Identification of neural-relevant toxcast high-throughput assay intended gene targets: Applicability to neurotoxicity and neurotoxicant putative molecular initiating events.

The US EPA's Toxicity Forecaster (ToxCast) is a suite of high-throughput in vitro assays to screen environmental toxicants and predict potential toxicity of uncharacterized chemicals. This work examines the relevance of ToxCast assay intended gene targets to putative molecular initiating events (MIEs) of neurotoxicants. This effort is needed as there is growing interest in the regulatory and scientific communities about developing new approach methodologies (NAMs) to screen large numbers of chemicals for neurotoxicity and developmental neurotoxicity. Assay gene function (GeneCards, NCBI-PUBMED) was used to categorize gene target neural relevance (1 = neural, 2 = neural development, 3 = general cellular process, 3 A = cellular process critical during neural development, 4 = unlikely significance). Of 481 unique gene targets, 80 = category 1 (16.6 %); 16 = category 2 (3.3 %); 303 = category 3 (63.0 %); 97 = category 3 A (20.2 %); 82 = category 4 (17.0 %). A representative list of neurotoxicants (548) was researched (ex. PUBMED, PubChem) for neurotoxicity associated MIEs/Key Events (KEs). MIEs were identified for 375 compounds, whereas only KEs for 173. ToxCast gene targets associated with MIEs were primarily neurotransmitter (ex. dopaminergic, GABA)receptors and ion channels (calcium, sodium, potassium). Conversely, numerous MIEs associated with neurotoxicity were absent. Oxidative stress (OS) mechanisms were 79.1 % of KEs. In summary, 40 % of ToxCast assay gene targets are relevant to neurotoxicity mechanisms. Additional receptor and ion channel subtypes and increased OS pathway coverage are identified for potential future assay inclusion to provide more complete coverage of neural and developmental neural targets in assessing neurotoxicity.

Perspective on halogenated organic compounds.

During the past century, a vast number of organic chemicals have been manufactured and used in industrial, agricultural, public health, consumer products, and other applications. The widespread use in bulk quantities of halogenated organic chemicals (HOCs; also called Organohalogens), including chlorinated, brominated, and fluorinated compounds, and their persistent nature have resulted in global environmental contamination. Increasing levels of HOCs in environmental media (i.e., air, water, soil, sediment) and in human tissues including adipose tissue, breast milk, and placenta continue to be a cause of ecological and human health concern. Human exposure can occur through multiple pathways including direct skin contact, inhalation, drinking water, and mainly through food consumption. HOCs exposure has been implicated in a myriad of health effects including reproductive, neurological, immunological, endocrine, behavioral, and carcinogenic effects in both wildlife and humans. In addition, recent studies indicate that exposure to HOCs contributes to obesity and type 2 diabetes. Because of these adverse health effects, several regulatory agencies either banned or placed severe restrictions on their production and usage. In turn, many industries withdrew from production and usage of HOCs. This action resulted in decline of older HOCs such as polychlorinated biphenyls (PCBs), but more recent HOCs such as polybrominated diphenyl ethers (PBDEs) and perfluoroalkyl substances (PFAS) show a steady increase/stable with time in the global environment. Based on their use pattern and their persistent chemical properties, human exposure to HOCs will likely continue. Hence, understanding human health effects and taking preventive measures for such exposures are necessary.

Influence of Mild Chronic Stress and Social Isolation on Acute Ozone-Induced Alterations in Stress Biomarkers and Brain-Region-Specific Gene Expression in Male Wistar-Kyoto Rats.

