Inhibition of cigarette smoke-related DNA adducts in rat tissues by indole-3-carbinol

Dietary selenium fails to influence cigarette smoke-induced lung tumorigenesis in A/J mice

The goal of the study was to determine if dietary selenium inhibited the induction of lung tumorigenesis by cigarette smoke in A/J mice. Purified diets containing 0.15, 0.5, or 2.0mg/kg selenium in the form of sodium selenite were fed to female A/J mice. Half of the mice in each dietary group were exposed to cigarette smoke 6h/day, 5days/week for five months followed by a four month recovery period in ambient air, while the other half were used as controls. After the recovery period, the mice were euthanized, and their lungs were removed for further analysis. Mice exposed to smoke had a higher tumor incidence and a higher tumor multiplicity, whereas dietary Se did not affect either the tumor incidence or tumor multiplicity. An increase in dietary selenium led to increased levels of selenium in the lung as well as GPx protein levels, but dietary Se did not affect lung SOD protein levels. In conclusion, these data confirm the carcinogenic activity of cigarette smoke in mice but show that dietary Se provided as sodium selenite does not affect smoke-induced carcinogenesis in this model.

Indole-3-carbinol inhibits nasopharyngeal carcinoma

This study explored the effects of indole-3-carbinol on the proliferation of human nasopharyngeal carcinoma, both in vitro and in vivo, and the underlying mechanisms in inducing apoptosis of CNE1 cells. Proliferation, apoptosis, malondialdehyde, superoxide dismutase, glutathione peroxidase, expressions of caspase-9, and caspase-3 in human nasopharyngeal carcinoma cells CNE1 were examined. Indole-3-carbinol suppressed proliferation, induced apoptosis, decreased malondialdehyde level, increased the activity of superoxide dismutase and glutathione peroxidase, and up-regulated the expression of active fragments of caspase-9 and caspase-3 both in vitro and in vivo. It was concluded that indole-3-carbinol could inhibit proliferation and induce apoptosis of CNE1 cells and inhibit tumor growth in mice. Increased activity of superoxide dismutase and glutathione peroxidase and activated expression of caspase-9 and caspase-3 were also observed in indole-3-carbinol-treated tumors or tumor cells, suggesting that stress- and apoptosis-related molecules are involved in the indole-3-carbinol-induced apoptosis and inhibition of tumor growth.

Induced expression of drug metabolizing enzymes by preventive agents: role of the antioxidant response element

Identifying agents that block tumor initiation is a goal of cancer prevention. The ability of a chemically varied group of agents to induce various drug metabolizing genes in livers of rats was examined. Sprague-Dawley rats were treated for 7 days with various agents in the diet or by gavage. The agents examined, which might be expected to respond via specific nuclear receptors (CAR, AhR) as well as antioxidant response elements (AREs), included Phase I/II inducers [5,6-benzoflavone (BF, 5000mg/kg diet), diallyl sulfide (DAS, 500mg/kg BW/day), ethoxyquin (EXO, 300mg/kg BW/day) and phenobarbital (PB, 500mg/kg diet)] or pure Phase II inducers [1,2-dithiol-3-thione (DTT, 500mg/kg diet), and cyclopentadithiolthione (CPDTT, 175mg/kg BW/day)]. Liver RNA expression was analyzed employing oligonucleotide microarrays. The agents yielded unique expression profiles. In genes with known AREs, the induction ratios (Levels Treated/Levels Controls) were: quinone oxidoreductase (BF, 8:1; DTT, 3.2:1; CPDTT, 3:1; DAS, 1.8:1; Exo, 1.7:1), glutatione transferase Pi (DTT, 36:1; CPDTT, 34:1; EXO, 8:1; DAS, 5:1; BF, 2.5:1), and aldehyde keto reductase 7A3 (AFAR) (DTT and CPDTT, 14:1; DAS, 6:1; EXO, 4:1; PB, 1.5:1). When the search included a wider variety of Phase II drug metabolizing enzymes, no clear pattern was observed. Agent induced gene expression and preventive activity in published carcinogen induced tumor models showed limited correlation; questioning whether measuring the induction of one or two genes (e.g., quinone reductase) is a surrogate for overall Phase II inducing (antioxidant) and potential anti-tumor activity.

