Stimulation of calmodulin by cadmium ion

Associations of serum lead, cadmium, and mercury concentrations with all-cause and cause-specific mortality among individuals with cardiometabolic multimorbidity

Epidemiological evidence indicates an association between exposure to toxic metals and the occurrence of cardiometabolic diseases (CMDs). However, the impact of exposure to harmful metallic elements, such as lead (Pb), cadmium (Cd), and mercury (Hg), on mortality in individuals with cardiometabolic multimorbidity (CMM) remains uncertain. Therefore, in this study, we analyzed data from 4139 adults diagnosed with CMM from the National Health and Nutrition Examination Survey 1999-2016. CMM was defined as the presence of at least two CMDs (hypertension, diabetes, stroke, and coronary artery disease). Over an average follow-up period of 9.0 years, 1379 deaths from all causes, 515 deaths related to cardiovascular disease (CVD), and 215 deaths attributable to cancer were recorded. After adjusting for potential covariates, serum Pb concentrations were not associated with all-cause, CVD, or cancer mortality. Participants exposed to Cd had an elevated risk of all-cause mortality (hazard ratio [HR], 1.23; 95 % CI, 1.16-1.30), CVD-related mortality (HR, 1.23; 95 % CI, 1.12-1.35), and cancer-related mortality (HR, 1.29; 95 % CI, 1.13-1.47). Participants with serum Hg levels in the highest quantile had lower risks of all-cause (HR, 0.64; 95 % CI, 0.52-0.80) and CVD-related (HR, 0.62; 95 % CI, 0.44-0.88) mortality than did those in the lowest quantile. Stratified analyses revealed significant interactions between serum Cd concentrations and age for CVD-related mortality (P for interaction =0.011), indicating that CMM participants aged < 60 years who were exposed to Cd were at a greater risk of CVD-related mortality. A nonlinear relationship was observed between serum Cd concentrations and all-cause (P for nonlinear relationship = 0.012) and CVD-related (P for nonlinear relationship < 0.001) mortality. Minimizing Cd exposure in patients with CMM may help prevent premature death.

Cadmium inhibits calcium activity in hippocampal CA1 neurons of freely moving mice

Cadmium (Cd) is a ubiquitous toxic heavy metal and a potential neurotoxicant due to its wide use in industrial manufacturing processes and commercial products, including fertilizers. The general population is exposed to Cd through food and smoking due to high transfer rates of Cd from contaminated soil. Cd has been shown to mimic calcium ions (Ca2+) and interfere with intracellular Ca2+ levels and Ca2+ signaling in in vitro studies. However, nothing is known about Cd's effects on Ca2+ activity in neurons in live animals. This study aimed to determine if Cd disrupts Ca2+ transients of neurons in CA1 region of the hippocampus during an associative learning paradigm. We utilized in vivo Ca2+ imaging in awake, freely moving C57BL/6 mice to measure Ca2+ activity in CA1 excitatory neurons expressing genetically encoded Ca2+ sensor GCaMP6 during an associative learning paradigm. We found that a smaller proportion of neurons are activated in Cd-treated groups compared with control during fear conditioning, suggesting that Cd may contribute to learning and memory deficit by reducing the activity of neurons. We observed these effects at Cd exposure levels that result in blood Cd levels comparable with the general U.S. population levels. This provides a possible molecular mechanism for Cd interference of learning and memory at exposure levels relevant to U.S. adults. To our knowledge, our study is the first to describe Cd effects on brain Ca2+ activity in vivo in freely behaving mice. This study provides evidence for impairment of neuronal calcium activity in hippocampal CA1 excitatory neurons in freely moving mice following cadmium exposure.

Toxic Effects of Cadmium on Fish

Large amounts of enriched cadmium (Cd) in the environment seriously threatens the healthy and sustainable development of the aquaculture industry and greatly restricts the development of the food processing industry. Studying the distribution and toxic effects of Cd in fish, as well as the possible toxic effects of Cd on the human body, is very significant. A large number of studies have shown that the accumulation and distribution of Cd in fish are biologically specific, cause tissue differences, and seriously damage the integrity of tissue structure and function, the antioxidant defense system, the reproductive regulation system, and the immune system. The physiological, biochemical, enzyme, molecular, and gene expression levels change with different concentrations and times of Cd exposure, and these changes are closely related to the target sites of Cd action and tissues in fish. Therefore, the toxic effects of Cd on fish occur with multiple tissues, systems, and levels.

Low-Level Cadmium Exposure and Atherosclerosis

PURPOSE OF REVIEW

Cadmium has been recognized as a potential risk factor for cardiovascular disease (CVD). We present a review of cadmium toxicity, its effect on cellular activities, and a summary of reported association between environmental cadmium exposure and CVD. We also discuss the possible therapeutic benefit of cadmium chelation.

RECENT FINDINGS

Experimental data suggest that cadmium affects several signaling pathways which may lead to endothelial dysfunction and vascular tissue damage, promoting atherosclerosis. This is further supported by epidemiological studies that have shown an association of even low-level cadmium exposure with an increased risk of clinical cardiovascular events. The Trial to Assess Chelation Therapy (TACT) provided inferential evidence for the cardiovascular benefit of treating toxic metal burden. However, at the present time, there is no direct evidence, but suggestive findings from clinical trials indicating that removal of cadmium from body stores may be associated with improved cardiovascular outcomes. An evolving body of evidence supports environmental cadmium exposure as a pro-atherosclerosis risk factor in CVD; however, the mechanisms for the proatherogenic effect of cadmium are still not completely understood. Further studies in translational toxicology are needed to fill the knowledge gaps regarding the molecular mechanisms of cadmium toxicity and the promotion of atherosclerosis.

Cadmium, nickel, copper, and zinc influence on microfilament organization in Arabidopsis root cells

The plant cytoskeleton orchestrates such fundamental processes in cells as division, growth and development, polymer cross-linking, membrane anchorage, etc. Here, we describe the influence of Cd²⁺ , Ni²⁺ , Zn²⁺ , and Cu²⁺ on root development and vital organization of actin filaments into different cells of Arabidopsis thaliana line expressing GFP-FABD2. CdSO₄ , NiSO₄ , CuSO₄ , and ZnSO₄ were used in concentrations of 5-20 µM in this study. It was found that Cd, Ni, and Cu cause dose-dependent primary root growth inhibition and alteration of the root morphology, whereas Zn slightly stimulates root growth and does not affect the morphology of Arabidopsis roots. This growth inhibition/stimulation correlated with the various sensitivities of microfilaments to Cd, Ni, Cu, and Zn action. It was established that Cd, Ni, and Cu affected predominantly the actin filaments of meristematic cells. Cells of transition and elongation zones demonstrated strong actin filament sensitivity to Cd and Cu. Microfilaments of elongating root cells were more sensitive to Ni and Cu. Although Cd, Ni, and Cu stimulated root hair growth after long-term treatment, actin filaments were destroyed after 1 h exposure with these metals. Zn did not disrupt native actin filament organization in root cells. Thus, our investigation shows that microfilaments act as sensitive cellular targets for Cd, Ni, and Cu. More data on effects on native actin filaments organization would contribute to a better understanding of plant tolerance mechanisms to the action of these metals.

