Endocannabinoids in Bladder Sensory Mechanisms in Health and Diseases

Novel pharmacotherapeutic avenues for bladder storage dysfunction in men

INTRODUCTION

Bladder storage dysfunction is associated with low quality of life in men and remains a challenging field in pharmacotherapy because of low persistence followed by patient-perceived lack of efficacy and adverse effects. The persistent desire for the development of novel pharmacotherapy is evident, leading to numerous research efforts based on its pathophysiology.

AREAS COVERED

This review describes the pathophysiology, current pharmacotherapeutic strategies, and emerging novel drugs for male bladder storage dysfunction. The section on emerging pharmacotherapy provides an overview of current research, focusing on high-potential target molecules, particularly those being evaluated in ongoing clinical trials.

EXPERT OPINION

As pharmacotherapies targeting alpha-adrenergic, beta-adrenergic, and muscarinic receptors - the current primary targets for treating male bladder storage dysfunction - have demonstrated insufficient efficacy and side effects, researchers are exploring various alternative molecular targets. Numerous targets have been identified as central to regulating bladder afferent nerve activity, and their pharmacological effects and potential have been evaluated in animal-based experiments. However, there is a limited number of clinical trials for these new pharmacotherapies, and they have not demonstrated clear superiority over current treatments. Further research is needed to develop new effective pharmacotherapies for bladder storage dysfunction in men.

Aging and urinary control: Alterations in the brain-bladder axis

Age-associated alterations in bladder control affect millions of older adults, with a heavy burden added to families both economically and in quality of life. Therapeutic options are limited with poor efficacy in older adults, lending to a growing need to address the gaps in our current understanding of urinary tract aging. This review summarizes the current knowledge of age-associated alterations in the structure and function of the brain-bladder axis and identifies important gaps in the field that have yet to be addressed. Urinary aging is associated with decreased tissue responsiveness, decreased control over the voiding reflex, signaling dysfunction along the brain-bladder axis, and structural changes within the bladder wall. Studies are needed to improve our understanding of how age affects the brain-bladder axis and identify genetic targets that correlate with functional outcomes.

Serum anandamide and lipids associated with linoleic acid can distinguish interstitial cystitis/bladder pain syndrome from overactive bladder: An exploratory study

OBJECTIVES

Diagnosing interstitial cystitis/bladder pain syndrome presents a major challenge because it relies on subjective symptoms and empirical cystoscopic findings. A practical biomarker should discriminate diseases that cause increased urinary frequency, particularly overactive bladder. Therefore, we aimed to identify blood biomarkers that can discriminate between interstitial cystitis/bladder pain syndrome and overactive bladder.

METHODS

We enrolled patients with Hunner-type interstitial cystitis (n = 20), bladder pain syndrome (n = 20), and overactive bladder (n = 20) and without lower urinary tract symptoms (controls, n = 15) at Ueda Clinic and Nara Medical University Hospital from February 2020 to August 2021. The degree of interstitial cystitis/bladder pain syndrome symptoms was evaluated using the interstitial cystitis symptom and problem indices. Metabolomics analysis was performed on 323 serum metabolites using liquid chromatography time-of-flight mass spectrometry.

RESULTS

In the Hunner-type interstitial cystitis or bladder pain syndrome group, we observed smaller relative areas, including anandamide, acylcarnitine (18:2), linoleoyl ethanolamide, and arachidonic acid, compared to those in the overactive bladder or control group. Notably, the differences in the relative areas of anandamide were statistically significant (median: 3.950e-005 and 4.150e-005 vs. 8.300e-005 and 9.800e-005), with an area under the curve of 0.9321, demonstrating its ability to discriminate interstitial cystitis/bladder pain syndrome.

CONCLUSIONS

Serum anandamide may be a feasible diagnostic biomarker for interstitial cystitis/bladder pain syndrome. Reduced serum anandamide levels may be associated with pain and inflammation initiation, reflecting the pathology of interstitial cystitis/bladder pain syndrome. Furthermore, our findings suggest that abnormal linoleic acid metabolism may be involved in the pathogenesis of interstitial cystitis/bladder pain syndrome.

