Metallothionein--aspects related to copper and zinc metabolism

Study of Serum Copper and Zinc Levels and Serum Cu/Zn Ratio among Polish Women with Endometrial Cancer

BACKGROUND

Micronutrients are important components for the homeostasis of the human body. The studies available in the literature of the subject on their impact on the risk of population diseases, including malignant neoplasms, are ambiguous. In this paper, the relationship between Cu and Zn serum levels and the occurrence of endometrial cancer have been analyzed.

METHODS

306 patients (153 test group and 153 control group) matched for age were analyzed for Cu and Zn levels. Microelements levels were determined for sera collected during the hospitalization of patients by means of an inductively coupled plasma mass spectrometry. In addition, the Cu/Zn ratio in the population included in the study was analyzed. Univariable and multivariable analyzes were used to examine the relationship between the factors under study and the incidence of endometrial cancer.

RESULTS

Lower levels of elements were observed in the study group compared with the control group (Cu: 959.39 μg/L vs. 1176.42 μg/L, p < 0.001; Zn: 707.05 μg/L vs. 901.67 μg/L, p < 0.001). A statistically significant relationship with the occurrence of endometrial cancer was observed for Cu and Zn. The patients with the lowest Cu level had a significantly higher occurrence of endometrial cancer compared with reference tertile (OR 8.54; p < 0.001). Similarly, compared with the reference tertile, the patients with the lowest Zn levels had a significantly greater incidence of endometrial cancer (OR 15.0; p < 0.001).

CONCLUSION

The results of the study suggest an association of endometrial cancer occurrence with lower Cu and Zn serum levels.

Re-evaluation of the existing health-based guidance values for copper and exposure assessment from all sources

Copper is an essential micronutrient and also a regulated product used in organic and in conventional farming pest management. Both deficiency and excessive exposure to copper can have adverse health effects. In this Scientific Opinion, the EFSA 2021 harmonised approach for establishing health-based guidance values (HBGVs) for substances that are regulated products and also nutrients was used to resolve the divergent existing HBGVs for copper. The tightly regulated homeostasis prevents toxicity manifestation in the short term, but the development of chronic copper toxicity is dependent on copper homeostasis and its tissue retention. Evidence from Wilson disease suggests that hepatic retention is indicative of potential future and possibly sudden onset of copper toxicity under conditions of continuous intake. Hence, emphasis was placed on copper retention as an early marker of potential adverse effects. The relationships between (a) chronic copper exposure and its retention in the body, particularly the liver, and (b) hepatic copper concentrations and evidence of toxicity were examined. The Scientific Committee (SC) concludes that no retention of copper is expected to occur with intake of 5 mg/day and established an Acceptable Daily Intake (ADI) of 0.07 mg/kg bw. A refined dietary exposure assessment was performed, assessing contribution from dietary and non-dietary sources. Background copper levels are a significant source of copper. The contribution of copper from its use as plant protection product (PPP), food and feed additives or fertilisers is negligible. The use of copper in fertilisers or PPPs contributes to copper accumulation in soil. Infant formula and follow-on formula are important contributors to dietary exposure of copper in infants and toddlers. Contribution from non-oral sources is negligible. Dietary exposure to total copper does not exceed the HBGV in adolescents, adults, elderly and the very elderly. Neither hepatic copper retention nor adverse effects are expected to occur from the estimated copper exposure in children due to higher nutrient requirements related to growth.

Copper and Zinc Feud: Is This Myelodysplasia or Myelodysplastic Syndrome?

We report a case of a 59-year-old male who developed pancytopenia and multiorgan failure attributed to copper deficiency from exogenous consumption of zinc tablets. During the six months preceding his presentation, he had experienced increasing shortness of breath, lightheadedness, and fatigue. Laboratory studies revealed pancytopenia with profound anemia (hemoglobin level 2.8 g/dL) along with evidence of acute kidney injury and acute heart failure; the patient was presumed to have multiorgan failure due to profound anemia. Bone marrow biopsy revealed dyspoiesis suggestive of myelodysplastic syndrome (MDS). There were no cytogenetic abnormalities observed. However, the blood workup analysis found low copper and ceruloplasmin levels, whereas zinc levels were excessively elevated (257 mg/dL). Upon inquiry, the patient reported taking an over-the-counter zinc supplement of an unknown quantity for over a year. After two months of copper treatment, his blood count returned to normal. This case highlights a rare presentation of zinc-induced copper deficiency resulting in pancytopenia and severe anemia-related multiorgan failure. A growing number of hematological disorders are being linked to copper deficiency. Copper deficiency pancytopenia is a reversible condition that often goes unnoticed and can be misdiagnosed as MDS because it has similar hematological characteristics.

Treatment-resistant schizophrenia: focus on the transsulfuration pathway

Treatment-resistant schizophrenia (TRS) is a severe form of schizophrenia. The severity of illness is positively related to homocysteine levels, with high homocysteine levels due to the low activity of the transsulfuration pathway, which metabolizes homocysteine in synthesizing L-cysteine. Glutathione levels are low in schizophrenia, which indicates shortages of L-cysteine and low activity of the transsulfuration pathway. Hydrogen sulfide (H2S) levels are low in schizophrenia. H2S is synthesized by cystathionine β-synthase and cystathionine γ-lyase, which are the two enzymes in the transsulfuration pathway. Iron-sulfur proteins obtain sulfur from L-cysteine. The oxidative phosphorylation (OXPHOS) pathway has various iron-sulfur proteins. With low levels of L-cysteine, iron-sulfur cluster formation will be dysregulated leading to deficits in OXPHOS in schizophrenia. Molybdenum cofactor (MoCo) synthesis requires sulfur, which is obtained from L-cysteine. With low levels of MoCo synthesis, molybdenum-dependent sulfite oxidase (SUOX) will not be synthesized at appropriate levels. SUOX detoxifies sulfite from sulfur-containing amino acids. If sulfites are not detoxified, there can be sulfite toxicity. The transsulfuration pathway metabolizes selenomethionine, whereby selenium from selenomethionine can be used for selenoprotein synthesis. The low activity of the transsulfuration pathway decreases selenoprotein synthesis. Glutathione peroxidase (GPX), with various GPXs being selenoprotein, is low in schizophrenia. The dysregulations of selenoproteins would lead to oxidant stress, which would increase the methylation of genes and histones leading to epigenetic changes in TRS. An add-on treatment to mainline antipsychotics is proposed for TRS that targets the dysregulations of the transsulfuration pathway and the dysregulations of other pathways stemming from the transsulfuration pathway being dysregulated.

