After a decade of intravesical vanilloid therapy: still more questions than answers

Regulation of Carcinogenesis by Sensory Neurons and Neuromediators

Simple Summary

Sensory nerve fibers extensively innervate the entire body. They are the first to sense danger signals, including the ones coming from newly formed cancer cells. Various studies have demonstrated that the inactivation of sensory nerve fibers as well as the vagus nerve enhances tumor growth and spread in models including breast, pancreatic, and gastric cancer. On the other hand, there are also contradictory findings that show the opposite, namely that the inactivation of nerve fibers inhibits tumor growth. These discrepancies are likely caused by the stage and the level of aggressiveness of the tumor model used. Hence, further studies are required to determine the factors involved in neuro-immunological mechanisms of tumor growth and spread.

Abstract

Interactions between the immune system and the nervous system are crucial in maintaining homeostasis, and disturbances of these neuro-immune interactions may participate in carcinogenesis and metastasis. Nerve endings have been identified within solid tumors in humans and experimental animals. Although the involvement of the efferent sympathetic and parasympathetic innervation in carcinogenesis has been extensively investigated, the role of the afferent sensory neurons and the neuropeptides in tumor development, growth, and progression is recently appreciated. Similarly, current findings point to the significant role of Schwann cells as part of neuro-immune interactions. Hence, in this review, we mainly focus on local and systemic effects of sensory nerve activity as well as Schwann cells in carcinogenesis and metastasis. Specific denervation of vagal sensory nerve fibers, or vagotomy, in animal models, has been reported to markedly increase lung metastases of breast carcinoma as well as pancreatic and gastric tumor growth, with the formation of liver metastases demonstrating the protective role of vagal sensory fibers against cancer. Clinical studies have revealed that patients with gastric ulcers who have undergone a vagotomy have a greater risk of stomach, colorectal, biliary tract, and lung cancers. Protective effects of vagal activity have also been documented by epidemiological studies demonstrating that high vagal activity predicts longer survival rates in patients with colon, non-small cell lung, prostate, and breast cancers. However, several studies have reported that inhibition of sensory neuronal activity reduces the development of solid tumors, including prostate, gastric, pancreatic, head and neck, cervical, ovarian, and skin cancers. These contradictory findings are likely to be due to the post-nerve injury-induced activation of systemic sensory fibers, the level of aggressiveness of the tumor model used, and the local heterogeneity of sensory fibers. As the aggressiveness of the tumor model and the level of the inflammatory response increase, the protective role of sensory nerve fibers is apparent and might be mostly due to systemic alterations in the neuro-immune response. Hence, more insights into inductive and permissive mechanisms, such as systemic, cellular neuro-immunological mechanisms of carcinogenesis and metastasis formation, are needed to understand the role of sensory neurons in tumor growth and spread.

Botulinum toxin in the treatment of overactive bladder

Clinical effectiveness of botulinum toxin (BTX) in the treatment of both neurogenic and idiopathic detrusor overactivity has been demonstrated in several studies. However, different protocols and techniques have been used by authors.

Methods.

Literature review on intradetrusor injection of BTX for detrusor overactivity.

Results.

The greatest clinical experience reports the use of 200 and 300 U Botox®. Available data suggest that clinical efficacy, duration, and the side effect profile is similar at these doses. Very few data, on the other hand, are available regarding the clinical outcomes using the Dysport® preparation; isolated reports support that efficacy is similar when using a dosing range of 500 to 1000 SU with increased risk of systemic side effects using 1000 SU. A variety of injection volumes was used, demonstrating similar efficacy and tolerability profile. Clinical effect duration extends six to ten months in the majority of studies. Data suggest that a repeated injection scheme proves successful in the vast majority of initial responders.

Conclusions.

Safety, effectiveness, specificity and reversibility make BTX a new attractive treatment modality for overactive bladder syndrome. However, more experience is needed to standardize the injection protocol with respect to therapeutic outcomes and adverse effects.

