Dietary iron lowers the intestinal uptake of cadmium-metallothionein in rats.

It has been shown that addition of extra calcium/phosphorus (Ca/P), zinc (Zn) and iron (Fe2+) to the diet results in a significant protection against cadmium (Cd) accumulation and toxicity in rats fed inorganic Cd salt. However, it is not clear whether the presence of these mineral supplements in the diet also protects against the Cd uptake from cadmium-metallothionein. The present study examines the influence of Ca/P, Zn and Fe2+ on the Cd disposition in rats fed diets containing either 1.5 and 8 mg Cd/kg diet as cadmium-metallothionein (CdMt) or as cadmium chloride (CdCl2) for 4 weeks. The feeding of Cd resulted in a dose-dependent increase of Cd in intestine, liver and kidneys. The total Cd uptake in liver and kidneys after exposure to CdMt was lower than after exposure to CdCl2. At the low dietary Cd level and after addition of the mineral supplement, the kidney/liver concentration ratio increased. However, this ratio was always higher with CdMt than with CdCl2, suggesting a selective renal disposition of dietary CdMt. The uptake of Cd from CdCl2 as well as from CdMt was significantly decreased by the presence of a combined mineral supplement of Ca/P, Zn and Fe2+. The protection which could be achieved was 72 and 75% for CdMt and 85 and 92% for CdCl2 after doses of 1.5 mg/kg and 8 mg/kg respectively. In a following experiment it was shown that the protective effect of the mineral mixture against CdMt was mainly due to the presence of Fe2+. It seems clear that Cd speciation and the mineral status of the diet have a considerable impact on the extent of Cd uptake in rats.     

Comparison of Renal Toxicity after Long-Term Oral Administration of Cadmium Chloride and Cadmium-Metallothionein in Rats

There is a clear lack of information on the toxicological riskof dietary intake of cadmium-metallothionein (CdMt). The presentstudy aimed at establishing dose-dependent cadmium (Cd) dispositionand to investigate differences in renal toxicity after long-termdietary exposure to CdMt or cadmium chloride (CdCl₂ in rats.Male Wistar rats were fed diets containing 0.3, 3, 30, or 90mg Cd/kg either as CdMt or as CdCl₂ for 10 months. In rats fed30 and 90 mg/kg Cd as CdCl₂ the Cd concentrations in intestine,liver, and kidneys were all higher than in rats fed the samedoses in the form of CdMt. The kidney/liver Cd concentrationratio was higher with CdMt than with CdCl₂. At the lower Cdconcentrations (0.3 and 3 mg/kg), no differences in Cd accumulationbetween CdMt and CdCl₂ groups were observed and the kidney/liverCd ratio was also similar. When based on the amount of CdMtper milligram Cd in the tissue, rats fed CdMt and those fedCdCl₂ had a similar relative CdMt concentration in liver andkidney. First signs of renal injury, indicated by an increaseof urinary lactate dehydrogenase (LDH) activity, were seen 4months after exposure to 90 mg/kg Cd as CdCl₂. After 8 and 10months the renal effect of 90 mg/kg Cd as CdCl₂ became morepronounced and urinary enzyme activities of LDH, N-acetyl-ß-D-glucosaminidaseand alkaline phosphatase were all elevated. The only clinicaleffect of CdMt at the dose level of 90 mg/kg was a slight increasein urinary -glutamyl transpeptidase activity at 8 and 10 months.Histopathological changes (e.g., glomerulonephrosis and basophilictubules) were observed after 10 months of exposure in rats fed30 and 90 mg/kg Cd as CdCl₂. Rats fed 90 mg/kg as CdMt alsoshowed slight histomorphological changes, but the effect wasless pronounced than that of CdCl₂ and was mainly restrictedto the tubules. In conclusion, no difference was observed inrenal disposition between CdMt and CdCl₂ after long-term exposureto low (3 mg/kg) dietary doses. Nephrotoxicity was mainly relatedto the total renal Cd concentration and, in contrast to Cd administeredintravenously, not to a difference in sensitivity between CdMtand CdCl₂ Therefore, the health risk of dietary intake of Cdat low doses does not seem to differ between CdMt and CdCl₂.     

