Passive transport and binding of lead by human red blood cells

Surface functionalization of hydroxyapatite nanoparticles for biomedical applications

This review completely covers the various aspects of hydroxyapatite (HAp) nanoparticles and their role in different biological situations, and provides the surface and interface contents on (i) hydroxyapatite nanoparticles and their hybridization with organic molecules, (ii) surface designing of hydroxyapatite nanoparticles to provide their biocompatibility and photofunction, and (iii) coating technology of hydroxyapatite nanoparticles. In particular, we summarized how the HAp nanoparticles interact with the different ions and molecules and highlighted the potential for hybridization between HAp nanoparticles and organic molecules, which is driven by the interactions of the HAp nanoparticle surface ions with several functional groups of biological molecules. In addition, we highlighted the studies focusing on the interfacial interactions between the HAp nanoparticles and proteins for exploring the enhanced biocompatibility. Such studies focus on how these interactions affect the hydration layers and protein adsorption. However, the hydration layer state involves diverse molecular interactions that can alter the shape of the adsorbed proteins, thereby affecting cell adhesion and spreading on the surfaces. We also summarized the relationship between the surface properties of the HAp nanoparticles and the hydration layer. Furthermore, we spotlighted the cytocompatible photoluminescent probes that can be developed by designing HAp/organic nanohybrid structures. We then emphasized the importance of photofunctionalization in theranostics, which involves the integration of diagnostics and therapy based on the surface design of the HAp nanoparticles. Furthermore, the coating techniques using HAp nanoparticles and HAp nanoparticle/polymer composites were outlined for fusing base biomaterials with biological tissues. The advantages of HAp/biocompatible polymer composite coatings include the ability to effectively cover porous or irregularly shaped surfaces while controlling the thickness of the coating layer, and the addition of HAp nanoparticles to the polymer matrix improves the mechanical properties, increases the roughness, and forms the morphologies that mimic bone nanostructures. Therefore, the fundamental design of hydroxyapatite nanoparticles and their surfaces was suggested from various aspects for biomedical applications.

Plasma Thallium Concentration, Kidney Function, Nephrotoxicity and Graft Failure in Kidney Transplant Recipients

The nephrotoxic effects of heavy metals have gained increasing scientific attention in the past years. Recent studies suggest that heavy metals, including cadmium, lead, and arsenic, are detrimental to kidney transplant recipients (KTR) even at circulating concentrations within the normal range, posing an increased risk for graft failure. Thallium is another highly toxic heavy metal, yet the potential consequences of the circulating thallium concentrations in KTR are unclear. We measured plasma thallium concentrations in 672 stable KTR enrolled in the prospective TransplantLines Food and Nutrition Biobank and Cohort Study using inductively coupled plasma mass spectrometry. In cross-sectional analyses, plasma thallium concentrations were positively associated with kidney function measures and hemoglobin. We observed no associations of thallium concentration with proteinuria or markers of tubular damage. In prospective analyses, we observed no association of plasma thallium with graft failure and mortality during a median follow-up of 5.4 [interquartile range: 4.8 to 6.1] years. In conclusion, in contrast with other heavy metals such as lead, cadmium, and arsenic, there is no evidence of tubular damage or thallium nephrotoxicity for the range of circulating thallium concentrations observed in this study. This is further evidenced by the absence of associations of plasma thallium with graft failure and mortality in KTR.

The impacts of different anticoagulants and long-term frozen storage on multiple metal concentrations in peripheral blood: a comparative study

It is important but remains unclear whether ethylenediaminetetraacetic acid (EDTA) and sodium heparin anticoagulants have different impacts on the levels of various metals in peripheral blood after long-term frozen storage. The concentrations of 22 metals (Al, As, Ba, Ca, Cd, Cr, Co, Cu, Mn, Mg, Mo, Ni, Fe, Pb, Rb, Se, Sn, Sb, Sr, Ti, V, Zn) in whole blood, blood cells and plasma from 22 healthy participants were determined twice, 18 months apart, using inductively coupled plasma mass spectrometry (ICP-MS). The mean percentage error (MPE) and intraclass correlation coefficient (ICC) were calculated to evaluate the impact of the anticoagulants and long-term frozen storage on metal concentrations, respectively. The concentrations of Sb and Ba in whole blood, blood cells and plasma were significantly altered by EDTA and sodium heparin at two measurement timepoints (P < 0.05 and MPE > 80%). In EDTA tubes, the Ti and Ni concentrations in blood cells were changed significantly; and in heparin tubes, the concentrations of Ni and Mo in blood cells and Sb in plasma were also altered (P < 0.05 and MPE > 80%). The ICCs of 11 metals in whole blood, 15 metals in blood cells and 16 metals in plasma remained unchanged in EDTA tubes, and 16 metals in whole blood, 15 metals in blood cells and 17 metals in plasma remained unchanged in heparin tubes (ICC > 0.40). Our study suggested the use of EDTA tubes to determine Sb concentrations in peripheral blood and heparin tubes to determine Ba concentrations. Additionally, heparin tubes may be more suited for determining multiple metal concentrations in whole blood, whereas for blood cells and plasma either EDTA or heparin tubes could be used.

The Effects of Calcium, Magnesium, Phosphorus, Fluoride, and Lead on Bone Tissue

Bones are metabolically active organs. Their reconstruction is crucial for the proper functioning of the skeletal system during bone growth and remodeling, fracture healing, and maintaining calcium-phosphorus homeostasis. The bone metabolism and tissue properties are influenced by trace elements that may act either indirectly through the regulation of macromineral metabolism, or directly by affecting osteoblast and osteoclast proliferation or activity, or through becoming part of the bone mineral matrix. This study analyzes the skeletal impact of macroelements (calcium, magnesium, phosphorus), microelements (fluorine), and heavy metals (lead), and discusses the concentration of each of these elements in the various bone tissues.

