Differences between pregnant and nulliparous rats in basal and stress levels of metallothionein

The present experiment was designed to examine the influence of pregnancy on basal and stress levels of serum and liver metallothionein (MT). Eighteen-day pregnant rats showed higher serum MT levels and lower liver MT levels than nulliparous rats, suggesting that a great MT mobilization from the liver into the serum was present in the former rats. Serum MT levels were not changed by either restraint or starvation. It is unlikely that the lower liver MT levels showed by pregnant rats were due to competition by progesterone for glucocorticoid receptors, as previously suggested, since the corticosterone/progesterone ratio was unchanged in pregnant rats. Liver MT response to food and water deprivation with or without restraint was somewhat different in nulliparous and pregnant rats. Thus, food and water deprivation for 24 h caused higher liver MT induction in pregnant than in nulliparous rats. When food and water deprivation was accompanied by restraint stress a further increase in liver MT was observed in nulliparous but not in pregnant rats. This suggests that food and water deprivation may be a more severe stress in pregnant rats because of the additional demands of the growing fetuses. Fetal liver MT was increased by restraint stress but not by food and water deprivation. The role of Zn influx into the liver is discussed.

N-alkyl-N-dithiocarboxy-D-glucamine analogs as cadmium antagonists: synthesis and evaluation of the n-propyl, n-butyl, and n-amyl derivatives

N-(n-Propyl)-, N-(n-butyl)-, and N-(n-amyl)-N-dithiocarboxy-D-glucamine were newly synthesized by (a) addition of each n-alkylamine to glucose, (b) high-pressure catalytic reduction of each glucosamine thus formed to the corresponding glucamine, and (c) reaction of the resultant secondary amines with CS2 to form the dithiocarboxy derivatives. Each compound was evaluated as an antagonist of acute cadmium (Cd) toxicity and as a complexing agent for intracellular metallothionein-bound Cd (Cd-MT) in mice. N-Benzyl-N-dithiocarboxy-D-glucamine (BDCG) was used as a positive control compound. Each congener afforded partial or complete protection against the lethal effects of 10.0 mg/kg CdCl2.2.5 H2O, and retarded accumulation of Cd in livers and kidneys when given 2 h after the acutely toxic dose of Cd. Each derivative was also effective in mobilizing Cd from MT-bound sites in livers and kidneys of mice which had received a sub-lethal dose of CdCl2 along with 109CdCl2 2 weeks earlier. Excretion of mobilized Cd was almost exclusively by the fecal route. Potency of the analogs, as well as the octanol/aqueous partition coefficients, increased with the overall length of the N-(n-alkyl) carbon chain. Each compound readily complexed Cd from partially purified Cd-MT in vitro. Serum Cd from mice treated with BDCG was associated principally with proteins of high molecular weight.

Cadmium-induced synthesis of metallothioneins in human lymphocytes and monocytes

Cd2+-binding proteins of peripheral blood lymphocytes and monocytes have not well been characterized so far, although they are expected to be a clue for understanding Cd2+ toxicity in those immune competent cells. We separated a family of Cd2+-binding proteins from Cd2+-exposed human peripheral blood lymphocytes by gel filtration chromatography, and characterized them by SDS-gel electrophoresis. The proteins showed electrophoretic behaviours closely similar to metallothioneins (MTs) of HeLa cells derived from human cervical carcinoma. The proteins were also found in Cd2+-exposed monocytes, and were inducible by Cd2+ in both lymphocytes and monocytes. Anti-MT serum specifically precipitated these proteins, which were thus identified as MTs. These results suggest that the two classes of the cells involved in the immune system possess a protective mechanism against Cd2+ through MTs. A variety of human lymphoid cell lines derived from both T and B cells were also found to have capacity to synthesize MTs in response to Cd2+.

Sex and restraint stress differences in rat metallothionein and Zn levels

Sex differences in serum and liver metallothionein (MT) levels were studied in adult male and female rats. Whereas it was found that female rats had higher hepatic MT levels than male rats in basal, unstressed conditions, no significant differences were found in serum MT levels. Restraint stress increased both serum and liver MT in both sexes. The increase in serum MT was greater in male than in female rats, whereas no significant differences between sexes were found in liver MT content after restraint stress. It is suggested that MT regulation might be sex-dependent and that MT might play some extrahepatic function during stress.

