Inflammation-Like Glial Response in Lead-Exposed Immature Rat Brain

Exposure to toxic metals might accelerate aging

BACKGROUND

Biological aging (BA) trajectory can capture the characteristics of the dynamic process of aging. Although toxic metals were associated with various health effects, there was limited study of their single and joint effects on BA trajectory.

METHODS

A total of 2688 community-based older adults (≥65 years) were enrolled in this study, and we measured a composite BA indicator based on 9 clinical and anthropometric measures using Klemera and Doubal methods at four time points from baseline to the last follow-up. Group-based trajectory modeling was used to identify the aging trajectories. The associations between toxic metals and BA trajectories were analyzed by multivariable multinomial logistic regression. Quantile g-computing was used to explore the mixed effect of toxic metals. Pairwise interactions of toxic metals were further assessed.

RESULTS

Three BA trajectories including slow aging, normal aging, and accelerated aging were identified in this study. Quantile g-computing showed toxic metals mixture was associated with higher risk of being in normal aging trajectory (OR = 1.14, 95%CI: 1.01, 1.29) or accelerated aging trajectories (OR = 1.53, 95%CI: 1.25, 1.88), with Pb as the dominant contributor. An interquartile range (IQR) increase in ln-transformed Pb was associated with an increased risk of being in normal aging (OR = 1.21, 95%CI:1.08, 1.35) or accelerated BA trajectory (OR = 1.54, 95%CI:1.31, 1.82) compared with slow aging trajectory. Similarly, per IQR increase in As was associated with a higher risk of being in accelerated BA trajectory (OR = 1.18, 95%CI: 1.01, 1.39). The interaction between toxic metals exposure was not significant.

CONCLUSION

This study identified three BA trajectories and found the association between mixed toxic metals and increased risk of accelerated BA trajectories, with Pb as the dominant contributor. These findings highlight the importance of reducing toxic metals in the environment and may assist in developing effective anti-aging interventions in older adults.

Antioxidant Potential of Selected Apiaceae Plant Extracts: A Study Focused on the Chemical Composition and Neuroprotective Effect of Coriandrum sativum L. Extract Against Lead (Pb)-Induced Neurotoxicity in Rats

Lead is a common environmental pollutant. It can affect several body systems including the central nervous system (CNS). Lead can disrupt the nervous system by different mechanisms including oxidative stress, inflammation, disruption of neurotransmission, and aberrant autophagy. Apiaceous species have been used traditionally as food flavoring and medicine, representing a rich source of bioactive compounds. In the current study, the antioxidant power of four Apiaceous extracts (Foeniculum vulgare L., Pimpinella anisum L., Coriandrum sativum L., and Cuminum cyminum L.) was evaluated. Additionally, the metabolite profiles of the selected species were comprehensively investigated by untargeted liquid chromatography electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) coupled to chemometry. Coriander (Coriandrum sativum L.) extract showed the highest radical scavenging activity and reducing power. Coriander was further subjected to in vivo evaluation of its protective effect against Lead (Pb)-induced neurotoxicity. Administration of coriander extracts improved the short- and long-term memory performance and decreased hippocampal Pb content in Pb-intoxicated rats. Moreover, it attenuated hippocampal oxidative stress, neurochemical changes, and exhibited anti-inflammatory effect in the hippocampal tissue. Further, coriander extracts attenuated Pb inhibitory effect on the mammalian target of Rapamycin (mTORC1) pathway resulting in upregulation of Phospho-p70 S6 Kinase (P-P70S6K) and Phospho-S6 Ribosomal Protein (PS6) and downregulation of Beclin-1. Additionally, some selected coriander ingredients were subjected to molecular docking to examine their regulatory effect on mTORC-1 and IκB kinase complex (Ikk-β). The present findings highlight the future pharmaceutical utilization of coriander extract as valuable source of phenolic compounds that can be used as antioxidant, anti-inflammatory, and neuroprotective agents against Pb-induced neurotoxicity.

Heavy metals: toxicity and human health effects

Heavy metals are naturally occurring components of the Earth's crust and persistent environmental pollutants. Human exposure to heavy metals occurs via various pathways, including inhalation of air/dust particles, ingesting contaminated water or soil, or through the food chain. Their bioaccumulation may lead to diverse toxic effects affecting different body tissues and organ systems. The toxicity of heavy metals depends on the properties of the given metal, dose, route, duration of exposure (acute or chronic), and  extent of bioaccumulation. The detrimental impacts of heavy metals on human health are largely linked to their capacity to interfere with antioxidant defense mechanisms, primarily through their interaction with intracellular glutathione (GSH) or sulfhydryl groups (R-SH) of antioxidant enzymes such as superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx), glutathione reductase (GR), and other enzyme systems. Although arsenic (As) is believed to bind directly to critical thiols, alternative hydrogen peroxide production processes have also been postulated. Heavy metals are known to interfere with signaling pathways and affect a variety of cellular processes, including cell growth, proliferation, survival, metabolism, and apoptosis. For example, cadmium can affect the BLC-2 family of proteins involved in mitochondrial death via the overexpression of antiapoptotic Bcl-2 and the suppression of proapoptotic (BAX, BAK) mechanisms, thus increasing the resistance of various cells to undergo malignant transformation. Nuclear factor erythroid 2-related factor 2 (Nrf2) is an important regulator of antioxidant enzymes, the level of oxidative stress, and cellular resistance to oxidants and has been shown to act as a double-edged sword in response to arsenic-induced oxidative stress. Another mechanism of significant health threats and heavy metal (e.g., Pb) toxicity involves the substitution of essential metals (e.g., calcium (Ca), copper (Cu), and iron (Fe)) with structurally similar heavy metals (e.g., cadmium (Cd) and lead (Pb)) in the metal-binding sites of proteins. Displaced essential redox metals (copper, iron, manganese) from their natural metal-binding sites can catalyze the decomposition of hydrogen peroxide via the Fenton reaction and generate damaging ROS such as hydroxyl radicals, causing damage to lipids, proteins, and DNA. Conversely, some heavy metals, such as cadmium, can suppress the synthesis of nitric oxide radical (NO·), manifested by altered vasorelaxation and, consequently, blood pressure regulation. Pb-induced oxidative stress has been shown to be indirectly responsible for the depletion of nitric oxide due to its interaction with superoxide radical (O2·-), resulting in the formation of a potent biological oxidant, peroxynitrite (ONOO-). This review comprehensively discusses the mechanisms of heavy metal toxicity and their health effects. Aluminum (Al), cadmium (Cd), arsenic (As), mercury (Hg), lead (Pb), and chromium (Cr) and their roles in the development of gastrointestinal, pulmonary, kidney, reproductive, neurodegenerative (Alzheimer's and Parkinson's diseases), cardiovascular, and cancer (e.g. renal, lung, skin, stomach) diseases are discussed. A short account is devoted to the detoxification of heavy metals by chelation via the use of ethylenediaminetetraacetic acid (EDTA), dimercaprol (BAL), 2,3-dimercaptosuccinic acid (DMSA), 2,3-dimercapto-1-propane sulfonic acid (DMPS), and penicillamine chelators.

Hazardous or Advantageous: Uncovering the Roles of Heavy Metals and Humic Substances in Shilajit (Phyto-mineral) with Emphasis on Heavy Metals Toxicity and Their Detoxification Mechanisms

Shilajit is a phyto-mineral diffusion and semi-solid matter used as traditional medicine with extraordinary health benefits. This study provides a comprehensive data on Shilajit with emphasis on heavy metal profile, associated toxicities, and metal detoxification mechanisms by humic substances present in Shilajit. Data was searched across papers and traditional books using Google Scholar, PubMed, Science Direct, Medline, SciELO, Web of Science, and Scopus as key scientific databases. Findings showed that Shilajit is distributed in almost 20 regions of the world with uses against 20 health problems as traditional medicine. With various humic substances, almost 11 biological activities were reported in Shilajit. This phyto-mineral diffusion possesses around 65 heavy metals including the toxic heavy metals like Cu, Al, Pb, As, Cd, and Hg. However, humic substances in Shilajit actively detoxify around 12 heavy metals. The recommended levels of heavy metals by WHO and FDA in herbal drugs is 0.20 and 0.30 ppm for Cd, 1 ppm for Hg, 10.00 ppm for As and Pb, 20 ppm for Cu, and 50 ppm for Zn. The levels of reported metals in Shilajit were found to be lower than the permissible limits set by WHO and FDA, except in few studies where exceeded levels were reported. Shilajit consumption without knowing permissible levels of metals is not safe and could pose serious health problems. Although the humic substances and few metals in Shilajit are beneficial in terms of chelating toxic heavy metals, the data on metal detoxification still needs to be clarified.

Enhancing Heavy Metal Detection through Electrochemical Polishing of Carbon Electrodes

Our research addresses the pressing need for environmental sensors capable of large-scale, on-site detection of a wide array of heavy metals with highly accurate sensor metrics. We present a novel approach using electrochemically polished (ECP) carbon screen-printed electrodes (cSPEs) for high-sensitivity detection of cadmium and lead. By applying a range of techniques, including scanning electron microscopy, energy-dispersive spectroscopy, Raman spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry, we investigated the impact of the electrochemical potential scan range, scan rate, and the number of cycles on electrode response and its ability to detect cadmium and lead. Our findings reveal a 41 ± 1.2% increase in voltammogram currents and a 51 ± 1.6% decrease in potential separations (n = 3), indicating a significantly improved active electrode area and kinetics. The impedance model elucidates the microstructural and electrochemical property changes in the ECP-treated electrodes, showing an 88 ± 2% (n = 3) decrease in the charge transfer resistance, leading to enhanced electrode electrical conductivity. A bismuth-reduced graphene oxide nanocomposite-modified, ECP-treated electrode demonstrated a higher cadmium and lead sensitivity of up to 5 ± 0.1 μAppb-1cm-2 and 2.7 ± 0.1 μAppb-1cm-2 (n = 3), respectively, resulting in sub-ppb limits of detection in spiked deionized water samples. Our study underscores the potential of optimally ECP-activated electrodes as a foundation for designing ultrasensitive heavy metal sensors for a wide range of real-world heavy metal-contaminated waters.

