Date of Graduation
School of Medicine
Microbiology, Immunology, and Cell Biology
Cytochrome P450s (CYPs) form a superfamily of enzymes crucial for the oxidative metabolism of a wide variety of endogenous and exogenous (xenobiotic) compounds. Cytochrome P4501A1 (CYP1A1) is a member of the CYP1A subfamily that is involved in pulmonary carcinogenesis. CYP1A1 metabolizes polycyclic aromatic hydrocarbons (PAH), such as benzo[a]pyrene in cigarette smoke into DNA-binding reactive metabolites resulting in gene mutation and carcinogenesis. Silicosis and coal workers' pneumoconiosis (CWP) are two pulmonary diseases associated with occupational exposure to silica and coal dust (CD), respectively. Most coal miners are smokers or ex-smokers and epidemiologic studies of coal dust carcinogenesis are confounded by the presence of both cigarette smoke and respirable particles. To clarify the nature of this interaction, we investigated the hypotheses that (1) CYP1A1 induction and activity (EROD) are inhibited by CD and silica. (2) CYP1A1 inhibition by particle exposure is associated with changes in the cellular populations in the exposed lung. Western blot analysis, immunofluorescent-labeling, bronchoalveolar lavage fluid analysis, biochemical assays, and histopathology were used to evaluate our hypotheses. Because of a current debate about using the rat to extrapolate particle-induced pulmonary alterations to humans, the rabbit silicosis and sheep CWP model, were also used. The results indicate that (1) CYP1A1 induction and its metabolic activity (EROD) were suppressed by CD exposure in rats and sheep; and by silica in rabbits; (2) CYP1A1 expression was reduced in alveolar epithelial cells by CD or silica exposure; (3) silica and CD increased the size (hypertrophy) and number (hyperplasia) of alveolar type II cell with reduction of CYP1A1 expression in these cells; (4) CD particles induced dose-dependent pulmonary inflammation, manifested by recruitment of alveolar macrophages and polymorphonuclear leucocytes; (5) CD particles induced the preapoptotic Bax protein expression in alveolar epithelial cells and triggered apoptosis; (6) inhibition of apoptosis and Bax by the caspase inhibitor, Q-VD-OPH, did not alter CYP1A1 induction; (7) suppression of CYP1A1 induction was associated with pulmonary inflammation. These findings are consistent with the hypothesis that CYP1A1 induction and its metabolic activity are inhibited by particle exposure and associated with pulmonary inflammation.
Ghanem, Mohamed Mohamedy, "Genetic, metabolic, and histopathological studies of particle -associated respiratory alterations" (2003). Graduate Theses, Dissertations, and Problem Reports. 1868.