Protective role of renal metallothionein against Cd nephropathy in rats

Rats were treated with four types of Cd compound: CdCl2, Cd bound (Cd-peptide), and Cd bound to metallothionein (Cd-MT). This treatment caused no nephropathy. Subsequently, toxic doses of Cd compounds were administered to these pretreated rats and their effects on renal function were examined. When 1.4 mg Cd/kg as Cd-Cys was administered, marked increases in urinary protein, glucose, and amino acid were observed. However, when the animals were pretreated with 1 mg Cd/kg/day as CdCl2 for 3 days, and 1.4 mg Cd/kg as Cd-Cys was administered 24 hr later, no renal damage was observed. Such a protective effect against the nephrotoxic action of Cd-Cys was also shown by pretreatment with Cd-Cys, Cd-peptide, or Cd-MT. Furthermore such a phenomenon was also observed when the nephropathy was caused by Cd-peptide or Cd-MT. The efficacy of pretreatment depended on the time before subsequent administration of Cd and the dose used for pretreatment. Incorporation of Cd into the liver and the kidney was not altered by the pretreatment. No matter in which form the nephrotoxic dose of Cd was administered, the incorporated Cd was distributed between particulates and cytosol; 3 hr after administration, cytosolic Cd was present in almost equal amounts in the high-molecular-weight and the MT fractions in the nonpretreated rats. However, after pretreatment, more of the Cd subsequently administered was found in the MT fraction. These results suggest that MT participates in the detoxication mechanism against Cd in the kidney, as it does in the liver.     

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.     

Exogenous metallothionein and renal toxicity of cadmium and mercury in rats.

The relative tissue distribution and toxicity of cadmium (Cd) and mercury (Hg) in the liver and kidneys of rats when the metals are administered as either inorganic salts or complexed with MT were studied. Male Sprague-Dawley rats were injected (i.v.) with Cd or Hg inorganic salt of chloride or in a complex of MT at a dose of 0.3 mg/kg body weight. The concentration of MT and metals in plasma and urine was monitored for 7 days, at the end of which the rats were killed. Injection of both HgCl2 and Hg-MT induced the synthesis of MT only in the kidney but not in the liver, whereas CdCl2 and Cd-MT injections induced MT synthesis in both liver and kidney, respectively. Plasma MT levels increased 3 days after CdCl2 but not after HgCl2 injection, suggesting that hepatic MT may be an important source of plasma MT under our experimental conditions. Renal toxicity was observed morphologically and by an increase in blood urea nitrogen, plasma creatinine, proteinuria in rats injected with Cd-MT and both forms of Hg. Urinary MT excretion was significantly elevated in Cd-MT injected rats compared with those injected with CdCl2. However, HgCl2 and Hg-MT injected rats showed no significant difference in urinary MT excretion. The magnitude in the renal accumulation of Hg is similar after the administration of Hg-MT or HgCl2, but our findings suggest that the site of epithelial injury may be different. Injury effects of Hg-MT localized mainly in the terminal portions of the proximal convoluted tubule and the initial portions of the proximal straight tubule whereas inorganic Hg caused necrosis in pars recta segments of the proximal tubule.     

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.     

Nephrotoxicity of Intravenously Injected Cadmium-Metallothionein: Critical Concentration and Tolerance

Nephrotoxicity of Intravenously Injected Cadmium-Metallothionein:Critical Concentration and Tolerance. MAITANI, T., CUPPAGE,F. E. AND KLAASSEN, C. D. (1988). Fundam. Appl Toxicol. 10,98-108. The nephrotoxicity of Cd-metallothionein (Cd-MT) wasexamined after iv administration of various dosages to mice.The lowest dosage of Cd-MT that produced renal injury was 0.2mg Cd/kg. This dosage of Cd-MT resulted in 10 µ Cd/g inthe kidneys 24 hr after administration. A time-course experimentutilizing a higher (0.3 mg Cd/kg) nephrotoxic dose of Cd-MTdemonstrated that the renal Cd concentration at 4 and 12 hrwas much higher than the critical concentration, but thereafterdecreased to about 10 Mg Cd/g wet tissue by 24 hr. Thus, Cdin excess of 10 Mg/g appears to damage the kidney and then distributesto other tissues and/or is excreted into urine. When a totalof 0.3, 0.4, and 0.8 mg of Cd/kg as Cd-MT was administered individed dosages over 4 days, as much as 30 Mg Cd/g was detectedin the kidney but no renal injury was observed. Thus, the criticalconcentration for producing renal injury after acute administrationof Cd-MT is estimated to be approximately 10 Mg Cd/g wet weight.However, with repeated exposure to Cd-MT, this acute criticalconcentration can be exceeded without producing renal injury,as tolerance to the nephrotoxic effects of Cd-MT develops.     

