Free peritoneal grafts for patch urethroplasty in male rabbits

Cell-Based Therapy for Urethral Regeneration: A Narrative Review and Future Perspectives

Urethral stricture is a common urological disease that seriously affects quality of life. Urethroplasty with grafts is the primary treatment, but the autografts used in clinical practice have unavoidable disadvantages, which have contributed to the development of urethral tissue engineering. Using various types of seed cells in combination with biomaterials to construct a tissue-engineered urethra provides a new treatment method to repair long-segment urethral strictures. To date, various cell types have been explored and applied in the field of urethral regeneration. However, no optimal strategy for the source, selection, and application conditions of the cells is available. This review systematically summarizes the use of various cell types in urethral regeneration and their characteristics in recent years and discusses possible future directions of cell-based therapies.

Urethral Reconstruction Using Mesothelial Cell-Seeded Autogenous Granulation Tissue Tube: An Experimental Study in Male Rabbits

Objective. This study was to evaluate the utility of the compound graft for tubularized urethroplasty by seeding mesothelial cells onto autogenous granulation tissue. Methods. Silastic tubes were implanted subcutaneously in 18 male rabbits, of which nine underwent omentum biopsies simultaneously for in vitro expansion of mesothelial cells. The granulation tissue covering the tubes was harvested 2 weeks after operation. Mesothelial cells were seeded onto and cocultured with the tissue for 7 days. A pendulous urethral segment of 1.5 cm was totally excised. Urethroplasty was performed with mesothelial cell-seeded tissue tubes in an end-to-end fashion in nine rabbits and with unseeded grafts in others as controls. Serial urethrograms were performed at 1, 2, and 6 months postoperatively. Meanwhile, the neourethra was harvested and analyzed grossly and histologically. Results. Urethrograms showed cell-seeded grafts maintained wide at each time point, while strictures formation was found in unseeded grafts. Histologically, layers of urothelium surrounded by increasingly organized smooth muscles were observed in seeded grafts. In contrast, myofibroblasts accumulation and extensive scarring occurred in unseeded grafts. Conclusions. Mesothelial cell-seeded granulation tissue tube can be successfully used for tubularized urethroplasty in male rabbits.

Onlay foreskin flap anastomosed directly to the tunica albuginea: a short-term experimental study in rabbits

INTRODUCTION

In severe hypospadias, urethral plate division is necessary for curvature correction. To configure the new urethra, an approach has been described using a foreskin flap directly anastomosed in an 'onlay' fashion to the tunica albuginea of the corpora cavernosa. Results suggest that it is possible to use the corpus cavernosum albuginea as the posterior wall of the neourethra without the need of a dorsal graft.

OBJECTIVE

The present experimental study aimed to evaluate the histological characteristics and healing pattern of this procedure.

STUDY DESIGN

Sixteen New Zealand male rabbits were divided into two groups of eight animals. Eight animals underwent 1-cm longitudinal dorsal incision of the penile urethra and the edges were anastomosed to the tunica albuginea (Group 1). Eight other animals underwent complete excision of 1.0 cm of penile urethra. Urethroplasty was performed using a foreskin flap directly anastomosed as an onlay to the albuginea, as shown in the figure (Group 2). Sacrifice and histological assessment was performed 2, 4, 8 and 12 weeks postoperatively.

RESULTS

In Group 1, a mild inflammatory process was noted that became almost imperceptible at 12 weeks. Fibrosis was mild at all stages in this group. Over time, a regenerative epithelium covered the corpus cavernosum. Immunohistochemistry using specific CK-7 and CK-20 confirmed the presence of urothelium. No complications were microscopically detected in this group. Group 2 presented with a more intense inflammatory infiltrate, which also resolved over time. Fibrosis was slightly more intense in this group, especially in animals that had urethral strictures. Group 2 presented with three fistulas, two were associated with urethral stricture. Histological evaluation showed the presence of epithelization over the albuginea, which turned out to be similar to the normal urothelium over time and was confirmed by immunohistochemistry. Non-keratinized stratified squamous epithelium of the foreskin flap showed good integration to the urethra.

DISCUSSION

Microscopic analysis showed that inflammation, fibrosis and complications were similar to previous studies. At 12 weeks there was a well-developed epithelium similar to normal urethra, which was confirmed by immunohistochemistry; this was similar to what occurs in the TIP technique, as previously demonstrated. It was hypothesized that the epithelium regeneration developed from the urethral edges, as demonstrated in other experimental studies.

CONCLUSION

The albuginea was covered by mature urothelium after 12 weeks, which presumably grew from the urethral edges. The foreskin flap onlay that was directly anastomosed to the albuginea completely integrated and constituted the roof of the neourethra.

