Association of Acute, High-dose Cadmium Exposure with Alterations in Vascular Endothelial Barrier Antigen Expression and Astrocyte Morphology in the Developing Rat Central Nervous System

Cerebellar injury induced by cadmium via disrupting the heat-shock response

Cadmium (Cd) is a food contaminant that poses serious threats to animal health, including birds. It is also an air pollutant with well-known neurotoxic effects on humans. However, knowledge on the neurotoxic effects of chronic Cd exposure on chicken is limited. Thus, this study assessed the neurotoxic effects of chronic Cd on chicken cerebellum. Chicks were exposed to 0 (control), 35 (low), and 70 (high) mg/kg of Cd for 90 days, and the expression of genes related to the heat-shock response was investigated. The chickens showed clinical symptoms of ataxia, and histopathology revealed that Cd exposure decreased the number of Purkinje cells and induced degeneration of Purkinje cells with pyknosis, and some dendrites were missing. Moreover, Cd exposure increased the expression of heat-shock factors, HSF1, HSF2, and HSF3, and heat-shock proteins, HSP60, HSP70, HSP90, and HSP110. These changes indicate that HSPs improve the tolerance of the cerebellum to Cd. Conversely, the expressions of HSP10, HSP25, and HSP40 were decreased significantly, which indicated that Cd inhibits the expression of small heat-shock proteins. However, HSP27 and HSP47 were upregulated following low-dose Cd exposure, but downregulated under high-dose Cd exposure. This work sheds light on the toxic effects of Cd on the cerebellum, and it may provide evidence for health risks posed by Cd. Additionally, this work also identified a novel target of Cd exposure in that Cd induces cerebellar injury by disrupting the heat-shock response. Cd can be absorbed into chicken's cerebellum through the food chain, which eventually caused cerebellar injury. This study provided a new insight that chronic Cd-induced neurotoxicity in the cerebellum is associated with alterations in heat-shock response-related genes, which indicated that Cd through disturbing heat-shock response induced cerebellar injury.

Environmental exposure of the general population to cadmium as a risk factor of the damage to the nervous system: A critical review of current data

Nowadays, more and more attention has been focused on the risk of the neurotoxic action of cadmium (Cd) under environmental exposure. Due to the growing incidence of nervous system diseases, including neurodegenerative changes, and suggested involvement of Cd in their aetiopathogenesis, this review aimed to discuss critically this element neurotoxicity. Attempts have been made to recognize at which concentrations in the blood and urine Cd may increase the risk of damage to the nervous system and compare it to the risk of injury of other organs and systems. The performed overview of the available literature shows that Cd may have an unfavourable impact on the human's nervous system at the concentration >0.8 μg Cd/L in the urine and >0.6 μg Cd/L in the blood. Because such concentrations are currently noted in the general population of industrialized countries, it can be concluded that environmental exposure to this xenobiotic may create a risk of damage to the nervous system and be involved in the aetiopathogenesis of neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease, as well as worsening cognitive and behavioural functions. The potential mechanism of Cd neurotoxicity consists in inducing oxidative stress, disrupting the activity of enzymes essential to the proper functioning of the nervous system and destroying the homoeostasis of bioelements in the brain. Thus, further studies are necessary to recognize accurately both the risk of nervous system damage in the general population due to environmental exposure to Cd and the mechanism of this action.

APP/PS1 Gene-Environmental Cadmium Interaction Aggravates the Progression of Alzheimer's Disease in Mice via the Blood-Brain Barrier, Amyloid-β, and Inflammation

BACKGROUND

There is limited information about gene-environment interaction on the occurrence and the progression of Alzheimer's disease.

OBJECTIVE

To explore the effect of environmental low-dose cadmium (Cd) exposure on the progress of Alzheimer's disease and the underlining mechanism.

METHODS

We administered 1 mg/L, 10 mg/L cadmium chloride (treated groups), and water (control group) to C57BL/6J and APP/PS1 mice through drinking water, from one week before mating, until the offspring were sacrificed at 6 months of age. The behaviors, Cd level, blood-brain barrier (BBB) leakage, Aβ1-42 deposition, and inflammation expression were evaluated in these mice.

RESULTS

Mice of both genotypes had similar blood Cd levels after exposure to the same dose of Cd. The toxic effects of Cd on the two genotypes differed little in terms of neuronal histomorphology and BBB permeability. Cd caused a series of pathological morphological changes in the mouse brains and more fluorescent dye leakage at higher doses. Furthermore, the APP/PS1 mice had more severe damage than the C57BL/6J mice, based on the following five criteria. They were increasing anxiety-like behavior and chaos movement, spatial reference memory damage, Aβ plaque deposition in mouse brains, increasing microglia expression in the brain, and IL-6 higher expression in the cortex and in the serum.

