Reversal of desferrioxamine induced auditory neurotoxicity during treatment with Ca-DTPA

Hearing Loss in Beta-Thalassemia: Systematic Review

In the last half century, the life expectancy of beta-thalassemia patients has strikingly increased mostly due to regular blood transfusions and chelation treatments. The improved survival, however, has allowed for the emergence of comorbidities, such as hearing loss, with a non-negligible impact on the patients' quality of life. This thorough review analyzes the acquired knowledge regarding hearing impairment in this hereditary hemoglobinopathy, aiming at defining its prevalence, features, course, and possible disease- or treatment-related pathogenic factors. Following PRISMA criteria, we retrieved 60 studies published between 1979 and 2021. Diagnostic tools and criteria, forms of hearing impairment, correlations with beta-thalassemia phenotypes, age and sex, chelation treatment and laboratory findings including iron overload, were carefully searched, analyzed and summarized. In spite of the relatively high number of studies in the last 40 years, our knowledge is rather limited, and large prospective studies with homogeneous diagnostic tools and criteria are required to define all the aforementioned issues. According to the literature, the overall prevalence rate of hearing impairment is 32.3%; age, sex, and laboratory findings do not seem to correlate with hearing deficits, while the weak relationship with clinical phenotype and chelation treatment seems to highlight the presence of further yet to be identified pathogenic factors.

Safety profiles of iron chelators in young patients with haemoglobinopathies

BACKGROUND

This review describes the safety of deferoxamine (DFO), deferiprone (DFP), deferasirox (DFX) and combined therapy in young patients less than 25 yr of age with haemoglobinopathies.

METHODS

Searches in electronic literature databases were performed. Studies reporting adverse events associated with iron chelation therapy were included. Study and reporting quality was assessed using AHRQ Risk of Bias Assessment Tool and McMaster Quality Assessment Scale of Harms. Prospective clinical studies were pooled in a random-effects meta-analysis of proportions.

RESULTS

Safety data of 2040 patients from 34 studies were included. Ninety-two case reports of 246 patients were identified. DFX (937 patients) and DFP (667 patients) possess the largest published safety evidence. Fewer studies on combination regimens are available. Increased transaminases were seen in all regimens (3.9-31.3%) and gastrointestinal disorders with DFP and DFX (3.7-18.4% and 5.8-18.8%, respectively). Therapy discontinuations due to adverse events were low (0-4.1%). Reporting quality was selective and poor in most of the studies.

CONCLUSION

Iron chelation therapy is generally safe in young patients, and published data correspond to summary of product characteristics. Each iron chelation regimen has its specific safety risks. DFO seems not to be associated with serious adverse effects in recommended doses. In DFP and DFX, rare, but serious, adverse reactions can occur. Data on combined therapy are scarce, but it seems equally safe compared to monotherapy.

Incidence of ototoxicity in pediatric patients with transfusion-dependent thalassemia who are less well-chelated by mono- and combined therapy of iron chelating agents

Ototoxicity due to iron chelation therapy, especially deferoxamine (DFO), is frequently observed in patients who have a higher chelation index (>0.025). However, there is limited data on patients who are less well-chelated and on other chelating regimens, including deferiprone (L1), deferasirox (DFX), and a combination of DFO and L1. To determine the incidence of ototoxicity from iron chelators, we retrospectively analyzed our clinical records from January 1997 to December 2010. All transfusion-dependent thalassemia (TDT) patients received iron chelation therapy with mono DFX, DFO, L1, or a combination. All patients underwent routine otolaryngologic examination and pure-tone audiometry before starting each chelation regimen and were regularly followed every 6 months. One hundred thalassemic patients were enrolled and analyzed (48 males and 52 females), with a mean age of 12.11 ± 4.48 years (range 2.5-22.5 years). Total summative duration of iron chelation therapy in all patients was 596.50 years. Nine patients were found to have conductive hearing loss. Sensorineural hearing loss (SNHL) was identified in seven patients but only four were determined to be associated with iron chelators; three patients were detected while undergoing DFO therapy and one patient with L1 therapy. None of patients undergoing DFO therapy had reached over the levels of chelation index. In our resource-limited setting with poor treatment compliance, there was a rather low incidence of ototoxicity after exposure to iron chelators. However, a routine audiometry remains recommended for early detection and intervention since SNHL still develops and results in a long-term morbidity.