Studies on Mechanisms of the Toxic Effects of Cadmium in Mouse Tracheal Organ Culture

Exposure of tracheal organ cultures to 10μM cadmium acetate resulted in a reduction of ciliary activity by 89% and a profound swelling of the epithelial cells within 4 hours. Substances with specific effects on ion transport systems did not interact with these cadmium induced effects. The swelling took place without any significant alterations of the intracellular electrolyte content (Na+, K+). Trifluoperazine (0.1mM), a calmodulin-specific drug, resulted in a reduction of ciliary activity similar to that induced by 10μM cadmium acetate, and induced a prominent swelling in part of the epithelial cell layer. A possible mechanism for the toxicity of cadmium could thus be binding of Cd2+ to the Ca2+ sites on calmodulin, causing dysfunctions of its normal regulatory role in both ciliary activity and volume control.

Female oxidative status in relation to calcium availability, metal pollution and offspring development in a wild passerine

Both Ca deficiency and metal exposure may affect physiological and nutritional condition of breeding females altering their ability to deposit essential resources (e.g. Ca, antioxidants) into the eggs. This effect of the maternal investment into egg quality is not strictly limited to the embryonic period, but may persist after hatching, since nutrient levels in yolks can compromise nestling antioxidant status, growth and fledging success. The goal of this study was to investigate how metal pollution and Ca availability during the breeding season affect oxidative stress biomarkers and plasma biochemistry in adult female pied flycatchers (Ficedula hypoleuca). In addition, we aim to evaluate how maternal antioxidant status and body condition relate to breeding parameters and offspring oxidative balance. Females breeding in a metal-polluted area in SW Finland showed higher metal concentrations compared to the control area, although current levels were below the toxic level able to affect female physiology. In addition, Ca availability was not constraining female oxidative status and general health in the study area. Interestingly, our results suggested that antioxidant response to metals was better when Ca concentrations were high enough to cover the physiological Ca requirements in breeding females. There seems to be a subtle balance between the concentrations of Ca in the organism and the tolerance to metal-related effects that requires further research. This study supports that offspring oxidative balance and nestling development are affected by maternal body condition and antioxidant status.

Cadmium exposure enhances organic cation transporter 2 trafficking to the kidney membrane and exacerbates cisplatin nephrotoxicity

Renal accumulation and exposure of cadmium originating from pollution in agricultural land and the prevalence of cigarette smoking remains an unneglectable human health concern. Whereas cadmium exposure has been correlated with increased incidence of a variety of kidney diseases, little is known pertaining to its effect on renal drug disposition and response in patients. Here, we report that cadmium exposure significantly increased the activity of organic cation transporter 2 (OCT2), a critical renal drug transporter recommended in United States Federal Drug Administration guidance for assessment during drug development. Cadmium enhanced OCT2 trafficking to the cell membrane both in vitro and in vivo. Mechanistically cadmium-mediated OCT2 translocation was found to involve protein-protein interaction between serine/threonine-protein kinase AKT2, calcium/calmodulin and the AKT substrate AS160 in in vitro cellular studies. The formed protein complex could selectively facilitate phosphorylation of AKT2 at T309, which induced translocation of OCT2 to the plasma membrane. Moreover, cadmium exposure markedly exacerbated nephrotoxicity induced by cisplatin, an OCT2 substrate, by increasing its accumulation in the mouse kidney. Consistently, there was a significant correlation between plasma cadmium level and alteration of renal function in cervical cancer patients who underwent chemotherapy with cisplatin. Thus, our studies suggest that membrane transporter distribution induced by cadmium exposure is a previously unrecognized factor for the broad variation in renal drug disposition and response.

Effects of calcium supplementation on oxidative status and oxidative damage in great tit nestlings inhabiting a metal-polluted area

Calcium has been proposed to diminish metal toxicity by the modulation of the oxidative stress. This study explores the effects of Ca availability and metal exposure on oxidative stress biomarkers in great tit (Parus major) nestlings. Nests were supplemented with Ca (Ca-supplemented group) or not supplemented (Control group) in a metal-polluted and a background zone in SW Finland. Metal concentrations were analyzed from feces. We analyzed antioxidants (tGSH, GSH:GSSG ratio, CAT, GST, GPx, SOD), protein carbonylation and lipid peroxidation in red cells of nestlings. Ca-supplemented and fast-growing nestlings showed higher CAT activity to cope with reactive oxygen species (ROS) generated during intensive growth and metabolism. SOD and GPx (the latter not statistically significant) were more active in the polluted area, possibly reflecting higher ROS production in nestlings from this zone due to the enhanced metal exposure and smaller size. Antioxidant levels changed over the range of metal concentrations depending on the Ca levels in plasma, suggesting that higher Ca levels stimulate antioxidants and mitigate the impacts of metals. Ca supplementation may improve nestling traits and reproductive output when antioxidants are enhanced in a situation of oxidative challenge. Therefore, Ca should be considered in future studies assessing metal exposure and effects on wild birds.

Cadmium association with DREAM promotes DREAM interactions with intracellular partners in a similar manner to its physiological ligand, calcium

Cd²⁺exposure has been associated with neurodegenerative diseases and other pathologies, but the underlying mechanism through which it exerts toxic effects remain unresolved.

Defining potential roles of Pb(2+) in neurotoxicity from a calciomics approach

Metal ions play crucial roles in numerous biological processes, facilitating biochemical reactions by binding to various proteins. An increasing body of evidence suggests that neurotoxicity associated with exposure to nonessential metals (e.g., Pb(2+)) involves disruption of synaptic activity, and these observed effects are associated with the ability of Pb(2+) to interfere with Zn(2+) and Ca(2+)-dependent functions. However, the molecular mechanism behind Pb(2+) toxicity remains a topic of debate. In this review, we first discuss potential neuronal Ca(2+) binding protein (CaBP) targets for Pb(2+) such as calmodulin (CaM), synaptotagmin, neuronal calcium sensor-1 (NCS-1), N-methyl-d-aspartate receptor (NMDAR) and family C of G-protein coupled receptors (cGPCRs), and their involvement in Ca(2+)-signalling pathways. We then compare metal binding properties between Ca(2+) and Pb(2+) to understand the structural implications of Pb(2+) binding to CaBPs. Statistical and biophysical studies (e.g., NMR and fluorescence spectroscopy) of Pb(2+) binding are discussed to investigate the molecular mechanism behind Pb(2+) toxicity. These studies identify an opportunistic, allosteric binding of Pb(2+) to CaM, which is distinct from ionic displacement. Together, these data suggest three potential modes of Pb(2+) activity related to molecular and/or neural toxicity: (i) Pb(2+) can occupy Ca(2+)-binding sites, inhibiting the activity of the protein by structural modulation, (ii) Pb(2+) can mimic Ca(2+) in the binding sites, falsely activating the protein and perturbing downstream activities, or (iii) Pb(2+) can bind outside of the Ca(2+)-binding sites, resulting in the allosteric modulation of the protein activity. Moreover, the data further suggest that even low concentrations of Pb(2+) can interfere at multiple points within the neuronal Ca(2+) signalling pathways to cause neurotoxicity.

