Effects of short-term exposure to diesel exhaust on lung cell proliferation and phospholipid metabolism.

The effect of exposure to diesel exhaust (DE) on DNA synthesis in lung tissue and type II cells was investigated. Parallel experiments with carbon black (CB) and NO2 were designed to mimic exposure to individual components of DE. Continuous exposure to 6 mg/m3 DE particulate or 7 ppm NO2 elicited significant increases in DNA synthesis and type II cell labeling index. The maximal response occurred after 2 days of exposure, and all measures returned to control levels after one week. Exposure to 6 mg/m3 CB did not cause similar changes, suggesting that the initial wave of cell proliferation elicited by DE exposure may be related to the presence of NO2 in the exhaust. In investigations of the effect of DE exposure on lung lipid metabolism, the incorporation in vivo of 14C-palmitic acid into lung tissue phosphatidylcholine increased three-fold after the first exposure day, when tissue palmitic acid content was significantly decreased and lavaged phospholipid (PL) increased. In vitro measures of PL biosynthesis showed no changes. These results suggest that exposure to a high concentration of DE results in immediate, transient changes in fatty acid and PL metabolism, but that these effects are not necessarily related to a stimulation of PL biosynthesis.