Unraveling the role of zinc in memory

Impact of Solute Carrier Transporters in Glioma Pathology: A Comprehensive Review

Solute carriers (SLCs) are essential for brain physiology and homeostasis due to their role in transporting necessary substances across cell membranes. There is an increasing need to further unravel their pathophysiological implications since they have been proposed to play a pivotal role in brain tumor development, progression, and the formation of the tumor microenvironment (TME) through the upregulation and downregulation of various amino acid transporters. Due to their implication in malignancy and tumor progression, SLCs are currently positioned at the center of novel pharmacological targeting strategies and drug development. In this review, we discuss the key structural and functional characteristics of the main SLC family members involved in glioma pathogenesis, along with their potential targeting options to provide new opportunities for CNS drug design and more effective glioma management.

Pathophysiological Roles of Transient Receptor Potential (Trp) Channels and Zinc Toxicity in Brain Disease

Maintaining the correct ionic gradient from extracellular to intracellular space via several membrane-bound transporters is critical for maintaining overall cellular homeostasis. One of these transporters is the transient receptor potential (TRP) channel family that consists of six putative transmembrane segments systemically expressed in mammalian tissues. Upon the activation of TRP channels by brain disease, several cations are translocated through TRP channels. Brain disease, especially ischemic stroke, epilepsy, and traumatic brain injury, triggers the dysregulation of ionic gradients and promotes the excessive release of neuro-transmitters and zinc. The divalent metal cation zinc is highly distributed in the brain and is specifically located in the pre-synaptic vesicles as free ions, usually existing in cytoplasm bound with metallothionein. Although adequate zinc is essential for regulating diverse physiological functions, the brain-disease-induced excessive release and translocation of zinc causes cell damage, including oxidative stress, apoptotic cascades, and disturbances in energy metabolism. Therefore, the regulation of zinc homeostasis following brain disease is critical for the prevention of brain damage. In this review, we summarize recent experimental research findings regarding how TRP channels (mainly TRPC and TRPM) and zinc are regulated in animal brain-disease models of global cerebral ischemia, epilepsy, and traumatic brain injury. The blockade of zinc translocation via the inhibition of TRPC and TRPM channels using known channel antagonists, was shown to be neuroprotective in brain disease. The regulation of both zinc and TRP channels may serve as targets for treating and preventing neuronal death.

Zinc supplement reverses short-term memory deficit in sodium benzoate-induced neurotoxicity in male Wistar rats by enhancing anti-oxidative capacity via Nrf 2 up-regulation

Sodium benzoate (SB) is a commonly-used food preservative, with a controversial report to its neurological benefit and toxicity. Zinc (Zn) is a trace element that plays a crucial role in memory, inflammation and oxidative stress. This study was to investigate the effect of SB on rat cognition and memory and the possible modulatory effect of Zn supplement. Twenty four male Wistar rats were divided into four groups of six animals each. Animals in groups 1-4 were treated with normal saline 1 ml/kg, SB 200 mg/kg, zinc sulphate 10 ml/kg and SB 200 mg/kg + zinc sulphate 10 ml/kg/day daily respectively for three weeks. After treatment, the animals were subjected to different behavioural tests, and then sacrificed. Their blood samples were collected for catalase(CAT), superoxide dismutase(SOD) and interleukin-1B(IL-1B) assay. Brain samples were also collected for nuclear factor-erythroid-related factor 2(Nrf2), and acetylcholinesterase (AchE) mRNA gene expression. The serum levels of CAT and SOD were (p < 0.0001; p < 0.0001) reduced in the SB only-treated group compared to the other groups. Nrf2 gene expression was totally shut down in the SB only-treated group but, up-regulated in the Zn-treated groups (p < 0.0001). The serum level of IL-1B was higher in the SB only-treated group compared to the other groups. SB-treated group spent longer time in the close arm (p = <0.0001), shorter time in the open arm (p = <0.0001) and had higher anxiety index (p = 0.0045) than the Zn-treated groups. Conclusively, Zinc improves memory deficit, has anxiolytic, anti-oxidant and anti-inflammatory properties.

