The toxic effects of desferrioxamine

Cytoprotection and iron mobilization in rat hepatocyte cultures by a new synthetic dihydroxamate chelator

The cytoprotection and iron mobilization effect of a new dihydroxamate chelator 1,1 bis [(11-N-hydroxy)-2,5,11-triaza-1,6,10-trioxo dodecanyl] ethane or KD was studied in primary rat hepatocyte cultures exposed to iron-citrate. Lactate dehydrogenase (LDH) release and malondialdehyde (MDA) production were measured as indexes of cytotoxicity. Cell viability was evaluated using the [3-(4,5-dimethyl-thiazol-2-yl) 2,5-diphenyl tetrazolium bromide] (MTT) reduction test. To demonstrate that this chelator was able to decrease iron uptake or increase iron release from the hepatocytes, labelled cells were obtained by maintaining the cultures in the presence of 0.02 microM 55Fe-citrate. The efficacy of KD was compared to desferrioxamine B (DFO) at stoechiometry concentrations. After 24 h of exposure to 50 microM of iron-citrate, a significant release of LDH and MDA was observed. Cell viability was also significantly decreased. When 100 microM of KD were added at the same time as iron, LDH and MDA release was decreased and cell viability was improved. In the presence of the same chelator concentration, a net decrease of iron uptake by the cells was observed as attested by the low intracellular 55Fe level. Moreover, in the 55Fe loaded hepatocytes, the chelator increased the iron extracellular level indicating its iron release effect from the cells. In all tested experimental conditions, the efficacy of 100 microM of the dihydroxamate chelator KD was close to that of 50 microM of the trihydroxamate chelator DFO. In conclusion, KD is effective at a level comparable to DFO in protecting rat hepatocytes against the toxic effect of iron-citrate by decreasing the uptake of the metal and increasing its release from the cells. This synthetic compound appears to have some potential therapeutical interest and the results obtained encourage the synthesis of new hydroxamate ligands.

Deferiprone: a review of its clinical potential in iron overload in beta-thalassaemia major and other transfusion-dependent diseases

Patients with beta-thalassaemia and other transfusion-dependent diseases develop iron overload from chronic blood transfusions and require regular iron chelation to prevent potentially fatal iron-related complications. The only iron chelator currently widely available is deferoxamine, which is expensive and requires prolonged subcutaneous infusion 3 to 7 times per week or daily intramuscular injections. Moreover, some patients are unable to tolerate deferoxamine and compliance with the drug is poor in many patients. Deferiprone is the most extensively studied oral iron chelator to date. Non-comparative clinical studies mostly in patients with beta-thalassaemia have demonstrated that deferiprone 75 to 100 mg/kg/day can reduce iron burden in regularly transfused iron-overloaded patients. Serum ferritin levels are generally reduced in patients with very high pretreatment levels and are frequently maintained within an acceptable range in those who are already adequately chelated. Deferiprone is not effective in all patients (some of whom show increases in serum ferritin and/or liver iron content, particularly during long term therapy). This may reflect factors such as suboptimal dosage and/or severe degree of iron overload at baseline in some instances. Although few long term comparative data are available, deferiprone at the recommended dosage of 75 mg/kg/day appears to be less effective than deferoxamine; however, compliance is superior with deferiprone, which may partly compensate for this. Deferiprone has additive, or possibly synergistic, effects on iron excretion when combined with deferoxamine. The optimum dosage and long term efficacy of deferiprone, and its effects on survival and progression of iron-related organ damage, remain to be established. The most important adverse effects in deferiprone-treated patients are arthropathy and neutropenia/agranulocytosis. Other adverse events include gastrointestinal disturbances, ALT elevation, development of antinuclear antibodies and zinc deficiency. With deferiprone, adverse effects occur mostly in heavily iron-loaded patients, whereas with deferoxamine adverse effects occur predominantly when body iron burden is lower.

