Chemistry and biological activities of constituents from Morus australis

A novel constituent named australone B (1) was further isolated from the cortex of Morus australis (Moraceae). The structure of 1 has been elucidated by one- and two-dimension spectra. In human citrated platelet-rich plasma, 1 showed strong inhibition of aggregation induced by adrenaline in a concentration-dependent manner with an IC(50) value of about 33.3 microM. Compound 1 (30 microM) also showed inhibitory effects on superoxide anion formation from rat neutrophils stimulated with formyl-Met-Leu-Phe (fMLP)/cytochalasin B (CB). Morusin (2) inhibited superoxide anion formation from rat neutrophils stimulated with phorbol myristate acetate (PMA) in a concentration-dependent manner with an IC(50) value of 66.9+/-2.5 microM.

Follow-up in the micronucleus frequencies and its subsets in human population with chronic low-dose gamma-irradiation exposure

Forty-eight individuals, who received protracted low-dose rate gamma-irradiation from radioactive environments for 2-10 years, have been evaluated repetitively for cytogenetic damage by the cytochalasin-B micronuclei assay (CBMN) after they relocated from radioactive buildings. These subjects were shown to have a significant decrease in the CBMN frequencies during 26.2+/-8.4 months of follow-up. By the mixed effect multiple linear regression analysis, the CBMN frequencies in these 48 subjects during repetitive measurements were significantly associated with the relocation duration since leaving the radioactive environments (relocation time or RT in months; estimate -0.47, standard error 0. 0016, p value 0.0074). The alteration rate in the proportions of binucleates carrying a single micronucleus and those with multiple micronuclei was further compared among 26 of these exposed individuals. The proportions of binucleates with multi-micronuclei were shown to decline significantly faster than those with a mono-micronucleus between these two repetitive assays (proportional Z-test, p value 0.003). Moreover, some of the exposed subjects were shown to have a persistent increase in the total micronuclei frequencies or carrying multi-micronuclei in the binuclei even 3-4 years post-cessation of exposure. This suggests potential genomic instability in stem cells of the exposed individuals and the phenomenon deserves further closer monitoring. Understanding the dynamics of micronucleus expression in lymphocytes in subjects with previous mutagenic exposure would be of significant importance for human population monitoring.

Chromosomal damage and ageing: effect on micronuclei frequency in peripheral blood lymphocytes

BACKGROUND

Instability in the organization and expression of the genetic material has been hypothesized as the basic mechanism of ageing.

OBJECTIVE

To quantify the effect of ageing on chromosomal damage as measured by spontaneous micronuclei (MN) frequency in peripheral blood lymphocytes.

METHOD

Analysis of a large population sample from two laboratories applying the cytokinesis-block technique and a third using traditional interphase analysis. The age-related effect on baseline level of micronuclei frequency and on cell proliferation measures was further investigated in a study of peripheral blood samples from healthy subjects.

RESULTS

There was an increase of MN frequency with age. The regression lines showed a positive slope and were statistically significant (P< 0.01) with a steeper trend for cytochalasin B-treated samples. An inverse correlation with age was detected for the percentage of binucleated cells in laboratories using cytochalasin B. This study confirms the increase of basal level of MN with age. A decrease by age in proliferation efficiency measured by the percentage of binucleated cells suggests an interference of age-related factors on cell division.

CONCLUSION

There is an increase in MN frequency with increasing age.

