Effect of aurothioglucose on liver and kidney concentrations of copper, iron, manganese and zinc

Gold stimulates Ca2+ entry into and subsequent suicidal death of erythrocytes

The suicidal death of erythrocytes, eryptosis, is characterized by cell shrinkage and cell membrane scrambling leading to phosphatidylserine exposure at the erythrocyte surface. Erythrocyte cell membrane scrambling is stimulated by increase of cytosolic Ca2+ concentration ([Ca2+](i)) and formation of ceramide. Phosphatidylserine (PS) exposing cells are rapidly cleared from circulating blood. Ca2+ entry and/or ceramide formation and thus eryptosis are triggered by lead, mercury, aluminium, and copper ions. The present study explored whether eryptosis could be similarly triggered by exposure to gold. To this end, erythrocytes from healthy volunteers were exposed to AuCl and phosphatidylserine exposure (annexin V binding), cell volume (forward scatter), [Ca2+](i) (Fluo3-dependent fluorescence), and ceramide formation (anti-ceramide-FITC fluorescence) were determined by flow cytometry. Exposure of erythrocytes to low concentrations of AuCl (> or =0.75microg/ml) increased [Ca2+](i) but did not affect ceramide formation. AuCl at concentrations > or =0.5microg/ml significantly increased the number of PS exposing erythrocytes and decreased forward scatter at low concentrations of AuCl pointing to cell shrinkage. Aurothiomalate (> or =1microg/ml), a gold containing drug effective against rheumatoid arthritis, similarly triggered PS exposure of erythrocytes. The present observations disclose a novel action of gold, which may well contribute to side effects during treatment with gold preparations.

Influences of gold on zinc, copper and metallothionein kinetics in liver and kidney of the rat

1. Single, very low dose of gold (500 micrograms/kg body weight) was given intramuscularly to male Sprague-Dawley rats (mean body weight: 200 g) as aurothiokeratinate (Auro-Detoxin(R) dissolved in 0.9% NaCl. 2. Blood, liver and kidney were samples at autopsy 0.5, 1, 2, 3, 6 and 12 h after the gold injection (six animals per time). 12 rats were treated with 0.9% saline only as controls. The zinc (Zn), copper (Cu), gold and metallothionein (MT) concentrations were determined in homogenates and cytosols of liver and kidney using atomic absorption spectrometry and gel chromatography, respectively. 3. The main changes in metal and MT concentrations occurred in the kidney, where an increase of gold was found 0.5 h after the injection, followed by an increase in Cu and MT concentrations after 6 h. Zn homeostasis did not change. 4. The results suggest that gold by itself induces an increase of MT-like peptides in the kidney cytosol, which was accompanied by an increase in the concentration of Cu mainly bound to these MT-like peptides.

The effect of sodium aurothiomalate (myochrysin) on the distribution of calcium, magnesium, copper, zinc and iron in the rat

Sodium aurothiomalate was given to male Wistar rats (initial body weights: 150 g) by subcutaneous (s.c.) injection at doses of up to 7.5 mg/kg (corresponding to 4.27 mg gold/kg), twice a week, for 4-5 weeks. The concentrations of Ca, Mg, Fe, Cu and Zn were measured in serum, urine, faeces and in the liver, kidney, spleen, heart, lung, testis, bone and muscle. Kidney cytosol was separated by gel chromatography and the fractions analysed for protein, copper, zinc, iron and gold concentrations. The concentration of copper was increased 5-fold in kidney while smaller increases of zinc in kidney, copper in muscle, iron in muscle and testis and calcium in spleen were found. There was a significant reduction in the concentration of copper in serum. Kidney cytosol from gold-treated but not from control animals contained a low molecular weight protein which was associated with copper, zinc and gold. The rats developed proteinuria and microscopic changes to renal tubular cell structure were also observed. It is suggested that the gold-induced accumulation of copper may follow from an increased rate of synthesis of metallothionein and could be responsible for the renal dysfunction which develops in a proportion of rheumatoid arthritis patients who are treated with gold.

