| Recently many growth factors were investigated to participate wound tissue repairing and healing. The wound tissue recovery itself generally has biologic process, but many growth factors could be involved in this process and these factors could accelerate the period of wound healing and stimulalte the speed and quality of this healing. In clinical field, some growth factors have been used to promote tissue repairing and showed good effects. The activation of platelets could be induced by many agents and then these plateltes could release multiple growth factors. These growth factors can improve and accommodate tissue repairing. Platelets contain innerαparticle with rich growth factors, having biological activity to proliferate fibroblast, smooth muscle cell and sclerocyte, and also induce MSCs and endothelial cell differentiation and matrix biosynthesis. Platelet-rich plasma (PRP) is a fraction of plasma that contains high levels of multiple growth factors released by platelets after activiation and could be potentially used to heal skin wound.Objective:The experimental apheresis platelets were used to investigate CD62p expression and the levels of VEGF, TGF-β1, PDGF, at different storage time phase. Meanwhile, the platelet count and activation level in microparticle platelets frozen powder were tested and compared with the results from fresh plasma, and then analyzed their relationships among VEGF, TGF-β1, PDGF, and CD62p expression in these samples. To explore the method of outdated platelets to prepare microparticle platelet frozen-powder, and to research the potential use for wound healing in animal model.Materials and methodsThe levels of VEGF, TGFβ1 and PDGF in plasma, fresh apheresis platelets and platelets with storage by shaking at 22℃for 5 days were measured and evaluated by ELISA. The expression of CD62p was measured by flow cytometry in two experimertal groups. A comparison was made in terms of difference between the two groups. The levels of VEGF, TGFβ1, and PDGF in apheresis platelets and microparticle platelet frezone-powder were measured and evaluated by ELISA. The animal model with back skin wounds was used to research the role of wound healing. Kunming mice were randomly divided into blank control group, plasma group, microparticle platelet frezone-powder and commercial bFGF group with six mice in each group. A 1.2 centimeter-diameter full-thickness wound was made on each side of the mouse mid-back. The treatment was applied to each wound once daily for 14 consecutive days after wounding. The wound area, the percentage of wound contraction and CD31 expression at days 5, 7, 10, and 14 after wounding were also measured.ResultsThe number of platelets in RPR is about 6.3 times than that in the whole blood. The expression of CD62p is higher to 13 times in platelets with storage by shaking at 22℃for 5 days than storage at day 1.The levels of VEGF, TGF-β11 and PDGF in fresh apheresis platelets were markedly higher than that in the blood plasma group (P <0.01).The levels of VEGF, TGFβ1, and PDGF in apheresis platelets at day 1 were significantly lower than platelets activated by shaking at 22℃for 5 days(P < 0.05) . There were significantly positive correlations among the levels of VEGF, TGF-β1, PDGF of apheresis platelets and platelet counts and activation ratios. There were also significantly positive correlations among the levels of VEGF, TGF-β1and PDGF.The levels of VEGF were not significantly different in fresh apheresis platelet and microparticle platelet frozen powder(P>0.05). The levels of TGF-β1 and PDGF in microparticle platelet frozen powder were higher than that in fresh platelet(P< 0.05).The wounding area was decreased in the microparticle platelet frozen powder group, compared with those in the saline control group and plasma control group at day 5, 7 and 10 after wounding(P<0.05). The percentage of wound contraction was enhanced in the microparticle platelet frozen powder group compared with those in the saline control group and plasma control group at day 5, 7 and 10 after wounding(P< 0.01, P< 0.05). The expression of CD31 was higher in the microparticle platelet frozen powder group compared with those in the saline control group and plasma control group at day 5, 7 and 10 after wounding(P< 0.01, P< 0.05) ConclusionsThe expression levels of VEGF, TGF-β1, and PDGF in apheresis platelet were significantly related to platelet counts and the platelet activation ratio after collection. The levels of TGF-β1 and PDGF in microparticle platelet frozen powder increased significantly and were higher than that in fresh apheresis platelets.This study showed good results of using microparticle platelet frozen powder to treat mouse full-thickness skin defects, comparing with the widely used commerical bFGF agent. It suggests that the microparticle platelet frozen powder has potential use in clinical wound healing.The microparticle platelet frozen powder is easy to preserve and carry, so it may provide a wide range of blood resources.
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