Expression of nitric oxide synthase in bladder smooth muscle cells: regulation by cytokines and L-arginine

Bladder Oversensitivity Is Associated with Bladder Outlet Obstruction in Men

Objective: The aim of this study was to assess whether there is an objective association between bladder outlet obstruction (BOO) and abnormal sensation parameters during filling cystometry in men. Methods: This was a prospective study. Consecutive patients referred for urodynamic examination were assessed for eligibility. Patients with permanent catheters, BPH related surgery, neurologic disease, or inability to complete the urodynamic study were excluded. All patients underwent full physical examination, as well as renal and bladder ultrasound including prostate size estimation, post void residual volume, and PSA, and they completed the International Prostate Symptoms Score (IPSS) questionnaire. The cohort was divided into obstructed and un-obstructed groups according to the Bladder Outlet Obstruction Index. Results: Ninety of the 115 patients recruited were obstructed (78%). Obstructed patients had significantly higher PSA, larger prostate volume, and higher IPSS. Detrusor overactivity did not differ between the two groups (45.6% vs. 48.1%, p = 0.83). First, normal, strong, and urgent desires to void were significantly lower in obstructed men: median (IQR) 118 (57−128) vs. 180 (80−200), 171 (85−257) vs. 227 (125−350), 221 (150−383) vs. 307 (180−477), and 276 (197−480) vs. 344 (280−535), respectively. First desire to void (FDV) had the highest area under the curve (AUC = 0.83, 95% CI = 0.76−0.90, p < 0.001) for predicting BOO with a Youden index of 0.78 at 140 mL. Conclusions: Our results suggest that there is a strong association between bladder oversensitivity and BOO in men. Men with FDV <140 mL had a significantly increased probability of being obstructed. These findings may shed a light on the pathophysiological connection between obstruction and enhanced afferent signaling from the bladder.

Bladder outlet obstruction is associated with bladder oversensitivity in women

INTRODUCTION AND HYPOTHESIS

Bladder outlet obstruction (BOO) in women might be associated with significant lower urinary tract storage symptoms such as increased frequency, urgency, and incontinence. This prospective study was designed to assess whether there is an objective association between BOO and abnormal parameters during filling cystometry in women.

METHODS

A total of 169 consecutive women (mean age 56 ± 14 years) who were referred for urodynamic investigation were prospectively recruited. Comprehensive medical, obstetric, and gynecological histories were recorded. All patients underwent physical examination, renal and bladder ultrasound, and filled out the International Prostate Symptoms Score (IPSS) questionnaire. The cohort was divided into obstructed and un-obstructed groups based on pressure flow results (Obstruction: Q_max <12 ml/s and P_det @ Q_max >25 cmH₂O).

RESULT

There was no significant difference in the frequency of detrusor overactivity between the obstructed and non-obstructed group (37% vs 32%, p = 0.71). All bladder sensation volumes were significantly lower in obstructed women than non-obstructed women in univariate and multivariate logistic regression analyses. Of the sensation parameters, first desire to void (FDV) had the highest area under the curve (AUC = 0.75, 95% CI = 0.672-0.837, p < 0.001) for predicting BOO. FDV < 105 ml showed a strong association with BOO with OR = 9.84 (95% CI 4.122-23.508, p < 0.0001). On univariate and multivariate analyses adjusted to 50 cc reduction in sensation volume, all sensation parameters, were associated with bladder outlet obstruction.

CONCLUSION

Our results suggest that there might be a strong association between bladder oversensitivity and BOO in women. This may shed light on the pathophysiological connection between obstruction and enhanced afferent signaling from the bladder.

Recent insights into the cell biology of bladder smooth muscle

Much of current biomedical research is focused on the development of 'targeted therapies' based on detailed knowledge about the signals that mediate aberrant cellular behavior in a given disease. Although this concept has been used most widely in cancer treatment, the same strategy applies to nonmalignant conditions such as pathologic tissue expansion in the genitourinary tract. A rigorous understanding of the key molecular events and pathways that underlie normal and pathologic activity of the bladder would allow us to identify potential targets for rational drug design. In this review, I will summarize our current understanding of cell signaling in bladder smooth muscle and highlight potential targets for drug-based treatment of tissue remodeling in the lower urinary tract.

