Simple differential Giemsa staining of sister chromatids after treatment with photosensitive dyes and exposure to light and the mechanism of staining

Mitigation of X-ray induced DNA damages and expression of DNA-repair genes by antioxidative Potentilla fulgens root extract and its ethyl-acetate fraction in mammalian cells

Potentilla fulgens is a medicinal plant in North-East India whose root is reported to have anti-diabetic, anticarcinogenic and antioxidant properties. The potential of hydro-alcoholic extract of P. fulgens root (PRE) for providing protection to mammalian cells exposed to ionising radiation was investigated in this study. The methanolic extract of PRE shows an enhanced radical scavenging ability in a concentration dependent manner. PRE-pre-treatment to stimulated human blood lymphocytes (HBLs) reduced the frequency of deletion and exchange aberrations induced by X-irradiation. Similar protection of chromosome aberrations was also observed in mouse bone marrow cells (BMCs) where mice were given PRE extract (1 mg extract/day/mice) ad libitum in the drinking water for 45 days before whole-body X-irradiation. Of the various extracts prepared by partitioning of the methanol extract, the ethyl-acetate (EA) fraction was found to possess better antioxidant, radical scavenging and DNA-damage reduction activities. PRE-pre-treatment also reduced the radiation-induced cell-cycle delay effectively in HBL. In HEK-293 cells, PRE reduced radiation-induced G2-block in cell kinetics. Interestingly, PRE-treatment alone increased the concentration of endogenous glutathione (GSH) in mouse BMC and in stimulated HBL along with the elevated expression of γ-glutamyl-cysteine synthetase heavy/catalytic subunit, a key determinant of GSH synthesis. Studies on expression of two DNA-repair genes revealed that there was a marked increase in the expression of GADD45 and H2AX genes after X-irradiation in stimulated HBL, and such expression was reduced significantly if PRE-treatment was given prior to radiation. The present findings show the ability of PRE to reduce radiation-induced DNA damages probably by free radical scavenging whereas modulation of expression of DNA-repair genes' and endogenous GSH-increment emerge as effective strategies. The present study is the first report on the selected medicinal plant species that suggests it to be a potential natural radioprotector when used as root extract or its EA fraction for mitigating radiation toxicity.

Monocyte clearance of apoptotic neutrophils is unhindered in the presence of NETosis, but proteins of NET trigger ETosis in monocytes

Resolution of inflammation needs effective and timely removal of dead cells and other toxic products of neutrophils, monocytes, and macrophages. In this study, we evaluated the role of monocytes in the clearance of neutrophil extracellular trap (NET) and apoptotic neutrophils in the inflammation site. For this, monocytes were observed microscopically after exposing them with NETs and/or apoptotic bodies. A subset of monocytes exposed to NETs ejected extracellular traps and this was shown to be mediated by proteins like elastase and citrullinated histones present in NET supernatant. Monocytes showed a preference for the internalisation of the apoptotic body when both NET and apoptotic bodies were present in the medium. The study provides new insight into the role of monocytes in the clearance of NET and apoptotic neutrophils and this information may open up a way in formulating therapeutic strategies for accelerating resolution of inflammation.

The N-terminal-truncated recombinant fibrin(ogen)olytic serine protease improves its functional property, demonstrates in vivo anticoagulant and plasma defibrinogenation activity as well as pre-clinical safety in rodent model

An N-terminal truncated fibrino(geno)lytic serine protease gene encoding a ~42kDa protein from Bacillus cereus strain AB01 was produced by error prone PCR, cloned into pET19b vector, and expressed in E5 coli BL21 DE3 cells. The deletion of 24 amino acid residues from N-terminal of wild-type Bacifrinase improves the catalytic activity of [Bacifrinase (ΔN24)]. The anticoagulant potency of [Bacifrinase (ΔN24)] was comparable to Nattokinase and Warfarin and results showed that its anticoagulant action is contributed by progressive defibrinogenation and antiplatelet activities. Nonetheless, at the tested concentration of 2.0μM [Bacifrinase (ΔN24)] did not show in vitro cytotoxicity or chromosomal aberrations on human embryonic kidney cells-293 (HEK-293) and human peripheral blood lymphocytes (HPBL) cells. [Bacifrinase (ΔN24)], at a dose of 2mg/kg, did not show toxicity, adverse pharmacological effects, tissue necrosis or hemorrhagic effect after 72h of its administration in Swiss albino mice. However, at the tested doses of 0.125 to 0.5mg/kg, it demonstrated significant in anticoagulant effect as well as defibrinogenation after 6h of administration in mice. We propose that [Bacifrinase (ΔN24)] may serve as prototype for the development of potent drug to prevent hyperfibrinogenemia related disorders.

Influence of reduced glutathione on end-joining of DNA double-strand breaks: Cytogenetical and molecular approach

Radiation induced DNA double-strand breaks (DSB) are the major initial lesions whose misrejoining may lead to exchange aberrations. However, the role of glutathione (GSH), a major cellular thiol, in regulating cell's sensitivity to DNA damaging agents is not well understood. Influence of endogenous GSH on the efficiency of X-rays and bleomycin (Blem) induced DNA DSBs end-joining has been tested here cytogenetically, in human lymphocytes and Hct116 cells. In another approach, oligomeric DNA (75bp) containing 5'-compatible and non-compatible overhangs mimicking the endogenous DSB were for rejoining in presence of cell-free extracts from cells having different endogenous GSH levels. Frequency of aberrations, particularly exchange aberrations, was significantly increased when Blem was combined with radiation. The exchange aberration frequency was further enhanced when combined treatment was given at 4°C since DNA lesions are poorly repaired at 4°C so that a higher number of DNA breaks persist and interact when shifted from 4°C to 37°C. The exchange aberrations increased further when the combined treatment was given to Glutathione-ester (GE) pre-treated cells, indicating more frequent rejoining of DNA lesions in presence of higher cellular GSH. This is further supported by the drastic reduction in frequency of exchange aberrations but significant increase in incidences of deletions when combined treatment was given to GSH-depleted cells. End-joining efficiency of DNA DSBs with compatible ends was better than for non-compatible ends. End-joining efficiency of testicular and MCF7 cell extracts was better than that of lungs and Hct116 cells. Cell extract made from GE-treated MCF-7 cells provided more efficient end-joining than from untreated and GSH-depleted cells. However, direct addition of GSH to the cell-free extracts showed considerable reduction in end-joining efficiency. Present data indicate that higher endogenous GSH favours rejoining of DNA DSBs (both restitution and illegitimate reunion) which in turn produce more exchange aberrations.

