Turnover of parenterally administered zinc and cadmium and the redistribution of metallothionein bound zinc in newborn rats

The whole body retention, tissue distribution and protein binding patterns of 65Zn were compared with 109Cd in newborn rats during postnatal development. One-day-old pups received a single injection of either 65Zn (2.5 microCi) or 109Cd (2.5 microCi plus 1 mg Cd/kg as CdCl2). During the 22 days of age, the whole body retention of 109Cd was higher than that for 65Zn. The biological half times were 466 and 46.3 days for 109Cd and 65Zn, respectively. There were marked differences in tissue deposition of these metals. Both liver and kidney accumulated more 109Cd than other tissues while the 65Zn showed a uniform distribution, with a gradual decrease in radioactivity with age. At the time of weaning, 109Cd had accumulated mainly in liver and kidney whereas, 65Zn was found predominantly in bone and skin. The specific binding of 109Cd to hepatic MT in newborn rats did not change with growth. Although a significant amount of 65Zn initially accumulated in the MT fractions in the liver, it was transferred gradually to high molecular weight protein fractions during development. The administration of these 2 metals had no effect on the body weight, liver weight and total hepatic zinc concentration. However, a significantly high content of MT and zinc in MT fractions was detected in the livers of Cd-treated rats at 22 days of age. The results show the transfer of the essential metal, zinc from hepatic MT to other proteins and the specific binding of cadmium, the non-essential metal to MT during postnatal development in rats.     

Dynamics of (Cd,Zn)-metallothioneins in gills, liver and kidney of common carp Cyprinus carpio during cadmium exposure

Cadmium concentrations, (Cd,Zn)-metallothionein (MT) concentrations, MT synthesis and the relative amounts of cadmium bound to (Cd,Zn)-MTs were determined in gills, liver and kidney of common carp Cyprinus carpio exposed to 0, 0.5 microM (0.06 mg.l(-1)), 2.5 microM (0.28 mg.l(-1)) and 7 microM (0.79 mg.l(-1)) Cd for up to 29 days. Cadmium accumulation was in the order kidney > liver > gills. Control levels of hepatic (Cd,Zn)-MT were four times higher compared to those of gills and kidney. No increases in (Cd,Zn)-MT concentrations were observed in liver during the exposure period. In comparison with control carp, (Cd,Zn)-MT concentrations increased up to 4.5 times in kidney and two times in gills. In both these organs, (Cd,Zn)-MT concentrations were linearly related with cadmium tissue levels and with the de novo synthesis of MTs. Hepatic cadmium was almost completely bound to (Cd,Zn)-MT, while percentages of non-MT-bound cadmium were at least 40% in gills and 25% in kidney. This corresponded with a total saturation of (Cd,Zn)-MT by cadmium in kidney and a saturation of approximately 50 and 60% in gills and liver, respectively. The final order of non-MT-bound cadmium was kidney > gills > liver. Our results indicate that cadmium exposure causes toxic effects, which cannot be correlated with the accumulated levels of the metal in tissues. Although cadmium clearly leads to the de novo synthesis of MT and higher (Cd,Zn)-MT concentrations, the role of this protein in the detoxification process is clearly organ-specific and its synthesis does not keep track with cadmium accumulation.     

Induction and binding of Cd, Cu, and Zn to metallothionein in carp (Cyprinus carpio) using HPLC-ICP-TOFMS.

