Intravesical resiniferatoxin desensitizes rat bladder sensory fibres without causing intense noxious excitation. A c-fos study

Resiniferatoxin: Nature's Precision Medicine to Silence TRPV1-Positive Afferents

Resiniferatoxin (RTX) is an ultrapotent capsaicin analog with a unique spectrum of pharmacological actions. The therapeutic window of RTX is broad, allowing for the full desensitization of pain perception and neurogenic inflammation without causing unacceptable side effects. Intravesical RTX was shown to restore continence in a subset of patients with idiopathic and neurogenic detrusor overactivity. RTX can also ablate sensory neurons as a "molecular scalpel" to achieve permanent analgesia. This targeted (intrathecal or epidural) RTX therapy holds great promise in cancer pain management. Intra-articular RTX is undergoing clinical trials to treat moderate-to-severe knee pain in patients with osteoarthritis. Similar targeted approaches may be useful in the management of post-operative pain or pain associated with severe burn injuries. The current state of this field is reviewed, from preclinical studies through veterinary medicine to clinical trials.

Safety and efficacy of intravesical instillation of resiniferatoxin in healthy cats: A preliminary study

Objectives

To evaluate the safety of intravesical application of resiniferatoxin (RTX) in healthy cats and its effects on calcitonin gene-related peptide (CGRP) and substance P (SP) produced by C-fibers.

Methods

Seven adult female cats received either 25 mL of saline (control; n = 1), or intravesical RTX at 5, 25, or 50 μg in 25 mL of saline to a final concentration of 0.2 μg/mL (318 nM), 1 μg/mL (1,591 nM), and 2 μg/mL (3,181 nM) (n = 2 per group). The treatment was instilled into the urinary bladder for 20 min. Plasma concentrations of RTX were measured at 0, 0.5, 1, and 4 h. Physical exam, complete blood count, and serum biochemical analysis were performed on day 0, 7, and 14. After 14 days, the sacral dorsal root ganglia (DRG) and the urinary bladder were harvested for histological and immunofluorescence analysis.

Results

Intravesical RTX was well tolerated and plasma concentrations were below the quantifiable limits except for one cat receiving 1 μg/mL. Mild to moderate histopathological changes, including epithelial changes, edema, and blood vessel proliferation, were observed at lower doses (0.2 and 1 μg/mL), and were more severe at the higher dose (2 μg/mL). C-fiber ablation was observed in the urinary bladder tissue at all doses, as shown by an apparent reduction of both CGRP and SP immunoreactive axons.

Conclusion

A dose of 25 μg (1 μg/mL) of RTX instilled in the urinary bladder of healthy cats appeared to decrease the density of SP and CGRP nerve axons innervating bladder and induced moderate changes in the bladder tissue.

The urethra in continence and sensation: Neural aspects of urethral function

AIMS

Traditionally, the urethra has been considered a mere conduit to guide urine from the bladder to the external side of the body. Building evidence indicates that the urethra may directly influence bladder function via mechanisms restricted to the lower urinary tract (LUT).

METHODS

Here, we discuss the tissue arrangement of the urethra and addressed the contribution of new paraneuronal cells to LUT function. We also briefly reviewed two frequent LUT pathologies associated with urethral dysfunction.

RESULTS

Continence depends on an intact and functional urethral sphincter, composed of smooth, and striated muscle fibers and regulated by somatic and autonomic fibers. Recent studies suggest the existence of an urethro-vesical reflex that also contributes to normal LUT function. Indeed, the urethral lumen is lined by a specialized epithelium, the urothelium, in the proximal urethra. In this region, recent evidence demonstrates the presence of specific paraneuronal cells, expressing the neurotransmitters acetylcholine and serotonin. These cells are in close proximity of nerve fibers coursing in the lamina propria and are able to release neurotransmitters and rapidly induce detrusor contractions, supporting the existence of an urethro-vesical crosstalk.

CONCLUSION

The mechanism underlying the fast communication between the urethra and thebladder are beginning to be understood and should involve the interaction between specificepithelial cells and fibres innervating the urethral wall. It is likely that this reflex should bealtered in pathological conditions, becoming an attractive therapeutic target.

Effects of early intravesical administration of resiniferatoxin to spinal cord-injured rats in neurogenic detrusor overactivity

OBJECTIVES

To investigate if intravesical administration during spinal shock of resiniferatoxin (RTX), an ultrapotent desensitizing agonist of transient receptor potential vanilloid-1 (TRPV1), would silence TRPV1-expressing bladder afferents at an early stage of disease progression and modulate neurogenic detrusor overactivity (NDO) emergence.

MATERIALS AND METHODS

Rats submitted to largely incomplete spinal cord transection at T8/9 spinal segment were treated with intravesical RTX (50 nM) or its vehicle during spinal shock. Four weeks after spinal lesion, bladder-reflex activity was evaluated by cystometry under urethane anesthesia, after which the bladder, spinal cord, and dorsal root ganglia were collected and processed.

RESULTS

We found improvements on bladder function several weeks after early intravesical RTX administration, including a marked decrease of intravesical pressures and amplitude of bladder contractions. Such strong long-lasting urodynamic effects resulted from the very potent desensitizing activity of RTX on peripheral terminals of sensory afferents, an effect restricted to the bladder.

CONCLUSION

Our results support that an early intervention with RTX could potentially attenuate NDO development and ensuing urinary incontinence, with a dramatic impact on the quality of life of spinal cord injury patients.