CONCLUSION

Low-dose Cd exposure for 6 months increases Aβ plaque deposition and BBB permeability, exacerbates inflammatory responses, and activates microglia, in APP/PS1 mice. APP/PS1 gene-environmental Cd interaction aggravates the progression of Alzheimer's disease in mice.

Nano-selenium alleviates cadmium-induced cerebellar injury by activating metal regulatory transcription factor 1 mediated metal response

This study aims to investigate the role of metal regulatory transcription factor 1 (MTF1)-mediated metal response in cadmium (Cd)-induced cerebellar injury, and to evaluate the antagonistic effects of nano-selenium (Nano-Se) against Cd toxicity. A total of 80 chicks (1 d old, male, Hy-Line Variety White) were randomly allocated to 4 treatment groups for 3 months: the control group (fed with a basic diet, n = 20), the Nano-Se group (basic diet with 1 mg/kg nano-Se 1 mg/kg Nano-Se in basic diet, n = 20), the Nano-Se + Cd group (basic diet with 1 mg/kg Nano-Se and 140 mg/kg CdCl₂, n = 20) and the Cd group (basic diet with 140 mg/kg CdCl₂ , n = 20). The results of the experiment showed that the Purkinje cells were significantly decreased with their degradation and indistinct nucleoli after Cd exposure. Moreover, exposure to Cd caused a significant accumulation of Cd and cupper. However, the contents of Se, iron, and zinc were decreased, thereby disturbing the metal homeostasis in the cerebellum. The Cd exposure also resulted in high levels of malondialdehyde (MDA) and down regulation of selenoprotein transcriptome. Furthermore, the expressions of MTF1, metallothionein 1 (MT1), MT2, zinc transporter 3 (ZNT3), ZNT5, ZNT10, zrt, irt-like protein 8 (ZIP8), ZIP10, transferrin (TF), ferroportin 1 (FPN1), ATPase copper transporting beta (ATP7B), and copper uptake protein 1 (CTR1) were inhibited by Cd exposure. However, all these changes were significantly alleviated by the supplementation of Nano-Se. This study proved that Cd could disorder metal homeostasis and induce oxidative stress, whereas Nano-Se could relieve all these negative effects caused by Cd via activating the MTF1-mediated metal response in the cerebellum of chicken.

Effect of cadmium administration on the antioxidant system and neuronal death in the hippocampus of rats

Cadmium (Cd) is a heavy metal classified as a carcinogen whose exposure could affect the function of the central nervous system. Studies suggest that Cd modifies neuronal morphology in the hippocampus and affects cognitive tasks. The oxidative stress pathway is proposed as a mechanism of toxicity. However, this mechanism is not precise yet. This study aimed to evaluate the effect of Cd administration on oxidative stress markers in the male rat's hippocampus. Male Wistar rats were divided into (1) control (drinking water) and (2) treatment with Cd (32.5 ppm of cadmium chloride (CdCl₂ ) in water). The Cd was administered for 2, 3, and 4 months. The results show that the oral administration of CdCl₂ increased the concentration of Cd in plasma and hippocampus, and this response is time-dependent on its administration. Likewise, it caused an increase in lipid peroxidation and nitrosative stress markers. Moreover, it increased reactive astrogliosis and antioxidant enzyme activity. Consequently, the progression of the oxidative response exacerbated neurodegeneration in hippocampal cells. Our results suggest that Cd exposure induces a severe oxidative response that contributes critically to hippocampal neurodegeneration. It is suggested that exposure to Cd increases the risk of developing neurological diseases, which contributes to a decrease in the quality of life of the human and the environment in which it lives.

The Effect of Short-Term Exposure to Cadmium on the Expression of Vascular Endothelial Barrier Antigen in the Developing Rat Forebrain and Cerebellum: A Computerized Quantitative Immunofluorescent Study

Clinical and laboratory studies have shown that environmental exposure to cadmium produces damage to several organs, including bones, lungs, and kidneys. The involvement of cadmium in central nervous system (CNS) disorders has also been widely reported, but the precise pathophysiological mechanism is not yet fully understood. Children who were exposed to cadmium during pregnancy are known to suffer from developmental delays, learning difficulties, attention deficit hyperactivity disorder (ADHD), and other cognitive and neurobehavioral deficits. Results from numerous studies suggest that dysfunction of the blood-brain barrier (BBB) structures is an important step in the neurotoxicity of cadmium. A rat-specific BBB marker protein, the endothelial barrier antigen (EBA), has been previously isolated and classified by Sternberger and others. The mouse IgG1 clone, anti-endothelial barrier antigen (anti-EBA), detects a protein triplet (23.5kDa, 25 kDa, and 30kDa) localized to the luminal surface of central and peripheral nervous system (CNS and PNS) vascular endothelial cells with selective permeability barrier functions. This marker has been widely used for characterizing BBB alterations under demyelinating, inflammatory, and other CNS pathologies. Many studies have been published using the rat model system for studying the neurotoxic effect of acute and chronic exposure to cadmium.

