The isolation of metallothionein and its protective role in cadmium poisoning

Differentiated Zn(II) binding affinities in animal, plant, and bacterial metallothioneins define their zinc buffering capacity at physiological pZn

Metallothioneins (MTs) are small, Cys-rich proteins present in various but not all organisms, from bacteria to humans. They participate in zinc and copper metabolism, toxic metals detoxification, and protection against reactive species. Structurally, they contain one or multiple domains, capable of binding a variable number of metal ions. For experimental convenience, biochemical characterization of MTs is mainly performed on Cd(II)-loaded proteins, frequently omitting or limiting Zn(II) binding features and related functions. Here, by choosing 10 MTs with relatively well-characterized structures from animals, plants, and bacteria, we focused on poorly investigated Zn(II)-to-protein affinities, stability-structure relations, and the speciation of individual complexes. For that purpose, MTs were characterized in terms of stoichiometry, pH-dependent Zn(II) binding, and competition with chromogenic and fluorescent probes. To shed more light on protein folding and its relation with Zn(II) affinity, reactivity of variously Zn(II)-loaded MTs was studied by (5,5'-dithiobis(2-nitrobenzoic acid) oxidation in the presence of mild chelators. The results show that animal and plant MTs, despite their architectural differences, demonstrate the same affinities to Zn(II), varying from nano- to low picomolar range. Bacterial MTs bind Zn(II) more tightly but, importantly, with different affinities from low picomolar to low femtomolar range. The presence of weak, moderate, and tight zinc sites is related to the folding mechanisms and internal electrostatic interactions. Differentiated affinities of all MTs define their zinc buffering capacity required for Zn(II) donation and acceptance at various free Zn(II) concentrations (pZn levels). The data demonstrate critical roles of individual Zn(II)-depleted MT species in zinc buffering processes.

Relationship between osteoid formation and iron deposition induced by chronic cadmium exposure in ovariectomized rats

Itai-itai (Japanese, "It hurts! It hurts!") disease (IID), a form of osteomalacia, can be induced in ovariectomized rats by long-term administration of cadmium (Cd). This IID rat model shows severe anemia, severe nephropathy, and osteomalacia accompanied by iron (Fe) deposition at the mineralization front. We characterized the pathogenesis of Cd-induced bone lesions by investigating the relationship between Fe deposition and osteoid tissue formation in ovariectomized rats. The rats were injected with CdCl₂ (0.5 mg/kg) for 70 weeks, with or without co-injection of erythropoietin (EPO) for varying lengths of time to elucidate whether EPO prevents and/or cures anemia, and, with the restoration from anemia, lessens the osteoid tissue formation. Necropsies were performed at 25, 50, or 70 weeks. Fe deposition at the mineralization front of bone was found at 50 weeks and increased thereafter. Animals injected with EPO showed decreased Fe deposition, although there was no relation between EPO administration and osteoid formation in the femur. Because the increase in bone lesion severity was independent of the amount of Fe deposition, we suggest that Fe deposition is not involved in the etiology of Cd-induced femoral bone lesions.

Differences in the susceptibility to cadmium-induced renal tubular damage and osteoporosis according to sex

This study aimed to estimate the risks for renal tubular damage and osteoporosis in individuals with long-term environmental Cd exposure. This cross-sectional study comprised 1086 residents living in the vicinity of a copper refinery plant. As the urinary Cd levels increased, the proportion of female subjects with β₂-MG ≥300 μg/g creatinine also increased significantly, but this was not observed in the male subjects. The prevalence of osteoporosis was significantly higher in men with urinary Cd >5 μg/g creatinine than in those with urinary Cd ≤5 μg/g creatinine. This difference was not observed in the corresponding female groups. The association between increased urinary excretion of β₂-MG and decreased BMD was statistically significant only in the female subjects. We suggest that an increased Cd body burden directly decreases the BMD in male subjects; however, in female subjects, it first induces renal microtubular damage, which can lead to osteoporosis.

Cadmium-induced apoptosis and necrosis in human osteoblasts: role of caspases and mitogen-activated protein kinases pathways

Cadmium is a widespread environmental pollutant which induces severe toxic alterations, including osteomalacia and osteoporosis, likely by estrogen receptor-dependent mechanisms. Indeed, cadmium has been described to act as an endocrine disruptor and its toxicity is exerted both in vivo and in vitro through induction of apoptosis and/or necrosis by not fully clarified intracellular mechanism(s) of action. Aim of the present study was to further investigate the molecular mechanism by which cadmium might alter homeostasis of estrogen target cells, such as osteoblast homeostasis, inducing cell apoptosis and/or necrosis. Human osteoblastic cells (hFOB 1.19) in culture were used as an in vitro model to characterize the intracellular mechanisms induced by this heavy metal. Cells were incubated in the presence/ absence of 10-50 μM cadmium chloride at different times and DNA fragmentation and activation of procaspases- 8 and -3 were induced upon CdCl(2) treatment triggering apoptotic and necrotic pathways. Addition of caspase-8 and -3 inhibitors (Z-IETD-FMK and Z-DQMD-FMK) partially blocked these effects. No activation of procaspase-9 was observed. To determine the role of mitogen-activated protein kinases (MAPK) in these events, we investigated c-jun N-terminal kinase (JNK), p38 and extracellular signal-regulated protein kinase (ERK1/2) phosphorylation which were activated by 10 μM CdCl(2). Chemical inhibitors of JNK, p38, and ERK1/2, SP600125, SB202190, and PD98059, significantly reduced the phosphorylation of the kinases and blunted apoptosis. In contrast, caspase inhibitors did not reduce the cadmium-induced MAPK phosphorylation, suggesting an independent activation of these pathways. In conclusion, at least 2 pathways appear activated by cadmium in osteoblasts: a direct induction of caspase-8 followed by activation of caspase-3 and an indirect induction by phosphorylation of ERK1/2, p38, and JNK MAPK triggering activation of caspase-8 and -3.

Mammalian metallothionein in toxicology, cancer, and cancer chemotherapy

The present paper centers on mammalian metallothionein 1 and 2 in relationship to cell and tissue injury beginning with its reaction with Cd²⁺ and then considering its role in the toxicology and chemotherapy of both metals and non-metal electrophiles and oxidants. Intertwined is a consideration of MTs role in tumor cell Zn²⁺ metabolism. The paper updates and expands on our recent review by Petering et al. (Met Ions Life Sci 5:353-398, 2009).

Expression of metallothionein cDNA in a freshwater crab, Sinopotamon yangtsekiense, exposed to cadmium

This paper aims at evaluating the induction of metallothionein (MT) synthesis in gills, heart and hepatopancreas of a freshwater crab, Sinopotamon yangtsekiense. Crabs were exposed to different cadmium concentrations (from 0 to 5 mg/L) from 24 to 96 h. The amount of cadmium (Cd) accumulated in gills, heart and hepatopancreas of the crab showed an increase with an increase in the treatment concentration. Furthermore, the amount of Cd accumulated in these tissues showed an increase with an increase in duration. On the other hand, MT and β-actin genes were amplified using reverse transcription PCR (RT-PCR). Metallothionein gene expression induced by Cd was analyzed using real-time quantitative polymerase chain reaction. Its expression levels were correlated to duration time and increased with cadmium concentrations in water, whilst β-actin was expressed at a relatively constant level. The MT transcript levels in gills and hepatopancreas were higher than that in heart. Furthermore, the MT mRNA expression was not time dependent, and no relationship with Cd accumulation followed the time course of treatment at the same dose Cd treatment. But the clear dose response of MT to cadmium exposure of S. yangtsekiense is a proof of the feasibility of MT as a biomarker for testing cadmium pollution.

