Induction of hepatic metallothionein I in tumour-bearing mice

[Heavy metal responses of the human metallothionein isoform genes]

Metallothioneins (MTs) are proteins known to be involved in defense mechanisms against heavy metals and reactive oxygen species. In human, more than ten MT isoform genes have been identified, in contrast to much fewer isoforms in other mammalian species. The increased number of isoforms in human may have some biological significance; for example, isoforms may have been functionally differentiated to deal with various environmental factors in the evolutional process. However, we know little about the functions of the individual MT isoforms. To clarify functional differences between human MT isoforms, we developed a method to determine individual isoform mRNA levels using real-time polymerase chain reaction (PCR), and studied responses of the isoform genes against heavy metals (Zn, Cd, Cu) and As in HeLa cells. These metals induced all MT isoforms except for MT-1A by Cu, though their induced levels were different. Furthermore, these metals preferentially induced isoforms MT-2A and MT-1X suggesting that these isoforms may be important in protecting from their cytotoxicity.

An improved diagnostic method for chronic hepatic disorder: analyses of metallothionein isoforms and trace metals in the liver of patients with hepatocellular carcinoma as determined by capillary zone electrophoresis and inductively coupled plasma-mass spectrometry

It is desirable to diagnose hepatocellular carcinoma (HCC) in the early stages during its development since its treatment is usually difficult. We previously proposed a new diagnostic method that made use of the total metallothionein (MT), zinc (Zn), and copper (Cu) concentrations in the liver of the HCC patients. We recently found that MT-1 is involved in the metabolism or detoxification of toxic metals, such as cadmium; on the other hand, MT-2 is responsible for the homeostasis of essential metals such as copper, in experimental models such as Long Evans Cinnamon (LEC) rats. In order to device a better diagnostic method than the one we proposed previously, in this study, we newly propose an improved method that includes the discriminative determination data regarding the MT isomers, namely, MT-1 and MT-2, in the liver of patients with or without HCC as compared with the total MT level. The total MT and Zn concentrations in the HCC patients were confirmed to be significantly lower than those in patients without hepatic disorders (Ctrl). In contrast, Cu concentrations of the HCC patients were higher than those of the Ctrl patients. In addition, in the juxta-tumor portion with HCC, MT-1 concentrations were significantly higher than those of MT-2. In contrast, the MT-1 concentrations in the tumor portion were significantly lower than that in the juxta-tumor portion. In addition, MT-1/MT-2 ratio in the tumor portion was significantly lower than that of the juxta-tumor portion. By using parameters such as concentrations of Cu, Zn, total MT, and MT isomers, we performed the multivariate discriminative analysis (MDA). The results suggest that the concentrations of MT isomers change depending on the progress of the tumor, and information on MT isomers and trace elements is very useful in determining the stage of the chronic hepatic disorder.

Comparison of viral vectors: gene transfer efficiency and tissue specificity in a bladder cancer model

PURPOSE

Gene transfer efficiency and specific cell targeting of vectors is a major obstacle in preclinical studies of gene therapy for malignant disease. Previous attempts at gene transfer in bladder cancer models have resulted in variable urothelial and tumor transgene expression after intravesical administration of recombinant viral vectors. In the current study we compared the gene transfer efficiencies of different viral vectors.

MATERIALS AND METHODS

We compared the gene transfer efficiencies of the viral vectors replication-deficient adenovirus, attenuated vaccinia virus (NYVAC) and canarypox virus (ALVAC) in vitro and in an orthotopic murine bladder cancer model. We used beta-galactosidase and firefly luciferase reporter gene expression to compare gene transfer efficiency.

RESULTS

Significantly higher transgene expression was observed in vitro when these cells were infected with NYVAC or ALVAC compared with adenovirus vectors. Similarly the efficiency of adenovirus vectors to transfer genetic material into bladder urothelium and orthotopic bladder tumors was inferior to that of ALVAC and NYVAC vectors, which interestingly appeared to have a predilection to infect the orthotopic tumor. Analysis of the expression of coxsackie-adenovirus receptor using reverse transcriptase-polymerase chain reaction revealed the bladder tumor cell lines were lacking this adenovirus receptor. While adenovirus transferred genes poorly to normal bladder, coxsackie-adenovirus receptor expression was high in bladder tissue.

CONCLUSIONS

The viral vectors examined in these experiments resulted in significantly different gene transfer in the orthotopic bladder cancer model, underscoring the importance of vector selection in gene therapy protocols.

