Effects of acute exposure to aluminum on blood–brain barrier and the protection of zinc

A review of the epidemiological and laboratory evidence of the role of aluminum exposure in pathogenesis of cardiovascular diseases

The objective of the present study was to review the epidemiological and laboratory evidence on the role of aluminum (Al) exposure in the pathogenesis of cardiovascular diseases. Epidemiological data demonstrated an increased incidence of cardiovascular diseases (CVD), including hypertension and atherosclerosis in occupationally exposed subjects and hemodialysis patients. In addition, Al body burden was found to be elevated in patients with coronary heart disease, hypertension, and dyslipidemia. Laboratory studies demonstrated that Al exposure induced significant ultrastructural damage in the heart, resulting in electrocardiogram alterations in association with cardiomyocyte necrosis and apoptosis, inflammation, oxidative stress, inflammation, and mitochondrial dysfunction. In agreement with the epidemiological findings, laboratory data demonstrated dyslipidemia upon Al exposure, resulting from impaired hepatic lipid catabolism, as well as promotion of low-density lipoprotein oxidation. Al was also shown to inhibit paraoxonase 1 activity and to induce endothelial dysfunction and adhesion molecule expression, further promoting atherogenesis. The role of Al in hypertension was shown to be mediated by up-regulation of NADPH-oxidase, inhibition of nitric oxide bioavailability, and stimulation of renin-angiotensin-aldosterone system. It has been also demonstrated that Al exposure targets cerebral vasculature, which may be considered a link between Al exposure and cerebrovascular diseases. Findings from other tissues lend support that ferroptosis, pyroptosis, endoplasmic reticulum stress, and modulation of gut microbiome and metabolome are involved in the development of CVD upon Al exposure. A better understanding of the role of the cardiovascular system as a target for Al toxicity will be useful for risk assessment and the development of treatment and prevention strategies.

Local and Systemic Hypoxia as Inductors of Increased Aluminum and Iron Brain Accumulation Promoting the Onset of Alzheimer's Disease

Human environment is highly contaminated with aluminum, and aluminum is toxic to majority of tissues, particularly to neurons. In previous decades, aluminum exposure was frequently linked with the onset of Alzheimer's disease (AD), and increased levels of Al were detected in the brains of individuals with AD. People who live in a certain area are exposed to aluminum in a similar way (they eat the same vegetable and other foodstuffs, use similar cosmetics, and buy medications from the same manufacturer), nevertheless not all of them develop Alzheimer's disease. Majority of known risk factors for AD promote atherosclerosis and consequently reduce brain blood supply. In this review, we highlighted the significance of local (carotid disease and atherosclerosis of intracranial blood vessels) and systemic hypoxia (chronic obstructive pulmonary disease and anemia) in the development of AD. Nerve tissue is very sophisticated and sensitive to hypoxia and aluminum toxicity. As a side effect of compensatory mechanisms in case of hypoxia, neurons start to uptake aluminum and iron to a greater extent. This makes perfect a background for the gradual onset and development of AD.

Aluminum exposure induces central nervous system impairment via activating NLRP3-medicated pyroptosis pathway

PURPOSE

Aluminum is an environmental toxicant whose long-term exposure is closely associated with nervous system impairment. This study mainly investigated neurological impairment induced by subchronic aluminum exposure via activating NLRP3-medicated pyroptosis pathway.

METHODS

In vivo, Kunming mice were exposed to AlCl3 (30.3 mg/kg, 101 mg/kg and 303 mg/kg) via drinking water for 3 months, and administered with Rsv (100 mg/kg) by gavage for 1 month. Cognitive impairment was assessed by Morris water maze test, and pathological injury was detected via H&E staining. BBB integrity, pyroptosis and neuroinflammation were evaluated through western blotting and immunofluorescence methods. In vitro, BV2 microglia was treated with AlCl3 (0.5 mM, 1 mM and 2 mM) to sensitize pyroptosis pathway. The protein interaction was verified by co-immunoprecipitation, and neuronal damage was estimated via a conditioned medium co-culture system with BV2 and TH22 cells.

RESULTS

Our results showed that AlCl3 induced mice memory disorder, BBB destruction, and pathological injury. Besides, aluminum caused glial activation, sensitized DDX3X-NLRP3 pyroptosis pathway, released cytokines IL-1β and IL-18, initiating neuroinflammation. BV2 microglia treated with AlCl3 emerged hyperactivation and pyroptotic death, and Ddx3x knockdown inhibited pyroptosis signaling pathway. DDX3X acted as a live-or-die checkpoint in stressed cells by regulating NLRP3 inflammasome and G3BP1 stress granules. Furthermore, aluminum-activated microglia had an adverse effect on co-cultured neurons and destroyed nervous system homeostasis.

CONCLUSION

Aluminum exposure could induce pyroptosis and neurotoxicity. DDX3X determined live or die via selectively regulating pro-survival stress granules or pro-death NLRP3 inflammasome. Excessive activation of microglia might damage neurons and aggravate nerve injury.

Synthesis and Degradation of Poly(ADP-ribose) in Zebrafish Brain Exposed to Aluminum

Poly(ADPribosyl)ation is a post-translational protein modification, catalyzed by poly(ADP-ribose) polymerase (PARPs) enzymes, responsible for ADP-ribose polymer synthesis (PAR) from NAD⁺. PAR turnover is assured by poly(ADPR) glycohydrolase (PARGs) enzymes. In our previous study, the altered histology of zebrafish brain tissue, resulting in demyelination and neurodegeneration also with poly(ADPribosyl)ation hyperactivation, was demonstrated after aluminum (Al) exposure for 10 and 15 days. On the basis of this evidence, the aim of the present research was to study the synthesis and degradation of poly(ADP-ribose) in the brain of adult zebrafish exposed to 11 mg/L of Al for 10, 15, and 20 days. For this reason, PARP and PARG expression analyses were carried out, and ADPR polymers were synthesized and digested. The data showed the presence of different PARP isoforms, among which a human PARP1 counterpart was also expressed. Moreover, the highest PARP and PARG activity levels, responsible for the PAR production and its degradation, respectively, were measured after 10 and 15 days of exposure. We suppose that PARP activation is related to DNA damage induced by Al, while PARG activation is needed to avoid PAR accumulation, which is known to inhibit PARP and promote parthanatos. On the contrary, PARP activity decrease at longer exposure times suggests that neuronal cells could adopt the stratagem of reducing polymer synthesis to avoid energy expenditure and allow cell survival.

