Zinc distribution and metallothionein in the liver and kidney of mice treated with cadmium

Cadmium in the liver and kidney increased with the dosage of this injection. There was a parallel relation between the increase of cadmium in the whole liver and that in the metallothionein. In the liver and kidney, zinc highly increased in the low dose group than in the high dose group. In the 5.0 mg/kg group, zinc in the liver was not different from that of the control group, and about 30% of zinc in the 30,000 g supernatant existed in the metallothionein. By the DEAE-cellulose chromatography of metallothionein, two forms of metallothionein were obtained.

Effect of selenium on the organ distribution and binding of bismuth in rat tissues

Subcutaneous administration of bismuth, both single and multiple, resulted in deposition of this metal mainly in the kidneys which contained over 50% of the 'accessible pool' of bismuth. In the kidneys bismuth was bound mainly by the soluble fraction in which it was complexed with a protein of molecular weight of about 7000. Multiple administration of bismuth increased the level of this protein. Selenite administration brought about an increase in the 'accessible pool' of bismuth, probably due to a drop in excretion, and also changes in the organ distribution of this metal. The retention in the kidneys was diminished while those in the liver and in other tissues were augmented. These changes were accompanied by a change in the chemical form of bismuth present in the kidneys manifested by the total disappearance of the protein complex of molecular weight of 7000. The increased synthesis of this protein due to bismuth administration was not abolished completely.

Role of metallothioneins in disease

Metallothioneins are small proteins (6,000 to 10,000 mw) with similar amino acid compositions, high content of sulfhydryl amino acids and no aromatic amino acids. Emax at 250 nm is due to cadmium mercaptide bond. Synthesis is induced by a number of metals including zinc, cadmium, mercury, copper, bismuth, gold and silver. These proteins function as a mechanism of intracellular storage of some essential metals such as zinc and copper. Binding of potentially toxic metals like cadmium may be protective; but with saturation of protein by metal, toxicity may occur. Excessive cadmium-thionein may have a role in the pathogenesis of cadmium induced kidney disease. A more sensitive method for detection adn measurement of this protein will greatly enhance future studies, particularly the potential for clinical application.

Induction of cadmium-thionein in isolated rat liver cells

The uptake of cadmium by isolated liver cells was linearly related to the cadmium concentration to which the cells were exposed in the medium. Cadmium-treated cells synthesized proteins de novo with the characteristics of cadmium-thionein induced in the liver of cadmium-treated animals. Thionein from liver cells incorporated cadmium and [35S]cysteine, had a Ve/Vo (Sephadex G-50) of 1.8-1.9, and was separated into two subfractions by DEAE-cellulose ion-exchange chromatography. Cycloheximide and actinomycin D when added after a cadmium exposure prevented the synthesis of thionein. However, addition of actinomycin D after synthesis had started only decreased the total amount of thionein synthesized. The concentration of cadmium to which the cells were exposed affected the amount of cadmium-thionein synthesized in 6h. The maximum response occurred when cells were exposed to 0.5 microgram of cadmium/ml; at higher metal concentrations the total amount of cadmium-thionein synthesized declined. The system described in the present paper can be used to study the mode of metal toxicity and the mechanism of cadmium-thionein synthesis.

Postinductive actinomycin D effects on the concentrations of cadmium thionein, zinc thionein, and copper chelatin in rat liver

The time courses of induction in rat liver of copper chelatin by copper, cadmium thionein by cadmium, and zinc thionein by copper, cadmium, and zinc were monitorg metal were used in order to avoid toxic effects, being 5 mg zinc, 0.5 mg copper, and 0.25 mg cadmium per kg body weight. Peak times of induction and half times of decay observed were: copper chelatin (9 h, 8.6 h), cadmium thionein (18 h, 6.80 days), and zinc thionein (zinc rats, 18 h, 10.1 h; copper rats, 9 h, 18.2 h; cadmium rats, 24 h, 4.53 days). Administration of actinomycin D (1 mg per kg body weight) at the peak times of induction of the various proteins had no effect on the concentrations of chelatin or cadmium thionein observed up to 24 hours later, but in the case of zinc thionein, induced by zinc, copper, or cadmium, elevated concentrations were observed up to 23 h after administration of the drug. Such behavior is reminiscent of superinduction previously seen with other proteins and enzymes. We postulate that the intracellular concentration of free zinc in liver is of fundamental importance in the induction of zinc thionein, and this can be distributed by exogenous copper or cadmium resulting in the induction of synthesis of zinc thionein.

