Slashdot Mirror
Air Pollution Causes Sperm Mutations In Mice
Reservoir Hill writes "Epidemiological studies in humans have suggested a link between air pollution and reduced male fertility, but such studies are often confounded by other lifestyle differences such as diet, genetic background, and economic class. Now a study of mice, reared in cages kept in a shed downwind of two steel mills and a busy highway in a Canadian city, showed a host of genetic changes compared to similarly housed mice breathing filtered air. DNA in the sperm of the mice in the polluted area contained 60% more mutations, had more strand breaks, and had more bases that had been chemically modified via the addition of a methyl group. Precisely how the pollution caused the DNA damage remains unclear but changes may be a more general response to particulate pollution. 'It's important to move this forward to the next step: determining whether there are any human corollaries to this,' says Jonathan Samet, an epidemiologist at Johns Hopkins University."
As is mentioned in the article, I would take the wild guess that one of the culprits in this situation is probably the collection of good old reactive oxygen species--hydroxyl radicals from peroxides formed via enzymatic transformation of superoxide ions, for instance. Naturally, the guess is worthless without being tested and proven. However, increased free radical production is fairly well implicated in similar DNA damage (base damage, double and single strand breaks, etc.) due to some types of ionizing radiation. You can show that cells in a high-oxygen environment will "respond better" (i.e. be more likely to be "killed" (i.e. transformed in a way that makes them not reproduce)) upon low-LET radiation exposure compared to cells that are poorly oxygenated. This implicates oxygen (and, eventually, reactive oxygen species) as a _partial_ explanation for DNA damage due to ionizing radiation. (This happens to be important when you consider that cells that are closer to the centers of some tumors are poorly oxygenated--not enough that they necessarily die, but enough so that they are not as easily killed as those cells on the periphery.) Similar damage might be caused by similar chemical, if not physical, processes, but my speculation is just that: speculation.
It bears mentioning, though, that much like the picture for radiation, it is just about certain that there is more to the story than just oxygenation. High LET radiation (think alpha particles compared to, say, low-energy x-rays) cause damage that is virtually unaffected by oxygen concentration, so we know there's more to the story.
Given how relatively poorly understood are the biological changes due to ionizing radiation, it's a little surprising to me, at least, that we don't know more about the mechanistics of damage due to "pollution." Many, many more people deal with high doses of pollution than deal with high doses of radiation, and it's a lot easier (usually) to control who gets the radiation as opposed to who breathes in the pollution. Anyhow, I suppose what I'm saying is that it shouldn't be surprising that ROS-es might be fingered as _a_ cause, but it'd be shortsighted to think of them as the only cause--not that it seems that's happened here, fortunately.