Changes in metallothionein level in rat hepatic tissue after administration of natural mouldy wheat

Mycotoxins are secondary metabolites produced by microfungi that are capable of causing disease and death in humans and other animals. This work was aimed at investigation of influence of mouldy wheat contaminated by pathogenic fungi producing mycotoxins on metallothionein levels in hepatic tissue of rats. The rats were administrating feed mixtures with different contents of vitamins or naturally mouldy wheat for 28 days. It was found that the wheat contained deoxynivalenol (80 +/- 5 microg per kg of mouldy wheat), zearalenone (56 +/- 3 microg/kg), T2-toxin (20 +/- 2 microg/kg) and aflatoxins as a sum of B1, B2, G1 and G2 (3.9 +/- 0.2 microg/kg). Rats were fed diets containing 0, 33, 66 and 100% naturally moulded wheat. Control group 0, 33, 66 and 100% contained vitamins according to Nutrient Requirements of Rats (NRC). Other four groups (control group with vitamins, vit33, vit66 and vit100%) were fed on the same levels of mouldy wheat, also vitamins at levels 100% higher than the previous mixtures. We determined weight, feed conversion and performed dissection to observe pathological processes. Changes between control group and experimental groups exposed to influence of mouldy wheat and experimental groups supplemented by higher concentration of vitamins and mouldy wheat were not observed. Livers were sampled and did not demonstrate significant changes in morphology compared to control either. In the following experiments the levels of metallothionein as a marker of oxidative stress was determined. We observed a quite surprising trend in metallothionein levels in animals supplemented with increased concentration of vitamins. Its level enhanced with increasing content of mouldy wheat. It was possible to determine a statistically significant decline (p<0.05) between control group and groups of animals fed with 33, 66 and 100% mouldy wheat. It is likely that some mycotoxins presented in mouldy wheat are able to block the mechanism of metallothionein synthesis.

Experimental studies on the bone metabolism of male rats chronically exposed to cadmium intoxication using dual-energy X-ray absorptiometry

Cadmium (Cd) has been identified as the etiologic agent of itai-itai disease. The purpose of this study was to investigate whether chronic Cd exposure affects bone metabolism in a male rat model and to estimate the bone mineral density (BMD) differences in lumbar and femoral bone because of Cd exposure. Six-week-old male Hos Donryu rats were used in this experiment. Cadmium was administered at a dose of 200 ppm to rats in the diet to produce experimental chronic Cd poisoning. Bone mineral density was measured using dual-energy X-ray absorptiometry (DEXA) with a high-resolution scan collimator (0.25 mm diameter) (Hologic QDR-2000). The Cd content in renal tissue reached a critical concentration of 128.42 ± 14.38 μg/g 10 months after the administration of the element (Table 3). The average blood urea nitrogen (BUN) value was increased throughout the period of the experiment, and the serum creatinine value of the experimental group showed an increase after 2 months of Cd administration (0.46 ± 0.09 mg/dL). The concentration of urinary calcium changed in the experimental group after exposure to Cd for 12 months (15.4 ± 0.13 mg/dL). DEXA showed a greater reduction in the bone mineral density of the 5th vertebral body (L5) in rats that had ingested Cd for 4 months (0.359 ± 0.013 g/cm2) than in control rats (0.372 ± 0.012 g/cm2, P < 0.01). On the contrary, the difference in bone mineral content between rats ingesting Cd for 6–8 months and control rats was not significant. However, significant reductions in bone mineral content were again noted in rats that had ingested Cd for 12 months (0.339 ± 0.023 g/cm2) compared with the control group (0.385 ± 0.012 g/cm2, P < 0.01). The bone mineral density of the right femoral bone in control rats was 0.328 ± 0.018 g/cm2 and that in experimental rats was 0.306 ± 0.012 g/cm2, and a meaningful difference was recognized ( P < 0.05). Histological examination of the rats exposed to Cd for 12 months showed that the 5th lumbar vertebral body (L5) exhibited osteomalacia. The results of our studies show that Cd stimulated a loss of bone mineral at an early stage to a great extent in male rats. In the examination of male rats, bone injury and renal functional disorder were encountered simultaneously. This study suggested that osteomalacia was induced by a direct action of Cd on the bone through abnormal calcium homeostasis at an early stage in male rats.

Low-volume, high-sensitivity assay for cadmium in blood and urine using conventional atomic absorption spectrophotometry

An assay for cadmium in whole blood and urine using deuterium background-correction electrothermal atomic absorption spectroscopy (D(2)-ETAAS) was developed. Cadmium (in a 1- to 2-ml sample) was bound to 15 mg anion-exchange resin, interfering ions were removed in a 2-ml Bio-Spin column, and cadmium was extracted into 100 microl 1M nitric acid for analysis. Cadmium in the sample extract was concentrated 7-fold for blood and 10-fold for urine over the starting material. These steps produced cadmium atomic absorption traces with high signal to background ratios and allowed analysis against aqueous standards. At approximately 0.1 ng Cd/ml, mean intra- and interassay coefficients of variation were 11-12%. Cadmium recovery for 0.1 to 0.6 ng added cadmium was 107+/-4% for blood and 94+/-4% for urine (mean+/-SE, n=3). The mean detection limit (mean + 3 x SD of blank) was 0.008 ng/ml for blood and 0.003 ng/ml for urine. Samples from "unexposed" animals including humans ranged from 0.051+/-0.000 to 0.229+/-0.035 ng/ml. Values were approximately 10-fold lower than those obtained by the method of Stoeppler and Brandt using Zeeman background-correction ETAAS. This new high-sensitivity, low-volume assay will be useful for epidemiological studies, even those involving children, and will provide a means to help determine the contribution of cadmium to disease incidence in the general population.

Urinary cadmium excretion is correlated with calcaneal bone mass in Japanese women living in an urban area

Nine hundred eight women aged 40-88 years living in a non-Cd-polluted area in Japan were analyzed for urinary cadmium (Cd), N-acetyl-beta-D-glucosaminidase (NAG) activity, beta(2)-microglobulin (B2MG) concentration, and for the stiffness index (STIFF) of calcaneal bone using an ultrasound method. The urinary Cd in the subjects, with a mean and range of 2.87 and 0.25-11.4 microg/g creatinine, respectively, showed a significant correlation with NAG but not with B2MG. STIFF was significantly inversely correlated with urinary Cd, and the association remained significant after adjusting for age, body weight, and menstrual status, suggesting a significant effect of Cd on the bone loss in these subjects without signs of Cd-induced kidney damage. A two-fold increase in urinary Cd was accompanied by a decrease in STIFF corresponding to a 1.7-year rise in age. These results emphasize the need for reassessment of the significance of Cd exposure in the general Japanese population.