Individuals with psychosocial stress often experience an exaggerated response to air pollutants. Ozone (O3) exposure has been associated with the activation of the neuroendocrine stress-response system. We hypothesized that preexistent mild chronic stress plus social isolation (CS), or social isolation (SI) alone, would exacerbate the acute effects of O3 exposure on the circulating adrenal-derived stress hormones, and the expression of the genes regulating glucocorticoid stress signaling via an altered stress adaptation in a brain-region-specific manner. Male Wistar-Kyoto rats (5 weeks old) were socially isolated, plus were subjected to either CS (noise, confinement, fear, uncomfortable living, hectic activity, and single housing), SI (single housing only, restricted handling and no enrichment) or no stress (NS; double housing, frequent handling and enrichment provided) for 8 weeks. The rats were then exposed to either air or O3 (0.8 ppm for 4 h), and the samples were collected immediately after. The indicators of sympathetic and hypothalamic-pituitary axis (HPA) activation (i.e., epinephrine, corticosterone, and lymphopenia) increased with O3 exposure, but there were no effects from CS or SI, except for the depletion of serum BDNF. CS and SI revealed small changes in brain-region-specific glucocorticoid-signaling-associated markers of gene expression in the air-exposed rats (hypothalamic Nr3c1, Nr3c2 Hsp90aa1, Hspa4 and Cnr1 inhibition in SI; hippocampal HSP90aa1 increase in SI; and inhibition of the bed nucleus of the stria terminalis (BNST) Cnr1 in CS). Gene expression across all brain regions was altered by O3, reflective of glucocorticoid signaling effects, such as Fkbp5 in NS, CS and SI. The SI effects on Fkbp5 were greatest for SI in BNST. O3 increased Cnr2 expression in the hypothalamus and olfactory bulbs of the NS and SI groups. O3, in all stress conditions, generally inhibited the expression of Nr3c1 in all brain regions, Nr3c2 in the hippocampus and hypothalamus and Bdnf in the hippocampus. SI, in general, showed slightly greater O3-induced changes when compared to NS and CS. Serum metabolomics revealed increased sphingomyelins in the air-exposed SI and O3-exposed NS, with underlying SI dampening some of the O3-induced changes. These results suggest a potential link between preexistent SI and acute O3-induced increases in the circulating adrenal-derived stress hormones and brain-region-specific gene expression changes in glucocorticoid signaling, which may partly underlie the stress dynamic in those with long-term SI.

Acute Ozone-Induced Transcriptional Changes in Markers of Oxidative Stress and Glucocorticoid Signaling in the Rat Hippocampus and Hypothalamus Are Sex-Specific.

Exposure to a prototypic air pollutant ozone (O3) has been associated with the activation of neuroendocrine stress response along with neural changes in oxidative stress (OS), inflammation, and Alzheimer's disease-like pathologies in susceptible animal models. We hypothesized that neural oxidative and transcriptional changes induced by O3 in stress responsive regions are sex-dependent. Male and female adult Long-Evans rats were exposed to filtered air or O3 for two consecutive days (0.8 ppm, 4 h/day) and brain regions were flash-frozen. Activities of cerebellar OS parameters and mitochondrial complex I, II, and IV enzymes were assessed to confirm prior findings. We assessed transcriptional changes in hypothalamus (HYP) and hippocampus (HIP) for markers of OS, microglial activity and glucocorticoid signaling using qPCR. Although there were no O3 or sex-related differences in the cerebellar activities of OS and mitochondrial enzymes, the levels of protein carbonyls and complex II activities were higher in females regardless of O3. There were no statistical differences in baseline expression of genes related to OS (Cat, Dhcr24, Foxm1, Gpx1, Gss, Nfe2l2, Sod1) except for lower HYP Sod1 expression in air-exposed females than males, and higher HIP Gss expression in O3-exposed females relative to matched males. Microglial marker Aif1 expression was higher in O3-exposed females relative to males; O3 inhibited Itgam only in males. The expression of Bdnf in HIP and HYP was inhibited by O3 in both sexes. Genes related to glucocorticoid signaling (Fkbp4, Fkbp5, Hsp90aa1, Hspa4, nr3c1, nr3c2) showed sex-specific effects due to O3 exposure. Baseline expression of HIP Fkbp4 was higher in females relative to males. O3 inhibited Nr3c1 in female HIP and male HYP, but Nr3c2 was inhibited in male HYP. Fkbp4 expression was higher in O3-exposed females when compared to matched males, whereas Fkbp5 was expressed at higher levels in both brain regions of males and females. These results indicate that sex-specific brain region responses to O3 might, in part, be caused by OS and regulation of glucocorticoid signaling.

Social isolation exacerbates acute ozone inhalation induced pulmonary and systemic health outcomes.

