Relative oral efficacy and acute toxicity of hydroxypyridin-4-one iron chelators in mice [see comments]

The relationship between the oral efficacy and the acute toxicity of hydroxypyridin-4-one iron chelators has been investigated to clarify structure-function relationships of these compounds in vivo and to identify compounds with the maximum therapeutic safety margin. By comparing 59Fe excretion following oral or intraperitoneal administration of increasing doses of each chelator to iron-overloaded mice, the most effective compounds have been identified. These have partition coefficients (Kpart) above 0.3 in the iron-free form with a trend of increasing oral efficacy with increasing Kpart values (r = .6). However, this is achieved at a cost of increasing acute toxicity, as shown by a linear correlation between 59Fe excretion increase per unit dose and 1/LD50 (r = .83). A sharp increase in the LD50 values is observed for compounds with Kpart values above 1.0, suggesting that such compounds are unlikely to possess a sufficient therapeutic safety margin. Below a Kpart of 1.0, acute toxicity is relatively independent of lipid solubility. All the compounds are less toxic by the oral route than by the intraperitoneal route, although iron excretion is not significantly different by these two routes. At least five compounds (CP51, CP94, CP93, CP96, and CP21) are more effective orally than the same dose of intraperitoneal desferrioxamine (DFO) (P less than or equal to .02) or orally administered L1(CP20) (P less than or equal to .02).     

Iron mobilization from hepatocyte monolayer cultures by chelators: the importance of membrane permeability and the iron-binding constant

A series of bidentate hydroxypyridinone iron chelators that have therapeutic potential as oral iron chelators, have been studied systematically to determine which properties are the most critical for the mobilization of hepatocyte iron. The relationship between lipid solubility of the free and complexed forms of each chelator and hepatocyte iron release has been investigated as well as the contribution of the binding constant for iron (III). Hydroxypyridin-4- ones that were approximately equally soluble in lipid and aqueous phases were the most active compounds, the partition coefficient of the free chelator appearing to be more critical in determining iron release than that of the iron-complexed form. Highly hydrophilic chelators did not mobilize intracellular iron pools, whereas highly lipophilic compounds were toxic to hepatocytes. The contribution of the binding constant for iron (III) to cellular iron release was assessed by comparing hydroxypyridin-4-ones (log beta 3 = 36) and hydroxypyridin-2- ones (log beta 3 = 32), which possess similar partition coefficients. The results show that the binding for iron (III) is particularly important at low concentrations of chelator (less than 100 mumol/L) and that at higher concentrations (greater than 500 mumol/L) iron mobilization is limited by the available chelatable pool. Measurement of iron release with other chelators confirms the importance of both the lipid solubilities and iron (III)-binding constants to iron mobilization. The most active hydroxypyridin-4-ones released more hepatocyte iron than did deferoxamine when compared at equimolar concentrations. The results suggest that the ability of an iron chelator to enter the cell is crucial for effective iron mobilization and that once within the cell the binding constant of the chelator for iron (III) becomes a dominant factor.     

Effect of iron chelators on paraquat toxicity in rats and alveolar type II cells.

There is general agreement that the lung damage seen in paraquat poisoning is due to the generation of free radicals in alveolar epithelial cells. We have recently shown that the iron chelator and antioxidant deferoxamine (DF) reduces the mortality caused by paraquat in vitamin-E-deficient rats. In the present study we investigated the effect of DF and the lipid soluble iron chelator compound 51 (CP51) of the hydroxypyridin-4-one family on paraquat poisoning in rats with a normal vitamin E status and on isolated alveolar type II cells (ATTC). Adult rats were intravenously injected with a lethal dose of paraquat (40 mg/kg) while concurrent treatment with a continuous intravenous infusion of DF or CP51 was started. Survival of rats receiving DF at 25 and 50 mg/kg/24 h was not significantly increased compared with PBS-treated control animals. CP51, however, significantly (p less than 0.01) reduced the mortality caused by paraquat. When rats were treated with 25 mg/kg/24 h, eight of 15 rats survived the study period of 35 days compared with three in the PBS-treated control group (n = 27). In ancillary in vitro studies radiolabeled [51Cr]ATTC were incubated in a medium containing 100 microM paraquat in the absence or presence of DF and CP51. Paraquat-induced ATTC lysis increased to approximately 25% after 7 h of incubation. At the highest tested concentration (500 microM) of chelator, injury decreased markedly (80%), whereas at the lowest tested concentration (50 microM) cytotoxicity was not prevented.(ABSTRACT TRUNCATED AT 250 WORDS)     