Pleiotropic roles of Ca+2/calmodulin-dependent pathways in regulating cadmium-induced toxicity in human osteoblast-like cell lines

The heavy metal cadmium is a widespread environmental contaminant that has gained public attention due to the global increase in cadmium-containing electronic waste. Human exposure to cadmium is linked to the pathogenesis of osteoporosis. We previously reported cadmium induces apoptosis and decreases alkaline phosphatase mRNA expression via extracellular signal-regulated protein kinase (ERK) activation in Saos-2 bone-forming osteoblasts. This study examines the mechanisms of cadmium-induced osteotoxicity by investigating roles of Ca⁺²/calmodulin-dependent protein kinase (CAMK) pathways. Saos-2 or MG-63 cells were treated for 24 or 48h with 5μM CdCl₂ alone or in combination with calmodulin-dependent phosphodiesterase (PDE) inhibitor CGS-9343β; calmodulin-dependent kinase kinase (CAMKK) inhibitor STO-609; or calmodulin-dependent kinase II (CAMKII) inhibitor KN-93. CGS-9343β protected against cadmium-induced toxicity and attenuated ERK activation; STO-609 enhanced toxicity and exacerbated ERK activation, whereas KN-93 had no detectable effect on cadmium-induced toxicity. Furthermore, CGS-9343β co-treatment attenuated cadmium-induced apoptosis; but CGS-9343β did not recover cadmium-induced decrease in ALP activity. The major findings suggest the calmodulin-dependent PDE pathway facilitates cadmium-induced ERK activation leading to apoptosis, whereas the CAMKK pathway plays a protective role against cadmium-induced osteotoxicity via ERK signaling. This research distinguishes itself by identifying pleiotropic roles for CAMK pathways in mediating cadmium's toxicity in osteoblasts.

Effects of dietary lead exposure on vitamin levels in great tit nestlings - An experimental manipulation

Exposure to metal pollution negatively affects animal physiology, including nutrient metabolism, but in the wild an effect can seldom be attributed to a single metal. Moreover, little is known about how the metabolism of vitamins, essential micronutrients for developing juveniles, is affected by toxic metals. Therefore we experimentally investigated the effects of lead (Pb), a widespread toxic metal, on four fat-soluble vitamins A (total and retinol), D3, E (total and α-tocopherol) and K and carotenoids (lutein, zeaxanthin and unidentified) in great tit (Parus major) nestlings. In addition to a control group where no Pb was provided, two Pb-dosed groups were compared to a metal exposed group in the vicinity of a Ni-Cu smelter. We examined whether Pb treatment affects vitamin homeostasis and how the response of Pb-treated birds relates to that of a population under industrial exposure of Pb and other metals. For this purpose, vitamin and carotenoid levels were quantified with UPLC-MS from plasma of 7 days-old nestlings. All metal exposed groups showed increased vitamin A and retinol levels. However, vitamin levels were not directly associated with fecal Pb levels, with the exception of retinol, which was positively correlated with fecal Pb. Alpha-tocopherol, lutein and zeaxanthin levels were positively associated with body mass and wing growth rate. To conclude, Pb exposure increased plasma vitamin A and retinol levels while the levels of other vitamins and carotenoids rather reflected secondary pollution effects via differences in habitat and diet quality at the smelter site. Our findings suggest Pb exposed nestlings may allocate the vitamins needed for growth and development to fight the physiological stress thus compromising their fitness.

Effects of calcium supplementation on growth and biochemistry in two passerine species breeding in a Ca-poor and metal-polluted area

Several studies provide evidence of calcium (Ca)-limited reproduction in birds. A Ca-supplementation experiment was carried out in 2014 in a Ca-poor area associated with metal pollution in SW Finland. We aimed to evaluate the relationship between Ca availability and heavy metal exposure in free-living passerines, and to compare Ca levels in plasma and feces and the effects of Ca supplementation and metals on breeding, nestling growth, and plasma biochemistry in great tits and pied flycatchers. Although the Ca supplement was used by parents, in general the treatment had limited effects on growth and biochemistry, suggesting that parents are capable of finding sufficient Ca-rich foods to allow nestlings to grow properly. Snail shells were an abundant Ca source in the moderately polluted zone for pied flycatcher, and great tits likely combines the intake of snail shells and other anthropogenic Ca-rich items. Great tits had higher Ca concentrations in feces and plasma than pied flycatcher nestlings, suggesting that they need and sustain higher Ca levels and seem to be more opportunistic in search for Ca than pied flycatcher, since they consumed more of the supplemented Ca. Negative effects of pollution in nestling size and fledgling number were found in great tit. This species may suffer especially from the lower food quality and quantity in the polluted area. The pied flycatcher seems to be adapted to low Ca availability and they can successfully breed when metal concentrations are not too high. Our results show that great tits and pied flycatchers may employ different strategies in response to low Ca availability.

Effects of experimental calcium availability and anthropogenic metal pollution on eggshell characteristics and yolk carotenoid and vitamin levels in two passerine birds

The maternal investment into egg quality depends on the condition of the female, the quality of the mate, and the quality of the environment. In that sense, availability of nutrients and exposure to pollutants are essential parameters to consider. The main aim of this study is to assess the effects of calcium (Ca) availability and anthropogenic metal pollution on early-stage reproduction in two passerine species, great tits (Parus major) and pied flycatchers (Ficedula hypoleuca), inhabiting a Ca-poor and metal-polluted area in SW Finland. Both species were able to obtain sufficient Ca for eggshell formation, and metal pollution was below the level of having negative effects in the egg size and eggshell characteristics. However, metal polluted environment negatively affected yolk lutein and vitamin D3 levels in both species, probably because of a lower access to carotenoid-rich diet and higher metal interference with vitamin D3 metabolism. The higher levels of vitamin D3 in yolks in the unpolluted zone could also be due to upregulated D3 levels as a response to the lower natural Ca availability. Yolk carotenoids and vitamin D3 were positively associated with nestling growth and size, supporting their importance for the appropriate chick development. The interspecific differences in yolk nutrient concentrations possibly reflect the different growth rate of these species. Pied flycatchers are likely adapted to low Ca availability through an efficient vitamin D3 metabolism, but their Ca intake could be close to a deficient level.

Cadmium Induces Apoptosis in Freshwater Crab Sinopotamon henanense through Activating Calcium Signal Transduction Pathway

Calcium ion (Ca²⁺) is one of the key intracellular signals, which is implicated in the regulation of cell functions such as impregnation, cell proliferation, differentiation and death. Cadmium (Cd) is a toxic environmental pollutant that can disturb cell functions and even lead to cell death. Recently, we have found that Cd induced apoptosis in gill cells of the freshwater crab Sinopotamon henanense via caspase activation. In the present study, we further investigated the role of calcium signaling in the Cd-induced apoptosis in the animals. Our data showed that Cd triggered gill cell apoptosis which is evidenced by apoptotic DNA fragmentation, activations of caspases-3, -8 and -9 and the presence of apoptotic morphological features. Moreover, Cd elevated the intracellular concentration of Ca²⁺, the protein concentration of calmodulin (CaM) and the activity of Ca²⁺-ATPase in the gill cells of the crabs. Pretreatment of the animals with ethylene glycol-bis-(b-aminoethyl ether)-N,N,N’,N’-tetraacetic acid (EGTA), Ca²⁺ chelator, inhibited Cd-induced activation of caspases-3, -8 and -9 as well as blocked the Cd-triggered apoptotic DNA fragmentation. The apoptotic morphological features were no longer observed in gill cells pretreated with the Ca²⁺ signaling inhibitors before Cd treatment. Our results indicate that Cd evokes gill cell apoptosis through activating Ca²⁺-CaM signaling transduction pathway.

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+).

