Respiratory and Olfactory Cytotoxicity of Inhaled 2,3-Pentanedione in Sprague-Dawley Rats

Abstract

Flavorings-related lung disease is a potentially disabling disease of food industry workers associated with exposure to the α-diketone butter flavoring, diacetyl (2,3-butanedione). To investigate the hypothesis that another α-diketone flavoring, 2,3-pentanedione, would cause airway damage, rats that inhaled air, 2,3-pentanedione (112, 241, 318, or 354 ppm), or diacetyl (240 ppm) for 6 hours were sacrificed the following day. Rats inhaling 2,3-pentanedione developed necrotizing rhinitis, tracheitis, and bronchitis comparable to diacetyl-induced injury. To investigate delayed toxicity, additional rats inhaled 318 (range, 317.9-318.9) ppm 2,3-pentanedione for 6 hours and were sacrificed 0 to 2, 12 to 14, or 18 to 20 hours after exposure. Respiratory epithelial injury in the upper nose involved both apoptosis and necrosis, which progressed through 12 to 14 hours after exposure. Olfactory neuroepithelial injury included loss of olfactory neurons that showed reduced expression of the 2,3-pentanedione-metabolizing enzyme, dicarbonyl/L-xylulose reductase, relative to sustentacular cells. Caspase 3 activation occasionally involved olfactory nerve bundles that synapse in the olfactory bulb (OB). An additional group of rats inhaling 270 ppm 2,3-pentanedione for 6 hours 41 minutes showed increased expression of IL-6 and nitric oxide synthase-2 and decreased expression of vascular endothelial growth factor A in the OB, striatum, hippocampus, and cerebellum using real-time PCR. Claudin-1 expression increased in the OB and striatum. We conclude that 2,3-pentanedione is a respiratory hazard that can also alter gene expression in the brain.

Evaluation of Electronic Cigarette Liquids and Aerosol for the Presence of Selected Inhalation Toxins

“…14 Toxicological studies in animals have shown that it has adverse effects on respiratory epithelium similar to DA and at similar levels. 15,28 Study Implications A wide range of DA and AP concentrations were found in the samples, indicating that in some cases the chemicals were used deliberately as ingredients while in others they were probably contaminants. Overall the estimated daily exposure from EC use was approximately 100 times lower for DA and 10 times lower for AP compared to tobacco cigarettes; therefore, it is still plausible to classify ECs as tobacco harm reduction products.…”

“…Unfortunately, the risks associated with inhalation of AP may well be as high as from DA, based on inhalation studies performed on rats. 15 Due to the potential hazards associated with inhalation exposure to DA and AP, regulatory agencies have set specific Occupational Exposure Limits (OELs 10,16 For AP, NIOSH has set a TWA limit of 9.3 ppb (38 µg/m 3 ) and an STEL of 31 ppb (127 µg/m 3 ). 10 The purpose of this study was to examine the presence of DA and AP in a large sample of EC liquids obtain from European and US manufacturers and retailers.…”

Accumulation of Ubiquitin and Sequestosome-1 Implicate Protein Damage in Diacetyl-Induced Cytotoxicity

“…Mice were exposed in a glass and stainless steel whole-body inhalation exposure chamber, as previously described for diacetyl and 2,3-pentanedione exposures in rats but modified for exposing mice. 3,16 In brief, a computer-controlled syringe pump injected diacetyl into stainless steel tubing, which was heated to 150 C. Diluent air flowed through the tubing so that the air in the tubing was at 70 C when the diacetyl was vaporized and then flowed into the inhalation chamber, where the concentration was monitored using a volatile organic compound meter (PGM-760; RAE Systems, San Jose, CA). The temperature in the chamber was maintained between 27.0 C and 28.0 C. Each mouse was housed individually in a wire cage during the exposures.…”

“…For the immunofluorescence assays, antigenicity was retrieved with 1 mmol/L EDTA, as previously described. 16 Slides were then rinsed in distilled water and blocked for 2 hours at room temperature using 10% donkey serum (Jackson ImmunoResearch). Primary antibodies were applied using capillary action with pairs of ProbeOn Plus slides (Fisher Scientific, Pittsburgh, PA), which were incubated overnight at 4 C. Nonimmune serum or immunoglobulin was used in place of the primary antibodies in the negative control slides.…”

“…13,14 The importance of these adjacent carbonyl groups was recently underlined by the discovery that another a-dicarbonyl butter flavoring, 2,3-pentanedione, caused airway epithelial injury and airway fibrosis in rats, which was similar to diacetyl-induced airway injury. 15,16 Protein damage, particularly at arginine residues, can be caused by chemical interactions between proteins and diacetyl or the structurally related 3-carbon a-dicarbonyl compound, methylglyoxal. 17,18 Although most studies of adicarbonyl compounds are conducted in vitro, a recent study demonstrated arginine adducts in hemoglobin and albumin of rats and mice after intratracheal instillation or oropharyngeal aspiration of [ 14 C]diacetyl in vivo.…”