The new research, forthcoming in Toxicology Letters, found that more new blood vessels sprouted in mice exposed to diesel exhaust than in mice exposed to clean filtered air. The growth occurred in both healthy and diseased animals—meaning that even healthy bodies are susceptible to the damaging effects of diesel.
The problem lies in the size of inhaled diesel particles. Most are less than 0.1 micron in diameter—that's less than one-tenth of a millionth of a meter. Such tiny particles penetrate the blood stream, organs, and tissues to damage practically any part of the body.
Exposure levels in the study mimicked the exposures of people living in urban areas and of people commuting in heavy traffic. The levels were lower than, or similar to, those typically experienced by workers using diesel-powered equipment and those working along railroads, in mines, tunnels, vehicle maintenance garages, on bridges, farms, and at loading docks.
According to co-author Qinghua Sun, via The Ohio State University: "The message from our study is that exposure to diesel exhaust for just a short time period of two months could give even normal tissue the potential to develop a tumor."
The researchers found three types of blood vessel development after exposure to the diesel exhaust: angiogenesis, the development of new capillaries; arteriogenesis, the maturation or regrowth of existing vessels; and vasculogenesis, the formation of new blood vessels. All are associated with tumor growth but angiogenesis in particular can wreak havoc in the human body.
The researchers observed four ways that exposure to diesel exhaust facilitated tumor growth:
- By activating a chemical signal, vascular endothelial growth factor, associated with new blood vessel development
- By increasing levels of a protein, hypoxia-inducible factor 1, essential to blood vessel development when oxygen levels are low
- By lowering the activity of an enzyme with a role in producing substances that suppress tumor growth
- By inducing low-grade inflammation, often associated with tumor development, in tissues exposed to exhaust
"We need to raise public awareness so people give more thought to how they drive and how they live so they can pursue ways to protect themselves and improve their health," says Sun. "And we still have a lot of work to do to improve diesel engines so they generate fewer particles and exhaust that can be released into the ambient air."