Cooling and freezing damage platelet membrane integrity

Cytoskeletal rearrangements and a membrane lipid phase transition (liquid crystalline to gel) occur in platelets on cooling from 23 to 4 degrees C. A consequence of these structural alterations is irreversible cellular damage. We investigated whether platelet membrane integrity could be preserved by (a) previously studied combinations of a calcium chelator (EGTA) and microfilament stabilizer (cytochalasin B) with apparent benefit in protecting platelets from cooling injury or (b) agents of known benefit in protecting membranes and proteins from freezing injury. Platelet function and activation before and after freezing or cooling were measured by agglutination with ristocetin, aggregation with thrombin or ADP, platelet-induced clot retraction (PICR), and expression of P-selectin. Platelets were loaded with 10 nM fluorescein diacetate. After freezing or cooling, the preparations were centrifuged and the supernatant was measured for fluorescein. For cooling experiments, fresh platelets were chilled at 4 degrees C for 1 to 21 days with or without the combination of 80 microM EGTA/AM and 2 microM cytochalasin B (EGTA/AM-CytoB) and then warmed rapidly at 37 degrees C. For freezing experiments, 5% dimethyl sulfoxide (Me2SO) or 5 mM glycerol were added to fresh platelets. The preparations were then frozen at -1 degrees C/min to -70 degrees C and then thawed rapidly at 37 degrees C. Platelet membrane integrity, as measured by supernatant levels of fluorescein, correlated inversely with platelet function. Chilling platelets at 4 degrees C with EGTA/AM-CytoB showed a gradual loss of membrane integrity, with maximum loss reached on day 7. The loss of membrane integrity preceded complete loss of function as demonstrated by PICR. In contrast, platelets chilled without these agents had complete loss of membrane integrity and function after 1 day of storage. Freezing platelets in Me2SO resulted in far less release of fluorescein than did freezing with or without other cryoprotectants (P < 0.001). This result correlated with enhanced function as demonstrated by PICR and supports earlier observations that Me2SO protects platelet membranes from freezing injury. Release of fluorescein into the surrounding medium reflected loss of membrane integrity and function in both cooled and frozen platelets. Membrane cytoskeletal rearrangements are linked to membrane changes during storage. These results may be generally applicable to the study of platelet storage.

Cell cycle dependent aneuploidy induction by X-rays in vitro in human lymphocytes

Although ionising radiation mainly induces DNA strand breaks leading to chromosomal aberrations, there are indications that it also might induce numerical chromosome aberrations (aneuploidy). The existing data, however, do not provide evidence for a mechanism. To assess the relative sensitivity of the G1 vs. G2 cellular targets, whole blood cultures of lymphocytes were irradiated in vitro with different doses of X-rays (0.5, 1 and 2 Gy). The lymphocytes were harvested after cytochalasin-B blockade to allow the selective study of binucleated cells, having undergone only one division in culture. Harvesting was performed at different sampling times (70, 74, and 78 hours). To evaluate the micronuclei, regarding whole chromosomes or acentric fragments, an oligonucleotide probe that recognises the centromeric region of all human chromosomes was used. The relative percentage of centromere-positive micronuclei ranged from 5 up to 18% depending on the cell cycle stage and on the received dose. Cells exposed during the G1 phase exhibited a slightly higher frequency of centromere-positive micronuclei than cells that were in G2 at the time of exposure. G1 exposure induced a centromere-positive micronuclei dose-effect relationship that was not observed after G2 exposure. The observed difference in response of both phases on the centromere-positive micronuclei yields may be due to the involvement of different targets.

The butadiene metabolite, 1,2:3,4-diepoxybutane, induces micronuclei but is only weakly mutagenic at lacI in the Big Blue Rat2 lacI transgenic cell line

1,3-Butadiene (BD) is a genotoxic carcinogen that is bioactivated to at least two mutagenic metabolites, 1,2-epoxybutene (EB) and 1,2:3,4-diepoxybutane (DEB). We investigated the mutagenicity and induction of micronuclei by DEB in vitro in Rat2 lambda/lacI transgenic fibroblasts (Big Blue Rat2 cells, Stratagene, LaJolla, CA). Assays for mutagenicity and micronuclei induction were carried out at concentrations of 0, 2, 5, or 10 microM DEB for 24 hours. Exposure of cells to these concentrations of DEB resulted in approximately 100, 50, and 10% survival, respectively, compared with media controls. In independent replicate experiments, no statistically significant increase in lacI mutant frequency was observed in Rat2 cells at any of the DEB exposure concentrations when compared to media or solvent controls. However, regression analyses indicated a trend toward increasing mutant frequency with increasing DEB exposure concentration. Experiments to examine the induction of micronuclei by DEB revealed a concentration-dependent increase in micronuclei in Rat2 cells following exposure to DEB. These results indicate that DEB induces micronuclei in the absence of detectable gene mutation at lacI in Big Blue Rat2 cells. The induction of micronuclei but only weak mutagenicity at the lacI transgene is likely due to the poor recovery of deletions using this lambda shuttle vector system, demonstrating the need to investigate multiple endpoints of genotoxicity when considering the mutational activity of a compound.

