The intensity of internalization and cytotoxicity of superparamagnetic iron oxide nanoparticles with different surface modifications in human tumor and diploid lung cells.

The human lung adenocarcinoma epithelial (A549) cells and the human embryo lung (HEL 12469) cells were used to investigate the uptake and cytotoxicity of magnetite nanoparticles (MNPs) with different chemically modified surfaces. MNPs uptake was an energy-dependent process substantially affected by the serum concentration in the culture medium. Internalized MNPs localized in vesicle-bound aggregates were observed in the cytoplasm, none in the nucleus or in mitochondria. All MNPs induced a dose- and time-dependent increase in cytotoxicity in both human lung cell lines. The cytotoxicity of MNPs increased proportionally with the particle size. Since the cytotoxicity of MNPs was nearly identical when the doses were equalized based on particle surface area, we suppose that the particle surface area rather than the surface modifications per se underlay the cytotoxicity of MNPs. In general, higher internalized amount of MNPs was found in HEL 12469 cells compared with A549 cells. Accordingly, the viability of the human embryo lung cells was reduced more substantially than that of the adenocarcinoma lung cells. The weak MNPs uptake into A549 cells might be of biomedical relevance in cases where MNPs should be used as nanocarriers for targeted drug delivery in tumor tissue derived from alveolar epithelial cells.

Significance of amino acid substitution variants of DNA repair genes in radiosusceptibility of cervical cancer patients; a pilot study.

The present pilot study was designed to elucidate the functional significance of amino acid substitution variants of DNA repair genes. Using the peripheral blood lymphocytes (PBLs) from healthy donors and cervical cancer patients, the contribution of four non-synonymous single nucleotide polymorphisms (SNPs) in three base excision repair genes (BER), XRCC1 (Arg194Trp and Arg399Gln), hOGG1 (Ser326Cys), and APE1 (Asp148Glu), to the susceptibility to ionizing radiation were evaluated. The level of initial, oxidative and residual DNA damage produced by 2 Gy was measured by the alkaline single cell gel electrophoresis (the comet assay), and the SNPs were determined by PCR-restriction fragment length polymorphism (RFLP) assay. No significant differences in the allele frequencies between cancer patients and controls for any of these four SNPs were detected. Although the initial DNA damage levels were approximately similar, significantly higher level of Fpg-sensitive sites were found in patients compared with controls (p<0.001) irrespective of genotype distribution. A trend towards increased values of EndoIII-sensitive sites was determined in PBLs from cancer patients compared with healthy women, mainly carriers of the XRCC1 and OGG1 variant alleles; however, the mean value of EndoIII-sensitive sites does not reach any significance. A substantial delay in DNA strand-break rejoining was ascertained in patients who carried APE1 Glu variant allele in comparison with healthy donors 15 and 60 minutes after irradiation (p< 0.05 and p< 0.01, respectively). In contrast, slightly higher but statistically significant level of residual DNA damage was estimated in controls (APE1Asp/Asp) compared with patients. An association between single nucleotide polymorphism (SNP) of two DNA repair genes functioning in the same biochemical pathway and susceptibility to radiation was found. In the combined genotype APE1/XRCC1 and APE1/hOGG1, a decreased level of residual DNA damage was detected in carriers of wild type APE1 genotype. In addition, a possible modulating effect of hOGG1 gene on the kinetics of strand-break rejoining was estimated. The lowest residual DNA damage level was determined in subjects with the combined APE1(Asp/Asp)/hOGG1(Ser/Cys+Cys/Cys) genotypes. Based on these preliminary data we suppose that a combination of several amino acid substitution variants of DNA repair genes involved in the same repair pathway rather than one low-penetrance SNP in a single gene may contribute to DNA repair outcomes. Larger study with more subjects is needed to verify these findings.

Radiosensitivity of peripheral blood lymphocytes from healthy donors and cervical cancer patients; the correspondence of in vitro data with the clinical outcome.

