Modifying effect of triadimefon on the development of preneoplastic lesions and tumours in rat multi-organ carcinogenesis

  • Authors: N.M. Nedopytanska, E.A. Bagley, O.V. Reshavska, V.S. Lisovska, L.V. Tkachenko
  • UDC: 615.9:616-006.6:632.95
  • DOI: 10.33273/2663-4570-2018-84-4-5-18
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State Enterprise “L. I. Medved’s Research Center of Preventive Toxicology, Food and Chemical Safety of the Ministry of Health of Ukraine”, Kyiv, Ukraine

ABSTRACT. Throughout life, the human body is exposed to multiple environmental carcinogens that may stimulate carcinogenesis in different organs. Critical place among these carcinogens belongs to nitroso compounds. Triadimefon belongs to the chemical class of triazoles that are widely used as fungicides in pesticides and medicinal products.

Objective is to investigate the effect of triadimefon on the development of preneoplastic lesions of the tissues and tumours in carcinogenesis induced in different organs by nitroso compounds.

Materials and Methods. Experiments were performed in male Wistar Han rats in which nitroso compounds - N-nitrosodiethylamine, N-methylnitrosourea, N-nitrosobis(2-hydroxypropyl) amine induced multi-organ carcinogenesis according to the N.Ito. protocol. Triadimefon at the doses: 16.0 and 80.0 mg/kg body weight that corresponded to the no-observed-effect and observed effect level by carcinogenic effect were administered intragastrically on a daily basis for 20 weeks. Clinical studies were conducted throughout the experiment. The general condition of animals, their body weight and body weight gain were assessed. After necropsy, gross examination, including aberrant multiple crypts of the colonic mucosa, and histological examinations were conducted. Nodules positive for γ-glutamyl transpeptidase (γ-GTP) were determined by histochemistry in the hepatic tissue.

Results. No clinical signs of toxic action of triadimefon in rat body induced by nitroso compounds to carcinogenesis were established. No specific organotrophic action of triadimefon was found by changes in the internal organ weight, except for liver. High dose resulted in the increase of liver weight, as well as in the number and size of γ-GTP positive nodules suggesting an increase in the pool of transformed hepatocytes.

Histological examination of internal organs allowed detecting proliferative processes that are criterial markers of carcinogenicity of chemical substances upon their study in multi-organ model. The tendency to the increase in the rate of dose-dependent thyroid adenoma has been established. Increase in the rate of epithelium hyperplasia of oesophagus and forestomach, prostatic gland, as well as the total rate of benign tumours in different organs of animals on the tumour-inducing dose of triadimefon was found. The rate of malignancies in these animals do not differ from the control.

Conclusion. The tumour-inducing dose of triadimefon shows weak promotor effect on the development of preneoplastic lesions of tissues of the thyroid gland, liver, oesophagus and forestomach, prostatic gland, as well as on the development of benign tumours in rats induced by carcinogenic nitroso compounds. No-observed-effect level of triadimefon by oncogenic effect established in chronic experiments ensures its safety upon exposure in the body of rats initiated by carcinogenic nitroso compounds. Regulations developed on this parameters ensure oncological safety of its use in human.

Key words: multi-organ carcinogenesis, carcinogenesis by nitroso compounds, triadimefon, triazoles, proliferative processes, preneoplastic lesions, male Wistar Han rats.

Annual growth of oncological morbidity and mortality of population remains an urgent challenge in the world that is more or less associated with the action of carcinogenic environmental factors in everyday life and in industry. Use of pesticides also belongs to these factors by epidemiological data [1, 2]. According to the international and national standards, active substances undergo extensive and thorough trials, including carcinogenicity, for their safe use [3]. It can be believed that carcinogenicity found in epidemiological studies develops under circumstances that were not considered by the protocol of these trials, namely — concomitant action of pesticides and other substances in the human body.

Currently, it is proved that carcinogenesis is a multistage process, where the most combined stages are: initiation, promotion, and progression. Transformation of the normal stem cells into tumour ones takes place at the stage of initiation under the effect of different exogenous and endogenous factors. Among exogenous factors, chemical substances take a significant place. Such substances may initiate carcinogenesis in different organs, and pesticides may act on other stages as a promotor of this process creating such conditions for selection and proliferation of tumour stem cells [4, 5].

