Toluene effects on oxidative stress in brain regions of young-adult, middle-age, and senescent Brown Norway rats

Association of volatile organic compounds exposure with the risk of depression in U.S. adults: a cross‑sectional study from NHANES 2013-2016

BACKGROUND

Volatile organic compounds (VOCs) are a broad class of chemicals, and previous studies showed that VOCs could increase the risk of central nervous system disorders. However, few studies have comprehensively explored their association with depression among general adults.

OBJECTIVE

We aimed to explore the association between blood VOCs and depression risk based on a large cross-sectional study of the National Health and Nutrition Examination Survey (NHANES).

METHODS

We analyzed data from 3449 American adults in the NHANES 2013-2016. Survey-weighted logistic regression model was used to explore the association of ten blood VOCs with depression. Subsequently, the relative importance of the selected VOCs was determined using the XGBoost model. The weighted quantile sum (WQS) regression model was used to explore the overall association of 10 blood VOCs with depression. Subgroup analyses were performed to identify high-risk populations. Finally, restricted cubic spline (RCS) analysis was utilized to explore the dose-response relationship between blood VOCs and the risk of depression.

RESULTS

XGBoost Algorithm model identified blood 2,5-dimethylfuran was the most critical variable in depression. The logistic regression model showed that blood benzene, blood 2,5-dimethylfuran, and blood furan showed a positive correlation with depression. In subgroup analysis, we found that the effects of the above VOCs on depression existed among the female, young middle-aged, and overweight-obese population. Mixture VOCs exposure was positively associated with depression risk (OR = 2.089, 95% CI: 1.299-3.361), and 2,5-dimethylfuran had the largest weights in WQS regression. RCS displayed that blood benzene, blood 2,5-dimethylfuran, and blood furan were positively associated with depression.

CONCLUSION

The results of this study indicated that VOCs exposure was associated with an increased prevalence of depression in U.S. adults. Women, young and middle-aged, and overweight-obese populations are more vulnerable to VOCs.

Toluene Can Disrupt Rat Ovarian Follicullogenesis and Steroidogenesis and Induce Both Autophagy and Apoptosis

Toluene has been shown to be highly toxic to humans and animals and can cause damage to various tissues. However, studies reporting its effects on ovarian function are still limited. In this study, we investigated the in vivo effect of toluene using female Wistar rats. We found that toluene exposure decreased ovarian weight and affected ovarian structure by increasing the number of abnormally growing follicles. Moreover, it significantly increased progesterone and testosterone levels. We also showed that toluene exposure decreased GDF-9 protein and its encoding gene. In addition, it inhibited the expression of most of the genes involved in granulosa cell proliferation and differentiation, such as Insl3, ccnd2 and actb. The TUNEL assay showed that apoptosis occurred at the middle and high doses only (4000 and 8000 ppm, respectively), whereas no effect was observed at the low dose (2000 ppm). Interestingly, we showed that toluene exposure induced autophagy as LC3 protein and its encoding gene significantly increased for all doses of treatment. These results may suggest that the activation of autophagy at a low dose of exposure was to protect ovarian cells against death by inhibiting apoptosis, whereas its activation at high doses of exposure triggered apoptosis leading to cell death.

Spatial distribution of health risks for residents located close to solvent-consuming industrial VOC emission sources

Emissions derived from the consumption of organic solvents have been proven to be the primary industrial source of volatile organic compounds (VOCs). In conjunction with epidemiologic studies, water-based paints (WBPs) and solvent-based paints (SBPs) were selected as representatives of newly developed solvents and traditional solvents, respectively, to simulate the effects of consuming solvents emitted during industrial production. And non-carcinogenic and carcinogenic risks to residents near emission sources were studied in detail. The results showed that the spatial distribution of health risks varied with meteorological conditions and type of emission source, and the prevailing wind direction strongly affected the distribution range and shape of the influenced area. The areas of influence maximized on heavy-polluting days for both WBP and SBP emission sources with the total span reaching 804 m and 16 km, respectively; meanwhile, the areas of influence for carcinogenic risk resulting from WBP emission sources were 1.2 and 2.3 times greater than those measured on fine and rainy days, respectively, and 1.8 and 2.9 times greater for SBP emission sources. Compared with WBPs, the total spans of negatively influenced regions resulting from SBP emission sources were 10.4, 12.5 and 19.9 times greater on fine, rainy and heavy-polluting days, respectively. Therefore, carcinogenic risk was the dominant health threat for populations residing close to solvent-consuming industrial emission sources. The findings suggest that newly developed solvents are capable of significantly reducing consequent health threats, nevertheless, they could still pose occasional threats to nearby residents under specific meteorological conditions.

