Assessment of Endogenous and Therapeutic Arteriogenesis by Contrast Ultrasound Molecular Imaging of Integrin Expression

Abstract

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. Methods and 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 ␣ v -and ␣ 5 ␤ 1 -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 ␣ 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. (Circulation. 2005;111:3248-3254.)

Acoustically-active microbubbles conjugated to liposomes: Characterization of a proposed drug delivery vehicle

“…In addition to the use of microbubbles with ultrasound for molecular imaging approaches, combining microbubbles and therapeutics has recently been considered [13][14][15][16][17]. The thin microbubble shell and gas core each have limited drug-carrying capacity, and therefore, do not yield an efficient therapeutic delivery vehicle.…”

Retrograde Perfusion and Filling of Mouse Coronary Vasculature as Preparation for Micro Computed Tomography Imaging

“…One technique, Contrast Enhanced High Resolution Ultrasound (CEHRUS), utilizes gas filled microbubbles as a contrast agent. Injection of these microbubbles into the blood stream allows for visualization of the flow of blood with real-time flow measurements down to the capillary level, but it does not provide a 3D view of the imaged vessels 2,[27][28][29][30][31] . Another method, Magnetic Resonance Angiography (MRA) has also been used to image coronary vessels [32][33][34] , and recent advances in MRA have extended its imaging capabilities to obtain real-time blood flow measurements 35,36 …”

Impaired recovery of hind limb muscle perfusion following ischemic injury in rodents receiving B vitamin supplementation

“…Ligation was performed blinded to animal treatment and all animals were ligated on the same day in random order. This model of ischemia has been well established resulting in an immediate reduction (approximately 70% reduction in blood flow) in the ischemic limb compared to the contralateral non-ischemic limb and increases over the next 1-2 weeks post ligation, as measured by laser Doppler and contrast enhanced ultrasound, peaking and reaching a plateau at five weeks post-ligation [14].…”