Renal cortical mitochondrial dysfunction upon cadmium metallothionein administration to Sprague-Dawley rats

Mitochondrial Oxidative Stress Is the General Reason for Apoptosis Induced by Different-Valence Heavy Metals in Cells and Mitochondria

This review analyzes the causes and consequences of apoptosis resulting from oxidative stress that occurs in mitochondria and cells exposed to the toxic effects of different-valence heavy metals (Ag+, Tl+, Hg2+, Cd2+, Pb2+, Al3+, Ga3+, In3+, As3+, Sb3+, Cr6+, and U6+). The problems of the relationship between the integration of these toxic metals into molecular mechanisms with the subsequent development of pathophysiological processes and the appearance of diseases caused by the accumulation of these metals in the body are also addressed in this review. Such apoptosis is characterized by a reduction in cell viability, the activation of caspase-3 and caspase-9, the expression of pro-apoptotic genes (Bax and Bcl-2), and the activation of protein kinases (ERK, JNK, p53, and p38) by mitogens. Moreover, the oxidative stress manifests as the mitochondrial permeability transition pore (MPTP) opening, mitochondrial swelling, an increase in the production of reactive oxygen species (ROS) and H2O2, lipid peroxidation, cytochrome c release, a decline in the inner mitochondrial membrane potential (ΔΨmito), a decrease in ATP synthesis, and reduced glutathione and oxygen consumption as well as cytoplasm and matrix calcium overload due to Ca2+ release from the endoplasmic reticulum (ER). The apoptosis and respiratory dysfunction induced by these metals are discussed regarding their interaction with cellular and mitochondrial thiol groups and Fe2+ metabolism disturbance. Similarities and differences in the toxic effects of Tl+ from those of other heavy metals under review are discussed. Similarities may be due to the increase in the cytoplasmic calcium concentration induced by Tl+ and these metals. One difference discussed is the failure to decrease Tl+ toxicity through metallothionein-dependent mechanisms. Another difference could be the decrease in reduced glutathione in the matrix due to the reversible oxidation of Tl+ to Tl3+ near the centers of ROS generation in the respiratory chain. The latter may explain why thallium toxicity to humans turned out to be higher than the toxicity of mercury, lead, cadmium, copper, and zinc.

Hazards related to the presence of cadmium in food - Studies on the European soil centipede, Lithobius forficatus

The soil is an environment rich in numerous potentially toxic substances/elements when present at elevated concentrations. They can be transported through the successive levels of the trophic chain. Animals living in a contaminated environment or eating contaminated food can accumulate potentially toxic elements in their bodies. One of the potentially toxic metals is cadmium, which accumulates significantly in soils. The aim of our research was to evaluate the changes caused by cadmium supplied with the food administered to invertebrates living in uncontaminated soil. The results were compared with those obtained for animals raised in contaminated soil, where cadmium entered the body via the epidermis. As the material for studies, we chose a common European soil centipede, Lithobius forficatus. Adult specimens were divided into the following experimental groups: C - control animals, Cd12 and Cd45 - animals fed with Chironomus larvae maintained in water containing 80 mg/l CdCl₂, for 12 and 45 days, respectively. The material was analyzed using qualitative and quantitative analysis (transmission electron microscopy, confocal microscopy, flow cytometry, atomic absorption spectrometry). Eventually, we can conclude that the digestive system is an effective barrier against the effects of toxic metals on the entire organism, but among the gonads, ovaries are more protected than testes, however, this protection is not sufficient. Accumulation of spherites and mitochondrial alterations are probably involved in survival mechanisms of tissues after Cd intoxication.

Involvement of caspase-3 in apoptosis of human lymphocytes exposed to cadmium chloride

BACKGROUND

Lymphocytes are a group of white blood cells with a variety of roles their integrity is crucial for the body's immune responses. Cadmium, a heavy metal and environmental pollutant, is known as a toxicant to exert its adverse effects on some sort of cells including blood cells.

RESEARCH DESIGN

In this study, human lymphocytes were divided into 3 groups: (1) lymphocytes at 0-h, (2) lymphocytes at 24 h (control), (3) lymphocytes treated with cadmium chloride (15 μM). Lymphocyte viability and plasma membrane integrity were assessed in these groups. In addition, the occurrence of apoptosis was investigated by assessment of nucleus diameter and flow cytometry. Activation of caspase-3 was also detected by immunocytochemistry.

RESULTS

Result showed that lymphocyte's viability and plasma membrane integrity decreased in lymphocytes treated with cadmium as compared with the control group. Decreased nucleus diameter and result of flow cytometry demonstrated cadmium-induced apoptosis in human lymphocytes. Furthermore, lymphocytes treated with cadmium displayed intensely activated caspase-3 immunoreactivity in their cytoplasm.

CONCLUSION

In conclusion, cadmium not only negatively effect on viability and plasma membrane, but also induces caspase-dependent apoptosis in human lymphocytes.

Functional Food Product Based on Nanoselenium-Enriched Lactobacillus casei against Cadmium Kidney Toxicity

This paper demonstrates the ability of a functional food based on probiotics and selenium nanoparticles (SeNPs) to annihilate the toxic effect of cadmium on the kidneys. SeNPs were obtained by eco-friendly method used Lactobacillus casei. The morphological features and size of SeNPS were characterized by Atomic Force Microscopy (AFM) and Dynamic Light Scattering (DLS). Two kind of SeNPs were used, purified and Lacto-SeNPs (LSeNPs), administered by gavage at three concentrations (0.1, 0.2, and 0.4 mg/Kg b.w.) for 30 days in a mouse model of cadmium renal toxicity. The blood marker of renal injury (creatinine) significantly decreased in groups where the mice were treated with both form of SeNPs. The antioxidant capacity of plasma was evaluated by Trolox Equivalent Antioxidant Capacity (TEAC) assay and revealed that SeNPs in co-treatment with Cd, promotes maintaining antioxidant activity at the control level. Histopathological analysis of kidneys demonstrated morphological alteration in the group that received only cadmium and restored after administration of SeNPs or LSeNPs. In addition, immunohistochemical analysis revealed anti-apoptotic effects through reduction of pro-apoptotic bax and increasing of anti-apoptotic Bcl-2 protein expressions. Moreover, co-administration of Cd with SeNPs significantly decreased gene expression of kidneys inflammatory markers (TNF-α, IL-6, NF-ĸB) in a dose dependent manner, with the best results for LSeNPs at highest dose (0.4 mg/kg). Therefore, the L. casei strain is a potential SeNPs-enriched probiotic for application as functional food in the future to annihilate cadmium-induced kidneys toxicity.

Exposure to waterborne cadmium induce oxidative stress, autophagy and mitochondrial dysfunction in the liver of Procypris merus

The present study was performed to determine the effect of waterborne cadmium (Cd) exposure on oxidative stress, autophagy and mitochondrial dysfunction, and to explore the mechanism of Cd-induced liver damage in freshwater teleost Procypris merus. To this end, P. merus were exposed to waterborne 0, 0.25 and 0.5 mg/L Cd for 30 days (equal to 0, 2.22 and 4.45 μmol Cd/l). The waterborne Cd exposure significantly increased hepatic Cd accumulation and impaired histological structure of the liver of P. merus. both low and high-dose waterborne Cd exposure induced oxidative stress in the liver of P. merus, through increases Malondialdehyde (MDA) and reactive oxide species (ROS) accumulation in the liver. The Cd-induced oxidative stress in liver may result from reduction of enzyme activities (superoxide dismutases (SOD), catalases (CAT), GSH-S-transferases (GST)) and transcriptional expression of antioxidant related genes (gpx1, gpx2, cata, gsta1, sod1). Furthermore, the present study showed that waterborne Cd exposure decreased the transcriptional factor (nrf2) expression, which might lead to the down-regulation of antioxidant gene expression. Transmission electron microscopy (TEM) observations demonstrated that waterborne Cd exposure induced autophagy in the liver of P. merus. Gene expression analysis showed that waterborne Cd exposure also induced mRNA expression of a set of genes (beclin1, ulk1, atg5, lc3a, atg4b, atg9a, and p62) involved in the autophagy process, indicating that the influence of Cd on autophagy involved transcription regulation of autophagy gene expression. Waterborne Cd exposure induced a sharp decrease in ATP content in the liver of P. merus. In addition, the expression of mitochondrial function genes (sdha, cox4i1, cox1, atp5f1, and mt-cyb) are significantly decreased in the liver of P. merus in Cd treated groups, manifesting the suppression of Cd on mitochondrial energy metabolism. Taken together, our experiments demonstrate that waterborne Cd exposure induced oxidative stress, autophagy and mitochondrial dysfunction in the liver of P. merus. These results may contribute to the understanding of mechanisms that hepatotoxicity of Cd in teleost.

