Oral and subcutaneous administration of cadmium chloride and the distribution of metallothionein and cadmium along the villus-crypt axis in rat jejunum

Damage to the Testicular Structure of Rats by Acute Oral Exposure of Cadmium

Cadmium (Cd) is one of the most important heavy metal toxicants, used throughout the world at the industrial level. It affects humans through environmental and occupational exposure and animals through the environment. The most severe effects of oral exposure to Cd on the male reproductive system, particularly spermatogenesis, have not been discussed. In this study, we observed the damage to the testes and heritable DNA caused by oral exposure to Cd. Adult male Sprague–Dawley rats were divided into four groups: a control group and three groups treated with 5, 10, and 15 mg Cd/kg/day for 17 days by oral gavage. Our results revealed that Cd significantly decreases weight gain in 10 and 15 mg/kg groups, whereas the 5 mg/kg groups showed no difference in weight gain. The histopathology showed adverse structural effects on the rat testis by significantly reducing the thickness of the tunica albuginea, the diameter of the tubular lumen, and the interstitial space among seminiferous tubules and increasing the height of the epithelium and the diameter of the seminiferous tubules in Cd treated groups. Comet assay in epididymal sperms demonstrated a significant difference in the lengths of the head and comet in all the 3 Cd treated groups, indicating damage in heritable DNA, although variations in daily sperm production were not significant. Only a slight decrease in sperm count was reported in Cd-treated groups as compared to the control group, whereas the tail length, percentage of DNA in head, and tail showed no significant difference in control and all the experimental groups. Overall, our findings indicate that Cd toxicity must be controlled using natural sources, such as herbal medicine or bioremediation, with non-edible plants, because it could considerably affect heritable DNA and induce damage to the reproductive system.

Metals and metalloids in whole blood and tissues of Olive Ridley turtles (Lepidochelys olivacea) from La Escobilla Beach (Oaxaca, Mexico)

Concentrations of eight metals and metalloids (Pb, Cd, Cu, Zn, Mn, Se, Ni and As) were evaluated from 41 nesting females (blood) and 13 dead (tissues) Olive Ridley turtles (Lepidochelys olivacea), a species classified as vulnerable and also listed in Appendix I of the Convention of International Trade in Endangered Species (CITES). The mean blood, liver and kidney lead concentration were 0.02 ± 0.01, 0.11 ± 0.08 and 0.06 ± 0.03 μ gg(-1) ww respectively, values lower than other turtle species and locations, which it could be due to the gradual disuse of leaded gasoline in Mexico and Central America since the 1990s. Mean concentration of cadmium was 0.17 ± 0.08 (blood), 82.88 ± 36.65 (liver) and 150.88 ± 110.9 9μg g(-1) (kidney). To our knowledge, the mean renal cadmium levels found is the highest ever reported worldwide for any sea turtle species, while other six elements showed a concentration similar to other studies in sea turtles.

A study of metal concentrations and metallothionein binding capacity in liver, kidney and brain tissues of three Arctic seal species

Arctic seals are known to accumulate relatively high concentrations of potential toxic heavy metals in their vital organs, such as livers and kidneys, as well as in their central nervous system. We therefore decided to determine whether mercury, copper, cadmium and zinc levels in liver, kidney and brain tissues of three Arctic seal species were associated with the intracellular metal-binding protein metallothionein (MT) as a sign of toxic exposure. Samples from four ringed (Phoca hispida), five harp (P.groenlandica) and five hooded (Cystophora cristata) seals taken during field trips to Central West Greenland (Godhavn) and the Barents Sea in the spring of 1999 were used for the present study. In all three seal species concentrations of mercury, zinc and copper were highest in the liver, except for cadmium which was highest in the kidneys. Metal concentrations increased significantly in the order: ringed seal<harp seal<hooded seal for both kidney and liver tissues. MT concentrations were highest in the kidneys and the concentrations increased in the order: ringed seal<hooded seal<harp seal. MT metal-binding capacity was highest in the kidneys for all three species and increased in the same order: ringed seals (2-10%)<hooded seals (8-15%)<harp seals (27-63%). We therefore suggest that there are species-specific differences in the sub-cellular handling of heavy metals which indicate differences in sensitivity and health implications. However, a larger sample size is needed in order to test the relationship between metal concentrations and MT up-regulation in order to decide which metals are the most important and to elucidate whether the MT binding capacity is sufficient to protect tissues (i.e. kidney) from metal toxicosis. MT with its binding capacity could be a useful marker for environmental exposure to metals and their potential toxicity in the Arctic.

