Biomedical subjects

Keiichirou Morimura

Publications and source records attributed to Keiichirou Morimura.

At least 55 records · Page 3Linked to original sources

PubMed2003

Phenobarbital at low dose exerts hormesis in rat hepatocarcinogenesis by reducing oxidative DNA damage, altering cell proliferation, apoptosis and gene expression.

Our recent research indicated that phenobarbital (PB) may inhibit the development of N-diethylnitrosamine (DEN)-initiated pre-neoplastic lesions at low doses in a rat liver medium-term bioassay (Ito test), while high doses exhibit promoting activity. This raises the question of whether treatment with low doses of PB might reduce cancer risk. For clarification, male 6-week-old F344 rats were treated with PB at doses of 0, 2, 15 and 500 p.p.m. in the diet for 10 or 33 weeks after initiation of hepatocarcinogenesis with DEN. In a second, short-term experiment, animals were given PB at doses of 2, 4, 15, 60 and 500 p.p.m. for 8 days. Formation of glutathione S-transferase placental form (GST-P) positive foci and liver tumors was inhibited at 2 p.p.m. Generation of oxidative DNA damage marker, 8-hydroxy-2'-deoxyguanosine (8-OHdG), cellular proliferation within the areas of GST-P positive foci and apoptosis in background liver parenchyma were suppressed. Suppression of 8-OHdG formation by PB at low dose might be related to the enhanced mRNA expression of 8-OHdG repair enzyme, oxoguanine glycosylase 1 (Ogg1). Moreover, as detected by cDNA microarray analysis, PB treatment at low dose enhanced mRNA expression of glutamic acid decarboxylase (GAD65), an enzyme involved in the synthesis of gamma-aminobutyric acid (GABA), and suppressed MAP kinase p38 and other intracellular kinases gene expression. On the contrary, when PB was applied at a high dose, GST-P positive foci numbers and areas, tumor multiplicity, hydroxyl radicals and 8-OHdG levels were greatly elevated with the increase in CYP2B1/2 and CYP3A2 mRNA, protein, activity and gene expression of GST, nuclear tyrosine phosphatase, NADPH- cytochrome P-450 reductase and guanine nucleotide binding protein G(O) alpha subunit. These results indicate that PB exhibits hormetic effect on rat hepatocarcinogenesis initiated with DEN by differentially altering cell proliferation, apoptosis and oxidative DNA damage at high and low doses.

8-Hydroxy-2'-Deoxyguanosine↗

PubMed2003

High susceptibility of p53 knockout mice to esophageal and urinary bladder carcinogenesis induced by N, N-dibutylnitrosamine.

In human cancer, alterations in the p53 tumor suppressor gene are the most common genetic alterations. The aim of the present study was to detect sensitivity of the p53 (+/-) mice and their littermates p53 (+/+) mice to N, N-dibutylnitrosamine (DBN) carcinogenicity. In experiment 1, 6-7-week-old p53 (+/-) and p53 (+/+) mice were treated with 0, 0.025 and 0.05% DBN, respectively, in drinking water for 20 weeks. Esophageal squamous cell and urinary bladder transitional cell carcinomas (TCCs) and fibrosarcomas were found to be significantly increased in p53 (+/-) mice treated with doses of DBN compared to p53 (+/+) mice administered similar doses. In experiment 2, 6-7-week-old p53 (+/-) and p53 (+/+) mice were administered 0 or 0.05 % DBN in drinking water for 8 weeks. Immunohistochemical staining revealed a significant increase in numbers of p53 and bromodeoxyuridine (BrdU) positive cells in the esophageal and urinary bladder epithelia of DBN-treated p53 (+/-) mice compared to p53 (+/+) mice administered DBN. Molecular analysis revealed point mutations in the residual p53 allele in four of eight (50%) esophageal mucosa of DBN-treated p53 (+/-) mice, and in three of eight (38%) of treated p53 (+/+) mice. The results show that p53 (+/-) mice were sensitive to DBN treatment with respect to esophageal and bladder tumor development, with a mechanism that could be confined to early mutations of the residual p53 allele and increased cellular proliferation in the target organs.

