Toxic equivalency factors (TEFs) for PCBs, PCDDs, PCDFs for humans and wildlife

An expert meeting was organized by the World Health Organization (WHO) and held in Stockholm on 15-18 June 1997. The objective of this meeting was to derive consensus toxic equivalency factors (TEFs) for polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) and dioxinlike polychlorinated biphenyls (PCBs) for both human, fish, and wildlife risk assessment. Based on existing literature data, TEFs were (re)evaluated and either revised (mammals) or established (fish and birds). A few mammalian WHO-TEFs were revised, including 1,2,3,7,8-pentachlorinated DD, octachlorinated DD, octachlorinated DF, and PCB 77. These mammalian TEFs are also considered applicable for humans and wild mammalian species. Furthermore, it was concluded that there was insufficient in vivo evidence to continue the use of TEFs for some di-ortho PCBs, as suggested earlier by Ahlborg et al. [Chemosphere 28:1049-1067 (1994)]. In addition, TEFs for fish and birds were determined. The WHO working group attempted to harmonize TEFs across different taxa to the extent possible. However, total synchronization of TEFs was not feasible, as there were orders of a magnitude difference in TEFs between taxa for some compounds. In this respect, the absent or very low response of fish to mono-ortho PCBs is most noticeable compared to mammals and birds. Uncertainties that could compromise the TEF concept were also reviewed, including nonadditive interactions, differences in shape of the dose-response curve, and species responsiveness. In spite of these uncertainties, it was concluded that the TEF concept is still the most plausible and feasible approach for risk assessment of halogenated aromatic hydrocarbons with dioxinlike properties.

Postoperative morbidity and mortality after D1 and D2 resections for gastric cancer: preliminary results of the MRC randomised controlled surgical trial. The Surgical Cooperative Group

BACKGROUND

In Japan the surgical approach to treatment of potentially curable gastric cancer, including extended lymphadenectomy, seems in retrospective surveys to give better results than the less radical procedures favoured in Western countries. There has, however, been no evidence from randomised trials that extended lymphadenectomy (D2 gastric resection) confers a survival advantage. This question was addressed in a trial involving thirty-two surgeons in Europe.

METHODS

In a prospective randomised controlled trial, D1 resection (level 1 lymphadenectomy) was compared with D2 resection (levels 1 and 2 lymphadenectomy). Central randomisation (200 patients in each arm) followed a staging laparotomy.

FINDINGS

The D2 group had greater postoperative hospital mortality (13% vs 6.5%; p=0.04 [95% Cl 9-18% for D2, 4-11% for D1] and higher overall postoperative morbidity (46% vs 28%; p<0.001); their postoperative stay was also longer. The excess postoperative morbidity and mortality in the D2 group was accounted for by distal pancreaticosplenectomy and splenectomy. In the whole group (400 patients), survival beyond three years was 30% in patients whose gastrectomy included en-bloc pancreatico-splenic resection versus 50% in the remainder.

INTERPRETATION

D2 gastric resections are followed by higher morbidity and mortality than D1 resections. These disadvantages are consequent upon additional pancreatectomies and distal splenectomies, and in long-term follow-up the higher mortality when the pancreas and spleen are resected may prove to nullify any survival benefit from D2 procedures.

The organization of replication and transcription

Models for replication and transcription often display polymerases that track like locomotives along their DNA templates. However, recent evidence supports an alternative model in which DNA and RNA polymerases are immobilized by attachment to larger structures, where they reel in their templates and extrude newly made nucleic acids. These polymerases do not act independently; they are concentrated in discrete "factories," where they work together on many different templates. Evidence for models involving tracking and immobile polymerases is reviewed.

Kinetics of core histones in living human cells: little exchange of H3 and H4 and some rapid exchange of H2B

Histones H2A and H2B form part of the same nucleosomal structure as H3 and H4. Stable HeLa cell lines expressing histones H2B, H3, and H4 tagged with green fluorescent protein (GFP) were established; the tagged molecules were assembled into nucleosomes. Although H2B-GFP was distributed like DNA, H3-GFP and H4-GFP were concentrated in euchromatin during interphase and in R-bands in mitotic chromosomes. These differences probably result from an unregulated production of tagged histones and differences in exchange. In both single cells and heterokaryons, photobleaching revealed that H2B-GFP exchanged more rapidly than H3-GFP and H4-GFP. About 3% of H2B exchanged within minutes, whereas approximately 40% did so slowly (t(1/2) approximately 130 min). The rapidly exchanging fraction disappeared in 5,6-dichloro-1-beta-d-ribofuranosylbenzimidazole and so may represent H2B in transcriptionally active chromatin. The slowly exchanging fraction was probably associated with chromatin domains surrounding active units. H3-GFP and H4-GFP were assembled into chromatin when DNA was replicated, and then >80% remained bound permanently. These results reveal that the inner core of the nucleosome is very stable, whereas H2B on the surface of active nucleosomes exchanges continually.

