In vitro induction of SCE in human lymphocytes by epichlorohydrin with and without metabolic activation

Toxic, DNA-Damaging and Mutagenic Activity of Epichlorohydrin on Human Cells Cultured in Vitro

Epichlorohydrin (ECHH) highly inhibited the tritiated thymidine uptake by human lymphocytes cultured in vitro, although the corresponding cell viability was unaffected. Furthermore, it elicited unscheduled DNA synthesis, acting as a DNA-damaging agent after its metabolic activation. ECHH also showed a clear toxic and mutagenic activity toward a human epithelial-like cell line, causing a decrease in cell viability and an increase in mutants resistant to 0.05 Lf/ml of diphtheria toxin.

A comparative study of chemically induced DNA damage in isolated nasal mucosa cells of humans and rats assessed by the alkaline comet assay

Single-cell microgel electrophoresis (comet) assay was used to study genotoxic effects in human nasal mucosa cells and rat nasal and ethmoidal mucosa cells in vitro. Human cells were obtained from tissue samples of 10 patients (3 females/7 males), who underwent surgery (conchotomy) for treatment of nasal airway obstruction. Rat nasal mucosa cells were derived from male Sprague-Dawley rats. Cells were exposed for 1 h to either N-nitrosodiethanolamine (NDELA), epichlorohydrin (EPI), 1,2-epoxybutane (EPB), ethylene dibromide (EDB), or 1,2-dibromo-3-chloropropane (DBCP). Dimethyl sulfoxide (DMSO) was used as negative control. Alkaline comet assay was performed according to a standard protocol and DNA damage was quantified as Olive tail moment using image analysis system. All test substances induced an increase in DNA damage in human and rat cells. The absolute amount of DNA damage in rat nasal mucosa cells was usually higher than in ethmoidal mucosa cells. Human nasal mucosa cells were found to be less sensitive than rat mucosa cells to the genotoxic activities of DBCP (lowest effective concentration in human cells [LEC(human)]: 1.5, in rat cells [LEC(rat)]: 0.01 mM) and NDELA (LEC(human): 25, LEC(rat): 12.5 mM), whereas EPB-treated cells were almost equal (LEC(human) and LEC(rat) 0.78 mM). NDELA induced a marked concomitant cytotoxicity. For EPI (LEC(human) and LEC(rat): 0.097 mM) and EDB (LEC(human): 0.195, LEC(rat): 0.048 mM), pronounced interindividual differences were observed in human samples.

Genetic toxicology of epichlorohydrin: a review

Epichlorohydrin (ECH) is one of the more commercially important aliphatic epoxides used extensively as an industrial intermediate, a laboratory reagent, and as an insecticide. It is a volatile, colourless liquid with an ethereal odour. It behaves as an alkylating agent. Reports have shown it to cause the respiratory and dermal toxicity in animals and humans. It has also been reported to be carcinogenic in experimental models. Thus, the wide-spread use of this aliphatic epoxide is of great concern in human health problem. The purpose of this paper is to critically review and update the mutagenic and clastogenic effects of ECH based on available literature.

Reaction of epichlorohydrin with 2'-deoxynucleosides: characterization of adducts