Psychosocially-stressed individuals might have exacerbated responses to air pollution exposure. Acute ozone exposure activates the neuroendocrine stress response leading to systemic metabolic and lung inflammatory changes. We hypothesized chronic mild stress (CS) and/or social isolation (SI) would cause neuroendocrine, inflammatory, and metabolic phenotypes that would be exacerbated by an acute ozone exposure. Male 5-week-old Wistar-Kyoto rats were randomly assigned into 3 groups: no stress (NS) (pair-housed, regular-handling); SI (single-housed, minimal-handling); CS (single-housed, subjected to mild unpredicted-randomized stressors [restraint-1 h, tilted cage-1 h, shaking-1 h, intermittent noise-6 h, and predator odor-1 h], 1-stressor/day*5-days/week*8-weeks. All animals then 13-week-old were subsequently exposed to filtered-air or ozone (0.8-ppm) for 4 h and immediately necropsied. CS, but not SI animals had increased adrenal weights. However, relative to NS, both CS and SI had lower circulating luteinizing hormone, prolactin, and follicle-stimulating hormone regardless of exposure (SI > CS), and only CS demonstrated lower thyroid-stimulating hormone levels. SI caused more severe systemic inflammation than CS, as evidenced by higher circulating cytokines and cholesterol. Ozone exposure increased urine corticosterone and catecholamine metabolites with no significant stressor effect. Ozone-induced lung injury, and increases in lavage-fluid neutrophils and IL-6, were exacerbated by SI. Ozone severely lowered circulating thyroid-stimulating hormone, prolactin, and luteinizing hormone in all groups and exacerbated systemic inflammation in SI. Ozone-induced increases in serum glucose, leptin, and triglycerides were consistent across stressors; however, increases in cholesterol were exacerbated by SI. Collectively, psychosocial stressors, especially SI, affected the neuroendocrine system and induced adverse metabolic and inflammatory effects that were exacerbated by ozone exposure.

Persistent autism-relevant behavioral phenotype and social neuropeptide alterations in female mice offspring induced by maternal transfer of PBDE congeners in the commercial mixture DE-71.

Polybrominated diphenyl ethers (PBDEs) are ubiquitous persistent organic pollutants (POPs) that are known neuroendocrine disrupting chemicals with adverse neurodevelopmental effects. PBDEs may act as risk factors for autism spectrum disorders (ASD), characterized by abnormal psychosocial functioning, although direct evidence is currently lacking. Using a translational exposure model, we tested the hypothesis that maternal transfer of a commercial mixture of PBDEs, DE-71, produces ASD-relevant behavioral and neurochemical deficits in female offspring. C57Bl6/N mouse dams (F0) were exposed to DE-71 via oral administration of 0 (VEH/CON), 0.1 (L-DE-71) or 0.4 (H-DE-71) mg/kg bw/d from 3 wk prior to gestation through end of lactation. Mass spectrometry analysis indicated in utero and lactational transfer of PBDEs (in ppb) to F1 female offspring brain tissue at postnatal day (PND) 15 which was reduced by PND 110. Neurobehavioral testing of social novelty preference (SNP) and social recognition memory (SRM) revealed that adult L-DE-71 F1 offspring display deficient short- and long-term SRM, in the absence of reduced sociability, and increased repetitive behavior. These effects were concomitant with reduced olfactory discrimination of social odors. Additionally, L-DE-71 exposure also altered short-term novel object recognition memory but not anxiety or depressive-like behavior. Moreover, F1 L-DE-71 displayed downregulated mRNA transcripts for oxytocin (Oxt) in the bed nucleus of the stria terminalis (BNST) and supraoptic nucleus, and vasopressin (Avp) in the BNST and upregulated Avp1ar in BNST, and Oxtr in the paraventricular nucleus. Our work demonstrates that developmental PBDE exposure produces ASD-relevant neurochemical, olfactory processing and behavioral phenotypes that may result from early neurodevelopmental reprogramming within central social and memory networks.

The Role of Hepatic Vagal Tone in Ozone-Induced Metabolic Dysfunction in the Liver.

Air pollution has been associated with metabolic diseases and hepatic steatosis-like changes. We have shown that ozone alters liver gene expression for metabolic processes through neuroendocrine activation. This study aimed to further characterize ozone-induced changes and to determine the impact of hepatic vagotomy (HV) which reduces parasympathetic influence. Twelve-week-old male Wistar-Kyoto rats underwent HV or sham surgery 5-6 days before air or ozone exposure (0 or 1 ppm; 4 h/day for 1 or 2 days). Ozone-induced lung injury, hyperglycemia, glucose intolerance, and increases in circulating cholesterol, triglycerides, and leptin were similar in rats with HV and sham surgery. However, decreases in circulating insulin and increased HDL and LDL were observed only in ozone-exposed HV rats. Ozone exposure resulted in changed liver gene expression in both sham and HV rats (sham > HV), however, HV did not change expression in air-exposed rats. Upstream target analysis revealed that ozone-induced transcriptomic changes were similar to responses induced by glucocorticoid-mediated processes in both sham and HV rats. The directionality of ozone-induced changes reflecting cellular response to stress, metabolic pathways, and immune surveillance was similar in sham and HV rats. However, pathways regulating cell-cycle, regeneration, proliferation, cell growth, and survival were enriched by ozone in a directionally opposing manner between sham and HV rats. In conclusion, parasympathetic innervation modulated ozone-induced liver transcriptional responses for cell growth and regeneration without affecting stress-mediated metabolic changes. Thus, impaired neuroendocrine axes and parasympathetic innervation could collectively contribute to adverse effects of air pollutants on the liver.

