Acellular Matrix Tube for Canine Urethral Replacement:: is It Fact or Fiction?

[Appllication of human acellular dermal matrix in surgical treatment of genitourinary disease]

Humanacellular dermal matrix (HADM) is widely used in the field of burn wound repair and tissue engineering plastic surgery. HADM is manufactored by physical and chemical decellular process to remove the antigenic components that might cause immune rejection in dermis.The extracellular matrix of three-dimensional cell scaffold structure with collagen fibers had been used for wound repair and tissue regeneration, while HADM characterized with low absorption rate after implantation and strong ability to induce angiogenesis in host tissue. Studies reported that after the HADM was implanted into the patient, the host cells, such as fibroblasts and myofibroblasts, as well as lymphocytes, macrophages, granulocytes and mast cells, rapidly infiltrated the graft. The connective tissue and neovascularization were then formed within the HADM three-dimensional cell scaffold, the lymphatic system also appears after vascular reconstruction. Traditional urethral reconstruction using autologous skin flaps has some defects, such as complexity of the technology, risk of necrosis of the skin flaps after transplantation, and failure to achieve functional repair of the urethral epithelium. It has been reported that using HADM to reconstruct the urethra in patients with urethral stricture, hypospadias and bladder-vaginal fistula, showed promising results. Others have reported the experience of using HADM to repair and reconstruct congenital classic bladder exstrophy. HADM has also been used for tissue repair in patients with penile skin defect caused by Fonier's gangrene and hidradenitis suppurativa, and implanted under Bucks' fascia to enlarge the penis. The report of HADM implantation for treating premature ejaculation also deserves attention. Researchers found that HADM implantation can form a tissue barrier between the skin and corpus cavernosum, which can effectively reduce penile sensitivity and treat premature ejaculation. The safety and effectiveness of HADM implantation in the treatment of premature ejaculation need to be further standardized by data from multi-center, large-sample clinical studies. In summary, HADM is the extracellular matrix and three-dimensional cell scaffold of human dermis. As a new type of tissue repair material, new blood vessels are formed actively after implantation, which shows good histocompatibility. HADM has shown increasingly broad application prospects in treatment of genitourinary diseases including penis, urethra and bladder diseases. HADM has also been used in the treatment of premature ejaculation in recent clinical studies, and its long-term safety and efficacy need to be further investigated.

Fiber density of collagen grafts impacts rabbit urethral regeneration

There is a need for efficient and “off-the-shelf” grafts in urethral reconstructive surgery. Currently available surgical techniques require harvesting of grafts from autologous sites, with increased risk of surgical complications and added patient discomfort. Therefore, a cost-effective and cell-free graft with adequate regenerative potential has a great chance to be translated into clinical practice. Tubular cell-free collagen grafts were prepared by varying the collagen density and fiber distribution, thereby creating a polarized low fiber density collagen graft (LD-graft). A uniform, high fiber density collagen graft (HD-graft) was engineered as a control. These two grafts were implanted to bridge a 2 cm long iatrogenic urethral defect in a rabbit model. Histology revealed that rabbits implanted with the LD-graft had a better smooth muscle regeneration compared to the HD-graft. The overall functional outcome assessed by contrast voiding cystourethrography showed patency of the urethra in 90% for the LD-graft and in 66.6% for the HD-graft. Functional regeneration of the rabbit implanted with the LD-graft could further be demonstrated by successful mating, resulting in healthy offspring. In conclusion, cell-free low-density polarized collagen grafts show better urethral regeneration than high-density collagen grafts.

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.

