K-ras mutations in lung tumors from p53 mutant mice exposed to cigarette smoke

Indoor PM2.5, tobacco smoking and chronic lung diseases: A narrative review

The lung is one of the most important organs exposed to environmental agents. People spend approximately 90% of their time indoors, and risks to health may thus be greater from exposure to poor air quality indoors than outdoors. Multiple indoor pollutants have been linked to chronic respiratory diseases. Environmental tobacco smoke (ETS) is known as an important source of multiple pollutants, especially in indoor environments. Indoor PM_2.5 (particulate matter with aerodynamic diameter < 2.5 μm) was reported to be the most reliable marker of the presence of tobacco smoke. Recent studies have demonstrated that PM_2.5 is closely correlated with chronic lung diseases. In this paper, we reviewed the relationship of tobacco smoking and indoor PM_2.5 and the mechanism that underpin the link of tobacco smoke, indoor PM_2.5 and chronic lung diseases.

An Updated Review of Inhalation Studies with Cigarette Smoke in Laboratory Animals

Until recently, the published literature on inhalation studies with laboratory animals and cigarette smoke consisted entirely of negative findings, as far as neoplastic disease is concerned. This paper brings readers up to date, with analyses of recent studies that do indeed appear to report success after so many years of failure. The paper consists of a brief analysis of the literature up until a couple of years ago, giving brief, representative examples of inhalation studies with the five main species of laboratory animals that have been used: rat, mouse, hamster, dog, and nonhuman primate. A brief examination of the various technologies used to expose laboratory animals is given, along with an analysis of the histopathology and related toxicology data (specifically, biomarkers of exposure) that have been reported. The paper concludes by briefly mentioning the most recent studies, where positive results have been reported.

Molecular damage and lung tumors in cigarette smoke-exposed mice

Cigarette smoke (CS) induces lung cancer through a multistep process that is now being depicted by molecular analyses. During the early phase (weeks), DNA damage occurs in nuclear and mitochondrial DNA, triggering adaptive responses activated by transient microRNA downregulation in the expression of defensive genes and proteins. During the intermediate phase (months), damaged cells are removed by apoptosis and the resulting cell loss is counteracted by a recruitment of stem cells that are highly sensitive to genotoxic damage. In parallel, microRNA downregulation becomes irreversible because of an accumulation of molecular damage in DICER. During the late phase (years), apoptosis efficacy is decreased by fragile histidine triad loss, while irreversible microRNA downregulation triggers the expression of mutated oncogenes, resulting in adenoma appearance. Furthermore, deletions occur in microRNA-encoding genes, causing carcinoma formation and uncontrolled growth. All reported pathogenic steps are required to obtain a fully developed lung cancer. This complex pathogenesis develops over a long period of time; therefore, it is difficult to induce cancer in short-living animals exposed to CS, whereas in humans there is a long latency from the start of smoke exposure to the onset of cancer.

Impact of AhR, CYP1A1 and GSTM1 genetic polymorphisms on TP53 R273G mutations in individuals exposed to polycyclic aromatic hydrocarbons

This study was to undertaken to investigate the impacts of AhR, CYP1A1, GSTM1 genetic polymorphisms on the R273G mutation in exon 8 of the tumor suppressor p53 gene (TP53) among polycyclic aromatic hydrocarbons (PAHs) exposed to coke-oven workers. One hundred thirteen workers exposed to PAH and 82 control workers were recruited. We genotyped for polymorphisms in the AhR, CYP1A1, GSTM1, and TP53 R273G mutation in blood by PCR methods, and determined the levels of 1-hydroxypyrene as PAH exposure marker in urine using the high pressure liquid chromatography assay. We found that the distribution of alcohol users and the urinary excretion of 1-OHP in the exposed workers were significantly higher than that of the control workers (p=0.004, p<0.001, respectively). Significant differences were observed in the p53 genotype distributions of smoking subjects (p=0.01, 95%CI: 1.23-6.01) and PAH exposure (p=0.008, 95%CI: 1.24-4.48), respectively. Further, significant differences were observed in the p53 exon 8 mutations for the genetic polymorphisms of Lys/Arg for AhR (p=0.02, 95%CI: 0.70-15.86), Val/Val for CYP1A1 (p=0.04, 95%CI: 0.98-19.09) and null for GSTM1 (p=0.02, 95%CI: 1.19-6.26), respectively. Our findings indicated that polymorphisms of PAH metabolic genes, such as AhR, CYP1A1, GSTM1 polymorphisms may interact with p53 genetic variants and may contribute to PAH related cancers.

