Control of disease by selective iron depletion: a novel therapeutic strategy utilizing iron chelators

Functional consequence of Iron dyshomeostasis and ferroptosis in systemic lupus erythematosus and lupus nephritis

Systemic lupus erythematosus (SLE) and its renal manifestation Lupus nephritis (LN) are characterized by a dysregulated immune system, autoantibodies, and injury to the renal parenchyma. Iron accumulation and ferroptosis in the immune effectors and renal tubules are recently identified pathological features in SLE and LN. Ferroptosis is an iron dependent non-apoptotic form of regulated cell death and ferroptosis inhibitors have improved disease outcomes in murine models of SLE, identifying it as a novel druggable target. In this review, we discuss novel mechanisms by which iron accumulation and ferroptosis perpetuate immune cell mediated pathology in SLE/LN. We highlight intra-renal dysregulation of iron metabolism and ferroptosis as an underlying pathogenic mechanism of renal tubular injury. The basic concepts of iron biology and ferroptosis are also discussed to expose the links between iron, cell metabolism and ferroptosis, that identify intracellular pro-ferroptotic enzymes and their protein conjugates as potential targets to improve SLE/LN outcomes.

Cardiotoxicity and ROS Protection Assessment of three Structure-Related N-Acylhydrazones with Potential for the Treatment of Neurodegenerative Diseases

The senescence process is associated with accumulated oxidative damage and increased metal concentration in the heart and brain. Besides, abnormal metal-protein interactions have also been linked with the development of several conditions, including Alzheimer's and Parkinson's diseases. Over the years we have described a series of structure-related compounds with different activities towards models of such diseases. In this work, we evaluated the potential of three N-acylhydrazones (INHHQ: 8-hydroxyquinoline-2-carboxaldehyde isonicotinoyl hydrazone, HPCIH: pyridine-2-carboxaldehyde isonicotinoyl hydrazone and X1INH: 1-methyl-1H-imidazole-2-carboxaldehyde isonicotinoyl hydrazone) to prevent oxidative stress in cellular models, with the dual intent of being active on this pathway and also to confirm their lack of cardiotoxicity as an important step in the drug development process, especially considering that the target population often presents cardiovascular comorbidity. The 8-hydroxyquinoline-contaning compound, INHHQ, exhibits a significant cardioprotective effect against hydrogen peroxide and a robust antioxidant activity. However, this compound is the most toxic to the studied cell models and seems to induce oxidative damage on its own. Interestingly, although not possessing a phenol group in its structure, the new-generation 1-methylimidazole derivative X1INH showed a cardioprotective tendency towards H9c2 cells, demonstrating the importance of attaining a compromise between activity and intrinsic cytotoxicity when developing a drug candidate.

DTPA-Bound Planar Catechin with Potent Antioxidant Activity Triggered by Fe3+ Coordination

In diseases related to oxidative stress, accumulation of metal ions at the site of pathogenesis results in the generation of reactive oxygen species (ROS) through the reductive activation of oxygen molecules catalyzed by the metal ions. If these metals can be removed and the generated ROS can be strongly scavenged, such diseases can be prevented and treated. Planar catechins exhibit stronger radical scavenging activity than natural catechins and can efficiently scavenge hydroxyl radicals generated by the Fenton reaction without showing pro-oxidant effects, even in the presence of iron ions. Hence, in the current study, we designed a compound in which diethylenetriaminepentaacetic acid (DTPA), a metal chelator, was bound to a planar catechin with enhanced radical scavenging activity by immobilizing the steric structure of a natural catechin to be planar. This compound showed almost no radical scavenging activity due to intramolecular hydrogen bonding of DTPA with the planar catechins; however, when coordinated with Fe³⁺, it showed more potent radical scavenging activity than planar catechins. Owing to its potent antioxidant activity triggered by metal coordination and its inhibition of ROS generation by trapping metal ions, this compound might exert excellent preventive and therapeutic effects against oxidative stress-related diseases.

Biochanin A protects against iron overload associated knee osteoarthritis via regulating iron levels and NRF2/System xc-/GPX4 axis

BACKGROUND

Iron homeostasis plays a positive role in articular cartilage health. Excessive iron or iron overload can induce oxidative stress damage in chondrocytes and ferroptosis cell death, advancing knee osteoarthritis (KOA). However, up to date, few effective agents treat iron overload-induced KOA (IOKOA). Chinese herbal medicine (CHM) provides abundant resources for drug selection to manage bone metabolic conditions, including osteoporosis. Biochanin A (BCA) is a novel bioactive multifunctional natural compound isolated from Huangqi, which has protective effects on bone loss. Nevertheless, the function and mechanism of BCA in treating IOKOA are still elusive.

PURPOSE

This study seeks to uncover the potential therapeutic targets and mechanisms of BCA in the management of KOA with iron accumulation.

METHODS

Iron dextrin (500 mg/kg) was intraperitoneally injected into mice to establish the iron overloaded mice model. OA was induced through surgery, and the progression was evaluated eight weeks following surgery. OA severity was evaluated with micro-CT and Safranin-O/Fast green staining in vivo. Iron deposition in the knee joint and synovium was assessed using Perl's Prussian blue staining. Ferric ammonium citrate (FAC) was then administered to primary chondrocytes to evaluate iron regulators mediated iron homeostasis. Toluidine blue staining was utilized to identify chondrocytes in vitro. The vitality of the cells was assessed using the CCK-8 test. The apoptosis rate of cells was measured using Annexin V-FITC/PI assay. The intracellular iron level was detected utilizing the calcein-AM test. Reactive oxygen species (ROS), lipid-ROS, and mitochondrial membrane potentiality were reflected via fluorescence density. Utilizing RT-qPCR and western blotting, the expression level was determined.

RESULTS

Micro-CT and histological staining of knee joints showed greater cartilage degradation and higher iron buildup detected in iron-overloaded mice. BCA can reduce iron deposition and the severity of KOA. Toluidine blue staining and the CCK-8 assay indicated that BCA could rescue chondrocytes killed by iron. Cell apoptosis rates were increased due to iron overload but improved by BCA. Further, the intracellular content of iron, ROS, and lipid-ROS was increased with ferric ammonium citrate (FAC) treatment but restored after treatment with different concentrations of BCA. JC-1 staining revealed that BCA could reduce mitochondrial damage induced by iron overload.

CONCLUSION

Iron overload was shown to promote chondrocyte ferroptosis in vivo and in vitro. Moreover, iron overload suppressed the expression of collagen II and induced MMP expression by catalyzing ROS generation with mitochondrial dysfunction. Our results showed that BCA could directly reduce intracellular iron concentration by inhibiting TfR1 and promoting FPN but also target the Nrf2/system xc-/GPX4 signaling pathway to scavenge free radicals and prevent lipid peroxidation. The results of this research indicate that BCA regulates iron homeostasis during the progression of osteoarthritis, which can open a new field of treatment for KOA.