A huge range of toxicants and extent of their use in human activities, as well as environmental pollution, complicates identification of initiators. Therefore, an experimental model was proposed, where initiation was performed in different organs by well-studied carcinogenic nitroso compounds, as the most probable factors that may be formed during cultivation of agricultural products and cooking of food products [6, 7].

Triadimefon (1-(4-chloropehoxy)-3,3-dimethyl-1-(1H -1,2,4-triazol-1-yl) butanone, CAS 43121-43-3) belongs to chemical class of triazoles. Biological action of this substance involves inhibition of the synthesis of steroids, impairment of the function of cellular membranes that provides treatment and continuous protective fungicidal effect [8].

Objective of this work is to investigate the effect of triadimefon on the development of preneoplastic lesions of the tissues and tumours in carcinogenesis induced in different organs by nitroso compounds.

Materials and methods. The experiment was conducted at the Center of Preventive and Regulatory Toxicology of the State Enterprise “L. I. Medved’s Research Center of Preventive Toxicology, Food and Chemical Safety of the Ministry of Health of Ukraine” in accordance with GLP requirements. Studies correspond to the requirements of the Bioethics Committee on animal welfare, legislation of Ukraine and international organizations.

The experiment included 45 white male Wistar Han rats (SPF) with a body weight of 130 ± 5.8, received from the nursery of the Center. After quarantine and randomization, animals were divided into three groups. The control group (1) and experimental groups (2, 3), 15 animals in each.

According to the protocol (Fig. 1), all animals received 98 % N-nitrosodiethylamine (NDEA) at the dose of 100 mg/kg, then 4 times — 98 % N-methyl-N-nitrosourea (MNU) at the dose of 20 mg/kg body weight. 98 % N-nitrosobis(2-hydroxypropyl)amine (NDHPA) with drinking water in the form of 0.1 % solution. All carcinogens are manufactured by TRC, Canada.

Fig. 1. Diagram of experiments, where ↓ – intraperitoneal injection of 100 mg/kg NDEA;
▼ – intraperitoneal injection of 20 mg/kg MNU;
 – addition of 0.01 % NDHPA to the drinking water;
 – intragastric administration of the test substance.


97 % triadimefon — generic manufactured by China Communications Import & Export Corporation, China,, provided by the private enterprise Chemiline Agro, Ukraine, corresponded to the appropriate international standards [9]. The substance was administered in rats intragastrically at the doses of 16.0 and 80.0 mg/kg body weight during 20 weeks. According to the literature data of toxicological evaluation of the prototype of this substance, selected doses correspond to the no-observed and observed effect level by the oncogenicity [8].

Solutions of the test product were prepared on a daily basis, ex tempore, as triadimefon aqueous suspension with OP-10. Concentrations of solutions: for a low dose, 0.16 % aqueous solution, for high — 8.0 %. The concentration of the solutions was selected considering the volume of liquid administered into the stomach of a rat. Control animals received water with OP-10 (0.05 %).

Animals were managed in a “clean” zone of the barrier-type vivarium, by 5 animals in a cage. Sterile chlorinated food-grade paper was used for bedding. Room was equipped with forced ventilation (12 volumes per hour) with prepared air. Temperature and relative humidity of air were 19–21 оС and 53–56 %. Lightning of the room — daylight lamps (12 hours of light, 12 hours of darkness). Throughout the experiment, animals received balanced pelletized feed Altromin (Germany) and decontaminated filtered water.

During the experiment, daily examination of animals was performed to establish any deviations associated with the action of substances, namely: behaviour, mobility, appetite, the condition of the hair coat, skin and mucous membranes of the animals. Also, such parameters as survival rate, body weight changes over time, body weight gain were considered and registered every week during exposure. At the same time, the adjustment of triadimefon doses was performed.

