Ferrostatin-1 mitigates cellular damage in a ferroptosis-like environment in Caenorhabditis elegans

Although iron (Fe) is the most biologically abundant transition metal, it is highly toxic when it accumulates as Fe2+, forming a labile Fe pool and favoring the Fenton reaction. This oxidative scenario leads to a type of caspase-independent programmed cell death, referred to as ferroptosis, where following processes take place: 1) Fe2+ overload; 2) glutathione peroxidase 4 inactivation; 3) lipid peroxidation and 4) glutathione depletion. The present study sought to evaluate the consequences of Fe2+ administration on ferroptosis induction in Caenorhabditis elegans. We demonstrated higher mortality, increased lipid peroxidation, reduced glutathione peroxidase activity, and morphological damage in dopaminergic neurons upon Fe2+ overload. Pharmacological intervention at the level of lipid peroxidation with ferrostatin-1 (250 μM) mitigated the damage and returned the biochemical parameters to basal levels, revealing the potential of this therapeutical approach. Finally, to assess the relationship between ferroptosis and dopamine in a Parkinsonian background, we evaluated the UA44 worm strain which overexpresses the alpha-synuclein protein in cherry-labeled dopaminergic neurons. We demonstrated that Fe2+ administration reduced lethality associated with similar alterations in biochemical and dopaminergic morphological parameters in wild-type animals. These experiments provide mechanistic-based evidence on the efficacy of a pharmacological approach to mitigate the physiological, biochemical, and morphological consequences of Fe2+ overload. At the same time, they encourage further research on the impact of the combined effects resulting from the genetic background and dopamine signaling in a Parkinsonian phenotype.

Enduring Ethanol-Induced Behavioral Alterations in Caenorhabditis elegans After Developmental Lead Exposure

The roundworm Caenorhabditis elegans (C. elegans) has become a powerful tool to evaluate the deleterious effects of early-life exposure to xenobiotics, including metals. The present chapter describes a detailed protocol for developmental lead (Pb)-exposure in C. elegans. Preliminary assays as well as the final procedure are described in detail. In addition, further protocols aimed to assess ethanol exposure at later stages of life demonstrate the impact of this drug on locomotor behavior, revealing the enduring effects that Pb can imprint on this organism when exposure occurs during development.

Dissecting the role of cadmium, lead, arsenic, and mercury in non-alcoholic fatty liver disease and non-alcoholic steatohepatitis

The objective of the present study was to review the existing epidemiological and laboratory findings supporting the role of toxic metal exposure in non-alcoholic fatty liver disease (NAFLD). The existing epidemiological studies demonstrate that cadmium (Cd), lead (Pb), arsenic (As), and mercury (Hg) exposure was associated both with an increased risk of NAFLD and altered biochemical markers of liver injury. Laboratory studies demonstrated that metal exposure induces hepatic lipid accumulation resulting from activation of lipogenesis and inhibition of fatty acid β-oxidation due to up-regulation of sterol regulatory element-binding protein 1 (SREBP-1), carbohydrate response element binding protein (ChREBP), peroxisome proliferator-activated receptor γ (PPARγ), and down-regulation of PPARα. Other metabolic pathways involved in this effect may include activation of reactive oxygen species (ROS)/extracellular signal-regulated kinase (ERK) and inhibition of AMP-activated protein kinase (AMPK) signaling. The mechanisms of hepatocyte damage during development of metal-induced hepatic steatosis were shown to involve oxidative stress, endoplasmic reticulum stress, pyroptosis, ferroptosis, and dysregulation of autophagy. Induction of inflammatory response contributing to progression of NAFLD to non-alcoholic steatohepatitis (NASH) upon toxic metal exposure was shown to be mediated by up-regulation of nuclear factor κB (NF-κB) and activation of NRLP3 inflammasome. Moreover, epigenetic effects of the metals, as well as their effect on gut microbiota and gut wall integrity were also shown to mediate their role in NAFLD development. Despite being demonstrated for Cd, Pb, and As, the contribution of these mechanisms into Hg-induced NAFLD is yet to be estimated. Therefore, further studies are required to clarify the intimate mechanisms underlying the relationship between heavy metal and metalloid exposure and NAFLD/NASH to reveal the potential targets for treatment and prevention of metal-induced NAFLD.

From Mechanisms to Implications: Understanding the Molecular Neurotoxicity of Titanium Dioxide Nanoparticles

Titanium dioxide nanoparticles (TiO2NPs) are widely produced and used nanoparticles. Yet, TiO2NP exposure may possess toxic effects to different cells and tissues, including the brain. Recent studies significantly expanded the understanding of the molecular mechanisms underlying TiO2NP neurotoxicity implicating a number of both direct and indirect mechanisms. In view of the significant recent progress in research on TiO2NP neurotoxicity, the objective of the present study is to provide a narrative review on the molecular mechanisms involved in its neurotoxicity, with a special focus on the studies published in the last decade. The existing data demosntrate that although TiO2NP may cross blood-brain barrier and accumulate in brain, its neurotoxic effects may be mediated by systemic toxicity. In addition to neuronal damage and impaired neurogenesis, TiO2NP exposure also results in reduced neurite outgrowth and impaired neurotransmitter metabolism, especially dopamine and glutamate. TiO2NP exposure was also shown to promote α-synuclein and β-amyloid aggregation, thus increasing its toxicity. Recent findings also suggest that epigenetic effects and alterations in gut microbiota biodiversity contribute to TiO2NP neurotoxicity. Correspondingly, in vivo studies demosntrated that TiO2NPs induce a wide spectrum of adverse neurobehavioral effects, while epidemiological data are lacking. In addition, TiO2NPs were shown to promote neurotoxic effects of other toxic compounds. Here we show the contribution of a wide spectrum of molecular mechanisms to TiO2NP-induced neurotoxicity; yet, the role of TiO2NP exposure in adverse neurological outcomes in humans has yet to be fully appreciated.

