Iron chelators and iron toxicity

Biochemical effects of deferasirox and deferasirox-loaded nanomicellesin iron-intoxicated rats

Deferasirox (DFX) was formulated into oil-in-water microemulsions in the presence of pluronicto improve its oral bioavailability. The size of the DFX-loadedmicroemulsions system measured by dynamic light scattering (DLS) was about 9 nm. The anti-proliferative and anti-lipid peroxidation effects of DFX and DFX-loaded microemulsions were assessed on Human umbilical vein endothelial (HUVEC) cells. Our in vitro results showed that HUVEC cells are more susceptible to free DFX as compared to DFX-loaded microemulsions. Although both free and encapsulated DFX attenuated FeCl₃-induced lipid peroxidation, after 6 and 12 h treatment, DFX-loaded microemulsions did not appear a better ameliorator than DFX. To compare the in vivo efficacy of free DFX and DFX-loaded microemulsions in iron- intoxicated rats, the animals were orally administered with 25 mg/kg DFX, or 25 mg/kg DFX microemulsions, respectively. In vivo gavage handling of free DFX significantly increased serum biochemical parameters. There was also a significant increase in lipid peroxidation in rats who received free DFX compared to those in the control rats. Treatment with DFX-loaded microemulsions restored the elevated levels of serum AST, ALT, and creatinine levels and also reduced liver MDA content. Histopathological analysis of renal and hepatic tissues was in line with the biochemical results. In conclusion, DFX-loaded microemulsions induce less toxicity than free DFX and appear a more desirable and safer drug carrier in combating the iron-overload complications. Theoretical simulations are performed to get better insight regarding interactions between DFX and surfactant F127.

Current understanding of the metabolism of micronutrients in chronic alcoholic liver disease

Alcoholic liver disease (ALD) remains an important health problem worldwide. Perturbation of micronutrients has been broadly reported to be a common characteristic in patients with ALD, given the fact that micronutrients often act as composition or coenzymes of many biochemical enzymes responsible for the inflammatory response, oxidative stress, and cell proliferation. Mapping the metabolic pattern and the function of these micronutrients is a prerequisite before targeted intervention can be delivered in clinical practice. Recent years have registered a significant improvement in our understanding of the role of micronutrients on the pathogenesis and progression of ALD. However, how and to what extent these micronutrients are involved in the pathophysiology of ALD remains largely unknown. In the current study, we provide a review of recent studies that investigated the imbalance of micronutrients in patients with ALD with a focus on zinc, iron, copper, magnesium, selenium, vitamin D and vitamin E, and determine how disturbances in micronutrients relates to the pathophysiology of ALD. Overall, zinc, selenium, vitamin D, and vitamin E uniformly exhibited a deficiency, and iron demonstrated an elevated trend. While for copper, both an elevation and deficiency were observed from existing literature. More importantly, we also highlight several challenges in terms of low sample size, study design discrepancies, sample heterogeneity across studies, and the use of machine learning approaches.

Prognostic Value of Serum Iron, Ferritin, and Transferrin in Chronic Alcoholic Liver Disease

Ethanol increases iron absorption. Therefore, increased amount of iron reaches the liver, and exerts pro-oxidant effects and stimulates ferritin synthesis and hepatic stellate cell activation, promoting fibrosis and inflammation. These mechanisms would theoretically support a role of ferritin as a marker of the transition to liver cirrhosis, and, consequently, as a prognostic factor, but there is controversy regarding its behavior in alcoholics. We analyzed among 238 severe alcoholics the prognostic value of iron, ferritin, transferrin, transferrin saturation index (TSI) and total iron binding capacity (TIBC), and the relationships of these variables with liver function, proinflammatory markers (C-reactive protein (CRP), interleukin (IL)-6, IL-8, and tumor necrosis factor α), and the presence of cirrhosis. Patients showed higher serum ferritin (Z = 2.50, p = 0.031) but lower transferrin (t(264) = 4.81, p < 0.001), TIBC (t(262) = 4.44, p < 0.001), and iron (Z = 3.19, p = 0.001) values compared with 32 age- and sex-matched controls. Ferritin was related to inflammatory cytokines such as IL-8 (ρ = 0.18, p = 0.012) and to IL-6 (ρ = 0.16, p = 0.016), but not to liver function. On the contrary, cirrhotics showed lower transferrin (t(234) = 4.77, p < 0.001) and TIBC (t(232) = 4.67, p < 0.001), but higher TSI (Z = 3.35, p < 0.001) than non-cirrhotics. Transferrin, TSI, and TIBC were related to liver function impairment (marked differences among the Child's groups regarding transferrin (KW (2) = 22.83, p < 0.001), TSI (KW (2) = 15.81, p < 0.001), and TIBC (KW (2) = 21.38, p < 0.001) but only weakly to inflammation (inverse relationships between IL-6 and total iron (ρ = - 0.16, p = 0.017), TIBC (ρ = - 0.20, p = 0.002), and transferrin (ρ = - 0.20, p = 0.003). In accordance, albumin, IL-6, alcohol quitting, and TSI, in this order, were independently related to mortality, but not ferritin or iron.

CN128: A New Orally Active Hydroxypyridinone Iron Chelator

Deferoxamine, deferiprone, and deferasirox are used for the treatment of systemic iron overload, although they possess limitations due to lack of oral activity, lower efficacy, and side effects. These limitations led to a search for an orally active iron chelator with an improved therapeutic index. The lower efficacy of deferiprone is due to rapid glucuronidation, leading to the formation of a nonchelating metabolite. Here, we demonstrate that the influence of metabolism can be reduced by introducing a sacrificial site for glucuronidation. A log P-guided investigation of 20 hydroxpyridinones led to the identification of CN128. The Fe(III) affinity and metal selectivity of CN128 are similar to those of deferiprone, the log P value is more lipophilic, and its iron scavenging ability is superior. Overall, CN128 was demonstrated to be safe in a range of toxicity assessments and is now in clinical trials for the treatment of β-thalassemia after regular blood transfusion.

