Auranofin modulated cytoplasmic free calcium in neutrophils by mobilizing intracellular calcium and inhibiting protein kinase

Auranofin, an anti-rheumatic gold compound, modulates apoptosis by elevating the intracellular calcium concentration ([ca2+]I) in mcf-7 breast cancer cells

Auranofin, a transition metal complex is used for the treatment of rheumatoid arthritis but is also an effective anti-cancer drug. We investigate the effects of Auranofin in inducing cell death by apoptosis and whether these changes are correlated to changes of intracellular calcium concentration ([Ca²⁺]_i) in breast cancer cells (MCF-7). Cytotoxicity of Auranofin was evaluated using MTS assay and the Trypan blue dye exclusion method. With fluorescent dyes SR-FLICA and 7-AAD apoptotic death and necrotic death were differentiated by Flow cytometry. A concentration dependent decrease in the viability occurred and cells were shifted to the apoptotic phase. Intracellular calcium ([Ca²⁺]_i) was recorded using florescence microscopy and a calcium sensitive dye (Fluo-4 AM) with a strong negative correlation (r = −0.713) to viability. Pharmacological modulators 2-APB (50 μM), Nimodipine (10 μM), Caffeine (10 mM), SKF 96365(20 μM) were used to modify calcium entry and release. Auranofin induced a sustained increase of [Ca²⁺]_i in a concentration and time dependent manner. The use of different blockers of calcium channels did not reveal the source for the rise of [Ca²⁺]_i. Overall, elevation of [Ca²⁺]_i by Auranofin might be crucial for triggering Ca²⁺-dependent apoptotic pathways. Therefore, in anti-cancer therapy, modulating [Ca²⁺]_i should be considered as a crucial factor for the induction of cell death in cancer cells.

Gold drug auranofin could reduce neuroinflammation by inhibiting microglia cytotoxic secretions and primed respiratory burst

Neuroinflammation contributes to the pathogenesis of neurological disorders. Anti-inflammatory treatments could potentially be used to slow down the progression of these diseases. We studied the anti-neuroinflammatory activity of gold compounds which have been used to treat rheumatoid arthritis. Non-toxic concentrations of auranofin (0.1-1 μM) significantly reduced the cytotoxic secretions by primary human microglia and microglia-like THP-1 promonocytic cells. Auranofin inhibited primed NADPH-oxidase dependent respiratory burst and secretion of tumor necrosis factor (TNF)-α and nitric oxide by monocytic cells. It had a direct neuroprotective effect on SH-SY5Y neuronal cells. Auranofin could have a novel application in the treatment of neurodegenerative diseases.

Pivotal Advance: Inhibition of HMGB1 nuclear translocation as a mechanism for the anti-rheumatic effects of gold sodium thiomalate

Gold compounds such as gold sodium thiomalate (GST) can reduce the symptoms of rheumatoid arthritis (RA), although their mechanism of action is not well defined. As the proinflammatory mediator high mobility group box chromosomal protein 1 (HMGB1) may play a role in the pathogenesis of RA, we have performed in vitro studies to investigate whether GST inhibits HMGB1 release as the basis of its mode of action. Murine RAW 264.7 or human THP-1 macrophage cells were stimulated in culture with agents causing extracellular HMGB1 release, including LPS, IFN-gamma, polyinosinic:polycytidylic acid, IFN-beta, or NO in the presence of GST, ranging from 0 microM to 250 microM. Secretion and intracellular location of HMGB1 were assessed by Western blotting, HMGB1-specific ELISPOT assay, and immunofluorescent staining. In parallel, TNF and IFN-beta levels were analyzed by ELISPOT and/or ELISA. Supernatant NO production was analyzed by the Griess method. At pharmacologically relevant doses, GST inhibited the extracellular release of HMGB1 from activated macrophages and caused the nuclear retention of this protein; in contrast, no effects were observed on the secretion or production of TNF. Release of the key endogenous mediators of HMGB1 translocation, IFN-beta and NO, was inhibited by GST. This inhibition required gold, as sodium thiomalate did not affect the responses measured. Furthermore, gold chloride also inhibited release of HMGB1. Together, these results suggest a new mechanism for the anti-rheumatic effects of gold salts in RA and the potential of drugs, which interfere with intracellular HMGB1 transport mechanisms, as novel agents to treat RA.

