UP-REGULATION OF BRADYKININ RESPONSE IN RAT AND HUMAN BLADDER SMOOTH MUSCLE

Signaling Pathways Mediating Bradykinin-Induced Contraction in Murine and Human Detrusor Muscle

Bradykinin (BK) has been proposed to modulate urinary bladder functions and implicated in the pathophysiology of detrusor overactivity. The present study aims to elucidate the signaling pathways of BK-induced detrusor muscle contraction, with the goal of better understanding the molecular regulation of micturition and identifying potential novel therapeutic targets of its disorders. Experiments have been carried out on bladders isolated from wild-type or genetically modified [smooth muscle-specific knockout (KO): Gαq/11-KO, Gα12/13-KO and constitutive KO: thromboxane prostanoid (TP) receptor-KO, cyclooxygenase-1 (COX-1)-KO] mice and on human bladder samples. Contractions of detrusor strips were measured by myography. Bradykinin induced concentration-dependent contractions in both murine and human bladders, which were independent of secondary release of acetylcholine, ATP, or prostanoid mediators. B2 receptor antagonist HOE-140 markedly diminished contractile responses in both species, whereas B1 receptor antagonist R-715 did not alter BK's effect. Consistently with these findings, pharmacological stimulation of B2 but not B1 receptors resembled the effect of BK. Interestingly, both Gαq/11- and Gα12/13-KO murine bladders showed reduced response to BK, indicating that simultaneous activation of both pathways is required for the contraction. Furthermore, the Rho-kinase (ROCK) inhibitor Y-27632 markedly decreased contractions in both murine and human bladders. Our results indicate that BK evokes contractions in murine and human bladders, acting primarily on B2 receptors. Gαq/11-coupled and Gα12/13-RhoA-ROCK signaling appear to mediate these contractions simultaneously. Inhibition of ROCK enzyme reduces the contractions in both species, identifying this enzyme, together with B2 receptor, as potential targets for treating voiding disorders.

Bradykinin modulates spontaneous nerve growth factor production and stretch-induced ATP release in human urothelium

The urothelium plays a crucial role in integrating urinary bladder sensory outputs, responding to mechanical stress and chemical stimulation by producing several diffusible mediators, including ATP and, possibly, neurotrophin nerve growth factor (NGF). Such urothelial mediators activate underlying afferents and thus may contribute to normal bladder sensation and possibly to the development of bladder overactivity. The muscle-contracting and pain-inducing peptide bradykinin is produced in various inflammatory and non-inflammatory pathologies associated with bladder overactivity, but the effect of bradykinin on human urothelial function has not yet been characterized. The human urothelial cell line UROtsa expresses mRNA for both B1 and B2 subtypes of bradykinin receptors, as determined by real-time PCR. Bradykinin concentration-dependently (pEC50=8.3, Emax 4434±277nM) increased urothelial intracellular calcium levels and induced phosphorylation of the mitogen-activated protein kinase (MAPK) ERK1/2. Activation of both bradykinin-induced signaling pathways was completely abolished by the B2 antagonist icatibant (1μM), but not the B1 antagonist R715 (1μM). Bradykinin-induced (100nM) B2 receptor activation markedly increased (192±13% of control levels) stretch-induced ATP release from UROtsa in hypotonic medium, the effect being dependent on intracellular calcium elevations. UROtsa cells also expressed mRNA and protein for NGF and spontaneously released NGF to the medium in the course of hours (11.5±1.4pgNGF/mgprotein/h). Bradykinin increased NGF mRNA expression and accelerated urothelial NGF release to 127±5% in a protein kinase C- and ERK1/2-dependent manner. Finally, bradykinin up-regulated mRNA for transient-receptor potential vanilloid (TRPV1) sensory ion channel in UROtsa. In conclusion, we show that bradykinin represents a versatile modulator of human urothelial phenotype, accelerating stretch-induced ATP release, spontaneous release of NGF, as well as expression of sensory ion channel TRPV1. Bradykinin-induced changes in urothelial sensory function might contribute to the development of bladder dysfunction.

Effects of kinin B(1) and B(2) receptor antagonists on overactive urinary bladder syndrome induced by spinal cord injury in rats

BACKGROUND AND PURPOSE

Kinin B(1) and B(2) receptors have been implicated in physiological and pathological conditions of the urinary bladder. However, their role in overactive urinary bladder (OAB) syndrome following spinal cord injury (SCI) remains elusive.

EXPERIMENTAL APPROACH

We investigated the role of kinin B(1) and B(2) receptors in OAB after SCI in rats.

KEY RESULTS

SCI was associated with a marked inflammatory response and functional changes in the urinary bladder. SCI resulted in an up-regulation of B(1) receptor mRNA in the urinary bladder, dorsal root ganglion and spinal cord, as well as in B(1) protein in the urinary bladder and B(1) and B(2) receptor protein in spinal cord. Interestingly, both B(1) and B(2) protein expression were similarly distributed in detrusor muscle and urothelium of animals with SCI. In vitro stimulation of urinary bladder with the selective B(1) or B(2) agonist elicited a higher concentration-response curve in the SCI urinary bladder than in naive or sham urinary bladders. Cystometry revealed that treatment of SCI animals with the B(2) selective antagonist icatibant reduced the amplitude and number of non-voiding contractions (NVCs). The B(1) antagonist des-Arg(9) -[Leu(8) ]-bradykinin reduced the number of NVCs while the non-peptide B(1) antagonist SSR240612 reduced the number of NVCs, the urinary bladder capacity and increased the voiding efficiency and voided volume.

CONCLUSIONS AND IMPLICATIONS

Taken together, these data show the important roles of B(1) and B(2) receptors in OAB following SCI in rats and suggest that blockade of these receptors could be a potential therapeutic target for controlling OAB.

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.

Characterization of kinin receptors in human cultured detrusor smooth muscle cells

BACKGROUND AND PURPOSE

Kinins have an important role in inflammatory cystitis and in animal pathophysiological models, by acting on epithelium, fibroblasts, sensory innervation and smooth muscle. The aim of this study was to characterize the receptors responsible for direct motor responses induced by kinins on human detrusor.

EXPERIMENTAL APPROACH

Human detrusor cells from biopsies were isolated and maintained in culture. B(1) and B(2) kinin receptors were characterized by means of radioligand and functional experiments (PI accumulation and PGE(2) release).

KEY RESULTS

[(3)H]-[desArg(9)]-Lys-BK and [(3)H]-BK saturation studies indicated receptor density (B(max)) and K (d) values of 19 or 113 fmol mg(-1), and 0.16 or 0.11 nM for the B(1) or B(2) receptors, respectively. Inhibition binding studies indicated the selectivity of the B(1) receptor antagonist [desArg(9)Leu(8)]-Lys-BK and of the B(2) receptor antagonists Icatibant and MEN16132. [DesArg(9)]-Lys-BK and BK induced PI accumulation with an EC(50) of 1.6 and 1.4 nM and different maximal responses (E(max) of [desArg(9)]-Lys-BK was 10% of BK). BK also induced prostaglandin E(2) release (EC(50) 2.3 nM), whereas no response was detected with the B(1) receptor agonist. The incubation of detrusor smooth muscle cells with interleukin 1beta (IL-1beta) or tumour necrosis factor-alpha (TNF-alpha) (10 ng ml(-1)) induced a time-dependent increase in radioligand-specific binding, which was greater for the B(1) than for the B(2) receptor.

CONCLUSIONS AND IMPLICATIONS

Human detrusor smooth muscle cells in culture retain kinin receptors, and represent a suitable model to investigate the mechanisms and changes that occur under chronic inflammatory conditions.

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.