Histological and immunohistochemical changes in the rat oral mucosa used as an autologous urethral graft

Evaluation of Bi-layer Silk Fibroin Grafts for Onlay Urethroplasty in a Female Porcine Model of Long Urethral Strictures

BACKGROUND

Buccal mucosa urethroplasty represents the primary strategy for reconstruction of long urethral strictures (US). However, significant complications including stricture recurrence and donor site morbidity currently hamper this approach. The goal of this study was to determine the efficacy of acellular, bi-layer silk fibroin (BLSF) biomaterials to serve as superior alternatives to buccal mucosal (BM) grafts for repair of 4 cm long US in female swine.

METHODS

Urethral mucosal damage was induced over 4-5 cm long segments via electrocoagulation in adult female swine (N = 10) to promote US over the course of 2-4 weeks. Onlay urethroplasty with BLSF scaffolds or autologous BM grafts (N = 5 per group, ~ 4 cm2) was subsequently performed and animals were maintained for 3 months. Outcome analyses included urethroscopy, retrograde urethrography (RUG), and histological and immunohistochemical (IHC) analyses. Non operated urethral segments served as internal controls (N = 10).

RESULTS

All swine survived the study with no severe complications and exhibited US formation following electrocoagulation with a 43-57% reduction in baseline calibers. At 3 months post-op, imaging modalities revealed both graft cohorts promoted > 80% restoration of native urethral calibers. Histological and IHC evaluations showed BLSF grafts supported the formation of innervated, vascularized urethral-like neotissues with α-smooth muscle actin + and SM22α + smooth muscle bundles as well as pan-cytokeratin + epithelia reminiscent of controls. In contrast, BM grafts primarily retained native oral tissue morphology after urethral transposition exhibiting cytokeratin 1 + stratified, squamous epithelia and scant muscle formation.

CONCLUSIONS

BLSF matrices can promote functional restoration of long US via regeneration of native urethral tissues.

Histological, histochemical, and immunohistochemical characterization of NANOULCOR nanostructured fibrin-agarose human cornea substitutes generated by tissue engineering

BACKGROUND

Human artificial corneas (HAC) generated by tissue engineering recently demonstrated clinical usefulness in the management of complex corneal diseases. However, the biological mechanisms associated to their regenerative potential need to be elucidated.

METHODS

In the present work, we generated HAC using nanostructured fibrin-agarose biomaterials with cultured corneal epithelial and stromal cells, and we compared the structure and histochemical and immunohistochemical profiles of HAC with control native corneas (CTR-C) and limbus (CTR-L) to determine the level of biomimicry of the HAC with these two native organs.

RESULTS

HAC tissues consisted of a stratified epithelium and a cellular stromal substitute. The interface between stroma and epithelium was similar to that of CTR-C, without the finger-shaped palisades of Vogt found in CTR-L, and contained a poorly developed basement membrane as determined by PAS histochemistry. Analysis of the stromal layer revealed that HAC contained significantly lower amounts of extracellular matrix components (collagen, proteoglycans, decorin, keratocan, and lumican) than CTR-C and CTR-L, with all samples being devoid of elastic and reticular fibers. At the epithelial level, HAC were strongly positive for several cytokeratins, although KRT5 was lower in HAC as compared to CTR-C and CTR-L. The expression of crystallin lambda was lower in HAC than in control tissues, whereas crystallin alpha-a was similar in HAC and CTR-C. No differences were found among HAC and controls for the cell-cell junction proteins CX43 and TJP1. When specific markers were analyzed, we found that HAC expression profile of KRT3, KRT19, KRT15, and ΔNp63 was more similar to CTR-L than to CTR-C.

CONCLUSIONS

These results suggest that HAC generated in the laboratory could be structurally and functionally more biomimetic to the structure found at the corneal limbus than to the central cornea, and open the door to the use of these artificial tissues in patients with limbal deficiency.

Direct oral mucosal epithelial transplantation supplies stem cells and promotes corneal wound healing to treat refractory persistent corneal epithelial defects

Persistent corneal epithelial defects (PED) can lead to irreversible blindness, seriously affecting the social function and life quality of these patients. When it comes to refractory PED, such as limbal stem cell deficiency (LSCD), that does not respond to standard managements, stem cell therapy is an ideal method. Oral mucosal epithelium (OME) abundant with stem cells within the base, is a promising autologous biomaterial, with much resemblance to corneal epithelial structures. In this experiment, uncultured autologous rat OME was directly applied to alkali burned corneas. Clinical evaluations and histological analyses showed that the transplantation accelerated the healing process, presenting faster re-epithelization and better formation of corneal epithelial barrier. To further investigate the therapeutic mechanism, oral epithelium was transplanted to de-epithelialized cornea in vitro for organ culture. It could be observed that the oral epithelial cells could migrate to the corneal surface and form smooth and stratified epithelium. Immunofluorescence staining results showed that the re-formed epithelium derived from OME, maintained stemness and transformed to corneal epithelial phenotype to some extent. Corneal stroma may provide the suitable microenvironment to promote the trans-differentiation of oral stem cells. Thus, both in vivo and in vitro experiments suggested that oral epithelium could play a positive role in treating refractory PED.