Inhibition of micturition reflex by activation of somatic afferents in posterior femoral cutaneous nerve

This study determined if activation of somatic afferents in posterior femoral cutaneous nerve (PFCN) could modulate the micturition reflex recorded under isovolumetric conditions in α-chloralose anaesthetized cats. PFCN stimulation inhibited reflex bladder activity and significantly (P <0.05) increased bladder capacity during slow infusion of saline or 0.25% acetic acid (AA). The optimal frequency for PFCN stimulation-induced bladder inhibition was between 3 and 10 Hz, and a minimal stimulation intensity of half of the threshold for inducing anal twitching was required. Bilateral pudendal nerve transection eliminated PFCN stimulation-induced anal twitching but did not change the stimulation-induced bladder inhibition, excluding the involvement of pudendal afferent or efferent axons in PFCN afferent inhibition.Mechanical or electrical stimulation on the skin surface in the PFCN dermatome also inhibited bladder activity. Prolonged (2 × 30 min) PFCN stimulation induced a post-stimulation inhibition that persists for at least 2 h. This study revealed a new cutaneous-bladder reflex activated by PFCN afferents. Although the mechanisms and physiological functions of this cutaneous-bladder reflex need to be further studied, our data raise the possibility that stimulation of PFCN afferents might be useful clinically for the treatment of overactive bladder symptoms.

New insights into the pharmacology of the bladder

PURPOSE OF REVIEW

Pharmacotherapy of a number of bladder disorders has traditionally focused on targeting the 'sensory' component or bladder nerves and the smooth muscle. This review aims to provide an insight into recent (experimental and clinical) developments in mechanisms of existing therapies as well as novel targets.

RECENT FINDINGS

Traditionally, sensory signaling in the urinary bladder has been attributed to activation of bladder afferents, but new findings have pointed to the urothelium and interstitial cells as key participants in the transduction of sensory events. Recent advances provide strong support for the development of subtype selective receptor agonists/antagonists, the modulation of signal transduction cascades and new and expanded uses for various neurotoxins.

SUMMARY

The development of therapeutic options for the treatment of a number of bladder disorders is complicated, and most treatments are associated with an increased incidence of side effects or lack of specificity. Recent studies suggest that selective targeting of receptors/ion channels or a disease-specific (i.e. phosphorylated) form of the receptor may represent a viable therapeutic target. Though the mechanisms regulating ion channel expression under pathological conditions are not fully known, an increased understanding of these pathways has important implications for drug development.

Modulation of bladder myofibroblast activity: implications for bladder function

Bladder suburothelial myofibroblasts may modulate both sensory responses from the bladder wall and spontaneous activity. This study aimed to characterize further these cells in their response to exogenous agents implicated in mediating the above activity. Detrusor strips, with or without mucosa, and isolated suburothelial myofibroblasts were prepared from guinea pig bladders. Isometric tension, intracellular Ca²⁺, and membrane current were recorded. Cell pairs were formed by pushing two cells together. Tension, intracellular Ca²⁺, and membrane potential were also recorded from bladder sheets using normal or spinal cord-transected (SCT) rats. Spontaneous contractions were greater in detrusor strips with an intact mucosa and were augmented by 10 μM UTP. ATP, UTP, or reduced extracellular pH elicited Ca²⁺ transients and inward currents (E_rev −30 mV) in isolated cells. Capsaicin (5–30 μM) reduced membrane current (37 ± 12% of control) with minor effects on Ca²⁺ transients: sodium nitroprusside reduced membrane currents (40 ± 21% of control). Cell pair formation, without an increase in cell capacitance, augmented ATP and pH responses (180 ± 58% of control) and reduced the threshold to ATP and acidosis. Glivec (20–50 μM) reversibly blocked the augmentation and also reduced spontaneous activity in bladder sheets from SCT, but not normal, rats. Glivec also disrupted the spread of Ca²⁺ waves in SCT sheets, generating patterns similar to normal bladders. Suburothelial myofibroblasts respond to exogenous agents implicated in modulating bladder sensory responses; responses augmented by physical intercellular contact. The action of glivec and its selective suppression of spontaneous activity in SCT rats identifies a possible pathway to attenuate bladder overactivity.

Analgesic compound from sea anemone Heteractis crispa is the first polypeptide inhibitor of vanilloid receptor 1 (TRPV1)

Venomous animals from distinct phyla such as spiders, scorpions, snakes, cone snails, or sea anemones produce small toxic proteins interacting with a variety of cell targets. Their bites often cause pain. One of the ways of pain generation is the activation of TRPV1 channels. Screening of 30 different venoms from spiders and sea anemones for modulation of TRPV1 activity revealed inhibitors in tropical sea anemone Heteractis crispa venom. Several separation steps resulted in isolation of an inhibiting compound. This is a 56-residue-long polypeptide named APHC1 that has a Bos taurus trypsin inhibitor (BPTI)/Kunitz-type fold, mostly represented by serine protease inhibitors and ion channel blockers. APHC1 acted as a partial antagonist of capsaicin-induced currents (32 +/- 9% inhibition) with half-maximal effective concentration (EC(50)) 54 +/- 4 nm. In vivo, a 0.1 mg/kg dose of APHC1 significantly prolonged tail-flick latency and reduced capsaicin-induced acute pain. Therefore, our results can make an important contribution to the research into molecular mechanisms of TRPV1 modulation and help to solve the problem of overactivity of this receptor during a number of pathological processes in the organism.

