Susceptibility of insulinoma cells to cadmium and modulation by L-type calcium channels

The impact of environmental cadmium exposure on type 2 diabetes risk: a protocol for an overview of systematic reviews

BACKGROUND

Type 2 diabetes mellitus (T2DM) is a worldwide epidemic, and while its etiology is polygenic, the role of environmental contaminant exposure in T2DM pathogenesis is of increasing importance. However, the evidence presented in systematic reviews on the relationship between cadmium exposure and T2DM development is inconsistent. This overview aims to assess existing evidence from systematic reviews linking cadmium exposure to T2DM and select metabolic disorders in humans.

METHODS

Searches will be conducted in Medline, Embase, Web of Science, GEOBASE, BIOSIS Previews, and Cochrane Database of Systematic Reviews. Two reviewers (J.H and S.T.) will independently complete screening, data abstraction, risk of bias evaluation, and quality assessment. The primary outcome will be the association between cadmium exposure and T2DM prevalence. Secondary outcomes will include prediabetes, obesity, dyslipidemia, hypertension, and non-alcoholic fatty liver disease. We will perform a meta-analysis if two or more studies assess similar populations, utilize analogous methods, have related study designs, and evaluate similar outcomes.

DISCUSSION

This overview will assess current evidence from systematic reviews for the association between cadmium exposure and risk of T2DM and other metabolic morbidities. This overview may be helpful for policy-makers and healthcare teams aiming to mitigate T2DM risk in populations at risk of cadmium exposure.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42019125956.

Fucoidan inhibits Ca2+ responses induced by a wide spectrum of agonists for G‑protein‑coupled receptors

Fucoidan, a sulfated polysaccharide extracted from brown seaweed, has been used in traditional Chinese herbal medicine to treat thyroid tumors for many years. Although a number of its cellular effects have been investigated, the role of fucoidan in molecular signaling, particularly in Ca²⁺ signaling, remains largely unknown. In the present study, the effects of fucoidan on Ca²⁺ responses in HeLa cells, human umbilical vein endothelial cells and astrocytes were investigated using a wide range of receptor agonists. Fucoidan inhibited the increase in intracellular free calcium concentration that was induced by histamine, ATP, compound 48/80 and acetylcholine. The responses induced by the same agonists in the absence of extracellular Ca²⁺ were also markedly suppressed by fucoidan. Reverse transcription-polymerase chain reaction demonstrated that 0.5 and 1.0 mg/ml fucoidan treatment for 3 h decreased histamine receptor 1 expression in HeLa cells. Similarly, the expressions of purinergic receptor P2Y, G-protein coupled (P2YR)1, P2YR2 and P2YR11 were significantly downregulated within cells pretreated with 1.0 mg/ml fucoidan for 3 h, and 0.5 mg/ml fucoidan significantly inhibited P2YR1 and P2YR11 expression. The results demonstrated that fucoidan may exert a wide spectrum of inhibitory effects on Ca²⁺ responses and that fucoidan may inhibit a number of different G-protein coupled receptors associated with Ca²⁺ dynamics.

Characterization of cadmium transport in hepatopancreatic cells of a mangrove crab Ucides cordatus: The role of calcium

Cadmium is a toxic metal, present in batteries and discarded in estuaries and mangrove habitats. Apart from that, it is a non-essential metal that causes toxic effects in many organisms. Cadmium accumulates in gills and hepatopancreas of crustaceans and its route into the cell is unknown. It is possible that occurs by calcium channels or calcium transporters. The objective of this study was to characterize the transport of cadmium and the role of calcium in different cell types from hepatopancreas of the mangrove crab Ucides cordatus. For this, the hepatopancreas was dissociated by magnetic stirring and after that separated by a sucrose gradient. Then, the cells were labeled with FluoZin-3 AM and different CdCl₂ concentrations were added together with a variety of inhibitors. The results showed that Cd²⁺ transport occurs differently in each cell type from hepatopancreas and is partially explained by the function the cells perform in this organ. Embryonic (E) and Resorptive (R) cells transported more Cd²⁺ compared to Fibrillar (F) and Blister (B) cells. R cells responded to Ca²⁺ channel inhibitors and intracellular Ca²⁺ manipulations positively, as the other cell types and in a stronger way. B cells were the least responsive to Ca²⁺ channel inhibitors and, unlike the other cells, showed a competition of Cd²⁺ with intracellular Ca²⁺ manipulations. The results indicate that Ca²⁺ affects the transport of Cd²⁺ in hepatopancreatic cells of Ucides cordatus and uses Ca²⁺ channels to enter these cells. In addition, information about Ca concentration could be used as a mitigating factor for Cd accumulation in crabs' hepatopancreas.

