Choroid plexus protects cerebrospinal fluid against toxic metals

Choroid Plexus Modulates Subventricular Zone Adult Neurogenesis and Olfaction Through Secretion of Small Extracellular Vesicles

The choroid plexus (CP) in brain ventricles secrete cerebrospinal fluid (CSF) that bathes the adjacent subventricular zone (SVZ); the latter is the largest neurogenic region in adult brain harboring neural stem/progenitor cells (NSPCs) and supplies newborn neurons to the olfactory bulb (OB) for normal olfaction. We discovered the presence of a CP-SVZ regulatory (CSR) axis in which the CP, by secreting small extracellular vesicles (sEVs), regulated adult neurogenesis in the SVZ and maintained olfaction. The proposed CSR axis was supported by 1) differential neurogenesis outcomes in the OB when animals treated with intracerebroventricular (ICV) infusion of sEVs collected from the CP of normal or manganese (Mn)-poisoned mice, 2) progressively diminished SVZ adult neurogenesis in mice following CP-targeted knockdown of SMPD3 to suppress CP sEV secretion, and 3) compromised olfactory performance in these CP-SMPD3-knockdown mice. Collectively, our findings demonstrate the biological and physiological presence of this sEV-dependent CSR axis in adult brains.

HIGHLIGHTS

CP-secreted sEVs regulate adult neurogenesis in the SVZ.CP-secreted sEVs modulate newborn neurons in the OB.Suppression of sEV secretion from the CP deteriorates olfactory performance.

GSH and Zinc Supplementation Attenuate Cadmium-Induced Cellular Stress and Stimulation of Choline Uptake in Cultured Neonatal Rat Choroid Plexus Epithelia

Choroid plexus (CP) sequesters cadmium and other metals, protecting the brain from these neurotoxins. These metals can induce cellular stress and modulate homeostatic functions of CP, such as solute transport. We previously showed in primary cultured neonatal rat CP epithelial cells (CPECs) that cadmium induced cellular stress and stimulated choline uptake at the apical membrane, which interfaces with cerebrospinal fluid in situ. Here, in CPECs, we characterized the roles of glutathione (GSH) and Zinc supplementation in the adaptive stress response to cadmium. Cadmium increased GSH and decreased the reduced GSH-to-oxidized GSH (GSSG) ratio. Heat shock protein-70 (Hsp70), heme oxygenase (HO-1), and metallothionein (Mt-1) were induced along with the catalytic and modifier subunits of glutamate cysteine ligase (GCL), the rate-limiting enzyme in GSH synthesis. Inhibition of GCL by l-buthionine sulfoximine (BSO) enhanced stress protein induction and stimulation of choline uptake by cadmium. Zinc alone did not induce Hsp70, HO-1, or GCL subunits, or modulate choline uptake. Zinc supplementation during cadmium exposure attenuated stress protein induction and stimulation of choline uptake; this effect persisted despite inhibition of GSH synthesis. These data indicated up-regulation of GSH synthesis promotes adaptation to cadmium-induced cellular stress in CP, but Zinc may confer cytoprotection independent of GSH.

Cadmium promotes glycolysis upregulation and glutamine dependency in human neuronal cells

Cadmium is a widespread pollutant, which easily accumulates inside the human body with an estimated half-life of 25-30 years. Many data strongly suggest that it may play a role in the pathogenesis of neurodegenerative diseases. In this paper we investigated cadmium effect on human SH-SY5Y neuroblastoma cells metabolism. Results showed that, although SH-SY5Y cells already showed hyperactivated glycolysis, cadmium further increased basal glycolytic rate. Both glycolytic capacity and reserve were also increased following cadmium administration, endowing the cells with a higher compensatory glycolysis when oxidative phosphorylation was inhibited. Cadmium administration also led to an increase in glycolytic ATP production rate, paralleled by a decrease in ATP production by oxidative phosphorylation, due to an impairment of mitochondrial respiration. Moreover, following cadmium administration, mitochondria increased their dependency on glutamine, while decreasing lipids oxidation. On the whole, our data show that cadmium exacerbates the Warburg effect and promotes the use of glutamine as a substrate for lipid biosynthesis. Although increased glutamine consumption leads to an increase in glutathione level, this cannot efficiently counteract cadmium-induced oxidative stress, leading to membrane lipid peroxidation. Oxidative stress represents a serious threat for neuronal cells and our data confirm glutathione as a key defense mechanism.

An efficient autometallography approach to localize lead at ultra-structural levels of cultured cells

Understanding the precise intracellular localization of lead (Pb) is a key in deciphering processes in Pb-induced toxicology. However, it is a great challenge to trace Pbin vitro, especially in cultured cells. We aimed to find an innovative and efficient approach to investigate distribution of Pb in cells and to validate it through determining the subcellular Pb content. We identified its ultra-structural distribution with autometallography under electron microscopy in a choroidal epithelial Z310 cell line. Electron microscopy in combination with energy-dispersive X-ray spectroscope (EDS) was employed to provide further evidence of Pb location. In addition, Pb content was determined in the cytosol, membrane/organelle, nucleus and cytoskeleton fractions with atomic absorption spectroscopy. Pb was found predominantly inside the nuclear membranes and some was distributed in the cytoplasm under low-concentration exposure. Nuclear existence of Pb was verified by EDS under electron microscopy. Once standardized for protein content, Pb percentage in the nucleus fraction reached the highest level (76%). Our results indicate that Pb is accumulated mainly in the nucleus of choroid plexus. This method is sensitive and precise in providing optimal means to study the ultra-structural localization of Pb forin vitromodels. In addition, it offers the possibility of localization of other metals in cultured cells. Some procedures may also be adopted to detect target proteins via immunoreactions.

Zika virus infects pericytes in the choroid plexus and enters the central nervous system through the blood-cerebrospinal fluid barrier

Zika virus (ZIKV) can infect and cause microcephaly and Zika-associated neurological complications in the developing fetal and adult brains. In terms of pathogenesis, a critical question is how ZIKV overcomes the barriers separating the brain from the circulation and gains access to the central nervous system (CNS). Despite the importance of ZIKV pathogenesis, the route ZIKV utilizes to cross CNS barriers remains unclear. Here we show that in mouse models, ZIKV-infected cells initially appeared in the periventricular regions of the brain, including the choroid plexus and the meninges, prior to infection of the cortex. The appearance of ZIKV in cerebrospinal fluid (CSF) preceded infection of the brain parenchyma. Further the brain infection was significantly attenuated by neutralization of the virus in the CSF, indicating that ZIKV in the CSF at the early stage of infection might be responsible for establishing a lethal infection of the brain. We show that cells infected by ZIKV in the choroid plexus were pericytes. Using in vitro systems, we highlight the possibility that ZIKV crosses the blood-CSF barrier by disrupting the choroid plexus epithelial layer. Taken together, our results suggest that ZIKV might exploit the blood-CSF barrier rather than the blood-brain barrier to invade the CNS.

