Single-walled carbon nanotube-induced mitotic disruption.

Carbon nanotubes were among the earliest products of nanotechnology and have many potential applications in medicine, electronics, and manufacturing. The low density, small size, and biological persistence of carbon nanotubes create challenges for exposure control and monitoring and make respiratory exposures to workers likely. We have previously shown mitotic spindle aberrations in cultured primary and immortalized human airway epithelial cells exposed to 24, 48 and 96 µg/cm(2) single-walled carbon nanotubes (SWCNT). To investigate mitotic spindle aberrations at concentrations anticipated in exposed workers, primary and immortalized human airway epithelial cells were exposed to SWCNT for 24-72 h at doses equivalent to 20 weeks of exposure at the Permissible Exposure Limit for particulates not otherwise regulated. We have now demonstrated fragmented centrosomes, disrupted mitotic spindles and aneuploid chromosome number at those doses. The data further demonstrated multipolar mitotic spindles comprised 95% of the disrupted mitoses. The increased multipolar mitotic spindles were associated with an increased number of cells in the G2 phase of mitosis, indicating a mitotic checkpoint response. Nanotubes were observed in association with mitotic spindle microtubules, the centrosomes and condensed chromatin in cells exposed to 0.024, 0.24, 2.4 and 24 µg/cm(2) SWCNT. Three-dimensional reconstructions showed carbon nanotubes within the centrosome structure. The lower doses did not cause cytotoxicity or reduction in colony formation after 24h; however, after three days, significant cytotoxicity was observed in the SWCNT-exposed cells. Colony formation assays showed an increased proliferation seven days after exposure. Our results show significant disruption of the mitotic spindle by SWCNT at occupationally relevant doses. The increased proliferation that was observed in carbon nanotube-exposed cells indicates a greater potential to pass the genetic damage to daughter cells. Disruption of the centrosome is common in many solid tumors including lung cancer. The resulting aneuploidy is an early event in the progression of many cancers, suggesting that it may play a role in both tumorigenesis and tumor progression. These results suggest caution should be used in the handling and processing of carbon nanotubes.

Microscale exoglycosidase processing and lectin capture of glycans with phospholipid assisted capillary electrophoresis separations.

Capillary electrophoresis separations of glycans labeled with 1-aminopyrene-3,6,8-trisulfonic acid were achieved with separation efficiencies ranging from 480,000 to 640,000 theoretical plates in a 60.2 cm, 25 µm inner diameter fused silica capillary. Under these separation conditions, the coefficient of variation in peak area is 10%, and if labeling efficiency is estimated at 100%, the limit of detection is 15 fM. The capillary electrophoresis method incorporated phospholipid additives to enhance the separation of glycans with slight differences in hydrodynamic volume. In addition, the phospholipid additives supported the integration of the lectin concanavalin A as well as the enzymes α1-2,3 mannosidase or ß1-4 galactosidase to provide structural and compositional information about the glycans subject to separation. The use of in-capillary cleavage of terminal glycan residues with exoglycosidases offers a number of advantages over benchtop enzymatic sequencing, including reduced consumption of analyte, as well as enzyme. These methods were used to evaluate glycans derived from the glycoproteins α1-acid glycoprotein, fetuin, and ribonuclease B, as well as from glycoproteins collected from MCF7 cells.

Induction of aneuploidy by single-walled carbon nanotubes.

Engineered carbon nanotubes are newly emerging manufactured particles with potential applications in electronics, computers, aerospace, and medicine. The low density and small size of these biologically persistent particles makes respiratory exposures to workers likely during the production or use of commercial products. The narrow diameter and great length of single-walled carbon nanotubes (SWCNT) suggest the potential to interact with critical biological structures. To examine the potential of nanotubes to induce genetic damage in normal lung cells, cultured primary and immortalized human airway epithelial cells were exposed to SWCNT or a positive control, vanadium pentoxide. After 24 hr of exposure to either SWCNT or vanadium pentoxide, fragmented centrosomes, multiple mitotic spindle poles, anaphase bridges, and aneuploid chromosome number were observed. Confocal microscopy demonstrated nanotubes within the nucleus that were in association with cellular and mitotic tubulin as well as the chromatin. Our results are the first to report disruption of the mitotic spindle by SWCNT. The nanotube bundles are similar to the size of microtubules that form the mitotic spindle and may be incorporated into the mitotic spindle apparatus.

