Effects of copper metabolism on neurological functions in Wistar and Wilson’s disease model rats

Adverse neurological effects after exposure to copper, manganese, and mercury mixtures in a Spraque-Dawley rat model: an ultrastructural investigation

Exposure to environmental metal pollutants is linked to oxidative stress and the subsequent development of neurological disease. In this study, the effects of copper, manganese, and mercury, were evaluated at X100 the World Health Organization safety limits for drinking water. Using a Sprague-Dawley rat model, following exposure for 28 days, the effects of these metals on biochemical blood parameters and tissue and cellular structure of the brain were determined. Biochemical analysis revealed no hepatocellular injury with minor changes associated with the hepatobiliary system. Minimal changes were found for renal function and the Na+/K+ ratio was reduced in the copper and manganese (Cu + Mn) and copper, manganese, and mercury (Cu, Mn + Hg) groups that could affect neurological function. Light microscopy of the brain revealed abnormal histopathology of Purkinje cells in the cerebellum and pyramidal cells in the cerebrum as well as tissue damage and fibrosis of the surface blood vessels. Transmission electron microscopy of the cerebral neurons showed microscopic signs of axonal damage, chromatin condensation, the presence of indistinct nucleoli and mitochondrial damage. Together these cellular features suggest the presence and influence of oxidative stress. Exposure to these metals at X100 the safety limits, as part of mixtures, induces changes to neurological tissue that could adversely influence neurological functioning in the central nervous system.

Atp7b-dependent choroid plexus dysfunction causes transient copper deficit and metabolic changes in the developing mouse brain

Copper (Cu) has a multifaceted role in brain development, function, and metabolism. Two homologous Cu transporters, Atp7a (Menkes disease protein) and Atp7b (Wilson disease protein), maintain Cu homeostasis in the tissue. Atp7a mediates Cu entry into the brain and activates Cu-dependent enzymes, whereas the role of Atp7b is less clear. We show that during postnatal development Atp7b is necessary for normal morphology and function of choroid plexus (ChPl). Inactivation of Atp7b causes reorganization of ChPl' cytoskeleton and cell-cell contacts, loss of Slc31a1 from the apical membrane, and a decrease in the length and number of microvilli and cilia. In ChPl lacking Atp7b, Atp7a is upregulated but remains intracellular, which limits Cu transport into the brain and results in significant Cu deficit, which is reversed only in older animals. Cu deficiency is associated with down-regulation of Atp7a in locus coeruleus and catecholamine imbalance, despite normal expression of dopamine-β-hydroxylase. In addition, there are notable changes in the brain lipidome, which can be attributed to inhibition of diacylglyceride-to-phosphatidylethanolamine conversion. These results identify the new role for Atp7b in developing brain and identify metabolic changes that could be exacerbated by Cu chelation therapy.

Non-Ceruloplasmin Copper as a Stratification Biomarker of Alzheimer's Disease Patients: How to Measure and Use It

Alzheimer's disease (AD) is a type of dementia very common in the elderly. A growing body of recent evidence has linked AD pathogenesis to copper (Cu) dysmetabolism in the body. In fact, a subset of patients affected either by AD or by its prodromal form known as Mild Cognitive Impairment (MCI) have been observed to be unable to maintain a proper balance of Cu metabolism and distribution and are characterized by the presence in their serum of increased levels of Cu not bound to ceruloplasmin (non-ceruloplasmin Cu). Since serum non-ceruloplasmin Cu is a biomark- er of Wilson's disease (WD), a well-known condition of Cu-driven toxicosis, in this review, we pro- pose that in close analogy with WD, the assessment of non-ceruloplasmin Cu levels can be exploit- ed as a cost-effective stratification and susceptibility/risk biomarker for the identification of some AD/MCI individuals. The approach can also be used as an eligibility criterion for clinical trials aim- ing at investigating Cu-related interventions against AD/MCI.

Copper Imbalance in Alzheimer's Disease: Meta-Analysis of Serum, Plasma, and Brain Specimens, and Replication Study Evaluating ATP7B Gene Variants

Evidence indicates that patients with Alzheimer's dementia (AD) show signs of copper (Cu) dyshomeostasis. This study aimed at evaluating the potential of Cu dysregulation as an AD susceptibility factor. We performed a meta-analysis of 56 studies investigating Cu biomarkers in brain specimens (pooled total of 182 AD and 166 healthy controls, HC) and in serum/plasma (pooled total of 2929 AD and 3547 HC). We also completed a replication study of serum Cu biomarkers in 97 AD patients and 70 HC screened for rs732774 and rs1061472 ATP7B, the gene encoding for the Cu transporter ATPase7B. Our meta-analysis showed decreased Cu in AD brain specimens, increased Cu and nonbound ceruloplasmin (Non-Cp) Cu in serum/plasma samples, and unchanged ceruloplasmin. Serum/plasma Cu excess was associated with a three to fourfold increase in the risk of having AD. Our replication study confirmed meta-analysis results and showed that carriers of the ATP7B AG haplotype were significantly more frequent in the AD group. Overall, our study shows that AD patients fail to maintain a Cu metabolic balance and reveals the presence of a percentage of AD patients carrying ATP7B AG haplotype and presenting Non-Cp Cu excess, which suggest that a subset of AD subjects is prone to Cu imbalance. This AD subtype can be the target of precision medicine-based strategies tackling Cu dysregulation.