Traces matter: Targeted optimization of monoclonal antibody N-glycosylation based on/by implementing automated high-throughput trace element screening

The use of high-throughput systems in cell culture process optimization offers various opportunities in biopharmaceutical process development. Here we describe the potential for acceleration and enhancement of product quality optimization and de novo bioprocess design regarding monoclonal antibody N-glycosylation by using an iterative statistical Design of Experiments (DoE) strategy based on our automated microtiter plate-based system for suspension cell culture. In our example, the combination of an initial screening of trace metal building blocks with a comprehensive DoE-based screening of 13 different trace elemental ions at three concentration levels in one run revealed most effective levers for N-glycan processing and biomass formation. Obtained results served to evaluate optimal concentration ranges and the right supplementation timing of relevant trace elements at shake flask and 2 L bioreactor scale. This setup identified manganese, copper, zinc, and iron as major factors. Manganese and copper acted as inverse key players in N-glycosylation, showing a positive effect of manganese and a negative effect of copper on glycan maturation in a zinc-dependent manner. Zinc and iron similarly improved cell growth and biomass formation. These findings allowed determining optimal concentration ranges for all four trace elements to establish control on desired product quality attributes regarding premature afucosylated and mature galactosylated glycan species. Our results demonstrates the power of combining robotics with DoE screening to enhance product quality optimization and to improve process understanding, thus, enabling targeted product quality control.

A disease-modifying treatment for Alzheimer's disease: focus on the trans-sulfuration pathway

High homocysteine levels in Alzheimer's disease (AD) result from low activity of the trans-sulfuration pathway. Glutathione levels are also low in AD. L-cysteine is required for the synthesis of glutathione. The synthesis of coenzyme A (CoA) requires L-cysteine, which is synthesized via the trans-sulfuration pathway. CoA is required for the synthesis of acetylcholine and appropriate cholinergic neurotransmission. L-cysteine is required for the synthesis of molybdenum-containing proteins. Sulfite oxidase (SUOX), which is a molybdenum-containing protein, could be dysregulated in AD. SUOX detoxifies the sulfites. Glutaminergic neurotransmission could be dysregulated in AD due to low levels of SUOX and high levels of sulfites. L-cysteine provides sulfur for iron-sulfur clusters. Oxidative phosphorylation (OXPHOS) is heavily dependent on iron-sulfur proteins. The decrease in OXPHOS seen in AD could be due to dysregulations of the trans-sulfuration pathway. There is a decrease in aconitase 1 (ACO1) in AD. ACO1 is an iron-sulfur enzyme in the citric acid cycle that upon loss of an iron-sulfur cluster converts to iron regulatory protein 1 (IRP1). With the dysregulation of iron-sulfur cluster formation ACO1 will convert to IRP1 which will decrease the 2-oxglutarate synthesis dysregulating the citric acid cycle and also dysregulating iron metabolism. Selenomethionine is also metabolized by the trans-sulfuration pathway. With the low activity of the trans-sulfuration pathway in AD selenoproteins will be dysregulated in AD. Dysregulation of selenoproteins could lead to oxidant stress in AD. In this article, we propose a novel treatment for AD that addresses dysregulations resulting from low activity of the trans-sulfuration pathway and low L-cysteine.

The Functions of Metamorphic Metallothioneins in Zinc and Copper Metabolism

Recent discoveries in zinc biology provide a new platform for discussing the primary physiological functions of mammalian metallothioneins (MTs) and their exquisite zinc-dependent regulation. It is now understood that the control of cellular zinc homeostasis includes buffering of Zn²⁺ ions at picomolar concentrations, extensive subcellular re-distribution of Zn²⁺, the loading of exocytotic vesicles with zinc species, and the control of Zn²⁺ ion signalling. In parallel, characteristic features of human MTs became known: their graded affinities for Zn²⁺ and the redox activity of their thiolate coordination environments. Unlike the single species that structural models of mammalian MTs describe with a set of seven divalent or eight to twelve monovalent metal ions, MTs are metamorphic. In vivo, they exist as many species differing in redox state and load with different metal ions. The functions of mammalian MTs should no longer be considered elusive or enigmatic because it is now evident that the reactivity and coordination dynamics of MTs with Zn²⁺ and Cu⁺ match the biological requirements for controlling—binding and delivering—these cellular metal ions, thus completing a 60-year search for their functions. MT represents a unique biological principle for buffering the most competitive essential metal ions Zn²⁺ and Cu⁺. How this knowledge translates to the function of other families of MTs awaits further insights into the specifics of how their properties relate to zinc and copper metabolism in other organisms.

Arsenic toxicity to cladocerans isolated and associated with iron: implications for aquatic environments

ABSTRACT Arsenic is an ametal ubiquitous in nature and known by its high toxicity. Many studies have tried to elucidate the arsenic metabolism in the cell and its impact to plants, animals and human health. In aqueous phase, inorganic arsenic is more common and its oxidation state (As III and As V) depends on physical and chemical environmental conditions. The aim of this study was to evaluate toxicity of arsenic to Daphnia similis and Ceriodaphnia silvestrii, isolated and associated with iron. The results showed differences in toxicity of As III and As V to both species. Effective concentration (EC50) mean values were 0.45 mg L-1 (As III) and 0.54 mg L-1 (As V) for D. similis, and 0.44 mg L-1 (As III) and 0.69 mg L-1 (As V) for C. silvestrii. However, As V IC25 mean value was 0.59 mg L-1, indicating that C. silvestrii has mechanisms to reduce arsenic toxicity. On the other hand, when associated with iron at 0.02 and 2.00 mg L-1, EC50 values decreased for D. similis (0.34 and 0.38 mg L-1) as well as C. silvestrii (0.37 and 0.37 mg L-1), showing synergistic effect of these substances.

Metallothioneins I/II expression in rat strains with genetically different susceptibility to experimental autoimmune encephalomyelitis

OBJECTIVES

Compared to the Dark Agouti (DA), the Albino Oxford (AO) rat strain exhibits lower susceptibility to the induction of experimental autoimmune encephalomyelitis (EAE). Here, we investigated the potential contribution of the heavy metal-binding proteins metallothioneins (MTs) I/II to these effects.

METHODS

Rats were immunized with bovine brain homogenate emulsified in complete Freund's adjuvant or only with complete Freund's adjuvant. The expression patterns of MTs mRNA and proteins and tissue concentrations of Zn2+ and Cu2+ were estimated in the brain and in the liver on days 7 and 12 after immunization, by real-time PCR, immunohistochemistry and inductively coupled plasma spectrometry, respectively. Additionally, the hepatic transforming growth factor beta and nuclear factor kappa B immunoreactivities were tested.

