Chromosomal analysis in bone-marrow cells of Chinese hamsters after treatment with mycotoxins

Interaction of aflatoxin G1 with free DNA in vitro and possibility of its application in removing aflatoxin G1

The present study sought to evaluate the interaction between aflatoxin G₁ and free DNA in vitro through different analytical techniques. The UV-visible spectra results showed that the structure of DNA might be changed with a new aflatoxin G₁-DNA complex forming, which indicated that the interacting mode between them was the intercalating mode. The DNA melting temperature increased by 12.80 °C, suggesting that the DNA double helix structure was more compact and stable through intercalation. The circular dichroism (CD) spectra results indicated that the interaction of aflatoxin G₁ with DNA induced the DNA base stacking changes. The results of agarose gel electrophoresis and fluorescence microscope further verified that the interacting mode between aflatoxin G₁ and DNA was intercalation mode. According to the fluorescence spectrum data, the binding constant was calculated 6.24 × 10⁴ L·mol^-1. The thermodynamic results demonstrated that the reaction of aflatoxin G₁ intercalating to DNA was a spontaneous reaction. The elimination results suggested that aflatoxin G₁ could be enriched and removed by DNA intercalation through magnetic beads separation, with the removal efficiency of 93.73%. The study results would provide a theoretical basis for establishing a new aflatoxin removal method based on DNA intercalation.

Mycotoxin patulin in food matrices: occurrence and its biological degradation strategies

Patulin is a mycotoxin produced by a number of filamentous fungal species. It is a polyketide secondary metabolite which can gravely cause human health problems and food safety issues. This review deals with the occurrence of patulin in major food commodities from 2008 to date, including historical aspects, source, occurrence, regulatory limits and its toxicity. Most importantly, an overview of the recent research progress about the biodegradation strategies for contaminated food matrices is provided. The physical and chemical approaches have some drawbacks such as safety issues, possible losses in the nutritional quality, chemical hazards, limited efficacy, and high cost. The biological decontamination based on elimination or degradation of patulin using yeast, bacteria, and fungi has shown good results and it seems to be attractive since it works under mild and environment-friendly conditions. Further studies are needed to make clear the detoxification pathways by available potential biosorbents and to determine the practical applications of these methods at a commercial level to remove patulin from food products with special reference to their effects on sensory characteristics of foods.

Isotopic Labeling Studies Reveal the Patulin Detoxification Pathway by the Biocontrol Yeast Rhodotorula kratochvilovae LS11

Patulin (1) is a mycotoxin contaminant in fruit and vegetable products worldwide. Biocontrol agents, such as the yeast Rhodotorula kratochvilovae strain LS11, can reduce patulin (1) contamination in food. R. kratochvilovae LS11 converts patulin (1) into desoxypatulinic acid (DPA) (5), which is less cytotoxic than the mycotoxin (1) to in vitro human lymphocytes. In the present study, we report our investigations into the pathway of degradation of patulin (1) to DPA (5) by R. kratochvilovae. Isotopic labeling experiments revealed that 5 derives from patulin (1) through the hydrolysis of the γ-lactone ring and subsequent enzymatic modifications. The ability of patulin (1) and DPA (5) to cause genetic damage was also investigated by the cytokinesis-block micronucleus cytome assay on in vitro human lymphocytes. Patulin (1) was demonstrated to cause much higher chromosomal damage than DPA (5).

A core in vitro genotoxicity battery comprising the Ames test plus the in vitro micronucleus test is sufficient to detect rodent carcinogens and in vivo genotoxins