Toxic milk mice models of Wilson's disease

Wilson's disease (WD) is a rare genetic disorder inherited as an autosomal recessive trait. The signs and symptoms of this disease are related to dysfunctional ATP7B protein which leads to copper accumulation and cellular damage. The organs that are most commonly affected by WD are the liver and brain. The dysfunctional ATP7B homolog has previously been identified in many different species, including two naturally occurring murine models called toxic milk mice. The aim of this paper was to compare the toxic milk mouse described by Rauch (tx) to that from Jackson Laboratory (txJ) through a review of studies on these two groups of mice. The two mice strains differ in the type of carried mutation and the phenotype of the disease. The data of the studies showed that the tx mice developed mild chronic hepatitis but suffered severe organ destruction with faster progression to full-liver cirrhosis. No changes were noted in the neurological and behavioral status of this strain despite the described toxic accumulation of copper and neuronal destruction in their brain. On the other hand, though the Jackson toxic milk mice (txJ) also presented chronic hepatitis, the condition was a bit milder with slower progression to end-stage disease. Moreover, hepatocyte suitable to perform neurobehavioral research as their phenotype characterized by tremors and locomotor disabilities better corresponds with the cliniconeurological picture of the humans.

Cobalt protoporphyrin decreases food intake, body weight, and the number of neurons in the Nucleus Accumbens in female rats

Cobalt protoporphyrin (CoPP) is a potent heme oxygenase-1 inductor that produces temporary hypophagia and chronic weight loss. A complete description of this effect and the underlying mechanisms are unknown. In this work, we challenged the ability of CoPP to produce changes in rat behavior and cellular alterations in the Nucleus Accumbens that would explain those effects. We subcutaneously administered 25 µmol/kg_{body weight} CoPP in female rats and determined body weight, food intake, hyperactivity, and anxiety-like behavior, as well as the number of neurons and glial cells in the Nucleus Accumbens. CoPP significantly reduced food intake, water consumption, and body weight. Behavioral tests showed that anxiety-like behaviors and locomotor activity were not modified five days after the administration of CoPP. We also found a reduced number of neurons in the Nucleus Accumbens Shell. The above results could be relevant to diseases like anorexia, so it is necessary to deepen the study about the molecular mechanisms involved in reducing the food intake and weight loss elicited by CoPP.

Copper Toxicity Links to Pathogenesis of Alzheimer's Disease and Therapeutics Approaches

Alzheimer's disease (AD) is an irreversible, age-related progressive neurological disorder, and the most common type of dementia in aged people. Neuropathological lesions of AD are neurofibrillary tangles (NFTs), and senile plaques comprise the accumulated amyloid-beta (Aβ), loaded with metal ions including Cu, Fe, or Zn. Some reports have identified metal dyshomeostasis as a neurotoxic factor of AD, among which Cu ions seem to be a central cationic metal in the formation of plaque and soluble oligomers, and have an essential role in the AD pathology. Cu-Aβ complex catalyzes the generation of reactive oxygen species (ROS) and results in oxidative damage. Several studies have indicated that oxidative stress plays a crucial role in the pathogenesis of AD. The connection of copper levels in AD is still ambiguous, as some researches indicate a Cu deficiency, while others show its higher content in AD, and therefore there is a need to increase and decrease its levels in animal models, respectively, to study which one is the cause. For more than twenty years, many in vitro studies have been devoted to identifying metals' roles in Aβ accumulation, oxidative damage, and neurotoxicity. Towards the end, a short review of the modern therapeutic approach in chelation therapy, with the main focus on Cu ions, is discussed. Despite the lack of strong proofs of clinical advantage so far, the conjecture that using a therapeutic metal chelator is an effective strategy for AD remains popular. However, some recent reports of genetic-regulating copper transporters in AD models have shed light on treating this refractory disease. This review aims to succinctly present a better understanding of Cu ions' current status in several AD features, and some conflicting reports are present herein.

Activation of HIF-1 signaling ameliorates liver steatosis in zebrafish atp7b deficiency (Wilson's disease) models

Wilson's disease is an autosomal recessive disease characterized by excess copper accumulated in the liver and brain. It is caused by mutations in the copper transporter gene ATP7B. However, based on the poor understanding of the transcriptional program involved in the pathogenesis of Wilson's disease and the lack of more safe and efficient therapies, the identification of novel pathways and the establishment of complementary model systems of Wilson's disease are urgently needed. Herein, we generated two zebrafish atp7b-mutant lines using the CRISPR/Cas9 editing system, and the mutants developed hepatic and behavioral deficits similar to those observed in humans with Wilson's disease. Interestingly, we found that atp7b-deficient zebrafish embryos developed liver steatosis under low-dose Cu exposure, and behavioral deficits appeared under high-dose Cu exposure. Analyses of publicly available transcriptomic data from ATP7B-knockout HepG2 cells demonstrated that the HIF-1 signaling pathway is downregulated in ATP7B-knockout HepG2 cells compared with wildtype cells following Cu exposure. The HIF-1 signaling pathway was also downregulated in our atp7b-deficient zebrafish mutants following Cu exposure. Furthermore, we demonstrate that activation of the HIF-1 signaling pathway with the chemical compound FG-4592 or DMOG ameliorates liver steatosis and reduces accumulated Cu levels in zebrafish atp7b deficiency models. These findings introduce a novel prospect that modulation of the HIF-1 signaling pathway should be explored as a novel strategy to reduce copper toxicity in Wilson's disease patients.