Altered clearance of beta-amyloid from the cerebrospinal fluid following subchronic lead exposure in rats: Roles of RAGE and LRP1 in the choroid plexus

Formation of amyloid plaques is the hallmark of Alzheimer's disease. Our early studies show that lead (Pb) exposure in PDAPP transgenic mice increases β-amyloid (Aβ) levels in the cerebrospinal fluid (CSF) and hippocampus, leading to the formation of amyloid plaques in mouse brain. Aβ in the CSF is regulated by the blood-CSF barrier (BCB) in the choroid plexus. However, the questions as to whether and how Pb exposure affected the influx and efflux of Aβ in BCB remained unknown. This study was conducted to investigate whether Pb exposure altered the Aβ efflux in the choroid plexus from the CSF to blood, and how Pb may affect the expression and subcellular translocation of two major Aβ transporters, i.e., the receptor for advanced glycation end-products (RAGE) and the low density lipoprotein receptor protein-1 (LRP1) in the choroid plexus. 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 (2.5 μg/mL) was infused to rat brain via a cannulated internal carotid artery. Subchronic Pb exposure at both dose levels significantly increased Aβ levels in the CSF and choroid plexus (p < 0.05) by ELISA. Confocal data showed that 4-wk Pb exposures prompted subcellular translocation of RAGE from the choroidal cytoplasm toward apical microvilli. Furthermore, it increased the RAGE expression in the choroid plexus by 34.1 % and 25.1 % over the controls (p < 0.05) in the low- and high- dose groups, respectfully. Subchronic Pb exposure did not significantly affect the expression of LRP1; yet the high-dose group showed LRP1 concentrated along the basal lamina. The data from the ventriculo-cisternal perfusion revealed a significantly decreased efflux of Aβ40 from the CSF to blood via the blood-CSF barrier. Incubation of freshly dissected plexus tissues with Pb in artificial CSF supported a Pb effect on increased RAGE expression. Taken together, these data suggest that Pb accumulation in the choroid plexus after subchronic exposure reduces the clearance of Aβ from the CSF to blood by the choroid plexus, which, in turn, leads to an increase of Aβ in the CSF. Interaction of Pb with RAGE and LRP1 in choroidal epithelial cells may contribute to the altered Aβ transport by the blood-CSF barrier in brain ventricles.

Role of Astrocytes in Manganese Neurotoxicity Revisited

Manganese (Mn) overexposure is a public health concern due to its widespread industrial usage and the risk for environmental contamination. The clinical symptoms of Mn neurotoxicity, or manganism, share several pathological features of Parkinson's disease (PD). Biologically, Mn is an essential trace element, and Mn in the brain is preferentially localized in astrocytes. This review summarizes the role of astrocytes in Mn-induced neurotoxicity, specifically on the role of neurotransmitter recycling, neuroinflammation, and genetics. Mn overexposure can dysregulate astrocytic cycling of glutamine (Gln) and glutamate (Glu), which is the basis for Mn-induced excitotoxic neuronal injury. In addition, reactive astrocytes are important mediators of Mn-induced neuronal damage by potentiating neuroinflammation. Genetic studies, including those with Caenorhabditis elegans (C. elegans) have uncovered several genes associated with Mn neurotoxicity. Though we have yet to fully understand the role of astrocytes in the pathologic changes characteristic of manganism, significant strides have been made over the last two decades in deciphering the role of astrocytes in Mn-induced neurotoxicity and neurodegeneration.

Quantitative analysis of Gd in the protein content of the brain following single injection of gadolinium-based contrast agents (GBCAs) by size exclusion chromatography

OBJECTIVE

To investigate the role of transporter proteins in gadolinium (Gd) distribution and retention in the brain after one high-dose injection of Gd-based contrast agent (GBCA).

METHODS AND MATERIALS

30 ddY mice were randomly divided into three treatment groups to be intravenously injected with either Gadodiamide (linear GBCA), Gadobutrol (macrocyclic GBCA), or Gadoterate (macrocyclic GBCA) at a dose of 5 mmol/kg, while five mice in the control group received 250 µL saline. Five minutes (5 min) and ten days (10d) post-injection, the cerebrospinal fluid (CSF), choroid plexus (CP), and meninges and associated vasculature (MAV) were collected. The brain was then dissected to obtain the olfactory bulb, cerebral cortex, hippocampus, cerebellum, and brainstem. Proteins were extracted and separated by a size-exclusion high-performance liquid chromatography (SEC) system, and Gd concentrations were quantified by inductively coupled plasma mass spectrometry (ICP-MS).

RESULTS

5 m post-injection, the Gadodiamide group had the highest Gd concentration, while Gadoterate had the lowest Gd concentration in all parts of the brain (p < .05). Gd concentration was highest in the cerebrospinal fluid (CSF) of the Gadodiamide group (578.4 ± 135.3 nmol), while Gd concentration was highest in MAV in the Gadobutrol group (379.7 ± 75.4 nmol) at 5 min post-injection. At 10d, in spite of the significant decrease of Gd from all GBCAs ( p < 0.01), retained Gd from Gadodiamide was detected all over the brain in several molecules that varied in size. Gd from Gadobutrol detected in the olfactory bulb (8.7 ± 4.5 nmol) was significantly higher than in other parts of the brain. Although most Gd from Gadobutrol was found in molecules similar in size to Gadobutrol, it was also found in several protein molecules of molecular size larger than the contrast agents. Only a small amount of Gd from Gadoterate was found in the brain.

CONCLUSION

GBCAs may be able to pass through intact brain barriers, and the chemical structures of GBCAs may affect the penetration capability of Gd into the brain. Retained Gd in the brain tissue from Gadodiamide and Gadobutrol may be bound to some organic molecules, including proteins.

ADVANCES IN KNOWLEDGE

Intact GBCA are able to penetrate a series of brain barrier immediately after administration regardless the type of the chelate. Gd may be bound with macromolecules that may cause Gd retention in the brain.

Correlation of regional deposition dosage for inhaled nanoparticles in human and rat olfactory

Background

Nose-to-brain transport of airborne ultrafine particles (UFPs) via the olfactory pathway has been verified as a possible route for particle translocation into the brain. The exact relationship between increased airborne toxicant exposure and neurological deterioration in the human central nervous system, is still unclear. However, the nasal olfactory is undoubtedly a critical junction where the time course and toxicant dose dependency might be inferred.

Method

Computational fluid-particle dynamics modeling of inhaled nanoparticles (1 to 100 nm) under low to moderate breathing conditions (5 to 14 L/min – human; and 0.14 to 0.40 L/min – rat) were performed in physiologically realistic human and rat nasal airways. The simulation emphasized olfactory deposition, and variations in airflow and particle flux caused by the inter-species airway geometry differences. Empirical equations were developed to predict regional deposition rates of inhaled nanoparticles on human and rat olfactory mucosa in sedentary breathing. Considering, breathing and geometric differences, quantified correlations between human and the rat olfactory deposition dose against a variety of metrics were proposed.

Results

Regional deposition of nanoparticles in human and the rat olfactory was extremely low, with the highest deposition (< 3.5 and 8.1%) occurring for high diffusivity particles of 1.5 nm and 5 nm, respectively. Due to significant filtering of extremely small particles (< 2 nm) by abrupt sharp turns at front of the rat nose, only small fractions of the inhaled nanoparticles (in this range) reached rat olfactory than that in human (1.25 to 45%); however, for larger sizes (> 3 nm), significantly higher percentage of the inhaled nanoparticles reached rat nasal olfactory than that in human (2 to 32 folds). Taking into account the physical and geometric features between human and rat, the total deposition rate (#/min) and deposition rate per unit surface area (#/min/mm²) were comparable for particles> 3 nm. However, when body mass was considered, the normalized deposition rate (#/min/kg) in the rat olfactory region exceeded that in the human. Nanoparticles < 1.5 nm were filtered out by rat anterior nasal cavity, and therefore deposition in human olfactory region exceeded that in the rat model.

Conclusion

Regional deposition dose of inhaled nanoparticles in a human and rat olfactory region was governed by particle size and the breathing rate. Interspecies correlation was determined by combining the effect of deposition dosage, physical\geometric features, and genetic differences. Developed empirical equations provided a tool to quantify inhaled nanoparticle dose in human and rat nasal olfactory regions, which lay the ground work for comprehensive interspecies correlation between the two species. Furthermore, this study contributes to the fields in toxicology, i.e., neurotoxicity evaluation and risk assessment of UFPs, in long-term and low-dose inhalation exposure scenarios.