In 24 hours after the last administration of the test substance, rats were sacrificed in СО2 chamber. All animals were exposed to autopsy. The following organs were removed for measurement of internal organ weight: brain, pituitary gland, both lobes of the thyroid gland with parathyroid gland, lungs, heart, liver, pancreatic gland, pair of adrenal glands, pair of kidneys, spleen, prostatic gland and pair of testicles. Their absolute and relative weight was measured. Both lobes of the thyroid gland were weighed simultaneously. Paired organs: kidneys, adrenal glands and testicles were weighed simultaneously, left and right organ from the pair. Lungs and liver were weighed with all lobes, each organ separately. The relative weight of the organ was measured by the percentage to the body weight of the animal, and it was expressed in %.

All thin-walled cavity organs, in particular: oesophagus, stomach, intestine and bladder were preliminary washed and fixed in full. After required consolidation in the fixing solution, the entire mucous membrane was studied using binocular stereomicroscope for the presence of papillomas and other neoplasms, and in the colon — for the presence of aberrant mutations following preliminary staining of mucous membrane with methylene blue [10].

For further histological examination, the following organs were removed independently of change: thyroid gland, specimens of the lung, liver, adrenal, kidney tissue, material from two parts of the stomach, oesophagus, rectum, prostatic gland, bladder. Histological specimens were prepared using common morphological methods with haematoxylin-eosin staining of sections.

For histochemical analysis, specimens of the liver were taken directly after the autopsy. Five-micron slices were prepared from selected specimens using freezing microtome. After fixing of slices in cold acetone, the histochemical reaction on determination of γ-GTP, market of transformed hepatocytes, was performed [12]. γ-glutamyl transpeptidase positive nodules are formed in the hepatic tissue during cell transformation. Total area, standardised per conditional unit (cm2), number and size of these nodules, are the principal criteria in determining promotor activity of the test product. After the histochemical reaction, statistical processing of the detected nodules was performed. Number and area of nodules per conditional unit (cm2) of the liver slice plane were counted. For determination of the number and area of nodules in the liver slice, special software was used.

Statistical analysis of the experimental findings has been performed for the following parameters: body weight and its gain, weight of internal organs, number of cases of detected pathology in gross and histological examinations, as well as parameters of histochemical examinations (total area standardised per conditional unit (cm2) and total number of nodules, as well as mean nodule area). Mean and median values per group and the standard deviation were determined. Distribution law in the population was determined by methods of Kolmogorov and Shapiro — Wilk.

For determination of differences between experimental groups of animals and control, parametric paired Student’s t-test for independent samples was used upon the normal distribution of variables, and upon the absence — non-parametric Kruskal-Wallis (ANOVA) and Mann — Whitney tests were used.

Analysis of the rate of tumours and other histopathological changes was performed using χ2 test or one-sided Fischer exact test. Dose-effect dependence of the product was determined using regression analysis. Difference between parameters of the control and experimental animals was achieved at ≤ 0.05 [3].

Statistical calculations were performed using Excell 2010, Statistica 2010 application software.

Results and discussion. Throughout the period of exposure, experimental groups did not show animal death, and behaviour, appearance, motor activity in the majority of rats was unchanged. Animals readily ate feed and drank water. In group 3, 4 animals (27 %) showed increased excitement and body weight reduction during the follow-up period. Upon comparative assessment of the grown rates (Fig. 2) in male Wistar Han rats under conditions of the experiment, somewhat body weight gain was observed in animals on triadimefon at the dose of 16 mg/kg (р ≤ 0.05). Animals on the low dose, body weight was by 5–6 % higher beginning from week 9 and till the end of the experiment, compared with the control group.

Fig. 2. Diagram of the animal body weight:
Group 1 - control;
Group 2 - triadimefon dose 16.0 mg/kg;
Group 3 - triadimefon dose 80.0 mg/kg.

 

No statistically significant changes in the body weight of animals on high dose were registered; although the tendency towards its decrease by 1–4 % is detected. Cumulative body weight gain did not fall below the control value.

After sacrification, external examination of animals in the experimental groups did not find any differences in appearance compared with the control. According to autopsy findings, rats showed limited cases of gross changes in the condition of internal organs and tissues compared with the control. As for these cases, foci of aberrant crypts in the rectum were found in the animals of the first and third group.

