LONG-TERM EFFICACY OF A VAGINAL SLING PROCEDURE IN A RAT MODEL OF STRESS URINARY INCONTINENCE

Stem cell homing factor, CCL7, expression in mouse models of stress urinary incontinence

OBJECTIVES

Animal models of vaginal distention (VD) have demonstrated increased expression of chemokine (C-C motif) ligand 7 (CCL7) In this study, we investigated the expression of CCL7 in mice models of simulated birth trauma-induced urinary incontinence using VD and pudendal nerve transection (PNT).

METHODS

Forty-nine mice were divided into 6 groups: VD, sham VD, PNT, sham PNT, anesthesia, and age-matched controls. The urethra, vagina, and rectum were harvested for the expression of CCL7 immediately or 24 hours after assigned procedure. Venous sampling for quantification of serum CCL7 was also performed. An analysis of variance model was used to compare the relative expression of CCL7 in each group.

RESULTS

Urethral CCL7 expression in the VD group was significantly higher than control group after 24 hours (P < 0.01). There was no difference in the urethral CCL7 expression in PNT, sham PNT, sham VD, or anesthesia groups compared with the controls. No statistically significant difference was noted in the vaginal and rectal expression of CCL7 between any of the groups except for sham PNT. Statistically significant differences were noted in the serum CCL7 expression in the VD, PNT, and sham PNT (P < 0.01 in all) groups after 24 hours compared with the control group.

CONCLUSIONS

This study demonstrates overexpression of urethral CCL7 after VD but not PNT. This suggests that nerve injury does not contribute to the CCL7 overexpression. The overexpression of CCL7 in the serum of mice after VD suggests a translational potential where CCL7 measurement could be used as a surrogate for injury after delivery.

Animal models of stress urinary incontinence

Stress urinary incontinence (SUI) is a common health problem significantly affecting the quality of life of women worldwide. Animal models that simulate SUI enable the assessment of the mechanism of risk factors for SUI in a controlled fashion, including childbirth injuries, and enable preclinical testing of new treatments and therapies for SUI. Animal models that simulate childbirth are presently being utilized to determine the mechanisms of the maternal injuries of childbirth that lead to SUI with the goal of developing prophylactic treatments. Methods of assessing SUI in animals that mimic diagnostic methods used clinically have been developed to evaluate the animal models. Use of these animal models to test innovative treatment strategies has the potential to improve clinical management of SUI. This chapter provides a review of the available animal models of SUI, as well as a review of the methods of assessing SUI in animal models, and potential treatments that have been tested on these models.

Transplantation of muscle-derived stem cells plus biodegradable fibrin glue restores the urethral sphincter in a pudendal nerve-transected rat model

We investigated whether fibrin glue (FG) could promote urethral sphincter restoration in muscle-derived stem cell (MDSC)-based injection therapies in a pudendal nerve-transected (PNT) rat, which was used as a stress urinary incontinence (SUI) model. MDSCs were purified from the gastrocnemius muscles of 4-week-old inbred female SPF Wistar rats and labeled with green fluorescent protein. Animals were divided into five groups (N = 15): sham (S), PNT (D), PNT+FG injection (F), PNT+MDSC injection (M), and PNT+MDSC+FG injection (FM). Each group was subdivided into 1- and 4-week groups. One and 4 weeks after injection into the proximal urethra, leak point pressure (LPP) was measured to assess urethral resistance function. Histology and immunohistochemistry were performed 4 weeks after injection. LPP was increased significantly in FM and M animals after implantation compared to group D (P < 0.01), but was not different from group S. LPP was slightly higher in the FM group than in the M group but there was no significant difference between them at different times. Histological and immunohistochemical examination demonstrated increased numbers of surviving MDSCs (109 ± 19 vs 82 ± 11/hpf, P = 0.026), increased muscle/collagen ratio (0.40 ± 0.02 vs 0.34 ± 0.02, P = 0.044), as well as increased microvessel density (16.9 ± 0.6 vs 14.1 ± 0.4/hpf, P = 0.001) at the injection sites in FM compared to M animals. Fibrin glue may potentially improve the action of transplanted MDSCs to restore the histology and function of the urethral sphincter in a SUI rat model. Injection of MDSCs with fibrin glue may provide a novel cellular therapy method for SUI.