Dose- and route-dependent hormonal activity of the metalloestrogen cadmium in the rat uterus

The toxic heavy metal cadmium (Cd) is regarded as a potential endocrine disruptor, since Cd exerts estrogen-like activity in vitro and can elicit some typical estrogenic responses in rodents upon intraperitoneal (i.p.) injection. But estrogenic effects have not been documented in vivo with other more relevant routes of exposure, although it is known that Cd absorption and distribution in the body is strongly affected by the application route. Therefore, we investigated its hormonal activity in ovariectomized Wistar rats after oral administration of CdCl(2) (0.05-4 mg/kg b.w. on 3 days by gavage and 0.4-9 mg/kg b.w. for 4 weeks in drinking water) in comparison with i.p. injection of CdCl(2) (0.00005-2 mg/kg b.w.). Uterus wet weight, height of uterine epithelium, and modulation of estrogen-regulated gene expression, i.e. uterine complement component 3 (C3), were determined, and also Cd-levels in uterus and liver were measured by atomic absorption spectrometry. The analysis revealed pronounced differences in Cd tissue levels and hormonal potency for the two routes of administration: a single i.p. injection of Cd increased dose-dependently uterine wet weight and thickness of the uterine epithelium. Interestingly, C3 mRNA expression in the uterus was down regulated at low doses of CdCl(2) (0.00005-0.05 mg/kg b.w.), but strongly stimulated at the highest dose of 2 mg/kg b.w. Other than i.p. injection, oral treatment with Cd, by gavage or in drinking water, did neither increase uterine wet weights nor epithelial thickness. But, both 3-day- and 4-week oral Cd administration resulted in a dose-dependent stimulation of C3 expression in the uterus, significant at and above 0.5 mg/kg b.w. In summary, our data demonstrate an estrogenic effect in the uterus upon i.p. injection of Cd, but considerably lower hormonal potency with oral administration: short and long-term oral treatment with Cd did not affect uterus weight or histology, whilst on the molecular level, an induction of estrogen sensitive uterine gene expression was observed, albeit at dose levels far exceeding those of dietary exposure in humans.

Characterization of cadmium uptake in human intestinal crypt cells HIEC in relation to inorganic metal speciation

Cadmium (Cd) uptake was studied under inorganic exposure conditions in normal human intestinal crypt cells HIEC. The uptake time course of 0.3 microM Cd in a serum-free chloride medium was analyzed according to a first order equation with rapid initial (U0) and maximal (Umax) accumulation values of 14.1+/-1.4pmol/mgprotein and 41.4+/-2.0 pmol/mgprotein, respectively. The presence of a 300-fold excess of unlabeled Cd dramatically decreased tracer uptake, showing the involvement of specific mechanism(s) of transport. Our speciation studies revealed the preferential uptake of the free ion Cd2+, but also suggested that CdCln(2-n) species may contribute to Cd accumulation. Specific mechanisms of transport of very high and similar affinity (Km approximately 5 microM) have been characterized under both chloride and nitrate exposure conditions, but a two-fold higher capacity (Vmax) was estimated in the nitrate medium used to increase [Cd2+] over chlorocomplex formation. A clear inhibition of 109Cd uptake was observed at external acidic pH under both exposure media. An La-inhibitible 46% increase in 109Cd uptake was obtained in nominally Ca-free nitrate medium, whereas Zn provided additional inhibition. These results show different kinetic parameters for Cd uptake as a function of inorganic metal speciation. Cd2+ uptake would not involve the H+-coupled symport NRAMP2 but would be related instead to the Ca and/or Zn pathways. Because proliferative crypt cells play a critical role in the renewal process of the entire intestinal epithelium, studies on the impact of Cd on HIEC cell functions clearly deserve further investigation.

Changes in Carboxypeptidase A, Dipeptidase and Na+/K+ ATPase Activities in the Intestine of Rats Orally Exposed to Different Doses of Cadmium