Induction and distribution of damage in CHO-K1 and the X-ray-sensitive hamster cell line xrs5, measured by the cytochalasin-B-cytokinesis block micronucleus assay

The micronucleus assay holds promise as a method for determining clastogenic effects of particular agents and for examining relative sensitivities of eukaryotic cells to such clastogens. In the following work, a detailed examination of the induction of micronuclei in radio-resistant Chinese hamster ovary fibroblasts (CHO-K1) and the DNA double-strand break repair-defective daughter cell line, xrs5, was performed. Cells were exposed to gamma-irradiation, bleomycin, etoposide, camptothecin and the restriction endonuclease PvuII. By a simplified statistical analysis of data, information on the expression of chromosomal damage, the distribution of damage and the role of cell cycle effects on damage expression was obtained from a relatively small number of cells. All 5 clastogens resulted in elevated levels of micronuclei in xrs5 compared to CHO-K1. An analysis of the distribution of micronuclei within treated populations revealed differences between the modes of damage. Significant deviation from the expected values indicated that expression of micronuclei does not follow an expected Poisson distribution. The frequencies of binucleated cells indicated micronucleus frequencies do not always correlate with inhibition of cell cycle progression. This work also demonstrates that caution is required in the interpretation of data obtained through micronucleus assays. In particular, it does not appear possible to proscribe simple numerical values of relative sensitivity or clastogenicity based on the relative number of micronuclei induced alone.

[Primary study on the sensitivity of cytokinesis blocked micronucleus assay in CHL cells]

Studies were performed to determine the cytochalasin B induced binucleated cell percentage influenced by clastogens and aneuploidgens and to compare the efficacy of cytokinesis blocked binucleated cells for scoring micronuclei with that of the conventional mononucleated method following the treatment with mitomycin C, methyl methanesulforate, colchicin and chloral hydrate. The results showed that mitomycin C decreased the binucleated cell percentage induced by cytochalasin B, whereas colchicin increased the frequencies of binucleated cells. The frequencies of micronuclei in binucleated cells were not significantly higher than those in the conventional mononucleated cells. The results suggest that cytokinesis blocked method is not more sensitive than the conventional method for scoring micronuclei. The factors that may influence the cytokinesis blocked micronucleus assay have been discussed.

Human lymphocytes micronucleus assay in Europe. An international survey

The human lymphocytes micronucleus assay has been extensively used in Europe since the cytochalasin-B method was introduced. However, a large range of inter-laboratory variability has been reported, limiting its applicability in European coordinated projects as well as its acceptance in international regulatory guidelines. Thus, an European survey was proposed in order to (a) determine the present state of the human lymphocytes micronuclei assay, (b) review methodological and scientific aspects, and (c) identify discrepancies in the criteria employed by different laboratories that could account for the lack of reproducible results. The outcome of the study with 30 European laboratories surveyed, reflects an immature state of the micronuclei assay in Europe, with (a) disparity in criteria and methodologies, (b) high diversity in the methods of statistical analyses employed, (c) non-uniform criteria for determining positive responses, and (d) a still rare use of new or emerging methodologies. The reported average baseline frequency of micronuclei in human lymphocytes was 7.8 +/- 5.2 per 1000 cells (ranging from 3 to 23), with age and sex but not smoking as being main confounding factors. The general opinion was that more basic research on the micronucleus assay itself is required before considering this technique as an alternative to the chromosomal aberration assay, and that it is a suitable method to detect aneuploidy, mainly in vitro, and specially when coupled with molecular cytogenetic techniques.

The advantages and disadvantages of the cytokinesis-block micronucleus method

There is current interest in adopting the micronucleus test instead of metaphase analysis of chromosomes to assess the in vitro genotoxic potential of chemical and physical agents. In this paper, the advantages and disadvantages of the cytokinesis-block micronucleus technique relative to metaphase analysis of chromosomes and the conventional micronucleus technique that does not distinguish between dividing and non-dividing cells are discussed. Furthermore, additional features, such as the measurement of non-disjunction, excision-repairable DNA lesions and HPRT variants and possibilities for further improving the application of the cytokinesis-block method are proposed.

