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ABSTRACT: The aryl-hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that mediates the toxicity of certain halogenated aromatic hydrocarbons including 2,3,7,8-tetra-chlorodibenzo-p-dioxin (TCDD). These compounds are potent developmental toxicants that can alter gene expression and disrupt processes of proliferation and differentiation. It has not yet been determined which tissues during development are most sensitive to these compounds, nor which genes are directly associated with the toxicities. We developed a transgenic (TG) mouse model to delineate the temporal and spatial context of transcriptionally active AhR by utilizing a dioxin responsive element-linked LacZ reporter system. The present study focuses on the pattern of TCDD-induced transgene expression localized to the footpad and digits of the paws between gestational days (GD) 13 and 18. Paw morphology was evaluated at several developmental stages following TCDD exposure. Gene expression profiles acquired by microarray technology were evaluated in the paws of fetuses exposed at GD 14.5. The results showed that TCDD exposure in utero induced LacZ expression in the developing paws. This expression appeared to be localized to the mesenchymal cell layer. Gross morphological changes were not observed in the paws prior to or after birth following TCDD exposure in utero. However, significant alterations in gene expression profiles in the developing paws were observed at 24 h following TCDD exposure in utero. These results indicate that the developing paw is a target tissue of TCDD in terms of altered gene expression, further validating the use of this AhR responsive reporter gene TG mouse model in studying AhR ligand-mediated responsiveness. However, the linkage of these changes to detectable biological outcomes in the paw remains unclear.
Toxicological Sciences 02/2007; 95(1):240-8. · 4.65 Impact Factor
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ABSTRACT: Rickettsiae, a diverse group of obligately intracellular gram-negative bacteria, include etiologic agents of the spotted fever and typhus groups of diseases. Rocky Mountain spotted fever and boutonneuse fever, due to Rickettsia rickettsii and R. conorii, respectively, are characterized by widespread infection of the vascular endothelium, microvascular injury, and vasculitis. Cultured human endothelial cells (EC) are highly susceptible to infection and respond by altering the expression of adhesion molecules, regulatory cytokines, and the antioxidant enzyme heme oxygenase (HO). In the vasculature, HO regulates the cyclooxygenase (COX) enzymes, among which the inducible isozyme COX-2 facilitates the synthesis of prostaglandins (PGs). Using in vitro and ex vivo models of infection, we demonstrate here that R. rickettsii infection of human EC causes robust induction of COX-2 mRNA and protein expression but has no apparent effect on the constitutive COX-1 isoform. Cells infected with viable rickettsiae consistently displayed significantly increased secretion of 6-keto-PGF(1alpha) and PGE(2). R. rickettsii-induced COX-2 was sensitive to inhibitors of de novo transcription and the pyridinylimidazole-based compound SB 203580, suggesting that this transcriptional host cell response involves signaling through p38 mitogen-activated protein kinase. PG production by infected cells was abrogated by NS 398 (a selective COX-2 inhibitor) and indomethacin (a pan-COX inhibitor). Immunohistochemical staining of sections of infected umbilical cords and corresponding uninfected controls revealed comparatively more intense and abundant staining for COX-2 in infected endothelia. Induction of the endothelial COX-2 system and the resultant enhanced release of vasoactive PGs may contribute to the regulation of inflammatory responses and vascular permeability changes during spotted fever rickettsioses.
Infection and Immunity 10/2006; 74(9):5067-74. · 4.16 Impact Factor
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ABSTRACT: To characterize the voiding function in a transgenic adenocarcinoma of murine prostate (TRAMP) mouse of advanced age, because it might provide a useful model of slow-onset bladder outlet obstruction. Spontaneous death from urinary outlet obstruction occurs in the TRAMP mouse.
A metabolic cage without a fecal separation screen was placed above a precision balance that reported the mass of the excreta pan every 100 ms. A computational algorithm identified voids suitable for uroflow assessment from other excretory events. A series of images were obtained automatically before and during the excretory events.
The TRAMP mouse displayed a pulsatile voiding pattern characterized by a reduction in uroflow, prolongation of voiding, and droplet formation at the tip of the prepuce. Postmortem histologic examination revealed gross enlargement of the prostate, a suburethral tumor, dilation of the lumen of the urethra, and proteinaceous debris in the urethra and bladder.
