Effect of fetal calf serum on the cadmium clastogenicity

Cytome micronucleus assays with a metabolically competent human derived liver cell line (Huh6): A promising approach for routine testing of chemicals?

One of the main problems of in vitro genotoxicity tests is the inadequate representation of drug metabolizing enzymes in most indicator cell lines which are currently used. We identified recently a human derived liver cell line (Huh6) which detected induction of DNA damage by representatives of different groups of promutagens without enzyme mix and showed that these cells are more suitable in terms of reproducibility and sensitivity as other currently used liver derived lines. We developed a protocol for micronucleus (MN) cytome assays with these cells and validated the procedure in experiments with representatives of different groups of directly and indirectly acting genotoxic carcinogens (MMS, cisplatin, PhIP, IQ, NDMA, B(a)P, AFB1, etoposide, and H₂ O₂ ). The optimal cytochalasin B concentration in combination with 48 hr treatment was found to be 1.5 μg/mL and leads to a cytokinesis block proliferation index in the range between 1.7 and 2.0. The morphological characteristics of different nuclear anomalies which reflect DNA damage (MN, nuclear bridges, and buds) and their baseline frequencies in untreated cells were characterized, and the rates which are required to cause significant effects were calculated. All compounds caused dose dependent induction of MN when the cells were treated for 24 hr, longer and shorter exposure times were less effective. Experiments with different serum levels (fetal bovine serum [FBS]) showed that 10% FBS in the medium (instead of 4%) causes a substantial increase of the sensitivity of the cells. Our results indicate that the new protocol is a promising approach for routine testing of chemicals. Environ. Mol. Mutagen. 60: 134-144, 2019. © 2018 The Authors. Environmental and Molecular Mutagenesis published by Wiley Periodicals, Inc. on behalf of Environmental Mutagen Society.

A study on the investigation of cadmium chloride genotoxicity in rat bone marrow using micronucleus test and chromosome aberration analysis

In this study, we investigated the genotoxic and cytotoxic potential of cadmium chloride (CdCl2)in Wistar rat tibia bone marrow cells, using the structural chromosomal aberration (SCA) and micronucleus (MN) test systems. CdCl2 was administered to adult female rats as repeated i.p. doses of 0.5 mg/kg b.w. for 18 week (four months) at 48 h intervals. Mitomycin C (MMC) was used as a positive control (2 mg/kg b.w.). This study shows that cadmium chloride treatment significantly induced the frequency of micronucleus in polychromatic erythrocytes in tibia bone marrow. This increase in micronucleus frequency shows that cadmium has a genotoxic effect on bone marrow at this level. Also, in order to determine cytotoxicity in bone marrow, the ratio of polychromatic erythrocytes to normochromatic erythrocytes was calculated in bone marrow. The results of this study indicate that CdCl2 decreased this ratio. The decrease of this ratio in bone marrow shows CdCl2 may lead to cytotoxicity. We have reported that 0.5 mg/kg-level chronic exposure to cadmium (Cd) has an injurious effect on bone marrow. Our findings indicate that CdCl2 has a cytotoxic and genotoxic effect on rat bone marrow at chronic exposure.

Cytotoxic and clastogenic activity of CdCl2 in human lymphocytes from different donors

The sensitivity of human lymphocytes from different donors to CdCl2 using a complex of methods for determination of cytotoxicity and genotoxicity was studied. As endpoints for cytotoxicity the mitotic index (MI) and apoptosis were evaluated. To indicate genotoxicity chromosome aberrations test (CA) was used. The results indicate an individual sensitivity of lymphocytes to CdCl2-induced damage, which is directly depending on the concentration (10(-6), 10(-5), 5×10(-5), 10(-4)mol/l) applied. The assessment of the toxic and genotoxic effect using various endpoints allows more complete risk estimation for organisms exposed to heavy metals. The results have direct practical significance for threat evaluation in humans.

Cadmium chloride-induced oxidative stress and DNA damage in the human Jurkat T cell line is not linked to intracellular trace elements depletion

Cadmium (Cd) is a widespread environmental contaminant. Cd affects the cellular homeostasis and generates damage via complex mechanisms involving interactions with other metals, induction of oxidative stress and apoptotic or necrotic cell death, depending on the cell type and the concentration. The goal of the present study was to investigate the effect of exposure to CdCl(2) on the intracellular trace elements levels, the antioxidant enzyme activities and on DNA damage in the Jurkat T cell line. Cells were exposed to 5, 25 and 50 μM of CdCl(2) for 24 h. Cd significantly reduced the viability of Jurkat T cells and induced a dose-dependent increase in DNA damage with statistically significant differences relative to controls (p<0.001); the superoxide dismutase and glutathione peroxidase activities were significantly decreased. Lipid peroxidation and protein carbonyl levels were significantly increased while glutathione and the total intracellular sulfhydryl groups were decreased showing clearly that an oxidative stress was generated by Cd. Surprisingly the treatment with Cd induced a significant increase in the intracellular levels of all the trace elements measured. The results indicate that cellular pro-oxidative stress induced by Cd is most likely mediated by disruption of redox homeostasis associated to a mishandling of redox-active transition metals and causes lipid and protein oxidation and oxidative DNA damage in Jurkat T cells.

