Low Doses Of Cadmium Research Articles

Responses of Lemna trisulca L. (Duckweed) exposed to low doses of cadmium: thiols, metal binding complexes, and photosynthetic pigments as sensitive biomarkers of ecotoxicity

Lemna species are reported to accumulate a variety of metals from contaminated/polluted sites. Cadmium is a nonessential element for plant metabolism. In this work, we aimed to investigate physiological responses to low doses of cadmium (up to 100 microM). From exposure to the lowest Cd concentration (1 microM) to the highest (100 microM), photosynthetic pigments (Chl a, b, carotenoids) and the ratios of Chl a/b, Chl (a + b)/carotenoids decreased as a function of the Cd dose. The content of soluble proteins decreased in a dose-dependent manner, while total soluble thiols drastically increased. In Cd-treated fronds, the dose-dependent accumulation of a polypeptide with an apparent molecular weight of 24 kDa, as well as the appearance of two smaller polypeptides with molecular weights <6.5 kDa, was observed in sodium dodecyl sulfate polyacrylamide gel electrophoresis. Our results show that in Lemna trisulca, different adaptative mechanisms may be involved in counterbalancing low and high doses of a particular toxicant (cadmium). This feature makes this plant potentially useful material in biomonitoring and phytotoxicity testing.

Quantitative Study of Leydig Cell Populations in Mice Exposed to Low Doses of Cadmium

Leydig cell morphological changes were evaluated using morphometric and stereological methods in male mice exposed to low doses of cadmium. A possible reversibility of the changes after cadmium withdrawal was also considered. Nuclear morphological parameters and stereological densities of the Leydig cell population were lower in the cadmium-exposed groups than in the control. The withdrawal of cadmium did not lead to any significant recovery of the morphological parameters. Nevertheless, numerical density increased significantly in the withdrawn groups, suggesting that the hyperplasia of interstitial cells could try to relieve morphological damage after cadmium withdrawal.

Long‐term extracellular signal‐related kinase activation following cadmium intoxication is negatively regulated by a protein kinase C‐dependent pathway affecting cadmium transport

Extracellular signal-related kinase (ERK) is a well-known kinase taking part in a signal transduction cascade in response to extracellular stimuli. ERK is generally viewed as a kinase that is rapidly and transiently phosphorylated following mitogenic stimulation. This activation results in ERK phosphorylating further downstream targets, thus transmitting and amplifying the original stimulus, and ultimately resulting in the onset of cellular proliferation and/or protection against apoptosis. More recently, several groups have identified a strikingly new type of ERK activation that results in cell death. This activation is very different from conventional ERK activation, as it occurs several hours after the original stimulation, and results in the sustained phosphorylation of ERK, which can be observed for up to several days. One way of inducing this delayed ERK activation is by low-dose cadmium treatment. We show here that sustained ERK activation induced by cadmium in human kidney-derived cells is inhibited following protein kinase C (PKC) activation, even when this activation occurs hours before intoxication. Furthermore, PKC inhibition results in an enhanced ERK activation in response to cadmium, even when inhibition is induced hours before intoxication. PKCepsilon appears to be the most implicated isotype in this phenomenon. Finally, we present evidence suggesting that the ZIP8 transporter is involved in this process, as multiple small interfering RNAs against ZIP8 have a protective effect against cadmium treatment. Our results indicate that PKC activation negatively affects ZIP8 transporter activity, thus protecting cells against cadmium poisoning.

The changes of the immune circumstance in the testicular tissues of mice treated with low dose of cadmium