Zinc availability from zinc lipoate and zinc sulfate in growing rats

The purpose of this study was to investigate the effect of zinc lipoate and zinc sulfate on zinc availability in growing rats. 6 . 6 male albino rats were fed purified diets based on corn starch, egg albumen, sucrose, soy bean oil and cellulose over a 4-week period (diet Ia: 10 mg Zn/kg as zinc sulfate, diet Ib: 10 mg Zn/kg as zinc lipoate, diet IIa: 10 mg Zn/kg as zinc sulfate +0.4% phytic acid, diet IIb: 10 mg Zn/kg as zinc lipoate +0.4% phytic acid, diet IIIa: 20 mg Zn/kg as zinc sulfate + 0.4% phytic acid, diet IIIb: 20 mg Zn/kg as zinc lipoate + 0.4% phytic acid). Zinc lipoate and zinc sulfate both proved to be highly available zinc sources. When 0.4% phytic acid were present in the diets, apparent zinc absorption was generally depressed but was higher from zinc lipoate in tendency than from zinc sulfate. Comparable results were evident for femur zinc, plasma zinc and metallothionein concentrations in liver tissues. This indicates that zinc lipoate could be a valuable zinc source under conditions of low zinc availability. Nevertheless the absence or presence of phytic acid was a more important factor influencing zinc availability than the type of zinc source investigated.

Effects of cadmium intake on bone metabolism of mothers during pregnancy and lactation

Cadmium (Cd) is a heavy metal that exists ubiquitously in the environment, and it interacts with essential elements such as zinc, copper, iron, and calcium (Ca). Particularly, Cd interferes with Ca and vitamin D metabolism in bone kidney and intestine. The interaction between Cd and Ca in bone, intestine, and kidney may result in the disorder of bone metabolism. On the other hand, pregnancy and lactation are also important physiological factors affecting bone metabolism in the mother. Ca absorption is decreased by competition with Cd in the intestine, and more Ca is released from maternal bone and transferred to neonate by lactation. In the intestine, Cd uptake competes with Ca uptake. Cd causes a marked decrease in bone density compared to the normal decrease in bone mineral density during lactation. Lactation is an important factor contributing to the decrease in bone mineral density and Cd has an additive effect of decreasing bone metabolism of mother animal, although the Cd intake level is relatively low (approximately 3-14 microgCd/kg/day). The relationship among maternal Cd intake, renal function and bone metabolism and the interaction between Cd and Ca during lactation are reviewed herein, together with additional data obtained recently in our laboratory.

Metallothionein expression and localization in rat bone tissue after cadmium injection

We investigated the induction of metallothionein (MT) by cadmium (Cd) in the bone tissue of rats. To clarify the cell response to Cd in bone, the isoform-specific expression of MT mRNAs (MT-I and MT-II) was examined by reverse transcriptase-polymerase chain reaction (RT-PCR). Both MT-I and MT-II mRNA levels were increased within 3 h by Cd administration. MT (MT-I/MT-II) localization after single Cd injection were also confirmed by immunohistochemical studies. Notably, MT-positive cells were time-dependently increased, and the positive cells were mainly localized in osteocytes. The cell-specific induction of MT may be associated with Cd accumulation and Cd-induced bone injury in vivo. Furthermore, we also found that MT was consecutively expressed in some osteoclasts of control rats. This finding suggested a new role of osteoclasts in bone metabolism.

Localization of metallothionein (MT) and expression of MT isoforms induced by cadmium in rat dental pulp

We investigated the induction of metallothionein (MT) by cadmium (Cd) in the dental pulp of rat incisors. Time-course studies of MT mRNA expression after single Cd injection were observed by Northern-blot analysis. The isoform-specific expressions of MT mRNAs (MT-I, MT-II and MT-III) were observed using the reverse transcriptase-polymerase chain reaction (RT-PCR) method. Both MT-I and MT-II mRNA levels increased within 3 h, peaked at 3 h and then decreased. These findings demonstrated that MT-I and MT-II mRNA were rapidly induced by Cd in dental pulp. MT-III mRNA was constitutively expressed in rat dental pulp, but the expression level did not change by Cd treatment. The localization of MT protein in Cd-treated rat dental pulp was determined by immunohistochemical staining using anti-MT antibody against MT-I and MT-II. MT protein was localized in the specific cell type of odontoblasts (secretory odontoblasts and resting odontoblasts). In conclusion, it is likely that stained MT in the immunohistochemical study should be MT-I and/or MT-II. Furthermore, MT-I and/or MT-II in Cd-treated rat dental pulp was localized in odontoblasts, in which accumulation of Cd were reported. The cell-specific synthesis of MT may be associated with its metal storage and detoxification role in dental tissues.

109Cd accumulation in the calcified parts of rat bones

A recent epidemiological study showed an increased risk for bone fractures after chronic low-level cadmium exposure. This finding agrees with those of cadmium accumulation in rat bones after chronic oral exposure which reduced the mechanical strength of the bones. There are indications that ossicular cadmium uptake may be higher during growth and may contribute over proportion to life long cadmium accumulation in the skeleton. The present study investigates this hypothesis in 59 male Sprague-Dawley rats. 109Cd distribution showed no differences after intravenous (i.v.) administration of different doses (0.02-2.00 micromol 109Cd/kg body weight) and at different time points after injection (3 and 10 days). Iron-deficiency had no impact on 109Cd distribution, neither during growth nor in adult animals. Age, however, showed an impact on cadmium distribution. Hepatic 109Cd accumulation was significantly higher in adult rats while 109Cd distribution in the bones as well as 109Cd concentration in cortical and trabecular bone tissue was significantly higher during growth. No difference in 109Cd uptake was found between femur epiphysis and diaphysis after one-dose i.v. application, which is in contrast to earlier results after chronic oral cadmium administration to rats. This difference may be explained by a different saturation for cadmium uptake in these two bone sections. Cadmium exposure during growth, thus, seems to contribute considerably to cumulative ossicular cadmium accumulation over a lifetime and possibly to cadmium-derived bone fragility in advanced age.

Zinc and copper levels in ribs of cadmium-exposed persons with special reference to osteomalacia

Cadmium (Cd), zinc (Zn), copper (Cu), calcium (Ca), phosphorus (P), and magnesium (Mg) were determined in ribs obtained at autopsy from 38 Cd-exposed and 17 nonexposed subjects to determine how levels of these elements in bone are affected by Cd exposure and whether they are associated with the bone lesions due to Cd exposure, osteomalacia, and osteoporosis. Cd in ribs was significantly higher in the Cd-exposed subjects than in nonexposed subjects. Zn tended to be higher, while Cu, Ca, P, and Mg tended to be lower in the ribs of Cd-exposed subjects, though these differences were not statistically significant. Zn, Ca, P, and Mg were highly correlated with each other in both Cd-exposed and nonexposed groups, but the associations of Ca, P, and Mg in the ribs with Zn concentrations differed in subjects and controls. Ca to Zn ratios were low in the Cd-exposed subjects, and the higher the grade of osteomalacia, the lower the Ca/Zn ratio. The decrease in Ca/Zn ratio was significantly correlated with increases in Cd. Cu showed a significant positive correlation with Cd and significant inverse correlation with Ca, P, and Mg in the Cd-exposed group. Cu and its relation to other elements did not show any association with osteomalacia. In conclusion, Ca/Zn ratio in bone was related to Cd exposure and the degree of osteomalacia in the Cd-exposed subjects.

