Bladder acellular matrix graft in rats: its neurophysiologic properties and mRNA expression of growth factors TGF-alpha and TGF-beta

What's in the Pipeline about Bladder Reconstructive Surgery? Some Remarks on the State of the Art

The fusion of engineering with cell biology and advances in biomaterials may lead to de novo construction of implantable organs. Engineering of neobladder from autologous urothelial and smooth muscle cells cultured on biocompatible, either synthetic or naturally-derived substrates, is now feasible in preclinical studies and may have clinical applicability in the near future. The development of a bioartificial bladder would warrant the prevention of both the metabolic and neoplastic shortcomings of the intestinal neobladder. Two tissue-engineering techniques for bladder reconstruction have been tested on animals: 1) the in vivo technique involves the use of naturally-derived biomaterials for functional native bladder regeneration 2) the in vitro technique involves the establishment of autologous urothelial and smooth muscle cell culture from the host's urinary tract, after which the cells are seeded on the biodegradable matrix-scaffold to create a composite graft that is implanted into the same host for complete histotectonic regeneration. Waiting for the creation of a complete tissue-engineered bladder with a trigone-shaped base, we suggest, in surgical oncology after radical cystectomy, the realization of conduit or continent pouch using tissue-engineered material.

Ex vivo Functional Evaluation of Isolated Strips in BAMG Tissue-Engineered Bladders

Although gastrointestinal segments have been widely used for bladder augmentation, they are still not considered ideal sources due to the possibility of complications. In this study, with the aim of reducing complications, we performed bladder augmentation in pigs using bladder acellular matrix grafts (BAMG) as a scaffold. Three months after surgery, the BAMG tissue-engineered bladders revealed bladder reconstruction that morphologically resembled that of the normal bladder. Functional experiments were performed to evaluate the contractile characteristics of isolated strips from both normal and BAMG tissue-engineered bladders 3 months after augmentation. No significant differences between these two groups were found in spontaneous contraction and contraction after electric stimulation; in the relaxing effect of epinephrine on potassium chloride-induced twitch height; in the contracting effects of acetylcholin; or in the antagonistic effect of atropine on acetylcholine-induced contraction.

These results demonstrate that not only can BAMG tissue-engineered bladders be histologically reconstructed, they also possess electrophysiological and pharmacological characteristics similar to normal bladders. This further confirms BAMG as an ideal scaffold for bladder augmentation.

Seeding Homologous Adipose-Derived Stem Cells and Bladder Smooth Muscle Cells Into Bladder Submucosa Matrix for Reconstructing the Ureter in a Rabbit Model

BACKGROUND

Congenital or acquired abnormalities may result in ureteral malformation, trauma, or defect. Traditional reconstructive methods are often associated with numerous complications. Tissue engineering technology may provide an alternate avenue for ureteral reconstruction. In this study, we constructed tissue-engineered tubularized grafts (TETGs) by seeding homologous adipose-derived stem cells (ADSCs) and bladder smooth muscle cells (SMCs) into bladder submucosa matrix (BSM) for ureteral reconstruction in rabbit models.

METHODS

ADSCs and bladder SMCs were seeded onto 2 sides of the BSM, respectively. Then the grafts were used to construct TETGs of 4.0 cm length and 8.0 mm diameter and were transplanted into the omentum of rabbits for 2 weeks before ureteral reconstruction. The 4.0-cm segment of the ureter was replaced by the TETG. Evolutionary formation of tissue structures and degree of epithelization were evaluated with the use of histologic and immunohistochemical techniques at 2, 4, 8, and 16 weeks after implantation.

RESULTS

All of the rabbits were alive until they were killed. Histologic and immunohistochemical analyses showed consistent regeneration of mature and functional urothelium. At 16 weeks after TETG implantation, multilayered urothelium covered the entire lumen, with visible neovascularization in the center and formation of organized smooth muscle bundles.

CONCLUSIONS

We successfully constructed a tissue-engineered transplanted graft by seeding ADSCs and SMCs onto the BSM for ureteral repair and reconstruction in a rabbit model.