精細管内のhaploid germ cellsは、様々な自己抗原を含むことがわかっているが、Sertoli細胞間の結合で構成される血液−精巣関門 (blood-testis barrier=BTB) によって免疫系 (精巣間質マクロファージを含む) からある程度守られているとされている。しかしながら、直精細管および精巣網には、投与された抗体やhorseradish peroxidase (HRP) が管内へ若干入り込むため、その部位のBTBは生理学的に脆弱なことが明らかとなってきている。精巣毒性物質として知られているカドミウム (CdCl2) は、主に精巣毛細血管障害を引き起こし、BTBの破壊や精上皮壊死を伴うことが報告されているが、本研究では、精子形成障害を惹起しない程度のCdCl2微量投与 (1mg/kgおよび3mg/kg) による精巣の免疫学的組織環境変化 (CdCl2投与12および72時間後の外来性HRPと内在性IgGの精巣内分布の変化) を、8週齢雄A/Jマウスを用いて組織化学的に検討した。その結果、CdCl2投与によって、HRP (屠殺30分前に投与) は直精細管・精巣網周囲の間質に強い集積を認めたが、間質の定住マクロファージによるHRP取り込みは精巣全域で逆に弱くなった。また、基底膜を超えて管内 (精細管→直精細管→精巣網) の上皮細胞に取り込まれたり上皮細胞間に侵入するHRP像を一部に認めたが、特に直精細管・精巣網に選択的に起こるものでなかった。一方、内在性のIgGは、HRPのような局在性分布や定住マクロファージによる取り込みを、対照群、CdCl2投与群ともに認めず、精細管→直精細管→精巣網への侵入像も精細管の一部に観察するのみであった。よって、精子形成障害を引き起こさない程度の微量CdCl2投与によっても、精巣間質における微小循環やマクロファージの機能に障害が起こることが示唆された。また、明らかなBTBの破綻とは異なる精細管→直精細管→精巣網の基底膜の一部に破壊が起こることが示唆された。しかし、その破壊は生理学的にBTBが脆弱とされる直精細管・精巣網に強く起こるということはないことがわかった。

Role of Oxidative Stress, Apoptosis, and Intracellular Homeostasis in Primary Cultures of Rat Proximal Tubular Cells Exposed to Cadmium

Cadmium (Cd) is a known nephrotoxic element. In this study, the primary cultures of rat proximal tubular (rPT) cells were treated with low doses of cadmium acetate (2.5 and 5 microM) to investigate its cytotoxic mechanism. A progressive loss in cell viability, together with a significant increase in the number of apoptotic and necrotic cells, were seen in the experiment. Simultaneously, elevation of intracellular [Ca(2+)]i and reactive oxygen species (ROS) levels, significant depletion of mitochondrial membrane potential(Delta Psi) and cellular glutathione (GSH), intracellular acidification, and inhibition of Na(+), K(+)-ATPase and Ca(2+)-ATPase activities were revealed in a dose-dependent manner during the exposure, while the cellular death and the apoptosis could be markedly reversed by N-acetyl-L-cysteine (NAC). Also, the calcium overload and GSH depletion were significantly affected by NAC. In conclusion, exposure of rPT cells to low-dose cadmium led to cellular death, mediated by an apoptotic and a necrotic mechanism. The apoptotic death might be the chief mechanism, which may be mediated by oxidative stress. Also, a disorder of intracellular homeostasis induced by oxidative stress and mitochondrial dysfunction is a trigger of apoptosis in rPT cells.

Suppressive effects of cadmium on neurons and affected proteins in cultured developing cortical cells

The purpose of the present study was to examine the in vitro effects of low-dose cadmium (Cd) on developing cortical cells. The cortical cells removed from fetuses (embryonic day 15) were treated with 10 nM of Cd for 24 h. The effects of Cd on dendritic and synaptic development were immunocytochemically observed with anti-microtubule associated protein-2 (MAP2) and anti-synapsin I antibodies, respectively. Administration of Cd suppressed dendritic as well as synaptic development at 10 nM. By two-dimensional gel electrophoresis and liquid chromatography–tandem mass spectrometric (LC/MS/MS) analysis, we identified three proteins with different expression after Cd-treatment; dihydropyrimidinase-related protein 2 (DRP-2/CRMP-2), 14-3-3-epsillon and calmodulin (CaM). Though the number of identified proteins was small, these proteins are known to be involved in neuronal development. The present study demonstrated the morphological effects as well as affected proteins in Cd-treated cortical cells, providing tools and insights in elucidating mechanisms how low-dose Cd distorts brain development.

Transcriptome analyses in normal prostate epithelial cells exposed to low-dose cadmium: oncogenic and immunomodulations involving the action of tumor necrosis factor.

