Can the Bladder Itself “Measure” Volume, and Thereby Help to Determine When Initiation of Voiding Should Occur? ICI‐RS 2024

ABSTRACT

Aims

To answer the question of whether the bladder itself can to any extent control or modulate the initiation of voiding.

Methods

This subject was discussed at the International Consultation on Incontinence‐Research Society (ICI‐RS) 2024 conference in Bristol, UK in a proposal session.

Results

Cells in the bladder wall sense the local environment via a diverse array of ion channels and receptors which together provide input to motor‐sensory and signal transduction mechanisms. A purinergic signal transduction system provides a high‐gain mucosal chemosensitive transduction pathway between bladder wall stretch during filling and graded afferent activation. Recent studies established cross‐species similarities in the regulation of urine storage which include the upregulation of aquaporin (water) channels during bladder filling/wall stretch, in the bladder. In addition to the endocrine hypothalamus/pituitary axis production, urothelial production of arginine vasopressin acts on urothelial vasopressin receptors in a paracrine manner causing aquaporin channel upregulation, reducing the bladder volume and delaying sensation of fullness. Bladder shape influences the sensory systems involved in the perception of bladder volume; moreover irregular bladder shapes may correlate with overactive bladder.

Conclusions

Volume measuring and signaling threshold‐determining mechanisms in the bladder along with shape and permeability act to influence the timing and type of signaling to the CNS; although this is not always followed by a consecutive action. The hierarchical grading of the signals originating from the bladder among other peripheral bodily or central signals are crucial factors that determine whether the bladder is “allowed” to initiate voiding.

1. Introduction

Bladder sensation is necessary for adequate storage and voiding functions of the urinary bladder. Dysfunctional bladder sensation is suggested to be one of the key causative factors in both the overactive bladder symptom complex and the underactive bladder. Therefore, the regulation of bladder storage and filling, mediated by bladder sensation, needs to be understood for the development of both diagnostic and therapeutic interventions for functional bladder disorders.

The question whether the bladder itself can measure volume and can harness that information to determine when voiding should occur is a crucial question. The answer to this may determine the level of influence the bladder itself has on the switch from storage to voiding.

2. Methods and Collection of Data

Important factors that may determine whether the bladder has the abovementioned functionality were proposed and discussed by a group of experts in the field. This occurred during a Proposal session at the 2024 meeting of the International Consultation on Incontinence Research Society (ICI‐RS) in Bristol, UK. These factors comprise: the sensors present in the bladder wall, the regulatory mechanisms inside the bladder wall driving and modulating afferent signaling, the physical properties such as shape and permeability of the bladder, communication with the central nervous system (CNS) and consecutive processing inside the CNS. Remaining research questions and proposals for further research are suggested in the Discussion following an overview of the factors discussed in the Results section.

3. Results

The bladder wall has several mechanisms by which its local environment is sensed—this information is relayed to the brain where it is interpreted and an appropriate action is planned and executed, for example, planning and initiating an appropriate void or further maintaining the storage phase. Importantly, local bladder sensing information does not always translate to conscious sensations.

3.1. Sensors Inside the Urinary Bladder

Environmental cues detected by the bladder include fullness, pressure, pain, urine pH and osmolality, and temperature. The bladder has a portfolio of sensors, such as transient receptor potential (TRP) channels, purinergic receptors and mechanosensing Piezo ion channels as well as classic voltage‐gated, Ca²⁺‐activated and ligand‐gated channels [1]. TRP channels comprise a diverse family of canonical (TRPC), melastatin (TRPM), polycystin (TRPP), mucolipin (TRPML) and vanilloid TRPs (TRPV) that sense the environment, many of which are expressed in the bladder [1, 2, 3].

