EFFECT OF ROUTE OF ADMINISTRATION ON THE CARCINOGENIC ACTION OF DIETHYLNITROSAMINE (N-NITROSODIETHYLAMINE)

Systemic Carcinogens (N-Nitroso Compounds) and Synergistic or Additive Effects in Respiratory Carcinogenesis

Systemic carcinogens induce respiratory tract tumors in various animals species. Typical examples of systemic carcinogens are the N-nitroso compounds, which require metabolic conversion to exert their carcinogenic effect. In this review particular emphasis is put on the comparative studies performed in the same species with different nitrosamines, providing an experimental model in which is possible to examine and correlate the biochemical changes preceding the development of detectable tumors and the carcinogenic effect. In addition studies describing synergistic or additive effects in respiratory carcinogenesis are reviewed and discussed.

Nasal Tumorigenesis in B6C3F1 Mice Following Intraperitoneal Diethylnitrosamine

Diethylnitrosamine (DEN) is a chemical broadly used in animal models as a hepatocarcinogen, reported to also cause pulmonary neoplasms in mice. The original objective was to evaluate the impact of a Western diet with or without 10% broccoli on DEN-induced on liver cancer. We administered DEN (45 mg/kg) intraperitoneally to young adult male B6C3F1 mice by 6 weekly injections and evaluated liver cancer 6 months after the DEN treatments. Here, we report unexpected primary tumorigenesis in nasal epithelium, independent of dietary treatment. More than 50% of DEN-treated B6C3F1 mice developed nasal neoplasm-related lesions, not reported previously in the literature. Only one of these neoplasms was visible externally prior to postmortem examination. Intraperitoneal DEN treatment used as a model for liver cancer can have a carcinogenic effect on the nasal epithelium in B6C3F1 mice, which should be carefully monitored in future liver cancer studies.

Tea polyphenols EGCG and TF restrict tongue and liver carcinogenesis simultaneously induced by N-nitrosodiethylamine in mice

The aim of this study is to understand the molecular mechanisms of N-nitrosodiethylamine (NDEA) induced multi-organ carcinogenesis in tongue and liver of the same mouse and restriction of carcinogenesis by Epigallocatechin gallate (EGCG) and Theaflavin (TF), if any. For that purpose, cellular proliferation/apoptosis, prevalence of CD44 positive stem cell population and expressions of some key regulatory genes of self renewal Wnt and Hedgehog (Hh) pathways and some of their associated genes were analyzed in the NDEA induced tongue and liver lesions in absence or presence of EGCG/TF. Chronic NDEA exposure in oral cavity could decrease mice body weights and induce tongue and liver carcinogenesis with similar histological stages (severe dysplasia up to 30thweeks of NDEA administration). Increasing mice body weights were seen in continuous and post EGCG/TF treated groups. EGCG/TF treatment could restrict both the carcinogenesis at similar histological stages showing potential chemopreventive effect in continuous treated groups (mild dysplasia) followed by pre treatment (moderate dysplasia) and therapeutic efficacy in post treated groups (mild dysplasia) up to 30thweek. The mechanism of carcinogenesis by NDEA and restriction by the EGCG/TF in both tongue and liver were similar and found to be associated with modulation in cellular proliferation/apoptosis and prevalence of CD44 positive population. The up-regulation of self renewal Wnt/β-catenin, Hh/Gli1 pathways and their associated genes Cyclin D1, cMyc and EGFR along with down regulation of E-cadherin seen during the carcinogenesis processes were found to be modulated during the restriction processes by EGCG/TF.

Kupffer Cell Metabolism and Function

Kupffer cells are resident liver macrophages and play a critical role in maintaining liver functions. Under physiological conditions, they are the first innate immune cells and protect the liver from bacterial infections. Under pathological conditions, they are activated by different components and can differentiate into M1-like (classical) or M2-like (alternative) macrophages. The metabolism of classical or alternative activated Kupffer cells will determine their functions in liver damage. Special functions and metabolism of Kupffer cells suggest that they are an attractive target for therapy of liver inflammation and related diseases, including cancer and infectious diseases. Here we review the different types of Kupffer cells and their metabolism and functions in physiological and pathological conditions.