Interaction of DNA-lesions induced by sodium fluoride and radiation and its influence in apoptotic induction in cancer cell lines

Fluoride is an essential trace element but also an environmental contaminant with major sources of exposure being drinking water, food and pesticides. Previous studies showed that sodium fluoride (NaF) at 5 mM or more is required to induce apoptosis and chromosome aberrations and proposed that DNA damage and apoptosis play an important role in toxicity of excessive fluoride. The aim of this study is directed to understand the nature of DNA-lesions induced by NaF by allowing its interaction with radiation induced DNA-lesions. NaF 5 mM was used after observing inability to induce DNA damages and apoptosis by single exposure with 50 μM or 1 mM NaF. Co-exposure to NaF and radiation significantly increased the frequency of aberrant metaphases and exchange aberrations in human lymphocytes and arrested the cells in G1 stage instead of apoptotic death. Flow cytometric analysis, DNA fragmentation and PARP-cleavage analysis clearly indicated that 5 mM NaF together with radiation (1 Gy) induced apoptosis in both U87 and K562 cells due to down regulation of expression of anti-apoptotic proteins, like Bcl2 in U87 and inhibitors of apoptotic proteins like survivin and cIAP in K562 cells. This study herein suggested that single exposure with extremely low concentration of NaF unable to induce DNA lesions whereas higher concentration induced DNA lesions interact with the radiation-induced DNA lesions. Both are probably repaired rapidly thus showed increased interactive effect. Coexposure to NaF and radiation induces more apoptosis in cancer cell lines which could be due to increased exchange aberrations through lesions interaction and downregulating anti-apoptotic genes.

The relationship between dioxin congeners in the breast milk of Vietnamese women and sister chromatid exchange

The aim of this study was to clarify the relationship between dioxin concentrations in breast milk and the sister chromatid exchange (SCE) frequency in women from herbicide-sprayed and non sprayed areas. Blood samples were taken from 21 women with high TCDD (tetrachlorodibenzo-p-dioxin) levels from sprayed areas, 23 women with moderate TCDD levels from sprayed areas, and 19 women from non sprayed areas to determine their SCE frequency. The SCE frequencies for the high and moderate TCDD groups from the sprayed area and for the non sprayed area group were 2.40, 2.19, and 1.48 per cell, respectively. Multiple regression analysis showed that the standardized β values for 1,2,3,6,7,8-hexaCDD (β = 0.60), 1,2,3,4,6,7,8-heptaCDD (β = 0.64), and octaCDD (β = 0.65) were higher than those for TCDD (β = 0.34) and 1,2,3,7,8-pentaCDD (β = 0.42). The adjusted R² value for polyCDDs (R² = 0.38) was higher than that for polyCDD toxic equivalents (TEQ (toxic equivalents); R² = 0.23). This study therefore shows that levels of hexa-, hepta-, and octaCDD, which were previously regarded as being less toxic than TCDD, are closely related to SCE frequency and that the level of dioxin (pg/g lipid) is potentially more useful as an indicator than TEQ value for explaining SCE frequency.

The in vivo induction of sister chromatid exchange by the demethylating agent 5-aza-2'-deoxycytidine

Previously, we observed that the demethylating agent 5-azacytidine (azaC) induces a constant and limited low frequency of sister chromatid exchange (SCE), seemingly due to a limited number of SCE-prone sites whose expression is related to DNA demethylation. An alternative explanation for the low frequency of SCE induction may be its inefficient incorporation into DNA, as it has a higher incorporation into RNA. The aim of the present work is to determine if the frequency of SCE induction is increased after exposure to 5-aza-2'-deoxycytidine (azadC), a compound with the same mechanism of demethylation as azaC but more efficiently incorporated into DNA. Groups of mice were treated with 2.2, 4.4, 6.6 and 8.8 μmol azadC per kilogram body weight, and the SCE frequency, the mitotic index and the average generation time were determined after two cell division cycles. The dose-response data of SCE induction showed two components: (i) a dose-dependent increase between 0 and 4.4 μmol and (ii) almost a same level of two SCEs per cell at 4.4 and 8.8 μmol. Although azadC is incorporated more efficiently into DNA, as shown by a lower dose required for a maximal effect, the highest frequency of SCE induction is similar to that observed with azaC. These results indicate that the low incorporation of azaC into DNA seems not to be the factor that limits SCE induction, but the limited number of specific SCE-prone sites in demethylated DNA. Perhaps, there are a restricted number of sites prone to homologous recombination due to DNA demethylation.

Genotoxic assessment in peripheral blood lymphocytes of post-polio individuals using sister chromatid exchange analysis and micronucleus assay

Environmental pollution is a complex issue because of the diversity of anthropogenic agents, both chemical and physical, that have been detected and catalogued. The consequences to biota from exposure to genotoxic agents present an additional problem because of the potential for these agents to produce adverse change at the cellular and organism levels. Past studies in virus have focused on structural damage to the DNA of environmental species that may occur after exposure to genotoxic agents and the use of this information to document exposure and to monitor remediation. In an effort to predict effects at the population, community and ecosystem levels, in the present study, we attempt to characterize damage occurring through genotoxic agents like 5-bromo-2-deoxyuridine, BrdU, using sister chromatid exchange technique and the formation of micronuclei (MN) in the peripheral lymphocytes of the post-polio syndrome sequelae affected by poliovirus. Analysis of structural chromosomal aberrations (CAs) and involvement of the specific chromosome break were pursued in this study. They revealed a significantly higher incidence of CAs (chromatid and chromosome breaks) in patients compared with controls, where the specific chromosome break has emerged as specific. Also, the maximum numbers of breaks were found to be in chromosome 1 at the position 1p36.1. The results also suggest a correlation between CAs and content of MN.

The influence of reduced glutathione on chromosome damage induced by X-rays or heavy ion beams of different LETs and on the interaction of DNA lesions induced by radiations and bleomycin

It is thought that high linear energy transfer (LET) radiation induces more complex DNA damage than low-LET particles, specifically clustered DNA damage that causes cells to repair DNA double strand breaks (DSB) more slowly and leads to severe biological consequences. The present study aimed to investigate the role of exogenously added glutathione (GSH) on (12)C-beam (287keV/mum) and (7)Li-beam (60keV/mum) induced chromosome aberration (CA) formation, particularly on exchange aberration formation. In order to characterize the role of GSH in the joining of DNA DSBs, we induced DNA lesions with bleomycin (Blem) in conjunction with either high- or low-LET radiation (X-rays) since the chemistry of the free DNA ends created by Blem and X-rays is similar. CHO cells were exposed to reduced GSH at a concentration of 2mM for 3h before radiation. Treatment with Blem (20mug/ml) was carried out for 2h before the cells were exposed to radiation. Our results show that the frequency of chromosomal aberration increases with increased LET. Heavy ion exposed cells show a higher frequency of CA over time than do X-irradiated cells. An analysis of the first post-irradiation mitosis of exposed CHO cells shows that high-LET radiation induces more breaks than exchange-type aberrations and exogenous GSH has no influence on high-LET radiation-induced DNA damage. The DNA lesions induced by low-LET radiation interact relatively strongly with Blem-induced lesions whereas interaction between Blem and high-LET radiations was poor. This could be attributed to differences in repair kinetics and qualitative differences in the DNA lesions induced by Blem and high-LET radiation.