RESULTS

Clinical signs of EAE were not induced in AO rats, but they upregulated the expression of MT I/II proteins in the brain (hippocampus and cerebellum) and in the liver, similarly as DA rats. The transcriptional activation of MT-I occurred, however, only in DA rats, which accumulated also more zinc in the brain and in the liver. In contrast, intact AO rats had greater hepatic MT-I mRNA immunoreactivity and more Cu2+ in the hippocampus. Besides, in immunized AO rats a high upregulation of transforming growth factor beta and nuclear factor kappa B immunoreactivities was found in several hepatic structures (vascular endothelium, Kupffer cells and hepatocytes).

CONCLUSIONS

Our data show that AO and DA rats differ in constitutive and inductive MT-I gene expression in the brain and in the liver, as well as in the hepatic cytokine profile, suggesting that these mechanisms may contribute to the discrepancy in the susceptibility to EAE.

Alterations in fear response and spatial memory in pre- and post-natal zinc supplemented rats: remediation by copper

The role of zinc in the nervous system is receiving increased attention. At a time when dietary fortification and supplementation have increased the amount of zinc being consumed, little work has been done on the effects of enhanced zinc on behavior. Both zinc and copper are essential trace minerals that are acquired from the diet; under normal conditions the body protects against zinc overload, but at excessive dosages, copper deficiency has been seen. In order to examine the effect of enhanced metal administration on learning and memory, Sprague Dawley rats were given water supplemented with 10ppm Zn, 10ppm Zn+0.25ppm Cu, or normal lab water, during pre- and post-natal development. Fear conditioning tests at 4months showed significantly higher freezing rates during contextual retention and extinction and cued extinction for rats drinking water supplemented with zinc, suggesting increased anxiety compared to controls raised on lab water. During the MWM task at 9months, zinc-enhanced rats had significantly longer latencies to reach the platform compared to controls. The addition of copper to the zinc supplemented water brought freezing and latency levels closer to that of controls. These data demonstrate the importance of maintaining appropriate intake of both metals simultaneously, and show that long-term supplementation with zinc may cause alterations in memory.

Antioxidants and metallothionein levels in mercury-treated mice

Acute effects of mercury on mouse blood, kidneys, and liver were evaluated. Mice received a single dose of mercuric chloride (HgCl2, 4.6 mg/kg, subcutaneously) for three consecutive days. We investigated the possible beneficial effects of antioxidant therapy (N-acetylcysteine (NAC) and diphenyl diselenide (PhSe)2) compared with the sodium salt of 2,3-dimercapto-1-propanesulfonic acid (DMPS), an effective chelating agent in HgCl2 exposure in mice. We also verified whether metallothionein (MT) induction might be involved in a possible mechanism of protection against HgCl2 poisoning and whether different treatments would modify MT levels and other toxicological parameters. The results demonstrated that HgCl2 exposure significantly inhibited delta-aminolevulinate dehydratase (delta-ALA-D) activity in liver and only DMPS treatment prevented the inhibitory effect. Mercuric chloride caused an increase in renal non-protein thiol groups (NPSH) and none of the treatments modified renal NPSH levels. Urea concentration was increased after HgCl2 exposure. NAC plus (PhSe)2 was partially effective in protecting against the effects of mercury. DMPS and (PhSe)2 were effective in restoring the increment in urea concentration caused by mercury. Thiobarbituric acid-reactive substances (TBARS), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) activities and ascorbic acid levels were not modified after mercury exposure. Mercuric chloride poisoning caused an increase in hepatic and renal MT levels and antioxidant treatments did not modify this parameter. Our data indicated a lack of therapeutic effect of the antioxidants tested.

Metallothionein-1 and -2 expression in cadmium- or arsenic-derived human malignant urothelial cells and tumor heterotransplants and as a prognostic indicator in human bladder cancer

The goal of this study was to determine if the expression of the metallothionein (MT)-1/2 proteins might serve as a biomarker for the development of bladder cancer. A retrospective analysis of MT-1/2 staining was performed on 343 tissue sections from patients referred for the diagnosis of bladder cancer. The specimens were subdivided into six categories: benign, dysplastic, low-grade cancer, high-grade cancer with no evidence of invasion, high-grade cancer with evidence of invasion, and carcinoma in situ. There was no expression of MT-1/2 in benign lesions and low-grade cancers, a low incidence of expression in dysplastic lesions and high-grade cancers with no evidence of muscle invasion, and a significantly increased incidence of MT-1/2 in high-grade cancers that had invaded the underlying matrix. The expression of MT-1/2 varied in intensity from sample to sample and was focal in its expression. It was concluded from these findings that MT-1/2 may be a prognostic marker for cancers that are progressing to invade the underlying stroma of the bladder wall. The expression of MT-1/2 was also determined in a cell culture model of human urothelium that had been malignantly transformed by Cd2+ and As3+ and shown to be capable of tumor formation in nude mice. It was demonstrated that the expression of MT-1/2 in the tumor heterotransplants was similar to the pattern found in archival specimens of high-grade bladder cancers. The MT-1/2 staining in the heterotransplants was focal in pattern, varied in intensity, and highest in the less differentiated cells of the tumor. These findings indicate that the cell culture model may serve to help define the role of MT-1/2 expression in bladder cancer invasion.

Expression of metallothoinein isoform 3 is restricted at the post-transcriptional level in human bladder epithelial cells

This study was designed to define the effect that overexpression of MT-3 would have on a cell culture model of bladder urothelium. Stable and inducible transfection was used to achieve overexpression of the MT-3 gene in the UROtsa cell line. When the UROtsa cells were stably transfected with the MT-3 coding sequence, there was highly elevated expression of MT-3 mRNA, but no MT-3 protein. An inducible vector showed that low basal levels of MT-3 mRNA and protein could be produced, but that induction only increased MT-3 mRNA and not protein. The clones expressing low basal levels of MT-3 protein also had reduced growth rates compared to control cells. Site directed mutagenesis was used to produce an MT-3 coding sequence where the prolines in positions 7 and 9 were converted to threonines. When this altered MT-3 was stably transfected into the UROtsa cells, the cells were able to accumulate the mutated form of the MT-3 protein. These studies show that MT-3 protein expression is inhibited by post-transcriptional control in the urothelial cell. Modifying the MT-3 protein to resemble the MT-1 isoform removes this component of post-transcriptional control and allows accumulation of the mutated MT-3 protein. The altered sequence involved in post-transcriptional control of MT-3 protein expression is the same sequence implicated in the neuronal growth inhibitory activity associated specifically with the MT-3 isoform of the MT gene family.

