Tissue functions mediated by β 3-adrenoceptors - Findings and challenges

Archiv für Experimentelle Pathologie und Pharmakologie (Impact Factor: 2.47). 08/2010; 382(2):103-8. DOI: 10.1007/s00210-010-0529-2
Source: PubMed


As β3-adrenoceptor agonists metamorphose from experimental tools into therapeutic drugs, it is vital to obtain a comprehensive
picture of the cell and tissue functions mediated by this receptor subtype in humans. Human tissues with proven functions
and/or a high expression of β3-adrenoceptors include the urinary bladder, the gall bladder, and other parts of the gastrointestinal tract. While several
other β3-adrenoceptor functions have been proposed based on results obtained in animals, their relevance to humans remains uncertain.
For instance, β3-adrenoceptors perform an important role in thermogenesis and lipolysis in rodent brown and white adipose tissue, respectively,
but their role in humans appears less significant. Moreover, the use of tools such as the agonist BRL 37344 and the antagonist
SR59230A to demonstrate functional involvement of β3-adrenoceptors may lead in many cases to misleading conclusions as they can also interact with other β-adrenoceptor subtypes
or even non-adrenoceptor targets. In conclusion, we propose that many responses attributed to β3-adrenoceptor stimulation may need re-evaluation in the light of the development of more selective tools. Moreover, findings
in experimental animals need to be extended to humans in order to better understand the potential additional indications and
side effects of the β3-adrenoceptor agonists that are beginning to enter clinical medicine.

