Implications of an elevated sister-chromatid exchange frequency in rat lymphocytes cultured in the absence of erythrocytes

Flow cytometric lymphocyte subset analysis using material from frozen whole blood

Multicenter immune monitoring programs commonly rely on storing and shipping cryopreserved peripheral blood mononuclear cells (PBMC), isolated from whole blood before freezing. However, under many conditions in the field, facilities to separate PBMC are absent. Here, we investigate the feasibility of using whole blood (WB) frozen at -80°C as a source of viable lymphocytes for use in immunological studies. We compare the percentage of CD4 and CD8 T lymphocytes and their subsets from frozen WB with results from cryopreserved PBMC in five random healthy blood donors (three female, two male). We report that CD4 and CD8 values in lymphocytes from WB frozen up to 120 days were very similar to those of PBMC frozen up to 10 days. These data suggest that within the limits of parameters investigated in this study, contrary to our original assumptions, whole blood frozen at -80°C may in fact be an appropriate source of viable lymphocytes for T cell enumeration assays in immunological and epidemiological studies.

Chromosome aberrations in Chinese hamster and human cells: a comparison using compounds with various genotoxicity profiles

Chromosome aberrations (Cabs) can be induced in vitro by non-DNA damaging compounds, often associated with cytotoxicity and DNA synthesis inhibition, and under conditions that would not be relevant in vivo. Such misleading positive results are reported both in Chinese hamster cell lines and in human peripheral blood lymphocytes (HL). We assessed the response of HL to compounds with varied genetic toxicity profiles, all of which induced Cabs in CHO cells Seven of 10 compounds were negative or equivocal in HL. Results in purified lymphocytes for four verified that the difference was not due to the presence of blood in cultures. Two compounds that were weakly positive in the Ames test and one that induced DNA adducts were negative or equivocal in the HL assay; their overall mutagenic potential in vivo is not clear. Of four Ames-negative compounds, three of which inhibited DNA synthesis in CHO cells, three were negative and one was equivocal in the HL assay. A potent Cab inducer, which also induced micronuclei in vivo (but was negative in the Ames test) was clearly positive in the HL assay. Two compounds were clearly positive in HL only when the mitotic indices (MI) were below 50% of control. These are genotoxic in other assays but our evidence suggests that Cab induction is related more to toxicity than to primary DNA damage. For this limited set of 10 compounds, HL were more likely than CHO cells to give negative or equivocal results. It is likely that more stringent checkpoint controls in human cells prevent damaged cells reaching mitosis, and may also influence the reported greater sensitivity to induction of aneuploidy and polyploidy of normal rodent compared with human cells. In the studies reported here, two strong inducers of polyploidy in CHO cells gave weaker increases in HL. Human lymphocytes have disadvantages as a routine screening assay (finding donors, known individual variability, increased time required and the inadequacy of the MI as a toxicity measure), but may be useful in follow-up testing to assess weight of evidence about genotoxic risk to humans, for compounds that are positive in the Chinese hamster cell Cabs assays.

Cryopreserving whole blood for functional assays using viable lymphocytes in molecular epidemiology studies

There is an increasing need for viable lymphocytes in performing phenotypic assays for biomarker studies. Both fresh and cryopreserved lymphocytes have been used for cell culture-based functional assays. However, fresh lymphocytes do not allow assays to be done in batches and cryopreservation of isolated lymphocytes results in a considerable loss of viable cells. To investigate the feasibility of using cryopreserved whole blood as a source of viable lymphocytes in molecular epidemiology studies, two well-established biomarkers, the host-cell reactivation (HCR) and mutagen sensitivity assays, were used to compare the method of cryopreserving whole blood with the traditional methods. In 25 paired blood samples assayed for DNA repair capacity (DRC) by the HCR assay, the DRC values of frozen whole blood (mean +/- SD, 11.59 +/- 3.07) were similar to those of frozen isolated lymphocytes (11.08 +/- 3.50). The correlation between the paired DRC values was 0.77 (P < 0.001). In 31 paired blood samples assayed for the gamma-radiation-induced chromatid breaks by the mutagen sensitivity assay, there was no significant difference between the baseline level of chromatid breaks in lymphocytes from frozen blood (0.05 +/- 0.03) and fresh blood (0.06 +/- 0.03). The blastogenic rate and mitotic index of the cells used for the two assays were compared between the different processing methods. The lymphocytes from frozen whole blood were more sensitive to gamma-radiation, with a higher mean level of chromatid breaks (0.68 +/- 0.21) than that in fresh blood (0.42 +/- 0.12, P < 0.01), and the correlation between the numbers of chromatid breaks in the paired samples was statistically significant (r = 0.61, P < 0.001). These data suggest that within the limits of the parameters investigated here, cryopreserved whole blood is a good source of viable lymphocytes for biomarker assays in molecular epidemiological studies.

