Metal-metal interactions among dietary toxic and essential trace metals in the rat

Exposure to e-cigarette aerosol over two months induces accumulation of neurotoxic metals and alteration of essential metals in mouse brain

Despite a recent increase in e-cigarette use, the adverse human health effects of exposure to e-cigarette aerosol, especially on the central nervous system (CNS), remain unclear. Multiple neurotoxic metals have been identified in e-cigarette aerosol. However, it is unknown whether those metals accumulate in the CNS at biologically meaningful levels. To answer this question, two groups of mice were whole-body exposed twice a day, 5 days a week, for two months, to either a dose of e-cigarette aerosol equivalent to human secondhand exposure, or a 5-fold higher dose. After the last exposure, the olfactory bulb, anterior and posterior frontal cortex, striatum, ventral midbrain, cerebellum, brainstem, remaining brain tissue and spinal cord were collected for metal quantification by inductively coupled plasma mass spectrometry and compared to tissues from unexposed control mice. The two-month exposure caused significant accumulation of several neurotoxic metals in various brain areas - for some metals even at the low exposure dose. The most striking increases were measured in the striatum. For several metals, including Cr, Cu, Fe, Mn, and Pb, similar accumulations are known to be neurotoxic in mice. Decreases in some essential metals were observed across the CNS. Our findings suggest that chronic exposure to e-cigarette aerosol could lead to CNS neurotoxic metal deposition and endogenous metal dyshomeostasis, including potential neurotoxicity. We conclude that e-cigarette-mediated metal neurotoxicity may pose long-term neurotoxic and neurodegenerative risks for e-cigarette users and bystanders.

NMR-based lipidomics of fish from a metal(loid) contaminated wetland show differences consistent with effects on cellular membranes and energy storage

Metals and metalloids are priority contaminants due to their non-degradable and bioaccumulative nature, and their ability to regulate and perturb diverse physiological processes in various species. Metal(loid)s are known to cause oxidative stress through production of reactive oxygen species (ROS), thus related endpoints like lipid peroxidation (LPO) have received considerable attention as biomarkers of exposure. However, the implications of metal(loid) toxicity including LPO on actual lipid profiles of species inhabiting contaminated systems are poorly understood. Here we applied Nuclear Magnetic Resonance (NMR) spectroscopy for untargeted lipidomics of mosquitofish (Gambusia holbrooki) collected from reference and metal(loid)-contaminated wetlands. We measured a range of trace elements in water and fish using inductively coupled plasma - mass spectrometry (ICP-MS), and interpreted site differences in the lipid profiles of mosquitofish in the context of known physiological responses to sub-lethal metal(loid) exposure. Results indicate deregulation of cellular membrane lipids (i.e., glycerophospholipids, cholesterol and sphingolipids) and increased energy storage molecules (i.e., triacylglycerols and fatty acids) in fish from the contaminated wetland. These responses are consistent with the recognised induction of oxidative stress pathways in organisms exposed to metal(loid)s and could also be symptomatic of mitochondrial dysfunction and endocrine disruption. It is difficult to attribute metal(loid)s as the sole factor causing differences between wetlands, and a more controlled experimental approach is therefore warranted to further explore mechanistic pathways. Nevertheless, our study highlights the benefits of untargeted ¹H NMR-based lipidomics as a relatively fast and simple approach for field-scale assessment and monitoring of organisms inhabiting metal(loid) contaminated environments.

Mixture risk assessment due to ingestion of arsenic, copper, and zinc from milkfish farmed in contaminated coastal areas

Human health risks associated with the consumption of metal-contaminated fish over extended periods have become a concern particularly in Taiwan, where fish is consumed on a large scale. This study applied the interaction-based hazard index (HI) to assess the mixture health risks for fishers and non-fishers who consume the arsenic (As), copper (Cu), and zinc (Zn) contaminated milkfish from As-contaminated coastal areas in Taiwan, taking into account joint toxic actions and potential toxic interactions. We showed that the interactions of As-Zn and Cu-Zn were antagonistic, whereas As-Cu interaction was additive. We found that HI estimates without interactions considered were 1.3-1.6 times higher than interactive HIs. Probability distributions of HI estimates for non-fishers were less than 1, whereas all 97.5%-tile HI estimates for fishers were >1. Analytical results revealed that the level of inorganic As in milkfish was the main contributor to HIs, indicating a health risk posed to consumers of fish farmed in As-contaminated areas. However, we found that Zn supplementation could significantly decrease As-induced risk of hematological effect by activating a Zn-dependent enzyme. In order to improve the accuracy of health risk due to exposure to multiple metals, further toxicological data, regular environmental monitoring, dietary survey, and refinement approaches for interactive risk assessment are warranted.