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.     

肝脏损害对染镉大鼠镉分布的影响

大鼠腹腔内注射ＣｄＣｌ２０．５ｍｇＣｄ＾２＋／Ｋｇ体重，每周三次，共１０周。注射ＣｄＣｌ２第４周末，其中一组动物灌胃ＣＣｌ４９００ｍｇ／ｋｇ体重。结果表明ＣｄＣｌ２＋ＣＣｌ４组动物肝脏损害后肝镉浓度明显低于单纯ＣｄＣｌ２组，同时伴随血镉，肾镉水平显著升高。肝、肾中金属硫蛋白浓度也与相应组织中隔浓度呈类似的变化形式。ＣｄＣｌ２＋ＣＣｌ４组动物尿镉和尿金属硫蛋白浓度均明显高于ＣｄＣｌ２组。这些实验     

The dose-dependent deposition of cadmium into organs of Japanese quail following oral administration

The accumulation and disposition of Cd2+ as CdCl2 administered orally to Japanese quail (Coturnix coturnix) was investigated. Birds received 0.01, 0.10, 1.0, 50, 500, 5000, or 50,000 micrograms Cd/kg/day for 4 consecutive days by gastric tube, and were killed 4 days after the final dose. The percentage of the total administered dose recovered in liver + kidneys + duodenum was 0.7% or less in all but the highest dose, for which recovery was approximately 2%. Only at the highest dose did the hepatic Cd concentration exceed that of the kidney, and only at this dose was there any appreciable increase in metallothionein (MT) concentrations in the liver and kidney. Duodenal cytosol was found to contain high levels (300-1300 micrograms/g) of endogenous MT-like proteins, probably due to the relatively high Zn concentration (approximately 185 ppm) of the commercial diet eaten by the quail. In the small intestine, Cd2+ taken up after trace doses of oral 109Cd2+ was found to be exclusively bound to these 10,000-MW, or lower MW, ligands. In the liver, MT synthesis was accompanied by increased concentrations of Cd and Zn (but not Cu) associated with the MT fractions, whereas in the kidney, all three metals were elevated in response to Cd-induced MT synthesis. A major conclusion of the present study is that, in response to environmentally relevant (less than 10 micrograms/kg/day po) doses of Cd2+, absorbed Cd is transported in blood primarily in a form which enhances deposition in the kidney. This behavior is consistent with the pharmacokinetics of Cd-MT.     

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.     

Renal glutathione depletion and nephrotoxicity of cadmium-metallothionein in rats

Renal glutathione (GSH) concentrations were reduced approximately 80% at 4 hr after a single injection of buthionine sulfoxime (BSO) (4 mmol/kg body wt) and remained reduced for at least 16 hr in male rats. Following BSO injection, rats were injected with a nephrotoxic dose of cadmium-metallothionein (Cd-MT) (0.3 mg Cd as Cd-MT/kg body wt) and killed 1, 4, or 12 hr later. Damage to the kidney was assessed histologically and by measurement of p-aminohippuric acid (PAH) uptake into renal cortical slices. Although the renal accumulation of Cd following Cd-MT injection was significantly lower in BSO-pretreated rats as compared to nonpretreated rats, the damage to kidney was more severe. At 4 and 12 hr, both Cd-MT-induced inhibition of PAH uptake and morphological damage were significantly increased in BSO-pretreated rats. In certain experiments, the induction of renal intracellular MT synthesis by zinc pretreatment slightly decreased the renal toxicity of Cd-MT in the BSO-treated rats. The results demonstrate that although GSH depletion decreases the renal accumulation of Cd in rats injected with Cd-MT, the nephrotoxicity of Cd-MT is increased. Preinduction of MT in the kidney can only partially overcome this increase in toxicity. Therefore both GSH and intracellular MT levels can influence the renal toxicity of injected Cd-MT.     

