The metabolism of desferrioxamine B and ferrioxamine B

Long-term and oxidative-responsive alginate–deferoxamine conjugates with a low toxicity for iron overload

Long-term and oxidative-responsive alginate–deferoxamine conjugates.

Iron: a target for the management of Kaposi's sarcoma?

BACKGROUND

Kaposi's sarcoma (KS) is a mesenchymal tumour associated with human herpesvirus-8 infection. However, the incidence of human herpesvirus-8 infection is far higher than the prevalence of KS, suggesting that viral infection per se is not sufficient for the development of malignancy and that one or more additional cofactors are required.

DISCUSSION

Epidemiological data suggest that iron may be one of the cofactors involved in the pathogenesis of KS. Iron is a well-known carcinogen and may favour KS growth through several pathways. Based on the apoptotic and antiproliferative effect of iron chelation on KS cells, it is suggested that iron withdrawal strategies could be developed for the management of KS. Studies using potent iron chelators in suitable KS animal models are critical to evaluate whether iron deprivation may be a useful anti-KS strategy.

SUMMARY

It is suggested that iron may be one of non-viral co-factors involved of KS pathogenesis and that iron withdrawal strategies might interfere with tumour growth in patients with KS.

Oral iron chelation with deferiprone

Deferiprone is the most widely studied oral iron chelator and, at present, the only one shown to be effective in achieving negative iron balance in long-term clinical trials for chronic iron overload. Because of its adverse effects (e.g., agranulocytosis and arthropathy) its use is presently restricted to clinical trials and to countries where desferrioxamine is unavailable. Deferiprone was licensed for clinical use in India in 1995. Clinical trials are in progress in many centers worldwide that will provide further information on the long-term effectiveness of deferiprone as well as on the incidence of serious adverse effects in patients with iron overload. Trials of combined use of deferiprone and desferrioxamine are also in progress. In the meantime, deferiprone is an acceptable alternative for patients who cannot use desferrioxamine because of serious adverse effects, lack of compliance, or unavailability. Elucidation of the mechanisms involved in the agranulocytosis and arthropathy associated with deferiprone is still needed, as are methods to predict individual susceptibility to these adverse effects and ways of preventing them. In addition, new indications for iron-chelating therapy are continuously being explored.

Clinically achievable plasma deferoxamine concentrations are therapeutic in a rat model of Pneumocystis carinii pneumonia

The iron-chelating drug deferoxamine (DFO) has been shown to be active in animal models of Pneumocystis carinii pneumonia (PCP), with effective daily intraperitoneal bolus dosages being 400 and 1,000 mg of DFO mesylate kg of body weight-1 in mouse and rat models, respectively. Continuous infusion produced a moderately improved response in a rat model. The data reported here demonstrate that the response achieved by continuous infusion of 195 and 335 mg of DFO mesylate kg-1 day-1 in the rat model is associated with mean concentrations in plasma of 1.3 and 2.5 micrograms of DFO ml-1 and mean concentrations in lung tissue of 4.9 and 6.0 micrograms of DFO g of lung tissue-1, respectively. Since current clinical use of DFO mesylate for the treatment of iron overload produces higher concentrations in the plasma of patients, DFO may prove to be a useful anti-PCP treatment. The 2.4- to 3.8-fold higher DFO concentration observed in lung tissue compared with that observed in plasma may be important in the response of PCP to DFO.

Response of rat model of Pneumocystis carinii pneumonia to continuous infusion of deferoxamine

The iron-chelating drug deferoxamine mesylate (DFO) is active against Pneumocystis carinii in vitro and in rat and mouse models of P. carinii pneumonia. Because DFO has a short half-life, daily divided or continuous dosage was expected to improve the dose response, as is the case with DFO treatment of malaria. Therefore, results of single daily intraperitoneal injections were compared with results of an evenly divided four-times-daily dosage and the efficacy of delivery with implanted infusion pumps. The highest bolus dosage (1,000 mg kg-1 of body weight day-1) was as effective as the standard combination of trimethoprim with sulfamethoxazole. Unexpectedly, very little improvement was observed with the divided or continuous dosage, and several mechanisms that could account for this are discussed.

Desferrioxamine treatment reduces histological evidence of lung damage in rats after acute nitrogen dioxide (NO2) intoxication

1. In previous studies a rat inhalation model was developed to investigate the efficacy of treatment in acute NO2 intoxication. 2. Desferrioxamine was administered intravenously to study its effect on histological alterations in lung tissue in rats after acute NO2 exposure. 3. Twenty four hours after exposure to 175 ppm NO2 for 10 minutes the lung injury observed by light microscopy in the desferrioxamine treated rats was less pronounced than in the saline treated rats. 4. Desferrioxamine appeared to provide more protection with a dose of 100 mg kg-1 24 h-1 than with 200 mg kg-1 24 h-1.