Chromosome aberrations in peripheral blood lymphocytes of high-risk HPV-infected women with HGSIL

Genomic instability is one of the main characteristics of malignant tumors, including HPV-induced cervical cancer. The aim of this study was to explore the use of assessing chromosome aberrations (CA) in peripheral blood lymphocytes as a biomarker for genomic instability in high-risk HPV-infected women with high-grade squamous intraepithelial lesions (HGSIL). A total of 120 women were recruited for this study, following cytology/colposcopy evaluation and HPV DNA detection. The study groups consisted of 30 HPV(+) women with histologically confirmed cervical intraepithelial neoplasia grade 2/3 and 30 HPV(+) women with carcinoma in situ (CIS). Two control groups, including 30 women HPV(-) and 30 women HPV(+), were recruited among women who were reported as cytology negative. Lymphocyte cell cultures were established for 52 hr, and 100 complete metaphase cells were evaluated per subject for CA analysis. The results show that women with CIS had significantly higher frequencies of both aneuploidy (0.67 +/- 0.20 vs. 0.14 +/- 0.08, P = 0.020) and tetraploidy (0.88 +/- 0.23 vs. 0.17 +/- 0.08, P = 0.013) in comparison with HPV(-) controls. These findings suggest the usefulness of peripheral blood lymphocytes to detect genomic instability associated with HPV-induced HGSIL.

p53-dependent antiproliferative and antitumor effect of novel alkyl series of diorganotin(IV) compounds

PURPOSE

A series of diorganotin(IV) dichloride complexes of N-(2-pyridylmethylene)arylamine (nitrogen-chelating ligands) have been synthesized and characterized. The present study was carried out to investigate the comparative anti-proliferative and anti-tumor effect of Me(2)SnCl(2.)L(1) (OTC-1), Et(2)SnCl(2.)L(2) (OTC-2) and (n)Bu(2)SnCl. L(2) (OTC-3) in combination with X-rays (1.5 Gy).

METHOD

The cytotoxicity of these diorganotin(IV) compounds was studied in human peripheral lymphocytes and the antitumor activity was assessed in Dalton's lymphoma cells. The involvement of proteins that regulate cell cycle and apoptosis was investigated to elucidate the mechanism of their action.

RESULTS

5 mg kg(-1) of OTC-3 showed better antiproliferative and antitumor activity than OTC-1 and OTC-2, both as alone or in combination with X-rays. The maximum enhancement of exchange aberrations and the level of p53 and p16 proteins were observed in the OTC-3 treated samples. Upregulated expression of p53 caused a significant down-regulated transcriptionally repression of Survivin in OTC-3 treated human lymphocytes.

CONCLUSION

It could be possible that after treatment with either OTC-3 alone or in combination with X-rays the Dalton's lymphoma cells may die apoptotically after inducing initial delay in cell cycle and thereby survivality of mouse bearing Dalton's Lymphoma cells was increased significantly.

Cell proliferation inhibition and antitumor activity of novel alkyl series of diorganotin(IV) compounds

Diorganotin(IV) compounds, R2SnCl2 are often tetrahedral, and structurally resemble the active platinum compounds, i.e. cisplatin, and consequently a large number of such complexes have been tested for antitumor activity. A structural correlation with biological activity for diorganotin(IV) complexes has shown that active species are associated with complexes having Sn-N bonds longer than 2.39 A which in turn determines the formation of a tin-DNA complex. In view of these, a series of diorganotin(IV) dichloride complexes of N-(2-pyridylmethylene)arylamine (nitrogen-chelating ligands) has been synthesized and characterized on the basis of IR, NMR and 119Sn-Mössbauer studies. In the present study, an attempt was made to determine the comparative antiproliferative and antitumor effect of diorganotin(IV) complexes with different alkyl groups [Me2SnCl2.L1 (OTC-1), Et2SnCl2.L2 (OTC-2) and (n)Bu2SnCl2.L2 (OTC-3)]. The present study in human lymphocytes demonstrated that these diorganotin(IV) complexes could block the cell cycle progression and induce sister chromatid exchanges (SCEs) significantly, however, with respect to the induction of chromosome aberrations (CAs) it was very mild. Both the levels of p53 and p16 proteins were raised after diorganotin(IV) treatment and such induction was maximum in the OTC-3 treated samples. The antitumor activity was determined in accordance with the US National Cancer Institute (NCI) standard protocol for primary screening in Dalton's lymphoma that was maintained by serial intraperitoneal transplantation. The T/C (treated/control) value was increased (186% with OTC-3) when diorganotin(IV) was given after transplantation. The data suggest that the OTC-3 has better antiproliferative and antitumor activity and endogenous glutathione level has no influence on the effect of OTC-3.

Identification of a high frequency of chromosomal rearrangements in the centromeric regions of prostate cancer patients

The aim of the present investigation was to study the major chromosomal aberrations (CA) like deletion, translocation, inversion and mosaic in prostate cancer patients of Tamilnadu, Southern India. Totally 45 blood samples were collected from various hospitals in Tamilnadu, Southern India. Equal numbers of normal healthy subjects were chosen after signing a consent form. Volunteers provided blood samples (5 ml) to establish leukocyte cultures. Cytogenetic studies were performed by using Giemsa-banding technique and finally the results were ensured by spectral karyotyping (SKY) technique. In the present investigation, major CA like deletion, translocation, inversion and mosaic were identified in experimental subjects. Results showed frequent CA in chromosomes 1, 3, 5, 6, 7, 9, 13, 16, 18 and X. In comparison with experimental subjects, the control subjects exhibited very low levels of major CA (P<0.05). In the present study, the high frequency of centromeric rearrangements indicates a potential role for mitotic irregularities associated with the centromere in prostate cancer tumorigenesis. Identification of chromosome alterations may be helpful in understanding the molecular basis of the disease in better manner.

