Involvement of calcium channels in the sexual dimorphism of cadmium-induced hepatotoxicity

Recombinant human metallothionein-III alleviates oxidative damage induced by copper and cadmium in Caenorhabditis elegans

Recombinant human metallothionein III (rh-MT-III) is a genetically engineered product produced by Escherichia coli fermentation technology. Its molecules contain abundant reducing sulfhydryl groups, which possess the ability to bind heavy metal ions. The present study was to evaluate the binding effects of rh-MT-III against copper and cadmium in vitro and to investigate the antioxidant activity of rh-MT-III using Caenorhabditis elegans in vivo. For in vitro experiments, the binding rates of copper and cadmium were 91.4% and 97.3% for rh-MT-III at a dosage of 200 μg/mL at 10 h, respectively. For in vivo assays, the oxidative stress induced by copper (CuSO₄ , 10 μg/mL) and cadmium (CdCl₂ , 10 μg/mL) was significantly reduced after 72 h of exposure to different doses of rh-MT-III (5-500 μg/mL), indicated by restoring locomotion behavior and growth, and reducing malondialdehyde and reactive oxygen species levels in C. elegans. Moreover, rh-MT-III decreased the deposition of lipofuscin and fat content, which could delay the progression of aging. In addition, rh-MT-III (500 μg/mL) promoted the up-regulation of Mtl-1 and Mtl-2 gene expression in C. elegans, which could enhance the resistance to oxidative stress by increasing the enzymatic activity of antioxidant defense system and scavenging free radicals. The results indicated that supplemental rh-MT-III could effectively protect C. elegans from heavy metal stress, providing an experimental basis for the future application and development of rh-MT-III.

Effects of Environmental Cadmium Exposure on the Liver in Korean Adults: Cross-Sectional and Longitudinal Studies

Cadmium (Cd) is a ubiquitous environmental pollutant with an exceptionally long biological half-life. The liver is a major organ for Cd metabolism, but the toxicity of Cd is unclear. This study sought to determine whether blood Cd (BCd) level (representing recent exposure [months] to Cd) was associated with liver function in Korean adults, both cross-sectionally and longitudinally. The baseline cross-sectional study involved 2,086 adults (male: 908, female: 1,178) in 2010 - 2011, and 503 of them (male: 207, female: 296) were followed up in 2014 - 2015. BCd was measured by graphite-furnace atomic absorption spectrometry, and liver function indices (aspartate aminotransferase [AST], alanine aminotransferase [ALT], and γ-glutamyltransferase [GGT]) were determined. Liver damage was defined as an abnormal elevation of more than one liver function index. The geometric mean of BCd (1.07 μg/L) was higher in females than in males (1.16 vs. 0.96 μg/L). Liver function indices increased significantly in a dose-dependent manner according to the BCd levels, except for ALT in males, and were higher in males than in females. BCd level was also associated with the risk of liver damage in both sexes. No significant changes in BCd were observed between baseline and follow-up. The liver function indices in 2014 - 2015 were comparable to those in 2010 - 2011 in males, while ALT and GGT were significantly increased in 2014 - 2015 compared to 2010 - 2011 in females with relatively high BCd. These findings suggest that even a low level of environmental Cd exposure, short- and long-term, may affect liver function, and females appear more susceptible than males.

Role of Autophagy in Cadmium-Induced Hepatotoxicity and Liver Diseases

Cadmium (Cd) is a toxic pollutant that is associated with several severe human diseases. Cd can be easily absorbed in significant quantities from air contamination/industrial pollution, cigarette smoke, food, and water and primarily affects the liver, kidney, and lungs. Toxic effects of Cd include hepatotoxicity, nephrotoxicity, pulmonary toxicity, and the development of various human cancers. Cd is also involved in the development and progression of fatty liver diseases and hepatocellular carcinoma. Cd affects liver function via modulation of cell survival/proliferation, differentiation, and apoptosis. Moreover, Cd dysregulates hepatic autophagy, an endogenous catabolic process that detoxifies damaged cell organelles or dysfunctional cytosolic proteins through vacuole-mediated sequestration and lysosomal degradation. In this article, we review recent developments and findings regarding the role of Cd in the modulation of hepatotoxicity, autophagic function, and liver diseases at the molecular level.