Alleles↗

PubMed2003

Enhancement of lung carcinogenesis by nonylphenol and genistein in a F344 rat multiorgan carcinogenesis model.

The modifying effects of nonylphenol and genistein on cancer induction were assessed in a multi-organ carcinogenesis model in male F344 rats initially treated with five different carcinogens. In experiment 1 rats received 250 or 25 ppm nonylphenol, or 250 or 25 ppm genistein in their diet for 28 weeks. The total incidences of adenomas and carcinomas in the lungs of animals treated with nonylphenol and genistein were significantly higher than in the control group. 5-Bromo-2'-deoxyuridine labeling indices, reflecting cell proliferation, were also significantly elevated in the lungs of rats given 250 and 25 ppm nonylphenol and 250 ppm genistein. In experiment 2, rats were treated with nonylphenol or genistein at concentrations of 250 ppm after DHPN initiation. In the lung, formation of 8-hydroxy-2'-deoxyguanosine, a marker of oxygen radical-mediated DNA damage, was significantly increased. These results indicate that nonylphenol and genistein have the potential to promote rat lung carcinogenesis, possibly via a mechanism involving stimulation of cell proliferation and DNA damage caused by oxygen radicals.

Animals↗

PubMed2003

Enhancing risk of ethanol on MeIQx-induced rat hepatocarcinogenesis is accompanied with increased levels of cellular proliferation and oxidative stress.

We investigated promotion potential of ethanol after initiation of hepatocarcinogenesis in male, 21-day-old, F344 rats by exposure to 10 ppm 2-amino-3, 8-dimethylimidazo[4,5-f]quinoxaline pellet diet for 8 weeks. The rats in group 1 were then fed on liquid control diet for 16 weeks, group 2 receiving the same diet containing 5% ethanol for 8 weeks followed by 8 weeks on the control diet, while group 3 animals were given 5% ethanol containing liquid diet for the entire16 weeks. On sacrifice at the end of week 24, glutathione S-transferase placental form positive foci, putative preneoplastic lesions in the liver, cell proliferation as indicated by proliferating cell nuclear antigen immunohistochemical staining and levels of 8-hydroxydeoxyguanosine, a marker of oxidative DNA damage, were significantly increased in the liver of group 3 along with non significant alteration of 8-oxoguanine DNA glycosylase mRNA expression. Lack of persistent increase of above parameters was found in transient ethanol exposure group. These results suggest that chronic consumption of ethanol promotes hepatocarcinogenesis by increasing oxidative stress and cell proliferation. It is also evident that abstinence of ethanol during the second stage stops its persistent promotion effect.

8-Hydroxy-2'-Deoxyguanosine↗

PubMed2003

Lack of initiation activity in rat liver of low doses of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline.

It has been generally accepted that genotoxic carcinogens have no threshold in exerting their potential for cancer induction. However, the non-threshold theory can be challenged for cancer risk assessment in humans. Here we examined low dose carcinogenicity of a food-derived, genotoxic hepatocarcinogen, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), using an in vivo medium-term bioassay to detect initiating activity for rat hepatocarcinogenesis. With MeIQx initiation at various doses followed by administration of phenobarbital, a well known hepatopromoter, no induction of glutathione S-transferase placental form-positive foci, assessed as preneoplastic lesions, was noted at doses of 0.001-1 ppm. The results imply a no-observed effect level for hepatocarcinogenicity with this genotoxic agent.

Animals↗

PubMed2003

Carcinogenicity of dimethylarsinic acid in p53 heterozygous knockout and wild-type C57BL/6J mice.

