Metallothionein in cadmium-exposed workers

Metallothionein and brain inflammation

Since the seminal discoveries of Bert Vallee regarding zinc and metallothioneins (MTs) more than 50 years ago, thousands of studies have been published concerning this fascinating story. One of the most active areas of research is the involvement of these proteins in the inflammatory response in general, and in neuroinflammation in particular. We describe the general aspects of the inflammatory response, highlighting the essential role of the major cytokine interleukin-6, and review briefly the expression and function of MTs in the central nervous system in the context of neuroinflammation. Particular attention is paid to the Tg2576 Alzheimer disease mouse model and the preliminary results obtained in mice into which human Zn(7)MT-2A was injected, which suggest a reversal of the behavioral deficits while enhancing amyloid plaque load and gliosis.

Application of covalent affinity chromatography with thiol-disulphide interchange for determination of environmental exposure to heavy metals based on the quantitative isolation of Cd-thionein from human breast milk

The aim of this study was to test a new chromatographic method for the quantitative determination of Cd-thionein (Cd-Th) in human breast milk, in order to determine the level of exposure to heavy metals. Cd-thionein was isolated by covalent affinity chromatography with thiol-disulphide interchange, which is a modern separation technique of high affinity, good repeatability and reproducibility, allowing specific isolation of the thiolproteins. The fundamentals of indirect determination of the contents of metallothionein protein from human milk were worked out through estimation of the quantities of cadmium bound with Cd-thionein and adsorbed on covalent affinity chromatography gel during a separation process.

The application of affinity chromatography for quantitative determination of metallothionein in physiological fluids by an indirect method based on analysis of metal contents

An indirect method, based on the analysis of metal contents, for the determination of metallothionein (MT) in body fluids is described. Affinity chromatography gel was used as a solid phase extraction (SPE) support for preconcentration of MT Proteins and metals bound to MT from spiked water and human urine samples. The results showed a good correlation between the concentration of MT proteins added to water or physiological human urine and the concentration of protein indirectly determined by atomic absorption spectrometry (AAS) recovered by the SPE-affinity chromatography technique and calculated from the metal concentration. The present method can be used in toxicological analysis for determination of MT concentration in physiological fluids in subjects exposed to heavy metals.

Increased urinary cadmium excretion and its relationship to urinary N-acetyl-beta-D-glucosaminidase activity in smokers

To assess the renal effects of low-level exposure to cadmium due to smoking we examined blood and urinary levels of cadmium and urinary excretions of N-acetyl-beta-D-glucosaminidase (NAG), beta 2-microglobulin (BMG) and metallothionein in 94 male workers aged 18-55 years. Both blood and urinary cadmium levels indicated excess exposure to cadmium caused by smoking. The urinary cadmium concentration ranged between 0.1 and 5.0 micrograms/g creatinine and increased significantly with age in the smokers. Neither urinary NAG nor BMG was increased in the smokers compared from non-smokers. A positive relationship between urinary cadmium and metallothionein was obtained not only in the smokers but also in the non-smokers. Furthermore, in the smokers urinary cadmium and metallothionein was positively related with urinary NAG. Since NAG in urine mostly originates from tubular cells by lysosomal exocytosis, the results may reflect an early cadmium effect on the lysosomal functions. Inhibitory effect of cadmium on the lysosomal degradation activities was discussed as a possible explanation of the positive relationship of urinary cadmium and metallothionein to urinary NAG.

Determination and purification of metallothioneins by high performance liquid chromatography

A rapid, reproducible and sensitive high performance liquid chromatography (HPLC) method for the determination and purification of metallothionein-I (MT-I) and metallothionein-II (MT-II) in mouse and rabbit livers has been developed. Methallothioneins (MTs) were separated by an HPLC anion exchange column, eluted through a linear gradient of Tris buffer and the peak containing MTs was determined by atomic absorption spectrophotometry. Furthermore, the content of MT-I or MT-II was calculated by protein peak area in a short time (about 20 min). The sample to be tested was homogenized, centrifuged and saturated by cadmium. MT-I and MT-II were eluted at 15.9 and 19.3 min, respectively. The following mouse liver cytosols were tested: controls, Cd-injected samples and 60Co-irradiated samples. A detection limit of 5 micrograms/g liver was established for this method. We have analysed more than 100 biological samples and obtained satisfactory results.

