Mechanism of Action,Pharmacology, Clinical Efficacy and Side Effects of Auranofin: An Orally Administered Organic Gold Compound for the Treatment of Rheumatoid Arthritis

The mechanism of action of auranofin, an oral organic gold compound used in the treatment of rheumatoid arthritis, is probably similar to the previously available parenteral gold compounds. Auranofin affects polymorphonuclear cells and monocytes at lower concentrations than gold sodium thiomalate and generally affects humoral and cell-mediated immunity in the same direction as the latter drug. The pharmacokinetics of auranofin are different from the intramuscular gold compounds. Auranofin is 20–25% orally absorbed and has less total body retention, greater fecal excretion, and less urinary excretion than gold sodium thiomalate. This may be due in part to its differing chemistry, including its lipophilicity and monomeric structure (at least in vitro). While many clinical studies are not yet complete, auranofin (6 mg/day) is clearly more effective than placebo for treating rheumatoid arthritis. Its efficacy relative to gold sodium thiomalate is not clear. Auranofin may be slightly less effective than gold sodium thiomalate, but because it is generally less toxic than intramuscular gold compounds, its therapeutic index may be more favorable.     

Action of gold sodium thiomalate on experimental thrombosis in vivo

In order to study the effect of gold compounds on the action of thrombin in vivo, experiments were performed to measure platelet survival and the weight of thrombus formation in experimental models of intra-aortic thrombosis by two indwelling aortic catheter methods. We have called these the long and short catheter methods. Platelet survival was reduced in all gold-treated and control animals which had indwelling aortic catheters. In the long catheter model, New Zealand White male rabbits were treated with one of the following: gold sodium thiomalate, sterile water, gold thioglucose, gold sodium thiosulfate, disodium thiomalate. Gold sodium thiomalate-treated rabbits had a reduced weight of experimentally induced intra-aortic thrombi compared with animals treated with sterile water or equimolar concentrations of gold thioglucose, gold sodium thiosulfate, or disodium thiomalate. This reduction in thrombus weight in the animals treated with gold sodium thiomalate was not reflected by changes in platelet survival or fibrinolysis. The serum gold levels achieved in these in vivo experiments was in the range of 5.0 X 10(-5) to 1.0 X 10(-4) M. These values are comparable to levels which can be achieved in human subjects immediately after a gold injection. In the short catheter model, New Zealand White male rabbits were treated with either gold sodium thiomalate, gold thioglucose, disodium thiomalate, or auranofin. Controls were given either water or 0.05% chlorocresol. Water-treated and gold sodium thiomalate-treated animals were also given 51Cr-labeled platelets and 125I-fibrinogen before insertion of the catheter.(ABSTRACT TRUNCATED AT 250 WORDS)     

Clinical pharmacology of gold

Since the dawn of civilization, elemental gold and gold compounds have been revered and utilized by Shamen and medical practitioners alike for many varied pathological problems. In the 20(th) century following the observations of Jacques Forestier, injectable gold compounds were successfully used for the treatment of rheumatoid arthritis. Of the many compounds developed, gold sodium thiomalate has been the most extensively studied by basic scientists and by clinicians. In the1980s, the oral gold compound auranofin showed promise as a therapeutic contender to injectable gold, but the clinical side effect profile and fear of long term effects of immune suppression by auranofin, resulted in gold sodium thiomalate continuing as the preferred gold compound for rheumatoid treatment. However, the increased use and demonstration of effectiveness of low dose Methotrexate (MTX) in rheumatoid treatment over the last 20 years has resulted in a significant decline in the use of injectable gold sodium thiomalate, this despite the claims and evidence that it remains a useful agent in the management of rheumatoid arthritis. Several authors still contend that the injectable gold compounds can still play a valuable role, and indeed may be the correct first choice in the management of rheumatoid arthritis.     