Characterization of platelet-activating factor-induced cytosolic calcium mobilization in human eosinophils

BACKGROUND

Activated eosinophils play an important role in the pathogenesis of bronchial asthma and other allergic diseases, and platelet-activating factor (PAF) is a potent activator of eosinophils.

OBJECTIVE

To characterize the cytosolic Ca2+ ([Ca2+]i) mobilization in human eosinophils in response to PAF.

METHODS

[Ca2+]i responses to PAF were examined in human eosinophils using a microscopic fura-2 fluorescence-ratio imaging system.

RESULTS

PAF caused a significant and dose-dependent increase in (Ca2+)i, which consisted of an initial rapid rise followed by a sustained elevation. This PAF-induced (Ca2+)i rise was inhibited by WEB 2086, a specific PAF receptor antagonist. The addition of 5 mM EGTA or 1 mM Ni2+ to a nominally Ca2+-free solution did not appreciably reduce the initial rise but significantly inhibited the sustained rise. The application of a protein kinase C inhibitor, Ro31-8220, augmented the sustained increase by PAF. Thapsigargin, a microsomal Ca2+ ATPase inhibitor, induced no appreciable change in a nominally Ca2+-free solution but induced a marked increase in (Ca2+)i when changed to a Ca2+-containing solution.

CONCLUSIONS

The initial rapid rise and the following sustained rise in (Ca2+)i by PAF depends on Ca2+ release from the intracellular Ca2+ stores and Ca2+ influx, respectively, which are regulated by protein kinase C in human eosinophils. Furthermore, the so called Ca2+-capacitative entry is possibly involved in the Ca2+ influx from the extracellular solution in human eosinophils.

Auranofin inhibits interleukin-1beta-induced transcript of cyclooxygenase-2 on cultured human synoviocytes

The aim of this study was to characterize the effects of auranofin (2,3,4,6-tetra-O-acetyl-l-thio-beta-D-gluco-pyranosato-S) on cyclooxygenase expression and prostaglandin E(2) synthesis on cultured human synovial fibroblast-like cells (synoviocytes). Synoviocytes were treated with auranofin in the presence or absence of interleukin-1beta. Cultured supernatants were harvested for prostaglandin E(2) synthesis. Cyclooxygenase-1 and -2 expression was analyzed with Western and Northern blotting. Translocation of nuclear factor-kappa B p65 was determined by immunostaining. Cytotoxicity was measured with 51Cr release assay. Auranofin attenuated interleukin-1beta-induced prostaglandin E(2) production of the cells in a dose-dependent fashion. Auranofin selectively suppressed interleukin-1beta-induced cyclooxygenase-2 mRNA and protein expression of the cells without alteration of cyclooxygenase-1 expression. Also, auranofin interfered with interleukin-1beta-induced translocation of nuclear factor-kappa B. These inhibitory effects did not originate in the cytotoxicity of the agent. Our data indicate that auranofin inhibits interleukin-1beta-induced prostaglandin E(2) synthesis and cyclooxygenase-2 expression via suppression of nuclear factor-kappa B activation on synoviocytes.

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.

Effects of antirheumatic drugs on adhesiveness of endothelial cells and neutrophils

