128. Systemic Exogenous Estrogen and Reduced Endogenous Estrogen Alter Wound Healing in a Rat Model

PURPOSE: Poor wound healing causes major morbidity following gender-affirming surgery. While it has been demonstrated that estradiol exerts pro-wound repair effects in XX animal models, it is not well understood how exogenous estrogen impacts wound healing in XY models. We have previously demonstrated that exogenous testosterone may worsen wound healing, however the impact of systemic estrogen, particularly in XY mice, remains unknown. This project investigates the impact of systemic exogenous estrogen in XY rats, and the removal of endogenous estrogen from XX rats, on wound healing. METHODS: Rats were assigned to three groups: no exogenous hormone (OVX/-H, n=8), bi-weekly 1 mg/kg testosterone cypionate (TC) from POD0 to POD24 (OVX/2T, n=8), or subcutaneous silastic capsule (SC) containing 17β-estradiol from POD7 to POD24 (OVX/E2 SC, n=6). After sterilization, bilateral dorsal wounding occurred on POD14 and wound harvest occurred on POD24. Silastic capsules were implanted on POD7. Wound histology and immunofluorescent staining were performed. Differences were analyzed with ANOVA or Welch’s t-test. In a second cohort, wounds were created in gonadectomized XX (n=10) and XY (n=7) rats. At day 42 postoperatively, peri-wound tissue was collected for histology and qPCR analysis to compare markers of wound healing in XX and XY rats where endogenous hormones were removed. RESULTS: In the exogenous model, immunofluorescence staining demonstrated significantly higher CD31 (p<0.01) and MYH11 (p<0.01) in the OVX/E2 group compared to OVX/-H but no significant difference in ER, VEGF, or CD68. Significantly higher blood vessel density was observed in OVX/E2 wound tissue compared to OVX/-H (p<0.01). When endogenous hormones were removed from XX and XY rats, Col-1 expression was on average 2.5-fold higher in XY versus XX rats (p<0.01), CD68 expression was 28.1% higher (p=0.03), and F4/80 was 14.8% higher (p=0.02). There was no significant difference between Col-3, VEGF, IFNy, or CD4 expression. On trichrome histology, scar thickness was not significantly different, however perineural scar area (p=0.03) and epineural scar area (p=0.03) were both more than doubled in XY versus XX rats. CONCLUSION: Increased endothelial cell marker CD31, smooth muscle cell marker MYH11, and vessel density in estrogen-exposed wounds suggests that exogenous estrogen in XY rats significantly increases cutaneous angiogenesis, which may facilitate improved wound healing. No significant differences between OVX/E2 and OVX/-H groups for pan-macrophage markers suggests that exogenous estrogen via silastic capsule implants in XY rats may not impact peri-wound inflammation. Future studies will investigate systemic estrogen administered via subcutaneous injection to determine if mode of administration impacts outcomes. Decreased expression of Col-1, CD68, and F4/80 in peri-wound tissue and smaller scar area values on histology for gonadectomized XX versus XY rats suggests that sex-specific differences in wound healing and the peri-wound inflammatory milieu may persist when endogenous estrogen and testosterone are removed.