In vitro genotoxicity testing needs to include tests in both bacterial and mammalian cells, and be able to detect gene mutations, chromosomal damage and aneuploidy. This may be achieved by a combination of the Ames test (detects gene mutations) and the in vitro micronucleus test (MNvit), since the latter detects both chromosomal aberrations and aneuploidy. In this paper we therefore present an analysis of an existing database of rodent carcinogens and a new database of in vivo genotoxins in terms of the in vitro genotoxicity tests needed to detect their in vivo activity. Published in vitro data from at least one test system (most were from the Ames test) were available for 557 carcinogens and 405 in vivo genotoxins. Because there are fewer publications on the MNvit than for other mammalian cell tests, and because the concordance between the MNvit and the in vitro chromosomal aberration (CAvit) test is so high for clastogenic activity, positive results in the CAvit test were taken as indicative of a positive result in the MNvit where there were no, or only inadequate data for the latter. Also, because Hprt and Tk loci both detect gene-mutation activity, a positive Hprt test was taken as indicative of a mouse-lymphoma Tk assay (MLA)-positive, where there were no data for the latter. Almost all of the 962 rodent carcinogens and in vivo genotoxins were detected by an in vitro battery comprising Ames+MNvit. An additional 11 carcinogens and six in vivo genotoxins would apparently be detected by the MLA, but many of these had not been tested in the MNvit or CAvit tests. Only four chemicals emerge as potentially being more readily detected in MLA than in Ames+MNvit--benzyl acetate, toluene, morphine and thiabendazole--and none of these are convincing cases to argue for the inclusion of the MLA in addition to Ames+MNvit. Thus, there is no convincing evidence that any genotoxic rodent carcinogens or in vivo genotoxins would remain undetected in an in vitro test battery consisting of Ames+MNvit.

Protective effects of selenium against sister chromatid exchange induced by AFG 1 in human lymphocytes in vitro

Aflatoxins have been shown to be hepatotoxic, carcinogenic, mutagenic and teratogenic to different species of animals. Besides, at low concentrations, Selenium (Se(4+)) is antimutagenic and anticarcinogenic while it is toxic, mutagenic and carcinogenic at high concentrations. In this study, we aimed to evaluate the effect of Se(4+) against aflatoxin GAFG(1) (AFG(1)) on blood cultures in relation to induction of sister chromatid exchange (SCE). The results showed that at 0.4 and 0.8 parts per million (ppm) concentration of AFG(1), the frequency of SCE increased in cultured human lymphocytes. When different concentration of Se(4+) (0.08 and 8 ppm) were added to AFG(1), the frequencies of SCE decreased. Howewer, when 800 ppm concentration of Se(4+) together with 0.08 ppm AFG(1) were added to cell division inhibited in the cultures. Results suggested that Se(4+) could effectively inhibit AFG(1)-induced SCE. Besides, the protective role of Se(4+) against AFG(1)-induced SCE is probably related to its doses.

Evaluation of different biological test systems to assess the toxicity of metabolites from fungal biocontrol agents

The development of fungal biocontrol agents (BCAs) as alternatives to chemical pesticides is of increasing public interest. Tools to assess the toxicity of the secondary metabolites that these BCAs produce are often not available or existing methods have not yet been evaluated for these compounds. This study compares five different test systems, which include a representative bacterium, protozoan, arthropod and insect and human cell lines, as regards their sensitivity. It also compares the cost in time and resources for conducting the tests. Pure metabolites and crude extracts from two fungal BCAs as well as two chemical pesticides (hoestar and chlorpyrifos) and the mycotoxin patulin were employed as test compounds. All tests systems proved to be suitable for toxicity studies of metabolites from fungal BCAs and showed different grades of sensitivity to the different substances. The possibility of employing an array of test systems to determine ecotoxicological properties is discussed.

Evaluation of genotoxic risk and oxidative DNA damage in mammalian cells exposed to mycotoxins, patulin and citrinin

Mycotoxins are fungal secondary metabolites with very diversified toxic effects in humans and animals. In the present study, patulin (PAT) and citrinin (CTN), two prevalent mycotoxins, were evaluated for their genotoxic effects and oxidative damage to mammalian cells, including Chinese hamster ovary cells (CHO-K1), human peripheral blood lymphocytes, and human embryonic kidney cells (HEK293). PAT, but not CTN, caused a significant dose-dependent increase in sister chromatid exchange (SCE) frequency in both CHO-K1 and human lymphocytes. PAT also elevated the levels of DNA gap and break in treated CHO-K1. In the single cell gel electrophoresis (SCGE) assay, exposure of HEK293 to concentrations above 15 microM of PAT induced DNA strand breaks; the tail moment values also greatly increased after posttreatment with formamidopyrimidine-DNA glycosylase (Fpg). This suggests that in human cells PAT is a potent clastogen with the ability to cause oxidative damage to DNA. However, no significant change in the tail moment values in CTN-treated cultures was found, suggesting that CTN is not genotoxic to HEK293. Incubation of HEK293 with CTN increased the mRNA level of heat shock protein 70 (HSP70), but not that of human 8-hydroxyguanine DNA glycosylase 1 (hOGG1). PAT treatment did not modulate the expression of either HSP70 or hOGG1 mRNA.

