Gene expression levels of matrix metalloproteinases in human atherosclerotic plaques and evaluation of radiolabeled inhibitors as imaging agents for plaque vulnerability

Nucl Med Biol. 2014 Aug;41(7):562-9. doi: 10.1016/j.nucmedbio.2014.04.085. Epub 2014 Apr 21.

Abstract

Introduction: Atherosclerotic plaque rupture is the primary cause for myocardial infarction and stroke. During plaque progression macrophages and mast cells secrete matrix-degrading proteolytic enzymes, such as matrix metalloproteinases (MMPs). We studied levels of MMPs and tissue inhibitor of metalloproteinases-3 (TIMP-3) in relation to the characteristics of carotid plaques. We evaluated in vitro two radiolabeled probes targeting active MMPs towards non-invasive imaging of rupture-prone plaques.

Methods: Human carotid plaques obtained from endarterectomy were classified into stable and vulnerable by visual and histological analysis. MMP-1, MMP-2, MMP-8, MMP-9, MMP-10, MMP-12, MMP-14, TIMP-3, and CD68 levels were investigated by quantitative polymerase chain reaction. Immunohistochemistry was used to localize MMP-2 and MMP-9 with respect to CD68-expressing macrophages. Western blotting was applied to detect their active forms. A fluorine-18-labeled MMP-2/MMP-9 inhibitor and a tritiated selective MMP-9 inhibitor were evaluated by in vitro autoradiography as potential lead structures for non-invasive imaging.

Results: Gene expression levels of all MMPs and CD68 were elevated in plaques. MMP-1, MMP-9, MMP-12 and MMP-14 were significantly higher in vulnerable than stable plaques. TIMP-3 expression was highest in stable and low in vulnerable plaques. Immunohistochemistry revealed intensive staining of MMP-9 in vulnerable plaques. Western blotting confirmed presence of the active form in plaque lysates. In vitro autoradiography showed binding of both inhibitors to stable and vulnerable plaques.

Conclusions: MMPs differed in their expression patterns among plaque phenotypes, providing possible imaging targets. The two tested MMP-2/MMP-9 and MMP-9 inhibitors may be useful to detect atherosclerotic plaques, but not the vulnerable lesions selectively.

Keywords: Atherosclerosis; Autoradiography; Carotid artery plaque; Inflammation; Matrix metalloproteinases; Tissue inhibitor of metalloproteinase-3.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Aged, 80 and over
  • Animals
  • Antigens, CD / genetics
  • Antigens, CD / metabolism
  • Antigens, Differentiation, Myelomonocytic / genetics
  • Antigens, Differentiation, Myelomonocytic / metabolism
  • Arteries / metabolism
  • Benzoic Acid / chemistry
  • Female
  • Gene Expression Regulation, Enzymologic*
  • Humans
  • Isotope Labeling
  • Macrophages / metabolism
  • Male
  • Matrix Metalloproteinase Inhibitors* / chemistry
  • Matrix Metalloproteinases / genetics
  • Matrix Metalloproteinases / metabolism*
  • Mice
  • Middle Aged
  • Molecular Imaging / methods*
  • Plaque, Atherosclerotic / diagnosis*
  • Plaque, Atherosclerotic / genetics
  • Plaque, Atherosclerotic / metabolism*
  • Protein Transport
  • Tissue Inhibitor of Metalloproteinase-3 / genetics
  • Tissue Inhibitor of Metalloproteinase-3 / metabolism
  • Tritium*

Substances

  • Antigens, CD
  • Antigens, Differentiation, Myelomonocytic
  • CD68 antigen, human
  • Matrix Metalloproteinase Inhibitors
  • Tissue Inhibitor of Metalloproteinase-3
  • Tritium
  • Benzoic Acid
  • Matrix Metalloproteinases