Hepatic Metallothionein Levels Research Articles

The effect of orally administered melatonin on tissue accumulation and toxicity of cadmium in mice

The aim of this study was to determine whether an oral administration of melatonin, a known antioxidant, free radical scavenger and metal chelator, influences tissue accumulation and toxicity of cadmium (Cd) in mice exposed subchronically to the metal. The animals received drinking water containing 50 μg Cd/mL only or with additional 2, 4 or 6 μg/mL melatonin for 8 weeks. Melatonin co-treatment brought about a dose-dependent decrease in the renal, hepatic and intestinal Cd concentrations, and the renal and hepatic metallothionein levels followed a pattern similar to that of the Cd accumulation. Histopathological changes occurred only in the kidneys (glomerular swelling and focal tubular degeneration) in all mice from the Cd alone group. In mice co-treated with melatonin, only slight (2 μg/mL melatonin) or no damage (4 and 6 μg/mL melatonin) was seen. The Cd and melatonin treatments did not affect renal lipid peroxidation and iron concentration. These data indicate that orally administered melatonin together with Cd reduces tissue accumulation of this metal; in particular, the reduction of renal Cd accumulation by melatonin is probably responsible for the prevention of Cd-induced injury in this organ.

Augmented hepatic injury followed by impaired regeneration in metallothionein-I/II knockout mice after treatment with thioacetamide

A previous study (Oliver, J.R., Mara, T.W., Cherian, M.G. 2005. Impaired hepatic regeneration in metallothionein-I/II knockout mice after partial hepatectomy. Exp. Biol. Med. 230, 61-67) has shown an impairment of liver regeneration following partial hepatectomy (PH) in metallothionein (MT)-I and MT-II gene knockout (MT-null) mice, thus suggesting a requirement for MT in cellular growth. The present study was undertaken to investigate whether MT may play a similar role in hepatic injury and regeneration after acute treatment with thioacetamide (TAA). Hepatotoxicity of TAA is caused by the generation of oxidative stress. TAA was injected ip to both wild-type (WT) and MT-null mice. Mice were killed at 6, 12, 24, 48, 60, and 72 h after injection of TAA (125 mg/kg) or 48 h after injection of saline (vehicle control), and different parameters of hepatic injury were measured. The levels of hepatic lipid peroxidation were increased at 12 h in both types of mice; however, lipid peroxidation was significantly less in WT mice than MT-null mice at 48 h after injection of TAA. Analysis of hepatic glutathione (GSH) levels after TAA injection showed depletion of GSH at 12 h in WT mice and at 6 h in MT-null mice; however, significantly more GSH was depleted early (6-24 h) in MT-null mice than WT mice. An increase in hepatic iron (Fe) levels was observed in both types of mice after injection of TAA, but Fe levels were significantly higher in MT-null mice than WT mice at 6-60 h. The levels of hepatic copper (Cu) and zinc (Zn) were significantly higher in WT mice than MT-null mice at 6-60 h for Cu, and at 24 h and 60 h for Zn, respectively. Histopathological examination showed hemorrhagic necrosis in the liver of both types of mice at 12-72 h, with hepatic injury being more prominent in MT-null mice than WT mice. The hepatic MT levels were increased in WT mice after injection of TAA, and were highest at 24-72 h. Immunohistochemical staining for MT in WT mice indicated the presence of MT in both nucleus and cytoplasm of hepatocytes at 24-72 h after TAA injection. Cell proliferation, as assessed by immunohistochemical staining for proliferating cell nuclear antigen, was detected mainly in the livers of WT mice at 48-72 h after TAA treatment. Hepatic proliferation index in MT-null mice was very low as compared to WT mice during liver regeneration after injection of TAA. These results show that the liver cells of MT-null mice with no functional MT are unable to regenerate after TAA-induced hepatic injury, demonstrating an important role for MT in cellular regeneration.

