Susceptibility to kainate-induced seizures under dietary zinc deficiency

Zinc homeostasis in the brain is altered by dietary zinc deficiency, and its alteration may be associated with the etiology and manifestation of epileptic seizures. In the present study, susceptibility to kainate-induced seizures was enhanced in mice fed a zinc-deficient diet for 4 weeks. When Timm's stain was performed to estimate zinc concentrations in synaptic vesicles, Timm's stain in the brain was attenuated in the zinc-deficient mice. In rats fed the zinc-deficient diet for 4 weeks, susceptibility to kainate-induced seizures was also enhanced. When the release of zinc and neurotransmitters in the hippocampal extracellular fluid of the zinc-deficient rats was studied using in vivo microdialysis, the zinc concentration in the perfusate was less than 50% of that of the control rats and the increased levels of zinc by treatment with kainate were lower than the basal level in control rats, suggesting that vesicular zinc is responsive to dietary zinc deficiency. The levels of glutamate in the perfusate of the zinc-deficient rats were more increased than in the control rats, whereas the levels of GABA in the perfusate were not at all increased in the zinc-deficient rats, unlike in the control rats. The present results demonstrate an enhanced release of glutamate associated with a decrease in GABA concentrations as a possible mechanism for the increased seizure susceptibility under zinc deficiency.     

Zinc metabolism and homeostasis: The application of tracer techniques to human zinc physiology

Tracer kinetic techniques based on zinc stable isotopes have a vital role in advancing knowledge of human zinc physiology and homeostasis. These techniques have demonstrated the complexity of zinc metabolism, and have been critical to estimating the size and interrelationships of those pools of zinc that exchange rapidly with zinc in plasma and which are likely to be especially important for zinc dependent biology. This paper presents findings from recent research linking a steady state compartmental model with non-steady state post-prandial sampling from the intestine, utilizing a combination of intestinal intubation/perfusion and stable isotope tracer kinetic techniques. The gastrointestinal tract has a central role in maintaining whole body zinc homeostasis. While the fractional absorption of zinc from a meal depends on the quantity of exogenous zinc and on such dietary factors as phytic acid, the fractional absorption does not appear to be dependent on the size of the rapidly exchanging pool of the host. In contrast, the quantity of endogenous zinc excreted via the intestine is positively correlated with both the amount of absorbed zinc and the zinc `status' of the host, and thus this process has an equally critical role in maintaining zinc homeostasis. The observed alterations in zinc metabolism in some disease states can be understood in the context of known homeostatic processes. In other conditions, however, such alterations as inflammation-associated hyperzincuria and zinc redistribution, the links between homeostatic perturbation and cellular biology are yet to be explained. Thus the challenge remains for research at the whole body level to carefully characterize zinc distribution and exchange under diverse circumstances, while research at the cellular level must elucidate the regulatory processes and the factors to which they respond.     

Resveratrol–zinc combination for prostate cancer management

Zinc, an essential trace element, plays a critical role in cell signaling, and defect(s) in zinc homeostasis may contribute to adverse physiological and pathological conditions, including cancer. Zinc is present in healthy prostate at a very high concentration, where it is required for important prostatic functions. However, zinc levels are significantly diminished in cancerous tissue, and intracellular zinc level is inversely correlated with prostate cancer progression. During neoplastic transformation, zinc-accumulating, citrate-producing normal prostate cells are metabolically transformed to citrate oxidizing cells that lose the ability to accumulate zinc. Interestingly, zinc has been shown to function as chemopreventive agent against prostate cancer, albeit at high doses, which may lead to many adverse effects. Therefore, novel means to enhance bioaccumulation of sufficient zinc in prostate cells via increasing zinc transport could be useful against prostate cancer. On the basis of available evidence, we present a possibility that the grape antioxidant resveratrol, when given with zinc, may lead to retuning the zinc homeostasis in prostate, thereby abolishing or reversing malignancy. If experimentally verified in in vivo model(s) of prostate cancer, such as transgenic mouse models, this may lead to novel means toward management of prostate cancer and other conditions with compromised zinc homeostasis.     