Smoke-induced microRNA and related proteome alterations. Modulation by chemopreventive agents

Dysregulation of microRNAs (miRNAs) has important consequences on gene and protein expression since a single miRNA targets a number of genes simultaneously. This article provides a review of published data and ongoing studies regarding the effects of cigarette smoke (CS), either mainstream (MCS) or environmental (ECS), on the expression of miRNAs and related proteins. The results generated in mice, rats, and humans provided evidence that exposure to CS results in an intense dysregulation of miRNA expression in the respiratory tract, which is mainly oriented in the sense of downregulation. In parallel, there was an upregulation of proteins targeted by the downregulated miRNAs. These trends reflect an attempt to defend the respiratory tract by means of antioxidant mechanisms, detoxification of carcinogens, DNA repair, anti-inflammatory pathways, apoptosis, etc. However, a long-lasting exposure to CS causes irreversible miRNA alterations that activate carcinogenic mechanisms, such as modulation of oncogenes and oncosuppressor genes, cell proliferation, recruitment of undifferentiated stem cells, inflammation, inhibition of intercellular communications, angiogenesis, invasion, and metastasis. The miRNA alterations induced by CS in the lung of mice and rats are similar to those observed in the human respiratory tract. Since a number of miRNAs that are modulated by CS and/or chemopreventive agents are subjected to single nucleotide polymorphisms in humans, they can be evaluated according to toxicogenomic/pharmacogenomics approaches. A variety of cancer chemopreventive agents tested in our laboratory modulated both baseline and CS-related miRNA and proteome alterations, thus contributing to evaluate both safety and efficacy of dietary and pharmacological agents.

Interplay between histopathological alterations, cigarette smoke and chemopreventive agents in defining microRNA profiles in mouse lung

We have investigated alterations of microRNA expression profiles in the apparently healthy lung of mice and rats as an early response to exposure to cigarette smoke, either mainstream (MCS) or environmental, and/or to treatment with chemopreventive agents. Further on, we evaluated microRNA alterations at a later stage, when lung tumors were detectable in MCS-exposed mice. Lung samples were available from previous studies, in which strain H mice had been exposed to MCS for 4 months, starting immediately after birth, and then kept in filtered air for an additional 3 months. Some samples were from MCS-exposed mice treated either with N-acetyl-l-cysteine during pregnancy or with phenethyl isothiocyanate after weaning. The analysis of 576 mouse microRNAs showed that MCS strongly dysregulated microRNA expression and that both chemopreventive agents efficiently attenuated this trend, especially in noncancer tissue. MicroRNA expression was affected by histopathology, with specific signatures related to occurrence of pneumonia, adenoma, or bronchoalveolar carcinoma. Within pairs of samples from individual mice, microRNA analysis discriminated adenomatous tissue and especially carcinomatous tissue from the surrounding normal appearing tissue. A series of microRNA alterations characterized the sequential stages of pulmonary carcinogenesis. The involved functions included oncogene activation, inhibition of oncosuppressor genes, recruitment of undifferentiated stem cells, inflammation, inhibition of gap-junctional intercellular communications, angiogenesis, invasiveness, and metastatization. Thus, microRNA expression profiles in lung are dysregulated by MCS along all steps of the carcinogenesis process and depend on the interplay among exposure to noxious agents, treatment with dietary and pharmacological agents, and occurrence of pulmonary diseases.

