This Month in Investigative Urology

Article Outline

• Antimicrobial Peptides and Urinary Tract Sterility
• Mature, Adipocyte Derived, Dedifferentiated Fat Cells and Bladder Tissue Regeneration
• Holmium:YAG Laser Optical Fibers for Flexible Ureteroscopy
• Intraurethral Stimulation and Bladder Responses
• Identification of Potassium Channel Subunit in Bladder Smooth Muscle
• Copyright

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Antimicrobial Peptides and Urinary Tract Sterility 

Urinary tract infection is one of the most common bacterial infections encountered in clinical practice. Emergence of bacterial resistance following overuse of traditional antibiotics requires the urgent development of alternative treatment strategies. Ali et al (page 21) from Newcastle Upon Tyne, United Kingdom performed an extensive review of the current level of knowledge concerning the role of innate immunity and specifically antimicrobial peptides (AMPs) within the human urinary tract.

AMPs are a ubiquitous component of innate immunity expressed by neutrophils or epithelial cells either constitutively or via induction by pathogens. AMPs are small (less than 10 kDa), cationic and amphipathic peptides of variable length, sequence and structure with broad spectrum killing activity against a wide range of microorganisms including gram-positive and gram-negative bacteria. Five AMPs have been identified in the urinary tract, including α- and β-defensins, cathelicidin and hepcidin. The amount and type of AMPs expressed varies according to tissue source and disease state. These differences may reflect altered levels of innate response and, thus, susceptibility to infection. AMPs are already being exploited therapeutically for skin and endovascular catheter infection, and prospects for useful application in the urinary tract are emerging. The authors conclude that although investigation of AMP function in the human urinary tract is at an early stage, there is considerable potential for the future design of novel therapeutic strategies. More knowledge is needed concerning the pathway of involvement of AMPs in the maintenance of urinary tract sterility and the ways in which this is altered during active infection.

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Mature, Adipocyte Derived, Dedifferentiated Fat Cells and Bladder Tissue Regeneration 

Tissue engineering and autologous cell therapy techniques have been developed to reconstitute urological tissues including the bladder. Mature, adipocyte derived dedifferentiated fat (DFAT) cells exhibit high proliferative activity and multilineage differentiation potential. Sakuma et al (page 355) from Tokyo, Japan investigated whether DFAT cells could differentiate into a smooth muscle cell (SMC) lineage and contribute to bladder tissue regeneration in a mouse bladder cryo-injury model. The investigators used human DFAT cells cultured for 1 week under conditions favorable for SMC differentiation and immunostained for α-smooth muscle actin (ASMA). The expression of SMC marker genes for differentiating DFAT cells was measured by real-time reverse transcriptase-polymerase chain reaction (RT-PCR). Green fluorescence protein labeled DFAT cells were injected into cryo-injured bladder walls in mice. The ability of DFAT cells to regenerate smooth muscle tissue was examined immunohistochemically 14 and 30 days after transplantation.

Immunohistochemical analysis revealed that more than 50% of DFAT cells were successfully differentiated into ASMA positive cells under the optimum culture conditions. Real-time RT-PCR revealed increased expression of SM22α, ASMA and smooth muscle-myosin heavy chain in DFAT cells during week 1 of differentiation culture. Cells expressing ASMA and green fluorescence protein were observed at the bladder wall injection sites in mice 14 and 30 days after transplantation. ASMA positive areas in injured bladder tissue in mice with DFAT cell injection were significantly larger than those in saline injected control mice. However, no functional studies were performed. The authors concluded that DFAT cells can differentiate into SMC lineages and contribute to the regeneration of bladder smooth muscle tissue. They also suggested that because adipose tissue is abundant and easily accessible at most ages in humans, DFAT cell transplantation may be an attractive therapeutic strategy for reconstituting the injured bladder.

