Dose Of Dioxin Research Articles

Low-Dose Dioxin Reduced Glucose Uptake in C2C12 Myocytes: The Role of Mitochondrial Oxidative Stress and Insulin-Dependent Calcium Mobilization.

Chronic exposure to some environmental polluting chemicals (EPCs) is strongly associated with metabolic syndrome, and insulin resistance is a major biochemical abnormality in the skeletal muscle in patients with metabolic syndrome. However, the causal relationship is inconsistent and little is known about how EPCs affect the insulin signaling cascade in skeletal muscle. Here, we investigated whether exposure to 100 pM of 2,3,7,8-tetrachlorodibenzodioxin (TCDD) as a low dose of dioxin induces insulin resistance in C2C12 myocytes. The treatment with TCDD inhibited the insulin-stimulated glucose uptake and translocation of glucose transporter 4 (GLUT4). The low-dose TCDD reduced the expression of insulin receptor β (IRβ) and insulin receptor substrate (IRS)-1 without affecting the phosphorylation of Akt. The TCDD impaired mitochondrial activities, leading to reactive oxygen species (ROS) production and the blockage of insulin-induced Ca2+ release. All TCDD-mediated effects related to insulin resistance were still observed in aryl hydrocarbon receptor (AhR)-deficient myocytes and prevented by MitoTEMPO, a mitochondria-targeting ROS scavenger. These results suggest that low-dose TCDD stress may induce muscle insulin resistance AhR-independently and that mitochondrial oxidative stress is a novel therapeutic target for dioxin-induced insulin resistance.

Ultrastructure of rat cerebral cortex cells in normal and experimental dioxin poisoning

Purpose the study of the ultrastructure of the cerebral cortex of rats in normal and experimental poisoning with dioxin.
 Materials and methods. We studied the ultrastructure of the cells of the pyramidal layer of the cerebral cortex of rats of the control and experimental groups that were chronic poisoned with small doses of dioxin (2,3,7,8-tetrachlorodibenzo-para-dioxin or TCDD). Morphometric analysis was carried out to determine the length of synaptic clefts, the number of synapses per unit area, the thickness of the myelin layer of the processes and the number of wrappers of myelin sheaths.
 Results. The pathology of neurons has been observed both at the optical and ultrastructural levels. It is characterized by a decrease in nuclei, cell death, thinning of myelin sheaths and demyelination. The dose of poisoning correlates with the degree of destruction of neurons: with an increase in the dose of dioxin, changes become more significant. The number of synaptic contacts decreases but there is a significant increase in their average length.
 Conclusions. The processes of demyelination, impaired cellular respiration and destruction of synaptic contacts indicate the ability of dioxin to indirectly cause accelerated aging of neurons and their death (apoptosis).

Female mice exposed to low doses of dioxin during pregnancy and lactation have increased susceptibility to diet-induced obesity and diabetes

ObjectiveExposure to persistent organic pollutants is consistently associated with increased diabetes risk in humans. We investigated the short- and long-term impact of transient low-dose dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin, TCDD) exposure during pregnancy and lactation on glucose homeostasis and beta cell function in female mice, including their response to a metabolic stressor later in life. MethodsFemale mice were injected with either corn oil (CO; vehicle control) or 20 ng/kg/d TCDD 2x/week throughout mating, pregnancy and lactation, and then tracked for 6–10 weeks after chemical exposure stopped. A subset of CO- and TCDD-exposed dams was then transferred to a 45% high-fat diet (HFD) or remained on a standard chow diet for an additional 11 weeks to assess the long-term effects of TCDD on adaptability to a metabolic stressor. To summarize, female mice were transiently exposed to TCDD and then subsequently tracked beyond when TCDD had been excreted to identify lasting metabolic effects of TCDD exposure. ResultsTCDD-exposed dams were hypoglycemic at birth but otherwise had normal glucose homeostasis during and post-TCDD exposure. However, TCDD-exposed dams on a chow diet were modestly heavier than controls starting 5 weeks after the last TCDD injection, and their weight gain accelerated after transitioning to a HFD. TCDD-exposed dams also had an accelerated onset of hyperglycemia, impaired glucose-induced plasma insulin levels, reduced islet size, increased MAFA-ve beta cells, and increased proinsulin accumulation following HFD feeding compared to controls. Overall, our study demonstrates that low-dose TCDD exposure during pregnancy has minimal effects on metabolism during the period of active exposure, but has detrimental long-term effects on metabolic adaptability to HFD feeding. ConclusionsOur study suggests that transient low-dose TCDD exposure in female mice impairs metabolic adaptability to HFD feeding, demonstrating that dioxin exposure may be a contributing factor to obesity and diabetes pathogenesis in females.