Pb induces the release of CXCL10 and CCL2 chemokines via mtROS/NF-κB activation in BV-2 cells

Lead (Pb), a well-known environmental pollutant, could cause damage of microglia, the resident macrophages vitally regulating inflammation in brain. Previous studies have found that Pb exposure induces typical pro-inflammatory factors release, such as tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), but what effects of Pb treatment below the dose causing these factors release are unknown. Thus, cytokines assay was performed to identify the factors released from Pb-treated BV-2 cells at 2.5 μM, causing no effects on TNF-α, IL-1β, and IL-6 release and cell death. Cytokines assay identified low doses of Pb exposure mainly induce an increase in specific chemokines, including CXCL10, CCL2, and CXCL2, which were confirmed by ELISA. Subsequent assessment found Pb could damage mitochondria function and generate mitochondrial reactive oxygen species (mtROS), and Mito TEMPO, a specific inhibitor of mtROS, suppressed Pb-caused upregulation of CXCL10 and CCL2, but not CXCL2. Finally, we determined that mtROS mediated Pb-induced activation of NF-κB pathway, as Mito TEMPO treatment inhibited P-p65/p65 escalation during Pb treatment. Inhibition of NF-κB pathway by Bay11-7821 suppressed the release of CXCL10 and CCL2. Collectively, low dose of Pb induces the release of CXCL10 and CCL2 chemokines, but not TNF-α and IL-1β, via mtROS/NF-κB activation in BV-2 cells.

Early-Life Lead Exposure: Risks and Neurotoxic Consequences

BACKGROUND

Lead (Pb) does not have any biological function in a human, and it is likely no safe level of Pb in the human body. The Pb exposure impacts are a global concern for their potential neurotoxic consequences. Despite decreasing both the environmental Pb levels and the average blood Pb levels in the survey populations, the lifetime redistribution from the tissues-stored Pb still poses neurotoxic risks from the low-level exposure in later life. The growing fetus and children hold their innate high-susceptible to these Pb-induced neurodevelopmental and neurobehavioral effects.

OBJECTIVE

This article aims to evaluate cumulative studies and insights on the topic of Pb neurotoxicology while assessing the emerging trends in the field.

RESULTS

The Pb-induced neurochemical and neuro-immunological mechanisms are likely responsible for the high-level Pb exposure with the neurodevelopmental and neurobehavioral impacts at the initial stages. Early-life Pb exposure can still produce neurodegenerative consequences in later life due to the altered epigenetic imprints and the ongoing endogenous Pb exposure. Several mechanisms contribute to the Pb-induced neurotoxic impacts, including the direct neurochemical effects, the induction of oxidative stress and inflammation through immunologic activations, and epigenetic alterations. Furthermore, the individual nutritional status, such as macro-, micro-, or antioxidant nutrients, can significantly influence the neurotoxic impacts even at low-level exposure to Pb.

CONCLUSION

The prevention of early-life Pb exposure is, therefore, the critical determinant for alleviating various Pb-induced neurotoxic impacts across the different age groups.

Maternal suboptimal selenium intake and low-level lead exposure affect offspring's microglial immune profile and its reactivity to a subsequent inflammatory hit

Micronutrients such as selenium (Se) are essentials since prenatal life to support brain and cognitive development. Se deficiency, which affects up to 1 billion people worldwide, can interact with common adverse environmental challenges including (Pb), exacerbating their toxic effects. Exploiting our recently validated rat model of maternal Se restriction and developmental low Pb exposure, our aims were to investigate: (i) the early consequences of suboptimal Se intake and low-Pb exposure on neuroinflammation in neonates' whole brains; (ii) the potential priming effect of suboptimal Se and low-Pb exposure on offspring's glial reactivity to a further inflammatory hit. To these aims female rats were fed with suboptimal (0.04 mg/kg; Subopt) and optimal (0.15 mg/kg; Opt) Se dietary levels throughout pregnancy and lactation and exposed or not to environmentally relevant Pb dose in drinking water (12.5 µg/mL) since 4 weeks pre-mating. We found an overall higher basal expression of inflammatory markers in neonatal brains, as well as in purified microglia and organotypic hippocampal slice cultures, from the Subopt Se offspring. Subopt/Pb cultures were highly activated than Subopt cultures and showed a higher susceptibility to the inflammatory challenge lipopolysaccharide than cultures from the Opt groups. We demonstrate that even a mild Se deficiency and low-Pb exposure during brain development can influence the neuroinflammatory tone of microglia, exacerbate the toxic effects of Pb and prime microglial reactivity to subsequent inflammatory stimuli. These neuroinflammatory changes may be responsible, at least in part, for adverse neurodevelopmental outcomes.

Association between serum iron, blood lead, cadmium, mercury, selenium, manganese and low cognitive performance in old adults from National Health and Nutrition Examination Survey (NHANES): a cross-sectional study

Cognitive decline is a public health problem for the world's ageing population. This study was to evaluate the relationships between serum Fe, blood Pb, Cd, Hg, Se and Mn and cognitive decline in elderly Americans. Data of this cross-sectional study were extracted from the National Health and Nutritional Examination Survey (NHANES 2011-2014). Cognitive performance was measured by the Consortium to Establish a Registry for Alzheimer's Disease (CERAD), Animal Fluency and Digit Symbol Substitution Test (DSST) tests. Weighted univariable and multivariate logistic regression analyses were used to assess the associations between six trace elements and low cognitive performance. Subgroup analyses based on diabetes and hypertension history were further assessed the associations. A total of 2002 adults over 60 years old were included. After adjusting covariates, elevated serum Fe levels were associated with the decreased risk of low cognitive performance, especially in the elderly without diabetes history and with hypertension history. High blood Cd levels were associated with the high odds of low cognitive performance in old adults with diabetes and hypertension history. Elevated blood Mn levels were connected with low cognitive performance in old hypertensive people. High blood Pb levels were related to the high odds of low cognitive performance, especially in the elderly without diabetes and hypertension history. High blood Se levels were linked to the decreased risk of low cognitive performance in all the elderly. Appropriate Fe, Se supplementation and Fe-, Se-rich foods intake, while reducing exposure to Pb, Cd and Mn may be beneficial for cognitive function in the elderly.

The Exposure to Lead (Pb) Exacerbates Immunological Abnormalities in BTBR T+ Itpr3tf/J Mice through the Regulation of Signaling Pathways Relevant to T Cells

Autism spectrum disorder (ASD) is a common neurodevelopmental illness characterized by abnormal social interactions, communication difficulties, and repetitive and limited behaviors or interests. The BTBR T+ Itpr3tf/J (BTBR) mice have been used extensively to research the ASD-like phenotype. Lead (Pb) is a hazardous chemical linked to organ damage in the human body. It is regarded as one of the most common metal exposure sources and has been connected to the development of neurological abnormalities. We used flow cytometry to investigate the molecular mechanism behind the effect of Pb exposure on subsets of CD4+ T cells in the spleen expressing IFN-γ, T-bet, STAT1, STAT4, IL-9, IRF4, IL-22, AhR, IL-10, and Foxp3. Furthermore, using RT-PCR, we studied the effect of Pb on the expression of numerous genes in brain tissue, including IFN-γ, T-bet, STAT1, STAT4, IL-9, IRF4, IL-22, AhR, IL-10, and Foxp3. Pb exposure increased the population of CD4+IFN-γ+, CD4+T-bet+, CD4+STAT1+, CD4+STAT4+, CD4+IL-9+, CD4+IRF4+, CD4+IL-22+, and CD4+AhR+ cells in BTBR mice. In contrast, CD4+IL-10+ and CD4+Foxp3+ cells were downregulated in the spleen cells of Pb-exposed BTBR mice compared to those treated with vehicle. Furthermore, Pb exposure led to a significant increase in IFN-γ, T-bet, STAT1, STAT4, IL-9, IRF4, IL-22, and AhR mRNA expression in BTBR mice. In contrast, IL-10 and Foxp3 mRNA expression was significantly lower in those treated with the vehicle. Our data suggest that Pb exposure exacerbates immunological dysfunctions associated with ASD. These data imply that Pb exposure may increase the risk of ASD.

Possible role of selenium in ameliorating lead-induced neurotoxicity in the cerebrum of adult male rats: an experimental study

Chronic lead (Pb) poisoning is one of the greatest public health risks. The nervous system is the primary and most vulnerable target of Pb poisoning. Selenium (Se) has been shown to be a potential protection against heavy metal toxicity through anti-inflammatory and antioxidant properties. Therefore, the present study aimed to elucidate the possible protective role of Se in ameliorating the effects of Pb on rat cerebral structure by examining oxidative stress and markers of apoptosis. The rats were divided into 6 groups: control group, Se group, low Pb group, high Pb group, low Pb + Se group, high Pb + Se group. After the 4-week experiment period, cerebral samples were examined using biochemical and histological techniques. Pb ingestion especially when administered in high doses resulted in cerebral injury manifested by a significant increase in glial fibrillary acidic protein, malondialdehyde (MDA) marker of brain oxidation and DNA fragmentation. Moreover, Pb produced alteration of the normal cerebral structure and cellular degeneration with a significant reduction in the total number of neurons and thickness of the frontal cortex with separation of meninges from the cerebral surface. There was also a decrease in total antioxidant capacity. All these changes are greatly improved by adding Se especially in the low Pb + Se group. The cerebral structure showed a relatively normal histological appearance with normally attached pia and an improvement in neuronal structure. There was also a decrease in MDA and DNA fragmentation and an increase TAC. Selenium is suggested to reduce Pb-induced neurotoxicity due to its modulation of oxidative stress and apoptosis.