Effects of lead exposure on salivary glands of rats: insights into the oxidative biochemistry and glandular morphology

This study aimed to investigate the effects of lead (Pb) exposure on parotid and submandibular glands through morphological aspects as well as the systemic and salivary gland redox state. Male Wistar rats were exposed to 50 mg/kg/day of Pb-acetate or distilled water by intragastric gavage for 55 days (n = 40). Blood samples were used for lipid peroxidation (LPO), glutathione (GSH), and trolox equivalent antioxidant capacity (TEAC) assays. Samples of salivary glands were analyzed by LPO, nitrites (NO), and antioxidant capacity against peroxyl radicals (ACAP) levels. Morphometric analyses (total stromal area [TSA], total parenchyma area [TPA], total ductal area [TDA], and total acinar area [TAA]) and immunohistochemistry for cytokeratin-19 (CK-19), metallothionein I/II (MT I/II), and anti-smooth muscle actin (α-SMA) were performed. The results revealed that exposure to Pb triggered systemic oxidative stress represented by lower GSH levels and increased TBARS/TEAC ratio in blood plasma. ACAP was reduced, while NO and LPO were increased in both parotid and submandibular. The morphological analyses showed increase on MT I/II expression, reduced CK-19 expression in both glands, and α-SMA reduced the immunostaining only in the parotid glands. The morphometric analyses revealed an increase in TPA in both glands, while TAA was reduced only in submandibular glands and TDA was increased only in parotid glands. Our findings are pioneer in showing that long-term exposure to Pb is able to promote blood and glandular oxidative stress associated with cellular, morphological, and biochemical damage in both parotid and submandibular glands.

Lead (Pb) Accumulation in Human THP-1 Monocytes/Macrophages In Vitro and the Influence on Cell Apoptosis

In this study, we investigated the ability of THP-1 monocytes and macrophages to accumulate lead (Pb) in vitro, relative to Pb concentration and length of exposure. Moreover, we also evaluated the effect of Pb accumulation on cell viability and apoptosis. THP-1 monocytes and macrophages were cultured in the presence of Pb at 1.25 μg/dL, 2.5 μg/dL, 5 μg/dL, and 10 μg/dL. Pb accumulation was examined by inductively coupled plasma and confocal microscopy. The influence of Pb on cell viability, apoptosis, and necrosis was assessed using flow cytometry. The results showed that Pb was toxic to THP-1 monocytes/macrophages even at very low environmental concentrations. Despite the use of low concentrations, both monocytes and macrophages showed dose-dependent and time-dependent decreases in viability, with a simultaneous increase in the percentage of early and late apoptotic cells. Macrophages reacted more strongly to Pb than monocytes. When exposed to the same Pb concentrations, they showed lower viability and a higher percentage of necrotic cells. The incubation time positively correlated with Pb accumulation in a dose-dependent manner. The obtained results indicate that environmental exposure to low Pb concentrations may significantly impair the function of macrophages, with the increased number of apoptotic cells potentially contributing to the development of many pathologies in the brain and whole body.

Effect of Physico-Chemical Properties of Nanoparticles on Their Intracellular Uptake

Cellular internalization of inorganic, lipidic and polymeric nanoparticles is of great significance in the quest to develop effective formulations for the treatment of high morbidity rate diseases. Understanding nanoparticle–cell interactions plays a key role in therapeutic interventions, and it continues to be a topic of great interest to both chemists and biologists. The mechanistic evaluation of cellular uptake is quite complex and is continuously being aided by the design of nanocarriers with desired physico-chemical properties. The progress in biomedicine, including enhancing the rate of uptake by the cells, is being made through the development of structure–property relationships in nanoparticles. We summarize here investigations related to transport pathways through active and passive mechanisms, and the role played by physico-chemical properties of nanoparticles, including size, geometry or shape, core-corona structure, surface chemistry, ligand binding and mechanical effects, in influencing intracellular delivery. It is becoming clear that designing nanoparticles with specific surface composition, and engineered physical and mechanical characteristics, can facilitate their internalization more efficiently into the targeted cells, as well as enhance the rate of cellular uptake.

Treatment with Lead Chloride During Pregnancy and the Postnatal Period Alters Cell Proliferation and Immune Function in Swiss Albino Mice

In the current study, we investigated the effect of lead chloride (PbCl₂) administration (50 and 100 ppm) on organ and body weight as well as its bioaccumulation during pregnancy and the postnatal period in mice. We showed that lead has no effect on the body weight of mice. However, spleen weight is affected by the two doses of PbCl₂ while liver and kidney weights are altered only by the 100-ppm dose. Inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis showed that lead accumulates in the blood, spleen, and thymus. Both doses of PbCl₂ significantly reduced splenocyte and thymocyte cell counts after stimulation with lipopolysaccharide (LPS) and phytohemagglutinin A (PHA), respectively. On the other hand, we showed that the levels of Th1 cytokines (interleukin-2 (IL-2), interferon gamma (IFN-γ)), and tumor necrosis factor alpha (TNF-α) were reduced in the serum of mice treated with PbCl₂ in a dose-dependent manner, as measured by ELISA. The levels of interleukin-4 (IL-4) and interleukin-10 (IL-10) were very low in untreated mice and were also reduced by treatment with PbCl₂. The levels of IL-2, IFN-γ, IL-4, IL-10, and TNF-α secretion differentially decreased in LPS-stimulated splenocytes in lead-treated mice. Using PHA-stimulated thymocytes, we observed a reduction in the levels of IL-2, IL-4, IL-10, and TNF-α in the PbCl₂-treated groups. However, IFN-γ concentration in the supernatant of these cells was not decreased when mice were treated with 50 ppm of lead.

Angiogenesis and lead (Pb): is there a connection?

