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Henk Van Loveren - One of the best experts on this subject based on the ideXlab platform.
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The immunosuppressant Tributyltin Oxide blocks the mTOR pathway, like rapamycin, albeit by a different mechanism.
Journal of Applied Toxicology, 2013Co-Authors: Ahmed M. Osman, Henk Van LoverenAbstract:We treated the thymoma cell line (EL4) with two model immunosuppressants, rapamycin and Tributyltin Oxide (TBTO), and compared their effects on the expression levels of proteins that are downstream targets of mTOR kinase 1 (mammalian target of rapamycin, known also as mechanistic target of rapamycin): p70 ribosomal S6 kinase1 and 4E-binding protein 1, a repressor of the cap-binding protein eIF4E. In addition, we evaluated the levels of ribosomal protein S6, p-eIF4B, substrates of p70S6 kinase1, matrin 3 and ribonucleotide reductase, subunit RRM2. The levels of these proteins were evaluated in cell lysates by immunoblot. We found that both compounds inhibited the phosphorylation state of p70S6 kinase 1 and its substrates; however, TBTO, in contrast to rapamycin, reduced the level of the total p70S6k1. Besides, we detected a band with a molecular weight of c. 32 kDa only in the TBTO-treated lysates. This band was detected with a monoclonal antibody specific for S6k1, suggesting that this band might be a degradation product of the kinase. Further, TBTO and rapamycin differentially affected 4E-binding protein 1; the former compound stimulated its phosphorylation state whereas the latter inhibited it. The two immunosuppressants did not affect the level of ribonucleotide reductase, but TBTO downregulated matrin3, in agreement with a previous report, whereas rapamycin had no effect on the expression level of this latter protein. We conclude that TBTO inhibits, like rapamycin, the p70 S6 kinase 1 pathway, but with a different mechanism. However, in contrast to rapamycin, which inhibits the cap-dependent translation, TBTO increases the phosphorylation of 4E-binding protein1. Copyright © 2013 John Wiley & Sons, Ltd.
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phosphoproteomic analysis of mouse thymoma cells treated with Tributyltin Oxide tbto affects proliferation and energy sensing pathways
Toxicological Sciences, 2012Co-Authors: Ahmed M. Osman, Henk Van LoverenAbstract:We report the results of phosphoproteomic analysis of mouse thymoma cells treated with Tributyltin Oxide (TBTO), an immunotoxic compound. After cell lysis, phosphoproteins were isolated using Phosphoprotein Purification Kit, separated by SDS-PAGE and subsequently digested with trypsin. Phosphopeptides were enriched employing titanium diOxide, and the obtained fractions were analyzed by nano-LC-MS/MS. A total of 160 phosphoproteins and 328 phosphorylation sites were identified in thymoma cells. Among the differentially phosphorylated proteins identified in TBTO-treated cells were key enzymes, which catalyze rate-limiting steps in pathways that are sensitive to cellular energy status. These proteins included acetyl-CoA carboxylase isoform 1, which catalyzes the rate-limiting step of fatty acid synthesis. Another enzyme was glutamine: fructose-6-phosphate amidotransferase, GFAT1, the first and rate-limiting enzyme for the hexoamine synthesis pathway. Pyruvate dehydrogenase (PDH), a multicomplex enzyme that catalyzes the rate-limiting step of aerobic oxidation of fuel carbohydrates, was identified in both TBTO-treated and control cells; however, phosphorylation at residue S293, known to inhibit PDH activity, was identified only in control cells. A lower expression level of ribosomal protein S6 kinase 1, a downstream kinase of the mammalian target of rapamycin signaling pathway implicated in protein synthesis through phosphorylation of 40 ribosomal S6, was observed in the treated cells. Giant kinases like AMP-activated protein kinase (AMPK) and cAMP-dependent protein kinase (PKAR1A), which are known to mediate the phosphorylation of these enzymes, were identified in TBTO-treated cells. Downregulation of proteins, such as MAPK, matrin-3 and ribonucleotide reductase, subunit RRM2, which are implicated in cell proliferation, was also observed in TBTO-treated cells. Together, the results show that TBTO affects proliferation and energy sensor pathways.
