Bladder function in a cannabinoid receptor type 1 knockout mouse

Cannabinoid receptor type 1 activation causes a water diuresis by inducing an acute central diabetes insipidus in mice

Cannabis and synthetic cannabinoid consumption are increasing worldwide. Cannabis contains numerous phytocannabinoids that act on the G protein-coupled cannabinoid receptor type 1 (CB1R) and cannabinoid receptor type 2 expressed throughout the body, including the kidney. Essentially every organ, including the kidney, produces endocannabinoids, which are endogenous ligands to these receptors. Cannabinoids acutely increase urine output in rodents and humans, thus potentially influencing total body water and electrolyte homeostasis. As the kidney collecting duct (CD) regulates total body water, acid/base, and electrolyte balance through specific functions of principal cells (PCs) and intercalated cells (ICs), we examined the cell-specific immunolocalization of CB1R in the mouse CD. Antibodies against either the C-terminus or N-terminus of CB1R consistently labeled aquaporin 2 (AQP2)-negative cells in the cortical and medullary CD and thus presumably ICs. Given the well-established role of ICs in urinary acidification, we used a clearance approach in mice that were acid loaded with 280 mM NH4Cl for 7 days and nonacid-loaded mice treated with the cannabinoid receptor agonist WIN55,212-2 (WIN) or a vehicle control. Although WIN had no effect on urinary acidification, these WIN-treated mice had less apical + subapical AQP2 expression in PCs compared with controls and developed acute diabetes insipidus associated with the excretion of large volumes of dilute urine. Mice maximally concentrated their urine when WIN and 1-desamino-8-d-arginine vasopressin [desmopressin (DDAVP)] were coadministered, consistent with central rather than nephrogenic diabetes insipidus. Although ICs express CB1R, the physiological role of CB1R in this cell type remains to be determined.NEW & NOTEWORTHY The CB1R agonist WIN55,212-2 induces central diabetes insipidus in mice. This research integrates existing knowledge regarding the diuretic effects of cannabinoids and the influence of CB1R on vasopressin secretion while adding new mechanistic insights about total body water homeostasis. Our findings provide a deeper understanding about the potential clinical impact of cannabinoids on human physiology and may help identify targets for novel therapeutics to treat water and electrolyte disorders such as hyponatremia and volume overload.

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.

Expression of cannabinoid 1 and, 2 receptors and the effects of cannabinoid 1 and, 2 receptor agonists on detrusor overactivity associated with bladder outlet obstruction in rats

Background

This study investigated changes in the expression of cannabinoid (CB) receptors and the effects of CB1 and CB2 agonists on detrusor overactivity (DO) associated with bladder outlet obstruction (BOO) in rats.

Methods

Male Sprague Dawley rats were randomly assigned to four groups (n = 10) in each group. The control group comprised sham-operated rats. A animals in the BOO, CB1 agonist and CB2 agonist groups all underwent BOO surgery. Three weeks postoperatively, cystometrography (CMG) was performed on all rats. After confirming the presence of DO in the CB1 and CB2 agonist groups, a CB1 agonist (WIN 55,212–2) and a CB2 agonist (CB65) were instilled intravesically, and CMG was repeated. CMG parameters, including the contraction interval (CI) and contraction pressure (CP) were then analyzed. The bladders of rats in all four groups were excised following CMG. Immunofluorescence staining and Western blotting were performed to localize CB1 and CB2 and measure their expression levels in the urothelium and detrusor muscle.

Results

The CI was significantly longer and the CP was significantly lower in the CB1 agonist group than in the BOO group. CI and CP in the CB2 agonist group showed the same results. CB1 receptor immunofluorescence staining signals and immunoreactive bands in Western blotting were increased in the BOO group compared with results in the control group. Similarly, results for the CB2 receptor were also increased in the BOO group, although this difference was not significant. The CMG parameters in the BOO group were significantly improved by the inhibitory effects of CB1 and CB2 agonists on BOO-associated DO. The expression of CB1 was significantly increased in the urothelium and detrusor muscle in BOO-associated DO, but no significant change in CB2 expression was observed.