The reliability of a particular in vitro parameter as potential prognostic biomarker of individual radiosensitivity is still discussed. Therefore, several in vitro radiation-induced cellular endpoints including initial, oxidative and residual DNA damage and the rate of DNA repair were assessed in peripheral blood lymphocytes (PBL) from healthy donors and patients with carcinoma of the cervix using the alkaline single cell gel electrophoresis (the comet assay). PBL from cancer patients were analyzed three times during the course of therapy, prior, in the middle (25-27 Gy) and after the radiotherapy. Interindividual differences in radiation-induced DNA damage and in the kinetics of strand break rejoining were determined within both groups. Significantly higher level of mean background and oxidative DNA damage was estimated in the cancer patient cohort than in the healthy subject group; however similar mean values of the initial DNA damage and the rate of DNA repair kinetics were found in both groups. No adaptive response was determined in PBL from cancer patients due to radiotherapy. The acute radiation toxicity and the clinical outcome were scored according to the criteria as proposed by the National Cancer Institute. A substantial delay in DNA strand break rejoining was determined in cancer patients suffering from adverse side effects (G2+) in comparison to persons with no or very mild radiation toxicity (G0-G1) (p<0.05). The recurrence of disease has been associated with a lower initial DNA damage and slope value of dose-response effect, and increased rate of DNA repair. Results from this pilot study suggest that the residual DNA damage level might be a promising prognostic biomarker of acute radiation morbidity; however, further study is necessary to validate this finding.

Radiosensitivity of cervical cancer cell lines: the impact of polymorphisms in DNA repair genes.

The aim of this study was to evaluate radiosensitivity of cervical cancer cells in vitro and to assess the relationship between genetic polymorphisms in DNA repair genes and the response of cells to ionizing radiation. The alkaline comet assay as a predictive assay of radiosensitivity was used to examine the susceptibility of four human cervical cancer cell lines (CaSki, C-33A, HeLa and SiHa) to radiation damages. The initial DNA damage and the residual DNA damage at 15, 30, 45 and 60 min after irradiation were assessed. Genotypes of DNA repair genes (XRCC1, hOGG1, PARP, XPD, XRCC3 and XRCC4) were analyzed by PCR-RFLP assays. The comet data clearly indicate a variable but dose-dependent increase in the initial DNA damage in all cell lines. The highest slope of dose response curve was observed in C-33A cells and this cell line was assumed to be radiosensitive. All cell lines repaired DNA damage in a similar manner, the level of DNA strand breakage has returned near the background level within 45 min after irradiation. According to the genotype we found that C-33A cells are polymorphic in the majority of analyzed DNA repair genes. This pilot study indicated associations between polymorphisms in DNA repair genes and cell radiosensitivity.

Effect of cytosine arabinoside and hydroxyurea on micronucleus formation induced by model clastogens in Chinese hamster V79 cells.

Post-cultivation of treated cells in the presence of DNA repair inhibitors has been proposed as a new methodological approach of the micronucleus (MN) assay to increase the sensitivity of this technique. In order to assess the advantages and limitations of this promising methodological approach, several genotoxic/clastogenic agents with different mechanisms of activity were chosen to assess the effect of DNA repair inhibitors on the level of micronuclei (MNi) induced by particular agent using Chinese hamster V79 cells. Both UV light (UV) and benzo(a)pyrene (BaP) increased significantly the micronucleus level in V79 cells (p<0.01-0.001). In contrast, only at cytotoxic concentration (>0.8 mM) a slight but statistically significant rise of MNi was determined in cells exposed to N-methyl-N-nitroso urea (MNU). However, post-cultivation of MNU-treated cells in the presence of DNA repair inhibitors (cytosine arabinoside, AraC and hydroxyurea, HU) led to an additional rise of MNi. While AraC had a synergistic effect on MN formation (0.4 mM and 0.8 mM, DS=2.14 and 1.13, respectively), HU had less than additive effect (DS=0.86 and 0.66) and the combined treatment of cells with AraC and HU was least effective (Cf=0.36 and 0.28). On the other hand, post-cultivation of UV- and BaP-treated cells in the presence of AraC did not result in any synergistic effect on MN formation. No effect or even a decrease of MNi was measured particularly due to HU or combined treatment of HU and AraC. Incubation of control untreated cells with AraC gave rise to a significant increase of MN formation (2- to 2.5-fold) as well. Hydroxyurea or the combined treatment of HU with AraC had lower effect on the spontaneous level of MNi. Our study shows, that the combination of MNU treatment with DNA repair inhibitors increased the number of MNi on well proliferating V79 cells; in case UV light and BaP treatment, the involvement of DNA repair inhibitors did not contribute to an increase of sensitivity of MN assay. On the basis of our results we suppose that the AraC/CBMN assay might be a promising approach in genetic toxicology applied only to lymphocytes.