There is abundant epidemiological evidence that arsenic is an environmental carcinogen related to human cancers of the skin, lung, liver and urinary bladder, in particular. Dimethylarsinic acid (DMA) has also been reported to act as a carcinogen/or a promoter in rat models. To elucidate molecular mechanisms, we conducted an 18 month carcinogenicity study of DMA in p53 heterozygous (+/-) knockout mice, which are susceptible to early spontaneous development of various types of tumors, and wild-type (+/+) C57BL/6J mice. Totals of 88-90 males, 7-8 weeks of age, were divided into three groups each administered 0, 50 or 200 p.p.m. DMA in their drinking water for 18 months. Mice that were found moribund or died before the end of the study were autopsied to evaluate the tumor induction levels, as well as those killed at the end. Both p53(+/-) knockout and wild-type mice demonstrated spontaneous tumor development, but lesions were more prevalent in the knockout case. Carcinogenic effect of DMA was evident by significant early induction of tumors in both treated p53(+/-) knockout and wild-type mice, significant increase of the tumor multiplicity in 200 p.p.m.-treated p53(+/-) knockout mice, and by significant increase in the incidence and multiplicity of tumors (malignant lymphomas) in the treated wild-type mice. By the end of 80 weeks, tumor induction, particularly malignant lymphomas and sarcomas, were similar in treated and control p53(+/-) knockout mice. No evidence for organ-tumor specificity of DMA was obtained. Molecular analysis using PCR-SSCP techniques revealed no p53 mutations in lymphomas from either p53(+/-) knockout or wild-type mice. In conclusion, DMA primarily exerted its carcinogenic effect on spontaneous development of tumors with both of the animal genotypes investigated here.

Animals↗

PubMed2003

Significance of overexpression of metallothionein in mouse urinary bladder focal lesions induced by treatment with N-butyl-N-(4-hydroxybutyl)-nitrosamine.

Metallothionein (MT) is expressed in various types of human tumors, including transitional cell carcinomas of the urinary bladder, but its biological significance remains unclear. In the present study, the role of MT in urinary bladder carcinogenesis induced by N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) treatment was investigated using C57BL/6 mice. One hundred 5-week-old male C57BL/6 mice were divided into two groups, which were given drinking water with or without 0.05% BBN throughout the experimental period. Subgroups of ten animals from each group were sacrificed at weeks 5, 10, 15, 20 and 25, and urinary bladder samples were examined immunohistochemically for MT, proliferating cell nuclear antigen (PCNA) and apoptosis. MT was found to be abundant in normal-looking mucosa, but decreased with progression from precancerous lesions to invasive carcinoma in the urinary bladder obtained from BBN-treated mice. Lesions could be divided into MT-positive and negative. There was a tendency for greater MT expression in PCNA-positive lesions, while apoptosis was rather associated with MT-negativity. These data suggest that the overexpression of MT may play a role in mouse urinary bladder carcinogenesis.

Animals↗

PubMed2003

Urinary bladder lesions induced by persistent chronic low-dose ionizing radiation.

The incidence of urinary bladder cancer in the Ukraine increased from 26.2 to 43.3 per 100,000 population between 1986 and 2001 after the Chernobyl accident. The present study was conducted to evaluate the development of radiation-dependent lesions in the urinary bladders of people living in cesium 137 ((137)Cs) radio-contaminated areas of the Ukraine. Bladder urothelial biopsies from 159 male and 5 female patients were subjected to histological examination and immunohistochemical study of p38 mitogen-activated protein kinase (MAPK), as well as the p50 and p65 subunits of nuclear factor kappa B (NF-kappa B). A pattern of chronic proliferative atypical cystitis accompanied with large areas of sclerosis of connective tissue in the lamina propria was commonly observed in all cases. Interestingly, these lesions were associated with a dramatic increase in the incidences of dysplasia/carcinoma in situ, and, moreover, small urothelial carcinomas were incidentally detected. We defined the overall condition as "Chernobyl cystitis." Greatly elevated levels of p38, p65 and p50 expression in the urothelium were evident and the patients showed increased (137)Cs in urine. The data support conclusions from our previous studies of a critical role for increased oxidative stress in generation of urinary bladder urothelial lesions in individuals chronically exposed to low-dose (137)Cs radiation. Alterations in the p38 MAPK cascade and accumulation of NF-kappa B subunits could be crucial early molecular events in the pathogenesis of Chernobyl cystitis.