Contrasting interspecies efficacy and toxicology of 1, 2 -diethy 1–3 -hydroxypyridin-4-one, CP9 4, relates to differing metabolism of the iron chelating site

Summary. In order to define a predictive animal model for the effects of hydroxypyridinone (HPO) iron chelators in humans, we have compared the 28 d oral efficacy and toxicology of the HPO, 1,2-diethyI-3–hydroxypyridin-4–one (CP94) in rats and guinea-pigs and related the results to the contrasting metabolism of this compound in the two species. CP94 was highly effective at mobilizing liver iron in rats but showed toxicity at higher doses, whereas in the guinea-pig the compound lacked toxicity but was ineffective at mobilizing liver iron. These differences can be explained by the contrasting metabolism of the drug between the two species. In rats, at the top dose of 300 mg/kg intragastrically, all animals died before the end of the study, with no deaths or weight loss at lower doses. At 100 mg/kg, rat liver non-haem iron concentrations were reduced by 53% and 44% in females and males respectively (P<0.001). At this dose, adrenal medullary cell vacuolation, increased mammary secretory activity, vacuolation of corpora luteal cells and single cell hepatocyte necrosis were seen. There were no reductions in the white cell count. At 50 mg/kg rat liver non-haem iron concentrations were decreased by 50% and 34% in females and males respectively (P<0.02). In female rats this was associated with increased mammary secretory activity. In iron-overloaded rats given 100 mg/kg by gavage for 28 d, liver non-haem iron concentration was reduced by 39% (P<0.01) and serum ferritin by 71% (P<0.001). Ovarian and mammary changes were not influenced by iron loading. In guinea-pigs, CP94 was evaluated at 50 mg/kg, 100 mg/kg or 200 mg/kg by oral insufflation for 28 d. No reduction in liver iron was seen and no systematic dose related histological, biochemical or haematological effects were observed. Whereas in guinea-pigs 99% of urinary recovery following an oral dose of CP94 (100 mg/kg) was as the inactive glucuronide metabolite, in the rat only 23% of the dose was excreted in the urine as the glucuronide with remainder as the free drug or an iron binding metabolite. The lack of both efficacy and toxicity in the guinea-pig may therefore be explained by the rapid inactivation of CP94 by glucuronidation. This metabolism of CP94 in the guinea-pig is closer to humans than the rat, suggesting that both the efficacy and toxicity of this compound in humans may also be limited by glucuronidation.     

Effect of orally active hydroxypyridinone iron chelators on human lymphocyte function

Several iron chelators, 3-hydroxypyridin-4-ones (CP) and desferrioxamine (DF) were compared for their effect on DNA synthesis, cell viability and expression of cell proliferation markers. Short-term (4 h) exposure of human peripheral blood mononuclear cells to CP or DF inhibited the proliferative response of cells to concanavalin A (Con A). Inhibition by CP and DF showed a dose-dependent effect with CP compounds more active than DF. Increased inhibitory activity of CP over DF was partly due to the lipophilic properties of CP. Pre-saturation of CP and DF with exogenous ferric ion either diminished or prevented the inhibitory effect. At high chelator concentrations or prolonged (72 h) exposure of the cells to chelators, inhibition occurred but poor cell viability was observed. In contrast to their inhibition of DNA synthesis, these iron chelators showed little effect on protein synthesis and the expression of transferrin receptors and interleukin-2 (IL-2) receptors. These findings suggest that both DF and CP compounds exert their effect by chelation of ferric ion with subsequent inhibition of DNA synthesis.     