The effect of cadmium exposition on the structure and mechanical properties of rat incisors

Alterations in the structure and mechanical properties of teeth in adult Wistar rats exposed to cadmium were investigated. Analyses were conducted on two sets of incisors from female and male specimens, that were intoxicated with cadmium (n = 12) or belonged to the control (n = 12). The cadmium group was administered with CdCl2 dissolved in drinking water with a dose of 4mg/kgbw for 10 weeks. The oral intake of cadmium by adult rats led to the range of structural changes in enamel morphology and its mechanical features. A significant increase of cadmium levels in the teeth in comparison to the control, a slight shift in the colour and reduction of pigmented enamel length, higher surface irregularity, a decrease of hydroxyapatite crystals size in the c-axis and simultaneous increase in pigmented enamel hardness were observed. The extent of these changes was sex-dependent and was more pronounced in males.

Impact of chronic and low cadmium exposure of rats: sex specific disruption of glucose metabolism

BACKGROUND

Several epidemiological and animal studies suggest a positive association between cadmium (Cd) exposure and incidence of type 2 diabetes, but the association remains controversial. Besides, the experimental data have mainly been obtained with relatively high levels of Cd, over various periods of time, and with artificial routes of administration.

OBJECTIVES

Do environmental exposures to Cd induce significant disruption of glucose metabolism?

METHODS

Adults Wistar rats were exposed for three months to 0, 5, 50 or 500 μg.kg^-1.d^-1 of CdCl₂ in drinking water. Relevant parameters of glucose homeostasis were measured.

RESULTS

Cd accumulated in plasma, kidney and liver of rats exposed to 50 and 500 μg.kg^-1.d^-1, without inducing signs of organ failure. In rats drinking 5 μg.kg^-1.d^-1 for 3 months, Cd exposure did not lead to any significant increase of Cd in these organs. At 50 and 500 μg.kg^-1.d^-1 of Cd, glucose and insulin tolerance were unchanged in both sexes. However, females exhibited a significant increase of both fasting and glucose-stimulated plasma insulin that was assigned to impaired hepatic insulin extraction as indicated by unaltered fasting C-peptide plasma levels.

CONCLUSIONS

Glucose homeostasis is sensitive to chronic Cd exposure in a gender-specific way. Moreover, this study proves that an environmental pollutant such as Cd can have, at low concentrations, an impact on the glucose homeostatic system and it highlights the importance of a closer scrutiny of the underlying environmental causes to understand the increased incidence of type 2 diabetes.

Effects of diallyl tetrasulfide on cadmium-induced oxidative damage in the liver of rats

The protective efficacy of diallyl tetrasulfide (DTS) from garlic on liver injury induced by cadmium (Cd) was investigated. In this study, Cd (3 mg/kg body weight) was administered subcutaneously for 3 weeks to induce toxicity. DTS was administered orally (10, 20 and 40 mg/kg body weight) for 3 weeks with subcutaneous (sc) injection of Cd. Cd-induced liver damage was evidenced from increased activities of serum hepatic enzymes, namely aspartate transaminase, alanine transaminase, alkaline phosphatase and lactate dehydrogenase, with significant elevation of lipid peroxidation indices (thiobarbituric acid reactive substances and hydroperoxides) and protein carbonyl groups in the liver. Rats subjected to Cd toxicity also showed a decline in the levels of total thiols, reduced glutathione (GSH), vitamin C and vitamin E, accompanied by an increased accumulation of Cd, and significantly decreased activities of superoxide dismutase, catalase (CAT), glutathione peroxidase, glutathione-S-transferase (GST), glutathione reductase, and glucose-6-phosphate dehydrogenase in the liver. Administration of DTS at 40 mg/kg body weight significantly normalised the activities of hepatic marker enzymes, compared to other doses of DTS (10 and 20 mg/kg body weight). In addition, DTS (40 mg/kg body weight) significantly reduced the accumulation of Cd and the level of lipid peroxidation, and restored the level of antioxidant defense in the liver. Histological studies also showed that administration of DTS to Cd-treated rats resulted in a marked improvement of hepatocytes morphology with mild portal inflammation. Our results suggest that DTS might play a vital role in protecting Cd-induced oxidative damage in the liver. Human & Experimental Toxicology(2007) 26, 527—534