In situ tissue regeneration through host stem cell recruitment

The field of tissue engineering has made steady progress in translating various tissue applications. Although the classical tissue engineering strategy, which involves the use of culture-expanded cells and scaffolds to produce a tissue construct for implantation, has been validated, this approach involves extensive cell expansion steps, requiring a lot of time and laborious effort before implantation. To bypass this ex vivo process, a new approach has been introduced. In situ tissue regeneration utilizes the body's own regenerating capacity by mobilizing host endogenous stem cells or tissue-specific progenitor cells to the site of injury. This approach relies on development of a target-specific biomaterial scaffolding system that can effectively control the host microenvironment and mobilize host stem/progenitor cells to target tissues. An appropriate microenvironment provided by implanted scaffolds would facilitate recruitment of host cells that can be guided to regenerating structural and functional tissues.

Equine cellular therapy--from stall to bench to bedside?

Pioneering clinical stem cell research is being performed in the horse, a recipient of cutting edge veterinary medicine as well as a unique animal model, paving the way for human medical applications. Although demonstrable progress has been made on the clinical front, in vitro characterization of equine stem cells is still in comparatively early stages. To translate the promising results of clinical stem cell therapy in the horse, advances must be made in the characterization of equine stem cells. Aiming to improve communication between veterinarians and other natural scientists, this review gives an overview of veterinary "bedside" achievements, focusing on stem cell therapies in equine orthopedics as well as the current state of in vitro characterization of equine multipotent mesenchymal stromal cells (MSCs) and equine embryonic stem cells (ESCs).

Adrenal extracellular matrix scaffolds support adrenocortical cell proliferation and function in vitro

Transplantation of functional adrenal cortex cells could reduce morbidity and increase the quality of life of patients with adrenal insufficiency. Our aim was to determine whether adrenal extracellular matrix (ECM) scaffolds promote adrenocortical cell endocrine function and proliferation in vitro. We seeded decellularized porcine adrenal ECM with primary human fetal adrenocortical (HFA) cells. Adrenocortical function was quantified by cortisol secretion of HFA-ECM constructs after stimulation with adrenocorticotropic hormone. Proliferation was assessed by adenosine triphosphate assay. HFA-ECM construct morphology was evaluated by immunofluorescence microscopy and scanning electron microscopy. Adrenal HFA-ECM constructs coated with laminin were compared to uncoated constructs. Laminin coating did not significantly affect HFA morphology, proliferation, or function. We demonstrated HFA cell attachment to adrenal ECM scaffolds. Cortisol production and HFA cell proliferation were significantly increased in HFA-ECM constructs compared to controls (p < 0.05), and cortisol secretion rate per cell is comparable to that of human adult and fetal explants. We conclude that adrenal ECM supports endocrine function and proliferation of adrenocortical cells in vitro. Adrenal ECM scaffolds may form the basis for biocompatible tissue-engineered adrenal replacements.

Nerve growth factor combined with vascular endothelial growth factor enhances regeneration of bladder acellular matrix graft in spinal cord injury-induced neurogenic rat bladder

OBJECTIVE

To determine the combined effects of nerve growth factor (NGF) and vascular endothelial growth factor (VEGF) on regeneration of the bladder acellular matrix graft (BAMG) in spinal cord injury (SCI)-mediated neurogenic bladder in rats.

MATERIALS AND METHODS

In all, 40 female Sprague-Dawley rats were used. At 8 weeks after spinalization surgery (neurogenic bladder), they were divided into five groups consisting of untreated controls and those whose bladders were injected with either no growth factor, NGF (2 microg/rat), VEGF (2 microg/rat) or both at partial BAMG replacement surgery. After 8 weeks, bladder function was assessed by urodynamic studies and the bladders were harvested for histological examination. Smooth muscle induction, collagen and nerve fibre regeneration were assessed immunohistochemically using antibodies to smooth muscle actin (alpha-actin), Masson's trichrome and protein gene product 9.5, respectively.

RESULTS

Bladder capacity and compliance were significantly increased in all BAMG groups 8 weeks after surgery compared with that before bladder replacement surgery. Bladder capacity and compliance were much higher in the VEGF and NGF combined group than in the control, or NGF and VEGF alone groups. There was no significant difference in the residual volume ratio among all groups.

