Inhibition by salbutamol of the proliferation of human airway smooth muscle cells grown in culture

Abstract

1 P2-Adrenoceptor agonists may exacerbate asthma by reducing the release of the anti-proliferative and anti-inflammatory molecule, heparin from mast cells in the airway. In this study, the direct effects of the clinically used bronchodilator, salbutamol, on the proliferation of airway smooth muscle cells grown in culture and stimulated with a range of mitogens have been examined.2 In mitogen-stimulated cells, salbutamol (0.1-I00 nM) inhibited [3H]-thymidine incorporation in a concentration-dependent manner. Salbutamol (100 nM) pretreatment reduced the mitogenic responses to thrombin (0.3 u ml-1), epidermal growth factor (EGF) (300 pM) and U46619 (100 nM) by 61.7 ± 6.1%, 46.9 ± 13.9% and 57.6 ± 12.7%, respectively. However, salbutamol pretreatment did not appear to reduce the small mitogenic response to endothelin-1. 3 Increases in [3H]-leucine incorporation in thrombin (0.3 u ml-')-stimulated cells were reduced by salbutamol (100 nM) by 27.7 ± 2.8%. Similarly, thrombin (0.3 u ml`)-stimulated increases in cell number were also inhibited by salbutamol (100 nM) pretreatment. Thus, the effect of salbutamol in decreasing thrombin-induced [3H]-leucine incorporation may, at least in part, be explained by inhibition of cell proliferation. 4 The inhibition of cell proliferation by salbutamol was prevented by pretreatment with either the non-selective P-adrenoceptor antagonist, propranolol (0.3 JAM) or the selective P2-adrenoceptor antagonist, ICI 118551 (50 nM).5 These results indicate that salbutamol, through activation of a P2-adrenoceptor, has a direct inhibitory effect on proliferation elicited by the mitogens thrombin, EGF, and U46619. Thus, it seems likely that this direct inhibitory action of P2-adrenoceptor agonists would override any indirect action to accelerate airway smooth muscle proliferation. These observations lead us to suggest that R2-adrenoceptor agonists exacerbate asthma by mechanisms unrelated to airway smooth muscle proliferation.

Exchange Protein Directly Activated by cAMP (epac): A Multidomain cAMP Mediator in the Regulation of Diverse Biological Functions

“…Exposure to mitogenic stimuli switches the airway smooth muscle phenotype from a (normo)contractile to a proliferative, hypocontractile state characterized by increased expression of proliferative markers and decreased contractile responses associated with decreased expression of contractile proteins, a process reversible in nature Amrani, 2003, Dekkers et al, 2009). Mitogen-induced airway smooth muscle cells proliferation is reduced in response to b 2 -agonists and even more pronounced in response to PGE 2 (Tomlinson et al, 1994;Stewart et al, 1999;Lee et al, 2001;Kassel et al, 2008;Roscioni et al, 2011a;Yan et al, 2011). PGE 2 may act antimitogenic or promitogenic via distinct EP receptor subtypes (Yan et al, 2011).…”

Mechanisms of serum potentiation of GM-CSF production by human airway smooth muscle cells

“…The mitogen stocks were freshly diluted in serum free medium and added to wells of untreated or cytokine-primed ASMC at concentrations that had previously been shown to induce human ASMC proliferation: 40 ng/ml PDGF (10), 100 ng/ml EGF (17), 100 ng/ml IGF (14), and 0.1, 1.0, and 10 U/ml thrombin (22). A vehicle control of 1.0 M acetic acid in serum-free medium was included for PDGF-AB and EGF.…”

Phenotypic diversity and molecular mechanisms of airway smooth muscle proliferation in asthma

“…Various diverse stimuli have now been demonstrated to increase the proliferation of airway smooth muscle cells in cell culture, and have been reviewed in detail elsewhere [13,47,48]. Broadly, the substances now implicated in mitogenesis of airway smooth muscle, in addition to the action of serum itself (discussed in [49]), include pro-inflammatory mediators (histamine [46], 5-hydroxytryptamine (5-HT) [50], phenylephrine [51], tachykinins [52], endothelin (ET)-1 [53±56] and leukotriene D 4 [57]), several inflammatory cell-and plasma-derived enzymes (a-thrombin [58], tryptase [59], b-hexosaminidase and b-glucuronidase [60]), polypeptide growth factors (platelet-derived growth factor (PDGF) [61], epidermal growth factor (EGF) [62], fibroblast growth factor-2 (FGF-2) [63] and insulin-like growth factors (IGFs) [64]) and thromboxanes [65]. Pro-inflammatory cytokines (interleukin-1b [66], interleukin-6 [67], and tumour necrosis factor-a [68]) also induce a proliferative response in airway smooth muscle, which is revealed only under conditions of cyclo-oxygenase inhibition [69], in which the production and action of inhibitory prostanoids such as prostaglandin E 2 is limited.…”

“…b 2 -Adrenoceptor agonists represent another class of drugs used in the management of asthma which inhibit proliferation of mitogen-stimulated airway smooth muscle cells in culture [62,157]. The action of b 2 -adrenoceptor agonists is considered to be dependent largely on increases in intracellular cyclic adenosine monophosphate (AMP) levels, consistent with the antiproliferative effect of agents which directly increase cyclic AMP levels [158].…”