Unexpected calcification after direct intravascular injection of autologous bone marrow-derived cells in a chronic total occlusion model.

AIMS: Patients with symptomatic chronic total occlusions (CTO) remain a therapeutic challenge. Enhancement of intraluminal neovascularisation by pro-angiogenic therapies has been proposed as a new strategy to improve percutaneous revascularisation. The aim of this study was to investigate the effects of intraluminal injection of bone marrow-derived cells (BMC) into experimental CTO. METHODS AND RESULTS: CTO were created in the femoral arteries of 43 New Zealand White rabbits using the thrombin injection model. At 12 weeks following CTO creation, 33 rabbits were injected with either cultured BMC (n=19) or control DMEM alone (n=14) directly into the CTO. Ten rabbits were used for cell tracking (seven BMC and three control). BMC labelled with fluorescent Qdot® nanocrystals were identified in the CTO up to one week after injection. Animals were sacrificed at three to five weeks post-treatment and arterial samples were excised for micro-CT imaging and histologic morphometric analysis. There was a significant but modest increase in neovascularisation in BMC-treated arteries compared to controls (7.47±4.75% vs. 4.35±2.97%, p<0.05). However, unexpected intravascular calcification was only detected within the CTO in BMC cell treated arteries. Western blot for conditioned medium from BMC showed up-regulation of osteogenic proteins (BMP-2 and -7). CONCLUSIONS: Although direct delivery of BMC into CTO increases neovascularisation, undesirable vascular calcification will limit this therapeutic approach.

Intravascular and extravascular microvessel formation in chronic total occlusions a micro-CT imaging study.

OBJECTIVES: The purpose of this study was to characterize the 3-dimensional structure of intravascular and extravascular microvessels during chronic total occlusion (CTO) maturation in a rabbit model. BACKGROUND: Intravascular microchannels are an important component of a CTO and may predict guidewire crossability. However, temporal changes in the structure and geographic localization of these microvessels are poorly understood. METHODS: A total of 39 occlusions were created in a rabbit femoral artery thrombin model. Animals were sacrificed at 2, 6, 12, and 24 weeks (n > or =8 occlusions per time point). The arteries were filled with a low viscosity radio-opaque polymer compound (Microfil) at 150 mm Hg pressure. Samples were scanned in a micro-computed tomography system to obtain high-resolution volumetric images. Analysis was performed in an image processing package that allowed for labeling of multiple materials. RESULTS: Two distinct types of microvessels were observed: circumferentially oriented "extravascular" and longitudinally oriented "intravascular" microvessels. Extravascular microvessels were evident along the entire CTO length and maximal at the 2-week time point. There was a gradual and progressive reduction in extravascular microvessels over time, with very minimal microvessels evident beyond 12 weeks. In contrast, intravascular microvessel formation was delayed, with peak vascular volume at 6 weeks, followed by modest reductions at later time points. Intravascular microvessel formation was more prominent in the body compared with that in the proximal and distal ends of the CTO. Sharply angulated connections between the intravascular and extravascular microvessels were present at all time points, but most prominent at 6 weeks. At later time points, the individual intravascular microvessels became finer and more tortuous, although the continuity of these microvessels remained constant beyond 2 weeks. CONCLUSIONS: Differences are present in the temporal and geographic patterns of intravascular and extravascular microvessel formation during CTO maturation.