Preclinical Experiments for Hypospadias Surgery: Systematic Review and Quality Assessment

Background: There is a steadily growing number of different reconstructive surgical procedures for hypospadias that were tested on animal models prior to their human application. However, the clinical translatability and reproducibility of the results encountered in preclinical urethral reconstruction experiments is considered poor, with significant factors contributing to the poor design and reporting of animal experiments. Our objective was to evaluate the quality of the design and reporting in published articles of urethral reconstructive preclinical studies. Methods: Both PubMed and EMBASE databases were searched for animal urethral repair experiments between January 2014 and September 2019. Internal quality (bias) was evaluated through several signaling questions arising from the Systematic Review Centre for Laboratory animal Experimentation (SYRCLE), while the quality of reporting was assessed by the Animal Research: Reporting of In vivo Experiments (ARRIVE) guidelines by scoring of a 20-item checklist. Results: A total of 638 articles were initially screened after the literature search. Employing the inclusion and exclusion criteria, 30 studies were chosen for full-text screening and 21 studies were considered eligible for the quality assessment. The mean score of the checklist was 66%. The elements that accomplished the highest grades included the number of animals utilized, the number in each investigational and control group, and the delineation of investigational conclusions. The items that were least commonly stated comprised information about the experimental method, housing and husbandry, rationalization of the number of animals, and reporting of adverse events. No paper stated the sample size estimation. Conclusion: We found that several critical experiment design principles were poorly reported, which hinders a rigorous appraisal of the scientific quality and reproducibility of the experiments. A comprehensive implementation of the ARRIVE guidelines in animal studies exploring urethral repair is necessary to facilitate the effective translation of preclinical research findings into clinical therapies.

Buccal Mucosa Tube Graft for Failed Hypospadias Repair: Worth it or Not?

OBJECTIVE

To report the outcome of buccal mucosa tube graft (BMTG) over time in correcting failed hypospadias.

METHODS

We conducted a retrospective analysis, reviewing charts of all 69 patients who underwent BMTG to repair hypospadias between January 2005 and October 2016. Twenty-one patients were excluded, leaving 48 eligible study subjects. In patients with penile curvatures, corrective procedures (including urethral division, corporoplasty, and local skin flap) took place prior to grafting.

RESULTS

Mean age at surgery was 8.96 years, and mean duration of follow-up was 73.10 ± 30.31 months. A mean of 1.88 previous surgeries was recorded. During follow-up, only 7 patients (14.5%) were complication free. The other 41 patients required at least 1 additional procedure. Stricture-free rates were 50%, 35.4%, and 27% at 1, 3, and 12 months after BMTG, respectively. Among 37 patients with postoperative stricture, 25 were treated only by endoscopic procedures. Single operation prior to BMTG (P= .004) and usage of larger catheter size (>8Fr) (P = .029) were confirmed significant factors associated with better stricture-free survival after BMTG by log-rank test. After several additional procedures, 46 patients (95.8%) reported normal urination with mean maximal urinary flow of 9.55 mL/s and post-void residual of 16.08 mL for at least 12 months on last visit.

CONCLUSION

BMTG after failed hypospadias repair seems prone to complications, primarily urethral stricture. However, a large number of patients with postoperative stricture could be treated simply by endoscopic procedures. Given the better results of staged approach, BMTG should be only applied to highly selected patients with failed hypospadias.

Tissue engineering of urethra: Systematic review of recent literature

The purpose of this article was to perform a systematic review of the recent literature on urethral tissue engineering. A total of 31 articles describing the use of tissue engineering for urethra reconstruction were included. The obtained results were discussed in three groups: cells, scaffolds, and clinical results of urethral reconstructions using these components. Stem cells of different origin were used in many experimental studies, but only autologous urothelial cells, fibroblasts, and keratinocytes were applied in clinical trials. Natural and synthetic scaffolds were studied in the context of urethral tissue engineering. The main advantage of synthetic ones is the fact that they can be obtained in unlimited amount and modified by different techniques, but scaffolds of natural origin normally contain chemical groups and bioactive proteins which increase the cell attachment and may promote the cell proliferation and differentiation. The most promising are smart scaffolds delivering different bioactive molecules or those that can be tubularized. In two clinical trials, only onlay-fashioned transplants were used for urethral reconstruction. However, the very promising results were obtained from animal studies where tubularized scaffolds, both non-seeded and cell-seeded, were applied. Impact statement The main goal of this article was to perform a systematic review of the recent literature on urethral tissue engineering. It summarizes the most recent information about cells, seeded or non-seeded scaffolds and clinical application with respect to regeneration of urethra.