Induction of micronuclei by 7H-dibenzo[c,g]carbazole and its tissue specific derivatives in Chinese hamster V79MZh1A1 cells.

The clastogenicity/aneugenicity of N-heterocyclic polycyclic aromatic pollutant 7H-dibenzo[c,g]carbazole (DBC) and its two synthetic derivatives N-methyl DBC (MeDBC) and 5,9-dimethyl DBC (diMeDBC) was evaluated in the genetically engineered Chinese hamster V79 cell line V79MZh1A1 with stable expression of human cytochrome P4501A1 and in the parental V79MZ cell line without any cytochrome P450 activity. While none of the three carbazoles changed significantly the level of micronuclei in the parental V79MZ cells, a variable, but statistically significant rise of micronucleus frequencies was assessed in V79MZh1A1 cells. DBC induced dose-dependent increase in the number of micronuclei at harvest times of 24 and 48h and MeDBC at sampling time of 48h in V79MZh1A1 cells in comparison to untreated cells, however, no significant time-dependent increase in micronucleus frequencies was found. The use of the antikinetochore immunostaining revealed that DBC and MeDBC induced approximately equal levels of both kinetochore positive (C+) and kinetochore negative (C-) micronuclei. DiMeDBC, a strict hepatocarcinogen, did not manifest any effect on micronucleus induction in V79MZh1A1 cells. These studies suggest that genetically engineered Chinese hamster V79 cell lines expressing individual CYP cDNAs are a useful in vitro model for evaluation the role of particular cytochromes P450 in biotransformation of DBC and its tissue and organ specific derivatives.

Role of cytochrome P4501A1 in biotransformation of a tissue specific sarcomagen N-methyldibenzo[c,g]carbazole.

7H-dibenzo[c,g]carbazole (DBC) is a potent liver and skin carcinogen, while its synthetic methyl derivative N-methyldibenzo[c,g]carbazole (MeDBC) is tissue specific sarcomagen. It is supposed that sarcomagenic activity of DBC depends on biotransformation at ring-carbon atoms, as with PAH, whereas the heterocyclic nitrogen plays an important role in liver carcinogenicity. The objective of this study was to elucidate the role of cytochrome P4501A1 in metabolic activation of sarcomagenic derivatives of DBC and to characterize the DNA damage profiles induced by DBC and MeDBC in relation to the mode of metabolic activation. The genetically engineered V79MZh1A1 cell line with stable expression of cDNA of human cytochrome P4501A1, the parental V79MZ cell line lacking any cytochrome P450 activity and human hepatocarcinoma Hep G2 cells were used as a model cells. Dose-dependent decrease in colony forming ability (CFA) was found in the V79MZh1A1 cell line after treatment of cells with DBC and MeDBC; however, no change in CFA was induced in parental V79MZ cells. These results were in a good correlation with DNA damaging effects of these two derivatives measured by the alkaline DNA unwinding (ADU) and the modified single cell gel electrophoresis (SCGE) techniques. Differences in DNA damage profiles induced by DBC and MeDBC were found in V79MZh1A1 and Hep G2 cells. These differences were probably the result of different reactive metabolite formation depending on chemical structure of the molecule and ways of biotransformation. This study showed that the cytochrome P4501A1 took part in activation of sarcomagenic DBC derivatives. Moreover, V79 cell lines with stable expression of different cytochromes P450 in combination with DNA repair endonucleases should be a useful tool for characterization of the role of individual cytochromes in metabolic activation pathways of DBC and MeDBC.

Radiation-induced DNA damage and repair evaluated with 'comet assay' in human ovarian carcinoma cell lines with different radiosensitivities.