The binding of Cd, Cu, and Zn to metallothionein in carp was studied under control and acute Cd exposure scenarios. Carp were exposed to different Cd concentrations for 96 h. Total (Cu, Cd, Zn)-MT levels were determined by the cadmium thiomolybdate saturation assay. Total tissue and cytosolic Cd, Cu, and Zn concentrations were determined by ICP-MS. The cytosolic metal speciation was determined by high pressure liquid chromatography (size-exclusion [SE] in combination with anion exchange [AE]) directly coupled to an inductively coupled plasma time of flight mass spectrometer (ICP-TOFMS). This coupled technique allows the chromatographic separation and online determination of the metals associated to the protein fractions separated. Very strong differences in the tissue compartmentalization and cytosolic speciation of the metals were observed. For example, over 30% of cytosolic zinc was bound to MT in liver while this was only 2% in the kidneys although total cytosolic levels were considerably higher. Induction of metallothionein during cadmium exposure was also tissue specific, displaying different response patterns in gills, liver, and kidney. Cadmium accumulated much stronger in liver and kidney compared to the gills and the latter also showed much lower MT levels. The renal MT-induction was more sensitive to Cd exposure than the hepatic MT induction since a significant increase of Cd-MT and total MT levels occurred at lower tissue Cd concentrations in the kidney in comparison to the liver, except for the highest Cd exposure level where a drastic 10-fold increase in hepatic Cd-MT was observed. At this Cd exposure level also an apparent spill over of zinc to the high molecular weight fraction was observed in the kidneys.     

Effects of Zn pre-exposure on Cd and Zn bioaccumulation and metallothionein levels in two species of marine fish

Zinc is an essential trace metal but also a potential toxicant to aquatic organisms. In this study, two juvenile marine fish species, the black sea bream Acanthopagrus schlegeli and the grunt Teraponjarbua, were pre-exposed to Zn either from waterborne (0.74-170 microg L-1) or dietary (39-5926 microg g-1) Zn for 1 or 3 weeks. The concentrations of Zn and metallothionein (MT) in the whole body of the black sea bream and in the gills, viscera and carcass of the grunt were then measured during this pre-exposure. Following the pre-exposure, both fish species were then exposed to 109Cd and 65Zn labeled food or water to quantify the dietary assimilation efficiency (AE) and the uptake rate of dissolved Cd and Zn. Zn concentrations in both fish species were enhanced after pre-exposure, but the increases were much less than the increase of ambient Zn pre-exposure concentration. Following Zn pre-exposure, MT concentrations in the viscera and carcass were significantly elevated, whereas the MT levels were not significantly elevated in the gills. Waterborne and dietary Zn exposure enhanced the uptake rates of dissolved Cd and Zn in both fish. The maximum increases of uptake rate constants of dissolved Cd and Zn were up to 1.9-2.8 and 2.1-2.6 times, respectively, in the seabream and grunt. In contrast, dietary assimilation efficiency of Cd and Zn was not significantly enhanced following Zn pre-exposure. A positive linear relationship was found between the uptake rate constants of dissolved metals and Zn or MT concentrations in the fish. The results suggested that Zn pre-exposure increased the potential of metal uptake from ambient water, but had little effect on dietary metal uptake. Furthermore, the Zn body concentration and metal uptake from the dissolved phase were significantly dependent on the fish body size.     

Effects of long term sublethal Cd exposure in rainbow trout during soft water exposure: implications for biotic ligand modelling

The objectives of the study were to determine the physiological and toxicological effects of chronic cadmium exposure on juvenile rainbow trout in soft water. Particular attention focused on acclimation, on comparison to an earlier hard water study, and on whether a gill surface binding model, originally developed in dilute soft water, could be applied in this water quality to fish chronically exposed to Cd. Juvenile rainbow trout, on 3% of body weight daily ration, were exposed to 0 (control), 0.07, and 0.11 microg l(-1) Cd [as Cd(NO(3))(2).4H(2)O] in synthetic soft water (hardness=20 mg l(-1) as CaCO(3), alkalinity=15 mg l(-1) as CaCO(3), pH 7.2) for 30 days. Mortality was minimal for all treatments (up to 14% for 0.11 microg l(-1) Cd). No significant effects of chronic Cd exposure were seen in growth rate, swimming performance (stamina), routine O(2) consumption, or whole body/plasma ion levels. In contrast to the hard water study, no acclimation occurred in either exposure group in soft water, with no significant increases in 96-h LC(50) values. Cadmium accumulated in a time-dependent fashion to twice the control levels in the gills and only marginally in the liver by 30 days. No significant Cd accumulation occurred in the gall bladder or whole body. Cadmium uptake/turnover tests were run using radioactive 109Cd for acute (3 h) exposures. Saturation of the gills occurred for control fish but not for Cd-exposed fish when exposed to up to 36 microg l(-1) Cd for 3 h. Cd-exposed trout accumulated less 'new' Cd in their gills compared to controls and they internalized less 109Cd than control fish. This effect of lowered Cd uptake by the gills of acclimated trout was earlier seen for the fish acclimated to 10 microg l(-1) Cd in hard water. The affinity of the gill for Cd was greater in hard water (logK(Cd-gill)=7.6) than in soft water (logK(Cd-gill)=7.3) but the number of binding sites (B(max)=0.20 microg g(-1) gill) was similar in both media. In addition, there was a shift in affinity of the gill for Cd (i.e. lowered logK(Cd-gill)) and increased B(max) with chronic Cd exposure in both soft water and hard water. We conclude that the present gill modelling approach (i.e. acute gill surface binding model or Biotic Ligand Model) does work for soft and hard water exposures but there are complications when applying the model to fish chronically exposed to cadmium.     