Dietary iron lowers the intestinal uptake of cadmium-metallothionein in rats

It has been shown that addition of extra calcium/phosphorus (Ca/P), zinc (Zn) and iron (Fe²⁺) to the diet results in a significant protection against cadmium (Cd) accumulation and toxicity in rats fed inorganic Cd salt. However, it is not clear whether the presence of these miniral supplements in the diet also protects against the Cd uptake from cadmium-metallothionein. The present study examines the influence of Ca/P, Zn and Fe²⁺ on the Cd disposition in rats fed diets containing either 1.5 and 8 mg Cd/kg diet as cadmium-metallothionein (CdMt) or as cadmium chloride (CdCl₂) for 4 weeks. The feeding of Cd resulted in a dose-dependent increase of Cd in intestine, liver and kidneys. The total Cd uptake in liver and kidneys after exposure to CdMt was lower than after exposure to CdCl₂. At the low dietary Cd level and after addition of the mineral supplement, the kidney/liver concentration ratio increased. However, this ratio was always higher with CdMt than with CdCl₂, suggesting a selective renal disposition of dietary CdMt. The uptake of Cd from CdCl₂ as well as from CdMt was significantly decreased by the presence of a combined mineral supplement of Ca/P, Zn and Fe²⁺. The protection which could be achieved was 72 and 75% for CdMt and 85 and 92% for CdCl₂ after doses of 1.5 mg/kg and 8 mg/kg respectively. In a following experiment it was shown that the protective effect of the mineral mixture against CdMt was mainly due to the presence of Fe²⁺. It seems clear that Cd speciation and the mineral status of the diet have a considerable impact on the extent of Cd uptake in rats.     

Comparative toxicity and accumulation of cadmium chloride and cadmium-metallothionein in primary cells and cell lines of rat intestine, liver and kidney

The protective role of metallothionein (Mt) in the toxicity of cadmium (Cd) is controversial, since Cd bound to Mt is more nephrotoxic than ionic Cd after parenteral exposure and less hepatotoxic than ionic Cd after oral exposure. This study compared the uptake and toxicity in vitro of CdCl₂ and two isoforms of rat cadmium-metallothionein (CdMt-1 and CdMt-2) using primary rat kidney cortex cells, primary rat hepatocytes, liver hepatoma cell line H-35, kidney epithelial cell line NRK52-E and intestinal epithelial cell line IEC-18. The molar ratio of Cd was 2.1 and 1.4 mol Cd/mol Mt for CdMt-1 and CdMt-2, respectively. Monolayer cultures were incubated for 22 hr with CdCl₂, CdMt-1 or CdMt-2 and Cd accumulation was examined at Cd levels of 0.25–10 μM-Cd. Cells exposed to CdCl₂ accumulated more Cd in 22 hr than cells exposed to an equimolar amount of CdMt. For CdCl₂ the Cd accumulation is directly related to the Cd concentration in the medium; however, for CdMt an increase in Cd concentration in the medium above 2 μM had no effect on the Cd accumulation in the cells. At Cd concentrations above 2 μM, therefore, the difference in Cd accumulation between CdCl₂ and CdMt was greater (5–6 times) than at concentrations below 2 μM (1–2 times). Cytotoxicity was examined in the Cd-concentration range from 0.25 to 100 μM by determining the lactate dehydrogenase (LDH) release in the medium and the neutral red uptake in the cells. Under these culture conditions CdCl₂ was at least 100 times more toxic than CdMt-1 or CdMt-2 in all cell types tested. Primary hepatocyte cultures were 10 times more sensitive (50% LDH release at 1–2 μM) to CdCl₂ intoxication than primary cultures of renal cortical cells or the intestinal cell line (50% LDH release at 10–20 μM). Hepatic and renal cell lines were less sensitive (50% LDH release at 20–35 μM) than the corresponding primary cultures. No difference in sensitivity towards CdMt-1 or CdMt-2 was found for the various cell types tested. To investigate the influence of the molar Cd ratio of CdMt on cytotoxicity, the Cd content of CdMt-1 (2.1 mol Cd/mol Mt) was artificially raised in vitro to 5 mol/mol Mt. Compared with native CdMt, CdMt with a high molar Cd ratio in primary renal cultures showed a 15% increase in LDH release at a Cd concentration of 1500 μM in the medium. In conclusion, exogenous CdMt is far less toxic than CdCl₂ to cell cultures in a serum-free medium. Whereas CdCl₂ in all cases showed dose-dependent Cd accumulation, Cd accumulation due to CdMt exposure in all cell types tested reached a plateau at medium Cd concentrations of 2 μM. The low cellular Cd uptake of CdMt and the corresponding low cytotoxicity supports previously reported results in vivo, showing that the difference in toxicity between CdMt and CdCl₂ is associated with a difference in Cd distribution.     