Pharmacology of the lower urinary tract: basis for current and future treatments of urinary incontinence

The lower urinary tract constitutes a functional unit controlled by a complex interplay between the central and peripheral nervous systems and local regulatory factors. In the adult, micturition is controlled by a spinobulbospinal reflex, which is under suprapontine control. Several central nervous system transmitters can modulate voiding, as well as, potentially, drugs affecting voiding; for example, noradrenaline, GABA, or dopamine receptors and mechanisms may be therapeutically useful. Peripherally, lower urinary tract function is dependent on the concerted action of the smooth and striated muscles of the urinary bladder, urethra, and periurethral region. Various neurotransmitters, including acetylcholine, noradrenaline, adenosine triphosphate, nitric oxide, and neuropeptides, have been implicated in this neural regulation. Muscarinic receptors mediate normal bladder contraction as well as at least the main part of contraction in the overactive bladder. Disorders of micturition can roughly be classified as disturbances of storage or disturbances of emptying. Failure to store urine may lead to various forms of incontinence, the main forms of which are urge and stress incontinence. The etiology and pathophysiology of these disorders remain incompletely known, which is reflected in the fact that current drug treatment includes a relatively small number of more or less well-documented alternatives. Antimuscarinics are the main-stay of pharmacological treatment of the overactive bladder syndrome, which is characterized by urgency, frequency, and urge incontinence. Accepted drug treatments of stress incontinence are currently scarce, but new alternatives are emerging. New targets for control of micturition are being defined, but further research is needed to advance the pharmacological treatment of micturition disorders.

Physiologic role of nitric oxide and nitric oxide synthase in female lower urinary tract

PURPOSE OF REVIEW

In recent years nitric oxide (NO) has gained increasing recognition as an important neurotransmitter and cell signaling molecule with a broad range of functions in the lower urinary tract. This review discusses recently published data related to the physiologic and pathophysiologic roles of NO and nitric oxide synthase (NOS) in the female lower urinary tract.

RECENT FINDINGS

Expression of three isoforms of NOS, namely endothelial NOS, neuronal NOS and inducible NOS, has been identified in various tissues of the lower urinary tract in animals and humans. In addition to its relaxation effects on bladder and urethra, NO also serves as a neurotransmitter in the lower urinary tract. The physiologic roles of NO in overactive bladder, bladder outlet obstruction, diabetic cystopathy, interstitial cystitis, and bladder inflammation have been demonstrated.

SUMMARY

NO plays an important role in the micturition process and in disorders of the lower urinary tract. Improved understanding of the pathophysiologic role of NO/NOS system and of the L-arginine-NO-cGMP pathway may allow us to identify suitable therapeutic targets for lower urinary tract disorders. However, there is a need for further investigation to determine the precise function of NO in human lower urinary tract because most work thus far has been done in animal models.

Urinary bladder contraction and relaxation: physiology and pathophysiology

The detrusor smooth muscle is the main muscle component of the urinary bladder wall. Its ability to contract over a large length interval and to relax determines the bladder function during filling and micturition. These processes are regulated by several external nervous and hormonal control systems, and the detrusor contains multiple receptors and signaling pathways. Functional changes of the detrusor can be found in several clinically important conditions, e.g., lower urinary tract symptoms (LUTS) and bladder outlet obstruction. The aim of this review is to summarize and synthesize basic information and recent advances in the understanding of the properties of the detrusor smooth muscle, its contractile system, cellular signaling, membrane properties, and cellular receptors. Alterations in these systems in pathological conditions of the bladder wall are described, and some areas for future research are suggested.

