Air pollution exposure–DNA adduct dosimetry in humans and rodents: evidence for non-linearity at high doses

https://doi.org/10.1016/S0027-5107(97)00097-3Get rights and content

Abstract

The impact of air pollution exposure on the level of total DNA adducts in human white blood cells (WBCs) was evaluated in two populations in the Czech Republic and compared to the exposure–DNA adduct relationship in other populations in the US and China in human lung cells and rodent lung tissue. The human populations examined were exposed to respirable particles (<2.5 μm) (PM2.5) in urban, rural, and occupational settings where the particles originated from coal and petroleum fuel combustion, coke production, and other coal-tar aerosols (e.g., used in aluminum production). These particles contain carcinogenic polycyclic aromatic hydrocarbons (PAHs) that are known to form DNA adducts through covalent binding. Personal exposure to PM2.5 and PAHs were measured prior to collection of blood samples for DNA adduct analysis by 32P-postlabeling. Coke oven workers (n=76), in 10 job categories on the top and side of a coke oven in Ostrava, CZ, were studied and compared to a different population exposed to environmental levels of PAHs from air pollution in Teplice, CZ. Personal exposures to airborne particles ranged from <1 to more than 15 000 μg/m3 and carcinogenic PAHs exposure ranged from <5 to >200 000 ng/m3. At low to moderate environmental exposures to carcinogenic PAHs, DNA adduct levels in the WBCs were significantly correlated with exposure. However, at the higher occupational levels found on the coke oven, the exposure–DNA adduct relationship became non-linear. Under these high exposure conditions, the relative DNA adduct level per unit of exposure (DNA-binding potency) was significantly lower than measured at environmental exposures. This finding is consistent with observations in lung cells from bronchoalveolar lavage of humans exposed to a wide range of PAH. This same high exposure–dose non-linearity was also observed in lung DNA from rats exposed by inhalation to a coal-tar pitch aerosol. DNA adduct levels in all these cases show evidence of a form of non-linearity at high doses that has been described by Lutz (W.K. Lutz, Dose–response relationship and low dose extrapolation in chemical carcinogenesis, Carcinogenesis, 11 (1990) 1243–1247) as a superlinear dose response. This superlinear response may be due to saturation of metabolic activation enzymes, induction of either DNA repair processes or detoxification enzymes, or other mechanisms. Regardless of the mechanism, this decrease in the DNA-binding potency at moderate to high doses of PAH has important implications for dose-response extrapolation in risk assessment.

Introduction

Dose–response extrapolation in risk assessment may include both rodent to human species extrapolation and human high- to low-dose extrapolation. The uncertainties associated with this component of risk assessment are often difficult to assess due in part to limited quantitative data in humans. One of the greatest limitations in developing valid extrapolation models is the lack of quantitative data on the relationship between external exposure (e.g., a delivered dose) and an effective dose to specific target molecules, cells or organs in humans. The development of molecular and biochemical methods to measure internal exposure (e.g., urinary metabolites) and biologically effective doses (e.g., DNA and protein adducts) [2] has facilitated human exposure–dosimety biomarker studies. The development of 32P-postlabeling methods for quantifying a wide range of DNA adducts in both humans and animals even at very low doses has had the greatest impact in advancing the data available for future dose–response extrapolation studies. This methodology allows the evaluation of DNA adducts in humans at background levels so that the question of low-dose extrapolation in humans with respect to exposure–dosimetry can be addressed.

Recent technological advances in the development of monitoring and analytical methods for measurement of personal and total human exposure to environmental pollutants now make it possible to measure human exposure in relationship to biomarkers of dose. The development of personal exposure monitors (PEMs) has facilitated the investigation of the relationship between personal exposure to carcinogenic PAHs associated with respirable particulate matter (PM2.5) in the air and biomarkers of internal exposure and dose.

Biomarker studies to measure seasonal differences in exposure and genetic damage from environmental pollution were first conducted in a population from a high polluted area in Silesia (Poland) 3, 4, 5. In these population groups, seasonal variations in several biomarkers were related to seasonal changes in air pollution 4, 5. Personal exposure data in these populations were not evaluated at that time. Therefore, the investigators were not able to determine the relationship between individual exposure to air pollution and biomarkers of exposure and genetic damage. It is possible that much of the inter-individual variation observed in these studies within the exposure groups is actually due to differences in individual personal exposures.

The objectives of this study were to evaluate personal exposure to air pollution in conjunction with DNA adducts as a molecular measure of DNA dosimetry. Carcinogenic PAHs adsorbed to respirable particulate matter (<2.5 μm) (RSP) were selected as the air pollution marker for monitoring personal exposure in this study. The major sources of regional pollution are combustion of petroleum and coal and related fuels that produce PAHs and other genotoxic polycyclic organic matter (POM) adsorbed to fine soot particles. Exposures to PAH and POM have been estimated to represent the greatest potential source of lung cancer risk outside of tobacco smoke [6]. PAHs are rapidly metabolized via microsomal oxidative pathways to reactive intermediates that may bind to protein and DNA or that may be excreted as phenols and diols in the urine. DNA adducts, as measured by 32P-postlabeling, were selected as the biomarker of dose for this study [7].

