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Biomedical subjects

A Brouwer

Publications and source records attributed to A Brouwer.

At least 55 records · Page 3Linked to original sources
PubMed1998

Prx1 and Prx2 in skeletogenesis: roles in the craniofacial region, inner ear and limbs.

Prx1 and Prx2 are closely related paired-class homeobox genes that are expressed in very similar patterns predominantly in mesenchyme. Prx1 loss-of-function mutants show skeletal defects in skull, limbs and vertebral column (Martin, J. F., Bradley, A. and Olson, E. N. (1995) Genes Dev. 9, 1237-1249). We report here that mice in which Prx2 is inactivated by a lacZ insertion had no skeletal defects, whereas Prx1/Prx2 double mutants showed many novel abnormalities in addition to an aggravation of the Prx1 single mutant phenotype. We found defects in external, middle and inner ear, reduction or loss of skull bones, a reduced and sometimes cleft mandible, and limb abnormalities including postaxial polydactyly and bent zeugopods. A single, or no incisor was present in the lower jaw, and ectopic expression of Fgf8 and Pax9 was found medially in the mandibular arch. A novel method to detect &bgr ;-galactosidase activity in hydroxyethylmethacrylate sections allowed detailed analysis of Prx2 expression in affected structures. Our results suggest a role for Prx genes in mediating epitheliomesenchymal interactions in inner ear and lower jaw. In addition, Prx1 and Prx2 are involved in interactions between perichondrium and chondrocytes that regulate their proliferation or differentiation in the bones of the zeugopods.

Amino Acid Sequence↗
PubMed1997

Thyroxine binding to transthyretin Met 119. Comparative studies of different heterozygotic carriers and structural analysis.

The majority of the known transthyretin (TTR) variants are associated with amyloidosis, but there are also variants associated with euthyroid hyperthyroxinemia and others are apparently nonpathogenic. TTR Met 119 is a nonpathogenic variant found to be frequent in the Portuguese population. Previous studies on thyroxine (T4) binding to semi-purified TTR from heterozygotic carriers of TTR Met 119, reported by us and other groups, revealed different results. Therefore, to further characterize T4 binding to TTR Met 119 we performed T4-TTR binding studies in homotetrameric-recombinant TTR Met 119 variant and normal TTR. We also studied T4 binding to TTR purified from serum of different heterozygotic carriers of TTR Met 119 including compound heterozygotic individuals carriers of a TTR mutation in the other allele. We observed an increased T4 binding affinity to TTR Met 119 from heterozygotic individuals and compound heterozygotes and this effect of increasing T4 binding affinity was consistent and independent from the mutation present in the other allele. Recombinant homotetrameric TTR Met 119 and heterotetrameric protein from heterozygotic carriers of TTR Met 119 presented similar T4 binding affinity demonstrating the increased T4 binding affinity of TTR Met 119. X-ray crystallography studies performed on the recombinant TTR Met 119 variant revealed structural alterations mainly at the level of residue Leu 110 allowing a closer contact between the hormone and the mutant protein. These results are consistent with the observed T4 binding results.

Binding, Competitive↗
PubMed1997

Impaired cellular immune response in rats exposed perinatally to Baltic Sea herring oil or 2,3,7,8-TCDD.