Different behavior of SCE-eliciting lesions induced by low and high doses of busulfan

Our previous studies suggested a dose-dependent transition in the types of DNA lesions induced by busulfan, as measured using the comet assay and by micronuclei analyses. The aim of the present study was to investigate the dose-dependent induction of different sister-chromatid exchange-eliciting lesions; lesions were distinguished by their efficiency in producing sister-chromatid exchange (SCE), and by their reparability during G1. Synchronously dividing murine salivary gland cells were assayed in vivo. Groups of mice were intraperitoneally injected with either 30 or 80 micromol busulfan/kg body weight solution at early or late G1. The rate of SCE/micromol busulfan/kg body weight obtained by exposure at late G1 with the high dose was twice that of the low dose. SCE induction during early G1 was higher than at late G1 with both doses; only the low-dose response was statistically significant. The frequency distribution of SCEs per cell demonstrated that cells exposed at the late G1 phase showed typical profiles that closely fit a Gaussian curve. However, an irregular profile was obtained for cells treated during early G1, which showed some cells with high-SCE frequency. Cells treated in early G1 have more time to repair lesions before DNA synthesis; therefore, the results suggest that instead of repair, secondary SCE-eliciting lesions during G1 were produced, especially at the lower dose. The results obtained in this study indicate that there are dose-dependent differences in the types of SCE-eliciting lesions induced by busulfan.

Mechanism of in vivo sister-chromatid exchange induction by 5-azacytidine

The aim of the present study was to explore the in vivo mechanism of sister-chromatid exchange (SCE) induction by 5-azacytidine (5-azaC) in murine bone marrow cells. Experiments were performed to examine SCE induction in response to different doses of 5-azaC as well as several exposures. Additionally, we examined the persistence of SCE induction and the effect of bromodeoxiuridine (BrdU) incorporation. Sister-chromatid differentiation was obtained by injecting mice intraperitoneally with BrdU absorbed to activated charcoal. Before BrdU injection, different doses of 5-azaC were administered intraperitoneally either singly or in multiples. Colchicine in an aqueous solution was administered subcutaneously 22 h after BrdU injection. Two hours later, animals were sacrificed by cervical dislocation and both femurs were dissected. Bone marrow cells were processed to obtain chromosome preparations, which were stained by the fluorescence plus Giemsa method. Results indicate that 5-azaC caused SCE, albeit to a limited extent. In order to discern whether the limitation was due to cytotoxicity or to partial 5-azaC incorporation, we administered multiple sub-toxic doses of 5-azaC. This treatment increased 5-azaC incorporation and reduced cytotoxicity, but did not raise SCE frequency, indicating that the limitation was not due to either of the two factors mentioned above. SCE frequency induced by 5-azaC persisted for at least eight cell divisions, confirming that this agent had caused inhibition of DNA methyltransferase and subsequently the reduction of DNA re-methylation, which in turn induced the expression of a number of SCE-prone sites. Finally, SCE induction in response to 5-azaC was completely dependent on BrdU incorporation. The data allow us to conclude that 5-azaC causes SCE to a limited extent; limited SCE induction was not due to the direct effect of incorporation or cytotoxicity of 5-azaC, but rather the generation of a number of SCE-prone sites, the expression of which persists for at least eight cell divisions and is dependent on BrdU incorporation.

Influence of endogenous glutathione level on X-ray induced cell cycle delay in human lymphocytes

Here, induction of chromosomal aberration after X-irradiation and the pattern of cell cycle kinetics have been investigated in human lymphocytes, after exogenous addition of reduced glutathione or by depleting levels of reduced glutathione endogenously. Involvement of cell cycle regulator proteins such as p53 and p21 has been investigated to elucidate their role in induction of delay in cell cycle progression after irradiation.

Interaction of radiation- and bleomycin-induced lesions and influence of glutathione level on the interaction

Radiation-induced exchange aberrations are thought to arise as a consequence of misrejoining of free ends of DNA double strand breaks (dsbs). In quiescent mammalian cells this process of misrejoining is prevalently taken up by the non-homologous end joining (NHEJ) process. In order to investigate the role of glutathione (GSH) in DNA dsb rejoining, the interaction of the lesions induced by bleomycin (Blem) and by radiation was studied since the lesions caused by both have similar and apparent rapid rates of repair. Endogenous GSH was depleted by buthionine sulfoximine (BSO) and chromosome aberrations (CAs) of human lymphocytes were scored from first cycle metaphases. Gamma radiation was administered 2 h after Blem treatment in combined studies. In the case of BSO, the treatment was given 3 h before Blem treatment. The BSO-treated samples showed higher sensitivity to radiation than BSO-untreated ones. Combined treatment of Blem and radiation induced higher frequency of CAs, in particular the exchange aberrations and interstitial deletions. However, such increased frequency of exchange aberrations was reduced drastically and the frequency of terminal deletions was increased significantly when combined treatment was given to BSO-pretreated cells. The consistent level of Ku70 protein in all the treated samples, with undetectable level of Rad51 in the G0-lymphocytes indicates the involvement of NHEJ pathway in misrejoining of DNA dsbs. It may be hypothesized that reduction in the frequency of exchange aberrations as induced by Blem + radiation combined treatment in BSO-treated samples could be because of reduced NHEJ pathway.

Chromosome aberrations among cigarette smokers in Colombia

Worldwide, the annual morbimortality caused by cigarette smoking is a major public health concern. In Colombia, up to 33% of the adult population has smoked at some point in life, raising important national issues on the disease burden from tobacco. The aim of this study was to establish whether cigarette smoking increases the frequency of chromosome aberrations (CA) in peripheral blood lymphocytes of smokers (n = 52) compared with non-smokers (n = 52) in Popayán, Colombia. After signing a consent form, volunteers provided a blood sample (20 ml) to establish cell cultures at 52 h. For CA analysis, 100 complete metaphase cells from each subject were evaluated. The CA frequency was significantly higher in smokers (8.38 +/- 0.61) than in non-smokers (3.13 +/- 0.29), showing the highest number of CA (14.83 +/- 1.01) among heavy smokers (>20 pack-years). Interestingly, light smokers (< or =10 pack-years) also showed a significant increase in CA when compared to non-smokers (6.62 +/- 0.53 versus 3.13 +/- 0.29, P < 0.01, respectively). In addition, a significant positive correlation was found between the frequency of CA and the intensity of smoking in pack-years (R2 = 0.60). Our study indicates that the genotoxic effects in lymphocytes from smokers are most likely caused by cigarette smoke constituents, providing scientific evidence to encourage national campaigns to prevent tobacco consumption.