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.

Minocycline prevents neuronal hyperexcitability and neuroinflammation in medial prefrontal cortex, as well as memory impairment caused by repeated toluene inhalation in adolescent rats

Toluene can be intentionally misused by adolescents to experience psychoactive effects. Toluene has a complex mechanism of action and broad behavioral effects, among which memory impairment is reported consistently. We have previously reported that repeated toluene inhalation (8000 ppm) increases layer 5 prelimbic pyramidal cells' excitability in the medial prefrontal cortex (mPFC) of adolescent rats. Toluene also produces reactive oxygen species (ROS), which activate glial cells. Here, we tested the hypothesis that the anti-inflammatory agent minocycline would decrease toluene's effects because it inhibits NF-κB (nuclear factor enhancer of the kappa light chains of activated B cells) and reduces pro-inflammatory cytokine and ROS production. Our results show that minocycline (50 mg/kg, ip, for 10 days) prevents the hyperexcitability of mPFC neurons observed after repeated 8000 ppm toluene exposure (30 min/day, 2×/day for 10 days). Minocycline prevents toluene-induced hyperexcitability by a mechanism that averts the loss of the slow calcium-dependent potassium current, and normalizes mPFC neurons' firing frequency. These effects are accompanied by significant decreased expression of astrocytes and activated microglia in the mPFC, reduced NLRP3 inflammasome activation and mRNA expression levels of the pro-inflammatory cytokine interleukin 1β (IL-1β), as well as increased mRNA expression of the anti-inflammatory cytokine transforming growth factor β (TGF-β). Minocycline also prevents toluene-induced memory impairment in adolescent rats in the passive avoidance task and the temporal order memory test in which the mPFC plays a central role. These results show that neuroinflammation produces several effects of repeated toluene administration at high concentrations, and minocycline can significantly prevent them.

Effect of Initial Aging and High-Fat/High-Fructose Diet on Mitochondrial Bioenergetics and Oxidative Status in Rat Brain

Middle age is an early stage of the aging process, during which the consumption of diets rich in saturated fats and/or simple sugars might influence brain function, but only few data are available on this issue. We therefore investigated the impact of a diet rich in saturated fat and fructose (HFF) on mitochondrial physiology in hippocampus and frontal cortex of middle-aged rats (1 year old), by including a group of adult rats (90 days) as a "negative control," lacking the putative effect of aging. Middle-aged rats were fed HFF or control diet for 4 weeks. Mitochondrial function was analyzed by high-resolution respirometry and by assessing the amount of respiratory complexes. Markers of oxidative balance, as well as the protein content of uncoupling protein 2 (UCP2), peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), and peroxisome proliferator-activated receptor alpha (PPARα), were also assessed. A decrease in the activity of complex I was detected in both brain areas of middle-aged rats. In hippocampus, mitochondrial respiratory capacity and complex IV content decreased with age and increased with HFF diet. Higher protein oxidative damage, decreased antioxidant defenses, and increased UCP2 and PGC-1α content were found in hippocampus of middle-aged rats. HFF feeding induced a significant reduction in the amount of UCP2, PGC-1α, and PPARα, together with higher protein oxidative damage, in both brain areas. Overall, our results point to middle age as a condition of early brain aging for mitochondrial function, with hippocampus being an area more susceptible to metabolic impairment than frontal cortex.

Acute and Chronic Exposure of Toluene Induces Genotoxicity in Different Regions of the Brain in Normal and Allergic Mouse Models

Toluene is a widely used industrial organic solvent and is ubiquitous in our environment. The neurobehavioral and neurotoxic effects of toluene are well recognized; however, its genotoxicity is still under discussion. Toluene biotransformation leads to the generation of reactive oxygen species that cause oxidative stress and DNA damages. Individuals with different immunogenetic backgrounds have different sensitivities to toxic chemical exposure. Previous studies have suggested that allergic stimulation may influence the threshold for toluene sensitivity due to the modulation of neurotrophin-related genes. Therefore, we aimed to investigate toluene-induced genotoxicity in different brain regions following acute and chronic exposure in vivo and to further examine whether allergic stimulation may influence the sensitivity to toluene-induced genotoxicity. In this present study, we found that exposure of toluene induced oxidative DNA damages resulting in genotoxicity in different brain regions including cortex, cerebellum, and hippocampus using comet assay. Higher genotoxicity induced by toluene was observed in the hippocampus of control mice compared to OVA-immunized mice. These results provide evidence that toluene-induced genotoxicity may contribute to its neurotoxicity in different immunogenetic individuals.