Protective Effect of L-Theanine on Cadmium-Induced Apoptosis in PC12 Cells by Inhibiting the Mitochondria-Mediated Pathway

L-Theanine is an amino acid derivative from green tea. The present work was aimed at the effect of L-theanine on neuron-like rat pheochromocytoma (PC12) cells stimulated with cadmium chloride. Treatment with L-theanine before cadmium exposure increased cell viability; the experiments of Annexin V/PI staining indicated that L-theanine inhibited cadmium-induced cell apoptosis. Meanwhile, L-theanine decreased ROS production and protected from cadmium-induced disruption of mitochondrial transmembrane potential. Compared with cadmium-treated cells, L-theanine could also decrease the ratio of Bax/Bcl-2, as well as the level of cleaved caspase-9, caspase-3 and poly(ADP-ribose) polymerase. Furthermore, L-theanine depresses cadmium-induced up regulation of phosphorylations of PI3K/Akt, MAPK ERK1/2, and JNK signaling. These data suggest that L-theanine pretreatment reduces severity of cadmium toxicity probably via antioxidant action. Therefore, it may be concluded that L-theanine could be exploited for prevention of cadmium-induced diseases.

The influence of biological and environmental factors on metallothionein concentration in the blood

The concentration of metallothionein (MT), a low-molecular-weight protein, is regulated by many factors, primarily metals (zinc, cadmium, copper), cytokines, glucocorticoides and free radicals. These factors are determined by such aspects of human biology as gender, pregnancy and age, as well as by environmental factors including the use of oral contraceptives and cigarette smoking, all which may affect MT levels in the body. The aim of this study was to investigate the influence of these biological and environmental factors on MT concentrations in erythrocyte lysate and in plasma. MT concentrations were determined by a two-step direct enzyme-linked immunosorbent assay. Evaluation of exposure to cigarette smoking was performed by checking cotinine levels in the plasma of subjects. The studies showed higher MT concentrations in both the erythrocyte lysate and plasma of women when compared to men. Furthermore, pregnancy causes an increase of MT concentration in plasma, while oral contraceptives cause an elevated concentration of MT in erythrocyte lysate. Age impacts plasma MT concentrations in men, whereas it does not affect concentrations of MT in erythrocyte lysate.

Oxidative stress and Ca(2+) signals involved on cadmium-induced apoptosis in rat hepatocyte

Cadmium (Cd) is an important industrial and environmental pollutant. In animals, the liver is the major target organ of Cd toxicity. In this study, rat hepatocytes were treated with 2.5∼10 μM Cd for various durations. Studies on nuclear morphology, chromatin condensation, and apoptotic cells demonstrate that Cd concentrations ranging within 2.5∼10 μM induced apoptosis. The early-stage marker of apoptosis, i.e., decreased mitochondrial membrane potential, was observed as early as 1.5 h at 5 μM Cd. Significant (P < 0.01) reactive oxygen species (ROS) production at 5 μM Cd and 0.75 h occurred prior to the decrease of the mitochondrial membrane potential, suggesting the involvement of ROS in mitochondrial membrane damage. Glutathione (GSH) level significantly decreased after cell treatment with 5 and 10 μM Cd after 12 h (P < 0.01). Meanwhile, the intracellular free Ca(2+) concentration ([Ca(2+)] i ) of Cd-exposed cells significantly increased (P < 0.01) at 1.5 h, and pretreatment with the calcium chelator Bapta-AM partially blocked Cd-induced apoptosis. This finding indicated that the elevation of [Ca(2+)] i may play an important role in apoptosis. Overall, these results showed that oxidative stress and Ca(2+) signaling were critical mediators of the Cd-induced apoptosis of rat hepatocytes.