Relationship between toxicity and cadmium accumulation in rats given low amounts of cadmium chloride or cadmium-polluted rice for 22 months

To clarify toxic effects of long-term oral administration of low dose cadmium (Cd) on the liver and kidney, six groups of female Sprague-Dawley rats were fed a diet containing Cd-polluted rice or CdCl2 at concentrations up to 40 ppm, and killed after 12, 18, and 22 months. With toxicological parameters, including histopathology, there was no evidence of Cd-related hepato-renal toxicity, despite a slight decrease of mean corpuscular volume and mean corpuscular hemoglobin of red blood cells with 40 ppm CdCl2. Dose-dependent accumulation of Cd was observed in the liver and kidneys with peak levels of 130 +/- 42 micrograms/g and 120 +/- 20 micrograms/g, respectively, at 18 months in animals treated with 40 ppm CdCl2. A dose-dependent increase in urinary Cd levels became evident with time. Induction of metallothionein (MT) was also observed in the liver and kidney with a high correlation to the corresponding Cd levels. In the proximal renal tubular epithelia of 40 ppm CdCl2-treated rats at 22 months, prominent accumulation of Cd was observed in secondary lysosomes associated with MT deposits in their exocytotic residual bodies. The results demonstrated that, in contrast to the case with high-dose Cd-administration, renal toxicity is not induced by long-term oral administration of low amounts of Cd, although tissue accumulation does occur. Possible protective mechanisms may be operating.     

Metallothionein-I/II null mice are sensitive to chronic oral cadmium-induced nephrotoxicity.

Chronic exposure to cadmium (Cd) via food and drinking water is a major human health concern. We have previously shown that metallothionein (MT), a metal-binding protein, plays an important role in protecting against Cd toxicity produced by repeated sc injections. However, it is unclear whether MT protects against Cd-induced nephrotoxicity following chronic oral exposure, a route with obvious human relevance. To clarify this issue, MT-I/II knockout (MT-null) and background-matched wild-type (WT) mice were allowed free access to drinking water containing CdCl(2) (30, 100, and 300 ppm Cd), or feed containing CdCl(2) (100 ppm Cd) for 6 months, and the resultant nephrotoxicity was examined. Chronic oral Cd exposure produced a dose-dependent accumulation of Cd in liver and kidney of WT mice, reaching levels up to 50 microg Cd/g tissue. Immunohistological localization of renal MT indicated that chronic oral Cd exposure in WT mice greatly increased MT in the proximal tubules and the medulla, with cellular localization in both the cytoplasm and nuclei. As expected, no MT was detected in kidneys of MT-null mice. After 6 months of Cd exposure, tissue Cd concentrations in MT-null mice were only about one-fifth of that in WT mice. Even though the renal Cd concentrations were much lower in the MT-null mice, they were more sensitive than WT mice to Cd-induced renal injury, as evidenced by more severe nephropathic lesions, increased urinary excretion of gamma-glutamyl-transferase and glucose, and elevated blood urea nitrogen. Six months of Cd exposure to MT-null animals resulted in greater increases in renal caspase-3 activity, an indicator of apoptosis, than to WT mice. In conclusion, this study demonstrates that lack of MT renders MT-null mice vulnerable to Cd-induced nephrotoxicity after chronic oral exposure, the primary route of human Cd exposure.     

