Seeding cell approach for tissue-engineered urethral reconstruction in animal study: A systematic review and meta-analysis

Follow-up and histocompatibility observation of urethral reconstruction with different materials

OBJECTIVE

Our objective is to observe the long-term surgical results of urethral reconstruction using either pedicled penile flaps or lingual mucosa grafts. We also assess the histocompatibility of the reconstructed urethra.

MATERIALS AND METHODS

Clinical data of patients with anterior urethral stenosis undergoing urethra reconstruction by applying different materials were collected from 2014 to 2022 in the Second Hospital of Hebei Medical University. We assessed their efficacy and the occurrence of complications. Patients who required reoperation due to complications were selected. Sections of the reconstructed urethra created with various materials were excised during repair procedures. The excised tissues underwent hematoxylin-eosin staining and immunohistochemistry. Comparison with the original histological morphology was conducted to evaluate histocompatibility.

RESULTS

42 of the 55 patients were cured which showed a surgical success rate of 76.36%. The success rate of urethra reconstruction surgery utilizing lingual mucosa is 71.43% and that of surgeries using pedicled penis flaps is 79.41%. The long-term prognosis of the two groups is similar (P > 0.05). Observations show that the histological morphology of the original epithelium gradually disappeared, leading to adaptive changes to the urinary environment with favorable histocompatibility.

CONCLUSION

The application of lingual mucosal and pedicled penis flaps for urethral reconstruction both have a high surgical success rate. The long-term follow-up results are positive. Both methods are viable for urethral reconstruction and exhibit favorable histocompatibility.

Acellular dermal matrix in urethral reconstruction

The management of severe urethral stricture has always posed a formidable challenge. Traditional approaches such as skin flaps, mucosal grafts, and urethroplasty may not be suitable for lengthy and intricate strictures. In the past two decades, tissue engineering solutions utilizing acellular dermal matrix have emerged as potential alternatives. Acellular dermal matrix (ADM) is a non-immunogenic biological collagen scaffold that has demonstrated its ability to induce layer-by-layer tissue regeneration. The application of ADM in urethral reconstruction through tissue engineering has become a practical endeavor. This article provides an overview of the preparation, characteristics, advantages, and disadvantages of ADM along with its utilization in urethral reconstruction via tissue engineering.

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.

Sources, Selection, and Microenvironmental Preconditioning of Cells for Urethral Tissue Engineering

Urethral stricture is a common urinary tract disorder in men that can be caused by iatrogenic causes, trauma, inflammation, or infection and often requires reconstructive surgery. The current therapeutic approach for complex urethral strictures usually involves reconstruction with autologous tissue from the oral mucosa. With the goal of overcoming the lack of sufficient autologous tissue and donor site morbidity, research over the past two decades has focused on cell-based tissue-engineered substitutes. While the main focus has been on autologous cells from the penile tissue, bladder, and oral cavity, stem cells from sources such as adipose tissue and urine are competing candidates for future urethral regeneration due to their ease of collection, high proliferative capacity, maturation potential, and paracrine function. This review addresses the sources, advantages, and limitations of cells for tissue engineering in the urethra and discusses recent approaches to improve cell survival, growth, and differentiation by mimicking the mechanical and biophysical properties of the extracellular environment.

Creation of Tissue-Engineered Urethras for Large Urethral Defect Repair in a Rabbit Experimental Model

Introduction: Tissue engineering is a potential source of urethral substitutes to treat severe urethral defects. Our aim was to create tissue-engineered urethras by harvesting autologous cells obtained by bladder washes and then using these cells to create a neourethra in a chronic large urethral defect in a rabbit model. Methods: A large urethral defect was first created in male New Zealand rabbits by resecting an elliptic defect (70 mm²) in the ventral penile urethra and then letting it settle down as a chronic defect for 5-6 weeks. Urothelial cells were harvested noninvasively by washing the bladder with saline and isolating urothelial cells. Neourethras were created by seeding urothelial cells on a commercially available decellularized intestinal submucosa matrix (Biodesign® Cook-Biotech®). Twenty-two rabbits were divided into three groups. Group-A (n = 2) is a control group (urethral defect unrepaired). Group-B (n = 10) and group-C (n = 10) underwent on-lay urethroplasty, with unseeded matrix (group-B) and urothelial cell-seeded matrix (group-C). Macroscopic appearance, radiology, and histology were assessed. Results: The chronic large urethral defect model was successfully created. Stratified urothelial cultures attached to the matrix were obtained. All group-A rabbits kept the urethral defect size unchanged (70 ± 2.5 mm²). All group-B rabbits presented urethroplasty dehiscence, with a median defect of 61 mm² (range 34-70). In group-C, five presented complete correction and five almost total correction with fistula, with a median defect of 0.3 mm² (range 0-12.5), demonstrating a significant better result (p = 7.85 × 10^-5). Urethrography showed more fistulas in group-B (10/10, versus 5/10 in group-C) (p = 0.04). No strictures were found in any of the groups. Group-B histology identified the absence of ventral urethra in unrepaired areas, with squamous cell metaplasia in the edges toward the defect. In group-C repaired areas, ventral multilayer urothelium was identified with cells staining for urothelial cell marker cytokeratin-7. Conclusions: The importance of this study is that we used a chronic large urethral defect animal model and clearly found that cell-seeded transplants were superior to nonseeded. In addition, bladder washing was a feasible method for harvesting viable autologous cells in a noninvasive way. There is a place for considering tissue-engineered transplants in the surgical armamentarium for treating complex urethral defects and hypospadias cases.