Zinc deficiency and supplementation in autism spectrum disorder and Phelan-McDermid syndrome

Approximately 1 in 36 children are diagnosed with autism spectrum disorder (ASD). The disorder is four times more common in males than in females. Zinc deficiency and mutations in SHANK2 and SHANK3 (members of a family of excitatory postsynaptic scaffolding proteins) are all risk factors that may contribute to the pathophysiology of the disease. The presence of shankopathies (loss of one copy of the SHANK3 gene) can lead to the development of Phelan-McDermid syndrome (PMDS)-a rare genetic disorder characterized by developmental delay, intellectual disability, poor motor tone, and ASD-like symptoms. We reviewed the relationship between zinc, ASD, and PMDS as well as the effect of zinc supplementation in improving symptoms of ASD and PMDS based on 22 studies published within 6 years (2015-2020). Zinc deficiency (assessed by either dietary intake, blood, hair, or tooth matrix) was shown to be highly prevalent in ASD and PMDS patients as well as in preclinical models of ASD and PMDS. Zinc supplements improved the behavioral deficits in animal models of ASD and PMDS. Clinical trials are still needed to validate the beneficial therapeutic effects of zinc supplements in ASD and PMDS patients.

Potentials of Musa Species Fruits against Oxidative Stress-Induced and Diet-Linked Chronic Diseases: In Vitro and In Vivo Implications of Micronutritional Factors and Dietary Secondary Metabolite Compounds

Nutritional quality and the well-being of the body system are directly linked aspects of human survival. From the unborn foetus to adulthood, the need for sustainable access to micronutrient-rich foods is pertinent and the global consumption of banana and plantain fruits, in effect, contributes to the alleviation of the scourge of malnutrition. This review is particularly aimed at evaluating the pharmacological dimensions through the biological mechanisms of Musa fruits in the body, which represent correlations with their constituent micronutrient factors and dietary polyphenolic constituents such as minerals, vitamin members, anthocyanins, lutein, α-,β- carotenes, neoxanthins and cryptoxanthins, epi- and gallo catechins, catecholamines, 3-carboxycoumarin, β-sitosterol, monoterpenoids, with series of analytical approaches for the various identified compounds being highlighted therein. Derivative value-products from the compartments (flesh and peel) of Musa fruits are equally highlighted, bringing forth the biomedicinal and nutritional relevance, including the potentials of Musa species in dietary diversification approaches.

Zinc Deficiency Leads to Lipid Changes in Drosophila Brain Similar to Cognitive-Impairing Drugs: An Imaging Mass Spectrometry Study

Several diseases and disorders have been suggested to be associated with zinc deficiency, especially learning and memory impairment. To have better understanding about the connection between lipid changes and cognitive impairments, we investigated the effects of a zinc-chelated diet on certain brain lipids of Drosophila melanogaster by using time-of-flight secondary ion mass spectrometry (ToF-SIMS). The data revealed that there are increases in the levels of phosphatidylcholine and phosphatidylinositol in the central brains of the zinc-deficient flies compared to the control flies. In contrast, the abundance of phosphatidylethanolamine in the brains of the zinc-deficient flies is lower. These data are consistent with that of cognitive-diminishing drugs, thus providing insight into the biological and molecular effects of zinc deficiency on the major brain lipids and opening a new treatment target for cognitive deficit in zinc deficiency.

Camel milk rescues neurotoxic impairments induced by fenpropathrin via regulating oxidative stress, apoptotic, and inflammatory events in the brain of rats

This study explored the camel milk (CM) efficacy to ameliorate the fenpropathrin (FNP) induced neurotoxic impacts in rats. Six groups were orally administered physiological saline, corn oil, CM (2ml/rat/day), FNP (15 mg/kg bw daily for 60 days), CM/FNP (protective) or FNP + CM (therapeutic). Sensorimotor functions, memory, exploratory, and locomotor activities were assessed. The levels of dopamine (DOPA) neurotransmitter, acetylcholinesterase (AChE) enzyme, oxidative stress, and inflammatory markers were determined. Brain histopathology and apoptotic markers immunohistochemical detection were performed. The results revealed that FNP exposure resulted in deficit sensorimotor functions, impaired memory, and less exploration. DOPA and AChE Levels were significantly reduced. FNP exposure increased nitric oxide, malondialdehyde, myeloperoxidase, Caspase-3, and tumor necrosis factor-alpha levels but interleukin 10, total antioxidant capacity, and Bcl-2 levels were declined. Also, FNP exposure induced obvious encephalopathy. Additionally, neurodegenerative changes were seen in the hippocampi of FNP-treated rats. FNP Exposure induced a significant decrease of Bcl-2 immunolabelling but Caspase-3 immunoexpression was increased in cerebral cortices and hippocampus tissues. CM significantly counteracted the FNP injurious impacts, especially when used as a prophylactic routine than a therapeutic one. Conclusively, these findings confirmed that CM could be a biologically effective protective agent against FNP induced neurobehavioral aberrations and neurotoxic impacts.