Influence of culture time on the frequency and contents of human lymphocyte micronuclei with and without cytochalasin B

The effects of culture time (52, 64 and 76 h) and cytochalasin B (Cyt-B, 3 micrograms/ml) on the frequency of micronuclei (MN) harbouring whole chromosomes and acentric fragments was investigated in purified lymphocyte cultures of five nonsmoking male donors aged 41-50 years. Centromere-positive (C+) MN were identified by fluorescence in situ hybridization, using an alphoid DNA oligomer probe (SO-alpha AllCen) hybridizing to all human centromeres. For each culture time, 2000 cells and 60 MN were scored per donor, both with and without Cyt-B, making a total of 60,000 cells and 1800 MN. The frequency of MN and the proportion of C+ MN were higher at 64 h and 76 h than at 52 h, irrespective of Cyt-B. The culture time-dependent increase in MN frequency was mainly due to C+ MN which were about 1.5-times more frequent at 64 h and 72 h than at 52 h. The frequencies of C+ MN, expressed per 1000 nuclei, were similar with and without Cyt-B, although the prevalence of C+ MN was consistently about 10 percent units higher in the former type of culture. This effect was due to a decreased frequency of centromere-negative (C-) MN in the binucleate cells, possibly reflecting, e.g. increased inclusion of acentric chromosomal fragments within the main nuclei of such cells, enhanced expulsion of C- MN, or selection against binucleate cells carrying such MN. In conclusion, the present findings indicate that MN harbouring whole chromosomes become more frequent at long culture times with and without Cyt-B and that Cyt-B-induced binucleate cells show a reduced frequency of MN containing acentric fragments. Due to the high background of whole-chromosome-containing MN (mean C+ MN proportions ranged from 42.3% to 62.7%), it may be recommended that centromeric fluorescence in situ hybridization is routinely applied when lymphocyte MN are used as a biomarker of human exposure to clastogens.

Micronuclei, centromere-positive micronuclei and chromosome nondisjunction in cytokinesis blocked human lymphocytes following mitomycin C or vincristine treatment

The influence of sampling time on the frequencies of micronuclei, centromere-positive micronuclei and chromosome nondisjunction was investigated in binucleated lymphocytes following treatment with a known clastogen (mitomycin C) or an aneuploidy-inducing agent (vincristine sulfate). Cytochalasin B (6 micrograms/ml) was added 44 h after mitogen stimulation and cultures were harvested 12, 28, 36 and 48 h thereafter. Micronucleated cells and micronuclei were significantly induced by the two treatments at all sampling times. Furthermore, in situ hybridization with an 'all centromeres' probe showed that vincristine-induced micronuclei were prevalently centromere-positive whereas in mitomycin C-treated cultures only a minor fraction of induced micronuclei contained the hybridization signals. Chromosome nondisjunction rates, as measured by in situ hybridization with chromosome 7- and 11-specific alphoid probes, significantly increased following vincristine treatment. Chromosome nondisjunction and total micronucleus frequencies were found to increase with time both in controls and in mutagen-treated cultures, whereas the percentage of centromere-positive micronuclei in the different treatments was not influenced by the sampling time. Our data suggest that even in the presence of 6 micrograms/ml cytochalasin B, the abnormal segregation of binucleated cells may contribute to the baseline level of micronuclei and influence the results obtained. The introduction of a short cytochalasin B treatment (between 12 and 28 h) in the cytokinesis-blocked micronucleus assay may avoid the cytochalasin B effect on micronucleus frequencies.

