In vivo quantification of VCAM-1 expression in renal ischemia reperfusion injury using non-invasive magnetic resonance molecular imaging.
OBJECTIVE
Vascular cell adhesion molecule-1 (VCAM-1) is upregulated in ischemia reperfusion injury (IRI), persisting after restoration of blood flow. We hypothesized that microparticles of iron oxide targeting VCAM-1 (VCAM-MPIO) would depict "ischemic memory" and enable in vivo assessment of VCAM-1 expression.


RESULTS
Mice subject to unilateral, transient (30 minutes) renal ischemia and subsequent reperfusion received intravenous VCAM-MPIO (4.5 mg iron/kg body weight). Contrast agent bound rapidly (<30 minutes) in IRI-kidneys and appeared as intensely low signal areas by MRI in vivo. Automated segmentation and quantification yielded MPIO contrast volumes of 5991±354×10(6) µm(3) in IRI vs. 87±7×10(6) µm(3) in kidneys with no surgical intervention (P<0.001); 90±8×10(6) µm(3) in IRI kidneys exposed to control (IgG-MPIO) and 625±80×10(6) µm(3), in IRI kidneys pre-treated with a blocking dose of VCAM-1 antibody (P<0.001). In keeping with quantitative MRI data, VCAM-1 mRNA expression in IRI was 65-fold higher than in kidneys without surgical intervention (3.06±0.63 vs. 0.05±0.02, P<0.001). Indeed VCAM-1 mRNA expression and VCAM-MPIO contrast volume were highly correlated (R(2)=0.901, P<0.01), indicating that quantification of contrast volume reflected renal VCAM-1 transcription. Serial imaging showed VCAM-MPIO accumulation at target within 30 minutes, persisting for ≥90 minutes, while unbound VCAM-MPIO was cleared rapidly from blood, with sequestration by mac-3 positive Kupffer cells in the liver and monocyte/macrophages in the spleen.


CONCLUSIONS
(1) VCAM-MPIO detected VCAM-1 expression and defined its 3-dimensional distribution, revealing "ischemic memory" in renal IRI; (2) automated volumetric quantification of VCAM-MPIO accurately reflected tissue levels of VCAM-1 mRNA; and (3) VCAM-MPIO bound rapidly to target with active sequestration of unbound MPIO in the liver and spleen.
Akhtar
Asim M
AM
Department of Cardiovascular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom.
Schneider
Jurgen E
JE
Chapman
Stephanie J
SJ
Jefferson
Andrew
A
Digby
Janet E
JE
Mankia
Kulveer
K
Chen
Ye
Y
McAteer
Martina A
MA
Wood
Kathryn J
KJ
Choudhury
Robin P
RP
D000818:Animals; D003287:Contrast Media / Q000032:analysis / Q000378:metabolism; D004195:Disease Models, Animal; D005290:Ferric Compounds / Q000032:analysis / Q000378:metabolism; D015870:Gene Expression; D006801:Humans; D007668:Kidney / Q000098:blood supply / Q000000981:diagnostic imaging* / Q000378:metabolism; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D011859:Radiography; D015427:Reperfusion Injury / Q000000981:diagnostic imaging / Q000235:genetics / Q000378:metabolism*; D019010:Vascular Cell Adhesion Molecule-1 / Q000032:analysis* / Q000235:genetics / Q000378:metabolism*
D003287:Contrast Media; D005290:Ferric Compounds; D019010:Vascular Cell Adhesion Molecule-1; C000499:ferric oxide