Effects of Experimental Hemosiderosis on Pancreatic Tissue Iron Content and Structure

The effects of iron overload on pancreatic ironcontent and morphology were investigated. Sprague-Dawleyrats were randomized into an iron-overloaded group,which received a single subcutaneous injection of 1.2 g/kg elemental iron as iron-dextrancomplex, and placebo-treated pair-fed controls. Animalswere studied after a 10-month observation period. Tissuenonheme iron content was measured, and histologic examination was carried out. Chroniciron-overloaded animals showed significant increases intissue iron content. There was a statisticallysignificant increase in stainable iron in perivascular,parenchymal, and lymphoid tissue in the iron-overloadedgroup. Although pancreatic fibrosis was present in theiron-overload group, it was not statisticallysignificant. The iron-overloaded animals showed someislet cell destruction. In contrast, no significantislet cell destruction was seen in the control group.However, the difference was not statisticallysignificant. Moreover, the serum glucose levels were the same in both groups, suggesting that there wasno significant impairment of pancreatic endocrinefunction. Thus, chronic experimental iron overload inrats leads to significant increases in tissue iron content, but no significant morphologicalterations of the pancreas with the dose and route ofiron administered in this animal model.     

Iron mobilization from myocardial cells by 3-hydroxypyridin-4-one chelators: studies in rat heart cells in culture

The ability of 3-hydroxypyridin-4-ones (CP), a family of bidentate orally effective iron chelators, to remove iron and to prevent iron-induced lipid peroxidation was studied in beating rat myocardial cells in culture. The iron (III) binding constant (log beta 3) of all CP compounds is 36, but their lipophilicity may be modified by altering the length of the R2 substituent on the ring nitrogen. There was a direct relation between lipid solubility and chelating efficiency. Although at high concentrations all CP compounds were more effective in iron mobilization than deferoxamine, the opposite was true for low concentrations. Further studies with 1,2-diethyl-3-hydroxypyridin-4-one (CP94), the most effective CP compound, have shown that iron mobilization is completed within 6 hours, that effective mobilization requires a drug: iron molar ratio exceeding 3:1 permitting the formation of a hexadentate complex, and that the beneficial effects of iron mobilization are manifested in a marked reduction in membrane lipid peroxidation as indicated by cellular malonaldehyde content. Our study represents the first demonstration of a direct interaction between myocardial cells and an orally effective iron chelator, and underlines the need for high molar concentrations for achieving an optimal therapeutic effect.     

Effects of experimental hemosiderosis on intestinal morphology,permeability, and tissue iron content

Effects of iron overload on intestinal function and structure are unknown and were, therefore, investigated. Sprague-Dawley rats were randomized into an iron-overloaded group, which received a single subcutaneous injection of 1,2 g/kg elemental iron-dextran complex, and placebo-treated pair-fed controls. Animals were studied after a 10-month observation period. Intestinal permeability was assessed by measuring the urinary excretion of lactulose, rhamnose, and mannitol after oral administration. In addition, tissue nonheme iron content was measured, and histologic examination and morphometric measurements were carried out. The chronic iron-overloaded group showed a significant increase in intestine tissue iron content and stainable iron in the submucosa and muscularis propria and adipose tissue of the small intestine and lamina propria and muscularis mucosa of the large intestine. There was a significant decrease in the crypt depths without discernible change in the intestine permeability to any of the markers used. In addition, the iron-overloaded animals showed a significant number of iron-laden cells, which primarily consisted of macrophages, fibroblasts, myocytes, and adipocytes. In contrast, no iron-laden cells were present in tissues obtained from the normal control group. Thus, chronic experimental iron overload in rats leads to significant morphologic, but no permeability, alterations of the alimentary tract.     