A systematic review of animal and clinical studies on the use of scaffolds for urethral repair

Replacing urethral tissue with functional scaffolds has been one of the challenging problems in the field of urethra reconstruction or repair over the last several decades. Various scaffold materials have been used in animal studies, but clinical studies on use of scaffolds for urethral repair are scarce. The aim of this study was to review recent animal and clinical studies on the use of different scaffolds for urethral repair, and to evaluate these scaffolds based on the evidence from these studies. PubMed and OVID databases were searched to identify relevant studies, in conjunction with further manual search. Studies that met the inclusion criteria were systematically evaluated. Of 555 identified studies, 38 were included for analysis. It was found that in both animal and clinical studies, scaffolds seeded with cells were used for repair of large segmental defects of the urethra, such as in tubular urethroplasty. When the defect area was small, cell-free scaffolds were more likely to be applied. A lot of pre-clinical and limited clinical evidence showed that natural or artificial materials could be used as scaffolds for urethral repair. Urinary tissue engineering is still in the immature stage, and the safety, efficacy, cost-effectiveness of the scaffolds are needed for further study.

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.

Acellular matrix in urethral reconstruction

The treatment of severe urethral stenosis has always been a challenge even for skilled urologists. Classic urethroplasty, skin flaps and buccal mucosa grafting may not be used for long and complex strictures. In the quest for an ideal urethral substitute, acellular scaffolds have demonstrated the ability to induce tissue regeneration layer by layer. After several experimental studies, the use of acellular matrices for urethral reconstruction has become a clinical reality over the last decade. In this review we analyze advantages and limitations of both biological and polymeric scaffolds that have been reported in experimental and human studies. Important aspects such as graft extension, surgical technique and cell-seeding versus cell-free grafts will be discussed.

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.

Cell-seeded tubular acellular matrix for replacing a long circumferential urethral defect in a canine model: Is it clinically applicable?

Objective

To evaluate the feasibility of replacing a relatively long segment of the canine urethra by a tube of cell-seeded acellular collagen bladder matrix.

Materials and methods

The study included 14 female mongrel dogs in which a 3-cm segment of the whole urethral circumference was excised and replaced by a tube of acellular matrix seeded with autologous urothelial cells. The acellular matrix was obtained from the excised bladder of female donor dogs that were not included in the study. Autologous cells were obtained from the study dogs by open bladder biopsy, with subsequent in vitro expansion and cultivation. Urethroplasty was performed over a 16 F urethral catheter that was kept for 4 weeks. The dogs were killed humanely (one every week for 4 weeks and then one monthly for 10 months). After stent removal, retrograde urethrography was used each month in the living dogs. If retention occurred a urethrogram was taken and then the dog was killed humanely. All grafts from dogs were harvested and sent for histopathological examination.

Results

Exploration at 1, 2, 3 and 4 weeks showed progressive shrinkage in length, together with relative narrowing of the lumen. Three dogs developed retention within a week after stent removal and the other seven developed retention within 4 months. Retrograde urethrograms showed evidence of stricture and/or fistula at the graft site in all dogs. On exploration, grafts showed marked shrinkage (0.6–1.2 cm in length) with complete obliteration of their lumens. Histopathological examination showed extensive fibrosis of the matrix with no evident urothelial architecture.

Conclusion

Cell-seeded acellular matrix tube is insufficient to replace a 3-cm circumferential urethral defect in dogs.

Mechanical stimuli-induced urothelial differentiation in a human tissue-engineered tubular genitourinary graft

BACKGROUND

A challenge in urologic tissue engineering is to obtain well-differentiated urothelium to overcome the complications related to other sources of tissues used in ureteral and urethral substitution.

OBJECTIVE

We investigated the effects of in vitro mechanical stimuli on functional and morphologic properties of a human tissue-engineered tubular genitourinary graft (TTGG).

DESIGN, SETTING, AND PARTICIPANTS

Using the self-assembly technique, we developed a TTGG composed of human dermal fibroblasts and human urothelial cells without exogenous scaffolding. Eight substitutes were subjected to dynamic flow and hydrostatic pressure for up to 2 wk compared to static conditions (n=8).

MEASUREMENTS

Stratification and cell differentiation were assessed by histology, electron microscopy, immunostaining, and uroplakin gene expression. Barrier function was determined by permeation studies with carbon 14-urea.