CONCLUSION

Deferiprone is the most promising oral iron chelator under development at present. Further studies are required to determine the best way to use this new drug. Although it appears to be less effective than deferoxamine at the recommended dosage and there are concerns regarding its tolerability, it may nevertheless offer a therapeutic alternative in the management of patients unable or unwilling to receive the latter drug. Deferipone also shows promise as an adjunct to deferoxamine therapy in patients with insufficient response and may prove useful as a maintenance treatment to interpose between treatments.

HBED: The Continuing Development of a Potential Alternative to Deferoxamine for Iron-Chelating Therapy

To further examine the potential clinical usefulness of the hexadentate phenolic aminocarboxylate iron chelatorN,N′-bis(2-hydroxybenzyl)ethylenediamine-N,N′-diacetic acid (HBED) for the chronic treatment of transfusional iron overload, we performed a subchronic toxicity study of the HBED monosodium salt in rodents and have evaluated the iron excretion in primates induced by HBED. The HBED-induced iron excretion was determined for the monohydrochloride dihydrate that was first dissolved in a 0.1-mmol/L sodium phosphate buffer at pH 7.6 and administered to the primates either orally (PO) at a dose of 324 μmol/kg (149.3 mg/kg, n = 5), subcutaneously (sc) at a dose of 81 μmol/kg (37.3 mg/kg, n = 5), sc at 324 μmol/kg (n = 5), and sc at 162 μmol/kg (74.7 mg/kg) for 2 consecutive days for a total dose of 324 μmol/kg (n = 3). In addition, the monosodium salt of HBED in saline was administered to the monkeys sc at a single dose of 150 μmol/kg (64.9 mg/kg, n = 5) or at a dose of 75 μmol/kg every other day for three doses, for a total dose of 225 μmol/kg (n = 4). For comparative purposes, we have also administered deferoxamine (DFO) PO and sc in aqueous solution at a dose of 300 μmol/kg (200 mg/kg). In the iron-loadedCebus apella monkey, whereas the PO administration of DFO or HBED even at a dose of 300 to 324 μmol/kg was ineffective, the sc injection of HBED in buffer or its monosodium salt, 75 to 324 μmol/kg, produced a net iron excretion that was nearly three times that observed after similar doses of sc DFO. In patients with transfusional iron overload, sc injections of HBED may provide a much needed alternative to the use of prolonged parenteral infusions of DFO.  Note: After the publication of our previous paper (Blood, 91:1446, 1998) and the completion of the studies described here, it was discovered that the HBED obtained from Strem Chemical Co (Newburyport, MA) that was labeled and sold as a dihydrochloride dihydrate was in fact the monohydrochloride dihydrate. Therefore, the actual administered doses were 81, 162, or 324 μmol/kg; not 75, 150, or 300 μmol/kg as was previously reported. The new data have been recalculated accordingly, and the data from our earlier study, corrected where applicable, are shown in parentheses.

HBED: The Continuing Development of a Potential Alternative to Deferoxamine for Iron-Chelating Therapy

To further examine the potential clinical usefulness of the hexadentate phenolic aminocarboxylate iron chelatorN,N′-bis(2-hydroxybenzyl)ethylenediamine-N,N′-diacetic acid (HBED) for the chronic treatment of transfusional iron overload, we performed a subchronic toxicity study of the HBED monosodium salt in rodents and have evaluated the iron excretion in primates induced by HBED. The HBED-induced iron excretion was determined for the monohydrochloride dihydrate that was first dissolved in a 0.1-mmol/L sodium phosphate buffer at pH 7.6 and administered to the primates either orally (PO) at a dose of 324 μmol/kg (149.3 mg/kg, n = 5), subcutaneously (sc) at a dose of 81 μmol/kg (37.3 mg/kg, n = 5), sc at 324 μmol/kg (n = 5), and sc at 162 μmol/kg (74.7 mg/kg) for 2 consecutive days for a total dose of 324 μmol/kg (n = 3). In addition, the monosodium salt of HBED in saline was administered to the monkeys sc at a single dose of 150 μmol/kg (64.9 mg/kg, n = 5) or at a dose of 75 μmol/kg every other day for three doses, for a total dose of 225 μmol/kg (n = 4). For comparative purposes, we have also administered deferoxamine (DFO) PO and sc in aqueous solution at a dose of 300 μmol/kg (200 mg/kg). In the iron-loadedCebus apella monkey, whereas the PO administration of DFO or HBED even at a dose of 300 to 324 μmol/kg was ineffective, the sc injection of HBED in buffer or its monosodium salt, 75 to 324 μmol/kg, produced a net iron excretion that was nearly three times that observed after similar doses of sc DFO. In patients with transfusional iron overload, sc injections of HBED may provide a much needed alternative to the use of prolonged parenteral infusions of DFO.  Note: After the publication of our previous paper (Blood, 91:1446, 1998) and the completion of the studies described here, it was discovered that the HBED obtained from Strem Chemical Co (Newburyport, MA) that was labeled and sold as a dihydrochloride dihydrate was in fact the monohydrochloride dihydrate. Therefore, the actual administered doses were 81, 162, or 324 μmol/kg; not 75, 150, or 300 μmol/kg as was previously reported. The new data have been recalculated accordingly, and the data from our earlier study, corrected where applicable, are shown in parentheses.

