MOLECULAR MECHANISMS OF LEAD NEUROTOXICITY

Neurotoxic effects of aluminum and manganese: From molecular to clinical effects

The existing data demonstrate that aluminum (Al) and manganese (Mn) possess neurotoxic effects upon overexposure due to induction of neuronal oxidative stress and apoptosis, synaptic dysfunction and neurotransmitter metabolism, neuroinflammation, and cytoskeletal pathology. However, systematic evidence regarding contribution of these metals to development of neurological diseases are lacking. Therefore, in this review we provide a summary of the existing data on contribution of Al and Mn exposure to brain diseases and its symptoms. Causal relations were demonstrated for development of parkinsonism upon exposure to high doses of Mn, whereas Al overload is considered the key contributor to dialysis encephalopathy. Certain studies demonstrate that Al and Mn overexposure is associated with neurodegenerative diseases including Alzheimer's and Parkinson's diseases, as well as neurodevelopmental disorders like autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD). Although laboratory studies demonstrate the potential contribution of Al and Mn to molecular pathogenesis of these diseases, clinical findings supporting the causal role of metals is these pathologies are yet insufficient. Therefore, estimation of the contribution of these metals to neurological disorders is essential for development of more effective early diagnostics and prevention of diseases under exposure to adverse neurological effects of Al and Mn compounds.

Unravelling the developmental toxicity of heavy metals using zebrafish as a model: a narrative review

Developmental toxicity is the disruption of an organism's normal development which may occur in either the parent before conception or in the growing creature itself. Zebrafish (Danio rerio) are being employed as effective vertebrate models to evaluate the safety and toxicity of chemicals because they can breed multiple times in a year so we can observe the toxic effects in the next generation and their development mental stages can be observed and define clearly because their 1 cell stage to prime stage is transparent so we can observe the development of every organ also they have nearly about 80% genetic similarity with humans and shares the similar neuromodulatory structure along with multiple neurotransmitter. The recent research endeavours to examine the harmful outcome of various heavy metals such as cadmium, chromium, nickel, arsenic, lead, mercury, bismuth, iron, manganese, and thallium along with microplastics on zebrafish embryos when subjected to environmentally acceptable levels of every single metal in addition to co-exposure at various points in time. These heavy metals can alter the mRNA expression levels, increase the reactive oxygen species (ROS) generation, decrease antioxidant expression, damage neuronal function, alter neurotransmitter release, alter the expression of several apoptotic proteins, interfere with the different signalling pathways, decrease heat rates, increase malformations like - pericardial oedema, heart oedema, reduce in length tail bending abnormal formation in fins. Thereafter we concluded that due to its involvement in the food chain, it also causes severe effects on human beings.

Ameliorative role of bioactive compounds against lead-induced neurotoxicity

Lead (Pb) is an environmental toxin ubiquitously present in the human environment due to anthropogenic activities and industrialization. Lead can enter the human body through various sources and pathways, such as inhalation, ingestion and dermal contact, leading to detrimental health effects. The majority of lead that enters the body is removed by urine or feces; however, under chronic exposure conditions, lead is not efficient, as lead is absorbed and transferred to numerous organs, such as the brain, liver, kidney, muscles, and heart, and it is ultimately stored in mineralizing tissues such as bones and teeth. The central nervous system is the most affected among all the organs and systems affected, as lead is a known neurotoxin. Lead absorption is elevated in the fasting state than in the fed state. Chelation therapy, which is used to treat lead poisoning, has various adverse effects, making this treatment detrimental because it disrupts the levels of other essential elements and redistributes lead to various tissues. One of the main mechanisms by which lead induces toxicity is through the generation of reactive oxygen species. Hence, bioactive compounds that are the source of antioxidants if consumed along with ongoing lead exposure can ameliorate the toxic effects of lead.

A new quinoline-based fluorescent-colorimetric chemosensor for sensitive and selective "on-off" detection of Pb2+ ions

For the first time, a novel mono Schiff base of a quinoline-based reversible fluorescent-colorimetric receptor (L) has been designed for the detection of Pb2+ ions in a semi-aqueous medium. The receptor L exhibited a very good selective fluorescent-colorimetric quick on-off response when exposed to Pb2+. The colorimetric assay showed a sensitivity of 1.2 × 10-6 M, while the fluorescent assay exhibited a sensitivity of 9.9 × 10-7 M for Pb2+. A 1 : 1 stoichiometric complexation between L and Pb2+ was determined using ESI-MS spectra and Job's plot measurements. Pb2+ was successfully measured using receptor L in both real samples and in an aqueous solution of the protein bovine serum albumin, as well as in the construction of an INHIBIT-type molecular logic gate.

From contamination to detection: The growing threat of heavy metals

Heavy metals like lead, mercury, cadmium, and arsenic are environmental pollutants that accumulate in ecosystems and pose significant health risks to humans and wildlife, primarily through food chain contamination where plants absorb heavy metals, affecting their growth and threatening consumer health. Cognitive and cardiovascular functions are particularly affected by exposure to heavy metals even at low concentrations through the induction of oxidative stress. Various analytical techniques are used in measuring heavy metals in different environmental and biological samples. The atomic absorption spectroscopy (AAS) offers low cost, simplicity, and portability but lacks sensitivity for certain metals. Although more sensitive, the high cost of inductively coupled plasma mass spectrometry (ICP-MS) may limit laboratory accessibility. The inductively coupled plasma with atomic emission spectrometry (ICP-AES) is known for its broad dynamic linear range and ability to identify minute variations in concentration. Atomic fluorescence spectrometry (AFS) is considered a powerful tool for quantifying heavy metals due to its high sensitivity, low detection limits, and wide linear range. The current article reviews heavy metal pollution's impact on health and spectrometric techniques for the detection of these contaminants. This may help efforts of international, and regional policies towards preventing this health hazard problem.

Mitigating lead acetate-induced histopathologic and physiologic disorders in rats receiving vitamin C and glutathione supplement

The present work examines the extreme impact of lead acetate and the preventive function of co-supplementation with vitamin C and glutathione. It hypothesizes that these supplements can alleviate the poisonous effects of lead exposure. Eighty male albino rats, weighing 100 ± 15 g, were categorized into four groups: the control group, the second group receiving daily supplements of 100 mg/kg of body weight glutathione and 1 mg/100 g of body weight vitamin C orally, the third group receiving 100 mg/kg body weight of lead acetate orally daily, and the fourth group receiving similar oral dosages of lead acetate along with glutathione and vitamin C. Lead exposure significantly decreased body weight and relative testis weight, while relative organ weights for the liver, kidney, and spleen increased significantly. Additionally, lead acetate increased plasma glutamic pyruvic transaminase and glutamic oxaloacetic transaminase activities and plasma creatinine concentration (p < 0.05). Lead concentration rose significantly in blood, urine, liver, and kidney (p < 0.05). Examinations revealed that lead acetate exposure induced apoptotic DNA fragmentation in hepatocytes, significantly increasing caspase-3 activity (91 %) and annexin V indicators. Moreover, lead exposure induced a decrease in sperm count and motility, along with an increase in abnormal sperm morphology. However, vitamin C and glutathione supplementation significantly improved these adverse impacts, suggesting their protective function in counteracting the harmful impacts of lead acetate in different organs.

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.