CONCLUSIONS

This is the first report showing that NGF has a significant synergistic effect on the development, differentiation and functional restoration of the BAMG when administered with VEGF in neurogenic bladder. Our results indicate that NGF may be a useful cytokine for enhancing the regeneration of a functional bladder following acellular matrix grafting in a neurogenic rat model.

Time-Dependent Neovasculogenesis and Regeneration of Different Bladder Wall Components in the Bladder Acellular Matrix Graft in Rats

OBJECTIVES

To determine the time-dependent regeneration of different cellular components in the bladder acellular matrix graft (BAMG) and the involvement of hematopoietic stem cells in BAMG vascular regeneration.

METHODS AND MATERIALS

Thirty-three male Sprague Dawley rats underwent partial cystectomy and the acellular matrices were grafted to the remaining host bladder. At 4, 7, 14, 30, 60, 90, and 180 d after grafting, animals were sacrificed and their bladders were excised and paraffin-embedded. Tissue sections were stained for determination of CD3, CD20, CD34, CD31, CD68, smooth muscle cell (SMC) alpha-actin, and neurofilament protein as well as elastin fibers and collagen typing. Cystometric evaluation of grafted bladders was also performed 3 mo after procedure.

RESULTS

In acellular matrices, there was no expression of cellular markers and type-1 collagen fibers were predominant. One month after surgery, all grafted matrices were completely lined with urothelium. Polymorphonuclear cells and lymphocytes densely infiltrated BAMG during the first 2 wk after grafting; however the inflammation resolved by the first post-surgical mo. CD34+ endothelial progenitor cells (EPCs) were found in all grafts 4 d after surgery. The number of CD34+ cells increased continuously and peaked 2 mo after grafting. The increment in number of CD31+ microvessels in grafted matrices followed that of CD34+ cells and reached 144.5% of control values at third post-surgical mo. The mean number of CD34+ and CD31+ cells returned to control ranges by 6 mo after grafting. Expression of SMC alpha-actin was first visualized on day 4 and alpha-actin intensity reached to control values 6 mo after grafting. Neural elements appeared 1 wk after grafting and just 60% of normal intensity was achieved by the sixth post-surgical mo; however complete nerve bundles were found in all grafted matrices after 1 mo. Cystometric studies revealed higher bladder capacity and compliance but lower maximum intravesical pressure in grafted bladders in comparison with controls, 3 mo after surgery.

CONCLUSIONS

Our results demonstrate the effective cellular regeneration in BAMG and propose a considerable role for the CD34+ EPCs in the neo-vasculogenesis of the grafts.

Functional improvement in spinal cord injury-induced neurogenic bladder by bladder augmentation using bladder acellular matrix graft in the rat

Spinal cord injury (SCI) rostral to the lumbosacral level causes bladder hyperreflexia and detrusor-sphincter dyssynergia (DSD), which are accompanied by bladder hypertrophy. We hypothesize that bladder augmentation using a bladder acellular matrix graft (BAMG) can improve the function of SCI-mediated neurogenic bladder. In female rats (n = 35), SCI was induced by transection of the spinal cord at the lower thoracic level. Eight weeks following spinalization, bladder augmentation using BAMG was performed after hemicystectomy of the hypertrophic bladder. Cystometrography was performed at 8 weeks after spinalization and again at 8 weeks after augmentation. Several urodynamic parameters were measured and the grafted bladder was histologically evaluated. Thirty one rats were alive 8 weeks after spinalization. Twenty two (71%) rats developed hyperreflexic bladders and nine (29%) rats had underactive bladders before bladder augmentation. Twenty six rats survived until 8 weeks after augmentation. Urodynamic parameters showed improvement in some bladder functions in both hyperreflexic and underactive bladders after augmentation. In addition, bladder compliance was increased in hyperreflexic bladders and decreased in underactive bladders. Bladder augmentation decreased bladder capacity in high-capacity rats and increased it in low-capacity rats. Histological evaluation showed complete regeneration of BAMG in SCI-induced neurogenic bladder at 8 weeks after augmentation. This is the first report suggesting that the voiding function in SCI-induced neurogenic bladder can be improved by augmentation using BAMG. Improved voiding function was accompanied by histological regeneration of BAMG.

Bladder acellular matrix grafting regenerates urinary bladder in the spinal cord injury rat

OBJECTIVES

To assess the feasibility of bladder acellular matrix (BAM) grafting onto the bladder of rats with spinal cord injury (SCI).