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Phosphoproteomic Analysis of Mouse Thymoma Cells Treated With Tributyltin Oxide: TBTO Affects Proliferation and Energy Sensing Pathways
2011Co-Authors: Ahmed M. Osman, Henk Van LoverenAbstract:We report the results of phosphoproteomic analysis of mouse thymoma cells treated with Tributyltin Oxide (TBTO), an immuno-toxic compound. After cell lysis, phosphoproteins were isolated using Phosphoprotein Purification Kit, separated by SDS-PAGE and subsequently digested with trypsin. Phosphopeptides were enriched employing titanium diOxide, and the obtained fractions were analyzed by nano-LC-MS/MS. A total of 160 phosphoproteins and 328 phosphorylation sites were identified in thymoma cells. Among the differentially phosphorylated proteins identified in TBTO-treated cells were key enzymes, which catalyze rate-limiting steps in pathways that are sensitive to cellular energy status. These proteins included acetyl-CoA carboxylase isoform 1, which catalyzes the rate-limiting step of fatty acid synthesis. Another enzyme was glutamine: fructose-6-phosphate amidotransferase, GFAT1, the first and rate-limiting enzyme for the hexoamine synthesis pathway
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bis Tributyltin Oxide tbto decreases the food allergic response against peanut and ovalbumin in brown norway rats
Toxicology, 2007Co-Authors: Jonathan D De Jonge, Janine Ezendam, Leon M J Knippels, Jennie Odink, Milanthy S Pourier, Andre Penninks, Raymond Pieters, Henk Van LoverenAbstract:Other factors than the allergen itself may be of importance in the development of food allergy. This report describes the influence of the immunosuppressive compound bis(Tributyltin)Oxide (TBTO), present in the food chain, on the development of food allergy to peanut or ovalbumin in Brown Norway (BN) rats. To study these effects BN rats were sensitized to either 1 or 10 mg peanut or ovalbumin by daily oral gavage and the TBTO-groups were fed a diet containing 80 mg TBTO per kg diet. Co-exposure to TBTO not only resulted in decreased general immunologic parameters such as weights of mesenteric lymph nodes and Peyer's patches, lymphocyte proliferation rates in splenocytes, but also on allergic parameters. In the peanut allergen-model TBTO decreased allergen-specific Th2 cytokine production by spleen cells, number of eosinophilic and basophilic granulocytes in the blood and production of mast cell protease II after oral food challenge. In the ovalbumin allergen-model TBTO decreased the number of eosinophilic and basophilic granulocytes, allergen-specific IgE and production of mast cell protease II after oral food challenge. The data imply that in the process of risk assessment of food allergy attention should be given to immunomodulating compounds present in the diet. © 2007 Elsevier Ireland Ltd. All rights reserved.
Sunao Fujimoto - One of the best experts on this subject based on the ideXlab platform.
