Quantitation of Cu-containing metallothionein by a Cd-saturation method

Understanding mercury accumulation in mosses of two subalpine forests in China

The role of forest ecosystems in the global mercury (Hg) biogeochemical cycle is widely recognized; however, using litterfall as a surrogate to assess the Hg sink function of forests encounters limitations. We investigated the accumulation characteristics and influencing factors of Hg in mosses from two remote subalpine forests in southwestern China. The results indicated that there was high Hg accumulation in subalpine forest mosses, with average concentrations of 82 ± 49 ng g-1 for total mercury (THg) and 1.3 ± 0.8 ng g-1 for methylmercury (MeHg). We demonstrated that the accumulation capacity of Hg in mosses was significantly dependent on species and substrates (micro-habitats), the mosses on tree trunks exhibited significantly elevated Hg accumulation levels (THg 132 ± 56 ng g-1, MeHg 1.6 ± 0.2 ng g-1) compared to mosses in other substrates. The surface morphologies and biochemical components of leaf (phyllidia), such as cation exchange capacity (CEC), pectin, uronic acid, and metallothionein, play a crucial role in the accumulation of Hg by mosses. These findings provide valuable insights into Hg accumulation in forest mosses. Suggesting that the contribution of mosses Hg accumulation should be considered when assessing atmospheric Hg sinks of forests.

Cadmium binding during leaf senescence in Festuca arundinacea: Promotion phytoextraction efficiency by harvesting dead leaves

Phytoextraction by harvesting dead leaves is a novel cadmium (Cd) phytoremediation strategy in tall fescue (Festuca arundinacea), which provides feasibility for the phytoremediation of Cd-polluted soils and cleaner food production. The highest Cd in dead leaves is the result of Cd accumulation during the process of leaf senescence. However, it is not known the mechanism of Cd accumulation during the leaf senescence, which limits the phytoextraction efficiency of this technology. In this study, we found that the contents of phytochelatins (PC), glutathione (GSH), and non-protein thiols (NPT) were increased during the process of leaf senescence and Cd stress significantly promoted PC, GSH, and NPT. Transcriptome analysis showed that the pathway of glutathione metabolism was significantly enriched in the senescent leaf under Cd stress. 19 genes encoding GST, enzymes catalyzing GSH-Cd binding, were up-regulated in the senescent leaf. The increases of PC, GSH, and NPT in the senescent leaf for Cd-binding could be from the pathways of the protein degradation rather than their synthesis, because genes encoding cysteine protease (catalyzes protein degradation) were significantly promoted, but both GSH synthetase (GS) and PC synthetase (PCS) did not show the significant changes between the young and senescent leaves. Our results indicated that Cd accumulation during the leaf senescence could be the result of the promotion of Cd-binding by PC, GSH, and NPT, which provide insights into the regulatory mechanism and further genetic engineering to promote the phytoextraction efficiency by harvesting dead leaves in tall fescue.

A multibiomarker approach for evaluating environmental contamination: Common carp (Cyprinus carpio) transplanted along a gradient of metal pollution

Environmental monitoring and risk assessment approaches which include a more holistic view on the effects of pollutants on biota are increasingly sought by regulators and policy makers. Therefore, caged carp juveniles (Cyprinus carpio) were transplanted for 7 weeks along a known Cd and Zn pollution gradient. Metal (Cu, Cd and Zn) accumulation in gill and liver tissue and effect biomarkers (growth, condition factor (CF), hepatosomatic index (HSI), oxygen consumption, swimming capacity, Na⁺/K⁺-ATPase activity (NKA) and metallothionein (MT) levels) were compared. Up to 10-fold higher cadmium concentrations were measured in the gills of the fish at the most polluted locations compared to the laboratory control fish. Similarly, cadmium concentrations in liver tissues of field-exposed fish were significantly higher than those measured in laboratory control fish. Cu and Zn concentrations in the gills were not significantly different between field-exposed and control organisms, whereas higher levels in liver tissues were measured in carps deployed in some locations. Effects on liver MT levels were up to 10 times greater for organisms exposed to the field, whereas no clear effect of the metal exposure on NKA in the gill tissue was observed. A decrease in muscle glycogen stores was observed for all organisms deployed in the field, while liver glycogen levels decreased only in fish exposed to two of the 5 sites compared to the laboratory control fish. Additionally, significant drops in liver protein- and lipid stores were observed. No effect on oxygen consumption rates and swimming capacity was observed. The CF and HSI of caged fish reflected the pollution gradient in the river and considerable loss of weight was observed for fish transplanted in the most polluted site. Overall, this active biomonitoring study successfully revealed differences in metal accumulation, physiological and organismal endpoints as a direct consequence of field exposure.

Methanobactin reverses acute liver failure in a rat model of Wilson disease

In Wilson disease (WD), functional loss of ATPase copper-transporting β (ATP7B) impairs biliary copper excretion, leading to excessive copper accumulation in the liver and fulminant hepatitis. Current US Food and Drug Administration- and European Medicines Agency-approved pharmacological treatments usually fail to restore copper homeostasis in patients with WD who have progressed to acute liver failure, leaving liver transplantation as the only viable treatment option. Here, we investigated the therapeutic utility of methanobactin (MB), a peptide produced by Methylosinus trichosporium OB3b, which has an exceptionally high affinity for copper. We demonstrated that ATP7B-deficient rats recapitulate WD-associated phenotypes, including hepatic copper accumulation, liver damage, and mitochondrial impairment. Short-term treatment of these rats with MB efficiently reversed mitochondrial impairment and liver damage in the acute stages of liver copper accumulation compared with that seen in untreated ATP7B-deficient rats. This beneficial effect was associated with depletion of copper from hepatocyte mitochondria. Moreover, MB treatment prevented hepatocyte death, subsequent liver failure, and death in the rodent model. These results suggest that MB has potential as a therapeutic agent for the treatment of acute WD.

Accumulation and detoxification of metals and arsenic in tissues of cattle (Bos taurus), and the risks for human consumption

The aim of this study was to investigate metal accumulation and detoxification processes in cattle from polluted and unpolluted areas. Therefore dairy cows from farms and free ranging Galloway cows from nature reserves were used as study animals. The concentrations of Ag, Cd, Pb, Al, Cr, Mn, Fe, Co, Ni, Cu, Zn and As were determined in muscle, kidney, liver and lungs of cattle from polluted and reference areas in Belgium. In kidney and liver also the metallothionein concentrations were measured. For Ag, Mn, Co, Cu, Zn and As the concentrations in the different tissues were significantly higher in the sampled Galloways than in the sampled dairy cows. On the other hand Cd and Pb were significantly higher in tissues of both cattle breeds from polluted sites. Cadmium seemed to be the most important metal for metallothionein induction in kidneys whereas Zn seemed to be the most important metal for the induction of metallothionein in the liver. This study also suggested that only for Mn and Cd a significant part of the uptake occurs via the lungs. Although in muscle none of the Cd and Pb levels exceeded the European limits for human consumption, 40% of the livers and 85% of the kidneys of all examined cows were above the European limit for cadmium. Based on the existing minimum risk levels (MRLs) for chronic oral exposure, the present results suggested that a person of 70kg should not eat more than 150g cow meat per day because of the Cr levels in the muscles.