While the immunotoxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been well established, the effects of complex environmental mixtures of polyhalogenated aromatic hydrocarbons (PHAHs) are poorly understood. Many PHAHs, including the polychlorinated-biphenyls (PCBs), -dibenzofurans (PCDFs), and dibenzo-p-dioxins (PCDDs), possess 'dioxin-like' activities, and accumulate in the aquatic food chain. Organisms occupying high trophic levels may therefore be exposed to concentrations which may present an immunotoxic risk. In this study, pregnant PVG rats were administered a daily oral dose of 1 ml of the following during pregnancy and lactation: (1) oil extracted from herring caught in the relatively uncontaminated Atlantic Ocean; (2) oil extracted from herring caught in the contaminated Blastic Sea; or (3) the Atlantic herring oil extract spiked with 2,3,7,8-TCDD. The daily intakes of aryl hydrocarbon (Ah)-receptor dependent toxic equivalents (TEQ) for mothers were 0.3 in the Atlantic group, 2.1 in the Baltic group, and 134 ng/kg body wt. in the 2,3,7,8-TCDD positive control group. Immune function and host resistance to rat cytomegalovirus (RCMV) were assessed in offspring aged 11, 25, 46 or 59 days. Rat pups in the positive control TCDD-spiked group exhibited immunosuppression characterized by reduced thymus weight and cellularity, reduced thymocyte and splenocyte proliferative responses to T-dependent mitogens in vitro, reduced virus-associated natural killer (NK) cell and specific antibody responses. While less pronounced, a similar pattern of effects was observed in the rat pups exposed only to the Baltic Sea herring oil. These immunotoxic effects were transient in both exposure groups, with a time-related recovery in immune function possibly due to the half-life of TCDD in rats and the waning exposure levels in the rapidly growing pups. We previously demonstrated that the same Baltic Sea herring led to impaired natural killer cell and T-lymphocyte function in harbour seals during the course of a long-term captive feeding study. The collective results of these studies in rats and seals indicate the immunotoxic potential of environmental mixtures at current levels in the aquatic environment, and suggest that the developing immune system of young mammals may be at particular risk.

Animals↗
PubMed1997

Extrathyroidal effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on thyroid hormone turnover in male Sprague-Dawley rats.

Treatment of rats with different polyhalogenated aromatic hydrocarbons strongly decreases plasma T4, with little or no decrease in plasma T3. The extrathyroidal effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on thyroid hormone turnover were studied by i.p. administration of a single dose of 10 microg TCDD/kg BW or vehicle (corn oil) to euthyroid (Eu) rats, thyroidectomized (Tx) rats, and Tx rats infused with 1 microg T4 (Tx+T4) or 0.4 microg T3 (Tx+T3)/100 g BW x day by osmotic minipumps. Tx rats showed decreased plasma T4 and T3 and increased plasma TSH levels, decreased hepatic type I deiodinase (D1) and malic enzyme activities, and increased brain type II deiodinase (D2) activities. All parameters were largely restored to Eu levels in Tx+T4 rats and, except for plasma T4 and brain D2 activity, in Tx+T3 rats, validating the thyroid hormone-replaced Tx rats as models to study the peripheral effects of TCDD. Three days after TCDD administration, plasma T4 and free T4 levels were significantly reduced in Eu and Tx+T4 rats, and plasma T3 was significantly reduced in Tx+T3, but not in Eu or Tx+T4 rats. Plasma TSH was not affected by TCDD in any group. Hepatic T4 UDP-glucuronyltransferase (UGT) activity was induced approximately 5-fold by TCDD, whereas T3 UGT activity was only increased by about 20% (P = NS) in the different groups. TCDD produced an insignificant decrease in liver D1 activity in Tx rats and an insignificant increase in brain D2 activity in Tx rats and hormone-replaced Tx rats. Hepatic malic enzyme activity was significantly increased by TCDD in all groups, except Tx rats. These results strongly suggest that the thyroid hormone-decreasing effects of TCDD are predominantly extrathyroidal and mediated by the marked induction of hepatic T4 UGT activity.

Animals↗
PubMed1996

Modulation of intercellular communication between smooth muscle cells by growth factors and cytokines.

We recently reported that tumor necrosis factor alpha is able to cause a dose-dependent and persistent reduction in gap junctional intercellular communication between primary human smooth muscle cells. In order to study whether this observed persistent reduction in gap junctional intercellular communication is a unique feature for tumor necrosis factor alpha, the present study focuses on the effects of other growth factors and cytokines on gap junctional intercellular communication. Platelet-derived growth factor AA and BB (PDGF-AA, PDGF-BB), basic fibroblast growth factor (bFGF), interleukin-6 and interferon-gamma were able to modulate gap junctional intercellular communication between primary human smooth muscle cells in vitro. However, our results demonstrate that the magnitude and nature of the observed effects are growth factor- and cytokine-specific. PDGF-AA, PDGF-BB and interleukin-6 caused a transient reduction in gap junctional intercellular communication, while bFGF induced a transient increase in gap junctional intercellular communication. Interferon-gamma was shown to be capable of causing a persistent reduction in gap junctional intercellular communication. In addition, PDGF-AA, PDGF-BB, bFGF, interleukin-6, interferon-gamma and tumor necrosis factor alpha all stimulated smooth muscle cell proliferation. These observations suggest a more complex relationship between modulation of gap junctional intercellular communication and cell proliferation than current hypotheses imply. The implications of the observed effects of growth factors and cytokines on gap junctional intercellular communication between smooth muscle cells in relation to the process of atherosclerosis is discussed.