Adult↗

PubMed2002

Promoting effects of monomethylarsonic acid, dimethylarsinic acid and trimethylarsine oxide on induction of rat liver preneoplastic glutathione S-transferase placental form positive foci: a possible reactive oxygen species mechanism.

Dimethylarsinic acid (DMA) is a major metabolite of inorganic arsenicals, which are epidemiologically significant chemicals in relation to liver cancer in mammals. The present study was conducted to determine the promoting effects of organic arsenicals related to DMA [monomethylarsonic acid (MMA) and trimethylarsine oxide (TMAO)] on rat liver carcinogenesis using a liver medium-term bioassay (the Ito test). Male, 10-week-old, F344 rats were given a single i.p. injection of diethylnitrosamine at a dose of 200 mg/kg b.w. as an initiator. Starting 2 weeks thereafter they received 100 ppm of MMA, DMA or TMAO in their drinking water, or no supplement as a control, for 6 weeks. All animals underwent 2/3 partial hepatectomy in week 3 after initiation. Quantification of glutathione S-transferase placental form (GST-P)-positive foci as preneoplastic lesions in liver sections revealed significantly increased numbers and areas in all 3 treated groups compared with controls. Hepatic microsome cytochrome P-450 content was markedly increased with all 3 arsenic treatments. Markedly elevated CYP 2B1 protein levels and CYP 2B1/2 mRNA levels were thus observed in all cases. The potency of promotion was similar for MMA, DMA and TMAO. Since hydroxyradicals were found to be generated in the relatively early phase while methylated arsenicals were metabolized in liver, the resultant oxidative stress might have promoted lesion development.

8-Hydroxy-2'-Deoxyguanosine↗

PubMed2002

Etiology-specific gene expression profiles in rat mammary carcinomas.

Identification of etiology of human cancers is important for effective cancer prevention, and attempts to estimate the roles of a variety of environmental carcinogens in human cancers are being made. Here, we applied cDNA microarray technology to estimate whether gene expression profiles of cancers would reflect their etiology. Using rat mammary carcinoma models, expression profiles were analyzed in two groups of carcinomas induced by distinct carcinogens but with the same histological classification. Four carcinomas induced by 7,12-dimethylbenz[a]anthracene (DMBA) and three carcinomas induced by 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and a high-fat diet were analyzed by a GeneChip oligonucleotide microarray that contained approximately 8000 rat genes. By hierarchical clustering analysis, the seven carcinomas were classified into two groups that exactly coincided with the DMBA-induced and the PhIP-induced groups. The correlation coefficient between the two groups was 0.63, and those between any carcinomas within each group ranged from 0.78 to 0.95. In addition, characteristic clusters of genes were also identified that highlighted distinct and common characteristics of both groups. Seventeen genes were down-regulated in the DMBA and up-regulated in the PhIP-induced groups. Thirty-three genes were regulated in the opposite manner. Our results indicated that gene expression profiles in cancers reflect their etiology and suggested a possibility that etiology of cancers could be retrospectively estimated from their expression profiles.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed2002

Role of oxidative DNA damage caused by carbon tetrachloride-induced liver injury -- enhancement of MeIQ-induced glutathione S-transferase placental form-positive foci in rats.