Cigarette-Smoke-Induced Dysregulation of MicroRNA Expression and Its Role in Lung Carcinogenesis

Dysregulation of microRNAs (miRNAs), particularly their downregulation, has been widely shown to be associated with the development of lung cancer. Downregulation of miRNAs leads to the overactivation of their oncogene targets, while upregulation of some miRNAs leads to inhibition of important tumor suppressors. Research has implicated cigarette smoke in miRNA dysregulation, leading to carcinogenesis. Cigarette smoke may lead to genetic or epigenetic damage to miRNAs, many of which map to fragile sites and some of which contain single nucleotide polymorphisms. Cigarette smoke may also cause dysregulation by affecting regulatory mechanisms controlling miRNA expression. Researchers have shown a correlation between smoke-exposure-induced dysregulation of miRNAs and age. Furthermore, dysregulation seems to be associated with intensity and duration of smoke exposure and duration of cessation. Longer exposure at a threshold level is needed for irreversibility of changes in expression. Better understanding of miRNA dysregulation may allow for improved biomonitoring and treatment regimens for lung cancer.

Dose-responsiveness and persistence of microRNA expression alterations induced by cigarette smoke in mouse lung

Our previous studies demonstrated that exposure to cigarette smoke (CS), either mainstream or environmental, results in a remarkable downregulation of microRNA expression in the lung of both mice and rats. The goals of the present study were to evaluate the dose responsiveness to CS and the persistence of microRNA alterations after smoking cessation. ICR (CD-1) neonatal mice were exposed whole-body to mainstream CS, at the doses of 119, 292, 438, and 631mg/m(3) of total particulate matter. Exposure started within 12h after birth and continued daily for 4 weeks. The levels of bulky DNA adducts and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) were measured by (32)P postlabeling procedures, and the expression of 697 mouse microRNAs was analyzed by microarray. The highest CS dose was lethal. Exposure to CS caused a dose-dependent increase of DNA alterations. DNA adducts and, even more sharply, 8-oxodGuo were reverted 1 and 4 weeks after smoking cessation. Exposure to CS resulted in an evident dysregulation of microRNA expression profiles, mainly in the sense of downregulation. The two lowest doses were not particularly effective, while the highest nonlethal dose produced extensive microRNA alterations. The expression of most downregulated microRNAs, including among others 7 members of the let-7 family, was restored one week after smoking cessation. However, the recovery was incomplete for a limited array of microRNAs, including mir-34b, mir-345, mir-421, mir-450b, mir-466, and mir-469. Thus, it appears that microRNAs mainly behave as biomarkers of effect and that exposure to high-dose, lasting for an adequate period of time, is needed to trigger the CS-related carcinogenesis process in the experimental animal model used.

A further review of inhalation studies with cigarette smoke and lung cancer in experimental animals, including transgenic mice

CONTEXT

The lack of an effective animal model for pulmonary carcinogenesis in smokers is a continuing problem for researchers trying to design Potentially Reduced Risk Products for those smokers who are either unwilling or unable to quit smoking. The major failing of inhalation assays with cigarette smoke in laboratory animals is that these assays produce only small percentages of animals with pulmonary tumors (e.g. adenomas, with the occasional adenocarcinoma), as opposed to the highly invasive carcinomas (e.g. small cell and squamous cell) seen in smokers.

OBJECTIVE

To update previous reviews on animal models, and to add different types of transgenic (Tg) mice to the review.

METHODS

Reviews were made of articles retrieved from PubMed and elsewhere.

RESULTS

The addition of Tg mice to the arsenal of tests used for the evaluation of the carcinogenic potential of cigarettes did not result in any better understanding of the inability of such testing to reflect the epidemiological evidence for lung cancer in smokers.

CONCLUSION

As in previous reviews on the subject, the best assay providing support for the epidemiology data is still the 5-month whole-body exposure of male A/J mice to a combination of mainstream/sidestream smoke, followed by a 4-month recovery.

