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Gastroenterology Oct 1995Rat colon neoplasms are distributed 60% in the distal colon (DC) and 40% in the proximal colon (PC), similar to distribution of colon cancers in the industrialized...
BACKGROUND & AIMS
Rat colon neoplasms are distributed 60% in the distal colon (DC) and 40% in the proximal colon (PC), similar to distribution of colon cancers in the industrialized world. The effects of chemopreventive agents that affect colon tumor incidence on the distribution of colon tumors were studied.
METHODS
Colon tumor distribution, numbers, and volumes were measured in the DC and PC of rats administered azoxymethane (15 mg/kg subcutaneously 2x) as an initiating agent and fed diets containing various chemopreventive agents.
RESULTS
In control rats, azoxymethane-induced tumor incidence in the DC exceeded that in the PC, but tumor volume was greater in the PC than the DC. Ellagic acid showed no chemopreventive effect and maintained the PC-DC colon tumor gradient. Oltipraz, a modestly effective chemopreventive agent, principally reduced the incidence of DC tumors. DL-d-difluoromethylornithine also greatly altered tumor number in the DC compared with the PC. In contrast, piroxicam (400 ppm) reduced PC tumors by 82% but DC tumors only by 57%. With all regimens, tumor volume remained greater in the PC than the DC.
CONCLUSIONS
Chemopreventive agents have a selective regional effect on colon tumorigenesis in the rat. Elucidation of the mechanism for these differences may help clarify the modes of action of chemopreventive agents in colon cancer.
Topics: Animals; Anticarcinogenic Agents; Azoxymethane; Colonic Neoplasms; Eflornithine; Ellagic Acid; Male; Piroxicam; Pyrazines; Rats; Rats, Inbred F344; Thiones; Thiophenes
PubMed: 7557082
DOI: 10.1016/0016-5085(95)90575-8 -
American Journal of Transplantation :... Jan 2015Activating transcription factor 3 (ATF3) is a stress-induced transcription factor that has been shown to repress inflammatory gene expression in multiple cell types and...
Activating transcription factor 3 (ATF3) is a stress-induced transcription factor that has been shown to repress inflammatory gene expression in multiple cell types and diseases. However, little is known about the roles and mechanisms of ATF3 in liver ischemia/reperfusion injury (IRI). In warm and cold liver IRI models, we showed that ATF3 deficiency significantly increased ischemia/reperfusion (IR)-stressed liver injury, as evidenced by increased serum alanine aminotransferase levels, histological liver damage, and hepatocellular apoptosis. These may correlate with inhibition of the intrahepatic nuclear factor erythroid-derived 2-related factor 2/heme oxygenase-1 (NRF2/HO-1) signaling pathway leading to enhancing Toll-like receptor 4/nuclear factor kappa beta (TLR4/NF-κB) activation, pro-inflammatory programs and macrophage/neutrophil trafficking, while simultaneously repressing anti-apoptotic molecules in ischemic liver. Interestingly, activation of NRF2/HO-1 signaling using an NRF2 activator, oltipraz (M2), during hepatic IRI-rescued ATF3 anti-inflammatory functions in ATF3-deficient mice. For in vitro studies, ATF3 ablation in lipopolysaccharide (LPS)-stimulated bone marrow-derived macrophages (BMMs) depressed levels of NRF2/HO-1 and PI3K/AKT, resulting in enhanced TLR4/NF-κB activation. Pretreatment of LPS-stimulated BMMs with M2 increased NRF2/HO-1 expression, promoted PI3K/AKT, which in turn suppressed TLR4/NF-κB-mediated proinflammatory mediators. Thus, our results first demonstrate ATF3-mediated NRF2/HO-1 signaling in the regulation of TLR4-driven inflammatory responses in IR-stressed livers. Our findings provide a rationale for a novel therapeutic strategy for managing IR-induced liver injury.
Topics: Activating Transcription Factor 3; Animals; Apoptosis; Blotting, Western; Cell Proliferation; Cells, Cultured; Enzyme-Linked Immunosorbent Assay; Heme Oxygenase-1; Immunity, Innate; Liver; Macrophages; Male; Membrane Proteins; Mice; Mice, Inbred C57BL; Mice, Knockout; NF-E2-Related Factor 2; NF-kappa B; Phosphatidylinositol 3-Kinases; RNA, Messenger; Real-Time Polymerase Chain Reaction; Reperfusion Injury; Reverse Transcriptase Polymerase Chain Reaction; Signal Transduction; Toll-Like Receptor 4
PubMed: 25359217
DOI: 10.1111/ajt.12954 -
Cancer Prevention Research... Jan 2010We previously showed that exposure to environmental cigarette smoke (ECS) for 28 days causes extensive downregulation of microRNA expression in the lungs of rats,...