The strong association between chronic inflammation and development of cancer is well-established in chronic inflammatory states. Nitric oxide (NO) is generated by inflammatory cytokines due to the action of inducible nitric oxide (iNOS), oxidizing DNA to form 8-hydroxy-2'-deoxyguanosine (8-OHdG) adducts, a major species of oxidative DNA damage. In the present study, we investigated the enhancing effect of carbon tetrachloride, a typical hepatotoxic chemical, on rat 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) hepato-carcinogenesis. A total of 420, 21-day-old, male Fisher 344 rats were given MeIQx at a concentration of 0, 0.001 ppm (human exposure level), 0.01, 0.1, 1, 10 and 100 ppm in the diet, and each group was separated into carbon tetrachloride-treated and vehicle-treated subgroups. Carbon tetrachloride was given by subcutaneous (s.c.) injection twice a week at a dose of 0.125 ml/kg body weight (b.w.) for the first 10 weeks and then at 0.25 ml/kg b.w. during the next 10 weeks. All rats were sacrificed at the end of week 22. In the vehicle-treated animals, only 100 ppm MeIQx significantly increased the number of glutathione S-transferase placental form (GST-P)-positive foci in the liver compared with 0 ppm MeIQx. Co-administration of carbon tetrachloride enhanced the induction of GST-P-positive foci by MeIQx in each group and the curve was almost the same pattern as that of vehicle-treated group but their numbers were significantly enhanced with 10 ppm and above compared with 0 ppm MeIQx. Persistent liver injury and liver cell proliferation were histopathologically observed in carbon tetrachloride-treated groups. Increase of 8-hydroxydeoxyguanosine (8-OHdG) formation and iNOS overexpression were observed by co-administration of carbon tetrachloride in MeIQx-treated rat liver. Our results indicate that carbon tetrachloride enhances MeIQx hepato-carcinogenicity through increase in oxidative DNA damage but non-effect levels of MeIQx carcinogenic activity still exist.

Animals↗

PubMed2002

Lack of promoting effect due to oral administration of dimethylarsinic acid on rat lung carcinogenesis initiated with N-bis(2-hydroxypropyl)nitrosamine.

Dimethylarsinic acid (DMA), a major metabolite of inorganic arsenics, and arsenic exposure is associated with tumor development in a wide variety of human tissues. In the present study, we examined whether DMA has tumor-promoting activity on rat lung carcinogenesis initiated with N-bis(2-hydroxypropyl)nitrosamine (DHPN). Male, 8-week-old, F344 rats were treated with DHPN at a concentration of 0.1% in drinking water for 1 week, and starting 1 week thereafter, DMA was administered at concentrations of 0, 100, 200 or 400 ppm in the drinking water for 30 weeks. Induction of epithelial lesions, classified as alveolar epithelial hyperplasia, adenoma, and adenocarcinoma was evident in the lungs of DHPN-initiated animals, but no significant differences were found between DMA-treated groups and control groups. Furthermore, no significant differences in 5-bromo-2'-deoxyuridine labeling indices, as a marker of cell proliferation were observed among the groups. An additional group treated with DMA at concentrations of 200 ppm alone, without prior DHPN initiation was found to develop no epithelial lesions in the lung. There was no significant gain in 8-hydroxydeoxyguanosine formation, as a marker of oxidative stress, in the lungs of rats treated with DMA in their drinking water. In conclusion, oral-administered DMA does not exert promoting effects on rat lung carcinogenesis initiated with DHPN.

8-Hydroxy-2'-Deoxyguanosine↗

PubMed2002

Lack of modification of rat hepatocarcinogenesis by fernane-type triterpenoids, isolated from a Euphorbia genus.

Inhibitors of topoisomerases, enzymes that produce an unusual type of DNA damage, are considered as antitumor agents. Recently it has been reported that the fernane-type triterpenoid EC-2 and its hydroxyl derivative, isolated from Euphorbia, are potent topoisomerase II inhibitors. In this study, the modifying effects of EC-2 and EC-4 on the development of putative preneoplastic lesions, glutathione S-transferase placental form (GST-P)-positive foci, in the liver of rats were investigated using a medium-term bioassay system. Fisher 344 male, 6-week-old rats were given a single intraperitoneal injection (200 mg/kg b.w.) of diethylnitrosamine or saline at the beginning of the experiment and subjected to 2/3 partial hepatectomy at the 3rd week. The test compounds were administered five times/week by i.g. gavage at a dose of 1 mg/kg b.w. from 2 to 8 weeks. Quantitation of the numbers and areas per cm(2) of induced GST-P positive foci did not demonstrated any significant differences among the groups and no variation in cell proliferation as indicated by 5-bromo- 2'-deoxyuridine (BrdU) labeling. Our results suggest that EC-2 and EC-4 have no modifying effects on rat hepatocarcinogenesis.