Iron deposition at mineralization fronts and osteoid formation following chronic cadmium exposure in ovariectomized rats

To investigate whether chronic exposure of cadmium (Cd) chloride induces osteomalacic lesions similar to Itai-itai disease (IID), ovariectomized rats were injected intravenously with the cadmium at doses of 0.05 and 0.5 mg/kg/day, 5 days per week, for 50 weeks. In six rats in the 0.5 mg/kg group, the administration was continued for up to 70 weeks. In the 0.5 mg/kg group, the plasma concentration of calcium was similar in the treatment and control groups throughout the treatment period. The urinary excretion of calcium increased from 20 weeks and the increase became marked from 40 weeks. Histopathologically, osteoid seams in the femur, tibia, and humerus were increased from 50 weeks, and these changes became prominent at 70 weeks. Hypertrophy and hyperplasia of chief cells in the parathyroid were also observed from 50 weeks. The osteoid morphometry of the trabecular bone of the femur and sternum revealed a dose-dependent increase in osteoid/bone volumes. Roentgenographs of the antebrachial and metacarpal bones taken at 70 weeks showed so-called paper bone. The bone Cd content markedly increased until 25 weeks, but thereafter decreased linearly for up to 70 weeks. In contrast to the Cd content, the iron content decreased until 25 weeks, but thereafter increased until 70 weeks. Undecalcified section of the humerus showed the deposition of iron and formation of osteoid at mineralization fronts. Our data suggest that osteomalacic lesions were caused by chronic Cd intoxication, and that iron, as well as Cd, was involved in osteoid formation.

Metallothionein in physiological and physiopathological processes

The multipurpose nature of MT that we have presented in this review has drawn attention from many different fields of research: biochemistry, molecular biology, toxicology, pharmacology, etc. In recent years, considerable advances have been made concerning the regulation of MT genes by metals. Little, however, is known at the molecular level about the mechanisms of MT induction by nonmetallic inducers such as growth factors. This is of particular interest since MT is highly expressed during liver regeneration, an event orchestrated by a series of growth stimulators and inhibitors. The significance of the nuclear distribution of MT in growing cells and what controls its translocation are questions that remain unanswered at the present time. The possibility that MT could participate in a DNA synthesis-related process through donation or abstraction of Zn to and from transcription factors has been inferred from in vitro studies. Such transfer mechanisms, however, have yet to be confirmed in vivo. Overexpression of MT is often accompanied by increased resistance towards a variety of alkylating agents and chemotherapeutic drugs. The mechanisms by which MT protects cells against these agents may depend on their distinct mode of toxic action. For some, MT cysteines can be the target of the direct attack from the parent compound. For others such as N-methyl-N-nitroso compounds, MT cysteines may serve as a sink for the reactive oxygen species now known to be derived from their metabolism. In either case, a primary consequence of such interactions is the release of the metals initially bound to MT. Therefore, the metal composition of MT appears to be an important factor to consider in determining the overall effect of MT in the resistance process.

Characterisation of the effects of cadmium on the release of calcium and on the activity of some enzymes from neonatal mouse calvaria in culture

Exposure to cadmium (Cd) causes skeletal impairments, such as osteoporosis and osteomalacia, in many mammalian species, including humans. There is, however, some controversy about the mechanism of action of these Cd-induced skeletal effects, although both a direct influence on bone cells and effects that are secondary to renal damage caused by the metal have been demonstrated. In the present study, we cultured calvarial bones from neonatal mice and exposed them to Cd to study the effects of the metal on calcium release and on the activity of some enzymes of importance for bone resorption and bone formation. Cd dose-dependently stimulated calcium release from the bones. Maximal release was noted at Cd concentrations of 0.4-0.8 microM, which was similar to the level of release in the presence of maximal stimulatory concentrations of parathyroid hormone (10 nM) and prostaglandin E2 (10 microM). Cykloheximide (1 microM) inhibited calcium release elicited by Cd, prostaglandin E2 and parathyroid hormone. Cd-induced calcium release was linearly increased from 24 to 72 hr of culture. Production of prostaglandin E2 by the bone specimens was dose-dependently stimulated by Cd and inhibited by 1 microM indomethacin. Cd-induced calcium release was inhibited by acetazolamide (100 microM), indomethacin (1 microM) and ibuprofen (10 microM). Prostaglandin E2-stimulated calcium release was not inhibited by indomethacin. Exposure to 32 microM Cd, present during a 48-hr incubation period, significantly decreased prostaglandin E2-stimulated calcium release from 38.9% to 29.8%. Calcium release induced by parathyroid hormone was more sensitive to inhibition by the metal (i.e., Cd concentrations of 0.2 and 32 microM decreased the release from 37.7% to 31% and 19%, respectively). Cd present in the culture medium during a 48-hr incubation dose-dependently inhibited the activity of alkaline phosphatase and tartrate-resistant acid phosphatase in the bones but did not influence the activity of carbonic anhydrase. We conclude that Cd has a direct stimulatory effect on bone resorption, and this effect is dependent on prostaglandin production and also on protein synthesis. On the other hand, Cd also has an inhibitory effect on bone resorption (i.e., resorption is inhibited by higher concentrations of the metal). Moreover, Cd may impair bone formation by impeding the activity of alkaline phosphatase.

Effect of cadmium on bone repair in young rats

The effect of cadmium (Cd) in drinking water on repair of bone at a site of hole injury to the tibia of young rats was followed using quantitative methods. The rats (3-4 wk old) were given 20 ppm and 200 ppm Cd for 5 wk and compared to a control group. A slight reduction (about 10%) in body weight and water and food consumption was observed in cadmium-exposed rats as compared to control rats. Clinical chemistry tests in the blood and histology of kidney, liver, and bone did not indicate changes related to Cd toxicity. A significant reduction (43%) in alkaline phosphatase (ALP) and tartarate-resistant acid phosphatase (TRAP) (46%) enzymatic activity was observed at 4 and 7 d postinjury respectively, in the site of injury in the rats receiving 200 ppm Cd in drinking water as compared to control rats. Calcium accumulation in the newly formed repair tissue at the site of injury was also significantly reduced (53%) at 13 d postinjury in the Cd-treated (200 ppm) rats as compared to control rats. It is concluded that Cd probably exhibits an effect on the bone repair process as reflected by reduction in ALP activity (osteoblastic cells) and mineralization at the site of injury in the tibia of young rats.

