Extenuation of in utero toxic effects of MeHg in the developing neurons by Fisetin via modulating the expression of synaptic transmission and plasticity regulators in hippocampus of the rat offspring

Molecular crosstalk and putative mechanisms underlying mitochondrial quality control: The hidden link with methylmercury-induced cognitive impairment

Methylmercury (MeHg) is a neurotoxin associated with foetal neurodevelopmental and adult cognitive deficits. Neurons are highly dependent on the tricarboxylic acid cycle and oxidative phosphorylation to produce ATP and meet their high energy demands. Therefore, mitochondrial quality control (MQC) is critical for neuronal homeostasis. While existing studies have generated a wealth of data on the toxicity of MeHg, the complex cascades and molecular pathways governing the mitochondrial network remain to be elucidated. Here, 0.6, 1.2 and 2.4 mg/kg body weight of MeHg were administered intragastrically to pregnant Sprague Dawley rats to model maternal MeHg exposure. The results of the in vivo study revealed that MeHg-treated rats tended to perform more directionless repetitive strategies in the Morris Water Maze and fewer target-orientation strategies than control offspring. Moreover, pathological injury and synaptic toxicity were observed in the hippocampus. Transmission electron microscopy (TEM) demonstrated that the autophagosomes encapsulated damaged mitochondria, while showing a typical mitochondrial fission phenotype, which was supported by the activation of PINK1-dependent key regulators of mitophagy. Moreover, there was upregulation of DRP1 and FIS1. Additionally, MeHg compensation promoted mitochondrial biogenesis, as evidenced by the activation of the mitochondrial PGC1-α-NRF1-TFAM signalling pathway. Notably, SIRT3/AMPK was activated by MeHg, and the expression and activity of p-AMPK, p-LKB1 and SIRT3 were consistently coordinated. Collectively, these findings provide new insights into the potential molecular mechanisms regulating MeHg-induced cognitive deficits through SIRT3/AMPK MQC network coordination.

N-acetylcysteine protects against neurodevelopmental injuries induced by methylmercury exposure during pregnancy and lactation

As an extremely dangerous environmental contaminant, methylmercury (MeHg) results in detrimental health effects in human brain nervous system, one of its main targets. However, as a developmental toxicant, the brain of offspring is vulnerable to MeHg during pregnancy and lactation exposure. Unfortunately, mechanisms of neurodevelopmental injuries induced by MeHg have not been fully elucidated. N-acetylcysteine (NAC) has been used for several decades as an antioxidant to antagonize oxidative stress. However, the molecular mechanisms of NAC alleviating MeHg-induced neurodevelopmental toxicity are not clear. Here, for evaluation of the dose-dependent effects of MeHg exposure on neurodevelopmental injuries of offspring, and the possible protective effects of NAC, the pregnant female mice were exposed to MeHg (4, 8, 12 mg/L, respectively) and NAC (50, 100, 150 mg/kg, respectively) from gestational day 1 (GD1) to postnatal day 21 (PND21). Our results indicated that administering MeHg caused behavioral impairment and neuronal injuries in the cerebral cortex of newborn mice. MeHg dose-dependently caused reactive oxygen species (ROS) overproduction and oxidative stress aggravation, together with expression of Nrf2, HO-1, Notch1, and p21 up-regulation, and CDK2 inhibition. NAC treatment dose-dependently antagonized MeHg-induced oxidative stress that may contribute to alleviating neurobehavioral and neurodevelopmental impairments. These results give insight into that NAC can protect against MeHg-induced neurodevelopmental toxicity by its antioxidation capacity.

Prenatal amoxicillin exposure induces developmental toxicity in fetal mice and its characteristics

Amoxicillin, a widely used antibiotic in human and veterinary pharmaceuticals, is now considered as an "emerging contaminant" because it exists widespreadly in the environment and brings a series of adverse outcomes. Currently, systematic studies about the developmental toxicity of amoxicillin are still lacking. We explored the potential effects of amoxicillin exposure on pregnancy outcomes, maternal/fetal serum phenotypes, and fetal multiple organ development in mice, at different doses (75, 150, 300 mg/(kg·day)) during late-pregnancy, or at a dose of 300 mg/(kg·day) during different stages (mid-/late-pregnancy) and courses (single-/multi-course). Results showed that prenatal amoxicillin exposure (PAmE) had no significant influence on the body weights of dams, but it could inhibit the physical development and reduce the survival rate of fetuses, especially during the mid-pregnancy. Meanwhile, PAmE altered multiple maternal/fetal serum phenotypes, especially in fetuses. Fetal multi-organ function results showed that PAmE inhibited testicular/adrenal steroid synthesis, long bone/cartilage and hippocampal development, and enhanced ovarian steroid synthesis and hepatic glycogenesis/lipogenesis, and the order of severity might be gonad (testis, ovary) > liver > others. Further analysis found that PAmE-induced multi-organ developmental and functional alterations had differences in stages, courses and fetal gender, and the most obvious changes might be in high-dose, late-pregnancy and multi-course, but there was no typical rule of a dose-response relationship. In conclusion, this study confirmed that PAmE could cause abnormal development and multi-organ function alterations, which deepens our understanding of the risk of PAmE and provides an experimental basis for further exploration of the long-term harm.

