Molecular determinants of afferent sensitization in a rat model of cystitis with urothelial barrier dysfunction

Bladder infection with uropathogenic Escherichia coli increases the excitability of afferent neurons

Urinary tract infections (UTIs) cause bladder hyperactivity and pelvic pain, but the underlying causes of these symptoms remain unknown. We investigated whether afferent sensitization contributes to the bladder overactivity and pain observed in mice suffering from experimentally induced bacterial cystitis. Inoculation of mouse bladders with the uropathogenic Escherichia coli strain UTI89 caused pelvic allodynia, increased voiding frequency, and prompted an acute inflammatory process marked by leukocytic infiltration and edema of the mucosa. Compared with controls, isolated bladder sensory neurons from UTI-treated mice exhibited a depolarized resting membrane potential, lower action potential threshold and rheobase, and increased firing in response to suprathreshold stimulation. To determine whether bacterial virulence factors can contribute to the sensitization of bladder afferents, neurons isolated from naïve mice were incubated with supernatants collected from bacterial cultures with or depleted of lipopolysaccharide (LPS). Supernatants containing LPS prompted the sensitization of bladder sensory neurons with both tetrodotoxin (TTX)-resistant and TTX-sensitive action potentials. However, bladder sensory neurons with TTX-sensitive action potentials were not affected by bacterial supernatants depleted of LPS. Unexpectedly, ultrapure LPS increased the excitability only of bladder sensory neurons with TTX-resistant action potentials, but the supplementation of supernatants depleted of LPS with ultrapure LPS resulted in the sensitization of both population of bladder sensory neurons. In summary, the results of our study indicate that multiple virulence factors released from UTI89 act on bladder sensory neurons to prompt their sensitization. These sensitized bladder sensory neurons mediate, at least in part, the bladder hyperactivity and pelvic pain seen in mice inoculated with UTI89.NEW & NOTEWORTHY Urinary tract infection (UTI) produced by uropathogenic Escherichia coli (UPEC) promotes sensitization of bladder afferent sensory neurons with tetrodotoxin-resistant and tetrodotoxin-sensitive action potentials. Lipopolysaccharide and other virulence factors produced by UPEC contribute to the sensitization of bladder afferents in UTI. In conclusion, sensitized afferents contribute to the voiding symptoms and pelvic pain present in mice bladder inoculated with UPEC.

Acid-sensing ion channels modulate bladder nociception

Sensitization of neuronal pathways and persistent afferent drive are major contributors to somatic and visceral pain. However, the underlying mechanisms that govern whether afferent signaling will give rise to sensitization and pain are not fully understood. In the present report, we investigated the contribution of acid-sensing ion channels (ASICs) to bladder nociception in a model of chemical cystitis induced by cyclophosphamide (CYP). We found that the administration of CYP to mice lacking ASIC3, a subunit primarily expressed in sensory neurons, generates pelvic allodynia at a time point at which only modest changes in pelvic sensitivity are apparent in wild-type mice. The differences in mechanical pelvic sensitivity between wild-type and Asic3 knockout mice treated with CYP were ascribed to sensitized bladder C nociceptors. Deletion of Asic3 from bladder sensory neurons abolished their ability to discharge action potentials in response to extracellular acidification. Collectively, the results of our study support the notion that protons and their cognate ASIC receptors are part of a mechanism that operates at the nerve terminals to control nociceptor excitability and sensitization.NEW & NOTEWORTHY Our study indicates that protons and their cognate acid-sensing ion channel receptors are part of a mechanism that operates at bladder afferent terminals to control their function and that the loss of this regulatory mechanism results in hyperactivation of nociceptive pathways and the development of pain in the setting of chemical-induced cystitis.