The Effect of Cerebrolysin in an Animal Model of Forebrain Ischemic-Reperfusion Injury: New Insights into the Activation of the Keap1/Nrf2/Antioxidant Signaling Pathway

Forebrain ischemia-reperfusion (IR) injury causes neurological impairments due to decreased cerebral autoregulation, hypoperfusion, and edema in the hours to days following the restoration of spontaneous circulation. This study aimed to examine the protective and/or therapeutic effects of cerebrolysin (CBL) in managing forebrain IR injury and any probable underlying mechanisms. To study the contribution of reperfusion to forebrain injury, we developed a transient dual carotid artery ligation (tDCAL/IR) mouse model. Five equal groups of six BLC57 mice were created: Group 1: control group (no surgery was performed); Group 2: sham surgery (surgery was performed without IR); Group 3: tDCAL/IR (surgery with IR via permanently ligating the left CA and temporarily closing the right CA for 30 min, followed by reperfusion for 72 h); Group 4: CBL + tDCAL/IR (CBL was given intravenously at a 60 mg/kg BW dose 30 min before IR); and Group 5: tDCAL/IR + CBL (CBL was administered i.v. at 60 mg/kg BW three hours after IR). At 72 h following IR, the mice were euthanized. CBL administration 3 h after IR improved neurological functional recovery, enhanced anti-inflammatory and antioxidant activities, alleviated apoptotic neuronal death, and inhibited reactive microglial and astrocyte activation, resulting in neuroprotection after IR injury in the tDCAL/IR + CBL mice group as compared to the other groups. Furthermore, CBL reduced the TLRs/NF-kB/cytokines while activating the Keap1/Nrf2/antioxidant signaling pathway. These results indicate that CBL may improve neurologic function in mice following IR.

Combined exposure to lead and high-fat diet induced neuronal deficits in rats: Anti-neuroinflammatory role of SIRT1

INTRODUCTION

Lead (Pb) exposure and high-fat diet (HFD) trigger neurotoxicity, which may involve neuroinflammation. However, the mechanism by which combined Pb and HFD exposure induces nucleotide oligomerization domain-like receptor family pyrin domain 3 (NLRP3) inflammasome activation has not been fully elucidated.

MATERIAL AND METHODS

The Sprague-Dawley (SD) rat model of exposure to Pb and HFD was established to reveal the influence of co-exposure on cognition and identify signaling clues that mediate neuroinflammation and synaptic dysregulation. PC12 cells was treated with Pb and PA in vitro. Silent information regulator 1 (SIRT1) agonist (SRT 1720) was employed as intervention agent.

RESULTS

Our results showed that Pb and HFD exposure induced cognitive impairment and lead to neurological damage in rats. Meanwhile, Pb and HFD could stimulate the NLRP3 inflammasome assembly and activate caspase 1, releasing proinflammatory cytokines interleukin-1β (IL-1β) and interleukin-18 (IL-18), further promoting neuronal cell activation and amplifying neuroinflammatory responses. Additionally, our findings suggest that SIRT1 plays a role in Pb and HFD induced neuroinflammation. However, the use of SRT 1720 agonists showed some potential in alleviating these impairments.

CONCLUSION

Pb exposure and HFD intake could induce neuronal damage through activation of the NLRP3 inflammasome pathway and synaptic dysregulation, while the NLRP3 inflammasome pathway may be rescued via activating SIRT1.

Microglia and Astroglia-The Potential Role in Neuroinflammation Induced by Pre- and Neonatal Exposure to Lead (Pb)

Neuroinflammation is one of the postulated mechanisms for Pb neurotoxicity. However, the exact molecular mechanisms responsible for its pro-inflammatory effect are not fully elucidated. In this study, we examined the role of glial cells in neuroinflammation induced by Pb exposure. We investigated how microglia, a type of glial cell, responded to the changes caused by perinatal exposure to Pb by measuring the expression of Iba1 at the mRNA and protein levels. To assess the state of microglia, we analyzed the mRNA levels of specific markers associated with the cytotoxic M1 phenotype (Il1b, Il6, and Tnfa) and the cytoprotective M2 phenotype (Arg1, Chi3l1, Mrc1, Fcgr1a, Sphk1, and Tgfb1). Additionally, we measured the concentration of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α). To assess the reactivity and functionality status of astrocytes, we analyzed the GFAP (mRNA expression and protein concentration) as well as glutamine synthase (GS) protein level and activity. Using an electron microscope, we assessed ultrastructural abnormalities in the examined brain structures (forebrain cortex, cerebellum, and hippocampus). In addition, we measured the mRNA levels of Cxcl1 and Cxcl2, and their receptor, Cxcr2. Our data showed that perinatal exposure to Pb at low doses affected both microglia and astrocyte cells' status (their mobilization, activation, function, and changes in gene expression profile) in a brain-structure-specific manner. The results suggest that both microglia and astrocytes represent a potential target for Pb neurotoxicity, thus being key mediators of neuroinflammation and further neuropathology evoked by Pb poisoning during perinatal brain development.

Curcumin-loaded cockle shell-derived calcium carbonate nanoparticles ameliorates lead-induced neurotoxicity in rats via attenuation of oxidative stress

A substantial global health burden is associated with neurotoxicity caused by lead (Pb) exposure and the common mechanism of this toxicity is mainly via oxidative damage. Curcumin has remarkable pharmacological activities but remains clinically constrained due to its poor bioavailability when orally administered. Currently, cockle shell-derived calcium carbonate nanoparticle (CSCaCO3NP) is gaining more acceptance in nanomedicine as a nanocarrier to various therapeutics. This study aimed at investigating the ameliorative effect of curcumin-loaded CSCaCO3NP (Cur-CSCaCO3NP) on lead-induced neurotoxicity in rats. A total of 36 male Sprague-Dawley rats were randomly assigned into five groups. Each group consists of 6 rats apart from the control group which consists of 12 rats. During the 4 weeks induction phase, all rats received a flat dose of 50 mg/kg of lead while the control group received normal saline. The treatment phase lasted for 4 weeks, and all rats received various doses of treatments as follows: group C (Cur 100) received 100 mg/kg of curcumin, group D (Cur-CSCaCO3NP 50) received 50 mg/kg of Cur-CSCaCO3NP, and group E (Cur-CSCaCO3NP 100) received 100 mg/kg of Cur-CSCaCO3NP. The motor function test was carried out using the horizontal bar method. The cerebral and cerebellar oxidative biomarker levels were estimated using ELISA and enzyme assay kits. Lead-administered rats revealed a significant decrease in motor scores and SOD activities with a resultant increase in MDA levels. Furthermore, marked cellular death of the cerebral and cerebellar cortex was observed. Conversely, treatment with Cur-CSCaCO3NP demonstrated enhanced ameliorative effects when compared with free curcumin treatment by significantly reversing the aforementioned alterations caused by lead. Thus, CSCaCO3NP enhanced the efficacy of curcumin by ameliorating the lead-induced neurotoxicity via enhanced attenuation of oxidative stress.

Intermittent Lead Exposure Induces Behavioral and Cardiovascular Alterations Associated with Neuroinflammation

The nervous system is the primary target for lead exposure and the developing brain appears to be especially susceptible, namely the hippocampus. The mechanisms of lead neurotoxicity remain unclear, but microgliosis and astrogliosis are potential candidates, leading to an inflammatory cascade and interrupting the pathways involved in hippocampal functions. Moreover, these molecular changes can be impactful as they may contribute to the pathophysiology of behavioral deficits and cardiovascular complications observed in chronic lead exposure. Nevertheless, the health effects and the underlying influence mechanism of intermittent lead exposure in the nervous and cardiovascular systems are still vague. Thus, we used a rat model of intermittent lead exposure to determine the systemic effects of lead and on microglial and astroglial activation in the hippocampal dentate gyrus throughout time. In this study, the intermittent group was exposed to lead from the fetal period until 12 weeks of age, no exposure (tap water) until 20 weeks, and a second exposure from 20 to 28 weeks of age. A control group (without lead exposure) matched in age and sex was used. At 12, 20 and 28 weeks of age, both groups were submitted to a physiological and behavioral evaluation. Behavioral tests were performed for the assessment of anxiety-like behavior and locomotor activity (open-field test), and memory (novel object recognition test). In the physiological evaluation, in an acute experiment, blood pressure, electrocardiogram, and heart and respiratory rates were recorded, and autonomic reflexes were evaluated. The expression of GFAP, Iba-1, NeuN and Synaptophysin in the hippocampal dentate gyrus was assessed. Intermittent lead exposure induced microgliosis and astrogliosis in the hippocampus of rats and changes in behavioral and cardiovascular function. We identified increases in GFAP and Iba1 markers together with presynaptic dysfunction in the hippocampus, concomitant with behavioral changes. This type of exposure produced significant long-term memory dysfunction. Regarding physiological changes, hypertension, tachypnea, baroreceptor reflex impairment and increased chemoreceptor reflex sensitivity were observed. In conclusion, the present study demonstrated the potential of lead intermittent exposure inducing reactive astrogliosis and microgliosis, along with a presynaptic loss that was accompanied by alterations of homeostatic mechanisms. This suggests that chronic neuroinflammation promoted by intermittent lead exposure since fetal period may increase the susceptibility to adverse events in individuals with pre-existing cardiovascular disease and/or in the elderly.

