Comparative toxicity of gold preparations in treatment of rheumatoid arthritis

Next Generation Gold Drugs and Probes: Chemistry and Biomedical Applications

The gold drugs, gold sodium thiomalate (Myocrisin), aurothioglucose (Solganal), and the orally administered auranofin (Ridaura), are utilized in modern medicine for the treatment of inflammatory arthritis including rheumatoid and juvenile arthritis; however, new gold agents have been slow to enter the clinic. Repurposing of auranofin in different disease indications such as cancer, parasitic, and microbial infections in the clinic has provided impetus for the development of new gold complexes for biomedical applications based on unique mechanistic insights differentiated from auranofin. Various chemical methods for the preparation of physiologically stable gold complexes and associated mechanisms have been explored in biomedicine such as therapeutics or chemical probes. In this Review, we discuss the chemistry of next generation gold drugs, which encompasses oxidation states, geometry, ligands, coordination, and organometallic compounds for infectious diseases, cancer, inflammation, and as tools for chemical biology via gold-protein interactions. We will focus on the development of gold agents in biomedicine within the past decade. The Review provides readers with an accessible overview of the utility, development, and mechanism of action of gold-based small molecules to establish context and basis for the thriving resurgence of gold in medicine.

The thyroid hormone converting enzyme human deiodinase 1 is inhibited by gold ions from inorganic salts, organic substances, and by small-size nanoparticles

The selenocysteine-containing enzyme class deiodinases (DIO) consists of three isoforms. DIOs play a role in regulation of thyroid hormone (TH) signaling through the removal of iodide from TH leading to TH that interact with the hypothalamic-pituitary-thyroid (HPT) axis with differing potency. Some gold-containing organic substances are known to inhibit many selenoenzymes, including DIOs. It is, however, unclear whether the Au-containing substances or the Au ions are causing the inhibition. In this study, five organic and inorganic gold substances as well as three gold nanoparticles (AuNPs) were tested for their potential to inhibit DIO1. The enzyme activity was tested using human liver microsomes as an enzyme source and reverse T3 as a substrate; iodide release was measured by the Sandell-Kolthoff method. The three organic gold substances aurothioglucose, auranofin and sodium aurothiomalate inhibited DIO1 with IC₅₀ between 0.38 and 0.75 μM while their structural analogues lacking the gold ion did not. Likewise, the two tested gold salts, Au(I) and Au(III) chloride, showed a concentration-dependent inhibition of the DIO1 with IC₅₀ values of 0.95 and 0.57 μM. Further, AuNPs of different sizes (100, 30 and 5 nm diameter) were tested with only the 5 nm AuNPs leading to inhibition with an IC₅₀ of 8 × 10¹⁴ AuNP/L. This inhibition was not caused by the Au ions released by the AuNP into the incubation media. The exact mechanism of inhibition of DIO1 by 5 nm AuNPs should be further examined. In conclusion, the microsomal DIO1 assay demonstrated the inhibition of DIO1 by gold ions originating from different gold-containing substances, but not by Au released from AuNPs; rather DIO1 is inhibited by 5 nm, but not larger, AuNPs.

GOLD: human exposure and update on toxic risks

Gold is ubiquitous in the human environment and most people are in contact with it through wearing jewelry, dental devices, implants or therapies for rheumatoid arthritis. Gold is not a nutrient but people are exposed to it as a food colorant and in food chains. The present review discusses the hazards faced in personal and domestic use of gold and the far greater risks presented through occupational exposure to the metal in mining and processing gold ores. In the last situation, regular manual contact or inhalation of toxic or carcinogenic materials like mercury or arsenic, respectively, presents far greater hazard and greatly complicates the evaluation of gold toxicity. The uses and risks presented by new technology and use of nanoparticulate gold in anti-cancer therapies and diagnostic medicine forms a major consideration in gold toxicity, where tissue uptake and distribution are determined largely by particle size and surface characteristics. Many human problems arise through the ability of metallic gold to induce allergic contact hypersensitivity. While gold in jewelry can evoke allergic reactions, other metals such as nickel, chromium and copper present in white gold or alloys exhibit more serious clinical problems. It is concluded that toxic risks associated with gold are low in relation to the vast range of potential routes of exposure to the metal in everyday life.

Aurothioglucose overdosage in five patients with rheumatoid arthritis

Five patients with active seronegative, rheumatoid arthritis, HLA-DR3 negative, received inadvertently 250 to 500 mg of aurothioglucose instead of their usual weekly dose, during standard remission-inducing chrysotherapy. Subsequently a rapid and sustained clinical remission appeared in all five patients.

