Induction Of Metallothionein In Liver Research Articles

Role of non-enzymatic antioxidants in stimulation of Metallothionein against metal toxicity

Metallothionein (MT) is a low molecular-weight protein considered to be protective in function. It has been estimated in the liver and kidney of cadmium, mercury, copper and zinc treated rats offered antioxidative protection by selenium (Se), vitamin E and glutathione (GSH). These antioxidants stimulated induction of MT in liver and kidney of metal treated rats. Induction was greater in liver than kidney. α -tocopherol induced maximum synthesis of MT in the liver of mercury treated rats during lipid peroxidation, whereas maximum induction of MT in Cd fed rats was observed after GSH treatment. Minimum accumulation of mercury in comparison to other metals was observed in liver as well as kidney in glutathione treated rats. It is suggested that different metal species induced specific metallothionein(s) that express specific effects. The mechanism for maintaining high levels of MT might result from increased translation and transcription of MT. Present results suggest that these proteins not only scavenge free radicals (FR) but also decrease accumulation of metals in soft tissue.

Cadmium-induced oxidative stress and DNA damage in kidney of pregnant female rats

In the present study, we have investigated the influence of sub-acute treatment with cadmium (Cd) on some parameters indicative of oxidative stress and DNA damage in tissues of pregnant female rats. Pregnant female rats ( n = 6 ) were injected subcutaneously, daily with a dose of cadmium chloride of 3 mg/kg body weight (b.w.) from day 6 to day 19 of pregnancy, and they were allowed to deliver normally. MDA level and GPx, CAT and SOD activities were used as markers of oxidative stress in liver and kidney. The 8-oxo-dG level was measured by the HPLC-EC system. Cd treatment increased MDA (+116%, p < 0.01 ) in kidney. Moreover, Cd treatment also decreased CuZn-SOD (−11%, p < 0.05 ) and GSH level (−52%, p < 0.05 ) in kidney. Treated rats displayed an increase of the liver metallothionein (MT) level. Induction of MT in liver was probably implicated in the detoxification of Cd. The high level of Cd (3 mg/kg) used in the present study is partially neutralized by MT in liver, whereas the free fraction could be implicated in the oxidative stress and DNA oxidation observed in kidney. Cd treatment failed to alter 8-oxodGuo, indicating the absence of DNA oxidation in liver; by contrast, the same treatment increased the 8-oxodGuo level (+51%, p < 0.05 ) in the kidney of pregnant female rats, indicating an oxidative stress associated with DNA damage only in kidney. To cite this article: S. Chater et al., C. R. Biologies 331 (2008).

Arctic char (Salvelinus alpinus) metallothionein: cDNA sequence, expression, and tissue‐specific inhibition of cadmium‐mediated metallothionein induction by 17β‐estradiol, 4‐OH‐PCB 30, and PCB 104

AbstractIn this study, we haveexamined the basallevel expression and tissue‐specificexpressionpatternsof metallothionein (MT) in Arctic char following metal and E2 (17β‐estradiol) treatment. To study the gene regulation in Arctic char, the two MT isoforms were isolated from a lambda‐ZAP hepatic cDNA library and characterized. Determination of basal MT mRNA and MT expression for 10 different tissues revealed a lack of correlation between MT mRNA and MT levels. The inducibility of MT mRNA and the correlation to resulting MT levels were then determined for liver and kidney. We found a more rapid and stronger induction of MT mRNA in liver than in kidney at day 1 and 3 postinjection, whereas the MT protein quantification showed higher MT levels in kidney than in liver at days 3 and 7 postinjection. These discrepancies indicate that differences in metal handling or posttran‐scriptional regulation of MT exists between tissues. Whereas metals induce MT synthesis, E2 inhibit the hepatic MT expression. To examine the tissue specificity of this inhibition, we determined the effect of 17pj‐estradiol (E2) and two estrogenic PCBs (4′‐OH‐PCB 30 and PCB 104) on Cd‐mediated MT induction in liver and kidney. Although E2 and the estrogenic PCBs inhibited cadmium‐mediated hepatic MT induction, these compounds did not interfere with renal MT induction.

Zinc-specific response in metallothionein induction in liver of tumor-bearing mice

The response of trace metals to host liver in tumor-bearing mice was studied based on the data that an increase of hepatic zinc metallothionein (Zn-MT) was correlated with tumor growth rates. Zn concentration and 65Zn uptake in liver, unlike pancreas, were elevated 9 days after tumor transplantation. When zinc sulfate was subcutaneously (s.c.) injected into the tumor-bearing mice, hepatic MT, unlike pancreatic MT, was induced dose-dependently and much more than that in control mice. In the case of s.c. injection with cadmium chloride or copper chloride, however, hepatic MT in both control and tumor-bearing mice was induced dose-dependently. Yet, the induction efficiency by these two metals was nearly the same between control and tumor-bearing mice. These results indicate the unique response to exogenous Zn in host liver of tumor-bearing mice. An efficient induction of hepatic MT by Zn may lead to a retention of Zn in liver of tumor-bearing mice. J. Trace Elem. Exp. Med. 10:243–248, 1997. © 1997 Wiley-Liss, Inc.

