Action of sodium aurothiomalate on erythrocyte membrane

The anti-rheumatic gold salt aurothiomalate suppresses interleukin-1beta-induced hyaluronan accumulation by blocking HAS1 transcription and by acting as a COX-2 transcriptional repressor

Gold compounds are among the oldest disease-modifying drugs and are still widely used today for treating rheumatoid arthritis. Despite decades of use, little is known about the mode of action of this class of drugs. Here we have demonstrated that aurothiomalate (AuTM) suppresses hyaluronan accumulation by blocking interleukin (IL)-1beta-induced hyaluronan synthase-1 transcription. We have further demonstrated that, in fibroblast-like synoviocytes (FLSs), AuTM acts as a specific COX-2 transcriptional repressor in that IL-1beta-induced COX-2 transcription is blocked, whereas COX-1 transcription and translation is unaffected. As a consequence, PGE2 levels released by FLS are dose-dependently reduced in cells exposed to AuTM. Of similar importance is the demonstration that AuTM does block NFkappaB-DNA interaction. In addition, two other transcription factors implicated in inflammatory events, namely AP-1 and STAT3, are blocked as well. The effect on NFkappaB likely explains the inhibition of COX-2 as well as that of HAS1, as both are genes that depend on the activation of NFkappaB. Interestingly, AuTM does not interfere with IL-1beta-induced IkappaB alpha degradation, in most cases a prerequisite for subsequent NFkappaB activation. Furthermore, evidence is presented that, in FLS, AuTM blocks NFkappaB-DNA interaction neither by binding to NFkappaB binding sites nor by interacting with activated NFkappaB proteins. Taken together, AuTM treatment of FLS blocks two of the most important proinflammatory events that are associated with rheumatoid arthritis. AuTM blocks the release of PGE2 and prevents the activation of NFkappaB, therefore blocking IL-1beta-induced hyaluronan accumulation and likely a series of other pro-inflammatory NFkappaB-dependent genes.

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.

Myocrisin-mediated oxidative stress

This study reports on the ability of myocrisin to mediate in the production and detoxification of oxidants (principally hydrogen peroxide) in the monocyte in-vivo and in-vitro. The hydrogen peroxide produced by the monocyte derived from rheumatoid arthritis patients being treated with myocrisin was found to be 14.9 +/- 1.6 nmoles/10(6) cells and is elevated above levels found in monocytes obtained from patients either being treated with non-steroidal anti-inflammatory drugs (NSAIDs) (11.3 +/- 0.4 nmoles/10(6) cells; P < 0.01) or normal healthy volunteers (11.2 +/- 1.2 nmoles/10(6) cells; P < 0.01). A comparative study on glutathione (GSH) oxidation indicated that levels of monocyte GSH were elevated in myocrisin-treated patients (2.4 +/- 0.49 mmol/l) over normal healthy volunteers (0.83 +/- 0.18 mM; P < 0.01) and that levels of monocyte diglutathione (GSSG) were depressed (myocrisin, 0.97 +/- 0.41 micromol/l; normal, 5.71 +/- 0.73 micromol/l; P < 0.01). The non-inhibition of glutathione reductase and the inhibition of glutathione peroxidase by gold provides the link between these two observations. Thus, gold therapy would seem to elevate monocyte hydrogen peroxide, increase monocyte reduced glutathione and decrease plasma glutathione peroxidase activity. Subsequently, the data from this small group of patients (n = 10) provides an indication that, in-vivo, myocrisin contributes to an increase in oxidative stress.

A comparative study of the interaction of Myocrisin with albumin and gamma-globulin

The reactions of Myocrisin with albumin and gamma-globulin have been investigated using atomic absorption spectrometry and gel filtration. Albumin rapidly binds gold up to the levels predicted from the concentration of free sulphydryl groups present in the protein. However, in the presence of glutathione, gold incorporation is increased, suggesting that in vivo, free thiols (glutathione, thiomalate) may facilitate gold uptake by the protein. In comparison, gamma-globulin is found to be capable of binding up to one atom of gold per molecule of protein in a slow reaction which requires high Myocrisin concentrations.