Dose-rate sparing for micronucleus induction in lymphocytes of controls and ataxia-telangiectasia heterozygotes exposed to 60Co gamma-irradiation in vitro

We investigated the reproducibility of the cytochalasin B micronucleus (MN) assay in irradiated human lymphocytes to assess its suitability in predicting cancer predisposition and response to radiotherapy by virtue of defects in the processing of clastogenic lesions. G0 lymphocytes were exposed to 3.0 Gy 60Co gamma-rays at high (HDR) or low dose-rate (LDR). Six healthy donors were assayed three times each in nine experiments and compared with six ataxia-telangiectasia (A-T) heterozygotes. In controls, significant interexperiment variability in MN yields was observed at HDR and LDR, also in dose-rate sparing (i.e. reduction in MN yield at LDR compared with HDR). Significant inter-individual variability was seen at HDR, but not at LDR or for sparing. Average sparing was 66.4 +/- 4.8%. In spite of the experimental variability, a significant difference between controls and A-T heterozygotes was detected at LDR, and 5/6 heterozygotes had sparing values below the control range. This gives encouragement for the use of this assay in predictive testing if sources of experimental variability can be identified so as to improve discrimination between individuals. HDR and to a lesser extent LDR irradiation induced significant mitotic inhibition, seen as a reduction in binucleate cells after cytocholasin treatment. A positive correlation between mitotic inhibition and MN frequency suggests that similar lesions may be involved in these effects.

Mitotic non-disjunction as a mechanism for in vitro aneuploidy induction by X-rays in primary human cells

A collaborative study of three laboratories compared the induction of aneuploidy by X-rays in human lymphocytes and fibroblasts. The induction of non-disjunction versus chromosome loss by X-rays was investigated using a variety of aneuploidy detection methods. Chromosome loss was determined by fluorescence in situ hybridization (FISH) with pan-centromeric probes in cytochalasin-B-blocked binucleated cells. Chromosome non-disjunction was estimated by FISH with chromosome-specific centromeric probes in binucleated interphase cells. Chromosomes were counted in parallel in lymphocyte metaphase cells; chromosome counts of the whole karyotype and counts of chromosomes 2 and 8 using chromosome paints. A major observation in spontaneous non-disjunction frequencies concerned the clear difference in frequencies observed between the two painted chromosomes in the same primary cells. When cells were irradiated elevated frequencies were observed for all the different cytogenetic endpoints. Although only a small number of the micronuclei were positive for the centromeric signal and presumably contained whole chromosomes, the absolute number %oC+ increased with dose. Higher rates of non-disjunction were found for irradiated cells; in fibroblasts a statistically significant increase was observed at a dose of 0.5 Gy. The detection of hyperdiploidy by means of chromosome counts and chromosome painting revealed an increase from doses of 1 Gy and higher. Comparison of the different methods detecting different endpoints indicates that non-disjunction may be an important mechanism leading to spontaneous and X-ray-induced aneuploidy. The relative radiosensitivity of aneuploidy induction was compared in two types of primary human cells - lymphocytes and fibroblasts. For chromosome loss both cell types showed similar results, whereas for non-disjunction fibroblasts seemed to be more sensitive. However, these differences may reflect a different sensitivity in the scoring methods used.

The regulation of GLUT5 and GLUT2 activity in the adaptation of intestinal brush-border fructose transport in diabetes

The adaptation of d-fructose transport in rat jejunum to experimental diabetes has been studied. In vivo and in vitro perfusions of intact jejunum with d-fructose revealed the appearance of a phloretin-sensitive transporter in the brush-border membrane of streptozotocin-diabetic rats which was not detectable in normal rats. The nature of the transporters involved was investigated by Western blotting and by d-fructose transport studies using highly purified brush-border and basolateral membrane vesicles. GLUT5, the major transporter in the brush-border membrane of normal rats, was not inhibited by d-glucose or phloretin. In contrast, GLUT2, the major transporter in the basolateral membrane of normal rats, was strongly inhibited by both D-glucose and phloretin. In brush-border membrane vesicles from diabetic rats, GLUT5 levels were significantly enhanced; moreover the presence of GLUT2 was readily detectable and increased markedly as diabetes progressed. The differences in stereospecificity between GLUT2 and GLUT5 were used to show that both transporters contributed to the overall enhancement of d-fructose transport measured in brush-border membrane vesicles and in vitro isolated loops from diabetic rats. However, overall d-fructose uptake in vivo was diminished. The underlying mechanisms and functional consequences are discussed.

Targeting of glucose transport proteins for tumor imaging: is it feasible?

If glucose transport proteins (Glut) are elevated in tumors they may be good targets for tumor imaging. For targeting, the overexpression of Glut should be a general characteristic of tumors. Moreover agents which bind to Glut should accumulate selectively in tumors.

