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

The Severity of Interstitial Inflammation in the Renal Parenchyma of Albino Rats Is Subjected to the Dose of Heavy Metals

Aim

This study aimed to determine the relationship between irreversible morphological changes in the renal interstitium and the duration of exposure to heavy metals such as copper in albino rats.

Materials and methods

An experimental research design was used to conduct this study from November 2019 to May 2020. All experiments were performed in the Department of Pathology of the Services Institute of Medical Sciences, University of Health Sciences (UHS) (animal house), Lahore, Pakistan. A total of 30 albino rats equally divided into three groups were included in the study. Group I (control) was given tap water and a typical rodent pellet diet. Groups II and III (experimental) were fed with copper (heavy metal) at a dose of 0.15 and 0.30 mg/kg body weight, respectively, for 18 weeks on alternate days. At the end of the experiment, the kidneys were extracted from the rats, stained with hematoxylin and eosin, and processed for histological observation. Renal histopathological changes were evaluated in terms of edema, inflammation, and fibrosis.

Results

The collected data were analyzed using the Chi-square test, with p < 0.05 considered significant. Renal histopathology in terms of interstitium showed that edema, inflammation, and fibrosis were significantly different in all groups. In Group I, none of the rats had edema, inflammation, and fibrosis, while in Groups II and III, these characteristics were observed; the difference was significant between the experimental and control groups.

Conclusions

Heavy metals, such as copper, can induce renal parenchymal changes in a dose-dependent manner, resulting in edema, fibrosis, and inflammation.

Arsenic bioaccumulation and biotransformation in aquatic organisms

Arsenic exists universally in freshwater and marine environments, threatening the survival of aquatic organisms and human health. To elucidate arsenic bioaccumulation and biotransformation processes in aquatic organisms, this review evaluates the dissolved uptake, dietary assimilation, biotransformation, and elimination of arsenic in aquatic organisms and discusses the major factors influencing these processes. Environmental factors such as phosphorus concentration, pH, salinity, and dissolved organic matter influence arsenic absorption from aquatic systems, whereas ingestion rate, gut passage time, and gut environment affect the assimilation of arsenic from foodstuffs. Arsenic bioaccumulation and biotransformation mechanisms differ depending on specific arsenic species and the involved aquatic organism. Although some enzymes engaged in arsenic biotransformation are known, deciphering the complicated synthesis and degradation pathway of arsenobetaine remains a challenge. The elimination of arsenic involves many processes, such as fecal excretion, renal elimination, molting, and reproductive processes. This review facilitates our understanding of the environmental behavior and biological fate of arsenic and contributes to regulation of the environmental risk posed by arsenic pollution.

The Potential of Bone Marrow Stem Cells to Correct Liver Dysfunction in a Mouse Model of Wilson's Disease

Metabolic liver diseases are excellent targets for correction using novel stem cell, hepatocyte, and gene therapies. In this study, the use of bone marrow stem cell transplantation to correct liver disease in the toxic milk (tx) mouse, a murine model for Wilson's disease, was evaluated. Preconditioning with sublethal irradiation, dietary copper loading, and the influence of cell transplantation sites were assessed. Recipient tx mice were sublethally irradiated (4 Gy) prior to transplantation with bone marrow stem cells harvested from normal congenic (DL) littermates. Of 46 transplanted tx mice, 11 demonstrated genotypic repopulation in the liver. Sublethal irradiation was found to be essential for donor cell engraftment and liver repopulation. Dietary copper loading did not improve cell engraftment and repopulation results. Both intravenously and intrasplenically transplanted cells produced similar repopulation successes. Direct evidence of functionality and disease correction following liver repopulation was observed in the 11 mice where liver copper levels were significantly reduced when compared with mice with no liver repopulation. The reversal of copper loading with bone marrow cells is similar to the level of correction seen when normal congenic liver cells are used. Transplantation of bone marrow cells partially corrects the metabolic phenotype in a mouse model for Wilson's disease.