The effect of N-alkyl modification on the antimalarial activity of 3-hydroxypyridin-4-one oral iron chelators

The antimalaria effect of iron chelators is attributed to their interaction with a labile iron pool within parasitised erythrocytes, and it was postulated that increased affinity to iron as well as increased lipophilicity may improve antimalarial activity. In the present study we have examined the antimalarial effect of 3-hydroxypyridin-4-ones, a family of bidentate orally effective iron chelators whose lipophilicity may be modified by altering the length of the R2 substituent on the ring nitrogen. A significant dose-related suppression of Plasmodium falciparum cultures was observed with all drugs tested in vitro at concentrations of 5 mumol/L or higher. In contrast, there was a clear segregation of the in vivo effect on P berghei in rats (300 mg/kg/d subcutaneous) into two categories: compounds CP20, 38, and 40 failed to suppress malaria, whereas CP51, 94, and 96 had a strong antimalarial effect, similar or better than deferoxamine. There was a close linear correlation between the suppression of peak parasite counts and the reduction in hepatic nonheme iron induced by the various drugs tested (r = .9837). The most lipophilic compounds were also the most effective in suppressing malaria and in depleting hepatic iron stores. These data indicate that 3-hydroxypyrydin-4-ones are able to suppress malaria in vivo and in vitro. Because lipid solubility is an important determinant of antimalarial action, our study provides useful information regarding the selection of orally effective iron-chelating compounds that may be suitable for clinical application as antimalarial agents.     

The C57BL/6 genetic background confers cardioprotection in iron-overloaded mice

Background

Chronic transfusion therapy causes a progressive iron overload that damages many organs including the heart. Recent evidence suggests that L-type calcium channels play an important role in iron uptake by cardiomyocytes under conditions of iron overload. Given that beta-adrenergic stimulation significantly enhances L-type calcium current, we hypothesised that beta-adrenergic blocking drugs could reduce the deleterious effects of iron overload on the heart.

Methods

Iron overload was generated by intraperitoneal injections of iron dextran (1g/kg) administered once a week for 8 weeks in male C57bl/6 mice, while propranolol was administered in drinking water at the dose of 40 mg/kg/day. Cardiac function and ventricular remodelling were evaluated by echocardiography and histological methods.

Results

As compared to placebo, iron injection caused cardiac iron deposition. Surprisingly, despite iron overload, myocardial function and ventricular geometry in the iron-treated mice resulted unchanged as compared to those in the placebo-treated mice. Administration of propranolol increased cardiac performance in iron-overloaded mice. Specifically, as compared to the values in the iron-overloaded group, in iron-overloaded animals treated with propranolol left ventricular fractional shortening increased (from 31.6% to 44.2%, P =0.01) whereas left ventricular end-diastolic diameter decreased (from 4.1±0.1 mm to 3.5±0.1 mm, P =0.03). Propranolol did not alter cardiac systolic function or left ventricular sizes in the placebo group.

Conclusions

These results demonstrate that C57bl/6 mice are resistant to iron overload-induced myocardial injury and that treatment with propranolol is able to increase cardiac performance in iron-overloaded mice. However, since C57bl/6 mice were resistant to iron-induced injury, it remains to be evaluated further whether propranolol could prevent iron-overload cardiomyopathy.     

Enhancement of methyl-aminolevulinate photodynamic therapy by iron chelation with CP94: an in vitro investigation and clinical dose-escalating safety study for the treatment of nodular basal cell carcinoma

PURPOSE: Methyl-aminolevulinate (MAL) photodynamic therapy (PDT) is a cancer therapy that combines the selective accumulation of a photosensitizer in tumor tissue with visible light (and tissue oxygen) to produce reactive oxygen species. This results in cellular damage and ablation of tumor tissue. Combining iron chelators with MAL has the potential to increase the accumulation of the photosensitizer protoporphyrin IX (PpIX) by reducing its bioconversion to heme. This paper investigates this method of enhancement both in vitro and for the first time clinically for the treatment of nodular basal cell carcinoma (BCC). METHODS: Enhancement of MAL-induced PpIX accumulation by the iron chelator CP94 was quantified fluorometrically in human cultured cells (including three dermatological cell types). An open, dose-escalating, pilot study was then conducted in patients with nodular BCC, to determine the safety of this pharmacological modification. RESULTS: Large enhancements in PpIX accumulation were observed in the cultured cells when co-incubated with the iron chelator CP94. Clinically the addition of CP94 was found to be feasible and safe. In addition greater reductions in tumor depth were observed in the CP94 co-incubated tumors. CONCLUSION: Iron chelation by CP94 is an effective enhancer of MAL-induced PpIX accumulation in vitro. This method of enhancement was safely applied to a clinical PDT protocol with no unexpected adverse effects reported. Although the clinical investigation was only intended to be a small pilot to assess safety, enhancements in tumor clearance were observed both clinically and histologically when CP94 was included in the photosensitizing cream.     