Interacting effects of zinc and cadmium on the cadmium distribution in the mouse

Effects of zinc (Zn) on cadmium (Cd) distribution in the mouse body were investigated after intranasal administration. The amounts of Cd (2 x 10(-6) M/0.02 ml) reaching respiratory organs increased as the ip dose of pentobarbital increased. Administration of Zn with Cd (2 x 10(-6) M Zn + 2 x 10(-6) M Cd /0.02 ml) further increased the Cd amounts reaching respiratory organs and increased mouse mortality. A single administration of Cd increased Cd levels in blood, liver, kidney and respiratory organs. High levels of Cd were maintained for at least 90 days in these organs after single administrations of Cd. The administration of Cd plus Zn further increased the Cd content in these organs during 0-60 min after administration. However, simultaneous administration of Zn with Cd inhibited prolonged Cd accumulation in kidney and liver. These results suggest that intranasally administered Zn (2 x 10(-6) M) has dual effects on Cd movement. Zn further increases the Cd levels in the lung and mouse mortality increases. On the contrary, Zn inhibits prolonged Cd accumulation in mice and decreases the chronic toxicity in mice that survive the acute phase.     

Calcium effects on cadmium uptake,redistribution, and elimination in minnows,Phoxinus phoxinus,acclimated to different calcium concentrations

A short ‘pulse’ of ¹⁰⁹Cd (0.01 μg Cd/l) was given in the synthetic experimental water to four groups of minnows, Phoxinus phoxinus, acclimated to different calcium concentrations (0.2, 0.5, 2, and 5 mM Ca). The fate of the radioactive metal within the fish was followed during an elimination period. The study was designed as an uptake-release study and the main effect of calcium was observed on the ¹⁰⁹Cd uptake in the gills which decreased with increasing Ca levels. This caused a lower metal accumulation in the liver and kidney. Increased Ca levels resulted in a slower transfer of ¹⁰⁹Cd from the gills to the blood indicated both by the slower ¹⁰⁹Cd elimination rates in the gills and slower accumulation rates in liver and kidney. This effect may not have been caused by Ca directly since the ¹⁰⁹Cd transfer rate could have been dependent on the amount of ¹⁰⁹Cd retained in the gill. Liming of acidified fresh waters increases the calcium concentrations in the water. One of the positive effects of this increase might be a lower heavy-metal uptake in fish and a subsequent decreased metal toxicity to fish.     

Plasma clearance of cadmium and zinc in non-acclimated and metal-acclimated trout

