On-Disc Observations of Flux Rope Formation Prior to Its Eruption

Coronal mass ejections (CMEs) are one of the primary manifestations of solar activity and can drive severe space weather effects. Therefore, it is vital to work towards being able to predict their occurrence. However, many aspects of CME formation and eruption remain unclear, including whether magnetic flux ropes are present before the onset of eruption and the key mechanisms that cause CMEs to occur. In this work, the pre-eruptive coronal configuration of an active region that produced an interplanetary CME with a clear magnetic flux rope structure at 1 AU is studied. A forward-S sigmoid appears in extreme-ultraviolet (EUV) data two hours before the onset of the eruption (SOL2012-06-14), which is interpreted as a signature of a right-handed flux rope that formed prior to the eruption. Flare ribbons and EUV dimmings are used to infer the locations of the flux rope footpoints. These locations, together with observations of the global magnetic flux distribution, indicate that an interaction between newly emerged magnetic flux and pre-existing sunspot field in the days prior to the eruption may have enabled the coronal flux rope to form via tether-cutting-like reconnection. Composition analysis suggests that the flux rope had a coronal plasma composition, supporting our interpretation that the flux rope formed via magnetic reconnection in the corona. Once formed, the flux rope remained stable for two hours before erupting as a CME.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (doi:10.1007/s11207-017-1093-4) contains supplementary material, which is available to authorized users.

Characterization of accelerated iron-ion-induced damage in gap junction-competent and -incompetent thyroid follicular cells

Early- and late-passage cultures of Fischer rat thyroid cells differ in their growth properties and gap junction competency. Previous studies comparing early- and late-passage cultures exposed to gamma rays and proton beams revealed that differences in growth rate did not influence their responses; however, the presence of connexin 32 gap junctions conferred resistance to gamma radiation. To further assess differences in radiation quality, suspension cultures of early- and late-passage cells were exposed to accelerated iron ions, and their comparative biological responses were measured. The iron-ion-irradiated cells displayed sustained levels of incorporated dUTP, reflecting persistent DNA damage. These results were supported by the frequency of chromosomal damage measured by micronucleus formation. Iron-ion irradiation induced micronuclei at a rate of eight per gray per 100 binucleated cells scored in early-passage cells and nine per gray per 100 binucleated cells scored in late-passage cells. Relative to photons, the calculated radiobiological effectiveness for frequency of micronuclei was 5.7 and 6.4 for the early- and late-passage cultures, respectively (P > 0.05). Levels of apoptosis fluctuated as a function of dose, and modest increases above basal levels persisted throughout the 48-h period. The comparison of retained follicular structures revealed differences in the alpha components of the linear-quadratic dose-response curves (0.60 Gy(-1) for early-passage and 0.71 Gy(-1) for late-passage cultures, P < 0.014). Cell cycle phase redistribution resulted in a G2 arrest (P < 0.001) for both early- and late-passage cultures. In conclusion, the response of thyroid follicular cells to high-LET radiation was not influenced by the presence of gap junctions or the proliferative status of the target cells.

Thyrocytes isolated from autoimmune-diseased thyroids secrete soluble tumor necrosis factor-R1 that is related to their elevated protein kinase C activity

Soluble tumor necrosis factor (TNF)-alpha receptors have the potential to modulate TNF-alpha activity during autoimmune thyroiditis. In this study we examined cell-surface TNF-alpha receptors and soluble TNF-alpha receptor production by thyrocytes from normal and MRL-lpr(-/-) (diseased) mice, which spontaneously develop autoimmune thyroiditis. We found that murine thyrocytes possess the 55-kd receptor (TNF-R1). Examination of soluble TNF-R1 production revealed that diseased thyrocytes produced sevenfold more soluble TNF-R1 than normal thyrocytes. Furthermore, basal protein kinase C (pKC) activity in diseased thyrocytes was 67% higher than that found in normal murine thyrocytes. The elevated basal pKC activity in diseased thyrocytes was related to their enhanced production of soluble TNF-R1 because inhibition of pKC activity with calphostin C caused soluble TNF-R1 production to decrease significantly. Additionally, soluble TNF-R1 production by murine thyrocytes was not a result of cell-surface receptor shedding but through secretion of a truncated version of TNF-R1. This was evident when cell-surface TNF-R1 levels were unchanged after treatment of diseased thyrocytes with calphostin C. Also, the 28-kd form of TNF-R1, which corresponds to the soluble receptor, was present in the intracellular membranes of the diseased thyrocytes.

Response of thyroid follicular cells to gamma irradiation compared to proton irradiation: II. The role of connexin 32

The objective of this study was to determine whether connexin 32-type gap junctions contribute to the "contact effect" in follicular thyrocytes and whether the response is influenced by radiation quality. Our previous studies demonstrated that early-passage follicular cultures of Fischer rat thyroid cells express functional connexin 32 gap junctions, with later-passage cultures expressing a truncated nonfunctional form of the protein. This model allowed us to assess the role of connexin 32 in radiation responsiveness without relying solely on chemical manipulation of gap junctions. The survival curves generated after gamma irradiation revealed that early-passage follicular cultures had significantly lower values of alpha (0.04 Gy(-1)) than later-passage cultures (0.11 Gy(-1)) (P < 0.0001, n = 12). As an additional way to determine whether connexin 32 was contributing to the difference in survival, cultures were treated with heptanol, resulting in higher alpha values, with early-passage cultures (0.10 Gy(-1)) nearly equivalent to untreated late-passage cultures (0.11 Gy(-1)) (P > 0.1, n = 9). This strongly suggests that the presence of functional connexin 32-type gap junctions was contributing to radiation resistance in gamma-irradiated thyroid follicles. Survival curves from proton-irradiated cultures had alpha values that were not significantly different whether cells expressed functional connexin 32 (0.10 Gy(-1)), did not express connexin 32 (0.09 Gy(-1)), or were down-regulated (early-passage plus heptanol, 0.09 Gy(-1); late-passage plus heptanol, 0.12 Gy(-1)) (P > 0.1, n = 19). Thus, for proton irradiation, the presence of connexin 32-type gap junctional channels did not influence their radiosensitivity. Collectively, the data support the following conclusions. (1) The lower alpha values from the gamma-ray survival curves of the early-passage cultures suggest greater repair efficiency and/or enhanced resistance to radiation-induced damage, coincident with the expression of connexin 32-type gap junctions. (2) The increased sensitivity of FRTL-5 cells to proton irradiation was independent of their ability to communicate through connexin 32 gap junctions. (3) The fact that the beta components of the survival curves from both gamma rays and proton beams were similar (average 0.022 +/- 0.008 Gy(-2), P > 0.1, n = 39) suggests that at higher doses the loss of viability occurs at a relatively constant rate and is independent of radiation quality and the presence of functional gap junctions.