How does exposure to nickel and cadmium affect the transcriptome of yellow perch (Perca flavescens)--results from a 1000 candidate-gene microarray

The molecular mechanisms underlying nickel (Ni) and cadmium (Cd) toxicity and their specific effects on fish are poorly understood. Documenting gene transcription profiles offers a powerful approach toward identifying the molecular mechanisms affected by these metals and to discover biomarkers of their toxicity. However, confounding environmental factors can complicate the interpretation of the results and the detection of biomarkers for fish captured in their natural environment. In the present study, a 1000 candidate-gene microarray, developed from a previous RNA-seq study on a subset of individual fish from contrasting level of metal contamination, was used to investigate the transcriptional response to metal (Ni and Cd) and non metal (temperature, oxygen, and diet) stressors in yellow perch (Perca flavescens). Specifically, we aimed at (1) identifying transcriptional signatures specific to Ni and Cd exposure, (2) investigating the mechanisms of their toxicity, and (3) developing a predictive tool to identify the sublethal effects of Ni and Cd contaminants in fish sampled from natural environments. A total of 475 genes displayed significantly different transcription levels when temperature varied while 287 and 176 genes were differentially transcribed at different concentrations of Ni and Cd, respectively. These metals were found to mainly affect the transcription level of genes involved in iron metabolism, transcriptional and translational processes, vitamin metabolism, blood coagulation, and calcium transport. In addition, a linear discriminant analysis (LDA) made using gene transcription levels yielded 94% correctly reassigned samples regarding their level of metal contamination, which indicates the potential of the microarray to detect perch response to Cd or Ni effects.

Metal toxicity and opportunistic binding of Pb(2+) in proteins

Lead toxicity is associated with various human diseases. While Ca(2+) binding proteins such as calmodulin (CaM) are often reported to be molecular targets for Pb(2+)-binding and lead toxicity, the effect of Pb(2+) on the Ca(2+)/CaM regulated biological activities cannot be described by the primary mechanism of ionic displacement (e.g., ionic mimicry). The focus of this study was to investigate the mechanism of lead toxicity through binding differences between Ca(2+) and Pb(2+) for CaM, an essential intracellular trigger protein with two EF-Hand Ca(2+)-binding sites in each of its two domains that regulates many molecular targets via Ca(2+)-induced conformational change. Fluorescence changes in phenylalanine indicated that Pb(2+) binds with 8-fold higher affinity than Ca(2+) in the N-terminal domain. Additionally, NMR chemical shift changes and an unusual biphasic response observed in tyrosine fluorescence associated with C-terminal domain sites EF-III and EF-IV suggest a single higher affinity Pb(2+)-binding site with a 3-fold higher affinity than Ca(2+), coupled with a second site exhibiting affinity nearly equivalent to that of the N-terminal domain sites. Our results further indicate that Pb(2+) displaces Ca(2+) only in the N-terminal domain, with minimal perturbation of the C-terminal domain, however significant structural/dynamic changes are observed in the trans-domain linker region which appear to be due to Pb(2+)-binding outside of the known calcium-binding sites. These data suggest that opportunistic Pb(2+)-binding in Ca(2+)/CaM has a profound impact on the conformation and dynamics of the essential molecular recognition sites of the central helix, and provides insight into the molecular toxicity of non-essential metal ions.

Disarrangement of actin filaments and Ca²⁺ gradient by CdCl₂ alters cell wall construction in Arabidopsis thaliana root hairs by inhibiting vesicular trafficking

Cadmium (Cd), one of the most toxic heavy metals, inhibits many cellular and physiological processes in plants. Here, the involvement of cytoplasmic Ca²⁺ gradient and actin filaments (AFs) in vesicular trafficking, cell wall deposition and tip growth was investigated during root (hair) development of Arabidopsis thaliana in response to CdCl₂ treatment. Seed germination and root elongation were prevented in a dose- and time-dependent manner by CdCl₂ treatment. Fluorescence labelling and non-invasive detection showed that CdCl₂ inhibited extracellular Ca²⁺ influx, promoted intracellular Ca²⁺ efflux, and disturbed the cytoplasmic tip-focused Ca²⁺ gradient. In vivo labelling revealed that CdCl₂ modified actin organization, which subsequently contributed to vesicle trafficking. Transmission electron microscopy revealed that CdCl₂ induced cytoplasmic vacuolization and was detrimental to organelles such as mitochondria and endoplasmic reticulum (ER). Finally, immunofluorescent labelling and Fourier transform infrared (FTIR) analysis indicated that configuration/distribution of cell wall components such as pectins and cellulose was significantly altered in response to CdCl₂. Our results indicate that CdCl₂ induces disruption of Ca²⁺ gradient and AFs affects the distribution of cell wall components in root hairs by disturbing vesicular trafficking in A. thaliana.

Structural differences between Pb2+- and Ca2+-binding sites in proteins: implications with respect to toxicity

Pb(2+) is known to displace physiologically-relevant metal ions in proteins. To investigate potential relationships between Pb(2+)/protein complexes and toxicity, data from the protein data bank were analyzed to compare structural properties of Pb(2+)- and Ca(2+)-binding sites. Results of this analysis reveal that the majority of Pb(2+) sites (77.1%) involve 2-5 binding ligands, compared with 6+/-2 for non-EF-Hand and 7+/-1 for EF-Hand Ca(2+)-binding sites. The mean net negative charge by site (1.7) fell between values noted for non-EF-Hand (1+/-1) and EF-Hand (3+/-1). Oxygen is the dominant ligand for both Pb(2+) and Ca(2+), but Pb(2+) binds predominantly with sidechain Glu (38.4%), which is less prevalent in both non-EF-Hand (10.4%) and EF-Hand (26.6%) Ca(2+)-binding sites. A comparison of binding geometries where Pb(2+) has replaced Ca(2+) in calmodulin (CaM) and Zn(2+) in 5-aminolaevulinic acid dehydratase (ALAD) revealed protein structural changes that appear to be unrelated to ionic displacement. Structural changes observed with CaM may be related to opportunistic binding of Pb(2+) in regions of high electrostatic charge, whereas ALAD may bind multiple Pb(2+) ions in the active site. These results suggest that Pb(2+) adapts to structurally-diverse binding geometries and that opportunistic binding may play an active role in molecular metal toxicity.

The Pmr1 protein, the major yeast Ca2+-ATPase in the Golgi, regulates intracellular levels of the cadmium ion

Cadmium is a nonessential, highly toxic heavy metal that shows ionic properties similar to calcium. These ionic similarities imply that the cadmium ion, Cd2+, is a calcium ion, Ca2+, receptor-agonist, affecting the same biochemical pathways involved in Ca2+ homeostasis. In the yeast Saccharomyces cerevisiae, the PMC1 and PMR1 genes encode vacuolar and Golgi Ca2+-ATPases, respectively. The PMR1 protein product Pmr1p is involved in both Ca2+ and Mn2+ homeostasis. This study investigated the importance of Pmc1p and Pmr1p for Cd2+ cellular detoxification. Using the standard techniques of yeast molecular research and a multielemental procedure named particle-induced X-ray emission, Pmr1p was identified as a protein that directly participates in the detoxification of Cd2+, possibly through the secretory pathway. The results allow us to posit a model of Cd2+ detoxification where Pmr1p has a central role in cell survival in a Cd2+-rich environment.

