Brain barrier systems: a new frontier in metal neurotoxicological research

The molecular interplay between human and bacterial amyloids: Implications in neurodegenerative diseases

Neurodegenerative disorders such as Parkinson's (PD) and Alzheimer's diseases (AD) are linked with the assembly and accumulation of proteins into structured scaffold called amyloids. These diseases pose significant challenges due to their complex and multifaceted nature. While the primary focus has been on endogenous amyloids, recent evidence suggests that bacterial amyloids may contribute to the development and exacerbation of such disorders. The gut-brain axis is emerging as a communication pathway between bacterial and human amyloids. This review delves into the novel role and potential mechanism of bacterial amyloids in modulating human amyloid formation and the progression of AD and PD.

Imaging gastrointestinal damage due to acute mercury poisoning using a mitochondria-targeted dual near-infrared fluorescent probe

Mercury (Hg) is one of the most widespread pollutants that pose serious threats to public health and the environment. People are inevitably exposed to Hg via different routes, such as respiration, dermal contact, drinking or diet. Hg poisoning could cause gingivitis, inflammation, vomiting and diarrhea, respiratory distress or even death. Especially during the developmental stage, there is considerable harm to the brain development of young children, causing serious symptoms such as intellectual disability and motor impairments, and delayed neural development. Therefore, it's of great significance to develop a specific, quick, practical and labor-saving assay for monitoring Hg2+. Herein, a mitochondria-targeted dual (excitation 700 nm and emission 728 nm) near-infrared (NIR) fluorescent probe JZ-1 was synthesized to detect Hg2+, which is a turn-on fluorescent probe designed based on the rhodamine fluorophore thiolactone, with advantages of swift response, great selectivity, and robust anti-interference capability. Cell fluorescence imaging results showed that JZ-1 could selectively target mitochondria in HeLa cells and monitor exogenous Hg2+. More importantly, JZ-1 has been successfully used to monitor gastrointestinal damage of acute mercury poisoning in a drug-induced mouse model, which provided a great method for sensing Hg species in living subjects, as well as for prenatal diagnosis.

Circadian ABCG2 Expression Influences the Brain Uptake of Donepezil across the Blood-Cerebrospinal Fluid Barrier

Donepezil (DNPZ) is a cholinesterase inhibitor used for the management of Alzheimer's disease (AD) and is dependent on membrane transporters such as ABCG2 to actively cross brain barriers and reach its target site of action in the brain. Located in the brain ventricles, the choroid plexus (CP) forms an interface between the cerebrospinal fluid (CSF) and the bloodstream, known as the blood-CSF barrier (BCSFB). Historically, the BCSFB has received little attention as a potential pathway for drug delivery to the central nervous system (CNS). Nonetheless, this barrier is presently viewed as a dynamic transport interface that limits the traffic of molecules into and out of the CNS through the presence of membrane transporters, with parallel activity with the BBB. The localization and expression of drug transporters in brain barriers represent a huge obstacle for drug delivery to the brain and a major challenge for the development of therapeutic approaches to CNS disorders. The widespread interest in understanding how circadian clocks modulate many processes that define drug delivery in order to predict the variability in drug safety and efficacy is the next bridge to improve effective treatment. In this context, this study aims at characterizing the circadian expression of ABCG2 and DNPZ circadian transport profile using an in vitro model of the BCSFB. We found that ABCG2 displays a circadian pattern and DNPZ is transported in a circadian way across this barrier. This study will strongly impact on the capacity to modulate the BCSFB in order to control the penetration of DNPZ into the brain and improve therapeutic strategies for the treatment of AD according to the time of the day.

The Progress in Molecular Transport and Therapeutic Development in Human Blood-Brain Barrier Models in Neurological Disorders

The blood-brain barrier (BBB) is responsible for maintaining homeostasis within the central nervous system (CNS). Depending on its permeability, certain substances can penetrate the brain, while others are restricted in their passage. Therefore, the knowledge about BBB structure and function is essential for understanding physiological and pathological brain processes. Consequently, the functional models can serve as a key to help reveal this unknown. There are many in vitro models available to study molecular mechanisms that occur in the barrier. Brain endothelial cells grown in culture are commonly used to modeling the BBB. Current BBB platforms include: monolayer platforms, transwell, matrigel, spheroidal, and tissue-on-chip models. In this paper, the BBB structure, molecular characteristic, as well as its dysfunctions as a consequence of aging, neurodegeneration, or under hypoxia and neurotoxic conditions are presented. Furthermore, the current modelling strategies that can be used to study BBB for the purpose of further drugs development that may reach CNS are also described.

What does scientometry tell us about mercury toxicology and its biological impairments?

Mercury is a toxic pollutant that poses risks to both human and environmental health, making it a pressing public health concern. This study aimed to summarize the knowledge on mercury toxicology and the biological impairments caused by exposure to mercury in experimental studies and/or diagnosis in humans. The research was conducted on the main collection of Web of Science, employing as a methodological tool a bibliometric analysis. The selected articles were analyzed, and extracted data such as publication year, journal, author, title, number of citations, corresponding author's country, keywords, and the knowledge mapping was performed about the type of study, chemical form of mercury, exposure period, origin of exposure, tissue/fluid of exposure measurement, mercury concentration, evaluation period (age), mercury effect, model experiments, dose, exposure pathway, and time of exposure. The selected articles were published between 1965 and 2021, with Clarkson TW being the most cited author who has also published the most articles. A total of 38% of the publications were from the USA. These studies assessed the prenatal and postnatal effects of mercury, emphasizing the impact of methylmercury on neurodevelopment, including motor and cognitive evaluations, the association between mercury and autism, and an evaluation of its protective effects against mercury toxicity. In observational studies, the blood, umbilical cord, and hair were the most frequently used for measuring mercury levels. Our data analysis reveals that mercury neurotoxicology has been extensively explored, but the association among the outcomes evaluated in experimental studies has yet to be strengthened. Providing metric evidence on what is unexplored allows for new studies that may help governmental and non-governmental organizations develop guidelines and policies.

Association between multiple sclerosis and urinary levels of toxic metals and organophosphates: A cross-sectional study in Israel

BACKGROUND

Multiple sclerosis (MS) is a multifactorial disease of uncertain etiology damaging myelin sheaths around axons of the central nervous system. Myelin protects the axon from potentially harmful exogenous factors. The aetiological role of environmental exposure metals and organophosphates is unclear.

OBJECTIVE

Identify whether urinary levels of metals and organophosphates differed in MS patients and controls.

METHODS

We recruited MS patients from Ziv Medical Centre and healthy controls. MS patients were evaluated according to Expanded Disability Status Scale into mild and moderate-severe conditions. Each participant provided a urine sample and completed epidemiological questionnaires. The levels of six metal (Aluminum, Cadmium, Chromium, Lead, Mercury, Nickel) and one metalloid (Arsenic) and common organophosphates pesticide metabolites (6 dialkylphosphates, DAP) were measured in urine using inductively coupled plasma-mass spectrometry and gas-chromatography mass-spectrometry. We compared cases with controls in terms of urinary levels of these compounds using Mann-Whitney and Kruskall-Wallis tests.