Pathophysiological Role of Transient Receptor Potential Ankyrin 1 in a Mouse Long-Lasting Cystitis Model Induced by an Intravesical Injection of Hydrogen Peroxide

Chronic inflammatory bladder disorders, such as interstitial cystitis/bladder pain syndrome, are associated with poor quality of life. The exact pathological processes remain unclear, but accumulating evidence suggests that reactive oxidative species (ROS) are involved in urinary bladder disorders. Transient receptor potential ankyrin 1 (TRPA1), the most sensitive TRP channel to ROS, was shown to be responsible for urinary bladder abnormalities and hyperalgesia in an acute cystitis model. However, the roles of TRPA1 in chronic inflammatory bladder are not fully understood. We previously established a novel mouse cystitis model induced by intravesical injection of hydrogen peroxide (H₂O₂), resulting in long-lasting frequent urination, bladder inflammation, pain-related behavior, and histopathological changes. In the present study, we investigated the pathophysiological role of TRPA1 in the H₂O₂-induced long-lasting cystitis mouse model. Under anesthesia, 1.5% H₂O₂ solution was introduced transurethrally into the bladder of female wild-type (WT) and TRPA1-knockout mice and maintained for 30 min. This increased the number of voids in WT mice at 1 and 7 days after injection, but reduced the number in TRPA1-knockout mice at 1 day but not 7 days after injection. Spontaneous locomotor activities (increase in freezing time and decrease in distance moved) were reduced at 3 h after injection in WT mice, whereas the spontaneous visceral pain-related behaviors were attenuated in TRPA1-knockout mice. Furthermore, upregulation of c-fos mRNA in the spinal cord at 1 day after injection was observed in WT but not TRPA1-knockout mice. However, there was no difference in histopathological changes in the urinary bladder, such as edematous thickening in the submucosa, between WT and TRPA1-knockout mice at 1 or 7 days after injection. Finally, Trpa1 mRNA levels in the L5-S1 dorsal root ganglion were not altered, but levels in the urinary bladder were drastically increased at 1 and 7 days after injection. Taken together, these results suggest that TRPA1 contributes to acute bladder hyperactivity such as frequent urination and bladder pain, but does not appear to play a major role in the pathological processes of long-lasting cystitis.

Capsaicin, Nociception and Pain

Capsaicin, the pungent ingredient of the hot chili pepper, is known to act on the transient receptor potential cation channel vanilloid subfamily member 1 (TRPV1). TRPV1 is involved in somatic and visceral peripheral inflammation, in the modulation of nociceptive inputs to spinal cord and brain stem centers, as well as the integration of diverse painful stimuli. In this review, we first describe the chemical and pharmacological properties of capsaicin and its derivatives in relation to their analgesic properties. We then consider the biochemical and functional characteristics of TRPV1, focusing on its distribution and biological effects within the somatosensory and viscerosensory nociceptive systems. Finally, we discuss the use of capsaicin as an agonist of TRPV1 to model acute inflammation in slices and other ex vivo preparations.

Assessment of bladder sensation in mice with a novel device

OBJECTIVE

To develop and test the efficacy of an implantable bladder electrode device that can be used with the Neurometer electrodiagnostic stimulator to assess fiber-specific afferent bladder sensation in the mouse.

METHODS

We constructed a ball-tipped platinum electrode and surgically implanted it into the mouse bladder. The Neurometer was connected to the electrode to apply selective nerve fiber stimuli (250 Hz for Aδ fibers and 5 Hz for C fibers) of increasing intensities to the bladder mucosa in the mouse to determine bladder sensory threshold (BST) values. Using 58 female C57BL/6J mice, we measured the temporal and interobserver consistency of BST measurements, the effects of intravesical administration of lidocaine and resiniferatoxin on the BST, and the effects of our device on voiding behavior and bladder mucosal integrity.

RESULTS

BST values at 250 and 5 Hz did not vary significantly when measured 2, 4, and 6 days after device implantation, or when obtained by 2 blinded independent observers. Intravesical lidocaine yielded a transient increase in BST values at both 250 Hz and 5 Hz, whereas resiniferatoxin yielded a significant increase only at the 5 Hz stimulus frequency after 24 hours. Moderately increased micturition frequency and decreased volume per void were observed 4 and 6 days after device implantation. Histology revealed mild inflammatory changes in the area of the bladder adjacent to the implanted BST device.

CONCLUSION

Assessment of neuroselective bladder sensation in mice is feasible with our device, which provides reproducible BST values for autonomic bladder afferent nerve fibers.

Anatomical and functional characterization of a duodeno-pancreatic neural reflex that can induce acute pancreatitis

Neural cross talk between visceral organs may play a role in mediating inflammation and pain remote from the site of the insult. We hypothesized such a cross talk exists between the duodenum and pancreas, and further it induces pancreatitis in response to intraduodenal toxins. A dichotomous spinal innervation serving both the duodenum and pancreas was examined, and splanchnic nerve responses to mechanical stimulation of these organs were detected. This pathway was then excited on the duodenal side by exposure to ethanol followed by luminal mustard oil to activate transient receptor potential subfamily A, member 1 (TRPA1). Ninety minutes later, pancreatic inflammation was examined. Ablation of duodenal afferents by resiniferatoxin (RTX) or blocking TRPA1 by Chembridge (CHEM)-5861528 was used to further investigate the duodeno-pancreatic neural reflex via TRPA1. ~40% of dorsal root ganglia (DRG) from the spinal cord originated from both duodenum and pancreas via dichotomous peripheral branches; ~50% splanchnic nerve single units responded to mechanical stimulation of both organs. Ethanol sensitized TRPA1 currents in cultured DRG neurons. Pancreatic edema and myeloperoxidase activity significantly increased after intraduodenal ethanol followed by mustard oil (but not capsaicin) but significantly decreased after ablation of duodenal afferents by using RTX or blocking TRPA1 by CHEM-5861528. We found the existence of a neural cross talk between the duodenum and pancreas that can promote acute pancreatitis in response to intraduodenal chemicals. It also proves a previously unexamined mechanism by which alcohol can induce pancreatitis, which is novel both in terms of the site (duodenum), process (neurogenic), and receptor (TRPA1).