Research activities at the Loma Linda University and Proton Treatment Facility--an overview

The Loma Linda University (LLU) Radiobiology Program coordinates basic research and proton beam service activities for the university and extramural communities. The current focus of the program is on the biological and physical properties of protons and the operation of radiobiology facilities for NASA-sponsored projects. The current accelerator, supporting facilities and operations are described along with a brief review of extramural research projects supported by the program. These include space craft electronic parts and shielding testing as well as tumorigenesis and animal behavior experiments. An overview of research projects currently underway at LLU is also described. These include: 1) acute responses of the C57Bl/6 mouse immune system, 2) modulation of gene expression in the nematode C. elegans and rat thyroid cells, 3) quantitation of dose tolerance in rat CNS microvasculature, 4) behavioral screening of whole body proton and iron ion-irradiated C57Bl/6 mice, and 5) investigation of the role of cell integration into epithelial structures on responses to radiation.

Circulating antibodies to guanosine in systemic lupus erythematosus: correlation with nephritis and polyserositis by acute and longitudinal analyses

Systemic lupus erythematosus (SLE) is characterized by autoantibodies, including antibodies to the nucleosides of DNA. Guanosine is the most immunogenic nucleoside. In this study serum antiguanosine antibody levels were compared with disease activity, determined by their SLEDI score, in 86 patients with SLE. Sera from these patients were tested, by ELISA, for autoantibodies to guanosine, single-stranded DNA (ssDNA), and double-stranded DNA (dsDNA). Anti-double-stranded DNA levels were also measured by RIA. Resultant values from these assays were correlated with SLE disease activity, and compared with specific features of SLE. The strongest correlation was higher levels of antiguanosine antibodies in patients with active lupus nephritis and polyserositis compared to patients with inactive disease (P < 0.0001). Antiguanosine levels also correlated with arthritis (P < 0.006), CNS lupus (P < 0.005), and hematologic manifestations of SLE (P < 0.002). To test the validity of this association in chronic SLE, serum antiguanosine antibodies were measured in patients with SLE at various phases of disease activity. Twelve patients with SLE had serum samples drawn at active, active-improved, and inactive phases over a 3-7 y period. Differences were significant for serum antiguanosine antibodies in the active group compared to the inactive group (P < 0.05) and the active vs the active-improved group (P < 0.02), unlike those for dsDNA and ssDNA by ELISA or RIA. Antiguanosine antibodies correlated more closely with disease activity in SLE patients in this longitudinal study than either anti-dsDNA or ssDNA antibodies. Thus, antibodies to guanosine correlated as well or better with disease activity than the other anti-DNA antibodies measured and should be considered to contribute to the pathology of SLE, especially lupus nephritis.

Evaluation of polysaccharopeptide effects against C6 glioma in combination with radiation

Long-term control of high-grade brain tumors is rarely achieved with current therapeutic regimens. The major goal of this study was to determine whether polysaccharopeptide (PSP), a crude polysaccharide peptide extract derived from Coriolus versicolor, a fungus, could enhance the effects of radiation against glioma cells in culture and in xenografted tumors in vivo. PSP significantly augmented radiation-induced damage to C6 rat glioma cells in vitro. Nude mice injected subcutaneously with the C6 cells were treated with PSP (injected intraperitoneally at 2 mg/injection) and radiation (2 Gy/fraction, 8 Gy in total) using three different time-dose protocols. Tumor volumes were consistently smaller in all treated groups compared to the non-treated tumor-bearing controls except in one group which received PSP prior to tumor implantation. The administration of radiation alone resulted in the slowest tumor progression, whereas PSP alone had no effect. Furthermore, PSP in combination with radiation treatment did not increase radiation efficacy. Natural killer cell, lymphocyte and granulocyte counts in blood and spleen were significantly higher in PSP-treated animals, demonstrating that PSP has protective effects on immunological function. Collectively, these results warrant further investigation to determine if PSP can be effectively utilized to upregulate immune responsiveness in case of neoplasia and other diseases in which immunosuppression is a prominent feature.

A spontaneously arising mutation in connexin32 with repeated passage of FRTL-5 cells coincides with increased growth rate and reduced thyroxine release

In this study we examine changes in the cellular properties of FRTL-5 cells as a function of passage number, with particular emphasis on gap junction expression, karyotype, morphology, growth rate and thyroxine (T(4)) release. Early passage FRTL-5 follicular cells transfer dye through gap junctions from injected cell(s) to third-order neighboring cells and beyond within their respective follicles and have immuno-detectable connexin32 (Cx32) type gap junctional plaques in their lateral contacting plasma membranes. By contrast, FRTL-5 cells established as monolayers, or as follicles from cultures passed more than 15 times, did not transfer microinjected Lucifer Yellow dye to contiguous neighboring cells and did not express any immuno-detectable rat thyroid specific connexins (Cx43, Cx32 or Cx26). Western blots confirmed that total, membrane and cytosolic Cx32 protein was present only in early pass follicular cultures. To better understand the passage-dependent loss of Cx32 expression, RT-PCR primers were made to the most unique sequences of the rat Cx32 molecule, the cytoplasmic and carboxyl-terminal regions. These primers were used to screen FRTL-5 RNA from cultures of various passage numbers. The results revealed that later passage cultures had a single base deletion in the middle of the Cx32 cytoplasmic loop region at nucleotide position 378. This base deletion was in the middle position of the codon for amino acid 116, which is normally a CAC (histidine) but read with the frame shift was a CCC (proline). The four amino acids that followed this deletion were also altered with the fourth one becoming UAA, the ochre translation stop codon. This premature stopping of translation resulted in a truncation of 60% of the protein, which included the remaining cytoplasmic loop, third and fourth transmembrane regions and the carboxyl-terminus. The later passage cultures did not produce a carboxyl-terminal RT-PCR product, indicating that the mRNA was also truncated. These regions of the Cx32 molecule contain the sequences and epitopes to which probes and antibodies are directed, and as such alterations of these regions with repeated passage explains reports by others that FRTL-5 cells do not express Cx32, and implies that cultures used for these assessments were passed more than 15 times. To determine if genetic or epigenetic abnormalities existed in FRTL-5 cells we performed chromosome spreads from various passage cultures. FRTL-5 cells have been reported to be diploid and more recently non-diploid; however, we found them to be fully tetraploid. This tetraploidy appears to be unstable in that later passes are tetraploid plus two or three extra chromosomes. There were no obvious translocations, breaks or large-scale interstitial deletions of any chromosomes in the FRTL-5 cultures tested. As FRTL-5 cells were repeatedly passed their morphology changed. Monolayer areas spread from beneath the follicles, and the follicles became flattened in appearance. These physical changes were coincident with dramatically increased growth rates. Early cultures (passed 3-12 times) divided on average every 49+/-1 h, whereas later passes (passes 20-25) divided every 28+/-3 h. To correlate these changes with a measure of thyroid function we assayed T(4) output. Early passage follicular cultures incubated for 6 h with sodium iodide, released on average 5.27+/- 0.33 ng/ml of T(4)/100 follicles. Later passes, or early passes treated with heptanol to down-regulate Cx32, released an average of 3.84+/-0.50 ng/ml of T(4)/100 follicles. There was a 27% difference in T(4) release between early follicular cultures, that were coupled by Cx32, and late or down-regulated early follicular cultures, that were uncoupled (P<0.0001). Collectively, the physical changes documented in this study were coincident with the loss of functional Cx32. This implies a relationship between the loss of intercellular communication and changes in morphogenic appearance, growth rate and reduced thyroid function and supports the previously postulated, tumor-suppressor role for Cx32. FRTL-5 cultures from low passage numbers are an excellent model of primary thyroid cells. However, many reports in the literature ascribe features to FRTL-5 cells that are mutually inconsistent. These differences may be resolved in the future by addressing the passage number and the conditional differences of the cultures being studied.