Supplementation with zinc in rats enhances memory and reverses an age-dependent increase in plasma copper

Zinc and copper are essential trace elements. Dyshomeostasis in these two metals has been observed in Alzheimer's disease, which causes profound cognitive impairment. Insulin therapy has been shown to enhance cognitive performance; however, recent data suggest that this effect may be at least in part due to the inclusion of zinc in the insulin formulation used. Zinc plays a key role in regulation of neuronal glutamate signaling, suggesting a possible link between zinc and memory processes. Consistent with this, zinc deficiency causes cognitive impairments in children. The effect of zinc supplementation on short- and long-term recognition memory, and on spatial working memory, was explored in young and adult male Sprague Dawley rats. After behavioral testing, hippocampal and plasma zinc and copper were measured. Age increased hippocampal zinc and copper, as well as plasma copper, and decreased plasma zinc. An interaction between age and treatment affecting plasma copper was also found, with zinc supplementation reversing elevated plasma copper concentration in adult rats. Zinc supplementation enhanced cognitive performance across tasks. These data support zinc as a plausible therapeutic intervention to ameliorate cognitive impairment in disorders characterized by alterations in zinc and copper, such as Alzheimer's disease.

Revised stability constant, spectroscopic properties and binding mode of Zn(II) to FluoZin-3, the most common zinc probe in life sciences

2-[2-[2-[2-[bis(carboxylatomethyl)amino]-5-methoxyphenoxy]ethoxy]-4-(2,7-difluoro-3-oxido-6-oxo-4a,9a-dihydroxanthen-9-yl)anilino]acetate (FluoZin-3) is used very broadly in life sciences as intra- and extracellular Zn(II) sensor selective for Zn(II) over Co(II), Ca(II) and Mg(II) ions at their physiological concentrations. It has been used for determination of relative and absolute levels of exchangeable Zn(II) in cells and extracellular fluids. Despite its popularity, the knowledge of its acid/base and Zn(II) coordination abilities and of its spectroscopic properties remained very limited. Also the published conditional dissociation constant ((C)Kd) values at pH7.4 are slightly discrepant, (15nM or 8.9nM). In this work we determined the (C)Kd for Zn(II) complexation by FluoZin-3 at pH7.4 with nitrilotriacetic acid (NTA) as competitor using two independent methods: fluorimetry and UV-Vis spectroscopy. For the first time, we investigated FluoZin-3 alone and complexed with Zn(II) in the wide range of pH, determining the total of eight pKa values from fluorescence spectra and from various regions of UV-Vis spectra. The validated values of (C)Kd (9.1±0.4nM; -log (C)Kd=8.04) and of the absolute (pH-independent) stability constant log βZnL (8.16±0.05) were provided by fluorescence spectroscopy experiments performed at 1μM concentrations. Our experiments demonstrated that both of aminocarboxylate moieties of FluoZin-3 bind the Zn(II) ion synergistically.

Zinc Chloride and Zinc Acetate Injected into the Neostriatum Produce Opposite Effect on Locomotor Behavior of Rats

Zinc chloride and zinc acetate solutions injected in a dose of 1 μg into the rostral neostriatum produced opposite effect on locomotor behavior of rats. Zink chloride disturbed conditioned avoidance and reduced spontaneous motor activity. Zink acetate virtually did not modify avoidance behavior and stimulated motor activity with elements of motor stereotypy. It was hypothesized that important factors here were the relationship between the effect and the level of metal released after salt dissociation and different reactivity of the synaptic substrate of the neostriatum to the presence of zinc ions.

Gestational and early postnatal hypothyroidism alters VGluT1 and VGAT bouton distribution in the neocortex and hippocampus, and behavior in rats