Comparative tissue distributions of cadmium chloride and cadmium-based quantum dot 705 in mice: Safety implications and applications

Cadmium (Cd) is a component in quantum dot 705 (QD705). Whether QD705 behaves similar to Cd in vivo is of great concern. We compared the distributional kinetics of cadmium chloride (CdCl(2)) and QD705 in mice after intravenous injection. QD705 showed a longer plasma and body retention than CdCl(2) and could be detected in the brain during early exposure. While both the liver and spleen demonstrated a constant Cd concentration for 28 days after QD705 injection, it is likely that this represents intact QD705 stored in mononuclear phagocytes. The kidneys showed a time-dependent accumulation of Cd in the QD705-exposed animals. By day 28, Cd in the kidneys from QD705 was 3-fold that of CdCl(2). QD705 and CdCl(2) have very different kinetics in distribution and metabolism. The long body retention of QD705 in the kidneys may mean that QD705 has even more renal toxicity than CdCl(2).     

Assessment of renal toxicity by analysis of regeneration of tubular epithelium in rats given low-dose cadmium chloride or cadmium-polluted rice for 22 months

To determine whether low-dose oral administration of cadmium (Cd) induces renal toxicity, six groups of female Sprague-Dawley rats were fed a diet containing low amounts of CdCl2 or Cd-polluted rice at concentrations up to 40 ppm, and were killed after 12, 18, and 22 months (experiment 1). In addition to the determination of cortical Cd levels and histopathological assessment of kidneys, labeling indices (LIs) for proliferating cell nuclear antigen (PCNA) in the renal cortical tubular epithelium of Cd-treated rats were determined as a measure of regenerative activity. For comparison, the kidneys of rats given diets containing small to large amounts of CdCl2 up to 600 ppm for 4 months were similarly examined (experiment 2). Animals in experiment 1 demonstrated spontaneous chronic nephropathy and fluctuation in the tubular PCNA LI, but these findings were not correlated with renal Cd levels at 22 months. PCNA LI on the other hand, appeared to be linked to the severity of chronic nephropathy. In experiment 2, levels of CdCl2 of 200 ppm or more clearly induced degeneration and apoptosis of proximal tubules with high correlations between renal Cd levels, PCNA LI, and the severity of tubular degeneration. The results demonstrated that, in contrast to high-dose Cd administration, treatment with 40 ppm or less for 22 months did not influence tubular regeneration as a component of nonspecific chronic nephropathy, suggesting that long-term oral administration of low levels of Cd does not injure renal tubules in female rats.     

Dietary calcium restriction enhances cadmium-induced metallothionein synthesis in rats.

Experiments were conducted with adult male rats to investigate the effects of dietary calcium (Ca) restriction upon intake and tissue distribution of cadmium (Cd), and Cd-metallothionein (Mt) synthesis. Four groups of animals were fed either a low-Ca, semisynthetic diet (0.1% Ca) or the same diet supplemented with 0.8% Ca (normal diet). The caloric intake was similar in all groups. Two groups (low-Ca and normal diet) were used as controls, and two groups (low-Ca and normal diet) received 100 mg/l Cd (as CdCl2) in drinking water. Cd levels in liver, kidney, spleen and red cells were measured in all animals after 8 weeks of treatment. Concomitantly, Mt levels in plasma, liver and kidney were evaluated by radioimmunoassay. Ca deficiency entailed marked and significant increases in accumulation of Cd and synthesis of Mt in all assayed tissues. It is concluded that dietary Ca restriction, independent of caloric intake, enhances Cd intestinal absorption and tissue accumulation, which is followed by increased tissue Mt synthesis.     

Kidney synthesizes less metallothionein than liver in response to cadmium chloride and cadmium-metallothionein