Conclusions

CB1 and CB2 receptors, especially CB1, play a role in the pathophysiology of BOO-associated DO, and could serve as therapeutic targets.

Serotonin Receptor 5-HT3A Affects Development of Bladder Innervation and Urinary Bladder Function

The autonomic and sensory nervous systems are required for proper function of all visceral organs, including the lower urinary tract (LUT). Despite the wide prevalence of bladder dysfunction, effective treatment options remain limited. Pelvic innervation regenerative strategies are promising, but surprisingly little is known about the molecular factors driving the development of bladder innervation. Given prior evidence that serotonin receptor 5-HT3A is expressed early in LUT development and is an important mediator of adult bladder function, we sought to determine if 5-HT3A is required for the development of autonomic innervation of the bladder. We found that 5-HT3A is expressed early in fetal mouse pelvic ganglia and is maintained through adulthood. Htr3a knockout male mice, but not females, exhibit increased urinary voiding frequency compared to wild type littermates. Analysis of LUT function via anesthetized cystometry revealed decreased voiding efficiency in male Htr3a mutants. Htr3a^−/− mutant animals exhibit a transient disturbance of autonomic neuronal subtype markers (tyrosine hydroxylase and choline acetyl transferase) within the fetal pelvic ganglia, although the imbalance of neuronal subtype markers assayed is no longer apparent in adulthood. Loss of 5-HT3A activity results in a higher density of autonomic and sensory neuronal fibers supplying bladder smooth muscle in both fetal and adult mice. Collectively, our findings highlight 5-HT3A as a critical component in the autonomic control of micturition and identify a novel role for this serotonin receptor in peripheral nervous system development.

Impaired Excitatory Neurotransmission in the Urinary Bladder from the Obese Zucker Rat: Role of Cannabinoid Receptors

Metabolic syndrome (MS) is a known risk factor for lower urinary tract symptoms. This study investigates whether functional and expression changes of cannabinoid CB₁ and CB₂ receptors are involved in the bladder dysfunction in an obese rat model with insulin resistance. Bladder samples from obese Zucker rat (OZR) and their respective controls lean Zucker rat (LZR) were processed for immunohistochemistry and western blot for studying the cannabinoid receptors expression. Detrusor smooth muscle (DSM) strips from LZR and OZR were also mounted in myographs for isometric force recordings. Neuronal and smooth muscle CB₁ and CB₂ receptor expression and the nerve fiber density was diminished in the OZR bladder. Electrical field stimulation (EFS) and acetylcholine (ACh) induced frequency- and concentration-dependent contractions of LZR and OZR DSM. ACh contractile responses were similar in LZR and OZR. EFS-elicited contractions, however, were reduced in OZR bladder. Cannabinoid receptor agonists and antagonists failed to modify the DSM basal tension in LZR and OZR In LZR bladder, EFS responses were inhibited by ACEA and SER-601, CB₁ and CB₂ receptor agonists, respectively, these effects being reversed by ACEA plus the CB₁ antagonist, AM-251 or SER-601 plus the CB₂ antagonist, AM-630. In OZR bladder, the inhibitory action of ACEA on nerve-evoked contractions was diminished, whereas that SER-601 did not change EFS responses. These results suggest that a diminished function and expression of neuronal cannabinoid CB₁ and CB₂ receptors, as well as a lower nerve fiber density is involved in the impaired excitatory neurotransmission of the urinary bladder from the OZR.

Spinal neuronal cannabinoid receptors mediate urodynamic effects of systemic fatty acid amide hydrolase (FAAH) inhibition in rats

AIMS

To test if urodynamic effects from systemic Fatty Acid Amide Hydrolase (FAAH) inhibition involve sacral spinal cannabinoid type 1 (CB1) or type 2 (CB2) receptors.