Evidence for an interaction between p-glycoprotein and cadmium toxicity in cadmium-resistant and -susceptible strains of Drosophila melanogaster

The role of an ATP-dependent membrane protein, p-glycoprotein (pgp), in cadmium toxicity and resistance in Drosophila melanogaster was investigated. Two strains were compared, a wild-type and a cadmium-resistant strain. Verapamil (1, 10, and 100 mciroM) was added to the larval diet of Drosophila in both the presence and the absence of 80 ppm cadmium chloride. Adult emergence of wild-type but not of cadmium-resistant flies was reduced in the presence of cadmium. Verapamil in the larval diet without cadmium had no effect on adult emergence in either strain. Verapamil in the diet spiked with cadmium significantly reduced adult emergence in both strains. This result is indicative of an interaction between the efflux of cadmium and verapamil and demonstrates that pgps have a role in regulating the toxicity of cadmium in Drosophil. These results do not rule out pgps as putative cadmium resistance genes.

Metallothionein isoform 3 and proximal tubule vectorial active transport

BACKGROUND

Metallothionein isoform 3 (MT-3) is expressed in the proximal tubule cells of the human kidney. The goal of the present study was to further characterize the basal expression of MT-3 in the proximal tubule and to determine if MT-3 participates in the maintenance of proximal tubule cell function.

METHODS

Expression of MT-3 mRNA was determined in the intact proximal tubule using microdissection and reverse transcription-polymerase chain reaction (RT-PCR). Basal expression of MT-3 mRNA and protein was determined in cultured human proximal tubule (HPT) cells and an immortalized proximal tubular cell line, HK-2 cells, using RT-PCR and immunoblotting. The MT-3 gene was stably transfected into the HK-2 cell line using the pcDNA3.1/Hygro (+) vector.

RESULTS

MT-3 mRNA was detected in the proximal tubule of the in situ kidney with relative expression in excess to that of the beta-actin housekeeping gene. The mortal HPT cells were shown to express both MT-3 mRNA and protein and to form domes, while immortal HK-2 cells were shown to have no expression of MT-3 mRNA and protein nor to form domes. The stable transfection of MT-3 in HK-2 restored MT-3 expression and dome formation to the HK-2 cells.

CONCLUSIONS

MT-3 mRNA is present in the human proximal tubule, and MT-3 expression is involved in the transport function of a human renal cell line that retains properties of the proximal tubule.

Possible role of metal redistribution, hepatotoxicity and oxidative stress in chelating agents induced hepatic and renal metallothionein in rats

A study was planned to investigate possible role of oxidative stress, hepato- and nephrotoxicity and essential metal redistribution following administration of amino and thiol chelating agents on hepatic and renal metallothionein (MT) and the levels of some metalloenzymes in male rats. Animals were administered 50 mg/kg, intraperitoneally, twice daily for 15 consecutive days; a dose of three amino and four thiol chelators and were sacrificed 24 h after the last dose. The results indicate no evidence of oxidative stress in hepatic and renal tissues of rats administered thiol and amino chelators, except for some marginal changes in the animals treated with calcium disodium ethylenediaminetetraacetic acid (EDTA) and D-penicillamine (DPA). Redistribution of essential metal (particularly zinc), hepato- and nephrotoxicity seems to play a significant role in influencing the MT induction by amino chelators. Redistribution of essential metals may also be playing a significant role in a number of metalloenzymes, especially by amino chelators compared to thiol chelators. It can thus be concluded that toxic effects of chelating agents, including metal redistribution and hepatotoxicity, might be playing a crucial role in the metallothionein induction.

Induction of metallothionein in the liver of carbon tetrachloride intoxicated rats: an immunohistochemical study

Metallothioneins (MTs), are low molecular weight proteins, mainly implicated in metal ion detoxification. In the present study, we investigated the expression of hepatic MT in a rat model of injury and regeneration, induced by carbon tetrachloride (CCl(4)) administration. A single intraperitoneal injection of 1 ml CCl(4)/kg body weight was performed in male Wistar rats, killed at different time points post-administration. The enzymatic activities of aspartate and alanine aminotransferases in serum were determined, in addition to the liver histological findings, to estimate hepatotoxicity. The rate of tritiated thymidine incorporation into hepatic DNA, the enzymatic activity of thymidine kinase in liver tissue and the assessment of the mitotic index in hepatocytes, were used as indices of regeneration. MT was detected immunohistochemically in liver tissue sections. CCl(4) administration caused severe hepatic injury, followed by regeneration. MT expression became prominent as early as 12 h after the administration of CCl(4), in the nuclei of hepatocytes, while at 24 and 36 h intense cytoplasmic staining for MT appeared in the hepatocytes in the vicinity of necrotic areas. The peak of hepatocyte proliferative capacity, occurring at 48 h post-CCl(4) administration coincides with the maximum nuclear and cytoplasmic MT expression. At further time points MT expression presented a decreasing trend. Induction of MT expression was observed in the liver after a single administration of CCl(4), being more prominent at the time of maximum hepatocellular proliferation, participating actively in the replication of hepatocytes.

Metallothionein isoform 3 expression in the human prostate and cancer-derived cell lines

BACKGROUND

Expression of metallothionein isoform 3 (MT-3) was initially reported to be confined to neural tissues. However, it was recently demonstrated that MT-3 is expressed in epithelial cells of the human kidney. This motivated the current examination of the expression of MT-3 in the human prostate.

METHODS

Immunohistochemistry (IHC) was used to localize the expression of MT-3, RT-PCR to determine the expression of MT-3 mRNA, and Western blot analysis to determine the level of MT-3 protein.

RESULTS

Selected epithelial and stromal cells of the normal human prostate were shown to have low levels of MT-3 expression. MT-3 was increased in prostatic intraepithelial neoplasia (PIN) lesions and further increased in a highly variable fashion in prostatic adenocarcinoma. In some adenocarcinomas, MT-3 expression exceeded that of nerve. Three cell culture models of prostate cancer were also shown to variably express MT-3. Restriction enzyme analysis confirmed the expression of MT-3 in the cells and tissues.

CONCLUSIONS

MT-3 is expressed in the normal human prostate, and expression is enhanced and highly variable in PIN lesions and primary prostate cancer cells. The variable nature of MT-3 expression was also noted in commonly utilized prostate cancer cell lines.