Arteriosclerosis↗
PubMed1996

Binding of a 3,3', 4,4'-tetrachlorobiphenyl (CB-77) metabolite to fetal transthyretin and effects on fetal thyroid hormone levels in mice.

The present study was conducted in order to study the effect of the PCB congener 3,3', 4,4'-tetrachlorobiphenyl (CB-77) on fetal thyroxin homeostasis in the mouse, and to examine a possible underlying mechanism behind the effect. C57BL mice were treated with 14C-labelled or unlabelled CB-77 (1 or 10 mg/kg body wt.) on day 13 of gestation, and control animals were treated with corn oil. The experiment was terminated at 4 days after exposure. Maternal and fetal plasma and livers, and whole fetuses for homogenate preparation, were collected and analysed for total radioactivity, in vitro binding of 125I-thyroxin to plasma transthyretin (TTR; a thyroxin-transporting protein), and free and total thyroxin (FT4, TT4) levels. Maternal plasma, fetal plasma and homogenates were also analyzed for presence of CB-77 and metabolites. Results showed a dose-dependent uptake of radioactivity in plasma and liver, fetal plasma 14C-levels being about five-times higher in 10 mg/kg dosed animals as after 1 mg/kg. Fetal; plasma levels of total radioactivity were four- to nine-times above maternal levels and corresponded to only one compound, the metabolite 4-OH-3,3', 4',5-tetrachlorobiphenyl (4-OH-tCB). 4-OH-tCB was the major metabolite also in whole fetuses, with only small amounts of the parent compound (approximately 15% of the 4-OH-tCB) and traces (approximately 6%) of two other metabolites, 2-OH-3,3, 4,4'-tetrachlorobiphenyl and 5-OH-3,3', 4,4'-tetrachlorobiphenyl. Polyacrylamide gel electrophoresis confirmed that the 14C-radioactivity in fetal plasma was bound to TTR, and revealed that in vitro binding of 125I-T4 to fetal TTR was reduced to 50% of control values in treated animals (10 mg/kg body wt.). Fetal plasma FT4 and TT4 levels were significantly decreased (64 and 55% of control fetuses) after 10 mg/kg treatment. In conclusion, exposure of pregnant mice to CB-77 results in the accumulation of the metabolite 4-OH-tCB in fetal mouse plasma. The metabolite binds to TTR and is accompanied by a significant decrease in fetal plasma T4 levels. A causative correlation between TTR binding and effects on T4 levels is suggested.

Animals↗
PubMed1996

Differential expression of alpha-6 and other subunits of laminin binding integrins during development of the murine heart.

The development of the heart from a single heart tube to a four chambered organ with two separated unidirectional flows is a highly complex process. Events like looping, septation, tissue remodelling, and development of valves take place in a time period in which the heart already exerts its pump function. Adhesion of cells to each other and to their extracellular matrix as well as the capability to migrate in such a dynamic environment are extremely important. Integrins and extracellular matrix components have already been implicated in this process. In this report, we describe in detail the differential expression of the alpha-6 integrin subunit during late murine heart development, e.g., in the process from looping to the end of septation. We compare mRNA and protein expression patterns with those of beta-1 and other subunits of laminin-binding integrins, alpha-3 and alpha-7. We show a constant and high expression of alpha-6 in the atrial myocardium and a decrease in expression in the ventricular trabecular myocardium. The compact myocardial wall and the ventricular septum do not express alpha-6, except for the myocardium of the distal outflow tract at early stages. Moreover, we describe expression of this integrin subunit in the endocardial cushions that contribute to the development of the atrioventricular and semilunar valves. We propose a role for the alpha-6-beta-1 laminin receptor in the adhesion of cells to their extracellular matrix at sites of high stress due to cardiac contraction or blood flow induced shear stress. Moreover, site specific endothelial expression within the heart and surrounding extracardiac tissue is discussed. This study suggests a distinct role for alpha-6-beta-1 in the heart and provides insight concerning probably important roles of integrins and their extracellular matrix ligands during embryonic development.