Chronic liver iron overload in the baboon by ferric nitrilotriacetate

Two baboons receiving intramuscular injections of ferric nitrilotriacetate over a two-year period were compared with two control baboons. The results indicate that in iron-overloaded animals: liver iron excess was major (maximal liver iron concentration values of 42 mumol/100 mg dry weight for both animals vs 1.3 +/- 0.2 (mean +/- SD) in controls) and chronic (for 15 months liver iron concentrations were higher than 15); iron deposition, although less abundant than in sinusoidal cells, was pronounced within parenchymal cells; serum transaminase activities were markedly increased; rare foci of perisinusoidal fibrosis were observed in areas of massive iron overload; and a dramatic decrease in hepatic 4-prolyl-hydroxylase activity was found, in contrast with unchanged glucosyltransferase and galactosyltransferase activities. In conclusion these findings suggest that, in our model, chronic liver iron overload: exerts a marked biochemical cytolytic effect; and does not produce significant hepatic fibrosis, possibly related to an inhibiting effect of ferric nitrilotriacetate complex on 4-prolyl-hydroxylase activity.     

Selection of a new generation of orally active α-ketohydroxypyridine iron chelators intended for use in the treatment of iron overload

The prospect of selecting oral α-ketohydroxypyridine chelators intended for clinical use in iron overload has been examined using several animal models of efficacy and toxicity. Studies using iron dextran-loaded mice labelled with ⁵⁹Fe have shown that only the 1-substituted methyl, ethyl, (n)propyl, allyl, cyclopropyl, 2′-methoxyethyl, 3′-ethoxypropyl, or 2-methyl- or 2-ethyl- 3-hydroxypyrid-4-one chelators were orally effective in increasing iron (⁵⁹Fe) excretion by comparison to intraperitoneally administered desferrioxamine at the same dose (250 mg/kg). In contrast, chelators containing -H, mono- or dihydroxyalkyl and diethoxyethyl 1-substituents caused very little or no increase in iron (⁵⁹Fe) excretion by the oral or intraperitoneal routes. In vitro studies using ferritin and haemosiderin have shown that equivalent iron release took place with both groups of chelators irrespective of their in vivo effects. In most cases there was no correlation between the n-octanol/water partition coefficient (K_par) and iron removal efficacy but positive correlation between the lipophilicity and acute or subacute toxicity of these chelators in rats. The most toxic chelator in the chronic toxicity studies in rats was the lipophilic 1, 2-diethyl-3-hydroxypyrid-4-one (EL1NEt). The most effective chelator in increasing iron excretion in mice and rabbits was 1-allyl-2-methyl-3-hydroxypyrid-4-one (L1NAll), and the chelator with the highest safety margin in mice and rats was 1, 2-dimethyl-3-hydroxypyrid-4-one (L1). Overall the oral effectiveness in increasing iron excretion by these chelators in animals does not appear to be related to their lipophilicity or their ability to mobilise polynuclear iron in vitro but rather to other properties possibly related to their rate of biotransformation and excretion. © 1993 Wiley-Liss, Inc.     

Iron-chelating therapy with the new oral agent ICL670 (Exjade)

Iron-chelation therapy is essential in iron-overloaded patients. The long-term efficacy of this approach has been demonstrated unequivocally with deferoxamine, which effectively controls iron concentrations, thereby limiting organ damage and preventing premature death. However, as deferoxamine is administered parenterally, poor compliance is a significant limitation to successful patient management. ICL670 (Exjade) is a highly efficient and selective oral iron chelator. The results of phase I and phase II clinical studies indicate that ICL670 is at least as effective as current standard therapy (deferoxamine), with a tolerability and safety profile suitable for chronic, once-daily administration. These encouraging results have provided the rationale for the ongoing phase III programme, and offer physicians and patients the promise of an oral, once-daily, iron-chelating agent for the prevention and management of iron overload.     