Disruption of the zinc metabolism in rat fœtal brain after prenatal exposure to cadmium

This study was carried out to investigate the effects of maternal Cd and/or Zn exposure on some parameters of Zn metabolism in fetal brain of Wistar rats. Thus, female controls and other exposed by the oral route during the gestation period to Cd (50 mg CdCl2/L) and/or Zn (ZnCl2 60 mg/L) were used. The male fetuses at age 20 days of gestation (GD20) were sacrificed and their brains were taken for histological, chemical and molecular analysis. Zn depletion was observed in the brains of fetuses issued from mothers exposed to Cd. Histological analysis showed that Cd exposure induces pyknosis in cortical region and CA1 region of the hippocampus compared to controls. Under Cd exposure, we noted an overexpression of the genes coding for membrane transporter involved in the intracellular incorporation of Zn (ZIP6) associated with inhibition of that encoding the transporters involved in the output of the Zn into the extracellular medium (ZnT1 and ZnT3). A decrease in the expression of the gene encoding the neuro-trophic factor (BDNF) associated with overexpression of the encoding the metal regulatory transcription factor 1 (MTF1), factor involved in the homeostasis of Zn, was also noted in Cd group. Interestingly, Zn supply provided a total or partial restauration of the changes induced by the Cd exposure. The depletion of brain Zn contents as well as the modification of the profile of expression of genes encoding membrane Zn transporters, suggest that the toxicity of Cd observed in fetal brain level are mediated, in part, by impairment of Zn metabolism.

Lead, cadmium and mercury in cerebrospinal fluid and risk of amyotrophic lateral sclerosis: A case-control study

Exposure to neurotoxic chemicals such as pesticides, selenium, and heavy metals have been suggested to play a role in the etiology of amyotrophic lateral sclerosis (ALS). We assessed exposure to lead, cadmium, and mercury in 38 ALS patients (16 men and 22 females) and 38 hospital-admitted controls by using their cerebrospinal fluid (CSF) content as biomarker. We determined CSF heavy metal levels with inductively coupled plasma sector field mass spectrometry, according to a methodology specifically developed for this biological matrix. ALS patients had higher median values for Pb (155 vs. 132ng/L) but lower levels for Cd (36 vs. 72ng/L) and Hg (196 vs. 217ng/L). In the highest tertile of exposure, ALS odds ratio was 1.39 (95% CI 0.48-4.25) for Pb, 0.29 (0.08-1.04) for Cd and 3.03 (0.52-17.55) for Hg; however, no dose-response relation emerged. Results were substantially confirmed after conducting various sensitivity analyses, and after stratification for age and sex. Though interpretation of these results is limited by the statistical imprecision of the estimates, and by the possibility that CSF heavy metal content may not reflect long-term antecedent exposure, they do not lend support to a role of the heavy metals cadmium, lead and mercury in ALS etiology.

Influence of age on arsenic-induced behavioral and cholinergic perturbations: Amelioration with zinc and α-tocopherol

This study was planned to determine arsenic (As) (10 mg/kg body weight given through oral gavage) induced behavioral and cholinergic perturbations in three different age groups of rats; young (postnatal day 21), adult (3 months), and aged (18 months) at 7 days post-acute exposure ( n = 6 for each of the four groups of all three age points). Further, we also evaluated the ameliorative effect of essential metal zinc (Zn; 0.02% through drinking water) and an antioxidant, α-tocopherol (vitamin E; 125 mg/kg body weight through oral gavage) against As-induced neurotoxicity. As exposure showed significant alterations in behavioral functions (open-field behavior, total locomotor activity, grip strength, exploratory behavior, and water maze learning). Cholinergic studies in three brain regions (cerebral cortex, cerebellum, and hippocampus) of different age groups also showed significant increase in acetylcholine levels and a decrease in acetylcholinesterase activity. These effects were more pronounced in hippocampus followed by cerebral cortex and cerebellum. Among the three different age points, aged animals were found to be more vulnerable to the As-induced toxicity as compared to young and adult animals suggesting that As neurotoxicity is age dependent. These As-induced alterations were significantly reversed following supplementation with Zn or vitamin E. However, vitamin E was found to elicit greater protection as compared to Zn in restoring the altered behavioral and cholinergic perturbations, providing evidence for As-induced oxidative damage.

The blood–cerebrospinal fluid barrier – first evidence for an active transport of organic mercury compounds out of the brain

Hg strongly transfers across the blood–CSF barrier towards the blood side after incubation with organic Hg compounds.

Stress-induced stimulation of choline transport in cultured choroid plexus epithelium exposed to low concentrations of cadmium

The choroid plexus epithelium forms the blood-cerebrospinal fluid barrier and accumulates essential minerals and heavy metals. Choroid plexus is cited as being a "sink" for heavy metals and excess minerals, serving to minimize accumulation of these potentially toxic agents in the brain. An understanding of how low doses of contaminant metals might alter transport of other solutes in the choroid plexus is limited. Using primary cultures of epithelial cells isolated from neonatal rat choroid plexus, our objective was to characterize modulation of apical uptake of the model organic cation choline elicited by low concentrations of the contaminant metal cadmium (CdCl₂). At 50-1,000 nM, cadmium did not directly decrease or increase 30-min apical uptake of 10 μM [(3)H]choline. However, extended exposure to 250-500 nM cadmium increased [(3)H]choline uptake by as much as 75% without marked cytotoxicity. In addition, cadmium induced heat shock protein 70 and heme oxygenase-1 protein expression and markedly induced metallothionein gene expression. The antioxidant N-acetylcysteine attenuated stimulation of choline uptake and induction of stress proteins. Conversely, an inhibitor of glutathione synthesis l-buthionine-sulfoximine (BSO) enhanced stimulation of choline uptake and induction of stress proteins. Cadmium also activated ERK1/2 MAP kinase. The MEK1 inhibitor PD98059 diminished ERK1/2 activation and attenuated stimulation of choline uptake. Furthermore, inhibition of ERK1/2 activation abated stimulation of choline uptake in cells exposed to cadmium with BSO. These data indicate that in the choroid plexus, exposure to low concentrations of cadmium may induce oxidative stress and consequently stimulate apical choline transport through activation of ERK1/2 MAP kinase.

Regional distribution and accumulation of lead in caprine brain tissues following a long-term oral dosing regimen

It is well known that the brain is a key target organ for lead (Pb)-induced toxicity, with exposure potentially resulting in numerous adverse neurological effects. However, information on the distribution and accumulation of Pb within different brain regions is scarce. In this study, Pb uptake and accumulation were characterized in brain and related tissues obtained from a convenience sample of goats dosed with Pb. Tissues were harvested postmortem from 10 animals (9 dosed and 1 undosed) that are used to produce blood Pb pools for the New York State Department of Health's Proficiency Testing program. Whole brains were subdivided into 14 distinct anatomical regions to explore interregional differences. Related tissues included the olfactory epithelium and spinal cord. Where sufficient tissue mass permitted, further subdivision into smaller sections was carried out to examine intraregional Pb variability. Determination of Pb content in these tissues was accomplished using inductively coupled plasma mass spectrometry (ICP-MS), with accuracy assessed using reference materials certified for Pb. Lead content (dry weight) varied from <10 ng/g, that is, below the method detection limit, to as much as 4.45 × 10(4) ng/g Pb. Olfactory epithelium Pb content was several orders of magnitude greater than found in other regions analyzed. Enrichment of Pb was also observed in the olfactory bulb and choroid plexus. Data for each region analyzed were pooled from all goats to identify regions with the greatest propensity for Pb accumulation. Data related to Pb content were also assessed individually within each goat and significant differences in Pb content between regions were determined.