On the origin of bladder sensing: Tr(i)ps in urology

The mammalian TRP family consists of 28 channels that can be subdivided into 6 different classes: TRPV (vanilloid), TRPC (canonical), TRPM (Melastatin), TRPP (Polycystin), TRPML (Mucolipin), and TRPA (Ankyrin). TRP channels are activated by a diversity of physical (voltage, heat, cold, mechanical stress) or chemical (pH, osmolality) stimuli and by binding of specific ligands, enabling them to act as multifunctional sensors at the cellular level. Currently, a lot of scientific research is devoted to these channels and their role in sensing mechanisms throughout the body. In urology, there's a growing conviction that disturbances in afferent (sensory) mechanisms are highly important in the pathogenesis of functional problems. Therefore, the TRP family forms an interesting new target to focus on. In this review we attempt to summarize the existing knowledge about TRP channels in the urogenital tract. So far, TRPV1, TRPV2, TRPV4, TRPM8, and TRPA1 have been described in different parts of the urogenital tract. Although only TRPV1 (the vanilloid receptor) has been extensively studied so far, more evidence is slowly accumulating about the role of other TRP channels in the (patho)physiology of the urogenital tract.

TRPV1 is involved in stretch-evoked contractile changes in the rat autonomous bladder model: a study with piperine, a new TRPV1 agonist

AIM

Vanilloids like capsaicin and resiniferatoxin (RTX) have been used for more than a decade in the treatment of neurogenic detrusor overactivity. Recently, the vanilloid molecule piperine (PIP) has been shown to have similar pharmacological properties as these drugs. In this study, we looked at PIP-effects on autonomous bladder contractile activity, with particular interest for its selectivity for the transient receptor potential channel 1 (TRPV1) receptor. Additionally, we studied the role of TRPV1 in volume-induced contractile changes using selective and non-selective TRPV1 antagonists.

METHODS

The acute and prolonged effects of PIP were studied on rat bladders. Each bladder was excised and placed in a heated organ bath, where intravesical pressures were measured. In acute experiments, PIP was added directly to the bathing solution. For prolonged effects, animals were pre-treated intravesically with vehicle (ethanol 5%) or PIP (10(-4) M) and sacrificed 72 hr later. The effects of selective (capsazepine (CZP)) and non-selective (ruthenium red (RR)) TRPV1 antagonists on volume-evoked contractile parameters were also studied.

RESULTS

Acute administration of PIP 10(-4) M significantly increased amplitude of bladder contractions (P < 0.05). These effects were significantly antagonized (P < 0.05) by the TRPV1-selective antagonist CZP (10(-5) M) and the non-selective TRP-antagonist RR (10(-5) M). Intravesical pre-treatment with PIP induced shorter contractions with more periods of non-activity (P < 0.05) compared to controls. Inhibition of TRPV1 with CZP and RR significantly reduced the volume-evoked rise in contractile amplitude in isolated bladders (P < 0.05).

CONCLUSION

We found evidence for acute and prolonged effects of PIP on bladder contractility, which seem to be mediated through TRPV1. Furthermore, we found evidence for involvement of TRPV1 in afferent signaling of mechanical stimuli.

The molecular basis of urgency: regional difference of vanilloid receptor expression in the human urinary bladder

AIM

Treatments targeting vanilloid receptor TRPV1 are effective in some bladder disorders. Our aim was to determine the expression profiles of TRPV1 in regions of human bladder and test the hypothesis that there would be an upregulation of TRPV1 in mucosa of patients with bladder hypersensitivity but not idiopathic detrusor overactivity (IDO).

MATERIALS AND METHODS

Women with sensory urgency (SU), interstitial cystitis (IC), and IDO were investigated by videourodynamics and cystoscopy. Control biopsies were used for comparison. Biopsies were dissected into mucosa and muscle, and evaluated for TRPV1 mRNA expression using quantitative competitive RT-PCR (QC-RT-PCR).

RESULTS

TRPV1 mRNA from SU trigonal mucosa was significantly higher than control trigonal mucosa or SU bladder body mucosa. In contrast, in IDO patients, there was no difference between trigonal mucosa and body mucosa. In IC biopsies, RNA quality was substandard and unable to be used for analysis. The most striking finding was that TRPV1 mRNA expressed in SU trigonal mucosa was significantly inversely correlated with the bladder volume at first sensation of filling during cystometry. No such relationship was seen for IDO trigonal mucosa. No difference was seen in bladder body mucosa from any disease groups compared with age-matched control.

