Differential inducibility of rat pulmonary CYP1A1 by cigarette smoke and wood smoke

Cytochromes P450: Role in Carcinogenesis and Relevance to Cancers

Abstracts:

Cancer is a leading factor of mortality globally. Cytochrome P450 (CYP) enzymes play a pivotal role in the biotransformation of both endogenous and exogenous compounds. Evidence from numerous epidemiological, animal, and clinical studies points to instrumental role of CYPs in cancer initiation, metastasis, and prevention. Substantial research has found that CYPs are involved in activating different carcinogenic chemicals in the environment, such as polycyclic aromatic hydrocarbons and tobacco-related nitrosamines. Electrophilic intermediates produced from these chemicals can covalently bind to DNA, inducing mutation and cellular transformation that collectively result in cancer development. While bioactivation of procarcinogens and promutagens by CYPs has long been established, the role of CYP-derived endobiotics in carcinogenesis has emerged in recent years. Eicosanoids derived from arachidonic acid via CYP oxidative pathways have been implicated in tumorigenesis, cancer progression and metastasis. The purpose of this review is to update on the current state of knowledge about the cancer molecular mechanism involving CYPs with focus on the biochemical and biotransformation mechanisms in the various CYP-mediated carcinogenesis, and the role of CYP-derived reactive metabolites, from both external and endogenous sources, on cancer growth and tumour formation.

Genotoxic bioactivation of constituents of a diesel exhaust particle extract by the human lung

The ability of the human lung to catalyze genotoxic bioactivation of constituents of diesel exhaust particle (DEP) extract (DEPE) and the identity of the lung enzymes involved in the bioactivation were investigated using human lung tissues obtained from surgical resections. Genotoxicity was determined by lung S9-catalyzed mutagenicity of DEPE constituents to Salmonella typhimurium TA98NR in the Ames test and by DEPE-induced pneumocyte DNA damage response as determined by γH2Ax expression in ex vivo tissues. S9 was prepared from lung explants treated ex vivo with either DEPE to induce pulmonary enzymes (DEPE-S9) or vehicle only (CON-S9). TA98NR served as the tester strain for the purpose of enhancing and minimizing the contribution of lung S9 and Salmonella, respectively, to DEPE bioactivation. DEPE-S9 was 2.2-fold more active than CON-S9 or rat liver S9 in DEPE bioactivation and the bioactivation was inhibited 58, 45, 22, and 16% by α-naphthoflavone, dicumarol, ketoconazole, and ticlopidine, respectively. Alveolar S9 was less active than bronchioalveolar S9 in DEPE bioactivation. DEPE and diesel exhaust particles (DEP) induced γ-pH2Ax expression in pulmonary cells. Pulmonary CYP1A1 and NQO1 were induced by DEPE treatment, with the constitutive and induced CYP1A1 distributed throughout all peripheral lung regions, whereas NQO1 was limited in distribution to bronchiolar epithelium. The results show that the human lung is highly active in catalyzing genotoxic bioactivation of diesel emission constituents and that CYP1A and NQO1 play major roles in the reaction. The findings underscore the usefulness of human lung tissues in studies of the pneumotoxicity potential of chemicals to humans.

Biomass smoke exposures: toxicology and animal study design

The International Biomass Smoke Health Effects (IBSHE) conference was convened in Missoula, MT, to define our current knowledge of smoke exposure and the potential health effects. In an effort to ascertain the relative health effects of an exposure to biomass smoke, numerous studies have utilized either animal or in vitro systems. A wide variety of systems that have been employed ranged from more mainstream animal models (i.e., rodents) and transformed cell lines to less common animal (piglets and dogs) and explant models. The Toxicology and Animal Study Design Workgroup at IBSHE was tasked with an analysis of the use of animal models in the assessment of the health effects of biomass smoke exposure. The present article contains a mini-review of models utilized historically, in addition to the adverse health effects assessed, and an overview of the discussion within the breakout session. The most common question that arose in discussions at the IBSHE conference was from local and federal health departments: What level of smoke is unhealthy? The present workgroup determined categories of exposure, common health concerns, and the availability of animal models to answer key health questions.