Taurine and deferiprone against Al-linked apoptosis in rat hippocampus

BACKGROUND

Aluminium (Al) overload has toxic effects on multiple organ systems, especially the nervous system. Al accumulation in the brain, especially the hippocampus, is an important factor contributing to Alzheimer's disease (AD). Deferiprone (DFP), a metal chelator, is used as a potential treatment for AD. In this study, we investigated the combined effect of taurine and DFP on Al chelation and hippocampal apoptosis in Al-exposed rats, as well as the underlying mechanisms of these effects to explore a possible therapy for AD.

METHODS

Male Wistar rats were divided into seven groups: negative control group (administered saline), Al-exposure group (administered AlCl₃ and saline), and five experimental groups (administered AlCl₃ and taurine, varying doses of DFP, or taurine with varying doses of DFP). After 8 weeks of treatment, the rats were sacrificed, and the terminal deoxyribonucleotidyl transferase (TDT)-mediated dUTP-digoxigenin nick end labelling (TUNEL) assay was used to detect hippocampal apoptotic cells. Real-time quantitative PCR was used to assess the expression of the Bcl2 and Bax genes, and a western blotting assay was used to evaluate BCL2, BAX, and cleaved caspase-3 levels.

RESULTS

Compared to the negative control group, the number of apoptotic cells in the hippocampus increased, Bcl2 expression significantly decreased, and BAX and cleaved caspase-3 levels increased in the Al-exposure group. The combination of taurine and DFP exerted a protective effect by inhibiting hippocampal cell apoptosis through the BCL2, BAX, and caspase-3 signalling pathways. Compared with the taurine-administered group, the group administered taurine with DFP showed a significantly increased Bcl2 and decreased Bax expression.

CONCLUSION

The combination of taurine and DFP is a potential candidate for the treatment of AD induced by Al exposure.

Zinc oxide calcium silicate composite attenuates acute tramadol toxicity in mice

BACKGROUND

Seizures are considered to be the most common symptom encountered in emergency- rushed tramadol-poisoned patients; accounting for 8% of the drug-induced seizure cases. Although, diazepam clears these seizures, the risk of central respiratory depression cannot be overlooked. Henceforth, three adsorbing composites were examined in a tramadol acute intoxication mouse model.

METHODS

Calcium Silicate (Wollastonite) either non-doped or wet doped with iron oxide (3%Fe₂O₃) or zinc oxide (30% ZnO) were prepared. The composites' adsorption capacity for tramadol was determined in vitro. Tramadol intoxication was induced in Swiss albino mice by a parenteral dose of 120 mg/kg. Proposed treatments were administered within 1 min at 5 increasing doses, i.p. The next 30 min, seizures were monitored as an intoxication symptom. Plasma tramadol concentration was recorded after two hours of administration.

RESULTS

The 3% Fe₂O₃-containing composite (CSFe3), was found to be composed of mainly wollastonite with very little alpha-hematite. On the other hand, hardystonite and wellimite were developed in the 30%ZnO-containing composite (CSZn3). Micro-round and irregular nano-sized microstructures were established (The particle size of CS was 56 nm, CSFe3 was 49 nm, and CSZn3 was 42 nm). The CSZn3 adsorption capacity reached 1497 mg of tramadol for each gram. Tramadol concentration was reduced in plasma and seizures were inhibited after its administration to mice at three doses.

CONCLUSION

The calcium silicate composite doped with ZnO presented a good resolution of tramadol-induced seizures accompanied by detoxification of blood, indicating its potential for application in such cases. Further studies are required.

Maternal and Newborn Blood Aluminum Levels and Neurodevelopment of Infants: Is there a Need for Concern?

Aluminum is a neurotoxic element that enters the human body due to its widespread usage in daily life. It has the potential to affect the neurological development of the fetus and infant adversely. This study aimed to evaluate the relationship between maternal and umbilical cord serum aluminum level and infant neurodevelopment. Over a period of March 2018 to September 2019, we conducted a prospective cohort study; 173 Mother-new-born pairs were enrolled. Aluminum levels were measured using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The correlation with Bayley Scales of Infant Development (BSID) -3rd edition score and maternal and cord serum aluminum were assessed via linear regression model. The mean concentration of maternal and cord serum aluminum was 2.58 ± 1.14 µg/dL and 1.44 ± 0.62 µg/dL, respectively. There was a significant correlation in aluminum level between maternal and umbilical cord serum (Pearson's r = 0.591, p < 0.000). There is no significant correlation between maternal and serum aluminum level, and BSID-3rd edition (cognitive, motor, language, and social-emotion) score at the average age of 6.5 months. In conclusion, maternal and cord serum aluminum levels were significantly correlated but did not correlate with infant neurodevelopment. Thus, low serum aluminum concentration and their association with child neurodevelopment deserve further investigation longitudinally in a large cohort.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s12291-021-01002-y.

Neurobehavioral and Immunohistochemical Studies of the Cerebral Cortex Following Treatment with Ethyl Acetate Leaf Fraction of Tamarindus indica During Prenatal Aluminum Chloride Exposure in Wistar Rats

Purpose

The recent increase in aluminum exposure and its effect on the development of the brain call for serious attention. The study investigated the behavioral and immunohistochemical changes in the cerebral cortex of Wistar rats following prenatal co-administration of ethyl acetate leaf fraction of Tamarindus indica (EATI) and aluminum chloride (AlCl₃).

Methods

Pregnant Wistar rats were divided into 5 groups (n=4). Group I (negative control), Group II-V were experimental groups treated with 200 mg/kg of AlCl₃ s/c. Group III and IV received an additional 400 mg/kg and 800 mg/kg of EATI respectively, while Group V received an additional 300 mg/kg of Vitamin E for 14 days (prenatal days 7-21) via the oral route. The pups were then exposed to cliff avoidance, negative geotaxis, and elevated plus maze (EPM) test on the post-natal day (PoND) 4-6, 7-10, and 18 respectively. On PoND 21 pups were sacrificed, and the skull dissected to remove the brain. The harvested brain tissues were processed for Cresyl fast (CF) and glial fibrillary acid protein (GFAP).

