Target organ specificity of cell proliferation induced by various carcinogens

Chemopreventive Potential of Phyllanthus emblica Fruit Extract against Colon and Liver Cancer Using a Dual-Organ Rat Carcinogenesis Model

Humans are frequently exposed to various carcinogens capable of inducing cancer in multiple organs. Phyllanthus emblica (P. emblica) is known for its strong antioxidant properties and potential in cancer prevention. However, its effectiveness against combined carcinogens remains relatively unexplored. This study aimed to assess the chemopreventive potential of the ethanolic extract of P. emblica fruits against preneoplastic lesions in the liver and colon using a rat model. Rats were administered with diethylnitrosamine (DEN) and 1,2-dimethylhydrazine (DMH) to induce hepato- and colon carcinogenesis, respectively. The ethanolic extract of P. emblica fruit at 100 and 500 mg/kg bw significantly reduced the number of preneoplastic lesions in the liver by 74.7% and 55.6%, respectively, and in the colon by 39.2% and 40.8%, respectively. Similarly, the extract decreased the size of preneoplastic lesions in the liver by 75.2% (100 mg/kg bw) and 70.6% (500 mg/kg bw). Furthermore, the extract significantly reduced the cell proliferation marker in the liver by 70.3% (100 mg/kg bw) and 61.54% (500 mg/kg bw), and in the colon by 62.7% (100 mg/kg bw) and 60.5% (500 mg/kg bw). The ethanolic extract also enhanced liver antioxidant enzyme activities and demonstrated free radical scavenging in DPPH, ABTS, and FRAP assays. Additionally, the dichloromethane fraction of P. emblica showed significant cancer prevention potential by reducing intracellular ROS and NO production by 61.7% and 35.4%, respectively, in RAW 264.7 macrophages. It also exhibited antimutagenic effects with a reduction of 54.0% against aflatoxin B1 and 52.3% against 2-amino-3,4-dimethylimidazo[4,5-f]quinoline-induced mutagenesis in Salmonella typhimurium. Finally, this study highlights the chemopreventive activity of P. emblica fruit extract against the initiation of early-stage carcinogenic lesions in the liver and colon in rats treated with dual carcinogens.

Increased Cell Proliferation as a Key Event in Chemical Carcinogenesis: Application in an Integrated Approach for the Testing and Assessment of Non-Genotoxic Carcinogenesis

In contrast to genotoxic carcinogens, there are currently no internationally agreed upon regulatory tools for identifying non-genotoxic carcinogens of human relevance. The rodent cancer bioassay is only used in certain regulatory sectors and is criticized for its limited predictive power for human cancer risk. Cancer is due to genetic errors occurring in single cells. The risk of cancer is higher when there is an increase in the number of errors per replication (genotoxic agents) or in the number of replications (cell proliferation-inducing agents). The default regulatory approach for genotoxic agents whereby no threshold is set is reasonably conservative. However, non-genotoxic carcinogens cannot be regulated in the same way since increased cell proliferation has a clear threshold. An integrated approach for the testing and assessment (IATA) of non-genotoxic carcinogens is under development at the OECD, considering learnings from the regulatory assessment of data-rich substances such as agrochemicals. The aim is to achieve an endorsed IATA that predicts human cancer better than the rodent cancer bioassay, using methodologies that equally or better protect human health and are superior from the view of animal welfare/efficiency. This paper describes the technical opportunities available to assess cell proliferation as the central gateway of an IATA for non-genotoxic carcinogenicity.

