Lead and cadmium synergistically enhance the expression of divalent metal transporter 1 protein in central nervous system of developing rats

Polystyrene microplastics mitigate lead-induced neurotoxicity by reducing heavy metal uptake in zebrafish larvae

The combined pollution of lead (Pb) and polystyrene microplastics (PS-MPs) is common in aquatic environments. However, the combined neurotoxicity of these two pollutants is still poorly understood. In this study, zebrafish (Danio rerio) larvae were used to assess the combined neurotoxicity and mechanism of Pb and PS-MPs at environmentally relevant concentrations. The results showed that Pb (10 μg/L) induced abnormal behavior including significantly reduced movement distance, maximum acceleration, and average velocity (P < 0.05) along with altered expression of neurodevelopment-related genes (gap43 and α1-tubulin) (P < 0.05). PS-MPs (25 μg/L, 250 μg/L; diameter at 25 μm) co-exposure not only significantly reduced the concentration of Pb in the exposed solution (P < 0.01), but also decreased the uptake of Pb by downregulating the divalent metal transporter 1 gene (dmt1) (P < 0.01), thereby alleviating Pb-induced neurotoxicity. However, to demonstrate that PS-MPs alleviate the neurotoxicity of Pb by reducing Pb uptake, upregulation of dmt1 by addition of deferoxamine (DFO, an efficient iron chelator, 100 μM) significantly increased the Pb uptake and exacerbated neurotoxicity in zebrafish. In summary, our results demonstrated that PS-MPs alleviate Pb neurotoxicity by downregulating the mRNA level of dmt1 and decreasing the Pb uptake. This study provides a new insight into the combined neurotoxicity and underlying mechanisms of PS-MPs and Pb on zebrafish.

Lead and cadmium co-exposure modified PC12 viability and ER stress: study from a 3 × 3 factorial design

Background

Although exposure to individual metal does exhibit its toxicity, combined exposures provide a more effective representation of the toxic effects of different heavy metal exposures on public health as well as ecosystems. Furthermore, there are few studies on composite exposure to low concentrations of heavy metals, which is more consistent with real-life exposure. The purpose of this study was to explore the neurotoxicity induced by combined exposure to low concentrations of Lead (Pb) and cadmium (Cd) and the potential interaction of their mixture in vitro.

Methods

PC12 cells were incubation with the corresponding concentration of cadmium chloride and/or lead acetate. Viability of PC12 cells was measured by CCK8 assay after 12, 24 and 48h incubation. Next, We measured the ROS, mitochondrial membrane potential (MMP) and apoptosis produced by different treated cells using ROS assay kit, JC-1 MMP assay kit and annexin V-FITC/propidium iodide (PI) apoptosis assay kit, respectively. Expression of proteins related to PI3K/AKT and endoplasmic reticulum (ER) stress in PC12 cells were tested by western blotting. Our study was the first to analyze the interaction between Pb and Cd using a 3 × 3 factorial design approach to observe neurotoxicity.

Results

The results showed that the combined exposure of them was more cytotoxic than the single metal. The activation of PI3K/AKT signaling pathway and several parameters related to oxidative stress and ER stress were significantly altered in combined exposure to low concentrations of Pb and Cd compared with the Pb or Cd. Regarding apoptosis and ER stress, a synergistic interaction between Pb and Cd was evident. Moreover, evoked ER stress as a mechanism involved in the apoptosis of PC12 cells by the combined exposure to Pb and Cd.

Conclusion

The present study provides a theoretical basis used for the toxicological assessment of metal mixtures induced neurotoxicity of concern in terms of public health, and more effective control measures should be taken for the environmental pollution caused by various mixed heavy metals discharged from industry and agriculture.

Cadmium reduces growth of male fetuses by impairing development of the placental vasculature and reducing expression of nutrient transporters