Response of thyroid follicular cells to gamma irradiation compared to proton irradiation. I. Initial characterization of DNA damage, micronucleus formation, apoptosis, cell survival, and cell cycle phase redistribution

The RBE of protons has been assumed to be equivalent to that of photons. The objective of this study was to determine whether radiation-induced DNA and chromosome damage, apoptosis, cell killing and cell cycling in organized epithelial cells was influenced by radiation quality. Thyroid-stimulating hormone-dependent Fischer rat thyroid cells, established as follicles, were exposed to gamma rays or proton beams delivered acutely over a range of physical doses. Gamma-irradiated cells were able to repair DNA damage relatively rapidly so that by 1 h postirradiation they had approximately 20% fewer exposed 3' ends than their counterparts that had been irradiated with proton beams. The persistence of free ends of DNA in the samples irradiated with the proton beam implies that either more initial breaks or a quantitatively different type of damage had occurred. These results were further supported by an increased frequency of chromosomal damage as measured by the presence of micronuclei. Proton-beam irradiation induced micronuclei at a rate of 2.4% per gray, which at 12 Gy translated to 40% more micronuclei than in comparable gamma-irradiated cultures. The higher rate of micronucleus formation and the presence of larger micronuclei in proton-irradiated cells was further evidence that a qualitatively more severe class of damage had been induced than was induced by gamma rays. Differences in the type of damage produced were detected in the apoptosis assay, wherein a significant lag in the induction of apoptosis occurred after gamma irradiation that did not occur with protons. The more immediate expression of apoptotic cells in the cultures irradiated with the proton beam suggests that the damage inflicted was more severe. Alternatively, the cell cycle checkpoint mechanisms required for recovery from such damage might not have been invoked. Differences based on radiation quality were also evident in the alpha components of cell survival curves (0.05 Gy(-1) for gamma rays, 0.12 Gy(-1) for protons), which suggests that the higher level of survival of gamma-irradiated cells could be attributed to the persistence of nonlethally irradiated thyrocytes and/or the capacity to repair damage more effectively than cells exposed to equal physical doses of protons. The final assessment in this study was radiation-induced cell cycle phase redistribution. Gamma rays and protons produced a similar dose-dependent redistribution toward a predominantly G(2)-phase population. From our cumulative results, it seems likely that a majority of the proton-irradiated cells would not continue to divide. In conclusion, these findings suggest that there are quantitative and qualitative differences in the biological effects of proton beams and gamma rays. These differences could be due to structured energy deposition from the tracks of primary protons and the associated high-LET secondary particles produced in the targets. The results suggest that a simple dose-equivalent approach to dosimetry may be inadequate to compare the biological responses of cells to photons and protons.

Impact of patient characteristics, complications, and facility volume on the costs and time of cardiac catheterization and coronary angioplasty in 70 catheterization laboratories

Although over 1 million procedures are performed in cardiac catheterization laboratories (CCLs) annually, little comparative data exist on costs or resource use in these settings. In this study, data from 70 CCLs were used to profile CCL times and total direct costs for 2 high-volume procedures: left heart catheterization (LHC) and percutaneous transluminal coronary angioplasty (PTCA) with or without stent placement. In total, 70,677 consecutive patient examinations for a 12-month period from January 1, 1998 to December 31, 1998 were analyzed. For LHC mean total direct costs averaged $306, whereas for PTCA catheterization laboratory costs averaged $3,172. The average total times for these procedures were 63 and 108 minutes, respectively. Seventy-two percent of the PTCA patients underwent coronary stenting with an associated incremental cost of $1,244. By multivariate linear regression, baseline patient characteristics such as age, gender, and clinical factors had little impact on total time and total costs. The major determinants of CCL time and cost were procedural factors (e.g., number and type of interventions) and in-lab complications, including profound hypotension, abrupt vessel closure, and emergency bypass surgery. Using facility procedure volume as a proxy for potential economies of scale, we found no relation between CCL volume and total direct CCL costs. There did appear to be a significant inverse relation between facility volume and total procedural time with CCLs that performed the highest volumes of LHC and PTCA procedures saving an average of 5 to 9 minutes per procedure. These findings may be useful in defining specific time and cost benchmarks for these commonly performed procedures and serve to underscore the critical role of reducing complications in both quality improvement and cost-saving efforts.

Distribution and activation of uterine mononuclear phagocytes in peripartum endometrium and myometrium of the mouse

The present study tested the hypothesis that macrophage distribution and activation are enhanced in the uterus before term. Mid-uterine horn tissue strips from mice on Days 15 and 18 of pregnancy, the day of birth (= Day 19), and one day postpartum were paraffin-embedded and then sectioned, stained with a monoclonal pan-macrophage marker (BM8), and processed for visualization and quantification of resident macrophages per nuclear area. Macrophages were dispersed throughout the endometrium and subluminal epithelium; cell numbers declined on the day before term, then increased postpartum. Within myometrium, macrophages congregated in stroma surrounding muscle bundles, and staining was enhanced near term. Macrophage numbers were similar in pregnant and postpartum uteri, enhanced more than 2-fold over those in nonpregnant controls. Uterine sections were also analyzed by laser-scanning cytometry to enumerate activated macrophages (i.e., those that express the intercellular adhesion molecule marker CD54+) and to determine cell cycle (propidium iodide fluorescence). Activated macrophages were directly proportional to cell numbers and, by cell cycle analysis, were not terminally differentiated. Highest cell numbers occurred on Day 15: 4-fold greater than those in nonpregnant controls and 2-fold higher than those at Day 18 or in postpartum groups. These findings indicate a decline in endometrial macrophage numbers at least one day before the onset of parturition and raise the possibility that trafficking of this immune cell may contribute to onset of labor.

P-glycoprotein and multidrug resistance-associated protein, but not lung resistance protein, lower the intracellular daunorubicin accumulation in acute myeloid leukaemic cells

The in vitro intracellular daunorubicin accumulation (IDA) of blast cells from 69 patients with newly diagnosed acute myeloid leukaemia (AML) was correlated with the expression and functional activity of the multidrug resistance (MDR) proteins, P-glycoprotein (Pgp), multidrug resistance-associated protein (MRP) and lung-resistance protein (LRP). An inverse and significant association was found between IDA and Pgp-related efflux activity (r = -0.31, P = 0.01) and also MRP (r = -0.25, P = 0.04) but not with LRP (r = -0.13, P = 0.28). Coexpression of the MDR proteins had an additive effect in further lowering of IDA levels, suggesting that the clinical MDR phenotype is dependent on the sum of multiple MDR factors available to the leukaemic cell. Thus, the median IDA of leukaemic cells without any MDR proteins was significantly higher than that of blasts carrying two MDR proteins (0.466 vs. 0.296, P = 0.046). Seven patients with no expression of Pgp, MRP and LRP still had low IDA levels, suggesting the presence of efflux MDR mechanisms other than those studied. The relation of IDA to clinical parameters known to be associated with poor prognosis, such as age, secondary AML, karyotype, peripheral blood blast and CD34 counts, was also studied, but no significance was found on multifactorial analysis. There was a non-significant trend for earlier relapse in patients with low IDA levels (leukaemia-free survival of 16.3 months compared with 21.1 months in patients with high IDA levels). Our data suggest that, while the IDA assay is a quick and relatively easy test for the combined efflux MDR phenotype, it is unable to detect other MDR mechanisms, such as LRP, which may be important to the clinical outcome of patients with AML.