Sublethal concentrations of diverse gold compounds inhibit mammalian cytosolic thioredoxin reductase (TrxR1)

Thioredoxin reductase (TrxR) reduces thioredoxin (Trx), thereby contributing to cellular redox balance, facilitating the synthesis of deoxy-ribose sugars for DNA synthesis, and regulating redox-sensitive gene expression. Auranofin is a gold compound that potently inhibits TrxR. This inhibition is one suspected mechanism of auranofin’s therapeutic benefit in the treatment of rheumatoid arthritis. The use of other gold compounds to treat cancer or inflammatory disease may rely on their ability to inhibit TrxR. In the current study, we tested the hypothesis that a variety of gold compounds may inhibit TrxR.Methods: We exposed rat-TrxR1 to auranofin, gold sodium thiomalate, sodium aurothiosulfate, triphenyl phosphine gold chloride, or gold acetate, and measured TrxR activity ex vivo. We then compared TrxR1 inhibitory levels of gold compounds to those that inhibited mitochondrial activity of THP1 monocytes and OSC2 epithelial cells, estimated by succinate dehydrogenase activity.Results: All gold compounds inhibited TrxR1 at concentrations ranging from 5 to 4000 nM (50% inhibitory concentration). The oxidation state of gold did not correlate with inhibitory potency, but ligand configuration was important. Au(I)-phosphine compounds (triphenyl phosphine gold chloride and auranofin) were the most potent inhibitors of TrxR. All TrxR1 inhibitory concentrations were sublethal to mitochondrial activity in both THP1 and OSC2 cells.Conclusions: Diverse types of gold compounds may be effective inhibitors of TrxR1 at concentrations that do not suppress cellular mitochondrial function. Inhibition may be optimized to some degree by altering the ligand configuration of the compounds. These results support future study of a variety of Au compounds for therapeutic development as inhibitors of TrxR1.     

The anti-inflammatory effect of auranofin

The anti-inflammatory effects of auranofin were studied and compared with those of indomethacin, gold sodium thiomalate (GST) and D-penicillamine. Auranofin was active as indomethacin in inhibiting carrageenan induced paw edema in rats, but was less potent than indomethacin in inhibiting UV-induced erythema in guinea pigs. Auranofin inhibited Arthus type paw edema and reverse PCA reaction in rats, on which indomethacin was ineffective. The inhibitory activity of auranofin on adjuvant arthritis was weaker than that of indomethacin. In in vitro experiments, auranofin did not show any suppression of cyclooxygenase activity, but was capable of suppression of lysosomal enzyme release and chemotaxis of neutrophils and macrophages. In addition to these anti-inflammatory activities, auranofin had almost equal anti-analgesic and anti-pyretic activity to that of indomethacin. The above results indicated that the anti-inflammatory profiles of auranofin and indomethacin differ, so we can expect new therapeutic activities of auranofin. GST had similar anti-inflammatory and anti-analgesic profiles to those of auranofin; however, the activities were less potent than auranofin and devoid of anti-pyretic activity. D-penicillamine did not show any anti-inflammatory, anti-analgesic or anti-pyretic activity.     

Effects of gold coordination complexes on neutrophil function are mediated via inhibition of protein kinase C

Previous studies have shown that the gold compounds auranofin (AUR) and gold sodium thiomalate (GST) inhibit responses of various cells and tissues. We found that superoxide anion generation induced in human neutrophils by the chemotactic tripeptide fmet-leu-phe (1 microM), fluoride (18 mM), or phorbol myristate acetate (PMA, 100 nM) was inhibited by pretreatment of cells with 5-100 microM AUR. The extent of inhibition was dependent on AUR concentration and duration of the preincubation. GST was much less potent, inasmuch as only weak effects were observed at 5 times higher concentrations. The ineffectiveness of GST was attributed to its slower rate of penetration into cells, compared with AUR. The finding that mobilization of internal Ca2+ stores was not blocked in AUR-treated cells suggests that phospholipase C-mediated hydrolysis of polyphosphoinositides to inositol 1,4,5-trisphosphate was not inhibited by the drug. Because PMA is known to mimic the action of diacylglycerol in activating protein kinase C (PKC), we investigated the possibility that gold compounds might be interfering with signal transduction at this level. Enzymatic assays indicated that both gold compounds reduced the level of PKC activity associated with the cytosol; however, translocation of PKC to the plasma membrane was not found. Immunoblot analyses carried out with polyclonal anti-PKC antisera revealed that the gold compounds did not cause degradation of PKC or increase translocation to the membrane. Further studies indicated that enhanced endogenous protein phosphorylation resulting from PMA stimulation was attenuated in cells co-treated with AUR. Finally, in vitro enzymatic assays showed that both AUR and GST inhibited partially purified PKC in a concentration-dependent manner. It is suggested that modulation of PKC represents a mechanism of action of gold coordination complexes at the cellular level.     