Mitochondria in the Spotlight: C. elegans as a Model Organism to Evaluate Xenobiotic-Induced Dysfunction

Mitochondria play a crucial role in cellular respiration, ATP production, and the regulation of various cellular processes. Mitochondrial dysfunctions have been directly linked to pathophysiological conditions, making them a significant target of interest in toxicological research. In recent years, there has been a growing need to understand the intricate effects of xenobiotics on human health, necessitating the use of effective scientific research tools. Caenorhabditis elegans (C. elegans), a nonpathogenic nematode, has emerged as a powerful tool for investigating toxic mechanisms and mitochondrial dysfunction. With remarkable genetic homology to mammals, C. elegans has been used in studies to elucidate the impact of contaminants and drugs on mitochondrial function. This review focuses on the effects of several toxic metals and metalloids, drugs of abuse and pesticides on mitochondria, highlighting the utility of C. elegans as a model organism to investigate mitochondrial dysfunction induced by xenobiotics. Mitochondrial structure, function, and dynamics are discussed, emphasizing their essential role in cellular viability and the regulation of processes such as autophagy, apoptosis, and calcium homeostasis. Additionally, specific toxins and toxicants, such as arsenic, cadmium, and manganese are examined in the context of their impact on mitochondrial function and the utility of C. elegans in elucidating the underlying mechanisms. Furthermore, we demonstrate the utilization of C. elegans as an experimental model providing a promising platform for investigating the intricate relationships between xenobiotics and mitochondrial dysfunction. This knowledge could contribute to the development of strategies to mitigate the adverse effects of contaminants and drugs of abuse, ultimately enhancing our understanding of these complex processes and promoting human health.

ALDH2 Inhibition by Lead and Ethanol Elicits Redox Imbalance and Mitochondrial Dysfunction in SH-SY5Y Human Neuroblastoma Cell Line: Reversion by Alda-1

Lead (Pb), a common environmental contaminant, and ethanol (EtOH), a widely available drug of abuse, are well-known neurotoxicants. In vivo, experimental evidence indicates that Pb exposure affects oxidative EtOH metabolism with a high impact on living organisms. On these bases, we evaluated the consequences of combined Pb and EtOH exposure on aldehyde dehydrogenase 2 (ALDH2) functionality. In vitro exposure to 10µM Pb, 200mM EtOH, or their combination for 24h reduced ALDH2 activity and content in SH-SY5Y human neuroblastoma cells. In this scenario, we observed mitochondrial dysfunction characterized by reduced mass and membrane potential, decreased maximal respiration, and spare capacity. We also evaluated the oxidative balance in these cells finding a significant increase in reactive oxygen species (ROS) production and lipid peroxidation products under all treatments accompanied by an increase in catalase (CAT) activity and content. These data suggest that ALDH2 inhibition induces the activation of converging cytotoxic mechanisms resulting in an interplay between mitochondrial dysfunction and oxidative stress. Notably, NAD⁺ (1mM for 24h) restored ALDH2 activity in all groups, while an ALDH2 enhancer (Alda-1, 20µM for 24h) also reversed some of the deleterious effects resulting from impaired ALDH2 function. Overall, these results reveal the crucial role of this enzyme on the Pb and EtOH interaction and the potential of activators such as Alda-1 as therapeutic approaches against several conditions involving aldehydes accumulation.

Low-dose N-acetyl cysteine prevents paraquat-induced mortality in Caenorhabditis elegans

Exposure to the herbicide paraquat (PQ; 1,1'-dimethyl-4,4'-bipyridinium dichloride) affects the redox balance of the cell, an effect that can be restored by antioxidants, including N-acetyl cysteine (NAC). One hour of exposure to PQ (0 mM, 10 mM, 50 mM, or 100 mM) dose-dependently increased mortality in Caenorhabditis elegans after exposure (immediate toxicity), while this effect was more evident 24 hours thereafter (delayed toxicity). Importantly, pretreatment with NAC 0.5 mM for one hour partially prevented mortality in the immediate assay, while it had no effect in the delayed test, revealing the importance of long-term studies when evaluating toxicity.

Developmental lead exposure affects dopaminergic neuron morphology and modifies basal slowing response in Caenorhabditis elegans: effects of ethanol

Lead (Pb) and ethanol (EtOH) are neurotoxicants that affect the dopaminergic (DAergic) system. We first sought to assess the morphology of the DAergic neurons in the Caenorhabditis elegans BY200 strain. The results demonstrated dose-dependent damage in these neurons induced by developmental Pb exposure. Secondly, transgenic worms exposed to 24μM Pb and administered with 200mM EtOH were evaluated in the basal slowing response (BSR). Pb induced impairment in the BSR in the wild-type strain that did not improve in response to EtOH, an effect also observed in strains that lack the DOP-1, DOP-2, and DOP-3 receptors. The animals that overexpress tyrosine hydroxylase (TH), or lack the vesicular transport (VMAT) showed a Pb-induced impairment in the BSR that seemed to improve after EtOH. Interestingly, a dramatic impairment in the BSR was observed in the Pb group in strains lacking the DOP-4 receptor, resembling the response of the TH-deficient strain, an effect that in both cases showed a non-significant reversal by EtOH. These results suggest that the facilitatory effect of EtOH on the impaired BSR observed in Pb-exposed null mutant strains may be the result of a compensatory effect in the altered DAergic synapse present in these animals.

Environmental exposure to lead and oxidative stress biomarkers among healthy children in La Plata, Argentina

INTRODUCTION

Environmental exposure to lead is still a major public health problem, especially in children. Oxidative stress may be a primary mechanism associated with toxicity. The objective of this study was to measure blood lead levels (BLLs) in children aged 1 to 6 years exposed to lead in La Plata and suburban areas and their relation to oxidative stress biomarkers.

POPULATION AND METHODS

Cross-sectional, analytical study. Clinically healthy children aged 1 to 6 years were analyzed. BLLs, antioxidant enzyme activity, and extent of lipid peroxidation were measured. The statistical software package R, version 3.5.1, was used.

