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 chelator N, 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 micromol/kg (149.3 mg/kg, n = 5), subcutaneously (sc) at a dose of 81 micromol/kg (37.3 mg/kg, n = 5), sc at 324 micromol/kg (n = 5), and sc at 162 micromol/kg (74.7 mg/kg) for 2 consecutive days for a total dose of 324 micromol/kg (n = 3). In addition, the monosodium salt of HBED in saline was administered to the monkeys sc at a single dose of 150 micromol/kg (64.9 mg/kg, n = 5) or at a dose of 75 micromol/kg every other day for three doses, for a total dose of 225 micromol/kg (n = 4). For comparative purposes, we have also administered deferoxamine (DFO) PO and sc in aqueous solution at a dose of 300 micromol/kg (200 mg/kg). In the iron-loaded Cebus apella monkey, whereas the PO administration of DFO or HBED even at a dose of 300 to 324 micromol/kg was ineffective, the sc injection of HBED in buffer or its monosodium salt, 75 to 324 micromol/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 micromol/kg; not 75, 150, or 300 micromol/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.     

Noise-induced hearing loss in young adults: the role of personal listening devices and other sources of leisure noise

CONCEPT: No consensus exists regarding the magnitude of the risk of noise-induced hearing loss (NIHL) associated with leisure noise, in particular, personal listening devices in young adults. OBJECTIVE: Examine the magnitude of hearing loss associated with personal listening devices and other sources of leisure noise in causing NIHL in young adults. STUDY DESIGN: Prospective auditory testing of college student volunteers with retrospective history exposure to home stereos, personal listening devices, firearms, and other sources of recreational noise. METHODS: Subjects underwent audiologic examination consisting of estimation of pure-tone thresholds, speech reception thresholds, and word recognition at 45 dB HL. RESULTS: Fifty subjects aged 18 to 30 years were tested. All hearing thresholds of all subjects (save one-a unilateral 30 dB HL threshold at 6 kHz) were normal, (i.e., 25 dB HL or better). A 10 dB threshold elevation (notch) in either ear at 3 to 6 kHz as compared with neighboring frequencies was noted in 11 (22%) subjects and an unequivocal notch (15 dB or greater) in either ear was noted in 14 (28%) of subjects. The presence or absence of any notch (small or large) did not correlate with any single or cumulative source of noise exposure. No difference in pure-tone threshold, speech reception threshold, or speech discrimination was found among subjects when segregated by noise exposure level. CONCLUSION: The majority of young users of personal listening devices are at low risk for substantive NIHL. Interpretation of the significance of these findings in relation to noise exposure must be made with caution. NIHL is an additive process and even subtle deficits may contribute to unequivocal hearing loss with continued exposure. The low prevalence of measurable deficits in this study group may not exclude more substantive deficits in other populations with greater exposures. Continued education of young people about the risk to hearing from recreational noise exposure is warranted.     

Iron uptake from ferrioxamine and from ferrirhizoferrin by germinating spores of Rhizopus microsporus

Mucormycosis caused by the fungus Rhizopus has been documented in iron overloaded patients and more particularly in dialysis patients, both when treated with desferrioxamine B (DFO). This iron and aluminium chelator is thought to play a role in the pathogenesis of this infection. We therefore investigated in vitro the cellular pharmacology of iron chelated by DFO in the fungus Rhizopus. In a medium, designed for fungal cultivation, Rhizopus microsporus var. rhizopodiformis takes up iron from ferric-DFO complex (55Fe.DFO) and from 55Fe.rhizoferrin, the siderophore synthesized and secreted by Rhizopus [Drechsel et al., Biol. Metals 4: 238-243, 1991]. In both cases, iron accumulation is partially saturable with the duration of exposure and the chelator concentration. Fe.DFO binds to Rhizopus; iron becomes trapped and remains associated with the fungus, whereas the iron-depleted siderophore is released in the extracellular medium. In a medium designed for mammalian cell cultivation and in the absence of human serum, the fungal iron accumulation both from 55Fe.DFO and from 55Fe.rhizoferrin is proportional to the chelator concentration. Human serum at 40% does not influence the iron accumulation from Fe.DFO but it significantly affects that from Fe.rhizoferrin which, in the presence of serum, only occurs at concentration > 5 microM. This difference finds its explanation in the iron transfer observed between Fe.rhizoferrin and seric apotransferrin, the latter making the metal unavailable to Rhizopus. By contrast, no iron transfer takes place between Fe.DFO and apotransferrin, allowing fungal iron utilization from this complex, even at very low concentrations. The iron uptake, being inhibited by NaN3 and KCN, is energy-dependent; being inhibited by bipyridyl, it requires prior reduction of ferric iron; being unaffected by the covalent linkage of Fe.DFO to albumin, it does not require the entry of Fe.DFO within the fungus. These in vitro results strongly suggest that, upon administration of DFO to iron overloaded or dialysis patients, the formed Fe.DFO is efficiently used as an iron source by Rhizopus, even in the presence of serum apotransferrin or rhizoferrin. The consequent promotion of the growth of Rhizopus helps explain the increased risk of mucormycosis in DFO-treated patients.     