Clinical pharmacokinetics of oral and injectable gold compounds

The pharmacokinetics of oral gold (auranofin) in some respects resemble, and in other respects differ from, those of existing parenteral gold compounds such as gold sodium thiomalate (GST). This may in part relate to physicochemical differences as GST is a water-soluble polymeric compound in vitro whereas auranofin is lipid-soluble and characteristically monomeric. Furthermore, intramuscularly administered gold is greater than 95% bioavailable, whereas only 20 to 30% of an orally administered dose of auranofin is absorbed. Following a standard 50mg intramuscular injection of GST, serum gold concentrations rise sharply, peaking between 4 and 8 mg/L in approximately 2 hours and declining to an average of 3 mg/L by 7 days. With repeated injections of GST stable serum concentrations of gold (3 to 5 mg/L) are eventually achieved (usually within 5 to 8 weeks) although absolute concentrations may vary widely between patients. On the other hand, long term treatment with auranofin is associated with lower and more stable serum concentrations of gold (0.5 to 0.7 mg/L), on the standard dosing regimen of 6 mg daily. Both compounds are retained within the body for prolonged periods. However, the amount of gold retained with auranofin is significantly less compared with GST (less than 5% of a tracer dose of auranofin--about 20% of the absorbed dose--is retained by 100 days whereas the retention for a single labelled dose of GST over a similar interval is greater than 50%). Excretory patterns of GST and auranofin also differ. Most of an absorbed dose of GST (greater than 70%) is excreted by the kidneys whereas only 50% of an absorbed (15% of an administered) dose of auranofin is excreted in the urine. Both compounds are avidly bound by plasma proteins and auranofin shows a particularly strong association with circulating cellular elements. In human subjects, parenterally administered gold is widely distributed among bodily tissues, showing a predilection for tissues of the reticuloendothelial system as well as the kidney and adrenal cortex. Comparable studies in humans are not available for auranofin but animal studies have shown comparatively less affinity for the liver, kidney and spleen. Valuable insight has been gained in analysing the comparative pharmacokinetics of oral and injectable gold compounds. Unfortunately, attempts to correlate pharmacokinetic findings with clinical response or pharmacodynamic changes, as a whole, remain largely unsuccessful with these agents.     

Alteration of interleukin-1 activity and the acute phase response in adjuvant arthritic rats treated with disease modifying antirheumatic drugs

Interleukin-1 (IL-1) activity and the acute phase response, as measured by plasma CRP and iron, were used to determine if the standard disease modifying antirheumatic drugs (DMARDs), gold, chloroquine and D-penicillamine had a common profile of activity in the adjuvant arthritic (AA) rat. All drugs were tested at a dose which significantly reduced noninjected paw swelling in AA rats. Inhibition of paw edema ranged from 37% for D-penicillamine (100 mg/kg) to 69% for auranofin (10 mg/kg). Two week medication of AA rats with gold sodium thiomalate (GST, 10 mg/kg, i.m.) or auranofin (10 mg/kg, p.o.) resulted in a significant decrease in splenic IL-1 activity, as measured in the standard lymphocyte activating factor (LAF) assay. The acute phase response, often associated with elevated IL-1 activity, was also significantly reduced following treatment of AA rats with 10 mg/kg of GST or auranofin (oral gold). Inhibition of the acute phase response by gold was determined by a significant reduction of plasma CRP levels (56-71% reduction) and enhancement of plasma iron levels (27-52% enhancement). In contrast to the effect of GST and auranofin on IL-1, CRP and iron, treatment with chloroquine (20, 30 and 35 mg/kg) and D-penicillamine (55 and 100 mg/kg) failed to reduce the acute phase response (as measured by plasma CRP and iron) or alter LAF activity from AA rat spleen cell supernatants. Based on its ability to reduce LAF activity in spleen cell supernatants and reduce the acute phase response, it is possible that the activity of gold in the AA rat may in part be due to its ability to inhibit IL-1 production in vivo. The inability of chloroquine and D-penicillamine to alter LAF activity and the acute phase response in AA rats does not preclude their possession of an immunoregulatory mechanism of action, but it does indicate that their mechanism of action in the AA rat probably differs from that of GST and auranofin.     