Endogenous purinergic control of bladder activity via presynaptic P2X3 and P2X2/3 receptors in the spinal cord

P2X(3) and P2X(2/3) receptors are localized on sensory afferents both peripherally and centrally and have been implicated in various sensory functions. However, the physiological role of these receptors expressed presynaptically in the spinal cord in regulating sensory transmission remains to be elucidated. Here, a novel selective P2X(3) and P2X(2/3) antagonist, AF-792 [5-(5-ethynyl-2-isopropyl-4-methoxy-phenoxy)-pyrimidine-2,4-diamine, previously known as RO-5], in addition to less selective purinoceptor ligands, was applied intrathecally in vivo. Cystometry recordings were made to assess changes in the micturition reflex contractions after drug treatments. We found that AF-792 inhibited micturition reflex activity significantly (300 nmol; from baseline contraction intervals of 1.18 +/- 0.07 to 9.33 +/- 2.50 min). Furthermore, inhibition of P2X(3) and P2X(2/3) receptors in the spinal cord significantly attenuated spinal activation of extracellular-signal regulated kinases induced by acute peripheral stimulation of the bladder with 1% acetic acid by 46.4 +/- 12.0% on average. Hence, the data suggest that afferent signals originating from the bladder are regulated by spinal P2X(3) and P2X(2/3) receptors and establish directly an endogenous central presynaptic purinergic mechanism to regulate visceral sensory transmission. Identification of this spinal purinergic control in visceral activities may help the development of P2X(3) and P2X(2/3) antagonist to treat urological dysfunction, such as overactive bladder, and possibly other debilitating sensory disorders, including chronic pain states.

Sequestration of brain derived nerve factor by intravenous delivery of TrkB-Ig2 reduces bladder overactivity and noxious input in animals with chronic cystitis

Brain derived nerve factor (BDNF) is a trophic factor belonging to the neurotrophin family. It is upregulated in various inflammatory conditions, where it may contribute to altered pain states. In cystitis, little is known about the relevance of BDNF in bladder-generated noxious input and bladder overactivity, a matter we investigated in the present study. Female rats were intraperitoneally (i.p.) injected with cyclophosphamide (CYP; 200 mg/kg). They received saline or TrkB-Ig(2) via intravenously (i.v.) or intravesical administration. Three days after CYP-injection, animals were anaesthetized and cystometries performed. All animals were perfusion-fixed and the spinal cord segments L6 collected, post-fixed and processed for c-Fos and phosphoERK immunoreactivity. BDNF expression in the bladder, as well as bladder histology, was also assessed. Intravesical TrkB-Ig(2) did not change bladder reflex activity of CYP-injected rats. In CYP-animals treated with i.v. TrkB-Ig(2) a decrease in the frequency of bladder reflex contractions, in comparison with saline-treated animals, was observed. In spinal sections from the latter group of animals, the number of phosphoERK and c-Fos immunoreactive neurons was lower than in sections from saline-treated CYP-animals. BDNF immunoreactivity was higher during cystitis but was not changed by TrkB-Ig(2) i.v. treatment. Evaluation of the bladder histology showed similar inflammatory signs in the bladders of inflamed animals, irrespective of the treatment. Data show that i.v. but not intravesical administration of TrkB-Ig(2) reduced bladder hyperactivity in animals with cystitis to levels comparable to those observed in unirritated rats. Since i.v. TrkB-Ig(2) also reduced spinal extracellular signal-regulated kinase (ERK) activation, it is possible that BDNF contribution to inflammation-induced bladder hyperactivity is via spinal activation of the ERK pathway. Finally, the reduction in c-Fos expression indicates that TrkB-Ig(2) also reduced bladder-generated noxious input. Our results show that sequestration of BDNF may be considered a new therapeutic strategy to treat chronic cystitis.

Bladder sensory desensitization decreases urinary urgency

Background

Bladder desensitization has been investigated as an alternative treatment for refractory detrusor overactivity. Most open and controlled clinical trials conducted with intravesical RTX showed that desensitization delays the appearance of involuntary detrusor contractions during bladder filling and decreases the number of episodes of urgency incontinence.

Urgency is being recognised as the fundamental symptom of overactive bladder (OAB), a symptomatic complex which recent epidemiological studies have shown to affect more than 10% of the Western population. As anti-muscarinic drugs, the first line treatment for OAB, are far from being able to fully control urgency, the opportunity to test other therapeutic approaches is created. The present work was, therefore, designed as an exploratory investigation to evaluate the effect of bladder desensitization on urinary urgency.

Methods

Twenty-three OAB patients with refractory urgency entered, after given informed consent, a 30 days run-in period in which medications influencing the bladder function were interrupted. At the end of this period patients filled a seven-day voiding chart where they scored, using a 0–4 scale, the bladder sensations felt before each voiding. Then, patients were instilled with 100 ml of 10% ethanol in saline (vehicle solution) and 30 days later a second seven-day voiding chart was collected. Finally, patients were instilled with 100 ml of 50 nM RTX in 10% ethanol in saline. At 1 and 3 months additional voiding charts were collected.

At the end of the vehicle and 3 months period patients were asked to give their subjective impression about the outcome of the treatment and about the willingness to repeat the previous instillation.