Expression of MT-3 protein in the human kidney

The objective of the present study was to determine the expression of MT-3 in the human kidney. To accomplish this, an antibody was generated against a unique 8 amino acid sequence present in MT-3 that is not shared by any other MT family member. Western analysis demonstrated that the resulting antibody reacted with a protein band of approximately 6 kDa, corresponding to the known molecular weight of MT-3. Immunohistochemical staining using this antibody demonstrated reactivity with several epithelial components of the nephron. In the glomerulus, moderate intensity was demonstrated in parietal epithelial cells of Bowman's capsule and in visceral epithelial cells of the glomerular tuft. Proximal convoluted tubule cells exhibited moderate cytoplasmic MT-3 reactivity. Distal tubules showed strong cytoplasmic staining for MT-3, particularly in the medullary rays. In the medulla, MT-3 staining was the most variable, with weak to moderate staining in the medullary collecting ducts and a general absence of staining in the thin loops of Henle and in the transitional epithelium of the renal pelvis. The finding that MT-3 is constitutively expressed in several glomerular and tubular epithelial elements of the human kidney warrants consideration of an expanded role for this protein family in maintaining renal homeostasis.

Brain injury and growth inhibitory factor (GIF)--a minireview

Growth inhibitory factor (GIF) is a small (7 kDa), heat-stable, acidic, hydrophilic metallothionein (MT)-like protein. GIF inhibits the neurotrophic activity in Alzheimer's disease (AD) brain extracts on neonatal rat cortical neurons in culture. GIF has been shown to be drastically reduced and down-regulated in AD brains. In neurodegenerative diseases in humans, GIF expression levels are reduced whereas GFAP expression levels are markedly induced in reactive astrocytes. Both GIF and GIF mRNA are present at high levels in reactive astrocytes following acute experimental brain injury. In chronological observations the level of GIF was found to increase more slowly and remain elevated for longer periods than that of glial fibrillary acidic protein (GFAP). These differential patterns and distribution of GIF and GFAP seem to be important in understanding the mechanism of brain tissue repair. The most important point concerning GIF in AD is not simply the decrease in the level of expression throughout the brain, but the drastic decrease in the level of expression in reactive astrocytes around senile plaques in AD. Although what makes the level of GIF decrease drastically in reactive astrocytes in AD is still unknown, supplements of GIF may be effective for AD, based on a review of current evidence. The processes of tissue repair following acute brain injury are considered to be different from those in AD from the viewpoint of reactive astrocytes.

Heavy metal content (Hg2+, Cd2+, Pb2+) in various body parts: its impact on cholinesterase activity and binding glycoproteins in the grasshopper Aiolopus thalassinus adults

Various toxicological symptoms were observed in Aiolopus thalassinus (Fabr.) adults which resulted from either contaminated soil or from being fed HgCl2-, CdCl2-, and PbCl2-treated diet. Many insects had abnormal wings which were present until the F3 untreated generation. Heavy metals were stored in different body parts, most of Cd2+ and Hg2+ were found in the testes, followed by the gut. Lead was enriched in all organs and body parts of the treated grasshoppers compared to the control. The highest lead concentrations were found in testes, wings, gut, and ovaries. In the treated generation ChE activity was reduced to about 23% compared to the untreated grasshoppers. In contrast to this, lead increased ChE activity to about 14%. In the following F2 untreated adults, ChE activity was normal; no long-term effect was found. In the supernatant of treated adults a Cd-type glycoprotein was found which can bind Cd ions; its MW was determined by electrophoresis and reference proteins at about 14,450 Da.

Metallothionein expression in normal, hyperplastic, and neoplastic thyroid follicular and parafollicular C cells using monoclonal antimetallothionein antibody E9

Metallothioneins (MTs) are a set of ubiquitous low molecular proteins with a high affinity for metal ions, such as zinc, copper, and cadmium. MT overexpression can be induced by these metal ions as well as by other endogenous and exogenous factors. In this study, normal, hyperplastic, and neoplastic thyroid tissues of both follicular and C-cell origin were immuno-histochemically investigated with a monoclonal antibody against I- and II-isoforms of MTs. MT immunoreactivity was demonstrated in the follicular epithelium of 19 normal thyroid glands and in all 32 cases of Graves' disease investigated; 26 of 30 follicular adenomas and 25 of 28 follicular carcinomas showed MT immunoreactivity, whereas only 7 of 20 papillary carcinomas were MT-positive (p < 0.0001 ). In 3 of the 7 positive samples, positivity was restricted to follicular areas of differentation. No MT could be immunolocalized in normal and hyperplastic C cells and medullary thyroid carcinomas (n = 20). In mixed medullary-follicular carcinomas (n = 4), MT staining patterns resembled those seen for thyroglobulin. In anaplastic carcinomas, MTs were mainly immunolocalized in nonspindle cell areas. MT expression in thyroid tumors may reflect the different biological behavior of follicular and papillary carcinomas. Antibodies to MTs may also serve as fairly specific immunohistochemical markers of follicular cell differentiation in thyroid neoplasia.

Influence of thyroparathyroidectomy and thyroxine replacement on Cu and Zn cellular distribution and on the metallothionein level and induction in rats

Thyroid hormones are involved in copper and zinc distribution in rat tissues. We examined the influence of thyroparathyroidectomy (TPTY) and of a replacement therapy by T4 on Cu and Zn organ distribution. MT levels were also measured both in basal conditions and after induction by cadmium. The results confirm that a lack of T4 modified Cu and Zn in serum and tissues. In serum, TPTY increased Cu (+15%) and ceruloplasmin (+18%), and decreased Zn (-18%). In tissues, Cu was altered in liver (+13%), kidney (-24%), heart (-16%) duodenum (-18%), and Zn in liver (+25%) and kidney (-10%). The soluble fractions (100,000 g supernatant) were mainly affected in liver and kidney, and the subcellular fractions in heart and duodenum. MT levels were modified in basal conditions only in liver (+57%) and kidney (-36%). T4 administration partially prevented the effect of TPTY on both elements and MT concentrations. Therefore, no evidence is provided for a direct role of T4 in the metabolism of MT in a way comparable to the effects of glucocorticoids. However, MT could mediate the consequences of TPTY on metal distribution in certain organs, such as liver and kidney.

Effect of methoxyethanol, cyclophosphamide and cadmium on metallothionein levels during prenatal development in the mouse

Three known teratogenic agents--methoxyethanol (ME), cyclophosphamide (CP) and cadmium (Cd)--are possible inducers of metallothionein (MT) in the embryo and/or in the fetus. Their effect on the MT levels of forelimbs, brain and liver during prenatal development and in dam's liver was studied in the mouse to elucidate whether MT could be used as an early biochemical indicator of teratogenicity. Pregnant mice were injected with 2 doses of each teratogen at different days of the middle gestational phase and their embryos and fetuses were obtained thereafter. Quantitative estimation of MT in the S9 from homogenates of the embryo/fetal tissues and organs and maternal liver showed major alterations in the dam's hepatic MT content but only small changes in prenatal MT levels. These results do not support MT as an early indicator of teratogenicity. However, a causal relationship between the maternal MT changes induced by the tested agents and their teratogenic effect could be possible.

