Grantee Research Project Results
2007 Progress Report: Diesel-induced Vascular Dysfunction: Role of Endothelin
EPA Grant Number: R831860Title: Diesel-induced Vascular Dysfunction: Role of Endothelin
Investigators: Kanagy, Nancy L. , Campen, Matthew J. , Walker, Benjimen R.
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, 2006 through October 29,2007
Project Amount: $1,500,000
RFA: The Role of Air Pollutants in Cardiovascular Disease (2003) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Air , Human Health , Particulate Matter
Objective:
Recent studies have substantiated the premise of this proposal that air pollution exposure is associated with cardiovascular morbidity and mortality. In addition, multiple reports have demonstrated that a portion of this is due to alterations in vascular function. However, the mechanisms leading to the vascular dysfunction are not clear. Multiple inhaled pollutants have been shown to decrease the ability of vascular endothelium to release vasodilator substances and to increase the production of vasoactive cytokines such as endothelin. Therefore we have been examining specific cellular changes associated with exposure to diesel exhaust. We proposed to use a novel model of endothelin- dependent hypertension and endothelial dysfunction, paired with state-of-the-art methods for generating whole diesel exhaust, to investigate cardiovascular effects of PM.
These studies were designed to determine the mechanisms 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 was that inhalation of whole DE augments ET-vasoconstriction in ET-sensitized hypertension. Studies carried out under each of the orginal aims are described below.
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.
The initial studies established the time course of increases in plasma and tissue ET and ET-receptors following acute inhalation of whole DE. Those studies were completed in the first year of the grant and demonstrated that there was only a modest increase in ET-1 synthesis and only in a few tissues. This was in contrast to earlier studies using much higher concentrations of DE. However, parallel studies in mice found that there is a cumulative increase in ET-1 synthesis 3 validating the focus on this peptide. Additional studies evaluated the changes in hemodynamics and found evidence of sympathetic activation following acute exposure to DE but no significant changes in arterial pressure. These studies are part of a manuscript submitted for publication.
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 under aim 2 were the primary focus of research in the study period. Vasoconstrictor responses to ET, a thromboxane mimetic, U46619, and depolarizing potassium solution were evaluated in air and DE exposed rats. Endothelium-dependent vasodilation will be analyzed in the final year of the project.
Approach:
Our specific aims are: 1) To determine the effect of 6 hours of DE inhalation on plasma and tissue ET levels in Sham and IH hypertensive rats. These studies will test the hypothesis that DE stimulated ET synthesis is augmented in IH rats. We will examine tissue and plasma levels of ET-1, -2, and -3 and vascular expression of ETA- and ETB-receptors. 2) To determine the role of ROS in ET synthesis in IH and Sham rats at baseline and following DE inhalation. These studies will determine if elevated basal ROS levels sensitize IH rats to DE stimulation of ET vasoconstriction and if DE stimulation of ROS is necessary for increased ET synthesis. Tissue and plasma thiobarbiturate reactive substances (TBARS) will be measured at baseline and following DE inhalation as a measure of ROS generation. The effect of systemic antioxidants (Tempol 30 mg/kg/day) on ET synthesis will determine the contribution of ROS to DE stimulation of ET synthesis.
Progress Summary:
RNA and protein analyses were conducted on samples from air and DE exposed rats. We found 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 (intermittent hypoxia/hypercapnia during sleep, 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. This data was presented at the SOT conference in spring 2007 and is part of a submitted manuscript.
Studies last year found that IH/HC exposure alone leads to augmented endothelin 1 (ET-1) constriction in coronaries from IH/HC rats. In addition, acetylcholine-induced endothelium-dependent dilation was impaired in arteries from 3 of the 7 IH/HC rats. However, the lack of a clear synergism between the two conditions led us to focus on the effects of diesel alone. Following exposure to DE, ET-1 constriction was greatly augmented and endothelium-dependent dilation was profoundly decreased. The mechanism of these effects was investigated in preliminary studies appears to be uncoupling of eNOS.
To begin addressing the role of ROS in mediating these vascular changes, we examined the level of dihydroethidium staining in hearts from DE and air rats. We observed increased levels of superoxide in the DE hearts. We also examined the effect of antioxidants on the augmented ET-induced coronary constriction and found that it partially restored the sensitivity in the DE arteries. However, it had an even larger effect in the control arteries so that the data are still inconclusive. A portion of these studies were presented at the World Congress of the Microcirculatory Society in the Spring 2007 and are part of a manuscript in preparation. Ongoing studies are using eNOS substrates and co-factors to further evaluate the mechanism of the eNOS uncoupling by DE exposure.
Expected Results:
These studies are expected to determine mechanisms underlying the increased vascular pathology in response to DE inhalation in patients with pre-existing vascular disease. The widespread incidence of sleep apnea makes this relevant to a large segment of the population. This collaboration between NLK and BRW at the University of New Mexico and MJC at LRRI uniquely brings together expertise in environmental exposure toxicology and cardiovascular/hypertension physiology as part of the research consortium in the New Mexico NIEHS Center.
Future Activities:
Studies planned for year four will complete the coronary reactivity studies to further evaluate the mechanism of the eNOS uncoupling. A potential contribution of oxidative stress to this response will be examined by measuring levels of antioxidants (SOD, HO-1) in vascular tissues and by directly measuring O2- and H2O2 production in heart tissue and coronary arteries.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 22 publications | 14 publications in selected types | All 14 journal articles |
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Type | Citation | ||
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Lund AK, Knuckles TL, Akata CO, Shohet R, McDonald JD, Gigliotti A, Seagrave JC, Campen MJ. Gasoline exhaust emissions induce vascular remodeling pathways involved in atherosclerosis. Toxicological Sciences 2007;95(2):485-494. |
R831860 (2007) R831860 (Final) CR831455 (Final) R830839 (2005) R830839 (Final) |
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Supplemental Keywords:
particulates, pre-existing vascular disease, sudden cardiac death, physiology, hemodynamics, 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, Scientific Discipline, Health, PHYSICAL ASPECTS, Air, HUMAN HEALTH, Toxicology, particulate matter, Environmental Chemistry, Health Risk Assessment, air toxics, Exposure, Susceptibility/Sensitive Population/Genetic Susceptibility, Risk Assessments, Physical Processes, mobile sources, Ecological Risk Assessment, genetic susceptability, Biology, copollutant exposures, sensitive populations, atmospheric particulate matter, engine exhaust, airway epithelial cells, cardiopulmonary responses, fine particles, inhaled pollutants, acute lung injury, diesel engines, air pollution, susceptible subpopulations, endothelial function, diesel exhaust, automotive exhaust, chronic health effects, lung inflammation, oxidant gas, particulate exposure, cardiopulmonary response, heart rate, ambient particle pollution, Acute health effects, inhaled, highrisk groups, human susceptibility, diesel exhaust particles, cardiotoxicity, cardiopulmonary, diesel exhaust particulate, concentrated particulate matter, air contaminant exposure, air quality, environmental hazard exposures, toxics, airborne urban contaminants, cardiovascular disease, acute exposureProgress and Final Reports:
Original AbstractThe 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.