Mirabegron induces relaxant effects via cAMP signaling‐dependent and ‐independent pathways in detrusor smooth muscle

Abstract

Objective: We previously found that mirabegron exerts a relaxant effect in the presence of the β 3 -adrenoceptor antagonist SR58894A during carbachol-induced contraction in human and pig detrusor. The aim of this study was to explore the possible mechanism underlying the relaxant effects of mirabegron using detrusor smooth muscle. Methods: Human tissue was obtained from urinary bladders of patients undergoing radical cystectomy at Kyushu University and Harasanshin Hospital. Pig tissue was obtained from an abattoir. Tension force (organ bath experiments) was measured in intact or permeabilised (α-toxin or β-escin) detrusor smooth muscle strips. The contribution of cAMP-dependent signaling and the inhibition of Ca 2+ sensitization to the relaxant effects of mirabegron were characterized using 1 μM SR58894A, 100 μM SQ22536 (an adenylyl cyclase inhibitor), 10 μM H-89 (a protein kinase [PK] A inhibitor), 10 μM Y-27632 (a selective Rho kinase inhibitor), and 10 μM GF-109203X (a selective PKC inhibitor). Results: 30 μM Mirabegron impaired carbachol (0.03-1 μM)-induced contraction in human detrusor smooth muscle. SR58894A only partially attenuated the relaxant effects of mirabegron in human and pig detrusor strips precontracted with 1 μM carbachol. In α-toxin-permeabilized detrusor strips, tension force at 1 μM [Ca 2+ ] i was decreased by mirabegron in a concentrationdependent manner. The relaxant effect of mirabegron was only slightly attenuated by H-89 and not significantly affected by SQ22536. Y-27632 potentiated the relaxation response to mirabegron, but attenuated responses to cAMP; GF-109203X had little effect. Mirabegron but not cAMP had a notable relaxant effect in the pig detrusor smooth muscle permeabilized with β-escin. Conclusions: Mirabegron-induced relaxation of pig and human detrusor smooth muscle occurs via both a β 3 -adrenoceptor/cAMP-dependent and -independent pathway. K E Y W O R D S β 3 -Adrenoceptors, mirabegron, smooth muscle, urinary bladder

Everything You Always Wanted to Know about β3-AR * (* But Were Afraid to Ask)

“…Furthermore, pre-incubation with adenylate cyclase inhibitor SQ22536 markedly suppressed both of these effects [92]. However, Maki et al recently reported a milder effect of SQ22536 on human and pig pre-contracted detrusor strips treated with mirabegron supporting the hypothesis of a cAMP-independent mechanism, potentially via activation of myosin light chain phosphatase [93]. Along the same line, Frazier et al previously showed that only Rp-cAMPS, among other PKA inhibitors had a small significant effect on isoproterenol responses against passive tension on non-contracted rat bladder strips, not supporting a major role for cAMP and/or PKA in β-AR-mediated bladder relaxation.…”

β3 Adrenoceptor‐induced cholinergic inhibition in human and rat urinary bladders involves the exchange protein directly activated by cyclic AMP 1 favoring adenosine release

“…In conclusion, data suggest that the therapeutic success of β 3adrenoceptor agonists in the treatment of OAB syndromes involves activation of an EPAC1-PKC intracellular pathway downstream of cAMP production, resulting in adenosine release, via ENT1, from the detrusor and retrograde activation of inhibitory A 1 receptors on cholinergic nerves. The adenosine-mediated inhibitory effect on cholinergic neurotransmission (this study; Silva et al, 2017) may add to cAMP-dependent and -independent mechanisms whenever β 3adrenoceptor agonists reach the micromolar concentration range required to cause direct relaxation of detrusor smooth muscle fibres (Maki et al, 2019;Michel & Korstanje, 2016). Although still premature, manipulation of the activity of EPAC1 and conventional PKC isoforms may provide additional therapeutic targets to improve bladder overactivity, alongside β 3 -adrenoceptor agonists, also counting on the possibility that the cAMP-dependent EPAC1 signalling may prevent fibroblast-induced irreversible bladder remodelling that is often observed as a consequence of bladder obstruction and/or chronic overactivation (see Certal et al, 2015).…”

“…Intracellular effects of cAMP are most often attributed to protein kinase A (PKA; Wang et al, ). However, detrusor relaxation owing to downstream activation of the AC/PKA pathway by β‐adrenoceptors has been questioned (Frazier, Mathy, Peters, & Michel, ; Maki et al, ), raising the hypothesis that PKA‐independent effects are also involved (de Rooij et al, ; Kawasaki et al, ; reviewed in Dekkers, Racké, & Schmidt, ). The exchange protein directly activated by cAMP (EPAC) is a cAMP‐regulated guanine nucleotide exchange factor that favours GDP/GTP exchange and activation of small Ras‐like GTPases (Li et al, ).…”

“…Intracellular effects of cAMP are most often attributed to protein kinase A (PKA; Wang et al, 2017). However, detrusor relaxation owing to downstream activation of the AC/PKA pathway by β-adrenoceptors has been questioned (Frazier, Mathy, Peters, & Michel, 2005;Maki et al, 2019), raising the hypothesis that PKA-independent effects are also involved (de Rooij et al, 1998;Kawasaki et al, 1998;reviewed in Dekkers, Racké, & Schmidt, 2013).…”

Can mirabegron facilitate ureteral access sheath placement during flexible ureterorenoscopy?

“…Mirabegron is a drug that is used in patients with overactive bladder and acts by stimulating selective beta-3 receptors. Mirabegron increases the capacity of the bladder by relaxing mechanism and affecting its filling function without affecting its contractility or flow rates [10,11]. Animal experiments have also demonstrated dilatation of the ureter and a decrease in ureteral intraluminal pressure with the use of mirabegron [12].…”