Reduction of diepoxybutane-induced sister chromatid exchanges by glutathione peroxidase and erythrocytes in transgenic Big Blue mouse and rat fibroblasts

We have investigated the effect of glutathione peroxidase (GSH-Px) and mammalian erythrocytes (RBCs) on spontaneous and diepoxybutane (DEB)-induced sister chromatid exchange (SCE) in primary Big Blue(R) mouse (BBM1) and Big Blue(R) rat (BBR1) fibroblasts. DEB is the putative carcinogenic metabolite of 1,3-butadiene (BD) for which inhalation exposure yields a high rate of malignancies in mice but not in rats. BD is metabolized differently in mice and rats, producing much higher levels of DEB in mice than in rats, which may partly explain the different carcinogenic responses. However, other factors may contribute to the observed differences in the rodent carcinogenic response to BD. DEB is a highly reactive compound. Upon epoxide hydrolysis, DEB can covalently bind to DNA bases. Likewise, DEB generates reactive oxygen species that, in turn, can either damage DNA or produce H(2)O(2). Reduced glutathione (GSH) is known to play a role in the metabolism and detoxification of DEB; and GSH is reduced by GSH-Px in the presence of H(2)O(2). GSH-Px is a constitutive enzyme that is found at high concentrations in mammalian RBCs. Therefore, we were interested in examining the role of RBCs and GSH-Px on DEB-induced SCE in rat and mouse cells for detection of possible differences in the species response. Transgenic BBM1 and BBR1 fibroblasts were treated with either 0, 2 or 4 microM DEB plus 0, 2 or 20 units of GSH-Px with and without 2x10(8) species-specific RBCs. DEB effectively induced SCEs in both rat and mouse cells. The relative induction of SCEs in both cell types was comparable. Both GSH-Px and RBCs alone and in combination were effective in significantly reducing DEB-induced SCEs in both mouse and rat fibroblasts, although there was more variability in the SCE response in rat cells. The present study suggests that GSH-Px may be important in the detoxification of DEB-induced DNA damage that results in the formation of SCEs.

Effects of prenatal exposure to 5-bromo-2'-deoxyuridine on reproductive function in male mouse offspring

The effect of the halogenated pyrimidine analog 5-bromo-2'-deoxyuridine (BrdU), on reproductive functions of male mouse offspring treated prenatally was studied. BrdU was administered intraperitoneally to pregnant ICR mice at 100 mg/kg/d on days 8 through 13 of gestation, and at 100 or 200 mg/kg/d on days 14 through 18 of gestation. Dams were allowed to deliver naturally. Male offspring were aged for 10 weeks and then cohabited with untreated female mice for assessment of reproductive performance. Histopathologic examination of the testes and pituitary, sperm analysis, and determination of plasma testosterone concentrations of offspring at 12 weeks of age were performed. In the subsequent study, pregnant ICR mice were treated with 200 mg BrdU/kg on day 10, 13, or 15 of gestation. The embryos or fetuses were obtained from mothers from 6 to 48 h after treatment, and pyknotic cells in the ventricular zone of the telencephalon were counted. There was a significant decrease in body weight gain of offspring in all of the BrdU-treated groups. A marked decrease in copulation rate was noted in the male offspring of dams treated on days 8 through 13 of gestation, whereas no significant decreases in copulation and fertility rates were found in the male offspring of dams treated on days 14 through 18 of gestation. Neither histopathologic examination of testes nor sperm analyses revealed adverse effects of this compound, whereas cysts in the pars distalis of the pituitary were observed in the male offspring treated on days 8 through 13 of gestation. Dilatation of the lateral ventricles was also observed in male offspring at 12 weeks of age in the group treated on days 8 through 13 of gestation. The incidence of pyknotic cells in the ventricular zone of embryos was markedly increased 24 h after treatment on day 10 of gestation. These results indicate that the impaired fertility of the male offspring of dams treated with BrdU on days 8 through 13 of gestation may be due to the effects of BrdU exposure on central nervous system function that result in loss of libido rather than to the direct effects of this compound on the male reproductive organs.