Lead (Pb) is a toxic heavy metal ubiquitously distributed around the world, especially in industrial areas. Occupational and environmental exposures to Pb have detrimental effects on human health. Pb affects functioning of many systems of the human body, including the cardiovascular system. Angiogenesis, the process of new blood vessel formation, which makes critical contribution throughout life is deranged in various diseases. Excessive angiogenesis may result in different diseases including cancer. On the other spectrum, insufficient angiogenesis is observed in many diseases, such as atherosclerosis, hypertension, and cardiovascular disease. These disorders are also associated with occupational Pb exposure. In this paper, epidemiological and experimental studies are reviewed selectively for evidence in support of this hypothesis, that is, interactions between Pb and angiogenesis. We discuss the evidence for the possible mechanism of Pb impact on concentrations of angiogenic factors. Studies suggested that Pb exposure affects the level of angiogenic factors associated with angiogenesis regulation and promotion. Further research is needed, especially in the mechanisms in which Pb-induced vascular endothelial growth factor (VEGF) disregulation is present. We believe that characterizing the connection between Pb and angiogenesis will provide helpful information for the development of intervention strategies to reduce the adverse effects of Pb exposure.

Chronic lead (Pb) exposure results in diminished hemocyte count and increased susceptibility to bacterial infection in Drosophila melanogaster

Heavy metal Pb is a common toxic pollutant present in our environment adversely affecting health of the living organisms. Recent studies suggest positive correlation between heavy metal exposure and immune dysfunction and present work utilizes Drosophila to address this issue in relation to Pb exposure. In-vivo Pb toxicity was established by dietary intake where essential parameters like development and life span were found to be hampered and augmented upon metallothionein B (mtnB) downregulation hinting towards potential role of mtnB in Pb detoxification. Further response of Drosophila to B. subtilis bacterial infection was monitored by carrying out oral infections. Pb fed flies showed increased susceptibility to infection as compared to their controls. Since Drosophila hemocytes play dual role as immune cells, we checked for the total hemocyte count and found significant decrease in hemocyte numbers in Pb fed larvae. Both crystal cells and plasmatocytes, the two major hemocytes in third instar larval hemolymph were reduced. However we did not find any visible morphological changes in Giemsa stained hemocytes. Crystal cells are crucial for synthesis and release of phenoloxidase (PO), an enzyme required for melanin clot synthesis and deposition. PO activity assessed from total hemolymph protein isolates was found to be substantially decreased in Pb raised animals. Results were also confirmed by spot test and native gel activity assay of PO. Overall our results suggest immunotoxic effect of Pb through decrease in hemocyte count including crystal cell which in turn leads to decreased PO activity and increased susceptibility to B. subtilis.

Bioaccumulation and morphological traits in a multi-generation test with two Daphnia species exposed to lead

Anthropic pressure negatively affects natural environments. Lead (Pb) is a non-essential highly toxic metal that is present in aquatic ecosystems. Two daphnid species from two different latitudes, the temperate Daphnia magna and the tropical Daphnia similis were used as test-organisms to evaluate a long-term Pb exposure. Both species were exposed for nine generations to a chronic concentration of Pb (50 μg/L) and the effects were explored, considering some endpoints not commonly used in toxicity tests: body burden of Pb and presence of granules in the dorsal region of neonates, hemoglobin contents, carapace deformation and morphology, production of males and ephippia (or dormant haploid egg), changes in the eggs' colour and eggs abortion. This multi-generation test was conducted under two food regimes, the usual (3 × 10⁵ cells/mL) and the restricted (1.5 × 10⁵ cells/mL) regime. On generation F6, Pb acclimated neonates were changed to a clean media for three generations, to evaluate exposure retrieval (recovery period). Negative and adverse effects occurred through generations, but no disparity was shown between D. magna and D. similis. The D. magna Pb accumulation showed different patterns regarding food regime. Bioaccumulation was faster under usual food, rapidly reaching a saturation point, whereas a gradual increase occurred under food restriction. A successful retrieval happened regarding Pb in D. magna, since no difference between control and recovering organisms was evidenced regarding their Pb body burdens. Generational Pb exposure led to carapace malformations, Pb aggregation in neonates' dorsal region, reddish extremities, production of males, ephippia (or dormant haploid egg), and aborted eggs, and changes in the eggs' colour (green and white). Food restriction also induced the production of males. Reddish extremities disappeared in recovering organisms and ephippia (or dormant haploid egg) did not occurred during the recovery period. Existent males revealed a shorter lifespan than females (under stress). D. magna and D. similis presented similar responses, for the endpoints analysed; however, it does not mean that this lack of sensitivity difference will be observed when other endpoints (e.g. survival, reproduction) are considered. Bioaccumulation of Pb and adverse effects occurred at the tested concentration of 50μg/L, although higher Pb levels are allowed in the environment as safe concentrations, as reported by the Brazilian legislation and the literature where effects are evidences above 400 μg/L of Pb. Pb effects on reproduction, respiration, malformation, and other adverse effects suggest that a chronic generational exposure can be harmful to both D. magna and D. similis, and that such chronic contaminated environments should not be disregarded when it comes to environmental monitoring.

Copper transporters and copper chaperones: roles in cardiovascular physiology and disease

Copper (Cu) is an essential micronutrient but excess Cu is potentially toxic. Its important propensity to cycle between two oxidation states accounts for its frequent presence as a cofactor in many physiological processes through Cu-containing enzymes, including mitochondrial energy production (via cytochrome c-oxidase), protection against oxidative stress (via superoxide dismutase), and extracellular matrix stability (via lysyl oxidase). Since free Cu is potentially toxic, the bioavailability of intracellular Cu is tightly controlled by Cu transporters and Cu chaperones. Recent evidence reveals that these Cu transport systems play an essential role in the physiological responses of cardiovascular cells, including cell growth, migration, angiogenesis and wound repair. In response to growth factors, cytokines, and hypoxia, their expression, subcellular localization, and function are tightly regulated. Cu transport systems and their regulators have also been linked to various cardiovascular pathophysiologies such as hypertension, inflammation, atherosclerosis, diabetes, cardiac hypertrophy, and cardiomyopathy. A greater appreciation of the central importance of Cu transporters and Cu chaperones in cell signaling and gene expression in cardiovascular biology offers the possibility of identifying new therapeutic targets for cardiovascular disease.