RESULTS

A total of 131 children participated; their median age was 2.33 years. The geometric mean of BLLs was 1.90 μg/dL; 32% showed a measurable BLL and 3%, BLLs ≥ 5 μg/dL (international reference). The comparison of oxidative stress biomarkers based on BLLs showed a significant difference in median thiobarbituric acid reactive substances (TBARS): 12.0 versus 10.0 nmol MDA/mL of plasma; p = 0.02. In addition, the correlation between BLLs and TBARS was positive (r = 0.24; p = 0.012).

CONCLUSIONS

Most children had a BLL below the limit recommended by international agencies; although such BLLs do not affect antioxidant enzyme activity, they can induce lipid peroxidation. These results demonstrate the usefulness of this biomarker as an early diagnosis tool to assess subtoxic lead effects.

Iron overload and neurodegenerative diseases: What can we learn from Caenorhabditis elegans?

Iron (Fe) is an essential trace element required for several physiological processes. It plays important roles in mitochondrial function, synthesis, and metabolism of the neurotransmitter, as well as oxygen transport. However, excess Fe can cause toxicity. Particularly, Fe overload may result in neurotoxicity, contributing to the development and progression of neurodegenerative diseases, although the molecular mechanisms underlying Fe-induced neurodegeneration have yet to be entirely understood. Alternative (non-rodent) experimental models have been pointed as important approaches to elucidate molecular and physiological events mediating Fe-induced pathology. Among such alternative strategies, an advantageous experimental worm-model system, Caenorhabditis elegans ( C. elegans), has been used to investigate Fe-induced neurotoxicity and neurodegenerative disorders. Its genome has been fully sequenced, corroborating that it shares significant homology with mammalians, and has approximately 40% of human disease-related genes. As part of this review, we discuss studies using the C. elegans model to study molecular mechanisms such as oxidative stress, mitochondrial dysfunction, disturbed homeostasis, and its potential contribution to the study of metal-induced neurodegenerative diseases such as Parkinson’s disease (PD) and Alzheimer’s disease (AD).

Early Cognitive Impairment Behind Nigrostriatal Circuit Neurotoxicity: Are Astrocytes Involved?

Cognitive dysfunction is one of the most severe nonmotor symptoms of nigrostriatal impairment. This occurs as a result of profound functional and morphological changes of different neuronal circuits, including modifications in the plasticity and architecture of hippocampal synapses. Such alterations can be implicated in the genesis and progression of dementia associated with neurodegenerative diseases including Parkinson-like symptoms. There are few studies regarding cognitive changes in nigrostriatal animal models. The aim of this study was to characterize the onset of memory deficit after induction of neurotoxicity with 6-hydroxydopamine (6-OHDA) and its correlation with hippocampal dysfunction. For this, we bilaterally microinjected 6-OHDA in dorsolateral Caudate-Putamen unit (CPu) and then, animals were tested weekly for working memory, spatial short-term memory, and motor performance. We evaluated tyrosine hydroxylase (TH) as a dopamine marker, aldehyde dehydrogenase 2 (ALDH2), a mitochondria detoxification enzyme and astrocyte glial fibrillar acid protein (GFAP) an immunoreactivity marker involved in different areas: CPu, substantia nigra, prefrontal cortex, and hippocampus. We observed a specific prefrontal cortex and nigrostriatal pathway TH reduction while ALDH2 showed a decrease-positive area in all the studied regions. Moreover, GFAP showed a specific CPu decrease and hippocampus increase of positively stained area on the third week after toxicity. We also evaluated the threshold to induce long-term potentiation in hippocampal excitability. Our findings showed that reduced hippocampal synaptic transmission was accompanied by deficits in memory processes, without affecting motor performance on the third-week post 6-OHDA administration. Our results suggest that 3 weeks after neurotoxic administration, astrocytes and ALDH2 mitochondrial enzyme modifications participate in altering the properties that negatively affect hippocampal function and consequently cognitive behavior.

CB1R activation in nucleus accumbens core promotes stress-induced reinstatement of cocaine seeking by elevating extracellular glutamate in a drug-paired context

Preclinical models of stress-induced relapse to drug use have shown that the dysregulation of glutamatergic transmission within the nucleus accumbens (NA) contributes notably to the reinstatement of cocaine-seeking behavior in rodents. In this sense, there has been increasing interest in the cannabinoid type-1 receptor (CB1R), due to its crucial role in modulating glutamatergic neurotransmission within brain areas involved in drug-related behaviors. This study explored the involvement of CB1R within the NA subregions in the restraint stress-induced reinstatement of cocaine-conditioned place preference (CPP), as well as in the regulation of glutamatergic transmission, by using a pharmacological approach and the in vivo microdialysis sampling technique in freely moving rats. CB1R blockade by the antagonist/inverse agonist AM251 (5 nmol/0.5 μl/side) or CB1R activation by the agonist ACEA (0.01 fmol/0.5 μl/side), prevented or potentiated restraint stress-induced reinstatement of cocaine-CPP, respectively, after local administration into NAcore, but not NAshell. In addition, microdialysis experiments demonstrated that restraint stress elicited a significant increase in extracellular glutamate in NAcore under reinstatement conditions, with the local administration of AM251 or ACEA inhibiting or potentiating this, respectively. Interestingly, this rise specifically corresponded to the cocaine-associated CPP compartment. We also showed that this context-dependent change in glutamate paralleled the expression of cocaine-CPP, and disappeared after the extinction of this response. Taken together, these findings demonstrated the key role played by CB1R in mediating reinstatement of cocaine-CPP after restraint stress, through modulation of the context-specific glutamate release within NAcore. Additionally, CB1R regulation of basal extracellular glutamate was demonstrated and proposed as the underlying mechanism.

MOLECULAR MECHANISMS OF LEAD NEUROTOXICITY

Lead (Pb2+) is a non-essential metal with numerous industrial applications that have led to ts ubiquity in the environment. Thus, not only occupational-exposed individuals' health is compromised, but also that of the general population and in particular children. Notably, although the central nervous system is particularly susceptible to Pb2+, other systems are affected as well. The present study focuses on molecular mechanisms that underlie the effects that arise from the presence of Pb2+ in situ in the brain, and the possible toxic effects that follows. As the brain barriers represent the first target of systemic Pb2+, mechanisms of Pb2+ entry into the brain are discussed, followed by a detailed discussion on neurotoxic mechanisms, with special emphasis on theories of ion mimicry, mitochondrial dysfunction, redox imbalance, and neuroinflammation. Most importantly, the confluence and crosstalk between these events is combined into a cogent mechanism of toxicity, by intertwining recent and old evidences from humans, in vitro cell culture and experimental animals. Finally, pharmacological interventions, including chelators, antioxidants substances, anti-inflammatory drugs, or their combination are reviewed as integrated approaches to ameliorate Pb2+ harmful effects in both developing or adult organisms.