Results

At the end of the run-in period the mean number of episodes of urgency per week was 71 ± 12 (mean ± SEM). After vehicle instillation, the mean number of episodes of urgency was 56 ± 11, but only 4 patients (17%) considered that their urinary condition had improved enough to repeat the treatment. At 1 and 3 months after RTX the number of episodes of urgency decreased to 39 ± 9 (p = 0.002) and 37 ± 6 (p = 0.02), respectively (p indicates statistical differences against vehicle). The percentage of patients with subjective improvement after RTX and willing to repeat the instillation at a later occasion was 69%.

Conclusion

In OAB patients with refractory urgency bladder desensitization should be further investigated as an alternative to the standard management. Additionally, the specific effect of RTX on TRPV1 receptors suggests that urothelium and sub-urothelial C-fibers play an important role to the generation of urgency sensation.

Urodynamic effect of intravesical resiniferatoxin in patients with neurogenic detrusor overactivity of spinal origin: results of a double-blind randomized placebo-controlled trial

OBJECTIVES

To access by a placebo-controlled randomized clinical trial the effect of intravesical resiniferatoxin on the urodynamic parameters of patients with neurogenic detrusor overactivity (NDO) of spinal origin.

METHODS

Twenty eight patients with spinal NDO were randomised to receive intravesically 50 nM resiniferatoxin dissolved in 10% ethanol in saline (RTX group) or only the vehicle solution (placebo group). Filling cystometries were obtained in each patient at 1 month and 1 week before and at 1 and 3 months after treatment. In a visual analog scale patients were asked to estimate the discomfort induced by treatment. Patients were also persuaded to fill a micturition chart during the 3 days preceding each cystometry.

RESULTS

The RTX and placebo groups were homogeneous in what respects the volume to first involuntary detrusor contraction (FDC, 143+/-95 ml and 115+/-58 ml, respectively, p=0.3) and maximal cystometric capacity (MCC, 189+/-99 ml and 198+/-111 ml, respectively, p=0.8). At the end of the study, mean FDC and MCC in the RTX group, 184+/-93 ml and 314+/-135 ml, respectively were significantly higher than in the placebo group, 115+/-61 ml (p=0.03) and 204+/-92 ml (p=0.02). In the visual analogue scale discomfort caused by treatment was similar. Only 10 patients in the RTX group and 6 patients in the placebo group completed adequately the micturition chart. Mean frequency and urinary incontinence decreased significantly only in the RTX group.

CONCLUSIONS

Intravesical RTX is effective in increasing bladder capacity in spinal NDO patients. Such increment might contribute to decrease urinary frequency and incontinence of these patients.

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.

Anandamide-evoked activation of vanilloid receptor 1 contributes to the development of bladder hyperreflexia and nociceptive transmission to spinal dorsal horn neurons in cystitis

The role of anandamide in the development of inflammatory hyperalgesia and visceral hyperreflexia was studied in the rat urinary bladder. Animals were given intraperitoneal cyclophosphamide injection, which evokes painful hemorrhagic cystitis accompanied by increased bladder reflex activity. The vanilloid receptor 1 [transient receptor potential vanilloid 1 (TRPV1)] antagonist capsazepine, applied onto the serosal surface of bladders, significantly reduced the hyperreflexia. Mass spectrometric analysis revealed that cyclophosphamide injection significantly and persistently increased the anandamide content of bladder tissues. The increase in the anandamide content paralleled the development of reflex hyperactivity. Anandamide (1-100 microm), applied onto the serosal surface of naive bladders, increased the reflex activity in a concentration-dependent manner. Repeated anandamide applications did not produce desensitization of the response. The anandamide-evoked effect was blocked by capsazepine or by instillation of resiniferatoxin, the ultrapotent TRPV1 agonist, into the bladders 24 hr before the anandamide challenge. The cannabinoid 1 receptor antagonist SR141716A [N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methylpyrazole-3-carboxamide] significantly increased the potency of anandamide in enhancing bladder reflex activity in naive but not in cyclophosphamide-injected animals. Application of the fatty acid amide hydrolyze inhibitor palmitoylisopropylamine onto the serosal surface of bladders also increased the reflex activity both in naive and cyclophosphamide-injected rats. This latter effect in naive animals was blocked by capsazepine and by resiniferatoxin pretreatment. Finally, intravesical instillation of anandamide (50 microm) increased c-fos expression in the spinal cord, which was reduced by capsazepine or by resiniferatoxin pretreatment. These results suggest that anandamide, through activating TRPV1, contributes to the development of hyperreflexia and hyperalgesia during cystitis.

Increased spinal cord phosphorylation of extracellular signal-regulated kinases mediates micturition overactivity in rats with chronic bladder inflammation

Spinal processing of somatosensory and viscerosensory information is greatly facilitated in some persistent pain states. Growing evidence suggests that the so-called central sensitization depends in part on intracellular activation and signalling via specific MAP kinases. Here we studied the expression of phosphorylated extracellular signal-regulated kinases 1 and 2 (phosphoERK), the active form of these kinases, in spinal neurons following innocuous and noxious distension of non-inflamed and cyclophosphamide (CYP)-inflamed rat urinary bladders. Additionally, we investigated the nature of bladder primary afferents responsible for spinal ERK activation. Finally, we used a specific inhibitor of ERK phosphorylation to study the influence of these kinases on the bladder reflex activity of normal and inflamed bladders. Results indicated that, in non-inflamed rats, noxious but not innocuous bladder distension significantly increased spinal phosphoERK immunoreactivity from its normal very low level. However, in CYP-inflamed rats, innocuous and noxious bladder distension significantly increased the number of spinal neurons immunoreactive to phosphoERK. ERK activation was rapid (within minutes) and transient. Desensitization of vanilloid-sensitive afferents by intravesical resiniferatoxin, a capsaicin analogue, did not decrease phosphoERK immunoreactivity in normal or CYP-inflamed rats. ERK inhibition by intrathecal PD 98059 had no effect on bladder reflex contractions of non-inflamed bladders but significantly decreased its frequency in inflamed animals. Our results suggest that spinal ERK intervene in acute and chronic inflammatory pain perception and mediate bladder reflex overactivity accompanying chronic bladder inflammation. In addition, bladder noxious input conveyed in vanilloid-resistant primary afferents is important to spinal ERK phosphorylation in both noninflamed and CYP-inflamed animals.

