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Searching for the molecular underpinnings of asthma exacerbations

little boy using asthma inhaler

It’s long been known that colds, flu and other respiratory illnesses are major triggers for asthma exacerbations, says asthma expert Stephen J. Teach, M.D., MPH. Consequently, a significant body of research has focused on trying to figure out what’s happening on the cellular or molecular level as these illnesses progress to exacerbations.

People with asthma can be indistinguishable from people who don’t have this chronic airway disease – until they have an asthma attack, also known as an exacerbation. During these events, their airways become inflamed and swollen and produce an abundance of mucus, causing dangerous narrowing of the bronchial tubes that leads to coughing, wheezing and trouble breathing. These events are a major cause of morbidity and mortality, leading to the deaths of 10 U.S. residents every day, according to the Centers for Disease Control and Prevention.

It’s long been known that colds, flu and other respiratory illnesses are major triggers for asthma exacerbations, says Children’s National in Washington, D.C., asthma expert Stephen J. Teach, M.D., MPH. Consequently, a significant body of research has focused on trying to figure out what’s happening on the cellular or molecular level as these illnesses progress to exacerbations. Targeted searches have identified several different molecular pathways that appear to be key players in this phenomenon. However, Dr. Teach says researchers have been missing a complete and unbiased snapshot of all the important pathways in illness-triggered exacerbations and how they interrelate.

To develop this big picture view, Dr. Teach and  Inner-City Asthma Consortium colleagues recruited 208 children ages 6-17 years old with severe asthma – marked by the need for daily doses of inhaled corticosteroids, two hospitalizations or systemic corticosteroid treatments over the past year, and a high concentration of asthma-associated immune cells – from nine pediatric medical centers across the country, including Children’s National. (Inhaled corticosteroids are a class of medicine that calms inflamed airways.) The researchers collected samples of nasal secretions and blood from these patients at baseline, when all of them were healthy.

Then, they waited for these children to show symptoms of respiratory illnesses. Within six days of cold symptoms, the researchers took two more samples of nasal secretions and blood. They also administered breathing tests to determine whether these respiratory illnesses led to asthma exacerbations and recorded whether these patients were treated with systemic corticosteroids to stem the associated respiratory inflammation.

The researchers examined nasal fluid samples for evidence of viral infection during illness and used analytical methods to identify the causative virus. They analyzed all the samples they collected for changes in concentrations of various immune cells. They also looked globally in these samples for changes in gene expression compared with baseline and between the two collection periods during respiratory illness.

Together, this information told the molecular story about what took place after these children got sick and after some of them developed exacerbations. Of the 208 patients recruited, 106 got respiratory illnesses during the six-month study period, leading to a total of 154 illness events. Of those, 47 caused exacerbations, and 107 didn’t.

About half the exacerbations appeared to have been triggered by a rhinovirus, a cause of common colds, the research team reports in a study published online April 8, 2019, in Nature Immunology. The other children’s cold-like symptoms could have been triggered by pollution, allergens or other irritants.

In most exacerbations, virally triggered or not, the researchers saw early activation of a network of genes that appeared to be associated with SMAD3, a signaling molecule already known to be involved in airway inflammation. At the same time, genes that control a set of immune cells known as lymphocytes were turned down. However, as the exacerbation progressed and worsened, the researchers saw gene networks turned on that related to airway narrowing, mucus hypersecretion and activation of other immune cells.

Exacerbations triggered by viruses were associated with multiple inflammatory pathways, in contrast to those in which viruses weren’t found, which were associated with molecular pathways that affected cells in the airway lining.

The researchers validated these findings in 19 patients who each got respiratory illnesses at least twice during the study period but only developed an exacerbation during one of these episodes, finding the same upregulated and downregulated molecular pathways in these patients as in the study population as a whole. They also identified a set of molecular risk factors in patients at baseline – signatures of gene activation that appeared to put patients at risk for exacerbations when they got sick. When patients were treated with systemic corticosteroids during exacerbations, these medicines appeared to restore only some of the affected molecular pathways to normal, healthy levels. Other molecular pathways remained markedly changed.

Each finding could represent a new target for drugs that could prevent or more effectively treat exacerbations, keeping more patients with asthma healthy and out of the hospital.

“Our consortium study found increased gene expression of enzymes that produce molecules that contribute to narrowed airways and dilated blood vessels,” Dr. Teach adds. “This is especially intriguing because drugs that target kallikreins or bradykinin may help treat asthma attacks that aren’t caused by viruses.”

In addition to Dr. Teach, study co-authors include Lead Author Matthew C. Altman, University of Washington; Michelle A. Gill, Baomei Shao and Rebecca S. Gruchalla, all of University of Texas Southwestern Medical Center; Elizabeth Whalen and Scott Presnell of Benaroya Research Institute; Denise C. Babineau and Brett Jepson of Rho, Inc.; Andrew H. Liu, Children’s Hospital Colorado; George T. O’Connor, Boston University School of Medicine; Jacqueline A. Pongracic, Ann Robert H. Lurie Children’s Hospital of Chicago; Carolyn M. Kercsmar and Gurjit K. Khurana Hershey, , Cincinnati Children’s Hospital; Edward M. Zoratti and Christine C. Johnson, Henry Ford Health System; Meyer Kattan, Columbia University College of Physicians and Surgeons; Leonard B. Bacharier and Avraham Beigelman, Washington University, St. Louis; Steve M. Sigelman, Peter J. Gergen, Lisa M. Wheatley and Alkis Togias, National Institute of Allergy and Infectious Diseases; and James E. Gern, William W. Busse and Senior author Daniel J. Jackson, University of Wisconsin School of Medicine and Public Health.