Assessment of Neurotoxic Mechanisms of Individual and Binary Mixtures of Cobalt, Nickel and Lead in Hippocampal Neuronal Cells

Many studies have focused on the neurotoxic effects of single metals, while investigation on the exposure to metal mixtures, which mainly occur in real-life situations, is scarce. This study sought to assess the neurotoxic effect of Ni, Co, and Pb binary mixtures and their individual effects in hippocampal neuronal cells (HT-22). Cells were exposed to Ni, Co, and Pb separately for 48 h at 37°C and 5% CO2, and cell viability was assessed. Morphological assessment of the cells exposed to binary mixtures of Co, Ni, and Pb and single metals was assessed using a microscope. Furthermore, acetylcholinesterase (AChE) activity, oxidative stress biomarkers (glutathione [GSH] and malondialdehyde [MDA] levels, catalase [CAT], and glutathione-S transferase [GST] activities) and nitric oxide [NO] levels were evaluated after treatment with the binary mixtures and single metals. Binary mixtures of the metals reduced cell viability, exerting an additivity action. The combinations also exerted synergistic action, as revealed by the combination index. Furthermore, a significant reduction in AChE activity, GSH levels, CAT and GST activities, and high MDA and NO levels were observed in neuronal cells. The additive interactions and synergistic actions of the binary mixtures might contribute to the significant reduction of AChE activity, GSH levels, GST, and CAT activities, and an increase in MDA and NO levels. The findings from this study revealed significant evidence that binary mixtures of Co, Pb, and Ni may induce impaired neuronal function and, ultimately, neurodegeneration.

Novel plasma cytokines identified and validated in children during lead exposure according to the new updated BLRV

Lead is a pervasive environmental contaminant with significant health risks, particularly to children. It is known for its neurotoxic and immunotoxic effects, causing developmental, cognitive, and behavioral impairments. Despite extensive research, the mechanisms of lead toxicity remain unclear. Cytokines, which are critical in immune response and inflammation, have emerged as potential biomarkers for lead toxicity. The recent Centers for Disease Control and Prevention (CDC) update to the blood lead reference value (BLRV) to 3.5 µg/dL emphasizes the need to explore novel biomarkers and mechanisms. The study involved 100 healthy children aged 1 to 5 years, divided into two groups based on BLRV: elevated (≥ 3.5 µg/dL) and low (< 3.5 µg/dL). The research consisted of two phases: discovery and validation. Plasma samples were analyzed using RayBio® Human Cytokine Antibody Arrays and Enzyme-linked immunosorbent assay (ELISA) for cytokine levels. Ethical approval was obtained, and statistical analyses included t-tests, chi-squared tests, pearson correlations, and multivariate logistic regression. Protein-protein interaction (PPI), Gene Ontology (GO) enrichment, and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were conducted to explore the roles of significant differentially expressed proteins (DEPs). No significant differences in age, gender, or BMI between the two groups, but BLRV levels were significantly higher in the elevated BLRV group compared to the low BLRV group. In the discovery phase, significant changes in cytokine expression were identified, including increased levels of IL-6, IL-8, and IL-17, and decreased levels of BDNF, BMP-4, IGF-1, IL-7, IL-10, and Leptin. These findings were validated in the second phase using ELISA. Significant positive correlations were found between BLRV and IL-6, IL-8, and IL-17. Negative correlations were observed with BDNF, BMP-4, IGF-1, IL-7, IL-10, and Leptin. Multivariate regression confirmed that BLRV significantly affects these cytokine levels. PPI networks revealed that DEPs had strong interactions with multiple proteins, indicating their central role in lead toxicity. GO and KEGG analyses highlighted pathways related to neurotoxicity and inflammatory responses, including "negative regulation of myotube differentiation," "neurotrophin signaling pathway," and "alcoholism." This study provides insights into the role of cytokines as biomarkers for lead toxicity and offers a comprehensive analysis of the mechanisms involved. The findings underscore the importance of early detection and intervention based on updated BLRV thresholds.

ATF5-mediated mitochondrial unfolded protein response protects against Pb-induced mitochondria damage in SH-SY5Y cell

Mitochondria is the primary target of lead (Pb) in neural cells, and Pb exposure can cause impairment to mitochondrial function and morphology. Recent studies have reported that a conserved cellular stress response, called mitochondrial unfolded protein response (mtUPR), is activated in response to mitochondrial dysfunction and protein misfolding and play protective roles in aging and neurodegeneration, but it's unknown whether mtUPR could protect against Pb-induced neurotoxicity. In this study, we found that sublethal level exposure of PbAc (2.5 μM) could cause mitochondria damage and then activate mtUPR by promoting the expression of mitochondrial proteases (LonP1 and ClpP), molecular chaperone (HSPA1A). ATF5 mediated mtUPR activation as knocking out ATF5 significantly inhibited Pb-induced LonP1 and ClpP expression. Moreover, ATF5 deficiency exacerbated Pb-induced mitochondrial morphological and oxidative phosphorylation (OXPHOS) functional damage, resulting in oxidative stress and ultimately promoting cell death. Conversely, overexpression of ATF5 confers protection against Pb-induced oxidative stress and cell death. Collectively, thess results highlight that mtUPR mediated by ATF5 safeguards against mitochondria damage caused by Pb exposure, providing insights into the development of new strategies for mitigating the Pb neurotoxicity.

Silibinin-loaded Nanostructured Lipid Carriers (NLCs) Ameliorated Lead-induced Acute Nephrotoxicity in Male Rats

As a toxic heavy metal, lead (Pb) is well known for impairment of renal function due to oxidative injuries. In contrast, the antioxidant activity of silibinin has been approved. Given the role of silibinin antioxidant activity, the present study investigated the effectiveness of silibinin-loaded nanostructured lipid carriers (Sili-NLCs) against Pb-induced acute nephrotoxicity in rats. The emulsification-solvent evaporation method was applied to prepare Sili-NLCs. Sixty male Wistar rats were divided into ten separate groups. Pb (20 mg/kg/day, i.p.) was applied to induce nephrotoxicity and in the treatment groups animals received the same concentration of silibinin and Sili-NLCs (25, 50, and 100 mg/kg/day, p.o.) for five days. After sacrificing rats, kidney tissue samples were collected to assess the oxidative stress parameters, including lipid peroxidation (LPO), nitric oxide (NO), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activity. Also, histopathological examination using Hematoxylin-Eosin (H&E) was studied. Not only did Pb injection significantly increase the renal levels of LPO and NO, but also decreased the levels of antioxidant enzyme activity. On the other hand, Sili-NLCs were more effective than silibinin in decreasing renal oxidative damage by increasing the antioxidant defense system. Moreover, the histopathological examination correlated well with biochemical findings. Our data suggested that Sili-NLCs are potentially superior to pure silibinin for attenuating Pb-induced acute nephrotoxicity.

Exploring serum trace element shifts: Implications for cervical intraepithelial neoplasia

BACKGROUND

Cervical intraepithelial neoplasia (CIN) represents a premalignant state presumably related to perturbations in circulating levels of trace elements.

MATERIALS AND METHODS

Employing inductively coupled plasma mass spectrometry (ICP-MS), we quantified essential and toxic trace elements in the sera of 60 women diagnosed with CIN and 60 age-matched healthy counterparts.

RESULTS

Our investigation revealed a noteworthy higher levels in serum of Mn, Zn, and Pb, as well as lower levels in Ni, Se, Rb, and Mo levels within the CIN cohort. Levels of Mn, Zn, and Pb were higher by approximately 5.5-fold, 3.0-fold, and 7.5-fold, respectively, while Mo levels exhibited an approximate 4.5-fold reduction in CIN sera compared to the control group. While the study provided valuable insights into trace element variations, it's important to note that the adult Serbian population is considered Zn-deficient, so the Zn data should be interpreted with caution. Age stratification (30-40 vs. 40-50 vs. 50-60 years), smoking status (smokers vs. nonsmokers), and CIN severity (CIN 2 vs. CIN 3) yielded no significant disparities in elemental profiles. Among the 10 proposed ratios, 5 demonstrated a significant surge in CIN sera relative to controls: Mn/Se, Mn/Mo, Zn/Se, Zn/Mo, and Se/Mo. Correlation analysis of trace element levels revealed a predominantly consistent pattern between CIN cases and healthy subjects, except for Zn and its negative correlations (antagonistic interactions) with other analyzed trace elements.

CONCLUSION

Our findings underscore differences in serum levels of specific trace elements in CIN cases versus controls, implicating their potential involvement in the underlying pathophysiological cascades culminating in cervical neoplasms.