Results

The study showed that EATI administration during AlCl₃ exposure was associated with significant improvement in sensory-motor development. The EPM, CF, and GFAP results revealed significant improvement in anxiety-like behavior, motor activities, GFAP expression, pyramidal cell count, and Nissl staining following prenatal EATI administration during AlCl₃ exposure.

Conclusion

The present study concludes that EATI was associated with some protective potential during prenatal AlCl₃ exposure in Wistar rats.

The Protection of Zinc against Acute Cadmium Exposure: A Morphological and Molecular Study on a BBB In Vitro Model

Cadmium (Cd) is a well-known occupational and environmental pollutant worldwide, and its toxicity is widely recognised. Cd is reported to increase the permeability of the blood–brain barrier (BBB) and to penetrate and accumulate in the brain. Although many lines of evidence show that Cd toxicity is induced by different mechanisms, one of the best known is the Cd-dependent production of reactive oxygen species (ROS). Zinc is a trace element known as coenzyme and cofactor for many antioxidant proteins, such as metallothioneins and superoxide dismutase enzymes. To date, very little is known about the role of Zn in preventing Cd-induced blood–brain barrier (BBB) alterations. The goal of this study was to test the Zn antioxidant capacity against Cd-dependent alterations in a rat brain endothelial cell line (RBE4), as an in vitro model for BBB. In order to mimic acute Cd poisoning, RBE4 cells were treated with CdCl₂ 30 µM for 24 h. The protective role of ZnCl₂ (50 µM) was revealed by evaluating the cell viability, reactive oxygen species (ROS) quantification, cytochrome C distribution, and the superoxide dismutase (SOD) protein activity. Additionally, the effectiveness of Zn in counteracting the Cd-induced damage was investigated by evaluating the expression levels of proteins already known to be involved in the Cd signalling pathway, such as GRP78 (an endoplasmic reticulum (ER) stress protein), caspase3 pro- and cleaved forms, and BAX. Finally, we evaluated if Zn was able to attenuate the alterations of zonula occludens-1 (ZO-1), one of the tight-junction (TJ) proteins involved in the formation of the BBB. Our data clearly demonstrate that Zn, by protecting from the SOD activity impairment induced by Cd, is able to prevent the triggering of the Cd-dependent signalling pathway that leads to ZO-1 dislocation and downregulation, and BBB damage.

Micronutrient Improvement of Epithelial Barrier Function in Various Disease States: A Case for Adjuvant Therapy

The published literature makes a very strong case that a wide range of disease morbidity associates with and may in part be due to epithelial barrier leak. An equally large body of published literature substantiates that a diverse group of micronutrients can reduce barrier leak across a wide array of epithelial tissue types, stemming from both cell culture as well as animal and human tissue models. Conversely, micronutrient deficiencies can exacerbate both barrier leak and morbidity. Focusing on zinc, Vitamin A and Vitamin D, this review shows that at concentrations above RDA levels but well below toxicity limits, these micronutrients can induce cell- and tissue-specific molecular-level changes in tight junctional complexes (and by other mechanisms) that reduce barrier leak. An opportunity now exists in critical care—but also medical prophylactic and therapeutic care in general—to consider implementation of select micronutrients at elevated dosages as adjuvant therapeutics in a variety of disease management. This consideration is particularly pointed amidst the COVID-19 pandemic.

Zinc as a Neuroprotective Nutrient for COVID-19-Related Neuropsychiatric Manifestations: A Literature Review

The outbreak of the pandemic associated with Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2) led researchers to find new potential treatments, including nonpharmacological molecules such as zinc (Zn2+). Specifically, the use of Zn2+ as a therapy for SARS-CoV-2 infection is based on several findings: 1) the possible role of the anti-inflammatory activity of Zn2+ on the aberrant inflammatory response triggered by COronaVIrus Disease 19 (COVID-19), 2) properties of Zn2+ in modulating the competitive balance between the host and the invading pathogens, and 3) the antiviral activity of Zn2+ on a number of pathogens, including coronaviruses. Furthermore, Zn2+ has been found to play a central role in regulating brain functioning and many disorders have been associated with Zn2+ deficiency, including neurodegenerative diseases, psychiatric disorders, and brain injuries. Within this context, we carried out a narrative review to provide an overview of the evidence relating to the effects of Zn2+ on the immune and nervous systems, and the therapeutic use of such micronutrients in both neurological and infective disorders, with the final goal of elucidating the possible use of Zn2+ as a preventive or therapeutic intervention in COVID-19. Overall, the results from the available evidence showed that, owing to its neuroprotective properties, Zn2+ supplementation could be effective not only on COVID-19-related symptoms but also on virus replication, as well as on COVID-19-related inflammation and neurological damage. However, further clinical trials evaluating the efficacy of Zn2+ as a nonpharmacological treatment of COVID-19 are required to achieve an overall improvement in outcome and prognosis.

High-fat diet exacerbates lead-induced blood-brain barrier disruption by disrupting tight junction integrity

Environmental exposure to lead (Pb) can damage to the central nervous system (CNS) in humans. High-fat diet (HFD) also has been suggested to impair neurocognitive function. Blood-brain barrier (BBB) is a rigorous permeability barrier for maintaining homeostasis of CNS. The damage of BBB caused by tight junctions (TJs) disruption is central to the etiology of various CNS disorders. This study aimed to investigate whether HFD could exacerbate Pb exposure induced the destruction of BBB integrity by TJs disruption. To this end, we measured cell viability assay, trans-endothelial electrical resistance assay, horseradish peroxidase flux measurement, Western blot analysis, and immunofluorescence experiments. The results showed that palmitic acid (PA), the most common saturated fatty acid found in the human body, can increase the permeability of the BBB in vitro which formed in bEnd.3 cells induced by Pb exposure, and decrease the expression of TJs, such as zonula occludins-1 (ZO-1) and occludin. Besides, we found that PA could promote the up-regulation of matrix metalloproteinase (MMP)-9 expression and activate the c-Jun N-terminal kinase (JNK) pathway induced by Pb. MMP-9 inhibitor or JNK inhibitor could increase BBB integrity and up-regulate the expressions of ZO-1 and occludin after treatment, respectively. Moreover, the JNK inhibitor could down-regulate the expression of MMP-9. In conclusion, these results suggested that HFD exacerbates Pb-induced BBB disruption by disrupting TJs integrity. This may be because PA promotes the activation of JNK pathway and then up-regulated the expression of MMP-9 after Pb-exposure. It is suggested that people with HFD exposed to environmental Pb may cause more serious damage to the CNS.