Quantification of desferrioxamine and its iron chelating metabolites by high-performance liquid chromatography and simultaneous ultraviolet-visible/radioactive detection

An HPLC-based method for quantification of desferrioxamine (DFO) and its iron chelating metabolites in plasma has been developed. This assay overcomes stability problems associated with DFO by the addition of radioactive iron to convert unbound drug and metabolites to radio-iron-bound species. A dual detection system utilizing uv-vis absorption and radioactive (beta-particle) detector was used to quantify total and radio-iron-bound species. The use of octadecyl silanol solid phase extraction cartridges permits concentration of samples and allows accurate quantification of drug and metabolites down to 0.1 nmol/ml.

Hyperoxic inhibition of newborn rat lung development: protection by deferoxamine

Prolonged exposure to hyperoxia markedly inhibits normal lung development (alveolarization and respiratory surface area expansion) in immature animals. Since (a) hyperoxia results in excess hydroxyl radical (OH.) formation, (b) (OH.) is implicated in O2-induced lipid peroxidation and DNA alterations, and (c) both OH. formation and its interaction with DNA are Fe++ dependent; chelation of Fe++ should act to protect against pulmonary O2 toxicity and hyperoxic inhibition of lung development. We therefore treated litters of newborn rats with the iron chelator Deferoxamine mesylate (DES) (150 mg/kg/day) during a 10-day exposure to greater than 95% O2. Morphometric analysis demonstrated that compared to the mean airspace size in air control rat pups (Lm = 44.5 microns), hyperoxic exposure resulted in a 34% larger mean air space diameter in O2-saline rat lungs (59.5 microns) versus only an 11% enlargement in O2-DES lungs (51.1 microns*). Lung internal surface area (cm2) per 100-g body weight were air control = 4480, O2-saline = 3570 (decreases 20.3%), and O2-DES = 4125* (decreases 7.9%) (*p less than 0.05 versus O2-saline group). DES-treated animals also had significantly decreased lung conjugated diene levels during hyperoxic exposure and increased lung elastin content (reflective of preserved lung alveolar formation) compared to O2-saline rats. These results indicate that DES treatment substantially ameliorated the inhibitory effects of neonatal hyperoxic exposure on normal lung development.

Separation and identification of desferrioxamine and its iron chelating metabolites by high-performance liquid chromatography and fast atom bombardment mass spectrometry: choice of complexing agent and application to biological fluids

An HPLC-based method capable of separating desferrioxamine (DFO) and its iron chelating metabolites from uv-absorbing species present in biological fluids has been developed. This method relies on the use of nitrilotriacetic acid (NTA) as the complexing agent in the mobile phase, instead of EDTA, previously used in HPLC methods. The use of NTA ensures that iron contamination present in buffers and bound to the column does not interfere with analysis. The disadvantages of using EDTA are discussed. The identity of the iron chelating metabolites of DFO present in the urine of patients with beta-thalassemia major has been established using FAB mass spectrometry. The metabolism of DFO, reported in this study, takes place almost exclusively at the N-terminal region of the molecule and is in many respects similar to the degradation of the amino acid lysine. In addition, a metabolite which corresponds to N-hydroxylation of the terminal amino group has been identified.

Ferrioxamine and its hexadentate iron-chelating metabolites in human post-desferal urine studied by high-performance liquid chromatography and fast atom bombardment mass spectrometry

Three iron-containing fractions were detected by high-performance liquid chromatography (HPLC) on a reverse-phase column in the 24-h urine of two patients with hereditary hemochromatosis following the injection of deferoxamine mesylate (Desferal). These fractions have virtually identical absorption spectra in the visible range, with a broad maximum around 430 nm. Molecular weight determination of these fractions was performed by fast atom bombardment mass spectrometry (FAB-MS), which gave intense ion signals for the protonated molecular ions of the intact iron chelates, namely, at m/z 614 for ferrioxamine (FOA; Mr 613), at m/z 629 for metabolite I (FOA-MI; Mr 628), and at m/z 601 for metabolite II (FOA-MII; Mr 600). The molecular weight of FOA-MI is compatible with deamination of the terminal amino function and oxidation of the adjacent carbon atom to a carboxyl group; the molecular weight of FOA-MII is compatible with loss of a C2H4 unit from FOA-MI by beta oxidation. Quantification of iron in post-Desferal urine samples either by atomic absorption spectrometry (AAS) or by HPLC leads to results which are identical within experimental error. In ten subsequent 12-h urine samples of a patient under therapy (subcutaneous infusion of Desferal), the following distribution of urinary iron was found: FOA-MI, 58.4 +/- 4.7% (arithmetic mean +/- SD); FOA, 33.2 +/- 4.9%; FOA-MII, 8.4 +/- 1.7%. Addition of 2 mM ethylenediaminetetraacetic acid (EDTA) to the chromatographic solvents was used as a stability test for FOA and its two metabolites MI and MII.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological models for studying iron chelating drugs

