Grantee Research Project Results
Final Report: The Consequences of Prolonged Inhalation of Ozone on Rats: An Integrative Summary of the Results of Eight Collaborative Studies
EPA Grant Number: R828112C065XISubproject: this is subproject number 065XI , established and managed by the Center Director under grant R828112
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: Health Effects Institute (Prior to 2000)
Center Director: Greenbaum, Daniel S.
Title: The Consequences of Prolonged Inhalation of Ozone on Rats: An Integrative Summary of the Results of Eight Collaborative Studies
Investigators:
Institution:
EPA Project Officer: Chung, Serena
Project Period:
RFA: Health Effects Institute (1996) RFA Text | Recipients Lists
Research Category: Air , Human Health
Objective:
Ozone is a highly reactive gas that formed when components of emissions from mobile and industrial sources react in the presence of sunlight. Ozone is a major component of urban smog and a public health concern. It has been well documented that short-term exposure to ozone can cause transient health effects in some people. Symptoms include cough, pulmonary function changes, and the appearance of inflammatory cells in the lungs. What is not known is whether repeated exposures to ozone over a period of many years cause damage to the respiratory tract and lead to the development or worsening of chronic lung diseases such as chronic obstructive pulmonary disease, asthma, or diffuse pulmonary fibrosis. This is of serious concern because chronic lung diseases are major contributors to morbidity and mortality in developed countries, where over half of the population is exposed to elevated levels of ozone, especially during the summer months. In order to protect public health, the U.S. Environmental Protection Agency sets National Ambient Air Quality Standards for ozone. The current ozone standard is 0.12 parts per million (ppm), a level that is not to be exceeded for more than one hour once per year.Recently, the National Toxicology Program (NTP) conducted an animal bioassay designed to evaluate whether prolonged exposure to ozone causes cancer in rodents. The NTP bioassay presented a unique opportunity to examine noncancer endpoints as well. Therefore, the NTP and HEI set up a collaboration that allowed HEI-funded investigators access to rats that were exposed to ozone using the same rigorous exposure protocol and quality assurance procedures as the NTP bioassay animals. The HEI studies addressed respiratory diseases other than cancer. The results of the individual studies have already been published. The Integrative Summary that is discussed in this Statement highlights the major findings, integrates the results, and discusses their implications for human health.
Summary/Accomplishments (Outputs/Outcomes):
Healthy male and female F344/N rats were exposed to filtered air or to one of three concentrations of ozone for six hours per day, five days per week, for twenty months: 1.0 ppm ozone (the highest level the animals would tolerate), 0.12 ppm ozone (the National Ambient Air Quality Standard), or 0.5 ppm ozone (an intermediate concentration). (It should be noted that the cumulative annual ozone exposure, even for the low-dose group, was much higher than that received by individuals who live in polluted areas of the United States.) The HEI funded eight independent research studies, including investigations of lung biochemical constituents, structural and cellular changes, lung function, and nasal structure and function. In addition, a Biostatistical Advisory Group developed an animal allocation scheme that allowed several investigators to measure endpoints on the same set of animals, assisted the individual investigators with data analyses, and developed a statistical approach for analyzing multiple endpoints across the individual studies.Twenty months of exposure to ozone, even at the highest concentration, had no effect on animal survival and only minimal effect on weight gain. Some of the most striking effects of prolonged ozone exposure were observed in the nose. They included structural alterations of the epithelium that lines the nasal cavity and impairment in the flow of mucus; the severity of both of these changes depended on ozone concentration. These effects were seen when rats exposed to 0.5 or 1.0 ppm ozone were compared with rats that had breathed clean air. Exposure to 0.12 ppm ozone had no effect on nasal structure or function.
Prolonged exposure to ozone had mild to moderate effects on other regions of the respiratory tract. The most notable changes occurred in the centriacinar region of the lung, which is the anatomical site that is the junction of the conducting airways and gas exchange region. In rats exposed to 0.5 or 1.0 ppm ozone, the thin epithelial cells that normally line the alveolar ducts were replaced by thicker cells that are more characteristic of the small bronchioles, and the volume of the underlying interstitium increased. These changes were specific to the centriacinar region and were not seen in randomly chosen alveolar ducts. Some alterations were reported in the epithelial cells of the centriacinar region of rats exposed to 0.12 ppm ozone; however, these are difficult to interpret because the changes were small, they were found in some lung regions but not in others, and some of them occurred only in male rats. Thus, whether prolonged exposure to 0.12 ppm ozone causes alternations in the respiratory tract requires further steady.
Biochemical studies indicated small ozone-induced changes in some components of connective tissue (collagen and glycosaminoglycans), substances that provide structural support to the lung. Analyses by light microscopy showed an increase in collagen fibrils in the centriacinar region of animals exposed to 0.5 or 1.0 ppm compared with rats that breathed clean air. Other analyses indicated that the increase in collagen most likely occurred early in the exposure period.
