Butter flavouring used in microwave popcorn which was thought to be safe has been shown to be a respiratory hazard for workers who inhale the substance, causing ‘popcorn workers’ lung’.
The ingredient 2,3-pentanedione (PD) replaced the use of another butter flavouring, diacetyl, which was found to cause bronchiolitis obliterans; but far from being a safer alternative, researchers have found that PD has a respiratory toxicity comparable to diacetyl in laboratory animals.
“Our study demonstrates that PD, like diacetyl, damages airway epithelium in laboratory studies,” said lead researcher Ann F Hubbs from the Health Effects Laboratory Division of the National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention. “This finding is important because the damage is believed to be the underlying cause of bronchiolitis obliterans.”
Groups of rats were exposed to different concentrations of PD, diacetyl or filtered air and monitored for toxicity. The rats’ brains, lungs and nasal tissues were microscopically examined and further investigations were carried out on changes in gene expression in discrete brain regions.
The researchers found respiratory epithelial injury in the upper nose of rats exposed to PD that was comparable to that cause by diacetyl. They also found PD exposure caused necrosis and apoptosis in the olfactory neuroepithelium and activation of caspase 3 - a protein involved in cell death - in axons of olfactory nerve bundles.
Several signs of toxicity were found, including increased expression of interleukin-6 and nitric oxide synthase-2. In addition, the researchers found decreased expression of vascular endothelial growth factor A in the olfactory bulb, striatum, hippocampus and cerebellum.
“Our study is a reminder that a chemical with a long history of being eaten without any evidence of toxicity can still be an agent with respiratory toxicity when appropriate studies are conducted,” said Hubbs.
“It suggests several intriguing potential mechanisms for the toxicity of inhaled volatile α-diketones, reveals mRNA changes in the brain, documents olfactory neurotoxicity and clearly demonstrates that the remarkable airway toxicity of diacetyl is shared with its close structural relative, PD.”
The research findings were published in The American Journal of Pathology.