Different effects of two gold compounds on muscle contraction, membrane potential and ryanodine receptor.

Effects of gold sodium thiomalate and NaAuCl4 on skeletal muscle function were studied using intact single fibres of frog skeletal muscle and fragmented sarcoplasmic reticulum prepared from frog and rabbit skeletal muscles. Gold sodium thiomalate at a concentration of 500 microM decreased tension amplitude by 27% and resting membrane potential by 5.3% after 30 and 22 min, respectively. The duration of tetanus tension was markedly shortened by 500 microM gold sodium thiomalate. When 10 microM NaAuCl4 was applied to gold sodium thiomalate-pretreated fibres, the fibres lost the ability to contract upon electrical stimulation, similar to the effects of 10 microM NaAuCl4 alone. In the presence of thiomalic acid, on the other hand, NaAuCl4 did not completely block tetanus tension even at 50 microM. Thiomalic acid also inhibited NaAuCl4-induced membrane depolarization. These findings suggest that thiomalate masks the effects of gold ion on muscle function. When sarcoplasmic reticulum vesicles were incorporated into lipid bilayers, exposure of the cis side of the Ca2+-release channel to 100 microM gold sodium thiomalate rapidly increased the open probability of the channel 3.3-fold, from 0.032 in controls to 0.105, with an increase in number of open events and a decrease in mean closed time. The ability of NaAuCl4 to activate the Ca2+-release channel was much stronger than that of gold sodium thiomalate. Only 1 microM NaAuCl4 was enough to activate the channel and this gold was effective from either side of the channel. These results suggest that gold sodium thiomalate could be used as an antirheumatic drug without considering severe side-effects on skeletal muscle. Coexistent thiomalate probably contributes to protection of muscle function from side-effects of gold ion.     

Gold-induced reactive oxygen species (ROS) do not mediate suppression of monocytic mitochondrial or secretory function.

The toxicity of anti-rheumatic gold compounds has limited their use and development, yet both the toxicological and therapeutic actions of these compounds remain unclear. In the current study, we tested the hypothesis that intracellular reactive oxygen species (ROS) induced by Au(I) or Au(III) compounds mediate their ability to suppress mitochondrial activity. METHODS: Human THP1 monocytes were exposed to HAuCl(4) x 3H(2)O (Au(III)), or the anti-rheumatic compounds auranofin (AF) or gold sodium thiomalate (GSTM) for 6-72 h, after which mitochondrial activity (succinate dehydrogenase) was measured. To assess the role of cellular redox status as a mediator of mitochondrial suppression, monocytes were pre-treated with a pro-oxidant (t-butyl hydroquinone, t-BHQ) or antioxidant (N-acetyl cysteine, NAC ). ROS levels were measured 0-24h post-gold addition to determine their role as mediators of mitochondrial activity suppression. RESULTS: AF was the most potent inhibitor of mitochondrial activity, followed by Au(III) and GSTM. Only Au(III) induced intracellular ROS; no ROS formation was observed in response to AF or GSTM exposure. Although anti- and pro-oxidants had some effects on mitochondrial suppression of Au compounds, collectively the data do not support redox effects or ROS formation as major mediators of Au-compound mitochondrial suppression. CONCLUSIONS: Our results do not indicate that ROS and redox effects play major roles in mediating the cytotoxicity of AF, GSTM or Au(III).     

Anti-rheumatic gold compounds as sublethal modulators of monocytic LPS-induced cytokine secretion.

The objective of this study was to quantify the ability of sublethal concentrations of several gold compounds to differentially modulate the monocytic secretion of key cytokines that are important in the etiology of rheumatic diseases. Human THP1 monocytic cells were exposed to the anti-rheumatic drugs auranofin (AF), gold sodium thiomalate (GSTM) or HAuCl4 (Au(III)) for 24-72 h. Succinate dehydrogenase (SDH) activity of the monocytes was used to determine sublethal concentrations. Monocytes were then exposed to sublethal concentrations of gold compounds for 72 h, and the activator lipopolysaccharide (LPS) was added (or not) to cultures for the last 6h. The secretion of IL6, IL8, IL10, and TNFalpha were measured in cell supernatants using ELISA. Cytokine secretion was compared among concentrations and gold compounds. SDH experiments established a sublethal concentration range of 0-75 microM for GSTM and Au(III) and 0-0.5 microM for AF. In cytokine experiments, none of the compounds alone activated secretion of any of the cytokines, but all differentially (50-440%, p<0.05) increased LPS-induced secretion of IL6 and IL8 over TNFalpha and IL10. In conclusion, sublethal concentrations of AF, GSTM, and Au(III) all may differentially modulate activation of monocytic cells, and this differential modulation may be important in the mechanisms of action of these compounds.     