Shifts in Relative Tissue δ15N Values in Snowy Egret Nestlings with Dietary Mercury Exposure: A Marker for Increased Protein Degradation

Shifts in tissue nitrogen isotope composition may be a more sensitive general indicator of stress than measurement of high-turnover defensive biomolecules such as metallothionein and glutathione. As a physical resource transmitted along the trophic web, perturbations in protein nitrogen metabolism may also help resolve issues concerning the effects of contaminants on organisms and their consequential hierarchical linkages in ecotoxicology. Snowy egret nestlings (Egretta thula) fed mercury-contaminated diets of constant nitrogen isotope composition exhibited increased relative delta15N values in whole liver (p = 0.0011) and the acid-soluble fraction (ASF) of the liver (p = 0.0005) when compared to nestlings fed a reference diet. When nitrogen isotope data were adjusted for the source term of the diet, liver mercury concentrations corresponded with both whole liver relative 15N enrichment (r2 = 0.79, slope 0.009, p < 0.0001) and relative 15N enrichment in the acid-soluble fraction of the liver (r2 = 0.85, slope 0.026, p < 0.0001). Meanwhile, significant differences were not observed in hepatic levels of the metal-binding peptides metallothionein and glutathione despite a nearly 3-fold difference in liver mercury content. Because increases in tissue delta15N values result from increased rates of protein breakdown relative to synthesis, we propose that the increased relative liver delta15N values reflect a shift in protein metabolism. The relationship between ASF and mercury was significantly stronger (p < 0.0001) than that for whole liver, suggesting that the relationship is driven by an increase in bodily derived amino acids in the acid-soluble, free amino acid pool.

Interferon alpha induction of metallothionein in rat liver is not linked to interleukin-1, interleukin-6, or tumor necrosis factor alpha

Synthesis of metallothionein (MT) is induced by interferon-alpha (IFN-α) in vitro and in vivo. In addition, IFN-α promotes redistribution of zinc (Zn) from the plasma to the liver in mice. However, it is not clear if IFN-α induces hepatic MT synthesis directly or indirectly via liberation of other cytokines. In order to address this issue, we determined hepatic MT levels, Zn concentration in plasma, liver, and urine, and plasma levels interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor-α (TNFα) in rats following intramuscular injection of human IFN-α (1.5 × 10 6 UI/m 2). Animals were housed in metabolic cages and sacrificed at various times after IFN-α administration. Zn concentrations in serum, urine, and hepatic tissue were determined by atomic absorption spectrophotometry. MT protein was measured using the MT silver saturation method and expression of MT-1 and MT-2 mRNA was measured by RT-PCR. Plasma levels of rat IL-1, IL-6, and TNFα were determined using an ELISA method. Hepatic MT levels began to increase at 2 h following IFN-α administration and reached maximum levels at 12 h post-treatment. Induction of MT gene expression was confirmed by increases in MT-1 and MT-2 mRNA levels 6, 12, and 18 h after IFN-α administration. IFN-α treatment also resulted in biphasic increases in hepatic Zn, with levels peaking at 2 h, the time-point when MT levels are first increased, and again at 18 h. Concurrently, there were decreases in serum Zn levels at these time points, suggesting IFN-α induced movement of Zn from the blood to hepatic tissue. The decrease in serum Zn was not due to increased excretion since urinary Zn levels were unaffected following IFN-α treatment. IFN-α administration had no effect on plasma IL-1, IL-6, and TNFα levels. These results show that IFN-α promotes the increase of hepatic MT levels and plasma/liver redistribution directly, without IL-1, IL-6, or TNFα participation.

Impaired Hepatic Regeneration in Metallothionein-I/II Knockout Mice After Partial Hepatectomy

Although the translocation of metallothionein (MT) from cytoplasm to nucleus has been demonstrated in liver during times of high requirement for zinc (fetal development and the neonatal period), the role of MT in cellular growth is not well understood. In this study, a potential role of MT in liver regeneration was investigated in wild type (WT) and MT-I and MT-II gene knockout (MT-null) mice after 35% partial hepatectomy (PH) or sham laparotomy. Hepatic MT levels and proliferation index were measured at 0, 5, 15, 24, 36, 48, and 60 hrs after PH and 48 hrs after sham laparotomy (control). MT levels were increased in WT mice (peak at 24 hrs after PH) and declined to normal levels by 60 hrs after PH. Immunohistochemical staining for MT in WT mice indicated the presence of MT in both nucleus and cytoplasm of hepatocytes at 24 hrs after PH, whereas MT was present mainly in the cytoplasm at 36-60 hrs after PH and 48 hrs after sham laparotomy. Hepatic proliferation index in both WT and MT-null mice, as determined by argyrophilic nucleolar organizing region staining and proliferating cell nuclear antigen immunohistochemical staining, reached a peak at 48 hrs and declined by 60 hrs after PH. Cell proliferation was significantly less in MT-null mice as compared to WT mice during liver regeneration after PH. These results suggest that MT may play a positive role in hepatic regeneration after PH.