Study of metallothionein using capillary zone electrophoresis

Metallothioneins (MTs) have many different functions in tissues, but the roles of individual isoforms are still not entirely clear. Capillary zone electrophoresis (CZE) is a powerful method for the separation of substances because of its small sample requirement, rapid analysis, high sensitivity and high resolution. The separation and identification of mammalian MT-1, MT-2, and MT-3 and class III MTs by CZE has been reported. Uncoated and polyacrylamide-coated capillary tubes were recently used for the separation of MTs, and a UV detector is usually employed for observations of peaks of MTs. Small changes to the structure and metal components of MTs are reflected in the migration times of the peaks. N-acetylated and non-acetylated MTs can be separated and identified by CZE-mass spectrometry (MS). In addition, metal complexes with MTs can be characterized by CZE-proton-induced X-ray emission (PIXE) detector and CZE-inductively coupled plasma (ICP)-MS. For the quantification of an MT isoform, the peak area of UV absorption is used, but the technique has problems. One is lack of a purified isoform standard. The other is the need for a suitable internal standard substance. CZE-ICP-isotope dilution (ID)-MS is also reported to be able to quantify MT isoforms. CZE combined with other techniques is very effective for separation and quantitative and qualitative analyses of MT isoforms in biological materials.

Determination of metallothionein-1/metallothionein-2 ratios in the mouse liver and pancreas by capillary zone electrophoresis using a polyacrylamide-coated capillary at neutral pH

Metallothionein (MT) isoforms, MT-1 and MT-2, in biological specimens are clearly separated by capillary zone electrophoresis (CZE) using a polyacrylamide-coated capillary. The effectiveness of CZE analysis in the study of MT isoforms in biological specimens is discussed. We did two experiments to determine the MT-1/MT-2 ratio in biological specimens. The ratio of MT-1/MT-2 can be determined by CZE under a neutral pH without any detergents. One of these studies is time-dependent changes of the MT-1/MT-2 ratio in the cytosol of the pancreas and liver in mice after Zn or Cd injection. In the pancreas, both isoforms were detected in the control mice and the ratio of MT-1/MT-2 was below 1.0. When Zn was injected, the maximum peak areas of both isoforms were obtained at 24 h, and the ratios increased over a value of 1.0 at 3 h and peaked at 10 h. However, in the Cd-injected mice, the peak areas of both isoforms increased up to 72 h, and the ratios were below 1.0 up to 72 h. On the contrary, neither isoform was detected in the livers of control mice. The ratios of Zn-injected mice liver were near the value 1.0 between 6 and 72 h, although the areas of both isoforms showed peaks at 48 h. The ratios of Cd-injected mice livers were detected to be over 1.0 from 10 h, but there were no significant difference between 10 and 72 h, and the areas of both isoforms showed peaks at 24 h. The other experiment investigated the ratio in each fraction of cell fractionation. Cell fractionation was done in the livers of Zn-treated mice. Twenty-four hours after the injection, the ratio of MT-1/MT-2 was 0.80+/-0.12 and 1.19+/-0.21 (mean+/-SD) in nuclear and cytosol fractions, respectively. Neither isoform was detected in mitochondrial or microsomal fraction. From the present results, CZE analysis is a suitable method for observation of the ratio of MT-1/MT-2 in biological specimens, and dynamic changes in both isoforms can be detected.

Identification of genes differentially expressed between gastric cancers and normal gastric mucosa with cDNA microarrays

To identify genes whose alterations lead to gastric cancer, gene expression profiles have been obtained from 22 gastric cancer tissues and their surrounding gastric mucosa tissues. A total of 16 genes were differentially expressed in more than 50% of gastric cancer tissues compared with surrounding gastric mucosa tissues. Genes such as HMG-Y, fibroblast collagenase inhibitor, and osteopontin are among those that are overexpressed in over 50% of the gastric cancer tissues. Dihydrodiol dehydrogenase, ribonuclease A, and glutathione peroxidase are among those genes that are underexpressed in over 50% of the gastric cancer tissues. We identified genes that are associated with clinical phenotypes of patients with gastric cancers. Alpha-II spectrin, Na/K-ATPase and KIAA0111 are those that are enhanced in intestinal type of gastric cancer. Gene such as platelet-endothelial tetraspan antigen 3 was enhanced in highly metastatic gastric cancer tissues.