RESULTS

Urinary cadmium and mercury levels were higher in the 49 MS patients than the 37 controls (p < 0.01). Cadmium levels were higher in moderate-severe MS patients (n = 24) than mild MS patients (n = 25) (p = 0.003).

CONCLUSION

Urinary cadmium and mercury levels were higher among MS patients than controls. Cadmium levels correlated with disease severity. Further studies are needed to explore potential causal pathways between these compounds and MS pathogenesis.

Mendelian randomization reveals apolipoprotein B shortens healthspan and possibly increases risk for Alzheimer's disease

Apolipoprotein B-100 (APOB) is a component of fat- and cholesterol-transporting molecules in the bloodstream. It is the main lipoprotein in low-density lipoprotein cholesterol (LDL) and has been implicated in conditions that end healthspan (the interval between birth and onset of chronic disease). However, APOB's direct relationship with healthspan remains uncertain. With Mendelian randomization, we show that higher levels of APOB and LDL shorten healthspan in humans. Multivariable Mendelian randomization of APOB and LDL on healthspan suggests that the predominant trait accounting for the relationship is APOB. In addition, we provide preliminary evidence that APOB increases risk for Alzheimer's disease, a condition that ends healthspan. If these relationships are causal, they suggest that interventions to improve healthspan in aging populations could include strategies targeting APOB. Ultimately, given that more than 44 million people currently suffer from Alzheimer's disease worldwide, such interventions are needed.

Vulnerability of the Hippocampus to Insults: Links to Blood-Brain Barrier Dysfunction

The hippocampus is a critical brain substrate for learning and memory; events that harm the hippocampus can seriously impair mental and behavioral functioning. Hippocampal pathophysiologies have been identified as potential causes and effects of a remarkably diverse array of medical diseases, psychological disorders, and environmental sources of damage. It may be that the hippocampus is more vulnerable than other brain areas to insults that are related to these conditions. One purpose of this review is to assess the vulnerability of the hippocampus to the most prevalent types of insults in multiple biomedical domains (i.e., neuroactive pathogens, neurotoxins, neurological conditions, trauma, aging, neurodegenerative disease, acquired brain injury, mental health conditions, endocrine disorders, developmental disabilities, nutrition) and to evaluate whether these insults affect the hippocampus first and more prominently compared to other brain loci. A second purpose is to consider the role of hippocampal blood-brain barrier (BBB) breakdown in either causing or worsening the harmful effects of each insult. Recent research suggests that the hippocampal BBB is more fragile compared to other brain areas and may also be more prone to the disruption of the transport mechanisms that act to maintain the internal milieu. Moreover, a compromised BBB could be a factor that is common to many different types of insults. Our analysis indicates that the hippocampus is more vulnerable to insults compared to other parts of the brain, and that developing interventions that protect the hippocampal BBB may help to prevent or ameliorate the harmful effects of many insults on memory and cognition.

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.

Impairments of Spatial Memory and N-methyl-d-aspartate Receptors and Their Postsynaptic Signaling Molecules in the Hippocampus of Developing Rats Induced by As, Pb, and Mn Mixture Exposure

Exposure to metal mixtures is recognized as a real-life scenario, needing novel studies that can assess their complex effects on brain development. There is still a significant public health concern associated with chronic low levels of metal exposure. In contrast to other metals, these three metals (As, Pb, and Mn) are commonly found in various environmental and industrial contexts. In addition to additive or synergistic interactions, concurrent exposure to this metal mixture may also have neurotoxic effects that differ from those caused by exposure to single components. The NMDA receptor and several important signaling proteins are involved in learning, memory, and synaptic plasticity in the hippocampus, including CaMKII, postsynaptic density protein-95 (PSD-95), synaptic Ras GTPase activating protein (SynGAP), a negative regulator of Ras-MAPK activity, and CREB. We hypothesized that alterations in the above molecular players may contribute to metal mixture developmental neurotoxicity. Thus, the aim of this study was to investigate the effect of these metals and their mixture at low doses (As 4 mg, Pb 4 mg, and Mn 10 mg/kg bw/p.o) on NMDA receptors and their postsynaptic signaling proteins during developing periods (GD6 to PD59) of the rat brain. Rats exposed to As, Pb, and Mn individually or at the same doses in a triple-metal mixture (MM) showed impairments in learning and memory functions in comparison to the control group rats. Declined protein expressions of NR2A, PSD-95, p- CaMKII, and pCREB were observed in the metal mix-exposed rats, while the expression of SynGAP was found to be enhanced in the hippocampus as compared to the controls on PD60. Thereby, our data suggest that alterations in the NMDA receptor complex and postsynaptic signaling proteins could explain the cognitive dysfunctions caused by metal-mixture-induced developmental neurotoxicity in rats. These outcomes indicate that incessant metal mixture exposure may have detrimental consequences on brain development.

Evaluating Manganese, Zinc, and Copper Metal Toxicity on SH-SY5Y Cells in Establishing an Idiopathic Parkinson's Disease Model

Parkinson's disease (PD) is a neurodegenerative condition marked by loss of motor coordination and cognitive impairment. According to global estimates, the worldwide prevalence of PD will likely exceed 12 million cases by 2040. PD is primarily associated with genetic factors, while clinically, cases are attributed to idiopathic factors such as environmental or occupational exposure. The heavy metals linked to PD and other neurodegenerative disorders include copper, manganese, and zinc. Chronic exposure to metals induces elevated oxidative stress and disrupts homeostasis, resulting in neuronal death. These metals are suggested to induce idiopathic PD in the literature. This study measures the effects of lethal concentration at 10% cell death (LC10) and lethal concentration at 50% cell death (LC50) concentrations of copper, manganese, and zinc chlorides on SH-SY5Y cells via markers for dopamine, reactive oxygen species (ROS) generation, DNA damage, and mitochondrial dysfunction after a 24 h exposure. These measurements were compared to a known neurotoxin to induce PD, 100 µM 6-hydroxydopamine (6-ODHA). Between the three metal chlorides, zinc was statistically different in all parameters from all other treatments and induced significant dopaminergic loss, DNA damage, and mitochondrial dysfunction. The LC50 of manganese and copper had the most similar response to 6-ODHA in all parameters, while LC10 of manganese and copper responded most like untreated cells. This study suggests that these metal chlorides respond differently from 6-ODHA and each other, suggesting that idiopathic PD utilizes a different mechanism from the classic PD model.

Chronic Pb Exposure Induces Anxiety and Depression-like Behaviors in Mice via Excitatory Neuronal Hyperexcitability in Ventral Hippocampal Dentate Gyrus

Lead (Pb) is a widespread neurotoxic pollutant. Pb exposure is associated with mood disorders, with no well-established neural mechanisms elucidated. In the present study, we aimed to investigate whether excitatory neurons in the dentate gyrus subregion of the ventral hippocampus (vDG) played a key role in Pb-induced anxiety and depression-like behaviors. C57BL/6 mice were exposed to 100 ppm Pb starting on day 1 of pregnancy until experiments were performed using the offspring. Behavioral studies suggested that chronic Pb exposure triggered anxiety and depression-like behaviors. A combination of electrophysiological, optogenetic, and immunohistochemistry experiments was conducted. Results showed that Pb exposure resulted in excitatory neuronal hyperexcitability in vDG and that the behavioral deficits caused by Pb exposure could be rescued by inhibition of excitatory neuronal activity. Moreover, it was found that the action potential (AP) threshold of excitatory neurons was decreased by electrophysiological recordings. Our study demonstrates a significant role for excitatory neurons in vDG in Pb-induced anxiety and depression-like behaviors in mice, which is likely a result of decreased AP threshold. These outcomes can serve as an important basis for understanding mechanisms of anxiety and depression under environmental Pb exposure and help in the design of therapeutic strategies.

