Abstract
The cytochrome P450 (CYP) enzyme system in human lung is an essential component
in the pulmonary carcinogenicity of several inhaled xenobiotic compounds. The
aim of this study was to elucidate the expression and regulation of
xenobiotic-metabolizing CYP enzymes in human lung.
To evaluate which of the two is a better surrogate cell model for lung tissue,
the expression patterns of CYP enzymes in alveolar macrophages and peripheral
blood lymphocytes were clarified by reverse transcriptase-polymerase chain
reaction (RT-PCR) and compared to the expression in lung tissue. The pattern of
CYP expression in alveolar macrophages was found to closely resemble the
expression pattern in human lung tissue, while the pattern in lymphocytes was
markedly different. The expression of CYP2B6, CYP2C, CYP3A5, and CYP4B1 mRNAs in
alveolar macrophages was demonstrated for the first time.
To facilitate mechanistic studies on human pulmonary CYP induction, the A549
lung adenocarcinoma cell line was characterized by RT-PCR, and the CYP
expression
pattern was found to compare reasonably well to human lung epithelial cells. The
induction of CYP1A1 by 2,3,7,8-tetrachlorodibenzo-p-dioxin
(TCDD) behaved as predicted, and CYP1B1 and CYP3A5 were also inducible by TCDD
and dexamethasone, respectively. TCDD elevated the level of CYP1A1 mRNA
(56-fold), while the induction of CYP1B1 mRNA was more modest (2.5-fold). The
tyrosine kinase inhibitor genistein and the protein kinase C inhibitor
staurosporine blocked CYP1A1 induction by TCDD, but did not affect CYP1B1
induction. The serine/threonine protein phosphatase inhibitor calyculin A and
okadaic acid enhanced CYP1B1 induction slightly, but did not alter CYP1A1
induction.
The expression of CYP3A forms in human pulmonary tissues was studied with RT-PCR
and
immunohistochemistry, and both methods established CYP3A5 as the main CYP3A
form. CYP3A4 was expressed in only about 20% of the cases. In A549 cells, CYP3A5
was induced about 4-fold by the glucocorticoids budesonide, beclomethasone
dipropionate, and dexamethasone. Maximal induction was achieved by
concentrations as low as ~100 nM, suggesting that CYP3A5 could be induced
in vivo in patients using inhaled glucocorticoids. However,
there were no differences in CYP3A5 expression in alveolar macrophages in
current glucocorticoid users, ex-users, and non-users. Cigarette smoking had a
marked decreasing effect on CYP3A5 levels in alveolar macrophages. The presence
and possible induction of CYP3A5 by glucocorticoids in human lung could have
consequences for the maintenance of physiological steroid hormone balance in
lung and the individual susceptibility to lung cancer of patients using
glucocorticoids.
| Identifer | oai:union.ndltd.org:oulo.fi/oai:oulu.fi:isbn951-42-5864-9 |
| Date | 21 December 2000 |
| Creators | Hukkanen, J. (Janne) |
| Publisher | University of Oulu |
| Source Sets | University of Oulu |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/doctoralThesis, info:eu-repo/semantics/publishedVersion |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess, © University of Oulu, 2000 |
| Relation | info:eu-repo/semantics/altIdentifier/pissn/0355-3221, info:eu-repo/semantics/altIdentifier/eissn/1796-2234 |
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