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(Hypertension. 2006;48:950.)
© 2006 American Heart Association, Inc.

Original Articles

NO Modulates NADPH Oxidase Function Via Heme Oxygenase-1 in Human Endothelial Cells

Fan Jiang; Sarah J. Roberts; Srinivasa raju Datla; Gregory J. Dusting

From the Bernard O’Brien Institute of Microsurgery, University of Melbourne, Fitzroy, Victoria 3065, Australia.

Correspondence to Fan Jiang, Bernard O’Brien Institute of Microsurgery, 42 Fitzroy St, Fitzroy, Victoria 3065, Australia. E-mail fjiang{at}unimelb.edu.au

NO is known to induce expression of heme oxygenase-1, an antioxidant enzyme in blood vessels. We tested whether NO might modulate the endothelial NADPH oxidase function via heme oxygenase-1. In human microvascular endothelial cells, the NO donor DETA-NONOate (0.1 to 1 mmol/L) strongly induced expression of heme oxygenase-1 but not Cu/Zn superoxide dismutase. This was associated with a reduction of the superoxide-generating capacity of NADPH oxidase, an effect that depended on de novo gene transcription and heme oxygenase-1 activity. Activation of NADPH oxidase by tumor necrosis factor (TNF) increased generation of reactive oxygen species. DETA-NONOate alone had little effect on TNF-stimulated reactive oxygen species, but it enhanced the TNF response when: (1) heme oxygenase-1 expression was blocked with specific small-interfering RNA; (2) heme oxygenase-1 activity was blocked by zinc-protoporphyrin; or (3) NADPH oxidase activity was blocked by diphenyleneiodonium. Moreover, the heme oxygenase-1 end product bilirubin directly inhibited fully functional NADPH oxidase and seemed to interrupt the assembly and activation of the oxidase. In conclusion, NO may modulate superoxide production by NADPH oxidase in human vascular endothelial cells, at least partly by inducing heme oxygenase-1. Our results indicate that suppression of NADPH oxidase-dependent reactive oxygen species formation may represent a novel mechanism underlying the cardiovascular protective actions of heme oxygenase-1 and bilirubin.

Key Words: bilirubin • endothelium • heme oxygenase-1 • NADPH oxidase • nitric oxide • oxidant stress

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Heme Oxygenase-1 Inhibition of Nox Oxidase Activation Is a Microvascular Endothelial Antioxidant Effect of NO

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