Nephroprotective role of bromelain against oxidative injury induced by aluminium in rats

The present study was designed to investigate the nephroprotective effect of bromelain against oxidative stress stimulated by aluminium chloride in rats. Rats were grouped as follows; group one was used as control while groups 2, 3 and 4 were treated orally with bromelain (250 mg/kg, daily), aluminium chloride (AlCl₃; 34 mg/kg BW, every other day) and bromelain plus AlCl₃ for 30 days, respectively. Administration of AlCl₃ caused a significant reduction in rats' body and kidney weights, and increased Al accumulation in kidney tissue. Also, AlCl₃ treatment elevated thiobarbituric acid reactive substances, hydrogen peroxide, kidney functions biomarkers levels and lactate dehydrogenase activity. While enzymatic (SOD, CAT, GPx, GR, GST) and non-enzymatic (GSH) antioxidants, protein content, and alkaline phosphatase activity were significantly decreased. In addition, significant alterations in lipid and protein profiles were detected. Furthermore, histopathological and immunohistochemical variations were seen in kidney sections supporting the obtained biochemical changes. Otherwise, rats supplemented with bromelain singly declined lipid peroxidation and improved most of the studied parameters. Moreover, rats pretreated with bromelain followed by AlCl₃ intoxication showed significant alleviation in lipid peroxidation, antioxidant status and biochemical indices with respect to AlCl₃ treated group. Conclusively, bromelain has beneficial protective effects and has the capability to counteract the toxic influence of AlCl₃. So, bromelain might represent a novel approach in the therapy of metal toxicity because of its antioxidant and chelating properties.

The role of different SIRT1-mediated signaling pathways in toxic injury

Common environmental pollutants and drugs encountered in everyday life can cause toxic damage to the body through oxidative stress, inflammatory stimulation, induction of apoptosis, and inhibition of energy metabolism. Silent information regulator 1 (SIRT1), a nicotinamide adenine dinucleotide-dependent deacetylase, is a member of the evolutionarily highly conserved Sir2 (silent information regulator 2) superprotein family, which is located in the nucleus and cytoplasm. It can deacetylate protein substrates in various signal transduction pathways to regulate gene expression, cell apoptosis and senescence, participate in the process of neuroprotection, energy metabolism, inflammation and the oxidative stress response in living organisms, and plays an important role in toxic damage caused by toxicants and in the process of SIRT1 activator/inhibitor antagonized toxic damage. This review summarizes the role that SIRT1 plays in toxic damage caused by toxicants via its interactions with protein substrates in certain signaling pathways.

Cadmium Complexed with β2-Microglubulin, Albumin and Lipocalin-2 rather than Metallothionein Cause Megalin:Cubilin Dependent Toxicity of the Renal Proximal Tubule

Cadmium (Cd²⁺) in the environment is a significant health hazard. Chronic low Cd²⁺ exposure mainly results from food and tobacco smoking and causes kidney damage, predominantly in the proximal tubule. Blood Cd²⁺ binds to thiol-containing high (e.g., albumin, transferrin) and low molecular weight proteins (e.g., the high-affinity metal-binding protein metallothionein, β2-microglobulin, α1-microglobulin and lipocalin-2). These plasma proteins reach the glomerular filtrate and are endocytosed at the proximal tubule via the multiligand receptor complex megalin:cubilin. The current dogma of chronic Cd²⁺ nephrotoxicity claims that Cd²⁺-metallothionein endocytosed via megalin:cubilin causes renal damage. However, a thorough study of the literature strongly argues for revision of this model for various reasons, mainly: (i) It relied on studies with unusually high Cd²⁺-metallothionein concentrations; (ii) the K_D of megalin for metallothionein is ~10⁵-times higher than (Cd²⁺)-metallothionein plasma concentrations. Here we investigated the uptake and toxicity of ultrafiltrated Cd²⁺-binding protein ligands that are endocytosed via megalin:cubilin in the proximal tubule. Metallothionein, β2-microglobulin, α1-microglobulin, lipocalin-2, albumin and transferrin were investigated, both as apo- and Cd²⁺-protein complexes, in a rat proximal tubule cell line (WKPT-0293 Cl.2) expressing megalin:cubilin at low passage, but is lost at high passage. Uptake was determined by fluorescence microscopy and toxicity by MTT cell viability assay. Apo-proteins in low and high passage cells as well as Cd²⁺-protein complexes in megalin:cubilin deficient high passage cells did not affect cell viability. The data prove Cd²⁺-metallothionein is not toxic, even at >100-fold physiological metallothionein concentrations in the primary filtrate. Rather, Cd²⁺-β2-microglobulin, Cd²⁺-albumin and Cd²⁺-lipocalin-2 at concentrations present in the primary filtrate are taken up by low passage proximal tubule cells and cause toxicity. They are therefore likely candidates of Cd²⁺-protein complexes damaging the proximal tubule via megalin:cubilin at concentrations found in the ultrafiltrate.

The interaction between AtMT2b and AtVDAC3 affects the mitochondrial membrane potential and reactive oxygen species generation under NaCl stress in Arabidopsis

AtMT2b interacts with AtVDAC3 in mitochondria in Arabidopsis. The overexpression of the AtMT2b and AtVDAC3 T-DNA insertion mutant confers tolerance to NaCl stress in Arabidopsis. Both AtMT2b and AtVDAC3 are involved in the regulation of the mitochondrial membrane potential (MMP) and reactive oxygen species (ROS) under NaCl stress. Metallothioneins (MTs) are small, cysteine rich, metal-binding proteins that perform multiple functions, such as heavy metal detoxification and reactive oxygen species (ROS) scavenging. MTs have been reported to be involved in mitochondrial function in mammals. However, whether a direct relationship exists between MTs and mitochondrial proteins remains unclear. In the present study, we used yeast two-hybrid and bimolecular fluorescence complementation assays to demonstrate that AtMT2b, which is a type 2 MT in Arabidopsis, interacts with the outer mitochondrial membrane voltage-dependent anion channel AtVDAC3. AtMT2b bound AtVDAC3, leading to its co-localization in mitochondria. AtMT2b transgenic seedlings exhibited increased tolerance to salt stress, and the atvdac3 mutant showed a similar phenotype. The mitochondrial membrane potential (MMP) was maintained, and ROS generation was reduced following AtMT2b overexpression and AtVDAC3 knockout under NaCl stress. Both AtMT2b and AtVDAC3 were shown to be involved in MMP regulation and ROS production under NaCl stress but showed opposite effects. We conclude that AtMT2b might negatively interact with AtVDAC3 in mitochondria, and both proteins are involved in the regulation of MMP and ROS under NaCl stress.