Protection of U937 cells against oxidative injury by a novel series of iron chelators

A new series of iron chelators designed to protect tissues against iron-catalysed oxidative damage is described. These compounds are aminocarboxylate derivatives bearing pendant aromatic groups. They were designed to have a relatively low affinity for both ferrous and ferric iron and to be site-specifically oxidizable by hydrogen peroxide through intramolecular aromatic hydroxylation into species with strong iron binding capacity which do not catalyse hydroxyl radical formation. Thus, at the cellular level, oxidative injury is used to convert weak iron chelators into strong iron chelators in order to promote cell survival. The purpose of this local activation process is to minimise toxicity compared to strong iron chelators which may interfere with normal iron metabolism. Compounds within this series were evaluated in vitro in view of their capacity to undergo intramolecular hydroxylation and to protect cultured cells against oxidative injury. Results show that the intramolecular aromatic hydroxylation capacity is critically dependent upon the amino carboxylate chelating moieties and the substituents of the aromatic rings. Cell protection against oxidative injury is only observed with compounds possessing sufficient lipophilicity. The monohydroxylation product of N,N'-dibenzylethylenediamine N,N'-diacetic acid, protects cells against both H2O2 and tBuOOH toxicity with IC50's of 12 and 60 microM, respectively, in agreement with the oxidative activation concept. These results represent the first step toward the development of a new strategy to safe iron chelation for the prevention of oxidative damage.

Quantification of desferrioxamine, ferrioxamine and aluminoxamine by post-column derivatization high-performance liquid chromatography. Non-linear calibration resulting from second-order reaction kinetics

Desferrioxamine B is widely used as therapeutic agent for removal of excess body iron and, more recently, for removal of aluminium. A HPLC-based method for direct sensitive and reliable determination of ferrioxamine, desferrioxamine, aluminoxamine and related metabolites has been developed for use in pharmacokinetic studies. The method consists of complete separation of the analytes by an optimized mobile phase avoiding conversion of desferrioxamine to ferrioxamine by the analytical system and overcoming problems due to peak tailing properties of desferrioxamine. A post-column derivatization reaction with colourless fluoro-complexed iron converts all iron free species to ferrioxamine and allows quantification at 430 nm avoiding interference of UV-absorbing coelutes. This reaction might be of interest for other analytical procedures concerning iron chelators. The influence of the post-column reaction system on the column plate number is characterized. As the reaction rate of desferrioxamine and aluminoxamine with iron(III) is of second-order kinetics, a quadratic calibration function is observed, resulting from a compromise between residence time and peak broadening. A solid-phase extraction procedure is presented for extraction of the analytes from plasma. Limits of detection (S/N ratio of 3) were determined as 1.95 ng for ferrioxamine, 3.9 ng for aluminoxamine and 15.7 ng for desferrioxamine, expressed as on-column load. A new iron-free metabolite was identified with fast atom bombardment-mass spectrometry as N-hydroxylated desferrioxamine.