Uptake of cadmium and metallothionein by rat everted intestinal sacs

The gastrointestinal uptake and transport of cadmium (Cd) and the role of metallothionein (MT) were studied in everted sacs of rat intestine (ESRI). When ESRI were incubated for 30 min in a medium containing various Cd concentrations (1-5 x 10(-4) M) as CdCl2, Cd-cysteine (Cd-Cyst) or rat liver Cd-MT-II (Cd-MT), a dose-dependent tissue uptake of Cd was observed. In ESRI incubated with Cd-MT, total Cd uptake was lower than that of CdCl2 (25% of CdCl2). Fractionation of the tissue showed that about 80% of Cd in the tissue was recovered in the particulate fraction after CdCl2 and Cd-Cyst incubation, while that after Cd-MT incubation was present mainly in the cytosol fraction (about 80%). Most of the Cd in the cytosol fraction of Cd-MT-incubated ESRI was associated with a 10,000 molecular weight protein on Sephadex G-75 column fractionation. Similar results were obtained after incubation of ESRI from Zn-pretreated rats with 109CdCl2 solution. In addition to the Cd-MT peak, there was a small peak of Cd associated with a high molecular weight fraction. Only a small percentage of Cd was leaked to serosal fluid in the everted sacs incubated at a low concentration of CdCl2 (0.8%) but this leakage of cadmium was increased at higher concentration and was higher after incubation with Cd-MT. The results suggest that the uptake of Cd from CdCl2 and Cd-MT is different. Although Cd-MT was taken up intact by everted sacs, the uptake was slow as compared to Cd salts. The intracellular presence of MT had little effect on the uptake of CdCl2 but the Cd was sequestered by MT in the intestine.     

Influence of cadmium-metallothionein pretreatment on tolerance of rat kidney cortical cells to cadmium toxicity in vitro and in vivo

Kidney cells were isolated from rats pretreated by daily subcutaneous doses of cadmium metallothionein (CdMT: 0.05-0.2 mg Cd/kg X 5) and from non-pretreated rats. Upon exposure to CdCl2 in vitro (0-200 micrograms Cd/ml), a concentration dependent decrease in viability was observed in the non-pretreated cells, while no such decrease occurred in the pretreated cells indicating that these cells were more resistant to the toxic action of cadmium. There was a higher in vitro uptake of Cd+2 and an increased metallothionein (MT) concentration in the pretreated cells (compared to non-pretreated cells). Subcellular distribution studies revealed that Cd was mainly recovered in the "cytosol" fraction. The higher total cadmium uptake in pretreated cells corresponded to an increase of Cd in "cytosol" and "nuclear" fractions. This observation may be explained by MT-binding of Cd in the cells and is in accordance with a possible protective effect of induced MT in the pretreated cells. In order to assess whether pretreatment-induced tolerance to cadmium toxicity--indicated by the cellular studies--could also be observed in vivo, some whole animal experiments were also performed. A dose-related proteinuria was observed in non-pretreated rats after a single subcutaneous administration of 109Cd-MT at doses of 0.05 and 0.4 mg Cd/kg. Urinary total Cd, 109Cd and MT was also increased in a dose-related fashion. Cadmium concentrations in kidney were dose related and reached 19 micrograms/g wet weight. In contrast, in animals repeatedly pretreated with CdMT according to 1), no proteinuria was observed after administration of the same single doses of 109CdMT. Total Cd. 109Cd and particularly MT-concentrations in urine were lower in such pretreated animals than in in non-pretreated ones in spite of the accumulation of higher tissue concentrations of total Cd (up to 80 micrograms/g). The pretreatment was thus shown to prevent some of the acute nephrotoxicity of CdMT, possibly by means of induction of MT synthesis.     

Effect of N-benzyl-d-glucamine dithiocarbamate on renal toxicity induced by cadmium-metallothionein in rats

The effect of N-benzyl-D-glucamine dithiocarbamate (BGD) on the renal toxicity induced by acute exposure to cadmium-metallothionein (Cd-MT) in rats was studied. Rats were injected intraperitoneally with BGD (400 mumol/kg) 6, 12, or 24 h after intraperitoneal injection of Cd-MT (1.78 mumol Cd as Cd-MT/kg) and thereafter they received three injections of BGD (400 mumol/kg) daily for 3 days. Urinary protein concentration and aspartate aminotransferase (AST) activity significantly increased 1 day after Cd-MT treatment and decreased to control levels at 9 days after the treatment. Urinary excretion of glucose and amino acids rose gradually reaching maximum levels 5 days after Cd-MT treatment and returned to the control levels at 9 days. BGD injection significantly reduced the increases in the urinary excretion of protein, AST, glucose and amino acid, which were produced by Cd-MT treatment. Significant increases in urine volume were observed after Cd-MT treatment. BGD injection inhibited the increase in urine volume caused by Cd-MT treatment. A long time interval (12 and 24 h) between the administrations of Cd-MT and BGD resulted in a decreased protective effect of BGD against Cd-MT-induced renal damage. Following Cd-MT injection, the major route of excretion of cadmium (Cd) was via the urine and the kidney was the major site of accumulation of Cd. BGD injection remarkably increased the urinary excretion of Cd, resulting in a significant reduction in the kidney Cd concentration. The results of this study indicate that BGD injection is effective in decreasing the Cd concentration in the kidney, resulting in the protective effect on Cd-MT-induced renal damage.     