Arsenic-Copper Interaction in the Kidney of the Rat

1 The interaction between As and three toxic metals (Cd, Ni and Pb) and Cu (an essential trace metal) in the kidney was investigated in the rat by feeding diets containing various concentrations of As whilst maintaining constant concentrations of the other elements.

After 1, 3, 7 and 15 weeks of feeding, metal contents in the renal cortex and medulla, red blood cells and plasma were determined by atomic emission spectrometry (ICP-AES). 2 As accumulated in the whole kidney, whereas Cu accumulated only in the cortex. Accumulation of Cu was found to depend on the feeding period and dietary As concentration.

3 As was also accumulated in red blood cells, where saturation was found at 550 μg As g-1 cells.

4 Although Cd was also accumulated in the cortex, its accumulation was independent of the dietary As concentration. Ni and Pb were not detected by ICP-AES.

5 Chromatography of the supernatants from cortical homogenates of control and As-treated rat kidney suggested that Cu accumulated in renal metallothionein (MT). Its accumulation in this fraction was independent of that of Cd, indicating that the As-Cu interaction was not a result of MT induction, but rather that it might result from altered renal handling of Cu with subsequent incorporation into MT.

Exposure to multiple metals from groundwater-a global crisis: geology, climate change, health effects, testing, and mitigation

This paper presents an overview of the global extent of naturally occurring toxic metals in groundwater. Adverse health effects attributed to the toxic metals most commonly found in groundwater are reviewed, as well as chemical, biochemical, and physiological interactions between these metals. Synergistic and antagonistic effects that have been reported between the toxic metals found in groundwater and the dietary trace elements are highlighted, and common behavioural, cultural, and dietary practices that are likely to significantly modify health risks due to use of metal-contaminated groundwater are reviewed. Methods for analytical testing of samples containing multiple metals are discussed, with special attention to analytical interferences between metals and reagents. An overview is presented of approaches to providing safe water when groundwater contains multiple metallic toxins.

[Anemia induced by cadmium intoxication]

Anemia is commonly induced by chronic cadmium (Cd) intoxication. Three main factors are involved in the development of Cd-induced anemia: hemolytic, iron-deficiency, and renal. Intravascular hemolysis can occur at the early stage of Cd exposure owing to the direct damaging effect on erythrocytes. In addition, Cd that accumulates in erythrocytes affects membrane cytoskeletons and decreases cell deformability, and these cells are then trapped and destroyed in the spleen. Iron deficiency can be detected in animals after an oral exposure to Cd, which competes with iron for absorption in the intestines, leading to anemia. However, an increase in body iron content along with anemia is often observed in cases of parenteral exposure or itai-itai disease. Therefore, it is estimated that Cd disrupts the efficient usage of iron in hemoglobin synthesis in the body. Renal anemia is observed during the very last phase of chronic, severe Cd intoxication, such as itai-itai disease, showing a decrease in the production of erythropoietin from renal tubular cells. Because the renal anemia is based on the same pathophysiology as Cd-induced osteomalacia, which is derived from the disturbance of mineral metabolism due to renal tubular dysfunction, it is reasonable to include renal anemia in the criteria for the diagnosis of itai-itai disease. Hemodilution could also contribute to the development of Cd-induced anemia. Bone marrow hypoplasia or the inhibition of heme synthesis might only be involved in Cd-induced anemia in severe cases of Cd intoxication.

Proteomic Profiling in the Sera of Workers Occupationally Exposed to Arsenic and Lead: Identification of Potential Biomarkers

Arsenic (As) and lead (Pb) are important inorganic toxicants in the environment. Frequently, humans are exposed to the mixtures of As and Pb, but little is known about the expression of biomarkers resulting from such mixed exposures. In this study, we analyzed serum proteomic profiles in a group of smelter workers with the aim of identifying protein biomarkers of mixed As and Pb exposure. Forty-six male workers co-exposed to As and Pb were studied. Forty-five age-matched male office workers were chosen as controls. Urine As and blood Pb concentrations were determined. Serum proteomic profiles were analyzed by Surface-Enhanced Laser Desorption/Ionization Time-Of-Flight (SELDI-TOF) mass spectrometer on the WCX2 ProteinChip. Using Recursive support vector machine (RSVM) algorithm, a panel of five peptides/proteins (2097 Da, 2953 Da, 3941 Da, 5338 Da, and 5639 Da) was selected based on their collective contribution to the optional separation between higher metal mixture exposure and non-exposure controls. Among these five selected markers, the 3941 Da was down-regulated and the four other proteins were up-regulated. Descriptive statistics confirmed that these five proteins differed significantly between metal exposure and non-exposure. Interestingly, the combined use of the five selected biomarkers could achieve higher discriminative power than single marker. These results demonstrated that proteomic technology, in conjunction with bioinformatics tools, could facilitate the discovery of new and better biomarkers of mixed metal exposure.