Testicular toxicity induced by dietary cadmium is associated with decreased testicular zinc and increased hepatic and renal metallothionein and zinc in the bank vole (Clethrionomys glareolus)

Mechanism of testicular toxicity induced by dietary cadmium (Cd) has been less investigated than that following acute Cd injection. In the present study we characterized testicular injury in a small rodent, the bank vole, exposed subchronically to dietary Cd in a quantity of 0.9 micromol/g, and determined the importance of some factors (Cd accumulation, metallothionein (MT), oxidative stress, and zinc (Zn)) in the injury. Dietary Cd induced moderate histopathological changes (hemorrhage in interstitium, necrosis and apoptosis in seminiferous tubule epithelium) in young (1 month old) bank voles fed, for 6 weeks, Fe-adequate (1.1-1.4 micromol/g) and Fe-enriched (4.5-4.8 micromol/g) diets. In contrast, adult (5 months old) bank voles appeared to be resistant to the toxic effects of dietary Cd, despite the fact that testicular Cd contents were higher and MT levels lower than those in the young animals. The Cd-induced histopathological changes and apoptosis were accompanied by increased testicular lipid peroxidation, decreased testicular Zn concentration and elevated levels of hepatic and renal MT and Zn. Supplemental dietary Zn (1.7-1.8 micromol/g) prevented the Cd-induced testicular Zn depletion and injury. The data indicate that dietary Cd produces testicular lesions indirectly, through decreasing testicular Zn, which seems to be due to the sequestration of this element by the Cd-induced hepatic and renal MT.

Induction of hepatic metallothionein synthesis by endoplasmic reticulum stress in mice

Metallothionein (MT) is a small sulfhydryl-rich protein whose levels are elevated by various inducers of organelle stresses, such as nuclear stress (cisplatin), mitochondrial stress (antimycin A, 2,4-dinitrophenol) and lysosomal stress (paraquat). Although abnormal folding of protein in the endoplasmic reticulum (ER) causes ER stress, induction of MT synthesis by ER stress has never been investigated. In this study, we examined the induction of MT by an inducer of ER stress, tunicamycin (Tun), which induces ER stress by inhibiting N-linked glycosylation of protein in the ER. Administration of Tun (0.5–1.5 mg/kg, sc) increased hepatic MT levels in C57BL/6J mice (3.1-fold). The maximal increase in hepatic MT was observed 48–96 h after the administration of Tun (1.0 mg/kg). Expressions of MT-I, II and glucose-regulated protein 78 (Bip/GRP78), which is a molecular chaperone induced by ER stress, mRNA were also detected by administration of Tun. Thapsigargin (Thap), a generator of ER stress by inhibiting ER Ca 2+-ATPase, also increased both hepatic MT levels and expression of MT-I and -II mRNA. The level of expression of Bip/GRP78 mRNA induced by Tun administration in MT-null mice was greater than that in wild-type mice. Taken together, these findings suggest that inhibitors of ER are potent inducers of MT.

Effects of Iron Overload on Hepatic and Renal Metallothionein Levels in Rats

Metallothionein (MT) is one of the stress proteins induced by various heavy metals and oxidative stress. Although induction by Fe has not been well established, its overload is documented to cause oxidative stress in experimental animals. To investigate alteration in tissue MT levels that were possibly caused by Fe overload, male Wistar rats were fed a diet containing 3.5% Fe(II) fumarate (1.2% as Fe) for up to 21 days. Tissue Fe levels in liver and kidney increased in time-dependent manners up to 7.2 and 2-fold, respectively, by the end of the experiment. Interestingly, plasma Fe levels showed a maximum on day 3, then decreased to the control level. The hepatic MT levels showed a transient decrease on day 3, then turned to increase throughout the experiment period, with the final level higher than that in control animals that fed on a normal diet. MT levels in the kidney decreased to nearly 1/3 of the control on day 3, with the values unchanged thereafter. Although Zn levels in liver, plasma and kidney showed a transient but significant reduction on day 3 of the Fe feeding, they recovered to the control values in the later period. Thus, a time-dependent change in the hepatic MT levels was quite similar to that of the tissue Zn levels. The renal Zn levels could not account for the change in the tissue MT levels, at least in the latter period of the experiment. Hybridization analysis of the MT mRNA in the kidney of Fe-fed rats did not differ from control-diet rats, suggesting Fe feeding would not alter synthetic rates of the renal MT. The turnover rates of the renal MT estimated from a time-dependent alteration after its induction by HgCl2 treatment seemed to be enhanced in Fe-fed rats. Thus, the Fe-induced decrease in the renal MT level could possibly be due to an enhanced turnover rate. Despite the reduced renal MT levels, the Fe-treated rats showed no sign of a renal failure indicated by a stable plasma creatinine levels and sustained increase of body weight, suggesting that the Fe-induced suppression of the renal MT levels would not be one of the toxic effects by this metal. Nevertheless, the HgCl2 injection experiment revealed Fe-fed rats had a slightly higher susceptibility against HgCl2 nephrotoxicity than the control-diet rats.