Pharmacologic modulation of TNF production by endotoxin stimulated macrophages: in vitro and in vivo effects of auranofin and other chrysotherapeutic compounds

The gold compounds, auranofin, sodium aurothiomalate, and triethyl gold phosphine have been demonstrated to inhibit various effector functions associated with monocyte-macrophage populations. Incubation of human peripheral blood monocytes and murine peritoneal macrophages with auranofin or triethyl gold phosphine inhibited TNF production in lipopolysaccharide [LPS] stimulated murine peritoneal macrophages. The inhibitory effect of auranofin and triethyl gold phosphine on LPS stimulated monokine production was reversible when these compounds were incubated with macrophage cultures at concentrations between 0.1-0.5 micrograms/ml. These compounds also inhibited both TNF and IL-1 production by human peripheral blood monocytes. Sodium aurothiomalate at these concentrations had no inhibitory effect on TNF or IL-1 production. Auranofin and triethyl gold phosphine also inhibited TNF production in vivo when compounds were administered orally or intraperitoneally 2 hours prior to a lethal dose of endotoxin. Serum TNF levels from Balb/c mice were significantly reduced when animals were predosed with 1-25 mg/kg of auranofin. The data suggest that the inhibition of TNF production by activated macrophages may contribute to the therapeutic role of gold compounds in the management of chronic inflammatory disease.     

Differential effects of anti-arthritic agents on subnormal plasma iron levels in adjuvant arthritic rats

Nonsteroidal anti-inflammatory drugs (NSAID's) and other antirheumatic compounds such as disease modifying antirheumatic drugs (DMARD's), immunosuppressives and glucocorticoids were tested to determine if daily medication for two weeks could elevate subnormal levels of plasma iron in adjuvant-arthritic (AA) rats. Aspirin, indomethacin, ibuprofen and phenylbutazone were chosen as representative carboxylic acids and pyrazole NSAID's. Although NSAID's at all doses significantly reduced noninjected paw swelling, no NSAID significantly enhanced subnormal plasma iron levels in AA rats. In contrast, the standard DMARD's auranofin and gold sodium thiomalate, as well as the glucocorticoid, dexamethasone and the immunosuppressives, methotrexate and cyclosporin-A all significantly restored plasma iron levels 28 to 100 percent. Plasma iron depression, a parameter of the acute phase response probably under regulation by pro-inflammatory cytokines, is not reversed by NSAID treatment. This appears to be a useful method for distinguishing NSAID's from other anti-arthritic compounds.     

Gold complex research in medical science. Difficulties with experimental design

Despite the use of gold complexes in modern medicine for over 100 years and the use of gold complexes in the management of rheumatoid disease for more than 60 years, the definitive mechanisms of action for efficacy and for toxicity have not been established. Gold is a group 1b metal in the periodic table with several oxidation states but it is only Au(I) which is active in the biological milieu. Gold sodium thiomalate is not only a polymeric structure, but also has the chiral ligand, thiomalic acid. Gold sodium thiomalate thus can exist in several different physical states which may have different biological activity. In addition the pharmacokinetic profile of gold complexes has been of little value in the understanding of either the mechanism of action, efficacy or toxicity for both the injectable and the oral gold complexes. Many authors have misinterpreted research data on the activities of gold complexes because they compared gold complexes of different structures, and gold complexes which exist at different pH. Experimental work in our laboratory has identified that gold sodium thiomalate is a mixture and can exist as either a yellow or a colourless solution. These have some similar but several different biological activities. Many factors contribute to the lack of understanding of the action of gold complexes. Some of these factors are related to the wide variation in physical structure and biological activities exhibited by these compounds.     