Mouse Models Incorporating Alterations In The Major Tumor Suppressor Genes P53 And P16: Their Use In Screening For Potential Carcinogens, Developing Further Relevant Mouse Models, And Screening For Potential Chemopreventive And Chemotherapetutic Agents

This review is primarily a follow up to an initial review on this subject that the authors published 4 years ago [Lubet et al., Exp Lung Res. 2000; 581-593]. The present review gives a brief discussion of certain background points and rationale for development of these specific models, which had been presented in greater detail in the earlier article. In that initial article the authors identified the potential use of mutant mice in screening for carcinogens as well as preventive or therapeutic agents, discussed the relevance of the dominant-negative P53 mutation, as contrasted with knockout P53 mice, and briefly discussed the pros and cons of mice with a germline mutation in tumor suppressor genes in developing mouse models. The primary objective of the present review is to describe more recent studies using mice the dominant-negative P53 mutation as well as to introduce studies with mice with a heterozygous knockout of the P16/Ink4A ARF locus.

The inhibitory effect of vitamin E on cigarette smoke-induced oxidative damage to the rat urothelium: can it prevent transitional cell carcinoma?

INTRODUCTION

We aimed to detect reactive oxygen species (ROS) and assess subsequent carcinogenesis in terms of cellular proliferation in the bladder and kidney epithelial tissues of rats exposed to cigarette smoke (CS), and to investigate the changes following vitamin E treatment.

MATERIALS AND METHODS

Twenty-four male Sprague-Dawley rats were divided into 3 groups: group 1 was kept intact; group 2 was subjected to CS exposure for 8 weeks, and group 3 received intraperitoneal vitamin E injections (200 mg/kg/week) for 8 weeks in addition to CS exposure. Histological examination and Ki67 antigen expression measurements were made from bladder and renal pelvic tissue sections. Luminol-amplified chemiluminescence was used to measure ROS levels. All results were compared using a one-way ANOVA test.

RESULTS

In CS-exposed rats, light microscopy of renal and bladder tissues revealed nonspecific epithelial changes; however, Ki67 expression was significantly increased in bladder tissues compared to other groups (17.5 +/- 4.7, 35 +/- 2.9 and 18.7 +/- 5.1% in groups 1, 2 and 3, respectively, p < 0.05). Chemiluminescence levels in bladder and renal tissues were also significantly higher in the CS-exposed animals (78.1 +/- 11.4, 148 +/- 13.3, 97.8 +/- 6.1 rlu/mg for the bladder, and 99.8 +/- 12.2, 176.1 +/- 27.9, 67.1 +/- 9 rlu/mg, for renal pelvic tissues, respectively, p < 0.05).

CONCLUSIONS

Vitamin E can alleviate CS-induced oxidative damage in rat bladder and kidney epithelium suggesting a potential role for vitamin E in the prevention of CS-mediated carcinogenesis.

The effects of erdosteine, N-acetylcysteine, and vitamin E on nicotine-induced apoptosis of pulmonary cells

This study was conducted to investigate the frequency of apoptosis in the pulmonary epithelial cells of rats after intratraperitoneal nicotine injection, in order to examine the role of inflammatory markers [myeloperoxidase (MPO) and tumor necrosis factor-alpha (TNF-alpha)] in nicotine-induced lung damage, and to determine the protective effects of three known antioxidant agents [N-acetylcysteine (NAC), erdosteine, and vitamin E] on the lung toxicity of nicotine in the lungs. Female Wistar rats were divided into seven groups, each composed of nine rats: two negative control groups, two positive control groups, one erdosteine-treated group (500 mg/kg), one NAC-treated group (500 mg/kg), and one vitamin E-treated group (500 mg/kg). Nicotine was injected intraperitoneally at a dosage of 0.6 mg/kg for 21 days. Following nicotine injection, the antioxidants were administered orally, treatment was continued until the rats were killed. Lung tissue samples were stained with hematoxylin-eosin (H&E) for histopathological assessments. The apoptosis level in the lung bronchiolar and alveolar epithelium was determined by using the terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) method. Cytoplasmic TNF-alpha in the bronchiolar and alveolar epithelial cells and the lung MPO activity were evaluated immunohistochemically. The protective effect of vitamin E on lung histology was stronger than that of erdosteine or NAC. Treatment with erdosteine, NAC, and vitamin E significantly reduced the rate of nicotine-induced pulmonary epithelial cell apoptosis, and there were no significant differences in apoptosis among the three antioxidants groups. Erdosteine, NAC, and vitamin E significantly reduced the increases in TNF-alpha staining and lung MPO activity. The effects of erdosteine on the increases in the local TNF-alpha level and lung MPO activity were weaker than that of NAC or vitamin E. This findings suggest that erdosteine and NAC can be as effective as vitamin E in protecting against nicotine-induced pulmonary cell apoptosis.

