Extracellular biotransformation potential in mouse airways

The aims of this study were to determine if freshly isolated bronchiolar Clara cells retained biotransformation potential and whether components of phase 1 and/or phase 2 metabolism were present in the extracellular lining fluid of the lung airways. Approximately 550 μl of lavage fluid was obtained from the mouse lung, which had been totally perfused of blood in order to facilitate the isolation of Clara cells from the same animal. Samples of acellular lavage fluid and aliquots of purified Clara cells were frozen at — 20°C prior to analysis. Minimum numbers of cells and lavage fluid volumes, pooled from 2 CD-1 mice, were assayed for ethoxycoumarin- O-deethylase, NADPH-dependent cytochrome c reductase, glutathione- S-transferase(s) and non-protein sulphydryls (mostly reduced glutathione). Isolated Clara cells retained a high activity/level of all these parameters confirming their functional status for subsequent studies of xenobiotic metabolism in vitro. Acellular lavage fluid, from all the healthy animals, also contained mono-oxygenase, reductase and transferase activities and high non-protein sulphydryl levels suggesting that phase 1 and 2 reactions with xenobiotics could take place in the extracellular environment of the lung. Clara cells are known to undergo apocrine secretion and this removal of the apical cap containing secretory granules and smooth endoplasmic reticulum could account for the airway biotransformation potential that was observed.