Acute exposure to Cd produces liver injury, whereas chronic exposure results in kidney injury. Tolerance to the hepatotoxicity is observed during chronic exposure to Cd due to the induction of metallothionein (MT). The nephrotoxicity produced by chronic Cd exposure purportedly results from renal uptake of Cd-metallothionein (CdMT) synthesized in liver. The change in target organ from liver to kidney might be due to a lower amount of MT synthesized in the kidney in response to CdMT. Therefore, the purpose of the present study was to quantitate hepatic and renal MT induced by CdCl2 and CdMT. MT levels in mice were quantitated using the Cd-heme assay 24 hr after administration of CdCl2 (0.5-3.0 mg Cd/kg) and CdMT (0.1-0.5 mg Cd/kg). In both liver and kidney, MT reached higher levels following administration of CdCl2 (220 and 60 micrograms/g, respectively) than of CdMT (25 and 35 micrograms/g, respectively), probably because higher dosages of CdCl2 than CdMT are tolerated. CdMT produced 19 and 3 micrograms MT/micrograms Cd in liver and kidney, respectively, while CdCl2 produced 11 and 6 micrograms MT/micrograms Cd, respectively. In conclusion, induction of MT occurs in both the liver and kidney after administration of CdCl2 and CdMT. However, the kidney is less responsive than the liver to the induction of MT by both forms of Cd, which may contribute to making the kidney the target organ of toxicity during chronic Cd exposure.     

Interaction of dietary Ca, P, Mg, Mn, Cu, Fe, Zn and Se with the accumulation and oral toxicity of cadmium in rats

The toxicity of Cd was examined in rats fed diets containing 30 mg Cd/kg as CdCl2 for 8 wk. The Cd-containing diets were supplemented with various combinations of the minerals Ca, P, Mg, Mn, Cu, Fe, Zn and Se in order to investigate the protective effect of these mineral combinations on Cd accumulation and toxicity. The mineral combinations were chosen such that the effect of the individual components could be analysed. At the end of the 8-wk feeding period, the Cd concentrations in the liver and renal cortex were 13.9 and 19.5 mg/kg body weight, respectively. The feeding of 30 mg Cd/kg diet alone resulted in well known Cd effects, such as growth retardation, slight anaemia, increased plasma transaminase activities and alteration of Fe accumulation. Only supplements that contained extra Fe resulted in a significant protection against Cd accumulation and toxicity. The most pronounced effect was obtained using a supplement of Ca/P, Fe and Zn, which resulted in a 70-80% reduction in Cd accumulation in the liver and kidneys, as well as a reduction in Cd toxicity. The protective effect of the mineral combinations was mainly due to the presence of Fe2+, but in combinations with Ca/P and Zn the effect of Fe was most pronounced. Compared with Fe2+ the protective effect of Fe3+ was significantly lower. Addition of ascorbic acid to Fe in both forms improved the Fe uptake, but consequently did not decrease Cd accumulation. Thus, the mineral status of the diet may have a considerable impact on the accumulation and toxicity of Cd, fed as CdCl2 in laboratory animals. For the risk assessment of Cd intake, special consideration should be given to an adequate intake of Fe.     

Cadmium absorption in mice: effects of broiling on bioavailability of cadmium in foods of animal origin

The absorption and organ distribution of organic Cd from raw and broiled horse kidney was compared to that of CdCl2 at two dose levels (0.05 and 3 mg Cd/kg feed) in a feeding study in mice. The high Cd concentration in the horse kidney (raw 112 mg/kg; broiled 53 mg/kg) made it possible to mix kidney into mouse feed without marked effects on the composition of the feed. The weight of the mice, feed and water consumption, and Cd levels in the feed were determined once a week. After 9 wk of exposure, the liver and kidneys of the mice were sampled and Cd was analyzed. The Cd concentration in horse kidney was halved by broiling, and the content of soluble Cd decreased from 12% in raw kidney to 5% in broiled kidney. The majority of the soluble Cd was associated with proteins with the same molecular weight as metallothionein (MT) in both raw and broiled kidney. Broiling of the kidney had no marked effect on the fractional accumulation of organic Cd in mice. The fractional accumulation of inorganic CdCl2, on the other hand, was significantly higher than that of organic Cd in the low dose groups but not in the high dose groups. The ratio between Cd accumulation in kidney and that in liver was higher in the group receiving raw kidney compared to the ratio in the group receiving CdCl2 at both the high and low exposure levels. This indicates that the raw kidney contained a Cd form that was more preferentially distributed to the kidneys.     

Effects of mucosal metallothionein in small intestine on tissue distribution of cadmium after oral administration of cadmium compounds.

