An automated alkaline elution system: DNA damage induced by 1,2-dibromo-3-chloropropane in vivo and in vitro

Genotoxic and mutagenic studies of teratogens in developing rat and mouse

In this review, genotoxic and mutagenic effects of teratogenic chemical agents in both rat and mouse have been reviewed. Of these chemicals, 97 are drugs and 33 are pesticides or belong to other groups. Large literature searches were conducted to determine the effects of chemicals on chromosome abnormalities, sister chromatid exchanges, and micronucleus formation in experimental animals such as rats and mice. In addition, studies that include unscheduled DNA synthesis, DNA adduct formations, and gene mutations, which help to determine the genotoxicity or mutagenicity of chemicals, have been reviewed. It has been estimated that 46.87% of teratogenic drugs and 48.48% of teratogenic pesticides are positive in all tests. So, all of the teratogens involved in this group have genotoxic and mutagenic effects. On the other hand, 36.45% of the drugs and 21.21% of the pesticides have been found to give negative results in at least one test, with the majority of the tests giving positive results. However, only 4.16% of the drugs and 18.18% of the pesticides were determined to give negative results in the majority of the tests. Among tests with major negative results, 12.50% of the teratogenic drugs and 12.12% of the teratogenic pesticides were negative in all conducted tests.

Genotoxicity of Aflatoxin B1 and Ochratoxin A after simultaneous application of the in vivo micronucleus and comet assay

Aflatoxin B1 (AFB1) and Ochratoxin A (OTA) are genotoxic mycotoxins that can contaminate a variety of foodstuffs, the liver and the kidney being their target organs, respectively. The micronucleus (MN) assay (bone marrow) and the comet assay (liver and kidney) were performed simultaneously in F344 rats, treated with AFB1 (0.25 mg/kg b.w.), OTA (0.5 mg/kg b.w.) or both mycotoxins. After AFB1 treatment, histopathology and biochemistry analysis showed liver necrosis, focal inflammation and an increase in Alanine Aminotransferase and Aspartate Aminotransferase. OTA alone did not cause any alteration. The acute hepatotoxic effects caused by AFB1 were less pronounced in animals treated with both mycotoxins. With regard to the MN assay, after 24 h, positive results were obtained for AFB1 and negative results were obtained for OTA, although both toxins caused bone marrow toxicity. In the combined treatment, OTA reduced the toxicity and the number of MN produced by AFB1. In the comet assay, after 3 h, positive results were obtained for AFB1 in the liver and for OTA in the kidney. The combined treatment reduced DNA damage in the liver and had no influence in the kidney. Altogether, these results may be indicative of an antagonistic relationship regarding the genotoxicity of both mycotoxins.

Genotoxic effects of two-generational selenium deficiency in mouse somatic and testicular cells

Many studies have investigated genotoxic effects of high Se diets but very few have addressed the genotoxicity of Se deprivation and its consequences in germ cells and none in somatic cells. To address these data gaps, C57BL/6 male mice were subjected to Se deprivation starting in the parental generation, i.e. before conception. Mice were given a diet of either low (0.01mg Se/kg diet) or normal (0.23mg Se/kg diet) Se content. Ogg1-deficient (Ogg1 (-/-) ) mice were used as a sensitive model towards oxidative stress due to their reduced capacity to repair oxidised purines. Ogg1 (-/-) mice also mimic the repair characteristics of human post-meiotic male germ cells which have a reduced ability to repair such lesions. The genotoxicity of Se deficiency was addressed by measuring DNA lesions with the alkaline single cell gel electrophoresis (+ Fpg to detect oxidised DNA lesions) in somatic cells (nucleated blood cells and lung cells) and male germ cells (testicular cells). Total Se concentration in liver and GPx activity in plasma and testicular cells were measured. Gene mutation was evaluated by an erythrocyte-based Pig-a assay. We found that Se deprivation of F1 from their conception and until early adulthood led to the induction of DNA lesions in testicular and lung cells expressed as significantly increased levels of DNA lesions, irrespective of the mouse genotype. In blood cells, Se levels did not appear to affect DNA lesions or mutant cell frequencies. The results suggest that the testis was the most sensitive tissue. Thus, genotoxicity induced by the low Se diet in the spermatozoal genome has potential implications for the offspring.

Octyl methoxycinnamate modulates gene expression and prevents cyclobutane pyrimidine dimer formation but not oxidative DNA damage in UV-exposed human cell lines

Octyl methoxycinnamate (OMC) is one of the most widely used sunscreen ingredients. To analyze biological effects of OMC, an in vitro approach was used implying ultraviolet (UV) exposure of two human cell lines, a primary skin fibroblast (GM00498) and a breast cancer (MCF-7) cell lines. End points include cell viability assessment, assay of cyclobutane pyrimidine dimers (CPDs) and oxidated DNA lesions using alkaline elution and lesion-specific enzymes, and gene expression analysis of a panel of 17 DNA damage–responsive genes. We observed that OMC provided protection against CPDs, and the degree of protection correlated with the OMC-mediated reduction in UV dose. No such protection was found with respect to oxidative DNA lesions. Upon UV exposure in the presence of OMC, the gene expression studies showed significant differential changes in some of the genes studied and the expression of p53 protein was also changed. For some genes, the change in expression seemed to be delayed in time by OMC. The experimental approach applied in this study, using a panel of 17 genes in an in vitro cellular system together with genotoxicity assays, may be useful in the initial screening of active ingredients in sunscreens.

In vitro investigations of glycidamide-induced DNA lesions in mouse male germ cells and in mouse and human lymphocytes

The industrial compound and food contaminant acrylamide (AA) is a probable human carcinogen, also known to induce male-mediated reproductive effects in animals. Most data suggest that its metabolite glycidamide (GA) is involved in the observed toxicity. We have investigated in vitro effects of AA/GA in mouse male germ cells (prior to spermatid elongation) and human and mouse peripheral blood lymphocytes, to assess inter-species and cell-type differences in susceptibility, and to explore the nature of the DNA lesion(s) as well as their potential repair. The comet assay was used in combination with the DNA-repair enzymes Fpg and hOGG1 to measure specific DNA lesions. In contrast to AA, GA induced significant levels of DNA lesions (strand breaks and alkali-labile sites) at millimolar concentrations in mouse testicular cells and human peripheral blood lymphocytes (hPBL). Using Fpg, the GA-induced DNA damage was measured at 20-50-fold higher sensitivity, in all cell types investigated. GA-induced DNA damage could not be recognised by hOGG1, suggesting that, based on the known affinities of these repair enzymes, alkylation of guanine is involved, rather than oxidation. Human lymphocytes appeared to be more susceptible to GA-induced lesions than both types of mouse cells. Mouse testicular cells and lymphocytes seemed to respond similarly to GA-induced Fpg-sensitive DNA lesions. The persistence of lesions was explored with cells from mice either proficient or deficient in Ogg1 (mouse 8-oxoguanine DNA glycosylase). Low in vitro repair of GA-induced Fpg-sensitive lesions was observed in primary male germ cells and lymphocytes from both Ogg1(+/+) and Ogg1(-/-) mice. We conclude that there may be differences between mice and humans in AA/GA-induced genotoxicity, and DNA from mouse male germ cells does not appear to be more sensitive to GA than DNA from peripheral blood lymphocytes in vitro. The usefulness of the comet assay in combination with DNA-repair enzymes is demonstrated.

Safety assessment and risk–benefit analysis of the use of azodicarbonamide in baby food jar closure technology: Putting trace levels of semicarbazide exposure into perspective – A review

The discovery of trace levels of semicarbazide (SEM) in bottled foods (especially baby foods) led to a consideration of the safety of this hydrazine compound by regulatory agencies worldwide. Azodicarbonamide, which is used in the jar-sealing technology known as Press On-Twist Off (or Push-Twist/PT) closures for the formation of a hermetic, plastisol seal, partially degrades with the heat of processing to form trace amounts of SEM. This review has evaluated the potential toxicological risks of resulting exposure to SEM and also the benefit of the PT technology (with azodicarbonamide) in the context of possible microbial contamination. It also considers the potential impact on infant nutrition if parents come to the conclusion that commercial baby foods are unsafe. SEM shows limited genotoxicity in vitro that is largely prevented by the presence of mammalian metabolic enzymes. Negative results were found in vivo in DNA alkaline elution, unscheduled DNA synthesis and micronucleus assays. This pattern is in contrast to the genotoxic hydrazines that also have been shown to cause tumours. Carcinogenicity studies of SEM are of limited quality, show a questionable weak effect in mice at high doses, which are not relevant to human exposure at trace levels, and show no effect in the rat. The IARC has assigned SEM as Group 3, 'Not classifiable as to its carcinogenicity to humans'. Based on estimates of exposure to infants consuming baby foods (with the assumption of SEM levels at the 95th percentile of 20 ng g(-1) in all of the consumed 'ready-to-eat' foods) compared with a no observed adverse effect level (NOAEL) in developmental toxicity studies, the margin of safety is more than 21 000. Since the risk of an adverse effect is negligible, it is clear that any theoretical risk is outweighed by the benefits of continuing use of the PT closure (with azodicarbonamide blowing agent) to ensure both the microbial integrity and availability of commercial baby foods as a valuable source of infant nutrition.