Childhood lead exposure increases the risk of attention-deficit-hyperactivity disorder: A meta-analysis

Environmental lead exposure has been a much-discussed risk factor for the development of ADHD for decades. However, due to methodological shortcomings, the existing research on this topic is highly inconsistent. We will attempt to clarify this question by performing a meta-analysis based on a systematic literature search until February 2024 including different databases such as Pubmed and Google Scholar. The effects of environmental lead exposure were synthesized by odds ratios. A random effects model was deployed with a Paule-Mandel estimator using Hedges' invariance weighting. In addition, we carried out sensitivity analyses to examine the robustness of effects, including the detection of outliers, publication bias, p-hacking and moderating variables. In total, 14 studies with 14 effect sizes were included which had investigated the effects of lead exposure on the development of ADHD. The analyses were based on a final sample size of N = 7618 with n = 2554 ADHD cases (33,53 %) and n = 5064 healthy controls (66.47 %). Our results show that lead exposure was significantly associated with a higher risk of ADHD development. Regression analyses demonstrated that increased age of participants and increased lead significantly enhanced the risk of ADHD. Summing up we present novel results concerning the relationship between environmental lead exposure and the development of ADHD, while discussing underlying pathomechanisms as well as limitations. Finally, we provide recommendations for future studies and public health policies.

Estrogen replacement therapy reverses spatial memory loss and pyramidal cell neurodegeneration in the prefrontal cortex of lead-exposed ovariectomized Wistar rats

Background

Although menopause is a component of chronological aging, it may be induced by exposure to heavy metals like lead. Interestingly, lead exposure, just like the postmenopausal state, has been associated with spatial memory loss and neurodegeneration; however, the impact of hormone replacement therapy (HRT) on menopause and lead-induced spatial memory loss and neurodegeneration is yet to be reported.

Aim

The present study investigated the effect and associated mechanism of HRT on ovariectomized-driven menopausal state and lead exposure-induced spatial memory loss and neurodegeneration.

Materials and methods

Thirty adult female Wistar rats were randomized into 6 groups (n = 5 rats/group); the sham-operated vehicle-treated, ovariectomized (OVX), OVX + HRT, lead-exposed, OVX + lead, and OVX + Lead + HRT groups. Treatment was daily via gavage and lasted for 28 days.

Results

Ovariectomy and lead exposure impaired spatial memory deficit evidenced by a significant reduction in novel arm entry, time spent in the novel arm, alternation, time exploring novel and familiar objects, and discrimination index. These findings were accompanied by a marked distortion in the histology of the prefrontal cortex, and a decline in serum dopamine level and pyramidal neurons. In addition, ovariectomy and lead exposure induced metabolic disruption (as depicted by a marked rise in lactate level and lactate dehydrogenase and creatinine kinase activities), oxidative stress (evidenced by a significant increase in MDA level, and decrease in GSH level, and SOD and catalase activities), inflammation (as shown by significant upregulation of myeloperoxidase activity, and TNF-α and IL-1β), and apoptosis (evidenced by a rise in caspase 3 activity) of the prefrontal cortex. The observed biochemical and histological perturbations were attenuated by HRT.

Conclusions

This study revealed that HRT attenuated ovariectomy and lead-exposure-induced spatial memory deficit and pyramidal neurodegeneration by suppressing oxidative stress, inflammation, and apoptosis of the prefrontal cortex.

Demyelination and impaired oligodendrogenesis in the corpus callosum following lead exposure

The corpus callosum is an oligodendrocyte-enriched brain region, replenished by newborn oligodendrocytes from oligodendrocyte progenitor cells (OPCs) in subventricular zone (SVZ). Lead (Pb) exposure has been associated with multiple sclerosis, a disease characterized by the loss of oligodendrocytes. This study aimed to investigate the effects of Pb exposure on oligodendrogenesis in SVZ and myelination in the corpus callosum. Adult female mice were used for a disproportionately higher prevalence of multiple sclerosis in females. Acute Pb exposure (one ip-injection of 27 mg Pb/kg as PbAc2 24 hr before sampling) caused mild Pb accumulation in the corpus callosum. Ex vivo assay using isolated SVZ tissues collected from acute Pb-exposed brains showed a diminished oligodendrogenesis in SVZ-derived neurospheres compared with controls. In vivo subchronic Pb exposure (13.5 mg Pb/kg by daily oral gavage 4 wk) revealed significantly decreased newborn BrdU+/MBP+ oligodendrocytes in the corpus callosum, suggesting demyelination. Mechanistic investigations indicated decreased Rictor in SVZ OPCs, defective self-defense pathways, and reactive gliosis in the corpus callosum. Given the interwined pathologies between multiple sclerosis and Alzheimer's disease, the effect of Pb on myelination was evaluated in AD-modeled APP/PS1 mice. Myelin MRI on mice following chronic exposure (1,000 ppm Pb in drinking water as PbAc2 for 20 wk) revealed a profound demyelination in the corpus callosum compared with controls. Immunostaining of the choroid plexus showed diminished signaling molecule (Klotho, OTX2) expressions in Pb-treated animals. These observations suggest that Pb caused demyelination in the corpus callosum, likely by disrupting oligodendrogenesis from SVZ OPCs. Pb-induced demyelination represents a crucial pathogenic pathway in Pb neurotoxicity, including multiple sclerosis.

Influence of lead on cAMP-response element binding protein (CREB) and its implications in neurodegenerative disorders

Lead (Pb2+) is one of the most common toxic metals present in the environment, and lead exposure causes serious health issues in humans. Lead is widely used because of its physio-chemical characteristics, which include softness, corrosion resistance, ductility, and low conductivity. Lead affects almost all human organs, specifically the central nervous system. Lead neurotoxicity is connected to various neural pathways, including brain-derived neurotrophic factor (BDNF) protein level alterations, cyclic adenosine 3',5'-monophosphate (cAMP) response element binding protein (CREB) pathway changes, and N-methyl-D-aspartate receptors (NMDARs) changes. Lead primarily affects protein kinase C (PKC) through the replacement of calcium (Ca2+) ions in the CREB pathway. In this review, we have discussed the effect of lead on the CREB pathway and its implications on the nervous system, highlighting its effects on learning, synaptic plasticity, memory, and cognitive deficits. This review provides an understanding of the lead-induced alterations in the CREB pathway, which can lead to the future prospect of its use as a diagnostic marker as well as a therapeutic target for neurodegenerative disorders.

Co-administration of resveratrol rescued lead-induced toxicity in Drosophila melanogaster

Lead toxicity poses a significant environmental concern linked to diverse health issues. This study explores the potential mitigating effects of resveratrol on lead-induced toxicity in Drosophila melanogaster. Adult fruit flies, aged three days, were orally exposed to lead (60 mg/L), Succimer (10 mg), and varying concentrations of resveratrol (50, 100, and 150 mg). The investigation encompassed the assessment of selected biological parameters, biochemical markers, oxidative stress indicators, and antioxidant enzymes. Resveratrol exhibited a dose-dependent enhancement of egg-laying, eclosion rate, filial generation output, locomotor activity, and life span in D. melanogaster, significantly to 150 mg of diet. Most of the investigated biochemical parameters were significantly rescued in lead-exposed fruit flies when co-treated with resveratrol (p < 0.05). However, oxidative stress remained unaffected by resveratrol. The findings suggest that resveratrol effectively protects against lead toxicity in Drosophila melanogaster and may hold therapeutic potential as an agent for managing lead poisoning in humans.

Exploring the link between toxic metal exposure and ADHD: a systematic review of pb and hg

INTRODUCTION

Attention-Deficit/Hyperactivity Disorder (ADHD) is a recognized neurodevelopmental disorder with a complex, multifactorial origin. Lead (Pb) and mercury (Hg) are highly toxic substances that can potentially impair brain development and have been implicated in the development of ADHD. This systematic review aims to analyze the epidemiological literature regarding the association between Pb and Hg exposure and the diagnosis of ADHD.

