Toxicological Sciences 58, 173-181 (2000)
Copyright © 2000 by the Society of Toxicology
Respiratory Toxicology |
Inhalation Toxicity of 1,6-Hexamethylene Diisocyanate Homopolymer (HDI-IC) Aerosol: Results of Single Inhalation Exposure Studies
Institute of Toxicology, Bayer AG, Building 514, 42096 Wuppertal, Germany
The early acute pulmonary response of female Wistar rats exposed nose-only to a mixture of 1,6-hexamethylene diisocyanate homopolymer (HDI-IC) aerosol was examined. This study was designed to investigate the time course of the relationship between acute pulmonary irritation and ensuing disturbances of the air/blood barrier in rats exposed to concentrations of 3.9, 15.9, 54.3, or 118.1 mg HDI-IC/m3. The duration of exposure was 6 h, followed by serial sacrifices 0 h, 3 h, 1 day, 3 days, and 7 days postexposure. Concentrations were selected based on the results of a 4-h acute inhalation study in rats (LC50 = 462 mg/m3). Bronchoalveolar lavage (BAL) fluid was analyzed for markers indicative of injury of the bronchoalveolar region, including phospholipids as proxy of altered surfactant homeostasis. Glutathione (GSH) was determined in BAL fluid and lung tissue. BAL cells with increased intracellular phospholipids were observed on day 1 and especially day 3, with some residual increase on day 7. Increased intracellular phospholipids and activity of acid phosphatases appear to suggest that phagocytized phospholipids may transiently affect lysosomal function. Following exposure to 15.9 mg/m3, changes returned almost entirely to the level of the air-exposed control on day 7. Especially at higher exposure concentrations, lung weights and total number of cells in BAL were still statistically significantly elevated at this time point. Experimental evidence suggests that markers indicative of a dysfunction of the air/blood barrier, such as angiotensin-converting enzyme, total protein, and phospholipids engulfed by alveolar macrophages, were most sensitive to probe this type of changes. Although GSH in BALF was increased following exposure, there was an apparent depletion of tissue GSH immediately after cessation of exposure. In summary, this study suggests that respirable HDI-IC aerosol appears to cause a transient dysfunction of the air/blood barrier indicated by an increased extravasation of plasma constituents. Despite the remarkable extent of effects observed, most changes were reversible within a postexposure period as short as 7 days. First evidence of increased leakage of pulmonary epithelial barrier was observed at 3.9 mg/m3. With respect to changes of early markers of pulmonary epithelial barrier dysfunction, 
3 mg HDI-IC/m3 was considered to be the threshold concentration for acute pulmonary irritation.
Key Words: isocyanate aerosol inhalation; pulmonary edema; aerosol of HDI-homopolymer; HDI-isocyanurate; surfactant; polyurethane coating.