Because disease-modifying antirheumatic drugs might exert part of their effects on adhesion of polymorphonuclear neutrophils (PMN) to endothelial cells, this being the first step for PMN migration to inflammatory lesions, we evaluated such drug effects in vitro. Gold sodium thiomalate (GSTM) impaired the ability of interleukin 1beta (IL-1beta)-stimulated human umbilical vein endothelial cells (HUVEC) to express E-selectin and to bind PMN but had no effect on the expression of intercellular adhesion molecule 1 (ICAM-1) or on hyperadhesivity of N-formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated PMN. Auranofin (AF) interacted with HUVEC and PMN adhesiveness but in opposite directions: this drug hampered IL-1beta-induced HUVEC hyperadhesiveness and expression of E-selectin and intercellular adhesion molecule 1, but augmented PMN adherence and CD18 expression. The net effect of auranofin was a reduction of cytokine-driven adhesiveness and enhancement of formylpeptide-induced adhesion. Salazopyrin did not affect HUVEC or PMN adhesiveness or E-selectin and intercellular adhesion molecule 1 expression. Thus, the gold-containing drugs modulated HUVEC and PMN adhesiveness by different mechanisms but ones involving surface adhesion molecules.

Signaling mechanisms of elevated neutrophil O2- generation after burn injury

A full skin thickness burn injury was produced in anesthetized rats by exposing 25% of total body surface area to 98 degrees C water for 10 s. Sham (exposed to 37 degrees C water) and burn rats were killed 1, 3, 7, or 10 days later. The role of Ca2+ signaling and Ca(2+)-related protein kinase C (PKC) activation in neutrophil O2- generation was ascertained by evaluating the effect of treatment of the rats with the Ca2+ entry blocker, diltiazem. There was an overt enhancement of O2- generation by polymorphonuclear leukocytes from burn rats on days 1, 3, and 7 postburn, with the peak release occurring on day 3 postburn. O2- generation comparable to the sham was noted on day 10 after the burn. O2- releases on days 1, 3, and 7 postburn were accompanied by marked elevation of Cai2+ and PKC responses. Like the O2- release, intracellular Ca2+ concentration ([Ca2+]i) response on day 10 after burn was suppressed to levels found in the sham group. The treatment of burn rats with diltiazem prevented the upregulation of both [Ca2+]i and PKC responses as well as O2- generation in neutrophils in rats on days 1, 3, and 7 after the burn. Because previous studies have shown that increases in [Ca2+]i precede O2- generation and degranulation, our results suggest that neutrophil O2- release enhancement in the early stages after burn injury (e.g., days 1-7 postburn) results from an overactivation of the Cai2+ and PKC signaling pathways. The heightened O2- generation during the early burn injury phase might play a role in tissue damage in one or more of host organs.

Auranofin inhibits calcium uptake into opsonized-zymosan-stimulated neutrophils obtained from rats

In order to study the pharmacological action site of auranofin during the functional suppression of leukocytes, especially neutrophils, we investigated the influence of auranofin on the calcium-45 (45Ca2+) uptake into peripheral blood neutrophils and peritoneal resident macrophages isolated from normal and adjuvant-induced arthritis (AA) rats. Calcium-45 uptake into neutrophils and macrophages obtained from normal and AA rats was increased by stimulation with opsonized-zymosan, while auranofin inhibited the increase in the 45Ca2+ uptake into neutrophils, but not into macrophages. There was a tendency that auranofin more strongly inhibited the increase in the 45Ca2+ uptake into neutrophils obtained from AA rats than normal rats, but no statistically significant difference between them was observed in the inhibitory potency of auranofin. From these results, it is suggested that auranofin would show anti-rheumatic and anti-inflammatory effects by the inhibition of Ca2+ uptake into neutrophils which infiltrate into local lesions during the early and active phases of rheumatoid arthritis.

N-acetylsphingosine (C2-ceramide) inhibited neutrophil superoxide formation and calcium influx