Electrospinning: Application and Prospects for Urologic Tissue Engineering

Functional disorders and injuries of urinary bladder, urethra, and ureter may necessitate the application of urologic reconstructive surgeries to recover normal urine passage, prevent progressive damages of these organs and upstream structures, and improve the quality of life of patients. Reconstructive surgeries are generally very invasive procedures that utilize autologous tissues. In addition to imperfect functional outcomes, these procedures are associated with significant complications owing to long-term contact of urine with unspecific tissues, donor site morbidity, and lack of sufficient tissue for vast reconstructions. Thanks to the extensive advancements in tissue engineering strategies, reconstruction of the diseased urologic organs through tissue engineering have provided promising vistas during the last two decades. Several biomaterials and fabrication methods have been utilized for reconstruction of the urinary tract in animal models and human subjects; however, limited success has been reported, which inspires the application of new methods and biomaterials. Electrospinning is the primary method for the production of nanofibers from a broad array of natural and synthetic biomaterials. The biomimetic structure of electrospun scaffolds provides an ECM-like matrix that can modulate cells' function. In addition, electrospinning is a versatile technique for the incorporation of drugs, biomolecules, and living cells into the constructed scaffolds. This method can also be integrated with other fabrication procedures to achieve hybrid smart constructs with improved performance. Herein, we reviewed the application and outcomes of electrospun scaffolds in tissue engineering of bladder, urethra, and ureter. First, we presented the current status of tissue engineering in each organ, then reviewed electrospun scaffolds from the simplest to the most intricate designs, and summarized the outcomes of preclinical (animal) studies in this area.

Regenerative and engineered options for urethroplasty

Surgical correction of urethral strictures by substitution urethroplasty - the use of grafts or flaps to correct the urethral narrowing - remains one of the most challenging procedures in urology and is frequently associated with complications, restenosis and poor quality of life for the affected individual. Tissue engineering using different cell types and tissue scaffolds offers a promising alternative for tissue repair and replacement. The past 30 years of tissue engineering has resulted in the development of several therapies that are now in use in the clinic, especially in treating cutaneous, bone and cartilage defects. Advances in tissue engineering for urethral replacement have resulted in several clinical applications that have shown promise but have not yet become the standard of care.

Tissue engineering of the urethra: where are we in 2019?

Purpose

The purpose of this review is to assess the potential role of tissue engineering for urethral reconstruction. It is well- recognised that urethrotomy remains the first-line therapy in the treatment of urethral stricture. Following on from the randomised study which recommended no difference between urethrotomy and urethral dilation, Steenkamp et al. reported long-term success rates of only 20%. Patients with longer strictures, penile or distal urethral strictures, and extensive periurethral spongiofibrosis typically do not respond well to repeated incisions. This report reviews the potential role of tissue engineering as applied to augmentation urethroplasty, which is the treatment of choice following failed urethrotomy.

Methods

A review of the literature was carried out. The principal emphasis was on tissue engineering as applied to augmentation urethroplasty, but an introductory section reviews the use of urethrotomy and the background to contemporary practise with augmentation urethroplasty using oral mucosa.

Results

It is evident that a cellular matrix which requires the ingrowth of cells is unlikely to be successful except for very short strictures. Other approaches such as injection of stem cells have not been adequately trialled in humans to date. Tissue-engineered substitute for autologous oral mucosa has been used and the results relating to this are reviewed.

Conclusions

Tissue engineering of autologous tissue for urethroplasty is expensive. It is unnecessary for the majority of cases, but could be potentially useful for very lengthy strictures, for instance, relating to lichen sclerosis. Whilst tissue-engineered oral mucosa has been successfully used, a great deal more work would be necessary to develop an appropriate matrix. Another study has looked at a larger series using an alternative tissue-engineered substitute, but the results have been very disappointing. At present, it has to be concluded that there is no effective and validated tissue engineering solution for the management of urethral stricture disease.