Electrophilic properties of patulin. Adduct structures and reaction pathways with 4-bromothiophenol and other model nucleophiles

The mycotoxin patulin (PAT) is believed to exert its cytotoxic and chromosome-damaging effects by forming covalent adducts with essential cellular thiols. Since the chemical structures of such adducts are unknown to date, we have studied the reaction of PAT and its O-acetylated derivative with the monofunctional thiol model compound 4-bromothiophenol (BTP), which was chosen due to analytical advantages. By means of analytical and preparative high-performance liquid chromatography, 16 adducts of PAT and 3 adducts of acetyl-PAT were isolated and their chemical structures elucidated by (1)H and (13)C NMR, IR, and UV spectroscopy. Time course studies and analysis of daughter product formation from isolated intermediate adducts led to a detailed scheme for the reaction of PAT with BTP. The structures of adducts of PAT formed with other model nucleophiles, e. g., the aliphatic thiol 2-mercaptoethanol and the aromatic amine 4-bromoaniline, were also elucidated and found to corroborate the reaction scheme. In addition, one further reaction pathway was observed with 2-mercaptoethanol, which appears to be independent from those found for BTP. Our study with model nucleophiles provides insights into the electrophilic reactivity of PAT and proved to be useful for the structure elucidation of PAT adducts with biological nucleophiles of toxicological relevance, as will be reported by Fliege and Metzler [(2000) Chem. Res. Toxicol. 13, 373-381].

The mycotoxin patulin induces intra- and intermolecular protein crosslinks in vitro involving cysteine, lysine, and histidine side chains, and alpha-amino groups

As previous studies have indicated a multiple electrophilic reactivity of patulin (PAT) towards simple thiol nucleophiles, we have methodically investigated the ability of PAT to covalently crosslink proteins in vitro. By means of sodium dodecylsulphate polyacrylamide gel electrophoresis, the formation of PAT-induced intermolecular protein-protein crosslinks was clearly demonstrated for bovine serum albumin containing one thiol group per molecule, but also for the thiol-free hen egg lysozyme. Characterization of the crosslink sites was carried out by (1) modulation of the thiol groups with N-ethylimaleimide and 2-iminothiolane; (2) comparison with various known crosslinking agents, i.e. phenylenedimaleimide, glutardialdehyde, and dimethylsuberimidate, and (3) fluorescence incorporation studies using dansyl-labeled amino acids and a fluorescent glutathione derivative. The thiol group of cysteine was preferred for PAT-mediated crosslink reactions, but the side chains of lysine and histidine, and alpha-amino groups also exhibited reactivity. PAT can act both as a homobifunctional as well as a heterobifunctional crosslinking agent. The initial formation of a monoadduct with a thiol group appears to activate PAT for the subsequent reaction with an amino group, but also leads to rapid loss of further electrophilic properties when no second nucleophile for crosslink completion is available. Studies using microtubule proteins as a protein with experimentally controllable quarternary structure and a proposed cellular target for PAT toxicity emphasized the influence of specific sterical conditions on crosslink formation at low protein concentrations. Non-polymerized microtubule proteins, i.e. tubulin alpha,beta-dimers, formed a defined product with PAT consisting of an intramolecularly crosslinked beta-tubulin, whereas guanosine triphosphate- or paclitaxel-induced polymerization to microtubule-like quarternary structures prior to treatment with PAT gave rise to intermolecular crosslink formation between alpha- and beta-tubulin. In contrast, denaturated tubulin yielded none of those two new protein species, but only unspecific intramolecular crosslinks and highly crosslinked aggregates. Thus, in addition to the amino acid composition, the tertiary and quarternary superstructures of proteins appear to markedly influence their reactivity towards PAT. Under appropriate conditions, the generation of protein crosslinks could easily be observed at concentrations of PAT equal to or even below the concentration of the protein. The relevance of these novel reaction pathways of PAT demonstrated in vitro for its in vivo mechanisms of toxicity remains to be investigated.