Matching target dose to target organ

In vitro assays have become a mainstay of modern approaches to toxicology with the promise of replacing or reducing the number of in vivo tests required to establish benchmark doses, as well as increasing mechanistic understanding. However, matching target dose to target organ is an often overlooked aspect of in vitro assays, and the calibration of in vitro exposure against in vivo benchmark doses is often ignored, inadvertently or otherwise.  An example of this was recently published in Environmental Health Perspectives by Wagner et al (2016), where neural stems cells were used to model the molecular toxicity of lead.  On closer examination of the in vitro work, the doses used in media reflected in vivo lead doses that would be at the highest end of lead toxicity, perhaps even lethal.  Here we discuss the doses used and suggest more realistic doses for future work with stem cells or other neuronal cell lines.

Matching target dose to target organ

In vitro assays have become a mainstay of modern approaches to toxicology with the promise of replacing or reducing the number of in vivo tests required to establish benchmark doses, as well as increasing mechanistic understanding. However, matching target dose to target organ is an often overlooked aspect of in vitro assays, and the calibration of in vitro exposure against in vivo benchmark doses is often ignored, inadvertently or otherwise.  An example of this was recently published in Environmental Health Perspectives by Wagner et al (2016), where neural stems cells were used to model the molecular toxicity of lead.  On closer examination of the in vitro work, the doses used in media reflected in vivo lead doses that would be at the highest end of lead toxicity, perhaps even lethal.  Here we discuss the doses used and suggest more realistic doses for future work with stem cells or other neuronal cell lines.

In vitro evaluation of cell death induced by cadmium, lead and their binary mixtures on erythrocytes of Common buzzard (Buteo buteo)

Cadmium and lead are persistent and ubiquitous metals that can cause several deleterious effects in living beings. Apoptosis and necrosis are two types of cell death that can be found after in vivo and in vitro exposure to these metals. In this study, isolated red blood cells from living captive Common buzzard (Buteo buteo) were exposed in vitro to different concentrations of lead, cadmium, and the mixture lead-cadmium in a proportion of 1:10 (similar to that found in previous field studies). Data obtained from dose-response curves were used to evaluate the interactive effects of metal mixtures on cell viability. In general, except for the exposure to NOEC, additivity was the most frequently observed response. As described in human, after in vitro exposure, lead was highly accumulated in buzzard erythrocytes, while cadmium accumulation was scarce. Finally, the type of cell death (apoptosis or necrosis) induced by the exposure to different concentrations of these heavy metals and their mixtures was evaluated in the red blood cells. Apoptosis was found to be the main type of cell death observed after cadmium and/or lead exposure. However, this exposure caused an increase in lysis or necrosis, especially if red blood cells were exposed to high doses.

Effects of lead chloride on human erythrocyte membranes and on kinetic anion sulphate and glutathione concentrations

Our study concerns the effects of exposure to lead chloride on the morphology, K⁺ efflux, SO₄⁻ influx and GSH levels of the human erythrocyte. Blood was collected in heparinized tubes and washed three times. The cells were suspended at 3% hematocrit and incubated for 1 h at 25°C in a medium containing increasing concentrations of lead chloride (0, 0.3, 0.5 and 1 μM). After incubation, the suspensions were centrifuged and the erythrocyte pellets were divided into three aliquots for testing. The results show: an increase in the permeability of erythrocytes treated with lead chloride with consequent damage and cellular death, especially in the presence of high concentrations; an increase in potassium ion efflux; alterations in the morphology and membrane structure of the red blood cells; and a decrease in sulphate uptake, due either to the oxidative effect of this compound on the band 3 protein, which loses its biological valence as a carrier of sulphate ions, or to a decrease in the ATP erythrocyte concentration. In conclusion, the exposure of erythrocytes to Pb²⁺ ions leads to a reduction in the average lifetime of the erythrocytes and the subsequent development of anemia. These data are discussed in terms of the possible effect of lead on the reduction-oxidation systems of the cell. Oxidant agents, such as lead, are known to cross-link integral membrane proteins, leading to K/Cl-cotransport. The increased K⁺ efflux affects the altered redox state.

Acquisition of dietary copper: a role for anion transporters in intestinal apical copper uptake

Copper is an essential micronutrient in humans and is required for a wide range of physiological processes, including neurotransmitter biosynthesis, oxidative metabolism, protection against reactive oxygen species, and angiogenesis. The first step in the acquisition of dietary copper is absorption from the intestinal lumen. The major human high-affinity copper uptake protein, human copper transporter hCTR1, was recently shown to be at the basolateral or blood side of both intestinal and renal epithelial cell lines and thus does not play a direct role in this initial step. We sought to functionally identify the major transport pathways available for the absorption of dietary copper across the apical intestinal membrane using Caco2 cells, a well-established model for human enterocytes. The initial rate of apical copper uptake into confluent monolayers of Caco2 cells is greatly elevated if amino acids and serum proteins are removed from the growth media. Uptake from buffered saline solutions at neutral pH (but not at lower pH) is inhibited by either d- or l-histidine, unaltered by the removal of sodium ions, and inhibited by ∼90% when chloride ions are replaced by gluconate or sulfate. Chloride-dependent copper uptake occurs with Cu(II) or Cu(I), although Cu(I) uptake is not inhibited by histidine, nor by silver ions. A well-characterized inhibitor of anion exchange systems, DIDS, inhibited apical copper uptake by 60-70%, while the addition of Mn(II) or Fe(II), competitive substrates for the divalent metal transporter DMT1, had no effect on copper uptake. We propose that anion exchangers play an unexpected role in copper absorption, utilizing copper-chloride complexes as pseudo-substrates. This pathway is also observed in mouse embryonic fibroblasts, human embryonic kidney cells, and Cos-7 cells. The special environment of low pH, low concentration of protein, and protonation of amino acids in the early intestinal lumen make this pathway especially important in dietary copper acquisition.