METHODS

Male rats with or without partial urethral obstruction were used for cystometry or immunohistochemistry. Urodynamic effects of intravenous (IV) 0.3 mg/kg Oleoyl Ethyl Amide (OEtA; FAAH inhibitor), and intrathecal (IT) 5 μg rimonabant (CB1 antagonist) or 5 μg SR144528 (CB2 antagonist) were studied in awake rats.

RESULTS

After administration of rimonabant or SR144528, non-obstructed rats with normal bladder function developed bladder overactivity (BO), which was counteracted by OEtA. OEtA also counteracted BO in obstructed rats. SR144528 did not affect bladder function in obstructed rats but counteracted the urodynamic effects of OEtA. Surprisingly, rimonabant (and AM251, another CB1 antagonist) reduced BO in obstructed rats, whereafter OEtA produced no additional urodynamic effects. CB1 expression increased in the sacral spinal cord of obstructed rats whereas no changes were observed for CB2 or FAAH.

CONCLUSIONS

Urodynamic effects of systemic FAAH inhibition involve activities at spinal neuronal CB1 and CB2 receptors in normal and obstructed rats. Endogenous spinal CB receptor ligands seem to regulate normal micturition and BO. Altered spinal CB receptor functions may be involved in the pathogenesis of obstruction-induced BO. Neurourol. Urodynam. 35:464-470, 2016. © 2015 Wiley Periodicals, Inc.

Genetic Manipulation of the Endocannabinoid System

The physiological and pathophysiological functions of the endocannabinoid system have been studied extensively using transgenic and targeted knockout mouse models. The first gene deletions of the cannabinoid CB(1) receptor were described in the late 1990s, soon followed by CB(2) and FAAH mutations in early 2000. These mouse models helped to elucidate the fundamental role of endocannabinoids as retrograde transmitters in the CNS and in the discovery of many unexpected endocannabinoid functions, for example, in the skin, bone and liver. We now have knockout mouse models for almost every receptor and enzyme of the endocannabinoid system. Conditional mutant mice were mostly developed for the CB(1) receptor, which is widely expressed on many different neurons, astrocytes and microglia, as well as on many cells outside the CNS. These mouse strains include "floxed" CB(1) alleles and mice with a conditional re-expression of CB(1). The availability of these mice made it possible to decipher the function of CB(1) in specific neuronal circuits and cell populations or to discriminate between central and peripheral effects. Many of the genetic mouse models were also used in combination with viral expression systems. The purpose of this review is to provide a comprehensive overview of the existing genetic models and to summarize some of the most important discoveries that were made with these animals.

Protective effect of palmitoylethanolamide in a rat model of cystitis

PURPOSE

PEA is an endogenous mediator released together with the endocannabinoid anandamide from membrane phospholipids. It is a plant derived compound with analgesic and anti-inflammatory properties. We verified whether the pathophysiology of experimental cystitis involves changes in the levels of PEA and of some of its targets, ie CB1 and CB2 receptors, and PPARα. We also determined whether exogenously administered PEA could be proposed as a preventive measure for cystitis.

MATERIALS AND METHODS

Cystitis was induced by cyclophosphamide in female rats. Nociceptive responses, voiding episodes, gross damage, myeloperoxidase activity, bladder weight, bladder PEA and endocannabinoid levels (measured by liquid chromatography-mass spectrometry) and the expression of PEA targets (measured by quantitative reverse transcriptase-polymerase chain reaction) were recorded.

RESULTS

Cyclophosphamide induced pain behavior, bladder inflammation and voiding dysfunction associated with increased bladder levels of PEA, up-regulation of CB1 receptor mRNA expression, down-regulation of PPARα mRNA and no change in CB2 receptor mRNA expression. Exogenously administered, ultramicronized PEA attenuated pain behavior, voids and bladder gross damage. The CB1 antagonist rimonabant and the PPARα antagonist GW6471 counteracted the beneficial effect of PEA on gross damage. Also, GW6471 further decreased voiding episodes in rats treated with PEA.

CONCLUSIONS

The current study provides strong evidence for a protective role of PEA as well as an alteration in bladder levels of PEA and of some of its targets in cyclophosphamide induced cystitis.