Iron-induced oligomerization of human FXN81-210 and bacterial CyaY frataxin and the effect of iron chelators

Patients suffering from the progressive neurodegenerative disease Friedreich's ataxia have reduced expression levels of the protein frataxin. Three major isoforms of human frataxin have been identified, FXN42-210, FXN56-210 and FXN81-210, of which FXN81-210 is considered to be the mature form. Both long forms, FXN42-210 and FXN56-210, have been shown to spontaneously form oligomeric particles stabilized by the extended N-terminal sequence. The short variant FXN81-210, on other hand, has only been observed in the monomeric state. However, a highly homologous E. coli frataxin CyaY, which also lacks an N-terminal extension, has been shown to oligomerize in the presence of iron. To explore the mechanisms of stabilization of short variant frataxin oligomers we compare here the effect of iron on the oligomerization of CyaY and FXN81-210. Using dynamic light scattering, small-angle X-ray scattering, electron microscopy (EM) and cross linking mass spectrometry (MS), we show that at aerobic conditions in the presence of iron both FXN81-210 and CyaY form oligomers. However, while CyaY oligomers are stable over time, FXN81-210 oligomers are unstable and dissociate into monomers after about 24 h. EM and MS studies suggest that within the oligomers FXN81-210 and CyaY monomers are packed in a head-to-tail fashion in ring-shaped structures with potential iron-binding sites located at the interface between monomers. The higher stability of CyaY oligomers can be explained by a higher number of acidic residues at the interface between monomers, which may result in a more stable iron binding. We also show that CyaY oligomers may be dissociated by ferric iron chelators deferiprone and DFO, as well as by the ferrous iron chelator BIPY. Surprisingly, deferiprone and DFO stimulate FXN81-210 oligomerization, while BIPY does not show any effect on oligomerization in this case. The results suggest that FXN81-210 oligomerization is primarily driven by ferric iron, while both ferric and ferrous iron participate in CyaY oligomer stabilization. Analysis of the amino acid sequences of bacterial and eukaryotic frataxins suggests that variations in the position of the acidic residues in helix 1, β-strand 1 and the loop between them may control the mode of frataxin oligomerization.

Deferoxamine alleviates liver fibrosis induced by CCl4 in rats

Several chronic liver diseases can lead to the occurrence of hepatic fibrosis through the accumulation of iron, which causes induction of oxidative stress and consequently activation of fibrogenesis. The present study was designed to investigate the potential antifibrotic and anti-oxidant effects of deferoxamine (DFO), a well-known iron chelator in an experimental rat model of liver injury using carbon tetrachloride (CCl4 ). First, the potential effective dose of DFO was screened against CCl4 -induced acute hepatotoxicity. Then, rats were co-treated with DFO (300 mg/kg, i.p.) for 6 weeks starting from the third week of CCl4 induction of chronic hepatotoxicity. Liver function was assessed in addition to histopathological examination. Furthermore, oxidative stress and fibrosis markers were assessed. It was found that treatment of animals with DFO significantly counteracted the changes in liver function; histopathological lesions and hepatic iron deposition that were induced by CCl4 . DFO also significantly counteracted the CCl4 -induced lipid peroxidation increase and reduction in antioxidant activities of superoxide dismutase and glutathione peroxidase enzymes. In addition, DFO ameliorated significantly liver fibrosis markers including hydroxyproline, collagen accumulation, and the expression of the hepatic stellate cells (HSCs) activation marker; alpha smooth muscle actin and transforming growth factor-beta (TGF-β). Together, these findings indicate that DFO possesses a potent antifibrotic effect due to its antioxidant properties that counteracted oxidative stress and lipid peroxidation and restored antioxidant enzymes activities as well as reducing HSCs activation and fibrogenesis.

Redox cycling metals: Pedaling their roles in metabolism and their use in the development of novel therapeutics

Essential metals, such as iron and copper, play a critical role in a plethora of cellular processes including cell growth and proliferation. However, concomitantly, excess of these metal ions in the body can have deleterious effects due to their ability to generate cytotoxic reactive oxygen species (ROS). Thus, the human body has evolved a very well-orchestrated metabolic system that keeps tight control on the levels of these metal ions. Considering their very high proliferation rate, cancer cells require a high abundance of these metals compared to their normal counterparts. Interestingly, new anti-cancer agents that take advantage of the sensitivity of cancer cells to metal sequestration and their susceptibility to ROS have been developed. These ligands can avidly bind metal ions to form redox active metal complexes, which lead to generation of cytotoxic ROS. Furthermore, these agents also act as potent metastasis suppressors due to their ability to up-regulate the metastasis suppressor gene, N-myc downstream regulated gene 1. This review discusses the importance of iron and copper in the metabolism and progression of cancer, how they can be exploited to target tumors and the clinical translation of novel anti-cancer chemotherapeutics.

Antifibrotic mechanism of deferoxamine in concanavalin A induced-liver fibrosis: Impact on interferon therapy

Iron-overload is a well-known factor of hepatotoxicity and liver fibrosis, which found to be a common finding among hepatitis C virus patients and related to interferon resistance. We aimed to elucidate the potential antifibrotic effect of deferoxamine; the main iron chelator, and its additional usefulness to interferon-based therapy in concanavalin A-induced immunological model of liver fibrosis. Rats were treated with deferoxamine and/or pegylated interferon-α for 6 weeks. Hepatotoxicity indices, oxidative stress, inflammatory and liver fibrosis markers were assessed. Concanavalin A induced a significant increase in hepatotoxicity indices and lipid peroxidation accompanied with a significant depletion of total antioxidant capacity, glutathione level and superoxide dismutase activity. Besides, it increased CD4(+) T-cells content and the downstream inflammatory cascades, including NF-κB, TNF-α, iNOS, COX-2, IL-6 and IFN-γ. Furthermore, α-SMA, TGF-β1 and hydroxyproline were increased markedly, which confirmed by histopathology. Treatment with either deferoxamine or pegylated interferon-α alone reduced liver fibrosis markers significantly and improved liver histology. However, some of the hepatotoxicity indices and oxidative stress markers did not improve upon pegylated interferon-α treatment alone, besides the remarkable increase in IL-6. Combination therapy of deferoxamine with pegylated interferon-α further improved all previous markers, ameliorated IL-6 elevation, as well as increased hepcidin expression. In conclusion, our study provides evidences for the potent antifibrotic effects of deferoxamine and the underlying mechanisms that involved attenuating oxidative stress and subsequent inflammatory cascade, as well as the production of profibrogenic factors. Addition of deferoxamine to interferon regimen for HCV patients may offer a promising adjuvant modality to enhance therapeutic response.