METHODS

From November 1983 to June 2, 2023, a comprehensive search was conducted in multiple databases and search engines, including PubMed, Web of Science, Scopus, and Google Scholar. Observational studies (case-control, cohort, and cross-sectional) measuring Pb and Hg levels in various biological samples (blood, hair, urine, nail, saliva, teeth, and bone) of children with ADHD or their parents and their association with ADHD symptoms were included.

RESULTS

Out of 2059 studies, 87 met the inclusion criteria and were included in this systematic review. Approximately two-thirds of the 74 studies investigating Pb levels in different biological samples reported associations with at least one subtype of ADHD. However, most studies examining Hg levels in various biological samples found no significant association with any ADHD subtype, although there were variations in exposure periods and diagnostic criteria.

CONCLUSION

The evidence gathered from the included studies supports an association between Pb exposure and the diagnosis of ADHD, while no significant association was found with Hg exposure. Importantly, even low levels of Pb were found to elevate the risk of ADHD. Further research is needed to explore the comprehensive range of risk factors for ADHD in children, considering its significance as a neurodevelopmental disorder.

Selected Functions and Disorders of Mitochondrial Metabolism under Lead Exposure

Mitochondria play a fundamental role in the energy metabolism of eukaryotic cells. Numerous studies indicate lead (Pb) as a widely occurring environmental factor capable of disrupting oxidative metabolism by modulating the mitochondrial processes. The multitude of known molecular targets of Pb and its strong affinity for biochemical pathways involving divalent metals suggest that it may pose a health threat at any given dose. Changes in the bioenergetics of cells exposed to Pb have been repeatedly demonstrated in research, primarily showing a reduced ability to synthesize ATP. In addition, lead interferes with mitochondrial-mediated processes essential for maintaining homeostasis, such as apoptosis, mitophagy, mitochondrial dynamics, and the inflammatory response. This article describes selected aspects of mitochondrial metabolism in relation to potential mechanisms of energy metabolism disorders induced by Pb.

Lead induced cerebellar toxicology of developmental Japanese quail (Coturnix japonica) via oxidative stress-based Nrf2/Keap1 pathway inhibition and glutathione-mediated apoptosis signaling activation

Lead (Pb) is a heavy metal that has been recognized as a neurotoxin, meaning it can cause harmful effects on the nervous system. However, the neurotoxicology of Pb to birds still needs further study. In this study, we examined the neurotoxic effects of Pb exposure on avian cerebellum by using an animal model-Japanese quail (Coturnix japonica). The one-week old male chicks were exposed to 50, 200 and 500 mg/kg Pb of environmental relevance in the feed for five weeks. The results showed Pb caused cerebellar microstructural damages charactered by deformation of neuroglia cells, granule cells and Purkinje cells with Nissl body changes. Moreover, cerebellar neurotransmission was disturbed by Pb with increasing acetylcholine (ACh) and decreasing acetylcholinesterase (AChE), dopamine (DA), γ-Aminobutyric Acid (GABA) and Na+/K+ ATPase. Meanwhile, cerebellar oxidative stress was caused by Pb exposure represented by increasing reactive oxygen species (ROS) and malondialdehyde (MDA) as well as decreasing catalase (CAT), glutathione peroxidase (GPX), glutathione (GSH) and superoxide dismutase (SOD). Moreover, RNA-Seq analysis showed that molecular signaling pathways in the cerebellum were disrupted by Pb exposure. In particular, the disruption of nuclear factor erythroid-2-related factor 2 (Nfr2)/kelch-like ECH-associated protein 1 (Keap1) pathway and glutathione metabolism pathway indicated increasing cell apoptosis and functional disorder in the cerebellum. The present study revealed that Pb induced cerebellar toxicology through structural injury, oxidative stress, neurotransmission interference and abnormal apoptosis.

Empirical analysis of lead neurotoxicity mode of action and its application in health risk assessment

The mode of action (MOA) framework is proposed to inform a biological link between chemical exposures and adverse health effects. Despite a significant increase in knowledge and awareness, the application of MOA in human health risk assessment (RA) remains limited. This study aims to discuss the adoption of MOA for health RA within a regulatory context, taking our previously proposed but not yet validated MOA for lead neurotoxicity as an example. We first conducted a quantitative weight of evidence (qWOE) assessment, which revealed that the MOA has a moderate confidence. Then, targeted bioassays were performed within an in vitro blood-brain barrier (BBB) model to quantitatively validate the scientific validity of key events (KEs) in terms of essentiality and concordance of empirical support (dose/temporal concordance), which increases confidence in utilizing the MOA for RA. Building upon the quantitative validation data, we further conducted benchmark dose (BMD) analysis to map dose-response relationships for the critical toxicity pathways, and the lower limit of BMD at a 5% response (BMDL5) was identified as the point of departure (POD) value for adverse health effects. Notably, perturbation of the Aryl Hydrocarbon Receptor (AHR) signaling pathway exhibited the lowest POD value, measured at 0.0062 μM. Considering bioavailability, we further calculated a provisional health-based guidance value (HBGV) for children's lead intake, determining it to be 2.56 μg/day. Finally, the health risk associated with the HBGV was assessed using the hazard quotient (HQ) approach, which indicated that the HBGV established in this study is a relative safe reference value for lead intake. In summary, our study described the procedure for utilizing MOA in health RA and set an example for MOA-based human health risk regulation.

Heavy metal exposure and metabolomics analysis: an emerging frontier in environmental health

Exposure to heavy metals in various populations can lead to extensive damage to different organs, as these metals infiltrate and bioaccumulate in the human body, causing metabolic disruptions in various organs. To comprehensively understand the metal homeostasis, inter-organ "traffic," and extensive metabolic alterations resulting from heavy metal exposure, employing complementary analytical methods is crucial. Metabolomics is pivotal in unraveling the intricacies of disease vulnerability by furnishing thorough understandings of metabolic changes linked to different metabolic diseases. This field offers exciting prospects for enhancing the disease prevention, early detection, and tailoring treatment approaches to individual needs. This article consolidates the existing knowledge on disease-linked metabolic pathways affected by the exposure of diverse heavy metals providing concise overview of the underlying impact mechanisms. The main aim is to investigate the connection between the altered metabolic pathways and long-term complex health conditions induced by heavy metals such as diabetes mellitus, cardiovascular diseases, renal disorders, inflammation, neurodegenerative diseases, reproductive risks, and organ damage. Further exploration of common pathways may unveil the shared targets for treating associated pathological conditions. In this article, the role of metabolomics in disease susceptibility is emphasized that metabolomics is expected to be routinely utilized for the diagnosis and monitoring of diseases and practical value of biomarkers derived from metabolomics, as well as determining their appropriate integration into extensive clinical settings.

Gender-Specific Effects on the Cardiorespiratory System and Neurotoxicity of Intermittent and Permanent Low-Level Lead Exposures

Lead exposure is a significant health concern, ranking among the top 10 most harmful substances for humans. There are no safe levels of lead exposure, and it affects multiple body systems, especially the cardiovascular and neurological systems, leading to problems such as hypertension, heart disease, cognitive deficits, and developmental delays, particularly in children. Gender differences are a crucial factor, with women's reproductive systems being especially vulnerable, resulting in fertility issues, pregnancy complications, miscarriages, and premature births. The globalization of lead exposure presents new challenges in managing this issue. Therefore, understanding the gender-specific implications is essential for developing effective treatments and public health strategies to mitigate the impact of lead-related health problems. This study examined the effects of intermittent and permanent lead exposure on both male and female animals, assessing behaviours like anxiety, locomotor activity, and long-term memory, as well as molecular changes related to astrogliosis. Additionally, physiological and autonomic evaluations were performed, focusing on baro- and chemoreceptor reflexes. The study's findings revealed that permanent lead exposure has more severe health consequences, including hypertension, anxiety, and reactive astrogliosis, affecting both genders. However, males exhibit greater cognitive, behavioural, and respiratory changes, while females are more susceptible to chemoreflex hypersensitivity. In contrast, intermittent lead exposure leads to hypertension and reactive astrogliosis in both genders. Still, females are more vulnerable to cognitive impairment, increased respiratory frequency, and chemoreflex hypersensitivity, while males show more reactive astrocytes in the hippocampus. Overall, this research emphasizes the importance of not only investigating different types of lead exposure but also considering gender differences in toxicity when addressing this public health concern.

