RECONSTRUCTIVE UROLOGY

Growth of Bone Marrow Stromal Cells on Small Intestinal Submucosa: An Alternative Cell Source for Tissue Engineered Bladder
Zhang Y, Lin HK, Frimberger D, Epstein RB, Kropp BP
Department of Urology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA
BJU Int. 2005; 96: 1120-5

• Objective: To assess the potential use of bone marrow stromal cell (BMSC)-seeded biodegradable scaffold for bladder regeneration in a canine model, by characterizing BMSCs and comparing them to bladder smooth muscle cells (SMCs) by immunohistochemistry, growth capability, and contractility.
• Materials and Methods: Bone marrow was taken by direct needle aspiration from the femurs of five beagle dogs for the in vitro study. Mononuclear cells were isolated by Ficoll-Paque density gradient centrifugation and cultivated in medium 199 with 10% fetal bovine serum. BMSCs were characterized by cell proliferation, in vitro contractility, immunohistochemical analysis, and the growth pattern on small intestinal submucosa (SIS) scaffolds compared to bladder SMC cultures from the same dogs. Another six dogs had a hemicystectomy and bladder augmentation with BMSC-seeded (two), bladder cells including urothelial cells plus SMC-seeded SIS (two) and unseeded SIS scaffolds (two). The six dogs were followed for 10 weeks after augmentation.
• Results: In vitro BMSCs had a significant contractile response to calcium-ionophore, with a mean (sem) 36 (2) %, relative contraction (P < 0.01), which was similar to bladder SMCs but markedly different from fibroblasts. BMSCs also expressed alpha-smooth muscle actin by immunohistochemical staining and Western blotting, but did not express desmin or myosin. In vivo, both BMSC-seeded and bladder cell-seeded SIS grafts had solid smooth-muscle bundle formation throughout the graft.
• Conclusions: BMSCs had a similar cell proliferation, histological appearance and contractile phenotype as primary cultured bladder SMCs. SIS supported three-dimensional growth of BMSCs in vitro, and BMSC-seeded SIS scaffold promoted bladder regeneration in a canine model. BMSCs may serve as an alternative cell source in urological tissue engineering.
  
  
• Editorial Comment
  During recent years, biodegradable scaffolds demonstrated a good source for bladder wall regeneration. Some performed better than others, such as polyglycolic acid and other produced scaffolds, in comparison to small intestine submucosa (SIS) or organ specific acellular matrix (bladder acellular matrix graft (BAMG)) which demonstrated the potential to support tissue regeneration. All have in common that the cells migrate from the host to the center of the scaffold. This might be too slow in that fibrotic changes can happen in the center of the implant before the migration line reaches the center. The result is a scar without function or even worse, shrinking tissue dependent.
  To avoid this effect, cell seeding prior to the implantation gives faster recovery, function and reduction of possible scaring. Zhang et al. differentiated bone marrow stromal cells (BMSC’s) into smooth muscle cells. For comparison, they cultured bladder smooth muscle cells (SMC’s) of the same animal. In addition to an almost equal histological outcome, the intensity for a-smooth muscle actin was brighter in the differentiated BMSC’s with a better contractility in Ca2+-ionophore conditions. Both types of cells grew on and into the SIS scaffold in several layers. Finally augmented to the bladder, cell-matrix implants demonstrated bladder wall regeneration, which was better for BMSC differentiated cells throughout the complete SIS.
  The comparison between BMSC and bladder SMC nicely demonstrates the advantage of bone marrow-derived stromal cells, which do have the potency to differentiate myogenically. The seeded scaffold regenerates faster in comparison to the unseeded, but the results are preliminary because each in-vivo group consists of just two animals. The disadvantage is the requirement of 10% fetal bovine serum, which is not in accordance with the principles of Good Medical Practices (GMP) and currently makes impossible to introduce this technique into the clinic.

Reference
1. Chung SY, Krivorov NP, Rausei V, Thomas L, Frantzen M, Landsittel D, Kang YM, Chon CH, Ng CS, Fuchs GJ: Bladder reconstitution with bone marrow derived stem cells seeded on small intestinal submucosa improves morphological and molecular composition. J Urol. 2005; 174: 353-9.

Dr. Karl-Dietrich Sievert,
Dr. Gerhard Feil, & Dr. Arnulf Stenzl
Department of Urology
Eberhard-Karls-University Tuebingen
Tuebingen, Germany