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Holmium:YAG Laser Optical Fibers for Flexible Ureteroscopy 

The holmium:YAG laser is the modality of choice for intracorporeal lithotripsy. Industry has produced multiple optical fibers that vary in flexibility and diameter (core and total diameter), and prior study has shown that holmium:YAG laser fiber performance differs among manufacturers. Mues et al (page 348) from Columbus, Ohio determined the performance and threshold for failure of 24 commercially available holmium:YAG laser fibers. Single use and reusable fibers were tested in small (150 to 300 μm) and medium (300 to 400 μm) core diameter sizes. All fibers were evaluated for flexibility, failure threshold and true fiber diameter. Flexibility was measured by maximally deflecting a Stryker® U-500 ureteroscope with the fiber in the working channel. The diameter of each fiber was measured by digital micrometer. The failure threshold was assessed by bending the fibers to 180 degrees, beginning with a radius of 1.25 cm. A VersaPulse® 100 W holmium:YAG laser was operated at 1.2 J and 10 Hz for 1 minute or until fiber fracture. The bend radius was decreased in 0.25 cm increments and testing repeated until a minimum bend radius of 0.5 cm was reached or until the fiber failed. Of the small core fibers the SureFlex™ LLF-150 and LLF-273, OptiLite™ SMH1020F and Dornier® LG Super 270 had the highest threshold for failure. The Accuflex® 200 had the lowest failure threshold failing at the largest bend radius (1.75 cm). Of the medium core fibers the SureFlex LLF-365, Accuflex 365 and Lumenis® SL 365 had the highest failure threshold while the Dornier LG 400 and Lumenis EZ SL 365 were the lowest. The reusable Lumenis 365 fiber had a higher failure threshold than the single use Lumenis 365. The authors summarized the characteristics for the ideal fiber as a small true diameter, high flexibility, ergonomic ease of handling and capability of delivering a large amount of optical energy without thermal breakdown. They concluded that commercially available holmium:YAG laser fibers differ significantly in performance characteristics and that currently no single fiber is best in all these categories.

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Intraurethral Stimulation and Bladder Responses 

Previous animal studies have shown that electrical activation of somatovesical reflexes by stimulation of pudendal nerve afferents allows inhibition and activation of the bladder. Two distinct sensory pathways, originating from the cranial sensory branch and the dorsal penile nerve (DNP) of the pudendal nerve, can produce bladder activation and inhibition in adult cats. Woock et al (page 366) from Durham, North Carolina examined intraurethral electrical stimulation (IES) as a minimally invasive means of selectively activating these pathways in α-chloralose anesthetized male cats at different stimulation frequencies, stimulation intensities and intraurethral locations. IES evoked inhibitory and excitatory bladder reflexes depending on stimulation frequency and location. Stimulation in the penile urethra 0 to 3 cm from the urethral meatus at 33 Hz stimulation evoked bladder contraction and at 10 Hz stimulation it evoked bladder relaxation. These responses were abolished after bilateral transection of the dorsal penile nerves. Stimulation in the membranous urethra 5 to 7 cm from the urethral meatus at 2, 10 and 33 Hz stimulation evoked bladder contractions. These responses were abolished following bilateral transection of the cranial sensory nerves. Following acute spinal cord transection bladder contractions were still evoked by 33 Hz stimulation in the penile urethra but not by stimulation at any frequency in the membranous urethra. The authors concluded that the bladder responses evoked by IES were dependent on stimulation location, frequency and intensity. Two distinct reflex pathways were activated by IES to evoke bladder responses but only the DNP mediated pathway was present following spinal cord injury. Therefore, they suggested that the DNP pathway should be the target for restoring bladder function in spinal cord injured humans.

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Identification of Potassium Channel Subunit in Bladder Smooth Muscle 

In bladder smooth muscle (BSM) the large conductance voltage and Ca²⁺ activated K⁺ (BK) channels are key regulators of cell membrane excitability, action potential formation and contractility. In BSM the BK channel pore forming α subunit (BKα) is associated in homotetramers with 4 regulatory smooth muscle specific β1 subunits (BKβ1). Chen and Petkov (page 374) from Columbia, South Carolina challenged this concept in identifying whether other regulatory BKβ subunits exist in mouse and rat BSM. They used a novel approach combining single cell RT-PCR and immunocytochemical studies in freshly isolated mouse and rat BSM cells. Their results indicated that in addition to BKα and BKβ1, the neuronal specific BKβ4 is expressed in mouse and rat BSM cells. BKβ4 expression was also revealed by Western blotting. Immunocytochemistry was further applied to confirm the specific expression of BKβ4 protein directly in freshly isolated mouse and rat BSM cells. The authors conclude that the BSM BK channel identified has a distinctive architecture involving pore forming BKα and regulatory BKβ1/β4, and suggest that further studies on the functional roles of the BKα, BKβ1 and BKβ4 directly in human BSM may help the development of alternative therapeutic strategies to control bladder dysfunction.