Origin, Function, and Fate of Metallothionein in Human Blood

Toxic heavy metals, toxic organic compounds, reactive oxygen species (ROS), infections, and temperature are well-known metallothionein (MT) inducers in human blood. The current review aims to summarize synthesis, function, and fate of human blood MT in response to the known MT inducers. Part of the MTs that are synthesized in different organs such as the liver, kidney, and spleen is transported and stored in different blood cells and in plasma. Cells of the circulatory system also synthesize MT. From the circulation, MT returns to the kidney where the metal-bound MTs are degraded to release the metal ion that in turn induces MT expression therein. The blood MTs play important roles in metal detoxification, transportation, and storage. By neutralizing ROS, MTs protect blood cells from oxidative stress-induced cytotoxicity and genotoxicity. Arguably, MTs are also involved in immune suppression. Given the permeating distribution of blood MT throughout the body as well as its diverse role in the protection against harmful environmental factors and in metal homeostasis, MT could be better recognized as a major public health protein.

The Physiological Roles of Extracellular Metallothionein

Metallothionein (MT) is a low-molecular-weight protein with a number of roles to play in cellular homeostasis. MT is synthesized as a consequence of a variety of cellular stressors, and has been found in both intracellular compartments and in extracellular spaces. The intracellular pool of this cysteine-rich protein can act as a reservoir of essential heavy metals, as a scavenger of reactive oxygen and nitrogen species, as an antagonist of toxic metals and organic molecules, and as a regulator of transcription factor activity. The presence of MT outside of cells due to the Influence of stressors suggests that this protein may make important contributions as a “danger signal” that influences the management of responses to cellular damage. While conventional wisdom has held that extracellular MT is the result of cell death or leakage from stressed cells, there are numerous examples of selective release of proteins by nontraditional mechanisms, including stress response proteins. This suggests that MT may similarly be selectively released, and that the pool of extracellular MT represents an important regulator of various cellular functions. For example, extracellular MT has effects both on the severity of autoimmune disease, and on the development of adaptive immune functions. Extracellular MT may operate as a chemotactic factor that governs the trafficking of inflammatory cells that move to resolve damaged tissues, as a counter to extracellular oxidant-mediated damage, and as a signal that influences the functional behavior of wounded cells. A thorough understanding of the mechanisms of MT release from cells, the conditions under which MT is released to the extracellular environment, and the ways in which MT Interacts with sensitive cells may both illuminate our understanding of an important control mechanism that operates in stressful conditions, and should indicate new opportunities for therapeutic management via the manipulation of this pool of extracellular MT.

Decreased erythrocyte CCS content is a biomarker of copper overload in rats

Copper (Cu) is an essential trace metal that is toxic in excess. It is therefore important to be able to accurately assess Cu deficiency or overload. Cu chaperone for Cu/Zn superoxide dismutase (CCS) protein expression is elevated in tissues of Cu-deficient animals. Increased CCS content in erythrocytes is particularly sensitive to decreased Cu status. Given the lack of a non-invasive, sensitive and specific biomarker for the assessment of Cu excess, we investigated whether CCS expression in erythrocytes reflects Cu overload. Rats were fed diets containing normal or high levels of Cu for 13 weeks. Diets contained 6.3 +/- 0.6 (Cu-N), 985 +/- 14 (Cu-1000) or 1944 +/- 19 (Cu-2000) mg Cu/kg diet. Rats showed a variable response to the high Cu diets. Some rats showed severe Cu toxicity, while other rats showed no visible signs of toxicity and grew normally. Also, some rats had high levels of Cu in liver, whereas others had liver Cu concentrations within the normal range. Erythrocyte CCS protein expression was 30% lower in Cu-2000 rats compared to Cu-N rats (P < 0.05). Notably, only rats that accumulated high levels of Cu in liver had lower erythrocyte CCS (47% reduction, P < 0.05) compared to rats fed normal levels of Cu. Together, these data indicate that decreased erythrocyte CCS content is associated with Cu overload in rats and should be evaluated further as a potential biomarker for assessing Cu excess in humans.