Bergamot essential oil attenuate aluminum-induced anxiety-like behavior through antioxidation, anti-inflammatory and GABA regulation in rats

A large number of studies showed that aluminum (Al) has potential neurotoxicity to human and animal bodies. Al-treated animals showed anxiety-like behavior, oxidative stress, neuroinflammation and γ-aminobutyric acid (GABA) changes. Bergamot essential oil (BEO) is a kind of well-known plant extract from the fresh fruit of bergamot. Previous studies suggested that BEO improved mood and relieved symptoms of stress-induced anxiety. This study was designed to study the effects of BEO on anxiety-like behavior, oxidative stress, neuroinflammation and GABA system in aluminum trichloride (AlCl₃) treated rats. Results showed that AlCl₃ exposure induced anxiety-like behavior in the elevated plus maze and the open field test. Moreover, AlCl₃ exposure decreased the level of GABA and the activity of glutathione peroxidase (GPx), catalase (CAT) and superoxide dismutase (SOD) in the hippocampus (HP) and the frontal cortex (FC). In addition, AlCl₃ exposure increased the levels of malondialdehyde (MDA) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) and the levels of interleukin-1 beta (IL-1β), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) in the HP and the FC. To the contrary, co-administration of BEO and AlCl₃ improved the anxiety-like behavior, GABA system, oxidative stress and neuroinflammation. These results indicated that BEO can alleviate the anxiety-like behavior of AlCl₃-exposed rats through the combined action of antioxidant, anti-inflammatory and GABA regulation.

The Possible Neuroprotective Effect of Silymarin against Aluminum Chloride-Prompted Alzheimer's-Like Disease in Rats

Alzheimer's disease (AD) is a worldwide rapidly growing neurodegenerative disease. Here, we elucidated the neuroprotective effects of silymarin (SM) on the hippocampal tissues of aluminum chloride (AlCl3)-induced Alzheimer-like disease in rats using biochemical, histological, and ultrastructural approaches. Forty rats were divided into control, SM, AlCl3, and AlCl3 + SM groups. Biochemically, AlCl3 administration resulted in marked elevation in levels of lipid peroxidation (LPO) and nitric oxide (NO) and decrease in levels of reduced glutathione (GSH), catalase (CAT), and superoxide dismutase (SOD). Moreover, AlCl3 significantly increased tumor necrosis factor-α (TNF-α), interleukin-1beta (IL-1β), and acetylcholinesterase (AChE) activities. Furthermore, myriad histological and ultrastructural alterations were recorded in the hippocampal tissues of AlCl3-treated rats represented as marked degenerative changes of pyramidal neurons, astrocytes, and oligodendrocytes. Additionally, some myelinated nerve fibers exhibited irregular arrangement of their myelin coats, while the others revealed focal degranulation of their myelin sheaths. Severe defects in the blood-brain barrier (BBB) were also recorded. However, co-administration of SM with AlCl3 reversed most of the biochemical, histological, and ultrastructural changes triggered by AlCl3 in rats. The results of the current study indicate that SM can potentially mend most of the previously evoked neuronal damage in the hippocampal tissues of AlCl3-kindled rats.

Oral exposure to aluminum leads to reduced nicotinic acetylcholine receptor gene expression, severe neurodegeneration and impaired hippocampus dependent learning in mice

Aluminum (Al) is known for its neurotoxicity for over a century and is reported to have specifically high toxicity for cholinergic system. The effect of Al on muscarinic acetylcholine receptors is widely reported, but its effect on nicotinic acetylcholine receptors (nAChRs) is less well known. The aim of this study was to determine the effects of Al on hippocampus dependent learning and memory, function and expression of nAChRs in the hippocampus. Al concentration and neurodegeneration were also measured in the hippocampus following Al treatment. The mice were treated with 250 mg/kg AlCl₃.6H₂O in drinking water for a period of 42 days. Results show that Al treated animals have significantly reduced spatial reference memory as compared to control animals in Morris water maze test. Similarly, Al treated animals showed reduced contextual memory for Pavlovian fear compared to control animals. Al treated animals show higher anxiety in elevated plus maze as compared to control animals. The analysis of nAChR expression via RT-PCR showed reduced expression of α7, α4 and β2 nAChR gene expression in the hippocampus of Al treated animals. High Al accumulation was observed in Al-treated animals (688.14 ± 242.82 μg/g) compared to the control group (115.14 ± 18.18 μg/g) that resulted in severe neurodegeneration in the hippocampus. These results demonstrated that Al exposure caused neurotoxicity in mice hippocampus which is manifested by reduced memory and elevated anxiety. The results were further validated by high Al accumulation in the hippocampus, severe neurodegeneration and reduced expression of nAChRs.

Lanthanum Chloride Impairs the Blood-Brain Barrier Integrity by Reduction of Junctional Proteins and Upregulation of MMP-9 in Rats

Lanthanum could cause cognitive impairment in children and rodent animals. The normal blood-brain barrier (BBB) integrity is essential for protecting the brain from systemic toxins and maintaining the homeostasis for proper neuronal function. BBB dysfunction has been implicated as a potential mechanism of heavy metal-induced neurotoxicity. The present study was aimed to investigate effects of lanthanum on BBB integrity and endothelial junctional complexes in the cerebral cortex of young rats. Animals were exposed to lanthanum chloride (LaCl₃) through drinking water under 0, 0.25, 0.5, and 1.0% concentrations from postnatal day 0 until 30 days after weaning. LaCl₃-exposure increased BBB permeability, caused ultrastructure changes in cerebral capillaries, and reduced protein expression of claudin-5, occludin, and VE-cadherin. Due to the critical role of matrix metalloproteinases (MMPs) in BBB integrity, we further examined alterations in MMPs activity and expression. Enhanced gelatinase activity and upregulated MMP-9 expression were observed after LaCl₃-exposure, concurrently with decreased expression of endogenous inhibitor tissue inhibitors of metalloproteinase (TIMP)-1. Taken together, this study demonstrated that postnatal lanthanum exposure caused leakage of BBB in young rats, partially attributed to upregulation of MMP-9 and reduction of junctional proteins expression.