Benchmarking cardiac catheterization laboratories: the impact of patient age, gender and risk factors on variable costs, device costs, total time and procedural time in 53 catheterization laboratories

Coronary catheterization laboratories (CCLs) are the cornerstones of the delivery system for many cardiovascular procedures performed in the United States. However, few comprehensive data exist benchmarking physician activities in CCLs. This study benchmarks cost and time data on 82,548 consecutive patient encounters in 53 CCLs for the 18-month period of January 1997 through June 1998. The data are compiled from the OEP program, a relational database developed by Boston Scientific/Scimed (Maple Grove, Minnesota) for use in CCLs. CCL productivity (total time and procedure time) and cost (variable costs and device costs) benchmarks are created for: 1) left heart catheterization; 2) right and left heart catheterization; 3) percutaneous transluminal coronary balloon angioplasty (PTCA); 4) atherectomy; and 5) coronary stents. Results show the variable costs (those costs that vary in direct proportion to changes in CCL activities) for the five procedures are: $308, left heart catheterization; $395, right and left heart catheterization; $841, PTCA; $2,768, atherectomy; and $3,186, coronary stent. These variable costs are lower than the typical average costs reported for these procedures because they do not include hospital, laboratory, and physician costs, only the procedure-specific activity-related costs most directly controlled and/or influenced by CCL physicians or administrators. The total time for the left heart catheterization averaged 64 minutes and 84 minutes for the right and left heart catheterization, respectively, and procedural times averaged 25 and 32 minutes, respectively. For the major interventional procedures N PTCA, atherectomy, and coronary stents, total times averages were 102, 135, and 117 minutes, respectively. Procedural times for these procedures averaged between 60 and 65 percent of the total time. The major implications of these findings are discussed and limitations noted.

A case-control study of childhood leukemia in southern Ontario, Canada, and exposure to magnetic fields in residences

A population-based case-control study was conducted in Ontario, Canada, to assess the relation between the risk of childhood leukemia and residential exposure to magnetic fields. Participating subjects consisted of 201 cases, diagnosed at 0 to 14 years of age during 1985-1993, ascertained from the records at the Hospital for Sick Children (Toronto), and 406 individually matched controls. Where possible, point-in-time measurements of magnetic fields were made in all residences occupied by subjects during the period of inquiry in the defined catchment area. Three different classification schemes of wire code were assigned to each residence. Detailed information was collected by interviewer-administered questionnaires, which enabled risk estimates to be adjusted for socio-economic characteristics, medical history of parent(s) and child and environmental exposures. Inconsistent elevations in risk were associated with time-weighted averages of magnetic fields both inside and outside the home for subjects having residential point-in-time measurements that represented at least 70% of their etiological period. These risks increased in magnitude when analysis was restricted to children under 6 years of age at diagnosis or to those with acute lymphoblastic leukemia. For children younger than 6 years at diagnosis, outside perimeter measurements of the residence, > or = 0.15 microT, were associated with increased leukemia risk (OR = 3.45, 95% CI = 1.14-10.45). Evaluation of different exposure times for point-in-time magnetic field measurements and wire configuration suggested that exposures earliest in the etiological period were associated with greater risks for children diagnosed at a younger age (OR = 2.50, 95% CI = 1.14-5.49). Our findings did not support an association between leukemia and proximity to power lines with high current configuration.

Childhood leukemia and personal monitoring of residential exposures to electric and magnetic fields in Ontario, Canada

OBJECTIVES

To evaluate the risk of childhood leukemia in relation to residential electric and magnetic field (EMF) exposures.

METHODS

A case control study based on 88 cases and 133 controls used different assessment methods to determine EMF exposure in the child's current residence. Cases comprised incident leukemias diagnosed at 0-14 years of age between 1985-1993 from a larger study in southern Ontario; population controls were individually matched to the cases by age and sex. Exposure was measured by a personal monitoring device worn by the child during usual activities at home, by point-in-time measurements in three rooms and according to wire code assigned to the child's residence.

RESULTS

An association between magnetic field exposures as measured with the personal monitor and increased risk of leukemia was observed. The risk was more pronounced for those children diagnosed at less than 6 years of age and those with acute lymphoblastic leukemia. Risk estimates associated with magnetic fields tended to increase after adjusting for power consumption and potential confounders with significant odds ratios (OR) (OR: 4.5, 95% confidence interval (CI): 1.3-15.9) observed for exposures > or = 0.14 microTesla (microT). For the most part point-in-time measurements of magnetic fields were associated with non-significant elevations in risk which were generally compatible with previous research. Residential proximity to power lines having a high current configuration was not associated with increased risk of leukemia. Exposures to electric fields as measured by personal monitoring were associated with a decreased leukemia risk.

CONCLUSIONS

The findings relating to magnetic field exposures directly measured by personal monitoring support an association with the risk of childhood leukemia. As exposure assessment is refined, the possible role of magnetic fields in the etiology of childhood leukemia becomes more evident.

Prostaglandin E2 regulates vitamin D receptor expression, vitamin D-24-hydroxylase activity and cell proliferation in an adherent human myeloid leukemia cell line (Ad-HL60)

The effects of prostaglandin E2, forskolin, and phorbol 12-myristate 13-acetate on cell proliferation, cell surface antigen expression, vitamin D-24-hydroxylase activity and vitamin D receptor (VDR) expression have been studied in an adherent variant (Ad-HL60) of the human HL60 promyelomonocytic leukemia cell line. Ad-HL60 cells have a more differentiated phenotype than the nonadherent HL60 cells from which they were derived and, unlike the parent cell line, constitutively express vitamin D-24-hydroxylase activity. Treatment of Ad-HL60 cells with 1 microM PGE2 resulted in a decrease in the rate of cell proliferation (cell numbers were approximately 23% of control values after 72 h treatment), a change in expression of leukocyte surface antigens (decreased CD13 and CD14, increased CD11b and CD49d expression), an increase in the synthesis of 24,25-dihydroxyvitamin D3 from substrate 25-hydroxyvitamin D3 (control 5.76 +/- 0.17, 72 h PGE2-treated cells 12.10 +/- 1.90 pmol/h/10(6) cells), and an increase in receptors for the active metabolite of vitamin D, 1 alpha,25-dihydroxyvitamin D3, from 3910 to 11285 receptors per cell in control and 7-day treated cells, respectively. Prostaglandin E2 may be acting via a mechanism involving cyclic AMP in these cells, as we have also demonstrated that 10 microM forskolin, an adenylate cyclase activator, has similar effects. Phorbol 12-myristate 13-acetate had little effect on any of the parameters measured in this cell line.