The results of extensive pulmonary function tests indicated that ozone exposure had little or no measureable impact on lung function. A small decrease in residual volume (the amount of air remaining in the lungs at the end of an expiration) was the only change that was found; however, when compared with control animals, the change was statistically significant only in the group exposed to 0.5 ppm ozone. Thus, one can conclude that the minor alterations in lung structure and biochemistry did not affect overall lung function.
Because the 20-month exposure to ozone resulted in some biochemical and structural changes in the rat lungs that were protective in nature, and because the effects on overall pulmonary function were minimal or not measurable, the authors suggest that the animals had become tolerant to the injurious effects of ozone. Although this is a reasonable hypothesis, the study design, in which the animals were examined at only one time point, did not a true test of whether tolerance had, indeed, developed. Examining the animals at multiple time points would be required to determine conclusively if the rats developed tolerance as a result of repeated exposures to ozone.
The investigators used three analytical approaches to integrate the results of the multiple studies. One innovative technique involved combing data for a set of related parameters that were measured in different animals. Using a statistical technique called median polish analysis, composite scores for the combined data were developed. This analytical technique, when applied to three disease surrogates (defined by the investigators as a collection of endpoints "potentially related to different pathogenic processes"), revealed new relationships among the structural, biochemical, and functional endpoints investigated in the individual studies. When ozone exposure was clearly related to a disease process, as it was with rhinitis, the composite scores showed highly significant differences between the control rats and those exposed to 0.5 or 1.0 ppm ozone, but no differences between rats exposed to 0 or 0.12 ppm ozone. However, for the other disease surrogates, centriacinar fibrosis and airway disease, the analyses were heavily influenced by the structural changes in the centriacinar region, or were sensitive to the inclusion or exclusion of some endpoints.
The results for the NTP/HEI Collaborative Ozone Project provide insight into the question of whether prolonged exposure to ozone leads to permanent injury of the respiratory tract or to the development of chronic diseases. The nasal changes in rats exposed to 0.5 or 1.0 ppm ozone are very similar to the lesions that have been observed in humans living in areas with high levels of ozone in the ambient atmosphere, and suggest that rhinitis may be a consequence of exposure to high ambient concentrations of ozone. However, because of marked differences in the structures of the nasal cavities of rats and humans, it is difficult to draw conclusions about this aspect of the human response, and to extrapolate exposure-response data from rats to humans. Although rats exposed to 0.5 or 1.0 ppm ozone developed mild to moderate fibrotic lesions in the centriacinar region of the lungs, they did not develop diffuse pulmonary fibrosis analogous to the human condition. In humans, pulmonary fibrosis of either known or unknown origin has characteristic clinical, physiologic, and pathologic features, including diffuse inflammatory response and a reduction in some pulmonary function measurements. The rats exposed to ozone for 20 months, even at the highest ozone concentrations, did not show any of the characteristic features of human diffuse pulmonary fibrosis, including the inflammatory changes that might lead to fibrotic lesions. The lesions observed in the centriacinar region of the rat lungs were very similar to respiratory bronchiolitis in humans, which is asymptomatic and is associated with either no measureable functional abnormalities or only minimal functional abnormalities.
Some limitations must be considered when extrapolating the results of the NTP/HEI Collaborative Ozone Project to humans. First, the protocol for exposing the rats to ozone did not simulate the ambient exposure pattern of humans, which is intermittent and includes extended periods during which peak ozone levels are less than 0.12 ppm. Second, despite the fact that both the exposure and experimental components of the study were conducted rigorously and thoroughly, the results are directly applicable only to healthy animals exposed to a single pollutant. Prolonged ozone exposure may have a more severe effect in animals with lungs already compromised by previous injury or disease, or when the exposure includes other air pollutants.
Supplemental Keywords:
Air, ambient air quality, air toxics, epidemiology, health effects, particulate matter, ozone, inhalation studies, animal models, disease, cumulative effects., RFA, Scientific Discipline, Health, Air, Toxicology, particulate matter, air toxics, Environmental Chemistry, Health Risk Assessment, Risk Assessments, mobile sources, Disease & Cumulative Effects, Biochemistry, ambient air quality, lung injury, particulates, carbohydrate content of lungs, motor vehicles, mercury, exposure and effects, lung disease, air pollutants, human health effects, inhalability, lung, engines, ozone, animal model, airway disease, ambient air, chronic ozone inhalation, air pollution, environmental health effects, automobiles, emissions, human exposure, ambient particle health effects, inhalation, particulate exposure, lung inflammation, effects of ozone in the lung, inhalation toxicology, inhaled, lung content, human health, human health riskMain Center Abstract and Reports:
R828112 Health Effects Institute (Prior to 2000) Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R828112C042 Does Inhalation of Methanol Vapor Affect Human Neurobehavior?