Piezo1 and Piezo2 mechanosensing channels are expressed in urothelium and afferents of mouse [4, 5, 6] and human [7] bladder urothelium. Conditional knockout (KO) mice demonstrate that urothelial Piezo1 KO has a limited phenotype concerning voiding behavior, Piezo2 KO males exhibit incontinence (increased number of secondary void spots in void‐spot assays) during the active, nocturnal dark (awake) phase; moreover, double KOs have a more affected phenotype [7]. The latter group exhibited incontinence during the dark phase in both sexes; furthermore anaesthetized females had bladder hypoactivity (increased compliance and prolonged intervoid intervals during cystometry recordings). In urothelium from double KO, there were decreased urothelial responses to mechanical stimulation and reduced ATP release, together showing the importance of urothelial Piezo1/2 in mechano‐transduction and normal voiding. These findings align with observations of urinary dysfunction in patients, deficient in Piezo2 who exhibit decreased voiding frequency, limited/absent sensation of the need to void and many patients reported the experience of sudden urgency incontinence [6]. The observation that individuals with mutant Piezo2 have difficulty in sensing bladder fullness and experience urinary dysfunction highlights the need to better interrogate Piezo‐signaling and its cross‐talk with relevant mechanisms, for example, cholinergic, adrenergic and purinergic pathways in physiology and pathophysiology.

3.2. Motor‐Sensory Mechanism for Sensing Bladder Fullness

Spontaneous contractions, also known as non‐voiding contractions (NVCs) recorded from in vitro bladder strips or ex vivo bladder pressure recordings, have been used experimentally to advance our knowledge of basic bladder physiology and pharmacology. Interestingly, these events represent a sensing pathway within the detrusor layer, which is neurogenic and tetrodotoxin (TTX)‐insensitive Moreover, evidence from ex vivo rodent or pig bladder recordings, show a concomitant increase in frequency and amplitude during filling [8, 9]. Single NVCs precede a burst of afferent nerve signaling, indicating that NVCs transduce filling status to the afferents [8], not the other way round. Removal of the outer detrusor layer of mouse bladder, leaving a mucosal preparation (urothelium and lamina propria) demonstrated that a “detrusor‐free” bladder could accommodate similar volumes at given pressures, but with a striking lack of NVCs [10]. Mechanisms exist to limit the extent of NVCs during filling, potentially preventing generation of unwanted voiding contractions. Small‐conductance, Ca²⁺‐activated K⁺ channels (SK channels), which are preferentially expressed on detrusor interstitial cells rather than detrusor smooth muscle, interact with mechanosensitive TRPV4 channels to generate a hyperpolarization that has been proposed to act as a biological “brake” on neighboring smooth muscle [11]. This SK‐mechanism may translate to human bladder physiology as application of the SK blocker, apamin, to ex vivo strips of human bladder, markedly enhanced spontaneous contractions (NVCs) [12]. To date, the question remains whether the SK‐mechanism in detrusor interstitial cells can directly affect smooth muscle NVCs [13].

3.3. A Purinergic Chemotransduction Mechanism to Measure Bladder Filling

Gradual mechanical stretch of isolated bladder wall segments or filling isolated bladders with a physiological solution evokes graded increases of afferent nerve firing suggestive of a sensory transduction system relating stretch of the bladder wall to increased afferent nerve activity [14, 15]. Purinergic P2X3 receptors are associated with afferent nerve endings. Thus, the observation that afferent firing is attenuated in bladders from which these receptors have been genetically knocked‐out suggests an involvement of adenosine triphosphate (ATP) in sensory transduction [15]. Moreover, the bladder mucosa has an abundant afferent nerve supply, especially just beneath the urothelium [16], suggesting a sensory role for this part of the bladder wall. Artificial stretch of small (≈1 mm diameter) mucosa strips also releases ATP into the extracellular space [17, 18, 19, 20], whilst substantially less release is recorded from detrusor‐only preparations, that is, with the mucosa removed [18]. In addition, spontaneous contractions of the mucosa are associated with transient increases of extracellular ATP, suggestive of local contractions stretching adjacent tissues to release ATP [17].

However, the mucosa is composed of multiple cell types, ranging from abundant interstitial cells, blood vessels, a muscularis mucosae in many species including humans, and a multi‐layered urothelium. Suspensions of viable urothelial cells, prepared by gentle enzymatic digestion of the mucosa, release ATP, as well as acetylcholine (ACh), when subject to mechanical stimulation by forcing a cell suspension sample through a narrow tube [21, 22]. All cells of the urothelium (umbrella, intermediate and basal) release ATP and ACh [22]. Moreover, the amounts of ATP and ACh released were a function of the magnitude of the forcing stimulus, as required for a sensory transduction mechanism. A linkage between urothelial ATP and ACh release in a sensory pathway is also suggested from several lines of evidence using urothelial cell suspensions or mucosa strips:

• ACh release from urothelial suspensions is more sensitive to the forcing stimuli than ATP [21, 22];

• With mucosal strips, addition of a cholinergic receptor agonist, in the absence of stretch, is associated with release of comparable amounts of ATP compared to that released by stretch alone [20];

• Carbachol‐induced ATP release is inhibited by the M3‐selective antagonist 4‐DAMP and the M2‐selective antagonist methoctramine [17, 18].