The effect of slow acting antirheumatic drugs on the production of cytokines by human monocytes

The mode of action of slow acting antirheumatic drugs (SAARDs) is poorly understood. Interleukin (IL)-1α, IL-1β, IL-6 and tumour necrosis factor (TNF)α are pleiotropic cytokines produced predominantly by macrophages which have been implicated in the pathogenesis of rheumatoid arthritis. We have investigated the potential of the following drugs to modulate the production of those cytokines by purified human monocytes stimulated by either lipopolysaccharide (LPS) or cytokines in vitro: gold sodium thiomalate (GST), auranofin, hydroxychloroquine (HCQ),d-penicillamine (d-Pen), sulphasalazine and its metabolites, sulphapyridine and 5-aminosalicylic acid (5-ASA). Auranofin, HCQ and sulphasalazine, at therapeutically relevant concentrations, inhibited the production of all four cytokines in vitro. There were some differential effects suggesting that HCQ was less effective at inhibiting cell-associated IL-1 production compared with IL-1 release, and the reverse seemed to be the case for sulphasalazine which did not inhibit IL-1 secretion as effectively as cell-associated IL-1 production. Sulphasalazine was also less effective at inhibiting IL-6 production compared with the other three cytokines. GST had only a minor inhibitory effect (on IL-1β release) andd-Pen, sulphapyridine and 5-ASA did not inhibit cytokine production. Finally, low concentrations of gold compounds (GST and auranofin) stimulated IL-1 and IL-6 production directly and potentiated IL-1, IL-6 and TNFα production induced by LPS. These results suggest that some SAARDs may inhibit cytokine production as part of their antirheumatic effect and that the enhancement of cytokine production by low doses of gold may potentially exacerbate rheumatoid disease at the early stages of chrysotherapy.     

Effects of coordinated gold compounds on in vitro and in situ DNA replication

Auranofin, a coordinated gold compound, inhibits in vitro DNA synthesis and displays in vivo antitumor activity. To understand the mechanisms of inhibition of DNA replication, we have examined the effects of auranofin and other gold complexes on the activities of purified cellular and herpesvirus-induced DNA polymerases, and on in situ DNA replication in permeabilized S phase KB cells. Evaluation of the data suggests the following conclusions. (1) The gold compounds varied in their abilities to inhibit DNA polymerase activities. DNA polymerase alpha was more sensitive to inhibition by gold compounds than DNA polymerase beta; (2) Inhibition of purified DNA polymerases by gold (I) compounds was noncompetitive with both DNA template and triphosphate substrates. Inhibition by SKF 101675, a gold (III) complex was competitive with DNA. (3) None of the gold compounds tested preferentially inhibited herpesvirus-induced DNA polymerases. (4) The gold complexes that inhibited in vitro DNA replication also inhibited in situ DNA synthesis. However, the potency and order of potency of the compounds varied between the in vitro and in situ systems. (5) Auranofin and other gold compounds inhibited the clonogenic capacity of KB cells in a concentration-dependent manner. The IC50 values measured in the clonogenic assay were significantly lower than those obtained from the in vitro and in situ DNA replication assays.     

Auranofin. A preliminary review of its pharmacological properties and therapeutic use in rheumatoid arthritis

Auranofin is the first orally active gold compound for the treatment of rheumatoid arthritis. Like other chrysotherapeutic agents, its exact mechanism of action is unknown, but it probably acts via immunological mechanisms and alteration of lysosomal enzyme activity. Although long term clinical experience with auranofin is limited, its efficacy appears to approach that of sodium aurothiomalate. Further comparative studies with aurothioglucose, hydroxychloroquine and D-penicillamine are required before definitive statements can be made regarding the relative efficacy of auranofin and these agents. While patients have demonstrated clinical remission of rheumatoid arthritis in response to auranofin therapy, radiological studies have been inconclusive regarding its effect on the occurrence or progression of erosive lesions. Auranofin is relatively well tolerated in most patients, but diarrhoea, skin rash, and pruritus are sometimes troublesome, and thrombocytopenia and proteinuria are potentially serious side effects which may occur during therapy. Whereas mucocutaneous side effects are more frequent with injectable gold compounds, gastrointestinal reactions are the most common adverse effect seen with auranofin. The frequency of side effects has been similar with auranofin and sodium aurothiomalate, but they are generally less severe with auranofin. While some of the side effects are controlled by a reduction in dosage, temporary or permanent withdrawal of auranofin may be necessary. Auranofin is clearly a useful addition to the limited list of agents with disease-modifying potential presently available for the treatment of rheumatoid arthritis. It will doubtless generate much interest as its final place in therapy becomes better defined through additional well-designed studies and wider clinical experience.     

