No Evidence of Persisting Unrepaired Nuclear DNA Single Strand Breaks in Distinct Types of Cells in the Brain,Kidney, and Liver of Adult Mice after Continuous Eight-Week 50 Hz Magnetic Field Exposure with Flux Density of 0.1 mT or 1.0 mT

Background

It has been hypothesized in the literature that exposure to extremely low frequency electromagnetic fields (50 or 60 Hz) may lead to human health effects such as childhood leukemia or brain tumors. In a previous study investigating multiple types of cells from brain and kidney of the mouse (Acta Neuropathologica 2004; 107: 257–264), we found increased unrepaired nuclear DNA single strand breaks (nDNA SSB) only in epithelial cells of the choroid plexus in the brain using autoradiographic methods after a continuous eight-week 50 Hz magnetic field (MF) exposure of adult mice with flux density of 1.5 mT.

Methods

In the present study we tested the hypothesis that MF exposure with lower flux densities (0.1 mT, i.e., the actual exposure limit for the population in most European countries, and 1.0 mT) shows similar results to those in the previous study. Experiments and data analysis were carried out in a similar way as in our previous study.

Results

Continuous eight-week 50 Hz MF exposure with 0.1 mT or 1.0 mT did not result in increased persisting unrepaired nDNA SSB in distinct types of cells in the brain, kidney, and liver of adult mice. MF exposure with 1.0 mT led to reduced unscheduled DNA synthesis (UDS) in epithelial cells in the choroid plexus of the fourth ventricle in the brain (EC-CP) and epithelial cells of the cortical collecting duct in the kidney, as well as to reduced mtDNA synthesis in neurons of the caudate nucleus in the brain and in EC-CP.

Conclusion

No evidence was found for increased persisting unrepaired nDNA SSB in distinct types of cells in the brain, kidney, and liver of adult mice after continuous eight-week 50 Hz magnetic field exposure with flux density of 0.1 mT or 1.0 mT.     

Genome-Wide Microarray Expression and Genomic Alterations by Array-CGH Analysis in Neuroblastoma Stem-Like Cells

Neuroblastoma has a very diverse clinical behaviour: from spontaneous regression to a very aggressive malignant progression and resistance to chemotherapy. This heterogeneous clinical behaviour might be due to the existence of Cancer Stem Cells (CSC), a subpopulation within the tumor with stem-like cell properties: a significant proliferation capacity, a unique self-renewal capacity, and therefore, a higher ability to form new tumors. We enriched the CSC-like cell population content of two commercial neuroblastoma cell lines by the use of conditioned cell culture media for neurospheres, and compared genomic gains and losses and genome expression by array-CGH and microarray analysis, respectively (in CSC-like versus standard tumor cells culture). Despite the array-CGH did not show significant differences between standard and CSC-like in both analyzed cell lines, the microarray expression analysis highlighted some of the most relevant biological processes and molecular functions that might be responsible for the CSC-like phenotype. Some signalling pathways detected seem to be involved in self-renewal of normal tissues (Wnt, Notch, Hh and TGF-β) and contribute to CSC phenotype. We focused on the aberrant activation of TGF-β and Hh signalling pathways, confirming the inhibition of repressors of TGF-β pathway, as SMAD6 and SMAD7 by RT-qPCR. The analysis of the Sonic Hedgehog pathway showed overexpression of PTCH1, GLI1 and SMO. We found overexpression of CD133 and CD15 in SIMA neurospheres, confirming that this cell line was particularly enriched in stem-like cells. This work shows a cross-talk among different pathways in neuroblastoma and its importance in CSC-like cells.     

