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.
The Rayne Laboratory, Respiratory Medicine Unit, Department of Medicine, University of Edinburgh, Edinburgh EH8 9AG, United Kingdom.
I
I
Rahman
A
A
Bel
B
B
Mulier
K
K
Donaldson
W
W
MacNee
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