In Vivo Quantification of Vcam-1 Expression in Renal Ischemia Reperfusion Injury Using Non-Invasive Magnetic Resonance Molecular Imaging

Rationale and 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. Methodology and Findings: 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 +/- 354x10(6) mu m(3) in IRI vs. 87 +/- 7x10(6) mu m(3) in kidneys with no surgical intervention (P<0.001); 90 +/- 8x10(6) mu m(3) in IRI kidneys exposed to control (IgG-MPIO) and 625 +/- 80x10(6) mu m(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 +/- 60.63 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.