In summary, these data reveal that lateral wall stretch releases ACh from urothelial cells which acts in an autocrine manner on M2/M3 receptors on urothelial cells. In addition, activation of M2/M3 receptors stimulates release of ATP from urothelial cells and ATP diffuses to P2X3 receptors on afferent nerve fibers to initiate action potential firing. This system provides a high‐gain mucosal chemosensitive transduction pathway between bladder wall stretch during filling and graded afferent activation.

3.4. Translational Evidence for Regulation Mechanisms of Stored Urine Volume and Associated Signaling Modulation

The uninterrupted sleep of healthy individuals is ensured by an equilibrium reached between urine production rate of the kidney and reabsorption rate of stored urine in the bladder [23], the latter indexed by tritiated water reabsorption rate of 1 mL/min at instilled volumes of ~200 mL [24] and increasing at higher distended volumes [25, 26]. Meanwhile, a mismatch between urine production and reabsorption in the bladder results in nocturia, defined by an estimated nocturnal urine production rate of >1.5 mL/min representing a summation of production and reabsorption rate [27]. The reabsorption of stored urine from the bladder is facilitated by constitutive and inducible expression of aquaporins, urea transporters, mineralocorticoid receptors, amiloride‐sensitive Na⁺‐channels, and Na⁺/K⁺‐ATPase pumps on the basolateral surface of umbrella cells and intermediate cells of mammalian urothelium [25]. The activity of aquaporin channels in the urothelium is sensitive to endocrine signaling by arginine vasopressin (AVP) released by the hypothalamus/pituitary axis and a paracrine signaling mechanism in human and mouse bladder urothelium, recently discovered [25, 28, 29]. The distension‐evoked upregulation of aquaporin 2 (AQP2) channels in rodent urothelium [30] facilitates water flux from the lumen via paracellular diffusion into the extracellular space of the urothelium and then into the intravascular space of capillaries [25, 28, 29, 31, 32] As a result, perfusion [33] is essential [25] for delaying full sensation of bladder fullness during sleep by ensuring prompt washout of diffused urine constituents from bladder mucosa to preclude the irritation of bladder afferent nerve endings [32, 33].

AVP synthesized locally in the urothelium activates vasopressin 1 and vasopressin 2 receptors (VR1/VR2) in mouse and human bladders to complement the endocrine signaling of AVP in the dilution of plasma osmolality through reduction in the urine volume and amelioration of the filling sensations arising from the bladder wall via a rise in bladder compliance. While human urothelium can accelerate the reabsorption of Na⁺ bound water for homeostasis of plasma electrolytes and hydration status to offset polyuria [26], mammalian urothelium lacks the biochemical machinery to absorb oil [31] or to upregulate Na‐glucose cotransporters (SGLT) or GLUT‐1 glucose transporters for homeostasis of glycemia by acceleration of concentration‐dependent reabsorption of 5%–50% glucose instilled in human bladder [34]. A three times slower reabsorption rate of glucose bound water (glucosuria) than that of Na⁺ or Cl⁻ bound water (polyuria) [32] during closed cystometry of the rat underlines the pathologic significance of the glucosuria in the Streptozotocin‐induced diabetes model. Instead of polyuria, glucosuria is culpable in prolonged distension of bladder causing a threefold rise in ATP/NO release from the urothelium to stimulate the firing of bladder afferent nerves for causing dramatically higher urinary frequency accompanied with the rise in bladder weight [35]. Accordingly, the causality of recently reported treatment‐associated adverse effects of OAB in non‐insulin dependent diabetes patients [36] after treatment with SGLT2 inhibitors (new antidiabetic drugs): canagliflozin, dapagliflozin, and empagliflozin is the evoked glucosuria instead of polyuria. Evidently, the receptors and channels expressed by the human urothelium can offset the effect of polyuria but not of glucosuria evoked by saturation of SGLT in diabetes or by inhibitors of SGLT. Overall, these reports provide clinical, and basic scientific evidence on the modulation of bladder permeability as a homeostatic lever to delay the full sensation of fullness and forestall urgency, the hallmark symptom of OAB.