In utero exposure to the toxic metal cadmium (Cd) alters fetoplacental growth in rodents and has been inversely associated with birth weight and infant size in some birth cohorts. Moreover, studies suggest that Cd may have differential effects on growth and development according to offspring sex. The purpose of the current study was to evaluate changes in male and female fetoplacental development following a single injection of saline (5 ml/kg ip) or cadmium chloride (CdCl2, 2.5, 5 mg/kg, ip) on gestational day (GD) 9. By GD18, no changes in fetal or placental weights were observed after treatment with 2.5 mg/kg CdCl2. By comparison, the weight and length of male fetuses and their placentas were reduced following treatment with 5 mg/kg CdCl2 whereas no change was observed in females. In addition, the area of maternal and fetal blood vessels as well as the expression of the glucose transporters, Glut1 and Glut3, and the endothelial marker, CD34, were reduced in the placentas of CdCl2-treated male offspring compared to females. Interestingly, the placentas of females accumulated 80% more Cd than males after CdCl2 (5 mg/kg) administration. Female placentas also had higher concentrations of zinc and the zinc transporter Znt1 compared to males which may explain the limited changes in fetal growth observed following CdCl2 treatment. Taken together, disruption of vasculature development and reduced expression of glucose transporters in the placenta provide potential mechanisms underlying reduced fetal growth in male offspring despite the greater accumulation of Cd in female placentas.

Cadmium induced cerebral toxicity via modulating MTF1-MTs regulatory axis

Metal-responsive transcription factor 1 (MTF1) participates in redox homeostasis and heavy metals detoxification via regulating the expression of metal responsive genes. However, the exact role of MTF1 in Cd-induced cerebral toxicity remains unclear. Herein, we explored the mechanism of Cd-elicited cerebral toxicity through modulating MTF1/MTs pathway in chicken cerebrum exposed to different concentrations of Cd (35 mg, 70 mg, and 140 mg/kg CdCl₂) via diet. Notably, cerebral tissues showed varying degrees of microstructural changes under Cd exposure. Cd exposure significantly up-regulated the expression of metal transporters (DMT1, ZIP8, and ZIP10) with concomitant elevated Cd level, as determined by ICP-MS. Cd significantly altered other cerebral biometals concentrations (particularly, Zn, Fe, Se, Cr, Mo, and Pb) and redox balance, resulting in increased cerebral oxidative stress. More importantly, Cd exposure suppressed MTF1 mRNA and nuclear protein levels and its target metal-responsive genes, notably metallothioneins (MT1 and MT2), and Fe and Cu transporter genes (FPN1, ATOX1, and XIAP). Moreover, Cd disrupted the regulation of expression of selenoproteome (particularly, GPxs and SelW), and cerebral Se level. Overall, our data revealed that molecular mechanisms associated with Cd-induced cerebral damage might include over-expression of DMT1, ZIP8 and ZIP10, and suppression of MTF1 and its main target metal-responsive genes as well as several selenoproteins.

Redox and essential metal status in the brain of Wistar rats acutely exposed to a cadmium and lead mixture

Most Pb and Cd neurotoxicity studies investigate exposure to either of the toxic metals alone, while data on co-exposure are scarce. The aim of our study was to fill that gap by investigating acute combined effects of Pb and Cd on redox and essential metal status in the brain of Wistar rats. Animals were randomised in four groups of six to eight rats, which received 15 or 30 mg/kg of Cd, 150 mg/kg of Pb, or 150 mg/kg of Pb + 15 mg/kg of Cd by gavage. The fifth, control, group received distilled water only. Co-treatment with Pb and Cd induced significant increase in malondialdehyde (MDA) and thiobarbituric acid-reactive substances (TBARS) compared to control and groups receiving either metal alone. This is of special importance, as MDA presence in the brain has been implicated in many neurodegenerative disorders. The groups did not significantly differ in Zn, Cu, Mn, and Fe brain levels. Our findings highlight the importance of metal mixture studies. Neurotoxicity assessments of single chemicals do not provide a real insight into exposure to mixtures in real life. Further research should look into interactions between these metals to reveal complex molecular mechanisms of their neurotoxicity.

Chemical mixtures and neurobehavior: a review of epidemiologic findings and future directions

Background Epidemiological studies have historically focused on single toxicants, or toxic chemicals, and neurodevelopment, even though the interactions of chemicals and nutrients may result in additive, synergistic, antagonistic, or potentiating effects on neurological endpoints. Investigating the impact of environmentally-relevant chemical mixtures, including heavy metals and endocrine disrupting chemicals (EDCs), is more reflective of human exposures and may result in more refined environmental policies to protect the public. Objective In this review, we provide a summary of epidemiological studies that have analyzed chemical mixtures of heavy metals and EDCs and neurobehavior utilizing multi-chemical models, including frequentist and Bayesian methods. Content Studies investigating chemicals and neurobehavior have the opportunity to not only examine the impact of chemical mixtures, but they can also identify chemicals from a mixture that may play a key role in neurotoxicity, investigate interactive effects, estimate non-linear dose response, and identify potential windows of susceptibility. The examination of neurobehavioral domains is particularly challenging given that traits emerge and change over time and subclinical nuances of neurobehavior are often unrecognized. To date, only a handful of epidemiological studies examining neurodevelopment have utilized multi-pollutant models in the investigation of heavy metals and EDCs. However, these studies were successful in identifying contaminants of importance from the exposure mixtures. Summary and Outlook Investigators are encouraged to broaden their focus to include more environmentally relevant mixtures of chemicals using advanced statistical approaches, particularly to aid in identifying potential mechanisms underlying associations.

