ALTERED NGF REGULATION MAY LINK A GENETIC PREDISPOSITION FOR HYPERTENSION WITH HYPERACTIVE VOIDING

Are blood vessels a target to treat lower urinary tract dysfunction?

Bladder dysfunction is common in the general population (Stewart et al. 2010) and even more so among patients seeing a physician for any reason (Goepel et al. 2002). It often manifests as lower urinary tract symptoms (LUTS), a term originally coined to describe voiding and storage symptoms in men with benign prostatic hyperplasia (BPH) but now more universally used to describe any type of voiding and storage symptoms in both sexes. Studies into possible causes of urinary bladder dysfunction have long focused on detrusor smooth muscle cells (Turner and Brading 1999). More recently, it became clear that several other types of cells and organs contribute to regulating detrusor smooth muscle function. These include the urothelium (Andersson and McCloskey 2014; Michel 2015), afferent nerves (Michel and Igawa 2015; Yoshimura et al. 2014b), and the central and autonomic nervous systems (Fowler and Griffiths 2010; Yoshimura et al. 2014a). Alterations in any of these may at least partly be responsible for detrusor dysfunction and, accordingly, be potential targets for the treatment of bladder dysfunction. As highlighted by an article in this issue of Naunyn-Schmiedeberg's Archives of Pharmacology (Bayrak et al. 2015), there is an additional suspect, the bladder vasculature. This article will discuss the currently available experimental and clinical evidence for a role of the vasculature in causing bladder dysfunction, and how existing and emerging treatments may modulate bladder function by acting on blood vessels. Due to a similarity in concept, data on prostate perfusion will also be discussed to some extent.

The urinary bladder of spontaneously hypertensive rat demonstrates bladder hypertrophy, inflammation, and fibrosis but not hyperplasia

AIMS

The present study aims to systemically characterize the factors that are associated with urinary bladder organ enlargement in spontaneously hypertensive rats (SHR).

MAIN METHODS

We compared the SHR to age-matched normotensive Wistar-Kyoto (WKY) control rats in the levels of bladder pro-inflammatory factors, collagen expression (type I), and detrusor smooth muscle growth.

KEY FINDINGS

Our results showed that enhanced inflammatory responses and fibrosis were key factors that were closely associated with bladder wall thickening in SHR. Specifically the mRNA levels of inflammatory factors interleukin (IL)-1α, IL-6 and TNFα were significantly higher in SHR than those in WKY rats. The SHR also had a higher number of mast cells in the suburothelium space. Type I collagen production was also significantly higher in SHR when compared to that in control rats. However, the smooth muscle content stayed the same in SHR and WKY rats. This was shown by the results that the ratio of α-smooth muscle actin (SMA) to the nuclear protein histone H3 had no difference between these two rat strains. The mRNA and protein levels of proliferating cell nuclear antigen (PCNA) also showed no change in the urinary bladder of SHR and WKY rats. Further study showed that the phosphorylation level of Akt in the urinary bladder was not changed in SHR when compared to WKY rats. In contrast, the phosphorylation level of ERK1/2 was significantly higher in SHR bladder when compared to that of WKY rats.

SIGNIFICANCE

These results suggest that inflammation and fibrosis are primary factors that may lead to urinary bladder hypertrophy in SHR.

Nonselective Blocking of the Sympathetic Nervous System Decreases Detrusor Overactivity in Spontaneously Hypertensive Rats

The involuntary dual control systems of the autonomic nervous system (ANS) in the bladder of awake spontaneously hypertensive rats (SHRs) were investigated through simultaneous registrations of intravesical and intraabdominal pressures to observe detrusor overactivity (DO) objectively as a core symptom of an overactive bladder. SHRs (n = 6) showed the features of overactive bladder syndrome during urodynamic study, especially DO during the filling phase. After injection of the nonselective sympathetic blocking agent labetalol, DO disappeared in 3 of 6 SHRs (50%). DO frequency decreased from 0.98 ± 0.22 min⁻¹ to 0.28 ± 0.19 min⁻¹ (p < 0.01), and DO pressure decreased from 3.82 ± 0.57 cm H₂O to 1.90 ± 0.86 cm H₂O (p < 0.05). This suggests that the DO originating from the overactive parasympathetic nervous system is attenuated by the nonselective blocking of the sympathetic nervous system. The detailed mechanism behind this result is still not known, but parasympathetic overactivity seems to require overactive sympathetic nervous system activity in a kind of balance between these two systems. These findings are consistent with recent clinical findings suggesting that patients with idiopathic overactive bladder may have ANS dysfunction, particularly a sympathetic dysfunction. The search for newer and better drugs than the current anticholinergic drugs as the mainstay for overactive bladder will be fueled by our research on these sympathetic mechanisms. Further studies of this principle are required.