CONCLUSIONS

The symptoms of SU were associated with the increased expression of TRPV1 mRNA in the trigonal mucosa. No upregulation or regional differences of TRPV1 mRNA were seen in IDO patients. TRPV1 may play a role in SU and premature first bladder sensation on filling.

Botulinum toxin injection: a review of injection principles and protocols

Despite the favorable outcomes seen using botulinum toxin (BTX) for voiding dysfunction using BTX, a standardized technique and protocol for toxin injection is not defined. We reviewed the current literature on intravesical BTX injection for DO (detrusor overactivity). Specific attention was placed on defining optimal injection protocol, including dose, volume, and injection sites. In addition, we sought to describe a standard technique to BTX injection.

Autonomous contractile activity in the isolated rat bladder is modulated by a TRPV1 dependent mechanism

AIMS

Resiniferatoxin (RTX), a vanilloid compound and agonist of the transient receptor potential channel 1 (TRPV1), is known for its beneficial effects on neurogenic detrusor overactivity. The mainstream rationale for its use is the desensitization of TRPV1 on sensory bladder afferents. However, recent findings showed that TRPV1 is present in other cell types in the bladder. To eliminate the effects of RTX on spinal and central neural circuits, we investigated autonomous contractility in normal and neurogenic rat bladders after treatment with RTX.

METHODS

Female Wistar rats were made paraplegic at vertebral level T8-T9. Animals were intravesically pre-treated with vehicle (ethanol 5%) or RTX (100 nM) and sacrificed after 72 hr. Each bladder was excised and placed in a heated organ bath, where intravesical pressures were measured. Effects on contractile parameters of intravesical volume load, the non-selective muscarinic receptor agonist carbachol (CA) and electrical stimulation (ES) of nerves were studied in both groups.

RESULTS

In RTX-treated normal bladders we found shorter contractions with higher amplitude than in control bladders (P < 0.05). In RTX-treated neurogenic bladders the amplitude and duration of autonomous contractions were increased compared with controls (P < 0.05). Furthermore RTX induced an increased response to CA and to ES (P < 0.05).

CONCLUSIONS

RTX significantly affected the properties of autonomous bladder contractile activity. This provides evidence for local effects of RTX on bladder contractile activity, which are not mediated by afferent neural pathways and which may contribute to the beneficial effects on detrusor overactivity. TRPV1 and TRPV1(+) cells seem to play an important role in (autonomous) bladder contractility.

Neuromodulatory therapies in female pelvic medicine and reconstructive surgery: biological agents

In recent years, important improvements in the management of patients with neurogenic or non-neurogenic detrusor overactivity and urge incontinence have been brought about by the introduction of vanilloids and botulinum toxins in urology. In this review we introduce the new therapeutic options, provides basic information, and summarize the results experienced so far.

Botulinum toxin type a inhibits calcitonin gene-related peptide release from isolated rat bladder

PURPOSE

Increasing evidence suggests that sensory nerve dysfunction may underlie several urological disorders, including interstitial cystitis and sensory urgency. We determined the effect of botulinum toxin type A (Allergan, Irvine, California) on baseline and chemically evoked release of the sensory neuropeptide, calcitonin gene-related peptide in an isolated bladder preparation.

MATERIALS AND METHODS

Whole rat bladders were incubated in a series of tissue baths containing physiological salt solution. Following bladder equilibration in PSS sequential incubation was performed and this sample was used to measure baseline CGRP release. To evoke CGRP release tissue was subsequently incubated in PSS containing capsaicin (30 nM) and adenosine triphosphate (10 microM). To measure the effect of BTX-A on baseline and evoked CGRP release bladders were incubated for 6 hours in an organ bath containing BTX-A (50 microM) or vehicle prior to bladder equilibration. CGRP release was determined by radioimmunoassay.

RESULTS

Mean baseline release of CGRP +/- SEM was 346 +/- 44 pg/gm. Adenosine triphosphate/capsaicin application increased CGRP release by 75% over baseline (606 +/- 98 pg/gm, p < 0.005). BTX-A application resulted in a 19% decrease in baseline release of CGRP, although this difference did not achieve statistical significance. BTX-A application significantly decreased evoked CGRP by 62% vs control (606 +/- 98 vs 229 +/- 21 pg/gm, p < 0.005).

CONCLUSIONS

BTX-A application inhibits the evoked release of CGRP from afferent nerve terminals in isolated rat bladder. This finding suggests a potential clinical benefit of BTX-A for the treatment of interstitial cystitis or sensory urgency.