Estrogenic effects of environmental chemicals: an interspecies comparison

The development of various in vitro screening methods has led to identification of novel estrogenic chemicals of natural and anthropogenic origin. In this study, the (anti)estrogenic potential of several environmental chemicals were compared in an array of in vitro test systems comprising: (i) competitive binding to estrogen receptors derived from the human breast cancer cell line MCF-7 (hER) and rainbow trout (Oncorhynchus mykiss) (rtER), (ii) a proliferation assay with MCF-7 cells (E-SCREEN), and iii) induction of vitellogenin (rtVtg) in isolated rainbow trout hepatocytes. The results showed substantial differences in assay sensitivity for potent estrogens like 17beta-estradiol, diethylstilbestrol and zearalenone (ranking order of sensitivity: E-SCREEN > hER approximately rtER approximately rtVtg). Chemicals like 4-n-nonylphenol and bisphenol A had higher relative binding affinity to the hER, whereas 4-t-butylphenol and 4-n-butylphenol showed highest affinity to the rtER. Zearalenone and the novel estrogen 4-t-butylhexanol displayed a considerable higher relative potency in the E-SCREEN than the rtVtg assay, whereas alkylphenols and the novel estrogen mimic 4-t-butyl-nitrobenzene were most potent in fish cells. Correlation analysis of data from the test systems suggest that interspecies differences is largely due to inter-assay variation of the ER-dependent cellular responses, whereas binding to the ER are fairly similar in the two species tested.

Antiepileptic drugs inhibit cell growth in the human breast cancer cell line MCF7

Several antiepileptic drugs (AEDs) are associated with anti-cancer activity. At the same time, many AEDs alter endocrine function with phenytoin (PHT) and phenobarbital (PB) causing-reduced free fractions of sex-steroid hormones, while VPA induces hyperandrogenism. Changes in sex-steroid hormone levels are known to affect apoptosis in endocrine tissue. The aim of the study was to investigate the influence of the antiepileptic drugs PHT, PB, VPA and lamotrigine (LTG) on estrogen-stimulated cell growth of human breast cancer cells (MCF-7), and to evaluate whether this effect could be related to a direct estrogen receptor (ER) binding. VPA reduced cell growth at therapeutically relevant concentrations; half-maximum effect of VPA on cell growth was 230 microM. PHT (100 microM) and PB (10 microM) reduced cell growth by 47 and 21%, respectively. None of the drugs had affinity to isolated estrogen receptors, and excess of estrogen was not able to abolish the growth inhibition provoked by VPA. However, sub-therapeutic concentrations of VPA (100 microM) mimicked estrogen by inducing cell growth (11%) in an estrogen-depleted medium, an effect that was abolished by adding an estrogen receptor antagonist. In conclusion; the estrogen receptor appear to be indirectly activated by sub-therapeutic concentrations of VPA, but therapeutic concentrations of VPA inhibits cell growth by mechanisms that do not seem to involve the estrogen receptor or estrogen stimulation.

Effects of the environmental oestrogens bisphenol A, tetrachlorobisphenol A, tetrabromobisphenol A, 4-hydroxybiphenyl and 4,4'-dihydroxybiphenyl on oestrogen receptor binding, cell proliferation and regulation of oestrogen sensitive proteins in the human breast cancer cell line MCF-7

Bisphenol A is extensively used in the manufacturing of epoxy resins and polycarbonate plastics, whereas several brominated and chlorinated analogues are used as flame retardants and intermediates in the plastic industry. Due to the structural relationship between these chemicals and the high production volumes, we wanted to characterize and compare their potential oestrogen-like potency using several end-points in MCF-7 cells: induction of pS2 protein and progesterone receptor, reduction of oestrogen receptor level, and stimulation of cell growth. Bisphenol A, tetrachloro- and tetrabromo-bisphenol A, 4-hydroxybiphenyl and 4,4'-dihydroxybiphenyl all showed oestrogen-like properties in MCF-7 cells. The chemicals tested had affinity to the oestrogen receptor isolated from MCF-7 cells, although their EC50s were 1,000 to 80,000 times higher than the EC50 of 17beta-oestradiol. Bisphenol A and 4-hydroxybiphenyl induced cell growth in MCF-7 cells, and the highest test concentrations induced responses, apparently exceeding the cell growth induced by 17beta-oestradiol. The other chemicals tested induced less than 50% of the maximum 17beta-oestradiol-stimulated cell growth. Bisphenol A, 4-hydroxybiphenyl, tetrabromobisphenol A and tetrachlorobisphenol A all increased the level of the oestrogen-regulated proteins, progesterone receptor and pS2, whereas 4,4'-dihydroxybiphenyl showed no such effect. Bisphenol A was the only chemical tested that clearly mimicked 17beta-oestradiol in its ability to reduce the level of cytosolic oestrogen receptors in MCF-7 cells. By measuring several oestrogen-dependent endpoints it seems that some xeno-oestrogens cause an imbalanced oestrogen-response. Their ability and potency in mimicking 17beta-oestrogen in one parameter is not necessarily accompanied by a similar effect in another oestrogen-linked parameter.

Limited repair of 8-hydroxy-7,8-dihydroguanine residues in human testicular cells

Oxidative damage in testicular DNA is associated with poor semen quality, reduced fertility and increased risk of stillbirths and birth defects. These DNA lesions are predominantly removed by base excision repair. Cellular extracts from human and rat testicular cells and three enriched populations of rat male germ cells (primary spermatocytes, round spermatids and elongating/elongated spermatids) all showed proficient excision/incision of 5-hydroxycytosine, thymine glycol and 2,6-diamino-4-hydroxy-5-formamidopyrimidine. DNA containing 8-oxo-7,8-dihydroguanine was excised poorly by human testicular cell extracts, although 8-oxoguanine-DNA glycosylase-1 (hOGG1) was present in human testicular cells, at levels that varied markedly between 13 individuals. This excision was as low as with human mononuclear blood cell extracts. The level of endonuclease III homologue-1 (NTH1), which excises oxidised pyrimidines, was higher in testicular than in somatic cells of both species. Cellular repair studies of lesions recognised by formamidopyrimidine-DNA glycosylase (Fpg) or endonuclease III (Nth) were assayed with alkaline elution and the Comet assay. Consistent with the enzymatic activities, human testicular cells showed poor removal of Fpg-sensitive lesions but efficient repair of Nth-sensitive lesions. Rat testicular cells efficiently repaired both Fpg- and Nth-sensitive lesions. In conclusion, human testicular cells have limited capacity to repair important oxidative DNA lesions, which could lead to impaired reproduction and de novo mutations.

Anguilla anguilla L. biochemical and genotoxic responses to benzo[a]pyrene

Eels (Anguilla anguilla L.) were exposed for 2, 4, 6, 8, 16, 24, 48, 72, 144, and 216 h to 0 (control), 0.3, 0.9, and 2.7 microM benzo[a]pyrene (BaP). The biotransformation induced by BaP was measured as liver ethoxyresorufin O-deethylase (EROD) activity and cytochrome P450 content, and compared with the genotoxic effects, such as erythrocytic nuclear abnormalities (ENA), and blood and liver DNA strand breaks. The liver exhibited a highly significant EROD activity increase from 2 up to 216 h exposure to 0.9 and 2.7 microM BaP, whereas 0.3 microM BaP exposure induced a significant liver EROD increase from 2 up to 144 h. Liver cytochrome P-450 content was significantly increased at 8 h to 2.7 microM BaP exposure. Liver DNA integrity was decreased at 16 h, from 8 up to 144 h and 8 up to 72 h exposure to 0.3, 0.9, and 2.7 microM BaP, respectively. A significant decrease in blood DNA integrity was observed at 48, 72, 144 h, from 8 up to 72, and from 6 up to 72 h exposure to 0.3, 0.9, and 2.7 microM BaP, respectively. The A. anguilla L. genotoxic response to BaP, measured as ENA induction, was significantly increased at 144 h exposure to 0.3 microM BaP. The intermediate BaP concentration tested (0.9 microM) induced a significant three fold ENA increase at 48 and 72 h exposure compared to their controls. The highest BaP concentration (2.7 microM) induced a significant increase in ENA frequency at 72, 144 and 216 h exposure.

