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1 The Rayne Laboratory,
We studied the regulation of GSH and the enzymes
involved in GSH regulation,
-glutamylcysteine synthetase (
-GCS)
and
-glutamyl transpeptidase (
-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
-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.
-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
-GCS activity at 24-96 h. The activity of
-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
-GT and
-GCS by different mechanisms. We suggest that the increase in
-GCS activity but not in
-GT activity may be required for the
increase in intracellular GSH under oxidative stress in alveolar
epithelial cells.
-glutamylcysteine synthetase;
-glutamyl transpeptidase; A549
cells
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