DExH-box helicase 9 modulates hippocampal synapses and regulates neuropathic pain

Experimental studies have shown that neuropathic pain impairs hippocampal synaptic plasticity. Here, we sought to determine the underlying mechanisms responsible for synaptic changes in neuropathic painful mouse hippocampal neurons. Beyond demonstrating proof-of-concept for the location of DExH-box helicase 9 (DHX9) in the nucleus, we found that it did exist in the cytoplasm and DHX9 depletion resulted in structural and functional changes at synapses in the hippocampus. A decrease of DHX9 was observed in the hippocampus after peripheral nerve injury; overexpression of DHX9 in the hippocampus significantly alleviated the nociceptive responses and improved anxiety behaviors. Mimicking DHX9 decrease evoked spontaneous pain behavioral symptoms and anxiety emotion in naïve mice. Mechanistically, we found that DHX9 bound to dendrin (Ddn) mRNA, which may have altered the level of synaptic- and dendritic-associated proteins. The data suggest that DHX9 contributes to synapses in hippocampal neurons and may modulate neuropathic pain and its comorbidity aversive emotion.

The Neuroprotective Role of Fisetin in Different Neurological Diseases: a Systematic Review

Neurological diseases place a substantial burden on public health and have a serious impact on the quality of life of patients. Despite the multifaceted pathological process involved in the occurrence and development of these neurological diseases, each disease has its own unique pathological characteristics and underlying molecular mechanisms which trigger their onset. Thus, it is unlikely to achieve effective treatment of neurological diseases by means of a single approach. To this end, we reason that it is pivotal to seek an efficient strategy that implements multitherapeutic targeting and addresses the multifaceted pathological process to overcome the complex issues related to neural dysfunction. In recent years, natural medicinal plant-derived monomers have received extensive attention as new neuroprotective agents for treatment of neurological disorders. Fisetin, a flavonoid, has emerged as a novel potential molecule that enhances neural protection and reverses cognitive abnormalities. The neuroprotective effects of fisetin are attributed to its multifaceted biological activity and multiple therapeutic mechanisms associated with different neurological disorders. In this review article, we summarize recent research progression regarding the pharmacological effects of fisetin in treating several neurological diseases and the potential mechanisms.

An Overview of Recent Advances in the Neuroprotective Potentials of Fisetin against Diverse Insults in Neurological Diseases and the Underlying Signaling Pathways

The nervous system plays a leading role in the regulation of physiological functions and activities in the body. However, a variety of diseases related to the nervous system have a serious impact on human health. It is increasingly clear that neurological diseases are multifactorial pathological processes involving multiple cellular systems, and the onset of these diseases usually involves a diverse array of molecular mechanisms. Unfortunately, no effective therapy exists to slow down the progression or prevent the development of diseases only through the regulation of a single factor. To this end, it is pivotal to seek an ideal therapeutic approach for challenging the complicated pathological process to achieve effective treatment. In recent years, fisetin, a kind of flavonoid widely existing in fruits, vegetables and other plants, has shown numerous interesting biological activities with clinical potentials including anti-inflammatory, antioxidant and neurotrophic effects. In addition, fisetin has been reported to have diverse pharmacological properties and neuroprotective potentials against various neurological diseases. The neuroprotective effects were ascribed to its unique biological properties and multiple clinical pharmacological activities associated with the treatment of different neurological disorders. In this review, we summarize recent research progress regarding the neuroprotective potential of fisetin and the underlying signaling pathways of the treatment of several neurological diseases.

Prenatal exposure to corn oil, CMC-Na or DMSO affects physical development and multi-organ functions in fetal mice

