A practical guide to the preparation and use of metal ion-buffered systems for physiological research

Identification of Cadmium Compounds in a Solution Using Graphene-Based Sensor Array

Rapid detection of heavy metals in solution is necessary to ensure human health and environmental protection. Some heavy-metal compounds are present in solution as compounds instead of as ions owing to their low ionization. Therefore, the development of sensor devices for the detection of heavy-metal compounds is important. In this study, as a proof of concept, we propose a sensor device using graphene and a chelating agent, which were used to develop an identification technique for three types of cadmium compounds. Pristine-graphene and two types of chelator-modified graphene-based sensors were successfully used to detect cadmium compounds at concentrations ranging from 50 to 1000 μM. The detection time was less than 5 min. The three type of graphene-based sensors responded differently to each cadmium compound, which indicates that they detected cadmium as a cadmium compound instead of as cadmium ions. Furthermore, we successfully identified cadmium compounds by operating these three types of sensors as a sensor array on the same substrate. The results indicate that sensors that focus on heavy-metal compounds instead of heavy-metal ions can be used for the detection of heavy metals in solution.

Zinc improved erythrocyte deformability and aggregation in patients with beta-thalassemia: An in vitro study

BACKGROUND

Thalassemia patients have reduced red cell deformability and decreased plasma zinc levels in their blood.

OBJECTIVE

This study aimed to evaluate the effects of zinc (Zn) on the hemorheological parameters and antioxidant enzyme activities in β-thalassemia major (TM) and healthy volunteers (HV).

METHODS

Hemorheological parameters were measured using LORCA (laser-assisted optical rotational cell analyzer) after adjusting the hematocrit to 40%. Zinc sulfate (ZnSO4.7H2O) was used for Zn incubation with a concentration of 0.5μg/dl. Oxidative stress and antioxidant status were determined using commercial kits.

RESULTS

Data showed that after Zn incubation, EImax, the area under the EI-osmolarity curve (Area), and Omax decreased in TM. However, no significant difference was observed in the osmotic deformability parameters of HV. The increased elongation index was obtained at different shear stresses for TM and HV, and SS1/2 decreased in both groups. The AMP and aggregation index (AI) decreased in TM, and the required time for half of the maximum aggregation (t1/2) increased in HV. However, Zn did not affect oxidative parameters in both groups.

CONCLUSIONS

This study showed that Zn incubation increased deformability and decreased aggregation in thalassemic erythrocytes. It means that Zn supplementation will contribute to microcirculation in thalassemia patients.

Hydroxypyridinones in nitrogen-fixing bacterial cultures: A metal buffer for molybdenum and simulation of natural conditions

Organic matter regulates the availability of important trace elements in aquatic and terrestrial ecosystems by acting as a source and container for microbes. To overcome the limitation of trace elements, nitrogen-fixing bacteria, for example, release low-molecular-weight chelators (metallophores), which scavenge the essential cofactors of the nitrogenase, iron and molybdenum, via complexation and subsequent uptake. The formation of metallophores is triggered by limiting conditions, which must be replicated in the laboratory in order to study metallophores as a mediator in metal cycling. While EDTA-based buffer systems for metal cations are well established, there is limited knowledge regarding the buffering of oxoanions such as molybdate in a bacterial growth medium. To mimic the availability of molybdenum in nature under laboratory conditions, this study created a Mo-buffer system for bacterial growth media of the model organisms Azotobacter vinelandii and Frankia sp. CH37. We investigated selected hydroxypyridinones (HPs) as potential molybdenum-chelating agents, determining the amount required for efficient molybdenum complexation by calculating speciation plots of the various candidate complexes in artificial growth media at various pH values. The Mo-maltol system was identified as an ideal, non-toxic molybdenum-buffer system. In the presence of the Mo-maltol system, the growth of Frankia sp. was limited under diazotrophic conditions, whereas A. vinelandii could acquire molybdenum through the release of protochelin and subsequent molybdenum uptake. The study paves the way for unravelling molybdenum recruitment and homeostasis under limiting conditions in bacteria.

Effects of Axonal Demyelination, Inflammatory Cytokines and Divalent Cation Chelators on Thalamic HCN Channels and Oscillatory Bursting