Experimental models for studying the biological effects of iron chelators range from in vitro cell cultures to in vivo models in a variety of animals. Apart from screening for chelating efficacy, such models have been useful in providing information on the pharmacology of desferrioxamine and a number of other, orally effective iron chelators; in the identification of the biological source of iron mobilized by such chelators; in defining optimal methods of drug delivery; in providing evidence for the ability of iron chelators to prevent or reverse iron toxicity; and in exploring the potential usefulness of iron chelating therapy in conditions unrelated to iron overload, where iron may fulfil a central role in the pathogenesis of disease. Although cell cultures are inexpensive and permit the rapid screening of large numbers of new chelating compounds, they may overlook alternative sources of chelatable iron, pro-drugs, and orally effective compounds. In vivo models provide information on drug toxicity, allow comparison of oral versus parenteral efficacy, routes of excretion of chelated iron, monitoring of selective interaction with various iron pools, and promotion of the excretion of various trace metals. Although iron metabolism in large animals such as dogs and monkeys closely resembles that of humans, small animals such as mice and rats are usually preferred because of their low cost and ease of handling. Thorough knowledge of the pharmacology of iron chelators is a prerequisite for their successful therapeutic application. Interaction with a rapidly exchanging, intracellular, low molecular weight chelatable iron pool requires a steady supply of a drug capable of penetrating the relevant effector cells. The high effectiveness of continuous desferrioxamine infusion illustrates this point and underlines the need for developing new orally effective iron chelators which, by virtue of their slower absorption, would be more suitable for providing a continuous supply of circulating drug.

High-performance liquid chromatographic analysis of desferrioxamine. Pharmacokinetic and metabolic studies

A high-performance liquid chromatographic method has been developed that permits determination and quantitation of desferrioxamine and metabolites as their iron (III) complexes in small samples of mammalian plasma at levels encountered with ion-specific chelation treatments. The technique permits measurement of desferrioxamine and metabolite concentrations which can be used in pharmacokinetic studies. A human study is presented as an example.

Iron-chelating therapy

Because of the catalytic action of iron in one-electron redox reactions, it has a key role in the formation of harmful oxygen derivatives and production of peroxidative damage to vital cellular structures. The clinical manifestations of iron overload may be prevented and even reversed by the effective administration of the iron-chelating drug deferoxamine (DF). Recent experimental evidence suggests that DF may also be useful in modifying disease conditions unrelated to iron overload by preventing the formation of free radicals, the powerful final effectors of tissue damage resulting from the respiratory burst of granulocytes and macrophages participating in the inflammatory response. Although much experimental work is still needed, this novel approach in iron-chelating therapy may have far-reaching implications in the management of autoimmune disease, adult respiratory distress syndrome, and organ transplantation. The poor intestinal absorption of DF, its almost prohibitive price, and short duration of action underline the need for new, orally effective iron chelators. A number of very promising orally effective drugs have been identified in recent years, such as the polyanionic amines, aryl hydrazones, and hydroxypyridones. Further development for clinical use of this new generation of iron-chelating drugs is a major challenge for future research.

Pharmacokinetics of desferrioxamine and of its iron and aluminium chelates in patients on haemodialysis

We have used a new analytical micromethod to study the pharmacokinetics of desferrioxamine and its aluminium chelates in patients with chronic renal failure on haemodialysis. Desferrioxamine (Desferal, CIBA, Basle) was given by 1-h infusion just after the haemodialysis at 20, 40, 80 mg/kg body wt. and during the first and the last hour of the haemodialysis at 40 mg/kg. The concentrations of desferrioxamine during infusions showed a linear increase with increasing doses. The maximum concentrations and the AUC obtained when desferrioxamine was infused during the haemodialysis were not statistically different but slightly lower than those obtained in post dialysis administration. This result indicates that the loss of desferrioxamine by transfer in the dialysate is quite moderate within 1 h. During the interdialysis period, there was a decrease of plasma desferrioxamine concentrations with a mean half-life of 18.7 +/- 5.2 h and an increase in plasma concentrations of aluminium desferrioxamine chelate. In vitro studies show that a lengthy contact between desferrioxamine and plasma is necessary for complete chelation of A1 already present in plasma. During the following dialysis session, there was an important decrease of desferrioxamine and of its iron and aluminium chelates in blood plasma representing their transfer to the dialysis fluid.

