[Safety and efficacy of interferon alfa-2b in the adjuvant treatment of uveal melanoma]. / Verträglichkeit und Wirksamkeit einer adjuvanten Interferon-alfa-2b-Behandlung beim Aderhautmelanom.

PURPOSE: In this manuscript, the safety and efficacy of adjuvant interferon alfa 2b treatment of uveal melanoma is described. PATIENTS AND METHODS: A total of 39 patients (23 male and 16 female, mean age 56.5 years, range 35-78 years) with uveal melanoma were treated with interferon alfa 2b, 3 million units three times a week subcutaneously for 1 year after therapy of the primary tumor. In all patients age, gender, primary melanoma data, therapeutic interventions, treatment side effects and outcome were documented. RESULTS: Of the 39 patients, 31 (80%) finished the treatment as scheduled after 1 year. In 18 patients (46%) the initial dose had to be reduced due to leucopenia, thrombopenia, cardiac symptoms, elevated of liver function or vertigo (WHO grade I-III). In eight patients, therapy had to be withdrawn because of serious side effects (five patients) and the appearance of metastases (three patients). Neither a univariate approach nor a multivariate approach could show a protective effect of interferon treatment on survival. CONCLUSIONS: Adjuvant treatment of uveal melanoma with interferon alfa should be abandoned until the question of dose and administration for cutaneous melanoma is solved.

Long term experience of gamma knife radiosurgery for benign skull base meningiomas.

OBJECTIVES: As most reports on the gamma knife have related only to short or mid-term results, we decided to evaluate the effectiveness and toxicity of radiosurgical treatment for benign skull base meningiomas in 200 patients with a follow up of 5-12 years to define the role of gamma knife radiosurgery (GKRS) for basal meningiomas and to provide further data for comparison with other treatment options. METHODS: In total, 99 patients were treated with a combination of microsurgical resection and GKRS. In 101 patients, GKRS was performed as the sole treatment option. Tumour volumes ranged from 0.38 to 89.8 cm3 (median 6.5 cm3), and doses of 7-25 Gy (median 12 Gy) were given to the tumour borders at covering isodose volume curves (range 20-80%, median 45%). RESULTS: The actuarial progression free survival rate was 98.5% at 5 years and 97.2% at 10 years. Passing radiation induced oedema occurred in two patients (1%). The neurological status improved in 83 cases (41.5%), remained unaltered in 108 (54%), and deteriorated in 9 (4.5%). Worsening was transient in seven patients (3.5%) and unrelated to tumour or treatment in one (0.5%). Repeated microsurgical resection was performed in five patients following GKRS (2.5%). CONCLUSIONS: GKRS has proved to be an effective alternative to microsurgical resection, radiotherapy, and Linac based radiosurgery for adjunctive and primary treatment of selected patients with basal meningiomas. Because of the excellent long term tumour control rate and low morbidity associated with GKRS, this treatment option should be used more frequently in the therapeutic management of benign skull base meningiomas.

Combined endoscopic surgery and radiosurgery as treatment modality for olfactory neuroblastoma (esthesioneuroblastoma).

OBJECT: Treatment of esthesioneuroblastoma (olfactory neuroblastoma) has been considerably improved by microsurgical techniques. Nevertheless, these rare tumours of the frontal skull base are still associated with high rates of tumour recurrence and mortality, thus remaining a challenge even for experienced surgeons. A novel therapeutic approach that combines endoscopic sinus surgery and Gamma Knife radiosurgery is presented here. Taking into account the rarity of the disease the present study comprises a relatively large series of patients treated in a similar manner. METHODS: 14 patients (8 males, 6 females) aged 27-75 years (median 38) were treated between May 1993 and December 2003. This series comprises 12 newly diagnosed esthesioneuroblastomas. Two more patients had already previously undergone surgery (24/39 months earlier). Paranasal and nasal endoscopic sinus surgery was performed. Marginal irradiation doses ranging from 15-34 Gy were given to the residual tumours by means of radiosurgery (Gamma Knife) involving 1-7 isocentres within 3 months after surgery. Median follow-up is 58 months (range 13-128). RESULTS: There was no mortality. In all patients tumour control was achieved within the treated area. 4 patients underwent a second radiosurgical procedure 6-79 months (median 34 months) after initial radiosurgery. One patients had to undergo an additional craniotomy because of extensive neoplastic infiltration, 1 developed postoperative liquorrhea, 1 case was complicated by bilateral frontal sinusitis. All patients complained of nasal discharge and crusts. Karnovsky Index--preoperatively ranging from 80%-100%--remained stable in 12 patients, an improvement was observed in 2 cases. CONCLUSIONS: Based on the favourable results recorded so far, the combination of endoscopic sinus surgery and radiosurgery can be considered a promising treatment option for esthesioneuroblastoma that merits further consideration.

