This Month in Investigative Urology

Article Outline

• Bladder Reduction Surgery Accelerates Spontaneous Voiding Appearance
• Bladder Trigone Origin and Mesenchymal-Epithelial Interaction
• Silodosin and Naftopidil Effects on Ureter and Cardiovascular System
• Bikunin Loss in Urine as Useful Bladder Cancer Marker
• Immunological Response to Cryoablation in Renal Cell Carcinoma Model
• Copyright

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Bladder Reduction Surgery Accelerates Spontaneous Voiding Appearance 

Children with nocturnal enuresis may have a small functional bladder capacity or decreased ability to sense a full bladder. These mechanisms are usually considered unrelated but it cannot be ruled out that a small bladder capacity leads to the inability to sense bladder fullness. Ng et al (page 370) from Hong Kong, China investigated whether decreasing bladder volume would affect the central inhibition of voiding, which is normally present between birth and 2 weeks of life in neonatal rats. During this period the pups cannot void by themselves but require their mother to lick the perigenital area to activate the perigenital-to-bladder spinal voiding reflex. This primitive perigenital-to-bladder reflex is then replaced by a more complex bladder-to-bladder supraspinal reflex at 3 weeks. Ng et al reduced bladder volume by 50% in 1 and 3-week-old Sprague-Dawley rats by suture closure of the bladder dome. In selected animals T8-T10 spinal cord injury was done, and perigenital-bladder reflex latency, spontaneous voiding onset and body weight were measured. Cystometry was performed using urethane anesthesia, and in vitro spontaneous and KCl evoked contractions were recorded.

Bladder reduction surgery led to the immediate appearance of spontaneous voiding in 1-week-old rats. Cystometry at 2 weeks showed voiding contractions in rats that had undergone bladder reduction, which could be abolished by acute T8-T10 spinalization. Voiding contractions were not seen in animals that underwent sham surgery or concurrent T8-T10 spinalization and bladder reduction. The perigenital-bladder reflex, somatic growth, spontaneous bladder contractions and bladder contractility were not affected by bladder reduction. Bladder capacity at 9 weeks was significantly larger in animals that underwent bladder reduction at 1 week compared to sham animals, but not in animals that underwent bladder reduction at 3 weeks. The authors conclude that bladder reduction in the neonatal rat removes the central inhibition of spontaneous voiding. Although neonatal rats and human infants have different voiding reflexes, the data presented suggest that neonatal changes in bladder capacity can turn off bladder regulatory pathways in the brain.

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Bladder Trigone Origin and Mesenchymal-Epithelial Interaction 

The classic view of bladder development postulates that the trigone originates from the mesoderm derived wolffian ducts while the remainder of the bladder originates from the endoderm derived urogenital sinus. However, recent molecular developmental studies have suggested an endodermal origin for the trigone. Tanaka et al (page 386) from Nashville, Tennessee hypothesized that if trigone epithelium were derived from mesoderm as proposed in the classic view, fetal urogenital sinus mesenchyme (UGM) would induce adult trigone epithelium to differentiate to seminal vesicle epithelium.

To test this hypothesis they studied the mesenchymal-epithelial interactions between trigone epithelium and UGM to infer the germ layer of origin of the trigone. Mouse trigone epithelium was recombined with fetal rat UGM in tissue recombinant grafts that were placed beneath the renal capsule of athymic mouse hosts. Grafts were harvested at 4 weeks. Control grafts with bladder dome and ureteral epithelium were also examined. Tissues were evaluated with hematoxylin and eosin, and Hoechst dye 33258 to confirm cell species origin. Immunohistochemistry was performed with androgen receptor, broad spectrum uroplakin, dorsal lateral prostate secretions and seminal vesicle secretions to differentiate prostatic and seminal vesicle differentiation. Grafts of mouse trigone epithelium with fetal rat UGM yielded epithelial tissue which stained for dorsolateral prostate secretions but not for seminal vesical secretions. Control grafts of bladder dome epithelium yielded the expected endodermal prostate differentiation and control grafts of ureteral epithelium yielded the expected mesodermal seminal vesicle differentiation. The authors conclude that the consistent finding of prostatic epithelium in tissue recombinants of trigone epithelium and fetal UGM reinforces the hypothesis that the trigone is derived from the endoderm and not the mesoderm as commonly accepted. Their study provides independent confirmation of recently published work that refutes the classically accepted view of trigone development from the mesoderm.

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Silodosin and Naftopidil Effects on Ureter and Cardiovascular System 

Urolithiasis is observed in 12% of the general population with a mean recurrence rate of 75% in the 20 years after the first diagnosis of the disease. Distal ureteral stone is the most common form of the disease (more than 70% of cases). Since the spontaneous stone expulsion rate is less than approximately 50% in distal ureteral stone cases, various medical treatments have been used to accelerate the expulsion rate. Published data indicate that α₁-adrenoceptor (AR) antagonists can increase the stone expulsion rate in patients with distal ureteral stones and have a favorable impact on the clearance of residual fragments after extracorporeal shock wave lithotripsy. The α_1A-AR is the main mediator of contraction in the human isolated ureter, which also seems to be the case in the dog.