Stimulation of erythrocyte phosphatidylserine exposure by lead ions

Pb+ intoxication causes anemia that is partially due to a decreased life span of circulating erythrocytes. As shown recently, a Ca(2+)-sensitive erythrocyte scramblase is activated by osmotic shock, oxidative stress, and/or energy depletion, leading to exposure of phosphatidylserine at the erythrocyte surface. Because macrophages are equipped with phosphatidylserine receptors, they bind, engulf, and degrade phosphatidylserine-exposing cells. The present experiments were performed to explore whether Pb+ ions trigger phosphatidylserine exposure of erythrocytes. The phosphatidylserine exposure was estimated on the basis of annexin binding as determined using fluorescence-activated cell sorting (FACS) analysis. Exposure to Pb+ ions [> or =0.1 microM Pb(NO3)2] significantly increased annexin binding. This effect was paralleled by erythrocyte shrinkage, which was apparent on the basis of the decrease in forward scatter in FACS analysis. The effect of Pb+ ions on cell volume was virtually abolished, and the effect of Pb+ ions on annexin binding was blunted after increase of extracellular K+ concentration. Moreover, both effects of Pb+ ions were partially prevented in the presence of clotrimazole (10 microM), an inhibitor of the Ca(2+)-sensitive K+ channels in the erythrocyte cell membrane. Whole cell patch-clamp experiments disclosed a significant activation of a K(+)-selective conductance after Pb+ ion exposure, an effect requiring higher (10 microM) concentrations, however. In conclusion, Pb+ ions activate erythrocyte K+ channels, leading to erythrocyte shrinkage, and also activate the erythrocyte scramblase, leading to phosphatidylserine exposure. The effect could well contribute to the reported decreased life span of circulating erythrocytes during Pb+ intoxication.

The Gárdos channel: a review of the Ca2+-activated K+ channel in human erythrocytes

Ca(2+)-dependent K(+) efflux from human erythrocytes was first described in the 1950s. Subsequent studies revealed that a K(+)-specific membrane protein (the Gárdos channel) was responsible for this phenomenon (the Gárdos effect). In recent years several types of Ca-activated K(+) channel have been identified and studied in a wide range of cells, with the erythrocyte Gárdos channel serving as both a model for a broader physiological perspective, and an intriguing component of erythrocyte function. The existence of this channel has raised a number of questions. For example, what is its role in the establishment and maintenance of ionic distribution across the red cell membrane? What role might it play in erythrocyte development? To what extent is it active in circulating erythrocytes? What are the cell-physiological implications of its dysfunction?This review summarises current knowledge of this membrane protein with respect to its function and structure, its physiological roles (some putative) and its contribution to various disease states, and it provides an introduction to adaptable NMR methods, which is our own area of technical expertise, for such ion transport analysis.

The effect of lead ions on the energy metabolism of human erythrocytes in vitro

The aim of this work was to evaluate the influence of chronic exposure to lead ions on the parameters of energetic status of human erythrocytes in vitro. Umbilical cord erythrocytes were incubated with lead acetate at final lead ion concentrations ranging from 10 to 200 microg/dl. ATP, ADP, AMP, adenosine, GTP, GDP, GMP, guanosine, IMP, inosine, hypoxanthine, NAD and NADP concentrations in erythrocytes were determined using HPLC. Scanning electron micrographs of erythrocytes were taken. The mean concentrations of ATP, GTP, NAD and NADP, and mean values of adenylate energy charge (AEC) and GEC in cells incubated at the presence of lead ions were significantly lower after 20 h of incubation. Concentrations of purine degradation products (Ado, Guo, Ino) and Hyp were significantly higher. It is suggested that lead ions affect the energy metabolism of erythrocytes. Morphological changes in erythrocytes correspond to the increase of lead ions in the incubation mixture and to the decrease of ATP concentration in erythrocytes. A decrease in NAD and ATP concentration in erythrocytes could be a sensitive indicator of energy process disturbance, useful in monitoring in case of chronic lead exposure.

Effect of DMT1 knockdown on iron, cadmium, and lead uptake in Caco-2 cells

DMT1 (divalent metal transporter 1) is a hydrogen-coupled divalent metal transporter with a substrate preference for iron, although the protein when expressed in frog oocytes transports a broad range of metals, including the toxic metals cadmium and lead. Wild-type Caco-2 cells displayed saturable transport of lead and iron that was stimulated by acid. Cadmium and manganese inhibited transport of iron, but zinc and lead did not. The involvement of DMT1 in the transport of toxic metals was examined by establishing clonal DMT1 knockdown and control Caco-2 cell lines. Knockdown cell lines displayed much lower levels of DMT1 mRNA and a smaller V(max) for iron uptake compared with control cell lines. One clone was further characterized and found to display an approximately 50% reduction in uptake of iron across a pH range from 5.5 to 7.4. Uptake for cadmium also decreased 50% across the same pH range, but uptake for lead did not. These results show that DMT1 is important in iron and cadmium transport in Caco-2 cells but that lead enters these cells through an independent hydrogen-driven mechanism.