The interaction of zinc and the blood-brain barrier under physiological and ischemic conditions

Zinc is the second most abundant metal in human and serves as an essential trace element in the body. During the past decades, zinc has been found to play important roles in central nervous system, such as the development of neurons and synaptic activities. An imbalance of zinc is associated with brain diseases. The blood-brain barrier (BBB) maintains the homeostasis of the microenvironment, regulating the balance of zinc in the brain. A compromised BBB is the main cause of severe complications in cerebral ischemic patients, such as hemorrhage transformation, inflammation and edema. Recent studies reported that zinc in the brain may be a potential target for integrative protection against ischemic brain injury. Although zinc has long been regarded as important transmitters in central nervous system, the critical role of zinc dyshomeostasis in damage to the BBB has not been fully recognized. In this review, we summarize the role of the BBB in regulating homeostasis of zinc in physiological conditions and the effects of changes in zinc levels on the permeability of the BBB in cerebral ischemia. The integrity of BBB maintains the homeostasis of zinc in pathological conditions, while the balance of zinc in the brain and the circulation maintains the normal function of the BBB. Interrupting the zinc/BBB system will disturb the microenvironment in the brain, leading to pathological diseases. In stroke patients, zinc may serve as a potential target for protecting the BBB and reducing hemorrhage transformation, inflammation and edema.

Analysis of aluminum, minerals and trace elements in the milk samples from lactating mothers in Hamadan, Iran

The present cross-sectional study is aimed at analyzing the breast milk of lactating mothers in Hamadan, Iran for aluminum and several minerals and trace elements. Ten governmental health care centers were utilized to facilitate collection of breast milk samples. The breast milk samples were collected at 1, 2, 6, 7, and 12 months postpartum from one hundred healthy lactating women, who delivered full-term newborns. Detection of sodium (Na), zinc (Zn), calcium (Ca), iron (Fe), copper (Cu), magnesium (Mg) and aluminum (Al) levels was conducted with the use of Inductively Coupled Plasma Mass Spectrometry (ICP-MS). This method has shown high accuracy, precision, sensitivity, and linearity for the wide range of concentrations. The accumulated data were not normally distributed; thus, the non-parametric Mann-Whitney U test was used in the statistical analysis of the results. Mean concentrations of Fe, Zn, Cu, Ca, Mg, and Na were 0.75, 1.38, 0.35, 255, 34.58, and 155.72 μg/mL, respectively. The mean level of Al, a well-known neurotoxic metal, was determined to be an alarming 0.191 μg/mL. Moreover, 95% of participants contained very harmful concentrations of Al in their milk. This study also revealed Zn deficiency in about 50% of milk samples. Further investigation is needed to elucidate sources of exposure and factors that may influence maternal and fetal exposure to aluminum.

Entry and Deposit of Aluminum in the Brain

Aluminum, as a known neurotoxicant, contributes to cognitive dysfunction and may contribute to Alzheimer's disease. The important reason is that aluminum can enter and be deposited in the brain. There have been three routes by which aluminum could enter the brain from systemic circulation or the site of absorption. Aluminum fluxes into brain across the blood-brain barrier (BBB), the choroid plexuses and the nasal cavity. Some factors, such as the increasing of the blood-brain barrier permeability, citric acid and parathyroid hormone (PTH), and vitamin D, can promote aluminum to enter the brain. But the redistribution of aluminum out of the brain is slow, so aluminum can be deposited in the brain for a long time.

Evidence of Zinc in Affording Protection Against X-Ray-Induced Brain Injury in Rats

In the present world, X-rays have been regarded as one of the most efficient tools in medicine, industry and research. On the contrary, extensive human exposure to these rays is responsible for causing detrimental effects on physiological system. The aim of the present study was to investigate the role of zinc (Zn), if any, in mitigating the adverse effects induced by fractionated X-irradiation on rat brain. Female Sprague-Dawley rats weighing 170-200 g were divided into four different groups viz.: (a) normal control, (b) X-irradiated (21Gy), (c) zinc treated (227 mg/L in drinking water) and (d) X-irradiated + zinc treated. The skulls of animals belonging to groups (b) and (d) were exposed to X-rays in 30 fractions. Each fraction delivered a radiation dose of 70 rads, and rats were exposed to two fractions every day for 15 days, consecutively. X-ray treatment resulted in significant alterations in the neurobehavior, neurotransmitter levels and neuro-histoarchitecture of rats, whereas zinc co-treatment with X-rays resulted in significant improvement in these parameters. X-ray exposure also caused a significant increase in the levels of lipid peroxidation as well as activities of catalase and superoxide dismutase, which however were decreased upon simultaneous Zn treatment. On the contrary, X-ray treatment down-regulated the glutathione system, which were found to be up-regulated by zinc co-treatment. Further, protein expressions of p53 and NF-ҚB were found to be significantly elevated after X-irradiation, which were reversed following Zn supplementation. Hence, Zn seems to be an effective agent in mitigating the detrimental effects caused by exposure to X-rays.