Iron depletion participates in the suppression of cell proliferation induced by lipin1 overexpression

Lipin1 participates in numerous cellular processes, including in the dephosphorylation of phosphatidic acid to diacylglycerol and as a co-transcriptional regulator. Iron is also essential in various critical biological processes. Previous studies have shown that compared to normal tissue cells, lipin1 expression and iron metabolism are abnormal in cancer cells. However, the involvement of lipin1 in the regulation of iron metabolism is unknown. In this study, we compared the contents of eight metal ions (potassium, calcium, sodium, magnesium, manganese, zinc, iron and copper) in human hepatoma carcinoma BEL7402 control cells as well as stable cells overexpressing lipin1 by using ICP-AES. Our results showed that only intracellular iron content was significantly decreased by lipin1 overexpression. Meanwhile, we observed that lipin1 overexpression could inhibit cell proliferation, similar to iron chelator deferoxamine. Western blotting showed that the up-regulation of p53-p21-p27 elicited cell cycle G0/G1 arrest in the stable cells overexpressing lipin1. Conversely, after lipin1 was down regulated with siRNA, we found that cell proliferation was promoted, accompanied by an increase in iron content, and the downregulation of p53 and p21. Our data indicate that lipin1 overexpression may cause reduction of intracellular iron content, which could activate the p53-p21-p27 signaling pathways, leading to cell cycle arrest at the G0/G1 phase in the hepatic carcinoma cells. Subsequently, we identified the putative cause for the decrease of the intracellular iron content induced by lipin1 overexpression. Our results suggested that the intracellular iron reduction was due to the increase in the expression of ferroportin, an iron export protein in the stable cells overexpressing lipin1. In contrast, after transfection with lipin1 siRNA, the decreased expression of ferroportin contributed to an increase in the iron content in BEL7402 cells. It was further confirmed that the intracellular iron content was increased after ferroportin was knocked down by siRNA in BEL7402 cells. Taken together, our findings demonstrate for the first time that lipin1 participates in the regulation of iron metabolism in human hepatic carcinoma cells. This suggests that lipin1 may play an important protective role in inhibiting the development of cancer through the reduction of iron content in tumors, which further demonstrates that iron reduction could be a potential strategy of cancer prevention and treatment.

Structure-guided design of anti-cancer ribonucleotide reductase inhibitors

Ribonucleotide reductase (RR) catalyses the rate-limiting step of dNTP synthesis, establishing it as an important cancer target. While RR is traditionally inhibited by nucleoside-based antimetabolites, we recently discovered a naphthyl salicyl acyl hydrazone-based inhibitor (NSAH) that binds reversibly to the catalytic site (C-site). Here we report the synthesis and in vitro evaluation of 13 distinct compounds (TP1-13) with improved binding to hRR over NSAH (TP8), with lower K_D’s and more predicted residue interactions. Moreover, TP6 displayed the greatest growth inhibiting effect in the Panc1 pancreatic cancer cell line with an IC₅₀ of 0.393 µM. This represents more than a 2-fold improvement over NSAH, making TP6 the most potent compound against pancreatic cancer emerging from the hydrazone inhibitors. NSAH was optimised by the addition of cyclic and polar groups replacing the naphthyl moiety, which occupies the phosphate-binding pocket in the C-site, establishing a new direction in inhibitor design.

Structure-Guided Synthesis and Mechanistic Studies Reveal Sweetspots on Naphthyl Salicyl Hydrazone Scaffold as Non-Nucleosidic Competitive, Reversible Inhibitors of Human Ribonucleotide Reductase

Ribonucleotide reductase (RR), an established cancer target, is usually inhibited by antimetabolites, which display multiple cross-reactive effects. Recently, we discovered a naphthyl salicyl acyl hydrazone-based inhibitor (NSAH or E-3a) of human RR (hRR) binding at the catalytic site (C-site) and inhibiting hRR reversibly. We herein report the synthesis and biochemical characterization of 25 distinct analogs. We designed each analog through docking to the C-site of hRR based on our 2.7 Å X-ray crystal structure (PDB ID: 5TUS). Broad tolerance to minor structural variations preserving inhibitory potency is observed. E-3f (82% yield) displayed an in vitro IC50 of 5.3 ± 1.8 μM against hRR, making it the most potent in this series. Kinetic assays reveal that E-3a, E-3c, E-3t, and E-3w bind and inhibit hRR through a reversible and competitive mode. Target selectivity toward the R1 subunit of hRR is established, providing a novel way of inhibition of this crucial enzyme.

The Eltrombopag antitumor effect on hepatocellular carcinoma

Currently, sorafenib is the only available chemotherapeutic agent for advanced hepatocellular carcinoma (HCC), but it cannot be used in patients with liver cirrhosis (LC) or thrombocytopenia. In these cases, sorafenib is likely effective if given in combination with treatments that increase the number of platelets, such as thrombopoietin (TPO) receptor agonists. Increasing the platelet count via TPO treatment resulted in reduction of LC. Eltrombopag (EP), a TPO receptor agonist, has been reported to have antitumor effects against certain cancers, despite their lack of TPO receptor expression. We hypothesized that EP may possess antitumor activity against HCC in addition to its ability to suppress hepatic fibrosis by increasing the platelet count. In the present study, the antitumor activity of EP was examined by assessing the inhibition of cell proliferation and then ascertaining the ability of iron supplementation to reverse these effects in HepG2, Hep3B and Huh7 cells. In addition, a cell cycle assay was performed using flow cytometry, and signal transduction was evaluated by analyzing cell cycle-related protein expression. The results of EP were compared with those of the most common iron chelator, deferoxamine (DFO). The combined effect of EP and sorafenib was also assessed. The results revealed that EP exerts antitumor activity in HCC that is mediated by the modulation of intracellular iron content. EP suppressed the expression of the cell cycle-related protein cyclin D1 and elicited cell cycle arrest in the G0/G1 phase. The activity of EP was comparable to that of DFO in HCC, and EP did not compete with sorafenib at low concentrations. In conclusion, our findings suggest that EP is a good candidate chemotherapeutic agent for the treatment of HCC in patients with LC and thrombocytopenia.

Deferoxamine inhibits TRAIL-mediated apoptosis via regulation of autophagy in human colon cancer cells

Deferoxamine (DFO), an iron chelator, has numerous clinical applications for patients presenting with iron overload in regards to the improvement in the quality of life and overall survival. In addition, experimental iron chelators have demonstrated potent anticancer properties. The present study investigated the effects of DFO on TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in colon cancer cells and and the mechanism involved. The experimental results showed that DFO treatment inhibited TRAIL-mediated cancer cell apoptosis by increasing Akt activation and decreasing caspase activation in human colon cancer cells. Furthermore, DFO treatment induced autophagy flux, and chloroquine, an autophagy inhibitor, blocked DFO-mediated inhibition of TRAIL-induced apoptosis. The present study demonstrated that DFO inhibited TRAIL-mediated tumor cell death via the autophagy pathway, and the results suggest that potent anticancer agent, DFO, can be an inhibitor against antitumor therapy including TRAIL protein.

Transfusion related iron overload in pediatric oncology patients treated at a tertiary care centre and treatment with chelation therapy

We conducted a retrospective chart review to determine prevalence of, risk factors for, and liver toxicity associated with Transfusion Related Iron Overload (TRIO) in pediatric cancer patients, and report our experience with Iron Chelation Therapy (ICT). Total number of transfusions was identified as the major risk factor, with a prevalence of 37% in patients receiving ≥10 transfusions. Four patients with TRIO and abnormal liver function tests (LFT) received ICT. Significant decrease in serum ferritin and improvement in LFT were observed, with no serious adverse effects from ICT noted. Guidelines for screening and treatment of TRIO in pediatric oncology are needed.

