Experimental studies on acute health effects of acrolein and other aldehydes

Aldehydes are reactive and ubiquitous in indoor as well as outdoors and can give rise to significant health problems in humans, e.g. irritation of the eyes and toxic effects on the upper respiratory tract. This thesis focuses on the irritating and inflammatory properties of three commonly occurring aldehydes; acrolein, crotonaldehyde and hexanal. Male and female volunteers were exposed in a controlled environment at six occasions for 2 hours to clean air only, 15 ppm ethyl acetate (EA) only and 0.05 ppm and 0.1 ppm acrolein with and without EA (Paper I). No significant exposure-related adverse effects (pulmonary function, nasal swelling, and inflammatory markers, coagulation markers, cell differentials, breathing frequency, symptom ratings except eye irritation) were found. The ratings of eye irritation were slightly but significantly increased during exposure to 0.1 ppm acrolein alone as well as combined with EA. Blinking frequency was only increased at 0.1 ppm acrolein alone. Employing a novel olfactometer developed in-house, we determined odor (OT) and lateralization (LT) thresholds in naïve subjects (Paper II). The median OTs was similar to or lower than previously reported: 17 ppb (acrolein), 0.8 ppb (crotonaldehyde) and 97 ppb (hexanal). We compared pulmonary pro-inflammatory and oxidative stress responses in seven inbred strains of mice after 11 weeks of whole body exposure to 1 ppm acrolein with filtered air as the control (Paper III). The responses varied widely between strains, and were in general agreement with that expected from previously reported survival times in the same mouse strains after acute exposure to 10 ppm acrolein. The inflammatory and toxic effects of acrolein (0-0.5 ppm), crotonaldehyde (0-5 ppm) and hexanal (0-50 ppm) were further studied in a newly developed exposure system allowing for airborne exposure of differentiated human pulmonary bronchial epithelial cells (PBEC) co- cultured with fibroblasts at an air- liquid interface (Paper IV). The release of inflammatory markers and the corresponding mRNA expressions increased. These effects were not observed with exposure of PBECs under submerged conditions. The findings herein provide new insights in the acute effects of environmentally realistic exposure-concentrations of acrolein, crotonaldehyde and hexanal. The results may prove helpful in future risk assessment and risk management efforts, such as setting health-based occupational exposure limits

Analysis of Acrolein Exposure Induced Pulmonary Response in Seven Inbred Mouse Strains and Human Primary Bronchial Epithelial Cells Cultured at Air-Liquid Interface

Background. Acrolein is a major component of environmental pollutants, cigarette smoke, and is also formed by heating cooking oil. We evaluated the interstrain variability of response to subchronic inhalation exposure to acrolein among inbred mouse strains for inflammation, oxidative stress, and tissue injury responses. Furthermore, we studied the response to acrolein vapor in the lung mucosa model using human primary bronchial epithelial cells (PBEC) cultured at an air-liquid interface (ALI) to evaluate the findings of mouse studies. Methods. Female 129S1/SvlmJ, A/J, BALB/cByJ, C3H/HeJ, C57BL/6J, DBA/2J, and FVB/NJ mice were exposed to 1 part per million (ppm) acrolein or filtered air for 11 weeks. Total cell counts and protein concentrations were measured in bronchoalveolar lavage (BAL) fluid to assess airway inflammation and membrane integrity. PBEC-ALI models were exposed to acrolein vapor (0.1 and 0.2 ppm) for 30 minutes. Gene expression of proinflammatory, oxidative stress, and tissue injury-repair markers was assessed (cut off: ≥2 folds; p<0.05) in the lung models. Results. Total BAL cell numbers and protein concentrations remained unchanged following acrolein exposure in all mouse strains. BALB/cByJ, C57BL/6J, and 129S1/SvlmJ strains were the most affected with an increased expression of proinflammatory, oxidative stress, and/or tissue injury markers. DBA/2J, C3H/HeJ, A/J, and FVB/NJ were affected to a lesser extent. Both matrix metalloproteinase 9 (Mmp9) and tissue inhibitor of metalloproteinase 1 (Timp1) were upregulated in the strains DBA/2J, C3H/HeJ, and FVB/NJ indicating altered protease/antiprotease balance. Upregulation of lung interleukin- (IL-) 17b transcript in the susceptible strains led us to investigate the IL-17 pathway genes in the PBEC-ALI model. Acrolein exposure resulted in an increased expression of IL-17A, C, and D; IL-1B; IL-22; and RAR-related orphan receptor A in the PBEC-ALI model. Conclusion. The interstrain differences in response to subchronic acrolein exposure in mouse suggest a genetic predisposition. Altered expression of IL-17 pathway genes following acrolein exposure in the PBEC-ALI models indicates that it has a central role in chemical irritant toxicity. The findings also indicate that genetically determined differences in IL-17 signaling pathway genes in the different mouse strains may explain their susceptibility to different chemical irritants