Desferrioxamine and vitamin E protect against iron and MPTP-induced neurodegeneration in mice

To elucidate the neuroprotective effects of the iron chelator desferrioxamine (DFO) and the antioxidant vitamin E on excessive iron-induced free radical damage, a chronic iron-loaded mice model was established. The relationship between striatal iron content, oxidized to reduced glutathione ratio, hydroxyl radical (.OH) levels and dopamine concentrations were observed in DFO or vitamin E pretreated iron-loaded/1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated C57BL/6 mice. The results demonstrated that both DFO and vitamin E inhibit the iron accumulation and thus reverses the increase in oxidized glutathione (GSSG), oxidized to reduced glutathione ratios, .OH and lipid peroxidation levels. The striatal dopamine concentration was elevated to normal value. Our data suggested that: (1) iron may induce neuronal damage and thus excessive iron in the brain may contribute to the neuronal loss in PD; (2) iron chelators and antioxidants may serve as potential therapeutic agents in retarding the progression of neurodegeneration.     

Iron mobilisation and cellular protection by a new synthetic chelator O-Trensox

We tested a new synthetic, 8-hydroxyquinoline-based, hexadentate iron chelator, O-Trensox and compared it with desferrioxamine B (DFO). Iron mobilisation was evaluated: (i) in vitro by using ferritin and haemosiderin; DFO mobilised iron much more rapidly from ferritin at pH 7.4 than did O-Trensox, whereas at pH 4, ferritin and haemosiderin iron mobilisation was very similar with both chelators; (ii) in vitro by using cultured rat hepatocytes which had been loaded with 55Fe-ferritin; here DFO was slightly more effective after 100 hr than O-Trensox; (iii) in vivo administration i.p. to rats which had been iron-loaded with iron dextran; O-Trensox mobilised 51.5% of hepatic iron over two weeks compared to 48.8% for DFO. We also demonstrated the effect of O-Trensox in decreasing the entry of 55Fe citrate into hepatocyte cultures. The protective effect of O-Trensox against iron toxicity induced in hepatocyte cultures by ferric citrate was shown by decreased release of the enzymes lactate dehydrogenase (LDH), aspartate aminotransferase (AST), and alanine aminotranferase (ALT) from the cultures and, using electron paramagnetic resonance (EPR) measurements, decreased production of lipid radicals. O-Trensox was more effective than DFO in quenching hydroxyl radicals in an acellular system.     

Reactive oxygen species produced in metal-catalyzed oxidation of bis(trifluoromethyl)disulfide and protection by ZE

Bis(trifluoromethyl)disulfide (TFD), used as an industrial fumigant, was found to generate a thiyl free radical as seen by EPR/spin trapping. Oxygen appears to be an absolute requirement for radical production. The results obtained in this investigation implicate the production of thiyl and reactive oxygen species (ROS), superoxide radical anion and hydroxyl radicals, during TFD autoxidation. The rate of production of these free radical intermediates was found to increase in the presence of iron(III) and copper(II). In addition, the metal ion chelator DETAPAC and ROS scavengers ethanol, mannitol, and PEG-SOD/catalase were found to inhibit free radical production. Reactive oxygen species were not formed when a high-potency zinc plus antioxidant, ZE caps, was present. These results provide support for the pro-oxidation of TFD and a protective role for zinc.     