Visualization of focal sites of transcription within human nuclei

HeLa cells were encapsulated in agarose microbeads, permeabilized and incubated with Br-UTP in a 'physiological' buffer; then sites of RNA synthesis were immunolabelled using an antibody that reacts with Br-RNA. After extending nascent RNA chains by < 400 nucleotides in vitro, approximately 300-500 focal synthetic sites can be seen in each nucleus by fluorescence microscopy. Most foci also contain a component of the splicing apparatus detected by an anti-Sm antibody. alpha-amanitin, an inhibitor of RNA polymerase II, prevents incorporation into these foci; then, using a slightly higher salt concentration, approximately 25 nucleolar foci became clearly visible. Both nucleolar and extra-nucleolar foci remain after nucleolytic removal of approximately 90% chromatin. An underlying structure probably organizes groups of transcription units into 'factories' where transcripts are both synthesized and processed.

Visualization of replication factories attached to nucleoskeleton

HeLa cells in early S phase were encapsulated in agarose microbeads, permeabilized, and incubated with biotin-11-dUTP in a "physiological" buffer. Sites of DNA synthesis were then immunolabeled. As others have found, approximately 150 focal sites of synthesis were visible in each nucleus by light microscopy; they also contained DNA polymerase alpha and proliferating cell nuclear antigen. Electron microscopy of thick resinless sections from which approximately 90% of the chromatin had been removed revealed a similar number of dense, morphologically discrete ovoid bodies strung along a nucleoskeleton. The ovoids remained morphologically and functionally intact despite the removal of most of the chromatin. After 2.5 min of incubation with biotin-11-dUTP, the incorporated analog was associated only with ovoids; after 5 min it began to spread into the adjacent chromatin, which became extensively labeled after 1 hr. This provides visual evidence for polymerization "factories" fixed to a skeleton, with replication occurring as the template moves through them.

Evaluation of an instrument to assess the needs of patients with cancer. Supportive Care Review Group

BACKGROUND

This study aimed to assess the face, content, and construct validity and the internal reliability of a tool for assessing the generic needs of patients with cancer (the Supportive Care Needs Survey).

METHODS

A total of 1,492 consecutive patients attending the surgical, radiation, or medical oncology departments of 9 cancer treatment centers in New South Wales, Australia, were asked to participate. Of the 1,370 eligible patients, 1,354 (99%) consented to participate and 888 (65%) completed the survey. Eligible consenting patients were given a Supportive Care Needs Survey to complete at home and return by mail within 7 days.

RESULTS

In the assessment of construct validity, the principal components method of factor analysis identified 5 factors with eigenvalues greater than 1, which together accounted for 64% of the total variance (patients' needs in the domains of psychologic, health system and information, physical and daily living, patient care and support, and sexuality). Face and content validity were found to be high following pilot tests and tests of reading ease. Internal reliability coefficients (Cronbach alpha) of all 5 factor-based scales were found to be substantial, ranging from 0.87 to 0.97.

CONCLUSIONS

These findings suggest that the Supportive Care Needs Survey provides a reliable and valid index of the global needs of oncology patients. The standardized and widespread application of this instrument is recommended following further refinement and evaluation.

Active RNA polymerases are localized within discrete transcription “factories' in human nuclei

Nascent transcripts in permeabilized HeLa cells were elongated by approximately 30–2,000 nucleotides in Br-UTP or biotin-14-CTP, before incorporation sites were immunolabelled either pre- or post-embedding, and visualized by light or electron microscopy. Analogues were concentrated in approximately 2,100 (range 2,000-2,700) discrete sites attached to a nucleoskeleton and surrounded by chromatin. A typical site contained a cluster (diameter 71 nm) of at least 4, and probably about 20, engaged polymerases, plus associated transcripts that partially overlapped a zone of RNA polymerase II, ribonucleoproteins, and proteins rich in thiols and acidic groups. As each site probably contains many transcription units, these results suggest that active polymerases are confined to these sites, which we call transcription ‘factories’. Results are consistent with transcription occurring as templates slide past attached polymerases, as nascent RNA is extruded into the factories.