Brominated phenols: characterization of estrogen-like activity in the human breast cancer cell-line MCF-7

A large number of halogenated phenols are detected in the blood of humans, fish and wild-animals. We have characterized the estrogen-like activity of phenol, 4-bromophenol (4-BP), 2,4-dibromophenol (2,4-DBP), 2,4,6-tribromophenol (2,4,6-TBP) and 4-tert-butylphenol (tert-BP) using the estrogen-dependent human breast cancer cell line MCF-7. 4-BP, 2,4-DBP and 4-tert-BP all bind to the estrogen receptor (ER) with approximately 10,000-fold less affinity than 17 beta-estradiol (17 beta-E). 2,4,6-TBP was only able to displace 43% of radiolabelled estrogen when tested at concentrations up to 1 microM, whereas phenol had no affinity for the ER. 4-tert-BP stimulated cell growth and induced estrogen-regulated proteins such as the progesterone receptor (PgR) and pS2. The brominated phenols, however, although binding to the ER, did not stimulate cell growth or increase the levels of the PgR or pS2, or reduce the level of 17 beta-E induced pS2. On the contrary, 4-BP, 2,4-DBP and partly 4-tert-BP reduced 17 beta-E-stimulated cell growth apparently by an ER independent mechanism.

DNA damage induced by the drinking water mutagen 3-chloro-4-(dichloromethyl)-5-hydroxy-2[5H]-furanone (MX) in mammalian cells in vitro and in mice

3-chloro-4-(dichloromethyl)-5-hydroxy-2[5H]-furanone (MX) formed during chlorination of water containing natural organic substances, is a very potent bacterial mutagen. Recently, tumours at multiple sites were reported in rats given MX-containing drinking water. We have investigated the genotoxicity of MX in mammalian cells exposed in vitro and in vivo using alkaline filter elution to detect DNA single-strand breaks and/or alkali-labile sites (SSBs). Concentrations as high as 100 and 300 microM MX were required to induce detectable levels of SSBs in the HL-60 cells. If MX treatment was carried out in the presence of DNA repair inhibitors (AraC plus hydroxyurea), the sensitivity of the assay to detect MX-induced SSBs was increased by a factor of 100. The presence of serum proteins during exposure resulted in a minor reduction of the MX-induced DNA damage in HL-60 cells at the lowest MX concentrations. In primary cultures of testicular cells as well as in resting human peripheral blood mononuclear cells (PBMC), a slightly increased level of SSBs was observed at MX-concentrations above 30 microM, this effect was not further increased by repair inhibitors. In LLC-PK1 renal proximal tubular epithelial cells and in growth stimulated human peripheral PBMC, increased SSBs were detected at MX concentrations as low as low as 3-10 microM and higher using repair inhibitors, and at 10 times higher concentrations without repair inhibitors. No dose dependent DNA damage was detected in the liver, kidney, spleen and colon of male B6C3F1 mice administrated high doses of MX (40 and 80 mg kg-1). Moderately increased and dose dependent SSBs were detected in the liver and kidney in the presence of DNA repair inhibitors during MX treatment, but no such increase was observed in the spleen and colon.

Metabolism and activation of cyclopenta polycyclic aromatic hydrocarbons in isolated human lymphocytes, HL-60 cells and exposed rats

The metabolism of radiolabelled benz(j)aceanthrylene (B(j)A) was studied in suspensions of isolated human peripheral mononuclear blood cells (lymphocytes), using high performance liquid chromatography (HPLC). The only known metabolite found after 24 h exposure to 30 microg/ml (120 microM) B(j)A, was B(j)A-1,2-dihydrodiol, representing approximately 35% of the total metabolites formed. B(j)A, benz(l)aceanthrylene (B(l)A) and benzo(a)pyrene (B(a)P) all caused DNA adducts in human lymphocytes, as well as in the human promyelocytic cell line HL-60 cells, as measured by the 32P-postlabelling technique (30 microg/ml, 24 h). The total DNA adduct levels in human lymphocytes exposed to B(j)A, B(l)A or B(a)P were 0.13 +/- 0.03, 1.10 +/- 0.62 and 0.37 +/- 0.10 fmol/microg DNA, respectively, and similar levels were obtained in HL-60 cells (0.18 +/- 0.14, 0.97 +/- 0.35 and 0.29 +/- 0.17 fmol/microg DNA, respectively). For each compound, the human lymphocytes and HL-60 cells in addition showed similar DNA adduct patterns. Cells exposed to B(j)A revealed only one DNA adduct, which, judged by its TLC properties, resulted from B(j)A-1,2-epoxide. As measured by the alkaline filter elution technique, only low levels of single strand DNA breaks (SSB) were observed in both human lymphocytes and HL-60 cells after exposure to B(j)A, B(l)A or B(a)P (24 h, 30 microg/ml). By adding cytosine-1-beta-D-arabinofuranoside (Are C) and hydroxyurea (HU) 1 h prior to analysis to prevent strand break rejoining, some increase in SSB (2-3 times) was observed in the lymphocytes. Co-incubation of human lymphocytes with liver microsomes from PCB-treated rats for 1 h and exposure to B(j)A or B(l)A, increased the DNA adduct levels in the lymphocytes to 12.3 and 37.8 fmol/microg DNA, respectively. A large increase in SSB was also observed, whereas no such increase was observed after co-incubation with human liver microsomes. In vivo exposure of rats to 30 mg/kg B(j)A (i.p.) for 24 h revealed one major DNA adduct in lymphocytes and lung tissue (only one of three rats showed an adduct in liver tissue), apparently resulting from B(j)A-1,2-epoxide. The total DNA adduct level in the lymphocytes was 0.09 fmol/microg DNA, and in lung tissue between 0.10 and 0.62 fmol/microg DNA. Overall, the present data suggests that oxidation at the cyclopenta-ring is an important activation pathway for B(j)A in rats as well as in humans.

Apoptosis in HL-60 cells induced by 3-chloro-4-(dichloromethyl)-5-hydroxy-2[5H]-furanone (MX)

The potent bacterial mutagen 3-chloro-4-(dichloromethyl)-5-hydroxy-2[5H]-furanone (MX), which is formed during chlorination of drinking water, has been studied with respect to induction of cell death in promyelocytic leukemic HL-60 cells. Cells exposed to MX for 1 h and further incubated for 3 h, revealed no significant increase in the proportion of cells with compromised plasma membrane damage as judged by trypan blue or propidium iodide exclusion. However, flow cytometric studies and microscopic analysis of HL-60 cells after staining with Giemsa or Hoechst 33342, revealed that more than 30% of the cells exposed to 30-100 microM of MX, showed the characteristic morphology and biochemical markers of apoptosis. On the other hand, in cultures exposed to 300 microM MX, less than 5% of the cells appeared to be apoptotic (< G1 DNA) 3 h after treatment, which is similar to control values. Microscopic analysis of Hoechst 33342-stained cells revealed that they were 'arrested' in the early stages of chromatin condensation, but these cells eventually became necrotic. Some decrease in the percentage of cells in S-phase was observed 3 h after exposure to MX (10, 30 and 100 microM), but the induced cell death was not markedly cell stage specific. The characteristic ladder pattern of apoptotic cells was observed when DNA isolated from MX-exposed HL-60 cells was electrophoresed in agarose. The apoptotic process could also be detected by analysis with alkaline filter elution (AE), as a decrease in the total DNA recovered; and by single cell gel electrophoresis, as a decrease in the average number of cells/comets observable on each slide. With the protocols used no apparent increase in values in the normalized area above the curve (NAAC) (alkaline elution) or tail moments (single cell gel electrophoresis (SCGE)) were detected, indicating that apoptotic cells are not necessarily a confounding factor when assaying for genotoxicity with these techniques.

