Looking at Developmental Neurotoxicity Testing from the Perspective of an Invertebrate Embryo

Developmental neurotoxicity (DNT) of chemical compounds disrupts the formation of a normal brain. There is impressive progress in the development of alternative testing methods for DNT potential in chemicals, some of which also incorporate invertebrate animals. This review briefly touches upon studies on the genetically tractable model organisms of Caenorhabditis elegans and Drosophila melanogaster about the action of specific developmental neurotoxicants. The formation of a functional nervous system requires precisely timed axonal pathfinding to the correct cellular targets. To address this complex key event, our lab developed an alternative assay using a serum-free culture of intact locust embryos. The first neural pathways in the leg of embryonic locusts are established by a pair of afferent pioneer neurons which use guidance cues from membrane-bound and diffusible semaphorin proteins. In a systematic approach according to recommendations for alternative testing, the embryo assay quantifies defects in pioneer navigation after exposure to a panel of recognized test compounds for DNT. The outcome indicates a high predictability for test-compound classification. Since the pyramidal neurons of the mammalian cortex also use a semaphorin gradient for neurite guidance, the assay is based on evolutionary conserved cellular mechanisms, supporting its relevance for cortical development.     

Photoinitiierte Polymerisation mit Dialkoxythiocarbonyldisulfiden – eine Polymerisationsreaktion mit Primärradikalabbruch

Photoinitiated Polymerization with Dialkoxy Thiocarbonyl Disulfides – a Polymerization Reaction with Primary Radical Termination The photoinduced free radical polymerization of methyl methacrylate (MMA) and some other vinyl monomers using dialkoxy thiocarbonyl disulfides ( 1 – 4 ) as photoinitiators was studied. The photolysis of these initiators leads to cleavage of the S S bond, which was determined by spin trapping experiments with phenyl tert-butyl nitrone. No evidence was found for a further thermal decomposition of the primary alkoxy thiocarbonyl sulfide radicals (R·) at room temperature. In the absence of scavengers the primary radicals react back exclusively to the initial compounds, due to a strong cage effect. By means of UV spectroscopic measurements and in the presence of MMA the quantum yields of the initiator decomposition were detected to be 0.8. The polymerization of acrylic and methacrylic derivatives can be initiated by the R·, contrary to the situation with fumarates and maleates. The mechanism of MMA polymerization depends on the light intensity absorbed by the initiators. At high intensities the combination of primary and polymer radicals terminates the chain reaction. This follows from the measured monomer exponent of α = 2, the light intensity exponent of β = 0,2 and the number of thiocarbonyl end groups of 2 in the polymers isolated. Contrary to this, in the low intensity region the experimental data obey the ideal kinetic equation. Kinetic modelling gives evidence for an interaction of the monomer with the cage radicals.     

Stabilität von Ionenaustauschern gegen Salpetersäure und Bestrahlung. I. Nitrosierender Abbau der Iminodiessigsäuregruppen in Chelonaustauschern

The Stability of Ion Exchangers towards Nitric Acid and Radiation. I. Nitrosative Cleavage of the Iminodiacetic Acid Groups in Chelating Ion Exchangers The behaviour of the chelating ion exchangers Wofatit MC 50, Dowex A 1 and Chelex 100 with aminoacetic acid – and iminodiacetic acid-groups towards nitric acid in the range of the concentration 1…︁10,5 mol/l and at temperatures ⩽68°C was determined. It is found that the COOH capacity and the N content are rapidly reduced leading to the formation of CO₂ and N₂. If the exposure to HNO₃ continues there is again a rise in the COOH capacity. The i.r.- and mass spectra show that the iminodiacetic acid-groups are destroyed by nitrosative cleavage and CHO groups result, which are then oxidized to COOH groups. The mass spectrum shows that the aminoacetic acid-groups of the resin are nitrosated, which has also been confirmed by the use of nitric acid labelled with ¹⁵N.     

Azoperoxide. VI. Selektive Spaltungen von β-Azo-acylperoxiden

Azoperoxides. VI. Selective Decomposition of β-Azoacylperoxides The selective decomposition of the O O-Groups in the azoperoxides 1 and 2 is possible by reaction with dimethylaniline at 35°C. Rate constants were measured and the decomposition products were analyzed. Intermediates are azoalkyl radicals. The radical yield of the amine induced decomposition of 2 in ethylbenzene is 8.2% at 35°C. UV irradiation of the azoperoxides 1 and 2 at 20°C in ethylbenzene results in a quantitative and selective decomposition of the azo groups. Intermediates are C-radicals with intact peroxide groups. The reaction of 1 and 2 with triethylstannane yields reduction products of the O O-groups and the NN-groups, respectively.     

Individual and combined effects of subclinical doses of deoxynivalenol and fumonisins in piglets

Scope: Deoxynivalenol (DON) and fumonisins (FB) are the most frequently encountered mycotoxins produced by Fusarium species and most commonly co‐occur in animal diets. These mycotoxins were studied for their toxicity in piglets on several parameters including plasma biochemistry, organ histopathology and immune response. Methods and results: Twenty‐four 5‐wk‐old animals were randomly assigned to four different groups, receiving separate diets for 5 wk, a control diet, a diet contaminated with either DON (3 mg/kg) or FB (6 mg/kg) or both toxins. At days 4 and 16 of the trial, the animals were subcutaneously immunized with ovalbumin to assess their specific immune response. The different diets did not affect animal performance and had minimal effect on hematological and biochemical blood parameters. By contrast, DON and FB induced histopathological lesions in the liver, the lungs and the kidneys of exposed animals. The liver was significantly more affected when the two mycotoxins were present simultaneously. The contaminated diets also altered the specific immune response upon vaccination as measured by reduced anti‐ovalbumin IgG level in the plasma and reduced lymphocyte proliferation upon antigenic stimulation. Because cytokines play a key role in immunity, the expression levels of IL‐8, IL‐1β, IL‐6 and macrophage inflammatory protein‐1β were measured by RT‐PCR at the end of the experiment. The expression of these four cytokines was significantly decreased in the spleen of piglets exposed to multi‐contaminated diet. Conclusion: Taken together, our data indicate that ingestion of multi‐contaminated diet induces greater histopathological lesions and higher immune suppression than ingestion of mono‐contaminated diets.     

