Search

The reaction of equine renal metallothionein (MT) with excess K2PtCl4 at pH 2 results in a polymeric adduct containing 17 +/- 2 mol Pt/mol MT. A monomeric adduct containing 7 mol Pt/mol MT is obtained at neutral pH. Rates of reaction of Pt7MT with DTNB and iodoacetic acid are consistent with Pt2+ to cysteine thiolate coordination, and the extent of reaction in both cases is 11 +/- 2 mol cys/mol MT. Adducts from the reaction of K2PtCl4 with apoMT chemically modified at the N-terminal methionine residue, Cd7MT, and native MT are also reported. A structural model of Pt7MT is proposed in which the square planar tetrathiolate Pt(II) unit is incorporated into a three-metal beta cluster. Implications for the metabolism of platinum anticancer drugs are discussed.

The concentration of metallothionein (MT) in the liver of the perinatal rat is relatively high at term and 7 days after birth and then decreases to barely detectable levels by day 28. The developmental pattern MT-zinc parallels that of MT. When challenged with a single injection of cadmium chloride, the 26-day-old rat responds with a dose-related increase in hepatic MT which sequesters both cadmium and zinc. When the 5-day-old rat is similarly challenged, induction of MT occurs only at the highest dose tested (6 mg Cd/kg); however, due to the pre-existence of MT in these younger rats, cadmium administered at the lower doses still binds to the MT in a dose-related manner. Despite the induction of MT seen in both age groups following the 6.0 mg/kg dose, exposure to that level of the metal produced death in 30% of the younger animals but in only 4% of the older animals. When cadmium was administered to pregnant rats on day 19 of gestation, it was found to produce a dose-related induction of maternal hepatic MT over the following 48 hr. In contrast, maternal exposure to the metal led to a significant depression of fetal hepatic MT over the same time interval.

Pregnant rats were injected subcutaneously on day 10 of pregnancy with 0.0, 0.25, 0.50, 1.0 or 3.0 mg cadmium/kg and sacrificed at term (day 21). There were no fetal or maternal deaths following the cadmium exposure with the exception of the e.0 mg/kg level where a 54% fetal mortality rate was observed. At doses of 1.0 mg/kg or less, non-specific parameters of fetal toxicity including body weight, crown-rump length, and liver weight were not significantly different from control values. The same was true of term placental weight as well as maternal weight gain over the 48-h treatment period. Following gel-filtration of hepatic cytosols from control fetuses, over 70% of the endogenous cytosolic zinc was associated with a peak previously described as metallothionein. It was found that cadmium exposure at sub-lethal doses caused a depression in both total cytosolic zinc and metallothionein-bound zinc levels in the fetus, whereas both these parameters increased in the maternal liver. In vitro cadmium saturation prior to gel filtration revealed that the cadmium-binding capacity of the metallothionein peak was significantly reduced at all dosage levels in the fetus but increased in maternal liver. These findings suggest that maternal administration of cadmium can depress fetal metallothionein levels and cytosolic zinc levels at doses which do not produce overt fetal toxicity. This reduction in fetal metallothionein is in sharp contrast with the well established finding of induction of metallothionein seen in the adult following exposure to cadmium.

Two inbred strains of mice were used in this study, the C57BL/6J which is reported to be a high interferon producer and the C3H/HeJ which is reported to be a low interferon producer. Each mouse received a single i.p. injection of either Newcastle disease virus (NDV) or the double-stranded nucleotide, polyinosinic acid-polycytidilic acid (poly (rI.rC], both type I interferon inducers, or cadmium chloride, a known inducer of metallothionein (MT), and were killed 24-hr later. Treatment of the C57BL and C3H mice with 1 mg Cd/kg caused a 14- and 16-fold increase in hepatic MT concentrations, respectively. In both strains, this induction was accompanied by an increase in the hepatic concentration of zinc but not copper. There were no observed changes in the circulating levels of interferon. In the C57BL mice, both the administration of poly (rI.rC), at a dose of 10 mg/kg, and NDV, at a dose of 512 hemagglutinating units/mouse, produced a 4-fold increase in the hepatic concentration of MT. Although both treatments caused an increase in levels of interferon, the increase seen with NDV was greater than that seen with poly (rI.rC). In the C3H mice, the results were quite different. Although both treatments induced hepatic MT concentrations 4- to 5-fold, the increase in interferon levels observed following the administration of poly (rI.rC) was higher than that seen with NDV and some 50-fold higher than the increase produced by the polynucleotide in the C57BL mice. The results of this study indicate that two interferon-inducing agents, poly (rI.rC) and NDV, are also capable of inducing hepatic metallothionein.

Seven American alligators, Alligator mississippiensis, were each administered a single, intracardiac injection of cadmium chloride, at a dose of 1.0 mg Cd/kg body wt. At sacrifice, the highest concentration of Cd was found in the liver, bound to a cytosolic protein with characteristics similar to mammalian metallothionein (MT). Gel filtration (Sephadex G-75) of the cytosol revealed a peak containing Cd and to a lesser extent, zinc (Zn), having the same relative elution volume (Ve/Vo) as rat hepatic Cd, Zn-MT. Anion-exchange chromatography (DEAE-Sephacel) of material having a Ve/Vo of 1.7-1.9 revealed a major Cd-peak corresponding to rat Cd, Zn-MT(I) and a minor peak corresponding to Cd, Zn-MT(II). Neither peak contained significant amounts of Zn. Heat treatment of alligator hepatic cytosol, followed by selective acetone precipitation, yielded material having a molar Cd:Zn ratio of 9.15:1 compared to 0.67:1 in material purified from Cd-pretreated rat liver. Spectral analysis of the material purified from both sources showed an absorbance peak between 250 and 260 nm and no absorbance peak at 280 nm, characteristic of mammalian MT.