Influence of iron deficiency and lead treatment on behavior and cerebellar and hippocampal polyamine levels in neonatal rats

Iron homeostasis and post-hemorrhagic hydrocephalus: a review

Iron physiology is regulated by a complex interplay of extracellular transport systems, coordinated transcriptional responses, and iron efflux mechanisms. Dysregulation of iron metabolism can result in defects in myelination, neurotransmitter synthesis, and neuronal maturation. In neonates, germinal matrix-intraventricular hemorrhage (GMH-IVH) causes iron overload as a result of blood breakdown in the ventricles and brain parenchyma which can lead to post-hemorrhagic hydrocephalus (PHH). However, the precise mechanisms by which GMH-IVH results in PHH remain elusive. Understanding the molecular determinants of iron homeostasis in the developing brain may lead to improved therapies. This manuscript reviews the various roles iron has in brain development, characterizes our understanding of iron transport in the developing brain, and describes potential mechanisms by which iron overload may cause PHH and brain injury. We also review novel preclinical treatments for IVH that specifically target iron. Understanding iron handling within the brain and central nervous system may provide a basis for preventative, targeted treatments for iron-mediated pathogenesis of GMH-IVH and PHH.

Spatially Resolved Co-Imaging of Polyhalogenated Xenobiotics and Endogenous Metabolites Reveals Xenobiotic-Induced Metabolic Alterations

A large group of polyhalogenated compounds has been added to the list of persistent organic pollutants in a global convention endorsed by over 100 nations. Once entering the biotas, these pollutants are transported to focal sites of toxicological action and affected endogenous metabolites, which exhibited distinct tissue or organ distribution patterns. However, no study is available to achieve simultaneous mapping of the spatial distributions of xenobiotics and endogenous metabolites for clarifying the molecular mechanism of toxicities. Herein, we present a sensitive mass spectrometry imaging method─tetraphenyl phosphonium chloride-enhanced ionization coupled with air flow-assisted ionization-Orbitrap mass spectrometry─which simultaneously determined the spatial distributions of polyhalogenated xenobiotics and endogenous metabolites. The spatially resolved toxicokinetics and toxicodynamics of typical polyhalogenated compounds (chlorinated paraffins (CPs) and hexabromocyclododecane (HBCD)) were assessed in zebrafish. Co-imaging of polyhalogenated compounds and metabolites visualized the major accumulation organs and maternal transfer of HBCD and CPs, and it clarified the reproductive toxicity of HBCD. CPs were accumulated in the liver, heart, and brain and decreased the concentrations of polyamine/inosine-related metabolites and lipid molecules in these organs. HBCD accumulated in the ovary and was effectively transferred to eggs, and it also disrupted normal follicular development and impaired the production of mature eggs from the ovary by inhibiting expressions of the luteinizing hormone/choriogonadotropin receptor gene. The toxic effects of metabolic disruptions were validated by organ-specific histopathological examinations. These results highlight the necessity to assess the distributions and bioeffects of pollutants in a spatial perspective.

Brain Iron Homeostasis: A Focus on Microglial Iron

Iron is an essential trace element required for important brain functions including oxidative metabolism, synaptic plasticity, myelination, and the synthesis of neurotransmitters. Disruptions in brain iron homeostasis underlie many neurodegenerative diseases. Increasing evidence suggests that accumulation of brain iron and chronic neuroinflammation, characterized by microglia activation and secretion of proinflammatory cytokines, are hallmarks of neurodegenerative disorders including Alzheimer’ s disease. While substantial efforts have led to an increased understanding of iron metabolism and the role of microglial cells in neuroinflammation, important questions still remain unanswered. Whether or not increased brain iron augments the inflammatory responses of microglial cells, including the molecular cues that guide such responses, is still unclear. How these brain macrophages accumulate, store, and utilize intracellular iron to carry out their various functions under normal and disease conditions is incompletely understood. Here, we describe the known and emerging mechanisms involved in microglial cell iron transport and metabolism as well as inflammatory responses in the brain, with a focus on AD.