Ceramide, a product arising from sphingomyelinase activity, has been shown to act as an intracellular second messenger in effecting growth inhibition, cellular differentiation, and apoptosis. In the present study, the relative effects of cell-permeable ceramides, N-acetylsphingosine (C2-ceramide) and N-hexanoylsphingosine (C6-ceramide), on neutrophil responses were measured. When cells were activated with fMet-Leu-Phe, C2-ceramide both potentiated (< 1 microM) and inhibited (> 1 microM) superoxide generation. C2- and C6-ceramide inhibited phorbol ester-induced superoxide release from neutrophils at IC50 values of 5 and 120 microM, respectively. C2-ceramide had no effect on semipurified protein kinase C activity. Neither ceramide affected significantly the general level of phosphorylated proteins in phorbol ester-treated cells. C2-ceramide (1-20 microM) alone did not change cytosolic free Ca2+ levels but inhibited Ca2+ and Mn2+ influx in fMet-Leu-Phe-activated neutrophils. In contrast, sphingosine enhanced Ca2+ entry; thus, ceramide conversion to sphingosine was not significant. Unlike C2-ceramide, C2-dihydroceramide failed to block superoxide generation or Ca2+ influx. Preincubation of cells with 10 nM okadaic acid reversed slightly the effects of C2-ceramide. Calyculin A, tautomycin, and much higher concentrations of okadaic acid inhibited agonist-induced Ca2+ influx. We postulate that C2-ceramide may inhibit neutrophil superoxide release by activation of type 2A protein phosphatases. Results suggest that protein phosphatase type 1 up-regulates Ca2+ entry, whereas type 2A (or a ceramide-activated subtype) forestalls Ca2+ entry by inactivating a calcium influx factor.

Staurosporine induces hydrolysis of phosphatidyl inositol 4,5-bisphosphate in human platelets

Staurosporine in the micromolar range raised inositol trisphosphate in intact human platelets to levels comparable to that mediated by thrombin. This response was inhibited by neomycin, a phospholipase C antagonist. Staurosporine alone induced a weak, transient rise in cytosolic free calcium levels ([Ca2+]i) from release of internal Ca2+ stores but potentiated the effect induced by thrombin. Therefore, it is unlikely that this alkaloid suppressed inositol trisphosphate mobilization of Ca2+. Additional studies show that staurosporine, 0.5-5 microM, stimulated GTPase activity in platelet membranes while 2 microM K252a and 20 microM H7 were inactive. Present results suggest that staurosporine may activate platelet phospholipase C at the level of G proteins or receptors.

Receptor-operated Ca2+ signaling and crosstalk in stimulus secretion coupling

In the cells of higher eukaryotic organisms, there are several messenger pathways of intracellular signal transduction, such as the inositol 1,4,5-trisphosphate/Ca2+ signal, voltage-dependent and -independent Ca2+ channels, adenylate cyclase/cyclic adenosine 3',5'-monophosphate, guanylate cyclase/cyclic guanosine 3',5'-monophosphate, diacylglycerol/protein kinase C, and growth factors/tyrosine kinase/tyrosine phosphatase. These pathways are present in different cell types and impinge on each other for the modulation of the cell function. Ca2+ is one of the most ubiquitous intracellular messengers mediating transcellular communication in a wide variety of cell types. Over the last decades it has become clear that the activation of many types of cells is accompanied by an increase in cytosolic free Ca2+ concentration ([Ca2+]i) that is thought to play an important part in the sequence of events occurring during cell activation. The Ca2+ signal can be divided into two categories: receptor- and voltage-operated Ca2+ signal. This review describes and integrates some recent views of receptor-operated Ca2+ signaling and crosstalk in the context of stimulus-secretion coupling.

Sphingosine mobilizes intracellular calcium in human neutrophils

The effect of sphingosine on the cytosolic free Ca2+ concentrations, [Ca2+]i, of human neutrophils was re-examined using Fura-2 loaded cells. We found that sphingosine induced a dose-dependent elevation of [Ca2+]i. At sphingosine concentrations > or = 10 microM, the rise in [Ca2+]i was biphasic; an initial phase increasing basal [Ca2+]i by 100% was succeeded by a second phase which raised [Ca2+]i to several microM. The enhanced signal was sustained and slowly approached the Fmax of Fura-2 over 10 min. Although cytotoxicity assays indicate that Fura-2 leakage contributed to the rise in fluorescence, EGTA, surprisingly, had no effect on the time course of this response. The explanation was that EGTA blocked Fura-2 leakage from and trypan blue uptake by neutrophils. Thus, in the presence of EGTA, biphasic increases in the fluorescent signal can be attributed mainly to release of intracellular Ca2+. Mn2+ quenching studies confirmed that sphingosine mobilized Ca2+ in two distinct phases and promoted the influx of Mn2+. Mn2+ entry, however, was not matched by substantial Ca2+ influx. Sphingosine elevation of [Ca2+]i was insensitive to pertussis toxin treatment of neutrophils and was not correlated with (1,4,5)IP3 formation. Studies with semi-permeabilized cells show that sphingosine, up to 80 microM, neither mobilized Ca2+ significantly nor inhibited active Ca2+ sequestration. Sphingosylphosphorylcholine induced a small but dose-dependent release of Ca2+. We hypothesize that a metabolite of sphingosine may release Ca2+ directly in intact neutrophils.