Radiation-induced DNA damage and kinetics of DNA repair was evaluated in three human ovarian carcinoma cell lines (i.e. CH-1, A-2780 and SKOV-3) with different sensitivities to ionizing radiation and radiation-induced apoptosis with the aid of single cell gel electrophoresis (SCGE, the comet assay). A good correlation was found between the initial level of DNA breaks and radiation induced apoptosis in CH-1 and SKOV-3 cell lines. While the radiation-sensitive CH-1 cell line manifested the highest level of initial DNA breakage and a significant delay in DNA break rejoining, the inverse correlation was found in the radiation-resistant cell line SKOV-3. Intermediate initial level of breaks was induced in the A-2780 cell line characterized by the intermediate sensitivity to X-ray radiation in comparison to CH-1 and SKOV-3 cells, however, the kinetics of DNA repair was comparable with radiation-resistant cell line SKOV-3. Our data suggest that the comet assay could be a promising tool for prediction of intrinsic cell radiosensitivity. This method might be considered as a supplementary technique to the more reliable but time consuming clonogenic assay.

Failure of carboxymethylglucan to inhibit oxidative DNA damage induced by hydroxyl radicals or singlet oxygen.

The ability of carboxymethylglucan (CMG), a high molecular water-soluble derivative of glucan, was evaluated to act as a scavenger of reactive oxygen species. Hydrogen peroxide and methylene blue plus visible light, well-defined oxidant factors, were used as a model agents for induction ofoxidative DNA damage in CaCo-2 cells. Both hydrogen peroxide and visible light gave rise to dose-dependent increase of DNA damage mediated by hydroxyl radicals (*OH) or singlet oxygen (1O2), respectively. While DNA lesions generated by hydrogen peroxide dominated by strand breakage, exposure of CaCo-2 cells to visible light led mainly to base modifications sensitive to formamidopyrimidine DNA-glycosylase (Fpg). Neither CMG nor ascorbic acid, a known antioxidant, induced any DNA damage in CaCo-2 cells. Pretreatment of cells with ascorbic acid prior to H2O2 or visible light exposure resulted into statistically significant reduction of DNA lesions induced by particular agent. However, pretreatment of CaCo-2 cells with CMG in concentration range from 0.01 microM to 1 microM reduced neither the level of strand breaks induced by hydrogen peroxide nor the number of Fpg-sensitive base modifications generated by visible light.

Cytotoxic and genotoxic effect of inhibitor of vulcanisation N-cyclohexylthiophthalimide in a battery of in vitro assays.

Mutagenicity of N-cyclohexylthiophthalimide (Duslin P) was tested first by the Ames test in the bacteria, Salmonella typhimurium. The negative results of the Ames test suggested that this compound does not induce mutations in the genome of S. typhimurium under the conditions used. To estimate the cytotoxicity of Duslin P to human cells, we measured cellular DNA and protein as well as cell proliferation, i.e., the mitotic index of treated and control cells. The genotoxic effects were assayed by two biochemical methods developed for detection of single-strand breaks of DNA in mammalian cells, i.e., by the alkaline single cell gel electrophoresis (comet assay) and by the DNA unwinding method, respectively. The DNA unwinding method showed that this compound did not induce DNA damage at concentrations < 7 micrograms/ml. Alkaline single cell gel electrophoresis revealed approximately double the level of DNA damage (in comparison to untreated control DNA) at a concentration of 2 micrograms/ml, which reduced proliferation to approximately 30%, and triple the level of DNA damage at higher concentrations (6 and 7 micrograms/ml), which inhibited completely both DNA synthesis and proteosynthesis. Cells with moderately damaged DNA were more common than cells with heavily damaged DNA. Parallel experiments with the strong mutagen and carcinogen MNNG showed that MNNG induced in cells a high level of DNA damage at concentrations which did not reduce the mitotic index or proteosynthesis, while DNA synthesis inhibited only partially. After treatment with MNNG, cells with heavily damaged DNA were more common than cells with moderately damaged DNA. Duslin P-treated VH10 cells were also tested cytogenetically, confirming that Duslin P induced neither chromosomal aberrations nor aneuploidy. We conclude that Duslin P has no mutagenic effect on bacteria, does not induce chromosomal aberrations and CREST positive or CREST negative micronuclei in human cells and induces only a small increase of DNA damage in human cells which is consistent with DNA fragmentation due to cell death.

