Tissue disposition and excretion of gold and 14C in rats treated with sodium aurothio[1,4-14C]malate or thio [1,4-14C] malic acid

Interaction and Aggregation of Sodium Aurothiomalate and Poly l-Lysine

This report describes the interaction and aggregation of sodium aurothiomalate with polylysine, a potentially useful property, both as a model for drug-protein interaction and as a means of reversibly immobilizing sodium aurothiomalate. Sodium aurothiomalate formed stable precipitates with polylysine at neutral pH, ionic strengths below 1m NaCl, and optimally, at sodium aurothiomalate to lysine ratios of less than one. The interaction could be demonstrated both by precipitation (which was sensitive to the size of polylysine polymer) and by using polylysine immobilized to Sepharose. Precipitation could be inhibited by addition of the organic thiomalate moiety alone. These findings indicate that the interaction of sodium aurothiomalate with polylysine is by electrostatic bonding of the thiomalate (mercaptosuccinate) moiety and the ε-amino groups of lysine residues. At suitable molar ratios this will link together many polylysine chains leading to precipitation. This represents a potentially valuable interaction for immobilization of the drug and in the formation of conjugates.

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.