Oxidative stress caused by lead (Pb) induces iron deficiency in Drosophila melanogaster

Toxic elements exposure disturbs the homeostasis of essential elements in organisms, but the mechanism remains elusive. In this study, we demonstrated that Drosophila melanogaster exposed to Lead (Pb, a pervasive environmental threat to human health) exhibited various health defects, including retarded development, decreased survival rate, impaired mobility and reduced egg production. These phenotypes could be significantly modulated by either intervention of dietary iron levels or altering expression of genes involved in iron metabolism. Further study revealed that Pb exposure leads to systemic iron deficiency. Strikingly, reactive oxygen species (ROS) clearance significantly increased iron uptake by restoring the expression of iron metabolism genes in the midgut and subsequently attenuated Pb toxicity. This study highlights the role of ROS in Pb induced iron dyshomeostasis and provides unique insights into understanding the mechanism of Pb toxicity and suggests ideal ways to attenuate Pb toxicity by iron supplementation therapy or ROS clearance.

Increased DMT-1 expression in placentas of women living in high-Cd-contaminated areas of Thailand

Cadmium (Cd) is a toxic heavy metal and contamination was reported in soil and rice in several areas of Thailand. Humans are normally exposed to environmental Cd, leading to gradual Cd accumulation in their bodies, including the placenta. DMT-1 is a divalent metal transporter which is found in placental tissue and plays a vital role in the transportation of Fe²⁺ and Cd²⁺. This study investigated DMT-1 protein and mRNA expressions in full term human placentas comparing those from high-Cd-contaminated areas (high-Cd group) and low-Cd-contaminated areas (low-Cd group), n = 6 per group. The maternal blood Cd (B-Cd) and placental Cd (P-Cd) of the high-Cd group was significantly raised in comparison with those in the low-Cd group. DMT-1 in the fetal portion of the placentas was localized in the apical and basal portions of the cytoplasm of the syncytiotrophoblastic cells, the endothelium of fetal capillaries which is functional structure of the placental barrier, and was also found in the cytoplasm of Hofbauer cells. Moreover, DMT-1 localization in the maternal portion was also detected in most decidual cells. In addition, the DMT-1 protein and mRNA expressions in the high-Cd group were significantly higher than those in the low-Cd group. Therefore, we suggest that pregnant women, who are exposed to environmental Cd, show an increased level of Cd in their maternal blood and this Cd can accumulate in the placenta. Intracellular Cd may induce DMT-1 mRNA transcription which further translates into DMT-1 protein, which can then function as a reciprocal Cd transporter in placental tissue.

Neurotoxicity Linked to Dysfunctional Metal Ion Homeostasis and Xenobiotic Metal Exposure: Redox Signaling and Oxidative Stress

SIGNIFICANCE

Essential metals such as copper, iron, manganese, and zinc play a role as cofactors in the activity of a wide range of processes involved in cellular homeostasis and survival, as well as during organ and tissue development. Throughout our life span, humans are also exposed to xenobiotic metals from natural and anthropogenic sources, including aluminum, arsenic, cadmium, lead, and mercury. It is well recognized that alterations in the homeostasis of essential metals and an increased environmental/occupational exposure to xenobiotic metals are linked to several neurological disorders, including neurodegeneration and neurodevelopmental alterations. Recent Advances: The redox activity of essential metals is key for neuronal homeostasis and brain function. Alterations in redox homeostasis and signaling are central to the pathological consequences of dysfunctional metal ion homeostasis and increased exposure to xenobiotic metals. Both redox-active and redox-inactive metals trigger oxidative stress and damage in the central nervous system, and the exact mechanisms involved are starting to become delineated.