Nasal cytotoxic and carcinogenic activities of systemically distributed organic chemicals

Toxicity and carcinogenicity in the mucosa of the nasal passages in rodents has been produced by a variety of organic chemicals which are systemically distributed. In this review, 14 such chemicals or classes were identified that produced rodent nasal cytotoxicity, but not carcinogenicity, and 11 were identified that produced nasal carcinogenicity. Most chemicals that affect the nasal mucosa were either concentrated in that tissue or readily activated there, or both. All chemicals with effects in the nasal mucosa that were DNA-reactive, were also carcinogenic, if adequately tested. None of the rodent nasal cytotoxins has been identified as a human systemic nasal toxin. This may reflect the lesser biotransformation activity of human nasal mucosa compared to rodent and the much lower levels of human exposures. None of the rodent carcinogens lacking DNA reactivity has been identified as a nasal carcinogen or other cancer hazard to humans. Some DNA-reactive rodent carcinogens that affect the nasal mucosa, as well as other tissues, have been associated with cancer at various sites in humans, but not the nasal cavity. Thus, findings in only the rodent nasal mucosa do not necessarily predict either a toxic or carcinogenic hazard to that tissue in humans.

Metabolism-dependent activation and toxicity of chemicals in nasal glands

The mucosae of the nasal passages contain a large amount of glands which express secretory proteins as well as phase I and phase II biotransformation enzymes. In this review the metabolic activation, covalent binding and toxicity of chemicals in the Bowman's glands in the olfactory mucosa, in the sero-mucous glands in the nasal septum and in the lateral nasal glands and maxillary glands around the maxillary sinuses are discussed. Light microscopic autoradiographic studies have demonstrated a selective covalent binding of nasal toxicants and carcinogens such as halogenated hydrocarbons and N-nitrosamines, especially in the Bowman's glands following a single systemic exposure, suggesting a high rate of metabolic activation of chemicals in these glands. Special attention is put on the herbicide dichlobenil which induces necrosis in the olfactory mucosa following a cytochrome-P450-mediated metabolic activation and covalent binding in the Bowman's glands.

Induction of carcinomas and sarcomas by 9,10-dimethyl-1,2-benzanthracene administration into the hamster maxillary sinus

To determine whether the local administration of 9,10-dimethyl-1,2-benzanthracene (DMBA) into the hamster maxillary sinus induced carcinoma at the injected site, hamsters were injected with 30 microliters of 0.5% solution of DMBA in dimethyl sulfoxide (DMSO) through the infraorbital foramen into the maxillary sinus once weekly for 10 weeks (Group 2). Another group of hamsters (Group 1) received similar injections of 30 microliters of DMSO only. In a third group of animals (Group 3), a roll of oxycellulose was inserted into the maxillary sinus and 40 microliters of a 2% solution of DMBA in DMSO was injected once. Sinonasal carcinomas were demonstrated in 73% (8/11) of the hamsters in Group 2 and sarcomas were shown in 73% (8/11) of the hamsters in Group 3, as well as some carcinomas. No tumors were seen in the Group 1 hamsters. Histologic examination revealed squamous cell carcinomas arising from the surface epithelium and submucous glands of the nasal cavity and maxillary sinus. These findings indicate that the intrasinal administration of a 0.5% solution of DMBA in DMSO is a reliable method for inducing maxillary sinus cancer.

Modulation of N-nitrosodiethylamine-induced hamster lung tumors by ozone

Male Syrian Golden hamsters were treated with subcutaneous injections of N-nitrosodiethylamine (DEN), 20 mg/kg, twice a week for 24 weeks. Half the animals were kept in filtered air and the other half was exposed continuously to an atmosphere of 0.8 ppm of ozone. After 6 months, no more DEN injections were given and all animals were kept in air until termination of the experiment at 7 months. It was found that the animals kept in ozone developed half as many peripheral lung tumors as did the animals kept in air; however, the difference was not statistically significant. Tumors of the trachea, bronchi, nasal cavity and liver developed with the same incidence whether the animals were exposed to ozone or not. It was concluded that ozone, an agent known to produce cell proliferation in the respiratory tract, does not enhance the development of tumors in the peripheral lung or in the nasal cavity of hamsters.