Tissue engineering in urothelium regeneration

The development of therapeutic treatments to regenerate urothelium, manufacture tissue equivalents or neourethras for in-vivo application is a significant challenge in the field of tissue engineering. Many studies have focused on urethral defects that, in most cases, inadequately address current therapies. This article reviews the primary tissue engineering strategies aimed at the clinical requirements for urothelium regeneration while concentrating on promising investigations in the use of grafts, cellular preparations, as well as seeded or unseeded natural and synthetic materials. Despite significant progress being made in the development of scaffolds and matrices, buccal mucosa transplants have not been replaced. Recently, graft tissues appear to have an advantage over the use of matrices. These therapies depend on cell isolation and propagation in vitro that require, not only substantial laboratory resources, but also subsequent surgical implant procedures. The choice of the correct cell source is crucial when determining an in-vivo application because of the risks of tissue changes and abnormalities that may result in donor site morbidity. Addressing an appropriately-designed animal model and relevant regulatory issues is of fundamental importance for the principal investigators when a therapy using cellular components has been developed for clinical use.

Tubularized urethral replacement using tissue-engineered peritoneum-like tissue in a rabbit model

INTRODUCTION

This study aims to investigate whether mesothelial cells could function as seed cells to construct tissue-engineered peritoneum-like tissue for urethral reconstruction in a rabbit model.

MATERIALS AND METHODS

Bladder acellular matrices were prepared and trimmed to 1.5 × 1 cm. Nine male rabbits underwent omentum biopsy and autologous mesothelial cells were isolated. After in vitro expansion, the cells were seeded onto the matrices and incubated for 7 days. In 18 rabbits, a pendulous urethral segment 1.5 cm long was totally excised and urethroplasty was performed with tubularized matrices seeded with cells in 9 animals and without cells in 9 as controls. Urethrography was performed at 1, 2 and 6 months postoperatively. Meanwhile, the neourethras were harvested and analyzed grossly and histologically.

RESULTS

Histological analysis of the cell-seeded grafts revealed a loose collagen matrix covered with a single layer of mesothelim. Serial urethrography indicated a wide urethral caliber without stricture formation in animals implanted with cell-seeded matrices, while all animals of the control group developed stricture. Histological analysis of the implanted cell-seeded matrices demonstrated a normal urethral architecture by 1 month, composed of multilayers of urothelium surrounded by smooth muscle bundles, which became increasingly organized with time. By 6 months, the neourethra could be hardly distinguished from native urethra both grossly and histologically.

CONCLUSIONS

Autologous mesothelial cells could be successfully used as seed cells for tubularized urethral reconstruction in male rabbits.

Urethral substitution using autologous lingual mucosal grafts: an experimental study

OBJECTIVE

To investigate the feasibility of urethral substitution using free lingual mucosa grafts (LMGs) in a dog model.

MATERIALS AND METHODS

The study included 10 female mongrel dogs in which a 4 x 1 cm(2) section of urethral mucosa was excised. The defect was immediately repaired with a size-matched free LMG harvested from the inferior lateral surface of the tongue. A 12 F urethral catheter was kept inside the urethra for a mean of 7 days. At 3 months after the procedure, the patency of the urethra was assessed by both insertion of a 12 F catheter and by retrograde urethrography. Dogs were killed, the grafted areas excised, and evaluated by gross and histopathological examination.

RESULTS

All dogs survived the procedure and there were no tongue complications. One of the 10 dogs developed a slight urethral stricture near the proximal anastomosis. The remaining nine dogs voided spontaneously with no difficulty. Retrograde urethrography showed that no strictures or fistulas had formed. The LMGs shortened by 9.5% after surgery, from a mean (sd) of 4 (0.13) to 3.62 (0.11) cm (statistically significant, P < 0.05). Histological examination showed that the LMGs were well-incorporated into the urethral walls and covered by a keratinized squamous epithelium. Neovascularization was evident beneath the grafts.

CONCLUSION

We successfully developed an dog model for free LMGs and showed the feasibility of this approach for urethral substitution.