NLRP3 activation in microglia contributes to learning and memory impairment induced by chronic lead exposure in mice

Lead (Pb)-induced microglial activation and neuroinflammation has been considered as one of the main pathological events of Pb neurotoxicity. The NLRP3 inflammasome signaling pathway is a major contributor to the neuroinflammatory process in the central nervous system. However, the relationship between chronic Pb exposure and neurogenic NLRP3 inflammasome is unclear. Therefore, the aim of this study was to characterize the role of NLRP3 inflammasome activation during the chronic Pb exposure using in vitro and in vivo models. Our results showed that chronic Pb exposure induce learning and memory impairment in mice, mainly related to the activation of microglia and NLRP3 inflammasome. This phenomenon was reversed in mice by treating with the NLRP3 inhibitor MCC950 and using NLRP3-/- mice. In addition, Pb caused the activation of NLRP3 inflammasome, the production of mitochondrial ROS (mtROS), and mitochondrial Ca2+ overload in BV2 cells. Amelioration of mtROS abolished Pb-induced NLRP3 inflammasome activation. Moreover, after regulation of Ca2+ redistribution, mtROS and NLRP3 inflammasome activation was restored. In conclusion, NLRP3 inflammasome activation in microglia plays a vital role in Pb neurotoxicity, by a novel mechanism of enhancing mtROS production and Ca2+ redistribution.

Microglial Activation in Metal Neurotoxicity: Impact in Neurodegenerative Diseases

Neurodegenerative processes encompass a large variety of diseases with different pathological patterns and clinical features, such as Alzheimer's and Parkinson's diseases. Exposure to metals has been hypothesized to increase oxidative stress in brain cells leading to cell death and neurodegeneration. Neurotoxicity of metals has been demonstrated by several in vitro and in vivo experimental studies, and most probably, each metal has its specific pathway to trigger cell death. As a result, exposure to essential metals, such as manganese, iron, copper, zinc, and cobalt, and nonessential metals, including lead, aluminum, and cadmium, perturbs metal homeostasis at the cellular and organism levels leading to neurodegeneration. In this contribution, a comprehensive review of the molecular mechanisms by which metals affect microglia physiology and signaling properties is presented. Furthermore, studies that validate the disruption of microglia activation pathways as an essential mechanism of metal toxicity that can contribute to neurodegenerative disease are also presented and discussed.

Epigenome-wide DNA methylation in leukocytes and toenail metals: The normative aging study

BACKGROUND

Environmental metal exposures have been associated with multiple deleterious health endpoints. DNA methylation (DNAm) may provide insight into the mechanisms underlying these relationships. Toenail metals are non-invasive biomarkers, reflecting a medium-term time exposure window.

OBJECTIVES

This study examined variation in leukocyte DNAm and toenail arsenic (As), cadmium (Cd), lead (Pb), manganese (Mn), and mercury (Hg) among elderly men in the Normative Aging Study, a longitudinal cohort.

METHODS

We repeatedly collected samples of blood and toenail clippings. We measured DNAm in leukocytes with the Illumina HumanMethylation450 K BeadChip. We first performed median regression to evaluate the effects of each individual toenail metal on DNAm at three levels: individual cytosine-phosphate-guanine (CpG) sites, regions, and pathways. Then, we applied a Bayesian kernel machine regression (BKMR) to assess the joint and individual effects of metal mixtures on DNAm. Significant CpGs were identified using a multiple testing correction based on the independent degrees of freedom approach for correlated outcomes. The approach considers the effective degrees of freedom in the DNAm data using the principal components that explain >95% variation of the data.

RESULTS

We included 564 subjects (754 visits) between 1999 and 2013. The numbers of significantly differentially methylated CpG sites, regions, and pathways varied by metals. For example, we found six significant pathways for As, three for Cd, and one for Mn. The As-associated pathways were associated with cancer (e.g., skin cancer) and cardiovascular disease, whereas the Cd-associated pathways were related to lung cancer. Metal mixtures were also associated with 47 significant CpG sites, as well as pathways, mainly related to cancer and cardiovascular disease.

CONCLUSIONS

This study provides an approach to understanding the potential epigenetic mechanisms underlying observed relations between toenail metals and adverse health endpoints.

Dietary fiber ameliorates lead-induced gut microbiota disturbance and alleviates neuroinflammation

Dietary fiber (DF) is a carbohydrate from the edible part of plants and has the functions of promoting gastrointestinal motility, regulating gut microbiota (GM) and improving health. Lead is a non-essential toxic heavy metal that can accumulate in the environment over time and enter the body through the respiratory tract, skin and gastrointestinal tract. Lead not only causes disturbances in GM but also leads to loss of homeostasis of immune functions, causes neuronal damage and results in neuroinflammation. The scientific literature has reported that DF had anti-inflammatory activity as a natural product. This review highlights the role of DF and its metabolic products in alleviating lead-induced neuroinflammation by inducing changes in the species and quantity of GM and regulating the immune system, providing a potential dietary protective strategy for lead-induced disease. © 2022 Society of Chemical Industry.

Impact of chronic exposure to legacy environmental contaminants on the corpus callosum microstructure: A diffusion MRI study of Inuit adolescents

Exposure to environmental contaminants is an important public health concern for the Inuit population of northern Québec, who have been exposed to mercury (Hg), polychlorinated biphenyls (PCBs) and lead (Pb). During the last 25 years, the Nunavik Child Development Study (NCDS) birth cohort has reported adverse associations between these exposures and brain function outcomes. In the current study, we aimed to determine whether contaminant exposure is associated with alterations of the corpus callosum (CC), which plays an important role in various cognitive, motor and sensory function processes. Magnetic resonance imaging (MRI) was administered to 89 NCDS participants (mean age ± SD = 18.4 ± 1.2). Diffusion-weighted imaging was assessed to characterize the microstructure of the CC white matter in 7 structurally and functionally distinct regions of interest (ROIs) using a tractography-based segmentation approach. The following metrics were computed: fiber tract density, fractional anisotropy (FA), axial diffusivity (AD) and radial diffusivity (RD). Multiple linear regression models adjusted for sex, age, current alcohol/drug use and fish nutrients (omega-3 fatty acids and selenium) were conducted to assess the association between diffusion-weighted imaging metrics and Hg, PCB 153 and Pb concentrations obtained at birth in the cord blood and postnatally (mean values from blood samples at 11 and 18 years of age). Exposures were not associated with fiber tract density. Nor were significant associations found with cord and postnatal blood Pb concentrations for FA. However, pre- and postnatal Hg and PCB concentrations were significantly associated with higher FA of several regions of the CC, namely anterior midbody, posterior midbody, isthmus, and splenium, with the most pronounced effects observed in the splenium. FA results were mainly associated with lower RD. This study shows that exposure to Hg and PCB 153 alters the posterior microstructure of the CC, providing neuroimaging evidence of how developmental exposure to environmental chemicals can impair brain function and behavior in late adolescence.

Sesamin: Insights into its protective effects against lead-induced learning and memory deficits in rats

BACKGROUND

Lead (Pb) is one of the most hazardous pollutants that induce a wide spectrum of neurological changes such as learning and memory deficits. Sesamin, a phytonutrient of the lignan class, exhibits anti-inflammatory, anti-apoptotic, and neuroprotective properties. The present study was designed to investigate the effects of sesamin against Pb-induced learning and memory deficits, disruption of hippocampal theta and gamma rhythms, inflammatory response, inhibition of blood δ-aminolevulinic acid dehydratase (δ-ALA-D) activity, Pb accumulation, and neuronal loss in rats.

METHODS

Sesamin treatment (30 mg/kg/day; P.O.) was started simultaneously with Pb acetate exposure (500 ppm in standard drinking water) in rats, and they continued for eight consecutive weeks.

RESULTS

The results showed that chronic exposure to Pb disrupted the learning and memory functions in both passive-avoidance and water-maze tests, which was accompanied by increase in spectral theta power and theta/gamma ratio, and a decrease in spectral gamma power in the hippocampus. Additionally, Pb exposure resulted in an enhanced tumor necrosis factor-alpha (TNF-α) content, decreased interleukin-10 (IL-10) production, inhibited blood δ-ALA-D activity, increased Pb accumulation, and neuronal loss of rats. In contrast, sesamin treatment improved all the above-mentioned Pb-induced pathological changes.

CONCLUSION

This data suggests that sesamin could improve Pb-induced learning and memory deficits, possibly through amelioration of hippocampal theta and gamma rhythms, modulation of inflammatory status, restoration of the blood δ-ALA-D activity, reduction of Pb accumulation in the blood and the brain tissues, and prevention of neuronal loss.