Role of megalin and the soluble form of its ligand RAP in Cd-metallothionein endocytosis and Cd-metallothionein-induced nephrotoxicity in vivo

Orally administered Cd is predominantly distributed to the intestine, and the majority of this mucosal Cd is bound to metallothionein (MT). MT attenuates heavy metal-induced cytotoxicity by sequestering these metals and lowering their intracellular concentrations. In addition, MT acts as an extracellular transporter of orally administered Cd to the kidney. Because of its low molecular weight, the Cd-MT complex is freely filtered at the glomerulus, and the filtered Cd-MT is then incorporated into renal proximal tubular cells. Megalin, a multiligand endocytic receptor (also known as low-density lipoprotein receptor-related protein 2 or Lrp2), acts as the receptor for Cd-MT in a renal proximal tubular cell model. Here, we used the soluble form of 39-kDa receptor-associated protein (sRAP; also known as Lrpap1), a ligand of megalin, to inhibit megalin function, and then analyzed the effect of megalin loss on Cd-MT distribution and Cd-MT-induced nephrotoxicity in an animal model. Administration of sRAP to mice caused acute loss of megalin function by removing megalin in the brush border membrane. The pre-injection of sRAP decreased renal Cd content and decreased Cd-MT-induced kidney damage. Our results demonstrate that sRAP reduces Cd-MT-induced kidney toxicity in vivo.     

Cadmium accumulation and metallothionein concentrations after 4-week dietary exposure to cadmium chloride or cadmium-metallothionein in rats.

The distribution of cadmium was examined in rats fed diets containing either cadmium-metallothionein (CdMt) or cadmium chloride (CdCl2) for 4 weeks. The test diets contained 3, 10, or 30 mg Cd/kg diet (3, 10, or 30 ppm) as CdMt or 30 mg Cd/kg diet (30 ppm) as CdCl2. A second study was performed to establish the Cd content in liver and kidneys after exposure to low doses of both CdMt and CdCl2 (1.5 and 8 ppm Cd). The feeding of CdMt resulted in a dose- and time-dependent increase of the Cd concentration in liver, kidneys, and intestinal mucosa. Rats fed 30 ppm CdMt consistently showed less Cd accumulation in liver and intestinal mucosa than did rats fed 30 ppm CdCl2. However, renal accumulation in rats fed 30 ppm was similar until Day 28 regardless of Cd form. At lower dietary Cd levels (1.5 and 8 ppm), relatively more Cd is deposited in the kidneys, although even at these doses the kidney/liver ratio of Cd is still higher with CdMt than with CdCl2. Tissue metallothionein (Mt) levels in the intestinal mucosa were relatively constant but always higher after CdCl2 exposure than after CdMt exposure. Mt levels in both liver and kidney increased after CdCl2 or CdMt exposure during the course of study. Although Mt levels in liver were higher after CdCl2 intake (30 ppm) than after CdMt intake (30 ppm), renal Mt concentrations were the same for both groups. In fact on Day 7, CdMt administration resulted in slightly higher Mt levels than CdCl2 administration, suggesting a direct accumulation of exogenous CdMt in the kidneys. In conclusion, after oral exposure to CdMt in the diet there is a relatively higher Cd accumulation in the kidneys. However, the indirect renal accumulation via redistribution of Cd from the liver might be lower than after CdCl2 exposure. Which of these two phenomena is decisive in the eventual level of renal toxicity of Cd after long-term oral intake could determine the toxicological risk of the chronic intake of biologically incorporated Cd.     

Effect of cadmium chloride and Cd-metallothionein on the nervous tissue culture

Influence of metallothionein (MT) isolated from rat liver on rat cerebellum in culture was investigated by comparison with that of CdCl2. Cd-MT at 0.2 X 10(-5) M as Cd significantly depressed the outgrowth of nerve fibers, fibroblasts and glial cells as compared to the control culture. In the range from 0.2 X 10(-5) M to 2.7 X 10(-5) M Cd, the toxicity of Cd-MT was the same as that of CdCl2. Above 5 X 10(-5) M Cd, however, the toxicity of Cd-MT was less than that of CdCl2. Cadmium added as CdCl2 was perfectly recovered at a region of higher Mr than MT on the Sephadex G-75 column. Cadmium added as Cd-MT was detected in part at the higher Mr region and in part at the MT region, depending on incubation time and Cd concentration in the medium. The toxic action of Cd-MT was proportional to the recovery level of Cd at the higher Mr region.     