Mustafa H, Abdulraouf Saleh H, M.O. El-Fark2 M. Zingiber Officinale Alleviates Maternal and Fetal Hepatorenal Toxicity Induced by Prenatal Cadmium

This study was designed to address the protective effects of Zingiber officinale on the toxic outcomes of prenatal Cadmium administration on pregnancy outcome. Pregnant female Sprague-Dawley rats were randomly divided into four groups (eight rats/each), control group received distilled water, 2nd group treated with 8.8 mg of CdCl2/kg b. wt, 3rd group treated with 250 mg of Zingiber officinale/kg b. wt, and 4th group treated with 250 mg of Zingiber officinale/kg b. wt, followed by 8.8 mg of CdCl2/kg b.wt. Daily body weight of pregnant was recorded from GD1-GD20, and then pregnant rats were sacrificed at GD20. Samples of maternal and fetal livers and kidneys were processed for histological examination. Administration of Cd to pregnant rats showed adverse effects on pregnant mothers and their fetuses; reduced maternal weight gain, reduced absolute organ weights, reduced fetal growth parameters and placental weights together with altered histological appearance of the maternal and fetal livers and kidneys. While co-administration of Zingiber officinale showed an improvement of these toxic alterations. Zingiber officinale through its antioxidant activity could be beneficial against toxic outcomes of Cd exposure during pregnancy.

Oxidative stress and mitochondrial dysfunction mediated Cd-induced hepatic lipid accumulation in zebrafish Danio rerio

The present study was performed to determine the effect of waterborne CdCl₂ exposure influencing lipid deposition and metabolism, oxidative stress and mitochondrial dysfunction, and explore the underlying molecular mechanism of cadmium (Cd)-induced disorder of hepatic lipid metabolism in fish. To this end, adult zebrafish were exposed to three waterborne CdCl₂ concentrations (0(control), 5 and 25 μg Cd/l, respectively) for 30 days. Lipid accumulation, the activities of enzymes related to lipid metabolism and oxidative stress, as well as the expression level of genes involved in lipid metabolism and mitophagy were determined in the liver of zebrafish. Waterborne CdCl₂ exposure increased hepatic triglyceride (TG) and Cd accumulation, the activities of fatty acid synthase (FAS), 6-phosphogluconate dehydrogenase (6PGD), glucose 6-phosphate dehydrogenase (G6PD) and malic enzyme (ME), and the mRNA level of fatty acid synthase (fas), acetyl-CoA carboxylase alpha (acaca), glucose 6-phosphate dehydrogenase (g6pd) and malic enzyme (me), but reduced the mRNA level of carnitine palmitoyl transferase 1 (cpt1), hormone-sensitive lipase alpha (hsla), and adipose triacylglyceride lipase (atgl). The activities of superoxide dismutase (SOD), glutathoinine peroxidase (GPx) and cytochrome c oxidase (COX) and the ATP level were significantly reduced after CdCl₂ exposure. CdCl₂ exposure significantly increased the mRNA level of genes (microtubule-associated protein light chain 3 alpha (lc3a), PTEN-induced putative kinase 1 (pink1), NIP3-like protein X (nix) and PARKIN (parkin)) related to mitophagy. To elucidate the mechanism, reactive oxygen species (ROS) scavenger N-acetylcysteine (NAC) and the mitochondrial permeability transition (MPT) inhibitor cyclosporine A (CsA) were used to verify the role of ROS and mitochondrial dysfunction in Cd-induced disorder of lipid metabolism. NAC pretreatment reversed the Cd-induced up-regulation of TG accumulation and activities of lipogenic enzymes, and the Cd-induced down-regulation of mRNA levels of lipolytic genes. Meanwhile, NAC pretreatment also blocked the mitochondrial membrane potential (MMP) collapse and decreased the ATP level, suggesting that ROS played a crucial role in regulating the Cd-induced mitochondrial dysfunction. Taken together, our findings, for the first time, highlight the importance of the oxidative stress and mitochondrial dysfunction in Cd-induced disorder of hepatic lipid metabolism, which proposed a novel mechanism for elucidating metal element exposure inducing the disorder of lipid metabolism in vertebrates.

Effect of cadmium exposure on hepatopancreas and gills of the estuary mud crab (Scylla paramamosain): Histopathological changes and expression characterization of stress response genes

Cadmium (Cd) is a heavy metal that accumulates easily in organisms and causes several detrimental effects, including tissue damage. Cd contamination from anthropogenic terrestrial sources flows into rivers, and through estuaries to the ocean. To evaluate the toxic effects of Cd on estuary crustaceans, we exposed the mud crab Scylla paramamosain to various Cd concentrations (0, 10.0, 20.0, and 40.0mg/L) for 24h. We also exposed mud crabs to a fixed Cd concentration (20.0mg/L) for various periods of time (0, 6, 12, 24, 48, and 72h). We observed that after exposure to Cd, the surfaces of the gill lamellae were wrinkled, and the morphologies of the nuclei and mitochondria in the hepatopancreas were altered. We analyzed the expression profiles of 36 stress-related genes after Cd exposure, including those encoding metallothioneins, heat shock proteins, apoptosis-related proteins, and antioxidant proteins, with quantitative reverse transcription PCR. We found that exposure to Cd altered gene expression, and that some genes might be suitable bioindicators of Cd stress. Gene expression profiles were organ-, duration-, and concentration-dependent, suggesting that stress-response genes might be involved in an innate defense system for handling heavy metal exposure. To the best of our knowledge, this study is the first one of histopathology and stress-response gene expression pattern of Scylla paramamosain after Cd exposure. Our work could increase our understanding of the effect of environmental toxins on estuary crustaceans.

Iron transport in the kidney: implications for physiology and cadmium nephrotoxicity

The kidney has recently emerged as an organ with a significant role in systemic iron (Fe) homeostasis. Substantial amounts of Fe are filtered by the kidney, which have to be reabsorbed to prevent Fe deficiency. Accordingly Fe transporters and receptors for protein-bound Fe are expressed in the nephron that may also function as entry pathways for toxic metals, such as cadmium (Cd), by way of "ionic and molecular mimicry". Similarities, but also differences in handling of Cd by these transport routes offer rationales for the propensity of the kidney to develop Cd toxicity. This critical review provides a comprehensive update on Fe transport by the kidney and its relevance for physiology and Cd nephrotoxicity. Based on quantitative considerations, we have also estimated the in vivo relevance of the described transport pathways for physiology and toxicology. Under physiological conditions all segments of the kidney tubules are likely to utilize Fe for cellular Fe requiring processes for metabolic purposes and also to contribute to reabsorption of free and bound forms of Fe into the circulation. But Cd entering tubule cells disrupts metabolic pathways and is unable to exit. Furthermore, our quantitative analyses contest established models linking chronic Cd nephrotoxicity to proximal tubular uptake of metallothionein-bound Cd. Hence, Fe transport by the kidney may be beneficial by preventing losses from the body. But increased uptake of Fe or Cd that cannot exit tubule cells may lead to kidney injury, and Fe deficiency may facilitate renal Cd uptake.