The observed changes were consistent with urethral obstruction induced by prostate enlargement and/or suburethral tumor. Additional studies are required to ascertain whether prostate enlargement per se is sufficient to produce urethral obstruction in the TRAMP mouse. This transgenic mouse strain may provide a model of slow-onset outlet obstruction that is more representative of bladder outlet obstruction caused by benign prostatic hyperplasia than is the obstruction produced by urethral ligation.
Urology 07/2006; 67(6):1324-8. · 2.43 Impact Factor
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ABSTRACT: We have shown previously that fibrin(ogen) binds fibroblast growth factor 2 (FGF-2) and potentiates stimulation of endothelial-cell (EC) proliferation. We have now used 2 FGF-2 mutants differing only in the 5 residues constituting the binding site to characterize the importance of this interaction in angiogenesis. The nonbinding (2212) and binding (221*2) mutants stimulated EC proliferation by 2.2 +/- 0.4-fold and 2.9 +/- 0.3-fold over control, respectively, and both were similar to wild-type (wt) FGF-2 (2.5 +/- 0.3-fold). Proliferation was augmented by fibrinogen to 5.3 +/- 1.2-fold and 4.8 +/- 0.8-fold with wtFGF-2 and 221*2, whereas no augmentation occurred with 2212 and fibrinogen. Using a placental explant model in a fibrin matrix, wtFGF-2 resulted in 2.6 +/- 0.9-fold more growth over control, and 221*2 increased growth 3.3 plus or minus 0.9-fold. Vessel outgrowth with 2212 was minimal and comparable to control. Similarly, fibrinogen potentiated wtFGF-2 or 221*2-mediated angiogenesis in the chicken chorioallantoic membrane model. In a mouse Matrigel implant model, fibrinogen significantly increased angiogenesis with either wtFGF-2 or 221*2, whereas there was no augmentation with 2212. These results demonstrate that binding of FGF-2 to fibrin(ogen) mediated by the 5-residue FGF-2-fibrin(ogen) interactive site is required for augmented angiogenesis.
Blood 02/2006; 107(1):126-31. · 9.90 Impact Factor
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Lawrence S Taylor,
Deborah J Rubens,
Brian C Porter,
Zhe Wu, Raymond B Baggs,
P Anthony di Sant'Agnese,
Gyongyi Nadasdy,
David Pasternack,
Edward M Messing,
Priya Nigwekar,
Kevin J Parker
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ABSTRACT: To prospectively evaluate the accuracy of three-dimensional (3D) sonoelastographic imaging, relative to that of gray-scale ultrasonography (US), in the in vitro detection of prostate cancer.
The study was approved by the institutional review board and was HIPAA compliant. Informed consent was obtained from all patients. Nineteen prostatectomy specimens from patients aged 46-70 years with biopsy-proved prostate cancer were scanned in three dimensions by using conventional B-mode US and sonoelastography with vibrations of more than 100 Hz. Step-sectioned whole-mount histologic specimens were used to create a 3D volume of the prostate and the tumors within it. B-mode US scans and regions of low vibration on the sonoelastographic images (hard regions) were formatted in three dimensions. The lesions in the 19 cases were classified into two groups, as follows: G1 lesions were pathologically confirmed tumors with a volume of at least 1.0 cm3, and G2 lesions were pathologically confirmed tumors smaller than 1.0 cm3. G1 lesions were evaluated with B-mode US and sonoelastography and classified as true-positive, false-positive, true-negative, or false-negative; G2 lesions were evaluated only with sonoelastography. Findings at histologic examination were used as the reference standard. True-positive findings necessitated 3D lesion correlation between pathologic and imaging data. Conventional definitions of accuracy and sensitivity were used for statistical analysis.
For G1 lesions (seven lesions with a volume of at least 1.0 cm3), sonoelastography had an accuracy of 55% and a sensitivity of 71% and B-mode US had an accuracy of 17% and a sensitivity of 29%. The mean tumor volume was 3.1 cm3 +/- 2.1 (standard deviation). For G2 lesions (22 lesions with a volume of less than 1.0 cm3), the mean tumor volume was 0.32 cm3 +/- 0.21. Sonoelastography had an accuracy of 34% and a sensitivity of 41%; there were six false-positive findings.
Sonoelastography performed considerably better than did gray-scale US in the depiction of prostate cancer for tumors with volumes of more than 1 cm3.