Peripheral Cannabinoid-1 Receptor Blockade Ameliorates Cystitis Severity

Background: The endocannabinoid system (ECS) plays a key physiological role in bladder function and it has been suggested as a potential target for relieving lower urinary tract symptoms (LUTSs). Whereas most studies indicate that activating the ECS has some beneficial effects on the bladder, some studies imply the opposite. In this study, we investigated the therapeutic potential of peripheral cannabinoid-1 receptor (CB1R) blockade in a mouse model for LUTSs. Materials and Methods: To this end, we used the cyclophosphamide (CYP; 300 mg/kg, intraperitoneal)-induced cystitis model of bladder dysfunction, in which 12-week-old, female C57BL/6 mice were treated with the peripherally restricted CB1R antagonist, JD5037 (3 mg/kg), or vehicle for three consecutive days. Bladder dysfunction was assessed using the noninvasive voiding spot assay (VSA) as well as the bladder-to-body weight (BW) ratio and gene and protein expression levels; ECS tone was assessed at the end of the study. Results: Peripheral CB1R blockade significantly ameliorated the severity of CYP-induced cystitis, manifested by reduced urination events measured in the VSA and an increased bladder-to-BW ratio. Moreover, JD5037 normalized CYP-mediated bladder ECS tone imbalance by affecting both the expression of CB1R and the endocannabinoid levels. These effects were associated with the ability of JD5037 to reduce CYP-induced inflammatory response, manifested by a reduction in levels of the proinflammatory cytokine, tumor necrosis factor alpha (TNFα), in the bladder and serum. Conclusions: Collectively, our results highlight the therapeutic relevance of peripheral CB1R blockade in ameliorating CYP-induced cystitis; they may further support the preclinical development and clinical use of peripherally restricted CB1R antagonism for treatment of LUTSs.

Antibacterial and Analgesic Properties of Beta-Caryophyllene in a Murine Urinary Tract Infection Model

Beta-caryophyllene has demonstrated anti-inflammatory effects in a variety of conditions, including interstitial cystitis. These effects are mediated primarily via the activation of the cannabinoid type 2 receptor. Additional antibacterial properties have recently been suggested, leading to our investigation of the effects of beta-caryophyllene in a murine model of urinary tract infection (UTI). Female BALB/c mice were intravesically inoculated with uropathogenic Escherichia coli CFT073. The mice received either beta-caryophyllene, antibiotic treatment using fosfomycin, or combination therapy. After 6, 24, or 72 h, the mice were evaluated for bacterial burden in the bladder and changes in pain and behavioral responses using von Frey esthesiometry. In the 24 h model, the anti-inflammatory effects of beta-caryophyllene were also assessed using intravital microscopy. The mice established a robust UTI by 24 h. Altered behavioral responses persisted 72 h post infection. Treatment with beta-caryophyllene resulted in a significant reduction in the bacterial burden in urine and bladder tissues 24 h post UTI induction and significant improvements in behavioral responses and intravital microscopy parameters, representing reduced inflammation in the bladder. This study demonstrates the utility of beta-caryophyllene as a new adjunct therapy for the management of UTI.

Cannabis and Cannabinoids in Multiple Sclerosis: From Experimental Models to Clinical Practice-A Review

BACKGROUND

As far as 80% of people diagnosed with multiple sclerosis (MS) experience disabling symptoms in the course of the disease, such as spasticity and neuropathic pain. As first-line symptomatic therapy is associated with important adverse reactions, cannabinoids have become increasingly popular among patients with MS. This review intends to provide an overview of the evidence of the role of cannabinoids in treating symptoms related to MS and to encourage further research on this matter.

AREAS OF UNCERTAINTY

To date, the evidence supporting the role of cannabis and its derivatives in alleviating the MS-related symptoms comes only from studies on experimental models of demyelination. To the best of our knowledge, relatively few clinical trials inquired about the therapeutic effects of cannabinoids on patients with MS, with variable results.

DATA SOURCES

We conducted a literature search through PubMed and Google Scholar from the beginning until 2022. We included articles in English describing the latest findings regarding the endocannabinoid system, the pharmacology of cannabinoids, and their therapeutic purpose in MS.