Hepatoprotective effect of grape seed proanthocyanidins on Cadmium-induced hepatic injury in rats: Possible involvement of mitochondrial dysfunction, inflammation and apoptosis

The present study was undertaken to evaluate the possible ameliorative role of grape seed proanthocyanidins (GSP) against Cadmium (Cd) induced hepatic inflammation, apoptosis and hepatic mitochondrial toxicity in rats. Male Wistar rats were distributed in four experimental groups: control, GSP, Cd and Cd + GSP. Exposure to a hepatotoxic dose of Cd (5 mg/kg BW) caused liver damage, coupled with enhanced reactive oxygen species (ROS) generation, increased inflammation and apoptosis in liver with increased DNA damage in hepatocytes of rats. Mitochondria were isolated from the hepatic tissues of rats from each group. Our results showed significant decrease in the tri-carboxylic acid cycle enzymes, increased mitochondrial swelling, inhibition of cytochrome c oxidase activity and complex I-III, II-III and IV mediated electron transfer, decreased mitochondrial ATPases, a reduction in calcium content and mitochondrial oxygen consumption in Cd treated rats. All these molecular changes caused by Cd were alleviated by the pre-supplementation with GSP (100 mg/kg BW). The ultra structural changes in the liver also support our findings. From our results, it is clearly indicated that the free radical scavenging, metal chelating and antioxidant potentials of GSP might be the possible reason, responsible for the rescue action against Cd induced mitochondrial damage in the liver of rats.

Modulatory effect of protocatechuic acid on cadmium induced nephrotoxicity and hepatoxicity in rats in vivo

Introduction

This study sought to investigate the effect of protocatechuic acid (PCA); a phenolic compound readily available in most plant foods on cadmium-induced nephrotoxicity and hepatoxicity in rats.

Case description

Thirty six adult male rats weighing about 150–160 g were acclimatized for 2 weeks and subsequently divided into six groups: Group 1 rats received normal saline (control group), group 2 rats were administered 5 mg Cd/kg body weight in form of solution orally (induced group), groups 3 and 4 received cadmium solution and different doses of PCA (10 and 20 mg/kg body weight) respectively, while groups 5 and 6 were the normal rats administered different doses of PCA (10 and 20 mg/kg) respectively in an experiment that lasted for twenty one days. The animals were sacrificed, the blood was collected and the serum was subsequently prepared. Furthermore, the liver was excised, homogenized and centrifuged to obtain the tissue homogenate used for the analyses. The serum was used for the determination of the total protein, urea, creatinine and uric acid levels while the liver homogenate was used for the estimation of alanine aminotransferase (ALT), aspartate transaminase (AST), and alkaline phosphatase (ALP).

Discussion and evaluation

The result revealed that total protein level was reduced in cadmium induced toxicity rat group which was elevated upon treatment with PCA. Conversely, the elevated levels of urea, uric acid and creatinine in cadmium induced toxicity kidney rats were significantly (p < 0.05) reduced in PCA treated groups. Similarly, marked elevation in the ALT, AST and ALP activity were observed in cadmium induced toxicity rat group when compared with the control group. However, significant (p < 0.05) decrease in ALT, AST and ALP activity were noticed in groups administered different doses of PCA.

Conclusions

The results from this study suggest that PCA may protect against cadmium-induced toxicity in the kidney and liver.

Hesperidin ameliorates heavy metal induced toxicity mediated by oxidative stress in brain of Wistar rats

Cadmium (Cd) induces neurotoxicity owing to its highly deleterious capacity to cross the blood brain barrier (BBB). Recent studies have provided insights on antioxidant properties of bioflavonoids which have emerged as potential therapeutic and nutraceutical agents. The aim of our study was to examine the hypothesis that hesperidin (HP) ameliorates oxidative stress and may have mitigatory effects in the extent of heavy metal-induced neurotoxicity. Cd (3mg/kg body weight) was administered subcutaneously for 21 days while HP (40 mg/kg body weight) was administered orally once every day. The results of the current investigation demonstrate significant elevated levels of oxidative stress markers such as lipid peroxidation (LPO) and protein carbonyl (PC) along with significant depletion in the activity of non-enzymatic antioxidants like glutathione (GSH) and non-protein thiol (NP-SH) and enzymatic antioxidants in the Cd treated rats' brain. Activity of neurotoxicity biomarkers such as acetylcholinesterase (AchE), monoamine oxidase (MAO) and total ATPase were also altered significantly and HP treatment significantly attenuated the altered levels of oxidative stress and neurotoxicity biomarkers while salvaging the antioxidant sentinels of cells to near normal levels thus exhibiting potent antioxidant and neuroprotective effects on the brain tissue against oxidative damage in Cd treated rodent model.

Mitochondrial gene expression, antioxidant responses, and histopathology after cadmium exposure

The present study investigates cadmium effects on the transcription of mitochondrial genes of Procambarus clarkii after acute (0.05, 0.5, and 5 mg Cd/L; 4-10 days) and chronic exposures (10 μg Cd/L; 30-60 days). Transcriptional responses of cox1, atp6, and 12S using quantitative real-time RT-PCR were assessed in gills and hepatopancreas. Additionally, the expression levels of genes involved in detoxification and/or oxidative stress responses [mt, sod(Mn)] and enzymatic activities of antioxidants (SOD, CAT, GPX, and GST) were analyzed. The histopathological effects in hepatopancreas of crayfish were evaluated by light microscopy. Relationships between endpoints at different levels of biological organization and Cd bioaccumulation were also examined. Cd induced high levels of bioaccumulation, which was followed by mitochondrial dysfunction and histological alterations in both experiments. Moreover, perturbations in the defence mechanisms against oxidative stress tended to increase with time. Results also showed that molecular responses can vary depending on the intensity and duration of the chemical stress applied to the organisms and that the study of mt gene expression levels seemed to be the best tool to assess Cd intoxication.

The protective effect of grape seed procyanidin extract against cadmium-induced renal oxidative damage in mice

As an important environmental pollutant, cadmium (Cd) can lead to serious renal damage. Grape seed procyanidins extract (GSPE), a biological active component of grape seed, has been shown to possess antioxidative effects. Here, we assessed the protective effect of GSPE on Cd-induced renal damage using animal experiment. After 30 days, the oxidative damage of kidney was evaluated through measurement of superoxide dismutase (SOD), glutathione peroxidation (GSH-Px) and malondialdehyde (MDA). Since, oxidative stress could lead to apoptosis, the renal apoptosis was measured using flow cytometer. Moreover, the expression of apoptosis-related protein Bax and Bcl-2 was analyzed by immunohistochemistry and Western blot. The results showed that Cd led to the decrease of SOD and GSH-Px activities, and the increase of MDA level, induced renal apoptosis. However, the coadministration of GSPE attenuated Cd-induced lipid peroxidation, and antagonized renal apoptosis, probably associated with the expression of Bax and Bcl-2. These data suggested that GSPE has protective effect against renal oxidative damage induced by Cd, which provide a potential natural chemopreventive agent against Cd-poisoning.

Differential susceptibility to cadmium-induced liver and kidney injury in wild and laboratory-bred bank voles Myodes glareolus

The objective of the study was to compare the sensitivity of wild and laboratory-bred bank voles to cadmium (Cd)-induced histopathological changes in the liver and kidneys. For 4 weeks, the male bank voles-both wild and laboratory-bred-were provided with diet containing Cd in quantities <0.1 (control), 30, and 60 μg/g dry weight. At the end of exposure period, histopathology and analyses of Cd, metallothionein (MT), glutathione (GSH), zinc (Zn), copper (Cu), iron (Fe), and lipid peroxidation-all considered to be critical factors during the development of Cd toxicity in the liver and kidneys-were carried out. Histopathological changes (focal hepatocyte swelling, vacuolation and inflammation [leukocyte infiltration] in the liver, and focal proximal tubule degeneration [including epithelial cell swelling] in the kidneys) occurred only in the wild bank voles fed a diet containing 60 μg Cd/g. There were no differences in concentrations of Cd, MT, GSH, Zn, and Cu in liver and kidney between the respective groups of wild and laboratory-bred animals. However, a decrease of hepatic Fe and lipid peroxidation was observed in the wild voles exhibiting histopathological changes. These data indicate the following: (1) wild bank voles are more susceptible to Cd-induced liver and kidney injury than those bred and raised in the laboratory; (2) the difference in sensitivity may be associated with a distinct decrease of hepatic Fe in response to Cd exposure between the two groups of bank voles; and (3) dietary Cd may produce histopathological changes indirectly through decreasing the hepatic Fe and Fe-dependent oxidative processes. These results also suggest that histopathology in the liver and kidney of wild bank voles living in a contaminated environment may occur at relatively low levels of tissue Cd.