Distribution of Iron, Copper, Zinc and Cadmium in Glia, Their Influence on Glial Cells and Relationship with Neurodegenerative Diseases

Recent data on the distribution and influence of copper, zinc and cadmium in glial cells are summarized. This review also examines the relationship between those metals and their role in neurodegenerative diseases like Alzheimer disease, multiple sclerosis, Parkinson disease and Amyotrophic lateral sclerosis, which have become a great challenge for today's physicians. The studies suggest that among glial cells, iron has the highest concentration in oligodendrocytes, copper in astrocytes and zinc in the glia of hippocampus and cortex. Previous studies have shown neurotoxic effects of copper, iron and manganese, while zinc can have a bidirectional effect, i.e., neurotoxic but also neuroprotective effects depending on the dose and disease state. Recent data point to the association of metals with neurodegeneration through their role in the modulation of protein aggregation. Metals can accumulate in the brain with aging and may be associated with age-related diseases.

High affinity of β-amyloid proteins to cerebral capillaries: implications in chronic lead exposure-induced neurotoxicity in rats

Lead (Pb) is a known environmental risk factor in the etiology of Alzheimer's disease (AD). The existing reports suggest that Pb exposure increases beta-amyloid (Aβ) levels in brain tissues and cerebrospinal fluid (CSF) and facilitates the formation of amyloid plaques, which is a pathological hallmark for AD. Pb exposure has long been associated with cerebral vasculature injury. Yet it remained unclear if Pb exposure caused excessive Ab buildup in cerebral vasculature, which may damage the blood-brain barrier and cause abnormal Ab accumulation. This study was designed to investigate the impact of chronic Pb exposure on Aβ accumulation in cerebral capillary and the expression of low-density lipoprotein receptor protein-1 (LRP1), a critical Aβ transporter, in brain capillary and parenchyma. Sprague-Dawley rats received daily oral gavage at doses of 0, 14 (low-dose), and 27 (high-dose) mg Pb/kg as Pb acetate, 5 d/wk, for 4 or 8 wks. At the end of Pb exposure, a solution containing Aβ40 was infused into the brain via the cannulated internal carotid artery. Data by ELISA showed a strikingly high affinity of Ab to cerebral vasculature, which was approximately 7-14 times higher than that to the parenchymal fractions collected from control brains. Pb exposure further aggravated the Aβ accumulation in cerebral vasculature in a dose-dependent manner. Western blot analyses revealed that Pb exposure decreased LRP1 expression in cortical capillaries and hippocampal parenchyma. Immunohistochemistry (IHC) studies further revealed a disrupted distribution of LRP1 alongside hippocampal vasculature accompanied with a decreased expression in hippocampal neurons by Pb exposure. Taken together, the current study demonstrated that the cerebral vasculature naturally possessed a high affinity to Aβ present in circulating blood. Pb exposure significantly increased Aβ accumulation in cerebral vasculature; such an increased Aβ accumulation was due partly to the diminished expression of LRP1 in response to Pb in tested brain regions. Perceivably, Pb-facilitated Ab aggravation in cerebral vasculature may contribute to Pb-associated amyloid alterations.

Insufficient evidence to link human exposure to heavy metals with biomarkers of glioma

Information on molecular mechanisms has implicated potential association between the concentrations of heavy metals and incidences of glioma, but experimental data on human brain tissue remain sparse. To address this data gap, 13 heavy metals were measured in 137 glioma and 35 non-glioma samples collected from 161 alive patients in Guangdong Province, China in 2019 - 2020. All target heavy metals were detected, suggesting they could cross the blood-brain barrier. Concentrations of Mn, Cu, and Zn were higher in glioma than in non-glioma samples, while those of Ni and Se were higher in non-glioma samples, probably suggesting that these five heavy metals are more prone to be altered by changing pathological conditions. In addition, Cu/Zn, Cr/Mn, Cr/Se, Ni/Se, Pb/Mn, and Pb/Se were statistically different between glioma and non-glioma samples by a difference test and a multiple logistic regression model. These concentration ratios may serve as chemical markers to assist pathological analysis for differentiating between tumor and healthy tissues. However, no direct link between heavy metal concentrations or concentration ratios and biomarkers of glioma (i.e., tumor grade, P53, and Ki-67) was observed. No sufficient evidence was obtained to implicate the role of heavy metals in inducing glioma, largely caused by the limited number of samples. Different concentrations and concentration ratios of heavy metals may be the consequence rather than the cause of pathological changes in brain tumors.

Metal concentrations in cerebrospinal fluid, blood, serum, plasma, hair, and nails in amyotrophic lateral sclerosis: A systematic review and meta-analysis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease with progressive muscle wasting, paralysis, and respiratory failure. Whereas approximately 10-15 % of ALS cases are familial, the etiology of the remaining, sporadic ALS cases remains largely unknown. Environmental exposures have been suggested as causative factors for decades, and previous studies have found elevated concentrations of metals in ALS patients.

PURPOSE

This meta-analysis aims to assess metal concentrations in body fluids and tissues of ALS patients.

METHODS

We searched the MEDLINE and EMBASE databases on December 7th, 2022 for cross-sectional, case-control, and cohort studies which measure metal concentrations in whole blood, blood plasma, blood serum, cerebrospinal fluid (CSF), urine, erythrocytes, nail, and hair samples of ALS patients. Meta-analysis was then performed when three or more articles existed for a comparison.

FINDINGS

Twenty-nine studies measuring 23 metals were included and 13 meta-analyses were performed from 4234 screened entries. The meta-analysis results showed elevated concentrations of lead and selenium. Lead, measured in whole blood in 6 studies, was significantly elevated by 2.88 µg/L (95 % CI: 0.83-4.93, p = 0.006) and lead, measured in CSF in 4 studies, was significantly elevated by 0.21 µg/L (95 % CI: 0.01 - 0.41, p = 0.04) in ALS patients when compared to controls. Selenium, measured in serum/plasma in 4 studies, was significantly elevated by 4.26 µg/L (95% CI: 0.73 - 7.79, p = 0.02) when compared to controls.Analyses of other metal concentrations showed no statistically significant difference between the groups.

CONCLUSION

Lead has been discussed as a possible causative agent in ALS since 1850. Lead has been found in the spinal cord of ALS patients, and occupational exposure to lead is more common in ALS patients than in controls. Selenium in the form of neurotoxic selenite has been shown to geochemically correlate to ALS occurrence in Italy. Although no causal relationship can be established from the results of this meta-analysis, the findings suggest an involvement of lead and selenium in the pathophysiology of ALS. After a thorough meta-analysis of published studies on metal concentrations in ALS it can only be concluded that lead and selenium are elevated in ALS.