The Protective Effect of Xanthohumol on the Content of Selected Elements in the Bone Tissue for Exposed Japanese Quails to TCDD.

Dioxins (including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) are highly toxic and persistent chemicals widely distributed in the environment in trace amounts, and are side products of industrial and chemical processes. Exposure to dioxins leads to multiorgan morphological and functional abnormalities, including within the bone tissue, disrupting its microarchitecture and mechanical properties. Xanthohumol (XN) is a chemical compound classified as a prenylated flavonoid, distinguished by multidirectional biological action. The aim of the study is to assess whether xanthohumol, as a substance with strong antioxidant and anti-inflammatory properties, has the ability to eliminate the negative effects of TCDD on bone tissue. The experiment was conducted on adult Japanese quails. Two different doses of TCDD and xanthohumol were administered to birds. After euthanasia of animals, the research material in the form of cranial vault and hind limb bone was collected, and their mineral compositions of calcium, phosphorus, magnesium, zinc, and iron concentrations were determined using atomic emission spectrometry in an acetylene-air flame method. Our results indicate that the administration of TCDD at a low dose causes more dynamic changes in the concentration of elements in bone, in comparison to a higher dose of dioxin. Results show also that higher doses of the XN cause the linear increase in the concentration of phosphorus and iron in the bone of the hind limb, and calcium in the bones of the cranial vault. In conclusion, our experiment shows that the use of TCDD and XN in Japanese quails together in various doses influences the content of phosphorus, magnesium, zinc, and iron in the research material.

Risk Factors for Environmental Pollution with Dioxin-Containing Compounds

Introduction. It has been demonstrated that the use of 2,4-D herbicide contaminates the environment with polychlorinated compounds, including dioxins. Additional risk factors for population health and the environment include climatic conditions of Siberia, processes of translocation of compounds from soil to plants, their ability to reach the human body along trophic chains and to have a toxic effect. The objective of this study was to analyze the behavior of the 2,4-D herbicide and dioxins in the environment and to justify health risk factors. Materials and methods. We used the method of gas chromatography-mass spectrometry that combines high efficiency of separation of impurities, the possibility of determining their molecular composition, selectivity of recording, and high sensitivity. We used a chromatographic method to determine residual amounts of the 2,4-dichlorophenoxyacetic acid amine salt (2,4-D) in soil, feed, and food of plant and animal origin. The calculation of average and statistical errors of indicators was performed using t-test in MS Excel. Results. Contamination of water of open reservoirs of the Irkutsk Region with the 2,4-D herbicide amine salt was found in concentrations as high as 7.7 μg/L with a positive sample count of 49%. In spring and summer, the water of open reservoirs is also polluted. In soils, the 2,4-D amine salt is immobile, concentrated in the surface layer at the level of 0.42–0.37 mg/kg. The maximum total soil concentration of dioxins reached 1,479 ng/kg exceeding the maximum permissible soil concentration of dioxins by 306 times. The maximum concentration of dioxins in feed was found at the end of the growing season (317–322 ng/kg). Dioxins accumulate in fat-containing food; thus, measured dioxin concentrations in butter averaged 680.6 ng/kg demonstrating a 10-fold excess of the permissible level. The estimated daily intake of dioxins with food can be as high as 26.2 pg/kg, which is 2.6 times higher than the permissible daily dose. We conducted the environmental and medico-hygienic analysis of outcomes of using the effective herbicide that poses a serious danger to human health due to the possibility of dioxin formation. We identified risk factors and substantiated the daily dose of dioxins for humans as a temporary value.

