Intracellular dialysis disrupts Zn2+ dynamics and enables selective detection of Zn2+ influx in brain slice preparations

Zinc regulates reactive oxygen species generation in platelets

Vascular complications resulting from atherosclerosis development are a major cause of death. Reactive oxygen species (ROS) are produced by platelets during activation, and have been demonstrated to positively regulate platelet activatory responses. Zn2+ is also an important hemostatic cofactor in platelets, acting both as a platelet agonist and second messenger. Whilst the effect of Zn2+-dependent signaling mechanisms on ROS production in nucleated cells has been demonstrated, comparable roles in platelets have yet to be investigated. In this study we investigated the relationship between fluctuations in cytosolic Zn2 [Zn2+]i and platelet ROS production. Agonist-evoked ROS production, GSH levels and GPx activity are abrogated in platelets treated with the Zn2+-chelator, TPEN. Conversely, increasing platelet [Zn2+]i using Zn2+ ionophores potentiated ROS generation and decreased GSH levels and GPx activity. Zn2+-dependent ROS production was sensitive to pretreatment with DPI or mitoTEMPO, NADPH oxidase and mitochondria inhibitors respectively. Increasing [Zn2+]i resulted in increases of Erk1/2 and JNK phosphorylation. Our data are consistent with a functional association between [Zn2+]i and ROS production in platelets that could influence thrombus formation in a clinical context.

Serum zinc and copper levels in a sample of Egyptian epileptic children

Background

Epilepsy is among the most common disabling neurological disorders among children. Altered serum levels of zinc and copper may facilitate seizure occurrence and repetition, and antiepileptic drugs may disturb their serum levels affecting disease control and outcome.

Objective

To investigate the association between serum levels of zinc and copper and epilepsy and antiepileptic treatment in a group of Egyptian epileptic children.

Methods

Case-control study on 100 epileptic patients, aged from 2 to 16 years, from neurology outpatient clinic and 50 apparently healthy children with matched age and sex. Venous samples were withdrawn from patients and controls then serum levels of zinc and copper were measured with graphite furnace atomic absorption spectrometer-A Analyst 800.

Results

Serum zinc level of patients’ group was significantly lower than that of controls with a mean of 59.1 μ/dL ± 22.7 and 85 μ/dL ± 22.2, respectively (P < 0.01). Serum zinc level of patients with history of febrile seizures was significantly decreased compared to patients without history of febrile seizures with a mean of 41.5 μ/dL ± 20.1 and 67.9 μ/dL ± 19.3, respectively (P < 0.01). Patient on carbamazepine intake showed significantly lower zinc serum level than patients without carbamazepine intake, with a mean of 49.0 μ/dL ± 17 and 61.8 μ/dL ± 23.4, respectively (P < 0.01). A significant negative correlation was noted between the duration of illness of epilepsy and the mean copper serum level (P < 0.05).

Conclusion

Zinc and copper altered homeostasis have mounting evidence about their role in the pathogenesis of epilepsy. Designing treatment plans that selectively restore zinc and copper normal levels may be a beneficial strategy in the future.

Agonist-Evoked Increases in Intra-Platelet Zinc Couple to Functional Responses

Background  Zinc (Zn ²⁺ ) is an essential trace element that regulates intracellular processes in multiple cell types. While the role of Zn ²⁺ as a platelet agonist is known, its secondary messenger activity in platelets has not been demonstrated.

Objectives  This article determines whether cytosolic Zn ²⁺ concentrations ([Zn ²⁺ ] _i ) change in platelets in response to agonist stimulation, in a manner consistent with a secondary messenger, and correlates the effects of [Zn ²⁺ ] _i changes on activation markers.

Methods  Changes in [Zn ²⁺ ] _i were quantified in Fluozin-3 (Fz-3)-loaded washed, human platelets using fluorometry. Increases in [Zn ²⁺ ] _i were modelled using Zn ²⁺ -specific chelators and ionophores. The influence of [Zn ²⁺ ] _i on platelet function was assessed using platelet aggregometry, flow cytometry and Western blotting.