The purpose of the present study was to evaluate the effect of cadmium on some protein digestive and absorption enzymes in rats. Thirty-six rats were grouped into three groups of 12 animals each; one group received deionised water and acted as control. One group received 445 microM Cd and the last group received 890 microM Cd in their drinking water for a period of one month. The results obtained indicate that increasing the level of cadmium from 445 microM to 890 microM in the drinking water of the rats led to 29% and 23% increase in accumulated cadmium in the proximal and distal small intestine respectively. The body weight gain of rats exposed to 445 microM and 890 microM Cd was decreased by about 24% and 43% respectively when compared with the control. The activities of carboxypeptidase A, dipeptidase and Na+/K+ ATPase were reduced in the mucosa of the proximal end of the small intestine of cadmium exposed rats. The reduction was dose dependent; with the 890 microM Cd exposed rats displaying the least activities. In the distal small intestine, the activities of these enzymes were restored in the 445 microM Cd exposed rats to levels that were not statistically different (P > 0.05) from those observed in the controls. In the 890 microM Cd exposed rats, dipeptidase activity improved by about 80% compared with the activity of the enzyme in the proximal small intestine. Likewise, Na+/K+ ATPase activity increased by about 125% compared with the observed level in the proximal small intestine. The study suggests that cadmium given to rats in drinking water compromise protein digestion and absorption of nutrients particularly in the proximal region of small intestine and could account for weight reduction associated with cadmium toxicity.

Marginal nutritional status of zinc, iron, and calcium increases cadmium retention in the duodenum and other organs of rats fed rice-based diets

Dietary minerals Zn, Fe, and Ca are antagonistic to Cd absorption. We showed earlier that rats fed a rice-based diet with a marginal content of these nutrients absorbed more Cd than rats fed adequate Zn-Fe-Ca (Environ. Sci. Technol., 36 (2002) 2684-2692). The present experiment was designed to determine the effects of marginal dietary Zn, Fe, and Ca on the uptake and turnover of Cd in the gastrointestinal tract. Two groups of weanling female rats (six per treatment) were fed a diet containing 40% cooked, dried rice containing 0.6 mg Cd/kg. The diet of one group contained adequate Zn (35 mg/kg), Fe (30 mg/kg), and Ca (5000 mg/kg), while that of the other group contained marginal Zn (6 mg/kg), Fe (9 mg/kg), and Ca (2500 mg/kg). Rats were fed for 5 weeks and then orally dosed with 1g of diet containing rice extrinsically labeled with 109Cd. From 0.25 to 64 days after dosing, 109Cd and total Cd concentrations were determined in intestinal segments. Shortly after dosing, 109Cd, as a percentage of the dose, was about 4 times higher in the duodenum of marginally fed rats than in that of control rats (10% vs 40%, respectively). Sixty-four days after dosing, 109Cd was 10 times higher in marginally fed rats than in controls; however, of the amount at day 1, <0.1% remained at day 64. After 5 weeks, the concentration of elemental Cd in the duodenum of the marginally fed rats was 8 times higher than that of control rats (24 microg/g dry wt. vs 2.9 microg/g dry wt., respectively). Cd concentrations in liver and kidney were 5 times higher in the marginally fed rats than those in controls (liver, 0.81 microg/g dry wt. vs 0.14 microg/g dry wt.; kidney, 4.7 microg/g dry wt. vs 0.92 microg/g dry wt., respectively). These data suggest that marginal intakes of Zn, Fe, and Ca cause the accumulation of Cd in the duodenum, which results in a greater rate of Cd absorption and a greater accumulation in the internal organs. Results are discussed in relation to mineral nutrient status and risk assessment of Cd in natural food sources.

Jejunal transfer rates of 109cadmium chloride increase in rats in vitro and in vivo after oral pretreatment with cadmium or zinc chloride

An increased body retention of Cd in rats orally pretreated with Cd or Zn is explained by induction of hepatic and renal metallothionein. Whether intestinal absorption of Cd increases after such treatments is not clear yet. To approach this problem we measured jejunal transfer rates of 109Cd in vitro and in vivo in pretreated rats (0.44 mmol Cd/l or 4.6 mmol Zn/l in the drinking water for 10 days) and compared them with those of untreated controls. Isolated jejunal segments were used for in vitro perfusion. In vivo perfusion was performed in anaesthetized rats with blood collected from mesenteric venules substituting corresponding losses by reinfusion of rat blood. Water and glucose transfer did not differ between controls and pretreated rats. At a luminal concentration of 5 micromol 109CdCl2/l, Cd and Zn pretreatment significantly increased the transfer rate of 109Cd in vitro and in vivo similarly. The 109Cd transfer rates in controls in the final perfusion intervals (80-120 min) were 0.06 (pmol/cm/min) in vivo and 0.05 in vitro; the corresponding rates in Cd or Zn pretreated rats were significantly higher (P<0.05) and amounted to 0.11 and 0.18 or 0.15 and 0.23, respectively. Mucosal concentrations of 109Cd measured at the end of the perfusion period tended to be lower in the pretreated animals than in the controls. This suggests that pretreatment with Cd or Zn reduces the amount of 109Cd bound to the tissue leaving more 109Cd for the transfer step. As compared to a level of mucosal metallothionein of 8 microg/g wet weight in controls, increased amounts of 67 or 52 microg/g wet weight in the Cd or Zn pretreated rats, respectively, thus did not decrease but increased transfer rates of 109Cd. Therefore, increased small intestinal transfer rates of Cd can contribute to increase the body retention of Cd seen after oral pretreatment with Cd or Zn.