Classical Conditioning of Metallothionein Synthesis in Mice

To clarify the role of metallothionein (MT), an anti-stress protein, induced by psychological stress, we carried out an experiment to determine whether hepatic MT synthesis induced by restraint stress can be classically conditioned by an olfactory odor cue of camphor. Mice were conditioned by exposure to the odor of camphor 1 hr before restraint stress and partly during restraint stress. Although exposure to the odor of camphor did not elevate hepatic MT levels in itself, the odor stimuli significantly elevated hepatic MT levels in mice conditioned for 3 days. The results indicate that MT synthesis is induced by an association of the central nervous system with psychological stress.

Antioxidant property of metallothionein in fasted mice

Metallothionein (MT) is a low-molecular-weight and sulfur-rich protein that is induced by not only heavy metals but also physiological stresses such as fasting and restraint stresses. Although MT plays a role as a radical scavenger and a regulator of metabolism of metals, the biological function of MT induced by fasting stress has not been elucidated. In this study, we investigated the antioxidative role of MT in fasted mice. In fasted mice, the lipid peroxidation level of the liver was elevated by 24-h fasting stress, and pre-induction of hepatic MT by Zn diminished hepatic lipid peroxidation. Although 24-h fasting stress induced MT synthesis in the liver, other antioxidants such as catalase, manganese-superoxide dismutase (Mn-SOD), and glutathione peroxidase (GSHPx) were not activated in the liver. Moreover, the hepatic MT level was still elevated by fasting stress after seven cycles of repetition of alternate fasting and feeding every 24 h, but the activities of catalase, Mn-SOD and GSHPx were unchanged. These results indicate that MT induced by fasting stress plays partly as an antioxidant.

Hepatic metallothionein in patients with chronic hepatitis C: relationship with severity of liver disease and response to treatment

Objectives Reactive oxygen species may be involved in the pathogenesis of chronic hepatitis C virus infection. Metallothionein (MT) is an essential protein for the protection of cells against reactive oxygen species. The aim of this prospective study was to assess the influence of the hepatic level and cellular distribution of MT in hepatitis C virus (HCV) infection and in the liver disease outcome. Methods In liver biopsy samples of 32 patients with chronic HCV infection and of 12 control subjects, quantification of MT was performed by radioimmunoassay, MT, interleukin (IL)-1 and -6, and tumor necrosis factor (INF)–α mRNA by reverse transcription–polymerase chain reaction (PCR) and cellular distribution by immunohistochemistry. Results In HCV-infected patients, MT liver protein level was 3-fold lower than in control specimens. A significant inverse linear regression between MT protein or mRNA expression and the Histological Activity Index, the necroinflammatory grade, and the stage of fibrosis was observed. MT immunostaining was located in the nucleus and cytoplasm in hepatocytes of control subjects, whereas it was mainly cytoplasmic in HCV-infected patients. Before interferon (IFN) therapy, the hepatic MT level in patients that were nonsustained responders was half that of sustained responders. Intrahepatic IL-6 and MT were simultaneously down-regulated, but no correlation was found between MT and intrahepatic cytokine mRNA expression in patients with chronic HCV infection. Conclusions This study shows that hepatic MT expression could reflect the severity of chronic HCV infection and could be one of the factors associated with a favorable clinical outcome in the response to interferon therapy.