Spirulina platensis attenuates the associated neurobehavioral and inflammatory response impairments in rats exposed to lead acetate

Heavy metals are well known as environmental pollutants with hazardous impacts on human and animal health because of their wide industrial usage. In the present study, the role of Spirulina platensis in reversing the oxidative stress-mediated brain injury elicited by lead acetate exposure was evaluated. In order to accomplish this aim, rats were orally administered with 300 mg/kg bw Spirulina for 15 d, before and simultaneously with an intraperitoneal injection of 50 mg/kg bw lead acetate [6 injections through the two weeks]. As a result, the co-administration of Spirulina with lead acetate reversed the most impaired open field behavioral indices; however, this did not happen for swimming performance, inclined plane, and grip strength tests. In addition, it was observed that Spirulina diminished the lead content that accumulated in both the blood and the brain tissue of the exposed rats, and reduced the elevated levels of oxidative damage indices, and brain proinflammatory markers. Also, because of the Spirulina administration, the levels of the depleted biomarkers of antioxidant status and interleukin-10 in the lead-exposed rats were improved. Moreover, Spirulina protected the brain tissue (cerebrum and cerebellum) against the changes elicited by lead exposure, and also decreased the reactivity of HSP70 and Caspase-3 in both cerebrum and cerebellum tissues. Collectively, our findings demonstrate that Spirulina has a potential use as a food supplement in the regions highly polluted with heavy metals.

Mechanisms of divalent metal toxicity in affective disorders

Metals are required for proper brain development and play an important role in a number of neurobiological functions. The divalent metal transporter 1 (DMT1) is a major metal transporter involved in the absorption and metabolism of several essential metals like iron and manganese. However, non-essential divalent metals are also transported through this transporter. Therefore, altered expression of DMT1 can modify the absorption of toxic metals and metal-induced toxicity. An accumulating body of evidence has suggested that increased metal stores in the brain are associated with elevated oxidative stress promoted by the ability of metals to catalyze redox reactions, resulting in abnormal neurobehavioral function and the progression of neurodegenerative diseases. Metal overload has also been implicated in impaired emotional behavior, although the underlying mechanisms are not well understood with limited information. The current review focuses on psychiatric dysfunction associated with imbalanced metabolism of metals that are transported by DMT1. The investigations with respect to the toxic effects of metal overload on behavior and their underlying mechanisms of toxicity could provide several new therapeutic targets to treat metal-associated affective disorders.

Brain iron deficiency and excess; cognitive impairment and neurodegeneration with involvement of striatum and hippocampus

While iron deficiency is not perceived as a life threatening disorder, it is the most prevalent nutritional abnormality in the world, and a better understanding of modes and sites of action, can help devise better treatment programs for those who suffer from it. Nowhere is this more important than in infants and children that make up the bulk of iron deficiency in society. Although the effects of iron deficiency have been extensively studied in systemic organs, until very recently little attention was paid to its effects on brain function. The studies of Oski at Johns Hopkin Medical School in 1974, demonstrating the impairment of learning in young school children with iron deficiency, prompted us to study its relevance to brain biochemistry and function in an animal model of iron deficiency. Indeed, rats made iron deficient have lowered brain iron and impaired behaviours including learning. This can become irreversible especially in newborns, even after long-term iron supplementation. We have shown that in this condition it is the brain striatal dopaminergic-opiate system which becomes defective, resulting in alterations in circadian behaviours, cognitive impairment and neurochemical changes closely associated with them. More recently we have extended these studies and have established that cognitive impairment may be closely associated with neuroanatomical damage and zinc metabolism in the hippocampus due to iron deficiency, and which may result from abnormal cholinergic function. The hippocampus is the focus of many studies today, since this brain structure has high zinc concentration and is highly involved in many forms of cognitive deficits as a consequence of cholinergic deficiency and has achieved prominence because of dementia in ageing and Alzheimer's disease. Thus, it is now apparent that cognitive impairment may not be attributed to a single neurotransmitter, but rather, alterations and interactions of several systems in different brain regions. In animal models of iron deficiency it is apparent that dopaminergic interaction with the opiate system and cholinergic neurotransmission may be defective.

Behavioral impairments related to lead-induced developmental neurotoxicity in chicks

Lead intoxication affects the central nervous system and produces structural disorders and behavioral deficits in several animal species. Although lead neurotoxicity is a well-reported phenomenon, studies on the developmental neurotoxicity induced by this metal in avian are scarce. The aim of this study was to evaluate how a single dose of 28 mug lead acetate administered into the yolk sac on the fifth incubation day of Gallus domesticus can affect the behavior and the brain tissue in the first postnatal week. Several behavioral tests, mainly those related to the motor and exploratory functions were evaluated at fifth and sixth postnatal days (PN). The lead deposition into mesencephalon and cerebellum was investigated by autometallography (AMG) method. Congenital anomalies, as failure on closure of body's ventral midline and leg dysfunction, were observed in treated chicks. During the first postnatal week, inactivity and anomalous movements were significantly high in lead treated chicks in comparison to control animals. Lead impregnation was observed in both mesencephalon and cerebellum and the cerebellar molecular layer presented higher lead deposition in comparison to granular layer and Purkinje cells. Our results indicate that the in ovo exposure to lead induces important deficits on motor behavior of chicks during the first postnatal week and such phenomena are related to lead deposition in the cerebellar tissue during embryonic development. The proposed exposure schedule represents an interesting experimental approach for studding behavioral and cellular mechanisms related to lead-induced developmental neurotoxicity.