In vitro assessment of the effects of cadmium and zinc on mammalian nerve fibres

Zinc and cadmium are environmental contaminants that have a wide range of effects on the nervous system, but zinc is also considered to be an important metal in the human body. In this study the effect of CdCl(2) and ZnCl(2), at concentrations of 50,150, 250 and 500 microM, on the nerve fibres of the sciatic nerve of the rat isolated in a three-chamber recording bath were studied. At the same concentrations, CdCl(2) and ZnCl(2) were found to have almost the same inhibitory effect on the compound action potential (CAP) of the nerve fibres. Their concentration-effect curves almost overlap and there was no significant difference in their EC(50) which for CdCl(2) is 250.1+/-18 microM (n=5) and for ZnCl(2) is 282.2+/-25 microM (n=5) correspondingly (P>0.05). The no-observed-effect concentration (NOEC) was estimated to be 50-100 microM for both metals. The identical inhibitory effect of both metals on the sciatic nerve fibres indicates a common mode of action which is related to their potential to generate reactive oxygen species (ROS).

Cadmium activates CaMK-II and initiates CaMK-II-dependent apoptosis in mesangial cells

Cadmium is a toxic metal that initiates both mitogenic responses and cell death. We show that Cd(2+) increases phosphorylation and activity of Ca(2+)/calmodulin-dependent protein kinase II (CaMK-II) in mesangial cells, in a concentration-dependent manner. Activation is biphasic with peaks at 1-5 min and 4-6 h. Cadmium also activates Erk, but this appears to be independent of CaMK-II. At 10-20 microM, Cd(2+) initiates apoptosis in 25-55% of mesangial cells by 6h. Inhibition of CaMK-II, but not of Erk, suppresses Cd(2+)-induced apoptosis. We conclude that activation of CaMK-II by Cd(2+) contributes to apoptotic cell death, independent of Erk activation.

Cadmium restores in vitro splicing activity inhibited by zinc-depletion

Zinc (Zn)-depletion inhibits the second step of RNA splicing, namely exon-ligation. To investigate the effects of cadmium (Cd) and other metal ions on RNA splicing inhibited by Zn-depletion, we measured in vitro splicing activities in the presence of these metals. Zn-depletion in the splicing reaction mixture was achieved by addition of a Zn-chelator, 1,10-phenanthroline. Cd(II) at 1, 5 and 10 microM restored the splicing activity to 2, 24 and 72% of that in the control reaction mixture, while higher concentrations of Cd(II) decreased the splicing activity, and more than 50 microM Cd(II) showed a complete absence of spliced products. Hg(II) also restored the splicing activity, albeit to a lesser extent, since 5 and 10 microM Hg(II) restored the splicing activity to 3 and 4% of the control value. The other metal ions examined in this study, Co(II), Cu(II), Mg(II) and Mn(II), did not show any restoration of the splicing activity. We concluded that Cd(II) could restore the in vitro splicing activity inhibited by Zn-depletion, although higher concentrations of Cd(II) prevented progress of the RNA splicing reaction. These results suggest that Cd(II) has a bifunctional property regarding RNA splicing, and is stimulatory at low concentrations and inhibitory at high concentrations.

Involvement of gelsolin in cadmium-induced disruption of the mesangial cell cytoskeleton

Cadmium (Cd2+) is known to cause a selective disruption of the filamentous actin cytoskeleton in the smooth muscle-like renal mesangial cell. We examined the effect of Cd2+ on the distribution of the actin-severing protein, gelsolin. Over 8 h, CdCl2 (10 microM) caused a progressive shift of gelsolin from a diffuse perinuclear and cytoplasmic distribution to a pattern decorating F-actin filaments. Over this time filaments were decreased in number in many cells, and membrane ruffling was initiated. Western blotting and 125I-F-actin gel overlays demonstrated an increase in actin-binding gelsolin activity in the cytoskeletal fraction of cell extracts following Cd2+ treatment. In in vitro polymerization assays, gelsolin acted as a nucleating factor and increased the rate of polymerization. Cytosolic extracts also increased the polymerization rate. Addition of Cd2+ together with gelsolin further increased the rate of polymerization. Gelsolin enhanced depolymerization of purified actin, and Cd2+ partially suppressed this effect. However, cytoskeletal extracts from Cd2+-treated cells also markedly increased depolymerization, suggesting further that Cd2+ may activate cellular component(s) such as gelsolin for actin binding. We conclude that a major effect of Cd2+ on the mesangial cell cytoskeleton is manifest through activating the association of gelsolin with actin, with gelsolin's severing properties predominating under conditions found in Cd2+-treated cells.

Hsp27, Hsp70, and metallothionein in MDCK and LLC-PK1 renal epithelial cells: effects of prolonged exposure to cadmium

Cadmium is a widely distributed industrial and environmental toxin. The principal target organ of chronic sublethal cadmium exposure is the kidney. In renal epithelial cells, acute high-dose cadmium exposure induces differential expression of proteins, including heat shock proteins. However, few studies have examined heat shock protein expression in cells after prolonged exposure to cadmium at sublethal concentrations. Here, we assayed total cell protein, neutral red uptake, cell death, and levels of metallothionein and heat shock proteins Hsp27 and inducible Hsp70 in cultures of MDCK and LLC-PK1 renal epithelial cells treated with cadmium for 3 days. Treatment with cadmium at concentrations equal to or greater than 10 microM (LLC-PK1) or 25 microM (MDCK) reduced measures of cell vitality and induced cell death. However, a concentration-dependent increase in Hsp27 was detected in both cell types treated with as little as 5 microM cadmium. Accumulation of Hsp70 was correlated only with cadmium treatment at concentrations also causing cell death. Metallothionein was maximally detected in cells treated with cadmium at concentrations that did not reduce cell vitality, and further increases were not detected at greater concentrations. These results reveal that heat shock proteins accumulate in renal epithelial cells during prolonged cadmium exposure, that cadmium induces differential expression of heat shock protein in epithelial cells, and that protein expression patterns in epithelial cells are specific to the cadmium concentration and degree of cellular injury. A potential role for Hsp27 in the cellular response to sublethal cadmium-induced injury is also implicated by our results.

Early steps in the oxidative burst induced by cadmium in cultured tobacco cells (BY-2 line)

The rapid generation of H(2)O(2) by Cd(2+)-treated plant cells was investigated in cultured tobacco (Nicotiana tabacum L.) BY-2 cells. The starting point for the generation of H(2)O(2) has been located at the cell plasma membrane using cytochemical methods. Treatment of the cells with diphenyleneiodonium (DPI) and imidazol, both inhibitors of the neutrophil NADPH oxidase, prevented the generation of H(2)O(2) induced by Cd(2+). These data suggest the involvement of an NADPH oxidase-like enzyme leading to H(2)O(2) production through O(2)(*-) dismutation by superoxide dismutase enzymes. To investigate the implication of Ca(2+) channels in a Cd(2+)-induced oxidative burst, different inhibitors of Ca(2+) channels were used. Only La(3+) totally inhibited the generation of H(2)O(2) induced by Cd(2+). However, verapamil and nifedipine, inhibitors of Ca(2+) channels, were not effective. Calmodulin or a Ca(2+)-dependent protein kinase is also implicated in the signal transduction sequence, based on the results obtained with two types of calmodulin antagonists, fluphenazine and N-(-6-amino-hexyl)-5-chloro-1-naphthalenesulphonamide (W-7) and staurosporine, an inhibitor of protein kinases. However, neomycin, an inhibitor of the phosphoinositide cycle, did not inhibit the generation of H(2)O(2) induced by Cd(2+), suggesting mainly an induction of the oxidative burst mediated by calmodulin and/or calmodulin-dependent proteins.