Adult rainbow trout were pre-exposed to a sublethal concentration of waterborne cadmium (Cd, 26.7 nmol/l) or waterborne zinc (Zn, 2294 nmol/l) for 30 days to induce acclimation. A single dose of radiolabeled Cd (64.4 nmol/kg) or Zn (183.8 nmol/kg) was injected into the vascular system of non-acclimated and Cd- or Zn-acclimated trout through indwelling arterial catheters. Subsequently, repetitive blood samples over 10 h and terminal tissue samples (liver, heart, bile, stomach, intestine, kidney, gills, muscle, and spleen) were taken to characterize the effect of metal acclimation on clearance kinetics in vivo. Plasma clearance of Cd in Cd-acclimated fish (0.726+/-0.015 and 0.477+/-0.012 ml/min per kg for total and newly accumulated Cd, respectively), was faster than that in non-acclimated trout (0.493+/-0.013 and 0.394+/-0.009 ml/min per kg). Unlike plasma Cd, the levels of Cd in red blood cells (RBCs) were 1.2-2.2 times higher in Cd-acclimated fish than in non-acclimated fish. At 10 h post-injection, the liver accumulated the highest proportion ( approximately 22%) of the injected Cd dose in both non-acclimated and Cd-acclimated fish but did not account for the difference in plasma levels of Cd between two groups. Plasma clearance of Zn ( approximately 0.23 ml/min per kg for new Zn) was substantially lower than Cd clearance. Pre-acclimation to waterborne Zn reduced the new Zn levels in RBCs, but did not affect the clearance of Zn from blood plasma or tissue burdens of Zn in fish. Bile concentrations of both Cd and Zn were elevated in acclimated fish, but total bile burden accounted for <1% of the injected metal dose. The results suggest that the detoxification process of injected plasma Cd is stimulated by pre-acclimation to waterborne Cd, and that Zn levels are homeostatically controlled in both non-acclimated and acclimated trout.     

Hepatic and renal metallothionein induction by an oral equimolar dose of zinc, cadmium or mercury in mice.

The hepatic and the renal subcellular distribution of zinc, cadmium or mercury and induction of tissue metallothionein (MT) at 24, 48 and 72 h following an oral equimolar dose (15 micro;mol metal/kg) of zinc (II) chloride, cadmium (II) chloride or mercury (II) chloride in male albino mice were investigated. There was a moderate increase in hepatic and renal zinc levels mainly in their nuclear mitochondrial fraction (NMF) 24 h post zinc chloride administration. Subsequently, the hepatic zinc increased and the renal zinc declined with time. The zinc-induced hepatic MT level was maximum at 48 h, which decreased slightly thereafter, while there was no marked increase in renal MT level at any time interval. The cadmium was equally distributed in liver and kidney more in their supernatant cytosol fraction (SCF) than in their NMF at 24 h after a dose of cadmium chloride. The cadmium levels showed a decreasing trend in hepatic fractions and an increasing trend in renal fractions with time. The cadmium-induced hepatic and renal MT were substantial at 24 h post cadmium administration, the former decreased thereafter while the latter enhanced at 48 h before declining. The accumulation of mercury in kidney was 1.5 times that in liver, which was localised more in their SCF than in their NMF at 24 h in response to a dose of mercuric chloride. The mercury levels of hepatic and renal subcellular fractions started declining after 24 h and at 72 h they were significantly lower. The induction of hepatic and renal MT was maximum at 24 h after mercuric chloride administration, which declined thereafter concomitant with the decrease in their mercury levels. However, the MT levels in both the organs remained considerably higher than in normal animals at 72 h post exposure. The results show that the accumulation of metal in liver and kidney follows the order: Hg > Cd > Zn and the induction of MT follows Hg > Cd > Zn in liver and Cd > Hg > Zn in kidney. The alterations in zinc and copper homeostasis were more marked in liver than in kidney and follows the order: Hg > Cd > Zn.     

Effects of sodium pyridinethione on the uptake and distribution of nickel, cadmium and zinc in pregnant and non-pregnant mice

Oral administration of sodium pyridinethione together with 63Ni2+, 109Cd2+ or 65Zn2+ to non-pregnant mice resulted in very markedly increased levels of the metals in several tissues in comparison with animals given the metals alone. For 63Ni2+ the sodium pyridinethione induced a strong labelling of the pancreatic islets and of the melanin of pigmented tissues. A considerable radioactivity was also obtained in the peripheral and central nervous system. For 109Cd2+ a strong radioactivity was observed in the red pulp of the spleen and the neurohypophysis and, in addition, in the liver and the kidney. For 65Zn2+ the distribution pictures in mice given 65Zn2+ only were similar to those seen in mice given the metal together with sodium pyridinethione, although the radioactivity in all tissues of the latter animals was much higher than in the former. All 3 metals were shown to form lipophilic complexes with pyridinethione (the nickel and zinc complexes being more lipophilic than the cadmium complex) and a facilitated penetration of the complexed metals through the cellular membranes is probably important for the observed results. Differences in the stability of the complexes in the body may be one factor of importance for the marked differences in the obtained distribution pictures but other factors may also be involved, as discussed in the paper. Experiments in pregnant mice showed markedly increased levels of 63Ni2+ and 65Zn2+ in the foetuses as a result of the sodium pyridinethione administration, whereas for 109Cd2+ only a small increase was observed. Our results suggest that effects on the disposition of metals may be important for the toxicity of the pyridinethiones.     