Effect of lead on ALA-D activity, metallothionein levels, and lipid peroxidation in blood, kidney, and liver of the toadfish Halobatrachus didactylus

The effects of lead (Pb) on ALA-D activity, metallothionein (MT) levels, and lipid peroxidation in liver, kidney, and blood of the toadfish Halobatrachus didactylus were investigated. A time-course experiment was performed with sampling on days 0, 2, 5, and 7 following intraperitoneal Pb injection. This indicated a rank order for lead concentration of kidney>liver>blood in fish exposed to Pb. No significant variation of ALA-D activity was observed in liver and kidney while in blood, a slight decrease of ALA-D activity was found but this was not attributed to acute metal stress. Hepatic and renal MT levels were both affected in different ways by metal uptake. The progressive decrease of MDA concentration in the liver and the lack of a clear induction in kidney suggested the hypothesis that Pb is not a good inductor of lipid peroxidation. The histological and histochemical results demonstrated degenerative effects of lead accumulation on the tissues and the activation of lysosomal responses to induced stress.

Protective role of metallothionein (I/II) against pathological damage and apoptosis induced by dimethylarsinic acid.

To better clarify the main target organs of dimethylarsinic acid toxicity and the role of metallothionein (MTs) in modifying dimethylarsinic acid (DMAA) toxicity. MT-I/II null (MT(-/-)) mice and the corresponding wild-type mice (MT(+/+)), six in each group, were exposed to DMAA (0-750 mg/kg body weight) by a single oral injection. Twenty four hours later, the lungs, livers and kidneys were collected and undergone pathological analysis, induction of apoptotic cells as determined by TUNEL and MT concentration was detected by radio-immunoassay. Remarkable pathological lesions were observed at the doses ranging from 350 to 750 mg/kg body weight in the lungs, livers and kidneys and MT(+/+) mice exhibited a relatively slight destruction when compared with that in dose matched MT(-/-) mice. The number of apoptotic cells was increased in a dose dependent manner in the lungs and livers in both types of mice. DMAA produced more necrotic cells rather than apoptotic cells at the highest dose of 750 mg/kg, however, no significant increase was observed in the kidney. Hepatic MT level in MT(+/+) mice was significantly increased by DMAA in a dose-dependent manner and there was no detectable amount of hepatic MT in untreated MT(-/-) mice. DMAA treatment can lead to the induction of apoptosis and pathological damage in both types of mice. MT exhibits a protective effect against DMAA toxicity.

Copper kinetics and hepatic metallothionein levels in the frog Rana ridibunda, after exposure to CuCl2.

Adult female frogs Rana ridibunda were exposed to 50 and 100 ppm of Cu (as CuCl2) dissolved in water for 5, 15 and 30 days. We measured the Cu content in the liver, kidneys, ventral skin, and large intestine. Hepatic metallothionein (MT) was also measured and we identified by elution the type of proteins bound to copper. Gross morphological characteristics of the frogs were not affected by Cu accumulation. Cu uptake took place first across the skin, then accumulated first in the large intestine, and then in the liver which was continuously accumulating Cu at all exposure concentrations and times. The highest concentration of the metal was recorded in the kidneys at 30 days and 100 ppm exposure. It appears that the kidneys act as the secondary route of Cu detoxification, probably after a Cu overload of liver. The concentration of hepatic MT increased with the increase of Cu concentration in liver at the 5th and 15th day of exposure but we observed a decrease by the end of the experiment. Cu was observed in the MT-fraction, and in the high-molecular weight protein fraction.

Enhancement of MT synthesis by leptin in fasted mice

It is known that metallothionein (MT) synthesis occurs in the liver in various stressful situations such as immobilization and fasting. However, the mechanism of MT synthesis in stressful situations is not fully understood. In this study, we examined the involvement of leptin, the obese gene product, in MT synthesis induced by fasting stress. Despite an increase in hepatic MT levels induced by 24-hr fasting in wild-type mice, both wild-type and MT-null mice showed decreases in plasma leptin levels after 24 hr of fasting. Hepatic MT levels increased to levels comparable with that in control mice in ICR, C3H, 129Sv and Balb/c mice fasted for 24 hr, and plasma leptin levels decreased significantly. Repetition of fasting and feeding in turn every 24 hr caused a gradual decrease in hepatic MT levels after the fasting period. In contrast, the reduced plasma leptin levels increased after the fasting period with repetition of fasting-feeding cycles. The findings indicate that there is an adaptation to starvation. On the other hand, subcutaneous leptin infusion in fasted mice via an osmotic pump resulted in increases in hepatic MT levels compared to the levels in vehicle-treated mice after 24 hr of fasting. Only leptin infusion had no effect on hepatic MT levels. These results suggest that MT synthesis in fasting stress is not correlated with decrease in plasma leptin levels but that leptin itself is a potent inducer of MT in a fasting situation.