[Dose-volume histogram regression analysis of uveal melanomas after single fraction gamma knife radiosurgery]. / Dosis-Volumen-Histogramm-Regressionsanalyse von Aderhautmelanomen nach einzeitiger Leksell-Gamma-Knife-Radiochirurgie.

BACKGROUND: To evaluate tumor regression and sequelae in 30 uveal melanomas treated with Gamma Knife radiosurgery between 1992 and 1995 at the Gamma Knife center in Graz. PATIENTS: A total of 30 uveal and ciliary body melanomas were treated with a single fraction of the Gamma Knife. The mean marginal dose was 52.1 Gy, (median 50 Gy). Of the tumors, 15 were large (higher than 8 mm), 14 were medium sized (3-8 mm) and one was a small melanoma (<3 mm). Among them were 6 juxtapapillary, 10 (juxta-) maculary melanomas, 5 tumors located in the midperiphery and 9 ciliary body melanomas. METHOD: Dose-volume histogram analysis. RESULTS: After a maximum follow up of 9 years and 7 months, 8 tumors regressed into a scar, 17 tumors into a residual prominence between 50% and 80% of the initial tumor height, 3 tumors showed no change and in 2 patients recurrence was obvious. Sequelae were classified as mild (in 3 patients), moderate (3), severe (5) and very severe (19). CONCLUSIONS: Significant factors for the development of severe sequelae were the tumor volume and the marginal dose, the mean dose proved to be more important than the marginal dose and the irradiated volume more important than the selective critical dose.

Long term results of radiosurgery for vestibular schwannomas.

UNLABELLED: Radiosurgery is either a primary or an adjunct management approach used to treat patients with vestibular schwannomas. The goals are long-term tumour growth control, maintenance of cranial nerve function and prevention of new neurologic deficiencies. We sought to determine long-term outcomes measuring the potential benefits against the neurological risks of radiosurgery. METHODS: 278 patients with vestibular schwannomas underwent Gamma Knife radiosurgery as a treatment modality for from April 1992 to November 2001. The long-term results of 60 patients were evaluated who received radiosurgery as primary treatment. 12 cases presented with previously performed subtotal microsurgical resection or recurrence of disease (12-96 months, median 39). The median treatment volume was 3.8 ccm and the median dose to the tumour margin was 12 Gy. The median patient follow-up time was 88 months (range 72-114 months). RESULTS: Four tumours progressed after primary radiosurgery. Tumour control rate was 93%. Useful hearing (Gardner-Robertson I/II) was preserved in 16 patients (55%). Clinical neurological improvement occurred in 36 patients (60%). Adverse effects comprised neurological symptoms (incomplete facial palsy) (House-Brackman II/III) in five cases (three recovered completely), mild trigeminal neuropathy in three cases, and morphological changes displaying rapid enlargement of preexisting macrocysts in two patients and tumour growth in two other ones. Microsurgical resection was performed in three cases (5%) and one patient underwent a shunting procedure because of hydrocephalus formation. In patients who had undergone previous microsurgery, neither new cranial nerve deficit nor any tumour growth was observed. CONCLUSIONS: Radiosurgery performed with current techniques proved to be an effective method for growth control of vestibular schwannomas with both a low mortality rate and a good quality of life. An increasing percentage of patients will undergo radiosurgery as accessibility to this alternative increases, and more data regarding long-term follow-up are available. It is a post-operative complementary treatment for partially removed tumours. Accordingly, radiosurgery is a useful method for the management of properly selected patients.