There were no statistically significant changes upon a comparative analysis of the absolute and relative weight of the brain, heart, lungs, thyroid gland, pancreatic gland, prostatic gland, kidneys and testicles in experimental rats compared with control (Table 1).

Table 1

Weight of internal organs in rats

Note: * – Statistically significant difference compared with the control at ≤ 0.05.

 

At the same time, a statistically significant increase in absolute weight of pituitary gland compared with control in low and high doses by 29 and 43 5, respectively, as well as adrenal glands by 20 and 15 % was established. No changes in the absolute hypophysis weight were observed. Similar changes were typical for relative adrenal gland weight. Increase in the absolute weight of adrenal glands was not accompanied by histological changes in their structure. It is expected that this effect is associated with stress due to concomitant administration of carcinogens and triadimefon.

A statistically non-significant dose-dependent increase in the absolute weight (5 and 10.5 %) of the liver was found. However, relative weight in a low dose did not change compared with the control and increase by 12 % for high dose (р ≤ 0.05).

Therefore, no specific organotropic action of triadimefon was found by changes in the internal organ weight, except for the liver. Changes in the weight of the liver suggest the hepatotoxic effect of triadimefon that was described in the literature [8].

Multiple experimental studies have established that NDEA and MNU are carcinogens [6]. Preneoplastic loci and further — hyperplastic nodules are formed in the hepatic tissue upon proliferation and selection of clones of carcinogen-transformed cells. Carcinogen-transformed cells express enzyme γ-glutamyl transpeptidase (γ-GTP) that is the histochemical marker of preneoplastic changes. The number and size of hyperplastic γ-GTP positive nodules in the hepatic tissue are the principal criteria in determining promotor activity of the test compound. Table 2 provides information on the effect of triadimefon on the formation and growth of γ-GTP positive nodules in the hepatic tissue of the rats.

Table 2

Number and size of hyperplastic γ-GTP positive nodules in the rat liver

Note: * – Statistically significant difference compared with the control at ≤ 0.05.

 

Upon assessment of the parameters of γ-GTP positive nodules in the liver of the rats, non-parametric statistics method was applied, since the sample of the obtained results did not meet the law of normal distribution. For a more precise comparison of the parameters with control, the median of the obtained data was determined along with means. Upon comparison of the median with control, a statistically significant increase in the mean area of γ-glutamyl transpeptidase positive nodules in the liver of 51 5 of animals on 80 mg/kg of triadimefon (р ≤ 0.01) was found. Mean total area of nodules per cm2 and the mean a number of nodules per cm 2 was without statistically significant changes, however, increased by 99 and 67 %, respectively, compared with the control. In our opinion, such an increase is biologically significant. At the background of these results in animals on low triadimefon doses, values of the above parameters did not differ from control.

Therefore, triadimefon at the dose of 16 mg/kg did not induce an increase in the number of γ-GTP positive nodules and their size that allows concluding the lack of promotor effect in hepatic carcinogenesis in these animals. Triadimefon induced the increase in the number and size of γ-GTP positive nodules only at the dose of 80 mg/kg. Previously, promotor effect of triadimefon was found in the model of hepatic carcinogenesis in rats “NDEA-hepatectomy” [6].

Histological examination of sampled internal organs allowed to detect proliferative processes that became criterial markers of carcinogenicity of chemical substances upon their study in multi-organ model [6]. Table 3 provides the data on proliferative processes and tumours found in control and experimental animals.

Table 3

Proliferative processes in tumour, found in rats

Note: * – Statistically significant difference compared with the control at ≤ 0.05.

 

For example, these processes were at the same level in the thyroid tissue of the experimental and control rats. However, the tendency to the increase in the rate of dose-dependent gland adenoma has been established. A statistically significant dose-dependent increase in the number of cases of hyperplasia of the squamous oesophageal epithelium and forestomach in animals on triadimefon was registered. Low triadimefon doses showed no statistical differences (р ≥ 0.05), whereas they were significant for high doses (р ≤ 0.01). It should be noted that the intensity of this effect also increases in animals, which received a dose of 80 mg/kg. Three cases of papilloma were registered in the forestomach of rats compared with 0 in the control group. These data suggest further progression of oncogenesis.