R828112C043 Human Responses to Nitrogen Dioxide
R828112C044 The Role of Inflammation in Ozone-Induced Lung Injury
R828112C045 How Does Exercise Affect the Dose of Inhaled Air Pollutants?
R828112C046 How Do Chemicals in Diesel Engine Exhaust Damage DNA?
R828112C047 Effect of Nitrogen Dioxide on Bacterial Respiratory infectionin Mice
R828112C048 Effects of Ozone Exposure on Airway Epithelium
R828112C049 Inhalation of Aldehydes and Effects on Breathing
R828112C050 Does Ozone Cause Precancerous Changes in Cells?
R828112C051 Effects of Formaldehyde on Human Airway Epithelial Cells Exposed in a Novel Culture System
R828112C052 Carbon Monoxide and Cardiac Arrhythmias
R828112C053 Effects of Formaldehyde and Particle-Bound Formaldehyde on Lung Macrophage Functions
R828112C054 Mechanisms for Protecting Lung Epithelial Cells Against Oxidant Injury
R828112C055 Relationship of Nitropyrene-Derived DNA Adducts to Carcinogenesis
R828112C056 Particle Trap Effects on Heavy-Duty Diesel Engine Emissions
R828112C057 Carbon Monoxide and Atherosclerosis
R828112C058 Nitrogen Dioxide and Respiratory Illness in Children
R828112C059 Noninvasive Methods for Measuring Ventilation in Mobile Subjects
R828112C060 Oxidant Air Pollutants and Lung Cancer: An Animal Model
R828112C061 Detection of Carcinogen-DNA Adducts: Development of New Methods
R828112C062 Effects of Carbon Monoxide on Heart Muscle Cells
R828112C063 Development of Personal Ozone Samplers: Three Approaches
R828112C064 Development of Biomarkers to Monitor Carcinogen Exposure
R828112C065 Effects of Prolonged Ozone Inhalation on Collagen Structure and Content in Rat Lungs
R828112C065II Prolonged Ozone Exposure and the Contractile Properties of Isolated Rat Airways
R828112C065III Changes in Complex Carbohydrate Content and Structure in Rat Lungs Caused by Prolonged Ozone Inhalation
R828112C065IV Genetic Control of Connective Tissue Protein Synthesis After Prolonged Ozone Inhalation
R828112C065V Pulmonary Function Alterations in Rats After Chronic Ozone Inhalation
R828112C065VII Prolonged Ozone Exposure Leads to Functional and Structural Changes in the Rat Nose
R828112C065VIII - IX Studies of Changes in Lung Structure and Enzyme Activitiesin Rats After Prolonged Exposure to Ozone
R828112C065X An Innovative Approach to Analyzing Multiple Experimental Outcomes: A Case Study of Rats Exposed to Ozone
R828112C065XI The Consequences of Prolonged Inhalation of Ozone on Rats:
An Integrative Summary of the Results of Eight Collaborative Studies
R828112C066 Interactive Effects of Nitropyrenes in Diesel Exhaust
R828112C067 Detection of FormaldehydeDNA Adducts: Development of New Methods
R828112C068I Comparison of the Carcinogenicity of Diesel Exhaust and Carbon Black in Rat Lungs
R828112C068II An Investigation of DNA Damage in the Lungs of Rats Exposed to Diesel Exhaust
R828112C068III No Evidence For Genetic Mutations Found In Lung Tumors From Rats Exposed To Diesel Exhaust or Carbon Black
R828112C069 Noninvasive Determination of Respiratory Ozone Absorption: The Bolus-Response Method
R828112C070 The Effects of Inhaled Oxidants and Acid Aerosols on Pulmonary Function
R828112C071 Biochemical Consequences of Ozone Reacting with Membrane Fatty Acids
R828112C072 DNA Mutations in Rats Treated with a Carcinogen Present in Diesel Exhaust
R828112C073 Developmental Neurotoxicity of Inhaled Methanol in Rats
R828112C074 Methanol Distribution in Non Pregnant and Pregnant Rodents
R828112C075 Is Increased Mortality Associated with Ozone Exposure in Mexico City?