Modulation of Ethanol-Metabolizing Enzymes by Developmental Lead Exposure: Effects in Voluntary Ethanol Consumption

This review article provides evidence of the impact of the environmental contaminant lead (Pb) on the pattern of the motivational effects of ethanol (EtOH). To find a mechanism that explains this interaction, the focus of this review article is on central EtOH metabolism and the participating enzymes, as key factors in the modulation of brain acetaldehyde (ACD) accumulation and resulting effect on EtOH intake. Catalase (CAT) seems a good candidate for the shared mechanism between Pb and EtOH due to both its antioxidant and its brain EtOH-metabolizing properties. CAT overactivation was reported to increase EtOH consumption, while CAT blockade reduced it, and both scenarios were modified by Pb exposure, probably as the result of elevated brain and blood CAT activity. Likewise, the motivational effects of EtOH were enhanced when brain ACD metabolism was prevented by ALDH2 inhibition, even in the Pb animals that evidenced reduced brain ALDH2 activity after chronic EtOH intake. Overall, these results suggest that brain EtOH metabolizing enzymes are modulated by Pb exposure with resultant central ACD accumulation and a prevalence of the reinforcing effects of the metabolite in brain against the aversive peripheral ACD accumulation. They also support the idea that early exposure to an environmental contaminant, even at low doses, predisposes at a later age to differential reactivity to challenging events, increasing, in this case, vulnerability to acquiring addictive behaviors, including excessive EtOH intake.

Age-related effects of chronic restraint stress on ethanol drinking, ethanol-induced sedation, and on basal and stress-induced anxiety response

Adolescents are sensitive to the anxiolytic effect of ethanol, and evidence suggests that they may be more sensitive to stress than adults. Relatively little is known, however, about age-related differences in stress modulation of ethanol drinking or stress modulation of ethanol-induced sedation and hypnosis. We observed that chronic restraint stress transiently exacerbated free-choice ethanol drinking in adolescent, but not in adult, rats. Restraint stress altered exploration patterns of a light-dark box apparatus in adolescents and adults. Stressed animals spent significantly more time in the white area of the maze and made significantly more transfers between compartments than their non-stressed peers. Behavioral response to acute stress, on the other hand, was modulated by prior restraint stress only in adults. Adolescents, unlike adults, exhibited ethanol-induced motor stimulation in an open field. Stress increased the duration of loss of the righting reflex after a high ethanol dose, yet this effect was similar at both ages. Ethanol-induced sleep time was much higher in adult than in adolescent rats, yet stress diminished ethanol-induced sleep time only in adults. The study indicates age-related differences that may increase the risk for initiation and escalation in alcohol drinking.

Enkephalin is essential for the molecular and behavioral expression of cocaine sensitization

Behavioral sensitization to cocaine is associated to neuroadaptations that contribute to addiction. Enkephalin is highly expressed in mesocorticolimbic areas associated with cocaine-induced sensitization; however, their influence on cocaine-dependent behavioral and neuronal plasticity has not been explained. In this study, we employed a knockout (KO) model to investigate the contribution of enkephalin in cocaine-induced behavioral sensitization. Wild-type (WT) and proenkephalin KO mice were treated with cocaine once daily for 9 days to induce sensitization. Additionally, to clarify the observations in KO mice, the same procedure was applied in C57BL/6 mice, except that naloxone was administered before each cocaine injection. All animals received a cocaine challenge on days 15 and 21 of the treatment to evaluate the expression of locomotor sensitization. On day 21, microdialysis measures of accumbal extracellular dopamine, Western blotting for GluR1 AMPA receptor (AMPAR), phosphorylated ERK2 (pERK2), CREB (pCREB), TrKB (pTrkB) were performed in brain areas relevant for sensitization from KO and WT and/or naloxone- and vehicle pre-treated animals. We found that KO mice do not develop sensitization to the stimulating properties of cocaine on locomotor activity and on dopamine release in the nucleus accumbens (NAc). Furthermore, pivotal neuroadaptations such as the increase in pTrkB receptor, pERK/CREB and AMPAR related to sensitized responses were absent in the NAc from KO mice. Consistently, full abrogation of cocaine-induced behavioral and neuronal plasticity after naloxone pre-treatment was observed. We show for first time that the proenkephalin system is essential in regulating long-lasting pivotal neuroadaptations in the NAc underlying behavioral sensitization to cocaine.

Participation of catalase in voluntary ethanol consumption in perinatally low-level lead-exposed rats

BACKGROUND

Environmental lead (Pb) exposure and alcohol abuse pose significant public health problems for our society. One of the proposed mechanisms of action of the developmental neurotoxicant Pb is related to its ability to affect antioxidant enzymes, including catalase (CAT). Ethanol's (EtOH) motivational effects are postulated to be mediated by the CAT-dependent acetaldehyde generated in the brain. The current study sought to investigate the role of this enzyme in the elevated EtOH intake previously reported in perinatally Pb-exposed rats.

METHODS

Thirty-five-day-old male Wistar rats exposed to 220 ppm Pb during gestation and lactation were offered escalating EtOH solutions (2 to 10%) or water, 2 h/d for 28 days. Once baseline 10% EtOH intake was achieved, they were injected with (i) saline (SAL), (ii) 3-amino 1,2,4 triazole (aminotriazole [AT], a CAT inhibitor, 250 mg/kg intraperitoneally [i.p.], 5 hours before the last 8 EtOH intake sessions), or (iii) 3-nitropropionic acid (3NPA; a CAT activator, 20 mg/kg subcutaneously [s.c.], 45 minutes before the last 4 EtOH intake sessions). Rats were then sacrificed, blood collected, and brain regions harvested for CAT activity determination. Additional studies evaluated EtOH intake and CAT activity in response to 10 and 30 mg/kg 3NPA. Both 3NPA and AT were evaluated for striatal cytotoxicity.