Tight junction proteins and oxidative stress in heavy metals-induced nephrotoxicity

Kidney is a target organ for heavy metals. They accumulate in several segments of the nephron and cause profound alterations in morphology and function. Acute intoxication frequently causes acute renal failure. The effects of chronic exposure have not been fully disclosed. In recent years increasing awareness of the consequences of their presence in the kidney has evolved. In this review we focus on the alterations induced by heavy metals on the intercellular junctions of the kidney. We describe that in addition to the proximal tubule, which has been recognized as the main site of accumulation and injury, other segments of the nephron, such as glomeruli, vessels, and distal nephron, show also deleterious effects. We also emphasize the participation of oxidative stress as a relevant component of the renal damage induced by heavy metals and the beneficial effect that some antioxidant drugs, such as vitamin A (all-trans-retinoic acid) and vitamin E (α-tocopherol), depict on the morphological and functional alterations induced by heavy metals.

Cadmium-Induced Pathologies: Where Is the Oxidative Balance Lost (or Not)?

Over the years, anthropogenic factors have led to cadmium (Cd) accumulation in the environment causing various health problems in humans. Although Cd is not a Fenton-like metal, it induces oxidative stress in various animal models via indirect mechanisms. The degree of Cd-induced oxidative stress depends on the dose, duration and frequency of Cd exposure. Also the presence or absence of serum in experimental conditions, type of cells and their antioxidant capacity, as well as the speciation of Cd are important determinants. At the cellular level, the Cd-induced oxidative stress either leads to oxidative damage or activates signal transduction pathways to initiate defence responses. This balance is important on how different organ systems respond to Cd stress and ultimately define the pathological outcome. In this review, we highlight the Cd-induced oxidant/antioxidant status as well as the damage versus signalling scenario in relation to Cd toxicity. Emphasis is addressed to Cd-induced pathologies of major target organs, including a section on cell proliferation and carcinogenesis. Furthermore, attention is paid to Cd-induced oxidative stress in undifferentiated stem cells, which can provide information for future therapies in preventing Cd-induced pathologies.

Thiol/disulfide redox states in signaling and sensing

Rapid advances in redox systems biology are creating new opportunities to understand complexities of human disease and contributions of environmental exposures. New understanding of thiol-disulfide systems have occurred during the past decade as a consequence of the discoveries that thiol and disulfide systems are maintained in kinetically controlled steady states displaced from thermodynamic equilibrium, that a widely distributed family of NADPH oxidases produces oxidants that function in cell signaling and that a family of peroxiredoxins utilize thioredoxin as a reductant to complement the well-studied glutathione antioxidant system for peroxide elimination and redox regulation. This review focuses on thiol/disulfide redox state in biologic systems and the knowledge base available to support development of integrated redox systems biology models to better understand the function and dysfunction of thiol-disulfide redox systems. In particular, central principles have emerged concerning redox compartmentalization and utility of thiol/disulfide redox measures as indicators of physiologic function. Advances in redox proteomics show that, in addition to functioning in protein active sites and cell signaling, cysteine residues also serve as redox sensors to integrate biologic functions. These advances provide a framework for translation of redox systems biology concepts to practical use in understanding and treating human disease. Biological responses to cadmium, a widespread environmental agent, are used to illustrate the utility of these advances to the understanding of complex pleiotropic toxicities.

Histochemical changes in muscle of rats exposed subchronically to low doses of heavy metals

Heavy metals are ubiquitous in the environment and exposure through food and water as well as occupational sources can constitute a potential threat to human health. The mechanisms of heavy metal damage include the production of free radicals that alter mitochondrial activity, affecting cellular types like neurons and muscular fibres. We examined whether rats exposed subchronically via drinking water to low doses of heavy metals can produce alterations in muscle. Results showed that the proportion of ragged red fibres increased in muscle of rats exposed to lead and thallium, likewise slight changes in enzymatic activity of muscular fibres were also observed.

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.

Cadmium stress: an oxidative challenge

At the cellular level, cadmium (Cd) induces both damaging and repair processes in which the cellular redox status plays a crucial role. Being not redox-active, Cd is unable to generate reactive oxygen species (ROS) directly, but Cd-induced oxidative stress is a common phenomenon observed in multiple studies. The current review gives an overview on Cd-induced ROS production and anti-oxidative defense in organisms under different Cd regimes. Moreover, the Cd-induced oxidative challenge is discussed with a focus on damage and signaling as downstream responses. Gathering these data, it was clear that oxidative stress related responses are affected during Cd stress, but the apparent discrepancies observed in between the different studies points towards the necessity to increase our knowledge on the spatial and temporal ROS signature under Cd stress. This information is essential in order to reveal the exact role of Cd-induced oxidative stress in the modulation of downstream responses under a diverse array of conditions.

Heavy metal poisoning: the effects of cadmium on the kidney

The heavy metal cadmium (Cd) is known to be a widespread environmental contaminant and a potential toxin that may adversely affect human health. Exposure is largely via the respiratory or gastrointestinal tracts; important non-industrial sources of exposure are cigarette smoke and food (from contaminated soil and water). The kidney is the main organ affected by chronic Cd exposure and toxicity. Cd accumulates in the kidney as a result of its preferential uptake by receptor-mediated endocytosis of freely filtered and metallothionein bound Cd (Cd-MT) in the renal proximal tubule. Internalised Cd-MT is degraded in endosomes and lysosomes, releasing free Cd(2+) into the cytosol, where it can generate reactive oxygen species (ROS) and activate cell death pathways. An early and sensitive manifestation of chronic Cd renal toxicity, which can be useful in individual and population screening, is impaired reabsorption of low molecular weight proteins (LMWP) (also a receptor-mediated process in the proximal tubule) such as retinol binding protein (RBP). This so-called 'tubular proteinuria' is a good index of proximal tubular damage, but it is not usually detected by routine clinical dipstick testing for proteinuria. Continued and heavy Cd exposure can progress to the clinical renal Fanconi syndrome, and ultimately to renal failure. Environmental Cd exposure may be a significant contributory factor to the development of chronic kidney disease, especially in the presence of other co-morbidities such as diabetes or hypertension; therefore, the sources and environmental impact of Cd, and efforts to limit Cd exposure, justify more attention.

Effect of treatment with cadmium on structure-function relationships in rat liver mitochondria: studies on oxidative energy metabolism and lipid/phospholipids profiles

Effects of treatment with a single intraperitoneal injection of cadmium (Cd) on oxidative energy metabolism and lipid/phospholipid profiles of rat liver mitochondria were examined at the end of 1 week and 1 month. Following Cd treatment the body weight increased only in the 1 month group, whereas the liver weight increased in both groups. State 3 and 4 respiration rates in general decreased significantly, with the maximum effect being seen with succinate. The 1 week Cd group showed decreased respiratory activity with glutamate, pyruvate + malate, and succinate as the substrates. In the 1 month Cd-treated group respiration rates recovered with glutamate and pyruvate + malate but not with succinate. All cytochrome contents decreased in the 1 week Cd-treated group but recovered in the 1 month group. ATPase activity registered an increase in both Cd-treated groups. Dehydrogenase activities increased in the 1 week group but decreased in the 1 month Cd-treated group. The mitochondrial cholesterol content increased in the 1 week Cd-treated group. In the 1 week Cd-treated group the lysophospholipid (Lyso), sphingomyelin (SPM), and diphosphatidylglycerol (DPG) components increased. By contrast, the phosphatidylethanolamine (PE) component decreased. In the 1 month Cd-treated group the phosphatidylinositol, phosphatidylserine, and DPG components increased, whereas the Lyso, SPM, and phosphatidylcholine components decreased. The results demonstrate that single-dose Cd treatment can have adverse effects on liver mitochondrial oxidative energy metabolism and lipid/phosphopholipid profiles, which in turn can affect membrane structure-function relationships.