Pyridoxal isonicotinoyl hydrazone and its analogs: potential orally effective iron-chelating agents for the treatment of iron overload disease

At present, the only iron (Fe) chelator in clinical use for the treatment of Fe overload disease is the tris-hydroxamate deferoxamine (DFO). However, DFO suffers from a number of disadvantages, including the need for subcutaneous infusion (12 to 24 hours a day, 5 or 6 times per week), its poor intestinal absorption, and high cost. Therefore, there is an urgent need for an efficient, economical, and orally effective Fe chelator. Pyridoxal isonicotinoyl hydrazone (PIH) is a tridentate Fe-chelating agent that shows high Fe chelation efficacy both in vitro in cell culture models and also in vivo in rats and mice. In addition, this chelator is relatively nontoxic, economical to synthesize, and orally effective, and it shows high selectivity and affinity for Fe. However, over the last 10 years the development of PIH and its analogs has largely been ignored because of justifiable interest in other ligands such as 1,2-dimethyl-3-hydroxypyrid-4-one (L1). Unfortunately, recent clinical trials have shown that significant complications occur with L1 therapy, and it is controversial whether this chelator is effective at reducing hepatic Fe levels in patients. Because of the current lack of a clinically useful Fe chelator to replace DFO, PIH and its analogs appear to be potential candidate compounds that warrant further investigation. In this review we will discuss the studies that have been performed to characterize these chelators at the chemical and biologic levels as effective agents for treating Fe overload. The evidence from the literature suggests that these ligands deserve further careful investigation as potential orally effective Fe chelators.     

Adverse health effects of PM10 particles: involvement of iron in generation of hydroxyl radical

OBJECTIVES: Environmental particles < 10 microns average aerodynamic diameter (PM10) are associated with mortality, exacerbation of airways diseases, and decrement in lung function. It is hypothesised that PM10 particles, along with other pathogenic particles, generate free radicals at their surface in reactions involving iron, and that this is a factor in the pathogenicity of PM10 particles. Identification of free radical activity in PM10 and examination of the content and role of iron in this process was undertaken. METHODS: Free radical activity was detected with a supercoiled plasmid, phi X174 RF1 DNA, and measured as scission of the supercoiled DNA (mediated by free radicals) by scanning laser densitometry. The role of the hydroxyl radical was confirmed by the use of the specific scavenger mannitol, and the role of iron investigated with the iron chelator desferrioxamine-B (DSF-B). Iron released from PM10 particles at pH 7.2 and pH 4.6 (to mimic conditions on the lung surface and in macrophage phagolysosomes, respectively) was assessed spectrophotometrically with the Fe++ chelator ferrozine and the Fe+ + + chelator DSF-B. RESULTS: PM10 particles showed significant free radical activity by their ability to degrade supercoiled DNA. A substantial part of this activity was due to the generation of hydroxyl radicals, as shown by partial protection with mannitol. Similarly, DSF-B also conferred protection against the damage caused to plasmid DNA indicating the role of iron in generation of hydroxyl radicals. Negligible Fe++ was released at either pH 7.2 or pH 4.6 by contrast with Fe+ + +, which was released in substantial quantities at both pHs, although twice as much was released at pH 4.6. CONCLUSIONS: PM10 particles generate the hydroxyl radical, a highly deleterious free radical, in aqueous solution. This occurs by an iron dependent process and hydroxyl radicals could play a part in the pathogenicity of PM10 particles. Iron release was greatest at the pH of the lysosome (pH 4.6) indicating that iron may be mobilised inside macrophages after phagocytosis, leading to oxidative stress in the macrophages.     

Survival of AIDS patients according to type of AIDS-defining event. The AIDS in Europe Study Group

The ability of hemoglobin, modified by H2O2 or HOCl/OCl-, to induce lipid peroxidation (LPO) in low density lipoproteins (LDL) was studied, as well as the effects of haptoglobin. It was found that Hb modification by H2O2 or HOCl/OCl- increased generation of TBA-reactive substances in low density lipoproteins. Modified Hb was as double or more reactive compared to intact Hb. Free radical scavengers (ethanol and mannitol) gave no effect on LPO in LDL. On the other hand, ferric iron chelator desferrioxamine decreased LPO 5-6 times. Ferrous iron chelator- o-phenanthroline was effective only in the case of LPO, induced by H2O2 modified Hb. Haptoglobin (plasma protein forming complexes with Hb) decreased LPO induced by both intact or HOCl/OCl modified Hb. The results of the paper show that modification of Hb by H2O2 or HOCl/OCl- increase the ability of Hb to induce LPO in LDL, probably due to metHb, ferrylHb or free iron production.     