The role of catecholamines and glucagon on serum and liver metallothionein response to restraint stress

The role of glucagon and catecholamines on serum and liver metallothionein (MT) concentrations in basal and stress conditions has been studied. Glucagon showed no effect on serum MT either in basal (unstressed) or stress (20 hours of restraint) conditions. In contrast, glucagon administration increased both unstressed and stressed levels of liver MT. No effect of the alpha + beta-catecholamine blocker labetalol on serum MT levels was observed in unstressed rats. However, the administration of labetalol abolished the increase in serum MT levels caused by stress. These data suggest that catecholamines might be involved in serum MT regulation during stress, while they might not be important in the maintenance of basal serum MT levels. Finally, no significant effect of adrenergic blockade was found on basal and stress levels MT, in agreement with previous data from this laboratory.

Effects of changes in dietary zinc, copper and selenium supply and of endotoxin administration on metallothionein I concentrations in blood cells and urine in the rat

These studies were designed to investigate the effects of low dietary zinc, copper or selenium intake of certain types of stress and of injection of zinc, copper or cadmium on metallothionein I (MT-I) concentrations in the blood and urine of rats. The aim was to establish whether such measurements could be of value in the diagnosis of zinc deficiency. Marginal zinc deficiency rapidly caused a major decrease in MT-I levels in the blood cells and to a lesser extent in urine. Injection of zinc and also of cadmium and copper had the opposite effect and increased MT-I concentrations in both samples, although the effects of zinc on blood cells and urine were relatively transient. The MT-I in the blood cells was associated mainly with the erythrocytes. No changes in blood or urine MT-I levels were found in copper- and selenium-deficient rats. Neither cold stress nor restriction of food intake for 24 h had any significant effect on MT-I levels in the blood cells or urine. Endotoxin injection increased urinary MT-I excretion in both zinc-adequate and zinc-deficient rats but did not affect blood cell MT-I levels in either group of animals. It appears therefore that assay of erythrocyte MT levels could be of particular value in the diagnosis of zinc deficiency, especially when it is accompanied by stress or infection.

Effect of maternal zinc supply on blood and tissue metallothionein I concentrations in suckling rats

Changes in metallothionein I (MT-I) levels were measured in blood and tissues of rat pups from dams given diets containing 6, 9 or 40 mg zinc/kg from wk 1 or gestation and throughout lactation. After 1, 2 and 3 wk of lactation, litters from each group were killed and tissues analyzed for MT-I. The relatively mild degree of zinc deficiency, which had no effect on fetal viability or litter size and caused only slightly lower pup weight, caused significantly lower MT-I concentrations in pup liver, thymus, plasma and red cells, particularly in pups from dams receiving 6 mg zinc/kg. Maternal zinc supply is therefore a major determinant of MT-I concentrations in neonatal tissues, and assay of this protein in blood plasma and red cells may give a useful indication of zinc status.

Occupational exposure to cadmium: effect on metallothionein and other biological indices of exposure and renal function

The effect of duration of employment at a North American cadmium smelter on urinary metallothionein (MT), total protein, beta 2-microglobulin (beta 2-MG), glucose, cadmium, copper and zinc of 53 men was studied. The levels of all urinary parameters increased with the duration of employment. Smoking history did not affect any of the above parameters studied. Although age was responsible for some of the changes noted in protein, glucose and beta 2-MG levels, its effect on MT and cadmium was insignificant. All urinary parameters were significantly related with each other. The relationship of elevated urinary MT levels with respect to renal dysfunction was also examined. Subjects with abnormal renal function excreted significantly higher amounts of MT than did those with normal renal function. The results confirm not only that occupational exposure to cadmium over long periods results in renal dysfunction but also that urinary MT could be used to monitor exposure and ultimately the appearance of the renal dysfunction.

Synthesis and degradation of erythrocyte metallothionein in cadmium-administered mice

The origin of erythrocyte metallothionein (MT) in cadmium (Cd) administered mice and its fate were studied in connection with erythrocyte kinetics. It was shown that Cd-MT in the erythrocyte is synthesized in the precursor cells of the erythropoietic tissues, and Cd-MT containing erythrocytes come into the circulation after maturation. In regard to the degradation, it was found that Cd-MT is stable in the erythrocyte, but decomposed in the spleen or liver with the breakdown of erythrocyte when its life span is over.

Age-dependent effects of acute and chronic intermittent stresses on serum metallothionein

Prepuberal and adult male rats were chronically stressed for a month with several acute stressors in a random schedule. Some of the animals were killed approximately 20 hours after the last stress session without any additional stress. Other animals from both control and chronic stress groups were subjected to an acute restraint stress for 15 min before being killed. While chronic stress did not alter hepatic metallothionein (MT) either in prepuberal or in adult rats, this treatment significantly increased serum MT levels in young but not in adult rats. Likewise, 15 min of restraint stress increased serum MT levels in young rats only, regardless of whether they were control or chronically stressed rats. The present data indicate that acute and chronic stressors may alter serum MT in an age-dependent fashion.

