Grantee Research Project Results

2006 Progress Report: Diesel-induced Vascular Dysfunction: Role of Endothelin

EPA Grant Number: R831860
Title: Diesel-induced Vascular Dysfunction: Role of Endothelin
Investigators: Kanagy, Nancy L. , Campen, Matthew J. , Walker, Benjimen R.
Institution: University of New Mexico
Current Institution: University of New Mexico , Lovelace Biomedical & Environmental Research Institute
EPA Project Officer: Chung, Serena
Project Period: October 1, 2004 through September 30, 2008 (Extended to September 30, 2010)
Project Period Covered by this Report: October 1, 2005 through September 30, 2006
Project Amount: $1,500,000
RFA: The Role of Air Pollutants in Cardiovascular Disease (2003) RFA Text | Recipients Lists
Research Category: Particulate Matter , Air Quality and Air Toxics , Human Health , Air

Objective:

There is a clear association between air pollution exposure and cardiovascular mortality. However, the mechanisms linking air pollution to cardiovascular events are poorly understood. Inhalation of particulate matter (PM) air pollution has been shown to increase the release of vasoactive cytokines such as endothelin (ET), whereas individuals with vascular disease have augmented vasoconstrictor responses to this peptide. Therefore, diesel exhaust (DE)-released ET could contribute to air pollution-induced cardiovascular events in sensitized individuals. We propose to use a novel model of ET dependent hypertension and endothelial dysfunction, paired with state-of-the-art methods for generating whole DE, to investigate cardiovascular effects of PM. Our preliminary studies demonstrated that simulating sleep apnea by exposing rats to 90 second episodes of intermittent hypoxia/hypercapnia (IH) for 8 hours a day causes hypertension that is reversed by ET antagonists and associated with increased ET synthesis, augmented ET vasoconstriction and both right and left ventricular hypertrophy. Our preliminary studies also demonstrated that whole DE stimulates ET-1 synthesis and increases oxidative stress.

Thus a potential mechanism for IH and air pollution to synergistically augment ET vasoconstriction is through the generation of reactive oxygen species (ROS). ROS are a potent stimulus for ET synthesis and augment ET vasoconstriction. Others have demonstrated ROS generation by multiple pollutants and our preliminary data show that diesel exposure alone stimulates the generation of ROS. Therefore DE exposure may increase ROS release of ET thereby exacerbating ET-dependent vasoconstriction in already compromised individuals. Our central hypothesis is that inhalation of whole DE augments ET-vasoconstriction in ET-sensitized hypertension. The following aims will test this hypothesis.

Objective 1: Identify the Role of ET in DE-Induced Vasoconstriction in IH and Sham Rats

Hypothesis: Inhalation of Whole DE Releases ET to Increase Vascular Resistance, Blood Pressure, and Venous Return in IH Rats but not in Sham Rats. Specifically, studies are designed to first establish the time course of increases in plasma and tissue ET and ET-receptors following acute inhalation of whole DE. After that is completed, we will evaluate the role of ROS in mediating increased ET synthesis following acute inhalation of whole DE. Finally, studies will establish time-course of hemodynamic changes following acute inhalation of whole DE and the role of ET in these changes.

Objective 2: Identify the Effect of Inhaled Whole DE on Vascular Smooth Muscle and Endothelial Cell Function in IH and Sham Rats

Hypothesis: DE Inhalation Augments ET Vasoconstriction and Decreases Endothelium-Induced Vasodilation in IH Rats but not in Sham Rats. Studies will first evaluate vasoconstrictor responses to ET in blood vessels from air and DE exposed IH and Sham rats. We will also evaluate endothelium-dependent vasodilation in blood vessels from air and DE exposed IH and Sham rats. Finally, specific blockers and assays will be used to determine the role of ROS in changes in vascular reactivity to ET following diesel exposure in IH and Sham rats.

