Ascorbic Acid Attenuates Lead-Induced Alterations in the Synapses in the Developing Rat Cerebellum

Effects of Gestational and Lactational Lead Exposure and High Fat Diet Feeding on Cerebellar Development of Postnatal Rat Offspring

Obesity and heavy metals, such as lead (Pb), are detrimental to the adult brain because they impair cognitive function and structural plasticity. However, the effects of co-administration of Pb and a high-fat diet (HFD) on the developing cerebellum is not clearly elucidated. We investigated the effects of Pb exposure (0.3% lead acetate) on developing cerebellum in the pups of an HFD-fed obese rat model. One week before mating, we fed a chow diet (CD) or HFD to the rats for one week and additionally administered Pb to HFD-fed female SD rats. Thereafter, treatment with Pb and a HFD was continued during the gestational and lactational periods. On postnatal day 21, the pups were euthanized to sample the brain tissue and blood for further analysis. Blood Pb levels were significantly higher in HFD-fed rats than in CD-fed rats. Histologically, the prominent degeneration of Purkinje cells was induced by the co-administration of Pb and HFD. The calbindin-28Kd-, GAD67-, NMDAR1-, and PSD95-immunopositive Purkinje cells and inhibitory synapse-forming pinceau structures were significantly decreased following Pb and HFD co-administration. MBP-immunoreactive myelinated axonal fibers were also impaired by HFD but were significantly damaged by the co-administration of HFD and Pb. Oxidative stress-related Nrf2-HO1 signaling was activated by HFD feeding, and Pb exposure further aggravated oxidative stress, as demonstrated by the consumption of endogenous anti-oxidant in HFD-Pb rats. The pro-inflammatory response was also increased by the co-administration of HFD and Pb in the cerebellum of the rat offspring. The present results suggest that HFD and Pb treatment during the gestational and lactational periods are harmful to cerebellar development.

Lead-induced neurodevelopmental lesion and epigenetic landscape: Implication in neurological disorders

Lead (Pb) was implicated in multiple genotoxic, neuroepigenotoxic, and chromosomal-toxic mechanisms and interacted with varying synaptic plasticity pathways, likely underpinning previous reports of links between Pb and cognitive impairment. Epigenetic changes have emerged as a promising biomarker for neurological disorders, including cognitive disorders, Alzheimer's disease (AD), and Parkinson's disease (PD). In the present review, special attention is paid to neural epigenetic features and mechanisms that can alter gene expression patterns upon environmental Pb exposure in rodents, primates, and zebrafish. Epigenetic modifications have also been discussed in population studies and cell experiment. Further, we explore growing evidence of potential linkage between Pb-induced disruption of regulatory pathway and neurodevelopmental and neurological disorders both in vivo and in vitro. These findings uncover how epigenome in neurons facilitates the development and function of the brain in response to Pb insult.

Functional role of ascorbic acid in the central nervous system: a focus on neurogenic and synaptogenic processes

Ascorbic acid, a water-soluble vitamin, is highly concentrated in the brain and participates in neuronal modulation and regulation of central nervous system (CNS) homeostasis. Ascorbic acid has emerged as a neuroprotective compound against neurotoxicants and neurodegenerative diseases, including Alzheimer's disease, multiple sclerosis and amyotrophic lateral sclerosis. Moreover, it improves behavioral and biochemical alterations in psychiatric disorders, including schizophrenia, anxiety, major depressive disorder, and bipolar disorder. Some recent studies have advanced the knowledge on the mechanisms associated with the preventive and therapeutic effects of ascorbic acid by showing that they are linked to improved neurogenesis and synaptic plasticity. This review shows that ascorbic acid has the potential to regulate positively stem cell generation and proliferation. Moreover, it improves neuronal differentiation of precursors cells, promotes adult hippocampal neurogenesis, and has synaptogenic effects that are possibly linked to its protective or therapeutic effects in the brain.

A single administration of ascorbic acid rapidly reverses depressive-like behavior and hippocampal synaptic dysfunction induced by corticosterone in mice