Evaluation of the oxidative stress in liver of crucian carp (Carassius auratus) exposed to 3,4,4'-tri-CDE, 2-MeO-3',4,4'-tri-CDE, and 2-HO-3',4,4'-tri-CDE

Polychlorinated diphenyl ethers (PCDEs) are a class of potential persistent organic contaminants, which have been widely detected in aquatic environment. In the present study, the effects of 3,4,4'-tri-CDE and its two possible metabolites (2-MeO-3',4,4'-tri-CDE and 2-HO-3',4,4'-tri-CDE) on oxidative stress biomarkers in liver of Carassius auratus were evaluated. The fish were treated with these three compounds at different doses (0.1, 1, and 10 μg/L) via semi-static water exposure. The liver samples were individually taken at 3, 7, and 21 days for analysis of oxidative stress indicators, including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), reduced glutathione (GSH), and malondialdehyde (MDA). Compare to the control group, the hepatic antioxidant enzyme activity and GSH contents showed significant decreases (p < 0.05) at high-dose treatment (10 μg/L) and prolonged exposure time (21 days) in most of the toxicant-treated groups, indicating the occurrence of oxidative stress in fish liver. However, no consistent trend of the variations of antioxidant parameters was observed at low doses (0.1 and 1 μg/L). Meanwhile, the lipid peroxidation was significantly induced with extending exposure time and increasing dose. In addition, the toxicity order of three compounds was discussed using the integrated biomarker response (IBR) index. Notably, 2-HO-3',4,4'-tri-CDE was indicated to cause the most severe hepatic oxidative stress.

Amyotrophic lateral sclerosis-A case report and mechanistic review of the association with toluene and other volatile organic compounds

Unmasking of latent neurodegenerative disease has been reported following exposure to chemicals that share one or more mechanisms of action in common with those implicated in the specific disease. For example, unmasking of latent Parkinson's disease (PD) has been associated with exposure to anti-dopaminergic agents, while the progression of pre-existing mild cognitive impairment and unmasking of latent Alzheimer's disease has been associated with exposure to general anesthetic agents which promote Aβ protein aggregation. This literature review and clinical case report about a 45-year-old man with no family history of motor neuron disease who developed overt symptoms of a neuromuscular disorder in close temporal association with his unwitting occupational exposure to volatile organic compounds (VOCs) puts forth the hypothesis that exposure to VOCs such as toluene, which disrupt motor function and increase oxidative stress, can unmask latent ALS type neuromuscular disorder in susceptible individuals.

Continuous Inhalation Exposure to Fungal Allergen Particulates Induces Lung Inflammation While Reducing Innate Immune Molecule Expression in the Brainstem

Continuous exposure to aerosolized fine (particle size ≤2.5 µm) and ultrafine (particle size ≤0.1 µm) particulates can trigger innate inflammatory responses in the lung and brain depending on particle composition. Most studies of manmade toxicants use inhalation exposure routes, whereas most studies of allergens use soluble solutions administered via intranasal or injection routes. Here, we tested whether continuous inhalation exposure to aerosolized Alternaria alternata particulates (a common fungal allergen associated with asthma) would induce innate inflammatory responses in the lung and brain. By designing a new environmental chamber able to control particle size distribution and mass concentration, we continuously exposed adult mice to aerosolized ultrafine Alternaria particulates for 96 hr. Despite induction of innate immune responses in the lung, induction of innate immune responses in whole brain samples was not detected by quantitative polymerase chain reaction or flow cytometry. However, exposure did trigger decreases in Arginase 1, inducible nitric oxide synthase, and tumor necrosis factor alpha mRNA in the brainstem samples containing the central nervous system respiratory circuit (the dorsal respiratory group, ventral respiratory group, and the pre-Bötzinger and Bötzinger complexes). In addition, a significant decrease in the percentage of Toll-like receptor 2-expressing brainstem microglia was detected by flow cytometry. Histologic analysis revealed a significant decrease in Iba1 but not glial fibrillary acidic protein immunoreactivity in both the brainstem and the hippocampus. Together these data indicate that inhalation exposure to a natural fungal allergen under conditions sufficient to induce lung inflammation surprisingly causes reductions in baseline expression of select innate immune molecules (similar to that observed during endotoxin tolerance) in the region of the central nervous system controlling respiration.