The dioxin regulation criteria in the agro-industrial complex of Russia

The article studies the reactions of biochemical, hematological, pathomorphological, immunological and ultrastructural changes in the organisms of laboratory animals that were subjected to chronic dioxin poisoning at threshold doses were studied. There were hold toxicological experiments on white rats of both sexes weighing 155–215 g in order to detect threshold doses. For two months, 2,3,7,8-tetrachlorodibenzo-para-dioxin (2,3,7,8- TCDD) in amounts corresponding to 1/100 and 1/200 LD 50. After each decade, some of the animals were euthanized and weighed to calculate the mass coefficient of internal organs. The obtained data comparison revealed no statistically significant changes in organ. Continued observation of animals in the experiment for up to two months, characteristic intoxication 2,3,7,8-TCDD clinical signs did not give. The correlation dependence of the minimum effective doses of 2,3,7,8-TCDD, namely 1/400 of LD50 with LD50, was determined. The obtained threshold dose of dioxin can be recommended as the basis for the normalization of dioxin in the Russian agro-industrial complex. There were determined biochemical, hematological and ultrastructural changes in the body of animals exposed to chronic poisoning of 2,3,7,8-TCDD in doses of 1/200, 1/300 of LD50. The article describes a statistically significant dependence of the respiratory activity of the liver mitochondria in laboratory animals (white rats and rabbits) on chronic poisoning with threshold doses of various degrees. Based on laboratory animals’ experiments, threshold concentrations are determined and the maximum permissible levels of dioxin in the feed of some animals are tentatively calculated.

Effects of dioxin on testicular histopathology, sperm parameters, and CatSper2 gene and protein expression in Naval Medical Research Institute male mice.

The CatSper gene family is known to be solely expressed in sperm cells and is possibly associated with sperm motility and penetration through the zona pellucida. Despite its vital role in male fertility, factors regulating its expression are not widely known. The present study aimed at evaluating the effects of dioxin on CatSper2 gene and protein expression, testicular histopathology, sperm quality and biochemical parameters in a mice model. The experiments were performed on 32 Naval Medical Research Institute male mice (2-3months). The animals were divided into four groups in a random manner: (a) control; (b) dioxin 1; (c) dioxin 2; and (d) dioxin 3. The treatment groups received 0.1, 0.5 and 1µg/kg of dioxin intraperitoneally every day for 2weeks. Administration of dioxin significantly downregulated the CatSper2 gene and protein expression. A greater reduction in gene and protein expression was found at higher doses of dioxin. At the same time, sperm parameters, especially sperm motility and count, decreased in mice exposed to dioxin. The results of testicular histopathology showed necrotic degeneration and epithelium thickness reduction in the dioxin groups in comparison with the controls. Besides, oxidative stress increased in seminiferous tubules.

BIOCHEMICAL AND HISTOLOGICAL CHANGES IN THE LIVER OF DIOXIN (TCDD)- INTOXICATED RABBITS

2,3,7,8- Tetrachlorodibenzo-p-dioxin (TCDD) is a highly persistent trace environmental contaminant that represents one of the most potent toxicants known to man. Dioxin is the name generally given to a class of super-toxic chemicals, formed as a by–product of the manufacture, molding, or burning of organic chemicals and plastics that contain chlorine. Oxidative stress may play a role in the toxic manifestations of dioxin. Therefore, the aim of this study was to investigate the dose-dependent effects of dioxin on various indices of oxidative stress along with other biochemical parameters in blood and liver of male rabbit, and to examine the histopathological consequences in the liver. Twenty four male rabbits were divided randomly into three groups. The first group (12 rabbits) served as control and vehicle-carrier. The other two groups, six rabbits each, received different oral doses of dioxin (3 and 6 µg/kg body weight) on seven consecutive days. Dioxin caused exaggerated oxidative stress response in dioxin-treated rabbits as indicated by significant changes in total antioxidant capacity, malondialdehyde (MDA), hydrogen peroxide (H2O2), and reduced glutathione (GSH) levels. Other biochemical parameters analyzed were also altered either slightly or significantly. The dioxin-mediated oxidative stress appears to cause hepatic histological changes. The hepatic tissue displayed microvesicular steatosis, and degenerative as well as necrotic changes. These changes were particularly prominent with the higher dose. In conclusion the results indicated that, the treatment of rabbits with dioxin may cause oxidative stress response and changes in some biochemical parameters and hepatic histological architecture in a dose-dependent manner.

Chronic Exposure to Low Doses of Dioxin Promotes Liver Fibrosis Development in the C57BL/6J Diet-Induced Obesity Mouse Model.