Proliferative processes also have shown a dose-dependent tendency towards the increase in the number of cases of nodular hyperplasia of the prostatic gland. Their 2.5-fold increase was found when a high dose was administered.

In general, 21 tumours were found in animals, 15 out of which are benign, and 6 malignant. The highest number of tumours was found in animals on high triadimefon doses: in the thyroid gland and stomach — 3 cases versus 1 and 0 in the control group, respectively. In animals on 16 mg/kg of triadimefon, 2 ademonas were found in the thyroid gland, and sarcoma and adenocarcinoma in the prostatic gland. Tumours were isolated in other organs. Therefore, papilloma of the forestomach and adenoma of the thyroid gland may be those tumours associated with the exposure to triadimefon.

The rate of tumours in the group of animals on triadimefon at the dose of 80 mg/kg was statistically significantly higher compared with control (р ≤ 0.05). It should be noted that animals in the experimental groups have 2.6 and 3.3-fold more tumours compared with the control. Multiplicity factor in these groups was also higher compared with control. The highest value of this parameter was established in animals, which received the dose of 16 mg/kg. The number of malignant tumours in these animals is higher. However, the proportion between malignant tumours and benign tumours in this group does not virtually differ from the control, whereas animals on high dose have 2-fold lower parameter. Therefore, detected oncogenicity is due to the development of benign tumours, the number of which in the experimental group is increased depending on triadimefon dose.

Thus, a tumour-inducing dose of triadimefon of 80 mg/kg body weight shows weak promotor effect on the development of preneoplastic lesions of tissues of the thyroid gland, liver, oesophagus and forestomach, prostatic gland, as well as on the development of benign tumours in rats induced by NDEA, MNU, NDHPA.

Triadimefon belongs to the chemical class of triazoles. This substance is an inhibitor of synthesis of steroids, and it has a strong fungitoxic action. Compounds of this class are used as fungicides. As with other pesticides, triadimefon has been studied in the chronic experiments in rats and nice, where the induction of thyroid tumours in male rats and hepatic tumours in mice was established [8]. No genotoxic properties were found upon investigation of triadimefon in a range of standard mutagenicity tests. Carcinogenicity of triadimefon was studied in the medium-term test on the model of hepatic carcinogenesis “HDEA hepatectomy” in rats. The positive effect was established [8].

Currently, common phenobarbital-like mechanism of carcinogenic action of triazole in rats and mice that involves activation of the family of nuclear constitutive receptors: androstane (CAR) and pregnane X-receptor has been established (PXR) [13-14]. This results in the induction of cytochrome P-450 enzymes, in particular in mice Cyp2b 10 and Cyp3а 11, in rats Cyp2b 1 and Cyp3а 3, hepatocellular hypertrophy, increased DNA synthesis, development of oxidative stress and hepatocellular proliferative processes, the formation of foci of changed hepatocytes, and, finally, development of the tumour. Development of thyroid tumour occurs as the secondary effect due to hepatic impairment. This is accompanied by increased elimination of the thyroid hormones from the body that results in increased secretion of the thyroid-stimulating hormone by hypophysis which stimulates proliferative processes in the gland. Actually, upon studying the promotor effect of phenobarbital on the similar model, a significant increase in the number of cases of hyperplasia, adenoma and carcinoma of the thyroid gland was registered [6]. However, the hypothesis that triadimefon-induced thyroid tumours develop through the specific mechanism of the increase of the level of the thyroid-stimulating hormone has not been confirmed in the article [5]. Authors using male Wistar Han rats on triadimefon and also on propiconazole and myclobutanil that do not cause thyroid tumours, have shown that the efficiency of uridine-diphospho-glucoronyl transferase that metabolises thyroxine increases at the same degree in a month and 90 days for all three conazoles. In rats on tumour-inducting dose, hypertrophy of hepatocytes developed only at the end of the experiment, whereas hypertrophy, reduction of colloid and proliferation of the follicular thyroid epithelium was observed earlier in animals on other conazoles in as little as 30 days. Dose-dependent reduction of thyroxine was registered in 4 days of exposure in all 3 groups. However, the low concentration of thyroxine in 30 days was registered only in rats on the tumour-inducing dose of triadimefon. Concentration of triiodothyronine showed dose-dependent reduction only in animals who received triadimefon from Day 4 to 90. Concentration of thyroid-stimulating hormone in animal plasma throughout the experiment did not increase in any of the groups [16].