Radiology 01/2006; 237(3):981-5. · 5.73 Impact Factor
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Robert J Siegel,
Valentina N Suchkova,
Takashi Miyamoto,
Huai Luo, Raymond B Baggs,
Yoram Neuman,
Michael Horzewski,
Veijo Suorsa,
Sergio Kobal,
Todd Thompson,
Debra Echt,
Charles W Francis
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ABSTRACT: We evaluated whether ultrasound improves myocardial tissue perfusion in 14 animals with coronary artery occlusion.
A recent study demonstrated that low-frequency ultrasound improves tissue perfusion in the rabbit ischemic limb, but there are no data on ultrasound enhancement of myocardial perfusion.
Fourteen animals (9 dogs, 5 pigs) underwent thoracotomy and occlusion of a diagonal branch of the left anterior descending coronary artery. Myocardial tissue perfusion units (TPUs) and pH were measured before coronary occlusion, after occlusion, and after direct exposure of the ischemic myocardium in the presence of fixed occlusion to low-frequency ultrasound (27 kHz).
The TPU decreased from 100.9 +/- 13 at baseline to 71.1 +/- 13 (p < 0.01) after 60 min occlusion but rose by 19.7% to 85.1 +/- 8 (p < 0.01) after ultrasound exposure for 60 min. After 60-min coronary occlusion, myocardial pH fell from 7.43 +/- 14 to 7.05 +/- 0.15 (p < 0.01) but then improved to normal (7.46 +/- 0.32) after ultrasound for 60 min. Administration of L-Nomega-nitro-arginine methyl esther (L-NAME), an inhibitor of nitric oxide synthase, before ultrasound exposure, blocked improvement in myocardial tissue perfusion and pH by ultrasound. Quantitative histomorphology showed a significant increase in the capillary area of myocardium exposed to ultrasound versus non-exposed myocardium (16.2 +/- 7.9 vs. 8.2 +/- 2.1, p < 0.02).
Low-frequency, low-intensity ultrasound improves myocardial tissue perfusion and pH in the presence of a fixed coronary artery occlusion.
Journal of the American College of Cardiology 11/2004; 44(7):1454-8. · 14.16 Impact Factor
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ABSTRACT: The involvement of oxidative mechanisms in the pathogenesis of rickettsiosis was investigated using infection of C3H/HeN mice with sub-lethal and lethal infectious doses of Rickettsia conorii, the causative agent of Mediterranean spotted fever. Microscopic examination of tissues at 48 and 96 h post-infection revealed characteristic pathologic features and the presence of rickettsiae in the endothelium of infected tissues. Activities of key antioxidant enzymes, namely glutathione peroxidase, glutathione reductase, glucose-6-phosphate dehydrogenase, and superoxide dismutase, at these times exhibited a pattern of differential and selective modulation in brain, lungs, and testes of mice infected with viable organisms, whereas heat-inactivated or sonically disrupted rickettsiae had no effect. Of these, most significant changes were evident in the lungs of infected animals. Adaptive alterations in oxidant-scavenging enzymes occurred in apparent correlation with the dose and duration of infection. Treatment with an antioxidant, alpha-lipoic acid, protected against infection-induced oxidative injury via regulation of antioxidant enzyme activities and maintenance of reduced glutathione levels. These results suggest the involvement of regulatory enzymes of glutathione redox and superoxide scavenging systems in the antioxidant response during in vivo infection, the extent of which varies with the titer of viable rickettsiae in different organs of the host.
Microbial Pathogenesis 07/2004; 36(6):293-301. · 1.94 Impact Factor
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ABSTRACT: A whole mount histology protocol for 3-D tissue reconstruction to compare the size and spatial location of tumors (and other components) identified in histology data with that from 3-D ultrasound (US) images is presented. Prostate specimens are imaged in 3-D using B-mode (US) and sonoelastography. The prostate surface is outlined in each B-mode image and a 3-D surface reconstruction is made. The specimen is then prepared for whole mount histology and the histology slides are digitally reconstructed to make a 3-D surface. These two surfaces are then aligned using a 3-D correlation algorithm, and the tumor boundary determined by the pathologist is compared with that using sonoelastography. 3-D images showing the overlapping histology and sonoelastography of prostate surface reconstructions for one prostate are presented to illustrate the technique; results for four prostates yielded an accuracy of 92% +/- 3%.
