Mesenchymal cells infiltrating a bladder acellular matrix gradually lose smooth muscle characteristics in intraperitoneally regenerated urothelial lining tissue in rats

Urinary bladder augmentation with acellular biologic scaffold-A preclinical study in a large animal model

Current strategies in urinary bladder augmentation include use of gastrointestinal segments, however, the technique is associated with inevitable complications. An acellular biologic scaffold seems to be a promising option for urinary bladder augmentation. The aim of this study was to evaluate the utility of bladder acellular matrix (BAM) for reconstruction of clinically significant large urinary bladder wall defects in a long-term porcine model. Urinary bladders were harvested from 10 pig donors. Biological scaffolds were prepared by chemically removing all cellular components from urinary bladder tissue. A total of 10 female pigs underwent hemicystectomy and subsequent bladder reconstruction with BAM. The follow-up study was 6 months. Reconstructed bladders were subjected to radiological, macroscopic, histological, immunohistochemical, and molecular evaluations. Six out of ten animals survived the 6-month follow-up period. Four pigs died during observation due to mechanical failure of the scaffold, anastomotic dehiscence between the scaffold and native bladder tissue, or occluded catheter. Tissue engineered bladder function was normal without any signs of postvoid residual urine in the bladder or upper urinary tracts. Macroscopically, graft shrinkage was observed. Urothelium completely covered the luminal surface of the graft. Smooth muscle regeneration was observed mainly in the peripheral graft region and gradually decreased toward the center of the graft. Expression of urothelial, smooth muscle, blood vessel, and nerve markers were lower in the reconstructed bladder wall compared to the native bladder. BAM seems to be a promising biomaterial for reconstruction of large urinary bladder wall defects. Further research on cell-seeded BAM to enhance urinary bladder regeneration is required.

Use of the extracellular matrix from the porcine esophagus as a graft for bladder enlargement

INTRODUCTION

Some patients with diseases that involve increased bladder pressure or low-capacity bladders may need bladder enlargement surgery. In current techniques for bladder enlargement, autologous tissue such as small intestine or colon tissue is used to perform cystoplasties, which is far from ideal for these patients. In search of biomaterials with appropriate regeneration and safety profiles, tissue engineering has resulted in preclinical studies with acellular matrices in animal models that have yielded positive preliminary results with respect to the urothelial cell and smooth muscle repopulation; these studies have primarily been performed with matrices originating from the bladder or intestinal submucosa.

OBJECTIVE

The aim of the study was to assess an extracellular matrix device derived from the porcine esophagus for augmentation cystoplasty in an animal model.

STUDY DESIGN

Seven male Wistar rats weighing 357-390 g were subjected to augmentation cystoplasty with a circular segment of the acellular matrix from the porcine esophagus. Daily postoperative follow-up was performed with evaluation of changes in body weight, behavior, and wound status.

RESULTS

During follow-up, there were no complications associated with the process. Three specimens were sacrificed at day 30, and three, at day 60. Necropsy was performed, with a description of the macroscopic findings and a morphological study. Epithelialization was observed, with different stages of mucosal development in all specimens analyzed. Repopulation of smooth muscle cells, mixed inflammatory infiltrate, and vascular neoformation were identified in the matrices.

DISCUSSION

The urothelium and fibers of the smooth muscle were observed inside the implanted matrix. Additional investigations in larger animal models that allow urodynamic evaluation of the bladder with the matrix implanted are needed. However, to compare the results of this study model with those reported in the literature, a matrix derived from an organ different from the bladder was used because it could prevent the use of an intestinal segment in augmentation cystoplasty.

CONCLUSION

The acellular porcine esophagus matrix offers positive results regarding the repopulation of the urothelium and smooth muscle when used in augmentation cystoplasty in a murine model.

Application of bladder acellular matrix in urinary bladder regeneration: the state of the art and future directions

Construction of the urinary bladder de novo using tissue engineering technologies is the “holy grail” of reconstructive urology. The search for the ideal biomaterial for urinary bladder reconstruction has been ongoing for decades. One of the most promising biomaterials for this purpose seems to be bladder acellular matrix (BAM). In this review we determine the most important factors, which may affect biological and physical properties of BAM and its regeneration potential in tissue engineered urinary bladder. We also point out the directions in modification of BAM, which include incorporation of exogenous growth factors into the BAM structure. Finally, we discuss the results of the urinary bladder regeneration with cell seeded BAM.

Tissue engineering for the oncologic urinary bladder

Urinary diversion after radical cystectomy in patients with bladder cancer normally takes the form of an ileal conduit or neobladder. However, such diversions are associated with a number of complications including increased risk of infection. A plausible alternative is the construction of a neobladder (or bladder tissue) in vitro using autologous cells harvested from the patient. Biomaterials can be used as a scaffold for naturally occurring regenerative stem cells to latch onto to regrow the bladder smooth muscle and epithelium. Such engineered tissues show great promise in urologic tissue regeneration, but are faced with a number of challenges. For example, the differentiation mesenchymal stem cells from various sources can be difficult and the smooth muscle cells formed do not precisely mimic the natural cells.