Under conditions of the same experiment, S.D. Hester et al. [16,17] have studied gene expression of the liver and thyroid gland in male Wistar Han rats. The number of changed genes varied depending on the dose and time of triazole exposure.

The highest number of changes genes induced by triadimefon and propiconazole in the liver was registered at the end of experiment at Day 90, whereas in the thyroid gland — at Day 30. Myclobutanil that did not have oncogenicity, however, showed minimal effects.

A significant number of changed genes was associated with signalling pathways that controlled the metabolism of cholesterol, activation of the nuclear receptors and N-ras and K-ras signalling, growth and metabolism. There was a clear separation in the difference of gene expression in no-observed-effect and tumour-inducing doses. Therefore, all of the specified changes in the liver and thyroid gland may be explained by changes in the gene expression in the cells of these organs that developed as the result of triadimefon exposure.

Upon studying the promotor effect of phenobarbital on a similar model, there were no proliferative processes in the oesophagus and forestomach of the rats and other organs that are targets for carcinogens-initiators. A statistically significant increase in the number of cases of hyperplasia of the oesophagus and forestomach in rats was found upon exposure to high triadimefon dose, and it could be associated with its irritating effect. According to the literature, triadimefon has a very weak irritating action on mucous membranes, and subchronic and chronic administration did not result in changes in the epithelium of oesophagus and forestomach in rats [8,15]. However, following intragastric administration, this weak effect may be sufficient for the development of a chronic inflammatory process, hyperplasia and papilloma, respectively [18].

On the similar model, hyperplasia of the oesophagus and forestomach was found following administration of such carcinogens in rats: N-nitrozodibutilamine, methyl-nitro-nitroguanidine, dimethylbenzanthracene, as well as catechol [6]. N-nitrozodibutilamine in the chronic experiments induced tumours of the liver, bladder, and forestomach in rats. Methyl-nitro-nitroguanidine is a direct carcinogen that induces tumours of the oesophagus, forestomach, intestine and other locations in rats. Dimethylbenzanthracene induces breast tumours, as well as epithelial tumours of different locations. Catechol also induces gastric tumours. Therefore, the authors believe that this effect is predictive in terms of the development of gastric tumours in rats.

It should be noted that triadimefon, as well as N-nitrozodibutilamine, dimethylbenzanthracene, and catechol induced not only hyperplasia but also contributed to the development of papillomas.

Therefore, a tumour-inducing dose of triadimefon enhances proliferative processes in the mucous membrane of the oesophagus and stomach in rats exposed to carcinogens.

Triadimefon results in a dose-dependent increase of prostatic hyperplasia in rats. Such effect may probably occur due to the common mechanism of action of triazoles — a reduction of synthesis of steroids and associated processes of impaired homeostasis of the testosterone level [19]. Actually, the development of prostatic hyperplasia in rats in our experiment developed at the background of atrophic processes in testicles that may be induced by carcinogens. At the same time, it was shown on the puberty model in male Wistar Han rats that high doses of triadimefon and other triazoles may have a stimulating effect on the genital tissues, in particular, result in the increase of weight of testicles and ventral prostatic gland, content of testosterone in the blood serum and testicles [19].

Carcinogens used as an initiator of carcinogenesis are strong genotoxicants of the wide spectrum of action. Their administration in the body may increase the pool of mutant stem cells not only in target organs but also in other tissues of the body [20]. Therefore, a total number of animals with tumours in the experimental and control group was analysed. The number of animals with tumours in the group of animals on triadimefon at the dose of 80 mg/kg was statistically significantly higher compared with control (р ≤ 0.05). Multiplicity factor in triadimefon groups was also higher compared with control. The detected oncogenicity is due to the development of benign tumours, the number of which in the experimental group is increased depending on triadimefon dose, whereas the rate of malignant tumours is virtually unchanged.