Metal ratios as possible biomarkers for amyotrophic lateral sclerosis

BACKGROUND AND OBJECTIVES

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease with unknown aetiology. Metals have been suspected to contribute to ALS pathogenesis since mid-19th century, yet studies on measured metal concentrations in ALS patients have often yielded conflicting results, with large individual variation in measured values. Calculating metal concentration ratios can unveil possible synergistic effects of neurotoxic metals in ALS pathogenesis. The aim of this study was to investigate if ratios of different metal concentrations in cerebrospinal fluid (CSF) and blood plasma, respectively, differ between ALS patients and healthy controls.

METHODS

Cerebrospinal fluid and blood plasma were collected from 17 ALS patients and 10 controls. Samples were analysed for 22 metals by high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS), and all possible 231 metal ratios calculated in each body fluid.

RESULTS

Fifty-three metal ratios were significantly elevated in ALS cases as compared to controls (p < 0.05); five in blood plasma, and 48 in CSF. The finding of fewer elevated ratios in blood plasma may indicate specific transport of metals into the central nervous system. The elevated metal ratios in CSF include Cd/Se (p = 0.031), and 16 ratios with magnesium, such as Mn/Mg (p = 0.005) and Al/Mg (p = 0.014).

CONCLUSION

Metal ratios may be used as biomarkers in ALS diagnosis and as guidelines for preventive measures.

Among Gerontogens, Heavy Metals Are a Class of Their Own: A Review of the Evidence for Cellular Senescence

Advancements in modern medicine have improved the quality of life across the globe and increased the average lifespan of our population by multiple decades. Current estimates predict by 2030, 12% of the global population will reach a geriatric age and live another 3-4 decades. This swelling geriatric population will place critical stress on healthcare infrastructures due to accompanying increases in age-related diseases and comorbidities. While much research focused on long-lived individuals seeks to answer questions regarding how to age healthier, there is a deficit in research investigating what aspects of our lives accelerate or exacerbate aging. In particular, heavy metals are recognized as a significant threat to human health with links to a plethora of age-related diseases, and have widespread human exposures from occupational, medical, or environmental settings. We believe heavy metals ought to be classified as a class of gerontogens (i.e., chemicals that accelerate biological aging in cells and tissues). Gerontogens may be best studied through their effects on the "Hallmarks of Aging", nine physiological hallmarks demonstrated to occur in aged cells, tissues, and bodies. Evidence suggests that cellular senescence-a permanent growth arrest in cells-is one of the most pertinent hallmarks of aging and is a useful indicator of aging in tissues. Here, we discuss the roles of heavy metals in brain aging. We briefly discuss brain aging in general, then expand upon observations for heavy metals contributing to age-related neurodegenerative disorders. We particularly emphasize the roles and observations of cellular senescence in neurodegenerative diseases. Finally, we discuss the observations for heavy metals inducing cellular senescence. The glaring lack of knowledge about gerontogens and gerontogenic mechanisms necessitates greater research in the field, especially in the context of the global aging crisis.

Pb induces ferroptosis in choroid plexus epithelial cells via Fe metabolism

Pb can enhance blood-cerebrospinal fluid barrier (BCSFB) permeability and accumulate in brain tissue, leading to central nervous system (CNS) dysfunction. Choroid plexus (CP) epithelial cells are the main components of the BCSFB with crucial functions in BCSFB maintenance. However, the mechanism by which Pb exposure affects CP epithelial cells remains unclear. Here, ferroptosis was identified as the major programmed cell death modality by sophisticated high-throughput sequencing and biochemical investigations in primary cultured CP epithelial cells following Pb exposure. Bioinformatics analysis using the ferroptosis database revealed that 16 ferroptosis-related genes were differentially expressed in primary cultured CP epithelial cells following Pb exposure. Among them, Gpx4, Slc7a11, Tfrc, and Slc40a1 were hub ferroptosis-related genes. In addition, CP epithelial cells can be impaired when the concentration of the Pb²⁺ reached 2050 μg/L (10 μM PbAc), which included the decrease of cell viability, Gpx4 and Slc7a11 proteins expression, etc. Moreover, inhibition of ferroptosis enhanced CP epithelial cell viability and reduced BCSFB permeability in vitro following Pb exposure. In summary, ferroptosis of CP epithelial cells is involved in BCSFB dysfunction following Pb exposure. Gpx4, Slc7a11, Tfrc, and Slc40a1 are hub ferroptosis-related genes in CP epithelial cells.

Toxic and carcinogenic effects of hexavalent chromium in mammalian cells in vivo and in vitro: a recent update

Chromium VI (Cr (VI)) can cross cell membranes readily and causes the formation of Cr-DNA adducts, genomic damages, elevation of reactive oxygen species (ROS) and alteration of survival signaling pathways, as evidenced by the modulation in p53 signaling pathway. Mammals, including humans are exposed to Cr, including Cr (VI), frequently through inhalation, drinking water, and food. Several studies demonstrated that Cr (VI) induces cellular death through apoptosis and autophagy, genotoxicity, functional alteration of mitochondria, endocrine and reproductive impairments. In the present review, studies on deleterious effects of Cr (VI) exposure to mammalian cells (in vivo and in vitro) have been documented. Special attention is paid to the underlying molecular mechanism of Cr (VI) toxicity.

Metal Profiles in Autism Spectrum Disorders: A Crosstalk between Toxic and Essential Metals

Since hundreds of years ago, metals have been recognized as impacting our body's physiology. As a result, they have been studied as a potential cure for many ailments as well as a cause of acute or chronic poisoning. However, the link between aberrant metal levels and neuropsychiatric illnesses such as schizophrenia and neurodevelopmental disorders, such as autism spectrum disorders (ASDs), is a relatively new finding, despite some evident ASD-related consequences of shortage or excess of specific metals. In this review, we will summarize past and current results explaining the pathomechanisms of toxic metals at the cellular and molecular levels that are still not fully understood. While toxic metals may interfere with dozens of physiological processes concurrently, we will focus on ASD-relevant activity such as inflammation/immune activation, mitochondrial malfunction, increased oxidative stress, impairment of axonal myelination, and synapse formation and function. In particular, we will highlight the competition with essential metals that may explain why both the presence of certain toxic metals and the absence of certain essential metals have emerged as risk factors for ASD. Although often investigated separately, through the agonistic and antagonistic effects of metals, a common metal imbalance may result in relation to ASD.

Alzheimer's Disease: Treatment Strategies and Their Limitations

Alzheimer's disease (AD) is the most frequent case of neurodegenerative disease and is becoming a major public health problem all over the world. Many therapeutic strategies have been explored for several decades; however, there is still no curative treatment, and the priority remains prevention. In this review, we present an update on the clinical and physiological phase of the AD spectrum, modifiable and non-modifiable risk factors for AD treatment with a focus on prevention strategies, then research models used in AD, followed by a discussion of treatment limitations. The prevention methods can significantly slow AD evolution and are currently the best strategy possible before the advanced stages of the disease. Indeed, current drug treatments have only symptomatic effects, and disease-modifying treatments are not yet available. Drug delivery to the central nervous system remains a complex process and represents a challenge for developing therapeutic and preventive strategies. Studies are underway to test new techniques to facilitate the bioavailability of molecules to the brain. After a deep study of the literature, we find the use of soft nanoparticles, in particular nanoliposomes and exosomes, as an innovative approach for preventive and therapeutic strategies in reducing the risk of AD and solving problems of brain bioavailability. Studies show the promising role of nanoliposomes and exosomes as smart drug delivery systems able to penetrate the blood-brain barrier and target brain tissues. Finally, the different drug administration techniques for neurological disorders are discussed. One of the promising therapeutic methods is the intranasal administration strategy which should be used for preclinical and clinical studies of neurodegenerative diseases.