Species differences in arsenic-mediated renal copper accumulation: a comparison between rats, mice and guinea pigs

1. Administration of arsenite leads to an accumulation of copper in the rat kidney. Owing to the high retention of arsenic in the erythrocytes, however, the rat is considered to possess special toxicokinetics of arsenic and is therefore considered less comparable with other species in this respect. 2. Therefore, we compared the effect of dietary arsenite in mice and guinea pigs with that in rats. Each species was divided into four groups of animals according to the diets fed which contained increasing concentrations of sodium arsenite (NaAsO2; 0, 10, 30 and 60 mg As/kg of diet). Animals were killed after 1, 2 and 3 weeks. Tissues were sampled and analyzed for arsenic and other trace metals (Cu, Fe, Zn and Mn). 3. Compared to controls with copper levels of about 10 microg Cu/g wet wt. in the renal cortex, dietary administration of arsenite up to 60 mg As/kg of diet for 3 weeks to rats increased cortical levels to 65 microg Cu/g wet wt. An increase of renal copper levels similar to that in rats, was only observed in guinea pigs but not in mice. Renal copper accumulation in guinea pigs was time- and concentration-dependent as in rats. Feeding a diet with 60 mg As/kg for 3 weeks increased cortical copper levels from about 6 - 40 microg Cu/g wet wt. Renal copper levels in mice as well as other trace metal levels in guinea pigs and mice were not essentially altered by dietary arsenite. 4. The study shows that the renal copper-arsenic interaction is not restricted to the rat. Since in rats and guinea pigs, but not in mice, arsenic accumulated in the kidney rather similarly, a common mechanism is suggestive. As it was previously shown in rats that only inorganic arsenic is involved in this interaction, a rapid conversion of the inorganic form into methylated metabolites as in mice may diminish the extent of the renal copper accumulation whereas the lack of, or a less efficient, methylation as in guinea pigs or rats increases it.

Small-intestinal absorption of cadmium and the significance of mucosal metallothionein

1 Although food intake is among the most important routes of Cd exposure, not many details are known about the intestinal absorption mechanisms of Cd. In this respect Cd is representative of most other nonessential, merely toxic metals. 2 Based on a concept of two distinguishable steps, intestinal absorption of Cd is characterized by high accumulation within the intestinal mucosa and a low rate of diffusive transfer into the organism. 3 After uptake into the mammalian organism, Cd is sequestered into hepatic metallothionein (MT). It is assumed that hepatic Cd-MT then gradually redistributes Cd to the kidney, which is the main target organ for chronic Cd toxicity. 4 When feeding low levels of dietary CdCl2, however, Cd accumulates preferentially in the kidney and to a lesser degree in the liver, a distribution pattern also found after intravenous and peroral administration of the Cd-MT complex itself. As dietary Cd induces intestinal MT, intestinal Cd-MT complexes could be at least partly responsible for the renal accumulation of dietary Cd. 5 For this mechanism, however, serosal release of mucosal Cd-MT is required. In fact, in vitro findings in rats reveal a concentration-dependent release of intestinal MT to the serosal side of the small intestine. These results indicate that endogenous intestinal MT may deliver Cd-MT to other inner organs, thus contributing to the preferential renal accumulation of ingested Cd.