A comparison of free skin graft, fascia lata, alloderm, bovine pericardium and primary repair in urethrocutaneous fistulas without diversion: an experimental study

The purpose of this study is to compare primary repair procedure with those that use bio-concordant materials in the treatment of urethrocutaneous fistula. Twenty-five New Zealand rabbits were randomly placed into five groups (primary repair, free graft, allograft fascia lata, alloderm and bovine pericardium repair groups). A single dose of 20 mg/kg of ceftriaxon was applied intramuscularly as a prophylactic dose. Urethrocutaneous fistula was formed on midpenile level. Later, while primary repair was applied in one group, repair with free grafts and with other bio-concordant materials were performed in other groups. Urinary diversion was not used in any of the rabbits. The macroscopic observation was evaluated with urethrography obtained 21 days after the operation and then the rabbits were sacrificed. A total point was obtained by awarding a point to each good parameter in the histopathological evaluation and all the groups were compared. The urethrographic findings and macroscopic examinations were normal in all groups. In histopathological examinations, ranging from the best to worst results, bovine pericardium group (8 points) had a better total score than primary repair group (7 points), allograft fascia lata group (7 points) and alloderm group (7 points). The free graft group had the worst total point (6 points). Bio-concordant materials can be used in urethrocutaneous fistula repair as an alternative to primary repair or to the grafts obtained from body tissues.

The rectus abdominis musculoperitoneal (RAMP) flap for the reconstruction of complicated pharyngoesophageal defects

In the advanced stage of hypopharyngeal cancer, extensive resection may sometimes leave both the cervical soft tissue and pharyngoesophageal defects that must be reconstructed at the same time. In this study, a new reconstructive method using the rectus abdominis musculoperitoneal flap is described. Three patients underwent pharyngoesophageal reconstruction by this method. Complete survival of the flaps was seen in all patients, but one patient developed a fistula due to rapid local recurrence of the tumour. We believe that the rectus abdominis musculoperitoneal flap can be an alternative choice for reconstruction of pharyngoesophageal defect, especially when there is a large area of cervical soft tissue defect at the same time.

Comparison of Angiogenic Activities after Urethral Reconstruction Using Free Grafts in Rabbits

OBJECTIVE

To determine the most suitable type of graft-free penile skin grafts or mucosal grafts from bladder or buccal regions - for urethral reconstruction in an animal model, as evaluated on the basis of angiogenic activity.

METHODS

Twenty-two male White New Zealand rabbits were randomly divided into four groups. In the control group (group O, n=4) a simple urethrotomy and closure was performed, whereas a ventral urethral defect was created in groups A, B, and C and then bridged using the following onlay patches: free penile skin (group A, n=6), buccal mucosal graft (group B, n=6), and bladder mucosal graft (group C, n=6). On the 21st postoperative day, the animals were sacrificed and the retrieved implants were subjected to macroscopic and microscopic analysis. The angiogenic activity was assessed with immunohistochemistry, using the anti-CD31 MoAb and the phosphatase antialkaline phosphatase procedure. The native vascularity of penile skin as well as buccal and bladder mucosa was assessed in rabbits from group O (n=3). Statistical analysis was performed using the one-way ANOVA.

RESULTS

The angiogenesis in a magnification of x200 in groups O, A, B, and C was 34.1+/-4.1 (mean+/-SD), 61.7+/-6.4, 94.3+/-6.4, and 91.5+/-7.2 vessels per optical field, respectively. There were, statistically significant differences (p<0.001) between groups A and B and between groups A and C, but not (p>0.05) between groups B and C. The native vascularity of penile skin, buccal mucosa and bladder mucosa was 23.3+/-3.0, 24.6+/-3.7 and 17.0+/-2.6 vessels per optical field, respectively.

CONCLUSION

The viability of mucosal grafts from bladder or buccal regions is better than that of a free penile graft because of higher angiogenic activity. Although the mucosal grafts showed the same angiogenic activity, the buccal mucosa graft is preferable because of its easier harvesting.

Patch Urethroplasty Using a Fascia lata Autograft in Male Rabbits

INTRODUCTION

Urethral reconstruction is difficult when the genital skin is not available for surgery. We evaluate the feasibility of using the autologous fascia lata as a graft for urethral repair.

MATERIALS AND METHODS

10 male rabbits underwent urethroplasty after creation of a ventral urethral defect. The defect was repaired using a graft harvested from the fascia lata. The animals were divided into three groups and sacrificed at 2, 4 and 12 weeks postoperatively. Radiologic control was performed after 10-12 days and before sacrifice.

RESULTS

In the 10 rabbits subjected to surgery, no case of death or wound infection was observed. During urethrography, a fistula was observed in 2 animals. In the remainder (n = 8), histological analysis showed the preservation of the original laminar structure without graft shrinkage or fibrosis. On the luminal side of the patch, a new line of urothelium appeared in the 2nd week after surgery. After 3 months, the new epithelium was multilayered and the graft edges were not detectable. No voiding dysfunction was detectable in 8 rabbits.

CONCLUSIONS

Our study suggests the feasibility of using the autologous fascia lata for urethral patch repair.