Adipose Tissue Exract for Wound Healing: Operating room preparation, in vitro and clinical use

With the number of acute and chronic wounds rapidly increasing worldwide, there is a crucial need for improved treatment methods. The mainstream treatment includes wound dressings, mechanical or chemical debridement and surgery. However, to date, no single method has yielded optimal wound healing. Some products are chemically enhanced, but most are bioactively inert. Most tissue engineered treatments are based on cell therapy, but their methods of preparation are expensive, lengthy, require training and are not without potential adverse effects. Wounds heal thanks to a cascade of orchestrated mechanisms resulting in cell proliferation, chemotaxis, migration, angiogenesis and extracellular matrix production. Key to wound healing, growth factors (GFs) are secreted by most cells within the zone of injury, i.e. platelets, endothelial cells, macrophages, lymphocytes, fibroblasts, adipocytes and epithelial cells. These proteins attach to membrane receptors and stimulate nuclear transcription, leading to wound closure. Attempts have been made to bioengineer single recombinant GFs for clinical use, but a combination of GFs is known to better mimic physiological healing. Bone marrow, blood and adipose tissue are known autologous sources of GFs. The use of platelet- rich plasma (PRP), has not gained much popularity due to varying clinical results in randomized controlled trials. Adipose tissue can easily be harvested and contains adipocytes and stromal vascular cells. Adipose tissue extract (ATE), is a cell-free, GF-rich secretome with proven adipogenic and angiogenic properties. The aim of the current study was to describe the effects of ATE within the wound healing setting.

The first study aimed at developing a new operating-room method to obtain ATE. Adipose tissue was obtained from the lipoaspirates of 27 healthy female donors and processed at different incubation time periods, temperatures, and employing different filter types. We compared the protein and GF values produced in the operating room to those in the laboratory. The second study focused on discovering the in vitro effects of ATE (13 samples) and PRP (11 samples) on the proliferation and migration of cells involved in wound healing: keratinocytes, fibroblasts, adipose stem cells and endothelial cells. We also measured the GF content of these samples. The third study was dedicated to unravelling ATE’s clinical effects. In patients with an indication for split-thickness skin graft reconstruction, two or more grafts were harvested. Autologous ATE or PRP was topically applied to one donor site while the other was left untreated. 15 ATE and 13 PRP-treated donor sites were studied. Wound re-epithelialization was evaluated with digital photography on postoperative days 5, 7, 10 and 15. Scars were measured using spectral imaging and scored with the Vancouver-Manchester modified scar scale on days 30 and 60.

In the first study we found that the ATE prepared in the operating theatre incubated for 30 min at room temperature and employing a 0.2 µm pore syringe filter recovered protein and GFs comparable to ATE produced in a laboratory setting. Although PRP had overall higher GF measurements, we found that the ATE was a rich source of keratinocyte GF. This reflected positively in vitro (Study II) showing improved keratinocyte proliferation on culture day 6. The ATE also accelerated fibroblast and adipose stem cell migration. ATE and PRP promoted keratinocyte migration. In the clinical study (Study III), we found that ATE stimulated early re- epithelialization on days 5 (p 0.003) and 7 (p 0.04) while PRP promoted healing on day 7 (p 0.001), compared with controls. The ATE-treated sites demonstrated improved scar scores on days 30 and 60 (p 0.0005 and 0.02, respectively).

Angiogenesis and re-epithelialization are key events in wound healing. The current study encourages further investigation to better understand the mechanisms behind ATE’s healing potential. This study opens new doors in the area of tissue engineering and unveils important findings: an acellular extract is effective in concentrating the adequate combination of GFs to promote healing, and that wound repair does not require extremely high GF values to occur.