β-adrenoceptor agonist effects in experimental models of bladder dysfunction

β-adrenoceptor stimulation can enhance the storage function of the urinary bladder by acting on detrusor smooth muscle tone, mediator release from the urothelium and/or afferent nerve activity. In humans this may occur predominantly if not exclusively via the β₃-subtype. The effects of β-adrenoceptor agonists including several β₃-selective agonists have been studied in vitro and in vivo, in healthy animals of both genders and various age groups and in a wide range of animal (mostly rat) models of genetic or acquired bladder dysfunction. Such models included bladder irritation by intravesical instillation of acetic acid or prostaglandin E₂, bladder outlet obstruction, stroke, diabetes, spontaneously hypertensive rats, and NO synthase inhibition. Across all of these models β-adrenoceptor agonists had effects consistent with improved bladder storage function. β₃-adrenoceptor effects are resistant to agonist-induced desensitization in many cell types, but whether this also applies to the human bladder is unknown. The efficacy of β-adrenoceptor agonists appears to be largely unaffected by common polymorphisms of the β₃-adrenoceptor gene. Taken together these findings suggest that β₃-adrenoceptor agonists may become useful drugs for the treatment of bladder storage dysfunction, a view supported by recent phase III clinical studies for one such agent, mirabegron.

Glial cell line-derived neurotrophic factor protein content in rat skeletal muscle is altered by increased physical activity in vivo and in vitro

Current evidence suggests that exercise and glial cell line-derived neurotrophic factor (GDNF) independently cause significant morphological changes in the neuromuscular system. The aim of the current study was to determine if increased physical activity regulates GDNF protein content in rat skeletal muscle. Extensor Digitorum Longus (EDL) and Soleus (SOL) hind limb skeletal muscles were analyzed following 2 weeks of involuntary exercise and 4 h of field stimulation or stretch in muscle bath preparations. GDNF protein content was measured via enzyme-linked immunosorbent assay (ELISA). Two weeks of exercise increased GDNF protein content in SOL as compared to sedentary controls (4.4±0.3 pg GDNF/mg tissue and 3.1±0.6 pg GDNF/mg tissue, respectively) and decreased GDNF protein content in EDL as compared to controls (1.0±0.1 pg GDNF/mg tissue and 2.3±0.7 pg GDNF/mg tissue, respectively). GDNF protein content in the EDL decreased following both field stimulation (56%±18% decrease from controls) and stretch (66%±10% decrease from controls). SOL responded to field stimulation with a 38%±7% increase from controls in GDNF protein content, but showed no change following stretch. Pre-treatment with α-bungarotoxin abolished the effects of field stimulation in both muscles and blocked the effect of stretch in EDL. α-bungarotoxin pre-treatment and stretch increased GDNF protein content to 240%±10% of controls in the SOL. Exposure to carbamylcholine decreased GDNF protein content to 51%±28% of controls in the EDL but not SOL. These results suggest that GDNF protein content in skeletal muscle may be controlled by stretch, where it may increase GDNF protein content, and membrane depolarization/acetylcholine (ACh) which acts to decrease GDNF protein content.