Use of single cell gel electrophoresis (comet assay) modifications for analysis of DNA damage.

Single cell gel electrophoresis (SCGE) or comet assay is a rapid and sensitive fluorescent microscopic method which allows measurement of DNA strand breaks in individual cells. Modifications of SCGE conditions permitted to detect different types of DNA damage. In order to characterize DNA damage induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and hydrogen peroxide (H2O2) in Chinese hamster V79 cells, two approaches were used: (1) two pH values of unwinding and electrophoresis solutions (pH > or = 13.0 and pH = 12.1) to specify the type of DNA lesions [the alkali-labile sites and true DNA single-strand breaks (ssb)] and (2) DNA glycosylases [endonuclease III (EndoIII) and formamidopyrimidine-DNA glycosylase (FaPy)] or DNA inhibitors [hydroxyurea (HU) + 1-(beta-D-arabinofuranosyl)cytosine (AraC)] to characterize the types of DNA damage. Our results showed that the lesions induced by H2O2 represented mainly the true DNA ssb, while MNNG formed predominantly alkali-labile sites, which were converted to DNA ssb under strong alkaline conditions (pH > or = 13.0). The effects of DNA repair enzymes and DNA inhibitors were more significant under lower pH (pH = 12.1) of unwinding and electrophoresis solution. Both, DNA glycosylases and DNA inhibitors increased the level of DNA ssb.

Use of repair endonucleases for characterization of DNA damage induced by N-heterocyclic aromatic hydrocarbons.

Several repair endonucleases were used to characterize and quantify various types of DNA damage induced by 7H-dibenzo[c,g]carbazole (DBC) and its methyl derivative, N-methyldibenzo[c,g]carbazole (MeDBC). Differences in the DNA damage profile induced by these two derivatives were found to be related to their chemical structure and dependent on the way of their metabolic activation. Different ways of activation gave rise to different numbers of single strand breaks and DNA modifications or, at least, to different ratios of common modifications. DBC induced the highest level of breaks in human hepatal cell line Hep G2, while MeDBC induced most of the breaks in V79 cell line with stable expression of human cytochrome P4501A1. Our results support the idea of two different pathways of biotransformation of DBC and MeDBC.

Preculturing of Chinese hamster V79 cells with sublethal concentration of theophylline sensitizes cells to cytotoxic effects of MNNG.

In our previous work concerning the biologic effects of theophylline, we found that cells incubated during 48 h at low concentrations of theophylline (0.3 mg/ml of medium) manifested short-term deviations in the rate of DNA replication; however, this short-term inhibition of DNA replication did not reduce either the growth rate or the colony-forming ability of cells. In the present study, we concentrated on cytotoxic and DNA-damaging effects of MNNG on V79 cells precultured with sublethal concentration of methylxanthine theophylline. Cytotoxicity was evaluated on the basis of growth rate of treated cells as well as by colony-forming ability (plating efficiency) test and by trypan blue exclusion test. The level of DNA lesions (strand breaks) induced by MNNG was measured by alkaline DNA unwinding and by the comet assay. In an effort to explain higher cytotoxic effects of MNNG on precultured cells, we studied rejoining of damaged parental DNA after 4 h incubation post-MNNG-treatment as well. We found differences as against the controls in theophylline-precultured cells after treatment with the mutagen and carcinogen MNNG. The higher cytotoxic effect of MNNG in precultured cells was accompanied by a higher level of ss breaks of DNA and by more unrepaired lesions which remained after 4 h in parental DNA. Our results demonstrate that theophylline belongs to the group of agents inhibiting repair of potentially lethal DNA lesions.

The nature and origin of DNA single-strand breaks determined with the comet assay.