Nonneoplastic changes in the olfactory epithelium--experimental studies

Interest in the olfactory mucosa has increased in recent years, since it has been shown to possess a considerable amount of cytochrome P-450-dependent monooxygenase activity and a wide variety of chemicals have been identified as olfactory toxins. Many chemicals induce lesions of a general nature in the olfactory mucosa, i.e., inflammation, degeneration, regeneration, and proliferation, whereas others cause more specific effects. Changes in the olfactory mucosa with reference to chemicals that initiate them are reviewed in this paper. Studies with 3-trifluoromethyl pyridine (3FMP) illustrate some of these general changes and show the importance of examining the olfactory mucosa at early time periods. The earliest damage seen by light microscopy was 6 hr after a single inhalation exposure to 3FMP, and by day 3, early regenerative changes were observed. Changes were seen by electron microscopy 30 min after an oral dose, and the primary site of toxicity appeared to be the Bowman's glands. Although atrophy of nerve bundles in the lamina propria would be the expected consequence of severe necrosis of the sensory cells, this is not always the case. Exposure to irritants such as acetaldehyde, formaldehyde, and dimethylamine results in nerve bundle atrophy, but with chemicals such as 3FMP, 3-methylindole, and 3-methylfuran--which are activated by mixed-function oxidases--the nerve bundles remain intact. Future work, including metabolism studies, will provide information on the mode of action of these chemicals.

Generation of high yields of Syrian hamster cholangiocellular carcinomas and hepatocellular nodules by combined nitrite and aminopyrine administration and Opisthorchis viverrini infection

Combined administration of 0.1% nitrite and 0.1% aminopyrine in the drinking water for eight to ten weeks resulted in subsequent development of both hepatocellular nodules and cholangiofibrotic lesions/cholangiocellular carcinomas in Syrian golden hamsters. Additional prior dosing with Opisthorchis viverrini metacercariae (100/animal) induced inflammatory and proliferative changes in the livers of infected hamsters and was associated with a significant increase in yields of hepatocellular and cholangiocellular preneoplastic and neoplastic lesions. Thus, environmental factors thought to be casually related to the high levels of human liver cancer observed in the Northeastern provinces of Thailand were sufficient to bring about development of equivalent tumors in experimental animals. The results indicate that parasite associated liver injury and non-specific compensatory regeneration may play an important role in generation of both hepatocellular and cholangiocellular carcinomas in man.

Formation and accumulation of O6-ethylguanine in DNA of enriched populations of Clara cells, alveolar type II cells, and macrophages of hamsters exposed to diethylnitrosamine

The concentration of O6-ethylguanine (O6EG) in DNA of enriched populations of hamster Clara cells, alveolar type II cells, and macrophages was determined following acute diethylnitrosamine (DEN) exposure, 100 and 200 mg/kg body wt, and during subchronic DEN exposure, 20 mg/kg body wt, 2 times/week. Pulmonary cells were separated by centrifugal elutriation. DNA was collected on polycarbonate filters and hydrolyzed by mild acid. Purines bases were separated by high-pressure liquid chromatography, and O6EG was quantitated by optical methods. O6EG levels in DNA of Clara cell-enriched populations were found to be higher than O6EG levels in DNA of alveolar type II cell-enriched populations and macrophages following acute DEN treatment. In Clara cell-enriched populations, O6EG levels found after 200 mg/kg body wt dose were approximately 50% the levels found after the 100 mg/kg body wt dose, and O6EG levels found at 24 h post-treatment were approximately 50% the levels found at 12 h post-treatment for both the 100 and 200 mg/kg body wt doses. O6EG accumulated in DNA of Clara cell-enriched populations during subchronic DEN exposure. The differential distribution of O6EG in target and non-target cell populations suggests the involvement of this promutagenic base in the initiation process of DEN pulmonary carcinogenesis.