DNA damage, gadd153 expression, and cytotoxicity in plateau-phase renal proximal tubular epithelial cells treated with a quinol thioether

2-Bromo-bis-(glutathion-S-yl)hydroquinone [2-Br-bis-(GSyl)HQ] causes DNA single-strand breaks (SSB), causes growth arrest, induces the expression of gadd153 (a gene inducible by growth arrest and DNA damage), and decreases histone H2B mRNA in log-phase renal proximal tubular epithelial cells (LLC-PK1). Renal epithelial cells in vivo normally exhibit a low mitotic index, therefore experiments in both plateau- and log-phase cells are necessary for a comprehensive understanding of the stress response to 2-Br-bis-(GSyl)HQ. In the present article we demonstrate that not all features of the stress response in log-phase cells are reproduced in plateau-phase cells. Thus, although 2-Br-bis-(GSyl)HQ causes concentration and time-dependent increases in DNA SSB, and increases the expression of gadd153, histone H2B mRNA levels are unaltered in plateau-phase cells. The relationship between reactive oxygen species, DNA damage, gene expression, and cytotoxicity was also investigated. Our findings suggest that (i) 2-Br-bis-(GSyl)HQ-mediated DNA damage in LLC-PK1 cells is mediated by the generation of H2O2; (ii) DNA damage, either directly or indirectly, contributes to cell death; and (iii) DNA damage, either directly or indirectly, provides the initial signal for gadd153 expression. In addition, DNA repair is rapid in LLC-PK1 cells, and the DNA-repair inhibitors 1-beta-D-arabinofuranosylcytosine and hydroxyurea have no effect on the amount of DNA SSB. Although the addition of 3-aminobenzamide following 2-Br-bis-(GSyl)HQ exposure has no effect on the removal of DNA SSB, it causes a slight but significant increase in gadd153 expression and cell viability, indicating that activation of poly(ADP-ribose)polymerase may exacerbate toxicity. Finally, aurintricarboxylic acid did not prevent DNA SSB or cytotoxicity in 2-Br-bis-(GSyl) HQ-treated LLC-PK1 cells, implying that activation of endonucleases does not play a role in these processes.

DNA damage induced by 3-chloro-4-(dichloromethyl)-5-hydroxy-2[5H]-furanone (MX) in HL-60 cells and purified DNA in vitro

Chlorinated tap water often contains 3-chloro-4-(dichloromethyl)-5-hydroxy-2[5H]-furanone (MX), which is a potent directly acting bacterial mutagen. We have investigated the induction of DNA damage by MX in a promyelocytic human leukaemia cell line (HL-60 cells). Exposure of HL-60 cells to 100-300 microM MX resulted in increased levels of DNA single-strand breaks and/or alkali-labile sites (SSBs) as detected by alkaline filter elution. When adding inhibitors of DNA break repair (AraC plus hydroxyurea), increased levels of DNA SSBs were observed at very low concentrations (1-3 microM) of MX, as observed by both alkaline filter elution and the single-cell gel electrophoresis assay. Increased DNA SSBs could also be observed if DNA repair inhibitors were added immediately after exposure to 10 microM MX, indicating that low concentrations of MX cause a relatively stable modification of DNA that may be recognized and incised by DNA repair enzyme activities. Further studies with DNA break repair inhibitors indicated that HL-60 cells exposed to 10 microM MX for 1 h repaired 50% of their initial DNA damage during a 2-h period and the repair appeared to be complete at 22 h. Analysis of MX-treated DNA by sequencing methods indicated that MX preferentially reacts with guanines in DNA.

Photoprotection by furocoumarin-induced melanogenesis against DNA photodamage in mouse epidermis in vivo

The photoprotective properties of furocoumarin plus UVA-induced epidermal melanogenesis were assessed in hairless mice. The ear and dorsal surfaces were topically treated with 6,4,4'-trimethylangelicin (TMA), 5-methoxypsoralen (5-MOP), 8-methoxypsoralen (8-MOP) or psoralen and exposed to UVA for 12 consecutive week-days. The TMA treatment induced intense tanning whereas modest tanning was seen with the other compounds. Seven days after the last treatment, the mice were challenged with a DNA damaging dose of UV radiation. Single strand breaks (SSB) in epidermal DNA were assessed by alkaline elution. Photoprotection was assessed by comparing SSB in furocoumarin-treated mice with control mice (vehicle plus UVA and also no treatment). No photoprotection was seen, with any compound, in dorsal epidermis despite intense pigmentation induced by TMA. Modest photoprotection with all compounds was seen in ear epidermis that was independent of the level of pigmentation. These data show that induced melanogenesis is not always associated, with photoprotection.

A comparative study of chemically induced DNA damage in isolated human and rat testicular cells

Testicular cells prepared from human organ transplant donors or from Wistar rats were used to compare 15 known reproductive toxicants with respect to their ability to induce DNA damage, measured as single-strand DNA breaks and alkali labile sites (ssDNA breaks) with alkaline filter elution. The compounds tested included various categories of chemicals (i.e., pesticides, industrial chemicals, cytostatics, and mycotoxins) most of which are directly acting genotoxicants (i.e., reacting with DNA either spontaneously or via metabolic activation). In addition, a few indirect genotoxic and nongenotoxic reproductive toxicants were included. Six of the chemicals induced no significant levels of ssDNA breaks in human and rat testicular cells; methoxychlor (10 to 100 microM, human and rat), benomyl (10 to 100 microM, human and rat), thiotepa (10 to 1000 microM, human and rat), cisplatin (30 to 1000 microM, human; 100 to 1000 microM, rat), Cd2+ (30 to 1000 microM, human; 100 to 1000 microM, rat), and acrylonitrile (30 to 1000 microM, human; 30 to 300 microM, rat). Four chemicals induced significant levels of ssDNA breaks in testicular cells from both species: styrene oxide (> or = 100 microM, rat and human), 1,2-dibromoethane (EDB) (> or = 100 microM, rat; 1000 microM human), thiram (> or = 30 microM, rat; > or = 100 microM, human), and chlordecone (300 microM, rat; > or = 300 microM, human). Finally, five chemicals induced ssDNA breaks in one of the two species. Four chemicals induced significant ssDNA breaks in rat testicular cells only: 1,2-dibromo-3-chloropropane (DBCP) (> or = 10 microM), 1,3-dinitrobenzene (1,3-DNB) (> or = 300 microM), Cr6+ (1000 microM), and aflatoxin B1 (> or = 100 microM), the last two of these produced only a minor positive response. One chemical, acrylamide, induced a marginal increase in ssDNA breaks in human at 1000 microM, but not in rat testicular cells. Although based on a limited number of donors, the data indicate a close correlation between the induction of DNA damage in human and rat testicular cells in vitro. For some chemicals, however, there appears to be differences in the susceptibility to chemically induced ssDNA breaks of isolated testicular cells from the two species. The data indicate that the parallel use of human and rat testicular cells provides a valuable tool in the assessment of human testicular toxicity.

DNA damage induced by etoposide; a comparison of two different methods for determination of strand breaks in DNA

Etoposide induces DNA damage to cells by interacting with the nuclear enzyme topoisomerase II. In this investigation the human lymphoblastic leukemia cell line (CEM) was used to study induction of DNA-strand breaks and cellular drug uptake after treatment with etoposide at a concentration of 0.5-2 micrograms/ml. High performance liquid chromatography was used for determination of etoposide concentrations. The alkaline elution assay and the DNA unwinding technique were compared for quantifying strand breaks in DNA induced by etoposide. The concentrations required to increase the level of DNA damage significantly was as follows: the DNA unwinding technique, 0.20 microgram/ml; the alkaline elution assay with proteinase K, 0.45 microgram/ml; the alkaline elution assay without proteinase K, 0.60 microgram/ml. When the half-life was adjusted, considering the efflux time of etoposide from cells, it was found to be only a few minutes. The present data show that the DNA unwinding technique is to be preferred for the screening of DNA damage. This technique is easier and quicker to perform than the alkaline elution technique.

