中药对再障染色体损伤的修复作用

目的　观察中药对由再生障碍性贫血 (AA)引起的染色体损伤的修复作用和对机体免疫功能的改善情况。方法　通过AA患者服用SB前后SCE率的变化和淋巴细胞转化的差别 ,观察生白片对再障患者遗传物质的保护和促进淋巴细胞转化作用。结果　AA患者在服用SB前的SCE值显著高于正常对照的P <0 .0 5 ) ,服用SB后SCE值显著降低 (P <0 .0 5 ) ;淋巴细胞转化率 (cpm)在服药前后也有显著差异(P>0 .0 5 ) 。结论　①AA患者具有染色体不稳定性 ,SB对AA的染色体不稳定性具有明显的修复作用 ;②SCE和淋巴细胞转化率可作为观察指标来研究中药的疗效机理。     

Malignant melanoma: sister chromatid exchange analysis in three families

Sister chromatid exchange (SCE) was analyzed in stimulated lymphocytes and skin fibroblasts in members of three families with cutaneous malignant melanoma (CMM). Two of these families were characterized by familial CMM; the other family had one patient affected by CMM and two others with other cutaneous melanocytic lesions. All the patients had undergone surgery but no chemotherapy. Higher and differing SCE rates were found in lymphocytes and in fibroblasts of all patients. A wide range of SCE distribution was found in patients with high SCE rate. A few healthy close relatives also showed relatively high SCE rates and wide range distributions. These subjects may be regarded as a subset of family members at high risk for developing cancer. The variability of SCE rates and distribution may reflect genetic heterogeneity of CMM.     

Beneficial effects of ascorbic acid on preimplantation mouse embryos after exposure to cyclophosphamide in vivo

To study mechanisms of embryotoxicity in early pregnancy, we have evaluated the genotoxic and embryolethal effects of ascorbic acid (AA) alone or in combination with cyclophosphamide (CPA). Female mice were exposed on day 3 of pregnancy. Embryotoxicity was investigated at term and genotoxicity shortly after treatment using the chromosomal aberration test and the sister chromatid exchange (SCE) assay as sensitive end points. Additionally, cytotoxic effects were determined by a proliferation test. AA was not found to be embryotoxic, cytotoxic, or genotoxic when given alone. In combination with 10 mg/kg CPA, however, which induced 50% aberrant metaphases, 100% increase SCE frequency, and a strong inhibition of cell proliferation, AA in a dose range of 25-1,600 mg/kg did not change SCE and proliferation, but reduced the rate of aberrant metaphases significantly. This anticlastogenic effect was clearly correlated to a beneficial effect on embryolethality at term when 200 mg/kg ascorbic acid was given in combination with 40 mg/kg CPA. The results suggest that during early pregnancy AA is not genotoxic even at so-called megadoses doses, but it seems to protect early embryos against damage induced by genotoxic agents like CPA.     

Sister chromatid exchange in malignant lymphomas

Sister chromatid exchange (SCE) was evaluated in peripheral lymphocytes from 20 untreated patients with malignant lymphomas: 6 with Hodgkin's disease (HD), 14 with non-Hodgkin lymphoma (NHL), and 5 with lymphadenitis. The mean SCE frequency (+/- SE) was: 11.2 +/- 0.6, 11.0 +/- 0.6, and 7.2 +/- 0.3 for HD, NHL, and lymphadenitis patients, respectively, and 8.7 +/- 0.2 for the control group. No differences in SCE score were observed in HD and NHL. These results allowed us to consider both groups (HD and NHL) as a single neoplastic population (mean +/- SE, 11.0 +/- 0.4). No significant differences were found between the lymphadenitis and control groups. On the other hand, significantly higher SCE scores were seen in neoplastic populations than in the control and lymphadenitis groups (p less than 0.001 and p less than 0.01, respectively). When SCE was compared by chromosome number and group between neoplastic patients and controls, a higher SCE frequency was observed in chromosomes #1, #2, #3, and B, C + X, E, F chromosome groups than in controls. SCE levels were significantly higher in lymphoma patients in all chromosome numbers and groups mentioned than in patients with lymphadenitis. It is suggested that the high SCE rate in the malignant lymphoma population is possibly related to an increased chromosomal instability.     

