Methylene chloride: an inhalation study to investigate toxicity in the mouse lung using morphological, biochemical and Clara cell culture techniques.
Single exposures of mice to methylene chloride (MC) cause vacuolation and necrosis of the bronchiolar Clara cells which subsequently recover normal morphology on continued exposure. Both cytochrome P-450 (CYP)- and glutathione S-transferase (GST)-dependent metabolism of MC are known to occur. The current studies have investigated the metabolism of MC in mouse lung using inhibitors of both GST and CYP-dependent routes of metabolism, the consequences of metabolic inhibition on the Clara cell vacuolation, and any changes in cell proliferation, assessed in vitro, in Clara cells cultured from exposed individuals. Vacuolated bronchiolar cells were seen in mice exposed to 2000 and 4000 ppm MC but were not seen at lower concentrations, while addition of the CYP inhibitor, piperonyl butoxide, significantly reduced the bronchiolar cell vacuolation seen following exposure to 2000 ppm MC. Treatment of mice with the glutathione depletor, buthionine sulphoximine, had no effect on the number of vacuolated bronchiolar cells following MC. Exposure of mice to 1000 ppm MC and above for 6 h caused a burst of DNA synthesis in bronchiolar Clara cells cultured in vitro from the lungs of exposed animals. The results suggest that the Clara cell vacuolation following MC exposure is mediated via CYP metabolism, that depression of the CYP metabolic pathway occurs following exposure, and that Clara cell vacuolation may have a priming role in stimulating cell proliferation in the unaffected cell population.
Foster
J R
JR
Pathology Section, Zeneca Central Toxicology Laboratory, Alderley Park, Macclesfield, Cheshire, UK.
Green
T
T
Smith
L L
LL
Tittensor
S
S
Wyatt
I
I
D000280:Administration, Inhalation; D000818:Animals; D000963:Antimetabolites / Q000494:pharmacology; D001980:Bronchi / Q000187:drug effects* / Q000201:enzymology / Q000473:pathology; D019328:Buthionine Sulfoximine; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D003600:Cytosol / Q000187:drug effects / Q000201:enzymology; D004848:Epithelium / Q000187:drug effects / Q000201:enzymology / Q000473:pathology; D005978:Glutathione / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism*; D008297:Male; D008717:Methionine Sulfoximine / Q000031:analogs & derivatives / Q000494:pharmacology; D008752:Methylene Chloride / Q000008:administration & dosage / Q000378:metabolism / Q000633:toxicity*; D051379:Mice; D008861:Microsomes / Q000187:drug effects / Q000201:enzymology; D010882:Piperonyl Butoxide / Q000494:pharmacology; D014617:Vacuoles / Q000187:drug effects
D000963:Antimetabolites; D065607:Cytochrome P-450 Enzyme Inhibitors; D008717:Methionine Sulfoximine; D019328:Buthionine Sulfoximine; D008752:Methylene Chloride; D003577:Cytochrome P-450 Enzyme System; D005982:Glutathione Transferase; D005978:Glutathione; D010882:Piperonyl Butoxide