Lead (Pb) exposure exacerbates behavioral and immune abnormalities by upregulating Th17 and NF-κB-related signaling in BTBR T+ Itpr3tf/J autistic mouse model

Autism spectrum disorder (ASD) is a highly prevalent neurodevelopmental disorder that are characterized by abnormal social interaction impairments in communication and repetitive and restricted activities or interests. Even though the exact etiology of ASD remains unknown. Lead (Pb) is a toxin known to harm many organs in the body, it is one of the most ubiquitous metal exposures which is associated with neurological deficits. Previous studies have shown that the exposure to Pb may play a role in ASD. BTBR T⁺ Itpr3^tf/J (BTBR) mouse model is commonly used as a preclinical model for ASD. In this study, we investigated the effects of Pb exposure on sociability, self-grooming and marble burying behaviors tests in BTBR mice. We further examined the effects of Pb on IL-17A- RORγT-, STAT3-, NF-κB p65-, iNOS-, TLR-2- and TLR-4-producing CD45⁺ cells in spleen using flow cytometry. We also explored the effects of Pb on IL-17A, RORγT, STAT3, NF-κB p65, and TLR-2 mRNA expression in the brain tissue using RT-PCR analysis. Our results demonstrated that Pb exposure substantially increased repetitive behavior, marble burying and decrease social interactions in BTBR mice. In addition, in spleen cells, Pb exposure exaggerated CD45⁺IL-17A⁺, CD45⁺RORγT⁺, CD45⁺STAT3⁺, CD45⁺NF-κB p65⁺, CD45⁺iNOS⁺, CD45⁺TLR-2⁺ and CD45⁺TLR-4⁺ in BTBR mice. We also found that Pb significantly increased IL-17A, RORγT, STAT3, NF-κB p65, and TLR-2 mRNA in the brain tissue. Therefore, Pb exposure exacerbates behavioral and neuroimmune function in BTBR mice, suggesting a potentially strong role for Pb in ASD.

CCL21 contributes to Th17 cell migration in neuroinflammation in obese mice following lead exposure

Obesity and lead exposure can independently cause neuroinflammation, which is associated with neurodegenerative diseases. Although Th17 cells play critical roles in inflammatory diseases of the central nervous system, few studies have evaluated their role in neuroinflammation in the background of obesity and lead exposure. In this study, the mechanism underlying inflammatory injury was evaluated in a mouse model of high fat diet-induced obesity following lead exposure. Neuroinflammation was aggravated in mice with obesity following lead exposure, and this was accompanied by increases in Th17 cells in the brain and IL-17A and IL-22 secretion. An antibody array using Z310, a choroid plexus epithelium cell line, revealed that CCL21 was the most highly altered chemokine. CCL21 expression was higher in the choroid plexus of obese mice treated with lead than in mice with obesity or lead treatment alone and was higher in Z310 cells treated with lead and palmitic acid. CCL21 knockout reduced chemotaxis. Our findings suggest that lead exposure can aggravate inflammation in brain tissues of obese mice, possibly by the CCL21-mediated regulation of the passage of Th17 cells through the blood-cerebrospinal fluid barrier. Our findings provide new insights into the mechanism underlying the combined effects of lead and obesity.

Therapeutic Effects of Sodium Para-Aminosalicylic Acid on Cognitive Deficits and Activated ERK1/2-p90RSK/NF-κB Inflammatory Pathway in Pb-Exposed Rats

Lead (Pb) is a toxic heavy metal and environmental pollutant that adversely affects the nervous system. However, effective therapeutic drugs for Pb-induced neurotoxicity have yet to be developed. In the present study, we investigated the ameliorative effect of sodium para-aminosalicylic acid (PAS-Na) on Pb-induced neurotoxicity. Male Sprague-Dawley rats were treated with (CH₃COO)₂ Pb•4H₂O (6 mg/kg) for 4 weeks, followed by 3 weeks of PAS-Na (100, 200, and 300 mg/kg). The results showed that subacute Pb exposure significantly decreased rats body-weight gains and increased liver coefficient, and impaired spatial learning and memory. HE staining showed that Pb damaged the structure of the hippocampus. Moreover, Pb activated the ERK1/2-p90^RSK/ NF-κB pathway concomitant with increased inflammatory cytokine IL-1β levels in rat hippocampus. PAS-Na reversed the Pb-induced increase in the liver coefficient as well as the learning and memory deficits. In addition, PAS-Na reduced the phosphorylation of ERK1/2, p90^RSK and NF-κB p65, decreasing IL-1β levels in hippocampus. Our findings indicated that PAS-Na showed efficacy in reversing Pb-induced rats cognitive deficits and triggered an anti-inflammatory response. Thus, PAS-Na may be a promising therapy for treating Pb-induced neurotoxicity.

Association between blood metals mixtures concentrations and cognitive performance, and effect modification by diet in older US adults

BACKGROUND

Chronic exposure to heavy metals has been associated with adverse neurological outcomes in older adults. Inflammatory processes are suspected as an underlying pathway by which metals exert their neurotoxicity. In parallel, a diet rich in antioxidant and anti-inflammatory components may protect against chronic inflammation.

OBJECTIVES

We examined the associations of blood concentrations of lead, cadmium, and manganese as a mixture with cognitive performance in older US adults and potential modification of these associations by diet as measured by the Healthy Eating Index 2015 (HEI-2015) and the Adapted Dietary Inflammatory Index (ADII).

METHODS

We used data on 1,777 adults ≥60 years old from the US National Health and Nutrition Examination Survey (NHANES; 2011-2014). We derived the ADII and the HEI-2015 from two nonconsecutive 24-hour diet recalls. Cognitive performance was measured by the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) Word Learning subtest, the animal fluency test, and the Digit Symbol Substitution Test (DSST). We also constructed a composite z-score reflecting overall cognitive performance. We used quantile g-computation to evaluate the joint associations of a mixture of metals with cognitive performance test scores. We also evaluated effect modification by sex and diet quality indices using Cochran Q tests.

RESULTS

The median (interquartile range) of blood metals were 0.38 μg/L (0.35), 14.70 μg/L (11.70), and 8.74 μg/L (4.06) for cadmium, lead, and manganese, respectively. Increasing blood concentrations of all metals by one quartile was associated with a decrease in overall cognitive performance (-0.04; 95% confidence interval [CI] = -0.09, 0.02), CERAD (-0.04; 95% CI = -0.12, 0.03), animal fluency (-0.02; 95% CI, -0.11, 0.06), and DSST (-0.05; 95% CI = -0.11, 0.02) test scores. These associations were more pronounced in adults with high pro-inflammatory or low-diet quality and null or positive though imprecise associations in participants with a high anti-inflammatory. These associations also varied by sex with inverse associations in men and positive associations in women.

CONCLUSIONS

Our findings suggest that adherence to an antioxidant and anti-inflammatory diet may prevent blood metals adverse cognitive effects among older adults. If confirmed, strategies based on diet could provide a potential complementary and efficient approach to counteract effects of environmental pollutants.

Heavy Metal Contamination of Natural Foods Is a Serious Health Issue: A Review

Heavy metals play an important role in the homeostasis of living cells. However, these elements induce several adverse environmental effects and toxicities, and therefore seriously affect living cells and organisms. In recent years, some heavy metal pollutants have been reported to cause harmful effects on crop quality, and thus affect both food security and human health. For example, chromium, cadmium, copper, lead, and mercury were detected in natural foods. Evidence suggests that these elements are environmental contaminants in natural foods. Consequently, this review highlights the risks of heavy metal contamination of the soil and food crops, and their impact on human health. The data were retrieved from different databases such as Science Direct, PubMed, Google scholar, and the Directory of Open Access Journals. Results show that vegetable and fruit crops grown in polluted soil accumulate higher levels of heavy metals than crops grown in unpolluted soil. Moreover, heavy metals in water, air, and soil can reduce the benefits of eating fruits and vegetables. A healthy diet requires a rational consumption of foods. Physical, chemical, and biological processes have been developed to reduce heavy metal concentration and bioavailability to reduce heavy metal aggregation in the ecosystem. However, mechanisms by which these heavy metals exhibit their action on human health are not well elucidated. In addition, the positive and negative effects of heavy metals are not very well established, suggesting the need for further investigation.

Salivary biomarkers and neuropsychological outcomes: A non-invasive approach to investigate pollutants-associated neurotoxicity and its effects on cognition in vulnerable populations

The occurrence of neurotoxicity caused by xenobiotics such as pesticides (dichlorodiphenyltrichloroethane, organophosphates, pyrethroids, etc.) or metals (mercury, lead, aluminum, arsenic, etc.) is a growing concern around the world, particularly in vulnerable populations with difficulties on both detection and symptoms treatment, due to low economic status, remote access, poor infrastructure, and low educational level, among others features. Despite the numerous molecular markers and questionnaires/clinical evaluations, studying neurotoxicity and its effects on cognition in these populations faces problems with samples collection and processing, and information accuracy. Assessing cognitive changes caused by neurotoxicity, especially those that are subtle in the initial stages, is fundamentally challenging. Finding accurate, non-invasive, and low-cost strategies to detect the first signals of brain injury has the potential to support an accelerated development of the research with these populations. Saliva emerges as an ideal pool of biomarkers (with interleukins and neural damage-related proteins, among others) and potential alternative diagnostic fluid to molecularly investigate neurotoxicity. As a source of numerous neurological biomarkers, saliva has several advantages compared to blood, such as easier storage, requires less manipulation, and the procedure is cheaper, safer and well accepted by patients compared with drawing blood. Regarding cognitive dysfunction, neuropsychological batteries represent, with their friendly interface, a feasible and accurate method to evaluate the eventual cognitive deficits associated with neurotoxicity in people from diverse cultural and educational backgrounds. The association of these two tools, saliva and neuropsychological batteries, to cover the molecular and cognitive aspects of neurotoxicity in vulnerable populations, could potentially increase the prevalence of early intervention and successful treatment.