Mechanisms underlying the recovery of lower urinary tract function following spinal cord injury

The lower urinary tract has two main functions, the storage and periodic expulsion of urine, which are regulated by a complex neural control system in the brain and lumbosacral spinal cord. This neural system coordinates the activity of two functional units in the lower urinary tract: (1) a reservoir (the urinary bladder) and (2) an outlet (consisting of bladder neck, urethra and striated muscles of the pelvic floor). During urine storage the outlet is closed and the bladder is quiescent, thereby maintaining a low intravesical pressure over a wide range of bladder volumes. During micturition the outlet relaxes and the bladder contracts to promote the release of urine. This reciprocal relationship between bladder and outlet is generated by visceral reflex circuits, some of which are under voluntary control. Experimental studies in animals indicate that the micturition reflex is mediated by a spinobulbospinal pathway passing through a coordination center (the pontine micturition center) located in the rostral brainstem. This reflex pathway is in turn modulated by higher centers in the cerebral cortex that are presumably involved in the voluntary control of micturition. Spinal cord injury at cervical or thoracic levels disrupts voluntary control of voiding as well as the normal reflex pathways that coordinate bladder and sphincter functions. Following spinal cord injury, the bladder is initially areflexic but then becomes hyperreflexic due to the emergence of a spinal micturition reflex pathway. Studies in animals indicate that the recovery of bladder function after spinal cord injury is dependent in part on plasticity of bladder afferent pathways and the unmasking of reflexes triggered by capsaicin-sensitive C-fiber bladder afferent neurons. The plasticity is associated with changes in the properties of ion channels and electrical excitability of afferent neurons, and appears to be mediated in part by neurotrophic factors released in the spinal cord and the peripheral target organs.

Integrative control of the lower urinary tract: preclinical perspective

Storage and periodic expulsion of urine is regulated by a neural control system in the brain and spinal cord that coordinates the reciprocal activity of two functional units in the lower urinary tract (LUT): (a) a reservoir (the urinary bladder) and (b) an outlet (bladder neck, urethra and striated muscles of the urethral sphincter). Control of the bladder and urethral outlet is dependent on three sets of peripheral nerves: parasympathetic, sympathetic and somatic nerves that contain afferent as well as efferent pathways. Afferent neurons innervating the bladder have A-delta or C-fibre axons. Urine storage reflexes are organized in the spinal cord, whereas voiding reflexes are mediated by a spinobulbospinal pathway passing through a coordination centre (the pontine micturition centre) located in the brainstem. Storage and voiding reflexes are activated by mechanosensitive A-delta afferents that respond to bladder distension. Many neurotransmitters including acetylcholine, norepinephrine, dopamine, serotonin, excitatory and inhibitory amino acids, adenosine triphosphate, nitric oxide and neuropeptides are involved in the neural control of the LUT. Injuries or diseases of the nervous system as well as disorders of the peripheral organs can produce LUT dysfunctions including: (1) urinary frequency, urgency and incontinence or (2) inefficient voiding and urinary retention. Neurogenic detrusor overactivity is triggered by C-fibre bladder afferent axons, many of which terminate in the close proximity to the urothelium. The urothelial cells exhibit 'neuron-like' properties that allow them to respond to mechanical and chemical stimuli and to release transmitters that can modulate the activity of afferent nerves.

Sacral neuromodulation in lower urinary tract dysfunction

Vesico-urethral dysfunction is a major problem in daily medical practice due to its psychological disturbances, its social costs and its high impact on quality of life. Recently, sacral neuromodulation, namely the electrical stimulation of the sacral nerves, appears to have become an alternative for radical bladder surgery particularly in cases of idiopathic bladder overactivity. The mechanism of action is only partially understood but it seems to involve a modulation in the spinal cord due to stimulation of inhibitory interneurons. Temporary sacral nerve stimulation is the first step. It comprises the temporary application of neuromodulation as a diagnostic test to determine the best location for the implant and to control the integrity of the sacral root. If test stimulation is successful, a permanent device is implanted. This procedure is safe in experienced hands. So-called idiopathic bladder overactivity still the major indication for this technique. Patients not likely to benefit from the procedure were those with complete or almost complete spinal lesions, but incomplete spinal lesions seemed to be a potential indication. This technique is now also indicated in the case of idiopathic chronic retention and chronic pelvic pain syndrome. When selection is performed, more than three-quarters of the patients showed a clinically significant response with 50% or more reduction in the frequency of incontinent episodes, but the results vary according to the author's mode of evaluation. From the economic point of view, the initial investment in the device is amortized in the mid-term by savings related to lower urinary tract dysfunction. Finally, this technique requires an attentive follow-up and adjustments to the electric parameters so as to optimize the equilibrium between the neurological systems.