An excitatory role for peripheral EP3 receptors in bladder afferent function

The excitatory roles of EP3 receptors at the peripheral afferent nerve innervating the rat urinary bladder have been evaluated by using the selective EP3 antagonist (2 E)-3-{1-[(2,4-dichlorophenyl)methyl]-5-fluoro-3-methyl-1 H-indol-7-yl}- N-[(4,5-dichloro-2-thienyl)sulfonyl]-2-propenamide (DG-041). The bladder rhythmic contraction model and a bladder pain model measuring the visceromotor reflex (VMR) to urinary bladder distension (UBD) have been used to evaluate DG-041 in female rats. In addition, male rats [spontaneously hypertensive rat (SHR), Wistar-Kyoto (WKY), and Sprague-Dawley (SD)] were anesthetized with pentobarbital sodium, and primary afferent fibers in the L6 dorsal root were isolated for recording the inhibitory response to UBD following intravenous injection of DG-041. Intravenous injection of DG-041 (10 mg/kg), a peripherally restricted EP3 receptor antagonist, significantly reduced the frequency of bladder rhythmic contraction and inhibited the VMR response to bladder distension. The magnitude of reduction of the VMR response was not different in the different strains of rats (SD, SHR, and WKY). Furthermore, quantitative characterization of the mechanosensitive properties of bladder afferent nerves in SHR, WKY, and SD rats did not show the SHR to be supersensitive to bladder distension. DG-041 selectively attenuated responses of mechanosensitive afferent nerves to UBD, with strong suppression on the slow-conducting, high-threshold afferent fibers, with equivalent activity in the three strains. We conclude that sensitization of afferent nerve activity was not one of the mechanisms of bladder hypersensitivity in SHR. EP3 receptors are involved in the regulation of bladder micturition and bladder nociception at the peripheral level.

Alterations of M 2,3 -Muscarinic Receptor Protein and mRNA Expression in the Bladder of the Fructose Fed Obese Rat

PURPOSE

The effects of metabolic syndrome on bladder function and M2,3-muscarinic receptor expression were studied using the fructose fed obese rat.

MATERIALS AND METHODS

Male Wistar rats were divided into 2 groups, including group 1-normal control rats and group 2-6-week fructose fed rats. In vivo cystometry using anesthesia was performed. In vitro the bladder was divided into the urothelium and muscle layer by microdissection. Tissue M2,3-muscarinic receptor protein levels were measured by Western blotting. Expression of the mRNAs that encode M2,3-muscarinic receptors was estimated using reverse transcriptase-polymerase chain reaction.

RESULTS

Premicturition unstable bladder contractions suggestive of detrusor overactivity were noted in 62.5% of fructose fed rats but in no controls. M2,3-muscarinic receptor protein and mRNA expression was noted in the urothelium and muscle layer of the rat bladder. In control rats the M2-to-M3-muscarinic receptor protein expression ratio was 1:0.68 in urothelium and 1:0.28 in the muscle layer, and that for mRNA expression was 1:0.32 and 1:0.36, respectively. Compared to controls bladder M2,3-muscarinic receptor protein expression in the urothelium and muscle layer of 8 preparations each was significantly increased in fructose fed rats by 89% and 90% for M2-muscarinic receptor (each p <0.001), and by 35% and 93% for M3-muscarinic receptor (p <0.01 and <0.001, respectively). Correspondingly M2,3-muscarinic receptor mRNA expression in the fructose fed rat bladder urothelium and muscle layer of 8 preparations each was also significantly increased by 31% and 49% for M2-muscarinic receptor (each p <0.01), and by 121% and 117% for M3-muscarinic receptor (each p <0.001, respectively).

CONCLUSIONS

Metabolic syndrome induces increased expression of M2,3-muscarinic receptor mRNA and protein in the urothelium as well as the muscle layer of the bladder in 6-week fructose fed rats. The receptor alterations are associated with functional evidence of detrusor overactivity.

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.

Mechanistic insights into the role of α1-adrenergic receptors in lower urinary tract symptoms

Although alpha(1)AR antagonists have been used for more than two decades to treat lower urinary tract symptoms (LUTS), we have little understanding of the mechanistic basis of their efficacy and their role in the development of LUTS. It is clear that alpha(1)ARs play a critical role in bladder dysfunction and recent data suggest that alpha(1)AR subtype switching may play a key role in this pathophysiology, providing support for use of alpha(1)(d)AR-selective antagonists in treating irritative symptoms. This review seeks to summarize current levels of understanding in this field and discusses new concepts that suggest increased levels of complexity involving cross-talk in multiple receptor systems. Effective therapeutic modalities likely will involve increased subtype selective alpha(1)AR antagonists and other pharmacodynamic factors.