Review on methods for determination of metallothioneins in aquatic organisms

One aspect of environmental degradation in coastal areas is pollution from toxic metals, which are persistent and are bioaccumulated by marine organisms, with serious public health implications. A conventional monitoring system of environmental metal pollution includes measuring the level of selected metals in the whole organism or in respective organs. However, measuring only the metal content in particular organs does not give information about its effect at the subcellular level. Therefore, the evaluation of biochemical biomarker metallothionein may be useful in assessing metal exposure and the prediction of potential detrimental effects induced by metal contamination. There are some methods for the determination of metallothioneins including spectrophotometric method, electrochemical methods, chromatography, saturation-based methods, immunological methods, electrophoresis, and RT-PCR. In this paper, different methods are discussed briefly and the comparison between them will be presented.

Metal accumulation and metallothionein induction in the spotted dogfish Scyliorhinus canicula

Recent studies indicate that elasmobranch fish respond differently to metal exposure than marine teleosts. Accumulation rates can be high, which despite the fact that normal background levels for metals in the marine environment are low, is worrying due to the long life span and late fecundity of most shark. The goals of the present study were to examine differences in accumulation rates and toxicity of a range of metals at equimolar concentrations (10microM) in the Mediterranean or spotted dogfish, Scyliorhinus canicula. For this purpose, we exposed the dogfish to Ni (587microg/L), Cd (1124microg/L), Pb (2072microg/L), Cu (635microg/L), and Ag (1079microg/L and two additional exposures at 10microg/L and 1microg/L) for one week and measured total metal accumulation, metallothionein induction, and parameters related to osmoregulation. Our study confirms the high toxicity and accumulation rates of Ag for elasmobranch fish, even at levels 100 to 1000 times lower than exposure levels of other metals. Also Pb accumulated readily in all organs, but did not cause any osmoregulatory disturbance at the exposure levels used. Ni and Cd seem to accumulate primarily in the kidney while Cu mainly accumulated in liver. In contrast to Ni and Cd, the three other metals Ag, Cu and Pb accumulated in the rectal gland, an important organ for osmoregulation and possible target organ for metal toxicity. Only Cu succeeded in initiating a protective response by inducing MT synthesis in liver and gills.

Heavy metals in the fishery products of low Lazio and the use of metallothionein as a biomarker of contamination

This study aims to investigate the use of metallothionein as a biomarker and its environmental impact on aquatic systems. According to the species' characteristics, the interactions of toxic elements with living organisms in marine water can lead to biomagnifications in the trophic chain or bioconcentration of what is in the water. In many aquatic organisms, the presence of metallothionein proteins was studied. The chemical analysis of these bioindicators establishes, therefore, a sensitive method for the measurement of bioavailability which, over the years, allows for the quantification of the current pollution agents in the environment. Two study areas were selected along the Latium coasts. They are differentiated by their economic activities and their kind and level of environmental impact (mainly on marine pollution). These areas were selected in order to differentiate the maximum degree of both economic development and environmental quality. In particular, the presence of pollutants in the sea due to land activities was evaluated to compare the quality of the fishing products obtained from locations subject to various environmental impacts. The heavy metal concentrations were evaluated in water samples taken from different 30 sections of the fishes in order to understand the metabolism and origin of these contaminants. The primary metals studied were: mercury (Hg), zinc (Zn), nickel (Ni), lead (Pb), cadmium (Cd), and copper (Cu). All data produced were analyzed via multivariate analyses in order to provide a final and reliable indicator.

Induction and activity of oxidative stress-related proteins during waterborne Cd/Zn-exposure in brown trout (Salmo trutta)

We studied how transcript levels of metallothionein (MT), Cu/Zn-superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX) and glutathione reductase (GR) as well as functional protein levels of MT, SOD and CAT in brown trout tissues changed during a 15-days waterborne exposure to Cd and Zn. Trout from a river with low levels of metals (the Stribekken River) was transferred to a river with high levels of Cd and Zn (the Naustebekken River) and exposed up to 15 days. The aim of this transfer experiment was to investigate how exposure to Cd and Zn induced transcription and activities of central antioxidant enzymes and proteins in an environmental setting. Significant uptake of both Cd and Zn was observed in gills during the 15 days exposure, and Cd levels was found to correlate significantly with transcript levels of MT-A, SOD, GPx and GR. Gill concentrations of Zn did not correlate significantly with the transcript levels of the stress genes studied, but Zn might have triggered transcription of proteins which dealt with subsequent accumulation of Cd. SOD and CAT activities increased in gills after transfer, but MT protein levels decreased. In liver, SOD activity and MT protein levels increased, while in kidney only MT protein concentrations were elevated after transfer. There was a general lack of consistency between mRNA transcription and enzyme activities, indicating that these proteins and enzymes are not solely under transcriptional control.

Induction and activity of oxidative stress-related proteins during waterborne Cu-exposure in brown trout (Salmo trutta)

Induction of gene transcription for proteins and enzymes involved in metal-mediated oxidative stress were studied in brown trout transferred to a Cu-contaminated river in the Røros region in Central Norway. In addition to metallothionein (MT-A), Cu/Zn-superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione reductase (GR) gene transcription, protein levels of MT and enzyme activities of SOD and CAT were analyzed in gill, liver and kidney. MT-A, SOD and GR transcription increased significantly along with uptake of Cu in gills, while only transcription of MT-A was found to respond in liver and kidney during the exposure. Already present MT proteins in gills seemed to be oxidized during the exposure, probably caused by Cu-mediated oxidative stress, and no increase in MT protein levels were observed in gills. SOD and CAT enzyme levels were affected in all tissues during the exposure. A negative correlation between SOD and CAT activities was observed in gills, and we suggest that the activities of these enzymes were influenced not only through transcription. GPx and GR transcription levels correlated positively with each other in gills and liver, indicating their shared function in GSH-turnover. Levels of MT and activity of SOD and CAT dealing with metal-induced oxidative stress appear to be regulated not only through gene transcription, but also through post-translational mechanisms.

Antioxidative stress proteins and their gene expression in brown trout (Salmo trutta) from three rivers with different heavy metal levels

Three populations of brown trout (Salmo trutta) exposed to different metal levels in their natural environments, were studied with respect to antioxidants metallothionein (MT), superoxide dismutase (SOD) and catalase (CAT) as well as for corresponding mRNA levels. In addition, mRNA levels were studied for glutathione peroxidase (GPx) and glutathione reductase (GR). The Cd/Zn-exposed trout (Naustebekken River) had higher accumulated levels of Cd, Cu and Zn in gills, and higher levels of MT (both protein and mRNA) in liver and kidney as well as in gills compared to the Cu-exposed trout (Rugla River) and trout from an uncontaminated reference river (Stribekken River). Less MT found in the Cu-exposed trout may increase susceptibility to oxidative stress, but no higher levels of antioxidant mRNAs were found in gills of these trouts. The data indicated that chronic exposures of brown trout to Cd, Zn and/or Cu did not involve maintenance of high activities of SOD and CAT enzymes in gills, although SOD mRNA levels were higher in the Cd/Zn-exposed trout. In livers, mRNA levels of SOD, CAT and GPx were higher in the metal-exposed trout, but in the case of GR this was only seen in kidneys of Cd/Zn-exposed trout. However, both metal-exposed groups had higher activities of SOD enzyme in liver compared to the unexposed reference trout, and CAT activity was found to be higher in kidneys of Cu-exposed trout. The Cu-exposed trout did not seem to rely on MT production to avoid Cu toxicity in gills, but rather by keeping the Cu uptake at a low level. A coordinated expression of different stress genes may also be important in chronic metal exposure. It may be concluded that the observed metal effects relies on acclimation rather than on genetic adaptation in the metal exposed populations.

