The secondary alcohol metabolite of doxorubicin irreversibly inactivates aconitase/iron regulatory protein-1 in cytosolic fractions from human myocardium

The iron regulatory proteins: targets and modulators of free radical reactions and oxidative damage

Iron acquisition is a fundamental requirement for many aspects of life, but excess iron may result in formation of free radicals that damage cellular constituents. For this reason, the amount of iron within the cell is carefully regulated in order to provide an adequate level of a micronutrient while preventing its accumulation and toxicity. A major mechanism for the regulation of iron homeostasis relies on the post-transcriptional control of ferritin and transferrin receptor mRNAs, which are recognized by two cytoplasmic iron regulatory proteins (IRP-1 and IRP-2) that modulate their translation and stability, respectively. IRP-1 can function as a mRNA binding protein or as an aconitase, depending on whether it disassembles or assembles an iron-sulfur cluster in response to iron deficiency or abundancy, respectively. IRP-2 is structurally and functionally similar to IRP-1, but does not assemble a cluster nor exhibits aconitase activity. Here we briefly review the role of IRP in iron-mediated damage induced by oxygen radicals, nitrogen-centered reactive species, and xenobiotics of pharmacological and clinical interest.

Nitric oxide and peroxynitrite activate the iron regulatory protein-1 of J774A.1 macrophages by direct disassembly of the Fe-S cluster of cytoplasmic aconitase

Posttranscriptional regulation of iron homeostasis involves, among other factors, a reversible conversion of the Fe-S enzyme cytoplasmic aconitase to a mRNA-binding iron regulatory protein (IRP-1) that lacks an Fe-S cluster. Previous studies have shown that aconitase/IRP-1 may be a target of *NO or peroxynitrite (ONOO(-)), formed after reaction of *NO with superoxide anion (O(2)(*-)); however, the mechanisms and consequences of such interactions have remained uncertain. In this study, recombinant aconitase/IRP-1 was exposed to SIN-1, whose thermal decomposition releases *NO and O(2)(*-). Results showed that SIN-1 was able to induce concomitant inactivation of aconitase and activation of IRP-1, attributable to cluster disassembly induced by ONOO(-). SIN-1 was used also in lysates of J774A.1 mouse macrophages grown under control conditions, or subjected to iron loading or starvation by treatment with hemin or desferrioxamine, respectively. Three lines of evidence confirmed that ONOO(-) activated IRP-1 by removing iron from the Fe-S cluster of cytoplasmic aconitase. First, IRP-1 activation was accompanied by iron release and loss of aconitase activity. Second, aconitase activity was recovered by reassembling Fe-S clusters with cysteine and ferrous ammonium sulfate. Third, iron release and IRP-1 activation were observed in lysates from control or iron-loaded macrophages, containing increasing levels of Fe-S clusters, but not in lysates from iron-starved macrophages, in which aconitase had already undergone cluster disassembly and switched to IRP-1. *NO was less efficient than ONOO(-) in attacking the Fe-S cluster of cytoplasmic aconitase; in fact, SIN-1-dependent iron release and IRP-1 activation were diminished by superoxide dismutase, which scavenged O(2)(*-) before it reacted with *NO to form ONOO(-). Under comparable conditions, however, both *NO and ONOO(-) inactivated an IRP-2 unable to assemble an Fe-S cluster. These results indicate that *NO and ONOO(-) may activate IRP-1 by attacking the Fe-S cluster of cytoplasmic aconitase, while also inactivating the cluster-deficient IRP-2. Such divergent actions offer clues to explain links between iron homeostasis and reactive nitrogen species in macrophages involved in inflammation or other pathophysiologic conditions.

Transferrin receptor-dependent iron uptake is responsible for doxorubicin-mediated apoptosis in endothelial cells: role of oxidant-induced iron signaling in apoptosis