Regulation of the isoforms of metallothionein

The objective of this research was to study the regulation of hepatic MT-I and MT-II in rats. Induction of MTs following Cd, Zn, and glucocorticoid treatments was studied in adult rats and the ontogeny of MTs was evaluated in developing rats. The isoforms were quantitated by anion-exchange HPLC and their respective mRNAs were evaluated by Northern blot hybridization with mouse cRNA probes. In untreated adult rat liver, MT-II was more abundant than MT-I. Cd treatment increased MT-I and MT-II to similar concentrations. Low dosages of Zn increased MT-II levels three times higher than MT-I levels, whereas higher dosages increased the isoforms to similar levels. Differences in the degradation of Zn-induced MTs were observed: apparent half-lives for MT-I and MT-II were 12.2 and 21.9 h, respectively. MT-II was the predominant glucocorticoid-inducible isoform. MT-I and MT-II mRNAs increased coordinately after glucocorticoid treatment, but MT-II mRNA was more abundant than MT-I mRNA. In immature rats, MT-I and MT-II were first detected in fetal liver on gestation day 18 and increased to maximum hepatic concentrations during the first week postpartum. Thereafter, MT levels decreased, reaching adult levels by 35 d. In contrast, MT mRNAs reached maximal levels during late gestation that were maintained throughout the first three weeks postpartum. Discoordination between MT mRNA and protein levels is suggestive of translational control of MTs in developing rats. In summary, MT-II is more abundant than MT-I in untreated rats and in rats treated with glucocorticoids or low dosages of zinc. In addition to transcriptional regulations of MTs, translational control of MTs may be important in regulating hepatic MT concentrations, particularly in developing rats, and differences in the degradation of MT-I and MT-II may influence tissue concentrations of the isoforms.

Characterization and development of metallothionein in fetal forelimbs, brain and liver from the mouse

The presence of the low molecular weight protein metallothionein (MT) has been investigated in fetal forelimbs, brain and liver from the mouse with the aim of using the protein as a biochemical marker for the early recognition of potential teratogenic agents in the future. Forelimbs, brain and liver were taken from mouse fetuses at ages ranging from 12 to 18 d. Each type of organ was homogenized and centrifuged at 9000 x g. The analysis of MT in the supernatants (S9) with the Cd-heme saturation method detected in all three cases the presence of a low molecular weight, Cd-binding protein whose concentration increased with the age of the fetus. Analysis of the S9 fractions using gel- and anion exchange-chromatography and polyacrylamide gel electrophoresis demonstrated the existence of a protein analogue to the hepatic MT in forelimbs and brain.

Distribution of 14 elements in various rat tissues following hypophysectomy, thyroparathyroidectomy, adrenalectomy, and castration

The tissue distribution of 14 elements was simultaneously determined in rats 28 d after hypophysectomy (HPY), thyroparathyroidectomy (TPTY), adrenalectomy (ADY), and castration (CTN). The elements Na, K, Ca, Mg, Fe, S, P, Rb, Sr, Mn, Cu, and Zn were investigated in whole blood, plasma, brain, liver, kidney, heart, skeletal muscle, and bone. Additionally Mo was determined in kidney and liver. The following results were obtained: 1) With regard to hormone deficiency: HPY induced the most noticeable variations on all the elements tested owing probably to the direct and indirect effects of adenohypophyseal hormones. ADY led to the expected modification of Na and K but also to a Sr accumulation and a Rb depletion. TPTY induced a sharp decrease in plasma and tissues Ca, an increase in plasma P, but did not disturb the two elements in bone. An increase of Rb in many tissues and of Fe in heart, kidney, and liver were also observed. CTN had little consequences except in bone whose Cu and Fe contents were increased; 2) With regard to element variations: K, Mg, and S underwent little change. Discriminations were revealed between elements such as K and Rb, Ca and Sr, Ca and Mg, and Cu and Zn. The changes of Rb and Sr were consistent with regulatory mechanisms. The accumulation of Fe and Cu in tissues such as liver after HPY, TPTY, and ADY, suggest that the hormonal deficiencies could worsen the hemochromatosis and Wilson's disease; 3) With regard to plasma and tissues: No correlation appeared in element levels between plasma and other tissues. Brain was the least affected and liver, kidney and bone the most.

Effects of adrenalectomy and of adrenal hormones on the tissue distribution of 14 elements in the rat

The effects of adrenalectomy (ADY) and of replacement therapy using a mineralocorticoid, deoxycorticosterone (DOC) and a glucocorticoid, dexamethasone (DEX) on the tissue distribution of elements in the rat, were studied under semichronic conditions. The elements Na, K, Ca, Mg, Fe, S, P, Rb, Sr, Mn, Cu, and Zn were determined in whole blood, plasma, brain, liver, kidney, heart, skeletal muscle, spleen, thymus, and bone. Additionally, Mo was determined in kidney and liver and Ba in bone. ADY modified concentrations of all elements tested. Small changes were observed for K, Mg, Ca, S, and P, whereas much larger changes were noted for Na, Rb, and Sr. Cu, Zn, and Fe were mainly modified in liver and kidney, organs involved in storage and/or elimination. The consequences of ADY were corrected fairly well by DEX for Mg, Mn, Ca, Cu, and Mo; by DOC for Na and K, and by the two corticoids for Zn, Fe, Sr, and Rb. This study revealed that corticoids, mainly glucocorticoids, play an important role in the plasma and tissue balance of elements. It is suggested that these results may have a pathological and clinical significance.

Mechanisms of regulation of rat hepatic metallothionein-I and metallothionein-II levels following administration of zinc

The purpose of this study was to determine the role of transcription, translation, and protein degradation on the accumulation of metallothionein-I (MT-I) and metallothionein-II (MT-II) in rat liver following induction of these proteins by Zn. The time course of MT induction indicated that concentrations of MT-I and MT-II, quantitated by high-performance liquid chromatography, were similar at 6 hr after administration of 1000 mumol Zn/kg (sc), but thereafter the concentration of MT-II was always higher than that of MT-I. By 24 hr after Zn administration, the concentration of MT-II in liver was more than two times that of MT-I. This difference increased with time such that by 96 hr the concentration of MT-II was more than five times that of MT-I. MT-I and MT-II mRNA levels, measured by Northern blot hybridization with mouse cRNA probes, increased coordinately following administration of Zn. MT mRNAs increased to maximum levels 6-9 hr after Zn administration, at which times MT-II mRNA was about two times more abundant than MT-I mRNA. MT mRNA levels remained elevated above control for as long as 36 hr after Zn administration. The relative rates of synthesis for MT-I and MT-II were determined by quantitating incorporation of [35S]cysteine into MTs during a 2-hr period. For both proteins, the maximum relative rates of synthesis were observed 6-9 hr after administration of Zn, in parallel with the increase in mRNA levels. When MT synthesis was at maximal levels, there was approximately two times more [35S]cysteine incorporated into MT-II than MT-I, but at no other times were differences observed. In contrast to MT mRNA levels, MT synthesis returned to control levels by 24 hr after administration of Zn. Half-lives of the isometallothioneins, determined by pulse-labeling experiments, were calculated to be 12.2 +/- 0.8 and 21.9 +/- 3.0 hr for MT-I and MT-II, respectively. Thus, Zn treatment increases transcription of both MT-I and MT-II genes and the synthesis of MT-I and MT-II. However, Zn-induced MT-II is more stable than MT-I. These results suggest that differences in the rate of synthesis and degradation of MT-I and MT-II lead to a greater and more prolonged induction of MT-II following administration of Zn.