Phenomenon of Hepatic Overload of Copper in Mugil cephalus: Role of Metallothionein and Patterns of Copper Cellular Distribution

In this work we describe a phenomenon of accumulation of copper (Cu) in livers of a teleost fish commonly known as mullet, Mugil cephalus. High levels of Cu, up to 1936 microg/g wet weight were found. The high Cu levels seem not to be associated with environmental Cu contamination, since the fish were collected from widely separated regions with low Cu concentrations. Other fish species sharing the same environment did not show high levels of Cu. The accumulation of Cu in mullet was seen in liver and most of the hepatic Cu was located in the non-cytosolic fraction. The intrahepatic distribution of Cu in mullet seems to depend on the total Cu content in the liver; as the total liver burden of Cu rose, Cu was increasingly recovered from the non-cytosolic fraction. Metallothionein in hepatic cytosols from mullet contained the most Cu. However, the Cu concentration not bound to metallothionein rose when total cytosolic Cu increased; which show that metallothionein, particularly at higher Cu levels, is not the major hepatic Cu-binding protein in cytosols of mullet. This report shows mullet as a very useful model to study the accumulation of Cu in the liver, which may lead to a better understanding of cellular mechanisms which control Cu homeostasis.

Copper in Helix pomatia (Gastropoda) is regulated by one single cell type: differently responsive metal pools in rhogocytes

Like all other animal species, terrestrial pulmonate snails require Cu as an essential trace element. On the other hand, elevated amounts of Cu can exert toxic effects on snails. The homeostatic regulation of Cu must therefore be a pivotal goal of terrestrial pulmonates to survive. Upon administration of Cu, snails accumulate the metal nearly equally in most of their organs. Quantitative studies in connection with HPLC and electrospray ionization mass spectrometry reveal that a certain fraction of Cu in snails is bound to a Cu-metallothionein (Cu-MT) isoform that occurs in most organs at constant concentrations, irrespective of whether the animals had been exposed to physiological or elevated amounts of Cu. In situ hybridization demonstrates that at the cellular level, the Cu-binding MT isoform is exclusively expressed in the so-called pore cells (or rhogocytes), which can be found in all major snail organs. The number of pore cells with Cu-MT mRNA reaction products remains unaffected by Cu exposure. Rhogocytes also are major storage sites of Cu in a granular form, the metal quickly entering the snail tissues upon elevated exposure. The number of rhogocytes with granular Cu precipitations strongly increases upon Cu administration via food. Thus, whereas Cu-MT in the rhogocytes represents a stable pool of Cu that apparently serves physiological tasks, the granular Cu precipitations form a second, quickly inducible, and more easily available pool of the metal that serves Cu regulation by responding to superphysiological metal exposure.

Tetrathiomolybdate in the treatment of acute hepatitis in an animal model for Wilson disease

BACKGROUND/AIMS

Tetrathiomolybdate (TTM) is a potent copper-chelating agent that has been shown to be effective in Wilson disease patients with neurological symptoms. Here, we investigate the potential use of TTM in treating the acute hepatic copper toxicosis in Long-Evans Cinnamon (LEC) rats, an authentic model for Wilson disease.

METHODS

After the onset of acute hepatitis, LEC rats were treated once with 10 mg TTM/kg. After 1 and 4 days, parameters of liver toxicity and the subcellular distribution and binding of copper and iron were studied.

RESULTS

In 11 out of 12 rats TTM rapidly improved acute hepatitis. Hepatic copper decreased through removal from cytosolic metallothionein and lysosomal metallothionein polymers. The remaining lysosomal copper forms a metallothionein-copper-TTM complex. In an almost moribund rat, however, TTM caused severe hepatotoxicity with fatal outcome.

CONCLUSIONS

TTM is effective in treating acute hepatitis in LEC rats when applied before the animals become moribund. TTM appears to act by removing the presumable reactive copper associated to lysosomal metallothionein polymers. The remaining lysosomal copper seems to be inactivated by forming a complex with TTM. Moreover, TTM removes copper from cytosolic copper-containing metallothionein. As a consequence, metallothionein is degraded and the uptake of copper-metallothionein into the lysosomes and the formation of the metallothionein polymer associated copper is reduced.

Differential metallothionein induction patterns in three freshwater fish during sublethal copper exposure

We assessed whether fish that tolerate higher levels of Cu exposure have a higher capacity to induce metallothionein (MT) synthesis than other, more sensitive, fish species. Furthermore, we examined if a correlation could be found between tissue Cu accumulation and MT levels. Cu accumulation and MT concentrations in gill, liver, kidney and muscle of rainbow trout (Oncorhynchus mykiss), common carp (Cyprinus carpio) and gibel carp (Carassius auratus gibelio) were measured during a 1 week exposure to a sublethal Cu (1 microM). Different patterns were observed for the three species regarding Cu accumulation as well as MT induction. Virtually no Cu accumulation was seen in rainbow trout gill, while in both cyprinid species gill Cu levels increased three- to four-fold. Cu accumulated fast in common carp (within the first day), but slow in gibel carp (1 week). Gill MT induction was obvious in gibel carp only, with an increase of 156% after 1 week of exposure. Liver accumulated most Cu in rainbow trout (235% increase) and common carp (144% increase), with Cu levels in liver being significantly higher in rainbow trout compared to the carp species from the start. MT induction was pronounced in common carp liver only (138% increase). In gibel carp liver, there was no clear Cu accumulation or MT induction. In contrast, gibel carp was the only species to show Cu accumulation in kidney after 3 days of exposure (83% increase), after which levels returned to normal. Concomitantly, gibel carp kidney was also the only kidney tissue to show MT induction (192-195% increase after 3 and 7 days). In common carp, a significant decrease of kidney MT levels was observed from day 1 onwards. In muscle, Cu accumulation was clear for the two cyprinid species (three- to four-fold increase) but not for rainbow trout. Of the species studied, gibel carp is the most resistant to copper polluted environments, and showed a positive significant relationship between tissue copper concentrations and MT levels in gill, liver and muscle tissues. Common carp showed an intermediate response, with significant correlations in liver and muscle tissue. In contrast, we found low MT induction in rainbow trout, the most sensitive species, and no correlation at all between MT concentrations and tissue copper contents. Possibly, the regulatory capacity for copper homeostasis was exceeded in rainbow trout, and MT synthesis inhibited.