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.
Topics: Acetylcysteine; Animals; Anticarcinogenic Agents; Chemoprevention; Cluster Analysis; Enzyme Inhibitors; Gene Expression; Indoles; Isothiocyanates; Lung; Male; MicroRNAs; Oligonucleotide Array Sequence Analysis; Principal Component Analysis; Pyrazines; Rats; Rats, Sprague-Dawley; Reverse Transcriptase Polymerase Chain Reaction; Thiones; Thiophenes; Tobacco Smoke Pollution; beta-Naphthoflavone
PubMed: 20051373
DOI: 10.1158/1940-6207.CAPR-09-0202 -
Cancer Letters Jun 2000The risk of liver cancer is greatest in people both infected with hepatitis B virus (HBV) and highly exposed to aflatoxin B(1) (AFB(1)). The tree shrew (Tupaia belangeri...
The risk of liver cancer is greatest in people both infected with hepatitis B virus (HBV) and highly exposed to aflatoxin B(1) (AFB(1)). The tree shrew (Tupaia belangeri chinensis) is a unique species that can be infected with human HBV, is susceptible to AFB(1)-induced liver cancer, and shows a synergistic interaction between HBV and AFB(1) for liver cancer. In this regard, the tree shrew may be useful for evaluating experimental chemoprevention strategies relevant to high-risk human populations as it mirrors the human epidemiology of liver cancer. To begin developing the model for chemoprevention study, two groups of tree shrews were fed 400 microg AFB(1)/kg b.wt. in milk daily for 4 weeks. One week prior to AFB(1) administration, one group also received oltipraz (0.5 mmol/kg, p.o.) daily for 5 weeks. At weekly intervals, 1 ml of blood and a 24-h urine sample were obtained from each animal. Aflatoxin-albumin adducts in serum were determined by a radioimmunological assay and aflatoxin-N(7)-guanine adducts in urine were measured by HPLC. Aflatoxin-albumin adducts increased rapidly in 2 weeks to plateau at 20 pmol/mg protein, and they diminished after cessation of AFB(1) exposure. Oltipraz significantly attenuated the overall burden of aflatoxin-albumin adducts throughout the exposure period with a median reduction of 80%. In a single cross-sectional analysis at the end of AFB(1) dosing, oltipraz treatment decreased urinary aflatoxin-N(7)-guanine by 93%. Collectively, these results indicate that oltipraz reduces AFB(1) risk biomarkers in the tree shrew in a manner similar to that observed in rodents and humans, and establishes a rationale to evaluate cancer chemoprevention by oltipraz in human HBV-infected, AFB(1) exposed tree shrews.
Topics: Aflatoxin B1; Animals; Anticarcinogenic Agents; Antiviral Agents; Biomarkers; Chromatography, High Pressure Liquid; DNA Adducts; Female; Hepatitis B virus; Humans; Liver Neoplasms; Male; Pyrazines; Radioimmunoassay; Thiones; Thiophenes; Time Factors; Tupaiidae
PubMed: 10799742
DOI: 10.1016/s0304-3835(00)00382-7 -
Bioorganic & Medicinal Chemistry Aug 2010Dithiolethiones upregulate the expression of cancer-preventive proteins via modification of thiol residues in the Keap1-Nrf2 transcription factor complex. In addition to...
Dithiolethiones upregulate the expression of cancer-preventive proteins via modification of thiol residues in the Keap1-Nrf2 transcription factor complex. In addition to Keap1-Nrf2, dithiolethiones have the potential to modify a variety of cysteine-containing proteins in the cell. Such 'off target' reactions could contribute to either side effects or cancer-preventive efficacy. Evidence is presented here that cancer chemopreventive dithiolethiones inactivate protein tyrosine phosphatases via covalent, but thiol-labile, modification of active site residues. This observation may explain a number of previously reported cellular responses to dithiolethiones.
Topics: Anticarcinogenic Agents; Catalytic Domain; Humans; Mass Spectrometry; Protein Tyrosine Phosphatase, Non-Receptor Type 1; Protein Tyrosine Phosphatase, Non-Receptor Type 11; Protein Tyrosine Phosphatases; Pyrazines; Reactive Oxygen Species; Recombinant Proteins; Thiones; Thiophenes
PubMed: 20655236
DOI: 10.1016/j.bmc.2010.06.084 -
Archives of Toxicology Dec 2008Non-alcoholic steatohepatitis (NASH) is a disease that compromises hepatic function and the capacity to metabolize numerous drugs. Aryl hydrocarbon receptor (AhR),...
