Changes in endogenous Zn and Cu distribution in different cytosolic protein fractions in mouse liver after administration of a single sublethal dose of CdCl(2)

The environment and male reproductive system: the potential role and underlying mechanisms of cadmium in testis cancer

Cadmium is a known human carcinogen, and has been shown to profoundly affect male reproductive function, at multiple levels, by exerting both endocrine and non-endocrine actions. Nevertheless, the potential role of cadmium in the etiology of testis cancer has been scantly investigated in humans, and, currently, available epidemiological observational studies are insufficient to draw definitive conclusions in this regard. On the contrary, experimental studies in laboratory animals demonstrated that cadmium is a strong inducer of testis tumors, mostly represented by benign Leydig cell adenoma; moreover, malignant transformation was also reported in few animals, following cadmium treatment. Early experimental studies in animals proposed an endocrine-dependent mechanism of cadmium-induced testis tumorigenesis; however, more recent findings from cell-free assays, in vitro studies, and short-term in vivo studies, highlighted that cadmium might also contribute to testis tumor development by early occurring endocrine-independent mechanisms, which include aberrant gene expression within the testis, and genotoxic effects, and take place well before the timing of testis tumorigenesis. These endocrine-independent mechanisms, however, have not been directly investigated on testis tumor samples retrieved from affected, cadmium-treated animals so far. The present review focuses on the relationship between cadmium exposure and testis cancer, by reporting the few epidemiological observational human studies available, and by providing animal-based experimental evidences of cadmium implication in the pathogenesis and progression of testis tumor. Moreover, the relevance of experimental animal studies to human cadmium exposure and the translational potential of experimental findings will be extensively discussed, by critically addressing strengths and weaknesses of available data.

The environment and male reproduction: The effect of cadmium exposure on reproductive function and its implication in fertility

Cadmium is an environmental pollutant known as endocrine disruptor. Testis is particularly susceptible to cadmium, and testis injury occurs at high but even low levels of exposure. Cadmium reproductive toxicity is mediated by multiple mechanisms, including structural damage to testis vasculature and blood-testis barrier, inflammation, cytotoxicity on Sertoli and Leydig cells, oxidative stress mainly by means of mimicry and interference with essential ions, apoptosis, interference with selected signaling pathways and epigenetic regulation of genes involved in the regulation of reproductive function, and disturbance of the hypothalamus-pituitary-gonadal axis. The current review outlines epidemiological observational findings from environmental and occupational exposure in humans, and reports experimental studies in humans and animals. Lastly, a focus on the pathogenetic mechanisms of cadmium toxicity and on the specific mechanisms of cadmium sensitivity and resistance, particularly assessed in animal models, is included. Despite convincing experimental findings in animals and supporting evidences in humans identifying cadmium as reproductive toxicant, observational findings are controversial, suffering from heterogeneity of study design and pattern of exposure, and from co-exposure to multiple pollutants.

Chronic Cadmium Exposure Lead to Inhibition of Serum and Hepatic Alkaline Phosphatase Activity in Wistar Rats

Alkaline phosphatase (ALP) activity in the serum and liver from rats administered with cadmium (Cd) in drinking water was studied. After metal administration, Cd showed a time-dependent accumulation in the liver, meanwhile metallothionein had a maximum increase at 1 month, remaining in this level until the end of the study. On the other hand, serum and liver ALP activity was decreased after 3 months exposure. To determine if Cd produced an inhibition on enzyme, apo-ALP prepared from both nonexposed and exposed rats was reactivated with Zn, showing 60% more activity as compared with the enzyme isolated from nonexposed rats. In vitro assays showed that Cd-ALP was partially reactivated with Zn; however, in the presence of cadmium, Zn-ALP was completely inhibited. Kinetic studies indicate a noncompetitive inhibition by Cd; these results suggest that Cd can substitute Zn, and/or Cd can interact with nucleophilic ligands essential for the enzymatic activity.

A combination of metallomics and metabolomics studies to evaluate the effects of metal interactions in mammals. Application to Mus musculus mice under arsenic/cadmium exposure

Arsenic and cadmium are toxic metals of environmental significance with harmful effects on man. To study the toxicological and biochemical effects of arsenic/cadmium in mammals a combined metallomic and metabolomic approach has been developed, complemented with the measurement of biochemical parameters in blood and histopathological evaluation of liver injury in mice Mus musculus under exposure to both xenobiotics. Size-exclusion chromatography (SEC) was combined with affinity chromatography (AF) and ICP-MS detection using species unspecific isotopic dilution analysis (SUID) to characterize the biological effects of As/Cd on selenium containing proteins in the bloodstream of exposed mice. On the other hand, both direct infusion mass spectrometry (DIMS) and gas chromatography-mass spectrometry (GC-MS) provided information about changes in metabolites caused by metals. The results show that As/Cd exposure produces interactions in the distribution of both toxics between organs and plasma of mice and antagonistic interactions with selenium containing proteins in the bloodstream. Interplay with essential metabolic pathways, such as energy metabolism and breakdown of membrane phospholipids were observed, which are more pronounced under As/Cd exposure. In addition, heavy metal and metalloid causes differential liver injury, manifested by steatosis (non-alcoholic fatty liver disease, NAFLD) and infiltration of blood cells into the space of Disse.