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system that is characterized by the progressive loss of oligodendrocytes and myelin and is associated with thalamic dysfunction. Cuprizone (CPZ)-induced general demyelination in rodents is a valuable model for studying different aspects of MS pathology. CPZ feeding is associated with the altered distribution and expression of different ion channels along neuronal somata and axons. However, it is largely unknown whether the copper chelator CPZ directly influences ion channels. Therefore, we assessed the effects of different divalent cations (copper; zinc) and trace metal chelators (EDTA; Tricine; the water-soluble derivative of CPZ, BiMPi) on hyperpolarization-activated cyclic nucleotide-gated (HCN) channels that are major mediators of thalamic function and pathology. In addition, alterations of HCN channels induced by CPZ treatment and MS-related proinflammatory cytokines (IL-1β; IL-6; INF-α; INF-β) were characterized in C57Bl/6J mice. Thus, the hyperpolarization-activated inward current (I_h) was recorded in thalamocortical (TC) neurons and heterologous expression systems (mHCN2 expressing HEK cells; hHCN4 expressing oocytes). A number of electrophysiological characteristics of I_h (potential of half-maximal activation (V_0.5); current density; activation kinetics) were unchanged following the extracellular application of trace metals and divalent cation chelators to native neurons, cell cultures or oocytes. Mice were fed a diet containing 0.2% CPZ for 35 days, resulting in general demyelination in the brain. Withdrawal of CPZ from the diet resulted in rapid remyelination, the effects of which were assessed at three time points after stopping CPZ feeding (Day1, Day7, Day25). In TC neurons, I_h was decreased on Day1 and Day25 and revealed a transient increased availability on Day7. In addition, we challenged naive TC neurons with INF-α and IL-1β. It was found that I_h parameters were differentially altered by the application of the two cytokines to thalamic cells, while IL-1β increased the availability of HCN channels (depolarized V_0.5; increased current density) and the excitability of TC neurons (depolarized resting membrane potential (RMP); increased the number of action potentials (APs); produced a larger voltage sag; promoted higher input resistance; increased the number of burst spikes; hyperpolarized the AP threshold), INF-α mediated contrary effects. The effect of cytokine modulation on thalamic bursting was further assessed in horizontal slices and a computational model of slow thalamic oscillations. Here, IL-1β and INF-α increased and reduced oscillatory bursting, respectively. We conclude that HCN channels are not directly modulated by trace metals and divalent cation chelators but are subject to modulation by different MS-related cytokines.

Chemical speciation of trace metals in mammalian cell culture media: looking under the hood to boost cellular performance and product quality

Upstream process development seeks to optimize media formulations to promote robust cell culture conditions and regulate product quality attributes such as glycosylation, aggregation, and charge variants. Transition metal ions Mn, Fe, Cu, and Zn present in cell culture media have a significant impact on cell growth, metabolism and product quality. These metals and other media components can have different chemical associations or speciation in media that are poorly characterized but may significantly impact their properties and effect on cellular performance. Computer-based equilibrium models are a good starting point for exploring metal speciation, bioavailability and conditions where precipitation may occur. However, some equilibrium constants, especially for newly introduced medium components, have not been experimentally determined. Owing to concurrent physical and biological processes, speciation may also be controlled by reaction kinetics rather than by equilibrium. These factors highlight the importance of analytically interrogating medium speciation to gain insights into the complex interconnections between media components and bioprocess performance.

Zn2+-induced changes in Cav2.3 channel function: An electrophysiological and modeling study

Loosely bound Zn²⁺ ions are increasingly recognized as potential modulators of synaptic plasticity and neuronal excitability under normal and pathophysiological conditions. Ca_v2.3 voltage-gated Ca²⁺ channels are among the most sensitive targets of Zn²⁺ and are therefore likely to be involved in the neuromodulatory actions of endogenous Zn²⁺. Although histidine residues on the external side of domain I have been implicated in the effects on Ca_v2.3 channel gating, the exact mechanisms involved in channel modulation remain incompletely understood. Here, we use a combination of electrophysiological recordings, modification of histidine residues, and computational modeling to analyze Zn²⁺-induced changes in Ca_v2.3 channel function. Our most important findings are that multiple high- and low-affinity mechanisms contribute to the net Zn²⁺ action, that Zn²⁺ can either inhibit or stimulate Ca²⁺ influx through Ca_v2.3 channels depending on resting membrane potential, and that Zn²⁺ effects may persist for some time even after cessation of the Zn²⁺ signal. Computer simulations show that (1) most salient features of Ca_v2.3 channel gating in the absence of trace metals can be reproduced by an obligatory model in which activation of two voltage sensors is necessary to open the pore; and (2) most, but not all, of the effects of Zn²⁺ can be accounted for by assuming that Zn²⁺ binding to a first site is associated with an electrostatic modification and mechanical slowing of one of the voltage sensors, whereas Zn²⁺ binding to a second, lower-affinity site blocks the channel and modifies the opening and closing transitions. While still far from complete, our model provides a first quantitative framework for understanding Zn²⁺ effects on Ca_v2.3 channel function and a step toward the application of computational approaches for predicting the complex actions of Zn²⁺ on neuronal excitability.

