The alpha-dicarbonyl butter flavoring, diacetyl (2,3-butanedione), is associated with flavorings-related constrictive bronchiolitis in workers who make or use flavorings. Diacetyl causes protein damage in a process believed to be dependent upon the alpha-dicarbonyl structure. A protective response to damaged protein is ubiquitination with subsequent proteasomal processing. Diacetyl is also metabolized to the less reactive alpha-hydroxyketone, acetoin, by dicarbonyl/L-xylulose reductase (Dcxr). We examined the role of Dcxr and gender on acute toxicity of inhaled diacetyl by exposing Dcxr knockout and wildtype mice of both sexes to diacetyl at target concentrations of 0, 100, 200 or 300 ppm for 6 hr. At 1 day post-exposure, endpoints were semi-quantitative histopathology and morphometric measurement of ubiquitin immunofluorescence in nose and lung sections. Ubiquitin was principally localized to nasal and intrapulmonary airways, increased in large bronchioles at concentrations > / = 100 ppm, and in the nose at 300 ppm. Diacetyl-induced ubiquitin in the nose and lung was modified by both gender and Dcxr. In lung histopathology, diacetyl caused vacuolation of airway epithelium of large bronchioles at concentrations > / = 100 ppm. In olfactory bulb (OB) of male mice inhaling 300 ppm diacetyl, mRNA expression of inflammatory mediators and olfactory marker protein (Omp), a marker of olfactory neuron axons, were assayed by real-time PCR. Diacetyl elevated Il6, Cxcl2, and TNFalpha and decreased Omp in OB. The data suggest that ubiquitin expression is a sensitive biomarker of diacetyl-induced protein damage in airway epithelium. Further, diacetyl causes neuroinflammation and potential loss of axons of olfactory neurons in OB, suggestive of neurotoxicity.
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