CRITICAL ISSUES

In this review, we aim to appraise the role of essential metals in determining the redox balance in the brain and the mechanisms by which alterations in the homeostasis of essential metals and exposure to xenobiotic metals disturb the cellular redox balance and signaling. We focus on recent literature regarding their transport, metabolism, and mechanisms of toxicity in neural systems.

FUTURE DIRECTIONS

Delineating the specific mechanisms by which metals alter redox homeostasis is key to understand the pathological processes that convey chronic neuronal dysfunction in neurodegenerative and neurodevelopmental disorders. Antioxid. Redox Signal. 28, 1669-1703.

Arsenic ototoxicity

High levels of arsenic are found in many parts of the world and more than 100 million people may have been exposed to it. There is growing evidence to indicate that arsenic has a deleterious effect on the auditory system. This paper provides the general information of arsenic and its ototoxic effects.

Mechanisms of divalent metal toxicity in affective disorders

Metals are required for proper brain development and play an important role in a number of neurobiological functions. The divalent metal transporter 1 (DMT1) is a major metal transporter involved in the absorption and metabolism of several essential metals like iron and manganese. However, non-essential divalent metals are also transported through this transporter. Therefore, altered expression of DMT1 can modify the absorption of toxic metals and metal-induced toxicity. An accumulating body of evidence has suggested that increased metal stores in the brain are associated with elevated oxidative stress promoted by the ability of metals to catalyze redox reactions, resulting in abnormal neurobehavioral function and the progression of neurodegenerative diseases. Metal overload has also been implicated in impaired emotional behavior, although the underlying mechanisms are not well understood with limited information. The current review focuses on psychiatric dysfunction associated with imbalanced metabolism of metals that are transported by DMT1. The investigations with respect to the toxic effects of metal overload on behavior and their underlying mechanisms of toxicity could provide several new therapeutic targets to treat metal-associated affective disorders.

Oxaliplatin-Induced Peripheral Neuropathy via TRPA1 Stimulation in Mice Dorsal Root Ganglion Is Correlated with Aluminum Accumulation

Oxaliplatin is a platinum-based anticancer drug used to treat metastatic colorectal, breast, and lung cancers. While oxaliplatin kills cancer cells effectively, it exhibits several side effects of varying severity. Neuropathic pain is commonly experienced during treatment with oxaliplatin. Patients describe symptoms of paresthesias or dysesthesias that are triggered by cold (acute neuropathy), or as abnormal sensory or motor function (chronic neuropathy). In particular, we found that aluminum levels were relatively high in some cancer patients suffering from neuropathic pain based on clinical observations. Based on these findings, we hypothesized that aluminum accumulation in the dorsal root ganglion (DRG) in the course of oxaliplatin treatment exacerbates neuropathic pain. In mice injected with oxaliplatin (three cycles of 3 mg/kg i.p. daily for 5 days, followed by 5 days of rest), we detected cold allodynia using the acetone test, but not heat hyperalgesia using a hot plate. However, co-treatment with aluminum chloride (AlCl3∙6H2O; 7 mg/kg i.p. for 14 days: equivalent 0.78 mg/kg of elemental Al) and oxaliplatin (1 cycle of 3 mg/kg i.p. daily for 5 days, followed by 5 days of rest) synergistically induced cold allodynia as well as increased TRPAl mRNA and protein expression. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) analysis showed a significant increase in aluminum concentrations in the DRG of mice treated with aluminum chloride and oxaliplatin compared to aluminum chloride alone. Similarly, in a mouse induced-tumor model, aluminum concentrations were increased in DRG tissue and tumor cells after oxaliplatin treatment. Taken together, these findings suggest that aluminum accumulation in the DRG may exacerbate neuropathic pain in oxaliplatin-treated mice.

Toxic effect of palladium on embryonic development of zebrafish

Since palladium (Pd) is now increasingly used in modern industry, it progressively accumulates in the environment, especially in aquatic ecosystem. The potential toxicity of Pd has therefore caused extensive concern worldwidely. In the present study, we investigated the toxic effect of Pd on zebrafish development. Acute Pd exposure significantly decreased both the survival rate (LC50: 292.6 μg/L, viz. 2.75 μM) and hatching rate (IC50: 181.5 μg/L, viz. 1.71 μM) of zebrafish during embryonic development. The most common developmental defect observed in Pd treated embryos is pericardiac edema, which occurs in a dose-dependent manner. Whole mount immunostaining and histological studies revealed that Pd exposure would produce the elongated, string-like heart. The heartbeat rate of zebrafish embryos was also decreased after Pd exposure. Consistently, mRNA expression levels of several cardiac-related genes were affected by Pd, suggesting a potential molecular mechanism of Pd-induced cardiac malformation of zebrafish embryo. Moreover, similar to other metals, Pd exposure resulted in the elevated expression of general metal-inducible genes. It was also found that the expression of several antioxidant enzymes was significantly down-regulated in the presence of Pd. Taken together, our study investigated the effects of Pd on zebrafish embryonic development and its potential molecular mechanisms, paving the way for the full understanding of Pd toxicity.