Animals↗

PubMed2002

DNA damage repair in bladder urothelium after the Chernobyl accident in Ukraine.

PURPOSE: We determined whether base and nucleotide excision repair is activated in bladder urothelium by chronic persistent low doses of ionizing radiation in male patients with benign prostate hyperplasia and females with chronic cystitis living more than 15 years in Cs contaminated areas after the Chernobyl accident in Ukraine. MATERIALS AND METHODS: Bladder urothelial biopsies from 204 patients were subjected to histological examination and biopsies from 35 were subjected to immunohistochemical study of 8-hydroxy-2'deoxyguanosine, 8-oxoguanine-DNA-glycosylase, apurinic/apyrimidinic endonuclease and xeroderma pigmentosum A endonuclease. RESULTS: Chronic proliferative atypical cystitis with multiple foci of dysplasia and carcinoma in situ were observed in 139 (89%) and in 91 (58%) of 156 group 1 patients from radio contaminated areas, respectively, as well as 10 small transitional cell carcinomas. Chronic cystitis with areas of dysplasia was detected in 9 of 48 patients (19%) in control group 2 from clean (without radio contamination) areas of Ukraine. Greatly elevated levels of 8-hydroxy-2'deoxyguanosine, 8-oxoguanine-DNA-glycosylase, apurinic/apyrimidinic endonuclease and xeroderma pigmentosum A were evident in the urothelium in group 1, accompanied by increased Cs in the urine. CONCLUSIONS: These findings support the hypothesis that significant activation of DNA damage repair (base and nucleotide excision repair) is induced by the oxidative stress generated by long-term low doses of ionizing radiation. The levels of DNA oxidative adducts pointing to mutagenic and carcinogenic potential were in line with the histopathologically diagnosed urothelial lesions.

8-Hydroxy-2'-Deoxyguanosine↗

PubMed2002

Different genetic alterations in rat forestomach tumors induced by genotoxic and non-genotoxic carcinogens.

Human beings are exposed to a multitude of carcinogens in their environment, and most cancers are considered to be chemically induced. Here we examined differences in genetic alterations in rat forestomach tumors induced by repeated exposure to a genotoxic carcinogen, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) or N-methylnitrosourethane (MNUR), and chronic treatment with a non-genotoxic carcinogen, butylated hydroxyanisole (BHA) or caffeic acid (CA). A total of 132, 6-week-old male F344 rats were employed. Forty rats were treated with MNNG by intragastric administration at a dose of 20 mg/kg body wt once a week for 32 weeks, and 20 rats received 20 p.p.m. MNUR in their drinking water for 48 weeks. Further groups of 20 animals were administered 2% BHA or 2% CA in the diet for 104 weeks. The remaining rats were maintained without any supplement as controls. Multiple forestomach tumors were observed in all rats of the MNNG-, MNUR-, BHA- and CA-treated groups. Histopathologically, MNUR- and CA-treated groups showed almost the same pattern. On polymerase chain reaction-single strand conformation polymorphism analysis, H-ras and p53 gene mutations were observed at high and relatively low frequencies, respectively, in forestomach tumors induced by MNNG and MNUR. Most H-ras gene mutations were G-->A transitions in codons 7 and 12 of exon 1. On the other hand, forestomach tumors due to the non-genotoxic carcinogens, BHA and CA, had almost no mutations of the H-ras and p53 genes. Moreover, relative overexpression of cyclin D1 and p53 was detected in forestomach tumors induced by the genotoxic carcinogens, while their non-genotoxic counterparts had a tendency to show low expression of those molecules. Mutations of the beta-catenin gene were not detected in any group. The present study demonstrates that rat forestomach tumors induced by genotoxic and non-genotoxic carcinogens have different underlying genetic alterations, even if their pathological features are similar.