Modulation of gut microbiota with probiotics as a strategy to counteract endogenous and exogenous neurotoxicity

The existing data demonstrate that probiotic supplementation affords protective effects against neurotoxicity of exogenous (e.g., metals, ethanol, propionic acid, aflatoxin B1, organic pollutants) and endogenous (e.g., LPS, glucose, Aβ, phospho-tau, α-synuclein) agents. Although the protective mechanisms of probiotic treatments differ between various neurotoxic agents, several key mechanisms at both the intestinal and brain levels seem inherent to all of them. Specifically, probiotic-induced improvement in gut microbiota diversity and taxonomic characteristics results in modulation of gut-derived metabolite production with increased secretion of SFCA. Moreover, modulation of gut microbiota results in inhibition of intestinal absorption of neurotoxic agents and their deposition in brain. Probiotics also maintain gut wall integrity and inhibit intestinal inflammation, thus reducing systemic levels of LPS. Centrally, probiotics ameliorate neurotoxin-induced neuroinflammation by decreasing LPS-induced TLR4/MyD88/NF-κB signaling and prevention of microglia activation. Neuroprotective mechanisms of probiotics also include inhibition of apoptosis and oxidative stress, at least partially by up-regulation of SIRT1 signaling. Moreover, probiotics reduce inhibitory effect of neurotoxic agents on BDNF expression, on neurogenesis, and on synaptic function. They can also reverse altered neurotransmitter metabolism and exert an antiamyloidogenic effect. The latter may be due to up-regulation of ADAM10 activity and down-regulation of presenilin 1 expression. Therefore, in view of the multiple mechanisms invoked for the neuroprotective effect of probiotics, as well as their high tolerance and safety, the use of probiotics should be considered as a therapeutic strategy for ameliorating adverse brain effects of various endogenous and exogenous agents.

Yucca schidigera Extract Mitigates the Oxidative Damages, Inflammation, and Neurochemical Impairments in the Brains of Quails Exposed to Lead

The present study explored the neurotoxic impacts of lead (Pb) and the potential alleviating effect of Yucca schidigera extract (YSE) in Japanese quails. About 360 adult Japanese quails (8 weeks old) were used. Quails were randomly distributed to six groups with 4 replicates each: the control group (fed basal diet, BD), the BD + YSE1 and BD + YSE2 groups (BD + 100 and 200 mg/kg diet of YSE, respectively), the Pb group (BD + 100 mg/kg Pb), and the Pb + YSE1 and Pb + YSE2 groups (BD + Pb + 100 and 200 mg/kg YSE, respectively). This feeding trial lasted for 8 weeks. The exposure to Pb in the diet induced oxidative damage stress in the brain of exposed quails reflected by the significant increase in the oxidative markers including malonaldehyde (MDA) and protein carbonyl (PC) and the significant reduction in the activities of antioxidants including catalase (CAT), superoxide dismutase (SOD), and the reduced glutathione (GSH). Brain neurochemistry and enzyme activities were also altered following Pb exposure. Pb significantly reduced serotonin, dopamine, norepinephrine, GABA, Ach, and Na + /K + -ATPase activities. Pb dietary intoxication markedly increased brain inflammatory biomarkers, including tumor necrosis factor (TNF-α), myeloperoxidase, and nitric oxide. Peripherally, Pb toxicity decreased the amino acid neurotransmitters (glutamic acid, glycine, and aspartic acid) in the serum of birds. At the transcriptomic level, Pb exposure upregulated the transcription patterns of CASP3, TNF-α, HSP70, and IL-1β. The single effect of YSE maintained that all the assessed parameters were not changed compared to the control. Interestingly, the YSE co-supplementation with Pb alleviated the Pb-induced neuro-oxidative damages by lowering the lipid, protein, and DNA damage, and the inflammatory biomarkers.

Evaluation of the Potential Protective Effect of Ellagic Acid against Heavy Metal (Cadmium, Mercury, and Lead) Toxicity in SH-SY5Y Neuroblastoma Cells

Ellagic acid (EA), a polyphenolic constituent of plant origin, has been thoroughly investigated for its hypothesised pharmacological properties among which antioxidant and neuroprotective activities are included. The present study was designed to explore whether EA could attenuate heavy metal (cadmium, mercury, and lead)-induced neurotoxicity in SH-SY5Y cells, which were utilized as a model system for brain cells. MTT and LDH assays were performed to examine the viability of the SH-SY5Y cells after exposure to Cd, Hg, and Pb (either individually or in combination with EA) as well as the effects of necrotic cell death, respectively. Furthermore, 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA), a cell-based assay, was performed to determine whether EA could protect SH-SY5Y from heavy metal-induced oxidative stress. Results allowed us to assess the capability of EA to enhance the number of viable SH-SY5Y cells after exposure to heavy metal toxicity. Pre-treatment with EA showed a considerable, concentration-dependent, cytoprotective effect, particularly against Cd2+-induced toxicity. This effect was confirmed through the reduction of LDH release after the simultaneous cell treatment with Cd2+ and EA compared with Cd2+-treated cells. Furthermore, a significant, concentration-dependent decrease in reactive oxygen species (ROS) production, induced by H2O2 or heavy metals, was observed in the same model. Overall, the obtained results provide further insight into the protective role of EA against heavy metal-induced neurotoxicity and oxidative stress, thus indicating the potential beneficial effects of the consumption of EA-rich foods. However, to confirm its effects, well-designed human randomized controlled trials are needed to fill the existing gap between experimental and clinical research.

Heavy metals, oxidative stress, and the role of AhR signaling

The Aryl Hydrocarbon Receptor (AhR) is a ligand-activated transcriptional factor pivotal in responding to environmental stress and maintaining cellular homeostasis. Exposure to specific xenobiotics or industrial compounds in the environment activates AhR and its subsequent signaling, inducing oxidative stress and related toxicity. Past research has also identified and characterized several classes of endogenous ligands, particularly some tryptophan (Trp) metabolic/catabolic products, that act as AhR agonists, influencing a variety of physiological and pathological states, including the modulation of immune responses and cell death. Heavy metals, being non-essential elements in the human body, are generally perceived as toxic and hazardous, originating either naturally or from industrial activities. Emerging evidence indicates that heavy metals significantly influence AhR activation and its downstream signaling. This review consolidates current knowledge on the modulation of the AhR signaling pathway by heavy metals, explores the consequences of co-exposure to AhR ligands and heavy metals, and investigates the interplay between oxidative stress and AhR activation, focusing on the regulation of immune responses and ferroptosis.

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.

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.