Audiologic and vestibular assessment in patients with β-thalassemia major receiving long-term transfusion therapy

BACKGROUND

Life-long transfusion therapy with chelators is a treatment choice for patients with β-thalassemia major. Some investigators have proposed auditory impairment related to the use of deferoxamine, but the mechanisms remain unclear and whether or not deferiprone has similar side effects needs to be evaluated.

PROCEDURE

Thirty-seven patients with β-thalassemia major who received regular transfusion in our hospital were enrolled. Chelation agents, including deferoxamine and deferiprone, were used. To assess audiologic function, otoscopy, pure tone audiometry (PTA), tympanometry, transient evoked oto-acoustic emission (TEOAE), and auditory brainstem response (ABR) were conducted. Bithermal caloric test was performed to evaluate vestibular function.

RESULTS

All of the 37 patients had normal findings on otoscopic evaluation and their tympanograms were type A. Thirteen patients (35.1%) had hearing impairment at one or more frequencies as detected by PTA. Compared to those without hearing impairment, patients with hearing impairment had lower serum ferritin levels (P = 0.01). Seven of 21 patients (33.3%) failed to pass the TEOAE, while 13 (61.9%) had abnormal ABR findings. Sixteen patients (80%) had canal paresis in the caloric test.

CONCLUSIONS

The incidence of auditory impairment and vestibular dysfunction was high in patients with β-thalassemia major receiving long-term transfusion therapy. Potential lesions of auditory impairment may exist anywhere along the auditory pathway, from the inner ear to the brainstem. Lower serum ferritin levels may be associated with hearing impairment. Therefore, regular check-ups of serum ferritin levels and periodic audiologic assessment are mandatory.

Marrow proliferation as a cause of hearing loss in beta-thalassaemia major

OBJECTIVE

The aim of this report was to highlight the fact that hearing loss in thalassaemia patients can be related to marrow expansion affecting the ossicles, resulting in a conductive loss.

CASE REPORT

A six-year-old boy with transfusion-dependent beta-thalassaemia developed a unilateral hearing loss shortly after commencing desferrioxamine therapy. Ototoxicity was assumed, but the deficit was later found to be of a conductive nature, due to marrow proliferation within the ossicular chain as a consequence of the disease process--a phenomenon previously unreported in the literature.

CONCLUSION

It is important to elucidate the precise nature of new onset hearing loss in patients receiving iron chelation therapy, in order to avoid unnecessary cessation of much needed medication, on the assumption of ototoxicity.

Neurophysiologic and intellectual evaluation of beta-thalassemia patients

In order to detect involvement of the central and peripheral nervous system in beta-thalassemic patients, 32 children and young adults (mean age 14.5 +/- 6.4 years) participated in a systematic neurophysiologic and intellectual prospective study. All patients were in a regular transfusion program, receiving subcutaneous desferrioxamine chelation and maintaining a mean serum ferritin level of 2,101.56 +/- 986.32 ng/ml. Study patients underwent neurophysiologic evaluation consisting of brainstem auditory, visual and somatosensory evoked potential examination (BAEP, VEP, SEP) as well as motor and sensory nerve conduction velocity studies (MCV, SCV). Additionally, the verbal, performance and total IQ were assessed in patients under 16 years of age using the Weschler Intelligence Scale for Children (WISC-III). The incidence of abnormal BAEP, VEP, SEP and NCVs was 0, 3.12, 3.12 and 18.75%, respectively, findings comparative to or better than previously reported. On the contrary, the prevalence of abnormal total IQ score was considerably high (36.4%), not correlating, however, to any of the parameters assessed (age, sex, ferritin level, BAEP, VEP, SEP, NCV). Factors associated with chronic illness, rather than the disease per se, could play a potential role in the development of cognitive dysfunction in beta-thalassemia patients.

Auditory and visual toxicity during deferoxamine therapy in transfusion-dependent patients

Deferoxamine is a chelating agent that has extended the life expectancy of patients with thalassemia. In the 1980s, many investigators reported otologic and visual toxicity caused by deferoxamine. In July 1999 and 2 years later, the authors performed audiologic and ophthalmologic assessments in 30 transfusion-dependent patients receiving deferoxamine therapy (40-50 mg/kg per dose, subcutaneously for 8-10 hours, 4-7 days per week). In 1999, six patients (20%) had deferoxamine-related hearing impairment (>25 dB), all at high frequencies. Because the authors believed the benefits of chelation therapy outweighed the risk of ototoxicity, the dose of deferoxamine was not reduced. Two years later, the hearing impairment had not progressed in any of the patients. There was no association between ototoxicity and ferritin level. No patients had abnormalities of visual acuity or funduscopy in either 1999 or 2001. Based on this experience, deferoxamine at doses lower than 50 mg/kg/d was safe for the eyes and slightly toxic to the ears. The ototoxicity probably relates to individual susceptibility. Regular monitoring of auditory function and close follow-up of abnormal findings are recommended. According to this limited experience, reducing the dose or withdrawing deferoxamine might not be necessary if the hearing loss is stable in the face of ferritin levels above 2,000 ng/mL. Because of the relatively small patient numbers, more data are needed to confirm these conclusions.