Aluminium distribution and excretion: a comparative study of a number of chelating agents in rats

The present study was conducted to assess in rats the comparative effects of a number of chelating agents on the urinary excretion and tissue distribution of A1. Adult male Sprague-Dawley rats received a single intraperitoneal dose of aluminium (A1) nitrate nonahydrate (0.24 mmol/kg). Ten min. after A1 injection 1,2-dimethyl-3-hydroxypyrid-4-one, 2,3-dihydroxybenzoic acid, picolinic acid, methylmalonic acid, ethylenediamine-di(o-hydroxyphenylacetic) acid, 1-benzyl-2-methyl-3-hydroxypyrid-4-one, 1-(p-methylbenzyl)-2-methyl-3-hydroxypyrid-4-one, 1-(p-methoxy-benzyl)-2-methyl-3-hydroxypyrid-4-one, 1-(p-chlorobenzyl)-2-methyl-3-hydroxypyrid-4-one, 1-benzyl-2-ethyl-3-hydroxypyrid-4-one, 1-(p-methyl-benzyl)-2-ethyl-3-hydroxypyrid-4-one, 1-[3-hydroxy-2-methyl-4-oxopyridyl]-2-ethanesulfonic acid and 1-benzyl-(4-carboxylic acid)-3-hydroxy-2-methyl-4-oxopyridine were given by gavage at 1.79 mmol/kg. A control group received similar volumes of distilled water. An additional group of rats received a subcutaneous injection of desferrioxamine at 1.79 mmol/ kg. Urine samples were collected daily for three consecutive days and the animals were killed after this period. Samples of brain, bone, liver, kidney and spleen were collected. Although desferrioxamine, 1,2-dimethyl-3-hydroxypirid-4-one, 1-(p-methylbenzyl)-2-methyl-3-hydroxypyrid-4-one, 1-(p-methoxybenzyl)-2-methyl-3- hydroxypyrid-4-one, 1-(p-methylbenzyl)-2-ethyl-3-hydroxypyrid-4-one, 1-[3-hydroxy-2-methyl-4-oxopyridyl]-2-ethanesulfonic acid and 1-benzyl-(4-carboxylic acid)-3-hydroxy-2-methyl-4-osopyridine significantly enhanced the total excretion of A1 into urine, only treatment with 1-(p-chlorobenzyl)-2-methyl-3-hydroxypyrid-4-one and 1-benzyl-2-ethyl-3-hydroxypyrid-4-one significantly reduced A1 concentrations in all analyzed tissues. No beneficial effects of the remaining chelators on Al mobilization were observed. Further studies on the effects of some 3-hydoxrypyrid-4-ones on A1 removal can be of interest for the treatment of A1 accumulation and toxicity.

Inhibition of iron toxicity in human hepatocyte cultures by pyoverdins Pa A and Pf, the peptidic siderophores of Pseudomonas aeruginosa and fluorescens

The protective effect of pyoverdins Pa A and Pf, peptidic siderophores secreted respectively by Pseudomonas aeruginosa and fluorescens, was studied in primary cultures of human hepatocytes exposed to iron (50 or 100 microM of iron-citrate). AST, ALT and MDA releases were measured as indexes of cytotoxicity. In order to demonstrate that these chelators were able to decrease iron uptake or increase iron release from the hepatocytes, labelled cells were obtained by maintaining the cultures in the presence of 1 microM 55Fe ferric chloride plus 50 microM iron citrate. One day after iron treatment, an increase in AST, ALT and MDA release was observed with 50 or 100 microM of iron citrate; it appeared that the concentrations 50 and 100 microM of iron were highly toxic for human hepatocytes. In the presence of 50 or 100 microM of iron, the addition of 50 or 100 microM of Pa A or Pf was effective to inhibit the increase observed in the enzyme leakage and the MDA production resulting from iron exposure. In human hepatocytes cultured for 1 day in the presence of 1 microM 55Fe-50 microM iron citrate plus 50 or 100 microM Pa A or Pf, a net decrease of iron uptake by the cells was observed, as demonstrated by the low intracellular iron level. When the hepatocytes were cultured for 1 day in the presence of 1 microM 55Fe-50 microM iron citrate and then for a further day in the presence of 50 or 100 microM Pa A or Pf without additional iron, the chelators increased the extracellular iron level, indicating their iron release from the loaded cells; however, the effects of Pa A and Pf on iron release did not differ significantly. In conclusion, iron loading achieved by adding iron citrate to the culture medium is highly toxic for human hepatocytes. Pyoverdins Pa A and Pf are effective in protecting human hepatocytes against the toxic effect of iron by both decreasing the uptake of the metal and increasing its release from the loaded cells.