Genotoxic effect of raw betel-nut extract in relation to endogenous glutathione levels and its mechanism of action in mammalian cells

The mutagenic and carcinogenic potency of betel-nut components is well established. This study was undertaken to determine the genotoxic potency of an aqueous extract of raw betel nut (AEBN) in relation to the endogenous glutathione (GSH) level in mouse bone marrow cells (BMC) and human peripheral blood lymphocytes (PBLs), and to find out whether arecoline (ARC), an alkaloid of betel nut, could generate reactive oxygen species (ROS) in these cells. It was observed that AEBN has genotoxic properties, which is further enhanced by depletion of endogenous GSH levels. However, the degree of enhancement varies with the type of parameter and cell system studied. The present data indicate that the generation of ROS by ARC could partially contribute to the induction of chromosomal aberrations (CAs), since the frequency of ARC-induced CAs was reduced either by post-treatment with superoxide dismutase (SOD) or in anoxic conditions. However, the induction of sister chromatid exchanges (SCEs) probably involves p53-dependent changes in cell proliferation and allowing some repair of DNA damage. The extent of damage for each parameter was higher when the mice were exposed to AEBN for 30 days than 5 days. Longer exposure showed higher level of p53 expression in mouse BMC, which could block the damaged cells from proliferation and allow the cells to repair the DNA damage.

Fenvalerate-induced chromosome aberrations and sister chromatid exchanges in the bone marrow cells of mice in vivo

Fenvalerate, a synthetic pyrethroid insecticide, is commonly used in agriculture and other domestic applications due to its high insecticidal activity and low mammalian-, avian- and phyto-toxicities. However, the genotoxic effect of fenvalerate is highly equivocal. In the present study the genotoxic effects of fenvalerate was evaluated using structural chromosome aberration (CA) and sister chromatid exchange (SCE) assays in mice. Out of the three doses (5, 10 and 20 mg/kg) tested, statistically significant increase in CA was found following intra peritoneal (i.p.) treatment of 2 0 mg/kg of fenvalerate for 24 h (P<0.01) and 48 h (P<0.05) only. Neither the acute doses of 5 and 10 mg/kg, nor the sub-acute dose (5x4 mg/kg) of fenvalerate could induce any significant effect. All the three acute doses induced significant increase in the frequency of SCEs (P<0.01) in the bone marrow cells, which showed a significant dose-response correlation (r=0.9541, P<0.05). With certain reservations to possible impurities, from the present findings technical grade fenvalerate may be considered as a weak clastogen and a potent inducer of SCEs in mice.

Genotoxic effects of malathion: an organophosphorus insecticide, using three mammalian bioassays in vivo

The genotoxic effects of malathion was evaluated using chromosome aberration, sister chromatid exchange (SCE) and sperm abnormality assays in mice. All the three acute doses (2.5, 5 and 10mg/kg) of malathion tested in the present study, induced significant dose-dependent increase in the frequency of chromosome aberrations and sperm abnormalities, but did not affect the total sperm count. The highest acute dose induced a >12-fold increase in the frequency of chromosome aberrations, two-fold increase in the frequency of SCEs and four-fold increase in the frequency of sperms with abnormal head morphology following intraperitoneal (i.p.) exposure. Further, a significant increase in the frequency of SCEs was observed, but the increase was not dose-dependent. At higher doses, malathion induced a moderate delay in cell cycle as evident from the increase in average generation time (AGT). The present findings suggest that technical grade malathion is a potent genotoxic agent and may be regarded as a potential germ cell mutagen also.

Antiproliferative and cytotoxic effect of a novel organotin compound on mammalian cells both in vitro and in vivo

Organotin compounds are organometallic compounds showing various toxicological properties. Several organotin compounds also showed an antineoplastic effect. However, their relative mutagenic potential is not well established. In this study Et(2)SnCl(2).L [L=N-(2-pyridylmethylene)-4-toluidine] (OTC) has been subjected to investigation for its cytotoxic effect in mouse bone marrow cells (BMCs) and human peripheral blood lymphocyte cells (HPBLs). The Sn [bond] N bond in OTC is 2.46A which is greater than 2.39A and therefore, a better formation of tin-DNA complex can be expected. The present data indicate that OTC induced significant delay in cell kinetics and sister chromatid exchanges (SCEs) in both BMCs and HPBLs, whereas, induction of chromosome aberrations was found only in HPBLs. The presence of buthionine sulfoximine (BSO) modulated cellular sensitivity towards OTC in both cell systems. It may be inferred that the OTC could bind on DNA more easily owing to its structural advantage and this may explain the induction of DNA damage and the delay in cell proliferation. Since the cytotoxic effect of OTC is more in glutathione depleted cells, the concentration of OTC may be reduced to get an antitumour effect in GSH-depleted cells and thus minimizes its toxic side effect.

Differences in sensitivity of murine spermatogonia and somatic cells in vivo to sister-chromatid exchange induction by nitrosoureas

Previously published data indicate that spermatogonia (SPG) are less sensitive to a sister-chromatid exchange (SCE) induction for different mutagens. In an earlier study, we have observed that bromodeoxyuridine (BrdU) substituted murine SPG are less sensitive to SCE induction by gamma ray in cells, than bone marrow (BM) and salivary gland (SG) cells in vivo. This was interpreted to mean that SPG are more efficient in DNA repair or are less prone to SCE induction. That the lower induction of SCE could be due to a reduced accessibility of mutagens to the SPG by virtue of a physiological barrier, was discarded by using gamma radiation. The aim of the present study was to establish whether or not there are differences in SCE induction by nitrosoureas among SPG, SG and BM cells with BrdU substituted or unsubstituted DNA. It was observed that SCE induction by methylnitrosourea (MNU) or by ethylnitrosourea (ENU) in SPG was, respectively, five and two times lower than in SG, and ten and three times lower than in BM. In SPG after BrdU incorporation, there was no increase in efficiency of SCE induction; in fact, there was even a slight decrease by exposure to MNU or ENU. BM and SG cells showed an increased efficiency in SCE induction after BrdU incorporation. This implies that SPG are also less sensitive to SCE induction by nitrosoureas, which cause a different kind of damage from previously assayed mutagens.

Chromosome diversity of the genus Aotus from Colombia

Description of six Colombian karyomorphs is completed through an extensive cytogenetic characterization of 35 Aotus (owl monkeys) specimens. The description of a new karyomorph for Colombian Aotus by chromosome on Q, G, R, and C, sequential banding is included. Pairs of karyomorphs 2 and 3 and 6 and 9 with 2n of 54, and 50, respectively, as well as karyomorphs 7 and 8 with 46 and 58 chromosomes were strongly suspected to represent different species on the grounds of large karyotypic differences. A proposal for a chromosome nomenclature of Aotus karyomorphs that aims to clarify Aotus taxonomy is presented which achieves a precise correspondence of different banding patterns, based on Q, G, R, and C sequential banding and chromosome measurements. Although our contribution is not a universal nomenclature system, unique criteria for chromosome denomination within Aotus karyomorphs are established. Previous systems of chromosome nomenclature have not successfully addressed the nomenclature of chromosomes of the same karyotype.