膳食锌对小鼠脑组织微管相关蛋白2表达的影响

本工作观察了膳食锌与脑组织微管相关蛋白２（ＭＡＰ２）之间的联系,并探讨了微量元素锌调节微管聚合作用的可能机制。ＩＣＲ初孕小鼠８０ 孕期和哺乳局喂不同锌水平饲料,随机分为５组：严重缺锌组,轻度缺锌组,轻度缺锌组,适锌组,高锌对喂组及高锌组,它们饲料的锌水平分别为１,５,３０,１００和１００ｍｇ／ｋｇ。     

Loss of COMMD1 and copper overload disrupt zinc homeostasis and influence an autism-associated pathway at glutamatergic synapses

Recent studies suggest that synaptic pathology in autism spectrum disorder (ASD) might be caused by the disruption of a signaling pathway at excitatory glutamatergic synapses, which can be influenced by environmental factors. Some factors, such as prenatal zinc deficiency, dysfunction of metallothioneins as well as deletion of COMMD1, all affect brain metal-ion homeostasis and have been associated with ASD. Given that COMMD1 regulates copper levels and that copper and zinc have antagonistic properties, here, we followed the idea that copper overload might induce a local zinc deficiency affecting key players of a putative ASD pathway such as ProSAP/Shank proteins as reported before. Our results show that increased copper levels indeed interfere with intracellular zinc concentrations and affect synaptic ProSAP/Shank levels, which similarly are altered by manipulation of copper and zinc levels through overexpression and knockdown of COMMD1. In line with this, acute and prenatal copper overload lead to local zinc deficiencies in mice. Pups exposed to prenatal copper overload furthermore show a reduction in ProSAP/Shank protein levels in the brain as well as a decreased NMDAR subunit 1 concentration. Thus, it might be likely that brain metal ion status influences a distinct pathway in excitatory synapses associated with genetic forms of ASD.     

Synaptically released zinc: Physiological functions and pathological effects

In addition to its familiar role as a component of metalloproteins, zinc is also sequestered in the presynaptic vesicles of a specialized type of neurons called `zinc-containing' neurons. Here we review the physiological and pathological effects of the release of zinc from these zinc-containing synaptic terminals. The best-established physiological role of synaptically released zinc is the tonic modulation of brain excitability through modulation of amino acid receptors; prominent pathological effects include acceleration of plaque deposition in Alzheimer's disease and exacerbation of excitotoxic neuron injury. Synaptically released zinc functions as a conventional synaptic neurotransmitter or neuromodulator, being released into the cleft, then recycled into the presynaptic terminal. Beyond this, zinc also has the highly unconventional property that it passes into postsynaptic neurons during synaptic events, functioning analogously to calcium in this regard, as a transmembrane neural signal. To stimulate comparisons of zinc signals with calcium signals, we have compiled a list of the important parameters of calcium signals and zinc signals. More speculatively, we hypothesize that zinc signals may loosely mimic phosphate `signals' in the sense that signal zinc ions may commonly bind to proteins in a lasting manner (i.e., `zincylating' the proteins) with consequential changes in protein structure and function.     

Targeting of the mouse Slc39a2 (Zip2) gene reveals highly cell-specific patterns of expression, and unique functions in zinc, iron, and calcium homeostasis

Fourteen members of the Slc39a superfamily of metal ion uptake transporters have been identified in mice and humans, but the physiological functions of most remain obscure. Herein, we created mice with Zip2 (Slc39a2) genes in which the open reading frame was replaced with that of the enhanced green fluorescent protein (EGFP), to study temporal and spatial patterns of Zip2 gene expression and examine the physiological roles of this transporter. Expression of this gene was remarkably cell-type specific and developmentally regulated in pericentral hepatocytes, developing keratinocytes, and a subset of immature dendritic cells in the immune system. In addition, the Zip2 gene was transiently expressed in giant trophoblast cells in the placenta. Although the Zip2 gene was not essential under conditions of normal dietary zinc, it played an important role in adapting to dietary zinc deficiency during pregnancy, and in the homeostasis of iron in the liver as well as iron and calcium in developing embryos. These studies suggest that active expression of the Zip2 gene in these few specific cell types, aforementioned, plays a particularly important role during zinc deficiency. These studies further reveal novel interactions between zinc transporter function and the homeostasis of other essential metals.     