Dysregulated Choline, Methionine, and Aromatic Amino Acid Metabolism in Patients with Wilson Disease: Exploratory Metabolomic Profiling and Implications for Hepatic and Neurologic Phenotypes

Wilson disease (WD) is a genetic copper overload condition characterized by hepatic and neuropsychiatric symptoms with a not well-understood pathogenesis. Dysregulated methionine cycle is reported in animal models of WD, though not verified in humans. Choline is essential for lipid and methionine metabolism. Defects in neurotransmitters as acetylcholine, and biogenic amines are reported in WD; however, less is known about their circulating precursors. We aimed to study choline, methionine, aromatic amino acids, and phospholipids in serum of WD subjects. Hydrophilic interaction chromatography-quadrupole time-of-flight mass spectrometry was employed to profile serum of WD subjects categorized as hepatic, neurologic, and pre-clinical. Hepatic transcript levels of genes related to choline and methionine metabolism were verified in the Jackson Laboratory toxic milk mouse model of WD (tx-j). Compared to healthy subjects, choline, methionine, ornithine, proline, phenylalanine, tyrosine, and histidine were significantly elevated in WD, with marked alterations in phosphatidylcholines and reductions in sphingosine-1-phosphate, sphingomyelins, and acylcarnitines. In tx-j mice, choline, methionine, and phosphatidylcholine were similarly dysregulated. Elevated choline is a hallmark dysregulation in WD interconnected with alterations in methionine and phospholipid metabolism, which are relevant to hepatic steatosis. The elevated phenylalanine, tyrosine, and histidine carry implications for neurologic manifestations and are worth further investigation.

Subcommissural organ-Reissner's fiber complex plasticity in two animal models of copper intoxication and modulatory effect of curcumin: Involvement of serotonin

Metal neurotoxicity is a universal health preoccupation. Previous data revealed an obvious neurochemical impairment induced by metal elements as copper. This investigation was conducted to study the subcommissural organ (SCO) response to acute and subchronic Cu exposure as well as its serotoninergic innervation in Wistar rats, and the probable protective potential of curcumin in these toxicological circumstances. By mean of immunohistochemistry using antibodies against Reissner's fiber (RF) and serotonin (5-HT) in acute model (10 mg/kg i.p. for 3 days) and subchronic model (0.125% in drinking water for six weeks), we noted a significant decrease of RF-immunoreactivity and a whole amplified 5-HT innervation of SCO and ventricular borders in intoxicated rats. Co-treatment with curcumin-I (30 mg/kg B.W) has shown a beneficial effect, reinstating both SCO secretory activity and serotoninergic innervation damaged by Cu exposure. This data revealed for the first time an obvious response of SCO-RF complex to Cu intoxication as well as the neuroprotective effect of curcumin-I. Thus, SCO could play a fundamental role in the strategies of brain resistance to neurotoxicity induced by metal elements in rats, and may be used as biomarker to assist in the diagnosis of this neurotoxicological conditions in rodents.

Low, but Not High, Doses of Copper Sulfate Impair Synaptic Plasticity in the Hippocampal CA1 Region In Vivo

Previous studies have shown the inhibitory effect of the in vitro application of copper sulfate on hippocampal long-term potentiation. While in vivo administration of copper did not affect spatial learning and memory. To find possible answers to this controversial issue, we evaluate the effect of different doses of copper sulfate on in vivo long-term potentiation, synaptic transmission, and paired-pulse behavior of CA1 pyramidal cells. Thirty-two male Wistar rats were divided into four groups: control, 5, 10, and 15 mg of copper sulfate. Field excitatory postsynaptic potential from the stratum radiatum of CA1 neurons was recorded following Schaffer collateral stimulation in rats. Spike amplitude, long-term potentiation and paired-pulse index were measured in all groups. The results of this study showed that 5 mg/kg copper sulfate increased synaptic transmission and inhibited long-term potentiation and decreased the hippocampal paired-pulse ratio, while 10 and 15 mg/kg copper sulfate did not affect CA1 synaptic transmission properties. Low, but not high, doses of copper sulfate affect synaptic plasticity. This finding may explain the difference between the effect of copper on synaptic plasticity and spatial learning and memory.