Ozone-induced changes in oxidative stress parameters in brain regions of adult, middle-age, and senescent Brown Norway rats.

A critical part of community based human health risk assessment following chemical exposure is identifying sources of susceptibility. Life stage is one such susceptibility. A prototypic air pollutant, ozone (O3) induces dysfunction of the pulmonary, cardiac, and nervous systems. Long-term exposure may cause oxidative stress (OS). The current study explored age-related and subchronic O3-induced changes in OS in brain regions of rats. To build a comprehensive assessment of OS-related effects of O3, a tripartite approach was implemented focusing on 1) the production of reactive oxygen species (ROS) [NADPH Quinone oxidoreductase 1, NADH Ubiquinone reductase] 2) antioxidant homeostasis [total antioxidant substances, superoxide dismutase, γ-glutamylcysteine synthetase] and 3) an assessment of oxidative damage [total aconitase and protein carbonyls]. Additionally, a neurobehavioral evaluation of motor activity was compared to these OS measures. Male Brown Norway rats (4, 12, and 24 months of age) were exposed to air or O3 (0.25 or 1 ppm) via inhalation for 6 h/day, 2 days per week for 13 weeks. A significant decrease in horizontal motor activity was noted only in 4-month old rats. Results on OS measures in frontal cortex (FC), cerebellum (CB), striatum (STR), and hippocampus (HIP) indicated life stage-related increases in ROS production, small decreases in antioxidant homeostatic mechanisms, a decrease in aconitase activity, and an increase in protein carbonyls. The effects of O3 exposure were brain area-specific, with the STR being more sensitive. Regarding life stage, the effects of O3 were greater in 4-month-old rats, which correlated with horizontal motor activity. These results indicate that OS may be increased in specific brain regions after subchronic O3 exposure, but the interactions between age and exposure along with their consequences on the brain require further investigation.

The effects of ozone exposure and sedentary lifestyle on neuronal microglia and mitochondrial bioenergetics of female Long-Evans rats.

Ozone (O3) is a widespread air pollutant that produces cardiovascular and pulmonary dysfunction possibly mediated by activation of central stress centers. Epidemiological data suggest that sedentary lifestyles may exacerbate responses to air pollutants such as O3. We sought to assess neurological changes in response to O3 exposure and an active lifestyle. We developed an animal model in which female Long-Evans rats were either sedentary or active with continuous access to running wheels starting at postnatal day (PND) 22 until the age of PND 100 and then exposed to O3 (0, 0.25, 0.5 or 1.0 ppm) 5 h/day for two consecutive days. We found significantly more reactive microglia within the hippocampus (HIP) in animals exposed to O3 in both sedentary and active rats. No changes were detected in astrocytic coverage. We next analyzed mitochondrial bioenergetic parameters (complex I, complex II and complex IV). Complex I activity was significantly affected by exercise in hypothalamus (HYP). Complex II activity was significantly affected by both exercise and O3 exposure in the HIP. Concomitant with the changes in enzymatic activity, there were also effects on expression of genes related to mitochondrial bioenergetics and antioxidant production. These results demonstrate that O3 induces microglia reactivity within stress centers of the brain and that mitochondrial bioenergetics are altered. Some of these effects may be augmented by exercise, suggesting a role for lifestyle in O3 effects on brain mitochondrial bioenergetics parameters in agreement with our previous reports on other endpoints.

Acute in vitro effects on embryonic rat dorsal root ganglion (DRG) cultures by in silico predicted neurotoxic chemicals: Evaluations on cytotoxicity, neurite length, and neurophysiology.