3.5. Physical Properties of the Bladder Wall That Influence or Modulate Sensing

Bladder shape is important for sensation related to bladder volume. As a simple example, consider two latex balloons, with one manufactured to be spherical and the other to be cylindrical. If the balloons are filled to the same volume without any external forces constraining their shape, they fill as a sphere and a cylinder, respectively, and develop pressure that is related to the volume and the material properties of the balloon. If the cylindrical balloon is either constrained to fill as a sphere or filled as a cylinder and then squeezed into a spherical shape, then the internal pressure for that volume will increase and some areas of the balloon will have increased stretch. This also occurs if a spherical balloon is forced into a cylindrical shape. Thus, the balloon's shape can influence pressure and wall stretch, and also the related wall tension, for a given volume.

Now, consider the bladder, which is much more complex than a balloon. This review has referenced several studies that provide evidence for mechanisms that respond to local strain, strain rate, and/or stress in one or more layers or cell types in the bladder wall. As illustrated by the balloon example, changes in isovolumetric bladder shape due to posture, fullness of the gut, size and positioning of other organs, etc. would influence bladder pressure and the relative stretch and stress in localized areas of the bladder wall, and would therefore influence the level of stimulation of local sensory mechanisms at that bladder volume [37]. Thus, the relationships between local bladder wall stretch, bladder wall tension, organ‐level pressure and bladder volume are complex and depend on the shape of the bladder, as well as bladder wall material properties [38], and the orientation, distribution and coordination of the sensory mechanisms within the bladder tissue with multiple interacting layers and cell types. Despite this complexity, bladder filling sensation has been shown to be repeatable during urodynamics in individuals with and without an overactive bladder [39], and voided volumes at different levels of fullness sensation, measured using frequency–volume charts and measured during urodynamics are comparable [40]. This suggests that each individual's bladder sensory mechanisms are relatively well calibrated to a particular volume.

Anecdotally, if someone's bladder is full to the extent that they have a desire to void and they push relatively hard on their abdomen near the bladder, they will likely feel a change in bladder sensation without a change in volume. Furthermore, research studies have shown the effect of bladder shape on filling mechanics [41] and others that suggest that irregular bladder shapes may correlate with overactive bladder (OAB) in some individuals [42, 43]. Effects of bladder internal or extrinsic factors, past resections, or scarring adherent to the bladder, are likely to influence the filling mechanics similarly causing comparable dysfunctions. Other studies have proposed that bladder compression due to chronic constipation may contribute to overactive bladder [44] and that treatment of constipation improves OAB symptoms [45]. Bladder compression has also been proposed as a potential cause of OAB during pregnancy [46]. Together, these studies suggest that bladder shape influences the sensory systems involved in the perception of bladder volume.

3.6. Bladder–Brain Signaling Mechanisms During Urine Storage

Close communication between the lower urinary tract (LUT) and CNS is not only essential for the switch between storage and voiding of urine, but also seems to actively facilitate urine storage. The significant role of afferent nerves, both mucosal and muscular afferents, in bladder sensing was discussed at the ICS‐2023 and is reviewed in [47]. Afferent signaling from the LUT arrives in the brain at the level of the PAG where it is relayed to higher cortical and subcortical areas that determine when attentional awareness should be shifted to the LUT and when voiding should be initiated [48].

Earlier research suggests the existence of a region in the pons that is involved in urine storage, the pontine storage center (PSC). Lesioning of this region in animal models induces retention [49] and positron emission tomography studies in humans show activity in this region during the storage phase [50]. Other studies indicate that electrical stimulation of the dorsolateral PAG promotes storage and can interrupt an ongoing voiding contraction [51]. This effect appears to be dependent on GABAergic signaling to Barrington's nucleus, also known as the pontine micturition center (PMC) [52]. The PAG and PMC are strongly interconnected, and excitation of the PMC immediately induces voiding [53]. Inhibition of the PMC from upstream brain areas may underlie active suppression of voiding during the storage phase. Human neuroimaging research using ultrahigh field functional magnetic resonance imaging (fMRI) indicates that communication between different functional areas of the PAG changes as a function of bladder filling, as well as communication with the PMC [54, 55].