Reactive oxygen species mediated T lymphocyte abnormalities in an iron-overloaded mouse model and iron-overloaded patients with myelodysplastic syndromes

The adverse effects of iron overload have raised more concerns as a growing number of studies reported its association with immune disorders. This study aimed to investigate alterations in the immune system by iron overload in patients with myelodysplastic syndrome (MDS) and an iron-overloaded mouse model. The peripheral blood from patients was harvested to test the effect of iron overload on the subsets of T lymphocytes, and the level of reactive oxygen species (ROS) was also evaluated. The data showed that iron-overloaded patients had a lower percentage of CD3⁺ T cells and disrupted T cell subsets, concomitant with higher ROS level in lymphocytes. In order to explore the mechanism, male C57Bl/6 mice were intraperitoneally injected with iron dextran at a dose of 250 mg/kg every 3 days for 4 weeks to establish an iron-overloaded mouse model and the blood of each mouse was collected for the analysis of the T lymphocyte subsets and T cell apoptosis. The results showed that iron overload could reduce the percentage of CD3⁺ T cells and the ratio of Th1/Th2 and Tc1/Tc2 but increase the percentage of regulatory T (Treg) cells and the ratio of CD4/CD8. We also found that iron overload induced the apoptosis of T lymphocytes and increased its ROS level. Furthermore, these effects could be partially recovered after treating with antioxidant N-acetyl-l-cysteine (NAC) or iron chelator deferasirox (DFX). Taken together, these observations indicated that iron overload could selectively affect peripheral T lymphocytes and induce an impaired cellular immunity by increasing ROS level.     

Sustained normalization of cardiac function by chelation therapy in thalassaemia major

The effect of iron chelation using subcutaneous desferrioxamine on the iron-overloaded heart was studied prospectively over 4 years in 23 asymptomatic patients (mean age 13.2 +/- 5.3 years) with thalassaemia major and transfusion-dependent anaemia. The haemoglobin was maintained greater than 10 g/dl by transfusion and chelation therapy to achieve a negative iron balance. Chelation was closely supervised to ensure compliance. Despite an increase in calculated iron load due to transfusion from 34 +/- 27 g to 63 +/- 28 g, there was a sequential fall in serum ferritin levels from 3148 +/- 1956 ng/ml to 2228 +/- 1825 ng/ml (P less than 0.05). Abnormalities of left ventricular (LV) function, assessed by radionuclide angiography, were present at rest or during exercise in 18 of 23 patients (78%) prior to therapy. Normal LV function was restored in 11 of these 18 patients, five continuing to have abnormal function and two dying. There was a significant increase in resting LVEF from 50 +/- 8% to 57 +/- 6% (P less than 0.01). Peak exercise LVEF rose from 51 +/- 11% to 65 +/- 7% (P less than 0.001). We conclude that the common subclinical abnormalities of LV function induced by iron overload in unchelated patients with thalassaemia major can be reversed with long-term subcutaneous infusions of desferrioxamine.     

Experimental hepatic iron overload in the baboon: Results of a two-year study

Four baboons receiving intramuscular iron for 15 months were compared with two control baboons. From the overall two-year observation period the following data emerge: (1) The baboon is a suitable animal for obtaining a massive and chronic iron overload. Liver iron concentrations reached very high levels (ranging from 41.3 to 180.6 mumol/100 mg dry weight vs 1.7 +/- 0.5, mean +/- SEM, in controls), and a major liver iron overload (ie, with concentration values greater than or equal to 18) was present in all four animals for an average period of 16.5 months (range 14-19). (2) When compared with human hepatic iron-overload disorders, iron distribution was similar to that observed in secondary (transfusional) hepatic siderosis since iron deposits were found primarily in sinusoidal cells. However, a marked parenchymal siderosis was also obtained close to that observed in primary (genetic) siderosis. Iron toxicity was present biologically as indicated by an increase in serum transaminases. Histologically, a slight fibrosis was observed in the most heavily iron-overloaded baboon. On the whole, this study of subhuman primates brings new evidence that iron per se has only a minor hepatic damaging effect. It also suggests that the iron-overloaded baboon liver provides a promising tool for the study of liver cell disturbances in human iron overload.     