Radiosurgery of residual and recurrent vestibular schwannomas.

Radiosurgery is either a primary or an adjunctive management approach used to treat patients with vestibular schwannomas. We sought to determine outcomes measuring the potential benefits against the neurological risks in patients who underwent radiosurgery after previous microsurgical subtotal resection or recurrence of the tumour after total resection. Gamma Knife radiosurgery was applied as an adjunctive treatment modality for 86 patients with vestibular schwannomas from April 1992 to August 2001. We evaluated the results of 50 patients who had a follow-up of at least 3.5 years (median 75 months, range 42-114 months). In 16 patients a recurrence of disease was observed after previous total resection. The median treatment volume was 3.4 ccm with a median dose to the tumour margin of 13 Gy. Tumour control rate was 96%. Two tumours progressed after adjunctive radiosurgery. Useful hearing (Gardner-Robertson II) (4 patients (8%)) and residual hearing (Gardner-Roberson III) (10 patients (20%)) remained unchanged in all patients, who presented with it before radiosurgery, respectively. Clinical neurological improvement was observed in 24 patients (46%). Adverse effects comprised transient neurological symptoms and signs (incomplete facial palsy, House-Brackman II/III) in five cases (recovered completely), mild trigeminal neuropathy in four cases, and morphological changes displaying rapid enlargement of a pre-existing macrocyst in one patient and tumour growth in another one. No permanent new cranial nerve deficit was observed. Radiosurgery appears to be an effective adjunctive method for growth control of vestibular schwannomas and is associated with both a low mortality rate and a good quality of life. Accordingly, radiosurgery is a rewarding therapeutic approach for the preservation of cranial nerve function in the management of patients with vestibular schwannoma in whom prior microsurgical resection failed.

Olfactory neuroblastoma (esthesioneuroblastoma): report of six cases treated by a novel combination of endoscopic surgery and radiosurgery.

Microsurgical techniques have considerably improved the results of surgical treatment for esthesioneuroblastoma (olfactory neuroblastoma). Nevertheless, these rare tumours of the frontal skull base are still associated with high rates of tumour recurrence and mortality, thus remaining a challenge even for experienced surgeons. A novel therapeutic approach that combines endoscopic sinus surgery and radiosurgery (gamma knife) is presented here. Six patients (3 males, 3 females) aged between 27 and 75 years (median 38 years) were treated between August 1993 and July 1999. Following paranasal and nasal endoscopic sinus surgery, marginal irradiation doses ranging from 16 to 34 Gy were applied radiosurgically involving up to 7 isocentres. At present, the median follow-up period is 57 months (range: 9 - 79 months). Without mortality, tumour control was achieved in all patients. One patient, who had to undergo additional craniotomy because of extensive neoplastic infiltration, developed postoperative liquorrhea. In another case the clinical course was complicated by a bilateral frontal sinusitis. All patients complained of nasal discharge and crusts. However, a preoperative Karnovsky Index ranging from 80 to 100 % remained stable in four patients whereas an improvement was observed in two patients. Based on the favourable results observed so far, the combination of endoscopic sinus surgery and radiosurgery can be considered as promising new option for the treatment of esthesioneuroblastoma that merits further investigation.

Staged radiosurgical treatment for large benign cerebral lesions.