In the past, investigators have successfully used iron chelators to mitigate the cardiotoxicity of doxorubicin (DOX), a widely used anticancer drug that induces reactive oxygen species (ROS), oxidative damage, and apoptosis. Although intracellular iron plays a critical role in initiating DOX-induced apoptosis, the molecular mechanism(s) that link iron, ROS, and apoptosis are still unknown. In this study, we demonstrate that apoptosis results from the exposure of bovine aortic endothelial cells to DOX and that the apoptotic cell death is accompanied by a significant increase in cellular iron ((55)Fe) uptake and activation of iron regulatory protein-1. Furthermore, DOX-induced iron uptake was shown to be mediated by the transferrin receptor (TfR)-dependent mechanism. Treatment with the anti-TfR antibody (IgA class) dramatically inhibited DOX-induced apoptosis, iron uptake, and intracellular oxidant formation as measured by fluorescence using dichlorodihydrofluorescein. Treatment with cell-permeable iron chelators and ROS scavengers inhibited DOX-induced cellular (55)Fe uptake, ROS formation, and apoptosis. Based on these findings, we conclude that DOX-induced iron signaling is regulated by the cell surface TfR expression, intracellular oxidant levels, and iron regulatory proteins. The implications of TfR-dependent iron transport in oxidant-induced apoptosis in endothelial cells are discussed.

Doxorubicin and C-13 deoxydoxorubicin effects on ryanodine receptor gene expression

Chronic anthracycline administration to rabbits causes impairment of cardiac contractility and decreased gene expression of the calcium-induced calcium release channel of sarcoplasmic reticulum (SR), the ryanodine receptor (RYR2). The C-13 hydroxy metabolite (doxorubicinol), formed in the heart, has been hypothesized to contribute to anthracycline cardiotoxicity. C-13 deoxydoxorubicin is an analog unable to form the C-13 hydroxy metabolite. Therefore, doxorubicin, C-13 deoxydoxorubicin, or saline was administered to rabbits (1 mg/kg iv twice weekly for 8 weeks). Left ventricular fractional shortening (LVFS) was decreased by chronic treatment with doxorubicin (28 +/- 2%; P < 0.05), but not C-13 deoxydoxorubicin (33 +/- 2%) compared to age-matched pair-fed controls. Doxorubicin, but not C-13 deoxydoxorubicin, caused a significant reduction (P < 0.02) in the ratio of RYR2/Ca-Mg ATPase (SERCA2) mRNA levels (0.57 +/- 0.1 vs 1.22 +/- 0.2, respectively) in the left ventricle. This suggests that doxorubicinol may contribute to the downregulation of cardiac RYR2 expression in chronic doxorubicin cardiotoxicity.

Impairment of myocardial contractility by anticancer anthracyclines: role of secondary alcohol metabolites and evidence of reduced toxicity by a novel disaccharide analogue

1. The anticancer anthracycline doxorubicin (DOX) causes cardiotoxicity. Enzymatic reduction of a side chain carbonyl group converts DOX to a secondary alcohol metabolite that has been implicated in cardiotoxicity. We therefore monitored negative inotropism, assessed as inhibition of post-rest contractions, in rat right ventricle strips exposed to DOX or to analogues forming fewer amounts of their alcohol metabolites (epirubicin, EPI, and the novel disaccharide anthracycline MEN 10755). 2. Thirty microM EPI exhibited higher uptake than equimolar DOX, but formed comparable amounts of alcohol metabolite due to its resistance to carbonyl reduction. MEN 10755 exhibited also an impaired uptake, and consequently formed the lowest levels of alcohol metabolite. Accordingly, DOX and EPI inhibited post-rest contractions by approximately 40-50%, whereas MEN 10755 inhibited by approximately 6%. 3. One hundred microM EPI exhibited the same uptake as equimolar DOX, but formed approximately 50% less alcohol metabolite. One hundred microM MEN 10755 still exhibited the lowest uptake, forming approximately 60% less alcohol metabolite than EPI. Under these conditions DOX inhibited post-rest contractions by 88%. EPI and MEN 10755 were approximately 18% (P<0.05) or approximately 80% (P<0.001) less inhibitory than DOX, respectively. 4. The negative inotropism of 30-100 microM DOX, EPI, or MEN 10755 correlated with cellular levels of both alcohol metabolites (r=0.88, P<0.0001) and carbonyl anthracyclines (r=0.79, P<0.0001). Nonetheless, multiple comparisons showed that alcohol metabolites were approximately 20-40 times more effective than carbonyl anthracyclines in inhibiting contractility. The negative inotropism of MEN 10755 was therefore increased by chemical procedures, like side chain valeryl esterification, that facilitated its uptake and conversion to alcohol metabolite but not its retention in a carbonyl form. 5. These results demonstrate that secondary alcohol metabolites are important mediators of cardiotoxicity. A combination of reduced uptake and limited conversion to alcohol metabolite formation might therefore render MEN 10755 more cardiac tolerable than DOX and EPI.

