Serum gold. I. Estimation by atomic absorption spectroscopy

Auranofin versus injectable gold. Comparison of pharmacokinetic properties

The new oral gold compound auranofin differs pharmacokinetically from the existing injectable gold compounds such as gold sodium thiomalate. Following a standard 50 mg intramuscular injection of gold sodium thiomalate, plasma gold levels rise sharply, peak between 400 and 800 micrograms/dl in approximately two hours, then decline to approximately 300 micrograms/dl by seven days. With repeated 50 mg weekly injections, stable plasma concentrations are gradually achieved, although absolute levels vary greatly among individual subjects. On the other hand, auranofin is associated with lower (50 to 70 micrograms/dl) and more predictable plasma concentrations. Single-dose kinetic studies using isotopically labelled gold show that the plasma disappearance half-time for gold sodium thiomalate is relatively rapid (approximately six days) compared with 17 days for auranofin. Both compounds are retained within the body over prolonged periods. Retention of auranofin is much less, about 1 percent of the original tracer dose remaining at 180 days, compared with more than 30 percent retention of gold sodium thiomalate. Excretory pathways are notable different. The majority of gold sodium thiomalate (greater than 70 percent) is excreted by the kidneys, with the remaining fraction appearing erratically in the stool. In contrast, the enteric pathway represents the major excretory route for auranofin, with nearly 85 percent of the dose eventually recoverable in the stool and less than 15 percent in the urine. In human subjects, parenterally administered gold is almost universally dispersed among body tissues, although highest concentrations occur in the organs of the reticuloendothelial system and the adrenal and renal cortices. Comparable studies are not available for auranofin, but animal studies show comparatively less affinity for liver, kidney, and spleen. To date, attempts to correlate the pharmacokinetics of the injectable gold compounds with clinical response and toxicity have been largely unsuccessful. The distinctive pharmacokinetic profile of auranofin, when compared with gold sodium thiomalate, may nonetheless account in part for the clinical and pharmacologic differences between these compounds.

Binding of gold to bovine serum albumin using flameless atomic absorption

A graphite furnace atomic absorption spectrophotometric assay capable of accurately determining nanogram amounts of gold in biological fluids was developed. The presence of bovine serum albumin and/or phosphate in the sample reduced the method sensitivity without affecting the linear response. Binding of gold was studied by ultrafiltration using cones with a molecular weihght cutoff of 25,000. The binding of gold at various concentrations to 2 and 4% bovine serum albumin in 0.1 M phosphate buffer, pH 7.4, was independent of the gold and protein concentrations. In the 2-10 microgram/ml range, the overall binding values (mean +/- SD) of gold to 2 and 4% bovine serum albumin were 98 +/- 1.6 (n = 35) and 99 +/- 1.0% (n = 15), respectively. When ultrafiltration cones with a molecular weight cutoff of 50,000 were used, the extent of binding to 2% bovine serum albumin was 85.4 +/- 1.6% (n=11). This statistically significant difference (p less than 0.001) was due to variations in the protein retention of the two cone types. Interaction studies showed that gold was not displaced from the binding sites by salicylic acid (200 microgram/ml) or vice versa.

Rapid determination of gold in whole blood of arthritis patients using flameless atomic absorption spectrophotometry

An assay for gold in whole blood of arthritis patients was developed using the graphite furnace atomic absorption spectrophotometer. This method involves no pretreatment of the whole blood except for simple dilution, thereby eliminating some variables and saving laboratory time and expense.

Determination of gold in plasma and plasma fractions by atomic absorption spectrometry and by neutron activation analysis

Three techniques of gold analysis, flame and electrothermal atomic absorption spectrometry and neutron activation analysis, have been compared, using plasma and plasma fractions (derived by gel chromatography) from rheumatoid patients receiving aurothiomalate therapy and from plasma samples incubated with aurothiomalate in vitro. The three methods correlated well in the analysis of gold in whole plasma, but only neutron activation analysis was suitable for the assay of all the plasma fractions. The susceptibility of the two atomic absorption methods to interference by sodium chloride was investigated.