Corn oil, sodium carboxymethyl cellulose (CMC-Na), and dimethyl sulfoxide (DMSO) are widely used as solvents or suspensions in animal experiments, but the effects of prenatal exposure to them on fetal development have not been reported. In this study, Kunming mice were given a conventional dose of corn oil (9.2g/kg·d), CMC-Na (0.05g/kg·d) or DMSO (0.088g/kg·d) during gestation days 10-18, and the pregnancy outcome, fetal physical development, serum phenotype, and multi-organ function changes were observed. The results showed that corn oil decreased serum triglyceride level in males but increased their serum testosterone and CORT levels, and affected female placenta and female/male multi-organ functions (mainly bone, liver, kidney). CMC-Na increased female/male body lengths and tail lengths, decreased serum glucose and total cholesterol levels in males as well as increased their serum LDL-C/HDL-C ratio and testosterone level, decreased female serum bile acid level, and affected male/female placenta and multi-organ functions (mainly bone, liver, hippocampus). DMSO decreased male body weight and serum glucose level, decreased male/female serum bile acid levels, and affected male/female placenta and multi-organs functions (mainly bone, hippocampus, adrenal gland). In conclusion, prenatal exposure to a conventional dose of corn oil, CMC-Na or DMSO could affect fetal physical development and multi-organ functions, and has the characteristics of "multi-pathway, multi-organ and multi-target". This study provides the experimental basis for the rational selection of solvents or suspensions in pharmacology and toxicology studies. DATA AVAILABILITY: Data will be made available on request.

Cognitive outcomes caused by low-level lead, cadmium, and mercury mixture exposure at distinct phases of brain development

Contaminated water and food are the main sources of lead, cadmium, and mercury in the human body. Long-term and low-level ingestion of these toxic heavy metals may affect brain development and cognition. However, the neurotoxic effects of exposure to lead, cadmium, and mercury mixture (Pb + Cd + Hg) at different stages of brain development are rarely elucidated. In this study, different doses of low-level Pb + Cd + Hg were administered to Sprague-Dawley rats via drinking water during the critical stage of brain development, late stage, and after maturation, respectively. Our findings showed that Pb + Cd + Hg exposure decreased the density of memory- and learning-related dendritic spines in the hippocampus during the critical period of brain development, resulting in hippocampus-dependent spatial memory deficits. Only the density of learning-related dendritic spines was reduced during the late phase of brain development and a higher-dose of Pb + Cd + Hg exposure was required, which led to hippocampus-independent spatial memory abnormalities. Exposure to Pb + Cd + Hg after brain maturation revealed no significant change in dendritic spines or cognitive function. Further molecular analysis indicated that morphological and functional changes caused by Pb + Cd + Hg exposure during the critical phase were associated with PSD95 and GluA1 dysregulation. Collectively, the effects of Pb + Cd + Hg on cognition varied depending on the brain development stages.

The Roles of Histone Modifications in Metal-Induced Neurological Disorders

Increasing research is illuminating the intricate roles of metal ions in neural development as well as neurological disorders, which may stem from misregulation or dysfunction of epigenetic modifiers. Lead (Pb), cadmium (Cd), aluminum (Al), and arsenic were chosen for critical review because they have become serious public health concerns due to globalization and industrialization. In this review, we will introduce various modes of action of metals and consider the role of two posttranslational modifications: histone acetylation and methylation and how each of them affects gene expression. We then summarize the findings from previous studies on the neurological outcomes and histone alterations in response to the metals on each of the previously described histone modifications mechanisms. Understanding metal-induced histone modifications changes could provide better insight on the mechanism through which neurotoxicity occurs, to propose and validate these modifications as possible biomarkers for early identification of neurological damage, and can help model targeted therapies for the diseases of the brain.

Effect of methylmercury on fetal neurobehavioral development: an overview of the possible mechanisms of toxicity and the neuroprotective effect of phytochemicals

Methylmercury (MeHg) is a global environmental pollutant with neurotoxic effects. Exposure to MeHg via consumption of seafood and fish can severely impact fetal neurobehavioral development even when MeHg levels in maternal blood are as low as about 5 μg/L, which the mother tolerates well. Persistent motor dysfunctions and cognitive deficits may result from trans-placental exposure. The present review summarizes current knowledge on the mechanisms of MeHg toxicity during the period of nervous system development. Although cerebellar Purkinje cells are MeHg targets, the actions of MeHg on thiol components in the neuronal cytoskeleton as well as on mitochondrial enzymes and induction of disturbances of glutamate signaling can impair extra-cerebellar functions, also at levels well tolerated by adult individuals. Numerous herbal substances possess neuroprotective effects, predominantly represented by natural polyphenolic molecules that might be utilized to develop natural drugs to alleviate neurotoxicity symptoms caused by MeHg or other Hg compounds.

Methylmercury plus Ethanol Exposure: How Much Does This Combination Affect Emotionality?