Epichlorohydrin (ECH) is a simple 3-carbon epoxide of industrial importance and thus has the potential for human exposure in the workplace. It has been shown to be genotoxic in several systems and is a compound capable of reacting with biological nucleophiles. This study details the products formed from the reaction of ECH with 2'-deoxynucleosides at pH 7 and 37 degrees C for 6 h. Reaction with 2'-deoxyguanosine yielded 7-(3-chloro-2-hydroxypropyl) guanine (7-CHP-Gua) resulting from alkylation at N-7 of 2'-deoxyguanosine followed by depurination. Two unusual adducts were also partially characterized which resulted from further reaction of 7-CHP-Gua with another molecule of ECH to yield 1,7-bis(3-chloro-2-hydroxypropyl)guanine (1,7-bis-CHP-Gua) which could then cyclize with the exocyclic amino group to yield 1,N2-(2-hydroxypropano)-7-(3-chloro-2-hydroxypropyl) guanine (1,N2-HP-7-CHP-Gua). Reaction with 2'-deoxyadenosine gave only one product, namely 1,N6-(2-hydroxypropano)-2'-deoxyadenosine (1,N6-HP-dAdo). The reaction of 2'-deoxythymidine with ECH also yielded one product which was identified as 3-(3-chloro-2-hydroxypropyl)-2'-deoxythymidine (3-CHP-dThd). A 3-(3-chloro-2-hydroxypropyl)-2'-deoxyuridine (3-CHP-dUrd) product was isolated from the reaction of ECH with 2'-deoxycytidine. This product most likely resulted from the deamination of an initially formed 3-(3-chloro-2-hydroxypropyl) -2'-deoxycytidine (3-CHP-dCyd), a phenomenon which we have previously reported to occur during the reaction of 2'-deoxycytidine with other aliphatic epoxides. Evidence is also presented that 3-CHP-dUrd is converted to 3-(2,3-dihydroxypropyl)-2'deoxyuridine (3-DHP-dUrd) under physiological conditions, with a half-life of 213 h. Reaction of ECH with calf thymus DNA (pH 7.0, 37 degrees C, 3 h) resulted in the formation of 7-CHP-Gua (200 nmol/mg DNA.

Sister-chromatid exchange: second report of the Gene-Tox Program

This paper reviews the ability of a number of chemicals to induce sister-chromatid exchanges (SCEs). The SCE data for animal cells in vivo and in vitro, and human cells in vitro are presented in 6 tables according to their relative effectiveness. A seventh table summarizes what is known about the effects of specific chemicals on SCEs for humans exposed in vivo. The data support the concept that SCEs provide a useful indication of exposure, although the mechanism and biological significance of SCE formation still remain to be elucidated.

Micronucleated reticulocyte induction by ethylating agents in mice

Six model ethylating agents were tested for clastogenic potency by means of a new technique of the micronucleus assay with mouse peripheral blood cells using acridine orange (AO)-coated slides, to evaluate the test. The alkylating agents were: N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG), N-ethyl-N-nitrosourea (ENU), diethylsulfate (DES), ethyl methanesulfonate (EMS), epichlorohydrin (ECH) and ethylene dibromide (EDB). The animals were given a single intraperitoneal injection of the following doses of the chemicals: ENNG and ENU, 25, 50 and 100 mg/kg; EMS and DES, 100, 200 and 400 mg/kg body weight. For EDB and ECH, the doses were 50, 100 and 200 mg/kg, given twice, 24 h apart. Before and after the injection, blood samples were taken from the tails at 24-h intervals up to 72 h and preparations were made on AO-coated slides. For each dose group, 4 animals were used and 1000 reticulocytes were examined per slide for the presence of micronuclei. At the optimum induction time of 48 h, ENU induced micronucleated reticulocytes (MNRETs) at all 3 doses. ENNG and EMS induced MNRETs significantly at 2 dose levels each and DES only at the highest dose. ECH and EDB failed to induce MNRETs. On the basis of the dose of chemical needed to double the spontaneous frequency, the order of clastogenic potency was ENU greater than ENNG greater than EMS greater than DES. The results obtained compared favorably with those from other in vivo methods. The present technique proves to be simple, flexible and relatively sensitive. Shifts in the optimum induction peak in individual animals and by some chemicals can be picked up easily which is important when testing weak mutagens and chemicals with an unknown mechanism of action.

