[Effect of adipose-derived stem cell derived exosomes on angiogenesis after skin flap transplantation in rats].

[OBJECTIVE] To investigate the effect of adipose-derived stem cell derived exosomes (ADSC-Exos) on angiogenesis after skin flap transplantation in rats.

[METHODS] ADSCs were isolated and cultured by enzymatic digestion from voluntary donated adipose tissue of patients undergoing liposuction. The 3rd generation cells were observed under microscopy and identified by flow cytometry and oil red O staining at 14 days after induction of adipogenesis. After cells were identified as ADSCs, ADSC-Exos was extracted by density gradient centrifugation. And the morphology was observed by transmission electron microscopy, the surface marker proteins (CD63, TSG101) were detected by Western blot, and particle size distribution was measured by nanoparticle size tracking analyzer. Twenty male Sprague Dawley rats, weighing 250-300 g, were randomly divided into ADSC-Exos group and PBS group with 10 rats in each group. ADSC-Exos (ADSC-Exos group) and PBS (PBS group) were injected into the proximal, middle, and distal regions of the dorsal free flaps with an area of 9 cm×3 cm along the long axis in the two groups. The survival rate of the flap was measured on the 7th day, and then the flap tissue was harvested. The tissue morphology was observed by HE staining, and mean blood vessel density (MVD) was measured by CD31 immunohistochemical staining.

[RESULTS] ADSCs were identified by microscopy, flow cytometry, and adipogenic induction culture. ADSC-Exos was a round or elliptical membrane vesicle with clear edge and uniform size. It has high expression of CD63 and TSG101, and its size distribution was 30-200 nm, which was in accordance with the size range of Exos. The distal necrosis of the flaps in the ADSC-Exos group was milder than that in the PBS group. On the 7th day, the survival rate of the flaps in the ADSC-Exos group was 64.2%±11.5%, which was significantly higher than that in the PBS group (31.0%±6.6%; =7.945, =0.000); the skin appendages in the middle region of the flap in the ADSC-Exos group were more complete, the edema in the proximal region was lighter and the vasodilation was more extensive. MVD of the ADSC-Exos group was (103.3±27.0) /field, which was significantly higher than that of the PBS group [(45.3±16.2)/field; =3.190, =0.011].

[CONCLUSION] ADSC-Exos can improve the blood supply of skin flaps by promoting the formation of neovascularization after skin flap transplantation, thereby improve the survival rate of skin flaps in rats.