Progress Summary:

Samples were collected from Fischer and Sprague Dawley (SD) rats exposed to IH/HC and DE or air exposure. RNA and protein analysis has not yet been completed on these samples but preliminary data suggest that ET-1 mRNA is decreased in the heart in the SD rats. These studies will be completed in the next few weeks. Heart rate variability (HRV) analysis was performed using ECG traces from rats were exposed to either simulated sleep apnea (IH/HC) or Sham apnea for 14 days and then to DE for 4 hours. Data suggested that there was an increase in cardiac sympathetic activity in the IH/HC rats exposed to DE but not in the Sham rats or in the air-exposed IH/HC. We also observed basal differences in HRV between IH/HC rats and Sham prior to DE or Air exposure suggestive of greater sympathetic activity in the IH/HC rats. Therefore it appears that there is sensitization of the sympathetic nervous system following IH/HC that is sustained during the response to DE.

Contractility studies in small intraseptal coronary arteries were performed using a videomicroscopy system. This study demonstrated that IH/HC exposure alone leads to augmented ET-1 constriction in coronaries from IH/HC rats. In addition, acetylcholine-induced endothelium-dependent dilation was impaired in arteries from three of the seven IH/HC rats. Following exposure to DE, ET-1 constriction was further augmented and endothelium-dependent dilation was profoundly decreased. This suggests that IH/HC exposure should sensitize coronary arteries to vasoconstrictors.

To begin addressing the role of ROS in mediating these vascular changes, we developed an assay using ferric cytochrome C as a spin trap detector of superoxide (O₂^-). Preliminary studies found that IH/HC exposure for 14 days greatly increased basal O₂^- generation in small mesenteric arteries. This signal was quenched by the superoxide dismutase (SOD) mimetic, tiron, but not by catalase. Thus new data confirm our preliminary data that IH/HC increases vascular oxidative stress. Ongoing studies are using this system to determine if DE exposure further increases ROS production in resistance arteries from the IH/HC and Sham rats.

Future Activities:

Studies planned for Year 3 of the project will complete the RNA and protein analysis on samples collected from the Fischer and SD rats exposed to IH/HC and DE protocols. We also will conduct chronic exposure studies to determine if repeat exposures (5 to 15 days) to DE cause more profound effects on coronary reactivity than a single exposure. Tissues will be collected for coronary reactivity studies and for mRNA analysis of the ET system. Oxidative stress will be examined by measuring levels of antioxidants (SOD, HO-1) in vascular tissues and by directly measuring O₂^- and H₂O₂ production in mesenteric and coronary arteries.

Journal Articles:

No journal articles submitted with this report: View all 22 publications for this project

Supplemental Keywords:

sleep apnea, diesel exhaust, toxicology, endothelin, blood pressure, cardiac, coronary, endothelial dysfunction, autonomic nervous system, sympathetic nervous system, heart rate variability, reactive oxygen species, superoxide, hydrogen peroxide, SOD, catalase,, RFA, Health, Scientific Discipline, Air, PHYSICAL ASPECTS, HUMAN HEALTH, Susceptibility/Sensitive Population/Genetic Susceptibility, Ecological Risk Assessment, Health Risk Assessment, Physical Processes, Risk Assessments, particulate matter, Biology, genetic susceptability, mobile sources, Environmental Chemistry, Exposure, Toxicology, air toxics, inhaled, air quality, environmental hazard exposures, inhaled pollutants, sensitive populations, diesel exhaust, fine particles, lung inflammation, oxidant gas, acute lung injury, endothelial function, DEP, engine exhaust, cardiopulmonary responses, particulate exposure, Acute health effects, airway epithelial cells, copollutant exposures, cardiotoxicity, acute exposure, diesel exhaust particulate, chronic health effects, susceptible subpopulations, concentrated particulate matter, air contaminant exposure, toxics, atmospheric particulate matter, heart rate, air pollution, highrisk groups, human susceptibility, airborne urban contaminants, cardiovascular disease, cardiopulmonary, ambient particle pollution, cardiopulmonary response, automotive exhaust, diesel engines

Relevant Websites:

http://hsc.unm.edu/som/cbp/kanagy.shtml Exit
http://www.lrri.org/staff/directoryofscientists/campen.html Exit
http://hsc.unm.edu/som/cbp/walker.shtml Exit

Progress and Final Reports:

Original Abstract

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.