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sweat gland toxicity induced by bis Tributyltin Oxide an ultrastructural and x ray microanalysis study
Archives of Toxicology, 2000Co-Authors: Osamu Yamamoto, Yoshiaki Doi, Hideaki Kudo, Mitsuaki Yoshizuka, Sunao FujimotoAbstract:Acute toxicity of bis (Tributyltin) Oxide in the sweat glands in the rat footpad was investigated by electron microscopy and an energy-dispersive X-ray microanalyzer. Male Wistar rats received an intramuscular injection of 0.5 ml/kg bis (Tributyltin) Oxide. After 6–8 h, swelling of mitochondria appeared in the secretory cells of the sweat glands. After 12 h, the secretory cells began to show intracytoplasmic edema. After 16–20 h, secretory cells in some sweat glands showed marked hydropic degeneration with swollen cytoplasm. Using X-ray microanalysis, tin peaks were preferentially obtained from the swollen mitochondria of the affected secretory cells. Mitochondria dysfunction due to the toxic effects of bis (Tributyltin) Oxide induced changes in the secretory cells of rat sweat glands. After 24–48 h, the secretory portion of the sweat glands contained three types of cells: degenerating dark cells, regenerating cells carrying injured mitochondria, and light cells which were morphologically very similar to the cells in the transitional portion of the sweat gland. These light cells appeared to differentiate into active secretory cells after settling down in the secretory portion. Based on these observations, we concluded that the cells in the transitional portion could play an important role at least as reserve cells against secretory cell toxicity. In association with the regenerating process of the damaged secretory portions, increased mitotic activities were seen in different areas of all the dermal sweat ducts. The above-mentioned morphological observations for cell damage and subsequent regeneration and renewal of secretory cells in sweat gland intoxication have not been reported so far.
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toxic effects of bis Tributyltin Oxide on the synthesis and secretion of zymogen granules in the rat exocrine pancreas
Archives of Histology and Cytology, 1994Co-Authors: Kazuo Hara, Mitsuaki Yoshizuka, Sunao FujimotoAbstract:Toxic effects of bis (Tributyltin) Oxide (TBTO) on the rat exocrine pancreas were studied with an electron microscope and X-ray microanalyzer. To measure tin concentrations in the blood, atomic absorption spectrophotometry was carried out. Adult male Wistar rats received an intramuscular injection of TBTO (0.5 ml/kg). At 2 h after injection, a marked swelling of mitochondria and an enlargement of the cisterns of the rough endoplasmic reticulum appeared in the pancreatic acinar cells. Using X-ray microanalysis, tin peaks were preferentially obtained from the swollen mitochondria. Heterogeneous zymogen granules with an electron dense core and a pale central zone increased in number in the acinar cells between 4 and 8 h after TBTO treatment. By 24 h after TBTO injection, the acinar cells had been ultrastructurally restored. Atomic absorption analyses showed that blood tin concentrations peaked at approximately 1 h after TBTO injection and then progressively declined, reaching the zero level at 12 h after injection. The effects of TBTO on the synthesis and secretion of zymogen granules were investigated with and without caerulein as a stimulant of secretion. Data obtained from these experiments indicated that TBTO inhibited both the synthesis and secretion of zymogen granules. The inhibition of the protein synthesis and secretion might be caused partly by mitochondrial dysfunctions due to the toxic effects of TBTO.
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the toxic effects of bis Tributyltin Oxide on the rat thoracic aorta
Histology and Histopathology, 1992Co-Authors: M Yoshizuka, Mitsuru Yokoyama, Kazuo Hara, Naoki Mori, Y Doi, E Ono, Sunao FujimotoAbstract:The toxic effects of bis (Tributyltin) Oxide (TBTO) on the ultrastructure and permeability of rat thoracic aorta were studied electron microscopically and the accumulation sites of tin were determined with an X-ray microanalyzer. Male Wistar rats received 0.05ml/kg of TBTO as an emulsion in 1 ml of distilled water through a stomach tube. After time intervals of 2, 4, 6, 8, 10, 12 h after intubation, thoracic aortae were isolated and prepared for electron microscopy. Marked swelling of mitochondria in the aortic endothelial cells appeared at 4 h after TBTO treatment. By x-ray microanalysis, tin L-alpha peaks (3.44 keV) were obtained from these swollen mitochondria. Subendothelial edema progressed between 6 and 8 h after TBTO treatment. By tracer experiment, it was seen that large amounts of peroxidase reaction products filled the expanded subendothelial space. At 12 h after TBTO treatment, degenerative changes of the endothelial cells were prominent. These results indicated that orally administered TBTO accumulated in the mitochondria of the endothelial cells of thoracic aorta. The direct toxic effects of TBTO on mitochondria might induce severe damage to the endothelial cells and cause disturbance of the permeability barrier function of the endothelial layer and subendothelial edema.