Deferitazole, a new orally active iron chelator

Deferitazole possesses a high affinity and selectivity for iron(iii), forming an equilibrium mixture of two Fe^III(deferitazole)₂complexes, under biological conditions.

The exochelins of pathogenic mycobacteria: unique, highly potent, lipid- and water-soluble hexadentate iron chelators with multiple potential therapeutic uses

SIGNIFICANCE

Exochelins are lipid- and water-soluble siderophores of Mycobacterium tuberculosis with unique properties that endow them with exceptional pharmacologic utility. Exochelins can be utilized as probes to decipher the role of iron in normal and pathological states, and, since they rapidly cross cell membranes and chelate intracellular iron with little or no toxicity, exochelins are potentially useful for the treatment of a number of iron-dependent pathological phenomena.

RECENT ADVANCES

In animal models, exochelins have been demonstrated to have promise for the treatment of transfusion-related iron overload, restenosis after coronary artery angioplasty, cancer, and oxidative injury associated with acute myocardial infarction and transplantation.

CRITICAL ISSUES

To be clinically effective, iron chelators should be able to rapidly enter cells and chelate iron at key intracellular sites. Desferri-exochelins, and other lipid-soluble chelators, can readily cross cell membranes and remove intracellular free iron; whereas deferoxamine, which is lipid insoluble, cannot do so. Clinical utility also requires that the chelators be nontoxic, which, we hypothesize, includes the capability to prevent iron from catalyzing free radical reactions which produce •OH or other reactive oxygen species. Lipid-soluble iron chelators currently available for clinical application are bidentate (deferiprone) or tridentate (desferasirox) molecules that do not block all six sites on the iron molecule capable of catalyzing free radical reactions. In contrast, desferri-exochelins are hexadentate molecules, and by forming a one-to-one binding relationship with iron, they prevent free radical reactions.

FUTURE DIRECTIONS

Clinical studies are needed to assess the utility of desferri-exochelins in the treatment of iron-dependent pathological disorders.

Cell penetrating peptide (CPP)-conjugated desferrioxamine for enhanced neuroprotection: synthesis and in vitro evaluation

Iron overload causes progressive and sometimes irreversible damage due to accelerated production of reactive oxygen species. Desferrioxamine (DFO), a siderophore, has been used clinically to remove excess iron. However, the applications of DFO are limited because of its inability to access intracellular labile iron. Cell penetrating peptides (CPPs) have become an efficient delivery vector for the enhanced internalization of drugs into the cytosol. We describe, herein, an efficient method for covalently conjugating DFO to the CPPs TAT(47-57) and Penetratin. Both conjugates suppressed the redox activity of labile plasma iron in buffered solutions and in iron-overloaded sera. Enhanced access to intracellular labile iron compared to the parent siderophore was achieved in HeLa and RBE4 (a model of blood-brain-barrier) cell lines. Iron complexes of both conjugates also had better permeability in both cell models. DFO antioxidant and iron binding properties were preserved and its bioavailability was increased upon CPP conjugation, which opens new therapeutic possibilities for neurodegenerative processes associated with brain iron overload.

Changes of the corrosion potential of iron in stagnation and flow conditions and their relationship with metal release

This study examined the behavior of corrosion potential (Ecorr) of iron exposed to drinking water during episodes of stagnation and flow. These measurements showed that during stagnation episodes, Ecorr values decrease prominently and consistently. This decrease is initially rapid but it becomes slower as the stagnation time increases. During flow episodes, the Ecorr values increase and reach a quasi-steady state. Experiments with varying concentrations of dissolved oxygen showed that the decrease of Ecorr values characteristic for stagnation is likely to be associated with the consumption of dissolved oxygen by the exposed metal. The corrosion potential of iron and its changes during stagnation were sensitive to the concentrations of sulfate and chloride ions. Measurements of iron release showed that both the absolute values of Ecorr measured prior to or after stagnation episodes were well correlated with the logarithms of concentrations of total iron. The slope of this dependence showed that the observed correlations between Ecorr values and Fe concentrations corresponded to the coupling between the oxidant consumption and changes of Fe redox status. These results demonstrate that in situ Ecorr measurements can be a sensitive method with which to ascertain effects of hydrodynamic conditions and short-term variations of water chemistry on metal release and corrosion in drinking water. This approach is valuable practically because Ecorr measurements are precise, can be carried out in situ with any desired time resolution, do not affect the state of exposed surface in any extent and can be carried out with readily available equipment.

Quercetin protects rat hepatocytes from oxidative damage induced by ethanol and iron by maintaining intercellular liable iron pool

Accumulating evidence has shown that ethanol-induced iron overload plays a crucial role in the development and progression of alcoholic liver disease. We designed the present study to investigate the potential protective effect of quercetin, a naturally occurring iron-chelating antioxidant on alcoholic iron overload and oxidative stress. Ethanol-incubated (100 mmol/L) rat primary hepatocytes were co-treated by quercetin (100 µmol/L) and different dose of ferric nitrilotriacetate (Fe-NTA) for 24 h. When the hepatic enzyme releases in the culture medium, redox status of hepatocytes and the intercellular labile iron pool (LIP) level were assayed. Our data showed that Fe-NTA dose dependently induced cellular leakage of aspartate transaminase and lactate dehydrogenase, glutathione depletion, superoxide dismutase inactivation, and overproduction of malondialdehyde) and reactive oxygen species (ROS) of intact and especially ethanol-incubated hepatocytes. The oxidative damage resulted from ethanol, Fe-NTA, and especially their combined treatment was substantially alleviated by quercetin, accompanying the corresponding normalization of intercellular LIP level. Iron in excess, thus, may aggravate ethanol hepatotoxicity through Fenton-active LIP, and quercetin attenuated ethanol-induced iron and oxidative stress. To maintain intercellular LIP contributes to the hepatoprotective effect of quercetin besides its direct ROS-quenching activity.