A field study examining metal elimination kinetics in juvenile yellow perch (Perca flavescens)

Currently little is known about how and at what rate fish eliminate metals in natural environments. To address this knowledge gap we examined metal elimination kinetics in the field using juvenile yellow perch (Perca flavescens) that were caught in a metal-contaminated lake (elevated levels of Cd, Cu and Zn) and transplanted to cages held within a reference lake. Fish were sampled from the cages over 75 d and changes in metal concentrations were measured in the gills, gut, liver and kidney. In transplanted fish, Cd concentrations decreased most rapidly in the gills and gut, i.e. from organs in contact with the ambient water and food; biological half lives (t1/2) were 18 and 37 d, respectively, for each organ. Longer half-lives were observed in the liver (75 d) and kidney (52 d) for this metal. Elimination of excess Cu by the liver and gut occurred much more rapidly, with estimated half-lives of labile Cu being 8 and 4 d, respectively, for these two organs. In contrast to Cd and Cu, there was little Zn elimination. To compare how the liver handles different metals during elimination, we used a differential centrifugation approach to examine changes in metal concentrations (Cd and Cu) at the sub-cellular level. Consistent with the long half-life observed for Cd at the whole organ level, there was no significant loss of Cd from any of the sub-cellular fractions. Copper, on the other hand, was lost from both the organelle and cellular debris fractions. As these fractions likely contain structures such as lysosomes, we suggest that Cu is depurated from the liver by direct elimination of these sub-cellular vesicles. These field results clearly demonstrate how the liver handles essential (Cu, Zn) and non-essential metals (Cd) differently during depuration.     

Metal bioaccumulation in selected tissues of barb (Barbus sp.) and common carp (Cyprinus carpio,Linnaeus 1758) from the Keban Dam Lake,Turkey

Abstract

The aquatic life has been negatively influenced by harmful effects of environmental toxic elements, including heavy metals. The elevated concentrations of metals may be harmful for aquatic animals and human health. Herein, the present study deals with assessment of the bioavailability of metals [cadmium (Cd), chrome (Cr), copper (Cu), zinc (Zn), iron (Fe), lead (Pb), manganese (Mn), mercury (Hg), nickel (Ni), and selenium (Se)] in organs such as muscle, gills, liver, kidney, and gonad of the commercially consumed Barbus sp. and Cyprinus carpio (Linnaeus, 1758) collected from Keban Dam Lake, eastern Turkey. The fish were captured from four different stations of Keban Dam Lake. Our results indicated that Fe and Zn concentrations were the highest in all tissues of two fish species while Cd concentrations were the lowest levels. In addition, detected metals accumulated in the muscle of common carp at higher levels compared to Barbus sp. The results from the present study also demonstrated significant variations and considerable differences in the concentrations of all 10 elements between the four stations and different fish tissues. Overall, the concentrations of detected metals in the muscle were many folds higher than the permissible level prescribed by some national and international legislation, which raises health risk concerns.     

Antioxidant enzymes activity and lipid peroxidation in liver and kidney of rats exposed to cadmium and ethanol.