Prospective, randomized, double-blind study of safety and tolerability of intravesical resiniferatoxin (RTX) in interstitial cystitis (IC)

OBJECTIVE

To determine the safety and tolerability of intravesical resiniferatoxin (RTX) in interstitial cystitis (IC) patients.

MATERIALS AND METHODS

IC patients were instilled with 50 cc of test solution containing either placebo, 0.05 microM or 0.10 microM RTX in the bladder. Plasma concentration of RTX and its degradant resiniferonol 9-, 13-, 14-orthophenylacetate was measured. Immediate post-treatment blood sampling and cystoscopy were performed. Symptoms were evaluated before treatment, at 4- and at 12-week follow-ups, using VAS indicator for pain, voiding diary, and O'Leary's IC symptom/problem indices.

RESULTS

Among 22 patients observed (ten in 0.10 microM RTX, eight in 0.05 microM RTX, and four in placebo groups), the most commonly reported adverse event was pain during instillation (80.0%, 87.5%, and 25.0%). No serious adverse events were reported.

CONCLUSIONS

Use of intravesical RTX in IC patients is associated with important tolerability issues but safe at 0.10 microM and 0.05 microM.

Current status in the pharmacological management of interstitial cystitis

Interstitial cystitis is a clinical condition occurring predominantly in women characterised by irritative voiding symptoms in the form of urinary frequency, urgency and pain. Patient symptoms have the potential to significantly affect quality of life, posing a challenge to some to perform activities of daily living. Those who reach an eventual diagnosis of interstitial cystitis have typically done so through an emotionally charged and circuitous route, the product of numerous physician encounters and stigmatising experiences. As such, these patients require considerate care. Overall, current pharmacological agents for the treatment of those with interstitial cystitis, provide a measure of symptomatic benefit, however, a universally effective regimen remains to be reported. As a definitive disease aetiopathogenesis is not fully determined, trials of pharmacological therapy are ongoing.

Sensory nerves, neurogenic inflammation and pain: missing components of alternative irritation strategies? A review and a potential strategy

The eyes and skin are highly innervated by sensory nerves; stimulation of these nerves by irritants may give rise to neurogenic inflammation, leading to sensory irritation and pain. Few in vitro models of neurogenic inflammation have been described in conjunction with alternative skin and eye irritation methods, despite the fact that the sensory innervation of these organs is well-documented. To date, alternative approaches to the Draize skin and eye irritation tests have proved largely successful at classifying severe irritants, but are generally poor at discriminating between agents with mild to moderate irritant potential. We propose that the development of in vitro models for the prediction of sensory stimulation will assist in the re-classification of the irritant potential of agents that are under-predicted by current in vitro strategies. This review describes the range of xenobiotics known to cause inflammation and pain through the stimulation of sensory nerves, as well as the endogenous mediators and receptor types that are involved. In particular, it focuses on the vanilloid receptor, its activators and its regulation, as these receptors function as integrators of responses to numerous noxious stimuli. Cell culture models and ex vivo preparations that have the potential to serve as predictors of sensory irritation are also described. In addition, as readily available sensory neuron cell line models are few in number, stem cell lines (with the capacity to differentiate into sensory neurons) are explored. Finally, a preliminary strategy to enable assessment of whether incorporation of a sensory component will enhance the predictive power of current in vitro eye and skin testing strategies is proposed.

Intravesical resiniferatoxin decreases spinal c-fos expression and increases bladder volume to reflex micturition in rats with chronic inflamed urinary bladders

OBJECTIVE

To evaluate the effect of intravesical resiniferatoxin on spinal c-fos expression and bladder volume at reflex micturition in rats with chronic urinary bladder inflammation.

MATERIALS AND METHODS

Of three groups of female Wistar rats, group 1 received cyclophosphamide (75 mg/kg body weight) intraperitoneally every third day (cyclophosphamide is an antitumoral agent that induces bladder inflammation after urinary excretion of its metabolite, acrolein); group 2 comprised sham-inflamed rats that received saline instead of cyclophosphamide, and group 3 received cyclophosphamide, as group 1, every third day but plus 10 nmol/L resiniferatoxin intravesically, through a urethral catheter, at 7 days. At 8 days, under urethane anaesthesia, a needle was inserted in the bladder dome and saline infused at 6 mL/h for 2 h. Finally the animals were perfusion-fixed through the ascending aorta with 4% paraformaldehyde. Transverse sections cut from L6 spinal cord segments were immunoreacted for Fos protein and positive cells in the dorsal horn counted. In a further set of equal groups the bladders were prepared in the same way under urethane anaesthesia and after 30-min of stabilization, saline was infused at 6 mL/h and the volume evoking reflex micturition determined.

RESULTS

The mean (SD) number of positive c-fos cells per spinal cord section was 85 (21), 42 (9) (P = 0.002) and 55 (10) in groups 1 to 3, respectively; the values for group 2 and 3 were similar (P = 0.22) and statistically less than that of group 1 (P = 0.02). Reflex micturition occurred at, respectively, 0.26 (0.09), 0.49 (0.18) and 0.52 (0.11) mL, being similar in group 2 and 3 (P = 0.74) but lower in group 1 (P = 0.003).