Pharmacokinetics and renal elimination of desferrioxamine and ferrioxamine in healthy subjects and patients with haemochromatosis

1 Desferrioxamine mesylate (DM) (10 mg kg-1 = 15.24 mumol kg-1) was given by intramuscular injection to five healthy subjects and to six patients with haemochromatosis, after informed consent. 2 Desferrioxamine (DFA), ferrioxamine (FeA), aluminoxamine (AlA), aluminium (Al) and iron (Fe) were measured in plasma, before and 10, 20, 30, 60 min and 2, 4, 6, 8, 12 h after DM injection and in urine collected over a 6 h period the day before and the day of administration. 3 The predominant form in plasma from control subjects was DFA whereas FeA predominated in plasma from patients. In controls, rapid and slow phases of decline in plasma DFA concentrations were found, with half-lives of 1.0 h and 6.1 h, respectively. In the patients, only a single phase of decline was observed, with a half-life of 5.6 h. Total clearances of DFA were 296 ml h-1 kg-1 in controls and 239 ml h-1 kg-1 in patients. 4 The amount of FeA eliminated in urine during 6 h was significantly lower in controls (8.0 +/- 4.6 mumol) than in patients (129.2 +/- 40.0 mumol), with respective renal clearances estimated over 6 h of 516 ml h-1 kg-1 and 1,716 ml h-1 kg-1. DFA elimination was similar in both groups and its renal clearance estimated over 6 h was 91 ml h-1 kg-1 in controls and 85 ml h-1 kg-1 in patients. 5 Since there was no overlap in the 1 h DFA/FeA plasma ratio between controls and patients, this might be useful as an index of iron overload.

Cellular pharmacology of deferrioxamine B and derivatives in cultured rat hepatocytes in relation to iron mobilization

Two radiolabelled derivatives of deferrioxamine B (DF) have been synthesized: methyl-DF and acetyl-DF. Both derivatives are non cytotoxic and stable in cell culture but they are degraded in human plasma and more extensively in rat plasma. Methyl-DF, acetyl-DF and DF mobilize radioiron to the same extent from hepatocytes loaded with 59Fe citrate in the same range of extracellular concentrations. The uptake and release of the 3H-labelled derivatives and their corresponding iron complexes have been measured and appear to represent a passive phenomenon resulting from the gradient of concentration between the cellular compartment and the extracellular medium. The results indicate that only a limited pool of cellular iron is accessible for chelation and that neither the permeability of the cellular membrane, nor the intracellular concentration of the chelators are the limiting factors for iron mobilization. On the basis of the subcellular distribution of the 3H-DF analogues, methylamine inhibition of iron chelation by siderophores in cell cultures and the positive effect of acidic pH and hydrolysis by lysosomal enzymes on in vitro iron mobilization from radiolabelled ferritin, we suggest that iron mobilization by DF and its derivatives occurs in lysosomes where they complex iron released from ferritin under the conjugate actions of acidic pH and lysosomal enzymes.

Studies in desferrioxamine and ferrioxamine metabolism in normal and iron-loaded subjects

Plasma concentrations of desferrioxamine and ferrioxamine were measured following bolus injections of desferrioxamine and during 24 h infusions of the drug. [59Fe]ferrioxamine clearance and urinary iron excretion were also measured. Higher plasma ferrioxamine concentrations were found in iron loaded subjects and higher desferrioxamine concentrations in subjects with normal ironloads. There is a correlation between the circulating concentration of ferrioxamine during an infusion and the 48 h urinary iron excretion. The data suggests that the amount of iron chelated in vivo is related to an increase in the size of an intermediate chelatable pool rather than the total amount of the iron load. The well-recognized delay in urinary iron excretion appears to be related to active tubular reabsorption of ferrioxamine.

Quantitative measurement of iron stores with diethylenetriamine penta-acetic acid

The use of the chelating agent diethylenetriamine penta-acetic acid (DTPA) for measuring body storage iron was investigated in patients with iron excess whose stores could be determined by venesection. Iron excretion after DTPA bore a close semi-logarithmic relationship to body iron stores when these were increased. The excretion of DTPA-bound (59)Fe was similarly related to the size of the stores, indicating that the increased iron excretion produced by DTPA in iron overload states reflects both increased tissue iron available for chelation and greater stability of the iron-chelate complex. Evidence was obtained that injected (59)Fe-DTPA could be used as a marker for chelated tissue iron enabling the DTPA-chelatable body iron pool to be calculated. There was a highly significant correlation between DTPA-chelatable iron and body storage iron. The regression intercept approximated to the origin, implying a specific relation between the DTPA effect and storage iron. The SE of the mean estimate for storage iron on DTPA-chelatable iron was 0.25 g (5.6%). Mean storage iron values of 392 mg for males and 243 mg for females were predicted from the findings in control subjects.