar epithelial cells