The disposition and metabolism of N-nitrosodiethylamine in adult, infant and foetal tissues of the Syrian golden hamster

Low-temperature whole-body autoradiography in Syrian golden hamsters, 11 and 15 days pregnant, given N-14C-nitrosodiethylamine, indicated an ability of the non-metabolized substance to freely pass the cellular membranes of the maternal, placental and foetal tissues. Experiments in vitro with tissues of adult hamsters showed a capacity of the nasal olfactory and respiratory mucosa, the trachea, the lung, the lateral nasal gland, the liver and the kidney to degrade the N-nitrosodiethylamine. Autoradiography showed a localization of non-volatile N-14C-nitrosodiethylamine metabolites in these tissues in vivo. Since the mentioned tissues are the targets for the N-nitrosodiethylamine-induced neoplastic or preneoplastic lesions in the hamster, our results indicate that the ability of the sensitive tissues to perform the degradation of the substance is correlated to the tumour organotrophy. The main targets for the N-nitrosodiethylamine carcinogenicity - the nasal olfactory and respiratory mucosa and the trachea - were found to be very active in degrading the substance, and it was shown that cytochrome P450 is present in these tissues. Microautoradiography of the nasal mucosa showed the highest labelling over the subepithelial glands (Bowman's glands) in the olfactory region, but other areas were also labelled. In the 15 day pregnant hamster, autoradiography showed a marked in vivo localization of non-volatile metabolites in the foetal nasal and tracheo-bronchial mucosa and liver, which was not observed in the 11 day pregnant hamster. The in vivo data were shown to correlate to an in vitro capacity by the nasal mucosa, the lung and the liver of the 15 day old foetus to metabolize the substance. N-nitrosodiethylamine is a transplacental carcinogen only when administered on one of the last four days of pregnancy (day 12-15), and our results are in accord with the assumption that only at this late stage of pregnancy has the differentiation of the sensitive tissues reached a stage at which the substance can be metabolized to its ultimate carcinogen. In vitro experiments in 4, 10, and 20 day old infant hamsters showed a high capacity of the nasal mucosa, the lung and the liver to metabolize the N-nitrosodiethylamine at these early stages of life.

Spindle cell carcinoma of the hamster trachea induced by N-methyl-N-nitrosourea

The tracheas of 63 male Syrian golden hamsters were exposed once each week for 12 weeks to a flowing stream of 0.5% N-methyl-N-nitrosourea in phosphate-buffered saline (pH 4.5) with a specially designed intratracheal cannula. The animals were killed when moribund or 6 months after the final exposure, and the respiratory tracts were examined grossly, histologically, and ultrastructurally for tumor formation. A total of 13 neoplasms was found in the larynx or trachea. Six were papillomas, 3 were carcinomas, and 4 were diagnosed as spindle-cell carcinomas. The average time of observation of the various tumor types was 33, 31, and 21 weeks, respectively. The spindle cell carcinomas contained an exophytic portion protruding into the tracheal or laryngeal lumen and an infiltrating portion growing circumferentially between the intact mucosa and the cartilage rings or plates. They were composed of sheets of elongated and spindle-shaped cells. Ultrastructurally, the cells contained bundles of tonofilaments and keratohyalin, and were connected by numerous desmosomes. These findings are consistent with a squamous origin of the tumor cells and a diagnosis of spindle cell carcinoma.

Pathogenesis of diethylnitrosamine-induced tumors in the trachea of the Syrian golden hamster

The pathogenesis of tracheal tumors induced in Syrian hamsters by subcutaneous treatment of N-nitrosodiethylamine (DEN) was examined in a serial sacrifice study using light and electron microscopy. Initial ultrastructural changes were noted in ciliated and mucous cells, and basal cells were identified as source of the later developing papillary polyps and squamous carcinomas.

Comparative studies of neoplastic response to a single dose of nitroso compounds. 6. The effect of diethylnitrosamine in Syrian golden hamsters

The effect of a single subcutaneous injection of different DEN doses was examined in adult Syrian hamsters observed for life. The minimal effective dose (threshold dose) for neoplastic response, reflected by induction of papillary polyps in the larynx and/or trachea, was 1.03 mg DEN/kg body weight. No tumors were found which could be related to treatment in other segments of the respiratory epithelium nor in other tissues.

