Response of Human Endothelial Cell Antioxidant Enzymes to Hyperoxia

Abstract

To explore the level of regulation of the expression of the major antioxidant enzymes in response to hyperoxia, we exposed human umbilical vein endothelial cells to 95% O2 for 3 and 5 days and measured (1) the steady-state mRNA levels, (2) the activities, and (3) the immunoreactive content of CuZn and Mn superoxide dismutases (SOD), catalase (CAT), and glutathione peroxidase (GP). We found that a 3-day exposure to 95% O2 caused (1) an increase in CuZnSOD mRNA (by 41%), CAT mRNA (by 26%), and GP mRNA (by 173%); (2) an increase in CuZnSOD activity (by 30%), a decrease in CAT activity (by 37%), and an increase in GP activity (by 60%); and (3) an increase in CuZnSOD immunodetectable protein (by 26%) and a loss in CAT immunoreactive protein (by 27%). After a 5-day exposure to 95% O2, there was (1) a 93% increase in CuZnSOD mRNA, a 71% increase in CAT mRNA, and a 127% increase in GP mRNA; (2) a 56% increase in CuZnSOD activity, a 70% decrease in CAT activity, and an 89% increase in GP activity; and (3) a 35% increase in CuZnSOD immunoreactive protein and a 55% loss in CAT immunoreactive protein. There was no change in the steady-state MnSOD mRNA level after 3 days in 95% O2, but a 100% increase was observed on day 5 of oxygen exposure. MnSOD activity was unchanged in cells exposed to hyperoxia for 3 and 5 days. These data suggest that, in human umbilical vein endothelial cells, the regulation of antioxidant enzymes expression in response to O2 is complex and exerted at different levels.

Reactive Oxygen Species in Inflammation and Tissue Injury

“…Oxidized GSSG is converted back to its monomeric GSH form by glutathione reductase. The expression and activity of GPx is induced by hyperoxia in endothelial cells (202). However, GPx knockout mice showed no hypersensitivity to hyperoxia-induced lung injury, indicating the compensation from other antioxidant enzymes (180).…”

“…Arita et al have shown that targeting of catalase directly to the mitochondria in lung epithelial cells protects them from H 2 O 2 -induced apoptosis (14). Despite this important physiological link, no increase in the activity of catalase was reported after hyperoxia in endothelial cells (202) and bronchial epithelial cells, which made them more susceptible to hyperoxia-induced injury (110). Moreover, the LPS treatment decreased the expression and activity of catalase in mouse lung, a response preceding NF-jB activation (67).…”

Positive Regulation of Pulmonary Antioxidant Enzyme Gene Expression by Prenatal Thyrotropin Releasing Hormone Plus Dexamethasone Treatment in Premature Rats Exposed to Hyperoxia

“…Other studies suggest this is true also under hyperoxic conditions. For example, differential regulation of specific AOE in response to oxidants (21) or to hyperoxia (22) The premature rat model using 21-d gestation rat pups (7) in the present study provides an appropriate model for investigating prenatal TRH and glucocorticoid treatment (relevant to the human clinical prenatal use), especially because the previously reported full-term animal data (6) strongly imply negative effects on hyperoxic tolerance asso ciated with prenatal TRH + DEX treatment. Our original hypothesis in the present study was that premature rat pups prenatally treated with TRH + DEX would demonstrate inferior tolerance to prolonged hyperoxia, similar to what had been found for full-term TRH + DEX-treated rat pups.…”

“…Because of this negative regulation of AOE gene expression in the late fetal lung, we hypothesized that hormonally pretreated prematurely delivered rats might demonstrate inferior tolerance to prolonged hyperoxia. Litters of prenatal TRH+DEX-treated and shamtreated prematurely delivered rat pups (gestational d 21 of 22) were randomized to either >95% O 2 or room air for up to 14 d. The right lungs of 2-and 7-d exposure pups were assayed for AOE activities; the left lungs of the same pups were used to quantitate the concentrations of AOE mRNA by solution hybridization. The prenatal TRH+ DEX-treated pups were able to induce adaptive lung AOE mRNA and activity responses to hyperoxia by 2 d of exposure; and by 7 d in O 2 they showed greater increases in AOE mRNA concentrations and AOE activities in response to hyperoxic challenge compared with the sham-treated controls.…”

Glutathione peroxidase-1 as a novel therapeutic target for COPD

“…42 Primary bronchial epithelial cells, alveolar macrophages and other lung cell lines can synthesize classical Gpx and extracellular Gpx and also secrete the extracellular enzyme. 56 Classical Gpx is induced by hyperoxia 57 and by the combination of hyperoxia and TNF. 58 The levels of both classical Gpx and extracellular Gpx are decreased after exposure to ozone.…”