Prevention of postasphyxia electroretinal dysfunction with a pyridoxal hydrazone

The newborn retina is particularly sensitive and frequently subjected to peroxidative stresses that result in visual sequelae. We compared two iron chelators, deferoxamine and a newer compound, pyridoxal isonicotinoyl hydrazone (PIH), in protecting the retina of newborn pigs (1-3 d old) from asphyxia-reoxygenation insults. Animals were treated IV with either saline, deferoxamine 15.2 mumol/kg (10 mg/kg) or PIH 34.8 mumol/kg (10 mg/kg); n = 10 in each treatment group. Scotopic and photopic electroretinograms (ERG) were recorded before and 40 min after drug treatment as well as 45 min following a 5-min period of asphyxia by interrupting ventilation. In separate animals the indices of peroxidation, malondialdehyde (MDA: TBARS) and hydroperoxides, were measured in retina at the same times. In saline-treated animals, there was a marked increase in MDA and hydroperoxide concentrations in the retina following the asphyxia-reoxygenation period. This was associated with a decrease in the a- (photoreceptor generated) and b-wave (generated by Müller and bipolar cells) amplitudes measured under photopic (cone-mediated response) and scotopic (rod-mediated response) conditions, and an increase in their implicit times. PIH and deferoxamine prevented the postasphyxial increase in MDA and hydroperoxides. However, only PIH prevented the postasphyxial changes in a- and b-wave amplitudes and implicit times, whereas deferoxamine markedly altered the preasphyxial ERG and provided only partial postasphyxial protection simply to the retinal outer segment. Our findings indicate that the iron chelator PIH effectively inhibits peroxidation and retinal electrophysiological alterations secondary to asphyxia-reoxygenation-induced oxidative stresses to newborn animals, whereas deferoxamine adversely affects retinal function; hence, PIH may be a preferred alternative to deferoxamine.

Sensorineural hearing loss in children with thalassemia major in Northern Greece

Eighty eight (88) beta-thalassemic patients undergoing regular transfusion- chelation therapy with desferrioxamine (DFO) were studied for ENT problems from 1988 to 1993, as DFO has been implicated for auditory neurotoxicity. The mean age of the patients was 9.66 +/- 3.1 years, their pre-transfusion haemoglobin level was 9 +/- 2 g/dl, serum ferritin level was 2065 +/- 898 ng/ml and the daily DFO dose was 50.7 +/- 9.5 mg/kg for 5 days/week. The ENT study included, ENT examination, pure tone audiometry, speech audiometry, tympanometry, tone decay test and ABR. During this 6-year study 24/88 (27%) patients developed bilateral or ipsilateral sensorineural hearing loss in high tone frequencies, sometimes exceeding 80 dB, which was attributed to DFO toxicity. Therefore, a reduction or temporary withdrawal of DFO followed. After this intervention 12/24 patients recovered almost completely, 7/24 remained stable and 5/24 presented aggravation of their hearing loss. This study confirms the DFO induced auditory neurotoxicity and the necessity of periodical audiology control of beta-thalassemic patients for prompt diagnosis and management of this complication.

Ototoxicity in hemoglobinopathy patients chelated with desferrioxamine

PURPOSE

Ototoxicity often limits the dose of desferrioxamine (DFO) tolerated by patients who are transfusion dependent. Current recommendations advise doses of < 50 mg/kg/day after early reports noted higher rates of oxotoxicity with increasing doses. There have been no follow-up studies to determine the effect of this recommendation on oxotoxicity and iron overload.