Toxic Mechanisms of Five Heavy Metals: Mercury, Lead, Chromium, Cadmium, and Arsenic

The industrial activities of the last century have caused massive increases in human exposure to heavy metals. Mercury, lead, chromium, cadmium, and arsenic have been the most common heavy metals that induced human poisonings. Here, we reviewed the mechanistic action of these heavy metals according to the available animal and human studies. Acute or chronic poisonings may occur following exposure through water, air, and food. Bioaccumulation of these heavy metals leads to a diversity of toxic effects on a variety of body tissues and organs. Heavy metals disrupt cellular events including growth, proliferation, differentiation, damage-repairing processes, and apoptosis. Comparison of the mechanisms of action reveals similar pathways for these metals to induce toxicity including ROS generation, weakening of the antioxidant defense, enzyme inactivation, and oxidative stress. On the other hand, some of them have selective binding to specific macromolecules. The interaction of lead with aminolevulinic acid dehydratase and ferrochelatase is within this context. Reactions of other heavy metals with certain proteins were discussed as well. Some toxic metals including chromium, cadmium, and arsenic cause genomic instability. Defects in DNA repair following the induction of oxidative stress and DNA damage by the three metals have been considered as the cause of their carcinogenicity. Even with the current knowledge of hazards of heavy metals, the incidence of poisoning remains considerable and requires preventive and effective treatment. The application of chelation therapy for the management of metal poisoning could be another aspect of heavy metals to be reviewed in the future.

Saikosaponin a attenuates lead-induced kidney injury through activating Nrf2 signaling pathway

Saikosaponin a (SSa), a triterpene saponin extracted from Bupleurumfalcatum L., has been reported to have anti-inflammatory activity. In the present study, we investigated the effects of SSa on lead-induced kidney injury in common carp. Kidney histological changes were detected by H&E staining. The levels of TNF-α, IL-1β, MPO, MDA, GSH, and SOD activity were also measured. Furthermore, the NF-κB and Nrf2 signaling pathways were tested by western blot analysis. The results showed that lead-induced kidney histological change was attenuated by SSa. Lead-induced TNF-α, IL-1β, MPO, and MDA production were also suppressed by SSa. Meanwhile, lead could decrease GSH level and SOD activity and the decreases were inhibited by SSa. Furthermore, we found SSa significantly inhibited lead-induced NF-κB translocation. In addition, the expression of Nrf2 and HO-1 were increased by the treatment of SSa and Keap1 expression was decreased by SSa. In conclusion, this study indicated that SSa inhibited lead-induced kidney injury in carp through suppressing inflammatory and oxidative responses, and the mechanism may be involved in the inhibition of NF-κB and activation of Nrf2 signaling pathway.

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.

Signal transduction associated with lead-induced neurological disorders: A review

Lead is a heavy metal pollutant that is widely present in the environment. It affects every organ system, yet the nervous system appears to be the most sensitive and primary target. Although many countries have made significant strides in controlling Pb pollution, Pb poisoning continuous to be a major public health concern. Exposure to Pb causes neurotoxicity that ranges from neurodevelopmental disorders to severe neurodegenerative lesions, leading to impairments in learning, memory, and cognitive function. Studies on the mechanisms of Pb-induced nervous system injury have convincingly shown that this metal can affect a plethora of cellular pathways affecting on cell survival, altering calcium dyshomeostasis, and inducing apoptosis, inflammation, energy metabolism disorders, oxidative stress, autophagy and glial stress. This review summarizes recent knowledge on multiple signaling pathways associated with Pb-induced neurological disorders in vivo and in vitro.

Role of metallic pollutants in neurodegeneration: effects of aluminum, lead, mercury, and arsenic in mediating brain impairment events and autism spectrum disorder

Autism spectrum disorder (ASD) is a developmental disorder of the brain characterized by shortfall in the social portfolio of an individual and abbreviated interactive and communication aspects rendering stereotypical behavior and pitfalls in a child's memory, thinking, and learning capabilities. The incidence of ASD has accelerated since the past decade, portraying environment as one of the primary assets, comprising of metallic components aiming to curb the neurodevelopmental pathways in an individual. Many regulations like Clean Air Act and critical steps taken by countries all over the globe, like Sweden and the USA, have rendered the necessity to study the effects of environmental metallic components on ASD progression. The review focuses on the primary metallic components present in the environment (aluminum, lead, mercury, and arsenic), responsible for accelerating ASD symptoms by a set of general mechanisms like oxidative stress reduction, glycolysis suppression, microglial activation, and metalloprotein disruption, resulting in apoptotic signaling, neurotoxic effects, and neuroinflammatory responses. The effect of these metals can be retarded by certain protective strategies like chelation, dietary correction, certain agents (curcumin, mangiferin, selenium), and detoxification enhancement, which can necessarily halt the neurodegenerative effects.

Protection of lead-induced cytotoxicity using paramagnetic nickel–insulin quantum clusters

Pb-toxicity is associated with inflammation which leads to delay in wound healing. Pb²⁺ utilizes calcium ion channels to enter the cell. Therefore, to achieve effective healing in a Pb-poisoned system, capturing Pb²⁺ from the circulatory system would be an effective approach without hampering the activity of the calcium ion channel. In this work insulin–nickel fluorescent quantum clusters (INiQCs) have been synthesized and used for the specific detection of Pb²⁺ ions in vitro and in cell-free systems. INiQCs (0.09 μM) can detect Pb²⁺ concentrations as low as 10 pM effectively in a cell-free system using the fluorescence turn-off method. In vitro INiQCs (0.45 μM) can detect Pb²⁺ concentrations as low as 1 μM. INiQCs also promote wound healing which can easily be monitored using the bright fluorescence of INiQCs. INiQCs also help to overcome the wound recovery inhibitory effect of Pb²⁺in vitro using lead nitrate. This work helps to generate effective biocompatible therapeutics for wound recovery in Pb²⁺ poisoned individuals.

Receptor targeted ferromagnetic Insulin–Nickel Quantum fluorescence Clusters (INiQCs) can specifically detect Pb²⁺ and prevents Pb²⁺ poisoning.

Exposure to multiple heavy metals associate with aberrant immune homeostasis and inflammatory activation in preschool children

Heavy metals generate adverse health effects by interfering with immune homeostasis and promoting inflammation in individuals. Our objective was to explore the induction of immune and inflammatory responses by multiple heavy metals in children living in the e-waste contaminated area. A total of 147 preschool children were recruited, including 73 children from Guiyu, a typical e-waste recycling area, and 74 from a reference group. Blood levels of heavy metals, including lead (Pb), cadmium (Cd), mercury (Hg) and arsenic (As), were detected using an inductively coupled plasma mass spectrometry (ICP-MS). Immune cell counts (neutrophils, monocytes, lymphocytes) were determined by an automatic blood cell analyzer, pro-inflammatory cytokines (IL-1β, IL-6, IL-8, TNF-α) and anti-inflammatory cytokines (IL-1RA, IL-4, IL-10, IL-13) were analyzed by a Luminex 200 multiplex immunoassay instrument. Multiple correspondences and linear regression analyses were applied to investigate the relationships between heavy metal exposure and relevant parameters. Results shows Guiyu children had higher levels of Pb, Cd, Hg, As, IL-1β and IL-6, but decreased lymphocyte, IL-1RA and IL-13. Neutrophil count was positively correlated with Pb, Cd and Hg exposure. Anti-inflammatory IL-1RA concentration was negatively related with Pb, Cd, Hg and As, while pro-inflammatory IL-1β and IL-6 were positively correlated with Pb. Guiyu children may have dysregulated immune response and high inflammation risk. Exposure to Pb, Cd, Hg and As could be harmful for immune response and inflammatory regulation. Our finding of decreased IL-RA production in children exposed to Pb, Cd, Hg, and As is novel and could be an opportunity for future research.

Pre- and Neonatal Exposure to Lead (Pb) Induces Neuroinflammation in the Forebrain Cortex, Hippocampus and Cerebellum of Rat Pups

Lead (Pb) is a heavy metal with a proven neurotoxic effect. Exposure is particularly dangerous to the developing brain in the pre- and neonatal periods. One postulated mechanism of its neurotoxicity is induction of inflammation. This study analyzed the effect of exposure of rat pups to Pb during periods of brain development on the concentrations of selected cytokines and prostanoids in the forebrain cortex, hippocampus and cerebellum. Methods: Administration of 0.1% lead acetate (PbAc) in drinking water ad libitum, from the first day of gestation to postnatal day 21, resulted in blood Pb in rat pups reaching levels below the threshold considered safe for humans by the Centers for Disease Control and Prevention (10 µg/dL). Enzyme-linked immunosorbent assay (ELISA) method was used to determine the levels of interleukins IL-1β, IL-6, transforming growth factor-β (TGF-β), prostaglandin E2 (PGE2) and thromboxane B2 (TXB2). Western blot and quantitative real-time PCR were used to determine the expression levels of cyclooxygenases COX-1 and COX-2. Finally, Western blot was used to determine the level of nuclear factor kappa B (NF-κB). Results: In all studied brain structures (forebrain cortex, hippocampus and cerebellum), the administration of Pb caused a significant increase in all studied cytokines and prostanoids (IL-1β, IL-6, TGF-β, PGE2 and TXB2). The protein and mRNA expression of COX-1 and COX-2 increased in all studied brain structures, as did NF-κB expression. Conclusions: Chronic pre- and neonatal exposure to Pb induces neuroinflammation in the forebrain cortex, hippocampus and cerebellum of rat pups.