Growth rate and sister chromatid exchange (SCE) incidence of bone marrow cells in Acute Myeloblastic Leukemia (AML)

The sister chromatid exchange (SCE) incidence and growth kinetics have been studied by means of an in vitro bromodeoxyuridine (BrdU) chromosome labeling method in the bone marrow cells of 17 acute myeloblastic leukemia (AML) patients with only diploid cells at diagnosis, remission, and relapse of the disease. At diagnosis, the cells tended to exhibit a low SCE frequency as compared to that during remission. An increased SCE frequency was observed after chemotherapy during remission or relapse. At diagnosis and relapse, when leukemic blast cells predominated in the marrow, they were characterized by the predominance of cells that had undergone only one cell cycle after BrdU exposure. In contrast, the marrow cells during remission tended to resemble the control pattern of growth kinetics, with a predominance of cells undergoing second and third cell cycles in the presence of BrdU. These results suggest that the growth rate of leukemic and nonleukemic cells is different, and that chemotherapy can cause an increased SCE frequency in the marrow cells of AML patients irrespective of the state of the disease.     

The role of ascorbic acid on titanium dioxide-induced genetic damage assessed by the comet assay and cytogenetic tests

Titanium dioxide (TiO₂) is used in several commercial products such as cosmetics, sunscreen, toothpaste and pharmaceuticals. However, some recent investigations have revealed that titanium particles generate potential harmful effects on the environment and humans. Because of its strong antioxidant activity, ascorbic acid (AA) is admitted to act as an anti-mutagenic agent. The present study was undertaken to investigate the protective effect of AA against TiO₂-induced genotoxicity. Sister chromatid exchange (SCE), micronucleus (MN) and the comet assays were used to assess TiO₂-induced genotoxicity and to establish the protective effects of AA. There were significant increases (P<0.05) in both SCE and MN frequencies of cultures treated with TiO₂ as compared to controls. However, co-application of AA (4.87 and 9.73 μM) and TiO₂ resulted in decreases of SCE and MN rates as compared to the group treated with titanium alone. Besides, significant reductions of primary DNA damage (comet assay) were determined when the AA was added to the cell culture medium simultaneously with TiO₂. In conclusion, the preventive role of AA in alleviating TiO₂-induced DNA damage was indicated for the first time in the present study.     

Baseline and mitomycin-c-induced sister chromatid exchanges in a melanoma and a colon tumor cell line

Baseline and mitomycin C (MMC)-induced sister chromatid exchanges (SCEs) in two human tumor cell lines (a colon tumor and a melanoma) and in a normal fibroblast cell line were analyzed and compared. The tumor cells showed numerical and structural chromosomal abnormalities. Their baseline SCE rate was slightly, but not significantly, higher than that of the control. Each tumor cell line showed a dose-dependent increase in SCE frequency above the spontaneous level in its own specific manner. The response in the malanoma cell was consistantly below that of the control, but only the response to the highest dose of MMC (10^?9 M) was significantly lower than that of the control. The response of the colon tumor cells varied with respect to that of the control. Thus, it appears that karyotypic instability in tumor cells is not necessarily associated with elevated baseline or induced SCE/chromosome rates. In addition, within each cell line dose group, the SCE frequency was proportional to the number of chromosomes. Thus, the SCE/chromosome is a better expression of genetic damage than SCE/metaphase in analyses involving heteroploid cells.     

Induction and reduction of sister chromatid exchange by CCNU in human lymphocytes in vitro

Sister chromatid exchange (SCE) was studied in human lymphocytes treated with 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) in vitro. A dose-dependent increase of SCE was observed in cells exposed to 10(-5) - 10(-4) M CCNU. The maximal increase was 25-35 SCEs/cell over the control level, which is similar to the increase found in patients treated with CCNU in vivo. In the presence of rat liver microsomes (S-9 fraction) the frequency of CCNU-induced SCE was slightly higher than in parallel cultures without S-9, suggesting that microsomal metabolism may enhance the rate of decomposition of CCNU into reactive products. The CCNU-induced increase of SCE was greater in cells treated for longer time periods (up to 70 hr) than in cells subjected to a 1-hr treatment. This effect was most pronounced at higher concentrations of the drug (5 X 10(-5) M). The frequency of CCNU-induced SCE was also found to be dependent on the time of treatment in the cell cycle. A treatment for 1 hr during early G1-phase (about 20 hr before the first S-phase) gave rise to a higher increase of SCE than a 1 hr treatment immediately before or during the first or second S-phase. Thus, the CCNU-induced DNA damage leading to SCE seems to persist and may even increase during the prereplicative phase of the cell cycle. After replication in BrdUrd-free medium, the frequency of CCNU-induced SCEs decreased to the control level. The present results, taken together with other studies of strand break and cross-link formation by CCNU in mammalian cells in vitro, suggest that the major SCE-inducing damage by CCNU is DNA interstrand cross-links. These lesions then appear to be slowly removed, if at all, during the prereplicative phase of the cell cycle, and to disappear during or after replication in BrdUrd-free medium in vitro.     