Ultrasound in Medicine & Biology 03/2004; 30(2):161-8. · 2.29 Impact Factor
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ABSTRACT: While advancing age is the only unequivocally accepted risk factor for idiopathic Parkinson's disease, it has been postulated that exposure to environmental neurotoxicants combined with ageing could increase the risk for developing Parkinson's disease. The current study tested this hypothesis by exposing C57BL/6 mice that were 6 weeks, 5 months or 18 months old to the herbicide paraquat, the fungicide maneb or paraquat + maneb, a combination that produces a Parkinson's disease phenotype in young adult mice. Paraquat + maneb-induced reductions in locomotor activity and motor coordination were age dependent, with 18-month-old mice most affected and exhibiting failure to recover 24 h post-treatment. Three months post-treatment, reductions in locomotor activity and deficits in motor coordination were sustained in 5-month-old and further reduced in 18-month-old paraquat + maneb groups. Progressive reductions in dopamine metabolites and dopamine turnover were greatest in 18-month-old paraquat + maneb and paraquat groups 3 months post-treatment. Increased tyrosine hydroxylase enzyme activity compensated for striatal tyrosine hydroxylase protein and/or dopamine loss following treatment in 6-week-old and 5-month-old, but not 18-month-old paraquat and paraquat + maneb mice. Numbers of nigrostriatal dopaminergic neurons were reduced in all age groups following paraquat alone and paraquat + maneb exposure, but these losses, along with decreases in striatal tyrosine hydroxylase protein levels, were progressive in 18-month-old paraquat and paraquat + maneb groups between 2 weeks and 3 months post-exposure. Collectively, these data demonstrate enhanced sensitivity of the ageing nigrostriatal dopamine pathway to these pesticides, particularly paraquat + maneb, resulting in irreversible and progressive neurotoxicity.
European Journal of Neuroscience 09/2003; 18(3):589-600. · 3.63 Impact Factor
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ABSTRACT: Dichloroacetic acid (DCA), chlorofluoroacetic acid (CFA), and difluoroacetic acid (DFA) are inhibitors of pyruvate dehydrogenase kinase. DCA is used for the clinical management of congenital lactic acidosis. Glutathione transferase zeta (GSTZ1-1) catalyzes the biotransformation of DCA and CFA, and DCA is a mechanism-based inactivator of GSTZ1-1. In rodents, DCA causes multiorgan toxicities and is hepatocarcinogenic. The toxic effects of CFA, which is an excellent substrate but a poor inactivator of GSTZ1-1, have not been investigated. The objective of this study was to investigate the nephrotoxicity of CFA. Rats given a single dose of 1.5 mmol/kg CFA became anuric and died within 24 h. Urinalysis and light microscopic analysis showed that rats given 0.6-1.2 mmol/kg CFA developed polyuria, glycosuria, and renal proximal tubular damage. Electron microscopic analysis indicated a role for apoptosis in CFA-induced cell death. The nephrotoxicity of CFA was associated with a dose-dependent increase in inorganic fluoride excretion. Treatment of rats with DCA for 5 days to inactivate GSTZ1-1 failed to prevent metabolism of CFA to fluoride and did not block CFA-induced renal damage. A role for GSTZ1-1-catalyzed release of fluoride from CFA is proposed but a role for other enzymes cannot be excluded. DFA, which is not metabolized to fluoride by GSTZ1-1, was given to rats as a control and was also nephrotoxic: rats given 1.2 mmol DFA/kg/day for 5 days had normal urine volumes but showed proximal and distal tubular damage; fluoride excretion was not elevated. The mechanism of DFA-induced nephrotoxicity is not known but appears to differ from that of CFA.
Toxicological Sciences 01/2003; 70(2):261-8. · 4.65 Impact Factor
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ABSTRACT: Ultrasound accelerates enzymatic fibrinolysis in vitro and in animal models and may be used as an adjunct to thrombolytic therapy. Ultrasound can also affect vascular tone directly, and we have now investigated the effect of ultrasound on tissue perfusion in a rabbit model of acute muscle ischemia to characterize the magnitude and temporal course of vasodilation and determine its mechanism. After ligation of the femoral artery of rabbits, tissue perfusion in the gracilis muscle as determined using a laser Doppler probe declined by 53% from 13.7 +/- 0.3 U to 6.4 +/- 0.2 U. The tissue became acidotic as pH declined from normal to 7.05 +/- 0.2. Application of 40 kHz ultrasound at intensities from 0.25 to 0.75 W/cm(2) progressively improved perfusion over 60 min and reversed acidosis, but these effects were both completely blocked by pre-treatment with the nitric oxide synthase inhibitor L-NAME. Nitric oxide synthase activity in muscle was measured using an assay based on the conversion of radiolabeled L-arginine to L-citrulline and demonstrated an increase of 3.6-fold following ultrasound exposure. This effect was greatest at locations close to the transducer and declined progressively away from it. Histologic examination showed greater capillary circumference in ultrasound exposed muscle compared to unexposed tissue with no other histologic changes. We conclude that the application of 40 kHz at low intensity improves perfusion and reverses acidosis in acutely ischemic muscle through a nitric oxide dependent mechanism.