Overexpression of lung-resistance protein and increased P-glycoprotein function in acute myeloid leukaemia cells predict a poor response to chemotherapy and reduced patient survival

We investigated the role of the drug resistance-related proteins LRP, MRP and Pgp and the apoptotic suppressor, bcl-2, in relation to other clinical characteristics, with respect to response and survival in 91 patients with newly diagnosed AML, treated with standard chemotherapy. Multivariate analysis showed that poor response to chemotherapy was associated with increasing age (P=0.0004), LRP expression (P=0.0001) and Pgp function (P=0.015). The significant predictors of both leukaemia-free survival (LFS) and overall survival (OS) were LRP (LFS, P=0.01; OS, P=0.0001), Pgp function (LFS, P=0.0001; OS, P=0.0003) and cytogenetic abnormalities (LFS, P=0.0001; OS. P=0.0005). Patients with the lowest expression of LRP and Pgp function and favourable karyotype (group I) had an LFS of 30.2 months compared to 8 5 months in the group with the highest expression of LRP and Pgp and poor prognosis karyotype (group III, P=0.002). OS decreased from 75.4 months in group I to 7.9 months in group III patients (P <0.0001). Neither MRP nor bcl-2 were significantly associated with chemotherapy response and survival. Correlations were found between increasing expression of LRP and older age (P=0.05) and an unfavourable karyotype (P=0.005), but these variables were independent of each other in analysis of treatment response and patient survival. Our findings suggest that both LRP and Pgp are clinically relevant drug-resistance proteins and it may be necessary to modulate both LRP and Pgp functions in order to reverse the multidrug resistance phenotype in AML.

Elevation of protein kinase C in thyrocytes isolated from a Lewis rat model of autoimmune thyroiditis prevents assembly of immunodetectable connexin43 gap junctions and reduces intercellular communication

In the Lewis rat model of experimental autoimmune thyroiditis (EAT), decreased immunodetectable connexin assembly into gap junctions and diminished intercellular communication are associated with the loss of thyroid function (hypothyroidism) that occurs prior to significant tissue destruction. The current study explores the hypothesis that the loss of connexin 43 (Cx43)-mediated intercellular communication in these cells is caused by upregulation of protein kinase C (pKC) activity. Thyrocytes isolated from EAT rats exhibited a 78% increase in basal pKC activity; whereas, basal protein kinase A (pKA) activity was unchanged. Increased pKC activity was a result of increased isozyme protein levels. Thyroid cells expressed pKC isozymes gamma and lambda and had elevated levels of alpha (40%), beta (30%), delta (31%), and epsilon (25%) as quantified by western blot analyses. Furthermore, modulation of pKC activity inversely altered Cx43 assembly and function in monolayer thyrocytes. For example, octoacetyl glycerol (OAG) treatment of normal thyrocyte monolayers to increase pKC activity resulted in deficient Cx43 gap junction assembly and reduced intercellular communication indistinguishable from the deficits in EAT thyrocytes. Conversely, calphostin C inhibition of pKC activity in EAT thyrocyte monolayers restored these parameters to normal. Thus, pharmacological modulations of pKC activity in cultured thyrocytes support a causal relation between the changes in pKC activity and Cx43-mediated intercellular communication. Abnormalities in autoimmune diseased thyroid tissue (eg, increased pKC) appear to contribute to reduced intercellular coordination of thyroid follicles and thereby can affect subsequent thyroid function. The persistence of target cell abnormalities in the absence of infiltrating lymphocytes and their products supports an alternative mechanism by which thyroid function can be affected that does not depend on the loss of thyroid glandular epithelium.

Risk of congenital anomalies in children of parents occupationally exposed to low level ionising radiation

OBJECTIVES

To evaluate the risk of having a child with a congenital anomaly in relation to occupational exposure to low level ionising radiation in the pre-conception period.

METHODS

A case-control study based on the Canadian congenital anomalies registry used record linkage techniques to identify congenital anomalies among male and female workers in Canada's largest electric company. Cases were defined as parents of a child with a congenital anomaly born between April 1979 and December 1986 who had a congenital anomaly diagnosed within the first year of life. Controls were an individually matched sample of parents of a liveborn child without an anomaly. Risk of congenital anomaly was assessed in relation to parental exposure to ionising radiation acquired through work within a nuclear generating station of an electric power company. Exposure was assessed according to employment, whether or not the worker was monitored for radiation exposure, and quantitative estimates of radiation dose.

RESULTS

Employment within the electric power industry was not associated with an increased risk of congenital anomalies in the offspring of mothers or fathers. Risk estimates for workers monitored (those who are likely to be exposed to ionising radiation) were 1.75 (95% confidence interval (95% CI) 0.86 to 3.55) for mothers and 0.84 (95% CI 0.68 to 1.05) for fathers. Exposure for fathers before conception, defined cumulatively and for six months before conception, was not associated with increased risk of anomalies in their offspring. There were no significant increases in risk found between type of anomaly and any measure of exposure, although the statistical power in these groups was limited. The study had insufficient numbers to evaluate the effects of ionising radiation in mothers as only three mothers had recorded doses > 0 mSv.

CONCLUSIONS

Overall, workers in a nuclear power industry, and specifically those exposed before conception to low levels of ionising radiation, do not appear to be at an increased risk of having a liveborn child with a congenital anomaly.

Leukemia following occupational exposure to 60-Hz electric and magnetic fields among Ontario electric utility workers

In a nested case-control study of 1,484 cancer cases and 2,179 matched controls from a cohort of 31,543 Ontario Hydro male employees, the authors evaluated associations of cancer risk with electric field exposure and reevaluated the previously reported findings for magnetic fields. Pensioners were followed from January 1, 1970, and active workers (including those who left the corporation) from January 1, 1973, with both groups followed through December 31, 1988. Exposures to electric and magnetic fields and to potential occupational confounders were estimated through job exposure matrices. Odds ratios were elevated for hematopoietic malignancies with cumulative electric field exposure. After adjustment, the odds ratio for leukemia in the upper tertile was 4.45 (95% confidence interval (CI) 1.01-19.7). Odds ratios were also elevated for acute nonlymphoid leukemia, acute myeloid leukemia, and chronic lymphoid leukemia. For cumulative magnetic field exposure, there were similar elevations that fell with adjustment. Evaluation of the combined effect of electric and magnetic fields for leukemia showed significant elevations of risk for high exposure to both, with a dose-response relation for increasing exposure to electric fields and an inconsistent effect for magnetic fields. There was some evidence of a nonsignificant association for brain cancer and benign brain tumors with magnetic fields. For lung cancer, the odds ratio for high exposure to electric and magnetic fields was 1.84 (95% CI 0.69-4.94).