We applied the indirect immunofluorescent techniques using the anti-EBA antibody in conjunction with the Olympus cellSens computerized image analysis to detect and quantify the surface areas of BBB-competent microvessel profiles in paraformaldehyde-fixed, paraffin-embedded brains of term-delivered young rats after intraperitoneal injection of a single dose of cadmium chloride. We detected a statistically significant reduction in EBA-positive microvessel surface areas in the forebrain (t = 5.86, df = 1789, p-value < 0.001) and cerebellum (t=73.40, df=1337, p < 0.001) of cadmium-treated rats compared to the normal controls. Thus, this study supports the hypothesis that the EBA is a sensitive and measurable indicator for quantitative assessment of the impact of cadmium exposure in the developing rat brain.

Exposure to cadmium induces neuroinflammation and impairs ciliogenesis in hESC-derived 3D cerebral organoids

Cadmium (Cd) is an environmental heavy metal toxicant with central nervous system toxicity and has a greater negative impact on fetal neurodevelopment. However, the causative mechanisms for the neurodevelopmental toxicity of Cd have remained unclear. The human cerebral organoids can better mimic the three-dimensional structure of the early fetal nerve tissue, which can be used to study the developmental neurotoxicity under the condition of maternal exposure to Cd. Our study identified that Cd exposure specifically induced apoptosis in neurons and inhibited the proliferation of neural progenitor cells, but neural differentiation was not significantly affected in cerebral organoids. Cd exposure also elicited overexpression of GFAP, a marker of astrocytes and resulted in IL-6 release. This study revealed that mineral absorption was significantly disturbed with metallothioneins expression up-regulation. Moreover, we found Cd exposure inhibited cilium-related gene expression and reduced ciliary length with increasing dose. In conclusion, our study has shown that Cd exposure regulated neural cell proliferation and death, induced neuroinflammation, enhanced metal ion absorption, and impaired ciliogenesis, which hinder the normal development of the fetal brain.

Single-cell RNA sequencing of mouse neural stem cell differentiation reveals adverse effects of cadmium on neurogenesis

Cadmium (Cd) is a toxic heavy metal and widely exists in the environment. Extensive studies have revealed that Cd exposure can elicit neurotoxicity and potentially interfere with neurogenesis. However, underlying mechanisms by which Cd exposure affects neurogenesis remain unclear. In this study, we performed single-cell RNA sequencing (scRNA-seq) of the differentiated mixture from neonatal mouse Neural Stem Cells (mNSCs) that were exposed to Cd for 24 h and differentiated for 7 days. Our results showed that Cd exposure led to an increase in the differentiation of NSCs into astrocytes while a decrease into neurons. Besides, Cd induced subtype-specific response and dysregulated cell-to-cell communication. Collectively, our scRNA-seq data suggested that Cd had toxic effects on NSCs differentiation at the single-cell level, which offered insight into the potential molecular mechanism of Cd on neurogenesis. Furthermore, our findings provided a new method for assessing the neurodevelopmental toxicity of environmental pollutants.

Heavy Metal-Induced Cerebral Small Vessel Disease: Insights into Molecular Mechanisms and Possible Reversal Strategies

Heavy metals are considered a continuous threat to humanity, as they cannot be eradicated. Prolonged exposure to heavy metals/metalloids in humans has been associated with several health risks, including neurodegeneration, vascular dysfunction, metabolic disorders, cancer, etc. Small blood vessels are highly vulnerable to heavy metals as they are directly exposed to the blood circulatory system, which has comparatively higher concentration of heavy metals than other organs. Cerebral small vessel disease (CSVD) is an umbrella term used to describe various pathological processes that affect the cerebral small blood vessels and is accepted as a primary contributor in associated disorders, such as dementia, cognitive disabilities, mood disorder, and ischemic, as well as a hemorrhagic stroke. In this review, we discuss the possible implication of heavy metals/metalloid exposure in CSVD and its associated disorders based on in-vitro, preclinical, and clinical evidences. We briefly discuss the CSVD, prevalence, epidemiology, and risk factors for development such as genetic, traditional, and environmental factors. Toxic effects of specific heavy metal/metalloid intoxication (As, Cd, Pb, Hg, and Cu) in the small vessel associated endothelium and vascular dysfunction too have been reviewed. An attempt has been made to highlight the possible molecular mechanism involved in the pathophysiology, such as oxidative stress, inflammatory pathway, matrix metalloproteinases (MMPs) expression, and amyloid angiopathy in the CSVD and related disorders. Finally, we discussed the role of cellular antioxidant defense enzymes to neutralize the toxic effect, and also highlighted the potential reversal strategies to combat heavy metal-induced vascular changes. In conclusion, heavy metals in small vessels are strongly associated with the development as well as the progression of CSVD. Chelation therapy may be an effective strategy to reduce the toxic metal load and the associated complications.