Epithelium integrity is crucial for the relaxant activity of brain natriuretic peptide in human isolated bronchi

Abstract

BACKGROUND AND PURPOSEBrain natriuretic peptide (BNP) plays an important role in several biological functions, including bronchial relaxation. Here, we have investigated the role of BNP and its cognate receptors in human bronchial tone. EXPERIMENTAL APPROACHEffects of BNP on responses to carbachol and histamine were evaluated in non-sensitized, passively sensitized, epitheliumintact or denuded isolated bronchi and in the presence of methoctramine, N w -nitro-L-arginine methyl ester (L-NAME) and aminoguanidine. Natriuretic peptide receptors (NPRs) were investigated by immunohistochemistry, RT-PCR and real-time PCR. Release of NO and acetylcholine from bronchial tissues and cultured BEAS-2B bronchial epithelial cells was also investigated. KEY RESULTSBNP reduced contractions mediated by carbachol and histamine, with decreased Emax (carbachol: 22.7 Ϯ 4.7%; histamine: 59.3 Ϯ 1.8%) and increased EC50 (carbachol: control 3.33 Ϯ 0.88 mM, BNP 100 Ϯ 52.9 mM; histamine: control 16.7 Ϯ 1.7 mM, BNP 90 Ϯ 30.6 mM); BNP was ineffective in epithelium-denuded bronchi. Among NPRs, only atrial NPR (NPR1) transcripts were detected in bronchial tissue. Bronchial NPR1 immunoreactivity was detected in epithelium and inflammatory cells but faint or absent in airway smooth muscle cells. NPR1 transcripts in bronchi increased after incubation with BNP, but not after sensitization. Methoctramine and quinine abolished BNP-induced relaxant activity. The latter was associated with increased bronchial mRNA for NO synthase and NO release, inhibited by L-NAME and aminoguanidine. In vitro, BNP increased acetylcholine release from bronchial epithelial cells, whereas NO release was unchanged. CONCLUSIONS AND IMPLICATIONSEpithelial cells mediate the BNP-induced relaxant activity in human isolated bronchi. AbbreviationsASM, airway smooth muscle; BNP, brain natriuretic peptide; COPD, chronic obstructive pulmonary disease; E, effect; Emax, maximal response; eNOS, endothelial nitric oxide synthase; iNOS, inducible nitric oxide synthase; KH, KrebsHenseleit buffer solution; L-NAME, N w -nitro-L-arginine methyl ester hydrochloride; MTT, 3-[4,5-dimethylthiazol-2-yl]2,5-diphenyl tetrazolium bromide; NPR, natriuretic peptide receptor; pGC, particulate guanylate cyclase; Ki, receptor binding affinity BJP British Journal of Pharmacology

Epithelial-smooth muscle cooperation is needed for brain natriuretic peptide-dependent bronchorelaxant activity

“…This finding suggests that BNP may interact with the muscarinic receptor signalling, mainly with the M 2 receptor subtype, regulating the airway smooth muscle function [6]. BNP-dependent relaxant activity is also coupled to the increase of iNOS transcript levels in the isolated bronchi but not in bronchial epithelial cells, and the inhibition NO synthesis by aminoguanidine abolished bronchial relaxant effects [4].…”

“…The BNP-related relaxation of human isolated bronchi, particularly in passively sensitized tissues, suggests that many local factors might regulate the biological activity of BNP [3]. In effect, epithelial integrity is needed for BNP-related post-transductional mechanisms regulating human bronchial contractility in response to both cholinergic and histaminergic stimulation [4]. In humans, acetylcholine has been found in epithelial cells and several studies confirm the pathobiological role of the non-neuronal cholinergic system [5,6].…”

“…In humans, acetylcholine has been found in epithelial cells and several studies confirm the pathobiological role of the non-neuronal cholinergic system [5,6]. Effectively, recently it has been demonstrated that, in human isolated bronchi, the BNP-dependent bronchial relaxant effect is inhibited by quinine, an inhibitor of organic cation transporters that reduces acetylcholine release [4]. This finding suggests that BNP may interact with the muscarinic receptor signalling, mainly with the M 2 receptor subtype, regulating the airway smooth muscle function [6].…”

Endocrine regulation of airway contractility is overlooked

“…BNP mechanism of action also involved ASM relaxation (Matera et al 2009, Edelson et al 2013). However, the relaxing effect is mediated indirectly through the epithelium (Matera et al 2011).…”

Pharmacology and Therapeutics of Bronchodilators

“…Moreover, in humans, exogenous ANP reverses airway hyper-responsiveness when given intravenously or by inhalation in high doses, although it seems to be less effective when administered by inhalation (Angus et al, 1993(Angus et al, , 1994a, and has also been shown to modify bronchial responsiveness to inhaled histamine (Angus et al, 1995) and nebulized water (Mcalpine et al, 1992). We have documented that BNP, which is able to induce a time-and concentration-dependent increase of cGMP levels in human ASM cells (Hamad et al, 2003), induces a weak but intriguing relaxant effect on human ASM (Matera et al,476 CAZZOLA ET AL. 2009) through the activation of the natriuretic peptide receptor-A (Matera et al, 2011a). The incubation of human ASM with BNP can elicit a significant reduction of cholinergic and histaminergic responses (Matera et al, 2011a).…”