Endothelial differentiation of adipose-derived stem cells: effects of endothelial cell growth supplement and shear force.

BACKGROUND: Adipose tissue is a readily available source of multipotent adult stem cells for use in tissue engineering/regenerative medicine. Various growth factors have been used to stimulate acquisition of endothelial characteristics by adipose-derived stem cells (ASC). Herein we study the effects of endothelial cell growth supplement (ECGS) and physiological shear force on the differentiation of ASC into endothelial cells. MATERIALS AND METHODS: Human ASC (CD13(+)29(+)90(+)31(-)45(-)) were isolated from periumbilical fat, cultured in ECGS media (for up to 3 wk), and exposed to physiological shear force (12 dynes for up to 8 d) in vitro. Endothelial phenotype was defined by cord formation on Matrigel, acetylated-low density lipoprotein (acLDL) uptake, and expression of nitric oxide synthase (eNOS), von Willebrand factor (vWF), and CD31 (platelet endothelial cell adhesion molecule, PECAM). Additionally, cell thrombogenicity was evaluated by seeding canine autologous ASC onto vascular grafts implanted within the canine arterial circulation for 2 wk. RESULTS: We found that undifferentiated ASC did not display any of the noted endothelial characteristics. After culture in ECGS, ASC formed cords in Matrigel but failed to take up acLDL or express the molecular markers. Subsequent exposure to shear resulted in stem cell realignment, acLDL uptake, and expression of CD31; eNOS and vWF expression was still not observed. Grafts seeded with cells grown in ECGS (+/- shear) remained patent (six of seven) at 2 wk but had a thin coat of fibrin along the luminal surfaces. CONCLUSIONS: This study suggests that (1) ECGS and shear promote the expression of several endothelial characteristics in human adipose-derived stem cells, but not eNOS or vWF; (2) their combined effects appear synergistic; and (3) stem cells differentiated in ECGS appear mildly thrombogenic in vitro, possibly related, in part, to insufficient eNOS expression. Thus, while the acquisition of several endothelial characteristics by adult stem cells derived from adipose tissue suggests these cells are a viable source of autologous cells for cardiovascular regeneration, further stimulation/modifications are necessary prior to using them as a true endothelial cell replacement.

Transrectal endoscopic retrorectal access (TERA): a novel NOTES approach to the peritoneal cavity.

BACKGROUND: As the field of natural orifice translumenal endoscopic surgery (NOTES) expands, new access sites are being investigated. One access site to the peritoneal cavity, which has not been the subject of much investigation, is transrectal access. The aim of this article is to describe a new method to peritoneal access: transrectal endoscopic retrorectal access (TERA). MATERIALS AND METHODS: Three pigs were placed in the supine position under general anesthesia, and an umbilical port was placed for the pneumoperitoneum, as well as visualization of the pelvic dissection and access. A rectotomy was made under direct vision above the dentate line posteriorly. The flexible endoscope was introduced into the retrorectal space, balloon dilation was used to open and dissect the retrorectal plane, and the peritoneal cavity was entered with a needle knife. After peritoneal exploration, the endoscope was withdrawn and the rectotomy was closed under direct vision. RESULTS: Each of the 3 cases was successful with entry into the peritoneal cavity to the right of the sacral promontory. Direct visualization allowed the avoidance of injury to the ureter, vessels, and nervous structures of the pelvis. The flexible endoscope allowed an easy direct visualization of the upper abdominal organs. In addition, retroflexion allowed a view of the pelvic organs. Mean operative time was 40 minutes. CONCLUSIONS: TERA is a novel access route to the peritoneal cavity that can be performed by using readily available instrumentation. When performed under direct view, injury to the adjacent structures can be avoided while obtaining access. Unresolved issues include sterility of the procedure and reproducibility, and future survival studies will delineate long-term safety.