Propylene oxide in blood and soluble nonprotein thiols in nasal mucosa and other tissues of male Fischer 344/N rats exposed to propylene oxide vapors - Relevance of glutathione depletion for propylene oxide-induced rat nasal tumors

High concentrations of propylene oxide (PO) induced inflammation in the respiratory nasal mucosa (RNM) of rodents. Concentrations ≥ 300 ppm caused nasal tumors. In order to investigate if glutathione depletion could be relevant for these effects, we determined in PO exposed male Fischer 344/N rats PO in blood and soluble non-protein SH-groups (NPSH) in RNM and other tissues. Rats were exposed once (6 h) to PO concentrations between 0 and 750 ppm, and repeatedly for up to 20 days (6 h, 5 days/week) to concentrations between 0 and 500 ppm. At the end of the exposures, PO in blood and NPSH in tissues were determined. PO in blood was dependent on concentration and duration of exposure. After the 1-day exposures, NPSH depletion was most distinctive (RNM > liver > lung). Compared to controls, NPSH levels were 43% at 50 ppm PO in RNM and 16% at ≥ 300 ppm in both RNM and liver. Lung NPSH fell linearly to 20% at 750 ppm. After repeated exposures over 3 and 20 days to 5,25, 50, 300, and 500 ppm, NPSH losses were less pronounced. At both time points, NPSH were 90%, 70%, 50%, 30%, and 30% of the control values in RNM. Liver NPSH decreased to 80% and 50% at 300 and 500 ppm, respectively. After 20 days, lung NPSH declined to 70% (300 ppm) and 50% (500 ppm). We conclude that continuous, severe perturbation of GSH in RNM following repeated high PO exposures may lead to inflammatory lesions and cell proliferation, critical steps on the path towards tumorigenicity.