Tiny air pollutants inflame airways and harm heart | Science News for Students

Tiny air pollutants inflame airways and harm heart

New data from animals and people show how inhaled particles do their dirty work
May 31, 2017 — 7:10 am EST
Los Angeles

Tiny bits of air pollution can cause chronic runny noses, blood-vessel changes and other problems, new studies show.  


If your nose runs year-round, air pollution could be part of the problem. A new study in mice shows how tiny airborne particles affect the nose and sinus areas. Those particles can also build up within fatty deposits in blood vessels, a second new study finds. Boosting these fatty build-ups could lead to more strokes and heart attacks. Together, these new data show that when inhaled, teeny particles can lead to big harm.

Winter sniffles
Air pollution can lead to sinus problems even when it’s not cold or allergy season, new data suggest.
nicoletaionescu / iStockphoto

Particulates (Par-TIK-yu-lets) are a big category of small pollutants in the air. They include soot, smoke, dust, mists and other specks of material. Huge amounts come from burning coal, oil and wood. Particulates also spew from factories, farms and construction sites. The material is tiny — less than 10 micrometers (4 ten-thousandths of an inch) in diameter. Yet ongoing exposure to it raises the risk of lung disease, heart disease and other illnesses. Because of particulates, air pollution is the fourth leading cause of deaths worldwide, scientists reported last year.

Even when this pollution doesn’t kill, it can harm health, notes Murray Ramanathan. He’s a head and neck surgeon at Johns Hopkins University School of Medicine in Baltimore, Md. He and other scientists sometimes work with mice to learn more about what happens in human diseases of the nose, throat and sinuses. The animals are models that stand in for people.

In one of the new studies, Ramanathan’s team showed how particle pollution can cause or worsen chronic sinusitis (Sign-yu-SY-tis). Patients with this condition have stuffy and runny noses, facial pain behind the cheeks and other soreness. “Chronic” means that these symptoms last for 12 weeks or more.

More than 29 million people in the United States alone have the illness, reports the Centers for Disease Control and Prevention. This disease “has a huge impact on quality of life,” Ramanathan says. Patients have higher rates of depression than people who don’t have the disease. They miss more days of work. They’re also less productive and have lower well-being overall, he adds. Now his team has shown that pollution may be part of the problem.

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Relative PMs
This graphic shows the relative sizes of different types of particulate matter (PMs), in terms of their diameters (in micrograms).

Nosing around

For 16 weeks, the researchers exposed mice to particulates smaller than 2.5 micrometers. (That’s less than one ten-thousandth of an inch in diameter). The mice breathed this dirty air for six hours per day, five days each week. The time would be comparable to years of exposure in a person. The level of pollution was “probably about half of what we would see in India, or less,” Ramanathan says. India has some of the highest levels of air pollution in the world. So the mice experienced poor air quality, but not as bad as some people encounter in their daily lives. A control group of mice breathed only clean, filtered air.

At the end of the trial, the team rinsed the nose and sinus areas of each mouse with water. Then they examined the flushed-out water.

The rinse water from mice that had been breathing the polluted air showed that the inhaled particulates had triggered the immune systems in these rodents. For example, this water had an excess of macrophages (MAK-roh-fayj-es) — a type of white blood cells. These cells engulf and destroy foreign bodies, such as germs. Compared to the control group, the pollution-breathing mice had almost four times as many macrophages. Rinse water from these animals also had more proteins linked to inflammation. This inflammation is one way the body responds to injury. Its symptoms include swelling, heat and pain.

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Mouse sinuses
A mouse that inhaled clean air had a protein called E-cadherin (left, in red); it helps hold cells in the sinus surface together. That protein was mostly gone (right) from the sinus surface of a mouse that breathed polluted air.
Ramanathan Lab, Johns Hopkins University

The researchers also looked at the nose and sinus tissues of these mice using a high-powered microscope. Tissues from the pollution-breathing mice showed signs of damage. It seemed like the particulates were “basically punching holes in the wall [of the sinuses],” Ramanathan says. That would make it easier for microbes and allergens to get through. (Allergens are things, such as pollen and pet dander, which can trigger allergies.)

The group’s work “adds to a growing list of ways that particles of air pollution have harmful effects around the body,” says Mark Miller. He’s a cardiovascular scientist at the University of Edinburgh in Scotland. He studies diseases of the heart and blood system.

Particulate levels in the United States are generally lower than those used in the study. Still, Ramanathan notes, exposure depends on location. A school playground near a busy highway, he points out, could have particulate levels two or three times higher than what is typical for a region.

The team published its new findings online February 28 in the American Journal of Respiratory Cell and Molecular Biology.

Chronic sinusitis isn’t life-threatening. But “it can be debilitating for those affected,” says Michael Brauer. He’s an epidemiologist (Ep-ih-dee-me-OL-oh-jizt) at the University of British Columbia in Vancouver, Canada. “We have quite strong evidence of effects of particulate matter on the lungs,” he says. “While not unexpected, this study provides evidence supporting effects on the sinuses.”