Chromosomes and stress

The present investigation examines genotoxic effects of: prolonged periods of stress; the role of the endocrine system; and the relationship between psychogenic stress and chemical mutagens. Increased levels of both Sister Chromatid Exchanges (SCEs) and Chromosome Aberrations (CAs) were observed in male rats subjected to white noise of either 72 or 240 hrs duration, demonstrating that damage occurs during chronic stress. Rats subjected to foot-shock after having been either hypophysectomized or sham-operated, showed elevation of both SCEs and CAs, indicating that hormones in the hypothalamic-pituitary-adrenal axis do not play a role in genotoxic damage. Rats subjected to foot-shock, and/or the mutagen Mitomycin-C(MMC) showed elevated SCEs, both separately and together. The combined effect was the sum of the individual effects, demonstrating that synergism was not involved. This investigation establishes that psychogenic stress plays a role in genotoxic damage.

Genotoxic effect of arecoline given either by the peritoneal or oral route in murine bone marrow cells and the influence of N-acetylcysteine

The carcinogenic potentiality of the major alkaloid of betel nut, arecoline (ARC), is well established. This study was undertaken to determine the differences in genotoxic effects of ARC when given by two different routes (oral administration (OA) and intraperitoneal injection (IP)) in mouse bone marrow cells (BMC) since ARC carcinogenicity was observed only when ARC was given orally. The data indicate that ARC-OA induced a higher frequency of cancers, a greater delay in the cell cycle and greater sister chromatid exchanges than ARC-IP. The presence of N-acetyl cysteine along with ARC-OA significantly reduced the effect of ARC.

In vivo repair during G1 of DNA lesions eliciting sister chromatid exchanges induced by methylnitrosourea or ethylnitrosourea in BrdU substituted or unsubstituted DNA in murine salivary gland cells

The difference in efficiency of methylnitrosourea (MNU) and ethylnitrosourea (ENU) to induce SCE in early or late G1 was determined in synchronized murine salivary gland cells in vivo, as a measure of the capacity of this tissue to repair the lesions involved in SCE formation during G1. The repair during G1 was determined by treating the cells in early or late G1. Treatment was in the first cycle (G1 before incorporation of 5-bromodeoxyuridine (BrdU)) or in G1 of the second cycle (after a single round of BrdU incorporation). It was observed that 50% of the lesions induced by MNU that elicit SCE are repaired during G1. BrdU incorporation into DNA increases the sensitivity of the cell to SCE induction by MNU nearly 40%; however under this circumstance a slightly lower SCE frequency was observed in the cells exposed to MNU at early G1, indicating that during G1 only few lesions are repaired. The ENU-induced DNA-lesions involved in SCE production are nearly 100% persistent along G1; besides, a slight but significantly higher SCE frequency was observed in cells exposed at early G1, suggesting the formation of SCE-inducing lesions during G1. BrdU incorporation to DNA sensitizes the cell to SCE induction by ENU, increasing the SCE frequency to nearly to a 40%, although these additional lesions involved in SCE induction seem to be susceptible to repair during G1.

The DNA helicase activity of BLM is necessary for the correction of the genomic instability of bloom syndrome cells

Bloom syndrome (BS) is a rare autosomal recessive disorder characterized by growth deficiency, immunodeficiency, genomic instability, and the early development of cancers of many types. BLM, the protein encoded by BLM, the gene mutated in BS, is localized in nuclear foci and absent from BS cells. BLM encodes a DNA helicase, and proteins from three missense alleles lack displacement activity. BLM transfected into BS cells reduces the frequency of sister chromatid exchanges and restores BLM in the nucleus. Missense alleles fail to reduce the sister chromatid exchanges in transfected BS cells or restore the normal nuclear pattern. BLM complements a phenotype of a Saccharomyces cerevisiae sgs1 top3 strain, and the missense alleles do not. This work demonstrates the importance of the enzymatic activity of BLM for its function and nuclear localization pattern.

Modulation of mitomycin C-induced sister chromatid exchanges and cell cycle delay by buthionine sulfoximine and reduced glutathione in mouse bone marrow cells in vivo

Mitomycin C (MMC) is a bifunctional alkylating agent and a chemotherapeutic drug, covalently binds to the DNA of cells and produces monoadducts and DNA-DNA, DNA-protein crosslinks, induces damages at chromosomal level and slows down the rate of cell proliferation. Reduced glutathione (GSH), a major non-protein thiol substance plays an important role in detoxification of cells against the toxic effect of exogenous compounds. In order to understand the role of factor which affects MMC sensitivity, we have made an attempt to establish a relationship between MMC-induced DNA damages and the endogenous GSH-status of the cells. MMC was treated to normal and buthionine sulfoximine (BSO; GSH-depleting agent)-treated mice. Exogenous GSH was also added to MMC-treated normal mice. Cells were fixed at 24 h and sister chromatid exchanges (SCEs) and average generation time (AGT) were scored. MMC-induced SCEs and cell cycle delay significantly with respect to control and the frequency of SCEs was increased considerably while MMC treatment combined with either GSH or BSO. The induction of cell cycle delay by MMC was reduced significantly when GSH or BSO was present along with MMC. These observations indicate that the factor responsible for inducing delay in cell cycle after MMC treatment may not be relevant for SCE-induction.

Variation in arsenic-induced sister chromatid exchange in human lymphocytes and lymphoblastoid cell lines

This study was undertaken to compare the genotoxic effects of arsenite in cultured human lymphocytes and lymphoblastoid cell lines from a group of normal human volunteers. The goal was to determine whether, as found with other genotoxins, subgroups might exist which showed relative high or low sensitivity to induction of sister chromatid exchanges (SCEs) by this metal. Primary lymphoblast cultures were established by treatment with phytohemagglutinin (PHA-L). Lymphoblastoid cell lines were established by transformation with Epstein-Barr virus. Cultures were exposed for 40 h to sodium arsenite (AsIII) and SCEs assayed by 5-bromo-2'-deoxyuridine incorporation and staining by fluorescence plus Giemsa. SCEs were increased by arsenite in a dose-dependent manner over the concentration range of 10(-7)-10(-5) M. SCEs could not be scored above 10(-5) M because of cytotoxicity. Comparison of SCE frequency in primary lymphocyte cultures among individuals showed substantial variation in sensitivity to arsenite, with some showing no significant effect while others showed a 2-3-fold increase in SCE frequency. In one lymphoblastoid cell line especially sensitive to arsenite, arsenic acid (AsV) or dimethylarsinic acid (DMA) at concentrations up to 10(-5) M did not increase the SCE frequency suggesting that AsIII is the active form of arsenic. When pooled data from the primary lymphocytes was compared to that obtained with the lymphoblastoid cells, the slopes of the dose-response curves for ASIII-induced SCEs were similar. The sensitivity of the majority of the individual primary lymphocyte cultures to SCE induction by arsenite was correlated with the sensitivity of the lymphoblastoid cultures established from the same individual. However, in three individuals no correlation was found. Individual lymphoblastoid cell lines retained their As sensitivity after cryopreservation and subsequent revival. Whether the genotoxic response to As is genetically controlled or the result of phenotypic selection is being explored in these stable lymphoblastoid cell lines.

