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Chemical exposure-response relationship between air pollutants and reactive oxygen species in the human respiratory tract

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ABSTRACT

Air pollution can cause oxidative stress and adverse health effects such as asthma and other respiratory diseases, but the underlying chemical processes are not well characterized. Here we present chemical exposure-response relations between ambient concentrations of air pollutants and the production rates and concentrations of reactive oxygen species (ROS) in the epithelial lining fluid (ELF) of the human respiratory tract. In highly polluted environments, fine particulate matter (PM2.5) containing redox-active transition metals, quinones, and secondary organic aerosols can increase ROS concentrations in the ELF to levels characteristic for respiratory diseases. Ambient ozone readily saturates the ELF and can enhance oxidative stress by depleting antioxidants and surfactants. Chemical exposure-response relations provide a quantitative basis for assessing the relative importance of specific air pollutants in different regions of the world, showing that aerosol-induced epithelial ROS levels in polluted megacity air can be several orders of magnitude higher than in pristine rainforest air.

No MeSH data available.


Chemical exposure-response relations for reactive oxygen species (ROS) produced in the human respiratory tract upon inhalation of fine particulate matter (PM2.5).It is shown as a function of PM2.5 concentrations with redox-active components as observed at various geographic locations around the world (Supplementary Tables 4–7). (A) ROS production rates induced by copper (Cu), iron (Fe), secondary organic aerosol (SOA), and quinones. (B) Characteristic concentration levels of different types of ROS and (C) total ROS concentration in the epithelial lining fluid after two hours of inhalation and deposition of ambient PM2.5. In panel (C), the green-striped horizontal bar indicates the ROS level characteristic for healthy humans (~100 nmol L−1), and the gray envelope represents the range of aerosol-induced ROS concentrations obtained with the approximate upper and lower limit mass fractions of redox-active components typically observed in ambient PM2.5. Total water-soluble fractions of iron and copper can range from ~5–25% and ~20–60%, respectively, in a wide range of different environments, which are represented by the error bars. (D) Fractional change of ROS concentrations upon removal of 50% of redox-active components from PM2.5 calculated for selected geographic locations with different PM2.5 concentration levels and composition (Supplementary Table 7).
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f2: Chemical exposure-response relations for reactive oxygen species (ROS) produced in the human respiratory tract upon inhalation of fine particulate matter (PM2.5).It is shown as a function of PM2.5 concentrations with redox-active components as observed at various geographic locations around the world (Supplementary Tables 4–7). (A) ROS production rates induced by copper (Cu), iron (Fe), secondary organic aerosol (SOA), and quinones. (B) Characteristic concentration levels of different types of ROS and (C) total ROS concentration in the epithelial lining fluid after two hours of inhalation and deposition of ambient PM2.5. In panel (C), the green-striped horizontal bar indicates the ROS level characteristic for healthy humans (~100 nmol L−1), and the gray envelope represents the range of aerosol-induced ROS concentrations obtained with the approximate upper and lower limit mass fractions of redox-active components typically observed in ambient PM2.5. Total water-soluble fractions of iron and copper can range from ~5–25% and ~20–60%, respectively, in a wide range of different environments, which are represented by the error bars. (D) Fractional change of ROS concentrations upon removal of 50% of redox-active components from PM2.5 calculated for selected geographic locations with different PM2.5 concentration levels and composition (Supplementary Table 7).

Mentions: Figure 2A shows ROS production rates calculated for each location and each redox-active component plotted against the ambient concentration of PM2.5. The data points fall into corridors outlining the relative importance of different chemical components for ROS production in the ELF. The highest ROS production rates are caused by copper and iron ions followed by quinones and SOA. As illustrated in Fig. 2B, the far most abundant form of ROS in the ELF are H2O2 molecules, which are three to four orders of magnitude more abundant than the O2− radicals initially produced from molecular oxygen, six to seven times more abundant than the HO2 radicals formed by proton transfer to O2−, and approximately ten orders of magnitude more abundant than the OH radicals formed by Fenton-like reactions of H2O2 (Fig. 1). The wide range of concentration levels reflects the vastly different chemical reactivities and lifetimes of the different ROS species. Due to its relatively low reactivity and decomposition rates, H2O2 is a reservoir species with a chemical lifetime of several hours, whereas the lifetime of OH radicals is less than a microsecond due to their rapid reactions with antioxidants.