Role of the urothelium in urinary bladder dysfunction following spinal cord injury

A consequence of spinal cord injury is a change in bladder reflex pathways resulting in the emergence of detrusor hyperreflexia and increased activity of the urethral sphincter. A basis for some of these alterations could be changes in the environment of bladder sensory nerve endings at the target organ. Recent evidence suggests that the urothelium (the lining of the urinary bladder) plays a prominent role in modulating bladder sensory nerve ending excitability. It is conceivable that factors and processes affecting the plasticity of bladder neurons after spinal cord injury may be partly due to changes occurring in the urothelium. Although the urothelium has classically been thought of as a passive barrier to ions/solutes, a number of novel properties have been recently attributed to these cells. Our work and that of others clearly demonstrates that the urothelium exhibits both "sensor" (expression of sensor molecules or response to thermal, mechanical and chemical stimuli) as well as "transducer" (release of factors/transmitters) properties. Taken together, these and other findings discussed in this chapter suggest a sensory function for the urothelium and that alterations in urothelial properties may contribute to afferent abnormalities following spinal cord injury.

Capsaicin‐sensitive sensory neurons regulate myocardial function and gene expression pattern of rat hearts: a DNA microarray study

We have previously shown that capsaicin-sensitive sensory nerves contribute to the regulation of normal cardiac function and to the development of cardiac adaptation to ischemic stress; however, the underlying molecular mechanisms remain unknown. Therefore, here we assessed cardiac functional alterations and relative gene expression changes by DNA microarray analysis of 6400 genes in rat hearts 7 days after the end of systemic capsaicin treatment protocol leading to selective sensory chemodenervation. Capsaicin pretreatment resulted in a cardiac dysfunction characterized by elevation of left ventricular end-diastolic pressure and led to altered expression of 80 genes of known function or homology to known sequences. Forty-seven genes exhibited significant up-regulation and 33 genes were down-regulated (changes ranged from -3.9 to +4.8-fold). The expression changes of 10 selected genes were verified, and an additional 11 genes were examined by real-time quantitative PCR. This is the first demonstration that gene expression changes in the heart due to capsaicin pretreatment included vanilloid receptor-1 (capsaicin receptor), transient receptor potential protein, GABA receptor rho-3 subunit, 5-hydroxytryptamine 3 receptor B, neurokinin receptor 2, endothelial nitric oxide synthase, matrix metalloproteinase-13, cytochrome P450, farnesyl-transferase, ApoB, and leptin. None of the genes have been previously shown to be involved in the mechanism of the cardiac functional effects of sensory chemodenervation by capsaicin. We conclude that capsaicin-sensitive sensory nerves play a significant role in the regulation of a variety of neuronal and non-neuronal genes in the heart and possibly in other tissues as well.

More than just a barrier: urothelium as a drug target for urinary bladder pain

Although the urinary bladder urothelium has classically been thought of as a passive barrier to ions/solutes, a number of novel properties have been recently attributed to these cells. Studies have revealed that the urothelium is involved in sensory mechanisms (i.e., ability to express a number of sensor molecules or respond to thermal, mechanical, and chemical stimuli) and can release chemical mediators. Localization of afferent nerves next to the urothelium suggests these cells may be targets for transmitters released from bladder nerves or that chemicals released by urothelial cells may alter afferent excitability. Taken together, these and other findings highlighted in this review suggest a sensory function for the urothelium. Elucidation of mechanisms impacting on urothelial function may provide insights into the pathology of bladder dysfunction.

An open-label pilot study of cannabis-based extracts for bladder dysfunction in advanced multiple sclerosis

The majority of patients with multiple sclerosis (MS) develop troublesome lower urinary tract symptoms (LUTS). Anecdotal reports suggest that cannabis may alleviate LUTS, and cannabinoid receptors in the bladder and nervous system are potential pharmacological targets. In an open trial we evaluated the safety, tolerability, dose range, and efficacy of two whole-plant extracts of Cannabis sativa in patients with advanced MS and refractory LUTS. Patients took extracts containing delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD; 2.5 mg of each per spray) for eight weeks followed by THC-only (2.5 mg THC per spray) for a further eight weeks, and then into a long-term extension. Assessments included urinary frequency and volume charts, incontinence pad weights, cystometry and visual analogue scales for secondary troublesome symptoms. Twenty-one patients were recruited and data from 15 were evaluated. Urinary urgency, the number and volume of incontinence episodes, frequency and nocturia all decreased significantly following treatment (P <0.05, Wilcoxon's signed rank test). However, daily total voided, catheterized and urinary incontinence pad weights also decreased significantly on both extracts. Patient self-assessment of pain, spasticity and quality of sleep improved significantly (P <0.05, Wilcoxon's signed rank test) with pain improvement continuing up to median of 35 weeks. There were few troublesome side effects, suggesting that cannabis-based medicinal extracts are a safe and effective treatment for urinary and other problems in patients with advanced MS.

