When laboratory mice inhaled diacetyl vapors for three months, they developed lymphocytic bronchiolitis - a potential precursor of OB. None of the mice, however, were diagnosed with OB.
"This is one of the first studies to evaluate the respiratory toxicity of diacetyl at levels relevant to human health. Mice were exposed to diacetyl at concentrations and durations comparable to what may be inhaled at some microwave popcorn packaging plants," said Daniel L. Morgan, Ph.D., head of the Respiratory Toxicology Group at the NIEHS and co-author on the paper that appears online in the journal, Toxicological Sciences. The study was done in collaboration with Duke University researchers.
The authors conclude that these findings suggest that workplace exposure to diacetyl contributes to the development of OB in humans, but more research is needed.
Although exposure of laboratory animals by inhalation closely duplicates the way humans are exposed to airborne toxicants, the study points out that some anatomical differences between the mice and humans may account for why the nasal cavity of mice is more susceptible to reactive vapours than that of humans. Another reason may be that mice breathe exclusively through their noses.
The researchers also speculate that the extensive reaction of diacetyl vapours in the nose and upper airways of mice may have prevented toxic concentrations from penetrating deeper in the lung to the bronchioles or tiny airways where obstruction occurs in humans.
When the mice were exposed to high concentrations of diacetyl using a method that bypasses the nose, the researchers found lesions partially obstructing the small airways. More studies are under way to determine if these lesions progress to OB in mice.
The National Toxicology Program, headquartered at the NIEHS, plans to do a larger set of studies to provide inhalation toxicity data on artificial butter flavouring and the two major components, diacetyl and another compound called acetoin. The NTP studies will help pinpoint more definitively the toxic components of artificial butter flavouring and potentially help identify biomarkers for early detection. The NTP data will then be shared with public health and regulatory agencies so they can set safe exposure levels for these compounds and develop guidance to protect the health of workers in occupations where these chemicals are used.