Organ-specific and transplacental DNA damage and its repair in rats treated with 1,2-dibromo-3-chloropropane

An in vivo genotoxicity assay system based on alkaline elution has been used to study the formation and removal of DNA damage induced by 1,2-dibromo-3-chloropropane (DBCP). Cells/nuclei from different tissues and organs of Wistar rats were prepared by a rapid mincing/homogenization technique. Thirty-six samples of which up to 11 were from different organs of the same animal, were then assayed in parallel for DNA damage (DNA single-strand breaks plus alkali-labile sites = SSBs) with a semi-automated alkaline elution system. A single i.p. injection of DBCP gave dose-(5 and 10 mg/kg) and time-(20 min-4 h) dependent SSBs in kidney and liver DNA from male rats. At 10 mg/kg DBCP, SSBs were formed in all organs examined except the bone marrow and colon; however, an increased dose of 40 mg/kg produced SSBs also in the latter two organs. The relative susceptibilities to DBCP-induced DNA damage were: kidney approximately duodenum > liver > lung approximately brain approximately urinary bladder approximately glandular stomach > spleen approximately testis > bone marrow approximately colon. These relative levels correlate with previous data on tissue distribution and organ necrosis in liver, kidney and testis of rats given a single i.p. dose of DBCP. When female rats were injected i.p. with 5, 10 or 20 mg/kg (nonhepatotoxic doses) at day 20 of pregnancy, similar levels of SSBs were detected in the livers of the dam and the fetuses. In adult male rats, time-dependent changes in SSBs were followed in the liver and kidney after DBCP exposure. In both organs SSBs peaked around 4 h post-exposure, 50% had been removed by 12-24 h, whereas at day 2-3 SSB frequencies had returned to control levels. Pretreatment of rats with phenobarbital prior to DBCP exposure reduced the maximum level of DNA damage as well as its persistence. In cultured primary hepatocytes from male rats exposed in vitro to DBCP (2-20 microM. 1 h), 50% of the initial DNA damage had been repaired within approximately 100 min. In conclusion, the experiments indicate that the distribution characteristics of DBCP are of major importance for DNA damage and its persistence in various organs of rats. The data are also in accordance with glutathione-S-transferase, rather than P450, being the most important pathway for metabolic activation of DBCP in rat extrahepatic tissues including the fetal liver. It appears that alkaline elution of cells/nuclei prepared from exposed animals constitutes a sensitive, rapid and versatile technique to study organ- and cell-specific genotoxicity in vivo.

DNA filter elution: a window on DNA damage in mammalian cells

This personal account traces a series of studies that led from DNA physical chemistry to anticancer drug mechanisms. Chemical crosslinking as a basis for anticancer drug actions had been suspected since the time of the first clinical reports of the effectiveness of nitrogen mustard in 1946. After the elucidation of the DNA helix-coil transition, several nearly concurrent findings in the early 1960s established the paradigm of DNA interstrand crosslinking. The DNA filter elution phenomenon was discovered in the early 1970s, and lent itself to the development of practical assays for DNA crosslinks and other DNA lesions in mammalian cells. The assays allowed studies of the effects of DNA damaging agents at pharmacologically or toxicologically relevant doses, and have been widely applied in studies of mutagenic and chemotherapeutic agents. During the period 1979-1986, DNA filter elution studies led to the paradigm of DNA topoisomerases as targets of anticancer drug action, and this has become one of the most active areas of anticancer drug development.

Mutagenicity and genotoxicity of the mycotoxin ochratoxin A

Natural occurrence of the mycotoxin ochratoxin A in food commodities has been linked to endemic diseases in certain human populations, where a high incidence of nephropathy is observed (Balkan endemic nephropathy). The increase of renal disease is accompanied with a high risk for urinary tract tumours. Despite epidemiological and experimental evidence for the carcinogenicity of ochratoxin A the underlying mechanism needs to be established. The pivotal role of cytochrome P450 in the mutagenicity of ochratoxin A could be demonstrated in experiments with cell lines stably expressing the human cytochrome P450 enzymes. CYP1A1, 1A2, 2C10 and 3A4, which were able to activate the non-mutagenic ochratoxin A into mutagenic metabolites. In the cell lines the bacterial lacZ' gene was used as reporter gene for mutagenicity. Sequencing of the lacZ' gene resulted in the detection of large deletions. In addition, in metabolically competent rat hepatocytes an increase of single strand breaks could be observed by means of the DNA alkaline elution assay. These DNA alterations could be related to biotransformation processes, indicating extensive metabolism of ochratoxin A. The discrepancies found between microsomal and cellular metabolism leads to the conclusion that ochratoxin A mediated mutagenicity requires additional processing of cytochrome P450 derived metabolism.

Induction and repair of DNA damage in UV-irradiated human lymphocytes. Spectral differences and repair kinetics

The alkaline elution assay has been employed to study the induction and repair kinetics of DNA damage in human lymphocytes after irradiation with biologically relevant doses of UVB (297 and 302 nm) or UVA (365 nm) radiation. At 365 nm, when the predominant lesions are single-strand breaks, the rate of lesion induction was 1.5 x 10(-3) per 10(8) Da per kJ m-2. The number of breaks decayed with a half-life of about 50 min after a dose of 20 kJ m-2. In the UVB region, cyclobutyl pyrimidine dimers and 6-4 photoproducts are formed, both of which are repairable via the nucleotide excision repair pathway. By using repair inhibitors, the rate of induction of such lesions at 297 and 302 nm was found to be 0.07 per 10(8) Da per J m-2. Lesions were removed with a half-life of about 100 min. Mathematical modelling of the excision repair process revealed a time-dependent polymerization-ligation rate: after an initial lag phase the polymerization-ligation rate increased, reaching 50% of its maximum rate at 80-100 min after the start of repair incubation. This course of development might be due to a damage-associated regulation of DNA precursors synthesis.

Metabolism of 1,2-dibromo-3-chloropropane by glutathione S-transferases

The metabolism of 1,2-dibromo-3-chloropropane (DBCP), measured as the formation of water soluble metabolites and metabolites covalently bound to macromolecules, was studied in isolated rat liver, kidney, and testicular cells, in subcellular fractions, and with purified rat and human glutathione S-transferases (GSTs). The rate of formation of water soluble metabolites in the cells were in the order liver > kidney > testis. The rate of covalent macromolecular binding of reactive DBCP metabolites in the different cell types was of the same relative order. Pretreatment of the cells with the GSH depleting agent diethyl maleate (DEM) markedly decreased the rate of covalent binding in all cell types. Both the overall metabolism and the formation of DBCP metabolites that covalently bound to macromolecules, were substantially higher in rat testicular cells compared to hamster testicular cells. Rat liver cytosol and microsomes, and various purified rat and human GSTs extensively metabolized DBCP to water soluble metabolites in the presence of GSH. When compared to isolated cells, substantially lower rates of binding per mg protein could be observed in subcellular fractions. Binding of DBCP was detected in the microsomal and cytosolic fractions in the absence of NADPH, though in microsomes fortified with a NADPH-regenerating system, the generation of reactive DBCP metabolites was approximately doubled. Studies with purified rat GST isozymes showed that the relative overall GSH conjugation activity with DBCP was in the following order: GST form 3-3 > 2-2 approximately 12-12 > 1-1 > 4-4 approximately 8-8 approximately 7-7. Furthermore, human GST forms also readily metabolized DBCP with activities of GST A1-2 > A2-2 approximately A1-1 > M1a-1a > M3-3 approximately P1-1.

DNA damage in lung cells in vivo and in vitro by 1,3-butadiene and nitrogen dioxide and their photochemical reaction products

A UV-irradiated mixture of 1,3-butadiene and nitrogen dioxide (NO2) was tested for its potency to induce DNA damage measured as single-strand breaks (SSB) in lungs of mice. Both gases were also tested separately. After 16 h exposure a UV-irradiated mixture of 40 ppm butadiene + 20 ppm NO2, but not 20 ppm butadiene + 10 ppm NO2 + UV, induced a significant increase in SSB as measured by the alkaline unwinding technique. There was no increase in the level of SSB using the alkaline elution technique during the same testing conditions. However, after 5 h exposure to 60 ppm butadiene + 30 ppm NO2 + UV both methods demonstrated a significant increase in SSB. Mice were also exposed to butadiene at 80 and 200 ppm for 16 h and at 500 ppm for 5 h. DNA damage was demonstrated in both liver and lung after 5 and 16 h (only at 200 ppm) of exposure using the unwinding technique. Using the alkaline elution assay, a significant increase in the level of SSB in lung and liver was found only after 5 h of exposure. When mice were exposed to 30 ppm NO2 for 16 h or 50 ppm for 5 h, a significant increase in SSB was found with the unwinding technique. Alveolar macrophages from mice were also exposed in vitro to the gas mixture and to butadiene and NO2 separately. In these experiments, the DNA damage was studied with the unwinding technique. A significant effect was demonstrated with 40 ppm butadiene + 20 ppm NO2 + UV. NO2 itself contributed to some extent to the increase. Reasons for the discrepancies between the unwinding and the alkaline elution techniques are discussed.