Animals↗
PubMed1996

Expression of the beta 4 integrin subunit in the mouse heart during embryonic development: retinoic acid advances beta 4 expression.

Using immunohistochemical techniques as well as in situ hybridization we were able to elicit the expression pattern of the beta 4 integrin subunit in the murine heart during development. We show that beta 4 is not expressed in the heart before E13 and is afterwards restricted to the endocardium of the atrioventricular canal, the outflow tract, and the venous valves in the right atrium. As these are all sites of high shear stress in the heart, we propose a role for alpha 6 beta 4 in the tight adhesion of the endocardial cells to their basement membranes in these segments. Moreover, mouse embryos were treated with all-trans retinoic acid, which was previously shown to induce congenital malformations, among which malformations of the heart. We show an advanced expression without ectopic localization of cardiac beta 4 after the administration of retinoic acid. This advanced appearance of beta 4 was also shown in extracardiac tissue like migrating neural crest cells. Several hypotheses on the mechanism of beta 4 up-regulation and a possible role for alpha 6 beta 4 in the development of heart malformations after the administration of retinoic acid are discussed.

Animals↗
PubMed1996

Species-specific recombinant cell lines as bioassay systems for the detection of 2,3,7,8-tetrachlorodibenzo-p-dioxin-like chemicals.

Exposure to specific polychlorinated diaromatic hydrocarbons (PCDH), such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin), produces a wide variety of species- and tissue-specific toxic and biological effects. Many of these responses are mediated by the Ah receptor (AhR) and are modulated by the interaction of the PCDH:AhR complex with its DNA recognition sequence (the dioxin-responsive element (DRE)). We have constructed a recombinant expression plasmid which contains the luciferase gene under TCDD-inducible control of several DREs and responds to TCDD-like chemicals with the induction of firefly luciferase. Stable transfection of this vector into various cell lines has produced a series of species-specific cell bioassay systems that respond to TCDD-like chemicals with the induction of luciferase in a time-, dose-, and AhR-dependent manner. In addition, these cell lines have been used to demonstrate that 2,2',5,5'-tetrachlorobiphenyl can act as a species-specific AhR antagonist. Overall, these recombinant cell lines can be used for the detection and relative quantitation of AhR agonists/antagonists in complex mixtures of environmental and biological samples, for identification and characterization of novel AhR agonists, and for examination of species differences in PCDH responsiveness.

Animals↗
PubMed1996

Chemical-activated luciferase gene expression (CALUX): a novel in vitro bioassay for Ah receptor active compounds in sediments and pore water.

This study demonstrates that the novel in vitro CALUX (chemical-activated luciferase expression) assay is a rapid, sensitive assay for assessing the toxic potency of (mixtures of) aryl hydrocarbon receptor (AhR)-active compounds in sediments and pore waters. A rat hepatoma (H4IIE) cell line, stably transfected with a construct containing the dioxin-responsive element (DRE) sequence and the luciferase reporter gene, was used to determine the relative potency or the total activities of AhR-active compounds in sediment and pore water extracts. This novel CALUX assay had a detection limit of 0.5 fmol of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The sensitivity and linear working range was slightly better than for the ethoxyresorufin O-deethylase (EROD) assay in H4IIE wild type cells. The primary improvement of the CALUX assay compared to the EROD assay, however, is that the CALUX assay is insensitive to substrate inhibition. The CALUX activity induced by organic extracts from 450-mg aliquots of sediment or 250-microl aliquots of pore water corresponded with the instrumentally analyzed degree of pollution of the sediment. Using pore water, only a simple and rapid extraction procedure was needed, without additional clean-up to prevent cell death. The response from pore water samples in an 8-day early life stage test with zebra fish (Branchydanio rerio) corresponded with the CALUX induction, although the correlation was sometimes disturbed by heavy metals. Two polychlorinated terphenyl mixtures, the PCB-substitute Ugilec 141, polybrominated diphenylethers, and the PCB-mixture Clophen A50 were tested in the CALUX assay and had induction potencies that were 10(-4)-10(-7) compared to TCDD.

