Ambient air pollution exposure and damage to male gametes: human studies andin situ‘sentinel’ animal experiments

Abstract

Globally there is concern that adverse reproductive outcomes and fertility impairment in humans may be caused by exposure to environmental contaminants. Air pollution in particular has been linked to DNA damage, abnormal sperm morphology, and reduced sperm performance in men. Experimental studies using model species (mice and rats) exposed in situ provide evidence that ambient air pollution can cause damage to the respiratory system and other tissues or organs. This can take the form of DNA damage and other genetic changes throughout the body, including induced mutations, DNA strand breaks, and altered methylation patterns in male germ cells. Human and animal studies together provide strong evidence that air pollution, especially airborne particulate matter, at commonly occurring ambient levels is genotoxic to male germ cells. The mechanistic link between air pollution exposure and induced genetic changes in male germ cells is currently unclear. 'Sentinel' animal experiments explicitly examining air pollution affects on sperm quality in laboratory rodents have not been conducted and would provide a critical link to observations in humans. The importance of air pollution compared to other factors affecting fertility and reproductive outcomes in humans is not clear and warrants further investigation.

Declaring the existence of human germ‐cell mutagens

“…b There are two studies, both in mice [Yauk et al, 2007;Marchetti et al, 2011]. These agents induce similar biomarker effects in humans as they do in animals, such as DNA damage in sperm, as reviewed for ionizing radiation and chemotherapy [Kamiguchi and Tateno, 2002], smoking [DeMarini, 2004], and air pollution [Somers, 2011]. Thus, there is sufficiently strong mechanistic evidence for how these agents affect animals and humans.…”

“…Of 48 agents evaluated for induction of germ-cell mutations in rodents, 39 of them are positive [Shelby 1996;Witt and Bishop, 1996;Russell, 2004;Marchetti and Wyrobek 2005;Glen et al, 2008;Marchetti et al, 2011;Somers, 2011]. The published rodent germ-cell mutagens include ionizing radiation; cancer chemotherapy agents; food components (acrylamide); environmental contaminants (benzo[a]pyrene); and common complex mixtures to which nearly everyone is exposed, such as main-and side-stream tobacco smoke, diesel exhaust, and the particulate fraction of air pollution [Yauk et al, 2007;Marchetti et al, 2011;Ritz et al, 2011;Somers, 2011]. Table I illustrates that some of these agents are carcinogenic and somatic-cell mutagens in both humans and rodents, as well as germ-cell mutagens in rodents.…”

Air Pollution Exposure During Pregnancy and Reproductive Outcomes

“…Epidemiological studies demonstrated exposure to ambient levels of air pollutants, especially airborne particulate matter, has been linked in particular to DNA fragmentation (Selevan et al, 2000) (Evenson et al, 2005) and in general to abnormal sperm morphology and reduced sperm performance in men. (Somers 2011;Hammoud et al, 2010). Recent experimental animal data indicated that female fertility is also affected by air pollutants (Veras et al, 2010).…”

Spermatozoa as biomarkers for the assessment of human male infertility and genotoxicity

“…Perhaps this level of DNA damage can be tolerated. The association with the birth of the healthy child is not yet known although animal studies appear to be leading the way (reviewed in Somers 2011]). However, the long-term consequences remain unknown.…”