Noninvasive MRI monitoring of the effect of interventions on endothelial permeability in murine atherosclerosis using an albumin-binding contrast agent

Abstract

Background--Endothelial dysfunction promotes atherosclerosis. We investigated whether in vivo magnetic resonance imaging (MRI) using an albumin-binding contrast agent, gadofosveset, could monitor the efficacy of minocycline and ebselen in reducing endothelial permeability and atherosclerotic burden in the brachiocephalic artery of high-fat diet (HFD)-fed ApoE-/- mice. Methods and Results--ApoE-/- mice were scanned 12 weeks after commencement of either a normal diet (controls) or an HFD. HFD-fed ApoE-/- mice were either untreated or treated with minocycline or ebselen for 12 weeks. Delayed-enhancement MRI and T1 mapping of the brachiocephalic artery, 30 minutes after injection of gadofosveset, showed increased vessel wall enhancement and relaxation rate (R1, s-1) in untreated HFD-fed ApoE-/- mice (R1=3.8±0.52 s-1) compared with controls (R1=2.15±0.34 s-1, P < 0.001). Conversely, minocycline-treated (R1=2.7±0.17 s-1, P < 0.001) and ebselen-treated (R1=2.7±0.23 s-1, P<0.001) ApoE-/- mice showed less vessel wall enhancement compared with untreated HFD-fed ApoE-/- mice. Mass spectroscopy showed a lower gadolinium concentration in the brachiocephalic artery of treated (minocycline=28.5±3 μmol/L, ebselen= 32.4±4 μmol/L) compared with untreated HFD-fed ApoE-/- mice (191±4.8 μmol/L) (P < 0.02). Both interventions resulted in a lower plaque burden as measured by delayed-enhancement MRI (minocycline=0.14±0.02 mm2, ebselen=0.20±0.09 mm2, untreated=0.44±0.01 mm2; P<0.001) and histology (minocycline=0.13±0.05 mm2, ebselen=0.18±0.02 mm2, untreated= 0.32±0.04 mm2; P<0.002). Endothelium cells displayed fewer structural changes and smaller gap junction width in treated compared with untreated animals as seen by electron microscopy (minocycline=42.3±8.4 nm, ebselen=56.5±17 nm, untreated=2400±39 nm; P < 0.001). Tissue flow cytometry of the brachiocephalic artery showed lower monocyte/macrophage content in both ebselen- and minocycline-treated mice (8.06±3.2% and 7.62±1.73%, respectively) compared with untreated animals (20.1±2.2%) (P=0.03), with significant attenuation of the proinflammatory Ly6Chigh subtype (untreated mice, 42.64±6.1% of total monocytes; ebselen, 14.07±9.5% of total monocytes; minocycline, 26.42±0.6% of total monocytes). Conclusions--We demonstrate that contrast-enhanced MRI with an albumin-binding contrast agent can be used to noninvasively monitor the effect of interventions on endothelial permeability and plaque burden. Blood albumin leakage could be a surrogate marker for the in vivo evaluation of interventions that aim at restoring endothelial integrity.