Multiparametric analysis of the effectiveness of cisplatin on cutaneous squamous carcinoma cells using two different types of adjuvants

The objective of this study was to regulate the cytotoxicity of cisplatin (cisPt) minimizing its adverse effects. For this purpose, the lowest cisPt concentration needed to obtain a significant positive response in cutaneous squamous cell carcinoma (cSCC) was explored. Two adjuvant agents as gold nanoparticles (AuNP) and chelating tricine were tested as enhancers in cisPt treatment. Effectiveness of all treatments was assessed by means of biochemical techniques, which offer quantitative data, as well as two microscopy–based techniques that provided qualitative cell imaging. The present work confirms the effectiveness of free cisplatin at very low concentrations. In order to enhance its effectiveness while the side effects were probably diminished, cisPt 3.5 μM was administered with AuNP 2.5 mM, showing an effectiveness practically equal to that observed with free cisPt. However, the second treatment investigated, based on cisPt 3.5 μM combined with tricine 50 mM, enhanced drug effectiveness, increasing the percentage of cells dying by apoptosis. This treatment was even better in terms of cell damage than free cisPt at 15 μM. Images obtained by TEM and cryo-SXT confirmed these results, since a notable number of apoptotic bodies were detected when cisPt was combined with tricine. Thus, tricine was clearly a better adjuvant for cisPt treatments.

Ionized concentrations in Ca2+ and Mg2+ buffers must be measured, not calculated

NEW FINDINGS

What is the topic of this review? The [Ca²⁺ ]/[Mg²⁺ ] in buffers are usually calculated using one of eight programs. These all give different values, thus [Ca²⁺ ]/[Mg²⁺ ] must be measured. What advances does it highlight? The ligand optimization method (LOM) using electrodes is an accurate method to do this. The limitations of the method are described. The LOM has been generalized to include calibration of fluorochromes and aequorin. It is the method of choice to measure intracellular equilibrium constants. Owing to the uncertainties for the values of resting [Ca²⁺ ], ∆[Ca²⁺ ] and the pK' values for intracellular Ca²⁺ /Mg²⁺ binding used in modelling, these values must now be re-examined critically.

ABSTRACT

Modelling intracellular regulation of Ca²⁺ /Mg²⁺ is now an established part of physiology. However, the conclusions drawn from such studies depend on accurate knowledge of intracellular [Ca²⁺ ], ∆[Ca²⁺ ] and the pK' values for the intracellular binding of Ca²⁺ /Mg²⁺ . Calculation of [Ca²⁺ ]/[Mg²⁺ ] in buffers is normal. The eight freely available programs all give different values for the [Ca²⁺ ]/[Mg²⁺ ] in the buffer solutions, varying by up to a factor of 4.3. As a result, concentrations must be measured. There are two methods to do this, both based on the ligand optimization method (LOM): (1) calibration solutions from 0.5 to 4 mmol l^-1 ; and (2) calibration solutions from 0.1 µmol l^-1 to 2 mmol l^-1 . Both methods can be used to calibrate Ca²⁺ /Mg²⁺ electrodes. Only Method 2 can be used directly to calibrate fluorochromes and aequorin. Software in the statistical program R to calculate the [Ca²⁺ ]/[Mg²⁺ ] in buffers is provided for both methods. The LOM has now been generalized for use with electrodes, fluorochromes and aequorin, making it the ideal method to determine the pK' values for intracellular binding of Ca²⁺ /Mg²⁺ . The [Ca²⁺ ]/[Mg²⁺ ] in buffers must be measured routinely, which is best done by calibrating electrodes with the LOM and software written in R. If [Ca²⁺ ]/[Mg²⁺ ] in buffers are calculated, the parameters used in modelling show the same degree of variability as the software programs. Uncritical acceptance of such parameters means that conclusions reached from such studies are relative, not absolute, and must now be re-examined.

Metal Chelation Therapy and Parkinson's Disease: A Critical Review on the Thermodynamics of Complex Formation between Relevant Metal Ions and Promising or Established Drugs

The present review reports a list of approximately 800 compounds which have been used, tested or proposed for Parkinson's disease (PD) therapy in the year range 2014-2019 (April): name(s), chemical structure and references are given. Among these compounds, approximately 250 have possible or established metal-chelating properties towards Cu(II), Cu(I), Fe(III), Fe(II), Mn(II), and Zn(II), which are considered to be involved in metal dyshomeostasis during PD. Speciation information regarding the complexes formed by these ions and the 250 compounds has been collected or, if not experimentally available, has been estimated from similar molecules. Stoichiometries and stability constants of the complexes have been reported; values of the cologarithm of the concentration of free metal ion at equilibrium (pM), and of the dissociation constant Kd (both computed at pH = 7.4 and at total metal and ligand concentrations of 10-6 and 10-5 mol/L, respectively), charge and stoichiometry of the most abundant metal-ligand complexes existing at physiological conditions, have been obtained. A rigorous definition of the reported amounts is given, the possible usefulness of this data is described, and the need to characterize the metal-ligand speciation of PD drugs is underlined.