Pig plasma modulates cell cycle kinetics but not the baseline frequency of sister-chromatid exchanges in human lymphocytes

The effect of human and pig plasma on the baseline frequency of sister-chromatid exchanges (SCEs) in human and porcine plasma leukocyte cultures was studied. Human plasma leukocyte cultures, but not porcine plasma leukocyte cultures, showed at least a twofold increase in SCE frequency over whole blood culture values. Addition of pig plasma to human plasma leukocyte cultures and human plasma to pig plasma leukocyte cultures did not modify the baseline SCE frequencies. In both human and porcine cultures, cell proliferation was slower in plasma leukocyte cultures than in whole blood cultures. The addition of pig plasma to human plasma leukocyte cultures, but not the incorporation of human plasma in pig plasma leukocyte cultures, accelerated the cell cycle progression of lymphocytes. With 10% pig plasma in the plasma leukocyte culture medium, lymphocyte proliferation was similar to that in whole blood cultures. Smaller concentrations of pig plasma rendered cell cycle progression intermediate between the basal plasma leukocyte culture and whole blood culture values. Exchanging fetal calf serum for human AB serum in human plasma leukocyte cultures did not affect the cell cycle kinetics of lymphocytes but it did decrease their baseline SCE frequency.

Induction of micronuclei by X-radiation in human, mouse and rat peripheral blood lymphocytes

We compared the radiosensitivity of human, rat and mouse peripheral blood lymphocytes (PBLs) by analyzing micronuclei (MN) in cytochalasin B-induced binucleated (BN) cells. For each species and dose 4-ml aliquots of whole blood were X-irradiated to obtain doses of 38, 75, 150 or 300 cGy. Controls were sham-irradiated. After exposure to X-rays, mononuclear leukocytes were isolated using density gradients and cultured in RPMI 1640 medium containing phytohemagglutinin to stimulate mitogenesis. At 21 h cytochalasin B was added to produce BN PBLs, and all cultures were harvested at 52 h post-initiation using a cytocentrifuge. Significant dose-dependent increases in the percentage of micronucleated cells and the number of MN per BN cell were observed in all three species. The linear-quadratic regression curves for the total percentage of micronucleated cells for the three species were similar; however, the curve for the mouse PBLs had a larger quadratic component than either of the curves for the rat or human PBLs. Although the correlation between the percentage of cells with MN and those with chromosome aberrations was high (r2 greater than 0.95), the mouse and rat PBLs were over twice as efficient as human PBLs in forming MN from presumed acentric fragments. These data indicate that the induction of MN in BN cells following ionizing radiation is similar in human, rat and mouse PBLs, but care must be taken in using the MN results to predict frequencies of cells with chromosomal aberrations.

The genetic toxicology of 5-bromodeoxyuridine in mammalian cells

The thymidine analog, BrdUrd, induces many biological responses which are of importance to the field of genetic toxicology and related disciplines. These include the induction of SCE, specific-locus mutations, and toxicity, inhibition of cell proliferation, and the expression of fragile sites in the human genome. In early models which addressed the mechanisms of the biological effects of BrdUrd exposure, two pathways were proposed to account for the induction of the biological responses. Incorporation of the enol form of BrdUrd into the nascent DNA strand after pairing with deoxyguanosine was proposed as one pathway, whereas the incorporation of BrdUrd opposite adenosine in place of thymidine was proposed as the second pathway. Many novel and sophisticated techniques have been applied to the study of the mechanism of the induction of biological effects by BrdUrd leading to a substantial increase in our understanding of these mechanisms. However, the experimental evidence clearly supports the contention that BrdUrd exerts its effects on eukaryotic cells through mechanisms similar to those originally proposed to explain the genotoxicity of BrdUrd.