Matrix alteration and not residual sodium dodecyl sulfate cytotoxicity affects the cellular repopulation of a decellularized matrix

It has been suggested that residual cytotoxic sodium dodecyl sulfate (SDS) is responsible for the low levels of cell in-growth observed in SDS decellularized tissues. To determine whether this is the case, we used 2 washing methods to remove residual SDS and extensive biochemical, mechanical, and structural analyses to determine the effects of SDS-based decellularization on porcine anterior cruciate ligament (ACL) tissue and its propensity for cellular repopulation. The level of residual SDS in decellularized tissue was reduced using 2 different washing techniques (pH = 9 buffer, 75% ethanol). After washing in pH = 9 or 75% ethanol, residual SDS concentrations in decellularized tissues were found to be approximately 8 and 23 times less than reported SDS cytotoxic levels, respectively. It was found that SDS treatment significantly reduced glycosaminoglycan levels, increased collagen crimp amplitude and periodicity, and increased susceptibility of collagen to degradation by the gelatinase enzyme trypsin. The level of repopulation and viability of autologous ACL fibroblasts in the decellularized tissue after 28 days of culture were found to be the same regardless of the washing technique and resulting level of residual SDS in the tissue. This strongly indicates that alterations in tissue matrix biochemistry or structure from SDS treatment and not residual SDS cytotoxicity are responsible for the low cell re-population observed in SDS decellularized tissues.

Changing concepts of bladder regeneration

During the last decade, there has been a dramatic increase in studies aimed at regeneration of the urinary bladder. Many studies employed animal-derived or synthetic materials as grafts for experimental bladder augmentation models, with or without additional measures to promote regeneration, such as autologous cell transplantation or growth factor loading. However, in spite of encouraging results in several reports, few methodologies have shown proven definitive clinical utility. One major problem in these studies is the lack of a clear distinction between native and regenerated bladder in total bladder function after augmentation. Another crucial problem is the absorption and shrinkage of larger grafts, which may result from insufficient vascular supply and smooth muscle regeneration. In contrast, researchers have recently attempted to establish alternative regenerative strategies for treating bladder diseases, and have employed far more diverse approaches according to the various pathological conditions to be treated. For total replacement of the bladder after cystectomy for invasive bladder cancer, urothelium-covered neobladder with non-urinary tract backbone remains a viable choice. In addition, functional bladder diseases such as urinary incontinence, weak detrusor, or non-compliant fibrotic bladder have also been major targets for many leading research groups in this field. These conditions are studied much more from different therapeutic standpoints, aiming at the prevention or reversal of pathological conditions in muscle remodeling or neural control. Such altered research direction would inevitably lead to less surgically based basic biological research, and also would include a far wider spectrum of adult and pediatric bladder diseases, from overactive bladder to dysfunctional voiding.

Detection of Residual Tumor Cells in Bladder Biopsy Specimens: Pitfalls in the Interpretation of Cytokeratin Stains

Some patients who have had prior bladder biopsies or transurethral resections undergo a repeat resection within several months for various reasons. The detection of a few residual tumor cells in bladder specimens with prior biopsy site changes can be challenging based on histology alone. Immunohistochemistry for cytokeratins may be used as an adjunct in this situation. We have noted several cases in which keratin stains were performed and positive cells were noted, raising the issue as to whether the cytokeratin positive cells were residual tumor cells or stromal cells. Immunohistochemistry for a panel of antibodies [AE1/AE3, CAM 5.2, high molecular weight cytokeratin, smooth muscle actin (SMA), desmin, and anaplastic lymphoma kinase (ALK)] was performed on 29 cases of bladder biopsies with prior biopsy site changes. Of 29 patients, 25 had a prior history of bladder tumor: 17 had invasive high-grade urothelial carcinoma (T1, 5 cases; T2, 11 cases; T3,1 case); 7 had noninvasive high-grade papillary urothelial carcinoma; 1 had noninvasive low-grade papillary urothelial carcinoma). One of the patients with noninvasive high-grade papillary urothelial carcinoma and one of the patents with invasive high-grade urothelial carcinoma had associated carcinoma in-situ. Four patients had prior benign bladder diagnoses: cystitis cystica et glandularis; polypoid cystitis; follicular cystitis; and neurogenic bladder with benign prostate hyperplasia. Of the 29 cases, 6 (21%) had cells with staining for at least 2 of the cytokeratin markers. Cytokeratin (CK) AE1/ AE3 was positive for cells in 8/29 cases (28%). In 6 of these cases, cells displayed a spindle cell and 2 cases a more epithelioid morphology. CAM 5.2 was positive in cells in 5/29 cases (17%); 3 of the cases had spindle cell and 2 cases epithelioid morphology. High molecular weight cytokeratin was expressed in cells in 2/29 cases (7%) with 1 case having spindle cell and 1 epithelioid morphology. SMA was positive in cells with a spindle cell morphology and negative in the more epitheloid cytokeratin positive cells. Desmin was positive in 3/6 keratin positive spindle cells and negative in keratin positive epithelioid cells. ALK was negative in all the cases. Three cases with spindle cell morphology and positivity for at least 1 of the keratins and SMA stains were interpreted as aberrant keratin expression in myofibroblastic cells based on the staining and the morphology of the spindle cells. Another 3 cases with concurrent staining for at least 1 of the keratins, SMA and desmin were consistent with smooth muscle cells on the basis of their cellular morphology. Another 2 cases had cells, which expressed at least 2 CK markers but did not express SMA, desmin, or ALK and a more epithelioid morphology. These cells were interpreted as residual tumors cells. When interpreting CK stains for the detection of residual tumor cells, one should pay attention to the nature of the cells and not assume all CK staining cells are residual tumor cells.