BackgroundCadmium is implicated in prostate carcinogenesis, but its oncogenic action remains unclear.ObjectivesIn this study we aimed to decipher changes in cell growth and the transcriptome in an immortalized human normal prostate epithelial cell line (NPrEC) following exposure to low-dose Cd.MethodsSynchronized NPrEC cells were exposed to different doses of Cd and assayed for cell viability and cell-cycle progression. We investigated changes in transcriptome by global profiling and used Ingenuity Pathways Analysis software to develop propositions about functional connections among differentially expressed genes. A neutralizing antibody was used to negate the effect of Cd-induced up-regulation of tumor necrosis factor (TNF) in NPrEC cells.ResultsExposure of NPrEC to 2.5 μM Cd enhanced cell viability and accelerated cell-cycle progression. Global expression profiling identified 48 genes that exhibited ≥ 1.5-fold changes in expression after 4, 8, 16, and 32 hr of Cd treatment. Pathway analyses inferred a functional connection among 35 of these genes in one major network, with TNF as the most prominent node. Fourteen of the 35 genes are related to TNF, and 11 exhibited an average of > 2-fold changes in gene expression. Real-time reverse transcriptase-polymerase chain reaction confirmed the up-regulation of 7 of the 11 genes (ADAM8, EDN1, IL8, IL24, IL13RA2, COX2/PTGS2, and SERPINB2) and uncovered a 28-fold transient increase in TNF expression in Cd-treated NPrEC cells. A TNF-neutralizing antibody effectively blocked Cd-induced elevations in the expression of these genes.ConclusionsNoncytotoxic, low-dose Cd has growth-promoting effects on NPrEC cells and induces transient overexpression of TNF, leading to up-regulation of genes with oncogenic and immunomodulation functions.

Biochemical Evaluation of The Effects of Vitamin C in Rats Exposed to Sub-Chronic Low Doses of Cadmium

In this study, the effects of vitamin C in cadmium-induced toxicity were investigated. Wister rats in different groups were exposed to cadmium (as CdSO4.8H2O), by sub-cutaneous injection, at doses of 1.0, 2.0 and 3.0 μg/kg body weight, with or without vitamin C supplementation, for four weeks. The serum alkaline phosphatase, of group III of the vitamin C untreated rats significantly (p<0.05) increased, all the groups of the vitamin C treated rats also had significantly (p<0.05) increased serum alkaline phosphatase. The bone protein level and serum calcium of the vitamin C untreated group of rats, significantly (p<0.05) decreased relative to its control. The bone calcium of the vitamin C treated rats significantly (p<0.05) decreased (group IIIc from 2896.30±344.64 mg Ca/dl to 1049±101.43 mg Ca/dl) while the bone phosphate of this same group of rats, significantly (p<0.05) increased. For some parameters evaluated, the effects of cadmium on the vitamin C treated rats were less pronounced, indicating that vitamin C may be protective against cadmium-induced toxicity. Place of research: Department of Biochemistry, University of Benin, Benin City, Nigeria. Research funding: The research was privately funded.

Prevention of HIF-1 activation and iNOS gene targeting by low-dose cadmium results in loss of myocardial hypoxic preconditioning in the rat

This study aimed to underline the interaction between hypoxia-inducible factor-1 (HIF-1) and the inducible nitric oxide synthase (iNOS) gene in vivo and their contribution to the delayed myocardial preconditioning induced by acute intermittent hypoxia (IH) in the rat using chromatin immunoprecipitation and pharmacological inhibition by low-dose cadmium. Langendorff-perfused hearts of Wistar rats exposed to normoxia or IH 24 h earlier were submitted to global ischemia and reperfusion. Effects of iNOS inhibition by aminoguanidine (100 microM) before ischemia or of low-dose injection of cadmium chloride (1 mg/kg) before normoxia or IH were tested. Myocardial HIF-1 and iNOS quantification and in vivo chromatin immunoprecipitation of HIF-1 bound to the iNOS gene promoter were performed. IH-induced delayed cardioprotection resulted in an improvement in coronary flow and functional recovery at reperfusion and a decrease in infarct size. Myocardial HIF-1 activity was increased with resulting targeting of the iNOS gene. Aminoguanidine abolished the cardioprotective effects of IH. Cadmium chloride treatment before IH prevented myocardial HIF-1 activation (72.3 +/- 4.0 vs. 42.1 +/- 9.7 arbitrary units after cadmium chloride; P < 0.05), targeting of the iNOS gene, iNOS expression, and preconditioning (infarct size: 15.9 +/- 5.6 vs. 30.1 +/- 5.4% after cadmium chloride; P < 0.05). This study is the first to demonstrate the interaction of HIF-1 with the myocardial iNOS gene in situ after hypoxic preconditioning. Prevention of HIF-1 activation and iNOS gene targeting by a single low dose of cadmium abolished the delayed cardioprotective effects, bringing insight into the cardiovascular consequences of cadmium exposure.