Thrombosis and Haemostasis 12/2002; 88(5):865-70. · 5.04 Impact Factor
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ABSTRACT: Idiopathic Parkinson's disease (PD) is associated with advanced age, but it is still unclear whether dopaminergic neuronal death results from events initiated during development, adulthood, or represents a cumulative effect across the span of life. This study hypothesized that paraquat (PQ) and maneb (MB) exposure during critical periods of development could permanently change the nigrostriatal dopamine (DA) system and enhance its vulnerability to subsequent neurotoxicant challenges. C57BL/6 mice were treated daily with saline, 0.3 mg/kg PQ, 1 mg/kg MB or PQ + MB from post-natal (PN) days 5 to 19. At 6 weeks, a 20% decrease in activity was evident only in the PQ + MB group, with a further decline (40%) observed at 6 months. A subset of mice were re-challenged as adults with saline, 10 mg/kg PQ, 30 mg/kg MB, or PQ + MB 2 x a week for 3 weeks. Mice exposed developmentally to PQ + MB and rechallenged as adults were the most affected, showing a 70% reduction in motor activity 2 weeks following the last rechallenge dose. Striatal DA levels were reduced by 37% following developmental exposure to PQ + MB only, butfollowing adult re-challenge levels were reduced by 62%. A similar pattern of nigral dopaminergic cell loss was observed, with the PQ + MB treated group exhibiting the greatest reduction, with this loss being amplified by adult re-challenge. Developmental exposure to PQ or MB alone produced minimal changes. However, following adult re-challenge, significant decreases in DA and nigral cell counts were observed, suggesting that exposure to either neurotoxicant alone produced a state of silent toxicity that was unmasked following adult re-exposure. Taken together, these findings indicate that exposure to pesticides during the PN period can produce permanent and progressive lesions of the nigrostriatal DA system, and enhanced adult susceptibility to these pesticides, suggesting that developmental exposure to neurotoxicants may be involved in the induction of neurodegenerative disorders and/or alter the normal aging process.
NeuroToxicology 11/2002; 23(4-5):621-33. · 3.10 Impact Factor
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ABSTRACT: Glutathione transferase zeta (GSTZ1-1) catalyzes the biotransformation of a range of alpha-haloacids, including dichloroacetic acid (DCA), and the penultimate step in the tyrosine degradation pathway. DCA is a rodent carcinogen and a common drinking water contaminant. DCA also causes multiorgan toxicity in rodents and dogs. The objective of this study was to determine the expression and activities of GSTZ1-1 in rat tissues with maleylacetone and chlorofluoroacetic acid as substrates. GSTZ1-1 protein was detected in most tissues by immunoblot analysis after immunoprecipitation of GSTZ1-1 and by immunohistochemical analysis; intense staining was observed in the liver, testis, and prostate; moderate staining was observed in the brain, heart, pancreatic islets, adrenal medulla, and the epithelial lining of the gastrointestinal tract, airways, and bladder; and sparse staining was observed in the renal juxtaglomerular regions, skeletal muscle, and peripheral nerve tissue. These patterns of expression corresponded to GSTZ1-1 activities in the different tissues with maleylacetone and chlorofluoroacetic acid as substrates. Specific activities ranged from 258 +/- 17 (liver) to 1.1 +/- 0.4 (muscle) nmol/min/mg of protein with maleylacetone as substrate and from 4.6 +/- 0.89 (liver) to 0.09 +/- 0.01 (kidney) nmol/min/mg of protein with chlorofluoroacetic acid as substrate. Rats given DCA had reduced amounts of immunoreactive GSTZ1-1 protein and activities of GSTZ1-1 in most tissues, especially in the liver. These findings indicate that the DCA-induced inactivation of GSTZ1-1 in different tissues may result in multiorgan disorders that may be associated with perturbed tyrosine metabolism.