Characterisation and mapping of the human SOX14 gene

The effects of nimodipine, a calcium channel blocker, on noise-induced hearing loss were examined in gerbils. Animals were implanted subcutaneously with a timed-release pellet containing either nimodipine (approximately 10 mg/kg/day) or placebo and exposed to either 102 or 107 dBA noise. Serum levels were tested in two subjects and were in the range known to protect humans from cerebral artery vasospasm and ischemia-related neurologic deficits. Nimodipine and control groups had similar amounts of noise-induced (a) permanent threshold shift; (b) reductions in distortion product otoacoustic emissions; (c) reductions in tuning and suppression of the compound action potential; and (d) loss of outer hair cells. The results suggest that nimodipine, at a dose which results in clinically relevant serum levels, does not provide protection from the effects of moderately intense noise exposures.     

Differential effects of diazepam on anxiety in streptozotocin induced diabetic and non-diabetic rats

In the absence of added Fe2+, the ATPase activity of isolated Schizosaccharomyces pombe plasma membranes (5-7 mumol P(i) per mg protein per min) is moderately inhibited by H2O2 in a concentration-dependent manner. Sizable inactivation occurs only at 50-80 mmol/L H2O2. The process, probably a direct oxidative action of H2O2 on the enzyme, is not induced by the indigenous membrane-bound iron (19.3 nmol/mg membrane protein), is not affected by the radical scavengers mannitol and Tris, and involves a decrease of both the K(m) of the enzyme for ATP and the V of ATP splitting. On exposing the membranes to the Fenton reagent (50 mumol/L Fe2+ + 20 mmol/L H2O2), which causes a fast production of HO. radicals, the ATPase is 50-60% inactivated and 90% of added Fe2+ is oxidized to Fe3+ within 1 min. The inactivation occurs only when Fe2+ is added before H2O2 and can thus bind to the membranes. The lack of effect of radical scavengers (mannitol, Tris) indicates that HO. radicals produced in the bulk phase play no role in inactivation. Blockage of the inactivation by the iron chelator deferrioxamine implies that the process requires the presence of Fe2+ ions bound to binding sites on the enzyme molecules. Added catalase, which competes with Fe2+ for H2O2, slows down the inactivation but in some cases increases its total extent, probably due to the formation of the superoxide radical that gives rise to delayed HO. production.     

Attenuation of neomycin ototoxicity by iron chelation

Increasing evidence suggests that aminoglycoside ototoxicity is mediated by the formation of an aminoglycoside-iron complex and that the creation of this complex is a preliminary step in generation of free radical species and subsequent hair cell death. In this study we have assessed the ability of the iron chelator deferoxamine to attenuate the hearing loss induced by an ototoxic dose of the aminoglycoside neomycin (100 mg/kg per day for 14 days). Experiments were carried out on pigmented guinea pigs weighing 250 to 300 g. Changes in auditory sensitivity were characterized by monitoring shifts in compound action potential (CAP) thresholds, recorded through indwelling electrodes implanted at the round window, vertex, and contralateral mastoid. Results show that animals receiving neomycin alone suffered a mean threshold shift exceeding 35 dB at all test frequencies (2.0, 4.0, and 8.0 kHz) 30 days after initiation of treatment. In comparison, all animals receiving cotherapy of neomycin and deferoxamine (150 mg/kg twice daily for 14 days) maintained their CAP threshold, suggesting significant protection from neomycin ototoxicity. A statistical comparison of treatment groups showed that in the animals receiving cotherapy with neomycin and deferoxamine, deferoxamine produced a significant protective effect against neomycin-induced ototoxicity (P < 0.001). These results provide further evidence of the intrinsic role of iron in aminoglycoside ototoxicity and suggest that deferoxamine may have a therapeutic role in attenuating the cytotoxic action of aminoglycoside antibiotics.     