Metallothionein as bioindicator of freshwater metal pollution: European eel and brown trout

The aim of this work was to evaluate the potential of metallothionein (MT) as a bioindicator of heavy metal pollution in brown trout and European eel in the field situation. River Ferrerias (North Spain) provided a good gradient of metal contamination: concentrations of heavy metals were elevated both in water and in sediments at the downstream (polluted) site and were low at the upstream (unpolluted) site. MT levels of brown trout exhibited statistically significant differences between sites. Although European eel at the polluted site had a higher MT content, differences were not significant. It is concluded that MT is a good bioindicator of heavy metal pollution in brown trout.

Metal accumulation and metallothionein in brown trout, Salmo trutta, from two Norwegian rivers differently contaminated with Cd, Cu and Zn

In this work we have studied the accumulation of heavy metals in two brown trout (Salmo trutta) populations in their natural environment and the participation of metal binding to metallothionein (MT) in this process. Cd, Cu and Zn concentrations, total MT (including Cu MT) and Cd/Zn MT were measured in the gills, liver and kidney of trout inhabiting two rivers, one Cu-contaminated and the other Cd/Zn-contaminated, located at Røros, Central Norway. In both populations, high levels of Cu were found in the liver, whereas Cd was accumulated in liver and particularly in the kidney. The proportions of Cd/Zn MT and Cu MT in liver and kidney, but not in gills, reflected the accumulated and the environmental concentrations of these metals. The total Cu MT concentrations in the investigated tissues, however, were highest in trout from the river with the lowest ambient Cu concentration. It is suggested that MTs are of less importance in Cu-acclimated trout. The data also suggest that acclimation to a Cu-rich environment involves reduced Cu accumulation or increased Cu elimination. In trout from the Cd-rich environment, this metal was mainly bound to MT, whereas in trout from the Cu-rich environment Cd was also associated with non-MT proteins. These findings emphasize the importance to determine both Cd/Zn MT and Cu MT levels, when the participation of this protein in metal handling in trout tissues is investigated.

Studies on the influence of a Se-restricted diet on the effects of long-term increased copper intake in guinea pigs

Guinea pigs were exposed to Se-restriction/deficiency in combination with drinking water containing 200 or 300 mg Cu/l for 6-30 weeks. Under the influence of Se-restriction/deficiency Cu excretion by bile was diminished, the Cu content of the kidneys was increased and disturbances of liver function were seen in animals exposed for prolonged periods. Some parameters of the immune system, such as the phagocytic activity of peritoneal macrophages, mitogenicity of spleen lymphocytes and the amount of lymphatic spleen tissue were also adversely affected. These effects correlated in part with the liver damage and the copper content of the kidneys. Conclusion are drawn with respect to the Idiopathic Copper Toxicosis/Indian Childhood Cirrhosis.

Dissolution of copper-rich granules in hepatic lysosomes by D-penicillamine prevents the development of fulminant hepatitis in Long-Evans cinnamon rats

BACKGROUND/AIM

The Long-Evans cinnamon rat has a mutation homologous to the human Wilson disease gene, leading to gross copper accumulation and the development of hepatitis. D-penicillamine, a copper-chelating drug widely and efficiently used in treating Wilson disease, has also been shown to prevent hepatitis in Long-Evans cinnamon rats. The objectives of this study were: i) to investigate the effectiveness of D-penicillamine when administered to the already affected animals, and ii) to elucidate the mechanism of action of the drug.

METHODS

Long-Evans cinnamon rats were divided into groups according to age and treatment with D-penicillamine. The drug was administered orally before and after the onset of hepatitis. Livers were examined by light and electron microscopy. The effect of D-penicillamine on the subcellular distribution and binding of copper was investigated in more detail. Finally, the interaction between D-penicillamine and specific hepatic copper-binding proteins was studied in vitro.

RESULTS

D-penicillamine when given to either healthy or diseased animals prevented or reversed hepatitis, respectively. The drug particularly inhibited the disease-specific accumulation of copper in lysosomes of hepatocytes, tissue macrophages and Kupffer cells. When administered to diseased animals, the drug sequestered copper particularly from insoluble lysosomal particles. According to results obtained in vitro, the mobilization of this copper is likely to proceed through the solubilization of these particles. In contrast and as supported by the in vitro data, D-penicillamine had only a minor effect on copper bound to metallothionein in the cytosol.

CONCLUSION

Our findings on the Long-Evans cinnamon rat provide some conclusions on the mechanism of action of D-penicillamine in Wilson disease therapy. The drug prevents the formation or promotes the solubilization of copper-rich particles which occur in lysosomes of hepatocytes and Kupffer cells in the livers of patients with Wilson disease. Once chelated with D-penicillamine copper might then be excreted into urine. However, the mobilization of copper by D-penicillamine seems to be limited due to the binding of the metal to metallothionein in liver cytosol. This copper, even at relatively high concentrations, apparently may be well tolerated.

Metallothionein and heavy metals in brown trout (Salmo trutta) and European eel (Anguilla anguilla): a comparative study

The levels and the cellular distribution of heavy metals, and the extent by which the metals binds to metallothionein (MT) in brown trout (Salmo trutta) and European eel (Anguilla anguilla), were analyzed in order to assess the natural conditions of MT and heavy metals in these two fish species. There were no differences in heavy metals and MT concentrations between males and females of brown trout in a nonreproductive status and between adult brown trout individuals. Brown trout presented higher Cu content than European eel. The cellular distribution of Cu was also different between the two fish species; while in brown trout most of the Cu was in the noncytosolic fraction, Cu was mainly located in the cytosol in European eel. However, the cellular distribution of Zn, Cd, and Pb was similar in the two fish species. There was also an important difference in the metal content of MT between both species. Whereas, in brown trout, Cu-binding MT represented 75% of total metal-binding MT, this value was 25% in European eel. The between-species differences found in this study are intrinsic characteristics not associated with environmental factors. These results establish the basis to use MT as a bioindicator.

Liver fibrosis in guinea pigs experimentally induced by combined copper and aflatoxin application

Aflatoxin B1 alone (0.05 mg resp. 0.037 mg/kg/d), copper alone (6.6 mg/kg/d or 200 mg/l drinking water) or a combination of both was administrated orally for 6 months to young guinea pigs from the first/second day of life. In the copper group there were no pathomorphological changes. For the aflatoxin B1 group liver damage was established. In the combined group liver injury was more frequent and more severe compared to the aflatoxin B1 group. Compared with the copper group biliary copper excretion was diminished and the kidney copper content was elevated in the Afl. B1 + Cu group. While copper concentrations in bile and kidney correlated with other parameters, notably the pathological lesions of the liver, no such correlation was found for liver copper. Therefore in this experiment the degree of Cu accumulation was not decisive for the liver lesions. The livers' capacity for excreting Cu by bile seems to be a much more important factor. Histologically only the livers of the combined group exhibited degeneration, atrophy and steatosis of liver cells, and a fibrosis more or less pronounced. For childhood cirrhosis (ICC and ICT), a combined etiology--a liver damaging agent plus elevated alimentary copper--is a plausible hypothesis.

