Source of iron overload in multiple sclerosis

Iron deposition in multiple sclerosis: overall load or distribution alteration?

Background

Though abnormal iron deposition has been reported in specific brain regions in multiple sclerosis (MS), no data exist about whether the overall quantity of iron in the brain is altered or not. We aimed to determine whether the noted aberrant iron deposition in MS brains was a problem of overall load or regional distribution in a cohort of MS patients.

Methods

An experienced neuroradiologist, a radiology software engineer, and four neurologists analysed data from quantitative susceptibility maps reconstructed from 3-T magnetic resonance brain images of 30 MS patients and 15 age- and sex-matched healthy controls. Global brain iron load was calculated, and the regional iron concentrations were assessed in 1,000 regions of interest placed in MS lesions in different locations, normal appearing white matter, thalami, and basal ganglia.

Results

Global brain iron load was comparable between patients and controls after adjustment for volume (p = 0.660), whereas the regional iron concentrations were significantly different in patients than in control (p ≤ 0.031). There was no significant correlation between global iron load and clinical parameters, whereas regional iron concentrations correlated with patients’ age, disease duration, and disability grade (p ≤ 0.039).

Conclusions

The aberrant iron deposition noted in MS seems to be a problem of regional distribution rather than an altered global brain iron load.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41747-022-00279-9.

Nuclear prelamin a recognition factor and iron dysregulation in multiple sclerosis

Dysregulation of iron metabolism and aberrant iron deposition has been associated with multiple sclerosis. However, the factors that contribute to this pathological state remain to be understood. In this study, human multiple sclerosis and mice brain samples were analyzed through mass spectrometry as well as histological and immunoblot techniques, which demonstrated that iron deposition is associated with increased levels of nuclear prelamin A recognition factor (NARF). NARF is a protein associated with the mitochondria which has also been linked to mitochondrial defects in multiple sclerosis. We report NARF to be associated in multiple sclerosis pathology and aberrant iron deposition.

Blood Perfusion and Cellular Microstructural Changes Associated With Iron Deposition in Multiple Sclerosis Lesions

Background and Purpose: Susceptibility-weighted imaging (SWI) has emerged as a useful clinical tool in many neurological diseases including multiple sclerosis (MS). This study aims to investigate the relationship between SWI signal changes due to iron deposition in MS lesions and tissue blood perfusion and microstructural abnormalities to better understand their underlying histopathologies.

Methods: Forty-six patients with relapsing remitting MS were recruited for this study. Conventional FLAIR, pre- and post-contrast T1-weighted imaging, SWI, diffusion tensor imaging (DTI), and dynamic susceptibility contrast (DSC) perfusion MRI were performed in these patients at 3T. The SWI was processed using both magnitude and phase information with one slice minimal intensity projection (mIP) and phase multiplication factor of 4. MS lesions were classified into 3 types based on their lesional signal appearance on SWI mIP relative to perilesional normal appearing white matter (peri-NAWM): Type-1: hypointense, Type-2: isointense, and Type-3: hyperintense lesions. The DTI and DSC MRI data were processed offline to generate DTI-derived mean diffusivity (MD) and fractional anisotropy (FA) maps, as well as DSC-derived cerebral blood flow (CBF) and cerebral blood volume (CBV) maps. Comparisons of diffusion and perfusion measurements between lesions and peri-NAWM, as well between different types of lesions, were performed.

Results: A total of 137 lesions were identified on FLAIR in these patients that include 40 Type-1, 46 Type-2, and 51 Type-3 lesions according to their SWI intensity relative to peri-NAWM. All lesion types showed significant higher MD and lower FA compared to their peri-NAWM (P < 0.0001). Compared to Type-1 lesions (likely represent iron deposition), Type-2 lesions had significantly higher MD and lower FA (P < 0.001) as well as lower perfusion measurements (P < 0.05), while Type 3 lesions had significantly higher perfusion (P < 0.001) and lower FA (P < 0.05). Compared to Type-2, Type-3 lesions had higher perfusion (P < 0.0001) and marginally higher MD and lower FA (P < 0.05).

Conclusion: The significant differences in diffusion and perfusion MRI metrics associated with MS lesions, that appear with different signal appearance on SWI, may help to identify the underlying destructive pathways of myelin and axons and their evolution related to inflammatory activities.

Correlation of geographic distributions of haptoglobin alleles with prevalence of multiple sclerosis (MS) - a narrative literature review

We have proposed that the myelin damage observed in multiple sclerosis (MS) may be partly mediated through the long-term release and degradation of extracellular hemoglobin (Hb) and the products of its oxidative degradation [Cellular and Molecular Life Sciences, 71, 1789-1798, 2014]. The protein haptoglobin (Hpt) binds extracellular Hb as a first line of defense, and can serve as a vascular antioxidant. Humans have two different Hpt alleles: Hpt1 and Hpt2, giving either homozygous Hpt1-1 or Hpt2-2 phenotypes, or a heterozygous Hpt1-2 phenotype. We questioned whether those geographic regions with higher frequency of the Hpt2 allele (conversely, lower frequency of Hpt1 allele) would correlate with an increased incidence of MS, because different Hpt phenotypes will have variable anti-oxidative potentials in protecting myelin from damage inflicted by extracellular Hb and its degradation products. To test this hypothesis, we undertook a systematic analysis of the literature on reported geographic distributions of Hpt alleles to compare them with data reported in the World Health Organization Atlas of worldwide MS prevalence. We found the frequency of the Hpt1 allele to be low in European and North American countries with a high prevalence of MS, consistent with our hypothesis. However, this correlation was not observed in China and India, countries with the lowest Hpt1 frequencies, yet low reported prevalence of MS. Nevertheless, this work shows the need for continued refinement of geographic patterns of MS prevalence, including data on ethnic or racial origin, and for new clinical studies to probe the observed correlation and evaluate Hpt phenotype as a predictor of disease variability and progression, severity, and/or comorbidity with cardiovascular disorders.

Iron and Neurodegeneration: Is Ferritinophagy the Link?

Mounting evidence indicates that the lysosome-autophagy pathway plays a critical role in iron release from ferritin, the main iron storage cellular protein, hence in the distribution of iron to the cells. The recent identification of nuclear receptor co-activator 4 as the receptor for ferritin delivery to selective autophagy sheds further light on the understanding of the mechanisms underlying this pathway. The emerging view is that iron release from ferritin through the lysosomes is a general mechanism in normal and tumour cells of different tissue origins, but it has not yet been investigated in brain cells. Defects in the lysosome-autophagy pathway are often involved in the pathogenesis of neurodegenerative disorders, and brain iron homeostasis disruption is a hallmark of many of these diseases. However, in most cases, it has not been established whether iron dysregulation is directly involved in the pathogenesis of the diseases or if it is a secondary effect derived from other pathogenic mechanisms. The recent evidence of the crucial involvement of autophagy in cellular iron handling offers new perspectives about the role of iron in neurodegeneration, suggesting that autophagy dysregulation could cause iron dyshomeostasis. In this review, we recapitulate our current knowledge on the routes through which iron is released from ferritin, focusing on the most recent advances. We summarise the current evidence concerning lysosome-autophagy pathway dysfunctions and those of iron metabolism and discuss their potential interconnections in several neurodegenerative disorders, such as Alzheimer's, Parkinson's and Huntington's diseases; amyotrophic lateral sclerosis; and frontotemporal lobar dementia.