Non-alcoholic steatohepatitis (NASH) is a disease that compromises hepatic function and the capacity to metabolize numerous drugs. Aryl hydrocarbon receptor (AhR), constitutive androstane receptor (CAR), pregnane X receptor (PXR), peroxisome proliferator-activated receptor alpha (PPARalpha), and nuclear factor-E2 related factor 2 (Nrf2) are xenobiotic activated transcription factors that regulate induction of a number of drug metabolizing enzymes (DMEs). The purpose of the current study was to determine whether experimental NASH alters the xenobiotic activation of these transcription factors and induction of downstream DME targets Cyp1A1, Cyp2B10, Cyp3A11, Cyp4A14 and NAD(P)H:quinone oxidoreductase 1 (Nqo1), respectively. Mice fed normal rodent chow or methionine-choline-deficient (MCD) diet for 8 weeks were then treated with microsomal enzyme inducers beta-naphoflavone (BNF), 1,4-bis-[2-(3,5-dichloropyridyloxy)] benzene (TCPOBOP), pregnenolone-16alpha-carbonitrile (PCN), clofibrate (CFB) or oltipraz (OPZ), known activators of AhR, CAR, PXR, PPARalpha and Nrf2, respectively. Results of this study show that (1) Hepatic PXR mRNA levels were significantly increased (1.4-fold) in mice fed MCD diet, while AhR, CAR, PPARalpha and Nrf2 were not affected. (2) The MCD diet did not alter hepatic inducibility of Cyp1A1, Cyp2B10, Cyp3A11 mRNA levels by their respective microsomal inducers. (3) Constitutive levels of Cyp4A14 mRNA were significantly increased in mice fed the MCD diet, yet further induction by clofibrate was not observed. (4) Hepatic Nqo1 mRNA levels were significantly increased by the MCD diet; however, additional induction of Nqo1 was still achievable following treatment with the Nrf2 activator OPZ.
Topics: Animals; Aryl Hydrocarbon Hydroxylases; Constitutive Androstane Receptor; Cytochrome P-450 CYP1A1; Cytochrome P-450 CYP3A; Cytochrome P-450 Enzyme System; Cytochrome P450 Family 2; Cytochrome P450 Family 4; Enzyme Induction; Fatty Liver; Gene Expression Regulation, Enzymologic; Liver; Male; Membrane Proteins; Mice; Mice, Inbred C57BL; NAD(P)H Dehydrogenase (Quinone); NADPH Dehydrogenase; NF-E2-Related Factor 2; PPAR alpha; Pharmaceutical Preparations; Pregnane X Receptor; RNA, Messenger; Receptors, Cytoplasmic and Nuclear; Receptors, Steroid; Steroid Hydroxylases; Transcription Factors
PubMed: 18488193
DOI: 10.1007/s00204-008-0312-z -
The Journal of Clinical Investigation Sep 1996Prolonged exposure to mutagenic substances is strongly associated with an individual's risk of developing colorectal cancer. Clinical investigation of oltipraz as a... (Clinical Trial)
Clinical Trial Comparative Study
Prolonged exposure to mutagenic substances is strongly associated with an individual's risk of developing colorectal cancer. Clinical investigation of oltipraz as a chemopreventive agent is supported by its induction of the expression of detoxication enzymes in various tissues, and its protective activity against the formation of chemically induced colorectal tumors in animals. The goals of the present study were: to determine if oltipraz could induce detoxicating gene expression in human tissues; to identify effective non-toxic doses for more extensive clinical testing; and to establish a relationship between effects in the colon mucosa and those in a more readily available tissue, the peripheral mononuclear cell. 24 evaluable patients at high risk for colorectal cancer were treated in a dose-finding study with oltipraz 125, 250, 500, or 1,000 mg/m2 as a single oral dose. Biochemical analysis of sequential blood samples and colon mucosal biopsies revealed increases in glutathione transferase activity at the lower dose levels. These effects were not observed at the higher doses. More pronounced changes were observed in detoxicating enzyme gene expression in both tissues at all doses. Peripheral mononuclear cell and colon mRNA content for gamma-glutamylcysteine synthetase (gamma-GCS) and DT-diaphorase increased after dosing to reach a peak on day 2-4 after treatment, and declined to baseline in the subsequent 7-10 d. The extent of induction of gene expression in colon mucosa reached a peak of 5.75-fold for gamma-GCS, and a peak of 4.14-fold for DT-diaphorase at 250 mg/m2 ; higher doses were not more effective. Levels of gamma-GCS and DT-diaphorase correlated closely (P < or = 0.001) between peripheral mononuclear cells and colon mucosa both at baseline and at peak. These findings demonstrate that the administration of minimally toxic agents at low doses may modulate the expression of detoxicating genes in the tissues of individuals at high risk for cancer. Furthermore, peripheral mononuclear cells may be used as a noninvasive surrogate endpoint biomarker for the transcriptional response of normal colon mucosa to drug administration.