Metallothionein in liver of eels Anguilla anguilla from the Thames Estuary: an indicator of environmental quality?

The purpose of this study was to examine the role of the cysteine-rich protein metallothionein (MT) in the detoxification and metabolism of metals in livers of eels Anguilla anguilla from the Thames Estuary, and to assess the value of MT measurements in environmental monitoring. Hepatic MT levels and associated metal concentrations were determined in A. anguilla collected on three occasions during 1998 at sites along the tidal Thames (from freshwater to the sea) and also from a reference site (Tamar Estuary) in southwest England. MT was present at basal levels of 2 mg g −1 dry weight (dw), predominantly in association with the essential metals Cu and Zn. MT concentrations were variable within each eel ‘population’ but were generally highest (up to 11 mg g −1 in individual eels) at the more contaminated upper- and mid-estuarine sites in the Thames (e.g. Brentford and Kew). Lowest MT levels were those in eels from Blythe Sands at the mouth of the estuary. Season, sex, reproductive status and salinity may have influenced MT levels to some extent, although metals were the most significant factor. Hepatic MT concentrations were highly correlated with associated metal burdens (Zn, Cu, Ag and Cd),—notably reflecting Cu and Ag enrichment in the upper- and mid-estuary. With the exception of Zn, metals in the supernatant fraction of eel livers were primarily associated with MT. Proportions of Cu, Ag and Cd bound to MT increased as a function of accumulated metal burdens, with no indication of saturation. Thus, despite causing induction of MT, excess bioavailable Cu, Ag and Cd appear to be successfully detoxified in eels over the range of environmental contamination encountered along the Thames Estuary. Paradoxically, it may be argued from conventional doctrine that the presence of raised levels of MT, at upstream sites, constitutes a response to contamination and, by definition, signals that the fish are affected by metals; however, obvious signs of deleterious effects were not detected. Superficially, from liver MT data, it would seem that eel populations have become biochemically adapted to metal contamination. The approach tested here has proved viable in helping to interpret trends in bioavailability and the toxicological significance of accumulated metal burdens in Thames eels. A. anguilla is a common inhabitant of estuarine and fresh waters throughout Europe, and related species occur world wide. Therefore, determination of hepatic MT (and associated metals) in eels could be useful for monitoring responses to metal exposure and environmental quality on a much broader basis. Ideally these determinations should be performed in tandem with other sublethal-effects measurements to maximise information.

Glucocorticoids Suppress the Inflammation-Mediated Tolerance to Acute Toxicity of Cadmium in Mice

Several compounds have been shown to cause acute toxicity to cadmium (Cd). The mechanism of tolerance to Cd toxicity induced by glucocorticoids or by inflammation involves induction of metallothionein (MT) synthesis via glucocorticoid response elements or by inflammatory cytokines. We have demonstrated previously that the synthetic glucocorticoid dexamethasone suppresses inflammation-mediated induction of hepatic MT synthesis. Here we investigated the effect of glucocorticoid on tolerance to Cd induced by inflammation in mice. The LD50 of Cd for mice with induced inflammation by injection with turpentine oil (Tur-mice) was higher than the LD50 in control mice. Pretreatment of Tur-mice with dexamethasone to the Tur-mice (Dex+Tur-mice) resulted in a decrease in LD50 after Cd treatment. A significant increase in plasma alanine aminotransferase and aspartate aminotransferase levels in the Dex+Tur-mice was observed at lower doses of Cd than in the Tur-mice and at higher doses of Cd than in control mice. Dexamethasone did not suppress tolerance to cadmium toxicity in the testes of the Tur-mice. Pretreatment of Tur-mice with dexamethasone resulted in suppression of both plasma interleukin (IL)-6 elevation and in suppression of hepatic MT levels when induced by inflammation but not when induced by Cd. These data suggest that suppression of tolerance to Cd toxicity induced by glucocorticoid may involve hepatic MT synthesis mediated by inflammatory cytokines, such as IL-6. We suggest that the inflammatory response can modulate Cd toxicity by induction of MT by inflammatory cytokines.