The Hard-Soft Acid and Base hypothesis can be used to predict the potential bio-reactivity (electrophilicity) of a chemical with intracellular proteins, resulting in neurotoxicity. Twelve chemicals predicted to be neurotoxic were evaluated in vitro in rat dorsal root ganglia (DRG) for effects on cytotoxicity (%LDH), neuronal structure (total neurite length/neuron, NLPN), and neurophysiology (mean firing rate, MFR). DRGs were treated acutely on days in vitro (DIV) 7 (1-100 µM) with test chemical; %LDH and NLPN were measured after 48 h. 4-cyclohexylhexanone (4-C) increased %LDH release at 50 (29%) and 100 µM (56%), citronellal (Cit) and 1-bromopropane increased %LDH at 100 µM (22% and 26%). 4-C, Cit, 2,5 Hexanedione (2,5Hex), phenylacetylaldehyde (PAA) and 2-ethylhexanal decreased mean NLPN at 48 h; 50 and 100 µM for 4-C (28% and 60%), 100 µM Cit (52%), 100 µM 2,5- Hex (37%) 100 µM PAA (41%) and 100 µM for 2-ethylhexanal (23%). Separate DRG cultures were treated on DIV 14 and changes in MFR measured. Four compounds decreased MFR at 50 or 100 µM: Acrylamide (-83%), 3,4-dichloro-1-butene (-93%), 4-C (-89%) and hexane (-79%, 50 µM). Changes in MFR and NLPN occurred in absence of cytotoxicity. While the current study showed little cytotoxicity, it gave insight to initial changes in MFR. Results provide insight for future chronic exposure experiments to evaluate neurotoxicity.

Age- and Organ-Specific Differences in Mitochondrial Bioenergetics in Brown Norway Rats.

Mitochondria play a central role in energy homeostasis and act as regulatory checkpoints for downstream metabolic responses and cell senescence processes during an entire life span. Acute or chronic environmental toxicant exposures have shown deleterious organ-specific human health issues at various life stages. Since mitochondria are a prime target for ensuing cellular bioenergetics responses and senescence, it is essential to understand mitochondrial bioenergetic responses in different organs over multiple life stages. Therefore, in the present study, we evaluated mitochondrial bioenergetic parameters in the liver, lung, and heart in four diverse age groups (young: 1 month; adult: 4 months; middle-aged: 12 months; old-aged: 24 month) using male Brown Norway rats as a model of aging (n = 5 sample size/organ/age group) and compared them with our previously published results on brain. Real-time mitochondrial bioenergetic parameters (i.e., State III, State IV, and State V) were measured using the Seahorse Extracellular Flux Analyzer. Additionally, mitochondrial enzyme pyruvate dehydrogenase complex (PDHC), Complex I, Complex II, and Complex IV activities were measured using Synergy HT plate reader. Our results indicated that nearly in all parameters, significant age- and organ-specific interactions were observed. We observed age-specific declines in State III (i.e., ATP synthesis rate) responses in both the heart and lung, where opposite was observed in the liver as age advances. Across the age, the heart has highest enzyme activities than the liver and lung. Interestingly, heart and liver mitochondrial bioenergetic rates and enzyme activities remain higher than the lung, which specifies their higher metabolic capabilities than the lung. Amongst all, bioenergetic rates and enzyme activities in the lung remain lowest suggesting the lung may display higher vulnerability and lower resilience to environmental toxicants during aging than other organs tested here. Overall, these age- and organ-specific findings may facilitate a more contextualized understanding of mitochondrial bioenergetic outcomes when considering the interactions of age-related sensitivities with exposure to chemical stressors from the environment.

Perinatal exposure to octabromodiphenyl ether mixture, DE-79, alters the vasopressinergic system in adult rats.

Polybrominated diphenyl ethers (PBDEs) are persistent environmental pollutants considered as neurotoxicants and endocrine disruptors with important biological effects ranging from alterations in growth, reproduction, and effects on the hypothalamus-pituitary-adrenal axis. The vasopressinergic (AVPergic) system is a known target for pentaBDEs mixture (DE-71) and the structurally similar chemicals, polychlorinated biphenyls. However, the potential adverse effects of mixtures containing octaBDE compounds, like DE-79, on the AVPergic system are still unknown. The present study aims to examine the effects of perinatal DE-79 exposure on the AVPergic system. Dams were dosed from gestational day 6 to postnatal day 21 at doses of 0 (control), 1.7 (low) or 10.2 (high) mg/kg/day, and male offspring from all doses at 3-months-old were subjected to normosmotic and hyperosmotic challenge. Male offspring where later assessed for alterations in osmoregulation (i.e. serum osmolality and systemic vasopressin release), and both vasopressin immunoreactivity (AVP-IR) and gene expression in the hypothalamic paraventricular and supraoptic nuclei. Additionally, to elucidate a possible mechanism for the effects of DE-79 on the AVPergic system, both neuronal nitric oxide synthase immunoreactivity (nNOS-IR) and mRNA expression were investigated in the same hypothalamic nuclei. The results showed that perinatal DE-79 exposure AVP-IR, mRNA expression and systemic release in adulthood under normosmotic conditions and more evidently under hyperosmotic stimulation. nNOS-IR and mRNA expression were also affected in the same nuclei. Since NO is an AVP regulator, we propose that disturbances in NO could be a mechanism underlying the AVPergic system disruption following perinatal DE-79 exposure leading to osmoregulation deficits.