Zinc‐specific response in metallothionein induction in liver of tumor‐bearing mice

The response of trace metals to host liver in tumor-bearing mice was studied based on the data that an increase of hepatic zinc metallothionein (Zn-MT) was correlated with tumor growth rates. Zn concentration and 65Zn uptake in liver, unlike pancreas, were elevated 9 days after tumor transplantation. When zinc sulfate was subcutaneously (s.c.) injected into the tumor-bearing mice, hepatic MT, unlike pancreatic MT, was induced dose-dependently and much more than that in control mice. In the case of s.c. injection with cadmium chloride or copper chloride, however, hepatic MT in both control and tumor-bearing mice was induced dose-dependently. Yet, the induction efficiency by these two metals was nearly the same between control and tumor-bearing mice. These results indicate the unique response to exogenous Zn in host liver of tumor-bearing mice. An efficient induction of hepatic MT by Zn may lead to a retention of Zn in liver of tumor-bearing mice. J. Trace Elem. Exp. Med. 10:243–248, 1997. © 1997 Wiley-Liss, Inc.

The physiology of waterborne silver toxicity in freshwater rainbow trout ( Oncorhynchus mykiss) 2. The effects of silver thiosulfate

The physiological responses of adult rainbow trout to a high level (30 000 μg l −1) of waterborne silver complexed by thiosulfate [Ag(S 2O 3) n −], as occurs in photoprocessing effluent, were compared with the responses to a low level of ionic Ag + (10 μg l −1 as AgNO 3). Ag(S 2O 3) n − was synthesized by combining one mole part AgCl with four mole parts of Na 2S 2O 3; responses to an equivalent level of Na 2S 2O 3 alone (1.11 mM) were examined as a control. Under flow-through conditions in moderately hard freshwater, 97% occurred as Ag(S 2O 3) 2 3−, 3% as AgS 2O 3 −, and a negligible fraction as ionic Ag + (< 0.003 μg l −1). Whereas 10 μg l −1 Ag (as AgNO 3) caused a variety of internal disturbances related to losses of plasma Na + and Cl −, 3000-fold greater Ag(S 2O 3) n − had very minor effects — a moderate, transient metabolic alkalosis and an apparent expansion of plasma volume. Plasma glucose declined slightly, but this also occurred in Na 2S 2O 3 controls. Plasma Na +, Cl −, Ca 2+, K +, lactate, arterial blood P O 2 and P CO 2 , and hematology were essentially unaffected. Nevertheless, by Day 6, total gill Ag was 3-fold greater than during AgNO 3 exposure, while plasma Ag was 3–4 times greater (stabilized by Day 2). There was also two-fold greater Ag accumulation in the liver than during AgNO 3 exposure, as well as accumulation in kidney, and an induction of metallothionein in liver, gills, and kidney. We conclude that acute toxic effects of waterborne silver are caused by ionic Ag + interacting with key functions at the gill surface and not by internal Ag accumulation. Even very high levels of waterborne silver are relatively benign when complexed by thiosulfate.

Interactions between metallothionein inducers in rat liver and primary cultures of rat hepatocytes

The interaction of Zn, stress and endotoxin on liver metallothionein (MT) regulation has been studied in the rat. Zn, stress and endotoxin increased liver MT levels significantly, by 12-, 5- and 8-fold, respectively. The previous administration of Zn to stress or endotoxin treatments increased MT levels by 35- and 42-fold, respectively, indicating a synergistic effect in both cases. In contrast, when liver MT was preinduced by stress, MT levels were further increased by endotoxin only in an additive manner. In another experiment where liver MT induction by stress was studied in control rats and in rats with preinduced MT by Zn, endotoxin or stress, it was found that Zn pretreated animals had higher MT-I mRNA levels than endotoxin- or stress-pretreated ones. No synergisms between dexamethasone, Zn, TNF and IFN were observed in primary culture of hepatocytes. These results suggest that the observed synergisms between Zn and other MT inducers in vivo in the liver is a consequence of increased Zn levels in the body and mobilization capacity, with concomitant MT synthesis.