OBJECT: Large brain lesions are considered unamenable to gamma knife treatment because of possible adverse effects. The proximity of eloquent brain to a target location, including some arteriovenous malformations (AVMs), still poses a challenge to the neurosurgeon. Because meningiomas and AVMs often show a slow or absent growth rate, partial radiosurgical treatment in cases with risk of unacceptable surgery-related morbidity is an alternative. The authors evaluated the results of staged treatment. METHODS: Since April 1992, 12 patients suffering from large benign tumors (meningiomas) and seven with AVMs considered inoperable underwent gamma knife radiosurgery in staged procedures. All patients with tumors underwent primary open surgery for partial removal of recurrent growth and subsequent radiosurgical treatment. Four men and eight women ranging in age from 26 to 73 years harbored tumors that ranged in volume from 19 to 90 cm3. Marginal dose ranged from 10 to 25 Gy prescribed in the 30 to 50% isodose. The time interval between the radiosurgical treatments varied from 1 to 8 months. Follow up ranged from 5 and 89 months. Three female and four male patients (age range 10-48 years) had undergone previous AVM embolization and were treated with margin doses of 18 to 22 Gy in the 40 to 50% isodose. The volume range of these AVMs was 11 to 25 cm3. The time interval between radiosurgical treatments ranged from 5 to 36 months. The mean follow up was 22.6 months. Neurological follow-up examinations showed clinical improvement in 11 patients (58%), whereas five (26%) remained unchanged. Among tumor patients no deterioration or further tumor growth was observed. Tumor necrosis demonstrated noticed in five patients (26%). One patient with an AVM suffered from seizures and hemiparesis. Follow-up magnetic resonance imaging of the residual nidus disclosed no rebleeding. CONCLUSIONS: For selected patients with large benign lesions staged gamma knife radiosurgery could be an alternative, as evidenced by the authors' series in which there was no mortality and low incidence morbidity.

Gamma knife treatment of subfoveal, classic neovascularization in age-related macular degeneration: a pilot study.

OBJECT: Age-related macular degeneration (AMD) is the leading cause of severe vision loss in people older than age 65 years in the western world. The visual acuity loss usually results from the ingrowth of new vessels from the choroid capillaries, so called choroidal neovascularization (CNV). The aim of this pilot study was to investigate the effect of a single-fraction gamma knife radiosurgery (GKS) on visual acuity and the growth pattern of CNV in patients with AMD. METHODS: Ten patients with a mean age of 75 years and with a subfoveal, classic CNV due to AMD were enrolled in this study. All patients were treated with GKS in one fraction with a prescription dose of 10 Gy. The treatment target was the CNV located in the macula. Computerized tomography scans of the globe were obtained. After a follow up of 1 year visual acuity was stable in six patients and decreased in four. The size of the CNV could be stabilized in four patients, and in six an enlargement of these neovascular complexes was shown. No side effects, such as cataract formation, development of radiation-induced retinopathy, or optic neuropathy, have been observed so far. CONCLUSIONS: Gamma knife radiosurgery seemed to have a beneficial effect on visual acuity in patients with AMD, but it failed to control growth of CNV in six patients. A longer follow up, a larger study population, and a randomized and controlled study are necessary for a final conclusion.

Gamma knife radiosurgery for uveal melanomas: an 8-year experience.

OBJECT: The authors report their experience using gamma knife radiosurgery (GKS) to treat uveal melanomas. METHODS: Between 1992 and 1998, 60 patients were treated with GKS at a prescription dose between 45 Gy and 80 Gy. The mean diameter of the tumor base was 12.2 mm (range 3-22 mm). The mean height of the tumor prominence was 6.7 mm (range 3-12 mm). The eye was immobilized. The follow-up period ranged from 16 to 94 months. Tumor regression was achieved in 56 (93%) of 60 patients. There were four recurrences followed by enucleation. The severe side effect of neovascular glaucoma developed in 21 (35%) patients in a high-dose group with larger tumors and in proximity to the ciliary body. A reduction in the prescription dose to 40 Gy or less and excluding treatment to tumors near the ciliary body decreased the rate of glaucoma without affecting the rate of tumor control. CONCLUSIONS: Gamma knife radiosurgery at a prescription dose of 45 Gy or more can achieve tumor regression in 85% of the uveal melanomas treated. Neovascular glaucoma can develop in patients when using this dose in tumors near the ciliary body. It is advised that such tumors be avoided and that the prescription dose be reduced to 40 Gy.

Possibilities and limitations of endoscopic management of nasal and paranasal sinus malignancies.