Genetic, Transcriptome, Proteomic, and Epidemiological Evidence for Blood-Brain Barrier Disruption and Polymicrobial Brain Invasion as Determinant Factors in Alzheimer's Disease

Diverse pathogens are detected in Alzheimer's disease (AD) brains. A bioinformatics survey showed that AD genome-wide association study (GWAS) genes (localized in bone marrow, immune locations and microglia) relate to multiple host/pathogen interactomes (Candida albicans, Cryptococcus neoformans, Bornavirus, Borrelia burgdorferri, cytomegalovirus, Ebola virus, HSV-1, HERV-W, HIV-1, Epstein-Barr, hepatitis C, influenza, Chlamydia pneumoniae, Porphyrymonas gingivalis, Helicobacter pylori, Toxoplasma gondii, Trypanosoma cruzi). These interactomes also relate to the AD hippocampal transcriptome and to plaque or tangle proteins. Upregulated AD hippocampal genes match those upregulated by multiple bacteria, viruses, fungi, or protozoa in immunocompetent cells. AD genes are enriched in GWAS datasets reflecting pathogen diversity, suggesting selection for pathogen resistance, as supported by the old age of AD patients, implying resistance to earlier infections. APOE4 is concentrated in regions of high parasitic burden and protects against childhood tropical infections and hepatitis C. Immune/inflammatory gain of function applies to APOE4, CR1, and TREM2 variants. AD genes are also expressed in the blood-brain barrier (BBB), which is disrupted by AD risk factors (age, alcohol, aluminum, concussion, cerebral hypoperfusion, diabetes, homocysteine, hypercholesterolemia, hypertension, obesity, pesticides, pollution, physical inactivity, sleep disruption, smoking) and by pathogens, directly or via olfactory routes to basal-forebrain BBB control centers. The BBB benefits from statins, NSAIDs, estrogen, melatonin, memantine, and the Mediterranean diet. Polymicrobial involvement is supported by upregulation of bacterial, viral, and fungal sensors/defenders in the AD brain, blood, or cerebrospinal fluid. AD serum amyloid-β autoantibodies may attenuate its antimicrobial effects favoring microbial survival and cerebral invasion leading to activation of neurodestructive immune/inflammatory processes, which may also be augmented by age-related immunosenescence. AD may thus respond to antibiotic, antifungal, or antiviral therapy.

The History, Status, Gaps, and Future Directions of Neurotoxicology in China

BACKGROUND

Rapid economic development in China has produced serious ecological, environmental, and health problems. Neurotoxicity has been recognized as a major public health problem. The Chinese government, research institutes, and scientists conducted extensive studies concerning the source, characteristics, and mechanisms of neurotoxicants.

OBJECTIVES

This paper presents, for the first time, a comprehensive history and review of major sources of neurotoxicants, national bodies/legislation engaged, and major neurotoxicology research in China.

METHODS

Peer-reviewed research and pollution studies by Chinese scientists from 1991 to 2015 were examined. PubMed, Web of Science and Chinese National Knowledge Infrastructure (CNKI) were the major search tools.

RESULTS

The central problem is an increased exposure to neurotoxicants from air and water, food contamination, e-waste recycling, and manufacturing of household products. China formulated an institutional framework and standards system for management of major neurotoxicants. Basic and applied research was initiated, and international cooperation was achieved. The annual number of peer-reviewed neurotoxicology papers from Chinese authors increased almost 30-fold since 2001.

CONCLUSIONS

Despite extensive efforts, neurotoxicity remains a significant public health problem. This provides great challenges and opportunities. We identified 10 significant areas that require major educational, environmental, governmental, and research efforts, as well as attention to public awareness. For example, there is a need to increase efforts to utilize new in vivo and in vitro models, determine the potential neurotoxicity and mechanisms involved in newly emerging pollutants, and examine the effects and mechanisms of mixtures. In the future, we anticipate working with scientists worldwide to accomplish these goals and eliminate, prevent and treat neurotoxicity.

CITATION

Cai T, Luo W, Ruan D, Wu YJ, Fox DA, Chen J. 2016. The history, status, gaps, and future directions of neurotoxicology in China. Environ Health Perspect 124:722-732; http://dx.doi.org/10.1289/ehp.1409566.

Zinc Improves Cognitive and Neuronal Dysfunction During Aluminium-Induced Neurodegeneration

Metals are considered as important components of a physiologically active cell, and imbalance in their levels can lead to various diseased conditions. Aluminium (Al) is an environmental neurotoxicant, which is etiologically related to several neurodegenerative disorders like Alzheimer's, whereas zinc (Zn) is an essential trace element that regulates a large number of metabolic processes in the brain. The objective of the present study was to understand whether Zn provides any physiological protection during Al-induced neurodegeneration. Male Sprague Dawley rats weighing 140-160 g received either aluminium chloride (AlCl₃) orally (100 mg/kg b.wt./day), zinc sulphate (ZnSO₄) in drinking water (227 mg/L) or combined treatment of aluminium and zinc for 8 weeks. Al treatment resulted in a significant decline in the cognitive behaviour of rats, whereas zinc supplementation caused an improvement in various neurobehavior parameters. Further, Al exposure decreased (p ≤ 0.001) the levels of neurotransmitters, acetylcholinesterase activity, but increased (p ≤ 0.001) the levels of L-citrulline as well as activities of nitric oxide and monoamine oxidase in the brain. However, zinc administration to Al-treated animals increased the levels of neurotransmitters and regulated the altered activities of brain markers. Western blot of tau, amyloid precursor protein (APP), glial fibrillary acidic protein (GFAP), ubiquitin, α-synuclein and Hsp 70 were also found to be elevated after Al exposure, which however were reversed following Zn treatment. Al treatment also revealed alterations in neurohistoarchitecture in the form of loss of pyramidal and Purkinje cells, which were improved upon zinc co-administration. Therefore, the present study demonstrates that zinc improves cognitive functions by regulating α-synuclein and APP-mediated molecular pathways during aluminium-induced neurodegeneration.

Modulation of (14) C-labeled glucose metabolism by zinc during aluminium induced neurodegeneration

Aluminium (Al) is one of the most prominent metals in the environment and is responsible for causing several neurological disorders, including Alzheimer's disease. On the other hand, zinc (Zn) is an essential micronutrient that is involved in regulating brain development and function. The present study investigates the protective potential of Zn in the uptake of (14) C-labeled amino acids and glucose and their turnover in rat brain slices during Al intoxication. Male Sprague Dawley rats (140-160 g) were divided into four different groups: normal control, Al treated (100 mg/kg body weight/day via oral gavage), Zn treated (227 mg/liter in drinking water), and Al + Zn treated. Radiorespirometric assay revealed an increase in glucose turnover after Al exposure that was attenuated after Zn treatment. Furthermore, the uptake of (14) C-labeled glucose was increased after Al treatment but was appreciably decreased upon Zn supplementation. In addition, the uptakes of (14) C-lysine, (14) C-leucine, and (14) C-aspartic acid were also found to be elevated following Al exposure but were decreased after Zn treatment. Al treatment also caused alterations in the neurohistoarchitecture of the brain, which were improved after Zn coadministration. Therefore, the present study suggests that Zn provides protection against Al-induced neurotoxicity by regulating glucose and amino acid uptake in rats, indicating that Zn could be a potential candidate for the treatment of various neurodegenerative disorders.