Prevalence of metallothioneinuria among the population living in the Kakehashi River basin in Japan--an epidemiological study

An epidemiological study to evaluate cadmium-induced renal dysfunction by urinary metallothionein levels was carried out in an environmentally-exposed Japanese population. The study population consisted of 3168 men and women from a cadmium-polluted area who were 50 years and older and 291 individuals from a non-polluted area. The mean metallothionein levels in urine of the control population were 138.2 +/- 2.1 and 198.6 +/- 1.9 microgram/g creatinine for men and women, respectively. The corresponding values for the cadmium-exposed population were 157.8 +/- 2.2 and 248.0 +/- 2.2. The 97.5% upper limits for men in the control population was determined to be 638 and for women 693 microgram MT/g creatinine. Based on these values as the cut-off levels, the prevalence of metallothioneinuria was calculated to be 4.6% in men and 8.4% in women from the cadmium-polluted area. Further selection of the population, based on life-time residence in the polluted area accompanied with the consumption of cadmium-containing rice, showed an even greater prevalence of metallothioneinuria: 5.4% in men and 10.9% in women of all ages. The prevalence of metallothioneinuria increased with age and duration of residence in the polluted area. These results suggest that metallothioneinuria can be used as an indicator of renal dysfunction due to environmental cadmium exposure.

Development of a radioimmunoassay for human metallothionein

We report the development of a radioimmunoassay (RIA) for human metallothionein (MT). The MT was isolated from the liver of a patient with primary biliary cirrhosis and used to raise high titer antibodies in rabbits. The RIA was developed using Bolton-Hunter labeled MT as label and purified MT as standard. The detection limit of the assay was 0.4 ng/ml and concentrations between 0.8 and 100 ng/ml could be routinely measured. Dilutions of plasma samples containing high endogenous MT concentrations and tissue extracts in assay buffer showed parallelism with the standard curve and MT added to plasma could be fully recovered.

Cadmium concentration in human kidney biopsies

This study reports the cadmium concentration and histopathology of kidney tissue from 29 patients with clinical findings that motivated a diagnostic percutaneous kidney biopsy and/or a history of possible exposure to cadmium. Cadmium was found in all specimens examined including those from controls. In the patients, the mean cadmium concentration was 12.9 (0.6-45.0) micrograms cadmium per g wet kidney tissue. The highest concentrations (30-45 micrograms/g) were found in three patients with morphological and clinical findings of tubulo-interstitial damage. Patients with signs of tubulo-interstitial disease had higher mean cadmium concentrations than those with glomerular changes, and patients with normal blood pressure had higher concentrations than those with diastolic hypertension. In a control group of 22 autopsies, the mean cadmium concentration was 8.7 (2.9-22.4) micrograms/g. The mean difference between the right and the left kidney was 2.3 (0.9-9.6) micrograms/g. Laboratory findings in patients with cadmium nephropathy were nonspecific. Thus, in patients with interstitial nephritis and cadmium exposure, a biopsy for the analysis of kidney cadmium concentration may be motivated. The combination of morphological and clinical findings of interstitial nephritis and a high concentration of cadmium in biopsied kidney tissue indicates cadmium nephropathy.

The relationships of urinary metallothionein with other indicators of renal dysfunction in people living in a cadmium-polluted area in Japan

An epidemiologic investigation was carried out to study the significance of urinary excretion of metallothionein (MT) in people aged 50 years and over living in a cadmium (Cd)-polluted area in Japan. The urinary level of MT was compared with various parameters (age, urinary alpha 1-microglobulin (alpha 1-MG), beta 2-microglobulin (beta 2-MG), total protein, Cd, copper (Cu), and zinc (Zn), and relative clearances to creatinine of alpha 1-MG, beta 2-MG, phosphate and uric acid). It was found that the urinary excretion of MT is closely associated with Cd and the indices of renal dysfunction listed above. This observation was more remarkable in women than men. When subjects with signs of renal dysfunction were compared as a group to those with normal renal functions, the excreted amount of MT in the former is significantly greater. The results support the notion that the urinary excretion of MT reflects not only Cd exposure levels but also renal dysfunction caused by long-term Cd exposure.

Influence of chemical and environmental stressors on acute cadmium toxicity

Previous investigations have demonstrated that the cytosolic protein metallothionein (MT) is induced not only by exposure to certain heavy metals but also by a variety of other factors, including environmental stress. While MT synthesis has been observed with exposure to cold temperatures, there is a paucity of data concerning the influence of cold on heavy-metal toxicity. The present investigation focused on the influence of metal and cold pretreatments on the acute toxicity of cadmium. Mortalities of 80% and 100% were observed for mice orally administered challenge doses of 100 mg Cd/kg and 150 mg Cd/kg, respectively. To determine a protective cadmium pretreatment dose, animals were administered 2.5, 5, 10, 20, 25, and 50 mg Cd/kg 24 h prior to cadmium challenge. In animals pretreated with 10 mg Cd/kg, mortalities of 20% and 70% were observed with the respective challenge doses. Immediately following cold stress (4 degrees C, 12 h), mortalities of 30% and 90% were observed with cadmium challenge doses of 100 and 150 mg Cd/kg, respectively. Significant correlations were demonstrated between induced hepatic MT concentrations and cadmium pretreatment (r = 0.99), as well as cold pretreatment (r = 0.87). Results of this investigation indicate that stressors, such as cold, influence the acute toxicity of cadmium to the same magnitude as metal pretreatment. This induced tolerance to cadmium was attributed, in part, to the induction of MT synthesis. Furthermore, the induced levels of MT resulting from cold stress may confound the simplistic approach of using MT as a biological monitor of occupational exposure to cadmium.