Ketamine is the prototype for glutamate-based fast-acting antidepressants. The establishment of ketamine-like drugs is still a challenge and ascorbic acid has emerged as a candidate. This study investigated the ascorbic acid's ability to induce a fast antidepressant-like response and to improve hippocampal synaptic markers in mice subjected to chronic corticosterone (CORT) administration. CORT was administered for 21 days, followed by a single administration of ascorbic acid (1 mg ∕Kg, p.o.), ketamine (1 mg ∕Kg, i.p.) or fluoxetine (10 mg ∕Kg, p.o.) in mice. Depressive-like behavior, hippocampal synaptic proteins immunocontent, dendrite spines density in the dentate gyrus (DG) were analyzed 24 h following treatments. The administration of ascorbic acid or ketamine, but not fluoxetine, counteracted CORT-induced depressive-like behavior in the tail suspension test (TST). CORT administration reduced PSD-95, GluA1, and synapsin (synaptic markers) immunocontent, and these alterations were reversed by ascorbic acid or ketamine, but only ketamine reversed the CORT-induced reduction on GluA1 immunocontent. In the ventral and dorsal DG, CORT decreased filopodia-, thin- and stubby-shaped spines, while ascorbic acid and ketamine abolished this alteration only in filopodia spines. Ascorbic acid and ketamine increased mushroom-shaped spines density in ventral and dorsal DG. Therefore, the results show that a single administration of ascorbic acid, in a way similar to ketamine, rapidly elicits an antidepressant-like response and reverses hippocampal synaptic deficits caused by CORT, an effect associated with increased levels of synaptic proteins and dendritic remodeling.

Neuroprotective effects of vitamin C and garlic on glycoconjugates changes of cerebellar cortex in lead-exposed rat offspring

The deteriorating effects of Lead (Pb) on central nervous system (CNS) such as cerebellum has been demonstrated in previous studies. Glycoconjugates with the important role in CNS development may be affected by Pb-exposure. Utilization of antioxidant agents and herbal plants has attracted a great deal of attention on attenuating neurotoxicants-induced damage. Thus, in this study the neuroprotective effects of vitamin C and garlic on content of glycoconjugates of cerebellar cortex in Pb-exposed animals were investigated. Wistar pregnant rats were divided into: control (C), Pb-exposed (Pb) (1500 ppm lead acetate in drinking water), Pb plus vitamin C (Pb + Vit C) (500 mg/kg) intraperitoneally, Pb plus garlic (Pb + G) (1 mL /100 g body weight fresh garlic juice via gavage), Pb plus vitamin C and garlic (Pb + Vit C + G), and sham groups (Sh). Finally, levels of Pb in blood were measured in both rats and offspring on postnatal day 50 (PND50). Also, the cerebellums were removed for measuring Pb-levels and performing lectin histochemistry. Blood and cerebellar Pb-levels were increased in Pb-exposed group compared to control group (P < 0.001), whereas they were decreased significantly in Pb + Vit C, Pb + G, and Pb + Vit C + G groups (P < 0.01). By using MPA, UEA-1, and WGA lectin histochemistry, Pb-exposed group showed weak staining intensity compared to other groups. Besides, significant decrease was observed in the density of lectin-positive neurons of Pb-exposed group compared to the control group (P < 0.001). Moreover, strong staining intensity and high lectin-positive neurons were found in Pb + Vit C, Pb + G and Pb + Vit C + G groups than Pb-exposed group (P < 0.001). The present study revealed that Pb-exposure can result in alteration in the cerebellar glycoconjugates contents and co-administration of vitamin C and garlic could attenuate the adverse effects of Pb. The findings of this study revealed the ameliorating effects of vitamin C and garlic against Pb, suggesting the potential use of vitamin C and garlic as preventive agents in Pb poisoning.

MOLECULAR MECHANISMS OF LEAD NEUROTOXICITY

Lead (Pb2+) is a non-essential metal with numerous industrial applications that have led to ts ubiquity in the environment. Thus, not only occupational-exposed individuals' health is compromised, but also that of the general population and in particular children. Notably, although the central nervous system is particularly susceptible to Pb2+, other systems are affected as well. The present study focuses on molecular mechanisms that underlie the effects that arise from the presence of Pb2+ in situ in the brain, and the possible toxic effects that follows. As the brain barriers represent the first target of systemic Pb2+, mechanisms of Pb2+ entry into the brain are discussed, followed by a detailed discussion on neurotoxic mechanisms, with special emphasis on theories of ion mimicry, mitochondrial dysfunction, redox imbalance, and neuroinflammation. Most importantly, the confluence and crosstalk between these events is combined into a cogent mechanism of toxicity, by intertwining recent and old evidences from humans, in vitro cell culture and experimental animals. Finally, pharmacological interventions, including chelators, antioxidants substances, anti-inflammatory drugs, or their combination are reviewed as integrated approaches to ameliorate Pb2+ harmful effects in both developing or adult organisms.