A Review of Diabetes Mellitus and Exposure to the Environmental Toxicant Cadmium with an Emphasis on Likely Mechanisms of Action

There is increasing interest in how exposure to environmental substances can contribute to the onset of Type II diabetes mellitus (T2DM). Impaired insulin release is a hallmark of type I diabetes mellitus and is involved in the progression of T2DM. Both epidemiological and experimental studies show that exposure to the environmental pollutant cadmium (Cd), is associated with hyperglycemia, T2DM and reduced serum insulin. The goal of this review is to examine likely mechanisms of action of Cd-induced dysglycemia based on experimental studies in the literature and from the most recent findings in the Edwards lab. The primary focus of this review will examine how Cd may cause islet dysfunction and subsequent impaired insulin release. Recent findings in the Edwards lab indicate that Cd causes timedependent and statistically significant changes in fasting leptin, Glucose-dependent Insulinotropic Polypeptide (GIP) and pancreas polypeptide hormone levels in a subchronic animal model of Cd-induced hyperglycemia. This review summarizes the most likely cellular mechanisms by which the ubiquitous environmental contaminant Cd disrupts glucose homeostasis. While individual cellular effects of Cd are reviewed it is likely that no one single mechanism is involved, rather multiple mechanisms exist and work synergistically resulting in islet dysfunction and ultimately dysglycemia.

Sublethal effects of cadmium on auditory structure and function in fathead minnows (Pimephales promelas)

Aquatic ecosystems are threatened by environmental contaminants, and many heavy metals can influence both the structure and function of sense organs in fishes. The use of these senses is vital to the survival and reproductive success of fish and therefore affects the health of the ecosystem as a whole. The current study examines the effects of cadmium on auditory structure and function in the fathead minnow (Pimephales promelas). In the laboratory, fish were exposed for 96 h to a range of cadmium concentrations and both hearing sensitivity and hair cell morphology were quantified. While hair cell numbers were unaffected, cadmium caused an increase in auditory threshold, with a critical range for toxic effects of cadmium estimated at 2.1-2.9 µg L(-1). Cadmium exposure also caused a decrease in response latency at higher cadmium concentrations. The current study demonstrates the sublethal effects of cadmium on fish sensory function while also pointing to the need for more careful interpretation of cadmium impacts on aquatic populations.

Characterization of cadmium plasma membrane transport in gills of a mangrove crab Ucides cordatus

Membrane pathway for intracellular cadmium (Cd(2+)) accumulation is not fully elucidated in many organisms and has not been studied in crab gill cells. To characterize membrane Cd(2+) transport of anterior and posterior gill cells of Ucides cordatus, a hypo-hyper-regulating crab, a change in intracellular Cd(2+) concentration under various experimental conditions was examined by using FluoZin, a fluorescent probe. The membrane Cd(2+) transport was estimated by the augmentation of FluoZin fluorescence induced by extracellular application of CdCl2 and different inhibitors. Addition of extracellular calcium (Ca(2+)) to the cells affected little the fluorescence of FluoZin, confirming that Cd(2+) was the main ion increasing intracellular fluorescence. Ca(2+) channels blockers (nimodipine and verapamil) decreased Cd(2+) influx as well as vanadate, a Ca(2+)-ATPase blocker. Chelating intracellular Ca(2+) (BAPTA) decreased Cd(2+) influx in gill cells, while increasing intracellular Ca(2+) (caffeine) augmented Cd influx. Cd(2+) and ATP added at different temporal conditions were not effective at increasing intracellular Cd(2+) accumulation. Ouabain (Na(+)/K(+)-ATPase inhibitor) increased Cd(2+) influx probably through a change in intracellular Na and/or a change in cell membrane potential. Routes of Cd(2+) influx, a non-essential metal, through the gill cell plasma membrane of crabs are suggested.