Mitochondrial Bioenergetics in Brain Following Ozone Exposure in Rats Maintained on Coconut, Fish and Olive Oil-Rich Diets.

Dietary supplementation with omega-3 and omega-6 fatty acids offer cardioprotection against air pollution, but these protections have not been established in the brain. We tested whether diets rich in omega-3 or -6 fatty acids offered neuroprotective benefits, by measuring mitochondrial complex enzyme I, II and IV activities and oxidative stress measures in the frontal cortex, cerebellum, hypothalamus, and hippocampus of male rats that were fed either a normal diet, or a diet enriched with fish oil olive oil, or coconut oil followed by exposure to either filtered air or ozone (0.8 ppm) for 4 h/day for 2 days. Results show that mitochondrial complex I enzyme activity was significantly decreased in the cerebellum, hypothalamus and hippocampus by diets. Complex II enzyme activity was significantly lower in frontal cortex and cerebellum of rats maintained on all test diets. Complex IV enzyme activity was significantly lower in the frontal cortex, hypothalamus and hippocampus of animals maintained on fish oil. Ozone exposure decreased complex I and II activity in the cerebellum of rats maintained on the normal diet, an effect blocked by diet treatments. While diet and ozone have no apparent influence on endogenous reactive oxygen species production, they do affect antioxidant levels in the brain. Fish oil was the only diet that ozone exposure did not alter. Microglial morphology and GFAP immunoreactivity were assessed across diet groups; results indicated that fish oil consistently decreased reactive microglia in the hypothalamus and hippocampus. These results indicate that acute ozone exposure alters mitochondrial bioenergetics in brain and co-treatment with omega-6 and omega-3 fatty acids alleviate some adverse effects within the brain.

Interaction of Diet and Ozone Exposure on Oxidative Stress Parameters within Specific Brain Regions of Male Brown Norway Rats.

Oxidative stress (OS) contributes to the neurological and cardio/pulmonary effects caused by adverse metabolic states and air pollutants such as ozone (O3). This study explores the interactive effects of O3 and diet (high-fructose (FRUC) or high⁻fat (FAT)) on OS in different rat brain regions. In acute exposure, there was a decrease in markers of reactive oxygen species (ROS) production in some brain regions by diet and not by O3. Total antioxidant substances (TAS) were increased in the cerebellum (CER) and frontal cortex (FC) and decreased in the striatum (STR) by both diets irrespective of O3 exposure. Protein carbonyls (PC) and total aconitase decreased in some brain regions irrespective of exposure. Following subacute exposure, an increase in markers of ROS was observed in both diet groups. TAS was increased in the FC (FAT only) and there was a clear O3 effect where TAS was increased in the FC and STR. Diet increased PC formation within the CER in the FAT group, while the hippocampus showed a decrease in PC after O3 exposure in controls. In general, these results indicate that diet/O3 did not have a global effect on brain OS parameters, but showed some brain region- and OS parameter-specific effects by diets.

Perinatal exposure to organohalogen pollutants decreases vasopressin content and its mRNA expression in magnocellular neuroendocrine cells activated by osmotic stress in adult rats.

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are environmental pollutants that produce neurotoxicity and neuroendocrine disruption. They affect the vasopressinergic system but their disruptive mechanisms are not well understood. Our group reported that rats perinatally exposed to Aroclor-1254 (A1254) and DE-71 (commercial mixtures of PCBs and PBDEs) decrease somatodendritic vasopressin (AVP) release while increasing plasma AVP responses to osmotic activation, potentially emptying AVP reserves required for body-water balance. The aim of this research was to evaluate the effects of perinatal exposure to A1254 or DE-71 (30mgkg/day) on AVP transcription and protein content in the paraventricular and supraoptic hypothalamic nuclei, of male and female rats, by in situ hybridization and immunohistochemistry. cFOS mRNA expression was evaluated in order to determine neuroendocrine cells activation due to osmotic stimulation. Animal groups were: vehicle (control); exposed to either A1254 or DE-71; both, control and exposed, subjected to osmotic challenge. The results confirmed a physiological increase in AVP-immunoreactivity (AVP-IR) and gene expression in response to osmotic challenge as reported elsewhere. In contrast, the exposed groups did not show this response to osmotic activation, they showed significant reduction in AVP-IR neurons, and AVP mRNA expression as compared to the hyperosmotic controls. cFOS mRNA expression increased in A1254 dehydrated groups, suggesting that the AVP-IR decrease was not due to a lack of the response to the osmotic activation. Therefore, A1254 may interfere with the activation of AVP mRNA transcript levels and protein, causing a central dysfunction of vasopressinergic system.