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.

Enzyme-linked immunosorbent assay (ELISA) for metallothionein

A heterogeneous, double-antibody, fluorometric enzyme-linked immunosorbent assay (ELISA) is described for the detection and quantitation of metallothionein(MT) The protocol uses the same immunological reagents as the radioimmunoassay(RIA) developed previously in this laboratory; fluorescence replaces radioactivity for detection of the reference antigen in the specific binding reaction. Present results indicate that the developed ELISA has approximately the same range of capability in detecting and quantitating MT as is characteristic of the RIA. The ELISA has the advantage that the time required to perform a typical assay is significantly less than that required for the RIA.

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.

Comparison of methods of metallothionein quantification: cadmium radioassay, mercury radioassay, and radioimmunoassay

A comparison of the Hg radioassay (i.e. "Piotrowski" assay), the Cd radioassay (i.e. "cadmium-hemolysate" assay), and the radioimmunoassay (RIA) for metallothionein (MT) was performed for livers from control, Cd-, and Zn-pretreated rats. Results indicate that the Cd and Hg radioassays gave similar results in all cases. The RIA values compared very favorably to those obtained by the metal saturation assays for livers from control rats. The values obtained for livers from Cd- or Zn-treated animals were generally lower in the RIA than in the Hg or Cd radioassay, ranging from 36 to 75% of the metal saturation assays. The source of this discrepancy cannot be discerned from the present data. However, the various assay systems employed did yield MT concentrations that followed similar intraassay patterns, being lowest in control, elevated to an intermediate level with Cd treatment, and highest following Zn treatment.

Chelation of cadmium

The toxicity of cadmium is determined by chelation reactions: in vivo, Cd2+ exists exclusively in coordination complexes with biological ligands, or with administered chelating agents. The Cd2+ ion has some soft character, but it is not a typical soft ion. It has a high degree of polarizability, and its complexes with soft ligands have predominantly covalent bond characteristics. Cd2+ forms the most stable complexes with soft donor atoms (S much greater than N greater than 0). The coordination stereochemistry of Cd2+ is unusually varied, including coordination numbers from 2 to 8. Even though the Cd2+ ion is a d10 ion, disturbed coordination geometries are often seen. Generally, the stability of complexes increases with the number of coordination groups contributed by the ligand; consequently, complexes of Cd2+ with polydentate ligands containing SH groups are very stable. Cd2+ in metallothionein (MT) is coordinated with 4 thiolate groups, and the log stability constant is estimated to 25.5. Complexes between Cd2+ and low molecular weight monodentate or bidentate ligands, e.g., free amino acids (LMW-Cd), seem to exist very briefly, and Cd2+ is rapidly bound to high molecular weight proteins, mainly serum albumin. These complexes (HMW-Cd) are rapidly scavenged from blood, mainly by the liver, and Cd2+ is redistributed to MT. After about 1 day the Cd-MT complex (MT-Cd) almost exclusively accounts for the total retained dose of Cd2+, independent of the route of exposure. MT-Cd is slowly transferred to and accumulated in kidney cortex. The acute toxicity and interorgan distribution of parenterally administered Cd2+ are strongly influenced by preceding MT induction, or decreased capacity for MT synthesis; however, the gastrointestinal (GI) uptake of Cd2+ seems unaffected by preceding MT induction resulting in considerable capacity for Cd2+ chelation in intestinal mucosa, and this finding indicates that endogenous MT is not involved in Cd2+ absorption. The toxicity of parenterally administered Cd2+ is strongly enhanced when administered as complexes with NTA or STPP , but it is much decreased when administered as a complex with EDTA. In chronic oral exposure the toxicity and GI uptake of Cd2+ is not changed when Cd2+ is administered as a complex with the detergent formula chelating agents NTA, EDTA and STPP . The uptake of Cd2+ from ligated intestine in vivo was not affected by administration of Cd2+ as complexes with CYS or GSH, but significantly reduced by complexation with EDTA or BAL. The acute toxicity of orally administered Cd2+ is reduced when Cd2+ is administered as a complex with EDTA.(ABSTRACT TRUNCATED AT 400 WORDS)

