Xie Jg

Efficacy of Contrast-enhanced US and Magnetic Microbubbles Targeted to Vascular Cell Adhesion Molecule–1 for Molecular Imaging of Atherosclerosis

PURPOSE To evaluate whether microbubbles targeted to vascular cell adhesion molecule-1 (VCAM-1) (CD106) coupled with a magnetic guidance system could improve the efficacy of contrast-enhanced molecular ultrasonography (US) of atherosclerosis in the aorta. MATERIALS AND METHODS The animal research committee at Southern Medical University approved all experiments. Adherence of magnetic VCAM-1-targeted microbubbles, control inactive magnetic microbubbles, and nonmagnetic VCAM-1-targeted microbubbles to VCAM-1-Fc was determined in vitro by using a flow chamber at variable shear stress (1-24 dyne/cm(2)) under magnetic field guidance. Attachment of microbubbles under magnetic field guidance was determined in vivo with fluorescent microscopy and contrast-enhanced US of the abdominal aorta in wild-type (C57BL/6) or apolipoprotein E (APOE)-deficient mice on a regular or hypercholesterolemic diet. General factorial analysis of variance was used to compare the targeted effect of the microbubbles among different animal groups to identify significant differences. RESULTS Attachment was noted for magnetic and nonmagnetic microbubbles but not for inactive magnetic microbubbles; firm attachment at high shear stress (16-20 dyne/cm(2)) was achieved only with magnetic microbubbles. Fluorescence intensity and video intensity were significantly higher in magnetic microbubbles with magnetic field guidance than in inactive magnetic microbubbles and nonmagnetic microbubbles (P < .05). Video intensity from retained magnetic microbubbles in APOE-deficient mice was significantly greater than that in wild-type mice (mean video intensity for APOE-deficient mice: 28.25 [interquartile range, or IQR, 26.55-29.20] with a hypercholesterolemic diet and 16.10 [IQR, 14.15-18.75] with a regular diet; mean video intensity for wild-type mice: 9.55 [IQR, 8.85-10.5] with a hypercholesterolemic diet and 2.90 [IQR, 1.25-3.85] with a regular diet; P < .001). CONCLUSION Use of a magnetic targeted microbubble system results in greater attachment to endothelial VCAM-1 in atherosclerotic aortas in conditions of high shear stress and improved detection of early inflammatory changes of atherosclerosis.

Mutant hypoxia inducible factor-1α improves angiogenesis and tissue perfusion in ischemic rabbit skeletal muscle.

Hypoxia-inducible factor-1α (HIF-1α) is one of the most potent angiogenic growth factors. It regulates genes involved in angiogenesis, but is inactivated rapidly by normoxia. Ad-HIF-1α-Trip was constructed by transforming Pro402, Pro564, and Asn803 in HIF-1α to alanine in order to delay degradation and create a constitutive transcriptional activator. In this study, we investigated whether Ad-HIF-1α-Trip could induce functional mature angiogenesis and the possible mechanisms involved. We found that Ad-HIF-1α-Trip increased the expression of multiple angiogenic genes in cultured HMVEC-Ls, including VEGF, PLGF, PAI-1, and PDGF. In a rabbit model of acute hind limb ischemia, Ad-HIF-1α-Trip improved tissue perfusion and collateral vessels, as measured by contrast-enhanced ultrasound (CEU), CT angiography, and vascular casting. Ad-HIF-1α-Trip also produced more histologically identifiable capillaries, which were verified by immunostaining, compared with controls. Interestingly, inhibition of CBP/p300 by curcumin prevented HIF-1α from inducing the expression of several angiogenic genes. The present study suggests that Ad-HIF-1α-Trip can induce mature angiogenesis and improve tissue perfusion in ischemic rabbit skeletal muscle. CBP/p300, which interacts with the transactivation domains of HIF-1α, is important for HIF-1α-induced transcription of angiogenic genes.

Ultrasound molecular imaging of angiogenesis induced by mutant forms of hypoxia-inducible factor-1α

AIMS Targeted point mutants of hypoxia-inducible factor-1α (HIF-1α) are potential optimal agents for angiogenesis therapy. Data are limited regarding the angiogenic response of HIF-1α mutants. We aimed to compare the angiogenic effect of wild-type and mutant HIF-1α by contrast ultrasound molecular imaging (UMI) of α(v)-integrin expression. METHODS AND RESULTS The wild-type gene of human HIF-1α, a gene with double mutations (HIF-1α(564/803)), a gene with triple mutations (HIF-1α(564/803/402)), or the LacZ gene (control) was transfected into the ischaemic hind limbs of C57BL/6 mice using an adenovirus vector. The video intensity of microbubbles targeted to α(v)-integrins in the ischaemic limbs increased along with the number of point mutations of HIF-1α. Immunohistochemical expression of endothelial α(v)-integrins was higher in the mutant HIF-1α(564/803/402) group than the other groups as was the density of both capillaries and arterioles in ischaemic muscle. Expression of both the mRNA and protein for HIF-1α and VEGF was significantly higher in the mutant HIF-1α(564/803/402) group than in the other groups. The half-life of HIF-1α and VEGF mRNA was longer in HIF-1α mutant-transfected cells than in wild-type HIF-1α or LacZ-transfected cells. CONCLUSION HIF-1α mutants were more effective for enhancing angiogenesis in ischaemic muscle tissue than wild-type HIF-1α, and the response could be qualitatively evaluated by UMI of α(v)-integrins expression.

EFFICACY OF NOVEL MAGNETIC MICROBUBBLES TARGETED TO VCAM-1 IN THE ASSESSMENT OF INFLAMMATION IN EARLY STAGE OF ATHEROSCLEROSIS

Background: Contrast-enhanced ultrasound imaging (CEU) with site-targeted microbubbles has a potential for the detecting of inflammation in atherosclerosis that plays an important role on the stability of atherosclerotic plaque. However, the achievement of this technique in the conditions of vigorous artery flow is currently difficult due to the limited binding. We, therefore, hypothesized that a “novel” microbubbles targeted to vascular cell adhesion molecule-1 (VCAM-1) with magnetic-guided can enhance the affinity of microbubbles and be used to detect the inflammation in early stage of atherosclerosis.