Hepatocyte growth factor protects human mesangial cells against apoptosis induced by lead damage

Lead is a kind of nephrotoxic metal which frequently threats human health. Hepatocyte growth factor (HGF) is a multifunctional growth factor that protects cell apoptosis. In this study, human mesangial cells (HMCs) were treated with a single HGF dose of 20 and 40 μl/ml in order to investigate the effect of HGF on proliferation and apoptosis ability of HMCs induced by lead acetate. In HGF-treated group, HMCs were incubated with HGF (20, 40 μl/ml) half an hour prior to lead inducing. After lead-induced damage 48 h, the proliferation of HMCs was measured by MTT assay, and the apoptosis was assessed by flow cytometry. RT-PCR was used to detect the expression of P53, Bcl-2, Bax, and caspase-3 mRNA. The expression of Bax protein was measured by Western blot analysis. The results showed that HGF inhibits proliferation of HMCs induced lead acetate in a dose-dependent manner (P < 0.05). HGF significantly promoted the proliferation of HMCs, and flow cytometry revealed that HGF can inhibit apoptosis of HMCs. RT-PCR and Western blot showed that P53, Bax, and caspase-3 expression decreased, while Bcl-2 expression increased. HGF may afford a protection to HMCs against lead-induced damage.

The effect of lead exposure on brain iron homeostasis and the expression of DMT1/FP1 in the brain in developing and aged rats

The relation between lead (Pb) and iron (Fe) becomes increasingly concerned because they are both divalent metals that are absorbed by the same intestinal mechanism, and Pb exposure and Fe deficiency in the developmental brain, as well as Fe overload in the aged brain, can cause cognitive deficits. However, the interaction between Pb exposure and Fe status in the brain has not been established. Therefore, in the current study, we examined the effects of maternal ingestion of Pb in drinking water during gestation and lactation on the Fe status and the expression of divalent metal transporter 1 (DMT1) and ferroportin 1 (FP1) in the brain of offspring. The offspring were followed through old age, with measurements taken at postnatal week 3 (PNW3), 41 (PNW41) and 70 (PNW70). Pb exposure increases the Fe content in the old-aged rats' brain, which might be not subjected to DMT1 mediating, but may be associated with the decrease expression of FP1. Furthermore, the effect of Pb on FP1 expression is regulated at transcriptional and posttranscriptional levels. The perturbation in Fe homeostasis may contribute to the neurotoxicology consequences induced by Pb exposure, and FP1 may play a role in Pb-induced Fe cumulation in the brain.

Cd, Cu, Zn, Se, and metallothioneins in two amphibians, Necturus maculosus (Amphibia, Caudata) and Bufo bufo (Amphibia, Anura)

The accumulation of cadmium, its affinity for metallothioneins (MTs), and its relation to copper, zinc, and selenium were investigated in the experimental mudpuppy Necturus maculosus and the common toad Bufo bufo captured in nature. Specimens of N. maculosus were exposed to waterborne Cd (85 μg/L) for up to 40 days. Exposure resulted in tissue-dependent accumulation of Cd in the order kidney, gills > intestine, liver, brain > pancreas, skin, spleen, and gonads. During the 40-day exposure, concentrations increased close to 1 μg/g in kidneys and gills (0.64-0.95 and 0.52-0.76; n = 4), whereas the levels stayed below 0.5 in liver (0.14-0.29; n = 4) and other organs. Cd exposure was accompanied by an increase of Zn and Cu in kidneys and Zn in skin, while a decrease of Cu was observed in muscles and skin. Cytosol metallothioneins (MTs) were detected as Cu,Zn-thioneins in liver and Zn,Cu-thioneins in gills and kidney, with the presence of Se in all cases. After exposure, Cd binding to MTs was clearly observed in cytosol of gills as Zn,Cu,Cd-thionein and in pellet extract of kidneys as Zn,Cu,Cd-thioneins. The results indicate low Cd storage in liver with almost undetectable Cd in liver MT fractions. In field trapped Bufo bufo (spring and autumn animals), Cd levels were followed in four organs and found to be in the order kidney > liver (0.56-5.0 μg/g >0.03-0.72 μg/g; n = 11, spring and autumn animals), with no detectable Cd in muscle and skin. At the tissue level, high positive correlations between Cd, Cu, and Se were found in liver (all r > 0.80; α = 0.05, n = 5), and between Cd and Se in kidney (r = 0.76; n = 5) of autumn animals, possibly connected with the storage of excess elements in biologically inert forms. In the liver of spring animals, having higher tissue level of Cd than autumn ones, part of the Cd was identified as Cu,Zn,Cd-thioneins with traces of Se. As both species are special in having liver Cu levels higher than Zn, the observed highly preferential Cd load in kidney seems reasonable. The relatively low Cd found in liver can be attributed to its excretion through bile and its inability to displace Cu from MTs. The associations of selenium observed with Cd and/or Cu (on the tissue and cell level) point to selenium involvement in the detoxification of excessive cadmium and copper through immobilization.