Hair cell loss from acoustic trauma in chloroquine-treated red, black and albino guinea pigs

In order to further elucidate the relationship between noise-induced hearing loss and pigmentation, a two-factor study was designed. Albino, red and black guinea pigs were divided into controls and chloroquine-treated groups and exposed to 1 kHz noise, 105 dB SPL, for 72 hours. One month later the animals were sacrificed and the loss of hair cells evaluated. The red guinea pigs developed a greater hair cell loss (OHC) in all three OHC rows than black or albino animals. Black and albino groups showed equal amounts of OHC loss. A high dosage of chloroquine seemed to reduce the OHC loss in albino, but not in black or red guinea pigs. The greater OHC loss in red compared with black animals is in accordance with the original hypothesis that melanin protects the inner ear against noise trauma. However, as red guinea pigs developed greater OHC loss than albinos, it is obvious that the original hypothesis needs to be modified to consider also the different melanin types, i.e., the black eumelanin and the red pheomelanin. The present results are interpreted as a toxic interaction in the strial melanocytes between pheomelanin and noise. It is suggested that the pathophysiology of noise-induced hearing loss involves cochlear mechanisms related to radical oxygen species (ROS) as melanin both generates and neutralizes ROS. A hypothesis about a linkage between dopamine, noise trauma and the cochlear melanocyte system is discussed.     

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

The prospect of selecting oral alpha-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 (Kpar) 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 (L1NAII), 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.     

Iron supplementation enhances response to high doses of recombinant human erythropoietin in preterm infants

AIMS: To determine whether iron supplementation would enhance erythropoiesis in preterm infants treated with high doses of human recombinant erythropoietin (r-HuEPO). METHODS: Sixty three preterm infants were randomly allocated at birth to one of three groups to receive: r-HuEPO alone, 1200 IU/kg/week (EPO); or r-HuEPO and iron, 1200 IU/kg/week of r-HuEPO plus 20 mg/kg/week of intravenous iron (EPO + iron); or to serve as controls. All three groups received blood transfusions according to uniform guidelines. RESULTS: Infants in the EPO + iron group needed fewer transfusions than controls--mean (95% CI) 1.0 (0.28-1.18) vs 2.9 (1.84-3.88) and received lower volumes of blood--mean (95% CI) 16.7 (4.9-28.6) vs 44.4 (29.0-59.7) ml/kg. The EPO group also needed lower volumes of blood than the controls--mean (95% CI) 20.1 (6.2-34.2) vs 44.4 (29.0-59.7) ml/kg, but the same number of transfusions, 1.3 (0.54-2.06) vs 2.9 (1.84-3.88). Reticulocyte and haematocrit values from postnatal weeks 5 to 8 were higher in the EPO + iron than in the EPO group, and both groups had higher values than the controls. Mean (SEM) plasma ferritin was lower in the EPO group-65 (55) micrograms/l than in the EPO + iron group 780 (182) micrograms/l, and 561 (228) micrograms/l in the control infants. CONCLUSIONS: Early administration of high doses of r-HuEPO with iron supplements significantly reduced the need for blood transfusion. Intravenous iron (20 mg/kg/week in conjunction with r-HuEPO yielded a higher reticulocyte count and haematocrit concentration after the forth week of life than r-HuEPO alone. Infants treated with r-HuEPO alone showed signs of reduced iron stores.     

Cardioprotective effect of alpha-tocopherol, ascorbate, deferoxamine, and deferiprone: mitochondrial function in cultured, iron-loaded heart cells

Because mitochondrial inner membrane respiratory complexes are important targets of iron toxicity, we used iron-loaded rat heart cells in culture to study the beneficial effect on mitochondrial enzymes of the iron chelators deferoxamine (DFO) and deferiprone (L1) and of antioxidants and reducing agents (ascorbate and alpha-tocopherol). Reduced nicotinamide adenine dinucleotide-cytochrome c oxidoreductase (complex I-III) and succinate dehydrogenase were the most-sensitive indicators of iron toxicity and cardioprotective effect. Although at concentrations below 0.3 mmol/L the iron-mobilizing effect of L1 was less than that of DFO, both were equally effective in protecting or restoring mitochondrial respiratory enzyme activity. At 1.0 mmol/L, L1 toxicity was manifested in respiratory enzyme inhibition, whereas DFO had no such effect. Ascorbate (0.057 to 5.7 mmol/L) had a mild cardioprotective effect at the highest concentration only, in association with decreased cellular iron uptake. By contrast, alpha-tocopherol (0.023 mmol/L) completely inhibited mitochondrial iron toxicity without affecting iron uptake or release, and irrespective of whether it was used before, during, or after in vitro iron loading. These observations illustrate the usefulness and limitations of iron chelators and other agents used for preventing iron toxicity to the heart and other vital organs, and they underline the need for exploring in more detail the effects of these agents in the clinical setting.     