Animals↗
PubMed1996

Alterations in rat brain thyroid hormone status following pre- and postnatal exposure to polychlorinated biphenyls (Aroclor 1254).

The effect of daily oral maternal exposure to 0, 5, or 25 mg/kg body wt of a polychlorinated biphenyl (PCB) mixture (Aroclor 1254) on Days 10 to 16 of gestation on plasma and brain thyroid hormone concentrations and peripheral thyroid hormone concentrations and peripheral thyroid hormone metabolism were examined in fetal and weanling rats. Plasma thyroid hormone levels and hepatic microsomal thyroid hormone glucuronidation were also examined in pregnant rats and the adult offspring. Plasma and brain levels of PCBs and hydroxylated PCB metabolites were analyzed in fetal, weanling, and adult offspring. Maternal exposure to Aroclor 1254 significantly decreased fetal (Gestation Day 20) and neonatal (Postnatal Day 4) plasma total thyroxine (T4) and free T4 levels in a dose-dependent manner. Effects of maternal Aroclor 1254 exposure on plasma total and free T4 concentrations were less pronounced in offspring at 21 days of age and absent 90 days after birth. Plasma concentrations of thyroid-stimulating hormone were unaltered in fetuses, neonates, weanling rats, and adult offspring following maternal treatment with Aroclor 1254. the concentration of T4 was severely depressed in the forebrain and cerebellum of fetal rats on Day 20 of gestation following maternal Aroclor 1254 exposure. Brain triiodothyronine (T3) concentrations in the Aroclor-exposed fetuses were significantly decreased relative to control values only in the low-dose group. On Day 21 postpartum T4 concentrations were significantly decreased in the forebrains of female weanling rats from the 25 mg Aroclor 1254/kg dose group, and no reductions were observed in forebrain T3 concentrations in male or female neonates. The deiodination of T4 to T3 was significantly increased in fetal forebrain homogenates by both PCB treatments. In female weanling brain homogenates the deiodination of T4 to T3 was significantly decreased in the low-dose group and unaltered in the high-dose group. No alterations in brain thyroid hormone metabolism were observed in forebrain homogenates from adult offspring exposed pre- and postnatally to Aroclor 1254. Hepatic microsomal T4 glucuronidation was significantly decreased in fetal microsomes following perinatal PCB exposure and significantly increased in weanling hepatic microsomes in a dose-dependent manner. An accumulation of mainly one PCB metabolite, 2,3,3',4',5-pentachloro-4-biphenylol was observed in fetal plasma and forebrain on Gestation Day 20 and in neonatal and weanling rat plasma on Postnatal Days 4, 21, and 90. The plasma level of 2,3,3',4',5-pentachloro-4-biphenylol was higher than that of the persistent PCB congener 2,2',4,4',5,5'-hexachlorobiphenyl in the control and PCB-exposed offspring up to Postnatal Day 21, and even after 90 days, the 2,3,3',4',5-pentachloro-4-biphenylol was present in amounts approximately equal to those of CB 153. Although PCB levels were relatively high in the weanling rat forebrain, no hydroxylated PCB metabolites were detected. On Day 90 postpartum, plasma levels of PCBs and 2,3,3',4',5-pentachloro-4-biphenylol were still elevated in the offspring of PCB-treated dams relative to controls. These results suggest that the accumulation of hydroxylated PCB metabolites in fetal plasma can reduce fetal plasma T4 levels and accordingly fetal brain T4 levels. However, in late gestational fetuses, the induction of brain type II thyroxine 5'-deiodinase activity compensates for decreases in brain T4 levels, so that brain T3 levels are maintained.

Animals↗
PubMed1996

Comparison of Ah receptor-mediated luciferase and ethoxyresorufin-O-deethylase induction in H4IIE cells: implications for their use as bioanalytical tools for the detection of polyhalogenated aromatic hydrocarbons.