The exact mechanisms by which the CNS contributes to the facilitation of urine storage are not completely understood, although this knowledge is essential to improve therapeutic approaches. It remains to be explored how active interaction between the LUT and CNS is organized. It is likely that local signaling processes in the bladder wall determine a potential threshold for CNS involvement in maintaining continence during bladder filling. Once the CNS is actively involved, the prolongation of the storage phase may be facilitated by active suppression of the PMC (likely from the PAG) or by activity of the PSC. However, it could also be argued that, since activity of the PMC is required to switch from storage to voiding of urine, merely the absence of excitation of the PMC should be sufficient to prolong the storage phase.

It is likely that brainstem switching mechanisms are affected in association with various lower urinary tract symptoms, either of neurogenic origin or with their origin in the LUT. An important knowledge gap centers around the question how pathophysiological changes in the LUT affect upstream processing of LUT sensory information in the CNS. Improved understanding of these relationships will enable identification of adaptive processes in the CNS that could be therapeutically targeted or exploited to improve patients' well‐being.

4. Discussion

Cells in the bladder wall have a number of interconnecting mechanisms to sense fullness and environmental conditions. The majority of studies have been performed in animal models, supported by some human studies. Besides the sensors themselves, sensing and modulating systems are found that integrate sensory information such as the motor sensory system and the purinergic chemotransduction system. In addition to diuresis regulation via the kidney, the bladder itself also has mechanisms that regulate urine volume by changing permeability and also active reabsorption. Moreover, the bladder shape can influence bladder pressure and stretch and wall stress in certain areas of the bladder. These factors interact with each other and are also likely to be influenced by factors such as sex, age and circadian rhythm. Therefore, an integrated approach is expected to provide more insight into the mechanism by which the bladder measures volume and is able to modulate the moment of voiding.

Table 1 below indicates the proposals for further research based on the research questions derived from the discussions during this proposal at ICI‐RS 2024:

Table 1.

Research questions and future directions.