Effects of long-term low-dose cadmium exposure on genomic DNA methylation in human embryo lung fibroblast cells

Cadmium is a toxic transition metal of continuing occupational and environmental concern. As a well-recognized human carcinogen, its carcinogenic mechanisms are still poorly understood. Cadmium has long been considered a non-genotoxic carcinogen and thought to act through epigenetic mechanisms. In the present study, we tested the effects of long-term low-dose cadmium exposure on DNA methylation in human embryo lung fibroblast (HLF) cells. After 2 months of exposure to 0–1.5 μmol/L cadmium, both the level of genomic DNA methylation and the enzyme activity of DNA methyltransferases (DNMTs) were increased in a concentration-related manner. Moreover, our results showed that cadmium exposure up-regulated the mRNA levels of DNMT1, DNMT3a and DNMT3b at higher concentrations. We further tested the growth dynamics of HLF cells, and observed significantly elevated growth rates, decreased cell population of G0/G1-phase and increased cell population of S-phase at 0.9, 1.2, and 1.5 μmol/L concentrations. Our study indicated that long-term low-dose cadmium exposure could disrupt DNA methylation, which may be one of the possible underlying carcinogenic mechanisms of cadmium.

Chronic exposure to environmentally-relevant, low-doses of cadmium (Cd) in a rat model mimics effects on spermatogenesis observed in infertile men with varicoceles

Infertile men with varicoceles typically exhibit reduced sperm count, reduced motility, round spermatid maturation arrest and altered Leydig cell function. Testicular Cd is elevated in 60% of biopsies of varicocele testes. Our goal was to determine, using an animal model, whether elevated Cd contributes to abnormal semen parameters and, if so, to identify underlying mechanisms with the aim of developing medical therapies. Rats were exposed to low level Cd in drinking water from puberty to maturity (PN weeks 5–21). We have previously reported that sperm motility is decreased in this model system. In this study, we looked for changes in sperm number, loss of testicular germ cells and changes in RNA expression profiles compared to controls. Male Wistar Hanover rats were fed a nutritionally complete solid diet without Cd and given deionized drinking water containing one of four levels of Cd (0, 5, 50 or 100 mg/L; corresponding to 0–13 mg/kg/d Cd) in the form of Cd Cl2 for 1,4, 8 or 16 weeks. At each time, epididymal sperm and testes were collected. Sperm count was assessed using a hemocytmeter, testicular Cd levels by atomic absorption, testicular testosterone (T) by RIA, histology by H&E staining, apoptosis by DAPI staining, and gene expression using Affymetrix GeneChip Rat Genome 230 2.0 microarrays. Cd accumulated in testes in response to time (ANOVA, P<0.001) and dose (ANOVA, P<0.001). T fell with Cd exposure (ANOVA, P<0.014–P<0.003), as did epididymal sperm count (ANOVA, P<0.007) while apoptosis increased (t-test, P<0.01). Testes sections showed selective loss of postmeiotic stages with increasing Cd. Cd exposures were associated with increased nitric oxide synthase mRNA levels (iNOS, eNOS), NOS inhibitor mRNA down-regulation (e.g., Prmt3), a decrease in mRNAs functioning in late stages of sperm maturation (TP1, TP2, protamines), disregulation of apoptosis factors (caspase 8 decreases; FasL, p53 and Bid increase), and up-regulation of genes involved in steroid hormone biosynthesis (e.g., HSD17β3). Cd alone induces many aspects of human varicocele-related infertility in this rat model: altered apoptosis, increased oxidative stress enzymes, endocrine disruption. Cd induces these changes by affecting levels of testicular mRNAs. This argues that Cd is a significant co-morbidity factor and suggests the need for the systematic study of specific supplements, e.g., antioxidants and antiestrogens.