Over the last decade, the use of rigid endoscopes in surgery of tumorous lesions of the nose, paranasal sinuses, nasopharynx and anterior skull base has extended and diversified. Endoscopic surgical approaches for malignant lesions are very controversially discussed as of today, yet. From 1989-1999 we have treated 43 patients with invasive/destructive tumors of the paranasal sinuses and the anterior skull base strictly endoscopically, transnasally. These included 5 patients with juvenile angiofibromas and 36 patients with various malignant tumors, one with a large invasive macroadenoma of the pituitary and one case of a craniopharyngeoma. The age range was 3 months to 82 years. Whereas the very first patients were approached endoscopically in a palliative intention, we have started endoscopic surgery for selected malignancies with curative intention in the last years. Histologically, patients with various carcinoma differentiation were operated (n = 18), as well as patients with malignant melanoma (n = 5), esthesioneuroblastoma (n = 8), clivus chordoma (n = 3), immature teratoma (n = 1) and leiomyosarcoma (n = 1). Our first results appear to indicate, that outcome is at least equal to standard external approaches, however with excellent functional terms and significantly better overall quality of life. The limitations result from the anatomical spread of the tumor, when extensive infiltration of orbit, dura/brain and other vital structures exist. However, in experienced hands, endoscopic surgery in this region can be rather radical, bone and even dura of the anterior skull base can be resected as can the periorbit, and all structures reconstructed in the same session. Endoscopic techniques lend themselves very well to cooperation with neighbouring specialities like neurosurgery. In individual cases, gamma-knife therapy has proven an extremely helpful adjunctive. With this combined approach, all 8 patients with esthesioneuroblastoma are alive and free of disease with a mean observation time of 37.2 months. We will therefore continue to use this procedure in selected cases as a reliable alternative to external approaches in the future. However we recommend, that these techniques are only applied at centers, where all other surgical approaches can be performed, should need for this arise.

[Radiosurgery of acoustic neurinoma as a minimally invasive alternative to microsurgery]. / Die Radiochirurgie des Akustikusneurinoms als minimal-invasive Alternative zur Mikrochirurgie.

From April 1992 to July 1998 stereotactic radiosurgery (Gamma Knife) was used to treat 1382 patients; 181 had acoustic neurinomas and were followed up, 44 of them for at least 4 years (48-75 months, median 60). With no mortality control of growth tumor was achieved in all cases but one. It was possible to preserve useful hearing in more than half of the patients (60%). In two patients complications due to the radiation with enlargement of the cystic component were observed. One patient needed additional microsurgical decompression. Three patients suffered transient incomplete facial palsy (one permanent, HBI III), and two patients complained of mild trigeminal neuropathy. One suffered from hydrocephalus and a shunting procedure was necessary. The neurological state improved in 23 patients (52%); five complained of new or worsened deficits. Radiosurgery is an effective alternative treatment for acoustic neurinomas with exceptionally low mortality and morbidity. With respect to preserving cranial nerve function the results are just as good as those of microsurgical resection. Short duration of hospitalization and quick return to normal activities make radiosurgery quite cost effective.

Radiosurgery of vestibular schwannomas: a minimally invasive alternative to microsurgery.

From April 1992 till December 1998 stereotactic radiosurgery (Gamma Knife) was applied to 192 patients with vestibular schwannomas. 56 of them had radiosurgery as primary treatment modality and were followed-up for at least 4 years (48-80 months, median 62). Without fatal complications, control of tumour growth was achieved in all but three cases, useful hearing being preserved in more than one half of the patients (62%). The neurological state improved in 30 patients (54%). Irradiation-associated adverse effects (18%) comprised neurological signs (incomplete facial palsy, four cases (two recovered completely), and mild trigeminal neuropathy, three cases, respectively) and morphological changes (three patients) marked by an enlargement of pre-existing cystic components calling for additional surgical treatment: Microsurgical decompression was performed in two cases, the third patient underwent a shunting procedure because of hydrocephalus formation. Based on the present data, radiosurgery represents an effective treatment for vestibular schwannomas associated with an exceptionally low mortality rate and a good quality of life. With respect to the preservation of cranial nerve function, results are comparable to microsurgical resection. A short duration of hospitalization and a quick return to normal activities constitute further advantages and contribute to cost effectiveness in public health care.