Thyroid hormones are fundamental for the expression of genes involved in the development of the CNS and their deficiency is associated with a wide spectrum of neurological diseases including mental retardation, attention deficit-hyperactivity disorder and autism spectrum disorders. We examined in rat whether developmental and early postnatal hypothyroidism affects the distribution of vesicular glutamate transporter-1 (VGluT1; glutamatergic) and vesicular inhibitory amino acid transporter (VGAT; GABAergic) immunoreactive (ir) boutons in the hippocampus and somatosensory cortex, and the behavior of the pups. Hypothyroidism was induced by adding 0.02% methimazole (MMI) and 1% KClO4 to the drinking water starting at embryonic day 10 (E10; developmental hypothyroidism) and E21 (early postnatal hypothyroidism) until day of sacrifice at postnatal day 50. Behavior was studied using the acoustic prepulse inhibition (somatosensory attention) and the elevated plus-maze (anxiety-like assessment) tests. The distribution, density and size of VGluT1-ir and VGAT-ir boutons in the hippocampus and somatosensory cortex was abnormal in MMI pups and these changes correlate with behavioral changes, as prepulse inhibition of the startle response amplitude was reduced, and the percentage of time spent in open arms increased. In conclusion, both developmental and early postnatal hypothyroidism significantly decreases the ratio of GABAergic to glutamatergic boutons in dentate gyrus leading to an abnormal flow of information to the hippocampus and infragranular layers of the somatosensory cortex, and alter behavior in rats. Our data show cytoarchitectonic alterations in the basic excitatory hippocampal loop, and in local inhibitory circuits of the somatosensory cortex and hippocampus that might contribute to the delayed neurocognitive outcome observed in thyroid hormone deficient children born in iodine deficient areas, or suffering from congenital hypothyroidism.

A comparative study on the possible zinc binding sites of the human ZnT3 zinc transporter protein

The brain specific zinc transporter protein ZnT3 can be related to the amyloid neuropathology of Alzheimer's disease. In order to analyze the metal binding ability of human ZnT3 protein, here we report a potentiometric and solution structural (UV-Vis, CD, EPR, NMR) study of nickel(II), copper(II) and zinc(II) complexes of three peptides mimicking the possible metal binding sequences of this protein. The peptide L¹ (Ac-RHQAGPPHSHR-NH2) is a minimalist, the cyclic peptide L² (cyclo(Ac-CKLHQAGPPHSHGSRGAEYAPLEEGPEEKC-NH2) is a more complete model of the intracellular His-rich loop, which is widely accepted as a putative metal binding site. The peptide L³ (Ac-PFHHCHRD-NH2) is the model of the conserved cytoplasmic N-terminal -HHCH- sequence. In the physiological pH-range, the ZnL¹, ZnH3L² and ZnL³ complexes are the major species in the corresponding binary systems, with {3N(im)}, {3N(im),2/3O(amide)} and {3N(im),S(-)} coordination environments, respectively. The species ZnL³ has 3-4 orders of magnitude higher stability than the other two complexes, indicating the presence of a high-affinity zinc-binding site at the N-terminal tail of the human ZnT3 transporter. Moreover, L³ shows preferred zinc binding as compared to nickel (log β(ZnL³) - log β(NiL³) = 2.3), probably due to the higher preference of zinc(II) for tetrahedral geometry. These facts suggest that zinc binding to the N-terminal -HHCH- sequence of human ZnT3 may be involved in the biological activity of this zinc transporter protein in zinc sensing, binding or translocation processes.

Inhibitory effect of zinc on glucose-stimulated zinc/insulin secretion in an insulin-secreting β-cell line

Diminished or inappropriate secretion of insulin is associated with type II diabetes. The cellular/molecular mechanism coupled with the regulation of insulin secretion is still under intense investigation. Divalent ion zinc (Zn(2+)) is co-packaged and co-secreted with insulin and is intimately involved in the process of insulin biosynthesis and the maturation of insulin secretory granules. The study reported here investigated glucose-stimulated zinc secretion (GSZS) and the effect of zinc on glucose-stimulated insulin secretion (GSIS) in the HIT-T15 pancreatic β-cell line. Zinc secretion was measured using a newly developed fluorescent zinc imaging approach, and the insulin secretion was measured using an enzyme-linked immunosorbent assay. There was apparent granular-like zinc staining in β-cells. The application of glucose induced detectable zinc secretion or GSZS. Like GSIS, GSZS was dependent on the glucose concentration (5-20 mm) and the presence of extracellular calcium. The application of a zinc chelator enhanced GSZS. When brief paired-pulse glucose stimulations, which involve the initial glucose stimulation followed by a second round of glucose stimulation, were applied, zinc secretion or GSZS that followed the first pulse was inhibited. This inhibition was reversed by zinc chelation, suggesting a feedback mechanism on GSZS by zinc secreted from β-cells. Finally, the application of zinc (50 μm) strongly inhibited GSIS as measured by enzyme-linked immunosorbent assay. The present study suggests that insulin secretion is regulated by co-secreted zinc that may act as an autocrine inhibitory modulator.