Signal transduction associated with lead-induced neurological disorders: A review

Lead is a heavy metal pollutant that is widely present in the environment. It affects every organ system, yet the nervous system appears to be the most sensitive and primary target. Although many countries have made significant strides in controlling Pb pollution, Pb poisoning continuous to be a major public health concern. Exposure to Pb causes neurotoxicity that ranges from neurodevelopmental disorders to severe neurodegenerative lesions, leading to impairments in learning, memory, and cognitive function. Studies on the mechanisms of Pb-induced nervous system injury have convincingly shown that this metal can affect a plethora of cellular pathways affecting on cell survival, altering calcium dyshomeostasis, and inducing apoptosis, inflammation, energy metabolism disorders, oxidative stress, autophagy and glial stress. This review summarizes recent knowledge on multiple signaling pathways associated with Pb-induced neurological disorders in vivo and in vitro.

Cognitive Impairment Induced by Lead Exposure during Lifespan: Mechanisms of Lead Neurotoxicity

Lead (Pb) is considered a strong environmental toxin with human health repercussions. Due to its widespread use and the number of people potentially exposed to different sources of this heavy metal, Pb intoxication is recognized as a public health problem in many countries. Exposure to Pb can occur through ingestion, inhalation, dermal, and transplacental routes. The magnitude of its effects depends on several toxicity conditions: lead speciation, doses, time, and age of exposure, among others. It has been demonstrated that Pb exposure induces stronger effects during early life. The central nervous system is especially vulnerable to Pb toxicity; Pb exposure is linked to cognitive impairment, executive function alterations, abnormal social behavior, and fine motor control perturbations. This review aims to provide a general view of the cognitive consequences associated with Pb exposure during early life as well as during adulthood. Additionally, it describes the neurotoxic mechanisms associated with cognitive impairment induced by Pb, which include neurochemical, molecular, and morphological changes that jointly could have a synergic effect on the cognitive performance.

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.

(Ascorb)ing Pb Neurotoxicity in the Developing Brain

Lead (Pb) neurotoxicity is a major concern, particularly in children. Developmental exposure to Pb can alter neurodevelopmental trajectory and has permanent neuropathological consequences, including an increased vulnerability to further stressors. Ascorbic acid is among most researched antioxidant nutrients and has a special role in maintaining redox homeostasis in physiological and physio-pathological brain states. Furthermore, because of its capacity to chelate metal ions, ascorbic acid may particularly serve as a potent therapeutic agent in Pb poisoning. The present review first discusses the major consequences of Pb exposure in children and then proceeds to present evidence from human and animal studies for ascorbic acid as an efficient ameliorative supplemental nutrient in Pb poisoning, with a particular focus on developmental Pb neurotoxicity. In doing so, it is hoped that there is a revitalization for further research on understanding the brain functions of this essential, safe, and readily available vitamin in physiological states, as well to justify and establish it as an effective neuroprotective and modulatory factor in the pathologies of the nervous system, including developmental neuropathologies.

Developmental lead (Pb)-induced deficits in redox and bioenergetic status of cerebellar synapses are ameliorated by ascorbate supplementation

Neurotoxicity induced by exposure to heavy metal lead (Pb) is a concern of utmost importance particularly for countries with industrial-based economies. The developing brain is especially sensitive to exposure to even minute quantities of Pb which can alter neurodevelopmental trajectory with irreversible effects on motor, emotive-social and cognitive attributes even into later adulthood. Chemical synapses form the major pathway of inter-neuronal communications and are prime candidates for higher order brain (motor, memory and behavior) functions and determine the resistance/susceptibility for neurological disorders, including neuropsychopathologies. The synaptic pathways and mechanisms underlying Pb-mediated alterations in neuronal signaling and plasticity are not completely understood. Employing a biochemically isolated synaptosomal fraction which is enriched in synaptic terminals and synaptic mitochondria, this study aimed to analyze the alterations in bioenergetic and redox/antioxidant status of cerebellar synapses induced by developmental exposure to Pb (0.2 %). Moreover, we test the efficacy of vitamin C (ascorbate; 500 mg/kg body weight), a neuroprotective and neuromodulatory antioxidant, in mitigation of Pb-induced neuronal deficits. Our results implicate redox and bioenergetic disruptions as an underlying feature of the synaptic dysfunction observed in developmental Pb neurotoxicity, potentially contributing to consequent deficits in motor, behavioral and psychological attributes of the organisms. In addition, we establish ascorbate as a key ingredient for therapeutic approach against Pb induced neurotoxicity, particularly for early-life exposures.