Cadmium and its neurotoxic effects

Cadmium (Cd) is a heavy metal that has received considerable concern environmentally and occupationally. Cd has a long biological half-life mainly due to its low rate of excretion from the body. Thus, prolonged exposure to Cd will cause toxic effect due to its accumulation over time in a variety of tissues, including kidneys, liver, central nervous system (CNS), and peripheral neuronal systems. Cd can be uptaken from the nasal mucosa or olfactory pathways into the peripheral and central neurons; for the latter, Cd can increase the blood brain barrier (BBB) permeability. However, mechanisms underlying Cd neurotoxicity remain not completely understood. Effect of Cd neurotransmitter, oxidative damage, interaction with other metals such as cobalt and zinc, estrogen-like, effect and epigenetic modification may all be the underlying mechanisms. Here, we review the in vitro and in vivo evidence of neurotoxic effects of Cd. The available finding indicates the neurotoxic effects of Cd that was associated with both biochemical changes of the cell and functional changes of central nervous system, suggesting that neurotoxic effects may play a role in the systemic toxic effects of the exposure to Cd, particularly the long-term exposure.

Culture of choroid plexus epithelial cells and in vitro model of blood-CSF barrier

Chemical homeostasis in the extracellular fluid of the central nervous system (CNS) is maintained by two brain barrier systems, i.e., the blood-brain barrier (BBB) that separates the blood circulation from brain interstitial fluid and the blood-cerebrospinal fluid barrier (BCB) that separates the blood from the cerebrospinal fluid (CSF). The choroid plexus, where the BCB is located, is a polarized tissue, with the basolateral side of the choroidal epithelium facing the blood and the apical microvilli in direct contact with the CSF. The tissue plays a wide range of roles in brain development, aging, nutrient transport, endocrine regulation, and pathogenesis of certain neurodegenerative disorders. This chapter describes two in vitro cultures that have been well established to allow for study of the BCB structure and function. The primary choroidal epithelial cell culture can be established from rat choroid plexus tissue, and a similar immortalized murine choroidal epithelial cell culture known as Z310 cells has also been established. Both cultures display a dominant polygonal morphology, and immunochemical studies demonstrate the presence of transthyretin, a thyroxine transport protein known to be exclusively produced by the choroidal epithelia in the CNS. These cultures have been adapted for use on freely permeable Transwell(®) membranes sandwiched between two culture chambers, facilitating transport studies of various compounds across this barrier in vitro. These choroidal epithelia cultures with the Transwell system will perceivably assist blood-CSF barrier research.

Ginsenoside Rd maintains adult neural stem cell proliferation during lead-impaired neurogenesis

Lead exposure attracts a great deal of public attention due to its harmful effects on human health. Even low-level lead (Pb) exposure reduces the capacity for neurogenesis. It is well known that microglia-mediated neurotoxicity can impair neurogenesis. Despite this, few in vivo studies have been conducted to understand the relationship between acute Pb exposure and microglial activation. We investigated whether the acute Pb exposure altered the expression of a marker of activated microglial cells (Iba-1), and markers of neurogenesis (BrdU and doublecortin) in aging rats. As compared to controls, Pb exposure significantly enhanced the expression of Iba-1 immunoreactivity; increased the expression levels of IL-1β, IL-6, and TNF-α and decreased the numbers of BrdU(+) and doublecortin(+) cells. Our prior work demonstrated that ginsenoside Rd (Rd), one of the major active ingredients in Panax ginseng, was neuroprotective in a variety of paradigms involving anti-inflammatory mechanisms. Thus, we further examined whether Rd could attenuate Pb-induced phenotypes. Compared with the Pb exposure group, Rd pretreatment indeed attenuated the effects of Pb exposure. These results suggest that Rd may be neuroprotective in old rats following acute Pb exposure, which involves limitation of microglial activation and maintenance of NSC proliferation.

Mercury in the spinal cord after inhalation of mercury

Amyotrophic lateral sclerosis (ALS) affects anterior horn cells of the spinal cord causing an indolent slow and steady deterioration of muscle strength leading inevitably to death in respiratory failure. ALS is a model condition for neurodegenerative disorders. Exposure to different agents dispersed in the environment has been suggested to cause neurodegeneration but no convincing evidence for such a link has yet been presented. Respiratory exposure to metallic mercury (Hg(0)) from different sources may be suspected. Body distribution of metallic mercury is fast and depends on solubility properties. Routes of transport, metabolism, excretion and biological half-life determine the overall toxic effects. Inhalation experiments were performed in 1984 where small marmoset monkeys (Callithrix jacchus) were exposed to (203) Hg(0 vapour) mixed into the breathing air (4-5 μg/l). After 1 hr of exposure, they were killed and whole body autoradiograms prepared to study the distribution of mercury within organs. Autoradiograms showed that Hg was deposited inside the spinal cord. Areas of enhanced accumulation anatomically corresponding to motor nuclei could be observed. This study describes a reinvestigation, with new emphasis on the spinal cord, of these classical metal exposure data in a primate, focusing on their relevance for the causation of neurodegenerative disorders. A comparison with more recent rodent experiments with similar findings is included. The hypothesis that long-time low-dose respiratory exposure to metals, for example, Hg, contributes to neurodegenerative disorders is forwarded and discussed.

Regulation of brain copper homeostasis by the brain barrier systems: effects of Fe-overload and Fe-deficiency

Maintaining brain Cu homeostasis is vital for normal brain function. The role of systemic Fe deficiency (FeD) or overload (FeO) due to metabolic diseases or environmental insults in Cu homeostasis in the cerebrospinal fluid (CSF) and brain tissues remains unknown. This study was designed to investigate how blood-brain barrier (BBB) and blood-SCF barrier (BCB) regulated Cu transport and how FeO or FeD altered brain Cu homeostasis. Rats received an Fe-enriched or Fe-depleted diet for 4 weeks. FeD and FeO treatment resulted in a significant increase (+55%) and decrease (-56%) in CSF Cu levels (p<0.05), respectively; however, neither treatment had any effect on CSF Fe levels. The FeD, but not FeO, led to significant increases in Cu levels in brain parenchyma and the choroid plexus. In situ brain perfusion studies demonstrated that the rate of Cu transport into the brain parenchyma was significantly faster in FeD rats (+92%) and significantly slower (-53%) in FeO rats than in controls. In vitro two chamber Transwell transepithelial transport studies using primary choroidal epithelial cells revealed a predominant efflux of Cu from the CSF to blood compartment by the BCB. Further ventriculo-cisternal perfusion studies showed that Cu clearance by the choroid plexus in FeD animals was significantly greater than control (p<0.05). Taken together, our results demonstrate that both the BBB and BCB contribute to maintain a stable Cu homeostasis in the brain and CSF. Cu appears to enter the brain primarily via the BBB and is subsequently removed from the CSF by the BCB. FeD has a more profound effect on brain Cu levels than FeO. FeD increases Cu transport at the brain barriers and prompts Cu overload in the CNS. The BCB plays a key role in removing the excess Cu from the CSF.

Lead exposure increases levels of β-amyloid in the brain and CSF and inhibits LRP1 expression in APP transgenic mice

Lead (Pb) is an environmental factor suspected of contributing to neurodegenerative diseases such as Alzheimer's disease (AD). In AD, it has been postulated that increased production and/or decreased metabolism/clearance of β-amyloid (Aβ) may lead to amyloid plaque deposition as well as a cascade of other neuropathological changes. It has been suggested that Pb exposure may be associated with AD-like pathology and severe memory deficits in humans. Therefore, we investigated whether Pb exposure could induce Aβ accumulation in the brain. In this study, we demonstrated that acute Pb treatments lead to increased levels of Aβ in the cerebrospinal fluid (CSF) and brain tissues. Interestingly, Pb treatments did not affect Aβ production in brain neurons. Furthermore, Pb treatments significantly decreased LRP1 protein expression in the choroid plexus (CP). Our results suggest disrupted LRP1-mediated transport of Aβ in this region may be responsible for the Aβ accumulation in brain.