Reduced heat sensitivity and epidermal nerve fiber immunostaining following single applications of a high-concentration capsaicin patch

Capsaicin-containing plant extracts have been used as topical treatments for a variety of pain syndromes for many centuries. Current products containing capsaicin in low concentrations (usually 0.025-0.075% w/w) have shown efficacy against a variety of pain conditions in clinical studies. However, in order to produce significant analgesic effects, these formulations require frequent re-dosing, often as much as three to five times daily for several weeks. Previous functional and immunohistochemical studies following prolonged exposures to low-concentration capsaicin cream suggested that the duration and onset of analgesic efficacy correlate with a reduction of cutaneous nociceptive sensory nerve fiber responsiveness and immunostaining. The purpose of the present study was to determine whether a single topical application of a high-concentration capsaicin-containing (8%w/w) patch for 120 min or less would induce similar effects on cutaneous nociceptive nerve fibers. Seven days following patch application, changes in heat and cold perception thresholds were determined by quantitative sensory testing and punch biopsies were collected to assess epidermal nerve fiber (ENF) immunostaining density at the application site using PGP 9.5 as a marker. The results show a significant reduction of heat, but not cold, sensitivity and reduction of ENF immunostaining with high-capsaicin concentration patch applications for 60 or 120 min, compared to placebo patch applications. Application sites exposed to low-capsaicin concentration (0.04%w/w) patches for 120 min or high-concentration patches for 30 min were not significantly different from placebo with respect to either thermal threshold detection or ENF immunostaining. The ability of a single 60 min high-concentration patch application to mimic effects produced by prolonged exposure to low-concentration capsaicin creams suggests a new approach to the management of chronic pain syndromes.

Development of the first ultra-potent "capsaicinoid" agonist at transient receptor potential vanilloid type 1 (TRPV1) channels and its therapeutic potential

Olvanil (N-9-Z-octadecenoyl-vanillamide) is an agonist of transient receptor potential vanilloid type 1 (TRPV1) channels that lack the pungency of capsaicin and was developed as an oral analgesic. Vanillamides are unmatched in terms of structural simplicity, straightforward synthesis, and safety compared with the more powerful TRPV1 agonists, like the structurally complex phorboid compound resiniferatoxin. We have modified the fatty acyl chain of olvanil to obtain ultra-potent analogs. The insertion of a hydroxyl group at C-12 yielded a compound named rinvanil, after ricinoleic acid, significantly less potent than olvanil (EC(50) = 6 versus 0.7 nM), but more versatile in terms of structural modifications because of the presence of an additional functional group. Acetylation and phenylacetylation of rinvanil re-established and dramatically enhanced, respectively, its potency at hTRPV1. With a two-digit picomolar EC(50) (90 pM), phenylacetylrinvanil (PhAR, IDN5890) is the most potent vanillamide ever described with potency comparable with that of resiniferatoxin (EC(50), 11 pM). Benzoyl- and phenylpropionylrinvanil were as potent and less potent than PhAR, respectively, whereas configurational inversion to ent-PhAR and cyclopropanation (but not hydrogenation or epoxidation) of the double bond were tolerated. Finally, iodination of the aromatic hydroxyl caused a dramatic switch in functional activity, generating compounds that behaved as TRPV1 antagonists rather than agonists. Since the potency of PhAR was maintained in rat dorsal root ganglion neurons and, particularly, in the rat urinary bladder, this compound was investigated in an in vivo rat model of urinary incontinence and proved as effective as resiniferatoxin at reducing bladder detrusor overactivity.

Cool (TRPM8) and hot (TRPV1) receptors in the bladder and male genital tract

PURPOSE

Overactive bladder symptoms due to various etiologies have been successfully treated with capsaicin by desensitization of the temperature sensitive vanilloid receptor TRPV1. Recently another temperature sensitive receptor, TRPM8, activated by menthol and cool temperatures (8C to 28C) was described that may be the proposed cool receptor, at least in part mediating the bladder response in the diagnostic ice water test. We defined the sites of mRNA and protein expression of TRPM8 and TRPV1 in the rat and human genitourinary tract.