METHODS

To test this, we quantitated Glut in isolated membranes from three human tumor xenografts, two murine tumor models and normal murine tissues using direct binding studies. Additionally, the biodistribution of two compounds which bind to Glut, 7-[[(2-(3-(125I-p-hydroxyphenyl)propionyl)aminoethyl)amino]carbonyl]-7-+ ++desacetyl-forskolin([125I]HPP forskolin) and [3H]cytochalasin B, were studied in a tumor model which overexpressed Glut.

RESULTS

There were multiple classes of binding sites for [3H]cytochalasin B and a percentage of these sites were competitive with D-glucose but not L-glucose. The rank potency and IC50 values for [3H]cytochalasin B binding were: 2-deoxy-D-glucose (4.5 mM) > or = D-glucose (7 mM) > mannose (25 mM) > galactose (35 mM) > rhamnose (1-3 mM) > sorbitol (1-3 mM) and were similar to reported values for transport. The average density of Glut in four tumor models and normal tissues was between 0.7 and 4 pmole/mg protein, but Kd values were not significantly different (69 nM). In LX-1 human lung tumor xenograft (LX-1) Glut were 10-to-20-fold higher than other tissues (21.6 +/- 0.6 pmole/mg protein, p<0.01). Immunostaining of Glut-1 was more prominent in LX-1 than other xenograft tumors, consistent with the binding data. Glut density was highest in poorly vascularized regions suggesting that Glut upregulation was related to a biofeedback mediated event. Iodine-125 HPP-forskolin and [3H]cytochalasin B did not localize in LX-1 tumors.

CONCLUSION

Glut overexpression was not a common characteristic of the five tumors tested. Iodine-125 HPP-forskolin and [3H]cytochalasin B did not localize in LX-1 tumors, indicating that these agents did not target tumors with upregulated Glut. Results suggest that Glut are not a promising target for tumor imaging.

Characterization of rat GLUT5 and functional analysis of chimeric proteins of GLUT1 glucose transporter and GLUT5 fructose transporter

To investigate the biological and biochemical properties of GLUT5, rat GLUT5 complementary DNA was transfected into Chinese hamster ovary cells. Rat GLUT5 was exclusively targeted to the plasma membrane and exhibited a transport activity, not for glucose, but for fructose. The affinity for fructose (Km = 11.6mM) was much higher than that of GLUT2, the other glucose transporter with fructose transport activity. Interestingly, rat GLUT5 was not photolabeled with 0.5 microM cytochalasin B, whereas a similar amount of GLUT1 was adequately photolabeled under the same experimental conditions. Next, to investigate the domains required for transport of glucose/fructose in GLUT1 and/or GLUT5, several chimeric GLUT1/GLUT5 proteins were expressed, and their glucose and/or fructose transport activities were studied. The intracellular middle loop and the region encompassing the membrane spanning domains 7-12 were observed to have crucial roles in GLUT1 glucose transport, whereas replacement of the N-terminal half or the intracellular C-terminal region with the corresponding region of GLUT5 produced no marked effects on glucose transport activity. In contrast, both the N-terminal half encompassing the region from the N-terminus through the 6th membrane spanning domain and the intracellular C-terminal region were mandatory for GLUT5 fructose transport. In conclusion, GLUT5 is a transporter exclusively for fructose and the structural requirements for fructose transport are more stringent than those for glucose transport among hexose transporter proteins.

Image processing algorithms for the automated micronucleus assay in binucleated human lymphocytes

The frequency of micronuclei in binucleated lymphocytes (cytochalasin B assay) may serve as a biological dosimeter after radiation exposure. The automation of the micronucleus assay in binucleated human lymphocytes has been considerably advanced in recent years. In our studies for this purpose the detection of binucleated cells (BNCs) and the scoring of micronuclei (MN) was divided into two parts. First, detection of BNCs was feasible with low microscopic magnification (x 100). The positions of classified BNCs were stored. Second, after an automatic change of microscope objective, the stored BNCs were automatically analyzed in sequence at high microscopic magnification (x 630) for occurrence of MN. For both phases of image analysis we used empirical methods based on mathematical morphology. The system is able to recognize nearly 65% of BNCs with false positive decisions of 6% and about 75% of the MN with false positive decisions of 7%.