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Studies on the hepatotoxicity induced by bis (Tributyltin) Oxide
Archives of Toxicology, 1992Co-Authors: Mitsuaki Yoshizuka, Yoshiaki Doi, Nobuya Haramaki, Mitsuru Yokoyama, Kazuo Hara, Akio Kawahara, Naoki Mori, Sunao FujimotoAbstract:The toxic effects of bis (Tributyltin) Oxide (TBTO) on the rat liver were studied with an electron microscope and the accumulation sites of tin were determined with an X-ray microanalyzer. The activities of serum enzymes and the concentration of serum bilirubin were also analyzed. Male Wistar rats received an intramuscular injection of 0.5 ml/kg of TBTO. Marked swelling of the mitochondria appeared in the hepatocytes 4 h after injection of TBTO. Cytoplasmic vacuoles, which contained degenerated mitochondria, gradually increased in number in these hepatocytes. This in turn may have caused a decrease in the volume of hepatic cell cords and an enlargement of sinusoids in the entire hepatic lobule. However, fine structures of intrahepatic bile ducts were not altered. By X-ray microanalysis, tin peaks were preferentially obtained from swollen mitochondria of the hepatocytes. By polarographic analysis of the respiratory responses of mitochondria, it was demonstrated that rates of state 4 respiration and respiratory control ratio were significantly disturbed in TBTO-treated rats in comparison with those of controls. The activities of AST (aspartate aminotransferase) and ALT (alanine aminotransferase) were significantly increased after TBTO treatment, but those of ALP (alkaline phosphatase), LAP (leucine aminopeptidase) and total bilirubin were not changed. These results indicated that parenterally administered TBTO accumulated in the liver cell mitochondria and disturbed oxidative phosphorylation. Mitochondrial dysfunction might induce severe damage of the hepatocytes. Four days after injection of TBTO, hepatic structures and chemical indices were almost restored by the regeneration of hepatocytes.
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the role of the rat submandibular gland in the excretion of bis Tributyltin Oxide electron microscopy x ray microanalysis and atomic absorption analysis
Tissue & Cell, 1992Co-Authors: Mitsuaki Yoshizuka, Yoshiaki Doi, Mitsuru Yokoyama, Kazuo Hara, Naoki Nagata, Tetsuya Sagara, Sunao FujimotoAbstract:The role of the submandibular glands in the excretion of parenterally administered bis (Tributyltin) Oxide (TBTO) was studied. Fine structural alterations of the submandibular glands were observed with an electron microscope. Accumulation sites of TBTO were determined with an X-ray microanalyzer and tin concentrations in saliva and blood were measured by atomic absorption spectrophotometry.
Jorg Rombke - One of the best experts on this subject based on the ideXlab platform.
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comparison of the effects of zinc nitrate tetrahydrate and Tributyltin Oxide on the reproduction and avoidance behavior of the earthworm eisenia andrei in laboratory tests using nine soils
Applied Soil Ecology, 2014Co-Authors: Adam Scheffczyk, Stephan Jansch, Silja Frankenbach, Jorg RombkeAbstract:The aim of this contribution was to evaluate whether the sensitivity of the earthworm avoidance test is comparable to that of the earthworm reproduction test (standard test guidelines for both are available). The objective was to determine if relatively simple short-term tests are useful as an initial screening step for the environmental risk assessment (ERA) of potentially contaminated soils prior to performing long-term, elaborate tests. Therefore, the effects of two model substances, zinc nitrate-tetrahydrate and Tributyltin-Oxide (TBT-O) on the reproduction and the avoidance behavior of the earthworm Eisenia andrei were compared using Organization for Economic Co-operation and Development (OECD) artificial soil as well as eight natural soils, including LUFA St. 2.2 soil, covering a wide range of pH-values, organic matter content and texture. Almost all tests fulfilled the validity criteria defined in the two standard guidelines published by the International Organization for Standardization (ISO), despite the fact that the properties of natural soils differed clearly from those of OECD artificial soil. The median effective concentration (EC50) values estimated for zinc nitrate-tetrahydrate in 48-h avoidance tests and in 56-day reproduction tests were often similar when using the same soil (seven out of nine soils). However, in the case of TBT-O, the outcome was more complex: in two test soils the avoidance EC50 values were by a factor >3 higher than the reproduction EC50 values. In one of the test soils it was the other way around and the remaining soils showed comparable EC50 values in both tests. Summarizing the results obtained here and according to experiences reported in the available literature, the earthworm avoidance test may be recommended as an initial screening tool in the ERA of potentially contaminated soils. However, further research is needed to understand the factors that contribute to the difference in sensitivity between reproduction and avoidance tests.