Association of copper to metallothionein in hepatic lysosomes of Long-Evans cinnamon (LEC) rats during the development of hepatitis [se e comments]

BACKGROUND

The Long-Evans cinnamon (LEC) rat has a mutation homologous to the human Wilson's disease gene, leading to copper-induced hepatotoxicity. The mechanism of how excess copper damages the liver or what chemical form of copper is toxic is still unclear.

RESULTS

In liver cytosol, copper levels were highest just before the onset of hepatitis and declined thereafter. In cytosol, total copper was bound to metallothionein (MT). Considerable amounts of both copper and iron accumulated in lysosomes with increasing age and development of liver damage. Lysosomal levels of presumably reactive non-MT-bound copper were increased. In severely affected livers, large amounts of copper were associated with insoluble material of high density which, upon ultrastructural information, was found to be derived from the lysosomes of Kupffer cells. This copper-rich material is considered to consist of polymeric degradation products of copper-MT.

CONCLUSION

We suggest that chronic copper toxicity in LEC rats involves the uptake of copper-loaded MT into lysosomes, where it is incompletely degraded and polymerizes to an insoluble material containing reactive copper. This copper, together with iron, initiates lysosomal lipid peroxidation, leading to hepatocyte necrosis. Subsequent to phagocytosis by Kupffer cells, the reactive copper may amplify liver damage either directly or through stimulation of these cells.

Copper in infant nutrition: safety of World Health Organization provisional guideline value for copper content of drinking water

BACKGROUND

Copper is an essential nutrient for humans. Recently, a limit of 31.48 micromol/l (2 mg/l) was proposed by the World Health Organization as the provisional guideline value for copper content of drinking water. The objective of the study was to determine the tolerance of chronic exposure to drinking water with low or high copper content in infants.

METHODS

Healthy infants (n = 128) were randomly assigned to receive drinking water with less than 1.57 micromol/l (<0.1 mg/l) (n = 48) or 31.48 micromol/l (2 mg/l) of copper (n = 80) from 3 to 12 months of age. At 6, 9, and 12 months of age, serum concentrations of copper, ceruloplasmin, and superoxide dismutase; erythrocyte metallothionein; bilirubin; transaminases; and gamma-glutamyl transferase were measured.

RESULTS

Small differences in biochemical indexes of copper nutrition were observed between the groups, but there was no evidence of adverse or toxic effects. These findings may be explained by an adaptive response to the higher copper intake, limiting copper absorption, and increasing biliary secretion, as well as by an increase in copper storage. It is also possible that the sensitivity of the biochemical indicators employed to detect differences in copper status is limited.

CONCLUSION

No acute or chronic adverse consequences of consuming water with copper content of 31.48 micromol/l (2 mg/l) were detected in infants during the first year of life. The results support the safety of the World Health Organization's provisional guideline value for copper in drinking water during infancy.

Primary structure of a copper-binding metallothionein from mantle tissue of the terrestrial gastropod Helix pomatia L

A novel copper-binding metallothionein (MT) has been purified from mantle tissue of the terrestrial snail Helix pomatia using gel-permeation chromatography, ion-exchange chromatography and reverse-phase HPLC. Copper was removed from the thionein by addition of ammonium tetrathiomolybdate. The resulting apothionein (molecular mass 6247 Da) was S-methylated and digested with trypsin, endoproteinase Arg-C and endoproteinase Lys-C. Amino acid sequences of the resulting peptides were determined by collision-induced dissociation tandem MS. The protein is acetylated at its N-terminus, and consists of 64 amino acids, 18 of which are cysteine residues. A comparison with the cadmium-binding MT isolated from the midgut gland of the same species shows an identical arrangement of the cysteines, but an unexpectedly high variability in the other amino acids. The two MT isoforms differ in total length and at 26 positions of their peptide chains. We suggest that the copper-binding MT isoform from the mantle of H. pomatia is responsible for regulatory functions in favour of copper, probably in connection with the metabolism of the copper-bearing protein, haemocyanin.

Experimental induction of liver fibrosis in young guinea pigs by combined application of copper sulphate and aflatoxin B1

Aflatoxin B1 alone (0.05 mg resp. 0.037 mg/kg/d), copper alone (6.6 mg/kg/d or 200 mg/l drinking water) or a combination of both was administered orally for 6 months to young guinea pigs from the first/second day of life. In the copper group there were no pathomorphological changes. For the aflatoxin B1 group, liver damage was established. In the combined group, liver injury was more frequent and more severe compared to the aflatoxin B1 group and biliary copper excretion was diminished compared with the copper group. Histologically, only the livers of this group exhibited degeneration, atrophy and steatosis of liver cells, inflammatory processes and a more or less prominent fibrosis. For childhood cirrhosis (ICC and ICT) a combined etiology--a liver damaging agent plus elevated alimentary copper--is a plausible hypothesis.

Visualization of yellowish-orange luminescence from cuprous metallothioneins in liver of Long-Evans Cinnamon rat

We describe the first use of an emission probe, based on the cuprous thiolate chromophore, for direct microscopical observation of cuprous metallothioneins located in liver of 15-week-old (just before spontaneous hepatitis) Long-Evans Cinnamon rats. The rats show remarkable accumulations of copper and cuprous metallothioneins. In the mildly fixed liver, we visualized the same yellowish-orange luminescence as the specific emission from cuprous metallothioneins, following excitation in 330-385 nm region. In liver from Long-Evans Agouti rat, a counter part of Long-Evans Cinnamon rat, no similar luminescence was found. So, it was thought that cuprous metallothioneins accumulated in the Long-Evans Cinnamon rat liver might emit the yellowish-orange light. To verify this presumption, we tentatively defined three histochemical criteria, quenching tests by oxidation, protonation and mercury treatment, based on the coordination chemical characteristics of metallothioneins. The emission completely satisfied these criteria. Furthermore, the reliability of these criteria was supported by immunocytochemical and biochemical results. Consequently, all results sufficiently indicate that the yellowish-orange luminescence in the Long-Evans Cinnamon rat liver is the emission from cuprous metallothioneins.

Metallothionein research in terrestrial invertebrates: synopsis and perspectives

While most of metallothionein research during the past years has been carried out on mammals or vertebrates, only relatively few studies have been directed towards invertebrates. Even fewer investigations have focussed on terrestrial invertebrates. The best studied metallothioneins and/or metallothionein genes among terrestrial invertebrates are those from an insect species (Drosophila melanogaster), a nematode (Caenorhabditis elegans) and some terrestrial gastropods (Helix pomatia, Arianta arbustorum). From these few examples it already appears that terrestrial invertebrate metallothioneins provide intriguing models to better understand the multiplicity of functions of these proteins and their evolution within the animal kingdom. Like in mammals, metallothioneins in terrestrial invertebrates seem to perform different functions simultaneously. This is exemplified by terrestrial gastropods, which are able to accumulate different metals in different tissues, in which metal-specific metallothionein isoforms or conformation forms are expressed, allowing these organisms to detoxify more efficiently nonessential trace elements such as cadmium, and at the same time to maintain the homeostasis of essential trace elements such as copper. A major proportion of metallothionein research in terrestrial invertebrates addresses the ecophysiological and ecotoxicological significance of these proteins with regard to the increasing risk due to chemical pollution. One promising aspect in this concern is the potential utilization of metallothioneins as biomarkers for risk assessment in terrestrial environments.