Synthesis and characterization of a triazine dendrimer that sequesters iron(III) using 12 desferrioxamine B groups

The synthesis of a third generation triazine dendrimer, 1, containing multiple, iron-sequestering desferrioxamine B (DFO) groups is described. Benzoylation of the hydroxamic acid groups of DFO and formation of a reactive dichlorotriazine provide the intermediate for reaction with the second generation dendrimer displaying twelve amines. This strategy further generalizes the 'functional monomer' approach to generate biologically active triazine dendrimers. Dendrimer 1 is prepared in seven steps in 35% overall yield and displays 12 DFO groups making it 56% drug by weight. Spectrophotometric titrations (UV-vis) show that 1 sequesters iron(III) atoms with neither cooperativity nor significant interference from the dendrimer backbone. Evidence from NMR spectroscopy and mass spectrometry reveals a limitation to this functional monomer approach: trace amounts of O-to-N acyl migration from the protected hydroxamic acids to the amine-terminated dendrimer occurs during the coupling step leading to N-benzoylated dendrimers displaying fewer than 12 DFO groups.

Amyloid precursor protein and alpha synuclein translation, implications for iron and inflammation in neurodegenerative diseases

Recent studies that alleles in the hemochromatosis gene may accelerate the onset of Alzheimer's disease by five years have validated interest in the model in which metals (particularly iron) accelerate disease course. Biochemical and biophysical measurements demonstrated the presence of elevated levels of neurotoxic copper zinc and iron in the brains of AD patients. Intracellular levels of APP holoprotein were shown to be modulated by iron by a mechanism that is similar to the translation control of the ferritin L- and H mRNAs by iron-responsive element (IRE) RNA stem loops in their 5' untranslated regions (5'UTRs). More recently a putative IRE-like sequence was hypothesized present in the Parkinsons's alpha synuclein (ASYN) transcript (see [A.L. Friedlich, R.E. Tanzi, J.T. Rogers, The 5'-untranslated region of Parkinson's disease alpha-synuclein messenger RNA contains a predicted iron responsive element, Mol. Psychiatry 12 (2007) 222-223. [6]]). Together with the demonstration of metal dependent translation of APP mRNA, the involvement of metals in the plaque of AD patients and of increased iron in striatal neurons in the substantia nigra (SN) of Parkinson's disease patients have stimulated the development of metal attenuating agents and iron chelators as a major new therapeutic strategy for the treatment of these neurodegenerative diseases. In the case of AD, metal based therapeutics may ultimately prove more cost effective than the use of an amyloid vaccine as the preferred anti-amyloid therapeutic strategy to ameliorate the cognitive decline of AD patients.

Iron chelation protects the retinal pigment epithelial cell line ARPE-19 against cell death triggered by diverse stimuli

PURPOSE

Cell death can be induced by exogenous reactive oxygen species (ROS). Endogenous ROS can also play a role in cell death triggered by agents that are not themselves ROS. One of the most potent ROS-generating systems is the iron-catalyzed Fenton reaction. Herein, the authors tested whether iron plays an important role in cell death induced by diverse stimuli in retinal pigment epithelial (RPE) cells.

METHODS

The ability of the iron chelator salicylaldehyde isonicotinoyl hydrazone (SIH) to chelate intracellular labile iron was tested in the human cell line ARPE-19. The ability of SIH to protect against RPE cell death induced by hydrogen peroxide, staurosporine, anti-Fas, and exposure to A2E plus blue light was determined. ROS production by staurosporine was assessed in the presence and absence of SIH. The protective activity of SIH was compared with that of other iron chelators and an antioxidant.

RESULTS

Acute exposure to SIH was nontoxic and at least partially protective against cell death induced by all tested agents. On a molar basis, SIH was more protective against hydrogen peroxide than other iron chelators and an antioxidant. SIH decreased levels of staurosporine-induced ROS.

CONCLUSIONS

Iron chelation with SIH can decrease levels of ROS and protect RPE cells against cell death induced by diverse stimuli. These results suggest a central role for iron in cell death pathways, potentially involving the generation of oxidative stress. SIH or related iron chelators may prove useful for protection against diseases involving RPE death, such as AMD.

Iron behaving badly: inappropriate iron chelation as a major contributor to the aetiology of vascular and other progressive inflammatory and degenerative diseases

BACKGROUND

The production of peroxide and superoxide is an inevitable consequence of aerobic metabolism, and while these particular 'reactive oxygen species' (ROSs) can exhibit a number of biological effects, they are not of themselves excessively reactive and thus they are not especially damaging at physiological concentrations. However, their reactions with poorly liganded iron species can lead to the catalytic production of the very reactive and dangerous hydroxyl radical, which is exceptionally damaging, and a major cause of chronic inflammation.

