Delayed Wound Healing in Hemophilia B Mice.

These studies use our previously reported wound healing model to establish the mechanisms behind the impaired wound healing we observed in hemophilia B animals. We hypothisized that thrombin mediated signals generated in response to the initial wound would be absent or reduced in hemophilia B mice, leading to an impaired course of wound healing and poor angiogenesis. All work was done in accord with the US Amended Animal Welfare Act and was monitored by the Institutional Animal Care and Use Committee of UNC. Three mm circular dermal wounds were made in normal and hemophilia B mice. All wounds were treated with an antibiotic gel at the time the wound was made. The mice were monitored for bleeding both at the time the wound was made and for delayed bleeding. Hemophilia B mice with excessive bleeding were treated. The wounds were monitored for regrowth of the epithelial layer. The size of the area not covered by epithelial tissue was measured and expressed as square millimeters (wound size). We have previously reported that there is a significant difference in the time to wound healing between untreated hemophilic (10 days) and normal animals (7 days). At the end of the time course, wound areas were excised and the skin was formalin fixed, paraffin embedded, and sectioned. Essentially all hemophilia but no normal animals showed unresolved subcutaneous hematoma. During the wound healing process, macrophage infiltration into the granulation tissue was significantly delayed. Unexpectedly, hemophilia B mice relative to wild type mice showed twice as many blood vessels in the healing wound. This difference persisted out to two weeks after the wound was made and well after reepithelialization. Pretreatment (30 minutes prior to wounding) of hemophilia B mice with a single bolus dose of human factor IX sufficient to give 1 U/mL corrected the wound healing time. Pretreated hemophilia B mice did not have obvious subcutaneous hematomoas. The observation that a single bolus dose of factor IX prior to wounding a hemophilia B animal normalized the wound healing time provides a starting point for determining how different doses or different administration times effect wound healing. It also provides a starting point from which to compare the effects of bypassing therapy on wound healing.