RESULTS

We observed that AT pretreatment blunted the increased EtOH intake, as well as the elevated CAT activity in blood, cerebellum, and hippocampus evidenced in the developmentally Pb-exposed rats that have consumed EtOH. Conversely, 20 mg/kg 3NPA further increased voluntary EtOH intake in these animals as compared with controls, concomitantly with a slight elevation in CAT activity both in blood and in the striatum, associated with no changes in striatal cytotoxicity.

CONCLUSIONS

These results suggest a participation of CAT, and possibly acetaldehyde, in Pb-induced high EtOH intake, and open up new avenues to elucidate the mechanism that underlies the Pb and EtOH interaction.

Blood lead levels and enzymatic biomarkers of environmental lead exposure in children in Cordoba, Argentina, after the ban of leaded gasoline

Lead (Pb) is a developmental neurotoxicant found in industrial activities, many of them already prohibited worldwide. This study aimed to evaluate current blood Pb (PbB) levels in children in Cordoba, Argentina, and to compare these with similar studies performed before Pb was banned in gasoline in 1996. We also sought to identify mechanistically relevant biomarkers by measuring δ-aminolevulinic acid dehydratase (δ-ALAD), superoxide dismutase (SOD), and catalase (CAT) activities. We finally aimed to determine whether sociodemographic characteristics are associated with Pb toxicity. Blood samples collected from 161 healthy children between September 2009 and February 2010 revealed mean PbB levels of 2.58 ± 0.30 µg/dl. Enzymatic δ-ALAD, CAT, and SOD activities showed no significant variations when plotted against PbB levels. Finally, children living in the suburbs have higher PbB levels than their city counterparts, while low socioeconomic status increased δ-ALAD inhibition compared with that of middle-income children. Overall, these results evidenced a substantial reduction in exposure to Pb in this pediatric population over a decade after Pb was restricted in gasoline and reveal the importance of pursuing novel biomarkers of toxicity along with the sociodemographic profile to complement Pb diagnosis.

Stress-induced sensitization to cocaine: actin cytoskeleton remodeling within mesocorticolimbic nuclei

This study investigated the consequence of repeated stress on actin cytoskeleton remodeling in the nucleus accumbens (NAc) and prefrontal cortex (Pfc), and the involvement of this remodeling in the expression of stress-induced motor cross-sensitization with cocaine. Wistar rats were restrained daily (2 h) for 7 days and, 3 weeks later, their NAc and Pfc were dissected 45 min after acute saline or cocaine (30 mg/kg i.p.). F-actin, actin-binding proteins (ABP) and GluR1 were quantified by Western blotting, and dendritic spines and postsynaptic density (PSD) size measured by electron microscopy. In the NAc from the stress plus cocaine group we observed a decrease in the phosphorylation of two ABPs, cofilin and cortactin, and an increase in the PSD size and the surface expression of GluR1, consistent with a more highly branched actin cytoskeleton. The Pfc also showed evidence of increased actin polymerization after stress as an increase was observed in Arp2, and in the number of spines. Inhibiting actin cycling and polymerization with latrunculin A into the NAc, but not the Pfc, inhibited the expression of cross-sensitization to cocaine (15 mg/kg i.p.) and restored the expression of GluR1 to control levels. This study shows that a history of repeated stress alters the ability of a subsequent cocaine injection to modulate dendritic spine morphology, actin dynamics and GluR1 expression in the NAc. Furthermore, by regulating GluR1 expression in the NAc, elevated actin cycling contributes to the expression of cross-sensitization between stress and cocaine, while stress-induced changes in the Pfc were not associated with cross-sensitization.

Enhanced stimulus sequence-dependent repeated learning in male offspring after prenatal stress alone or in conjunction with lead exposure

Both lead (Pb) exposure and prenatal stress (PS) can produce cognitive deficits, and in a prior study we demonstrated enhanced cognitive deficits in repeated learning of female rats exposed to both of these developmental insults (Cory-Slechta et al., 2010). However, PS can also lead to improved cognitive outcomes that are both gender- and context-dependent. Thus, the current study examined whether Pb ± PS likewise produced repeated learning deficits in males, either after maternal or lifetime Pb exposure. Repeated learning was evaluated using a multiple schedule of repeated learning and performance that required learning 3-response sequences in male offspring that had been subjected to either maternal Pb (0 or 150 ppm) or lifetime Pb exposure (0 or 50 ppm) beginning two months prior to dam breeding, to prenatal immobilization restraint stress (gestational days 16-17), or to both Pb and PS. Blood Pb, corticosterone, hippocampal glucocorticoid receptor density and brain monoamines were also measured. In contrast to outcomes in females, sequence-specific enhancements of repeated learning accuracy were produced by PS, particularly when combined with Pb, results that appeared to be more robust in combination with lifetime than maternal Pb exposure. A common behavioral mechanism of these improvements appears to be an increased reinforcement density associated with increased response rates and shorter session times seen with PS ± Pb that could shorten time to reinforcement. Trends toward lower levels of nucleus accumbens dopamine activity seen after both maternal Pb and lifetime Pb combined with PS suggest a possible role for this region/neurotransmitter in enhanced accuracy, whereas PS ± Pb-induced corticosterone changes did not exhibit an obvious systematic relationship to accuracy enhancements. While PS ± Pb-based increases in accuracy appear to be an improved outcome, the benefits of increased response rate are by no means universal, but highly context-dependent and can lead to adverse behavioral effects in other conditions.