Inhibitory effects of paracetamol on DNA repair in mammalian cells

Paracetamol blocks DNA replication by inhibiting deoxyribonucleotide (dNTP) synthesis and may therefore also interfere with DNA repair. In the present work various mammalian cell types were treated with genotoxic agents and allowed to repair in the presence or absence of paracetamol. Alkaline elution was used to assay DNA single-strand breaks plus alkali-labile sites (= SSBs). Resting human mononuclear blood cells (MNC) exposed to 4-nitroquinoline N-oxide (NQO, 3 microM) plus 0.3 mM paracetamol contained twice as many DNA SSBs compared to MNC exposed to NQO alone, and the level of SSBs decreased more slowly during repair in the presence of paracetamol. Deoxyribonucleosides reversed the effects of paracetamol. SSBs induced by MMS or X-rays (2.6 Gy) were not increased by paracetamol. Resting and growth-stimulated MNC, HL-60 cells, rat hepatocytes and human fibroblasts exposed to UV-C (3-12 J/m2) showed varying levels of transient SSBs formed during repair but these were consistently higher in the presence of paracetamol (0.3-1 mM). In rat testicular cells SSBs were induced by NQO and the levels were further increased in the presence of paracetamol, whereas after UV almost no SSBs were detected during repair. The cell-type specific levels of transient SSBs after UV did not correlate with the rate of incision of DNA lesions, measured as the rate of SSB accumulation in the presence of repair inhibitors Ara C plus hydroxyurea. Transient SSBs were present in resting MNC for at least 24 h after UV and paracetamol increased these breaks 4-fold however the overall rate of removal of excisable photodamage during repair did not appear to be reduced by the presence of paracetamol. The present data indicate that paracetamol interferes with nucleotide excision repair in several mammalian cell types. This constitutes a mechanism by which paracetamol may contribute to genotoxicity in humans.

Detection of UVR-induced DNA damage in mouse epidermis in vivo using alkaline elution

Alkaline elution has been used to detect ultraviolet radiation (UVR)-induced DNA damage in the epidermis of C3H/Tif hr/hr mice. This technique detects DNA damage in the form of single-strand breaks and alkali-labile sites (SSB) formed directly by UVA (320-400 nm) or indirectly by UVB (280-320 nm). The latter induces DNA damage such as cyclobutane pyrimidine dimers and pyrimidine-pyrimidone (6-4)-photoproducts, which are then converted into transient SSB by cellular endonucleases, during nucleotide excision repair (NER). The irradiation system used had a spectral output similar in effect to solar UVR, with the UVB component inducing 94% of the edema response observed in mice. Consequently, the majority of SSB detected were those formed via NER of UVB-induced photoadducts. The number of SSB detected immediately after 8 kJ/m2 (2.7 minimum erythema doses determined at 48 h post-UVR [MED]) was low, indicating the formation of only small numbers of transient SSB. When DNA repair inhibitors hydroxyurea and 1-beta-D-arabinofuranosylcytosine were administered (intraperitoneally) to mice 30 min before UVR, they prevented sealing of the DNA SSB formed during NER. A four-fold increase in the number of SSB detected resulted, which was found to be linearly related to the UVR dose. The SSB induced by 2 kJ/m2 (less than an MED) were readily detected, with the ear showing lower numbers of SSB than the dorsum. When repair inhibitors were added post-UVR, the rate of formation of SSB declined rapidly with time of administration, reflecting repair of DNA lesions. After a UVR dose of 6 kJ/m2 (2 MED), 50% of the initial repair-dependent SSB had been removed after approximately 2 h in the ear and 4 h in the dorsum; no more SSB appeared to be incised by 24 h post-UVR. The technique described is an efficient and highly sensitive one for the quantification of SSB induced in UV-irradiated skin samples in vivo.

Comparative toxicity of (+)-(R)- and (-)-(S)-1,2-dibromo-3-chloropropane

The haloalkane 1,2-dibromo-3-chloropropane (DBCP), an environmental pollutant that was widely used as a soil fumigant, is a carcinogen and a mutagen and displays target-organ toxicity to the testes and the kidneys. Because little is known about effects of stereochemistry on the metabolism and toxicity of halogenated alkyl compounds and because DBCP, which has a chiral center at C-2, may show enantioselectivity in its metabolism and/or toxicities, the optically pure enantiomers of DBCP were tested in vivo in rats for organ toxicity as well as for bacterial mutagenicity. Organ toxicity studies showed that (S)-DBCP was slightly more renal toxic than (R)-DBCP but was not significantly more toxic than the racemate, and that no significant differences were observed in the extents of testicular necrosis and atrophy caused by either enantiomer or the racemate. In contrast, (R)-DBCP was more mutagenic than either (S)-DBCP or the racemate to Salmonella typhimurium (S. typhimurium) strains TA 100 and TA104. However, there was little or no enantioselectivity in glutathione S-transferase (GST)-catalyzed conjugation reactions of glutathione with DBCP based on the lack of selectivity in the rates of disappearance of the enantiomers of DBCP in the presence of glutathione (GSH) and GSTs as monitored by chiral gas chromatography (GC).

Chemically induced DNA damage in isolated rabbit lung cells

By use of an isolation procedure including centrifugal elutriation and density gradient centrifugation, relatively pure fractions of Clara cells and type II cells were obtained from rabbit lungs. These cells and alveolar macrophages isolated by lavage were exposed to methyl methanesulfonate (MMS), 1,2-dibromo-3-chloropropane (DBCP), 1-nitropyrene (1-NP), 2-nitrofluorene (2-NF), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), N'-nitrosonornicotine (NNN), N-nitrosoheptamethyleneimine (NHMI) or phorbol 12-myristate 13-acetate (TPA). DNA damage measured as alkali-labile sites and/or single-strand breaks was then determined in the different lung cells by an automated alkaline elution system. The direct-acting compound MMS showed similar DNA-damaging effect in Clara cells, type II cells and alveolar macrophages. The nematocide DBCP, activated by both P450- and glutathione S-transferase(s)-dependent pathways, caused considerably less DNA damage in macrophages than in Clara or type II cells. Similar differences between the lung cells in induction of DNA damage as observed with DBCP were demonstrated after exposure to the activation-dependent nitrosamines NNK and NHMI and the tumor promoter TPA. The other test substances (1-NP, 2-NF, NNN) did not cause any marked DNA damage measured by the alkaline elution technique. These findings are in agreement with the known metabolic capacity of these cell types, indicating that Clara and type II cells are possible primary targets for lung toxic/carcinogenic compounds.

Fractionation of DNA from marine invertebrate (Maja crispata, Mytilus galloprovincialis) haemolymph by alkaline elution

1. An alkaline elution procedure for the detection of DNA damage in marine invertebrate haemolymph has been developed. 2. Provided that three criteria are optimized, such as buffer composition, small filter pores (0.22 microns GVWP 025 00, Millipore), and optimal amounts of haemolymph applied, flow rates may be changed within the range of 0.2 ml/min to 0.05 ml/min without adverse back-pressure on the filter and without blocking filter pores. 3. Under optimal conditions, 70% of mussel haemolymph DNA, and 80% of crab haemolymph DNA will be retained on the filter after 6 hr of elution, indicating shorter DNA in mussel haemolymph. 4. The technique is applicable for testing the in vivo effects of different compounds on DNA in marine invertebrates, and to measurements of DNA damage in naturally exposed mussels. 5. This argues an important case for the use of alkaline elution technique for assessment of environmental genotoxicity, and especially for investigation of DNA damage in different marine organisms which cover a broad range in their DNA molecular weights.

Organ-specific DNA damage of tris(2,3-dibromopropyl)-phosphate and its diester metabolite in the rat

The organ specificity of tris(2,3-dibromopropyl)phosphate(Tris-BP)-induced DNA damage was investigated in the rat 2 h after a single i.p. injection of 350 mumol/kg. Extensive DNA damage, measured with the alkaline elution method, was found in the kidney, liver and small intestine. Less, but significant DNA damage was detected in the brain, lung, spleen, large intestine and testis. The role of different pathways in the activation of Tris-BP to DNA damaging products was studied in isolated liver and testicular cells. Concentrations as low as 2.5-5 microM Tris-BP caused DNA damage in the hepatocytes, whereas an approximately 10-fold higher concentration was needed in testicular cells to produce a similar amount of DNA damage. Depletion of GSH by diethyl maleate (DEM) did not affect the extent of DNA damage caused by Tris-BP in the liver cells, but blocked the genotoxic effect in testicular cells. Two specifically deuterated Tris-BP analogs, C3D2-Tris-BP and C2D1-Tris-BP, were significantly less potent in causing DNA damage than the protio compound in isolated liver cells and were somewhat less potent in testicular cells. The major urinary metabolite of Tris-BP, bis(2,3-dibromopropyl)phosphate (Bis-BP), was less potent than Tris-BP in causing kidney DNA damage after in vivo exposure. Furthermore, Bis-BP induced substantially less DNA damage in isolated liver and testicular cells. Similar to the effect of DEM on the DNA damage caused by Tris-BP, the DNA damage caused by Bis-BP could be decreased by DEM-pretreatment in testicular cells but not in liver cells. The present study shows that Tris-BP is a potent multiorgan genotoxic agent in vivo. The in vitro data indicate that P-450 mediated metabolism of Tris-BP is more important than activation by glutathione S-transferases of Tris-BP in liver cells, whereas the latter activation pathway seems to be most important in testicular cells.