Erythrocytes modulate the baseline frequency of sister-chromatid exchanges and the kinetics of lymphocyte division in culture

The baseline sister-chromatid exchange (SCE) frequencies of human plasma lymphocyte cultures (PLC), but not pig PLC, were nearly twice as high as those of whole-blood cultures (WBC). Addition of human red blood cells (RBCs) to human PLC decreased the SCE frequency in proportion to the RBC-leukocyte co-incubation interval. When the period of RBC-leukocyte co-incubation was equivalent to the total length of the culture period (72 h), the SCE frequency was similar to that observed in WBC. Shorter co-incubation periods yielded SCE frequencies intermediate between those of PLC and WBC. Regardless of the species, cell proliferation was slower in PLC than in WBC. Experiments where RBCs were added to PLC showed that the time sequence of RBC incorporation also affects the cell-cycle progression of human and pig lymphocytes. When either human or pig RBCs were added immediately after PLC stimulation, the cell-cycle kinetics was similar to that of WBC. Shorter co-incubation periods made cell-cycle progression intermediate between PLC and WBC values. Thus, PBCs modulate the baseline frequency of SCEs in human PLC and the cell-cycle progression of both human and pig lymphocytes in a time-dependent manner. Two possible hypotheses for the heightened frequency of SCEs of human lymphocytes in RBC-free cultures were assessed. The loss of RBC-to-lymphocyte cellular contact in PLC did not influence the SCE frequencies of lymphocytes. Finally, the increase of SCEs in human PLC could not be related to differences in the generation time of lymphocytes in culture.

Genotoxic effects of a sub-acute low-level inhalation exposure to a mixture of carcinogenic chemicals

A study was conducted using a combined testing protocol (CTP), to determine whether short-term biological end-points, singly or in combination, are sufficiently sensitive to identify damage induced by exposure to ambient levels of industrial chemicals. A small-scale inhalation set-up which is both economical and easy to assemble was designed. Mice were exposed to 4 concentrations of a custom-blend mixture of benzene, chloroprene, epichlorohydrin and xylene in a ratio of 2:2:1:2, respectively. The concentrations for benzene, chloroprene and xylene were 0, 0.1, 1.0 and 10 ppm each. Concentrations for epichlorohydrin were half those for the other components. Groups of 22 males and 22 female mice were exposed to each concentration of the mixture for 3 and 6 weeks. Selected biological end-points including urine mutagenesis, bone marrow cell aberrations and micronuclei, spleen lymphocyte aberrations and liver enzyme induction were monitored. The spleen lymphocyte aberrations and liver enzyme induction were the most sensitive end-points. The lymphocytes showed a significant induction of chromosome aberrations from exposure for 3 weeks to all 3 concentrations of the mixtures. After 6 weeks of exposure, significant induction of aberrations was observed after exposure to low and medium concentrations but not to the high concentration. This lack of response at the high concentration after 6 weeks exposure, appeared to correlate with a significant induction of glutathione S-transferase in the liver. Since this enzyme is known to detoxify 3 of the 4 chemicals in our mixture, it may indicate a detoxification mechanism after enzyme induction. The present study indicates that the CTP is sufficiently sensitive to identify toxicological effects after exposure to ambient levels of a gas mixture.

Baseline and mutagen-induced sister-chromatid exchanges in cultures of human whole blood and purified fresh or frozen lymphocytes

Baseline and mutagen-induced levels of sister-chromatid exchanges were evaluated in 10 normal individuals. Cultures with whole blood or purified lymphocytes, either freshly isolated or after 1 or 6 months of cryopreservation, were analyzed to determine whether frozen lymphocytes are suitable for SCE studies. Whole blood and freshly isolated lymphocytes were cultured from samples taken at the beginning of the study (Time 0) and 6 months later (Time 6). Cryopreserved lymphocytes were recovered after 1 month (Time 1) and 6 months (Time 6) of cryopreservation and then challenged with mutagens in culture. The mutagens used were mitomycin C, 4-nitroquinoline-1-oxide, and N-methyl-N'-nitro-N-nitrosoguanidine. Purified lymphocytes had consistently and significantly higher baseline SCE frequencies than cells from whole blood cultures and were more sensitive to N-methyl-N'-nitro-N-nitrosoguanidine and 4-nitroquinoline-1-oxide. The response to mitomycin C was similar in all culture types. There was, overall, no consistent effect of freezing on baseline or induced sister-chromatid exchange frequencies in the purified lymphocytes. This suggests that purification and cryopreservation of human lymphocytes does not alter the baseline or mutagen-induced sister-chromatid exchange response and in certain epidemiological, occupational and monitoring situations may have logistical and technical advantages over the use of fresh whole blood.