Nephrotoxicities of Aluminium and/or Cadmium-Metallothionein in Rats: Creatinine Excretion and Metabolism of Selected Essential Metals

Abstract: The effects of exposure to aluminium (Al) and cadmium (Cd) on urinary creatinine and protein excretion, and the concentrations of calcium, magnesium and copper in kidney and urine were studied in 32 male adult Wistar rats. The animals were divided into 8 groups, groups 1–4 given a calcium-deficient diet (0.01%, i.e. 0.01 g calcium/100 g diet weight) and groups 5–8 a calcium-adequate diet (0.9%) for 6 weeks. Single daily intraperitoneal injections of AlCl₃ (10.8 mg Al/kg body weight, per day) were done on 6 consecutive days to groups 3, 4, 7 and 8 during the last week of the experiment. One single intraperitoneal injection of cadmium-metallothionein (Cd-MT, 0.4 mg Cd/kg) was administered 12 hr before the final Al dose to groups 2, 4, 6, and 8 and the rats were sacrificed 47 hr after the Cd-MT injection. The rate of creatinine clearance was significantly lower in rats injected intraperitoneally with either Cd-MT or Al, and the concentrations of magnesium and calcium in urine were lower in rats administered both Al and Cd-MT as compared to those in control groups. Histological examination showed that Al was toxic to the kidney tubule cells of rats, however, an adequate supply of calcium in food protected to some extent the renal tubules from Al toxicity as indicated by a higher creatinine clearance, and there was also less tubule damage as shown by histological examination. The copper concentrations in kidney tissue were lower in groups treated with either Al or Cd-MT. The above results indicate that: (1) Al administered by intraperitoneal injection is nephrotoxic in rats; (2) food deficient in calcium increases the vulnerability of the kidney to Al-induced toxicity; (3) the decreased creatinine clearance in Cd-MT-injected rats may explain the low calcium excretion in urine observed in these rats.     

Absorption and distribution of cadmium (Cd), copper and zinc following oral subchronic low level administration to rats of different binding forms of cadmium (Cd-acetate, Cd-metallothionein, Cd-glutathione)

Male Wistar rats received by gavage saline or about 25 micrograms cadmium (Cd)/kg/day as Cd-acetate (Cd-Ac), Cd-metallothionein (Cd-MT) or Cd-glutathione (Cd-GSH) 5 times per week for 28 times. At all treatments 0.2-0.3% of the totally administered Cd dose was found in liver, kidneys, small intestine and pancreas, whereas none of the Cd forms applied resulted in a Cd accumulation in testes. Cd in small intestine was not increased by Cd-MT. However, it was raised by Cd-Ac and even more by Cd-GSH. A smaller increase in hepatic and renal Cd resulted from Cd-GSH than from Cd-Ac or Cd-MT. Cd in pancreas increased after Cd-GSH but not after Cd-Ac or Cd-MT. Copper (Cu) rose in small intestine and testes but decreased in kidneys independent of either Cd treatment. Concomitantly, zinc (Zn) was decreased in small intestine and testes. The tissue concentration of metallothionein (MT) was only marginally increased by all treatments. The highest value (80%) above controls) was found in small intestine after Cd-GSH. Intestinal Cd as well as testicular Cu were related to the tissue MT. Therefore, the distribution of Cd between various organs depends on the Cd form applied. There is some relationship to the distribution of Cu and Zn.     

Role of intestinal metallothionein in absorption and distribution of orally administered cadmium

The effects of mucosal metallothionein (MT) preinduced by Zn on the intestinal absorption and tissue distribution of Cd were studied. 109CdCl2 was administered to control and Zn-pretreated rats. The total amount of Cd distributed to the liver and the kidney in the group pretreated with 100 mg/kg of Zn was about 70% that of the control group. In the control group, the Cd concentration in the intestinal mucosa reached a maximum 16-24 hr after its administration and then gradually decreased with time, unlike that in the liver and the kidney. The concentration of intestinal Cd in the pretreated group reached a maximum earlier than it did in the control group and most of the Cd was in the MT fraction. Pretreatment with Zn (100 mg/kg or higher, po) caused a reduction in the Cd concentration in the liver and an increase in the kidney. Pretreatment with Zn (5 X 10 mg/kg, sc) or Cd (5 mg/kg, po) also increased renal Cd concentration. This was effective at 24 hr but not at 0.5 hr after pretreatment. These effects of pretreatment with Zn (100 mg/kg, po) on tissue distribution of Cd were also observed after an intraintestinal injection of Cd but not after an iv injection. The results indicate that MT in intestinal mucosa plays a significant role not only in the absorption of Cd but also in its transport to the kidney.     

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.