METHODS

We followed 28 patients who were chronically chelated with serial audiograms over a 5-year period. Patients with and without oxotoxicity were compared with respect to age, disease, DFO dose, peak DFO dose, length of DFO therapy, ferritin, and therapeutic index.

RESULTS

Eight of the 28 patients (29%) had an abnormal audiogram during threshold testing. Two patients had two separate episodes with hearing deficit. Nine of the 10 episodes were high-frequency losses, with seven being moderate and three mild. All deficits were rapidly reversible with DFO dose reduction. No significant differences were found between the affected and unaffected groups with respect to age, DFO dose or duration, ferritin, or therapeutic index. Numbers of affected patients were small, but patients with SCD differed from patients with thalassemia in that they developed ototoxicity earlier and with lower doses of DFO and lower therapeutic indexes.

CONCLUSIONS

Despite DFO doses usually felt to be low risk for ototoxicity, we found a high rate of ototoxicity in our patients who we've chronically chelated. No variables were identified that reliably predicted ototoxicity. We stress the need for regular audiological exams and feel no dose of DFO is "safe" from the development of ototoxicity.

N,N'-bis-(3,4,5-trimethoxybenzyl) ethylenediamine N,N'-diacetic acid as a new iron chelator with potential medicinal applications against oxidative stress

N,N'-bis-(3,4,5-trimethoxybenzyl) ethylenediamine N,N,-diacetic acid dihydrochloride (OR10141) is a member of a recently described series of "oxidative stress activatable iron chelators." These chelators have a relatively low affinity for iron but can be site-specifically oxidized, in situations mimicking oxidative stress in vitro, into species with strong iron-binding capacity. It is hoped that this local activation process will minimise toxicity compared to strong iron chelators that may interfere with iron metabolism. The present paper describes the results of experiments aimed at characterising oxidative reactions between iron-OR10141 complexes and hydrogen peroxide. Incubation of ascorbate and hydrogen peroxide with the ferric chelate of OR10141 in neutral aqueous solution yields a purple solution with a chromophore at 560 nm, which is consistent with an o-hydroxylation of one of the trimethoxybenzyl rings. Oxidation of OR10141 also takes place, although more slowly, by incubating hydrogen peroxide with ferric OR10141 complex in the absence of reductant. HPLC analysis shows that OR10141 is consumed during the reaction and transformed principally into N-(2-hydroxy 3,4,5-trimethoxybenzyl) N'-(3,4,5-trimethoxybenzyl) ethylenediamine N,N'-diacetic acid. Minor products are also formed, some of which were identified by mass spectrometry. The protective effect of OR10141 in vitro against DNA single strand breaks, protein damage, and lipid peroxidation induced by Fenton chemistry suggests that this compound is able to compete for iron with biological molecules and, thus, that this strategy of protection against oxidative stress is feasible. In addition, preliminary results showing protective effects of OR10141 dimethyl ester against toxicity induced by hydrogen peroxide in cell culture are described. It is concluded that OR10141 and related prodrugs might be useful in vivo in chronic situations involving oxidative stress.

Rheumatological manifestations of haematological diseases

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Effects of deferoximine on chondrocyte alkaline phosphatase activity: proxidant role of deferoximine in thalassemia