Redox changes in the brains of reproductive female rats during aging

Reproduction is a critical and demanding phase of an animal's life. In mammals, females usually invest much more in parental care than males, and lactation is the most energetically demanding period of a female's life. Here, we tested whether oxidative stress is a consequence of reproduction in the brains of female Wistar rats. We evaluated the activities of glutathione peroxidase, glutathione S-transferase, and superoxide dismutase; H₂O₂ consumption; protein carbonylation; NO₂ & NO₃ levels; and total glutathione, as well as sex hormone levels in brain tissue of animals at 3, 6, 12, and 24months of age. Animals were grouped according to reproductive experience: breeders or non-breeders. Most of the studied parameters showed a difference between non-breeders and breeders at 12 and 24months. At 24months of age, breeders showed higher superoxide dismutase activity, H₂O₂ consumption, glutathione peroxidase activity, and carbonyl levels than non-breeders. In 12-month-old non-breeders, we observed a higher level of H₂O₂ consumption and higher superoxide dismutase and glutathione peroxidase activities than breeders. By evaluating the correlation network, we found that there were a larger number of influential nodes and positive links in breeder animals than in non-breeders, indicating a greater number of redox changes in breeder animals. Here, we also demonstrated that the aging process caused higher oxidative damage and higher antioxidant defenses in the brains of breeder female rats at 24months, suggesting that the reproduction process is costly, at least for the female brain. This study shows that there is a strong potential for a link between the cost of reproduction and oxidative stress.

Emerging trends in photodegradation of petrochemical wastes: a review

Various human activities like mining and extraction of mineral oils have been used for the modernization of society and well-beings. However, the by-products such as petrochemical wastes generated from such industries are carcinogenic and toxic, which had increased environmental pollution and risks to human health several folds. Various methods such as physical, chemical and biological methods have been used to degrade these pollutants from wastewater. Advance oxidation processes (AOPs) are evolving techniques for efficient sequestration of chemically stable and less biodegradable organic pollutants. In the present review, photocatalytic degradation of petrochemical wastes containing monoaromatic and poly-aromatic hydrocarbons has been studied using various heterogeneous photocatalysts (such as TiO₂, ZnO and CdS. The present article seeks to offer a scientific and technical overview of the current trend in the use of the photocatalyst for remediation and degradation of petrochemical waste depending upon the recent advances in photodegradation of petrochemical research using bibliometric analysis. We further outlined the effect of various heterogeneous catalysts and their ecotoxicity, various degradation pathways of petrochemical wastes, the key regulatory parameters and the reactors used. A critical analysis of the available literature revealed that TiO₂ is widely reported in the degradation processes along with other semiconductors/nanomaterials in visible and UV light irradiation. Further, various degradation studies have been carried out at laboratory scale in the presence of UV light. However, further elaborative research is needed for successful application of the laboratory scale techniques to pilot-scale operation and to develop environmental friendly catalysts which support the sustainable treatment technology with the "zero concept" of industrial wastewater. Nevertheless, there is a need to develop more effective methods which consume less energy and are more efficient in pilot scale for the demineralization of pollutant.

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.

Oxidative stress response and Nrf2 signaling in aging

Increasing oxidative stress, a major characteristic of aging, has been implicated in a variety of age-related pathologies. In aging, oxidant production from several sources is increased, whereas antioxidant enzymes, the primary lines of defense, are decreased. Repair systems, including the proteasomal degradation of damaged proteins, also decline. Importantly, the adaptive response to oxidative stress declines with aging. Nrf2/EpRE signaling regulates the basal and inducible expression of many antioxidant enzymes and the proteasome. Nrf2/EpRE activity is regulated at several levels, including transcription, posttranslation, and interactions with other proteins. This review summarizes current studies on age-related impairment of Nrf2/EpRE function and discusses the changes in Nrf2 regulatory mechanisms with aging.

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.