Quantum dot nanoparticles affect the reproductive system of Caenorhabditis elegans

Quantum dots (QDs) are an increasingly important class of nanoparticle, but little ecotoxicological data for QDs has been published to date. The effects of mercaptosuccinic acid (MSA)-capped QDs (QDs-MSA) and equivalent concentrations of cadmium (Cd) from cadmium chloride on growth and reproduction of the nematode Caenorhabditis elegans (Rhabditidae) were assessed in laboratory experiments. Growth from larvae to adults of C. elegans was unaffected by exposure to 1 µM fluorescent QDs-MSA, but adults produced more embryos and laid them prematurely. Furthermore, C. elegans exposed to QDs-MSA (1 µM) showed a high percentage of embryo mortality (19.2 ± 0.5, p < 0.001, percentage ± standard deviation) compared with unexposed nematodes (11.6 ± 0.4). An egg-laying defect phenotype was also observed at high frequency in response to 1 µM QDs-MSA exposure (38.3 ± 3.6%, p < 0.01; control 10.0 ± 2.2%). This resulted in a reduced mean life span (20.5 ± 1.1 d, p < 0.05) compared with the control (24.6 ± 1.0 d). Cadmium also caused reduced life span in C. elegans, but a low incidence of egg-laying defects was observed, suggesting that Cd and QDs-MSA affected C. elegans by different mechanisms. Furthermore, egg-laying defects caused by QDs-MSA responded to the addition of the anticonvulsant ethosuximide and to a lesser extent to the neurotransmitter serotonin, suggesting that QDs-MSA might have disrupted motor neurons during the reproduction process.

Effect of age-dependent exposure to lead on hepatotoxicity and nephrotoxicity in male rats

Lead is known to induce a broad range of physiological, biochemical, and behavioral dysfunctions in laboratory animals and humans. This includes age-specific variations in absorption, retention, and tissue distribution of lead. This study was carried out to investigate the effects of chronic exposure to lead (50 mg/L) on liver and kidneys of two different age groups of male rats treated with lead from delivery until puberty period (40 days) and postpuberty period (65 days). For this purpose, the concentrations of thiobarbituric acid reactive substance (TBARS), total thiol groups (SH), and superoxide dismutase (SOD) activity were measured in the liver and kidney of rats. Renal function was analyzed by determining creatinine, acid uric, and urea. Plasma activities of alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, and albumin were determined spectrophotometrically to evaluate hepatic function. These markers of damage were determined to assess the level of toxicity in these animals. Our results clearly show that the administration of lead produces oxidative damage in liver and kidney, as strongly suggested by the significant increase in TBARS, decrease in total SH, and the alteration of SOD activity. In young lead-exposed animals, lead-induced perturbations on the synthetic function of the liver and the kidney were more pronounced. However, nephropathy is evident for adult lead-exposed animals. It is concluded that lead induces severe hepatic and renal toxicity, which depends on the age of the animals and the target organ.

Gender differences in pulmonary inflammation following systemic cadmium administration in rats

OBJECTIVE

To examine the presence of gender differences in pulmonary inflammation evoked by acute systemic cadmium administration in rats.

METHODS

Presence of basic indicators of lung inflammation (inflammatory cytokine lung content, leukocyte infiltration and activity of cells recovered from lungs by enzyme digestion) was analyzed and compared in animals of the two sexes.

RESULTS

Intraperitoneal administration of cadmium (1.0 mg/kg) resulted in higher cadmium content in lungs of female rats. Higher tumor necrosis factor (TNF) content was noted in lung homogenates of male rats, while interleukin-6 (IL-6) content was slightly, but significantly greater in lungs of female rats. Increased leukocyte infiltration was observed in lungs of male rats, mainly due to neutrophils. Increased responsiveness to phorbol myristate acetate (PMA) stimulation was noted in cells recovered from lungs of male rats. Rise in intracellular content of myeloperoxidase (MPO) was noted in lung cells from cadmium-treated rats of both sexes, but higher in cells from male rats.

CONCLUSIONS

Presented data documented a more intense pulmonary inflammatory response to systemic cadmium administration in males, with higher IL-6 levels in lungs of female individuals. These sex differences in proinflamatory activity of cadmium in lungs should be taken into consideration in studying the remote toxicity of this heavy metal.