Effects of perinatal exposure to low-dose cadmium on thyroid hormone-related and sex hormone receptor gene expressions in brain of offspring

Perinatal cadmium (Cd) exposure has been shown to alter behaviors and reduce learning ability of offspring. A few studies have shown that Cd reduced serum thyroid hormones (THs), which are important for brain development during the perinatal period. Brain specific genes, neurogranin (RC3) and myelin basic protein (BMP), are known to be regulated by TH through TH receptors (TR). It has been suggested that RC3 may play roles in memory and learning. In addition, Cd has been suggested to have estrogen-like activity. To evaluate the effects of perinatal low-dose exposure to Cd on thyroid hormone-related gene (RC3, TR-β1, MBP, RAR-β) and sex hormone receptor gene (ER-α, ER-β and PgR) expressions in the brain and on behaviors of offspring, mice were administered with 10 ppm Cd (from gestational day 1 to postnatal day 10) and/or 0.025% methimazole (MMI; anti-thyroid drug) (from gestational day 12 to postnatal day 10) in drinking water. Also, 0.1% MMI was administered as a positive control (high MMI group). RC3 mRNA expression was reduced in the female brain of combined exposure and high MMI groups and was negatively correlated with the activity in the open-field. ER-α, ER-β and PgR mRNA expressions were decreased in male and female Cd, and female Cd + MMI groups, respectively; among these changes the reduced expression of PgR was opposite to estrogenic action. These results suggested that perinatal exposure to Cd disrupted the gene expressions of sex hormone receptors, which could not be considered to be a result of estrogenic action. Our study indicates that alteration in the gene expressions of RC3 and sex hormone receptors in the brain induced by perinatal Cd and MMI exposure might be one mechanism of developmental toxicity of Cd.

Effect of Low Level Cadmium Exposure on the Bone Density of the Residents Near a Closed Copper Mine

P-675 Introduction: Long-term environmental exposure to low dose cadmium can induce renal damage and bone loss. However, there is a controversy whether bone pathology can be developed without nephropathy. The authors evaluated the renal function and bone density in relation to long-term cadmium exposure among residents near an abandoned mine in rural Korea. Methods: One hundred two residents near the closed copper mine and 149 residents from two control villages were examined with urine and blood cadmium, urinary β2-microglobulin (β2-MG), α1-microglobulin (α1-MG) and N-acetyl-beta-glucosaminidase (NAG). Bone density was measured with portable DEXA and radiographic absorptiometry at heel, forearm, and carpal bone. Fifty eight residents with blood or urine cadmium greater than 95 percentile of controls (blood cadmium 3.8 μg/L or urine cadmium 3.7 μg/g cr) were screened and examined with 24 hour urine cadmium and bone density at femur and vertebra. Results: Mean level of urine cadmium was higher in the exposed population (2.1 μg/g cr, range 0.1–11.6 μg/g cr) compared to the controls (1.5 μg/g cr, range 0.1–14.7 μg/g cr)(p< 0.001). Urinary β 2-MG, α 1-MG and NAG level were not different between groups. Bone density in the exposed population had a decreasing tendency by the actual duration of residence after controlling for the age, gender, and body weight. Among 57 residents with high urine or blood cadmium level, bone density of heel had positive correlation with actual duration of residence. 24 hour urine cadmium (mean 4.4 μg/g cr) was highly correlated with bone density. On multiple regression, 24 hour urine cadmium was a strong predictor of bone density, but urinary proteins were not significant predictors. On bone density measurement of axial bones, 76% had osteoporotic change. Discussion and Conclusions: From this study, we found that high prevalence of osteoporosis in the exposed population was related to environmental exposure to cadmium. However, there was no evidence of renal dysfunction among exposed population and controls. It is suggested that the osteoporosis related to environmental cadmium exposure may develop without renal damage.