Metallothionein in blood, bile and urine

The development of radioimmunoassays for rat metallothionein-I (MT-I) has revealed that this protein is present in many extracellular fluids. Plasma concentrations are low in normal animals but may be substantially increased in animals with elevated tissue MT levels. MT-I is also excreted in varying amounts into urine and bile, and there is evidence for the presence of degradation products of MT-I, detectable by radioimmunoassay, in these fluids. Investigation of the secretion of MT can provide valuable information on the turnover of the protein in tissues and lead to the development of novel diagnostic tests for the assessment of trace metal status.

Copper transport from Cu(I)-thionein into apo-caeruloplasmin mediated by activated leucocytes

A study on the transfer of copper from Cu-thionein into apo-caeruloplasmin, using Cu-thionein that was previously oxidised by activated leucocytes, was performed. Cu(I)-thiolate oxidation was conveniently monitored by the progressive decline of the specific Cotton bands between 400 and 300 nm. The characteristic e.p.r. properties and NN-dimethyl-p-phenylenediamine oxidase activity indicated a successful formation of caeruloplasmin. Taking into account the simultaneous occurrence of leucocytes, apo-caeruloplasmin and Cu-thionein in blood plasma, such an interaction would favour a possible metabolic link between either copper protein.

Restraint stress induced changes in rat liver and serum metallothionein and in Zn metabolism

24 h of a psychogenic stress (restraint) caused a strong increase of liver metallothionein (MT) levels. 3 h of stress were sufficient to induce an increase in liver MT, measured 21 h later, but the increase was much lower than in continuously restrained rats. Stress induction of liver MT was not due to food deprivation, since rats deprived for 24 h showed lower MT levels than stressed ones. Zn on MT presented the same qualitative but not quantitative pattern of response as MT protein. Liver cytosolic Zn was increased by restraint in spite of their being no decrease in serum Zn. Any treatment altered serum MT. Liver and serum MT were not correlated. The present results demonstrate that basically psychogenic stresses increased liver but not serum MT levels. No positive evidence for a relationship between corticosterone secretion and MT induction was found.

Fluorometric ELISA for the detection and quantitation of metallothionein

The development of a heterogeneous fluorometric ELISA for the detection and quantitation of metallothionein (MT) is described. A radioimmunoassay (RIA) previously developed in our laboratory is used as a reference assay to characterize the performance of the ELISA. The standard curves (logit-log regressions) that are typical of either assay have similar ranges (customarily from 20 000 to 100 pg of competing antigen); both assays are capable of quantitating MT in unknowns with 5-10% accuracy. Aspects of MT measurement in cytosols and physiological fluids are discussed.

Effects of dietary copper supplementation of rats on the occurrence of metallothionein-I in liver and its secretion into blood, bile and urine

The appearance and excretion of metallothionein-I (MT-I) was studied in rats given a diet containing 1000 mg of Cu/kg for several weeks. No significant increase in MT-I concentrations in liver, plasma or bile was detected in rats with liver copper concentrations less than 600 micrograms of Cu/g fresh wt. Above this concentration, liver MT-I concentrations increased in proportion to the increase in hepatic copper content. Plasma and bile MT-I concentrations were directly related to those in the liver and were about 10 times those in normal rats. Urinary MT-I concentration also increased 10-fold within 1 week. Fractionation of bile and urine on Sephadex G-50 revealed the presence of monomeric MT-I and a range of possible degradation products of the isoprotein.

The origin of metallothionein in red blood cells

The origin of metallothionein (MT) in red blood cells (RBCs) from a mouse given cadmium was studied in connection with RBC kinetics. Plasma Cd concentration rapidly decreased 3 hr following 109CdCl2 (2 mg/kg, sc) administration, whereas RBC Cd increased from 2 to 4 days, followed by a gradual decrease. RBC Cd was found to be distributed more in the high-molecular-weight fraction than in the MT fraction 12 hr after administration. But, thereafter, Cd increased rapidly in the MT fraction to show changes with time similar to Cd level in RBCs. Hepatic damage induced in a mouse given 21 injections of Cd, with resultant marked elevation of plasma MT concentrations, did not cause any change in RBC Cd concentration. MT was hardly transferred to RBC when a mouse RBC suspension was incubated with mouse hepatic MT. To examine the relationship of Cd-MT and erythropoietic function, mice in the normal group, the phenylhydrazine-induced anemia group (PH), the transfusion-induced plethora group (TR), and the erythropoietin administered plethora group (TR + EP) were given 109CdCl2. Three days after administration, Cd concentration in its RBCs and its MT fraction remarkably increased in the PH group, and was greatly decreased in the TR group. A significant increase was noted in the TR + EP group as compared with the TR group. These results indicate that MT in the RBCs is formed in erythroblasts.