Drug Metabolism and Disposition 07/2002; 30(6):616-25. · 3.73 Impact Factor
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ABSTRACT: The possibility that bacteria may have evolved strategies to overcome host cell apoptosis was explored by using Rickettsia rickettsii, an obligate intracellular Gram-negative bacteria that is the etiologic agent of Rocky Mountain spotted fever. The vascular
endothelial cell, the primary target cell during in vivo infection, exhibits no evidence of apoptosis during natural infection and is maintained for a sufficient time to allow replication
and cell-to-cell spread prior to eventual death due to necrotic damage. Prior work in our laboratory demonstrated that R. rickettsii infection activates the transcription factor NF-κB and alters expression of several genes under its control. However, when
R. rickettsii-induced activation of NF-κB was inhibited, apoptosis of infected but not uninfected endothelial cells rapidly ensued. In addition,
human embryonic fibroblasts stably transfected with a superrepressor mutant inhibitory subunit IκB that rendered NF-κB inactivatable
also underwent apoptosis when infected, whereas infected wild-type human embryonic fibroblasts survived. R. rickettsii, therefore, appeared to inhibit host cell apoptosis via a mechanism dependent on NF-κB activation. Apoptotic nuclear changes
correlated with presence of intracellular organisms and thus this previously unrecognized proapoptotic signal, masked by concomitant
NF-κB activation, likely required intracellular infection. Our studies demonstrate that a bacterial organism can exert an
antiapoptotic effect, thus modulating the host cell’s apoptotic response to its own advantage by potentially allowing the
host cell to remain as a site of infection.
Proceedings of the National Academy of Sciences 04/1998; 95(8):4646-4651. · 9.68 Impact Factor
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ABSTRACT: The teratogenicity of methanol was investigated following a single oral exposure preceded by an equal volume of mineral oil to guard against local gastric irritation. Four groups of pregnant Long-Evans rats were gavaged on day 10 of gestation with the following solutions: 0.0 (n = 13), 1.3 (n = 12), 2.6 (n = 11), and 5.2 (n = 10) mL MeOH/kg. Wilson sectioning (head only), gross necropsy, and Alizarin red skeletal examinations were performed on day 20 of gestation. At 5.2 mL/kg, the dams demonstrated >20% decrease in weight gain in comparison to the control, which was the only clinical toxic manifestation or histopathologic change noted for the dams. Methanol at all doses failed to produce any significant change in standard reproductive indices (e.g., postimplantation loss). A significant decrease in fetal body weight (11 to 19.5%), however, was associated with prenatal oral ingestion of methanol. Both internal and external examination of the fetuses demonstrated a dose-dependent increase in anomalies [0 = 0.6%, 1.3 mL/kg = 3.7%, 2.6 mL/kg = 7%, 5.2 mL/kg = 16.5% (litter percents)]. The dose-related anomalies were undescended testes, exophthalmia, and anophthalmia. Thus, acute methanol given orally produces anomalies, even when there is no apparent maternal toxic response.
Reproductive Toxicology · 3.23 Impact Factor
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ABSTRACT: The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that mediates the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related halogenated aromatic hydrocarbons. Although the normal function and endogenous ligand for this receptor are not known, it is thought to have a role in growth regulation processes. The AhR has been found in both adult and certain developing tissues, and AhR agonists like the environmental contaminant TCDD cause a number of developmental anomalies. We sought to determine whether the AhR is directly activated to a transcriptionally functional form in tissues known to be adversely affected by AhR agonist exposure. To this end, a transgenic mouse model was developed that could be used to indicate the temporal and spatial context of transcriptionally active AhR following agonist exposurein vivo.A synthetic promoter containing two dioxin-responsive elements (DREs) and a minimal TATA box was strongly induced by TCDD in transfected cells when linked to thelacZor luciferase reporter gene. Transgenic mice harboring thelacZconstruct had TCDD-inducible β-galactosidase activity in tissues following adult andin uteroexposure. EmbryoniclacZexpression was induced in hard and soft palates, genital tubercle, certain facial regions, shoulder, as well as other tissues byin uteroexposure to 30 μg TCDD/kg at Gestational Day 13. The most intense reporter response was observed in the genital tubercle. Histopathology of the palate and tubercle demonstrated the reporter gene activity to be both cell- and region-specific. This is the first publication to correlate reported TCDD-elicited toxicity (e.g., cleft palate in mice) with TCDD-dependent AhR activation. These data indicate the ability of TCDD to initiate a signal transduction process leading to a transcriptionally active AhR in these tissues, thereby identifying potential targets of dioxin-induced toxicity during development. Weak activation of the reporter gene was consistently observed only in the genital tubercle in the absence of exogenous inducer. This indicates minimal or no endogenous AhR activators at the developmental stage examined. This mouse model will prove useful for both the examination of the endogenous role of the AhR in proliferation or differentiation and of the developmental targets of dioxin-like compounds.