Induction of chromosome aberrations in lymphocytes of mice after subchronic exposure to benzene

The induction of chromosome aberrations in lymphocytes of mice after subchronic exposure to benzene was investigated. 4 groups of 5 Swiss (ICR) male mice were given orally a solution of benzene every day for 14 days except days 5 and 10. The daily doses were 0, 36.6, 73.2 and 146.4 mg/kg. Mice were sacrificed on day 15, lymphocytes were obtained by perfusion of the spleen and the cells were cultured in RPMI 1640 medium. After 48 h of culture, cells were harvested for cytogenetic analysis. A significant dose-dependent increase in the frequency of cells with chromatid aberrations were found (p less than 0.001). A significant increase in polyploid cells were also observed (p less than or equal to 0.05). This study represents the first report on the induction of chromosome aberrations and polyploid cells in lymphocytes of mice after subchronic exposure to benzene. Such dual activity of benzene suggests that benzene may be responsible for more human health problems than currently estimated.

Variation in sister chromatid exchange frequencies between human and pig whole blood, plasma leukocyte, and mononuclear leukocyte cultures

Sister chromatid exchange (SCE) induction by ultraviolet (UV) light was studied in both human and pig whole blood cultures (WBC) and plasma leukocyte cultures (PLC). No variation in SCE frequency was observed between pig WBC and PLC in control as well as in treated cells. Conversely, SCE frequencies of human PLC were consistently higher than those of WBC in control and UV-exposed cells. Thus, red blood cells (RBCs) do not influence the sensitivity of lymphocytes to UV light exposure, and there must be some different culture condition(s) in the induction of SCEs between human WBC and PLC but not in swine lymphocyte cultures. Since the BrdUrd/lymphocyte ratio of WBC was halved in PLC, the effect of BrdUrd concentration in inducing the SCE baseline frequency of PLC may be ruled out. Also, Ficoll-Hypaque-separated human mononuclear leukocytes in culture (MLC), but not pig MLC, showed a two-fold increase in SCE frequency over WBC values. Thus, neither the cell separation technique nor polymorphonuclear leukocytes had a significant role in the elevated SCE frequency of human PLC or MLC. Experiments where human RBCs were titrated into human PLC showed that the induction of an elevated SCE frequency of PLC was suppressed in a dose-dependent manner by the presence of RBCs in the culture medium. Since the incorporation of pig or human RBCs into human PLC as well as into MLC reduced the SCE frequency to that of WBC, a common component and/or function existing in these cells is suggested. Analysis of different RBC components showed that RBCs, specifically RBC ghosts, release a diffusible but not dialyzable "corrective" factor into culture medium that is able to reduce the SCE frequencies of PLC. Antioxidant enzymes such as catalase and horseradish peroxidase were unable to reduce the SCE frequency of human PLC to WBC values.

Induction of cytogenetic damage in rodents after short-term inhalation of benzene