In vivo effect of gamma ray pretreatment on sister-chromatid exchange induction by mitomycin C in murine bone marrow cells

The effect of gamma ray pretreatment on sister-chromatid exchange induction by mitomycin C (MMC) was determined in murine bone marrow cells in vivo. A 30% reduction in the expected SCE frequency was observed assuming an additive effect. These results support the prediction of the replicative model for SCE formation with regard to the interactions between mutagens, and confirm previous results focused on the adaptive response.

Development of an in vivo genotoxicity assay using the marine worm Platynereis dumerilii (Polychaeta: Nereidae)

An in vivo genotoxicity test system has been developed using the embryo-larval stages of the marine annelid, Platynereis dumerilii (Polychaeta: Nereidae). This species is representative of an ecologically important group of marine invertebrates, it is amenable to laboratory culture and has a well defined and stable karyotype (2n=28) which is suitable for the analysis of a range of cytogenetic endpoints, including chromosomal aberrations (CAs) and sister chromatid exchanges (SCEs). An evaluation of the cell cycle kinetics using the embryo-larval stages allowed selection of exposure times for cytogenetic work. Subsequently, 12-h-old embryos were exposed to reference mutagens, dissolved in sea water, in the presence of 5-bromodeoxyuridine (BrdU) for 12 h (SCE analysis) or 8 h (CA analysis) at 15 +/- 1 degree C, by which time they had reached the first larval stage (20-24h). Dose response-relationships for cytotoxicity, SCEs and CAs were observed for both direct acting mutagens (methyl methanesulfonate, mitomycin C) and mutagens which require metabolic activation (cyclophosphamide, benzo[a]pyrene). The sensitivity of the embryo-larval stages of P. dumerilii to both direct and indirect acting mutagens, their suitability for laboratory culture, together with the presence of a good karyotype and chromosome morphology for cytogenetic analyses, makes this species a potentially valuable in vivo model for marine genotoxicity testing.

Psychogenic stress induces chromosomal and DNA damage

In this investigation, rats subjected to swim stress showed within 24 hours significant increases in both the level of chromosome aberrations and Sister Chromatid Exchanges (SCEs) in bone marrow cells. The generality of cytogenetic damage by behavioral stressors was demonstrated by exposing rats to both cold-and warm-water forced swims, to white noise, and to continuous or intermittent inescapable foot shock stress (IFS). The induction of chromosome aberrations and SCEs, to differing degrees, by stressors that differ both quantitatively and qualitatively, demonstrates that this is a general phenomenon of stress. The use of an additional measure, unscheduled DNA Synthesis (UDS) showed that stress-induced genotoxic damage can occur in a second cell type and on a molecular as well as chromosomal level. These results indicate that there may be a cellular genetic basis for some of the effects of stress.

Genotoxic effects produced by capsaicin in mouse during subchronic treatment

Capsaicin is the chemical responsible for the pungent, hot properties of Capsicum, a vegetable widely consumed in the diet of many countries in the world. In this work, the genotoxic capacity of capsaicin was studied in mouse during a 32-day treatment. We used the dosages of 1.46 and 1.94 mg/kg given by the i.p. route. Each week, the frequency of micronucleated normochromatic erythrocytes (MN-NE) and the ratio polychromatic/normochromatic erythrocytes (PE/NE) were scored. At the end of the experiment we also scored the frequency of sister chromatid exchanges (SCE). The results in the MN-NE analysis showed a genotoxic response with 1.94 mg/kg starting from day 16, while the 1.46 mg/kg dose produced a significant increase of MN-NE only at the 32nd day. The ratio PE/NE was only affected at the 32nd day with the high dose. Concerning the SCE frequency, the genotoxic effect was only observed with the highest dose. These results indicated that capsaicin is a genotoxicant, and due to the probable relation between an excessive consumption of Capsacum and an increase in gastric cancer, it is suggested that its consumption could be moderated until a definitive risk for humans is established.

1,3-Butadiene working group report

During the Workshop in North Carolina, the in vivo metabolism, adduct formation and genotoxicity data available from rodent and human exposure to 1,3-butadiente (BD) were reviewed and they are summarized in the present report. BD is metabolized by cytochrome P-450-dependent monoxygenases to the primary metabolite 1,2-epoxybutene-3 (epoxybutene, EB). EB is subjected to further metabolism: oxidation to 1,2:3,4-diepoxybutane (DEB), hydrolysis to 3-butene-1,2-diol and conjugation to glutathione. The first pathway seems to prevail in mice while the latter is characteristic for rats and possibly for humans. Species differences exist in adduct formation of the monoepoxide to hemoglobin, for which the following pattern has been found: mice > rats > humans. Genotoxity of BD was found in mice with all applied tests; however, negative results were obtained in rats. In exposed humans, the cytogenetic studies in peripheral blood lymphocytes did not show genotoxic effects, although one report described elevated hprt variant levels in peripheral blood lymphocytes of exposed workers. It was concluded that the presently available data are insufficient for the application of the parallelogram model to estimate genetic risk for humans. As an alternative approach, a tentative estimate of the doubling dose for induction of hprt mutations in somatic cells of mice and men was performed and the calculated values were surprisingly similar, i.e. 9000 ppmh. However, this estimate is burdened with a number of caveats which were discussed in detail. The working group identified a series of urgent research needs to provide the appropriate data for the application of the parallelogram model, such as identification of metabolic pathways in different rodent species and humans, metabolic studies in mice, rats and humans considering metabolic polymorphisms, studies of adducts to DNA and hemoglobin especially of DEB and other butadiene metabolites in rodents and humans, studies of mutational spectra (mutational fingerprinting) in somatic and germinal cells, confirmation of the human hprt mutation data, conformation of the rodent malformation data, dose-response studies in rodent germ cell tests and studies on repair kinetics of mono-adducts induced by EB as opposed to repair of cross-links produced by DEB. Finally, it was suggested that the original parallelogram consisting of data from somatic cell studies in rodents and humans plus studies of heritable effects in rodents to extrapolate to germ cell risk for humans should be supplemented with studies in sperm of experimental animals and exposed men.