Background:Exposure to persistent organic pollutants (POPs) has been associated with the progression of chronic liver diseases, yet the contribution of POPs to the development of fibrosis in non-alcoholic fatty liver disease (NAFLD), a condition closely linked to obesity, remains poorly documented.Objectives:We investigated the effects of subchronic exposure to low doses of the POP 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), an aryl hydrocarbon receptor ligand, on NAFLD progression in diet-induced obese C57BL/6J mice.Methods:Male C57BL/6J mice were fed either a 10% low-fat (LFD) or a 45% high-fat (HFD) purified diet for 14 weeks and TCDD-exposed groups were injected once a week with 5 μg/kg TCDD or the vehicle for the last 6 weeks of the diet.Results:Liver histology and triglyceride levels showed that exposure of HFD fed mice to TCDD worsened hepatic steatosis, as compared to either HFD alone or LFD plus TCDD and the mRNA levels of key genes of hepatic lipid metabolism were strongly altered in co-treated mice. Further, increased liver collagen staining and serum transaminase levels showed that TCDD induced liver fibrosis in the HFD fed mice. TCDD in LFD fed mice increased the expression of several inflammation and fibrosis marker genes with no additional effect from a HFD.Conclusions:Exposure to TCDD amplifies the impairment of liver functions observed in mice fed an enriched fat diet as compared to a low fat diet. The results provide new evidence that environmental pollutants promote the development of liver fibrosis in obesity-related NAFLD in C57BL/6J mice.Citation:Duval C, Teixeira-Clerc F, Leblanc AF, Touch S, Emond C, Guerre-Millo M, Lotersztajn S, Barouki R, Aggerbeck M, Coumoul X. 2017. Chronic exposure to low doses of dioxin promotes liver fibrosis development in the C57BL/6J diet-induced obesity mouse model. Environ Health Perspect 125:428–436; http://dx.doi.org/10.1289/EHP316

Inhalation Exposure to Dioxins and dl-PCBs Depending on the Season in Upper Silesia, Poland: A Pilot Study.

The aim of this study was to investigate the seasonal fluctuation of PCDD/Fs and dl-PCBs levels in the ambient air of Upper Silesia in the aspect of human inhalation exposure as well as the estimation of health risk attributed to this exposure pathway to dioxins and dl-PCBs. In the study air samples were taken in five urban districts of Upper Silesia, Poland, where the houses are heated with coal. The same sampling points in summer and winter were analyzed for dioxins/furans and dl-PCBs. In addition, information was collected on awareness of the residents about the co-incineration of plastic waste and effects of this activity on human health. The results show that the average daily exposure of residents of Upper Silesia to TCDD and DLCs in the heating season was about 6.5.-fold higher than in summer. The risk assessment showed that expected excess of cancer cases per 1,000,000 people ranged from 4.5 to 13.2 in winter and from 0.9 to 2.1 in summer. The practice of mixing waste with coal for houses heating has been confirmed by investigated families, who do not associate it with the possibility of negative health effects. Air pollution can be a significant source of dioxin and dl-PCB for people during the winter season, as a result of co-burning coal and waste containing plastics. The dose of dioxins inhaled through the respiratory pathway in winter can be associated with the higher cancer risk in the population of Upper Silesia.

Assessment of physical traits of rat offspring derived from mothers exposed to dioxin

Negative effects of dioxin action are associated with limited abilities of their bio-degradation along with continuously increasing production and long-term bio-accumulation of those toxins in living organisms. Dioxins penetrate through placenta to fetus indicating indirect toxic effects on offspring of mothers exposed to the action of these toxins. During lactation a significant part of dioxins is excreted from organism with milk, which contributes to further accumulation of those compounds and multiple exceeding of maximal permissible dose of dioxins in newborns feeding with mother's milk. The aim of the study was to determine how a single dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) administered to females 3 weeks before getting pregnant affects the parturition duration, labour delay, number and weight of offspring. The studies were performed on rat offspring deriving from primigravida females from the Buffalo strain, which 3 weeks before getting pregnant were administered with a single dose of TCDD. The obtained results revealed that labours in females exposed to dioxin effects were characterized by significant temporal range and their end occurred 3 weeks later compared to females from the control group, which gave birth within a very narrow temporal range ending within 2 days. Offspring obtained from females exposed to the TCDD action was smaller in number and was characterized by smaller rearing and smaller birth weight even after the first month of life; however weight gain in both groups was similar and it was twelve-fold increase.

