© 2003 by European Society of Cardiology
Copyright © 2003, European Society of Cardiology
Differential regulation of xanthine and NAD(P)H oxidase by hypoxia in human umbilical vein endothelial cells. Role of nitric oxide and adenosine
aMedizinische Poliklinik Innenstadt, Ludwig-Maximilians-University Munich, Ziemssenstrasse 1, 80336 Munich, Germany
bInstitute of Physiology, Ludwig-Maximilians-University Munich, Ziemssenstrasse 1, 80336 Munich, Germany
sohn{at}lrz.uni-muenchen.de
* Corresponding author. Tel.: +49-89-5160-2111; fax: +49-89-5160-2410.
Objectives: Although in tissue injury following hypoxia/reoxygenation (H/R) an increased endothelial formation of superoxide anions (O2–) plays an important role, it is still not fully understood which of the potential enzymatic sources of endothelial O2– are crucially involved. In this study, we particularly examined the activities of NAD(P)H oxidase and xanthine oxidase (XO) after 8 h of exposure to mild hypoxia. We further studied whether enzyme activities can be modified by NO and adenosine during hypoxic treatment. Methods and results: In human umbilical vein endothelial cells O2– production was measured immediately after exposure to hypoxia (‘early reoxygenation’) or after 2 h of reoxygenation at normoxic conditions (‘late reoxygenation’). In the early reoxygenation phase the O2– production was attenuated by 28.5% while it was enhanced by 58.2% after late reoxygenation. Using specific inhibitors of NAD(P)H oxidase and XO, gp91ds-tat and oxypurinol, respectively, we show that the constitutively active NAD(P)H oxidase was blocked following hypoxia while XO was activated. The presence of NO during hypoxia had no effect on NAD(P)H oxidase activity but it significantly inhibited the activation of XO. Inhibition of XO activation was, at least in part, caused by the release of adenosine from endothelial cells which induces an increased formation of NO by its A1 and A2 receptors. Conclusion: Our results indicate that during exposure to mild hypoxia for 8 h, a change in the enzymatic source of endothelial O2– occurs: a prolonged inhibition of NAD(P)H oxidase was found while an enhanced activity of XO occurs in the reoxygenation phase. These results suggest that different strategies of antioxidant therapy should be taken into consideration in oxidative stress related to chronic hypoxia when compared to normoxic atherosclerotic tissues with an activated vascular NAD(P)H oxidase as the main source of O2–.
KEYWORDS Endothelial function; Hypoxia/anoxia; Free radicals; Nitric oxide; Adenosine