A recombinant H4IIE rat hepatoma cell line (H4L1.1c4, H4IIE-luc), containing a luciferase reporter gene under control of dioxin-responsive enhancers, was examined for responsiveness to several polyhalogenated aromatic hydrocarbons (PHAHs). The recombinant cell system was compared with the widely used wild-type cell line (H4IIE-wt), which expresses Ah receptor-mediated cytochrome P450 1A induction. We also report an improved and down-scaled method for the H4IIE-wt bioassay which allows for the rapid screening of environmental samples for Ah-active PhAHs. This method employs 96-well plates, a plate-reading spectrofluorometer, and a fluorescence-based protein assay that enables the simultaneous measurement of resorufin and protein. Both cell lines demonstrated a dose-dependent increase in Ah receptor-mediated response upon exposure to a number of known Ah receptor agonists, including Halowax 1014. H4IIE-luc cells were 3-fold more sensitive than H4IIE-wt cells to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The detection limit and ED50 for EROD induction by TCDD were 0.6 and 4.9 fmol/well (2,4 and 20 pM), respectively; for luciferase induction they were 0.2 and 1.4 fmol/well (0.8 and 5.6 pM). The detection limit for EROD induction in H4IIE-wt cells was a 50-fold improvement over that reported previously (Tillitt et al., Environ. Sci. Technol. 25, 87-92, 1991) and comparable to that of a chicken embryo primary hepatocyte bioassay (Kennedy et al., Anal. Biochem. 211, 102-112, 1993). The tested PHAHs exhibited a similar structure-activity relationship in H4IIE-luc as in H4IIE-wt cells. Binary mixtures of TCDD, PCB-126, and PCB-77 showed no departure from additivity in their combined responses when tested in H4IIE-wt cells. PCB-153 at the highest tested dose of 14 nmol/well (56 microM) significantly reduced the potency of TCDD and PCB-126 without affecting their efficacy in both H4IIE-wt and H4IIE-luc cells. These findings support the use of H4IIE-luc cells as an alternative bioanalytical tool to the wild-type cells for the detection of Ah agonists in environmental samples.

Animals↗
PubMed1996

Persistent alterations in regional brain glial fibrillary acidic protein and synaptophysin levels following pre- and postnatal polychlorinated biphenyl exposure.

Pregnant Wistar WU rats were exposed to 0, 5, and 25 mg of the commercial polychlorinated biphenyl (PCB) mixture Aroclor 1254 per kilogram of body weight on Days 10 to 16 of gestation. Pregnant rats were sacrificed on Gestation Day 20 to observe effects on fetal body and brain weights. Male and female offspring were sacrificed on Postnatal Days 21 and 90 (PND21 and PND90, respectively) and examined for treatment-related effects on neurochemical parameters. The concentrations of the neuronal and glial cell markers, synaptophysin and glial fibrillary acidic protein (GFAP), were measured in diverse brain regions from the offspring using immunochemical techniques. The level of calcineurin (a calmodulin-regulated protein phosphatase) activity was measured in cerebellar homogenates. In addition, ethoxyresorufin O-deethylase (EROD) activity was determined in hepatic microsomes as a measure of a well-characterized response to PCB exposure in experimental animals. The major alterations of GFAP levels following maternal PCB treatment were significant increases in the lateral olfactory tract (LOT) and the cerebellum (CB) and significant decreases in the brain stem (BS) of the offspring on PND21 and 90. Synaptophysin levels were significantly decreased relative to controls in the LOT, prefrontal cortex, and striatum of the offspring on PND90. In the BS, synaptophysin levels were significantly decreased relative to controls in male and female weanlings on PND21 and males on PND90; however, significant increases were observed in the BS of females on PND90. No effect of maternal PCB treatment was observed on levels of GFAP and synaptophysin in the dorsal hippocampus on PND21 and 90. Due to analytical restrictions statistical comparisons of GFAP levels were limited to examining the effect of maternal PCB treatment per brain region per sex per time point. Calcineurin activity was decreased in the female CB on PND21, but a significant increase in activity was observed in the female CB on PND90. No effect of maternal PCB treatment was observed on the cerebellar calcineurin activity in male offspring on PND21 and 90. EROD activity was highly induced in maternal microsomes from both PCB treatment groups, but only slightly induced in fetal hepatic microsomes. On PND21 weanling hepatic microsomal EROD activity was highly induced following gestational and lactational PCB exposure; however, on PND90 EROD activity was unaffected by maternal PCB treatment in male offspring and significantly decreased in female offspring. The results of the present study indicate that gestational and lactational exposure to the commercial PCB mixture results in long-term alterations in a neuronal and glial cell markers in specific brain regions of rats. These marker proteins may be useful for determining the structure-activity relationships in PCB-induced developmental neurotoxicity.