In an anesthetized dog model Kobayashi et al (page 357) from Aichi, Japan compared the effects of silodosin (a selective α_1A-AR antagonist) and naftopidil (a modestly selective α_1D-AR antagonist) on intraureteral pressure (IUP), and evaluated their uroselectivities. The effects of silodosin and naftopidil were evaluated on phenylephrine induced increase in IUP and on blood pressure. Each drug was administered intravenously in progressively increasing doses. Values of ED₁₅ (the dose of each α₁-AR antagonist at which mean blood pressure was decreased by 15%) and ID₅₀ (the dose at which the phenylephrine induced increase in IUP was suppressed by 50%) were measured, and uroselectivity (ED₁₅/ID₅₀ value) was calculated. Silodosin dose dependently suppressed the phenylephrine induced increase in IUP but decreased mean blood pressure only at higher doses. In contrast, naftopidil decreased mean blood pressure at the same doses as those that reduced the phenylephrine induced increase in IUP. The uroselectivity of silodosin (58.6) was markedly higher than that of naftopidil (1.3). The authors conclude that selective α_1A-AR antagonism might facilitate distal ureteral stone passage, and suggest that selective α_1A-AR antagonists such as silodosin might be useful for facilitating the passage of distal ureteral stones at doses that do not lower systemic blood pressure.

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Bikunin Loss in Urine as Useful Bladder Cancer Marker 

Transitional cell carcinoma of the bladder is the second most common malignancy of the genitourinary tract and the second most common cause of death from genitourinary tumors. Cytological analysis of voided urine is the most commonly used noninvasive method for detecting transitional cell carcinoma, and several potential diagnostic markers for bladder cancer have been identified but the heterogeneity of bladder cancer implies that multiple rather than single biomarkers may be required for accurate diagnosis. Tsui et al (page 339) from Taiwan, China searched for bladder tumor markers and analyzed urine from patients with bladder cancer as well as normal individuals. Proteins in the urine samples were systematically examined by 2-dimensional electrophoresis combined with matrix assisted laser desorption ionization time-of-flight mass spectrometry.

Among the proteins analyzed bikunin was highly expressed, and expression was confirmed by Western blot analysis and further evaluated. Bikunin is a plasma proteinase inhibitor with a broad spectrum of biological functions. To correlate the urinary levels of bikunin with clinical significance urine samples from patients with bladder cancer and normal controls were examined for expression of bikunin in parallel with pro-urolinase-plasminogen activator (pro-u-PA) that was previously shown to be associated with advanced bladder carcinoma. A significant relationship was established between the low level and absence of bikunin, and pro-u-PA in urine samples from patients with bladder tumors. The authors conclude that analysis of urinary proteomes can be a feasible, noninvasive and efficient strategy for searching for potential bladder tumor biomarkers, and that there may be an important linkage among bikunin, pro-u-PA and u-PA in bladder carcinoma. They suggest that loss of bikunin and pro-u-PA in urine may serve as reliable bladder carcinoma markers.

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Immunological Response to Cryoablation in Renal Cell Carcinoma Model 

Cryoablation is an attractive therapeutic option for tumors due to its highly efficient and minimally invasive nature. Cryoablation is potentially immunogenic but the immunological consequences of cryoablation for renal cell carcinoma (RCC) are largely unknown. However, suitable models for study of the problem are lacking. Matin et al (page 333) from Houston, Texas describe the development of an animal model for delivery of in vivo renal cryotherapy to orthotopically implanted RCC and the results of multiple immunological interrogations after cryoablation. They used 4 to 6-week-old female Balb/c mice that underwent renal subcapsular implantation of Renca, a syngeneic murine RCC. Contact cryoablation was performed 2 weeks later on the tumor bearing kidneys. Another group of animals underwent cryoablation of normal kidneys. The animals were sacrificed 2 weeks after tumor injection or at 1 and 2 weeks after cryoablation. Kidneys, spleens and draining lymph nodes were harvested.

Evaluations consisted of immunohistochemistry, immunofluorescence and gene expression profiling using reverse-transcriptase polymerase chain reaction. Subcapsular tumor implantation was successful in all cases and could be confirmed histologically. No significant lymphocytic infiltrate was seen in the tumor only animals. However, animals treated with cryoablation (tumor and nontumor bearing) had a significant inflammatory response seen primarily in the areas of sublethal tissue injury and in perivascular areas. The majority of infiltrating cells after cryoablation were neutrophils, macrophages and T cells, respectively. Polymerase chain reaction indicated increased interferon-γ production in kidneys after cryoablation. This study demonstrates the potential feasibility of this animal model for the study of cryo-immunology. The authors show that cryoablation initiated an inflammatory response consisting of neutrophils, macrophages, CD4+ and CD8+ T cells, and suggest that cryoablation may provide an initial in situ immune reaction that can then be accelerated using immunostimulatory agents in a combination immunotherapy fashion. The orthotopic murine model can form the basis for future studies evaluating immunological responses after renal cryoablation, other forms of ablative therapy and combination immunotherapy strategies.