锌指类基因调控蛋白──生物无机化学和分子生物学发展的新领域

生命必需元素锌,除了以锌酶的形式,参与生物体的各类代谢过程外,近年来发现,锌还以各种锌蛋白的结构方式,包括锌指、锌纽、锌带和锌簇等,参与生物体的基因转录、复制及蛋白质的合成等各种基因调节和控制过程．联想到金属硫蛋白在锌的体内平衡中所扮演的角色,很有可能锌是通过金属硫蛋白和锌指类蛋白的逐级调控,成为生物体生长发育的调控中心．癌基因和人免疫缺陷病毒（HIV）的许多调节蛋白也具有锌指类结构,这给癌症和爱滋病的治疗提供了新思路．     

Dynamic action of neurometals at the synapse

There are synaptic vesicles that are labeled by Timm's sulfide-silver staining method in the brain, suggesting that synaptic vesicles contain metals such as zinc and copper. Zinc is co-released with glutamate and the importance of zinc signaling in the intracellular compartment, in addition to extracellular compartment, is becoming recognized. Zinc can pass through calcium channels, while blocking them. Calcium signaling plays a critical role for synaptic activity and crosstalk between zinc signaling with calcium signaling through calcium channels may participate in synaptic neurotransmission including synaptic plasticity such as long-term potentiation. Copper released into the synaptic cleft during synaptic excitation may also participate in synaptic neurotransmission. Other metals including copper potentially serve as calcium channel blockers and also influence calcium signaling and zinc signaling via the interaction with metal-binding proteins such as metallothioneins. Homeostasis of metals needs to be controlled spatiotemporally for proper brain function, and their dyshomeostasis is associated with neurological diseases. However, the data on the dynamic action of metals at synapses is limited and their significance poorly understood. This paper summarizes the action of metals in synaptic neurotransmission focused on calcium signaling at glutamatergic synapses.     

Extrasynaptic transmission and the diffusion parameters of the extracellular space

Extrasynaptic volume transmission, mediated by the diffusion of neuroactive substances in the extracellular space (ECS), plays an important role in short- and long-distance communication between nerve cells. The ability of a substance to reach extrasynaptic high-affinity receptors via diffusion depends on the ECS diffusion parameters, ECS volume fraction alpha (alpha=ECS volume/total tissue volume) and tortuosity lambda (lambda2=free/apparent diffusion coefficient), which reflects the presence of diffusion barriers represented by, e.g., fine astrocytic processes or extracellular matrix molecules. These barriers channel the migration of molecules in the ECS, so that diffusion may be facilitated in a certain direction, i.e. anisotropic. The diffusion parameters alpha and lambda differ in various brain regions, and diffusion in the CNS is therefore inhomogeneous. Changes in diffusion parameters have been found in many physiological and pathological states, such as development and aging, neuronal activity, lactation, ischemia, brain injury, degenerative diseases, tumor growth and others, in which cell swelling, glial remodeling and extracellular matrix changes are key factors influencing diffusion. Changes in ECS volume, tortuosity and anisotropy significantly affect the accumulation and diffusion of neuroactive substances and thus extrasynaptic transmission, neuron-glia communication, mediator "spillover" and synaptic crosstalk as well as, cell migration. The various changes occurring during pathological states can be important for diagnosis, drug delivery and treatment.     

Zinc homeostasis in the hippocampus of zinc-deficient young adult rats

On the basis of the evidence of the transient learning impairment of young adult rats fed a zinc-deficient diet for 4 weeks, zinc concentration in the hippocampus was examined in the zinc-deficient rats to understand the mechanism of brain dysfunction in zinc deficiency. Zinc concentration in the hippocampus, as well as that in other brain regions, was not decreased by 4-week zinc deprivation. When Timm's stain, with which histochemically reactive zinc in the presynaptic vesicles is detected, was compared between the control and zinc-deficient rats, the intensity of Timm's stain in the hippocampus was almost the same between them. In the hippocampus, zinc concentration in the synaptosomal fraction was not also decreased by 4-week zinc deprivation, whereas that in the crude nuclear fraction was significantly increased. These results suggest that zinc concentration in the presynaptic vesicles is not decreased in young adults rats by 4-week zinc deprivation. It is likely that zinc-requiring systems in the nucleus are more responsive to zinc deficiency than vesicular zinc. This responsiveness appears to be involved in the transient learning impairment.     

