Screening for specific blood-borne particles or proteins might reveal whether a smoker is developing emphysema, two new studies propose, raising the possibility that a test could catch some of the millions of undiagnosed people with the condition. Both studies appear in an upcoming issue of the American Journal of Respiratory and Critical Care Medicine.
Emphysema and chronic bronchitis are forms of chronic obstructive pulmonary disease. COPD is the third most common cause of death in the United States after heart disease and cancer, the Centers for Disease Control and Prevention determined last year. Most COPD patients are current or former smokers, and while the condition can be treated, there is no cure. It affects 24 million people in the United States, roughly half of whom are yet to be diagnosed, the National Institutes of Health estimates.
In one of the new studies, researchers at Weill Cornell Medical College in New York City examined blood from 32 nonsmokers and 60 largely healthy smokers who passed at least one in a pair of breathing tests.
The researchers found substantially more endothelial microparticles in smokers than in the nonsmokers. These microparticles come from tiny blood vessels called capillaries. Smokers who scored poorly on one of the breathing tests — a measure of the ability of cells in the lung to exchange carbon dioxide for oxygen — had more microparticles than did smokers who passed this test. Smoke damage causes capillary cells to die and shed microparticles into the blood.
The microparticles found in smokers were also more likely than those in nonsmokers to be attached to a protein called angiotensin converting enzyme. The enzyme shows up frequently on lung capillary cells that maintain air sacs called alveoli, which are central to oxygen exchange, thus tracing the origin of the microparticles.
Many smokers show no outward symptoms of COPD. Microparticles and other biomarkers may be valuable because smokers who are presented with clear evidence that their health is in danger are more apt to quit, says study coauthor Ronald Crystal, a pulmonary physician at Weill Cornell.
In the other new study, Australian researchers scanned blood from 21 asthma patients, five people with COPD and 17 healthy controls. Physician Peter Gibson of the University of Newcastle and his colleagues identified four proteins that show up in greater concentrations in COPD patients, three of which were also elevated in asthmatics. Combinations of one or more of these four proteins show promise as blood biomarkers for discerning whether a person has one or both of these conditions, the authors say.
“There are a number of biomarkers that people are now looking at in COPD,” says biochemist William Mattes of the COPD Foundation in Washington. “These are some of the new ones that are promising.” In addition to clarifying whether a person has COPD and if so its stage of development, he says, biomarkers may help researchers “as they work their way backward through the biological process of the disease,” with the added goal of finding other molecules that can be targeted by drugs to thwart COPD.