Effect of Disturbances of Zinc and Copper on the Physical and Mental Health Status of Patients with Alcohol Dependence

The concentrations of copper and zinc in the tissues of alcohol-addicted people can significantly correlate with the variables describing their mental state. Studies on the homeostasis of zinc in alcohol-dependent patients have often been characterized by low hypozincemia detection. This may be caused by a low content of zinc in blood serum (1%) compared to the average zinc level in the body. Unfortunately, most authors have identified extracellular zinc in their studies. In the available literature, data on the level of copper in patients suffering from alcohol dependence are inconsistent. Our study included 100 alcohol-addicted patients (the study group) and 50 healthy subjects (the control group). Mental state was measured using appropriate psychometric scales. We used inductively coupled plasma mass spectrometry (ICP-MS) to determine copper and zinc content. Our results confirm the purposefulness of the use of zinc concentration in erythrocytes as a diagnostic parameter for low zinc status in alcohol-dependent patients. Alcohol-dependent patients with reduced concentrations of zinc in erythrocytes/copper in blood plasma differed significantly from alcohol-dependent patients with normal concentrations in terms of clinical parameters. With regard to zinc in blood plasma and copper in erythrocytes, this situation has not been found. The clinical symptoms of hypozincemia and copper deficiency in patients addicted to alcohol usually relate to disorders in central nervous system functioning, and they result in a decreased quality of physical and mental life.

Copper influence on bank vole's (Myodes glareolus) sexual behavior

The impact of human activity on the environment has led to a steady increase of the amounts of copper in the ecosystems. This element accumulates in plants and water, potentially exposing rodents to its harmful effects. In industrial districts, a decrease in the density of small rodent populations has been observed. This decline may be caused by many factors, including mortality, decreased fertility, or impaired sexual behavior. The decline in the reproductive abilities of small rodents after copper exposure was demonstrated in our previous work (Miska-Schramm A, Kruczek M, Kapusta J, Ecotoxicology 23:1546-1554, 2014). The aim of the presented research was to determine how copper administered at concentrations similar to those recorded in industrial districts (Cu I-150 mg/kg, Cu II-600 mg/kg, C-control) affects the sexual behavior of small rodents. The model species was the bank vole (Myodes glareolus). The behavior and vocalizations of male-female pairs were recorded during open-field tests: ♂C vs. ♀C; ♂Cu I vs. ♀C; ♂Cu II vs. ♀C while in preference tests, female behavior was assessed in the following combinations: ♀C vs. ♂C & ♂Cu I; ♀C vs. ♂C & ♂Cu II. In the presented work, we show that copper decreased the males' sexual attractiveness. Females showed suppressed preference towards males treated with 600 mg/kg copper. The number of sniffs and a number of approaches towards Cu II males was significantly lower than towards control individuals. Also, in preference test with 150 mg/kg treated animals, total activity was lower towards copper treated animals. At the same time, copper did not influence intra-sexual interactions.

Role of Copper in the Onset of Alzheimer's Disease Compared to Other Metals

Alzheimer's disease (AD) is a neurodegenerative disorder that is characterized by amyloid plaques in patients' brain tissue. The plaques are mainly made of β-amyloid peptides and trace elements including Zn2+, Cu2+, and Fe2+. Some studies have shown that AD can be considered a type of metal dyshomeostasis. Among metal ions involved in plaques, numerous studies have focused on copper ions, which seem to be one of the main cationic elements in plaque formation. The involvement of copper in AD is controversial, as some studies show a copper deficiency in AD, and consequently a need to enhance copper levels, while other data point to copper overload and therefore a need to reduce copper levels. In this paper, the role of copper ions in AD and some contradictory reports are reviewed and discussed.

Measurements of serum non-ceruloplasmin copper by a direct fluorescent method specific to Cu(II)

BACKGROUND

Meta-analyses indicated the breakdown of copper homeostasis in the sporadic form of Alzheimer's disease (AD), comprising copper decreases within the brain and copper increases in the blood and the pool not bound to ceruloplasmin (non-Cp Cu, also known in the literature as "free" copper). The calculated non-Cp Cu (Walshe's) index has many limitations.

METHODS

A direct fluorescent method for non-Cp Cu detection has been developed and data are presented herein. The study included samples from 147 healthy subjects, 36 stable mild cognitive impairment (MCI) and 89 AD patients, who were tested for non-Cp Cu through the direct method, total serum copper, ceruloplasmin concentration and o-dianisidine ceruloplasmin activity. The indirect non-Cp Cu Walshe's index was also calculated.

RESULTS

The direct method was linear (0.9-5.9 μM), precise (within-laboratory coefficient variation of 9.7% for low and 7.1% for high measurements), and had a good recovery. A reference interval (0-1.9 μM) was determined parametrically in 147 healthy controls (27-84 years old). The variation of non-Cp Cu was evaluated according to age and sex. Non-Cp Cu was 1.5 times higher in AD patients (regarding the upper value of the reference interval) than in healthy controls. Healthy, MCI and AD subjects were differentiated through the direct non-Cp Cu method [areas under the curve (AUC)=0.755]. Considering a 95% specificity and a 1.91 μmol/L cut-off, the sensitivity was 48.3% (confidence interval 95%: 38%-58%). The likelihood ratio (LR) was 9.94 for positive test results (LR+) and 0.54 for negative test result (LR-).

CONCLUSIONS

The direct fluorescent test reliably and accurately measures non-Cp Cu, thereby determining the probability of having AD.