RESULTS

Evidence from preclinical studies showed that cannabinoids can limit the demyelination process, promote remyelination, and have anti-inflammatory properties by reducing immune cell infiltration of the central nervous system in mice with experimental autoimmune encephalomyelitis. Moreover, it has been established that experimental autoimmune encephalomyelitis mice treated with cannabinoids experienced a significant reduction of symptoms and slowing of the disease progression. Given the complexity of human immune and nervous systems, cannabinoids did not have the anticipated effects on human subjects. However, data obtained from clinical trials showed some beneficial results of cannabinoids as a single or as add-on therapy in reducing the spasticity and pain related to MS.

CONCLUSION

Considering their various mechanisms of action and good tolerability, cannabinoids remain an interesting therapy for spasticity and chronic pain related to MS.

Endocannabinoids, anandamide and 2-AG, regulate mechanosensitivity of mucosal afferents in the Guinea pig bladder

Bladder afferents play a crucial role in urine storage and voiding, and conscious sensations from the bladder. Endocannabinoids, anandamide (AEA) and 2-arachidonolylglycerol (2-AG), are endogenous ligands of G-protein coupled cannabinoid receptors 1 and 2 (CB1 and CB2) found in the CNS and peripheral organs. They also have off-target effects on some ligand- and voltage-gated channels. The aim of this study is to determine the role of AEA and 2-AG in regulation of mechanosensitivity of probable nociceptive neurons innervating the bladder - capsaicin-sensitive mucosal afferents. The activity of these afferents was determined by ex vivo single unit extracellular recordings in the guinea pig bladder. A stable analogue of anandamide, methanandamide (mAEA) evoked initial excitatory response of mucosal afferents followed by potentiation of their responses to mechanical stimulation. In the presence of TRPV1 antagonist (AMG9810), mAEA's effect on mechanosensitivity switched from excitatory to inhibitory. The inhibitory effect of mAEA is due to activation of both CB1 and CB2 cannabinoid receptors since it was abolished by combined application of selective CB1 (NESS0327) and CB2 (SR144528) antagonists. 2-AG application evoked a brief excitation of mucosal afferents, without potentiation of their mechanosensitivity, followed by the inhibition of their responses to mechanical stimulation. CB2 receptor antagonist, SR144528 abolished the inhibitory effect of 2-AG. Our data indicated that anandamide and 2-AG have opposite effects on mechanosensitivity of mucosal capsaicin-sensitive afferents in the guinea pig bladder; mAEA potentiated while 2-AG inhibited responses of mucosal afferents to mechanical stimulation. These findings are important for understanding of the role of endocannabinoids in regulating bladder sensation and function.

Role of circadian rhythms and melatonin in bladder function in heath and diseases

The circadian system modulates all visceral organ physiological processes including urine storage and voiding. The "master clock" of the circadian system lies within suprachiasmatic nucleus of the hypothalamus while "peripheral clocks" are found in most peripheral tissue and organs, including the urinary bladder. Disruptions of circadian rhythms can cause organ malfunction and disorder or exacerbate pre-existing ones. It has been suggested that nocturia, which develops mostly in the elderly, could be a circadian-related disorder of the bladder. In the bladder, many types of gap junctions and ion channels in the detrusor, urothelium and sensory nerves are likely under strict local peripheral circadian control. The pineal hormone, melatonin, is a circadian rhythm synchroniser capable of controlling a variety of physiological processes in the body. Melatonin predominantly acts via the melatonin 1 and melatonin 2 G-protein coupled receptors expressed in the central nervous system, and many peripheral organs and tissues. Melatonin could be beneficial in the treatment of nocturia and other common bladder disorders. The ameliorating action of melatonin on bladder function is likely due to multiple mechanisms which include central effects on voiding and peripheral effects on the detrusor and bladder afferents. More studies are warranted to determine the precise mechanisms of circadian rhythm coordination of the bladder function and melatonin influences on the bladder in health and diseases.

TRPV1 and TRPM8 antagonists reduce cystitis-induced bladder hypersensitivity via inhibition of different sensitised classes of bladder afferents in guinea pigs

BACKGROUND AND PURPOSE

Interstitial cystitis (=painful bladder syndrome) is a chronic bladder syndrome characterised by pelvic and bladder pain, urinary frequency and urgency, and nocturia. Transient receptor potential (TRP) channels are an attractive target in reducing the pain associated with interstitial cystitis. The current study aims to determine the efficacy of combination of TRP vanilloid 1 (TRPV1) and TRP melastatin 8 (TRPM8) channel inhibition in reducing the pain associated with experimental cystitis in guinea pigs.