The homozygous form of beta-thalassemia, the most common single gene disorder, is treated by red cell transfusion therapy. Following transfusion, the chelator, deferoximine, is administered to patients to remove excess iron. However, when this drug is given to young children, metaphyseal dysplasia and abnormalities of linear growth are frequently observed. To explore the notion that deferoximine interferes with endochondral growth by chelating zinc, we examined the effect of the drug on chondrocytes maintained in long-term culture. We found that deferoximine caused a dose-dependent inhibition of a wide range of functions including cell proliferation, protein synthesis (and possibly under-hydroxylation of type X collagen), and mineral deposition. Directly relevant to the mineralization process was the observation that the drug dramatically lowered the activity of alkaline phosphatase, a zinc-requiring enzyme. To test the hypothesis that enzyme inhibition was due to chelation of zinc by deferoximine, the cell culture medium was supplemented with excess zinc. However, this treatment did not overcome the deferoximine-dependent change in enzyme activity. We next examined the possibility that deferoximine, in the presence of ascorbate, could form a free radical system that would serve to inactivate the enzyme. Using alkaline phosphatase extracted from chick cartilage, we noted that the activity of the phosphatase was markedly reduced in the presence of deferoximine and ascorbate. These effects were consistant with the notion that deferoximine and ascorbate can act as a prooxidant couple. This conclusion was confirmed when we measured the oxidative activities of the system using nitrobule tetrazolium and cytochrome c. Indeed, we noted that deferoximine markedly activates the autocatalytic oxidation of ascorbate.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of the developmental toxicity of deferoxamine in mice

Deferoxamine (DFO), an efficient chelating agent available for the treatment of iron and aluminium overload, was evaluated for developmental toxicity in Swiss mice. Intraperitoneal injections of DFO were given to pregnant animals at 0, 44, 88, 176, and 352 mg/kg per day on gestational days 6 through 15. Maternal clinical status was monitored daily during and after treatment. Fetal parameters, including external, visceral, and skeletal malformations and variations, were assessed. Mice were killed on day 18. No maternal mortality was observed, but dams exhibited reduced body weight gain during treatment at 88, 176, and 352 mg/kg per day. Body weight at termination, corrected body weight, and food consumption were reduced in all groups. In contrast, the only significant treatment-related embryo/fetal effect was a decrease in the number of live fetuses per litter at 352 mg/kg per day. The no-observable-adverse-effect level (NOAEL) for maternal toxicity of DFO was < 44 mg/kg per day, whereas the NOAEL for developmental toxicity was 176 mg/kg per day. In summary, intraperitoneal administration of DFO to mice during organogenesis produced developmental toxicity in the presence of maternal toxicity. Because of the remarkable maternal toxicity of DFO, extreme caution in the use of this drug is recommended during pregnancy.

Iron-chelation therapy with oral deferiprone in patients with thalassemia major

BACKGROUND

To determine whether the orally active iron chelator deferiprone (1,2-dimethyl-3-hydroxy-pyridin-4-one) is efficacious in the treatment of iron overload in patients with thalassemia major, we conducted a prospective trial of deferiprone in 21 patients unable or unwilling to use standard chelation therapy with parenteral deferoxamine.

METHODS

Hepatic iron stores were determined yearly by chemical analysis of liver-biopsy specimens or magnetic-susceptibility measurements. Detailed clinical and laboratory studies were used to monitor safety and compliance.

RESULTS

The patients received deferiprone therapy for a mean (+/-SE) of 3.1 +/- 0.3 years. Ten patients in whom previous chelation therapy with deferoxamine had been ineffective had initial hepatic iron concentrations of at least 80 mumol per gram of liver, wet weight -- values associated with complications of iron overload. Hepatic iron concentrations decreased in all 10 patients, from 125.3 +/- 11.5 to 60.3 +/- 9.6 mumol per gram (P < 0.005), with values that were less than 80 mumol per gram in 8 of the 10 patients (P < 0.005). In all 11 patients in whom deferoxamine therapy had previously been effective, deferiprone maintained hepatic iron concentrations below 80 mumol of iron per gram.

CONCLUSIONS

Oral deferiprone induces sustained decreases in body iron to concentrations compatible with the avoidance of complications from iron overload. The risk of agranulocytosis associated with deferiprone may restrict its administration to patients who are unable or unwilling to use deferoxamine.

The importance of bone biopsy in managing renal osteodystrophy

A case is presented in which bone biopsy results helped to resolve not only difficult issues in the clinical management of the patient's renal osteodystrophy but also disruptive psychosocial problems surrounding her clinical course. The outcome was a satisfactory resolution based on rational medical treatment and directed supportive care. The presentation highlights important principles in the procurement, processing, and interpretation of the bone biopsy, while also addressing the importance of accurate diagnosis in facilitating the overall long-term management by the entire renal team.