Development of Higher Brain Function Tests in Rodents and Its Application to Neurotoxicity Assessment of Environmental Chemicals

The brain during developmental period is thought to be highly sensitive to environmental insults including exposure to chemicals. However, it has been extremely difficult to detect and assess the features and degree of adversity particularly at low exposure levels. I describe here the effects of maternal exposure to dioxin on higher brain functions later in life, which we detected using our originally developed behavioral tests for quantifying higher brain functions in rodents. We first found changes in the mRNA expression levels of glutamate NMDA receptor subunits that have critical roles in learning and memory function in the neocortex and hippocampus. To assess the neocortical and hippocampal functions in rats, we established novel behavioral tests for assessing paired-associate learning, which is the hippocampal and medial prefrontal NMDA-dependent function. Maternal exposure to dioxin, at a low level of which does not affect simple memory formation, resulted in the disturbance of the paired-associate learning. On the basis of the above learning paradigm, we next developed a behavioral flexibility task and a social competitive task for mice using the automated behavioral assessment system ‘IntelliCage’: this system can accommodate 16 mice at the same time to monitor and record their behavior. Using this system, we found that male mice born to dams exposed to very low doses of dioxin showed inflexibility in a serial reversal learning task and socially low-dominance behavior under a competitive situation. Immunohistochemical analysis of putative neuronal activity markers revealed hypoactivity in the medial prefrontal cortex (mPFC) of dioxin-exposed mice. We speculate that mPFC hypoactivity reflects the dioxin-induced higher brain dysfunction and may be associated with some psychiatric illnesses and related problems. These behavioral tests were found to be useful for studying the higher brain functions of rats and mice.

Dioxins, PCBs and heavy metals in Chinese mitten crabs from Dutch rivers and lakes

Chinese mitten crab is an invasive species in many European rivers and lakes. Data from the UK indicated high levels of dioxins and PCBs, in particular in the brown meat in the body. This was confirmed by studies in the Netherlands, showing average levels of dioxins and PCBs in the meat in the body of 43pgTEQg−1 ww in crabs caught in the large rivers. Levels in crab of lakes in the Northern part of the Netherlands were on average 3.7-fold lower. Consumption of crabs from polluted areas results in a relatively high dose of dioxins and dl-PCBs and could significantly increase the intake above the TWI. However, in general consumption of these crabs is low, even in the Asian sub-population in the Netherlands.Cadmium and lead levels were higher in crabs from contaminated areas, but for mercury and arsenic there was no clear difference. Consumption of crabs would not result in significant risks for cadmium and mercury. For lead the daily intake could be raised above the BMDL01 for neurodevelopmental toxicity, but this would only occur on a limited number of days. For arsenic the exposure would exceed the lower end of the BMDL01 values for certain cancers, but again, the infrequent consumption by most consumers reduces this risk. Furthermore, speciation showed that most arsenic in crabs was probably not a toxic inorganic form, but likely to be in an organic form.

Chitosan as a Hepato-Protective Agent against Single Oral Dose of Dioxin

Investigations revealed that tetrachlorodibenzo-p-dioxin (TCDD) induces hepatic damage. Chitosan exhibits antioxidant properties and supplementations with antioxidants can influence hepatotoxicity. We evaluate effect of dietary low molecular weight chitosan (106-110 kilodaltons) in 3 multiplied doses (1.2, 2.4 and 3.6 g/ kg diet) against hepato toxic effects caused by a single oral dose (5 µg TCDD/ kg body weight) for 6 weeks in adult male albino rats. TCDD decreased body weight gain, food intake, feeding efficiency ratio, serum albumin and albumin / globulin ratio. While it caused an increase in liver relative weight, serum total protein, globulin, aspartate and alanine amino transferases and alkaline phosphatase. Also, TCDD caused basophilic hyper chromatic nuclei, hepatic degeneration and fibrosis. Chitosan alone showed a significant positive effect in measured items except feed intake, body weight gain and feed efficiency ratio. Also it alleviated most of biochemical and histological hepatotoxic effects of dioxin. Chitosan is safe as a dietary supplement in rat's diet and can mitigate the hepatotoxic effects of TCDD by controlling the antioxidant status and free radicals production.

Executive function deficits and social-behavioral abnormality in mice exposed to a low dose of dioxin in utero and via lactation.