The effect of mucosal metallothionein (MT) preinduced by zinc (Zn) on tissue distribution of cadmium (Cd) after administration of Cd with several chelating agents was studied in rats. After Cd-cysteine (Cd-Cys) was incubated with intestinal Zn-MT in vitro, all the Cd dissociated from Cys and exchanged the Zn bound to MT. However, dissociation of Cd bound to EDTA (Cd-EDTA) was not observed in the incubation mixture containing intestinal Zn-MT. The concentration of Cd in intestinal mucosa reached a maximum 16 hr after oral administration of Cd-Cys. The Cd level in the intestine was higher than that in the liver and kidney and was similar to that occurring after oral administration of CdCl2. The amount of Cd distributed to the liver and kidney after Cd-EDTA administration was about 30% of the level after CdCl2 administration. Even at 15 mg Cd/kg Cd-EDTA, the Cd level in the intestinal mucosa reached a plateau after 2-4 hr, as it did in the liver and kidney. When Cd-Cys was administered po to control or to Zn-pretreated rats, it was found that Zn pretreatment increased the concentration of Cd in the kidney, as was the case after oral administration of CdCl2. This effect of Zn pretreatment was not observed after oral administration of Cd-EDTA. When Cd-MT was injected into the duodenum, the intestinal absorption of Cd was 60% of that after CdCl2 administration. After the duodenal administration of Cd-MT, at all doses, the concentration of Cd in the kidney was higher than that in the liver. These results suggest that mucosal MT in the small intestine might trap Cd absorbed from the intestinal lumen and transport it to the kidney.     

Distribution of cadmium after oral administration of cadmium-thionein to mice

Distribution of Cd was compared after oral administration of either Cd ions or Cd-thionein (Cd-TH). Mice received 0.5 mg Cd/kg, po as CdCl2 in saline, CdCl2 in control rat liver homogenate, Cd-TH in saline, Cd-TH in liver homogenate, or liver homogenate from Cd-treated rats. In all cases, 85-90% of the Cd dose was present in feces within 24 hr. However, in groups receiving CdCl2, more Cd was found in feces on Days 2 and 3 in comparison to those receiving Cd-TH. All treatments resulted in lower levels of Cd in liver than in kidney. In addition, tissue levels indicate that less Cd was absorbed when rats received Cd-TH in saline than CdCl2 in saline. Cd-TH added to liver homogenate or liver homogenate containing Cd-TH increased the absorption of Cd resulting in renal Cd levels similar to those in mice receiving CdCl2 in saline. The kidney/liver Cd concentration ratio (9) was the same for Cd-TH in all three media. Although Cd-TH gave much higher kidney/liver Cd ratios than CdCl2 (9 vs 2), renal Cd concentrations were the same or lower than after CdCl2 treatments. Results indicate that the high kidney/liver Cd ratio after Cd-TH treatment versus CdCl2 is due to lower concentrations of Cd in liver rather than marked increases in renal Cd levels. Heating of Cd-TH did not result in lower amounts of Cd in kidney. While the chemical form of Cd administered affects the absorption and distribution of Cd, the amount of Cd reaching the kidney after Cd-TH administration is similar to that after CdCl2 administration.     

Detection of cadmium exposure in rats by induction of lymphocyte metallothionein gene expression.

The induction of metallothionein (MT) gene expression in lymphocytes of rats was determined in order to detect exposure in vivo to cadmium. Both acute and chronic CdCl2 exposures resulted in the induction of the MT-1 gene in lymphocytes as measured by standard RNA Northern blot analysis. Twenty-four hours following an ip injection of 3.4 mg/kg CdCl2, a ninefold increase in MT gene expression was observed in lymphocytes, as well as five- and sevenfold increases in liver and kidney, respectively. Oral exposure of rats to 1-100 ppm CdCl2 via drinking water resulted in an approximate twofold enhanced MT signal in lymphocytes after 6 wk, and a threefold increase after 13 wk of exposure to 100 ppm Cd. No increases in lymphocyte MT gene expression were observed after 3 wk of Cd exposure. Liver MT gene expression was substantially induced following chronic Cd exposure, while kidney was not, although this organ had a higher basal expression of the MT-1 gene. Analysis of tissue Cd burdens demonstrated a dose-response Cd accumulation in liver and kidney, but only kidney burdens increased substantially with prolonged Cd exposure. These results demonstrate the utility of lymphocyte gene expression assays to detect in vivo toxicant exposure, and thus their applicability as molecular biomarker assays for human exposure assessment.     