Diminished molecular response to doxorubicin and loss of cardioprotective effect of dexrazoxane inEgr-1deficient female mice

Doxorubicin (DOX) and VP16 are DNA topoisomerase II inhibitors yet only DOX induces an irreversible cardiotoxicity, likely through DOX-induced oxidative stress. Egr-1 is overexpressed after many stimuli that increase oxidative stress in vitro and after DOX-injection into adult mice in vivo. To investigate Egr-1 function in the heart, we compared the molecular and histological responses of wild type (+/+) and Egr-1 deficient (–/–) female mice to saline, DOX, VP16, the cardioprotectant dexrazoxane (DZR), or DOX+DZR injection. DOX, and to a lesser extent VP16, induced characteristic increases in cardiac muscle and non-muscle genes typical of cardiac damage in +/+ mice, whereas only β-MHC and Sp1 were increased in –/– mice. DZR-alone treated +/+ mice showed increased cardiomyocyte transnuclear width without a change to the heart to body weight (HW/BW) ratio. However, DZR-alone treated –/– mice had an increased HW/BW, increased cardiomyocyte transnuclear width, and gene expression changes similar to DOX-injected +/+ mice. DZR pre-injection alleviated DOX-induced gene changes in +/+ mice; in DZR+DOX injected –/– mice the increases in cardiac and non-muscle gene expression were equal to, or exceeded that, detected after DOX-alone or DZR-alone injections. We conclude that Egr-1 is required for DOX-induced molecular changes and for DZR-mediated cardioprotection.Key words: mice, gene expression, doxorubicin, DNA topoisomerase II inhibitors, cardioprotection.

Anthracycline drug targeting: cytoplasmic versus nuclear--a fork in the road

The anthracycline antibiotics doxorubicin (Adriamycin; DOX) and daunorubicin (DNR) continue to be essential components of first-line chemotherapy in the treatment of a variety of solid and hematopoietic tumors. The overall efficacies of DOX and DNR are, however, impeded by serious dose-limiting toxicities, including cardiotoxicity, and the selection of multiple mechanisms of cellular drug resistance. These limitations have necessitated the development of newer anthracyclines whose structural and functional modifications circumvent these impediments. In this review, we will present recent strategies in anthracycline design and assess their potential therapeutic merits. Current anthracycline design has diverged to target either cytoplasmic or nuclear sites. Nuclear targets have been broadened to include not only topoisomerase II (topo II) inhibition through ternary complex stabilization and catalytic inhibition, but also topoisomerase I (topo I) inhibition and transcriptional inhibition. In contrast, cytoplasmic targeting focuses on anthracycline binding to protein kinase C (PKC) regulatory domain with consequent modulation of activity.

The cardioprotective effect of the iron chelator dexrazoxane (ICRF-187) on anthracycline-mediated cardiotoxicity

The cardiotoxic effect of anthracyclines limits their use in the treatment of a variety of cancers. The reason for the high susceptibility of cardiac muscle to anthracyclines remains unclear, but it appears to be due, at least in part, to the interaction of these drugs with intracellular iron (Fe). The suggestion that Fe plays an important role in anthracycline cardiotoxicity has been strengthened by observation that the chelator, dexrazoxane (ICRF-187), has a potent cardioprotective effect. In the present review, the role of Fe in the cardiotoxicity of anthracyclines is discussed together with the possible role of Fe chelation therapy as a cardioprotective strategy that may also result in enhanced antitumour activity.

Anthracycline metabolism and toxicity in human myocardium: comparisons between doxorubicin, epirubicin, and a novel disaccharide analogue with a reduced level of formation and [4Fe-4S] reactivity of its secondary alcohol metabolite