Reduced cell-cell communication in experimentally induced autoimmune thyroid disease

We have recently described a spontaneous murine model of autoimmune thyroid disease. The disorder was in part characterized by reduced thyroid epithelial cell-cell communication that was associated with abnormalities in three major connexins. To compare whether this finding was a common secondary occurrence in autoimmune thyroid disease, or unique to the spontaneous development in the MRL mice, we induced thyroiditis in Lewis rats. Immunization with thyroid extract and thyroglobulin resulted in extensive lymphocytic infiltration and increased expression of major histocompatibility gene complex (MHC) class II surface antigen in the diseased thyroid. Both experimental and control rat thyroid tissues produced gap junction proteins connexin 43, connexin 32, and connexin 26. The connexins in nondiseased tissue was located in the plasma membrane at points of cell-cell contact and labeled as discrete arrays of punctate fluorescence. The quantity of all three connexins were reduced in the diseased thyroid tissue. More importantly, the connexin proteins were not distributed as gap junctions at contacting cell interfaces. Both nondiseased and diseased thyroid tissue expressed messenger RNA (mRNA) for the three connexins, but the diseased tissue had reduced levels of mRNA for connexin 43 (45%), and to a lesser extent, connexin 26 (25%) and connexin 32 (20%). The reduced connexin mRNA, protein, and lack of assembled gap junctions measured in the diseased tissue were obtained under conditions where the infiltrating cells and their potent cytokine products were continuously present. To determine if this difference persisted when these inflammatory components were absent, primary cultures of thyroid cells from control and experimental rats were established and connexin localization experiments repeated. The diseased thyroid cells, like the diseased tissue, lacked plasma membrane associated connexin protein. The lack of gap junction assembly in the thyrocytes cultured from the diseased tissue was accompanied by a loss of functional coupling. Collectively, the data document that autoimmune diseased thyroid tissue from both the spontaneous mouse and induced rat models have reduced plasma membrane assembled gap junctions and deficient intercellular communication as determined by the inability to transfer lucifer yellow dye to contiguous cells. Nondiseased cultured thyrocyte monolayers and follicles transferred dye to second and third order neighboring cells in 80 and 95% of trials, respectively. In contrast, only 5-10% of the diseased thyrocytes transferred microinjected dye, and in these cases the transit was limited to primary contacting cells. Culturing removed inequities introduced by the infiltrating cells and their products. However, the established cultures of diseased thyroid cells retained their communication deficiency. This suggests that the loss of communication may be a common abnormality in autoimmune disease, and furthermore, this uncoupling could contribute to the loss of coordinated hormonal regulation (hypothyroidism) in the diseased thyroid gland in the absence of thyroid cell destruction.

Reduced cell-cell communication in a spontaneous murine model of autoimmune thyroid disease

MRL-lpr/lpr mice manifest a systemic lupus-like autoimmune disease. As part of this syndrome, the mice spontaneously develop autoimmune thyroiditis, which is morphologically and biochemically similar to human autoimmune thyroiditis. In this study we investigated whether thyroid tissue obtained from sites of chronic inflammation had altered gap junctional communication. Fresh tissue sections revealed that thyroid from the nondiseased mice (MRL-(+)/+) had connexins (Cx) localized to the plasma membrane at points of thyroid cell-cell contact. In contrast, the Cx in diseased mouse (MRL-lpr/lpr) thyroid tissue were not localized to the plasma membrane, and the fluorescent intensity was reduced for Cx43 and Cx26. Northern analysis confirmed that murine thyroid tissue expressed messenger RNA for these Cx. However, the diseased tissue expressed lower levels of Cx32 and Cx26 messenger RNA. The infiltrating cells and their biologically active products present in the diseased thyroid tissue may mediate the reduced Cx expression and aberrant gap junctional assembly. We established primary thyrocyte cultures to determine whether these differences persisted when the inflammatory factors were removed. The nondiseased thyroid cells were communication competent, with fluorescent dye transfer proceeding from the injected cell to primary contacts (95%) and to second and third order neighboring cells in 75% of the trials. Thyroid cells from the diseased mice were communication incompetent, in that 80% of microinjections failed to result in dye transfer to cells in direct contact. Immunocytochemistry indicated that the functional coupling in the normal mouse thyroid cells was associated with Cx43 located in the plasma membrane as assembled gap junctional plaques. The communication-deficient diseased thyroid cells had internalized Cx43 predominantly localized to perinuclear regions of the cells. Collectively, these data document altered Cx-protein distribution in the autoimmune diseased thyroid. The diseased thyroid tissue was devoid of plasma membrane identifiable gap junctions and deficient in intercellular communication. Culturing removed the inflammatory mediators; however, the disease cells retained their communication incompetence. These results suggest that if this deficiency was initiated by components of the inflammation process, then protracted changes must have occurred so that the continued presence of these factors was no longer required to sustain this difference.

Characterization of autoimmune thyroiditis in MRL-lpr/lpr mice

MRL-lpr/lpr mice are genetically predisposed to develop a systemic lupus erythematosus-like syndrome that is clinically very similar to the human disease. The results presented here demonstrate, for the first time to our knowledge, that MRL-lpr/lpr mice also develop thyroiditis as part of their systemic autoimmune disorder. The thyroid gland was infiltrated by immunocomponent cells with defined lymphoid follicular centers and extensive interstitial lymphocytes dispersed throughout the thyroid epithelium. All the diseased mice were hypothyroid with reduced, relative levels of thyroid hormone (free T4) and elevated levels of thyroid-stimulating hormone (TSH). They also had high concentrations of circulating IgG class autoantibodies directed against thyroglobulin, thyroperoxidase and double-stranded DNA. The MRL-+/+ age-matched allelic counterpart mice had relatively few lymphocytes in their thyroid tissue, and normal levels of thyroxine and TSH. The non-diseased mice also had undetectable levels of thyroid reactive autoantibodies tested for by enzyme-linked immunosorbent assays. Collectively these findings document that the MRL-lpr/lpr mice spontaneously develop autoimmune thyroiditis and can be used as a model for the study of thyroid-specific autoimmunity.

Serum soluble CD23 in patients with hypogammaglobulinaemia

Serum levels of the soluble form of the low-affinity receptor for IgE (FcERII, CD23) (sCD23) are elevated in autoimmune conditions associated with hypergammaglobulinaemia and B cell hyperactivity. Very high levels of sCD23 are found in patients with B-chronic lymphatic leukaemia (B-CLL) who are, however, frequently hypogammaglobulinaemic. We therefore compared the serum levels of sCD23 in healthy controls (n = 33) with three conditions associated with hypogammaglobulinaemia (HGG) and varying B cell numbers: X-linked agammaglobulinaemia (XLA, n = 12), common variable immunodeficiency (CVI, n = 20) and B-chronic lymphatic leukaemia (n = 33). Serum levels of sCD23 showed a significant correlation with the CD19+ B cell count in both normals and patients with CVI (r = 0.65, P < 0.0001). Amongst the different clinical groups, serum levels of sCD23 were increased in the order XLA < CVI < normals < CLL (medians 2.5, 7.7, 11.1 and 540, respectively; P < 0.001 for all comparisons except CVI versus normals P < 0.03 in a one-tailed test). In the CVI group, serum sCD23 was lowest amongst four patients with low B cell numbers. There was no overlap in sCD23 between patients with XLA and this subgroup of CVI patients. Serum sCD23 is, therefore, derived predominantly from B cells, and is significantly related to the peripheral blood B cell count.