The binding, transport and fate of aluminium in biological cells

Aluminium is the most abundant metal in the Earth's crust and yet, paradoxically, it has no known biological function. Aluminium is biochemically reactive, it is simply that it is not required for any essential process in extant biota. There is evidence neither of element-specific nor evolutionarily conserved aluminium biochemistry. This means that there are no ligands or chaperones which are specific to its transport, there are no transporters or channels to selectively facilitate its passage across membranes, there are no intracellular storage proteins to aid its cellular homeostasis and there are no pathways which evolved to enable the metabolism and excretion of aluminium. Of course, aluminium is found in every compartment of every cell of every organism, from virus through to Man. Herein we have investigated each of the 'silent' pathways and metabolic events which together constitute a form of aluminium homeostasis in biota, identifying and evaluating as far as is possible what is known and, equally importantly, what is unknown about its uptake, transport, storage and excretion.

Zinc modulates aluminium-induced oxidative stress and cellular injury in rat brain

Dysregulation of metal homeostasis has been perceived as one of the key factors in the progression of neurodegeneration. Aluminium (Al) has been considered as a major risk factor, which is linked to several neurodegenerative diseases, especially Alzheimer's disease, whereas zinc (Zn) has been reported as a vital dietary element, which regulates a number of physiological processes in central nervous system. The present study was conducted to explore the protective potential of zinc, if any, in ameliorating neurotoxicity induced by aluminium. Male Sprague Dawley rats received either aluminium chloride (AlCl3) orally (100 mg kg(-1) b.wt. per day), zinc sulphate (ZnSO4) at a dose level of 227 mg L(-1) in drinking water or combined treatment of aluminium and zinc for 8 weeks. Aluminium treatment significantly elevated the levels of lipid peroxidation and reactive oxygen species as well as the activities of catalase, superoxide dismutase and glutathione reductase, which however were decreased following Zn co-treatment of Al-treated rats. In contrast, Al treatment decreased the activities of glutathione-S-transferase as well as the levels of reduced glutathione, oxidised glutathione and total glutathione, but co-administration of Zn to Al-treated animals increased these levels. Furthermore, Al treatment caused a significant increase in the levels of Fe and Mn as well as of Al but decreased the Zn and metallothionein levels. In the Zn-supplemented animals, the levels of Al, Fe, Mn were found to be significantly decreased, whereas the levels of metallothionein as well as Zn were increased. Moreover, histopathological alterations such as vacuolization and loss of Purkinje cells were also evident following Al treatment, which showed improvement upon Zn supplementation. Therefore, zinc has the potential to alleviate aluminium-induced neurodegeneration.

Hippocampal neuronal metal ion imbalance related oxidative stress in a rat model of chronic aluminum exposure and neuroprotection of meloxicam

Neurodegenerative diseases remain a significant unresolved societal burden afflicting millions of people worldwide. Neurons in the brain are highly sensitive to oxidative stress, which can be induced by metal toxicity. In this paper, a chronic aluminum overload-induced model of neurodegeneration was used to investigate whether metal ions (Al, Fe, Mn, Cu and Zn)-related oxidative stress was involved in neurodegenerative mechanism and to identify the protective action of meloxicam against rat hippocampal neuronal injury. The metal ion contents, activity of superoxide dismutase (SOD), and content of malondialdehyde (MDA) were detected. The results showed that the spatial learning and memory (SLM) function was significantly impaired in chronic aluminum overload rats. Considerable karyopycnosis was observed in hippocampal neurons. The SOD activity was weakened and the MDA content increased both significantly. In the hippocampus, Al, Fe, Mn, Cu, and Zn contents increased by 184.1%, 186.1%, 884.2%, 199.4% and 149.2%, respectively. Meloxicam administration (without Al) had no effect compared with the control group, while meloxicam treatment with aluminum exposure significantly protected rats from SLM function impairment, neuron death, lower SOD activity, higher MDA content and brain metal ion imbalance. Our findings suggest that the cerebral metal ion imbalance-related oxidative stress is involved in mechanism of cerebral injury and neurodegeneration induced by chronic Al overload in rats, and that meloxicam protects neurons by reducing metal ion imbalance-related oxidative stress.

Cerebrovascular protection of β-asarone in Alzheimer's disease rats: a behavioral, cerebral blood flow, biochemical and genic study

AIM OF THE STUDY

Recent studies have suggested that β-asarone have neuroprotective and cardiovascular protective effects in animal model. However, the influence of β-asarone on cerebrovascular system has not been explored so far. Therefore, present study was designed to determine whether repeated exposures to β-asarone resulted in positive effects on cerebrovascular function in AD rats.

MATERIALS AND METHODS

Alzheimer's disease induced rats was established by injecting both D-galactose (D-gal) and aluminum chloride (AlCl(3)) into abdominal cavity for 42 days. After injection of AlCl(3) and D-gal or saline for 28 days, the rats were treated with volume-matched vehicle or β-asarone (25mg/kg, 50mg/kg or 100mg/kg, i.h.) or Nimodipine (40mg/kg, i.g) once daily for consecutive 14 days, respectively. Behavioral responses of animals were assessed in a Morris water maze. CBF was measured by laser Doppler flowmetry. At the end of this period all rats were sacrificed, lactic acid, pyruvic acid content, Na+K+ATPase activity were determined in brain tissue homogenate to estimate the brain biochemical changes and mRNA expression of ET-1, eNOS and APP was measured with real-time RT-PCR method.