Role of metallothionein in cadmium traffic and toxicity in kidneys and other mammalian organs

Metallothioneins are cysteine-rich, small metal-binding proteins present in various mammalian tissues. Of the four common metallothioneins, MT-1 and MT-2 (MTs) are expressed in most tissues, MT-3 is predominantly present in brain, whereas MT-4 is restricted to the squamous epithelia. The expression of MT-1 and MT-2 in some organs exhibits sex, age, and strain differences, and inducibility with a variety of stimuli. In adult mammals, MTs have been localized largely in the cell cytoplasm, but also in lysosomes, mitochondria and nuclei. The major physiological functions of MTs include homeostasis of essential metals Zn and Cu, protection against cytotoxicity of Cd and other toxic metals, and scavenging free radicals generated in oxidative stress. The role of MTs in Cd-induced acute and chronic toxicity, particularly in liver and kidneys, is reviewed in more details. In acute toxicity, liver is the primary target, whereas in chronic toxicity, kidneys are major targets of Cd. The intracellular MTs bind Cd ions and form CdMT. In chronic intoxication, Cd stimulates de novo synthesis of MTs; it is assumed that toxicity in the cells starts when loading with Cd ions exceeds the buffering capacity of intracellular MTs. CdMT, released from the Cd-injured organs, or when applied parenterally for experimental purposes, reaches the kidneys via circulation, where it is filtered, endocytosed in the proximal tubule cells, and degraded in lysosomes. Liberated Cd can immediately affect the cell structures and functions. The resulting proteinuria and CdMT in the urine can be used as biomarkers of tubular injury.

Glycine reduces cadmium-induced alterations in the viability and activation of macrophage U937 cells

This study investigates the effect of glycine on cadmium-induced alterations on the viability and activation of the cell line U-937. In this experiment, U-937 cells were pre-treated with 16 microM cadmium (as cadmium chloride). These cadmium-treated cells were later incubated with or without glycine (1-16 microM). After 72 h, it was revealed that glycine significantly (P<0.05) reduced the tendency of cadmium to reduce the viability of the cells. U-937 cells were also treated with phorbol, 12-myristate, 13-acetate to enhance their transition to the macrophage form. Thereafter, the cells were treated with cadmium with or without glycine (1-16 microM). Twenty-four hours later, the supernatants of each cell culture were assessed for the production of tumour necrosis factor alpha (TNF-alpha), interleukin 6 (IL-6), interleukin 1 (IL-1), nitric oxide (NO), and catalase activity as indices of the activation of macrophages. The results show that glycine significantly (P<0.05) reduced the cadmium-induced production of all the markers of the activation of macrophages in a concentration-dependent manner. The findings support the immense antioxidant role of glycine.

Gender differences in acute cadmium-induced systemic inflammation in rats

OBJECTIVE

To examine the presence of gender differences in pro-inflammatory potential of cadmium in rats by comparing systemic inflammatory response to acute cadmium intoxication in animals of the two sexes.

METHODS

Basic aspects of this response were evaluated, including plasma levels of inflammatory cytokines tumor necrosis factor (TNF) and interleukin-6 (IL-6) and of major rat acute phase protein alpha 2-macroglobulin (alpha2-M), as soluble indicators of inflammation, and the number and activity of peripheral blood leukocytes, as cellular indicators of inflammation.

RESULTS

Differential increases of IL-6 and alpha2-M (higher in males than in females) in peripheral blood cell counts and types (leukocytosis and shift in the ratio of granulocytes to lymphocytes more pronounced in males vs females) and in levels of neutrophil priming (higher in males vs females) were noted.

CONCLUSION

The data document a more intense inflammatory response to cadmium administration in males. The sex differences in inflammatory effects of cadmium might be taken into consideration in studying the toxicity of this heavy metal.

Gender differences in correlations between the content of elements in rain water and the frequency of hospitalization for arterial hypertension, chronic obstructive pulmonary disease, and psoriasis in Opole Voivodship, Poland, during 2000-2002