Biological function of metallothionein-IV. Biosynthesis and degradation of liver and kidney metallothionein in rats fed diets containing zinc or cadmium

The half-lives of liver and kidney metallothionein of rats fed diets containing either 2,000 ppm Zn or 100 ppm Cd were determined by a single injection of 14C-cystine. This protein was purified by Sephadex G-75 and DEAE cellulose column chromatography. Half-lives of liver metallothionein in rats fed the basal (18 ppm Zn), high Zn (2,000 ppm Zn), high Zn then basal, and high Cd (100 ppm) diet were, respectively, 3.4, 2.7 1.3, and 3.3 days, and that of kidney metallothionein were, respectively, 2.0, 2.2, 1.4, and 3.6 days. Thus, Cd-thionein has a longer half-life than Zn-thionein in both liver and kidney. The major species of metallothionein, which were separated on DEAE cellulose, had similar half-lives. Metallothionein, a protein having high content of metals and relatively short half-life, is possibly involved in cellular regulatory function.

Copper thionein in the kidneys of copper-poisoned sheep

A study has been made of the distribution of copper in the kidneys of copper-poisoned sheep, containing up to 240 microgram copper/g fresh cortex. About 64% of the copper in the cortex was present in the cytosol and 75% of this occurred in a form with molecular weight of approx. 12 000. This was partially purified by gel filtration on Sephadex G-75 and Bio-Gel P.10 and ion exchange chromatography on DEAE Sephadex A-25 to give three sub-fractions, which also contained zinc. The amino acid composition, copper content and chromatographic behaviour of these proteins indicated that they were copper-thioneins. No significant amounts of the proteins were detected in the plasma or erythrocytes of the copper-poisoned sheep when they were undergoing the haemolytic crisis typical of this syndrome. It is concluded that metallothionein constitutes the major copper-binding protein in the kidneys of copper-poisoned sheep. However the rapid accumulation of the protein in the kidney, and the development of kidney damage, are unlikely to have arisen from the release of the intact copper-protein from the liver and its transport via the blood to the kidneys.

Isolation of a non-thionein copper-binding protein from liver of copper-injected rats

1. The characterization of a low molecular weight, non-thionein, Cu-binding protein isolated from rat liver is reported. The protein was isolated following chronic administration of Cu(NO3)2 using a combination of Sephadex G75 and Sephadex DEAE A-25 chromatography. The protein did not bind to fully equilibrated Sephadex DEAE which formed the basis of the isolation procedure. 2. The final protein pereparation was found to be homogenous by a variety of electrophoretic techniques and was distinguished from metallothionein on the basis of its behaviour on ion exhcange and electrophoretic systems, spectral properties, and amino acid composition and metal content. It contains 6.8% cysteine and was found to bind Cu in a ration of 1.5:1 based on a molecular weight of 11 000. 3. These results confirm the necessity to use techniques other than gel filtration alone to obtain adequate separation of low molecular weight metal-binding protein fractions.

Distribution of copper and zinc in the liver of the developing sheep foetus

1. A study has been made of the copper- and zinc-binding proteins in the livers from sheep foetuses of 80-142 d gestational age. 2. Metallothionein was found to constitute the major Zn-binding component in the cytosol at all times and to be identical to Zn-thionein from adult sheep liver. 3. Zn also occurred in two fractions, not normally found in sheep liver, with approximate molecular weights of 28000 and 47000. The relative proportions of these were age-dependent. 4. Between 15 and 35% of the hepatic Cu, corresponding to most of the Cu in the cytosol, also occurred in the metallothionein-containing fraction.

Studies on the synthesis and metabolism of zinc-thionein in rats

The objectives of this investigation were to study the role of zinc-thionein in the metabolism of excessive amounts of zinc and the re-utilization of zinc bound to this protein. Rats were injected ip with 5 mg Zn/kg body weight as zinc chloride for 5 days to induce the synthesis of zinc-thionein. Proteins with molecular weight of 10,000 with high affinity for zinc were synthesized in rat liver and intestine. These proteins were heat stable. Large scale isolation of this protein from rat liver was achieved by a simple method consisting of a heating step and sephadex gel fractionation. Intravenous injection of isolated 65Zn-thionein to rats resulted in similar organ distribution of zinc as that after 65ZnCL2 injection. Gel filtration experiments with liver supernatant from rats injected with 65Zn-thionein showed that a major portion of 65Zn was transfered to other protein fractions and was re-ultilized similar to inorganic salts of zinc. Morphological studies showed no toxic effects after injection of zinc-thionein. These results show that zinc-thionein is metabolically active and non-toxic.