This study examines the influence of personal exposure to PAH on WBC DNA adducts in a population exposed to high occupational levels of PAH in Ostrava, CZ compared to an environmentally exposed population in Teplice, CZ. The personal exposure levels to RSP ranged from <1 to more than 15 000 μg/m3, the exposures to 8 carcinogenic PAHs ranged from <5 to >200 000 ng/m3, and exposures to benzo[a] pyrene (B[a]P), one of the most carcinogenic PAH, ranged from 0.1 to 42 000 ng/m3 (Table 1). DNA adduct dosimetry in WBCs under relatively low environmental exposures was compared to high occupational exposures in two different populations in the Czech Republic. In lung cells of individuals in the US exposed to relatively low concentrations of PAH, the DNA adduct dosimetry was compared to individuals in China exposed to both moderate urban concentrations of PAH (Kumming, China) and exceptionally high concentrations of PAH from burning smoky coal indoors in Xuan Wei, China. Evidence of high dose non-linearity and decreased DNA-binding potencies were found in both WBCs and lung cells of individuals exposed to high concentrations of PAH when compared to individuals exposed to lower environmental levels of PAH where evidence of a significant DNA adduct dose–response was found. The same high dose non-linearity was observed in lung DNA of rodents exposed by inhalation to coal-tar pitch aerosols.

Section snippets

Human subjects and sampling design

Coke oven workers (n=76) in 10 job categories, evenly distributed between the top and side of a coke oven and between smokers and non-smokers, were studied and compared to the population exposed to environmental levels of PAHs from air pollution. The coke oven workers were employed at a large coke oven battery located in Ostrava, Czech Republic. Personal exposure monitoring was initiated at the beginning of their working shift and continued for up to 8 h through their shift. Blood samples for

Dose–response relationship between personal exposure to carcinogenic PAH and DNA adducts in WBCs

The particle and PAH exposure range for the environmental and occupational groups is shown in Table 1. The environmental exposures to carcinogenic PAH ranged slightly more than one order of magnitude from 2 to 30 ng/m3 for the data used here [8]. The coke oven exposure range was much wider than the environmental exposure range, from 135 to 200 000 ng/m3. No significant difference was observed in the personal exposure to RSP, PAH or B[a]P between the smokers and non-smoker in either the

Discussion

The dose–response relationship for DNA adduct formation in experimental animals has been reviewed for a number of genotoxic chemicals that require metabolic activation 19, 20, 21. The most recent review by Lutz and Gaylor [22] supports earlier analyses concluding that the “…experimental (animal) data as well as theoretical considerations strongly favor low-dose linearity for DNA adduct formation”. At moderate and high dose levels, however, non-linearities are frequent. Lutz [1] has proposed

Acknowledgements

We thank Drs. Jane Gallagher and Werner Lutz for their critical comments on the manuscript. The authors acknowledge the support of the technical staff and Dr. J. Wolf, Director of the Regional Institute of Hygiene, Ostrava, Czech Republic and the cooperating coke oven workers and management at the Iron Works in Ostrava who made it possible to conduct the coke oven biomarker study. We also acknowledge the collaboration of Dr. Uwe Heinrich, Director of the Fraunhofer Institute of Toxicology and

References (28)

  • B. Binková et al.

    DNA adducts and personal air monitoring of carcinogenic polycyclic aromatic hydrocarbons in an environmentally exposed population

    Carcinogenesis

    (1995)
  • R. Williams, L. Brooks, R. Stevens, V. Marple, J. Lewtas, Field test and laboratory evaluation of a lightweight modular...
  • R. Watts et al.

    Czech–U.S. EPA health study: assessment of personal and ambient air exposures to PAH and organic mutagens in the Teplice district of Northern Bohemia

    Int. J. Environ. Anal. Chem.

    (1994)
  • R. Williams et al.

    Environmental tobacco smoke exposure of young children as assessed using a passive diffusion device for nicotine

    Indoor Environ.

    (1993)
  • Cited by (131)

    • Benzo(a)pyrene exposure in utero exacerbates Parkinson's Disease (PD)-like α-synucleinopathy in A53T human alpha-synuclein transgenic mice

      2021, Toxicology and Applied Pharmacology
      Citation Excerpt :

      And more genes related to neurotransmitter whose expression could be affected by B(a)P exposure like dopamine receptor D1A, glutamate receptor metabotropic 4 and dopamine receptor D2 were found with whole genome oligo microarrays by Qiu et al(Qiu et al., 2011) Robust neurotoxic effects will be caused by these changes and the mechanism under these discoveries remains unclear, it's likely that DNA adducts of genes and B(a)P could be one of the reasons.( Lewtas et al., 1997) B(a)P DNA adducts also can be found in 60 days adult mice who exposed to B(a)P in utero which means that expression of the offspring's genes can be affected too.( Arnould et al., 1997) In the present study it was declared that as the preliminary step of α-syn expression the SNCA transcription could be altered by B(a)P exposure in utero, and a dose-dependent increase was observed.

    View all citing articles on Scopus
    View full text