Current concepts in the treatment of rheumatoid arthritis

The treatment of RA is complex and often frustrating. The pathologic process of RA is composed of acute inflammation, chronic immunologic phenomenon, and chronic connective tissue degradation. It is important to understand not only the pathophysiology of RA but also the mechanism of action of our therapeutic drugs so that treatment can be tailored to affect the important aspects of the process leading to end-organ damage. Despite the many drugs available, therapy is still unsatisfactory. Many drugs work in only certain patients. This could be secondary to variability in the disease state or to difference in drug metabolism. A better understanding of both disease and therapeutic agents may lead to better use of our present agents and development of new, more effective treatment modalities.

The relationship between aurothioglucose- and D-penicillamine-induced proteinuria

We studied patients with rheumatoid arthritis who have been treated with aurothioglucose (Au) and subsequently with D-penicillamine (DP), and who developed drug-induced proteinuria, over a 10-year period. Twelve patients developed Au-induced and 19 DP-induced proteinuria. Of the 12 patients with Au-induced proteinuria, only 2 (17%) developed DP-induced proteinuria, indicating a slightly increased risk as compared with the overall incidence (9.3%) of this reaction in 168 DP-treated patients. In addition, only a minority (2 out of 19, 10.6%) of patients with DP-induced proteinuria had previous Au-induced proteinuria. These data may indicate that different mechanisms are operative in Au and DP-induced proteinuria, as is also suggested by the finding that HLA-DR3 was present more frequently in the latter (50%) than in the former (21%). A history of previous Au-induced proteinuria is insufficient reason to deny these patients the benefits of subsequent treatment with DP.

The effect of zinc and copper pretreatment on the binding of gold (I) to hepatic and renal metallothioneins

In the first part of this study, single s.c. injections of gold (I) sodium thiomalate were given to male Wistar rats at various dose levels and sacrificed either at 48 hr or 4 days later. The results indicate that though metallothioneins play a significant role in the sequestration of renal gold, the ability of gold itself to induce synthesis of the metalloprotein was limited in the kidneys and practically insignificant in the liver. Pre-injection with zinc however, (4 mg/kg body wt), significantly (P less than 0.01) enhanced the uptake of gold into the metallothioneins both, in the liver as well as the kidneys. The pretreatment increased the proportion of cytosolic gold incorporated into the thioneins from 29% to 48% in the kidneys and from 22% to 47% in the liver. Concurrent increases in the uptake of zinc and copper into the thioneins was also observed. Pre-injection with copper induced a similar effect in the kidneys only. There was no significant difference in the overall uptake of gold into the cytosol itself between the control animals (injected with gold only) and those pretreated with either zinc or copper. This indicated that the increased uptake of gold into the thioneins in the pretreated animals were due to enhanced synthesis of metallothioneins and subsequent increased binding of gold to thioneins rather than increased levels of intracellular gold itself. It is suggested that increased protection against the deposition and possible toxicity of gold in the cell organelles of the liver and kidney tissues may be provided by an increased binding of gold to metallothioneins through pretreatment with zinc, and to a lesser extent copper.

Antirheumatic drugs: clinical pharmacology and therapeutic use

With the exception of the treatment of gout and bacterial infections of joints, therapy in the rheumatic diseases remains inadequate. Although many patients gain symptomatic improvement on the drugs currently available, their impact on the underlying disease process remains uncertain. Hope for future therapeutic development is highest in rheumatoid arthritis with the second-line agents (e.g. gold, penicillamine), as unravelling their mechanism of action may lead to the design of more effective and less toxic medications. The cytotoxic agents appear to hold some promise in the therapy of vasculitis, but problems with their use have by no means been solved. In the major problem area of osteoarthritis, important gains are being made in the field of joint replacement, and the use of non-steroidal anti-inflammatory drugs in the interim has made symptoms more tolerable. Obviously much remains to be done in research in the area of antirheumatic drugs.

Postinjection nonvasomotor reactions during chrysotherapy. Constitutional and rheumatic symptoms following injections of gold salts

During gold sodium thiomalate (GST) therapy, 15% of 100 unselected patients described recurring postinjection reactions (PIRs), consisting of transient stiffness, arthralgias, myalgias, and constitutional symptoms. Six patients with more severe reactions requested discontinuation of chrysotherapy and for these, gold thioglucose (GTG) substitution abolished or amelioriated the reactions. The major significance of the PIR is that it may be a frequent cause of unwarranted premature abandonment of chrysotherapy.