Skeletal changes in multiparous and nulliparous mice fed a nutrient-deficient diet containing cadmium

Female mice were given nutrient-deficient, purified diets containing either 0.25 (environmental), 5, or 50 ppm Cd; the nutrient quality of each was patterned after deficiencies known to be present in food consumed by Japanese women who contracted Itai-Itai disease. One-half of the mice were bred for six consecutive, 42-day rounds of pregnancy/lactation (PL mice); remaining females were non-pregnant, virgin controls (NP mice). PL and NP mice were sacrificed at the end of rounds 1, 2, 3, 5, or 6. PL mice taken during the first three rounds were successively pregnant; those taken in later rounds experienced gestation/lactation either four (round 5) or three (round 6) non-successive times. No consistent round-by-round decreases in diet consumption or body weight occurred among NP mice during the 252 days of cadmium exposure, however a significant decrease in femur calcium content (11-17%) was observed in virgin groups exposed to 50 vs. 0.25 ppm Cd. Similar femur decalcification (14-20%) was observed in PL mice, however calcium loss at 50 ppm Cd paralleled decreases in food consumption (24%) and body weight (9-17%). Significant but smaller decreases in the calcium/dry weight (Ca/DW) ratio were found for NP and PL groups consuming 50 ppm dietary Cd. Over the 6-round experiment, exposure to cadmium was found to effect smaller decreases in both femur Ca content and Ca/DW ratio than either consumption of nutrient-deficient diet or multiparous experience. Demineralization results for PL mice provide evidence that the combination of chronic ingestion of cadmium in a nutrient-deficient diet and multiparous activity likely played a role in the etiology of Itai-Itai disease; results for NP mice additionally suggest that decalcification may have been initiated in human females at a time prior to the multiparous and menopausal stages of life.

Comparative effect of cadmium on osteoblastic cells and osteoclastic cells

Cadmium(Cd) has been thought to disturb the bone metabolism directly. The mechanism for the bone lesion is unknown, however. To examine the effects of cadmium on bone metabolism, we compared its effects on osteoblasts and osteoclasts in vitro. We used an established cell line, MC3T3-E1, as osteoblasts and tartrate resistant acid phosphatase (TRACP)-positive multi-nucleated cells (MNC) formed by a bone marrow culture system as osteoclasts. Alkaline phosphatase (ALP) activity was decreased by 10(-7) M Cd and DNA content and hydroxyproline content of osteoblastic cells were decreased by 10(-5) M Cd. Cadmium at 10(-7) M inhibited the osteoclastic cell formation from mouse bone marrow in the presence of 10(-8) M 1 alpha, 25(OH)2 vitamin D3. A 100-fold higher concentration of zinc(Zn) simultaneously added to the cadmium-containing medium prevented the toxicity of cadmium to osteoclastic cells as observed in the culture of osteoblastic cells. These results indicate that both bone formation and bone resorption are inhibited by cadmium. The responses of osteoclasts and osteoblasts to cadmium in this culture system were the same and the responses of cadmium-damaged osteoblasts and osteoclasts to zinc were also similar. These results suggest that another mechanism by which cadmium could cause bone damage should be considered in addition to the specific induction of osteoclastic cells by Cd.

Excessive accumulation of hepatic copper in LEC rats aged 80 days without hepatitis and 130 days with hepatitis

The Cu concentration was about 40 and 60 times higher in the liver in Long-Evans with a cinnamon-like coat color (LEC) rats aged 80 days (without hepatitis) and 130 days (with hepatitis), respectively than in the liver in Fischer rats. Most hepatic Cu was recovered in the cytosol fraction. Furthermore, about 96% and 84% of the cytosolic Cu was found in the metallothionein region on a Sephadex G-75 column in LEC rats aged 80 and 130 days, respectively. The hepatic metallothionein concentration was about 130 to 140 times higher in LEC rats than in Fischer rats when the concentration was expressed as metallothionein-bound Cu. Three forms of Cu-metallothionein were isolated by DEAE-cartridge. Although the concentration of hepatic Cu-metallothionein and its composition of polymorphic form were not changed greatly in hepatitis phase (in the 130-day-old LEC rats), activities of serum enzymes, aspartate aminotransferase (GOT) and alanine aminotransferase (GPT) were increased significantly. The LEC rat showed a significantly low concentration of biliary Cu and markedly low activity of ceruloplasmin (as ferroxidase). Serum Cu showed a low concentration in the 80-day-old LEC rats, but recovered to the control level in the 130-day-old LEC rats. The abnormal accumulation of Cu may be due to the inherent reduction of excretion of Cu into the bile and blood. Such deposition may be a trigger for the onset of the spontaneous hepatitis occurring at 90-120 days after birth and for the onset of hepatoma later.

Decrease in bone strength of cadmium-treated young and old rats

A decrease in mechanical strength of bones was observed both in young and old rats for long periods of administration of cadmium. Young (3-week-old) female rats were given 0 (control), 5 and 10 ppm cadmium in drinking water, respectively, for 20 weeks. Old (18-month-old) female rats were given 0 (control) and 40 ppm cadmium in drinking water, respectively, for 7 months. The compression strengths of bones of young rats which were given 10 ppm cadmium, and those of old rats which were given 40 ppm cadmium, significantly decreased at the distal end portion of femur. Cadmium contents in bones in the 10 ppm and 40 ppm groups were about 110 and 210 ng/g dry weight, respectively. The present result confirmed that cadmium has a lesional effect on the mechanical strength of bone at the concentration of 100-200 ng/g in dry weight of bone, for both young and old rats.

Effect of dietary cadmium and/or copper on the bone lysyl oxidase in copper-deficient rats relative to the metabolism of copper in the bone

Effects of cadmium (Cd) on lysyl oxidase activity and copper (Cu) metabolism in bone were studied using Cu-deficient rats supplemented with Cu and/or Cd in a diet. When fed for 8 weeks on a diet containing 0.3 ppm or less Cu (-Cu diet), weanling rats revealed anemia, and markedly decreased plasma ceruloplasmin activity and serum Cu to less than 15% of normal level, showing features of Cu-deficiency. These rats were divided into four groups and refed for another 2 weeks on the following diets: Group I, -Cu diet; Group II, -Cu diet with 50 ppm Cd (+Cd diet); Group III, -Cu diet supplemented with 15 ppm Cu (+Cu diet); group IV, -Cu diet with both Cu and Cd (+Cu/+Cd diet). After 2 weeks, serum Cu levels of Groups I, II, III and IV were 1.8, 0.8, 78 and 74% of the normal control level (1.438 +/- 0.060 micrograms/ml), respectively. Concentrations of Cu in epi- and metaphyses of the control group, Groups I, II, III and IV were 1.45 +/- 0.20, 0.67 +/- 0.08, 0.76 +/- 0.12, 1.40 +/- 0.31 and 1.22 +/- 0.05 micrograms/g wet tissue, in that order. Concentrations of Cd in epi- and metaphysis increased in only Groups II and IV and were 0.15 +/- 0.03 and 0.18 +/- 0.01 micrograms/g wet tissue, respectively. Thus, having both Cd and Cu supplements in a diet did not inhibit each other's uptake into the tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Toxicity of cadmium to rat osteosarcoma cells (ROS 17/2.8): protective effect of 1 alpha,25-dihydroxyvitamin D3

Inadequate vitamin D intake is an important cofactor in clinical and experimental bone disease induced by chronic cadmium exposure. The interaction was investigated by culture of rat osteoblastic osteosarcoma cells (ROS 17/2.8) in a serum-free medium with equimolar concentrations of cadmium chloride and 1 alpha,25-(OH)2 vitamin D3. After addition of cadmium alone to culture medium, the unstimulated secretion of osteocalcin and cellular alkaline phosphatase activity were inhibited at 10 pM, and of DNA synthesis and proline incorporation into collagen at 500 nM. In the presence of equimolar amounts of cadmium and 1 alpha,25-(OH)2 vitamin D3, all four responses paralleled those of 1 alpha,25-(OH)2 vitamin D3 alone up to the inhibitory concentration of 500 nM cadmium. Neither 10 nM 1 alpha,25-(OH)2 vitamin D3 nor 1 microM cadmium induced synthesis of metallothionein in these cells indicating that the protective effect of D3 was not related to the induction of a metallothionein-like protein in ROS 17/2.8 cells. In the presence or absence of D3, cadmium inhibited osteoblastic function at concentrations below the whole-organ concentration of cadmium in bone as reported in experimental and clinical cadmium-induced osteotoxicity. The extreme sensitivity of ROS 17/2.8 cells to cadmium may relate to the absence of metallothionein synthesis.