REVIEW

We review the considerable and wide-ranging evidence for the involvement of this combination of (su)peroxide and poorly liganded iron in a large number of physiological and indeed pathological processes and inflammatory disorders, especially those involving the progressive degradation of cellular and organismal performance. These diseases share a great many similarities and thus might be considered to have a common cause (i.e. iron-catalysed free radical and especially hydroxyl radical generation).The studies reviewed include those focused on a series of cardiovascular, metabolic and neurological diseases, where iron can be found at the sites of plaques and lesions, as well as studies showing the significance of iron to aging and longevity. The effective chelation of iron by natural or synthetic ligands is thus of major physiological (and potentially therapeutic) importance. As systems properties, we need to recognise that physiological observables have multiple molecular causes, and studying them in isolation leads to inconsistent patterns of apparent causality when it is the simultaneous combination of multiple factors that is responsible.This explains, for instance, the decidedly mixed effects of antioxidants that have been observed, since in some circumstances (especially the presence of poorly liganded iron) molecules that are nominally antioxidants can actually act as pro-oxidants. The reduction of redox stress thus requires suitable levels of both antioxidants and effective iron chelators. Some polyphenolic antioxidants may serve both roles.Understanding the exact speciation and liganding of iron in all its states is thus crucial to separating its various pro- and anti-inflammatory activities. Redox stress, innate immunity and pro- (and some anti-)inflammatory cytokines are linked in particular via signalling pathways involving NF-kappaB and p38, with the oxidative roles of iron here seemingly involved upstream of the IkappaB kinase (IKK) reaction. In a number of cases it is possible to identify mechanisms by which ROSs and poorly liganded iron act synergistically and autocatalytically, leading to 'runaway' reactions that are hard to control unless one tackles multiple sites of action simultaneously. Some molecules such as statins and erythropoietin, not traditionally associated with anti-inflammatory activity, do indeed have 'pleiotropic' anti-inflammatory effects that may be of benefit here.

CONCLUSION

Overall we argue, by synthesising a widely dispersed literature, that the role of poorly liganded iron has been rather underappreciated in the past, and that in combination with peroxide and superoxide its activity underpins the behaviour of a great many physiological processes that degrade over time. Understanding these requires an integrative, systems-level approach that may lead to novel therapeutic targets.

Alcohol and viral hepatitis: a mini-review

Due to their high prevalence in the general population, alcohol use and abuse can be associated with hepatitis B and C virus infections and it has been demonstrated that alcohol plays a role as a co-morbid factor in the development of liver disease. There is evidence that alcohol abuse accelerates the progression of liver fibrosis and affects the survival of patients with chronic hepatitis C. The mechanism by which alcohol worsens hepatitis C virus-related liver disease has not been fully clarified, but enhanced viral replication, increased oxidative stress, cytotoxicity and impairment of immune response could play a relevant role. Alcohol abuse also seems to reduce both sensitivity to interferon and adherence to treatment. It sounds reasonable to presume that the mechanisms enhancing liver damage in patients affected by hepatitis B are similar to those involved in hepatitis C virus infection. However, more studies are warranted to improve our knowledge about the interaction between alcohol intake and hepatitis B virus infection. In conclusion alcohol abuse is associated with an accelerated progression of liver injury, leading to an earlier development of cirrhosis, higher incidence of hepatocellular carcinoma, and higher mortality. Abstinence could reverse some of these deleterious effects.

Chelation of mitochondrial iron prevents seizure-induced mitochondrial dysfunction and neuronal injury

Chelatable iron is an important catalyst for the initiation and propagation of free radical reactions and implicated in the pathogenesis of diverse neuronal disorders. Studies in our laboratory have shown that mitochondria are the principal source of reactive oxygen species production after status epilepticus (SE). We asked whether SE modulates mitochondrial iron levels by two independent methods and whether consequent mitochondrial dysfunction and neuronal injury could be ameliorated with a cell-permeable iron chelator. Kainate-induced SE resulted in a time-dependent increase in chelatable iron in mitochondrial but not cytosolic fractions of the rat hippocampus. Systemically administered N,N'-bis (2-hydroxybenzyl) ethylenediamine-N,N'-diacetic acid (HBED), a synthetic iron chelator, ameliorated SE-induced changes in chelatable iron, mitochondrial oxidative stress (8-hydroxy-2' deoxyguanosine and glutathione depletion), mitochondrial DNA integrity and hippocampal cell loss. Measurement of brain HBED levels after systemic administration confirmed its penetration in hippocampal mitochondria. These results suggest a role for mitochondrial iron in the pathogenesis of SE-induced brain damage and subcellular iron chelation as a novel therapeutic approach for its management.

Redox mechanisms in hepatic chronic wound healing and fibrogenesis

Reactive oxygen species (ROS) generated within cells or, more generally, in a tissue environment, may easily turn into a source of cell and tissue injury. Aerobic organisms have developed evolutionarily conserved mechanisms and strategies to carefully control the generation of ROS and other oxidative stress-related radical or non-radical reactive intermediates (that is, to maintain redox homeostasis), as well as to 'make use' of these molecules under physiological conditions as tools to modulate signal transduction, gene expression and cellular functional responses (that is, redox signalling). However, a derangement in redox homeostasis, resulting in sustained levels of oxidative stress and related mediators, can play a significant role in the pathogenesis of major human diseases characterized by chronic inflammation, chronic activation of wound healing and tissue fibrogenesis. This review has been designed to first offer a critical introduction to current knowledge in the field of redox research in order to introduce readers to the complexity of redox signalling and redox homeostasis. This will include ready-to-use key information and concepts on ROS, free radicals and oxidative stress-related reactive intermediates and reactions, sources of ROS in mammalian cells and tissues, antioxidant defences, redox sensors and, more generally, the major principles of redox signalling and redox-dependent transcriptional regulation of mammalian cells. This information will serve as a basis of knowledge to introduce the role of ROS and other oxidative stress-related intermediates in contributing to essential events, such as the induction of cell death, the perpetuation of chronic inflammatory responses, fibrogenesis and much more, with a major focus on hepatic chronic wound healing and liver fibrogenesis.

Desferrithiocin analogues and nephrotoxicity

The syntheses of a series of 4'-O-alkylated ( S)-4,5-dihydro-2-(2,4-dihydroxyphenyl)-4-methyl-4-thiazole-carboxylic acid and 5'-O-alkylated ( S)-4,5-dihydro-2-(2,5-dihydroxyphenyl)-4-methyl-4-thiazolecarboxylic acid ligands are described. Their partition between octanol and water, log P(app), is determined, along with their iron-clearing efficiency (ICE) in both non-iron-overloaded, bile duct-cannulated rodents and in iron-overloaded primates. The ligand-promoted biliary ferrokinetics in rats are described for each of the chelators. Plots of log P(app) versus ICE in a rodent model for both the 4'-O-alkylated 2,4-dihydroxy and 5'-O-alkylated 2,5-dihydroxy series produced an inverse parabola plot with r(2) values of 0.97 and 0.81, respectively. The plots indicate an optimum log P(app)/ICE relationship. Because of the nature of the data spread in the 4'-O-alkylated 2,4-dihydroxy series, it will be used to help assess the origin of nephrotoxicity in desferrithiocin analogues: is toxicity simply related to lipophilicity, ICE, or a combination of these properties?