细菌锌离子调控体系与感染北大核心CSCD

锌(Zn)是生命体不可或缺的微量元素,对细菌和宿主同等重要。细菌体内锌离子稳态的维持依赖锌离子转运和调控体系。宿主通过限制锌离子或高锌离子中毒来控制细菌感染。为了在宿主体内生存,细菌必须表达高亲和力的锌离子转运系统,如ZnuABC,以获取足够的锌离子。由于锌与细菌大量的代谢和毒性通路密切相关,在细菌建立感染的过程中尤为重要,因此通过抑制锌离子转运系统来影响锌离子的稳态,将成为一个非常有发展前途的新型抗菌策略。     

Enhanced Susceptibility to Spontaneous Seizures of Noda Epileptic Rats by Loss of Synaptic Zn2+

Zinc homeostasis in the brain is associated with the etiology and manifestation of epileptic seizures. Adult Noda epileptic rats (NER, >12-week-old) exhibit spontaneously generalized tonic-clonic convulsion about once a day. To pursue the involvement of synaptic Zn²⁺ signal in susceptibility to spontaneous seizures, in the present study, the effect of zinc chelators on epileptogenesis was examined using adult NER. Clioquinol (CQ) and TPEN are lipophilic zinc chelotors, transported into the brain and reduce the levels of synaptic Zn²⁺. The incidence of tonic-clonic convulsion was markedly increased after i.p. injection of CQ (30–100 mg/kg) and TPEN (1 mg/kg). The basal levels of extracellular Zn²⁺ measured by ZnAF-2 were decreased before tonic-clonic convulsion was induced with zinc chelators. The hippocampal electroencephalograms during CQ (30 mg/kg)-induced convulsions were similar to those during sound-induced convulsions in NER reported previously. Exocytosis of hippocampal mossy fibers, which was measured with FM4-64, was significantly increased in hippocampal slices from CQ-injected NER that did not show tonic-clonic convulsion yet. These results indicate that the abnormal excitability of mossy fibers is induced prior to epileptic seizures by injection of zinc chelators into NER. The incidence of tonic-clonic convulsion induced with CQ (30 mg/kg) was significantly reduced by co-injection with aminooxyacetic acid (5–10 mg/kg), an anticonvulsant drug enhancing GABAergic activity, which did not affect locomotor activity. The present paper demonstrates that the abnormal excitability in the brain, especially in mossy fibers, which is potentially associated with the insufficient GABAergic neuron activity, may be a factor to reduce the threshold for epileptogenesis in NER.     

内质网应激与心肌肥大

肌浆网是调控心肌细胞钙稳态、蛋白质合成和细胞凋亡的重要亚细胞器。内质网应激是指内质网理化环境改变和过负荷等因素导致未折叠/误折叠蛋白在内质网聚集和钙稳态失衡等内质网功能紊乱状态。适度的内质网应激有利于心肌细胞代偿,持续而严重的内质网应激则触发内质网应激相关细胞凋亡,造成肥大心肌由代偿转向衰竭,是影响心肌肥大发生、发展的重要因素。本文综述了内质网应激反应在心肌肥大发生、发展中的作用。     

Erythrocyte metallothionein in relation to other biochemical zinc indices in pregnant and nonpregnant women

Erythrocyte metallothionein (E-MT) is considered a promising index of zinc status in humans, since it may be more sensitive than other biochemical indices to changes in dietary zinc. However, conditions of high zinc demand with substantial redistribution of tissue zinc and specific changes in hormone profile, such as pregnancy, may have an influence on E-MT levels in addition to dietary zinc. In this study, we compared E-MT concentrations in relation to other biochemical zinc indices in healthy pregnant women at delivery (n=40) and nonpregnant women (n=22) with similar habitual dietary zinc intakes (average 13.3 mg/d). Pregnant women had lower serum zinc and albumin-bound serum zinc, but higher levels of {ie115-1}-macroglobulin-bound serum zinc than the nonpregnant women. Erythrocyte zinc (E-Zn) was similar in both groups, but E-MT (mean±SE) was slightly but significantly (p<0.05) higher in the pregnant women (2.9±0.09 nmol/g protein) compared to nonpregnant women (2.6±0.06 nmol/g protein). A significant correlation was observed between E-MT and E-Zn in the nonpregnant women (r=0.70;p<0.001), consistent with the role of intracellular zinc in the regulation of metallothionein synthesis. However, such correlation was not observed in the pregnant women, suggesting that E-MT levels in pregnancy may be influenced by factors related to the pregnant state.     