Sister chromatid exchange in normal and Ph1-positive leukemic cells after mitomycin-C treatment in vitro

The sister chromatid exchange (SCE) frequency was investigated in normal bone marrow and Ph1-positive cells of chronic myelocytic leukemia (CML) patients with and without mitomycin-C (MMC) treatment in vitro. Even though the spontaneous SCE frequency was found to be significantly lower in CML cells, the absolute SCE values after MMC treatment did not differ between leukemic and normal cells, and this seems to indicate an equilization of SCE rates. However, the fact that leukemic cells with lower spontaneous SCE rates need a further increase of SCE to reach values equal to those of normal cells might indicate a somewhat higher susceptibility of leukemic cells to DNA damage by MMC. This interpretation appears to be confirmed by the fact that the inhibition of cellular proliferation at higher MMC doses considerably reduced the number of leukemic cells that was able to divide twice during a given culture time.     

Elevated sister chromatid exchange and cell cycle analysis in bone marrow in childhood ALL

Sister chromatid exchange (SCE) frequencies were analyzed in both stimulated and unstimulated bone marrow samples from eight patients recently found to have childhood acute lymphocytic leukemia (ALL). Six of the patients had elevated SCE frequencies in stimulated marrow when compared to control values. In unstimulated marrow, all four patients had elevated SCE frequencies. These data agree with peripheral leukocyte findings in ALL. Cell cycle analysis revealed no significant differences between the patient marrows and the control marrows. Since no correlation between cell cycle distribution and SCE frequency was found, it is suggested that the differences in SCE observed may be related to the type of proliferating cell.     

Sister chromatid exchanges in patients with carcinoma in situ of cervix uteri.

Sister chromatid exchange (SCE) was analyzed in lymphocytes of 21 patients with carcinoma in situ of cervix uteri and 19 control subjects. The mean SCE frequencies were 8.92 +/- 0.31 (n = 417) and 6.94 +/- 0.23, (n = 375) per metaphase in patients and controls, respectively. The increase of SCE levels in cancer patients was highly significant in respect to controls (p less than 0.001). Together with data of other authors in patients with precancerous and cancerous lesions of the cervix, our results suggest that there is no correlation between SCE rate and severity of cancerous lesions.     

Sister chromatid exchanges in leukemic patients

Sister chromatid exchange (SCE) was studied in PHA-stimulated peripheral blood lymphocytes from 36 newly diagnosed and untreated leukemic patients: 16 with acute lymphoblastic leukemia (ALL), 10 with acute nonlymphocytic leukemia (ANLL), and 10 with chronic myelocytic leukemia (CML). The metaphases analyzed show no chromosomal abnormalities. The mean SCE frequency (mean +/- SE) for each group of patients was: 6.8 +/- 0.4, 6.6 +/- 0.3, and 7.0 +/- 0.6 per mitosis, respectively, which was significantly lower than the mean SCE score for 30 controls (8.7 +/- 0.2). No differences in SCE score among ALL, ANLL, and CML and a similar SCE frequency by chromosome number and group allowed consolidation of all the cases into a single group of 36 leukemic patients (6.8 +/- 0.3). When the frequency of SCE was compared by chromosome number and group between the leukemic patients with the control group, a significant decrease in SCE frequency was observed due to a low SCE score in almost all the complements, except chromosome #1. It is suggested that the low SCE rate is related to the leukemic process itself.     

Establishment of B-lymphoid cell lines retaining cytogenetic characteristics of Bloom syndrome

The present study describes the establishment of and chromosomal changes in B-lymphoid cell lines from cells of Bloom syndrome (BS) patients using Epstein-Barr virus (EBV). Even though PHA-stimulated BS lymphocytes from all five patients studied showed high levels of sister chromatid exchange (SCE), three EBV-transformed BS-B-lymphoid cell lines had normal levels of SCE and two yielded two types of cell populations, i.e., one with increased SCE and chromosome instability (including breaks and quadriradials) and another with normal levels of SCE and without structural aberrations. The karyotypic abnormalities, as observed in the BS lines have not been seen in the cells of any established normal B-lymphoid lines transformed by EBV and strongly suggest that the chromosome abnormalities in the BS--B-cell lines with abnormal karyotypes originated in vivo and not through an in vitro effect of EBV. Furthermore, in the EBV-transformed B-cell lines, we found quadriradial formation between sister chromosomes during endomitoses instead of between homologous chromosomes, strongly suggesting that quadriradial formation may be closely related to SCE. The coexistence in BS subjects of abnormal and normal populations of cells with respect to the number of SCE awaits explanation.     

Some comments on sister chromatid exchange (SCE) in human neoplasia

The incidence of sister chromatid exchange (SCE) in bone marrow cells and/or lymphocytes of patients with various leukemias and the effects of drugs on the SCE incidence in the cells of patients with leukemia or cancer are presented and discussed. The possible use of SCE for screening antileukemic drugs, mutagenic and/or carcinogenic agents and susceptible human populations is presented.     

