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(Circulation. 2008;117:915-922.)
© 2008 American Heart Association, Inc.

Imaging

Monitoring of the Biological Response to Murine Hindlimb Ischemia With ⁶⁴Cu-Labeled Vascular Endothelial Growth Factor-121 Positron Emission Tomography

Jürgen K. Willmann, MD; Kai Chen, PhD; Hui Wang, PhD; Ramasamy Paulmurugan, PhD; Mark Rollins, MD, PhD; Weibo Cai, PhD; David S. Wang, MD; Ian Y. Chen, MSE; Olivier Gheysens, MD; Martin Rodriguez-Porcel, MD; Xiaoyuan Chen, PhD; Sanjiv S. Gambhir, MD, PhD

From The Molecular Imaging Program at Stanford, Department of Radiology and Bio-X Program (J.K.W., K.C., H.W., R.P., W.C., D.S.W., I.Y.C., O.G., M.R.-P., X.C., S.S.G.), and Department of Bioengineering (I.Y.C., S.S.G.), Stanford University School of Medicine, Stanford, Calif; and Department of Anesthesia and Perioperative Care (M.R.), University of California at San Francisco, San Francisco.

Correspondence to Sanjiv Sam Gambhir, MD, PhD, 318 Campus Dr, East Wing, 1st Floor, Stanford, CA 94305-5427. E-mail sgambhir{at}stanford.edu

Received August 10, 2007; accepted December 7, 2007.

Background— Vascular endothelial growth factor-121 (VEGF₁₂₁), an angiogenic protein secreted in response to hypoxic stress, binds to VEGF receptors (VEGFRs) overexpressed on vessels of ischemic tissue. The purpose of this study was to evaluate ⁶⁴Cu-VEGF₁₂₁ positron emission tomography for noninvasive spatial, temporal, and quantitative monitoring of VEGFR2 expression in a murine model of hindlimb ischemia with and without treadmill exercise training.

Methods and Results— ⁶⁴Cu-labeled VEGF₁₂₁ and a VEGF mutant were tested for VEGFR2 binding specificity in cell culture. Mice (n=58) underwent unilateral ligation of the femoral artery, and postoperative tissue ischemia was assessed with laser Doppler imaging. Longitudinal VEGFR2 expression in exercised and nonexercised mice was quantified with ⁶⁴Cu-VEGF₁₂₁ positron emission tomography at postoperative day 8, 15, 22, and 29 and correlated with postmortem -counting. Hindlimbs were excised for immunohistochemistry, Western blotting, and microvessel density measurements. Compared with the VEGF mutant, VEGF₁₂₁ showed specific binding to VEGFR2. Perfusion in ischemic hindlimbs fell to 9% of contralateral hindlimb on postoperative day 1 and recovered to 82% on day 29. ⁶⁴Cu-VEGF₁₂₁ uptake in ischemic hindlimbs increased significantly (P<0.001) from a control level of 0.61±0.17% ID/g (percentage of injected dose per gram) to 1.62±0.35% ID/g at postoperative day 8, gradually decreased over the following 3 weeks (0.59±0.14% ID/g at day 29), and correlated with -counting (R²=0.99). Compared with nonexercised mice, ⁶⁴Cu-VEGF₁₂₁ uptake was increased significantly (P0.0001) in exercised mice (at day 15, 22, and 29) and correlated with VEGFR2 levels as obtained by Western blotting (R²=0.76). Ischemic hindlimb tissue stained positively for VEGFR2. In exercised mice, microvessel density was increased significantly (P<0.001) compared with nonexercised mice.

Conclusions— ⁶⁴Cu-VEGF₁₂₁ positron emission tomography allows longitudinal spatial and quantitative monitoring of VEGFR2 expression in murine hindlimb ischemia and indirectly visualizes enhanced angiogenesis stimulated by treadmill exercise training.

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CLINICAL PERSPECTIVE

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Clinical Summaries
Circulation 2008 117: 857-859. [Full Text]