Persistent Effects on Cardiorespiratory and Nervous Systems Induced by Long-Term Lead Exposure: Results from a Longitudinal Study

Long-term lead (Pb) exposure alters the normal development of the nervous system and physiology. It affects multiple organ systems, causing hypertension, cardiorespiratory dysfunction, being a well-known neurotoxin, inducing changes in neurogenesis, neurodegeneration, and glial cells. However, studies of the developmental effects of lead and its outcomes throughout life are lacking. Determine morphofunctional, behavioral, and cognitive developmental effects of long-term lead exposure at three different ages. Wistar rats were exposed to a Pb-acetate solution from fetal period until adulthood and compared to a non-exposed control group. General behavior and cognitive skills were evaluated by behavioral tests and physiological data and cardiorespiratory reflexes measured. Neurodegeneration, neuroinflammation, and synaptic activity were assessed by immunohistochemistry. Lead exposure caused long-lasting anxiety-like behavior and strong long-term memory impairment without changes in locomotor and exploratory activity. Hypertension was observed at all time points, concomitant with baroreflex impairment and increased chemoreflex sensitivity. Persistent neuroinflammation, transient synaptic overexcitation without neurodegeneration was observed. Long-term Pb exposure, since fetal period, causes long-lasting anxiety-like behavior, concomitant with hypertension, without general motor skills impairment. Synaptic overexcitation, reactive astrogliosis, and microgliosis could underlie behavioral and long-term memory changes, which might have been caused during developmental phases and consolidated during adulthood. Also, alterations observed in the cardiorespiratory reflexes can explain persistent hypertension. This longitudinal study identifies and characterizes lead toxicity nature and magnitude, important to devise and test potential interventions to attenuate the long-term harmful effects of lead on the nervous and cardiovascular systems.

The Neuroprotective Role of Coenzyme Q10 Against Lead Acetate-Induced Neurotoxicity Is Mediated by Antioxidant, Anti-Inflammatory and Anti-Apoptotic Activities

Heavy metal exposure, in lead (Pb) particularly, is associated with severe neuronal impairment though oxidative stress mediated by reactive oxygen species, and antioxidants may be used to abolish these adverse effects. This study investigated the potential neuroprotective role of coenzyme Q10 (CoQ₁₀) against lead acetate (PbAc)-induced neurotoxicity. Twenty-eight male Wistar albino rats were divided into four equal groups (n = 7) and treated as follows: the control group was injected with physiological saline (0.9% NaCl); the CoQ₁₀ group was injected with CoQ₁₀ (10 mg/kg); PbAc group was injected with PbAc (20 mg/kg); PbAc + CoQ₁₀ group was injected first with PbAc, and after 1 h with CoQ₁₀. All groups were injected intraperitoneally for seven days. PbAc significantly increased cortical lipid peroxidation, nitrate/nitrite levels, and inducible nitric oxide synthase expression, and decreased glutathione content, superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase activity and mRNA expression, as well as nuclear factor erythroid 2–related factor 2 (Nrf2) and homoxygenase-1 (HO-1) expression. PbAc also promoted the secretion of interleukin-1ß and tumor necrosis factor-α, inhibited interleukin-10 production, triggered the activation of pro-apoptotic proteins, and suppressed anti-apoptotic proteins. Additionally, PbAc increased the cortical levels of serotonin, dopamine, norepinephrine, GABA, and glutamate, and decreased the level of ATP. However, treatment with CoQ₁₀ rescued cortical neurons from PbAc-induced neurotoxicity by restoring the balance between oxidants and antioxidants, activating the Nrf2/HO-1 pathway, suppressing inflammation, inhibiting the apoptotic cascade, and modulating cortical neurotransmission and energy metabolism. Altogether, our findings indicate that CoQ₁₀ has beneficial effects against PbAc-induced neuronal damage through its antioxidant, anti-inflammatory, anti-apoptotic, and neuromodulatory activities.

Protective Effects of Phyllanthus amarus Against Lipopolysaccharide-Induced Neuroinflammation and Cognitive Impairment in Rats

Background: Phyllanthus amarus (PA) is widely studied for its hepatoprotective properties but has recently received increasing attention due to its diverse anti-inflammatory effects. However, the effects of PA in modulating immune responses in the central nervous system leading to protection against functional changes remain unexplored. Therefore, we sought to examine the protective effects of 80% v/v ethanol extract of PA on lipopolysaccharide (LPS)-induced non-spatial memory impairment and neuroinflammation. Methods: Selected major phytoconstituents of PA extract were identified and quantified using high-performance liquid chromatography. Subchronic neurotoxicity was performed in male Wistar rats given daily oral administration of 100, 200, and 400 mg/kg of the PA extract. Their neurobehavioral activities (functional observation battery and locomotor activity) were scored, and the extracted brains were examined for neuropathological changes. Rats were treated orally with vehicle (5% Tween 20), PA extract (100, 200, and 400 mg/kg), or ibuprofen (IBF; 40 mg/kg) for 14 and 28 days before being subjected to novel object discrimination test. All groups were challenged with LPS (1 mg/kg) given intraperitoneally a day prior to the behavioral tests except for the negative control group. At the end of the behavioral tests, the levels of tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, nitric oxide (NO), inducible nitric oxide synthase (iNOS), CD11b/c integrin expression, and synaptophysin immunoreactivity were determined in the brain tissues. Results: Gallic acid, ellagic acid, corilagin, geraniin, niranthin, phyllanthin, hypophyllanthin, phyltetralin, and isonirtetralin were identified in the PA extract. Subchronic administration of PA extract (100, 200, and 400 mg/kg) showed no abnormalities in neurobehavior and brain histology. PA extract administered at 200 and 400 mg/kg for 14 and 28 days effectively protected the rodents from LPS-induced memory impairment. Similar doses significantly (p < 0.05) decreased the release of proteins like TNF-α, IL-1β, and iNOS in the brain tissue. NO levels, CD11b/c integrin expression, and synaptophysin immunoreactivity were also reduced as compared with those in the LPS-challenged group. Conclusion: Pre-treatment with PA extract for 14 and 28 days was comparable with pre-treatment with IBF in prevention of memory impairment and alleviation of neuroinflammatory responses induced by LPS. Further studies are essential to identify the bioactive phytochemicals and the precise underlying mechanisms.

Lead exposure-induced cognitive impairment through RyR-modulating intracellular calcium signaling in aged rats

Lead is widely distributed in the environment and has become a global public health issue. It is well known that lead exposure induces not only neurodevelopmental toxicity but also neurodegenerative diseases, with learning and memory impairment in the later stage. However, the molecular mechanisms remain elusive. The present study investigated the effects of early life and lifetime lead exposure on cognition and identified the molecular mechanisms involved in aged rats. The results herein demonstrated that the lead concentration in peripheral blood and brain tissues in aged rats was significantly increased in a lead dose-dependent manner. High-dose lead exposure caused cognitive functional impairment in aged rats, concomitant with a longer escape latency and a lower frequency of crossing the platform via Morris water maze testing compared to those in the control and low-dose lead exposure groups. Importantly, neuron functional defects were still observed even in early life lead exposure during the prenatal and weaning periods in aged rats. The neurotoxicity induced by lead exposure was morphologically evidenced by a recessed nuclear membrane, a swollen endoplasmic reticulum, and mitochondria in the neurons. Mechanistically, the exposure of aged rats to lead resulted in increasing free calcium concentration, reactive oxygen species, and apoptosis in the hippocampal neurons. Lead exposure increased RyR3 expression and decreased the levels of p-CaMKIIα/CaMKIIα and p-CREB/CREB in the hippocampus of aged rats. These findings indicated that early life lead exposure-induced cognition disorder was irreversible in aged rats. Lead-induced neurotoxicity might be related to the upregulation of RyR3 expression and high levels of intracellular free calcium with increasing lead concentration in injured neurons.

Memantine Is Protective against Cytotoxicity Caused by Lead and Quinolinic Acid in Cultured Rat Embryonic Hippocampal Cells

Quinolinic acid (QA) is an excitotoxic metabolite of the kynurenine pathway of tryptophan metabolism produced in response to inflammation and oxidative stress. Lead (Pb) causes oxidative stress and thus may produce neurotoxicity by increasing QA production. We investigated the in vitro cytotoxic effects of Pb and QA and the protective effects of the NMDA receptor antagonist memantine. Primary cultures of embryonic hippocampal cells from Wistar rats were treated with different concentrations of Pb, QA, and Pb + QA with and without memantine. Cell viability was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). Apoptosis was analyzed by flow cytometry after Annexin-V/propidium iodide staining. The numbers of immunostained neurons (with β3-Tubulin; Tuj1) and astrocytes (with glial fibrillary acidic protein) were counted. Pb at 20 μg/dL (0.97 μM) and QA at 500 nM concentrations showed significant cytotoxic effects, as evidenced by decreased cell viability, increased apoptosis, and a decrease in the number of both astrocytes and neurons. The combination of Pb and QA showed significant synergistic apoptotic effects at lower doses. Memantine (500 nM) was largely protective against the cytotoxic effects of both Pb and QA, suggesting that Pb's and QA's cytotoxicity involves NMDA receptor activation. Whereas the neuroprotection by memantine from QA-induced toxicity has been previously reported, this is the first study reporting the protection by memantine against Pb-induced cytotoxicity in cultured hippocampal cells. Protection by memantine against these neurotoxicants in vivo needs to be investigated.

