Two chemicals commonly found in e-cigarette liquid flavorings could impair the function of cilia in the human airway, according to a recent study conducted by the Harvard T.H. Chan School of Public Health.
Cilia are found in the middle ear, respiratory tract, as well as the lungs. They have beating motion or rhythmic waving which is important in keeping the human airways clear from dirt and mucus - allowing us to easily breathe without any hesitation. If cilia function has been impaired, it could lead to several lung diseases such as asthma and chronic obstructive pulmonary disease (COPD).
Quan Lu, the co-senior author of the study and associate professor of environmental genetics and pathophysiology, said their new study suggests chemicals usually found in e-cigarette liquids could harm the cilia by altering the gene expression associated with cilia production and function. The study was published in the Scientific Reports journal.
Millions of people are using e-cigarettes, and the number is rising among school-aged children which prompted concerns to public health experts. Joseph Allen - an assistant professor of exposure assessment science and also the co-senior author of the study - along with Harvard Chan colleagues tested e-cigarettes and found over 90 percent flavoring chemicals - primarily 2,3-pentanedione and diacetyl.
Diacetyl, in particular, is being used as a flavoring agent in foods like candy, baked goods, and butter-flavored microwave popcorn. The chemical is considered as a safe food ingredient, but previous studies pointed out it can be dangerous when inhaled.
Diacetyl has been also linked with bronchiolitis obliterans - a lung disease dubbed as "popcorn lung" since it first appeared in workers who inhaled artificial butter flavor in microwave popcorn processing facilities. Since the chemical was linked to popcorn lung, the 2,3-pentanedione was then used as a substitute.
Now, researchers in the new study applied novel lab techniques so they can properly examine both diacetyl and 2,3-pentanedione on epithelial cells - mimicking the human airway epithelium in vivo. The normal human bronchial epithelial (NHBE) cells were exposed to the chemicals, and they found out both chemicals caused changes in gene expression which could impair the production, as well as the function of cilia.
The research team also discovered that even low levels of these chemicals could already affect gene. Allen noted e-cigarette users are heating and inhaling such chemicals, but these products were never tested for inhalation safety. And even though some e-cigarette liquid manufacturers said they do not use diacetyl or 2,3-pentandione, researchers still question what flavoring chemicals they are using then?