Structure-activity relationships among desazadesferrithiocin analogues

Desferrithiocin, a natural product iron chelator (siderophore), offers an excellent platform from which to construct orally active iron chelators which have a good therapeutic window. A systematic structure-activity study on desferrithiocin identified the structural fragments necessary for the compound's oral iron-clearing activity. There are strict requirements regarding the distance between the ligating centers; they cannot be altered without loss of efficacy. The thiazoline ring must remain intact. Benz-fusions, which were designed to improve the ligands' tissue residence time and possibly iron-clearing efficiency, are ineffective. The maintenance of an (S)-configured C-4 carbon is optimal in the design of desferrithiocin-based iron chelators. With this information in hand, alteration of the redox potential of the aromatic ring was initiated. Introduction of a hydroxy in the 4'-position of at least three different desazadesferrithiocin analogues resulted in moderate to small changes in iron clearing efficacy yet dramatic reductions in the toxicity of the compounds were observed. Although the toxicity studies of these desferrithiocin analogues are continuing, it is clear that it is possible to alter a siderophore in such a way as to ameliorate its toxicity profile while maintaining its iron-clearing properties.

Neurophysiologic evaluation of long-term desferrioxamine therapy in beta-thalassemia patients

Forty patients with beta-thalassemia major (BTM), between 11 and 19 years of age and maintained on long-term desferrioxamine (DFO) treatment, were examined by evoked potential and nerve conduction velocity studies to investigate a possible involvement of the auditory, visual, somatosensory, or peripheral nervous pathways. Pathologic findings in brainstem auditory-, visual-, and somatosensory-evoked potentials, and nerve conduction velocity studies were demonstrated in 25%, 15%, 7.5%, and 25% of the patients, respectively, whereas 15% demonstrated involvement of multiple neural pathways. Subclinical involvement of the auditory pathway was statistically associated with higher mean daily DFO dose and longer duration of DFO therapy, whereas abnormalities regarding the somatosensory pathways were related to older age, longer mean duration of DFO therapy, and lower serum copper levels. Involvement of the peripheral nervous system was related to lower serum copper levels. Multiple involvement of neural pathways was related to longer mean duration of DFO therapy. We conclude that risk factors related to long-term DFO treatment are only partly responsible for the subclinical involvement of neural pathways demonstrated in beta-thalassemia major patients.

IRC011, a New Synthetic Chelator With Selective Interaction With Catabolic Red Blood Cell Iron: Evaluation in Hypertransfused Rats With Hepatocellular and Reticuloendothelial Radioiron Probes and in Iron-Loaded Rat Heart Cells in Culture

A major consideration in the selection of new and improved iron chelators for clinical use is preferential interaction with the most toxic iron compartment. We describe the biologic properties of a new synthetic hexadentate iron chelator (IRC011) that is a substituted polyaza compound. Unlike deferoxamine (DF ), the polyaza structure of IRC011 does not contain any readily hydrolyzable covalent bonds and is anticipated to resist in vivo biotransformation. In the present studies, the ability of IRC011 to remove radioiron from iron-loaded heart cells in vitro was similar to DF, with a decrease to 20.0 ± 0.4% and 19.7 ± 0.5% of initial values after 24 hours of incubation with 0.3 mmol/L of DF or IRC011, respectively. The in vivo interaction of IRC011 with specific iron stores was studied in hypertransfused rats using selective labeling of reticuloendothelial (RE) iron stores with 59Fe-heat-denatured red blood cells (DRBCs) and of hepatocellular stores with 59Fe-ferritin. The pattern of radioiron excretion with IRC011 was quite different from that with DF. Although with both compounds, hepatocellular iron excretion was through the bile, whereas RE iron excretion was mainly in the urine, the magnitude of these effects was quite different. After the administration of a single parenteral dose of 200 mg/kg representing a 53% higher iron-binding capacity for IRC011 compared with DF, 48-hour urinary excretion of RE iron with IRC011 was 22.8% ± 1.1% (% of total body 59Fe), but only 6.0% ± 3.6% with DF. By contrast, the corresponding biliary excretion of hepatocellular radioiron was 14.2% ± 3.2% with DF, but only 0.7% ± 0.3% with IRC011. Thus, the new iron chelator IRC011 is distinguished from DF by the following features: (1) a higher affinity to Fe(III), (2) anticipated resistance to in vivo catabolism, (3) preferential interaction with RE iron derived from RBC breakdown, and (4) selective renal excretion. Because RBC breakdown is the most likely source of the toxic nontranferrin plasma iron, IRC011 may be a useful iron chelator for protecting vital organs from peroxidative damage.