The zinc/thiolate redox biochemistry of metallothionein and the control of zinc ion fluctuations in cell signaling

Free zinc ions are potent effectors of proteins. Their tightly controlled fluctuations ("zinc signals") in the picomolar range of concentrations modulate cellular signaling pathways. Sulfur (cysteine) donors generate redox-active coordination environments in proteins for the redox-inert zinc ion and make it possible for redox signals to induce zinc signals. Amplitudes of zinc signals are determined by the cellular zinc buffering capacity, which itself is redox-sensitive. In part by interfering with zinc and redox buffering, reactive species, drugs, toxins, and metal ions can elicit zinc signals that initiate physiological and pathobiochemical changes or lead to cellular injury when free zinc ions are sustained at higher concentrations. These interactions establish redox-inert zinc as an important factor in redox signaling. At the center of zinc/redox signaling are the zinc/thiolate clusters of metallothionein. They can transduce zinc and redox signals and thereby attenuate or amplify these signals.

Lipid raft-dependent endocytosis of metallothionein in HepG2 cells

Human hepatocellular carcinoma (HepG2) cells take up metallothionein (MT) by endocytosis. MT co-localizes with albumin but not with transferrin, indicating uptake via a non-classical pathway rather than via clathrin-mediated endocytosis. A lipid raft-dependent uptake is indicated by pravastatin inhibition of cholesterol synthesis and methyl-beta-cyclodextrin inhibition of cholesterol translocation to the plasma membrane, reducing MT uptake by 29% and 69%, respectively. Subcellular fractionation after MT uptake reveals significant amounts of MT in vesicular fractions including lysosomes but virtually no MT in the cytosol. Metals bound to MT are released into the cytosol, however. The findings define a pathway for cellular metal acquisition. Together with results from other studies demonstrating secretion of MT from different cells and the presence of MT in extracellular fluids, the results suggest a function of MT in intercellular communication.

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.

Chronic exposure of HepG2 cells to excess copper results in depletion of glutathione and induction of metallothionein

Metallothionein (MT) and reduced glutathione (GSH) play an important role in the intracellular handling of copper by preventing the generation and favouring the removal of copper-derived free radicals. The present study addressed the changes in MT and GSH that follow chronic (2 or 5 weeks) exposure of human hepatoblastoma cells (HepG2) to excess copper. Copper treatment (100 microM, 2 weeks) led to a 28-fold elevation in intracellular copper. Concomitantly, cells exhibited a seven-fold increase in total MT and an increment in its saturation with copper from 45 to 86%. Around 38% of copper in the cytosolic fraction could be accounted for by MT. GSH equivalents were substantially lowered (to 37% of basal levels) in treated cells, with only part of it being accounted for by an increase in GSSG. Copper-treatment induced no changes in catalase or GSH-peroxidase activities but it was associated with a small reduction in SOD (20%) and GSH-reductase (26%) activities. Copper-loaded cells did not differ from controls in their basal oxidative tone; however, when exposed to tert-butylhydroperoxide they exhibited a markedly greater susceptibility to undergo both oxidative stress and cell lysis. It is proposed that chronic exposure of HepG2 cells to excess copper is accompanied by "adaptive changes" in GSH and MT metabolism that would render cells substantially more susceptibility to undergo oxidative stress-related cytotoxicity.

Effect of age and sex on liver damage due to excess dietary copper in Fischer 344 rats

OBJECTIVE

The aim of this study was to investigate the morphologic and biochemical effects of excess dietary copper in young and adult rats of different sex.

METHODS

Adult Fischer 344 male and female rats were given a diet containing 1500 ppm copper for 18 weeks. Young male and female rats were fed a similar copper-loaded diet from birth until 16 weeks of age. Age- and sex-matched control rats were fed a normal rodent diet (<10 ppm copper). Serum liver enzyme activity was determined in all rats. Livers were sampled for histology, histochemistry (rhodanine), immunohistochemical detection of metallothionein and copper analysis by atomic absorption spectrophotometry. Hepatic metallothionein and zinc concentrations were measured in adult rats.