Secondary alcohol metabolites have been proposed to mediate chronic cardiotoxicity induced by doxorubicin (DOX) and other anticancer anthracyclines. In this study, NADPH-supplemented human cardiac cytosol was found to reduce the carbonyl group in the side chain of the tetracyclic ring of DOX, producing the secondary alcohol metabolite doxorubicinol (DOXol). A decrease in the level of alcohol metabolite formation was observed by replacing DOX with epirubicin (EPI), a less cardiotoxic analogue characterized by an axial-to-equatorial epimerization of the hydroxyl group at C-4 in the amino sugar bound to the tetracyclic ring (daunosamine). A similar decrease was observed by replacing DOX with MEN 10755, a novel anthracycline with preclinical evidence of reduced cardiotoxicity. MEN 10755 is characterized by the lack of a methoxy group at C-4 in the tetracyclic ring and by intercalation of 2, 6-dideoxy-L-fucose between daunosamine and the aglycone. Multiple comparisons with methoxy- or 4-demethoxyaglycones, and a number of mono- or disaccharide 4-demethoxyanthracyclines, showed that both the lack of the methoxy group and the presence of a disaccharide moiety limited alcohol metabolite formation by MEN 10755. Studies with enzymatically generated or purified anthracycline secondary alcohols also showed that the presence of a disaccharide moiety, but not the lack of a methoxy group, made the metabolite of MEN 10755 less reactive with the [4Fe-4S] cluster of cytoplasmic aconitase, as evidenced by its limited reoxidation to the parent carbonyl anthracycline and by a reduced level of delocalization of Fe(II) from the cluster. Collectively, these studies (i) characterize the different influence of methoxy and sugar substituents on the formation and [4Fe-4S] reactivity of anthracycline secondary alcohols, (ii) lend support to the role of alcohol metabolites in anthracycline-induced cardiotoxicity, as they demonstrate that the less cardiotoxic EPI and MEN 10755 share a reduction in the level of formation of such metabolites, and (iii) suggest that the cardiotoxicity of MEN 10755 might be further decreased by the reduced [4Fe-4S] reactivity of its alcohol metabolite.

Prevention by dexrazoxane of down-regulation of ryanodine receptor gene expression in anthracycline cardiomyopathy in the rat

Anthracyclines can cause cumulative dose-related cardiotoxicity characterized by changes in Ca(2+) metabolism, including dysfunction of the sacroplasmic reticulum (SR) and decreased expression of Ca(2+)-handling proteins, such as the ryanodine receptor (RyR2). In this study, we examined the effect of dexrazoxane (ICRF-187), an iron chelator which prevents anthracycline cardiotoxicity, on RyR2 gene expression in rats treated chronically with daunorubicin. Daunorubicin (2.5 mg kg(-1) i.v. weekly for 6 weeks) produced cardiotoxicity as demonstrated by histopathologic changes. The ryanodine receptor/glyceraldehyde phosphate dehydrogenase (GAPDH) mRNA ratio was decreased by 38+/-3% (P<0.02) compared to values in control rats. Dexrazoxane pre-treatment (50 mg kg(-1); 1 h prior to each daunorubicin injection) prevented the decrease in RyR2/GAPDH mRNA ratio and histopathologic lesions in daunorubicin-treated rats. This is the first report that a protective agent such as dexrazoxane can ameliorate the decreased expression of a specific gene involved in anthracycline-induced cardiotoxicity.

Mass spectrometric measurement of formaldehyde generated in breast cancer cells upon treatment with anthracycline antitumor drugs

Selected ion flow tube-chemical ionization mass spectrometry was used to measure formaldehyde levels in human breast cancer cells in comparison with levels in cells treated with the antitumor drugs doxorubicin (DOX) and daunorubicin (DAU) and the daunorubicin-formaldehyde conjugate Daunoform (DAUF). The measurement was performed on cell lysates and showed only background levels of formaldehyde in untreated cells and drug-treated resistant cells (MCF-7/Adr cells) but levels above background in DOX- and DAU-treated sensitive cells (MCF-7 cells). The level of formaldehyde above background was a function of drug concentration (0.5-50 microM), treatment time (3-24 h), cell density (0.3 x 10(6) to 7 x 10(6) cells/mL), and cell viability (0-100%). Higher levels of formaldehyde were observed in lysates of MCF-7 cells treated at higher drug levels, unless the treatment resulted in low cell viability. Elevated levels were directly related to cell density and were observed even with 0.5 microM drug. A lower limit for excess formaldehyde in MCF-7 cells treated with 0.5 microM DAU for 24 h is 0.3 mM. Control experiments showed that formaldehyde was not produced after cell lysis. Lysates of sensitive and resistant cells treated with 0.5 micromolar equiv of the formaldehyde conjugate (DAUF) for 3 h showed only background levels of formaldehyde. The results support a mechanism for drug cytotoxicity which involves drug induction of metabolic processes leading to formaldehyde production followed by drug utilization of formaldehyde to virtually cross-link DNA.