Gold complexes and activation of human polymorphonuclear leukocytes. Dissociation of changes in membrane potential and oxidative burst

The effects of the gold compounds on the alteration of membrane potential of polymorphonuclear leukocytes (PMN) in response to various stimulants have been compared with their effects on the oxidative burst. The present studies have shown that gold complexes [auranofin (AF), aurothiomalate (Autm), aurocyanide (Au(CN)2-)] have contrasting effects on the membrane potential of 3,3'-dipentyloxacarbocyanine [di-O-C5(3)] loaded PMN. Au(CN)2- at concentrations which inhibit the oxidative burst of PMN did not affect the membrane depolarization after activation of PMN by phorbol myristate acetate (PMA) and N-formyl-methionyl-leucyl phenylalanine (FMLP); Autm slightly stimulated the oxidative burst but had no effect on the depolarization of PMN. In contrast, AF inhibited the depolarization of stimulated PMN to an extent depending upon the concentration of AF, the time of preincubation and the stimulus. The membrane depolarization of PMN caused by PMA, FMLP and concanavalin A (ConA) was inhibited by AF (5 microM) but the depolarization induced by calcium ionophore (A23187) was not affected. AF at the same conditions inhibits the oxidative burst of PMN induced by all these single stimuli including the calcium ionophore. Dissociation of membrane depolarization and superoxide generation caused by AF was also seen in PMN activated by two stimuli. AF (5 microM) had little initial inhibitory effect on the oxidative burst of PMN stimulated by combinations of PMA and ConA or PMA and FMLP whereas it almost totally blocked the depolarization caused by these combinations. Preincubation of cells with 5 microM AF for less than 5 min prior to the addition of PMA allowed membrane depolarization which was followed rapidly by repolarization. None of the gold complexes studied had any effect on the resting membrane potential of PMN.

Effect of gold compounds on the activity of adenylyl cyclase in human lymphocyte membranes

OBJECTIVE

To determine the effects of aurothioglucose, aurothiomalate, and auranofin on basal and forskolin-activated adenylyl cyclase activity in human total lymphocyte membranes, and in membranes of T and B lymphocyte subsets.

METHODS

Membranes were isolated from human total lymphocytes and T and B cell subsets. The effects of gold compounds on basal and forskolin-stimulated activity of adenylyl cyclase were measured by radioassay.

RESULTS

The gold compounds inhibited adenylyl cyclase activity. This inhibitory effect required the presence of both the sulfhydryl ligands and aurous cation.

CONCLUSION

Regulation of lymphocyte adenylyl cyclase by gold compounds represents a potential mode of action of these drugs in rheumatic diseases.

Polyamines enhance calcium mobilization in fMet-Leu-Phe-stimulated phagocytes

Spermidine and putrescine (50 microM-1 mM), found in exudates from infection sites, significantly enhance fMet-Leu-Phe-induced Ca2+ mobilization in differentiated HL-60 cells and polymorphonuclear leukocytes (PMNs) by delaying the return to basal cytosolic Ca2+ levels. This enhancement by polyamines is associated with inhibition of Ca2+ efflux across the plasma membrane. In parallel with their effects on Ca2+ signaling, polyamines also significantly prolong the kinetics of fMet-Leu-Phe-induced protein kinase C translocation. Thus, polyamines may play a novel role in modulating regulatory events in phagocytes.