Chronic exposure of mice to environmentally relevant, low doses of cadmium leads to early renal damage, not predicted by blood or urine cadmium levels

Mice were exposed to cadmium (Cd) concentrations ranging from 0 to 100mg CdCl2/l in the drinking water for 1, 4, 8, 16 and 23 weeks. Urine samples were taken regularly, Cd content was determined in blood, liver, kidney and urine and histological analyses of the kidney were performed.Kidney cortex Cd content increased linearly with time and dose, while blood levels reached a plateau at 8 weeks and liver at 16 weeks in mice exposed to 100mg CdCl2/l after which both started to decrease. Urinary Cd levels were not correlated with the kidney Cd content.A multivariate regression model taking into account the actual Cd intake, calculated from the volume of water taken in by each animal and the exposure concentration, confirmed that blood is an indicator of acute exposure, while kidney Cd content is a reliable indicator of chronic exposure. The urinary protein content was significantly increased from 16 weeks on in mice exposed to 100mg CdCl2/l (p<0.05), while other signs of proximal tubular damage (glucosuria, enzymuria) were not detected. Histologically more vacuoles and lysosomes were present in the proximal tubule cells with increasing time and dose.The results indicate that chronic exposure to low doses of Cd induced functional and histological signs of early damage at concentrations in or below the ones generally accepted as safe. Our study does not corroborate the statement that urine Cd levels are a reliable indicator of total Cd body burden, at least when the body burden is low.

Quantitative changes in the testicular structure in mice exposed to low doses of cadmium

The purpose of this study was to quantify the consequences of a long-term exposure to low doses of cadmium on the testicular structure. Sexually mature male mice were orally exposed to cadmium (0.015 g/1 of CdCl2 in drinking water) for 1, 3, 6 and 12 months and then sacrificed; cadmium withdrawal was also considered in two groups raised with cadmium for 3 and 6 months, and without cadmium for 3 and 6 months before sacrifice, respectively. Morphometrical and stereological estimations were applied to quantify the structural constituents of the testes. The morphological parameters (testicular mass and size) were significantly decreased at 6 and 12 months of cadmium exposure. Interstitium was the testicular constituent most sensitive to cadmium so that significant decreases in the volume fractions of interstitium and Leydig cells were recorded as from 3 months of cadmium exposure. Cadmium-exposed seminipherous tubules showed increased diameters and lumens together with decreased tubular densities and epithelial percentages.

Detection of toxic effects of Cd2+ on different fish species via liver cytochrome P450-dependent monooxygenase activities and FTIR spectroscopy

The in vivo and in vitro effects of Cd2+ and the CYP1A inductor beta-naphthoflavone(beta-NF) on the hepatic cytochrome P450 (Cyt 450) monooxygenases were studied in silver carp (Hypophthalmichtys molitrix V.), wels (Silurus glanis L.), and carp (Cyprinus carpio). In vivo treatment of carp with a high dose of Cd2+ (10 mg kg(-1), for 3 days) caused a strong inhibition of 7-ethoxyresorufin-O-deethylase (EROD) and a lower inhibition of 7-ethoxycoumarin-O-deethylase (ECOD) activity. The low-dose cadmium treatment (2 mg kg(-1) Cd2+, for 6+3 days) resulted in 4-fold increase in EROD and a 3-fold increase in ECOD activity. The combined treatment with Cd2+ and beta-NF in both cases led to a loss of EROD inducibility. The silver carp and wels were treated with 10 mg L(-1) Cd2+ for 72 h in water. The Cyt P450 content in the wels liver microsomes was increased significantly after treatment for 48 h, whereas there was only a slight, not significant increase in Cyt P450 content in the silver carp microsomes. While the Cd2+ treatment resulted in inhibition of the CYP1A isoenzymes (EROD and ECOD), the APND (aminopyrene-N-demethylase, CYP2B or CYP3A isoenzyme) activity was increased 3- to 4-fold in both fish species. In vitro experiments of the effect of Cd2+ led to a concentration-dependent inhibition in all three investigated fish species. The ECOD isoenzyme of silver carp was the most sensitive to Cd2+. The lowest concentration of Cd2+ resulted in 50% inhibition. The APND isoenzyme was similarly sensitive to Cd2+ in all three investigated fish species. The most sensitive species was the wels, and the least sensitive were the carp isoenzyme. FTIR spectroscopy confirmed that cadmium caused damage to the protein structure. These results support the enzyme activity measurements measured in vivo and in vitro.