Interactions of lifetime lead exposure and stress: behavioral, neurochemical and HPA axis effects

Lead (Pb) and stress co-occur as risk factors, share biological substrates and produce common adverse effects. We previously found that prenatal restraint stress (PS) or offspring stress (OS) could enhance maternal Pb-induced behavioral, brain neurotransmitter level and HPA axis changes. The current study examined how lifetime Pb exposure, consistent with human environmental exposure, interacts with stress. Dams were exposed to Pb beginning 2 mos prior to breeding (0, 50 or 150ppm in drinking water), PS on gestational days 16 and 17, or the combination. Offspring continued on the same Pb exposure as the dam. A subset of Pb+PS offspring also received 3 additional stress challenges (OS), yielding 9 exposure groups/gender: 0-NS, 0-PS, 0-OS, 50-NS, 50-PS, 50-OS, 150-NS, 150-PS and 150-OS. As with maternal Pb (Virgolini et al., 2008a), lifetime Pb and stress influenced Fixed Interval (FI) behavior primarily in females. Relative to 0-NS control, reductions in postreinforcement pause (PRP) times were seen only with combined Pb+PS (50-PS, 50-OS, 150-PS). Stress increased FI response rates when Pb alone was without effect (150-PS, 150-OS), but gradually mitigated rate increases produced by Pb alone (50-PS, 50-OS), effects that appear to be due primarily to PS, as they were of comparable magnitude in PS and OS groups. Individual subject data suggest that enhanced Pb and PS effects reflect increasing numbers of subjects shifting to the high end of the normal range of FI performance values, consistent with a dose-response type of Pb+stress additivity. Consistent with reports of cortico-striatal mediation of both interval timing (PRP) and FI rates, principal component analyses suggested potential mediation via altered frontal cortex norepinephrine, reduced nucleus accumbens dopaminergic control and enhanced striatal monoamine control. Altered FI performance, whether occurring through changes in response rate, PRP, or both, represent behavioral inefficiency and potentially sub-optimal or even dysfunctional resource/energy use.

Alterations in glucocorticoid negative feedback following maternal Pb, prenatal stress and the combination: a potential biological unifying mechanism for their corresponding disease profiles

Combined exposures to maternal lead (Pb) and prenatal stress (PS) can act synergistically to enhance behavioral and neurochemical toxicity in offspring. Maternal Pb itself causes permanent dysfunction of the body's major stress system, the hypothalamic pituitary adrenal (HPA) axis. The current study sought to determine the potential involvement of altered negative glucocorticoid feedback as a mechanistic basis of the effects in rats of maternal Pb (0, 50 or 150 ppm in drinking water beginning 2 mo prior to breeding), prenatal stress (PS; restraint on gestational days 16-17) and combined maternal Pb+PS in 8 mo old male and female offspring. Corticosterone changes were measured over 24 h following an i.p. injection stress containing vehicle or 100 or 300 microg/kg (females) or 100 or 150 microg/kg (males) dexamethasone (DEX). Both Pb and PS prolonged the time course of corticosterone reduction following vehicle injection stress. Pb effects were non-monotonic, with a greater impact at 50 vs. 150 ppm, particularly in males, where further enhancement occurred with PS. In accord with these findings, the efficacy of DEX in suppressing corticosterone was reduced by Pb and Pb+PS in both genders, with Pb efficacy enhanced by PS in females, over the first 6 h post-administration. A marked prolongation of DEX effects was found in males. Thus, Pb, PS and Pb+PS, sometimes additively, produced hypercortisolism in both genders, followed by hypocortisolism in males, consistent with HPA axis dysfunction. These findings may provide a plausible unifying biological mechanism for the reported links between Pb exposure and stress-associated diseases and disorders mediated via the HPA axis, including obesity, hypertension, diabetes, anxiety, schizophrenia and depression. They also suggest broadening of Pb screening programs to pregnant women in high stress environments.

CNS effects of developmental Pb exposure are enhanced by combined maternal and offspring stress

Lead (Pb) exposure and elevated stress are co-occurring risk factors. Both impact brain mesolimbic dopamine/glutamate systems involved in cognitive functions. We previously found that maternal stress can potentiate Pb-related adverse effects in offspring at blood Pb levels averaging approximately 40 microg/dl. The current study of combined Pb exposure and stress sought to extend those results to lower levels of Pb exposure, and to examine relationships among consequences in offspring for fixed interval (FI) schedule-controlled behavior, neurochemistry and corticosterone levels. Dams were exposed to maternal Pb beginning 2 months prior to breeding (0, 50 or 150 ppm in drinking water), maternal restraint stress on gestational days 16 and 17 (MS), or the combination. In addition, a subset of offspring from each resultant treatment group was also exposed intermittently to variable stressors as adults (MS+OS). Marked "Pb-stress"-related increases in response rates on a fixed interval schedule, a behavioral performance with demonstrated sensitivity to Pb, occurred preferentially in female offspring even at mean blood Pb levels of 11 microg/dl when 50 ppm Pb was combined with maternal and offspring stress. Greater sensitivity of females to frontal cortex catecholamine changes may contribute to the elevated FI response rates as mesocorticolimbic systems are critical to the mediation of this behavior. Basal and final corticosterone levels of offspring used to evaluate FI performance differed significantly from those of non-behaviorally tested (NFI) littermates, demonstrating that purported mechanisms of Pb, stress or Pb/stress effects determined in non-behaviorally trained animals cannot necessarily be generalized to animals with behavioral histories. Finally, the persistent and permanent consequences of Pb, stress and Pb+stress in offspring of both genders suggest that Pb screening programs should include pregnant women at risk for elevated Pb exposure, and that stress should be considered as an additional risk factor. Pb+stress effects observed in the absence of either risk factor alone (i.e., potentiated effects) raise questions about the capacity of current hazard identification approaches to adequately identify human health risks posed by neurotoxicants.