Design, synthesis, and testing of non-nephrotoxic desazadesferrithiocin polyether analogues

A series of iron-clearing efficiencies (ICEs), ferrokinetics, and toxicity studies for ( S)-2-(2,4-dihydroxyphenyl)-4,5-dihydro-4-methyl-4-thiazolecarboxylic acid (deferitrin, 1), ( S)-4,5-dihydro-2-[2-hydroxy-4-(3,6,9-trioxadecyloxy)phenyl]-4-methyl-4-thiazolecarboxylic acid ( 2), and (S)-4,5-dihydro-2-[2-hydroxy-3-(3,6,9-trioxadecyloxy)phenyl]-4-methyl-4-thiazolecarboxylic acid ( 3) are reported. The ICEs in rodents are shown to be dose-dependent and saturable for ligands 2 and 3 and superior to 1. Both polyether analogues in subcutaneous (sc) versus oral (po) administration in rodents and primates demonstrated excellent bioavailability. Finally, in a series of toxicity studies of ligands 1- 3, the dosing regimen was shown to have a profound effect in animals treated with ligand 1. When ligand 1 was given at doses of 237 micromol/kg/day twice a day (b.i.d.), there was serious proximal tubule damage versus 474 micromol/kg/day once daily (s.i.d.). With 2 and 3, in iron-overloaded and/or non-iron-loaded rodents, kidney histopathologies remained normal.

Role of iron in hepatic fibrosis: One piece in the puzzle

Iron is an essential element involved in various biological pathways. When present in excess within the cell, iron can be toxic due to its ability to catalyse the formation of damaging radicals, which promote cellular injury and cell death. Within the liver, iron related oxidative stress can lead to fibrosis and ultimately to cirrhosis. Here we review the role of excessive iron in the pathologies associated with various chronic diseases of the liver. We also describe the molecular mechanism by which iron contributes to the development of hepatic fibrosis.

Iron chelation, quo vadis?

Orally bioavailable chelators for transfusional iron overload have been sought since the introduction of deferoxamine (Desferal) in 1962. Despite tremendous efforts, to date, only deferiprone (Ferriprox) and deferasirox (Exjade) have successfully reached the market, reflecting the difficulty to combine oral activity and safety. Owing to the risk of failure, few new oral chelators can be expected in the future for the treatment of transfusional iron overload. As iron is involved in many disease processes, deferiprone and deferasirox have been proposed to be potentially useful in a variety of indications not characterized by general iron overload. Although it may be possible to obtain clinical benefit from current compounds, more selective chelators tailored to the particular target are needed for successful intervention in these indications.

Impact of the 3,6,9-trioxadecyloxy group on desazadesferrithiocin analogue iron clearance and organ distribution

The impact of introducing a 3,6,9-trioxadecyloxyl group at various positions of the desazadesferrithiocin (DADFT) aromatic ring on iron clearance and organ distribution is described. Three DADFT polyethers are evaluated: (S)-4,5-dihydro-2-[2-hydroxy-4-(3,6,9-trioxadecyloxy)phenyl]-4-methyl-4-thiazolecarboxylic acid [(S)-4'-(HO)-DADFT-PE, 3], (S)-4,5-dihydro-2-[2-hydroxy-5-(3,6,9-trioxadecyloxy)phenyl]-4-methyl-4-thiazolecarboxylic acid [(S)-5'-(HO)-DADFT-PE, 6], and (S)-4,5-dihydro-2-[2-hydroxy-3-(3,6,9-trioxadecyloxy)phenyl]-4-methyl-4-thiazolecarboxylic acid [(S)-3'-(HO)-DADFT-PE, 9]. The iron-clearing efficiency (ICE) in rodents and primates is shown to be very sensitive to which positional isomer is evaluated, as is the organ distribution in rodents. The polyethers had uniformly higher ICEs than their corresponding parent ligands in rodents, consistent with in vivo ligand-serum albumin binding studies. Ligand 9 is the most active polyether analogue in rodents and is also very effective in primates, suggesting a higher index of success in humans. In addition, this analogue is also shown to clear more iron in the urine of the primates than many of the other chelators. If this trend were also observed in patients, it would facilitate iron-balance studies in a clinical setting.

Calorimetric, spectroscopic, and model studies provide insight into the transport of Ti(IV) by human serum transferrin

Evidence suggests that transferrin can bind Ti(IV) in an unhydrolyzed form (without bound hydroxide or oxide) or in a hydrolyzed form. Ti(IV) coordination by N,N'-di(o-hydroxybenzyl)ethylenediamine-N,N'-diacetic acid (HBED) at different pH values models the two forms of Ti(IV)-loaded transferrin spectrally and structurally. 13C NMR and stopped-flow kinetic experiments reveal that when the metal is delivered to the protein using an unhydrolyzed source, Ti(IV) can coordinate in the typical distorted octahedral environment with a bound synergistic anion. The crystal structure of TiHBED obtained at low pH models this type of coordination. The solution structure of the complex compares favorably with the solid state from pH 3.0 to 4.0, and the complex can be reduced with E1/2 = -641 mV vs NHE. Kinetic and thermodynamic competition studies at pH 3.0 reveal that Ti(citrate)3 reacts with HBED via a dissociative mechanism and that the stability of TiHBED (log beta = 34.024) is weaker than that of the Fe(III) complex. pH stability studies show that Ti(IV) hydrolyzes ligand waters at higher pH but still remains bound to HBED until pH 9.5. Similarly, at a pH greater than 8.0 the synergistic anion that binds Ti(IV) in transferrin is readily displaced by irreversible metal hydrolysis although the metal remains bound to the protein until pH 9.5. Thermal denaturation studies conducted optically and by differential scanning calorimetry reveal that Ti(IV)-bound transferrin experiences only minimal enhanced thermal stability unlike when Fe(III) is bound. The C- and N-lobe transition Tm values shift to a few degrees higher. The stability, competition, and redox studies performed provide insight into the possible mechanism of Ti2-Tf transport in cells.