Do iron chelators increase the antiproliferative effect of trichostatin A through a glucose-regulated protein 78 mediated mechanism?

Histone deacetylase (HDAC) inhibitors, such as trichostatin A (TSA), and iron chelators, including deferoxamine (DFO) and phenanthroline (PHEN), appear to have anticancer effects. We hypothesized that the HDAC inhibitors and iron chelators would be synergistic with their effect on breast cancer cell line MCF7, because the HDAC inhibitors increase glucose-regulated protein 78 (Grp78) and the iron chelators reduce its expression. Although the administration of TSA alone resulted in a dose-related decrease in the cell index, it did not have an antiproliferative effect except the 62.5 and 500 nM of TSA. However, all doses of TSA produced a cytotoxic effect from the initial hours when combined with 150 μM of DFO and 25 μM of PHEN. DFO and PHEN downregulated Grp78, Grp94, and MRP1 expressions and upregulated CHOP and HO-1 expressions. TSA upregulated all the genes in various rates when used alone but resulted in decreased expression levels when combined with DFO and PHEN. Increased HDAC-1 levels in the Grp78 promoter region indicated that DFO and PHEN either promoted binding of HDAC-1 to this region or inhibited its detachment. We determined that the reduction of increased Grp78, Grp94, HO-1, and MRP1 expressions, which appears to inhibit the chemotherapeutic effect of TSA, through the combination with DFO or PHEN will contribute to the anticancer effect.

Iron, human growth, and the global epidemic of obesity

Iron is an essential nutrient utilized in almost every aspect of cell function and its availability has previously limited life. Those same properties which allow iron to function as a catalyst in the reactions of life also present a threat via generation of oxygen-based free radicals. Accordingly; life exists at the interface of iron-deficiency and iron-sufficiency. We propose that: (1) human life is no longer positioned at the limits of iron availability following several decades of fortification and supplementation and there is now an overabundance of the metal among individuals of many societies; (2) this increased iron availability exerts a positive effect on growth by targeting molecules critical in regulating the progression of the cell cycle; there is increased growth in humans provided greater amounts of this metal; and indices of obesity can positively correlate with body stores of iron; and (3) diseases of obesity reflect this over-abundance of iron. Testing potential associations between iron availability and both obesity and obesity-related diseases in populations will be difficult since fortification and supplementation is so extensively practiced.

Mechanism of protective effects of Danshen against iron overload-induced injury in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Danshen (Salvia miltiorrhiza) has been widely prescribed in traditional folk medicine for treatment of hepatic and cardiovascular diseases in China and other Asian countries for several hundred years.

MATERIALS AND METHODS

Sixty male mice were randomly divided into five groups: control, iron overload, low-dose Danshen (L-Danshen, 3g/kg/day), high-dose Danshen (H-Danshen, 6g/kg/day) and deferoxamine (DFO) groups (n=12 per group). Iron dextran was injected intraperitoneally (i.p.) at 50mg/kg body weight/day to establish the iron overload model. While control mice received saline, mice of the treated groups simultaneously received (i.p.) injections of L-Danshen, H-Danshen or DFO daily for 2 weeks. At the end of the experiment, changes in alanine aminotransferase (ALT) and aspartate aminotransferase (AST), glutathione peroxidase (GSH-Px), superoxide desmutase (SOD) and malondialdehyde (MDA) were measured, and histological changes were observed by Prussian blue or hematoxylin and eosin staining of the liver. Apoptosis was detected by terminal-deoxynucleotidyl transferase mediated nick end labeling.

RESULTS

Treatment of iron overloaded mice with either low or high doses of Danshen not only significantly attenuated the hepatic dysfunction (ALT/AST levels), decreased the content of MDA and increased the activities of GSH-Px and SOD, it also suppressed apoptosis in hepatocytes. Histopathological examination showed that treatment with Danshen reduced iron deposition and ameliorated pathological changes in the liver of iron overloaded mice.

CONCLUSIONS

Danshen demonstrated significant protective effects in the liver of iron overloaded mice, which were at least partly due to the decrease of iron deposition and inhibition of lipid peroxidation and hepatocyte apoptosis.

Bp44mT: an orally active iron chelator of the thiosemicarbazone class with potent anti-tumour efficacy

BACKGROUND AND PURPOSE

Our previous studies demonstrated that a thiosemicarbazone iron chelator (di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone; Dp44mT) possesses potent and selective anti-cancer activity but led to cardiotoxicity at non-optimal doses. In this study, we examined the in vivo anti-tumour efficacy and tolerability of a new-generation 2-benzoylpyridine thiosemicarbazone iron chelator (2-benzoylpyridine-4,4-dimethyl-3-thiosemicarbazone; Bp44mT) administered via the oral or i.v. routes.

EXPERIMENTAL APPROACH

BpT chelators were tested in vitro against human lung cancer cells (DMS-53) and in vivo in DMS-53 tumour xenografts in mice. The toxicity of Bp44mT in vivo and its effects on the expression of iron-regulated molecules involved in growth and cell cycle control were investigated.

KEY RESULTS

Administration of Bp44mT by either route resulted in marked dose-dependent inhibition of tumour growth. When administered at 50 mg·kg(-1) via oral gavage three times per week for 23 days, the net xenograft growth was inhibited by 75%, compared with vehicle-treated mice. Toxicological examination showed reversible alterations including slight reduction of RBC count, with a decrease of liver and splenic iron levels, which confirmed iron chelation in vivo. Importantly, in contrast to Dp44mT, the chelator-treated mice did not show cardiac histological abnormalities. There was also no significant weight loss in mice, suggesting oral administration of Bp44mT was well tolerated.

CONCLUSIONS AND IMPLICATIONS

This is the first study to show that Bp44mT can be given orally with potent anti-tumour efficacy. Oral administration of a novel and effective chemotherapeutic agent provides the benefits of convenience for chronic dosing regimens.

Iron chelators of the di-2-pyridylketone thiosemicarbazone and 2-benzoylpyridine thiosemicarbazone series inhibit HIV-1 transcription: identification of novel cellular targets--iron, cyclin-dependent kinase (CDK) 2, and CDK9

HIV-1 transcription is activated by HIV-1 Tat protein, which recruits cyclin-dependent kinase 9 (CDK9)/cyclin T1 and other host transcriptional coactivators to the HIV-1 promoter. Tat itself is phosphorylated by CDK2, and inhibition of CDK2 by small interfering RNA, the iron chelator 2-hydroxy-1-naphthylaldehyde isonicotinoyl hydrazone (311), and the iron chelator deferasirox (ICL670) inhibits HIV-1 transcription. Here we have analyzed a group of novel di-2-pyridylketone thiosemicarbazone- and 2-benzoylpyridine thiosemicarbazone-based iron chelators that exhibit marked anticancer activity in vitro and in vivo (Proc Natl Acad Sci USA 103:7670-7675, 2006; J Med Chem 50:3716-3729, 2007). Several of these iron chelators, in particular 2-benzoylpyridine 4-allyl-3-thiosemicarbazone (Bp4aT) and 2-benzoylpyridine 4-ethyl-3-thiosemicarbazone (Bp4eT), inhibited HIV-1 transcription and replication at much lower concentrations than did 311 and ICL670. Neither Bp4aT nor Bp4eT were toxic after a 24-h incubation. However, longer incubations for 48 h or 72 h resulted in cytotoxicity. Analysis of the molecular mechanism of HIV-1 inhibition showed that the novel iron chelators inhibited basal HIV-1 transcription, but not the nuclear factor-κB-dependent transcription or transcription from an HIV-1 promoter with inactivated SP1 sites. The chelators inhibited the activities of CDK2 and CDK9/cyclin T1, suggesting that inhibition of CDK9 may contribute to the inhibition of HIV-1 transcription. Our study suggests the potential usefulness of Bp4aT or Bp4eT in antiretroviral regimens, particularly where resistance to standard treatment occurs.