In situ regulation of cell-cell communication by the cAMP-dependent protein kinase and protein kinase C

The effects of cAMP-dependent protein kinase A and protein kinase C on cell-cell communication have been examined in primary ovarian granulosa cells microinjected with purified components of these two regulatory cascades. These cells possess connexin43 (alpha 1)-type gap junctions, and are well-coupled electrotonically and as judged by the cell-to-cell transfer of fluorescent dye. Within 2-3 min after injection of the protein kinase A inhibitor (PKI) communication was sharply reduced or ceased, but resumed in about 3 min with the injection of the protein kinase A catalytic subunit. A similar resumption also occurred in PKI-injected cells after exposure to follicle stimulating hormone. Microinjection of the protein kinase C inhibitor protein caused a transient cessation of communication that spontaneously returned within 15-20 min. Treatment of cells with activators of protein kinase C, TPA or OAG for 60 min caused a significant reduction in communication that could be restored within 2-5 min by the subsequent injection of either the protein kinase C inhibitor or the protein kinase A catalytic subunit. With a longer exposure to either protein kinase C activator communication could not be restored and this appeared to be related to the absence of aggregates of connexin43 in membrane as detected immunologically. In cells injected with alkaline phosphatase communication stopped but returned either spontaneously within 20 min or within 2-3 min of injecting the cell with either the protein kinase A catalytic subunit or with protein kinase C. When untreated cells were injected with protein kinase C communication diminished or ceased within 5 min. Collectively these results demonstrate that cell-cell communication is regulated by both protein kinase A and C, but in a complex interrelated manner, quite likely by multiple phosphorylation of proteins within or regulating connexin-43 containing gap junctions.

HIV induces deletion of T cell receptor variable gene product-specific T cells

Using a flow cytometric method, CD4+, CD8+, alpha beta TCR+ and TCR variable region gene product (TVRGP)-specific T cells were analysed in healthy heterosexual males (HHeM), HIV-seronegative homosexual males (SNHM), asymptomatic seropositive homosexual males (ASPH) and homosexual males with AIDS who were either well (AIDS-A), or unwell in hospital (AIDS-B). Total CD4+ and CD8+ T cell numbers were similar in HHeM and SNHM. CD4+ T cells were significantly reduced in ASPH relative to both HHeM and SNHM and in AIDS-A and AIDS-B relative to SNHM. TVRGP-specific T cells expressed as a percentage of TCR alpha beta + cells showed no significant difference in HHeM, SNHM and AIDS-B. The proportion of alpha beta + cells expressing the V beta 5.1, V beta 12 and V alpha 2 gene product (GP) was, however, significantly reduced in ASPH and AIDS-B relative to HHeM, SNHM and AIDS-A. Possible causes of TVRGP-specific T cell deletion are discussed.

NMR and computational evidence that high-affinity bradykinin receptor antagonists adopt C-terminal beta-turns

Three tetrapeptides were prepared, each corresponding to the four C-terminal amino acid residues of highly potent, second-generation bradykinin receptor antagonists. The tetrapeptides are (IA) Ser-D-Phe-Oic-Arg, (IIA) Ser-D-Tic-Oic-Arg, and (IIIA) Ser-D-Hype(trans-propyl)-Oic-Arg. Solution conformations for each were determined by incorporating interproton distance restraints, determined by 2D NMR experiments performed in water at neutral pH, into a series of distance geometry/simulated annealing model building calculations. Similarly, systematic conformational analyses were performed for each using molecular mechanics calculations. Both the NMR-derived structures, as well as the calculated structures, are shown to adopt a beta-turn as the primary conformation. Excellent agreement between the predicted structures and the NMR-derived structures is demonstrated. Aside from being the first examples of linear tetrapeptides reported to be ordered in aqueous solvent, the results presented support the hypothesis that high-affinity bradykinin receptor antagonists must adopt C-terminal beta-turn conformations.

A novel beta-turn mimic useful for mapping the unknown topology of peptide receptors

Ethers of cis or trans D-4-hydroxyproline (Hype), adjacent to octahydroindole-carboxylic acid (Oic), introduce a beta-turn into the backbone of peptides when positioned respectively at the i+1 and i+2 position of the turn. This is confirmed by NMR experiments performed on a model tetrapeptide in water. Synthetic alteration of the ether group allows simple probing of the steric limits and electrostatic potential of a receptor binding site, a technique applied successfully to the bradykinin receptor.

Dysplasia and the natural history of cervical cancer: early results of the Toronto Cohort Study

A sample of 176,808 Pap smears, taken from 70,236 women, was constructed from the records of a large cytopathology laboratory between 1962 and 1981. The prevalence of cervical dysplasia, based on the distribution of initial smear results, rose from 42.7 to 94.9 per 1000 during the study period. The relative risks (RR) for the manifestation of a malignancy (carcinoma in situ or worse) in a subsequent cervical smear were 1.48, 3.42, 20.9 and 71.5 for women with minimal, mild, moderate and severe dysplasia, respectively, compared with the entire cohort. The initial degree of dysplasia for women developing a malignancy was much more likely to be interpreted as moderate (RR = 5.0) or severe (RR = 42.3) than were those for controls. These results are strongly supportive of the hypothesis that the degree of dysplasia is related to the risk of development of cancer of the cervix.

Cancer mortality in workers exposed to chlorophenoxy herbicides and chlorophenols

Epidemiological studies have revealed an increased risk of cancer, notably soft-tissue sarcomas and non-Hodgkin's lymphomas, in people occupationally exposed to chlorophenoxy herbicides, including those contaminated by 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD). We report here a historical cohort study of mortality in an international register of 18,910 production workers or sprayers from ten countries. Exposure was reconstructed through questionnaires, factory or spraying records, and job histories. Cause-specific national death rates were used as reference. No excess was observed in all-cause mortality, for all neoplasms, for the most common epithelial cancers, or for lymphomas. A statistically non-significant two-fold excess risk, based on 4 observed deaths, was noted for soft-tissue sarcoma with a standardised mortality ratio (SMR) of 196 and 95% confidence interval (Cl) 53-502; this was concentrated as a six-fold statistically significant excess, occurring 10-19 years from first exposure in the cohort as a whole (SMR = 606 [165-1552]) and, for the same time period, as a nine-fold excess among sprayers (SMR = 882 [182-2579]). Risks appeared to be increased for cancers of the testicle, thyroid, other endocrine glands, and nose and nasal cavity, based on small numbers of deaths. The excess of soft-tissue sarcomas among sprayers is compatible with a causal role of chlorophenoxy herbicides but the excess does not seem to be specifically associated with those herbicides probably contaminated by TCDD.

An abnormal T cell repertoire in hypergammaglobulinaemic primary Sjögren's syndrome

T cell antigen specificity is determined by the products of the genes which encode the variable regions of their receptors. Of the T cell receptor (TCR) variable region gene products examined, only V beta 6.7a TCR-positive lymphocytes were reduced in primary Sjögren's syndrome patients with IgG1 hypergammaglobulinaemia compared with an age-, sex- and HLA-matched control population. The levels of V beta 6.7a T cells were also significantly reduced when these patients were compared with an age- and sex-matched but HLA-unmatched control group and non-tissue typed normal people of both sexes. Since published studies show no such abnormality in rheumatoid arthritis, systemic lupus erythematosus or other autoimmune diseases, this abnormality may reflect a pathogenic process specific to primary Sjögren's syndrome.