The O'Flaherty model of lead kinetics: an evaluation using data from a lead smelter population

The O'Flaherty model of lead kinetics is a physiologically based computer model of lead disposition in humans. The model is based on an age-dependent approach to human growth, with particular attention devoted to bone metabolism. As such, model output is well suited for comparison with noninvasive bone lead measurements made via X-ray fluorescence. A subset of workers from a lead smelter population were selected for an initial evaluation of the O'Flaherty model. Detailed blood lead records were used to define input. Simulated bone lead and blood lead output were compared with observation, enabling a refinement of model parameters. A revised version of the O'Flaherty model was then evaluated for the smelter population as a whole. Previously observed trends for the accumulation of lead in cortical bone and the release of lead from bone stores were well explained by the revised model. Model predictions for the accumulation of lead in trabecular bone were not in accord with observed levels in the calcaneus. Model results from the smelter population are consistent with the hypothesis that a polymorphism in the delta-aminolevulinate dehydratase enzyme modifies the kinetics of lead in humans. Further refinements are suggested, which may enhance the ability of the model to explain the underlying relationships between lead exposure and the distribution of lead in the body.

Bone lead as a biological marker in epidemiologic studies of chronic toxicity: conceptual paradigms

The skeleton contains the majority of the body's lead burden in both children and adults. The half-life of lead in bone is in the range of years to decades, depending on bone type, metabolic state, and subject age, among other things. Measurement of skeletal lead has benefited greatly from the recent development of X-ray fluorescence (XRF) instruments that can make rapid, safe, accurate, and relatively precise measurements of lead in bone. Two types of XRF technologies exist, LXRF and KXRF; this paper focuses on KXRF, which has been the most widely validated and used. KXRF is proving to be a powerful analytical methodology for evaluating bone lead levels as a measure of time-integrated (i.e., cumulative) lead dose in epidemiologic studies of the effects of chronic lead exposure. However, insufficient attention has been given to conceptualizing the paradigms by which bone lead levels reflect lead exposure and by which the skeleton serves as an endogenous source of lead. Consideration of these paradigms, which rely on bone lead kinetics, is necessary for the proper development of a priori hypotheses involving bone lead accumulation and release, the selection of bone sites for measurement by KXRF, and the design of epidemiologic studies involving bone lead dynamics. We discuss and present supporting evidence for a conceptual model that distinguishes two major paradigms of skeletal lead, including 1) bone lead as an indicator of cumulative lead exposure (bone lead as repository), and 2) bone lead as a source of body lead burden that is mobilizable into the circulation (bone lead as source). These two roles are not mutually exclusive. Instead, they are components of the processes controlling lead accumulation into and release from bone over time. Developing successful strategies for distinguishing these two processes in epidemiologic studies will require separate measurements of lead in cortical and trabecular bone and additional measurement of specific markers of bone mineral turnover and resorption. It may also involve developing accurate methods for evaluating lead in labile compartments of the circulation, such as plasma, as a potentially useful and responsive measure of bone lead release, of the partitioning of circulatory lead, and of the toxicological significance of lead released from bone to other target organs.

Lead transport in IEC-6 intestinal epithelial cells

This study evaluated the use of IEC-6 cells as a model for studying lead (Pb) transport by intestinal epithelial cells (IECs) and examined potential transport mechanisms for Pb uptake and extrusion. Pb accumulation in IEC-6 cells exposed to 5 and 10 microM Pb for up to 60 min was time- and dose-dependent. Reduction of incubation temperature significantly reduced the total cellular Pb content of IEC-6 cells. Simultaneous exposed of cells to zinc (Zn) and Pb resulted in decreased total cellular Pb contents compared to total cellular Pb contents of cells exposed to Pb only. IEC-6 cells treated with ouabain (1 mM) or sodium azide (1 mM) and 5 microM Pb accumulated more Pb than cells exposed to Pb only. Cells treated with p-chloromercuribenzensulfonic acid (50 microM), p-chloromercuribenzoic acid (50 microM), or iodoacetimide (50 microM) accumulated less Pb than cells treated with Pb only. We conclude that Pb uptake by IEC-6 cells depends on the extracellular Pb concentration. Our data suggest that the mechanism of Pb uptake by IECs is complex, and that Pb transport in IEC-6 cells is time- and temperature-dependent, involves sulfhydryl groups, and is decreased by the presence of Zn. Extrusion of Pb is at least partially dependent on metabolic energy.

Role of anion exchange and thiol groups in the regulation of potassium efflux by lead in human erythrocytes

Pb2+ is thought to enter erythrocytes through anion exchange (AE) and to remain in the cell by binding to thiol groups. To define the role of AE mechanisms and thiol groups in Pb2+ toxicity, we studied the effects of drugs and conditions that modify AE and that modify thiol groups on the ability of Pb2+ to stimulate potassium efflux as measured with 86Rb. The most potent stimulation of 86Rb efflux by Pb2+ occurred when conditions were optimal for the AE mechanism--that is, when bicarbonate was included in the buffer or a buffer made with Nal or NaCl rather than NaClO4 or NaNO3 was used. Furthermore, 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid and 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfuonic acid, potent inhibitors of the AE mechanism, completely inhibited stimulation of the 86Rb efflux by Pb2+. These conditions or inhibitors did not affect stimulation of the 86Rb efflux by ionomycin plus Ca2+. A role for Ca2+ channels was dismissed because the inorganic Ca2+ channel blockers, Cd2+ or Mn2+, did not prevent stimulation of 86Rb efflux by Pb2+ but did inhibit stimulation by ionomycin plus Ca2+. 86Rb efflux was more sensitive to Pb2+ if erythrocytes were treated for 15 min with thiol-modifying reagents that enter cells, such as iodoacetamide, N-ethylmaleimide, or dithiothreitol, than to reduced glutathione, a thiol-modifying reagent that is not permeable to the cell. Thus, in erythrocytes the AE mechanism and internal thiol groups are critical factors that affect the stimulation of a Ca(2+)-dependent process by Pb2+.