Lifetime consequences of combined maternal lead and stress

Elevated lead (Pb) exposure and high stress both target low socio-economic status populations. Both also act on the hypothalamic-pituitary-adrenal (HPA) axis. Pb disrupts cognition through effects on the mesocorticolimbic dopamine pathway. Stress hormones act on this same pathway via the HPA axis. The fact that Pb and stress are likely interactive risk factors served as the rationale for a series of studies in our laboratory. These demonstrate that stress can modify Pb effects, that Pb can modify stress responsivity, and, notably, that Pb + stress effects can occur in the absence of an effect of either alone in rats. Furthermore, maternal only Pb exposure can permanently alter basal corticosterone levels, stress responsivity (i.e. permanent modification of HPA axis function) and brain catecholamines in offspring of both genders. Interactive effects of Pb + stress are not limited to early development: even Pb exposures initiated post-weaning alter basal corticosterone and stress responsivity. Outcomes differ in relation to gender, brain region, stressor and time of measurement, making Pb + stress interactions complex. Altered HPA axis function may serve as a mechanism for the behavioural and catecholaminergic neurotoxicity associated with Pb, as well as for the increased incidence of disease and dysfunctions associated with low socio-economic status. The permanent consequences of maternal only Pb exposure suggest that Pb screening programmes should include pregnant women at risk for elevated Pb exposure, and that stress should be considered as an additional risk factor. Pb + stress effects observed in the absence of either risk factor alone raise questions about the capacity of current hazard identification approaches to adequately identify human health risks posed by neurotoxicants.

Permanent alterations in stress responsivity in female offspring subjected to combined maternal lead exposure and/or stress

Elevated lead (Pb) exposures preferentially impact low socioeconomic status (SES) populations, the same groups thought to sustain the highest levels of environmental stress. As co-occurring risk factors, therefore, Pb and stress could interact, a possibility further supported by the fact that both act on mesocorticolimbic dopamine systems of the brain. We recently demonstrated in rats that maternal Pb exposure could permanently increase basal corticosterone levels of offspring consistent with altered hypothalamic pituitary adrenal (HPA) axis function. The current study was thus designed to test the hypothesis that stress responsivity of offspring should likewise be altered, with the outcome differing in response to Pb, stress or Pb+stress. The impact of intermittent variable stress challenges (restraint, novelty, cold) on behavior sensitive to Pb exposure (fixed interval (FI) schedule-controlled responding) and on stress-induced corticosterone changes were evaluated in adult female offspring of dams that had been exposed to Pb (150 ppm) in drinking water from 2 months prior to breeding through lactation with or without maternal restraint stress on days 16 and 17 of gestation. This design yielded four treatment groups: (NS/0, no maternal Pb, no maternal stress; S/0, no maternal Pb, maternal stress; NS/150, maternal Pb, no maternal stress; and S/150, maternal Pb exposure and maternal stress). While maternal Pb alone and stress alone each altered components of stress responsivity, the greatest number of effects was seen in response to Pb + stress. This included alterations in FI performance following both restraint and cold stress and in the corticosterone response to cold stress. Collectively, these studies reveal that maternal Pb exposure alone can permanently alter stress responsivity and that the profile of effects produced by maternal Pb differ from those produced by maternal Pb in conjunction with stress, findings which have both mechanistic and risk assessment significance.

Interactions of chronic lead exposure and intermittent stress: consequences for brain catecholamine systems and associated behaviors and HPA axis function

Elevated lead (Pb) burden and high stress levels are co-occurring risk factors in low socioeconomic status (SES) children. Our previous work demonstrated that maternal Pb exposure can permanently alter hypothalamic-pituitary-adrenal (HPA) axis function and responsivity to stress challenges in offspring. The current study sought to determine the consequences of chronic Pb exposures initiated later in development combined with variable intermittent stress challenges. Male rats were exposed chronically from weaning to 0, 50, or 150 ppm Pb acetate drinking solutions (producing blood Pb levels of <5, 9-15, and 23-27 mug/dl, respectively). Pb itself decreased basal plasma corticosterone, with greater effects at 50 than 150 ppm; 150 ppm reduced both cytosolic and nuclear glucocorticoid receptor binding. Responsivity to stress challenges including novelty, cold, and restraint, was measured as changes in Fixed Interval (FI) schedule-controlled behavior in a subset of rats within each group. FI performance was modified by novelty stress only in Pb-treated rats, whereas cold and restraint stress effects were comparable across groups. Novelty elevated corticosterone equivalently across groups, but cold stress markedly increased corticosterone only in Pb-treated groups. The pattern of Pb-induced changes in serotonin (5-HT) or its metabolite 5-HIAA in frontal cortex, nucleus accumbens, striatum, and hypothalamus resembled that observed for basal corticosterone levels indicating a relationship between these variables. In addition to suggesting the potential for HPA axis-mediated effects of Pb on the central nervous system, these findings also raise questions about whether single chemicals studied in isolation from other relevant risk factors can adequately identify neurotoxic hazards.

Maternal stress modulates the effects of developmental lead exposure

Lead exposure is higher among children with low socioeconomic status (SES) compared with other children in the United States. Low SES itself is a known risk factor for various diseases and dysfunctions, effects that have been ascribed to chronic stress and associated elevation of glucocorticoids. Chronically elevated glucocorticoids and Pb provoke similar behavioral changes, and both can act on mesocorticolimbic systems of the brain. In this study we examined the hypothesis that these co-occurring risk factors, Pb and environmental stress, would interact and modulate each others' effects. Using a rodent model, we focused on the specific contributions of maternal stress (restraint) and maternal Pb exposure (150 ppm in drinking water) on corticosterone levels of offspring, as well as on neurotransmitter changes and a behavioral baseline (fixed-interval schedule-controlled performance) with known sensitivities to Pb. We observed interactions of Pb and stress that differed in relation to outcome measure and sex. In addition, potentiated effects (effects of Pb plus stress but showing no changes produced by either alone) were observed more frequently in females. Importantly, Pb alone (in males) and Pb plus stress (in females) permanently elevated corticosterone levels in offspring; even short-term Pb exposure to dams could cause this effect. Such increases could suggest a potential new mechanism by which Pb exposure could directly or indirectly enhance susceptibility to diseases and dysfunctions and induce cognitive deficits. Moreover, the interactive effects of Pb and stress, and particularly the potentiated effects of Pb plus stress, raise questions about whether current risk assessment strategies sufficiently consider the potential for modulation of toxicity that can accrue from intercurrent risk factors.