The effect of environmental lead exposure on human health and the contribution of inflammatory mechanisms, a review

Lead (Pb) pollution has been considered as a major threat for human health due to induction of inflammatory cascades in various tissues. The aim of present review is to summarize the literature on the effects of lead exposure on respiratory, neurologic, digestive, cardiovascular and urinary disorders and the role of inflammation as an underlying mechanism for these effects. Various databases such as ISI Web of Knowledge, Medline, PubMed, Scopus, Google Scholar and Iran Medex, were searched from 1970 to November 2017 to gather the required articles using appropriate keywords such as lead, respiratory disorders, neurologic disorders, digestive disorders, cardiovascular disorders, urinary disorders and inflammation. Disorders of various body systems and the role of inflammation due to lead exposure has been proven by various studies. These studies indicate that lead exposure may cause respiratory, neurologic, digestive, cardiovascular and urinary diseases. The results were also indicated the increased inflammatory cells and mediators due to lead exposure including cytokines and chemokines due to lead exposure which suggested to be the cause various organ disorders.

AST-120 Reduces Neuroinflammation Induced by Indoxyl Sulfate in Glial Cells

Chronic kidney disease (CKD) involves multiple organ dysfunction, and the neurological complications that are often present in CKD patients support the idea of a crosstalk between the kidneys and the brain. Evidence suggests a possible role for products accumulating in these patients as uremic toxins in various CKD complications, including neurodegeneration. Indoxyl sulfate (IS), derived from tryptophan metabolism, is well-known as a uremic nephron-vascular toxin, and recent evidence suggests it also has a role in the immune response and in neurodegeneration. Inflammation has been associated with neurodegenerative diseases, as well as with CKD. In this study, we demonstrated that sera of CKD patients induced a significant inflammation in astrocyte cells which was proportional to IS sera concentrations, and that the IS adsorbent, AST-120, reduced this inflammatory response. These results indicated that, among the uremic toxins accumulating in serum of CKD patients, IS significantly contributed to astrocyte inflammation. Moreover, being also chronic inflammation associated with CKD, here we reported that IS further increased inflammation and oxidative stress in primary central nervous system (CNS) cells, via Nuclear Factor-κB (NF-κB) and Aryl hydrocarbon Receptor (AhR) activation, and induced neuron death. This study is a step towards elucidating IS as a potential pharmacological target in CKD patients.

Toxic metal(loid)-based pollutants and their possible role in autism spectrum disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by deficits in social interaction, verbal and non-verbal communication, and stereotypic behaviors. Many studies support a significant relationship between many different environmental factors in ASD etiology. These factors include increased daily exposure to various toxic metal-based environmental pollutants, which represent a cause for concern in public health. This article reviews the most relevant toxic metals, commonly found, environmental pollutants, i.e., lead (Pb), mercury (Hg), aluminum (Al), and the metalloid arsenic (As). Additionally, it discusses how pollutants can be a possible pathogenetic cause of ASD through various mechanisms including neuroinflammation in different regions of the brain, fundamentally occurring through elevation of the proinflammatory profile of cytokines and aberrant expression of nuclear factor kappa B (NF-κB). Due to the worldwide increase in toxic environmental pollution, studies on the role of pollutants in neurodevelopmental disorders, including direct effects on the developing brain and the subjects' genetic susceptibility and polymorphism, are of utmost importance to achieve the best therapeutic approach and preventive strategies.

Intraventricular infusion of quinolinic acid impairs spatial learning and memory in young rats: a novel mechanism of lead-induced neurotoxicity

Background

Lead (Pb), a heavy metal, and quinolinic acid (QA), a metabolite of the kynurenine pathway of tryptophan metabolism, are known neurotoxicants. Both Pb and QA impair spatial learning and memory. Pb activates astrocytes and microglia, which in turn induce the synthesis of QA. We hypothesized increased QA production in response to Pb exposure as a novel mechanism of Pb-neurotoxicity.

Methods

Two experimental paradigms were used. In experiment one, Wistar rat pups were exposed to Pb via their dams’ drinking water from postnatal day 1 to 21. Control group was given regular water. In the second protocol, QA (9 mM) or normal saline (as Vehicle Control) was infused into right lateral ventricle of 21-day old rats for 7 days using osmotic pumps. Learning and memory were assessed by Morris water maze test on postnatal day 30 or 45 in both Pb- and QA-exposed rats. QA levels in the Pb exposed rats were measured in blood by ELISA and in the brain by immunohistochemistry on postnatal days 45 and 60. Expression of various molecules involved in learning and memory was analyzed by Western blot. Means of control and experimental groups were compared with two-way repeated measure ANOVA (learning) and t test (all other variables).

Results

Pb exposure increased QA level in the blood (by ~ 58%) and increased (p < 0.05) the number of QA-immunoreactive cells in the cortex, and CA1, CA3 and dentate gyrus regions of the hippocampus, compared to control rats. In separate experiments, QA infusion impaired learning and short-term memory similar to Pb. PSD-95, PP1, and PP2A were decreased (p < 0.05) in the QA-infused rats, whereas tau phosphorylation was increased, compared to vehicle infused rats.

Conclusion

Putting together the results of the two experimental paradigms, we propose that increased QA production in response to Pb exposure is a novel mechanism of Pb-induced neurotoxicity.

Dihydromyricetin Inhibits Lead-Induced Cognitive Impairments and Inflammation by the Adenosine 5'-Monophosphate-Activated Protein Kinase Pathway in Mice

Dihydromyricetin (DHM), a natural flavonoid derived from the medicinal and edible plant Ampelopsis grossedentata, exhibits antioxidant, antiapoptosis, antitumor, and anti-inflammatory bioactivities. This study evaluated the effects of DHM on Pb-induced neurotoxicity and explored the underlying mechanisms. DHM significantly ameliorated behavioral impairments of Pb-induced mice. It decreased the levels of lipid peroxidation and protein carbonyl and increased the activities of superoxide dismutase and catalase in the brains. DHM suppressed Pb-induced apoptosis, as indicated by the decreased levels of Bax and cleaved caspase-3. DHM also decreased inflammatory cytokines in the brains of Pb-treated mice. DHM decreased amyloid-beta (Aβ) level and nuclear factor-κB nuclear translocation. Moreover, DHM induced the adenosine 5'-monophosphate-activated protein kinase (AMPK) phosphorylation and inhibited the activation of p38, Toll-like receptor 4, myeloid differentiation factor 88, and glycogen synthase kinase-3. Collectively, this is the first report indicating that DHM could improve Pb-induced cognitive functional impairment by preventing oxidative stress, apoptosis, and inflammation and that the protective effect was mediated partly through the AMPK pathway.

Effect of developmental lead exposure on neurogenesis and cortical neuronal morphology in Wistar rats

Lead (Pb) is a neurotoxic heavy metal that largely affects the developing nervous system. The present study examined the temporal effect of perinatal Pb exposure on neurogenesis and cortical neuronal morphology. Wistar pregnant rats were exposed to 0.5% lead acetate throughout pregnancy and to postnatal day (PD) 28. Offspring were grouped as gestational day (GD) 18 and 21 and PD 7, 14, 21, and 28 in both control and experimental groups. Brain sections were processed for immunohistological staining with anti-proliferating cell nuclear antigen (PCNA) or glial fibrillary acidic protein (GFAP). Brains from 14, 21, and 28 PDs pups were processed for Golgi–Cox stain. Pb exposure significantly increased PCNA-positive nuclei in the ventricular and subventricular zones of the lateral ventricle at 18 and 21 GDs. Postnatally, the Pb-treated groups showed a significant decrease in PCNA-positivity and neuron density compared to control. This reduction was associated with an increase in damaged or apoptotic cell profiles in the experimental groups. At PD 21, there was a significant increase in GFAP immunoreactivity in Pb-exposed groups compared with control. Furthermore, the total apical and basal dendritic length of pyramidal neurons in layer 2–3 of the Golgi–Cox stained sensorimotor cortex was comparable in both control and Pb-exposed groups. Spine density per 10 µm was significantly increased at PD 14 and 21 on the apical dendrites but not basal dendrites of Pb-treated groups. In conclusion, developmental Pb exposure in rats induces a toxic effect on neurogenesis and on cortical neurons, which may be related to cognitive disabilities observed in children exposed to lead.

Chronic lead exposure enhances the sympathoexcitatory response associated with P2X4 receptor in rat stellate ganglia

Chronic lead exposure causes peripheral sympathetic nerve stimulation, including increased blood pressure and heart rate. Purinergic receptors are involved in the sympathoexcitatory response induced by myocardial ischemia injury. However, whether P2X4 receptor participates in sympathoexcitatory response induced by chronic lead exposure and the possible mechanisms are still unknown. The aim of this study was to explore the change of the sympathoexcitatory response induced by chronic lead exposure via the P2X4 receptor in the stellate ganglion (SG). Rats were given lead acetate through drinking water freely at doses of 0 g/L (control group), 0.5 g/L (low lead group), and 2 g/L (high lead group) for 1 year. Our results demonstrated that lead exposure caused autonomic nervous dysfunction, including blood pressure and heart rate increased and heart rate variability (HRV) decreased. Western blotting results indicated that after lead exposure, the protein expression levels in the SG of P2X4 receptor, IL-1β and Cx43 were up-regulated, the phosphorylation of p38 mitogen-activated protein kinase (MAPK) was activated. Real-time PCR results showed that the mRNA expression of P2X4 receptor in the SG was higher in lead exposure group than that in the control group. Double-labeled immunofluorescence results showed that P2X4 receptor was co-expressed with glutamine synthetase (GS), the marker of satellite glial cells (SGCs). These changes were positively correlated with the dose of lead exposure. The up-regulated expression of P2X4 receptor in SGCs of the SG maybe enhance the sympathoexcitatory response induced by chronic lead exposure.