Coupled transcription and translation within nuclei of mammalian cells

It is widely assumed that the vital processes of transcription and translation are spatially separated in eukaryotes and that no translation occurs in nuclei. We localized translation sites by incubating permeabilized mammalian cells with [3H]lysine or lysyl-transfer RNA tagged with biotin or BODIPY; although most nascent polypeptides were cytoplasmic, some were found in discrete nuclear sites known as transcription "factories." Some of this nuclear translation also depends on concurrent transcription by RNA polymerase II. This coupling is simply explained if nuclear ribosomes translate nascent transcripts as those transcripts emerge from still-engaged RNA polymerases, much as they do in bacteria.

Supercoils in human DNA

The three-dimensional structure of a double-stranded DNA molecule may be described by distinguishing the helical turns of the DNA duplex from any superhelical turns that might be superimposed upon the duplex turns. There are characteristic changes in the hydrodynamic properties of superhelical DNA molecules when they interact with intercalating agents. The hydrodynamic properties of nuclear structures released by gently lysing human cells are changed by intercalating agents in this characteristic manner. The characteristic changes are abolished by irradiating the cells with gamma-rays but may be restored by incubating the cells at 37 degrees C after irradiation. These results are interpreted as showing that human DNA is supercoiled. A model for the structure of the chromosome is suggested.

The depletion attraction: an underappreciated force driving cellular organization

Cellular structures are shaped by hydrogen and ionic bonds, plus van der Waals and hydrophobic forces. In cells crowded with macromolecules, a little-known and distinct force—the “depletion attraction”—also acts. We review evidence that this force assists in the assembly of a wide range of cellular structures, ranging from the cytoskeleton to chromatin loops and whole chromosomes.

Outbreak of vancomycin-, ampicillin-, and aminoglycoside-resistant Enterococcus faecium bacteremia in an adult oncology unit

An outbreak of bacteremia caused by Enterococcus faecium with high-level resistance to vancomycin (MIC of > or = 256 micrograms/ml), ampicillin (MIC of > or = 64 micrograms/ml), and gentamicin or streptomycin (MIC of > or = 2,000 micrograms/ml) occurred in an adult oncology unit from June 1991 to May 1992. Active surveillance for the presence of this organism in stool or perianal cultures was begun in September 1991. Between June 1991 and May 1992, seven patients with bacteremia and 22 noninfected carriers of the organism in stool were identified. The vanA gene, tested for by PCR and gene probe, was present in all isolates evaluated. All bacteremic patients also had resistant E. faecium present in a stool or perianal culture; the stool isolates tested were closely related to the respective blood isolates as determined by pulsed-field gel electrophoresis. Antibiotic regimens using high-dose ampicillin and an aminoglycoside were ineffective with four patients. Five patients (71%) had multiple positive blood cultures; four of these patients died. Following a multiple logistic regression analysis, it was found that bacteremic patients received a significantly greater number of total antibiotic days compared with noninfected stool carriers (P = 0.019). The emergence of E. faecium with high-level resistance to vancomycin, ampicillin, and aminoglycosides underscores the importance of performing susceptibility testing on all clinically significant isolates. In the neutropenic adult oncology patient, bacteremia with this organism is of probable gastrointestinal origin, is often persistent, and is refractory to treatment with ampicillin in combination with an aminoglycoside. Prolonged use of antibiotics may predispose patients with gastrointestinal colonization to develop bacteremia.

Characterization of nuclear structures containing superhelical DNA

Structures resembling nuclei but depleted of protein may be released by gently lysing cells in solutions containing non-ionic detergents and high concentrations of salt. These nucleoids sediment in gradients containing intercalating agents in a manner characteristic of DNA that is intact, supercoiled and circular. The concentration of salt present during isolation of human nucleoids affects their protein content. When made in I-95 M NaCl they lack histones and most of the proteins characteristic of chromatin; in 1-0 M NaCl they contain variable amounts of histones. The effects of various treatments on nucleoid integrity were investigated.

Equivalence of three or four cycles of bleomycin, etoposide, and cisplatin chemotherapy and of a 3- or 5-day schedule in good-prognosis germ cell cancer: a randomized study of the European Organization for Research and Treatment of Cancer Genitourinary Tract Cancer Cooperative Group and the Medical Research Council

PURPOSE

To test the equivalence of three versus four cycles of bleomycin, etoposide, and cisplatin (BEP) and of the 5-day schedule versus 3 days per cycle in good-prognosis germ cell cancer.