The oxidative status of liver and kidney of rats co-exposed to cadmium (50 mg Cd/l in drinking water) and ethanol (5 g EtOH/kg body weight/24 h, intragastrically) for 12 weeks was studied. The activities of antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT) as well as the concentration of malondialdehyde (MDA), as an indicator of lipid peroxidation, were measured in homogenates of the liver and kidney. Concentrations of zinc (Zn), copper (Cu), iron (Fe) and Cd in the serum or blood, and their content in the liver and kidney as well as EtOH concentration in the whole blood were assayed. Daily Cd intake in the Cd and Cd+EtOH groups was similar and ranged from 2.39 to 4.88 mg/kg body weight/24 h and from 2.64 to 4.14 mg/kg body weight/24 h, respectively. After the administration of EtOH alone, the activity of SOD increased in the kidney and decreased in the liver, whereas the activity of CAT decreased in both these organs, and MDA concentration increased in the liver and was unchanged in the kidney. The exposure to 50 mg Cd/l led to a decrease in the activities of SOD in the liver and CAT in the liver and kidney, and an increase in the kidney activity of SOD and MDA concentration in both these organs. In the rats co-exposed to Cd and EtOH, the kidney activity of SOD and the liver concentration of MDA were lower, whereas the kidney activity of CAT was higher compared to the Cd group. The concentration of Fe in the serum and its content in the liver of rats treated with EtOH increased, whereas the concentrations of Zn and Cu in the serum and the content of Zn, Cu and Fe in the kidney and that of Zn and Cu in the liver were unchanged. In the liver and kidney of rats treated with Cd alone, the content of Fe was decreased and that of Zn and Cu was enhanced. After EtOH administration to Cd-exposed rats, a decrease in Cu serum concentration and its liver content and an increase in Fe concentration in the serum and its content in the liver and kidney, compared to the group exposed to Cd alone, were noted. Moreover, EtOH decreased the blood Cd concentration and its accumulation in the liver and kidney of these animals. EtOH alone decreased Cd content in the liver and increased in the kidney, however the whole content of Cd in these organs was unchanged compared with control. The results of this study indicate that despite the ability of Cd and EtOH to induce the oxidative stress the effect in the liver and kidney is not intensified at simultaneous exposure to both substances. The changes in the studied indicators of oxidative stress (SOD, CAT and MDA) observed in the kidney and especially in the liver of the rats co-exposed to Cd and EtOH may result from an independent effect of Cd and/or EtOH and also from their interaction. The interactive effect may involve, among others, changes in Cd accumulation and content of Zn, Cu and Fe in these organs and their concentration in serum. Since the rats treated with Cd and Cd+EtOH had reduced drinking fluids intake that might result in dehydratation, the effect of the both xenobiotics on the oxidative status of the body may be not solely due to Cd and/or EtOH, but also the modyfing influence of accompanying alterations such as reduced water intake and dehydratation. The results of the study allow us to hypothesize that Cd-exposed alcohol misusers are not at enhanced risk of liver and kidney damage due to lipid peroxidation.     

Gastrointestinal absorption of cadmium in mice during gestation and lactation: II. Continuous exposure studies

The effect on cadmium retention of continuous exposure to drinking water containing low levels of cadmium during pregnancy and lactation was studied in mice. Female mice were provided drinking water ad libitum containing ¹⁰⁹CdCl₂ (0.03 μCi ¹⁰⁹Cd/ml, 0.11 ppb total cadmium) throughout either gestation, lactation, or a combined period of pregnancy and lactation. Nonpregnant control mice were exposed to the same cadmium solution for similar time periods. Dams in all three experimental groups retained two to three times more cadmium (expressed as percentage of ingested dose) than did nonpregnant controls. The ¹⁰⁹Cd contents of liver, kidney, mammary tissue, and duodenum increased strikingly in all three groups. Increases in kidney and mammary tissue were particularly apparent during lactation, with increases of fivefold for kidney and at least ninefold for mammary tissue, compared to levels in nonpregnant controls. Increases in ¹⁰⁹Cd retention by the duodenum were fivefold during gestation and three- to fourfold during lactation. The kidneys of dams exposed during lactation retained 53% of the whole body ¹⁰⁹Cd, while kidneys of nonpregnant controls retained only 27%. Results indicate that pregnant and lactating mice absorb and subsequently retain substantially more cadmium from their diets than do nonpregnant mice.     

