Nitrogen Oxides

In a follow-up study to previous research, Dr. Mercer and colleagues at Duke University exposed three groups of rats continuously for six weeks to 2 or 6 ppm nitric oxide (NO) or to filtered air to learn more about the toxicity of NO so as to compare it with two other important oxidants, ozone and nitrogen dioxide (NO₂). At the end of the exposure period he used an electron microscope to measure the number of holes in the alveolar septa and to observe other structural changes, such as in the surface area and the number and type of other abnormalities in the alveolar septa.

In two separate studies, Drs. Koenig and Utell examined the effects of exposing healthy subjects and subjects with asthma to combined oxidant and acid pollutants. Each team of investigators conducted studies in which human volunteers received either combined or sequential exposures to oxidant gases and acid aerosols and standard pulmonary function tests were performed and symptoms were recorded. Dr. Koenig and colleagues exposed 28 adolescents with asthma to varying concentrations of ozone, nitrogen dioxide, and sulfuric acid. Dr. Utell and colleagues examined the effects of sequential exposures to sulfuric acid and ozone on pulmonary function in 30 subjects with asthma and 30 healthy subjects between the ages of 18 and 45. 

Ozone and nitrogen dioxide are highly reactive oxidant gases that are derived from the combustion of fossil fuels and the atmospheric transformation of these combustion products. A major unanswered question is whether or not exposure to oxidant air pollutants contributes to lung cancer. Dr. Witschi and colleagues at the University of California at Davis examined whether exposure to ozone or nitrogen dioxide enhances the development of tumors induced by the chemical carcinogen diethylnitrosamine (DEN), particularly neuroendocrine tumors, in the respiratory tract of hamsters.

Nitrogen dioxide is an ubiquitous air pollutant resulting from the combustion of fossil fuels. When inhaled at high levels, it reacts with and damages lung cells, including those cells that fight infection. This damage can affect breathing and may increase the risk of respiratory infections. Dr. J.K. Davis and his colleagues at the University of Alabama, Birmingham examined whether exposure to lower levels of nitrogen dioxide (less than 5 ppm) compromises mouse lung defense.

Nitrogen dioxide is an ubiquitous air pollutant that can react with and damages lung cells when inhaled at high levels. Although outdoor and indoor levels of nitrogen dioxide are usually below the annual standard of 0.053 ppm, peaks can occur that reach up to 10 times this standard. Dr. Mark Utell and coworkers at the University of Rochester examined the human health impacts of higher (peak) levels of nitrogen dioxide that exceed the annual standard. The investigators exposed healthy, nonasthmatic, human volunteers to either nitrogen dioxide or filtered air for three hours.

This report describes a study by Dr. Mauderly and colleagues to examine the influence of preexisting pulmonary emphysema on adverse health effects induced by chronic exposure of rats to diesel engine exhaust (DEE) or NO₂. Rats were exposed 7 hours/day, 5 days/week for 24 months to 9.5 ppm NO₂ or 3.5 mg soot/m³ DEE. Prior to exposure, a subset of rats was instilled with the proteolytic enzyme elastase to induce pulmonary emphysema.

This report describes a study by Dr. Evans and colleagues to develop an early marker of lung injury that changes in response to exposure to NO₂, which is an important component of mobile source emissions. Rats were exposed to NO₂ in concentrations ranging from 0.5 to 30 ppm for 6 hours per day for periods ranging from 2 days to 4 weeks. Urine and bronchoalveloar lavage samples were collected and analyzed for the presence of the lung injury markers hydroxylysin, angiotensin-converting enzyme, and desmosine.

This report examined the effect of nitrogen dioxide exposure on the sensitivity of the lower respiratory tract to viral infection and reinfection. Dr. Rose and colleagues exposed mice to concentrations of nitrogen dioxide ranging from 1-10 ppm or to air prior to and after inoculation with varying doses of murine cytomegalovirus. A subset of mice was reinfected 30 days later. Infection status, macrophage phagocytic uptake, lymphocyte function, and virus-specific antibody levels were measured, and the results were compared by exposure condition.

This report investigated the influence of acute exposure to nitrogen dioxide on susceptibility to and severity of viral and bacterial infection in mice. Dr. Jakab exposed normal and immunosuppressed mice to concentrations of nitrogen dioxide ranging from 1 to 30 ppm before or after bacterial or viral challenge and measured host resistance to infection by physiologic parameters.