A cohort mortality study of forestry workers exposed to phenoxy acid herbicides

A cohort mortality study was undertaken of forestry workers at a public electrical utility who had worked for six months or more during 1950-82 and who were routinely exposed to herbicides including phenoxy acids. A total of 1222 men with 25 274 years at risk experienced 80 deaths. Ascertainment of vital state at the end of follow up was 95.5%. The male population of the province (Ontario) was used as the reference group. Overall, no excess mortality was found in this cohort relative to the reference population. A statistically significant increase in deaths occurred, however, due to suicide (SMR = 210, 95% confidence interval, 95% CI 105-376) for the cohort as a whole. No deaths were seen due to cancers such as soft tissue sarcoma and non-Hodgkin's lymphoma that have been cited by other authors as being associated with exposure to phenoxy acid herbicides. Although the cohort is not large, the absence of deaths due to these cancers is consistent with findings from other studies with sufficient numbers to allow examination of specific risks. The cohort is still young, however, and at the end of follow up most had not reached an age when increased incidence of cancer would normally be expected.

Retroviral nucleocapsid protein-metal ion interactions: folding and sequence variants

Retroviral nucleocapsid proteins contain one or two proposed metal-binding sequences of the form Cys-Xaa2-Cys-Xaa4-His-Xaa4-Cys. Previously, we reported that an 18-amino acid peptide derived from the nucleocapsid protein of Rauscher murine leukemia virus (RMLV) binds metals such as Co2+ and Zn2+. We have now synthesized the entire nucleocapsid protein from RMLV. We report here that the protein also binds Co2+ and Zn2+ and does so with a higher affinity than does the peptide. Limited proteolysis and circular dichroism studies reveal that metal binding induces folding of the metal-binding domain and, perhaps, the regions adjacent to it but the remainder of the protein remains in a relatively unstructured state. In addition, we have synthesized sequence variants of the metal-binding domain that correspond to viral mutations reported in the literature. In many cases, the metal-binding properties of these peptides correlate with the observed biological activity, providing further evidence for the importance of metal binding to nucleocapsid function.

A retroviral Cys-Xaa2-Cys-Xaa4-His-Xaa4-Cys peptide binds metal ions: spectroscopic studies and a proposed three-dimensional structure

Retroviral gag gene-encoded core nucleic acid binding proteins contain either one or two sequences of the form Cys-Xaa2-Cys-Xaa4-His-Xaa4-Cys. Previously, one of us has proposed that these sequences form metal-binding domains in analogy with the "zinc finger" domains first observed in transcription factor IIIA. We report that an 18-amino acid peptide derived from the core nucleic acid binding protein from Rauscher murine leukemia virus binds metal ions such as Co2+ and Zn2+. The absorption spectrum of the peptide-Co2+ complex is highly suggestive of tetrahedral coordination involving three cysteinates and one histidine. Titration experiments indicate that the dissociation constant for the peptide-Co2+ complex is 1.0 microM and that Zn2+ binds more tightly than Co2+. A detailed three-dimensional structure for this domain based on conserved substructures in other crystallographically characterized metalloproteins and on a detailed analysis of the Cys-Xaa2-Cys-Xaa4-His-Xaa4-Cys sequences from retroviruses and other related sources is proposed.

Cytotoxicity mediated by tumor necrosis factor in variant subclones of the ME-180 cervical carcinoma line: modulation by specific inhibitors of DNA topoisomerase II

The mechanism of tumor necrosis factor (TNF)-induced cytotoxicity has been investigated using two clonal variants of the ME-180 human cervical carcinoma cell line. The clonal lines were characterized with respect to their expression of TNF receptors, kinetics of cell death, and their ability to communicate intercellularly through gap junctions. The ME-180.4 and ME-180.8 clones were identified by their relative sensitivity to TNF induced lysis in a 24-h assay. The dose of TNF required to kill 50% of the target cells was 60 pM for the sensitive ME-180.4 and 2.5 nM for the ME-180.8. However, when assay times were extended, the dose response for both clones was the same, indicating that a difference in the kinetics of cell death and not absolute TNF sensitivity existed between the ME-180.4 and ME-180.8 clones. Both clones were gap junction deficient as judged by their inability to transfer Lucifer yellow or 6-carboxyfluorescein, a characteristic phenotype of cells sensitive to cytotoxicity by TNF. The level of surface receptor expressed on these clones was nearly identical with a Kd = 0.3 nM and 5,000 binding sites per cell. Measurement of the kinetics of cell death revealed that the time between the addition of TNF and the onset of observed cell death (induction phase) was much shorter for the ME-180.4 (32-55 h) than for the resistant ME-180.8 (55-80 h). Mitomycin C, a DNA alkylating agent, significantly reduced the length of the induction phase for both clones, although the kinetic difference between the clones remained unchanged. Two epipodophyllotoxins, VP-16 and VM-26, which specifically inhibit the rejoining activity of DNA topoisomerase II, showed a 10-100-fold synergistic effect when combined with TNF as shown by isobologram analysis. VM-26 when added to the resistant ME-180.8 clones decreased the length of induction phase and abolished the kinetic difference observed with the ME-180.4 clone. These results indicate that the variance in the TNF response of these two clones was closely associated with DNA topoisomerase II, and suggest that this enzyme may play an important role in TNF mediated cytotoxicity.

Cytotoxicity by tumor necrosis factor is linked with the cell cycle but does not require DNA synthesis

The relationship between the kinetics of cell death induced by TNF and the cell cycle in L929.10 target cells was investigated by comparison of growing, asynchronous cells with target cells synchronized at G1/S using a double thymidine block. The induction phase of lysis, the time following TNF addition but before loss of cell viability, was shortened in asynchronous cells by increasing the level of saturation of the TNF receptor. However, in synchronized target cells, the length of the induction phase showed no dependence on receptor occupancy. Almost all cell death occurred within a 3 hr period 4-7 hr after the addition of TNF regardless of the concentration of TNF. Target cell lysis in synchronized cells was concomitant with mitosis as verified by flow cytometry and DNA staining with propidium iodide. The narrow window of cytotoxicity was not due to cell cycle-related changes in the expression of the TNF receptor as measured by [125I]TNF binding. Treatment with TNF did not accelerate or retard the progression of cells through S and G2/M nor did target cells accumulate at G2/M. When the kinetic experiments were repeated in the presence of 2 mM thymidine, TNF-treated cells died with identical dose and kinetic responses as those in which the thymidine block had been removed. Under these conditions, flow cytometric analysis revealed that DNA synthesis remained inhibited. These results suggest that TNF-induced cytotoxicity is linked to cell cycle-associated processes and that TNF is capable of overriding the normal cellular controls that coordinately link the DNA replicative cycle with the mitotic cycle. In the L929.10 target cell, TNF may induce a fatal mitosis-linked event.