Histopathological, ultrastructural, and immunohistochemical assessment of hippocampus structures of rats exposed to TCDD and high doses of tocopherol and acetylsalicylic acid

Impacts of dioxin exposure on brain connectivity estimated by DTI analysis of MRI images in men residing in contaminated areas of Vietnam

Introduction

Effects of dioxin exposure on gray matter volume have been reported in previous studies, but a few studies reported effects of dioxin exposure on white matter structure. Therefore, this study was undertaken to investigate the impact of dioxin exposure on white matter microstructure in men living in the most severely dioxin-contaminated areas in Vietnam.

Methods

In 2019 brain MRI scans from 28 men living near Bien Hoa airbase were obtained at Dong Nai General Hospital, Vietnam, on a 3 T scanner using a conventional diffusion tensor imaging sequence. Two exposure markers were indicated by perinatal exposure estimated by assessment of maternal residency in a dioxin-contaminated area during pregnancy and by measurement of blood dioxin levels. A general linear model was used to compare fractional anisotropy (FA) values in 11 white matter tracts in both hemispheres between groups with and without perinatal dioxin exposure and groups with high and low blood dioxin levels after adjusting for covariates.

Results

The adjusted mean FA value in the left cingulum hippocampal part (CGH) was significantly lower in the perinatal dioxin exposure group compared with the group without perinatal dioxin exposure. The high blood TCDD group showed significantly reduced FA values in the left and right CGH and right uncinate fasciculus (UNC). Moreover, the high blood TEQ-PCDDs group showed significantly lower FA values in the left and right CGH and the left UNC. There were no significant differences in FA values between the groups with high and low TEQ-PCDFs levels or between the groups with high and low TEQ-PCDD/Fs levels.

Discussion

It was concluded that dioxin exposure during the perinatal period and adulthood may alter the microstructure of white matter tracts in individuals with neurodevelopmental disorders.

Exposure to dibutyl phthalate adsorbed to multi-walled carbon nanotubes causes neurotoxicity in mice by inducing the release of BDNF

Multi-walled carbon nanotubes (MWCNTs) and dibutyl phthalate (DBP) exist extensively in the environment, and they are easy to form compound pollution through π-π interactions in the environment. We investigate whether DBP, an environmental hormone disruptor, mediated by CNTs can more easily cross the blood-brain barrier, and whether DBP entering the brain has neurotoxic effects on the cells in the brain. Experimental subjects were 40 male Kunming (KM) mice randomly divided into 4 groups: the control group; the MWCNTs group; the DBP group; and the MWCNTs+DBP group. The mice were exposed via tail intravenous injection once every 3 days for 21 days, following which toxicology studies were carried out. The results of behavioral experiments showed that the mice in the combined exposure group (MWCNTs+DBP) exhibited spatial learning and memory impairment, and anxiety-like behavior. Staining of hippocampal sections of mouse brain tissue showed that, in the CA1, CA2, and DG areas, the number of neurons decreased, the nucleus was pyknotic, the cell body was atrophied, and levels of the microglia marker Iba-1 increased. By proteomic KEGG analysis, we found that the DEPs were mainly those related to neurodegenerative diseases. Immunohistochemistry in the hippocampus indicated that the level of brain-derived neurotrophic factor (BDNF) in the DG region was significantly increased. RT-PCR results revealed that the expression levels of P53, caspase3, and Bax genes related to apoptosis were up-regulated. The experimental results demonstrated that the mechanism of the combined-exposure injury to neurons in the hippocampus of mice may be that MWCNTs with adsorbed DBP can induce the release of BDNF, accelerate the apoptosis of neurons, and reduce the number of nerve cells, which activates microglia, causing neuroinflammation and nervous system toxicity.

Proper modulation of AHR signaling is necessary for establishing neural connectivity and oligodendrocyte precursor cell development in the embryonic zebrafish brain

2,3,7,8-tetrachlorodibenzo-[p]-dioxin (TCDD) is a persistent global pollutant that exhibits a high affinity for the aryl hydrocarbon receptor (AHR), a ligand activated transcription factor. Epidemiological studies have associated AHR agonist exposure with multiple human neuropathologies. Consistent with the human data, research studies using laboratory models have linked pollutant-induced AHR activation to disruptions in learning and memory as well as motor impairments. Our understanding of endogenous AHR functions in brain development is limited and, correspondingly, scientists are still determining which cell types and brain regions are sensitive to AHR modulation. To identify novel phenotypes resulting from pollutant-induced AHR activation and ahr2 loss of function, we utilized the optically transparent zebrafish model. Early embryonic TCDD exposure impaired embryonic brain morphogenesis, resulted in ventriculomegaly, and disrupted neural connectivity in the optic tectum, habenula, cerebellum, and olfactory bulb. Altered neural network formation was accompanied by reduced expression of synaptic vesicle 2. Loss of ahr2 function also impaired nascent network development, but did not affect gross brain or ventricular morphology. To determine whether neural AHR activation was sufficient to disrupt connectivity, we used the Gal4/UAS system to express a constitutively active AHR specifically in differentiated neurons and observed disruptions only in the cerebellum; thus, suggesting that the phenotypes resulting from global AHR activation likely involve multiple cell types. Consistent with this hypothesis, we found that TCDD exposure reduced the number of oligodendrocyte precursor cells and their derivatives. Together, our findings indicate that proper modulation of AHR signaling is necessary for the growth and maturation of the embryonic zebrafish brain.