MATERIALS AND METHODS

Prostate, testis, penis, bladder and dorsal root ganglion tissue was obtained from rats. Prostate, testicle, seminiferous tubules, corpus cavernosum, glans, overlying glans skin, scrotal skin and bladder were obtained from human patients. Reverse transcription-polymerase chain reaction was done using species specific primers for TRPM8 and TRPV1. Immunofluorescence staining for TRPM8 was performed in rat tissues as well as in cultured human urothelial cells.

RESULTS

TRPM8 and TRPV1 mRNA were detected in all rat tissues. Human samples demonstrated TRPM8 mRNA in prostate, testicle, seminiferous tubules, scrotal skin and bladder. No TRPM8 mRNA was identified in human corpus cavernosum, glans or overlying glans skin. Separation of layers in human bladder demonstrated mRNA for TRPM8 only in the urothelium and not in the detrusor. Immunofluorescence location of TRPM8 was found in rat prostate, DRG and bladder, and in human urothelial cells in culture. TRPV1 mRNA was detected in all human genitourinary tract tissues.

CONCLUSIONS

These results demonstrate that mRNA and protein for TRPM8 exist in multiple genitourinary organs in the rat and human, and it may be considered a possible new target, as is TRPV1, for the pharmacological treatment of detrusor overactivity or other urological disorders.

Intravesical resiniferatoxin versus botulinum-A toxin injections for neurogenic detrusor overactivity: a prospective randomized study

PURPOSE

We investigated the effectiveness and safety of intravesical resiniferatoxin (Sigma Chemical Co., St. Louis, Missouri) and botulinum-A toxin injections into the detrusor muscle in a group of spinal cord injured patients with neurogenic detrusor overactivity unresponsive to conventional anticholinergic therapy.

MATERIALS AND METHODS

A total of 25 patients were randomly assigned to receive intravesically 0.6 microM resiniferatoxin in 50 ml of 0.9% NaCl or injections into the detrusor muscle of 300 units botulinum A-toxin diluted in 30 ml 0.9% NaCl. Clinical evaluation and urodynamics were performed at baseline, and at 6, 12 and 18 months after treatment.

RESULTS

In both arms there was a significant decrease in catheterization and incontinent episodes, and a significant increase in first detrusor contraction and maximum bladder capacity at 6, 12 and 18-month followup. There were no local side effects with either treatment. Botulinum-A toxin induced a significant decrease in the frequency of daily incontinence episodes (p <0.05), a significant increase in first uninhibited detrusor contraction (p <0.01) in maximum bladder capacity (p <0.01), and a significant decrease in maximum pressure of uninhibited detrusor contractions (p <0.01) compared to resiniferatoxin at 6, 12 and 18-month followup.

CONCLUSIONS

In spinal cord injured patients with refractory neurogenic detrusor overactivity, intravesical resiniferatoxin and botulinum-A toxin injections into the detrusor muscle provided beneficial clinical and urodynamic results with decreases in detrusor overactivity and restoration of urinary continence in a large proportion of patients. Botulinum-A toxin injections provided superior clinical and urodynamic benefits compared to those of intravesical resiniferatoxin.

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.

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.

The perspective of a neurologist on treatment-related research in fecal and urinary incontinence

Afferent innervation is important in sensing the degree of bladder fullness and in forming the input limb to involuntary detrusor contractions in neurogenic and probably also non-neurogenic detrusor overactivity. It is likely that homologous mechanisms are involved in control of the bowel. Accumulating evidence now suggests that in conditions of bladder hypersensitivity as well as non-neurogenic detrusor overactivity, there is up-regulation of unmyelinated nerve fibers expressing both the vanilloid receptor and purinergic receptors. The development of a selective neurotoxin that could successfully "deafferent" the bladder would have major therapeutic consequences. Women who respond best to neuromodulation through sacral nerve stimulation are those with a primary disorder of sphincter relaxation and a very large capacity without sensations of urgency or a hyperactive sphincter. For these women, neuromodulation may counteract the inhibitory effects of overactive sphincter afferents on the detrusor, and determination of the central nervous system level at which this response occurs may provide an explanation for the paradoxical finding that both urge incontinence and urinary retention are responsive to this intervention. Experimental evidence suggests that the "procontinence" reaction consists of an inhibitory effect on the detrusor and presumably the lower rectum resulting from contraction of the pelvic floor and the anal or urethral sphincter. Development of methods of enhancing the inhibitory reflex effect could lead to improved voluntary control of micturition and defecation for patients with neurogenic bladder overactivity or spinal cord lesions.