Search

Purpose: To employ an off-resonance saturation method to measure the mineral-iron pool in the postmortem brain, which is an endogenous contrast agent that can give information on cellular iron status. Methods: An off-resonance saturation acquisition protocol was implemented on a 7 Tesla preclinical scanner, and the contrast maps were fitted to an established analytical model. The method was validated by correlation and Bland-Altman analysis on a ferritin-containing phantom. Mineral-iron maps were obtained from postmortem tissue of patients with neurological diseases characterized by brain iron accumulation, that is, Alzheimer disease, Huntington disease, and aceruloplasminemia, and validated with histology. Transverse relaxation rate and magnetic susceptibility values were used for comparison. Results: In postmortem tissue, the mineral-iron contrast colocalizes with histological iron staining in all the cases. Iron concentrations obtained via the off-resonance saturation method are in agreement with literature. Conclusions: Off-resonance saturation is an effective way to detect iron in gray matter structures and partially mitigate for the presence of myelin. If a reference region with little iron is available in the tissue, the method can produce quantitative iron maps. This method is applicable in the study of diseases characterized by brain iron accumulation and can complement existing iron-sensitive parametric methods.

Highlights • Ferrihydrite-iron is the most abundant iron form in the aceruloplasminemia brain. • Iron concentrations over 1 mg/g are found in deep gray matter structures. • The deep gray matter contains over three times more iron than the temporal cortex. • Iron-sensitive MRI contrast is primarily driven by the amount of ferrihydrite-iron. • R2* is more illustrative of the pattern of iron accumulation than QSM at 7 T., Aims Aceruloplasminemia is an ultra-rare neurodegenerative disorder associated with massive brain iron deposits, of which the molecular composition is unknown. We aimed to quantitatively determine the molecular iron forms in the aceruloplasminemia brain, and to illustrate their influence on iron-sensitive MRI metrics. Methods The inhomogeneous transverse relaxation rate (R2*) and magnetic susceptibility obtained from 7 T MRI were combined with Electron Paramagnetic Resonance (EPR) and Superconducting Quantum Interference Device (SQUID) magnetometry. The basal ganglia, thalamus, red nucleus, dentate nucleus, superior- and middle temporal gyrus and white matter of a post-mortem aceruloplasminemia brain were studied. MRI, EPR and SQUID results that had been previously obtained from the temporal cortex of healthy controls were included for comparison. Results The brain iron pool in aceruloplasminemia detected in this study consisted of EPR-detectable Fe3+ ions, magnetic Fe3+ embedded in the core of ferritin and hemosiderin (ferrihydrite-iron), and magnetic Fe3+ embedded in oxidized magnetite/maghemite minerals (maghemite-iron). Ferrihydrite-iron represented above 90% of all iron and was the main driver of iron-sensitive MRI contrast. Although deep gray matter structures were three times richer in ferrihydrite-iron than the temporal cortex, ferrihydrite-iron was already six times more abundant in the temporal cortex of the patient with aceruloplasminemia compared to the healthy situation (162 µg/g vs. 27 µg/g), on average. The concentrations of Fe3+ ions and maghemite-iron in the temporal cortex in aceruloplasminemia were within the range of those in the control subjects. Conclusions Iron-related neurodegeneration in aceruloplasminemia is primarily associated with an increase in ferrihydrite-iron, with ferrihydrite-iron being the major determinant of iron-sensitive MRI contrast.

PurposeTo employ an Off-Resonance Saturation (ORS) method to measure the ferritin-bound iron pool, which is an endogenous contrast agent which can give information on cellular iron status.MethodsAn ORS acquisition protocol was implemented on a 7T preclinical scanner and the contrast maps were fitted to an established analytical model. The method was validated by correlation and Bland-Altman analysis on a ferritin-containing phantom. Ferritin-iron maps were obtained from post-mortem tissue of patients with neurological diseases characterized by brain iron accumulation, i. e. Alzheimer’s disease, Huntington’s disease and aceruloplasminemia, and validated with histology. Transverse relaxation rate and magnetic susceptibility values were also obtained for comparison.ResultsIn post-mortem tissue, the ferritin-iron contrast strongly co-localizes with histological iron staining, in all the cases. Quantitative iron values obtained via the ORS method are in agreement with literature.ConclusionsOff-resonance saturation is an effective way to detect iron in grey matter structures, while mitigating for the presence of myelin. If a reference region with little iron is available in the tissue, the method can produce quantitative iron maps. This method is applicable in the study of brain diseases characterized by brain iron accumulation and complement existing iron-sensitive parametric methods.