Interplay of calcium and cadmium in mediating cadmium toxicity

The environmentally important toxic metal, cadmium, exists as the Cd(2+) ion in biological systems, and in this state structurally resembles Ca(2+). Thus, although cadmium exerts a broad range of adverse actions on cells by virtue of its propensity to bind to protein thiol groups, it is now well appreciated that Cd(2+) participates in a number of Ca(2+)-dependent pathways, attributable to its actions as a Ca(2+) mimetic, with a central role for calmodulin, and the Ca(2+)/calmodlin-dependent protein kinase II (CaMK-II) that mediates effects on cytoskeletal dynamics and apoptotic cell death. Cadmium interacts with receptors and ion channels on the cell surface, and with the intracellular estrogen receptor where it binds competitively to residues shared by Ca(2+). It increases cytosolic [Ca(2+)] through several mechanisms, but also decreases transcript levels of some Ca(2+)-transporter genes. It initiates mitochondrial apoptotic pathways, and activates calpains, contributing to mitochondria-independent apoptosis. However, the recent discovery of the role CaMK-II plays in Cd(2+)-induced cell death, and subsequent implication of CaMK-II in Cd(2+)-dependent alterations of cytoskeletal dynamics, has opened a new area of mechanistic cadmium toxicology that is a focus of this review. Calmodulin is necessary for induction of apoptosis by several agents, yet induction of apoptosis by Cd(2+) is prevented by CaMK-II block, and Ca(2+)-dependent phosphorylation of CaMK-II has been linked to increased Cd(2+)-dependent apoptosis. Calmodulin antagonism suppresses Cd(2+)-induced phosphorylation of Erk1/2 and the Akt survival pathway. The involvement of CaMK-II in the effects of Cd(2+) on cell morphology, and particularly the actin cytoskeleton, is profound, favouring actin depolymerization, disrupting focal adhesions, and directing phosphorylated FAK into a cellular membrane. CaMK-II is also implicated in effects of Cd(2+) on microtubules and cadherin junctions. A key question for future cadmium research is whether cytoskeletal disruption leads to apoptosis, or rather if apoptosis initiates cytoskeletal disruption in the context of Cd(2+).

Role of calcium channels in heavy metal toxicity

The role of voltage-dependent Ca channels (VDCC) in the membrane permeation of two toxic metals, lead (Pb) and cadmium (Cd), was studied in mammalian cells. Both metals interact with Ca-binding sites, but, while Cd influx appears to occur mainly through the same pathways as Ca, Pb is also rapidly taken up by different passive transport systems. Furthermore, I compared the effect of Cd in two Chinese hamster ovary (CHO) cell lines, a wild-type and a modified cell line, which were permanently transfected with an L-type VDCC. When cultures were subjected to a brief (30–60 min) exposure to 50–100 μM Cd, apoptotic features, metal accumulation, and death were comparable in both cell lines although, in transfected cells, the effect of Cd treatment was partially prevented by nimodipine (VDCC antagonist) and enhanced by BayK8644 (VDCC agonist). Thus, expression of L-type Ca channels is not sufficient to modify Cd accumulation and sensitivity to a toxicological significant extent and while both Cd and Pb can take advantage of VDCC to permeate the membrane, these transport proteins are not the only, and frequently not the most important, pathways of permeation.

Cadmium and selenium modulate slow vacuolar channels in rape (Brassica napus) vacuoles

Currents flowing through slow vacuolar SV channels of rape (Brassica napus) growing on media supplemented with Cd²+ (400 μM), and/or SeO₄(²⁻) (2μM) were examined. The aim of the study was to investigate the role of Cd²+ in modulation of SV channel activity and to determine whether Se reverses the effect of cadmium. Vacuoles were isolated using a quick surgical method to avoid application of any cell wall-degrading enzymes. Vacuoles of rape exhibited typical SV channel activity with slow activation at positive potentials and strong rectification into the vacuolar lumen. Single-channel conductance in cytoplasm-side-out tonoplast patches ranged between 68.8±1.9 pS in the control, 80.1±2.5pS, in Cd²+, 74.2±2.4 pS in Cd²+/selenate, and 80.1±1.8 pS in selenate-pretreated plants. The lack of a clear tendency was likely an effect of equilibration of the pipette solution (without Cd²+/SeO₄(²⁻) with that of the luminal side of the vesicles. In the vacuole-attached configuration, in which natural vacuolar solution was not exchanged, there was a significant reduction in single-channel conductance in the Cd²+ (40.3±2.8 pS), Cd²+/selenate (47.1±2.8 pS) and selenate-pretreated (42.3±1.4 pS) plants, compared to the control (60.2±1.7 pS). The reduction in single-channel conductance only partially explained the significant decline in the densities of ion current flowing through the vacuolar membrane in the whole-vacuole configuration in the plants growing on Cd²+ and Cd²+/selenate media. Thus, Cd²+ accumulation in the vacuole reduced the number of active SV channels from 0.28±0.05 μm⁻² in the control to 0.021±0.005 and 0.039±0.004 μm⁻² in Cd²+ and Cd²+/selenate-pretreated plants, respectively.