Detection of three novel translocations and specific common chromosomal break sites in malignant melanoma by spectral karyotyping.

Chromosomal aberrations in malignant melanoma cells have been reported using standard chromosome banding analysis and comparative genomic hybridization. To identify marker chromosomes and translocations that are difficult to characterize by standard banding analysis, 15 early passage malignant melanoma cell lines were examined using spectral karyotyping. All 15 tumor cell lines had lost all or part of 1p and 10q. Losses of material on chromosome arms 4p (12/15), 6q (12/15), 9p (15/15), 12p (13/15), 12q (13/15), 13q (11/15), and 19q (14/15) were the next most frequent events. Gain of chromosome arms 1q (11/15), 6p (13/15), and 20q11 (14/15) was also observed. Interestingly, we identified translocations der(12)t(12;20)(q15;q11), der(19)t(10;19)(q23;q13), and der(12)t(12;19)(q13;q13) in 4/15 tumors. Three recurring translocations involving four of the most frequent break points were detected. The identification of recurring translocations and unique chromosome break points in melanoma will aid in the identification of the genes that are important in the neoplastic process.

Nonrandom cytogenetic alterations in hepatocellular carcinoma from transgenic mice overexpressing c-Myc and transforming growth factor-alpha in the liver.

Identification of specific and primary chromosomal alterations during the course of neoplastic development is an essential part of defining the genetic basis of cancer. We have developed a transgenic mouse model for liver neoplasia in which chromosomal lesions associated with both the initial stages of the neoplastic process and the acquisition of malignancy can be analyzed. Here we analyze chromosomal alterations in 11 hepatocellular carcinomas from the c-myc/TGF-alpha double-transgenic mice by fluorescent in situ hybridization with whole chromosome probes, single-copy genes, and 4'-6-diamidino-2-phenylindole (DAPI-) and G-banded chromosomes and report nonrandom cytogenetic alterations associated with the tumor development. All tumors were aneuploid and exhibited nonrandom structural and numerical alterations. A balanced translocation t(5:6)(G1;F2) was identified by two-color fluorescent in situ hybridization in all tumors, and, using a genomic probe, the c-myc transgene was localized near the breakpoint on derivative chromosome der 6. Partial or complete loss of chromosome 4 was observed in all tumors with nonrandom breakage in band C2. Deletions of chromosome 1 were observed in 80% of the tumors, with the most frequent deletion at the border of bands C4 and C5. An entire copy of chromosome 7 was lost in 80% of the tumors cells. Eighty-five percent of the tumor cells had lost one copy of chromosome 12, and the most common breakpoint on chromosome 12 occurred at band D3 (28%). A copy of chromosome 14 was lost in 72%, and band 14E1 was deleted in 32% of the tumor cells. The X chromosome was lost in the majority of the tumor cells. The most frequent deletion on the X chromosome involved band F1. We have previously shown that breakages of chromosomes 1, 6, 7, and 12 were observed before the appearance of morphologically distinct neoplastic liver lesions in this transgenic mouse model. Thus breakpoints on chromosome 4, 9, 14, and X appear to be later events in this model of liver neoplasia. This is the first study to demonstrate that specific sites of chromosomal breakage observed during a period of chromosomal instability in early stages of carcinogenesis are later involved in stable rearrangements in solid tumors. The identification of the 5;6 translocation in all of the tumors has a special significance, being the first balanced translocation reported in human and mouse hepatocellular carcinoma and having the breakpoint near a tumor susceptibility gene and myc transgene site of integration. Moreover, its early occurrence indicates that this is a primary and relevant alteration to the initiation of the neoplastic process. In addition, the concordance between the breakpoints observed during the early dysplastic stage of hepatocarcinogenesis and the stable deletions of chromosomes 1, 4, 6, 7, 9, and 12 in the tumors provides evidence for preferential site of genetic changes in hepatocarcinogenesis.