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    • "A potential limitation to our choice for the rat to study β- AR pharmacology of phenomena such as NVA and MC in bladder function is that in rats both β 2 -and β 3 -AR are shown to be involved in relaxation of bladder smooth muscle, while mRNA for all β-AR subtypes was identified in rat bladder (Fujimura et al. 1999). This is a general problem assessing β 3 -AR functions across species and is extensively discussed by Michel et al. (2010). Nevertheless, this limits our conclusions for the present work to the rat. "
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    ABSTRACT: Spontaneous microcontractions and electrical field stimulation (EFS)-evoked contractions in isolated rat bladder strips from normal and from 6 weeks partial bladder outflow obstruction (pBOO) animals were studied to identify the potential site of action for the β3-adrenoceptor (AR) agonist mirabegron in detrusor overactivity in rats. For this, effects of the β-AR agonist isoprenaline and mirabegron were tested in presence or absence of selective antagonists for β-AR subtypes, namely CGP-20712A for β1-AR, ICI-118,551 for β2-AR, and L-748,337 for β3-AR. In detrusor strips from both normal and obstructed animals, EFS-induced contractions were weakly affected by isoprenaline and even less so by mirabegron. In contrast, microcontraction activity was more potently reduced by isoprenaline (pIC50 7.3; Emax ±85 %), whereas mirabegron showed a small effect. In pBOO strips, concentration response curves for isoprenaline and mirabegron at inhibition of EFS and spontaneous microcontractions were similar to those in normal strips. Isoprenaline-induced inhibition of microcontractions and EFS was antagonized by the β1-AR antagonist, but not by the β2- and β3-AR antagonists. In the context of β3-AR-mediated bladder functions for mirabegron in other experiments, the current data question a role for effects at spontaneous microcontractions, or neurogenic detrusor stimulation in the mode of action for mirabegron in vivo, since functional bladder effects for mirabegron are reported to occur at much lower concentrations.
    Archiv für Experimentelle Pathologie und Pharmakologie 06/2015; 388(7). DOI:10.1007/s00210-015-1136-z · 2.47 Impact Factor
    • "Interestingly, the susceptibility to agonist-induced down-regulation appears to differ between β-adrenoceptor subtypes (Marullo et al. 1995) with β 1 -adrenoceptors typically being less affected than β 2 -adrenoceptors, e.g., in the heart (Nanoff et al. 1989; Nanoff et al. 1990). β 3 -Adrenoceptors have been discovered more recently and mediate functions such as relaxation of urinary bladder smooth muscle (Michel et al. 2010) whereas their role in other tissues such as the human heart is controversial (Michel et al. 2011). Accordingly, selective β 3 -adrenoceptor agonists have recently been shown to be effective in the treatment of the overactive bladder syndrome (Khullar et al. 2013; Nitti et al. 2013; Ohlstein et al. 2012). "
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    ABSTRACT: β3-Adrenoceptors are resistant to agonist-induced desensitization in some cell types but susceptible in others including transfected human embryonic kidney (HEK) cells. Therefore, we have studied cellular and molecular changes involved in agonist-induced β3-adrenoceptor desensitization in HEK cells. Cells were treated with isoprenaline or forskolin, and following wash-out, cyclic adenosine monophosphate (cAMP) accumulation in response to freshly added agonist was quantified. Receptor and G protein expression were quantified by radioligand binding and immunoblot experiments, respectively. Treatment with isoprenaline induced a concentration- and time-dependent desensitization of cAMP accumulation in response to freshly added isoprenaline. This functional desensitization primarily consisted of reduced maximum responses with little change of agonist potency. Maximum desensitization was achieved by pre-treatment with 10 μM isoprenaline for 24 h. It was not accompanied by changes in β3-adrenoceptor density as assessed in saturation radioligand-binding studies. The desensitization was associated with a small reduction in immunoreactivity for α-subunits for Gs and Gi1, whereas that for Gi2, Gi3, and Gq/11 was not significantly altered. In cells treated with pertussis toxin, isoprenaline-induced cAMP accumulation as well as desensitization by isoprenaline pre-treatment remained unchanged. Isoprenaline pre-treatment also reduced forskolin-induced cAMP accumulation; conversely, pre-treatment with forskolin caused a similar desensitization of isoprenaline-induced cAMP accumulation. We conclude that agonist-induced β3-adrenoceptor desensitization in HEK cells does not involve reduced receptor numbers and small, if any, reduction of Gs expression; changes at the level of adenylyl cyclase function can fully explain this desensitization.
    Archiv für Experimentelle Pathologie und Pharmakologie 06/2013; 386(10). DOI:10.1007/s00210-013-0891-y · 2.47 Impact Factor
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    • "d effects of β 3 - adrenoceptor agonists in humans has been hampered by a lack of suitable tools to explore their expression pattern at the protein level ( Michel et al . 2011a ) . Thus , the expression pattern and tissue functions of β 1 - and β 2 - adrenoceptors have been well characterised , but those of β 3 - adrenoceptors remain ill defined ( Michel et al . 2010 ) . The only human tissue for which a large body of data exists on β 3 - adrenoceptors is the urinary bladder ( Michel and Vrydag 2006 ; Yamaguchi and Chapple 2007 ) . Progress in the identification of β 3 - adrenoceptor protein in other tissues is hampered by a lack of suitable tools such as radioligands or antibodies ( Vrydag and Mich"
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    ABSTRACT: β(3)-Adrenoceptors are a promising drug target for the treatment of urinary bladder dysfunction, but knowledge about their expression at the protein level and their functional role is limited, partly due to a lack of well validated tools. As many antibodies against G-protein-coupled receptors, including those against β(3)- and other β-adrenoceptor subtypes, lack selectivity for their target, we have evaluated the specificity of five antibodies raised against the full-length protein of the human β(3)-adrenoceptor (H155-B01), its N-terminus (LSA4198 and TA303277) and its C-terminus (AB5122, Sc1472) in immunoblotting and immunocytochemistry. Our primary test system were Chinese hamster ovary cells stably transfected to express each of the three human β-adrenoceptor subtypes at near physiological levels (100-200 fmol/mg protein). None of the five antibodies exhibited convincing target specificity in immunoblotting with Sc1472 apparently being least unsuitable. In immunocytochemistry, LSA4198 and Sc1472 appeared most promising, exhibiting at least some degree of specificity. As these two antibodies have been raised against different epitopes (N- and C-terminus of the receptor, respectively), we propose that concordant staining by both antibodies provides the most convincing evidence for β(3)-adrenoceptor labelling in cyto- or histochemistry studies.
    Archiv für Experimentelle Pathologie und Pharmakologie 06/2012; 385(9):875-82. DOI:10.1007/s00210-012-0767-6 · 2.47 Impact Factor
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