Results  Increases of intra-platelet Fluozin-3 (Fz-3) fluorescence occurred in response to stimulation by cross-linked collagen-related peptide (CRP-XL) or U46619, consistent with a rise of [Zn ²⁺ ] _i . Fluoresence increases were blocked by Zn ²⁺ chelators and modulators of the platelet redox state, and were distinct from agonist-evoked [Ca ²⁺ ] _i signals. Stimulation of platelets with the Zn ²⁺ ionophores clioquinol (Cq) or pyrithione (Py) caused sustained increases of [Zn ²⁺ ] _i , resulting in myosin light chain phosphorylation, and cytoskeletal re-arrangements which were sensitive to cytochalasin-D treatment. Cq stimulation resulted in integrin α _IIb β ₃ activation and release of dense, but not α, granules. Furthermore, Zn ²⁺ -ionophores induced externalization of phosphatidylserine.

Conclusion  These data suggest that agonist-evoked fluctuations in intra-platelet Zn ²⁺ couple to functional responses, in a manner that is consistent with a role as a secondary messenger. Increased intra-platelet Zn ²⁺ regulates signalling processes, including shape change, α _IIb β ₃ up-regulation and dense granule release, in a redox-sensitive manner.

Orchestration of NLRP3 Inflammasome Activation by Ion Fluxes

The assembly of the NLRP3 inflammasome can promote the release of IL-1β/IL-18 and initiate pyroptosis. Accordingly, the dysregulation of NLRP3 inflammasome activation is involved in a variety of human diseases, including gout, diabetes, and Alzheimer's disease. NLRP3 can sense a variety of structurally unrelated pathogen-associated molecular patterns (PAMPs) or danger-associated molecular patterns (DAMPs) to trigger inflammation, but the unifying mechanism of NLRP3 activation is still poorly understood. Increasing evidence suggests that intracellular ions, such as K⁺, Ca²⁺, and Cl^-, have a significant role in NLRP3 inflammasome activation. Here, we review the current knowledge about the role of ionic fluxes in NLRP3 inflammasome activation and discuss how disturbances in intracellular ionic levels orchestrate different signaling events upstream of NLRP3.

ZnT-1 extrudes zinc from mammalian cells functioning as a Zn(2+)/H(+) exchanger

ZnT-1 is a Cation Diffusion Facilitator (CDF) family protein, and is present throughout the phylogenetic tree from bacteria to humans. Since its original cloning in 1995, ZnT-1 has been considered to be the major Zn(2+) extruding transporter, based on its ability to protect cells against zinc toxicity. However, experimental evidence for ZnT-1 induced Zn(2+) extrusion was not convincing. In the present study, based on the 3D crystal structure of the ZnT-1 homologue, YiiP, that predicts a homodimer that utilizes the H(+) electrochemical gradient to facilitate Zn(2+) efflux, we demonstrate ZnT-1 dependent Zn(2+) efflux from HEK 293T cells using FluoZin-3 and Fura 2 by single cell microscope based fluorescent imaging. ZnT-1 facilitates zinc efflux in a sodium-independent, pH-driven and calcium-sensitive manner. Moreover, substitution of two amino acids in the putative zinc binding domain of ZnT-1 led to nullification of Zn(2+) efflux and rendered the mutated protein incapable of protecting cells against Zn(2+) toxicity. Our results demonstrate that ZnT-1 extrudes zinc from mammalian cells by functioning as a Zn(2+)/H(+) exchanger.

Chloroquine is a zinc ionophore

Chloroquine is an established antimalarial agent that has been recently tested in clinical trials for its anticancer activity. The favorable effect of chloroquine appears to be due to its ability to sensitize cancerous cells to chemotherapy, radiation therapy, and induce apoptosis. The present study investigated the interaction of zinc ions with chloroquine in a human ovarian cancer cell line (A2780). Chloroquine enhanced zinc uptake by A2780 cells in a concentration-dependent manner, as assayed using a fluorescent zinc probe. This enhancement was attenuated by TPEN, a high affinity metal-binding compound, indicating the specificity of the zinc uptake. Furthermore, addition of copper or iron ions had no effect on chloroquine-induced zinc uptake. Fluorescent microscopic examination of intracellular zinc distribution demonstrated that free zinc ions are more concentrated in the lysosomes after addition of chloroquine, which is consistent with previous reports showing that chloroquine inhibits lysosome function. The combination of chloroquine with zinc enhanced chloroquine's cytotoxicity and induced apoptosis in A2780 cells. Thus chloroquine is a zinc ionophore, a property that may contribute to chloroquine's anticancer activity.