It has been established that graft of cryopreserved dermal fibroblasts is able to improve wound healing. Transplantation of mesenchymal stem cells has the ability to undergo site-specific differentiation and participates in wound healing process. The wound healing process requires angiogenesis and the formation of a vascular network throughout the newly formed tissue. In this study we examined the effect of xenotransplantation of fresh human mesenchymal stem cells and dermal fibroblasts on the angiogenesis. Human mesenchymal stem cells and human fibroblasts were isolated from bone marrow and dermis of the same patients and grown in culture respectively. We have developed a porous polyethylene disc as a model experimental system for angiogenesis. The blocks of polyethylene were cut into discs that were 5 mm in diameter and 3 mm in length. Four discs were soaked in a solution containing 4,000,000 cells and 1 ml thrombin. After porous polyethylene discs were loaded with the cell-thrombin composite, they then were coated with fibrinogen. After the discs were cleaned of surrounding fibrin, they were implanted in the back of white rats. It group A and B, the discs were loaded with mesenchymal stem cells and fibroblasts respectively. In group C, the discs were filled with fibrin alone without cells. Eight white rats and 16 discs per group ( total 48 discs ) were used in this study. Following creating 6 pockets in the back of a rat, 6 discs ( 2 discs per group) were implanted. At three time intervals from 1 to 3 weeks, the implanted discs were harvested and processed for histological study. A longitudinal section was cut with a thickness of 3 micrometers in the very middle of a disc. Histological study was carried out to examine the formation of microvessels in the implants. Microvascular density was measured by counting the number of microvessels in the very middle of a biopsy specimen under 100 magnification field. Only fibrinoid materials and inflammatory cells were detected in most of specimens by the first week under 100 magnification field of the very middle. There was little difference in microvascular density among the 3 groups. By the second week, extracellular matrices including microvessels were detected in all the 3 groups. The microvascular density of group A (17.75 / 100 magnification field) was higher than that of group B (10.50 / 100 magnification field) and group C (10.25 / 100 magnification field). The third week specimens showed that most of the pores of the implants contained extracellular matrices. Significantly greater differences were seen in the microvascular density. The microvascular densities averaged 52.88, 26.12, and 17.50 per 100 magnification field for group A, B, and C respectively. The results indicate that transplantation of mesenchymal stem cells and dermal fibroblasts can significantly improve the angiogenesis in the wound healing process and mesenchymal stem cells are superior to dermal fibroblasts.
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