Tissue distribution of cadmium in rats given minimum amounts of cadmium-polluted rice or cadmium chloride for 8 months.

To investigate the relationship between cadmium (Cd) toxicity, intestinal absorption, and its distribution to various tissues in rats treated orally with minimum amounts of Cd, 14 female rats per dose group per time point were given diets consisting of 28% purified diet and 72% ordinary rice containing Cd-polluted rice (0. 02, 0.04, 0.12, or 1.01 ppm of Cd) or CdCl(2) (5.08, 19.8, or 40.0 ppm of Cd) for up to 8 months. At 1, 4, and 8 months after the commencement of Cd treatment, seven rats per group were euthanized for pathological examinations to determine the Cd concentrations in the liver and kidneys and metallothionein (MT) in the liver, kidneys, intestinal mucosa, serum, and urine. One week before each period of 1, 4, and 8 months, the remaining seven rats in each group were administered a single dosage of (109)Cd, a tracer, to match the amounts of the designated Cd doses (about 1.2 to 2400 microg/kg body wt). They were euthanized 5 days later to determine the distribution of Cd to various tissues. No Cd-related toxic changes were observed. The concentrations of Cd in the liver and kidneys at any time point and MT in the liver, kidney, serum, and urine at 4 and 8 months increased dose-dependently, whereas MT in the intestinal mucosa did not alter markedly at any time point. The distribution rates of Cd to the liver increased dose-dependently (40% at lower doses to 60% at higher doses), whereas those to the kidney decreased dose-dependently (20% at lower doses to 10% at higher doses). The Cd retention rates 5 days after (109)Cd administration (amounts of Cd in various tissues/amounts of Cd administered) ranged from 0.2 to 1. 0% at any time point. These results suggest that the distribution of Cd to the liver and kidneys after the oral administration vary depending on the dosage levels of Cd. The difference of the distribution pattern of Cd to the liver and kidney is probably due to the difference in the form of the absorbed Cd, i.e., free ion or Cd-MT complex, although not closely related to the MT in the intestinal mucosa.     

Early changes in the tissue distribution of cadmium after oral but not intravenous cadmium exposure

The kinetics of 109Cd distribution in tissues of male and female mice were measured at intervals of 5 min to 15 days after oral (100 micrograms Cd/kg; by gavage) or intravenous (1 micrograms Cd/kg; i.v.) administration of 109CdCl2. Unexpectedly, the ratio of 109Cd in liver to that in kidneys was greater than or equal to 10 within 1 h after administration by either route. However, after 4 h, route-dependent differences in distribution between liver and kidney became apparent. In mice receiving oral cadmium, the liver:kidney 109Cd ratio decreased with time to approximately 4 at 72 h after gavage. In contrast, in mice receiving IV cadmium, the liver:kidney 109Cd ratio remained high and relatively constant during the same time period. The time-dependent decrease in the liver:kidney 109Cd ratio after oral cadmium administration was caused by a 4-5-fold increase in cadmium content of the kidney that occurred between 30 min and 72 h after oral but not i.v. administration. During this time, there was no change in cadmium distribution in subcellular fractions of either liver or kidney. These results could be explained by the existence of 2 separate pathways for cadmium deposition after oral exposure. Early after exposure, cadmium may leave the intestine, bind to serum albumins or other high molecular weight proteins, and accumulate primarily in liver, as is also observed after IV cadmium administration. With time, cadmium may leave the intestinal mucosa bound to metallothionein and deposit primarily in the kidney. The different pathways of deposition after oral vs. i.v. exposure may in part explain why acute parenteral cadmium exposure causes liver toxicity, but chronic oral exposure causes renal toxicity.     

