Clin Res Cardiol 98, Suppl 1, April 2009

V238 - Heme oxygenase-1 controls NADPH oxidase activity and mitochondrial reactive oxygen species formation - insights from studies in heme oxygenase-1 deficient mice
P. Wenzel1, S. Schuhmacher2, T. Jansen1, M. Oelze2, E. Schulz1, A. Bhatnagar3, T. Münzel1, A. Daiber2
1II. Medizinische Klinik und Poliklinik, Klinikum der Universität Mainz, Mainz; 2II. Med. Klinik - Labor für Molekulare Kardiologie, Klinikum der Johannes Gutenberg-Universität, Mainz; 3Department of Medicine/Cardiology, University of Louisville, Louisville, USA;
Background: Heme oxygenase-1 (HO-1) catalyzes the breakdown of heme to yield potent intrinsic antioxidants like CO and biliverdin/bilirubin. We investigated HO-1+/+, HO-1+/- and HO-1-/- mice to test the hypothesis, that HO-1 controls the activity of the heme-containing NADPH oxidase and mitochondrial respiratory chain subunits, potential sources of reactive oxygen species (ROS).
Methods and results: Vascular endothelial and smooth muscle function as assessed by isometric tension studies in isolated aortic segments was impaired in HO-1-/-  and HO-1+/- as compared to HO-1+/+. This effect was even more pronounced when analyzed for age-dependency. Aging induced mtDNA strand breaks and oxidative DNA-damage increased in dependency of HO-1 deficiency, as measured by a modified fluorescence-assisted DNA alkaline unwinding-assay. Low-dose angiotensin-II (0.1mg/kg s.c., 7d) without apparent effect in HO-1+/+ evoked severe vascular dysfunction in HO-1+/- and HO-1-/- mice and a dramatic increase in NADPH oxidase activity, being already increased at baseline in HO-1 deficient mice. Dihydroethidium (DHE) staining of aortic cryosections revealed increased ROS formation in HO-1-deficiency throughout the vessel wall. The DHE-signal was unaffected by incubation of the cryosections with apocynin, an inhibitor of NADPH oxidase activation, indicating a long standing activity of this enzyme complex. Biliverdin reductase knockdown by siRNA led to an increase in superoxide formation in HUVECs, suggesting a potential antioxidant sequence heme/biliverdin/bilirubin.
Conclusion: Our results point toward a restraining role of HO-1 concerning the activity of heme-containing enzyme complexes that are important ROS-sources in cardiovascular disease. This feature of HO-1 can - at least partially - be attributed to biliverdin/bilirubin.