RESULTS

Excess dietary copper caused substantial liver injury, as evidenced by morphologic changes and increased activity of serum ALT, GGT, and SDH. All copper-loaded rats had significantly (p< 0.05) increased hepatic copper concentrations compared to controls. However, young copper-loaded rats accumulated more hepatic copper, had more severe liver changes, and had higher serum liver enzyme activities than adult rats. Histologic changes in copper-loaded rats consisted of multifocal hepatitis and widespread single-cell necrosis. Cytoplasmic copper was detected histochemically in centroacinar zone 1 (portal) and mid-zone in copper-loaded rats. Immunoreactivity for metallothionein was prominent in necrotic hepatocytes and within inflammatory foci in copper-loaded rats. However, differences in hepatic metallothionein concentrations were not detected between adult copper-loaded and control rats.

CONCLUSIONS

Young Fischer 344 rats are more susceptible than adults to copper-induced liver injury.

Metallothionein gene expression and secretion in white adipose tissue

White adipose tissue (WAT) has been examined to determine whether the gene encoding metallothionein (MT), a low-molecular-weight stress response protein, is expressed in the tissue and whether MT may be a secretory product of adipocytes. The MT-1 gene was expressed in epididymal WAT, with MT-1 mRNA levels being similar in lean and obese (ob/ob) mice. MT-1 mRNA was found in each of the main adipose tissue sites (epididymal, perirenal, omental, subcutaneous), and there was no major difference between depots. Separation of adipocytes from the stromal-vascular fraction of WAT indicated that the MT gene (MT-1 and MT-2) was expressed in adipocytes themselves. Treatment of mice with zinc had no effect on MT-1 mRNA levels in WAT, despite strong induction of MT-1 expression in the liver. MT-1 gene expression in WAT was also unaltered by fasting or norepinephrine. However, administration of a beta(3)-adrenoceptor agonist, BRL-35153A, led to a significant increase in MT-1 mRNA. On differentiation of fibroblastic preadipocytes to adipocytes in primary culture, MT was detected in the medium, suggesting that the protein may be secreted from WAT. It is concluded that WAT may be a significant site of MT production; within adipocytes, MT could play an antioxidant role in protecting fatty acids from damage.

Genes expressed in the mouse pituitary corticotrope AtT-20/D-16v tumor cell line

The pituitary corticotrope AtT-20 stable cell line has been used as a model system to study peptide secretion, glucocorticoid regulation, and several other processes. In order to better understand this model cell line, a phage cDNA library was generated from AtT-20/D-16v cell mRNA and cDNA sequences were obtained for 317 clones representing 203 known genes and 48 novel cDNAs. The sequencing results revealed the prevalence of the mouse leukemia virus in this cell line and also identified a number of putatively secreted molecules that were not previously recognized as being secreted from AtT-20/D-16v cells or pituitary corticotropes. Nine completely novel cDNAs and 39 cDNAs homologous to known ESTs were also identified. A listing of other genes known to be expressed in AtT-20/D-16v cells is also provided.

Identification of a novel copper-binding protein from the liver of Indian childhood cirrhosis: purification and physicochemical characterization [corrected]

A novel copper-binding protein was identified in the liver supernatant (100,000 x g) of Indian childhood cirrhosis (ICC), purified to apparent homogeneity and characterized [corrected]. Purified major copper-binding protein (MCuBP) is solely responsible for binding about 35% of the total supernatant copper. Elution profile of ICC liver supernatant on Sephadex G-75 column chromatography showed three peaks. About 60% of the total supernatant copper was resolved in peak II, whereas zinc content was insignificant in this peak. But peak II was almost missing in a gel elution profile of control liver supernatant. The control group included cases of various liver diseases viz. neonatal hepatitis, septicemia, and mixed nodular cirrhosis. Copper-binding proteins of peak II further purified on ion-exchange chromatography and elution profile showed that peak II was a MCuBP with high copper-binding capacity (10 g atoms/mol of native protein). SDS-PAGE of this protein also revealed the existence of a single band with molecular mass of about 50 kD. UV spectra of MCuBP showed the maximal absorbance at 254 nm. Unlike the classical metallothionein, the amino acid composition of MCuBP revealed the presence of aromatic amino acids and higher content of glutamic acid and aspartic acid followed by glycine and serine. The ratio (0.3) of basic amino acids to acidic amino acids strongly indicates that it is an acidic protein. The cysteine content in this protein was insignificant, which further corroborates the possibility that the acidic amino acids might be prominent candidates for binding copper. Thus, the 50-kD MCuBP apparently makes a major contribution to the total copper-binding activity in ICC liver cytosol and may play a significant role in hepatic intracellular copper accumulation.