Experiments were designed to investigate both the induction of sister chromatid exchanges (SCEs) in peripheral blood lymphocytes (PBLs) and micronuclei (MN) in bone marrow polychromatic erythrocytes (PCEs) of mice and rats after inhalation of benzene (BZ). Male DBA/2 mice (17-19 weeks old) were exposed to target concentrations of either 0, 10, 100, or 1,000 ppm BZ for 6 hr. Male Sprague-Dawley rats (11-14 weeks old) were exposed to target concentrations of either 0, 0.1, 0.3, 1, 3, 10, or 30 ppm BZ for 6 hr. Blood was obtained by cardiac puncture 18 hr after exposure, and PBLs were cultured in the presence of lipopolysaccharide (mouse B cells, 60 micrograms/ml) or concanavalin A (rat T cells, 30 micrograms/ml) to stimulate blastogenesis for SCE analysis. Femoral bone marrow smears from both species were analyzed for MN in PCEs 18 hr after BZ exposure. Mouse PBLs revealed a significant concentration-related increase in the SCE frequency over controls at 10, 100, or 1,000 ppm BZ. Mouse bone marrow showed a significant concentration-dependent increase in MN over controls after exposure to 10, 100, or 1,000 ppm BZ. Rat PBLs showed a significant increase in the SCE frequency after exposure to 3, 10, or 30 ppm BZ. The statistical significance of the 1 ppm BZ result was borderline and dependent on the statistical test chosen. Rat cells revealed a significant concentration-related increase in MN after inhalation of either 1, 3, 10, or 30 ppm BZ. PBLs from treated mice showed significant concentration-dependent decreases in mitotic indices; however, cell cycle kinetics and leucocyte counts remained unaffected. Rat PBLs showed significant decreases in mitotic activity only after exposure to 3 and 30 ppm BZ, whereas cell cycle kinetics and leucocyte counts were unaffected. These results show that BZ can induce statistically significant cytogenetic effects in PBLs and PCEs of both mice and rats after a 6-hr inhalation of BZ at low concentrations.

Induction of sister-chromatid exchange (SCE) and cell-cycle inhibition in mouse peripheral blood B lymphocytes exposed to mutagenic carcinogens in vivo

To determine the sensitivity of the mouse peripheral blood lymphocyte (PBL) culture system, male B6C3f1 mice were injected i.p. with either 2-acetylaminofluorene (AAF) (20, 40, 80, 160 mg/kg), benzo[a]pyrene (BP) 25, 75, 150, 300 mg/kg), dichlorvos (DCV) (5, 15, 25, 35 mg/kg), ethyl methanesulfonate (EMS) (10, 30, 90, 180, 270 mg/kg), or N-nitrosomorpholine (NM) (37.5, 75, 150, 300 mg/kg) dissolved in either RPMI 1640 (DCV, EMS, NM) or sunflower oil (AAF, BP). 24 h later blood was removed by cardiac puncture, and the lymphocytes were cultured in the presence of lipopolysaccharide for analysis of SCE in B lymphocytes. All 4 mutagenic carcinogens (AAF, BP, EMS, NM) induced significant dose-related increases in SCE frequency. DCV, a potent neurotoxicant, caused no change in the baseline SCE frequency. At the highest concentration of each chemical examined, AAF caused a 1.6-fold increase, EMS a 1.8-fold increase, NM a 3.0-fold increase, and BP a 3.1-fold increase in SCE frequency compared to concurrent controls. A comparison of these results for PBLs with those reported in the literature for bone marrow cells indicates that PBLs offer a good quantitative and qualitative estimate of the SCE-inducing potential for these 5 compounds in bone marrow cells.

Differences in the induction of SCEs between human whole blood cultures and purified lymphocyte cultures and the effect of an S9 mix

Studies for SCE induction are frequently performed on human blood cultures. Either whole blood cultures (WBC) or purified lymphocyte cultures (PLC) are employed. However, it has been shown that fundamental differences with respect to metabolic activity exist between these two systems. In order to further characterize the whole blood culture and the purified lymphocyte culture, differently acting substances were studied comparatively with and without an Aroclor-1254-induced S9 mix. Treatment with ethyl methanesulfonate (EMS), a direct mutagen, produced distinct SCE induction in both systems. Cyclophosphamide (CP) and benzo[a]pyrene (BP), two indirect mutagens, also led to a significant increase of SCEs both in WBC and PLC without S9 mix. Only with CP was this effect more pronounced after addition of S9 mix. Sodium selenite (Na2SeO3), which induced SCEs in WBC, did not show this effect in the PLC. After S9 mix was added to purified lymphocytes, an increase of SCEs by sodium selenite was observed as in WBC. H2O2, a radical former, led to SCE induction in purified lymphocytes but not in the whole blood culture. By adding S9 mix, a distinct reduction of the SCEs induced by H2O2 was established. These results show that human lymphocytes can metabolize indirect mutagens and that it should be kept in mind when using S9 mix that, besides mixed-function oxygenases, it also contains enzymes which influence the SCE-inducing effects of substances.