Doxorubicin metabolism and toxicity in human myocardium: role of cytoplasmic deglycosidation and carbonyl reduction

The anthracycline doxorubicin (DOX) is an exceptionally good antineoplastic agent, but its use is limited by formation of metabolites which induce acute and chronic cardiac toxicities. Whereas the acute toxicity is mild, the chronic toxicity can produce a life-threatening cardiomyopathy. Studies in laboratory animals are of limited value in predicting the structure and reactivity of toxic metabolites in humans; therefore, we used an ethically acceptable system which is suitable for exploring DOX metabolism in human myocardium. The system involves cytosolic fractions from myocardial samples obtained during aorto-coronary bypass grafting. After reconstitution with NADPH and DOX, these fractions generate the alcohol metabolite doxorubicinol (DOXol) as well as DOX deoxyaglycone and DOXol hydroxyaglycone, reflecting reduction of the side chain carbonyl group, reductase-type deglycosidation of the anthracycline, and hydrolase-type deglycosidation followed by carbonyl reduction, respectively. The efficiency of each metabolic route has been evaluated at low and high DOX:protein ratios, reproducing acute, single-dose and chronic, multiple-dose regimens, respectively. Low DOX:protein ratios increase the efficiency of formation of DOX deoxyaglycone and DOXol hydroxyaglycone but decrease that of DOXol. Conversely, high DOX:protein ratios facilitate the formation of DOXol but impair reductase- or hydrolase-type deglycosidation and uncouple hydrolysis from carbonyl reduction, making DOXol accumulate at levels higher than those of DOX deoxyaglycone and DOXol hydroxyaglycone. Structure-activity considerations have suggested that aglycones and DOXol may inflict cardiac damage by inducing oxidative stress or by perturbing iron homeostasis, respectively. Having characterized the influence of DOX:protein ratios on deglycosidation or carbonyl reduction, we propose that the benign acute toxicity should be attributed to the oxidant activity of aglycones, whereas the life-threatening chronic toxicity should be attributed to alterations of iron homeostasis by DOXol. This picture rationalizes the limited protective efficacy of antioxidants against chronic cardiomyopathy vis-à-vis the better protection offered by iron chelators, and forms the basis for developing analogues which produce less DOXol.

Epirubicin: a review of its efficacy as adjuvant therapy and in the treatment of metastatic disease in breast cancer

Epirubicin is a semisynthetic derivative of doxorubicin which has been extensively evaluated in patients with breast cancer. It is effective in the management of metastatic disease and as adjuvant therapy in patients with early breast cancer. In the adjuvant setting, epirubicin-based therapy appears to have efficacy at least equivalent to that of the standard therapy cyclophosphamide, methotrexate and fluorouracil (CMF), with the most recent trials, predominantly in premenopausal patients, reporting significant gains in relapse-free survival and overall survival for epirubicin-based vs CMF therapy. In a single trial, the 5-year relapse-free survival of postmenopausal patients receiving long term hormonal therapy (tamoxifen) was significantly increased when epirubicin was added as single-agent chemotherapy and compared with tamoxifen alone. In patients with metastatic disease, epirubicin- and doxorubicin-containing regimens (with cyclophosphamide and fluorouracil; FEC and FAC) are therapeutically equivalent. Increasing the dose of epirubicin appears to improve response rates in patients with either metastatic or early disease but, with the exception of 1 adjuvant study, improved overall survival has not been demonstrated. Quality of life (QOL) has yet to be adequately evaluated with epirubicin. The major adverse effects of epirubicin are acute dose-limiting haematotoxicity and cumulative dose-related cardiotoxicity. Other important adverse effects include mucositis, nausea and vomiting, reversible alopecia and local cutaneous reactions. However, the tolerability of epirubicin is better than that of doxorubicin at equimolar doses.

CONCLUSION

Epirubicin has been extensively investigated in patients with breast cancer and has been found to be a highly effective agent, both for the treatment of patients with metastatic disease and as an adjuvant therapy. Recent trials have confirmed that, in selected patients requiring adjuvant therapy, FEC therapy is at least as effective as CMF, a standard treatment. FEC is also therapeutically equivalent to FAC in patients with metastatic breast cancer, and because the therapeutic index appears to be better the opportunity exists to increase dose intensity in an effort to improve efficacy. Such trials, and those of combinations of epirubicin with newer or alternative agents, should result in the introduction of more effective and better tolerated epirubicin-based protocols for adjuvant therapy and the management of patients with advanced breast cancer. In the meantime there is sufficient evidence to justify consideration of epirubicin for inclusion in first-line therapies for patients with early or metastatic breast cancer.