Biomaterial-assisted drug delivery for interstitial cystitis/bladder pain syndrome treatment

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a chronic and painful bladder condition afflicting patients with increased urinary urgency and frequency as well as incontinence. Owing to the elusive pathogenesis of IC/BPS, obtaining effective therapeutic outcomes remains challenging. Current administrational routes such as intravesical-bladder injection improve the treatment efficacy and reduce systemic side effects. However, the bladder permeability barrier hinders drug penetration into the bladder wall to meet the desired therapeutic expectation. These issues can be addressed by encapsulating drugs into biomaterials. When appropriately exploited, they would increase the drug dwelling time in the bladder, enhance the penetration of mucosa and improve the therapeutic response of IC/BPS. In this review, we first elucidate the pathogenesis and animal models of IC/BPS. Then, we highlight recent representative biomaterial-assisted drug delivery systems for IC/BPS treatment. Finally, we discuss the challenges and outlook for further developing biomaterial-based delivery systems for IC/BPS management.

In vivo and ex vivo assessment of bladder hyper-permeability and using molecular targeted magnetic resonance imaging to detect claudin-2 in a mouse model for interstitial cystitis

OBJECTIVES

To determine if the URO-MCP-1 mouse model for bladder IC/BPS is associated with in vivo bladder hyper-permeability, as measured by contrast-enhanced MRI (CE-MRI), and assess whether molecular-targeted MRI (mt-MRI) can visualize in vivo claudin-2 expression as a result of bladder hyper-permeability. Interstitial cystitis/bladder pain syndrome (IC/BPS) is a chronic, painful condition of the bladder that affects primarily women. It is known that permeability plays a substantial role in IC/BPS. Claudins are tight junction membrane proteins that are expressed in epithelia and endothelia and form paracellular barriers and pores that determine tight junction permeability. Claudin-2 is a molecular marker that is associated with increased hyperpermeability in the urothelium.

MATERIALS AND METHODS

CE-MRI was used to measure bladder hyper-permeability in the URO-MCP-1 mice. A claudin-2-specific mt-MRI probe was used to assess in vivo levels of claudin-2. The mt-MRI probe consists of an antibody against claudin-2 conjugated to albumin that had Gd-DTPA (gadolinium diethylenetriamine pentaacetate) and biotin attached. Verification of the presence of the mt-MRI probe was done by targeting the biotin moiety for the probe with streptavidin-horse radish peroxidase (SA-HRP). Trans-epithelial electrical resistance (TEER) was also used to assess bladder permeability.

RESULTS

The URO-MCP-1 mouse model for IC/BPS was found to have a significant increase in bladder permeability, following liposaccharide (LPS) exposure, compared to saline-treated controls. mt-MRI- and histologically-detectable levels of the claudin-2 probe were found to increase with LPS -induced bladder urothelial hyper-permeability in the URO-MCP-1 IC mouse model. Levels of protein expression for claudin-2 were confirmed with immunohistochemistry and immunofluorescence imaging. Claudin-2 was also found to highly co-localize with zonula occlidens-1 (ZO-1), a tight junction protein.

CONCLUSION

The combination of CE-MRI and TEER approaches were able to demonstrate hyper-permeability, a known feature associated with some IC/BPS patients, in the LPS-exposed URO-MCP-1 mouse model. This MRI approach could be clinically translated to establish which IC/BPS patients have bladder hyper-permeability and help determine therapeutic options. In addition, the in vivo molecular-targeted imaging approach can provide invaluable information to enhance our understanding associated with bladder urothelium hyper-permeability in IC/BPS patients, and perhaps be used to assist in developing further therapeutic strategies.

The Urothelium: Life in a Liquid Environment

The urothelium, which lines the renal pelvis, ureters, urinary bladder, and proximal urethra, forms a high-resistance but adaptable barrier that surveils its mechanochemical environment and communicates changes to underlying tissues including afferent nerve fibers and the smooth muscle. The goal of this review is to summarize new insights into urothelial biology and function that have occurred in the past decade. After familiarizing the reader with key aspects of urothelial histology, we describe new insights into urothelial development and regeneration. This is followed by an extended discussion of urothelial barrier function, including information about the roles of the glycocalyx, ion and water transport, tight junctions, and the cellular and tissue shape changes and other adaptations that accompany expansion and contraction of the lower urinary tract. We also explore evidence that the urothelium can alter the water and solute composition of urine during normal physiology and in response to overdistension. We complete the review by providing an overview of our current knowledge about the urothelial environment, discussing the sensor and transducer functions of the urothelium, exploring the role of circadian rhythms in urothelial gene expression, and describing novel research tools that are likely to further advance our understanding of urothelial biology.