Specific chromosomal changes in albumin simian virus 40 T antigen transgenic rat liver neoplasms.

Hepatocytes isolated from 3-month-old female rats bearing the albumin promoter/enhancer SV40 T antigen construct as a transgene demonstrated a 20% aneuploidy rate and a significant duplication of chromosome 1. Other chromosome changes were observed but were not statistically significant. At this time in the development of hepatic lesions, only a relatively small number of microscopic altered hepatic foci could be noted. By contrast, hepatocytes isolated from the age-matched nontransgenic controls demonstrated only 1% aneuploidy. One hundred % of the metaphase spreads isolated from hepatocellular neoplasms in transgenic rats were aneuploid. Although there were many random changes, 70% of the neoplastic cells demonstrated an amplification of all or portions of chromosome 1q. Only 2% of the neoplastic cells had both a trisomy and a duplication. The smallest region of chromosome 1 that was duplicated was that between bands q3.7 and q4.3. A loss of chromosome 3 was detected in 50% of the neoplasms, as well as a loss of chromosome 6 in 72% of the neoplastic cells. The carcinomas with the highest proliferation rate had also lost at least one copy of chromosome 15 in 70% of the cells. The loss of chromosomes 3, 6, and 15 indicates that these regions may harbor one or more tumor suppressor genes. The amplification of a specific region of chromosome 1 is thus the first karyotypic alteration that can be identified in hepatocytes from livers from which hepatic neoplasms will arise. This indicates that expression or repression of one or more genes in this region may confer a growth advantage to preneoplastic hepatocytes, facilitating their transit to the neoplastic state in the stage of progression. Changes in chromosomes 3, 6, and 15 that occur subsequent to duplication of the q3.7-q4.3 region of chromosome 1 are changes possibly reflecting alteration of tumor suppressor genes with further enhancement of neoplastic growth.

Ploidy and karyotypic alterations associated with early events in the development of hepatocarcinogenesis in transgenic mice harboring c-myc and transforming growth factor alpha transgenes.

The cooperation of the c-myc oncogene with the growth factor transforming growth factor (TGF)-alpha in development of liver tumors in transgenic mice has been demonstrated previously. In this study, we analyzed the ploidy and karyotype of c-myc, TGF-alpha, parental control, and the double transgenic c-myc/TGF-alpha hepatocytes at 3 weeks of age when the liver is histologically normal and at 10 weeks when the c-myc/TGF-alpha liver is dysplastic and contains basophilic foci. Eighty % of the 10-week hepatocytes were aneuploid, and 32% had chromosomal breakage. Statistically significant breakage was observed in six different chromosomes. Breakage at band A5 and at the border of bands C4/5 of chromosome 1 was observed. Fragile sets on chromosome 4 were most frequent in the middle of the chromosome at bands C2 and C6. Chromosome 6 was fragile at band F2. The region of chromosome 7 at bands B5 and D3 was frequently broken and involved in translocations. Chromosome 12 was broken at bands D1 and D3. The breakage sites on chromosomes 1, 4, 7, and 12 correspond to sites of tumor susceptibility genes in the mouse. Although there was no consistent change in copy number, recurrent translocations between chromosomes 1, 4, 7, 12 and 19 were also observed. These studies demonstrate that the development of dysplasia and basophilic foci in the liver is correlated with aneuploidy and chromosome breakage. The specific fragile sites indicate genetic regions that are altered during early stages of hepatocarcinogenesis. Due to the conservation of genetic linkage groups between mice and humans, the identification of genetic alterations in the mouse during hepatocarcinogenesis may provide critical information about tumor susceptibility genes that are important in the early development of human hepatocellular carcinoma.

Induction of hepatic aneuploidy in vivo by tamoxifen, toremifene and idoxifene in female Sprague-Dawley rats.