PATIENTS AND METHODS

The study was designed as a 2 x 2 factorial trial. The aim was to rule out a 5% decrease in the 2-year progression-free survival (PFS) rate. The study included the assessment of patient quality of life. A cycle of BEP consisted of etoposide 500 mg/m(2), administered at either 100 mg/m(2) days 1 through 5 or 165 mg/m(2) days 1 through 3, cisplatin 100 mg/m(2), administered at either 20 mg/m(2) days 1 through 5 or 50 mg/m(2) days 1 and 2. Bleomycin 30 mg was administered on days 1, 8, and 15 during cycles 1 through 3. The randomization procedure allowed some investigators to participate only in the comparison of three versus four cycles.

RESULTS

From March 1995 until April 1998, 812 patients were randomly assigned to receive three or four cycles: of these, 681 were also randomly assigned to the 5-day or the 3-day schedule. Histology, marker values, and disease extent are well balanced in the treatment arms of the two comparisons. The projected 2-year PFS is 90.4% on three cycles and 89.4% on four cycles. The difference in PFS between three and four cycles is -1.0% (80% confidence limit [CL], -3.8%, +1.8%). Equivalence for three versus four cycles is claimed because both the upper and lower bounds of the 80% CL are less than 5%. In the 5- versus 3-day comparison, the projected 2-year PFS is 88.8% and 89.7%, respectively (difference, -0.9%, (80% CL, -4.1%, +2.2%). Hence, equivalence is claimed in this comparison also. Frequencies of hematologic and nonhematologic toxicities were essentially similar. Quality of life was maintained better in patients receiving three cycles; no differences were detected between 3 and 5 days of treatment.

CONCLUSION

We conclude that three cycles of BEP, with etoposide at 500 mg/m(2), is sufficient therapy in good-prognosis germ cell cancer and that the administration of the chemotherapy in 3 days has no detrimental effect on the effectiveness of the BEP regimen.

Numbers and organization of RNA polymerases, nascent transcripts, and transcription units in HeLa nuclei

Using HeLa cells, we have developed methods to determine 1) the number of RNA polymerases that are active at any moment, 2) the number of transcription sites, and 3) the number of polymerases associated with one transcription unit. To count engaged polymerases, cells were encapsulated in agarose, permeabilized, treated with ribonuclease, and the now-truncated transcripts extended in [32P]uridine triphosphate; then, the number of growing transcripts was calculated from the total number of nucleotides incorporated and the average increment in length of the transcripts. Approximately 15, 000 transcripts were elongated by polymerase I, and approximately 75,000 were elongated by polymerases II and III. Transcription sites were detected after the cells were grown in bromouridine for <2.5 min, after which the resulting bromo-RNA was labeled with gold particles; electron microscopy showed that most extranucleolar transcripts were concentrated in approximately 2400 sites with diameters of approximately 80 nm. The number of polymerases associated with a transcription unit was counted after templates were spread over a large area; most extranucleolar units were associated with one elongating complex. These results suggest that many templates are attached in a "cloud" of loops around a site; each site, or transcription "factory," would contain approximately 30 active polymerases and associated transcripts.

Lamin proteins form an internal nucleoskeleton as well as a peripheral lamina in human cells

The nuclear lamina forms a protein mesh that underlies the nuclear membrane. In most mammalian cells it contains the intermediate filament proteins, lamins A, B and C. As their name indicates, lamins are generally thought to be confined to the nuclear periphery. We now show that they also form part of a diffuse skeleton that ramifies throughout the interior of the nucleus. Unlike their peripheral counterparts, these internal lamins are buried in dense chromatin and so are inaccessible to antibodies, but accessibility can be increased by removing chromatin. Knobs and nodes on an internal skeleton can then be immunolabelled using fluorescein- or gold-conjugated anti-lamin A antibodies. These results suggest that the lamins are misnamed as they are also found internally.