Sensing of mercury ion using light induced aqueous leaf extract mediated green synthesized silver nanoparticles of Cestrum nocturnum L

In this study, a simple, one-pot, and eco-friendly biosynthesis of silver nanoparticles (AgNPs) was accomplished with the use of aqueous leaves extract of Cestrum nocturnum L.(AECN). Different techniques like ultraviolet-visible (UV-Vis) spectrophotometry, Fourier transform infrared (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning area electron diffraction were used to investigate the optical, operational, and physical properties of the green synthesized AECN-AgNPs.The AECN-AgNPs were further used for the detection of Hg²⁺ by UV-Vis and electrochemical methods. The disintegration of the AECN-AgNPs solution caused the formation of an Ag-Hg amalgam, which caused discoloration of the solution. Sensing performance for a variety of metals such as Na⁺, K⁺, Mg²⁺, Ca²⁺, Ni²⁺, Cu ²⁺, Fe³⁺, Zn²⁺, Co²⁺, Cd²⁺, Pb²⁺, As³⁺, and Mn²⁺ at 10-mM concentrations was measured in order to determine the selectivity of the sensor towards the Hg²⁺. For the electrochemical determination of 2 + Hg²⁺ , AECN-AgNPs were immobilized on a glassy carbon (GC) electrode, and the resulting modified electrode (GC/AECN-AgNPs) was characterized by cyclic voltammetry. This phenomenon is advantageously used for the sensitive determination of trace level Hg²⁺. GC/AECN-AgNPs demonstrated a linear calibration range of 100 nM to 10 μM and a limit of detection of 21 nM for Hg²⁺ determination.

Nanomedicine in the Face of Parkinson's Disease: From Drug Delivery Systems to Nanozymes

The complexity and overall burden of Parkinson's disease (PD) require new pharmacological approaches to counteract the symptomatology while reducing the progressive neurodegeneration of affected dopaminergic neurons. Since the pathophysiological signature of PD is characterized by the loss of physiological levels of dopamine (DA) and the misfolding and aggregation of the alpha-synuclein (α-syn) protein, new proposals seek to restore the lost DA and inhibit the progressive damage derived from pathological α-syn and its impact in terms of oxidative stress. In this line, nanomedicine (the medical application of nanotechnology) has achieved significant advances in the development of nanocarriers capable of transporting and delivering basal state DA in a controlled manner in the tissues of interest, as well as highly selective catalytic nanostructures with enzyme-like properties for the elimination of reactive oxygen species (responsible for oxidative stress) and the proteolysis of misfolded proteins. Although some of these proposals remain in their early stages, the deepening of our knowledge concerning the pathological processes of PD and the advances in nanomedicine could endow for the development of potential treatments for this still incurable condition. Therefore, in this paper, we offer: (i) a brief summary of the most recent findings concerning the physiology of motor regulation and (ii) the molecular neuropathological processes associated with PD, together with (iii) a recapitulation of the current progress in controlled DA release by nanocarriers and (iv) the design of nanozymes, catalytic nanostructures with oxidoreductase-, chaperon, and protease-like properties. Finally, we conclude by describing the prospects and knowledge gaps to overcome and consider as research into nanotherapies for PD continues, especially when clinical translations take place.

The development and function of the brain barriers - an overlooked consideration for chemical toxicity

It is well known that the adult brain is protected from some infections and toxic molecules by the blood-brain and the blood-cerebrospinal fluid barriers. Contrary to the immense data collected in other fields, it is deeply entrenched in environmental toxicology that xenobiotics easily permeate the developing brain because these barriers are either absent or non-functional in the fetus and newborn. Here we review the cellular and physiological makeup of the brain barrier systems in multiple species, and discuss decades of experiments that show they possess functionality during embryogenesis. We next present case studies of two chemical classes, perfluoroalkyl substances (PFAS) and bisphenols, and discuss their potential to bypass the brain barriers. While there is evidence to suggest these pollutants may enter the developing and/or adult brain parenchyma, many studies suffer from confounding technical variables which complicates data interpretation. In the future, a more formal consideration of brain barrier biology could not only improve understanding of chemical toxicokinetics but could assist in prioritizing environmental xenobiotics for their neurotoxicity risk.

Prenatal Co-Exposure to Manganese, Mercury, and Lead, and Neurodevelopment in Children during the First Year of Life

Lead (Pb), mercury (Hg), and manganese (Mn) are neurotoxic, but little is known about the neurodevelopmental effects associated with simultaneous prenatal exposure to these metals. We aimed to study the associations of Pb, Hg, and Mn prenatal levels (jointly and separately) with neurodevelopment in the first year of life. Methods: Pb, Hg, and Mn blood lead levels were measured in 253 pregnant women. Their offspring's neurodevelopment was assessed through the Bayley Scale of Infant Development III^® at one, three, six, and twelve months. The metals' mean blood levels (µg/L) were Pb = 11.2, Hg = 2.1, and Mn = 10.2. Mean language, cognitive, and motor development scores of the infants at each age were between low-average and average. Multilevel models' results showed that language development coefficients of the offspring decreased by 1.5 points per 1 µg/dL increase in maternal blood lead levels (p = 0.002); the magnitude of the aforementioned association increased in children with maternal blood Mn < 9.6 µg/L (ß = -1.9, p = 0.003) or Hg > 1.9 µg/L (ß = -1.6, p = 0.013). Cognitive and motor development had negative associations with maternal blood Pb levels; the latter was statistically significant when the interaction term between Pb, Mn, and Hg was included (ß = -0.037, p = 0.03). Prenatal exposure to low Pb levels may impair infants' neurodevelopment in the first year of life, even more so if they are exposed to Hg or deficient in Mn.

Geochemistry of multiple sclerosis in Finland

Multiple sclerosis (MS) affects some 3 million people around the world and the prevalence is increasing. The MS incidence increases with distance from the equator forming a north-to-south gradient. The cause of this gradient and the cause of MS in general are largely unknown. Sulphide-bearing marine and lake sediments, when exposed to oxygen after drainage, form sulphuric acid resulting in the development of acid sulphate soils. From these soils major neurotoxic metals such as iron, aluminum and manganese and trace metals such as nickel, copper and cadmium are released into the surrounding environment. As these soils are largely used for farming, obvious routes to human metal exposure exist. Here we compare the distribution of acid sulphate soils in Finland to the geographic localisation of MS cases using data from a national acid sulphate soil mapping project and historical MS distribution data. Finland has among the highest MS prevalences in the world and several independent nationwide surveys have shown the highest prevalence in western Finland, stable over time. Acid sulphate soil distribution colocalizes with MS, both on a regional (nationwide) scale and local (proximity to rivers) scale. A toxicokinetic LADME model for MS pathogenesis is presented. We propose that neurotoxic metals leaching from acid sulphate soils contribute to the clustering of MS in Finland.