Heavy metal toxicity: cadmium permeates through calcium channels and disturbs the plant water status

Because plant wilting has been described as a consequence of cadmium (Cd2+) toxicity, we investigate Cd2+ effects on plant water losses, gas exchanges and stomatal behaviour in Arabidopsis thaliana L. Effects of 1-week Cd2+ application in hydroponic condition (CdCl2 10-100 micro m) were analyzed. A 10- micro m Cd2+ concentration had no significant effect on the plant-water relationship and carbon assimilation. At higher Cd2+ concentrations, a Cd2+ -dependent decrease in leaf conductance and CO2 uptake was observed despite the photosynthetic apparatus appeared not to be affected as probed by fluorescence measurements. In epidermal strip bioassays, nanomolar Cd2+ concentrations reduced stomatal opening under light in A. thaliana, Vicia faba and Commelina communis. Application of 5 micro m ABA limited the root-to-shoot translocation of cadmium. However, the Cd2+-induced stomatal closure was likely ABA-independent, since a 5-day treatment with 50 micro m Cd2+ did not affect the plant relative water content. Additionally, a similar Cd2+-induced stomatal closure was observed in the ABA insensitive mutant abi1-1. Interestingly, this mutant displayed a higher transpiration rate than the wild type but did not accumulate more Cd2+, arguing that Cd2+ uptake is not dependent only on the transpiration flow. Application of putative calcium channels inhibitors suppressed the inhibitory effect of Cd2+ in epidermal strip experiments, suggesting that Cd2+ could enter the guard cell through calcium channels. Patch-clamp studies with V. faba guard cell protoplasts showed that plasma membrane K+ channels were insensitive to external Cd2+ application whereas Ca2+ channels were found permeable to Cd2+. In conclusion, we propose that Cd2+ affects guard cell regulation in an ABA-independent manner by entering the cytosol via Ca2+ channels.

The use of surrogate endpoints to assess potential toxicity in humans

Data on toxic effects in humans may come from epidemiology studies, accidental poisonings, surveillance schemes or following intentional exposures. In many cases, a surrogate endpoint related to the adverse effect is investigated. Effects produced following intentional exposures are usually restricted to readily reversible, mild surrogate endpoints of the adverse effect of concern. Not all initial interactions within the target organ are related to the toxic effect, and many measurements are biomarkers of exposure not response. Biomarkers of response represent surrogate endpoints of response only if they are critical to the mode of action. The use of biomarkers and the possible problems with using surrogate endpoints are illustrated with data on aniline, cadmium, carbon monoxide, erythrosine, paracetamol (acetaminophen) and styrene. In vivo surrogate endpoints are normally used in risk assessment directly, whereas in vitro surrogate endpoints can be incorporated by the development of a biologically based dose-response model, or used to replace a default uncertainty factor by a chemical-specific adjustment factor.

Effects of cadmium cell viability, trophoblastic development, and expression of low density lipoprotein receptor transcripts in cultured human placental cells

Previously, we have demonstrated that cadmium inhibits progesterone release in cultured human trophoblast cells. In the present study, we investigated potential mechanism(s) by which cadmium may elicit this effect. Cytotrophoblasts were obtained via enzymatic dispersion, purified by density gradient centrifugation, and cultured with increasing concentrations of cadmium. Cadmium-induced suppression of progesterone release seemed to be independent of cell death, as no significant decline in viability was observed with cadmium treatment. Further, immunocytochemical localization of cellular boundaries and nuclei indicated approximately 94% syncytial maturity was attained by both untreated and cadmium-treated cells, demonstrating that cadmium did not inhibit syncytial development. However, the abundance of LDL receptor (LDL-R) mRNA transcripts, as determined by competitive RT-PCR, was reduced (P < 0.05) by cadmium exposure in an apparent dose-dependent manner. Thus, the LDL-R, by which cholesterol substrate is supplied to the syncytiotrophoblast, is one site at which cadmium may interfere with placental progesterone production.

Risk assessment of nephrotoxicity of cadmium

Cadmium as an environmental or occupational toxin has been well studied. Exposure can fairly easily be detected by analysis of cadmium in biological material. Different routes of cadmium uptake, such as via airborne particles, cigarette smoke or contaminated food, have been identified. Urinary concentrations associated with renal effects vary, depending on urinary marker of effect, and are as low as 2 micrograms cadmium/g creatinine. Different segments of the nephron are affected by cadmium. Urinary enzymes and serum derived proteins, mainly low-molecular weight proteins, as well as eicosanoids or glycosaminoglycans are among the tubular or glomerular markers of effect. Predisposing factors, such as smoking, dietary habits and low body iron stores have been described. It is concluded that even for low level cadmium exposure effects can be detected with sensitive diagnostic tools.

Roles of lead-binding proteins in mediating lead bioavailability

The intracellular bioavailability of lead (Pb) at low dosage levels in major target organs such as the kidney and brain appears to be largely determined by complexation with a group of low molecular weight proteins. These proteins are rich in aspartic and glutamic dicarboxyl amino acids. The proteins are chemically similar but not identical across all species examined to date and the brain protein appears to be different from that found in the kidney. These proteins possess dissociation constant values for Pb on the order of 10(-8) M and appear to normally bind zinc. In rats, these proteins attenuate the Pb inhibition of the heme pathway enzyme delta-aminolevulinic acid dehydratase by a mechanism involving both Pb chelation and zinc donation to this highly Pb-sensitive zinc-dependent enzyme. Other studies in rats have shown that the kidney protein facilitates the intranuclear movement of Pb in vitro followed by chromatin binding, suggesting that this protein may be involved in alterations of the pathognomonic Pb intranuclear inclusion bodies in renal gene expression associated with the mitogenic effects of Pb in the kidney.

Effect of calmodulin-inhibitors and verapamil on the nephrotoxicity of cadmium in rat

Recent reports indicate that calmodulin inhibitors (CIs) can modify cadmium (Cd) toxicity in rodents. Pretreatment with CIs prevents Cd-induced testicular damage in mice and reduces the severity of such damage in rats. On the other hand it has been suggested that the cellular transport of Cd can be partly inhibited by the calcium-channel inhibitor, verapamil. The aim of this study was to determine whether these inhibitors can prevent the toxic effects of Cd on the kidney which is the critical organ. For that purpose, we have examined the effects of two CIs (trifluoperazine and chlorpromazine) and of verapamil on the development of tubular damage in female Sprague-Dawley rats. The animals were injected subcutaneously 5 days a week for 8 weeks with cadmium chloride (1 mg Cd/kg), alone or in association with trifluoperazine (20 mg/kg), chlorpromazine (15 mg/kg) or verapamil (2 x 5 mg/kg). The development of renal dysfunction was followed by measuring the urinary excretion of the low molecular weight protein Clara cell protein (CC16). In Cd-treated rats, the urinary excretion of CC16 started to increase from week 6 to reach at the end of experiment values more than 100-times above normal. CIs or verapamil did not influence the rise of urinary CC16 induced by Cd. The three inhibitors, by contrast, enhanced the accumulation of Cd in the liver and, at the exception of chlorpromazine, in the kidneys of Cd-treated rats. Although interfering with the metabolism of Cd, CIs and verapamil do not prevent renal damage in rats chronically exposed to this heavy metal.