The neuronal basis of copper induced modulation of anxiety state in rat

Recently, studies have provided strong evidence indicating the involvement of trace elements in the physiopathology of psychiatric disorders, particularly anxiety. We aimed, through the present study, to describe the effect of acute exposure to Cu (10mg/kg BW) on anxiety state together with the serotoninergic and dopaminergic systems in rat by means of neurobehavioral tests (elevated plus maze, dark light box) and immunohistochemistry using anti-serotonin (5HT) and anti-tyrosine hydroxylase (TH). Our data report that Cu enhanced 5HT innervation in the dorsal raphe nucleus (DRN) together with a loss of TH expression within the ventral tegmental area (VTA), Substantia nigra compacta (SNc) and their subsequent outputs including the medial forebrain bundle (MFB) and striatum. In the elevated plus maze Cu significantly increased the time and the number of entries into the open arms, and raised the time spent in the Dark Box indicating a clear reduced anxiety state induced by Cu. The present data show for the first time a powerful neuro-modulatory potential of Cu in rat which involves primarily a dysfunction of 5HT and DA neurotransmissions.

The absence of the SOD1 gene causes abnormal monoaminergic neurotransmission and motivational impairment-like behavior in mice

Copper/zinc superoxide dismutase (SOD1), a primary anti-oxidative enzyme, protects cells against oxidative stress. We report herein on a comparison of behavioral and neurobiological changes between SOD1 knockout (KO) and wild-type mice, in an attempt to assess the role of SOD1 in brain functions. SOD1 KO mice exhibited impaired motivational behavior in both shuttle-box learning and three-chamber social interaction tests. High levels of dopamine transporter protein and an acceleration of serotonin turnover were also detected in the cerebrums of the SOD1 KO mice. These findings suggest that SOD1 deficiency disturbs monoaminergic neurotransmission leading to a decrease in motivational behavior.

Non-ceruloplasmin bound copper and ATP7B gene variants in Alzheimer's disease

ATP7B, a protein mainly expressed in the hepatocytes, is a copper chaperone that loads the metal into the serum copper–protein ceruloplasmin during its synthesis and also escorts superfluous copper into the bile, by a sophisticated trafficking mechanism.

Regional Distribution of Copper, Zinc and Iron in Brain of Wistar Rat Model for Non-Wilsonian Brain Copper Toxicosis

In previous studies, we have reported first in vivo evidence of copper deposition in the choroid plexus, cognitive impairments, astrocytes swelling (Alzheimer type II cells) and astrogliosis (increase in number of astrocytes), and degenerated neurons coupled with significant increase in the hippocampus copper and zinc content in copper-intoxicated Wistar rats. Nonetheless, hippocampus iron levels were not affected by chronic copper-intoxication. Notwithstanding information on distribution of copper, zinc and iron status in different regions of brain due to chronic copper exposure remains fragmentary. In continuation with our previous study, the aim of this study was to investigate the effects of intraperitoneally injected copper lactate (0.15 mg Cu/100 g body weight) daily for 90 days on copper, zinc and iron levels in different regions of the brain using atomic absorption spectrophotometry. Copper-intoxicated group showed significantly increased cortex, cerebellum and striatum copper content (76, 46.8 and 80.7 % increase, respectively) compared to control group. However, non-significant changes were observed for the zinc and iron content in cortex, cerebellum and striatum due to chronic copper exposure. In conclusion, the current study demonstrates that chronic copper toxicity causes differential copper buildup in cortex, cerebellum and striatum region of central nervous system of male Wistar rats; signifying the critical requirement to discretely evaluate the effect of copper neurotoxicity in different brain regions, and ensuing neuropathological and cognitive dysfunctions.

A study of dose response and organ susceptibility of copper toxicity in a rat model

Copper (Cu) in higher concentration is toxic and results in various organ dysfunction. We report Cu concentration in liver, brain and kidney in the rat model following chronic exposure of oral copper sulphate at different subtoxic doses and correlate the tissue Cu concentrations with respective organ dysfunction. Fifty-four male wistar rats divided in 3 groups, the control group received saline water and the experimental group (Group-IIA and IIB) received oral copper sulphate in dose of 100 and 200mg/kg Body Weight. At the end of 30 days, 60 days and 90 days of exposure, six rats were sacrificed from each group. The maximum peak force in grip strength, latency to fall in rotarod and percentage attention score in Y-maze were significantly reduced in the copper sulphate exposed rats compared to the controls at all time points and these were more marked in Group-IIB compared to Group-IIA. Cu concentration was significantly higher in liver, kidney and brain in the Group-II compared to the Group-I. The Cu concentration was highest in the liver (29 folds) followed by kidney (3 folds) and brain (1.5 folds). Serum ALT, AST and bilirubin correlated with liver Cu, BUN with kidney Cu, and grip strength, rotarod and Y-maze findings correlated with brain Cu level. In rats, chronic oral copper sulphate exposure at subtoxic level results in neurobehavioral abnormality and liver and kidney dysfunctions due to increased Cu concentration in the respective organs. Liver is the most vulnerable organ and copper toxicity increases with increasing dose and duration of exposure.