The genotoxicity of trenbolone, a synthetic steroid

Trenbolone, a synthetic androgen is used as a growth promotant in animal husbandry. Because of its steroidal structure and properties it has been extensively evaluated in a series of in vitro and in vivo assays to assess its genotoxic and initiating properties. Both the parent molecule 17-beta-hydroxy-trenbolone and its metabolite 17-alpha-hydroxy-trenbolone, produced only in cattle, have been tested. 17-beta-hydroxy-trenbolone was not genotoxic in the Ames Salmonella/microsome assay, cytogenetics assays in human lymphocytes and CHO cells, a micronucleus assay in CHO cells, a DNA repair synthesis assay in HeLa cells, mammalian cell mutation assays with CHO and V79 cells, the mouse micronucleus assay, rat bone marrow or spermatogonial cytogenetics assays or in a test for initiators in the rat. In the mouse lymphoma cell mutation assay with L 5178Y TK+/- cells, equivocal responses were obtained, particularly at highly toxic concentrations. With 17-alpha-hydroxy-trenbolone a weak positive response was obtained in the L5178Y Tk +/- assay, particularly at highly toxic concentrations. Negative results were obtained in the Ames Salmonella/microsome assay, the cytogenetics assays using both human lymphocytes in vitro and rat bone marrow in vivo, the DNA repair assay and in the CHO mammalian cell mutation assay. It was also negative in the in vivo test for initiators. From this extensive battery of data, and also taking into account published data on trenbolone, it is concluded that 17-alpha-hydroxytrenbolone and 17-beta-hydroxy-trenbolone are devoid of genotoxic activity and are not initiators of cancer.

Genotoxicity of three-carbon compounds evaluated in the SCE test in vitro

Three-carbon chemicals (chlorinated and nonchlorinated, saturated and unsaturated, hydroxy- and oxo-hydrocarbons) were assayed for genotoxicity. The sister chromatid exchange test in vitro served as the test system. Without S9 mix, the nonchlorinated solvents 1-propanol, 2-propanol, and 2-propanone (acetone) did not increase the SCE frequencies. All chlorinated 3-C hydrocarbons, except 1,2,3-trichloropropane, proved to be potent SCE inducers in V79 cells without S9 mix. In the presence of S9 mix, the results obtained with the nonchlorinated solvents were also negative, whereas 1,2,3-trichloropropane was transformed to SCE-inducing metabolites. The addition of S9 mix resulted in an increased SCE rate for 2,3-dichloropropanol, whereas genotoxicity of 2,3-dichloropropene, 1,2-dichloropropane, 1,3-dichloropropene, and 1,3-dichloropropanone was reduced. 1,3-dichloropropanol, 1,3-dichloropropene, and epichlorohydrin were substantially inactivated by S9 mix in the V79/SCE test. It can be concluded that the reactivity of the saturated dichloro compounds in the SCE test depends on the degree of oxidation. There is no general difference between the reactivity of alpha, beta-dichloro and alpha, omega-dichloro compounds.

Chromosome-damaging effects of heraclenin in human lymphocytes in vitro

Heraclenin, a furocoumarin with an epoxide group in its side chain, was analyzed to see if it induced structural chromosome aberrations and sister-chromatid exchanges (SCEs) in human lymphocytes in vitro. The results were compared directly with those of imperatorin, which differs from heraclenin only in lacking an epoxide group. An equally strong clastogenic effect was found for both heraclenin and imperatorin: the number of metaphases with breaks was increased in both cases by approximately a factor of 6. Heraclenin produced a considerable dose-dependent increase in the SCE rate, i.e., by about 60 induced SCEs/metaphase, whereas imperatorin induced only about 4 SCEs/metaphase. The results are discussed with respect to the occurrence of structural aberrations, which are primarily due to the basic furocoumarin structure itself, whereas the large increase in the SCE rate produced by heraclenin is most probably significantly influenced by its epoxide group.

Mortality in an european cohort occupationally exposed to epichlorohydrin (ECH)

A study was undertaken on the mortality of workers exposed to ECH at four European sites with plants producing epichlorohydrin (ECH), epoxy resins, glycerin, and other specialty chemicals derived from ECH. The vital status of 606 individuals with at least one year of exposure to ECH, starting at least 10 years before the final date of the study on 31 December, 1978, were collected. Mortality was analysed for a subgroup with 10 or fewer years of exposure, and another subgroup with more than 10 years of exposure. Four deaths from different cancers were observed against five expected. No excess mortality from cancer was observed in either subgroup or the complete cohort, which could be related to ECH exposure. The small size of the cohort and the limited number of deaths due to low average age (42 years), as well as the short duration of the observation period, do not allow a firm conclusion to be reached regarding the potential carcinogenicity of ECH in man. Current exposure levels are low, but exposure in the early days of production occasionally reached levels high enough to be irritating. We recommend updating the study 5 years from the final date of the present study, i.e. on 31 December, 1983. Within their limitations this and other epidemiological studies so far provide no evidence for an association between occupational exposure to ECH and the occurrence of malignant neoplasms in man.