Ontogeny and induction of hepatic isometallothioneins in immature rats

It is well established that hepatic concentrations of metallothioneins (MTs) are very high in developing rats. In this study, the ontogeny of hepatic isometallothioneins (MT-I and MT-II) was determined. MTs were separated and quantitated with a high-performance liquid chromatography (HPLC) method. MT-I and MT-II, first detected in fetal liver on gestation Day 18, increased coordinately during late gestation and reached maximum hepatic concentrations of approximately 400 and 500 micrograms/g, respectively, which were maintained from postpartum Days 1 through 7. Thereafter, MT concentrations decreased, reaching concentrations similar to adult levels (approximately 10 micrograms/g liver) between 28 and 35 days of age. MT-II was significantly higher than MT-I in 14- and 21-day-old rats. In 35-day-old rats, MT-I was below the detection limit. MT-I and MT-II mRNA levels were quantitated by Northern blot hybridization with mouse cRNA probes. In contrast to protein concentrations, MT mRNA reached maximal levels during late gestation which were maintained throughout the first 3 weeks postpartum. Additional experiments indicated that Cd (1-30 mumol/kg), Zn (100-3000 mumol/kg), and dexamethasone (0.3-10 mumol/kg) increased hepatic concentrations of MT-I and MT-II and their respective mRNAs in 14-day-old rats, despite the preexisting high levels of protein and mRNA at this time. These results indicate that hepatic concentrations of MT-I and MT-II isoproteins and mRNA, which increase coordinately during fetal development, decline differently during neonatal development. In 14-day-old neonates, MT-I and MT-II genes are responsive to Cd, Zn, and dexamethasone when constitutive levels of both MT mRNA and isoproteins are high.

Metallothionein, cadmium, copper and zinc levels of human and rat tissues

Metallothionein (MT), zinc (Zn), copper (Cu) and cadmium (Cd) were determined in 10 tissues (brain, heart, kidney cortex, liver, lung, muscle, pancreas, small intestine, spleen and stomach) from human autopsies (10 male individuals, mean age 43 +/- 9 years, all smokers) and Wistar rats. The mean tissue concentrations of MT in the human samples varied between 3.8 and 495 micrograms/g wet weight in spleen and kidney cortex, respectively. In most tissues human MT levels were high as compared to rats; particularly in liver and kidney cortex human MT levels exceeded those of rats about 25- and 10-fold, respectively. Positive linear relationships were observed between Zn or Cu and MT in human liver and between Cd and MT in human kidney cortex.

Metallothionein messenger RNA regulation in the mottled mouse and Menkes kinky hair syndrome

Menkes kinky hair syndrome is an X-linked neurodegenerative disorder, causing tissue-specific increases in copper and metallothionein content. A mouse model is provided by hemizygotes for mutant alleles at the X-linked mottled locus. Herein we test the possibility that the primary defect in both species is in metallothionein gene regulation. We show that metallothionein-I messenger RNA (mRNA) (mouse) and metallothionein-II mRNA (human) are elevated in mutant fibroblasts. However, comparable dose-response curves in mutant and control cells are generated when mouse metallothionein-I mRNA concentrations are measured in cells exposed to varying concentrations of cadmium or copper (metallothionein inducers). Furthermore, when mutant and control cells are grown to achieve overlapping intracellular copper concentrations in the two cell types, metallothionein-I (mouse) and metallothionein-II (human) mRNA levels are proportional to the intracellular copper concentrations. Finally, in paired determinations in blotchy hemizygote and littermate kidneys containing comparable copper levels, metallothionein-I mRNA contents are very similar. The observations suggest that elevated intracellular copper in these mutants induces metallothionein synthesis by normal regulatory mechanisms.

Protective function of metallothionein against certain anticancer agents

The possible role of metallothioneins (MT) in the cellular protection against ionizing radiation and alkylating agent cytotoxicity has been investigated by the use of cultured cells with either low or high levels of MT. The cytotoxic activity of the drugs cis-dichlorodiammineplatinum (cis-DDP), chlorambucil and prednimustine was reduced 1,5-3 fold in cells containing high levels of MT, and furthermore about 70% of platinum and 30% chlorambucil was shown to be associated with the protein. Increased resistance was also demonstrated in MT-rich cells during exposure to ionizing radiation. Evidence that MT also may play a role in vivo as a resistance mechanism, was provided in studies of tumors derived from either the MT-rich or MT-poor cells which had been inoculated in nude mice. During treatment of the animals with cis-DDP, the MT-rich tumors exhibited a significant degree of resistance. These results indicate that MT may play an important role in the intrinsic protection of cells against these agents, and raises the question whether it also may be a factor in the acquired resistance of tumors against chemotherapy.

Variations in hepatic metallothionen, zinc and copper levels during an annual reproductive cycle in rainbow trout,Salmo gairdneri

The normal variations in hepatic levels of metallothionein, zinc and copper were studied during an annual reproductive cycle in rainbow trout of both sexes. In female fish, the total hepatic zinc levels closely followed the estradiol-17β and the LSI levels. Hence, the zinc levels rose in September, peaked in December and dropped in January. No distinct peaks were, however, observed in the whole-liver copper content. The hepatic metallothionein levels in female fish began to increase at the onset of exogenous vitellogenesis. Maximum levels were reached after estradiol-17β and LSI levels had dropped in January. In male fish no distinct peaks in either zinc or copper levels were observed. The metallothionein levels increased somewhat during the time of spermatogenesis. It is suggested that metallothionein may regulate the hepatic zinc distribution during the annual reproductive cycle in female rainbow trout, thereby ensuring the organism of a control mechanism to keep the pool of available zinc at an appropriate level.