Biological levels of cadmium and zinc in the small intestine of non-occupationally exposed human subjects

The objective of this study was to estimate the relationships between cadmium (Cd) levels in the small intestine and other organs (kidney, liver, lungs) and factors influencing the intestinal Cd levels in humans, as based on autopsy analysis of subjects not exposed to Cd occupationally. The study also involved estimating the levels of zinc (Zn) in these organs, as it is known that this element exerts interactions with Cd at the level of absorption and tissue binding. The levels of Cd and Zn were determined in the renal cortex, liver, lungs and three fragments of the small intestine (duodenum, jejunum, ileum) of 29 subjects deceased at the age 42 +/- 13 years. Flame atomic absorption spectrometry (AAS; kidneys, liver) and flameless AAS (lungs, intestine) were used. The level of Cd in the lungs was used as a marker of smoking habit. The determined levels (mean +/- SD) were: 0.28 +/- 0.16 microg Cd/g and 15.2 +/- 3.4 microg Zn/g in the duodenum; 0.26 +/- 0.15 microg Cd/g and 16.9 +/- 3.7 microg Zn/g in the jejunum; 0.13 +/- 0.07 microg Cd/g and 14.6 +/- 5.4 microg Zn/g in the ileum. Intestinal Cd levels are correlated with organ and total body Cd, and this was best expressed for Cd in ileum (r=0.67 with renal, r=0.71 with hepatic and r=0.68 with total Cd). In conclusions, the levels of Cd in the small intestine of humans are relatively low and reflect predominantly the whole body retention of this element. Somewhat higher levels of Cd are contained in the initial parts of the small intestines. In all fragments of small intestines the levels of Cd are higher in smokers. Also, the levels of Zn were relatively low and did not correlate with the levels of Cd.     

Gastrointestinal absorption of cadmium and metallothionein

Intestinal uptake and transport of cadmium (Cd) to different organs were studied in control and oral zinc pretreated rats using an in situ intestinal loop model. Intestinal loop was incubated with either CdCl2 or Cd-metallothionein (Cd-MT) for 30 and 60 min in rats under anesthesia. Induction of MT by oral Zn pretreatment had little effect on intestinal uptake of Cd ion. However, when intestinal loop was incubated with exogenous Cd-MT, the uptake of Cd was significantly smaller than that from CdCl2 incubation. About 50% of the Cd in the intestine of control rat after CdCl2 incubation was recovered in the cytosol fraction and bound to high-molecular-weight (greater than 60 kDa) proteins. In both Zn pretreated rats incubated with CdCl2 and control rats incubated with Cd-MT, Cd was mostly recovered in the intestinal cytosol fraction (75-85%) and was mainly bound to MT. After 60 min incubation of control intestinal loop with CdCl2. Cd was detected mainly in liver with small amounts in kidney and pancreas: with Cd-MT incubation, Cd was detected only in the kidney. The deposition of Cd in the liver was markedly decreased by Zn pretreatment. Both the uptake of Cd-MT by intestine and the induction of MT synthesis in the intestine by Zn pretreatment were demonstrated by immunohistochemistry using a specific antibody to rat liver MT. The results suggest a slow uptake of exogenous Cd-MT from the intestine and transport to kidney in contrast to deposition of Cd in the liver from CdCl2. Although the intracellular presence of MT does not affect the uptake of Cd from lumen, it may decrease both the release of Cd from the intestine and its deposition in liver.     

Mode of existence of cadmium in rat liver and kidney after prolonged subcutaneous administration

The relationship between the mode of existence of cadmium in cells and its concentration in the liver and kidney was studied. Male Wistar rats were injected with 0.3 mg of Cd (as CdCl₂) per kilogram sc for 6 days per week and sacrificed by bleeding at Weeks 1, 4, 9, 12, and 16. The cadmium concentration reached a near-maximum at 12 weeks. The 27,000g supernatants of the liver and kidney homogenates were chromatographed on Sephadex G-75. At 1 week more than 97% of the cadmium was bound to metallothionein in both organs. At 9, 12, and 16 weeks, most of the increased cadmium was bound to metallothionein, but four additional fractions of bound cadmium newly appeared. The cadmium content in these four fractions increased in a dose-related fashion. The ratios of the cadmium concentration in the fraction at 4, 9, 12, and 16 weeks to that of the fraction at 1 week were greater in the additional fractions than in metallothionein. If present in sufficiently high concentration, the cadmium ions in the additional fractions may cause damage to cells. Cd-induced hepatic and renal metallothioneins contained not only cadmium but also zinc, and the ratio of cadmium to zinc increased with the cadmium concentration in both organs. Though the cadmium tissue concentration was smaller in the kidney, the Cd/Zn ratio of metallothionein was greater in that organ. In conclusion, the distribution pattern of cadmium in the cells changes as the tissue concentration increases and the hepatic and renal metallothioneins differ significantly in the ratio of the cadmium content to the zinc content.     