Induction of c-fos proto-oncogene in mesangial cells by cadmium

Cadmium is mitogenic under some circumstances and has been shown to cause accumulation of transcripts for several proto-oncogenes in a variety of cells, but the mechanism(s) remain to be delineated. Here we show that CdCl2 causes an increase in c-fos mRNA within 30 min of exposure of mesangial cells. At 10 microM Cd2+, this increase persists for at least 8 h in both rat and human cells. The half-life of c-fos mRNA is the same whether it accumulates following 4 h of treatment with Cd2+ or is induced transiently by phorbol ester. Cycloheximide, which stabilizes the transcript, causes a synergistic increase when administered with CdCl2. Nuclear run-on analysis confirms that Cd2+ causes transcriptional activation of the c-fos gene. Calmodulin and Ca2+/calmodulin-dependent kinase, and classical protein kinase C (PKC) isoforms represent two Ca2+-dependent signaling pathways that can lead to induction of c-fos, and Cd2+ has been shown to activate both calmodulin and PKC in vitro, possibly by virtue of the similar ionic radii of Cd2+ and Ca2+. Therefore, we investigated the effect of Cd2+ on these pathways in vivo. 10 microM CdCl2 did not increase total PKC activity or Ca2+/calmodulin-dependent kinase II activity and inhibited the latter at higher concentrations, ruling out either pathway in the Cd2+-dependent induction of c-fos. However, Cd2+ did lead to a sustained activation of the Erk family mitogen-activated protein kinases (MAPK) that correlated with induction of c-fos. A specific inhibitor of the MAPK kinases, PD98059, partially inhibited the induction of c-fos by Cd2+. We conclude that Cd2+ induces c-fos at least in part by causing a sustained activation of MAPK independent of its ability to activate PKC and calmodulin in vitro.

Cadmium disrupts the signal transduction pathway of both inhibitory and stimulatory receptors regulating chloride secretion in the shark rectal gland

The heavy metal cadmium causes nephrotoxicity and alters the transport function of epithelial cells. In the shark rectal gland, chloride secretion is regulated by secretagogues and inhibitors acting through receptors coupled to G proteins and the cyclic AMP-protein kinase A pathway. We examined the effects of cadmium on the response to the inhibitory peptide somatostatin (SRIF), and to the stimulatory secretagogues forskolin and vasoactive intestinal peptide (VIP). In control experiments, SRIF (100 nM) entirely inhibited the chloride secretory response to 10 microM forskolin (maximum chloride secretion with forskolin 1984 +/- 176 microEq/h/g; with forskolin + SRIF 466 +/- 93 microEq/h/g, P < 0.001). Cadmium (25 microM) entirely reversed the inhibitory response to SRIF (chloride secretion 2143 +/- 222 microEq/h/g) and caused an overshoot (2917 +/- 293 microEq/h/g) that exceeded the response to forskolin (P < 0.01). Cadmium also enhanced forskolin-stimulated chloride secretion (2628 +/- 418 vs. 1673 +/- 340 microEq/h/g, P < 0.02) and reversed the declining phase of the forskolin response. Cadmium had a concentration-dependent, biphasic effect on the response to VIP. Cd (10-100 microM) increased both chloride secretion and tissue cyclic AMP content, whereas higher concentrations (1 mM) inhibited chloride secretion and cyclic AMP accumulation. Our findings provide evidence that Cd disrupts the signal transduction pathways of both inhibitory receptors and secretagogues regulating cAMP mediated transport in an intact epithelia. The results are consistent with direct effects of cadmium on adenylate cyclase and/or phosphodiesterase activity in this marine epithelial model.

Regulation of blood pressure with calcium-dependent dopamine synthesizing system in the brain and its related phenomena

The effects of calcium on blood pressure regulation remain controversial. Although the mechanism by which calcium increases blood pressure when it is given intravenously and acutely has been elucidated, that by which calcium reduces blood pressure when it is supplemented chronically and slightly through daily diet is unclear. From a number of animal experiments concerning the effects of calcium on blood pressure, we believe that calcium ions have two separate roles in the regulation of blood pressure through both central and peripheral systems: (1) calcium ions reduce blood pressure through a central, calcium/calmodulin-dependent dopamine-synthesizing system and (2) calcium ions increase blood pressure through an intracellular, calcium-dependent mechanism in the peripheral vasculature. These concepts were applied to elucidate the mechanisms underlying hypertension in spontaneously hypertensive rats (SHR) and changes in blood pressure in other experimental animals, and the following conclusions were reached. The decrease of the serum calcium level in spontaneously hypertensive rats (SHR) causes a decrease in calcium/calmodulin-dependent dopamine synthesis in the brain. The subsequent low level of brain dopamine induces hypertension. The increase in susceptibility to epileptic convulsions and the occurrence of hypertension in epileptic mice (El mice) may be linked through a lowering of calcium-dependent dopamine synthesis in the brain, and epilepsy and hypertension may be associated. Exercise leads to increases in calcium-dependent dopamine synthesis in the brain, and the increased dopamine levels induce physiological changes, including a decrease in blood pressure. Cadmium which is not distinguished from calcium by calmodulin, activates calmodulin-dependent functions in the brain, and increased dopamine levels may decrease blood pressure. In this report, our studies are considered in light of reports from many other laboratories.

The effect of intravenous cadmium on exocrine and endocrine pancreatic functions in conscious dogs

This study was conducted in conscious dogs to investigate the effect of cadmium on exocrine pancreatic secretion and plasma levels of pancreatic polypeptide (PP). Mongrel dogs weighing 20-25 kg were prepared with chronic gastric and pancreatic fistulas, and were acclimated for 3 wk prior to studies. The dogs were given iv infusion of saline, secretin at 25 U/kg/h, cadmium at 0.15 mg/kg/h, or various combinations of these compounds. During the infusion, pancreatic juice and blood samples were collected at regular intervals. Secretin infusion stimulated pancreatic secretions. Infusion of cadmium alone had no effect on pancreatic secretions and plasma levels of PP. When cadmium infusion was stopped with the background infusion of secretin, pancreatic secretions and plasma levels of PP were significantly increased. This latent effect of cadmium on pancreatic secretions and plasma levels of PP was abolished by an iv injection of 100 mg/kg atropine. These results indicate that cholinergic signaling may be involved in the effect of cadmium on pancreatic exocrine secretions and PP release. The current study suggests that cadmium may have diverse physiological functions in both exocrine and endocrine pancreatic cells.

Zinc alters actin filaments in Madin-Darby canine kidney cells

Exposure of semiconfluent cultures of Madin-Darby canine kidney cells to 10 microM zinc leads to a change in the organization of the actin filament system. Most of the stress fibers at the basal end of the cell are lost and the actin associated with the lateral membrane and junctional regions appears to retract into the cytoplasm. In addition, at the base of the cell in regions of cell-substratum contact, dense, actin-rich plaques appear. These alterations in actin filaments are associated with a change in cell shape. Microtubules were unaffected by exposure to 10 microM zinc. At zinc concentrations greater than or equal to 50 microM the microtubules depolymerized. Exposure to cadmium alters the actin filaments as well but the effect is different from the change seen with zinc. When the cells are exposed simultaneously to zinc and cadmium the cells appear the same as they would if exposed to zinc alone. Exposure of MDCK cells to either metal, individually or in combination, results in a significant and similar increase in F-actin content as determined spectrofluorometrically. The changes in organization and amount of F-actin are associated with a reduction in the ability of the cells to remain attached to the substrate, a toxic effect of these metals with regard to epithelial function. The results indicate that zinc, an essential metal, and cadmium, a highly toxic metal, interact with the actin cytoskeleton in intact cells.