METHODS

Female Wistar rats, weighing 100 to 150 g, were divided into four groups: neurologically intact groups with sham operation or BAM grafting and SCI rats with or without BAM grafting (grafted groups, n = 15 each; nongrafted groups, n = 5 each). The BAM was prepared from other normal rat bladder tissue. During BAM surgery, the rats underwent partial cystectomy, followed by BAM grafting as a bladder augmentation. The SCI was created by compressing the spinal cord at the 10th thoracic level. BAM grafting in SCI rats was performed 2 to 3 weeks after SCI. At 2, 4, and 12 weeks after grafting, cystometry was performed with the rats under pentobarbital anesthesia, and the bladders were subsequently harvested and immunostained with anti-PGP9.5, uroplakin III, and alpha-smooth muscle actin antibodies (n = 5 each time). For comparison, similar examinations were performed in the nongrafted groups (n = 5 each).

RESULTS

Regenerated urothelium, smooth muscles, and nerve fibers in the grafted BAM appeared at 2, 4, and 12 weeks, respectively, in both intact and SCI rats. Immunohistologic examination showed that these regenerated tissues inherited each characteristic of the host bladder tissue. The grafted BAM itself also showed the proper storage function of distensibility in the intact and SCI groups receiving BAM.

CONCLUSIONS

Our data have indicated that BAM grafting is feasible, even in animals with spinal injury, suggesting that BAM may be one of the alternatives for patients with a neurogenic bladder who require augmentation enterocystoplasty in clinical situations.

Effect of vascular endothelial growth factor on regeneration of bladder acellular matrix graft: Histologic and functional evaluation

OBJECTIVES

To evaluate the effect of vascular endothelial growth factor (VEGF) on regeneration of the bladder acellular matrix graft (BAMG).

METHODS

A total of 40 female rats were divided into two groups. In the experimental group (VEGF+), the BAMG was incubated in VEGF and VEGF was injected into the host bladder. In the control rats, sterile solution replaced VEGF. Urodynamic studies were performed at grafting and repeated at 2, 4, 8, and 12 weeks. The bladders were harvested for histologic examination. Immunostaining was used to monitor VEGF treatment by examining VEGF and VEGF-receptor 2 expression. Neovascularity, smooth muscle induction, and nerve regeneration were assessed immunohistochemically.

RESULTS

Increased VEGF and VEGF-receptor 2 were present in the VEGF+ rats 2 weeks after grafting. The maximal intravesical pressure was significantly greater in the VEGF+ group at 2 weeks than in the controls, despite the same bladder capacity. At 4 weeks, a significant increase in bladder capacity and a decrease in the postvoid residual volume ratio were observed. After 8 weeks, no differences were noted in the urodynamic parameters between the two groups. Numerous alpha-actin-positive spindle cells were observed in the VEGF+ rats at 2 weeks, and the smooth muscle content was significantly greater at all points. Enhanced angiogenesis was noted at 2 and 4 weeks. Nerve fibers were observed at 4 weeks and nerve growth factor-positive cells were significantly greater at 2, 4, and 8 weeks in the VEGF+ rats.

CONCLUSIONS

Administration of VEGF had significant effects on the BAMG at early periods after grafting. Our results have shown that VEGF enhances BAMG regeneration in rats as assessed by functional restoration and histologic examination.

Porosity of porcine bladder acellular matrix: impact of ACM thickness

The objectives of this study are to examine the porosity of bladder acellular matrix (ACM) using deionized (DI) water as the model fluid and dextran as the indicator macromolecule, and to correlate the porosity to the ACM thickness. Porcine urinary bladders from pigs weighing 20-50 kg were sequentially extracted in detergent containing solutions, and to modify the ACM thickness, stretched bladders were acellularized in the same manner. Luminal and abluminal ACM specimens were subjected to fixed static DI water pressure (10 cm); and water passing through the specimens was collected at specific time interval. While for the macromolecule porosity testing, the diffusion rate and direction of 10,000 MW fluoroescein-labeled dextrans across the ACM specimens mounted in Ussing's chambers were measured. Both experiments were repeated on the thin stretched ACM. In both ACM types, the fluid porosity in both directions did not decrease with increased test duration (3 h); in addition, the abluminal surface was more porous to fluid than the luminal surface. On the other hand, when comparing thin to thick ACM, the porosity in either direction was higher in the thick ACM. Macromolecule porosity, as measured by absorbance, was higher for the abluminal thick ACM than the luminal side, but this characteristic was reversed in the thin ACM. Comparing thin to thick ACM, the luminal side in the thin ACM was more porous to dextran than in the thick ACM, but this characteristic was reversed for the abluminal side. The porcine bladder ACM possesses directional porosity and acellularizing stretched urinary bladders may increase structural density and alter fluid and macromolecule porosity.