Sister chromatid exchanges in lymphocytes of patients with oral carcinoma

Sister chromatid exchanges (SCEs) were studied in cultured peripheral lymphocytes of 22 untreated patients with squamous cell carcinoma of the oral cavity and 29 age- and sex-matched controls. The SCE rate in cancer patients was not significantly higher compared with that found in controls, but there was a significant correlation between the SCE rate in lymphocytes of the cancer patients and the size of the primary tumor.     

Sister chromatid exchange in dyskeratosis congenita lymphocytes.

Sister chromatid exchange (SCE) frequency in chromosomes from lymphocytes of a patient with dyskeratosis congenita was 12-2 per mitosis. Our 33 normal controls had a mean of 5-4 SCE per mitosis and 5 patients with Fanconi's anaemia averaged 7-6 SCE per mitosis. The rate of chromosome breakage was only 0-5% in the dyskeratosis congenita patient and 0 to 2-5% in controls, while the Fanconi's anaemia patients showed higher values.     

Inhibition of bromodeoxyuridine-associated sister chromatid exchanges in Bloom's syndrome cells with cycloheximide

Effects of cycloheximide (CH) and deoxycytidine (dC) on the frequency of sister chromatid exchanges (SCEs) in normal and Bloom's syndrome (BS) cells labeled with bromodeoxyuridine (BrdU) during first, second, and third cell cycles were evaluated using endomitotic and three-way differentiation analyses. When CH at 0.2 and 2.0 ng/ml was added to normal and BS cultures of BrdU-labeled endomitoses, the rate of single SCEs was significantly decreased in BS cells, though the rate of reduction in single SCEs was slight in normal cells. No significant change was detected in the twin SCE rate. In BS cells, treatment with CH at 0.2 and 2.0 ng/ml produced significant reductions in SCEs in both the second (SCE2) and third (SCE3) cell cycles, sometimes reaching the normal level. Treatment with dC at 13 and 26 micrograms/ml resulted in almost no significant changes in rates of SCE during first, second, and third cell cycles. When CH was added to BrdU-labeled normal and BS cell cultures, the cell growth rates improved from 35% to 70% over the control level in the BS cells, though in normal cells, the addition of CH resulted in a close-dependent lower cell growth rate. Deoxycytidine did not noticeably affect the cell growth rates in BrdU-labeled normal and BS cultures. The finding that the reduction of BrdU-induced SCEs in BS is paralleled by cell growth improvement is of special interest.     

Evidence that the replication point is the site of sister chromatid exchange

DNA synthesis in Chinese hamster cells was blocked partially by treating the cells with either fluorodeoxyuridine (FUdR) or cycloheximide (CHM) for various lengths of time. Analyses of the population kinetics and measurement of incorporation of labeled nucleosides during the FUdR block strongly suggested that the number of growing points was accumulated by the treatment while the rate of chain growth was greatly reduced. No evidence for such an accumulation was obtained in the CHM-treated cells. To study the relation between DNA replication and sister chromatid exchange (SCE), bromodeoxyuridine-labeled cells were exposed to blue fluorescent light while DNA synthesis was blocked. The frequency of SCE induced by the light treatment appeared to increase as the number of growing points increased, implying that the site of exchange is confined to the replication forks. The induction of SCE by fluorescent light was inhibited completely by CHM-treatment. The reason for this finding remains to be elucidated.     

Sister chromatid exchange and chromosome abnormalities in uremic patients

Chronic renal failure heightens the risk of malignancy. We therefore examined lymphocytes from 44 uremic patients and 24 normal controls for chromosome abnormalities and sister chromatid exchange (SCE) rate. This is the first report of SCE in uremia. Uremia was found to increase structurally abnormal chromosomes and elevate the rate of SCE. These cytogenetic changes in uremia may play a role in the heightened risk of cancer.     

Sister chromatid exchanges induced by nitrogen mustard in Fanconi's anemia. Application to the detection of heterozygotes and interpretation of the results

Nitrogen mustard-induced SCE were studied on Fanconi's anemia (FA) patients, FA parents, and control lymphocyte cultures. When low doses of nitrogen mustard were added at the time cultures were initiated, a distinction could be made between FA heterozygotes and controls. In FA heterozygotes increase of SCE levels higher than that observed in controls was found, thus allowing the recognition of heterozygotes. FA cells appeared to be more sensitive to nitrogen mustard than FA heterozygous and control cells. The data argues in favor of an excision-repair defect, and is discussed in the light of possible repair and SCE production mechanisms.