Since tamoxifen is efficacious for the prevention of second primary breast neoplasms in humans and has a low reported incidence of acute side effects, several structurally related compounds have been developed for the treatment of breast cancer including toremifene and idoxifene. We have compared the karyotypic alterations that occur after a single per os administration of 35 mg/kg of tamoxifen, toremifene or idoxifene to female Sprague-Dawley rats. One day following treatment, the rats were sacrificed and the hepatocytes isolated and cultured. After 47 h in culture, colcemid was added for 3 h prior to harvest of the hepatocytes for karyotypic evaluation. At least 100 metaphase spreads were examined for each of five rats per treatment. Toremifene resulted in aneuploidy in 50 +/- 7% of the cells examined and idoxifene induced a 57 +/- 4% aneuploidy compared with the 85 +/- 7% level induced by tamoxifen. Since the level of aneuploidy in solvent-treated rats was 3 +/- 3 %, the induction of aneuploidy in at least 50% of the cells from rats treated with tamoxifen, toremifene or idoxifene was highly significant. Analysis of electron micrographs of cultures treated with these antiestrogens demonstrated a range of phenotypes including multipolar spindles in toremifene-treated rats and condensed chromosomes in the presence of an intact nuclear envelope in occasional idoxifene-treated rat hepatocytes. The exclusion of chromosomes from the spindle apparatus and the lagging of some chromosomes on the metaphase plate correlate with the high rate of induction of aneuploidy in the rat liver as determined by karyotypic analysis of hepatocytes from rats treated with these triphenylethylenes.

Tamoxifen induces hepatic aneuploidy and mitotic spindle disruption after a single in vivo administration to female Sprague-Dawley rats.

Tamoxifen has found extensive use in the treatment of all stages of human breast cancer. The efficacy of tamoxifen treatment for the prevention of second primary tumors and its chemosuppressive action in animal models have led to initiation of clinical trials to test its efficacy for prevention of this disease in women. Recently, tamoxifen has been shown to induce hepatocellular carcinomas in rats. For determination of the mechanism of induction of these tumors and assessment of the possibility of risk of human cancer development from tamoxifen treatment, female Sprague-Dawley rats (five rats per treatment) were administered tamoxifen at doses ranging from 0.3 to 35 mg/kg. One day after treatment, the rats were sacrificed, and the hepatocytes were isolated and cultured for 50 h. Colcemid was added 3 h prior to harvest, and the hepatocytes were then prepared for karyotypic evaluation. One hundred metaphase spreads were examined per animal. Tamoxifen treatment resulted in the induction of aneuploidy in approximately 70% of the examined hepatocytes at the doses used. In addition, premature condensation (2-10%) and endoreduplication (5-10%) were observed in hepatocytes of rats treated with tamoxifen. Furthermore, exchanges between chromosomes as well as chromosome breakage were observed. Examination of the cultured hepatocytes from rats treated with tamoxifen by electron microscopy demonstrated both unipolar spindles and incompletely elongated spindles. Exposure of rats to a single in vivo dose of tamoxifen produced multiple changes in rat hepatocytes including clastogenic damage at doses comparable to that administered to humans. The occurrence of aneuploidy induction, premature condensation, chromosome breakage, and improper mitotic spindle formation indicates that risk versus benefit of tamoxifen treatment should be carefully evaluated.

Ploidy and specific karyotypic changes during promotion with phenobarbital, 2,5,2',5'-tetrachlorobiphenyl, and/or 3,4,3'4'-tetrachlorobiphenyl in rat liver.

