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Breathing diesel exhaust induces DNA changes, study finds

Tests on asthmatic subjects showed altered genes associated with breathing stress

Asthmatics who inhaled diesel exhaust fumes for two hours in a study booth didn’t just get itchy eyes and a headache while breathing in the polluted air.

They also experienced effects on a micro level as genes associated with inflammatory and oxidative stress processes were altered.

Those are the findings from five researchers at the University of B.C. who put 16 asthma patients in a cubicle, exposing them — on separate occasions — to filtered air and diesel exhaust and later comparing blood samples collected before and after exposures.

Diesel exhaust induced DNA changes but filtered air did not, according to lead researcher Christopher Carlsten, a respirologist and associate professor in the division of respiratory medicine.

The study by the researchers at UBC and Vancouver Coastal Health is published in the journal Particle and Fibre Toxicology. It showed that just two hours of exposure to diesel exhaust fumes led to biological changes that meant some genes were switched on while others turned off. The air quality during the diesel fume exposures is said to be comparable to a Beijing highway or shipping ports in British Columbia.

Carlsten said study subjects aged 19 to 35 were each paid a total of $600 for the three times they visited the study lab. Since each visit was time-consuming because of blood tests and other investigations required, the hourly stipend given to the participants probably worked out to about $15 per hour, he said in response to questions about why individuals with asthma would want to breathe in polluted air for the sake of the experiment.

While some participants experienced eye discomfort and a mild headache, none got sick or required medication when exposed to the diesel air in the study, which was funded by grants from various publicly funded research agencies.

“More importantly, we had no evidence that such single, brief exposures exacerbate asthma in mild asthmatics — which is why we were able to ethically perform the study,” he said. “In fact, our studies [including this one] repeatedly bear that out. All we see are sub-clinical changes which help us understand how air pollution may be affecting health without actually hurting anyone.”

He said the next step is for researchers to study how changes in gene expression from air pollution affect the human body over the long term, since the study shows genes may be vulnerable to pollution without producing any obvious or immediate symptoms of ill health.

“Usually when we look at the effects of air pollution, we measure things that are clinically obvious — air flow, blood pressure, heart rhythm,” Carlsten said. “But asthma, higher blood pressure or arrhythmia might just be the gradual accumulation of (gene) changes. So we’ve revealed a window into how these long-term problems arise. We’re looking at changes deep under the hood.”

According to the provincial Ministry of Health, an “interagency” group is working on options to address diesel emissions.

The research is timely because the provincial AirCare program has ended and environmental advocates are concerned about the impacts of older vehicles and diesel engines.

Metro Vancouver recently announced it will enforce existing bylaw prohibitions on diesel engines as of this month.

“Older non-road diesel engines that have little or no emission controls are the main concern of the bylaw. Engines in machines like excavators, forklifts and generators are examples of those included in the bylaw,” said Greg Moore, chair of the Metro Vancouver board of directors.

“Diesel engine exhaust is a known carcinogen that is responsible for two-thirds of the lifetime cancer risk from air pollution in our region,” Moore said. “The prohibitions that come into effect in 2015 are essential to protect human health by reducing emissions of harmful diesel soot from industrial and construction machines.”