Indole-3-carbinol suppresses NF-kappaB and IkappaBalpha kinase activation, causing inhibition of expression of NF-kappaB-regulated antiapoptotic and metastatic gene products and enhancement of apoptosis in myeloid and leukemia cells

Indole-3-carbinol, found in Brassica species vegetables (such as cabbage, cauliflower, and brussels spouts), exhibits antitumor effects through poorly defined mechanisms. Because several genes that regulate apoptosis, proliferation, and metastasis are regulated by nuclear factor-kappaB (NF-kappaB), we postulated that indole-3-carbinol must mediate its activity through NF-kappaB modulation. We demonstrated that indole-3-carbinol suppressed constitutive NF-kappaB activation and activation induced by tumor necrosis factor (TNF), interleukin-1beta (IL-1beta), phorbol 12-myristate 13-acetate (PMA), lipopolysaccharide (LPS), and cigarette smoke; the suppression was not cell type specific, because activation was inhibited in myeloid, leukemia, and epithelial cells. This activation correlated with the sequential suppression of the IkappaBalpha kinase, IkappaBalpha phosphorylation, IkappaBalpha ubiquitination, IkappaBalpha degradation, p65 phosphorylation, p65 nuclear translocation, p65 acetylation, and NF-kappaB-dependent reporter gene expression. The NF-kappaB-regulated gene products cyclin D1, cyclooxygenase-2 (COX-2), matrix metalloproteinase-9 (MMP-9), survivin, inhibitor-of-apoptosis protein-1 (IAP1), IAP2, X chromosome-linked IAP (XIAP), Bcl-2, Bfl-1/A1, TNF receptor-associated factor-1 (TRAF1), and Fas-associated death domain protein-like interleukin-1beta-converting enzyme inhibitory protein (FLIP) were all down-regulated by indole-3-carbinol. This down-regulation led to the potentiation of apoptosis induced by cytokines and chemotherapeutic agents. Indole-3-carbinol suppressed constitutive NF-kappaB activation in mononuclear cells derived from bone marrow of acute myelogenous leukemia patients, and this correlated with inhibition of cell growth. Overall, our results indicated that indole-3-carbinol inhibits NF-kappaB and NF-kappaB-regulated gene expression and that this mechanism may provide the molecular basis for its ability to suppress tumorigenesis.

Genotoxicity of environmental tobacco smoke: a review

Environmental tobacco smoke (ETS), or second-hand smoke, is a widespread contaminant of indoor air in environments where smoking is not prohibited. It is a significant source of exposure to a large number of substances known to be hazardous to human health. Numerous expert panels have concluded that there is sufficient evidence to classify involuntary smoking (or passive smoking) as carcinogenic to humans. According to the recent evaluation by the International Agency for Research on Cancer, involuntary smoking causes lung cancer in never-smokers with an excess risk in the order of 20% for women and 30% for men. The present paper reviews studies on genotoxicity and related endpoints carried out on ETS since the mid-1980s. The evidence from in vitro studies demonstrates induction of DNA strand breaks, formation of DNA adducts, mutagenicity in bacterial assays and cytogenetic effects. In vivo experiments in rodents have shown that exposure to tobacco smoke, whole-body exposure to mainstream smoke (MS), sidestream smoke (SS), or their mixture, causes DNA single strand breaks, aromatic adducts and oxidative damage to DNA, chromosome aberrations and micronuclei. Genotoxicity of transplacental exposure to ETS has also been reported. Review of human biomarker studies conducted among non-smokers with involuntary exposure to tobacco smoke indicates presence of DNA adducts, urinary metabolites of carcinogens, urinary mutagenicity, SCEs and hypoxanthine-guanine phosphoribosyltransferase (HPRT) gene mutations (in newborns exposed through involuntary smoking of the mother). Studies on human lung cancer from smokers and never-smokers involuntarily exposed to tobacco smoke suggest occurrence of similar kinds of genetic alterations in both groups. In conclusion, these overwhelming data are compatible with the current knowledge on the mechanisms of carcinogenesis of tobacco-related cancers, occurring not only in smokers but with a high biological plausibility also in involuntary smokers.