EXPERIMENTAL APPROACH

A novel animal model of non-ulcerative interstitial cystitis has been developed using protamine sulfate/zymosan in female guinea pigs. Continuous voiding cystometry was performed in conscious guinea pigs. Ex vivo "close-to-target" single unit extracellular recordings were made from fine branches of pelvic nerves entering the guinea pig bladder. Visceromotor responses in vivo were used to determine the effects of TRP channel antagonists on cystitis-induced bladder hypersensitivity.

KEY RESULTS

Protamine sulfate/zymosan treatment evoked mild inflammation in the bladder and increased micturition frequency in conscious animals. In cystitis, high threshold muscular afferents were sensitised via up-regulation of TRPV1 channels, high threshold muscular-mucosal afferents were sensitised via TRPM8 channels, and mucosal afferents by both. Visceromotor responses evoked by noxious bladder distension were significantly enhanced in cystitis and were returned to control levels upon administration of combination of low doses of TRPV1 and TRPM8 antagonists.

CONCLUSIONS AND IMPLICATIONS

The data demonstrate the therapeutic promises of combination of TRPV1 and TRPM8 antagonists for the treatment of bladder hypersensitivity in cystitis.

Enhancing effect of nicotine on electrical field stimulation elicited contractile responses in isolated rabbit bladder straight muscle; the role of cannabinoid and vanilloid receptors

BACKGROUND

Nicotine acts as an agonist of nicotinic acetylcholine receptors (nAChR). These receptors belong to a superfamily of ligand-gated ion channels. We previously demonstrated that nicotine increased electrical field stimulation (EFS)-induced contractile or relaxation responses, possibly by facilitating neurotransmitter release from nerve terminals in various rabbit tissues. Studies have shown that there is an interaction between the endocannabinoid and nicotinic systems. This study aimed to investigate the interaction between nicotine and the endocannabinoid system in the rabbit urine bladder and also investigate the enhancing effect of nicotine on EFS-induced contractile responses in rabbit isolated bladder smooth muscle and its interaction with the endocannabinoid system.

METHODS

The New Zealand albino male adult rabbits were used for this study. Following scarification, the urine bladder was rapidly excised, and then uniform strips were prepared. Each strip was mounted under 1 g isometric resting tension in an organ bath containing 20 mL of Krebs-Henseleit solution. After obtaining EFS-induced contractile responses, 10-4 M concentrations of nicotine were applied to the preparations, and EFS was stopped after 5 stimulations. Following washing, the same experimental procedure was performed with the same tissue in the presence of AM251 (a cannabinoid CB1R antagonist, 10-6 M), AM630 (a cannabinoid CB2R antagonist, 10-6 M), and capsazepine (a vanilloid receptor antagonist, 3 × 10-6 M).

RESULTS

Nicotine enhanced the EFS-induced contraction responses by 17.16% ± 2.81% at a 4-Hz stimulation frequency. Cannabinoid receptor antagonists AM251 and AM630 reduced this increasing effect of nicotine although it was not significant and vanilloid receptor antagonist capsazepine did not significantly alter the nicotines' effect.

DISCUSSION

These results show that enhancing effect of nicotine in the smooth muscle of the rabbit bladder, even though it was not significant endocannabinoid system possibly have a role in nicotines' effect.

Melatonin inhibits muscular-mucosal stretch-sensitive bladder afferents via the MT2 receptors

Melatonin is a circadian rhythm regulator capable of controlling a variety of physiological processes in the body. It predominantly acts via the melatonin 1 (MT1) and MT2 receptors expressed in the CNS neurons and peripheral organs and tissues. Melatonin can modulate urinary bladder function, however, to date it is not known if melatonin can regulate activity of sensory neurons innervating the bladder. Bladder afferents play an important role in urine storage and voiding. Therefore, this study aims to determine if melatonin can regulate mechanosensitivity of 2 major classes of sensory neurons in the guinea pig bladder: stretch-insensitive mucosal and low threshold stretch-sensitive muscular-mucosal afferents. The effects of melatonin on the mechanosensitivity of mucosal and muscular-mucosal afferents were measured ex vivo using single unit extracellular recording. Melatonin did not affect the responses of mucosal afferents to stroking of their receptive fields but did concentration-dependently, significantly inhibit 69% of muscular-mucosal afferents responses to stroking and bladder stretch. This inhibitory effect was not affected by the MT1 receptor antagonist, S26131 but was blocked by the selective MT2 receptor antagonists, K-185 and 4-P-PDOT. Forskolin significantly potentiated the responses of muscular-mucosal afferents to stroking and stretch, which were prevented by melatonin. These findings demonstrate a direct inhibitory effect of melatonin on the mechanosensitivity of low threshold stretch-sensitive muscular-mucosal bladder afferents acting via MT2 receptors, which is independent from its action on detrusor muscle. This may have important clinical implications for the treatment of many common bladder disorders including nocturia.