The extracellular matrix as a scaffold for tissue reconstruction

The extracellular matrix (ECM) consists of a complex mixture of structural and functional proteins and serves an important role in tissue and organ morphogenesis, maintenance of cell and tissue structure and function, and in the host response to injury. Xenogeneic and allogeneic ECM has been used as a bioscaffold for the reconstruction of many different tissue types in both pre-clinical and human clinical studies. Common features of ECM-associated tissue remodeling include extensive angiogenesis, recruitment of circulating progenitor cells, rapid scaffold degradation and constructive remodeling of damaged or missing tissues. The ECM-induced remodeling response is a distinctly different phenomenon from that of scar tissue formation.

The bladder acellular matrix graft in a rat chemical cystitis model: functional and histologic evaluation

PURPOSE

We investigated the feasibility of augmentation in a diseased bladder with a bladder acellular matrix graft.

MATERIALS AND METHODS

In 50 female Sprague-Dawley rats chemical cystitis was induced by intravesical instillation of HCl repeated monthly to maintain chronic inflammation. Urodynamic studies were performed in all rats 1 week after the induction of chemical cystitis and repeated at sacrifice. The 29 rats in the experimental group underwent partial cystectomy (50% or greater), followed by bladder acellular matrix graft augmentation, while the 21 controls underwent monthly HCl instillation only. The rats were sacrificed at 2 weeks, 1, 2 and 3 months, respectively. The bladder was removed and examined for histological changes.

RESULTS

Urodynamic studies showed that bladder capacity and compliance were significantly higher in the grafted than in the control group (p = 0.008 and 0.006, respectively, at 3 months). Histological studies revealed urothelial and smooth muscle regeneration within the bladder acellular matrix graft at 1 month and nerve regeneration at 3. The number of mast cells was significantly lower in the grafted region than in the host bladder of all grafted rats (p <0.001).

CONCLUSIONS

In this rat chemical cystitis model bladder augmentation with a bladder acellular matrix graft led to functional and histological improvement over diseased host bladder.

Heterologous acellular matrix graft for reconstruction of the rabbit urethra: histological and functional evaluation

PURPOSE

In a rabbit model we evaluated urethral replacement by a free heterologous dog acellular matrix graft and compared these results with those of a homologous graft with the exclusion of antigenicity as a major goal.

MATERIALS AND METHODS

In 14 male New Zealand rabbits a 0.8 to 1.1 cm. segment of urethra was resected and replaced with a tubular acellular 1.0 to 1.5 cm. (mean 1.3) urethral matrix graft placed on an 8Fr feeding tube. Seven animals received a rabbit graft, 7 received a canine graft and 3 untreated rabbits served as controls. All animals underwent urethral pressure profile determination and retrograde urethrography before 8 and 6 were sacrificed at 6 and 8 months, respectively. Grafted and normal specimens were evaluated by histological testing.

RESULTS

In all animals the acellular matrix graft remained in its original position. Histological examination showed complete epithelialization and progressive vessel infiltration. At 6 months more than a third of the homologous grafts had smooth muscle bundles but the heterologous grafts had only poorly disseminated smooth muscle. Picrosirius red stain demonstrated a shift in the ratio of collagen types I-to-III with an increase in type III in the processed homologous and heterologous matrices that did not change significantly postoperatively. At 8 months the urethral pressure profile detected no difference in control and matrix grafted animals, and urethrography did not readily differentiate host from implant.