Regulation of endothelial cell morphogenesis by integrins, mechanical forces, and matrix guidance pathways

Basement membrane matrix is known to induce human endothelial cells to form cord-like structures that mimic those observed during early angiogenesis in vivo. Using this model, blocking antibody studies revealed a major role for the alpha 6 beta 1 integrin in cord formation. During this process, two alterations in the Matrigel structure were observed which suggested a mechanism for the precision of cord formation. First, Matrigel contracted and lifted off an agarose support and second, linear distortions became visible in the Matrigel that correspond to the migration pathways of endothelial cell processes. These pathways, which we have termed "matrix guidance pathways," appear to result from the generation of mechanical tension between endothelial cells. The above data support the concept that endothelial cell guidance during morphogenetic events could be controlled by the ability of these cells to exert mechanical forces on the surrounding extracellular matrix to create pathways for migration.

Characterization of the rabbit intestinal fructose transporter (GLUT5)

Recent studies suggest that the jejunal/kidney-type facilitative glucose transporter (GLUT5) functions as a high-affinity D-fructose transporter. However, its precise role in the small intestine is not clear. In an attempt to identify the fructose transporter in the small intestine, we measured fructose uptake in Xenopus oocytes expressing jejunal mRNA from five species (rat, mouse, rabbit, hamster and guinea-pig). Only jejunal mRNA from the rabbit significantly increased fructose uptake. We also cloned a rabbit GLUT5 cDNA from a jejunal library The predicted amino acid sequence of the 487-residue rabbit GLUT5 showed 72.3 and 67.1% identity with human and rat GLUT5 respectively. Northern-blot analysis revealed GLUT5 transcripts in rabbit duodenum, jejunum and, to a lesser extent, kidney. After separation of rabbit jejunal mRNA on a sucrose density gradient, the fractions that conferred D-fructose transport activity in oocytes also hybridized with rabbit GLUT5 cDNA. Hybrid depletion of jejunal mRNA with a GLUT5 antisense oligonucleotide markedly inhibited the mRNA-induced fructose uptake in oocytes. Immunoblot analysis indicated that GLUT5 (49 kDa) is located in the brush-border membrane of rabbit intestinal epithelial cells. Xenopus oocytes injected with rabbit GLUT5 cRNA exhibited fructose uptake activity with a Km of 11 mM for D-fructose. D-Fructose transport by GLUT5 was significantly inhibited by D-glucose and D-galactose. D-Fructose uptake in brush-border membrane vesicles shows a Km similar to that of GLUT5, but was not inhibited by D-glucose or D-galactose. Finally, cytochalasin B photolabelled a 49 kDa protein in rabbit brush-border-membrane preparations that was immunoprecipitated by antibodies to GLUT5. Our results suggest that GLUT5 functions as a fructose transporter in rabbit small intestine. However, biochemical properties of fructose transport in Xenopus oocytes injected with GLUT5 cRNA differed from those in rabbit jejunal vesicles.

Simultaneous detection of X-chromosome loss and non-disjunction in cytokinesis-blocked human lymphocytes by in situ hybridization with a centromeric DNA probe; implications for the human lymphocyte in vitro micronucleus assay using cytochalasin B

A methodology for the simultaneous detection of chromosome loss and gain in mammalian cells has been developed which is based upon the analysis of chromosome distribution in daughter nuclei of binucleated human lymphocytes. X-chromosome distribution was followed by in situ hybridization, using a commercial biotinylated DNA probe specific for the centromeric alphoid sequences of human X-chromosome. In order to optimize the experimental protocol for the use of cytokinesis-blocked lymphocytes in aneuploidy assays, the effect of harvest time and cytochalasin B (Cyt B) dosage upon chromosome distribution was investigated. To this end, lymphocyte cultures were treated 44 h after mitogen stimulation with different dosages of Cyt B and collected at 60, 66 and 72 h. High rates of binucleated cells with unbalanced chromosome distribution (two spots in one nucleus and none in the other in male cells; three spots in one nucleus and one in the other in female cells) and abnormal spot number (more than or less than two per male cell or four per female cell) were observed at 66 and 72 h in cultures treated with the lowest Cyt B dose (3 micrograms/ml). In contrast, low frequencies of unbalanced or abnormal binucleated cells were observed at 60 h with both 3 and 6 micrograms/ml Cyt B. These results indicate that binucleated lymphocytes with low background frequencies of malsegregation (required for the analysis of induced aneuploidy), can be obtained by harvesting lymphocyte cultures 60 h after stimulation (16 h after Cyt B block).(ABSTRACT TRUNCATED AT 250 WORDS)