Role of metallothionein in biliary metal excretion

We have studied the effect of acute induction of metallothionein on the biliary excretion of a bolus of metal in the rat. Female Sprague-Dawley rats were administered zinc chloride (6.5 mg/kg) or dexamethasone (2 mg/kg), ip in saline daily for 3 d; control animals received saline alone. Zinc causes a 17-fold induction in hepatic metallothionein levels, while dexamethasone caused a 5-fold induction. A bolus of metal chloride, either zinc, mercury, or cadmium, 1 mg/kg iv, was administered, and bile and plasma samples were collected and analyzed for metal content. At 3 h the rats were killed, livers excised, and both metallothionein and the metals associated with metallothionein estimated. Cadmium was excreted into the bile in inverse proportion to the hepatic metallothionein content, while metallothionein content did not appear to bear any relationship to biliary excretion of mercury or zinc. Metallothionein from rats pretreated with zinc contained twice as much zinc per molecule of metallothionein as that found in control rats. Cadmium, which exhibits a very high affinity for metallothionein, replaced this zinc found in association with metallothionein. Conversely, mercury only partially replaced the zinc associated with metallothionein, and a bolus of zinc was completely unable to bind to the already zinc-saturated metallothionein. Consequently, the bolus zinc was found associated with alternative cytosolic proteins, here termed the high-molecular-weight fraction. These findings support the hypothesis that the inhibitory effect of metallothionein on the biliary excretion of metals is dependent on the ability of the metal in question to replace any existing metals associated with metallothionein. Biliary metal excretion was directly proportional to the free metal content, regardless of the metal studied. Consequently, acute induction of metallothionein was inhibitory to biliary cadmium excretion, slightly inhibitory to biliary mercury excretion, and without effect on biliary zinc excretion.

Decrease in the mechanical strength of bones of rats administered cadmium

The mechanical properties of the bones of young, adult and old rats administered various concentrations of cadmium were measured to prove the direct effect of cadmium on the bones of young rats. The young rats were divided into three subgroups, which were administered 0 (control), 5 and 10 ppm cadmium, respectively. The adult rats were subdivided into six groups, administered 0, 10, 20, 40, 80 and 160 ppm cadmium, respectively. The old rats were divided into three subgroups, which were administered 0, 80, and 160 ppm cadmium, respectively. The length of the administration was 4 weeks in every group. The decrease in the mechanical strengths of bones of young rats administered with cadmium was observed. On the other hand, no change in mechanical strength of bones was observed in the case of adult and old rats, administered up to 160 ppm cadmium. The correlation between the cadmium in bones and the decrease in the strength of the bone shows that cadmium directly affects the mechanical properties of bones of young rats.

Cadmium accelerates bone loss in ovariectomized mice and fetal rat limb bones in culture

Loss of bone mineral after ovariectomy was studied in mice exposed to dietary cadmium at 0.25, 5, or 50 ppm. Results show that dietary cadmium at 50 ppm increased bone mineral loss to a significantly greater extent in ovariectomized mice than in sham-operated controls. These results were obtained from two studies, one in which skeletal calcium content was determined 6 months after ovariectomy and a second in which 45Ca release from 45Ca-prelabeled bones was measured immediately after the start of dietary cadmium exposure. Furthermore, experiments with 45Ca-prelabeled fetal rat limb bones in culture demonstrated that Cd at 10 nM in the medium, a concentration estimated to be in the plasma of mice exposed to 50 ppm dietary Cd, strikingly increased bone resorption, from 27 +/- 2% (mean +/- SEM) 45Ca release in cultures with no added cadmium to 68 +/- 6% release in cultures containing cadmium (n = 4). These in vitro results indicate that cadmium may enhance bone mineral loss by a direct action on bone. Results of the in vivo studies are consistent with a significant role of cadmium in the etiology of Itai-Itai disease among postmenopausal women in Japan and may in part explain the increased risk of postmenopausal osteoporosis among women who smoke.

Inhibitory effects of cadmium on in vitro calcification of a clonal osteogenic cell, MC3T3-E1

To examine an inhibitory mechanism of Cd on bone formation, the effects of Cd on calcification were investigated in a culture of a clonal osteogenic cell line, MC3T3-E1. At 3 days after inoculation, Cd was added to the medium containing 7 mM beta-glycerophosphate, and culture was continued for 8 days. Cd at 1.78 microM and above caused a significant decrease in 45Ca accumulation. The decrease in mineralization by Cd was similar to that in collagen content or alkaline phosphatase (ALP) activity. Histologically, the cell density and the mineralization degree were lower than those of the controls. Ultrastructurally, degenerated cells were observed with undifferentiated cells which had fewer rough-surfaced endoplasmic reticulum and many mitochondria. This suggests that Cd may inhibit the differentiation into osteoblasts as well as the cell function. On the other hand, calcification of cells at 8 days after inoculation was inhibited by Cd at 1.78 microM and above. The decrease in collagen content and ALP activity by Cd was much lower than that in calcification. Cd-treated cells were well differentiated into osteoblasts morphologically, but the mineralization degree was lower than that of the controls. Ultrastructurally, cell damage was not recognized so strongly compared with long-term Cd treatment. The mineralization of osteoblasts was also inhibited by Zn levels which left both collagen content and ALP activity unaffected. From these results, it was suggested that the inhibitory effect of Cd on in vitro calcification of MC3T3-E1 cells may be due to both a depression of cell-mediated calcification and a decrease in physiochemical mineral deposition.

Influence of several chelating agents on the distribution and binding of cadmium in rats

Male Sprague-Dawley rats were injected with 109CdCl2 (3 mumol Cd/kg) and killed between 1 h and 200 d afterwards. Metal concentration in the critical organs, i.e. liver and kidneys decreased very slowly. Within the cells Cd is found mainly in the cytosol and--at very early times--in the nuclei. Within the cytosol of the liver most of the metal is initially bound to proteins with high molecular weight but as early as 3 h after incorporation more than 90% is bound to metallothionein which is always the main binding site in the kidneys. Of the chelating agents tested only BAL and Puchel were able to reduce the body burden significantly. Both are lipophilic substances. Puchel cannot reduce the kidney Cd burden but removes Cd from the liver only while BAL is effective in both organs. Both chelating agents exert their effects at doses which are too near to the LD50 to be considered as safe enough for human use.