Relationship between toxicity and cadmium accumulation in rats given low amounts of cadmium chloride or cadmium-polluted rice for 22 months

To clarify toxic effects of long-term oral administration of low dose cadmium (Cd) on the liver and kidney, six groups of female Sprague-Dawley rats were fed a diet containing Cd-polluted rice or CdCl2 at concentrations up to 40 ppm, and killed after 12, 18, and 22 months. With toxicological parameters, including histopathology, there was no evidence of Cd-related hepato-renal toxicity, despite a slight decrease of mean corpuscular volume and mean corpuscular hemoglobin of red blood cells with 40 ppm CdCl2. Dose-dependent accumulation of Cd was observed in the liver and kidneys with peak levels of 130 +/- 42 micrograms/g and 120 +/- 20 micrograms/g, respectively, at 18 months in animals treated with 40 ppm CdCl2. A dose-dependent increase in urinary Cd levels became evident with time. Induction of metallothionein (MT) was also observed in the liver and kidney with a high correlation to the corresponding Cd levels. In the proximal renal tubular epithelia of 40 ppm CdCl2-treated rats at 22 months, prominent accumulation of Cd was observed in secondary lysosomes associated with MT deposits in their exocytotic residual bodies. The results demonstrated that, in contrast to the case with high-dose Cd-administration, renal toxicity is not induced by long-term oral administration of low amounts of Cd, although tissue accumulation does occur. Possible protective mechanisms may be operating.

Experimental observations in the rat on the influence of cadmium on skin wound repair

Wound healing in the skin depends upon the availability of appropriate trace metals as enzyme cofactors and structural components in tissue repair. The present study forms part of a series of experimental investigations to examine the influence of xenobiotic elements with no known nutritional function and which are known to compete with essential trace metals. It was designed to investigate further the importance of trace metals in wound healing as an aid to wound management and to identify mechanisms of nonhealing which constitute a major problem in human medicine. Surgically induced skin wounds in young adult male Wistar rats were exposed topically to 0.2 ml of 0.01, 0.10 or 1.0% cadmium chloride (aq.) daily for up to 10 days. Control wounds received de-ionized water only. Wounds exposed to cadmium chloride at 0.01 or 0.10% healed in a similar fashion to controls and exhibited a comparable histological profile with metallothionein distribution. Wounds receiving 1.0% cadmium chloride failed to heal or fully re-epithelialize within 7 days and animals were humanely killed. They showed a persistent mass of inflammatory cell infiltration, oedema, wound debris and aberrant epidermal cell growth. Metallothionein concentrations in the epidermis and fibroblasts of the papillary dermis increased greatly by 5 days postwounding and remained high through the observation period. Cadmium was identified in the liver, kidney and wound sites. In the wound, 1.0% cadmium chloride induced statistically significant (P > 0.001) changes in local concentrations of zinc and calcium at key stages in the healing process, and as a consequence disturbed the trace metal balance necessary for normal wound repair. Zinc levels were increased twofold after 7 days, but calcium was markedly reduced. Local changes in the distribution of metallothionein indicate interaction of cadmium and trace metal carrier proteins as a probable mechanism for impaired wound healing. The cytotoxicity of cadmium is considered to be largely responsible.

Induction, regulation, degradation, and biological significance of mammalian metallothioneins

MTs are small cysteine-rich metal-binding proteins found in many species and, although there are differences between them, it is of note that they have a great deal of sequence and structural homology. Mammalian MTs are 61 or 62 amino acid polypeptides containing 20 conserved cysteine residues that underpin the binding of metals. The existence of MT across species is indicative of its biological demand, while the conservation of cysteines indicates that these are undoubtedly central to the function of this protein. Four MT isoforms have been found so far, MT-1, MT-2, MT-3, and MT-4, but these also have subtypes with 17 MT genes identified in man, of which 10 are known to be functional. Different cells express different MT isoforms with varying levels of expression perhaps as a result of the different function of each isoform. Even different metals induce and bind to MTs to different extents. Over 40 years of research into MT have yielded much information on this protein, but have failed to assign to it a definitive biological role. The fact that multiple MT isoforms exist, and the great variety of substances and agents that act as inducers, further complicates the search for the biological role of MTs. This article reviews the current knowledge on the biochemistry, induction, regulation, and degradation of this protein in mammals, with a particular emphasis on human MTs. It also considers the possible biological roles of this protein, which include participation in cell proliferation and apoptosis, homeostasis of essential metals, cellular free radical scavenging, and metal detoxification.