Animals↗
PubMed1996

Host resistance to rat cytomegalovirus (RCMV) and immune function in adult PVG rats fed herring from the contaminated Baltic Sea.

The immunotoxic potential of many classes of environmental contaminants has been well established in laboratory studies, with much attention being focussed on aryl hydrocarbon (Ah)-receptor binding polychlorinated biphenyl (PCB), polychlorinated dibenzo-p-dioxin (PCDD), and polychlorinated dibenzofuran (PCDF) congeners. In a semi-field study, we previously showed that harbour seals (Phoca vitulina) fed herring from the contaminated Baltic Sea had lower natural killer cell activity, T-lymphocyte functionality and delayed-type hypersensitivity responses than seals fed herring from the relatively uncontaminated Atlantic Ocean. While ethical and practical constraints preclude in-depth studies in seals, specific reagents and a wider array of immune function tests allow such studies in laboratory rats. We therefore carried out a feeding study in rats aimed at extending our observations of contaminant-induced immunosuppression in harbour seals. The same two herring batches used in the seal study were freeze-dried, supplemented and fed to female adult PVG rats for a period of 4 1/2 months. Daily contaminant intakes of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxic equivalents (TEQ) were estimated to be 0.3 ng/kg body weight and 1.6 ng/kg in the Atlantic and Baltic groups, respectively. At the end of the feeding experiment, no contaminant-related changes in spleen CD4+/CD8+ cellularity, natural killer cell activity, or mitogen-induced proliferative responses of thymus or spleen cells could be detected. However, total thymocyte numbers and thymus CD4+/CD8+ ratios were reduced in the Baltic group. A novel model was established to assess the specific T-cell response to rat cytomegalovirus (RCMV). When applied to the feeding study, no differences between the Atlantic and Baltic groups in the RCMV-induced proliferative T-lymphocyte responses could be detected, but virus titres in salivary glands of infected rats of the Baltic Sea group were higher. These elevated RCMV titres and changes in thymus cellularity suggest that the dietary exposure to low levels of contaminants may have been immunotoxic at a level which our immune function test could not otherwise detect. While the herring diet per se appeared to have an effect on several immune function parameters, lower plasma thyroid hormone levels in the Baltic Sea group of rats confirmed that exposure to the environmental mixture of contaminants led to adverse PHAH-related health effects.

Animal Feed↗
PubMed1996

Low hepatic 7-ethoxyresorufin-O-deethylase (EROD) activity and minor alterations in retinoid and thyroid hormone levels in flounder (Platichthys flesus) exposed to the polychlorinated biphenyl (PCB) mixture, Clophen A50.

The effect of the polychlorinated biphenyl (PCB) mixture Clophen A50 on hepatic cytochrome P4501A1 dependent EROD (7-ethoxyresorufin-O-deethylase) activity, plasma thyroid hormone levels and plasma, kidney and liver retinoid concentrations of the euryhaline flatfish flounder (Platichthys flesus) was determined 2 and 10 days after i.p. (intraperitoneal) injection with 20, 100 and 500 mg Clophen A50/kg body weight. No effect of Clophen A50 on total cytochrome P450 content in flounder liver was observed at both time points. A six-fold, dose-dependent, significant increase in EROD activity was found at exposure day 10 in flounder receiving 100 or 500 mg Clophen A50/kg body weight. Plasma retinol concentrations were not altered at both time points after Clophen A50 administration, whereas renal retinol levels showed a minor dose-related increase at day 2 and day 10 of exposure. Significant alterations in hepatic retinoid concentrations were observed, which were not dependent on the dose of PCB administered. In addition Clophen A50 administration did not result in a dose-related alteration of total T4 concentrations in plasma. Total T3 concentrations in plasma were only significantly increased at day 2 after exposure, whereas free T4 concentrations were increased at both time points after Clophen A50 administration. These data indicate that with regard to the parameters investigated and in contrast to other fish species studied, the flounder is not a sensitive species to PCB exposure.