Functional restoration using basic fibroblast growth factor (bFGF) infusion in Kainic acid induced cognitive dysfunction in rat: neurobehavioural and neurochemical studies

Neurogenesis occurs in dentate gyrus of adult hippocampus under the influence of various mitogenic factors. Growth factors besides instigating the proliferation of neuronal progenitor cells (NPCs) in dentate gyrus, also supports their differentiation to cholinergic neurons. In the present study, an attempt has been made to investigate the neurotrophic effect of bFGF in Kainic acid (KA) induced cognitive dysfunction in rats. Stereotaxic lesioning using (KA) was performed in hippocampal CA3 region of rat's brain. Four-weeks post lesioning rats were assessed for impairment in learning and memory using Y maze followed by bFGF infusion in dentate gyrus region. The recovery was evaluated after bFGF infusion using neurochemical, neurobehavioural and immunohistochemical approaches and compared with lesioned group. Significant impairment in learning and memory (P < 0.01) observed in lesioned animals, four weeks post lesioning exhibited significant restoration (P < 0.001) following bFGF infusion twice at one and four week post lesion. The bFGF infused animals exhibited recovery in hippocampus cholinergic (76%)/ dopaminergic (46%) receptor binding and enhanced Choline acetyltransferase (ChAT) immunoreactivity in CA3 region. The results suggest restorative potential of bFGF in cognitive dysfunctions, possibly due to mitogenic effect on dentate gyrus neurogenic area leading to generation and migration of newer cholinergic neurons.

Iron status and neural functioning

Iron deficiency in early life is associated with delayed development as assessed by a number of clinical trials using similar global scales of development; this poor development during infancy persists in most cases after iron therapy has corrected iron status. If iron deficiency occurs in preschool and older children, the consequences appear reversible with treatment. The biologic understanding of this relationship between development, brain iron status, and functioning is sparse though animal studies repeatedly demonstrate alterations in dopamine metabolism and in the myelination process. Dietary iron deficiency can rapidly deplete brain iron concentrations and repletion is able to normalize them. Residual alterations in striatal dopamine metabolism and myelin production persist if neonatal animals are used. Future studies with more specific measures of neurodevelopment in iron-deficient human infants, and animal models, will allow investigators to more clearly define causal roles of brain iron in neural development and functioning.

Age-related morphological impairments in the rat hippocampus following developmental lead exposure: an MRI, LM and EM study

Lead is one of the most common neurotoxic metals present in our environment. Chronic developmental lead exposure is known to be associated with cognitive dysfunction in children. Functional and morphological impairment of the rat brain has also been reported in the hippocampus (Hi) following developmental lead exposure. The present study was carried out to further investigate age-related morphological impairments in the rat Hi following developmental lead exposure with three methods: (1) magnetic resonance imaging (MRI); (2) light microscopy (LM); and (3) electron microscopy (EM) techniques. Neonatal Wistar rats were exposed to lead from parturition to weaning via milk of dams drinking a 0.2% lead acetate solution. Age-related morphological alternations were investigated in the Hi of lead-exposed rats at various postnatal ages: postnatal day (PND) 17, 30 and 90. The MRI signal intensities (SIs) in the left, right, superior and inferior hippocampal regions of control and lead-exposed rats were analyzed. Compared with controls, the SIs of the four hippocampal regions of interest were significantly increased in lead-exposed rats at PND 17, 30 and 90. Moreover, the lead-induced impairment of the Hi showed an age-related decline and a specific topographical pattern. The impairment of inferior hippocampal regions was more severe than that of superior regions in lead-exposed rats at PND 17 and 30, while no significant difference of SIs was observed between left and right hippocampal regions in the three age groups, and between superior and inferior regions in the PND 90 lead-exposed rats. The LM observations indicated that the morphological injury of hippocampal neurons in lead-exposed rats was also age-related. The EM observations revealed that the endoplasmic reticular, Golgi complex and mitochondria of hippocampal CA1 and dentate gyrus neurons in lead-exposed rats were damaged. These results demonstrate that lead-induced morphological impairments of the rat Hi follow a specific age- and site-related pattern.