Effect of zinc supplementation on metallothionein, copper, and zinc concentration in various tissues of copper-loaded rats

The present study was designed to investigate the effects of Zn administration on metallothionein concentrations in the liver, kidney, and intestine of copper-loaded rats. Male CD rats were fed a diet containing 12 mg Cu and 67 mg Zn/kg body wt. They were divided into either acute or chronic experimental protocols. Rats undergoing acute experiments received daily ip injections of either Cu (3 mg/kg body wt) or Zn (10 mg/kg body wt) for 3 d. Chronic experiments were carried out on rats receiving Cu ip injections on d 1, 2, 3, 10, 17, and 24, Cu injections plus a Zn-supplemented diet containing 5 g Zn/kg solid diet, or a Zn-supplemented diet alone. Rats injected Zn or Cu had increased MT concentrations in liver and kidney. Zn produced the most important effects and the liver was the most responsive organ. Rats fed a Zn-supplemented diet had significantly higher MT concentrations in liver and intestine with respect to controls. Increased MT synthesis in the liver may contribute to copper detoxification; the hypothesis of copper entrapment in enterocytes cannot be confirmed.

Biliary excretion of copper in Fischer rats treated with copper salt and in Long-Evans cinnamon (LEC) rats with an inherently abnormal copper metabolism

Increased biliary Cu excretion was found in Fischer rats injected with Cu. The biliary Cu was located at the void (large-molecule region) and total (small-molecule region) volume of a Sephadex G-75 column. The most Cu was found in the total volume. The two Cu peaks comigrated with absorbance at 280 nm. Although the bile from Cu-untreated Fischer rats did not show Cu absorbance in the total volume, absorbance at 280 nm was also found in this region. Even though Long-Evans Cinnamon (LEC) rats deposited a gross amount of Cu (194.0 +/- 27.8 micrograms/g liver) in the liver, they conversely showed reduced Cu excretion into the bile. LEC bile did not show Cu absorbance but rather absorbance at 280 nm in the total volume. Therefore, it seems unlikely that the small molecules found in the Sephadex G-75 regulate biliary Cu excretion in Cu-loaded rats, although the molecules bind to Cu. When the bile from Cu-untreated Fischer and LEC rats was incubated with CuCl2 solution, the most Cu was recovered in the total volume of this column. Our results suggest that reduced biliary Cu excretion in LEC rats is not related to the small molecules, and that Cu cannot be excreted in the form of macromolecules in rats to decrease Cu from the Cu-loaded liver.

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.