Sex-specific effects of neonatal exposures to low levels of cadmium through maternal milk on development and immune functions of juvenile and adult rats

Cadmium (Cd) is a major environmental contaminant. Although immunotoxic effects have been associated with Cd exposure, the inconsistency of experimental results underlines the need of an experimental approach more closely related to environmental conditions. We investigated the effects of exposing neonatal Sprague-Dawley rats to environmentally relevant doses of Cd through maternal milk. Dams received 10 parts per billion (ppb) or 5 parts per million (ppm) Cd chloride (CdCl2) in drinking water from parturition until the weaning of the pups. Half of the offspring was sampled at weaning time. The remaining juvenile rats received water without addition of Cd until adulthood. Cd accumulation in kidneys of juvenile rats fed from dams exposed to Cd indicated the transfer of the metal from mother to pups through maternal milk. This neonatal exposure resulted in decreased body, kidney and spleen weights of just weaned females but not of males. This effect was more pronounced in the less exposed females fed from dams exposed to 10 ppb Cd, which also displayed lower hepatic metallothionein-1 (MT-1) mRNA levels. The effect of Cd exposure on body and organ weights did not persist to adulthood. In contrast, we observed gender-specific effects of neonatal Cd exposure on the cytotoxic activity of splenic NK-cells of both juvenile and adult rats. Cd also strongly inhibited the proliferative response of Con A-stimulated thymocytes in both male and female adult rats 5 weeks after the cessation of Cd exposure. These immunotoxic effects were observed at doses much lower than those reported to produce similar effects when exposure occurred during adulthood. In conclusion, neonatal exposures to environmentally relevant levels of Cd through maternal milk represent a critical hazard liable to lead to both transitory and persistent immunotoxic effects.     

Indirect and lactation-associated changes in renal alkaline phosphatase of newborn rats prenatally exposed to cadmium chloride.

Pregnant Sprague-Dawley rats were intraperitoneally injected with physiological saline solution (vehicle) or cadmium chloride (CdCl2) at 2.5 mg kg-1 body wt. on days 8, 10, 12 and 14 of gestation. Offspring were examined for renal alkaline phosphatase activity (ALP) on postnatal days (PND) 3 and 12, and for kidney metallothionein (MTh) and for liver, kidney and entire gastrointestinal tract 109Cd content at birth and on PND 3 and 12. No effects were observed on neonatal survival or on body, liver and kidney weights of pups up to PND 12. Newborns born and fed by mothers exposed to CdCl2 during pregnancy exhibited a significant decrease in ALP activity on PND 3. Conversely, no significant changes were observed in newborns lactated by surrogate non-treated mothers. Renal MTh increased with age but was not influenced by maternal treatment. Traces of 109Cd were present in the liver at birth (5-7 ng). Thereafter, 109Cd was mainly found in the gastrointestinal tract of newborns lactated by their biological mothers (610-690 ng on PND 12), with a marginal uptake in the liver (10-12 ng on PND 12). 109Cd was not detectable in the kidneys at any age (less than 4 ng). These results show that prenatal exposure to Cd cannot be the sole aetiological agent in the induction of the subtle and transitory changes in renal biochemistry observed in offspring born and fed by female rats intraperitoneally injected with 2.5 mg CdCl2 kg-1 body wt. on days 8, 10, 12 and 14 of gestation. The results also contradict the role of a direct effect on the kidney.     

Cadmium-induced enteropathy in domestic cocks: a biochemical and histological study after subchronic exposure

The biochemical and histological sequelae resulting from a diet containing 50.20 mg cadmium/kg were studied in Lohmann brown cockerels from hatching until 30 days of age. The additional cadmium chloride (CdCl(2)) to the diet induced the formation of lipid peroxides, which via a chain reaction led to accumulation of malondialdehyde in intestinal mucosa. At the end of the study (after 30 days of cadmium exposure) total protein and metallothionein levels in the intestinal mucosa and the relative ileal and duodenal weight increased. Histological data show that CdCl(2) causes an increase in number of goblet cells and granular lymphocytes in the intestinal mucosa. Down-regulation of the serotonin-positive cells in the cadmium-treated animals was observed. Growth retardation (by 27%) occurred in chicken fed the cadmium-enriched diet for 30 days. Cadmium accumulation in the intestine was markedly higher (154 times) in the cadmium-treated animals compared to the control group. Cadmium induced a decrease in zinc (but not copper) content in intestinal mucosa. We suggest that cadmium uptake triggers an inflammatory and secretory response in chicken small intestine.