Low ambient temperature decreases cadmium accumulation in the liver and kidneys of the bank vole (Clethrionomys glareolus)

The importance of photoperiod and ambient temperature on the accumulation of cadmium in the liver and kidneys of bank voles was determined in the present study. Males and females, aged 1 month, were given 3.0 micrograms Cd ml-1 drinking water and divided into four groups according to photoperiod (16 h light/8 h dark and 8 h light/16 h dark) and ambient temperature (20 or 5 degrees C); liver and kidneys were removed for cadmium as well as copper, iron and zinc analyses at the end of 6 weeks. Bank voles exposed to 5 degrees C in both photoperiods consumed approximately 30% less water containing cadmium than those kept at 20 degrees C. However, the total accumulation of cadmium in the liver and kidneys of males and females exposed to the low temperatures was 4.3-4.8 and 2.2-3.3 times less than that in animals maintained at room temperature in the long and short photoperiod, respectively. Simultaneously, the low temperature brought about an increase in the copper concentrations in the liver (12-43%) and kidneys (47-78%), giving rise to an inverse correlation between the cadmium accumulation and the tissue copper concentration. In contrast to cadmium and copper, the concentrations of iron and zinc were affected primarily by photoperiod. These findings indicate that ambient temperature is an important determinant of cadmium retention in the bank vole. It appears that low temperature decreases tissue cadmium accumulation not only by reducing cadmium intake but also through changes in copper metabolism.

Arsenic-copper interaction in the kidney of the rat: influence of arsenic metabolites

The present study was an attempt to investigate whether the renal accumulation of Cu observed in the kidneys of rats and guinea-pigs exposed to arsenite (As-III) was an effect of arsenite alone or also shared by its metabolites--arsenate (As-V), dimethylarsinic acid and monomethylarsonic acid. The four arsenic compounds were administered subcutaneously and separately to rats for 12 days in increasing doses. Kidney, liver and blood were taken and analysed for As, Cu and other trace elements by atomic emission spectrometry. Results indicate that administration of As-V leads to renal Cu accumulation similar to that observed on administration of As-III and that the accumulation in both cases is dependent on the dose of arsenic, although higher doses of As-V were required to achieve renal Cu levels comparable to that of As-III. A constant molar As:Cu ratio independent of arsenic dose was obtained in the kidney. Dimethylarsinic acid did not affect renal Cu levels at all. Administration of monomethylarsonic acid led to a slight increase in renal Cu levels which did not increase further in spite of increased doses of monomethylarsonic acid. It is concluded from these studies that neither the metabolic transformation of inorganic arsenic to its methylated products nor its metabolites (dimethylarsinic acid and monomethylarsonic acid) caused the observed renal Cu accumulation, rather, the inorganic form of As, either in the trivalent or pentavalent form is responsible.

Influence of dietary iron deficiency on nickel, lead and cadmium intoxication

The influence of dietary iron deficiency on acute nickel, lead or cadmium toxicity as reflected by the induction of hepatic, renal, and intestinal metallothionein (MT), disposition of the metals and alterations in hematological parameters, was investigated in young rats to ascertain whether the toxic effects of these metals modify under anemic conditions. The administration of Cd induced hepatic, renal and intestinal MT while that of Ni or Pb induced hepatic MT only. While dietary Fe deficiency did not affect MT induction by Cd, it enhanced the synthesis of renal and intestinal MT by Ni and Pb. The accumulation of Pb in liver and kidney and that of Cd in liver only, were enhanced by Fe deficiency; the tissue deposition of Ni remained unaffected by Fe deficiency. The induction of hepatic MT by Ni, Pb or Cd appears to be related to the concomitant rise in the hepatic Zn, Ca and Fe levels in normal rats. However, dietary Fe deficiency increased the hepatic Zn in response to Ni or Cd and the hepatic Ca in response to Pb administration.

The longitudinal distribution of cadmium, zinc, copper, iron, and metallothionein in the small-intestinal mucosa of rats after administration of cadmium chloride

Different routes of Cd intake may influence the intestinal distribution of Cd, metallothionein (MT), and trace metals differently. Therefore, we compared the effects of parenteral and enteral administration of Cd on the distribution of trace metals and MT along the small intestine. In a first experiment three groups of rats were employed: a control, one receiving CdCl2 within the drinking water, and another receiving sc injections of CdCl2. In a second experiment, rats were fed three different diets with either 0, 0.3, or 1 mmol CdCl2/kg for one and two weeks to study the time- and dose-dependent effects of orally administered Cd. Metal concentrations (Cd, Zn, Cu, Fe) were measured by atomic emission spectrometry and MT was determined by radioimmunoassay. Intestinal MT levels did not show proximodistal gradients in controls or after sc administration of Cd, but orally administered Cd increased mucosal MT levels longitudinally from the duodenum to the ileum. Cd levels paralleled those of MT. Compared with the metal concentrations in the controls, sc administration of Cd did not change intestinal Zn, Cu, and Fe levels. Oral administration of Cd, however, increased Cu and decreased Fe levels in the intestinal mucosa significantly. The second experiment revealed that only high dietary concentrations of Cd increase intestinal Cd and MT levels longitudinally toward the distal parts, whereas at lower dietary concentration the longitudinal distribution was reversed. This shows that different routes and doses of Cd intake lead to a different trace metal and MT distribution and emphasizes the role of dietary Cd in the local induction of small-intestinal MT.