Dietary administration of nickel: effects on behavior and metallothionein levels

Adult male rats were fed either 0, 10, or 20 mg Ni/kg body weight (as NiCl2) via a 10 g daily food ration. Following 14 days of exposure, animals were trained over a period of 61 days to lever press for food on a VI-2 operant training schedule while continuing to experience the indicated daily doses. Those rats treated with 20 mg/kg Ni lever pressed at a significantly lower rate than controls. Group 10 mg/kg subjects were not significantly different on this behavioral measure than control subjects. Atomic absorption spectrophotometric analysis revealed a dose/response accumulation of Ni in the kidney, but analyses of blood, bone, brain, hair, small intestine, liver, and testes did not show differential agent accumulations. Neither hepatic nor renal metallothionein levels were increased above control levels. These findings were discussed within the framework of other recent behavioral and biochemical studies of heavy metal toxicity.

Biliary excretion of metallothionein and a possible degradation product in rats injected with copper and zinc

The concentrations of metallothionein-I (MT-I) and related immunoreactive products in bile from adult female rats were measured by radioimmunoassay. Concentrations in normal animals were 20-30 ng/ml, but increased to 600 and 75 ng/ml after injection of Cu2+ and Zn2+ respectively (3 mg of metal/kg body wt.). However, only 1-2% of the biliary Cu was bound to MT, and less than 1% of the total liver MT in control or Cu2+-injected rats appeared to be secreted in intact form into bile. Other major immunoreactive components in bile from Cu2+-injected rats included an aggregated form of MT-I and a possible degradation product of the isoprotein.

Measurement of plasma metallothionein-I in the assessment of the zinc status of zinc-deficient and stressed rats

These studies were designed to investigate the effects of stress and of changes in zinc status on plasma and liver concentrations of metallothionein-I (MT-I) in rats and to assess the value of plasma MT-I assays in the diagnosis of zinc deficiency. No MT-I was detected by radioimmunoassay in the plasma or liver of rats made hypozincaemic by feeding diets with less than 1 or 3 mg Zn/kg. Injection of normal rats with endotoxin or CCl4 also decreased plasma zinc levels, but these treatments greatly increased MT-I concentrations in both liver and plasma. Moreover plasma MT-I levels in zinc-deprived rats given endotoxin were only slightly greater than those in untreated rats of normal zinc status. Neither plasma zinc nor MT-I levels were altered in starved rats despite increased levels of the protein in the liver, although a slight increase in plasma MT-I was found in rats pair-fed with zinc-deficient animals. It appears therefore that reduced plasma levels of both zinc and MT-I are indicative of a zinc deficiency state and that assay of plasma MT should be of value in the diagnosis of zinc deficiency.

Metallothionein-I in the plasma and liver of neonatal rats

The concentrations of metallothionein-I in the plasma and liver of neonatal rats were measured by radioimmunoassay. Plasma concentrations of the protein in male and female 4-day-old rats were 350 and 740 ng/ml respectively, and declined rapidly to only 3.5 ng/ml at 32 days of age. Concentrations in liver were also high in the newborn rats (200 micrograms/g), and declined from 12 days of age onwards.

Development of a radioimmunoassay for rat liver metallothionein-I and its application to the analysis of rat plasma and kidneys

A sensitive radioimmunoassay for rat liver metallothionein-I has been developed using avid and high-titre antibodies obtained from sheep that were immunized with a conjugate of metallothionein and rabbit immunoglobulin G. The assay was specific for metallothionein-I, and did not depend on the particular metal bound to the protein. There was no significant cross-reaction with rat liver metallothionein-II. The use of the assay to measure metallothionein concentrations in rat plasma and kidneys is described.

The identification of serum ligand-binding proteins using immuno-precipitation techniques and autoradiography

The identification of ligand-binding proteins in serum is important for understanding many metabolic pathways and for interpreting clinical measurements. Most techniques presently available lack the facility to identify specific binding proteins. This problem has been overcome by combining the specificity of immunological methods with the sensitivity of radioisotope detection. The methods comprise an adaptation of 2-dimensional immuno-electrophoresis, and radial immunodiffusion, combined with radiolabelled ligands and autoradiography. They have been used to determine the serum binding of calcium, cadmium, thyroxine and the beta blocking drug propranolol. This technique has wide application to other ligand-binding interactions.