BIOLOGICAL SIGNIFICANCE

This work presents new contributions in the study of arsenic/cadmium interactions in mice Mus musculus under controlled exposure. With the combination of metallomic and metabolomic approaches the traffic of As and Cd from liver to kidney by means of blood was observed and excretion of As (as arsenic metabolites) or Cd (as MTCd) is inhibited with the simultaneous administration of As/Cd, and these toxic elements have important influence in the levels of seleno-proteins in the plasma. In addition, the metabolomic approach reveals inhibition of different metabolic cycles such as tricarboxylic acid and phospholipid degradation that causes membrane damage and apoptosis that is histopathologically confirmed. This article is part of a Special Issue entitled: Environmental and structural proteomics.

Evolution of metallotionein isoforms complexes in hepatic cells of Mus musculus along cadmium exposure

Characterization of Cd-binding proteins has great analytical interest due to the high toxicity of Cd to living organisms. Metallothioneins (MTs), as Cd(II)-binding proteins are of increasing interest, since they form very stable Cd chelates and are involved in many detoxification processes. In this work, inductively coupled plasma octopole reaction cell mass spectrometry and nanospray ionization time-of-flight mass spectrometry were used in parallel and combined with two-dimensional chromatography: size exclusion followed by reversed-phase high performance liquid chromatography, to study metal complexes of MT isoforms produced in hepatic cytosols of Mus musculus during exposure experiments to Cd. Exposure experiments were carried out by subcutaneous injection of a growing dose of the toxic element ranging from 0.1 to 1.0 mg of Cd per kg of body weight per day during 10 days. A control group and three exposure groups at days 2, 6 and 10 of exposure were studied, and different cadmium, copper and zinc complexes with MTs isoforms were isolated and characterized from the two most exposed groups. The results allow gaining insight into the mechanisms involved in metal detoxification by MTs, showing the changes in the stoichiometry of metal complexes-MTs along cadmium exposure.

The toxicity redox mechanisms of cadmium alone or together with copper and zinc homeostasis alteration: its redox biomarkers

Cadmium (Cd) is a toxic metal and can induce and/or promote diseases in humans (cancer, aging diseases, kidney and bone diseases, etc.). Its toxicity involves many mechanisms including the alteration of copper (Cu) and zinc (Zn) homeostasis leading to reactive oxygen species (ROS) production, either directly or through the inhibition of antioxidant activities. Importantly, ROS can induce oxidative damages in cells. Cadmium, Cu and Zn are also able to induce glutathione (GSH) and metallothioneins (MT) synthesis in a cell-type-dependent manner. As a consequence, the effects induced by these three metals result simultaneously from the inhibition of antioxidant activities and the induction of other factors such as GSH and MT synthesis. MT levels are regulated not only by the p53 protein in a cell-type-dependent manner, or by transcription factors such as metal-responsive transcription factor 1 (MTF-1) and cellular Zn levels but also by cellular GSH level. As described in the literature, DNA damage, GSH and MT levels are sensitive biomarkers used to identify Cd-induced toxicity alone or together with Cu and Zn homeostasis alteration.

Study of cadmium-induced cytotoxicity using two-photon excitation endogenous fluorescence microscopy

We demonstrate that using time-resolved two-photon excitation endogenous fluorescence microscopy, the cadmium (Cd)-induced cellular toxic level can be assessed by the free-to protein-bound reduced nicotinamide adenine dinucleotide (free/bound NADH) ratio in a living cell. NADH fluorescence excited at 730 nm is captured at different times following exposure to cadmium at a variety of concentrations. The temporal characteristics of NADH fluorescence from mitochondrial and nuclear compartments are analyzed, respectively. The results show that cadmium induces a significant increase of the free/bound NADH ratio in mitochondria and nucleus, caused by the inhibition effect on the electron transport chain (ETC) and the stimulating effect on the glycolysis pathway, respectively. It is found that induction of metallothionein (MT) in cells occurs after 4 h of exposure to a sublethal concentration of Cd and reaches a peak at 6 h. More importantly, the increase in MT level can effectively suppress the elevation of the free/bound NADH ratio caused by a subsequent exposure to a higher concentration of Cd, indicating that MT plays a key role in protecting cells from Cd-induced toxicity. Our findings show that the free/bound NADH ratio can potentially be used as a sensitive indicator of toxic and carcinogenic actions induced by Cd.