Effects of antioxidants on oxygen toxicity in vivo and lipid peroxidation in vitro

Convulsions and pulmonary damage result when animals are exposed to hyperbaric oxygen at pressures above about 300 kPa. Several hydroxyl radical scavengers (namely dimethylsulphoxide, dimethylthiourea and mannitol), the iron chelator desferrioxamine and the lipid antioxidant butylated hydroxytoluene were tested for possible protection against such hyperbaric oxygen toxicity. Dimethylthiourea and dimethylsulphoxide prolonged the latency to the first convulsion, but, surprisingly, dimethylthiourea very significantly increased pulmonary damage at both pressures used (515 and 585 kPa). Desferrioxamine also slightly increased lung damage at 585 kPa. Other antioxidants did not alter neurotoxicity or pulmonary toxicity induced by hyperbaric oxygen at 515 or 585 kPa. The antioxidants were also tested for their ability to inhibit lipid peroxidation (TBARS formation) in vitro. Desferrioxamine (5 and 50 microM), and butylated hydroxytoluene (0.1 mM and 1 mM) greatly inhibited TBARS formation in brain and lung homogenates incubated at 37 degrees. None of the hydroxyl radical scavengers affected TBARS levels in homogenates. There was no correlation between in vitro inhibition of lipid peroxidation and in vivo protection against oxygen toxicity.

Desferrioxamine ameliorates retinal photic injury in albino rats

Albino rats were given intraperitoneal desferrioxamine before exposure to intense fluorescent light. Morphometric and morphologic studies of the retina indicated that there was better preservation of photoreceptor nuclei and fewer subretinal macrophages in rats treated with desferrioxamine than in the control rats. The results of the study imply that iron and hydroxyl radicals may be important mediators in photic retinal injury.

L1 (1,2-dimethyl-3-hydroxypyrid-4-one) for oral iron chelation in patients with beta-thalassaemia major

L1 was given to eight patients with beta-thalassaemia major who had previously been treated with deferoxamine (DF) for 4-10 years. The patients' ages ranged from 11 to 27 years. Serum ferritin values ranged from 1.3 to 11.5 x 10(3) micrograms/l. L1 was given twice daily at a daily dose of 55-80 mg/kg body weight and was continued for 10 months in two patients, 9 months in three, 7 months in two patients and 4 months in one patient. As previously observed with DF, each patient's urinary iron excretion (UIE) varied greatly from day to day. The mean UIE of the eight patients ranged from 11 to 49 mg/d (0.2-0.87 mmol/d) on subcutaneous DF and from 16 to 53 mg/d (0.28-0.95 mmol/d) on L1. Two patients excreted significantly more and one patient significantly less iron while on L1. If the UIE was calculated as mmol Fe/mmol creatinine there was no statistically significant difference. Serum ferritin values fluctuated widely in all, with a consistent downward trend in three, no change in four and an increase in one of two non-splenectomized patients. This patient's splenomegaly and need for transfusions continued to increase while on L1. No toxicities attributable to the drug were detected during the period of study and tolerance of the drug was excellent.

Desferrioxamine ototoxicity: evaluation of risk factors in thalassaemic patients and guidelines for safe dosage

Forty-seven patients with thalassaemia have been studied to define risk factors for development of sensorineural hearing loss, and to establish guidelines for safe chelation. Sensorineural hearing loss was only present in patients who had previously received desferrioxamine (DFO). The two most significant risk factors were the maximum dose of DFO previously received (P less than 0.01), and a serum ferritin of less than 2000 micrograms/l at that time (P less than 0.001). A therapeutic index obtained from the ratio of the mean daily dose of DFO mg/kg divided by the serum ferritin identifies patients with a ratio of greater than 0.025 as at risk of sensorineural hearing loss (P less than 0.001) and can be used as a guideline for safe DFO dosage. Follow-up audiometry of the affected patients over a 2-year period indicated that adjustment of the dose to a therapeutic index of less than 0.025 resulted in the stabilization of hearing loss in seven patients and improvement in two.