Animals↗

PubMed2002

Formation of 8-hydroxydeoxyguanosine and cell-cycle arrest in the rat liver via generation of oxidative stress by phenobarbital: association with expression profiles of p21(WAF1/Cip1), cyclin D1 and Ogg1.

To evaluate the risk of exposure to so-called non-genotoxic chemicals and elucidate mechanisms underlying their promoting activity on rat liver carcinogenesis the formation of 8-hydroxy-2'-deoxyguanosine (8-OHdG), cytochrome P-450 (P-450) and hydroxyl radicals induction, DNA repair and alteration to cellular proliferation and apoptosis in the rat liver were investigated during 2 weeks of phenobarbital (PB) administration at a dose of 0.05%. Significant increase of hydroxyl radical levels by day 4 of PB exposure accompanied the accumulation of 8-OHdG in the nucleus and P-450 isoenzymes CYP2B1/2 and CYP3A2 in the cytoplasm of hepatocytes. Conspicuous elevation of 8-OHdG and apoptosis in the liver tissue were associated with reduction of the proliferating cell nuclear antigen (PCNA) index after 8 days of PB application. Thereafter, 8-OHdG levels decreased with an increase in mRNA expression for the 8-OHdG repair enzyme, DNA glycosylase 1 (Ogg1). Analysis with LightCycler quantitative 2-step RT-PCR demonstrated induction of cyclin D1 (CD1) and p21(WAF1/Cip1) mRNA expression on days 4 and 6, respectively, preceding marked elevation of PCNA and apoptotic indices. These results suggest that similar to genotoxic, non-genotoxic chemicals might induce reversible alteration to nuclear 8-OHdG in the rat liver after several days of continuous application; however, by a different mechanism. Increased 8-OHdG formation is caused by developing oxidative stress or apoptotic degradation of DNA and coordinated with enhanced expression of CD1 mRNA and cell proliferation, subsequent increase of p21(WAF1/Cip1) mRNA expression, cell-cycle arrest and apoptosis, while activation of 8-OHdG repair mechanisms contributes to protection of tissue against reactive oxygen species-induced cell death.

8-Hydroxy-2'-Deoxyguanosine↗

PubMed2002

Carcinogenicity of dimethylarsinic acid in male F344 rats and genetic alterations in induced urinary bladder tumors.