Biological indicators of cadmium exposure and toxicity

The increasing environmental and occupational exposure of populations to cadmium creates the need for biological indicators of cadmium exposure and toxicity. The advantages and disadvantages of monitoring blood cadmium, urinary, fecal, hair, and tissue cadmium, serum creatinine, beta 2-microglobulin, alpha 1-antitrypsin and other proteins, and urinary amino acids, enzymes, total proteins, glucose, beta 2-microglobulin, retinol-binding protein, lysozyme, and metallothionein are discussed. It is concluded that urinary cadmium, metallothionein and beta 2-microglobulin may be used together to assess cadmium exposure and toxicity.

Significance of urinary metallothionein in workers exposed to cadmium

Cadmium in blood (Cd-B) and in urine (Cd-U) and metallothionein (Mt-U) and beta 2-microglobulin in urine (beta 2m-U) were measured in 94 male Cd workers. The results were examined according to the workers' current exposure to cadmium (group C, n = 73, workers currently exposed to Cd; group R, n = 21, Cd workers removed from exposure or retired) and according to their renal status (group N, n = 66, normal beta 2m-U; group I, n = 28, beta 2m-U greater than 200 micrograms/g creatinine). The interrelationships between Mt-U, Cd-U, Cd-B and years of cadmium exposure were examined in the various subgroups. The study of the correlations between these variables demonstrates that Mt-U is directly correlated with Cd-U but not with Cd-B or years of Cd exposure. The association between Cd-U and Mt-U is independent of the status of renal function and the intensity of current exposure to cadmium. Under moderate chronic exposure to cadmium, the fraction of Cd-U which is directly influenced by recent exposure (Cd-B) is small in comparison with that influenced by the cadmium body burden.

Urinary metallothionein as a new index of renal dysfunction in "Itai-Itai" disease patients and other Japanese women environmentally exposed to cadmium

The significance of elevated excretion of metallothionein in urine of women living in cadmium-polluted areas of Japan was studied with respect to renal dysfunction. The relationships between the concentrations of metallothionein in urine and those of other non-specific urinary indices of renal dysfunction, i.e., total protein, glucose, beta 2-microglobulin, retinol-binding protein, alpha-amino nitrogen and proline were examined. In addition, the relationships between urinary metallothionein and urinary cadmium and copper were also evaluated. It was found that the logarithm of the metallothionein concentration in urine was significantly correlated with the logarithm of the concentrations of each of the above parameters. When subjects with signs of renal dysfunction, including "itai'itai" disease patients and patients suspected of the disease, were compared with subjects with normal renal functions, as a group, the former excreted significantly higher concentrations of metallothionein in their urine than the latter. The results suggest that the elevated excretion of metallothionein is not only an index of excessive cadmium exposure, but also of renal dysfunction caused by chronic exposure to this metal.

Detection of circulating metallothionein in rats injected with zinc or cadmium

Circulating metallothionein was measured by radioimmunoassay over a 13-day period in male Sprague-Dawley rats that received a sequence of three intraperitoneal injections (at 3-day intervals) of either 5 milligrams of zinc or 0.8 milligrams of cadmium per kilogram of body weight. These amounts of zinc and cadmium produced metallothionein concentrations in the range of 2 to 5 nanograms per milliliter of serum (zinc) and 2 to 15 nanograms per milliliter of serum (cadmium). In control rats given saline injections over the same period the metallothionein concentration ranged from 1 to 3 nanograms per milliliter of serum.

Metallothionein excretion in urine upon cadmium exposure: its relationship with liver and kidney cadmium

The relationships between quantities of accumulated cadmium in the liver and kidney and those of metallothionein in urine was studied in occupationally exposed workers and experimentally exposed rats. Cadmium-exposed workers who had been employed at a cadmium production plant for periods of 8-29 years had significantly higher levels of cadmium in both liver and kidney and excreted significantly larger amounts of metallothionein in urine when compared with workers who had been employed for less than 1 year, with office workers at the plant or with control subjects having no known occupational exposure to cadmium. The excretion of metallothionein in urine of the cadmium-exposed workers appeared to be related to the levels of cadmium in both liver and kidney. A similar dose-effect relationship was also observed among rats given repeated subcutaneous injections of 5 mumol CdCl2/kg. However, in the rats the metallothionein excretion increased markedly when the liver and renal cortex Cd levels exceeded approximately 300 microgram/g and 200 microgram/g, respectively. It appears tht urinary metallothionein may be a useful biological indicator of liver and kidney cadmium levels.