Craniocerebral birth trauma caused by vacuum extraction: a case of growing skull fracture as a perinatal complication.

A case of growing skull fracture following birth trauma and caused by vacuum extraction is reported in order to emphasize the incidence of this peculiar head injury at the beginning of extrauterine life and to point out its relation to possible neuropsychological disturbances that may appear later in childhood. Delivery by vacuum extraction increases the incidence of perinatal injuries and consequently the incidence of neurological deficits in children. Neurosurgical repair is advocated as the appropriate treatment, with the aim not only of cosmetically correcting the lesion's typical subgaleal protuberance with cranioplasty, but also of performing a water-tight closure of the dura, enabling the cerebral cortex to "fill in" the intracerebral lesion. The surgical technique and gross pathology of the lesion are described together with radiological findings before and after surgery. Reports by other authors are reviewed in an attempt to identify the conditioning factors and pathological features of this traumatic injury to skull and brain in neonates and infants. The literature on cranial fractures associated with intracerebral lesions at this age shows a significant difference in recovery and outcome from that after similar lesions in older children.

Radiosurgery with the first Austrian cobalt-60 Gamma-unit. A one year experience.

During the period of one year, from the 21. 4. 1992 to 21. 4. 1993, a total of 201 radiosurgical sessions on 181 patients were performed with the first Austrian Gamma-unit in Graz. 42% of radiosurgical sessions were undertaken for malignomas, 20% for meningiomas, 11.5% for vascular malformations, 9% for neurinomas, 8.5% for low grade astrocytomas and glomus jugulare tumours, 5% for sellar and suprasellar lesions, and 4% for functional disorders. Dose plan data for all the lesions treated are shown. Clinical and imaging data of the first year which are available for 120 patients (66%) are presented and discussed.

A mixed-valent polyiron oxo complex that models the biomineralization of the ferritin core.

A novel polyiron oxo complex, [FeIII4FeII8(O)2(OCH3)18(O2CCH3)6(CH3OH) 4.67] (1), has been prepared from ferrous acetate and lithium methoxide in methanol by slow addition of dioxygen. The three-dimensional close-packed layered structure found in 1 closely mimics that proposed for the inorganic core in the iron storage protein ferritin. The Mössbauer spectra of 1 reveal superparamagnetic relaxation at temperatures below 15 K, a property characteristic of the ferritin core. The small size and mixed-valent nature of 1 suggest that it is a reasonable model for intermediates formed in the biomineralization of iron during ferritin core formation. A related compound, with the same iron-oxygen framework found in 1 but containing only two ferric ions, has also been structurally characterized. Because the clusters exhibit properties of both discrete molecules and extended solids, they are representative of a new class of nanometer-sized compounds that bridge the molecular solid-state boundary.

Primitive neuroectodermal tumor (PNET) extending into the cerebellopontine angle: case report.

The most common primary tumors of the cerebellopontine angle are growths of the 8th cranial nerve. The occurrence of other tumors in this area is very rare and may cause neuroradiological misinterpretation. We report the findings in a 37-year-old male patient suffering from a primitive neuroectodermal tumor (PNET) extending from the latero-basilar cerebellar hemisphere into the cerebellopontine angle (CPA) and causing cerebellar dysfunction as well as symptoms of typical cerebellopontine angle lesions. Differential diagnosis of tumors found in this area is given as well as a histological description of the tumor along with immunohistochemical findings and aspects of possible prognostic relevance.

Fe2+ and phosphate interactions in bacterial ferritin from Azotobacter vinelandii.