Mechanisms of metal transport across liver cell plasma membranes

The liver's pivotal role in the homeostasis of essential trace metals and detoxification of exogenous metals is attributed to its ability to efficiently extract metals from plasma, metabolize, store, and redistribute them in various forms either into bile or back into the bloodstream. Bidirectional transport across the sinusoidal plasma membrane allows the liver to control plasma concentrations and therefore availability to other tissues. In contrast, transport across the canalicular membrane is largely, but not exclusively, unidirectional and is a major excretory pathway. Although each metal has relatively distinct hepatic transport characteristics, some generalizations can be made. First, movement of metals from plasma to bile follows primarily a transcellular route. The roles of the paracellular pathway and of ductular secretion appear minimal. Second, intracellular binding proteins and in particular metallothionein play only indirect roles in transmembrane flux. The amounts of metallothionein normally secreted into plasma and bile are quite small and cannot account for total metal efflux. Third, metals traverse liver cell plasma membranes largely by facilitated diffusion, and by fluid-phase, adsorptive, and receptor-mediated endocytosis/exocytosis. There is currently no evidence for primary active transport. Because of the high rate of hepatocellular membrane turnover, metal transport via endocytic vesicles probably makes a larger contribution than previously recognized. Finally, there is significant overlap in substrate specificity on the putative membrane carriers for the essential trace metals. For example, zinc and copper share many transport characteristics and apparently compete for at least one common transport pathway. Similarly, canalicular transport of five of the metals discussed in this overview (Cu, Zn, Cd, Hg, and Pb) is linked to biliary GSH excretion. These metals may be transported as GSH complexes by the canalicular glutathione transport system(s). Unfortunately, none of the putative membrane carrier proteins have been studied at the subcellular or molecular level. Our knowledge of their biochemical properties is rudimentary and rests almost entirely on indirect evidence obtained in vivo or in intact cell systems. The challenge for the future is to isolate and characterize these putative metal carriers, and to determine how they are functionally regulated.

The protective role of metallothionein in copper-overload: II. Transport and excretion of immunoreactive MT-1 in blood, bile and urine of copper-loaded rats

The regulation of copper homeostasis in copper overloaded animals occurs by excretion of excess of the metal in bile and urine, which may be facilitated by metallothionein (MT) a copper binding protein. The role of MT in the mobilisation and excretion of copper excess has been studied in copper-loaded rats during the development of tolerance. Young male Wistar rats were fed a high copper (1 g/kg) diet for 16 weeks during which period they were killed after prior collection of bile, blood and urine for analysis for copper and immunoreactive MT-1. In addition bile was separated chromatographically and the eluant fractions were assessed likewise for copper and MT-1. Biliary excretion of copper and MT-1 rose to a maximum after 6 weeks, falling subsequently as the rats became copper tolerant. Early increases in circulating copper and MT-1 occurred likewise but whereas MT-1 fell subsequently during the recovery period, serum copper remained elevated. By contrast, urinary copper and MT-1 maintained an increased output throughout. Chromatographic separation of bile revealed the presence of a range of immunoreactive MT-1 degradation products. It was concluded that the close correspondence between bile and serum MT reflected their hepatic derivation and implicated liver MT as an export protein in the early stages of copper overload. By contrast, urine MT, maintained independently of circulating MT levels, established the active secretory participation of the kidney in promoting the continued depletion of excess copper.

Histochemical and immunocytochemical evaluation of copper and metallothionein in the liver and kidney of copper-loaded rats

Histochemical methods do not always show a good correlation with analytical measurement of copper content and consequently immunoreactive staining techniques for metallothionein (MT) have recently been employed for the differential diagnosis of copper-associated diseases. This study compares histochemical with immunocytochemical methods for the assessment of copper status. Male rats were fed a high copper (1 g/kg) diet for 16 weeks and killed sequentially during this period. The livers and kidneys were analysed for copper and zinc (atomic absorption spectrophotometry), and sections were stained with rubeanic acid and rhodanine for copper and for immunoreactive MT using the DNP localization system. Immunoreactive stains for MT corresponded better with copper content than histochemical stains and were more sensitive, albeit less selective, indicators of copper accumulation. Moreover, major differences in intracellular staining were apparent between the two methods, attributed to differences in copper binding and microcompartmentalization of metal.

Urinary excretion of metallothionein-I and its degradation product in rats treated with cadmium, copper, zinc or mercury

The metallothionein-I (MT-I) content of urine following administration of cadmium (Cd), copper (Cu), mercury (Hg) or zinc (Zn) to rats was determined by radioimmunoassay. Urinary excretion of MT-I was increased significantly after injection of each of these metals. Fractionation of urine from Cd-treated rats on Sephadex G-50 showed a single immunoreactive component corresponding to native MT-I, whereas in urine from Cu, Zn or Hg-treated rats 2 immunoreactive components corresponding to MT-I and a possible degradation production were observed. Since a comparable low molecular weight component corresponding to this degradation product was not detected to the same extent on fractionation of plasma from Cu-exposed rat, it seemed to be derived from degradation of MT in the kidney.