Design, Synthesis, and Testing of Polyamine Vectored Iron Chelators

Iron chelators have been shown to control the growth of cancer cells in culture by sequestering exogenous iron in the media. Thus, the ligands prevent cellular access to the metal. However, because transferrin provides iron to tumor cells in animals, chelators have not been effective antitumor agents. Polyamine chelator conjugates in which the polyamine vectored ligands into cells were far more active than the free chelators themselves. However, the free ligands were not released from the vector once in the cell. The current study focuses on the synthesis and preliminary evaluation of a polyamine chelator conjugate capable of releasing the free ligand intracellularly via a nonspecific esterase.

2-Acetylpyridine thiosemicarbazones are potent iron chelators and antiproliferative agents: redox activity, iron complexation and characterization of their antitumor activity

Through systematic structure-activity studies of the 2-benzoylpyridine thiosemicarbazone (HBpT), 2-(3-nitrobenzoyl)pyridine thiosemicarbazone (HNBpT) and dipyridylketone thiosemicarbazone (HDpT) series of iron (Fe) chelators, we identified structural features necessary to form Fe complexes with potent anticancer activity (J. Med. Chem. 2007, 50, 3716-3729). In this investigation, we generated the related 2-acetylpyridine thiosemicarbazone (HApT) analogues to examine the influence of the methyl group at the imine carbon. Four of the six HApT chelators had potent antitumor activity (IC(50): 0.001-0.002 microM) and Fe chelation efficacy that was similar to the most effective HBpT and HDpT ligands. The HApT Fe complexes had the lowest Fe(III/II) redox potentials of any thiosemicarbazone series we have generated. This property, in combination with their ability to effectively chelate cellular Fe, make the HApT series one of the most potent antiproliferative agents developed by our group.

Experimental tuberculosis: the role of comparative pathology in the discovery of improved tuberculosis treatment strategies

The use of laboratory animals is critical to the discovery and in vivo pre-clinical testing of new drugs and drug combinations for use in humans. M. tuberculosis infection of mice, rats, guinea pigs, rabbits and non-human primates are the most commonly used animal models of human tuberculosis. While granulomatous inflammation characterizes the most fundamental host response to M. tuberculosis aerosol infection in humans and animals, there are important species differences in pulmonary and extra-pulmonary lesion morphology which may influence responses to drug therapy. Lesions that progress to necrosis or cavitation are common, unfavorable host responses in naturally occurring tuberculosis of humans, but are not seen consistently in experimental infections in most animal model species. The importance of these unique lesion morphologies is that they represent irreversible tissue damage that can harbor persistent bacilli which are difficult to treat with standard therapies. Understanding the differences in host response to experimental tuberculosis infections may aid in selecting the most appropriate animal models to test drugs that have been rationally designed to have specific mechanisms of action in vivo. A better understanding of lesion pathogenesis across species may also aid in the identification of novel therapeutic targets or strategies that can be used alone or in combination with more conventional tuberculosis treatments in humans.

Drug development against metastasis-related genes and their pathways: a rationale for cancer therapy

It is well recognized that the majority of cancer related deaths is caused by metastatic diseases. Therefore, there is an urgent need for the development of therapeutic intervention specifically targeted to the metastatic process. In the last decade, significant progress has been made in this research field, and many new concepts have emerged that shed light on the molecular mechanism of metastasis cascade which is often portrayed as a succession of six distinct steps; localized invasion, intravasation, translocation, extravasation, micrometastasis and colonization. Successful metastasis is dependent on the balance and complex interplay of both the metastasis promoters and suppressors in each step. Therefore, the basic strategy of our interventions is aimed at either blocking the promoters or potentiating the suppressors in this disease process. Toward this goal, various kinds of antibodies and small molecules have been designed. These include agents that block the ligand-recepter interaction of metastasis promoters (HGF/c-Met), antagonize the metastasis-promoting enzymes (AMF, uPA and MMP) and inhibit the transcriptional activity of metastasis promoter (beta-Catenin). On the other hand, the intriguing roles of metastasis suppressors and their signal pathways have been extensively studied and various attempts have been made to potentiate these factors. Small molecules have been developed to restore the expression or mimic the function of metastasis-suppressor genes such as NM23, E-cadherin, Kiss-1, MKK4 and NDRG1, and some of them are under clinical trials. This review summarizes our current understanding of the molecular pathway of tumor metastasis and discusses strategies and recent development of anti-metastatic drugs.

Iron metabolism and malaria

Recent evidence from a large, randomized, controlled trial has suggested that the universal administration of iron to children in malaria-endemic areas is associated with an increase in adverse health outcomes. The purpose of this paper is to summarize the available ecologic and intervention trials related to iron and malaria in children, and to set these against current knowledge of the biology of host-pathogen interactions involving iron metabolism. We conclude that, although not fully consistent, the balance of evidence confirms that administration of iron (usually in combination with folic acid) increases the incidence of malaria when given without prophylaxis and in the absence of universal access to treatment. The mechanisms by which additional iron can benefit the parasite are far from clear. There is evidence to suggest that the apparent detrimental effect of iron supplementation may vary according to levels of antecedent iron status, the presence of hemoglobinopathies and glucose-6-phosphate dehydrogenase (G6PD) deficiency, and other host genetic variants, such as variants in haptoglobin. The effects of malaria on host iron metabolism are also reviewed and reveal that the key cause of malaria-induced anemia is a maldistribution of iron and suppression of erythropoiesis rather than an exacerbation of gross iron deficiency. We tentatively conclude that, if it is to be recommended, universal iron supplementation in malarious areas should only be considered in conjunction with some form of prophylaxis (e.g., intermittent preventive therapy [IPT]) or in the context of good health services with ready access to facilities for malaria diagnosis and treatment. An alternative approach would be to screen for anemia and target supplementation only to anemic children. With regard to treatment, there is good evidence that iron supplementation should be withheld until the treatment schedule is complete, both because iron may inhibit treatment and because the absorption of oral iron is blocked by the inflammatory response.