Targeted inactivation of the plastid ndhB gene in tobacco results in an enhanced sensitivity of photosynthesis to moderate stomatal closure

The ndh genes encoding for the subunits of NAD(P)H dehydrogenase complex represent the largest family of plastid genes without a clearly defined function. Tobacco (Nicotiana tabacum) plastid transformants were produced in which the ndhB gene was inactivated by replacing it with a mutant version possessing translational stops in the coding region. Western-blot analysis indicated that no functional NAD(P)H dehydrogenase complex can be assembled in the plastid transformants. Chlorophyll fluorescence measurements showed that dark reduction of the plastoquinone pool by stromal reductants was impaired in ndhB-inactivated plants. Both the phenotype and photosynthetic performance of the plastid transformants was completely normal under favorable conditions. However, an enhanced growth retardation of ndhB-inactivated plants was revealed under humidity stress conditions causing a moderate decline in photosynthesis via stomatal closure. This distinctive phenotype was mimicked under normal humidity by spraying plants with abscisic acid. Measurements of CO(2) fixation demonstrated an enhanced decline in photosynthesis in the mutant plants under humidity stress, which could be restored to wild-type levels by elevating the external CO(2) concentration. These results suggest that the plastid NAD(P)H:plastoquinone oxidoreductase in tobacco performs a significant physiological role by facilitating photosynthesis at moderate CO(2) limitation.     

Effect of GLG-V-13, a class III antiarrhythmic agent, on potassium currents in rabbit ventricular myocytes

The effects of a new Class III antiarrhythmic drug, GLG-V-13, on the 4-aminopyridine sensitive transient outward current, on the inward rectifier potassium current, on the ATP sensitive potassium current and on the rapid and slow components of the delayed rectifier potassium current were studied in single rabbit ventricular myocytes using the whole-cell voltage-clamp technique. GLG-V-13 blocked the rapid component of the delayed rectifier potassium current in a dose-dependent manner, with an estimated EC50 value of 0.36 microM. At high concentration, the slow component of the delayed rectifier potassium current was also depressed by the drug (40% effect at 10 microM concentration). The transient outward current, the inward rectifier potassium current and the ATP sensitive potassium current were not influenced by GLG-V-13, even at 10 microM concentration. Thus, GLG-V-13 blocks predominantly the rapid component of the delayed rectifier potassium current which may play a significant role in the prolongation of repolarization by the drug in ventricular tissue.     

Starvation- and xenobiotic-related transcriptomic responses of the sulfanilic acid-degrading bacterium,Novosphingobium resinovorum SA1

Applied Microbiology and Biotechnology - Novosphingobium resinovorum SA1 was the first single isolate capable of degrading sulfanilic acid, a widely used representative of sulfonated aromatic...     

The Heterogeneity of Structural and Functional Photosynthetic Characteristics of Mesophyll Chloroplasts in Various Parts of Mature or Senescing Leaf Blade of Two Maize (Zea Mays L.) Genotypes

Differences in ultrastructural parameters of mesophyll cell (MC) chloroplasts, contents of photosynthetic pigments, and photochemical activities of isolated MC chloroplasts were studied in the basal, middle, and apical part of mature or senescing leaf blade of two maize genotypes. A distinct heterogeneity of leaf blade was observed both for structural and functional characteristics of chloroplasts. In both mature and senescing leaves the shape of MC chloroplasts changed from flat one in basal part of leaf to nearly spherical one in leaf apex. The volume density of granal thylakoids decreased from leaf base to apex in both types of leaves examined, while the amount of intergranal thylakoids increased in mature leaves but decreased in senescing leaves. The most striking heterogeneity was found for the quantity of plastoglobuli, which strongly increased with the increasing distance from leaf base. The differences in chloroplast ultrastructure were accompanied by differences in other photosynthetic characteristics. The Hill reaction activity and activity of photosystem 1 of isolated MC chloroplasts decreased from leaf base to apex in mature leaves. Apical part of senescing leaf blade was characterised by low contents of chlorophyll (Chl) a and Chl b, whereas in mature leaves, the content of Chls as well as the content of total carotenoids (Car) slightly increased from basal to apical leaf part. This was reflected also in the ratio Chl (a+b)/total Car; the ratio of Chl a/b did not significantly differ between individual parts of leaf blade. Both genotypes examined differed in the character of developmental gradient observed along whole length of leaf blade.     