Effects of ascorbic acid treatment on developmental alterations in calcium-binding proteins and gamma-aminobutyric acid transporter 1 in the cerebellum of lead-exposed rats during pregnancy and lactation

In the present study, we investigated the effects of lead (Pb) and ascorbic acid co-administration on rat cerebellar development. Female rats were randomly divided into the following groups: control, Pb, and Pb plus ascorbic acid (PA) groups. From one week prior to mating, female rats were administered Pb (0.3% Pb acetate in drinking water) and ascorbic acid (100 mg/kg, oral intubation). The chemical administration was stopped on postnatal day 21 when the morphology of the offspring's cerebellum is similar to that of the adult brain. The blood Pb level was significantly increased following long-term Pb exposure. Ascorbic acid reduced Pb levels in the dams and offspring. Nissl staining demonstrated that the number of Purkinje cells was significantly reduced following Pb exposure, while ascorbic acid ameliorated this effect in the cerebellum of the offspring. Calcium-binding proteins, such as calbindin, calretinin, and parvalbumin were commonly expressed in Purkinje cells, and Pb exposure and ascorbic acid treatment resulted in similar patterns of change, namely Pb-induced impairment and ascorbic acid-mediated amelioration. The gamma-aminobutyric acid transporter 1 (GABAT1) is expressed in the pinceau structure where the somata of Purkinje cells are entwined in inhibitory synapses. The number of GABAT1-immunoreactive synapses was reduced following Pb exposure, and ascorbic acid co-treatment prevented this effect in the cerebellar cortex. Therefore, it can be concluded that ascorbic acid supplementation to mothers during gestation and lactation may have potential preventive effects against Pb-induced impairments in the developing cerebellum via protection of inhibitory neurons and synapses.

Ginseng Gintonin Attenuates Lead-Induced Rat Cerebellar Impairments during Gestation and Lactation

Gintonin, a novel ginseng-derived lysophosphatidic acid receptor ligand, improves brain functions and protects neurons from oxidative stress. However, little is known about the effects of gintonin against Pb-induced brain maldevelopment. We investigated the protective effects of gintonin on the developing cerebellum after prenatal and postnatal Pb exposure. Pregnant female rats were randomly divided into three groups: control, Pb (0.3% Pb acetate in drinking water), and Pb plus gintonin (100 mg/kg, p.o.). Blood Pb was increased in dams and pups; gintonin treatment significantly decreased blood Pb. On postnatal day 21, the number of degenerating Purkinje cells was remarkably increased while the number of calbindin-, GAD67-, NMDAR1-, LPAR1-immunoreactive intact Purkinje cells, and GABA transporter 1-immunoreactive pinceau structures were significantly reduced in Pb-exposed offspring. Following Pb exposure, gintonin ameliorated cerebellar degenerative effects, restored increased pro-apoptotic Bax, and decreased anti-apoptotic Bcl2. Gintonin treatment attenuated Pb-induced accumulation of oxidative stress (Nrf2 and Mn-SOD) and inflammation (IL-1β and TNFα,), restoring the decreased cerebellar BDNF and Sirt1. Gintonin ameliorated Pb-induced impairment of myelin basic protein-immunoreactive myelinated fibers of Purkinje cells. Gintonin attenuated Pb-induced locomotor dysfunctions. The present study revealed the ameliorating effects of gintonin against Pb, suggesting the potential use of gintonin as a preventive agent in Pb poisoning during pregnancy and lactation.

Effects of Ascorbic Acid on Osteopontin Expression and Axonal Myelination in the Developing Cerebellum of Lead-Exposed Rat Pups

Osteopontin (OPN) is a multi-functional protein that binds to integrin and calcium-binding phosphoprotein. OPN is required for normal neuronal development and its axonal myelination. We studied the combined effect of lead (Pb) and ascorbic acid treatment on OPN expression in the developing cerebellum. We randomly divided pregnant female rats into three groups: control, Pb (lead acetate, 0.3%, drinking water), and Pb plus ascorbic acid (PA; ascorbic acid, 100 mg/kg, oral intubation) groups. The blood level of Pb was significantly increased, while ascorbic acid reduced Pb levels in the dams and pups. At postnatal day (PND) 21, results from Nissl staining and OPN immunohistochemistry demonstrated that OPN was detected in the Purkinje cell layer in the cerebellum. Ascorbic acid treatment mitigated Pb exposure-induced reduction in the number of intact Purkinje cells and OPN immunoreactive Purkinje cells in the cerebellum of pups. In addition, Pb-induced reduction in the number of oligodendrocytes and myelin-associated glycoprotein is associated with the malformation of the myelin sheath. Ascorbic acid provided protection from Pb-induced impairments. Pb-induced structural deficits in the cerebellum resulted in functional deterioration observed during locomotive tests (bar holding test and wire mesh ascending test), while ascorbic acid ameliorated these harmful effects. Present results suggest that the change of OPN is associated with myelination in the developing cerebellum. The results also demonstrated that exposure to Pb is harmful, while ascorbic acid treatment is beneficial.