Hepatic and renal metallothionein induction by an oral equimolar dose of zinc, cadmium or mercury in mice

The hepatic and the renal subcellular distribution of zinc, cadmium or mercury and induction of tissue metallothionein (MT) at 24, 48 and 72 h following an oral equimolar dose (15 μmol metal/kg) of zinc (II) chloride, cadmium (II) chloride or mercury (II) chloride in male albino mice were investigated. There was a moderate increase in hepatic and renal zinc levels mainly in their nuclear mitochondrial fraction (NMF) 24 h post zinc chloride administration. Subsequently, the hepatic zinc increased and the renal zinc declined with time. The zinc-induced hepatic MT level was maximum at 48 h, which decreased slightly thereafter, while there was no marked increase in renal MT level at any time interval. The cadmium was equally distributed in liver and kidney more in their supernatant cytosol fraction (SCF) than in their NMF at 24 h after a dose of cadmium chloride. The cadmium levels showed a decreasing trend in hepatic fractions and an increasing trend in renal fractions with time. The cadmium-induced hepatic and renal MT were substantial at 24 h post cadmium administration, the former decreased thereafter while the latter enhanced at 48 h before declining. The accumulation of mercury in kidney was 1.5 times that in liver, which was localised more in their SCF than in their NMF at 24 h in response to a dose of mercuric chloride. The mercury levels of hepatic and renal subcellular fractions started declining after 24 h and at 72 h they were significantly lower. The induction of hepatic and renal MT was maximum at 24 h after mercuric chloride administration, which declined thereafter concomitant with the decrease in their mercury levels. However, the MT levels in both the organs remained considerably higher than in normal animals at 72 h post exposure. The results show that the accumulation of metal in liver and kidney follows the order: Hg>Cd>Zn and the induction of MT follows Hg>Cd>Zn in liver and Cd>Hg>Zn in kidney. The alterations in zinc and copper homeostasis were more marked in liver than in kidney and follows the order: Hg>Cd>Zn.

Effect of exercise training on metallothionein levels of hypertensive rats

Because oxidative stress may be involved in arterial hypertension by affecting the balance between relaxing and contracting factors of vascular smooth muscle, the training-induced adaptation of antioxidant defenses could be implicated in the antihypertensive effect of chronic exercise. It has been suggested that metallothionein (MT), a metal-binding protein, plays an antioxidant role in mammals. The aim of this experiment was to study whether chronic exercise (swimming) influences both the development of arterial hypertension in spontaneously hypertensive rats (SHR) and the modification of MT levels. Male SHR and Wistar Kyoto (WKY) rats as control were trained to swim 1 h.d-1 5 d.wk-1 for 8 wk and sacrificed 72 h after the last exercise period. MT and total thiol levels were then measured. Exercise training 1) reduced systolic blood pressure and heart rate in both SHR WKY rats, and 2) was associated with a decrease in hepatic and cardiac MT levels; there was an increase in the aortic MT amounts in exercised SHR only. No modifications were noted in the gastrocnemius muscle or kidneys. In exercised animals, total thiols were lower in the liver but not in kidneys. Chronic exercise induced a reduction in arterial hypertension development in SHR rats and an adaptation of the MT levels in cardiac, hepatic, and aortic tissues. Further experiments are needed to pinpoint the role of the MT in these two cases in which oxidative stress occurs.

Induction of hepatic metallothioneins in tumor-bearing IL-6-null mice.

Interleukin-6 (IL-6) has been thought to play a key role in the induction of hepatic metallothionein (MT) synthesis in tumor-bearing animals. In order to clarify the role of IL-6 and to distinguish its effect from those of other cytokines, we inoculated IL-6-null and B6J129Sv (wild-type control) mice SC with 1 x 10(7) Ehrlich carcinoma cells and examined tumor growth, hepatic MT, and serum cytokines. We have found that tumor growth was followed by an increase of hepatic MT in both IL-6-null and wild-type mice and that the two strains of mice had a similar hepatic MT induction followed by zinc accumulation in the liver. These results could be explained by our finding that tumor-bearing IL-6-null mice had a high level of tumor-secreted IL-6 in the blood. In conclusion, by utilizing tumor-bearing IL-6-null mice, we have demonstrated that IL-6 secreted from the tumor cells is responsible for the tumor-evoked increase of hepatic MT level.