Wound healing after thermal injury is improved by fat and adipose-derived stem cell isografts

Abstract

Patients with severe burns suffer functional, structural, and esthetic complications. It is important to explore reconstructive options given that no ideal treatment exists. Transfer of adipose and adipose-derived stem cells (ASCs) has been shown to improve healing in various models. The authors hypothesize that use of fat isografts and/or ASCs will improve healing in a mouse model of burn injury. Twenty 6 to 8 week old C57BL/6 male mice received a 30% surface area partial-thickness scald burn. Adipose tissue and ASCs from inguinal fat pads were harvested from a second group of C57BL/6 mice. Burned mice received 500 μl subcutaneous injection at burn site of 1) processed adipose, 2) ASCs, 3) mixed adipose (adipose and ASCs), or 4) sham (saline) injection (n = 5/group) on the first day postinjury. Mice were followed by serial photography until being killed at days 5 and 14. Wounds were assessed for burn depth and healing by hematoxylin and eosin (H&E) and immunohistochemistry. All treated groups showed improved healing over controls defined by decreased wound depth, area, and apoptotic activity. After 5 days, mice receiving ASCs or mixed adipose displayed a non-significant improvement in vascularization. No significant changes in proliferation were noted at 5 days. Adipose isografts improve some early markers of healing postburn injury. The authors demonstrate that addition of these grafts improves specific structural markers of healing. This improvement may be because of an increase in early wound vascularity postgraft. Further studies are needed to optimize use of fat or ASC grafts in acute and reconstructive surgery.

Figure 1. 5-Day Burn depth following partial thickness thermal injury

Thickness (5d) was measured at six points spread across each injury. A. Representative images collected from each experimental subset. B. Average of measurements of depth of burns. Error bars indicate SD. Samples for burn depth stained with H&E.

Figure 2. 14-Day Burn depth following partial thickness thermal injury

Thickness (14d) was measured at six points spread across each injury. A. Representative images collected from each experimental subset. B. Average of measurements of depth of burns. Error bars indicate SD. Samples for burn depth stained with H&E.

Figure 3. 14-Day Burn depth proximal and distal to treatment site

Skin samples were taken at sites distal and proximal to injection of treatment. Burn depth was measured at six points spread across each tissue sample. Error bars indicate SD. Samples for burn depth stained with H&E.

Figure 4. Burn area progression in mice

Thermal injuries days 1,2,5,9, and 14. Representative images collected from each experimental subset.

Figure 5. Apoptosis following partial thickness scald injury

Cell death (5d) was determined by direct count of Caspase staining cells deep to the burn and to the immediate periphery. A. Representative images collected from each experimental subset. B. Counts were measured in four equivalent regions and averages are represented above. Error bars indicate SD. Samples stained by IHC for Caspase (Arrows).

Figure 6. Vascularization following partial thickness scald injury

Angiogenesis (5d) was determined by direct count of CD-31 staining rings (capillary count) deep to the burn and to the immediate periphery. A. Representative images collected from each experimental subset. B. Counts were measured in six equivalent regions and averages are represented above. Error bars indicate SD. Samples stained by IHC for CD-31 (Arrows).