CONCLUSIONS

In the heterologous matrix all tissue components were present after 6 months with no signs of rejection and even gradual improvement with time. However, regenerated smooth muscle did not equal that in normal rabbit urethra and it was not well oriented. Even after 8 months only a few disseminated smooth muscle cells were evident. Most alpha-actin positive cells were surrounding the vessels. Although function was normal, the alteration in the collagen ratio effected by matrix production indicated that the matrix collagen appeared not to have been replaced by host collagen. The increase in collagen type III may explain the lack of stricture in the grafted animals on normal retrourethrography.

Biomaterials in functional reconstruction

Recent initiatives in the development of biomaterials for functional reconstruction involve the alloplasts, the biological and the bioengineered biomaterials. Anti-infective alloplastic biomaterials (Foley catheters coated with rifampicin/minocycline bonded to silicone or ciprofloxacin liposome-containing hydrogel) allow a reduction in the rate of bacterial contamination, but the risk of future bacterial resistance is a matter for concern. New generations of biologic collagen-based tissue-matrix grafts are derived from bladder (bladder acellular matrix graft and bladder submucosa collagen matrix), ureter or small intestine (subintestinal submucosa). There are high hopes that these materials may have applications in augmentation cystoplasty. Using tissue engineering (autologous cells expanded in vitro and grafted onto biodegradable matrix), biocompatible malleable penile prostheses have been obtained experimentally. Most of the results obtained with these new biomaterials are exclusively experimental, but they offer great hope for future functional reconstruction of the urinary tract.

Homologous bladder augmentation in dog with the bladder acellular matrix graft

OBJECTIVE

To determine the functional potential and antigenicity of the homologous bladder acellular matrix graft (BAMG) in a dog model.

MATERIALS AND METHODS

Seven mongrel dogs underwent partial cystectomy (20-50%) and grafting with an equal-sized BAMG; two control animals underwent partial cystectomy (40%) only. The dogs were killed after 30 (one), 120 (one) and 210 days (five dogs). Blood samples were obtained before and at 1, 2, 4, 7, 14, 30, 90 and 210 days after surgery. The dogs underwent cystography, intravenous pyelography and ultrasonography before and after surgery, and on the day they were killed, with cystoscopy carried out just before death. The grafted tissue was assessed using routine and immunohistochemical techniques.

RESULTS

All the dogs survived surgery; a complete blood cell count, chemical panel and white blood cell count showed no significant difference between the experimental and control animals. Cystography, cystoscopy and ultrasonography revealed no pathological changes in the upper urinary tract. After 7 months, the mean bladder capacity in the augmented dogs was significantly higher (P = 0.035) than in the controls (264 vs 172 mL). Histological evaluation showed an invasion of all bladder wall components during the first month; at 7 months, the morphological examination showed essentially complete regeneration.

CONCLUSION

In this dog model, the potential of the BAMG as a bladder augmentation graft was confirmed, having minimal antigenicity with maximal acceptance. The reconstructed bladder matched the morphological and functional properties of the normal bladder.

Composition and biomechanical properties of the bladder acellular matrix graft: comparative analysis in rat, pig and human

OBJECTIVE

To compare the composition and mechanical properties of the newly developed bladder acellular matrix graft (BAMG) with the normal urinary bladder in rat, pig and human.

MATERIALS AND METHODS

Rat, pig and human urinary bladders were harvested and divided into control and experimental groups. For the latter, BAMGs were prepared, and light and transmission electron microscopic studies performed. Strips from the normal bladders and the BAMGs (10 in each group) were tested under tension, and the ultimate tensile strength, maximum strain, and elastic modulus were determined from stress/strain curves.

RESULTS

Both types I and III collagen, as well as elastic fibres, were observed as major components of the matrix scaffold. There were more collagen type I fibres in the rat than in the pig and human BAMGs, whereas the pig, and particularly the human, both showed higher levels of type III collagen and elastic fibres. These different matrix scaffold patterns were confirmed by electron microscopy. Results from biomechanical testing showed no significant differences for strength, strain or elastic modulus between BAMG and control bladder strips, except in the rat where the maximum strain values were significantly lower.

CONCLUSION

There are variations in the acellular matrix structure with similar biomechanical properties between the BAMG and the normal urinary bladder in three different species. These results may underscore the potential of the BAMG. Furthermore, this in vitro model provides a suitable method to study the mechanical properties of the urinary bladder and may serve as a diagnostic tool for various investigations.