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comparison of the effects of zinc nitrate tetrahydrate and Tributyltin Oxide on the reproduction and avoidance behavior of the earthworm eisenia andrei in laboratory tests using nine soils
Applied Soil Ecology, 2014Co-Authors: Adam Scheffczyk, Stephan Jansch, Silja Frankenbach, Jorg RombkeAbstract:The aim of this contribution was to evaluate whether the sensitivity of the earthworm avoidance test is comparable to that of the earthworm reproduction test (standard test guidelines for both are available). The objective was to determine if relatively simple short-term tests are useful as an initial screening step for the environmental risk assessment (ERA) of potentially contaminated soils prior to performing long-term, elaborate tests. Therefore, the effects of two model substances, zinc nitrate-tetrahydrate and Tributyltin-Oxide (TBT-O) on the reproduction and the avoidance behavior of the earthworm Eisenia andrei were compared using Organization for Economic Co-operation and Development (OECD) artificial soil as well as eight natural soils, including LUFA St. 2.2 soil, covering a wide range of pH-values, organic matter content and texture. Almost all tests fulfilled the validity criteria defined in the two standard guidelines published by the International Organization for Standardization (ISO), despite the fact that the properties of natural soils differed clearly from those of OECD artificial soil. The median effective concentration (EC50) values estimated for zinc nitrate-tetrahydrate in 48-h avoidance tests and in 56-day reproduction tests were often similar when using the same soil (seven out of nine soils). However, in the case of TBT-O, the outcome was more complex: in two test soils the avoidance EC50 values were by a factor >3 higher than the reproduction EC50 values. In one of the test soils it was the other way around and the remaining soils showed comparable EC50 values in both tests. Summarizing the results obtained here and according to experiences reported in the available literature, the earthworm avoidance test may be recommended as an initial screening tool in the ERA of potentially contaminated soils. However, further research is needed to understand the factors that contribute to the difference in sensitivity between reproduction and avoidance tests.
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the effect of Tributyltin Oxide on earthworms springtails and plants in artificial and natural soils
Archives of Environmental Contamination and Toxicology, 2007Co-Authors: Jorg Rombke, Stephan Jansch, Thomas Junker, B Pohl, Adam Scheffczyk, H J SchallnassAbstract:Chemical bioavailability in Organisation for Economic Co-operation and Development (OECD) artificial soil can contrast with bioavailability in natural soils and produce ecotoxicologic benchmarks that are not representative of species’ exposure conditions in the field. Initially, reproduction and growth of earthworm and Collembolan species, and early seedling growth of a dicotyledonous plant species, in nine natural soils (with a wide range of physicochemical properties) and in OECD soil were evaluated. Soils that supported reproduction and growth of the test species were then used to investigate the toxicity of Tributyltin-Oxide (TBT-O). Natural soils caused greater toxicity of TBT-O to earthworms (EC50 values varied from 0.5 to 4.7 mg/kg soil dry weight [dw]) compared with toxicity in OECD soil (EC50 = 13.4 mg/kg dw). Collembolans were less sensitive to TBT-O than earthworms in natural soils, with EC50 values ranging from 23.4 to 177.8 mg/kg dw. In contrast, the toxicity of TBT-O to collembolans in OECD soil (EC50 = 104.0 mg/kg dw) was within the range of EC50 values in natural soils. Phytotoxicity tests revealed even greater difference between the effects in natural soils (EC50 values ranged from 10.7 to 189.2 mg/kg dw) and in OECD soil (EC50 = 535.5 mg/kg dw) compared with results of the earthworm tests. Studies also showed that EC50 values were a more robust end point compared with EC10 values based on comparisons of coefficients of variation. These results show that toxicity testing should include studies with natural soils in addition to OECD soil to better reflect exposure conditions in the field.