Oxidative stress: a possible mechanism for lead-induced apoptosis and nephrotoxicity

Lead-induced nephrotoxicity is a human health hazard problem. In this study, Human mesangial cells (HMCs) were treated with different concentration of lead acetate (5, 10, 20 μmol/l) in order to investigate the oxidative stress and apoptotic changes. It was revealed that lead acetate could induce a progressive loss in HMCs viability together with a significant increase in the number of apoptotic cells using 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium (MTT) assay and flow cytometry, respectively. The apoptotic morphological changes induced by lead exposure in HMCs were demonstrated by PI-Hochest33342 staining. A DNA laddering pattern in lead-treated cells was shown, which could indicate nuclear fragmentation. In addition, lead acetate significantly increased the levels of malondialehyde (MDA) content and lactate dehydrogenase (LDH) activity. Therefore, it might be concluded that lead could promote HMCs' oxidative stress and apoptosis, which may be the chief mechanisms of lead-induced nephrotoxicity.

Cellular transport and homeostasis of essential and nonessential metals

Metals can have a number of detrimental or beneficial effects in the cell, but first they must get in. Organisms have evolved transport mechanisms to get metals that are required, or essential into the cell. Nonessential metals often enter the cell through use of the machinery provided for essential metals. Much work has been done to advance our understanding of how these metals are transported across plasma and organelle membranes. This review provides an overview of essential and nonessential metal transport and homeostatic processes.

Ingestion of Mn and Pb by rats during and after pregnancy alters iron metabolism and behavior in offspring

Manganese (Mn) and lead (Pb) exposures during developmental period can impair development by direct neurotoxicity or through interaction with iron metabolism. Therefore, we examined the effects of maternal ingestion of Mn or Pb in drinking water during gestation and lactation on iron metabolism as well as behavior in their offspring. Pregnant dams were given distilled water, 4.79mg/ml Mn, or 2.84mg/ml Pb in drinking water during gestation and lactation. Pups were studied at time of weaning for (59)Fe absorption from the gut, duodenal divalent metal transporter 1 (DMT1) expression, hematological parameters, and anxiety-related behavior using an Elevated Plus Maze (EPM) test. Metal-exposed pups had lower body weights and elevated blood and brain concentrations of the respective metal. Pb-exposed pups had lower hematocrits and higher blood Zn protoporphyrin levels. In contrast, Mn exposed pups had normal hematological parameters but significantly reduced Zn protoporphyrin. Pharmacokinetic studies using (59)Fe showed that intestinal absorption in metal-exposed pups was not different from controls, nor was it correlated with duodenal DMT1 expression. However, intravenously injected (59)Fe was cleared more slowly in Pb-exposed pups resulting in higher plasma levels. The overall tissue uptake of (59)Fe was lower in Mn-exposed and lower in the brain in Pb-exposed pups. The EPM test demonstrated that Mn-exposed, but not Pb-exposed, pups had lower anxiety-related behavior compared to controls. We conclude that gestational and lactational exposures to Mn or Pb differentially alter Fe metabolism and anxiety-related behavior. The data suggest that perturbation in Fe metabolism may contribute to the pathophysiologic consequences of Mn and Pb exposure during early development.

