Defining the Deleterious Effects of Environmental Pollutants at a Mechanistic Level

Humans are constantly exposed to a complex mixture of damaging chemicals in the environment. Young children, especially those that are unborn, and the elderly are most at risk from environmental contaminants. Air pollution is a particular concern and has been linked to 3.7 million excess deaths worldwide each year, with diesel exhaust emissions being a major contributor. Contaminated foodstuffs - such as seafood contaminated by mercury - and pollution of water supplies by heavy metals such as arsenic also play a role, as do lifestyle factors, such as drinking and smoking. The World Health Organisation (WHO) estimates that 23% of global deaths, rising to 36% amongst children under 14 years of age, are attributable to environment factors such as these. Despite these alarming statistics, in most cases we do not understand how pollutants increase risk of disease. Our lack of understanding means that we cannot predict the likely health outcomes of exposure to specific pollutants. Nor are we in a position to develop public health interventions that might reduce the harmful impact of pollutants.

This work will test the hypothesis that pollutants associated with diesel engine emissions increase disease risk by causing damage to proteins, fats and DNA, the three major types of chemical that make up our bodies. We will do this using a panel of models we have generated that allow responses to damage to be measured following in vivo exposure.

This work will improve our understanding of how diesel exhaust fumes, and facilitate studies into how many other types of pollutants cause disease and also how pollutants exacerbate diseases such as asthma. It will allow us to identify affected organs and cell types and thus to predict the specific health outcomes that are likely to result from exposure to specific chemical mixtures. In the future, the models developed during this study will also allow us to evaluate the effectiveness of public-health interventions designed to reduce the impact of harmful pollutants. Finally, this work will provide us with potential biomarkers (chemicals that can be easily and safely measured in humans) that can be used to assess public exposure to dangerous levels of pollution.

Aim: Investigate whether pollutants associated with diesel emissions cause oxidative stress, DNA damage, and AhR pathway activation in vivo. We will evaluate in utero, neonatal and adult exposures and establish whether the responses observed are also observed in exposed human populations.

Methodology: This is a new collaboration between the University of Dundee and Queen Mary University London. The UoD will use its novel Hmox1, p21, and Cyp1a1 reporter mouse lines to evaluate oxidative stress, DNA damage, and AhR pathway activity, respectively, in response to chemicals associated with the semi-volatile organic fraction of diesel exhaust particles. We will also test ambient polluted air sampled from areas with high diesel emissions and provided by QMUL. Reporter mice will be randomized to control or treatment groups and reporter activities measured non-invasively by bioluminescent imaging for luciferase activity and post-mortem by LacZ staining of organ sections. The relevance of these rodent studies to humans will be assessed by measuring HMOX1, p21, and CYP1A1 levels in airway nasal epithelial biopsies and cultures taken before and after human volunteers have been exposed to polluted urban environments. Finally, to track the fate of cells damaged pre- and neonatally, we will exploit novel stress-shadowing (fate-mapping) mouse lines in which Cre recombinase driven from the Hmox1 or Cyp1a1 promoters and as a consequence permanently activates a silenced reporter system. For these studies, pure chemicals or particle mixtures will be administered to pregnant dams.

Benefits: Mechanistic insights into the relationship between diesel emissions and disease, including the highly susceptible in utero and neonatal phases of life. Pinpointing the organs and cell types affected will allow predictions of specific health outcomes for specific pollutants. Facilitate future studies on how the pathogenesis of human disease may be potentiated by the environment, i.e. asthma.

This project will have an impact on a broad range of stakeholders beyond academics, including the commercial private sector; regulatory bodies, policy-makers, and other organisations tasked with safeguarding the environment and public health; the wider public; and in the longer term public health itself.

The commercial private sector should derive both financial and intellectual benefits from our work, which will therefore contribute to the economic competitiveness of the UK. For example, the regulatory environment surrounding the chemical industry is becoming tougher; new EU REACH legislation, once in force, will require the chemical industry to undertake laborious and expensive general toxicity studies to establish the safety of bulk chemicals before importation into the EU and potential release into the environment. The cost and time required to generate the necessary data will be greatly reduced by performing regulatory toxicity studies in our reporter models. As a second example, British biotechnology and pharmaceutical companies developing drugs for use in man will be able to accelerate their pre-clinical drug safety and efficacy pipeline, and improve its predictive power, by using our models in place of standard mouse strains. This could greatly reduce the attrition rate of candidate drugs entering expensive clinical trials as well as animal use.

Regulatory authorities and policy-makers tasked with safeguarding human health will benefit though the incorporation of improved mechanism-based methods for risk assessment approaches. This should lead to improvements in public health policy, particularly if physiologically-based pharmacokinetic models can be developed for the extrapolation of in vitro and animal-based data to man.

The general public has an extremely keen interest on how the environment may affect their health and particularly that of their children. This is especially pertinent to individuals in developing countries who tend to suffer higher levels of air pollution. The ability to provide the public with more evidence based analysis of the health consequences of environmental exposure will help address the emotional and unscientific reactions to inaccurate press reports on this theme. The tools and datasets generated during this project will contribute to improving their health.

The final group that might benefit indirectly are public health services. It is recognized in the UK, for example, that an increasingly large percentage of public finances will be expended on the National Health Service in the future. This is largely due to a ballooning number of patients living with long-term, non-communicable diseases. As the aetiology of these diseases contains an environmental component, improvements to the environment driven by use of informative model systems to identify risk would help to reduce disease incidence and as a consequence associated health service costs.