Iron chelation and regulation of the cell cycle: 2 mechanisms of posttranscriptional regulation of the universal cyclin-dependent kinase inhibitor p21CIP1/WAF1 by iron depletion

Iron (Fe) plays a critical role in proliferation, and Fe deficiency results in G(1)/S arrest and apoptosis. However, the precise role of Fe in cell-cycle control remains unclear. We observed that Fe depletion increased the mRNA of the universal cyclin-dependent kinase inhibitor, p21(CIP1/WAF1), while its protein level was not elevated. This observation is unique to the G(1)/S arrest seen after Fe deprivation, as increased p21(CIP1/WAF1) mRNA and protein are usually found when arrest is induced by other stimuli. In this study, we examined the posttranscriptional regulation of p21(CIP1/WAF1) after Fe depletion and demonstrated that its down-regulation was due to 2 mechanisms: (1) inhibited translocation of p21(CIP1/WAF1) mRNA from the nucleus to cytosolic translational machinery; and (2) induction of ubiquitin-independent proteasomal degradation. Iron chelation significantly (P < .01) decreased p21(CIP1/WAF1) protein half-life from 61 (+/- 4 minutes; n = 3) to 28 (+/- 9 minutes, n = 3). Proteasomal inhibitors rescued the chelator-mediated decrease in p21(CIP1/WAF1) protein, while lysosomotropic agents were not effective. In Fe-replete cells, p21(CIP1/WAF1) was degraded in an ubiquitin-dependent manner, while after Fe depletion, ubiquitin-independent proteasomal degradation occurred. These results are important for considering the mechanism of Fe depletion-mediated cell-cycle arrest and apoptosis and the efficacy of chelators as antitumor agents.

Development and validation of HPLC-DAD methods for the analysis of two novel iron chelators with potent anti-cancer activity

Di-2-pyridylketone isonicotinoyl hydrazone (PKIH) and di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone (Dp44mT) novel iron chelators which possess marked anti-cancer activity in vivo. However, further progress in the development of these drug candidates requires precise and convenient methods for their qualitative and quantitative analysis. The aim of this study was to develop and validate HPLC methods suitable for the purity and stability evaluation of Dp44mT and PKIH and subsequently to employ these methods in stress tests addressing their chemical stability. The chromatographic analyses of both chelators were accomplished via HPLC using a Discovery HSF5 column (25 cm x 4 mm; 5 microm). For separation of Dp44mT and its synthetic precursors, the mobile phase was composed of a mixture of 2 mM EDTA and acetonitrile in a ratio 60:40 (v/v). A desirable separation of PKIH from its synthetic precursors was achieved with a mixture of 0.01 M phosphate buffer (pH 3.0), methanol and acetonitrile in a ratio of 65:21:14 (v/v/v) with the addition of EDTA (2 mM). In order to confirm the utility of these HPLC methods for measuring these drugs and their stability, Dp44mT and PKIH were subjected to chemical stress tests. These experiments showed that Dp44mT was relatively stable against hydrolytic degradation, but quite sensitive to oxidation. On the other hand, PKIH was slightly sensitive to acid-catalyzed hydrolysis, but it was relatively stable under other tested conditions. Furthermore, these studies confirmed the utility of these methods not only for appropriate evaluation of purity but also stability. The analytical methods developed and validated in this study, as well as the basic data on the chemical stability, should further support the development of both these novel anti-cancer chelators as promising drug candidates.

Iron chelation regulates cyclin D1 expression via the proteasome: a link to iron deficiency-mediated growth suppression

Iron (Fe) plays an important role in proliferation, and Fe deficiency results in G(1)/S arrest. Despite this, the precise role of Fe in cell-cycle control remains unclear. Cyclin D1 plays a critical function in G(1) progression by interacting with cyclin-dependent kinases. Previously, we examined the effect of Fe depletion on the expression of cell-cycle control molecules and identified a marked decrease in cyclin D1 protein, although the mechanism involved was unknown. In this study, we showed that cyclin D1 was regulated posttranscriptionally by Fe depletion. Iron chelation of cells in culture using desferrioxamine (DFO) or 2-hydroxy-1-naphthylaldehyde isonicotinoyl hydrazone (311) decreased cyclin D1 protein levels after 14 hours and was rescued by the addition of Fe. Cyclin D1 half-life in control cells was 80 +/- 15 minutes (n = 5), while in chelator-treated cells it was significantly (P < .008) decreased to 38 +/- 3 minutes (n = 5). Proteasomal inhibitors rescued the Fe chelator-mediated decrease in cyclin D1 protein, suggesting the role of the proteasome. In Fe-replete cells, cyclin D1 was degraded in an ubiquitin-dependent manner, while Fe depletion induced a ubiquitin-independent pathway. This is the first report linking Fe depletion-mediated growth suppression at G(1)/S to a mechanism inducing cyclin D1 proteolysis.

Desferal inhibits breast tumor growth and does not interfere with the tumoricidal activity of doxorubicin

Desferal is a clinically approved iron chelator used to treat iron overload. Doxorubicin is an anthracycline cancer chemotherapy drug used in the treatment of breast cancer. It can undergo redox cycling in the presence of iron to produce reactive oxygen species. The oxidant-generating activity of doxorubicin is thought to be responsible for the cardiotoxic side effects of the drug, but it is unclear whether it is also required for its anti-tumor activity. To test whether an iron-chelating antioxidant would interfere with the tumor-killing activity of doxorubicin, nude mice were transplanted with xenografts of human breast cancer MDA-MB 231 cells and then treated with doxorubicin and/or desferal. Not only did desferal not interfere with the anti-tumor activity of doxorubicin, it inhibited tumor growth on its own. In vitro studies confirmed that desferal inhibits breast tumor growth. However, it did not induce apoptosis, nor did it induce cell cycle arrest. Instead, desferal caused cytostasis, apparently through iron depletion. The cytostatic activity of desferal was partially ameliorated by pretreatment with iron-saturated transferrin, and transferrin receptor expression on breast cancer cells nearly doubled after exposure to desferal. In contrast to its effect on tumor cells, desferal did not inhibit growth of normal breast epithelial cells. The data indicate that the anti-tumor activity of doxorubicin is not dependent on iron-mediated ROS production. Furthermore, desferal may have utility as an adjunctive chemotherapy due to its ability to inhibit breast tumor growth and cardiotoxic side effects without compromising the tumor-killing activity of an anthracycline chemotherapy drug.

Study of daunorubicin cardiotoxicity prevention with pyridoxal isonicotinoyl hydrazone in rabbits

Risk of cardiotoxicity is the most serious drawback of the clinical usefulness of anthracycline antineoplastic antibiotics, which however, remain among the most powerful and widely employed anticancer drugs. In this study we have used daunorubicin-induced cardiomyopathy in rabbits as a model to investigate possible cardioprotective effects of pyridoxal isonicotinoyl hydrazone (PIH)-a principal representative of a novel group of aroylhydrazone iron chelators. Three groups of animals were used: a control group (n=11; i.v. saline), daunorubicin-treated animals (n=11; 3mg/kg, i.v.), and animals pretreated with PIH (n=9, 25 mg/kg, i.p.) 60 min before daunorubicin administration. All substances were administered once weekly for 10 weeks. Repeated administration of daunorubicin caused premature death in four animals and induced conspicuous histopathological changes in the myocardium, progressive and significant impairment of systolic heart function (a decrease in left ventricular dP/dt(max), ejection fraction, an increase in the pre-ejection period/left ventricular ejection time index), and a gradual increase in cardiac troponin T plasma concentrations. On the contrary, all the PIH-treated animals have survived all daunorubicin applications. Furthermore, in this group, the daunorubicin-induced cardiac changes were in most functional, biochemical as well as morphological parameters less pronounced than in the group receiving daunorubicin alone. Hence, PIH and other aroylhydrazones merit further investigation as potentially protective agents against anthracycline-induced cardiotoxicity.