After treatment with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), methyl methanesulfonate (MMS) and hydrogen peroxide, the level of alkali-labile sites and single-strand breaks (ssb) in DNA was investigated, using the comet assay. The ability of antioxidant pre-treatment to decrease DNA damage was assessed. Results showed the following. (a) All single-strand (ss) DNA breaks detected immediately after MNNG- and MMS-treatment in hamster V79 cells had the character of alkali-labile sites while true ssb of DNA were represented only as a minor statistically significant (p < 0.01) fraction at the highest MMS concentration. (b) Most ss DNA breaks detected immediately after H2O2-treatment had the character of true breaks in DNA and alkali-labile sites represented only a minor fraction. (c) Pre-treatment of hamster V79 and human CaCo2 cells with vitamin E significantly reduced the number of breaks induced by hydrogen peroxide, but has no effect on the level of breaks induced by MNNG or MMS. We suggest that MNNG and MMS do not induce significant oxidative damage of DNA. Most of breaks induced by hydrogen peroxide have the nature of oxidative lesions of DNA. (d) In contrast to the effect of vitamin E, stobadine (STB) decreased not only the breaks induced by hydrogen peroxide but also those induced by MNNG and MMS. The reduced level of DNA damage in STB pre-treated samples could be due to inactivation of these alkylating agents by STB.

The single cell gel electrophoresis: a potential tool for DNA analysis of the patients with hematological malignancies.

Single cell gel electrophoresis (SCGE) was used to evaluate the level of DNA damage in peripheral blood (PB), bone marrow (BM), and lymphatic node (LN) cells of patients with acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML), chronic lymphocytic leukemia (CLL), chronic myeloid leukemia (CML) and non-Hodgkin's lymphoma (NHL). The level of DNA damage was compared with the level of basal DNA damage in control group, represented by healthy donors. Statistically significant increase of basal DNA damage was found in leukemia/lymphoma cells of patients suffered from AML, CML, ALL of T-cell subtype (T-ALL), and NHL, however, no difference in basal DNA damage was found in patients with ALL of early B-cell subtype (B-ALL) and CLL in comparison to control group. The mean basal DNA damage increased in the order CLL

Detection of MNNG-induced DNA lesions in mammalian cells; validation of comet assay against DNA unwinding technique, alkaline elution of DNA and chromosomal aberrations.

Human cells (VH10 or Hep G2) and hamster cells V79 were exposed to different concentrations of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and the level of DNA lesions was evaluated by the DNA unwinding technique, alkaline elution of DNA and the comet assay. All three methods were able to detect the effects of MNNG but with a clear difference in sensitivity. At low concentrations of MNNG the most sensitive method appeared to be the comet assay. After the short-term treatment the comet assay was able to detect the lesions induced by MNNG at approx. 0.1 microgram/ml, alkaline elution of DNA at 1 microgram/ml and DNA unwinding at 1-2 micrograms/ml. MNNG treated VH10 cells, human lymphocytes and V79 cells were also tested cytogenetically, confirming that MNNG induced chromosomal aberrations at concentrations > 1 microgram/ml in VH10 cells (short-term treatment): > 0.2 microgram/ml in V79 cells (long-term treatment) and > 8 micrograms/ml in human lymphocytes (long-term treatment). In some experiments we tried to increase the level of MNNG-induced DNA breaks with help of DNA repair inhibitors cytosine arabinoside (Ara C) and hydroxyurea (HU) which were applied either after or during MNNG treatment. Our results showed that the level of MNNG-induced lesions was increased by simultaneous treatment of cells with MNNG and Ara C and HU. 2 x 10(-5) M Ara C and 2 x 10(-3) MHU were as effective as 10-times higher concentrations of inhibitors. Ara C and HU increased the level of MNNG-induced DNA breaks mainly in combination with lower concentrations of MNNG (< 2 micrograms/ml). Rejoining of DNA breaks was observed in human cells VH10 and Hep G2 as well as in Chinese hamster cells V79 damaged by both lower and higher MNNG-concentrations. All methods showed that MNNG-induced DNA breaks had been gradually rejoined.

DNA adduct formation in primary mouse embryo cells induced by 7H-dibenzo[c,g]carbazole and its organ-specific carcinogenic derivatives.

