Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCB071

Poster Communications

Effect of the endocannabinoid anandamide on airway tone in healthy and asthmatic mice

A. Simon1, M. Matthey1, J. M. Dietrich1, D. Wenzel1

1. Physiology 1, University of Bonn, Bonn, Germany.

The endocannabinoid system has emerged to be an important modulator of different organ functions. Anandamide (AEA), the currently best-characterized endocannabinoid, can act either via CB1 or CB2 receptors or via its degradation to eicosanoids by the enzyme fatty acid amide hydrolase (FAAH). In a recent study we could show that AEA is a key mediator of hypoxic vasoconstriction in the lung. Therefore, we wondered if endocannabinoids can also regulate airway function. We have investigated the effect of AEA on airway tone of mouse (C57BL/6 WT, FAAH-/-, Cnr1/2-/-) ex vivo. Large airways were examined by isometric force measurements in a wire-myograph and small intrapulmonary airways were analyzed in precision cut lung slices. We have also tested AEA in lung slices of ovalbumin (OVA)-induced asthmatic mice. Therefore, Balb/c mice were injected i.p. with 20 µg OVA in 2 mg Alum on days 0 and 14, then they were challenged by inhalation of 1% OVA 3 times a week and analysis was performed on d24 for acute asthma and on d37 for chronic asthma. Successful asthma induction was confirmed by a prominent cell invasion around the airways as determined in H&E stainings of lung sections. Moreover, qRT-PCR was performed to investigate the expression levels of FAAH in the airways of the upper and lower respiratory tract. In isometric force measurements AEA induced a strong airway relaxation in tracheal rings after serotonin (5-HT) pre-constriction (95.4±3.3%, n=8), while the effect was weaker after methacholine (MCh) pre-constriction (30.5±6.1%, n=12). In the small intrapulmonary airways of precision cut lung slices AEA induced a similar relaxation after 5-HT (51.0±3.9%, n=25) and MCh (35.3±4.6%; n=22) pre-constriction. This bronchorelaxing effect was mediated by FAAH-dependent metabolites as it was strongly reduced in FAAH-/- animals (18.2±3.0% n=8 (myograph after 5-HT)) but remained unaffected in Cnr1/2-/- mice. In lung slices of asthmatic animals AEA-dependent bronchorelaxation was unchanged compared to healthy mice (acute OVA: 62.6±5.4%, n=18 (5-HT); chronic OVA: 49.0±5.9, n=19 (5-HT). QRT-PCR experiments demonstrated that expression levels of FAAH were elevated in the lower respiratory tract (4.0±0.4 (2-△Ct x 106), n=3) compared to the trachea (2.2±0.4, n=3) or whole lung tissue (1.1±0.3, n=3). This may in part explain the limited relaxation by AEA in the upper respiratory tract after MCh pre-constriction. These results indicate that AEA is a strong airway relaxant in the upper and lower respiratory tract. The effect is mediated via metabolites of the FAAH enzyme and it is also present in asthmatic airways ex vivo. Thus, targeting the endocannabinoid system may be a promising approach for future therapies for obstructive airway disease.

Where applicable, experiments conform with Society ethical requirements