Isoquinoline alkaloids from Mahonia aquifolium stem bark are active against Malassezia spp

Bioassay directed fractionation of crude extract fromMahonia aquifolium led to the isolation of fraction A (bisbenzylisoquinoline alkaloid complex, BBI) and a fraction of protoberberine alkaloids, where the major compounds berberine and jatrorrhizine were isolated as their iodides. The antifungal activity of the crude extract, two protoberberine alkaloids and BBI fromM. aquifolium stem bark were evaluated against six strains ofMalassezia spp. The compounds tested were generally found to possess only weak to moderate antifungal properties: the MICs for individual strains were in the range ≤50–≥1000 mg/L.     

Carbon-source assimilation pattern of the astaxanthin-producing yeast Phaffia rhodozyma

Eleven Phaffia rhodozyma strains were assayed for their ability to utilize 99 compounds as single carbon source. Some of them showed modified coloration compared to colonies of the same strain grown on glucose medium.     

Molecular properties and metabolic effect on blood cells produced by a new toxin of Enterobacter cloacae

A new toxin of Enterobacter cloacae able to lyse erythrocytes and leukocytes was found. Purification of the toxin was performed by salt precipitation, gel filtration, ion exchange and HPLC in C₈ column. SDS-PAGE electrophoresis showed more than one bank corresponding to the leukotoxin able to form polymers and aggregate like some pore-forming cytotoxins (RTX). In culture supernatant the toxin showed 1 HU/ml (hemolytic unit) and 1.5 LU/ml (leukotoxic unit); after purification it reached 15 HU/ml and 20 LU/ml. The ratio between HU and percentage red cells affected the lytic capacity. E. cloacae toxin stimulated the oxidative metabolism of neutrophils, but over 50 μg toxin/ml the stimulus ceased as it was shown by NBT assay due to cell death. Chemiluminescence evidenced an increase in superoxide anion generation, but an excess of toxin interfered with this stimulus, as was previously observed in HlyA Escherichia coli toxin. Cross-reaction was found by immunoblotting with this HlyA. E. cloacae toxin presented higher amounts of proline, valine, aspartic and glutamic acids than HlyA. E. cloacae toxin was similar to HlyA in the prescence of a glycine-rich DNA sequence and in the observed effect of calcium on toxin activity. E. cloacae toxin did not cross-react by immunoblotting with hemolysin HmpA of Proteus. This revised version was published online in July 2006 with corrections to the Cover Date.     

Differential in vitro and in vivo behavior of mouse ascorbate/Fe3+ and diamide oxidized erythrocytes

Chemical oxidation of mouse erythrocytes has been carried out using two different oxidizing systems namely: Diamide and Ascorbate/Fe³⁺ together with different concentrations of the oxidant. These oxidation treatments produced different extents of modification in membrane proteins as was observed by electrophoretic analyses that showed a possible formation of high molecular weight aggregates. Lipid peroxidation was also observed as the result of these chemical treatments. The action of these two oxidation treatments produced different extents of lipid peroxidation in which the effect Ascorbate/Fe³⁺ reached higher values than that shown by diamide treatments. To study the resulting in vitro behavior of such oxidized erythrocytes, we have evaluated the recognition of oxidized erythrocytes by peritoneal macrophages. In the conditions used, diamide oxidized erythrocytes were more highly recognized by macrophages than Ascorbate/Fe³⁺ treated erythrocytes. However, in both cases an influence of serum factors in the recognition process can be inferred. Additionally, we have correlated on one side the action of different oxidation systems on mouse erythrocytes with different in vivo behavior and organ uptake of the oxidized erythrocytes. On the other side, differential targeting of oxidized erythrocytes to a liver or spleen was observed on dependence of the oxidant used.