Postpartum stress urinary incontinence: lessons from animal models

Postpartum stress urinary incontinence (SUI) is associated with chronic SUI in later life, which is 240% more likely to occur in women who deliver vaginally than those who did not. The etiology of SUI is multifactoral and has been associated with defects in both neuromuscular and structural components of continence. Specifically, clinical studies have demonstrated that pudendal nerve damage occurs during vaginal delivery, supporting the concept that neuromuscular damage to the continence mechanism can result in postpartum SUI. Urethral hypermobility and the loss of pelvic floor support, such as that involved in pelvic organ prolapse, have also been associated with SUI. Animal models provide an opportunity to investigate these injuries, individually and in combination, enabling researchers to gain further insight into their relative contributions to the development of SUI and the effectiveness of potential therapies for it. This article discusses the use of animal models of postpartum SUI in addition to the broad insights into treatment efficacy they provide.

Development of a device to standardize leak point pressure experiments in rats

AIMS

The objective of this study was to test a custom device aimed at increasing repeatability of abdominal leak point pressure (LPP) measurements in rodents.

METHODS

The device consisted of a soft-tipped force applicator with a force sensor which was moved in the vertical direction by a linear actuator, laser crosshairs for accurate positioning, and a hand-held wired remote control system. One expert and two novice experimenters acquired LPP measurements using manual and device methods by applying a gradually increasing force with the finger or the device, respectively, until a leak was visually observed at the urethral meatus. The device was tested at fast, medium, and slow speeds. A leak sensor was also tested to determine presence of a leak and reaction time of the user. The change in bladder pressure due to the externally applied force (LPP) was the primary outcome.

RESULTS

There were no significant differences in mean LPP value when compared across experiments (expert, novice), method (manual, device), or speeds. The pooled variance of LPP was significantly decreased (P < 0.05) compared to the manual method when using the device at medium speed; however the slower speed showed no further improvement over the medium speed. The wet sensor detected leaks 385 +/- 187 msec earlier than users' reaction.

CONCLUSIONS

Use of the device can decrease variability of the experiment but does not alter mean values. Reaction time, inherent in both the manual and device methods, has the potential for a significant impact on LPP outcomes.

Collagen remodeling and suburethral inflammation might account for preserved anti-incontinence effects of cut polypropylene sling in rat model

OBJECTIVES

To determine whether the inflammatory responses or collagen remodeling in suburethral tissue could have contributed to the preserved anti-incontinence effects of a cut polypropylene sling.

METHODS

Stress urinary incontinence was created in 60 age-matched female Sprague-Dawley rats that were subsequently randomized into 3 equal-size groups according to surgical procedure: placement of a vaginal suburethral sling, placement of a vaginal suburethral sling in which the suburethral portion of the sling was immediately cut, and sham surgery without placement of the sling. In a previous study, the leak point pressure measurements were obtained on these rats 6 weeks after surgery. The rats were then killed, the urethrovaginal tissue was harvested (cross-section of the entire urethra and anterior vagina) from 30 animals (10 from each experimental group), and the tissue was stained with hematoxylin-eosin and Masson's trichrome for histopathologic studies and picrosirius red for collagen fibers.

RESULTS

As previously published, the median leak point pressures were similarly and significantly increased in the rats in the intact and cut sling groups compared with those in the sham surgery group. The inflammatory mediators and interstitial edema were similarly increased in the intact and cut sling specimens compared with the sham surgery specimens. Under polarized light, picrosirius red-stained specimens from the sham surgery animals appeared to be composed of collagen that predominately birefringed red to yellow (typical of type I collagen). The picrosirius red-stained cut and intact sling specimens appeared to contain collagen fibers that predominately birefringed green (typical of type III collagen).

CONCLUSIONS

Histologic changes, including inflammation, localized edema, and differential collagen remodeling, might contribute to the preserved anti-incontinence mechanisms of cut or intact polypropylene slings observed clinically.