Different membrane modifications revealed by atomic force/lateral force microscopy after doping of human pancreatic cells with Cd, Zn, or Pb

The interaction of the cytotoxic metals cadmium, zinc, and lead with pancreatic cells was studied by atomic force/lateral Force microscopy (AFM/LFM), an approach that provides both topographic (with nanometer scale lateral resolution) and chemical information on the membrane. Different morphological modifications of the overall cell shape and roughness took place as consequence of 100 muM metal-dependent treatment. Furthermore, after exposure to Cd(Cl(2)) and Zn(Cl(2)), but not Pb(Cl(2)), the LFM images revealed several areas of the cell's surface showing lateral friction contrasts that have been interpreted as marker of different alterations of the cell physiology induced by the metal loading. Thus, the coupling of LFM detection to topographic AFM characterization allows to distinguish, through a nondestructive and surface characterising approach, between different metal-induced cytotoxic effects on cells. In this framework, the role of the LFM as an important tool to discriminate between different alteration of a biological system has to be highlighted.

Cadmium toxicity in animal cells by interference with essential metals

Cadmium is found in the environment as part of several, mainly zinc-rich, ores. It has been used in many technological applications, but biological systems generally failed to safely deal with this element. In mammalian biology, cadmium exposure jeopardizes health and mechanisms of cadmium toxicity are multifarious. Mainly because bioavailable cadmium mimics other metals that are essential to diverse biological functions, cadmium follows a Trojan horse strategy to get assimilated. Metals susceptible to cadmium deceit include calcium, zinc, and iron. The wealth of data addressing cadmium toxicity in animal cells is briefly reviewed with special emphasis on disturbance of the homeostasis of calcium, zinc, and iron. A limited number of tissues and cell types are considered as main targets for cadmium toxicity. Still, the diversity of pathways affected by cadmium exposure points to a more general threat to basic cellular functions. The poor efficiency of cellular export systems for cadmium explains the long residence time of the element in mammals. Therefore, proper disposal and educated uses of this technologically appealing, but biologically malicious, element should be favored in the future. The comprehensive knowledge of cadmium biological effects is indeed a necessary step to protect human and animal populations from environmental and anthropological exposures.

Zinc influx and physiological consequences in the beta-insulinoma cell line, Min6

In the mammalian pancreas, high concentrations of Zn(2+) are co-secreted with insulin, which may then permeate via abundant L-type Ca(2+) channels (LTCC) present on the beta-cells. Neither the mechanisms utilized by these cells to lower cytosolic Zn(2+) nor the implications of increased intracellular Zn(2+) on beta-cell survival are well understood. To address this, we employed cell imaging of Zn(2+) and Ca(2+) in the beta-insulinoma cell line, Min6. Depolarization induced an intense zinc influx that was blocked by nifedipine and verapamil, indicating that Zn(2+) permeates via the LTCC. Both Ca(2+) and Zn(2+) permeated concomitantly, yet while Ca(2+) was subsequently removed from the cytosol, Zn(2+) was retained in the cells. Fluorescent staining of vesicular Zn(2+) using ZP1 demonstrated that Zn(2+) could be slowly sequestered following a brief exposure to low concentration of Zn(2+). In contrast, cells were unable to sequester Zn(2+) following application of high concentrations, which was followed by massive cell death. Our results demonstrate homeostatic crosstalk between the plasma membrane and intracellular zinc transporters and suggest that attenuating zinc influx may enhance beta-cell survival.