An increasing prevalence of mental health problems has been partly ascribed to abnormal brain development that is induced upon exposure to environmental chemicals. However, it has been extremely difficult to detect and assess such causality particularly at low exposure levels. To address this question, we here investigated higher brain function in mice exposed to dioxin in utero and via lactation by using our recently developed automated behavioral flexibility test and immunohistochemistry of neuronal activation markers Arc, at the 14 brain areas. Pregnant C57BL/6 mice were given orally a low dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) at a dose of either 0, 0.6 or 3.0 µg/kg on gestation day 12.5. When the pups reached adulthood, they were group-housed in IntelliCage to assess their behavior. As a result, the offspring born to dams exposed to 0.6 µg TCDD/kg were shown to have behavioral inflexibility, compulsive repetitive behavior, and dramatically lowered competitive dominance. In these mice, immunohistochemistry of Arc exhibited the signs of hypoactivation of the medial prefrontal cortex (mPFC) and hyperactivation of the amygdala. Intriguingly, mice exposed to 3.0 µg/kg were hardly affected in both the behavioral and neuronal activation indices, indicating that the robust, non-monotonic dose-response relationship. In conclusion, this study showed for the first time that perinatal exposure to a low dose of TCDD in mice develops executive function deficits and social behavioral abnormality accompanied with the signs of imbalanced mPFC-amygdala activation.

Perinatal Exposure to Low Doses of Dioxin Can Permanently Impair Human Semen Quality

BackgroundIn recent decades, young men in some industrialized areas have reportedly experienced a decrease in semen quality.ObjectiveWe examined effects of perinatal dioxin exposure on sperm quality and reproductive hormones.MethodsWe investigated sperm quality and hormone concentrations in 39 sons (mean age, 22.5 years) born between 1977 and 1984 to mothers exposed to dioxin after the accident in Seveso, Italy (1976), and 58 comparisons (mean age, 24.6 years) born to mothers exposed only to background dioxin. Maternal dioxin levels at conception were extrapolated from the concentrations measured in 1976 serum samples.ResultsThe 21 breast-fed sons whose exposed mothers had a median serum dioxin concentration as low as 19 ppt at conception had lower sperm concentration (36.3 vs. 86.3 million/mL; p = 0.002), total count (116.9 vs. 231.1; p = 0.02), progressive motility (35.8 vs. 44.2%; p = 0.03), and total motile count (38.7 vs. 98 million; p = 0.01) than did the 36 breast-fed comparisons. The 18 formula-fed exposed and the 22 formula-fed and 36 breast-fed comparisons (maternal dioxin background 10 ppt at conception) had no sperm-related differences. Follicle-stimulating hormone was higher in the breast-fed exposed group than in the breast-fed comparisons (4.1 vs. 2.63 IU/L; p = 0.03) or the formula-fed exposed (4.1 vs. 2.6 IU/L; p = 0.04), and inhibin B was lower (breast-fed exposed group, 70.2; breast-fed comparisons, 101.8 pg/mL, p = 0.01; formula-fed exposed, 99.9 pg/mL, p = 0.02).ConclusionsIn utero and lactational exposure of children to relatively low dioxin doses can permanently reduce sperm quality.

Development of novel behavioral toxicity tests in rodents aimed for application to health risks in humans

We here introduce characteristic features of the novel behavioral tests, named Flavor Map and IntelliCage, recently developed to elucidate how maternal exposure to environmental chemicals affects executive brain functions in rats and mice. Flavor Map test requires rats to learn the existence of a schema of paired-associate of flavor and location, and enables to examine the short-term memory, long-term memory and paired-associative learning ability in adult rats. We have found that maternal exposure to a low dose of dioxin causes deficit in the paired-associative memory formation. Using the IntelliCage system, we have developed our own test protocol in mice. IntelliCage is versatile in terms of accommodation of as many as 16 mice at a time to monitor and record their basic physical activities and learning function. Our protocol successfully increases the efficiency of detection of the learning behavior with minimal variations between individual mice. We found that male mice born to dioxin-administered dams develop less behavioral flexibility. We believe that these behavioral tests can be used to study the executive functions in rats and mice, in biomedical research fields not only in toxicological study but also in animal psychology.

The Effect of TCDD Dioxin on the Rat Liver in Biochemical and Histological Assessment

Eighteen male Wistar rats were divided into 3 groups of 6 animals each. Two groups received different intraperitoneal doses of TCDD (0.75 and 8 microg) in DMSO solution and the third group (control) received only DMSO on days 0, 7 and 14. On day 21 the animals were sacrificed, and then blood tests, pathological examination and CYP1A1 activity measurement were performed. In rats that received a high dose of dioxin (8 microg) hepatic lobules revealed parenchymal degeneration and vacuolization of hepatocytes was observed, and also an increased CYP reaction was found in central parts of lobules, around the central vein. The reaction in control and low dose groups was weak. The resorufin level was significantly (P < 0.05) higher in the group receiving a low dose of dioxin as compared to the control group. The study confirmed that TCDD damages the rat liver in a dose-dependent manner. Administration of high TCDD doses causing major liver damage also damaged CYP1A1 (based on higher resorufin levels in epiluminescence). TCDD activates CYP1A1, which was confirmed by increased immunohistochemical reactivity of central areas ofhepatic lobules.