Topics: Adult; Aged; Aged, 80 and over; Anticarcinogenic Agents; Chemoprevention; Colon; Colorectal Neoplasms; Female; Gene Expression Regulation, Neoplastic; Glutamate-Cysteine Ligase; Humans; Inactivation, Metabolic; Intestinal Mucosa; Leukocytes, Mononuclear; Male; Middle Aged; Mutagenesis; NAD(P)H Dehydrogenase (Quinone); Pyrazines; Risk; Thiones; Thiophenes
PubMed: 8787684
DOI: 10.1172/JCI118904 -
Proceedings of the National Academy of... Mar 2001Induction of phase 2 enzymes, which neutralize reactive electrophiles and act as indirect antioxidants, appears to be an effective means for achieving protection against...
Induction of phase 2 enzymes, which neutralize reactive electrophiles and act as indirect antioxidants, appears to be an effective means for achieving protection against a variety of carcinogens in animals and humans. Transcriptional control of the expression of these enzymes is mediated, at least in part, through the antioxidant response element (ARE) found in the regulatory regions of their genes. The transcription factor Nrf2, which binds to the ARE, appears to be essential for the induction of prototypical phase 2 enzymes such as glutathione S-transferases (GSTs) and NAD(P)H:quinone oxidoreductase (NQO1). Constitutive hepatic and gastric activities of GST and NQO1 were reduced by 50-80% in nrf2-deficient mice compared with wild-type mice. Moreover, the 2- to 5-fold induction of these enzymes in wild-type mice by the chemoprotective agent oltipraz, which is currently in clinical trials, was almost completely abrogated in the nrf2-deficient mice. In parallel with the enzymatic changes, nrf2-deficient mice had a significantly higher burden of gastric neoplasia after treatment with benzo[a]pyrene than did wild-type mice. Oltipraz significantly reduced multiplicity of gastric neoplasia in wild-type mice by 55%, but had no effect on tumor burden in nrf2-deficient mice. Thus, Nrf2 plays a central role in the regulation of constitutive and inducible expression of phase 2 enzymes in vivo and dramatically influences susceptibility to carcinogenesis. Moreover, the total loss of anticarcinogenic efficacy of oltipraz in the nrf2-disrupted mice highlights the prime importance of elevated phase 2 gene expression in chemoprotection by this and similar enzyme inducers.
Topics: Animals; Anticarcinogenic Agents; Benzo(a)pyrene; Carcinogenicity Tests; Carcinogens; Cell Nucleus; DNA-Binding Proteins; Disease Models, Animal; Disease Susceptibility; Epoxide Hydrolases; FMN Reductase; Female; Gene Expression; Genotype; Glucuronosyltransferase; Glutathione Transferase; Mice; Mice, Inbred ICR; Mice, Knockout; NADH, NADPH Oxidoreductases; NF-E2-Related Factor 2; Pyrazines; Stomach Neoplasms; Thiones; Thiophenes; Trans-Activators
PubMed: 11248092
DOI: 10.1073/pnas.051618798 -
Toxicological Sciences : An Official... Apr 2009Alpha-naphthylisothiocyanate (ANIT) causes intrahepatic cholestasis by injuring biliary epithelial cells. Adaptive regulation of hepatobiliary transporter expression has...