Overview of Urethral Reconstruction by Tissue Engineering: Current Strategies, Clinical Status and Future Direction

BACKGROUND

Urinary tract is subjected to a variety of disorders such as urethral stricture, which often develops as a result of scarring process. Urethral stricture can be treated by urethral dilation and urethrotomy; but in cases of long urethral strictures, substitution urethroplasty with genital skin and buccal mucosa grafts is the only option. However a number of complications such as infection as a result of hair growth in neo-urethra, and stone formation restrict the application of those grafts. Therefore, tissue engineering techniques recently emerged as an alternative approach, aiming to overcome those restrictions. The aim of this review is to provide a comprehensive coverage on the strategies employed and the translational status of urethral tissue engineering over the past years and to propose a combinatory strategy for the future of urethral tissue engineering.

METHODs

Data collection was based on the key articles published in English language in years between 2006 and 2018 using the searching terms of urethral stricture and tissue engineering on PubMed database.

RESULTS

Differentiation of mesenchymal stem cells into urothelial and smooth muscle cells to be used for urologic application does not offer any advantage over autologous urothelial and smooth muscle cells. Among studied scaffolds, synthetic scaffolds with proper porosity and mechanical strength is the best option to be used for urethral tissue engineering.

CONCLUSION

Hypoxia-preconditioned mesenchymal stem cells in combination with autologous cells seeded on a pre-vascularized synthetic and biodegradable scaffold can be said to be the best combinatory strategy in engineering of human urethra.

Future Prospects for Human Tissue Engineered Urethra Transplantation: Decellularization and Recellularization-Based Urethra Regeneration

To evaluate the histological characteristics of decellularized human urethra after transplantation into the rat omentum and compare in vivo cell seeding with perfusion-based and cell sheet urethral regeneration. Eight adult human male urethras accompanied with the surrounding corpus spongiosum were obtained. The tissues were decellularized with detergent-based method. The efficacy of decellularization and extracellular matrix preservation was evaluated by several techniques. Decellularized scaffolds were transplanted into the omentum of 12 male rats and located into the scrotum. Biopsies were taken 1, 3, and 6 months postoperatively to assess the natural recellularization. Mesenchymal stem cells obtained from preputial tissue were seeded with perfusion-based and cell sheet techniques as well. Immunohistochemical staining with α-actin, cytokeratin AE1/AE3, synaptophysin, and CD31 antibodies were performed. Removal of nuclear components and preservation of biomechanical properties was confirmed. In-vivo recellularization revealed promising results in progressive angiogenesis and cell seeding of epithelium-like cells in the lining of the urethra as well as smooth muscle cells in the wall structure. In-vitro urethral regeneration revealed that cell sheet engineering was the technique of choice compared to perfusion-based technique. This study may paw the road for clinical application of acellular urethral matrix with the surrounding corpus spongiosum in urological reconstructive surgery.

Tissue Engineering of the Urethra: A Systematic Review and Meta-analysis of Preclinical and Clinical Studies

CONTEXT

Urethra repair by tissue engineering has been extensively studied in laboratory animals and patients, but is not routinely used in clinical practice.

OBJECTIVE

To systematically investigate preclinical and clinical evidence of the efficacy of tissue engineering for urethra repair in order to stimulate translation of preclinical studies to the clinic.

EVIDENCE ACQUISITION

A systematic search strategy was applied in PubMed and EMBASE. Studies were independently screened for relevance by two reviewers, resulting in 80 preclinical and 23 clinical studies of which 63 and 13 were selected for meta-analysis to assess side effects, functionality, and study completion. Analyses for preclinical and clinical studies were performed separately. Full circumferential and inlay procedures were assessed independently. Evaluated parameters included seeding of cells and type of biomaterial.

EVIDENCE SYNTHESIS

Meta-analysis revealed that cell seeding significantly reduced the probability of encountering side effects in preclinical studies. Remarkably though, cells were only sparsely used in the clinic (4/23 studies) and showed no significant reduction of side effects. ln 21 out of 23 clinical studies, decellularized templates were used, while in preclinical studies other biomaterials showed promising outcomes as well. No direct comparison to current clinical practice could be made due to the limited number of randomized controlled studies.

CONCLUSIONS

Due to a lack of controlled (pre)clinical studies, the efficacy of tissue engineering for urethra repair could not be determined. Meta-analysis outcome measures were similar to current treatment options described in literature. Surprisingly, it appeared that favorable preclinical results, that is inclusion of cells, were not translated to the clinic. Improved (pre)clinical study designs may enhance clinical translation.

PATIENT SUMMARY

We reviewed all available literature on urethral tissue engineering to assess the efficacy in preclinical and clinical studies. We show that improvements to (pre)clinical study design is required to improve clinical translation of tissue engineering technologies.