In vitro inhibition of human cytomegalovirus replication by calcium trinatrium diethylenetriaminepentaacetic acid

Desferrioxamine (DFO) has been shown to inhibit human cytomegalovirus (CMV) replication in vitro. In the present study, we compared antiviral effects of DFO in human foreskin fibroblast (HFF) cells against several CMV strains with those of other chelators that interact with iron and other ions from different pools. DFO, a hydrophilic chelator, that may chelate both intracellular and extracellular ions inhibited production of CMV late antigen at 50% effective concentrations (EC50S) ranging from 6.2 to 8.9 microM. EC50S for calcium trinatrium diethylenetriaminepentaacetic acid (CaDTPA) ranged from 6.1 to 9.9 microM. EC50S for 2,2'-bipyridine (BPD), a hydrophobic chelator, which diffuses into cell membranes ranged from 65 to 72 microM. Concentrations which inhibited BrdU incorporation into cellular DNA by 50% (IC50S) ranged from 8.2 to 12.0 microM (DFO), from 65 to 89 microM (BPD), and from 139 to 249 microM (CaDTPA). CaDTPA was the only chelator which completely inhibited production of infectious virus in HFF and vascular endothelial cells at concentrations which had no significant effects on cellular DNA synthesis and growth. Addition of stoichiometric amounts of Fe3+ in the culture medium of HFF cells completely eliminated antiviral effects of DFO while antiviral effects of CaDTPA and BPD were only moderately affected. Fe2+ and Cu2+ were stronger inhibitors of CaDTPA than Fe3+; however, Mn2+ and Zn2+ completely suppressed antiviral effects of CaDTPA. The results show that CaDTPA is a novel nontoxic inhibitor of CMV replication. The antiviral activity of CaDTPA is suppressed by metal ions with a decreasing potency order of Mn2+/Zn2+ > Fe2+ > Cu2+ > Fe3+.

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.

Zinc concentration in patients with iron overload receiving oral iron chelator 1,2-dimethyl-3-hydroxypyrid-4-one or desferrioxamine

AIMS

To determine the changes in serum zinc concentration and the extent of urinary zinc excretion in patients with iron overload receiving the oral iron chelator 1,2-dimethyl-3-hydroxypyrid-4-one (L1) or desferrioxamine (DFX), and to correlate these results with blood glucose concentration.

METHODS

Serum zinc and ferritin concentrations, urinary zinc and iron excretion were regularly assayed in 39 patients and the glucose tolerance test (GTT) was performed in each patient. Patients were segregated according to their GTT into normal, diabetic, and those with an abnormal GTT. The mean of L1- or DFX associated urinary zinc excretion for each group was determined and compared with the other two groups and with normal value. L1 associated urinary zinc excretion was also compared with L1 dose, serum ferritin values, and urinary iron excretion.

RESULTS

Both DFX and L1 were associated with a significantly increased urinary zinc excretion (15.1 (7.3) mumol/24 hours, 11.1 (6.0) mumol/24 hours, respectively) compared with normal subjects. In patients receiving DFX this increase only occurred in patients with diabetes mellitus. Both diabetic and non-diabetic patients receiving L1 treatment excreted more zinc than normal. Diabetic patients receiving L1 or DFX excreted more zinc than non-diabetics receiving the same treatment. No correlation was found between urinary zinc excretion and L1 dose or patients' serum ferritin concentrations. In seven patients receiving long term L1 treatment a fall in serum zinc was observed from an initial 13.6 (1.6) mumol/l to a final 9.6 (0.8) mumol/l. In one patient this was associated with symptoms of dry skin and itchy skin patches requiring treatment with oral zinc sulphate.

CONCLUSIONS

In contrast to DFX, L1 treatment is associated with increased zinc loss. This, however, is modest and does not lead in most patients to subnormal serum zinc concentrations. In a few patients whose negative zinc balance may give rise to symptoms, zinc supplementation rapidly corrects the deficit.