Neurologic manifestations of iron deficiency in childhood

Iron deficiency is a common disorder in pediatric patients. Although the most common manifestation is that of anemia, iron deficiency is frequently the source of a host of neurologic disorders presenting to general pediatric neurologic practices. These disorders include developmental delay, stroke, breath-holding episodes, pseudotumor cerebri, and cranial nerve palsies. Although frequent, the identification of iron deficiency as part of the differential diagnosis in these disorders is uncommon and frequently goes untreated. The purpose of the current review is to highlight what is understood regarding iron deficiency and it's underlying pathophysiology as it relates to the brain, and the association of iron deficiency with common neurologic pediatric disease.

Developmental lead exposure in rats: is a behavioral sequel extended at F2 generation?

Lead toxicity was studied in rats exposed from conception until weaning and assessed by monitoring offspring behavior in both the open field and elevated plus maze and by determining tissue lead in an assessment schedule extended to first (F1) and second (F2) generations. Dams utilized for the F1 generation were submitted to 750 ppm of lead (acetate) in drinking water during pregnancy and lactation. For F1 pups, behavioral alterations were not detected in the elevated plus maze, while in the open field, spontaneous locomotor activity as well as time of both grooming and rearing increased, while freezing time decreased in 30- and 90-day-old rats. Lead content was higher in tissues of 1- and 30-day-old pups. However, in 90-day-old rats, lead was detected only in the femur. F2 generation was lead-free but still presented alterations in both locomotor activity and grooming in 30- and 90-day-old pups. It appears that developmental lead exposure may cause behavioral effects during the developmental stage of the F1 generation, which remains throughout the animal's adult life as a sequel, regardless of lead accumulation, and is extended to the F2 generation of rats.

Intrahippocampal cholinergic-rich transplants restore lead-induced deficits: a preliminary study in rats

In the present study restorative potential of fetal cholinergic rich cell suspensions in ameliorating cognitive deficits in rats perinatally exposed to lead was studied. Lactating dams with 1-day old litters were given 0.2% (w/v) lead acetate in drinking water throughout lactation from postnatal day (PND) 1 to PND21 at the end of which the treatment was stopped and the animals were weaned. On PND42 lead exposed rats were given bilateral, intrahippocampal, cholinergic rich fetal neural transplants (approximately 60,000 cells per site) and subsequently assessed 3 and 6 months posttransplantation. Control animals (Sham operated and transplanted) were also run in parallel. Lead exposed rats exhibited a decreased learning ability and locomotor activity. A significant decrease in the levels of acetylcholinesterase and sodium potassium ATPase Na+,K+-ATPase activity was observed in hippocampal region of lead exposed rats. The levels of lead were increased by fivefold in the hippocampal region of lead exposed rats. Transplantation showed marginal improvement in the above impairments at 3 months which were more marked at 6 months. Lead levels at 6 months were not significantly higher in lead exposed rats as compared with the control. Results confirm previous findings that fetal neural transplants help in restoring the lost functional deficits and demonstrate their restorative potential in case of lead induced deficits.

Effects of micronutrients on metal toxicity

There is growing evidence that micronutrient intake has a significant effect on the toxicity and carcinogenesis caused by various chemicals. This paper examines the effect of micronutrient status on the toxicity of four nonessential metals: cadmium, lead, mercury, and arsenic. Unfortunately, few studies have directly examined the effect of dietary deficiency or supplementation on metal toxicity. More commonly, the effect of dietary alteration must be deduced from the results of mechanistic studies. We have chosen to separate the effect of micronutrients on toxic metals into three classes: interaction between essential micronutrients and toxic metals during uptake, binding, and excretion; influence of micronutrients on the metabolism of toxic metals; and effect of micronutrients on secondary toxic effects of metals. Based on data from mechanistic studies, the ability of micronutrients to modulate the toxicity of metals is indisputable. Micronutrients interact with toxic metals at several points in the body: absorption and excretion of toxic metals; transport of metals in the body; binding to target proteins; metabolism and sequestration of toxic metals; and finally, in secondary mechanisms of toxicity such as oxidative stress. Therefore, people eating a diet deficient in micronutrients will be predisposed to toxicity from nonessential metals.