Iron chelators with high antiproliferative activity up-regulate the expression of a growth inhibitory and metastasis suppressor gene: a link between iron metabolism and proliferation

Iron (Fe) is critical for proliferation, but its precise role in cell cycle progression remains unclear. In this study, we examined the mechanisms involved by assessing the effects of Fe chelators on the expression of molecules that play key roles in this process. In initial studies, gene arrays were used to assess gene expression after incubating cells with 2 Fe chelators, namely, desferrioxamine (DFO) and 2-hydroxy-1-naphthylaldehyde isonicotinoyl hydrazone (311), or the DNA-damaging agent, actinomycin D. From the genes assessed, only the N-myc downstream-regulated gene 1 (Ndrg1) was specifically up-regulated by Fe chelation. Although the function of Ndrg1 is unclear, previous studies showed it markedly slows tumor growth and acts as a potent metastasis suppressor. Incubation of cells with chelators markedly increased Ndrg1 mRNA and protein expression, but this was not found with their Fe complexes or when the Fe-binding site had been inactivated. Increased Ndrg1 expression following Fe chelation was related to the permeability and antiproliferative activity of chelators and could be reversed by Fe repletion. Moreover, Ndrg1 up-regulation after chelation occurred at the transcriptional level and was mediated by hypoxia inducible factor-1α (HIF-1α)-dependent and -independent mechanisms. Our investigation suggests Ndrg1 is a novel link between Fe metabolism and the control of proliferation.

Acyclonucleoside iron chelators of 1-(2-hydroxyethoxy)methyl-2-alkyl-3-hydroxy-4-pyridinones: potential oral iron chelation therapeutics

The method of synthesizing acyclonucleoside iron chelators is both convenient and cost effective compared to that of synthesizing ribonucleoside iron chelators. The X-ray crystal structural analysis shows that the 2-hydroxyethoxymethyl group does not affect the geometry of the iron chelating sites. Therefore, the iron binding and removal properties of the acyclonucleoside iron chelators should remain similar to the ribonucleoside iron chelators, which is confirmed by the titration and competition reaction of the acyclonucleoside chelators with iron and ferritin, respectively. The acyclonucleoside iron chelators are more lipophilic with measured n-octanol and Tris buffer distribution coefficients than ribonucleoside iron chelators.

Novel di-2-pyridyl-derived iron chelators with marked and selective antitumor activity: in vitro and in vivo assessment

Aroylhydrazone and thiosemicarbazone iron (Fe) chelators have potent antitumor activity. The aim of the current study was to examine the antitumor effects and mechanisms of action of a novel series of Fe chelators, the di-2-pyridyl thiosemicarbazones. Of 7 new chelators synthesized, 4 showed pronounced antiproliferative effects. The most active chelator was Dp44mT, which had marked and selective antitumor activity-for example, an IC(50) of 0.03 microM in neuroepithelioma cells compared with more than 25 microM in mortal fibroblasts. Indeed, this antiproliferative activity was the greatest yet observed for an Fe chelator. Efficacy was greater than it was for the cytotoxic ligand 311 and comparable to that of the antitumor agent doxorubicin. Strikingly, Dp44mT significantly (P <.01) decreased tumor weight in mice to 47% of the weight in the control after only 5 days, whereas there was no marked change in animal weight or hematologic indices. Terminal deoxyribonucleotidyl transferase (TdT)-mediated dUTP nick end-labeling (TUNEL) staining demonstrated apoptosis in tumors taken from mice treated with Dp44mT. This chelator caused a marked increase of caspase-3 activity in murine Madison-109 (M109) cells. Caspase activation was at least partially mediated by the release of mitochondrial holo-cytochrome c (h-cytc) after incubation with Dp44mT. In conclusion, Dp44mT is a novel, highly effective antitumor agent in vitro and in vivo that induces apoptosis.

Iron chelators for the treatment of iron overload disease: relationship between structure, redox activity, and toxicity

The success of the iron (Fe) chelator desferrioxamine (DFO) in the treatment of beta-thalassemia is limited by its lack of bioavailability. The design and characterization of synthetic alternatives to DFO has attracted much scientific interest and has led to the discovery of orally active chelators that can remove pathological Fe deposits. However, chelators that access intracellular Fe pools can be toxic by either inhibiting Fe-containing enzymes or promoting Fe-mediated free radical damage. Interestingly, toxicity does not necessarily correlate with Fe-binding affinity or with chelation efficacy, suggesting that other factors may promote the cytopathic effects of chelators. In this review, we discuss the interactions of chelators and their Fe complexes with biomolecules that can lead to toxicity and tissue damage.

Multidentate pyridinones inhibit the metabolism of nontransferrin-bound iron by hepatocytes and hepatoma cells

The therapeutic effect of iron (Fe) chelators on the potentially toxic plasma pool of nontransferrin-bound iron (NTBI), often present in Fe overload diseases and in some cancer patients during chemotherapy, is of considerable interest. In the present investigation, several multidentate pyridinones were synthesized and compared with their bidentate analogue, deferiprone (DFP; L1, orally active) and desferrioxamine (DFO; hexadentate; orally inactive) for their effect on the metabolism of NTBI in the rat hepatocyte and a hepatoma cell line (McArdle 7777, Q7). Hepatoma cells took up much less NTBI than the hepatocytes (< 10%). All the chelators inhibited NTBI uptake (80-98%) much more than they increased mobilization of Fe from cells prelabelled with NTBI (5-20%). The hexadentate pyridinone, N,N,N-tris(3-hydroxy-1-methyl-2(1H)-pyridinone-4-carboxaminoethyl)amine showed comparable activity to DFO and DFP. There was no apparent correlation between Fe status, Fe uptake and chelator activity in hepatocytes, suggesting that NTBI transport is not regulated by cellular Fe levels. The intracellular distribution of iron taken up as NTBI changed in the presence of chelators suggesting that the chelators may act intracellularly as well as at the cell membrane. In conclusion (a) rat hepatocytes have a much greater capacity to take up NTBI than the rat hepatoma cell line (Q7), (b) all chelators bind NTBI much more effectively during the uptake phase than in the mobilization of Fe which has been stored from NTBI and (c) while DFP is the most active chelator, other multidentate pyridinones have potential in the treatment of Fe overload, particularly at lower, more readily clinically available concentrations, and during cancer chemotherapy, by removing plasma NTBI.