Lead transport and binding by human erythrocytes in vitro

Transport and binding of Pb2+ by human erythrocytes were examined for cell Pb contents in the 1-10 microM range, using the 203Pb isotope. Pb2+ crosses the erythrocyte membrane by the anion exchanger, and can also leave erythrocytes by a vanadate-sensitive pathway, identified with the Ca2+ pump. However, Pb2+ exit is very much less than expected from earlier experiments with resealed erythrocyte ghosts [Simons TJB (1988) J Physiol (Lond) 405:105-113] and the distribution of Pb2+ across the erythrocyte membrane is close to equilibrium. The high ratio of erythrocyte to plasma Pb seen in vivo appears to be due to the presence of a labile Pb(2+)-binding component present in erythrocyte cytoplasm.

Mechanisms of cobalt(II) uptake into V79 Chinese hamster cells

V79 Chinese hamster cells were used as a model for the characterization of the Co(II) uptake into mammalian cells as well as the mechanisms involved. Co(II) was taken up in a dose and time dependent manner. The uptake was exponential without saturation in the tested concentration range up to 400 microM CoCl2. Furthermore, there was a high intracellular cobalt accumulation at elevated extracellular Co(II) doses (up to 16 fold at 200 microM). The time course of Co(II) uptake showed a maximum after about 8-12 h with no further change after the longest tested incubation time (24 h). The uptake of Co(II) into V79 cells seems to be mediated by multiple mechanisms: active, energy consuming transport like ion pumps and endocytosis, since the Co(II) uptake was significantly reduced by ouabain (an inhibitor of the Na+/K+ATPase), N-ethylmaleinimide (an inhibitor of the Ca2+/Mg2+ATPase and the Na+/K+ATPase), chlorpromazine (a calmodulin antagonist and inhibitor of the Ca2+/Mg2+ ATPase) as well as by the endocytosis inhibitor chloroquine. Furthermore, the two agents iodoacetate and potassium cyanide, which produce ATP depletion, resulted in a diminution of the intracellular cobalt concentration. An uptake through anion channels could be excluded, since 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid was not inhibitory.

Low level lead inhibits the human brain cation pump

The impact of low level lead exposure on human central nervous system function is a major public health concern. This study addresses the inhibition of the cation pump enzyme Na, K-ATPase by low level lead. Human brain tissue was obtained at autopsy and frozen until use. Brain homogenates were preincubated with PbCl2 for 20 min at 0 degrees C. Inhibition of K-paranitrophenylphosphatase (pNPPase), a measure of the dephosphorylation step of Na,K-ATPase, reached steady state within 10 min. K-pNPPase activity, expressed (mean +/- SEM) as a percentage of control (45.2 +/- 2.7 nmol/mg/min), fell to 96.3 +/- 0.9% at 0.25 uM [PbCl2] to 82.0 +/- 1.6% at 2.5 uM [PbCl2] in homogenates prepared from normal brain. Similar results were obtained with homogenates prepared from brains of patients with a history of alcohol abuse and of those with other miscellaneous conditions. Since the mean blood level of lead in the United States has ranged recently from 9.2 to 16.0 ug/dl (0.44 to 0.77 uM), these results indicate that current in vivo levels of lead exposure may impair important human brain function.

Transport of lead-203 at the blood-brain barrier during short cerebrovascular perfusion with saline in the rat

Lead transport at the blood-brain barrier has been studied by short (less than 1.5 min) vascular perfusion of one cerebral hemisphere of the rat with a buffered physiological salt solution at pH 7.4 without calcium, magnesium, or bicarbonate and containing 203 Pb-labelled lead chloride. In the absence of complexing agents, 203Pb uptake was rapid, giving a space of 9.7 ml/100 g of wet frontal cortex at 1 min. Lead-203 influx was linear with lead concentration up to 4 microM. Five percent albumin, 200 microM cysteine, or 1 mM EDTA almost abolished 203Pb uptake. Lead-203 entry into brain was uninfluenced by varying the calcium concentration or by magnesium or the calcium blocker methoxyverapamil. Similarly, 1 mM bicarbonate or 50 microM 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid was without effect. Increasing the potassium concentration reduced 203Pb uptake. Vanadate at 2 mM, 2 microM carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (a metabolic uncoupler), or 2 microM stannic chloride all markedly enhanced lead entry into brain, as did a more alkaline pH (7.80). In conclusion, there is a mechanism allowing rapid passive transport of 203Pb at the brain endothelium, perhaps as PbOH+. Lead uptake into brain via this system is probably made less important by active transport of lead back into the capillary lumen by the calcium-ATP-dependent pump.

Anionic mechanisms of zinc uptake across the human red cell membrane

1. Zinc is taken up into human red cells by two mechanisms that depend upon the presence of anions. One of these requires bicarbonate ions, is inhibited by 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) and appears to be catalysed by the anion exchanger. The second occurs in the presence of thiocyanate or salicylate ions and may represent transport of a neutral complex with Zn2+. 2. The initial rate of Zn2+ uptake via the anion exchanger is 64 +/- 13 mumol (10(13) cells x h)-1 microM-1 external Zn2+, in the presence of 5 mM-bicarbonate at pH 7.4 and 37 degrees C (+/- S.D.). This is about 1/250 of the corresponding rate of Pb2+ uptake by the anion exchanger. 3. The variation of transport with Zn2+ concentration, HCO3- concentration and pH suggests that the transported species may be ZnCO3Cl- or Zn(HCO3)Cl.OH-. 4. Zinc efflux could not be observed by either of the above routes. This observation suggests that the intracellular free Zn2+ concentration is below 3 nM.