Increased expression of neuronal nitric oxide synthase in bladder afferent cells in the lumbosacral dorsal root ganglia after chronic bladder outflow obstruction

Nitric oxide (NO), a neurotransmitter in autonomic reflex pathways, plays a role in functional neuroregulation of the lower urinary tract. Upregulation of the levels of neuronal nitric oxide synthase (nNOS), the enzyme system responsible for NO synthesis, has been documented in the peripheral, spinal and supraspinal segments of the micturition reflex in diseases such as cystitis, bladder/sphincter dyssynergia following spinal cord injury and bladder overactivity after cerebral infarction. These observations suggest that NO might play a role in the development of bladder overactivity. In this study, nNOS-immunoreactivity (IR) was evaluated in bladder afferent and spinal neurons following bladder outflow obstruction (BOO) in male and female rats. Chronic BOO was induced by placing lumen reducing ligatures around the proximal urethra. Six weeks following the obstructive or sham surgery, bladder function was evaluated by awake cystometry. Bladder afferent neurons in L1, L2, L6 and S1 dorsal root ganglia (DRG) were identified by retrograde neuronal labeling with injection of Fast Blue into the bladder smooth muscle. A differential distribution of nNOS-IR was subsequently evaluated in bladder afferent neurons in the DRG and in the associated spinal cord segments. The percentage of bladder afferent neurons expressing nNOS-IR was increased in L6 (1.8-fold in males and 1.9-fold in females) and S1 (2.8-fold in males and 5.3-fold in females) DRG. In contrast, no changes in nNOS-IR in neurons or fiber distribution were observed in any spinal cord segments examined.

Phenotypic modulation of cultured bladder smooth muscle cells and the expression of inducible nitric oxide synthase

Phenotypic modulation of smooth muscle is associated with various pathological conditions, including bladder dysfunction. Cytoskeletal dynamics modulate the cell phenotype and were recently shown to be involved in regulation of inducible nitric oxide synthase (iNOS). We tested the hypothesis that the cell differentiation status affects iNOS expression, and that iNOS is preferentially expressed in immature dedifferentiated bladder smooth muscle cells (BSMC). Isolated at BSMC were put into different stages of differentiation by serum deprivation on laminin-coated plates in the presence of IGF-I and by interaction with Rho signaling and actin polymerization. iNOS and smooth muscle-myosin heavy chain (SM-MHC) protein expression were investigated with Western blot analysis. Our results showed iNOS protein in BSMC exposed to interleukin-1 beta (2 ng/ml) + TNF-alpha (50 ng/ml). Growth of BSMC in serum-free medium on laminin in the presence of IGF-I increased SM-MHC expression, whereas cytokine-induced iNOS was inhibited. Disruption of F-actin with latrunculin B (0.5 microM) potentiated iNOS expression and decreased SM-MHC expression. Rho inhibition with C3 (2.5 microg/ml) increased iNOS expression, whereas SM-MHC expression was slightly decreased. Rho-kinase inhibition with Y-27632 (10 microM) mediated a decrease in iNOS and a slight increase in SM-MHC expression. In conclusion, the capacity of BSMC to express iNOS was negatively correlated to differentiation status measured as SM-MHC expression. Actin cytoskeletal dynamics and Rho signaling are involved in regulation of cytokine-induced iNOS expression in BSMC. Phenotypic changes and impairment in actin cytoskeleton formation may potentiate cytokine activation and in turn increase nitric oxide production in the bladder during disease.

Nerve-mediated bladder contraction is impaired by cytokines: involvement of inducible nitric oxide synthase

We investigated the possible involvement of inducible nitric oxide synthase (iNOS) in the effect of cytokines on neuromuscular function in isolated rat bladder strips. Bladder strips were incubated in cell culture medium for 24 h with or without tumour necrosis factor-alpha (TNF-alpha)+interleukin-1beta. Mechanical activity in response to electrical field stimulation and carbachol was recorded in organ baths. Both the electrical field stimulation- and carbachol-induced contractions were reduced by the incubation. The electrical field stimulation-induced contraction was significantly further impaired after prolonged exposure to TNF-alpha+interleukin-1beta. This impairment was restored by dexamethasone, the iNOS inhibitor aminoguanidine and partially by brain-derived neurotrophic factor (BDNF). In contrast, carbachol-induced contractions were not affected by cytokines. iNOS protein expression was detected in cytokine-incubated bladder strips by immunohistochemistry and Western blot analysis. The results demonstrated that TNF-alpha+interleukin-1beta impaired nerve-mediated bladder contractions. Aminoguanidine, and to some extent BDNF, exerted neuroprotective effects.