Slow dissociation kinetics of LAMAs contribute to the functional interactions with LABAs

Abstract

Introduction Combination therapy with long-acting anticholinergics (LAMA) and long-acting β-agonists (LABA) leads to improved lung function in COPD or asthma patients. We investigated whether this interaction is dependent on intracellular crosstalk, either via muscarinic M₃ receptors and PKC or via M₂ receptors (M₂R), or via other functional interactions.

Methods Contraction studies were performed using bovine tracheal smooth muscle strips and guinea pig precision cut lung slices. Contraction in response to methacholine was recorded after pre-incubation for 1h with tiotropium (1–30nM) and/or olodaterol (10-100nM), glycopyrrolate (1-100nM) and/or indacaterol (100-1000nM), and/or the PKC inhibitor GF109203X (1 µM), and/or the M₂R antagonist gallamine (10 µM).

Results Pre-incubation with the individual bronchodilators resulted in rightward-shifts of the methacholine dose response curves in strips and slices. Tiotropium, and to a lesser extent glycopyrrolate, showed Schild coefficients greater than unity and anticholinergic effects remained visible after 1h washout. Tiotropium inhibited the maximal effect (Emax) in strips, which was further enhanced by olodaterol. Similar effects on Emax were not observed for glycopyrrolate and indacaterol. Remarkably, pre-incubation with GF109203X or gallamine had no major impact on the size or nature of the LABA effects in both preparations.

Conclusions Tiotropium, and to a lesser extent glycopyrrolate, exhibits non-competitive functional characteristics, presumably due to slow dissociation kinetics. This behavior of LAMAs may contribute to the functional interactions with LABAs, also in view of the limited evidence for intracellular crosstalk via PKC or M₂R.