Into the blood

Inhaled particles don’t just cause breathing problems. They also increase risks for heart attacks, strokes and other diseases of the circulatory system. A new study shows how particles can move from the lungs into the heart and blood vessels to cause this harm.

Mark Miller’s team exposed people and mice to inhaled nanoparticles. Rather than have them breathe polluted outdoor air, the researchers exposed them to billionth-of-a-meter-size gold bits. These particles are “several thousand times smaller than the width of a human hair,” Miller explains. They are roughly the size of particles spewed in the exhaust of diesel engines.

Because gold does not react easily with other chemicals, it is “essentially harmless” to people, Miller explains. Yet special laboratory methods can easily detect where this faux pollution ends up within the body. Within a day of inhaling the nanoparticles, gold showed up in people’s blood and urine. And it was still there up to three months later! Gold also showed up in the mouse blood. But only the smallest nanoparticles made it into their urine.

Concludes Miller: “We showed that these tiny particles enter the blood and are carried around the body.” And the smaller the particles, the more likely they were to circulate in blood and end up in urine.

That’s not all. Some people in the study needed surgery (not for issues related to their taking part in the tests). These people had build-ups of certain fatty deposits, called plaque (PLAK), in the arteries that carry blood to the brain. When doctors removed some of that plaque, they found it contained gold bits. Gold also showed up in fatty plaques from mice that had similar build-ups. But the gold wasn’t present in tissue within healthy mouse arteries.

Fatty plaques are a sign of atherosclerosis (ATH-er-oh-skler-OH-sis). This disease contributes to heart attacks or strokes, Miller explains. Air pollution can make this plaque-based disease worse. Particles in air pollution carry harmful chemicals on their surface, he says — chemicals much more reactive than gold. If the tiny particles reach plaque, these pollutants might prompt the fatty deposits to break open. A heart attack or stroke could result. Miller’s team shared its findings April 26 in ACS Nano.

Many countries have laws meant to limit particulate pollution. It may seem that air in many places is getting cleaner. However, Miller notes, “levels of nanoparticles have been increasing with increasing amounts of [car and truck] traffic,” he says. And if the particles are especially small, they may not even be visible.

City air often contains up to 10,000 particles per cubic centimeter (or per 0.06 cubic inch). But, a team from Carnegie Mellon University in Pittsburgh showed that on days when the air appeared totally clear of pollution, up to 150,000 particles could pollute each cubic centimeter. The particulates were simply too small to affect visibility.

Adds Brauer: “We have more than enough evidence of the harmful effects of air pollution on human health.” And that “only increases the urgency to reduce air pollution exposure as a way to improve population health.”

Power Words

(more about Power Words)

allergen     A substance that causes an allergic reaction.

artery       Part of the body’s circulation system, one of the major tubes carries blood from the heart to all parts of the body.

blood vessel     A tubular structure that carries blood through the tissues and organs.

cardiovascular     An adjective that refers to things that affect or are part of the heart and the system of vessels and arteries that move blood through the heart and tissues of the body.

cell     The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells. Most organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.

Centers for Disease Control and Prevention, or CDC    An agency of the U.S. Department of Health and Human Services, CDC is charged with protecting public health and safety by working to control and prevent disease, injury and disabilities. It does this by investigating disease outbreaks, tracking exposures by Americans to infections and toxic chemicals, and regularly surveying diet and other habits among a representative cross-section of all Americans.

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

chronic     A condition, such as an illness (or its symptoms, including pain), that lasts for a long time.

circulation      (adj. circulatory) A term in medicine that refers to the pumping of blood through the arteries and smaller types of vessels (and from there into other organs and tissues).

control     A part of an experiment where there is no change from normal conditions. The control is essential to scientific experiments. It shows that any new effect is likely due only to the part of the test that a researcher has altered.

depression     (in medicine) A mental illness characterized by persistent sadness and apathy. Although these feelings can be triggered by events, such as the death of a loved one or the move to a new city, that isn’t typically considered an “illness” — unless the symptoms are prolonged and harm an individual’s ability to perform normal daily tasks (such as working, sleeping or interacting with others). People suffering from depression often feel they lack the energy needed to get anything done. They may have difficulty concentrating on things or showing an interest in normal events. Many times, these feelings seem to be triggered by nothing; they can appear out of nowhere.

epidemiologist     Like health detectives, these researchers figure out what causes a particular illness and how to limit its spread.