Neurodegenerative Diseases: Implications of Environmental and Climatic Influences on Neurotransmitters and Neuronal Hormones Activities

Neurodegenerative and neuronal-related diseases are major public health concerns. Human vulnerability to neurodegenerative diseases (NDDs) increases with age. Neuronal hormones and neurotransmitters are major determinant factors regulating brain structure and functions. The implications of environmental and climatic changes emerged recently as influence factors on numerous diseases. However, the complex interaction of neurotransmitters and neuronal hormones and their depletion under environmental and climatic influences on NDDs are not well established in the literature. In this review, we aim to explore the connection between the environmental and climatic factors to NDDs and to highlight the available and potential therapeutic interventions that could use to improve the quality of life and reduce susceptibility to NDDs.

Excited-State Intramolecular Hydrogen Transfer of Compact Molecules Controls Amyloid Aggregation Profiles

Developing chemical methodologies to directly modify harmful biomolecules affords the mitigation of their toxicity by persistent changes in their properties and structures. Here we report compact photosensitizers composed of the anthraquinone (AQ) backbone that undergo excited-state intramolecular hydrogen transfer, effectively oxidize amyloidogenic peptides, and, subsequently, alter their aggregation pathways. Density functional theory calculations showed that the appropriate position of the hydroxyl groups in the AQ backbone and the consequent intramolecular hydrogen transfer can facilitate the energy transfer to triplet oxygen. Biochemical and biophysical investigations confirmed that these photoactive chemical reagents can oxidatively vary both metal-free amyloid-β (Aβ) and metal-bound Aβ, thereby redirecting their on-pathway aggregation into off-pathway as well as disassembling their preformed aggregates. Moreover, the in vivo histochemical analysis of Aβ species produced upon photoactivation of the most promising candidate demonstrated that they do not aggregate into oligomeric or fibrillar aggregates in the brain. Overall, our combined computational and experimental studies validate a light-based approach for designing small molecules, with minimum structural complexity, as chemical reagents targeting and controlling amyloidogenic peptides associated with neurodegenerative disorders.

Phytochemical: a treatment option for heavy metal induced neurotoxicity

Heavy metals are known to be carcinogenic, mutagenic, and teratogenic. Some heavy metals are necessary while present in the growing medium in moderate concentrations known to be essential heavy metals as they required for the body functioning as a nutrient. But there are some unwanted metals and are also toxic to the environment and create a harmful impact on the body, which termed to be non-essential heavy metals. Upon exposure, the heavy metals decrease the major antioxidants of cells and enzymes with the thiol group and affect cell division, proliferation, and apoptosis. It interacts with the DNA repair mechanism and initiates the production of reactive oxygen species (ROS). It subsequently binds to the mitochondria and may inhibit respiratory and oxidative phosphorylation in even low concentrations. This mechanism leads to damage antioxidant repair mechanism of neuronal cells and turns into neurotoxicity. Now, phytochemicals have led to good practices in the health system. Phytochemicals that are present in the fruits and herbs can preserve upon free radical damage. Thus, this review paper summarized various phytochemicals which can be utilized as a treatment option to reverse the effect of the toxicity caused by the ingestion of heavy metals in our body through various environmental or lifestyles ways.

In Vitro Models of the Blood–Cerebrospinal Fluid Barrier and Their Applications in the Development and Research of (Neuro)Pharmaceuticals

The pharmaceutical research sector has been facing the challenge of neurotherapeutics development and its inherited high-risk and high-failure-rate nature for decades. This hurdle is partly attributable to the presence of brain barriers, considered both as obstacles and opportunities for the entry of drug substances. The blood–cerebrospinal fluid (CSF) barrier (BCSFB), an under-studied brain barrier site compared to the blood–brain barrier (BBB), can be considered a potential therapeutic target to improve the delivery of CNS therapeutics and provide brain protection measures. Therefore, leveraging robust and authentic in vitro models of the BCSFB can diminish the time and effort spent on unproductive or redundant development activities by a preliminary assessment of the desired physiochemical behavior of an agent toward this barrier. To this end, the current review summarizes the efforts and progresses made to this research area with a notable focus on the attribution of these models and applied techniques to the pharmaceutical sector and the development of neuropharmacological therapeutics and diagnostics. A survey of available in vitro models, with their advantages and limitations and cell lines in hand will be provided, followed by highlighting the potential applications of such models in the (neuro)therapeutics discovery and development pipelines.

Influence of heavy metals in Parkinson's disease: an overview

Parkinson's disease (PD) is an ageing disorder with deterioration of dopamine neurons which leads to motor complications like tremor, stiffness, slow movement and postural disturbances. In PD, both genetics as well as environmental factors both play a major role in causing the pathogenesis. Though there are surfeit of risk factors involved in PD occurrence, till now there is lack of an exact causative agent as a risk for PD with confirmative findings. The role of heavy metals reported to be a significant factor in PD pathogenesis. Heavy metal functions in cell maintenance but growing pieces of evidences reported to cause dyshomeostasis with increased PD rate. Metals disturb the molecular processes and results in oxidative stress, DNA damage, mitochondrial dysfunction, and apoptosis. The present review elucidates the role of cobalt, nickel, mercury, chromium, thallium metals in α-synuclein aggregation and its involvement in blood brain barrier flux. Also, the review explains the plausible role of aforementioned metals with a mechanistic approach and therapeutic recommendations in PD.

D-Ribose-LCysteine attenuates manganese-induced cognitive and motor deficit, oxidative damage, and reactive microglia activation

Due to overexposure, manganese (Mn) accumulation in the brain can trigger the inhibition of glutathione synthesis and lead to increased generation of reactive oxygen species (ROS) and oxidative stress. D-Ribose-L-Cysteine (RibCys) has been demonstrated to effectively support glutathione synthesis to scavenge ROS and protect cells from oxidative damage. In the present study, we examined the effects of RibCys on weight changes, cognitive and motor associated activities, oxidative stress markers, striatal and cortical histology, and microglia activation following Mn exposure. Rats were exposed to either saline, Mn or/and RibCys for two weeks. The Mn exposed rats received RibCys either as pre-, co-, or post-treatments. Mn caused a significant decrease in weight, memory and motor activities, increased lactate dehydrogenase level, overexpression of IBA1 reflecting microglia activation, and distortion of the neuronal cytoarchitecture of the striatum and motor cortex, respectively. Interventions with RibCys mitigated Mn-induced neurotoxic events. Our novel study demonstrates that RibCys effectively ameliorates the neurotoxicity following Mn treatment and maybe a therapeutic strategy against the neurological consequences of Mn overexposurec.