Subchronic treatment of rats with aurothioglucose; effects on plasma, hepatic, renal and urinary zinc, copper and metallothionein

Administration of sodium aurothioglucose (10 mg/kg per day) to female rats for up to 8 weeks resulted in no apparent effects on the kidney. Gold accumulated in kidney, liver, spleen, pancreas, skin and blood. Although plasma and hepatic gold levels increased with time, no remarkable change in either copper, zinc or metallothionein (MT) levels was observed. Gel filtration chromatography of plasma showed binding of gold to albumin, whereas copper was associated with albumin, ceruloplasmin and a protein eluting in the void volume of the Sephadex G-150 column. Almost all of the hepatic gold was bound to proteins other than MT. In the kidney, not only gold but also copper and MT increased rapidly, reached a maximum between 2 and 4 weeks and exhibited insignificant change thereafter. Gold-treated animals showed an increase in binding of copper to the very high molecular weight plasma protein, which may be involved in transport of copper to the kidneys. Urinary gold and MT followed a pattern similar to that in the kidney. Renal zinc also increased but returned to normal by week 8. In renal cytosol 57% and 54% of the gold and copper, respectively, were associated with MT. It appears that the elevated levels of copper and zinc, rather than gold, are responsible for the induction of MT synthesis. This then provides a mechanism by which gold and the inducing metals are retained by the kidney.

The effect of cadmium pretreatment on the disposition and excretion of methylmercury and trace elements (zinc, copper) in rats

Cadmium chloride (Cd) was injected s.c. into male rats at a dose rate of 3 mg Cd/kg 3 times a week for 4 weeks. The animals were maintained for administration of methylmercury (203 Hg) chloride at a dose of 3 mg CH3Hg/kg given p.o. 3 times a week for 2 weeks, followed by 3 weeks of recovery period. Animals were sacrificed 24 h after the final dose of MeHg, or 5 weeks after cessation of Cd administration. Cd-pretreatment significantly decreased total Hg concentration in the kidney and RBC and almost completely inhibited demethylation of MeHg in the kidney (from 32% to 3% of inorganic Hg). Cd-pretreatment did not affect urinary excretion of total Hg, but significantly increased daily excretion of total Hg in feces. MeHg given alone significantly increased renal but not hepatic copper levels and decreased copper in the plasma and brain. In Cd-pretreated rats, both renal and hepatic copper concentration were in the normal ranges. Zinc levels in Cd-pretreated rats significantly increased in the kidney, liver and brain but decreased in plasma (compared to control and MeHg-alone treated animals). From these results it can be concluded that Cd-pretreatment may decrease MeHg toxicity by increasing the fecal mercury excretion and by inhibiting the formation of inorganic mercury in the kidney, which is a more potent renal toxin than MeHg.

Effect of a chelating drug on balance and tissue distribution of four essential metals

Numerous drugs have structures that suggest that they and/or their metabolites are chelating agents, and therefore might affect trace metal metabolism. Ethambutol, used therapeutically in the treatment of tuberculosis, is an example. The objective of this study was to determine the effects of ethambutol on tissue concentrations and balance of 4 essential trace metals: copper, iron, manganese, and zinc. Eighteen male Sprague-Dawley rats (148 +/- 7 g) were housed individually in metabolic cages. Six rats received ethambutol (400 mg/kg/day) via the drinking water. There were 2 control groups of 6 rats each, an ad-lib and a pair-fed group. Iron concentrations in kidney, liver, heart, and spleen were significantly increased in both the pair-fed and ethambutol-dosed rats, an effect related to reduced food intake. However, the total iron content of these organs was comparable to that of the ad-lib controls, suggesting retention of iron by these organs with reduced food intake during growth. Trace element balance was not affected by ethambutol administration. Ethambutol produced significant decreases in heart copper, kidney zinc, plasma zinc, and liver copper and zinc not due to the associated reduced food intake. The latter results support the hypothesis that chelating drugs may alter trace metal metabolism.

Multielement analysis of metal-binding proteins in cytosol fractions

The distribution of 24 elements among the cytosol protein fractions was determined for specimens of the bivalve mollusc Macoma balthica obtained from three estuarine locations subject to varying levels of metal pollution and on specimens of Rangia cuneata from three areas subject to varying degrees of thermal pollution. Of the 24 elements examined 15 occurred at levels above detection limits and in association with one or more of four distinct protein fractions. Levels of Ag and Cu associated with high molecular weight proteins and with "metallothionein-like" proteins permitted identification of those Macoma balthica specimens exposed to the greatest degree of metal stress.