Amphetamine and stress responses in developmentally lead-exposed rats

In this study, pregnant Wistar dams were exposed to 220 ppm of lead (Pb) in drinking water during gestation and lactation. The response to the locomotor-stimulating effects of 0.5 mg/kg of amphetamine (AMPH) was evaluated in 35-day-old male offspring. The results demonstrated that developmental Pb exposure induced no differences in the response to the drug, although an increase in locomotor activity induced by a single saline (SAL) injection was observed selectively in the Pb-exposed group. Considering evidence that suggests a relationship between increased locomotor activity and stress response, a time course analysis of corticosterone (CS) secretion and locomotor performance was carried out. Higher basal levels of CS and elevated stress-induced secretion of this hormone in response to the injection were observed in Pb-exposed rats compared to controls, a pattern that showed a time-related increase in locomotor activity. Habituation to SAL injections prior to testing restored both CS secretion and locomotor response to SAL to levels comparable to controls and did not modify AMPH locomotor response measured in these new experimental conditions. Additionally, we demonstrated that these behavioral/hormonal disruptions were no longer detectable later in adulthood. Collectively, these data suggest that the stimulant-locomotor effect of AMPH in Pb-exposed rats is independent of the arousal of the animal at the time of its administration. They also support a unique profile of integrated behavioral and hormonal hyperresponsiveness in 35-day-old low-level Pb-exposed rats evidenced as hyperlocomotion and altered secretion of CS in response to an environmental manipulation, an effect that was no longer present later in life.

Glutamate and dopamine in nucleus accumbens core and shell: sequence learning versus performance

This study sought to determine whether neurochemical changes associated with chronic postweaning lead (Pb) exposure, namely, enhanced dopamine (DA) activity and/or blockade of NMDA function in nucleus accumbens (NAC), underlie the learning impairments also associated with this Pb regimen, and whether core or shell subregions of nucleus accumbens would be more important to such effects. If so, then mimicking these neurochemical changes in normal (control) rats should reproduce these Pb-induced learning impairments. For this purpose, the effects of DA (20-80 microg), the non-competitive NMDA antagonist MK-801 (1.0-2.5 microg) or DA+MK-801 (40+1.0, 80+2.5 microg) were infused in core or shell of nucleus accumbens in normal rats and effects on a multiple schedule of repeated learning (RL) and performance (P) evaluated. In core, MK-801 mimicked the effects of Pb exposure, selectively reducing RL accuracy with no corresponding changes in P accuracy, an effect derived from an increased frequency of perseverative errors. DA produced non-specific changes, reducing accuracy levels in RL and P components. Accuracy and rate effects of DA could be reversed by concurrent administration of the higher MK-801 dose. In shell, MK-801, primarily the lower dose, reduced accuracy in both the RL and P components, while DA did not produce any systematic effects. Collectively, these results point to a greater importance of core as compared to shell in the mediation of learning of spatial sequences, and suggest that inhibition of glutamatergic NMDA function may play a critical role in the selective learning impairments associated with chronic low level Pb exposure.

Behavioral responses to ethanol in rats perinatally exposed to low lead levels

Wistar rats were exposed to 220 ppm of lead (Pb) in the drinking water from conception to the end of the nursing period (postnatal day 25). Maternal blood Pb levels at this time were 25 microg/dl. Male offspring were tested at the age of 35 or 70 days. We studied the anxiolytic response to 0.5-2.0 g/kg ethanol in an elevated plus maze test and preference for increasing ethanol solutions (2%, 4%, and 6%, v/v) in a free-choice paradigm; we also determined basal blood levels of corticosterone. Results demonstrated that, at 35 days of age, experimental rats were hypersensitive to the anxiolytic effect of ethanol and showed greater voluntary intake of this drug. In addition, 35-day-old Pb-treated rats exhibited higher basal levels of corticosterone as compared with those of controls. These differences disappeared at 70 days. Our findings are discussed in terms of either Pb-induced alterations in the development of the CNS or higher levels of corticosterone in experimental animals. Possible Pb-ethanol effects interactions are also considered.

Spatial learning in rats exposed to acute ethanol intoxication on gestational day 8

Pregnant Wistar rats were treated on gestational day 8 (GD 8) with two IP injections of either ethanol (2.9 g/kg in 24% v/v saline solution) or saline. Offspring were tested in the water-maze task at 45 or 90 days of age. The escape latencies of rats trained with a submerged escape platform at a fixed location were similar between control and experimental rats. Analyses of responses on a probe trial carried out 10 days after the training period, revealed that 90-day-old females prenatally exposed to alcohol were less likely to swim in the target region. No differences were observed in this free-swim trial in 45- and 90-day-old male, and 45-day-old female animals. Binding studies of low-affinity GABAA sites in the hippocampus showed an increase in affinity of [3H]GABAA for their binding sites in 90-day-old female offspring prenatally intoxicated with ethanol. Our results demonstrate that acute intoxication with ethanol on GD 8 did not modify acquisition but impaired the retention of spatial learning only in adult female rats. It is possible that the impaired retention will be consequence of higher GABAA receptor affinity.

Effects of acute ethanol intoxication during pregnancy on central dopaminergic system in male rats

Pregnant albino rats received 2 IP injections, spaced by 4 h, of either ethanol (2.9 g/kg in 24% v/v saline solution) or saline, on gestational day (GD) 8. During adulthood, male rats prenatally exposed to alcohol exhibited an increased stereotyped behavioral response to 12 mg/kg of amphetamine (AMPH) or 1 mg/kg of apomorphine (APO), whereas the stereotypy induced by 6 mg/kg of AMPH showed no difference between control and experimental animals. Also, the hypoactivity response elicited by small doses of APO was not significantly affected by the prenatal treatment with alcohol. Analysis of dopaminergic function in the striatum and nucleus accumbens demonstrated no change on dopamine (DA) levels in both structures in alcohol pre-exposed 55- and 180-day-old rats. A reduction in striatum 3-4 dihydroxyphenylacetic acid levels was observed at both ages. These results indicate that an acute intoxication with alcohol on GD 8 induces a long-lasting decrease in striatal but not in nucleus accumbens DA metabolism. As a consequence, a lower striatal DA release might produce a compensatory supersensitivity of postsynaptic DA sites. This interpretation is consistent and correlates with behavioral results.