RESULTS AND LIMITATIONS

Dynamic conditions showed well-established stratified urothelium and basement membrane formation, whereas no stratification was observed in static culture. The first signs of cell differentiation were perceived after 7 d of perfusion and were fully expressed at day 14. Superficial cells under perfusion displayed discoidal and fusiform vesicles and positive staining for uroplakin 2, cytokeratine 20, and tight junction protein ZO-1, similar to native urothelium. Mechanical stimuli induced expression of the major uroplakin transcripts, whereas expression was low or undetectable in static culture. Permeation studies showed that mechanical constraints significantly improved the barrier function compared to static conditions (p<0.01 at 14 d, p<0.05 at 7 d) and were comparable to native urothelium.

CONCLUSIONS

Mechanical stimuli induced in vitro terminal urothelium differentiation in a human genitourinary substitute displaying morphologic and functional properties equivalent to a native urologic conduit.

Impact of state of arousal and stress neuropeptides on urodynamic function in freely moving rats

Corticotropin-releasing factor (CRF) is a neurotransmitter in Barrington's nucleus neurons. These neurons can coregulate parasympathetic tone to the bladder (to modulate micturition) and brain noradrenergic activity (to affect arousal). To identify the role of CRF in the regulation of micturition, the effects of CRF agonists and antagonists on urodynamics in the unanesthetized rat were characterized. Rats were implanted with bladder and intrathecal or intraperitoneal catheters under isoflurane anesthesia. Cystometry was performed in the unanesthetized, unrestrained state at least 24 h later. In some cases, cortical electroencephalographic activity (EEG) was recorded simultaneously to assess arousal state. During cystometry, the state of arousal often shifted between waking and sleeping and urodynamic function changed depending on the state. Micturition threshold, bladder capacity, and micturition volume were all increased during sleep. The CRF1/CRF2 receptor agonists CRF and urocortin 2 increased bladder capacity and micturition volume in awake but not in sleeping rats. Conversely, the CRF1 receptor antagonists antalarmin and NBI-30775 increased urinary frequency and decreased bladder capacity in awake rats. The present results demonstrate a profound effect of the state of arousal on urodynamic function and suggest that simultaneous monitoring of EEG and cystometry may provide a useful model for studying nocturnal enuresis and other urinary disorders. In addition, the results provide evidence for an inhibitory influence of CRF in the spinal pathway on micturition. Targeting the CRF system in the spinal cord may provide a novel approach for treating urinary disorders.

Canine ureteral replacement with long acellular matrix tube: is it clinically applicable?

PURPOSE

We evaluated the effectiveness of acellular matrix used as a tube for replacement of a relatively long segment of the canine ureter.

MATERIALS AND METHODS

Acellular matrix was obtained by excision of the whole ureter of donor dogs that were sacrificed and not included in the study group. Retrieved ureters were treated to have complete cell lysis, while maintaining the fiber framework. The study included 10 mongrel dogs in which a 3 cm segment was excised from 1 ureter and replaced by a tube of acellular matrix of the same length and width. The new tube was sutured proximal and distal by watertight interrupted sutures around a 5Fr Double-J stent (Medical Engineering Corp., New York, New York) that remained for 6 weeks. Excretory urography was done 1 and 2 weeks after stent removal and the dogs were then sacrificed. Before sacrifice the ureter was exposed and carefully examined, and the whole specimen was excised for histopathological examination.

RESULTS

All dogs survived surgery except 1, which died 1 week postoperatively of a malpositioned stent and urinary ascites. There was no clinically apparent postoperative complications during the presence or after the removal of the ureteral stents. One week after stent removal excretory urography showed ipsilateral mild to moderate hydroureteronephrosis in 3 dogs and no dye excretion in 6 with a normal contralateral kidney. One week later no dye excretion was detected in all except 1 dog, which showed more radiological deterioration. At the time of sacrifice there was moderate to marked hydroureteronephrosis above the level of the new tube in all dogs. Although the graft was intact in all subjects, marked shrinkage was observed. On ureteral calibration there was significant narrowing of the lumen up to complete occlusion. At 8 weeks histopathological examination showed extensive fibrosis.

CONCLUSIONS

An acellular matrix tube is not able to replace a 3 cm segment of the canine ureter.