Adam Scheffczyk - One of the best experts on this subject based on the ideXlab platform.
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comparison of the effects of zinc nitrate tetrahydrate and Tributyltin Oxide on the reproduction and avoidance behavior of the earthworm eisenia andrei in laboratory tests using nine soils
Applied Soil Ecology, 2014Co-Authors: Adam Scheffczyk, Stephan Jansch, Silja Frankenbach, Jorg RombkeAbstract:The aim of this contribution was to evaluate whether the sensitivity of the earthworm avoidance test is comparable to that of the earthworm reproduction test (standard test guidelines for both are available). The objective was to determine if relatively simple short-term tests are useful as an initial screening step for the environmental risk assessment (ERA) of potentially contaminated soils prior to performing long-term, elaborate tests. Therefore, the effects of two model substances, zinc nitrate-tetrahydrate and Tributyltin-Oxide (TBT-O) on the reproduction and the avoidance behavior of the earthworm Eisenia andrei were compared using Organization for Economic Co-operation and Development (OECD) artificial soil as well as eight natural soils, including LUFA St. 2.2 soil, covering a wide range of pH-values, organic matter content and texture. Almost all tests fulfilled the validity criteria defined in the two standard guidelines published by the International Organization for Standardization (ISO), despite the fact that the properties of natural soils differed clearly from those of OECD artificial soil. The median effective concentration (EC50) values estimated for zinc nitrate-tetrahydrate in 48-h avoidance tests and in 56-day reproduction tests were often similar when using the same soil (seven out of nine soils). However, in the case of TBT-O, the outcome was more complex: in two test soils the avoidance EC50 values were by a factor >3 higher than the reproduction EC50 values. In one of the test soils it was the other way around and the remaining soils showed comparable EC50 values in both tests. Summarizing the results obtained here and according to experiences reported in the available literature, the earthworm avoidance test may be recommended as an initial screening tool in the ERA of potentially contaminated soils. However, further research is needed to understand the factors that contribute to the difference in sensitivity between reproduction and avoidance tests.
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comparison of the effects of zinc nitrate tetrahydrate and Tributyltin Oxide on the reproduction and avoidance behavior of the earthworm eisenia andrei in laboratory tests using nine soils
Applied Soil Ecology, 2014Co-Authors: Adam Scheffczyk, Stephan Jansch, Silja Frankenbach, Jorg RombkeAbstract:The aim of this contribution was to evaluate whether the sensitivity of the earthworm avoidance test is comparable to that of the earthworm reproduction test (standard test guidelines for both are available). The objective was to determine if relatively simple short-term tests are useful as an initial screening step for the environmental risk assessment (ERA) of potentially contaminated soils prior to performing long-term, elaborate tests. Therefore, the effects of two model substances, zinc nitrate-tetrahydrate and Tributyltin-Oxide (TBT-O) on the reproduction and the avoidance behavior of the earthworm Eisenia andrei were compared using Organization for Economic Co-operation and Development (OECD) artificial soil as well as eight natural soils, including LUFA St. 2.2 soil, covering a wide range of pH-values, organic matter content and texture. Almost all tests fulfilled the validity criteria defined in the two standard guidelines published by the International Organization for Standardization (ISO), despite the fact that the properties of natural soils differed clearly from those of OECD artificial soil. The median effective concentration (EC50) values estimated for zinc nitrate-tetrahydrate in 48-h avoidance tests and in 56-day reproduction tests were often similar when using the same soil (seven out of nine soils). However, in the case of TBT-O, the outcome was more complex: in two test soils the avoidance EC50 values were by a factor >3 higher than the reproduction EC50 values. In one of the test soils it was the other way around and the remaining soils showed comparable EC50 values in both tests. Summarizing the results obtained here and according to experiences reported in the available literature, the earthworm avoidance test may be recommended as an initial screening tool in the ERA of potentially contaminated soils. However, further research is needed to understand the factors that contribute to the difference in sensitivity between reproduction and avoidance tests.
