INVESTIGATIVE UROLOGY

Urethral Replacement Using Epidermal Cell-Seeded Tubular Acellular Bladder Collagen Matrix
Fu Q, Deng CL, Liu W, Cao YL
Department of Urology, Shanghai 6th People’s Hospital, Shanghai Jiaotong University, Shanghai, China
BJU Int. 2007; 99: 1162-5

• Objectives: To investigate the feasibility of replacing urinary epithelium cells with foreskin epidermal cells to reconstruct engineered anterior urethra with an acellular collagen matrix.
• Materials and Methods: Acellular collagen matrices were generated from allogeneic rabbit bladder submucosa. In nine rabbits, autologous foreskin epidermal cells were isolated, expanded in vitro, and labelled with 5-bromo2'-deoxy-uridine (BrdU) before seeding onto a tubular acellular collagen matrix (1.5 x 1 cm). In male rabbits, a urethral mucosal defect was created, and urethroplasty performed with a tubular acellular collagen matrix seeded with epidermal cells (nine rabbits) or with a matrix with no cell seeding (nine rabbits; control group). Urethrography was done at 1, 2 and 6 months after grafting. The urethral grafts were harvested and analysed grossly and histologically.
• Results: In the control group, gross views and urethrography revealed stricture of repaired defects at the different sample times. In the experimental group, a wide urethral calibre was maintained with no sign of strictures. Histology in the control group showed a single layer of epithelium cells with disorganized muscle fibre bundles in the submucosa layer at 1 month after grafting, and a transitional cell layer surrounded by disorganized muscle fibre bundles at 2 and at 6 months. Grafts seeded with epidermal cells formed a single-layer structure by 1 month, and at 2 and 6 months there were several layers of epidermal cells with abundant vessels in the submucosa. There was an evident margin between graft epidermal cells and host epithelium at 6 months. The implanted cells expressed keratin, shown by staining with anti-pancytokeratins. Immunofluorescence for BrdU confirmed the presence of implanted epidermal cells at 1 month after grafting; there were fewer positive cells at the implantation site at 2 months. At 6 months, there were several layers of epidermal cells with no signs of BrdU staining.
• Conclusions: Urethral reconstruction was better with an acellular collagen matrix seeded with epidermal cells than with the acellular collagen matrix alone. Foreskin epidermal cells seem adequate in replacing urethral epithelium cells for urethral reconstruction.
  
  
• Editorial Comment
  It has been demonstrated that tissue engineering techniques are useful for urethral reconstruction and acellular collagen matrices derived from donor bladder submucosa have been used both experimentally and clinically for onlay urethral replacement with good success (1). Other materials have been also used with varied successful results, both for urethral and bladder replacement (2,3).
  In the present study, the authors examined the feasibility of using an epidermal cell-seeded or -unseeded scaffold for tubularized urethral replacement in a rabbit model. It was found that the acellular collagen matrix had a structure of loose collagen with no nucleoli, and proposed that it might be important for avoiding rejection. Histological analysis shown that the mucosal membrane of the graft is thin, and strictures were formed in the unseeded group, with many disorganized muscle fiber bundles around the urethral lumen. On the other hand, the study demonstrated that seeded implants had a thin epidermal cell layer at 1month, with normal multiple layers of epidermal cells at 2 and 6 months. Repeated urethrograms demonstrated that a wide urethral caliber was maintained with no sign of strictures.
  The authors must be commended for such well-designed experimental work, which provides more evidence in animal models that acellular matrix might be suitable for urethral repair. Nevertheless, it is still uncertain whether larger defects can be corrected with such a matrix.
  Although promised, tissue engineered for urethral substitution remains arguable, since buccal mucosa is easy to obtain and the buccal defect heals well. Also, the buccal mucosal grafts are tough, resilient, easy to harvest, and leave no scar as demonstrated recently (4,5). Also, these homologous grafts appear to be an optimal substitute even for anterior and posterior long urethral strictures in repeated urethroplasty (5).

References

1. Atala A: Experimental and clinical experience with tissue engineering techniques for urethral reconstruction. Urol Clin North Am. 2002; 29: 485-92.
2. Sievert KD, Wefer J, Bakircioglu ME, Nunes L, Dahiya R, Tanagho EA: Heterologous acellular matrix graft for reconstruction of the rabbit urethra: histological and functional evaluation. J Urol. 2001; 165: 2096-102.
3. Ayyildiz A, Nuhoglu B, Huri E, Ozer E, Gurdal M, Germiyanoglu C: Using porcine acellular collagen matrix (Pelvicol) in bladder augmentation: experimental study. Int Braz J Urol. 2006; 32: 88-92; discussion 92-3.
4. Kellner DS, Fracchia JA, Voigt E, Armenakas NA: Preliminary report on use of AlloDerm for closure of intraoral defects after buccal mucosal harvest. Urology. 2007; 69: 372-4.
5. Mehrsai A, Djaladat H, Salem S, Jahangiri R, Pourmand G: Outcome of buccal mucosal graft urethroplasty for long and repeated stricture repair. Urology. 2007; 69: 17-21; discussion 21.

Dr. Francisco J.B. Sampaio
Full-Professor and Chair, Urogenital Research Unit
State University of Rio de Janeiro
Rio de Janeiro, RJ, Brazil