Systematic Review to Compare Urothelium Differentiation with Urethral Epithelium Differentiation in Fetal Development, as a Basis for Tissue Engineering of the Male Urethra

BACKGROUND

Tissue-engineered (TE) urethra is desirable in men with urethral disease (stricture or hypospadias) and shortage of local tissue. Although ideally a TE graft would contain urethral epithelium cells, currently, bladder epithelium (urothelium) is widely used, but morphologically different. Understanding the differences and similarities of urothelium and urethral epithelium could help design a protocol for in vitro generation of urethral epithelium to be used in TE grafts for the urethra.

PURPOSE

To understand the development toward urethral epithelium or urothelium to improve TE of the urethra.

METHODS

A literature search was done following PRISMA guidelines. Articles describing urethral epithelium and bladder urothelium development in laboratory animals and humans were selected.

RESULTS

Twenty-nine studies on development of urethral epithelium and 29 studies on development of urothelium were included. Both tissue linings derive from endoderm and although adult urothelium and urethral epithelium are characterized by different gene expression profiles, the signaling pathways underlying their development are similar, including Shh, BMP, Wnt, and FGF. The progenitor of the urothelium and the urethral epithelium is the early fetal urogenital sinus (UGS). The urethral plate and the urothelium are both formed from the p63+ cells of the UGS. Keratin 20 and uroplakins are exclusively expressed in urothelium, not in the urethral epithelium. Further research has to be done on unique markers for the urethral epithelium.

CONCLUSION

This review has summarized the current knowledge about embryonic development of urothelium versus urethral epithelium and especially focuses on the influencing factors that are potentially specific for the eventual morphological differences of both cell linings, to be a basis for developmental or tissue engineering of urethral tissue.

Development of a multilayered palate substitute in rabbits: a histochemical ex vivo and in vivo analysis

Current tissue engineering technology focuses on developing simple tissues, whereas multilayered structures comprising several tissue types have rarely been described. We developed a highly biomimetic multilayered palate substitute with bone and oral mucosa tissues using rabbit cells and biomaterials subjected to nanotechnological techniques based on plastic compression. This novel palate substitute was autologously grafted in vivo, and histological and histochemical analyses were used to evaluate biointegration, cell function, and cell differentiation in the multilayered palate substitute. The three-dimensional structure of the multilayered palate substitute was histologically similar to control tissues, but the ex vivo level of cell and tissue differentiation were low as determined by the absence of epithelial differentiation although cytokeratins 4 and 13 were expressed. In vivo grafting was associated with greater cell differentiation, epithelial stratification, and maturation, but the expression of cytokeratins 4, 13, 5, and 19 at did not reach control tissue levels. Histochemical analysis of the oral mucosa stroma and bone detected weak signals for proteoglycans, elastic and collagen fibers, mineralization deposits and osteocalcin in the multilayered palate substitute cultured ex vivo. However, in vivo grafting was able to induce cell and tissue differentiation, although the expression levels of these components were always significantly lower than those found in controls, except for collagen in the bone layer. These results suggest that generation of a full-thickness multilayered palate substitute is achievable and that tissues become partially differentiated upon in vivo grafting.

Buccal grafts for urethroplasty in pre-pubertal boys: what happens to the neourethra after puberty?

OBJECTIVE

Buccal mucosa grafts (BMG) are often used in complex urethral reconstruction. Following pubertal endogenous androgen stimulation (EAS) in prepubertal boys, there are concerns that the neourethra may not grow proportionally to the phallus. To address the paucity of literature on the topic, this article reports on data for post-pubertal follow up after pre-pubertal BMG urethroplasties (BMGU).

PATIENTS AND METHODS

Retrospective chart review of boys who underwent staged BMGU before the age of 12 years at a single referral center between 2000 and 2010 and who were followed up until after puberty. Demographic information, initial meatal location, quality of graft before tubularization, flow rate parameters (FRP) and complications were captured.

RESULTS

Of the 137 patients who underwent staged BMGU during the study period, 10 satisfied the inclusion criteria. Mean patient age at first stage BMGU was eight years (range five to eleven years). The mean follow-up was 40.6 months (9-66 months). The grafts were harvested from the cheek and lower lip in seven and three cases, respectively. The mean interval between the first and second stage was 15.8 months (6-87 months). Complications included one urethro-cutaneous fistula and two cases of glanular dehiscence. The final position of the meatus was glanular in nine boys and coronal in one. Importantly, no recurrent ventral curvature (VC) was found during the second stage BMGU or reported after puberty. All patients demonstrated normal maximum flow after puberty (mean 25.7 ml/s).

CONCLUSION

Buccal mucosa grafts appear to grow proportionally to the phallus after pubertal EAS. No recurrent VC or inadequate FRP were observed in this series. Despite the small number of subjects, the results are reassuring and support continued use of BMG in the pediatric pre-pubertal population.