Accumulation and depletion of zinc in rat liver and kidney metallothionens

The accumulations of zinc in liver and kidneys of rats fed various dietary levels of this element was investigated. Zinc started to accumulate in rat liver when 1,000 ppm or higher levels of this element were fed in the diet, but not when the dietary zinc level was 500 ppm less. Almost all of the accumulated zinc in the soluble fraction was found to be present in the metallothionein (MT) fractions. When rats were fed a diet supplemented with 2,000 ppm, zinc, the metal rapidly accumulated in MT in the liver and kidneys. The accumulated zinc was, however, depleted to the pre-supplementation level after only 3 days of feeding a zinc deficient diet. While rats were fed the zinc deficient diet, in which the element was simultaneously depleted from MT, significant increased excretion of the metal occurred in the feces urine. No evidence was found to indicate that zinc was excreted in the bile in association with MT. It was therefore concluded that MT is probably, as one of its possible biological roles, more involved in accumulation of excessive zinc rather than in storage of the metal for later utilization.

Role of dietary calcium and calcium binding protein in cadmium toxicity in rats

Growing male rats were fed a purified diet containing 0.6% Ca (two groups) or 0.1% Ca (two groups) for 8 weeks. One 0.6% Ca group and one 0.1% Ca group received 25 ppm Cd (as CdC12) in the drinking water. Diets were fed on an equalized basis with the 0.1% Ca + Cd group determining the amount of diet fed to the other groups. Water was provided ad libitum. Terminal body weights were not different among the four groups. Packed cell volumes were depressed in the Cd-exposed groups, especially the 0.1% Ca + Cd group. The highest concentrations of Cd were found in the lungs, liver, and kidneys of the 0.1% Ca + Cd group. More Cd was bound to low molecular weight proteins of the intestinal mucosa from the 0.1% Ca + Cd group than the 0.6% Ca + Cd group. Rats fed the 0.1% Ca diet appeared to have a greater capacity to absorb either Ca or Cd than rats fed the 0.6% Ca diet, as shown by an enhanced binding of 45Ca and 115mCd to intestinal calcium-binding protein (CaBP) in the rats fed the low calcium diet. A portion of the mucosal Cd was accounted for as Cd bound to metallothionein. It was concluded, based upon these experiments, that cadmium retention and signs of toxicity are enhanced by feeding low Ca diet and that the increased CaBP activity due to Ca restrictions is responsible for the increased Cd uptake observed.

Cadmium-induced enteropathy: comparative toxicity of cadmium chloride and cadmium-thionein

In protecting the body against the noxious effects of dietary cadmium ions, cadmium is bound to metallothionein in the proximal intestine, and subsequently excreted into the lumen with desquamation of the epithelium. The purpose of this study was to determine the extent to which cadmium in the form of intestinal cadmium-thionein is absorbed from the intestinal lumen and to appraise the toxicity of cadmium-thionein on the intestinal mucosa. With open-ended duodenal perfusion, equivalent amounts of cadmium administered as CdCl2 or cadmium-thionein entered the mucosa, but significantly less cadmium from the perfusate of cadmium-thionein passed into the body. Exposure of the mucosa to CdCl2 for 1 hr led to minor abnormalities in the form of broadening of villi with pseudostratification of epithelium, and swelling of mitochondria, whereas cadmium-thionein produced extensive necrosis of absorptive cells. The results suggest that cadmium-thionein may play a paradoxical role, providing protection against the cadmium ion in the intracellular milieu, but promoting cadmium toxicity when it is present in sufficient amounts in the lumen of the intestine.

Degradation of hepatic zinc-thionein after parenteral zinc administration

A low-molecular-weight protein, zinc-thionein, a metallothionein, was implicated as having a regulatory function in zinc metabolism. The half-life (t 1/2) of hepatic zinc-thionein was determined by pulse-labelling with either L-[35S] cystine and/or 65Zn. In two experiments with L-[35S]cystine, the t 1/2 of zinc-thionein was 18h and 19h. Most of the soluble 35S-labelled hepatic proteins had a t 1/2 of 4 days. The t 1/2 of zinc-thionein calculated by using 65Zn was 20h. The close similarity between the calculated and measured t 1/2 values for zinc-thionein suggests that release of Zn2+ from zinc-thionein probably occurs simultaneously with degradation of the protein moiety.