Development of a rapid zebrafish model for lead poisoning research and drugs screening

Lead (Pb) contamination is a worldwide public health threaten. Besides close restraint of lead exposure, it's emergency to discover compounds that could help to cue toxicities caused by lead. Zebrafish embryos and early larvae can serve as valuable screening tools in early pre-clinical phase of drug screening and research. In order to establish a zebrafish lead poisoning model that could be used for drug screening and research, zebrafish embryos at 6 h post-fertilization (hpf) were treated with lead at different concentrations by soaking intermittently, raised in lead work solution at night while in fish water during the day. After treated for 90 h, death and severe trunk curvature were observed on zebrafish in 640 μM group, obvious dysplasia, blood toxicity, excessive reactive oxygen species (ROS), severe neurotoxicity, such as shorter length of peripheral motor neurons, neuronal apoptosis, and axonal injury, and neurobehavior impairment were induced by lead at 80, 160 and 320 μM, similar to phenotypes reported in rodent. Moreover, the mRNA level of genes related to neurodevelopment, memory, and antioxidation were significantly down regulated, and apoptosis-related genes were up regulated, consistent to zebrafish phenotypic change. Finally, zebrafish were intermittently exposed to 80 μM lead solution to establish the lead poisoning model, and the efficacy of a safe chelating agent Meso-2,3-Dimercaptosuccinic acid (DMSA) was tested at a series of concentrations to validate the zebrafish model. The result showed concentration-dependent decrease of lead content in zebrafish in DMSA treated groups compared with model group. The above data fully demonstrated a zebrafish model of lead poisoning suitable for drug screening was successfully developed, which was expected to provide a rapid and economic tools for discovering antidotes of lead and drugs of neuroprotection.

Interaction of Heavy Metal Lead with Gut Microbiota: Implications for Autism Spectrum Disorder

Autism Spectrum Disorder (ASD), a neurodevelopmental disorder characterized by persistent deficits in social interaction and communication, manifests in early childhood and is followed by restricted and stereotyped behaviors, interests, or activities in adolescence and adulthood (DSM-V). Although genetics and environmental factors have been implicated, the exact causes of ASD have yet to be fully characterized. New evidence suggests that dysbiosis or perturbation in gut microbiota (GM) and exposure to lead (Pb) may play important roles in ASD etiology. Pb is a toxic heavy metal that has been linked to a wide range of negative health outcomes, including anemia, encephalopathy, gastroenteric diseases, and, more importantly, cognitive and behavioral problems inherent to ASD. Pb exposure can disrupt GM, which is essential for maintaining overall health. GM, consisting of trillions of microorganisms, has been shown to play a crucial role in the development of various physiological and psychological functions. GM interacts with the brain in a bidirectional manner referred to as the "Gut-Brain Axis (GBA)". In this review, following a general overview of ASD and GM, the interaction of Pb with GM in the context of ASD is emphasized. The potential exploitation of this interaction for therapeutic purposes is also touched upon.

Mitochondrial Oxidative Stress Is the General Reason for Apoptosis Induced by Different-Valence Heavy Metals in Cells and Mitochondria

This review analyzes the causes and consequences of apoptosis resulting from oxidative stress that occurs in mitochondria and cells exposed to the toxic effects of different-valence heavy metals (Ag+, Tl+, Hg2+, Cd2+, Pb2+, Al3+, Ga3+, In3+, As3+, Sb3+, Cr6+, and U6+). The problems of the relationship between the integration of these toxic metals into molecular mechanisms with the subsequent development of pathophysiological processes and the appearance of diseases caused by the accumulation of these metals in the body are also addressed in this review. Such apoptosis is characterized by a reduction in cell viability, the activation of caspase-3 and caspase-9, the expression of pro-apoptotic genes (Bax and Bcl-2), and the activation of protein kinases (ERK, JNK, p53, and p38) by mitogens. Moreover, the oxidative stress manifests as the mitochondrial permeability transition pore (MPTP) opening, mitochondrial swelling, an increase in the production of reactive oxygen species (ROS) and H2O2, lipid peroxidation, cytochrome c release, a decline in the inner mitochondrial membrane potential (ΔΨmito), a decrease in ATP synthesis, and reduced glutathione and oxygen consumption as well as cytoplasm and matrix calcium overload due to Ca2+ release from the endoplasmic reticulum (ER). The apoptosis and respiratory dysfunction induced by these metals are discussed regarding their interaction with cellular and mitochondrial thiol groups and Fe2+ metabolism disturbance. Similarities and differences in the toxic effects of Tl+ from those of other heavy metals under review are discussed. Similarities may be due to the increase in the cytoplasmic calcium concentration induced by Tl+ and these metals. One difference discussed is the failure to decrease Tl+ toxicity through metallothionein-dependent mechanisms. Another difference could be the decrease in reduced glutathione in the matrix due to the reversible oxidation of Tl+ to Tl3+ near the centers of ROS generation in the respiratory chain. The latter may explain why thallium toxicity to humans turned out to be higher than the toxicity of mercury, lead, cadmium, copper, and zinc.

Association between Heavy Metals, Metalloids and Metabolic Syndrome: New Insights and Approaches

Metabolic syndrome (MetS) is an important public health issue that affects millions of people around the world and is growing to pandemic-like proportions. This syndrome is defined by the World Health Organization (WHO) as a pathologic condition characterized by abdominal obesity, insulin resistance, hypertension, and hyperlipidemia. Moreover, the etiology of MetS is multifactorial, involving many environmental factors, including toxicant exposures. Several studies have associated MetS with heavy metals exposure, which is the focus of this review. Environmental and/or occupational exposure to heavy metals are a major risk, contributing to the development of chronic diseases. Of particular note, toxic metals such as mercury, lead, and cadmium may contribute to the development of MetS by altering oxidative stress, IL-6 signaling, apoptosis, altered lipoprotein metabolism, fluid shear stress and atherosclerosis, and other mechanisms. In this review, we discuss the known and potential roles of heavy metals in MetS etiology as well as potential targeted pathways that are associated with MetS. Furthermore, we describe how new approaches involving proteomic and transcriptome analysis, as well as bioinformatic tools, may help bring about an understanding of the involvement of heavy metals and metalloids in MetS.

The association between lead exposure and crime: A systematic review

Prior research has demonstrated an association between lead exposure and criminal behavior at the population-level, however studies exploring the effect of lead exposure on criminal behavior at the individual-level have not been reviewed systematically. The intent of this study is to complete a systematic review of all studies assessing individual-level exposures to lead and the outcomes of crime and antisocial behavior traits. We included peer reviewed studies that were published prior to August 2022 and were classified as cohort, cross-sectional, or case-control. Studies measuring the outcomes of crime, delinquency, violence, or aggression were included. The following databases were searched using a standardized search strategy: ProQuest Environmental Science Database, PubMed, ToxNet and the Public Affairs Information Service (PAIS). Seventeen manuscripts met our inclusion criteria. Blood lead was measured in 12 studies, bone lead in 3 studies, and dentine lead levels in 2 studies. This systematic review identified a wide range of diverse outcomes between exposure to lead at multiple windows of development and later delinquent, criminal and antisocial behavior. A review of all potential confounding variables included within each study was made, with inclusion of relevant confounders into the risk of bias tool. There is limited data at the individual level on the effects of prenatal, childhood, and adolescent lead exposure and later criminal behavior and more evidence is necessary to evaluate the magnitude of the associations seen in this review. Our review, in conjunction with the available biological evidence, suggests that an excess risk for criminal behavior in adulthood exists when an individual is exposed to lead in utero or in the early years of childhood. The authors report no conflict of interest and no funding source. Clinical trial registration: PROSPERO ID: CRD42021268379.

Profile of N6-methyladenosine of Pb-exposed neurons presents epitranscriptomic alterations in PI3K-AKT pathway-associated genes

Lead (Pb) is a pervasive heavy metal with multi-organ toxicity. However, the molecular mechanisms of Pb-induced neurotoxicity are not fully understood. The dynamics of N6-methylademine (m6A) is an emerging regulatory mechanism for gene expression, which is closely related to nervous system diseases. To elucidate the association between m6A modification and Pb-mediated neurotoxicity, primary hippocampal neurons exposed to 5 μM Pb for 48 h were used as the paradigm neurotoxic model in this study. According to the results, Pb exposure reprogrammed the transcription spectrum. Simultaneously, Pb exposure remodeled the transcriptome-wide distribution of m6A while disrupting the overall level of m6A in cellular transcripts. United analysis of MeRIP-Seq and RNA-Seq was applied to further identify the core genes whose expression levels are regulated by m6A in the process of lead-induced nerve injury. GO and KEGG analysis unveiled that the modified transcripts were overrepresented by the PI3K-AKT pathway. Mechanically, we elucidated the regulatory role of the methyltransferase like3 (METTL3) in the process of lead-induced neurotoxicity and the downregulation of the PI3K-AKT pathway. In conclusion, our novel findings shed new light on the functional roles of m6A modification in the expressional alternations of downstream transcripts caused by lead, providing an innovative molecular basis to explain Pb neurotoxicity.

