June 26, 2013
Determining The Role Of Chemicals Found In Secondhand Smoke
April Flowers for redOrbit.com - Your Universe Online
Scientists have known for a while that tobacco smoke, diesel exhaust and oil combustion are sources of polycyclic aromatic hydrocarbons (PAHs) that are known to cause cancer. The vast majority of research attention has been paid to the obviously dangerous high-molecular-weight PAHs like benzo[a]pyrene (BaP). The low-molecular-weight variety have been overlooked for the most part, with previous studies showing that these compounds alone aren’t very successful at mutating genes in cancer-causing ways.A new study from the University of Colorado Cancer Center explores two of these low-molecular-weight (LMW) PAHs, showing that while they don’t necessarily cause cancer, at least one of them promotes conditions that would allow cancer to grow. The findings, published in PLoS ONE, examined the LMW PAHs 1-methylanthracene (1-MeA) and 2-methylanthracene (2-MeA).
“There’s a big distinction between initiating cancer and promoting it,” says Alison Bauer, PhD, CU Cancer Center investigator and assistant professor at the Colorado School of Public Health. The new study revealed that in a mouse cell model using a progenitor cell of lung cancer, the LMW 1-MeA promoted inflammation and increased mitogenic pathways, both of which are linked to tumor promotion. 2-MeA, while nearly structurally identical, did not.
“These LMW PAHs have been considered less of a concern,” Bauer says, “but we’re finding evidence that’s not the case. They’re not likely initiating the cancer, but it looks as if they could promote it.”
Bauer and her team discovered that 1-MeA disrupts communication between cells, affecting the “gap junctions” across which adjoining cells pass information, as well as upregulates the gene COX2. COX2 has been shown in previous studies to create an over-aggressive inflammatory response – and this inflammation in turn can promote tumor growth.
“There are many different PAHs in secondhand smoke,” Bauer says. “Some are obviously dangerous like BaP, which directly mutates genes. Others, like 1-MeA, we know very little about. Think about all these PAHs like chess pieces – first you have to know how each piece moves and then you can start looking at how they all work together.”
Understanding the effects of these PAH mixtures is the next step in research, according to Bauer. A better understanding could help evaluate the risks of different combustion products and lead to new targeted therapies if some of the changes promoted by the LMW PAHs are found to be preventable or reversible by medicines.
“With smoking rates decreasing, we think this problem is going away, but high levels of secondhand smoke still exist in the U.S., for example in some apartment buildings,” Bauer says. “And around the world, in China, Russia, Poland and many other countries, secondhand smoke is still a major issue. Knowing the effects of these LMW PAHs like 1-MeA could help us prevent or treat cancers associated with them.”