Identification of the di-pyridyl ketone isonicotinoyl hydrazone (PKIH) analogues as potent iron chelators and anti-tumour agents

(1) In an attempt to develop chelators as potent anti-tumour agents, we synthesized two series of novel ligands based on the very active 2-pyridylcarboxaldehyde isonicotinoyl hydrazone (PCIH) group. Since lipophilicity and membrane permeability play a critical role in Fe chelation efficacy, the aldehyde moiety of the PCIH series, namely 2-pyridylcarboxaldehyde, was replaced with the more lipophilic 2-quinolinecarboxaldehyde or di-2-pyridylketone moieties. These compounds were then systematically condensed with the same group of acid hydrazides to yield ligands based on 2-quinolinecarboxaldehyde isonicotinoyl hydrazone (QCIH) and di-2-pyridylketone isonicotinoyl hydrazone (PKIH). To examine chelator efficacy, we assessed their effects on proliferation, Fe uptake, Fe efflux, the expression of cell cycle control molecules, iron-regulatory protein-RNA-binding activity, and (3)H-thymidine, (3)H-uridine and (3)H-leucine incorporation. (2) Despite the high lipophilicity of the QCIH ligands and the fact that they have the same Fe-binding site as the PCIH series, surprisingly none of these compounds were effective. In contrast, the PKIH analogues showed marked anti-proliferative activity and Fe chelation efficacy. Indeed, the ability of these ligands to inhibit proliferation and DNA synthesis was similar or exceeded that found for the highly cytotoxic chelator, 311. In contrast to the PCIH and QCIH analogues, most of the PKIH group markedly increased the mRNA levels of molecules vital for cell cycle arrest. (3) In conclusion, our studies identify structural features useful in the design of chelators with high anti-proliferative activity. We have identified a novel class of ligands that are potent Fe chelators and inhibitors of DNA synthesis, and which deserve further investigation.

Effects of nitrogen monoxide and carbon monoxide on molecular and cellular iron metabolism: mirror-image effector molecules that target iron

Many effector functions of nitrogen monoxide (NO) and carbon monoxide (CO) are mediated through their high-affinity for iron (Fe). In this review, the roles of NO and CO are examined in terms of their effects on the molecular and cellular mechanisms involved in Fe metabolism. Both NO and CO avidly form complexes with a plethora of Fe-containing molecules. The generation of NO and CO is mediated by the nitric oxide synthase and haem oxygenase (HO) families of enzymes respectively. The effects of NO on Fe metabolism have been well characterized, whereas knowledge of the effects of CO remains within its infancy. In terms of the role of NO in Fe metabolism, one of the best characterized interactions includes its effect on the iron regulatory proteins. These molecules are mRNA-binding proteins that control the expression of the transferrin receptor 1 and ferritin, molecules that are involved in Fe uptake and storage respectively. Apart from this, activated macrophages impart their cytotoxic activity by generating NO, which results in marked Fe mobilization from tumour-cell targets. This deprives the cell of the Fe that is required for DNA synthesis and energy production. Considering that HO degrades haem, resulting in the release of CO, Fe(II) and biliverdin, it is suggested that a CO-Fe complex will form. This may account for the rapid Fe mobilization observed from macrophages after haemoglobin catabolism. Intriguingly, overexpression of HO results in cellular Fe mobilization, suggesting that CO has a similar effect to NO on Fe trafficking. Preliminary evidence suggests that, like NO, CO plays important roles in Fe metabolism.

Dietary flavonoid iron complexes as cytoprotective superoxide radical scavengers

Superoxide radicals have been implicated in the pathogenesis of ischemia/reperfusion, aging, and inflammatory diseases. In the present work, we have shown that the Fe(3+) complexes of flavonoids (polyphenols) were much more effective than the uncomplexed flavonoids in protecting isolated rat hepatocytes against hypoxia-reoxygenation injury. The 2:1 flavonoid-metal complexes of Cu(2+), Fe(2+), or Fe(3+) were more effective than the parent compounds in scavenging superoxide radicals generated by xanthine oxidase/hypoxanthine (an enzymatic superoxide-generating system). The 2:1 [flavonoid:Fe(3+)] complexes but not the [deferoxamine:Fe(3+)] complex readily scavenged superoxide radicals. These results suggest that the initial step in superoxide radical scavenging (SRS) activity involves a redox-active flavonoid:Fe(3+) complex. Flavonoid:Fe(3+) complexes should, therefore, be tested as a therapy for the treatment of ischemia/reperfusion injury.

Genetic analysis of iron citrate toxicity in yeast: implications for mammalian iron homeostasis

Deletion of the yeast homologue of frataxin, YFH1, results in mitochondrial iron accumulation and respiratory deficiency (petite formation). We used a genetic screen to identify mutants that modify iron-associated defects in respiratory activity in Deltayfh1 cells. A deletion in the peroxisomal citrate synthase CIT2 in Deltayfh1 cells decreased the rate of petite formation. Conversely, overexpression of CIT2 in Deltayfh1 cells increased the rate of respiratory loss. Citrate toxicity in Deltayfh1 cells was dependent on iron but was independent of mitochondrial respiration. Citrate toxicity was not restricted to iron-laden mitochondria but also occurred when iron accumulated in cytosol because of impaired vacuolar iron storage. These results suggest that high levels of citrate may promote iron-mediated tissue damage.

Novel "hybrid" iron chelators derived from aroylhydrazones and thiosemicarbazones demonstrate selective antiproliferative activity against tumor cells

We previously demonstrated that 2-hydroxy-1-naphthylaldehyde isonicotinoyl hydrazone (311) and other aroylhydrazone chelators possess potent antineoplastic activity because of their ability to bind iron (Fe). From these studies, we identified structural components of the hydrazones that provide antineoplastic activity, namely the salicylaldehyde and 2-hydroxy-1-naphthylaldehyde moieties. A related group of chelators known as the thiosemicarbazones also show pronounced antitumor activity because of their ability to inhibit ribonucleotide reductase. Considering this, we designed a new series of "hybrid ligands" by condensation of the aldehydes described above with a range of thiosemicarbazides. The parent compound of these ligands is 2-hydroxy-1-naphthylaldehyde thiosemicarbazone (NT). Of 8 NT analogues, 3 chelators, namely NT, N4mT (2-hydroxy-1-naphthylaldehyde-4-methyl-3-thiosemicarbazone), and N44mT (2-hydroxy-1-naphthylaldehyde-4,4-dimethyl-3-thiosemicarbazone), showed high antiproliferative activity against SK-N-MC neuroepithelioma cells (50% inhibitory concentration [IC(50)] = 0.5-1.5 microM). Indeed, their activity was significantly (P <.0001) greater than that of desferrioxamine (DFO) (IC(50) = 22 microM). We demonstrate that 311, a 311 analogue (311m), and several NT-series chelators have significantly (P <.001) greater antiproliferative activity against tumor cells than against a range of normal cell types. For example, the IC(50) values of NT and N4mT in SK-N-MC neuroepithelioma cells were 0.5 microM, whereas for fibroblasts the IC(50) values were greater than 25 microM. Further, the effect of one of the most potent chelators (311m) on preventing the growth of bone marrow stem cell cultures was far less than that of doxorubicin and similar to that of cisplatin. These studies support the further development of these chelators as antiproliferative agents.

Action of deferoxamine against Pneumocystis carinii

We found earlier that deferoxamine (DFO), a drug used for treatment of iron overload, is active against a rat model of Pneumocystis carinii pneumonia (PCP). We had assumed a mode of action by deprivation of nutritional iron; however, data here show that DFO penetrates P. carinii, causing irreversible damage, thus indicating a different mode of action. Penetration was demonstrated by showing DFO uptake by high-pressure liquid chromatography analysis. By using calcein-AM as an indicator, exposure to DFO was shown to cause a reduction in P. carinii cytoplasmic free iron. Exposure to >or=100 microM DFO for >or=8 h in vitro caused growth to cease and cell numbers to decline over several days. This direct and irreversible damage to P. carinii led to the prediction that infrequent delivery of DFO to the lungs via an aerosol would be an effective treatment in the animal model of PCP. This prediction was confirmed by demonstrating that a once-a-week aerosol treatment of rats was 100% effective both as a prophylactic and as a curative treatment in a rat model of PCP.