Chemoprevention of cigarette smoke-induced alterations of MicroRNA expression in rat lungs

We previously showed that exposure to environmental cigarette smoke (ECS) for 28 days causes extensive downregulation of microRNA expression in the lungs of rats, resulting in the overexpression of multiple genes and proteins. In the present study, we evaluated by microarray the expression of 484 microRNAs in the lungs of either ECS-free or ECS-exposed rats treated with the orally administered chemopreventive agents N-acetylcysteine, oltipraz, indole-3-carbinol, 5,6-benzoflavone, and phenethyl isothiocyanate (as single agents or in combinations). This is the first study of microRNA modulation by chemopreventive agents in nonmalignant tissues. Scatterplot, hierarchical cluster, and principal component analyses of microarray and quantitative PCR data showed that none of the above chemopreventive regimens appreciably affected the baseline microRNA expression, indicating potential safety. On the other hand, all of them attenuated ECS-induced alterations but to a variable extent and with different patterns, indicating potential preventive efficacy. The main ECS-altered functions that were modulated by chemopreventive agents included cell proliferation, apoptosis, differentiation, Ras activation, P53 functions, NF-kappaB pathway, transforming growth factor-related stress response, and angiogenesis. Some microRNAs known to be polymorphic in humans were downregulated by ECS and were protected by chemopreventive agents. This study provides proof-of-concept and validation of technology that we are further refining to screen and prioritize potential agents for continued development and to help elucidate their biological effects and mechanisms. Therefore, microRNA analysis may provide a new tool for predicting at early carcinogenesis stages both the potential safety and efficacy of cancer chemopreventive agents.

Relationships of microRNA expression in mouse lung with age and exposure to cigarette smoke and light

MicroRNAs provide a formidable tool not only in cancer research but also to investigate physiological mechanisms and to assess the effect of environmental exposures in healthy tissues. Collectively, cigarette smoke and sunlight have been estimated to account for 40% of all human cancers, and not only smoke but also, surprisingly, UV light induced genomic and postgenomic alterations in mouse lung. Here we evaluated by microarray the expression of 484 microRNAs in the lungs of CD-1 mice, including newborns, postweanling males and females, and their dams, either untreated or exposed to environmental cigarette smoke and/or UV-containing light. The results obtained highlighted age-related variations in microRNA profiles, especially during the weanling period, due to perinatal stress and postnatal maturation of the lung. UV light alone did not affect pulmonary microRNAs, whereas smoke produced dramatic changes, mostly in the sense of down-regulation, reflecting both adaptive mechanisms and activation of pathways involved in the pathogenesis of pulmonary diseases. Both gender and age affected smoke-related microRNA dysregulation in mice. The data presented provide supporting evidence that microRNAs play a fundamental role in both physiological and pathological changes occurring in mouse lung.

Cigarette smoke-induced emphysema in A/J mice is associated with pulmonary oxidative stress, apoptosis of lung cells, and global alterations in gene expression

Cigarette smoking is the major risk factor for developing chronic obstructive pulmonary disease, the fourth leading cause of deaths in the United States. Despite recent advances, the molecular mechanisms involved in the initiation and progression of this disease remain elusive. We used Affymetrix Gene Chip arrays to determine the temporal alterations in global gene expression during the progression of pulmonary emphysema in A/J mice. Chronic cigarette smoke (CS) exposure caused pulmonary emphysema in A/J mice, which was associated with pronounced bronchoalveolar inflammation, enhanced oxidative stress, and increased apoptosis of alveolar septal cells. Microarray analysis revealed the upregulation of 1,190, 715, 260, and 246 genes and the downregulation of 1,840, 730, 442, and 236 genes in the lungs of mice exposed to CS for 5 h, 8 days, and 1.5 and 6 mo, respectively. Most of the genes belong to the functional categories of phase I genes, Nrf2-regulated antioxidant and phase II genes, phase III detoxification genes, and others including immune/inflammatory response genes. Induction of the genes encoding multiple phase I enzymes was markedly higher in the emphysematous lungs, whereas reduced expression of various cytoprotective genes constituting ubiquitin-proteasome complex, cell survival pathways, solute carriers and transporters, transcription factors, and Nrf2-regulated antioxidant and phase II-responsive genes was noted. Our data indicate that the progression of CS-induced emphysema is associated with a steady decline in the expression of various genes involved in multiple pathways in the lungs of A/J mice. Many of the genes discovered in this study could rationally play an important role in the susceptibility to CS-induced emphysema.