Alpha-naphthylisothiocyanate (ANIT) causes intrahepatic cholestasis by injuring biliary epithelial cells. Adaptive regulation of hepatobiliary transporter expression has been proposed to reduce liver injury during cholestasis. Recently, the oxidative stress transcription factor Nrf2 (nf-e2-related factor 2) was shown to regulate expression of hepatobiliary transporters. The purpose of this study was to determine whether ANIT-induced hepatotoxicity and regulation of hepatobiliary transporters are altered in the absence of Nrf2. For this purpose, wild-type and Nrf2-null mice were administered ANIT (75 mg/kg po). Surprisingly, ANIT-induced hepatotoxicity was similar in both genotypes at 48 h. Accumulation of bile acids in serum and liver was lower in Nrf2-null mice compared with wild-types treated with ANIT. Transporter mRNA profiles differed between wild-type and Nrf2-null mice after ANIT. Bsep (bile salt export pump), Mdr2 (multidrug resistance gene), and Mrp3 (multidrug resistance-associated protein) efflux transporters were increased by ANIT in wild-type, but not in Nrf2-null mice. In contrast, mRNA expression of two hepatic uptake transporters, Ntcp (sodium-taurocholate cotransporting polypeptide) and Oatp1b2 (organic anion transporting peptide), were decreased in both genotypes after ANIT, with larger declines in Nrf2-null mice. mRNA expression of the transcriptional repressor of Ntcp, small heterodimeric partner (SHP), was increased in Nrf2-null mice after ANIT. Furthermore, hepatocyte nuclear factor 1alpha (HNF1alpha), which regulates Oatp1b2, was downregulated in ANIT-treated Nrf2-null mice. Preferential upregulation of SHP and downregulation of HNF1alpha and uptake transporters likely explains why Nrf2-null mice exhibited similar injury to wild-types after ANIT. A subsequent study revealed that treatment of mice with the Nrf2 activator oltipraz protects against ANIT-induced histological injury. Despite compensatory changes in Nrf2-null mice to limit ANIT toxicity, pharmacological activation of Nrf2 may represent a therapeutic option for intrahepatic cholestasis.
Topics: 1-Naphthylisothiocyanate; Animals; Bile; Bile Acids and Salts; Bilirubin; Blotting, Western; Carrier Proteins; Cholestasis, Intrahepatic; Fluorescent Antibody Technique, Indirect; Indicators and Reagents; Liver; Liver Function Tests; Mice; Mice, Inbred C57BL; Mice, Knockout; NF-E2-Related Factor 2; RNA; Signal Transduction
PubMed: 19181614
DOI: 10.1093/toxsci/kfp020 -
The Journal of Biological Chemistry Mar 1998UDP-glucuronosyltransferase UGT1A7 catalyzes the glucuronidation of benzo(a)pyrene metabolites and other bulky aromatic compounds. Both UGT1A7 mRNA and an associated...
UDP-glucuronosyltransferase UGT1A7 catalyzes the glucuronidation of benzo(a)pyrene metabolites and other bulky aromatic compounds. Both UGT1A7 mRNA and an associated enzyme activity (benzo(a)pyrene7, 8-dihydrodioltransferase activity) are markedly increased in livers of rats treated with beta-naphthoflavone or 4-methyl-5-pyrazinyl-3H-1,2-dithiole-3-thione (oltipraz). Nuclear runoff assays show that the effects of both inducers are primarily due to transcriptional activation. A 27-kilobase region that included the UGT1A7/UGT1A6 promoter regions was cloned. Primer extension and RNase protection studies indicated >/=30 transcription start sites in five clusters between bases -85 and -40 respective to the translation start codon. There was no recognizable TATA box, but the promoter region is TA-rich. Sequence analysis revealed potential binding sites for CCAAT enhancer-binding protein, activator protein 1, and hepatic nuclear factors 1, 3, and 4, but no xenobiotic response elements or antioxidant response elements, implicated in the regulation of other genes by beta-naphthoflavone or oltipraz, were found. A UGT1A7 gene reporter plasmid directed strong constitutive expression in transient transfection assays using primary rat hepatocytes. Treatment with 3-methylcholanthrene or oltipraz had no effect compared with similarly treated pGL3-Basic-transfected cells. These results suggest that the regulatory elements controlling xenobiotic inducibility of UGT1A7 transcription are located either 5' or 3' of bases -1600 to +54. One possibility is that the polycyclic aromatic-mediated regulation of UGT1A7 occurs via the xenobiotic response element flanking the UGT1A6 locus 7 kilobase pairs downstream.
Topics: Animals; Base Sequence; Cells, Cultured; Cloning, Molecular; Cytochrome P-450 Enzyme System; Genes, Reporter; Glucuronosyltransferase; Liver; Male; Molecular Sequence Data; Polycyclic Aromatic Hydrocarbons; Promoter Regions, Genetic; Pyrazines; RNA, Messenger; Rats; Rats, Sprague-Dawley; Receptors, Aryl Hydrocarbon; Sequence Analysis, DNA; Thiones; Thiophenes; Transcriptional Activation; Transfection
PubMed: 9488689
DOI: 10.1074/jbc.273.10.5607