Influence of dietary cadmium on the distribution of the essential metals copper, zinc and iron in tissues of the rat

The effect of long-term dietary cadmium treatment upon the distribution of the metals copper, iron and zinc has been compared in various organs of male and female rats. The renal accumulation of cadmium was similar in both sexes without a plateau being reached. In contrast, the hepatic accumulation of cadmium was higher in the female than in the male rat and a plateau was observed after 30-35 weeks of dietary cadmium treatment. Most of the cadmium which accumulated in these organs was recovered in the metallothionein fraction andthe concentration of hepatic cadmiumthionein in the female rat was correspondingly higher than in the male rat. Accumulation of cadmium was associated with an increased zinc concentration in the liver and an increased copper concentration in the kidney; these increases were correlated with increases in liver and kidney metallothioneins induced by cadmium. Uptake of cadmium into organs other than liver and kidney occurred to a small extent but was not associated with changes in the concentration of copper and zinc. Cadmium also accumulated in the intestinal mucosa where it could be recovered in a fraction corresponding to metallothionien. A loss of iron from the liver and kidney was also observed following dietary cadmium treatment and involved mainly a loss of iron from ferritin.

Prevention by copper of cadmium sequestration by metallothionein in liver

Following chronic CdCl2 administration to rats, more than 98% of the metal in liver supernatant is bound to the low molecular weight binding protein, metallothionein. Simultaneous administration of high doses of Cd and copper salts result in an increase in toxicity which is accompanied by a failure of Cd sequestration by metallothionein in vivo. This may be due to an aggregation of metallothionein which has been observed in the presence of copper in vitro.

[Significance of trace elements within the scope of parenteral feeding as illustrated on the example of the elements copper, zinc and chromium]

Biochemical function and biological significance of Cu, Zn and Cr are reviewed briefly. During a longterm perenteral nutrition a depletion of the organism of copper and zinc is to be expected. Therefore, in parenteral nutrition, an early substitution of zinc seems to be usefull. Up to now a similar recommendation for copper cannot be given. As many infusion solutions are contaminated with chromium, there is no need to substitute this element in parenteral nutrition.

Distribution of metallothionein-bound cadmium and cadmium chloride in mice: preliminary studies

Metallothionein from livers of mice was isolated by gel chromatography and isoelectric focusing. One of two forms thus obtained contained 32 percent cysteine. This form, labeled in vitro with 109Cd, was injected intravenously in mice, and the distribution of 109Cd was studied. Animals killed after 4 hrs had over 80 percent of the injected dose in the kidneys. Protein obtained after gel chromatography, containing both forms of cadmium-binding protein, was also labeled in vitro with 109Cd and injected intravenously. Animals killed 4 hrs after injection had 50 percent of the injected dose in the kidneys. Whole-body measurements and wholebody autoradiography demonstrated that approximately 40-60 percent of the injected dose had been excreted in urine. The results show a selective accumulation of metallothionein-bound cadmium in the kidney and indicate possible differences in distribution and excretion of cadmium depending on binding to different forms of low molecular weight cadmium-binding proteins.

A soluble cadmium-binding component in rat and dog spleen

The spleens of cadmium-treated Sprague-Dawley rats and mongrel dogs were examined for cytoplasmic soluble cadmium-binding moieties following the cessation of parenteral cadmium exposure. Cell homogenates prepared in 0.25M sucrose were centrifuged at 29,000 g and the supernatant fractionated on a fractionating column (Sephadex G-75). Ultraviolet absorbing peaks that showed characteristically high 250-nm to 280-nm absorbences were further analyzed for cadmium content by atomic absorption spectrophotometry. Cadmium-binding fractions isolated from the spleens of both species were characteristically similar to rat kidney metallothionein-like substances isolated and identified by the same procedure. Molecular weights for the canine and rat spleen cadmium-binding components were estimated at 14,783 +/- 343 and 13,916 +/- 490, respectively. These preliminary data indicate the production and persistence of soluble metallothionein-like substances in spleen that bind and retain cadmium ions long after cadmium exposure has ceased.

The induction of metallothionein in rat liver by zinc injection and restriction of food intake

The isolation of two forms of hepatic zinc-thioneins after either zinc injection into rats or partial restriction of their food intake is described. The proteins differed slightly in their amino acid composition and electrophoretic mobilities. Increases in liver zinc content after both treatments were synchronous with, and associated almost completely with, increased zinc-binding to these proteins. The time-course for the appearance and disappearance of the zinc proteins is shown. It is suggested that metallothionein is involved in the normal metabolism of zinc, perhaps in some temporary storage or detoxication capacity.