IntroductionAceruloplasminemia is an ultra-rare neurodegenerative disorder associated with massive brain iron accumulation. It is unknown which molecular forms of iron accumulate in the brain of patients with aceruloplasminemia. As the disease is associated with at least a fivefold increase in brain iron concentration compared to the healthy brain, it offers a unique model to study the role of iron in neurodegeneration and the molecular basis of iron-sensitive MRI contrast.MethodsThe iron-sensitive MRI metrics inhomogeneous transverse relaxation rate (R2*) and magnetic susceptibility obtained at 7T were combined with Electron Paramagnetic Resonance (EPR) and Superconducting Quantum Interference Device (SQUID) magnetometry to specify and quantify the different iron forms per gram wet-weight in a post-mortem aceruloplasminemia brain, with focus on the basal ganglia, thalamus, red nucleus, dentate nucleus, superior-and middle temporal gyrus and white matter. MRI, EPR and SQUID results that had been previously obtained from the temporal cortex of healthy controls were included for comparison.ResultsThe brain iron pool in aceruloplasminemia consisted of EPR-detectable Fe3+ ions, magnetic Fe3+ embedded in the core of ferritin and hemosiderin (ferrihydrite-iron), and magnetic Fe3+ embedded in oxidized magnetite/maghemite minerals (maghemite-iron). Of all the studied iron pools, above 90% was made of ferrihydrite-iron, of which concentrations up to 1065 µg/g were detected in the red nucleus. Although deep gray matter structures in the aceruloplasminemia brain were three times richer in ferrihydrite-iron than the temporal cortex, ferrihydrite-iron in the temporal cortex of the patient with aceruloplasminemia was already six times more abundant compared to the healthy situation (162 µg/g vs. 27 µg/g). The concentration of Fe3+ ions and maghemite-iron were 1.7 times higher in the temporal cortex in aceruloplasminemia than in the control subjects. Of the two quantitative MRI metrics, R2* was the most illustrative of the pattern of iron accumulation and returned relaxation rates up to 0.49 ms-1, which were primarily driven by the abundance of ferrihydrite-iron. Maghemite-iron did not follow the spatial distribution of ferrihydrite-iron and did not significantly contribute to MRI contrast in most of the studied regions.ConclusionsEven in extremely iron-loaded cases, iron-related neurodegeneration remains primarily associated with an increase in ferrihydrite-iron, with ferrihydrite-iron being the major determinant of iron-sensitive MRI contrast.

Background Aceruloplasminemia is a rare genetic iron overload disorder, characterized by progressive neurological manifestations. The effects of iron chelation on neurological outcomes have only been described in case studies, and are inconsistent. Aggregated case reports were analyzed to help delineate the disease-modifying potential of treatment. Methods Data on clinical manifestations, treatment and neurological outcomes of treatment were collected from three neurologically symptomatic Dutch patients, who received deferiprone with phlebotomy as a new therapeutic approach, and combined with other published cases. Neurological outcomes of treatment were compared between patients starting treatment when neurologically symptomatic and patients without neurological manifestations. Results Therapeutic approaches for aceruloplasminemia have been described in 48 patients worldwide, including our three patients. Initiation of treatment in a presymptomatic stage of the disease delayed the estimated onset of neurological manifestations by 10 years (median age 61 years, SE 5.0 vs. median age 51 years, SE 0.6, p = 0.001). Although in 11/20 neurologically symptomatic patients neurological manifestations remained stable or improved during treatment, these patients were treated significantly shorter than patients who deteriorated neurologically (median 6 months vs. median 43 months, p = 0.016). Combined iron chelation therapy with deferiprone and phlebotomy for up to 34 months could be safely performed in our patients without symptomatic anemia (2/3), but did not prevent further neurological deterioration. Conclusions Early initiation of iron chelation therapy seems to postpone the onset of neurological manifestations in aceruloplasminemia. Publication bias and significant differences in duration of treatment should be considered when interpreting reported treatment outcomes in neurologically symptomatic patients. Based on theoretical grounds and the observed long-term safety and tolerability in our study, we recommend iron chelation therapy with deferiprone in combination with phlebotomy for aceruloplasminemia patients without symptomatic anemia.