An evaluation of 6 short-term tests for detecting organic chemical carcinogens

A number of tests have been described which are thought to be capable of identifying carcinogens without using the actual induction of cancer as an endpoint. This study compared the performance of 6 such tests on a selection of 120 organic chemicals. The tests studies were: (1) mutation of Salmonella typhimurium; (2) cell transformation; (3) degranulation of endoplasmic reticulum; (4) sebaceous gland suppression; (5) tetrazolium reduction and (6) subcutaneous implant. A further 4 tests were examined briefly, but were not included in the complete evaluation. The chemicals were classified into carcinogens (58) and non-carcinogens (62) on the basis of published experimental data, and into 1 of 4 broad chemical classes. There was considerable variation between tests in their ability to predict carcinogenicity, with the cell-transformation test and the bacterial-mutation test being the most accurate (94% and 93% accurate respectively). These 2 tests were considered to be of general use in screening, since they were clearly more accurate than the others. Statistical consideration of various combinations of these tests showed that the use of cell transformation and bacterial mutation together, provide an advantage over the use of either test alone. The inclusion of the other 4 tests in a screening battery predictably resulted in a great increase in overall inaccuracy and loss of discrimination, even though the detection of carcinogens is improved. All the tests were shown to generate both false positive and false negative results, a situation which may be controlled by the use, where possible, of appropriate chemical-class controls, to identify the test which is optimal for the class of chemical under test. Structural analogy may have a part to play in the rapid detection of environmental carcinogens, and some general guidelines for its use are given.

Morphology of diethylnitrosamine-induced lung tumours in Dzungarian dwarf hamsters

After transplacental application of 30 mg/kg b.w. diethylnitrosamine 16 out of 21 Dzungarian dwarf hamsters developed lung tumours. The histological picture of these tumours is described. The neoplasms are classified as papillary, tubular, or alveolar adenomas or adenocarcinomas, respectively. Different histological architectures occur in one and the same animal or even in different parts of the same tumour. The neoplasms derive from outgrowths of the epithelium of small bronchioles. The significance of the Dzungarian dwarf hamster as a suitable tool for transplacental and postnatal cancer research is discussed.

Chemically induced esthesioneuroblastomas in rats

Malignant tumours of the nasal cavity were induced in 19 of 56 (34%) female MRC-Wistar rats by 1-nitrosopiperazine administered orally for life. These tumours were of neurogenic origin, according to classical histologic criteria.

Comparative study of the carcinogenic activities of nas and some chemical carcinogens when introduced into the buccal pouch of the Syrian hamster

Studies were carried out on the carcinogenic effects of nas, 7,12-dimethylbenz-[a]anthracene (DMBA), DMBA+nas, dimethylnitrosamine (DMNA), diethylnitrosamine (DENA), and N-methyl-N-nitrosourea (MNU) when introduced into the buccal pouch of the Syrian hamster. Nas alone induced no tumours in the buccal pouch but tumours at other sites occurred in 18.8% of the treated animals, compared with 4.4% of the controls. Three of 11 hamsters treated with DMBA alone developed tumours. No tumours appeared in the buccal pouch following treatment with DMBA + nas but they developed at other sites in 6 of the 11 hamsters treated. DMNA and DENA induced no macroscopic changes in the mucous membrane of the buccal pouch. Following DMNA administration, tumours developed only in the liver; no tumours developed following the application of DENA. Tumours developed at various sites, including the buccal pouch, in 20 of the 25 hamsters treated with MNU.

Susceptibility of gerbils (Meriones unguiculatus) to weekly subcutaneous and single intravenous injections of N-diethylnitrosamine

Weekly s.c. (24, 12, and 6 mg/kg b.w.) or a single i.v. (100 or 50 mg/kg b.w.) injections of N-diethylnitrosamine (DEN) to gerbils (meriones unguiculatus) resulted in tumours of the respiratory tract and liver. Carcinomata of the nasal olfactory region or respiratory-olfactory mucosal junction were most common; papillomata of the tracheobronchial system and adenomata or carcinomata of the lungs appeared in significantly lower incidences. The neoplasms of the liver were of cholangiocellular and in a few cases of hepatocellular origin.