Effect of cadmium on vitamin D-non-stimulated intestinal calcium absorption in rats

The present report demonstrates the effect of Cd on intestinal Ca transport and Ca-binding protein in rats adapted to vitamin D repletion and high Ca. There were significant decreases in in vitro intestinal Ca transport in animals exposed to Cd for 2 or 3 months as compared with controls. Ca transport from everted gut sacs of normal rats showed a dose-dependent decrease. 45Ca-binding activity to intestinal mucosa from Cd-exposed rats showed a lower level of decrease than that on control rat mucosa. The typical peak of Cd-binding protein obtained from Sephadex G-100 gel filtration of 109Cd added to mucosal supernatant agreed with results of gel filtration obtained after 45Ca had been added to the same supernatant. Although there were 2 proteins binding Cd or Ca in the intestinal mucosa, with the same molecular weight of 10,000, these proteins were shown to be different, since Cd did not bind with the Ca protein. It was concluded that inhibition of vitamin-D-non-stimulated Ca transport was not caused by Cd bound to Ca-binding protein, but by some other factor.

Cadmium, zinc and copper relationships in kidney and liver of humans exposed to environmental cadmium

Cadmium, copper and zinc have been determined in kidney cortex, kidney medulla and liver from 51 cadmium-polluted and 122 nonpolluted autopsied subjects. Liver cadmium and zinc were significantly higher in the cadmium-polluted subjects than in the nonpolluted subjects. Kidney cadmium, copper and zinc were lower in the cadmium-polluted subjects because of renal damage. Significant correlations of the three metals were found in the kidney. In the liver the correlation coefficients were significant only between cadmium and zinc.

Role of metallothionein in detoxification and tolerance to transition metals

Animal tolerance to the transition metals cadmium and zinc is hereditary. The evolution to a high level of resistance can be accelerated through mutation and selective pressure. We have studied inbred strains of mice and mutants of Chinese hamster ovary cells resistant to cadmium to further these understandings. Results with whole animals show that the difference in the rate and level of metallothionein accumulation is at most twofold between sensitive and resistant strains. However, with cadmium resistant CHO mutant cells, there is an over 60 fold increase in metallothionein and its mRNA upon induction. These mutants show over 60 fold amplification in metallothionein genes. These results offer a direct contrast in the correlation between elevation of metal resistance and increases in metallothionein between two genetic systems.

Mechanism for bone disease found in inhabitants environmentally exposed to cadmium: decreased serum 1 alpha, 25-dihydroxyvitamin D level

To investigate the mechanism for bone disease caused by exposure to cadmium serum samples were collected from 5 itai-itai disease patients, 36 Cd-exposed residents with renal tubular damage and 17 non-exposed individuals and analyzed for 1 alpha,25-dihydroxyvitamin D[1 alpha,25(OH)2D], parathyroid hormone, beta 2-microglobulin, calcium and inorganic phosphorus. Measurement of percentage tubular reabsorption of phosphate (%TRP) were performed only on the Cd-exposed subjects. Serum 1 alpha,25(OH)2D levels were lower in itai-itai disease patients and cadmium-exposed subjects with renal damage than in non-exposed subjects. Parathyroid hormone and beta 2-microglobulin concentrations in serum were higher in the Cd-exposed subjects. Decrease in serum 1 alpha,25(OH)2D levels were closely related to serum concentrations of parathyroid hormone, beta 2-microglobulin and %TRP. This study suggests that cadmium-induced bone effects were mainly due to a disturbance in vitamin D and parathyroid hormone metabolism, which was caused by the cadmium-induced kidney damage.

A possible mechanism of cadmium-copper interaction in embryonic chick bone in tissue culture

Femurs from 9-day-old embryo were cultured for 4 days by the roller-tube method in the presence of Cd and/or Cu. The combination of both Cd and Cu caused a significantly interactive decrease in hydroxyproline (Hyp) synthesis as well as bone growth compared with that in the presence of Cd (1.1 or 3.3 microM) or Cu (1.1 or 2.2 microM) alone. The presence of both 2.2 microM Cd and 3.3 microM Cu also showed a significantly interactive decrease in the incorporation of [3H]proline (Pro) into collagenase-digestible protein (CDP), but it showed no interactive inhibition of the hydroxylation of [3H]Pro in CDP. The two metals were also interactive with respect to the inhibition of the synthesis of protein, RNA and DNA. Culture of epiphysis in the presence of both Cd and Cu resulted in higher content of Cd and Cu compared to those cultured in Cd or Cu alone. Subcellular fractions from epiphysis cultured in Cd plus Cu contained more Cd than those cultured in Cd alone. Cu was increased in two fractions, nuclei and cytosol, following co-incubation. The cytosol from epiphysis cultured in the presence of both Cd and Cu contained more Cd in both a metallothionein (MT)-like protein and a high-molecular-weight (HM) protein than cytosol from Cd-treated bones. The amount (nmol) of Cu in the MT fraction was nearly equal to the sum of the increased amounts (nmol) of Cd in HM fraction of cytosol and particulate fractions. This indicates that some Cd in MT-like protein induced by Cd is replaced with Cu and the released Cd redistribution to HM fraction and particulate fractions. Most of the Cd in the solubilized particulate fractions was detected in the HM fraction. A marker enzyme or component in each fraction was interactively inhibited by both Cd and Cu. Therefore, the interactive inhibition of bone metabolism by both Cd and Cu in the cultured bone is at least partly due to the increase in Cd content of HM fraction of cytosol and particulate fractions.

Protection against cadmium toxicity by zinc: decrease in the Cd-high molecular weight protein fraction in rat liver and kidney on Zn pretreatment

The amounts of cadmium, associated with high molecular weight proteins, metallothionein and low molecular weight fractions obtained on Sephadex G-75 gel filtration, were determined in the liver and kidneys of rats treated with Cd. When rats were pretreated with zinc 24 h prior to the Cd injection, Cd associated with the high molecular weight proteins was decreased in both the liver and kidneys. Although the Cd concentration in the liver was increased, the liver showed less morphological damage in Zn-pretreated rats. The above results suggest that Cd-toxicity toward the liver and kidneys may be related to the accumulation of Cd in the high molecular weight proteins.

The effects of cadmium on a clonal osteogenetic cell, MC3T3-E1: inhibition of calcification and induction of metallothionein-like protein by cadmium

To clarify the effects of cadmium (Cd) on bone formation, a clonal osteogenetic cell, MC3T3-E1, was used in the present study. After 24 h of culture, Cd at 1 ppm and above decreased DNA synthesis and alkaline phosphatase activity, but Cd at 1.5 ppm caused no significant decrease in collagen content. The cells treated with Cd (0.03-1.0 ppm) for 24 h showed the dose-dependent effects on metallothionein-like protein synthesis. The marked increase of Cd content unbound to metallothionein (MT)-like protein with cadmium at 1 ppm may be responsible for the toxic effects of cadmium. After 10 days of culture, the accumulation of 45Ca to the cell layer decreased with increasing level of cadmium at 0.03 and 0.1 ppm. The cadmium-treated cell layer showed a weaker reaction to histochemical staining for mineral compared with control culture. This result suggests that Cd inhibits an initial process of calcification.

Concentrations of metallothionein and metals in malignant and non-malignant tissues in human liver

Concentration of metallothionein in the malignant and non-malignant tissues of the human liver was determined by the Cd-hem method. The concentration of metallothionein was high in the non-malignant tissue (471 +/- 306 micrograms/g). Metallothionein in the non-malignant tissue was mainly Zn-thionein and metallothionein-bound Zn was a major chemical form of Zn in the non-malignant tissue. The concentration of metallothionein in the malignant tissue was 75.6 +/- 79.6 micrograms/g, and significantly lower than that in the nonmalignant tissue. A strong, positive relationship was observed between the Zn and metallothionein concentrations, and the regression equation was MT (microgram/g) = -94.7 + 11.9 Zn (micrograms/g).