Cadmium and mitochondria

The heavy metal cadmium (Cd) a pollutant associated with several modern industrial processes, is absorbed in significant quantities from cigarette smoke, water, food and air contaminations. It is known to have numerous undesirable effects on health in both experimental animals and humans, targeting kidney, liver and vascular system. The molecular mechanism accounting for most of the biological effects of Cd are not well-understood and the toxicity targets are largely unidentified. The present review focuses on important recent advances about the effects of cadmium on mitochondria of mammalian cells. Mitochondria are the proverbial powerhouses of the cell, running the fundamental biochemical processes that produce energy from nutrients using oxygen. They are among the key intracellular targets for different stressors including Cd. This review provides new additional informations on the cellular and molecular aspects of the interaction between Cd and cells, emphasizing alterations of mitochondria as important events in Cd cytotoxicity, thus representing an important basis for understanding the mechanisms of cadmium effect on the cells.

Mitochondrial compartment: a possible target of cadmium effects on breast epithelial cells

Cadmium-breast epithelial cell interactions were studied by analyzing some mitochondria-related aspects of stress response. We treated immortalized non-tumor breast cells with 5 or 50 microM CdCl(2) for 24 or 96 h demonstrating that the exposure did not cause a significant mitochondrial proliferation, while it induced a significant increase in the respiratory activity and mitochondrial polarization. In addition, we found that hsp60 was up-regulated while hsp70 and COXII and COXIV were down-regulated. The mRNA for hsp70 remained constant and only the inducible form of the 70-kDa heat shock protein was over expressed. The mRNAs for COXII and COXIV remained constant after 24 h and increased after longer incubations while the respective proteins decreased. These findings provide additional information on the cellular and molecular aspects of the interaction between Cd and epithelial cells, and on alterations of mitochondria as early events in Cd cytotoxicity.

Protective effects of Chlorpromazine and Verapamil against cadmium-induced kidney damage in vivo

Overexposure to cadmium (Cd) can induce kidney damage, which was related to the oxidative damage and disturb intracellular Ca2+ homeostasis. Chlorpromazine (CPZ), targeting calmodulin (CaM), and the Ca2+ channel blocker Verapamil (Ver) are involved in intracellular Ca2+ homeostasis processes. The aim of the study was to investigate the kidney damage caused by Cd administrated for 6 weeks and to evaluate the effects of pre-treatment with either chlorpromazine or verapamil on Cd-induced kidney damage. Thirty-two Wistar rats were divided randomly into 4 groups by weight, i.e., control group, Cd-treated group, and CPZ or Ver pre-treated group. The Cd-treated group rats were subcutaneously (s.c.) injected with 7micromol CdCl2/kg body weight/day. The CPZ and Ver pre-treated group rats were intraperitoneally (i.p.) injected with 5mg CPZ/kg body weight/day, 4mg Ver/kg body weight/day, respectively, 1h before the s.c. administration of 7micromol CdCl2/kg body weight/day. The control group rats were injected s.c. with saline at the same time. The volume of injection was 2ml/kg body weight, 5 times per week, for up to 6 weeks. After 6 weeks, Cd concentrations in the renal cortex and urine were significantly higher in Cd-treated group than that in controls. Cd concentrations of the urine in CPZ and Ver pre-treated groups were significantly lower than that in Cd-treated group, but there were no significant changes in the renal cortex. Compared with the controls, urinary NAG, ALP activities, and the levels of GSH, MDA, and the activities of PKC, Na(+)-K(+)-ATPase, and Ca(2+)-ATPase in rats from the Cd-treated group were significantly increased. SOD activity was suppressed by Cd. Urinary NAG activity and the level of GSH and the activities of PKC and Ca(2+)-ATPase in both CPZ and Ver pre-treated groups were significantly lower than that in Cd-treated rats. The present results showed that Cd-induced kidney damage was related to the oxidative damage and disturb intracellular Ca2+ homeostasis. Both CPZ and Ver possess some ability to prevent cadmium-induced kidney damage via antioxidative action and by maintaining calcium homeostasis.

Risk assessment of low-level cadmium and arsenic on the kidney

Cadmium (Cd) and arsenic (As) are widely distributed in the environment and are known human carcinogens. Several studies reported that chronic exposure to Cd and As produced renal injuries in humans. As one of the mechanisms, oxidative stress was suggested to play a role in the early process of Cd- and/or As-induced tubular damage in the kidney. This study was performed to evaluate the significance of urinary biomarkers, role of oxidative stress, and effect of coexposure to environmental low-level exposure to Cd and/or As in the general population. Urine samples were collected from 290 adults (86 males and 204 females). Urinary concentrations of Cd and As were measured, and kidney biomarkers of toxicity such as beta(2)-microglobulin and N-acetyl-beta-D-glucosaminidase (NAG) activity determined in urine. Urinary malondialdehyde (MDA) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels were measured as oxidative stress indices. The mean concentration of Cd was 1.21 microg/L, 0.84 microg/g creatinine, and As was 5.7 microg/L, 3.95 microg/g creatinine in urine. NAG, MDA, and 8-OHdG were positively correlated with both Cd and As in urine. Positive correlations were also observed between NAG and oxidative indices. The effects of coexposure to Cd and As on biomarkers are more pronounced than for exposure to each metal alone. These findings suggest that chronic exposure to low levels of Cd and/or As might produce tubular damage in the kidney through oxidative stress in humans.

JWA gene is involved in cadmium-induced growth inhibition and apoptosis in HEK-293T cells

Cadmium (Cd) is widely dispersed in the environment due to occupational and personal (cigarette) emissions. Exposure of human embryonic kidney 293T (HEK-293T) cells to CdCl2 resulted in growth inhibition and apoptosis. Our previous studies demonstrated that JWA, a novel retinoic acid-inducible and cytoskeleton-associated gene, is a potential environmental-responsive gene with increased expression attributed to oxidative and heat-shock stresses. In the present study, JWA was also found to be responsive to Cd exposure. After treatment with 20 microM CdCl2 for 12 h, the expression level of JWA was increased with accompanied growth inhibition and apoptosis. In addition, knock-down JWA protein expression by using transient transfecting of HEK-293T cells with antisense JWA express vector showed a protective effect against Cd-induced apoptosis. To determine whether the upregulation of JWA by Cd involved regulation by transcriptional mechanisms, further reporter gene assays were employed, which demonstrated a marked increase in JWA promoter activity. In addition, elevated intracellular levels of ROS components (O2-* and H2O2) and activation of JNK, ERK, and MAPK were found with corresponding upregulation of JWA protein expression. These results suggest that Cd-induced growth inhibition and apoptosis may involve ROS generation and subsequent affect on MAPK signal pathway. JWA responsiveness to CdCl2 might be through both transcriptional and posttranslational mechanisms.