Genotoxic effects of chromium(VI) and cadmium(II) in human blood lymphocytes using the electron microscopy in situ end-labeling (EM-ISEL) assay

Evaluation of genotoxic effects of potassium chromate (K2CrO4) and cadmium chloride (CdCl2) was carried out in human blood lymphocytes in vitro as measured by the electron microscopy in situ end-labeling (EM-ISEL). EM-ISEL was used to assess DNA single-strand breaks (SSBs) expressed as number of immunogold particles per microm2 of chromatin at both chromosomal and nuclear DNA levels. Human lymphocytes were cultured in supplemented RPMI medium for 72 h including treatment for 2 h with K2CrO4 (0-150 microM), CdCl2 (0-150 microM) or methyl methanesulfonate (500 microM) as a positive control. Quantification of SSBs by EM-ISEL showed that both compounds are genotoxic agents at non-cytotoxic concentrations. This study brings new information on the utility of EM-ISEL for the evaluation of genotoxicity and confirms the genotoxic effects induced by chromium and cadmium.

Involvement of oxygen free radicals in the serum-mediated increase of benzoquinone genotoxicity

The genotoxicity of benzoquinone (BQ), a toxic benzene metabolite, is greatly enhanced by the presence of fetal calf serum (FCS) in the incubation medium. The FCS effect is abolished by heat denaturation of serum proteins and is slightly decreased by dialysis. In the present study, we have further investigated the serum effect on BQ genotoxicity by measuring DNA damage produced in peripheral blood mononuclear cells (PBMCs) using the Comet assay. We have also evaluated the effect of human serum and rat liver post-mitochondrial fraction (S9) on the DNA damage produced by BQ. Both human serum and a rat liver S9 enhanced the genotoxicity of BQ in a manner similar to FCS. Gel filtration experiments showed that all the enhancing activity of the serum eluted with the high molecular weight fractions, suggesting that low molecular weight serum constituents do not play an important role in modulating genotoxicity. The genotoxicity-enhancing activity of serum was inhibited by the iron chelator deferoxamine and by superoxide dismutase and catalase. Incubating PBMCs with BQ in the presence of FCS also resulted in the accumulation of intracellular peroxides as demonstrated by loading the cells with 2',7'-dichlorofluorescin diacetate and analyzing for peroxide formation by flow cytometry. These results indicate that oxygen free radicals are involved in the enhancement of BQ-induced DNA damage by serum. We hypothesize that enzyme activities that reduce BQ by transferring single electrons could be the source of the oxygen free radicals.

Evaluation of the relationship of the molecular aggregation state of amphotericin B in medium to its genotoxic potential

This work analyzes the genotoxicity potential, in the G2 phase of the cellular cycle, of an amphotericin B (AmB) commercially available form (Fungizone), and correlates it with the physicochemical properties of this product in aqueous media. The genotoxic studies were performed using peripheral blood lymphocytes from human donors. The chromosome aberrations and mitotic index were determined. Absorption spectra of Fungizone were obtained by dispersion of the stock solution in water for injection at various AmB concentrations, and using different cuvette path lengths for spectrophotometric determination. The absorption spectra of Fungizone in water are concentration dependent. High concentrations of Fungizone present a spectrum with an intense band at 340 nm, characteristic of AmB self-association. Conversely, at low concentrations, the spectra are similar to those obtained with AmB in methanol, with a positive band at 409 nm, assigned to AmB monomeric form. Similarly, the cytogenetic analysis shows an important decrease on the mitotic index, which is also concentration dependent when compared with control. Furthermore, the chromosome aberrations present a small, not statistically significant, increase only at the highest concentration. The results suggest that the Fungizone presents a cytotoxicity similar to membrane pore formation in mammalian cells that depends on the existence of self-associated AmB. In the presence of only monomeric forms, this phenomenon disappears. However, no genotoxicity was observed in this study.

The impairments of neoblast division in regenerating planarian Polycelis felina (Daly.) caused by in vitro treatment with cadmium sulfate

The effects of cadmium sulfate on the neoblast mitotic activity in regenerating planarian Polycelis felina (Daly.) were investigated. Mitotic abnormalities and chromosomal aberrations were evaluated after 6-h treatment and 24-h recovery period. The blastema were fixed, and examined cytologically through routine lactoorceine squash preparations. Mitotic indices were also determined. Cadmium sulfate induced a dose-dependent decrease in neoblast mitotic activity, accompanied with disturbances in distribution of cells over mitotic phases. Different cytological abnormalities with varying frequency were observed. Marked mitotic depression was concentration-dependent. Toxic effects of cadmium in regenerating planarian were mainly associated with mitotic spindle disturbances. Immediately after treatment mitotic abnormalities were prevalent over chromosomal and C-mitosis was the most prominent one. After 24-h recovery period a prevalence of mitotic over chromosomal aberrations was still present in animals treated with two higher concentrations of cadmium sulfate. However, the proportions of cells with chromosome stickiness in all treated animals were significantly increased compared to their post-treatment values. Observed mitotic impairments could be related to mitotic arrest contributing to retardations and delays, especially in animals treated with the highest concentration tested. The results obtained indicated usefulness of short term invertebrate assays as an alternative to in vitro pre-screening of toxic chemicals.