CONCLUSION

Intravesical resiniferatoxin decreases c-fos expression and increases bladder capacity in chronically inflamed rat bladders. These findings suggest that desensitizing the vanilloid receptor type 1 by intravesical resiniferatoxin is relevant to the treatment of pain and voiding frequency in patients with chronic inflammatory bladder conditions.

Bladder C-Fiber Desensitization Induces a Long-Lasting Improvement of BPH-Associated Storage LUTS: A Pilot Study

OBJECTIVES

To evaluate the effect of bladder C-fiber desensitization on BPH-associated storage LUTS.

METHODS

Twelve patients with predominant BPH-associated storage LUTS gave written informed consent to enter the study. IPSS and QoL scores, micturition chart, uroflowmetry, cystometry and post-void residual (PVR) were obtained at baseline and at 1, 3 and 6 months after a single intravesical administration of 50 nM resiniferatoxin (RTX) solution.

RESULTS

Mean IPSS score decreased from 20.1 +/- 6.0 to 10.5 +/- 4.4 at 1 month (p = 0.0001), to 10.3 +/- 4.4 at 3 months (p = 0.00001) and to 9.8 +/- 5.7 at 6 months (p < 0.00001). Mean QoL score decreased from 4.5 +/- 1 to 2.5 +/- 1 at 1 month (p = 0.0001), to 2.3 +/- 1 at 3 months (p = 0.0004) and to 2.6 +/- 1.2 at 6 months (p = 0.0003). Mean urinary frequency decreased from 15.2 +/- 8.5 to 10.8 +/- 7.3 at 1 month (p = 0.0002), to 10.2 +/- 4.9 at 3 months (p = 0.002) and to 11.7 +/- 9.2 at 6 months (p = 0.005). Urge incontinence, which was present in six cases, disappeared in 4 patients and decreased to less than half in the other two. Mean first desire to void and maximal cystometric capacity increased significantly after RTX whereas uroflowmetry and PVR were not altered.

CONCLUSIONS

Intravesical desensitization of bladder C fibres with intravesical RTX might be useful in the treatment of patients with predominant BPH associated storage LUTS.

Mechanisms involved in new therapies for overactive bladder

During the last few years, vanilloid substances and botulinum-A toxin were extensively investigated as new therapies for overactive bladder. Intravesical administration of capsaicin or resiniferatoxin--2 members of the vanilloid family--has been shown to increase bladder capacity and decrease urge incontinence in patients with neurogenic, as well as nonneurogenic, forms of detrusor overactivity. In addition, vanilloids have been shown also to reduce bladder pain in patients with hypersensitive disorders. Vanilloids are exogenous ligands of vanilloid receptor type 1 (VR1), an ion channel present in the membrane of type C primary afferent nerve fibers. This receptor, which plays a key role in pain perception and control of the micturition reflex, may be upregulated by nerve growth factor (NGF), a neurotrophic molecule detected in high concentrations in overactive detrusor tissue. Vanilloids, by reducing uptake of NGF through sensory neurons, may counteract VR1 upregulation. Intravesical injections of botulinum-A toxin, a neurotoxin produced by Clostridium botulinum, were shown to increase bladder capacity and to decrease urge incontinence episodes in patients with neurogenic detrusor overactivity. Botulinum-A toxin impedes the release of acetylcholine from cholinergic nerve endings at the neuromuscular junction, leading to paralysis of the detrusor smooth muscle.

Neurogenic inflammation of the bladder

Current evidence suggests multiple and redundant pathways through which the nervous system can initiate, amplify, and perpetuate inflammation. Many of the processes initiated by neurogenic inflammation have the capacity to recruit the participation of additional sensory nerves. These observations indicate that effective strategies for prevention or treatment of neurogenic inflammation of the bladder will entail or require intervention at multiple points. It has been observed that pain management in the future will be based on selective intervention tailored to the specific processes modulating pain perception in individual patients. It is exciting to contemplate the same approach to prevention and treatment of neurogenic bladder inflammation.

The effect of intravesical resiniferatoxin in patients with idiopathic detrusor instability suggests that involuntary detrusor contractions are triggered by C-fiber input

PURPOSE

We evaluated the role of bladder C-fiber input in involuntary detrusor activity in patients with idiopathic detrusor instability.

MATERIALS AND METHODS

Filling cystometry and a voiding chart were done in 13 patients with idiopathic detrusor instability. The first detrusor contraction, maximal cystometric capacity, daily frequency and the number of episodes of urinary incontinence were determined. A 50 nM. solution of resiniferatoxin, a specific C-fiber neurotoxin, was then instilled in the bladder for 30 minutes. Patients were reevaluated 30 and 90 days later.

RESULTS

Resiniferatoxin instillation delayed or suppressed involuntary detrusor contractions during filling cystometry. The mean first detrusor contraction plus or minus standard deviation increased from 170 +/- 109 ml. at baseline to 440 +/- 130 ml. (p = 0.0001) at 30 days and to 391 +/- 165 ml. (p = 0.008) at 90 days. Mean maximal cystometric capacity increased from 291 +/- 160 to 472 +/- 139 ml. (p = 0.01) at 30 days and to 413 +/- 153 ml. (p = 0.1) at 90 days. The mean number of episodes of urinary incontinence daily decreased from 4.3 +/- 2.7 to 0.9 +/- 2.7 (p = 0.001) at 30 days and to 0.7 +/- 0.9 (p = 0.009) at 90 days. Mean frequency daily also decreased from 12 +/- 3.2 to 9.7 +/- 3.2 (p = 0.003) and to 9.9 +/- 3.5 (p = 0.001) times at the same time points, respectively.