Arsenic is a well-documented human carcinogen, and contamination with this heavy metal is of global concern, presenting a major issue in environmental health. However, the mechanism by which arsenic induces cancer is unknown, in large part due to the lack of an appropriate animal model. In the present set of experiments, we focused on dimethylarsinic acid (DMA), a major metabolite of arsenic in most mammals including humans. We provide, for the first time, the full data, including detailed pathology, of the carcinogenicity of DMA in male F344 rats in a 2-year bioassay, along with the first assessment of the genetic alteration patterns in the induced rat urinary bladder tumors. Additionally, to test the hypothesis that reactive oxygen species (ROS) may play a role in DMA carcinogenesis, 8-hydroxy-2'-deoxyguanosine (8-OHdG) formation in urinary bladder was examined. In experiment 1, a total of 144 male F344 rats at 10 weeks of age were randomly divided into four groups that received DMA at concentrations of 0, 12.5, 50 and 200 p.p.m. in the drinking water, respectively, for 104 weeks. From weeks 97-104, urinary bladder tumors were observed in 8 of 31 and 12 of 31 rats in groups treated with 50 and 200 p.p.m. DMA, respectively, and the preneoplastic lesion, papillary or nodular hyperplasias (PN hyperplasia), was noted in 12 and 14 rats, respectively. DMA treatment did not cause tumors in other organs and no urinary bladder tumors or preneoplastic lesions were evident in the 0 and 12.5 p.p.m.-treated groups. Urinary levels of arsenicals increased significantly in a dose-responsive manner except for arsenobetaine (AsBe). DMA and trimethylarsine oxide (TMAO) were the major compounds detected in the urine, with small amounts of monomethylarsonic acid (MMA) and tetramethylarsonium (TeMa) also detected. Significantly increased 5-bromo-2'-deoxyuridine (BrdU) labeling indices were observed in the morphologically normal epithelium of the groups treated with 50 and 200 p.p.m. DMA. Mutation analysis showed that DMA-induced rat urinary bladder tumors had a low rate of H-ras mutations (2 of 20, 10%). No alterations of the p53, K-ras or beta-catenin genes were detected. Only one TCC (6%) demonstrated nuclear accumulation of p53 protein by immunohistochemistry. In 16 of 18 (89%) of the TTCs and 3 of 4 (75%) of the papillomas, decreased p27(kip1) expression could be demonstrated. Cyclin D1 overexpression was observed in 26 of 47 (55%) PN hyperplasias, 3 of 4 (75%) papillomas, and 10 of 18 (56%) TCCs. As a molecular marker of oxidative stress, increased COX-2 expression was noted in 17 of 18 (94%) TCCs, 4 of 4 (100%) papillomas, and 39 of 47 (83%) PN hyperplasias. In experiment 2, 8-OHdG formation in urinary bladder was significantly increased after treatment with 200 p.p.m. DMA in the drinking water for 2 weeks compared with the controls. The studies demonstrated DMA to be a carcinogen for the rat urinary bladder and suggested that DMA exposure may be relevant to the carcinogenic risk of inorganic arsenic in humans. Diverse genetic alterations observed in DMA-induced urinary bladder tumors imply that multiple genes are involved in stages of DMA-induced tumor development. Furthermore, generation of ROS is likely to play an important role in the early stages of DMA carcinogenesis.

8-Hydroxy-2'-Deoxyguanosine↗

PubMed2002

Induction of tumors in the colon and liver of the immunodeficient (SCID) mouse by 2-amino-3-methylimidazo[4,5-f ]quinoline (IQ)-modulation by long-chain fatty acids.

We have recently shown that immunodeficient (SCID) mice, which lack functional T and B cells, are highly susceptible to low dose site specific induction of colon aberrant crypt foci (ACF), surrogates for colon tumors, by 2-amino-3-methylimidazo[4,5-f ]quinoline (IQ). To test whether long-term exposure to a high dose in the diet might prove carcinogenic to the SCID mouse colon, in contrast to other mice strains tested to date, the compound was administered at 300 p.p.m. in the diet to female 6-7-week-old SCID mice for 32 weeks. IQ induced high numbers of ACF, hyperplastic polyps, dysplasia, and colon adenomas, as well as hepatocellular altered foci and liver adenomas. Induction of colon tumors did not correlate with the main sites where ACF developed, the proximal colon, however, being seen mainly in the mid and distal colon. Induction of colon tumors correlated significantly with the incidence of dysplasia, crypt height, the mitotic index, cell proliferation and numbers of 8-hydroxydeoxyguanosine (8-OHdG)-positive cells in the colon crypt, particularly in mid and distal colon. Administration of 20% omega-6 polyunsaturated fatty acids (corn oil), omega-3 polyunsaturated fatty acids (perilla oil), or monounsaturated fatty acids (olive oil) simultaneously with IQ in the diet resulted in: (i) inhibition of colon and liver tumor induction by corn and perilla oil, whereas olive oil showed no effects; (ii) no reduction in total numbers of ACF by corn oil or perilla oil but significant suppression in the olive oil treated group; (iii) inhibition of tumor development particularly by omega-3 polyunsaturated fatty acids in perilla oil, correlating significantly with decreased cell proliferation in both colon and liver and a marked decrease in crypt heights and mitotic indices. Selective reduction in the numbers of 8-OHdG-positive nuclei, mainly in the middle and distal colon crypts, was also found to correlate with tumor inhibition. Thus, the results indicate carcinogenicity of IQ in the colon of the SCID mouse and preventive effects of polyunsaturated fatty acids.

8-Hydroxy-2'-Deoxyguanosine↗