Atypical microglial response to biodiesel exhaust in healthy and hypertensive rats.

Accumulating evidence suggests a deleterious role for urban air pollution in central nervous system (CNS) diseases and neurodevelopmental disorders. Microglia, the resident innate immune cells and sentinels in the brain, are a common source of neuroinflammation and are implicated in air pollution-induced CNS effects. While renewable energy, such as soy-based biofuel, is of increasing public interest, there is little information on how soy biofuel may affect the brain, especially in people with preexisting disease conditions. To address this, male spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) rats were exposed to 100% Soy-based Biodiesel Exhaust (100SBDE; 0, 50, 150 and 500µg/m3) by inhalation, 4h/day for 4 weeks (5 days/week). Ionized calcium-binding adapter molecule-1 (IBA-1) staining of microglia in the substantia nigra revealed significant changes in morphology with 100SBDE exposure in rats from both genotypes, where SHR were less sensitive. Aconitase activity was inhibited in the frontal cortex and cerebellum of WKY rats exposed to 100SBDE. No consistent changes occurred in pro-inflammatory cytokine expression, nitrated protein, or arginase1 expression in brain regions from either rat strain exposed to 100SBDE. However, while IBA-1 mRNA expression was not modified, CX3CR1 mRNA expression was lower in the striatum of 100SBDE exposed rats regardless of genotype, suggesting a downregulation of the fractalkine receptor on microglia in this brain region. Together, these data indicate that while microglia are detecting and responding to 100SBDE exposure with changes in morphology, there is reduced expression of CX3CR1 regardless of genetic background and the activation response is atypical without traditional inflammatory markers of M1 or M2 activation in the brain.

Age- and brain region-specific differences in mitochondrial bioenergetics in Brown Norway rats.

Mitochondria are central regulators of energy homeostasis and play a pivotal role in mechanisms of cellular senescence. The objective of the present study was to evaluate mitochondrial bioenergetic parameters in 5 brain regions (brain stem [BS], frontal cortex, cerebellum, striatum, hippocampus [HIP]) of 4 diverse age groups (1 month [young], 4 months [adult], 12 months [middle-aged], 24 months [old age]) to understand age-related differences in selected brain regions and their possible contribution to age-related chemical sensitivity. Mitochondrial bioenergetic parameters and enzyme activities were measured under identical conditions across multiple age groups and brain regions in Brown Norway rats (n = 5/group). The results indicate age- and brain region-specific patterns in mitochondrial functional endpoints. For example, an age-specific decline in ATP synthesis (State III respiration) was observed in BS and HIP. Similarly, the maximal respiratory capacities (State V1 and V2) showed age-specific declines in all brain regions examined (young > adult > middle-aged > old age). Amongst all regions, HIP had the greatest change in mitochondrial bioenergetics, showing declines in the 4, 12, and 24-months age groups. Activities of mitochondrial pyruvate dehydrogenase complex and electron transport chain complexes I, II, and IV enzymes were also age and brain region specific. In general, changes associated with age were more pronounced with enzyme activities declining as the animals aged (young > adult > middle-aged > old age). These age- and brain region-specific observations may aid in evaluating brain bioenergetic impact on the age-related susceptibility to environmental chemical stressors.

Acute and subchronic toxicity of inhaled toluene in male Long-Evans rats: Oxidative stress markers in brain.