Toxicology and Applied Pharmacology.
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ABSTRACT: The temporal - and dose-related characteristics of hepatic enzymes induced and toxic responses elicited in the hamster by 2,3,7,8-tetrachlorodibenzo--dioxin were examined. The results demonstrate a dissociation of the induction of these hepatic enzymes from TCDD-elicited lethality, but not necessarily hepatic damage, in this species. Furthermore, the hyperthyroidism observed is suggestive of a role of these hormones in the relatively insensitive nature of this species to TCDD treatment.
Chemosphere 15:1749-1752. · 3.21 Impact Factor
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ABSTRACT: Sexually dimorphic patterns of cortical lateralization are documented extensively in both human and animal brains. Male rats tend to exhibit pronounced right hemisphere dominance compared with females, whereas females typically exhibit more diffuse lateralization patterns and greater left hemisphere bias compared with males. Prenatal TCDD (2,3,7,8 tetrachlorodibenzo-p-dioxin) exposure produces demasculinization of male offspring sexual behavior. In previous studies, we showed a reversal of cortical dominance in rats after prenatal TCDD exposure on gestational day 18 (GD 18). The current study aimed to determine the nature of changes observed in rats exposed to TCDD on GD 8. In addition, locomotor activity was measured in male and female offspring on postnatal day (PND) 30, 60 and 90. Pregnant females were given, via gavage, a single dose of 0, 20, 60 or 180 ng kg(-1) TCDD on GD 8. Cortical depth measurements were taken in selected brain regions in offspring 3 months old that had been exposed to the 180 ng kg(-1) dose. Areas 2, 3, 17, 18a and 39 at bregmas -1.8, -3.8 and -5.8 were analyzed by quantifying digitized, enhanced images produced by a photomicroscope fitted with a special color camera. In both male and female offspring, cortical thicknesses in control brains exceeded those of exposed brains. In several brain areas of male offspring exposed to TCDD, right hemispheric dominance reversed to left hemispheric dominance. Female offspring brains showed a contrary move towards right hemisphere dominance. Motor activity in juvenile and mature animals did not differ among dose groups. These data demonstrate that prenatal exposure to TCDD reduces cortical thickness and alters the normal pattern of cortical asymmetry, a finding consistent with the sexually dimorphic behavioral effects induced by this agent.
Journal of Applied Toxicology 22(2):129-37. · 2.48 Impact Factor
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ABSTRACT: Sex-specific patterns of cerebral cortical lateralization have been documented consistently in both the human and animal brain. Male rats tend to exhibit pronounced right hemisphere dominance compared with females, while females typically exhibit more diffuse lateralization patterns and greater left hemisphere bias compared with males. Prenatal TCDD (2,3,7,8 tetrachlorodibenzo-p-dioxin) exposure produces demasculinization of male offspring sexual behavior, suggesting interference with sexual differentiation of the brain. In previous studies, a reversal of cortical thickness patterns in rats was shown after prenatal TCDD exposure on gestational day 8 (GD 8). The current study, based on the same brain sections, attempted to define changes in the number of cortical cells and cell size distributions in brains of offspring from TCDD-treated dams. Pregnant females were given a single oral dose of 0 or 180 ng kg(-1) TCDD on GD 8. Cell counts and sizes were determined in 3-month-old offspring. Areas 17 and 18a at bregma -3.8 were analysed using digitized, enhanced images of brain sections produced by a photomicroscope fitted with a high-resolution digital camera. Prenatal TCDD exposure altered the relative proportions of smaller and larger cell sizes in male, but not in female offspring. Both exposed males and females, however, exhibited a significant reversal of hemispheric dominance based on cell number. These findings demonstrate that prenatal exposure to TCDD alters the normal patterns of cortical cell asymmetry in a manner consistent with our previous data on thickness patterns.
Journal of Applied Toxicology 26(1):25-34. · 2.48 Impact Factor