Summing up the above data, it may be concluded that tumour-inducing doses of triadimefon show promotor effect on the development of preneoplastic lesions and tumours according to the mechanism of action common for triazoles — activation of the family of nuclear constitutive receptors, impaired homeostasis of sexual hormones. This effect is provided through changes in gene expression associated with signalling pathways that control the metabolism of cholesterol, activation of nuclear receptors and N-ras and K-ras signalling, growth and metabolism of cells in the rat body under the action of tumour-inducing doses. Increase in the rate of preneoplastic lesions and tumours of the oesophagus and stomach is apparently associated with the irritating action of triadimefon on mucous membranes. The lack of promotor effect in the no-observed oncogenic effect dose established in the chronic experiments in rodents allows it use in the assessment of combined action of carcinogenic nitroso compounds and triadimefon on the body. Previously developed regulations developed on these parameters ensure oncological safety of its use in human.

The data obtained confirm the significant role of the external factors in the development of tumours of different organs in the framework of current discussion [21].

Conclusion

1. Tumour-inducing dose of triadimefon of 80 mg/kg body weight shows weak promotor effect on the development of preneoplastic lesions of tissues of the thyroid gland, liver, oesophagus and forestomach, prostatic gland, as well as on the development of benign tumours in rats, in which carcinogenesis was induced by N-nitrosodiethylamine (NDEA), N-methylnitrosourea (MNU), N-nitrosobis(2-hydroxypropyl) (NDHPA) — carcinogenic nitroso compounds of the wide spectrum of action.

2. Increase in the total rate of benign tumours in animals with carcinogenesis induced by nitroso compounds following exposure to tumour-inducing triadimefon dose has been established. The rate of malignancies in these animals do not differ from the control.

3. The rate of the detected preneoplastic lesions in tissues and tumours did not increase compared to the control in rats, in which carcinogenesis was initiated by nitroso compounds following the exposure of triadimefon at the dose that does not induce tumour in the chronic experiment.

4. No-observed-effect level of triadimefon by oncogenic effect established in chronic experiments ensures its safety upon exposure in the body of rats initiated by carcinogenic nitroso compounds.

 

REFERENCES

1. IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. Some Organophosphate Insecticides and Herbicides. International Agency for Research on Cancer, Lyon, France. - 2017. - V. 112.  - [Electronic resource]. - Available at: http://www.iarc.fr/en/pdf/Monograph Volume112.pdf.

2. Silver S.R. Cancer incidence and Metolachlor use in the Agricultural Health Study: An update / S.R. Silver, S.J. Bertke, C.J. Hines [et al.] // Int. J. Cancer. – 2015. – V. 137. – No. 11. – P. 2630-2643.

3. OECD, Guidance Document 116 on the Conduct and Design of Chronic Toxicity and Carcinogenicity Studies, Supporting Test Guidelines 451, 452 and 453. 2nd Edition.  Series on Testing and Assessment, Paris, OECD. – P. 2012-156.

4. Miller M.F. Low-Dose Mixture Hypothesis of Carcinogenesis Workshop: scientific underpinnings and research recommendations / M.F. Miller, W.H. Goodson, M.H. Manjili [et al.] // Environ. Health. Perspect. – 2017. – V. 125. – P. 163-169.

5. Assessing the carcinogenic potential of low-dose exposures to chemical mixtures in the environment: the challenge ahead \ W.H. Goodson, L. Lowe, D.O. Carpenter [et al.] // Carcinogenesis. – 2015. – V. 36. – P. S254–296. 

6. Ito N. Medium-term bioassays for carcinogens / N.Ito, T.Shirai, R.Hasegawa // Mechanisms of Carcinogenesis in Risk Identification. Lyon: - IARC Scientific Publication. – 1992 – No. 116. – P. 353-388.