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.

Neurotoxicity and the Global Worst Pollutants: Astroglial Involvement in Arsenic, Lead, and Mercury Intoxication

Environmental pollution is a global threat and represents a strong risk factor for human health. It is estimated that pollution causes about 9 million premature deaths every year. Pollutants that can cross the blood-brain barrier and reach the central nervous system are of special concern, because of their potential to cause neurological and development disorders. Arsenic, lead and mercury are usually ranked as the top three in priority lists of regulatory agencies. Against xenobiotics, astrocytes are recognised as the first line of defence in the CNS, being involved in virtually all brain functions, contributing to homeostasis maintenance. Here, we discuss the current knowledge on the astroglial involvement in the neurotoxicity induced by these pollutants. Beginning by the main toxicokinetic characteristics, this review also highlights the several astrocytic mechanisms affected by these pollutants, involving redox system, neurotransmitter and glucose metabolism, and cytokine production/release, among others. Understanding how these alterations lead to neurological disturbances (including impaired memory, deficits in executive functions, and motor and visual disfunctions), by revisiting the current knowledge is essential for future research and development of therapies and prevention strategies.

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.

Polysaccharide from Flammulina velutipes residues protects mice from Pb poisoning by activating Akt/GSK3β/Nrf-2/HO-1 signaling pathway and modulating gut microbiota

Lead (Pb) can cause damages to the brain, liver, kidney, endocrine and other systems. Flammulina velutipes residues polysaccharide (FVRP) has been reported to exhibit anti-heavy metal toxicity on yeast, but its regulating mechanism is unclear. Therefore, the protective effect and the underlying mechanism of FVRP on Pb-intoxicated mice were investigated. The results showed that FVRP could reduce liver and kidney function indexes, serum inflammatory factor levels, and increase antioxidant enzyme activity of Pb-poisoned mice. FVRP also exhibited a protective effect on histopathological damages in organs of Pb-intoxicated mice. Furthermore, FVRP attenuated Pb-induced kidney injury by inhibiting apoptosis via activating the Akt/GSK3β/Nrf-2/HO-1 signaling pathway. In addition, based on 16 s rRNA and ITS-2 sequencing data, FVRP regulated the imbalance of gut microbiota to alleviate the damage of Pb-poisoned mice by increasing the abundance of beneficial microbiota (Lachnospiraceae, Lactobacillaceae, Saccharomyces and Mycosphaerella) and decreasing the abundance of harmful microbiota (Muribaculaceae and Pleosporaceae). In conclusion, FVRP inhibited kidney injury in Pb-poisoned mice by inhibiting apoptosis via activating Akt/GSK3β/Nrf-2/HO-1 signaling pathway, and regulating gut fungi and gut bacteria. This study not only revealed the role of gut fungi in Pb-toxicity, but also laid a theoretical foundation for FVRP as a natural drug against Pb-toxicity.

Zebrafish as a Potential Model for Neurodegenerative Diseases: A Focus on Toxic Metals Implications

In the last century, industrial activities increased and caused multiple health problems for humans and animals. At this moment, heavy metals are considered the most harmful substances for their effects on organisms and humans. The impact of these toxic metals, which have no biological role, poses a considerable threat and is associated with several health problems. Heavy metals can interfere with metabolic processes and can sometimes act as pseudo-elements. The zebrafish is an animal model progressively used to expose the toxic effects of diverse compounds and to find treatments for different devastating diseases that human beings are currently facing. This review aims to analyse and discuss the value of zebrafish as animal models used in neurological conditions, such as Alzheimer's disease (AD), and Parkinson's disease (PD), particularly in terms of the benefits of animal models and the limitations that exist.

Effects of Salinomycin and Deferiprone on Lead-Induced Changes in the Mouse Brain

Lead (Pb) is a highly toxic heavy metal that has deleterious effects on the central nervous system. This study aimed to investigate the effects of salinomycin (Sal) and deferiprone (DFP) on brain morphology and on the content of some essential elements in Pb-exposed mice. Adult male Institute of Cancer Research (ICR) mice were exposed to a daily dose of 80 mg/kg body weight ( b.w.) Pb(II) nitrate for 14 days and subsequently treated with Sal (16 mg/kg b.w.) or DFP (19 mg/kg b.w.) for another 14 days. At the end of the experimental protocol, the brains were processed for histological and inductively coupled plasma mass spectrometry (ICP-MS) analyses. Pb exposure resulted in a 50-fold increase in Pb concentration, compared with controls. Magnesium (Mg) and phosphorus (P) were also significantly increased by 22.22% and 17.92%, respectively. The histological analysis of Pb-exposed mice revealed brain pathological changes with features of neuronal necrosis. Brain Pb level remained significantly elevated in Sal- and DFP-administered groups (37-fold and 50-fold, respectively), compared with untreated controls. Treatment with Sal significantly reduced Mg and P concentrations by 22.56% and 18.38%, respectively, compared with the Pb-exposed group. Administration of Sal and DFP ameliorated brain injury in Pb-exposed mice and improved histological features. The results suggest the potential application of Sal and DFP for treatment of Pb-induced neurotoxicity.

Lead and Other Trace Element Levels in Brains of Croatian Large Terrestrial Carnivores: Influence of Biological and Ecological Factors

Trace element pollution can adversely affect the brains of individuals and thus impact the entire population of apex predators, such as large European carnivores. We assessed exposure to prominent neurotoxicants As, Cd, Hg and Pb by measuring their brain stem levels in brown bears (n = 114), grey wolves (n = 8), Eurasian lynx (n = 3), and golden jackals (n = 2) sampled in 2015-2022 in Croatia. The highest of the non-essential elements was the Pb level in the bears' brains (median, Q1-Q3; 11.1, 7.13-24.1 μg/kg wet mass), with 4% of animals, all subadults, exceeding the established normal bovine levels (100 μg/kg wet mass). Species-specific differences were noted for Ca, Cd, Cu, Fe, Pb and Se brain levels. Female brown bears had higher As brain levels than males. Cubs and yearlings had lower brain Cd, but higher Zn, while subadults had higher Cu than adult bears. Hepatic As, Cd, Cu and Hg levels were shown to be a moderate proxy for estimating brain levels in bears (r_S = 0.30-0.69). Multiple associations of As, Cd, Hg and Pb with essential elements pointed to a possible interaction and disturbance of brain Ca, Cu, Fe, Se and Zn homeostasis. Non-essential element levels in the brains of four studied species were lower than reported earlier for terrestrial meso-carnivores and humans. The age and sex of animals were highlighted as essential factors in interpreting brain element levels in ecotoxicological studies of large carnivores.

Metabolic and genetic derangement: a review of mechanisms involved in arsenic and lead toxicity and genotoxicity

Urbanisation and industrialisation are on the rise all over the world. Environmental contaminants such as potentially toxic elements (PTEs) are directly linked with both phenomena. Two PTEs that raise greatest concern are arsenic (As) and lead (Pb) as soil and drinking water contaminants, whether they are naturally occurring or the consequence of human activities. Both elements are potential carcinogens. This paper reviews the mechanisms by which As and Pb impair metabolic processes and cause genetic damage in humans. Despite efforts to ban or limit their use, due to high persistence both continue to pose a risk to human health, which justifies the need for further toxicological research.