The transcription cycle of RNA polymerase II in living cells

RNA polymerase II transcribes most eukaryotic genes. Its catalytic subunit was tagged with green fluorescent protein and expressed in Chinese hamster cells bearing a mutation in the same subunit; it complemented the defect and so was functional. Photobleaching revealed two kinetic fractions of polymerase in living nuclei: approximately 75% moved rapidly, but approximately 25% was transiently immobile (association t1/2 approximately 20 min) and transcriptionally active, as incubation with 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole eliminated it. No immobile but inactive fraction was detected, providing little support for the existence of a stable holoenzyme, or the slow stepwise assembly of a preinitiation complex on promoters or the nuclear substructure. Actinomycin D decreased the rapidly moving fraction, suggesting that engaged polymerases stall at intercalated molecules while others initiate. When wild-type cells containing only the endogenous enzyme were incubated with [3H]uridine, nascent transcripts became saturated with tritium with similar kinetics (t1/2 approximately 14 min). These data are consistent with a polymerase being mobile for one half to five sixths of a transcription cycle, and rapid assembly into the preinitiation complex. Then, most expressed transcription units would spend significant times unassociated with engaged polymerases.

The unmet supportive care needs of patients with cancer. Supportive Care Review Group

BACKGROUND

The aim of this study was to determine the prevalence and predictors of the perceived unmet needs of cancer patients undergoing treatment for their disease at public treatment centers.

METHODS

A total of 1,492 consecutive patients attending the surgical, radiation, or medical oncology departments of 9 major public cancer treatment centers in New South Wales, Australia, were asked to participate. Of the 1,370 eligible patients, 1,354 (99%) consented to participate and 888 (65%) returned completed surveys. Eligible consenting patients were given a Supportive Care Needs Survey to complete at home and return by mail within 7 days.

RESULTS

Patients' perceived needs were assessed across the following five areas: psychologic, health system and information, physical and daily living, patient care and support, and sexuality. Patients' perceived needs were highest in the psychologic, health system and information, and physical and daily living domains. Logistic regression modeling revealed subgroups of patients with different types of needs. The significant predictors of reporting some unmet need for help varied according to the domain examined.

CONCLUSIONS

This statewide study shows that cancer patients experience high levels of unmet needs across the range of domains examined. The study provides information that may be valuable in identifying areas where interventions could be tested and evaluated in an attempt to address the unmet needs of people living with cancer.

Regional specialization in human nuclei: visualization of discrete sites of transcription by RNA polymerase III

Mammalian nuclei contain three different RNA polymerases defined by their characteristic locations and drug sensitivities; polymerase I is found in nucleoli, and polymerases II and III in the nucleoplasm. As nascent transcripts made by polymerases I and II are concentrated in discrete sites, the locations of those made by polymerase III were investigated. HeLa cells were lysed with saponin in an improved 'physiological' buffer that preserves transcriptional activity and nuclear ultrastructure; then, engaged polymerases were allowed to extend nascent transcripts in Br-UTP, before the resulting Br-RNA was immunolabelled indirectly with fluorochromes or gold particles. Biochemical analysis showed that approximately 10 000 transcripts were being made by polymerase III at the moment of lysis, while confocal and electron microscopy showed that these transcripts were concentrated in only approximately 2000 sites (diameter approximately 40 nm). Therefore, each site contains approximately five active polymerases. These sites contain specific subunits of polymerase III, but not the hyperphosphorylated form of the largest subunit of polymerase II. The results indicate that the active forms of all three nuclear polymerases are concentrated in their own dedicated transcription sites or 'factories', suggesting that different regions of the nucleus specialize in the transcription of different types of gene.

A model for all genomes: the role of transcription factories

A model for all genomes involving one major architectural motif is presented: DNA or chromatin loops are tethered to "factories" through the transcription machinery-a polymerase (active or inactive) or its transcription factors (activators or repressors). These loops appear and disappear as polymerases initiate and terminate (and as factors bind and dissociate), so the structure is ever-changing and self-organizing. This model is parsimonious, detailed (and so easily tested), and incorporates elements found in various other models.

Conformational constraints in nuclear DNA

We have investigated DNA superstructure in a wide range of nuclei of higher cells by gently lysing cells to release structures that resemble nuclei but are depleted of nuclear proteins. The sedimentation properties of these structures, which we call nucleoids, have been examined in sucrose gradients containing the intercalating agent, ethidium. The sedimentation rate of nucleoids derived from the growing cells of mammals, birds, amphibians and insects varies in the manner characteristic of circular and superhelical molecules of DNA. These characteristic changes in sedimentation rate are abolished by irradiating the nucleoids with low doses of gamma-rays, a procedure known to introduce single-strand scissions into DNA. We have also investigated by similar means DNA superstructure in nucleoids derived from a variety of different chick cells. Nucleoids derived from adult hen erythrocytes differ from the other nucleoids studied in that their sedimentation rate does not vary in the manner characteristic of supercoiled DNA.