7. Park J. Distribution of Seven N-Nitrosamines in Food/ Jong-eun Park, Jung-eun Seo, Jee-yeon Lee, and Hoonjeong Kwon // Toxicol. Res. – 2015. – V. 31. – No. 3. – P. 2630-2643.  doi:  10.5487/TR.2015.31.3.279

8. Triadimefon: National Library of Medicine HSDB Database. [Electronic resource]. - Toxnet. – Available at: https://toxnet.nlm.nih.gov/cgi-bin/sis/search/a?dbs

9. FAO SPECIFICATIONS AND EVALUATIONS FOR AGRICULTURAL PESTICIDES. Triadimefon.(RS)-1-(4-chlorophenoxy)-3,3-dimethyl-1-(1H-1,2,4-triazol-1-yl)butan-2-one FAO/WHO. - 2011.[Electronic resource]. - FAO/WHO  – Available at: http://www.fao.org.

10. Bilbin M. Induction of Aberrant Crypts in the Colons of Rats by Alkylating Agents/ M. Bilbin, B. Tudek, H. Czeczot // Acta Biochimica Polonica. – 1992. – V.39. – No. 1. – P.113–117.

11. Pathology of tumors in laboratory animals. Vol. 1 - Tumours in the rat. Second Edition. Edited by V.S. Turusov and U. Mohr. – Lyon: IARC Scientific Publications. – 1990. – No. 99. – 754 р.

12. Loida Z. Histochemistry of enzymes / Z. Loida, R. Gossaru, T. Shybler // Laboratory methods – M.: Mir. – 1982. – 270 p.

13. Nesnow S. Integration of toxicological approaches with omic and related technologies to elucidate mechanisms of carcinogenic action: propiconazole, an example / S.Nesnow// Cancer Lett. – 2013. – V. 334. - Р. 20-27.

14. Phenobarbital and propiconazole toxicogenomic profiles in mice show major similarities consistent with the key role that constitutive androstane receptor (CAR) activation plays in their mode of action/ R.A. Currie, R.C. Peffer, K. Amber [et al.] // Toxicology – 2014 – V. 321. – Issue null, – P. 80-88.

15. Toxicity profiles in rats treated with tumorigenic and nontumorigenic triazole conazole fungicides: Propiconazole, triadimefon, and myclobutanil / D.C. Wolf, J.W. Allen, M.H. George [et al.] Toxicol. Pathol. – 2006. – V. 34. – No. 7. – Р.895–902.

16. Transcriptional profiles in liver from rats treated with tumorigenic and non-tumorigenic triazole conazole fungicides: Propiconazole, triadimefon, and myclobutanil / S.D. Hester, D.C. Wolf,  S.Nesnow, [et al.] Toxicol. Pathol. – 2006 - V. 34. – No. 7. – Р.879–894.

17. Hester S.D. Transcriptional responses in thyroid tissues from rats treated with a tumorigenic and a non- tumorigenic triazole conazole fungicide / S.D. Hester, S. Nesnow // Toxicol. Appl. Pharmacol. – 2008. – V. 227. – No. 3. – Р. 357-369.

18. Chandra S. A. Chemical Carcinogenesis of the Gastrointestinal Tract in Rodents: An Overview with Emphasis on NTP Carcinogenesis Bioassays / S. A. Chandra, M.W. Nolan, D.E. Malarkey // Toxicol. Pathol. – 2010 – V. 38. – No. 1. – Р. 188-197.

19. Disruption of testosterone homeostasis as a mode of action for the reproductive toxicity of triazole fungicides in the male rat / A.K. Goetz, H. Ren, J.E. Schmid [et al.] Toxicol. Sci. – 2007. – V. 95. - No. 1. – Р. 227-239.

20. Multi-organ mapping of cancer risk/ L. Zhu, D. Finkelstein, C. Gao [et al.] // Cell. - 2016. – V. 166. – No. 1. – Р. 1132-1146.

21. Thomas F. Intrinsic versus Extrinsic Cancer Risks: The Debate Continues / F. Thomas, B. Roche, B.Ujvari // Trends Cancer. – 2016. – V. 2. – No. 2. – Р. 68-69.

 

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