Possible involvement of plasma histidine in differential brain permeability to zinc and cadmium

Zinc gets into the brain parenchyma across the blood-brain and the blood-cerebrospinal fluid barriers, while cadmium hardly gets into the brain parenchyma. Because histidine may be involved in zinc transport across the brain barrier systems, the binding to histidine was compared between zinc and cadmium to understand the difference in brain permeability to both metals. Sephadex G-10 gel filtration indicated that ¹⁰⁹Cd, unlike ⁶⁵Zn, does not bind to histidine. When the plasma incubated with ⁶⁵Zn or ¹⁰⁹Cd was dialyzed in physiological saline containing histidine (0-10 mM), ⁶⁵Zn concentration in the dialysate was increased with the increase of the histidine concentration, suggesting the transfer of zinc from plasma proteins to histidine. The low affinity of zinc to plasma proteins may be important for brain permeability to this metal. On the other hand, ¹⁰⁹Cd was not detected in the dialysate in the presence of 0.1 mM histidine, which is equal to the concentration in the plasma, suggesting no transfer of cadmium from plasma proteins to histidine. These results suggest that the avid binding of cadmium to plasma proteins is related to brain impermeability to this metal.     

Synaptically released zinc: neuromodulator and toxin

In addition to its familiar role as a component of metalloproteins, zinc is also sequestered in the presynaptic vesicles in ‘zinc‐containing’ neurons. The best‐established physiological role of synaptically released zinc is the tonic modulation of brain excitability through modulation of amino acid receptors; prominent pathological effects include acceleration of plaque deposition in Alzheimer's disease and exacerbation of excitotoxic neuron injury. Synaptically released zinc functions as a conventional synaptic neurotransmitter or neuromodulator being released into the cleft then recycled into the postsynaptic neurons during synaptic events, functioning analogously to calcium in this regard, as a transmembrane neural signal. To stimulate comparisons of zinc signals with calcium signals, we have compiled a list of the important parameters of calcium signals and zinc signals. More speculatively, we hypothesize that zinc signals may loosely mimic phosphate signals in the sense that signal zinc ions may commonly bind to proteins in a lasting manner, as a result changing their structure and function.     

Serum growth factors and neuroprotective surveillance

The adult brain requires a constant trophic input for appropriate function. Although the main source of trophic factors for mature neurons is considered to arise locally from glial cells and synaptic partners, recent evidence suggests that hormonal-like influences from distant sources may also be important. These include not only relatively well-characterized steroid hormones that cross the brain barriers, but also blood-borne protein growth factors able to cross the barriers and exert unexpected, albeit specific, trophic actions in diverse brain areas. Insulin-like growth factor I (IGF-I) is until now the serum neurotrophic factor whose actions on the adult brain are best-characterized. This is because IGF-I has been known for many years to be present in serum, whereas the presence in the circulation of other more classical neurotrophic factors has only recently been recognized. Thus, new evidence strongly suggests that IGF-I, and other blood-borne neurotrophic factors such as Fibroblast Growth Factor (FGF-2) or the neurotrophins, exert a tonic trophic input on brain cells, providing a mechanism for what we may refer to as neuroprotective surveillance. Protective surveillance includes "first-line" defense mechanisms ranging from blockade of neuronal death after a wide variety of cellular insults to upregulation of neurogenesis when defenses against neuronal death are overcome. Most importantly, surveillance should also encompass modulation of homeostatic mechanisms to prevent neuronal derangement. These will include modulation of basic cellular processes such as metabolic demands and maintainance of cell-membrane potential as well as more complex processes such as regulation of neuronal plasticity to keep neurons able to respond to constantly changing functional demands.