Increased copper concentrations in rat tissues after acute intoxication with 2,3,7,8-tetrachlorodibenzo-p-dioxin

Recently, acutely toxic doses of the environmental pollutant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) have been reported to affect the hepatic distribution of essential metals in the rat. However, the reduced food intake by TCDD was not taken into account. Therefore, metal concentrations were determined in different rat tissues at the end of a toxicity study with TCDD in which a pair-fed control group was introduced. Male Sprague-Dawley rats received a single i.p. injection of corn oil/acetone with or without TCDD at 125 micrograms/kg. Controls and TCDD-treated rats were fed ad libitum; additionally, pair-fed controls received the amount of food consumed by their TCDD-treated partners 1 day before. Twenty-one days after dosing rats were killed and samples of liver, kidney and jejunum were taken for the analysis of Ca, Cu, Fe, Mg, Mn, and Zn. After acid digestion of the tissues metals were determined by atomic emission spectrometry (AES). The most outstanding effect of TCDD treatment was an increase of the copper levels in the kidney (4-fold, versus pair-fed controls) and in the liver (greater than 2-fold, versus pair-fed controls). Other metals were mainly affected by the reduced food intake only. Since Cu represents a trace metal the homeostasis of which depends on its biliary excretion and since TCDD is known to impair biliary flow and excretion, an impaired biliary excretion of Cu by TCDD is suggested as the causal mechanism.

Effect of a metal mixture in diet on the toxicokinetics and toxicity of cadmium, mercury and manganese in rats

The purpose of this work was to determine whether a metal mixture added to diet influences the toxicokinetics and toxicity of some elements. The metal mixture (MM) used in these experiments was ash (slag) from a coal gasification plant. The effect of this mixture (5 percent in diet) on the toxicokinetic and on the acute or subchronic toxicity of Cd, Hg, Mn was determined in rats of different ages. Rats were exposed for five weeks in toxicokinetic and six weeks in acute toxicity experiments. Sucklings were exposed through their mothers, which received the MM in diet over the pregnancy and lactation period. In toxicokinetic studies, half of the animals additionally received Cd, Hg or Mn (100, 50 or 2000 ppm, respectively) in drinking water. In subchronic experiments, six-week-old albino rats of both sexes were given MM in the diet and Cd, Hg or Mn in drinking water for 16 weeks. In toxicokinetic studies, 115mCd, 203Hg or 54Mn were administered orally or intraperitoneally to mothers and pups. Exposure to MM had no effect on the absorption, retention and organ distribution of these elements determined six days after radioisotope administration. In acute toxicity studies, exposure to MM in diet had no effect on LD50 values obtained eight days after oral administration of Cd, Hg or Mn to rats of different ages. In subchronic experiments, the effect of individual metals (Cd, Hg or Mn) was similar in animals with and without simultaneous exposure to the metal mixture (only a slight potentiation of a few health-effect parameters of cadmium was noticed in some animals). It is concluded that oral exposure to MM in the diet had almost no effect on the toxicokinetics and toxicity of Cd, Hg and Mn. This could be explained by the low level or low bioavailability of elements from MM, by the metal-metal interaction within the mixture or by the choice of health effect indicators determined. These results are presented as one of the potential approaches for studying the health effect of a metal mixture as occurring in the environment.

Interaction of lead with some essential elements in rat's kidney in relation to age

The aim of this study was to evaluate the interaction of lead given orally with Fe, Zn, and Cu in adult female rats and in their pups. Kidney was chosen for studying this interaction. Four different doses of lead (acetate) from 1500 to 7500 ppm were administered to mature female albino rats in beverages during 6 wk. The exposure lasted from mating up to 3 wk after delivery. Pb, Fe, Zn, and Cu were determined in kidneys of mothers and pups. Histopathological examinations were also performed. Results showed significantly lower concentrations of Fe, Zn, and Cu in kidneys of mothers on all lead levels. Their pups showed no change in concentrations of essential elements and even increased Fe at the highest exposure level. Concentrations of Pb and histopathological changes in the kidney were similar in mothers and offspring, although pups received only a fraction of the mothers' doses. Our results indicate that in immature animals the interaction of Pb with essential elements in the kidney is different from that in their mothers.