Cyclophosphamide: review of its mutagenicity for an assessment of potential germ cell risks

Cyclophosphamide (CP) is used to treat a wide range of neoplastic diseases as well as some non-malignant ones such as rheumatoid arthritis. It is also used as an immunosuppressive agent prior to organ transplantation. CP is, however, a known carcinogen in humans and produces secondary tumors. There is little absorption either orally or intravenously and 10% of the drug is excreted unchanged. CP is activated by hepatic mixed function oxidases and metabolites are delivered to neoplastic cells via the bloodstream. Phosphoramide mustard is thought to be the major anti-neoplastic metabolite of CP while acrolein, which is highly toxic and is produced in equimolar amounts, is thought to be responsible for most of the toxic side effects. DNA adducts have been formed after CP treatment in a variety of in vitro systems as well as in rats and mice using 3H-labeled CP. 32P-postlabeling techniques have also been used in mice. However, monitoring of adducts in humans has not yet been carried out. CP has also been shown to induce unscheduled DNA synthesis in a human cell line. CP has produced mutations in base-pair substituting strains of Salmonella tryphimurium in the presence of metabolic activation, but it has been shown to be negative in the E. coli chromotest. It has also been shown to be positive in Saccharomyces cerevisiae in D7 strain for many endpoints but negative in D62.M for aneuploidy/malsegregation. It has produced positive responses in Drosophila melanogaster for various endpoints and in Anopheles stephensi. In somatic cells, CP has been shown to produce gene mutations, chromosome aberrations, micronuclei and sister chromatid exchanges in a variety of cultured cells in the presence of metabolic activation as well as sister chromatid exchanges without metabolic activation. It has also produced chromosome damage and micronuclei in rats, mice and Chinese hamsters, and gene mutations in the mouse spot test and in the transgenic lacZ construct of Muta Mouse. Increases in chromosome damage and gene mutations have been found in the peripheral blood lymphocytes of nurses, pharmacists and female workers occupationally exposured to CP during its production or distribution. Chromosome aberrations, sister chromatid exchanges and gene mutations have been observed in somatic cells of patients treated therapeutically with CP. In general, there is a maximum dose and an optimum time for the detection of genetic effects because the toxicity associated with high doses of CP will affect cell division. In germ cells, CP has been shown to induce genetic damage in mice, rats and hamsters although the vast majority of such studies have used male mice.(ABSTRACT TRUNCATED AT 400 WORDS)

Genotoxic evaluation of ammonium inactivated aflatoxin B1 in mice fed with contaminated corn

Aflatoxin B1 (AFB1) is a major contaminant in different agricultural products including maize. In an attempt to reduce this problem and the hazards to human health, an AFB1 inactivating system with ammonia has been developed. In this work we evaluated the efficiency of the system in mice using micronucleus (MN) and sister chromatid exchange (SCE) analysis. Four groups of animals were fed during 8 weeks with a special diet mainly composed of maize: (1) uncontaminated; (2) uncontaminated/inactivated; (3) contaminated/inactivated; and (4) contaminated. We evaluated MN at weekly intervals in peripheral blood, and in weeks 4 and 8 SCE frequencies were quantified in bone marrow cells. The results showed that animals fed with AFB1 contaminated/inactivated maize had a 45% lower level of induced cytogenetic damage than those animals fed with AFB1 contaminated, but not inactivated maize. A residual amount of AFB1 after the inactivating treatment and the reconversion back to AFB1 in the organism may account for the remaining increased levels of SCE and MN.

Dose and time dependence of chromosomal aberration yields of bone marrow cells in male Chinese hamsters after a single i.p. injection of aflatoxin B1

The frequency of chromosomal aberrations in bone marrow cells, after a single i.p. aflatoxin B1 (AFB1) dose, was examined in male Chinese hamsters (Cricetulus griseus). There was a significant increase in aberrant cells within 5 days of administration of a dose of 0.1 micrograms-5 mg AFB1/kg, and on the 36th day. After a single dose of 5 mg AFB1/kg the enhanced frequency of aberrant cells was monitored up to day 104 with no sign of a decrease to control level. The results indicate that the minimum mutagenic effect of an AFB1 dose in this system is 0.1 micrograms/kg. Attention is drawn to the long-term presence of chromosomal aberrations even after a single i.p. exposure to AFB1.