Cadmium pathways during gestation and lactation in control versus metallothoinein 1,2-knockout mice.

Effects of metallothionein (MT) on cadmium absorption and transfer pathways during gestation and lactation in mice were investigated. Female 129/SvJ metallothionein-knockout (MT1,2KO) and metallothionein-normal (MTN) mice received drinking water containing trace amounts of (109)CdCl(2) (0.15 ng Cd/ml; 0.074 micro Ci (109)Cd/ml). (109)Cd and MT in maternal, fetal, and pup tissues were measured on gestation days 7, 14, and 17 and lactation day 11. In dams, MT influenced both the amount of (109)Cd transferred from intestine into body (two- to three-fold higher in MT1,2KO than MTN dams) and tissue-specific (109)Cd distribution (higher liver/kidney ratio in MT1,2KO dams). Placental (109)Cd concentrations in MT1,2KO dams were three- and seven-fold higher on gestation days 14 and 17, respectively, than in MTN dams. Fetal (109)Cd levels were low in both mouse types, but at least 10-fold lower in MTN fetuses. MT had no effect on the amount of (109)Cd transferred to pups via milk; furthermore, 85-90% of total pup (109)Cd was recovered in gastrointestinal tracts of both types, despite high duodenal MT only in MTN pups. A relatively large percentage of milk-derived intestinal (109)Cd was transferred to other pup tissues in both MT1,2KO and MTN pups (14 and 10%, respectively). These results demonstrate that specific sequestration of cadmium by both maternal and neonatal intestinal tract does not require MT. Although MT decreased oral cadmium transfer from intestine to body tissues at low cadmium exposure levels, MT did not play a major role in restricting transfer of cadmium from dam to fetus via placenta and to neonate via milk.     

Effect of ethanol on the distribution of cadmium between the cadmium metallothionein- and non-metallothionein-bound cadmium pools in cadmium-exposed rats.

In an attempt to assess the effect of ethanol on cadmium accumulation, metallothionein (MT) synthesis, Cd-binding capacity and lipid peroxidation, rats were administered either Cd, ethanol or their combination for a period of 4 weeks. A significant increase in Cd accumulation was observed in all the organs of rats under study co-exposed to Cd and ethanol as compared to only Cd-treated rats. Increased MT levels in response to Cd were associated with a marked alteration in the distribution of Cd amongst the two pools of intracellular Cd i.e. Cd bound to MT (Cd-MT) and Cd not bound to MT (non-MT-Cd). Higher levels of non-MT-Cd were observed in liver, kidney and heart of Cd+ethanol-exposed rats as compared to only Cd-exposed rats. Lesser binding of 109Cd to the protein peak was observed in Cd+ethanol-exposed rats than the Cd-treated rats when hepatic supernatants from all the groups were chromatographed on Sephadex G-75 columns, suggesting that ethanol has a redistributing effect on Cd amongst the two pools. A marked increase in lipid peroxidation was observed which was linear to the increase in non-MT-Cd levels. A positive correlation between non-MT-Cd levels and lipid peroxidation was observed in liver, kidney and heart suggesting that non-MT-Cd levels are more crucial and toxicologically more important than total Cd levels.     

Effect of zinc on cadmium,copper and zinc contents in cadmium exposed rats

The effect of zinc (Zn) administration on the uptake and retention of cadmium (Cd), copper (Cu) and Zn in liver, kidneys and testes of cadmium exposed rats was investigated. Exposure to Cd caused a significant increase in the uptake of these metals in the 3 organs. The administration of Zn after the Cd exposure had little effect on the level of these metals.