Cytoprotective and antioxidant role of diallyl tetrasulfide on cadmium induced renal injury: An in vivo and in vitro study

Cadmium (Cd) is an environmental and industrial pollutant that affects various organs in humans and animals. A body of evidence has accumulated implicating the free radical generation with subsequent oxidative stress in the biochemical and molecular mechanisms of Cd toxicity. Since kidney is the critical target of Cd toxicity, we carried out this study to investigate the effects of diallyl tetrasulfide (DTS), an organosulfur compound derived from garlic on Cd induced toxicity in the kidney of rats and also in the kidney cell line (vero cells). In experimental rats, subcutaneous administration of Cd (3 mg/kg bw/day) for 3 weeks induced renal damage, which was evident from significantly increased levels of serum urea and creatinine with significant decrease in creatinine clearance. A markedly increased levels of lipid peroxidation markers (thiobarbituric acid reactive substances and lipid hydroperoxides) and protein carbonyl contents with significant decrease in nonenzymic antioxidants (total sulphydryl groups, reduced glutathione, vitamin C and vitamin E) and enzymic antioxidants (superoxide dismutase, catalase, glutathione peroxidase and glutathione-S-transferase) as well as glutathione metabolizing enzymes (glutathione reductase, and glucose-6-phosphate dehydrogenase) were also observed in Cd intoxicated rats. Coadministration of DTS (40 mg/kg bw/day) and Cd resulted in the reversal of the kidney function accompanied by a significant decrease in lipid peroxidation and increase in the antioxidant defense system. In vitro studies with vero cells showed that incubation of DTS (5-50 microg/ml) with Cd (10 microM) significantly reduced the cell death induced by Cd. DTS at 40 microg/ml effectively blocked the cell death and lipid peroxidation induced by Cd (10 microM) indicating its cytoprotective property. Further, the flow cytometric assessment on the level of intracellular reactive oxygen species using a fluorescent probe 2', 7'-dichlorofluorescein diacetate (DCF-DA) confirmed the Cd induced intracellular oxidative stress in vero cells, which was significantly suppressed by DTS (40 microg/ml). The histopathological studies in the kidney of rats also showed that DTS (40 mg/kg bw/day) markedly reduced the toxicity of Cd and preserved the architecture of renal tissue. The present study suggests that the cytoprotective potential of DTS in Cd toxicity might be due to its antioxidant and metal chelating properties, which could be useful for achieving optimum effects in Cd induced renal damage.

Protective effect of quercetin on experimental chronic cadmium nephrotoxicity in rats is based on its antioxidant properties

Oxidative stress can play a key role in Cd-induced dysfunctions. Quercetin is a potent oxygen free radicals scavenger and a metal chelator. Our aim was to study the effect of quercetin on Cd-induced kidney damage and oxidative stress as well as its mechanism of action. Wistar rats were distributed in four experimental groups: control rats; Cd; quercetin and Cd+quercetin. Renal toxicity was evaluated by measuring urinary excretion of proteins, albumin, glucose and enzymes markers of tubular necrosis, as well as plasma concentration of creatinine. Plasma TBARS concentration and activity of antioxidant enzymes in kidney were also measured. Renal cell damage was assessed by electron microscopy. Animals that received both Cd and quercetin showed a better renal function than those receiving Cd alone. Cd-induced tubular lesions were markedly reduced in rats that also received quercetin. Cd-induced increase in plasma TBARS was prevented by the administration of quercetin. Total plasma antioxidants and renal superoxide dismutase and glutathione-reductase activities were higher in the group that received Cd and quercetin than in rats that received Cd alone. Quercetin administration does not modify the renal content or the urinary excretion of Cd. In conclusion, quercetin treatment prevents renal tubular damage and increased oxidative stress induced by chronic Cd administration, most probably throughout its antioxidant properties.

Cadmium affects tobacco cells by a series of three waves of reactive oxygen species that contribute to cytotoxicity

Cadmium is suspected to exert its toxic action on cells through oxidative damage. However, the transition metal is unable to directly generate reactive oxygen species (ROS) via redox reactions with molecular oxygen in a biological environment. Here, we show that bright yellow-2 (BY-2) tobacco cells exposed to millimolar concentrations of CdCl(2) developed cell death within 2-3 h. The death process was preceded by two successive waves of ROS differing in their nature and subcellular localization. Firstly, these consisted in the transient NADPH oxidase-dependent accumulation of H(2)O(2) followed by the accumulation of O(2) (-*) in mitochondria. A third wave of ROS consisting in fatty acid hydroperoxide accumulation was concomitant with cell death. Accumulation of H(2)O(2) was preceded by an increase in cytosolic free calcium concentration originating from internal pools that was essential to activate the NADPH oxidase. The cell line gp3, impaired in NADPH oxidase activity, and that was unable to accumulate H(2)O(2) in response to Cd(2+), was nevertheless poisoned by the metal. Therefore, this first wave of ROS was not sufficient to trigger all the cadmium-dependent deleterious effects. However, we show that the accumulation of O(2) (-*) of mitochondrial origin and membrane peroxidation are key players in Cd(2+)-induced cell death.

Common mechanisms in nephropathy induced by toxic metals

Various metals of unknown function in the body (Cd, Cr, Hg, Pb, U), trace elements in excessive concentrations (Co, Cu, Fe, Zn), or metals used in cancer therapy (Pt, V), accumulate in the mammalian kidney, largely in the proximal tubule (PT) cells, and cause functional and structural damage that results in reabsorptive and secretory defects. The intracellular mechanisms of their toxicity in the PT cells are not well known. Recent studies have indicated an oxidative stress with associated lipid peroxidation, apoptosis, and necrosis as common phenomena in the course of nephrotoxicity of these metals. However, a number of other phenomena, such as the selective inhibition and/or loss of various membrane transporters, enhancement of ion conductances, increased cytoplasmic concentration of calcium, deranged cytoskeleton and cell polarity, impaired endocytosis, swelling and fragmentation of mitochondria, increased expression of metallothionein, heat-shock and multidrug resistance proteins, loss of cell membrane integrity, as well as the damage of mitochondrial and genomic DNAs have been fragmentarily demonstrated for the action of some toxic metals, but their importance for the course of nephrotoxicity and the sequence of events in relation to oxidative stress, apoptosis, and necrosis have not been clearly established. Recent studies of metal toxicity in various tissues and cells of non-renal and renal origin enable us to estimate 'causes and consequences' of various phenomena in the metal-induced nephrotoxicity, and to assemble them in a possible common, time-related sequence.

Cadmium induces cell cycle arrest in rat kidney epithelial cells in G2/M phase

Cadmium (Cd) has been reported to cause cell cycle arrest in various cell types by p53-dependent and -independent mechanisms. This study was designed to investigate cell cycle progression in kidney cells that are the target of chronic Cd toxicity. Rat renal proximal tubular epithelial cells, NRK-52E, were treated with up to 20 microM CdCl2 in DMEM containing 10% calf serum for up to 24 h. Flow cytometric analysis revealed time- and concentration-dependent increases in cells in G2/M phase of the cell cycle. As compared to the control cells, the cells exposed to 20 microM Cd showed a doubling of the number of cells in this phase after 24 h. The cell cycle arrest was associated with a decrease in protein levels of both cyclins A and B. Further investigation into the mechanism revealed that Cd treatment led to down-modulation of cyclin-dependent kinases, Cdk1 and Cdk2, apparently by elevating the expression of cyclin kinase inhibitors, KIP1/p27 and WAF1/p21. Furthermore, the wild-type p53 DNA-binding activity was up-regulated. Based on these observations, it appears that Cd causes G2/M phase arrest in NRK-52E cells via elevation of p53 activity, increasing the expression of cyclin kinase inhibitors p27 and p21, and decreasing the expression of cyclin-dependent kinases Cdk1 and 2, and of cyclins A and B.