Molybdenum and copper kinetics after tetrathiomolybdate injection in LEC rats: specific role of serum albumin

Chelation therapy with tetrathiomolybdate (TTM) was applied to Long-Evans rats with a cinnamon coat-color (LEC rats), an animal model for Wilson disease, to remove copper (Cu) accumulated in the liver in a form bound to metallothionein (MT). Changes in molybdenum (Mo) and Cu concentrations and their biological forms in serum of LEC rats determined at different times after a single intraperitoneal injection were compared with those of Wistar (normal) rats. The change in Mo concentration in serum of normal rats was mono-phasic, whereas in LEC rats it was bi-phasic. The phase in normal rats and the first phase in LEC rats appeared to reflect the process of uptake and disappearance of TTM in the livers of Wistar and LEC rats. On the other hand, the second phase in LEC rats paralleled the changes of Cu and appeared to reflect the complex formation (Cu/thiomolybdate complex) between Mo and Cu accumulated in the liver. The complex was specifically bound to albumin as determined by high performance liquid chromatography with inductively coupled plasma-mass spectrometry (HPLC/ICP-MS). The results suggested that the changes in the Mo concentration in serum reflected the amount of Cu in the liver.

Role of cytosolic copper, metallothionein and glutathione in copper toxicity in rat hepatoma tissue culture cells

Effects of metallothionein (MT) synthesis inhibiting compounds (actinomycin D, cycloheximide), MT synthesis stimulating compounds (dexamethasone, dibu-cAMP) and interfering metals (Cd, Zn) on copper accumulation were investigated in rat hepatoma tissue culture cells. Copper-metallothionein (Cu-MT) and MT-associated copper levels were determined to find a possible correlation between cytosolic copper concentrations and MT as a Cu-detoxifying protein. Further, intracellular non-MT associated copper levels and levels of GSH and SOD were determined. Cell viability was tested under all experimental conditions by measuring LDH-release, K+ uptake and total cell protein. Administration of dexamethasone and dibu-cAMP showed no effect on MT levels (compared with controls), and only a marginal effect on 64Cu and total Cu accumulation. Administration of actinomycin D resulted in increased copper accumulation in the particulate fraction, possibly due to inhibition of copper secretion processes and/or protein synthesis. Presence of zinc had no effect on MT levels nor on total Cu and 64Cu levels, in contrast with cadmium which drastically enhanced copper accumulation and MT levels in the cells. Cu/MT ratios varied from 1.0 +/- 0.3 to 3.3 +/- 1.2, which is far below the assumed maximum molar ratio of 8-12 mol Cu per mol MT. SOD levels appeared to be enhanced up to 2- or 3-fold in the presence of Cd2+, relative to control values. The role of GSH as Cu-intermediate in intracellular Cu distribution plus its role in copper defence mechanism(s) was tested by application of BSO, an inhibitor of GSH synthesis. It was found that BSO had no effect on intracellular MT level; it was found however that MT-bound copper levels were markedly decreased. The results presented support a model for copper metabolism in hepatoma tissue culture (HTC) cells, where Cu(I) is complexed by GSH immediately after entering the cell. GSH is capable of transferring copper to MT where it is stored. Depletion of GSH (by administration of Cd2+, actinomycin D, cycloheximide) almost instantaneously results in enhanced cellular toxicity. When also MT is depleted (by actinomycin D) non-MT associated, 'free' cytosolic Cu2+ is elevated, and HTC cells rapidly loose their resistance to copper toxicity, as also reflected in loss of cell viability (LDH, K+ and total cell protein).

Mechanisms for removal of copper from metallothionein by tetrathiomolybdate

Mechanisms for removal of copper (Cu) from metallothionein (MT) by tetrathiomolybdate (TTM) were examined in vivo and in vitro using the LEC rat, which accumulates Cu as MT owing to the hereditary disorder of this strain. In our previous experiment, repeated intraperitoneal injections of TTM were shown to remove approximately two-thirds of the Cu from the liver, and the Cu remaining in the liver changed from soluble MT-bound forms to nonsoluble unidentified forms. The present single intravenous injection of TTM changed only part of the distribution in the soluble fraction, and dimeric MT was assumed to be formed. The liver supernatant was treated in vitro with high and low doses of TTM. The former treatment removed all Cu bound to MT and the Cu distributed to high molecular weight proteins, while the latter treatment produced dimeric MT. The results indicate that Cu accumulated as MT can be removed differently by TTM according to its relative dose both in vivo and in vitro. Excess TTM removes Cu completely from MT, leaving apothionein, while lesser TTM than Cu removes Cu incompletely, leaving MT with unoccupied sulfhydryl groups which coordinate with Cu intermolecularly to form dimeric and polymeric MT through the -S-Cu-S- bridge.

Factors influencing the separation of metallothioneins by capillary zone electrophoresis

The factors influencing the separation of metallothioneins (MTs) by capillary zone electrophoresis (CZE) were studied using untreated fused-silica capillaries. A comparison was made between the various buffers of 20 mM Na2B4O7, 10 mM Na2B4O7-10 mM Na2HPO4 and 20 mM Na2B4O7-10 mM Tris for the separation of MTs in terms of migration time and UV-absorbance under the various applied voltages. The migration times for MT-I and MT-II decreased with increase in the applied voltage and column temperature. However, no significant change in UV absorbance was observed. When Na2B4O7-Tris buffer was chosen for the separation of MTs, the migration time, UV absorbance, theoretical plates and resolutions also increased with increasing buffer concentrations. The effect of buffer pH on migration time was relatively complicated. Under the optimal operating conditions the standard MTs were well separated. Determination of MTs in the real samples failed due to the adsorption of other proteins onto the capillary walls.

Effects of copper on rat hepatoma HTC cells and primary cultured rat hepatocytes

Cellular responses to copper, applied in concentrations varying from 0.5 to 200 microM Cu2+, were investigated in two different cell types: rat hepatoma cells (HTC) and primary cultured rat hepatocytes. Accumulation of 64Cu, copper (AAS) levels, cellular viability parameters (cell growth and proliferation, LDH leakage, total cell protein, K+ uptake, and ATP levels), and cell toxicity parameters (metallothionein (MT), glutathione (GSH) and superoxide dismutase (SOD)) were examined over 24 hr incubation periods. Accumulation of radiolabeled copper (applied copper concentrations: 15-200 microM Cu2+) showed a four-fold increase in HTC cells (0.88-3.45 nmol Cu/mg cell protein) and a three-fold increase in hepatocytes (4.94-14.66 nmol Cu/mg cell protein), although quantitative uptake in HTC cells was five times lower. Most of the copper accumulated in the hepatoma cells and hepatocytes was found predominantly in the particulate fraction (i.e., cell membranes and organelles), while only a small quantity was present in the soluble fraction (cell cytosol). Metallothionein concentrations in HTC cells were increased from 43 pmol/mg cell protein (0.5 microM Cu2+ application) up to 223 pmol/mg cell protein (200 microM Cu2+ application), whereas MT in rat hepatocytes were elevated from 139 pmol/mg cell protein to 546 pmol/mg cell protein over the same range of administered Cu2+. Metallothionein synthesis rendered both cell types well equipped to deal with increasing intracellular copper levels. In hepatocytes however, MT synthesis resulted in decreasing non-MT-associated copper levels in the cytosol for Cu administrations up to 100 microM. Above that point however, MT failed to stay in line with increasing cytosolic Cu levels, resulting in cytotoxic effects shown by changes in cell viability and GSH/SOD levels. In HTC cells MT synthesis suppressed the free Cu levels in the cytosol to below 0.1 nmol Cu/mg cell protein over the total range of copper concentrations applied. The results presented indicate that hepatoma HTC cells are more capable of dealing with high accumulated Cu levels than the better established rat hepatocytes. Furthermore, it is clear that comparison of these two cell types regarding their ability to respond on (sub)toxic Cu should be discussed with full consideration for the copper applications involved.