Artichoke Leaf Extract-Mediated Neuroprotection against Effects of Aflatoxin in Male Rats

Attenuation of adverse effects of aflatoxin (AFB₁) in brains of B₁ rats by extracts of leaves of artichoke was studied. The active ingredients in extracts of leaves of artichoke, Cynara scolymus L., were determined by HPLC analysis. In the 42-day experiment, rats were exposed to either sterile water, 4% DMSO, 100 mg artichoke leaf extract/kg body mass, 72 μg aflatoxin B₁/kg body mass, or AFB₁ plus artichoke leaf extract. Neurotoxicity of AFB₁ was determined by an increase in profile of lipids, augmentation of plasmatic glucose and concentrations of insulin, oxidative stress, increased activities of cholinergic enzymes, and a decrease in activities of several antioxidant enzymes and pathological changes in brain tissue. Extracts of artichoke leaf significantly reduced adverse effects caused by AFB₁, rescuing most of the parameters to values similar to unexposed controls, which demonstrated that adverse, neurotoxic effects caused by aflatoxin B₁ could be significantly reduced by simultaneous dietary supplementation with artichoke leaf extract, which itself is not toxic.

Phenolic Acids and Prevention of Cognitive Decline: Polyphenols with a Neuroprotective Role in Cognitive Disorders and Alzheimer's Disease

Cognitive impairment, also known as cognitive decline, can occur gradually or suddenly and can be temporary or more permanent. It represents an increasingly important public health problem and can depend on normal aging or be linked to different neurodegenerative disorders, including Alzheimer's disease (AD). It is now well-established that lifestyle factors including dietary patterns play an important role in healthy aging as well as in the prevention of cognitive decline in later life. Among the natural compounds, dietary polyphenols including phenolic acids have been recently the focus of major attention, with their supplementation being associated with better cognitive status and prevention of cognitive decline. Despite their therapeutic potential, human studies investigating the relation between phenolic acids intake and cognitive outcomes are rather scarce. In this review, we provide preclinical evidence that different dietary polyphenols such as rosmarinic acid, ellagic acid, and cinnamic aldehyde can exert neuroprotective and pro-cognitive activities through different molecular mechanisms including the modulation of pro-oxidant and antioxidant machinery as well as inflammatory status. Future and more numerous in vivo studies are needed to strengthen the promising results obtained at the preclinical level. Despite the excellent pharmacokinetic properties of phenolic acids, which are able to be accumulated in the brain at pharmacologically relevant levels, future studies should also identify which among the different metabolites produced as a consequence of phenolic acids' consumption may be responsible for the potential neuroprotective effects of this subgroup of polyphenols.

Phenolic Acids and Prevention of Cognitive Decline: Polyphenols with a Neuroprotective Role in Cognitive Disorders and Alzheimer's Disease

Cognitive impairment, also known as cognitive decline, can occur gradually or suddenly and can be temporary or more permanent. It represents an increasingly important public health problem and can depend on normal aging or be linked to different neurodegenerative disorders, including Alzheimer's disease (AD). It is now well-established that lifestyle factors including dietary patterns play an important role in healthy aging as well as in the prevention of cognitive decline in later life. Among the natural compounds, dietary polyphenols including phenolic acids have been recently the focus of major attention, with their supplementation being associated with better cognitive status and prevention of cognitive decline. Despite their therapeutic potential, human studies investigating the relation between phenolic acids intake and cognitive outcomes are rather scarce. In this review, we provide preclinical evidence that different dietary polyphenols such as rosmarinic acid, ellagic acid, and cinnamic aldehyde can exert neuroprotective and pro-cognitive activities through different molecular mechanisms including the modulation of pro-oxidant and antioxidant machinery as well as inflammatory status. Future and more numerous in vivo studies are needed to strengthen the promising results obtained at the preclinical level. Despite the excellent pharmacokinetic properties of phenolic acids, which are able to be accumulated in the brain at pharmacologically relevant levels, future studies should also identify which among the different metabolites produced as a consequence of phenolic acids' consumption may be responsible for the potential neuroprotective effects of this subgroup of polyphenols.

