Expansion mechanisms of the partially cystectomized bladder: an experimental study in rabbits

Human urinary bladder regeneration through tissue engineering - an analysis of 131 clinical cases

Replacement of urinary bladder tissue with functional equivalents remains one of the most challenging problems of reconstructive urology over the last several decades. The gold standard treatment for urinary diversion after radical cystectomy is the ileal conduit or neobladder; however, this technique is associated with numerous complications including electrolyte imbalances, mucus production, and the potential for malignant transformation. Tissue engineering techniques provide the impetus to construct functional bladder substitutes de novo. Within this review, we have thoroughly perused the literature utilizing PubMed in order to identify clinical studies involving bladder reconstruction utilizing tissue engineering methodologies. The idea of urinary bladder regeneration through tissue engineering dates back to the 1950s. Many natural and synthetic biomaterials such as plastic mold, gelatin sponge, Japanese paper, preserved dog bladder, lyophilized human dura, bovine pericardium, small intestinal submucosa, bladder acellular matrix, or composite of collagen and polyglycolic acid were used for urinary bladder regeneration with a wide range of outcomes. Recent progress in the tissue engineering field suggest that in vitro engineered bladder wall substitutes may have expanded clinical applicability in near future but preclinical investigations on large animal models with defective bladders are necessary to optimize the methods of bladder reconstruction by tissue engineering in humans.

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.

Urethroplasty using a bovine pericardium graft: an experimental study using normal urethras from dogs

The use of bovine pericardium as a urethral patch to substitute a ventral segment of canine urethras was studied. Healing, epithelial growth, urethral permeability, fistulas, and calcification were analyzed. Thirty male mongrel dogs of medium and large size underwent resection of a ventral segment of the medial urethra measuring 2.0 x 0.5 cm, which was replaced with a bovine pericardium graft, treated with buffered glutaraldehyde and preserved in formaldehyde. Two running sutures of polygalactin 5-0 were applied, one on each side of the patch. The corpus spongiosum was closed with uninterrupted suture and the skin with interrupted suture of polygalactin 5-0. Six months later, the animals were examined and sacrificed under anesthesia. Retrograde urethrograms showed that the urethral healing was complete in six of the 30 animals, without stenosis, fistulas or dilations. Microscopic examination showed complete epithelization of these six urethras. The remaining 24 animals presented urethrocutaneous fistulas without stenosis, demonstrated by urethral catheterism using a 10-Fr plastic catheter. These data show that a successful urethral reconstruction of the penile urethra was possible in only 20% of the operated animals. Infection and leakage may be the cause of the urethrocutaneous fistulas present in 80% of cases. Further studies are necessary to determine whether such fistulas are avoidable. If they are, the bovine pericardium may well be an option in the treatment of urethral lesions in dogs.

Regeneration of detrusor muscle after subtotal cystectomy in the rat: effects on contractile proteins and bladder mechanics

The aim of the present study was to determine to what extent adult rats can produce new contracting bladder muscle and to see if such newly formed bladder tissue possesses characteristic mechanical properties or whether the ability to recover mechanically is so pronounced that the prehistory of the bladder is unimportant. Subtotal cystectomy was performed in adult female rats, leading to a pronounced decrease in total bladder weight. At 10 weeks, bladder weight had normalized. The histological appearance of such bladders was similar to that of the controls. Active and passive length-tension relations for the detrusor muscle were determined in controls and up to 10 weeks after surgery. Immediately after surgery active and passive forces showed a leftward shift and maximum active force decreased markedly. With time the length-tension curves shifted back to normal, but a decreased active force still remained at 10 weeks. Detrusor actin concentration and detrusor myosin/actin ratio were unaffected by the subtotal cystectomy. Intermediate filament protein/actin ratio showed a significant but transitory increase. We conclude that there is a remarkable recovery of detrusor muscle function after subtotal cystectomy, leading to a normalization of optimum length for active force and a net synthesis of contractile and cytoskeletal proteins. The ability to produce active force does, however, not fully recover.