Fe2+ binding to both apo- and holo- bacterial ferritin from Azotobacter vinelandii (AVBF) was measured as a function of pH under carefully controlled anaerobic conditions. Fe2+ binding to apo-AVBF is strongly pH dependent with 25 Fe2+ ions/apo-AVBF binding tightly at pH 5.5 and over 150 Fe2+/apo-AVBF at pH 9.0. Holo-AVBF gave a similar pH-dependent binding profile with over 400 Fe2+/AVBF binding at pH of 9.0. Proton release per Fe2+ bound to either AVBF protein increases with increasing pH until a total of about two protons are released at pH 9.0. These binding results are both qualitatively and quantitatively different from corresponding measurements (Jacobs et al., 1989) on apo- and holo- mammalian ferritin (MF) where less Fe2+ binds in both cases. The high level of Fe2+ binding to holo-AVBF relative to that of mammalian ferritin is a consequence of the higher phosphate content in the core of AVBF. Reduction of AVBF by either dithionite or methyl viologen in the absence of chelating agents demonstrated that phosphate, but not Fe2+, is released from the AVBF core in amounts commensurate with the degree of iron reduction, although even at 100% reduction considerable phosphate remains associated with the reduced mineral core. Fe2+ binding to holo-AVBF made deficient in phosphate was lower than that of native AVBF, while the addition of phosphate to native holo-AVBF increased the Fe2+ binding capacity. These results clearly support the role of phosphate as the site of interaction of Fe2+ with the AVBF mineral core.(ABSTRACT TRUNCATED AT 250 WORDS)

Fe2+ binding to apo and holo mammalian ferritin.

The binding of Fe2+ to both apo and holo mammalian ferritin has been investigated under anaerobic conditions as a function of pH. In the pH range 6.0-7.5, 8.0 +/- 0.5 Fe2+ ions bind to each apoferritin molecule, but above pH 7.5, a pH-dependent Fe2+ binding profile is observed with up to 80 Fe2+ ions binding at pH 10.0. This Fe2+ binding is reversible and is accompanied by up to two H+ being released per Fe2+ bound at pH 10.0. The Fe2+ binding to apoferritin probably occurs in the 3-fold channels. A much larger and more complex pH-dependent Fe2+ binding stoichiometry was observed for holoferritin with up to 300 Fe2+ ions binding at pH 10.0. This pH-dependent Fe2+ binding was interpreted as Fe2+ interaction at the FeOOH mineral surface with displacement of H+ from -OH or phosphate surface groups by the incoming Fe2+ ions. Mossbauer spectroscopic measurements using 57Fe-labeled Fe2+ under anaerobic conditions showed that 57Fe2+ binding to holoferritin was accompanied by electron transfer to the core, yielding 57Fe3+, presumably bound to the mineral surface. Removal of added iron by Fe2+-specific chelating agents yielded 57Fe2+, demonstrating the reversibility of this electron-transfer process. The Fe2+ bound to apo- and holoferritin is readily converted to Fe3+ by exposure to O2 and strongly retained by the respective ferritin species.

Redox reactions associated with iron release from mammalian ferritin.

The early redox events involved in iron reduction and mobilization in mammalian ferritin have been investigated by several techniques. Sedimentation velocity measurements of ferritin samples with altered core sizes, prepared by partial reduction and Fe2+ chelation, suggest two different events occur during iron loss from the ferritin core. Reductive optical titrations confirm this biphasic behavior by showing that the first 20-30% of core reduction has different optical properties than the latter 70-80%. Proton uptake during initial core reduction is near zero, but as the percent core reduction increases, the proton uptake (H+/e) values increase to 2 H+/e (2 H+/Fe3+ reduced) as core reduction approaches 1 e/Fe3+. Coulometric reduction of ferritin by mediators of different redox potential and different cross-sectional areas show a two-phase sigmoidal reaction pattern in which initial core reduction occurs at a slower rate than later core reduction. The above experiments were all conducted in the absence of iron chelators so that the observed results were all attributed to core reduction rather than the combined effects of core reduction accompanied by Fe2+ chelation. The coulometric reduction of ferritin by various mediators shows a correlation more with reduction potential than with molecular cross-sectional area. The role of the ferritin channels in core reduction is considered in terms of the reported results.