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the effect of Tributyltin Oxide on earthworms springtails and plants in artificial and natural soils
Archives of Environmental Contamination and Toxicology, 2007Co-Authors: Jorg Rombke, Stephan Jansch, Thomas Junker, B Pohl, Adam Scheffczyk, H J SchallnassAbstract:Chemical bioavailability in Organisation for Economic Co-operation and Development (OECD) artificial soil can contrast with bioavailability in natural soils and produce ecotoxicologic benchmarks that are not representative of species’ exposure conditions in the field. Initially, reproduction and growth of earthworm and Collembolan species, and early seedling growth of a dicotyledonous plant species, in nine natural soils (with a wide range of physicochemical properties) and in OECD soil were evaluated. Soils that supported reproduction and growth of the test species were then used to investigate the toxicity of Tributyltin-Oxide (TBT-O). Natural soils caused greater toxicity of TBT-O to earthworms (EC50 values varied from 0.5 to 4.7 mg/kg soil dry weight [dw]) compared with toxicity in OECD soil (EC50 = 13.4 mg/kg dw). Collembolans were less sensitive to TBT-O than earthworms in natural soils, with EC50 values ranging from 23.4 to 177.8 mg/kg dw. In contrast, the toxicity of TBT-O to collembolans in OECD soil (EC50 = 104.0 mg/kg dw) was within the range of EC50 values in natural soils. Phytotoxicity tests revealed even greater difference between the effects in natural soils (EC50 values ranged from 10.7 to 189.2 mg/kg dw) and in OECD soil (EC50 = 535.5 mg/kg dw) compared with results of the earthworm tests. Studies also showed that EC50 values were a more robust end point compared with EC10 values based on comparisons of coefficients of variation. These results show that toxicity testing should include studies with natural soils in addition to OECD soil to better reflect exposure conditions in the field.
Ahmed M. Osman - One of the best experts on this subject based on the ideXlab platform.
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The immunosuppressant Tributyltin Oxide blocks the mTOR pathway, like rapamycin, albeit by a different mechanism.
Journal of Applied Toxicology, 2013Co-Authors: Ahmed M. Osman, Henk Van LoverenAbstract:We treated the thymoma cell line (EL4) with two model immunosuppressants, rapamycin and Tributyltin Oxide (TBTO), and compared their effects on the expression levels of proteins that are downstream targets of mTOR kinase 1 (mammalian target of rapamycin, known also as mechanistic target of rapamycin): p70 ribosomal S6 kinase1 and 4E-binding protein 1, a repressor of the cap-binding protein eIF4E. In addition, we evaluated the levels of ribosomal protein S6, p-eIF4B, substrates of p70S6 kinase1, matrin 3 and ribonucleotide reductase, subunit RRM2. The levels of these proteins were evaluated in cell lysates by immunoblot. We found that both compounds inhibited the phosphorylation state of p70S6 kinase 1 and its substrates; however, TBTO, in contrast to rapamycin, reduced the level of the total p70S6k1. Besides, we detected a band with a molecular weight of c. 32 kDa only in the TBTO-treated lysates. This band was detected with a monoclonal antibody specific for S6k1, suggesting that this band might be a degradation product of the kinase. Further, TBTO and rapamycin differentially affected 4E-binding protein 1; the former compound stimulated its phosphorylation state whereas the latter inhibited it. The two immunosuppressants did not affect the level of ribonucleotide reductase, but TBTO downregulated matrin3, in agreement with a previous report, whereas rapamycin had no effect on the expression level of this latter protein. We conclude that TBTO inhibits, like rapamycin, the p70 S6 kinase 1 pathway, but with a different mechanism. However, in contrast to rapamycin, which inhibits the cap-dependent translation, TBTO increases the phosphorylation of 4E-binding protein1. Copyright © 2013 John Wiley & Sons, Ltd.