Lead-induced accumulation of beta-amyloid in the choroid plexus: role of low density lipoprotein receptor protein-1 and protein kinase C

The choroid plexus (CP), constituting the blood-cerebrospinal fluid barrier, has the capacity to remove beta-amyloid (Abeta) from the cerebrospinal fluid. Our previous work indicates that exposure to lead (Pb) results in Abeta accumulation in the CP by decreasing the expression of low density lipoprotein receptor protein-1 (LRP1), a protein involved in the transport and clearance of Abeta. The current study was designed to explore the relationship between Abeta accumulation, protein kinase C (PKC) activity, and LRP1 status in the CP following Pb exposure. Confocal microscopy revealed that LRP1 was primarily localized in the cytosol of the CP in control rats and migrated distinctly towards the apical surface and the microvilli following acute Pb exposure (27 mg Pb/kg, i.p., 24h). Co-immunostaining revealed a co-localization of both PKC-delta and LRP1 in the cytosol of control rats, with a distinct relocalization of both towards the apical membrane following Pb exposure. Preincubation of the tissues with PKC-delta inhibitor rottlerin (2 microM) prior to Pb exposure in vitro, resulted in abolishing the Pb-induced relocalization of LRP1 to the apical surface. Importantly, a significant elevation in intracellular Abeta levels (p<0.01) was observed in the cytosol of the CP following Pb exposure, which was abolished following preincubation with rottlerin. In addition, rottlerin caused a relocalization of Abeta from the cytosol to the nucleus in both Pb-treated and control CP tissues. Finally, co-immunoprecipitation studies revealed a strong protein-protein interaction between LRP1 and PKC-delta in the CP. These studies suggest that Pb exposure disrupts Abeta homeostasis at the CP, owing partly to a Pb-induced relocalization of LRP1 via PKC-delta.

Involvement of insulin-degrading enzyme in the clearance of beta-amyloid at the blood-CSF barrier: Consequences of lead exposure

Background

Alzheimer's disease (AD) is characterized by the deposition of beta-amyloid (Aβ) peptides in the brain extracellular matrix, resulting in pathological changes and neurobehavioral deficits. Previous work from this laboratory demonstrated that the choroid plexus (CP) possesses the capacity to remove Aβ from the cerebrospinal fluid (CSF), and exposure to lead (Pb) compromises this function. Since metalloendopeptidase insulin-degrading enzyme (IDE), has been implicated in the metabolism of Aβ, we sought to investigate whether accumulation of Aβ following Pb exposure was due to the effect of Pb on IDE.

Methods

Rats were injected with a single dose of Pb acetate or an equivalent concentration of Na-acetate; CP tissues were processed to detect the location of IDE by immunohistochemistry. For in vitro studies, choroidal epithelial Z310 cells were treated with Pb for 24 h in the presence or absence of a known IDE inhibitor, N-ethylmaleimide (NEM) to assess IDE enzymatic activity and subsequent metabolic clearance of Aβ. Additionally, the expression of IDE mRNA and protein were determined using real time PCR and western blots respectively.

Results

Immunohistochemistry and confocal imaging revealed the presence of IDE towards the apical surface of the CP tissue with no visible alteration in either its intensity or location following Pb exposure. There was no significant difference in the expressions of either IDE mRNA or protein following Pb exposure compared to controls either in CP tissues or in Z310 cells. However, our findings revealed a significant decrease in the IDE activity following Pb exposure; this inhibition was similar to that seen in the cells treated with NEM alone. Interestingly, treatment with Pb or NEM alone significantly increased the levels of intracellular Aβ, and a greater accumulation of Aβ was seen when the cells were exposed to a combination of both.

Conclusion

These data suggest that Pb exposure inhibits IDE activity but does not affect its expression in the CP. This, in turn, leads to a disrupted metabolism of Aβ resulting in its accumulation at the blood-CSF barrier.

Increased beta-amyloid levels in the choroid plexus following lead exposure and the involvement of low-density lipoprotein receptor protein-1

The choroid plexus, a barrier between the blood and cerebrospinal fluid (CSF), is known to accumulate lead (Pb) and also possibly function to maintain brain's homeostasis of Abeta, an important peptide in the etiology of Alzheimer's disease. This study was designed to investigate if Pb exposure altered Abeta levels at the blood-CSF barrier in the choroid plexus. Rats received ip injection of 27 mg Pb/kg. Twenty-four hours later, a FAM-labeled Abeta (200 pmol) was infused into the lateral ventricle and the plexus tissues were removed to quantify Abeta accumulation. Results revealed a significant increase in intracellular Abeta accumulation in the Pb-exposed animals compared to controls (p<0.001). When choroidal epithelial Z310 cells were treated with 10 microM Pb for 24 h and 48 h, Abeta (2 microM in culture medium) accumulation was significantly increased by 1.5 fold (p<0.05) and 1.8 fold (p<0.05), respectively. To explore the mechanism, we examined the effect of Pb on low-density lipoprotein receptor protein-1 (LRP1), an intracellular Abeta transport protein. Following acute Pb exposure with the aforementioned dose regimen, levels of LRP1 mRNA and proteins in the choroid plexus were decreased by 35% (p<0.05) and 31.8% (p<0.05), respectively, in comparison to those of controls. In Z310 cells exposed to 10 microM Pb for 24 h and 48 h, a 33.1% and 33.4% decrease in the protein expression of LRP1 was observed (p<0.05), respectively. Knocking down LRP1 resulted in even more substantial increases of cellular accumulation of Abeta, from 31% in cells without knockdown to 72% in cells with LRP1 knockdown (p<0.05). Taken together, these results suggest that the acute exposure to Pb results in an increased accumulation of intracellular Abeta in the choroid plexus; the effect appears to be mediated, at least in part, via suppression of LRP1 production following Pb exposure.

Evidence for altered hippocampal volume and brain metabolites in workers occupationally exposed to lead: a study by magnetic resonance imaging and (1)H magnetic resonance spectroscopy

Environmental and occupational exposure to lead (Pb) remains to be a major public health issue. The purpose of this cross-sectional study was to use non-invasive magnetic resonance imaging (MRI) and proton magnetic resonance spectroscopy ((1)H MRS) techniques to investigate whether chronic exposure to Pb in an occupational setting altered brain structure and function of Pb-exposed workers. The Pb-exposed group consisted of 15 workers recruited from either a Pb-smelting factory or a Pb-battery manufacturer. The control group had 19 healthy volunteers who had no history of Pb exposure in working environment or at home. The average airborne Pb concentrations in fume and dust were 0.43 and 0.44 mg/m(3), respectively, in the smeltery, and 0.10 and 1.06 mg/m(3), respectively, in the Pb battery workshop. The average blood Pb concentrations (BPb) in Pb-exposed and control workers were 63.5 and 8.7 microg/dL, respectively. The MRI examination showed that brain hippocampal volume among Pb-exposed workers was significantly diminished in comparison to age-matched control subjects (p < 0.01), although the extent of this reduction was relatively small (5-6% of the control values). Linear regression analyses revealed significant inverse associations between BPb and the decreased hippocampal volume on both sides of brain hemisphere. Among five brain metabolites investigated by MRS, i.e., N-acetyl-aspartate (NAA), creatine (Cr), choline (Cho), inosine (mI), glutamate/glutamine (Glx) and lipids (Lip), a significant decrease in NAA/Cr ratio (7% of controls, p < 0.05) and a remarkable increase in Lip/Cr ratio (40%, p < 0.01) were observed in the brains of Pb-exposed workers as compared to controls. Furthermore, the increased Lip/Cr ratio was significantly associated with BPb (r = 0.46, p < 0.01). Taken together, this study suggests that occupational exposure to Pb may cause subtle structural and functional alteration in human brains. The MRI and MRS brain imaging techniques can be used as the non-invasive means to evaluate Pb-induced neurotoxicity.