Spatial distributions of O2, CO2 and SO2 in a pilot-scale fluidized bed combustor operated with different coals

Axial concentration profiles of O₂, CO₂ and SO₂ have been measured at different radial positions in a coal-fired fluidized bed combustor. The profiles show some spatial inhomogeneity in the bed, the degree of which depends on fluidizing velocity and amount of excess air. Comparison of SO₂- with CO₂-concentration profiles reveals that SO₂ is formed in proportion to CO₂ only with anthracite as fuel. With bituminous coals, SO₂ is preferentially formed near the coal feed point. These results are discussed with regard to characteristic times of mixing and chemical reaction in fluidized beds, and SO₂-formation characteristics of the employed coals obtained in a thermobalance.     

Thermochemical Treatment--Technologies for Recovery and Utilisation of Materials

The arc furnace technology is an ideally suited process for the treatment of hazardous and problematic waste. The operation conditions of the arc furnace can be adapted for optimal transformation of the waste material input into raw materials and usable products. The process can significantly reduce the impact of contaminated wastes and industrial residues, and enable material conversion and separation. Thus, the products of the process have various applications. The capability of the process is illustrated with three examples, the treatment of bottom ash and filter ash from waste incineration plants, of stainless steel slags and of chromium containing residues from the refractory industry.     

Dietary Fish Oil Alters DNA Methylation of Genes Involved in Polyunsaturated Fatty Acid Biosynthesis in Muscle and Liver of Atlantic Salmon (Salmo salar)

Adequate dietary supply of eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3) is required to maintain health and growth of Atlantic salmon (Salmo salar). However, salmon can also convert α-linolenic acid (18:3n-3) into eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3) by sequential desaturation and elongation reactions, which can be modified by 20:5n-3 and 22:6n-3 intake. In mammals, dietary 20:5n-3 + 22:6n-3 intake can modify Fads2 expression (Δ6 desaturase) via altered DNA methylation of its promoter. Decreasing dietary fish oil (FO) has been shown to increase Δ5fad expression in salmon liver. However, it is not known whether this is associated with changes in the DNA methylation of genes involved in polyunsaturated fatty acid synthesis. To address this, we investigated whether changing the proportions of dietary FO and vegetable oil altered the DNA methylation of Δ6fad_b, Δ5fad, Elovl2, and Elovl5_b promoters in liver and muscle from Atlantic salmon and whether any changes were associated with mRNA expression. Higher dietary FO content increased the proportions of 20:5n-3 and 22:6n-3 and decreased Δ6fad_b mRNA expression in liver, but there was no effect on Δ5fad, Elovl2, and Elovl5_b expression. There were significant differences between liver and skeletal muscle in the methylation of individual CpG loci in all four genes studied. Methylation of individual Δ6fad_b CpG loci was negatively related to its expression and to proportions of 20:5n-3 and 22:6n-3 in the liver. These findings suggest variations in dietary FO can induce gene-, CpG locus-, and tissue-related changes in DNA methylation in salmon.     

Effect of pasture vs. concentrate diet on CLA isomer distribution in different tissue lipids of beef cattle

This study examined the effects of feeding pasture vs. concentrate on the distribution of CLA isomers in the lipids of longissimus and semitendinosus muscle, liver and heart muscle, and subcutaneous fat in beef bulls. Sixty-four German Holstein and German Simmental bulls were randomly allocated to either an indoor concentrate system or periods of pasture feeding followed by a finishing period on a concentrate containing linseed to enhance their beef content of n−3 PUFA and CLA. The concentrations of CLA isomers in the different tissues were determined by GC and silver ion HPLC. The diet affected the distribution of individual CLA isomers in the lipids of the different tissues. The concentration (mg/100 g fresh tissue) of the most prominent isomer, cis-9,trans-11 18∶2, was increased up to 1.5 times in liver and heart tissue of bulls fed on pasture as compared with concentrate. However, no diet effect was observed for cis-9,trans-11 18∶2 in the lipids of longissimus muscle and subcutaneous fat. In all tissues, the second-most abundant CLA isomer in concentratefed bulls was trans-7,cis-9 18∶2. In contrast, trans-11,cis-13 18∶2 was the second-most abundant CLA isomer in all investigated tissue lipids of pasture-fed bulls. The concentration of the trans-11,cis-13 18∶2 isomer was up to 15 times higher in tissues of pasture-fed bulls as compared with concentrate-fed animals. Furthermone, diet affected the concentrations of the CLA trans,trans 18∶2 isomers. Pasture feeding significantly increased the concentrations of some trans,trans 18∶2 isomers as compared with concentrate, predominantly trans-12,trans-14 18∶2 and trans-11,trans-13 18∶2. Overall, pasture feeding resulted in significantly increased concentrations of the sum of CLA isomers in the lipids of longissimus, muscle, subcutaneous fat, heart and liver muscle of German Holstein and German Simmental bulls, but not in semitendinosus muscle.