P4478Noise pollution exacerbates the development of arterial hypertension via additive oxidative stress and impairment of NO signaling
Authors: Steven S , Frenis K , Kroeller-Schoen S , Kalinovic S , Helmstaedter J , Kvandova M , Oelze M , Daiber A , Munzel T 
Published: October 2019

Abstract

Background
Environmental noise pollution has been identified as a cardiovascular risk and is characterized by moderate hypertension, endothelial dysfunction, increased oxidative stress, and inflammation. We have gained insights into the mechanism by which these consequences occur by exposing mice lacking the critical NADPH oxidase subunit gp91phox to aircraft noise. Mice were protected from the effects of aircraft noise exposure. NADPH oxidase is believed to be the mediator by which angiotensin II increases oxidative stress, making investigation into the additive effect of noise and hypertension an important subject in modern cardiovascular health research.

Methods and results
C57Bl/6J mice were implanted with subcutaneous osmotic mini-pumps, delivering a moderate dose of 0.5mg/kg/d of angiotensin II for 7 days. Immediately following the implantation, half the mice were exposed to aircraft noise for 7 days at a maximum sound pressure level of 85 dB(A) and a mean sound pressure level of 72 dB(A), a level at which hearing loss does not occur*. Non-invasive blood pressure measurements revealed an additive increase in blood pressure in noise-exposed hypertensive mice. Following sacrifice, endothelial dysfunction was evaluated through isometric tension recordings of 3mm aortic ring segments. These recordings support the blood pressure measurements and indicate a more serious impairment in acetylcholine-induced vasorelaxation in hypertensive mice exposed to noise than the hypertensive or noise only controls. Whole blood stimulated with phorbol 12,13-dibutyrate (PDBu) or zymosan A showed an additive increase in oxidative burst in in noise-exposed hypertensive mice. Dihydroethidium (DHE) staining was used to assess the presence of vascular and cerebral oxidative stress, showing similar additive effects in mice with hypertension plus noise exposure. High performance liquid chromatography (HPLC) measurement of 2-hydroxyethidium further confirmed additive increase of oxidative stress in the aorta and brain. Western blot analysis of aortic tissue revealed highest levels of gp91phox in mice with hypertension plus noise exposure and indicated a decrease in the ratio of P-eNOSSer1177:eNOS as well as a decrease in the ratio of eNOS dimer:monomer, exposing eNOS uncoupling as a potential pathomechanism for endothelial dysfunction and gp91phox as a source for the oxidative stress.Ongoing immunohistochemical and flow cytometric investigations will characterize the role of immune cells in these adverse effects.

Conclusion
Herein, we present novel data demonstrating additive noise-induced cardiovascular consequences on developing hypertension. Noise has previously been established as a cardiovascular risk factor, but the effects have not been determined in pre-existing or developing cardiovascular disease. Our results show a cumulative effect between noise exposure and hypertension and forge an important link between environmental stressors and cardiovascular health.

Acknowledgement/Funding
Boehringer Ingelheim Foundation