RECONSTRUCTIVE UROLOGY

Phenotypic and functional characterization of in vivo tissue engineered smooth muscle from normal and pathological bladders
Lai J-Y, Yoon CY, Yoo JJ, Wulf T, Atala A
From the Laboratory for Cellular Therapeutics and Tissue Engineering, Department of Urology, Children’s Hospital and Harvard Medical School, Boston, Massachusetts
J Urol. 2002; 168:1853-8

• Purpose: The engineering of bladder tissue involves obtaining a biopsy from a host, expanding the cells, seeding them onto a matrix and implanting the cell-matrix composite back into the host. Clinically, cells used for these techniques may be harvested from abnormal bladders. It is not known whether abnormal bladder cells may be engineered into functionally normal tissue. We investigated the phenotypic and functional characteristics of tissue engineered bladder smooth muscle derived from patients with functionally normal bladders and functionally abnormal exstrophic and neuropathic bladders.
• Materials and Methods: Human smooth muscle cells derived from functionally normal bladders, exstrophic bladders and neurogenic bladders were grown, expanded and seeded onto polymer scaffolds. Sixteen cell seeded scaffolds were analyzed in vitro and 40 cell seeded scaffolds were implanted in athymic mice. The tissue engineered constructs were retrieved and analyzed at 2 weeks and 2 months. The scaffolds were evaluated immunocytochemically, histologically, with organ bath studies and with Western blot analyses.
• Results: Human bladder cells showed similar expression of smooth muscle marker proteins (alpha-actin and myosin) in vitro and after 2 months in vivo, regardless of their origin. All scaffolds showed similar muscle formation in vivo. The cell seeded scaffolds demonstrated the typical “contraction-relaxation” response to supramaximal electrical field and carbachol stimulation. There were no statistical differences among the experimental groups (normal, exstrophic, neurogenic).
• Conclusions: Tissue engineered muscle from normal and diseased bladders retain their phenotype in vitro and after implantation in vivo. The cells exhibited the same degree of contractility to electrical and chemical stimulation regardless of their origin. These results suggest that there are no phenotypic or functional differences between muscle cells obtained from urodynamically normal or pathological bladders, and that bladder muscle cells, regardless of their origin, may have the potential to be engineered into normal bladder tissues.
  
  
• Editorial Comment
  For reconstruction of neurogenic bladders gastrointestinal segments are the preferred substitution material. The authors of this manuscript belong to a group, which has tried to demonstrate in recent years that tissue engineering may be an option for bladder augmentation or even replacement, using in vitro cultivated urothelial cells with or without smooth muscle cells seeded onto a scaffold.
  Whereas the biomaterials for cell seeding may be autologous, homologous, heterologous or artificial in the clinical setting, the cells to be seeded must be from the individual who needs bladder reconstruction. It is an ongoing debate where to obtain bladder cells for tissue engineering in patients with malignant or neurogenic disease of the lower urinary tract.
  The current paper demonstrates that smooth muscle cells from patients with congenital or neurogenic diseases of the lower urinary tract had the same functional properties than engineered smooth muscle cells from normal patients. If this proves true in further studies it will not only widen the possibilities of using tissue engineered flaps for bladder reconstruction but may also give more clues as to the pathophysiology of neurogenic bladders. If there is no functional difference in the musculature of the bladder, the underlying pathomechanism could be e.g. a deficient mucosa (1) or a cerebrospinal disease.

Reference
1. Hohlbrugger G, Frauscher F, Strasser H, Stenzl A, Bartsch G: Evidence for the autoregulation of vesical circulation by intravesical potassium chloride and distension in the normal human bladder. BJU Int. 2000; 85: 412-5.

Dr. Arnulf Stenzl
Professor and Chairman of Urology
Eberhard-Karls-University Tuebingen
Tuebingen, Germany