Selective removal of copper bound to metallothionein in the liver of LEC rats by tetrathiomolybdate

LEC rats (Long-Evans with a cinnamon-like coat color) have a genetical defect in Cu metabolism. Male LEC rats aged 10 weeks were injected ip with TTM at a dose of 5 or 10 mg/kg body weight for 8 consecutive days and killed one day after the last injection. Cu that had accumulated in the liver at a concentration of 251 micrograms/g liver was decreased to 82.7 or 74.3 micrograms/g liver respectively, by the treatment. Although most of Cu was bound to MT as a soluble form before TTM treatment, the metal remaining in the liver after the treatment was present almost exclusively in the non-soluble fraction. Zinc (Zn) present, bound to MT before the treatment, was also partly removed from the liver by TTM, and the Zn remaining in the liver after the treatment was revealed to be bound to MT (Zn-MT) by high performance liquid chromatography-atomic absorption spectrophotometry. Iron (Fe) in the liver was not affected by TTM treatment. Cu in the kidneys and spleen increased by TTM treatment, while Zn and iron were not affected. Treatment of LEC rats with severe jaundice effectively cured the animals from otherwise lethal signs by only two ip injections of TTM at a dose of 10 mg/kg body weight.

Determination of zinc-65, copper-64 and sulphur-35 labelled rat hepatoma tissue culture metallothioneins by high-performance liquid chromatography with on-line radioactivity detection

Molecular size exclusion (MSE), reversed-phase (RP), and anion-exchange (AE) high-performance liquid chromatography (HPLC) techniques were employed in combination with on-line radioactivity detection, in a study on the kinetic behaviour of 65Zn-, 64Cu- and [35S]cysteine-labelled metallothionein (MT) in rat hepatoma tissue culture (HTC) cells. MSE-HPLC of [35S]cysteine-labelled HTC cell cytosol resulted in co-eluting MT-I and MT-II isoforms (tR 19.80 min; Ve/Vo: 1.85). AE-HPLC of 65Zn-treated HTC cell cytosol yielded separated 65Zn MT-I (tR 11.5 min; I = 64 mM) and 65Zn MT-II (tR 14.5 min; I = 104 mM). RP-HPLC of 64Cu-treated HTC cytosol resulted in separated 64Cu MT-I (tR 26.4 min) and 64Cu MT-II (tR 23.4 min). Determination of the amino acid composition, apparent molecular mass and cysteine content of HTC MT-I and MT-II isoforms showed the characteristics of class I metallothioneins. The rate of dissociation of Zn2+ from Zn-MT could be determined from the losses of 65Zn from MT during a single AE-HPLC run, showing a Zn-MT dissociation half-life of 0.66 h. RP-HPLC showed a delay in incorporation of newly accumulated 64Cu into MT, possibly owing to the appearance of reduced glutathione as an intracellular copper-transfer compound. Application of compartmental analysis in [35S]-cysteine accumulation experiments permitted the determination of the actual rate of MT degradation; when 200 microM of Zn were applied, the MT degradation half-life was 2.0 +/- 0.8 h. These results indicate the potential of combined HPLC techniques and application of radionuclides in studies on the synthesis and degradation of MT and metal-MT complexes.

Oxygen free radicals and metallothionein

It is generally accepted that the principal roles of metallothionein lie in the detoxification of heavy metals and regulation of the metabolism of essential trace metals. However, there is increasing evidence that it can act as a free radical scavenger. This article reviews the evidence supporting such a physiological role and describes induction of metallothionein synthesis by oxidative stress, possible mediators for this induction, and the radical scavenging capability of metallothionein in tissues and cells. The relationship between metallothionein and other antioxidant defense systems and the medical implications of the free radical scavenging properties of metallothionein are also discussed.

Separation of metallothionein isoforms by capillary zone electrophoresis

The potential of capillary zone electrophoresis (CZE) for the analysis of metallothionein (MT) isoforms was investigated. CZE was performed using two different systems, (1) a laboratory-constructed instrument with an ISCO UV detector and (2) a Waters Quanta 4000 system. Capillaries were of 75 microns I.D. x ca. 1 m in length and loading times were up to 40 s by gravity or 4 s by electrokinetic migration at 30 kV. Samples were dissolved in 10 mM Tris-HCl buffer, pH 9.1, and electrophoresis was performed at 30 kV using a 50 mM Tris-HCl, pH 9.1 running buffer. Detection was by UV absorbance at 185 or 214 nm. Purified and semipurified MT samples were analysed for qualitative assessment of purity, relative isoform abundance and separation characteristics of MT from different species. As progress towards the development of a quantitative assay, the linearity of calibration curves and simple methods of sample preparation for analysis by CZE were investigated. Complete separation of a mixture of the two major MT isoforms was achieved in less than 5 min and the technique was found to be very useful for qualitative analysis of MT. Using a rabbit liver MT standard (500 micrograms/ml-1), a linear relationship was found between the gravity load time and the integrated peak area. Standard calibration curves were also linear and the detection limit for both CZE instruments under our separation conditions was 1-10 micrograms MT ml-1. The successful use of two solvent extraction procedures for tissue samples demonstrated the potential of CZE for routine quantitative analysis of MT.

Effects of cadmium, copper and metallothionein synthesis inhibiting and stimulating compounds on zinc uptake and accumulation in rat hepatoma HTC cells

Experiments were carried out to investigate the uptake and accumulation of Zn in rat hepatoma HTC cells, as affected by interfering metals (Cd, Cu), metallothionein synthesis inhibiting compounds (Actinomycin D, cycloheximide) and metallothionein synthesis stimulating compounds (dexamethasone, dibu-cAMP). Cell viability was tested under all experimental conditions by the measurement of LDH leakage, K+ uptake and total cell protein. Determinations of Zn were performed by AAS (total Zn) or by gamma-ray spectrometry (65Zn). Metallothionein analysis was carried out by Cd-saturation tests. The results indicate that cellular responses in rat hepatoma HTC cells with respect to the uptake and accumulation of 65Zn are fully comparable with literature data existing for 65Zn accumulation in rat hepatocytes, under all experimental conditions applied. Cu2+ and dibutyryl-cAMP did not significantly affect rates of 65Zn accumulation. Cd2+, Actinomycin D and cycloheximide reduced 65Zn uptake, but dexamethasone additions resulted in increased 65Zn accumulation in the cells. Effects on 65Zn were shown both in cytosolic and in the membranes/organelles cell fractions. HPLC chromatography in control cells suggested that newly accumulated cytosolic 65Zn was predominantly MT-associated. Dexamethasone-induced 65Zn accumulation could not be related to elevated cellular MT levels, nor were the total cytosolic Zn levels significantly affected. Non-specific attenuations in MT levels (Actinomycin D, cycloheximide and dibu-cAMP) yielded linear relations between cytosolic 65Zn and MT levels, without any change in cytosolic Zn (AAS). Combined addition of Cd and dexamethasone yielded elevated MT levels, but severely reduced total cytosolic Zn and 65Zn concentrations. The results further indicate the non-Zn-specific nature of dexamethasone-action and suggest the relatively easy Zn-complexing and Zn-release of MT. The simultaneous determinations of total cytosolic zinc and cytosolic 65Zn levels showed that the application and sole measurement of radiotracers may yield only one-sided views of what is actually present or occurring in the cells.