Low-molecular weight metalloproteins in tissues of the narwhal (Monodon monoceros)

Narwhal (Monodon monoceros) liver and kidney cytosol were fractionated by gel chromatography, anion-exchange chromatography and electrophoresis. Cadmium was associated largely with low molecular weight proteins, while mercury was associated also with high molecular weight proteins, but apparently not because of saturation of the metallothionein mechanism. Eight different electrophoretic bands, four of which were metalloproteins, were found under the "metallothionein" peak. Anion-exchange chromatography yielded five metal peaks while further fractionation on G-50 gave two peaks, one containing almost pure metallothionein (Mt-1) and the other a metalloprotein having twice the molecular weight of metallothionein. Mt-2 was observed, at a much lower concentration than Mt-1, in liver but not kidney.

Effects of dexamethasone on metallothionein induction by Zn, Cu, and Cd in Chang liver cells

Metallothioneins (MTs) were induced in Chang liver cells by the metals, Zn, Cu and Cd, and the glucocorticoid hormone, dexamethasone. When 116 microM Zn, 32 microM Cu and 18 microM Cd, and 10(-7) M dexamethasone, respectively, were administered for 9 h, MTs induced by each inducer in the cells reached maximum levels. The maximum accumulation of MT level induced by dexamethasone was the lowest of the four inducers investigated; the levels induced by Zn, Cu and Cd were 4.7, 1.2 and 1.5 times of that induced by dexamethasone. When dexamethasone was added to the cells together with the heavy metals (Zn, Cu and Cd), dexamethasone had an additive effect on the maximum MT accumulations induced by heavy metals as compared to when induction was conducted using one of heavy metals alone or by dexamethasone alone. However, dexamethasone did almost not effect the metal accumulations in the cells, although the maximum MT levels induced by heavy metal increased by dexamethasone. These results suggest that the process of MT induction by heavy metals and that by dexamethasone are independent of one another. When dexamethasone was added to the cells together with a high concentration of Cu (32 microM) induced the maximum MT accumulation, Cu transport into the cells decreased by 20-40% of that into non-treated cells, which was statistically significant.

Induction and degradation of Zn-, Cu- and Cd-thionein in Chang liver cells

Human liver cells (Chang liver) were exposed to 5 micrograms Zn, 2.5 micrograms Cu or 1 microgram Cd/ml in cultured medium. These exogeneous heavy metals were accumulated by the cells and induced de novo synthesis of metallothionein after a 3-h incubation period. The production of Zn-, Cu- or Cd-thionein started in the cells with accumulation of 1 nmol Zn, 0.3 nmol Cu and 0.1 nmol Cd/mg cytosol protein and subsequently the amounts of metal-binding thioneins increased in agreement with the relative amount of metal accumulated in the cytosol over a 24-h period. When cells containing Zn- or Cu-thionein were placed in metal free medium, 70% or 25% of the zinc or copper bound to each original metallothionein was released after 3 h; bound metals decreased to 85% and 65% respectively after 24 h. The disappearance of metal from metallothionein correlated with increases of metal in the medium. On the other hand, 35S-counts incorporated into Zn- and Cu-thionein decreased only to 40% and 15% of the levels in the original metallothionein after 3 h; 35S-counts decreased to 65% and 45%, respectively, after 24 h, indicating that metals bound to metallothionein decreased more quickly than 35S-counts. These results suggest that metals were released from metallothionein and were excreted into the medium. However, 35S- and 109Cd-counts in Cd-thionein changed very little, if at all, in the cells even after a 24-h incubation period. Our data strongly suggest that Zn- and Cu-thionein are degraded in the cells, but that Cd-thionein remains longer than either Zn- or Cu-thionein. When cells containing Zn-thionein were incubated in metal-free medium, Zn-thionein was digested in the cells and peptide fragments ranging about 200-400 daltons were excreted from the cells.

Effect of dietary chronic cadmium exposure on cell-mediated immune response in rhesus monkeys (Macaca mulatta): role of calcium deficiency

The role of Ca deficiency on the immunomodulatory effects of chronic Cd exposure for a period of 10 weeks in male Rhesus monkeys were assessed by the blastogenic capacity of peripheral blood lymphocytes (PBL) in response to T-cell mitogens, phytohemagglutinin (PHA), and concanavalin A (Con A). Calcium deficiency significantly decreased the blastogenic response to PHA (P less than 0.01) and Con A (P less than 0.05). Although Cd exposure in normal monkeys significantly increased the blastogenic response to Con A (P less than 0.05), Cd exposure in Ca-deficient monkeys produced a further significant decrease in the blastogenic response to Con A (P less than 0.001). Total and ionic Ca were also significantly decreased in plasma of Ca deficient monkeys exposed to Cd. It is possible that these two observations may be related to each other. Thus, it is important to assess the nutritional status of the host while evaluating the immunotoxicological effects of an environmental pollutant.

The binding of cadmium ions to the smooth muscle of guinea-pig taenia coli

Taenia coli was used to study the property of binding of Cd2+. The Scatchard plots of cadmium uptake showed that two qualitative Cd2+ binding sites (high and low affinity binding sites) exist in taenia coli. Decrease in Ca2+ concentration in the medium did increase the cadmium binding. The Scatchard analysis of Cd2+ binding in taenia coli at 4 degrees indicated a single class of binding sites (only high affinity binding sites). These findings suggest that the greater number of high affinity Cd2+ binding sites in taenia coli may relate to the binding to cell membrane. Further, it was postulated that some of low affinity binding sites in taenia coli may reflect intracellular accumulation, indicating the action on the contractile system.

In vivo and ex vivo displacement of zinc from metallothionein by cadmium and by mercury

Divalent cadmium and mercury ions are capable in vitro of displacement of zinc from metallothionein. This process has now been studied in vivo and ex vivo, using the isolated perfused rat liver system, in order to determine if this process can occur in the intact cell. Rats with normal and elevated (via preinduction with zinc) levels of hepatic zinc thionein were studied. Cd(II) completely displaces zinc from normal levels of metallothionein and on a one-to-one basis from elevated levels of metallothionein, both in vivo and ex vivo. Hg(II) displaces zinc from metallothionein (normal or elevated) rather poorly, as compared with Cd(II), in vivo, probably due to the kidneys preference for absorbing this metal. Ex vivo Hg(II) displaces zinc from metallothionein (normal or elevated) on a one-to-one basis, with considerably more mercury being incorporated into the protein than in vivo. The results of double-label ex vivo experiments using metal and [35S]cysteine (+/- cycloheximide) were consistent with the above experiments, indicating that de novo thionein synthesis was not required for short term incorporation of cadmium and mercury into metallothionein. These data are supportive of the hypothesis that cadmium and mercury incorporation into rat hepatic metallothionein during the first few hours after exposure to these metals can occur primarily by displacement of zinc from preexisting zinc thionein by a process which does not require new protein synthesis.