Direct Assessment of Cumulative Aryl Hydrocarbon Receptor Agonist Activity in Sera from Experimentally Exposed Mice and Environmentally Exposed Humans

BackgroundAryl hydrocarbon receptor (AhR) ligands adversely affect many biological processes. However, assessment of the significance of human exposures is hampered by an incomplete understanding of how complex mixtures affect AhR activation/inactivation.ObjectivesThese studies used biological readouts to provide a broader context for estimating human risk than that obtained with serum extraction and gas chromatography/mass spectroscopy (GC/MS)-based assays alone.MethodsAhR agonist activity was quantified in sera from dioxin-treated mice, commercial human sources, and polychlorinated biphenyl (PCB)–exposed Faroe Islanders using an AhR-driven reporter cell line. To validate relationships between serum AhR agonist levels and biological outcomes, AhR agonist activity in mouse sera correlated with toxic end points. AhR agonist activity in unmanipulated (“neat”) human sera was compared with these biologically relevant doses and with GC/MS-assayed PCB levels.ResultsMouse serum AhR agonist activity correlated with injected dioxin dose, thymic atrophy, and heptomegaly, validating the use of neat serum to assess AhR agonist activity. AhR agonist activity in sera from Faroe Islanders varied widely, was associated with the frequency of recent pilot whale dinners, but did not correlate with levels of PCBs quantified by GC/MS. Surprisingly, significant “baseline” AhR activity was found in commercial human sera.ConclusionsAn AhR reporter assay revealed cumulative levels of AhR activation potential in neat serum, whereas extraction may preclude detection of important non-dioxin-like biological activity. Significant levels of AhR agonist activity in commercial sera and in Faroe Islander sera, compared with that from experimentally exposed mice, suggest human exposures that are biologically relevant in both populations.

For Dioxin-induced Birth Defects, Mouse or Human CYP1A2 in Maternal Liver Protects whereas Mouse CYP1A1 and CYP1B1 Are Inconsequential

Dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin) induces cleft palate and hydronephrosis in mice, when exposed in utero; these effects are mediated by the aryl hydrocarbon receptor. The Cyp1a1, Cyp1a2, and Cyp1b1 genes are up-regulated by the aryl hydrocarbon receptor. To elucidate their roles in dioxin-induced teratogenesis, we compared Cyp1a1(-/-), Cyp1a2(-/-), and Cyp1b1(-/-) knock-out mice with Cyp1(+/+) wild-type mice. Dioxin was administered (25 microg/kg, gavage) on gestational day 10, and embryos were examined on gestational day 18. The incidence of cleft palate and hydronephrosis was not significantly different in fetuses from Cyp1a1(-/-), Cyp1b1(-/-), and Cyp1(+/+) wild-type mice. To fetuses carried by Cyp1a2(-/-) dams, however, this dose of dioxin was lethal; this effect was absolutely dependent on the maternal Cyp1a2 genotype and independent of the embryonic Cyp1a2 genotype. Dioxin levels were highest in adipose tissue, mammary gland, and circulating blood of Cyp1a2(-/-) mothers, compared with that in the Cyp1(+/+) mothers, who showed highest dioxin levels in liver. More dioxin reached the embryos from Cyp1a2(-/-) dams, compared with that from Cyp1(+/+) dams. Fetuses from Cyp1a2(-/-) dams exhibited a approximately 6-fold increased sensitivity to cleft palate, hydronephrosis, and lethality. Using the humanized hCYP1A1_1A2 transgenic mouse (expressing the human CYP1A1 and CYP1A2 genes in the absence of mouse Cyp1a2 gene), the teratogenic effects of dioxin reverted to the wild-type phenotype. These data indicate that maternal mouse hepatic CYP1A2, by sequestering dioxin and thus altering the pharmacokinetics, protects the embryos from toxicity and birth defects; substitution of the human CYP1A2 trans-gene provides the same protection. In contrast, neither CYP1A1 nor CYP1B1 appears to play a role in dioxin-mediated teratogenesis.