Calcium/calmodulin-dependent phosphorylation and the effect of cadmium in cultured fish cells

1. Calmodulin constitutes approximately 0.7% of the soluble protein in rainbow trout gonadal cells (RTG-2). 2. Calcium-dependent phosphorylation of endogenous proteins was examined in vitro in cytosol fractions of RTG-2 cells. Phosphorylation of numerous proteins was stimulated by calmodulin and calcium, and inhibited by the calmodulin-binding phenothiazine, trifluoperazine. 3. Cadmium was as effective as calcium in stimulating calmodulin-dependent phosphorylations of endogenous substrates in cytosolic fractions of RTG-2 cells.

Interaction of metals with brain calmodulin purified from normal and cadmium exposed rats

Chronic exposure of cadmium (Cd) to rats (6 mg/kg body weight/day) led to a significant accumulation of Cd in brain and other organs. Calmodulin (CaM) isolated from brains of Cd exposed rats showed a decreased ability to stimulate CaM-dependent phosphodiesterase (PDE) as compared to that purified from unexposed animals. There was a dose dependent inhibition of CaM activity when CaM (from normal and Cd exposed rats) was incubated with different molar ratios of aluminium (Al3+), lead (Pb2+), manganese (Mn2+) and vanadium (V5+). Regression analysis of rat brain CaM activity versus varying metal ion concentration demonstrated negative slopes. However, CaM from the brains of Cd exposed rats was less sensitive to these metals in comparison to the normal rat brain CaM. These data suggest that CaM inhibition may be used as a biological marker of neurotoxicity and for elucidating the possible mechanism by which neurotoxic metals manifest toxic effects.

Short-term exposure to cadmium modifies phosphorylation of gill proteins in the sea mussel

1. Sea mussels were exposed to cadmium for short periods of time. The excised gills were incubated with radioactive orthophosphate. The gill proteins were separated by 1- and 2-dimensional gel electrophoresis and the phosphorylation state of the proteins was determined by image analysis of autoradiographs. 2. 1-Dimensional gel electrophoresis revealed that exposure of the animals to cadmium stimulated phosphorylation of the gill proteins in a cadmium concentration-dependent manner. 3. 2-Dimensional gel electrophoresis showed that cadmium differentially affected the phosphorylation of various proteins. Major alterations were observed in the basic, high mol. wt proteins and in the acidic, low mol. wt polypeptides.

Activation of troponin C by Cd2+ and Pb2+

Certain heavy metal actions such as Cd2+ and Pb2+ mimic Ca2+ effectively in stimulating calmodulin (CaM). We now show that these cations also activate skeletal muscle troponin C (TnC), a Ca2(+)-binding protein highly homologous to CaM. Like Ca2+, these cations allow TnC to alter its electrophoretic mobility on polyacrylamide gels, and to bind to phenyl-Sepharose. Moreover, they activate TnC to stimulate myofibrillar ATPase. When TnC was removed from the skeletal myofibrils by treatment with trans-1,2-cyclohexanediamine-N,N,N',N'-tetraacetic acid (CDTA), the ATPase activity was no longer stimulated by the cations. However, after reconstitution of CDTA-treated skeletal myofibril with TnC, the response of ATPase to Ca2+, Cd2+ or Pb2+ was restored. These findings suggest that the activation of myofibrillar ATPase by Cd2+ and Pb2+ is mediated through TnC. The ability of the heavy metals to stimulate TnC-supported ATPase activity correlated quite well with the ability to increase the extent of the myofibrillar superprecipitation. The activation of TnC by Cd2+ or Pb2+ could constitute a possible molecular basis for their toxicity.

A 1H-NMR comparison of calmodulin activation by calcium and by cadmium

Our previous reports based on pharmacological and histochemical evidence suggest that calcium and cadmium can both activate calmodulin (CaM)-dependent functions. The study reported here was carried out to explain these observations in molecular terms, using 400 MHz 1H-NMR. Changes in the spectrum of bovine brain CaM induced by 0 to 4 molar equivalents of calcium and cadmium were practically the same. In particular, the chemical shifts and line shape of signals due to Tyr-138, Phe-65, Phe-89 and Tml-115 were similarly affected by either ion. In addition, the effects of N-(6-aminohexyl)-5-chloro-1-naphthalene-sulfonamide (W-7, a CaM antagonist) on the phenylalanine aromatic regions, methionine methyl regions and high-field methyl regions of the spectra of both calcium- and cadmium-saturated proteins were practically identical. The effect of W-7 on calcium- and cadmium-saturated CaM was reflected in changes in the signals of Ile-27, Phe-68, Phe-92, Ile-100 and Val-142, as well as Met-71, Met-72, Met-76, Phe-89 and Phe-141. The results show that cadmium binds to all calcium-binding sites of CaM, and induces conformational changes that are as extensive as those brought about by calcium. W-7 also inhibits CaM activation by calcium and cadmium. Combined with our previous toxicological evidence, these results suggest that cadmium binds indiscriminately to CaM and that subsequent activation or modulation of CaM-dependent functions is confused as a result. This may be a mechanism contributing to cadmium poisoning.

A mechanism of cadmium poisoning: the cross effect of calcium and cadmium in the calmodulin-dependent system

The effects of the intraventricular (IVT) administration of cadmium on the amount of dopamine (DA) in various regions of the mice brain were analyzed immunohistochemically using a microphotometry system. DA levels in the neostriatum and nucleus accumbens were increased by approximately 30% (p less than 0.01) by the IVT administration of CdCl2 (1 mumol/kg). This effect was abolished by the calmodulin antagonist, W-7 (4.2 micrograms/mouse, IVT). The effects of cadmium on DA levels in the brain were very similar to those seen with calcium. Combining these results with our previous finding that calmodulin does not have the ability to distinguish between calcium and cadmium, a mechanism of cadmium poisoning is suggested in which cadmium activates catecholamine synthesizing enzyme and numerous other enzymes through calmodulin-dependent systems, thereby disturbing many functions in the organism.

Effects of cadmium treatment in vitro on the antioxidant protection mechanism and activation of human blood platelets

Interactions of human platelets with cadmium in vitro were studied with respect to the platelet activation process as indicated by malondialdehyde (MDA) formation and also to the components of the cellular antioxidant defence system such as catalase, glutathione peroxidase (GPx), glutathione reductase (GR), glutathione-S-transferase (GST), glucose-6-phosphate dehydrogenase (G6PDH), and reduced glutathione (GSH). Cadmium treatment stimulated platelet MDA formation after a lag phase of at least 15 min and this effect was completely blocked by either 1 mM aspirin or 1 mM CaCl2. Cadmium pretreated platelets also displayed a much higher (5 fold) MDA formation when stimulated by thrombin. Platelet catalase activity was decreased by almost 50% after incubation with cadmium. There was also a moderate decline in platelet GSH and GR activity along with a stimulation of GST and G6PDH activity. These results suggest: (1) the cadmium effect on platelets as observed by enhanced formation of MDA via the cyclooxygenase pathway involves intraplatelet accumulation of cadmium which is inhibited by calcium, (2) a modest decline in GSH, presumably due to the inadequacy of H2O2 detoxification mechanism, does not adversely affect platelet function because of the adaptive response of G6PDH, and (3) intracellular accumulation of cadmium may result in platelet hyperactivity through higher intraplatelet free calcium levels resulting directly through cadmium action or indirectly through higher H2O2 levels due to catalase inhibition.