Evaluation of the genotoxic potential of sorbic acid and potassium sorbate

The genotoxic potential of sorbic acid and potassium sorbate was investigated in vivo and in vitro. Oral administration of sorbic acid (up to 5000 mg/kg body weight) did not induce sister chromatid exchanges or the formation of micronuclei in bone marrow cells of mice. Intraperitoneal treatment of rats with 400-1200 mg potassium sorbate/kg body weight did not alter the elution profile of DNA from isolated liver cells in the in vivo alkaline elution assay. Sorbic acid did not induce DNA repair in cultured human A549 cells in the unscheduled DNA synthesis (UDS) assay. In vitro incubation of the cells with 1-1000 micrograms potassium sorbate/ml, in the absence or presence of rat liver homogenate, did not result in the formation of DNA single-strand breaks in the alkaline elution assay. These results demonstrate that sorbic acid and its potassium salt are not genotoxic in vivo or in vitro. In contrast to sorbic acid and potassium sorbate, sodium sorbate is very sensitive to oxidative degradation; the main oxidation product was identified to be 4,5-oxohexenoate, which was mutagenic in the Ames test.

Genotoxic effects of 2-amino-3,4-dimethylimidazo(4,5-f)quinoline (MeIQ) in rats measured by alkaline elution

The alkaline elution method was used to examine genotoxic effects of MeIQ in various organs of rats after in vivo exposure. No DNA damage could be observed in the stomach, small and large intestine, liver, kidney or testis of male Wistar rats 2 h after a single intraperitoneal dose of 80 mg/kg MeIQ. In rats that had been pretreated with Aroclor 1254 (PCB), MeIQ induced significant DNA damage in the liver after both oral and intraperitoneal injection. MeIQ induced DNA damage in the large intestine, liver and kidney of male F344 rats given a single intraperitoneal dose of 80 mg MeIQ/kg or fed 0.03% MeIQ for 13 days. The DNA damage did not seem to accumulate during the feeding period.

DNA damage and cell death induced by 1,2-dibromo-3-chloropropane (DBCP) and structural analogs in monolayer culture of rat hepatocytes: 3-aminobenzamide inhibits the toxicity of DBCP

1,2-Dibromo-3-chloropropane (DBCP) and a number of halogenated propane analogs induced DNA damage in rat hepatocytes in vitro measured by an automated alkaline elution method. Short-term (2 hrs) cytotoxic effects of DBCP were not observed until the DBCP concentration exceeded 1 mM. The short-term cytotoxicity of all the DBCP analogs occurred in the same concentration range. Significant membrane damage, measured as cell detachment, was observed after extended exposure to lower concentrations of DBCP (100 microM) for 20 hrs. The relative, delayed cytotoxic effect of DBCP and analogs correlated with their ability to cause DNA damage. In general, the halogenated propanes with more bromines relative to chlorines were the more potent compounds. Propane analogs lacking the third halogen had little cytotoxic activity. The addition of the proposed specific poly(ADP-ribosyl)transferase inhibitor 3-aminobenzamide (3-ABA) protected against DBCP-induced cytotoxic effects and NAD+ depletion. However, 3-ABA also reduced DBCP-induced DNA damage, DBCP metabolic loss, and the formation of water soluble and covalently bound DBCP metabolites. Thus, 3-ABA may block DBCP-induced cell death by decreasing the formation of reactive DBCP-metabolites.

The non-genotoxicity to rodents of the potent rodent bladder carcinogens o-anisidine and p-cresidine

The two potent rodent bladder carcinogens o-anisidine and p-cresidine, and the structurally related non-carcinogen 2,4-dimethoxyaniline, have been extensively evaluated for genotoxicity to rodents and found to be inactive. Most data were generated on o-anisidine, an agent that is also only marginally genotoxic in vitro. The two carcinogens induced methaemoglobinaemia in rodents indicating that the chemicals are absorbed and metabolically oxidized. Despite their total lack of genotoxicity in vivo, the two carcinogens have the hall-marks of being genotoxic carcinogens given that most test animals of both sexes of B6C3F1 mice and F344 rats are reported to have succumbed rapidly to malignant bladder cancer. No reasons for this dramatic conflict of test data are so far apparent. The experiments described involve, in one or other combination, 2 strains of mice (including B6C3F1) and 4 strains of rat (including F344), the use of oral and i.p. routes of exposure and observations made after 1, 3 or 6 doses of test chemical. 6 tissues (including the rat bladder) were assayed using 3 genetic endpoints (unscheduled DNA synthesis, DNA single-strand breaks and micronuclei induction). Aroclor-induced rats were employed in one set of experiments with o-anisidine. In the case of one set of mouse bone-marrow micronucleus experiments the same batch of the 3 chemicals as used in the cancer bioassays, and the same strain of mouse, were used. Possible further experiments and the implications of these findings are discussed.

Prevention of 1,2-dibromo-3-chloropropane (DBCP)-induced kidney necrosis and testicular atrophy by 3-aminobenzamide

The poly(ADP-ribosyl)transferase inhibitor, 3-aminobenzamide (3-ABA), reduced morphological evidence of 1,2-dibromo-3-chloropropane (DBCP)-induced DNA damage determined by alkaline elution. The DBCP plasma, kidney, and testis tissue doses determined between 1 and 8 hr after a single intraperitoneal injection were somewhat higher with than without 3-ABA pretreatment. Furthermore, the amount of DBCP metabolites covalently bound to macromolecules was reduced to about 20-30 percent of control, indicating that 3-ABA may have an effect on the formation/detoxication of reactive DBCP metabolites. Inhibitors of replicative DNA synthesis such as hydroxyurea or stimulation of DNA replication by nephrectomy did not affect the cytotoxicity, neither did inhibitors of DNA repair such as beta-cytosine arabinoside and beta-lapachone.

Genotoxic effects of the drinking water mutagen 3-chloro-4-(dichloromethyl)-5-hydroxy-2[5H]-furanone (MX) in mammalian cells in vitro and in rats in vivo

The potent bacterial mutagen 3-chloro-4-(dichloromethyl)-5-hydroxy-2[5H]- furanone) (MX), which is formed during chlorination of drinking water and accounts for about one third of the Ames mutagenicity of tap water, has been studied with respect to its genotoxicity in vitro and in vivo. Treatment with 30-300 microM MX (1 h) induced DNA damage in a concentration-dependent manner in suspensions of rat hepatocytes, as measured by an automated alkaline elution system. The effect was similar in hepatocytes from PCB-induced and uninduced rats. DNA damage was induced in V79 Chinese hamster cells and in isolated rat testicular cells, at the same concentration level as in hepatocytes. Pretreating testicular cells with diethylmaleate, which depletes 85% of cellular glutathione, had no significant effect on the DNA damage induced by MX. The treatment conditions used in the alkaline elution experiments were not cytotoxic to any of the cell types used, as determined by trypan blue exclusion. V79 cells exposed to 2-5 microM MX (2 h) showed an increased frequency of sister-chromatid exchanges (SCE) whereas no significant effect on HGPRT mutation induction was observed. Higher concentrations (greater than 10 microM, 2 h) apparently blocked cell division. The data indicate that MX can react directly with DNA or that MX is metabolized to an ultimate mutagen via some enzyme which is common in mammalian cells. The in vivo experiments showed no evidence of genotoxicity after intraperitoneal (18 mg/kg, 1 h) or oral (18, 63 or 125 mg/kg, 1 h) administration of MX, as measured by alkaline elution, in any of the following organs: the pyloric part of the stomach, the duodenum, colon ascendens, liver, kidney, lung, bone marrow, urinary bladder and the testes. In conclusion, MX is a direct-acting genotoxicant in vitro but no in vivo genotoxicity was detected.

Principles and practice of DNA filter elution

DNA filter elution assays have proved useful in studies of DNA strand breaks and crosslinks produced in mammalian cells or tissues by a wide variety of carcinogenic and cancer chemotherapeutic agents. The basic types of DNA lesions that can be measured include single and double-strand breaks, interstrand crosslinks and DNA-protein crosslinks. DNA filter elution has also been adapted to the assay of other lesions such as alkali-labile sites and the protein-associated strand breaks of topoisomerase DNA cleavage complexes. The essential concepts and theory of the technique are discussed and the applications of the technique to various types of studies are critically reviewed.