In vivo and in vitro analyses of amygdalar function reveal a role for copper

Mice with a single copy of the peptide amidating monooxygenase (Pam) gene (PAM(+/-)) are impaired in contextual and cued fear conditioning. These abnormalities coincide with deficient long-term potentiation (LTP) at excitatory thalamic afferent synapses onto pyramidal neurons in the lateral amygdala. Slice recordings from PAM(+/-) mice identified an increase in GABAergic tone (Gaier ED, Rodriguiz RM, Ma XM, Sivaramakrishnan S, Bousquet-Moore D, Wetsel WC, Eipper BA, Mains RE. J Neurosci 30: 13656-13669, 2010). Biochemical data indicate a tissue-specific deficit in Cu content in the amygdala; amygdalar expression of Atox-1 and Atp7a, essential for transport of Cu into the secretory pathway, is reduced in PAM(+/-) mice. When PAM(+/-) mice were fed a diet supplemented with Cu, the impairments in fear conditioning were reversed, and LTP was normalized in amygdala slice recordings. A role for endogenous Cu in amygdalar LTP was established by the inhibitory effect of a brief incubation of wild-type slices with bathocuproine disulfonate, a highly selective, cell-impermeant Cu chelator. Interestingly, bath-applied CuSO₄ had no effect on excitatory currents but reversibly potentiated the disynaptic inhibitory current. Bath-applied CuSO₄ was sufficient to potentiate wild-type amygdala afferent synapses. The ability of dietary Cu to affect signaling in pathways that govern fear-based behaviors supports an essential physiological role for Cu in amygdalar function at both the synaptic and behavioral levels. This work is relevant to neurological and psychiatric disorders in which disturbed Cu homeostasis could contribute to altered synaptic transmission, including Wilson's, Menkes, Alzheimer's, and prion-related diseases.

Biochemical, histological, and memory impairment effects of chronic copper toxicity: a model for non-Wilsonian brain copper toxicosis in Wistar rat

Animal models of copper toxicosis rarely exhibit neurological impairments and increased brain copper accumulation impeding the development of novel therapeutic approaches to treat neurodegenerative diseases having high brain Cu content. The aim of this study was to investigate the effects of intraperitoneally injected copper lactate (0.15 mg Cu/100 g body weight) daily for 90 days on copper and zinc levels in the liver and hippocampus, on biochemical parameters, and on neurobehavioral functions (by Morris water maze) of male Wistar rats. Copper-administered animals exhibited significantly decreased serum acetylcholinesterase (AChE) activity and impaired neuromuscular coordination and spatial memory compared to control rats. Copper-intoxicated rats showed significant increase in liver and hippocampus copper content (99.1 and 73 % increase, respectively), 40.7 % reduction in hepatic zinc content, and interestingly, 77.1 % increase in hippocampus zinc content with concomitant increase in copper and zinc levels in serum and urine compared to control rats. Massive grade 4 copper depositions and grade 1 copper-associated protein in hepatocytes of copper-intoxicated rats were substantiated by rhodanine and orcein stains, respectively. Copper-intoxicated rats demonstrated swelling and increase in the number of astrocytes and copper deposition in the choroid plexus, with degenerated neurons showing pyknotic nuclei and dense eosinophilic cytoplasm. In conclusion, the present study shows the first evidence in vivo that chronic copper toxicity causes impaired spatial memory and neuromuscular coordination, swelling of astrocytes, decreased serum AChE activity, copper deposition in the choroid plexus, neuronal degeneration, and augmented levels of copper and zinc in the hippocampus of male Wistar rats.

Visualizing hepatic copper release in Long-Evans cinnamon rats using single-photon emission computed tomography

The potential utility of an imaging agent for the detection of hepatic copper was investigated in a Wilson's disease animal model. Solid-phase peptide synthesis was used to construct an imaging agent which consisted of a copper-binding moiety, taken from the prion protein, and a gamma ray-emitting indium radiolabel. Long-Evans Cinnamon (LEC) rats were used for the Wilson's disease animal model. Our evaluation methodology consisted of administering the indium-labeled agent to both LEC and genetically healthy Long-Evans (LE) cohorts via a tail vein injection and following the pharmacokinetics with single-photon emission computed tomography (SPECT) over the course of an hour. The animals were then sacrificed and their livers necropsied. An additional control agent, lacking the copper-binding moiety, was used to gauge whether any change in the hepatic uptake might be caused by other physiological differences between the two animal models. LEC rats injected with the indium-labeled agent had roughly double the amount of hepatic radioactivity as compared to the healthy control animals. The control agent, without the copper-binding moiety, displayed a hepatic signal similar to that of the control LE animals. Additional intraperitoneal spiking with CuSO4 in C57BL/6 mice also found that the pharmacokinetics of the indium-labeled, prion-based imaging agent is profoundly altered by exposure to in vivo pools of extracellular copper. The described SPECT application with this compound represented a significant improvement over a previous MRI application using the same base peptide sequence.