Paragraph	Research question	Animal or Human	Type of study
Sensors inside the urinary bladder	Which signaling mechanisms do Piezo1/2 interact with in sensing bladder fullness?	Animal	Cell and tissue physiological and molecular studies and ex vivo recordings of bladder pressure/volume and afferent nerve signaling from knockout mouse models, utilizing pharmacological modulators, e.g., cholinergic, adrenergic, purinergic.
	Is the Piezo1/2 mechanism defective in spinal cord injury, type 2 diabetes, urinary tract infection and other diseases that are associated with LUTS?	Animal/human	As above, using validated disease models. Cell and tissue physiological studies in human tissue.
	What do we know about sex and circadian differences of Piezo2 sensing in humans?	Human	Larger scale studies (to date, data published from 12 patients) of lower urinary tract symptoms in patients with Piezo2 mutations and correlation with sex, circadian rhythm and other physiological parameters.
Purinergic chemotransduction mechanism	Identify the cellular signaling pathways that control ACh release from urothelial cells in response to imposition of mechanical forces on the cell.	Animal/human	In vitro studies to determine which sensor molecules mediate ACh release from urothelial cells.
	Describe the urothelial cellular signaling pathways that mediate muscarinic receptor activation and ATP release.	Animal/human	In vitro studies that identify intracellular signaling pathways that link muscarinic receptor activation and ATP secretion from urothelial cells.
	Determine if other mucosal cells release ATP when subject to mechanical forces, e.g., the abundant interstitial cells.	Animal/human	In vitro studies, as above but using suspensions of isolated interstitial cells.
	Identify which signaling pathways underly increased ATP release using tissue from overactive or fibrotic bladders.	Animal/human	In vitro studies using animal models or human tissue samples to determine up‐ or downregulation of key signaling pathways that regulate ATP release.
	Identify potential therapeutic mediators that moderate ATP release as a means to minimise excessive sensory perceptions of bladder filling.	Animal/human	In vivo studies to test if modulators of key signaling pathways that regulate ATP release alleviate excessive bladder filling sensations. Contenders include the P2X3 antagonist gefapixant [56] and an antifibrotic agent, cinaciguat [57].
Translational evidence for regulation mechanisms of stored urine volume and associated signaling modulation	How does endocrine or paracrine signaling of AVP decrease plasma osmolality and increase urine osmolarity?	Animal/Human	Studies measuring osmolarity changes in the urine due to systemic versus instilled AVP.
	What are potential mechanisms for increased uptake of instilled 3H‐water and/or 14C‐urea to the systemic circulation with increased bladder filling/stretch?	Animal/Human	In vivo studies using 3H‐water and/or 14C‐Urea instilled in bladder at different volumes with radioactivity measured from blood samples over time.
	Accepting that desmopressin (dAVP) stimulates VR2 in apical urothelial cells to increase the trafficking of aquaporin channels, what is a possible mechanism whereby dAVP treats nocturia?	Animal	In vivo studies of nocturnal urine production and bladder capacity in dAVP treated rats after systemic or local delivery to bladder. In vitro studies on dAVP evoked bladder relaxation.
	Does the osmolarity of urine in the renal pelvis and bladder differ and change under different conditions?	Human	Osmolarity measurements of simultaneously collected urine from renal pelvis and bladder using an endoscope and catheter, respectively.
	Does bladder volume decrease during sleep of healthy adults and patients with nocturia?	Human	Overnight continuous recording of bladder pressure and volume in healthy adults and those with nocturia.
	Can differences be seen between intravesical absorption of isotonic dextrose and isotonic saline?	Human	By measuring percent dose of instilled saline and dextrose absorbed in systemic circulation.
	Do SGLT2 inhibitors cause OAB/DO symptoms?	Animal	Studies on the incidence of OAB/DO in diabetic rodents with and without SGLT2 inhibitors.
Physical properties of the bladder wall that influence or modulate sensing	Does a change in bladder shape due to abdominal compression cause a change in bladder fullness sensation?	Human	In vivo study using an abdominal ultrasound probe to acutely compress the bladder. Quantify bladder shape, volume and sensation.
	Does bladder shape during filling correlate with bladder dysfunction and/or LUTS?	Human	In vivo quantification of the bladder shape/volume relationship during urodynamic filling and correlation with bladder dysfunction/LUTS.
	Are bladders with detrusor overactivity more spherical?	Human	Perform in vivo follow‐up studies to a study by Gray et al., that correlated bladder shape with detrusor overactivity [58].
Bladder–Brain signaling mechanisms during urine storage	Is the pontine micturition center actively suppressed during a strong desire to void state, before onset of micturition is desired?	Animal	Invasive recording of pontine micturition center activity during manipulation of bladder volumes in a rodent model.
	What are the neuroanatomical characteristics of the pontine storage center?	Animal	Histology and (spatial) transcriptomics of the cellular characteristics in the hypothesized area of the pontine storage center.
	Is sensory processing in the periaqueductal gray (and potential suppression of the pontine micturition center) altered in patients with overactive or underactive bladder complaints? What are the effects of therapies that target the sensory system (such as sacral neuromodulation) on brainstem activity?	Human	Functional neuroimaging of brainstem activity in healthy adults and OAB/UAB patients during bladder volume manipulation before and after therapeutic intervention.

5. Conclusions

Several new sensors and new sensing mechanisms have been recognized in the last decade. Combining these new sensing mechanisms with those previously described into a comprehensive hypothesis will enhance our understanding of volume measuring and signaling threshold mechanisms in the bladder itself. Bladder properties such as shape and permeability have an underrecognized influence on the moment of signaling to the central nervous system. The communication of peripheral afferent information to the central nervous system will be transmitted from the end organ in either a frequency‐dependent or amplitude‐modulated manner. The way by which these signals are presented to the central nervous system only in part determine the consecutive actions that will be taken. The hierarchical grading of the signals originating from the bladder among other peripheral bodily or central signals are crucial factors that determine whether the bladder is “allowed” to initiate voiding. New methods both in basic science (optogenetics) and clinical science (functional imaging) will allow more specific experiments to unravel these mechanisms.

Author Contributions

All authors contributed to: writing, reviewing, editing and final approval of the manuscript. In addition to the above G.V.K. also prepared the manuscript.

Ethics Statement

The authors have nothing to report.

Consent

The authors have nothing to report.

Conflicts of Interest

Gommert Van Koeveringe—Boston Scientific: consultant, surgical procter, research collaboration. Medtronic: clinical trial. Minze Health: research collaboration. Scannexus: research collaboration. Pradeep Tyagi—Lipella Pharmaceuticals: inventor.Vensica Therapeutics: consultant. Urogen Pharma: consultant. John E. Speich—Vesi Corporation: equity interest. Bright Uro: consultant. The remaining authors declare no conflicts of interest.

Data Availability Statement

The authors have nothing to report.