Absence of genotoxic activity of penbutolol in bacterial and mammalian cell screening systems

The genotoxic potential of the beta-adrenergic blocker penbutolol was assessed using the Ames and HGPRT tests, unscheduled DNA synthesis (UDS) and alkaline elution assays. In the Ames test, penbutolol was tested for cytotoxicity and genotoxic activity in concentration ranges of 0.8-500 micrograms/plate and 0.1-125 micrograms/ml in the HGPRT, UDS and alkaline elution assays. In the Ames test penbutolol showed significant toxicity above 500 micrograms/plate. In the mammalian cells (V79) used for the HGPRT test and A459 cells used for alkaline elution and UDS assays, penbutolol was cytotoxic at concentrations above 30 micrograms/ml. In another series of experiments, male Wistar rats were treated i.p. with penbutolol (1, 10 and 100 mg/kg) and after 2 h liver nuclei were isolated and formation of single DNA-strand breaks was measured. The results of the present study demonstrate the absence of genotoxic activity of penbutolol in the 5 strains of Salmonella typhimurium (TA98, TA100, TA1535, TA1537 and TA1538) and in the strain of Escherichia coli WP2 uvrA in the presence or absence of metabolic activation. In V79 cells, penbutolol showed no mutagenic effects at the HGPRT locus in the presence or absence of metabolic activation. Additionally, no significant incorporation of [3H]thymidine into the DNA in the UDS test or formation of DNA-strand breaks in the alkaline elution assay was detected in the non-toxic concentration range of penbutolol with or without metabolic activation. Furthermore, penbutolol did not cause DNA damage in liver nuclei isolated from penbutolol-treated rats.

Species differences in kidney necrosis and DNA damage, distribution and glutathione-dependent metabolism of 1,2-dibromo-3-chloropropane (DBCP)

Species differences and mechanisms of 1,2-dibromo-3-chloropropane (DBCP) nephrotoxicity were investigated by studying DBCP renal necrosis and DNA damage, distribution and glutathione-dependent metabolism in rats, mice, hamsters and guinea pigs. Extensive renal tubular necrosis was observed in rats 48 hr after a single intraperitoneal administration (21-170 mumol/kg) of DBCP. Significantly less necrosis was found in mice and guinea pigs, whereas no renal damage was evident (less than 680 mumol/kg) in hamsters. The activation of DBCP to DNA damaging intermediates in vivo, as measured by alkaline elution of DNA isolated from kidney nuclei 60 min. after intraperitoneal injection of DBCP, was compared in all four species. Distinct DNA damage was detected in rats, mice and hamsters as early as 10 min. after administration of DBCP and within 30 min. in guinea pigs. Rats and guinea pigs showed similar sensitivity towards DBCP-induced DNA damage (extensive DNA damage greater than 21 mumol/kg DBCP), whereas in mice and hamsters a 10-50 times higher DBCP dose was needed to cause a similar degree of DNA damage. Renal DBCP concentrations at various time-points (20 min., 1, 3 and 8 hr) after intraperitoneal administration (85 mumol/kg) revealed that the initial (20 min.) DBCP concentration was substantially higher in rats and guinea pigs compared to the other two species. Furthermore, kidney elimination of DBCP occurred at a significantly lower rate in rats than in mice, hamsters and guinea pigs.(ABSTRACT TRUNCATED AT 250 WORDS)

Species differences in testicular necrosis and DNA damage, distribution and metabolism of 1,2-dibromo-3-chloropropane (DBCP)

The human testicular toxicant 1,2-dibromo-3-chloropropane (DBCP) was studied for the same end-point in 4 different species of laboratory animals. Marked necrosis and atrophy of the seminiferous epithelium were observed in rats and guinea pigs 10 days after a single i.p. administration of DBCP (170-340 mumol/kg), whereas significantly less damage was observed in hamsters and mice. The testicular concentrations of DBCP measured at various time-points after the i.p. injection of DBCP indicated that factors in addition to tissue concentration were of importance for the observed species differences in sensitivity towards DBCP-induced testicular damage. Also, there did not seem to be any direct correlation between DBCP-induced in vivo testicular toxicity and in vitro GSH-dependent dehalogenation, inasmuch as the rate of bromide release from DBCP with hamster testicular cytosol was as fast as that with rat cytosol. Testicular DNA damage, as determined by alkaline elution 60 min after in vivo administration of 170 mumol/kg DBCP, was observed only in rats and guinea pigs. Thus, induction of DNA damage correlates with the relative susceptibilities of the species towards DBCP-induced testicular necrosis. To further study species differences in testicular activation of DBCP to DNA-damaging intermediate(s), cells isolated from the testes of the 4 species were incubated with DBCP. Testicular cells from rats and guinea pigs were the only preparations developing substantial DNA damage after 60 min incubation with low concentrations of DBCP (5-50 microM). The findings indicate that rats are sensitive towards DBCP-induced testicular necrosis because rat testicular cells easily activate DBCP to a DNA-damaging intermediate(s). The relative high testicular DBCP concentration as well as the ability to activate DBCP may explain the sensitivity of guinea pigs towards DBCP-induced testicular toxicity.

Role of P-450 activity and glutathione levels in 1,2-dibromo-3-chloropropane tissue distribution, renal necrosis and in vivo DNA damage

Treatments known to alter P-450 activity and glutathione levels were used to elucidate the involvement of P-450 and glutathione S-transferase metabolism in 1,2-dibromo-3-chloropropane (DBCP) organ toxicity in the rat. Phenobarbital pretreatment abolished DBCP-induced renal necrosis, whereas it had only a small effect on initial renal DNA damage. The DBCP levels in plasma and tissues were markedly reduced by phenobarbital pretreatment. Perdeuterated DBCP had much higher plasma and tissue levels than protio-DBCP in phenobarbital-pretreated animals, but perdeuteration was without effect in uninduced animals. This indicates that P-450 metabolism of DBCP is of major importance only in phenobarbital-pretreated animals. In order to study the effects of decreased glutathione levels on renal distribution and toxicity, rats were pretreated with either diethyl maleate or buthionine sulfoximine. The DBCP levels in plasma and tissues showed transitory elevations after diethyl maleate and buthionine sulfoximine pretreatment compared to the control situation. Despite the fact that diethyl maleate and buthionine sulfoximine pretreatments are known to block DBCP-induced DNA damage in vitro, these pretreatments did not significantly alter DBCP-induced renal necrosis nor DNA damage. Thus, a role for glutathione conjugation in DBCP-induced in vivo renal toxicity could not be established in the present study.

Testicular necrosis and DNA damage caused by deuterated and methylated analogs of 1,2-dibromo-3-chloropropane in the rat

To study the role of metabolism in 1,2-dibromo-3-chloropropane (DBCP)-induced testicular damage in rats, selectively deuterated and methylated analogs of DBCP were given as a single ip dose of 340 mumol/kg and testicular toxicity was determined 10 days after treatment. None of the four deuterated analogs C1-D2-, C2-D1-, C3-D2-, or C1-C2-C3-D5-DBCP reduced the degree of testicular damage compared to DBCP, indicating that metabolic cleavage of a C-H bond was not rate-limiting in DBCP-induced testicular toxicity. Of the five methylated analogs, C1-methyl-, C1-dimethyl-, C2-methyl-, and C3-methyl-DBCP and 1,2-dibromo-4-chlorobutane, only C3-methyl-DBCP caused testicular toxicity. DBCP treatment resulted in increased testicular DNA damage at doses of 85-170 mumol/kg as measured by alkaline elution of DNA from testicular cells isolated 3 hr after in vivo treatment. The perdeutero-DBCP analog induced testicular DNA damage that was at least as extensive as that induced by DBCP. Of the methylated analogs tested, only C3-methyl-DBCP gave a marked dose-dependent increase in testicular DNA damage between 170 and 540 mumol/kg. There were no significant differences in the testicular tissue distribution between DBCP, perdeutero-DBCP, and the methylated DBCP analogs. Furthermore, in distribution studies with DBCP, C1-methyl- and C3-methyl-DBCP, and 1,2-dibromo-4-chlorobutane, the highest tissue concentrations were found in the kidneys, followed by the liver and then the testes. The fact that testicular DNA damage of DBCP and its deuterated and methylated analogs paralleled their ability to cause testicular necrosis and atrophy makes measurement of DNA damage a very useful correlate in mechanistic studies of DBCP-induced testicular cell death.