Cadmium-Induced Apoptosis in Rat Kidney Epithelial Cells Involves Decrease in Nuclear Factor-Kappa B Activity

Renal epithelial cells undergo apoptosis upon exposure to cadmium (Cd). Transcription factors, such as nuclear factor-kappa B (NF-kappaB), mediate the expression of a number of genes involved in apoptosis. The present study was designed to examine the involvement of this transcription factor in Cd-induced apoptosis. Rat kidney proximal tubular epithelial cells, NRK-52E, were incubated with up to 20 microM CdCl2 in serum-free medium for 5 h followed by incubation in serum-containing medium (without Cd) for an additional 12 h. The cells accumulated 582 +/- 19 ng Cd/mg protein after 5-h exposure to 20 microM Cd. As a result of Cd exposure, the DNA-binding activity of the p65 subunit of NF-kappaB was decreased in a concentration- and time-dependent manner. The activity of tumor necrosis factor-alpha-induced inhibitor of kappa B (IkappaB) kinase alpha was also inhibited by Cd. In addition, the phosphorylation of IkappaB-alpha and NF-kappaB p65, as well as the levels of NF-kappaB target gene products, cIAP-1 and cIAP-2, were reduced. Pretreatment of the cells with the antioxidant U83836E or butylated hydroxytoluene preserved the DNA-binding activity and blocked the Cd-induced decease in IkappaB-alpha phosphorylation. Cd exposure caused the activation of caspase-3, -7, and -9 and DNA fragmentation. By flow cytometry, 14.6 and 30.5% apoptosis was detected at 6 and 12 h after stopping the Cd exposure. Overexpression of NF-kappaB p65 by transient transfection protected the cells from the Cd-induced apoptosis. Conversely, attenuation of NF-kappaB activity by pretreatment with SN50, an NF-kappaB nuclear translocation inhibitor, potentiated apoptosis. These results suggest that Cd-induced apoptosis involves suppression of NF-kappaB activity which may be mediated by oxidative stress.

Cadmium inhibits the electron transfer chain and induces reactive oxygen species

Recent research indicates that cadmium (Cd) induces oxidative damage in cells; however, the mechanism of the oxidative stress induced by this metal is unclear. We investigated the effects of Cd on the individual complexes of the electron transfer chain (ETC) and on the stimulation of reactive oxygen species (ROS) production in mitochondria. The activity of complexes II (succinate:ubiquinone oxidoreductase) and III (ubiquinol:cytochrome c oxidoreductase) of mitochondrial ETC from liver, brain, and heart showed greater inhibition by Cd than the other complexes. Cd stimulated ROS production in the mitochondria of all three tissues mentioned above. The effect of various electron donors (NADH, succinate, and 2,3-dimethoxy-5-methyl-6-decyl-1,4-benzoquinol) on ROS production was tested separately in the presence and in the absence of Cd. ESR showed that complex III might be the only site of ROS production induced by Cd. The results of kinetic studies and electron turnover experiments suggest that Cd may bind between semiubiquinone and cytochrome b566 of the Q0 site of cytochrome b of complex III, resulting in accumulation of semiubiquinones at the Q0 site. The semiubiquinones, being unstable, are prone to transfer one electron to molecular oxygen to form superoxide, providing a possible mechanism for Cd-induced generation of ROS in mitochondria.

Nephrotoxicity and the proximal tubule. Insights from cadmium

Cadmium (Cd(2+)) is a non-essential heavy metal, which is taken up from the environment into the body through pulmonary and enteral pathways. The S1 segment of the kidney proximal tubule (PT) is a major target of chronic Cd(2+) toxicity. Renal dysfunction develops in up to 7% of the general population and in its most severe form displays major features of Fanconi syndrome, such as a defective protein, amino acid, glucose, bicarbonate and phosphate reabsorption. The major pathway for Cd(2+) uptake by PT cells (PTCs) in vivo is apical endocytosis of Cd(2+) complexed to the high-affinity metal-binding protein metallothionein (MT), which may be receptor-mediated. MT is subsequently degraded in endo-lysosomes, and Cd(2+) is liberated for translocation into the cytosolic compartment, possibly using transporters for Fe(2+), Zn(2+) or Cu(2+), such as the divalent metal transporter DMT1. Free Cd(2+) ions in the extracellular space are translocated across apical and/or basolateral PTC membranes into the cytosol via transporters, whose identity remains unknown. Cytosolic Cd(2+) generates reactive oxygen species (ROS), which deplete endogenous radical scavengers. ROS also damage a variety of transport proteins, including the Na(+)/K(+)-ATPase, which are subsequently degraded by the proteasome and endo-lysosomal proteases. Cd(2+) causes mitochondrial swelling and release of cytochrome C. If these ROS-mediated stress events are not balanced by repair processes, affected cells undergo apoptosis. But Cd(2+) also induces the upregulation of cytoprotective stress and metal-scavenging proteins, such as MT. In addition, Cd(2+) upregulates the detoxifying pump multidrug resistance P-glycoprotein, which appears to protect PTCs against Cd(2+)-induced apoptosis. Thus, Cd(2+) interferes with various cellular events ranging from mechanisms of induction of programmed cell death to activation of cell survival genes. A better understanding of the cellular mechanisms involved in Cd(2+) nephrotoxicity should provide insights into other heavy metal (e.g. Pb(2+), Hg(2+)) nephropathies and various forms of acquired Fanconi syndrome.

Delayed apoptosis post-cadmium injury in renal proximal tubule epithelial cells

BACKGROUND

Accumulation of the widespread environmental toxin cadmium (Cd) in the kidney results initially in proximal tubule dysfunction. Exposure to Cd has been previously shown to induce apoptosis in LLC-PK (Lily Laboratory Culture, Porcine Kidney) cells, which are a model of proximal tubule epithelium.

HYPOTHESIS

We postulated that modulation of the components of the apoptotic pathway triggered by Cd is amenable to therapeutic intervention.

METHODS

We subjected confluent LLC-PK cells grown on two-compartment filters and on plastic to Cd (1-50 microM). Apoptosis and changes in components of the apoptotic pathway were measured by immunocytochemical and immunoblot analysis during the period of exposure and following Cd withdrawal.

RESULTS

Insignificant apoptosis was seen during exposure to Cd and immediately after removal of this metal. Two waves of apoptosis were noted 6 and 48 h after the Cd was removed from the apical compartment. The apoptosis 48 h post-Cd exposure was accompanied by a decrease in cellular ATP levels and transepithelial resistance and preceded by an increase in p38 phosphorylation. Inhibition of p38 mitogen-activated protein kinase activity decreased the delayed apoptotic peak, without affecting the rate of recovery of the integrity of the renal epithelium. IGF-1 neither altered the delayed apoptosis nor facilitated the rate of recovery of the integrity of the renal epithelium.

CONCLUSION

We demonstrate that following exposure to Cd, renal epithelial cells undergo significant apoptosis, which appears to involve p38 and is not amenable to IGF therapy.

Recent studies on metallothionein: protection against toxicity of heavy metals and oxygen free radicals

Metallothionein (MT) is a ubiquitous, cysteine-rich, metal-binding protein. MT synthesis is induced by various stimuli such as cadmium, mercury, zinc, oxidative stress, glucocorticoid, and anticancer agents. Recently, transgenic mice with loss-of-function mutations in the MT-I/-II genes were established. It has been assumed that MT plays a role in the detoxification of heavy metals. In recent studies using MT-null mice, the ability of MT to protect against cadmium-induced renal, liver and bone injuries has been confirmed. Moreover, MT is also capable of scavenging oxygen free radicals. MT is involved in the protection of tissues against various forms of oxidative injury, including radiation, lipid peroxidation, oxidative stress caused by anticancer drugs, and conditions of hyperoxia. However, MT still lacks an established biological function. Unexpectedly, the MT-null mice were apparently in good health, and the critical biological roles of MT have been questioned. MT seems to be a protective protein produced in response to a variety of stresses. Here, current studies on the protective roles of MT against toxicity of heavy metals and reactive oxygen species are reviewed, and the putative biological functions of MT are discussed.