Novel Marine Compounds: Anticancer or Genotoxic?

In the past several decades, marine organisms have generously gifted to the pharmaceutical industries numerous naturally bioactive compounds with antiviral, antibacterial, antimalarial, anti-inflammatory, antioxidant, and anticancer potentials. But till date only few anticancer drugs (cytarabine, vidarabine) have been commercially developed from marine compounds while several others are currently in different clinical trials. Majority of these compounds were tested in the tumor xenograft models, however, lack of anticancer potential data in the chemical- and/or oncogene-induced pre-initiation animal carcinogenesis models might have cost some of the marine anticancer compounds an early exit from the clinical trials. This review critically discusses importance of preclinical evaluation, failure of human clinical trials with certain potential anticancer agents, the screening tests used, and choice of biomarkers.

Genotoxicity of naturally occurring indole compounds: correlation between covalent DNA binding and other genotoxicity tests

3-Methylindole (3MI), melatonin (Mel), serotonin (Ser), and tryptamine (Tryp) were evaluated in vitro for their potential to induce DNA adducts, DNA strand breaks, chromosomal aberrations (Abs), inhibition of DNA synthesis, and mutations. All compounds produced DNA adducts in calf thymus DNA in the presence of rat liver S9. In cultured rat hepatocytes, all produced DNA adducts but none induced DNA strand breaks. In Chinese hamster ovary cells, 3MI and Mel produced DNA adducts, Abs, and inhibition of DNA synthesis with and without S9, except that Mel without S9 did not form adducts. Ser formed DNA adducts, was an equivocal Abs inducer, and suppressed DNA synthesis. Tryp induced neither adducts nor Abs, but did suppress DNA synthesis with S9. Ser and Tryp were less cytotoxic than 3MI and Mel. Mel, Ser, and Tryp failed to induce mutations in Salmonella and E. coli strains with or without S9. 3MI and Mel produced DNA adducts but not mutations in Salmonella TA100 with S9. 3MI and its metabolite indole 3-carbinol also did not induce mutations in a shuttle vector system in human cells. The lack of correlation between DNA adducts and other genotoxicity endpoints for these indole compounds may be due to the higher sensitivity of the (32)P-postlabeling adduct assay or it may indicate that the indole-DNA adducts per se are not mutagenic and are not able to induce strand breaks or alkali-labile lesions. The indole-induced Abs may result from cytotoxicity and suppression of DNA synthesis with minimal if any contribution from DNA adducts.

The micronutrient indole-3-carbinol: implications for disease and chemoprevention

This review provides a historical perspective for the development of indole-3-carbinol (I-3-C) as a chemopreventive or therapeutic agent. Early experiments in animal models clearly showed that feeding cruciferous vegetables reduced the incidence of chemical carcinogenesis. Excitement was generated by the finding that these vegetables contained a high content of indole-containing compounds, and I-3-C could by itself inhibit neoplasia. The mechanism of action was linked primarily to the ability of I-3-C and derived substances to induce mixed-function oxidases and phase II antioxidant enzymes by binding and activating the aryl hydrocarbon receptor. Most of the literature on chemoprotection by dietary indole compounds relates to this mechanism of action. Other mechanisms, however, are notable for this class of compounds, including their ability to act as radical and electrophile scavengers; the various ascorbate conjugates of I-3-C (ascorbigens) may be important in this regard. Exciting recent findings have demonstrated that I-3-C and its reaction products can affect cellular signaling pathways, regulate the cell cycle, and decrease tumor cell properties related to metastasis. It does not appear that I-3-C per se is the primary active compound in chemoprotection or chemoprevention. Rather, I-3-C and ascorbate provide the parent compounds for the formation of a myriad of nonenzymatic reaction products that have strong biological potency. We conclude with our thoughts regarding the current status and future directions for the use of I-3-C and related compounds.