The effects of exposure to volatile organic compounds (VOCs), which are of concern to the EPA, are poorly understood, in part because of insufficient characterization of how human exposure duration impacts VOC effects. Two inhalation studies with multiple endpoints, one acute and one subchronic, were conducted to seek effects of the VOC, toluene, in rats and to compare the effects between acute and subchronic exposures. Adult male Long-Evans rats were exposed to toluene vapor (n=6 per group) at a concentration of 0 or 1019 ± 14 ppm for 6h in the acute study and at 0 ± 0, 10 ± 1.4, 97 ± 7, or 995 ± 43 ppm for 6h/d, 5d/week for 13 weeks in the subchronic study. For the acute study, brains were dissected on ice within 30 min of the end of exposure, while for the subchronic study, brains were dissected 18 h after the last exposure. Frontal cortex, hippocampus, cerebellum, and striatum were assayed for a variety of oxidative stress (OS) parameters including total aconitase (TA), protein carbonyls, glutathione peroxidase (GPX), glutathione reductase (GRD), glutathione transferase (GST), γ-glutamylcysteine synthetase (GCS), superoxide dismutase (SOD), total antioxidants (TAS), NADPH quinone oxidoreductase-1 (NQO1), and NADH ubiquinone reductase (UBIQ-RD) activities using commercially available kits. Following acute exposure, UBIQ-RD, GCS and GRD were increased significantly only in the cerebellum, while TAS was increased in frontal cortex. On the other hand, subchronic exposure affected several OS markers including increases in NQO1 and UBIQ-RD. The effect of subchronic toluene exposure on SOD and TAS was greater in the striatum than in the other brain regions. TA activity (involved in maintaining iron homeostasis and an indicator of DNA damage) was inhibited in striatum and cerebellum, increased in hippocampus, and unchanged in frontal cortex. Protein carbonyls increased significantly in both the frontal cortex and cerebellum. In general, the results showed that acute exposure to toluene affected OS parameters to a lesser extent than did subchronic exposure. These results suggest that toluene exposure induces OS in the brain and this may be a component of an adverse outcome pathway for some of the neurotoxic effects reported following toluene exposure.

Developmental exposure to a commercial PBDE mixture: effects on protein networks in the cerebellum and hippocampus of rats.

BACKGROUND: Polybrominated diphenyl ethers (PBDEs) are structurally similar to polychlorinated biphenyls (PCBs) and have both central (learning and memory deficits) and peripheral (motor dysfunction) neurotoxic effects at concentrations/doses similar to those of PCBs. The cellular and molecular mechanisms for these neurotoxic effects are not fully understood; however, several studies have shown that PBDEs affect thyroid hormones, cause oxidative stress, and disrupt Ca2+-mediated signal transduction. Changes in these signal transduction pathways can lead to differential gene regulation with subsequent changes in protein expression, which can affect the development and function of the nervous system. OBJECTIVE: In this study, we examined the protein expression profiles in the rat cerebellum and hippocampus following developmental exposure to a commercial PBDE mixture, DE-71. METHODS: Pregnant Long-Evans rats were dosed perinatally with 0 or 30.6 mg/kg/day of DE-71 from gestation day 6 through sampling on postnatal day 14. Proteins from the cerebellum and hippocampus were extracted, expression differences were detected by two-dimensional difference gel electrophoresis, and proteins were identified by tandem mass spectrometry. Protein network interaction analysis was performed using Ingenuity® Pathway Analysis, and the proteins of interest were validated by Western blotting. RESULTS: Four proteins were significantly differentially expressed in the cerebellum following DE-71 exposure, whereas 70 proteins were significantly differentially expressed in the hippocampus. Of these proteins, 4 from the cerebellum and 47 from the hippocampus, identifiable by mass spectrometry, were found to have roles in mitochondrial energy metabolism, oxidative stress, apoptosis, calcium signaling, and growth of the nervous system. CONCLUSIONS: Results suggest that changes in energy metabolism and processes related to neuroplasticity and growth may be involved in the developmental neurotoxicity of PBDEs.

Flame retardant BDE-47 effectively activates nuclear receptor CAR in human primary hepatocytes.

Polybrominated diphenyl ether BDE-47 (2,2',4,4'-tetrabromodiphenyl ether) is a thyroid hormone disruptor in mice; hepatic induction of various metabolic enzymes and transporters has been suggested as the mechanism for this disruption. Utilizing Car (-/-) and Pxr (-/-) mice as well as human primary hepatocytes, here we have demonstrated that BDE-47 activated both mouse and human nuclear receptor constitutive activated/androstane receptor (CAR). In mouse livers, CAR, not PXR, was responsible for Cyp2b10 mRNA induction by BDE-47. In human primary hepatocytes, BDE-47 was able to induce translocation of YFP-tagged human CAR from the cytoplasm to the nucleus andCYP2B6 and CYP3A4 mRNAs expressions. BDE-47 activated human CAR in a manner akin to the human CAR ligand CITCO (6-(4-Chlorophenyl)imidazo[2,1-b][1,3]thiazole-5-carbaldehyde-O-(3,4-dichlorobenzyl)oxime) in luciferase-reporter assays using Huh-7 cells. In contrast, mouse CAR was not potently activated by BDE-47 in the same reporter assays. Furthermore, human pregnane X receptor (PXR) was effectively activated by BDE-47 while mouse PXR was weakly activated in luciferase-reporter assays. Our results indicate that BDE-47 induces CYP genes through activation of human CAR in addition to the previously identified pathway through human PXR.