Effect of a water-maze procedure on the redox mechanisms in brain parts of aged rats

The Morris water maze (MWM) is a tool for assessment of age-related modulations spatial learning and memory in laboratory rats. In our work was investigated the age-related decline of MWM performance in 11-month-old rats and the effect exerted by training in the MWM on the redox mechanisms in rat brain parts. Young adult (3-month-old) and aged (11-month-old) male rats were trained in the MWM. Intact animals of the corresponding age were used as the reference groups. The level of pro- and antioxidant capacity in brain tissue homogenates was assessed using the chemiluminescence method. A reduced performance in the MWM test was found in 11-month-old rats: at the first day of training they showed only 30% of successful MWM trials. However, at the last training day the percentage of successful trials was equal for young adult and aged animals. This indicates that the aged 11-month-old rats can successfully learn in MWM. Therewith, the MWM spatial learning procedure itself produces changes in different processes of redox homeostasis in 11-month-old and 3-month-old rats as compared to intact animals. Young adult rats showed a decrease in prooxidant capacity in all brain parts, while 11-month-old rats demonstrated an increase in antioxidant capacity in the olfactory bulb, pons + medulla oblongata and frontal lobe cortex. Hence, the MWM procedure activates the mechanisms that restrict the oxidative stress in brain parts. The obtained results may be an argument for further development of the animal training procedures aimed to activate the mechanisms that can prevent the age-related deterioration of performance in the learning test. This may be useful not only for the development of training procedures applicable to human patients with age-related cognitive impairments, but also for their rehabilitation.

1,3-dinitrobenzene induces age- and region-specific oxidation to mitochondria-related proteins in brain

Regions of the brain with high energy requirements are especially sensitive to perturbations in mitochondrial function. Hence, neurotoxicant exposures that target mitochondria in regions of high energy demand have the potential to accelerate mitochondrial damage inherently occurring during the aging process. 1,3-Dinitrobenzene (DNB) is a model neurotoxicant that selectively targets mitochondria in brainstem nuclei innervated by the eighth cranial nerve. This study investigates the role of age in the regional susceptibility of brain mitochondria-related proteins (MRPs) to oxidation following exposure to DNB. Male F344 rats (1 month old [young], 3 months old [adult], 18 months old [aged]) were exposed to 10 mg/kg DNB prior to mitochondrial isolation and histopathology experiments. Using a high-throughput proteomic approach, 3 important region- and age-related increases in DNB-induced MRP oxidation were determined: (1) brainstem mitochondria are ×3 more sensitive to DNB-induced oxidation than cortical mitochondria; (2) oxidation of brainstem MRPs is significantly higher than in cortical counterparts; and (3) MRPs from the brainstems of older rats are significantly more oxidized than those from young or adult rats. Furthermore, lower levels of DNB cause signs of intoxication (ataxia, chromodacryorrhea) and vacuolation of the susceptible neuropil in aged animals, while neither is observed in DNB-exposed young rats. Additionally, methemoglobin levels increase significantly in DNB-exposed adult and aged animals, but not young DNB-exposed animals. This suggests that oxidation of key MRPs observed in brainstem of aged animals is necessary for DNB-induced signs of intoxication and lesion formation. These results provide compelling evidence that environmental chemicals such as DNB may aid in the acceleration of injury to specific brain regions by inducing oxidation of sensitive mitochondrial proteins.

Review of toluene action: clinical evidence, animal studies and molecular targets

It has long been known that individuals will engage in voluntary inhalation of volatile solvents for their rewarding effects. However, research into the neurobiology of these agents has lagged behind that of more commonly used drugs of abuse such as psychostimulants, alcohol and nicotine. This imbalance has begun to shift in recent years as the serious effects of abused inhalants, especially among children and adolescents, on brain function and behavior have become appreciated and scientifically documented. In this review, we discuss the physicochemical and pharmacological properties of toluene, a representative member of a large class of organic solvents commonly used as inhalants. This is followed by a brief summary of the clinical and pre-clinical evidence showing that toluene and related solvents produce significant effects on brain structures and processes involved in the rewarding aspects of drugs. This is highlighted by tables highlighting toluene's effect on behaviors (reward, motor effects, learning, etc.) and cellular proteins (e.g. voltage and ligand-gated ion channels) closely associated the actions of abused substances. These sections demonstrate not only the significant progress that has been made in understanding the neurobiological basis for solvent abuse but also reveal the challenges that remain in developing a coherent understanding of this often overlooked class of drugs of abuse.