Metallothionein concentration in the liver of patients with Wilson's disease, primary biliary cirrhosis, and liver metastasis of colorectal cancer

In patients with primary biliary cirrhosis and Wilson's disease liver copper concentrations become elevated during the evolution of the disorder. The accumulated copper is thought to be detoxified by metallothionein, a protein which binds copper and zinc. In liver metastasis of colorectal cancer, copper and zinc concentrations are usually decreased compared to normal liver tissue, but little is known about the concomitant metallothionein levels. In the present study metallothionein concentrations were determined in archival liver samples from patients with primary biliary cirrhosis and Wilson's disease, and in both normal and malignancy-containing liver samples from patients with metastasis from a colorectal adenocarcinoma. Twenty-seven control liver samples contained 3.98 +/- 1.55 mg metallothionein/g protein. From the 21 liver samples of patients with primary biliary cirrhosis, which had a mean metallothionein concentration of 6.06 +/- 5.03 mg/g protein, 6 were above the highest control level. Liver metallothionein concentrations for the 8 patients with Wilson's disease were significantly elevated (10.98 +/- 6.93 mg/g protein, p < 0.005 vs. controls and p < 0.05 vs. primary biliary cirrhosis). In the 11 liver metastases from colorectal adenocarcinomas metallothionein concentrations (1.17 +/- 0.90 mg/g protein) were significantly (p < 0.005) lower than surrounding normal liver tissue (4.25 +/- 1.75 mg/g protein). We conclude that in primary biliary cirrhosis and Wilson's disease increased liver metallothionein concentrations may detoxify the accumulated copper. Furthermore, liver metastasis of colorectal cancer contains less metallothionein than the surrounding normal liver tissue.

Postnatal changes in subcellular distribution of copper, zinc and metallothionein in the liver of bank vole (Clethrionomys glareolus): a possible involvement of metallothionein and copper in cell proliferation

1. Dramatic interdependent changes in the intracellular concentrations of copper (Cu), zinc (Zn) and metallothionein (MT) in the liver of bank voles during the first 30 days of their life were observed. 2. The post-mitochondrial Cu, Zn and MT (Zn-MT) abruptly decreased between 1 and 3 days following birth but the nuclear MT (Cu-MT) and Cu increased at the same time, suggesting that Cu displaced Zn already bound to MT in the cytoplasm and subsequently the complex Cu-MT was translocated to the nuclei. 3. The nuclear Cu concentration reached the highest level (62-71% of the total tissue Cu) in the period from day 3 to day 20 post-partum, just prior to and during a rapidly growing liver. 4. The data indicate that MT and Cu may be involved in the hepatocyte proliferation.

On metallothionein, cadmium, copper and zinc relationships in the liver and kidney of adult rats

1. A short-term exposure of adult Wistar rats to Cu (50 micrograms/ml) and Cd (10.0 micrograms/ml drinking water) caused significant changes in the subcellular concentrations of Cd, Cu, Zn and metallothionein (MT) in the liver and kidney; the concentrations were close to the physiological values, however. 2. To establish a relationship between these changes in the subcellular concentrations of Cd, Cu, Zn and the level of MT in the post-mitochondrial fraction of the liver and kidney, the analytical data (N = 42) were subjected to the multiple regression analysis. 3. The analysis showed that MT synthesis in the liver was principally induced by small amounts of Cd (0.32-1.4 micrograms/g wet wt) whereas in the kidney a level of MT in the post-mitochondrial fraction correlated positively with the renal Cd and Cu, as well as with the level of this protein in the liver. 4. The above results together with the positive correlation between the level of MT in the post-mitochondrial fraction and the concentration of Cu in this fraction, as well as the fact that under normal physiological conditions the capacity of MT (beta-domain) in the liver and kidney was sufficient to bind 50-100% of the total post-mitochondrial Cu suggest that MT, first induced by small amounts of Cd, may be involved in the metabolism of Cu.

Metallothionein biodegradation in rat hepatoma cells: a compartmental analysis aided 35S-radiotracer study

Disappearance rates, synthesis and biodegradation of rat HTC cell metallothioneins (MT) were examined by measurements of [35S]MT, and expressed by their rate constants in experiments carried out under steady-state conditions, with physiological doses of zinc and copper. Overall rates of disappearance of [35S]MT did not obey first-order kinetics, apparently due to the presence of chemically and/or spatially distinguishable MT (sub)pools. Application of compartmental analysis yielded results indicating that: (a) MT in copper-treated cells is stabler than MT in zinc-treated cells, (b) apparent half-lives for MT disappearance are 22-25 h under the conditions as described, (c) addition of 0.1 mM chloroquine reduces the overall rate of MT disappearance by 25%, (d) total MT should be regarded as significantly consisting of at least two MT sub-forms, i.e., Apo-MT and M-MT and/or cytosolic MT and lysosomal MT, each being depleted and replenished at different rates, (e) mean half-lives for total MT, based on actual degradation rates, were 3-7 h, (f) addition of 0.1 mM chloroquine resulted in both increased synthesis and increased degradation of non-lysosomal MT, the latter probably due to free amino acid depletion in the cells, and (g) MT behaviour may be best examined by combination of tracer experiments (35S-labeled amino acids), simultaneous determination of MT levels in all (sub)MT pools, and application of compartmental analysis.

Metallothionein, copper and zinc in fetal and neonatal human liver: changes during development

Total and cytosolic zinc (Zn) and copper (Cu), cytosolic metallothionein (MT) and the Cu-load of MT were investigated in fetal (22, 24 and 32 gestational weeks) and neonatal (2-15 months) human liver. Whereas the fraction of cytosolic Zn remained constant at 66% of the total independent of the stage of development, the fraction of cytosolic Cu increased from 26% in preterm liver to about 100% within 12 months postnatally. The MT content was higher in fetal than in neonatal liver. There was a linear correlation (r = 0.996) between cytosolic MT and Zn in both fetal and neonatal liver but not between MT and Cu. In contrast to fetal liver, the Cu-load of MT in neonatal liver seems to be determined by the Zn/Cu ratio in the cytosol. The results suggest that MT is involved in the regulation of Cu and Zn metabolism during fetal and neonatal development.