Enhanced Susceptibility of Ogg1 Mutant Mice to Multiorgan Carcinogenesis

The role of deficiency of oxoguanine glycosylase 1 (Ogg1) Mmh homolog, a repair enzyme of the 8-hydroxy-2’-deoxyguanosine (8-OHdG) residue in DNA, was investigated using the multiorgan carcinogenesis bioassay in mice. A total of 80 male and female six-week-old mice of C57BL/6J background carrying a mutant Mmh allele of the Mmh/Ogg1 gene (Ogg1^−/−) and wild type (Ogg1^+/+) mice were administered N-diethylnitrosamine (DEN), N-methyl-N-nitrosourea (MNU), N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN), N-bis (2-hydroxypropyl) nitrosamine (DHPN) and 1,2-dimethylhydrazine dihydrochloride (DMH) (DMBDD) to induce carcinogenesis in multiple organs, and observed up to 34 weeks. Significant increase of lung adenocarcinomas incidence was observed in DMBDD-treated Ogg1^−/− male mice, but not in DMBDD-administered Ogg1^+/+ animals. Furthermore, incidences of lung adenomas were significantly elevated in both Ogg1^−/− males and females as compared with respective Ogg1^−/− control and DMBDD-treated Ogg1^+/+ groups. Incidence of total liver tumors (hepatocellular adenomas, hemangiomas and hemangiosarcomas) was significantly higher in the DMBDD-administered Ogg1^−/− males and females. In addition, in DMBDD-treated male Ogg1^−/− mice, incidences of colon adenomas and total colon tumors showed a trend and a significant increase, respectively, along with significant rise in incidence of simple hyperplasia of the urinary bladder, and a trend to increase for renal tubules hyperplasia in the kidney. Furthermore, incidence of squamous cell hyperplasia in the forestomach of DMBDD-treated Ogg1^−/− male mice was significantly higher than that of Ogg1^+/+ males. Incidence of small intestine adenomas in DMBDD Ogg1^−/− groups showed a trend for increase, as compared to the wild type mice. The current results demonstrated increased susceptibility of Ogg1 mutant mice to the multiorgan carcinogenesis induced by DMBDD. The present bioassay could become a useful tool to examine the influence of various targets on mouse carcinogenesis.

Arachidonate-enriched triglyceride oil does not promote tumor development in a rat medium-term multi-organ carcinogenesis model

The modifying potential on tumor development of arachidonate-enriched triglyceride oil (ARA-oil) containing approximately 40% arachidonic acid was investigated in a medium-term multi-organ carcinogenesis bioassay using male and female F344 rats. The animals were sequentially given five carcinogens with different target sites in the first 4 weeks, and then administered ARA-oil for 24 weeks at dietary levels of 0% (control), 1.25%, 2.5% or 5.0%. No statistically significant differences in incidences and multiplicities of hyperplastic and neoplastic lesions were showed in the large intestine in either sex. In the liver, kidney, and lung in both sexes, and the mammary gland and uterus in females, tumor promoting potential was not evident with ARA-oil treatment. ARA-oil did not affect the quantitative data for glutathione S-transferase placental form positive foci of the liver. Increased induction of hyperplastic or neoplastic lesions in the urinary bladder and thyroid in ARA-oil-treated groups was without dose dependence. In addition, a second experiment with ARA-oil only administration for 8-week revealed no effects on cellular proliferation in the urinary bladder or thyroid in either sex. These results indicate that ARA-oil has no tumor promoting potential in any organs or tissues initiated with the five carcinogens applied in the present study.

No enhancing effects of diacylglycerol oil on tumor development in a medium-term multi-organ carcinogenesis bioassay using male F344 rats

The modifying potential of diacylglycerol (DAG) oil on tumor development was investigated in a medium-term multi-organ carcinogenesis bioassay. DAG oil is a cooking oil that contains >80% diglycerides, <20% triglycerides and <5% monoglycerides. Male 6-week-old F344 rats (20 in each group) were sequentially treated with five carcinogens for initiation in different organ target sites for 4 weeks (DMBDD treatment), and then administered DAG oil at dietary levels of 0% (control), 1.375%, 2.75% or 5.5% [triacylglycerol (TGs), with the same fatty acid composition as DAG oil were also added at dietary levels of 5.5%, 4.125%, 2.75% and 0%, respectively, to maintain the same lipid level], or 5.5% high linoleic acid TG (HLTG), 5.5% high oleic acid TG (HOTG), or 5.5% medium-chain TG (MCTG) (as reference substances, mostly consisting of triacylglycerols) admixed into AIN-93G semi-synthetic diet, for an additional 24 weeks. Controls received standard diet without any supplementation as non-treated control. All animals were killed at the end of week 28, and the major organs were carefully examined for preneoplastic and neoplastic lesions. No DAG oil treatment-related changes were noted in survival, general conditions, body weights, food consumption and organ weights. Upon quantitative analysis of glutathione S-transferase placental form (GST-P) positive foci of the liver, DAG oil was not found to exert any effects. The incidence of colon adenomas was significantly increased in rats given 1.375% DAG oil, but not 2.75% and 5.5% DAG oil, when compared to the control (5.5% TG group) value. Furthermore, incidences and multiplicity of hyperplasias and adenomas and/or adenocarcinomas were comparable across all DAG oil-treated groups. In contrast, incidences of colon adenomas and/or adenocarcinomas were significantly increased in rats given 5.5% HOTG, and adenomas with MCTG, but not 5.5% HLTG, as compared to the 5.5% TG value. Preneoplastic and neoplastic lesions induced by DMBDD treatment in various organs other than the large intestine were comparable in all cases. Thus, the current results indicate that DAG oil may not exert modifying potential on tumor development, even in the colon because of the lack of dose-dependence. DAG oil was equivalent to HOTG (standard cocking oil composed of naturally occurring fatty acids), with regard to colon tumor development. Further dose-response study concerning HOTG may be needed to confirm whether the enhancing effect of large intestine carcinogenesis exert or not.

