Beta₂‐adrenergic ligand racemic formoterol exhibits enantioselective disposition in blood and skeletal muscle of humans, and elicits myocellular PKA signaling at therapeutic inhaled doses

Abstract

While studies have demonstrated substantial differences in beta2‐adrenergic agonist enantiomer pharmacology, enantioselective disposition of long‐acting beta2‐adrenergic ligand racemic (rac)‐formoterol in blood is inadequately explored after inhaled therapy given analytical challenges. Furthermore, information on enantioselective disposition and partitioning of beta2‐adrenergic agonist in skeletal muscle is absent despite its promising data on muscle anabolism in humans. Using a sensitive ultra‐high performance liquid chromatography−mass spectrometry (UPLC−MS/MS) assay, we determined disposition of (R,R)‐formoterol and (S,S)‐formoterol in plasma and skeletal muscle samples from 11 non‐asthmatic men who had inhaled rac‐formoterol at therapeutic doses (2 × 27 μg). Mean (SD) concentrations of (R,R)‐ and (S,S)‐formoterol in plasma and in muscle biopsies of the vastus lateralis 1 hour after inhalation of formoterol were 31 (15) and 45 (18) pg × mL−1 for (R,R)‐formoterol and (S,S)‐formoterol, respectively, in plasma, and 0.56 (0.32) and 0.51 (0.29) pg × mgwet wt−1, respectively, in muscle. Formoterol exhibited different enantioselective disposition in plasma and muscle (p < 0.0001). In plasma, mean log (R,R):(S,S)‐formoterol ratio was lower than 0 [−0.17(0.07), p < 0.0001], whereas in muscle, mean log (R,R):(S,S)‐formoterol ratio was slightly higher than 0 [0.04(0.07), p < 0.05]. Log (R,R):(S,S)‐formoterol ratio in muscle was related to muscle fiber‐type composition. Furthermore, formoterol induced an approximately two‐fold increase in muscle p‐PKASer/thr phosphorylation (p < 0.01), indicating a substantial beta2‐adrenergic response. Collectively, these findings suggest that formoterol exhibits modest enantioselective disposition in plasma after inhaled therapy in humans, which appear related to a greater (R,R)‐enantiomer disposition in skeletal muscle that may be dependent on fiber‐type composition.

Beta2‐adrenergic agonist clenbuterol increases energy expenditure and fat oxidation, and induces mTOR phosphorylation in skeletal muscle of young healthy men

“…We observed that clenbuterol effectively induced PKA and mTOR phosphorylation in skeletal muscle. Given that the PKA‐dependent signaling pathway is the canonical signaling pathway associated with the beta 2 ‐adrenoceptor, the observed increase in PKA substrate phosphorylation with clenbuterol was expected and was consistent with that observed for formoterol and salbutamol in human skeletal muscle . The increase of 121% in mTOR Ser2448 phosphorylation, however, was larger than expected, and may indicate anabolic signaling in the absence of exercise.…”

The beta2‐adrenergic receptor – a re‐emerging target to combat obesity and induce leanness?

“…−1 × day −1 (Kalinovich et al 2020) would yield a systemic exposure 80 times exceeding that recommended for humans (Maltin et al 1993;Kamalakkannan et al 2008;Koeberl et al 2018). Therefore, we encourage research to be conducted with newer-generation and enantioselective beta 2 -agonists because of their greater selectivity for the beta 2 -adrenergic receptor and fewer cardiac side effects (Jacobson et al 2018;Hostrup et al 2019), and in doses more closely resembling those clinically relevant. Pharmaceutical development of novel beta 2 -agonists that are more specific to skeletal muscle tissue is ongoing (Koziczak-Holbro et al 2019) and could, in combination with exercise, diet or other treatment regimens, prove useful in weight-loss management.…”

Anabolic and lipolytic actions of beta2‐agonists in humans and antidoping challenges

“…Upon agonist binding to the beta 2 ‐adrenoceptor, various intracellular signalling pathways are activated as shown in Figure . The cAMP/protein kinase A (PKA)‐dependent pathway is the canonical signalling pathway activated upon beta 2 ‐adrenergic stimulation as also shown in human skeletal muscle after treatment with salbutamol and formoterol . The cAMP/PKA‐dependent pathway has several downstream targets that regulate metabolism and gene programs in skeletal muscle fibres.…”

“…While muscle hypertrophy is scarcely explored for the inhaled route, daily inhalation of terbutaline at 4 mg (8 puffs from a 0.5 mg Turbohaler) for 4 weeks was recently shown to induce a 1 kg gain in lean mass in healthy young men . In addition, an inhaled dose of 54 μg formoterol (6 puffs from a 9 μg Turbohaler), a dose that lies within the current WADA threshold limit, induces skeletal muscle signalling and increases resting metabolic rate, fat oxidation, and peripheral glucose uptake . The same is the case for salbutamol, which via the inhaled route has been shown to induce lipolysis at therapeutic doses and to increase resting metabolic rate .…”