Active transport of lead by the calcium pump in human red cell ghosts

1. Resealed human red cell ghosts containing lead buffers bring about a net transfer of lead from the cell interior to the outside. This transfer is ATP dependent. 2. The active transport of lead is characterized by a Vmax (maximum velocity) of 11 mmol/(l cells.h) and a KM (Michaelis constant) of 5 x 10(-8) M for internal Pb2+, at pH 6.8 and 37 degrees C. 3. Lead efflux is antagonized by internal calcium, and is inhibited by vanadate with the same IC50 (inhibition constant) with which vanadate inhibits calcium pumping. 4. It is concluded that lead is transported by the calcium pump.

Action of lead(II) and aluminium (III) ions on iron-stimulated lipid peroxidation in liposomes, erythrocytes and rat liver microsomal fractions

Lead (Pb2+) ions accelerate the lipid peroxidation observed when Fe2+ ions are added to phospholipid liposomes at pH 5.5 or pH 7.4, although Pb2+ ions alone do not induce any peroxidation. Similarly, aluminium (Al3+) ions increase Fe2+-dependent liposomal peroxidation at pH 5.5. Both Pb2+ and Al3+ accelerate the peroxidation of erythrocytes induced by high concentrations of H2O2 in the presence of azide, and they also increase the peroxidation that occurs when Fe2+ or Fe2+-ADP is added to rat liver microsomes at pH 7.4. It is proposed that increased lipid peroxidation may contribute to the toxic actions of Pb2+ in humans.

All or none cell responses of Ca2+-dependent K channels elicited by calcium or lead in human red cells can be explained by heterogeneity of agonist distribution

We have studied the all or none cell response of Ca2+-dependent K+ channels to added Ca in human red cells depleted of ATP by incubation with iodoacetate and inosine. A procedure was used which allows separation and differential analysis of responding and nonresponding cells. Responding (H for heavy) cells incubated in medium containing 5 mM K lose KCl and water and increase their density to the point of sinking on diethylphthalate (specific gravity = 1.12) on centrifugation. Nonresponding (L for light) cells do not lose KCl at all. There is no intermediate behavior. Increasing the Ca concentration in the medium increases the fraction of cells which become H. No differences in the sensitivity to Ca2+ of the individual K+ channels were detected in inside-out vesicles prepared either from H or from L cells. The Ca content of H cells was higher than that of L cells. Cells depleted of ATP by incubation with iodoacetate and inosine sustain pump-leak Ca fluxes of about 15 mumol/liter cells per hour. ATP seems to be resynthesized in these cells at the expense of cell 2,3-diphosphoglycerate stores at a rate of about 150 mumol/liter cells per hour. Inhibition of 2,3-diphosphoglycerate phosphatase by tetrathionate increased 6-8 times the measured rate of uptake of external 45Ca. This was accompanied by an increase in the fraction of H cells. All or none cell responses of Ca2+-dependent K channels have also been evidenced in intact human red cells on addition of Pb. They have the same characteristics as those in responding and nonresponding cells. The detailed study of the kinetics of Pb-induced shrinkage of red cells suspended in medium containing 5 mM K showed that changes of Pb concentration changed not only the fraction of H cells but also the rate of shrinkage of responding cells. H cells generated by Pb treatment contained significantly more lead than L cells. The above results suggest that the two all or none cell responses studied here can be explained by heterogeneity of agonist distribution among cells. Since pump-leak fluxes exist in both cases, differences of agonist distribution could be generated by heterogeneity of pumping among cells. This interpretation turns interest from K channels to Ca pumps to explain the heterogeneous behavior of red cells in response to a uniform stimulus.

Lead enters bovine adrenal medullary cells through calcium channels

Agents that stimulate secretion also accelerate the rate of Pb uptake into adrenal medullary cells. For example, when cells are suspended in a medium containing 5 microM Pb2+, depolarization by 77 mM K increases the rate of Pb uptake from 12 +/- 1 to 47 +/- 5 mumol/(L cells X min). K-induced Pb uptake has an apparent Km for Pb2+ of 2.6 microM, and is antagonized by Ca2+ with a K0.5 of 1.4 mM. The Ca channel blocker D-600 inhibits Pb entry with a K0.5 of 0.4 microM. Pb uptake is also stimulated by the Ca channel agonist BAY K 8644. These observations suggest that Pb passes through Ca channels. The permeability of the channels to Pb appears to be at least 10 times the permeability to Ca.

The role of anion transport in the passive movement of lead across the human red cell membrane

Passive Pb transport across the red cell membrane has been studied by measuring Pb uptake from Pb-buffered solutions into resealed ghosts containing EGTA. Over 90% of Pb uptake occurs by a pathway which is inhibited by drugs which block anion transport. The order of effectiveness is 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS) and 4-acetamido-4'-isothiocyanostilbene-2,2'-disulphonic acid (SITS) greater than phloretin greater than furosemide and bumetanide. Ouabain and cytochalasin B are ineffective. This implicates the anion-exchange mechanism in Pb uptake. The rate of Pb uptake by this route is directly proportional to external Pb2+ and HCO3- concentrations, and inversely proportional to the H+ concentration. These findings suggest that Pb transport depends on the formation of PbCO3 in solution. Pb transport depends upon the presence of a second anion. In the presence of HCO3-, the rate is stimulated in the order ClO4- less than NO3- and CH3CO2- less than F- less than Cl- less than Br- less than I-. The temperature dependence of Pb uptake is similar to that of HCO3-(-)Cl- exchange. Changes in membrane potential appear to influence Pb transport. The effects are small and somewhat variable, but in general a negative internal potential accelerates uptake and reduces exit. A positive internal potential reduces uptake and accelerates exit. These results suggest that Pb is transported on the anion exchanger. Exchange of PbCO3 for a monovalent anion best fits the experimental data, although transport of a ternary PbCO3(-)anion- complex is a possibility.