Early lead exposure increases the leakage of the blood-cerebrospinal fluid barrier, in vitro

The cell type constructing the blood-brain barrier (BBB) and blood-cerebrospinal fluid barrier (BCB) is entirely different, ie, endothelia in BBB and epithelia in BCB. Nonetheless, both barriers share a common character--the tight junctions (TJ) between adjacent cells. This study investigated the consequence of lead (Pb) exposure on the tightness of BCB. In an in vitro BCB transwell model, using immortalized choroidal epithelial Z310 cells, we found that early exposure to Pb (prior to the formation of tight barrier) at 5 and 10 microM, significantly reduced the tightness of BCB, as evidenced by a 20% reduction in transepithelial electrical resistance (TEER) values (P <0.05), and >20% increase in the paracellular permeability of [(14)C]sucrose (P <0.05). Exposure to Pb after the formation of tight barrier, however, did not cause any detectable barrier dysfunction. RT-PCR and Western blot analyses on typical TJ proteins revealed that Pb exposure decreased both the mRNA and protein levels of claudin-1, with the membrane-bound claudin-1 more profoundly affected than cytosolic claudin-1. Pb exposure, however, had no significant effect on ZO1 and occludin. These data suggest that Pb exposure selectively alters the cellular level of claudin-1, which, in turn, reduces the tightness and augments the permeability of tight blood-CSF barrier. The immature barrier appears to be more vulnerable to Pb toxicity than the mature, well-developed, brain barrier, the fact possibly contributing to Pb-induced neurotoxicity among young children.

Cadmium neurotoxicity

The Cd has been recognized as one of the most toxic environmental and industrial pollutants due to its ability to induce disturbances in several organs and tissues following either acute or chronic exposure. This review accounts for the recent evidence on its mechanisms to induce neurotoxicity, the role of the blood-brain barrier, oxidative stress, interference with calcium, and zinc-dependent processes and apoptosis induction as well as the modulatory effect of metallothionein. Discussion about cadmium neurotoxicity is centered on mechanisms of induction of cellular disfunctions. Future investigations must address those neuronal mechanisms in detail in order to understand cadmium-induced neurotoxicity.

Arsenic in the cerebrospinal fluid of a patient receiving arsenic trioxide for relapsed acute promyelocytic leukemia with CNS involvement

We report on a 42-year-old patient whose relapse of acute promyelocytic leukaemia (APL) included meningeal infiltration. Since he had previously experienced ATRA syndrome, he received arsenic trioxide (ATO) plus intrathecal therapy with cytarabine, prednisone, and methotrexate. We measured the concentration of arsenic in his cerebrospinal fluid (CSF). Arsenic showed a peak CSF concentration of 0.008 mg/l (0.11 micromol/l) and a nadir of 0.002 mg/l (0.027 micromol/l), both representing about 14% of blood levels. ATO thus crosses the blood-CSF-barrier when administered intravenously, but the concentration in CSF is probably not sufficient for treatment of meningeal leukemia.

Iron supplement prevents lead-induced disruption of the blood-brain barrier during rat development

Children are known to be venerable to lead (Pb) toxicity. The blood-brain barrier (BBB) in immature brain is particularly vulnerable to Pb insults. This study was designed to test the hypothesis that Pb exposure damaged the integrity of the BBB in young animals and iron (Fe) supplement may prevent against Pb-induced BBB disruption. Male weanling Sprague-Dawley rats were divided into four groups. Three groups of rats were exposed to Pb in drinking water containing 342 microg Pb/mL as Pb acetate, among which two groups were concurrently administered by oral gavage once every other day with 7 mg Fe/kg and 14 mg Fe/kg as FeSO(4) solution as the low and high Fe treatment group, respectively, for 6 weeks. The control group received sodium acetate in drinking water. Pb exposure significantly increased Pb concentrations in blood by 6.6-folds (p<0.05) and brain tissues by 1.5-2.0-folds (p<0.05) as compared to controls. Under the electron microscope, Pb exposure in young animals caused an extensive extravascular staining of lanthanum nitrate in brain parenchyma, suggesting a leakage of cerebral vasculature. Western blot showed that Pb treatment led to 29-68% reduction (p<0.05) in the expression of occludin as compared to the controls. Fe supplement among Pb-exposed rats maintained the normal ultra-structure of the BBB and restored the expression of occludin to normal levels. Moreover, the low dose Fe supplement significantly reduced Pb levels in blood and brain tissues. These data suggest that Pb exposure disrupts the structure of the BBB in young animals. The increased BBB permeability may facilitate the accumulation of Pb. Fe supplement appears to protect the integrity of the BBB against Pb insults, a beneficial effect that may have significant clinical implications.

Molecular mechanism of distorted iron regulation in the blood-CSF barrier and regional blood-brain barrier following in vivo subchronic manganese exposure

Previous studies in this laboratory indicated that manganese (Mn) exposure in vitro increases the expression of transferrin receptor (TfR) by enhancing the binding of iron regulatory proteins (IRPs) to iron responsive element-containing RNA. The current study further tested the hypothesis that in vivo exposure to Mn increased TfR expression at both blood-brain barrier (BBB) and blood-cerebrospinal fluid (CSF) barrier (BCB), which contributes to altered iron (Fe) homeostasis in the CSF. Groups of rats (10-11 each) received oral gavages at doses of 5 mg Mn/kg or 15 mg Mn/kg as MnCl(2) once daily for 30 days. Blood, CSF, and choroid plexus were collected and brain capillary fractions were separated from the regional parenchyma. Metal analyses showed that oral Mn exposure decreased concentrations of Fe in serum (-66%) but increased Fe in the CSF (+167%). Gel shift assay showed that Mn caused a dose-dependent increase of binding of IRP1 to iron responsive element-containing RNA in BCB in the choroid plexus (+70%), in regional BBB of capillaries of striatum (+39%), hippocampus (+56%), frontal cortex (+49%), and in brain parenchyma of striatum (+67%), hippocampus (+39%) and cerebellum (+28%). Real-time RT-PCR demonstrated that Mn exposure significantly increased the expression of TfR mRNA in choroid plexus and striatum with concomitant reduction in the expression of ferritin (Ft) mRNA. Collectively, these data indicate that in vivo Mn exposure results in Fe redistribution in body fluids through regulating the expression of TfR and ferritin at BCB and selected regional BBB. The disrupted Fe transport by brain barriers may underlie the distorted Fe homeostasis in the CSF.

Blockade and enhancement of glutamate receptor responses in Xenopus oocytes by methylated arsenicals

Pentavalent and trivalent organoarsenic compounds belong to the major metabolites of inorganic arsenicals detected in humans. Recently, the question was raised whether the organic arsenicals represent metabolites of a detoxification process or methylated species with deleterious biological effects. In this study, the effects of trivalent arsenite (AsO(3) (3-); iA(III)), the pentavalent organoarsenic compounds monomethylarsonic acid (CH(3)AsO(OH)(2); MMA(V)) and dimethylarsinic acid ((CH(3))(2)AsO(OH); DMA(V)) and the trivalent compounds monomethylarsonous acid (CH(3)As(OH)(2), MMA(III)) and dimethylarsinous acid ((CH(3))(2)As(OH); DMA(III)) were tested on glutamate receptors and on voltage-operated potassium and sodium channels heterologously expressed in Xenopus oocytes. Membrane currents of ion channels were measured by conventional two-electrode voltage-clamp techniques. The effects of arsenite were tested in concentrations of 1-1,000 micromol/l and the organic arsenical compounds were tested in concentrations of 0.1-100 micromol/l. We found no significant effects on voltage-operated ion channels; however, the arsenicals exert different effects on glutamate receptors. While MMA(V) and MMA(III) significantly enhanced ion currents through N-methyl-D: -aspartate (NMDA) receptor ion channels with threshold concentrations <10 micromol/l, DMA(V) and DMA(III) significantly reduced NMDA-receptor mediated responses with threshold concentrations <0.1 micromol/l; iA(III) had no effects on glutamate receptors of the NMDA type. MMA(III) and DMA(V) significantly reduced ion currents through alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-receptor ion channels with threshold concentrations <10 micromol/l (MMA(III)) and <1 micromol/l (DMA(V)). MMA(V) and iA(III) had no significant effects on glutamate receptors of the AMPA type. The effects of MMA(V), MMA(III), DMA(V) and DMA(III )on glutamate receptors point to a neurotoxic potential of these substances.

