Studies in Fat Grafting

Abstract

Background Following radiation therapy, skin becomes fibrotic and can present a difficult problem for reconstructive surgeons. There is an increasing belief that fat grafting under radiated skin can reverse the damage caused by radiation. The present study evaluated the effect of fat grafting on irradiated skin, along with fat graft quality and retention rates in irradiated tissue. Methods Nine adult Crl:NU-Foxn1nu CD-1 mice received 30 Gy external beam radiation of the scalp. Four weeks following radiation, scalp skin from irradiated and non-irradiated mice was harvested and compared histologically for dermal thickness, collagen content, and vascular density. Human fat grafts were then injected in the subcutaneous plane of the scalp. Skin assessment was performed in the irradiated group at 2 and 8 weeks post-grafting, and fat graft retention was measured at baseline and every 2 weeks up to 8 weeks post-grafting using micro-CT. Finally, fat graft samples were explanted at 8 weeks, and quality scoring was performed. Results Fat grafting resulted in decreased dermal thickness, decreased collagen content, and increased vascular density in irradiated skin. CT analysis revealed significantly decreased fat graft survival in the irradiated group when compared to the non-irradiated group. Histological scoring of explanted fat grafts demonstrated no difference in quality between the irradiated and non-irradiated groups. Conclusions Fat grafting attenuates dermal collagen deposition and vessel depletion characteristic of radiation fibrosis. Although fat graft retention rates are significantly lower in irradiated than non-irradiated tissue, the quality of retained fat between the groups is similar.

Studies in Fat Grafting

“…Though the mice used were still to some degree immunocompetent and thus could not perfectly replicate conditions of human fat autografts, they are commonly used in xenograft experiments (35, 36), and represented a natural choice for our study. This model has been found to yield reproducible results and provides an accurate real-time assessment of small-volume fat transfer (29, 31, 37). …”

“…Mice were scanned in the ventral position using a MicroCAT-II in vivo X-ray micro-CT scanner (Imtek, Inc./Siemens, Munich, Bavaria), as described previously (29–31). Fat was distinguished from skin and bone by Hounsfield units, and a user-defined region of interest was established in coronal and sagittal slices.…”

“…A Leica DM5000B light microscope (Leica Microsystems, Buffalo Grove, IL) at the 10× objective was used for bright field imaging. Based on a previously-published method, histological scoring was performed by four blinded observers in order to assess overall fat graft integrity (presence of intact, nucleated adipocytes), presence of cysts and vacuoles (seen in degenerating adipose tissue), level of inflammatory infiltrate (evidenced by infiltration of lymphocytes, macrophages, and other immune cells), and fibrosis (level of collagen and elastic fibers present) (31–33). This histological scoring method is established in literature, and relies on a scaling system for evaluation of each of the four parameters: 0 = absent; 1 = minimally present, 2 = minimally to moderately present, 3 = moderately present, 4 = moderately to extensively present, and 5 = extensively present (33, 34).…”

Studies in Fat Grafting

“…Importantly, studies with human fat grafting using immunocompromised mice have been well described in recent literature, making this model well-suited to investigate ASC contribution to fat graft retention (1, 13–15). Whether this occurs through secretion of paracrine factors by ASCs or a direct contribution to fat through adipogenic differentiation remains undetermined.…”

“…Fat was harvested using the Coleman technique and injectable fat was isolated from the oil layer and blood/debris layer through gravity separation for 30 minutes, as previously described (13–15). Processed fat was then enriched with either 500,000 GFP+ ASCs or luciferase+ ASCs per 200 μl of fat and then transferred to a 1 cc Luer-lock syringe with a 16-gauge needle for injection into mice, all performed by a single surgeon (R.M.G.).…”