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.

Thymic lymphomas in Wistar rats exposed to N-methyl-N-nitrosourea (MNU)

The Brazilian Agency for the Environment (IBAMA) recently adopted an alternative medium-term multiple-organ assay system with the Wistar rat strain for detection of the carcinogenic potential of pesticides. Originally, this initiation-promotion protocol was established in Japan with the isogenic Fischer 344 male rat. Among the initiating agents used in that assay, N-methyl-N-nitrosourea (MNU) rapidly induces malignant lymphoma and leukemia and early mortality of rats from different strains. This study was developed to evaluate whether the outbred Wistar rats are also similarly susceptible to MNU. Particularly, it aimed to evaluate the dose-response relationship and to register the MNU-induced pre-neoplasia and neoplasia that may develop in the lympho-hematopoietic system (LHS) of the Wistar rat within a medium-term period. Four groups of male Wistar rats were treated during 2 weeks with vehicle or with MNU (80, 160 or 240 mg/kg body weight, i.p.). After sacrifice at the 12th and 20th weeks, the thymus, spleen, bone marrow, cervical and mesenteric lymph nodes and liver were collected for analysis. At the 20th week, LHS malignant tumors and benign vascular tumors occurred only in the high- and intermediate-dose MNU-treated animals. Four animals treated with 240 mg/kg developed diffuse thymic lymphomas; two others, treated respectively with 240 mg/kg and 160 mg/kg, developed spleen hemangiomas. The present observations indicate that the Wistar strain is as susceptible as other strains to the early development of MNU-induced LHS (pre)neoplasia. Therefore, this strain seems suitable to be used as test system in bioassay protocols that adopt MNU as an initiating agent for carcinogenesis.

Induction of lung lesions in female rats following chronic exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin

2,3,7,8,-Tetrachlorodibenzo-p-dioxin (TCDD) has been classified as a known human carcinogen, and epidemiologic studies identify the lung as one of the target organs. Few experimental studies have attempted to characterize pulmonary effects of TCDD exposure. In this study, we characterize the induction of lesions in the lung by chronic oral TCDD exposure in diethylnitrosamine (DEN)-initiated or noninitiated female Sprague-Dawley rats. Two or 18 weeks after initiation, rats were treated with TCDD continuously for 14, 30, or 60 weeks by biweekly oral gavage (1,750 ng TCDD/kg) at a dose equivalent to 125 ng/kg body weight per day (controls received corn oil). To assess the time dependence and reversibility of potential changes, some groups included withdrawal periods of 16 or 30 weeks after 30 weeks of TCDD treatment. TCDD treatment alone for 60 weeks caused significant increases in alveolar-bronchiolar (AB) metaplasia. TCDD treatment of DEN-initiated animals for 60 weeks resulted in a significant increase in bronchiolar epithelial hyperplasia. These increases were not observed in animals treated with TCDD for 30 weeks followed by corn oil for 30 weeks, indicating that the development of these lesions required continuous exposure to TCDD. AB hyperplasia increased in an age-dependent manner after DEN initiation but was unaffected by TCDD treatment. Expression of the aromatic hydrocarbon receptor (AHR) and induction of CYP1A1 was observed only in bronchiolar Clara and ciliated cells, indicating that the mechanism of induction of AB metaplasia may be mediated by the AHR. TCDD elimination half-life was monophasic in the lung, and serum and was estimated to be 39.7 days and 44.6 days, respectively, independent of age, tissue TCDD concentration, or body weight. This is the first report to identify the AB region as a target for TCDD-induced metaplastic and proliferative changes after chronic oral exposure.

