Differential regulation of glutathione by oxidants and dexamethasone in alveolar epithelial cells.
We studied the regulation of GSH and the enzymes involved in GSH regulation, gamma-glutamylcysteine synthetase (gamma-GCS) and gamma-glutamyl transpeptidase (gamma-GT), in response to the oxidants menadione, xanthine/xanthine oxidase, hyperoxia, and cigarette smoke condensate in human alveolar epithelial cells (A549). Menadione (100 microM), xanthine/xanthine oxidase (50 microM/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 gamma-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. gamma-GCS activity increased significantly at 4 h (P < 0.001), returning to control values after 12 h of exposure. Dexamethasone (3 microM) exposure produced a significant time-dependent decrease in the levels of GSH and gamma-GCS activity at 24-96 h. The activity of gamma-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 gamma-GT and gamma-GCS by different mechanisms. We suggest that the increase in gamma-GCS activity but not in gamma-GT activity may be required for the increase in intracellular GSH under oxidative stress in alveolar epithelial cells.
Rahman
I
I
The Rayne Laboratory, Respiratory Medicine Unit, Department of Medicine, University of Edinburgh, Edinburgh EH8 9AG, United Kingdom.
Bel
A
A
Mulier
B
B
Donaldson
K
K
MacNee
W
W
D002460:Cell Line; D003907:Dexamethasone / Q000494:pharmacology*; D004847:Epithelial Cells / Q000378:metabolism*; D005721:Glutamate-Cysteine Ligase / Q000378:metabolism*; D005978:Glutathione / Q000378:metabolism*; D006801:Humans; D018496:Hyperoxia; D007700:Kinetics; D008175:Lung Neoplasms; D016877:Oxidants / Q000494:pharmacology*; D011650:Pulmonary Alveoli / Q000378:metabolism*; D012907:Smoking; D014407:Tumor Cells, Cultured; D014812:Vitamin K / Q000494:pharmacology; D019820:Xanthine / Q000494:pharmacology; D005723:gamma-Glutamyltransferase / Q000378:metabolism
D016877:Oxidants; D014812:Vitamin K; D019820:Xanthine; D003907:Dexamethasone; D005723:gamma-Glutamyltransferase; D005721:Glutamate-Cysteine Ligase; D005978:Glutathione