Brain barrier systems: a new frontier in metal neurotoxicological research

The concept of brain barriers or a brain barrier system embraces the blood-brain interface, referred to as the blood-brain barrier, and the blood-cerebrospinal fluid (CSF) interface, referred to as the blood-CSF barrier. These brain barriers protect the CNS against chemical insults, by different complementary mechanisms. Toxic metal molecules can either bypass these mechanisms or be sequestered in and therefore potentially deleterious to brain barriers. Supportive evidence suggests that damage to blood-brain interfaces can lead to chemical-induced neurotoxicities. This review article examines the unique structure, specialization, and function of the brain barrier system, with particular emphasis on its toxicological implications. Typical examples of metal transport and toxicity at the barriers, such as lead (Pb), mercury (Hg), iron (Fe), and manganese (Mn), are discussed in detail with a special focus on the relevance to their toxic neurological consequences. Based on these discussions, the emerging research needs, such as construction of the new concept of blood-brain regional barriers, understanding of chemical effect on aged or immature barriers, and elucidation of the susceptibility of tight junctions to toxicants, are identified and addressed in this newly evolving field of neurotoxicology. They represent both clear challenges and fruitful research domains not only in neurotoxicology, but also in neurophysiology and pharmacology.

Transport of L-[125I]thyroxine by in situ perfused ovine choroid plexus: inhibition by lead exposure

Lead (Pb) exposure hinders brain development in children by mechanisms that remain unknown. Previous evidence shows that sequestration of Pb in the choroid plexus lowers the production and secretion of transthyretin (TTR), a thyroxine (T4) transport protein, from the choroid plexus into the cerebrospinal fluid (CSF). This study was undertaken to characterize the uptake kinetics of T4 by the choroid plexus and to determine if in vivo Pb exposure altered the T4 uptake in an in situ perfused ovine choroid plexus model. Sheep received i.p. injections of Pb acetate (20 mg Pb/kg) or Na acetate (as the controls) every 48 h for a period of 16 d. The [125I]T4 uptake was determined by a paired-tracer perfusion method using 0.5 microCi [125I]T4 and 2 microCi [14C]mannitol at various concentrations of unlabeled T4 (trace to 20 microM). The flux of [125I]T4 into the choroid plexus followed Michaelis-Menten kinetics with the maximum flux (Vmax) of 56.6 nmol/min/g and half-saturation constant (Km) of 10.7 mumol/L, suggesting an evident saturable influx of T4 into the choroid epithelium. In vivo Pb exposure in these sheep resulted in a significant accumulation of Pb in the choroid plexus and hippocampus. Pb treatment diminished the Vmax by 63.7% of control, but did not alter Km. The maximal cellular uptake (Umax) and net uptake (Unet) in Pb-treated animals were 2.1-fold and 1.9-fold, respectively, lower than those of control. Exposure to Pb, however, did not significantly change the flow rate through the choroid plexus. Data suggest that the choroid plexus may serve as a significant site for T4 transport into the CSF, and Pb exposure may hinder the influx of T4 from the blood into the choroid plexus.

Manganese distribution across the blood-brain barrier. I. Evidence for carrier-mediated influx of managanese citrate as well as manganese and manganese transferrin

Manganese (Mn) is an essential element and a neurotoxicant. Regulation of Mn movement across the blood-brain barrier (BBB) contributes to whether the brain Mn concentration is functional or toxic. In plasma, Mn associates with water, small molecular weight ligands and proteins. Mn speciation may influence the kinetics of its movement through the BBB. In the present work, the brain influx rates of 54Mn2+, 54Mn citrate and 54Mn transferrin (54Mn Tf) were determined using the in situ brain perfusion technique. The influx rates were compared to their predicted diffusion rates, which were determined from their octanol/aqueous partitioning coefficients and molecular weights. The in situ brain perfusion fluid contained 54Mn2+, 54Mn citrate or 54Mn Tf and a vascular volume/extracellular space marker, 14C-sucrose, which did not appreciably cross the BBB during these short experiments (15-180 s). The influx transfer coefficient (Kin) was determined from four perfusion durations for each Mn species in nine brain regions and the lateral ventricular choroid plexus. The brain Kin was (5-13) x 10(-5), (3-51) x 10(-5), and (2-13) x 10(-5) ml/s/g for 54Mn2+, 54Mn citrate, and 54Mn Tf, respectively. Brain Kin values for any one of the three Mn species generally did not significantly differ among the nine brain regions and the choroid plexus. However, the brain Kin for Mn citrate was greater than Mn2+ and Mn Tf Kin values in a number of brain regions. When compared to calculated diffusion rates, brain Kin values suggest carrier-mediated brain influx of 54Mn2+, 54Mn citrate and 54Mn Tf. 55Mn citrate inhibited 54Mn citrate uptake, and 55Mn2+ inhibited 54Mn2+ uptake, supporting the conclusion of carrier-mediated brain Mn influx. The greater Kin values for Mn citrate than Mn2+ and its presence as a major non-protein-bound Mn species in blood plasma suggest Mn citrate may be a major Mn species entering the brain.

A study on behavioral, neurotoxicological, and immunotoxicological effects of subchronic arsenic treatment in rats

Male Wistar rats were treated for 4, 8, and 12 wk with 3.33, 6.66, 13.3, or 26.6 mg/kg of inorganic arsenic (NaAsO(2)) per os by gavage. Changes in behavioral and electrophysiological parameters (spontaneous open-field exploration; electrocorticogram mean frequency and power spectrum; latency and duration of somatosensory, visual, and auditory evoked potentials; conduction velocity; and relative and absolute refractory period of a peripheral nerve) were determined. Treated rats exhibited hypoactivity of horizontal ambulation in the open field and showed depressed rates of grooming. The electrophysiological data, recorded from anesthetized rats, did not show any significant dose- and time-dependent changes. Changes in humoral immune response, tested after 4 wk of treatment, were not marked. The weight of organs responsible for immune response (thymus, spleen, adrenals), was significantly reduced, as were delayed-type hypersensitivity (DTH) reaction and mean cell volume (MCV) of red blood cells a hematological parameter. Plaque-forming cell (PFC) assay proved to be insensitive in this short-time exposure. These results suggest that subchronic low-level exposure to arsenic can affect immune responses and/or spontaneous behavior of rats.