The activation of gold complexes by cyanide produced by polymorphonuclear leukocytes--I. The effects of aurocyanide on the oxidative burst of polymorphonuclear leukocytes

It has been suggested that the antiarthritic gold complex, aurothiomalate (Autm), is activated by its conversion to aurocyanide by polymorphonuclear leukocytes (PMN) which generate cyanide from thiocyanate. In an examination of this hypothesis, a study has been conducted on the effects of aurocyanide on the oxidative burst of polymorphonuclear leukocytes (PMN) and monocytes activated by phorbol myristate acetate (PMA). Aurocyanide produced delayed inhibition of the oxidative burst as shown by its effect on both lucigenin and luminol-dependent chemiluminescence and on the production of superoxide. It was a more potent inhibitor of luminol-dependent chemiluminescence than free thiomalate and other by-products of the reaction between Autm and cyanide. Aurocyanide had a biphasic effect on the PMA-stimulated hexose monophosphate shunt of PMN, with enhancement at 0.1 microM and inhibition at 10 and 100 microM. The activity of aurocyanide was also compared with that of auranofin, an orally active gold complex, which inhibits a variety of functions of PMN and monocytes. At low concentrations, auranofin produced delayed inhibition of chemiluminescence in a similar fashion to aurocyanide but at high concentrations was an immediate inhibitor of the oxidative burst.     

The modulation of interleukin 1 production by interferon gamma, and the inhibitory effects of gold compounds

We have studied the in vitro effects of gold sodium thiomalate (GST) and auranofin (Auf) on the production of interleukin 1 (IL1) expressed as thymocyte co-stimulatory activity (TCSA), and interleukin 1 beta (IL1 beta) as modulated by interferon gamma (IFN gamma). Adherent cells (ADC), of which 80% were monocytes, were obtained from human peripheral blood, and stimulated with lipoprotein polysaccharide (LPS) for 24-48 h. TCSA and IL1 beta production by fresh ADC (0-24 h) was significantly higher than that of aged ADC (24-48 h). The addition of IFN gamma to ADC cultures, however, maintained the capacity of aging ADC to respond optimally to LPS. The addition of GST or Auf inhibited this modulatory effect of IFN gamma, resulting in a marked reduction of TCSA and IL1 beta production. The effects of IFN gamma on the production of IL1 may be important in the pathogenesis of rheumatoid arthritis (RA). The inhibition by GST and Auf of IFN gamma modulation may contribute to the therapeutic efficacy of these drugs in RA.     

The effect of slow-acting anti-rheumatic drugs (SAARDs) and combinations of SAARDs on monokine production in vitro.

The mode of action of slow-acting anti-rheumatic drugs (SAARDs) is complex but may often include effects on cytokine (interleukin-1, IL-1, and tumour necrosis factor, TNF) production by monocytes/macrophages. Different SAARDs may have variable effects on cytokine production in vitro depending on the concentration of drug, the presence of other SAARDs and individual variation. The gold compounds gold sodium thiomalate (GST) and auranofin (AF) had a bimodal effect on cytokine production. High concentrations of GST (greater than 1 microgram/ml) weakly inhibited IL-1-beta secretion (without affecting IL-1-alpha or TNF secretion and without affecting cell-associated IL-1-alpha and IL-1-beta accumulation), and although AF (greater than 100 ng/ml) inhibited cytokine production it did so at concentrations near to the toxic range for the drug (greater than 200 ng/ml). GST and AF when used in combination inhibited cytokine production in a synergistic manner even at concentrations that would potentiate cytokine production if used individually. Hydroxychloroquine (HCQ) and sulfasalazine (SAP) were two other inhibitory SAARDs which acted synergistically in combination. Combination of HCQ and SAP with gold drugs gave variable results. D-penicillamine (D-pen) and methotrexate (MTX) were two SAARDs that generally did not affect cytokine production individually or in combination with other SAARDs. These results suggest that combination SAARD therapy may more effectively target excessive cytokine production, which is a hallmark of rheumatoid arthritis.