The design, synthesis, and evaluation of organ-specific iron chelators

A series of iron chelators, three (S)-4,5-dihydro-2-(2-hydroxyphenyl)-4-methyl-4-thiazolecarboxylic acid (DADFT) and three (S)-4,5-dihydro-2-(2-hydroxyphenyl)-4-thiazolecarboxylic acid (DADMDFT) analogues are synthesized and assessed for their lipophilicity (log Papp), iron-clearing efficiency (ICE) in rodents and iron-loaded primates (Cebus apella), toxicity in rodents, and organ distribution in rodents. The results lead to a number of generalizations useful in chelator design strategies. In rodents, while log Papp is a good predictor of a chelator's ICE, chelator liver concentration is a better tool. In primates, log Papp is a good predictor of ICE, but only when comparing structurally very similar chelators. There is a profound difference in toxicity between the DADMDFT and DADFT series: DADMDFTs are less toxic. Within the DADFT family of ligands, the more lipophilic ligands are generally more toxic. Lipophilicity can have a profound effect on ligand organ distribution, and ligands can thus be targeted to organs compromised in iron overload disease, for example, the heart.

Deferiprone protects the isolated atria from cardiotoxicity induced by doxorubicin

AIM

To investigate the effects of deferiprone on doxorubicin-induced cardiotoxicity and determine its protection on cardiac contractility in vivo at tissue level.

METHODS

Spontaneously-beating isolated atria from rats were pretreated with deferiprone for 10 min at 1.2 mmol/L or 0.3 mmol/L, respectively before co-incubation with doxorubicin (DOX) at 0.03 mmol/L for 60 min. Contractility (dF/dt) was assessed every 10 min during the incubation. After that, the tissues around the sinuatrial nodes were fixed for ultrastructural study; succinate dehydrogenase (SDH) and Cu, Zn superoxide dismutase (Cu, Zn-SOD) activity, as well as malondialdehyde (MDA) level of the atria were assayed.

RESULTS

Treatment with DOX alone resulted in a 49.34% reduction of the contractility, mitochondria swelling, disruption of mitochondrial crista and decreased electron density of the matrices. Conversely, with the presence of deferiprone, the negative inotropic effect and lesions in the cardiac mitochondria structure induced by DOX were attenuated. Cu, Zn-SOD activity increased by 12.97%-12.11%, the MDA level decreased by 29.12%-39.82% and succinate dehydrogenase (SDH) activity was ameliorated by 25.15%-34.76%.

CONCLUSION

Deferiprone can efficiently preserve cardiac contractility. Moreover, the results of this study indicate that deferiprone is able to protect mitochondrial function and structure form damage induced by DOX. This cardiac protective potential of deferiprone could be due to its defense capability against oxidative damage.

Desferri-Exochelin, a lipid-soluble, hexadentate iron chelator, effectively removes tissue iron

Chronic iron-overload is damaging to the heart, liver, and other organs. Better iron chelators are needed to treat this serious medical condition. The uptake and distribution of the lipid-soluble, hexadentate iron chelator desferri-Exochelin 772SM (D-Exo) is studied and its efficacy in removing iron from tissue in rodent models is evaluated. After an intravenous bolus of tritiated D-Exo to rats, counts rapidly disappeared from the blood and rapidly appeared in 15 organs studied, usually peaking within 15 min. There was considerable uptake in the heart and liver, 2 organs especially susceptible to damage from clinical iron overload. To assess actual decreases in cardiac and hepatic iron in response to D-Exo, mice loaded with 42 mg of iron dextran (2100 mg/kg) were studied. Untreated, iron-loaded mice sacrificed 9 weeks later had a 4-fold increase in cardiac iron and a 20-fold increase in hepatic iron compared with controls that were not iron-loaded. In iron-loaded mice treated with 7 mg of D-Exo intraperitoneally (i.p.) 4 days/week for 8 weeks (total 224 mg), tissue iron, measured by atomic absorption, was reduced by 20% in the liver and 25% in the heart (P < 0.01 for each organ). During the first 8 h after a D-Exo dose, iron was excreted in the urine. Mice treated with D-Exo gained weight normally and showed no evidence of toxicity. In conclusion, in this iron-overload mouse model, D-Exo administered intravenously or i.p. rapidly diffuses into multiple organs, including the heart and liver, and effectively removes iron without apparent toxicity.

The Evolution of Iron Chelators for the Treatment of Iron Overload Disease and Cancer

The evolution of iron chelators from a range of primordial siderophores and aromatic heterocyclic ligands has lead to the formation of a new generation of potent and efficient iron chelators. For example, various siderophore analogs and synthetic ligands, including ICL670A [4-[3,5-bis-(hydroxyphenyl)-1,2,4-triazol-1-yl]-benzoic acid], 4'-hydroxydesazadesferrithiocin, and Triapine, have been developed from predecessors and illustrate potent iron-mobilizing or antineoplastic activities. This review focuses on the evolution of iron chelators from initial lead compounds through to the development of novel chelating agents, many of which show great potential to be clinically applied in the treatment of iron overload disease and cancer.