Species differences in mutagenicity testing: I. Micronucleus and SCE tests in rats, mice, and Chinese hamsters with aflatoxin B1

Three animal species used in in vivo mutagenicity testing--rats, mice and Chinese hamsters--were compared with respect to their mutagenic response to the mycotoxin aflatoxin B1 (AFB1). The micronucleus test and the SCE test with bone marrow cells were chosen as test methods, employing similar protocols for all species. The mutagenic potential of AFB1 was detected with rats and mice but not with Chinese hamsters. Rats were more susceptible to the mutagenic action of AFB1 than mice with regard to the effective dose. A difference in sensitivity between males and females was evident in rats and mice: male animals exhibited higher induced micronucleus frequencies than females, and a clear SCE-inducing effect was only detectable in male animals. These results are in agreement with those of in vitro and carcinogenicity studies. They may be due to metabolic differences between the species and sexes, predominantly differences in glutathione conjugation of the reactive AFB1 epoxide and in the formation of the metabolite aflatoxicol. Furthermore, it could be demonstrated that AFB1 seems to be a more potent inducer of micronuclei than of SCE. Since our results obtained with rats and mice were clearly positive, but with the Chinese hamster the mutagenic potential of AFB1 was not detectable with the test systems used, it can be concluded that the choice of an "inappropriate" test species may lead to a false negative judgment on the genotoxic potential of a test compound.

Morphological alterations induced by patulin on cultured hepatoma cells

Patulin is a mycotoxin produced by various Penicillium, Aspergillus and Byssochlamys species. To evaluate its inhibitory effect on cells, hepatoma tissue culture cells in suspension were incubated in presence of 30 microM of patulin for 7 h and investigated by transmission and scanning electron microscopy. By transmission electron microscopy, the most significant difference observed between treated and control cells was the disorganization of the cytoplasmic microfilaments in the treated cells. The disappearance of superficial membrane microvilli which contain microfibrillar material was visualized by scanning electron microscopy; the cells also presented protrusions. The effect of this toxin on the cytoskeleton can be compared to that exerted by colchicine or by cytochalasins.

Mycotoxin induction of somatic mosaicism in Drosophila and DNA repair in mammalian liver cell cultures

The genotoxic activity of four mycotoxins has been studied. A high level of somatic mutagenesis in imaginal disk of Drosophila melanogaster larvae and DNA repair synthesis in human embryo and adult rat liver cells cultures was induced only by the strong carcinogen aflatoxin B1. Patulin somewhat elevated the level of somatic mutations in D. melanogaster, but did not elicit DNA repair synthesis. Citrinin and stachybotryotoxin were inactive in both systems.

Comparison of somatic and germ cell models for cytogenetic screening

A variety of in vivo mammalian test models are available for screening of chemicals for mutagenicity at the chromosomal level. These models have been grouped into those focusing on somatic cell effects and those dealing with germ cell effects. An analysis of available literature indicates that 76 compounds have been tested from chromosome effects in both somatic and germ cells. Of these, concordant results (positive-positive or negative-negative) were obtained with 58 compounds. Of the remaining 18 compounds with discordant results, all were positive in somatic cells, but negative in germ cell assays. These results suggest an inherent relative insensitivity of germ cells themselves to mutagenic chemicals. In the context of screening for safety evaluation purposes, this analysis suggests that a negative somatic-cell response can be taken as highly predictive of negative results in a germ cell assessment.

Patulin, a further clastogenic mycotoxin, is negative in the SCE assay in Chinese hamster V79-E cells in vitro

Patulin is a potent inducer of chromatid-type aberrations in Chinese hamster V79-E cells, but loses its activity when 9000 g supernatant of rat-liver homogenate is added. The narrow dose range of patulin clastogenicity shows a quantitative relationship between absolute amount of mycotoxin applied and the number of indicator cells treated. Within a dose range permitting survival of V79-E, patulin does not induce an increase of the SCE rate. It is suggested that patulin clastogenicity is caused by interaction with chromosomal proteins and that DNA is not the virtual target of this mycotoxin.