BACKGROUND:
Radiation therapy has become a common practice in the treatment of numerous malignancies. Unfortunately, radiation is not selective for neoplastic cells; healthy tissues are also damaged, with progressive fibrosis and decreased vascularity seen in these tissues over time. Recent reports have demonstrated clinical improvement in radiation skin damage with microstructural fat grafting; however, the mechanism of improvement is still unknown. We hypothesize that microstructural fat grafting improves radiation skin damage by downregulating the fibrotic response and restoring the vascularity of these tissues.
METHODS:
The dorsum of adult wild-type FVB mice (n=20) was shaved and depilitated. Dorsal skin was then isolated and a Varian 2300 Linear Accelerator was used to irradiate the skin with 45 Gy. Four weeks following radiation, mice were either fat grafted with 1.5-cc of lipoaspirate or sham-grafted with sterile saline into the dorsal subcutaneous tissues (n=10/group). Syringe-assisted lipoaspirate harvested from human donors was centrifuged for 3 minutes at 300(x)g. The blood and oil fractions were removed, and the higher density processed lipoaspirate was transferred to 1-cc syringes. Progenitor cell number as well as VEGF and SDF concentrations were measured in the processed lipoaspirate. Hair growth, skin color, and degree of ulceration were analyzed photometrically every week following irradiation. Irradiated skin was harvested 4 weeks following grafting for analysis. Immunohistochemistry for Smad3 was performed to assess the fibrotic response in these tissues. Collagen production, vascular density, and architecture of irradiated tissue were assessed via gomori trichrome, CD31 staining, and H&E, respectively.
RESULTS:
The processed lipoaspirate used for fat grafting contained 2.5±.2x10⁵ progenitor cells/g, 28.0±0.7 pg/ml of VEGF, and 298.2±35.9 pg/ml of SDF prior to injection. Chronic ulceration and fibrotic skin thickening became stable 4 weeks post-irradiation. Alopecia, skin color/texture, and ulceration were improved in fat-grafted mice compared to sham-treated controls when analyzed photometrically. Smad3 production was significantly decreased in treated animals (18.16±0.5% vs 29.34±0.7%, p<0.03). Collagen production subsequently had a 2.3-fold decrease in fat grafted mice and adopted a more organized structure compared to controls. Vascular density of irradiated skin was also increased in fat grafted mice compared to controls (7.3±0.04% vs 5.2±0.09%, p<0.01). The epidermis was also thicker in sham-grafted mice compared to fat grafted mice.
CONCLUSIONS:
Microstructural fat grafting improves radiation skin damage. Four weeks post-grafting, treatment animals experienced a downregulation of the TGF-β/Smad3 response as evidenced by the decrease in Smad3 staining. These findings correlated with a decrease in collagen production, a known marker of fibrosis, and improved skin color, texture, and alopecia. Furthermore, there was an increase in the vascularity of previously irradiated skin following treated with fat grafting. Our findings suggest that fat grafting improves radiation skin damage by improving vascularity and downregulating the TGF- β/Smad3 pathway in a process likely mediated by progenitor cells and angiogenic adipokines present in processed lipoaspirate.