Mercury is a heavy metal found in organic and inorganic forms that represents an important toxicant with impact on human health. Mercury can be released in the environment by natural phenoms (i.e., volcanic eruptions), industrial products, waste, or anthropogenic actions (i.e., mining activity). Evidence has pointed to mercury exposure inducing neurological damages related to emotional disturbance, such as anxiety, depression, and insomnia. The mechanisms that underlie these emotional disorders remain poorly understood, although an important role of glutamatergic pathways, alterations in HPA axis, and disturbance in activity of monoamines have been suggested. Ethanol (EtOH) is a psychoactive substance consumed worldwide that induces emotional alterations that have been strongly investigated, and shares common pathophysiological mechanisms with mercury. Concomitant mercury and EtOH intoxication occur in several regions of the world, specially by communities that consume seafood and fish as the principal product of nutrition (i.e., Amazon region). Such affront appears to be more deleterious in critical periods of life, such as the prenatal and adolescence period. Thus, this review aimed to discuss the cellular and behavioral changes displayed by the mercury plus EtOH exposure during adolescence, focused on emotional disorders, to answer the question of whether mercury plus EtOH exposure intensifies depression, anxiety, and insomnia observed by the toxicants in isolation.

Fisetin, potential flavonoid with multifarious targets for treating neurological disorders: An updated review

Neurodegenerative disorders pose a significant health burden and imprint a debilitative impact on the quality of life. Importantly, aging is intricately intertwined with the progression of these disorders, and their prevalence increases with a rise in the aging population worldwide. In recent times, fisetin emerged as one of the potential miracle molecules to address neurobehavioral and cognitive abnormalities. These effects were attributed to its actions on several macromolecules and multiple molecular mechanisms. Fisetin belongs to a class of flavonoids, which is found abundantly in several fruits and vegetables. Fisetin has manifested several health benefits in preclinical models of neurodegenerative diseases such as Alzheimer's disease, Vascular dementia, and Schizophrenia. Parkinson's disease, Amyotrophic Lateral Sclerosis, Huntington's disease, Stroke, Traumatic Brain Injury (TBI), and age-associated changes. This review aimed to evaluate the potential mechanisms and pharmacological effects of fisetin in treating several neurological diseases. This review also provides comprehensive data on up-to-date recent literature and highlights the various mechanistic pathways pertaining to fisetin's neuroprotective role.

Combining in vitro assays and mathematical modelling to study developmental neurotoxicity induced by chemical mixtures

Prenatal and postnatal co-exposure to multiple chemicals at the same time may have deleterious effects on the developing nervous system. We previously showed that chemicals acting through similar mode of action (MoA) and grouped based on perturbation of brain derived neurotrophic factor (BDNF), induced greater neurotoxic effects on human induced pluripotent stem cell (hiPSC)-derived neurons and astrocytes compared to chemicals with dissimilar MoA. Here we assessed the effects of repeated dose (14 days) treatments with mixtures containing the six chemicals tested in our previous study (Bisphenol A, Chlorpyrifos, Lead(II) chloride, Methylmercury chloride, PCB138 and Valproic acid) along with 2,2'4,4'-tetrabromodiphenyl ether (BDE47), Ethanol, Vinclozolin and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)), on hiPSC-derived neural stem cells undergoing differentiation toward mixed neurons/astrocytes up to 21 days. Similar MoA chemicals in mixtures caused an increase of BDNF levels and neurite outgrowth, and a decrease of synapse formation, which led to inhibition of electrical activity. Perturbations of these endpoints are described as common key events in adverse outcome pathways (AOPs) specific for DNT. When compared with mixtures tested in our previous study, adding similarly acting chemicals (BDE47 and EtOH) to the mixture resulted in a stronger downregulation of synapses. A synergistic effect on some synaptogenesis-related features (PSD95 in particular) was hypothesized upon treatment with tested mixtures, as indicated by mathematical modelling. Our findings confirm that the use of human iPSC-derived mixed neuronal/glial models applied to a battery of in vitro assays anchored to key events in DNT AOP networks, combined with mathematical modelling, is a suitable testing strategy to assess in vitro DNT induced by chemical mixtures.

Cellular and Molecular Mechanisms Mediating Methylmercury Neurotoxicity and Neuroinflammation

Methylmercury (MeHg) toxicity is a major environmental concern. In the aquatic reservoir, MeHg bioaccumulates along the food chain until it is consumed by riverine populations. There has been much interest in the neurotoxicity of MeHg due to recent environmental disasters. Studies have also addressed the implications of long-term MeHg exposure for humans. The central nervous system is particularly susceptible to the deleterious effects of MeHg, as evidenced by clinical symptoms and histopathological changes in poisoned humans. In vitro and in vivo studies have been crucial in deciphering the molecular mechanisms underlying MeHg-induced neurotoxicity. A collection of cellular and molecular alterations including cytokine release, oxidative stress, mitochondrial dysfunction, Ca²⁺ and glutamate dyshomeostasis, and cell death mechanisms are important consequences of brain cells exposure to MeHg. The purpose of this review is to organize an overview of the mercury cycle and MeHg poisoning events and to summarize data from cellular, animal, and human studies focusing on MeHg effects in neurons and glial cells. This review proposes an up-to-date compendium that will serve as a starting point for further studies and a consultation reference of published studies.