Cardiac Metallothionein Induction Plays the Major Role in the Prevention of Diabetic Cardiomyopathy by Zinc Supplementation

Our previous studies showed that transgenic mice that overexpress cardiac-specific metallothionein (MT) are highly resistant to diabetes-induced cardiomyopathy. Zinc is the major metal that binds to MT under physiological conditions and is a potent inducer of MT. The present study therefore explored whether zinc supplementation can protect against diabetic cardiomyopathy through cardiac MT induction. Diabetes was induced in mice (C57BL/6J strain) by a single injection of streptozotocin. Half were supplemented intraperitoneally with zinc sulfate (5 mg/kg) every other day for 3 months. After zinc supplementation, mice were maintained for 3 more months and then examined for cardiomyopathy by functional and morphological analysis. Significant increases in cardiac morphological impairment, fibrosis, and dysfunction were observed in diabetic mice but not in diabetic mice supplemented with zinc. Zinc supplementation also induced a significant increase in cardiac MT expression. The role of MT in cardiac protection by zinc supplementation was examined in cultured cardiac cells that were directly exposed to high levels of glucose (HG) and free fatty acid (FFA) (palmitate), treatment that mimics diabetic conditions. Cell survival rate was significantly decreased for cells exposed to HG/FFA but did not change for cells exposed to HG/FFA and pretreated with zinc or low-dose cadmium, each of which induces significant MT synthesis. When MT expression was silenced with the use of MT small-interfering RNA, the preventive effect of pretreatment with zinc or low-dose cadmium was abolished. These results suggest that the prevention of diabetic cardiomyopathy by zinc supplementation is predominantly mediated by an increase in cardiac MT.

Headliners: Cadmium-Induced Disease: Discovery of Gene Responsible for Cadmium Transport in Mice

Dalton TP, He L, Wang B, Miller ML, Jin L, Stringer KF, Chang X, Baxter CS, Nebert DW. 2005. Identification of mouse SLC39A8 as the transporter responsible for cadmium-induced toxicity in the testis. Proc Natl Acad Sci USA 102:3401–3406. Cadmium is a toxic and carcinogenic nonessential metal released from mining, smelting, battery manufacturing, and coal burning. Among other routes, humans are exposed to cadmium by smoking cigarettes and eating contaminated seafood or plants grown in contaminated soil. Environmental levels of cadmium have risen along with advances in industrialization, and the role of cadmium in human disease is therefore of increasing concern. Now NIEHS grantee Daniel W. Nebert and colleagues have discovered a gene responsible for the transport of cadmium in mice, which hints at a target that could be employed to prevent the toxic effects of cadmium in humans. Cadmium is readily absorbed through the lungs, intestines, and skin, and accumulates in the kidneys. The toxic mechanisms of cadmium are not well understood, but it is known to act intracellularly, causing damage particularly to the lungs, kidneys, bone, central nervous system, and reproductive tissues. Cadmium is also known to cause abnormalities in the developing embryo. The testis is a sensitive marker of cadmium exposure; cadmium-induced testicular necrosis is common across all studied animal species having testes. Exposure to this metal is a significant problem in many developing countries, where undernourishment and iron deficiency are associated with increased cadmium toxicity. Nebert and colleagues administered low doses of cadmium to mice and demonstrated that the SLC39A8 (ZIP8) protein, coded by the Slc39a8 gene, transported cadmium to the testis, causing vascular endothelial cell injury and subsequent testicular tissue death. Using in vitro models, the research team found that vascular endothelial cells from cadmium-insensitive mice did not accumulate ZIP8 mRNA, whereas cells from cadmium-sensitive mice did. The team suggests, therefore, that loss of vascular endothelial ZIP8 mRNA expression in the insensitive strains protected the mice’s testes against cadmium toxicity. Nebert and colleagues suspect that ZIP8 is normally responsible for the transport of other metals such as manganese and zinc, and that cadmium “participates as an opportunistic hitchhiker.” Because humans carry the analogous SLC39A8 gene, these findings have identified a potential target for exploration in preventing the toxic effects of cadmium in exposed people.