GDNF is regulated in an activity-dependent manner in rat skeletal muscle

Glial cell line-derived neurotrophic factor (GDNF) is produced by skeletal muscle and affects peripheral motor neurons. Elevated expression of GDNF in skeletal muscle leads to hyperinnervation of neuromuscular junctions, whereas postnatal administration of GDNF causes synaptic remodeling at the neuromuscular junction. Studies have demonstrated that altered physical activity causes changes in the neuromuscular junction. However, the role played by GDNF in this process in not known. The objective of this study was to determine whether changes in neuromuscular activity cause altered GDNF content in rat skeletal muscle. Following 4 weeks of walk-training on a treadmill, or 2 weeks of hindlimb unloading, soleus, gastrocnemius, and pectoralis major were removed and analyzed for GDNF content by enzyme-linked immunosorbant assay. Results indicated that walk-training is associated with increased GDNF content. Skeletal muscle from hindlimb-unloaded animals showed a decrease in GDNF in soleus and gastrocnemius, and an increase in pectoralis major. The altered production of GDNF may be responsible for activity-dependent remodeling of the neuromuscular junction and may aid in recovery from injury and disease.

Lower urinary tract physiology and pharmacology

This review focuses on what we consider to be the most important findings of the last year relating to the smooth muscle of the lower urogenital system and the different levels of regulation that control its contraction and relaxation. One level is through modulation of the smooth muscle itself or its environment. Recent findings examining myosin isoform composition and collagen content as well as mechanisms that appear to be involved in inducing hyperplasia/hypertrophy of smooth muscle are described. Another method of regulation is via calcium-dependent phosphorylation of the regulatory light chain of myosin, which increases its activity. Interesting results indicating an uncoupling of force from calcium in the bladder are discussed. A third level of regulation is pharmacologic. Thus, the most recent findings related to receptor subtypes, including muscarinic, endothelin, alpha-adrenergic and nicotinic receptors, are presented. In addition, the effects of diabetes, incontinence, and partial bladder outlet obstruction on these modes of contractile regulation are also discussed.

Stretch-activated signaling of nerve growth factor secretion in bladder and vascular smooth muscle cells from hypertensive and hyperactive rats

Elevated vascular (VSMC) and bladder smooth muscle (BSMC) NGF are associated with altered visceral innervation in the spontaneously hypertensive rat (SHR: hypertensive, behaviorally hyperactive) compared with control Wistar-Kyotos (WKYs). Stretch stimulates increased NGF production in BSMCs. To elucidate whether stretch induces NGF synthesis in VSMCs, and to determine if disturbances in stretch-mediated NGF production contribute to the elevated tissue levels of NGF in SHRs, we subjected VSMCs and BSMCs cultured from four established inbred rat strains (WKY, WKHA: hyperactive; SHR and WKHT: hypertensive) to several stretch paradigms. For VSMCs, acute and cyclic stretch affected cells derived from hypertensive rats (80-100% increase over control) but not from normotensive strains. For BSMCs, cyclic and static stretch increased NGF secretion in all four strains, but had a two- to threefold greater effect in cells from SHRs and WKHTs (increase up to 600%) at early time points. At later time points of a 24-h experimental period, stretch increased NGF output up to 400% in SHR and WKHA cultures. Thus, defects that influence early induction of stretch-mediated SHR NGF secretion cosegregate with the hypertensive phenotype. Stretch-gated ion channel inhibitors, voltage-gated ion channel inhibitors, and protease inhibitors failed to affect stretch-induced BSMC NGF secretion. In contrast, gene transcription, intracellular calcium, protein kinase C (PKC), and autocrine release of an unknown factor may play a role in the elevated NGF secretion observed in smooth muscle from hypertensive animals. Altered stretch-induced smooth muscle NGF secretion may contribute to the augmented vascular and bladder NGF content associated with high blood pressure and hyperactive voiding in SHRs.