Cerebral Iron Deposition in Neurodegeneration

Disruption of cerebral iron regulation appears to have a role in aging and in the pathogenesis of various neurodegenerative disorders. Possible unfavorable impacts of iron accumulation include reactive oxygen species generation, induction of ferroptosis, and acceleration of inflammatory changes. Whole-brain iron-sensitive magnetic resonance imaging (MRI) techniques allow the examination of macroscopic patterns of brain iron deposits in vivo, while modern analytical methods ex vivo enable the determination of metal-specific content inside individual cell-types, sometimes also within specific cellular compartments. The present review summarizes the whole brain, cellular, and subcellular patterns of iron accumulation in neurodegenerative diseases of genetic and sporadic origin. We also provide an update on mechanisms, biomarkers, and effects of brain iron accumulation in these disorders, focusing on recent publications. In Parkinson’s disease, Friedreich’s disease, and several disorders within the neurodegeneration with brain iron accumulation group, there is a focal siderosis, typically in regions with the most pronounced neuropathological changes. The second group of disorders including multiple sclerosis, Alzheimer’s disease, and amyotrophic lateral sclerosis shows iron accumulation in the globus pallidus, caudate, and putamen, and in specific cortical regions. Yet, other disorders such as aceruloplasminemia, neuroferritinopathy, or Wilson disease manifest with diffuse iron accumulation in the deep gray matter in a pattern comparable to or even more extensive than that observed during normal aging. On the microscopic level, brain iron deposits are present mostly in dystrophic microglia variably accompanied by iron-laden macrophages and in astrocytes, implicating a role of inflammatory changes and blood–brain barrier disturbance in iron accumulation. Options and potential benefits of iron reducing strategies in neurodegeneration are discussed. Future research investigating whether genetic predispositions play a role in brain Fe accumulation is necessary. If confirmed, the prevention of further brain Fe uptake in individuals at risk may be key for preventing neurodegenerative disorders.

Current status and future directions for a neurotoxicity hazard assessment framework that integrates in silico approaches

Neurotoxicology is the study of adverse effects on the structure or function of the developing or mature adult nervous system following exposure to chemical, biological, or physical agents. The development of more informative alternative methods to assess developmental (DNT) and adult (NT) neurotoxicity induced by xenobiotics is critically needed. The use of such alternative methods including in silico approaches that predict DNT or NT from chemical structure (e.g., statistical-based and expert rule-based systems) is ideally based on a comprehensive understanding of the relevant biological mechanisms. This paper discusses known mechanisms alongside the current state of the art in DNT/NT testing. In silico approaches available today that support the assessment of neurotoxicity based on knowledge of chemical structure are reviewed, and a conceptual framework for the integration of in silico methods with experimental information is presented. Establishing this framework is essential for the development of protocols, namely standardized approaches, to ensure that assessments of NT and DNT based on chemical structures are generated in a transparent, consistent, and defendable manner.

Pb Induces MCP-1 in the Choroid Plexus

Lead (Pb) is an environmental element that has been implicated in the development of dementia and Alzheimer's disease (AD). Additionally, innate immune activation contributes to AD pathophysiology. However, the mechanisms involved remain poorly understood. The choroid plexus (CP) is not only the site of cerebrospinal fluid (CSF) production, but also an important location for communication between the circulation and the CSF. In this study, we investigated the involvement of the CP during Pb exposure by evaluating the expression of the monocyte chemoattractant protein-1 (MCP-1). MCP-1 is highly expressed in the CP compared to other CNS tissues. MCP-1 regulates macrophage infiltration and is upregulated in AD brains. Our study revealed that Pb exposure stimulated MCP-1 expression, along with a significantly increased macrophage infiltration into the CP. By using cultured Z310 rat CP cells, Pb exposure stimulated MCP-1 expression in a dose-related fashion and markedly activated both NF-κB and p38 MAP kinase. Interestingly, both SB 203580, a p38 inhibitor, and BAY 11-7082, an NF-κB p65 inhibitor, significantly blocked Pb-induced MCP-1 expression. However, SB203580 did not directly inhibit NF-κB p65 phosphorylation. In conclusion, Pb exposure stimulates MCP-1 expression via the p38 and NF-κB p65 pathways along with macrophage infiltration into the CP.

Synthesis of metal nanoclusters and their application in Hg2+ ions detection: A review

Mercuric (Hg²⁺) ions released from human activities, natural phenomena, and industrial sources are regarded as the global pollutant of world's water. Hg²⁺ ions contaminated water has several adverse effects on human health and the environment even at low concentrations. Therefore, rapid and cost-effective method is urgently required for the detection of Hg²⁺ ions in water. Although, the current analytical methods applied for the detection of Hg²⁺ ions provide low detection limit, they are time consuming, require expensive equipment, and are not suitable for in-situ analysis. Metal nanoclusters (MNCs) consisting of several to ten metal atoms are important transition missing between single atoms and plasmonic metal nanoparticles. In addition, sub-nanometer sized MNCs possess unique electronic structures and the subsequent unusual optical, physical, and chemical properties. Because of these novel properties, MNCs as a promising material have attracted considerable attention for the construction of selective and sensitive sensors to monitor water quality. Hence this review is focused on recent advances on synthesis strategies, and optical and chemical properties of various MNCs including their applications to develop optical assay for Hg²⁺ ions in aqueous solutions.

Brain copper clearance by the blood-cerebrospinal fluid-barrier: Effects of lead exposure

Lead (Pb) is a heavy metal commonly found in the environment and is known to have neurotoxic, hematological, and other toxic effects. It has been reported that Pb exposure can disturb metal regulation in the blood-cerebrospinal fluid-barrier (BCB). Copper (Cu) plays a key role in maintaining normal brain function and can accumulate in the brain after Pb exposure. However, the mechanism by which Pb affects Cu levels in the brain is still unknown. This study investigated Cu clearance by the BCB in the central nervous system (CNS) of Sprague-Dawley rats after Pb exposure by focusing on the Cu transporter protein CTR1/ATP7A. Inductively coupled plasma mass spectrometry (ICP-MS) was used to examine how heavy metal levels change in the hippocampus, cortex, and cerebrospinal fluid (CSF) after Pb exposure. Ventriculo-cisternal perfusion measurements suggested that the ability of the BCB to deliver Cu from the CSF to the blood decreased after Pb exposure. The presence of excess Cu in the choroid plexus led to CTR1/ATP7A shifting toward the apical microvilli facing the CSF after Pb exposure. We further evaluated microstructure of the choroid plexus by transmission electron microscopy, revealing altered mitochondrial morphology with decreased microvilli after Pb exposure. Conclusively, exposure to Pb alters the cellular structure of the BCB and its Cu clearance function, which can cause further brain damage.

Nanoparticles for Diagnosis and Target Therapy in Pediatric Brain Cancers

Pediatric brain tumors represent the most common types of childhood cancer and novel diagnostic and therapeutic solutions are urgently needed. The gold standard treatment option for brain cancers in children, as in adults, is tumor resection followed by radio- and chemotherapy, but with discouraging therapeutic results. In particular, the last two treatments are often associated to significant neurotoxicity in the developing brain of a child, with resulting disabilities such as cognitive problems, neuroendocrine, and neurosensory dysfunctions/deficits. Nanoparticles have been increasingly and thoroughly investigated as they show great promises as diagnostic tools and vectors for gene/drug therapy for pediatric brain cancer due to their ability to cross the blood–brain barrier. In this review we will discuss the developments of nanoparticle-based strategies as novel precision nanomedicine tools for diagnosis and therapy in pediatric brain cancers, with a particular focus on targeting strategies to overcome the main physiological obstacles that are represented by blood–brain barrier.