Fate of lesions that elicit sister chromatid exchanges (FLE-SCE) produced in DNA by alkylating agents in vivo

A study was made on the effect of ethyl methanesulfonate (EMS) or dimethylnitrosamine (DMN) on the frequency of SCE occurring in the first, in the second or at the same locus in both divisions. This was done with a previously reported in vivo protocol which allowed us to determine the fate of lesions that elicit SCE (FLE-SCE) in two cell divisions after mutagen treatment. The results showed that EMS-induced DNA lesions that cause SCE are persistent, and that some of them were produced in the second-division or were generated from SCE non-inducing lesions. We inferred this by the analysis of the response in cell populations. DMN seems to induce SCE mainly during the second division, but by inhibiting DNA synthesis as was interpreted from the cell frequency distribution with respect to the number of SCE in first and in second cell division.

In vivo radioprotective effect of chlorophyllin on sister chromatid exchange induction in murine spermatogonial cells

The radioprotective capacity of chlorophyllin was determined by measuring the reduction of gamma-ray-induced sister chromatid exchange (SCE) in murine spermatogonia in vivo. The results obtained in experiments using 100 and 200 micrograms of chlorophyllin per gram of body weight (bw) and irradiated either before or after BrdU incorporation, indicate that a chlorophyllin dose of 200 micrograms/g bw protects 100% against the induction of SCE by 0.75 Gy of gamma-rays and 100 micrograms/g bw protects less than 50%. Chlorophyllin per se did not have any effect on the SCE frequency.

Replication banding and molecular studies of a mosaic, unbalanced dic(X;15)(Xpter-->Xq26.1::15p11-->15qter)

We present a patient with a chromosomal mosaicism involving the X chromosome. One cell line is 45,X and the other has a de novo paternally derived dicentric X;15 translocation. Her karyotype is therefore 45,X/45,X,dic(X;15)(Xpter-->Xq26.1::15p11-->15 qter) based on G-banding. The presence of 2 centromeres on the derivative X was confirmed by fluorescence in situ hybridization (FISH) and a deletion of Xq26.1-->qter was confirmed by polymerase chain reaction (PCR) using DXS52 and DXYS154. Replication banding studies indicate that the derivative X is late replicating. Based on these studies, it is unclear whether inactivation has spread to proximal 15q. The patient has a unique phenotype distinct from Ullrich-Turner or Prader-Willi syndromes, but includes ataxia and language delay which are commonly seen in Angelman syndrome. These findings are contrary to those anticipated since deficiency of paternal genes at 15q12 typically leads to Prader-Willi syndrome. Molecular analysis of PCR-based polymorphisms of chromosome 15 and X indicates that uniparental disomy is not present for the X chromosome or chromosome 15 in either cell line. It is hypothesized that her phenotype results from the interaction of the 2 abnormal genotypes. Each abnormality may be diluted by the mosaicism and, in the derivative X line, by the possible variation among cells of inactivation spreading to chromosome 15.

Sister chromatid exchange (SCE) studies in breast cancer patients: a follow-up study

Sister chromatid exchanges (SCEs) were studied in 20 patients with breast cancer (stage II) before surgery, one month after surgery, and after three years as a follow-up study. Data from 50 age-matched, normal healthy females, preferably from the affected families, served as controls. In each patient, 50 well-spread metaphases were scored for SCEs. The mean values of SCEs per metaphase were 5.80, 4.69, and 5.98 in breast cancer patients before surgery, one month after surgery, and after a gap of three years as a follow-up, respectively. The one-way analysis of variance was applied and it was found that there was a highly significant difference in the frequency of sister chromatid exchanges in these patients before surgery, one month after surgical removal of cancerous tissue, and after three years as a follow-up study. The elevated level of SCEs three years after surgical removal of cancerous tissue predict the chances of development of another type of cancer.

Effect of glutathione on sister-chromatid exchanges in normal and buthionine sulfoximine-treated mice

Based on their ability to induce sister-chromatid exchanges (SCEs) it is evident that thiol-containing radioprotectors can induce DNA damage. However, there were contradictory findings when reduced glutathione (GSH) was tested using two cell lines. The present study demonstrated that GSH can induce SCEs and also delay in cell proliferation in mouse bone marrow cells in vivo. The presence of catalase significantly reduced GSH-induced SCE frequency down to catalase alone levels. An attempt was made to evaluate the effect of GSH treatment in buthionine sulfoximine (BSO)-treated mice (GSH-depleted mice) and the data indicate that induction of SCEs takes place without inducing a delay in cell proliferation or the generation of hydrogen peroxide. Probably, some unknown route is involved by which GSH-degraded product(s) induce SCEs in BSO-treated mice. Therefore, the induction of SCEs by GSH in normal mice may be largely due to hydrogen peroxide generation; however, the involvement of the binding ability of GSH to chromatin and the probable (unknown) route by which GSH-degraded product(s) may cause smaller fraction of SCEs cannot be ruled out.

Persistence during G1 of gamma ray- or mitomycin C-induced lesions eliciting SCE in murine salivary gland cells in vivo

The efficiency of mitomycin C or gamma rays to induce SCE in early or late G1 was determined in synchronized murine salivary gland cells in vivo, as a measure of the capacity of this tissue to repair the lesions involved in SCE formation before S. The SCE frequencies induced by MMC in the first division (before BrdU incorporation) were significantly lower in the early G1 compared to the late G1, indicating some repair of SCE-inducing lesions. In the second division (after BrdU incorporation), there was no difference between SCE induced in early and late G1, indicating that MMC-induced lesions in such conditions are very persistent and not repairable during G1. The radio induced SCE frequency at early G1 was significantly lower than that observed in late G1, in cells irradiated after BrdU incorporation, suggesting that half of gamma ray-induced DNA lesions that elicit SCEs were repaired.

Comparison of results from mouse bone marrow chromosome aberration and micronucleus tests

Tests for the induction of chromosomal aberrations (ABS) and micronuclei (MN) in bone marrow cells of mice have been conducted on 65 chemicals. Although these tests were not conducted with the purpose of comparing the outcomes of these two in vivo genetic toxicity endpoints, the availability of these test results permits such a comparison. Based on studies to date, results from the 2 tests agree for more than 80% of the chemicals; 17 gave positive results in both tests, and 36 gave negative results in both. Seven chemicals were positive only for ABS and 5 were positive only for MN. Three chemicals that were originally concluded to be positive for ABS but not for MN were found to induce MN when the MN protocol was modified to more closely reflect the ABS protocol. Among the 12 chemicals for which there are discrepant results, there are only 2 for which the difference is convincing. One of these, selenium sulfide (MN negative, ABS positive) remains an enigma; further studies are being conducted. The second, isoprene (MN positive, ABS negative) will be difficult to pursue because the studies reported here were done by inhalation exposure. Based on the outcomes of these comparisons, protocol factors, rather than endpoint specificity, appear to be the major source of discrepant test results. Thus, these results do not support a recommendation that both tests be conducted in a primary testing scheme for genetic toxicity.