Neurophysiologic study of beta-thalassemia patients

Neurophysiologic investigations were performed in 34 Chinese patients with beta-thalassemia major maintained on long-term desferrioxamine treatment to look for subclinical toxicity in the auditory, visual, peripheral, or central neural pathways. In the auditory pathway study, four patients (12%) had mild sensorineural hearing impairment. Two patients (6%) had increased P 100 latencies in the visual evoked potential study, and nine patients (26%) had abnormal electroretinogram results. All had normal electrooculograms. Ophthalmoscopic examination was abnormal in three patients (9%), and three (9%) had a visual field defect. In the peripheral or central nervous pathways, seven patients (21%) had sensory neuropathy, of which three cases were probably related to diabetes mellitus. All had normal motor conduction velocities. Four patients (12%) had increased cortical latencies of median or posterior tibial somatosensory evoked potential. Abnormalities in multiple neural pathways were seen in four patients (12%). There was a significant association between subclinical toxicity to the peripheral or central nervous systems and serum ferritin level (P < .03) and the presence of diabetes mellitus (P < .002). There was no significant relationship between the age, dosage, or duration of desferrioxamine used and the increased risk of neurotoxicity to the auditory, visual, peripheral, or central nervous systems. There was also no association between the risk of neurotoxicity and the serum zinc, copper, or fructosamine levels.

Deferoxamine (desferrioxamine). New toxicities for an old drug

Iron is an essential element for body homoeostasis, but there is no effective mechanism for elimination of an excess of this mineral. Deferoxamine (desferrioxamine) is currently the treatment of choice for iron overload states from both acute iron intoxication and transfusion-dependent anaemias. The pharmacokinetics of deferoxamine are confounded both by its ability to chelate endogenous and exogenous iron and by the laboratory techniques used for its determination. Its iron-complex (ferrioxamine) has different pharmacokinetic properties. Because of its effectiveness, the use of deferoxamine is becoming more common, involving long term and high dose regimens. As a result of this, more and more toxicities that were not known in the past have been described and characterised. The most serious of these include hypotension, renal insufficiency, neurotoxicity, growth retardation and opportunistic infections: some of these side effects may be attributed to or aggravated by ferrioxamine. The pharmacological and toxicological literature on deferoxamine, and possible mechanisms for its toxicity, are reviewed and discussed.

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.

The toxic effects of desferrioxamine

DF has a low general toxicity, perhaps because of its low lipid solubility, Kpart 0.01 (Porter et al, 1988b). This feature of the molecule may prevent it from penetrating most cells of the body. It appears that there may be a specific mechanism of uptake of the drug by hepatocytes (Porter et al, 1987), making the iron in these cells available for excretion via the bile, while the iron excreted in the urine may all come from extracellular chelation, particularly when iron leaves the reticuloendothelial cells (Hershko et al, 1978). On this hypothesis, cellular toxicity occurs only when DF penetrates sensitive cells in sufficient amounts so that some free DF remains after all the available iron in such cells has been chelated. Such a hypothesis accounts for the protection of cells by iron overload and therefore the greater sensitivity of unloaded patients. The retina and central nervous system are further protected by the blood-retinal or blood-brain barrier, and increased penetration of this barrier, mediated by high peak levels of DF, by drugs or other diseases would lead to the retinal or neurotoxic effects seen. In the ear, high levels of unliganded DF for a period of time may be necessary to cause deafness. Thus the very property that prevents its oral activity may be part of the reason for the low toxicity of DF. The severe toxic effects on vision, hearing and growth are all more likely at higher doses of DF and there appears to be partial protection against them by iron overload. These two conclusions have to be taken into account when deciding on the appropriate dosage for each patient. With care, the dosage can be adjusted to remove enough iron to prevent iron accumulation and therefore its toxic effects, whilst keeping doses low enough to prevent DF from being toxic itself. It appears that even in very iron-overloaded patients dosages higher than 125 mg kg-1 day-1 may cause visual disturbances and should be avoided. In patients on renal dialysis with aluminium toxicity great care is needed to avoid retinal toxicity even with dosages as low as 50 mg kg-1 day-1, although the drug should not be withheld if clinically indicated. The administration of DF to renal dialysis patients is described by Pogglitsch et al (1981, 1983), Pacitti et al (1983), Ihle et al (1986) and Molitoris et al (1987). DF should not be given to patients unless there is a clearly established clinical indication.(ABSTRACT TRUNCATED AT 400 WORDS)