D-penicillamine induces rat hepatic metallothionein

Intraperitoneal injection of D-Penicillamine (D-PA) at a dose range of 20-500 mg/kg increased rat hepatic but not renal and pancreatic metallothionein (MT). Elevated MT predominantly contained Zn. Maximal induction was obtained 18 h after a single injection of 200 mg D-PA/kg resulting in 148 +/- 18 micrograms MT/g liver which was 16.4-times the control level of 9 +/- 2 micrograms MT/g. At 48 h after injection, MT declined to 18 +/- 9 micrograms MT/g liver. At maximal MT increase the content of total hepatic Zn but not of Cu was elevated. Increased amounts of Zn in liver homogenate, cytosol and MT could be detected approximately 4 h after injection of 200 mg D-PA/kg. Concomitantly there was a decrease in Zn bound to cytosolic non-MT ligands. All Zn changes reversed at 18 h. These data show that already single doses of D-PA cause induction of Zn-thionein in rat liver and lead to synchronous redistribution of Zn from endogenous sources to newly synthesized MT.

Transfer of copper from metallothionein to nonmetallothionein proteins in cultured cells

Copper uptake and distribution with time among cytoplasmic proteins were followed in cultured cells under several conditions: (1) CHO cells, which cannot synthesize metallothioneins, were labeled with(67)Cu in the presence of 100 μM ZnCl2; (2) Cd(r)30F9 cells, which contain some constitutive metallothionein (MT), were labeled in the absence of additional ZnCl2 and; (3) Cd(r)30F9 cells were labeled in the presence of ZnCl2, under which conditions they synthesized additional metallothioneins. The exogenous(67)Cu and ZnCl2, where present, were then removed, and the distributions of(67)Cu among size fractions of the cellular proteins were observed at intervals for 16 h. In addition, a culture identical to condition (3) above was also treated with 100 μM ZnCl2 during the redistribution period. The(67)Cu was initially resolved into three peaks by Sephadex G-75 chromatography: high molecular weight, intermediate molecular weight, and MT. The(67)Cu in the MT fraction decreased with at 1/2 of 10-12 h. In contrast to this, generally, in cells with a higher initial(67)Cu bound to metallothionein, there was a progressive increase in the amount of(67)Cu eluting with the high- and intermediate-molecular-weight fractions. Since no other source of(67)Cu was available, these experiments suggest that copper stored in MT can be transferred to other proteins in these cells.

Zinc secretion in the oviduct of the coturnix quail

The oviduct from laying quail were used to investigate mechanisms of trace mineral secretion and the possible role of metallothionein in this process. Secretion of zinc occurred maximally at pH 5.4, which is close to the normal pH of the oviduct. Secretion occurred to a much greater extent in the isthmus and shell gland than in the magnum, the major protein-secretory section of the oviduct. Intraperitoneal administration of cadmium resulted in a marked reduction in Zn secretion from the oviduct of laying quail. This effect could not be correlated with metallothionein since metallothionein could not be detected in any section of the oviduct in control or Cd-induced quail. Small-molecular-weight metal-binding ligands were present in the isthmus and shell gland, which may play a role in trace mineral mobilization. Histological evaluation by light and elelctron microscopy show that Zn is transported from the smooth muscle cells through the connective tissue matrix in the extracellular space to the epithelial goblet cells. Presumably, Zn and other trace minerals are secreted from the secretory goblet cells into the egg.

Trace element metabolism in the fetus and neonate

The effects of trace metal nutrition on the fetus and neonate have been described. Since very little research has been done with the human fetus and neonate, much of our knowledge must be extrapolated from animal studies. In addition, most of the work centres around the effects of copper and zinc nutrition. Nutritional requirements (when known) for both enteral and total parenteral feeding of certain trace metals, as well as the bioavailability, have been discussed. Finally, methods of assessment of trace metal nutritional status have been discussed. These include direct measurement of metal concentrations and determination of biochemical indicators, such as metal-dependent enzyme activities--both of which are static indicators of nutritional status, and functional assessment of nutritional status which is a dynamic measure of trace metal nutrition and includes tests measuring the effects of metal nutrition on the function of cells, tissues, organs, and the host in general.

Copper malabsorption in coeliac disease

Copper uptake during three hours from an oral test dose of copper sulphate solution giving three mg Cu++, close to the recommended daily dietary intake, was significantly reduced in patients with proximal intestinal disease, compared with normal subjects. Three out of ten patients had abnormal and otherwise unexplained blood counts compatible with the known haematological effects of copper deficiency and were restored to normal levels on a gluten-free diet. Copper deficiency and proximal intestinal disease should be suspected in patients with otherwise unexplained anaemia, especially neutropenia.

Transport and storage of metals

Current understanding of the means by which the trace metals copper, iron, and zinc are transported and stored in the human body is reviewed. Although metal-related inherited metabolic diseases manifest themselves as deficiencies in metalloenzymes, these deficiencies in fact arise from disturbances in the absorption/rejection or transport or storage phases of the metal metabolism. The considerable information available on iron metabolism shows these phases to be closely interrelated with a number of feedback mechanisms operating as controls on the various metabolic stages. Copper and zinc have vastly different roles in their enzymes but, following their close coordination chemistry properties, have similar metabolic routes. Both make use of albumin for transport and of metallothionein at the absorption and hepatic-binding stages. In contrast to iron, copper and zinc have no well-defined storage system; instead they make use of body reserves distributed in various tissues. Our knowledge of the transport and storage systems of the trace metals is still very incomplete. More research is needed on the dynamics of movement of the trace metals between the various body tissues and fluids. Further advances will also come from the study of related metal inherited diseases in other animal species.

Some nutritional aspects of trace metals

A brief outline of the known biochemical roles of manganese and chromium is given before the problems of determining human trace metal status are discussed. The factors predisposing to trace metal deficiency are reviewed but particular emphasis is placed upon those which alter the bioavailability of essential trace metals from natural and synthetic diets. This is illustrated by practical examples which show the importance of investigating the bioavailability of the trace metal content of artificial diets used in paediatric care. The results of such studies highlight the need to assess similarly the adequacy of the trace element composition of the many meat substitutes and extenders available currently. Finally, some aspects of trace metal supplementation of intravenous feeding regimens are described.

Analytical procedures for diagnosis of trace element disorders

Trace elements levels in tissues show changes in various diseases including inborn errors of metabolism. Such changes may be primary or secondary due to stress or diseases of the liver and gastrointestinal tract. Measurement of trace elements in these cases may be essential both for diagnostic and therapeutic purposes. Trace element measurements can also be useful in other areas of clinical interest including nutrition, toxicity and therapy with inorganic pharmaceutical agents. The available techniques for measuring trace elements in tissues are summarized and the various problems of each are discussed.