Heavy metal intracellular balance and relationship with metallothionein induction in the liver of carp after contamination by silver, cadmium and mercury following or not pretreatment by zinc

Determination of metal levels (copper, zinc, cadmium, silver and mercury) in soluble and insoluble fractions of liver homogenates has been performed after 7 days exposure of carps (Cyprinus carpio) to moderate concentrations of cadmium, silver and mercury in water. Metallothionein (MT) levels have been quantified by a polarographic method before and after the contamination and a subsequent decontamination phase (7 days). The influence of pretreatment by zinc (7 days) has also been evaluated. MT level variations have been interpreted as having regard to inter-related flows of metal between subcellular fractions. Special interest has been focused on heat-stable compound (HSC)-bound heavy metal flows within the cytosol, taking in account that MT is the major component of these ligands. Our data showed differences between the ability of metals to bind cytosolic ligands and HSCs, and their respective potency for MT induction in liver. Regardless of pretreatment, mercury gave the highest increase of liver MT, but the MT level decreased during the decontamination step, especially after pretreatment by zinc. Cadmium and silver gave similar increases, but a significant difference with the control appeared only after the decontamination step with cadmium, while 1 week of contamintion was enough for silver. However, silver binding with MT was achieved only by the end of the decontamination step, while cadmium depicted the highest ratio for HSC-bound toxic metals after the contamination. Our experimental conditions gave the following order of potency for MT induction in liver: mercury ≫ silver > cadmium > zinc. Results are discussed comparatively with data obtained with carp gills.

Examination of potential mechanism(s) of metallothionein induction by diethyl maleate

Diethyl maleate (DEM) is a glutathione-depleting agent that can increase the levels of the sulfhydryl-rich protein metallothionein (MT) in liver. The purpose of the present study was to examine the mechanism(s) by which DEM increases mouse hepatic MT levels. DEM appears to be an indirect MT inducer as suggested by the lack of increase in MT levels when cultured mouse hepatocytes were exposed to DEM. Four possible mechanisms by which indirect MT inducers may cause an elevation in MT concentrations in liver were examined. Zn levels did not increase prior to the increase in hepatic MT, thus, a Zn redistribution to the liver is not the cause of the liver MT induction by DEM. The adrenal gland products were not required for MT induction in liver, as adrenalectomy did not abolish the increase in hepatic MT caused by DEM. The elevation in liver MT does not appear to be due solely to the decrease in liver glutathione (60%) in the initial hour after DEM, because phorone, which decreases liver glutathione (80%), produced only a fourfold increase in hepatic MT. Activation of macrophages does not seem to account for the rise in liver MT levels, as there was no increase in abundance of cytokine mRNAs for TNF-α, IL-1β, or IL-6 in the liver. These data suggest that the induction of hepatic MT by DEM does not occur in response to (1) an increase in liver Zn that precedes the increase in liver MT, (2) release of adrenal gland products, (3) decrease in liver glutathione, or (4) increased cytokine gene expression.

Metallothionein response to stress in rats: role in free radical scavenging.

The possibility that liver metallothionein (MT) can function as an antioxidant in vivo has been studied in the rat. It was found that the stress of food and water deprivation with or without physical immobilization consistently increased liver lipid peroxidation (LLP), suggesting that liver MT induction by stress might be related to the stress-induced LLP. This was supported by results with the lipid peroxidation promoter dimethyl sulfoxide (DMSO) and the natural antioxidant vitamin E. Whereas DMSO administration increased LLP levels in basal and stress situations, vitamin E decreased them. Liver MT levels were increased by DMSO in basal and stress situations, whereas they were decreased by vitamin E during stress. These in vivo results are consistent with an antioxidant role of liver MT suggested by previous in vitro results. However, liver MT preinduction by Zn treatment did not result in a lower MT response to stress. Instead a positive synergistic effect between Zn and stress appeared to be present. This result indicates that the mechanism of action of MT as antioxidant remains unclear.

Induction of metallothionein in liver and changes of essential metal levels in selected tissues by three dextran derivatives

Three dextran derivatives (dextran sulfate, DEAE-dextran and Dextran T500) were injected intraperitoneally into mice to study the induction of zinc-thionein in the liver, and the changes of essential metal levels in the liver, kidneys and spleen. The former was investigated with a high performance liquid chromatograph equipped with an atomic absorption spectrophotometer, and the latter with an inductively coupled plasma-atomic emission spectrometer. Dextran sulfate and DEAE-dextran induced a large amount of hepatic zinc-thionein dose-dependently, while Dextran T500 did not induce metallothionein substantially at the doses studied 20, 40 and 60 mg/kg body wt). The injection of dextran sulfate resulted in a significant increase of spleen weight, with a transitory increase of calcium concentration in the three tissues and a significant decrease of iron level in the spleen. In accord with the induction of zinc-thionein by dextran sulfate and DEAE-dextran, zinc concentration in the liver also increased transitorily after both injections and the time-course of the hepatic zinc level in dextran sulfate showed a close resemblance to that of the calcium one.