Analysis of mammalian metallothionein isoforms by high-resolution SDS-gel electrophoresis

Induction of metallothionein by zinc protects from daunorubicin toxicity in rats

Daunorubicin (DNR) is an anthracyline antibiotic used in the treatment of a variety of human cancers. Reactive oxygen species (ROS) produced in the metabolism of DNR have severe cardiotoxicity which consequently compromises its clinical use as anticancer drug. This study aimed to investigate the effect of DNR administration on both cardiac and hepatic tissues, and the possible protective role of zinc on the cardiotoxicity and hepatotoxicity produced by DNR. Administration of 10 or 20 mg/kg DNR to Sprague-Dawley rats, increases serum creatine kinase activity, and blood troponin T levels (as cardiotoxicity indices), alanine aminotransferase activity (as hepatotoxicity index), as well as cardiac and hepatic 2-thiobarbituric acid reactive substances (as an index of lipid peroxidation). Treatment with 20 mg/kg Zn prior to DNR, dramatically induced metallothionein-1 (MT-1) mRNA and MT protein in both heart and liver while DNR alone induced MT, but to a much lower degree than Zn. The analysis of MT protein isoforms revealed that MT-1 was the form induced, while metallothionein-2 (MT-2) levels remained practically unchanged. The increases in both MT protein and MT-1 mRNA ran parallel with the reduction of cardiac and hepatic toxicities. Our results indicate that MT induction by Zn is a highly effective approach in preventing cardiotoxicity and hepatotoxicity caused by DNR. These animal data suggest the use of Zn to reduce DNR-induced cardiotoxicity and hepatotoxicity in the chemotherapy of cancer patients.

Dynamics of (Cd,Zn)-metallothioneins in gills, liver and kidney of common carp Cyprinus carpio during cadmium exposure

Cadmium concentrations, (Cd,Zn)-metallothionein (MT) concentrations, MT synthesis and the relative amounts of cadmium bound to (Cd,Zn)-MTs were determined in gills, liver and kidney of common carp Cyprinus carpio exposed to 0, 0.5 microM (0.06 mg.l(-1)), 2.5 microM (0.28 mg.l(-1)) and 7 microM (0.79 mg.l(-1)) Cd for up to 29 days. Cadmium accumulation was in the order kidney > liver > gills. Control levels of hepatic (Cd,Zn)-MT were four times higher compared to those of gills and kidney. No increases in (Cd,Zn)-MT concentrations were observed in liver during the exposure period. In comparison with control carp, (Cd,Zn)-MT concentrations increased up to 4.5 times in kidney and two times in gills. In both these organs, (Cd,Zn)-MT concentrations were linearly related with cadmium tissue levels and with the de novo synthesis of MTs. Hepatic cadmium was almost completely bound to (Cd,Zn)-MT, while percentages of non-MT-bound cadmium were at least 40% in gills and 25% in kidney. This corresponded with a total saturation of (Cd,Zn)-MT by cadmium in kidney and a saturation of approximately 50 and 60% in gills and liver, respectively. The final order of non-MT-bound cadmium was kidney > gills > liver. Our results indicate that cadmium exposure causes toxic effects, which cannot be correlated with the accumulated levels of the metal in tissues. Although cadmium clearly leads to the de novo synthesis of MT and higher (Cd,Zn)-MT concentrations, the role of this protein in the detoxification process is clearly organ-specific and its synthesis does not keep track with cadmium accumulation.

Effect of non-toxic mercury, zinc or cadmium pretreatment on the capacity of human monocytes to undergo lipopolysaccharide-induced activation

1. Metal salts can inhibit cell activity through direct toxicity to critical cellular molecules and structures. On the other hand, they can also change cell behaviour by inducing specific genes (including genes encoding members of the metallothionein [MT] gene family). Therefore, transition metals may affect cell functions either by acting as a toxin, or by transmitting or influencing signals controlling gene expression. 2. To explore the latter possibility, we measured the ability of low, non-toxic metal pretreatment to alter immune cell behaviour. We previously found that pretreatment of human monocytes with zinc induces metallothionein gene expression and alters their capacity to undergo a bacterial lipopolysaccharide-induced respiratory burst. We showed here that cadmium and mercury salts, at concentrations that exert no discernible toxicity, inhibit activation of human monocytic leukemia (THP-1) cells. CdCl2 1 microM, ZnCl2 20-40 microM or HgCl2 2 microM pretreatment for 20 h induced MT-2 mRNA and total MT protein accumulation and had no effect on proliferation potential or metabolic activity, but significantly inhibited the ability of subsequent lipopolysaccharide treatment to induce the oxidative burst, increased adhesion to plastic, and MT-2 and interleukin-1 beta (IL-1 beta) mRNA accumulation. 3. The phenomenon of metal-induced suppression of monocyte activation, at metal concentrations that have no effect on cell viability, has important implications for assessment of acceptable levels of human exposure to cadmium, zinc and mercury.

Accumulation of metallothionein and its multiple forms by zinc, cadmium and dexamethasone in human peripheral T and B lymphocytes and monocytes

Metallothionein (MT) is produced at high rates in isolated monocytes, and T and B lymphocytes during induction in vitro. At optimal concentrations, 125 microM for Zn and 10 microM for Cd and dexamethasone (dex), MT was demonstrated after only 2 h in some cases, and in all cell types substantial levels were measured after 1 day of exposure to all three inductors. With Cd, lower amounts of MT were found, but maximum levels were reached faster than with Zn. The same result was found for dex compared to Zn. Zn and dex in combination showed the same accumulation rate as Zn alone. If the inductors were used in lower concentrations than optimal, reduced accumulation rates occurred, particularly during the first part of the exposure period. No MT was found for concentrations below 5 microM Zn, 1 microM Cd or 0.5 microM dex. The constitutive levels of MT (mean +/- S.E.M.) were 0.11 +/- 0.05, 0.54 +/- 0.3, 0.06 +/- 0.05 and 0.15 +/- 0.08 nmol Cd bound/5 x 10(6) unseparated mononuclear cells (MNC), monocytes, T lymphocytes and B lymphocytes, respectively. Monocytes accumulated 19 times and B lymphocytes 6 times more MT than T lymphocytes after 2 days of exposure to 125 microM Zn. Despite these differences in accumulated amounts of MT, the fold accumulation values were rather similar between the cell types, reflecting corresponding variations in background MT levels. After exposure of unseparated MNC to 125 microM Zn for 2 days, removal of the metal caused constitutive MT levels to be reestablished in 5 days. Five different MT forms, all capable of Cd complexation, were demonstrated in these cells. These forms had kinetically different behaviour during Zn exposure among the cell types, and the response to Cd was different from the Zn response. The results indicate metals to be closely controlled in MNC and emphasize a role for multiple MT forms in the process of regulation.