Cell-permeable superoxide dismutase and glutathione peroxidase mimetics afford superior protection against doxorubicin-induced cardiotoxicity: the role of reactive oxygen and nitrogen intermediates

The use of the potent antitumor antibiotic doxorubicin (DOX) is hampered because of its severe cardiac toxicity that leads to the development of cardiomyopathy and heart failure. In this study, we have developed a cell culture model for DOX-induced myocardial injury using primary adult rat cardiomyocytes that were cultured in serum-free medium and exposed to 1 to 40 microM DOX. DOX caused a dose-dependent release of sarcosolic enzyme lactate dehydrogenase (LDH) from cultured myocytes. The release of LDH was prevented by the cell-permeable superoxide dismutase (SOD) mimetic (MnTBAP), but was unaffected by either cell-impermeable SOD enzyme, or manganese (II) sulfate. Ebselen, a glutathione peroxidase (GPx) mimetic, enhanced the protection of cardiomyocytes afforded by MnTBAP. DOX caused the increased formation of oxidants in cardiomyocytes, and MnTBAP lowered the amount of intracellular oxidants induced by DOX. In addition, DOX selectively inactivated aconitase in cardiomyocytes, and MnTBAP partially reversed this inactivation. Ebselen further amplified the protective effect of MnTBAP on aconitase activity. These results suggest that the SOD mimetic MnTBAP prevents DOX-induced damage to cardiomyocytes and that the GPx mimetic ebselen synergistically enhanced the cardioprotection afforded by MnTBAP. Relevance of these findings to minimizing cardiotoxicity in cancer treatment is discussed.

Transition metal ion-catalyzed oxygen activation during pathogenic processes

Most pathological processes include the production of activated oxygen species augmented or attenuated by transition metal ions catalyzing one electron transitions. Inhalation of airborne particles, infections, ingestion of toxins or liberation from endogenous stores represent biological pathways for the induction of pathogenic processes by these metal ions. In this short review basic reactions involving transition metal ions operating during oxidative stress in certain diseases will be discussed.

Preferential activation of iron regulatory protein-2 in cell lines as a result of higher sensitivity to iron

Iron regulatory proteins (IRP)-1 and 2 are cytoplasmic mRNA-binding proteins that control intracellular iron homeostasis by regulating the translation of ferritin mRNA and stability of transferrin receptor mRNA in an iron-dependent fashion. Although structurally and functionally similar, the two IRP are different in their mode of regulation, pattern of tissue expression and modulation by multiple factors, such as bioradicals. In the present study RNA bandshift assays demonstrated that IRP-2, but not IRP-1, activity was higher in cultured cells than in tissues. Increased expression of IRP-2 in cell lines was not related to immortalization and differentiation but seemed associated to cell proliferation, although not closely dependent on cell growth rate. As a growing cell consumes more iron than its quiescent counterpart, we assessed the iron status of cell lines and found that ferritin content was lower than in tissues. Analysis of IRP activity in cell lines supplemented with heme or non-heme iron and in livers of iron-loaded and iron-deficient rats indicated that IRP-2 responds more promptly than IRP-1 to modulations of iron content. We propose that enhanced IRP-2 activity in cultured cells could be due to a proliferation-dependent, relative iron deficiency that is sensed first by IRP-2.

Diacerhein blocks iron regulatory protein activation in inflamed human monocytes

Iron Regulatory Proteins (IRPs), by modulating expression of ferritin, which stores excess iron in a non toxic form, and transferrin receptor, which controls iron uptake, are the main controller of cellular iron metabolism. During inflammation, modification of IRP activity may affect iron availability, free radical generation and cytokine gene response in inflammatory cells. In the present study we tested the effect of inflammatory stimuli on IRP function in a human monocytic-macrophagic cell line and the possibility of interfering with these pathways by using an antiinflammatory compound, diacerhein (DAR). IRP activity was enhanced by interferon gamma/lipopolysaccarhide (IFN/LPS), and this effect was consistently counteracted by increasing concentrations of DAR. No direct effect of DAR on IRP activity was found in vitro. However, in vivo, similar IRP activation was achieved by exposing cells to nitric oxide (NO) donors and the LPS/IFN-induced activation of IRP was reversed by NO inhibitors. Interestingly, NO-induced IRP activation was efficiently blocked by DAR. These data show for the first time that a clinically useful antiinflammatory compound, DAR, interferes with IRP activation by NO in inflammed human cells.