Chemical and ecotoxicological analyses of sediments and elutriates of contaminated rivers due to e-waste recycling activities using a diverse battery of bioassays

A multi-trophic, multi-exposure phase assessment approach was applied to characterize the toxicity of sediments collected from two rivers in Guiyu, China, an e-waste recycling centre. Elutriate toxicity tests (bacterium Vibrio fischeri and microalga Selenastrum capricornutum) and whole sediment toxicity test (crustacean Heterocypris incongruens) showed that most sediments exhibited acute toxicity, due to elevated heavy metals and PAHs levels, and low pH caused by uncontrolled acid discharge. The survival rates of crustaceans were negatively (p < 0.05) correlated with total PAHs in sediments (411-1755 mg kg(-1)); EC50s of V. fischeri on the elutriates were significantly correlated with elutriate pH (p < 0.01). Significant (p < 0.05) correlations between the induction of hepatic metallothionein in tilapia (Oreochromis mossambicus) and metal concentrations (Cu, Zn, Pb) in sediments were also observed, when fish were fed with diets containing sediment. The results showed that uncontrolled e-waste recycling activities may bring adverse effects to local aquatic ecosystem.

Importance of metallothioneins in the cadmium detoxification process in Daphnia magna

Good knowledge of the relationship between toxic metals and biological systems, particularly the sub-cellular fraction, could be a suitable early indicator of toxic effects. These effects and the sub-cellular behaviour of cadmium were studied with a widely used species in freshwater toxicity bioassays, Daphnia magna. In spite of this very commonplace usage in ecotoxicological studies, very few data are available on its toxicant metabolism and in particular metal homeostasis. Combining multi-tools analysis, a soluble protein was found: it is heat-stable, rich in sulfhydryl groups (differential pulse polarography), characterised by a molecular mass of approximately 6.5 kDa, with a G-75 chromatographic profile corresponding to the rabbit metallothioneins monomer, with few if any aromatic-containing amino acids, it binds metals (e.g. Cd, Cu), and its concentration increases with Cd exposure. This evidence led us to hypothesise that metallothioneins (MTs) are present in D. magna. Up to 75% of the Cd body burden with Cd exposure is bound to the MTs fraction. The increase in the Cd concentration in the surrounding medium and concomitantly in daphnids induces sub-cellular reorganisation of essential metals such as Cu and Zn. The rate of metals in the soluble cellular fraction and associated with MTs increases with the Cd body burden. Monitoring sub-cellular distribution of metals after exposure in the natural environment could be very useful for ecotoxicological assessment.

Histopathological changes in the liver, kidneys, and testes of bank voles environmentally exposed to heavy metal emissions from the steelworks and zinc smelter in Poland

Bank voles were trapped in the neighborhood of the Sendzimir steelworks in Krakow and the ZGH Boleslaw zinc smelter in Bukowno. The Borecka forest in the north of Poland served as a control area. Lead, cadmium, zinc, and iron concentrations were analyzed in the liver, kidneys, testes, and femur bones of the bank voles. Typically, high levels of lead and cadmium were found in the bones and kidneys, respectively. In the femurs of the rodents from Bukowno, 109.26 microg g(-1) dry weight of lead was detected. The kidneys of these animals had accumulated 32.98 microg g(-1) cadmium. Concentrations of zinc and iron in the tissues were at physiological levels. No damage was found in the tissues of the bank voles from the Borecka forest or in the testes of animals from other areas. Histopathological changes in the kidneys of the rodents from Krakow as well as changes to the liver and kidneys of the animals from Bukowno were demonstrated.

Damage to the liver, kidney, and testis with reference to burden of heavy metals in yellow-necked mice from areas around steelworks and zinc smelters in Poland

The influence of the steelworks in Warsaw and Krakow as well as the zinc smelters in Bukowno and Miasteczko Slaskie on lead, cadmium, zinc and iron concentrations and the structure of selected tissues of yellow-necked mice were analysed. The Borecka Forest was chosen as a control area. The highest concentrations of lead, 172.36 g/g dry weight, and cadmium, 23.58 g/g, were detected in the femurs and kidneys, respectively, of rodents caught in Bukowno. Zinc and iron concentrations ranged over physiological values. No histopathological changes were observed in analysed tissues of all rodents in the control area. Damage occurred in the liver and kidneys of animals from all other sites and in the testes of rodents from Bukowno. Decreased glycogen content, interstitial fibrosis, and increased number of pyknotic nuclei as well as necrosis were seen in hepatocytes. In the kidneys hyperplasia of the tubules, atrophy of glomeruli, interstitial fibrosis and necrosis were observed. Degenerate cells were present in the lumen of seminiferous tubules of animals from the Bukowno area. Even relatively low concentrations of lead and cadmium, like those found in the liver and kidneys of rodents from the neighbourhood of the steelworks, caused histopathological changes.