Complications of mid urethral slings: important outcomes for future clinical trials

PURPOSE

Mid urethral slings are becoming the first line surgical treatment for stress urinary incontinence in women. We reviewed the complications of mid urethral sling placement and their potential pathophysiology.

MATERIALS AND METHODS

We conducted a literature search on MEDLINE from 1995 to 2007 using the key words sling, complications, mid-urethral slings, transvaginal tape, transobturator tape, trials, pathophysiology and complications. The Cochrane database was also searched. The results were summarized according to the type of mid urethral slings reported.

RESULTS

There were 928 MEDLINE citations for sling and complications, 279 for sling and complications and bladder, and 68 for sling and complications and voiding dysfunction. The reported complication rates ranged from 4.3% to 75.1% for retropubic and 10.5% to 31.3% for transobturator mid urethral slings. Complications included bladder perforation, hemorrhage, bowel injury, vaginal extrusion, de novo urgency and urge incontinence, urinary tract infections and voiding dysfunction. Retropubic mid urethral slings led to a higher occurrence of complications such as bladder perforation and hematoma. In addition, the retropubic approach resulted in serious complications such as bowel injury, major vascular injury and death. Groin pain was more common after the transobturator approach. Experimental studies indicated that the potential mechanisms for sling complications may include vaginal dissection, denervation injury and bladder remodeling.

CONCLUSIONS

Mid urethral slings result in bothersome complications which should not be minimized. Awareness of these complications should encourage improvements in patient counseling as well as further investigation of the underlying mechanisms. Decreasing complications should be considered an important outcome for future clinical studies of mid urethral slings.

Animal models of female stress urinary incontinence

PURPOSE

Urinary incontinence affects 40% of women in the United States and stress urinary incontinence accounts for a large portion of affected patients. As defined by the International Continence Society, stress urinary incontinence is the involuntary leakage of urine upon effort, exertion, sneezing or coughing. Since the ultimate success of long-term management for any condition is based on an understanding of its pathophysiology, and because the pathophysiology of stress urinary incontinence is incompletely defined, animal models have recently been developed to better understand stress urinary incontinence and develop novel treatment alternatives.

MATERIALS AND METHODS

Several animal models for urethral dysfunction have emerged in the last few years, including those based on pathophysiological theories of urethral sphincter dysfunction that were designed to simulate maternal birth trauma. Other models have focused on the creation of a durable model of dysfunction for investigating novel treatments.

RESULTS

Since animals cannot express intent, these animal models have focused on measuring decreased urethral resistance. The most widely used methods are the sneeze test, the tilt table technique and the leak point pressure test. Newer techniques include abdominal leak point pressure, urethral pressure measurement and retrograde urethral perfusion pressure. In addition to the advantages and disadvantages of each technique, all methods measure the composite contribution to urethral resistance from smooth and striated muscle, urethral closure and connective tissue, although none measures intent.

CONCLUSIONS

We critically reviewed the different models of stress urinary incontinence and urethral dysfunction as well as the different methods of measuring urethral resistance.

A mouse model of simulated birth trauma induced stress urinary incontinence

AIMS

To facilitate future applications of transgenic or knockout technologies in studies of simulated birth trauma induced stress urinary incontinence (SUI), we aimed to create a mouse model of SUI and explore the possible pathogenesis of this condition.

METHODS

Thirty female C57BL/6 mice were randomly distributed into five groups. Four groups underwent vaginal distention (VD) for 1 hr, using a modified 6-Fr. Foley catheter with a balloon dilated to 0.3, 0.2, or 0.1 ml or sham distention. Four days after VD, all mice underwent leak-point pressure (LPP) measurement via an implanted suprapubic tube (SPT). The normal control group only had SPT placement and LPP measurement. After sacrifice, the urethras of the mice were harvested for routine histological examination and nerve staining.

