Iron is a sensitive biomarker for inflammation in multiple sclerosis lesions

PLoS One. 2013;8(3):e57573. doi: 10.1371/journal.pone.0057573. Epub 2013 Mar 14.

Abstract

MRI phase imaging in multiple sclerosis (MS) patients and in autopsy tissue have demonstrated the presence of iron depositions in white matter lesions. The accumulation of iron in some but not all lesions suggests a specific, potentially disease-relevant process, however; its pathophysiological significance remains unknown. Here, we explore the role of lesional iron in multiple sclerosis using multiple approaches: immunohistochemical examination of autoptic MS tissue, an in vitro model of iron-uptake in human cultured macrophages and ultra-highfield phase imaging of highly active and of secondary progressive MS patients. Using Perls' stain and immunohistochemistry, iron was detected in MS tissue sections predominantly in non-phagocytosing macrophages/microglia at the edge of established, demyelinated lesions. Moreover, iron-containing macrophages but not myelin-laden macrophages expressed markers of proinflammatory (M1) polarization. Similarly, in human macrophage cultures, iron was preferentially taken up by non-phagocytosing, M1-polarized macrophages and induced M1 (super) polarization. Iron uptake was minimal in myelin-laden macrophages and active myelin phagocytosis led to depletion of intracellular iron. Finally, we demonstrated in MS patients using GRE phase imaging with ultra-highfield MRI that phase hypointense lesions were significantly more prevalent in patients with active relapsing than with secondary progressive MS. Taken together, our data provide a basis to interpret iron-sensitive GRE phase imaging in MS patients: iron is present in non-phagocytosing, M1-polarized microglia/macrophages at the rim of chronic active white matter demyelinating lesions. Phase imaging may therefore visualize specific, chronic proinflammatory activity in established MS lesions and thus provide important clinical information on disease status and treatment efficacy in MS patients.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Biomarkers / metabolism
  • Brain / metabolism
  • Brain / pathology
  • Humans
  • Inflammation / pathology*
  • Iron / metabolism*
  • Macrophages / immunology
  • Macrophages / metabolism
  • Macrophages / pathology
  • Magnetic Resonance Imaging
  • Multiple Sclerosis / metabolism*
  • Multiple Sclerosis / pathology*
  • Multiple Sclerosis, Chronic Progressive / pathology
  • Multiple Sclerosis, Relapsing-Remitting / metabolism
  • Multiple Sclerosis, Relapsing-Remitting / pathology
  • Myelin Proteins / metabolism
  • Phagocytosis

Substances

  • Biomarkers
  • Myelin Proteins
  • Iron

Grant support

This study was funded in part by Teva Neuroscience. No additional external funding received for this study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.