The aim of this work is to show and give a plausible explanation to gender-dependent differences in correlations between the content of selected elements in rainwater and the frequency of hospitalization by reason of arterial hypertension, chronic obstructive pulmonary disease (COPD), and psoriasis in the area of Opolskie Voivodeship, Poland, during the period 2000-2002. The elements analyzed were sodium, potassium, calcium, magnesium, manganese, iron, total phosphorus, total nitrogen, ammonium nitrogen, zinc, copper, lead, cadmium, nickel, chromium, chloride, nitrate, and sulfate. Hospitalization due to arterial hypertension was more frequent in women, whereas those for COPD and psoriasis were more frequent in men. In the case of women hospitalized for arterial hypertension, the correlations were low, except for zinc (r = 0.47) and for cadmium (r = 0.43). In men hospitalized for COPD, all of the correlation coefficients were higher than 0.4, except for phosphorus. The coefficients for nickel, ammonia nitrogen, and total nitrogen ranged from 0.5 to 0.6 and the remaining elements from 0.6 to 0.7. In women, the correlation was limited to five elements where the coefficient was r > 0.4 for chloride, calcium, nitrate, phosphorus, and chromium. In cases of hospitalization for psoriasis, the correlation in men was between 0.4 and 0.5 for chloride, phosphorus, copper, lead, and total nitrogen and greater than 5 for sulfate, potassium, calcium, iron, manganese, nitrate, and ammonium nitrogen. The correlation in women was between 0.48 and 0.5 for ammonium nitrogen and phosphorus.

Cadmium-induced apoptosis in human normal liver L-02 cells by acting on mitochondria and regulating Ca(2+) signals

Cadmium is a well-known toxic compound for the liver. It has been demonstrated to induce hepatotoxicity partly via apoptosis, but no uniform mechanism of apoptosis has so far been proposed. This study was first to determine whether cadmium-induced apoptosis in L-02 cells, second to observe the mechanism of cadmium-induced apoptosis. Studies of morphology, DNA fragmentation and apoptotic rate demonstrated that 60μM cadmium induced apoptosis with strong effects on cell viability. A concomitant time-dependent decrease of Bcl-2 and mitochondrial transmembrane potential (ΔΨ(m)) was observed. Subsequently, increase of caspase-3 activity and release of mitochondrial AIF were detected. However, cell pretreatment with a broad-specificity caspase inhibitor (Z-Asp) did not abolish apoptosis. These data demonstrated that the apoptotic events involved a mitochondria-mediated apoptotic pathway but not necessarily caspase-dependent signaling. On the other hand, intracellular free Ca(2+) concentration ([Ca(2+)](i)) of cadmium-exposed cells had significant increases and the Bapta-AM, a well-known calcium chelator, pretreatment partially blocked cadmium-induced apoptosis, indicating that the elevation of [Ca(2+)](i) may play an important role in the apoptosis. Together, these results support the notion that cadmium-induced hepatotoxicity is comparable to effects in L-02 by inducing apoptotic pathways on the basis of acting on mitochondria and regulating Ca(2+) signals.

Multiple stressor effects of radiation and metals in salmon (Salmo salar)

These experiments were designed to look at the cellular effects in key organs in Atlantic salmon (Salmo salar) after exposure in vivo to radiation and subtoxic levels of aluminum (Al) and cadmium (Cd), alone or in combination. Salmon (25g) were exposed to a single 0.5Gy dose of gamma-irradiation in water containing Cd, Al or Cd+Al. Three fish per group were sacrificed after 1h and the liver, pronephros, fin and gill of each was dissected. Small explants of each tissue were set up. After 2 days, the culture medium was harvested and filtered then placed on a reporter cell line for determination of stress signal activity (bystander effects). Radiation in combination with Cd and/or Al, caused bystander effects in tissues harvested from in vivo exposed salmon. The effects vary between different organs and are not consistently additive or synergistic for a given treatment. Tissue type appears to be critical. Liver cultures produce a toxic factor which is lethal to reporter cells, and therefore no liver data could be obtained. It is hoped that this stress signal response will prove to be a useful indicator of environmental stress in species inhabiting aquatic ecosystems.