The early molecular processes underlying the neurological manifestations of an animal model of Wilson's disease

The Long-Evans Cinnamon (LEC) rat shows age-dependent hepatic manifestations that are similar to those of Wilson's disease (WD). The pathogenic process in the brain has, however, not been evaluated in detail due to the rarity of the neurological symptoms. However, copper accumulation is noted in LEC rat brain tissue from 24 weeks of age, which results in oxidative injuries. The current study investigated the gene expression profiles of LEC rat brains at 24 weeks of age in order to identify the important early molecular changes that underlie the development of neurological symptoms in WD. Biological ontology-based analysis revealed diverse altered expressions of the genes related to copper accumulation. Of particular interest, we found altered expression of genes connected to mitochondrial respiration (Sdhaf2 and Ndufb7), calcineurin-mediated cellular processes (Ppp3ca, Ppp3cb, and Camk2a), amyloid precursor protein (Anks1b and A2m) and alpha-synuclein (Snca). In addition to copper-related changes, compensatory upregulations of Cp and Hamp reflect iron-mediated neurotoxicity. Of note, reciprocal expression of Asmt and Bhmt is an important clue that altered S-adenosylhomocysteine metabolism underlies brain injury in WD, which is directly correlated to the decreased expression of S-adenosylhomocysteine hydrolase in hepatic tissue in LEC rats. In conclusion, our study indicates that diverse molecular changes, both variable and complex, underlie the development of neurological manifestations in WD. Copper-related injuries were found to be the principal pathogenic process, but Fe- or adenosylhomocysteine-related injuries were also implicated. Investigations using other animal models or accessible human samples will be required to confirm our observations.

Short-term effects of sibutramine on mineral status and selected biochemical parameters in obese women

The aim of this study was to assess the effect of sibutramine on mineral status and selected biochemical parameters in obese women. The study was conducted on 24 patients who received 15 mg daily doses of sibutramine for 12 weeks, and on 20 patients who received placebo. At the baseline, after the sixth and twelfth weeks of treatment, body weight and blood pressure were measured, the BMI was calculated, and samples of blood and of first morning urine were collected. Serum lipid profiles, glucose levels, and nitric oxide levels were determined. The iron (Fe), copper (Cu), zinc (Zn), calcium (Ca), and magnesium (Mg) present in the serum and urine samples were assessed. The erythrocyte hemolysate of the patients was use to assay the activity of glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD). No changes were observed in BMI, blood pressure, or nitric oxide during the study. After 12 weeks of treatment, a decrease was observed in total cholesterol, LDL cholesterol, triglyceride, glucose, and ferritin levels. GSH-Px and SOD activity increased after 12 weeks of sibutramine treatment. The Mg and Cu increases was observed in serum after the sixth and twelfth weeks of treatment. It was found that the Zn level decreased in serum after the twelfth week. The elimination of Ca, Mg, Fe, Zn, and Cu in urine also declined in the twelfth week. No differences were found in the women taking the placebo. In conclusion, we found that sibutramine had a positive effect on lipid and glucose status in obese women. However, the drug disturbed the balance of minerals, especially Zn and Mg, in the subjects.

Copper signaling in the mammalian nervous system: synaptic effects

Copper is an essential metal present at high levels in the CNS. Its role as a cofactor in mitochondrial ATP production and in essential cuproenzymes is well defined. Menkes and Wilson's diseases are severe neurodegenerative conditions that demonstrate the importance of Cu transport into the secretory pathway. In the brain, intracellular levels of Cu, which is almost entirely protein bound, exceed extracellular levels by more than 100-fold. Cu stored in the secretory pathway is released in a Ca(2+)-dependent manner and can transiently reach concentrations over 100 μM at synapses. The ability of low micromolar levels of Cu to bind to and modulate the function of γ-aminobutyric acid type A (GABA(A)) receptors, N-methyl-D-aspartate (NMDA) receptors, and voltage-gated Ca(2+) channels contributes to its effects on synaptic transmission. Cu also binds to amyloid precursor protein and prion protein; both proteins are found at synapses and brain Cu homeostasis is disrupted in mice lacking either protein. Especially intriguing is the ability of Cu to affect AMP-activated protein kinase (AMPK), a monitor of cellular energy status. Despite this, few investigators have examined the direct effects of Cu on synaptic transmission and plasticity. Although the variability of results demonstrates complex influences of Cu that are highly method sensitive, these studies nevertheless strongly support important roles for endogenous Cu and new roles for Cu-binding proteins in synaptic function/plasticity and behavior. Further study of the many roles of Cu in nervous system function will reveal targets for intervention in other diseases in which Cu homeostasis is disrupted.

Neuroinflammatory and behavioural changes in the Atp7B mutant mouse model of Wilson's disease

Wilson's disease (WD) is caused by mutations in the copper transporting ATPase 7B (Atp7b). Patients present with liver pathology or behavioural disturbances. Studies on rodent models for WD so far mainly focussed on liver, not brain. The effect of knockout of atp7b on sensori-motor and cognitive behaviour, as well as neuronal number, inflammatory markers, copper and synaptic proteins in brain were studied in so-called toxic milk mice. Copper accumulated in striatum and hippocampus of toxic milk mice, but not in cerebral cortex. Inflammatory markers were increased in striatum and corpus callosum, but not in cerebral cortex and hippocampus, whereas neuronal numbers were unchanged. Toxic milk mice were mildly impaired in the rotarod and cylinder test and unable to acquire spatial memory in the Morris water maze. Despite the latter observation only synaptophysin of a number of synaptic proteins, was altered in the hippocampus of toxic milk mice. In addition to disturbances in neuronal signalling by increased brain copper, inflammation and inflammatory signalling from the periphery to the brain might add to the behavioural disturbances in the toxic milk mice. These mice can be used to evaluate therapeutic strategies to alleviate behavioural disturbances and cerebral pathology observed in WD.