Journal Article↗
PubMed1996

Prevalence of the eaeA gene in verotoxigenic Escherichia coli strains from dairy cattle in Southwest Ontario.

This study determined the prevalence of the eaeA gene and its relationship to serotype and type of verotoxin produced in a collection of 432 verotoxigenic Escherichia coli (VTEC) obtained from the faeces of healthy cows and calves in a systematic random survey involving 80 dairy farms in Southwest Ontario. A PCR amplification procedure involving primer pairs which target the conserved central region of the O157:H7 eaeA gene showed that 151 (35.2%) strains were positive for the eaeA gene. All isolates (9-21 for each O group) of O groups 5, 26, 69, 84, 103, 111, 145 and 157 were positive, whereas all isolates (7-34 for each O group) of O groups 113, 132, and 153 and serotype O156:NM (38 isolates) were negative for eaeA. Seventy-three percent of 130 isolates of eaeA-positive serotypes produced VT1 only compared with 20% of 253 isolates of eaeA-negative serotypes. We conclude that there is a strong association between certain O groups and the eaeA gene, that serotypes of eaeA-positive and eaeA-negative VTEC implicated in human and cattle disease are present at high frequency in the faeces of healthy cattle, that VT1 is more frequently associated with eaeA-positive than with eaeA-negative serogroups, and that the eaeA gene is more frequently found in VTEC from calves compared with VTEC from adult cattle.

Animals↗
PubMed1996

Synergistic effect of 2,2',4,4',5,5'-hexachlorobiphenyl and 2,3,7,8-tetrachlorodibenzo-p-dioxin on hepatic porphyrin levels in the rat.

We studied the effect of polychlorinated biphenyls (PCBs) on hepatic porphyrin accumulation in female Sprague-Dawley rats by feeding them diets containing 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153), 2,3,3',4,4',5-hexachlorobiphenyl (PCB 156), 3,3',4,4',5-pentachlorobiphenyl (PCB 126), or combinations of the single PCB congeners with TCDD for 13 weeks. A dose-dependent increase in hepatic porphyrin accumulation occurred after TCDD, PCB 126, or PCB 156 administration, reaching maximal levels of about twice control values. The lowest dose levels for which a significant increase in hepatic porphyrin accumulation was found were 0.7 microgram TCDD/kg diet, 50 micrograms PCB 126/kg diet, or 6 mg PCB 156/kg diet. These doses are equivalent to 47 ng TCDD/kg/day, 3.2 micrograms PCB 126/kg/day, and 365 micrograms PCB 156/kg/day. Relative potencies for hepatic porphyrin accumulation, using TCDD as a reference, ranged from 0.015 to 0.06 for PCB 126 and from 0.0001 to 0.0003 for PCB 156. CYP1A2 activities significantly correlated with hepatic porphyrin levels, with coefficients of 0.629, 0.483, or 0.808 for TCDD, PCB 126, or PCB 156, respectively. Administration of PCB 153 alone did not result in hepatic porphyrin accumulation. Co-administration of PCB 153 and TCDD revealed a strong synergistic effect on porphyrin accumulation (about 800 times control levels). This synergistic effect was significant in rats fed diets containing any combination of PCB 153 with TCDD. Uroporphyrin III and heptacarboxylic porphyrin were accumulated in porphyrinogenic livers. These results suggest that TCDD induction of CYP1A2 may be involved, leading to oxidation of uroporphyrinogen III to uroporphyrin III, in combination with an increase in delta-aminolevulinic acid synthetase induced by PCB 153. Under porphyrinogenic conditions, an inhibitor of CYP1A2 activity may also be formed. The interactive effects on porphyrin accumulation after co-administration of dioxinlike and non-dioxinlike compounds may have significant implications for the risk assessment of these chemicals.

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