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phosphoproteomic analysis of mouse thymoma cells treated with Tributyltin Oxide tbto affects proliferation and energy sensing pathways
Toxicological Sciences, 2012Co-Authors: Ahmed M. Osman, Henk Van LoverenAbstract:We report the results of phosphoproteomic analysis of mouse thymoma cells treated with Tributyltin Oxide (TBTO), an immunotoxic compound. After cell lysis, phosphoproteins were isolated using Phosphoprotein Purification Kit, separated by SDS-PAGE and subsequently digested with trypsin. Phosphopeptides were enriched employing titanium diOxide, and the obtained fractions were analyzed by nano-LC-MS/MS. A total of 160 phosphoproteins and 328 phosphorylation sites were identified in thymoma cells. Among the differentially phosphorylated proteins identified in TBTO-treated cells were key enzymes, which catalyze rate-limiting steps in pathways that are sensitive to cellular energy status. These proteins included acetyl-CoA carboxylase isoform 1, which catalyzes the rate-limiting step of fatty acid synthesis. Another enzyme was glutamine: fructose-6-phosphate amidotransferase, GFAT1, the first and rate-limiting enzyme for the hexoamine synthesis pathway. Pyruvate dehydrogenase (PDH), a multicomplex enzyme that catalyzes the rate-limiting step of aerobic oxidation of fuel carbohydrates, was identified in both TBTO-treated and control cells; however, phosphorylation at residue S293, known to inhibit PDH activity, was identified only in control cells. A lower expression level of ribosomal protein S6 kinase 1, a downstream kinase of the mammalian target of rapamycin signaling pathway implicated in protein synthesis through phosphorylation of 40 ribosomal S6, was observed in the treated cells. Giant kinases like AMP-activated protein kinase (AMPK) and cAMP-dependent protein kinase (PKAR1A), which are known to mediate the phosphorylation of these enzymes, were identified in TBTO-treated cells. Downregulation of proteins, such as MAPK, matrin-3 and ribonucleotide reductase, subunit RRM2, which are implicated in cell proliferation, was also observed in TBTO-treated cells. Together, the results show that TBTO affects proliferation and energy sensor pathways.
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Phosphoproteomic Analysis of Mouse Thymoma Cells Treated With Tributyltin Oxide: TBTO Affects Proliferation and Energy Sensing Pathways
2011Co-Authors: Ahmed M. Osman, Henk Van LoverenAbstract:We report the results of phosphoproteomic analysis of mouse thymoma cells treated with Tributyltin Oxide (TBTO), an immuno-toxic compound. After cell lysis, phosphoproteins were isolated using Phosphoprotein Purification Kit, separated by SDS-PAGE and subsequently digested with trypsin. Phosphopeptides were enriched employing titanium diOxide, and the obtained fractions were analyzed by nano-LC-MS/MS. A total of 160 phosphoproteins and 328 phosphorylation sites were identified in thymoma cells. Among the differentially phosphorylated proteins identified in TBTO-treated cells were key enzymes, which catalyze rate-limiting steps in pathways that are sensitive to cellular energy status. These proteins included acetyl-CoA carboxylase isoform 1, which catalyzes the rate-limiting step of fatty acid synthesis. Another enzyme was glutamine: fructose-6-phosphate amidotransferase, GFAT1, the first and rate-limiting enzyme for the hexoamine synthesis pathway