Detection of iron-containing proteins contributing to the cellular labile iron pool by a native electrophoresis metal blotting technique

The labile iron pool (LIP) plays a role in generation of free radicals and is thus the target of chelators used for the treatment of iron overload. We have previously shown that the LIP is bound mostly to high molecular weight carriers (MW>5000). However, the iron does not remain associated with these proteins during native gel electrophoresis. In this study we describe a new method to reconstruct the interaction of iron with iron-binding proteins. Proteins were separated by native gradient polyacrylamide gel electrophoresis and transfered to polyvinilidene difluoride membrane under native conditions. The immobilized iron-binding proteins are then labeled by 59Fe using a 'titrational blotting' technique and visualized by storage phosphorimaging. At least six proteins, in addition to ferritin and transferrin, are specifically labeled in cellular lysates of human erythroleukemic cells. This technique enables separation and detection of iron-binding proteins or other metal-protein complexes under near-physiological conditions and facilitates identification of weak iron-protein complexes. Using a new native metal blotting method, we have confirmed that specific high molecular weight proteins bind the labile iron pool.

The outcome of Leishmania major experimental infection in BALB/c mice can be modulated by exogenously delivered iron

We previously established that Leishmania promastigotes express a transferrin receptor and that iron chelators inhibit promastigote growth in vitro. Thus, we were interested in modulating the vertebrate host iron pool and to monitor whether such changes will affect the outcome of L. major infection in BALB / c mice, inoculated in the footpad with 106 stationary phase promastigotes. Treatment of mice with desferrioxamine resulted in a slight delay of the development of cutaneous lesions. In contrast and unexpectedly, systemic iron delivery, at early time points of parasite delivery, significantly limited footpad pathology. Accordingly, parasite loads at the site of parasite delivery, the draining lymph node, liver and spleen were significantly reduced in iron-loaded mice. Importantly, the "protective" effect of iron delivery correlated with the presence, at the site of inoculation, of lower levels of IL-4 and IL-10 transcripts while both IFN-gamma and inducible nitric oxide synthase transcripts were at higher levels. The presence of more type 1 cytokine transcripts was further supported by the increased levels of IgG2a in their sera. These data strongly suggest that susceptibility to L. major as assessed in the footpad model is modifiable by interventions that alter the iron status of the host at early time points of parasite delivery.

Protection of erythrocytes against oxidative damage and autologous immunoglobulin G (IgG) binding by iron chelator fluor-benzoil-pyridoxal hydrazone

Iron is released in a free desferrioxamine-chelatable form when erythrocytes are challenged by an oxidative stress. The release of iron is believed to play an important role in inducing destructive damage (lipid peroxidation and hemolysis) or in producing membrane protein oxidation and generation of senescent cell antigens (SCA). In this report, we further tested the hypothesis that intracellular chelation of iron released under conditions of oxidative stress prevents erythrocyte damage or SCA formation. Fluor-benzoil-pyridoxal hydrazone (FBPH), an iron-chelating molecule of the family of aromatic hydrazones, was prepared by synthesis and used for the above purpose after the capacity of the product to enter cells had been ascertained. GSH-depleted mouse erythrocytes were incubated with the oxidant drug phenylhydrazine in order to produce iron release, lipid peroxidation, and hemolysis. FBPH at a concentration of 200 microM prevented lipid peroxidation and hemolysis in spite of equal values of iron release. FBPH was active even at a lower concentration (100 microM) when the erythrocytes were preincubated with it for 15 min. No preventive effect was seen when FBPH saturated with iron was used. Prolonged aerobic incubation (60 hr) of erythrocytes produced iron release and formation of SCA as determined by autologous immunoglobulin G (IgG) binding. The IgG binding was detected by using an anti-IgG antibody labeled with fluorescein and by examining the cells for fluorescence by confocal microscopy. FBPH prevented SCA formation in a dose-related manner. These results lend further support to the hypothesis that iron release is a key factor in erythrocyte ageing.

Free radical scavengers: chemical concepts and clinical relevance

Free radicals are involved in the pathology of many CNS disorders, like Parkinson's disease, Alzheimer's disease, or stroke. This discovery lead to the development of many radical scavengers for the clinical treatment of neurodegenerative diseases. In this review, the different chemical concepts for free radical scavenging will be discussed: nitrons, thiols, iron chelators, phenols, and catechols. Especially catechols, like the naturally occurring flavonols, the synthetic drug nitecapone, or the endogenous catacholamines and their metabolites, are of great interest, as they combine iron chelating with radical scavenging activity. We present data on the radical scvenging activity of dopamine and apomorphine, which prevent lipid peroxidation in rat brain mitochondria and protect PC12 cells against H2O2-toxicity.

Therapy by taking away: the case of iron

The recent finding of the beneficial effects of iron deprivation in the outcome of muscle necrosis in an animal model of genetic myopathy served as the basis of this commentary. Here, "taking away" iron by controlled dietary deprivation is proposed as a reasonable, feasible, cheap, and efficient clinical approach to many diverse diseases, all of which have a free radical component. Indeed, iron potentiates the generation of the highly reactive and toxic hydroxyl radical, and, thus, of oxidative damage. Iron deprivation may represent the first really efficient antioxidant, preventing oxidative stress in all subcellular compartments, tissues, and organs. Iron/iron deprivation also modulates programmed cell death (apoptosis), which should be the subject of further studies to better define the mechanisms mediating these complex effects. Finally, related to its antioxidant effects, iron deprivation may find applications in the anti-aging field, whether programmed or premature aging, and whether in cosmetics or in gerontology.

Increased serum concentrations of conjugated diens and malondialdehyde in patients with pulmonary tuberculosis

During pulmonary inflammation increased amounts of reactive oxygen species (ROS) and reactive nitrogen intermediates (RNI) are produced as a consequence of phagocyte respiratory burst. One of the manifestation of these free radical-mediated processes is lipid peroxidation (LP). The aim of our study was to assess the concentration of lipid peroxidation products (LPPs), conjugated diens (CD) and malondialdehyde (MDA), in patients with active TB. Forty-two patients were enrolled into the study. Half (group I) had advanced TB and were sputum smear-positive. The remainder (group II) had only small radiographical changes and were sputum smear-negative. Serum concentrations of CD and MDA were measured at days 0, 7, 14 and 28 in group I and day 0 in group II. We found that in all patients with active TB CCD (1.0 +/- 0.05A233) and CMDA (2.01 +/- 0.16 nmol dl-1) were significantly elevated compared to healthy controls (0.67 +/- 0.03A233 and 1.36 +/- 0.08 nmol dl-1, respectively) (P < 0.001). The highest levels of LPPs were in patients with advanced TB. These concentrations were stable during the first month of anti-tuberculous therapy. Our data indicated that, as in bacterial pneumonia, LPPs were enhanced in active TB. The levels of LPPs depended on the form of the disease as they were higher in subjects with advanced disease than in those with only small radiographical changes. Further studies are needed to assess the role of antioxidants as adjuvant therapy in patients with pulmonary TB.