The nuclease P1 modification of the 32P-postlabeling technique was used to study the biological activity of 7H-dibenzo[c,g]carbazole (DBC) and some of its derivatives, including N-methyldibenzo[c,g]carbazole (N-MeDBC), 5,9-dimethyldibenzo[c,g]carbazole (5,9-diMeDBC), 5,9,N-trimethyldibenzo[c,g]carbazole (5,9,N-triMeDBC), 6-methoxydibenzo[c,g]carbazole (6-McODBC), N-acetyldibenzo[c,g]carbazole (N-AcDBC), N-hydroxymethyldibenzo[c,g]carbazole (N-HMeDBC) in primary mouse embryo cells. A very good correlation was found between carcinogenic specificity in vivo of these N-heterocyclic aromatic hydrocarbons and their DNA-adduction in vitro. Primary mouse embryo cells were able to metabolize and detect tissue-specific sarcomagens N-MeDBC and 6-MeODBC as well as derivatives with both sarcomagenic and hepatocarcinogenic activity, DBC, N-AcDBC, and N-HMeDBC. The strong specific hepatocarcinogen 5,9-diMeDBC in vivo, did not induce any DNA-adducts in the embryo cells, which suggests that the enzymatic composition of the target tissue probably is the determining factor in the organ specificity of this derivative. 5,9,N-triMeDBC, derivative without any carcinogenic activity in vivo, did not induce any DNA-adducts in primary mouse embryo cells. Pretreatment of cells with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) apparently stimulated DNA-adduct formation in the cells exposed to DBC, 6-MeODBC, and N-MeDBC. No or a very slight effect of TCDD on DNA-adduct formation was found in cells exposed to N-HMeDBC and N-AcDBC. Preliminary results have shown that TCDD slightly induced cytochrome P4501A1-linked ethoxyresorufin O-deethylase (EROD) activity in primary mouse embryo cells. These data suggest the role of cytochrome P4501A1 in the metabolism of DBC derivatives with sarcomagenic activity.

DNA-synthesis inhibition and repair DNA-synthesis in CHO Ade-C cells: an alternative approach to genotoxicity testing.

We describe an alternative assay to determine genotoxicity. Its main feature is that it combines two measures in a single experiment; the inhibition of replicative DNA synthesis together with the stimulation of DNA repair. We show that, in tests of four different genotoxic agents, the assay gives results that are entirely consistent with what is known about the mode of action of these agents. In addition, we have demonstrated that chemical carcinogens requiring metabolic activation can be examined using a standard procedure of incubation with a microsomal activating fraction. We consider the combined assay for DNA synthesis inhibition and repair synthesis to be a useful way for the rapid prescreening of chemicals suspected of genotoxic activity on the level of mammalian cells.

Measurement of DNA strand breakage and DNA repair induced with hydrogen peroxide using single cell gel electrophoresis, alkaline DNA unwinding and alkaline elution of DNA.

Three techniques: single cell gel electrophoresis (SCGE), alkaline elution of DNA (AE), and alkaline DNA unwinding (ADU) were chosen to compare the sensitivity among these methods in detection of DNA damage and repair in human diploid VH10 cell line after short-term exposure to hydrogen peroxide. Using SCGE technique a dose-dependent increase in DNA migration was found in cells exposed to hydrogen peroxide in concentration range from 10 micromol/l to 100 micromol/l. Alkaline DNA unwinding method detected increased level of single strand breaks (ssb) in concentration range from 25 micromol/l to 100 micromol/l of H2O2, and alkaline elution of DNA estimated increased DNA elution rate from concentration 50 micromol/l of H2O2. In a time course study to evaluate the kinetics of DNA repair, both SCGE and ADU techniques showed that the repair of DNA strand breaks is very rapid; the level of ssb in treated cells has returned to near the background level within two hours. After this time damage remaining in the DNA was in the form of oxidised bases as revealed the incubation of treated cells with specific DNA repair endonuclease, formamidopyrimidine-DNA glycosylase.

Evaluation of mutagenic and cytotoxic effects of sodium fluoride on mammalian cells influenced by an acid environment.

The mutagenic activity of sodium fluoride at reduced pH was studied in the V79/HGPRT system. Statistical analysis of the results of mutagenicity testing suggests that, despite its high toxicity, sodium fluoride has no mutagenic effects at reduced pH on hamster V79 cells. Short-term treatment of cells with sodium fluoride at reduced pH inhibits growth activity of cells as well as synthesis of pulse-labeled nascent DNA and cumulative RNA synthesis and proteosynthesis. From the results of this study we suggest that an acid environment which supports formation of hydrogen fluoride increases toxic but not mutagenic potencies of sodium fluoride.