Partition-variant desferrithiocin analogues: organ targeting and increased iron clearance

Altering the lipophilicity (log P(app)) of desferrithiocin analogues can change the organ distribution of the chelators and lead to enhanced iron clearance. For example, alkylation of (S)-2-(2,4-dihydroxyphenyl)-4,5-dihydro-4-methyl-4-thiazolecarboxylic acid [(S)-4'-(HO)-DADFT] and its analogues to more lipophilic compounds, such as (S)-4,5-dihydro-2-(2-hydroxy-4-methoxyphenyl)-4-methyl-4-thiazolecarboxylic acid [(S)-4'-(CH3O)-DADFT], provides ligands that achieved between a 3- and 8-fold increase in chelator concentrations in the heart, liver, and pancreas (the organs most at risk in iron-overload disease) of treated rodents. The 4'-O-methylated compounds are demethylated to their hydroxylated counterparts in rodents; furthermore, this O-demethylation takes place in both rodent and human liver microsomes. The relationship between chelator lipophilicity and iron-clearing efficacy in the iron-overloaded Cebus apella primate is further underscored by a comparison of the iron-clearing efficiency of (S)-2-(2,3-dihydroxyphenyl)-4,5-dihydro-4-methyl-4-thiazolecarboxylic acid [(S)-3'-(HO)-DADFT] and its 3'-(CH3O) counterpart. Finally, these DFT analogues are shown to be both inhibitors of the iron-mediated oxidation of ascorbate as well as effective radical scavengers.

Changes of hepatic fibrosis induced by iron overload in SD rats

AIM: To study the histological changes of hepatic fibrosis induced by diet iron overload in SD rats.

METHODS: After living on an iron overload in diet for 63 d, the male SD rats were decollated and the livers were harvested to examine the liver indexes, morphology of hepatocytes, hepatic stellate cells (HSC), sinusoidal endothelial cells, sinusoid, peri-sinusoid, and distribution of collagen type III and laminin were also observed.

RESULTS: On model rats there were coagulation necrosis of hepatocytes, activated HSC, sinusoidal endothelial cells with less fenestrae, sinusoidal capillarization and light peri-sinusoid fibrosis, thickened basement of central vein, more collagen types I and II and laminin than those in normal controls.

CONCLUSION: Iron overload in diet for some time can injure hepatocytes, activate HSC, decrease the fenestrae of sinusoidal endothelial cell, and result in sinusoidal capillarization and peri-sinusoid fibrosis. It may be feasible to establish an ALD model with iron overload in diet.

Thalassemia

New developments in the epidemiology, treatment and prognosis of thalassemia have dramatically altered the approach to the care of affected patients, and these developments are likely to have an even greater impact in the next few years. Demographic changes have required an awareness and understanding of the unique features of thalassemia disorders that were previously uncommon in North America but are now seen more frequently in children and recognized more consistently in adults. New methods for measuring tissue iron accumulation and new drugs to remove excessive iron are advancing two of the most challenging areas in the management of thalassemia as well as other transfusion-dependent disorders. Improved survival of patients with thalassemia has given new importance to adult complications such as endocrinopathies and hepatitis that have a major impact on the quality of life. This chapter describes how these changes are redefining the clinical management of thalassemia.

In Section I, Dr. Renzo Galanello describes recent advances in iron chelation therapy. Several new chelators are either licensed in some countries, are in clinical trials or are in the late stages of preclinical development. Some of these iron chelators, such as deferiprone (DFP) and ICL670, are orally active. Others, such as hydroxybenzyl-ethylenediamine-diacetic acid (HBED) and starch deferoxamine, require parenteral administration but may be effective with less frequent administration than is currently required for deferoxamine. Chelation therapy employing two chelators offers the possibility of more effective removal of iron without compromising safety or compliance. Other strategies for chelation therapy may take advantage of the ability of particular chelators to remove iron from specific target organs such as the heart and the liver.

In Section II, Dr. Dudley Pennell addresses cardiac iron overload, the most frequent cause of death from chronic transfusion therapy. The cardiac complications related to excessive iron may result from long-term iron deposition in vulnerable areas or may be due to the more immediate effects of nontransferrin-bound iron. Cardiac disease is reversible in some patients with intensive iron chelation therapy, but identification of cardiac problems prior to the onset of serious arrhythmias or congestive heart failure has proven difficult. New methods using magnetic resonance imaging (MRI) have recently been developed to assess cardiac iron loading, and studies suggest a clinically useful relationship between the results using these techniques and critical measures of cardiac function. Measurements such as T2* may help guide chelation therapy in individual patients and may also enhance the assessment of new chelators in clinical trials. The use of MRI-based technology also holds promise for wider application of non-invasive assessment of cardiac iron in the management of patients with thalassemia.

In Section III, Dr. Melody Cunningham describes some of the important complications of thalassemia that are emerging as patients survive into adulthood. Hepatitis C infection is present in the majority of patients older than 25 years. However, antiviral therapy in patients with thalassemia has been held back by the absence of large clinical trials and concern about ribavirin-induced hemolysis. More aggressive approaches to the treatment of hepatitis C may be particularly valuable because of the additive risks for cirrhosis and hepatocellular carcinoma that are posed by infection and iron overload. Thrombosis is recognized with increasing frequency as a significant complication of thalassemia major and thalassemia intermedia, and pulmonary hypertension is now the focus of intense study. Risk factors for thrombosis such as splenectomy are being identified and new approaches to anticoagulation are being initiated. Pregnancies in women with thalassemia are increasingly common with and without hormonal therapy, and require a better understanding of the risks of iron overload and cardiac disease in the mother and exposure of the fetus to iron chelators.

In Section IV, Dr. Elliott Vichinsky describes the dramatic changes in the epidemiology of thalassemia in North America. Hemoglobin E-β thalassemia is seen with increasing frequency and poses a particular challenge because of the wide variability in clinical severity. Some affected patients may require little or no intervention, while others need chronic transfusion therapy and may be appropriate candidates for hematopoietic stem cell transplantation. Enhancers of fetal hemoglobin production may have a unique role in Hb E-β thalassemia since a modest increase in hemoglobin level may confer substantial clinical benefits. Alpha thalassemia is also being recognized with increasing frequency in North America, and newborn screening for Hemoglobin Barts in some states is leading to early detection of Hb H disease and Hb H Constant Spring. New data clarify the importance of distinguishing these two disorders because of the increased severity associated with Hb H Constant Spring. The use of intrauterine transfusions to sustain the viability of fetuses with homozygous alpha thalassemia has created a new population of patients with severe thalassemia and has raised new and complex issues in genetic counseling for parents with alpha thalassemia trait.