Arsenic trioxide in the treatment of newly diagnosed acute promyelocytic leukemia: a single center experience

Arsenic trioxide (As(2)O(3)) has been found effective in the treatment in the treatment of acute promyelocytic leukemia (APML). Most studies with As(2)O(3) involve patients with APML who have relapsed following standard therapy. Between January 1998 and July 2000, 14 patients were recruited for an ongoing trial of As(2)O(3) in the treatment of newly diagnosed APML. Arsenic trioxide was administered at a dose of 10 mg/day until complete remission (CR) was achieved. Afterward, a consolidation course and a maintenance schedule consisting of As(2)O(3) as a single agent were administered over 6 months. There were 3 early deaths related to intra-cerebral hemorrhage: two on day 3 and one on day 4. Of the 11 evaluable patients, one died on day 21 secondary to uncontrolled sepsis, while the remaining 10 (91%) have attained CR. The average time to CR was 52.3 days (range: 34-70 days). One patient developed an isolated central nervous system (CNS) relapse and subsequently went into a second CR following therapy with triple intrathecal chemotherapy, cranial irradiation, and an additional 4-week course of systemic As(2)O(3). This patient, as well as the remaining nine, has continued to remain in CR at a median follow up of 15 months (range: 2-33 months). Eight out of 10 patients achieved molecular remission at variable periods during their consolidation and maintenance schedules. One patient developed an ATRA syndrome and was administered daunorubicin (40 mg/day) for 2 days. The side effects with this therapy were minimal and did not require cessation of therapy in any patient. There was no significant hepatic toxicity. In our experience, arsenic trioxide is effective in inducing and maintaining remission in patients with APML with minimal side effects. The optimal regimen and total dose required need to be defined.

Strain differences in the toxicity of cadmium to trigeminal ganglia in mice

Cadmium (Cd) is toxic to sensory ganglia in many animal species. Cadmium uptake is low in the central nervous system, but it distributes preferentially to peripheral sensory and autonomic ganglia. Strain differences have been demonstrated in the sensitivity of mice to Cd-induced hepatotoxicity, testicular toxicity, and teratogenicity. To study the sensitivity of different mouse strains to Cd toxicity in sensory ganglia, eight strains of mice (four sensitive to testicular toxicity: 129/SVIM, AKR/J, DBA/1J, and C57BR/J; and four resistant: Balb/C, C3H/HeJ, A/J, and C57BL/6J) were given 15 micromol CdCl(2)/kg iv. Trigeminal ganglia (TG) were harvested 24 h later and examined by light microscopy for pathologic lesions. Cadmium induced degeneration of ganglion cells in five strains, namely 129/SVIM, AKR/J, DBA/1J, C57BR/J, and C3H/HeJ mice. These are the same strains that show sensitivity to testicular toxicity, except for C3H/HeJ, which is resistant to testicular toxicity. Cd also induced focal hemorrhages around the ganglion cells and nerve fibers in two of these strains (129/SVIM and AKR/J) and scattered foci of necrosis in C3H/HeJ and 129/SVIM strains. There was no morphologic abnormality in three strains, namely Balb/C, A/J, and C57BL/6J. To examine the mechanism of these strain differences in toxicity, all eight strains of mice were given a nontoxic dose of Cd (0.4 micromol CdCl(2)/kg, 20 microCi (109)Cd/kg iv). Cadmium distribution to the brain and trigeminal ganglia was determined 30 min later by gamma scintillation spectrometry. Cadmium content in the brain was very low and did not differ among the eight strains. In contrast, Cd content was higher in trigeminal ganglia of four of the five strains showing trigeminal ganglia sensitivity than in the three strains showing resistance. In conclusion, the toxicity of Cd to trigeminal ganglia is different among various strains of mice. This strain difference in toxicity appears to be due, at least in part, to differences in the distribution of Cd to the ganglia, but it is clearly not the only factor.

Transthyretin, thyroxine, and retinol-binding protein in human cerebrospinal fluid: effect of lead exposure

Transthyretin (TTR), synthesized by the choroid plexus, is proposed to have a role in transport of thyroid hormones in the brain. Our previous studies in animals suggest that sequestration of lead (Pb) in the choroid plexus may lead to a marked decrease in TTR levels in the cerebrospinal fluid (CSF). The objectives of this study were to establish in humans whether TTR and thyroxine (T(4)) are correlated in the CSF, and whether CSF levels of Pb are associated with those of TTR, T(4), and/or retinol-binding protein (RBP). Eighty-two paired CSF and blood/serum samples were collected from patients undergoing clinical diagnosis of CSF chemistry. Results showed that the mean value of CSF concentrations for TTR was 3.33 +/- 1.60 microg/mg of CSF proteins (mean +/- SD, n = 82), for total T(4) (TT(4)) was 1.56 +/- 1.68 ng/mg (n = 82), for RBP was 0.34 +/- 0.19 microg/mg (n = 82), and for Pb was 0.53 +/- 0.69 microg/dl (n = 61 for those above the detection limit). Linear regression analyses revealed that CSF TTR levels were positively associated with those of CSF TT(4) (r = 0.33, p < 0.005). CSF TTR concentrations, however, were inversely associated with CSF Pb concentrations (r = -0.29, p < 0.05). There was an inverse, albeit weak, correlation between CSF TT(4) and CSF Pb concentrations (r = -0.22, p = 0.09). The concentrations of TTR, TT(4), and Pb in the CSF did not vary as the function of their levels in blood or serum, but RBP concentrations in the CSF did correlate to those of serum (r = 0.39, p < 0.0005). Unlike TTR, CSF RBP concentrations were not influenced by PB: These human data are consistent with our earlier observations in animals, which suggest that TTR is required for thyroxine transport in the CSF and that Pb exposure is likely associated with diminished TTR levels in the CSF.

Toxicology of choroid plexus: special reference to metal-induced neurotoxicities

The chemical stability in the brain underlies normal human thinking, learning, and behavior. Compelling evidence demonstrates a definite capacity of the choroid plexus in sequestering toxic heavy metal and metalloid ions. As the integrity of blood-brain and blood-CSF barriers, both structurally and functionally, is essential to brain chemical stability, the role of the choroid plexus in metal-induced neurotoxicities has become an important, yet under-investigated research area in neurotoxicology. Metals acting on the choroid plexus can be categorized into three major groups. A general choroid plexus toxicant can directly damage the choroid plexus structure such as mercury and cadmium. A selective choroid plexus toxicant may impair specific plexus regulatory pathways that are critical to brain development and function, rather than induce massive pathological alteration. The typical examples in this category include lead-induced alteration in transthyretin production and secretion as well as manganese interaction with iron in the choroid plexus. Furthermore, a sequestered choroid plexus toxicant, such as iron, silver, or gold, may be sequestered by the choroid plexus as an essential CNS defense mechanism. Our current knowledge on the toxicological aspect of choroid plexus research is still incomplete. Thus, the future research needs have been suggested to focus on the role of choroid plexus in early CNS development as affected by metal sequestration in this tissue, to explore how metal accumulation alters the capacity of the choroid plexus in regulation of certain essential elements involved in the etiology of neurodegenerative diseases, and to better understand the blood-CSF barrier as a defense mechanism in overall CNS function.

Neurotoxicology of the brain barrier system: new implications

The concept of a barrier system in the brain has existed for nearly a century. The barrier that separates the blood from the cerebral interstitial fluid is defined as the blood-brain barrier, while the one that discontinues the circulation between the blood and cerebrospinal fluid is named the blood-cerebrospinal fluid barrier. Evidence in the past decades suggests that brain barriers are subject to toxic insults from neurotoxic chemicals circulating in blood. The aging process and some disease states render barriers more vulnerable to insults arising inside and outside the barriers. The implication of brain barriers in certain neurodegenerative diseases is compelling, although the contribution of chemical-induced barrier dysfunction in the etiology of any of these disorders remains poorly understood. This review examines what is currently understood about brain barrier systems in central nervous system disorders by focusing on chemical-induced neurotoxicities including those associated with nitrobenzenes, N-methyl-D-aspartate, cyclosporin A, pyridostigmine bromide, aluminum, lead, manganese, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and 3-nitropropionic acid. Contemporary research questions arising from this growing understanding show enormous promises for brain researchers, toxicologists, and clinicians.