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.

Interaction between cadmium exposure and infection with the intestinal parasite Moniliformis moniliformis (Acanthocephala) on the stress hormone levels in rats

The impact of an infection with the acanthocephalan Moniliformis moniliformis and a simultaneous Cd-exposure on the stress hormone levels of rats was studied. Immediately after the application of cadmium to some rats, cortisol levels in all groups of rats, as quantified by radioimmunoassay (RIA), significantly increased. However, infections with M. moniliformis as well as the uptake of Cd reduced significantly the cortisol release compared to untreated controls. While catecholamine concentrations, as determined by high-performance liquid chromatography (HPLC), showed no clear tendency during the experimental period, the ratio of C(adrenaline)/C(noradrenaline) in the controls showed the significantly lowest value of all four groups after killing the animals. Thus, the acanthocephalan infection as well as the Cd-exposure and the combination of both treatments affect hormone homeostasis in the rats which probably lead to negative effects on the health of the rat. Therefore parasite infections must be carefully considered in environmental impact studies, as an important factor affecting the host's health.

Tissue metallothionein, apoptosis and cell proliferation responses in Atlantic salmon (Salmo salar L.) parr fed elevated dietary cadmium

Atlantic salmon parr were reared for 4 months on experimental diets supplemented with 0 (control), 0.5, 5, 25, 125, or 250 mg Cd x kg(-1) feed to establish a threshold concentration for dietary cadmium exposure by assessing early adaptive cellular responses. At the end of the experiment, the lowest dietary Cd concentration that caused significant accumulation in the gut, kidney and muscle was 5 mg Cd x kg(-1) compared to the control group. Over time, dietary Cd accumulated first in the gut (after 1 month), followed by the kidney (2 months), and later by muscle (4 months). Highest Cd accumulation (100-fold) was found in the gut. A significant increase in regulated cell death and proliferation in salmon fed 125 mg Cd x kg(-1) compared to control fish appeared efficient in preventing gross histopathological damage in the intestine. The highest increase in metallothionein levels was found in the kidney, and metallothionein (MT) levels increased disproportionally to Cd accumulation at increased exposure concentrations. It was concluded that MT was not directly associated with long-term Cd accumulation. Atlantic salmon showed increased metallothionein levels in the kidney at a median effective concentration (concentration of dietary Cd giving 50% of the maximum increase in metallothionein, EC50) of 7 mg Cd x kg(-1), indicating toxic exposure at this concentration.

Energetics in Atlantic salmon (Salmo salar L.) parr fed elevated dietary cadmium

Atlantic salmon (Salmo salar L.) parr were reared for 4 months on experimental diets supplemented with Cd (0.5, 5, 25, 125, or 250 mg Cd x kg(-1)) to assess the long-term energetic changes based on the digestibility and biochemical deposition of the major dietary nutrients and to evaluate a maximum tolerable dietary toxicant concentration. Growth did not differ significantly (P>0.05) from the control groups. The biochemical composition of the carcass, but not the viscera, was negatively affected by dietary Cd exposure. The significant decreases in protein, lipid, and glycogen concentrations in the carcass (P<0.05, 25 mg x kg(-1) compared to control groups) caused a reduction in calculated whole-body energy content in fish fed 125 mg x kg(-1)compared to control groups. This reduction in calculated whole-body energy content was explained by a concurrent significant disturbance to the gastrointestinal function (measured as reduced digestibility). Only at the highest dietary Cd exposure (250 mg x kg(-1)), increased metabolic costs to cope with Cd toxicity was thought to contribute significantly to the reduction in carcass energy content. The most important factor effecting calculated total energetics was nutrient digestibility. Based on the logarithmic effective median concentration for reduced calculated energy digestibility (dietary Cd concentration corresponding to 50% reduction, EC50), the maximum tolerable dietary Cd concentration is 11 mg x kg(-1) diet.

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.