Polychlorinated biphenyls are a group of industrial chemicals that are widely distributed in the environment. Since these compounds occur as mixtures, studies of their possible interactive effects are important. In order to determine whether an interaction of 2,5,2',5'-tetrachlorobiphenyl (TCB) with 3,4,3',4'-TCB occurs during multistage hepatocarcinogenesis in vivo, like that previously observed in lymphocytes in vitro (L. M. Sargent et al., Mutat. Res., 224: 79-88, 1989), we exposed rats to a single initiating dose of diethylnitrosamine (DEN), 10 mg/kg after a 70% partial hepatectomy, and subsequently to 0.1 ppm 3,4,3',4'-TCB and/or 10 ppm 2,5,2',5'-TCB in the diet for 1 year. Administration of each of the TCBs alone after DEN initiation resulted in a low incidence of chromosomal damage in hepatocytes; but when the two were given together after DEN initiation, there was a more than additive effect on this parameter at both 7 and 12 months which was highly significant. Administration of the TCBs alone or in combination in the absence of DEN initiation also resulted in chromosomal damage, approaching that seen in livers of animals initiated with DEN when sacrificed at 12 months. In animals receiving 0.05% phenobarbital for a 12-month period after initiation with DEN, a significant degree of chromosomal breakage and fragment formation occurred both in hepatocytes expressing the ectoenzyme gamma-glutamyltranspeptidase (GGT) and in those that were GGT negative. However, the GGT-negative cells showed a significantly lower incidence of chromosomal damage than the GGT-positive hepatocytes. Exposure to phenobarbital for 7 months after DEN initiation resulted in no significant chromosomal damage in hepatocytes, whether GGT positive or GGT negative. Some degree of specificity in chromosomal alterations was seen in hepatocytes of animals initiated with DEN and promoted either with a combination of TCBs or with phenobarbital. The most frequent alterations seen were a trisomy of chromosome 1 or of its long arm and a monosomy of chromosome 3 or its short arm. Some chromosome 7 aberrations were also seen. The highest frequency of specific aberrations occurred in hepatocytes from rats that also bore hepatocellular carcinomas, suggestive of the hypothesis that genes involved in the development of hepatic carcinoma may reside in chromosome 1 and/or 3 of the rat.

Multiple cell cycles occur in rat hepatocytes cultured in the presence of nicotinamide and epidermal growth factor.

Multiple rounds of cell division were induced in primary cultures of rat hepatocytes in serum-free medium containing 10 mmol/L nicotinamide and 10 ng epidermal growth factor/ml. Cells per culture almost doubled between day 1 and day 5. The proliferating cells were predominantly mononucleate. The time course of DNA synthesis in cultured hepatocytes showed that peaks of the incorporation of 3H-thymidine were observed at 60 hr and 82 hr after plating. Labeling indices of the cells indicated that almost half the cells were labeled with 3H-thymidine in the periods 48 to 72 hr and 72 to 96 hr after plating. In addition, about 20% of the hepatocytes in culture initiated a second round of the cell cycle between 48 and 96 hr in culture, as demonstrated by the use of continuous treatments with 3H-thymidine and 5-bromo-2'-deoxyuridine. Furthermore, by day 4 of culture, about 40% and 15% of metaphases resulted from a second and third round of cell division, respectively. The cultured hepatocytes on day 5 stained with albumin immunocytochemically, and the activity of tyrosine aminotransferase was induced by dexamethasone and glucagon on day 3. In addition, electron micrographs revealed that dividing cells not only had many characteristics of liver mitochondria and bile canaliculus-like structures, but many also contained a few large peroxisomes with internal crystalline nucleoids.

Mechanisms in cyclophosphamide induction of cytogenetic damage in human lymphocyte cultures.

Low-dose cyclophosphamide treatment of human lymphocyte cultures in concentrations ranging from 0.001 to 0.00001 microgram/ml produced a statistically significant dose response in chromosome breakage and cell death. However, a dose as high as 0.2 micrograms/ml did not produce significant damage in comparably treated whole blood cultures. These results suggest that lymphocytes in culture have the ability to metabolize the nonmutagenic cyclophosphamide parent compound to its more mutagenic metabolite, but that such conversion may be prevented by binding of cyclophosphamide to red blood cells.

Comparison of prometaphase chromosome techniques with emphasis on the role of colcemid.

Six different techniques were evaluated to define better those technical factors that are most critical for obtaining prometaphase cells for banding analysis. Our results demonstrate: colcemid exposures of 30 min or less have no effect on increasing the yield of prometaphase cells, colcemid exposures of greater than 0.1 microgram/ml can be toxic, methotrexate depresses the mitotic index significantly and seems to increase the incidence of prometaphase cells only because it suppresses later forms; and (d) the optimum number of cytogenetically satisfactory prometaphase cells can be obtained with a 4-h exposure to a combination of low concentration actinomycin D (0.5 microgram/ml) and colcemid (0.1 microgram/ml). This technique inhibits chromosome condensation while permitting prometaphase cells to accumulate for 4 h.