Identification of Cytochrome P-450 Isozymes in Nonciliated Bronchiolar Epithelial (Clara) and Alveolar Type II Cells Isolated from Rabbit Lung

Abstract

Two forms of cytochrome P-450 (P-450I and P-450II) have been shown by several techniques to be present in both nonciliated bronchiolar cells (Clara) and alveolar type II cells isolated from rabbit lung. In contrast, the alveolar macrophage contains little or none of these cytochromes. Cross-reactivity between antibodies to cytochrome P-450I or P-450II and detergent-digested microsomes prepared from 80% type II or 70% Clara cell fractions was shown by Ouchterlony double immunodiffusion. The presence of both cytochromes was also demonstrated by histochemical immunofluorescence in smears of type II cells stained by a modified Papanicolaou procedure and Clara cells stained with nitroblue tetrazolium. However, this same fluorescent antibody technique used for localization of rabbit pulmonary cytochromes P-450I and P-450II in tissue sections showed most of the immunofluorescence in the Clara cells of the bronchiolar epithelium. SDS-polyacrylamide gel electrophoresis of microsomes from either the type II or Clara cell fractions produced bands which corresponded to cytochrome P-450I (52,000 daltons) and cytochrome P-450II (58,000 daltons).

Clara Cell Cultures from the Mouse and Their Reaction to Bronchiolar Toxins

“…The TD50 values, calculated from this data (Fig. 6) are plotted in Figure 7 and each compound given an arbitrary toxicity rating as very high (TD50 < 1 AM), high (1)(2)(3)(4)(5)(6)(7)(8)(9)(10) AM), moderately high (11-100 /M), weak (101-1000 AM), or minimal (> 1000 riM).…”

“…This aromatic hydrocarbon is converted to a reactive arene oxide by the P-450 system, and either the parent compound or the metabolite(s) selectively initiates bronchiolar Clara cell necrosis in mice (7). Two other compounds, 4-ipomeanol and 3-methylindole, which also produce extensive Clara cell necrosis in mice (8)(9)(10)(11), are very highly toxic (TD50 value < 0.1 MM) and highly toxic (TD50 = 5 MM), respectively, to Clara cell cultures (Figs. 6 and 7).…”

“…6 and 7). P-450 mediated oxidation of the furan ring of 4-ipomeanol yields reactive metabolites that bind to Clara cell proteins, thus, enhancing cell necrosis (8). Methylindole may not require activation to induce toxicity, but the compound is detoxified by P-450 enzymes and glutathione conjugation.…”

Isolation of Clara Cells from the Mouse Lung

“…One example is the furan ipomeanol, a reactive metabolite that binds preferentially to Clara cells and is considered responsible for the potent pulmonary cytotoxicity observed (5). Isolated Clara cells have been used to study the metabolism of ipomeanol (6).…”

Pulmonary Metabolism of Foreign Compounds: Its Role in Metabolic Activation

“…The pulmonary toxicity of 4-ipomeanol is apparently mediated by reactive metabolites generated in specific cells in the lung -that is, the mechanism shown in Figure 1. Recent work with isolated rabbit lung cells showed that isolated Clara cells activated [14C] ipomeanol to covalently bound species at a much higher rate than isolated alveolar Type II cells (63).…”