Metallothionein immunoreactivity in the liver and kidney of copper injected rats

Adult male rats were injected intraperitoneally with copper sulphate in physiological saline (3 mg copper/kg body wt). Metallothionein-I (MT-I) levels in liver, kidney, plasma and red blood cells were measured by radioimmunoassay (RIA), prior to the injection and after 7, 16 and 24 h. Copper and zinc levels in liver and kidneys were also monitored. Concentrations of MT-I in liver and kidneys showed a rapid increase and remained elevated for 24 h. Copper concentrations also increased in both tissues but zinc levels remained constant in the kidney and rose only slightly in the liver. MT-I levels increased gradually in plasma but decreased in the red blood cells. Immunochemistry of liver and kidney, using the direct peroxidase technique with antiserum to rat MT-I, revealed an increase in staining in both tissues after copper administration, consistent with the RIA results. The change in distribution of immunoreactive material with time after copper injection indicates a role for MT in the sequestration and excretion of copper in acutely loaded animals.

Cellular mechanisms of toxicity and tolerance in the copper-loaded rat. II. Pathogenesis of copper toxicity in the liver

The distribution of copper has been studied in the liver of the copper-loaded rat at the ultrastructural level by X-ray electron probe microanalysis in order to clarify the pathogenesis of copper-induced damage. Male rats fed a high copper diet (1500 ppm) for 16 weeks were killed at intervals; their livers were removed and fixed in 4% paraformaldehyde and 2% glutaraldehyde for electron microscopy and were analyzed for copper by AA spectrophotometry. Three different forms of lysosomes were identified with respect to their morphology and X-ray emission profiles: Type I lysosomes appeared early and contained iron and zinc in addition to markedly elevated copper peaks, whereas later appearing Type II lysosomes included sulfur and phosphorus in addition to copper. Type III lysosomes were associated with the recovery period and contained much reduced elemental residue. Degenerative changes were not observed in any of the three types of lysosomes. Copper and other elemental residues, including sulfur, were also identified within the hepatic parenchymal cell nuclei and by contrast were associated with irreversible nuclear damage. Nuclear copper is directly injurious to this organelle and responsible for the subsequent cell death whereas copper contained within lysosomes is apparently innocuous.

Metalloforms of metallothionein induced by parenteral copper: the influence of route of administration

Previous results regarding the two metalloforms of MT which accumulate in chick liver following the parenteral administration (ip) of copper were discussed. One metalloform, which is exclusively zinc, was suggested to reflect the marked accumulation of hepatic zinc following copper injection. The present report shows that there is a marked difference in hepatic zinc accumulation if copper is administered iv. Under these conditions there is virtually no change in hepatic zinc and thus MT produced under these conditions appears to contain only copper. We suggest the the changes in zinc metabolism as effected by copper when given intraperitoneally reflect a secondary response analogous to that observed when iron is similarly administered.

Metallothionein metabolism in the liver and kidney of the streptozotocin-diabetic rat

1. Elevated levels of metallothionein (MT)-I and -II were identified in the liver and kidney of insulin-deficient diabetic rats. 2. The relative rate of MT synthesis and the turnover of cytoplasmic MT were both accelerated in the liver of diabetic rats. 3. The rate of synthesis of MT, but not its cytoplasmic turnover, was increased in diabetic kidney. 4. Maximal relative rates of MT synthesis in liver and kidney were first observed at 4 and 10 days, respectively, after inducing the diabetic condition. 5. The altered metabolism of hepatic MT in diabetic rats was attributed primarily to disturbances in endocrine status, while the altered metabolism of renal MT was largely due to accumulation of excessive dietary copper in the kidney.