Air pollution can mess with our DNA
Air pollution can make it hard to breathe. It also can increase someone’s blood pressure and heart rate. Those problems are well known. Now research suggests breathing diesel fumes can trigger another toxic change. It can inappropriately turn some genes on, while turning others off.
A gene is a segment of DNA that tells cells of the body what to do — and when. Genes can be controlled by a type of chemical switch, known as a methyl group (a carbon atom attached to three hydrogen atoms). Methyl groups cause a chemical reaction — called methylation — affecting a component of DNA. This tends to happen near a gene. Added methyl groups usually turn some gene off. The opposite tends to occur when you take a methyl group away, or demethylate a gene. Either change can alter health.
And that can be a good thing. The body naturally produces methyl groups. This allows it to turn off genes when their action is no longer needed.
But factors outside the body — such as air pollutants — may inappropriately step in and add methyl groups to DNA. Or they might remove methyl groups. These environmental changes can, in a sense, hijack genes, changing when or what they instruct cells to do.
The study of methylation’s role in gene action is calledepigenetics (EH-pee-jen-EH-tiks). It describes changes that happen outside of your DNA. Indeed, these changes do not harm DNA. Instead, epigenetics may silence a gene (by inappropriately turning it off) or switch some gene on at the wrong time.
And breathing diesel fumes for just two hours can have such an epigenetic effect, a new study finds. It was conducted by researchers at the University of British Columbia in Vancouver, Canada. They put 16 volunteers — one at a time — in an enclosed booth. It was about the size of a small bathroom. Each person remained there for two hours. Half breathed in clean air. The other half breathed air polluted with diesel fumes. Levels of that pollution were equal to what might occur in air along a highway in Beijing, China. Such levels also might occur at busy ports, rail yards, mines and industrial sites elsewhere in the world.
To probe the effects of the pollution, the researchers looked at a volunteers' blood. They compared samples collected before the experiment to those taken 6 and 30 hours after someone had sat in the exposure booth. Methyl groups changed at about 2,800 different points on the DNA of people who breathed in diesel fumes. Those changes affected about 400 genes. No similar changes were seen among people breathing the clean air.
At some DNA locations, exposure to diesel fumes added methyl groups. More often it reduced how many were present. That means a switch that normally would turn off a gene was more often flipped the other way. That could lead to unusually high gene activity.
How these diesel-related changes might affect health is not yet clear, notes Ruiwei Jiang, an author of the new study. But the tests show that air pollution can alter DNA. The new data also suggest that diseases such as asthma might stem from prolonged episodes of methylation, Jiang says.
"Even short-term exposure can cause these changes," she says. "So the question is: What are the cumulative effects for someone who breathes in diesel fumes regularly?" Jiang hopes other researchers will now try to answer this.
Her team’s findings were published December 9 in the journal Particle and Fibre Toxicology.
Andrea Baccarelli studies environmental health and epigenetics at Harvard University in Boston, Mass. The new study is important because it shows that human DNA can be affected by short-term exposure to air pollution, he says. Until now, he says, scientists had largely thought that DNA "would respond primarily to long-term exposures."
Power Words
asthma A disease affecting the body’s airways,which are the tubes through which animals breathe. Asthma obstructs these airways through swelling, the production of too much mucus or a tightening of the tubes. As a result, the body can expand to breathe in air, but loses the ability to exhale appropriately. The most common cause of asthma is an allergy. It is a leading cause of hospitalization and the top chronic disease responsible for kids missing school.
atom The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and neutrally charged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.
carbon The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.
chemical A substance formed from two or more atoms that unite (become bonded together) in a fixed proportion and structure. For example, water is a chemical made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O.
DNA (short for deoxyribonucleic acid) A long, spiral-shaped molecule inside most living cells that carries genetic instructions. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.
diesel Heavier and oilier than gasoline, diesel is another type of fuel made from crude oil. It’s used to power many engines — not only in cars and trucks but also to power some industrial motors — that don’t rely on spark plugs to ignite the fuel.
epigenetic changes Molecular switches that can turn a gene on or off. Methyl groups — chemical clusters each made of one carbon and three hydrogen atoms — latch onto DNA near a gene. It’s these methyl groups that can alter the programmed activity of a gene. Individuals can acquire an epigenetic change at any time during their lives.
exhaust (in engineering) The gases and fine particles emitted — often at high speed and/or pressure — by combustion (burning) or by the heating of air. Exhaust gases are usually a form of waste.
gene A segment of DNA that codes, or holds instructions, for producing a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.
hydrogen The lightest element in the universe. As a gas, it is colorless, odorless and highly flammable. It’s an integral part of many fuels, fats and chemicals that make up living tissues.
methylation (in chemistry) The attachment to some molecule of a methyl group — a carbon atom holding onto three hydrogen atoms. Removal of this methyl group is known as demethylation.
methyl group (in chemistry) Three hydrogen atoms bonded, chemically, to a carbon atom. This amazingly common quartet of atoms is then attached — through the carbon — to some other molecule. (in genetics) When attached to a gene, the methyl group can act like a new switch to turn the gene’s activity on or off, up or down.
molecule An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).
toxic Poisonous or able to harm or kill cells, tissues or whole organisms. The measure of risk posed by such a poison is its toxicity.
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