Iron chelation therapy in the myelodysplastic syndromes and aplastic anemia: a review of experience in South Korea

Emerging clinical data indicate that transfusion-dependent patients with bone marrow-failure syndromes (BMFS) are at risk of the consequences of iron overload, including progressive damage to hepatic, endocrine, and cardiac organs. Despite the availability of deferoxamine (DFO) in Korea since 1998, data from patients with myelodysplastic syndromes, aplastic anemia, and other BMFS show significant iron overload and damage to the heart and liver. The recent introduction of deferasirox, a once-daily, oral iron chelator, may improve the availability of iron chelation therapy to iron-overloaded patients, and improve compliance in patients who may otherwise find adherence to the DFO regimen difficult.     

Deferasirox in MDS patients with transfusion-caused iron overload—a phase-II study

Blood transfusions represent a main component of supportive care in myelodysplastic syndromes (MDS). To avoid organ damage caused by transfusion-dependent iron overload, an adequate iron chelation therapy is required. Recently, a new oral iron chelator deferasirox (ICL670, Exjade) has become available. A study was conducted to demonstrate the efficacy and tolerability of deferasirox in transfusion-dependent iron-overloaded patients with MDS. The efficacy of deferasirox was monitored by changes in serum ferritin, bone marrow iron, and liver iron concentration (LIC), as determined by T2*-weighted magnetic resonance imaging. Twelve patients with MDS of different subtypes (median age 76 years, range 53-91) were enrolled. Deferasirox administered in a once-daily dose of 20-30 mg/kg for 12 months was effective in reducing median ferritin concentration from 1,515 microg/L (range 665-6,900) to 413 microg/L (range 105-3,052). Within the first 4 weeks of treatment before the continuous decline of ferritin levels, the values markedly rose in eight of 12 patients. The median LIC declined from 315 to 230 micromol/g (p=0.02) at the end of study, accompanied by a reduction of bone marrow siderosis. The most common adverse events were mild and transient gastrointestinal disturbances, skin rash, nonprogressive transient increases in serum creatinine and urine beta2-microglobulin, and a temporary reduction of the creatinine clearance. The renal parameters normalized after end of treatment. No hematologic toxicities were observed. Deferasirox proved to be effective in transfusion-dependent iron overload in MDS by mobilizing iron deposits in liver and at least stabilizing iron stores in bone marrow.     

Heme oxygenase-1-generated biliverdin ameliorates experimental murine colitis

BACKGROUND: Heme oxygenase-1 (HO-1) seems to have an important protective role in acute and chronic inflammation. The products of heme catalysis, biliverdin/bilirubin, carbon monoxide (CO), and iron (that induces apoferritin) mediate the beneficial effects of HO-1. Blockade of HO-1 activity results in exacerbation of experimental colitis. We tested whether HO-1 has protective effects in the development of colitis and determined that specific enzymatic products of HO-1 are responsible for these effects. METHODS: Colitis was induced by oral administration of dextran sodium sulfate (5%) to C57BL/6 mice for 7 days. HO-1 was up-regulated by cobalt-protoporphyrin (5 mg/kg, intraperitoneally). Biliverdin, exogenous CO, or the iron chelator desferrioxamine was administered to other groups. RESULTS: Cobalt-protoporphyrin treatment resulted in significant up-regulation of HO-1 protein in mucosal and submucosal cells. Induction of HO-1 was associated with significantly less loss of body weight in mice with induced colitis (-12% versus -22% in the control animals, P < 0.001). Development of diarrhea and gastrointestinal hemorrhage was substantially delayed in animals in which HO-1 was induced, and mucosal injury was significantly attenuated. Administration of CO or desferrioxamine alone had no significant effects, whereas enhanced protection with lesser evidence of bowel inflammation was observed with systemic biliverdin administration (50 micromol/kg, 3 times per day, intraperitoneally). CONCLUSIONS: We conclude that heightened HO-1 expression or administration of biliverdin ameliorates dextran sodium sulfate-induced experimental colitis. Novel therapeutic strategies based on HO-1 and/or biliverdin administration may have use in inflammatory bowel disease.