Functional restoration of rat bladder after subtotal cystectomy: in vivo cystometry and in vitro study of whole bladder

Functional restoration of the rat urinary bladder following subtotal cystectomy was studied via in vivo infusion cystometry and an in vitro whole bladder model. After the bladder had been separated from the prostate, subtotal cystectomy was achieved by ligating the bladder completely at a level just above the insertion of the ureters into the bladder. Bladder function was investigated immediately and 7, 14, and 28 days after surgery. Bladder weight was reduced to 17% that in sham-operated controls immediately after surgery, but recovered to 76% of that in controls 28 days after the operation. In vivo capacity also increased after surgery from 13% that of controls to 59% 28 days later. However, voiding pressure remained low (34% of control) 28 days later. An in vitro whole bladder study showed that the response to field stimulation decreased significantly on day 7, but had recovered considerably by day 28. The maximal response to bethanechol decreased significantly 7 days after surgery, but recovered thereafter. The response to phenylephrine increased significantly immediately after surgery, but gradually returned to the control level. An in vitro volume-pressure study showed that passive compliance of the cystectomized bladder decreased after surgery, but improved with time. The peak of the active pressure increase to field stimulation occurred at a low infusion volume immediately after surgery, but bladder capacity increased gradually until 28 days later, when the maximal active pressure was obtained. Our results suggest that restoration of the bladder following subtotal cystectomy may not derive simply from an expansion of the bladder wall. Functional alteration involving the bladder base was also observed.

Regenerative urinary bladder augmentation using small intestinal submucosa: urodynamic and histopathologic assessment in long-term canine bladder augmentations

PURPOSE

To evaluate small intestinal submucosa (SIS) as a possible bladder augmentation material.

MATERIALS AND METHODS

Nineteen male dogs underwent 35 to 45% partial cystectomy with immediate augmentation with SIS grafts. All dogs were evaluated pre- and postoperatively with blood chemistries, urine cultures, intravenous urograms, cystograms and cystometrograms. Postoperatively (1 to 15 months), bladders were examined with routine histology and image analysis.

RESULTS

All dogs survived their intended survival period without morbidity. All results were normal. Histologically, all 3 layers (mucosa, smooth muscle, serosa) of the normal bladder showed evidence of regeneration.

CONCLUSIONS

Small intestinal submucosa acts as a scaffold for bladder augmentation through regeneration and could be a potential option for bladder reconstruction.

Pharmacological responses of rabbit urinary bladder after subtotal cystectomy

Partial cystectomy is used clinically in specific circumstances. There have been some reports indicating that the bladder following subtotal cystectomy can regenerate to a certain degree. The present study investigates the physiology and pharmacology of bladder regeneration at eight weeks after resection of a major part of the bladder body in rabbits. The following studies were performed on control and cystectomy bladders: 1) in vivo cystometry (prior to and four weeks after the operation, and before the sacrifice at eight weeks); 2) sequential muscle strip study (the strips were obtained by dividing bladder transversely into upper body, lower body, mid-bladder, upper base and lower base); and 3) in vitro whole bladder studies. The results can be summarized as follows: 1) grossly there was no regeneration of the bladder body; the cystometric capacity was increased slowly after the operation primarily due to increased size and capacity of the bladder base. 2) The contractile response of the subtotal cystectomized bladder body to field stimulation and bethanechol stimulation was less than the response of normal bladder body. 3) The contractile response to epinephrine showed that the ratio of alpha/beta adrenergic response was much greater in the cystectomy bladder than in the normal bladder. 4) In the whole bladder study, the intravesical pressure response to field stimulation was about the same in both groups, the response to bethanechol was less for cystectomized bladder, and the response to methoxamine was greater for the cystectomized bladder. 5) The ability of cystectomy bladder to empty in response to both field stimulation and bethanechol was impaired whereas the control bladder fully emptied to both field stimulation and bethanechol. In conclusion, over the eight week period following subtotal cystectomy the capacity increased via distention (and hypertrophy) of the bladder base area as opposed to regeneration of the bladder body.