Biomarker responses in juvenile rainbow trout (Oncorhynchus mykiss) after single and combined exposure to low doses of cadmium, zinc, PCB77 and 17β-oestradiol

The objective of this study was to examine (i) the biochemical responses of rainbow trout exposed to sublethal water concentrations of the metals cadmium (Cd) (1.5 μg l−1) and zinc (Zn) (150 μg l−1); and (ii) the potential combined effects when applied in mixture (Cd/Zn) with and without co-exposure to model organic chemicals 3,3′,4,4′-tetrachlorobiphenyl (PCB77) (1 mg kg−1) and 17β-oestradiol (E2) (0.5 mg kg−1). After 21 days of exposure, several biomarkers were assessed in the liver (enzymatic and non-enzymatic antioxidants, heat shock proteins [HSP70 and HSP60], ethoxyresorufin-O-deethylase [EROD]) and in the plasma (vitellogenin [Vtg], aminotransferases). Plasma aminotransferases were not affected, whereas the other biomarkers showed different patterns of response depending on the treatment. For example, Cd, and Zn to a lesser extent, induced an adaptive response in the liver shown by an increase in antioxidant defences (total glutathione [GSH], superoxide dismutase, Trolox equivalent antioxidant capacity [TEAC]), without any impairment of GSH redox status or induction of heat shock proteins. Antagonistic effects were observed in GSH-related biomarkers after Cd/Zn exposure. PCB77 strongly induced EROD activity, HSP70 and TEAC. Co-exposure with metals did not modulate significantly the effects of PCB77. E2 induced Vtg and inhibited liver antioxidants and basal EROD activity. These inhibitory effects were suppressed in fishes exposed to E2 + Cd/Zn, suggesting additive effects of E2 and metals. In addition, E2-induced Vtg was not altered by metals. Multivariate analyses confirmed some correlation between the biomarkers. The use of complementary biomarkers is necessary to discriminate different treatments and to highlight interactive effects.

Effects of low-dose cadmium exposure on biological examinations

We conducted an epidemiological study to investigate the effects of low-dose cadmium (Cd) exposure on human health in a specific area of a town in Japan where low Cd concentration was detected in rice. We compared clinical findings, urinary and whole blood Cd concentrations, and indicators of renal dysfunction between the polluted area and the control area. The study employed 44 men and 54 women from the polluted area and 21 men and 29 women from the control area. In urine analysis, as indicators of Cd exposure and possible related renal dysfunction, Cd, β 2-microglobulin (β 2-MG), α 1-microglobulin (α 1-MG), N-acetyl-β- d-glucosaminidase (NAG), total protein, inorganic phosphorus, lysozyme and creatinine were quantitatively measured. In blood analysis, serum IP and creatinine and whole blood Cd were measured. No case of renal dysfunction due to Cd exposure was confirmed. However, both the urinary and whole blood Cd of the polluted area were significantly higher than those of the control area for both sexes. Urinary β 2-MG did not differ between the two areas. For women, urinary α 1-MG was significantly higher in the polluted area than in the control area. In correlation analysis, β 2-MG, α 1-MG and NAG, were positively correlated with both of urinary and whole blood Cd for men and women in the polluted area except for between urinary β 2-MG and urinary Cd for men. In the control area, the sole positive correlation observed was between urinary β 2-MG and whole blood Cd for men. We then examined the determinants of variations of parameters in urinary and blood tests. Potential determinants were age, sex, body mass index, an indicator of smoking habits (cigarette index) and the index of estimated Cd intake from rice (Cd-rice-index). Cd-rice-index was expressed as the product of Cd concentrations in homegrown rice multiplied by daily frequency multiplied by duration (years) of residence in the polluted area. In multiple regression analysis, whole blood Cd was independently associated with Cd-rice-index, age and gender. Variations in whole blood Cd accounted for a substantial portion of the variations in urinary Cd, although they were less influential in older individuals. Whole blood Cd was the sole independent variable related to variations in urinary β 2-MG. Cd-rice-index accounted for a portion of the variance in urinary NAG, while age was a more powerful determinant. It was thus revealed that the consumption of homegrown rice polluted with Cd in low concentration resulted in an elevation of whole blood Cd level and consequent increase in urinary Cd level. However, it was not clearly elucidated that the excretion of urinary low-molecular microglobulins could increase significantly in response to slight elevation of Cd body load.