Grantee Research Project Results

2005 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, 2004 through September 30, 2005
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/HC) 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:

Preliminary studies were conducted separately at the University of New Mexico (UNM) where the sleep apnea model was developed and at the Lovelace Respiratory Research Institute (LRRI) facilities where the DE exposure chambers were established and maintained. Therefore, we spent the first 6 months purchasing and installing the equipment to establish the sleep apnea model at the LRRI facility. Studies were conducted to verify that the exposure chambers for the IH/HC during sleep produced the same levels of IH/HC as the equipment in place at UNM. After validating the exposure paradigm, rats were exposed to either IH/HC (simulated sleep apnea) or Sham apnea for 14 days. On days 15, 16, and 17, rats from each group were exposed to either room air or DE for 6 hours/day. Blood pressure was recorded throughout the IH/HC and DE exposure periods.

In this study, we used Fischer rats (standard strain at LRRI) rather than Sprague Dawley (SD) rats (standard strain at UNM). We observed that the hypertension response to the IH/HC exposure alone was not as robust in the Fischer rats as that in SD rats. However, even though mean arterial pressure was only slightly elevated in the IH/HC rats at the time of DE exposure, there was a significant difference in the hemodynamic response. The IH/HC rats responded to the DE exposure with an increase in arterial pressure and heart rate while the Sham rats and air-exposed rats responded with a fall in both blood pressure and heart rate. This suggested that even in the absence of overt hypertension, sleep apnea simulation sensitized the rats to DE exposure. Similar to previous results in the SD rats, real-time PCR revealed that ET-1 mRNA was not increased in whole heart homogenates, but plasma ET-1 and plasma TBARS (a measure of oxidative stress) circulating was slightly elevated in DE exposed rats.

Future Activities:

Studies planned for Year 2 of the project will expose both Fischer and SD rats to the IH/HC and DE protocols to determine if one strain is more sensitive to the effects of the exposures and will record ECG along with the blood pressure and heart rate. This will be used to do heart rate variability analysis as a measure of autonomic nervous system activity to determine if the IH/HC and DE exposures act synergistically to stimulate sympathetic activation at the heart. We will also collect tissues to measure ET-1 mRNA from both strains of rats to see if the relatively lower response of blood pressure in the Fischer rats is accompanied by a diminished response in ET-1 synthesis. We will also begin the studies of vascular function and ROS generation as outlined in Objective 2.

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,, 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.