R828112C076 Effects of Fuel Modification and Emission Control Devices on Heavy-Duty Diesel Engine Emissions
R828112C077 Metabolic Studies in Monkeys Exposed to Methanol Vapors
R828112C078 Effects of Ozone on Pulmonary Function and Airway Inflammation in Normal and Potentially Sensitive Human Subjects
R828112C079 Improvement of a Respiratory Ozone Analyzer
R828112C080 Mechanism of Oxidative Stress from Low Levels of Carbon Monoxide
R828112C081 Long-Term Exposure to Ozone: Development of Methods to Estimate Past Exposures and Health Outcomes
R828112C082 Effects of Ambient Ozone on Healthy, Wheezy, and Asthmatic Children
R828112C083 Daily Changes in Oxygen Saturation and Pulse Rate Associated with Particulate Air Pollution and Barometric Pressure
R828112C084 Evaluation of The Potential Health Effects of the Atmospheric Reaction Products of Polycyclic Aromatic Hydrocarbons
R828112C085 Mechanisms of Response to Ozone Exposure: The Role of Mast Cells in Mice
R828112C086 Statistical Methods for Epidemiologic Studies of the Health Effects of Air Pollution
R828112C087 Development of New Methods to Measure Benzene Biomarkers
R828112C088 Alveolar Changes in Rat Lungs After Long-Term Exposure to Nitric Oxide
R828112C089 Effects of Prenatal Exposure to Inhaled Methanol on Nonhuman Primates and Their Infant Offspring
R828112C090 A Pilot Study of Potential Biomarkers of Ozone Exposure
R828112C091 Effects of Concentrated Ambient Particles on the Cardiac and Pulmonary Systems of Dogs
R828112C092 Cancer, Mutations, and Adducts in Rats and Mice Exposed to Butadiene and Its Metabolites
R828112C093 Effects of Concentrated Ambient Particles in Rats and Hamsters: An Exploratory Study
R828112C094I The National Morbidity, Mortality, and Air Pollution Study: Methods and Methodologic Issues
R828112C094II The National Morbidity, Mortality, and Air Pollution Study: Morbidity and Mortality from Air Pollution in the United States
R828112C095 Association of Particulate Matter Components with Daily Mortality and Morbidity in Urban Populations
R828112C096 Acute Pulmonary Effects of Ultrafine Particles in Rats and Mice
R828112C097 Identifying Subgroups of the General Population That May Be Susceptible to Short-Term Increases in Particulate Air Pollution
R828112C098 Daily Mortality and Fine and Ultrafine Particles in Erfurt, Germany
R828112C099 A Case-Crossover Analysis of Fine Particulate Matter Air Pollution and Out-of-Hospital Sudden Cardiac Arrest
R828112C100 Effects of Mexico City Air on Rat Nose
R828112C101 Penetration of Lung Lining and Clearance of Particles Containing Benzo[a]pyrene
R828112C102 Metabolism of Ether Oxygenates Added to Gasoline
R828112C103 Characterization and Mechanisms of Chromosomal Alterations Induced by Benzene in Mice and Humans
R828112C104 Acute Cardiovascular Effects in Rats from Exposure to Urban Ambient Particles
R828112C105 Genetic Differences in Induction of Acute Lung Injury and Inflammation in Mice
R828112C106 Effects on Mice of Exposure to Ozone and Ambient Particle Pollution
R828112C107 Emissions from Diesel and Gasoline Engines Measured in Highway Tunnels
R828112C108 Case-Cohort Study of Styrene Exposure and Ischemic Heart Disease Investigators
R828112C110 Effects of Metals Bound to Particulate Matter on Human Lung Epithelial Cells
R828112C111 Effect of Concentrated Ambient Particulate Matter on Blood Coagulation Parameters in Rats
R828112C112 Health Effects of Acute Exposure to Air Pollution
R828112C113 Benzene Metabolism in Rodents at Doses Relevant to Human Exposure from Urban Air
R828112C114 A Personal Particle Speciation Sampler
R828112C115 Validation and Evaluation of Biomarkers in Workers Exposed to Benzene in China
R828112C116 Biomarkers in Czech Workers Exposed to 1,3-Butadiene: A Transitional Epidemiologic Study
R828112C117 Peroxides and Macrophages in the Toxicity of Fine Particulate Matter in Rats
R828112C118 Controlled Exposures of Healthy and Asthmatic Volunteers to Concentrated Ambient Particles in Metropolitan Los Angeles
R828112C119 Manganese Toxicokinetics at the Blood-Brain Barrier
R828112C120 Effects of Exposure to Concentrated Ambient Particles from Detroit Air on Healthy Rats and Rats with Features of Asthma or Mild Bronchitis
R828112C121 Field Evaluation of Nanofilm Detectors for Measuring Acidic Particles in Indoor and Outdoor Air
R828112C123 Time-Series Analysis of Air Pollution and Mortality: A Statistical Review
R828112C126 Effects of Exposure to Ultrafine Carbon Particles in Healthy Subjects and Subjects with Asthma
R828112C128 Neurogenic Responses of Rat Lung to Diesel Exhaust
R828112C130-I Relationships of Indoor, Outdoor, and Personal Air (RIOPA). Part I. Collection Methods and Descriptive Analyses
R828112C132 An Updated Study of Mortality Among North American Synthetic Rubber Industry Workers
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.