Caco-2 cell permeability of a new (hydroxybenzyl)ethylenediamine oral iron chelator: correlation with physicochemical properties and oral activity

This study describes the transport of CGP 75254A, a novel oral iron chelator, across Caco-2 cells in an attempt to model intestinal epithelial cell permeability in man. CGP 75254A was dosed to the apical side of Caco-2 cell monolayers, together with [14C]mannitol as an internal permeability standard. The apparent permeability (Papp) was calculated from the cumulative appearance of drug in the basolateral fluid with time. The [14C]mannitol Papp indicated that the Caco-2 monolayers remained intact and that the iron chelator was not toxic to the cells. Permeabilities of CGP 75254A were compared with the Caco-2 permeabilities of compounds of known absorption in man. The results predict that absorption of CGP 75254A is likely to be virtually complete at pH values between 5.5 and 7.0. However, at pH 8.0 permeability is predicted as negligible. Cell permeability data are in full accordance with key physicochemical properties of CGP 75254A and suggest that the drug is passively absorbed. The results, which suggest likely quantitative absorption in vivo, are supported by preliminary pharmacological experiments in marmosets.     

Iron-balance and dose-response studies of the oral iron chelator 1,2-dimethyl-3-hydroxypyrid-4-one (L1) in iron-loaded patients with sickle cell disease

Several life-threatening complications of the common disorder sickle cell disease require management with red blood cell transfusions and, hence, long-term iron-chelating therapy. The efficacy of the oral iron chelator 1,2-dimethyl-3-hydroxypyrid-4-one (L1) has not previously been determined in patients with sickle cell disease. We compared the efficacy of L1 to that of standard-dose subcutaneous deferoxamine in four regularly transfused patients with homozygous sickle cell disease, who had evidence of severe iron overload and a history of poor compliance with deferoxamine. Determination of 24-hour urinary iron excretion conducted over 5 days immediately after transfusion showed that the mean daily urinary iron excretion induced by L1 at 75 mg/kg/d (0.48 +/- 0.23 mg/kg) was equivalent to that induced by deferoxamine at 50 mg/kg/d (0.39 +/- 0.06 mg/kg). In two of three patients studied, a significant (P < .025) increase in mean daily urinary iron excretion was achieved when the dose of L1 was increased to 100 mg/kg/d. Total iron balance studies, which quantitated both urinary and stool iron excretion on L1 and deferoxamine, determined that mean total daily iron excretion induced by deferoxamine (0.88 +/- 0.05 mg/kg) was significantly greater (P < .05) than that induced by L1 (0.53 +/- 0.17 mg/kg), attributable to the significantly greater stool iron excretion during deferoxamine treatment (0.50 +/- 0.16 mg/kg/d) compared with that measured during L1 treatment (0.12 +/- 0.08 mg/kg/d, P < .01). Stool iron excretion accounted for a significantly greater percentage of total iron excretion during deferoxamine treatment (59% +/- 20%) than during L1 treatment (23% +/- 14%, P < .01). These iron balance studies are the first to compare total iron excretion induced by L1 with that achieved by deferoxamine. They demonstrate that the mean total daily iron excretion during L1 treatment (0.53 +/- 0.17 mg/kg) is sufficient to maintain net negative iron balance in most regularly transfused patients with sickle cell disease. Because long-term compliance with L1 has been shown previously to be superior to that with deferoxamine in patients with homozygous beta-thalassemia, the use of L1 should increase the long-term effectiveness of iron chelation in patients with sickle cell disease.     

Liver iron and fibrosis during long-term treatment with deferiprone in Swiss thalassaemic patients

Serum ferritin levels, hepatic histology and iron concentration were studied in a 'veteran' group of seven Swiss beta-thalassaemic patients after 93-99 months of treatment with the oral iron chelator deferiprone (L1), and another four patients who had received 54-82 months of L1 therapy. Despite continuous compliance, unexplained resurgence of serum ferritin levels occurred in 4/7 patients of the 'veteran' group after 4-5 years on L1. In three of these a concomitant increase of liver iron was also observed. Hepatic histology revealed significantly higher degrees of fibrosis in 6/11 hepatitis C (HC)-positive patients (fibrosis scores 1-5, mean 3.0) than in the HC-negative group (fibrosis score 0-2, mean 0.8). Two HC-negative patients had no detectable fibrosis after 98 and 93 months on deferiprone. Therefore the hepatic pathology in these patients cannot definitely be attributed as a side-effect of deferiprone. Chronic active hepatitis C and the accumulation of iron are the major causative factors to be considered.