Protective effects of Rosemary extract and/or Fluoxetine on Monosodium Glutamate-induced hippocampal neurotoxicity in rat

The use of Monosodium Glutamate (MSG) as a food flavor enhancer is increasing worldwide despite its neurotoxic effects. Fluoxetine (FLX) and Rosemary extract (RE) are known to have beneficial neuroprotective properties. Rats were divided into five groups: control group; MSG group, rats received 2 g/kg/day intraperitoneal (i.p.) injections of MSG for seven days; RE/MSG group, rats received 50 mg/kg/day of oral RE for 28 days starting prior to MSG; FLX/MSG group, rats received 10 mg/kg/day of oral FLX for 28 days beginning before MSG; and RE/FLX/MSG group, received combined treatments as mentioned above. Rats underwent the Barnes maze test, in addition to histopathological, immunohistochemical, morphometric and ultrastructural evaluations for their hippocampi. MSG increased the number of errors and escaped latency in the Barnes maze test that was significantly minimized in the three treatment groups. The MSG group exhibited pyramidal cell (PC) degeneration, shrunken glial cells and massive vascular dilatation that were improved with RE and/or FLX treatment. The number of glial fibrillary acidic protein (GFAP)-immunopositive cells were increased, and the number of PCs was decreased in the MSG group, while these values were significantly reversed with the three treatment groups with the most significant improvement at RE/FLX/MSG one. Ultrastructurally, PCs were shrunken with degenerated nuclei, dilated endoplasmic reticulum, swollen mitochondria, and vacuolations in the MSG group that were improved with RE and/or FLX. In conclusion, the combined RE and FLX treatment can ameliorate the toxic effect of MSG on rat hippocampus probably through its antioxidant and anti-inflammatory effects.

Effects of endocrine disrupting chemicals on myelin development and diseases

In the central and peripheral nervous systems, myelin is essential for efficient conduction of action potentials. During development, oligodendrocytes and Schwann cells differentiate and ensure axon myelination, and disruption of these processes can contribute to neurodevelopmental disorders. In adults, demyelination can lead to important disabilities, and recovery capacities by remyelination often decrease with disease progression. Among environmental chemical pollutants, endocrine disrupting chemicals (EDCs) are of major concern for human health and are notably suspected to participate in neurodevelopmental and neurodegenerative diseases. In this review, we have combined the current knowledge on EDCs impacts on myelin including several persistent organic pollutants, bisphenol A, triclosan, heavy metals, pesticides, and nicotine. Besides, we presented several other endocrine modulators, including pharmaceuticals and the phytoestrogen genistein, some of which are candidates for treating demyelinating conditions but could also be deleterious as contaminants. The direct impacts of EDCs on myelinating cells were considered as well as their indirect consequences on myelin, particularly on immune mechanisms associated with demyelinating conditions. More studies are needed to describe the effects of these compounds and to further understand the underlying mechanisms in relation to the potential for endocrine disruption.

Integrated Epigenetics, Transcriptomics, and Metabolomics to Analyze the Mechanisms of Benzo[a]pyrene Neurotoxicity in the Hippocampus

Benzo[a]pyrene (B[a]P) is a common environmental pollutant that is neurotoxic to mammals, which can cause changes to hippocampal function and result in cognitive disorders. The mechanisms of B[a]P-induced impairments are complex .To date there have been no studies on the association of epigenetic, transcriptomic, and metabolomic changes with neurotoxicity after B[a]P exposure. In the present study, we investigated the global effect of B[a]P on DNA methylation patterns, noncoding RNAs (ncRNAs) expression, coding RNAs expression, and metabolites in the rat hippocampus. Male Sprague Dawley rats (SD rats) received daily gavage of B[a]P (2.0 mg/kg body weight [BW]) or corn oil for 7 weeks. Learning and memory ability was analyzed using the Morris water maze (MWM) test and change to cellular ultrastructure in the hippocampus was analyzed using electron microscope observation. Integrated analysis of epigenetics, transcriptomics, and metabolomics was conducted to investigate the effect of B[a]P exposure on the signaling and metabolic pathways. Our results suggest that B[a]P could lead to learning and memory deficits, likely as a result of epigenetic and transcriptomic changes that further affected the expression of CACNA1C, Tpo, etc. The changes in expression ultimately affecting LTP, tyrosine metabolism, and other important metabolic pathways.

Modulating effect of selected pharmaceuticals on bone in female rats exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

This paper discusses the problems connected with the influence of TCDD on the mechanical properties and structure of the bone tissue in female rats treated with the dioxin. Moreover an analysis of the protective role of tocopherol, acetylsalicylic acid, dexamethazone and levamisol was performed. Rat tibiae were assessed by mechanical testing, and histological and trace element analysis. It was proved that TCDD has negative effect on bone mechanical properties, histological microstructure and trace element content. The results indicate that usage of both steroid and non-steroid anti-inflammatory medicaments, along with tocopherol and levamisol, modulating their activity, can reduce the negative effect of dioxin activity on the bone tissue of female rats intoxicated with TCDD.

The Neuroprotective Effects of Phenolic Acids: Molecular Mechanism of Action

The neuroprotective role of phenolic acids from food has previously been reported by many authors. In this review, the role of phenolic acids in ameliorating depression, ischemia/reperfusion injury, neuroinflammation, apoptosis, glutamate-induced toxicity, epilepsy, imbalance after traumatic brain injury, hyperinsulinemia-induced memory impairment, hearing and vision disturbances, Parkinson’s disease, Huntington’s disease, anti-amyotrophic lateral sclerosis, Chagas disease and other less distributed diseases is discussed. This review covers the in vitro, ex vivo and in vivo studies concerning the prevention and treatment of neurological disorders (on the biochemical and gene expression levels) by phenolic acids.