Suppression of metallothionein gene expression in a rat hepatoma because of promoter-specific DNA methylation

Metallothionein I can be induced in response to a variety of agents that include heavy metals and oxidative stress. On the contrary, its induction was suppressed in some lymphoid-derived cancer cells. The mechanism of this repression has not been elucidated. Here, we show silencing of MT-I gene in a solid transplanted rat tumor as a result of promoter methylation at all the 21 CpG dinucleotides that span the region from -225 bp to +1 bp. By contrast, none of these CpG dinucleotides were methylated in the livers from the rats bearing the tumor, which was consistent with the efficient induction of the gene in this tissue by zinc sulfate. Genomic footprinting revealed lack of access of the transcriptional activators to the respective cis-acting elements of the methylated MT-I promoter in the hepatoma. The absence of footprinting was not due to inactivation of the metal regulatory transcription factor MTF-1, because it was highly active in the hepatoma. Treatment of the hepatoma bearing rats with 5-azacytidine, a demethylating agent, induced basal as well as heavy metal-activated MT-I gene expression in the hepatoma, implying that methylation was indeed responsible for silencing the gene. Bisulfite genomic sequencing showed significant (>90%) demethylation of CpG dinucleotides spanning MT-I promoter in the hepatoma following treatment with 5-AzaC. The hypermethylation of MT-I promoter was probably caused by significantly higher (as much as 7-fold) level of DNA methyl transferase activity as well as enhanced expression of its gene in the hepatoma relative to the host liver. These data elucidated for the first time the molecular mechanism for the silencing of a highly inducible gene in a solid tumor transplanted in an animal, as compared with the robust induction in the corresponding parental tissue and have discussed the probable reasons for the suppression of this gene in some tumors.

Investigations of urinary cadmium content in patients with urinary bladder carcinoma

In the present paper authors investigated urinary cadmium content in 10 patients with urinary bladder carcinoma using atomic spectrometry. It was found that in 60% of these patients it was increased. These results might indicate an involvement of cadmium in carcinogenesis.

Biodistribution of [64Cu]Cu2+ and variance of metallothionein during tumor treatment by copper

The kinetic distribution patterns of [64Cu]Cu2+ in normal mice and in mice bearing tumors (HepA, ascitic tumor) after i.v. injection were similar. The i.v. injected [64Cu]Cu2+ concentrated into mouse liver first and then went to other organs and tissues, such as kidney and tumor. Most of the [64Cu]Cu2+ injected concentrated into the liver within 4 h, and about 8% of the total [64Cu]Cu2+ injected concentrated into the tumor cells at 24 h after i.v. injection. About 80% and 90% of the soluble [64Cu]Cu in the livers of tumor-bearing mice and normal mice, respectively, existed as [64Cu]CuMT (metallothionein [MT] is a small protein with many cysteine residues) at 4 h after i.v. injection, while about 43% of the soluble [64Cu]Cu2+ in tumor cells combined with MT at 6 h after i.v. injection. After 10 days oral administration of 150 microg/g body weight copper acetate, the concentration of MT in tumor cells reduced sharply, from 316 microg/g tissue to 152 microg/g tissue, while it increased slightly, from 375 microg/g tissue to 439 microg/g tissue, in the livers of tumor-bearing mice (HepA, solid tumor). The results suggest that MT contributes to the metabolism of copper that is localized mainly in the liver after copper administration and that copper can concentrate into mouse tumor cells followed by the reduction of MT in tumor cells.

Zinc depletion suppresses tumor growth in mice

The hypothesis that in tumor-bearing animals an increase of host hepatic zinc metallothionein (Zn-MT) causes a restriction of zinc in the tumor tissue was studied. Three types of tumors were induced in laboratory mice by cell transplant. Tumor growth appears to be inhibited under zinc-deficient conditions, even in cases where zinc deficiency was started after tumor cell transplant. The survival times of tumor-bearing mice were prolonged by administration of cadmium chloride, which induces the synthesis of a combined zinc-cadmium metallothionein derivative in the host liver, but not in the tumor tissue, leading to an increase of hepatic zinc in the treated animals. The uptake of 65Zn by the liver of Cd-treated, tumor bearing mice was significantly higher than that of controls whereas uptake of 65Zn by tumor cells was significantly higher in controls than in the treated animals. These results suggest that restriction of zinc intake suppresses tumor growth.