In adult mammals, the nonciliated bronchiolar epithelial (Clara) cell is the principal site for cytotoxicity and metabolism of pulmonary environmental toxicants which require activation via the cytochrome P-450 monooxygenase system, whether these compounds enter the organism via inhalation or ingestion. A number of recent studies suggest that the lungs of fetuses whose mothers have been subjected to environmental toxins also may be at risk as a result of these exposures. The process by which fetal airway cells differentiate into functional Clara cells is both a pre- and postnatal phenomenon. Because there is virtually no information on which factors regulate differentiation of the Clara cell, nor on how bioactivated pulmonary cytotoxins may modulate this process, we have proposed to evaluate the effects on Clara cell differentiation of a series of compounds which inhibit or induce the cytochrome P-450 system. The overall hypothesis we will be testing is that compounds which alter the pulmonary cytochrome P- 450 system in the adult function as stimulators of Clara cell differentiation and maturation in the fetal and neonatal animal. We we evaluate the effects of hormones which have been shown to regulate other aspects of lung development (glucocorticoids and progesterone), inducers of hepatic P-450s in adults (sodium phenobarbital, Arochlor, beta-naphthoflavone), a bioactivated Clara cell-specific toxicant (4-ipomeanol) and inhibitors of cytochrome P-450 activity (SKF 525-A and aminobenzotriazole). The attainment of adult organelle composition by differentiated Clara cells will be assessed by ultrastructural morphometry. In addition, all three major functions of the Clara cell will be assessed: role as progenitor of bronchiolar epithelial cells, site of cytochrome P- 450-mediated metabolism, and source of bronchiolar mucosecretory proteins. 3H-Thymidine incorporation and cell turnover will be estimated by autoradiography, and bronchiolar epithelial population densities will be assessed quantitatively. Immunocytochemical, immunochemical, spectrophotometric and enzymatic activity assays will be used to measure the cytochrome P-450 system. Immunocytochemical and immunochemical methods will be used to evaluate alterations in secretory function. This proposal offers a unique opportunity to assess the degree of hazard faced by neonates and fetuses of mothers exposed to environmental toxins, to define the impact of environmental toxins on a lung cell type which is pivotal for a number of normal lung functions and to identify compounds which may serve as regulators of Clara cell differentiation.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL043032-02
Application #
3361470
Study Section
Human Embryology and Development Subcommittee 1 (HED)
Project Start
1989-07-01
Project End
1992-06-30
Budget Start
1990-07-01
Budget End
1991-06-30
Support Year
2
Fiscal Year
1990
Total Cost
Indirect Cost
Name
University of California Davis
Department
Type
Schools of Veterinary Medicine
DUNS #
094878337
City
Davis
State
CA
Country
United States
Zip Code
95618
Ji, C M; Cardoso, W V; Gebremichael, A et al. (1995) Pulmonary cytochrome P-450 monooxygenase system and Clara cell differentiation in rats. Am J Physiol 269:L394-402
Plopper, C G; Weir, A J; Nishio, S J et al. (1994) Elevated susceptibility to 4-ipomeanol cytotoxicity in immature Clara cells of neonatal rabbits. J Pharmacol Exp Ther 269:867-80
Cardoso, W V; Stewart, L G; Pinkerton, K E et al. (1993) Secretory product expression during Clara cell differentiation in the rabbit and rat. Am J Physiol 264:L543-52
Plopper, C G; Weir, A J; Morin, D et al. (1993) Postnatal changes in the expression and distribution of pulmonary cytochrome P450 monooxygenases during Clara cell differentiation in rabbits. Mol Pharmacol 44:51-61
Plopper, C G; Nishio, S J; Alley, J L et al. (1992) The role of the nonciliated bronchiolar epithelial (Clara) cell as the progenitor cell during bronchiolar epithelial differentiation in the perinatal rabbit lung. Am J Respir Cell Mol Biol 7:606-13
Plopper, C; St George, J; Cardoso, W et al. (1992) Development of airway epithelium. Patterns of expression for markers of differentiation. Chest 101:2S-5S