Neurotrophic support and oxidative stress: converging effects in the normal and diseased nervous system

Oxidative stress and loss of neurotrophic support play major roles in the development of various diseases of the central and peripheral nervous systems. In disorders of the central nervous system such as Alzheimer's, Parkinson's, and Huntington's diseases, oxidative stress appears inextricably linked to the loss of neurotrophic support. A similar situation is seen in the peripheral nervous system in diseases of olfaction, hearing, and vision. Neurotrophic factors act to up-regulate antioxidant enzymes and promote the expression of antioxidant proteins. On the other hand, oxidative stress can cause down-regulation of neurotrophic factors. We propose that normal functioning of the nervous systems involves a positive feedback loop between antioxidant processes and neurotrophic support. Breakdown of this feedback loop in disease states leads to increased oxidative stress and reduced neurotrophic support.

Lysophosphatidylcholine induces delayed myelination in the juvenile ventral hippocampus and behavioral alterations in adulthood

Maternal virus infection or maternal polyinosinic-polycytidilic acid injection confers behavioral alterations including deficit in prepulse inhibition on the offspring. We previously found delayed myelination specifically in the early postnatal hippocampus in the polyinosinic-polycytidilic acid-injection model. To test whether the transient delay in myelination in the juvenile hippocampus leads to abnormal behaviors after adolescence, we injected lysophosphatidylcholine, a potent demyelinating agent, into the ventral hippocampus of the 10-day-old rat. The lysophosphatidylcholine treatment yielded hypomyelination at postnatal day 16, but myelination reverted to normal level in the adult rat. Neuronal arrays and morphology were not disturbed in this model. We then performed a battery of behavioral tests on the lysophosphatidylcholine-treated and control PBS-injected rats. The lysophosphatidylcholine-treated rats showed deficit in prepulse inhibition, motor hyperactivity in response to methamphetamine and anxiety-related behaviors, all of which are typical behaviors observed in the maternal infection models. These findings suggest that the timing of myelination in the early postnatal hippocampus is crucial for the proper development of sensorimotor and emotional functions. The lysophosphatidylcholine-treated rat without a gross anatomical defect is useful as a model for psychotic disorders.

Realistic expectations of prepulse inhibition in translational models for schizophrenia research

INTRODUCTION

Under specific conditions, a weak lead stimulus, or "prepulse", can inhibit the startling effects of a subsequent intense abrupt stimulus. This startle-inhibiting effect of the prepulse, termed "prepulse inhibition" (PPI), is widely used in translational models to understand the biology of brainbased inhibitory mechanisms and their deficiency in neuropsychiatric disorders. In 1981, four published reports with "prepulse inhibition" as an index term were listed on Medline; over the past 5 years, new published Medline reports with "prepulse inhibition" as an index term have appeared at a rate exceeding once every 2.7 days (n=678). Most of these reports focus on the use of PPI in translational models of impaired sensorimotor gating in schizophrenia. This rapid expansion and broad application of PPI as a tool for understanding schizophrenia has, at times, outpaced critical thinking and falsifiable hypotheses about the relative strengths vs. limitations of this measure.

OBJECTIVES

This review enumerates the realistic expectations for PPI in translational models for schizophrenia research, and provides cautionary notes for the future applications of this important research tool.

CONCLUSION

In humans, PPI is not "diagnostic"; levels of PPI do not predict clinical course, specific symptoms, or individual medication responses. In preclinical studies, PPI is valuable for evaluating models or model organisms relevant to schizophrenia, "mapping" neural substrates of deficient PPI in schizophrenia, and advancing the discovery and development of novel therapeutics. Across species, PPI is a reliable, robust quantitative phenotype that is useful for probing the neurobiology and genetics of gating deficits in schizophrenia.

Cholesterol enhances classical conditioning of the rabbit heart rate response

The cholesterol-fed rabbit is a model of atherosclerosis and has been proposed as an animal model of Alzheimer's disease. Feeding rabbits cholesterol has been shown to increase the number of beta amyloid immunoreactive neurons in the cortex. Addition of copper to the drinking water of cholesterol-fed rabbits can increase this number still further and may lead to plaque-like structures. Classical conditioning of the nictitating membrane response in cholesterol-fed rabbits is retarded in the presence of these plaque-like structures but may be facilitated in their absence. In a factorial design, rabbits fed 2% cholesterol or a normal diet (0% cholesterol) for 8 weeks with or without copper added to the drinking water were given trace classical conditioning using a tone and periorbital electrodermal stimulation to study the effects of cholesterol and copper on classical conditioning of heart rate and the nictitating membrane response. Cholesterol-fed rabbits showed significant facilitation of heart rate conditioning and conditioning-specific modification of heart rate relative to normal diet controls. Consistent with previous research, cholesterol had minimal effects on classical conditioning of the nictitating membrane response when periorbital electrodermal stimulation was used as the unconditioned stimulus. Immunohistochemical analysis showed a significant increase in the number of beta amyloid positive neurons in the cortex, hippocampus and amygdala of the cholesterol-fed rabbits. Supplementation of drinking water with copper increased the number of beta amyloid positive neurons in the cortex of cholesterol-fed rabbits but did not produce plaque-like structures or have a significant effect on heart rate conditioning. The data provide additional support for our finding that, in the absence of plaques, dietary cholesterol may facilitate learning and memory.