Virtual measurements of paracellular permeability and chronic inflammation via color coded pixel-wise T1 mapping

To assess whether quantitative T₁ relaxometry can measure permeability, chronic inflammation and mural thickening of mouse bladder wall. Adult female C57BL6 mice unexposed to radiation (controls) or 40 wk postirradiation of 10 Gy were scanned at 9.4 T before and after instillation (0.1 mL) of aqueous, novel contrast mixture (NCM) containing 4 mM gadobutrol and 5 mM ferumoxytol. Rapid acquisition with refocused echo (RARE) sequence was used with variable repetition times (TR). Pixel-wise maps of T₁ relaxation times for the segmented bladder wall layers were generated from voxel-wise, nonlinear least square data fitting of TR-dependent signal intensity acquired with TR array of 0.4-10 s followed by the histology of harvested bladder. Significant differences between precontrast and postcontrast T₁ (ΔT₁) were noted in urothelium and lamina propria of both groups but only in detrusor of irradiated group (P < 0.001; 2-way ANOVA). Nearly twofold higher gadobutrol permeability (550 ± 73 vs. 294 ± 160 μM; P < 0.01) derived as per 1/ΔT₁ = r1. [C] in urothelium of irradiated group. Inflammation and bladder wall thickening (0.75 ± 0. vs. 0.44 ± 0.08 mm; P < 0.001) predicted by MRI was subsequently confirmed by histology and altered expression of CD45 and zonula occludens-1 (ZO-1) relative to controls. NCM enhanced MRI relies on the retention of large molecular weight ferumoxytol in lumen for negative contrast, while permeation of the non-ionic, small molecular weight gadobutrol through ZO-1 generates positive contrast in bladder wall for virtual measurement of paracellular permeability and assessment of chronic inflammation in thin and distensible bladder wall, which is also defined by its variable shape and location within pelvis.

Assessing bladder hyper-permeability biomarkers in vivo using molecularly-targeted MRI

The objective was to investigate if some of the key molecular players associated with bladder hyper-permeability in interstitial cystitis/bladder pain syndrome (IC/BPS) could be visualized with molecularly-targeted magnetic resonance imaging (mt-MRI) in vivo. IC/BPS is a chronic, painful condition of the bladder that affects primarily women. It has been demonstrated over the past several decades that permeability plays a substantial role in IC/BPS. There are several key molecular markers that have been associated with permeability, including glycolsaminoglycan (GAG), biglycan, chondroitin sulfate, decorin, E-cadherin, keratin 20, uroplakin, vascular endothelial growth factor receptor 1 (VEGF-R1), claudin-2 and zonula occludens-1 (ZO-1). We used in vivo molecularly-targeted MRI (mt-MRI) to assess specific urothelial biomarkers (decorin, VEGF-R1, and claudin-2) associated with bladder hyper-permeability in a protamine sulfate (PS)-induced rat model. The mt-MRI probes consisted of an antibody against either VEGF-R1, decorin or claudin-2 conjugated to albumin that had also Gd-DTPA (gadolinium diethylene triamine penta acetic acid) and biotin attached. mt-MRI- and histologically-detectable levels of decorin and VEGF-R1 were both found to decrease following PS-induced bladder urothelial hyper-permeability, whereas claudin-2, was found to increase in the rat PS model. Verification of the presence of the mt-MRI probes were done by targeting the biotin moiety for each respective probe with streptavidin-hose radish peroxidase (HRP). Levels of protein expression for VEGF-R1, decorin and claudin-2 were confirmed with immunohistochemistry. In vivo molecularly-targeted MRI (mt-MRI) was found to successfully detect alterations in the expression of decorin, VEGFR1 and claudin-2 in a PS-induced rat bladder permeability model. This in vivo molecularly-targeted imaging approach has the potential to provide invaluable information to enhance our understanding of bladder urothelium hyper-permeability in IC/BPS patients, and perhaps be used to assist in developing novel therapeutic strategies.