Development of rodent peripheral blood lymphocyte culture systems to detect cytogenetic damage in vivo

Peripheral blood lymphocytes (PBLs) offer many advantages for in vivo cytogenetic studies. They can be removed nonlethally from the animal allowing a subject to serve as its own control, permitting the analysis of cytogenetic damage over time. Furthermore, mature PBLs normally do not divide, and some populations are long-lived. Thus, they have the potential to accumulate DNA lesions during chronic exposures to genotoxicants. We have developed standard methodologies for the whole blood culture of rat and mouse PBLs to serve as models for determining the sensitivity of PBLs to cytogenetic damage. The cultures obtained with these protocols give reproducible results with high mitotic indices, stable baseline sister chromatid exchange (SCE) frequencies, and ample numbers of first-and second-division methaphases for scoring both chromosomal aberrations and SCEs. The methodologies have been especially useful for examining cytogenetic damage after inhalation exposures to toxicants such as ethylene oxide, formaldehyde, benzene, and nitrobenzene. Of these compounds, only benzene and ethylene oxide were found to induce significant dose-dependent increases in SCEs in PBLs. Also, dose-response curves have been obtained for several carcinogens administered by ip injection. These studies show that PBLs are sensitive indicators of the genotoxic effects of the carcinogens benzo (a)pyrene, 2-acetylaminofluorene, cyclophosphamide (CP), N-nitrosomorpholine, and ethylmethanesulfonate (EMS). In addition, because subpopulations of lymphocytes can be stimulated to divide using different mitogens, it has been possible to compare the sensitivity of murine B and T lymphocytes following in vitro and in vivo cyclophosphamide exposure. Once the sensitivity and selectivity of rodent lymphocyte cultures are determined, these assays should be valuable not only as a means for predicting which environmental agents could lead to increases in human cytogenetic damage, but also as a way to corroborate human cytogenetic studies.

The effect of erythrocytes and hemoglobin on sister chromatid exchange induction in cultured human lymphocytes exposed to aniline HCI

Erythrocytes [red blood cells (RBCs)] possess aniline hydroxylase activity. When aniline interacts with ferrohemoglobin in the presence of molecular oxygen, oxidation of nitrogen and ring carbons occurs. Thus, apart from the liver, RBCs may represent an important site of aniline metabolism. Because 2 metabolites of aniline, o-aminophenol and phenylhydroxylamine, can induce sister chromatid exchanges (SCEs), we examined the ability of RBCs and hemoglobin to activate aniline to genotoxic intermediates as evidenced by SCE induction in human lymphocytes. Aniline HCI (0.05-1.0 mM) induced significant concentration-related increases in the SCE frequency only in the whole blood cultures. Similarly, inhibition of cell cycle kinetics by aniline was observed only in the whole blood cultures, as shown by a concentration-dependent decrease in the percentage of third- (and later) division metaphases. Mitotic indices were not affected significantly at any concentration of aniline or hemoglobin. Hemoglobin (500 or 1,000 micrograms/ml) alone induced significant concentration-related increases in SCEs in the mononuclear leukocyte cultures. Therefore, human mononuclear leukocytes do not activate aniline to genotoxic intermediates capable of inducing SCEs during a 48-hr exposure. However, the inclusion of RBCs and granulocytes provides an activation system as demonstrated by a small, but statistically significant increase in the SCE frequency in the whole blood cultures. The weak genotoxicity of hemoglobin may be related to production of oxygen radicals during autoxidation to methemoglobin.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of cytogenetic damage in rat lymphocytes following in vivo exposure to nitrobenzene

Male F-344 rats were exposed to target concentrations of 0, 5, 16, or 50 ppm nitrobenzene for 6 h/day, 5 days a week, for 21 days during a 29-day period. Isolated spleen (ISLs) and peripheral blood lymphocytes (PBLs) were cultured in the presence of 2 microM 5-bromodeoxyuridine and scored for sister-chromatid exchange (SCE) and PBLs were also scored for chromosome aberrations. No significant increase in SCE frequency or chromosome aberrations was found in the PBLs, and no significant increase in SCEs was observed in the ISLs at any of the concentrations. Thus, cytogenetic analysis of ISLs and PBLs provide no evidence of a genotoxic potential for nitrobenzene.