Chemical exposure-response relationship between air pollutants and reactive oxygen species in the human respiratory tract
Chemical exposure-response relations for reactive oxygen species (ROS) produced in the human respiratory tract upon inhalation of fine particulate matter (PM2.5).It is shown as a function of PM2.5 concentrations with redox-active components as observed at various geographic locations around the world (Supplementary Tables 4–7). (A) ROS production rates induced by copper (Cu), iron (Fe), secondary organic aerosol (SOA), and quinones. (B) Characteristic concentration levels of different types of ROS and (C) total ROS concentration in the epithelial lining fluid after two hours of inhalation and deposition of ambient PM2.5. In panel (C), the green-striped horizontal bar indicates the ROS level characteristic for healthy humans (~100 nmol L−1), and the gray envelope represents the range of aerosol-induced ROS concentrations obtained with the approximate upper and lower limit mass fractions of redox-active components typically observed in ambient PM2.5. Total water-soluble fractions of iron and copper can range from ~5–25% and ~20–60%, respectively, in a wide range of different environments, which are represented by the error bars. (D) Fractional change of ROS concentrations upon removal of 50% of redox-active components from PM2.5 calculated for selected geographic locations with different PM2.5 concentration levels and composition (Supplementary Table 7).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5015057&req=5

f2: Chemical exposure-response relations for reactive oxygen species (ROS) produced in the human respiratory tract upon inhalation of fine particulate matter (PM2.5).It is shown as a function of PM2.5 concentrations with redox-active components as observed at various geographic locations around the world (Supplementary Tables 4–7). (A) ROS production rates induced by copper (Cu), iron (Fe), secondary organic aerosol (SOA), and quinones. (B) Characteristic concentration levels of different types of ROS and (C) total ROS concentration in the epithelial lining fluid after two hours of inhalation and deposition of ambient PM2.5. In panel (C), the green-striped horizontal bar indicates the ROS level characteristic for healthy humans (~100 nmol L−1), and the gray envelope represents the range of aerosol-induced ROS concentrations obtained with the approximate upper and lower limit mass fractions of redox-active components typically observed in ambient PM2.5. Total water-soluble fractions of iron and copper can range from ~5–25% and ~20–60%, respectively, in a wide range of different environments, which are represented by the error bars. (D) Fractional change of ROS concentrations upon removal of 50% of redox-active components from PM2.5 calculated for selected geographic locations with different PM2.5 concentration levels and composition (Supplementary Table 7).
Mentions: Figure 2A shows ROS production rates calculated for each location and each redox-active component plotted against the ambient concentration of PM2.5. The data points fall into corridors outlining the relative importance of different chemical components for ROS production in the ELF. The highest ROS production rates are caused by copper and iron ions followed by quinones and SOA. As illustrated in Fig. 2B, the far most abundant form of ROS in the ELF are H2O2 molecules, which are three to four orders of magnitude more abundant than the O2− radicals initially produced from molecular oxygen, six to seven times more abundant than the HO2 radicals formed by proton transfer to O2−, and approximately ten orders of magnitude more abundant than the OH radicals formed by Fenton-like reactions of H2O2 (Fig. 1). The wide range of concentration levels reflects the vastly different chemical reactivities and lifetimes of the different ROS species. Due to its relatively low reactivity and decomposition rates, H2O2 is a reservoir species with a chemical lifetime of several hours, whereas the lifetime of OH radicals is less than a microsecond due to their rapid reactions with antioxidants.

View Article: PubMed Central - PubMed

ABSTRACT

Air pollution can cause oxidative stress and adverse health effects such as asthma and other respiratory diseases, but the underlying chemical processes are not well characterized. Here we present chemical exposure-response relations between ambient concentrations of air pollutants and the production rates and concentrations of reactive oxygen species (ROS) in the epithelial lining fluid (ELF) of the human respiratory tract. In highly polluted environments, fine particulate matter (PM2.5) containing redox-active transition metals, quinones, and secondary organic aerosols can increase ROS concentrations in the ELF to levels characteristic for respiratory diseases. Ambient ozone readily saturates the ELF and can enhance oxidative stress by depleting antioxidants and surfactants. Chemical exposure-response relations provide a quantitative basis for assessing the relative importance of specific air pollutants in different regions of the world, showing that aerosol-induced epithelial ROS levels in polluted megacity air can be several orders of magnitude higher than in pristine rainforest air.

No MeSH data available.