Characterization of developmental neurotoxicity of As, Cd, and Pb mixture: synergistic action of metal mixture in glial and neuronal functions

Neurotoxicity of individual metals is well investigated but that of metal mixture (MM), an environmental reality, in the developing brain is relatively obscure. We investigated the combinatorial effect of arsenic (As), cadmium (Cd), and lead (Pb) on rat brain development, spanning in utero to postnatal development. MM was administered by gavage to pregnant and lactating rats, and to postweaning pups till 2 months. The pups exhibited behavioral disturbances characterized by hyperlocomotion, increased grip strength, and learning-memory deficit. Disruption of the blood-brain barrier (BBB) was associated with dose-dependent increase in deposition of the metals in developing brain. Astrocytes were affected by MM treatment as evident from their reduced density, area, perimeter, compactness, and number of processes, and increased apoptosis in cerebral cortex and cerebellum. The metals induced synergistic reduction in glial fibrillary acidic protein (GFAP) expression during brain development; however, postweaning withdrawal of MM partially restored the levels of GFAP in adults. To characterize the toxic mechanism, we treated rat primary astrocytes with MM at concentrations ranging from lethal concentration (LC)(10) to LC(75) of the metals. We observed synergistic downregulation in viability and increase in apoptosis of the astrocytes, which were induced by proximal activation of extra cellular signal-regulated kinase (ERK) signaling and downstream activation of Jun N-terminal kinase (JNK) pathway. Furthermore, rise in intracellular calcium ion ([Ca(2+)](i)) and reactive oxygen species generation promoted apoptosis in the astrocytes. Taken together, these observations are the first to show that mixture of As, Cd, and Pb has the capacity to induce synergistic toxicity in astrocytes that may compromise the BBB and may cause behavioral dysfunction in developing rats.

Lead affects apoptosis and related gene XIAP and Smac expression in the hippocampus of developing rats

Lead (Pb) exposure poses devastating effects on central nervous system development of children. To replicate aspects of this neurotoxicity, we examined the effect of lead on the expression of apoptosis and of apoptosis-related genes, XIAP (X chromosome-linked inhibitor of apoptosis protein) and Smac (second mitochondrial activator of caspase), in the hippocampus of developing rats. A total of 48 rats (30-day old) were randomly divided into four groups for intragastrical perfusion of lead acetate [Pb(Ac)2]: untreated, low (2 mg/kg/d), medium (20 mg/kg/d), and high (200 mg/kg/d) dose groups. Pb content was determined in blood, and the apoptosis indexes and XIAP and Smac gene expression were analyzed in the hippocampus. There was a significant difference in apoptosis indexes (AI) between the exposed and control groups (p < 0.01). AI was highest in the high exposure group. XIAP gene expression was reduced in the exposed groups and the expression was negatively correlated with blood lead levels (BLLs) (p < 0.05). But the four groups did not differ in the expression of Smac (p > 0.05). Our data indicate that exposure to Pb(Ac)2 caused a dose-dependent and significant increase of apoptosis in the hippocampus of developing rats through depressing the expression of the XIAP but not the Smac genes.

Involvement of DMT1 +IRE in the transport of lead in an in vitro BBB model

Homeostasis of the central nervous system (CNS) microenvironment is maintained by the blood-brain barrier (BBB). The BBB is particularly vulnerable to lead (Pb) insults. This study was designed to test the hypothesis that divalent metal transporter 1 (DMT1), which is a divalent cation membrane transporter, was involved in transcellular transport across the BBB. An in vitro BBB model, which was a co-culture system of human umbilical vascular endothelial cells (ECV304) and rat glioma cells (C6), was established. Transendothelial electrical resistance (TEER) and fluoresceinisothiocyanate (FITC)-dextran permeability results showed that Pb exposure at the tested concentrations had no significant effects on intercellular tightness. Pb transport displayed properties that were associated with iron response element (IRE) positive isoform of DMT1. Accordingly, Pb transport was significantly blocked by iron (Fe). Moreover, ECV304 cells that were depleted of Fe with the chelator deferoxamine (DFO) demonstrated increased Pb transport. By transfecting ECV-304 cells with a DMT1 expression vector, overexpression of DMT1 promoted an increase in Pb transport. Treatment of ECV304 cells with DMT1 antisense oligonucleotides (ASONs) MA1 significantly inhibited the transport of Pb. Our results suggest that Pb is transported in the in vitro BBB model by a transporter with biochemical properties similar to those of the DMT1 IRE-positive isoform.