CONCLUSIONS

C-fiber input seems to have an important role in the generation of involuntary detrusor contractions and lower urinary tract symptoms in patients with idiopathic detrusor instability. Substances that block C-fiber input may represent a new strategy for treating this bladder dysfunction.

Current management of interstitial cystitis

The management of patients with IC remains a challenge because no single agent has proven universally effective. DMSO and PPS have been evaluated through early placebo-controlled trials, and these two agents are FDA approved treatments for IC. BCG is currently undergoing a large placebo-controlled trial, and hyaluronic acid is receiving similar clinical evaluation. Sacral nerve root stimulation shows promise with early favorable results. As with any treatment algorithm, it is reasonable to begin with conservative treatment using time-dependent milestones, allowing adequate trials of successive therapy while ensuring an appropriate pace for timely symptom resolution.

Vanilloid receptor 1 expression in the rat urinary tract

Previous findings have shown that the capsaicin sensitivity of sensory fibres is due to the expression of a specific membrane protein, the vanilloid receptor type 1 (VR1). In the present work we studied the distribution, morphology and the neurochemical content of nerve fibres expressing this receptor in the rat urinary tract. Immunolabelling was performed against the VR1 and the positive fibres were examined by light and electron microscopy. Colocalisation of VR1 and substance P or calcitonin gene-related peptide immunoreactivities, and isolectin B4 binding, was evaluated under the confocal microscope. In addition, the effect of intravesical administration of resiniferatoxin, an ultra-potent vanilloid receptor agonist, in the receptor expression in the bladder was also studied. Numerous VR1-immunoreactive fibres were found in the mucosa and muscular layer of the entire urinary tract except the kidney. In the bladder, most fibres were also substance P- or calcitonin gene-related peptide-immunoreactive but did not bind isolectin B4. Under the electron microscope VR1 immunoreactivity was confined to unmyelinated axons and varicosities containing small clear and large dense-core synaptic vesicles. They occurred beneath or among epithelial cells or closely apposed to smooth muscle cells. Intravesical resiniferatoxin decreased VR1 immunoreactivity transiently. These data indicate that primary sensory fibres expressing VR1 are extremely abundant in the rat urinary tract and that, in contrast to the skin, they belong almost exclusively to the peptide-containing sub-population of primary afferents. As capsaicin-sensitive bladder afferents are involved in nociception and reflex micturition control, the numerous free terminal nerve endings expressing VR1 in the mucosa seem more adequate to accomplish the former function. However, the close apposition between VR1-expressing fibres and smooth muscle cells suggests that they may also encode the tonus of the muscular layer.

Vanilloid receptor and detrusor instability

Very recently, a membrane receptor (vanilloid receptor type 1 [VR-1]) sensitive to capsaicin or resiniferatoxin (RTX) was identified in small- and medium-sized dorsal root ganglion neurons that give rise to most unmyelinated sensory fibers. After vanilloid binding to VR-1, these neurons remain transiently desensitized; that is, less reactive to natural stimuli. It is this effect of vanilloid substances that is being investigated for its potential therapeutic utility. In the urinary bladder, VR-1-expressing fibers are extremely abundant in the mucosa and in the muscular layer. In the latter, VR-1 fibers are intimately apposed to smooth muscle cells. The demonstration, several years ago, that these fibers were involved in detrusor hyperreflexia of spinal origin and in bladder pain processing, justified the clinical application of intravesical capsaicin or RTX in humans with these bladder diseases. More recently, the experimental and clinical evidence that the same type of bladder sensory fibers were also involved in detrusor instability made a strong case for intravesical RTX assay in patients with idiopathic detrusor instability.

A light- and electron-microscopic histopathological study of human bladder mucosa after intravesical resiniferatoxin application

OBJECTIVE

To determine the morphology of bladder mucosa and the integrity of its mucin coat in patients with detrusor hyper-reflexia treated with intravesical resiniferatoxin.

PATIENTS AND METHODS

Seven patients with detrusor hyper-reflexia were treated intravesically with resiniferatoxin dissolved in 10% ethanol in saline (50 nmol/L solution in two and 100 nmol/L in five). Patients were clinically evaluated by a voiding chart and filling cystometry before and 3 months after each resiniferatoxin application. In addition, they underwent cystoscopy and bladder biopsies at 22-33 months after the first instillation and at 7-23 months after the last one. Tissue samples for light microscopy were fixed in 4% paraformaldehyde, embedded in paraffin and stained with haematoxylin-eosin or periodic acid-Schiff reagent (PAS). Those for electron microscopy were fixed in 5% glutaraldehyde and embedded in resin.

RESULTS

The resiniferatoxin instillation was not painful. Three months after treatment the mean voiding frequency decreased and five incontinent patients became continent. The maximum cystometric capacity increased in all patients; at cystoscopy the bladders appeared normal. On light microscopy the urothelium was of normal morphology and stained with PAS in the luminal cells and in the basement membrane. Mononuclear inflammatory cells were occasionally apparent in the lamina propria. On electron microscopy epithelial cells were visible in a thick basal lamina. Superficial cells had the usual irregular contour and contained numerous membrane-coated vesicles. In the lamina propria, unmyelinated axonal profiles with occasional varicosities could be identified.

CONCLUSIONS

Intravesical resiniferatoxin improved urinary frequency, incontinence and bladder capacity in patients with detrusor hyper-reflexia, causing no morphological change in the bladder mucosa. The PAS reactivity of the carbohydrate moieties present in the mucin coat and the basement membrane was unchanged by resiniferatoxin.