Alhagi maurorum Ethanolic Extract Rescues Hepato-Neurotoxicity and Neurobehavioral Alterations Induced by Lead in Rats via Abrogating Oxidative Stress and the Caspase-3-Dependent Apoptotic Pathway

This work investigated the probable protective effect of an Alhagi maurorum ethanolic extract on the hepatotoxicity and neurotoxicity accompanied by neurobehavioral deficits caused by lead in rats. Rats in four groups were orally administered distilled water, ethanolic extract of A. maurorum (300 mg/kg BW daily), lead (100 mg/kg BW daily for 3 months), and lead + A. maurorum extract. The results demonstrated that lead exposure resulted in elevated locomotor activities and sensorimotor deficits associated with a decrease in brain dopamine levels. Moreover, lead exposure significantly increased liver function markers. In addition, the lead-treated rats exhibited extensive liver and brain histological changes and apoptosis. The lead treatment also triggered oxidative stress, as demonstrated by the increase in malondialdehyde (MDA) concentrations with a remarkable reduction in the activities of antioxidant enzymes, reduced glutathione (GSH) levels, and transcriptional mRNA levels of antioxidant genes in the liver and brain. Nevertheless, co-treatment with the A. maurorum extract significantly ameliorated the lead-induced toxic effects. These findings indicate that the A. maurorum extract has the ability to protect hepatic and brain tissues against lead exposure in rats through the attenuation of apoptosis and oxidative stress.

The intertwining between lead and ethanol in the model organism Caenorhabditis elegans

Caenorhabditis elegans (C. elegans) is a model organism widely used to evaluate the mechanistic aspects of toxicants with the potential to predict responses comparable to those of mammals. We report here the consequences of developmental lead (Pb) exposure on behavioral responses to ethanol (EtOH) in C. elegans. In addition, we present data on morphological alterations in the dopamine (DA) synapse and DA-dependent behaviors aimed to dissect the neurobiological mechanisms that underlie the relationship between these neurotoxicants. Finally, the escalation to superior animals that parallels the observed effects in both experimental models with references to EtOH metabolism and oxidative stress is also discussed. Overall, the literature revised here underpins the usefulness of C. elegans to evidence behavioral responses to a combination of neurotoxicants in mechanistic-orientated studies.

Comparison between Macro and Trace Element Concentrations in Human Semen and Blood Serum in Highly Polluted Areas in Italy

Macro and trace elements are important regulators of biological processes, including those ones linked to reproduction. Among them, Ca, Cu, Fe, K, Mg, Mn, Na, Se, and Zn ensure normal spermatic functions. Hence, the aim of this study was to evaluate the concentrations of 26 macro and trace elements (Al, As, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Li, Mg, Mn, Na, Ni, Pb, Rb, Sb, Se, Sn, Sr, U, V, and Zn) in blood serum and also in semen of healthy young men, homogeneous for age, anthropometric characteristics, and lifestyle, living in three highly polluted areas in Italy. Furthermore, a comparison among three geographical areas was performed to highlight any difference in the investigated parameters and, overall, to speculate any correlations between chemical elements and semen quality. Statistically significant differences (p < 0.05) among the three areas were found for each investigated element, in both semen and serum samples, where inter-area differences were more evident in semen than in blood serum, suggesting human semen as an early environmental marker. Considering the homogeneity of three cohorts, these differences could be due more to environmental conditions in the recruiting areas, suggesting that variations in those involved in reproductive-associated pathways can have an impact on male fertility. Nevertheless, more research is needed to evaluate threshold values for sperm dysfunction and male infertility. Actually, the role of different dietary intake and environmental exposure underlying the observed differences in the recruiting areas is under further investigation for the same cohort.

From Molecular to Functional Effects of Different Environmental Lead Exposure Paradigms

Simple Summary

Our comparative study brings new insights regarding the effects of environmental lead exposure on the cardiorespiratory and nervous systems. We show how various kinds of exposure can lead to different toxicities, with various degrees of nefarious effects. The developmental period is of utmost importance to the toxicity of environmental lead; however, we found that the duration of exposure is the prime reason for stronger effects, even though the dual effect of intermittent exposure causes greater molecular neuronal alterations.

Abstract

Lead is a heavy metal whose widespread use has resulted in environmental contamination and significant health problems, particularly if the exposure occurs during developmental stages. It is a cumulative toxicant that affects multiple systems of the body, including the cardiovascular and nervous systems. Chronic lead exposure has been defined as a cause of behavioral changes, inflammation, hypertension, and autonomic dysfunction. However, different environmental lead exposure paradigms can occur, and the different effects of these have not been described in a broad comparative study. In the present study, rats of both sexes were exposed to water containing lead acetate (0.2% w/v), from the fetal period until adulthood. Developmental Pb-exposed (DevPb) pups were exposed to lead until 12 weeks of age (n = 13); intermittent Pb exposure (IntPb) pups drank leaded water until 12 weeks of age, tap water until 20 weeks, and leaded water for a second time from 20 to 28 weeks of age (n = 14); and the permanent (PerPb) exposure group were exposed to lead until 28 weeks of age (n = 14). A control group (without exposure, Ctrl), matched in age and sex was used. After exposure protocols, at 28 weeks of age, behavioral tests were performed for assessment of anxiety (elevated plus maze test), locomotor activity (open-field test), and memory (novel object recognition test). Metabolic parameters were evaluated for 24 h, and the acute experiment was carried out. Blood pressure (BP), electrocardiogram, and heart (HR) and respiratory (RF) rates were recorded. Baroreflex gain, chemoreflex sensitivity, and sympathovagal balance were calculated. Immunohistochemistry protocol for NeuN, Syn, Iba-1, and GFAP staining was performed. All Pb-exposed groups showed hypertension, concomitant with a decrease in baroreflex gain and chemoreceptor hypersensitivity, without significant changes in HR and RF. Long-term memory impairment associated with reactive astrogliosis and microgliosis in the dentate gyrus of the hippocampus, indicating the presence of neuroinflammation, was also observed. However, these alterations seemed to reverse after lead abstinence for a certain period (DevPb) and were enhanced when a second exposure occurred (IntPb), along with a synaptic loss. These results suggest that the duration of Pb exposure is more relevant than the timing of exposure, since the PerPb group presented more pronounced effects and a significant increase in the LF and HF bands and anxiety levels. In summary, this is the first study with the characterization and comparison of physiological, autonomic, behavioral, and molecular changes caused by different low-level environmental lead exposures, from the fetal period to adulthood, where the duration of exposure was the main factor for stronger adverse effects. These kinds of studies are of immense importance, showing the importance of the surrounding environment in health from childhood until adulthood, leading to the creation of new policies for toxicant usage control.

Lead (Pb) induced Oxidative Stress as a Mechanism to Cause Neurotoxicity in Drosophila melanogaster

The widespread use of lead (Pb) has caused global contamination, inevitable human exposure, and public health problems. Pb neurotoxicity has been linked to various human diseases, but its associated mechanism causing neurotoxicity is unknown. Drosophila melanogaster as a model organism has been used to study the mechanism involved in Pb-caused neurotoxicity and the potential role of antioxidants in ameliorating its harmful effects. The larval feeding technique was adopted to administer different concentrations of Pb (0.2-0.8 mM) to Oregon-R (ORR), superoxide dismutase (Sod), or catalase (Cat) overexpressing, and Sod or Cat knockdown flies to analyse Pb load, oxidative stress components, DNA damage, apoptosis and vacuolation in the brain. The results revealed that Pb accumulation in the Drosophila brain induces oxidative stress by generating reactive oxygen species (ROS) and lipid peroxidation (LPO), depleting antioxidant enzymes. Molecular docking studies have evidenced it. Pb directly binds to antioxidants and major grooves of DNA, leading to DNA damage. Increased DNA damage, apoptosis, vacuolation in brains of Pb-treated ORR, Sod, or Cat knockdown flies; and on the contrary, reduced oxidative DNA damage, apoptosis, and vacuolation in brains of Pb treated Sod or Cat overexpressed flies put forward that oxidative stress is the mechanism in Pb caused neurotoxicity.