Evaluation of epichlorohydrin (ECH) genotoxicity. Microsomal epoxide hydrolase-dependent deactivation of ECH mutagenicity in Schizosaccharomyces pombe in vitro

The mutagenic effect of epichlorohydrin (ECH) on the yeast Schizosaccharomyces pombe was studied in vitro in the presence of mouse-liver S9 mix and microsomal and cytosolic fractions. The incubations were always performed in the absence of NADPH-generating systems. S9 mix and microsomes from phenobarbital-pretreated mice significantly reduced ECH mutagenicity, whereas the cytosol did not result in any deactivating effect. The various protein contents of the subcellular fractions were not involved in any scavenger effect as regards ECH mutagenic activity. Moreover, the addition of reduced glutathione to the incubation mixtures indicated that it did not play an important role, either per se or through the enzyme(s) glutathione-S-epoxide transferase(s), in preventing ECH genotoxicity. Our results suggest that microsomal epoxide hydrolase(s) represents the major step in the detoxifying pathway of ECH. These observations were supported by measurements of the specific epoxide hydrolase activity in the various fractions on the same substrate.

Toxic activity of seventeen industrial solvents and halogenated compounds on human lymphocytes cultured in vitro

Seventeen chemicals (solvents, insecticides and intermediates in the production of textiles and resins) were tested in a short-term in vitro system with human lymphocytes to determine their toxic action. The parameters studied were the tritiated thymidine uptake and cell viability in cultures grown with or without a rat liver metabolizing system (S-9 mix). Data obtained showed that 1,3-dichlorobenzene, 1,2-dichlorobenzene, hexane, 1,2-diiodoethane, 1,4-dichlorobenzene, tetrachloroethylene, 2,3-dibromopropanol, chloromethyl methyl ether, 1,2- and 1,3-dibromopropane, in order, exerted the more toxic effects; ethyl acetate, cyclohexane, cyclohexanone and benzene showed lower toxic activity. The chemicals lost their toxic power in the presence of the metabolizing system with the exception of 1,2- and 1,3-dichlorobenzene which maintained in some degree their toxicity even in the presence of the S-9 mix. Only chloromethyl methyl ether elicited unscheduled DNA synthesis acting as DNA damaging agent.

Mutagenic action of structurally related alkene oxides on Schizosaccharomyces pombe: the influence, 'in vitro', of mouse-liver metabolizing system

A series of aliphatic epoxides were tested for their ability to induce forward mutations in the yeast Schizosaccharomyces pombe. For all the compounds under study, a linear dose-response relationship was found, and the ranking of the relative specific activity was: epichlorohydrin greater than ethylene oxide greater than glycidol greater than 1,2-epoxybutane greater than 1,1,1-trichloropropylene oxide greater than propylene oxide greater than 2,3-epoxybutane. The influence of the metabolic conversion of the epoxides by the mouse-liver S9 fraction was also investigated. In such conditions, except for the 2,3-epoxybutane, the genetic activity of epoxides seems to be reduced.

Evaluation of experimental parameters in an S9 /human leukocyte SCE test with cyclophosphamide

The experimental parameters S9 concentration, cofactor concentration and exposure time were investigated in a microsome test with human leukocyte cultures, To evaluate these parameters, their effects on cyclophosphamide-induced SCE frequencies and changes in cell proliferation were analyzed. By varying S9 concentration and exposure time, dose-effect relationships were found with respect to the induction of SCE. A relatively small effect was found when the concentrations of the cofactors NADP and G-6-P were varied. In general, an increase in SCE frequencies was accompanied by delayed cell proliferation. The importance of varying the experimental parameters to avoid false- negative results in microsome tests is discussed.