Hepatocarcinogenic activity of N-butyl-N-(4-hydroxybutyl)nitrosamine in rats is not modified by sodium L-ascorbate

Male F344 and Wistar Shionogi (WS) rats were treated with 0.05% N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) for 20 weeks and then killed at week 36 (experiment 1). Although reduction of body weight increase was found, no effects on liver weights were noted. Formalin-fixed and paraffin-embedded liver tissues from rats killed terminally were cut and stained for glutathione S-transferase placental form (GST-P) immunohistochemically. Marked elevation of quantitative values of small GST-P positive (GST-P+) foci were apparent in both strains of rat administered BBN. In experiment 2, both sexes of F344 rats were given 0.05% BBN in the drinking water for 4 weeks and then fed diet containing 0 or 5.0% sodium L-ascorbate (SA) for 32 weeks. No body and liver weight changes were evident in any group. Quantitative values for small GST-P+ foci were increased in both sexes of rats exposed to BBN but were not modified by additional SA treatment. Thus, it was confirmed that the selective bladder carcinogen BBN also acts as a liver carcinogen. These results, from the quantitative analysis of small GST-P+ foci as end point marker lesions, indicate that the liver tumor modifying potential of test chemicals can be evaluated in rats by using an initiation/promotion protocol for urinary bladder carcinogenesis.

Dose- and sex-related carcinogenesis by N-bis(2-hydroxypropyl)nitrosamine in Wistar rats

An initiation-promotion medium-term bioassay for detection of chemical carcinogens, developed in the male F344 rat, uses 0.1% N-bis(2-hydroxypropyl)nitrosamine (DHPN) among five genotoxic chemicals for the initiation of carcinogenesis in multiple organs. To establish this bioassay in the Wistar strain, the effects of two dose levels of DHPN were evaluated on the main DHPN rat target organs: lung, thyroid gland, kidneys and liver. Four groups of male and female animals were studied: Control -- untreated group; Multi-organ initiated group (also referred to as DMBDD, based on the initials of the five initiators) -- treated sequentially with N-diethylnitrosamine (DEN, i.p.), N-methyl-N-nitrosourea (MNU, i.p.), N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN, drinking water), N, N'-dimethylhydrazine (DMH, s.c.) and DHPN (drinking water) for 4 weeks; a third group treated with 0.1% DHPN in drinking water for 2 weeks and the last group treated with 0.2% DHPN in drinking water for 4 weeks. The animals were sacrificed after 30 weeks. DHPN at 0. 2% induced preneoplasia in the liver and kidneys of rats of both sexes, the number and area of the putative preneoplastic liver glutathione S-transferase-positive hepatocyte foci being significantly increased in these animals. It also induced benign and malignant tumors in female and in male rats. However, there was no relationship between the increased incidence of preneoplastic lesions and tumor development in the 0.2% DHPN-exposed groups of both sexes. DHPN at 0.1% induced only a few preneoplastic lesions in the liver and kidney and no tumors in both male and female rats. A clear dose and sex-related carcinogenic activity of DHPN was registered, although Wistar rats of both sexes showed a relative resistance to the carcinogenic activity of this compound.

Summation of initiation activities of low doses of the non-hepatocarcinogen 1,2-dimethylhydrazine in the liver after carbon tetrachloride administration

Summation of initiation by low doses of the indirect-acting non-hepatocarcinogen, 1,2-dimethylhydrazine (DMH) after proliferative stimulation with a necrogenic dose of carbon tetrachloride (CCl4) was investigated in terms of the induction of glutathione S-transferase placental form (GST-P) positive liver cell foci. Cell kinetics of liver after CCl4 i.g. treatment were examined with bromodeoxyuridine (BrdU) labeling (experiment I). To assess the correlation between cell proliferation and induction of liver cell foci, DMH (10 mg/kg i.g.) was administrated to 7-week-old male F344 rats at 12, 24, 36, 48, 60, 96 h after CCl4 i.g. and initiated populations expanded using the resistant hepatocyte model (experiment IIA). Subsequently, effects of repeated administration (10 mg/kg, four times, i.g.) of DMH were compared with the results of a single administration (40 mg/ kg, i.g.) with the same total dose (experiment IIB). In experiments I and IIA, the numbers and areas of GST-P-positive foci increased with the BrdU labeling index at the time of DMH treatment (maximum after 60 h). In experiment HB, repeated exposure of DMH at 10 mg/kg, four times resulted in significant (P<0.05) increase in number and area of GST-P-positive foci compared with the single administration (40 mg/kg). Thus, multiple low dose treatments during cell proliferation might be most effective for detection of weak initiation activity.