Pharmacology of the lower urinary tract

The functions of the lower urinary tract, to store and periodically release urine, are dependent on the activity of smooth and striated muscles in the urinary bladder, urethra, and external urethral sphincter. This activity is in turn controlled by neural circuits in the brain, spinal cord, and peripheral ganglia. Various neurotransmitters, including acetylcholine, norepinephrine, dopamine, serotonin, excitatory and inhibitory amino acids, adenosine triphosphate, nitric oxide, and neuropeptides, have been implicated in the neural regulation of the lower urinary tract. Injuries or diseases of the nervous system, as well as drugs and disorders of the peripheral organs, can produce voiding dysfunctions such as urinary frequency, urgency, and incontinence or inefficient voiding and urinary retention. This chapter will review recent advances in our understanding of the pathophysiology of voiding disorders and the targets for drug therapy.

Peptide immunoreactivity and ultrastructure of rat urinary bladder nerve fibers after topical desensitization by capsaicin or resiniferatoxin

In the present study the decrease of neuropeptide containing nerve fibers and the increase in the volume threshold to reflex micturition occurring in the rat bladder after intravesical application of capsaicin or resiniferatoxin were compared. The ultrastructure of bladder terminal axons was evaluated at the moment of maximal peptide depletion and compared to that of nerve fibers after systemic capsaicin application. Adult Wistar rats were treated intravesically for 30 min with 0.5 ml of 100 nM RTX, 1 mM capsaicin or 30% ethanol in saline, the vehicle solution. Twenty-four hours and 1, 2, 3, 4 and 8 weeks later the bladders were immunostained for CGRP, SP, VIP and NPY. Cystomanometric studies were performed 24 h and 1, 8, and 12 weeks after vanilloid instillation. Twenty-four hours after systemic capsaicin or intravesical capsaicin or RTX, bladders were prepared for electron microscopic (EM) observation. Intravesical capsaicin or RTX decreased, in a similar way, the number of CGRP and SP-IR (immunoreactive) fibers coursing in the muscular layer and the mucosa. IR fibers amounted to less than 20% of controls at 24 h and returned to normal levels in the eighth week. At the EM level, bladders treated with topical vanilloids did not show morphological changes in terminal axons coursing in the mucosa. In contrast, bladders from animals treated systemically with capsaicin contained numerous grossly degenerated nerve fibers. VIP and NPY-IR fibers were not affected by the treatment. Cystometrograms showed an increase of the volume threshold to reflex micturition that started at 24 h and disappeared at 12 weeks. We conclude that intravesical capsaicin or RTX were equally effective in terms of reducing the number of SP and CGRP-IR fibers and increasing the volume threshold for reflex micturition. Both changes were transient and were not associated with ultrastructural changes of the bladder nerve fibers, excluding terminal axon degeneration as the main mechanism of action of intravesical vanilloids.

Pharmacologic and potential biologic interventions to restore bladder function after spinal cord injury

Spinal cord injury disrupts voluntary control of voiding and the normal reflex pathways that coordinate bladder and urethral sphincter function. The present review addresses studies in animals and humans that have evaluated various therapeutic approaches for normalizing lower urinary tract function after spinal cord injury.

Intravesical resiniferatoxin for the treatment of hypersensitive disorder: a randomized placebo controlled study

PURPOSE

Present therapeutic approaches to control hypersensitive disorder of the lower urinary tract and bladder pain are clinically and scientifically unsatisfactory. We performed a randomized placebo controlled study with followup after 1 and 3 months using intravesical resiniferatoxin to treat hypersensitive disorder and bladder pain.

MATERIALS AND METHODS

We prospectively randomized 18 patients into 2 groups to receive a single dose of 10 nM. resiniferatoxin intravesically (group 1) or a placebo saline solution only (group 2). All patients had at least a 6-month history of frequency, nocturia, urgency and symptoms of pelvic pain as well as no urinary tract infection within the last 3 months, functional disorders of the lower urinary tract, or other vesical or urethral pathology. Pretreatment voiding pattern and pain score were recorded. Patients were evaluated after 30 days (primary end point) and 3 months (secondary end point).

RESULTS

The 2 groups were adequately homogeneous in regard to patient age, sex ratio, disease duration, voiding pattern and pain score. At the primary end point mean frequency plus or minus standard error of mean was decreased from 12. 444 +/- 0.70 voids to 7.111 +/- 0.67 and nocturia from 3.777 +/- 0. 27 to 1.666 +/- 0.16 (p <0.01). We observed a lesser significant improvement in mean frequency in group 1 at the secondary end point to 10.444 +/- 0.94 voids (p <0.05). No significant modification was noted in patients assigned to placebo. Mean pain score significantly decreased in group 1 at the primary end point from 5.555 +/- 0.29 to 2.666 +/- 0.23 (p <0.01) but not at the secondary end point (4.777 +/- 0.66, p >0.05). No statistically significant improvement in mean pain score was observed in placebo group 2. During resiniferatoxin infusion 4 group 1 patients noticed a light warm or burning sensation at the suprapubic and/or urethral level.

CONCLUSIONS

Intravesical resiniferatoxin may significantly improve the voiding pattern and pain score in patients with hypersensitive disorder and bladder pain. Because resiniferatoxin did not cause a significant warm or burning sensation at the suprapubic and/or urethral level, it may be considered a new strategy for treating hypersensitive disorder and bladder pain. However, further studies are necessary to confirm our results and define the resiniferatoxin mechanism of action, dose and necessary treatment schedule.