Funding for research described in this post was provided by the National Institute of Allergy and Infectious Diseases under award numbers 1UM1AI114271 and UM2AI117870; CTSA under award numbers UL1TR000150, UL1TR001422 and 5UL1TR001425; the National Institutes of Health under award number UL1TR000451;  CTSI under award number 1UL1TR001430; CCTSI under award numbers UL1TR001082 and 5UM1AI114271; and NCATS under award numbers UL1 TR001876 and UL1TR002345.

Human Rhinovirus

Finding the root cause of bronchiolitis symptoms

Human Rhinovirus

A new study shows that steroids might work for rhinovirus but not for respiratory syncytial virus.

Every winter, doctors’ offices and hospital emergency rooms fill with children who have bronchiolitis, an inflammation of the small airways in the lung. It’s responsible for about 130,000 admissions each year. Sometimes these young patients have symptoms reminiscent of a bad cold with a fever, cough and runny nose. Other times, bronchiolitis causes breathing troubles so severe that these children end up in the intensive care unit.

“The reality is that we don’t have anything to treat these patients aside from supportive care, such as intravenous fluids or respiratory support,” says Robert J. Freishtat, M.D., M.P.H., chief of emergency medicine at Children’s National Health System. “That’s really unacceptable because some kids get very, very sick.”

Several years ago, Dr. Freishtat says a clinical trial tested using steroids as a potential treatment for bronchiolitis. The thinking was that these drugs might reduce the inflammation that’s a hallmark of this condition. However, he says, the results weren’t a slam-dunk for steroids: The drugs didn’t seem to improve outcomes any better than a placebo.

But the trial had a critical flaw, he explains. Rather than having one homogenous cause, bronchiolitis is an umbrella term for a set of symptoms that can be caused by a number of different viruses. The most common ones are respiratory syncytial virus (RSV) and rhinovirus, the latter itself being an assortment of more than 100 different but related viruses. By treating bronchiolitis as a single disease, Dr. Freishtat says researchers might be ignoring the subtleties of each virus that influence whether a particular medication is useful.

“By treating all bronchiolitis patients with a single agent, we could be comparing apples with oranges,” he says. “The treatment may be completely different depending on the underlying cause.”

To test this idea, Dr. Freishtat and colleagues examined nasal secretions from 32 infants who had been hospitalized with bronchiolitis from 2011 to 2014 at 17 medical centers across the country that participate in a consortium called the 35th Multicenter Airway Research Collaboration. In half of these patients, lab tests confirmed that their bronchiolitis was caused by RSV; in the other half, the cause was rhinovirus.

From these nasal secretions, the researchers extracted nucleic acids called microRNAs. These molecules regulate the effects of different genes through a variety of different mechanisms, usually resulting in the effects of target genes being silenced. A single microRNA typically targets multiple genes by affecting messenger RNA, a molecule that’s key for producing proteins.

Comparing results between patients with RSV or rhinovirus, the researchers found 386 microRNAs that differed in concentration. Using bioinformatic software, they traced these microRNAs to thousands of messenger RNAs, looking for any interesting clues to important mechanisms of illness that might vary between the two viruses.

Their findings eventually turned up important differences between the two viruses in the NF-kB (nuclear factor kappa-light-chain-enhancer of activated B cells) pathway, a protein cascade that’s intimately involved in the inflammatory response and is a target for many types of steroids. Rhinovirus appears to upregulate the expression of many members of this protein family, driving cells to make more of them, and downregulate inhibitors of this cascade. On the other hand, RSV didn’t seem to have much of an effect on this critical pathway.

To see if these effects translated into cells making more inflammatory molecules in this pathway, the researchers searched for various members of this protein cascade in the nasal secretions. They found an increase in two, known as RelA and NFkB2.

Based on these findings, published online Jan. 17, 2018, in Pediatric Research, steroids might work for rhinovirus but not for RSV, notes Dr. Freishtat the study’s senior author.

“We’re pretty close to saying that you’d need to conduct a clinical trial with respect to the virus, rather than the symptoms, to measure any effect from a given drug,” he says.

Future clinical trials might test the arsenal of currently available medicines to see if any has an effect on bronchiolitis caused by either of these two viruses. Further research into the mechanisms of each type of illness also might turn up new targets that researchers could develop new medicines to hit.

“Instead of determining the disease based on symptoms,” he says, “we can eventually treat the root cause.”

Study co-authors include Kohei Hasegawa, study lead author, and Carlos A. Camargo Jr., Massachusetts General Hospital; Marcos Pérez-Losada, The George Washington University School of Medicine and Health Sciences; Claire E. Hoptay, Samuel Epstein and Stephen J. Teach, M.D., M.P.H., Children’s National; Jonathan M. Mansbach, Boston Children’s Hospital; and Pedro A. Piedra, Baylor College of Medicine.