RESULTS

The spatial navigation task latencies, the times through platform zone and the time for the first through platform zone in the target quadrant in probe task, rCBF of right parietal lobe, the contents of lactic acid, pyruvic acid, and the activity of Na-K-ATP of cortex, and ET-1 and eNOS mRNA expression in hippocampus of AG rats were different from those of BG, P<0.05; The level of APP mRNA expression in model control group rats was higher than that in BG, though there was not a statistically significant difference, P>0.05; Compared with AG, HG rats spatial navigation task latencies were shorter, in probe task the times through platform zone in the target quadrant were bigger, rCBF and blood cell concentration of right parietal lobe were higher, the contents of pyruvic acid was lower, the activity of Na-K-ATP was higher, and ET-1 mRNA expression in hippocampus was lower, P<0.05; The level of eNOS and APP mRNA expression in HG rats was lower than that in AG, though there was not a statistically significant difference, P>0.05;

CONCLUSION

The present results suggested that β-asarone may be useful in memory impairment due to its cerebrovascular protection in AD rats and may develop as a therapeutic drug for treatment of AD patients.

The neuroprotective role of boric acid on aluminum chloride-induced neurotoxicity

This study was designed to investigate the qualitative and quantitative changes in brain tissue following aluminum chloride (AlCl3) administration and to determine whether boric acid (BA) has a protective effect against brain damage induced by AlCl 3. For this aim, Sprague-Dawley rats were randomly separated into eight groups: (1) control, (2) AlCl3 (5 mg/kg/day), (3, 4 and 5) BA (3.25, 36 and 58.5 mg/kg/day), (6, 7 and 8) AlCl3 (5 mg/kg/day) plus BA (3.25, 36 and 58.5 mg/kg/day). After the animals were killed, the total numbers of neuron in the brain of all groups were determined using an unbiased stereological analysis. In addition to the stereological analysis, all brains were examined histopathologically by using light and electron microscopy. The stereological and histopathological results indicated a high damage of the rat brain tissues in the AlCl3 and AlCl3 + high dose BA (36 and 58.5) treatment groups. However, protective effects on neuron were observed in the AlCl3 + low dose BA (3.25) group when compared other AlCl3 groups. Our stereological and histopathological findings show that low-dose BA, as a proteasome inhibitor, can decrease the adverse effects of AlCl3 on the cerebral cortex.

Pharmacokinetics of clomipramine, an antidepressant, in poloxamer 407-induced hyperlipidaemic model rats

Objective

This study was undertaken to investigate the effects of hyperlipidaemia on the pharmacokinetics of clomipramine, an antidepressant, particularly addressing the change of clomipramine distribution to plasma components in poloxamer 407-induced hyperlipidaemia model rats.

Methods

Clomipramine pharmacokinetic studies in hyperlipidaemic rats were performed with clomipramine continuous infusion. Furthermore, clomipramine protein binding and distribution to the brain and plasma components such as lipoproteins were investigated.

Key findings

Mean plasma concentration of clomipramine at steady state during continuous infusion (17.5 µg/min/kg) in hyperlipidaemic rats (0.45 ± 0.01 µg/ml) was significantly higher than that in the control rats (0.30 ± 0.02 µg/ml). However, the amount of clomipramine in the brain in hyperlipidaemic rats (0.31 ± 0.06 µg/g) was dramatically lower than in the control rats (1.89 ± 0.13 µg/g). However, the plasma unbound fraction in hyperlipidaemic rats (0.98 ± 0.05%) was significantly lower than that of the control rats (6.51 ± 0.62%).

Conclusions

Lower distribution to the brain and lower plasma clearance of clomipramine in hyperlipidaemic rats resulted from lower plasma unbound fraction because of higher lipid-rich protein contents in blood. Results of this study provide useful information for dosage adjustment of clomipramine in hyperlipidaemia.

Looking at the blood-brain barrier: molecular anatomy and possible investigation approaches

The blood-brain barrier (BBB) is a dynamic and complex interface between blood and the central nervous system that strictly controls the exchanges between the blood and brain compartments, therefore playing a key role in brain homeostasis and providing protection against many toxic compounds and pathogens. In this review, the unique properties of brain microvascular endothelial cells and intercellular junctions are examined. The specific interactions between endothelial cells and basement membrane as well as neighboring perivascular pericytes, glial cells and neurons, which altogether constitute the neurovascular unit and play an essential role in both health and function of the central nervous system, are also explored. Some relevant pathways across the endothelium, as well as mechanisms involved in the regulation of BBB permeability, and the emerging role of the BBB as a signaling interface are addressed as well. Furthermore, we summarize some of the experimental approaches that can be used to monitor BBB properties and function in a variety of conditions and have allowed recent advances in BBB knowledge. Elucidation of the molecular anatomy and dynamics of the BBB is an essential step for the development of new strategies directed to maintain or restore BBB integrity and barrier function and ultimately preserve the delicate interstitial brain environment.

Uptake and intracellular distribution of various metal ions in human monocyte-derived dendritic cells detected by Newport Green DCF diacetate ester

BACKGROUND

The attempt to visualise intracellular protein metal complexes has currently been difficult due to the unavailability of probes for such molecular structures. Newport Green DCF diacetate ester is a cell permeant acetate ester, which becomes fluorescent after hydrolysis. This molecule is initially uncharged, allowing it to pass through cell membranes. Once in the cell, it is hydrolysed and becomes charged, hindering its escape from the cell and allowing it to bind charged protein metal complexes, which then become fluorescent.

METHODS

In this study, we exposed cultured human monocyte-derived dendritic cells (mDC) to a variety of metal ions with the aim of having the cells take up and process protein metal complexes. Newport Green DCF diacetate ester was used to fluorescently label intracellular protein metal complexes.

RESULTS

Flow cytometry analysis and confocal imaging showed specific staining for mDC exposed to aluminium, chromium, nickel, titanium and zirconium ions. The intensity of staining varied between ion types, whereby Ti(III) resulted in the brightest fluorescence signal. Aluminium, Cr(III), Ni, Ti(IV) and Zr(IV) were also clearly detectable.

CONCLUSION

For the first time, intracellular metal ion protein complexes undergoing cellular processing were successfully visualised in human mDC using flow cytometry and confocal microscopy.