Oxidative stress: its role in air pollution and adverse health effects.

Increasing concern exists over the adverse effects of air pollution on human health. Epidemiological studies have shown a clear association between cardiovascular morbidity, decreased lung function, increased hospital admissions, mortality, and airborne concentrations of photochemical and particulate pollutants. Human exposure chamber studies of specific pollutants have shown that short term exposure leads to an acute inflammatory effect on normal human airways in a small (10–20%) proportion of healthy individuals. The consequences of long term exposure to air pollution are more difficult to access but are generally believed to be much worse. Studies in both children and adults have shown that exposure to particulates, nitrogen dioxide and sulphur dioxide, are associated with symptoms of bronchitis. Moreover, exposure to particulates has been related to reduced lung function growth in children and is reversed if the family relocates to a area with lower particulate concentrations. As with any toxic challenge the obvious solution is to remove, or at least decrease to an acceptable level, the source of trouble. In many countries, air pollution levels have fallen in recent years, while additional measures are in place in several more to decrease concentrations further. It is unlikely however, that these practical measures will completely eliminate the problem, even in the medium term. As a consequence, it has been recognised for some time that there is also a need to improve our understanding of the impact of air pollution on biological systems. For example, a better appreciation of the mechanisms underlying air pollution induced health problems would allow a more targeted approach to remove the most toxic components of air pollution, and could possibly provide a means to decrease individual sensitivity to air pollution. As a consequence of recent research undertaken in a number of different countries, using a range of different approaches, oxidative stress has been identified as a unifying feature underlying the toxic actions of the air pollutants that are causing concern. Oxidative stress, resulting from either increased exposure to oxidants or the presence of decreased antioxidant defences, seems to trigger a number of redox sensitive signalling pathways. There is now a strong body of evidence to indicate that the pulmonary inflammatory response that arises following exposure to a pollution episode, is mediated via oxidant signalling pathways.Moreover, it appears likely that an individual’s sensitivity to pollution is related, in part, to their pulmonary antioxidant defences.