Characterization of cadmium uptake in human intestinal crypt cells HIEC in relation to inorganic metal speciation

Cadmium (Cd) uptake was studied under inorganic exposure conditions in normal human intestinal crypt cells HIEC. The uptake time course of 0.3 microM Cd in a serum-free chloride medium was analyzed according to a first order equation with rapid initial (U0) and maximal (Umax) accumulation values of 14.1+/-1.4pmol/mgprotein and 41.4+/-2.0 pmol/mgprotein, respectively. The presence of a 300-fold excess of unlabeled Cd dramatically decreased tracer uptake, showing the involvement of specific mechanism(s) of transport. Our speciation studies revealed the preferential uptake of the free ion Cd2+, but also suggested that CdCln(2-n) species may contribute to Cd accumulation. Specific mechanisms of transport of very high and similar affinity (Km approximately 5 microM) have been characterized under both chloride and nitrate exposure conditions, but a two-fold higher capacity (Vmax) was estimated in the nitrate medium used to increase [Cd2+] over chlorocomplex formation. A clear inhibition of 109Cd uptake was observed at external acidic pH under both exposure media. An La-inhibitible 46% increase in 109Cd uptake was obtained in nominally Ca-free nitrate medium, whereas Zn provided additional inhibition. These results show different kinetic parameters for Cd uptake as a function of inorganic metal speciation. Cd2+ uptake would not involve the H+-coupled symport NRAMP2 but would be related instead to the Ca and/or Zn pathways. Because proliferative crypt cells play a critical role in the renewal process of the entire intestinal epithelium, studies on the impact of Cd on HIEC cell functions clearly deserve further investigation.

C. elegans metallothioneins: new insights into the phenotypic effects of cadmium toxicosis

Metallothioneins are considered to be the primary player in the detoxification of and protection from cadmium, a teratogen, mutagen and potentially lethal heavy metal. The nematode Caenorhabditis elegans has only two metallothioneins, mtl-i and mtIl-2, thus making it an ideal organism to investigate the phenotypic effects of cadmium toxicosis. The functional importance of metallothioneins in cadmium trafficking was highlighted through the generation of viable green fluorescent protein (GFP) expressing transgenes, a metallothionein null allele, as well as RNAi mediated metallothionein knock-downs. A highly sensitive dose and temporal transcriptional response to cadmium, but not copper or zinc, was shown to be equally prevalent in both isoforms. No measurable compensatory up-regulation of mtl-l could be observed in the null allele of mtl-2, suggesting that both isoforms are independent and not synergistic in their mode of action. Exposure to cadmium affected all demographic indices measured, manifested by a reduction in body size, generation time, brood size and lifespan. These effects were magnified in the knock-out or wild-type subjected to a knock down by RNAi, however, only in the presence of cadmium. This substantiates the notion that metallothioneins play a pivotal role in the protection from cadmium toxicosis. Finally, an earthworm metallothionein-GFP construct could be activated in C. elegans upon exposure to cadmium, the results providing further evidence that the transcriptional control of metallothioneins is fundamentally divergent in lower invertebrates and not mediated via MTF-1 as in more complex organisms.

Cadmium uptake in rat hepatocytes in relation to speciation and to complexation with metallothionein and albumin

Cadmium (Cd) uptake has been studied in primary cultures of rat hepatocytes focusing on the impact of inorganic and organic speciation. Uptake time-course studies over a 60-min exposure to 0.3 microM (109)Cd revealed a zero-time uptake and a slower process of accumulation which proceeds within minutes. (109)Cd uptake showed saturation kinetics (K(m) = 3.5 +/- 0.8 microM), and was highly sensitive to inhibition by Zn and Hg. There was no evidence for sensitivity to the external pH nor for any preferential transport of the free cation Cd(2+) over CdCl(n) (2-n) chloro-complexes. According to the assumption that only inorganic metal species are available, metal uptake decreased upon albumin (BSA) addition to the exposure media. In contrast, higher levels of (109)Cd accumulation were obtained under optimal conditions for Cd complexation by MT. Comparison among uptake data obtained under inorganic and organic conditions revealed that Cd-MT would be taken up 0.4 times as rapidly as Cd(inorg). We conclude that uptake of Cd in rat hepatocytes involves specific transport mechanism(s) subjected to Zn or Hg interactions. Uptake of inorganic Cd is not proportional to the levels of free Cd(2+) and does not involve the divalent cation transporter DCT1 nor the co-transporter Fe(2+)-H(+) NRAMP2. We found Cd-MT but not Cd-BSA to be available for the liver cells, and have estimated a binding affinity four orders of magnitude higher for Cd complexation with MT compared to BSA; MT may have a significant role in Cd delivery to the liver.