Prevention of focal intimal hyperplasia in rat vein grafts by using a tissue engineering approach

The present study focused on the role of blood flow in the formation of focal intimal hyperplasia in vein grafts, as well as the development of an engineering approach that can be used to eliminate disturbed blood flow and prevent blood flow-related focal intimal hyperplasia. A rat vein graft model was constructed by interposing a jugular vein into the abdominal aorta with end-to-end anastomoses. Locally disturbed flow was identified by analyzing particle streak-lines in methyl salicylate-cleared and perfused vein grafts in vitro with a physiological Reynolds number. At day 10, 20, and 30 after surgery, focal intimal hyperplasia of the vein grafts was examined using a histological approach and the density of alpha-actin positive cells was determined using immunohistological and fluorescent approaches. Results showed that apparent eddy blood flow formed at the proximal, but not at the distal, end of the vein grafts due to graft-host diameter mismatch and local geometric distortions, and was associated with apparent focal intimal hyperplasia. The thickness of the alpha-actin positive layers of the proximal vein grafts was significantly higher than that of the distal grafts (192 +/- 27 vs. 94 +/- 18 microm, 278 +/- 55 vs. 124 +/- 20 microm, and 288 +/- 24 vs. 131 +/- 23 microm for day 10, 20. and 30, respectively). The density of the alpha-actin positive cells, however, was similar between the proximal and the distal regions (3569 +/- 361 vs. 3285 +/- 343 cells/mm2, 5540 +/- 650 vs. 5376 + 887 cells/mm2, and 5465 +/- 791 vs. 5278 +/- 524 cells/mm2 for day 10, 20, and 30, respectively). When eddy blood flow was eliminated by matching the graft-host diameters using a tissue engineering approach, the average thickness of the alpha-actin positive layers of the proximal (71 +/- 15, 86 +/- 16, and 85 +/- 14 microm for day 10, 20, and 30, respectively) and the distal vein grafts (68 +/- 13, 80 +/- 14, and 79 +/- 13 microm for day 10, 20, and 30, respectively) was reduced significantly. The density of the alpha-actin positive cells was also reduced significantly in the proximal (2946 +/- 359, 3261 +/- 295, 3472 +/- 599 cells/mm2 for day 10, 20, and 30, respectively) and in the distal regions (3151 +/- 511, 3466 +/- 687, 3593 +/- 688 cells/mm2 for day 10, 20, and 30, respectively). The thickness of the alpha-actin positive layers and the density of the alpha-actin positive cells were not significantly different between the proximal and distal regions of the engineered vein grafts at each observation time. These results suggest that eddy flow may develop in vein grafts and may facilitate the formation of focal intimal hyperplasia, and the vascular tissue engineering approach developed in this study may be used to prevent blood flow-related focal intimal hyperplasia in vein grafts.