Phagocytosis of a fluorescently labeled perflubron emulsion by a human monocyte cell line

We hypothesized that fluorocarbon-based lipid emulsions are phagocytosed by monocytes and that many of the in vivo side effects related to the infusion of these particulate emulsions are due to release of cytokines by these monocytes. To clarify whether these emulsions are actually phagocytosed we attempted to measure by flow cytometry the apparent uptake of a fluorescently labeled high-concentration (90%, w/v) perflubron (perfluorooctyl bromide [PFOB]) emulsion by a differentiated human monocyte cell line. A fluorescent chromophore (Zynaxis Cell Science) was used to label the egg yolk phospholipid in a perflubron emulsion. This phospholipid label was used to track the perflubron emulsion during overnight incubation with the human monocyte (THP-1) cell line which had been differentiated, by exposure to PMA, into macrophage-like cells. Our results indicate that after 24 hours of incubation with the labeled perflubron emulsion, 64.9% (+/- 11.0) of differentiated THP-1 cells had cell-associated emulsion (ingested and/or membrane bound) whereas 24.4 (+/- 6.8%) of the control cells had cell-associated emulsion. We speculate that this technique may be a useful method to track the intravascular persistence and extravascular distribution of such emulsions, and that the degree of uptake of the emulsion by macrophages in this assay may correlate with its in vivo half life.

Micronucleus assays using cytochalasin-blocked MCL-5 cells, a proprietary human cell line expressing five human cytochromes P-450 and microsomal epoxide hydrolase

The MCL-5 cell line is a human lymphoblastoid TK+/- cell line that constitutively expresses a relatively high level of native CYP1A1, four other human cytochromes (CYP1A2, CYP2A6, CYP3A4 and CYP2E1) and microsomal epoxide hydrolase, carried as cDNAs in plasmids. The aim of this study was to evaluate this cell line for its suitability for detecting chromosomal anomalies, employing micronucleus formation in cells blocked at cytokinesis as the indicator of clastogenicity. Results from two laboratories ('ICR' and 'Swansea') using different protocols are reported. In the ICR protocol, aflatoxin B1, sterigmatocystin, benzo[a]pyrene, dibenz[a,h]anthracene, 3-methylcholanthrene, cyclophosphamide, N-nitrosodimethylamine, 2-amino-3,8-dimethylimidazo[4,5-f]-quinoxaline, benzidine, 2-aminofluorene, benzene, tamoxifen and omeprazole were tested and gave positive results. Anthracene, phenanthrene and pyrene were negative. In the Swansea protocol, AHH-1 cells, the parent line which constitutively expresses CYP1A1, but does not contain the genetically engineered human cytochromes or epoxide hydrolase, were tested in parallel with MCL-5 cells. Aflatoxin B1, sterigmatocystin, benzo[a]pyrene, N-nitrosodiethylamine, 2-acetylaminofluorene, benzene, omeprazole and tamoxifen were tested and gave positive results. Of these, only benzo[a]pyrene was equally potent in both cell lines. Assays of tamoxifen and omeprazole included kinetochore staining. Omeprazole, but not tamoxifen, induced a significant level of kinetochore-positive micronuclei. The detection of micronucleus formation in these genetically engineered cells appears to be a rapid, eclectic and sensitive method for screening for genotoxic activity in vitro.

Removal of stainable cytoplasmic substances from cytogenetic slide preparations

A method to remove stainable cytoplasmic substances from cytogenetic preparation using RNase A treatment is reported. The preparations processed with this method are especially useful for the automated analysis of micronuclei of cultured cells with cytochalasin B and of chromosome aberrations induced by radiation.