Development of Pharmaceutical Nanomedicines: From the Bench to the Market

Nanotechnology plays a significant role in the field of medicine and in drug delivery, mainly due to the major limitations affecting the conventional pharmaceutical agents, and older formulations and delivery systems. The effect of nanotechnology on healthcare is already being felt, as various nanotechnology applications have been developed, and several nanotechnology-based medicines are now on the market. Across many parts of the world, nanotechnology draws increasing investment from public authorities and the private sector. Most conventional drug-delivery systems (CDDSs) have an immediate, high drug release after administration, leading to increased administration frequency. Thus, many studies have been carried out worldwide focusing on the development of pharmaceutical nanomedicines for translation into products manufactured by local pharmaceutical companies. Pharmaceutical nanomedicine products are projected to play a major role in the global pharmaceutical market and healthcare system. Our objectives were to examine the nanomedicines approved by the Food and Drug Administration (FDA) and the European Medicines Agency (EMA) in the global market, to briefly cover the challenges faced during their development, and to look at future perspectives. Additionally, the importance of nanotechnology in developing pharmaceutical products, the ideal properties of nanocarriers, the reasons behind the failure of some nanomedicines, and the important considerations in the development of nanomedicines will be discussed in brief.

Current understanding of hexavalent chromium [Cr(VI)] neurotoxicity and new perspectives

Hexavalent chromium [Cr(VI)] is a global environmental pollutant that increases risk for several types of cancers and is increasingly being recognized as a neurotoxicant. Traditionally, the brain has been viewed as a largely post-mitotic organ due to its specialized composition of neurons, and consequently, clastogenic effects were not considered in neurotoxicology. Today, we understand the brain is composed of at least eight distinct cell types - most of which continue mitotic activity throughout lifespan. We have learned these dividing cells play essential roles in brain and body health. This review focuses on Cr(VI), a potent clastogen and known human carcinogen, as a potentially neurotoxic agent targeting mitotic cells of the brain. Despite its well-established role as a human carcinogen, Cr(VI) neurotoxicity studies have failed to find a significant link to brain cancers. In the few studies that did find a link, Cr(VI) was identified as a risk for gliomas. Instead, in the human brain, Cr(VI) appears to have more subtle deleterious effects that can impair childhood learning and attention development, olfactory function, social memory, and may contribute to motor neuron diseases. Studies of Cr(VI) neurotoxicity with animal and cell culture models have demonstrated elevated markers of oxidative damage and redox stress, with widespread neurodegeneration. One study showed mice exposed to Cr(VI)-laden tannery effluent exhibited longer periods of aggressive behavior toward an "intruder" mouse and took longer to recognize mice previously encountered, recapitulating the social memory deficits observed in humans. Here we conducted a critical review of the available literature on Cr(VI) neurotoxicity and synthesize the collective observations to thoroughly evaluate Cr(VI) neurotoxicity - much remains to be understood and recognized.

Metal arsenic mediated enhancement of type-2 immunity in brains with altered locomotive activities in mice with autism-like behavioral characteristics

Exposure to metal arsenic (As) has been proposed as a risk factor for autism spectrum disorders (ASDs), which are neurodevelopmental disorders with worldwide increasing in its incidence. In the present study, BTBR T + tf/J (BTBR) mice with ASD-like behavioral characteristics and control highly social FVB mice were orally exposed to 0.1 mM arsenic(III)oxide for 4 weeks, and were compared to investigate neuroimmunological or behavioral abnormalities. IgG1:IgG2a ratios in brain tissues from BTBR mice exposed to As (BTBR-As) were significantly higher than those of BTBR-control mice (BTBR-C), but this change did not occur in FVB mice exposed to As. Levels of IL-4, IFN-γ, IL-1β, IL-17, and TNF-α in brain tissue were lowered in BTBR-As relative to BTBR-C, but this tendency was not observed with FVB mice. BTBR-As mice demonstrated decrease in relative travel distance and time spent in the center vs. the periphery of open field arena compared to BTBR-C. Sociability evaluation using three-way chamber test did not clearly demonstrate As-mediated alteration in social interaction in BTBR mice. These findings suggest the potential for As-driven predominant TH2-like reactivity profile in the brain microenvironment of BTBR mice and for As-mediated locomotive impairment probably associated with ASD.

Parkinson's Disease and the Metal-Microbiome-Gut-Brain Axis: A Systems Toxicology Approach

Parkinson's Disease (PD) is a neurodegenerative disease, leading to motor and non-motor complications. Autonomic alterations, including gastrointestinal symptoms, precede motor defects and act as early warning signs. Chronic exposure to dietary, environmental heavy metals impacts the gastrointestinal system and host-associated microbiome, eventually affecting the central nervous system. The correlation between dysbiosis and PD suggests a functional and bidirectional communication between the gut and the brain. The bioaccumulation of metals promotes stress mechanisms by increasing reactive oxygen species, likely altering the bidirectional gut-brain link. To better understand the differing molecular mechanisms underlying PD, integrative modeling approaches are necessary to connect multifactorial perturbations in this heterogeneous disorder. By exploring the effects of gut microbiota modulation on dietary heavy metal exposure in relation to PD onset, the modification of the host-associated microbiome to mitigate neurological stress may be a future treatment option against neurodegeneration through bioremediation. The progressive movement towards a systems toxicology framework for precision medicine can uncover molecular mechanisms underlying PD onset such as metal regulation and microbial community interactions by developing predictive models to better understand PD etiology to identify options for novel treatments and beyond. Several methodologies recently addressed the complexity of this interaction from different perspectives; however, to date, a comprehensive review of these approaches is still lacking. Therefore, our main aim through this manuscript is to fill this gap in the scientific literature by reviewing recently published papers to address the surrounding questions regarding the underlying molecular mechanisms between metals, microbiota, and the gut-brain-axis, as well as the regulation of this system to prevent neurodegeneration.

Association of autism with toxic metals: A systematic review of case-control studies

Environmental factors have been associated with the etiology of autism spectrum disorder ASD in recent times. The involvement of toxic metals in the generation of reactive oxygen species and their epigenetics effects have been implicated in ASD. This systemic review examines the association of toxic metals with autism in children. A systematic literature search was performed in scientific databases such as PubMed, Google scholar, and Scopus. Case-control studies evaluating toxic metal levels in different tissues of ASD children and comparing them to healthy children (control group) were identified. The Newcastle-Ottawa Scale was used to evaluate the risk of bias of the included studies. Six case-control studies with 425 study subjects met our inclusion criteria. A total of four studies indicated higher levels of As, Pb, Hg, Cd, Al, Sn, Sb, Ba, TI, W, and Zr in whole blood, RBC, in whole blood, RBC, and hair samples of children with autism compared with control suggestive of a greater toxic metal exposure (immediate and long-term). Three studies identified significantly higher concentrations of Cd, Pb and Hg in urine and hair samples of autistic children compared to control suggesting decreased excretion and possible high body burden of these metals. The findings from this review demonstrate that high levels of toxic metals are associated with ASD, therefore, critical care is necessary to reduce body burden of these metals in children with ASD as a major therapeutic strategy.