Molecular and cytogenetical alterations induced by environmental cigarette smoke in mice heterozygous for Fhit

Previous studies in humans and animal models provided evidence that the Fhit gene is an early target for cigarette smoke. We compared the induction of a variety of molecular and cytogenetical alterations in B6-129(F(1)) mice, either wild type or Fhit(+/-), after whole-body exposure to environmental cigarette smoke (ECS) for 15 consecutive days. Both mouse genotypes responded to ECS with a loss of Fhit protein in the bronchial epithelium, accompanied by induction of apoptosis and stimulation of cell proliferation. ECS induced formation of bulky DNA adducts in whole lung. In addition, ECS caused cytogenetical damage both in the respiratory tract and at a systemic level, as shown by a significant increase of micronucleus frequency in pulmonary alveolar macrophages, bone marrow polychromatic erythrocytes, and peripheral blood normochromatic erythrocytes of both wild-type and Fhit(+/-) mice. These results are compared with those generated in other species, strains, and genotypes of rodents exposed to ECS that we investigated previously. Although the loss of Fhit protein in the bronchial epithelium of ECS-exposed B6-129(F(1)) mice provides further evidence that the Fhit gene is an early molecular target for ECS, heterozygosity for Fhit does not seem to confer an increased susceptibility of mice in terms of the investigated early biomarkers.

Inhibitory effect of maxizyme on mutant-type p53 in hepatocellular carcinoma

AIM: To investigate the inhibitory effect of maxizyme on the mutant-type p53 (mtp53) gene at codon 249 in exon 7 (AGG→AGT) in cell-free system, hepatocellular carcinoma (HCC) cell line MHCC97, and nude mice bearing human HCC, and to explore a new method for gene therapy of HCC.

METHODS: Anti-mtp53 and control mutant maxizyme were designed and then cloned into the vector pBSKU6 and pEGFPC1, respectively. The ³²p-labeled mtp53 transcript was the target mRNA. Cold maxizyme transcript was incubated with ³²p-labeled target RNA in cell-free system. The products were quantified by measuring the radioautographed count per minute (cpm) in 1 mL solution. The MHCC97 cells were the target cells which contained a mutation at the third-base position of codon 249 of the p53 gene(AGG→AGT). PEGFPMz (recombinant eukaryotic vector) was transfected into MHCC97 cells by LipofectamineTM2000. The expression of mtp53 was analyzed by Northern Blot and Western Blot. The nude mice bearing human liver cancer were prepared and divided into blank control pEGFP and pEGFPMz group. The growth curve of the tumor in mice and the survival rate of mice were observed. The expression of mtp53 mRNA were detected by reverse transcription polymerase chain reaction (PT-PCR).

RESULTS: The established pEGFPMz had the correct structure. Maxizyme had a specific cleavage activity for mtp53 with a cleavage efficiency of 49% extracellularly, while the wild type p53 was not cleaved. The control maxizyme had no significant effect on both mutant and wile type p53. After pEGFPMz were transfected into MHCC97 cells, the expression of mtp53 mRNA and protein in pEGFPMz group were 65% and 67% respectively, which were significantly lower than those in blank control and pEGFP group (P<0.05). The tumor size decreased and mtp53 mRNA was down-regulated in mice treated with pEGFPMz as compared with those in mice of blank control and pEGFP group (mtp53 mRNA: 0.95±0.13 vs 1.44±0.14, 1.47±0.12; P<0.05), and also the survivals of the mice in pEGFPMz were improved.

CONCLUSION: Maxizyme can effectively inhibit the expression of mtp53 mRNA and protein as well as the growth of hepatocellular carcinoma cells.