Study of the potential oxidative stress induced by six solvents in the rat brain

The mechanisms of action involved in the neurotoxicity of solvents are poorly understood. In vitro studies have suggested that the effects of some solvents might be due to the formation of reactive oxygen species (ROS). This study assesses hydroxyl radical (OH) generation and measures malondialdehyde (MDA) levels in the cerebral tissue of rats exposed to six solvents (n-hexane, n-octane, toluene, n-butylbenzene, cyclohexane and 1,2,4-trimethylcyclohexane). Three of these solvents have been shown to generate ROS in studies carried out in vitro on granular cell cultures from rat cerebellum. We assessed OH production by quantifying the rate of formation of 3,4-dihydroxybenzoic acid using a trapping agent, 4-hydroxybenzoic acid, infused via the microdialysis probe, into the prefrontal cortex of rats exposed intraperitoneally to the solvents. Extracellular MDA was quantified in microdialysates collected from the prefrontal cortex of rats exposed, 6h/day for ten days, to 1000ppm of the solvents (except for n-butylbenzene, generated at 830ppm) in inhalation chambers. Tissue levels of free and total MDA were measured in different brain structures for rats acutely (intraperitoneal route) and sub-acutely (inhalation) exposed to solvents. None of the six solvents studied increased the production of hydroxyl radicals in the prefrontal cortex after acute administration. Nor did they increase extracellular or tissue levels of MDA after 10 days' inhalation exposure. On the other hand, a decrease in the concentrations of free MDA in brain structures was observed after acute administration of n-hexane, 1,2,4-trimethylcyclohexane, toluene and n-butylbenzene. Therefore, data of this study carried out in vivo did not confirm observations made in vitro on cell cultures.

Effect of landfill leachate on oxidative stress of brain structures and liver from rodents: modulation by photoelectrooxidation process

The decomposition of solid waste in landfill is responsible for the formation of leachate, a dark liquid with an unpleasant odor; studies investigating its toxicity on mammals are rare. Oxidative stress has been considered as an important biochemical mechanism of the toxicity of several xenobiotics. The aim of this study was to evaluate the effects of landfill leachate on oxidative parameters in striatum, hippocampus and liver homogenates of mice and rats. In order to propose a clean technology for the treatment of leachate, we also investigated the effects of landfill leachate submitted to photoelectrooxidation process (PEO). The homogenates of cerebral structures and liver of Swiss albino mice and Wistar rats were incubated with different concentrations of non-PEO landfill leachate and PEO-treated landfill leachate. After the incubation, the levels of free radicals, determined by 2',7'-dichlorofluorescein diacetate probe, and the lipoperoxidation, quantified by the thiobarbituric acid reactive substances, were evaluated. There was an increase on the levels of free radicals in striatum of both mice and rats when exposed to non-PEO leachate. Moreover, PEO-treated leachate increased the lipoperoxidation in striatum homogenates from rodents. However, both leachates did not alter any of the parameters evaluated in the hippocampus. In the liver, the incubation with leachates induced an augment on levels of free radicals only in samples of mice. In addition, PEO-treated leachate increased the lipoperoxidation indexes in the liver of mice and rats. These results suggest that the landfill leachate can induce an oxidative stress state in the liver and the striatum of rodents. Additionally, the PEO process was unable to efficiently alter the toxic compounds of landfill leachate.

Toluene effects on gene expression in the hippocampus of young adult, middle-age, and senescent Brown Norway Rats

Differential susceptibility to environmental exposures across life stages is an area of toxicology about which little is known. We examined the effects of toluene on transcriptomic changes and oxidative stress (OS) parameters (e.g., NQO1 and GPX) in the rat brain at different life stages to elucidate key molecular pathways responsible for toluene-induced neurotoxicity, as well as possible age-related interactions. Changes in assessed end points following acute oral toluene (0, 0.65, and 1.0 g/kg) were examined 4 h after exposure in hippocampi of Brown Norway Rats at 4, 12, and 24 months of age. Genomic data were analyzed by two-way ANOVA to identify the effects of age, toluene, and interactions between the two factors. Analysis by one-way ANOVA identified 183 genes whose expression changed ≥ 1.25-fold with age. The majority of the genes were upregulated between life stages (> 79%). Similar analysis for toluene-related genes found only two sequences to vary significantly with dose. Fifty-six genes were identified to have expression changes due to an age-toluene interaction. Expression of genes with roles in immune response, cytoskeleton, protein, and energy metabolism was changed with advancing life stage, indicating changes in basic cellular homeostasis. Toluene affected similar cell functions, enhancing the effects of aging. OS parameters also indicated age-related changes in response mechanisms, evidence of toluene damage, and supported an age-toluene interaction. The data indicate that life stage can alter the toxicity of acute toluene exposure in various and complex ways, highlighting the need for further investigation into the role of aging in susceptibility.