Assessment of endogenous and therapeutic arteriogenesis by contrast ultrasound molecular imaging of integrin expression.
BACKGROUND
We hypothesized that molecular imaging with contrast-enhanced ultrasound (CEU) and microbubbles targeted to endothelial integrins could be used to noninvasively assess early angiogenic responses to ischemia and growth factor therapy.


RESULTS
Hindlimb ischemia was produced in 48 rats by ligation of an iliac artery. Half of the animals received intramuscular sustained-release fibroblast growth factor-2 (FGF-2). Immediately after ligation and at subsequent intervals from 4 to 28 days, blood flow and oxygen tension in the proximal adductor muscles were measured by CEU perfusion imaging and phosphor quenching, respectively. Targeted CEU imaging of alpha(v)- and alpha5beta1-integrin expression was performed with microbubbles bearing the disintegrin echistatin. Iliac artery ligation produced a 65% to 70% reduction in blood flow and oxygen tension. In untreated ischemic muscle, muscle flow and oxygen tension partially recovered by days 14 to 28. In these animals, signal from integrin-targeted microbubbles was intense and peaked before flow increase (days 4 to 7). In comparison to untreated animals, FGF-2-treated muscle had a greater rate and extent of blood flow recovery and greater signal intensity from integrin-targeted microbubbles, which peaked before maximal recovery of flow. On immunohistology, arteriolar but not capillary density increased in the ischemic limb after ligation, the rate and degree of which were greater in FGF-2-treated rats. Immunofluorescence demonstrated intense staining for alpha(v) in arterioles, the temporal course of which correlated with targeted imaging.


CONCLUSIONS
Targeted CEU can be used to assess endogenous and therapeutic arteriogenesis before recovery of tissue perfusion. These results suggest that molecular imaging of integrin expression may be useful for evaluating proangiogenic therapies.
Leong-Poi
Howard
H
Cardiovascular Imaging Center and Cardiovascular Division, University of Virginia School of Medicine, Charlottesville, USA.
Christiansen
Jonathan
J
Heppner
Peter
P
Lewis
Christopher W
CW
Klibanov
Alexander L
AL
Kaul
Sanjiv
S
Lindner
Jonathan R
JR
D000818:Animals; D001158:Arteries / Q000000981:diagnostic imaging* / Q000254:growth & development; D015415:Biomarkers / Q000032:analysis; D002478:Cells, Cultured; D003287:Contrast Media; D016903:Drug Monitoring / Q000379:methods; D004730:Endothelium, Vascular / Q000737:chemistry / Q000000981:diagnostic imaging; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology / Q000627:therapeutic use*; D006614:Hindlimb; D006801:Humans; D039081:Integrin alpha5beta1 / Q000032:analysis; D039564:Integrin alphaV / Q000032:analysis; D016023:Integrins / Q000032:analysis*; D036341:Intercellular Signaling Peptides and Proteins; D007511:Ischemia / Q000188:drug therapy* / Q000473:pathology; D045423:Microbubbles; D018919:Neovascularization, Physiologic / Q000187:drug effects; D010455:Peptides; D016491:Peripheral Vascular Diseases / Q000188:drug therapy / Q000473:pathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D016896:Treatment Outcome; D014463:Ultrasonography / Q000379:methods
D015415:Biomarkers; D003287:Contrast Media; D039081:Integrin alpha5beta1; D039564:Integrin alphaV; D016023:Integrins; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; D016222:Fibroblast Growth Factor 2; C057986:echistatin