RESULTS

LPPs were significantly lower in groups after VD with 0.3- or 0.2-ml balloon than in control and sham distention groups (10.29 +/- 6.70, 14.65 +/- 6.51, 37.78 +/- 5.10, and 30.30 +/- 5.30 cm H(2)O, respectively). There were no significant differences in LPP between control and sham groups. Histology showed no significant differences in urethral striated muscle among the five groups. The density of immunoreactive neurofilaments in the urethra decreased after VD with 0.3- or 0.2-ml balloon.

CONCLUSION

As a model of birth trauma, VD can induce SUI in female mice, the severity of which is related to intravaginal balloon size. Partial urethral denervation plays a plausible role in the pathogenesis of SUI. This novel mouse model could be used for further mechanistic studies of female SUI.

Animal models in urological disease and sexual dysfunction

There are several conditions associated with dysfunction of the lower urinary tract or which result in a reduction in the ability to engage in satisfactory sexual function and result in significant bother to sufferers, partners and/or carers. This review describes some of the animal models that may be used to discover safe and effective medicines with which to treat them. While alpha adrenoceptor antagonists and 5-alpha-reductase inhibitors deliver improvement in symptom relief in benign prostatic hyperplasia sufferers, the availability of efficacious and well-tolerated medicines to treat incontinence is less well served. Stress urinary incontinence (SUI) has no approved medical therapy in the United States and overactive bladder (OAB) therapy is limited to treatment with muscarinic antagonists (anti-muscarinics). SUI and OAB are characterised by high prevalence, a growing ageing population and a strong desire from sufferers and physicians for more effective treatment options. High patient numbers with low presentation rates characterizes sexual dysfunction in men and women. The introduction of Viagra in 1998 for treating male erectile dysfunction and the success of the phosphodiesterase type 5 inhibitor class (PDE5 inhibitor) have indicated the willingness of sufferers to seek treatment when an effective alternative to injections and devices is available. The main value of preclinical models in discovering new medicines is to predict clinical outcomes. This translation can be established relatively easily in areas of medicine where there are a large number of drugs with different underlying pharmacological mechanisms in clinical usage. However, apart from, for example, the use of PDE5 inhibitors to treat male erectile dysfunction and the use of anti-muscarinics to treat OAB, this clinical information is limited. Therefore, current confidence in existing preclinical models is based on our understanding of the biochemical, physiological, pathophysiological and psychological mechanisms underlying the conditions in humans and how they are reflected in preclinical models. Confidence in both the models used and the pharmacological data generated is reinforced if different models of related aspects of the same disorder generate confirmatory data. However, these models will only be fully validated in retrospect once the pharmacological agents they have helped identify are tested in humans.

ROLE OF SLING INTEGRITY IN THE RESTORATION OF LEAK POINT PRESSURE IN THE RAT VAGINAL SLING MODEL

PURPOSE

We tested the hypothesis that cutting the sling at its suburethral section does not cancel its anti-incontinence effect. We also examined the long-term effects of the sling on bladder function in a recently validated rat model of vaginal sling.

MATERIALS AND METHODS

Stress urinary incontinence was created in 60 female Sprague-Dawley rats by the previously established method of bilateral pudendal nerve transection. Under anesthesia 20 animals received a vaginal sling, 20 received a vaginal sling in which the suburethral portion of the sling was cut immediately after placement and 20 received a sham vaginal sling. Six weeks after the procedures leak point pressure was determined and a cystometrogram was done using anesthesia in each animal via a previously implanted suprapubic catheter. Kruskal-Wallis and pairwise separate rank multiple comparison tests were performed with a significance level of 0.05.

RESULTS

The cut and intact slings increased leak point pressure similarly and these values were significantly higher than that of the sham sling (24.9 and 27.9 cm H2O, respectively, vs 20.7, p <0.0001). Peak micturition pressure was not significantly different among the 3 groups, indicating absent bladder outlet obstruction in the sling groups. Bladder compliance was significantly decreased 6 weeks after placement of a cut or intact sling compared with the sham sling (p = 0.007 and 0.05, respectively).

CONCLUSIONS

An intact suburethral portion is not a requirement for sling effectiveness in the rat model of stress urinary incontinence. However, the sling procedure decreases bladder compliance. This may explain the observed voiding dysfunction associated with sling procedures.