Tocopherol transfer protein deficiency modifies nuclear receptor transcriptional networks in lungs: Modulation by cigarette smoke in vivo

Dietary factors and environmental pollutants initiate signaling cascades that converge on AhR:Nrf2:NF-kappaB transcription factor (TF) networks and, in turn, affect the health of the organism through its effects on the expression of numerous genes. Reactive oxygen metabolites (ROMs) have been hypothesized to be common mediators in these pathways. alpha-Tocopherol (AT) is a potent, lipophilic, scavenger of ROMs in vitro and has been hypothesized to be a major chain-breaking anti-oxidant in lipoproteins and biological membranes in vivo. The lung offers a vital organ to test the various postulated actions of AT in vivo. Lung AT concentrations can be manipulated by several methods that include dietary and genetic techniques. In this study we have used mice with severe AT deficiency inflicted at birth by the deletion of AT transfer protein (ATTP) which is abundantly expressed in the liver and regulates systemic concentrations of AT. Mice and humans deficient in ATTP are AT deficient. Female ATTP-deficient (ATTP-KO) mice and their congenic ATTP normal (WT) mice fed a diet containing 35 IU AT/kg diet were used to test our hypothesis. The mice (n=5/group) were exposed to either air or cigarette smoke (CS, total suspended particles 60 mg/m(3), 6h/day), a source of ROM, for 3 or 10 days. Post-exposure lung tissue was dissected, RNA extracted from each lung and it was pooled group-wise and processed for GeneChip analysis (Affymetrix 430A 2.0). Differential analysis of the transcriptomes ( approximately 16,000 mRNAs) identified CS sensitive genes that were modulated by lung AT-concentration. CS activated AhR driven genes such as cyp1b1 whose induction was augmented in CS-exposed, AT-deficient lungs. However, CS-induced expression of some of the Nrf2 driven genes was not potentiated in the AT-deficient lungs. Largest clusters of CS-AT sensitive genes were lymphocyte and leukocyte specific genes. These gene-clusters included those encoding cytokines and immunoglobulins, which were repressed by CS and were modulated by lung AT concentrations. Our genome-wide analysis suggests reciprocal regulation of xenobiotic and immune response genes by CS and a modulatory role of lung AT concentration on the expression of these clusters of genes. These data suggest that in vivo network of AT, AT-metabolites and ATTP affects the transcription of genes driven by AhR, Nrf2 and NF-kappaB, transcription factor networks that transduce cellular metabolic signals and orchestrate adaptive responses of lungs to inhaled environmental pollutants.

Cytotoxicity and gene expression profiles in cell cultures exposed to whole smoke from three types of cigarettes

The purpose of this study was to evaluate and compare the cytotoxicity and gene expression profiles in cell cultures exposed to whole smoke generated from a full flavor cigarette (Test 1), a low tar cigarette (Test 2), and an ultra-low tar cigarette (Test 3). In addition, a reference cigarette 2R4F was evaluated for cytotoxicity. Neutral red (NR) cytotoxicity assay was performed to determine relative cell death at each exposure concentration (n = 6). LC(50) was generated using wet total particular matter (WTPM), cigarette number, or nicotine concentrations. The overall order of cytotoxicity was Test 1 >> 2R4F approximately Test 2 > Test 3. Cell culture samples were collected for RNA extraction at WTPM concentrations of each cigarette that gave similar nicotine concentrations. Affymetrix mouse whole genome 430 2.0 array was used to characterize the gene expression profiles for each cigarette. A total of 598 genes in Test 1, 176 genes in Test 2, and 234 genes in Test 3 samples were differentially expressed compared to the concurrent sham controls. The major biological processes associated with the changed genes in Test 1 samples were down-regulated DNA replication and cell proliferation; the same biological processes were much less affected in Test 2 and Test 3 samples. The common findings in all three cigarettes types were increased glutathione biosynthesis/consumption and inflammatory response, which are known biological effects caused by smoke exposure. The most significantly up-regulated genes were CYP1A1, GSTs, Hmox1, and Procr in smoke-exposed samples, which are either related to well-studied mechanisms of smoke exposure-related diseases or potential new biomarkers for assessing and monitoring biological effects of cigarette smoke exposure in vivo and in smokers. In summary, both the NR cytotoxicity assay and gene expression profiling were able to differentiate the three types of test cigarettes, and the results demonstrated reduced biological effects for the Test 2 and Test 3 cigarettes compared to the Test 1 cigarette in BALB/c-3T3 Cells.