Emerging drugs for the treatment of bladder storage dysfunction

INTRODUCTION

Current drug treatment of lower urinary tract disorders, for example, overactive bladder syndrome and lower urinary tract symptoms associated with benign prostatic hyperplasia, is moderately effective, has a low treatment persistence and some short- and long-term adverse events. Even if combination therapy with approved drugs may offer advantages in some patients, there is still a need for new agents.

AREAS COVERED

New b₃-adrenoceptor agonists, antimuscarinics, the naked Maxi-K channel gene, a novel 5HT/NA reuptake inhibitor and soluble guanylate cyclase activators are discussed. Focus is given to P2X3 receptor antagonists, small molecule blockers of TRP channels, the roles of cannabis on incontinence in patients with multiple sclerosis, and of drugs acting directly on CB1 and CB2 receptor or indirectly via endocannabinoids by inhibition of fatty acid aminohydrolase.

EXPERT OPINION

New potential alternatives to currently used drugs/drug principles are emerging, but further clinical testing is required before they can be evaluated as therapeutic alternatives. It seems that for the near future individualized treatment with approved drugs and their combinations will be the prevailing therapeutic approach.

Components of the Endogenous Cannabinoid System as Potential Biomarkers for Interstitial Cystitis/Bladder Pain Syndrome

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a chronic condition causing bladder pressure and pain. The condition is of unknown etiology and is often accompanied by other symptoms, including chronic pelvic pain, increased urinary urgency, and frequency. There is no definitive diagnosis for IC/BPS, and treatment options are currently limited to physical therapy and medications to help alleviate symptoms. The endogenous cannabinoid system (ECS) is an important regulator of numerous physiological systems, including the urinary system. Modulations of the ECS have been shown to be beneficial for IC/BPS-associated pain and inflammation in rodents. As an attempt to identify potential biomarkers for IC/BPS, we reviewed experimental studies where the components of the ECS have been quantified in experimental models of IC/BPS. Further investigations using well-defined animal models and patients’ data are required to obtain stronger evidence regarding the potential for ECS components to be definitive biomarkers for IC/BPS.

Time-of-day dependent changes in guinea pig bladder afferent mechano-sensitivity

The voiding of urine has a clear circadian rhythm with increased voiding during active phases and decreased voiding during inactive phases. Bladder spinal afferents play a key role in the regulation of bladder storage and voiding, but it is unknown whether they exhibit themselves a potential circadian rhythm. Therefore, this study aimed to determine the mechano- and chemo- sensitivity of three major bladder afferent classes at two opposite day-night time points. Adult female guinea pigs underwent conscious voiding monitoring and bladder ex vivo single unit extracellular afferent recordings at 0300 h and 1500 h to determine day-night modulation of bladder afferent activity. All guinea pigs voided a higher amount of urine at 1500 h compared to 0300 h. This was due to an increased number of voids at 1500 h. The mechano-sensitivity of low- and high-threshold stretch-sensitive muscular-mucosal bladder afferents to mucosal stroking and stretch was significantly higher at 1500 h compared to 0300 h. Low-threshold stretch-insensitive mucosal afferent sensitivity to stroking was significantly higher at 1500 h compared to 0300 h. Further, the chemosensitivity of mucosal afferents to N-Oleoyl Dopamine (endogenous TRPV1 agonist) was also significantly increased at 1500 h compared to 0300 h. This data indicates that bladder afferents exhibit a significant time-of-day dependent variation in mechano-sensitivity which may influence urine voiding patterns. Further studies across a 24 h period are warranted to reveal potential circadian rhythm modulation of bladder afferent activity.