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.

faux       Meaning false or fake. Faux fur, for instance, would not be made from animal products but from some manufactured fibers.

germ      Any one-celled microorganism, such as a bacterium or fungal species, or a virus particle. Some germs cause disease. Others can promote the health of more complex organisms, including birds and mammals. The health effects of most germs, however, remain unknown.

heart attack     Permanent damage to the heart muscle that occurs when one or more regions of it become starved of oxygen, usually due to a temporary blockage in blood flow.

immune system     The collection of cells and their responses that help the body fight off infections and deal with foreign substances that may provoke allergies.

inflammation     The body’s response to cellular injury and obesity; it often involves swelling, redness, heat and pain. It also is an underlying feature responsible for the development and aggravation of many diseases, especially heart disease and diabetes.

journal     (in science) A publication in which scientists share their research findings with experts (and sometimes even the public). Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject. The best journals are peer-reviewed: They send all submitted articles to outside experts to be read and critiqued. The goal, here, is to prevent the publication of mistakes, fraud or sloppy work.

macrophage     A type of white blood cell dispatched by the immune system. Like janitors of the body, they gobble up germs, wastes and debris for disposal. These cells also stimulate other immune cells by exposing them to small bits of the invaders.

microbe     Short for microorganism. A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.

micrometer     (sometimes called a micron) One thousandth of a millimeter, or one millionth of a meter. It’s also equivalent to a few one-hundred-thousandths of an inch.

microscope     An instrument used to view objects, like bacteria, or the single cells of plants or animals, that are too small to be visible to the unaided eye.

molecular biology     The branch of biology that deals with the structure and function of molecules essential to life. Scientists who work in this field are called molecular biologists.

nano     A prefix indicating a billionth. In the metric system of measurements, it’s often used as an abbreviation to refer to objects that are a billionth of a meter long or in diameter.

nanoparticle     A small particle with dimensions measured in billionths of a meter.

online     (n.) On the internet. (adj.) A term for what can be found or accessed on the internet.

particulate     A tiny bit of something. A term used by pollution scientists to refer to extremely tiny solid particles and liquid droplets in air that can be inhaled into the lungs. So-called coarse particulates are those with a diameter that is 10 micrometers or smaller. Fine particulates have a diameter no bigger than 2.5 micrometers (or 2,500 nanometers). Ultra-fine particulates tend to have a diameter of 0.1 micrometer (100 nanometers) or less. The smaller the particulate, the more easily it can be inhaled deeply into the lungs. Ultra-fine particulates may be small enough to pass through cell walls and into the blood, where they can then move throughout the body.

plaque     Fatty deposits that accumulate in vessels as a result of a disease known as atherosclerosis. This plaque is made up of fat, cholesterol and other substances carried by the blood. Eventually these deposits will harden and narrow the internal openings of the arteries. This reduces the flow of oxygen and blood to organs throughout body. (in dental medicine) A biofilm, or community of bacterial species, that grows on teeth and other surfaces in the mouth.

population     (in biology) A group of individuals from the same species that lives in the same area.

protein     A compound made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. Among the better-known, stand-alone proteins are the hemoglobin (in blood) and the antibodies (also in blood) that attempt to fight infections. Medicines frequently work by latching onto proteins.

reactive     (in chemistry) The tendency of a substance to take part in a chemical process, known as a reaction, that leads to new chemicals or changes in existing chemicals.

respiratory     Of or referring to parts of the body involved in breathing (called the respiratory system). It includes the lungs, nose, sinuses, throat and other large airways.

risk     The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)

sinus      Air-filled cavities (known as sinus cavities) around the nose and eyes. The tissue lining the sinuses makes mucus. It collects foreign materials and helps it drain into the nose. A painful inflammation of these tissues is known as sinusitis, which can create intense facial pressure and headaches around the cheeks and eyes.

smoke     Plumes of microscopic particles that float in the air. They can be comprised of anything very small. But the best known types are pollutants created by the incomplete burning of oil, wood and other carbon-based materials.

soot     Also known as black carbon particles, these are the residues of incompletely burned materials, from plastics, leaves and wood to coal, oil and other fossil fuels. The particles can be quite small — nanometers in diameter. If inhaled, they can end up deep within the lung.

stroke     (in biology and medicine) A condition where blood stops flowing to part of the brain or leaks in the brain.

symptom     A physical or mental indicator generally regarded to be characteristic of a disease. Sometimes a single symptom — especially a general one, such as fever or pain — can be a sign of any of many different types of injury or disease.

tissue     Made of cells, any of the distinct types of materials that make up animals, plants or fungi. Cells within a tissue work as a unit to perform a particular function in living organisms. Different organs of the human body, for instance, often are made from many different types of tissues.

white blood cells     Blood cells that help the body fight off infection.


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Journal:​ ​​M. Miller​ ​et​ ​al.​ Inhaled nanoparticles accumulate at sites of vascular disease.​ ​​ACS Nano.​ ​​Published online April 26, 2017. doi:​ 10.1021/acsnano.6b08551.

Journal: M. Ramanathan et al. Airborne particulate matter induces non-allergic eosinophilic sinonasal inflammation in mice. American Journal of Respiratory Cell and Molecular Biology. Published online February 28, 2017. doi: 10.1165/rcmb.2016-0351OC.